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.

NR 811.47(7)(d)1. 1. ‘Detention time.’ Plants with conventional sedimentation shall provide a minimum of 4 hours of settling time. This may be reduced to 2 hours for lime-soda softening facilities treating only groundwater. Also, reduced sedimentation time may be approved when equivalent effective settling is demonstrated or when overflow rate is not more than 0.5 gallons per minute per square foot.

NR 811.47(7)(d)2. 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 project several feet below the water surface to dissipate inlet velocities and provide uniform flows across the basin.

NR 811.47(7)(d)3. 3. ‘Outlet devices.’ Outlet devices 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 volume above the orifices for storage when there are fluctuations in flow.

NR 811.47(7)(d)4. 4. ‘Weir overflow rate.’ The rate of flow over the outlet weir may not exceed 20,000 gallons per day per foot of weir length. If submerged ports or orifices are used as an alternate for overflow weirs, they may not be lower than 3 feet below the flow line with flow rates equivalent to weir loadings. The entrance velocity through the submerged orifices shall not exceed 0.5 feet per second.

NR 811.47(7)(d)5. 5. ‘Drainage.’ Basins shall be provided with a means for dewatering. Basin bottoms shall slope toward the drain not less than one foot in 12 feet where mechanical sludge collection is not provided.

NR 811.47(7)(d)6. 6. ‘Covers.’ Covers or superstructures are required at all plants. Where covers are used, access hatches shall be provided as well as drop light connections so that observation of the floc can take place at the inlet, midpoint and outlet of the basin.

NR 811.47(7)(d)7. 7. ‘Velocity.’ The velocity through settling basins may 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.

NR 811.47(7)(d)8. 8. ‘Overflow.’ An overflow weir or pipe shall be installed, which will establish the maximum water level desired on top of the filters. It shall discharge by gravity with a downturned pipe elbow a minimum of one foot above a concrete splash pad and shall be covered with 4-mesh corrosion resistant screen at a location where the discharge is visible and where the water can be appropriately drained.

NR 811.47(7)(d)9. 9. ‘Safety.’ Guard rails shall be installed around openings which may be hazardous to maintenance personnel. Permanent holders or handholds shall be provided on the inside walls of basins above the water level.

NR 811.47(7)(d)10. 10. ‘Sludge collection.’ Mechanical sludge collection equipment may be provided.

NR 811.47(7)(d)11. 11. ‘Sludge removal.’ Facilities for disposal of sludge are required by the department. Sludge removal design shall provide:

NR 811.47(7)(d)11.a. a. Sludge pipes not less than 3 inches in diameter and so arranged as to facilitate cleaning.

NR 811.47(7)(d)11.b. b. Entrance to sludge withdrawal piping to prevent clogging.