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k14 KLFINFELDER I r FIELD EXPLORATIONS AND TESTING The subsurface conditions at the site were explored on May 23, 2002 using a Simco 2400 truck- mounted drill rig equipped with 6-inch O.D. solid-stem auger. 4-Percolation:borings-were drilledl to•depths-of about 3;5. feet below,.site grade. The approximate percolation test locations are presented as on the attached plate. Based on our findings, the subsurface soils encountered consistedredom' to dark gray/brown silty and sandy clays to the depths explored, p mantly of gray brown The percolation tests were performed on.May 24, 2002, 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 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 per 3 foot of percolation test depth above the gravel to the hole. From a fixed reference point, the drop in water level is measured over approximately 30-minutes since water remained in the holes overnight after presoaking. None of the locations tested percolated over the 30-minute period. Following our percolation testing, a representative of our firm obtained a sample of groundwater using clean procedures from a spigot near the on-site well. The same day, the water sample was submitted to Sequoia Analytical using chain-of-custody procedures for DBCP and nitrate testing. The results of our tests and a copy of the chain-of-custody are attached. NITRATE LOADING CALCULATIONS Per SJCPHS/EHD requirements, the following summarizes our nitrate loading calculations for the proposed leach field. The State drinking water standard for nitrate is 45 milligrams per liter (NO3) and 10 mg/1 as Nitrogen (N) in groundwater. In our evaluation of nitrate loading, we have used the Hantzsche mass balance equation (source: Predicting Ground-Water Nitrate-Nitrogen Impacts, Hantzsche and Finnemore (1992)), which is presented below with an explanation for each factor and the value used in our study. The selection of parameters was based on previous studies and investigations performed by our firm and others, San Joaquin County Sewage Standards, and information provided in a report dated March 19, 1997 prepared by the Questa Engineering Corporation and authored by Mr. Hantzsche for a development in the Stockton area. N, =AWNW 1-D } bR AW+R Where: N, = Average calculated nitrate-nitrogen in groundwater resulting from domestic sources and precipitation—mg/l, as N 16797.GO1/ST02R170 July 1,2002 ©2002 Kleinfelder,Inc. Page 2 of 4