NR 811.47(7)(e)7.d.d. Facilities for an operator to observe or sample sludge being withdrawn from the unit.

NR 811.47(7)(e)8.8. ‘Cross-connections.’ Sludge blow-off outlets and drains shall terminate and discharge at places approved by the department. Cross-connection control shall be included for all potable water lines such as those used to backflush sludge lines or flush basins if potable water could become contaminated by nonpotable water.

NR 811.47(7)(e)9.9. ‘Detention period.’ The detention time shall be established on the basis of the raw water characteristics and local conditions that affect the operation of the unit. Based on design flow rates, the minimum detention time shall be 2 to 4 hours for suspended solids contact clarifiers and softeners treating surface waters, and one to 2 hours for the suspended solids contact softeners treating only groundwater.

NR 811.47(7)(e)10.10. ‘Suspended slurry concentrate.’ Softening units shall be designed so that continuous slurry concentrates of 1% or more, by weight, can be effectively maintained.

NR 811.47(7)(e)11.b.b. Total water loss may not exceed 5% for clarifiers or 3% for softening units.

NR 811.47(7)(e)11.c.c. Solids concentration of sludge discharged to waste shall be at least 3% by weight for clarifiers and 5% by weight for softeners.

NR 811.47(7)(e)12.12. ‘Weir or orifices.’ The units shall be equipped with either overflow weirs or orifices. Weirs shall be adjustable, at least equivalent in length to the perimeter of the tank, and constructed so that surface water does not travel over 10 feet horizontally to the collection trough.

NR 811.47(7)(e)13.13. ‘Weir or orifice loading.’ Weir loading may not exceed 20 gallons per minute per foot of weir length for units used for softeners, or 10 gallons per minute per foot of weir length for units used for clarifiers. Where orifices are used, the loading rate per foot shall be equivalent to weir loadings. Orifices or weirs shall produce uniform rising rates over the entire area of the tank.

NR 811.47(7)(e)14.14. ‘Upflow rates.’ Unless supporting data is submitted to the department and the department grants an exception, the following rates may not be exceeded:

NR 811.47(7)(e)14.a.a. 1.75 gallons per minute per square foot of area at the slurry separation line if units are used for softeners.

NR 811.47(7)(e)14.b.b. 1.0 gallon per minute per square foot of area at the sludge separation line if units are used for clarifiers.

NR 811.47(7)(f)(f) Tube or plate settlers. Proposals for settler unit clarification shall include pilot plant or a full scale demonstration or both satisfactory to the department prior to the preparation of final plans and specifications for approval. Settler units consisting of variously shaped tubes or plates which are installed in multiple layers and at an angle to the flow, may be used for sedimentation, following flocculation. Tube or plate settler installations shall meet the following:

NR 811.47(7)(f)1.1. ‘Inlet and outlet considerations.’ Design the inlets and outlets to maintain velocities suitable for settling in the basin and to minimize short-circuiting.

NR 811.47(7)(f)2.2. ‘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.

NR 811.47(7)(f)3.3. ‘Protection from freezing.’ Units shall be located within a plant or within a covered basin.

NR 811.47(7)(f)4.4. ‘Application rate for tubes.’ A maximum application rate of 2 gallons per minute per square foot of cross-sectional area, unless higher rates are successfully shown through pilot plant or in-plant demonstration studies and are approved by the department.

NR 811.47(7)(f)5.5. ‘Application rate for plates.’ A maximum plate loading rate of 0.5 gallons per minute per square foot, based on 80 percent of the projected horizontal plate area.

NR 811.47(7)(f)6.6. ‘Flushing lines.’ Flushing lines shall be provided to facilitate maintenance and shall be properly protected against backflow or back siphonage.

NR 811.47(7)(f)7.7. ‘Placement.’ Modules shall be placed in zones of stable hydraulic conditions and in areas nearest effluent launders for basins not completely covered by the modules.

NR 811.47(7)(f)8.8. ‘Inlets and outlets.’ Inlets and outlets shall conform with par. (d) 2. and 3.

NR 811.47 HistoryHistory: CR 09-073: cr. Register November 2010 No. 659, eff. 12-1-10; CR 22-074: am. (intro.), (7) (b) 1. Register January 2024 No. 817, eff. 2-1-24.

NR 811.48(1)(a)(a) Type. The following types of chemical feed equipment may be used to feed chlorine: