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1.1/02/01 FRI 1x:49 FAX 10003 i HISTORICAL GROUNDWATER AND TESTING i At the time of the water well was installed, groundwater was recorded at a depth of about 14.5 feet kow site grade. On July 2 and 3, 2001, a soil suitability study was performed by Dwain Toseb, Civil Engineer,within the project area. At the time of the percolation testing,Mir- Tosch reported groundwater was at a depth of about 7.5 feet. According to our discussions we understand that groundwater fluctuates in the area mostly due to irrigation ern properties to the west_ The ground surface, although relatively level at the house site, apparently slopes downward toward the river at a general rate of 2 foot every 100 feet Regional maps and our experiewe also suggest a groundwater gradient to the east toward the Sau Joaquin River. We, understand that the gr undwater depth decreases during the winter months. One of the factors required by the SJCPHS is to determine the existing valuer of nitrate in the groundwater below the site. Accordingly, a sample of groundwater was obtained by a staff geologist fropn our firm usingr clean procedures from the recently installed well on the property. The results of our evaluation showed a nitrate as NO3 concentration of 20 mg/l, This value correlates to a nitrate as ° N concentration of about 4,5 mg/l. As requested, two additional water samples were obtained ' fl r 'water wells on adjacent properties to the north and south and the results are attached The adjacent wells we3 understand are also used for irrigation- Although the-well construction is h unknown,we suspect the screen interval lis relatively shallow which would allow ir6gation water to impact water quality. NITRATE LOADING CALCULATI"N Per San Joaquin County Public Health Services (St'CPHS) Department Environmental Health r 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(N%) and 10 mg/l as Nitrogen(N) in groundwater. In our evaluation of nitrate loading, we have used the Hantzsche mass balance equation (source: Predicting Groin d-Water Nitrate-Nitrogen Impacts, Hantzsche and Finnetnore (1992)), which is presented below with aux explanation for each faCt4r and the values used in our study. Since there -is currently no d ed restriction limiting ' the nirnxber of homes on the lot to one, we have calculated the average nitrate (NJ in g rouridwater assuming on both one and two homes on the lot as moired by W. Huggins with SJCPHS. The; selection of other parameters was based on previous studies by our firm, as well as a report dated March 19, 1997 prepared by the Questa Engineering Corporation and authored by Mr. Hantzscbe. We have chosen to use the same values considered appropriate by Mr. Hantzscher for his report,with the exception of an increased vahte for pmvent.denitrification(D) that has been modified based on rccer_t.local testing. N,=AM%Q-I1)+ r AW+r -Where: N„ — Average calculated nitrate in groundwater resulting from domestic sources and precipitation —mg/1,as N A = Number of dwelling units per acres on septic tanlcss (u>nitlacre) = 0.44 (single home per lot) emd 0.59(two homes per lot) W = Annual wastewater loading .per dwelling unit per acre (inches) = 2.0 inches (based on 150 2a-U67-01120111.743 Pale a of Copyright 2001 KlranNder,Inc. November 2,2001 e