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Soil Suitability/ Nitrate Loading Study -Addendum 1rerracon Soares Property : Escalon, CA March 10, 2020 Terracon Project No. NA197095 Based on Terracon's prior SSNLS report, "the average total 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)". Terracon revised the effluent concentration (Nw) from 45 mg/L-N to 40 mg/L-N (the average). The following table presents a summary of the nitrate loading calculation for the site based on the revised long term average discharge and revised net rainfall recharge. Summary of Nitrate Mass Balance Equation - Revised. Result Average Effluent Leachfield Net Rainfall Acres Concentration Land Use (Nc)* Daily Flow Denitrification Recharge (mg/L-N) (A) (Q)(gpd) (mg/L)N) (d) (R)(in/year) Proposed 3 Bedroom 11.5 0.81 200 40 25% 5.84 Residence Maximum contaminant level(MCL)for nitrate in drinking water is 10 mg/L-N. Based on the revised nitrate loading balance, nitrate levels for the proposed residence decreased from 24.2 milligrams per liter (mg/L) nitrate (N) to 11.5 mg/L-N which is slightly above the MCL of 10.0 mg/L-N. On March 5, 2020, Terracon collected groundwater samples (GW 1 through GW-4) from a faucet directly attached to the onsite groundwater well tank. Samples GW-1 and GW-3 were collected into two clean unpreserved plastic 125 milliliter (ml) bottle to be analyzed for nitrate as N by EPA Extraction Method E300.1. Sample GW-2 and GW-4 were collected into four clean glass 40 ml VOAs preserved with ascorbic and meleic acid to be analyzed for DBCP (1,2-Dibromo-3- chloropropane) by EPA Extraction Method E524.3. Samples GW-3 and GW-4 were placed on hold. The groundwater samples were immediately placed on ice and submitted to McCampbell Analytical Inc. for analysis. Nitrate as N was reported at 3.3 mg/L-N in groundwater sample GW- 1 below the MCL of 10 mg/L-N. Groundwater sample GW-2 reported below laboratory reporting limits of at 0.010 micrograms per liter (ug/L) for DBCP. In conclusion, the results of the revised nitrate loading analysis (11.5 mg/L-N), indicate there is a potential the proposed development may cause an increase of nitrates to groundwater slightly above allowable limits. Nitrate as N was not identified in the existing groundwater well above the MCL and DBCP was not identified in the groundwater sample above laboratory reporting limits. Responsive ■ Resourceful ■ Reliable 2