 liner, if needed B. Subsurface Collected Sand Filter Materials in A., except substitute 4. 0.049 yd3 of 0.75-in. to 2.5-in. coarse gravel/ft2 of filter area 7. clay or 18-mil plastic liner and add 8. 0.0093 yd3 of washed 0.25-in. to 0.75-in. gravel/ft2 of filter area (or filter fabric) C. Elevated Intermittent Sand Filter 1. concrete block, fiberglass, or other housing for filter sand (see septic tank materials list) with removable covers and two compartments 2. dosing chamber(s) (see dosing chamber materials list) 3. 4-in. unperforated PVC pipe to and from dosing chamber and from filter to disposal area or second dosing chamber 4. diversion mechanism or valves for alternating use of filter sections 5. 4-in. unperforated PVC distribution pipes with elbows 6. 4-in. perforated PVC distribution pipes with elbows 7. 2-in. unperforated vent pipe 8. 2 splashplates 9. 0.025 yd3 of 0.75-in. to 2.5-in. gravel/ft2 of filter area ONSITE WASTEWATER DISPOSAL 10. 0.0093 yd3 of washed 0.25-in. to 0.75-in. gravel/ft2 of filter area (or filter fabric) 11. 0.074 yd3 of washed coarse sand/ft2 of filter area D. Elevated Recirculating Sand Filter Materials in C., except substitute: 1. single-compartment housing for filter sand 4. recirculation mechanism or float valve 8. splashplate and include: 12. recirculation tank 13. sewage rated sump pump 14. time clock and switching mechanism Construction Construction of the uncollected subsurface sand filter follows the same general procedure described for a conventional absorption trench, although the materials are different. Stake out the filter area, following any surface contour to keep the depth of the trench (or bed) constant and the bottom surface level. Dig holes for the septic tank and dosing chamber if one is to be used. The bottoms of the trenches for the solid connecting pipe should slope about 0.25 in. per ft in the direction of flow. Allow an extra inch or two of depth if the soil is rocky and use bedding sand to protect the pipe. If a dosing chamber wll be installed, the trenc