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4 <br /> y �� KLEINFELDER <br /> HISTORICAL GROUNDWATER DEPTH <br /> At the time of the water well was installed, groundwater was recorded at a depth of about 14.5 <br /> feet below site grade. On July 2 and 3, 2001, a soil suitability study was performed by Dwain <br /> Tosch, Civil Engineer, within the project area. At the time of the percolation testing, Mr. Tosch <br /> reported groundwater was at a depth of about 7.5 feet. <br /> NITRATE LOADING CALCULATIONS J <br /> Per San Joaquin County Public Health Services (SJCPHS) Department Environmental Health <br /> Division (PHS/EHD) requirements, the following summarizes our nitrate loading calculations for <br /> the proposed leach field. The drinking water standard for nitrate is 45 milligrams per liter (NO3) <br /> and 10 mg/l as Nitrogen (N) in groundwater. In our evaluation of nitrate loading, we have used <br /> the Hantzsche mass balance equation (source: Predicting Ground-Water Nitrate-Nitrogen <br /> Impacts, Hantzsche and Finnemore (1992)), which is presented below with an explanation for <br /> each factor;and the values used in our study. Since there is currently no deed restriction limiting <br /> the number of homes on the lot to one, we have calculated the average nitrate (N,) in <br /> groundwater assum_ ng on both one and two homes on the lot as required by Mr. Huggins with <br /> SJCPHS. The selection of other parameters was based on previous studies by our firm, as well <br /> as a report dated March 19, 1997 prepared by the Questa Engineering Corporation and authored <br /> by Mr. Hantzsche. We have chosen to use the same values considered appropriate by Mr. <br /> Hantzsche for his report, with the exception of an increased value for percent denitrification (D) <br /> that has been modified based on recent local testing. <br /> N,=AWNW 1-D + Nr <br /> AW+r <br /> Where: <br /> N, = Average calculated nitrate in groundwater resulting from domestic sources and precipitation <br /> —mg/1, as N <br /> A = Number of dwelling units per acres on septic tanks (unit/acre) = 0.44 (single home per lot) <br /> and 0.89 (two homes per lot) <br /> W = Annual wastewater loading per dwelling unit per acre (inches) = 2.0 inches (based on 150 <br /> gpd/residence) <br /> N,, — 1 rates`—e con entration of nitrified ieachfield effluent (mg/1) — 45 mg/1 typical (Hantzsche and <br /> Finnemore (1992)) <br /> D — Percent dentrification of leachfield effluent = 0.3 percent (Selected since the near-surface36% <br /> soils are reported to consist of fine clays and silts that tend to increase denitrification) <br /> R = Annual deep percolation of precipitation (inches) = 3.0 inches (used by Mr. Hantzsche based <br /> on approximately 13.5 inches precipitation, 2 inches of runoff, and 8.5 inches ET.) <br /> Nb = Background nitrate concentration of the deep percolating precipitation—mg/1 =2.2 mg/1 as N <br /> 20-4667-01/2011L743 Page 2 of 3 <br /> Copyright 2001 Kleinfelder, Inc. October 26,2001 <br />