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MEMORANDUM <br />Civil, <br />Environmental <br />Et Water <br />Resources <br />ENGINEERING CORP. <br />TO: Kasey Foley, REHS <br />Interim Director, San Joaquin Environmental Health Department <br />FROM: Norman Hantzsche, PE, Questa Engineering Corporat A <br />DATE: December 10, 2019 <br />SUBJECT: OWTS Design Review for 4700 Lovely Road, Tracy <br />PROJECT OVERVIEW <br />The project is for the construction of an Agricultural Building that will be used for storage of <br />agricultural equipment and implements. The building will have an interior unisex bathroom. <br />The subject property consists of a 67 -acre parcel, primarily an almond orchard, located on the <br />west side of Bird Road, one-half mile south of Lovely Road, Tracy. An onsite wastewater <br />system (OWTS) will be installed to accommodate wastewater flows from restroom use by <br />employees, up to a maximum of five people. <br />Plans and supporting documentation for the OWTS are contained in the "Nitrate Loading Study, <br />Soil Suitability Study" by Chesney Consulting, dated October 14, 2019. Soils on the site are <br />reported to be loamy sand and sandy loam, with a percolation rate of approximately 11 min/inch <br />at 42 -inch depth, and an estimated water table depth of 18 feet below existing grade. The <br />proposed OWTS consists of a standard septic tank and gravity leaching bed, maintaining more <br />than the minimum required 8 -ft vertical separation to groundwater. The anticipated average <br />wastewater flow is about 30 gpd, based on projected annual wastewater generation of <br />approximately 10,000 gallons per year. <br />COMMENTS <br />The Nitrate Loading Study by Chesney Consulting projects an estimated resultant groundwater <br />nitrate—nitrogen concentration of 0.13 mg-N/L, well below the 10 mg-N/L drinking water <br />standard. I agree with the methodology and calculations presented by Chesney with the <br />exception of the value for rainfall recharge. The study states an assumption of 9.5 inches per <br />year for average annual rainfall recharge (R value in the Hantzsche-Finnemore equation), based <br />on the assumption that average recharge is equal to average annual rainfall. This is not <br />universally true, since there will always be some amount of rainfall lost to runoff, evaporation <br />from the soil/land surface, and/or transpiration by plants. However, in this particular case it is a <br />suitable approximation because of the very large size of the property in relation to the very small <br />wastewater volumes that will be generated. No further analysis or response is required. I <br />recommend acceptance of the Nitrate Loading Study as submitted. <br />Box 70356, 1220 Brickyard Cove Rd. Suite 206 Pt. Richmond, CA 94807 T. 510/236.6114 F: 510/236.2423 E: Questa@QuestaEC.com <br />