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27 April 2020 <br />Project No. 20-5084 <br />Page 11 of 15 <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 residential land, and is near agricultural land, which might provide a nitrate <br />source. There 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) Ripon Station #249. <br />Ripon Station #249 has been collecting ETo and precipitation data since July 2016. <br /> <br />Deep percolation (average annual rainfall recharge) was estimated utilizing the monthly <br />ETo and precipitation data collected from Ripon Station #249 in 2017 and 2018. The <br />annual rainfall average for the area was 12.88 inches in 2017 and 11.14 inches in 2018 <br />(CIMIS); the annual ETo average was 4.13 inches in 2017 and 2.11 inches in 2018. The <br />estimated deep percolation (R) was determined by calculating the average of the ETo in <br />2017 and 2018. The estimated ETo (R) is 3.12 inches (Appendix E). <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. <br /> <br />The current site usage includes a 932-square foot house with two bedrooms. Residential <br />use includes showering/bathing, clothes washing, cooking, and hand washing. The <br />reasonable or maximum usage of wastewater for the two-bedroom house is 100 gpd for <br />the first bedroom and 50 gpd for each additional bedroom for a total of 150 gpd. <br /> <br />The total nitrate-nitrogen (NO3_N) average concentrations in domestic waste ranges <br />between 20 to 85 milligram total nitrogen liter (mg/l-N) with an average of 45 mg/l-N when <br />washing and sanitation is considered. <br /> <br />The weighted average calculation for total nitrogen concentrations for onsite residential <br />flow is proposed as the following: <br /> <br />• Residential volume 150 gpd. <br />• Home use concentration 45 mg/l-N (EHD standard).