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MEMORANDUM ENGINEERING CORP. TO: Linda Turkatte, REHS Director, San Joaquin Enviromnental Health Department FROM: Norman Hantzsche, PE, Questa Engineering Corporation DATE: October 11, 2019 SUBJECT: Final - OWTS Design Review for Holly Commerce Center, Buildings A&B In my Memorandum of August 15, 2019 I provided review comments on the plans and supporting design and Nitrate Loading Study for an onsite wastewater treatment system (OWTS) to serve the subject project in the Holly Commerce Center, Buildings A&B, in San Joaquin County. My comments and recommendations pertained to two main items: (1) provisions for wastewater treatment and disposal to accommodate potential future changes in the uses and occupancy of the buildings; and (2) alternate nitrate loading methodology for sites developed with large impervious area. Revised plans, design analysis and responses addressing the review comments were prepared by Siegfried Engineering in a Memorandum, dated October 1, 2019. I've reviewed the Siegfried Memorandum and find it satisfactorily addresses the issues and recommendation raised in my initial review, with my concluding notes as follows: 1. Provisions for Future Wastewater Needs. Appropriate provisions are included for ongoing monitoring and reporting of wastewater flows under the County's program for OWTS monitoring. The Siegfried Memorandum includes calculations of projected wastewater flows and disposal needs for potential future occupancy of the facilities up to their architectural capacity as office space. A drawing is provided depicting locations for future leachfields in the areas that would no longer be needed/used for loading docks (current plan). This is a reasonable assessment of how a future hypothetical change in use could potentially be accommodated for wastewater disposal (leachfields). However, it does not address the significant increases in wastewater nitrate loading that can be expected to accompany future changes in use/wastewater flows. My preliminary calculations indicate this would most probably require the inclusion of a supplemental treatment system for nitrogen removal in order to meet discharge criteria. Given the limited percolation information for the site, it's also likely that supplemental treatment would be needed to overcome soil/percolation limitations in areas impacted by years of truck traffic. Recognition of the probable future need for supplemental treatment, and where it could be located, should be included in the plans and/or permit documents, as clear notice to all parties. 1 Box 70356, 1220 Brickyard Cove Rd. Suite 206 Pt. Richmond, CA 94607 T: 510236.6114 F: 510f 236.2423 E: Questa®QuestaEC.com