for Water Works
Policies for the Review and Approval
of Plans and Specifications for Public Water Supplies
A Report of the Water Supply Committee of the
Great Lakes--Upper Mississippi River Board
of State and Provincial Public Health and Environmental Managers
MEMBER STATES AND PROVINCE
Illinois Indiana Iowa Michigan Minnesota Missouri
New York Ohio Ontario Pennsylvania Wisconsin
Published by: Health Research Inc., Health Education Services Division,
P.O. Box 7126, Albany, NY 12224
Copyright © 2007 by the Great Lakes - Upper Mississippi River Board of State and Provincial
Public Health and Environmental Managers
This book, or portions thereof, may be reproduced without permission from the author if proper credit is given.
POLICY STATEMENT ON PRE-ENGINEERED WATER TREATMENT PLANTS
POLICY STATEMENT ON AUTOMATED/UNATTENDED OPERATION OF SURFACE WATER TREATMENT PLANTS
POLICY STATEMENT ON BAG AND CARTRIDGE FILTERS FOR PUBLIC WATER SUPPLIES
POLICY STATEMENT ON ULTRA VIOLET LIGHT FOR TREATMENT OF PUBLIC WATER SUPPLIES
POLICY STATEMENT ON INFRASTRUCTURE SECURITY FOR PUBLIC WATER SUPPLIES
POLICY STATEMENT ON ARSENIC REMOVAL
INTERIM STANDARD - NITRATE REMOVAL USING SULFATE SELECTIVE ANION EXCHANGE RESIN
INTERIM STANDARD - USE OF CHLORAMINE DISINFECTANT FOR PUBLIC WATER SUPPLIES
INTERIM STANDARD ON MEMBRANE TECHNOLOGIES FOR PUBLIC WATER SUPPLIES
1.1.1 General Information
1.1.2 Extent of water works system
1.1.3 Justification of project
1.1.4 Soil, groundwater conditions, and foundation problems
1.1.5 Water use data
1.1.6 Flow requirements
1.1.7 Sources of water supply
1.1.8 Proposed treatment processes
1.1.9 Sewerage system available
1.1.10 Waste disposal
1.1.12 Project sites
1.1.14 Future extensions
PART 2 - GENERAL DESIGN CONSIDERATIONS
2.1 DESIGN BASIS
2.2 PLANT LAYOUT
2.3 BUILDING LAYOUT
2.4 LOCATION OF STRUCTURES
2.5 ELECTRICAL CONTROLS
2.6 STANDBY POWER
2.7 SHOP SPACE AND STORAGE
2.8 LABORATORY FACILITIES
2.9 MONITORING EQUIPMENT
2.10 SAMPLE TAPS
2.11 FACILITY WATER SUPPLY
2.12 WALL CASTINGS
2.14 PIPING COLOR CODE
2.16 OPERATION AND MAINTENANCE MANUAL
2.17 OPERATOR INSTRUCTION
2.20 FLOOD PROTECTION
2.21 CHEMICALS AND WATER CONTACT MATERIAL
2.22 OTHER CONSIDERATIONS
3.2.4 Testing and records
3.2.5 General well construction
3.2.6 Aquifer types and construction methods - Special conditions
3.2.7 Well pumps, discharge piping and appurtenances
4.2.1 Rapid rate gravity filters
4.2.2 Rapid rate pressure filters
4.2.3 Diatomaceous earth filtration
4.2.4 Slow sand filters
4.2.5 Direct filtration
4.2.6 Deep bed rapid rate gravity filters
4.2.7 Biologically active filters
4.3.1 Chlorination equipment
4.3.2 Contact time and point of application
4.3.3 Residual chlorine
4.3.4 Testing equipment
4.3.5 Chlorinator piping
4.3.8 Chlorine dioxide
4.3.9 Ultra violet light
4.3.10 Other disinfecting agents
4.5.1 Natural draft aeration
4.5.2 Forced or induced draft aeration
4.5.3 Spray aeration
4.5.4 Pressure aeration
4.5.5 Packed tower aeration
4.5.6 Other methods of aeration
4.5.7 Protection of aerators
4.5.10 Corrosion control
4.5.11 Quality control
4.6.1 Removal by oxidation, detention, and filtration
4.6.2 Removal by the lime-soda softening process
4.6.3 Removal by manganese-coated media filtration
4.6.4 Removal by ion exchange
4.6.5 Biological removal
4.6.6 Sequestration by polyphosphates
4.6.7 Sequestration by sodium silicates
4.6.8 Sampling taps
4.6.9 Testing equipment shall be provided for all plants
4.8.1 Carbon dioxide addition
4.8.2 Acid addition
4.8.4 “Split treatment”
4.8.5 Alkali feed
4.8.6 Carbon dioxide reduction by aeration
4.8.7 Other treatment
4.8.8 Water unstable due to biochemical action in distribution system
4.9.3 Chlorine dioxide
4.9.4 Powdered activated carbon
4.9.5 Granular activated carbon
4.9.6 Copper sulfate and other copper compounds
4.9.8 Potassium permanganate
4.9.10 Other methods
5.1 FEED EQUIPMENT
5.1.1 Feeder redundancy
5.1.3 Dry chemical feeders
5.1.4 Positive displacement solution pumps
5.1.5 Liquid chemical feeders - siphon control
5.1.6 Cross-connection control
5.1.7 Chemical feed equipment location
5.1.8 In-plant water supply
5.1.9 Storage of chemicals
5.1.10 Solution tanks
5.1.11 Day tanks
5.1.12 Feed lines
5.3 OPERATOR SAFETY
6.1.1 Site protection
6.2 PUMPING STATIONS
6.4 BOOSTER PUMPS
7.0.2 Location of reservoirs
7.0.3 Protection from contamination
7.0.4 Protection from trespassers
7.0.6 Stored Water Turnover
7.0.10 Roof and sidewall
7.0.11 Construction materials
7.0.14 Internal catwalk
7.0.15 Silt stop
7.0.17 Painting and/or cathodic protection
7.0.19 Provisions for sampling
8.2 SYSTEM DESIGN
The Great Lakes‑Upper Mississippi River Board of State and Provincial Public Health and Environmental Managers in 1950 created a Water Supply Committee consisting of one associate from each state represented on the Board. A representative from the Province of Ontario was added in 1978. Throughout this document the term state shall mean a representative state or the Province of Ontario. The Committee was assigned the responsibility for reviewing existing water works practices, policies, and procedures, and reporting its findings to the Board. The report of the Water Supply Committee was first published in 1953, and subsequently has been revised and published in 1962, 1968, 1976, 1982, 1987, 1992, 1997, 2003 and 2007.
This document includes the following:
1. Policy Statements ‑ Preceding the standards are policy statements of the Board concerning water works design, practice, or resource protection. Some policy statements recommend an approach to the investigation of innovative treatment processes which have not been included as part of the standards because sufficient confirmation has not yet been documented to allow the establishment of specific limitations or design parameters. Other policy statements recommend approaches, alternatives or considerations in addressing a specific water supply issue and may not develop into standards.
2. Interim Standards - Following the policy statements are interim standards. The interim standards give design criteria which are currently being used for new treatment processes, but the use of the criteria is limited and insufficient for recognition as a recommended standard.
3. Recommended Standards ‑ The Standards, consisting of proven technology, are intended to serve as a guide in the design and preparation of plans and specifications for public water supply systems, to suggest limiting values for items upon which an evaluation of such plans and specifications may be made by the reviewing authority, and to establish, as far as practicable, uniformity of practice. Because statutory requirements and legal authority pertaining to public water supplies are not uniform among the states, and since conditions and administrative procedures and policies also differ, the use of these standards must be adjusted to these variations.
The terms shall and must are used where practice is sufficiently standardized to permit specific delineation of requirements or where safeguarding of the public health justifies such definite action. Other terms, such as should, recommended, and preferred, indicate desirable procedures or methods, with deviations subject to individual consideration.
Most quantified items in this document are cited in US customary units and are rounded off at two significant figures. Metric equivalent quantities, also rounded off at two significant figures, follow in brackets where compound units are involved. The metric unit symbols follow International System conventions. In the event of a conflict between quantities in US units and the metric equivalent the quantity in US units shall take precedence.
It is not possible to cover recently developed processes and equipment in a publication of this type. However, the policy is to encourage, rather than obstruct, the development of new processes and equipment. Recent developments may be acceptable to individual states if they meet at least one of the following conditions: 1) have been thoroughly tested in full scale comparable installations under competent supervision, 2) have been thoroughly tested as a pilot plant operated for a sufficient time to indicate satisfactory performance, or 3) a performance bond or other acceptable arrangement has been
made so the owners or official custodians are adequately protected financially or otherwise in case of failure of the process or equipment.
The Board recognizes that many states, other than those of the Great Lakes‑Upper Mississippi River Board of State and Provincial Public Health and Environmental Managers, utilize this publication as part of their design requirements for water works facilities. The Board welcomes this practice as long as credit is given to the Board and to this publication as a source for the standards adopted. Suggestions from non‑member states are welcome and will be considered.
Adopted April, 1997
Revised April, 2007
PRE-ENGINEERED WATER TREATMENT PLANTS
Pre-engineered water treatment plants are becoming available and being used for production of potable water at public water systems. Many applications being proposed are for small systems having relatively clean surface water sources which are now being required to provide filtration under the federal Safe Drinking Water Act.
Pre-engineered water treatment plants are normally modular process units which are pre-designed for specific process applications and flow rates and purchased as a package. Multiple units may be installed in parallel to accommodate larger flows.
Pre-engineered treatment plants have numerous applications but are especially applicable at small systems where conventional treatment may not be cost effective. As with any design the proposed treatment must fit the situation and assure a continuous supply of safe drinking water for water consumers. The reviewing authority may accept proposals for pre-engineered water treatment plants on a case-by-case basis where they have been demonstrated to be effective in treating the source water being used. In most cases an applicant will be required to demonstrate, through pilot studies and/or other data, adequacy of the proposed plant for the specific application. A professional engineer is required to prepare plans and specifications for submittal to the reviewing authority for approval. It is recommended that a professional engineer be on site to oversee the installation and initial startup of pre-engineered water treatment plants.
Factors to be considered include:
1. Raw water quality characteristics under normal and worst case conditions. Seasonal fluctuations must be evaluated and considered in the design.
2. Demonstration of treatment effectiveness under all raw water conditions and system flow demands. This demonstration may be on-site pilot or full scale testing or testing off-site where the source water is of similar quality. On-site testing is required at sites having questionable water quality or applicability of the treatment process. The proposed demonstration project must be approved by the reviewing authority prior to starting.
3. Sophistication of equipment. The reliability and experience record of the proposed treatment equipment and controls must be evaluated.
4. Unit process flexibility which allows for optimization of treatment.
5. Operational oversight that is necessary. At surface water sources full-time operators are necessary, except where the reviewing authority has approved an automation plan. See Policy Statement on Automated/Unattended Operation of Surface Water Treatment Plants.
6. Third party certification or approvals such as National Sanitation Foundation (NSF), International Underwriters Laboratory (UL) or other acceptable ANSI accredited third parties for; a) treatment equipment and b) materials that will be in contact with the water.
7. Suitable pretreatment based on raw water quality and the pilot study or other demonstration of treatment effectiveness. Pretreatment may be included as an integral process in the pre-engineered module.
8. Factory testing of controls and process equipment prior to shipment.
9. Automated troubleshooting capability built into the control system.
10. Start-up and follow-up training and troubleshooting to be provided by the manufacturer or contractor.
11. Operation and maintenance manual. This manual must provide a description of the treatment, control and pumping equipment, necessary maintenance and schedule, and a troubleshooting guide for typical problems.
12. In addition to any automation, full manual override capabilities must be provided.
13. Cross-connection control including, but not limited to the avoidance of single wall separations between treated and partially or untreated surface water.
4.On-site and contractual laboratory capability. The on-site
testing must include all required continuous and daily testing as specified by
the reviewing authority. Contract testing may be considered for other
15.Manufacturers warranty and replacement guarantee. Appropriate safeguards for the water supplier must be included in contract documents. The reviewing authority may consider interim or conditional project approvals for innovative technology where there is sufficient demonstration of treatment effectiveness and contract provisions to protect the water supplier should the treatment not perform as claimed.
16.Water supplier revenue and budget for continuing operations, maintenance and equipment replacement in the future.
17. Life expectancy and long-term performance of the units based on the corrosivity of the raw and treated water and the treatment chemicals used.
Additional information on this topic is given in the State Alternative Technology Approval Protocol dated June 1996, which was developed by the Association of State Drinking Water Administrators, U.S. Environmental Protection Agency and various industry groups.
Adopted April, 1997
Revised April, 2006
AUTOMATED/UNATTENDED OPERATION OF SURFACE WATER TREATMENT PLANTS
Recent advances in computer technology, equipment controls and Supervisory Control and Data Acquisition (SCADA) Systems have brought automated and off-site operation of surface water treatment plants into the realm of feasibility. Coincidentally, this comes at a time when renewed concern for microbiological contamination is driving optimization of surface water treatment plant facilities and operations and finished water treatment goals are being lowered to levels of <0.1 NTU turbidity and <20 total particle counts per milliliter.
Review authorities encourage any measures, including automation, which assist operators in improving plant operations and surveillance functions.
Automation of surface water treatment facilities to allow unattended operation and off-site control presents a number of management and technological challenges which must be overcome before an approval can be considered. Each facet of the plant facilities and operations must be fully evaluated to determine what on-line monitoring is appropriate, what alarm capabilities must be incorporated into the design and what staffing is necessary. Consideration must be given to the consequences and operational response to treatment challenges, equipment failure and loss of communications or power.
An engineering report shall be developed as the first step in the process leading to design of the automation system. The engineering report to be submitted to review authorities must cover all aspects of the treatment plant and automation system including the following information/criteria:
1. Identify all critical features in the pumping and treatment facilities that will be electronically monitored, have alarms and can be operated automatically or off-site via the control system. Include a description of automatic plant shut-down controls with alarms and conditions which would trigger shut-downs. Dual or secondary alarms may be necessary for certain critical functions.
2. Automated monitoring of all critical functions with major and minor alarm features must be provided. Automated plant shutdown is required on all major alarms. Automated startup of the plant is prohibited after shutdown due to a major alarm. The control system must have response and adjustment capability on all minor alarms. Built-in control system challenge test capability must be provided to verify operational status of major and minor alarms.
3. The plant control system must have the capability for manual operation of all treatment plant equipment and process functions.
4. A plant flow diagram which shows the location of all critical features, alarms and automated controls to be provided.
5. Description of off-site control station(s) that allow observation of plant operations, receiving alarms and having the ability to adjust and control operation of equipment and the treatment process.
6. A certified operator must be on "standby duty" status at all times with remote operational capability and located within a reasonable response time of the treatment plant.
7. A certified operator must do an on-site check at least once per day to verify proper operation and plant security.
8. Description of operator staffing and training planned or completed in both process control and the automation system.
9. Operations manual which gives operators step by step procedures for understanding and using the automated control system under all water quality conditions. Emergency operations during power or communications failures or other emergencies must be included.
10. A plan for a 6 month or more demonstration period to prove the reliability of procedures, equipment and surveillance system. A certified operator must be on-duty during the demonstration period. The final plan must identify and address any problems and alarms that occurred during the demonstration period. Challenge testing of each critical component of the overall system must be included as part of the demonstration project.
11. Schedule for maintenance of equipment and critical parts replacement.
12. Sufficient finished water storage shall be provided to meet system demands and CT requirements whenever normal treatment production is interrupted as the result of automation system failure or plant shutdown.
13. Sufficient staffing must be provided to carry out daily on-site evaluations, operational functions and needed maintenance and calibration of all critical treatment components and monitoring equipment to ensure reliability of operations.
14. Plant staff must perform as a minimum weekly checks on the communication and control system to ensure reliability of operations. Challenge testing of such equipment should be part of normal maintenance routines.
15. Provisions must be made to ensure security of the treatment facilities at all times. Incorporation of appropriate intrusion alarms must be provided which are effectively communicated to the operator in charge.
Adopted April 1997
BAG AND CARTRIDGE FILTERS
FOR PUBLIC WATER SUPPLIES
Bag and cartridge technology has been used for some time in the food, pharmaceutical and industrial applications. This technology is increasingly being used by small public water supplies for treatment of drinking water. A number of states have accepted bag and cartridge technology as an alternate technology for compliance with the filtration requirements of the Surface Water Treatment Rule and the Long Term 1 Enhanced Surface Water Treatment Rule. In addition, bag and cartridge filters are included in the microbial toolbox options for meeting the Cryptosporidium treatment requirements of the Long Term 2 Enhance Surface Water Treatment Rule.
The particulate loading capacity of these filters is low, and once expended the bag or cartridge filter must be discarded. This technology is designed to meet the low flow requirement needs of small systems. The operational and maintenance cost of bag and cartridge replacement must be considered when designing a system. These filters can effectively remove particles from water in the size range of Giardia cysts (5-10 microns) and Cryptosporidium (2-5 microns).
At the present time, filtration evaluation is based on Cryptosporidium oocyst removal.
With this type of treatment there is no alteration of water chemistry. So, once the technology has demonstrated the required removal efficiency, no further pilot demonstration may be necessary. The demonstration of filtration is specific to a specific housing and a specific bag or cartridge filter. Any other combinations of different bags, cartridges, or housings will require additional demonstration of filter efficiency.
Treatment of a surface water should include source water protection, filtration, and disinfection.
The following items should be considered in evaluating the applicability of bag or cartridge filtration.
1. The filter housing and bag/cartridge filter must demonstrate a filter efficiency of at least 2-log reduction in particles size 2 micron and above. Demonstration of higher log removals may be required by the reviewing authority depending on raw water quality and other treatment steps to be employed. The reviewing authority will decide whether or not a pilot demonstration is necessary for each installation. This filtration efficiency demonstration may be accomplished by:
a. Microscopic particulate analysis, including particle counting , sizing and identification, which determines occurrence and removals of micro-organisms and other particle across a filter or system under ambient raw water source condition, or when artificially challenged.
b. Cryptosporidium particle removal evaluation in accordance with procedures specified in NSF Standard 53 or equivalent. These evaluations must be conducted by NSF or by another third-party whose certification would be acceptable to the reviewing authority.
c. “Protocol for Equipment Verification Testing for Physical Removal of Microbiological and Particulate Contaminants” procedure specified by the EPA/NSF Environmental Technology Verification Program.
d. Challenge testing procedure for bag and cartridge filters presented in Chapter 8 of the Long Term 2 Enhanced Surface Water Treatment Rule Toolbox Guidance Manual.
e. "Nonconsensus" live Cryptosporidium challenge studies that have been designed and carried
out by a third-party agent recognized and accepted by the reviewing authority
for interim evaluations. At the present time uniform protocol procedures for
live Cryptosporidium challenge studies have not been established.
f. Methods other than these that are approved by the reviewing authority.
2. System components such as housing, bags, cartridges, membranes, gaskets, and O-rings should be evaluated under NSF Standard 61 or equivalent, for leaching of contaminants. Additional testing may be required by the reviewing authority.
3. The source water or pre-treated water should have a turbidity less than 3 NTU.
4. The flow rate through the treatment process shall be monitored with a flow valve and meter. The flow rate through the bag/cartridge filter must not exceed the maximum flow rate verified by filtration efficiency testing.
5. Pretreatment is strongly recommended (if not required by the reviewing authority). This is to provide a more constant water quality to the bag/cartridge filter and to extend bag and cartridge life. Examples of pretreatment include media filters, larger opening bag/cartridge filters, infiltration galleries, and beach wells. Location of the water intake should be considered in the pretreatment evaluation.
6. Particle count analysis can be used to determine what level of pretreatment should be provided. It should be noted that particulate counting is a 'snap shot' in time and that there can be seasonal variations such as algae blooms, lake turnover, spring runoff, and heavy rainfall events that will give varied water quality.
7. It is recommended that chlorine or another disinfectant be added at the head of the treatment process to reduce/eliminate the growth of algae, bacteria, etc., on the filters. The impact on disinfection-by-product formation should be considered.
8. A filter to waste component is strongly recommended (if not required by the reviewing authority), for any pretreatment pressure sand filters. At the beginning of each filter cycle and/or after every backwash of the prefilters a set amount of water should be discharged to waste before water flows into the bag/cartridge filter. Filter to waste shall be provided for the final filter(s) and a set amount of water shall be discharged to waste after changing the filters.
9. If pressure media filters are used for pretreatment they must be designed according to Section 4.2.2.
10. A sampling tap shall be provided ahead of any treatment so a source water sample can be collected.
11. Pressure gages and sampling taps shall be installed before and after the media filter and before and after the bag/cartridge filter.
12. An automatic air release valve shall be installed on top of the filter housing.
13. Frequent start and stop operation of the bag or cartridge filter should be avoided. To avoid this frequent start and stop cycle the following options are recommended:
a. a slow opening and closing valve ahead of the filter to reduce flow surges.
b. reduce the flow through bag or cartridge filter to as low as possible to lengthen filter run times.
c. install a recirculating pump that pumps treated water back to a point ahead of the bag or cartridge filter. Care must be taken to make sure there is no cross connection between the finished water and raw water.
14. A minimum of two bag or cartridge filter housings should be provided for water systems that must provide water continuously.
15. A pressure relief valve should be incorporated into the bag or cartridge filter housing.
16. Complete automation of the treatment system is not required. Automation of the treatment plant should be incorporated into the ability of the water system to monitor the finished water quality. It is important that a qualified water operator is available to run the treatment plant.
17. A plan of action should be in place should the water quality parameters fail to meet EPA or the local reviewing authorities standards.
1. The filtration and backwash rates shall be monitored so that the prefilters are being optimally used.
2. The bag and cartridge filters must be replaced when a pressure difference of 30 psi or other pressure difference recommended by the manufacturer or the reviewing authority is observed. It should be noted that bag filters do not load linearly. Additional observation of the filter performance is required near the end of the filter run.
