NR 811.48(9)(g)2.
2. When a centrifugal pump will discharge at a point not under continuous positive pressure, the outlet piping between the centrifugal pump and the point of chemical injection shall be installed with a vertical pipe loop that will extend to a height that is a minimum of 12 inches above the top of the solution tank and the location of the chemical addition pipe connection with the water system piping. A vacuum relief valve shall be installed on the top of the pipe loop. As an alternative to the installation of a vertical pipe loop, an electrically operated shut-off valve on the outlet piping, wired to operate in series with the operation of the well or service pump motor and the chemical feed pump, may be installed.
NR 811.48(9)(h)
(h) Centrifugal pump discharge piping. The outlet piping of a centrifugal pump shall also be provided with a check valve and a manually operated shut-off valve. These valves shall be installed upstream of any pipe loop or electrically operated shut-off valve as required by par.
(g) 2. NR 811.48(10)
(10)
Sodium chlorite for chlorine dioxide generation. Proposals for the storage and use of sodium chlorite shall be submitted to the department for approval. Department approval shall be obtained prior to the preparation of final plans and specifications. Provision shall be made for proper storage and handling of sodium chlorite to eliminate any danger of fire or explosion.
NR 811.48(10)(a)1.1. Sodium chlorite shall be stored by itself in a separate room and preferably shall be stored in an outside building detached from the water treatment facility. Sodium chlorite shall be stored away from organic materials with which it could react violently.
NR 811.48(10)(a)2.
2. Storage structures shall be constructed of noncombustible materials.
NR 811.48(10)(a)3.
3. If the storage structure is located in an area where a fire may occur, water shall be available to keep the sodium chlorite area cool enough to prevent heat induced explosive decomposition of the sodium chlorite.
NR 811.48(10)(b)2.
2. An emergency plan of operation shall be available for the clean up of any spillage.
NR 811.48(10)(b)3.
3. Storage drums containing sodium chlorite shall be thoroughly flushed and the waste shall be discharged to an acceptable location prior to recycling or disposal.
NR 811.48(10)(c)2.
2. Tubing for conveying sodium chlorite or chlorine dioxide solutions shall be Type 1 PVC, polyethylene or materials recommended by the manufacturer.
NR 811.48(10)(c)3.
3. Chemical feeders may be installed in chlorine gas rooms if sufficient space is provided or in separate rooms meeting the requirements of subs.
(5) and
(6).
NR 811.48(10)(c)4.
4. Feed lines shall be installed in a manner to prevent formation of gas pockets and shall terminate at a point of positive pressure.
NR 811.48(10)(c)5.
5. Check valves shall be provided to prevent the backflow of chlorine into the sodium chlorite line.
NR 811.48 History
History: CR 09-073: cr.
Register November 2010 No. 659, eff. 12-1-10;
CR 22-074: am. (1) (a) 2. to 4., (b), (4) (title), (5) (title), r. (5) (e), am. (6) (b), (7) (a), r. and recr. (8) Register January 2024 No. 817, eff. 2-1-24. NR 811.49
NR 811.49 Filtration — gravity. The application of any type of gravity filter and media shall be supported by water quality data representing a period of use sufficient to characterize any variations in water quality. Experimental or pilot plant treatment studies may be required to demonstrate the applicability of the method or rate of filtration proposed. Pressure filters will not be approved for surface water applications. The following specific requirements shall be met:
NR 811.49(1)(a)
(a)
Pretreatment. Rapid rate gravity filters may only be utilized after coagulation, flocculation and sedimentation.
NR 811.49(1)(b)
(b) Number. At least 2 filter units or cells shall be provided. Provisions shall be made to meet the plant design capacity at the approved filtration rate with one filter out of service. If only 2 units or cells are provided, each shall be capable of meeting the plant design capacity, normally the projected maximum daily demand.
NR 811.49(1)(c)
(c) Rate of filtration. The permissible rate of filtration shall be determined after consideration of factors such as raw water quality, degree of pretreatment provided, filter media, water quality control parameters, competency of operating personnel, and other factors required by the department. If effective coagulation, flocculation, sedimentation, and filtration processes are to be utilized with relatively clean water sources, the following filtration rates may be approved:
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See PDF for table 
In all cases, the filtration rate shall be proposed and justified by the design engineer and shall be approved by the department prior to the preparation of final plans and specifications. The department may approve higher rates than indicated in this paragraph with sufficient justification by the design engineer or through pilot testing under s.
NR 811.44.
