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Contech Engineered Solutions, LLC 2020-10-6 Page 1 of 2 October 6, 2020 Contech Engineered Solutions, LLC Attention: Joe Bratchie 4091 Quincy St. St Louis, MO 63116 RE: Cascade Separator Dear Mr. Bratchie, The Metropolitan St. Louis Sewer District (MSD) has reviewed the 08/12/2020 application for the Contech Cascade Separator and is pleased to provide Highway Use Level (HUL), and Redevelopment Use Level (RUL) for use as a stand-alone water quality BMP subject to the following provisions. • The Cascade Separator 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 (Rev. Jan. 2009). • The Cascade Separator 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. Model Manhole Diameter [ft] Max Treatment Flow [cfs] CS-4 4 1.48 CS-5 5 2.31 CS-6 6 3.33 CS-8 8 5.93 CS-10 10 9.27 CS-12 12 13.35 Table 1. Maximum Water Quality Treatment Flow Rate (WQf) by Model • Only concrete manholes are allowed at this time. • 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 (WQv) upstream of the unit. • All devices shall provide a minimum sediment storage capacity of 10 ft3. Page 2 of 2 • 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 the Cascade Separator does not satisfy MSD rules, requirements, or construction and material specifications. Sincerely, Robert A. Miller, PE BMP Committee Chair Engineering / Development Review