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30 August 2019 <br />AGE Project No. 19-4819 <br />Page 11 of 15 <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 (adjacent property to the west) are sources of <br />nitrates (fertilizers) present on or around the property. <br /> <br />The current site usage includes a 2,100-square foot house with four bedrooms and three <br />bathrooms, and an approximately 600-square foot annex/shed. Residential use includes <br />showering/bathing, clothes washing, cooking, and hand washing. The reasonable or <br />maximum usage of wastewater for the four-bedroom house is 140 gpd per bedroom for <br />a total of 560 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 560 gpd. <br /> Home use concentration 45 mg/l-N (EHD standard). <br /> The flow concentration of 25,200 mg/l-N gallon. <br /> <br /> <br />9.4. FUTURE ON-SITE SOURCES OF NITRATE <br /> <br />The future site usage includes the addition of a 2,100-square foot residence with two <br />bedrooms and two bathrooms for residential use. Residential use includes