Current through Register Vol. XLI, No. 36, September 6, 2024
Section 64-77-6 - Treatment (General and Clarification)6.1. General. -- 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. All treatment processes with only one (1) unit shall be capable of meeting the projected maximum daily demand in eight (8) hours of operation or less to provide "down time" for repairs and maintenance.6.2. Clarification. -- Clarification is generally considered to consist of any process or combination of processes which reduce the concentration of suspended matter in drinking water prior to filtration. Plants designed for processing surface water shall: provide a minimum of two (2) units each for rapid mix, flocculation and sedimentation; permit operation of the units either in series or parallel where softening is performed and shall permit series or parallel operation where plain clarification is performed; be constructed to permit units to be taken out of service without disrupting operation; be constructed with drains or pumps sized to allow dewatering in a reasonable period of time; provide multiple-stage treatment facilities when required by the BPH; be started manually following a shutdown; and minimize hydraulic head losses between units to allow future changes in processes without the need for repumping. For ground water systems under the direct influence of surface water, the requirements in this subsection may be modified by the BPH, depending on the raw water quality characteristics. 6.2.a. Presedimintation. -- Surface waters containing high turbidity may require pretreatment, usually sedimentation either with or without addition of coagulation chemicals. Presedimentation basins shall have hopper bottoms or be equipped with continuous mechanical sludge removal apparatuses, have provisions for dewatering, provide for incoming water to be dispersed across the full width of the line of travel, prevent short-circuiting, provide for bypassing the presedimentation basins, and have a minimum two (2) hour detention.6.2.b. Coagulation. -- Is 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, 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. 6.2.b.1. Equipment. -- Basins shall 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. The coagulation and flocculation basins shall be as close together as possible.6.2.b.2. Mixing. -- The detention period shall 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 shall determine the appropriate G value and detention time through jar testing.6.2.c. Flocculation. -- 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. 6.2.c.1. 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, or both, shall be provided to handle dewatering and sludge removal.6.2.c.2. 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-though velocity shall be not less than 0.5 or greater than 1.5 feet per minute.6.2.c.3. Equipment. -- Agitators shall be driven by variable speed drives with the peripheral speed of paddles ranging from 0.5 to three (3.0) feet per second. External, non-submerged motors are recommended.6.2.c.4. 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 or greater than 1.5 feet per second. Allowances shall be made to minimize turbulence at bends, elevation drops and changes in direction.6.2.c.5. Other Designs. -- The BPH may allow baffling to be used for flocculation in small plants if the design would permit the velocities and flows noted above to be maintained.6.2.c.6. Superstructure. -- The BPH may require a superstructure over the flocculation basins.6.2.d. Sedimentation. -- Sedimentation shall follow flocculation. 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: 6.2.d.1. Detention time. -- A minimum of four (4) hours of settling time shall be provided. This may be reduced to two (2) hours for lime-soda softening facilities treating only groundwater. Reduced sedimentation time may also be approved by the BPH when equivalent effective settling is demonstrated (i.e., tube settlers, lamella plates, etc.) but shall never be less than two (2) hours.6.2.d.2. 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 shall be constructed across the basin close to the inlet end and shall project several feet below the water surface to dissipate inlet velocities and provide uniform flows across the basin;6.2.d.3. Outlet devices. -- Outlet weirs or submerged orifices shall be designed to maintain velocities suitable for settling in the basin and to 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;6.2.d.4. Overflow rate. -- The rate of flow over the outlet weir shall not exceed twenty thousand (20,000) gallons per day per foot of the outlet launder. Where submerged orifices are used as an alternate for overflow weirs, they shall be not lower than three (3) feet below the flow line. The entrance velocity through the submerged orifices shall not exceed 0.5 feet per second;6.2.d.5. Velocity. -- The velocity through settling basins shall not exceed 0.5 feet per minute. The basins shall be designed to minimize short-circuiting. Fixed or adjustable baffles shall be provided as necessary to achieve the maximum potential for clarification;6.2.d.6. Overflow. -- An overflow weir or pipe shall be installed that will establish the maximum water level desired on top of the filters. It shall discharge by gravity with a free fall at a location where the discharge will be noted;6.2.d.7. Superstructure. -- The BPH may require a public water system to build a superstructure over the sedimentation basins. The BPH may allow a cover in lieu of a superstructure, if there is no mechanical equipment in the basins and if provisions are included for adequate monitoring under all expected weather conditions;6.2.d.8. Sludge collection. -- Shall be designed to ensure the collection of sludge from throughout the basin;6.2.d.9. Drainage. -- Basins shall be provided with a means for dewatering. Basin bottoms shall slope toward the drain not less than one (1) foot in twelve (12) feet where mechanical sludge collection equipment is not required;6.2.d.10. Flushing lines. -- Flushing lines or hydrants shall be provided and shall be equipped with backflow prevention devices acceptable to the BPH;6.2.d.11. Safety. -- Permanent ladders or handholds shall be provided on the inside walls of basins. Guard rails shall be included;6.2.d.12. Sludge removal. -- Sludge removal design shall provide that sludge pipes shall be not less than three (3) inches in diameter and so arranged as to facilitate cleaning. The entrance to sludge withdrawal piping shall prevent clogging. Valves shall be located outside the tank for accessibility. The operator shall be able to observe and sample sludge being withdrawn from the unit; and6.2.d.13. Sludge disposal. -- Facilities shall be provided for the proper disposal of sludge.6.2.e. Solids contact unit. -- Combined softening and clarification units are generally acceptable in situations where water characteristics, especially temperature, do not fluctuate rapidly, flow rates are uniform and operation is continuous. The BPH shall give specific approval to the public water system engineer before these units are considered as clarifiers without softening. The public water system engineer shall design clarifiers for the maximum uniform rate and shall be adjustable to changes in flow that are less than the design rate and for changes in water characteristics. The BPH requires a minimum of two (2) units for surface water treatment. 6.2.e.1. Installation of equipment. -- A representative of the manufacturer shall supervise the installation of mechanical equipment, trouble-shooting, problem solving times and start-up and initial operation.6.2.e.2. Operating equipment. -- The following shall be provided for plant operation: a complete outfit of tools and accessories; trouble shooting and problem solving manuals; necessary laboratory equipment; and adequate piping with suitable sampling taps located to permit the collection of samples of water from critical portions of the units.6.2.e.3. Chemical feed. -- Chemicals shall be applied at such points and by such means as to insure satisfactory mixing of the chemicals with the water.6.2.e.4. Mixing. -- The BPH may require a rapid mix device or chamber ahead of solids contact units to assure proper mixing of the chemicals applied. Mixing devices employed shall be constructed to provide mixing of the raw water with previously formed sludge particles, and prevent deposition of solids in the mixing zone.6.2.e.5. Flocculation. -- Flocculation equipment shall: be adjustable (speed or pitch, or both); provide for coagulation in a separate chamber or baffled zone within the unit; and provide the flocculation and mixing period to be not less than thirty (30) minutes.6.2.e.6. Sludge concentrators. -- The equipment shall provide either internal or external concentrators in order to obtain a concentrated sludge with a minimum of waste water. Large basins shall have at least two (2) sumps for collecting sludge with one (1) sump located in the central flocculation zone.6.2.e.7. Sludge removal. -- Sludge removal design shall provide that sludge pipes shall be not less than three (3) inches in diameter and so arranged as to facilitate cleaning. Entrance to sludge withdrawal piping shall prevent clogging. Valves shall be located outside the tank for accessibility. The design shall permit the operator to observe and sample sludge being withdrawn from the unit.6.2.e.8. Cross-connections. -- Blow-off outlets and drains shall terminate and discharge at places satisfactory to the BPH. Cross-connection control shall be included for the potable water lines used to backflush sludge lines.6.2.e.9. Detention period. -- The detention time shall be based on the raw water characteristics and other local conditions that effect the operation of the unit. Based on design flow rates, the detention time shall be two (2) to four (4) hours for suspended solids contact clarifiers and softeners treating surface water and one (1) to two (2) hours for the suspended solids contact softeners treating only groundwater.6.2.e.10. Suspended slurry concentrate. -- Softening units shall be designed so that continuous slurry concentrates of one per cent (1%) or more, by weight, can be satisfactorily maintained.6.2.e.11. Water losses. -- Units shall be provided with suitable controls for sludge withdrawal. Total water losses shall not exceed five percent (5%) for clarifiers and three percent (3%) for softening units. The solids concentration of sludge bed to waste shall be three percent (3%) by weight for clarifiers and five percent (5%) by weight for softeners.6.2.e.12. Weirs or orifices. -- The units shall be equipped with either overflow weirs or orifices constructed so that water at the surface of the unit does not travel more than ten (10) feet horizontally to the collection trough. Weirs shall be adjustable and at least equivalent in length to the perimeter of the tank. Weir loading shall not exceed ten (10) gallons per minute per foot of weir length for units used for clarifiers and twenty (20) gallons per minute per foot of weir length for units used for softeners. Where orifices are used, the loading rates per foot of launder rates shall be equivalent to weir loadings. Either weirs or orifices shall produce uniform rising rates over the entire area of the tank.6.2.e.13. Upflow rates. -- The BPH shall receive supporting data from the public water system's engineer to justify rates exceeding the following: one (1) gallon per minute per square foot of area at the sludge separation line for units used for clarifiers; and 1.75 gallons per minute per square foot of area at the slurry separation line; for units used for softeners.6.2.f. Tube or plate settlers. -- Commercial settler units consisting of variously shaped tubes or plates that are installed in multiple layers and at an angle to the flow may be used for sedimentation following flocculation. 6.2.f.1. General criteria. 6.2.f.1.A. Inlet and outlet considerations. -- The inlets and outlets shall be designed to maintain velocities suitable for settling in the basin and to minimize maldistribution acoss the units.6.2.f.1.B. Drainage. -- Drain piping from the settler units shall be sized to facilitate a quick flush of the settler units and to prevent flooding other portions of the plant.6.2.f.1.C. Protection from freezing. -- Although most units are located within a plant, outdoor installations shall provide sufficient freeboard above the top of settlers to prevent freezing in the units. A cover or enclosure is strongly recommended.6.2.f.1.D. Application rate for tube settlers. -- A maximum rate of two (2) gallons per square foot per minute of cross-sectional area is required, unless higher rates are successfully shown through pilot plant or in-plant demonstration studies.6.2.f.1.E. Application rate for plates. -- A maximum forward design flow through the inclined plate settler is 0.5 gallons per minute per square foot based on eighty percent (80%) of the projected horizontal plate area.6.2.f.1.F. Flushing lines. -- Flushing lines shall be provided to facilitate maintenance and shall be properly protected against backflow or back siphonage.6.2.f.1.G. Placement. -- Modules should be placed in zones of stable hydraulic conditions and in areas nearest effluent launders for basins not completely covered by modules.6.2.f.1.H. Inlets and Outlets. -- Inlets and outlets shall conform to paragraphs 6.2.d.2 and 6.2.d.3.6.2.f.1.I. Support. -- The support system must be able to carry the weight of the modules when the basin is drained plus any additional weight to support maintenance.6.2.f.1.J. Cleaning. -- Provisions shall be made to allow the water level to be dropped, and a water or an air jet system for cleaning the modules.6.2.g. High Rate Clarification Processes. -- The BPH may approve high rate clarification processes upon demonstration of full scale operation with similar raw water quality conditions. 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.6.3. Filtration. -- Acceptable filters that may be considered are rapid rate gravity filters, rapid rate pressure filters, diatomaceous earth filtration, slow sand filtration, direct filtration, deep bed rapid rate gravity filters, membrane filtration, bag and cartridge filters. The application of any type of filter shall 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. 6.3.a. Rapid rate gravity filters. 