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LOGE 1901: Armosino SS/NLS Addendum Page 2 <br /> March 19, 2019 <br /> The following table presents a summary of the assumptions for, and results of, the <br /> nitrate loading calculation for the Site when recharge is derived by the <br /> evapotranspiration reduction method with CIMIS data. A modified version of this <br /> method is currently being developed by the San Joaquin County Environmental Health <br /> Department for use in future studies. Details of the calculation are presented in Plate 2. <br /> Table 1. Inputs and Results for Nitrate Loading Calculation, <br /> Recharge Derived from Evapotranspiration Reduction Method <br /> Variable Value Units Description <br /> Q 560 gpd Effluent flow rateY <br /> T <br /> Nw 35 mg/L-N Effluent stream concentration <br /> A 2.43 acres Site area <br /> Nb 1.00 mg/L-N Concentration of rain <br /> d 0.25 constant Denitrification factor <br /> R 3.64 inches per year Recharge rate of rainfall <br /> W 3.1 inches per year Uniform waste water loading (calculated) <br /> Nc 12.6 mg/L-N Long-term average concentration of percolating <br /> effluent <br /> For this Site, the long-term average concentration of percolating effluent is found to be <br /> 12.6 mg/L-N when calculated as shown. This value exceeds the US EPA <br /> recommended MCL for nitrate in drinking water of 10 mg/L-N. <br /> There are several mitigating factors that should be considered, however, when <br /> evaluating whether or not this Site is likely to impact ground water with nitrate: <br /> • The map of Nitrate — Land Use Data (2019) prepared by San Joaquin County <br /> Environmental Health Department indicates that, within a one-half mile radius <br /> surrounding the Site, two wells have been tested for nitrate. Nitrate was detected <br /> between 0.1 to 5.0 mg/L-N in both wells, significantly below the MCL (Plate 3). <br /> Approximately 25 existing homes are located within this half-mile radius. <br /> • Additionally, depth to ground water beneath the Site is estimated to be 74 to 90 <br /> feet, as discussed in the original report. San Joaquin County experienced its <br /> highest recent ground-water levels in 1983 and 1999. Review of ground-water <br /> maps for these years (Plates 4 and 5) reveals that depth to water would have <br /> been approximately 60 feet during these high periods. Even assuming the most <br /> conservative (shallowest) ground-water depth, the vadose zone of the new septic <br /> system will be relatively deep, extending from the bottom of the 10-foot sumps (if <br />