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r October 12,2000 Job Number:LG00-312 Page 12 . adequate drainage for a conventional residential septic system utilizing leach lines and seepage pits. The septic permit review has shown that conventional septic systems with seepage pits are f used in the area. The depth to ground water is fairly deep, about 76 to 80 feet and the nitrate level measuredin the well appears to indicate the water is probably at or near"natural concentration levels"with respect to nitrates. No DBCP was found in the groundwater. The aquifer appears to be quite heterogeneous with many sand/clay layers ranging between 1 and 40 feet thick located within the unsaturated and saturated zones. This heterogeneity was observed in our shallow drilling to a maximum depth of 25 feet. The aquifer. ' confinement is unknown however it appears that no nitrate impacts from local dairy"operations, agriculture, cattle grazing, or septic systems are observable within the aquifer at the inlet depth and location of water well. Based on this information, it is possible that there is a real, apparent, or functional low permeable zone(s)located between the surface and ground water. If septic systems are to'be utilized, a discontinuous and heterogeneous zone consisting of many clay layers and fairly deep ground water is more preferable then say Manteca conditions consisting of clean sand and shallow ground water. Based on the information available,the soil and hydrogeologic conditions appear to be favorable for the proposed development. The _clay layers will vrobably inhibit the downwardercolation of the treated septic effluent-and rain fall. The benefit of evapotranspiration could be expected in the shallow septic field that will remove 64 moisture and consume nitrogen. The nitrate loading analysis suggests that the area can sustain the long term use of 3 and 4 bedroom homes. The minimum acreage to support the nitrate load from a three(3)bedroom home(three occupants) septic system is about 0.75 acre. The minimum acreage to safely support the nitrate load from a four(4)(bedroom home(four occupants) septic system is about 1.0 acre. Keep in mind that over the life of a home and family,the home will probably not be completely occupied. This fact adds an additional factor of safety. Regarding parcels 16, 18,20, and 22,the nitrate loading analysis has indicated that the parcels are too small in size (allowing potential high density growth)to safely support the use of a conventional septic system.. If at some time in the future the lots were increased in size to 0.75 acres or larger and satisfactory percolation rates were achieved,these lots would be suitable for similar residential development. Based on the results of this study,parcels 1-15, 17, 19, and 21 are suitable for use with a conventional septic system. The nitrate analysis has shown that based on the different sizes of the proposed parcels, parcel numbers i through 14 exceed the minimum acreage requirement for a 4- ti 4