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k' ■ NLEINFELDER be cut deep in order to intersect suitable percolating soils or shallow leach lines will lead to 1/S5 seepage pits or wells for disposal of effluent. PRESENT AND PAST USE OF THE SITE At the time of our exploration, the project site was sloping pasture land. Based on our X/) C3 3� discussions with Mr. Vorhees, we understand that the project site has been used for pasture land ll in the past. IrZ�3 HISTORICAL GROUNDWATER DEPTH In accordance with groundwater reports published by the San Joaquin County Flood Control and �'7— Water Conservation District (Spring 1989 to Spring 1999), high groundwater in the project area has been recorded at depths greater than 100 feet below ground surface. FIELD EXPLORATIONS AND TESTING The subsurface conditions at the 30-acre site were initially explored on September 30, 2002 as part of a geotechnical investigation by drilling three test borings to depths ranging from about 20.2 to 20.8 feet below existing grade. The borings were drilled using a Simco 2400 truck- mounted drill rig equipped with 4-inch O.D. solid-stem auger. Between November 18, 2002 and February 7, 2003, at least two percolation borings were drilled on each of the fifteen lots (P- 1 through P-30) at depths ranging from about 3.5 to 15.4 feet below site grade. Based on our test borings, the near-surface soils encountered consisted predominately of very stiff, sandy to clayey silt to a depth of about 1 foot below site grade. The near-surface silts were O 11 underlain predominately by interbedded strata of medium dense to very dense clayey to silty j•�� c / sands; very dense, cemented gravelly sand; very stiff to hard, sandy to clayey silts; and very stiff to hard, silty to sandy clays to the depths explored. A total of 30 percolation tests were performed, two for each 2-acre lot. The percolation tests were performed in accordance with accepted guidelines using clear potable water. The procedure calls for first placing about 2 inches of fine gravel at the bottom of the borehole. The 602'�03� hole is then pre-soaked with water at least 24 hours prior to performing the test. The test is performed by first adding 6 to 12 inches of water above the gravel. From a fixed reference point, l the drop in water level is measured in approximately 30 minute intervals for four hours, refilling as necessary to maintain about 6 to 12 inches of water over the gravel. Under the observation of a sanitarian from the San Joaquin County Environmental Health Department (SJCEHD), the last 30 minute reading of the four hour period is recorded and used to calculate the percolation rate in minutes per inch. The estimated percolation rates at each test location are as summarized below. A copy of our field percolation test results is attached. 4.G 23197.GOI/ST03R289 February 14,2003 ©2003 Kleinfelder,Inc. Page 2 of 5