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RESUB 2-BLD2022-0926+Water Quality Report+7.26.2023_2.27.44_PM+3690715Msro INSIGHT ENGINEERING CO. Water Quality Narrative For Iron Vista Road The proposed project Iron Vista Road is located at 9500 1901h St SW and 19128, 19126, 19124, and 19122 941h Ave W, Edmonds, Washington. The site area is 1.23 Acres. The site is currently undeveloped and exists as lawn with a few trees. The site contains one drainage basin that slopes steeply to the west. The proposal is to construct a drive aisle from 94th Ave W with associated utility stubs to the future development on parcels 00434600006102, 00434600006104, 00434600006105, and 00434600006106. Access to the site will be provided from 941h Ave W. The total new hard surface area will be 21,965 SF. Runoff treatment for the site is required because the total proposed PGHS is over 5,000 SF. Oil control for the site is not required because the project is not commercial or indstrial. Phosphorus treatment is not required because the project is not located within a watershed that is being managed to control phosphorus. Enhanced treatment is not required because the project is not industrial, commercial, multifamily, and does not have high AADT roads. Basic treatment will be provided for the site via a Contech Stormfilter located downstream of the detention system. Please refer to the following pages for sizing calculations for the filter. P.O. Box 1478 *Everett, WA 98206• P: 425.303.9363 info@insightengineering.net C7%o-NTECH` ENGINEERED SOLUTIONS J u ly 5, 2023 Nicole Neufeld Insight Engineering Company 2804 Grand Ave, Ste 308 Everett, WA 98201 RE: StormFilter Review, Iron Vista Contech Engineered Solutions LLC has reviewed the design information provided by Insight Engineering for the Iron Vista project in Edmonds, Washington. The treatment goal is Basic level treatment as defined by WA Ecology and this appears to be a good application for the StormFilter. The designer reports a water quality flow rate of 0.01 cfs and a peak hydraulic flow rate resulting from the 100- year storm event is 0.11 cfs. Contech recommends a StormFilter 48" diameter manhole with 1-18" filter cartridge with ZPG filter media. A single 18" ZPG StormFilter cartridge will treat 0.016 cfs, which exceeds the treatment requirement. The internal bypass capacity of the StormFilter manhole is 1.0 cfs and the StormFilter may be used online. Based on the information provided by the engineer, the system appears to be constructible, and the horizontal configuration of the pipe inlet and outlet pipe is acceptable for the StormFilter specified. The vertical separation between the inlet and outlet pipe provides the prescribed 2.3 feet of drop required for the filter cartridge to operate as designed. In summary, the StormFilter is expected to operate in accordance with Contech Engineered Solutions' design intent. Please note that Contech Engineered Solutions has not reviewed the hydraulics of the collection system upstream or downstream of the filter. Please do not hesitate to call if you have any questions or require more information. Sincerely, Doug Miller Stormwater Area Manager Cc: ©2012 Contech Engineered Solutions LLC 11835 NE Glenn Widing Dr., Portland OR 97220 www.ContechES.com Toll-free:800.548.4667 Fax:800.561.1271 Page 1 of 1 TS-P052 C=:: NTECK ENGINEERED SOLUTIONS Prepared by Stephanie Jacobsen on July 6, 2023 Size and Cost Estimate Iron Vista — Stormwater Treatment System Edmonds, WA Information provided: • Water quality flow, Qwq = 0.01 cfs • Peak hydraulic flow rate, Qpeak = 0.11 CfS • Presiding agency = City of Edmonds, WA Assumptions: • Media = ZPG cartridges • Cartridge flow rate = 7.5 gpm • Drop required from inlet to outlet = 2.3' minimum Size and cost estimates: The StormFilter is a flow -based system and is therefore sized by calculating the peak water quality flow rate associated with the design storm. The water quality flow rate provided to Contech Engineered Solutions LLC for the purposes of developing this estimate. The StormFilter for this site was sized based on a water quality flow rate of 0.01 cfs. To accommodate this flow rate, Contech Engineered Solutions recommends using a 48" StormFilter manhole with 1 cartridge (see attached detail). The estimated cost of this system is $15,800, complete and delivered to the job site. This estimate assumes that the vault is 15 feet deep. The final system cost will depend on the actual depth of the units and whether extras like doors rather than castings are specified. The contractor is responsible for setting the 48" StormFilter Manhole and all external plumbing. Typically, the precast StormFilters have internal bypass capacities of 1 cfs. If the peak discharge off the site is expected to exceed this rate, we recommend placing a high -flow bypass upstream of the StormFilter system. Contech Engineered Solutions could provide our high -flow bypass, the StormGate, which provides a combination weir -orifice control structure to limit the flow to the StormFilter. The estimated cost of this structure is $4,000. The final cost would depend on the actual depth and size of the unit. Stephanie Jacobsen, P.E. Sr. Design Engineer- Stormwater I Team Lead SW Washington Stormwater Consultant Contech Engineered Solutions ©2012 Contech Engineered Solutions LLC 11835 NE Glenn Widing Dr., Portland OR 97220 www.conteches.com Toll-free:800.548.4667 Fax:800.561.1271 Page 1 of 1 TS-P027