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. 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.