NR 811.49(1)(d)
(d) Structural details and hydraulics. The filter structure shall be designed to provide:
NR 811.49(1)(d)2.
2. No protrusion of the filter walls or other structures into the filter media or the area between the top of the media and the high water line during backwashing.
NR 811.49(1)(d)7.
7. Trapped effluent pipe to prevent backflow of air to the bottom of the filters.
NR 811.49(1)(d)8.
8. Prevention of floor drainage to the filter with a minimum 4-inch curb around the filters.
NR 811.49(1)(d)9.
9. Prevention of flooding by providing an overflow if this is not provided in a pretreatment unit.
NR 811.49(1)(d)10.
10. Maximum velocity of treated water in the pipe and conduits to the filter of 2 feet per second.
NR 811.49(1)(d)11.
11. Cleanouts and straight alignment for influent pipes or conduits where solids loading is heavy or following lime-soda softening.
NR 811.49(1)(d)14.
14. Safety handrails or walls around the filter areas adjacent to walkways.
NR 811.49(1)(d)15.
15. Construction to prevent cross connections and common walls between potable and nonpotable water.
NR 811.49(1)(e)
(e) Washwater troughs. Washwater troughs shall be designed to provide:
NR 811.49(1)(e)1.
1. A bottom elevation above the maximum level of expanded media during washing.
NR 811.49(1)(e)4.
4. Spacing so that each trough serves the same number of square feet of filter area.
NR 811.49(1)(e)5.
5. A maximum horizontal travel of suspended particles not exceeding 3 feet in reaching the trough.
NR 811.49(1)(f)
(f) Filter material. The media shall be clean silica sand or other natural or synthetic media approved by the department and shall meet the following general requirements: a depth of not less than 24 inches; an effective size of the smallest material no greater than 0.45 mm to 0.55 mm, depending upon the quality of the raw water; a uniformity coefficient of the smallest material not greater than 1.65; a minimum of 12 inches of media with an effective size range no greater than 0.45 mm to 0.55 mm; and a specific gravity greater than other filtering materials within the filter. The following specific requirements shall be met:
NR 811.49(1)(f)1.
1. `Sand.' Sand shall have an effective size of 0.45 mm to 0.55 mm, a uniformity coefficient of not greater than 1.65, specific gravity greater than 2.5 and an acid solubility less than 5 percent.
NR 811.49(1)(f)2.
2. `Anthracite.' Filter anthracite shall consist of clean, hard, and durable anthracite coal particles of various sizes. Non-anthracite material may not be blended. Anthracite used as the only media shall have an effective size from 0.45 mm to 0.55 mm and a uniformity coefficient not greater than 1.65. Anthracite used to cap sand filters shall have an effective size from 0.8 mm to 1.2 mm and a uniformity coefficient not greater than 1.7. Effective size of anthracite for iron and manganese removal from potable groundwater shall be a maximum of 0.8 mm. Effective sizes greater than 0.8 mm may be approved by the department based upon onsite pilot plant studies. Anthracite shall have a specific gravity greater than 1.4 and an acid solubility less than 5%.
NR 811.49(1)(f)3.a.a. Granular activated carbon as a single media may be considered only after pilot or full scale testing and with prior approval of the department.
NR 811.49(1)(f)3.b.
b. The media shall meet the basic specifications for filter media as provided in this paragraph except that larger size media may be allowed by the department where full scale tests have demonstrated that treatment goals can be met under all conditions.
NR 811.49(1)(f)3.c.
c. There shall be provisions for a free chlorine residual and adequate contact time in the water following the filters and prior to distribution.
NR 811.49(1)(f)3.d.
d. There shall be means for periodic treatment of filter material for control of bacterial and other growth.
NR 811.49(1)(f)3.e.
e. Provisions shall be made for frequent replacement or regeneration of granular activated carbon if used for filtration.
NR 811.49(1)(f)4.
4. `High density sand.' High density sand shall consist of hard durable, and dense grain garnet, ilmenite, hematite, magnetite, or associated minerals of those ores that will resist degradation during handling and use and shall meet all of the following:
NR 811.49(1)(f)4.a.
a. Contain at least 95% of the associated material with a specific gravity of 3.8 or higher.
NR 811.49(1)(f)5.
5. `Other media.' Other media may be approved, but only on the basis of pilot tests and experience which demonstrate that the requirements of this chapter will be met.
NR 811.49(1)(f)6.
