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Soil Suitability/ Nitrate Loading Study Lease Property ■ Acampo, California December 17, 2021 Terracon Project No. NA217090 Table 10. Summary of Nitrate Mass Balance Equation. Ircerr on * Maximum contaminant level (MCL) for nitrate in drinking water is 10.0 mg/L-N. Based on the nitrate loading balance, nitrate levels for the existing residence is 4.0 milligrams per liter nitrogen (mg/L-N) below the MCL of 10.0 mg/L-N. The proposed three bedroom modular is anticipated to increase nitrate levels to 6.4 mg/L-N, also below the MCL. 2.3.6 Impact of Nitrate Loading to Nearby Water Sources Based on the aerial photographs and topographic maps (Section 1.1), the nearest surface water source is an intermittent stream located on the northern portion of the site. Based on distance and gradient, the stream is not anticipated to be affected by percolating effluent. 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 (6.4 mg/L N) indicates that the development on the parcel is not anticipated to cause a buildup of nitrates in the aquifer above the MCL. 2.4.2 Methods of Mitigation Based on the nitrate loading results, mitigation measures appear unwarranted. 3.0 CONCLUSIONS AND RECOMMENDATIONS Based on the results of the field work, site soils consist primarily of lean clay and sandy silt from 3 to 3.5 feet bgs and clayey silt to 21 feet bgs. Based on the percolation test results (27.7 and 3.08 minutes/inch), the soils within the proposed sewage disposal area appear suitable for a standard septic system and seepage pits. Depth to groundwater is anticipated to be greater than 70 feet bgs. A domestic groundwater well is currently located on the site; therefore, groundwater samples were collected. Nitrate as N was reported at 3.5 milligrams per liter (mg/L) in groundwater sample GW -1 below the MCL of 10 Responsive ■ Resourceful ■ Reliable 17 Effluent Result Average Leachfield Net Rainfall Acres Concentration Land Use (Nc)* Daily Flow Denitrification Charge (R) (A) (Nw) (mg/L-N) (Q) (g pd) fid) (i n./ (mg/L-N) Existing Residence 4.0 2.92 200 40 25% 8.09 Existing Residence & 6.4 2.92 400 40 25% 8.09 Proposed Modular I I I I * Maximum contaminant level (MCL) for nitrate in drinking water is 10.0 mg/L-N. Based on the nitrate loading balance, nitrate levels for the existing residence is 4.0 milligrams per liter nitrogen (mg/L-N) below the MCL of 10.0 mg/L-N. The proposed three bedroom modular is anticipated to increase nitrate levels to 6.4 mg/L-N, also below the MCL. 2.3.6 Impact of Nitrate Loading to Nearby Water Sources Based on the aerial photographs and topographic maps (Section 1.1), the nearest surface water source is an intermittent stream located on the northern portion of the site. Based on distance and gradient, the stream is not anticipated to be affected by percolating effluent. 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 (6.4 mg/L N) indicates that the development on the parcel is not anticipated to cause a buildup of nitrates in the aquifer above the MCL. 2.4.2 Methods of Mitigation Based on the nitrate loading results, mitigation measures appear unwarranted. 3.0 CONCLUSIONS AND RECOMMENDATIONS Based on the results of the field work, site soils consist primarily of lean clay and sandy silt from 3 to 3.5 feet bgs and clayey silt to 21 feet bgs. Based on the percolation test results (27.7 and 3.08 minutes/inch), the soils within the proposed sewage disposal area appear suitable for a standard septic system and seepage pits. Depth to groundwater is anticipated to be greater than 70 feet bgs. A domestic groundwater well is currently located on the site; therefore, groundwater samples were collected. Nitrate as N was reported at 3.5 milligrams per liter (mg/L) in groundwater sample GW -1 below the MCL of 10 Responsive ■ Resourceful ■ Reliable 17