HomeMy Public PortalAboutCascade_ApprovalLetter_020723Metropolitan
St. Louis Sewer
District
2350 Market Street
St. Louis, MO 63103-2555
(314) 768-6200
February 7, 2023
Contech Engineered Solutions, LLC
Mr. Joe Bratchie
4091 Quincy St.
St. Louis, MO 63116
RE: Contech Cascade Separator Hydrodynamic Separator (HDS)
Highway Use Level (HUL) and Redevelopment Use Level (RUL)
Approval within the District
Dear Sir,
The Metropolitan St. Louis Sewer District (MSD) is pleased to
provide HUL and RUL approval for the use of the Cascade Separator
HDS unit 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 (Revised
Jan. 2009).
• The Cascade Separator must be sized such that the Maximum
Treatment Flow Rate (MTFR) for the unit exceeds the Water
Quality flow rate calculated for the unit's tributary area.
The Cascade Separator's approved MTFRs will be those shown in
Table 1 below, to match the certified flow rates provided by
the New Jersey Department of Environmental Protection
(NJDEP). Procedures for calculating the Water Quality flow
rate are provided in Appendix D.10 of the Maryland Stormwater
Design Manual (2000).
Table 1: Cascade Separator Models and Approved MTFRs
Model Manhole
Diameter (ft)
MTFR (cfs)50% Max.
Sediment
Storage
Volume (ft3)
CS-3 3 1.02 5.3
CS-4 4 1.80 9.4
CS-5 5 2.81 14.7
CS-6 6 4.05 21.2
CS-8 8 7.20 37.7
CS-10 10 11.3 58.9
CS-12 12 16.2 84.8
• The Cascade Separator will be configured as an off-line unit,
downstream from a diversion manhole. In most cases, the BMP
will be installed without the need to store the Water Quality
volume upstream of the unit.
• All devices shall provide a minimum sediment storage capacity
of 10 cubic feet.
• All proprietary lids and covers should be captive components.
The minimum size access hole is 30 inches in diameter.
• Confined space entry shall not be a requirement for routine
maintenance. No special tools or attachments should be
required to provide for routine maintenance with a vacuum
pumping truck.
• Project specific design calculations and maintenance plans
furnished by the manufacturer 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,
Curtis Zurliene, PE
Civil Engineer (BMP Committee Chairman)
Engineering / Development Review
Metropolitan St. Louis Sewer District