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Addendum Revised Soil Suitability Nitrate Loading Study Manteca Unified School District 241 4th Street, French Camp, CA Page 7 A simple mass balance formula, as discussed in the article by Hantzsche and Finnemore1, 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 property 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 the NRCS website for San Joaquin County, soils on the Site consist of clay with a Runoff Class of “High” and Natural Drainage Class of “somewhat poorly drained”. The capacity of the most limiting layer are considered very low. Potential for mass transport is not expected to be of concern. A copy of the soil report is provided in Appendix E. 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 April 12, 2019. At the time of Condor’s exploration, groundwater was encountered at a depth of 26 feet bgs but subsequently rose to a depth of approximately 20.5 feet in the drilling augers. Groundwater was not encountered in either of the percolation test holes excavated to a depth of 3 feet bgs on June 25, 2019. Groundwater has been reported as shallow as 9 feet bgs historically but has generally been below 20 feet bgs. While the depth to groundwater is expected to fluctuate in response to both seasonal rainfall and irrigation of the grassy areas of the school site as well as 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 an urban mixed commercial-residential area with surrounding farmland involved in agricultural practices. Chemical applications, livestock waste, fertilizers, and uncontained or failed septic tank waste from surrounding parcels can contribute to the occurrence of nitrate in groundwater. Data gathered from GeoTracker Gama indicates that both municipal wells on the Site are below the MCL of 45 mg/L for nitrate-NO3. Water samples gathered from well ID 3900712-008 contained arsenic and 1 Hantzsche, N. and, Finnemore, E.J., 1992, Predicting Ground-Water Nitrate-Nitrogen Impacts, Ground Water, Vol 30, No 4.