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Geotechnical Engincering Report <br /> , Proposed New Storm Watcr Vault <br /> Northwest Mitsubishi <br /> November 18, 2002 <br /> CG File No. 1397 <br /> Pagc 2 <br /> maximum water storage planned in the vau]t. Water will bc rcleased 1'rom the vault into an open <br /> treatment cell planned on thc west side of the vault. "I'hc water will flow through the treatment <br /> cell to an intake with a trash rack and then be routed into the existing manhole. A roughly 4-foot- <br /> high concrete retaining wall is shown along thc west side of the treatment cell near the west <br /> property line. The DEA plan appeared to indicate that the wall would be located about 5 feet <br /> from the praperty line and 9 feet Gom the vault. <br /> We understand that thc arca around the new vault will be filled and lhe surface covered with <br /> 6Ravel for additional parking area. Mr. Greg Gliege with Project Services, your contractor on the <br /> project, indicatcd he expects to werk on the site this wintec I le said a temporary diversion of thc <br /> water currently ilowing through the planned vault area will be in place prior to bcginning the <br /> excavation. Ile expects to stockpile some of the excavated material for use as backfill and export <br /> wet material that cannot be stockpilcd duc to high moisturc or that contains excessive organics for <br /> use as backfill. Greg indicateJ that imported soil, most likely glacial [ill from a nearby project, <br /> will bc brought in to providc cnaugh soil for thc planned backfill and parking cxpansion. <br /> 7'hc top of thc slab at ihe basc of thc vault is planned at Elcvation G32.4 fcet. Based on the <br /> drawings provided, �+�e estimatc that the bottom of the footings is planned at about elevation 63l <br /> fcet. <br /> SCOPE <br /> The purposc of this study is to explorc anJ characterize the subsurfacc conditions, and present <br /> recomniendations for site devclopment. Specifically, our scope of services will include the <br /> follo�+�ing: <br /> L G��aluate the subsurface conditions with a backhoe. The backhoe will be provided <br /> by your cantractor. <br /> 2. Provide foundation and retaining wall recommendations. <br /> 3. Provide general surface and subsin face drainage recommendations. <br /> �l. Prcpare a gcotechnical report summarizing our cone;usions and recommendations. <br /> Cornerstone Geotechnical, Inc. � <br />