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of 140 gallons per bedroom per day has been selected (personal communication, <br />January 6, 2017). <br />The maximum daily flow for the Site was estimated to be 420 gallons per day (gpd), <br />derived from 140 gallons per bedroom per day multiplied by three bedrooms. A typical <br />residential concentration of 35 mg/L of nitrate as N was selected for the proposed <br />residence (Crites and Tchobanoglous, 1998). <br />The estimated flow values discussed here should not be used for the design and sizing <br />of the septic system. The design and sizing of the septic system should utilize the San <br />Joaquin County Environmental Health Department On-Site Wastewater Treatment <br />Systems Standards which incorporate peak and surge flow factors. The estimates used <br />in the On-Site Wastewater Treatment Systems Standards may be greater than those <br />discussed here. <br />Denitrification Reductions <br />Denitrification is a process that occurs in the septic system drain field whereby certain <br />bacteria oxidize the nitrate (NO 3 ) in the wastewater and release nitrogen gas (N2 ) to the <br />atmosphere. Due to the biologic processes in the shallow soils, nitrogen in the drain <br />field will may undergo a reduction between 10 percent to 35 percent. Soils with higher <br />clay content, moist soil conditions, high pH, and organic material denitrify by about 35 <br />percent, and soils with high sand content tend to denitrify at a lower rate of about 10 <br />percent. <br />A standard denitrification factor of 25 percent (Hantzsche and Finnemore, 1992) was <br />selected for the Site because of the silty soil present at the percolation test location. <br />Nitrate Loading Estimate <br />Two nitrate loading scenarios were employed to determine the impact from the <br />proposed project to ground water. The scenarios utilize the variables discussed <br />previously, which represent the estimated conditions and uses associated with this <br />project. Because the method for selecting a recharge value is currently being <br />reevaluated by the San Joaquin County Environmental Health Department, the nitrate <br />loading calculation is presented twice so that both the evapotranspiration reduction <br />method and the reduced rainfall method can be evaluated. <br />LOGE 1906 Page 13