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5.1 TEST PIT SOIL DESCRIPTIONS <br /> A test pit was excavated in the vicinity of the new leachfield area that will be used <br /> in the planned Phase 2 expansion of the church to accommodate 250 people. A second <br /> test pit was excavated to the west of the existing septic system. <br /> Logs of both test pits are attached in Appendix D. Both surface soils were black <br /> clays (CH/CL) to a depth of 2 to 2.5 feet bgs — properties consistent with the description <br /> of the Stockton clay series described by the soil survey (USDA, 1992). Based on the <br /> description of these soils, percolation is likely to be very slow, requiring supplemental <br /> infiltration provided by seepage pits. <br /> 5.2 PERCOLATION TESTS <br /> A percolation test was performed in both test pits following the procedures <br /> outlined by the San Joaquin County Public Health Services. A copy of the procedures is <br /> attached (Appendix E). The test holes were constructed by removing surface soil with <br /> a backhoe to a depth of 22 inches, hand augering a hole 6 inches in diameter to an <br /> additional depth of 14 inches (36 inches bgs), and placing 2 inches of gravel in the base <br /> of the excavation. Water was added to presoak the holes for 24 hours prior to the test. <br /> In both test locations, water remained in the test hole, and so Procedure # 1 (see <br /> Appendix E) was followed to calculate the percolation rate. The measured percolation <br /> rates in the test pits were 3/8 inch and 1/4 inch per hour. <br /> The percolation tests indicate that infiltration in the shallow soils at the property <br /> is very slow. Slow infiltration, however, enhances cation exchange of ammonia and <br /> denitrification which increases loss of nitrogen. <br /> 5.3 REGIONAL SEPTIC SYSTEM DESIGN <br /> According to information provided by licensed septic system installers, both <br /> residential and developed non-residential property in the area utilize leach lines and <br /> seepage pits for sewage disposal. The seepage pits are used because of the low <br /> infiltration into clay soils which are predominant in the area and because there is <br /> substantial separation between the base of the pits and groundwater. <br /> To prevent liquid loading problems, septic systems at the property can utilize <br /> seepage pits similar to those incorporated in the current septic system. New septic <br /> SAC 125.12 6 <br /> DAMES &MOORE <br />