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civil, <br /> Environmental <br /> . &Water <br /> Resources <br /> MEMORANDUM <br /> ENGINEERING CORP. <br /> TO: Michael Kith, REHS <br /> Program Coordinator, San Joaquin Environmental Health Department <br /> FROM: Norman Hantzsche,PE, Questa Engineering CorporatiA$/. <br /> DATE: April 22, 2020 <br /> SUBJECT: OWTS Design Review for Nile Garden Elementary School,Manteca <br /> Project Overview and Initial Design <br /> The project is for modernization of the Nile Garden Elementary School located at 5700 East Nile <br /> Avenue in Manteca. The project includes the construction of a new multi-purpose building, <br /> kindergarten classroom building, and other improvements including upgrade and expansion of <br /> the onsite septic system(OWTS). The school has an existing student enrollment plus staff of <br /> 828,which is not projected to increase as a result of the project.The construction of the new <br /> OWTS facilities falls under the purview of the San Joaquin Environmental Health Department, <br /> which triggered the preparation of a Nitrate Loading Study (NLS)for County review. Questa <br /> was tasked with providing a third-party technical review of the NLS and OWTS design. <br /> Plans and supporting documentation for the OWTS were initially provided in: (1)engineering <br /> plans prepared by MCR Engineering(July 2019); and(2)"Soil Suitability-Nitrate Loading <br /> Study" (December 2019)by Condor Earth consultants. The subsurface conditions on the site <br /> consist of deep, unconsolidated alluvium. Surface soils in areas planned for the new/upgraded <br /> OWTS are reported to be well drained, silty sand/coarse loamy sands. Percolation tests at depths <br /> of 2 and 3 feet showed rates of 5.7 and 10 minutes per inch. Groundwater was reportedly <br /> encountered at a depth of 10 feet below ground surface in November 2018; it may rise higher by <br /> a few feet during other times of the year. <br /> Questa's initial review of the engineering plans and NLS raised questions about several issues, <br /> which were conveyed to the project engineer(MCR Engineering) in a conference call with <br /> Environmental Health on April 10,2020. The main review points centered on the projected <br /> nitrate loading impact of the OWTS as indicated in the Condor Earth Nitrate Loading Study. <br /> Nitrate mass balance loading calculations by Condor projected a resultant concentration of 25.4 <br /> mg-N/L , which is significantly above the target limiting criterion of 10 mg-N/L contained in <br /> County OWTS requirements. Condor did not propose any specific nitrate mitigation measures, <br /> but did point out the limited significance of the impacts due to the surrounding agricultural land <br /> uses in the area. <br /> 1 <br /> Box 70356, 1220 Brickyard Cove Rd.Suite 206 Pt.Richmond,CA 94807 T.•510/236.6114 P.510/236.2423 E.Questa@QuestaEC.com <br />