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17 January 2020 AdvancedGeo <br /> Project No. 19-4964 AnOwned Company <br /> Page 10 of 14 =`� X <br /> A review of the DTSC EnviroStor Database and the Geotracker Web site revealed one <br /> (1) LUST site just slightly outside a half-mile radius of the subject property. However, the <br /> site has been closed for over 20 years. Based on the status of the investigation and its <br /> distance and direction from the subject property, the closed investigation should not <br /> impact the subject property. The review did not reveal any other sites of environmental <br /> concern within a 0.5-mile radius of the site. Based on the information reviewed, there is <br /> no existing or known groundwater contamination at the site and the potential for <br /> groundwater contamination is de minimis. <br /> 8.3. CURRENT AND FUTURE USE OF GROUNDWATER AT THE SITE <br /> The existing water supply well at 438 West Mathews Road (site) conforms to DWR and <br /> EHD standards and is used to supply the subject property with a domestic water source. <br /> 9.0. IMPACT OF NITRATE TO GROUNDWATER <br /> Due to the residential use of the property and the potential for nitrate leaching into the <br /> groundwater from the existing and proposed septic systems, a nitrate loading analysis for <br /> the future use of the septic systems 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, governmental, and agricultural land, which might provide a <br /> nitrate 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 2018. <br /> The annual rainfall average for the area between 2014 and 2018 was 11.64 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 />