3. Maintenance (o-ring replacement) shall be performed in accordance with the manufacturers recommendations.
4. Sterile rubber gloves and a disposable face mask covering the nose and mouth should be worn when replacing or cleaning the cartridge or bag filters.
5. The filter system shall be properly disinfected and water shall be ran to waste each time the cartridge or bag filter vessels are opened for maintenance.
6. The following parameters should be monitored:
Flow rate, instantaneous
Flow rate, total
Adopted April, 1997
Revised April, 2007
ULTRA VIOLET LIGHT
FOR TREATMENT OF PUBLIC WATER SUPPLIES
The United States Environmental Protection Agency (EPA) has promulgated the Long Term 2 Enhanced Surface Water Treatment Rule (LT2ESWTR) to further reduce microbial contamination of drinking water. The rule requires additional treatment for some public water supplies based on their source water Cryptosporidium concentrations and current treatment practices. Ultraviolet Light (UV) disinfection is one option public water supplies have to comply with the additional treatment requirements. The EPA has released a document entitled ULTRAVIOLET DISINFECTION GUIDANCE MANUAL FOR THE FINAL LONG TERM 2 ENHANCED SURFACE WATER TREATMENT RULE. This guidance manual will be used as the basis for the validation, design, and operation of all UV systems used for public water systems and for the development of the recommended standards for those systems. UV disinfection may also be considered as primary disinfection for public water systems with microbiologically safe ground water and must meet the same requirements as UV systems used to meet LT2ESWTR. The reviewing authority shall be contacted regarding use of UV treatment.
Supplemental disinfection for additional virus inactivation or to provide a residual in the water distribution system may be required by the reviewing authority. When UV light treatment devices are used for non-health related purposes the UV device may provide doses less than indicated in the following criteria.
A. CRITERIA FOR UV WATER TREATMENT DEVICES
1. UV water treatment devices must be validated by a third-party entity in accordance with the USEPA Ultraviolet Light Disinfection Guidance Manual (USEPA UVDGM), the German Association for Gas and Water (UVGW), the Austrian Standards Institute (ONORM), the National Water Research Institute/ American Water Works Association Research Foundation (NWRI/AwwaRF), the Class A criteria under ANSI/NSF Standard 55 - Ultraviolet Microbiological Water Treatment Systems; or other standards acceptable to the reviewing authority. The validation must demonstrate that the unit is capable of providing a UV light dose of 40 millijoules per square centimeter (mJ/cm2). In addition to the requirements cited in the USEPA UVDGM each UV water treatment device shall meet the following;
a. The UV assemblies shall be accessible for visual observation, cleaning and replacement of the lamp, lamp jackets and sensor window/lens. A wiper assembly or chemical cleaning-in-place system may be installed to allow in-situ cleaning of lamp jackets. Adequate controls shall be in place to prevent contamination of the potable water with cleaning chemicals;
b. An automatic shutdown valve shall be installed in the water supply line ahead of the UV treatment system that will be activated whenever the water treatment system loses power or is tripped by a monitoring device when the dosage is below the validated operating design dose. When power is not being supplied to the UV unit the valve shall be in a closed (fail-safe) position.
c. The UV housing shall be stainless steel 304 or 316L;
2. A flow or time delay mechanism wired in series with the well or service pump shall be provided to permit a sufficient time for lamp warm-up per manufacturer recommendations before water flows from the unit upon startup. Where there are extended no-flow periods and fixtures are located a short distance downstream of the UV unit, consideration should be given to UV unit shutdown between operating cycles to prevent heat build-up in the water due to the UV lamp:
3. A sufficient number (required number plus one) of parallel UV treatment systems shall be provided to assure a continuous water supply when one unit is out of service unless other satisfactory disinfection can be provided when the unit is out of service;
4. No bypasses shall be installed;
5. All water from the well shall be treated. The well owner may request a variance to treat only that portion of the water supply that is used for potable purposes provided that the daily average and peak water use is determined and signs are posted at all non-potable water supply outlets.
6. The well or booster pump(s) shall have adequate pressure capability to maintain minimum water system pressure after the water treatment devices;
The reviewing authority will determine pre and post treatment on a specific case basis depending on raw water quality. See Section G for raw water quality limitations. If coliform bacteria or other microbiological organisms are present in the untreated water appropriate filtration shall be provided as minimum pretreatment. A 5 um sediment filter or equivalent is recommended for all UV installations.
C. ONLINE MONITORING, REPLACEMENT PARTS
UV light intensity of each installed unit shall be monitored continuously. Treatment units and the water system shall automatically shutdown if the UV dosage falls below the validated operating and approved design dose. Water systems that have source water exceeding 5 NTU turbidity may be required to install additional pretreatment and/or an online turbidimeter ahead of the UV water treatment device. An automatic shutdown valve shall be installed and operated in conjunction with the turbidimeter. Each owner shall have available on site at least one replacement lamp, a 5 micron replacement filter and, where applicable, a replacement cyst reduction filter and any other components necessary to keep the treatment system in service.
D. SEASONAL OPERATIONS
UV water treatment devices that are operated on a seasonal basis shall be inspected and cleaned prior to use at the start of each operating season. The UV water treatment system including the filters shall be disinfected prior to placing the water treatment system back into operation. A procedure for shutting down and starting up the UV treatment system shall be developed for or by each owner based upon manufacturer recommendations and submitted in writing to the review authority.
E. RECORD KEEPING AND ACCESS
A record shall be kept of the water quality test data, dates of lamp replacement and cleaning, a record of when the device was shutdown and the reason for shutdown, and the dates of prefilter replacement.
The reviewing authority shall have access to the UV water treatment system and records.
Water system owners will be required to submit operating reports and required sample results on a monthly or quarterly basis as required by the reviewing authority.
F. RAW WATER QUALITY CHARACTERISTICS
The water supply shall be analyzed for the following water quality parameters and the results shall be included in the UV application. Pretreatment is required for UV installations if the water quality exceeds any of the following maximum limits. When an initial sample exceeds a maximum limit, a check sample shall be taken and analyzed.
UV 254nm Absorption 0.155cm-1
Dissolved Iron 0.3 mg/L
Dissolved Manganese 0.05 mg/L
Hardness 120 mg/L
Hydrogen sulfide (if odor is present) Non-Detectable
Iron Bacteria None
pH 6.5 to 9.5
Suspended Solids 10 mg/L
Turbidity 1.0 NTU
Total Coliform 1,000/100 ML
E. Coli **
* Higher values may be acceptable to the reviewing authority if experience with similar water quality and reactors shows that adequate treatment is provided and there are no treatment problems or excessive maintenance required, or if the reactor was validated for parameters higher than these maximums.
** These organisms may indicate that the source is either a surface water or ground water under the direct influence of surface water and may require additional filtration pretreatment. Consult the reviewing authority for guidance.
Raw water quality shall be evaluated and pretreatment equipment shall be designed to handle water quality changes. Variable turbidity caused by rainfall events is of special concern.
Adopted April, 2003
Revised April, 2007
FOR PUBLIC WATER SUPPLIES
Review of public water system security infrastructure and practices has shown an industry-wide vulnerability to intentional acts of vandalism, sabotage and terrorism. Protection from these types of threats must be integrated into all design considerations. Many public drinking water systems have implemented effective security and operational changes to help address this vulnerability, but additional efforts are needed.
Security measures are needed to help ensure that public water suppliers attain an effective level of security. Design considerations need to address physical infrastructure security, and facilitate security related operational practices and institutional controls. Because drinking water systems cannot be made immune to all possible attacks, the design needs to address issues of critical asset redundancy, monitoring, response and recovery. All public water supplies need to identify and address security needs in design and construction for new projects and for retrofits of existing drinking water systems.
The following concepts and items should be considered in the design and construction of new water system facilities and improvements to existing water systems:
1. Security shall be an integral part of drinking water system design. Facility layout shall consider critical system assets and the physical needs of security for these assets. Requirements for submitting, identifying and disclosing security features of the design, and the confidentiality of the submission and regulatory review should be discussed with the reviewing authority.
2. The design should identify and evaluate single points of failure that could render a system unable to meet its design basis. Redundancy and enhanced security features should be incorporated into the design to eliminate single points of failure when possible, or to protect them when they cannot reasonably be eliminated.
3. Consideration should be made to ensure effective response and timely replacement of critical components that are damaged or destroyed. Critical components that comprise single points of failure (e.g., high volume pumps) that cannot be eliminated should be identified during design and given special consideration. Design considerations should include component standardization, availability of replacements and key parts, re-procurement lead times, and identification of suppliers and secure retention of component specifications and fabrication drawings. Readily replaceable components should be used whenever possible and provisions should be made for maintaining an inventory of critical parts.
4. Human access should be through controlled locations only. Intrusion deterrence measures (e.g., physical barriers such as fences, window grates and security doors; traffic flow and check-in points; effective lighting; lines of sight; etc.) should be incorporated into the facility design to protect critical assets and security sensitive areas. Effective intrusion detection should be included in the system design and operation to protect critical assets and security sensitive areas. All cameras and alarms installed for security purposes should include monitors at manned locations.
5. Vehicle access should be through controlled locations only. Physical barriers such as moveable barriers or ramps should be included in designs to keep vehicles away from critical assets and security sensitive areas. It should be impossible for any vehicle to be driven either intentionally or accidentally into or adjacent to finished water storage or critical components without facility involvement. Designated vehicle areas such as parking lots and drives should be separated from critical assets with adequate standoff distances to eliminate impacts to these assets from possible explosions of material in vehicles.
6. Sturdy, weatherproof, locking hardware must be included in the design of access for all tanks, vaults, wells, well houses, pump houses, buildings, power stations, transformers, chemical storage, delivery areas, chemical fill pipes, and similar facilities. Vents and overflows should be hardened through use of baffles or other means to prevent their use for the introduction of contaminants.
7. Computer based control technologies such as SCADA must be secured from unauthorized physical access and potential cyber attacks. Wireless and network based communications should be encrypted as deterrence to hijacking by unauthorized personnel. Vigorous computer access and virus protection protocols should be built into computer control systems. Effective data recovery hardware and operating protocols should be employed and exercised on a regular basis. All automated control systems shall be equipped with manual overrides to provide the option to operate manually. The procedures for manual operation including a regular schedule for exercising and insuring operator's competence with the manual override systems shall be included in facility operation plans.
8. Real time water quality monitoring with continuous recording and alarms should be considered at key locations to provide early warning of possible intentional contamination events.
9. Facilities and procedures for delivery, handling and storage of chemicals should be designed to ensure that chemicals delivered to and used at the facility cannot be intentionally released, introduced or otherwise used to debilitate a water system, its personnel, or the public. Particular attention should be given to potentially harmful chemicals used in treatment processes (e.g., strong acids and bases, toxic gases and incompatible chemicals) and on maintenance chemicals that may be stored on-site (e.g., fuels, herbicides, paints, solvents).
Adopted April, 2003
Revised April, 2007
Arsenic in groundwater is an issue that many water systems must deal with following the maximum contaminant level revision from 50 parts per billion (ppb) to 10 ppb on January 22, 2006. Several technologies are available to remove arsenic, from fairly simple to more complex. In much of the Upper Midwest, arsenic typically exists as As (III) in groundwater, and as As (V) in surface waters. Arsenic in the form of As (V) is easier to remove due to its insolubility and negative charge. Arsenic As (III) can be changed to As (V) by a simple oxidation process.
With the different removal technologies comes a wide range of monetary investment. In addition, the issue of discharging concentrated waste water and/or disposal of solid wastes must be resolved. The safe and proper disposal of all related treatment wastes must comply with all local, state, federal and provincial requirements. When the maximum contaminant limit (MCL) for arsenic is exceeded, it is recommended that the treatment is capable of reducing arsenic levels in the water to one-half the MCL (currently 5 ppb) or less. The following list provides information on different types of typical arsenic treatment technologies and options for optimization:
Adsorptive Media - Uses metal oxide coatings, usually iron, titanium or aluminum, on the filter media to remove arsenic. Pre- and post-adjustment of pH will enhance removal rates and reduce corrosivity. This method needs chemical oxidation of arsenic, iron and manganese (if present), a pre-filter to remove iron and manganese to prevent fouling of the adsorptive media (if iron levels are too high [near or above 1.0 ppm]), followed by the adsorptive filter media. Costs for implementing this technology may be low to moderate if a system currently has an iron and/or manganese filter. High levels of iron, sulfate, and dissolved solids may cause interference or reduce the treatment efficiency.
Oxidation/Filtration (Iron & Manganese removal) - This method uses chemical oxidation of arsenic, iron and manganese with free chlorine, potassium permanganate (KMnO4), ozone or manganese dioxide with a manganese greensand, anthracite, pyrolusite, or other proprietary filter media. The water is allowed detention time and filtration after chemical oxidation. Water with low iron (less than a 20 to 1 ratio of iron to arsenic) may need additional iron in the form of ferric chloride or ferric sulfate to increase arsenic removal efficiencies.
Coagulation/Filtration - Typically chemical oxidation of arsenic, iron and manganese, pre- and post-adjustment of pH (to enhance coagulation; reduce corrosivity), the use of ferric chloride, ferric sulfate, or alum as a coagulant, use a polymer (filter aid or enhanced coagulation), and settling time (sedimentation) to remove arsenic. Other contaminants may be removed in this process. Sulfate may cause interference or reduce treatment efficiency.
Other Types of Treatment Technologies
Anion Exchange - Chloride (strong-base) sulfate-selective or nitrate-selective resins, are used to remove contaminants. This process may also require the chemical oxidation of arsenic, iron and manganese (if present), and pre-filters to maximize contaminant removal, and to prevent fouling of the exchange resin. Post-treatment adjustment of pH is required to reduce corrosivity. Treatment columns may be in parallel or series (avoid sulfate, nitrate and arsenic breakthrough, and avoid lowered pH breakthrough immediately after regeneration). Treatment may use anion exchange after cation exchange to remove hardness (mixed beds not recommended - anion resins are lighter and column becomes service intensive). Other contaminants that can be removed include sulfate (sulfate-selective resins); nitrate (nitrate-selective resins); and hardness (mixed cation/anion beds). Iron, sulfate, and dissolved solids may cause interference or reduce treatment efficiency.
Electrodialysis/Electrodialysis Reversal - Uses an electrical charge of a reverse osmosis (R.O.) membrane to remove arsenic. Chemical oxidation of arsenic, iron and manganese with filtration is used to remove oxidized iron and manganese to prevent fouling of the R.O. membrane. Pre- and post-adjustment of pH may be needed to prevent scaling, to enhance filtration, and to reduce corrosivity. Other contaminants that may be removed using this technology include hardness, dissolved solids, nitrates, and sulfates. If iron and manganese are too high, this may cause interference with the arsenic removal process.
Membrane Filtration (Micro, Ultra, Nanofiltration, and Reverse Osmosis) - Membrane removal utilizes chemical pre-oxidation (except when using polypropylene membranes), a pre-filter to remove oxidized iron and manganese to prevent fouling of the membranes), pre- and post-adjust pH (prevent scaling, enhance filtration; reduce corrosivity). The treatment can also use ferric chloride or ferric sulfate as a coagulant. Iron, manganese, and other dissolved solids may cause interference or reduce treatment efficiency. Reverse osmosis membranes will also remove hardness in the water.
Lime Softening - This technology is based on the optimization of Mg(OH)2 precipitation. High iron concentrations are desired for optimal arsenic removal. Waters with low dissolved iron may require the addition of ferric chloride or ferric sulfate. Hardness may also be removed in this process. Other issues include the disposal of lime sludge, and the high labor intensity of handling lime.
Adopted April, 2007
USING SULFATE SELECTIVE
ANION EXCHANGE RESIN
Four treatment processes are generally considered acceptable for Nitrate/Nitrite removal. These are anion exchange, reverse osmosis, nanofiltration and electrodialysis. Although these treatment processes, when properly designed and operated will reduce the nitrate/nitrite concentration of the water to acceptable levels, primary consideration shall be given to reducing the nitrate/nitrite levels of the raw water through either obtaining water from an alternate water source or through watershed management. Reverse osmosis nanofiltration or electrodialysis should be investigated when the water has high levels of sulfate or when the chloride content or dissolved solids concentration is of concern.
Most anion exchange resins used for nitrate removal are sulfate selective resins. Although nitrate selective resins are available, these resins typically have a lower total exchange capacity.
If a sulfate selective anion exchange resin is used beyond bed exhaustion, the resin will continue to remove sulfate from the water by exchanging the sulfate for previously removed nitrates resulting in treated water nitrate levels being much higher than raw water levels. Therefore it is extremely important that the system not be operated beyond design limitations.
An evaluation shall be made to determine if pretreatment of the water is required if the combination of iron, manganese, and heavy metals exceeds 0.1 milligrams per liter.
Anion exchange units are typically of the pressure type, down flow design. Although a pH spike can typically be observed shortly before bed exhaustion, automatic regeneration based on volume of water treated should be used unless justification for alternate regeneration is submitted to and approved by the reviewing authority. A manual override shall be provided on all automatic controls. A minimum of two units must be provided. The total treatment capacity must be capable of producing the maximum day water demand at a level below the nitrate/nitrite MCL. If a portion of the water is bypassed around the unit and blended with the treated water, the maximum blend ratio allowable must be determined based on the highest anticipated raw water nitrate level. If a bypass is provided, a totaling meter and a proportioning or regulating device or flow regulating valves must be provided on the bypass line.
Anion exchange media will remove both nitrates and sulfate from the water being treated. The design capacity for nitrate and sulfate removal expressed as CaCO3 should not exceed 16,000 grains per cubic foot (37g/l) when the resin is regenerated with 10 pounds of salt per cubic foot (160 g/l) of resin when operating at 2 to 3 gallons per minute per cubic foot (0.27 to 0.4 L/min per litre). However, if high levels of chlorides exist in the raw water, the exchange capacity of the resin should be reduced to account for the chlorides.
The treatment flow rate should not exceed 7 to 8 gallons per minute per square foot of bed area (29 to 32 cm/minute down flow rate). The back wash flow rate should be 2 to 3 gallons per minute per square foot of bed area (8 to 12 cm/minute rise rate) with a fast rinse approximately equal to the service flow rate.
Adequate freeboard must be provided to accommodate the backwash flow rate of the unit.
The system shall be designed to include an adequate under drain and supporting gravel system, brine distribution equipment, and cross connection control.
When ever possible, the treated water nitrate/nitrite level should be monitored using continuous monitoring and recording equipment. The continuous monitoring equipment should be equipped with a high nitrate level alarm. If continuous monitoring and recording equipment is not provided, the finished water nitrate/nitrite levels must be determined (using a test kit) no less than daily, preferably just prior to regeneration of the unit.
Generally, waste from the anion exchange unit should be disposed in accordance with Section 4.11.2 of these Standards. However, prior to any discharge, the reviewing authority must be contacted for wastewater discharge limitations or NPDES requirements.
Certain types of anion exchange resins can tolerate no more than 0.05 mg/L free chlorine. When the applied water will contain a chlorine residual, the anion exchange resin must be a type that is not damaged by residual chlorine.
Adopted April, 1997
Revised April, 2007
USE OF CHLORAMINE DISINFECTANT
FOR PUBLIC WATER SUPPLIES
Chloramination is an application of ammonia and chlorine, with ammonia addition usually downstream of the application of chlorine at a proper mass ratio of chlorine to ammonia to produce a combined chlorine residual predominantly in form of monochloramine. Proper chlorine to ammonia ratio must be maintained to prevent the formation of dichloramine and trichloramine which create taste and odor in drinking water.
Monochloramine is rarely suitable for use as a primary disinfectant because it requires very long contact time to achieve adequate disinfection at the normally used concentration. Because of its high persistence characteristics, monochloramine is more commonly used to maintain a chlorine residual in the water distribution system as a secondary disinfectant.
Chloramine residual is more stable and longer lasting than free chlorine, and it provides better protection against bacterial re-growth in water distribution systems including large storage tanks, lower flow demand and dead-end water mains. As a result, it is more effective in controlling biofilm growth in the water distribution system. Chloramine is not as reactive as chlorine with organic material in water, thereby producing substantially less disinfection by-products such as trihalomethanes in the water distribution system. However, chloramine may provide less protection from contamination of the distribution system through cross connections, water main breaks and other causes.
Unlike most substances added to water for treatment purposes, chloramine cannot be prepared at high concentrations. It can only be made by addition of ammonia to pre-chlorinated water or by adding chlorine to water containing low concentrations of ammonia. Contact of high concentrations of chlorine with ammonia or ammonium salts must be avoided to prevent the formation of nitrogen trichloride which is a sensitive and violently explosive substance.
Operating authorities who wish to modify disinfectant practices by using chloramine must show the reviewing authority clear evidence that bacteriological and chemical protection of consumers will not be compromised in any way and that aspects of chloramination mentioned below are considered in any permit application.
1. Chloramine, which is less powerful than free chlorine, may be suitable for disinfection of some ground water supplies but it is inadequate in strength for primary disinfection of surface waters.
2. Chloramine can be suitable for protecting potable water in distribution systems against bacterial contamination. The chloramine tends to remain active for longer periods and at greater distances from the plant than free chlorine. Chloramine concentrations should be maintained higher than for chlorine to avoid nitrifying bacterial activity. A range of 1-2 mg/L, measured as combined chlorine, on entry to the distribution system and greater than 1 mg/L at the system extremities is recommended. Chloramine can be less odorous than chlorine so these concentrations may be tolerated well by consumers.
3. Suitable commercial sources of ammonia for chloramine production are either ammonia gas or water solutions of ammonia or ammonium sulphate. Ammonia gas is supplied as compressed liquid in cylinders which must be stored in separate facilities designed as for chlorine gas. Ammonia solutions must be stored in containment with adequate cooling to prevent gas release from storage and gas release must be handled with pressure relief systems. Absorption/neutralization systems for ammonia gas leaks/spills must be designed specially for ammonia. Ammonium sulphate is available as free flowing powdered solid which must be stored in cool dry conditions and dissolved in water for use.
