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L , July 24,2003 Job Number:LG03-206 . Page 9 Based on this estimate, the average deep percolation of rain for the Lodi area is estimated to be �- 6.84 inches. The nitrate concentration afxain fall was_estirr►aterl to hP1 mg(L N�arhnce mm,im r contaminate limit for drinking water.zs 10 mg/L-N(Hantzsche and Fizinemore, 1992). 6.4E Denitrification Estimate Denitrification is an important.process which occurs within the leach field whereby certain bacteria utilize the oxygen in the,nitrate (NO,) and release nitrogen gas (Nz) 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. Due to the presence of the dark colored, fine grained, surface soils.. is on te, the denitrification factor for the shallow disposal trench is estimated to a about 25 percent. 6.5 Nitrate Loadin ,Scenario One nitrate loading scenario was performed to measure the impact to water utilizing a k standard type septic system at the site: The previously described assumptions were unitized in the Hantzshe and Finnemore equation. Please refer to Table 6 for a summary of the results of the nitrate loading equation.' Please note the variable Nc represents the average, long-term nitrate concentration of percolating water for the site from rain water and treated domestic wastewater. Table 6. Summary of Nitrate Mass Balance Analysis. Scenario Resuit Acres Average Daily Effluent Leachfield Deep (Ne)* (A) Flow(Q) Concen-. Denitrifi- Percolation of (Table_S) tratiop(Nw) cation(d) Rainfall(R) (Plate 4) Standard Septic 8.4 mg/T-N 1.33 279 gpd' 35 mgt=N 25% 6.84 in System Plate 8) * Maximum contaminate level(MCL)for Nitrate iri drinking water is 10 rng/L=N.