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Farmington Murphy Prope, 1.01 Our Project Number: E072MA Page 5 December 24,2007 Table 2, Summa of Nitrate Mass Balance E uation Result Average Effluent Leachfield Deep Parcel (Nc)* Acres A Dail Flow Concentration Percolation ( ) Y Denitrification (mg/L-N) (Q) (gPd) (NW) (d) of Rainfall (mg/L-N) (R) (in) 1 10.0 4.0 237 85 350% 4.0 *Maximum contaminant level(MCL)for nitrdtf In drinking water is 10 mg/L-N. Based only on the nitrate loading calculation described previously, the result of the nitrate loading balance indicates that a project on the site with four acres of land with an effluent quality of 85-mg/L-N would require 237 gallons per day to result in a Nc value of 10.0 mg/L-N (Plate 2), Essentially, with a flow rate above 237 gallons per day, there is a potential that ground water quality may be impacted. However, the Site has fine-grained soils to a depth of 50 feet or deeper which would tend to mitigate the potential impact. 3.6 Impact of Nitrate Loading to Nearby Water Sources 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 Considering the potential impact to ground water, there is a possibility that percolating effluent may impact ground water. However, the San Joaquin County Ground Water Investigation prepared by DWR (1967) indicates an absence of sandy sediment in the area. It is our opinion that the fine grained soils below the site could potentially attenuate the nitrate in the percolating effluent to some degree. The prediction of the impact should be more thoroughly addressed when a specific use is proposed for the site, 4.2 Methods of Mitigation A project with the parameters indicated in Table 2 should not require mitigation. However, a project that raises the NC value above 10 mg/L-N may require a small to large waste water treatment system to reduce nitrate to or below 10 mg/L-N in percolating effluent. 5.0 CONCLUSIONS AND RECOMMENDATIONS Our office concludes that the Site is suitable for development with the use of a standard septic system provide the variables discussed in Table 2 are not exceeded. We recommend that a nitrate loading update be performed when a specific project is determined for the site. All septic system construction should follow the San Joaquin County On-Site Wastewater Disposal Standards where applicable. "44 9021ndustrial Way• Lodi,CA 95240.209,367.3701 •Fax 209.369.4228 n2007 Neil 0.Anderson k Assacialcs, Lrc