4. Thorough and reasonably rapid mixing of chlorine and ammonia in the main plant stream shall be arranged so as to avoid formation of organic chloramines and of odorous dichloramine. Sufficient ammonia must be added to provide at least a small excess (more than one part of ammonia to between 3 and 5 parts of chlorine) over that required to convert all the free chlorine present to chloramine.
5. Addition of ammonia gas or ammonia solution will increase the pH of the water and addition of ammonium sulphate depresses the pH. The actual pH shift may be small in well buffered water but the effects on disinfectant power and corrosiveness of the water may require consideration. Ammonia gas forms alkaline solutions which may cause local plugging by lime deposition. Where hard water is to be treated, a side stream of pre-softened water may be needed for ammonia dilution so as to reduce plugging problems.
6. The use of chloramine in distribution systems which are not well maintained by flushing, swabbing and other regular routine maintenance activities can lead to local loss of disinfectant residual, increased nitrifying bacterial activity and, possibly over a period of time, to persistent high coliform bacterial counts which may not respond to reversion to the use of free chlorine. Early detection of nitrifying bacteria activity may be made by checking for reduced dissolved oxygen, elevated free ammonia, elevated HPC, and elevated nitrite and nitrate levels.
7. Chloramine in water is considerably more toxic to fish and other aquatic organisms than free chlorine. Consideration must therefore be given to the potential for leaks to contaminate and damage natural water course eco-systems. Kidney dialysis treatment can be upset by use of chloraminated water. Medical authorities, hospitals and commercial and domestic aquarium keepers should be notified so they can arrange for precautions to be taken.
Policy Statement Adopted April, 1997
Re-Adopted as Interim Standard April, 2003
MEMBRANE TECHNOLOGIES FOR PUBLIC WATER SUPPLIES
Membrane technologies have a wide range of applications from the use of reverse osmosis for desalination, inorganic compound removal, and radionuclide removal to the use of lower pressure membranes for removal of surface water contaminants such as giardia and cryptosporidium. Membrane technologies are typically separated into four categories based on membrane pore size: reverse osmosis, nanofiltration, ultrafiltration, and microfiltration. When using membranes for treatment of surface water or groundwater under the direct influence of surface water the reviewing agency should be contacted to determine inactivation/removal credits for the specific membrane and treatment objective.
The following items should be considered when evaluating the applicability of membrane processes.
1. Treatment objectives. The selection of the specific membrane process should be matched to the desired treatment objectives. Removal is generally related to pore size and as such the larger pore size membranes are not appropriate for applications such as inorganic compound or radionuclide removal.
2. Water quality considerations. A review of historical source raw water quality data, including turbidity and/or particle counts, seasonal changes, organic loading, microbial activity, and temperature differentials as well as other inorganic and physical parameters should be conducted. The data should be used to determine feasibility and cost of the system. The degree of pre-treatment may also be ascertained from the data. Design considerations and membrane selection at this phase must also address the issue of target removal efficiencies and system recovery versus acceptable transmembrane pressure differentials. On surface water supplies, pre-screening or cartridge filtration may be required. The source water temperature can significantly impact the flux of the membrane under consideration. At low water temperatures, the flux can be reduced appreciably (due to higher water viscosity and resistance of the membrane to permeate), possibly impacting process economics by the number of membrane units required for a full scale facility. Seasonal variation of design flow rates may be based on documented lower demand during colder weather.
3. Pilot study/preliminary investigations. Prior to initiating the design of a membrane treatment facility, the reviewing agency should be contacted to determine if a pilot plant study will be required. In most cases, a pilot plant study will be required to determine the best membrane to use, the need for pretreatment, type of post treatment, the bypass ratio, the amount of reject water, system recovery, process efficiency, particulate/organism removal efficiencies, cold and warm water flux, fouling potential, operating and transmembrane pressure and other design and monitoring considerations. Any virus removal credit must also be documented through an appropriate piloting process. The reviewing authority should be contacted prior to conducting the pilot study to establish the protocol to be followed.
4. Challenge Testing. Membranes treating surface waters or groundwater under the direct influence of a surface water must be challenge tested to establish a product specific maximum Cryptosporidium log removal credit.
5. Pretreatment. Acceptable feedwater characteristics are dependent on the type of membrane and operational parameters of the system. Without suitable pretreatment or acceptable feed water quality, the membrane may become fouled or scaled and consequently shorten its useful life. For reverse osmosis and nanofiltration processes pretreatment is usually needed for turbidity reduction, iron or manganese removal, stabilization of the water to prevent scale formation, microbial control, chlorine removal (for certain membrane types), and pH adjustment. Usually, at a minimum, cartridge filters should be provided for the protection of the reverse osmosis or nanofiltration membranes against particulate matter.
6. Membrane materials. Two types of membranes are typically used for reverse osmosis and nanofiltration. These are cellulose acetate based and polyamide composites. Membrane configurations typically include tubular, spiral wound and hollow fiber. Microfiltration (MF) and nanofiltration (NF) membranes are most commonly made from organic polymers such as: cellulose acetate, polysulfones, polyamides, polypropylene, polycarbonates, and polyvinylidene. The physical configurations include: hollow fiber, spiral wound, and tubular. Operational conditions and useful life vary depending on type of membrane selected, quality of feed water, and process operating parameters. Some membrane materials are incompatible with certain oxidants. If the system must rely on pre-treatment oxidants for other purposes, for example, zebra mussel control, taste and odor control, or iron and manganese oxidation, the selection of the membrane material becomes a significant design consideration.
7. Useful life of membranes. Membrane replacement represents a major component in the overall cost of water production The life expectancy of a particular membrane under consideration should be evaluated during the pilot study or from other relevant available data. Membrane life may also be reduced by operating at consistently high fluxes. Membrane replacement frequency is a significant factor in operation and maintenance cost comparisons in the selection of the process
8. Treatment efficiency. Reverse osmosis (RO) and nanofiltration (NF) are highly efficient in removing metallic salts and ions from the raw water. Efficiencies, however, do vary depending on the ion being removed and the membrane utilized. For most commonly encountered ions, removal efficiencies will range from 85% to over 99%. Organics removal is dependent on the molecular weight, shape and charge of the organic molecule and the pore size of the membrane utilized. Removal efficiencies may range from as high as 99% to less than 30%, depending on the membrane type and organic being considered.
9. Power consumption. Power consumption may be a significant coast factor for reverse osmosis plants. The power consumption of a particular membrane under consideration should be evaluated during the pilot study or from other relevant data.
10. Bypass water. Reverse osmosis (RO) permeate will be virtually demineralized. Nanofiltration (NF) permeate may also contain less dissolved minerals than desirable. The design should provide for a portion of the raw water to bypass the unit to maintain stable water within the distribution system and to improve process economics as long as the raw water does not contain unacceptable contaminants. Alternative filtration is required for bypassed surface water or ground water under the direct influence of surface water.
11. Reject water. Reject water from reverse osmosis and nanofiltration membranes may range from 10% to 50% of the raw water pumped to the reverse osmosis unit. For most brackish waters and ionic contaminant removal applications, reject is in the 10-25% range while for seawater it could be as high as 50%. The reject volume should be evaluated in terms of the source availability and from the waste treatment availabilities. The amount of reject water from a unit may be reduced to a limited extent by increasing the feed pressure to the unit. However, this may result in a shorter membrane life. Acceptable methods of waste disposal typically include discharge to a municipal sewer system, to waste treatment facilities, or to an evaporation pond.
12. Backflushing or cross flow cleansing. Automated periodic backflushing and cleaning is employed on microfiltraion and ultrafiltration on a timed basis or once a target transmembrane pressure differential has been reached. Back flushing volumes can range from 5 -15 percent of the permeate flow depending upon the frequency of flushing/cleaning and the degree of fouling and this should be considered in the treatment system sizing and the capacity of the raw water source
13. Membrane cleaning. The membrane must be periodically cleaned with acid, detergents and possibly disinfection. Method of cleaning and chemicals used must be approved by the state reviewing agency. Care must be taken in the cleaning process to prevent contamination of both the raw and finished water system. Cleaning chemicals, frequency and procedure should follow membrane manufacturer’s guidelines. Cleaning chemicals should be NSF/ANSI Standard 60 certified.
14. Membrane integrity and finished water monitoring. An appropriate level of direct and indirect integrity testing is required to routinely evaluate membrane and housing integrity and overall filtration performance. Direct integrity testing may include pressure and vacuum decay tests for MF& UF and marker-based tests for NF & RO. These are usually conducted at least once per day. Indirect monitoring options may include particle counters and/or turbidity monitors and should be done continuously. Consult the appropriate regulatory agency regarding specific process monitoring requirements.
15. Cross connection control. Cross connection control considerations must be incorporated into the system design, particularly with regard to chemical feeds and waste piping used for membrane cleaning, waste stream and concentrate. Typical protection includes block & bleed valves on the chemical cleaning lines and air gaps on the drain lines.
16. Redundancy of critical components. Redundancy of critical control components including but not limited to valves, air supply, and computers shall be required as per the reviewing authority.
17. Post treatment. Post treatment of water treated using reverse osmosis or nanofiltration typically includes degasification for carbon dioxide (if excessive) and hydrogen sulfide removal (if present), pH and hardness adjustment for corrosion control and disinfection as a secondary pathogen control and for distribution system protection.
18. Operator training. The ability to obtain qualified operators must be evaluated in selection of the treatment process. The necessary operator training shall be provided prior to plant startup.
Interim Standard Adopted April, 2007
All reports, final plans specifications, and design criteria should be submitted at least 60 days prior to the date on which action by the reviewing authority is desired. Environmental Assessments, and permits for construction, to take water, for waste discharges, for stream crossings, etc., may be required from other federal, state, or local agencies. Preliminary plans and the engineer's report should be submitted for review prior to the preparation of final plans. No approval for construction can be issued until final, complete, detailed plans and specifications have been submitted to the reviewing authority and found to be satisfactory. Documents submitted for formal approval shall include but not be limited to:
a. engineer’s report, where pertinent,
b. summary of the design criteria,
c. operation requirements, where applicable,
d. general layout,
e. detailed plans,
g. cost estimates.
h. water purchase contracts between water supplies, where applicable,
i. other information as required by reviewing authority.
Where the Design/Build construction concept is to be utilized, special consideration must be given to: designation of a project coordinator; close coordination of design concepts and submission of plans and necessary supporting information to the reviewing authority; allowance for project changes that may be required by the reviewing authority; and reasonable time for project review by the reviewing authority.
The engineer's report for water works improvements shall, where pertinent, present the following
a. description of the existing water works and sewerage facilities,
b. identification of the municipality or area served,
c. name and mailing address of the owner or official custodian.
d. imprint of professional engineer's seal or conformance with engineering registration
requirements of the individual state or province.
a. description of the nature and extent of the area to be served,
b. provisions for extending the water works system to include additional areas,
c. appraisal of the future requirements for service, including existing and potential industrial, commercial, institutional, and other water supply needs.
Where two or more solutions exist for providing public water supply facilities, each of which is feasible and practicable, discuss the alternatives. Give reasons for selecting the one recommended, including financial considerations, operational requirements, operator qualifications, reliability, and water quality considerations.
a. the character of the soil through which water mains are to be laid,
b. foundation conditions prevailing at sites of proposed structures,
c. the approximate elevation of ground water in relation to subsurface structures.
a. a description of the population trends as indicated by available records, and the estimated
population which will be served by the proposed water supply system or expanded system 20 years in the future in five year intervals or over the useful life of critical structures/equipment,
b. present water consumption and the projected average and maximum daily demands,
including fire flow demand (see Section 1.1.6),
c. present and/or estimated yield of the sources of supply,
d. unusual occurrences.
a. hydraulic analyses based on flow demands and pressure requirements (See Section 8.1.1)
b. fire flows, when fire protection is provided, meeting the recommendations of the Insurance
Services Office or other similar agency for the service area involved.
Describe the proposed source or sources of water supply to be developed, the reasons for their selection, and provide information as follows:
a. hydrological data, stream flow and weather records,
b. safe yield, including all factors that may affect it,
c. maximum flood flow, together with approval for safety features of the spillway and dam
from the appropriate reviewing authority,
d. description of the watershed, noting any existing or potential sources of contamination
(such as highways, railroads, chemical facilities, land/water use activities, etc.) which may affect water quality,
e. summarized quality of the raw water with special reference to fluctuations in quality,
changing meteorological conditions, etc.
f. source water protection issues or measures, including erosion and siltation control structures, that need to be considered or implemented.
a. sites considered,
b. advantages of the site selected,
c. elevations with respect to surroundings,
d. probable character of formations through which the source is to be developed,
e. geologic conditions affecting the site, such as anticipated interference between proposed and existing wells,
f. summary of source exploration, test well depth, and method of construction; placement
of liners or screen; test pumping rates and their duration; water levels and specific yield;
g. sources of possible contamination such as sewers and sewage treatment/disposal facilities, highways, railroads, landfills, outcroppings of consolidated water‑bearing formations, chemical facilities, waste disposal wells, agricultural uses, etc.
Summarize and establish the adequacy of proposed processes and unit parameters for the
treatment of the specific water under consideration. Alternative methods of water treatment
and chemical use should be considered as a means of reducing waste handling and disposal
problems. Bench scale test, pilot studies, or demonstrations may be required to establish
adequacy for some water quality standards.
Describe the existing sewerage system and sewage treatment works, with special reference to
their relationship to existing or proposed water works structures which may affect the operation of the water supply system, or which may affect the quality of the supply.
Discuss the various wastes from the water treatment plant, their volume, proposed treatment
and points of discharge. If discharging to a sanitary sewerage system, verify that the system,
including any lift stations, is capable of handling the flow to the sewage treatment works and that
the treatment works is capable and will accept the additional loading.
Provide supporting data justifying automatic equipment, including the servicing and operator training to be provided. Manual override must be provided for any automatic controls. Highly sophisticated automation may put proper maintenance beyond the capability of the plant operator, leading to equipment breakdowns or expensive servicing. Adequate funding must be assured for maintenance of automatic equipment.
a. discussion of the various sites considered and advantages of the recommended ones,
b. the proximity of residences, industries, and other establishments,
c. any potential sources of pollution that may influence the quality of the supply or interfere with
effective operation of the water works system, such as sewage absorption systems, septic tanks, privies, cesspools, sink holes, sanitary landfills, refuse and garbage dumps, etc.
a. estimated cost of integral parts of the system,
b. detailed estimated annual cost of operation,
c. proposed methods to finance both capital charges and operating expenses.
Summarize planning for future needs and services.
Plans for waterworks improvements shall, where pertinent, provide the following:
a. suitable title,
b. name of municipality, or other entity or person responsible for the water supply,
c. area or institution to be served,
e. north point,
f. datum used,
g. boundaries of the municipality or area to be served,
h. date, name, and address of the designing engineer,
i. imprint of professional engineer's seal or conformance with engineering registration
requirements of the individual state,
j. legible prints suitable for reproduction,
k. location and size of existing water mains,
l. location and nature of existing water works structures and appurtenances affecting the
proposed improvements, noted on one sheet.
a. stream crossings, providing profiles with elevations of the stream bed and the normal and
extreme high and low water levels,
b. profiles having a horizontal scale of not more than 100 feet to the inch and a vertical scale
of not more than 10 feet to the inch, with both scales clearly indicated,
c. location and size of the property to be used for the groundwater development with respect
to known references such as roads, streams, section lines, or streets,
d. topography and arrangement of present or planned wells or structures, with contour intervals not greater than two feet,
e. elevations of the highest known flood level, floor of the structure, upper terminal of protective
casings and outside surrounding grade, using United States Coast and Geodetic Survey,
United States Geological Survey or equivalent elevations where applicable as reference,
f. plat and profile drawings of well construction, showing diameter and depth of drill holes,
casing and liner diameters and depths, grouting depths, elevations and designation of geological formations, water levels and other details to describe the proposed well completely,
g. location of all existing and potential sources of pollution which may affect the water source
or underground treated water storage facilities,
h. size, length, and materials of proposed water mains,
i. location of existing or proposed streets; water sources, ponds, lakes, and drains; storm,
sanitary, combined and house sewers; septic tanks, disposal fields and cesspools,
j. schematic flow diagrams and hydraulic profiles showing the flow through various plant units,
k. piping in sufficient detail to show flow through the plant, including waste lines,
l. locations of all chemical storage areas, feeding equipment and points of chemical application (see Part 5),
m. all appurtenances, specific structures, equipment, water treatment plant waste disposal units
and points of discharge having any relationship to the plans for water mains and/or water works structures,
n. locations of sanitary or other facilities, such as lavatories, showers, toilets, and lockers, when applicable or required by the reviewing authority,
o. locations, dimensions, and elevations of all proposed plant facilities,
p. locations of all sampling taps,
q. adequate description of any features not otherwise covered by the specifications.
Complete, detailed technical specifications shall be supplied for the proposed project, including
a. a program for keeping existing water works facilities in operation during construction of additional facilities so as to minimize interruption of service,
b. laboratory facilities and equipment,
c. the number and design of chemical feeding equipment (see Section 5.1),
d. procedures for flushing, disinfection and testing, as needed, prior to placing the project in service,
e. materials or proprietary equipment for sanitary or other facilities including any necessary backflow or back‑siphonage protection.
A summary of complete design criteria shall be submitted for the proposed project, containing but not limited to the following:
a. long‑term dependable yield of the source of supply,
b. reservoir surface area, volume, and a volume‑versus‑depth curve, if applicable,
c. area of watershed, if applicable,
d. estimated average and maximum day water demands for the design period,
e. number of proposed services,
f. fire fighting requirements,
g. flash mix, flocculation and settling basin capacities,
h. retention times,
i. unit loadings,
j. filter area and the proposed filtration rate,
k. backwash rate,
l. feeder capacities and ranges.
m. minimum and maximum chemical application rates.
Any substantial deviations from approved plans or specifications must be approved by the reviewing authority before such changes are made. These include, but are not limited to deviations in: capacity, hydraulic conditions, operating units, the functioning of water treatment processes, or the quality of water to be delivered. Revised plans or specifications should be submitted in time to permit the review and approval of such plans or specifications before any construction work, which will be affected by such changes, is begun.
The reviewing authority may require additional information which is not part of the construction drawings, such as head loss calculations, proprietary technical data, copies of deeds, copies of contracts, etc.
The design of a water supply system or treatment process encompasses a broad area. Application of this part is dependent upon the type of system or process involved.
The system including the water source and treatment facilities shall be designed for maximum day
demand at the design year.
Design shall consider
a. functional aspects of the plant layout,
b. provisions for future plant expansion,
c. provisions for expansion of the plant waste treatment and disposal facilities,
d. access roads,
e. site grading,
f. site drainage,
i. chemical delivery.
Design shall provide for:
a. adequate ventilation,
b. adequate lighting,
c. adequate heating,
d. adequate drainage,
e. dehumidification equipment, if necessary,
f. accessibility of equipment for operation, servicing, and removal,
g. flexibility of operation,
h. operator safety,
i. convenience of operation,
j. chemical storage and feed equipment in a separate room to reduce hazards and dust problems.
The appropriate regulating authority must be consulted regarding any structure which is so located that normal or flood stream flows may be impeded.
Main switch gear electrical controls shall be located above grade, in areas not subject to flooding. All electrical work shall conform to the requirements of the National Electrical Code or to relevant state and/or local codes.
Dedicated Standby power shall be required by the reviewing authority so that water may be treated and/or pumped to the distribution system during power outages to meet the average day demand. Alternatives to dedicated standby power may be considered by the reviewing authority with proper justification.
Carbon monoxide detectors are recommended when fuel-fired generators are housed.
Adequate facilities should be included for shop space and storage consistent with the designed
Each public water supply shall have its own equipment and facilities for routine laboratory testing necessary to ensure proper operation. Laboratory equipment selection shall be based on the characteristics of the raw water source and the complexity of the treatment process involved. Laboratory test kits which simplify procedures for making one or more tests may be acceptable. An operator or chemist qualified to perform the necessary laboratory tests is essential. Analyses conducted to determine compliance with drinking water regulations must be performed in an appropriately certified laboratory in accordance with Standard Methods for the Examination of Water and Wastewater or approved alternative methods. Persons designing and equipping laboratory facilities shall confer with the reviewing authority before beginning the preparation of plans or the purchase of equipment. Methods for verifying adequate quality assurances and for routine calibration of equipment should be provided.
As a minimum, the following laboratory equipment shall be provided:
a. Surface water supplies shall provide the necessary facilities for microbiological testing of
water from both the treatment plant and the distribution system. The reviewing authority may allow deviations from this requirement.
b. Surface water supplies shall have a nephelometric turbidimeter meeting the requirements of
Standard Methods for the Examination of Water and Wastewater.
c. Each surface water treatment plant utilizing flocculation and sedimentation, including
those which lime soften, shall have a pH meter, jar test equipment, and titration equipment for both hardness and alkalinity.
d. Each ion‑exchange softening plant, and lime softening plant treating only groundwater
shall have a pH meter and titration equipment for both hardness and alkalinity.
e. Each iron and/or manganese removal plant shall have test equipment capable of
accurately measuring iron to a minimum of 0.1 milligrams per liter, and/or test equipment
capable of accurately measuring manganese to a minimum of 0.05 milligrams per liter.
f. Public water supplies which chlorinate shall have test equipment for determining both free
and total chlorine residual by methods in Standard Methods for the Examination of Water and Wastewater.
g. Public water supplies which fluoridate shall have test equipment for determining fluoride
by methods in Standard Methods for the Examination of Water and Wastewater.
h. Public water supplies which feed poly and/or orthophosphates shall have test equipment
capable of accurately measuring phosphates from 0.1 to 20 milligrams per liter.
