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i %woe k`■ KLEINEELDER FIELD EXPLORATIONS AND TESTING The subsurface conditions at the proposed addition were explored on March 21, 2002, by drilling four borings to depths ranging from approximately 15.5 to 20.5 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. Based on our findings, the subsurface soils encountered generally consisted of loose to medium dense silty and relatively clean sands to depths of about 8 to 14 feet below site grade, underlain by approximately 0.5 to 2.5 feet of very stiff silt. These soils were underlain by soft to very stiff sandy clays and medium dense silty and relatively clean sands to the depth explored. A staff engineer with our firm obtained samples of groundwater using clean procedures from a valve on the water tank adjacent to the on-site well. The well was located approximately 300 feet east and 200 feet north of the existing office. 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 attacher— NITRATE LOA)DING CALCULATIONS Per SJCPHS/EHD requirements, the following summarizes our nitrate loading calculations for the existing leach field. The State drinking water standard for nitrate is 45 milligrams per liter (NOO 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, communications with Mr. Mike Huggins at SJCPHS/EHD, 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. Ne=AWNw(1-D) + NO R `/f �� f! GG ✓ AW+R io. y3G Where: -/ t •.G36 y rrG io. Y36 Ne = Average calculated nitrate-nitrogen in groundwater resulting from domestic sources and precipitation–mg/1, as N A = Number of dwelling units per acre on septic tanks (unit/acre) = 0.418 (estimated based on an estimated water usage of 1700 gal./day, a typical water usage for 50t employees at 30 gal/employee plus 20 visitors at 10 gal./visitor (per the SIC PHS/EHD Sewage Standards) divided by 150 gal./day to obtain an equivalent number of homes,divided by 27.12 acres) W = Annual wastewater loading per dwelling unit per acre (inches)= 2.0 inches (per year per dwelling unit assuming a flow of 150 gal./day/dwelling unit) 13257.G01/ST02R023 June 4,2002 ©2002 Kleinfelder,Inc. Page 2 of 3