West Virginia Code of State Rules › Agency 64 - Health › Title 64 - LEGISLATIVE RULE WEST VIRGINIA DEPARTMENT OF HEALTH AND HUMAN RESOURCES › Series 64-77 - Public Water Systems Design Standards › Section 64-77-6 - Treatment (General and Clarification)

Current through Register Vol. XLI, No. 28, July 12, 2024
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; and
6.2.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.