SR0082866_SSNL - Laserfiche WebLink

Home Browse Search

Discussion of Nitrate Loading Results Total Nitrate Impact Based on the method and assumptions described, the result of the nitrate loading estimate indicates that the existing home plus a one-bedroom second unit dwelling on the Site should not cause a buildup of nitrates in the aquifer above 10 mg/L-N. The existing home plus a two-bedroom second unit dwelling on the Site has the potential to cause a buildup of nitrates in the aquifer slightly over 10 mg/L-N. There are several mitigating factors that should be considered, however, when evaluating whether or not this Site is likely to impact ground water with nitrate: • The Hantzsche and Finnemore equation is a conservative method for determining potential impacts, and actual nitrate loading experienced on the Site over time may be less than predicted. The requirement by San Joaquin County Environmental Health Department that the calculation use rainfall and evapotranspiration data to determine ground-water recharge is particularly conservative, as it does not include consideration of recharge from irrigation water or surface water sources. • According to the map reviewed, several wells in the area have been tested for nitrate; none are exhibiting nitrate levels above 5 mg/L-N. The test results may indicate that residential development in the area is not adversely impacting water quality. • Based on the clay soil type present on the Site, it is likely that adsorption of nitrate ions to clay will occur as percolating effluent travels downward through the vadose zone. True nitrate reduction may exceed that accounted for by the soil denitrification factor included in the calculation. Because of these factors, Live Oak recommends that development of a one- or two- bedroom second unit dwelling be allowed with a standard septic system utilizing leach lines or a filter bed. LOGE 20-48 Page 13