6.3.a.1. Pretreatment. -- The use of rapid rate gravity filters shall require pretreatment.6.3.a.2. Rate of filtration. -- The BPH shall determine the rate of filtration through consideration of such factors as raw water quality, the degree of pretreatment provided, filter media, water quality control parameters, the competency of operation personnel, and other pertinent factors. The maximum rate shall be two (2) gallons per minute per square foot of filter area for sand media, four (4) gallons per minute per square foot of filter area for dual media, and six (6) gallons per minute per square foot of filter for mixed media. In any case, the filter rate shall be proposed and justified by the designing engineer to the satisfaction of the BPH prior to the preparation of final plans and specifications.6.3.a.3. Number. -- At least two (2) filter units are required. Where only two (2) 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 (2) filter units are provided, the filters shall be capable of meeting the plant design capacity at the approved filtration rate with one (1) filter removed from service. Where declining rate filtration is provided, the variable aspect of filtration rates and the number of filters shall be considered when determining the design capacity for the filters.6.3.a.4. Structural details and hydraulics. -- The filter structure shall be designed to provide for: vertical walls within the filter; no protrusion of the filter walls into the filter media; covering by superstructure; head room to permit normal inspection and operation; minimum depth of filter box of eight and one half (81/2) feet; minimum water depth over the surface of the filter media of three (3) feet; trapped effluent to prevent backflow of air to the bottom of the filters; prevention of floor drainage to the filter with a minimum four (4) inch curb around the filter; prevention of flooding by providing overflow; maximum velocity of treated water in pipe and conduits to filters of two (2) feet per second; cleanouts and straight alignment for influent pipes or conduits where solids loading is heavy, or following lime-soda softening; washwater drain capacity to carry maximum flow; walkways around filters, to be not less than twenty-four (24) inches wide; safety handrails or walls around filter areas adjacent to normal walkways; and construction to prevent cross connections and common walls between potable and non-potable water.6.3.a.5. Washwater troughs. -- Washwater troughs shall be constructed to have: the bottom elevation above the maximum level of expanded media during washing, a two-inch freeboard at the maximum rate of wash; the top edge level and all at the same elevation; spacing so that each trough serves the same number of square feet of filter area; and maximum horizontal travel of suspended particles to reach the trough not to exceed three (3) feet.6.3.a.6. Filter. -- The media shall be clean silica sand or other natural or synthetic media free from detrimental chemical or bacterial contaminants. The filter shall be constructed to provide the following characteristics: a total depth of not less than twenty-four (24) inches and generally not more than thirty (30) inches; and a minimum of twelve (12) inches of media with an effective size range no greater than 0.45 mm to 0.55 mm, and uniformity coefficient of the smallest material not greater than 1.65.6.3.a.7. Types of filter media. 6.3.a.7.A. 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 effective size of 0.45 mm to 0.55 mm with uniformity coefficient not greater than 1.65 when used alone; an effective size of 0.8 mm to 1.2 mm with a uniformity coefficient not greater than 1.85 when used as a cap; specific gravity of 1.4, acid solubility less than five (5) percent, a Mho's scale of hardness greater than 2.7 and an effective maximum size of 0.8 mm for anthracite used as a single media on potable groundwater for iron and manganese removal only (effective sizes greater than 0.8 mm may be approved by the BPH based upon on-site pilot plant studies).6.3.a.7.B. Sand. -- Sand shall be clean silica sand and have an effective size of 0.45 mm to 0.55 mm, a specific gravity greater than 2.5, an acid solubility less than 5 percent and a uniformity coefficient of not greater than 1.65.6.3.a.7.C. Granular activated carbon (GAC). -- Granular activated carbon media may be considered. The design shall include the following: the media shall meet the basic specifications for filter media as given in this section except that larger size media may be allowed by the BPH where full scale tests have demonstrated that treatment goals can be met under all conditions; there shall be provisions for a free chlorine residual and adequate contact time in the water following the filters and prior to distribution; there shall be means for periodic treatment of filter material for control of bacterial and other growth; and provisions shall be made for frequent replacement or regeneration if GAC is used for filtration.6.3.a.7.D. High Density Sand. -- High density sand shall consist of hard durable, and dense grain garnet, ilmente, hematite, magnetite, or associated minerals of those ores that resists degradation during handling and use. The high density sand shall contain at least ninety-five (95) percent of the associated material with a specific gravity of 3.8 or higher, have a uniformity coefficient of not greater than 1.65 and have an acid solubility less than five (5) percent.6.3.a.7.E. Other Media. -- The BPH shall consider other media based on experimental data and operating experience.6.3.a.7.F. Torpedo sand. -- A three (3) inch layer of torpedo sand shall be used as a supporting media for filter sand, and shall have an effective size of 0.8 mm to 2.0 mm and a uniformity coefficient not greater than 1.7.6.3.a.7.G. Gravel. -- Gravel, when used as the supporting media, shall consist of a cleaned and washed hard, durable, rounded silica particles and shall not include flat or elongated particles. The coarsest gravel shall be approximately two (2) inches in size when the gravel rests directly on the strainer system and shall extend above the top of the perforated laterals. Not less than four (4) layers of gravel shall be provided in accordance with the size and depth distribution when used with perforated laterals, as illustrated in Table 64-77C of this rule. Reduction of gravel depths or other size gradations may be considered upon justification to the BPH when proprietary filter bottoms are specified or for slow sand filtration.6.3.a.8. Filter bottoms and strainer systems. -- Departures from the standards under this rule may be acceptable for high rate filters and 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 minimize loss of head in the manifold and laterals and assure even distribution of washwater and even rate of filtration over the entire area of the filter. The ratio of the area of the final openings of the strainer systems to the area of the filter shall be about 0.003. The total cross-sectional area of the laterals shall be about twice the total area of the final openings. The cross-sectional area of the manifold shall be one and one-half (11/2) to two (2) times the total area of the laterals. Lateral perforations without strainers shall be directed downward.6.3.a.9. 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 the provision for water pressures of at least forty-five (45) pounds per square inch and a properly installed vacuum breaker or other device approved by the BPH to prevent back siphonage if connected to the filtered or finished water system. The rate of flow shall be two (2) gallons per minute per square foot of filter area with fixed nozzles or 0.5 gallons per minute per square foot with revolving arms. Air wash can be considered based on experimental data and operating experiences.6.3.a.10. Air scouring. -- Air scouring can be considered in place of surface wash. Air flow for air scouring the filter shall be three (3) to five (5) standard cubic feet per minute per square foot of filter area when the air is introduced in the underdrain; a lower air rate shall be used when the air scour distribution system is placed above the underdrains. A method for avoiding excessive loss of the filter media during backwashing shall be provided. Air scouring shall be followed by a fluidization wash sufficient to re-stratify the media. Air shall be free from contamination. Air scour distribution systems shall 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. Piping for the air distribution system shall not be flexible hose that will collapse when not under air pressure and shall not be a relatively soft material that may erode at the orifice opening with the passage of air at high velocity. Air delivery piping shall not pass down through the filter media nor shall there be any arrangement in the filter design that would allow short circuiting between the applied unfiltered water and the filtered water. Consideration shall be given to maintenance and replacement of air delivery piping. The backwash delivery system shall be capable of fifteen (15) gallons per minute per square foot of filter surface area; however, when air scouring is provided the backwash rate shall be variable and shall not exceed eight (8) gallons per minute per square foot unless operating experience shows that a higher rate is necessary to remove scoured particles from filter surfaces, and the filter underdrains shall be designed to accommodate air scour piping when the piping is installed in the underdrain.6.3.a.11. Appurtenances. -- The following shall be provided for every filter: influent and effluent sampling taps; loss of head gauge; rate of flow controls; and an indicating rate-of-flow meter. A modified rate controller that limits the rate of filtration to a maximum rate may be used; Provided, that, 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 BPH. Provisions shall be made for filtering to waste (rewash) with appropriate measures for cross connection prevention. For surface water systems or groundwater under the direct influence of surface water systems with three (3) or more filters, on-line turbidimeters shall be installed on the effluent line from each filter. All turbidimeters 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 shall be designed to accurately measure low-range turbidities and have an alarm that sounds when the effluent level exceeds 0.3 NTU. It is recommended the following be provided for every filter: wall sleeves providing access to the filter interior at several locations for sampling or pressure sensing; a flow rate controller capable of providing gradual rate increases when placing the filters back into operation and a pressure hose and storage rack at the operating floor for washing filter walls.6.3.a.12. Backwash. -- Provisions shall be made for washing filters with a minimum rate of fifteen (15) gallons per minute per square foot, consistent with water temperatures and specific gravity of the filter media. A rate of twenty (20) gallons per minute per square foot or a rate necessary to provide for a fifty percent (50%) expansion of the filter bed is recommended. A reduced rate of ten (10) gallons per minute per square foot may be acceptable for full depth anthracite or granular activated carbon filters. Filtered water shall be provided at the required rate by washwater tanks, a washwater pump, or from the high service main. Washwater pumps shall be in duplicate unless an alternate means of obtaining washwater is available. Washwater pumps shall run a minimum fifteen (15) minutes for the wash of one (1) filter at the design rate of wash. A washwater regulator or valve on the main washwater line shall be provided to obtain the desired rate of filter wash with the washwater valves on the individual filters open wide. A rate-of-flow indicator, preferably with a totalizer, on the main washwater line, shall be located so that it can be easily read by the operator during the washwater process. The design shall prevent rapid changes in backwash water flow. Backwash shall be operator initiated. Automated systems shall be operator adjustable.6.3.a.13. Miscellaneous. -- Roof drains shall not discharge into the filters or basins and conduits preceding the filters.6.3.b. Rapid rate pressure filters. -- The normal use of rapid rate pressure filters is for iron and manganese removal and may be used for surface supplies classified as groundwater under direct influence where turbidity is less than or equal to ten (10) NTU. Pressure filters shall not be used in the filtration of other surface supplies or following lime-soda softening. 6.3.b.1. General. -- Minimum criteria relative to rate of filtration, structural details, hydraulics, filter media, etc., provided for rapid rate gravity filters also apply to pressure filters where appropriate.6.3.b.2. Rate of filtration. -- The rate shall not exceed three gallons per minute per square foot of filter area except where in-plant testing, as approved by the BPH, has demonstrated satisfactory results at higher rates.6.3.b.3. Details of design. -- The filters shall be designed to provide for: loss of head gauges on the inlet and outlet pipes of each filter; an easily readable meter or flow indicator on each battery of filters (a flow indicator is recommended for each filtering unit); filtration and backwashing of each filter individually with an arrangement of piping as simple as possible to accomplish these purposes; minimum side wall shell height of five (5) feet (a corresponding reduction in side wall height is acceptable where proprietary bottoms permit reduction of the gravel depth); the top of the washwater collectors to be at least eighteen (18) inches above the surface of the media; the underdrain system to efficiently collect the filtered water and to uniformly distribute the backwash water at a rate not less than fifteen (15) gallons per minute per square foot of filter area; backwash flow indicators and controls that are easily readable while operating the control valves; an air release valve on the highest point of each filter; an accessible manhole of adequate size to facilitate inspection and repairs for filters thirty-six (36) inches in diameter; there are sufficient handholds for filters less than thirty-six (36) inches in diameter; manholes should be at least twenty-four (24) inches in diameter where feasible; and means to observe the wastewater during backwashing, and construction to prevent cross-connection.6.3.c. Diatomaceous earth filtration. -- The use of diatomaceous earth filters may be considered for application to surface waters with low turbidity and low bacterial contamination. 6.3.c.1. Conditions of use. -- Diatomaceous earth filters are expressly excluded from considerations for the following conditions: bacteria removal; color removal; turbidity removal where either the quantity of turbidity is high or the turbidity exhibits poor filterability characteristics; and filtration of waters with high algae counts.6.3.c.2. Pilot plant study. -- Installation of a diatomaceous earth filtration system shall be preceded by a pilot plant study on the water to be treated. Conditions of the study such as duration, filter rates, head loss accumulation, slurry feed rates, turbidity removal, bacteria removal, etc., shall be approved by the BPH prior to the study. Satisfactory pilot plant results shall be obtained prior to preparation of final construction plans and specifications. The pilot plant study shall demonstrate the ability of the system to meet applicable drinking water standards at all times.6.3.c.3. Types of filters. -- Pressure or vacuum diatomaceous earth filtration units may be considered for approval; however, the BPH prefers the vacuum type for its ability to accommodate a design that permits observation of the filter surfaces to determine proper cleaning, damage to a filter element, and adequate coating over the entire filter area.6.3.c.4. Treated water storage. -- Treated water storage capacity in excess of normal requirements shall be provided: to allow operation of the filters at a uniform rate during all conditions of system demand at or below the approved filtration rate; and to guarantee continuity of service during adverse raw water conditions without by-passing the system.6.3.c.5. Number of units. -- See subdivision 6.3.b. "Rapid Rate Gravity Filters."6.3.c.6. Pre-coat. -- When pre-coating is accomplished with a filter-to-waste system, 0.15 to 0.2 pounds per square foot of filter area is recommended. 6.3.c.6.A. Application. -- A uniform pre-coat 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.6.3.c.6.B. Quantity. -- Diatomaceous earth in the amount of two tenths (0.2) pounds per square foot of filter area or an amount sufficient to apply a one-eighths (1/8) inch coating shall be used with recirculation.6.3.c.7. 