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Soe ..i <br /> July 13,2001 <br /> Job Number:LGOl-191 <br /> Page 10 <br /> As a result of the analysis, a conventional septic system which relies on subsurface <br /> effluent disposal could potentially cause a build up of nitrates above the maximum contaminate <br /> level for nitrates (10 mg/L-N) on the subject property. The potential is greatest when the <br /> residence is occupied with five adults and when permeable soils were present which would allow <br /> nitrates to leach to an aquifer. The actual long term occupancy if the residence is an unknown <br /> however low permeable soils exist on the property. These clayey soils typically impede the <br /> downward flow of effluent which would greatly reduce the potential of nitrate buildup in ground <br /> water. <br /> VIII. CONCLUSIONS AND RECOMMENDATIONS <br /> In conclusion, the site generally has three challenges to over come regarding the septic <br /> system; an unsatisfactory percolation rate of 250 minutes per inch, shallow ground water depthti <br /> if 4.8 Wit, and ajoslightly above the drinking water standard of 10 mg/L-N <br /> when five persons occupy the home. <br /> Mr. Ray Borges, Senior Environmental Health Specialist with the San Joaquin County <br /> PHS-EHD, was contacted regarding the problems encountered with the project. He indicated <br /> that given the shallow ground water and slow percolation rate, an engineered septic system <br /> would probably be a good choice for the project. <br /> Since a minimum distance of 5-feet between ground water and the bottom of the disposal <br /> trench is required by San Joaquin County PHS-EHD sewage code, we recommend engineered <br /> soil fill be placed in the sewage field to achieve a minimum of five feet of separation from <br /> ground water which exists at a depth of 4.8 feet. Over the engineered fill, we recommend the <br /> construction of an engineered septic system which relies o_ a ano_ transviration as well as soil <br /> absorption. <br /> By utilizing an engineered septic system on semi-impervious clay soils, the nitrates <br /> generated from the home would be restricted to the shallow soils and may be consumed in the <br /> ` soils by shrubs, grasses and bacteria. The clayey soils should impede the downward flow of <br /> effluent into ground water. With the use of an engineered septic system, it should be possible to <br /> mitigate the three problems associated with the proposed septic system. <br /> rpE RSO <br /> r 1 <br /> r <br /> Z � <br /> O / <br /> dSpL <br /> r <br />