6. `Supporting media.' Torpedo sand and gravel shall be provided as supporting media except when proprietary filter bottoms are used. In that case, the department, on the basis of substantiating information provided by the owner, may allow elimination of certain layers of supporting media or a reduction in the depth of the layers. Otherwise, the following apply:
NR 811.49(1)(f)6.a.
a. A 3-inch layer of torpedo sand shall be used as a supporting media for the filter sand. The torpedo sand shall have an effective size of 0.8 mm to 2.0 mm, and a uniformity coefficient not greater than 1.7.
NR 811.49(1)(f)6.b.
b. Gravel, when used as the supporting media, shall consist of hard, rounded silica particles and may not include flat or elongated particles. The coarsest gravel shall be 2.5 inches in size when the gravel rests directly on the strainer system, and shall extend above the top of the perforated laterals or strainer nozzles. Not less than 3 layers of gravel, in addition to the layer of torpedo sand, shall be provided in accordance with the following size and depth distribution when used with perforated laterals or strainer nozzles. Reduction of gravel depths may be considered upon justification to the department when proprietary filter bottoms are specified.
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See PDF for table NR 811.49(1)(g)
(g) Filter bottoms and strainer systems. Departures from these standards by using proprietary bottoms may be approved by the department on a case-by-case basis if the effectiveness of the method is demonstrated. Porous plate bottoms may not be used where iron or manganese may clog them or with waters softened by lime. The design of manifold type collection systems shall:
NR 811.49(1)(g)2.
2. Assure even distribution of washwater and even rate of filtration over the entire area of the filter.
NR 811.49(1)(g)3.
3. Provide a ratio of the area of the final openings of the strainer systems to the area of the filter of about 0.003.
NR 811.49(1)(g)4.
4. Provide a total cross-sectional area of the laterals about twice the total area of the final openings of the strainer system.
NR 811.49(1)(g)5.
5. Provide a cross-sectional area of the manifold at 1.5 to 2 times the total cross-sectional area of the laterals.
NR 811.49(1)(g)6.
6. Lateral perforations without strainers shall be directed upwards.
NR 811.49(1)(h)
(h) Surface wash. Surface wash facilities consisting of either fixed nozzles or a revolving mechanism are required unless air scour equipment is provided. All surface wash devices shall be designed with:
NR 811.49(1)(h)2.
2. Volume of flow of 2.0 gallons per minute per square foot of filter area with fixed nozzles and 0.5 gallons per minute per square foot with revolving arms.
NR 811.49(1)(h)3.
3. A vacuum breaker installed above the high water elevation in the filter or other approved device to prevent back siphonage.
NR 811.49(1)(i)
(i) Air scouring. Air scouring may be provided in place of surface wash. The following requirements apply:
NR 811.49(1)(i)1.
1. Air flow for air scouring the filter shall be 2 to 5 standard cubic feet per minute per square foot of filter area when the air is introduced in the underdrain. Air scour distribution systems placed above the underdrains shall use the lower end of the range.
NR 811.49(1)(i)2.
2. A method for avoiding excessive loss of the filter media during backwashing shall be provided.
NR 811.49(1)(i)3.
3. Air scouring shall be followed by a fluidization wash sufficient to restratify the media.
NR 811.49(1)(i)5.
5. Air scour distribution systems shall normally be placed below the media and supporting bed interface; if placed at the interface the air scour nozzles shall be designed to prevent media from clogging the nozzles or entering the air distribution system.
NR 811.49(1)(i)6.
6. Piping for the air distribution system may not be flexible hose which will collapse when not under air pressure and may not be a relatively soft material which may erode at the orifice opening with the passage of air at high velocity.
NR 811.49(1)(i)7.
7. Air delivery piping may not pass down through the filter media nor may there be any arrangement in the filter design which would allow short circuiting between the applied unfiltered water and the filtered water except if all of the following criteria are met:
NR 811.49(1)(i)7.a.
a. The vertical piping is double wall, welded at top and bottom, schedule 40 stainless steel for the internal pipe and schedule 5 stainless steel for the external pipe.
NR 811.49(1)(i)7.c.
c. An air connection to the double-wall annulus shall be provided including piping with a pressure gauge, regulator, flow switch and ball valve along with an air reservoir and compressor.
NR 811.49(1)(i)7.d.
d. The flow switch shall alarm and trigger filter shutdown if a pressure drop of over 10 psi is detected.
NR 811.49(1)(i)8.
8. The backwash delivery system shall be capable of 15 gallons per minute per square foot of filter surface area; however, when air scour is provided, the backwash rate shall be variable and may not exceed 8 gallons per minute per square foot unless operating experience shows that a higher rate is necessary to remove scoured particles from filter surfaces.
