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Soil Suitability /Nitrate Loading Study Irerracon ALL STAR HEAVY HAUL & TOWING INCORPORATED Tracy, California July 1, 2022 Terracon Project No. NA217024 Table 10. Summary of Nitrate Mass Balance Equation. Maximum contaminant level (MGL) for nitrate In tlnnkmg water Is 1U mg/L-N Based on the nitrate loading balance, nitrate levels for the proposed Phase I development is anticipated to increase nitrate levels to 1.7 mg/L-N for the project area, but with the addition of the septic system for the residence. It will bring up the nitrate levels to 6.5 mg/L which is below the MCL of 10 mg/L-N. 2.3.6 Impact of Nitrate Loading to Nearby Water Sources The nearest surface water source is the Governor Edmund G Brown California Aqueduct which is located to the adjoining south of the site. The site is situated lower than the river and the proposed septic systems are proposed to be developed greater than 1,000 feet east; therefore, percolating effluent is not anticipated to affect the surface water source. 2.4 Discussion of Nitrate Loading Results 2.4.1 Total Nitrate Impact Based on the method and assumptions described, the result of the nitrate loading balance indicate that the proposed development is anticipated to be below the MCL. 2.4.2 Methods of Mitigation Nitrate mitigation measures appears unwarranted. 3.0 CONCLUSIONS AND RECOMMENDATIONS Three percolation tests (131 at 23.4 feet, B2 at 9 feet and B3 at 3.32 feet bgs) were conducted on the site. The soils encountered in the percolation test borings consisted primarily of clay, silty clay except for a small layer around 9 ft to 10 feet that has some silty sand. The soil borings demonstrated adequate percolation rates of 6.58 (132) and 19.23 (132) minutes per inch; therefore, the EHD recommends a minimum 8 -foot separation between the bottom of the dispersal system to groundwater. Responsive ■ Resourceful ■ Reliable 18 Effluent Average Leachfield Net Rainfall Proposed Result (Nc)" Acres Concentration Daily Flow Denitrification Recharge Development (mg/L-N) (A) (Nw) (Q) (gpd) (d) (in/year) (R) (mg/L-N) Phase I — Septic 1.7 2.53 17 85 15% 8.55 System 1 Residence 6.5 2.53 167 85 30 8.55 Maximum contaminant level (MGL) for nitrate In tlnnkmg water Is 1U mg/L-N Based on the nitrate loading balance, nitrate levels for the proposed Phase I development is anticipated to increase nitrate levels to 1.7 mg/L-N for the project area, but with the addition of the septic system for the residence. It will bring up the nitrate levels to 6.5 mg/L which is below the MCL of 10 mg/L-N. 2.3.6 Impact of Nitrate Loading to Nearby Water Sources The nearest surface water source is the Governor Edmund G Brown California Aqueduct which is located to the adjoining south of the site. The site is situated lower than the river and the proposed septic systems are proposed to be developed greater than 1,000 feet east; therefore, percolating effluent is not anticipated to affect the surface water source. 2.4 Discussion of Nitrate Loading Results 2.4.1 Total Nitrate Impact Based on the method and assumptions described, the result of the nitrate loading balance indicate that the proposed development is anticipated to be below the MCL. 2.4.2 Methods of Mitigation Nitrate mitigation measures appears unwarranted. 3.0 CONCLUSIONS AND RECOMMENDATIONS Three percolation tests (131 at 23.4 feet, B2 at 9 feet and B3 at 3.32 feet bgs) were conducted on the site. The soils encountered in the percolation test borings consisted primarily of clay, silty clay except for a small layer around 9 ft to 10 feet that has some silty sand. The soil borings demonstrated adequate percolation rates of 6.58 (132) and 19.23 (132) minutes per inch; therefore, the EHD recommends a minimum 8 -foot separation between the bottom of the dispersal system to groundwater. Responsive ■ Resourceful ■ Reliable 18