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Nitrate Loading Study Arellano Property _ Stockton, California Irerracon April 26, 2019 a Terracon Project No. NA187058 the proposed three bedroom conversion (12.2 mg/L-N) is anticipated to further increase nitrate levels to 24.4 mg/L-N, also above allowable limits for groundwater. _ 3.5.3 Impact of Nitrate Loading to Nearby Water Sources Based on a review of the USGS Stockton East (1987) California Quadrangle topographic map (Appendix A), the site is located at approximately 45 to 50 feet above mean sea level with a topographic gradient toward the west. The nearest surface water source to the site is Mormon Slough located approximately 2,300 feet south of the site. As the subject property is relatively flat, we do not foresee percolating effluent affecting the surface water resources. 4.0 DISCUSSION OF NITRATE LOADING RESULTS RELATIVE TO PROPOSED METHOD OF WASTEWATER DISPOSAL 4.1 Total Nitrate Impact Based on the method and assumptions described, the result of the nitrate loading balance (24.4 mg/L N) indicates that the existing residential use and proposed development on the parcel may cause a buildup of nitrates in the aquifer above the MCL of 10 mg/L-N. 4.2 Methods of Mitigation Mitigation may consist of the utilization of an advanced water treatment product such as those available by Orenco, which are specifically designed to lower nitrates at point of discharge. Other mitigation options include the use of a carbon source such wood chips. Based on the proposed usage, mitigation may be required by the EHD. 5.0 CONCLUSIONS AND RECOMMENDATIONS Based on the nitrate loading results, nitrate levels for the existing three bedroom residence (12.2 mg/L-N) exceeds the MCL of 10 mg/L-N for nitrate in drinking water when an average two person occupancy is calculated per bedroom. The construction of the proposed three bedroom residence (12.2 mg/L-N) is anticipated to further increase nitrate levels to 24.4 mg/L-N, also above allowable limits for groundwater. The soil conditions at the site are anticipated to consist of silty clay underlain by cemented soils. Depth to groundwater is anticipated to be greater than 90 feet bgs. Nitrate as N (4.7 mg/L) was identified in a groundwater sample collected from the onsite domestic well below the MCL of 10 mg/L-N. A second groundwater sample reported below laboratory detection limits for DBCP. If the EHD requires mitigation for the project, an advanced water treatment product or carbon source may be considered mitigation options. Responsive a Resourceful a Reliable 9