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09 August 2022 tt Project No. 22-6942 AnEmployreowne Company Page 11 of 16 9.0. IMPACT OF NITRATE TO GROUNDWATER Due to the planned use of the property and the potential for nitrate leaching into the groundwater from the proposed septic systems, a nitrate loading analysis for the future use of the septic system is required by the EHD. 9.1. CURRENT OFF-SITE SOURCES OF NITRATE Septic systems and agriculture are sources of nitrates in the area of the site. The property is bordered by agricultural and residential land, which might provide a nitrate source. There are several residences within 1,000 feet of the site. 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 2017 and 2021. The annual rainfall average for the area between 2017 and 2021 was 11.18 inches per year (CIMIS); the annual ETo average ranged from 0.48 inches in 2020 to 4.41 inches in 2017. The estimated deep percolation (R) was determined by calculating the average of the ETo between 2017 and 2021. The estimated deep percolation (R) is 2.99 inches (Appendix E). 9.3. CURRENT ON-SITE SOURCES OF NITRATE Septic systems, rainfall and agriculture are sources of nitrates (fertilizers) present on or around the property. The current site usage includes an 1,860 -square foot house with three bedrooms. Residential water use includes showering/bathing, clothes washing, cooking, and hand washing. The reasonable or maximum usage of wastewater for the two-bedroom house 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.