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. Rate of body feed is dependent on raw water quality and characteristics and shall be determined in the pilot plant study. Operation and maintenance can be simplified by providing accessibility to the feed system and slurry lines. Continuous mixing of the body feed slurry is required.6.3.c.8. Filtration. 6.3.c.8.A. Rate of filtration. -- The recommended nominal rate is one (1.0) gallon per minute per square foot of filter area with a recommended maximum of one and a half (1.5) gallons per minute per square foot. The filtration rate shall be controlled by a positive means.6.3.c.8.B. Head loss. -- The head loss shall not exceed thirty (30) pounds per square inch for pressure diatomaceous earth filters, or a vacuum of fifteen (15) inches of mercury for a vacuum system.6.3.c.8.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 one tenth (0.1) gallon per minute per square foot of filter area shall be provided.6.3.c.8.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 (1) inch is provided between elements or between any element and a wall.6.3.c.8.E. Inlet design. -- The filter influent shall be designed to prevent scour of the diatomaceous earth from the filter element.6.3.c.9. Backwash. -- A satisfactory method to thoroughly remove and dispose of spent filter cake shall be provided.6.3.c.10. Appurtenances. -- The following shall be provided for every filter: sampling taps for raw and filtered water; a loss of head or differential pressure gauge; a rate-of-flow indicator, preferably with a totalizer; evaluation of the need for body feed, recirculation and any other pumps; provisions for filtering to waste with appropriate measures for backflow prevention; and a throttling valve used to reduce rates below normal during adverse raw water conditions. Recommend a pressure hose and storage rack at the operating floor for washing the filter; a throttling valve used to reduce rates below normal during adverse raw water conditions; a flow rate controller capable of providing gradual rate increases when placing the filters back into operation; and a continuous monitoring turbidimeter with recorder on each filter effluent for plants treating surface water.6.3.d. Slow rate gravity filters. -- The use of slow rate gravity filters shall require prior engineering studies to demonstrate the adequacy and suitability of this method of filtration for the specific raw water supply. 6.3.d.1. Quality of raw water. -- Slow rate gravity filtration shall be limited to waters having maximum turbidities of ten (10) NTU and maximum color of fifteen (15) units; this turbidity shall not be attributable to colloidal clay. Raw water quality data shall include examinations for algae to determine the nature and extent of algae growths and their potential adverse affect on filter operation.6.3.d.2. Number. -- At least two (2) units shall be provided. Where only two (2) 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 (2) filter units are provided, the filters shall be capable of meeting the plant design capacity at the approved filtration rate with one (1) filter removed from service.6.3.d.3. Structural details and hydraulics. -- Slow rate gravity filters shall be designed to provide: a cover; headroom to permit normal movement by operation personnel for scraping and sand removal operations; adequate hatches and access ports for handling of sand and for ventilation; protection from freezing and an overflow at the maximum filter water level.6.3.d.4. 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 forty-five (45) to one hundred fifty (150) gallons per day per square foot of sand area; higher rates are acceptable when demonstrated to the satisfaction of the BPH.6.3.d.5. Underdrains. -- 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 spaced so that the maximum velocity of the water flow in the underdrain does not exceed 0.75 feet per second. The maximum spacing of laterals shall not exceed three (3) feet if pipe laterals are used.6.3.d.6. Filtering material. -- Filter sand shall be placed on graded gravel layers for a minimum depth of thirty (30) inches. The effective size shall be between 0.15 mm and 0.30 mm. The BPH may require a pilot study if larger sand is proposed. The uniformity coefficient shall not exceed 2.5. The sand shall be clean and free from foreign matter. The sand shall be rebedded when scraping has reduced the bed depth to no less than nineteen (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.6.3.d.7. Filter gravel. -- The supporting gravel shall conform to the size and depth distribution provided for rapid rate gravity filters.6.3.d.8. Depth of water on filter beds. -- The design shall provide a depth of at least three (3) to six (6) feet of water over the sand. Influent water shall not scour the sand surface.6.3.d.9. Control appurtenances. -- Each filter shall be equipped with: influent and effluent sampling taps; an indicating rate-of-flow meter (A modified rate controller that limits the rate of filtration to a maximum rate may be used, but 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 loss of head gauge or other means to measure head loss; an orifice, Venturi meter, or other suitable means of discharge measurement installed on each filter to control the rate of filtration; and an effluent pipe designed to maintain the water level above the top of the filter sand.6.3.d.10. Ripening. -- Slow sand filters shall be operated to waste after scraping or rebedding during ripening period until the filter effluent turbidity falls to consistently below the regulated drinking water standard established for the system.6.3.e. Direct filtration. -- Direct filtration, as used herein, refers to the filtration of a surface water or groundwater determined to be under the direct influence of surface water following chemical coagulation and possibly flocculation without prior settling. The nature of the treatment process shall depend upon the raw water quality. 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 the pilot plant or in-plant demonstration studies. 6.3.e.1. Engineering report. -- The engineering report shall include a historical summary of operating conditions and 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 shall be evaluated in the report: color; turbidity; bacterial concentration; microscopic biological organisms; temperature; total solids; general inorganic chemical characteristics; and additional parameters as required by the BPH. The report shall also include a description of methods and work to be done during a pilot plant study or, where appropriate, an in-plant demonstration study.6.3.e.2. Pilot plant studies. -- The BPH may, after approval of the engineering report, require a pilot study or in-plant demonstration study by the public water system or their engineer. The study shall 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: chemical mixing conditions including shear gradients and detention periods; chemical feed rates; use of various coagulants and coagulant aids; flocculation conditions; filtration rates; filter gradation; types of media and depth of media; filter breakthrough conditions; and the adverse impact of recycling backwash water due to microorganisms, solids, algae, trihalomethane formation and other similar problems; length of filter runs; length of backwash cycles; quantities and make-up of the wastewater. The public water system or their engineer, prior to the initiation of design plans and specifications, shall submit a final report including the engineer's design recommendations to the BPH. The pilot plant filter shall be of a similar type and operated in the same manner as proposed for full scale operation. The pilot study shall demonstrate the minimum contact time necessary for optimum filtration for each coagulant proposed.6.3.e.3. Pretreatment. -- The final coagulation and flocculation basin design should be based upon the pilot plant or in-plant demonstration studies augmented with applicable portions of subdivision 6.2.b. "Coagulation" and subdivision 6.2.c. "Flocculation."6.3.e.4. Filtration. -- 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 subdivision 6.3.a. "Rapid Rate Gravity Filters." Pressure filters or single media sand filters shall not be used.6.3.e.5. Appurtenances. -- Every filter shall have an influent and effluent sampling taps, an indicating loss of head gauge and an indicating rate-of-flow meter. A modified rate controller which limits the rate of filtration to a maximum rate may be used but the 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; and provisions for filtering to waste with appropriate measures for cross connection control. 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 turbidity 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 fifteen (15) minutes. Turbidimeters on individual filters should be designed to accurately measure low-range turbidities and have an alarm that sounds when the effluent level exceeds 0.3 NTUs. It is recommended that every filter have wall sleeves providing access to the filter interior at several locations for sampling or pressure sensing; a pressure hose and storage rack at the operating floor for washing filter walls; and a flow rate controller capable of providing gradual rate increases when placing the filters back into operation.6.3.e.6. Site requirements. -- The plant and its design and land ownership surrounding the plant shall allow for modifications of the plant.6.3.f. Deep bed rapid rate gravity filters. -- 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 forty-eight (48) inches. Filter media sizes are typically larger than those required in conventional rapid rate gravity sand filters. Deep bed rapid rate filters may be considered based upon pilot studies approved by the BPH and shall comply with all applicable portions of subdivision 6.3.a. of this section.6.3.g. Biologically active filters. -- 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 disinfection 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. 6.3.g.1. Pilot study. -- Biologically active filters may be considered based on pilot studies approved by the BPH. 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 greater than three (3) months. The pilot study shall establish empty bed contact time, biomass loading, and/or other parameters necessary for successful operation as required by the BPH. The final filter design shall be based on the pilot study studies and shall comply with all applicable portions of subdivision 6.3.a. of this section.6.3.h. Membrane Filtration Systems. -- Membrane filtration systems, as used herein, generally refer to a complete and fully functional treatment system employing the use of a selective, physical barrier, consisting of thin sheets or hollow fibers of polymeric and/or inorganic materials, for the removal of suspended and/or dissolved solids from the source water. Such systems are often comprised of several sub-systems, or components, including: Membrane modules or cassettes; the membrane filtration skids, basins, or arrays; backwash sub-systems for frequent removal of suspended solids; chemical clean-in-place sub-systems to maintain the membrane performance and treatment capacity; air compressors and air blowers for control, maintenance, and integrity testing of the membrane system components; pumps; valves; piping; and related motor and supervisory controls necessary to operate and monitor membrane filtration performance. Membrane filtration systems require consideration for prescreening, pre-treatment, post-treatment, and residuals handling to properly maintain long-term performance. 6.3.h.1. Applicability. -- Membrane filtration systems can be identified within four (4) categories, including microfiltration (MF), ultrafiltration (UF), nanofiltration (NF), and reverse osmosis (RO). These categories of membranes shall be used in the following three (3) types of membrane filtration systems; Provided, that the membranes may be used in other systems with the approval of BPH. 6.3.h.1.A. Low Pressure Membrane Filtration Systems. -- Microfiltration and ultrafiltration are specifically used for the removal of suspended solids, including pathogens [e.g., protozoa, bacteria, and viruses, particulate matter, and natural organic matter (NOM)] depending on the membrane material's effective pore size. These types of systems are recognized as a treatment technique for the removal of Giardia, Cryptosporidium, and other pathogens from surface water sources and groundwater sources under the influence of surface water.6.3.h.1.B. High Pressure Membrane Filtration Systems. -- Reverse osmosis and nanofiltration are specifically used for the removal of dissolved solids, including monovalent (e.g., sodium and chloride) and divalent (e.g., calcium and manganese) ions, depending on the membrane material's diffusive properties. These types of systems are recognized as a Best Available Technology (BAT) for the removal of inorganic constituents, e.g. radium and nitrates, from groundwater sources.6.3.h.1.C. Alternative Membrane Filtration Systems. -- Membrane filtration systems can be configured in various ways to target specific treatment objectives. For example, integrated membrane filtration systems can use a combination of both low and high pressure membrane filtration systems. Electrodialysis reversal (EDR) systems employ electrical charges placed on either side of the membrane filter material to promote ion specific removal through high pressure membrane filtration systems.6.3.h.2. Design Considerations. -- When considering the use of membrane filtration technologies, the BPH shall be contacted prior to the development of an Engineer's Report (subsection 3.2) to establish additional requirements necessary for approval, as identified in subdivision 3.2.j of this rule. Design criteria for the proposed membrane filtration system should consist, at a minimum, of data related to gross and net flux (gallons per day per square foot of active membrane area), range of backwash frequencies, backwash duration and rates, range of membrane system recovery as a percentage of production vs. feed water, membrane system area, membrane system configuration, clean-in-place frequencies and solutions, transmembrane pressure operating range, number of skids/basins/arrays, residuals quantity and quality, and related design parameters. To demonstrate treatment efficacy, approval of the Engineer's Report may be based on the following items: 6.3.h.2.A. Effective Removal Credit. -- The BPH shall make a determination based on the effective log removal value (LRV) credit given for pathogens based on treatment objectives and type of membrane system. Data demonstrating membrane system LRV credit shall be provided to the BPH, including, but not limited to, standard calculations, integrity testing procedures, and actual test data demonstrating performance based on applicable ASTM, AWWA, and other standards.6.3.h.2.B. Water Quality. -- Water quality can have a measureable and potentially deleterious impact on membrane system performance, impacting the membrane system feasibility and life cycle cost. Therefore, a review of source water quality data, including range of turbidity, pH, alkalinity, hardness, total and dissolved inorganics, total and dissolved organic carbon, water temperature, color, seasonal variations, microbial and algal activity, in addition to other physical parameters should be conducted. Anticipated feed water quality goals, based on the amount and type of pretreatment, shall be evaluated to compare the amount of membrane area and transmembrane pressure required to operate at design flows with seasonal fluctuations in water quality. In anticipation of extreme conditions (e.g., failure of pretreatment, high turbidity, cold temperature, high algal counts, and high organic carbon concentrations), data should be evaluated