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1 KLEINFELDER HISTORICAL GROUNDWATER DEPTH In accordance with groundwater reports published by the San Joaquin County Flood Control and Water Conservation District (Spring 1990 to Spring 1999), high groundwater in the project area has been recorded at depths in the range of about 20 to 30 feet below ground surface. No groundwater was encountered to the maximum depth explored of 16.5 feet below ground surface during our geotechnical investigation. FIELD EXPLORATIONS AND TESTING The subsurface conditions at the site were initially explored as part of a geotechnical investigation on September 18, 2001 by drilling four borings (B-1 through B-4) to depths ranging from about 11.5 to 16.5 feet below existing grade. The borings were drilled using a Simco 2400 truck-mounted drill rig equipped with 4.5-inch O.D. solid-stem auger. During the Ysame time period, two percolation borings were drilled in the leach field area of the;K office/apartment building (P-1 and P-2) at depths ranging from about 3 to 9 feet below site grade. Based on our findings, the subsurface soils encountered over the majority of the site consisted predominately of silty sands with interbedded sandy silts, clayey silts and occasional layers of poorly graded sands. The soils encountered at percolation holes P-1 and P-2 consisted of silty sands at the surface with interbedded poorly graded sand strata. A per5o lation test was performed in accordance with accepted guidelines using clear potable water.7-The procedure calls for first placing about 2 inches of fine gravel at the bottom of the bore hole. The 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, 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 Public Health Department, 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 rate at the test location is as summarized below. A copy of our field percolation test results is attached. / Test Number Depth, ft. Percolation Rate min./inch ✓/ P-1 3.0 10.9 Although two percolation test holes were drilled, only one percolation test was performed due to test number P-1 percolating faster than the minimum 60 minutes per inch requirement. NITRATE LOADING CALCULATIONS Per San Joaquin County Public Health Services (SJCPHS) Department Environmental Health Division (PHS/EHD)requirements,the following summarizes our nitrate loading calculations for the proposed leach field. The drinking water standard for nitrate is 45 milligrams per liter(NO3) and 10 mg/l as Nitrogen (l) in groundwater. In our evaluation of nitrate loading, we have used the Hantzsche mass balance equation (source: Predicting Ground-Water Nitrate-Nitrogen 20-4654-O1.G01/201 IR1357 November 6,2001 ©2001 Kleinfelder,Inc. Page 2 of