NR 811.46 History History: CR 09-073: cr. Register November 2010 No. 659, eff. 12-1-10.

NR 811.47 NR 811.47 Clarification. Clarification plants prior to filtration shall meet all of the following requirements unless other design criteria are justified through pilot testing under s. NR 811.44 or other specific information provided to the department supports the proposed design, as determined by the department:

NR 811.47(1) (1) Provide a minimum of 2 units each for rapid mix, flocculation and sedimentation.

NR 811.47(2) (2) Permit operation of the units either in series or parallel.

NR 811.47(3) (3) Be constructed to permit units to be taken out of service without disrupting operation with drains or pumps sized to allow dewatering in a reasonable period of time.

NR 811.47(4) (4) Provide multiple-stage treatment facilities if required by the department.

NR 811.47(5) (5) Be started manually following shutdown.

NR 811.47(6) (6) Minimize hydraulic head losses between units to allow future changes in processes without the need for repumping.

NR 811.47(7) (7) Meet the following specific requirements:

NR 811.47(7)(a) (a) Presedimentation. Waters containing high turbidity or having unusual treatment requirements may require pretreatment, usually sedimentation or detention either with or without the addition of coagulation chemicals.

NR 811.47(7)(a)1. 1. ‘Basin design.’ Presedimentation basins shall have the following:

NR 811.47(7)(a)1.a. a. Hopper bottoms or be equipped with continuous mechanical sludge removal apparatus, and provide arrangements for dewatering.

NR 811.47(7)(a)1.b. b. Cover or superstructure.

NR 811.47(7)(a)2. 2. ‘Inlet.’ Incoming water shall be dispersed across the full width of the line of travel as quickly as possible. Short circuiting shall be prevented.

NR 811.47(7)(a)3. 3. ‘Bypass.’ Provisions for bypassing presedimentation basins shall be included.

NR 811.47(7)(a)4. 4. ‘Detention time.’ Three hours detention is the minimum period required for presedimentation. Greater detention may be required in individual cases of chemical pretreatment.

NR 811.47(7)(a)5. 5. ‘Raw water samples.’ A means for collecting raw water samples prior to any chemical addition shall be provided.

NR 811.47(7)(b) (b) Rapid mix. Mixing shall mean the rapid dispersion of chemicals throughout the water to be treated, usually by violent agitation. For surface water plants using direct or conventional filtration, the use of a primary coagulant is required at all times.

NR 811.47(7)(b)1. 1. ‘Mixing.’ The detention period shall not be more than 30 seconds with mixing equipment capable of imparting a minimum velocity gradient (G) of at least 750 feet per second per foot or as determined through jar testing. The appropriate G value and detention time shall be determined through jar testing.

NR 811.47(7)(b)2. 2. ‘Equipment.’ Basins shall be equipped with mechanical mixing devices unless other methods, such as baffling, or injection of chemicals at a point of high velocity, are approved by the department after determining that the other requirements of this chapter will be met. Variable speed drive equipment is recommended.

NR 811.47(7)(b)3. 3. ‘Location.’ The rapid mix and flocculation basin shall be as close together as possible.

NR 811.47(7)(c) (c) Flocculation — slow mixing. Flocculation installations shall meet all of the following requirements:

NR 811.47(7)(c)1. 1. ‘Basin design.’ Inlet and outlet design shall prevent short circuiting and destruction of floc. Series compartments shall be provided to 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 or pumps or both shall be provided to allow dewatering and sludge removal.

NR 811.47(7)(c)2. 2. ‘Detention.’ Flow-through velocity may be not less than 0.5 nor greater than 1.5 feet per minute with a detention time for floc formation of at least 30 minutes. Tapered energy with diminishing velocity gradient shall be considered in the design of the flocculation basin.

NR 811.47(7)(c)3. 3. ‘Equipment.’ Agitators shall be driven by variable speed drives or other means which vary the peripheral speed of paddles in the range of 0.5 to 3.0 feet per second and the tip speed of vertical shaft impellors in the range of 6 to 10 feet per second. Uniform mixing shall be provided to prevent settling in the flocculation basin.

NR 811.47(7)(c)4. 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 may not be less than 0.5 nor greater than 1.5 feet per second. Allowances shall be made to minimize turbulence at bends and changes in direction.

NR 811.47(7)(c)5. 5. ‘Other designs.’ Baffling may be used to provide flocculation only after approval by the department. The design shall be such that the velocities and flows in this section shall be maintained.

NR 811.47(7)(c)6. 6. ‘Superstructure.’ A superstructure shall be provided over the flocculation basins.

NR 811.47(7)(d) (d) Sedimentation. Sedimentation shall follow flocculation. The detention time for effective clarification is dependent upon factors related to basin design as well as the nature of the raw water, such as turbidity, color and colloidal matter, and taste and odor causing compounds.