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28 September 2022 <br />Project No. 22-6994 <br />Page 11 of 15 <br />AdvancedGeo <br />An Employee Owned Company <br />r ♦� <br />nnn <br />information reviewed, there is no known groundwater contamination at the site and the <br />potential for groundwater contamination is de minimis. <br />8.3. CURRENT AND FUTURE USE OF GROUNDWATER AT THE SITE <br />It is presumed that the existing water supply well at 16402 Escalon Bellota (site) conforms <br />to DWR and EHD standards. The well is currently utilized for the potable water source at <br />the property and will continue to be used to supply the subject property with a domestic <br />water source. <br />9.0. IMPACT OF NITRATE TO GROUNDWATER <br />Due to the planned residential use of the property and the potential for nitrate leaching <br />into the groundwater from the proposed septic system, a nitrate loading analysis for the <br />future use of the septic system is required by the EHD. <br />9.1. CURRENT OFF-SITE SOURCES OF NITRATE <br />Septic systems and agriculture are sources of nitrates in the area of the site. The property <br />is bordered by agricultural and residential land, which might provide a nitrate source. <br />There are several residences within 1,000 feet of the site. <br />9.2. IMPACT OF RAINFALL CONTRIBUTION TO NITRATE LOAD <br />The rainfall of the area has been estimated for the nitrate loading analysis. Deep <br />percolation is estimated by calculating the average monthly rainfall and <br />evapotranspiration of the site area. If average monthly rainfall exceeds average monthly <br />potential for evapotranspiration (ETo) there is a potential for deep percolation without <br />consideration for runoff. Average potential ETo was estimated from data obtained from <br />the California Irrigation Management Information System (CIMIS) Oakdale Station #194. <br />Oakdale Station #194 has been collecting ETo and precipitation data since January 2014. <br />Deep percolation (average annual rainfall recharge) was estimated utilizing the monthly <br />ETo and precipitation data collected from Oakdale Station #194 between 2017 and 2021. <br />The annual rainfall average for the area between 2017 and 2021 was 11.11 inches per <br />year (CIMIS); the annual ETo average ranged from 0.54 inches in 2020 to 7.16 inches in <br />2021. The estimated deep percolation (R) was determined by calculating the average of <br />the ETo between 2017 and 2021. The estimated deep percolation (R) is 3.54 inches <br />(Appendix E). <br />