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H <br />1 <br />1 <br />1 <br />1 <br />1 <br />1 <br />1 <br />1 <br />1 <br />1 <br />E <br />1 <br />1 <br />1 <br />j <br />1 <br />1 <br />Technical Review Committee's Recommendation: <br />The TRC finds that: <br />• The Vortechs system, sized at 35 GPM/sf, should provide, at a minimum, equivalent <br />performance to a presettling basin as defined in the most recent Stornnvater Management <br />Manual for Western Washington), Volume V, Chapter 6. <br />Findings of Fact: <br />I. Laboratory testing was completed by CONTECH for sieved sand using a Vortechs Model <br />2000. Laboratory results for the "50 micron" particle range (included particles ranging from <br />38 to 75 microns) showed 80% removal at 13 GPM/sf operating rate. <br />2. Abbreviated laboratory testing was completed by CONTECH for Sil-Co-Sil 106, a ground <br />silica product with a mean particle size of about 20 microns. Removal rates at 5 to 10 <br />GPM/sf were around 40%. <br />3. Various field studies were completed by independent parties in the eastern and northeastern <br />United States (Lake George, NY; South Windsor, CT; Yarmouth, ME; Harding Township, <br />NJ; Lexington, MA; Burlington, VT; and Charlottesville, VA). Study details are provided in <br />the technical appendices. These studies generally show above 80% TSS removal rates. <br />However, the results from a particle size distribution analysis on sediment captured in the <br />Lake George Vortechs System indicate that mainly coarse particles were present. Because <br />the influent particle size distribution was not measured removal efficiency of specific particle <br />sizes could not be determined. <br />4. Three field studies were completed by independent parties in the Pacific Northwest (WSDOT <br />SR-405; Buffalo Slough/City of Portland; Unified Sewerage Agency, Oregon). Study details <br />were not included in CONTECH submissions. These studies generally show TSS removal <br />rates to support a 40% pretreatment rating by Ecology for systems in the PN W, where soils <br />range from a silt to silt loam. <br />5. The system is easily maintained using a vacuum truck. <br />6. There are over 4,400 and 100 Vortechs systems installed nationwide and in the Pacific <br />Northwest, respectively. <br />Technology Description: <br />CD-ROM of Vortechs System Technology Report, dated June 2003, may be requested from <br />CONTECH Stormwater Solutions Inc. <br />Design N.nual and technical bulletins can be downloaded from company's web site. <br />164.4 <br />