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MEMORANDUM <br />ENGINEERING CORP. <br />TO: Linda Turkatte, RENS <br />Director, San Joaquin Environmental Health Departments i <br />FROM: Norman Hantzsche, PE, Questa Engineering Corporati� <br />DATE: November 13, 2019 <br />SUBJECT: OWTS Design Review for Navu Farms, Inc., 7300 West Delta Ave, Tracy <br />PROJECT OVERVIEW <br />The project is for the construction of an Ag Building, an Abattoir and holding pens on <br />agricultural property at 7300 West Delta Avenue, Tracy. The project spans two adjacent <br />properties of 36.46 and 3.93 acres, respectively. The onsite wastewater system (OWTS) will be <br />located on the 36 -acre parcel to accommodate wastewater flows from restroom use by the owner <br />and customers. <br />Plans and supporting documentation for the OWTS are contained in the "Nitrate Loading Study, <br />Soil Suitability Study and Onsite Wastewater Treatment System Design" by Chesney <br />Consulting, dated September 6, 2019. Soils on the site are reported to be clay loam, with a <br />percolation rate of 20.8 min/inch at 364nch depth, and water table found at a depth of 5.7 feet <br />below existing grade. The proposed OWTS consists of at -grade leaching trenches to maintain a <br />5 -ft separation to groundwater. The anticipated wastewater flow is less than 50 gpd, based on <br />projected annual wastewater generation of 17,555 gallons per year. <br />COMMENTS <br />1. Groundwater Separation/PercolationBate. Based on a percolation rate of 20.8 min/inch, <br />San Joaquin County regulations require an 8 -ft vertical separation to groundwater, rather than <br />5 -ft separation as proposed. A 5 -ft separation is acceptable where the soil percolation rate is <br />>30 min/inch. Normally several percolation tests (3 to 6) are conducted to provide a <br />representative characterization of soil conditions in the planned leachfield area. The single <br />percolation test result of 20.8 min/inch seems fast for clay loam soils. I recommend <br />conducting additional percolation tests to confirm the percolation rate and corresponding <br />groundwater separation requirement. Alternatively, if the single percolation test remains as <br />the basis of design, an alternative wastewater dispersal method, such as a mound system, <br />would be necessary to address the reduced separation to groundwater provided. <br />1 <br />Box 70356, 1220 Brickyard Cove Rd. Suite 206 Pt. Richmond, CA 94807 T: 510236.6114 F.' 510236.2423 f: Questa®QuestaEC.com <br />