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01 October 2019 AdvancedGeo <br /> AGE Project No. 19-4850 Environmental <br /> Page 10 of 14 �I <br /> 8.3. CURRENT AND FUTURE USE OF GROUNDWATER AT THE SITE <br /> There are no immediate plans to use groundwater at the site. Potable water is currently <br /> supplied to the site by the California Water Service Company. <br /> 9.0. IMPACT OF NITRATE TO GROUNDWATER <br /> Due to the commercial use of the property and the potential for nitrate leaching into the <br /> groundwater from the existing septic system, a nitrate loading analysis for the future use <br /> of the existing septic system is required by the EHD. <br /> 9.1. CURRENT OFF-SITE SOURCES OF NITRATE <br /> Septic systems are sources of nitrates in the area of the site. The property is bordered by <br /> commercial and residential lands which might provide a nitrate source. There are several <br /> residences and commercial properties 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. Total monthly ETo and precipitation data for the site area was <br /> obtained from the California Irrigation Management Information System (CIMIS) Holt <br /> Station #248. CIMIS Holt Station #248 has been collecting ETo and precipitation data <br /> since July 2016. <br /> Deep percolation (average annual rainfall recharge) was estimated utilizing the monthly <br /> ETo and precipitation data collected from Holt Station #248 in 2017 and 2018. The annual <br /> rainfall average for the area was 12.05 inches in 2017 and 11 .96 inches in 2018; the <br /> annual ETo average was 4.36 inches in 2017 and 3.07 inches in 2018. The estimated <br /> deep percolation (R) was determined by calculating the average of the ETo in 2017 and <br /> 2018. The estimated ETo (R) is 3.72 inches (Appendix D). <br /> 9.3. CURRENT ON-SITE SOURCES OF NITRATE <br /> Septic systems and rainfall are sources of nitrates (fertilizers) present on or around the <br /> property. The current site usage includes one existing septic system that services a <br /> commercial warehouse and office trailer. The onsite business is open Monday through <br /> Friday from 8:00 AM to 5:00 PM; and the septic system is utilized 260 days a year by <br />