and summarized, demonstrating how water quality and membrane filtration system capacity can be maintained during and after these extreme conditions. If source water quality is unknown or insufficiently demonstrated, the BPH may require additional water quality sampling for specific constituents, specified frequency, and duration of time to understand potential variations in water quality.6.3.h.2.C. Redundancy. -- The amount of membrane surface area in operation at any given time shall be sufficient to maintain the rated design capacity, with a portion of the total membrane surface out of service, to maintain redundant systems. A redundant membrane filtration system design should be based on a minimum N-1 installation, where N is the total number of membrane system skids, basins or arrays that are supplied for the specific project, and N-1 is the total of membrane system skids, basins or arrays supplied minus one skid, basin or array out-of-service. Under N-1 operation, consideration shall be given to N being sufficient, such that clean-in-place, integrity, and backwash procedures can be performed with a reasonable impact on design capacity and operations. Additional redundancy shall be provided for critical membrane filtration system components including, but not limited to, valves, sensors, computers and related control systems, compressed air systems, certain pumps and other identified system components.6.3.h.2.D. Long Term Fouling Allowance. -- Membrane materials are susceptible to declining permeability, or decrease in the amount of water produced for the same transmembrane pressure, because of long term fouling. While water conditions vary, the design should consider space within each skid, basin or array to increase the total membrane surface area to at least one hundred ten percent (110%) of the installed design membrane filtration surface area, without the need to construct additional infrastructure. The reserved unused space shall be provided with false modules or cassettes to maintain uniform conditions within membrane skid, basin or array.6.3.h.3.E. Membrane Integrity. -- Based on the LRV credit established by the BPH, low pressure membrane systems shall be equipped with an automated membrane integrity test procedure that measures and calculates the effective LRV value of the membrane material on a daily basis. Integrity testing shall be based on the pressure decay test procedure established in ASTM D6908 - Integrity Testing of Water Filtration Membrane Systems or other approved method. When theta ([THETA]) is less than 1, as indicated within the ASTM D908 standard, procedures and data shall be provided on how the membrane material surface wetting angle should be verified to calculate the effective LRV. Concentration of suspended solids within each skid, basin, or array during normal operation may also contribute to the LRV calculation. The membrane filtration system shall be provided with a method for detecting broken or comprised membrane modules, cassettes, and related appurtenances, including equipment and materials necessary to restore membrane system integrity.6.3.h.3.F. Pretreatment. -- Membrane filtration system designs rely on an understanding of acceptable feedwater characteristics. The performance of the pretreatment process must be coordinated with the membrane system design. Without suitable pretreatment or acceptable feed water quality, membrane life is often shortened due to irreversible fouling or by more frequent, oxidant based clean-in-place procedures to maintain system capacity. At a minimum, the following pretreatment considerations shall be included: 6.3.h.3.F.1. Surface water systems. -- The following pretreatment systems shall be provided for low pressure membrane filtration systems including chemical coagulant and related storage and feed systems, disinfection, clarification consisting of: rapid mix; a combination of flocculation and a four (4) hour retention time based sedimentation basins (the BPH may allow a two (2) hour retention time if the raw water source is a reservoir with a minimum of six (6) months storage and a plate/tube settler is used in the sedimentation basins); or a four (4) hour retention time based solid contact units (the BPH may allow a 2 hour retention time if the raw water source is a reservoir with a minimum of six (6) months storage); and prescreening to protect the membrane filtration from exposure to environmental debris, e.g. leaves, dust, and biota. Four (4) hour retention time shall be based on design flows higher than the production capacity of the membrane filtration system to account for total of production water, backwash water, and clean-in-place make up water, sediment or sludge removal, and other water demand requirements of the planned facility.6.3.h.3.F.2. Groundwater and groundwater under the influence of surface water based systems. -- The following pretreatment systems shall be provided for high pressure membrane filtration systems for the removal of suspended solids, e.g. cartridge filters or low pressure membrane filtration systems, stabilization of the feed water to prevent scale formation, microbial control, and pH adjustment. Additional consideration shall be given for disinfection, aeration, and ion specific pretreatment depending on treatment objectives. For low pressure membrane filtration systems, pretreatment should minimally consist of at least disinfection to prevent microbial growth and oxidation techniques specific for iron and manganese removal. For both types of systems, additional pretreatment or other treatment techniques may be required based on conditions after well development and operation have been verified because of varying well borehole conditions, e.g. sand production and drawdown characteristics, geological strata, and water quality.6.3.h.3.G. Pilot studies. -- The BPH requires the development of a pilot system test protocol for evaluation of the proposed treatment process using membrane filtration. The pilot system test protocol shall adequately describe the proposed pilot system setup, sampling frequencies and location, system monitoring and controls, integrity testing procedures, treatment goals and objectives, quality control, and operating conditions, consistent with the planned operation of the full scale membrane filtration system and overall treatment process. Following approval of the pilot system test protocol by the BPH, the pilot study or in-plant demonstration shall be conducted by the public water system and/or their engineer. The pilot study should be conducted over a sufficient time (recommended 6 months to 12 months) to treat anticipated water quality conditions throughout the year for surface water systems, but shall not be less than six (6) weeks. Groundwater systems shall provide a pilot study of at least six (6) weeks, based on anticipated use, e.g., if the well is planned to operate eight (8) hours every day with sixteen (16) hours of recovery, the pilot should be run for a similar twenty-four (24) hour operating condition for up to a total of forty five (45) operational days. The pilot system study should target a range of operating and feed water quality and quantity conditions that could be expected during operation of the planned full scale system. For disposal or treatment of the membrane filtration system reject, concentrate, backwash, and/or spent clean-in-place solutions, additional bench or pilot scale studies may be required to demonstrate the quantity and quality of discharge for the assessment of disposal costs, waste treatment controls, and ability to meet permit requirements established by the BPH and other agencies.6.3.h.3.H. Total Life Cycle Cost. -- Full scale membrane filtration systems are associated with quantifiable costs for purchase, operation, and maintenance. Where possible, the evaluation and comparison of multiple membrane filtration systems shall be based on similar design parameters and treatment objectives. Capital costs should consider the equipment, appurtenances, infrastructure, and special services required for design, installation, startup, training, and post-startup assistance. Operational costs related to power consumption, chemical use, membrane replacement, maintenance replacement, residuals handling and disposal, and facility operations should also be identified and evaluated. The Engineering Report should be used to establish how operational costs are calculated based on planned production, transmembrane pressure, clean-in-place types and frequencies, membrane life, maintenance reserve, and facility operations. Conservative membrane replacement costs require specific attention to useful life and distribution of payments, and may be supported by operational data from other similar facilities. Pilot study data may be used to verify total life cycle costs prior to construction of full scale facilities.6.3.h.3.I. Cross-connection Control. -- Membrane skids, basins, or arrays shall be equipped with positive controls to prevent cross-connection of chemical clean-in-place and waste solutions with the treated water supplying the public water system. Methods incorporating block-and-bleed systems and air gaps are preferred for chemical clean-in-place solution piping. Following chemical clean-in-place procedures, rinsing procedures should be considered to reduce the impact of residual chemical clean-in-place solutions on finished water quality.6.3.h.3.J. NSF Applicability. -- Oils, greases, lubricants and in-situ clean-in-place chemicals in contact with the process water should be NSF/ANSI Standard 60 certified or of suitable food grade quality (FDA). Where applicable, membrane system components and materials in contact with the process water shall be NSF/ANSI Standard 61 certified.6.4. Disinfection. -- Chlorine is 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 may 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. Continuous disinfection is required for all public water systems. Since disinfection agents other than chlorine usually demonstrate shortcomings when applied to a public water system, proposals for use of disinfecting agents in combination with chlorine or other than chlorine require approval by the BPH prior to preparation of final plans and specifications. 6.4.a. Chlorination equipment. 6.4.a.1. Type. -- Solution-feed, gas chlorinators or hypochlorite feeders of the positive displacement type shall be provided.6.4.a.2. Capacity. -- The chlorinator capacity shall be such that a free chlorine residual of at least two (2) milligrams per liter can be maintained in the water to meet the CT for surface water and ground water when maximum flow rate coincides with anticipated maximum chlorine demand, maximum pH and minimum temperatures. The equipment shall be of such design that it operates accurately over the desired feeding range.6.4.a.3. Standby equipment. -- 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 shall be provided for each dose range to ensure accurate control of the chlorine feed. ` 6.4.a.4. Automatic switchover. -- Automatic switchover of chlorine cylinders shall be provided, where necessary, to assure continuous disinfection.
6.4.a.5. Automatic proportioning. -- Automatic proportioning chlorinators are required where the rate of flow or chlorine demand is not reasonably constant.6.4.a.6. Eductor. -- Each eductor shall be selected for the point of application with particular attention given to the quantity of chlorine to be added, the maximum injector water flow, 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 shall be provided.6.4.a.7. Injector/diffuser. -- The chlorine solution injector/diffuser shall 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.6.4.b. Contact time and point of application. 6.4.b.1. Due consideration shall be given to the contact time of the chlorine in water with relation to pH, ammonia, taste-producing substances, temperature, bacterial quality, disinfection byproduct formation potential and other pertinent factors. The disinfectant shall be applied at a point that provides adequate contact time. All basins used for disinfection shall be designed to minimize short circuiting. Additional baffling can be added to new or existing basins to minimize short circuiting and increase contact time.6.4.b.2. At plants treating surface water, provisions shall be made for applying disinfectant to the raw water, settled water, filtered water, and water entering the distribution system. The contact time as required shall be provided after filtration.6.4.b.3. 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.6.4.b.4. The minimum contact time for surface water sources and ground water sources shall be determined by "CT Calculations." Details for calculating "CT" values are contained in the West Virginia Bureau for Public Health's rule, Public Water Systems, 64CSR3. If primary disinfection is accomplished using ozone or some other chemical that does not provide a residual disinfectant, then chlorine shall be added to provide a residual disinfectant as provided in subdivision 6.4.c.6.4.c. Residual chlorine. -- Minimum total chlorine residual at all points in a water distribution system shall be two tenths (0.2) milligrams per liter. Higher residuals may be required depending on pH, temperature and other characteristics of the water. Booster chlorination may be required to maintain proper residuals.6.4.d. Testing equipment. -- Chlorine residual test equipment recognized in the latest edition of the Standard Methods for the Examination of Water and Wastewater publication, shall be provided and shall be capable of measuring residuals as contained in the West Virginia Bureau for Public Health's legislative rule, Public Water Systems, 64CSR3. Automatic chlorine residual recorders shall be provided where the chlorine demand varies appreciably over a short period of time. All surface water treatment plants designed to serve three thousand three hundred (3,300) people or more shall be equipped with recording chlorine analyzers and continuous recorders monitoring water entering the distribution system.6.4.e. Chlorinator piping. 6.4.e.1. 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 shall 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 is allowed.6.4.e.2. Pipe material. -- The pipes carrying elemental liquid or dry gaseous chlorine under pressure shall be Schedule Eighty (80) seamless steel tubing or other materials recommended by the Chlorine Institute, Inc. (never use poly vinyl chloride, PVC). Rubber, PVC, polyethylene, or other materials recommended by the Chlorine Institute, Inc. shall be used for chlorine solution piping and fittings. Nylon products are not acceptable for any part of the chlorine solution piping system.6.4.f. Housing. -- Adequate housing must be provided for the chlorination equipment and for storing the chlorine.6.4.g. Ozone. 6.4.g.1. Design considerations. -- Ozone 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, 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 residuals 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 disinfectant by-product (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 acute results: particularly sensitive measurements for gas flow rate, water flow rate, and ozone concentration. Following the use of ozone, the application of a disinfectant which maintains a measurable residual is required throughout the distribution system. Because of the sophisticated nature of the ozone process, the public water system managers must make a commitment to obtaining qualified operators that are trained in the ozone process prior to the startup of an ozone process. The production of ozone is an energy intensive process: substantial economics in electrical usage, reduction in equipment size, and waste heat removal requirements can be obtained using oxygen enriched air or 100% oxygen as feed, and by operating at increased electrical frequency. The 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.6.4.g.2. Feed gas preparation. 