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Soil Suitability Nitrate Loading Study <br />Manteca Unified School District <br />5700 East Nile Ave., Manteca, CA <br />Page 9 <br /> <br /> <br /> <br />A typical denitrification estimate of 15 percent was chosen based on the silty sands with low fines reported <br />for the Site. <br /> <br />2.3.5 Calculated Mass Balance of Nitrogen Loading Considering all Potential Sources Identified <br />A nitrate loading scenario was performed to assess the impact from the proposed project using the Hantzche <br />and Finnemore formula/model. The scenario utilizes the variables discussed previously which represent the <br />estimated conditions and uses associated with this project. Table 4 presents a summary of the nitrate loading <br />calculation for the parcel. A copy of the nitrate loading calculation sheet is included in Appendix F. <br /> <br />Table 4 <br />Summary of Nitrate Mass Balance Analysis <br />Parcel <br />Number <br />Concentration <br />Result <br />(Nc)* <br />(mg/L-N) <br />Parcel Size <br />in Acres <br />(A) <br />Design Average <br />Daily Flow <br />(Q in gpd) <br />Effluent <br />Concentration <br />(Nw) <br />(mg/L-N) <br />Leach Field <br />Denitrification <br />(d) <br />Deep <br />Percolation of <br />Rainfall <br />(R in inches) <br />1 25.4 15.36 6,378 35 15% 0.99 <br />Notes: * Maximum contaminant level (MCL) for nitrate in drinking water is 10 mg/L-N; <br />mg/L = milligrams per liter; gpd = gallons per day. <br /> <br />Based on the nitrate loading balance calculation, nitrate levels for the proposed use is 25.4 mg/L, which is <br />above the MCL of 10 mg/L for nitrate-N in drinking water. <br /> <br />2.3.6 Calculated Impact of Nitrogen Loading from Site Project to Down Gradient Wells, Rivers, <br />Lakes, Etc. <br />Based on the relatively flat topography of the site, we do not foresee percolating effluent affecting any <br />surface water resources. <br /> <br />2.4 DISCUSSION OF NITRATE LOADING RESULTS RELATIVE TO PROPOSED <br />METHOD OF WASTEWATER DISPOSAL <br />2.4.1 Total Nitrate Impact from Proposed Project <br />The nitrate MCL set by the US EPA is 45 mg/L-NO3 or 10 mg/L-N. This report concludes that the proposed <br />development of a multi-purpose building of 14,600 square feet, and a kindergarten classroom building of <br />4,500 square feet has a design capacity of approximately 6,378 gallons per day effluent into the proposed <br />septic system. The actual usage will be considerably less when completed but will increase over time as <br />additional students attend the school. The proposed development, if operated the design capacity, may result <br />in an estimated nitrate load of 25.4 mg/L-N and, without mitigation, could cause long-term build-up of <br />nitrate in groundwater above 10 mg/L-N. However due to existing degradation of groundwater documented <br />in groundwater samples collected from Site wells, the shallow aquifer at the Site is not utilized for drinking <br />water. <br /> <br />One must consider that nitrate-NO3 concentrations in groundwater inflow from up gradient areas may also <br />increase over time from other land uses such as agriculture and increased rural residential use. Nitrate in <br />groundwater occurs as a result of the application of fertilizers, livestock waste, and untreated septic tank <br />waste. Nitrate is mobile and often accumulates in the shallow groundwater zones. The proposed <br />development is located within a shallow depth to ground water zone surrounded by septic use parcels in the