HomeMy Public PortalAboutFilterra RUL HUL 1-26-18
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January 26, 2018
Mr. Joe Bratchie
CONTECH Engineered Solutions, LLC
8133 Whitburn Dr. Apt. C
Clayton, MO 63105
RE: Filterra
Redevelopment Use Level (RUL) and Highway Use Level (HUL) Approval within the
District
Dear Mr. Bratchie:
MSD has reviewed your application regarding use of Filterra as a Best Management Practice for
stormwater Management. MSD is pleased to provide Filterra with Redevelopment Use Level
(RUL) and Highway Use Level (HUL) approval for use as a stand alone water quality BMP on
those types of projects, subject to the following provisions:
• Filterra is only approved for use on redevelopment sites less than 5 acres and municipal
roadway projects. This approval is based on compliance with requirements listed in
MSD’s Proprietary Water Quality Products and the MSD’s Stormwater Management
Program (Jan. 2008), MSD’s Rules and Regulations, and our region’s MS4 permit.
• Filterra is normally applied as a self-contained treatment system with a typical section
consisting of a 3” thick layer of hydraulically unrestrictive mulch, 21” of Filterra media, a
minimum 6” of underdrain stone, and a 4” or 6” underdrain. Under that condition, the
following table shall be utilized to select the appropriately sized Filterra unit:
Tributary Area* (ac) Filterra Unit Size
0.066 4 x 4
0.098 4 x 6
0.13 4 x 8
0.146 6 x 6
0.195 6 x 8
0.244 6 x 10
0.293 6 x 12
0.37 7 x 13
*assumes a 100% impervious contributory drainage area
• Inlet and gutter capacity leading up to the throat of the Filterra unit shall be of sufficient
capacity to convey and capture the tributary area’s Peak Water Quality Flowrate (as
determined per the 2000 Maryland Manual, Volume II, Appendix D.10.)
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• Filterra may be configured to bypass high flows at the curb line to a suitable outfall
location, normally an immediately adjacent downstream inlet structure or curb cut and
swale. Bypass routes shall be configured to provide for an overland overflow path
capable of managing the 100yr-20min flowrate that is tributary to the Filterra unit in
accordance with MSD’s Rules and Regulations.
• When interfaced with MSD’s public storm sewer system, the Filterra units, and the first
reaches of pipes connecting to and exiting the unit shall be private, under MSD’s
inspection. When implemented on a municipal roadway project, the municipality/agency
having jurisdiction over the roadway will be responsible for maintaining the configuration
as described above.
• The Filterra media may be utilized on bioretention designs on redevelopment and
roadway projects where hazardous subsoil and environmental conditions exist, and,
after geotechnical investigation, it is determined that an infiltration design would be
detrimental to those existing conditions. In such instances a K=140 in/hr may be utilized
to size the filter bed area, and the subgrade beneath the filter bed must be lined with an
impermeable lining.
• 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.
• The initial installation of the Filterra system in the MSD shall include the following:
1) A manufacturer’s or vendor’s representative must be onsite during the
proprietary BMP installation to ensure the product’s installation requirements are
met.
2) Shop drawings indicating elevations of flowlines, weirs, pipe inverts, etc. will be
required prior to installation.
3) The manufacturer or vendor must arrange for an as-built survey of the
proprietary BMP to be performed by a Missouri-registered Professional Land
Surveyor once the device has been installed, and prior to any testing or
monitoring.
4) The manufacturer or vendor must perform quarterly inspections of the
proprietary BMP during its’ first year of operation, which will include visual
inspections and quantitative analysis of the service’s sediment removal
efficiency, especially as compared to its design efficiency. MSD requests to be
invited to these inspections to further enhance familiarity and understanding of
the device.
5) Formal reports shall be submitted to MSD, including as-builts and at each
quarterly inspection. The reports shall include summaries, quantitative analysis
mentioned in item 4, photographs of the structure, inlet, internal conditions of the
structure, the filters, and outfall conditions, etc. The reports shall also evaluate
the performance of the owner’s adherence to the approved maintenance
program, and offer suggestions for any areas of improvement.
Filterra is not approved for general use at this time.
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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.
Principal Engineer (Proprietary BMP Committee Chair)
Engineering/Planning-Development Review