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Soil Suitability/ Nitrate Loading Study Irerracon Buddhist Temple Proposed Dormitory ■ Stockton, California July 11, 2019 ■Terracon Project No. NAI 77056 2.4 Discussion of Nitrate Loading Results 2.4.1 Total Nitrate Impact Based on the nitrate loading calculations, nitrate levels for the proposed 12 bedroom dormitory would further increase nitrate as N levels between 21.4 mg/L-N if one person is calculated per bedroom or 33.3 mg/L-N if two people are calculated per bedroom. 2.4.2 Methods of Mitigation Mitigation y d water treatment product, which are sped �desi ned to lower nitrates at point of dischar e. iti ation ma consist of the utilization of an advanced p y g p g Ofh'er`mitigat'ion options include the use of a carbon source such wood chips. 3.0 CONCLUSIONS AND RECOMMENDATIONS In summary the site soils consisted of silty sands. Two soil borings B1 and B2 were excavated to a depth of 3.5 feet bgs and resulted in satisfactory percolation rates of 2.74 minutes per inch and 50 minutes per inch respectively. Based on the favorable percolation results, the site soils appear suitable for a standard septic system. In general, septic system construction should follow the San Joaquin County On-Site Wastewater Treatment Systems Standards where applicable. Depth to groundwater is anticipated between 20 and 40 feet bgs. Nitrate as N was reported at 27 l" mg/L-N above the MCL of 10 mg/L-N and/or 120 mg/L as nitrate in groundwater sample GW-1 above the MCL of 45 mg/L as nitrate. Groundwater sample GW-2 reported below laboratory reporting limits of 0.010 ug/L for DBCP. Elevated nitrate levels were identified on the site in 2006 at 161 mg/L above the MCL of 45 mg/L for nitrate. The site is currently developed with two septic systems and is proposed to be developed with a third septic system. Septic System No. 1 has a 1,200 gallon septic tank (number of leach lines unknown) which services the existing 5 bedroom residence and has a residential flow rate of 350 gallons per day when one person is calculated per bedroom, reflective of the existing residential land use. Based on the nitrate loading results, nitrate levels for the existing 5 bedroom residence is 6.7 mg/L-N when one person is calculated per bedroom. Septic System No. 2 services the commercial land use for the assembly hall, detached restroom building, and thirteen special events and has a long term average daily flow rate of 50.4 gallons per day. The system has a 1,200 gallon septic tank and filter bed. Nitrate levels for the assembly hall daily visitors and special events is 2.9 mg/L-N over the long term. The combined nitrate levels for the existing residential land use and commercial land use is 9.6 mg/L-N, below the MCL of 10 mg/L-N. Responsive ■ Resourceful ■Reliable 20