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[51 LOCAL GROUNDWATER AND SURFACE WATER INFORMATION <br /> The groundwater, or the zone of saturation is located at approximately 30 ft below grade <br /> according to maps published by the Flood Control District. There was no evidence of a perched <br /> water table condition during our exploratory boring procedures. Part of the southern boundary of <br /> the Designated Remainder next to the Stanislaus River is in flood zone. The well logs illustrate a <br /> sandy clay from 7 to 24 feet below grade. <br /> No water sample was taken for analysis of nitrate and DBCP per the Conditions of Approval from <br /> the County, dated January 20, 1994. There is no potential impact to surface waters in the area, <br /> particularly the Stanislaus River. <br /> [61 CONCLUSIONS <br /> The percolation test results suggest a septic system with an 8,000 to 10,000 square foot leachfield <br /> may be used. We are recommending sumps if it is determined from leach line emplacement that <br /> this septic structure is necessary. It would be a highly unusual situation under which a clay lens <br /> was to be encountered. The Permit Applications for additional drainage for the study area does <br /> not indicate sumps are warranted. <br /> For any development, the size or number of bedrooms the new structure will have, should also be <br /> taken into consideration for the final design of the leachfield and sumps. For example, a four- <br /> bedroom house should have between 8,000 and 10,000 square feet of leachfield area and possibly <br /> sumps. A 50% standby replacement area must also be incorporated into the design. The <br /> referenced leachfield areas will help ensure stability and guard against leachfield failure. A failure <br /> would primarily result from the formation of a "biomat" or 'clogging mat" on the wetted soil <br /> where the effluent enters the soil. This mat is composed mostly of aerobic and anaerobic bacteria <br /> and bacterial products consisting of a slime of polyuronides and polysaccharides. If the <br /> soil/effluent interface is well aerated, a variety of soil microfauna such as nematodes and protozoa <br /> may digest the clogging mat bacteria. <br /> _(�`�^ �a�ity (vontro� Inspection <br />