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30 July 2019 AdvancedGeo AGE Project No. 19-4772 E r�v i ro n m e n t a l Page 10 of 14 9.0. IMPACT OF NITRATE TO GROUNDWATER Due to the residential use of the property and the potential for nitrate leaching into the groundwater from the existing and proposed septic systems, a nitrate loading analysis for the future use of the septic systems has been 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 lands 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) Ripon Station #249. The average rain fall data for the area was gathered from the Western_eg cnal Climate Center summary. The averages were calculated based on data collected between 1981 and 2010, the annual rain fall average for the area is 13.13 inches. 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 an 1,862-square foot house with three bedrooms and three bathrooms and an approximately 300-square foot shed. Residential use includes showering/bathing, clothes washing, cooking, and hand washing. The reasonable or maximum usage of wastewater for the three-bedroom house is 150 gpd per bedroom for a total of 450 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 450 gpd.