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� t August 8, 2006 NOA Project Number: E06087A ' n The average total nitrogen concentration of domestic waste water.is normally considered to be 20-85 mg/L-N with 35 to 45 mg/L-N being typical (Crites and Tchobanoglous, 1998). It is estimated that religious facility use will be approximately 80 mg/L-N. A weighted average is therefore used to calculate the total mg/L-N over the long term in the flow for the site since this project will include both residential and commercial concentrations. Please see the following equation for further detail. Weighted Average Calculation for Total Nitrogen Concentration in Residential and Commercial Flow On-Site Commercial flow Commercial concentration Flow concentration 548.6 gallons per day average * 80 m L-N = 43.888 mg/L-N gal Residential flaw Residential concentration Flow concentration 490 gallons 12eLday 45 m L-N = 22,050 mg/L-N gal Sum of Com. and Res. Flory Concentrations ►-� 43,888 mg/L-Ngal + 22,050 mg/L-N gal = 65.938 mg/L-N gal � l ` Sum of Cam. and Res.gallons per day average 548.6 gallons per day average + 490 gallons per day average = 1038.6 gallons per.da average F lYfeighted Average of mg/L-N Concentration inflow of on-.lite waste water F65,938 mg/L-N gal- 1038.6 gallons per dgy average = 63.48 m L-N Based on the weighted average of mg/L-N concentrations in the flow of waste water,it is estimated that the average concentration for total nitrogen from both sources in waste water for the project is approximately 63.48 mg/L-N over the long term. 3.4.2 Denitrification Estimate Denitrification is an important process which occurs within the leach field whereby certain bacteria utilize the oxygen in the nitrate (NO3) and release nitrogen gas (No 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 by about 35 percent, and soils with high sand content and'fast percolation rates are �F estimated to denitrify at a lower rate, about 10 percent to 15 percent. A typical denitrification factor of 35 percent was selected for the Site because of the fine grained soils that exist at the site.