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Addendum Revised Soil Suitability Nitrate Loading Study Manteca Unified School District 241 4th Street, French Camp, CA Page 4 Condor reviewed additional groundwater information from the Department of Water Resources (DWR), San Joaquin County Flood Control and Conservation District (SJCFCCD), and nearby UST sites on the GeoTracker database. The data indicates that from 1955 to 1992, the depth to groundwater has ranged from 9 to 46 feet bgs but has predominantly been deeper than 20 feet bgs. Based on historical records, the regional direction of groundwater flow beneath the site is typically northeast toward a groundwater pumping depression northeast of Stockton. Copies of the historical groundwater data from the Water Data Library and SJCFCCD groundwater gradient map are provided in Appendix E. 1.4.2 Existing and/or Potential Groundwater Contamination Issues in the General Location The presence of nitrates is not uncommon in shallow groundwater aquifers in the San Joaquin County region. Nitrate in groundwater occurs as a result of the application of fertilizers, livestock waste, and untreated septic tank waste. The site is located within rural housing and agricultural farmlands and activities related to these practices and the use of existing septic systems should be considered potential contamination sources. A review of the GAMA Groundwater Information System database shows seven “municipal” wells located within approximately 1,800 feet of the Site, including one destroyed and one existing well on-site. A review of aerial photographs suggest that these wells include the Site wells, a domestic well, and irrigation wells. At least two of the wells, including the existing on-site well, consistently contain arsenic at concentrations exceeding the Maximum Contaminant Level (MCL) of 10 micrograms per liter (µg/L) and one well located approximately 1,800 feet south of the property contained nitrate as nitrate (nitrate-NO3) at concentrations ranging from 108 to 198 milligrams per liter (mg/L), which exceeds the MCL of 45 mg/L for nitrate-NO3. Analytical results from the GAMA database are included in Appendix E. 1.4.3 Location, Type, and Construction of Well Water Sample(s) Two water supply wells are known to have existed on-site. The older well, identified as 3900712-001 (Global ID W0603900712), was located inside the southern “wing” of the school building and was destroyed by permit in June 2006. The existing well, known as Main Well #3 3900712-008, (Global ID W0603900712), was completed to a depth of at least 265 feet, with 40 feet of screen and sanitary seal to 200 feet, according to the GAMA database. A copy of the well log for Main Well #3 is included in Appendix E. 1.4.4 Constituents Being Tested for in the Water Sample Copies of readily available testing results pertaining to the wells (DWR’s GAMA database) are included in Appendix E. 1.4.5 Sample Collection and Handling Methodology No groundwater samples were directly collected as part of this report. Available groundwater analytical results from Main Well #3 were downloaded from DWR’s GAMA database. 1.4.6 Complete Chain of Custody Documentation No chain of custody documentation is provided in DWR’s GAMA database. 1.5 SOIL PROFILE INFORMATION The Site is located in the northern San Joaquin Valley in the Great Valley Geomorphic Province of California. Based upon published geologic maps, near-surface geology underlying the Site consists of