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AdvancedGeo 20 January 2021 An Employee -Owned Compony Project No. 20-6284 Page 11 of 14 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) Manteca Station #70. Manteca Station #70 has been collecting ETo and precipitation data since January 2014. Deep percolation (average annual rainfall recharge) was estimated utilizing the monthly ETo and precipitation data collected from Manteca Station #70 between 2014 and 2019. The annual rainfall average for the area between 2014 and 2019 was 11.97 inches (CIMIS); the annual ETo average ranged from 0.96 inches in 2015 to 5.63 inches in 2014. The estimated deep percolation (R) was determined by calculating the average of the ETo between 2014 and 2019. The estimated deep percolation (R) is 3.69 inches (Appendix D). 9.3. CURRENT ON-SITE SOURCES OF NITRATE Septic systems, rainfall and agriculture are sources of nitrates (fertilizers) present on or around the property. There are currently no onsite sources of nitrates at the subject property. 9.4. FUTURE ON-SITE SOURCES OF NITRATE The future site usage includes the addition of a residence with three bedrooms for residential use. Residential use includes showering/bathing, clothes washing, cooking, and hand washing. The reasonable or maximum usage of wastewater for the three- bedroom home is 100 gpd for the first bedroom and 50 gpd for each additional bedroom for a total of 200 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 200 gpd. • Home use concentration 45 mg/1-N (EHD standard). • The flow concentration of 9,000 mg/1-N gallon.