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Soil Suitability Nitrate Loading Study Manteca Unified School District 5700 East Nile Ave.,Manteca,CA Page 7 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. 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 NRCS website for San Joaquin County, soils on site consist of loamy sand and coarse sands with a Runoff Class of"negligible"and Natural Drainage Class of"somewhat excessively drained." Percolation rates are considered high to very high (5.95 to 19.98 in/hr.). A copy of soil report is provided in Appendix E. The potential for mass transport of nitrates from surface soils to shallow groundwater beneath the Site exists but shallow groundwater beneath the Site has already been impaired by agricultural chemicals, including nitrates, TCP, and arsenic. 2.2 GROUNDWATER ANALYSIS 2.2.1 Depth to Groundwater, Seasonal Fluctuations of Groundwater Depth, Directional Flow and Gradient As stated in Section 1.4, Condor explored subsurface conditions by means of multiple soil borings at the Site on November 11, 2018. At the time of Condor's exploration groundwater was encountered at a depth of 10 feet bgs. Groundwater was not encountered in our percolation test hole excavated to a depth of 2 and 3 feet bgs on April 19, 2019 but has been reported as shallow as 5 feet bgs in 2004. While the depth to groundwater is expected to fluctuate in response to both seasonal rainfall and irrigation of surrounding farmland,there is a practical limit to the anticipated temporary rise in groundwater levels at the site 2.2.2 Existing or Potential Groundwater Contamination Issues in the General Location of the Site The Site is located in rural residential and farmland involved in agricultural practices. Chemical applications, livestock waste, fertilizers, and uncontained or failed septic tank waste can contribute to the occurrence of nitrate in groundwater. In addition, elevated concentrations of nitrate(as NO3), arsenic, and TCP have been detected in on-site water supply wells. In response, safe drinking water is being provided to the school using bulk storage tanks to deliver the drinking water. Copies of readily available testing results pertaining to the wells(DWR's GAMA database) are included in Appendix E. ' Hantzsche,N. and, Finnemore,E.J., 1992, Predicting Ground-Water Nitrate-Nitrogen Impacts,Ground Water,Vol 30,No 4. �i� CONDOR