Sufficient bench space, adequate ventilation, adequate lighting, storage room, laboratory sink, and auxiliary facilities shall be provided. Air conditioning may be necessary.
Water treatment plants should be provided with equipment (including recorders, where applicable) to monitor the water as follows:
a. Plants treating surface water and ground water under the direct influence of surface water should have the capability to monitor and record turbidity, free chlorine residual, water temperature and pH at locations necessary to evaluate adequate CT disinfection, and other important process control variables as determined by the reviewing authority. Continuous monitoring and recording may be required.
b. Plants treating ground water using iron removal and/or ion exchange softening should have the capability to monitor and record free chlorine residual.
c. Ion exchange plants for nitrate removal should continuously monitor and record the treated water nitrate level.
Sample taps shall be provided so that water samples can be obtained from each water source and from appropriate locations in each unit operation of treatment, and from the finished water. Taps shall be consistent with sampling needs and shall not be of the petcock type. Taps used for obtaining samples for bacteriological analysis shall be of the smooth-nosed type without interior or exterior threads, shall not be of the mixing type, and shall not have a screen, aerator, or other such appurtenance.
The facility water supply service line and the plant finished water sample tap shall be supplied from a
source of finished water at a point where all chemicals have been thoroughly mixed, and the required disinfectant contact time has been achieved (see Section 4.3.2). There shall be no cross‑connections between the facility water supply service line and any piping, troughs, tanks, or other treatment units containing wastewater, treatment chemicals, raw or partially treated water.
Consideration shall be given to providing extra wall castings built into the structure to facilitate future
uses whenever pipes pass through walls of concrete structures.
All water supplies shall have an acceptable means of measuring the flow from each source, the
washwater, the recycled water, any blended water of different quality, and the finished water.
To facilitate identification of piping in plants and pumping stations it is recommended that the following color scheme be utilized:
Raw or Recycle Olive Green
Settled or Clarified Aqua
Finished or Potable Dark Blue
Alum or Primary Coagulant Orange
Carbon Slurry Black
Caustic Yellow with Green Band
Chlorine (Gas and Solution) Yellow
Chlorine Dioxide Yellow with Violet Band
Fluoride Light Blue with Red Band
Lime Slurry Light Green
Ozone Yellow with Orange Band
Phosphate Compounds Light Green with Red Band
Polymers or Coagulant Aids Orange with Green Band
Potassium Permanganate Violet
Soda Ash Light Green with Orange Band
Sulfuric Acid Yellow with Red Band
Sulfur Dioxide Light Green with Yellow Band
Backwash Waste Light Brown
Sludge Dark Brown
Sewer (Sanitary or Other) Dark Gray
Compressed Air Dark Green
Other Lines Light Gray
For liquids or gases not listed above, a unique color scheme and labeling should be used. In situations where two colors do not have sufficient contrast to easily differentiate between them, a six‑inch band of contrasting color should be on one of the pipes at approximately 30 inch intervals. The name of the liquid or gas should also be on the pipe. In some cases it may be advantageous to provide arrows indicating the direction of flow.
All wells, pipes, tanks, and equipment which can convey or store potable water shall be disinfected in accordance with current AWWA procedures. Plans or specifications shall outline the procedure and include the disinfectant dosage, contact time, and method of testing the results of the procedure.
An operation and maintenance manual including a parts list and parts order form, operator safety procedures and an operational trouble-shooting section shall be supplied to the water works as part of any proprietary unit installed in the facility.
Provisions shall be made for operator instruction at the start‑up of a plant or pumping station.
Consideration must be given to the safety of water plant personnel and visitors. The design must comply with all applicable safety codes and regulations that may include the Uniform Building Code, Uniform Fire Code, National Fire Protection Association Standards, and state and federal OSHA standards. Items to be considered include noise arresters, noise protection, confined space entry, protective equipment and clothing, gas masks, safety showers and eye washes, handrails and guards, warning signs, smoke detectors, toxic gas detectors and fire extinguishers.
Security measures shall be installed and instituted as required by the reviewing authority. Appropriate design measures to help ensure the security of water system facilities shall be incorporated. Such measures, as a minimum, shall include means to lock all exterior doorways, windows, gates and other entrances to source, treatment and water storage facilities. Other measures may include fencing, signage, close circuit monitoring, real-time water quality monitoring, and intrusion alarms.
Other than surface water intakes, all water supply facilities and water treatment plant access roads shall be protected to at least the 100 year flood elevation or maximum flood of record, as required by the reviewing authority. A freeboard factor may also be required by the reviewing authority.
Chemicals and water contact materials shall be approved by the reviewing authority or meet the
appropriate ANSI/AWWA and/or ANSI/NSF standards.
Consideration must be given to the design requirements of other federal, state, and local regulatory
agencies for items such as safety requirements, special designs for the handicapped, plumbing and
electrical codes, construction in the flood plain, etc.
In selecting the source of water to be developed, the designing engineer must prove to the satisfaction of the reviewing authority that an adequate quantity of water will be available, and that the water which is to be delivered to the consumers will meet the current requirements of the reviewing authority with respect to microbiological, physical, chemical and radiological qualities. Each water supply should take its raw water from the best available source which is economically reasonable and technically possible.
A surface water source includes all tributary streams and drainage basins, natural lakes and artificial reservoirs or impoundments above the point of water supply intake. A source water protection plan enacted for continued protection of the watershed from potential sources of contamination shall be provided as determined by the reviewing authority.
The quantity of water at the source shall
a. be adequate to meet the maximum projected water demand of the service area as shown
by calculations based on a one in fifty year drought or the extreme drought of record, and
should include consideration of multiple year droughts. Requirements for flows downstream of the intake shall comply with requirements of the appropriate reviewing authority,
b. provide a reasonable surplus for anticipated growth,
c. be adequate to compensate for all losses such as silting, evaporation, seepage, etc.,
d. be adequate to provide ample water for other legal users of the source.
A sanitary survey and study shall be made of the factors, both natural and man made, which may affect water quality. Such survey and study shall include, but not be limited to
a. determining possible future uses of impoundments or reservoirs,
b. determining degree of control of watershed by owner,
c. assessing degree of hazard to the supply by agricultural, industrial, recreational, and
residential activities in the watershed, and by accidental spillage of materials that may be toxic, harmful or detrimental to treatment processes,
d. assessing all waste discharges (point source and non point sources) and activities that could impact the water supply. The location of each waste discharge shall be shown on a scale map,
e. obtaining samples over a sufficient period of time to assess the microbiological, physical,
chemical and radiological characteristics of the water,
f. assessing the capability of the proposed treatment process to reduce contaminants to
g. consideration of currents, wind and ice conditions, and the effect of confluencing streams.
a. The design of the water treatment plant must consider the worst conditions that may exist
during the life of the facility.
b. The minimum treatment required shall be determined by the reviewing authority.
c. Filtration preceded by appropriate pretreatment shall be provided for all surface waters.
Exemptions may be approved by the reviewing authority on a case‑by‑case basis.
a. withdrawal of water from more than one level if quality varies with depth,
b. separate facilities for release of less desirable water held in storage,
c. where frazil ice may be a problem, holding the velocity of flow into the intake structure
to a minimum, generally not to exceed 0.5 feet per second,
d. inspection of manholes every 1000 feet for pipe sizes large enough to permit visual
e. occasional cleaning of the inlet line,
f. adequate protection against rupture by dragging anchors, ice, etc.,
g. ports located above the bottom of the stream, lake or impoundment, but at sufficient
depth to be kept submerged at low water levels,
h. where shore wells are not provided, a diversion device capable of keeping large
quantities of fish or debris from entering an intake structure,
i when buried surface water collectors are used, sufficient intake opening area must be
provided to minimize inlet headloss. Particular attention should be given to the selection of backfill material in relation to the collector pipe slot size and gradation of the native material over the collector system.
a. have motors and electrical controls located above grade, and protected from flooding as
required by the reviewing authority
b. be accessible,
c. be designed against flotation,
d. be equipped with removable or traveling screens before the pump suction well,
e. provide for introduction of chlorine or other chemicals in the raw water transmission main if necessary for quality control,
f. have intake valves and provisions for backflushing or cleaning by a mechanical device
and testing for leaks, where practical,
g. have provisions for withstanding surges where necessary,
is a facility into which water is pumped during periods of good quality and high stream flow
for future release to treatment facilities. These off-stream raw water storage reservoirs shall be constructed to assure that
a. water quality is protected by controlling runoff into the reservoir,
b. dikes are structurally sound and protected against wave action and erosion,
c. intake structures and devices meet requirements of Section 22.214.171.124,
d. point of influent flow is separated from the point of withdrawal,
e. separate pipes are provided for influent to and effluent from the reservoir.
If it is determined that chemical treatment is warranted for the control of zebra mussels:
a. Chemical treatment shall be in accordance with Chapter 5 of the Recommended Standards for Water Works and shall be acceptable to the reviewing authority.
b. Plant safety items, including but not limited to ventilation, operator protective equipment, eyewashes/showers, cross connection control, etc. shall be provided.
c. Solution piping and diffusers shall be installed within the intake pipe or in a suitable carrier pipe. Provisions shall be made to prevent dispersal of chemical into the water environment outside the intake. Diffusers shall be located and designed to protect all intake structure components.
d. A spare solution line should be installed to provide redundancy and to facilitate the use of alternate chemicals.
e. The chemical feeder shall be interlocked with plant system controls to shut down automatically when the raw water flow stops.
f. When alternative control methods are proposed for the control of zebra mussels, appropriate piloting or demonstration studies, satisfactory to the reviewing authority, may be required.
a. removal of brush and trees to high water elevation,
b. protection from floods during construction,
c. abandonment of all wells which will be inundated, in accordance with requirements of the reviewing authority.
a. approval from the appropriate regulatory agencies of the safety features for stability and
b. a permit from an appropriate regulatory agency for controlling stream flow or installing
a structure on the bed of a stream or interstate waterway.
Water supply dams shall be designed and constructed in accordance with the requirements of the appropriate regulatory agency.
Adequate security should be provided to prevent unauthorized access to vulnerable components. Specific consideration should be given to installation of fencing, locks, surveillance cameras, etc.
A groundwater source includes all water obtained from dug, drilled, bored or driven wells, and infiltration lines.
The total developed groundwater source capacity, unless otherwise specified by the reviewing authority, shall equal or exceed the design maximum day demand with the largest producing well out of service.
A minimum of two sources of groundwater shall be provided, unless otherwise specified by the reviewing authority. Consideration should be given to locating redundant sources in different aquifers or different locations of an aquifer.
a. To ensure continuous service when the primary power has been interrupted, a standby
power supply shall be provided through
1. connection to at least two independent public power sources, or
2. dedicated portable or in‑place auxiliary power of adequate supply and connectivity.
b. When automatic pre‑lubrication of pump bearings is necessary, and an auxiliary power
supply is provided, the pre‑lubrication line shall be provided with a valved by‑pass around the automatic control, or the automatic control shall be wired to the emergency power source.
a. After disinfection of each new, modified or reconditioned groundwater source, one or more water samples shall be submitted to a laboratory satisfactory to the reviewing authority for microbiological analysis with satisfactory results reported to such agency prior to placing the well into service.
b. A ground water under the direct influence of surface water determination acceptable to
the reviewing authority shall be provided for all new wells.
a. Every new, modified or reconditioned groundwater source shall be examined for applicable physical, chemical and radiological characteristics as required by the reviewing authority by tests of a representative sample in a laboratory satisfactory to the reviewing authority, with results reported to such authority.
b. Samples shall be collected at the conclusion of the test pumping procedure and
examined as soon as practical.
c. Field determinations of physical and chemical constituents or special sampling
procedures may be required by the reviewing authority.
The reviewing authority shall be consulted prior to design and construction regarding a
proposed well location as it relates to required separation between existing and potential sources of contamination and groundwater development. The well location should be selected to minimize the impact on other wells and other water resources.
Continued sanitary protection of the well site from potential sources of contamination shall
be provided either through ownership, zoning, easements, leasing or other means acceptable
to the reviewing authority. Fencing of the site may be required by the reviewing authority.
A wellhead protection plan for continued protection of the wellhead from potential sources
of contamination shall be provided as determined by the reviewing authority.
a. A yield and drawdown test shall be conducted in accordance with a protocol pre-approved by the reviewing authority.
b. The test shall be performed on every production well after construction or subsequent
treatment and prior to placement of the permanent pump.
c. The test methods shall be clearly indicated in the project specifications.
d. The test pump should have a capacity at least 1.5 times the flow anticipated at maximum anticipated drawdown.
e. The test shall provide, as a minimum, for continuous pumping for at least 24 hours at the
design pumping rate or until stabilized drawdown has continued for at least six hours when test pumped at 1.5 times the design pumping rate, or as required by the reviewing authority.
f. The following data shall be submitted to the reviewing authority:
1. test pump capacity‑head characteristics,
2. static water level,
3. depth of test pump setting,
4. time of starting and ending each test cycle, and
5. the zone of influence for the well or wells.
g. A report shall be submitted which provides recordings and graphic evaluation of the following at one hour intervals or less as may be required by the reviewing authority:
1. pumping rate,
2. pumping water level,
3. drawdown, and
4. water recovery rate and levels.
h. At the discretion of the reviewing authority, more comprehensive testing may be required.
a. Every well shall be tested for plumbness and alignment in accordance with AWWA
b. The test method and allowable tolerance shall be clearly stated in the specifications.
c. If the well fails to meet these requirements, it may be accepted by the engineer if it does
not interfere with the installation or operation of the pump or uniform placement of grout.
a. be determined from samples collected at 5‑foot intervals and at each pronounced change in formation,
b. be recorded and samples submitted to the appropriate authority,
c. be supplemented with a driller=s log, accurate geographical location such as latitude and longitude or GIS coordinates, and other information on accurate records of drillhole diameters and depths, assembled order of size and length of casing, screens and liners, grouting depths, formations penetrated, water levels, and location of any blast charges.
The owner of each well shall retain all records pertaining to each well, until the well has been properly abandoned.
a. not impart any toxic substances to the water or promote bacterial contamination,
b. be acceptable to the reviewing authority.
Minimum protected depths of drilled wells shall provide watertight construction to such depth
as may be required by the reviewing authority, to
a. exclude contamination, and
b. seal off formations that are, or may be, contaminated or yield undesirable water.
Temporary steel casing used for construction shall be capable of withstanding the structural
load imposed during its installation and removal.
a. be new single steel casing pipe meeting AWWA Standard A‑100, ASTM or API
specifications for water well construction,
b. have minimum weights and thickness indicated in Table I,
c. have additional thickness and weight if minimum thickness is not considered sufficient
to assure reasonable life expectancy of a well,
d. be capable of withstanding forces to which it is subjected,
e. be equipped with a drive shoe when driven, and
f. have full circumferential welds or threaded coupling joints.
The reviewing authority may approve the use of PVC casing for all or for limited applications. Where approved, PVC casing, as a minimum,
a. shall be new pipe meeting ASTM F480 and ANSI/NSF Standard 61 and be appropriately marked;
b. shall have a minimum wall thickness equivalent to SDR (standard dimension ratio) 21; however, diameters of 8 inches or greater or deep wells may require greater thickness to meet collapse strength requirements;
c. shall not be used at sites where permeation by hydrocarbons or degradation may occur;
d. shall be properly stored in a clean area free from exposure to direct sunlight;
e. shall be assembled using couplings or solvent welded joints; all couplings and solvents shall meet ANSI/NSF Standard 14, ASTM F480, or similar requirements; and
f. shall not be driven.
a. Approval of the use of any nonferrous material as well casing shall be subject to
special determination by the reviewing authority prior to submission of plans and specifications.
b. Nonferrous material proposed as a well casing must be resistant to the corrosiveness of the water and to the stresses to which it will be subjected during installation, grouting and operation.
Packers shall be of material that will not impart taste, odor, toxic substances or bacterial contamination to the well water. Lead packers shall not be used.
a. be constructed of materials resistant to damage by chemical action of
groundwater or cleaning operations,
b. have size of openings based on sieve analysis of formation and/or gravel pack
c. have sufficient length and diameter to provide adequate specific capacity and low aperture entrance velocity. Usually the entrance velocity should not exceed 0.1 feet per second,
d. be installed so that the pumping water level remains above the screen under all
e. where applicable, be designed and installed to permit removal or replacement without adversely affecting water‑tight construction of the well, and
f. be provided with a bottom plate or washdown bottom fitting of the same material as the screen.
All permanent well casing shall be surrounded by a minimum of 1 1/2 inches of grout to the depth required by the review authority. Other forms of grouting may be approved for driven casing. All temporary construction casings shall be removed. Where removal is not possible or practical, the casing shall be withdrawn at least five feet to ensure grout contact with the native formation.
a. Neat cement grout
1. Cement conforming to AWWA A100, and water, with not more than six gallons of water per 94 pounds of cement, must be used for 1 1/2 inch openings.
2. Additives may be used to increase fluidity subject to approval by the reviewing authority.
b. Concrete grout
1. Equal parts of cement conforming to AWWA A100, and sand, with not more than six gallons of water per 94 pounds of cement may be used for
openings larger than 1½ inches.
2. Where an annular opening larger than four inches is available, gravel not larger than one‑half inch in size may be added.
c. Bentonite, where allowed by the reviewing authority.
This is a mixture of water and commercial sodium-bentonite clay manufactured for the purpose of water well grouting. Bentonite mixtures shall contain no less than 20 percent bentonite solids. Organic polymers used in the grout mixtures must meet ANSI/NSF Standard 60.
d. Clay seal
Where an annular opening greater than six inches is available a clay seal of clean local clay mixed with at least 10 per cent swelling bentonite may be used when approved by the reviewing authority.
1. Sufficient annular opening shall be provided to permit a minimum of 1½ inches of grout around permanent casings, including couplings.
2. Prior to grouting through creviced or fractured formations, bentonite or similar
materials may be added to the annular opening, in the manner indicated for grouting.
3. When the annular opening is less than four inches, grout shall be installed under pressure by means of a grout pump from the bottom of the annular opening upward in one continuous operation until the annular opening is filled.
4. When the annular opening is four or more inches and less than 100 feet in depth, and concrete grout is used, it may be placed by gravity through a grout pipe installed to the bottom of the annular opening in one continuous operation until the annular opening is filled.
5. When the annular opening exceeds six inches, is less than 100 feet in depth, and a clay seal is used, it may be placed by gravity.
6. After cement grouting is applied, work on the well shall be discontinued until the cement or concrete grout has properly set.
7. Grout placement must be sufficient to achieve proper density or percent solids throughout the annular space.
The casing must be provided with sufficient guides welded to the casing to permit unobstructed flow and uniform thickness of grout.
a. Permanent casing for all groundwater sources shall project at least 12 inches above the pumphouse floor or concrete apron surface and at least 18 inches above final ground surface.
b. Where a well house is constructed, the floor surface shall be at least six inches above the final ground elevation.
c. Sites subject to flooding shall be provided with an earth mound to raise the
pumphouse floor to an elevation at least two feet above the highest known flood elevation, or other suitable protection as determined by the reviewing authority.
d. The top of the well casing at sites subject to flooding shall terminate at least three feet above the 100 year flood level or the highest known flood elevation, whichever is higher, or as the reviewing authority directs.
e. Protection from physical damage shall be provided as required by the reviewing authority.
a. Every well shall be developed to remove the native silts and clays, drilling mud or
finer fraction of the gravel pack.
b. Development should continue until the maximum specific capacity is obtained from the completed well.
c. Where chemical conditioning is required, the specifications shall include provisions for the method, equipment, chemicals, testing for residual chemicals, and disposal of waste and inhibitors.
d. Where blasting procedures may be used, the specifications shall include the
provisions for blasting and cleaning. Special attention shall be given to assure that the grouting and casing are not damaged by the blasting.
a. shall be provided after completion of work, if a substantial period elapses prior to test pumping or placement of permanent pumping equipment, and
b. shall be provided after placement of permanent pumping equipment.
c. shall be done in accordance with AWWA C654 or method approved by the reviewing authority.
a. A welded metal plate or a threaded cap is the preferred method for capping a well.
