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1246 N Fine Road Project No. 2021-00025 Page 15 <br />Table 2. Laboratory Analytica Results, April 19, 2021 <br />Analytical <br />Method <br />units Well <br />1 Sample MCL <br />Nitrate (as Nitrogen) E300.1 mg/L 0.92 1 10 <br />DBCP E524.3 ug/L ND 0.2 <br />1. Based on EPA's MCL (Maximum Contaminant Level). <br />ND = non-detect to laboratory detection limit <br />Bold indicates sample is above the MCL <br />The laboratory report is available for review in Appendix B. <br /> <br />4.4 Current and Future On-Site Groundwater Uses <br />The use of ground water for drinking water is currently utilized and further planned for the proposed <br />development. There is currently one domestic well onsite which will serve both residential <br />structures. <br /> <br />5.0 SOURCES AND IMPACT OF NITRATE TO GROUNDWATER <br /> <br />5.1 Current Off-Site Sources of Nitrate <br />Septic systems and agriculture in the area may be the most significant sources of nitrate. In an <br />attempt to determine the septic system density for the vicinity of the site, our office reviewed a recent <br />aerial photograph (2020) available from GoogleEarthTM. We counted the clusters within <br />approximately one square mile of the site, with the assumption each building cluster has one septic <br />system. Using this method, we determined there are approximately 75 septic systems per square <br />mile in the immediate vicinity of the site, with the majority of the residential development south of <br />the site. This is a low number of septic systems, with the majority of these systems located on <br />moderately sized parcels surrounded by agricultural land. <br />As discussed above, the domestic well was sampled for Nitrate as N; the analysis reports the <br />groundwater is 0.92 mg/L, which is well below the EPA maximum contaminant level of 10 mg/L. <br /> <br />5.2 Contribution of Rainfall <br />An estimate of the quantity and quality of rainfall was required for the nitrate loading analysis. The <br />estimate of deep percolation of rain is based on the average monthly precipitation of rain fall for <br />South Stockton, California, based on the nearest weather station to the site available. The estimate <br />first determines whether the average monthly precipitation exceeds average monthly potential <br />evapotranspiration. If so, then the difference is potential deep percolation. This method does not <br />consider runoff. See Plate 8 for the data and calculation. <br />Average potential evapotranspiration was obtained from the California Irrigation Management <br />Information System (CIMIS). The site is located within evapotranspiration zone number 12, as well <br />as the South Stockton station (Station 048558) used in the analysis. The average rainfall for the area, <br />as well as the average evapotranspiration data, was obtained from CIMIS <br />(https://cimis.water.ca.gov/) where the average rain fall for the South Stockton area was found to be <br />13.78 inches per year for years 1948 to 2016. <br />Petraiogix Engineering, Inc. <br />26675 Bruella Road, Galt, Ca 95632 <br />(209)-400-5729 <br />www.petralogix.com