6.4.g.2.A. General. -- 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 (absorptive separation) technology. For high purity oxygen-fed systems, dryers typically are not required. Air handling equipment on conventional low pressure feed systems shall consist of an air compressor, water/air separator, refrigerant dryer, heat reactivated desiccant dryer, and particulate filters, Provided, that some "package" ozonation systems for small plants may work effectively operating at high pressure without the refriderant dryer and with a "heat-less" desiccant dryer and may not be required to have those elements. In all cases the design engineer shall ensure that the maximum dew point of -76oF (-60°C) is not exceeded at any time.6.4.g.2.B. Air compressor. -- 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. 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. 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. A compressed air after-cooler and/or entrainment separator with automatic drain shall be provided to the dryers to reduce the water vapor. A back-up air compressor shall be provided so that the ozone generation is not interrupted in the event of a break-down.6.4.g.2.C. Air drying. -- Dry, dust-free and oil-free feed gas shall 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) shall be provided at the end of the drying cycle. Drying for high pressure systems may be accomplished using heatless desiccant dryers only. For low pressure systems, a refrigeration air dryer I series with heat-reactivated desiccant dryers shall be used. A refrigeration dryer capable of reducing inlet air temperature to 40oF (4oC) shall be provided for low pressure air preparation systems. The dryer may be of the compressed refrigerant type or chiller water type. 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 is achieved during a minimum absorption cycle time of sixteen (16) hours while operating at the maximum expected moisture loading conditions. Multiple air dryers shall be provided so that the ozone generation is not interrupted in the event of a breakdown. 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".6.4.g.2.D. Air filters. -- 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. The filter before the desiccant dryers shall be of the coalescing type and be capable of removing aerosol and particulates larger than three tenths (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 one tenths (0.1) microns in diameter, or smaller if specified by the generator manufacturer.6.4.g.2.E. Preparation piping. -- Piping in the air preparation system may be common grade steel, seamless copper, stainless steel or galvanized steel. The piping shall be designed to withstand the maximum pressures in the air preparation system.6.4.g.3. Ozone Generator. 6.4.g.3.A. Capacity. -- The production rating of the ozone generators shall be stated in pounds per day and kilowatt hours per pound at a maximum cooling water temperature and maximum ozone concentration. The design shall ensure that the minimum concentration of ozone in the generator exit gas is not less than one (1%) percent by weight. Generators shall be sized to have sufficient reserve capacity so that the system does not operate at peak capacity for extended periods of time, which can result in premature breakdown of the dielectrics. The production rate of ozone generators may 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 the 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. Ozone backup equipment must be provided.6.4.g.3.B. Cooling. -- 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 shall 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.6.4.g.3.C. Materials. -- To prevent corrosion, the ozone generator shell and tubes shall be constructed of Type 316L stainless steel.6.4.g.4. Ozone Contactors. -- The selection of design of the contactor and method of ozone application depends on the purpose for which the ozone is being used. 6.4.g.4.A. Bubble diffusers. -- 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. The minimum contact time shall be ten (10) minutes. A shorter contact time may be approved by the BPH if justified by appropriate design and "CT" considerations. For ozone applications in which precipitates are formed, such as with iron and manganese removal, porous diffusers should be used with caution. Where taste and odor control is of concern, multiple application points and contactors shall be considered. Contactors should be separate closed vessels that have no common walls with adjacent rooms. The contactor must be kept under negative pressure and sufficient monitors shall be provided to protect worker safety. The contactor shall be placed where the entire roof is exposed to the open atmosphere. Large contact vessels shall be constructed of reinforced concrete. All reinforcement bars shall be covered with a minimum of one and one half (1.5) inches of concrete. Smaller contact vessels can be made of stainless steel, fiberglass or other material which is stable in the presence of residual ozone and ozone in the gas phase above the water level. When 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 tot the contactor or other location acceptable to the BPH. If foaming is expected to be excessive, then a potable water spray system shall be placed in the contactor head space. 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. Multiple sampling ports shall be provided to enable sampling of each compartment's effluent water and to confirm "CT" calculations. 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. The diffusion system should work on a countercurrent basis such that ozone is fed at the bottom of the vessel and water is fed at the top of the vessel. The depth of water in bubble diffuser contactors should be a minimum of eighteen (18) feet. The contactor should also have a minimum of three (3) feet of freeboard to allow for foaming. All contactors shall have provisions for cleaning, maintenance and drainage of the contactor. Each contactor compartment shall be equipped with an access hatchway. Aeration diffusers shall be fully serviceable by either cleaning or replacement.6.4.g.4.B. Other contactors. -- Other contactors, such as venture or aspirating turbine mixer contactor, may be approved by the BPH provided adequate ozone transfer is achieved and the required contact times and residuals can be met and verified.6.4.g.5. Ozone Destruction Unit. -- A system for treating the final off-gas from each contactor shall be provided in order to meet safety and air quality standards. Acceptable systems include thermal destruction and thermal/catalytic destruction units. 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. The maximum allowable ozone concentration in the discharge is 0.1 ppm by volume. At least two (2) units shall be provided that are each capable of handling the entire gas flow. Exhaust blowers shall be provided in order to draw off-gas from the contactor into the destruct unit. Catalysts shall be protected from froth, moisture and other impurities which may harm the catalysts. The catalysts and heating elements shall be located where they can easily be reached for maintenance.6.4.g.6. Piping Materials. -- Only low carbon 304L or 316L stainless steel shall be used for ozone service with 316L the preferred.6.4.g.7. Joints and Connections. -- Connections on piping used for ozone service shall be welded where possible. Connections with meters, valves, or other equipment are to be made with flanged joints with ozone resistant gaskets, such as Teflon or Hypalon. Screwed fittings shall not be used because of their tendency to leak. 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.6.4.g.8. Instrumentation. -- 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. Electric power meters shall be provided for measuring the electric power supplied to the ozone generators. Each generator shall have a trip that shuts down the generator when the wattage exceeds a certain preset level. 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 allows for proper adjustment of the dryer cycle. Where there is potential for moisture entering the ozone generator during shutdown, post generator dew point monitors shall be used. 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. 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. 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. Ozone monitors shall be installed to measure ozone 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. A minimum of one (1) ambient ozone monitor shall be installed in the vicinity of the contactor and a minimum of one (1) shall be installed in the vicinity of the generator. Ozone monitors shall also be installed in any areas where ozone may accumulate.6.4.g.9. Alarms. -- The following alarm/shutdown systems shall be considered at each installation: Dew point shutdown/alarm - this system should shut down the generator in the event the system dew point exceeds -76°F(-60oC). Ozone generator cooling water flow shutdown/alarm - this system shall shutdown the generator in the event that cooling water flows decrease to the point that generator damage could occur. Ozone power supply cooling water flow shutdown/alarm - this system shall shutdown the power supply in the event that cooling water flow decreases to the point that damage could occur to the power supply. Ozone generator cooling water temperature shutdown/alarm - this system shall shutdown the generator if either the inlet or outlet cooling water exceeds a certain preset temperature. Ozone power supply water temperature shutdown/alarm - this system shall shutdown the power supply if either the inlet or outlet cooling water exceeds a certain preset temperature. Ozone generator inlet feed-gas temperature shutdown/alarm - this system shall shutdown the generator if the feed-gas temperature is above a preset value. Ambient ozone concentration shutdown/alarm - the alarm shall sound when ozone level in the ambient air exceeds 0.1 ppm or a lower value chosen by the water supplier and ozone generator shutdown shall occur when ambient ozone levels exceed 0.3 ppm (or a lower level) in either the vicinity of the ozone generator or the contactor. Ozone destruct temperature alarm - this alarm shall sound when temperature exceeds a preset value.6.4.g.10. Safety. -- The maximum allowable ozone concentration in the air to which workers may be exposed shall not exceed 0.1 ppm (by volume). 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. High voltage and high frequency electrical equipment shall meet current electrical and fire codes. Emergency exhaust fans shall be provided in rooms containing the ozone generators to remove ozone gas if leakage occurs. A portable purge air blower shall be provided that removes residual ozone in the contactor prior to entry for repair or maintenance. 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.6.4.g.11. Construction considerations. -- Prior to connecting the piping from the desiccant dryers to the ozone generators the air compressors shall be used to blow the dust out of the desiccant. The contactor shall be tested for leakage after sealing the exterior and this can be done by pressurizing the contactor and checking for pressure losses. Connections on the ozone service line shall be tested for leakage using the soap-test method.6.4.h. Chlorine Dioxide. -- May be considered as a primary and residual disinfectant, a pre-oxidant to control taste 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. 6.4.h.1. Chlorine dioxide generators. -- Chlorine dioxide generation equipment shall be factory assembled pre-engineered units with a minimum efficiency of 95 percent (95%). The excess free chlorine shall not exceed three percent (3%) of the theoretical stoichiometric concentration required.6.4.h.2. Feed and storage facilities. -- Chlorine gas and sodium chlorite feed and storage facilities shall comply with subsection 7.0.6.4.h.3. Other design requirements. -- The design shall comply with all applicable portions of subdivisions 6.4.a, 6.4.b, 6.4.d and 6.4.e of this section. The minimum residual disinfectant shall be established by the BPH.6.4.h.4. 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.6.4.i. Ultraviolet light. -- 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 may 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. Supplemental disinfection for additional virus inactivation and to provide a residual in the water distribution system is required by the BPH. 6.4.i.1. Criteria for UV Water Treatment Devices. -- 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 of Gas and Water (UVGW), the Austrian Standards Institute (ONORM), the National Water Research Institute/American Water Works Association Research Foundation (NWR/AwwaRF), the Class A criteria under ANSI/NSF Standard 55- Ultraviolet Microbiological Water Treatment Systems; or other standards approved by the BPH. The validation must demonstrate that the unit is capable of providing a UV light dose of 40 millijoules per square centimeter (mJ/cm2) throughout the reactor based on water quality, specifically transmittance of the dose through the treated water. Higher dosages may be required depending on application, e.g., type of pathogen inactivation and water quality conditions. In addition to the requirements cited in the USEPA UVDGM each UV water treatment device shall meet the following: 1) 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-in-place system should be installed to allow in-situ cleaning of lamp jackets. Adequate controls shall be in place to prevent contamination of potable water with cleaning chemicals. 2) An automatic shutdown valve shall be installed in the water supply line ahead of the UV treatment system that is activated whenever the water treatment system losses power or is tripped by a monitoring devise 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. 3) The UV housing shall be stainless steel 304 or 316L. 4) A flow or time delay mechanism shall be provided to permit sufficient time for UV lamp warm-up before water flows from the unit upon startup. 5) 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 disinfection can be provided when the unit is out of service.6.4.i.2. Record keeping and access. -- A record shall be kept of the dates of lamp replacement and cleaning, a record of when the device was shut down and the reason for the shutdown. The BPH shall have access to the UV water treatment system and records.6.4.j. Other disinfecting agents. -- Proposals for use of disinfecting agents other than those listed must be pre-approved by the BPH, prior to preparation of the final plans and specifications.6.5. Softening. -- The softening process selected shall 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. 6.5.a. Lime or lime-soda process. -- Design standards for rapid mix, flocculation and sedimentation are in "Clarification," subsection 6.2. of this rule. Additional consideration shall be given to the following process elements. 