All well caps, temporary or permanent, shall be effectively located/sealed against the entrance of water and contaminants.
b. At all times during the progress of work, the contractor shall provide protection to
prevent tampering with the well or entrance of foreign materials.
a. Test wells and groundwater sources which are not in use shall be sealed by such methods as necessary to restore the controlling geological conditions which existed prior to construction or as directed by the appropriate regulatory agency.
b. Wells to be abandoned shall
1. be sealed to prevent undesirable exchange of water from one aquifer to another,
2. preferably be filled with neat cement grout,
3. have fill materials other than cement grout or concrete, disinfected and free of
foreign materials, and
4. when filled with cement grout or concrete, these materials shall be applied to the well hole through a pipe, tremie, or bailer.
a. If clay or hard pan is encountered above the water bearing formation, the permanent casing and grout shall extend through such materials.
b. If a sand or gravel aquifer is overlaid only by permeable soils the permanent
casing and grout shall extend to at least 25 feet below original or final ground elevation, whichever is lower. Excavation of topsoil around the well casing should be avoided.
c. If a temporary outer casing is used, it shall be completely withdrawn as grout is
a. Gravel pack shall be well rounded particles, 95 per cent siliceous material, that are
smooth and uniform, free of foreign material, properly sized, washed and then disinfected immediately prior to or during placement.
b. Gravel pack shall be placed in one uniform continuous operation.
c. Gravel refill pipes, when used, shall be Schedule 40 steel pipe incorporated within the pump foundation and terminated with screwed or welded caps at least 12 inches above the pump house floor or concrete apron.
d. Gravel refill pipes located in the grouted annular opening shall be surrounded by
a minimum of 1 1/2 inches of grout.
e. Protection from leakage of grout into the gravel pack or screen shall be provided.
f. Permanent inner and outer casings shall meet requirements of Section 126.96.36.199.
g. Minimum casing and grouted depth shall be acceptable to the reviewing authority.
a. Locations of all caisson construction joints and porthole assemblies shall be indicated.
b. The caisson wall shall be reinforced to withstand the forces to which it will be
c. Radial collectors shall be in areas and at depths approved by the reviewing authority.
d. Provisions shall be made to assure that radial collectors are essentially horizontal.
e. The top of the caisson shall be covered with a watertight floor.
f. All openings in the floor shall be curbed and protected from entrance of foreign
g. The pump discharge piping shall not be placed through the caisson walls. In unique situations where this is not feasible, a water tight seal must be obtained at the wall.
a. Infiltration lines should be considered only where geological conditions preclude the possibility of developing an acceptable drilled well.
b. The area around infiltration lines shall be under the control of the water purveyor for a distance acceptable to or required by the reviewing authority.
c. Flow in the lines shall be by gravity to the collecting well.
d. Water from infiltration lines shall be considered as groundwater under the direct
influence of surface water unless demonstrated otherwise.
a. Where the depth of unconsolidated formations is more than 50 feet, the permanent
casing shall be firmly seated in uncreviced or unbroken rock. Grouting requirements shall be determined by the reviewing authority.
b. Where the depth of unconsolidated formations is less than 50 feet, the depth of
casing and grout shall be at least 50 feet or as determined by the reviewing authority.
a. Shall require special consideration by the reviewing authority where there is an
absence of an impervious confining layer.
b. Flow shall be controlled. Overflows shall discharge at least 18 inches above grade and flood level, and be visible. Discharge shall be to an effective drainage structure.
c. Permanent casing and grout shall be provided.
d. If erosion of the confining bed appears likely, special protective construction may be required by the reviewing authority.
Wells equipped with line shaft pumps shall
a. have the casing firmly connected to the pump structure or have the casing inserted
into a recess extending at least one‑half inch into the pump base,
b. have the pump foundation and base designed to prevent water from coming into
contact with the joint, and
c. avoid the use of oil lubrication at pump settings less than 400 feet. Lubricants must meet ANSI/NSF Standard 61 or be approved by the reviewing authority.
Where a submersible pump is used
a. the top of the casing shall be effectively sealed against the entrance of water under all conditions of vibration or movement of conductors or cables, and
b. the electrical cable shall be firmly attached to the riser pipe at 20 foot intervals or less.
a. The discharge piping shall
1. be designed so that the friction loss will be low,
2. have control valves and appurtenances located above the pumphouse floor when an above‑ground discharge is provided,
3. be protected against the entrance of contamination,
4. be equipped with a check valve in or at the well, a shutoff valve, a pressure
gauge, a means of measuring flow, and a smooth nosed sampling tap located at a point where positive pressure is maintained,
5. where applicable, be equipped with an air release‑vacuum relief valve located
upstream from the check valve, with exhaust/relief piping terminating in a down‑turned position at least 18 inches above the floor and covered with a 24 mesh corrosion resistant screen,
6. be valved to permit test pumping and control of each well,
7. have all exposed piping, valves and appurtenances protected against physical
damage and freezing,
8. be properly anchored to prevent movement, and
9. be protected against surge or water hammer.
b. The discharge piping should be provided with a means of pumping to waste, but shall not be directly connected to a sewer.
a. The reviewing authority must be contacted for approval of specific applications of
b. Pitless units shall
1. be shop‑fabricated from the point of connection with the well casing to the unit cap or cover,
2. be threaded or welded to the well casing,
3. be of watertight construction throughout,
4. be of materials and weight at least equivalent and compatible to the casing,
5. have field connection to the lateral discharge from the pitless unit of threaded,
flanged or mechanical joint connection, and
6. terminate at least 18 inches above final ground elevation or three feet above the 100 year flood level or the highest known flood elevation, whichever is higher, or as the reviewing authority directs.
c. The design of the pitless unit shall make provision for
1. access to disinfect the well,
2. a properly constructed casing vent meeting the requirements of Section 188.8.131.52,
3. facilities to measure water levels in the well (see Section 184.108.40.206),
4. a cover at the upper terminal of the well that will prevent the entrance of
5. a contamination‑proof entrance connection for electrical cable,
6. an inside diameter as great as that of the well casing, up to and including casing diameters of 12 inches, to facilitate work and repair on the well, pump, or well screen, and
7. at least one check valve within the well casing or in compliance with requirements of the reviewing authority.
d. If the connection to the casing is by field weld, the shop‑assembled unit must be
designed specifically for field welding to the casing. The only field welding permitted will be that needed to connect a pitless unit to the casing.
Pitless adapters may be acceptable at the discretion of the reviewing authority. The use of any pitless adapter must be pre-approved by the reviewing authority.
Provisions shall be made for venting the well casing to atmosphere. The vent shall terminate in a downturned position, at or above the top of the casing or pitless unit, no less than 12 inches above grade or floor, in a minimum 1½ inch diameter opening covered with a 24 mesh, corrosion resistant screen. The pipe connecting the casing to the vent shall be of adequate size to provide rapid venting of the casing. Where vertical turbine pumps are used, vents into the side of the casing may be necessary to provide adequate well venting; installation of these vents shall be in accordance with the requirements of the reviewing authority.
a. Provisions shall be made for periodic measurement of water levels in the completed well.
b. Where pneumatic water level measuring equipment is used it shall be made using
corrosion resistant materials attached firmly to the drop pipe or pump column and in such a manner as to prevent entrance of foreign materials.
a. constructed in accordance with the requirements for permanent wells if they are to
remain in service after completion of a water supply well, and
b. protected at the upper terminal to preclude entrance of foreign materials.
The design of treatment processes and devices shall depend on evaluation of the nature and quality of the particular water to be treated, seasonal variations, the desired quality of the finished water and the mode of operation planned.
Clarification is generally considered to consist of any process or combination of processes which reduces the concentration of suspended matter in drinking water prior to filtration.
Plants designed to reduce suspended solids concentrations prior to filtration shall
a. provide a minimum of two units each for coagulation, flocculation and solids removal,
b. permit operation of the units either in series or parallel where softening is performed and should permit series or parallel operation where plain clarification is performed,
c. be constructed to permit units to be taken out of service without disrupting operation, and with drains or pumps sized to allow dewatering in a reasonable period of time,
d. provide multiple‑stage treatment facilities when required by the reviewing authority,
e. be started manually following shutdown,
f. minimize hydraulic head losses between units to allow future changes in processes without the need for repumping.
Waters containing high turbidity may require pretreatment, usually sedimentation either with or without the addition of coagulation chemicals.
a. Basin design ‑ Presedimentation basins should have hopper bottoms or be equipped with continuous mechanical sludge removal apparatus, and provide arrangements for dewatering.
b. Inlet ‑ Incoming water shall be dispersed across the full width of the line of travel as quickly as possible; short‑circuiting must be prevented.
c. Bypass ‑ Provisions for bypassing presedimentation basins shall be included.
d. Detention time ‑ Three hours detention is the minimum period recommended; greater
detention may be required.
Coagulation shall mean a process using coagulant chemicals and mixing by which colloidal and suspended material are destabilized and agglomerated into settleable or filterable flocs, or both. The engineer shall submit the design basis for the velocity gradient (G value) selected, considering the chemicals to be added and water temperature, color and other related water quality parameters. For surface water plants using direct or conventional filtration, the use of a primary coagulant is required at all times
a. Mixing – The detention period should not be more than thirty seconds with mixing equipment capable of imparting a minimum velocity gradient (G) of at least 750 fps/ft. The design engineer should determine the appropriate G value and detention time through jar testing.
b. Equipment ‑ Basins should be equipped with devices capable of providing adequate mixing for all treatment flow rates. Static mixing may be considered where the flow is relatively constant and will be high enough to maintain the necessary turbulence for complete chemical reactions.
c. Location ‑ The coagulation and flocculation basins shall be as close together as possible.
Flocculation shall mean a process to enhance agglomeration or collection of smaller floc particles into larger, more easily settleable or filterable particles through gentle stirring by hydraulic or mechanical means.
a. Basin Design ‑ Inlet and outlet design shall minimize short‑circuiting and destruction of floc. Series compartments are recommended to further minimize short-circuiting and to provide decreasing mixing energy with time. Basins shall be designed so that individual basins may be isolated without disrupting plant operation. A drain and/or pumps shall be provided to handle dewatering and sludge removal.
b. Detention – The detention time for floc formation should be at least 30 minutes with consideration to using tapered (i.e., diminishing velocity gradient) flocculation. The flow‑through velocity should be not less than 0.5 nor greater than 1.5 feet per minute.
c. Equipment ‑ Agitators shall be driven by variable speed drives with the peripheral speed of paddles ranging from 0.5 to 3.0 feet per second. External, non-submerged motors are preferred.
d. Piping ‑ Flocculation and sedimentation basins shall be as close together as possible. The velocity of flocculated water through pipes or conduits to settling basins shall be not less than 0.5 nor greater than 1.5 feet per second. Allowances must be made to minimize turbulence at bends and changes in direction.
e. Other designs ‑ Baffling may be used to provide for flocculation in small plants only after consultation with the reviewing authority. The design should be such that the velocities and flows noted above will be maintained.
f. Superstructure ‑ A superstructure over the flocculation basins may be required.
Sedimentation shall follow flocculation unless otherwise approved by the reviewing agency. The detention time for effective clarification is dependent upon a number of factors related to basin design and the nature of the raw water. The following criteria apply to conventional gravity sedimentation units:
a. Detention time ‑ shall provide a minimum of four hours of settling time. This may be reduced to two hours for lime‑soda softening facilities treating only groundwater. Reduced sedimentation time may also be approved when equivalent effective settling is demonstrated or when overflow rate is not more than 0.5 gpm per square foot (1.2 m/hr).
b. Inlet devices ‑ Inlets shall be designed to distribute the water equally and at uniform velocities. Open ports, submerged ports, and similar entrance arrangements are required. A baffle should be constructed across the basin close to the inlet end and should project several feet below the water surface to dissipate inlet velocities and provide uniform flows across the basin.
c. Outlet devices ‑ Outlet weirs or submerged orifices shall maintain velocities suitable for settling in the basin and minimize short‑circuiting. The use of submerged orifices is recommended in order to provide a volume above the orifices for storage when there are fluctuations in flow. Outlet weirs and submerged orifices shall be designed as follows:
1. The rate of flow over the outlet weirs or through the submerged orifices shall not exceed 20,000 gallons per day per foot (250 m3/day/m) of the outlet launder.
2. Submerged orifices should not be located lower than three (3) feet below the flow line.
3. The entrance velocity through the submerged orifices shall not exceed 0.5 feet per
d. Velocity ‑ The velocity through settling basins should not exceed 0.5 feet per minute. The basins must be designed to minimize short‑circuiting. Fixed or adjustable baffles must be provided as necessary to achieve the maximum potential for clarification.
e. Overflow ‑ An overflow weir or pipe designed to establish the maximum water level desired on top of the filters should be provided. The overflow shall discharge by gravity with a free fall at a location where the discharge will be noted.
f. Superstructure ‑ A superstructure over the sedimentation basins may be required. If there is no mechanical equipment in the basins and if provisions are included for adequate monitoring under all expected weather conditions, a cover may be provided in lieu of a superstructure.
g. Drainage ‑ Basins must be provided with a means for dewatering. Basin bottoms should slope toward the drain not less than one foot in twelve feet where mechanical sludge collection equipment is not required.
h. Flushing lines ‑ Flushing lines or hydrants shall be provided and must be equipped with backflow prevention devices acceptable to the reviewing authority.
i. Safety ‑ Permanent ladders or handholds should be provided on the inside walls of basins above the water level. Guard rails should be included. Compliance with other applicable safety requirements, such as OSHA, shall be required.
j. Sludge collection system - shall be designed to ensure the collection of sludge from throughout the basin.
k. Sludge removal ‑ Sludge removal design shall provide that
1. sludge pipes shall be not less than three inches in diameter and so arranged as to
2. entrance to sludge withdrawal piping shall prevent clogging,
3. valves shall be located outside the tank for accessibility,
4. the operator may observe and sample sludge being withdrawn from the unit.
l. Sludge disposal ‑ Facilities are required by the reviewing authority for disposal of sludge. (see Part 9).
Units are generally acceptable for combined softening and clarification where water characteristics, especially temperature, do not fluctuate rapidly, flow rates are uniform and operation is continuous. Before such units are considered as clarifiers without softening, specific approval of the reviewing authority shall be obtained. Clarifiers should be designed for the maximum uniform rate and should be adjustable to changes in flow which are less than the design rate and for changes in water characteristics. A minimum of two units are required for surface water treatment.
220.127.116.11 Installation of equipment
Supervision by a representative of the manufacturer shall be provided with regard to all mechanical equipment at the time of
a. installation, and
b. initial operation.
18.104.22.168 Operating equipment
The following shall be provided for plant operation:
a. a complete outfit of tools and accessories,
b. necessary laboratory equipment,
c. adequate piping with suitable sampling taps located to permit the collection of samples of water from critical portions of the units.
22.214.171.124 Chemical feed
Chemicals shall be applied at such points and by such means as to insure satisfactory mixing of the chemicals with the water.
A rapid mix device or chamber ahead of solids contact units may be required by the reviewing authority to assure proper mixing of the chemicals applied. Mixing devices employed shall be so constructed as to
a. provide good mixing of the raw water with previously formed sludge particles, and
b. prevent deposition of solids in the mixing zone.
a. shall be adjustable (speed and/or pitch),
b. must provide for coagulation in a separate chamber or baffled zone within the unit,
c. should provide that the flocculation and mixing period to be not less than 30 minutes.
126.96.36.199 Sludge concentrators
a. The equipment should provide either internal or external concentrators in order to obtain a concentrated sludge with a minimum of waste water.
b. Large basins should have at least two sumps for collecting sludge located in the central flocculation zone.
188.8.131.52 Sludge removal
Sludge removal design shall provide that
a. sludge pipes shall be not less than three inches in diameter and so arranged as to
b. entrance to sludge withdrawal piping shall prevent clogging,
c. valves shall be located outside the tank for accessibility, and
d. the operator may observe and sample sludge being withdrawn from the unit.
a. Blow‑off outlets and drains must terminate and discharge at places satisfactory to the reviewing authority.
b. Cross‑connection control must be included for the potable water lines used to backflush sludge lines.
184.108.40.206 Detention period
The detention time shall be established on the basis of the raw water characteristics and other local conditions that affect the operation of the unit. Based on design flow rates, the detention time should be
a. two to four hours for suspended solids contact clarifiers and softeners treating surface water, and
b. one to two hours for the suspended solids contact softeners treating only groundwater.
The reviewing authority may alter detention time requirements.
220.127.116.11 Suspended slurry concentrate
Softening units should be designed so that continuous slurry concentrates of one per cent or more, by weight, can be satisfactorily maintained.
18.104.22.168 Water losses
a. Units shall be provided with suitable controls for sludge withdrawal.
b. Total water losses should not exceed
1. five per cent for clarifiers,
2. three per cent for softening units.
c. Solids concentration of sludge bled to waste should be
1. three per cent by weight for clarifiers,
2. five per cent by weight for softeners.
22.214.171.124 Weirs or orifices
The units should be equipped with either overflow weirs or orifices constructed so that water at the surface of the unit does not travel over 10 feet horizontally to the collection trough.
a. Weirs shall be adjustable, and at least equivalent in length to the perimeter of the tank.
b. Weir loading shall not exceed
1. 10 gpm per foot of weir length (120 L/min/m) for units used for clarifiers,
2. 20 gpm per foot of weir length (240 L/min/m) for units used for softeners.
c. Where orifices are used the loading rates per foot of launder rates should be equivalent to weir loadings. Either shall produce uniform rising rates over the entire area of the tank.
126.96.36.199 Upflow rates
Unless supporting data is submitted to the reviewing authority to justify rates exceeding the following, rates shall not exceed
a. 1.0 gpm per square foot of area (2.4 m/hr) at the sludge separation line for units used for clarifiers,
b. 1.75 gpm per square foot of area (4.2 m/hr) at the slurry separation line, for units used for softeners.
Proposals for settler unit clarification must include pilot plant and/or full scale demonstration data on water with similar quality prior to the preparation of final plans and specifications for approval. Settler units consisting of variously shaped tubes or plates which are installed in multiple layers and at an angle to the flow may be used for sedimentation, following flocculation.
188.8.131.52 General criteria
a. Inlet and outlet considerations ‑‑ Design to maintain velocities suitable for settling in the basin and to minimize short‑circuiting. Plate units shall be designed to minimize maldistribution across the units.
b. Drainage ‑‑ Drain piping from the settler units must be sized to facilitate a quick flush of the settler units and to prevent flooding other portions of the plant.
c. Protection from freezing ‑‑ Although most units will be located within a plant, outdoor
installations must provide sufficient freeboard above the top of settlers to prevent freezing in the units. A cover or enclosure is strongly recommended.
d. Application rate for tubes ‑‑ A maximum rate of 2 gpm per square foot of cross‑sectional area (4.8 m/hr) for tube settlers, unless higher rates are successfully shown through pilot plant or in‑plant demonstration studies.
e. Application rates for plates -- A maximum plate loading rate of 0.5 gpm per square foot (1.2 m/hr), based on 80 percent of the projected horizontal plate area.
f. Flushing lines ‑‑ Flushing lines shall be provided to facilitate maintenance and must be
properly protected against backflow or back siphonage.
g. Placement modules should be placed:
1. In zones of stable hydraulic conditions.
2. In areas nearest effluent launders for basins not completely covered by the modules.
h. Inlets and Outlets
Inlets and outlets shall conform with Sections 4.1.4.b and 4.1.4.c.
The support system should be able to carry the weight of the modules when the basin is drained plus any additional weight to support maintenance.
j. Provisions should be made to allow the water level to be dropped, and a water or an air jet system for cleaning the modules.
High rate clarification processes may be approved upon demonstrating satisfactory performance under on-site pilot plant conditions or documentation of full scale plant operation with similar raw water quality conditions as allowed by the reviewing authority. Reductions in detention times and/or increases in weir loading rates shall be justified. Examples of such processes may include dissolved air flotation, ballasted flocculation, contact flocculation/clarification, and helical upflow, solids contact units.
Acceptable filters shall include, upon the discretion of the reviewing authority, the following types:
a. rapid rate gravity filters (4.2.1),
b. rapid rate pressure filters (4.2.2),
c. diatomaceous earth filtration (4.2.3),
d. slow sand filtration (4.2.4),
e. direct filtration (4.2.5),
f. deep bed rapid rate gravity filters (4.2.6),
g. biologically active filters (4.2.7),
h. membrane filtration (see Interim Standard on Membrane Technologies), and
i. bag and cartridge filters (see policy statement on Bag and Cartridge Filters for Public Water Systems).
The application of any one type must be supported by water quality data representing a reasonable period of time to characterize the variations in water quality. Pilot treatment studies may be required to demonstrate the applicability of the method of filtration proposed.
The use of rapid rate gravity filters shall require pretreatment.
184.108.40.206 Rate of filtration
The rate of filtration shall be determined through consideration of such factors as raw water quality, degree of pretreatment provided, filter media, water quality control parameters, competency of operating personnel, and other factors as required by the reviewing authority. Typical filtration rates are from 2 to 4 gpm/ft2. In any case, the filter rate must be proposed and justified by the design engineer to the satisfaction of the reviewing authority prior to the preparation of final plans and specifications.
At least two units shall be provided. Where only two units are provided, each shall be capable of meeting the plant design capacity (normally the projected maximum daily demand) at the approved filtration rate. Where more than two filter units are provided, the filters shall be
capable of meeting the plant design capacity at the approved filtration rate with one filter removed from service. Where declining rate filtration is provided, the variable aspect of filtration rates, and the number of filters must be considered when determining the design capacity for the filters.
220.127.116.11 Structural details and hydraulics
The filter structure shall be designed to provide for
a. vertical walls within the filter,
b. no protrusion of the filter walls into the filter media,
c. cover by superstructure,
d. head room to permit normal inspection and operation,
e. minimum depth of filter box of 8.5 feet,
f. minimum water depth over the surface of the filter media of three feet,
g. trapped effluent to prevent backflow of air to the bottom of the filters,
h. prevention of floor drainage to the filter with a minimum 4‑inch curb around the filters,
I. prevention of flooding by providing overflow,
j. maximum velocity of treated water in pipe and conduits to filters of two feet per second,
k. cleanouts and straight alignment for influent pipes or conduits where solids loading is heavy, or following lime‑soda softening,
l. washwater drain capacity to carry maximum flow,
m. walkways around filters, to be not less than 24 inches wide,
n. safety handrails or walls around all filter walkways,
o. construction to prevent cross connections and common walls between potable and
18.104.22.168 Washwater troughs
Washwater troughs should be constructed to have
a. the bottom elevation above the maximum level of expanded media during washing,
b. a two‑inch freeboard at the maximum rate of wash,
c. the top edge level and all at the same elevation,
d. spacing so that each trough serves the same number of square feet of filter area,
e. maximum horizontal travel of suspended particles to reach the trough not to exceed three feet.
22.214.171.124 Filter material
The media shall be clean silica sand or other natural or synthetic media free from detrimental chemical or bacterial contaminants, approved by the reviewing authority, and having the following characteristics:
a. a total depth of not less than 24 inches and generally not more than 30 inches,
b. a uniformity coefficient of the smallest material not greater than 1.65,
c. a minimum of 12 inches of media with an effective size range no greater than 0.45 mm to 0.55 mm
d. Types of filter media:
1. Anthracite - Filter anthracite shall consist of hard, durable anthracite coal particles of various sizes. Blending of non-anthracite material is not acceptable. Anthracite shall have an
a. effective size of 0.45 mm ‑ 0.55 mm with uniformity coefficient not greater than 1.65 when used alone,
b. effective size of 0.8 mm ‑ 1.2 mm with a uniformity coefficient not greater than 1.7 when used as a cap,
c. effective size for anthracite used as a single media on potable groundwater for iron and manganese removal only shall be a maximum of 0.8 mm (effective sizes greater than 0.8 mm may be approved based upon onsite pilot plant studies or other demonstration acceptable to the reviewing authority).
d. specific gravity greater than 1.4,
e. acid solubility less than 5 percent,
f. A Mho’s scale of hardness greater than 2.7.
