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i.Free-access sand filters shall be covered to minimize odors except when located <br /> greater than 50 ft.away from any occupied structure and the property line. The cover <br /> shall consist of a thin layer of washed stone or washed pea gravel,a removable water- <br /> proof,or equivalent. <br /> ii.If washed stone or pea gravel is used as the filter cover,it shall be of uniform <br /> thickness as needed to cover the distribution network. <br /> iii.If a removable waterproof cover is used it shall be designed to withstand a uniform <br /> live loading of 150 pounds per square foot and constructed of materials resistant to <br /> decay and degradation such as aluminum or fiberglass and reinforced with treated <br /> lumber. If constructed entirely of wood,it shall be made from tongue and groove <br /> lumber treated to avoid decay. Gaps between boards shall be filled after shrinkage has <br /> occurred. The cover shall fit snugly on top of the filter containment structure to <br /> minimize escape of sewage odors while still facilitating air exchange. The cover must <br /> be easily removable to facilitate inspection and routine maintenance. <br /> d. Type C pressure-dosed sand filter recirculation system: <br /> (1) The system shall be designed so that between 66 percent and 83 percent of the sand <br /> filter effluent is returned back into the recirculation tank after each dose for <br /> reapplication to the sand filter,with the remainder directed to the drainfteld. <br /> (2) Acceptable recirculation ratios range from 2:1 to 5:1. A 3:1 recirculation ratio returns 3 <br /> parts(3/4)of the sand filter effluent back to the recirculation tank while discharging <br /> part(1/4)of the sand filter effluent to the drainfteld. <br /> G. INSTALLATION AND TESTING PROCEDURES <br /> 1. A preconstruction conference shall be required to be attended by the sand filter system designer, <br /> installer,local health department,and licensed soil scientist and registered professional engineer,as <br /> applicable,prior to beginning construction of the sand filter and associated ground absorption system. <br /> 2. The pressure-dosed sand filter shall be located to prevent surface/subsurface water inflow/ <br /> infiltration. The filter location shall meet the horizontal setback requirements of Rule.1950(a),except <br /> uncovered Type B and C sand filters shall be located at least 50 feet away from occupied structures and <br /> property lines. <br /> 3. When a liner is used for the filter containment stricture,a minimum leveling layer of 3 inches of <br /> Group I or 11 soil shall be placed in the excavation below the liner. The liner support structure shall be <br /> constructed such that nail points cannot penetrate the liner.The liner shall come above the original <br /> ground surface and extend into a perimeter berm built to shed surface runoff away from the filter. <br /> 4.Watertightness of the liner,its underdrain penetration points,and the preconstructed box or built-in- <br /> place concrete containment structure shall be demonstrated by a 24-hour leakage test conducted at the <br /> installation site after the underdrain and bedding is in place and prior to p€acement of sand in the <br /> containment structure. Sediment must be excluded from the system while the sand filter is open for this <br /> leakage test. <br /> 5. Laboratory analysis ofthe effective diameter,uniformity coefficient and dust content of the proposed <br /> sand filter media must be provided to the health department prior to sand media being installed. This <br /> analysis shall be included with the Operation Permit to be issued for the system. <br /> 6. Pressure distribution lateral perforations shall be cleaned of all filings,not have any visible burrs,and <br /> be reamed with a hole reamer prior to placement with the protective sleeve. <br /> 9 <br /> 134 <br />