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29 May 2020 Advancedu% <br /> Project No. 20-6014 An Employee Owned Compon <br /> Page 10 of 14 <br /> reviewed, there is no existing or 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 /> There is currently no potable water source provided to the subject property. An out-of- <br /> service domestic water well is located at the subject property and may be used to provide <br /> a potable source to the proposed residence. <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 residential land, and is near agricultural land, which might provide a nitrate <br /> source. 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) Manteca Station #70. <br /> Manteca Station #70 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 Manteca Station #70 between 2014 and 2019. <br /> The annual rainfall average for the area between 2014 and 2019 was 11.97 inches <br /> (CIMIS); the annual ETo average ranged from 0.96 inches in 2015 to 5.63 inches in 2014. <br /> The estimated deep percolation (R) was determined by calculating the average of the <br /> ETo between 2014 and 2019. The estimated deep percolation (R) is 3.69 inches <br /> (Appendix D). <br />