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Soil Suitability/Nitrate Loading Study Irerracon Vacant Commercial Property■ Stockton, California December 7, 2018 ■ Terracon Project No. NA187056 2.4 Discussion of Nitrate Loading Results 2.4.1 Total Nitrate Impact Based on the nitrate loading balance calculation (Table 10), nitrate levels for the proposed future use is anticipated to be 33.6 mg/L-N which is above the MCL of 10.0 mg/L-N. 2.4.2 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 will likely be required by the EHD. 3.0 CONCLUSIONS AND RECOMMENDATIONS In summary, the site and adjoining eastern parcel (APN 085-310-11) are proposed to be developed with St. Luke's Church for up to 600 parishioners with an average daily flow rate of 6,000 gpd. Site land uses have included agricultural orchards with associated structure(s) and a gas station/food mart. A former septic system consisting of a 1,200-gallon septic tank with 40 to 80 foot long leach lines with 25 foot deep seepage pits were located near the southwestern corner of the site and removed in 2018. Based on a history of the site, agricultural activities and the use of septic systems in the area should be considered potential groundwater contamination sources of nitrates. During the course of this investigation, a groundwater sample was not collected from the site domestic groundwater well as the well was non-operational; therefore, information pertaining to levels of nitrate as N and DBCP was not available. A TPH release was reported at the Speedy Food Mart(8200 North Highway 99), a former gasoline station located at the southwestern corner of the site. Elevated levels of TPHg, BTEX, and MTBE were identified in soil and groundwater samples collected from the site. A TPHg and MTBE groundwater plume were reported at the southwestern corner of the site at depths greater than 50 feet bgs. Three 8,000-gallon gasoline USTs and approximately 166 tons of contaminated soil were removed. Remediation and monitoring included multiple groundwater monitoring wells, groundwater extraction wells and a soil vapor extraction system. During the final groundwater monitoring period in 2010, the majority of the wells reported below laboratory detection limits for the contaminants of concern; however, elevated levels of TPHg (13,000 ug/L), benzene (210 ug/L), toluene (350 ug/L), xylenes (2,100 ug/L) and MTBE (390 ug/L) were reported in groundwater samples collected from two wells during the final monitoring period, above ESLs. The remediation wells were destroyed and the case was granted regulatory closure in the year 2010. Responsive■ Resourceful ■ Reliable 20