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Mr. John Parks Page 3 t ; based on a simple mass balance formula which takes into account site denitrification, rain fall, and the proposed waste effluent. Assumptions and calculations for the analysis are contained on the attached Nitrate Loading Calculations sheet. t... Denitrification is the biological process in the soil whereby certain bacteria utilize the oxygen in the nitrate(NO3) and release nitrogen to the atmosphere. Denitrification is expressed as gen g as(N ) a percentage,and the normally accepted range is 10%to 25%. Sites with higher clay content,moist conditions,and organic material denitrify about 25%or more but sites with higher sand content and fast peculation rates are estimated to denitrify about 10%or less. In our approach to estimate the nitrate concentration, we calculated two scenarios, one conservative and one non conservative. Please see the following table for a summary of variables and the result of analysis. Summary of Variables for Mass Balance Equation Approach Result of Denitrif- Deep Rain Waste Quantity of Rain Acres Analysis cation Percolation level2 discharge Concentration fl (35 people) Conservative l.l6 mg/1 10% 5.86 in/yr 60 mg1l N 1225 0.17 mg,/1 N or 150 as N or or gal/day 5.31 mg/l 265 mgll as NO, as NO, t Non 0.68 nig/l 25% 6.31 in/yr 40 mg/l N 1225 0.17 mgll N or 150 conservative as N or or gal/day 3.01 mgll 177 mg/l as NO, as NO, The results of the analysis indicates that.viewing the 150-acre site as a system for a period of a year, the combined rain water and septic effluent after denitrification could range between 0.68 mgll as N to 1.16 mgll as N. This level is between 8.6 to 14 times lower then the maximum contaminate drinking water standard of 10 mg/1 as N. III CONCLUSIONS AND RECOMMENDATIONS Based on the results of the Nitrate Loading calculation, the analysis indicates the nitrate-N concentration of combined effluent and rainfall percolate concentration is estimated to be between 0.68 mg/l as N to 1.16 mg/l as N for the 150-acre site. With moist subsurface conditions, slow percolation rates, and high organic material commonly found in the delta, the denitrification factor may actually be higher than the commonly estimated 25%therefore reducing the concentration even further.