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TO: J. DON LAYSON, M.P.H. , Director, Environmental Health Division <br /> FROM: ROBERT C. HARRELL, Assistant Director <br /> RE: Sewage Disposal Facility, Morada West Subdivision <br /> DATE: March 4, 1974 <br /> 1. A review of the percolation rates obtained from percolation tests conducted <br /> indicates a design factor of one gallon per square foot per day. <br /> 2. A soil boring to 25 foot depth and a percolation test conducted indicated a <br /> rate of four gallons per square foot per day if seepage pits are used. <br /> 3. Based on the four gallons per square foot per day figure the following calcu- <br /> lations are made. <br /> Square feet of seepage pit = 235 sq. ft. (36" x 25') <br /> Average daily flow - 19 residences x 3.01 people x 100 gpd <br /> 19 x 3.01 x 100 = 5700 gpd <br /> 235 x 4 = 940 gals/pit <br /> 940/5700 = 6.5 pits <br /> Pits to be intermittent dosed every 30 days <br /> 2 x 6.5 = 13 pits + 1 pit for seepage flow = 14 pits 36" x 25' deep. <br /> 4. The percolation tests were conducted at a depth of 4 1/2 - 5 feet and not in the <br /> designed leach field area. Only one boring was tested for seepage pits, again <br /> not in the leach field area. <br /> 5. It is my recommendation that additional percolation tests be conducted in the <br /> specified leach field area restricting the depth of the test to 3 feet. Further, <br /> these tests should be conducted in our presence. Once a definite rate is established <br /> then design criteria can be specific for the 19 residential units proposed in phase I. <br /> 6. The original percolation tests varied from 5 - 21 minutes per inch. The engineer <br /> stated that there was too much of a variation in these tests and selected one inch <br /> in 20 minutes as a practical rate of fall. <br /> 7. The plant itself would have to be reduced in capacity from 15,000 gpd to serve the <br /> development at the rate of 5,700 gpd. <br /> 3/w�? M' M <br />