6.5.a.1. Hydraulics. -- When split treatment is used, the bypass line shall be sized to carry total plant flow, and an accurate means of measuring and splitting the flow shall be provided.6.5.a.2. Aeration. -- Determinations shall be made for the carbon dioxide content of the raw water. When concentrations exceed ten (10) milligrams per liter, the economics of removal by aeration as opposed to removal with lime shall be considered if it has been determined that dissolved oxygen in the finished water will not cause corrosion problems in the distribution system.6.5.a.3. Chemical feed point. -- Lime shall be fed directly into the rapid mix basin.6.5.a.4. Rapid mix. -- Rapid mix basins shall provide not more than thirty (30) seconds detention time with adequate velocity gradients to keep the lime particles dispersed.6.5.a.5. Stabilization. -- Equipment for stabilization of water softened by the lime or lime-soda process is required.6.5.a.6. Sludge collection. -- Mechanical sludge removal equipment shall be provided in the sedimentation basin. Sludge recycling to the rapid mix shall be provided not to exceed a rate of ten percent (10%) of the incoming flow.6.5.a.7. Sludge disposal. - Provisions shall be included in the water treatment plant design for proper disposal of softening sludge.6.5.a.8. Disinfection. -- The use of excess lime is not an acceptable substitute for disinfection.6.5.a.9. Plant start-up. -- The plant processes shall be manually started following shut-down.6.5.b. Cation exchange process. -- Alternative methods of hardness reduction shall be investigated when the sodium content and dissolved solids concentration is of concern. 6.5.b.1. Pre-treatment requirements. -- Iron, manganese, or a combination of the two, shall not exceed 0.3 milligrams per liter 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 (2), is one (1) milligram per liter or more. Waters having five (5) units or more turbidity shall not be applied directly to the cation exchange softener.6.5.b.2. Design. -- The units may be of pressure or gravity type, of either an upflow or downflow design. Automatic regeneration based on volume of water softened shall be used unless manual regeneration is justified and is approved by the BPH. A manual override shall be provided on all automatic controls.6.5.b.3. Exchange capacity. -- The design capacity for hardness removal shall not exceed twenty thousand (20,000) grains per cubic foot when resin is regenerated with 0.3 pounds of salt per kilogram of hardness removed.6.5.b.4. Depth of resin. -- The depth of the exchange resin shall not be less than three (3) feet.6.5.b.5. Flow rates. -- The rate of softening shall not exceed seven (7) gallons per minute per square foot of bed area, and the backwash rate shall be six (6) to eight (8) gallons per minute per square foot of bed area. Rate-of-flow controllers or the equivalent shall be installed for the rate of softening.6.5.b.6. Freeboard. -- The freeboard will depend upon the specific gravity of the resin and the direction of water flow. Generally, the washwater collector shall be twenty-four (24) inches above the top of the resin on downflow units.6.5.b.7. Underdrains and supporting gravel. -- The bottoms, strainer systems and support for the exchange resin shall conform to criteria provided for rapid rate gravity filters.6.5.b.8. Brine distribution. -- Facilities shall be included for even distribution of the brine over the entire surface of both upflow and downflow units.6.5.b.9. 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.6.5.b.10. Bypass piping and equipment. -- A bypass shall be provided around softening units to produce a blended water of desirable hardness. Totalizing meters shall be installed on the bypass line and on each softener unit. The bypass line shall 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.6.5.b.11. Additional limitations. -- Silica gel resins shall not be used for waters having a pH above 8.4 or containing less than six (6) milligrams per liter silica and shall 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 shall not be used.6.5.b.12. Sampling taps. -- Smooth-nose sampling taps shall 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 twenty (20) feet downstream from the point of blending. Petcocks are not acceptable as sampling taps. Sampling taps shall be provided on the brine tank discharge piping.6.5.b.13. Brine and salt storage tanks. 6.5.b.13.A. Salt dissolving or brine tanks and wet salt storage tanks shall be covered and shall be corrosion-resistant.6.5.b.13.B. The make-up water inlet shall be protected from back-siphonage. Water for filling the tank shall be distributed over the entire surface by pipes above the maximum brine level in the tank. The tanks shall be provided with an automatic declining level control system on the make-up water line.6.5.b.13.C. Wet salt storage basins shall be equipped with manholes or hatchways for access and for direct dumping of salt from truck or rail car. Openings shall 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.6.5.b.13.D. Overflows, where provided, shall be protected with corrosion resistant screens and shall terminate with either a turned down bend having a proper free fall discharge or a self-closing flap valve.6.5.b.13.E. Two (2) wet salt storage tanks or compartments designed to operate independently shall be provided.6.5.b.13.F. The salt shall be supported on graduated layers of gravel placed over a brine collection system.6.5.b.13.G. The public water system engineer may consider alternative designs that are conducive to frequent cleaning of the wet salt storage tank.6.5.b.14. Salt and brine storage capacity. -- Reserve salt and brine storage capacity for at least thirty (30) days of operation shall be available.6.5.b.15. 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 shall be provided to obtain proper dilution.6.5.b.16. Stabilization. -- Stabilization for corrosion control shall be provided. An alkali feeder shall be provided except when exempted by the BPH.6.5.b.17. Waste disposal. -- Suitable disposal shall be provided for brine waste. Where the volume of spent brine is reduced, consideration may be given to using a part of the spent brine for a subsequent regeneration.6.5.b.18. Construction materials. -- Pipes and contact materials shall be resistant to the aggressiveness of salt. Plastic and red brass are acceptable piping materials. Steel and concrete shall be coated with a non-leaching protective coating that is compatible with salt and brine.6.5.b.19. Housing. -- Bagged salt and dry bulk salt storage shall be enclosed and separated from other operating areas in order to prevent damage to equipment.6.6. Aeration. -- Aeration may be used to help remove offensive tastes and odors due to dissolved gases from decomposing organic matter, to reduce or remove objectionable amounts of carbon dioxide, hydrogen sulfide, etc., and to introduce oxygen to assist in iron or manganese removal, or both. The packed tower aeration process is an aeration process applicable to removal of volatile organic contaminants. 6.6.a. Natural draft aeration. -- The design shall provide: perforations in the distribution pan three-sixteenths (3/16) to one-half (1/2) inches in diameter, spaced one (1) to three (3) inches on centers to maintain a six (6) inch water depth, and eight (8) to ten (10) inches of inert media, such as coke or limestone that will not disintegrate due to freezing cycles; distribution of water uniformly over the top tray and discharge through a series of three (3) or more trays with separation of trays not less than twelve (12) inches; loading at a rate of one (1) to five (5) gallons per minute for each square foot of total tray area; trays with slotted, heavy wire [one half (1/2) inch openings] mesh or perforated bottoms and construction of durable material resistant to aggressiveness of the water and dissolved gases; protection from loss of spray water by wind carriage by enclosure with louvers sloped to the inside at an angle of approximately forty-five (45) degrees; protection from insects by twenty-four (24) mesh screen; and provisions for continuous disinfection feed shall be provided after aeration.6.6.b. Forced or induced draft aeration. -- Forced or induced draft aeration devices shall be designed to: include a blower with a weatherproof motor in a tight housing and screened enclosure and ensure adequate counter current of air through the enclosed aerator column; exhaust air directly to the outside atmosphere; include a down-turned and twenty-four (24)-mesh screened air outlet and inlet; ensure that air introduced in the column is as free from obnoxious fumes, dust, and dirt as possible; 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; provide loading at a rate of one (1) to five (5) gallons per minute for each square foot of total tray area; ensure that the water outlet is adequately sealed to prevent unwarranted loss of air; discharge though a series of five or more trays with separation of trays not less than six (6) inches; provide distribution of water uniformly over the top tray; be of durable material resistant to the aggressiveness of the water and dissolved gases; provide for continuous disinfection feed after aeration.6.6.c. Spray aeration. -- The design shall provide a hydraulic head of between five (5) and twenty five (25) feet; nozzles, with the size, number, and spacing of the nozzles being dependent on the flow rate, space and amount of head available; nozzle diameter in the range of one (1) to one and a half (1.5) inches to minimize clogging; an enclosed basin to contain the spray with any openings for ventilation, etc. being protected by a twenty-four (24)-mesh screen; and for continuous disinfection feed after aeration.6.6.d. Pressure aeration. -- Pressure aeration may be used for oxidation purposes only if the pilot plant study indicates the method is applicable; it is not acceptable for removal of dissolved gases. Filters following pressure aeration shall have adequate exhaust devices for the release of air. Pressure aeration devices shall be designed to give a thorough mixing of compressed air with the water being treated and provide screened and filtered air, free of obnoxious fumes, dust, dirt and other contaminants.6.6.e. Packed Tower Aeration. -- Packed tower aeration (PTA) that 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 one hundred (100) (expressed in atm mol/mol - at twelve (12) degrees C), but not normally feasible for removing compounds with a Henry's Constant less than ten (10). For values between ten (10) and one hundred (100), PTA may be feasible but shall be extensively evaluated using pilot studies. The Public Water Systems' engineer shall discuss values for Henry's Constant with the BPH prior to final design. 6.6.e.1. Process Design. 6.6.e.1.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 Public Water Systems' engineer shall provide justification to the BPH for the design parameters selected (i.e., height and diameter of the unit, air to water ratio, packing depth, surface loading rate, etc.). Pilot plant testing shall be provided. The pilot test shall evaluate a variety of loading rates and air to water ratios at the peak contaminant concentration. The public water systems' engineer shall give special consideration 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 BPH may approve the process design based on use of appropriate calculations without pilot testing. The Public Water Systems' engineer shall discuss proposals of this type with the BPH prior to submission of any permit applications.6.6.e.1.B. The tower shall be designed to reduce contaminants to below the maximum contaminant level (MCL) and to the lowest practical level.6.6.e.1.C. The ratio of the column diameter to packing shall be at least seven (7) to one (1) for the pilot unit and at least ten (10) to one (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.6.6.e.1.D. The minimum volumetric air to water ratio at peak water flow shall be twenty-five (25) to one (1). The maximum air to water ratio for which credit will be given is eighty (80) to one (1).6.6.e.1.E. The design shall consider potential fouling problems from calcium carbonate, manganese and iron precipitation and from bacterial growth. It may be necessary to provide pretreatment. Disinfection capability shall be provided prior to and after PTA.6.6.e.1.F. The effects of temperature shall be considered since a drop in water temperature can result in a drop in contaminant removal efficiency.6.6.e.2. Materials of Construction. -- The tower may 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 shall be provided with adequate support to prevent damage from wind. 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.6.6.e.3. Water Flow System. -- Water shall be distributed uniformly at the top of the tower using spray nozzles or orifice-type distributor trays that prevent short circuiting. A mist eliminator shall be provided above the water distributor system. A side wiper redistribution ring shall be provided at least every ten (10) feet to prevent water channeling along the tower wall and short circuiting. Smooth nosed sample taps shall be provided in the influent and effluent piping. 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. A blow-off line shall be provided in the effluent piping to allow for discharge of water and chemicals used to clean the tower. 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. The water flow to each tower shall be metered. An overflow line shall be provided that discharges twelve (12) to fourteen (14) inches above a splash pad or drainage inlet. Proper drainage shall be provided to prevent flooding of the area.6.6.e.4. Air Flow System. -- The air inlet to the blower and tower discharge vent shall be protected with a non-corrodible twenty-four (24) mesh downturned screen to prevent contamination from extraneous matter. The air inlet shall be in a protected location. An air flow meter shall be provided on the influent air line or an alternative method to determine the air flow shall be provided. A backup motor for the air blower shall be readily available.6.6.e.5. Other Features that Shall Be Provided. -- The following shall be provided: a sufficient number of access ports with a minimum diameter of twenty-four (24) inches to facilitate inspection, media replacement, media cleaning and maintenance of the interior; a method of cleaning the packing material when iron, manganese, or calcium carbonate fouling may occur; tower effluent collection and pumping wells constructed to clearwell standards; provisions for extending the tower height; a BPH approved alternative supply during periods of maintenance and operation interruptions; no bypass unless specifically approved by the BPH; disinfection application points both ahead of and after the tower to control biological growth; disinfection and adequate contact time after the water has passed through the tower and prior to the distribution system; adequate packing support to allow free flow of water and to prevent deformation with deep packing heights; adequate foundation to support the tower and lateral support to prevent overturning due to wind loading; fencing and locking gate to prevent vandalism; an access ladder with safety cage for inspection of the aerator including the exhaust port and de-mister; and electrical interconnection to allow simultaneous operation and disconnect of the blower, disinfectant feeder and well pump.6.6.e.6. Environmental Factors. -- The applicant shall contact the appropriate air quality office to determine if permits are required under the Clean Air Act. Noise control facilities shall be provided on PTA systems located in residential areas.6.6.f. Other methods of aeration. -- Other methods of aeration may be used if applicable to the treatment needs. These methods include but are not restricted to spraying, diffused air, cascades and mechanical aeration. The treatment process shall be designed to meet the particular needs of the water to be treated and is subject to the approval of the BPH.6.6.g. Protection of aerators. -- 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.6.6.h. Bypass. -- A bypass shall be provided for all aeration units except those installed to comply with maximum contaminant levels.6.6.i. Corrosion control. -- The aggressiveness of the water after aeration shall be determined and corrected by additional treatment, if necessary.6.6.j. Quality control. -- Equipment shall be provided to test for dissolved oxygen, pH and temperature to determine proper functioning of the aeration device. Equipment to test for iron, manganese and carbon dioxide should also be considered.6.6.k. Redundancy. -- Redundant equipment shall be provided for units to comply with the Safe Drinking Water Act primary contaminants, unless otherwise approved by the BPH.6.7. Iron and Manganese Control. -- Iron and manganese control, as used in this subsection, refers solely to treatment processes designed specifically for this purpose. The treatment process used depends upon the character of the raw water. The selection of one (1) or more treatment processes shall 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 BPH. It may be necessary to operate a pilot plant in order to gather all information pertinent to the design. Consideration shall be given to adjusting the pH of the raw water to optimize the chemical reaction. Testing equipment and sampling taps shall be provided. 