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Soil Suitability Nitrate Loading Study <br /> Manteca Unified School District <br /> 14600 Austin Rd.,Manteca,California <br /> Page 8 <br /> for Manteca, California was found to be 13.91 inches per year (in/yr) for the years 2010 through 2020. <br /> Adjustments to the evapotranspiration factor were made based on site specific landscape conditions, as <br /> referenced from the University of California Division of Agriculture and Natural Resources. Based on the <br /> average monthly rainfall totals and the adjusted monthly evapotranspiration totals, deep percolation of rain <br /> for the Site is estimated to be 8.31 in/yr. The nitrate concentration of rainfall was estimated to be 1 mg/L- <br /> N(Hantzsche and Finnemore, 1992).Average monthly rainfall and precipitation data,as well as a summary <br /> of calculations, are provided in Appendix F. <br /> 2.3.3 Current On-Site Sources of Nitrate to Soil and Groundwater and the Contribution of Nitrate <br /> Load from These Sources to the Project Site <br /> Current on-site sources of nitrate include existing septic tanks discussed and identified in Section 1.3 and <br /> agricultural use in the area. <br /> 2.3.4 Proposed Future On-Site Sources of Nitrate to Soil and Groundwater and the Contribution <br /> of Nitrate Load from These Sources to the Project Site <br /> Proposed on-site sources of nitrate are discussed in Section 1.3.7. <br /> 2.3.4.1 Denitrification Estimate <br /> Denitrification is an important process which occurs within the leach field whereby certain bacteria utilize <br /> the oxygen in the nitrate(NO3)and release nitrogen gas(N2)to the atmosphere.Denitrification is expressed <br /> as a percentage,and the normally accepted range is 10 percent to 35 percent. Soils with higher clay content, <br /> moist soil,high pH,and organic material denitrify by about 35 percent and soils with high sand content and <br /> fast percolation rates are estimated to denitrify at a lower rate, about 10 percent to 15 percent. <br /> A denitrification estimate of 35 percent was chosen based on the silty sand encountered in shallow soil, <br /> significant clay at approximately 15 feet bgs, and groundwater at approximately 45 feet bgs. <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 <br /> Hantzsche and Finnemore formula/model. The scenario utilizes the variables discussed previously which <br /> represent the estimated conditions and uses associated with this project. The table on the following page <br /> presents a summary of the nitrate loading calculation for the parcel.A copy of the nitrate loading calculation <br /> sheet is included in Appendix F. <br /> rs <br /> ;1? CONDOR <br />