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`/ vme Mr. Sandi De Jong October 10,2006 Page 5 4.4 Future On-Site Sources of Nitrate 1---4.4.1 Quantity and Quality ofDomestic Wastewater From Proposed Project See Section 3.6 for discussion of Quantity of Domestic Wastewater from the proposed project. 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 commercial use will have higher concentrations of total nitrogen when compared to residential use. It is estimated that the average concentration for total nitrogen in waste water for the project is approximately 65 mg/L-N over the long term. `4.4.2 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 (ND 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 estimated to denitrify at a lower rate, about 10 percent to 15 percent. A denitrification factor of 30 percent was selected for the Site due to the silty nature of the soils. x/4.5 Nitrate Loading Scenario A nitrate loading scenario was performed to determine the impact from the proposed project. The scenario utilizes the variables discussed previously which represent the estimated conditions and uses associated with this project. The following table presents a summary of the nitrate loading calculation for the property. Table 2. Summary of Nitrate Mass Balance Analysis. Result Average Daily Effluent Leachfield Deep Plate (Nc)* Acres Flow(Q) Concen- Denitrifi- Percolation of (mg/L-N) (A) (Table 3) traction(Nw) cation(d) P Rainfall in) (gP ) ( g/ N) ( 9) ( ) Site 7. 3.5 272.1514--1 65` 30%' 5.76- Maximum contaminant level(MCL) for nitrate in drinking water is 10 mg/L-N.