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13 August 2019 AdvancedGeo <br /> AGE Project No. 19-4782 Environmental <br /> Page 10 of 14 <br /> Groundwater was not encountered in the 40-inch deep percolation test hole on <br /> 18 July 2019. <br /> 8.2. EXISTING OR POTENTIAL GROUNDWATER CONTAMINATION <br /> The immediately adjacent and outlying land use from the subject property is residential, <br /> commercial, and agricultural. There are potential groundwater contamination issues <br /> associated with agricultural uses and septic systems. A review of the California DTSC <br /> EnviroStor Database and the Geotracker Web site revealed two LUST sites within a one- <br /> mile radius of the site. However, both sites have been closed for over 10 years. The sites <br /> were located approximately 500 feet and 2,500 feet from the subject property. Based on <br /> information reviewed on the Geotracker Web site, residual petroleum hydrocarbon <br /> contamination was not left remaining in place at either site. There is no existing or known <br /> groundwater contamination at the site and the potential for groundwater contamination is <br /> de minimis. <br /> 8.3. CURRENT AND FUTURE USE OF GROUNDWATER AT THE SITE <br /> The existing water supply well at 17699 ST RT 120 conforms to DWR and EHD standards <br /> and will be used to supply the subject property with a domestic water source. <br /> 9.0. IMPACT OF NITRATE TO GROUNDWATER <br /> Due to the proposed 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, commercial and residential lands 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 />