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April 17, 2019 BGG Job No. G001.05 Rainfall recharge (deep percolation of rain) is a significant factor in the nitrate loading estimate; however,data on rainfall recharge rates is not widely available. For H&F's study conducted in the Chico area,a recharge rate was calculated to be 75 percent of the average rainfall. Since the Chico area is similar geologically to San Joaquin County region, an estimated recharge rainfall was calculated for this study based upon 75 percent of annual rainfall for the project area. Rainfall data for the Manteca area were obtained from the San Joaquin County Flood Control and Water Conservation District Groundwater Report from Fall 2016. The Stockton Fire Station, the closest reported station to the site,reports the average total annual rainfall from 1941 through 20-15 �s to be 15.6 inches. Assuming 75 percent of this rain water percolates to the aquifer,a value of 11Ji inches of average recharge of rainfall is calculated. H&F estimates that the nitrate concentration rainfall is approximately 1 mg/L-N. Quantity and Quality of Domestic Wastewater The proposed Guard Station at Delicato Winery is anticipated to operated five days per week. A maximum of 4 employees per day is anticipated. No customers are expected. The guard station building will have 4 total employee work stations,with one shared single-fixture restroom. There will be no break room or kitchen in-the building. The estimated sewage flow rates for various uses are available from a number of references. The uses presented below were guided by the San Joaquin County On-Site Wastewater Treatment Systems Standards (2017)and US EPA (1980). A use of 13 gallons per day for each employee is typical for an office or industrial worker; this rate was used for the guard station employees. The estimated flow values discussed here should not be used for the design and sizing of the septic system. The design and sizing of the septic system should utilize the San Joaquin County Environmental Health Department On-Site Wastewater Treatment Systems Standards which incorporate peak and surge flow factors. The estimates used in the On-Site Wastewater Treatment Systems Standards may be greater than those discussed herein. The nitrate as nitrogen (N) concentration for non-showering employee use is estimated to be 85 mg/L (US EPA, 1980). This value was used in calculations for the guard station employees. No contributions from crop irrigation or soil amendments are considered for the Hantzsche/Finnemore method. It is reasonably assumed that the irrigation and soil amendments would be applied at close to agronomic rates for a net balance of plant irrigation and nutrients. The following tables present the calculated maximum average daily flow for the site and weighted average concentrations: Table 1 —Average Daily Flow Calculation Use Units Rate Subtotal Reduction' Average Daily Flow Employees full-time 2 13 gal/employee 26 gpd 5/7 18.6 gpd Employees art-time 2 10 gal/employee 20 gpd 5/7 1 14.3 gpd Total I 1 1 32.9 gpd I Reduction factors convert calculated flow into average daily flow over a one-year period; 5/7 converts for anticipated weekday operations. BAEZ GEOTECHNICAL GROUP Soil Suitability Study and Nitrate Loading Study-DFV Guard Station Page 8