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Mr.Raymond Vaz December 14,2001 Page 4 that the nitrate-nitrogen concentration of ground-water flow from up-gradient areas is lower."' The Hantzsche and Fennemore equation provides"...a conservative(worst case) first approximation of ground-water nitrate-nitrogen concentration resulting from the combined effect of on-site sewage disposal systems and precipitation. This (the equation and approach)is for estimation of long-term effect(i.e., over years) on ground-water,quality, and is not intended for prediction of seasonal changes."' The Hantzsche and Fennemore equation takes into account development area, soil denitrification factor,rainfall volume,rainfall nitrate concentration, the waste effluent quantity, and waste effluent nitrate concentration. The formula, assumptions and calculations used for the analysis are shown on Plates 1 through 3. The units of nitrate used in the mass balance equation are nitrate-N whose maximum drinking water contaminate level is 10 mg/l. Nitrate Loading Analysis Variables and Assumptions Denitrification is one of many important processes occurring in septic systems whereby certain bacteria utilize the oxygen in the nitrate(NO3) and release nitrogen gas(NZ)to the atmosphere. Denitrification is expressed as a percentage, and the normally accepted range is 10 percent to 35 percent. Soils with higher clay content, moist soil conditions,high pH, and organic material denitrify about 35 percent of effluent and soils with very high sand content and fast percolation rates are estimated to denitrify effluent at a lower rate, about 10 percent to 15 percent.' Due to the predominance of dark colored sandy silt soils,the denitrification factor is estimated to be 25 percent. An estimate of the quantity and quality of rainfall and effluent is required for the analysis. The following information was used in the calculation. The deep percolation of rain was estimated to be 2.12 inches (Plate 1). The nitrate concentration of rain fall was estimated to be 0.17 mg/L-N.' The quantity of household waste water was estimated to be about 75 gallons per person per day. In a four bedroom residence, the typical occupancy of the main residence would probably range between two to five persons resulting in a daily waste water flow between 150 to 375 gallons per day(see Table 1). The potential impact of a legally permitted second dwelling unit whose size is allowed up to 500 sq-ft(3-bedroom home),must be accounted in this analysis per San Joaquin County PHS-EHD. The average nitrate concentration of the typical residential p[gROry r� O'j�4