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Soil Suitability Nitrate Loading Study Manteca Unified School District 2414"Street,French Camp,CA Page 9 2.3.4.1 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(N2)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,at about 10 percent to 15 percent. A typical denitrification estimate of 35 percent was chosen based on the predominantly clay soils for the Site. 2.3.5 Calculated Mass Balance of Nitrogen Loading Considering all Potential Sources Identified A nitrate loading scenario was performed to assess the impact from the proposed project using the Hantzsche and Finnemore formula/model. The scenario utilizes the variables discussed previously which represent the estimated conditions and uses associated with this project.Table 4,below,presents a summary of the nitrate loading calculation for the school site, which consists of multiple contiguous parcels. A copy of the nitrate loading calculation sheet is included in Appendix F. Table 4 S mmary of Nitrate Mass Balance Analysis Effluent Deep Result Acres Average Daily Flow Concentration Leachfield Percolation of (Nc) * (A) (Q) (Nw) Denitrification Rainfall (mg/L-N) (gpd) (mg/L-N) (d) (R) inches 8.0 1 13.46 1 1.52 1 35 1 35% 3.21 * Maximum contaminant level(MCL)for nitrate in drinking water is 10 mg/L-N; mg/L=milligrams per liter;gpd=gallons per day. 2.3.6 Calculated Impact of Nitrogen Loading from Site Project to Down Gradient Wells, Rivers, Lakes,Etc. Based on the relatively flat topography of the Site, we do not foresee percolating effluent affecting any surface water resources. 2.4 DISCUSSION OF NITRATE LOADING RESULTS RELATIVE TO PROPOSED METHOD OF WASTEWATER DISPOSAL 2.4.1 Total Nitrate Impact from Proposed Project The nitrate MCL set by the US EPA is 45 mg/L-NO3 or 10 mg/L-N.This report concludes that the proposed development of a multi-purpose building of 11,300 square feet has a design usage calculated at 1,520 gallons per day effluent into the proposed septic system. The proposed development may result in an estimated nitrate load of 8.0 mg/N-L when calculated over the 13.46 acres that comprise the school site, which is below the drinking water MCL of 10 mg/L-N. One must consider that nitrate-NO3 concentrations in groundwater inflow from upgradient areas may also increase over time from other land uses such as agriculture.Nitrate in groundwater occurs as a result of the application of fertilizers, livestock waste, and untreated septic tank waste. Nitrate is mobile and often accumulates in the shallow groundwater zones. The proposed development is surrounded by agricultural use as well as rural residential to the southwest that relies predominantly on septic use. Elevated nitrates iia CONDOR