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Civil, <br /> Environmental <br /> . Et Water <br /> Resources <br /> MEMORANDUM , <br /> ENGINEEIkING CORP. <br /> TO: Kasey Foley,RENS <br /> Interim Director, San Joaquin Environmental Health Department <br /> FROM: Norman Hantzsche, PE, Questa Engineering Corporatik/ <br /> DATE: February 12, 2019 <br /> UBJECT: OWTS Design Review for 11065 N Alpine Road,Lodi <br /> PROJECT OVERVIEW <br /> The project is for the construction of a new 4-bedroom single family residence and onsite <br /> wastewater treatment system(OWTS)on a 1.5-acre parcel in an agricultural area about 7 miles <br /> southeast of the City of Lodi. The property was historically used for agriculture in the 1930s, <br /> with residential uses dating back to the 1950s. Presently the site is vacant with all prior buildings <br /> having been removed. <br /> Plans and supporting documentation for the OWTS are contained in the "Soil Suitability/Nitrate <br /> Loading Study" by Terracon Consultants, Inc.,dated November 20, 2019. Surface soils in the <br /> area are mapped as Hollenbeck silty clay with slow permeability. Soil borings and percolation <br /> testing to depths of 25 feet showed reported soils predominantly consisting of silty sand,silty <br /> clay and clay. Six percolation test were conducted at depths ranging from 3 to 25 feet, showing <br /> unsatisfactory results with the exception of one passing test of 27.7 minutes per inch at a depth of <br /> 21 feet. Groundwater in the project area is estimated from regional groundwater maps to be <br /> about 90 to 100 feet below ground surface. Groundwater from the onsite domestic well was <br /> found to have nitrate-nitrogen concentration of 15 mg-N/L. <br /> The nitrate loading study by Terracon Consultants utilized a water-nitrogen mass balance <br /> analysis following the Hantzsche/Finnelnore methodology. The resultant nitrate-nitrogen <br /> concentration impacting the groundwater from the new OWTS was estimated to be 15.9 mg-N/L, <br /> which exceeds the 10 mg-N/L drinking water criterion. On the basis of this result Terracon <br /> recommended the use of an advanced/supplemental treatment system to mitigate the potential <br /> groundwater nitrate impact of the project. <br /> COMMENTS <br /> My review comments pertain specifically to the nitrate loading study and recommendation for <br /> supplemental treatment for nitrogen reduction. I agree with the overall approach, methodology <br /> and information provided in the Teracon study. However, I believe some of the assumptions used <br /> 1 <br /> Box 70356, 1220 Brickyard Cove Rd.Suite 206 Pt.Richmond,CA 94807 T:510/236.6114 F 5101236.2423 E:QuestaGQuestaEC.com <br />