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October 1, 2008
Mr. David Mudd
Kirchner Block & Brick
12901 St. Charles Rock Road
Bridgeton, Missouri 63044
RE: Permeable Interlocking Concrete Pavements (PICP)
Structural BMP – Water Quantity and Quality
Dear Mr. Mudd,
The Metropolitan St. Louis Sewer District (MSD) has re-reviewed your application of
pervious paver blocks, including the Bio-Aquifer Storm System (BASS) that is a
proprietary pervious paver type of BMP. Please note this letter replaces our previous
letter of October 4, 2007. MSD hereby grants Provisional Use Level approval for the
pervious pavers with a storage bed. MSD understands that the pervious paver blocks
enhance surface permeability by the drainage openings created by the block’s notched
design. The drainage openings are filled with a permeable, clean, hard crushed aggregate
that allows stormwater to infiltrate below the pavers. Stormwater water quality objectives
can be achieved by infiltration into the surrounding subgrade soils or filtration via an
underground sand filter. In some applications, the stone storage bed underlying the
pavers could be designed to provide temporary storage (i.e., detention), such as that
needed to meet channel protection requirements.
MSD has determined that pervious pavers with storage bed systems may be used under
the following conditions:
1. Proposed uses and designs of the device must be in general conformance with the
information and methodologies provided in the Kirchner application dated August
31, 2007.
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 pavers and an
underdrain at the base of the storage bed, 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 61 61 74 80
4. The imperviousness used in calculating the Water Quality Volume (WQv) may be
reduced. The area of pervious paver areas may be considered as pervious area for
the purpose of calculating Rv, and accordingly WQv.
5. Pervious pavers 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 or New Jersey New Jersey
Stormwater Best Management Practices Manual (February 2004).
6. The application of pervious pavers shall be limited to low traffic areas. (See
additional discussion of WQv treatment provided below.)
7. Project specific design calculations and maintenance plans must be included
within the project’s “Stormwater Management Facilities Report” prepared by the
consulting Engineer.
Your BMP application provides several examples of pervious paver applications,
including the BASS system. As noted above to be used as a stand-alone WQv treatment
BMP the pervious pavement must be designed in conjunction with an infiltration
basin/trench or a sand filter.
The initial installation of the pavers 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) The manufacturer or vendor must perform quarterly inspections of the
proprietary BMP during its first year of operation, which will include
visual inspections. MSD requests to be invited to these inspections to
further enhance familiarity and understanding of the BMP.
3) Formal reports shall be submitted to MSD for each quarterly inspection.
The reports shall include summaries and photographs of the paver system.
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.
The Permeable Interlocking Concrete Pavement is not approved for general use at this
time. MSD reserves the ability to withdraw or modify this approval based on subsequent
information, including information indicating that pervious pavers with storage beds do
not satisfy MSD rules, requirements, or construction specifications.
Sincerely,
Michael T. Buechter, P.E.
Principal Engineer (BMP Committee Chairman)
Engineering/Design
Metropolitan St. Louis Sewer District