2. Sand ‑ sand shall have
a. an effective size of 0.45 mm to 0.55 mm,
b. a uniformity coefficient of not greater than 1.65.
c. a specific gravity greater than 2.5.
d. an acid solubility less than 5 percent.
3. High Density Sand
High density sand shall consist of hard durable, and dense grain garnet, ilmenite, hematite, magnetite, or associated minerals of those ores that will resist degradation during handling and use, and shall
a. contain at least 95 percent of the associated material with a specific gravity of 3.8 or higher.
b. have an effective size of 0.2 to 0.3 mm.
c. have a uniformity coefficient of not greater than 1.65.
d. have an acid solubility less than 5 percent.
4. Granular activated carbon (GAC) ‑ Granular activated carbon as a single media may be considered for filtration only after pilot or full scale testing and with prior approval of the reviewing authority. The design shall include the following:
a. The media must meet the basic specifications for filter media as given in Section 126.96.36.199.a through c.
b. There must be provisions for a free chlorine residual and adequate contact time in the water following the filters and prior to distribution (See 4.3.2.d and 4.3.3).
c. There must be means for periodic treatment of filter material for control of bacterial and other growth.
d. Provisions must be made for frequent replacement or regeneration.
5. Other media types or characteristics may be considered based on experimental data and operating experience.
e. Support media
1. Torpedo sand ‑ A three‑inch layer of torpedo sand shall be used as a supporting media for filter sand where supporting gravel is used, and shall have
a. effective size of 0.8 mm to 2.0 mm, and
b. uniformity coefficient not greater than 1.7.
2. Gravel ‑ Gravel, when used as the supporting media shall consist of cleaned and washed, hard, durable, rounded silica particles and shall not include flat or elongated particles. The coarsest gravel shall be 2.5 inches in size when the gravel rests directly on a lateral system, and must extend above the top of the perforated laterals. Not less than four layers of gravel shall be provided in accordance with the following size and depth distribution:
3/32 to 3/16 inches 2 to 3 inches
3/16 to 1/2 inches 2 to 3 inches
1/2 to 3/4 inches 3 to 5 inches
3/4 to 1 ½ inches 3 to 5 inches
1 ½ to 2 ½ inches 5 to 8 inches
Reduction of gravel depths and other size gradations may be considered upon justification to the reviewing authority for slow sand filtration or when proprietary filter bottoms are specified.
188.8.131.52 Filter bottoms and strainer systems
Departures from these standards may be acceptable for high rate filters and for proprietary bottoms. Porous plate bottoms shall not be used where iron or manganese may clog them or with waters softened by lime. The design of manifold‑type collection systems shall:
a. minimize loss of head in the manifold and laterals,
b. ensure even distribution of washwater and even rate of filtration over the entire area of the filter,
c. provide the ratio of the area of the final openings of the strainer systems to the area of the filter at about 0.003,
d. provide the total cross‑sectional area of the laterals at about twice the total area of the final openings,
e. provide the cross‑sectional area of the manifold at 1.5 to 2 times the total area of the laterals.
f. lateral perforations without strainers shall be directed downward.
184.108.40.206 Surface wash or subsurface wash
Surface or subsurface wash facilities are required except for filters used exclusively for iron, radionuclides, arsenic or manganese removal, and may be accomplished by a system of fixed nozzles or a revolving‑type apparatus. All devices shall be designed with
a. provision for water pressures of at least 45 psi (310 kPa),
b. a properly installed vacuum breaker or other approved device to prevent back siphonage if connected to the filtered or finished water system,
c. rate of flow of 2.0 gallons per minute per square foot of filter area (4.9 m/hr) with fixed nozzles or 0.5 gallons per minute per square foot (1.2 m/hr) with revolving arms,
d. air wash can be considered based on experimental data and operating experiences.
220.127.116.11 Air scouring
Air scouring can be considered in place of surface wash
a. air flow for air scouring the filter must be 3‑5 standard cubic feet per minute square foot of filter area (0.9 - 1.5 m3/min/m2) when the air is introduced in the underdrain; a lower air rate must be used when the air scour distribution system is placed above the underdrains,
b. a method for avoiding excessive loss of the filter media during backwashing must be provided,
c. air scouring must be followed by a fluidization wash sufficient to restratify the media,
d. air must be free from contamination,
e. air scour distribution systems should be placed below the media and supporting bed interface; if placed at the interface the air scour nozzles shall be designed to prevent media from clogging the nozzles or entering the air distribution system.
f. piping for the air distribution system shall not be flexible hose which will collapse when not under air pressure and shall not be a relatively soft material which may erode at the orifice opening with the passage of air at high velocity.
g. air delivery piping shall not pass down through the filter media nor shall there be any arrangement in the filter design which would allow short circuiting between the applied unfiltered water and the filtered water,
h. consideration should be given to maintenance and replacement of air delivery piping,
i. the backwash water delivery system must be capable of 15 gallons per minute per square foot of filter surface area (37 m/hr); however, when air scour is provided the backwash water rate must be variable and should not exceed 8 gallons per minute per square foot (20 m/hr) unless operating experience shows that a higher rate is necessary to remove scoured particles from filter media surfaces.
j. the filter underdrains shall be designed to accommodate air scour piping when the piping is installed in the underdrain, and
k. the provisions of Section 18.104.22.168 shall be followed.
a. The following shall be provided for every filter:
1. influent and effluent sampling taps,
2. an indicating loss of head gauge,
3. an indicating rate‑of flow meter. A modified rate controller which limits the rate of filtration to a maximum rate may be used. However, equipment that simply maintains a constant water level on the filters is not acceptable, unless the rate of flow onto the filter is properly controlled. A pump or a flow meter in each filter effluent line may be used as the limiting device for the rate of filtration only after consultation with the reviewing authority.
4. where used for surface water, provisions for filtering to waste with appropriate
measures for cross connection control.
5. For systems with three or more filters, on-line turbidimeters shall be installed on the effluent line from each filter. All turbidimeters shall consistently determine and indicate the turbidity of the water in NTUs. Each turbidimeter shall report to a recorder that is designed and operated to allow the operator to accurately determine the turbidity at least once every 15 minutes. Turbidimeters on individual filters should be
designed to accurately measure low-range turbidities and have an alarm that will sound when the effluent level exceeds 0.3 NTU.
b. It is recommended the following be provided for every filter:
1. wall sleeves providing access to the filter interior at several locations for sampling or pressure sensing,
2. a 1 to 1.5 inch pressure hose and storage rack at the operating floor for washing filter walls,
3. particle monitoring equipment as a means to enhance overall treatment operations where used for surface water,
4. a flow rate controller capable of providing gradual rate increases when placing the filters back into operation.
Provisions shall be made for washing filters as follows:
a. a minimum rate of 15 gallons per minute per square foot (37 m/hr), consistent with water temperatures and specific gravity of the filter media. A rate of 20 gallons per minute per square foot (50 m/hr) or a rate necessary to provide for a 50 percent expansion of the filter bed is recommended. A reduced rate of 10 gallons per minute per square foot (24 m/hr) may be acceptable for full depth anthracite or granular activated carbon filters,
b. filtered water provided at the required rate by washwater tanks, a washwater pump, from the high service main, or a combination of these,
c. washwater pumps in duplicate unless an alternate means of obtaining washwater is available,
d. not less than 15 minutes wash of one filter at the design rate of wash,
e. a washwater regulator or valve on the main washwater line to obtain the desired rate of filter wash with the washwater valves on the individual filters open wide,
f. a rate‑of‑flow indicator, preferably with a totalizer, on the main washwater line, located so that it can be easily read by the operator during the washing process,
g. design to prevent rapid changes in backwash water flow.
h. backwash shall be operator initiated. Automated systems shall be operator adjustable.
Roof drains shall not discharge into the filters or basins and conduits preceding the filters.
The normal use of these filters is for iron and manganese removal. Pressure filters shall not be used in the filtration of surface or other polluted waters or following lime‑soda softening.
Minimum criteria relative to rate of filtration, structural details and hydraulics, filter media, etc., provided for rapid rate gravity filters also apply to pressure filters where appropriate.
22.214.171.124 Rate of filtration
The rate shall not exceed three gallons per minute per square foot of filter area (7.2 m/hr) except where inplant testing as approved by the reviewing authority has demonstrated satisfactory results at higher rates.
126.96.36.199 Details of design
The filters shall be designed to provide for
a. loss of head gauges on the inlet and outlet pipes of each battery of filters,
b. an easily readable meter or flow indicator on each battery of filters. A flow indicator is recommended for each filtering unit,
c. filtration and backwashing of each filter individually with an arrangement of piping as simple as possible to accomplish these purposes,
d. minimum side wall shell height of five feet. A corresponding reduction in side wall height is acceptable where proprietary bottoms permit reduction of the gravel depth,
e. the top of the washwater collectors to be at least 18 inches above the surface of the media,
f. the underdrain system to efficiently collect the filtered water and to uniformly distribute the backwash water at a rate not less than 15 gallons per minute per square foot of filter area (37 m/hr),
g. backwash flow indicators and controls that are easily readable while operating the control valves,
h. an air release valve on the highest point of each filter,
i. an accessible manhole of adequate size to facilitate inspection and repairs for filters 36 inches or more in diameter. Sufficient handholds shall be provided for filters less than 36 inches in diameter. Manholes should be at least 24 inches in diameter where feasible,
j. means to observe the wastewater during backwashing,
k. construction to prevent cross‑connection.
The use of these filters may be considered for application to surface waters with low turbidity and low bacterial contamination.
188.8.131.52 Conditions of use
Diatomaceous earth filters are expressly excluded from consideration for the following conditions:
a. bacteria removal,
b. color removal,
c. turbidity removal where either the gross quantity of turbidity is high or the turbidity exhibits poor filterability characteristics,
d. filtration of waters with high algae counts.
184.108.40.206 Pilot plant study
Installation of a diatomaceous earth filtration system shall be preceded by a pilot plant study on the water to be treated.
a. Conditions of the study such as duration, filter rates, head loss accumulation, slurry feed rates, turbidity removal, bacteria removal, etc., must be approved by the reviewing authority prior to the study.
b. Satisfactory pilot plant results must be obtained prior to preparation of final construction plans and specifications.
c. The pilot plant study must demonstrate the ability of the system to meet applicable drinking water standards at all times.
220.127.116.11 Types of filters
Pressure or vacuum diatomaceous earth filtration units will be considered for approval. However, the vacuum type is preferred for its ability to accommodate a design which permits observation of the filter surfaces to determine proper cleaning, damage to a filter element, and adequate coating over the entire filter area.
18.104.22.168 Treated water storage
Treated water storage capacity in excess of normal requirements shall be provided to:
a. allow operation of the filters at a uniform rate during all conditions of system demand at or below the approved filtration rate, and,
b. guarantee continuity of service during adverse raw water conditions without by‑passing the system.
22.214.171.124 Number of units
See Section 126.96.36.199
a. Application ‑ A uniform precoat shall be applied hydraulically to each septum by introducing a slurry to the tank influent line and employing a filter‑to‑waste or recirculation system.
b. Quantity ‑ Diatomaceous earth in the amount of 0.2 pounds per square foot of filter area (0.98 kg/m2) or an amount sufficient to apply a 1/8 inch coating should be used with recirculation.
188.8.131.52 Body feed
A body feed system to apply additional amounts of diatomaceous earth slurry during the filter run is required to avoid short filter runs or excessive head losses.
a. Quantity ‑ Rate of body feed is dependent on raw water quality and characteristics and must be determined in the pilot plant study.
b. Operation and maintenance can be simplified by providing accessibility to the feed system and slurry lines.
c. Continuous mixing of the body feed slurry is required.
a. Rate of filtration ‑ The recommended nominal rate is 1.0 gallon per minute per square foot of filter area (2.4 m/hr) with a recommended maximum of 1.5 gallons per minute per square foot (3.7 m/hr). The filtration rate shall be controlled by a positive means.
b. Head loss ‑ The head loss shall not exceed 30 psi (210 kPa) for pressure diatomaceous earth filters, or a vacuum of 15 inches of mercury (-51 kPa) for a vacuum system.
c. Recirculation ‑ A recirculation or holding pump shall be employed to maintain differential pressure across the filter when the unit is not in operation in order to prevent the filter cake from dropping off the filter elements. A minimum recirculation rate of 0.1 gallon per minute per square foot of filter area (0.24 m/hr) shall be provided.
d. Septum or filter element ‑ The filter elements shall be structurally capable of withstanding maximum pressure and velocity variations during filtration and backwash cycles, and shall be spaced such that no less than one inch is provided between elements or between any element and a wall.
e. Inlet design ‑ The filter influent shall be designed to prevent scour of the diatomaceous earth from the filter element.
A satisfactory method to thoroughly remove and dispose of spent filter cake shall be provided.
a. The following shall be provided for every filter:
1. sampling taps for raw and filtered water,
2. loss of head or differential pressure gauge,
3. rate‑of‑flow indicator, preferably with totalizer,
4. a throttling valve used to reduce rates below normal during adverse raw water conditions,
5. evaluation of the need for body feed, recirculation, and any other pumps, in accordance with Section 6.3.
6. provisions for filtering to waste with appropriate measures for backflow prevention (see Part 9).
b. It is recommended the following be provided:
1. A 1 to 1.5 inch pressure hose and storage rack at the operating floor for washing the filter.
2. Access to particle counting equipment as a means to enhance overall treatment operations.
3. A throttling valve used to reduce rates below normal during adverse raw water conditions.
4. Evaluation of the need for body feed, recirculation, and any other pumps, in accordance with Section 6.3.
5. A flow rate controller capable of providing gradual rate increases when placing the filters back into operation.
6. A continuous monitoring turbidimeter with recorder on each filter effluent for plants treating surface water.
The use of these filters shall require prior engineering studies to demonstrate the adequacy and suitability of this method of filtration for the specific raw water supply.
184.108.40.206 Quality of raw water
Slow rate gravity filtration shall be limited to waters having maximum turbidities of 10 units and maximum color of 15 units; such turbidity must not be attributable to colloidal clay. Microscopic examination of the raw water must be made to determine the nature and extent of algae growths and their potential adverse impact on filter operations.
At least two units shall be provided. Where only two units are provided, each shall be capable of meeting the plant design capacity (normally the projected maximum daily demand) at the approved filtration rate. Where more than two filter units are provided, the filters shall be
capable of meeting the plant design capacity at the approved filtration rate with one filter removed from service.
220.127.116.11 Structural details and hydraulics
Slow rate gravity filters shall be so designed as to provide:
a. a cover,
b. headroom to permit normal movement by operating personnel for scraping and sand removal operations,
c. adequate access hatches and access ports for handling of sand and for ventilation,
d. an overflow at the maximum filter water level, and
e. protection from freezing.
18.104.22.168 Rates of filtration
The permissible rates of filtration shall be determined by the quality of the raw water and shall be on the basis of experimental data derived from the water to be treated. The nominal rate may be 45 to 150 gallons per day per square foot of sand area (1.8 - 6.1 m/day), with somewhat higher rates acceptable when demonstrated to the satisfaction of the approving authority.
Each filter unit shall be equipped with a main drain and an adequate number of lateral underdrains to collect the filtered water. The underdrains shall be placed as close to the floor as possible and spaced so that the maximum velocity of the water flow in the underdrain will not exceed 0.75 feet per second. The maximum spacing of laterals shall not exceed 3 feet if pipe laterals are used.
22.214.171.124 Filter material
a. Filter sand shall be placed on graded gravel layers for a minimum depth of 30 inches.
b. The effective size shall be between 0.15 mm and 0.30 mm. Larger sizes may be considered by the reviewing authority; a pilot study may be required.
c. The uniformity coefficient shall not exceed 2.5.
d. The sand shall be cleaned and washed free from foreign matter.
e. The sand shall be rebedded when scraping has reduced the bed depth to no less than 19 inches. Where sand is to be reused in order to provide biological seeding and shortening of the ripening process, rebedding shall utilize a “throw over” technique whereby new sand is placed on the support gravel and existing sand is replaced on top of the new sand.
126.96.36.199 Filter gravel
The supporting gravel should be similar to the size and depth distribution provided for rapid rate gravity filters. See 188.8.131.52.f.2.
184.108.40.206 Depth of water on filter beds
Design shall provide a depth of at least three to six feet of water over the sand. Influent water shall not scour the sand surface.
220.127.116.11 Control appurtenances
Each filter shall be equipped with:
a. influent and effluent sampling taps.
b. an indicating loss of head gauge or other means to measure head loss.
c. an indicating rate-of-flow meter. A modified rate controller that limits the rate of filtration to a maximum rate may be used. However, equipment that simply maintains a constant water level on the filters is not acceptable, unless the rate of flow onto the filter is properly controlled. A pump or a flow meter in each filter effluent line may be used as the limiting device for the rate of filtration only after consultation with the reviewing authority.
d. provisions for filtering to waste with appropriate measures for cross connection control.
e. an orifice, Venturi meter, or other suitable means of discharge measurement installed on each filter to control the rate of filtration,
f. an effluent pipe designed to maintain the water level above the top of the filter sand.
Slow sand filters shall be operated to waste after scraping or rebedding during a ripening period until the filter effluent turbidity falls to consistently below the regulated drinking water standard established for the system.
Direct filtration, as used herein, refers to the filtration of a surface water following chemical coagulation and possibly flocculation but without prior settling. The nature of the treatment process will depend upon the raw water quality. A full scale direct filtration plant shall not be constructed without prior pilot studies which are acceptable to the reviewing authority. In‑plant demonstration studies may be appropriate where conventional treatment plants are converted to direct filtration. Where direct filtration is proposed, an engineering report shall be submitted prior to conducting pilot plant or in‑plant demonstration studies.
18.104.22.168 Engineering report
In addition to the items considered in Section 1.1, "Engineering Report", the report should include a historical summary of meteorological conditions and of raw water quality with special reference to fluctuations in quality, and possible sources of contamination. The following raw water parameters should be evaluated in the report:
c. bacterial concentration,
d. microscopic biological organisms,
f. total solids,
g. general inorganic chemical characteristics,
h. additional parameters as required by the reviewing authority.
The report should also include a description of methods and work to be done during a pilot plant study or, where appropriate, an in‑plant demonstration study.
22.214.171.124 Pilot plant studies
After approval of the engineering report, a pilot study or in‑plant demonstration study shall be conducted. The study must be conducted over a sufficient time to treat all expected raw water conditions throughout the year. The study shall emphasize but not be limited to, the following items:
a. chemical mixing conditions including shear gradients and detention periods,
b. chemical feed rates,
c. use of various coagulants and coagulant aids,
d. flocculation conditions,
e. filtration rates,
f. filter gradation, types of media and depth of media,
g. filter breakthrough conditions, and
h. adverse impact of recycling backwash water due to solids, algae, trihalomethane formation and similar problems.
i. length of filter runs,
j. length of backwash cycles,
k. quantities and make-up of the wastewater.
Prior to the initiation of design plans and specifications, a final report including the engineer's design recommendations shall be submitted to the reviewing authority.
The pilot plant filter must be of a similar type and operated in the same manner as proposed for full scale operation.
The pilot study must demonstrate the minimum contact time necessary for optimum filtration for each coagulant proposed.
126.96.36.199 Pretreatment ‑ Coagulation and flocculation
The final coagulation and flocculation basin design should be based on the pilot plant or in‑plant demonstration studies augmented with applicable portions of Section 4.1.2, " Coagulation" and Section 4.1.3, "Flocculation."
Filters shall be rapid rate gravity filters with dual or mixed media. The final filter design shall be based on the pilot plant or in‑plant demonstration studies and all portions of Section 4.2.1, "Rapid Rate Gravity Filters." Pressure filters or single media sand filters shall not be used.
a. The following shall be provided for every filter:
1. influent and effluent sampling taps,
2. an indicating loss of head gauge,
3. an indicating rate‑of flow meter. A modified rate controller which limits the rate of filtration to a maximum rate may be used. However, equipment that simply maintains a constant water level on the filters is not acceptable, unless the rate of flow onto the filter is properly controlled. A pump or a flow meter in each filter effluent line may be used as the limiting device for the rate of filtration only after consultation with the reviewing authority.
4. where used for surface water, provisions for filtering to waste with appropriate
measures for cross connection control.
5. For systems with three or more filters, on-line turbidimeters shall be installed on the effluent line from each filter. All turbidimeters shall consistently determine and indicate the turbidity of the water in NTUs. Each turbidimeter shall report to a recorder that is designed and operated to allow the operator to accurately determine the turbidity at least once every 15 minutes. Turbidimeters on individual filters should be designed to accurately measure low-range turbidities and have an alarm that will sound when the effluent level exceeds 0.3 NTU.
b. It is recommended the following be provided for every filter:
1. wall sleeves providing access to the filter interior at several locations for sampling or pressure sensing,
2. a 1 to 1.5 inch pressure hose and storage rack at the operating floor for washing filter walls,
3. particle monitoring equipment as a means to enhance overall treatment operations where used for surface water,
4. a flow rate controller capable of providing gradual rate increases when placing the filters back into operation.
188.8.131.52 Siting requirements
The plant design and land ownership surrounding the plant shall allow for modifications of the plant.
Deep bed rapid rate gravity filters, as used herein, generally refers to rapid rate gravity filters with filter material depths equal to or greater than 48 inches. Filter media sizes are typically larger than those listed in Section 184.108.40.206 (d).
