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18 September 2020 AdvancedGeo Project No. 20-6116 AnEmployee-Owned Company Page 12 of 16 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 land, which might provide a nitrate source. There are also 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. Deep percolation (average annual rainfall recharge) was estimated utilizing the monthly ETo and precipitation data collected from Ripon Station #249 between 2017 and 2019. The annual rainfall average for the area between 2017 and 2019 was 12.32 inches (CIMIS); the annual ETo averages were 4.13 inches in 2017, 2.11 inches in 2018, and 2.77 inches in 2019. The estimated deep percolation (R) was determined by calculating the average of the ETo between 2017 and 2019. The estimated deep percolation (R) is 3.00 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. There are four (4) existing septic systems at the site; two systems service the residences and two systems service the nursery at the site. (Figure 3). The current residential site usage includes two residences with two bedrooms each. Residential use includes showering/bathing, clothes washing, cooking, and hand washing. The reasonable or maximum usage of wastewater for the two-bedroom homes is 100 gpd for the first bedroom and 50 gpd for each additional bedroom for a total of 150 gpd for each residence and a grand total of 300 gpd. The current commercial site usage includes two existing septic systems that service the main office and breakroom. The onsite business is open Monday through Friday from 7:00 AM to 4:00 PM; and the septic system is utilized 260 days a year by eleven (11)full- time employees. The reasonable or maximum usage of wastewater for the main office and breakroom is 20 gpd per person or 220 gpd (11 employees). 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.