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LOGE 1907: Bavaro SS/NLS Addendum 3 Page 6 March 15, 2019 The estimated flow values discussed here should not be used for the design and sizing of the septic system. The design and sizing of the septic system should utilize the San Joaquin County Environmental Health Department's On-Site Wastewater Treatment Systems Standards (2017) which incorporates peak and surge flow factors. The estimates used in the On-Site Wastewater Treatment Systems Standards may be greater than those discussed here. Denitrification Reductions Denitrification is a process that occurs in the septic system drain field whereby certain bacteria oxidize the nitrate (NO3) in the waste water and release nitrogen gas (N2) to the atmosphere. Due to the biologic processes in the shallow soils, nitrogen in the drain field may undergo a reduction between 10 percent to 35 percent. Soils with higher clay content, moist soil conditions, high pH, and organic material denitrify by about 35 percent, and soils with high sand content and fast percolation rates tend to denitrify at a lower rate of about 10 percent. A denitrification factor of 20 percent was selected for the Site because of the mixture of sand and silt present at the percolation test locations. Nitrate Loading Estimate Two nitrate loading scenarios were employed to determine the impact from the proposed project to ground water. The scenarios utilize the variables discussed previously, which represent the estimated conditions and uses associated with this project. Because the method for selecting a recharge value is currently being reevaluated by the San Joaquin County Environmental Health Department, the nitrate loading calculation is presented twice so that both the evapotranspiration reduction method and the reduced rainfall method can be evaluated. Evapotranspiration Reduction Method The following table presents a summary of the assumptions for, and results of, the nitrate loading calculation for the Site when recharge is derived by the evapotranspiration reduction method, as presented in Plate 2. A modified version of this method is currently being developed by the San Joaquin County Environmental Health Department; full details of the recommended method are not yet available.