Deep bed rapid rate filters may be considered based on pilot studies pre approved by the reviewing authority.
The final filter design shall be based on the pilot plant studies and shall comply with all applicable portions of Section 4.2.1. Careful attention shall be paid to the design of the backwash system which usually includes simultaneous air scour and water backwash at subfluidization velocities.
Biologically active filtration, as used herein, refers to the filtration of a surface water (or a ground water with iron, manganese or significant natural organic material) which includes the establishment and maintenance of biological activity within the filtration media.
Objectives of biologically active filtration may include control of disinfection byproduct precursors, increased disinfectant stability, reduction of substrates for microbial regrowth, breakdown of small quantities of synthetic organic chemicals, reduction of ammonia-nitrogen, and oxidation of iron and manganese. Biological activity can have an adverse impact on turbidity, particle and microbial pathogen removal, disinfection practices; head loss development; filter run times and distribution system corrosion. Design and operation should ensure that aerobic conditions are maintained at all times. Biologically active filtration often includes the use of ozone as a pre-oxidant/disinfectant which breaks down natural organic materials into biodegradable organic matter and granular activated carbon filter media which may promote denser biofilms.
Biologically active filters may be considered based on pilot studies pre-approved by the reviewing authority. The study objectives must be clearly defined and must ensure the microbial quality of the filtered water under all anticipated conditions of operation.
The pilot study shall be of sufficient duration to ensure establishment of full biological activity; often greater than three months is required. Also, the pilot study shall establish empty bed contact time, biomass loading, and/or other parameters necessary for successful operation as required by the reviewing authority.
The final filter design shall be based on the pilot plant studies and shall comply with all applicable portions of Section 4.2.1.
Chlorine is historically the preferred disinfecting agent. Disinfection may be accomplished with gas and liquid chlorine, calcium or sodium hypochlorites, chlorine dioxide, ozone, or ultraviolet light. Other disinfecting agents will be considered, providing reliable application equipment is available and testing procedures for a residual are recognized in "Standard Methods for the Examination of Water and Wastewater," latest edition or an equivalent means of measuring effectiveness exists. Disinfection is required for all surface water supplies, groundwater under the direct influence of surface water, and for any groundwater supply of questionable sanitary quality or where other treatment is provided. Disinfection with chloramines is not recommended for primary disinfection. The required amount of primary disinfection needed shall be specified by the reviewing authority. Continuous disinfection is recommended for all water supplies. Consideration must be given to the formation of disinfection byproducts (DBP)when selecting the disinfectant.
Solution‑feed gas chlorinators or hypochlorite feeders of the positive displacement type must be provided. (see Part 5).
The chlorinator capacity shall be such that a free chlorine residual of at least 2 mg/L can be maintained in the water once all demands are met after contact time of at least 30 minutes when maximum flow rate coincides with anticipated maximum chlorine demand. The equipment shall be of such design that it will operate accurately over the desired feeding range.
220.127.116.11 Standby equipment
Where chlorination is required for protection of the supply, standby equipment of sufficient capacity shall be available to replace the largest unit. Spare parts shall be made available to replace parts subject to wear and breakage. If there is a large difference in feed rates between routine and emergency dosages, a gas metering tube should be provided for each dose range to ensure accurate control of the chlorine feed.
18.104.22.168 Automatic switch-over
Automatic switch-over of chlorine cylinders should be provided, where necessary, to assure continuous disinfection.
22.214.171.124 Automatic proportioning
Automatic proportioning chlorinators will be required where the rate of flow or chlorine demand is not reasonably constant.
Each eductor must be selected for the point of application with particular attention given to the quantity of chlorine to be added, the maximum injector waterflow, the total discharge back pressure, the injector operating pressure, and the size of the chlorine solution line. Gauges for measuring water pressure and vacuum at the inlet and outlet of each eductor should be provided.
The chlorine solution injector/diffuser must be compatible with the point of application to provide a rapid and thorough mix with all the water being treated. The center of a pipeline is the preferred application point.
a. Due consideration shall be given to the contact time of the disinfectant in water with relation to pH, ammonia, taste‑producing substances, temperature, bacterial quality, disinfection byproduct formation potential and other pertinent factors. The disinfectant should be applied at a point which will provide adequate contact time. All basins used for disinfection must be designed to minimize short circuiting. Additional baffling can be added to new or existing basins to minimize short circuiting and increase contact time.
b. At plants treating surface water, provisions shall be made for applying the disinfectant to the raw water, settled water, filtered water, and water entering the distribution system.
c. As a minimum, at plants treating groundwater, provisions shall be made for applying the disinfectant to the detention basin inlet and water entering the distribution system.
d. The amount of contact time provided will depend on the type of disinfectant used along with the parameters mentioned in 4.3.2.a. As a minimum, for surface waters and groundwaters under the direct influence of surface water, the system must be designed to meet the CT standards set by the reviewing authority. If primary disinfection is accomplished using ozone or some other chemical that does not provide a residual disinfectant, then chlorine must be added to provide a residual disinfectant as mentioned in 4.3.3. Disinfection for groundwaters shall be as determined by the reviewing authority.
a. Minimum free chlorine residual in a water distribution system should be 0.2 mg/L. Minimum chloramine residuals, where chloramination is practiced, should be 1.0 mg/L at distant points in the distribution system.
b. Higher residuals may be required depending on pH, temperature and other characteristics of the water.
a. Chlorine residual test equipment recognized in the latest edition of Standard Methods for the Examination of Water and Wastewater shall be provided and should be capable of measuring residuals to the nearest 0.1 milligrams per liter. It is recommended that all systems, as a minimum, use an instrument using the DPD colorimetric method with a digital readout and a self contained light source.
b. Automatic chlorine residual recorders should be provided where the chlorine demand varies appreciably over a short period of time.
c. All treatment plants having a capacity of 0.5 million gallons per day or greater should be equipped with recording chlorine analyzers monitoring water entering the distribution system. (see Section 2.9).
d. All surface water treatment plants that serve a population greater that 3300 must have equipment to measure chlorine residuals continuously entering the distribution system.
e. Systems that rely on chlorination for inactivation of bacteria or other microorganisms present in the source water shall have continuous chlorine residual analyzers and other equipment that automatically shut down the facility when chlorine residuals are not met unless otherwise approved by the reviewing authority.
126.96.36.199 Cross‑connection protection
The chlorinator water supply piping shall be designed to prevent contamination of the treated water supply by sources of questionable quality. At all facilities treating surface water, pre‑ and post‑chlorination systems must be independent to prevent possible siphoning of partially treated water into the clear well. The water supply to each eductor shall have a separate shut‑off valve. No master shut‑off valve will be allowed.
188.8.131.52 Pipe material
The pipes carrying elemental liquid or dry gaseous chlorine under pressure must be Schedule 80 seamless steel tubing or other materials recommended by the Chlorine Institute (never use PVC). Rubber, PVC, polyethylene, or other materials recommended by the Chlorine Institute must be used for chlorine solution piping and fittings. Nylon products are not acceptable for any part of the chlorine solution piping system.
Adequate housing must be provided for the chlorination equipment and for storing the chlorine. (see Part 5).
184.108.40.206 Design considerations
Ozonation systems are generally used for the purpose of disinfection, oxidation and microflocculation. When applied, all of these reactions may occur but typically only one is the primary purpose for its use. The other reactions would become secondary benefits of the installation.
Effective disinfection occurs as demonstrated by the fact that the "CT" values for ozone, for inactivation of viruses and Giardia cysts, are considerably lower than the "CT" values for other disinfectants. In addition, recent research indicates that ozone can be an effective disinfectant for the inactivation of cryptosporidium. Microflocculation and enhanced filterability has been demonstrated for many water supplies but has not occurred in all waters. Oxidation of organic compounds such as color, taste and odor, and detergents and inorganic compounds such as iron, manganese, heavy metals and hydrogen sulfide has been documented. The effectiveness of oxidation has been varied, depending on pH and alkalinity of the water.
These parameters affect the formation of highly reactive hydroxyl radicals, or, conversely the scavenging of this oxidant. High levels of hydroxyl radicals cause lower levels of residual ozone. Depending on the desired oxidation reaction, it may be necessary to maximize ozone residual or maximize hydroxyl radical formation. For disinfection, residual ozone is necessary for development of "CT".
As a minimum, bench scale studies shall be conducted to determine minimum and maximum ozone dosages for disinfection "CT" compliance and oxidation reactions. More involved pilot studies shall be conducted when necessary to document benefits and DBP precursor removal effectiveness. Consideration shall be given to multiple points of ozone addition. Pilot studies shall be conducted for all surface waters. Extreme care must be taken during bench and pilot scale studies to ensure accurate results. Particularly sensitive measurements include gas flow rate, water flow rate, and ozone concentration.
Following the use of ozone, the application of a disinfectant which maintains a measurable residual will be required in order to ensure a bacteriologically safe water is carried throughout the distribution system.
Furthermore, because of the more sophisticated nature of the ozone process a higher degree of operator maintenance skills and training is required. The ability to obtain qualified operators must be evaluated in selection of the treatment process. The necessary operator training shall be provided prior to plant startup.
The production of ozone is an energy intensive process: substantial economies in electrical usage, reduction in equipment size, and waste heat removal requirements can be obtained by using oxygen enriched air or 100% oxygen as feed, and by operating at increased electrical frequency.
Use of ozone may result in increases in biologically available organics content of the treated water. Consideration of biologically active filtration may be required to stabilize some treated waters. Ozone use may also lead to increased chlorinated byproduct levels if the water is not stabilized and free chlorine is used for distribution protection.
220.127.116.11 Feed Gas Preparation
Feed gas can be air, oxygen enriched air, or high purity oxygen. Sources of high purity oxygen include purchased liquid oxygen; on site generation using cryogenic air separation; or temperature, pressure or vacuum swing (adsorptive separation) technology. For high purity oxygen-feed systems, dryers typically are not required.
Air handling equipment on conventional low pressure air feed systems shall consist of an air compressor, water/air separator, refrigerant dryer, heat reactivated desiccant dryer, and particulate filters. Some "package" ozonation systems for small plants may work effectively operating at high pressure without the refrigerant dryer and with a "heat‑less" desiccant dryer. In all cases the design engineer must ensure that the maximum dew point of -76oF (‑60oC) will not be exceeded at any time.
b. Air Compression
1. Air compressors shall be of the liquid‑ring or rotary lobe, oil‑less, positive displacement type for smaller systems or dry rotary screw compressors for larger systems.
2. The air compressors shall have the capacity to simultaneously provide for maximum ozone demand, provide the air flow required for purging the desiccant dryers (where required) and allow for standby capacity.
3. Air feed for the compressor shall be drawn from a point protected from rain, condensation, mist, fog and contaminated air sources to minimize moisture and hydrocarbon content of the air supply.
4. A compressed air after‑cooler and/or entrainment separator with automatic drain shall be provided prior to the dryers to reduce the water vapor.
5. A back‑up air compressor must be provided so that ozone generation is not interrupted in the event of a break‑down.
c. Air Drying
1. Dry, dust‑free and oil‑free feed gas must be provided to the ozone generator. Dry gas is essential to prevent formation of nitric acid, to increase the efficiency of ozone generation and to prevent damage to the generator dielectrics. Sufficient drying to a maximum dew point of -76oF (‑60oC) must be provided at the end of the drying cycle.
2. Drying for high pressure systems may be accomplished using heatless desiccant dryers only. For low pressure systems, a refrigeration air dryer in series with heat‑reactivated desiccant dryers shall be used.
3. A refrigeration dryer capable of reducing inlet air temperature to 40oF (4oC). shall be provided for low pressure air preparation systems. The dryer can be of the compressed refrigerant type or chilled water type.
4. For heat‑reactivated desiccant dryers, the unit shall contain two desiccant filled towers complete with pressure relief valves, two four‑way valves and a heater. In addition, external type dryers shall have a cooler unit and blowers. The size of the unit shall be such that the specified dew point will be achieved during a minimum adsorption cycle time of 16 hours while operating at the maximum expected moisture loading conditions.
5. Multiple air dryers shall be provided so that the ozone generation is not interrupted in the event of dryer breakdown.
6. Each dryer shall be capable of venting "dry" gas to the atmosphere, prior to the ozone generator, to allow start‑up when other dryers are "on‑line".
d. Air Filters
1. Air filters shall be provided on the suction side of the air compressors, between the air compressors and the dryers and between the dryers and the ozone generators.
2. The filter before the desiccant dryers shall be of the coalescing type and be capable of removing aerosol and particulates larger than 0.3 microns in diameter. The filter after the
desiccant dryer shall be of the particulate type and be capable of removing all particulates greater than 0.1 microns in diameter, or smaller if specified by the generator manufacturer.
e. Preparation Piping
Piping in the air preparation system can be common grade steel, seamless copper, stainless steel or galvanized steel. The piping must be designed to withstand the maximum pressures in the air preparation system.
18.104.22.168 Ozone Generator
1. The production rating of the ozone generators shall be stated in pounds per day and kWhr per pound at a maximum cooling water temperature and maximum ozone concentration.
2. The design shall ensure that the minimum concentration of ozone in the generator exit gas will not be less than 1 percent (by weight).
3. Generators shall be sized to have sufficient reserve capacity so that the system does not operate at peak capacity for extended periods of time. This can result in premature breakdown of the dielectrics.
4. The production rate of ozone generators will decrease as the temperature of the coolant increases. If there is to be a variation in the supply temperature of the coolant throughout the year, then pertinent data shall be used to determine production changes due to the temperature change of the supplied coolant. The design shall ensure that the generators can produce the required ozone at maximum coolant temperature.
5. Appropriate ozone generator backup equipment must be provided.
The generators can be low, medium or high frequency type. Specifications shall require that the transformers, electronic circuitry and other electrical hardware be proven, high quality components designed for ozone service.
Adequate cooling shall be provided. The required water flow to an ozone generator varies with the ozone production. Normally unit design provides a maximum cooling water temperature rise of 5oF (2.8oC). The cooling water must be properly treated to minimize corrosion, scaling and microbiological fouling of the water side of the tubes. A closed loop cooling water system is often used to insure proper water conditions are maintained. Where cooling water is treated cross connection control shall be provided to prevent contamination of the potable water supply in accordance with Section 8.10.2.
To prevent corrosion, the ozone generator shell and tubes shall be constructed of Type 316L stainless steel.
22.214.171.124 Ozone Contactors
The selection or design of the contactor and method of ozone application depends on the purpose for which the ozone is being used.
a. Bubble Diffusers
1. Where disinfection is the primary application a minimum of two contact chambers each equipped with baffles to prevent short circuiting and induce countercurrent flow shall be provided. Ozone shall be applied using porous‑tube or dome diffusers.
2. The minimum contact time shall be 10 minutes. A shorter contact time may be approved by the reviewing authority if justified by appropriate design and “CT” considerations.
3. For ozone applications in which precipitates are formed, such as with iron and manganese removal, porous diffusers should be used with caution.
4. Where taste and odor control is of concern, multiple application points and contactors shall be considered.
5. Contactors should be separate closed vessels that have no common walls with adjacent rooms. The contactor must be kept under negative pressure and sufficient ozone monitors shall be provided to protect worker safety. Placement of the contactor where the entire roof is exposed to the open atmosphere is recommended.
6. Large contact vessels should be made of reinforced concrete. All reinforcement bars shall be covered with a minimum of 1.5 inches of concrete. Smaller contact vessels can be made of stainless steel, fiberglass or other material which will be stable in the presence of residual ozone and ozone in the gas phase above the water level.
7. Where necessary a system shall be provided between the contactor and the off‑gas destruct unit to remove froth from the air and return the other to the contactor or other location acceptable to the reviewing authority. If foaming is expected to be excessive, then a potable water spray system shall be placed in the contactor head space.
8. All openings into the contactor for pipe connections, hatchways, etc. shall be properly sealed using welds or ozone resistant gaskets such as Teflon or Hypalon.
9. Multiple sampling ports shall be provided to enable sampling of each compartment's effluent water and to confirm “CT” calculations.
10. A pressure/vacuum relief valve shall be provided in the contactor and piped to a location where there will be no damage to the destruction unit.
11. The diffusion system should work on a countercurrent basis such that the ozone is fed at the bottom of the vessel and water is fed at the top of the vessel.
12. The depth of water in bubble diffuser contactors should be a minimum of 18 feet. The contactor should also have a minimum of 3 feet of freeboard to allow for foaming.
13. All contactors shall have provisions for cleaning, maintenance and drainage of the contactor. Each contactor compartment shall also be equipped with an access hatchway.
14. Aeration diffusers shall be fully serviceable by either cleaning or replacement.
b. Other contactors
Other contactors, such as the venturi or aspirating turbine mixer contactor, may be approved by the reviewing authority provided adequate ozone transfer is achieved and the required contact times and residuals can be met and verified.
126.96.36.199 Ozone Destruction Unit
a. A system for treating the final off‑gas from each contactor must be provided in order to meet safety and air quality standards. Acceptable systems include thermal destruction and thermal/catalytic destruction units.
b. In order to reduce the risk of fires, the use of units that operate at lower temperatures is encouraged, especially where high purity oxygen is the feed gas.
c. The maximum allowable ozone concentration in the discharge is 0.1 ppm (by volume).
d. At least two units shall be provided which are each capable of handling the entire gas flow.
e. Exhaust blowers shall be provided in order to draw off‑gas from the contactor into the destruct unit.
f. Catalysts must be protected from froth, moisture and other impurities which may harm the catalyst.
g. The catalyst and heating elements shall be located where they can easily be reached for maintenance.
188.8.131.52 Piping Materials
Only low carbon 304L and 316L stainless steels shall be used for ozone service with 316L the preferred.
184.108.40.206 Joints and Connections
a. Connections on piping used for ozone service are to be welded where possible.
b. Connections with meters, valves or other equipment are to be made with flanged joints with ozone resistant gaskets, such as Teflon of Hypalon. Screwed fittings shall not be used because of their tendency to leak.
c. A positive closing plug or butterfly valve plus a leak‑proof check valve shall be provided in the piping between the generator and the contactor to prevent moisture reaching the generator.
a. Pressure gauges shall be provided at the discharge from the air compressor, at the inlet to the refrigeration dryers, at the inlet and outlet of the desiccant dryers, at the inlet to the ozone generators and contactors and at the inlet to the ozone destruction unit.
b. Electric power meters should be provided for measuring the electric power supplied to the ozone generators. Each generator shall have a trip which shuts down the generator when the wattage exceeds a certain preset level.
c. Dew point monitors shall be provided for measuring the moisture of the feed gas from the desiccant dryers. Because it is critical to maintain the specified dew point, it is recommended that continuous recording charts be used for dew point monitoring which will allow for proper adjustment of the dryer cycle. Where there is potential for moisture entering the ozone generator from downstream of the unit or where moisture accumulation can occur in the generator during shutdown, post‑generator dew point monitors shall be used.
d. Air flow meters shall be provided for measuring air flow from the desiccant dryers to each of other ozone generators, air flow to each contactor and purge air flow to the desiccant dryers.
e. Temperature gauges shall be provided for the inlet and outlet of the ozone cooling water and the inlet and outlet of the ozone generator feed gas, and, if necessary, for the inlet and outlet of the ozone power supply cooling water.
f. Water flow meters shall be installed to monitor the flow of cooling water to the ozone generators and, if necessary, to the ozone power supply.
g. Ozone monitors shall be installed to measure zone concentration in both the feed‑gas and off‑gas from the contactor and in the off‑gas from the destruct unit. For disinfection systems, monitors shall also be provided for monitoring ozone residuals in the water. The number and location of ozone residual monitors shall be such that the amount of time that the water is in contact with the ozone residual can be determined.
h. A minimum of one ambient ozone monitor shall be installed in the vicinity of the contactor and a minimum of one shall be installed in the vicinity of the generator. Ozone monitors shall also be installed in any areas where ozone gas may accumulate.
The following alarm/shutdown systems should be considered at each installation:
a. Dew point shutdown/alarm ‑ This system should shut down the generator in the event the system dew point exceeds -76oF (‑60oC).
b. Ozone generator cooling water flow shutdown/alarm ‑ This system should shut down the generator in the event that cooling water flows decrease to the point that generator damage could occur.
c. Ozone power supply cooling water flow shutdown/alarm ‑ This system should shut down the power supply in the event that cooling water flow decreases to the point that damage could occur to the power supply.
d. Ozone generator cooling water temperature shutdown/alarm ‑ This system should shutdown the generator if either the inlet or outlet cooling water exceeds a certain preset temperature.
e. Ozone power supply cooling water temperature shutdown/alarm ‑ This system should shutdown the power supply if either the inlet or outlet cooling water exceeds a certain preset temperature.
f. Ozone generator inlet feed‑gas temperature shutdown/alarm ‑ This system should shutdown the generator if the feed‑gas temperature is above a preset value.
g. Ambient ozone concentration shutdown/alarm ‑ The alarm should sound when the ozone level in the ambient air exceeds 0.1 ppm or a lower value chosen by the water supplier. Ozone generator shutdown should occur when ambient ozone levels exceed 0.3 ppm (or a lower value) in either the vicinity of the ozone generator or the contactor.
h. Ozone destruct temperature alarm ‑ The alarm should sound when temperature exceeds a preset value.
a. The maximum allowable ozone concentration in the air to which workers may be exposed must not exceed 0.1 ppm (by volume).
b. Noise levels resulting from the operating equipment of the ozonation system shall be controlled to within acceptable limits by special room construction and equipment isolation.
c. High voltage and high frequency electrical equipment must meet current electrical and fire codes.
d. Emergency exhaust fans must be provided in the rooms containing the ozone generators to remove ozone gas if leakage occurs.
e. A portable purge air blower that will remove residual ozone in the contactor prior to entry for repair or maintenance should be provided.
f. A sign shall be posted indicating “No smoking, oxygen in use” at all entrances to the treatment plant. In addition, no flammable or combustible materials shall be stored within the oxygen generator areas.