6.7.a. Removal by oxidation, detention and filtration.6.7.a.1. Oxidation. -- Oxidation may be by aeration or by chemical oxidation with chlorine, potassium permanganate, sodium permanganate, ozone or chlorine dioxide.6.7.a.2. Detention. 6.7.a.2.A. Reaction. -- A minimum detention time of thirty (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 shall be designed as a holding tank with no provisions for sludge collection but with sufficient baffling to prevent short circuiting.6.7.a.2.B. Sedimentation. -- Sedimentation basins shall be provided when treating water with high iron or manganese content, or where chemical coagulation is used to reduce the load on the filters. Provisions for sludge removal shall be made.6.7.b. Removal by the lime-soda softening process, as in subdivision 6.5.a. of this rule.6.7.c. Removal by manganese greensand filtration. -- This process consists of a continuous or batch feed of potassium permanganate to the influent of a manganese coated media filter. Provisions shall be made to apply the permanganate as far ahead of the filter as practical and to a point immediately before the filter. Other oxidizing agents or processes such as chlorination or aeration may be used prior to the permanganate feed to reduce the cost of the chemical. An anthracite media cap of at least six inches shall be provided over manganese greensand. The normal filtration rate is three (3) gallons per minute per square foot or not to exceed the rate specified by manufacturer. The normal wash rate is eight (8) to ten (10) gallons per minute per square foot for manganese greensand and fifteen (15) to twenty (20) gallons per minute with manganese coated media. Air washing shall be provided. Smooth nosed sample taps shall be provided for the raw water, immediately ahead of filtration, at the filter effluent and at points between the anthracite media and the manganese coated media. Recommend potassium permanganate feed system have a means of automatic shut-off if overfeed occurs.6.7.d. Removal by ion exchange. -- The ion exchange process of iron and manganese removal shall not be used for water containing more than three tenths (0.3) milligrams per liter of iron, manganese or a combination thereof. This process is not acceptable where either the raw water or wash water contains dissolved oxygen.6.7.e. Sequestration by polyphosphates. -- The sequestration by polyphosphates process shall not be used when iron, manganese or a combination thereof exceeds one (1) milligram per liter (mg/l). The total phosphate applied shall not exceed ten (10) mg/l as PO4. Where phosphate treatment is used, satisfactory chlorine residuals shall be maintained in the distribution system. Stock phosphate solution must be kept covered and disinfected by carrying approximately ten (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 two (2.0) or less may be exempt from this requirement by the BPH. Feeding equipment shall conform to the requirements of "Chemical Application," in subdivision 7.1.b. of this rule. 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. The phosphate feed point shall be located as far ahead of the oxidant feed point as possible. Phosphate chemicals shall meet AWWA Standards and conform to ANSI/NSF Standard 60: Drinking Water Treatment Chemicals - Health Effects.6.7.f. Sequestration by sodium silicates. -- 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 shall accompany or closely precede the sodium silicate addition. Injection of sodium silicate more than fifteen (15) seconds after oxidation may cause a detectable loss of chemical efficiency. Dilution of feed solutions much below five per cent (5%) silica as silica dioxide shall also be avoided for the same reason. Sodium silicate addition is applicable to waters containing up to two (2) mg/l of iron, manganese or a combination thereof. Chlorine residuals shall be maintained throughout the distribution system to prevent biological breakdown of the sequestered iron. The amount of silicate added shall be limited to twenty (20) mg/l as silica dioxide, but the amount added and naturally occurring silicate shall not exceed sixty (60) mg/l as silica dioxide. Feeding equipment shall conform to the requirements of "Chemical Application," in section 7 of this rule. Sodium silicate shall not be applied ahead of iron or manganese removal treatment. Liquid sodium silicate shall meet AWWA Standard B404 and shall conform to ANSI/NSF Standard 60: Drinking Water Treatment Chemicals - Health Effects.6.7.g. Sampling taps. -- Smooth-nosed sampling taps shall be provided for control purposes. Taps shall be located on each raw water source, each treatment unit influent and each treatment unit effluent.6.7.h. Testing equipment shall be provided for all plants. The equipment shall have the capacity to accurately measure the iron content to a minimum of 0.1 milligrams per liter and the manganese content to a minimum of 0.05 milligrams per liter. Where polyphosphate sequestration is practiced, appropriate phosphate testing equipment shall be provided.6.8. Fluoridation. -- Sodium fluoride, sodium silicofluoride and hydrofluosilicic acid shall conform to the applicable AWWA standards and shall conform to ANSI/NSF Standard 60: Drinking Water Treatment Chemicals - Health Effects. Other fluoride compounds that may be available shall be approved by the BPH. The proposed method of fluoride feed shall be approved by the BPH prior to preparation of final plans and specifications. 6.8.a. Fluoride compound storage. -- Fluoride chemicals shall be isolated from other chemicals to prevent contamination. Compounds shall be stored in covered or unopened shipping containers and shall be stored inside a building. Storage of hydrofluosilicic acid shall be in sealed carboys unless the treatment plant is designed with bulk storage tanks. While being used, the unsealed storage units for hydrofluosilicic acid shall be vented to the atmosphere at a point outside any building. Bags, fiber drums and deldrums shall be stored on pallets.6.8.b. Chemical feed equipment and methods. -- In addition to the requirements in "Chemical Application," in section 7 of this rule, fluoride feed equipment shall meet the following requirements: scales, loss-of-weight recorders or liquid level indicators, as appropriate, accurate to within five percent (5%) of the average daily change in reading shall be provided for chemical feeds; feeders shall be accurate to within five percent (5%) of any desired feed rate; the fluoride compound shall be fed by a fluoride saturator, volumetric, gravimetric, or hydrofluosilicic acid fifteen (15) gallon carboy or fifty-five (55) gallon drum only (solution tanks are not permitted, exclusive of saturators); fluoride compound shall be added last, either directly into the clearwell or into the plant discharge line; the point of application for hydrofluosilicic acid or sodium fluoride, if into a horizontal pipe, shall be forty-five (45) degrees from the bottom of the pipe with the injector protruding into the pipe one-third (1/3) of the pipe diameter; a fluoride solution shall be applied by a positive displacement pump having a stroke rate not less than twenty (20) strokes per minute; anti-siphon devices shall be provided for all fluoride lines and dilution water lines; a device to measure the flow of water to be treated is required; water used for sodium fluoride saturated solution shall be softened if hardness exceeds seventy-five (75) mg/l as calcium carbonate; fluoride solutions shall not be injected to a point of negative pressure; the electrical outlet used for the fluoride feed pump shall have a nonstandard receptacle, unless it would void the pump warranty, and shall be interconnected with the well or high service pump; and saturators shall be of the upflow type and be provided with a meter and backflow protection on the makeup water line. Consideration shall be given to providing a separate room for florosilicic acid storage and feed.6.8.c. Secondary controls. -- Secondary control systems for fluoride chemical feed devices may be required by the BPH as a means of reducing the possibility for overfeed; these may include flow or pressure switches, break boxes or other devices.6.8.d. Protective equipment. -- Protective equipment as recommended by the compound manufacturer shall be provided for operators handling fluoride compounds. Deluge showers and eye wash devices shall be provided at all fluorosilicic acid installations.6.8.e. Dust control. -- Provision shall be made for the transfer of dry fluoride compounds from shipping containers to storage bins or hoppers in such a way as to minimize the quantity of fluoride dust that may enter the room in which the equipment is installed. The enclosure shall be provided with an exhaust fan and dust filter that place the hopper under a negative pressure. Air exhausted from fluoride handling equipment shall discharge through a dust filter to the atmosphere outside of the building. Provision shall be made for disposing of empty bags, drums or barrels in a manner that minimizes exposure to fluoride dusts. A floor drain shall be provided to facilitate the hosing of floors.6.8.f. Testing equipment. -- Equipment shall be provided for measuring the quantity of fluoride in the water. The equipment is subject to the approval of the BPH.6.9. Stabilization. -- Water that is unstable due either to natural causes or to subsequent treatment shall be stabilized. 6.9.a. Carbon dioxide addition. -- Recarbonation basin design shall provide a total detention time of twenty (20) minutes. Two compartments, with a depth that provides a diffuser submergence of not less than 7.5 feet nor greater submergence than recommended by the manufacturer are required. One compartment shall be a mixing compartment having a detention time of at least three minutes and the second compartment shall be a reaction compartment. The practice of on-site generation of carbon dioxide is discouraged. Where liquid carbon dioxide is used, adequate precautions shall be taken to prevent carbon dioxide from entering the plant from the recarbonation process. Consideration should be given to the installation of a carbon dioxide alarm system with light and audio warning, especially in low areas. Recarbonation tanks shall be located outside or be sealed and vented to the outside with adequate seals and adequate urge flow of air to ensure worker safety. Provisions shall be made for draining the carbonation basin and removing sludge.6.9.b. Acid addition. -- Feed equipment shall conform to "Chemical Application" subdivision 7.1.b. Adequate precautions shall be taken for operator safety, such as not adding water to the concentrated acid.6.9.c. Phosphates. -- The feeding of phosphates may be applicable for sequestering calcium, corrosion control, and in conjunction with alkali feed following ion exchange softening. Feed equipment shall conform to "Chemical Application," subdivision 7.1.b of this rule. Phosphate shall meet AWWA standards and shall conform to ANSI/NSF Standard 60: Drinking Water Treatment Chemicals - Health Effects. Stock phosphate solution shall be kept covered and disinfected by carrying approximately ten (10) milligrams per liter 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 two (2) or less may be exempted from this requirement by the BPH. Satisfactory chlorine residuals shall be maintained in the distribution system when phosphates are used.6.9.d. "Split treatment". -- Under some conditions, a lime-softening water treatment plant may be designed using "split treatment" in which raw water is blended with lime-softened water to partially stabilize the water prior to secondary clarification and filtration. Treatment plants designed to utilize "split treatment" shall also contain facilities for further stabilization by other methods.6.9.e. Alkali feed. -- Water with low alkalinity or pH should be treated with an alkali chemical.6.9.f. Carbon dioxide reduction by aeration. -- The carbon dioxide content of an aggressive water may be reduced by aeration.6.9.g. Other treatment. -- Other treatment for controlling corrosive waters by the use of calcium hydroxide, sodium silicate and sodium bicarbonate may be used where necessary. Any proprietary compound shall receive the specific approval of the BPH before use.6.9.h. Water unstable due to biochemical action in distribution system. -- Unstable water resulting from the bacterial decomposition of organic matter in water (especially in dead end mains), the biochemical action within tubercles, and the reduction of sulfates to sulfides shall be prevented by the maintenance of a free and/or combined chlorine residual throughout the distribution system.6.9.i. Control. -- Laboratory equipment shall be provided for determining the effectiveness of stabilization treatment.6.10. Taste and Odor Control. -- Provision shall be made for the control of taste and odor at all surface water treatment plants. Chemicals shall be added sufficiently ahead of other treatment processes to assure adequate contact time for effective and economical use of the chemicals. Where severe taste and odor problems are encountered, in-plant or pilot plant, or both, studies are required. 