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" k" KL EIN'FELDER HISTORICAL GROUNDWATER DEPTH According to groundwater reports published by the San Joaquin County Flood Control and Water Conservation District (Spring 1993 to Spring 1999), high groundwater in the project area has been recorded at depths in the range of about 70 to 100 feet below ground surface. h FIELD EXPLORATIONS AND TESTING F The subsurface conditions at the proposed leach field location were explored.on December 6, 2001,by drilling one boring to a depth of approximately 15 feet below existing grade, which was used for a percolation test. The boring was drilled using a Simco 2400 truck-mounted drill rig equipped with 6-inch O.D. solid-stem auger. During the same time period, percolation borings were drilled to depths of about 3.5 and 9 feet below site grade. When the testing on these three borings was performed on December 7, 2001, all the tests failed to adequately percolate. Via a E telephone call with our field representative, Mr. Rodney Estrada of San Joaquin County !Public Health Services (SJCPHS) stated that due to failing results, the percolation testing on, these borings could be terminated without SJCPHS inspection. On December 10, additional percolation tests were installed in the same potential leachfield area at depths of approximately 19 and 25 feet. These tests were performed on December 11, 2001. The approximate ,boring (and percolation tests) location is presented as P-1 on the attached plate. Based on our findings, the subsurface soils encountered consisted of approximately 4.5 feet of sandy clays over approximately 11 feet of sandy and clayey silts, underlain by approximately 6.5 feet of silty sands. Beneath the silty sands existed sandy clay soils to the maximum' depth explored of approximately 25 feet. A log of boring that describes the subsurface conditions encountered is attached. j The percolation tests were performed in accordance with accepted guidelines using clearpotable water. The procedure calls for first placing about 2 inches of fine gravel at the bottom) of the borehole. The hole is then pre-soaked with water at least 24 hours prior to performing the test. The test is performed by first adding about 6 inches of water er 3 foot of percolation test depth above the gravel to the hole. From a fixed reference point, the drop in water level is measured at approximate 30-minute intervals for four hours, refilling as necessary to maintain the prescribed amount of water over the gravel. Under the observation of a sanitarian from the SJCPHS, the ! last 30-minute reading of the four hour period was recorded and used to calculate the percolation rate in minutes per inch. The estimated percolation rates are summarized below. Copies of our field percolation test results for test numbers P-1 and P-2 are attached. Te t Number_- 'Percolation R. (Tindinch}- e_ft:- -._9 --- ._ -. P-1 3.5 Did not percolate P-2 9.0 Did not percolate P-3 15.0 Did not percolate P-4 19.0 2.2 P-5 25.0 35.7 20-4684-Ol.G01/201 181570 December 20,2001 ©2001 Kleinfelder,Inc. Page 2 of 4