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)1.1. Water pressures of at least 45 psi.

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)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)4.4. Air shall be free from contamination.

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)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.

NR 811.49(1)(i)9.9. The filter underdrains shall be designed to accommodate air scour piping when the piping is installed in the underdrain.

NR 811.49(1)(i)10.10. Backwash facilities shall meet the requirements of par. (k).

NR 811.49(1)(j)1.1. Sampling faucets on the individual and combined influent and effluent lines. Combined filter effluent sample faucets shall be located upstream of subsequent treatment processes.

NR 811.49(1)(j)2.2. Indicating loss-of-head gauge with appropriate cross-connection protection.

NR 811.49(1)(j)3.3. Indicating flow rate controls. A modified rate controller which limits the rate of filtration to a maximum rate may be used. However, equipment that simply maintains a constant water level on the filters will not be approved unless the rate of flow onto the filter is properly controlled. A pump in each filter effluent line may be used as the limiting factor for the rate of filtration only with approval from the department.

NR 811.49(1)(j)4.4. For surface water and groundwater under the direct influence of surface water, provisions for filtering to waste with appropriate measures for backflow prevention.

NR 811.49(1)(j)5.5. For surface water and groundwater under the direct influence of surface water, on-line continuous turbidimeters shall be installed on the effluent from each filter. All turbidimeters shall consistently determine and indicate the turbidity of the water in nephelometric turbidity units (NTUs). Each turbidimeter shall report to a recorder that is designed and operated to allow the operator to accurately determine the turbidity at least every 15 minutes. Turbidimeters on individual filters shall be designed to accurately measure low-range turbidities and trigger an alarm when the effluent level exceeds 0.3 NTU. Access to the filter interior through wall sleeves shall be provided in several locations to allow the installation of sampling lines, pressure sensors and other devices, at different depths in the filter media.