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4350 E.Acampo Road Project No.2018-0043 Page 15 I I 2.2 Mass Transport Soil Properties Layered soils and sediments, such as the fine sandy loam and coarse sandy loam soil layers of the Tokay at the site typically provide a moderate degree of protection between percolating effluent at the surface and ground water aquifers. Soils of this type typically present a moderate risk of excessive mass transport of nitrate or other constituents of concern. ' 3.0 GROUNDWATER ANALYSIS 3.1 Regional and Site-Specific Groundwater The San Joaquin County Flood Control and Water Conservation District(2016)groundwater reports were reviewed to determine the groundwater levels near the Site. The Fall 2016 and Spring 2016 maps are the most current official maps available from the County. According to these maps, (Plates 5 and 6) in Appendix A,groundwater elevation lies at approximately-15 feet below mean sea level 1 (msl) in the spring and fall. The elevation of the land, as previously mentioned in Section 1.1, is approximately 60 feet above mean sea level. Therefore, the depth to groundwater (the difference between the elevation of the Site and the elevation of groundwater),is approximately 75 feet below the ground surface (bgs),in the spring and fall. The groundwater in the vicinity of the Site appears to flow to the northeast,at a gradient of approximately 10 feet per mile. 3.2 Potential Groundwater Contamination Issues The site is located within a rural residential subdivision and near parcels involved in agricultural practices; groundwater contamination can result from activities related to farming practices where ' chemicals are applied to crops which may permeate to groundwater.According to a permit search on the online EHD database7 there is a septic system (tank size unknown) with at least one 40-foot leach line and one 25-foot seepage pit located on site.The surrounding properties also utilize septic ' systems; leakage from septic tanks or failed septic systems can introduce bacteria to groundwater. 3.3 Current and Future On-Site Groundwater Uses ' The use of ground water for drinking water is planned for the proposed development. There is currently a domestic well onsite. The onsite water well was tested for nitrate. Total nitrogen was reported at 3.8 mg/L. The lab results are included in Appendix B. 4.0 SOURCES AND IMPACT OF NITRATE TO GROUNDWATER 4.1 Current Off-Site Sources of Nitrate ' Septic systems and agriculture in the area may be the most significant sources of nitrate. In an attempt to determine the septic system density for the vicinity of the site,our office reviewed a recent aerial photograph available from GoogleEarthTM.We counted the clusters within approximately one square mile of the site, with the assumption each building cluster has one septic system. Using this method, we determined there are approximately 350 septic systems per square mile in the 2667 Bw lla load,Galt Ca 95632 ov.org/WebLink/Browse.aspx?dbid=l&cr=1 accessed April 1Q 2018. 26675 Bruella Road,Galt,Ca 95632 (209)-000-5729 w .petralogkcom