6.10.a. Flexibility. -- Plants treating water that is known to have taste and odor problems shall be provided with equipment that makes several of the control processes available so that the operator has flexibility in operation.6.10.b. Chlorination. -- Chlorination can be used for the removal of some objectionable odors. Adequate contact time shall be provided to complete the chemical reactions involved. Excessive potential disinfection byproduct production shall be investigated by adequate bench-scale testing prior to the design.6.10.c. Chlorine dioxide. -- Chlorine dioxide has been generally recognized as a treatment for tastes caused by industrial wastes, such as phenols. Chlorine dioxide may be used in the treatment of any taste and odor that is treatable by an oxidizing compound. Provisions shall be made for proper storing and handling of the sodium chlorite, so as to eliminate any danger of explosion.6.10.d. Powdered activated carbon. -- Powdered activated carbon shall be added as early as possible in the treatment process to provide maximum contact time. Flexibility to allow the addition of carbon at several points is preferred. Activated carbon shall not be applied near the point of chlorine application or any other oxidant. The carbon can be added as a pre-mixed slurry or by means of a dry-feed machine as long as the carbon is properly wetted. Continuous agitation or re-suspension equipment is necessary to keep the carbon from depositing in the slurry storage tank. Provision shall be made for adequate dust control. The required rate of feed of carbon in a water treatment plant depends upon the tastes and odors involved, but provision shall be made for adding from 0.1 milligrams per liter to at least forty (40) milligrams per liter. Powdered activated carbon shall be handled as a potentially combustible material. It shall be stored in a building or compartment as nearly fireproof as possible. Other chemicals shall not be stored in the same compartment. A separate room shall be provided for carbon feed installations. Carbon feeder rooms shall be equipped with explosion-proof electrical outlets, lights and motors.6.10.e. Granular activated carbon. -- Replacement of anthracite with GAC may be considered as a control measure for geosmin and methyl isoborneol (MIB) taste and odors from algae blooms. Demonstration studies may be required by the BPH.6.10.f. Copper sulfate and other copper compounds. -- Continuous or periodic treatment of water with copper compounds to kill algae or other growths shall be controlled to prevent copper in excess of one (1) milligram per liter as copper in the plant effluent or distribution system. Care shall be taken to assure an even distribution within the treatment area.6.10.g. Aeration. -- See "Aeration," subsection 6.6 of this rule.6.10.h. Potassium permanganate. -- Application of potassium permanganate may be considered, providing the treatment shall be designed so that the products of the reaction are not visible in the finished water.6.10.i. Ozone. -- Ozonation may be used as a means of taste and odor control. Adequate contact time shall be provided to complete the chemical reactions involved. Ozone is generally more desirable for treating water with high threshold odors.6.10.j. Other methods. -- The decision to use any other methods of taste and odor control shall be made only after careful laboratory or pilot plant, or both, tests and in consultation with the BPH.6.11. Microscreening. -- A microscreen is a mechanical supplement of treatment capable of removing suspended matter from the water by straining. It may be used to reduce nuisance organisms and organic loadings. It shall not be used in place of filtration, when filtration is necessary to provide satisfactory water nor used in place of coagulation in the preparation of water for filtration. 6.11.a. Design. -- Design shall give due consideration to: the nature of the suspended matter to be removed corrosiveness of the water, the effect of chlorination, when required as pre-treatment; the duplication of units for continuous operation during equipment maintenance: and automated backflushing operation when used in conjunction with microfiltration treatment. Design shall provide a durable, corrosion-resistant screen, by-pass arrangements, protection against back-siphonage when potable water is used for washing, and proper disposal of wash waters.6.12. Waste Handling and Disposal. -- Provisions shall be made for proper disposal of water treatment plant waste such as sanitary waste, laboratory waste, clarification sludge, softening sludge, iron sludge, filter backwash water, and brines. All waste discharges are governed by West Virginia Department of Environmental Protection (WVDEP) requirements. The requirements under this rule shall be considered minimum requirements as WVDEP may have more stringent requirements. In locating waste disposal facilities, due consideration shall be given to preventing potential contamination of the water supply. Alternative methods of water treatment and chemical use shall be considered as a means of reducing waste volumes and the associated handling and disposal problems. 6.12.a. Sanitary waste. -- The sanitary waste from water treatment plants, pumping stations, and other waterworks installations shall receive treatment. Waste from these facilities shall be discharged directly to a sanitary sewer system, when available and feasible, to an adequate on-site waste treatment facility approved by the County Health Department or to a treatment system approved by the BPH.6.12.b. Brine waste. -- Waste from ion exchange plants, demineralization plants, or other plants that produce a brine, may be disposed of by controlled discharge to a stream if adequate dilution is available. Surface water quality requirements of the WVDEP control the rate of discharge. Except when discharging to large waterways, a holding tank of sufficient size shall be provided to allow the brine to be discharged over a twenty-four (24) hour period. Where discharging to a sanitary sewer, a holding tank may be required to prevent the overloading of the sewer or interfering with the waste treatment processes. The effect of brine discharge to sewage lagoons may depend on the rate of evaporation from lagoons.6.12.c. Precipitative softening sludge. -- Sludge from plants using precipitative softening water varies in quantity and in chemical characteristics depending on the softening process and the chemical characteristics of the water being softened. Recent studies show that the quantity of sludge produced is much larger than indicated by stoichiometric calculations. Methods of treatment and disposal are as follows: 6.12.c.1. Lagoons. -- Temporary lagoons that are cleaned periodically shall be designed on the basis of 0.7 acres per million gallons per day per one hundred (100) milligrams per liter of hardness removed based on usable lagoon depth of five feet. This shall provide about 2 years storage. At least two (2) but preferably more lagoons shall be provided in order to give flexibility in operation. An acceptable means of final sludge disposal shall be provided. Provisions shall be made for convenient cleaning. Permanent lagoons shall have a volume of at least four (4) times that for temporary lagoons. The design of both temporary lagoons and permanent lagoons shall provide for: locations free from flooding; when necessary, dikes, deflecting gutters or other means of diverting surface water so that it does not flow into the lagoons; a minimum usable depth of five (5) feet; adequate freeboard of at least two (2) feet; an adjustable decanting device; an effluent sampling point; safety provisions; and parallel operation.6.12.c.2. Land Application. -- The application of liquid lime sludge or dewatered sludge to farm land shall be considered as a method of ultimate disposal. Approval from the WVDEP shall be obtained.6.12.c.3. Sanitary Sewers. -- Discharge of lime sludge to sanitary sewers is only permitted when the sewerage system has the capability to adequately handle the lime sludge.6.12.c.4. Mixing. -- Mixing of lime sludge with activated sludge waste may be considered as a means of co-disposal.6.12.c.5. Landfills. -- Disposal at a landfill may be done as either a solid or liquid if the landfill can accept such waste, depending on WVDEP requirements.6.12.c.6. Mechanical Dewatering. -- Mechanical dewatering of sludge may be considered. Pilot studies on a particular plant waste are recommended. The BPH may require operational data from similar water treatment facilities treating similar raw water and require performance guaranteed specifications for the mechanical equipment.6.12.c.7. Calcination. -- Calcination of sludge may be considered. Pilot studies on a particular plant waste are recommended. The BPH may require operational data from similar water treatment facilities treating similar raw water and require performance guaranteed specifications for the mechanical equipment.6.12.c.8. Drying Beds. -- Lime sludge drying beds are not recommended.6.12.d. Alum sludge. -- Lagooning may be used as a method of handling alum sludge. Lagoon size may be calculated using total chemicals used plus a factor for turbidity. Mechanical concentration may be considered. A pilot plant study is required before the design of a mechanical dewatering installation. Freezing changes the nature of alum sludge so that it can be used for fill. Acid treatment of sludge for alum recovery may be a possible alternative. Alum sludge may be discharged to a sanitary sewer; however, initiation of this practice depends on obtaining approval from the owner of the sewerage system as well as from the BPH before final designs are made. Lagoons shall be designed to produce an effluent satisfactory to the WVDEP and shall provide for: locations free from flooding; where necessary, dikes, deflecting gutters or other means of diverting surface water so that it does not flow into the lagoon; a minimum usable depth of five feet; freeboard of at least two (2) feet; an adjustable decanting device; an effluent sampling point; safety provisions; and a minimum two (2) cells, each with appropriate inlet/outlet structures to facilitate independent filling/dewatering operations. Mechanical dewatering shall be preceded by sludge concentration and chemical pre-treatment. Alum sludge may be disposed of by land application with approval from the WVDEP.6.12.e. "Red water" waste. -- Waste filter wash water from iron and manganese removal plants can be disposed of as follows: 6.12.e.1. Sand filters. -- Sand filters shall have the following features: 6.12.e.1.A. Total filter area, regardless of the volume of water to be handled, shall be no less than one hundred (100) square feet. Unless the filter is small enough to be cleaned and returned to service in one (1) day, two (2) or more cells are required;6.12.e.1.B. The "red water" filter shall have sufficient capacity to contain, above the level of the sand, the entire volume of wash water produced by washing all of the production filters in the plant, unless the production filters are washed on a rotating schedule and the flow through the production filters is regulated by true rate of flow controllers. Then sufficient volume shall be provided to properly dispose of the wash water involved;6.12.e.1.C. Sufficient filter surface area shall be provided so that, during any one (1) filtration cycle, no more than two (2) feet of backwash water may accumulate over the sand surface;6.12.e.1.D. The filter shall not be subject to flooding by surface runoff or flood waters. Finished grade elevation shall be established to facilitate maintenance, cleaning and removal of surface sand as required. Flash boards or other non-watertight devices shall not be used in the construction of filter side walls;6.12.e.1.E. The filter media shall consist of a minimum of twelve (12) inches of sand, three (3) to four (4) inches of supporting small gravel or torpedo sand and nine (9) inches of gravel in graded layers. All sand and gravel shall be washed to remove fines;6.12.e.1.F. Filter sand shall have an effective size of 0.3 to 0.5 mm and a uniformity coefficient not to exceed 3.5. The use of larger sized sands shall be justified by the designing engineer to the satisfaction of the BPH;6.12.e.1.G. The filter shall be provided with an adequate under-drainage collection system to permit satisfactory discharge of filtrate;6.12.e.1.H. Provision shall be made for the sampling of the filter effluent;6.12.e.1.I. Overflow devices from "red water" filters shall not be permitted;6.12.e.1.J. Where freezing is a problem, provisions shall be made for covering the filters during the winter months; and6.12.e.1.K. "Red water" filters shall comply with the common wall provisions that pertain to the possibility of contamination of finished water with unsafe water. The BPH shall be contacted for approval of any arrangement where a separate structure is not provided.6.12.e.2. Lagoons. -- Lagoons shall have the following features: be designed with volume ten (10) times the total quantity of wash water discharged during any twenty-four (24) hour period; a minimum usable depth of three (3) feet, length four (4) times width, and the width at least three (3) times the depth, as measured at the operating water level; an outlet at the end opposite the inlet; a weir overflow device at the outlet end with weir length equal to or greater than depth; and velocity dissipated at the inlet end.6.12.e.3. Discharge to community sanitary sewer. -- "Red water" may be discharged to a community sewer; however, approval of this method depends on obtaining approval from the owner of the sewerage system as well as from the BPH before final designs are made. A holding tank is recommended to prevent overloading the sewers. Design shall prevent cross connections and there shall be no common walls between potable and non-potable water.6.12.e.4. Recycling "Red Water" waste. -- Recycling of supernatant or filtrate from "red water" waste treatment facilities to the head end of an iron removal plant is not allowed except as approved by the BPH.6.12.e.5. Discharge to surface water. -- Plants shall have a permit from the WVDEP for disposal of backwash water into surface water.6.12.f. Waste filter wash water. -- Waste filter wash water from surface water treatment or lime softening plants shall have suspended solids reduced to a level acceptable to the WVDEP before being discharged. Many plants have constructed holding facilities and return this water to the inlet end of the plant. The holding facility shall be of such a size that it contains the anticipated volume of waste wash water produced by the plant when operating at design capacity. A plant that has two (2) filters shall have a holding facility that contains the total waste wash from both filters calculated by using a fifteen (15) minute wash at twenty (20) gallons per minute per square foot. In plants with more filters, the size of the holding facilities depends on the anticipated hours of operation. It is required that waste filter wash water be returned at a rate of less than ten percent (10%) of the raw water influent rate. Filter backwash water shall not be recycled when the raw water contains excessive algae, when finished water taste and odor problems are encountered, or when disinfection byproduct levels in the distribution system may exceed allowable levels. Particular attention must be given to the presence of protozoans such as Giardia and Cryptosporidium concentrating in the waste water stream. Water utilities may need to treat filter waste water prior to recycling to reduce pathogen population and improve coagulation or avoid reclaiming filter wash water given the increased risk to treated water quality.6.12.g. Radioactive materials. -- Radioactive materials include, but are not limited to, granulated activated carbon (GAC); ion-exchange regeneration waste from radium removal; and manganese greensand backwash solids from manganese removal systems, precipitative softening sludge, and reverse osmosis concentrates where radiological constituents are present. The buildup of radioactive decay products of radon shall be considered, and adequate shielding and safeguards shall be provided for operators and visitors. These materials may require disposal as radioactive waste in accordance with Nuclear Regulatory Commission regulations. Approval shall be obtained from the WVDEP prior to disposal of radioactive materials.6.12.h. Arsenic waste residuals. -- Arsenic-bearing wastes from an arsenic treatment facility may be considered hazardous. Under the Resource Conservation and Recovery Act (RCRA), a residual from an arsenic water treatment facility is defined as being hazardous waste if it exhibits a Toxicity Characteristic Leaching Procedure (TCLP) result of 5.0 mg/l. Approval shall be obtained from the WVDEP prior to disposal of arsenic waste residuals.