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12172 N Hibbard Road Project No.2021-00063 Page 15 4.4 Current and Future On-Site Groundwater Uses The use of ground water for drinking water is currently utilized and further planned for the proposed development. There is currently one domestic well onsite which will serve both residential structures. 5.0 SOURCES AND IMPACT OF NITRATE TO GROUNDWATER 5.1 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 (2020) 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 90 septic systems per square mile in the immediate vicinity of the site.This is a low number of septic systems,with the majority of these systems located on moderately sized parcels surrounded by agricultural land. As discussed above, the domestic well was sampled for Nitrate as N; the analysis reports the groundwater is 2.0 mg/L,which is well below the EPA maximum contaminant level of 10 mg/L. 5.2 Contribution of Rainfall An estimate of the quantity and quality of rainfall was required for the nitrate loading analysis. The estimate of deep percolation of rain is based on the average monthly precipitation of rain fall for Lodi, California, based on the nearest weather station to the site available. The estimate first determines whether the average monthly precipitation exceeds average monthly potential evapotranspiration. If so, then the difference is potential deep percolation. This method does not consider runoff. See Plate 8 for the data and calculation. Average potential evapotranspiration was obtained from the California Irrigation Management Information System (CIMIS). The site is located within evapotranspiration zone number 12, as well as the Lodi station (Station 045032) used in the analysis. The average rainfall for the area,as well as the average evapotranspiration data,was obtained from CIMIS (https://cimis.water.ca.gov/) where the average rain fall for the Lodi area was found to be 17.27 inches per year for years 1893 to 2015. Based on this method, the average deep percolation of rain for Lodi area is estimated to be 5.29 inches. The nitrate concentration of rain fall was estimated to be 1 mg/L-N (Hantzsche and Finnemore, 1992). 5.3 Current On-Site Sources of Nitrate The current onsite 3-bedroom residence, and associated septic system and rainfall are recognized as potential current on-site sources of nitrate. Petralogix Engineering,InC. - 26675 BruelIa Road,Galt,Ca 95632 (209)-40o-5729 www.petralogix.com