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Soil Suitability/ Nitrate Loading Study Thor Property ■ Stockton, CA Irerracon July 19, 2018 a Terracon Project No. NA187029 Based on the nitrate loading balance calculation (Table 6), nitrate levels for the proposed use is anticipated at 20.4 mg/L N above MCL of 10.0 mg/L-N. 2.3.6 Impact of Nitrate Loading to Nearby Water Sources Since the subject property building area is relatively flat, we do not foresee percolating effluent affecting any surface water resources. 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 indicates that the development on the parcel may cause a buildup of nitrates in the aquifer above the MCL of 10 mg/L-N. 2.4.2 Methods of Mitigation Based on the proposed usage, mitigation may be required by the County. Mitigation may consist of the utilization of an advanced water treatment product such as those available by Orenco and others, which are specifically designed to lower nitrates at point of discharge. 3.0 CONCLUSIONS AND RECOMMENDATIONS In summary, percolation rates failed to meet EHD minimum standards at 3.5 feet bgs; however, meet the minimum EHD standards for seepage pits at a depth of 25.0 feet bgs in the proposed septic leach field area.The parcel appears suitable for the use of a standard septic system utilizing shallow leach lines designed for the intended usage. The foregoing investigation and percolation test results indicate the site consists of clay soils where leach lines may be utilized, however as indicated, the area is known for subsurface clay statum and hardpan. For this reason seepage pits should be installed at the end of the leach lines as secondary absorption measure. All final septic system construction should follow the San Joaquin County On-Site Wastewater Disposal Standards where applicable. Based on the nitrate loading results, the proposed residential use has the potential to cause an increase in nitrates above the MCL when an average two person occupancy is calculated per bedroom. If the EHD requires site mitigation for the project, an engineered packaged septic system (such as those available by Orenco and others) specifically designed to lower nitrates at point of discharge may be used. The San Joaquin County Environmental Health Department did not require a physical water sample to be tested (Refer to Section 1.4.3). Responsive ■ Resourceful ■ Reliable 16