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07 Septmber 2021 <br />Project No. 21-6531 <br />Page 10 of 14 <br />8.3. CURRENT AND FUTURE USE OF GROUNDWATER AT THE SITE <br /> <br />The existing water supply well at 20157 Little John Road is permitted and likely 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 /> <br /> <br />9.0. IMPACT OF NITRATE TO GROUNDWATER <br /> <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 /> <br /> <br />9.1. CURRENT OFF-SITE SOURCES OF NITRATE <br /> <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 may have sources of nitrate. There <br />are several residences within 1,000 feet of the site. <br /> <br /> <br />9.2. IMPACT OF RAINFALL CONTRIBUTION TO NITRATE LOAD <br /> <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 /> <br />Deep percolation (average annual rainfall recharge) was estimated utilizing the monthly <br />ETo and precipitation data collected from Manteca Station #70 between 2015 and 2020. <br />The annual rainfall average for the area between 2015 and 2020 was 11.52 inches <br />(CIMIS); the annual ETo average ranged from 0.48 inches in 2020 to 4.41 inches in 2017. <br />The estimated deep percolation (R) was determined by calculating the average of the <br />ETo between 2015 and 2020. The estimated deep percolation (R) is 3.20 inches <br />(Appendix D). <br /> <br /> <br />9.3. CURRENT ON-SITE SOURCES OF NITRATE <br /> <br />Septic systems, rainfall and agriculture are sources of nitrates (fertilizers) present on or <br />around the property.