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496660MEM Metropolitan St. Louis Sewer District 2350 Market Street St. Louis, MO 63103-2555 (314) 768-6200 February 26, 2013 Mr. Josh Dickinson CONTECH Engineered Solutions LLC 6413 Lloyd Avenue St. Louis, MO 63139 RE: CONTECH CDS®: St. Louis MSD Submission Highway Use Level (HUL) and Redevelopment Use Level (RUL) Approval within District Dear Mr. Dickinson: The Metropolitan St. Louis Sewer District (MSD) has reviewed the results of the CONTECH CDS Quarterly Assurance Project Plan (QAPP) and is pleased to provide Highway Use Level (HUL) and Redevelopment Use Level (RUL) approval for use of the CDS® as a stand-alone water quality BMP, subject to the following provisions. • The CDS® is only approved for use on public highway and roadway projects and for redevelopment sites less than 5 acres. This approval is based upon compliance with requirements listed in MSD's Proprietary Water Quality Products and the MSD's Stormwater Management Program (Jan. 2008). • The CDS® must be sized to capture all floatable trash and free oil, and remove 80% of total suspended solids for the OK-110 particle size distribution at the site water quality flow -rate (WQf). Procedures for calculating WQf are provided in Appendix D.10 of the Maryland Stormwater Design Manual (2000). Table 1 provides a list of approved models and their respective instantaneous peak treatment WQf. The 2400 micron screen will be used. Table 1: CDS® Approved Models and Peak W System Model Max Treatment Flow (cfs) CDS2015-4 0.49 CDS2015 0.49 CDS2020 0.77 CDS2025 1.12 CDS3020 1.40 CDS3030 2.10 CDS4030 3.15 CDS4040 4.20 • Devices should be configured as off-line units, downstream from a diversion manhole. In most cases the BMP will be installed without the need to store the water quality volume (WQ,,) upstream of the unit. • All devices shall provide a minimum sediment storage capacity of 10 ft3. • Confined space entry shall not be a requirement for routine maintenance. No special tools or attachments should be required to provide routine maintenance with a vacuum pumping truck. • All proprietary lids and covers should be captive components. The minimum size access hole is 30 inches in diameter. • Project specific design calculations and maintenance plans furnished by CONTECH must be included within the project's "Stormwater Management Facilities Report" prepared by the consulting engineer. MSD reserves the ability to withdraw or modify this approval based on subsequent information, including information indicating that this BMP does not satisfy MSD rules, requirements, or construction specifications. Sincerely, Jason Peterein, P.E. Civil Engineer (BMP Committee Chairman) Engineering/Planning Metropolitan St. Louis Sewer District