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lierracon Soil Suitability / Nitrate Loading Study Morada Produce — Ag Processing Building Stockton, California May 14, 2021 Terracon Project No. NA217014 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 Mormon Slough located 0.68 miles south of the site. Based on distance and gradient, Mormon Slough 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 indicate that the existing septic systems (Septic Systems 1, 2 and 3) and the proposed development (Septic System 4) may cause a buildup of nitrates (less than 13.8 mg/L-N) in the aquifer above the MCL during the peak season; however, the nitrate levels (less than 3.2 mg/L-N) are anticipated to be below the MCL during the standard season. The annual average nitrate loading impacts is anticipated to be below 8.5 mg/L-N which is below the MCL. 2.4.2 Methods of Mitigation Based on the nitrate loading results, nitrate levels may increase up to 13.8 mg/L-N during the peak season; however, the annual nitrate loading averages are anticipated to be below the MCL over the long term therefore, mitigation measures appear unwarranted. 3.0 CONCLUSIONS AND RECOMMENDATIONS Site soils consisted primarily of clay in the upper three feet and silty sand at 23 to 25 feet. The satisfactory percolation test results at 23 feet and 25 feet deep bgs (3.12 and 5 minutes per inch) indicate the soils within the proposed sewage disposal area appear suitable for seepage pits. Depth to groundwater was reported at 134 feet bgs; therefore, an adequate soil column is anticipated between the bottom of the seepage pits and groundwater. Groundwater samples for the onsite Well #2 reported at 5.4 and 5.6 mg/L-N in June 2019 and 2020, below the MCL of 10 mg/L-N. DBCP was reported below laboratory detection limits of 0.2 pg/L during the same time period. The site is currently developed with three septic systems and is proposed to be developed with a fourth septic system. The facility operates year round with the peak season beginning from April to June and August to September. The expected onsite maximum septic tank usage for the existing facility operations is approximately 27,728 gpd (Septic Systems 1, 2, 3). The proposed Ag Processing Building (Septic System 4) is anticipated to add approximately 789 gallons of effluent per day for a combined maximum daily flow rate of approximately 28,517 gpd for the 19