SR0080845 SSNL - Laserfiche WebLink

Home Browse Search

of the ground-water aquifer, it is possible that any remaining surface contaminants may be transported to the first saturated zone of the aquifer. First ground water is predicted at 85 to 98 feet below ground surface for this Site, consequently, significant nitrate reduction would be anticipated as the septic effluent percolates downward. Sources of Nitrate Dairies, orchards that require fertilization in sandy soils, and septic systems have been found to be the most significant sources of nitrate in ground water. Percolating Recharge Waters One of the most determinant factors in the Hantzsche and Finnemore equation is the rate of recharge from percolating waters, which mix with the downward-percolating effluent generated by on-site septic systems. In the original Hantzsche and Finnemore paper, "average recharge rate of rainfall" was utilized. Based on San Joaquin County Environmental Health Department policy (personal communication, March 18, 2019), the recharge input for the Hantzsche and Finnemore equation should be derived from average monthly precipitation of rainfall and evapotranspiration rates for the area; the data should be obtained from the California Irrigation Management Information System (CIMIS). Recharge is calculated by first determining whether the average monthly precipitation exceeds average monthly potential evapotranspiration. If so, then the difference is the percolating recharge water into the aquifer. Runoff and stream infiltration drainage are not factored into the calculation. This approach likely under-estimates recharge to the aquifer and, consequently, over-estimates nitrate loading. For the project Site, the local percolation and evapotranspiration rates are presented in Plate 14. The closest CIMIS station to the Site is Staten Island (station 242). Data for the Staten Island station were available for the past three years; based on the calculation shown, the estimated rate of recharge from percolating waters for the Staten Island station is determined to be 12.60 inches. A statistical error of 49 percent is associated with this value. Quality of Rainwater Hantzsche and Finnemore listed 1 mg/L-N as the nitrate concentration of rainwater for their original calculation, in the past, Live Oak has also utilized this value for the nitrate loading calculation. In May 2019, Live Oak collected rainwater during two storm events in Lodi; the samples were analyzed for nitrate by FGL Environmental of Stockton. Each sample was LOGE 1933 Page 9