Section 58.01.08.520 - SURFACE WATER TREATMENT: CLARIFICATION PROCESSESTreatment facilities designed to include clarification for processing surface water must meet the following requirements:
01.Two Units Required. A minimum of two (2) units each must be provided for flocculation, sedimentation, and solids removal such that plant design capacity can be maintained with any component out of service for maintenance or repairs. Drains and pumps must be sized to allow dewatering in a reasonable period of time.02.Parallel or Serial Operation. The units must be capable of being operated either in series or parallel where softening is performed.03.Manual Start-Up. The units must be started manually following shutdown.04.Pre-Treatment. Waters exhibiting high turbidity may require pretreatment, usually sedimentation with or without the addition of coagulation chemicals. When presedimentation is provided, the following requirements must be met: a. Incoming water must be dispersed across the full width of the line of travel as quickly as possible. Short circuiting must be prevented.b. Provisions for bypassing pre-sedimentation basins must be included.c. The need for redundant pretreatment components must be evaluated according to the type and necessity of the pretreatment.05.Rapid Mix. Unless otherwise approved by the Department, a rapid mix device or chamber is required prior to flocculation, clarification, sedimentation, and settler units. The need for redundant rapid mix components must be evaluated. Rapid mix is the rapid dispersion of chemicals throughout the water to be treated, usually by violent agitation. The engineer must submit the design basis for the velocity gradient (G value) selected, considering the chemicals to be added and water temperature, color and other related water quality parameters. Basins or mixing chambers must be equipped with devices capable of providing adequate mixing for all treatment flow rates.06.Flocculation. Flocculation is the gathering together of fine particles in water by gentle mixing after the addition of coagulant chemicals to form larger particles and must include: a. Basin inlet and outlet design must minimize short-circuiting and destruction of floc. A drain, pumps, or a combination of both drain and pumps must be provided to accomplish dewatering and sludge removal.b. The flow-through velocity must not be less than one-half (0.5) nor greater than one and one-half (1.5) feet per minute with a detention time for floc formation of at least thirty (30) minutes unless otherwise approved by the Department.c. Agitators must be driven by variable speed drives.d. Flocculation and sedimentation basins must be as close together as possible. The velocity of flocculated water through pipes or conduits to settling basins must be not less than one-half (0.5) nor greater than one and one-half (1.5) feet per second. Allowances must be made to minimize turbulence at bends and changes in direction.07.Small Systems May Use Baffling. Baffling may be used to provide for flocculation in small treatment plants upon approval by the Department.08.Sedimentation Units. The following criteria apply to conventional sedimentation units: a. A minimum of two (2) hours of settling time must be provided following flocculation unless adequate settling in less time can be demonstrated.b. Inlets must be designed to distribute the water equally and at uniform velocities.c. Outlet weirs or submerged orifices must maintain velocities suitable for settling in the basin and minimize short-circuiting. Outlet weirs must be designed so that the rate of flow over the outlet weirs or through the submerged orifices will not exceed twenty-thousand (20,000) gallons per day per foot of the outlet launder. The entrance velocity through the submerged orifices must not exceed one-half (0.5) feet per second.d. The velocity through settling basins must not exceed one-half (0.5) feet per minute. The basins must be designed to minimize short-circuiting. Fixed or adjustable baffles must be provided as necessary to achieve the maximum potential for clarification.e. When an overflow weir or pipe is provided the overflow must discharge by gravity with a free fall at a location where the discharge will be noted.f. Adequate sludge collection equipment that ensures proper basin coverage must be provided and basins must be provided with a means for dewatering.g. Flushing lines or hydrants must be provided and must be equipped with backflow prevention devices acceptable under Section 543.h. Sludge removal design must provide that sludge pipes are not less than three (3) inches in diameter and arranged so as to facilitate cleaning. Entrance to sludge withdrawal piping must be designed to prevent clogging. Provision must be made for the operator to observe and sample sludge being withdrawn from the unit.i. Sludge must be disposed of in accordance with applicable regulations, as set forth in Section 540.09.Solids Contact Clarifiers. Solids contact clarifiers are generally acceptable for combined softening and clarification where water characteristics, especially temperature, do not fluctuate rapidly, flow rates are uniform and operation is continuous. A minimum of two (2) units are required for surface water treatment as required in Subsection 520.01.a. Chemicals must be applied at such points and by such means as to ensure satisfactory mixing of the chemicals with the water.b. Unless otherwise approved by the Department, a rapid mix device or chamber ahead of the solids contact clarifier is required to assure proper mixing of the chemicals applied. Mixing devices employed must be constructed so as to provide good mixing of the raw water with previously formed sludge particles and prevent deposition of solids in the mixing zone.c. Flocculation equipment must be adjustable as to speed, pitch, or a combination of speed and pitch and must provide for coagulation in a separate chamber or baffled zone within the unit.d. Sludge removal design must provide that sludge pipes are not less than three (3) inches in diameter and arranged so as to facilitate cleaning. Entrance to sludge withdrawal piping must be designed to prevent clogging. Provision must be made for the operator to observe and sample sludge being withdrawn from the unit.e. Blow-off outlets and drains must terminate and discharge at places acceptable to the Department in regard to control of potential cross connections. Cross connection control must be included for the potable water lines used to backflush sludge lines.f. The detention time must be established on the basis of the raw water characteristics and other local conditions that affect the operation of the unit. The Department may request data to support decisions made with respect to detention times.g. Controls for sludge withdrawal which minimize water losses must be provided.h. Unless otherwise approved by the Department, weirs must be adjustable and at least equivalent in length to the perimeter of the tank. Weir loading must not exceed ten (10) gallons per minute per foot of weir length for units used as clarifiers or twenty (20) gallons per minute per foot of weir length for units used for softening. Where orifices are used, the loading rates per foot of launder rates must be equivalent to weir loadings. Either must produce uniform rising rates over the entire area of the tank.i. Upflow rates must not exceed one (1) gallon per minute per square foot of area at the sludge separation line for units used as clarifiers or one and three-quarters (1.75) gallons per minute per foot of area at the slurry separation line for units used as softeners. The Department may consider higher rates if supporting data is provided.10.Settler Units. Settler units consisting of variously shaped tubes or plates installed in multiple layers and at an angle to the flow may be used for sedimentation following flocculation.a. Inlets and outlets must be designed to maintain velocities suitable for settling in the basin and to minimize short-circuiting. Plate units must be designed to minimize unequal distribution across the units.b. Drain piping from the settler units must be sized to facilitate a quick flush of the settler units and to prevent flooding other portions of the plant.c. Although most units will be located within a plant, outdoor installations must provide sufficient freeboard above the top of settlers to prevent freezing in the units.d. Water must be applied to tube settlers at a maximum rate of two (2) gallons per minute per square foot of cross-sectional area for tube settlers, unless higher rates are justified through pilot plant or in-plant demonstration studies in accordance with Subsection 501.19.e. Water must be applied to plate settlers at a maximum plate loading rate of one-half (0.5) gallons per minute per square foot, based on eighty (80) percent of the projected horizontal plate area.f. Flushing lines must be provided to facilitate maintenance and must be properly protected against backflow or back siphonage.11.High Rate Clarification. High rate clarification processes may be approved upon demonstrating satisfactory performance under on-site pilot in accordance with Subsection 501.19 or documentation of full scale plant operation with similar raw water quality conditions. Reductions in detention times or increases in weir loading rates must be justified. Examples of such processes include dissolved air flotation, ballasted flocculation, contact flocculation/clarification, and helical upflow.Idaho Admin. Code r. 58.01.08.520