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Aprik.25,2001 Job Number:LGOI-098 Page 12 VIII: CONCLUSIONS AND.RECOMMENDATIONS In conclusion, a satisfactory percolation rate was not.achieved on all parcels involved "with the lot lirie.adjustment.. Clay soils were encountered at the surface which impede the downward movement of percolating water: The septic permit review-has shown that conventional septic,systemsare"used in the area. A",conversation iXith.Mr.-Mike Huggins, ' Supervising Environmental Health Specialist with the San Joaquin County Envirournental Health 1 - Division, indicated that clay soils; shallow ground-water,-and nitrate problems exist in the area. Mr. Huggins mentioned.that an engineered"or"mounded e of se tic system has successfully been used in the area and would be a goo choice for the roject .� The depth to ground water"was found to be about 6:5 feet.on'aI1 parcels:The nitrate level measured in the water well.was found to be 79 tng/L as NO3 07.6 mg/L-N). The Environmental Protection Agency maximum contaminate level for drinking water for nitrate is 45 mg/L"and 10 ' mg/L-N. "No DBCP was found in the groundwater. The source of the nitrate detectedin the well water sample"is unknown but may be indicative of the overall quality of the shallow aquifer. " The,nitrate loading sis has shown that the of a"t'Yp ical" septic stem could . . g .anal Y p Y ] potentially cause a build up of nitrogen in the-shallow aquifer above the maximum contaminate level Of 10 mg/L-N for the three (3) proposed.2-acre parcels_ The predicted build up of nitrates " in the shallow ground water.is primarily due to the estimated low amount of deep percolating rain(recharge) in'the area. Deep percolating rain was determined from,rain gauge data and potential evapotranspiration (ET) data.from-the California Department of Water Resources California,Irrigation Management System(CIMS) weather station in Manteca which probably reflects the weather for southwestern San Joaquin County. . .Based on the resuhs.of this study, the troposed1)roject is suitable for use with a surface "Tnouded„ 'ty e se ties "stem or uivalent. Tlie effluent and nitrates from the waste water" would be disposed primarily by evapotranspiration. If this type of system is utilized, we estimate the proposed project will not negatively impact'ground.water quality. The recommendations for the project are as follows l} " An engineered septic system utilizing a mounded disposal field or equivalent �;- system. The use of a mounded disposal field will.rely on.evapotranspiratioi,i -�- effluent disposal. As an option, high water-consuming plants and high nitrate consuming'plants could be placed next to"(or on) the mound.to improve performance of the system. { 2) A qualified civil engineer such as Kjeldsen Sinnock & Neudeck Inc:should be . i _ r