220.127.116.11 Construction Considerations
a. Prior to connecting the piping from the desiccant dryers to the ozone generators the air compressors should be used to blow the dust out of the desiccant.
b. The contactor should be tested for leakage after sealing the exterior. This can be done by pressurizing the contactor and checking for pressure losses.
c. Connections on the ozone service line should be tested for leakage using the soap‑test method.
Chlorine dioxide may be considered as a primary and residual disinfectant, a pre-oxidant to control tastes and odors, to oxidize iron and manganese, and to control hydrogen sulfide and phenolic compounds. It has been shown to be a strong disinfectant which does not form THMs or HAAs.
When choosing chlorine dioxide, consideration must be given to formation of the regulated byproducts, chlorite and chlorate.
18.104.22.168 Chlorine dioxide generators
Chlorine dioxide generation equipment shall be factory assembled pre-engineered units with a minimum efficiency of 95 percent. The excess free chlorine shall not exceed three percent of the theoretical stoichiometric concentration required.
22.214.171.124 Feed and storage facilities
126.96.36.199 Other design requirements
b. The minimum residual disinfectant level shall be established by the reviewing authority.
188.8.131.52 Public notification
Notification of a change in disinfection practices and the schedule for the changes shall be made known to the public; particularly to hospitals, kidney dialysis facilities and fish breeders, as chlorine dioxide and its byproducts may have similar effects as chloramines.
Proposals for use of disinfecting agents other than those listed shall be approved by the reviewing authority prior to preparation of final plans and specification.
The softening process selected must be based upon the mineral qualities of the raw water and the desired finished water quality in conjunction with requirements for disposal of sludge or brine waste, cost of plant, cost of chemicals and plant location. Applicability of the process chosen shall be demonstrated.
Design standards for rapid mix, flocculation and sedimentation are in Section 4.1. Additional consideration must be given to the following process elements.
When split treatment is used, the bypass line should be sized to carry total plant flow, and an accurate means of measuring and splitting the flow must be provided.
Determinations should be made for the carbon dioxide content of the raw water. When concentrations exceed 10 mg/L, the economics of removal by aeration as opposed to removal with lime should be considered if it has been determined that dissolved oxygen in the finished water will not cause corrosion problems in the distribution system. (see Section 4.5).
184.108.40.206 Chemical feed point
Lime should be fed directly into the rapid mix basin.
220.127.116.11 Rapid mix
Rapid mix basins must provide not more than 30 seconds detention time with adequate velocity gradients to keep the lime particles dispersed.
Equipment for stabilization of water softened by the lime or lime‑soda process is required. (see Section 4.8).
18.104.22.168 Sludge collection
a. Mechanical sludge removal equipment shall be provided in the sedimentation basin.
b. Sludge recycling to the rapid mix should be provided. If it is not, the reviewing authority must approve the point of recycle.
22.214.171.124 Sludge disposal
Provisions must be included for proper disposal of softening sludges. (see Part 9).
The use of excess lime shall not be considered an acceptable substitute for disinfection. (see Section 4.3)
126.96.36.199 Plant start‑up
The plant processes must be manually started following shut‑down.
Alternative methods of hardness reduction should be investigated when the sodium content and dissolved solids concentration is of concern.
188.8.131.52 Pre‑treatment requirements
Iron, manganese, or a combination of the two, should not exceed 0.3 mg/L in the water as applied to the ion exchange resin. Pre‑treatment is required when the content of iron, manganese, or a combination of the two, is one milligram per liter or more. (see Section 4.6). Waters having 5 units or more turbidity should not be applied directly to the cation exchange softener.
The units may be of pressure or gravity type, of either an upflow or downflow design. Automatic regeneration based on volume of water softened should be used unless manual regeneration is justified and is approved by the reviewing authority. A manual override shall be provided on all automatic controls.
184.108.40.206 Exchange capacity
The design capacity for hardness removal should not exceed 20,000 grains per cubic foot (46 kg/m3) when resin is regenerated with 0.3 pounds (0.14 kg) of salt per kgr of hardness removed.
220.127.116.11 Depth of resin
The depth of the exchange resin should not be less than three feet.
18.104.22.168 Flow rates
The rate of softening should not exceed seven gallons per minute per square foot of bed area (17 m/hr) and the backwash rate should be six to eight gallons per minute per square foot (14 - 20 m/hr) of bed area. Rate‑of‑flow controllers or the equivalent must be installed for the above purposes.
The freeboard will depend upon the size and specific gravity of the resin and the direction of water flow. Generally, the washwater collector should be 24 inches above the top of the resin on downflow units.
22.214.171.124 Underdrains and supporting gravel
The bottoms, strainer systems and support for the exchange resin shall conform to criteria provided for rapid rate gravity filters. (see Sections 126.96.36.199 and 188.8.131.52).
184.108.40.206 Brine distribution
Facilities should be included for even distribution of the brine over the entire surface of both upflow and downflow units.
220.127.116.11 Cross‑connection control
Backwash, rinse and air relief discharge pipes shall be installed in such a manner as to prevent any possibility of back‑siphonage.
18.104.22.168 Bypass piping and equipment
Bypass must be provided around softening units to produce a blended water of desirable hardness. Totalizing meters must be installed on the bypass line and on each softener unit. The bypass line must have a shutoff valve and should have an automatic proportioning or regulating device. In some installations, it may be necessary to treat the bypassed water to obtain acceptable levels of iron and/or manganese in the finished water.
22.214.171.124 Additional limitations
Silica gel resins should not be used for waters having a pH above 8.4 or containing less than six milligrams per liter silica and should not be used when iron is present. When the applied water contains a chlorine residual, the cation exchange resin shall be a type that is not damaged by residual chlorine. Phenolic resin should not be used.
126.96.36.199 Sampling taps
Smooth‑nose sampling taps must be provided for the collection of representative samples. The taps shall be located to provide for sampling of the softener influent, effluent and blended water. The sampling taps for the blended water shall be at least 20 feet downstream from the point of blending. Petcocks are not acceptable as sampling taps. Sampling taps should be provided on the brine tank discharge piping.
188.8.131.52 Brine and salt storage tanks
a. Salt dissolving or brine tanks and wet salt storage tanks must be covered and must be corrosion‑resistant.
b. The make‑up water inlet must be protected from back‑siphonage. Water for filling the tank should be distributed over the entire surface by pipes above the maximum brine level In the tank. The tanks should be provided with an automatic declining level control system on the make‑up water line.
c. Wet salt storage basins must be equipped with manholes or hatchways for access and for direct dumping of salt from truck or railcar. Openings must be provided with raised curbs and watertight covers having overlapping edges similar to those required for finished water reservoirs. Each cover shall be hinged on one side, and shall have locking device.
d. Overflows, where provided, must be protected with corrosion resistant screens and must terminate with either a turned downed bend having a proper free fall discharge or a self‑closing flap valve.
e. Two wet salt storage tanks or compartments designed to operate independently should be provided.
f. The salt shall be supported on graduated layers of gravel placed over a brine collection system.
g. Alternative designs which are conducive to frequent cleaning of the wet salt storage tank may be considered.
184.108.40.206 Salt and brine storage capacity
Total salt storage should have sufficient capacity to store in excess of 1.5 carloads or truckloads of salt, and provide for at least 30 days of operation.
220.127.116.11 Brine pump or eductor
An eductor may be used to transfer brine from the brine tank to the softeners. If a pump is used, a brine measuring tank or means of metering should be provided to obtain proper dilution.
Refer to 4.8
18.104.22.168 Waste disposal
Suitable disposal must be provided for brine waste (See Part 9). Where the volume of spent brine must be reduced, consideration may be given to using a part of the spent brine for a subsequent regeneration.
22.214.171.124 Construction materials
Pipes and contact materials must be resistant to the aggressiveness of salt. Plastic and red brass are acceptable piping materials. Steel and concrete must be coated with a non‑leaching protective coating which is compatible with salt and brine.
Bagged salt and Dry bulk salt storage shall be enclosed and separated from other operating areas in order to prevent damage to equipment.
Test equipment for alkalinity, total hardness, carbon dioxide content, and pH should be provided to determine treatment effectiveness.
Aeration may be used to help remove offensive tastes and odors due to dissolved gases from decomposing organic matter, or to reduce or remove objectionable amounts of carbon dioxide, hydrogen sulfide, etc., and to introduce oxygen to assist in iron and/or manganese removal. The packed tower aeration process is an aeration process applicable to removal of volatile organic contaminants.
Design shall provide
a. perforations in the distribution pan 3/16 to 1/2 inches in diameter, spaced 1 to 3 inches on centers to maintain a six inch water depth,
b. for distribution of water uniformly over the top tray,
c. discharge through a series of three or more trays with separation of trays not less than 12 inches,
d. loading at a rate of 1 to 5 gallons per minute for each square foot of total tray area (2.5 - 12.5 m/hr),
e. trays with slotted, heavy wire (1/2 inch openings) mesh or perforated bottoms,
f. construction of durable material resistant to aggressiveness of the water and dissolved gases,
g. protection from loss of spray water by wind carriage by enclosure with louvers sloped to the inside at a angle of approximately 45 degrees,
h. protection from insects by 24‑mesh screen.
i. Provisions for continuous disinfection feed shall be provided after aeration.
Devices shall be designed to
a. include a blower with a weatherproof motor in a tight housing and screened enclosure,
b. insure adequate counter current of air through the enclosed aerator column,
c. exhaust air directly to the outside atmosphere,
d. include a down‑turned and 24‑mesh screened air outlet and inlet,
e. be such that air introduced in the column shall be as free from obnoxious fumes, dust, and dirt as possible,
f. be such that sections of the aerator can be easily reached or removed for maintenance of the interior or installed in a separate aerator room,
g. provide loading at a rate of 1 to 5 gallons per minute for each square foot of total tray area(2.5 - 12.5 m/hr),
h. insure that the water outlet is adequately sealed to prevent unwarranted loss of air,
i. discharge through a series of five or more trays with separation of trays not less than six inches or as approved by the reviewing authority,
j. provide distribution of water uniformly over the top tray,
k. be of durable material resistant to the aggressiveness of the water and dissolved gases.
l. provide for continuous disinfection feed after aeration.
Design shall provide
a. a hydraulic head of between 5 - 25 feet,
b. nozzles, with the size, number, and spacing of the nozzles being dependent on the flowrate, space, and the amount of head available,
c. nozzle diameters in the range of 1 to 1.5 inches to minimize clogging,
d. an enclosed basin to contain the spray. Any openings for ventilation, etc. must be protected with a 24-mesh screen.
e. for continuous disinfection feed after aeration.
Pressure aeration may be used for oxidation purposes only if pilot plant study indicates the method is applicable; it is not acceptable for removal of dissolved gases. Filters following pressure aeration must have adequate exhaust devices for release of air. Pressure aeration devices shall be designed to
a. give thorough mixing of compressed air with water being treated,
b. provide screened and filtered air, free of obnoxious fumes, dust, dirt and other contaminants.
Packed tower aeration (PTA) which is also known as air stripping involves passing water down through a column of packing material while pumping air counter‑currently up through the packing. PTA is used for the removal of volatile organic chemicals, trihalomethanes, carbon dioxide, and radon. Generally, PTA is feasible for compounds with a Henry's Constant greater than 100 atm mol/mol at 120C, but not normally feasible for removing compounds with a Henry’s Constant less than 10. For values between 10 and 100, PTA may be feasible but should be extensively evaluated using pilot studies. Values for Henry's Constant should be discussed with the reviewing agency prior to final design.
126.96.36.199 Process design
a. Process design methods for PTA involve the determination of Henry's Constant for the contaminant, the mass transfer coefficient, air pressure drop and stripping factor. The applicant shall provide justification for the design parameters selected (i.e. height and diameter of unit, air to water ratio, packing depth, surface loading rate, etc.). Pilot plant testing may be required.
The pilot test shall evaluate a variety of loading rates and air to water ratios at the peak contaminant concentration. Special consideration should be given to removal efficiencies when multiple contaminations occur. Where there is considerable past performance data on the contaminant to be treated and there is a concentration level similar to previous projects, the reviewing authority may approve the process design based on use of appropriate calculations without pilot testing. Proposals of this type must be discussed with the reviewing authority prior to submission of any permit applications.
b. The tower shall be designed to reduce contaminants to below the maximum contaminant level (MCL) and to the lowest practical level.
c. The ratio of the column diameter to packing diameter should be at least 7:1 for the pilot unit and at least 10:1 for the full scale tower. The type and size of the packing used in the full scale unit shall be the same as that used in the pilot work.
d. The minimum volumetric air to water ratio at peak water flow should be 25:1. The maximum air to water ratio for which credit will be given is 80:1.
e. The design should consider potential fouling problems from calcium carbonate and iron precipitation and from bacterial growth. It may be necessary to provide pretreatment. Disinfection capability shall be provided prior to and after PTA.
f. The effects of temperature should be considered since a drop in water temperature can result in a drop in contaminant removal efficiency.
188.8.131.52 Materials of construction
a. The tower can be constructed of stainless steel, concrete, aluminum, fiberglass or plastic. Uncoated carbon steel is not recommended because of corrosion. Towers constructed of light‑weight materials should be provided with adequate support to prevent damage from wind.
b. Packing materials shall be resistant to the aggressiveness of the water, dissolved gases and cleaning materials and shall be suitable for contact with potable water.
184.108.40.206 Water flow system
a. Water should be distributed uniformly at the top of the tower using spray nozzles or orifice‑type distributor trays that prevent short circuiting. For multi-point injection, one injection point for every 30 in2 ( 190 cm2) of tower cross-sectional area is recommended.
b. A mist eliminator shall be provided above the water distributor system.
c. A side wiper redistribution ring shall be provided at least every 10 feet in order to prevent water channeling along the tower wall and short circuiting.
d. Sample taps shall be provided in the influent and effluent piping.
e. The effluent sump, if provided, shall have easy access for cleaning purposes and be equipped with a drain valve. The drain shall not be connected directly to any storm or sanitary sewer.
f. A blow‑off line should be provided in the effluent piping to allow for discharge of water/chemicals used to clean the tower.
g. The design shall prevent freezing of the influent riser and effluent piping when the unit is not operating. If piping is buried, it shall be maintained under positive pressure.
h. The water flow to each tower shall be metered.
i. An overflow line shall be provided which discharges 12 to 14 inches above a splash pad or drainage inlet. Proper drainage shall be provided to prevent flooding of the area.
j. Butterfly valves may be used in the water effluent line for better flow control, as well as to minimize air entrainment.
k. Means shall be provided to prevent flooding of the air blower.
l. The water influent pipe should be supported separately from the tower's main structural support.
220.127.116.11 Air flow system
a. The air inlet to the blower and the tower discharge vent shall be downturned and protected with a non-corrodible 24‑mesh screen to prevent contamination from extraneous matter. It is recommended that a 4-mesh screen also be installed prior to the 24-mesh screen on the air inlet system.
b. The air inlet shall be in a protected location.
c. An air flow meter shall be provided on the influent air line or an alternative method to determine the air flow shall be provided.
d. A positive air flow sensing device and a pressure gauge must be installed on the air influent line. The positive air flow sensing device must be a part of an automatic control
system which will turn off the influent water if positive air flow is not detected. The pressure gauge will serve as an indicator of fouling buildup.
e. A backup motor for the air blower must be readily available.
18.104.22.168 Other features that shall be provided
a. A sufficient number of access ports with a minimum diameter of 24 inches to facilitate inspection, media replacement, media cleaning and maintenance of the interior.
b. A method of cleaning the packing material when fouling may occur.
c. Tower effluent collection and pumping wells constructed to clearwell standards.
d. Provisions for extending the tower height without major reconstruction.
e. An acceptable alternative supply must be available during periods of maintenance and operation interruptions. No bypass shall be provided unless specifically approved by the reviewing agency.
f. Disinfection application points both ahead of and after the tower to control biological growth.
g. Disinfection and adequate contact time after the water has passed through the tower and prior to the distribution system.
h. Adequate packing support to allow free flow of water and to prevent deformation with deep packing heights.
i. Operation of the blower and disinfectant feeder equipment during power failures.
j. Adequate foundation to support the tower and lateral support to prevent overturning due to wind loading.
k. Fencing and locking gate to prevent vandalism.
l. An access ladder with safety cage for inspection of the aerator including the exhaust port and de‑mister.
m. Electrical interconnection between blower, disinfectant feeder and well pump.
22.214.171.124 Environmental factors
a. The applicant must contact the appropriate air quality office to determine if permits are required under the Clean Air Act.
b. Noise control facilities should be provided on PTA systems located in residential areas.
Other methods of aeration may be used if applicable to the treatment needs. Such methods include but are not restricted to spraying, diffused air, cascades and mechanical aeration. The treatment processes must be designed to meet the particular needs of the water to be treated and are subject to the approval of the reviewing authority.
All aerators except those discharging to lime softening or clarification plants shall be protected from contamination by birds, insects, wind borne debris, rainfall and water draining off the exterior of the aerator.
Groundwater supplies exposed to the atmosphere by aeration must receive chlorination as the minimum additional treatment.
A bypass should be provided for all aeration units except those installed to comply with maximum contaminant levels.
The aggressiveness of the water after aeration should be determined and corrected by additional treatment, if necessary. (see Section 4.8).
Equipment should be provided to test for DO, pH, and temperature to determine proper functioning of the aeration device. Equipment to test for iron, manganese, and carbon dioxide should also be considered.
Redundant equipment shall be provided for units installed to comply with Safe Drinking Water Act primary contaminants, unless otherwise approved by the reviewing authority.
Iron and manganese control, as used herein, refers solely to treatment processes designed specifically for this purpose. The treatment process used will depend upon the character of the raw water. The selection of one or more treatment processes must meet specific local conditions as determined by engineering investigations, including chemical analyses of representative samples of water to be treated, and receive the approval of the reviewing authority. It may be necessary to operate a pilot plant in order to gather all information pertinent to the design. Consideration should be given to adjusting pH of the raw water to optimize the chemical reaction. Testing equipment and sampling taps shall be provided as outlined in Sections 2.8 and 2.10.
Oxidation may be by aeration, as indicated in Section 4.5, or by chemical oxidation with chlorine, potassium permanganate, sodium permanganate, ozone or chlorine dioxide.
a. Reaction ‑ A minimum detention time of 30 minutes shall be provided following aeration to insure that the oxidation reactions are as complete as possible. This minimum detention may be omitted only where a pilot plant study indicates no need for detention. The detention basin may be designed as a holding tank without provisions for sludge collection but with sufficient baffling to prevent short circuiting.
b. Sedimentation ‑ Sedimentation basins shall be provided when treating water with high iron and/or manganese content, or where chemical coagulation is used to reduce the load on the filters. Provisions for sludge removal shall be made.
Filters shall be provided and shall conform to Section 4.2.
See Section 4.4.1.
This process, consists of a continuous or batch feed of potassium permanganate to the influent of a manganese coated media filter.
a. Provisions should be made to apply the permanganate as far ahead of the filter as practical and to a point immediately before the filter.
b. Other oxidizing agents or processes such as chlorination or aeration may be used prior to the permanganate feed to reduce the amount of the chemical oxidant needed.
c. An anthracite media cap of at least six inches or more as required by the reviewing authority shall be provided over manganese coated media.
d. Normal filtration rate is three gallons per minute per square foot (7.2 m/hr).
e. Normal wash rate is 8 to 10 gallons per minute per square foot (20 - 24 m/hr) with manganese greensand and 15 to 20 gallons per minute (37 - 49 m/hr) with manganese coated media.
f. Air washing should be provided.
g. Sample taps shall be provided
1. for the raw water,
2. immediately ahead of filtration,
3. at the filter effluent, and
4. should be provided at points between the anthracite media and the manganese coated media.
This process of iron and manganese removal should not be used for water containing more than 0.3 milligrams per liter of iron, manganese or combination thereof. This process is not acceptable where either the raw water or wash water contains dissolved oxygen or other oxidants.
Biofiltration to remove manganese and/or iron requires on-site piloting to establish effectiveness. The final filter design shall be based on the on-site pilot plant studies and shall comply with all applicable portions of section 4.2.7. Continuous disinfection shall be provided for the finished water.
This process shall not be used when iron, manganese or combination thereof exceeds 1.0 mg/L. The total phosphate applied shall not exceed 10 mg/L as PO4. Where phosphate treatment is used, satisfactory chlorine residuals shall be maintained in the distribution system. Possible adverse affects on corrosion must be addressed when phosphate addition is proposed for iron sequestering. Polyphosphate treatment may be less effective for sequestering manganese than for iron.
a. Feeding equipment shall conform to the requirements of Part 5.
b. Stock phosphate solution must be kept covered and disinfected by carrying approximately 10 mg/L free chlorine residual unless the phosphate is not able to support bacterial growth and the phosphate is being fed from the covered shipping container. Phosphate solutions having a pH of 2.0 or less may also be exempted from this requirement by the reviewing authority.
c. Polyphosphates shall not be applied ahead of iron and manganese removal treatment. The point of application shall be prior to any aeration, oxidation or disinfection if no iron or manganese removal treatment is provided.
d. The phosphate feed point shall be located as far ahead of the oxidant feed point as possible.
Sodium silicate sequestration of iron and manganese is appropriate only for groundwater supplies prior to air contact. On‑site pilot tests are required to determine the suitability of sodium silicate for the particular water and the minimum feed needed. Rapid oxidation of the metal ions such as by chlorine or chlorine dioxide must accompany or closely precede the sodium silicate addition. Injection of sodium silicate more than 15 seconds after oxidation may cause detectable loss of chemical efficiency. Dilution of feed solutions much below five per cent silica as SiO2 should also be avoided for the same reason. Sodium silicate treatment may be less effe