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04 November 2019 AdvaneedGeo AGE Project No. 19-4819 Environmental Page 2 of 5 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) Ripon Station #249. Ripon Station #249 has been collecting ETo and precipitation data since July 2016. Deep percolation (average annual rainfall recharge) was estimated utilizing the monthly ETo and precipitation data collected from Ripon Station #249 in 2017 and 2018. The annual rainfall average for the area was 12.88 inches in 2017 and 11.14 inches in 2018 (CIMIS); the annual ETo average was 4.13 inches in 2017 and 2.11 inches in 2018. The estimated deep percolation (R) was determined by calculating the average of the ETo in 2017 and 2018. The estimated ETo (R) is 3.12 inches (CIMIS Table Attached). 9.3. CURRENT ON-SITE SOURCES OF NITRATE Septic systems, rainfall and agriculture (adjacent property to the west) are sources of nitrates (fertilizers) present on or around the property. The current site usage includes a 2,100-square foot house with four bedrooms and three bathrooms, and an approximately 600-square foot annex/shed. Residential use includes showering/bathing, clothes washing, cooking, and hand washing. The reasonable or maximum usage of wastewater for the four-bedroom house is 140 gpd per bedroom for a total of 560 gpd. The total nitrate-nitrogen (NO3_N) average concentrations in domestic waste ranges between 20 to 85 milligram total nitrogen liter(mg/1-N) with an average of 45 mg/1-N when washing and sanitation is considered. The weighted average calculation for total nitrogen concentrations for onsite residential flow is proposed as the following: • Residential volume 560 gpd. • Home use concentration 45 mg/1-N (EHD standard). • The flow concentration of 25,200 mg/1-N gallon.