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MSID
Metropolitan
St. Louis Sewer
District
2350 Market Street
St. Louis, MO 63103-2555
(314) 768-6200
June 16, 2009
Mr. Phil Hocher, President
Pace Construction, Inc.
1620 Woodson Road
St. Louis, Missouri 63114
RE: Porous Asphalt — Proprietary BMP Application
Dear Mr. Hocher,
The Metropolitan St. Louis Sewer District (MSD) has reviewed your application of
Porous Asphalt that is a proprietary pervious pavement type of BMP. MSD hereby
grants Provisional Use Level approval for the Porous Asphalt with the storage bed
underneath. MSD understands that the Porous Asphalt enhances surface permeability
with the porous openings in the asphalt. The open graded stone storage bed underlying
the Porous Asphalt provides temporary storage for the runoff.
MSD has determined that Porous Asphalt with open graded stone storage bed system
may be used under the following conditions:
1. Proposed uses and designs of the product must be in general conformance with
the information and methodologies provided in the Fred Weber Porous Asphalt
Pavement application dated March 18, 2009.
2. Channel Protection Volume (CPv) storage may be provided in the storage bed
underneath the pavement.
3. With a minimum gravel storage bed of 12" underneath the pavement and a
designed underdrain, the post -developed curve number (CN) may be reduced.
Except for type A soils, the CN number that should be used should be reflective
of Open Space Good Condition areas and the soil type of the underlying native
soil. For convenience, the CN numbers are provided below:
Soil A B C D
CN 6I 61 74 80
4. The imperviousness used in calculating the Water Quality Volume (WQv) may be
reduced. The area of porous pavement may be considered as pervious area for the
purpose of calculating Rv, and accordingly WQv.
5. Porous Asphalt may be used to provide WQv treatment, when used in conjunction
with a properly designed infiltration basin/trench or sand filter per the 2000
Maryland Stormwater Design Manual. However, Porous Asphalt is not to be used
as a stand-alone WQv treatment BMP. The Porous Asphalt pavement must be
designed in conjunction with an infiltration basin/trench, sand filter, or other
supplemental BMP in order to meet MSD WQv treatment criteria. It is noted that
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the supplemental BMP shall not be located underneath the Porous Asphalt or the
base system.
6. While Porous Asphalt is approved for provisional use, its application shall be
limited to low traffic areas.
7. Project specific designed calculations and maintenance plans 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 Porous Asphalt
with storage bed does not satisfy MSD rules, requirements, or construction
specifications. Please provide three pavement samples to MSD to serve as
representative samples of the pavement Iayer. The three samples shall be
minimum 4 inches in diameter.
Sincerely,
/,
BwAi
Michael T. Buechter, P.E.
Principal Engineer (BMP Committee Chairman)
Engineering/Design
Metropolitan St. Louis Sewer District
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