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Soil Suitability Nitrate Loading Study Manteca Unified School District 14600 Austin Rd.,Manteca,California Page 6 (60) MPI or less than one (1) MPI. Percolation rates for seepage pits shall be no greater than thirty (30) MPI. 1.6.8 Discussion of Percolation Rates in Relation to the Type, Size and Location of Future Leach Fields Needed at the Site In general, septic system construction should follow the San Joaquin County On-Site Wastewater Disposal Standards where applicable. A copy of the engineered septic design can be found in Appendix D. 2.0 NITRATE LOADING STUDY EHD recognizes nitrate contamination as a significant potential threat to the surface and groundwaters of the County. Groundwater quality may be impacted by nitrate contamination where percolating effluent leaches into the ground, should this effluent reach groundwater. Due to EHD's concerns regarding nitrate leaching into the surface and groundwaters from septic systems, a soil suitability and nitrate loading study is required by EHD for the proposed development to measure the potential concentration of percolating effluent and rainfall over a long period of time. This report has been prepared to meet the requirements of the San Joaquin County EHD's Soil Suitability Study Requirement Checklist (dated 9/25/07) and Nitrate Loading Study Requirement Checklist(dated 7/14/03). A simple mass balance formula,as discussed in the article by Hantzsche and Finnemore',provides a method for nitrate loading analysis to estimate long-term groundwater nitrate impacts for a wide area. Based on the Hantzsche and Finnemore study, water quality in the upper saturated groundwater zone approximates the quality of percolating recharge waters, which the authors believe is a reliable planning tool to estimate the potential impact to groundwater, as well as a useful source of analysis to official planning agencies. The equation utilized by the Hantzsche and Finnemore approach considers the development area, soil denitrification factor, rainfall volume, rainfall nitrate concentrations, waste effluent quantity, and waste effluent nitrate concentration. The study points out that "...the equation ignores dispersion, lateral flow, and mixing with groundwater flow from up-gradient areas. These processes would generally contribute to additional reduction of nitrate-nitrogen concentrations in groundwater to the extent that the nitrate-nitrogen concentration of groundwater flow from up-gradient areas is lower." Thus, the Hantzsche and Finnemore approach is "...a conservative (worst case) first approximation of groundwater nitrate-nitrogen concentration resulting from the combined effect of on-site sewage disposal systems and precipitation." 2.1 CHEMICAL AND PHYSICAL PROPERTIES OF SOIL 2.1.1 Chemical and Physical Properties of the Soils Underlying the Site A discussion of the physical properties of shallow soil at the Site is included in Section 1.5 of this report. 2.1.2 Mass Transport Properties of the Soils Underlying the Site with Respect to Nitrate and/or any Other Constituent of Concern Identified for the Project Site Based on review of the NRCS website for San Joaquin County, shallow Site soils consist of loamy sand and fine loamy sand with a Runoff Class of"negligible to very low" and a Natural Drainage Class of "moderately well drained to somewhat excessively drained". Percolation rates are considered high to very high(5.95 to 19.98 inch per hour). A copy of soil report is provided in Appendix E. Hantzsche,N. and, Finnemore,E.J., 1992,Predicting Ground-Water Nitrate-Nitrogen Impacts,Ground Water,Vol 30,No 4. ;a CONDOR