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n November 19, 2004 NOA Project Number: E040107A Table 2. Summary of Nitrate Mass Balance Analysis. Parcel Plate Result Acres Average Daily Effluent Leachfield Deep (Nc) * (A) Flow(Q) Concert- Denitrifi- Percolation of (mg/L-N) (Table 3) tration(Nw) cation(d) Rainfall(R) (gpd) (mg/L-N) (Plate 4) (in.) 1 5 18.9 1.12 Z 252 45 25% 2.52 * Maximum contarninant level(MCL) for nitrate in drinking water is 10 mg/L-N. 3.6 Impact of Nitrate Loading to Nearby Water Sources Based on the method and assumptions described, the result of the nitrate loading balance indicates that the proposed development on the parcel j j au a build up of nitrate in the_ group water k abgsze Q mg L-N over r the lop term. This result is due to the relatively small lot size and the estimate of minimal deep percolation of rain in the area. F1 Since the Site is relatively flat,we do not foresee percolating effluent affecting any surface water resources. 4.0 DISCUSSION OF NITRATE LOADING RESULTS 4.1 Total Nitrate Impact Based on the method and assumptions described, the result of the nitrate loading balance indicates that therx e Site may cause a build u of nitrate in the shallow ground water aquifer above 10 mg/L-N over the long term. a &0� -Z,L�z5 -v- �-A) �, , o .�..am.� 4.2 Methods of Mitigation S To reduce the potential impact of nitrates to shallow ground water discussed above,we recommend the use of a modified filter bed type septic system for the proposed project. Since there is no evidence of shallow water less then 8.5 feet in depth, the filter bed does not need to be raised above ground. We recommend that a_standard countVfilter bed could be upgraded for additional nitrate reduction b addin two inches o gar en com ost or eat on the ottom e bed. This will provlde�' an organic carbon source in e ilter bed for microbial digestion. This material will also slow the infiltration rate of the effluent. In addition,we would recommend the minimum size septic tank for this project be 2 000 ons. The larger tank size will provide more retention time in the primary compartment for nitrification and more anaerobic volume in the second compartment for denitrification. The denitrification reduction "benefit" from using a filter bed system, organic carbon enhancement j r6