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S 1 Soil Suitability/Nitrate Loading Study Addendum Letter Lange Twins Winery h Acampo, California Irerracon May 21, 2019 u.. Terracon Project No. NA197005 Average Daily Flow Rates (Max Flow x # Days used per year/ 365 days per year For the purpose of the nitrate loading analysis, a long term average daily flow rate was calculated for the facility. During standard operating hours the long term average daily flow for the existing facility is 313.86 gpd and 1,031.51 gpd during peak hours. The proposed development is anticipated to add an additional average daily flow rate of 403.95 gpd during standard operating hours or 481.30 gpd during peak hours. The special events are anticipated to add an additional 54.79 average daily flow. Therefore, the average daily flow for the facility is anticipated to be 772.60 gpd during standard operating hours or 1,567.61 gpd during peak hours. The average total nitrogen concentration of domestic wastewater is normally considered to be 20 to 85 mg/L-N with 35 to 45 mg/L-N being typical (Crites and Tchobanoglous, 1998). It is estimated that commercial use will have higher concentrations of total nitrogen when compared to residential use. The 2005 NOA SSNLS reported the average total nitrogen concentration of wastewater was reported at 60 mg/L-N for the winery facility with 25% denitrification factor. Terracon recommends an average concentration for total nitrogen in wastewater for the winery operations is approximately 85 mg/L-N over the long term and 45 mg/L-N for the residence. Deep percolation of rainfall was estimated to be 4.49 inches per year. Nitrate Loading A nitrate loading scenario was performed for each building with a septic tank to determine the impact of the existing facility and proposed development. The scenario utilizes the variables discussed previously which represent the estimated conditions and uses associated with this project. The following table presents a summary of the nitrate loading calculation for the site based on the highest average daily flow rates for each the facility buildings with septic tanks. A copy of the nitrate loading calculation is included in the Attachments. Table 3. Summary of Nitrate Mass Balance Equation. Result Effluent Deep Septic Leachfield Tank Land Use (Nc)* Acres `Average Daily Concentration Denitrification Percolation No. (mg/L- (A) Flow(Q)(gpd) (Nw) (d) of Rainfall N) (mg/L-N) (R)(in) 1 Truck South 1.3 41.38 70.32 85 25% 4.49 Restroom 2 Caretaker 1.7 41.38 280 45 25% 4.49 House 3 Bottling 2.2 41.38 275.03 85 25% 4.49 Building 4 Building#1 1.5 41.38 112.51 85 25% 4.49 5 Tasting Room 2.3 41.38 293.65 85 25% 4.49 Responsive ■ Resourceful ■ Reliable 6