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02 March 2020 AdvancedGeo Project No. 20-5001 An Employee-Owned Company Page 10 of 14 A review of the California DTSC EnviroStor Database and the Geotracker Web site revealed one (1) LUST site within a 0.5-mile of the subject property. However, the LUST site has been closed for over 20 years. Based on the status of the LUST and the distance and direction from the subject property, the LUST should not impact the subject property. The review did not reveal any other sites of environmental concern within a half-mile radius of the site. 8.3. CURRENT AND FUTURE USE OF GROUNDWATER AT THE SITE There is currently no potable water source supplied to the subject property. A domestic water well is planned to be installed to the east of the proposed residence and will provide potable water to the residence and property. 9.0. IMPACT OF NITRATE TO GROUNDWATER Due to the planned residential use of the property and the potential for nitrate leaching into the groundwater from the proposed septic system, a nitrate loading analysis for the future use of the septic system is required by the EHD. 9.1. CURRENT OFF-SITE SOURCES OF NITRATE Septic systems and agriculture are sources of nitrates in the area of the site. The property is bordered by residential land, and is near agricultural land, which might provide a nitrate source. There are several residences within 1 ,000-feet of the site. 9.2. IMPACT OF RAINFALL CONTRIBUTION TO NITRATE LOAD The rainfall of the area has been estimated for the nitrate loading analysis. Deep percolation is estimated by calculating the average monthly rainfall and evapotranspiration of the site area. If average monthly rainfall exceeds average monthly potential for evapotranspiration (ETo) there is a potential for deep percolation without consideration for runoff. Average potential ETo was estimated from data obtained from the California Irrigation Management Information System (CIMIS) Manteca Station #70. Manteca Station #70 has been collecting ETo and precipitation data since January 2014. Deep percolation (average annual rainfall recharge) was estimated utilizing the monthly ETo and precipitation data collected from Manteca Station #70 between 2014 and 2018. The annual rainfall average for the area between 2014 and 2018 was 11.64 inches (CIMIS); the annual ETo average ranged from 0.96 inches in 2015 to 5.63 inches in 2014. The estimated deep percolation (R) was determined by calculating the average of the ETo between 2014 and 2018. The estimated deep percolation (R) is 3.64 inches (Appendix D).