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' Nitrate Loading Study Irerracon Arriaga Property -w Stockton, California April 26, 2019 m Terracon Project No. NA187059 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 (25.2 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 two bedroom residence (12.6 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 two bedroom mobile home (12.6 mg/L-N) is anticipated to further increase nitrate levels to 25.2 mg/L-N, also above allowable limits for groundwater. The soil conditions at the site are anticipated to consist of clay to stratified sandy loam to clay loam underlain by cemented soils. Depth to groundwater is anticipated to be greater than 97 feet bgs. Nitrate as N (5.9 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. 6.0 LIMITATIONS As indicated, our study takes into account the subject property only with the sewage load applied over the property site area. The study does not take into account surrounding properties and/or lands. The method utilized for the nitrate loading analysis is based on a simple mass balance formula, discussed in a published article by Hantzsche and Finnemore (1992), which provides a convenient and simplified method to estimate long-term groundwater nitrate impacts on an area- wide basis. A more detailed analysis was not requested nor intended. Responsive m Resourceful ■ Reliable 10