CASE STUDIES - Low Impact Development and Sustainable Stormwater Management - page 211

During the 1990s, a number of states took the initiative and prepared BMP
manuals listing and explaining in some detail the various types of erosion con-
trol, sediment capture, and rate mitigation measures, again trying to design a
better detention basin, now including vegetative elements and, where possible,
infiltration elements.
Pennsylvania BMP Manual (2005)
The commonwealth of Pennsylvania followed the trend of other states, preparing
a BMP manual during the late 1990s directed at the local units of government
(2,560 throughout the state), not as regulations (because the issue of land use was
still considered a local issue and politically sensitive) but as “guidance.” Like
other state manuals, this largely failed to change the development process, and
the building of detention basins continued unabated as the appropriate stormwater
management system, augmented by a number of erosion control technologies to
contain the soil loss within the development site.
From 2003 through 2005, Cahill Associates helped the Pennsylvania Depart-
ment of Environmental Protection (PADEP) develop the Pennsylvania Stormwa-
ter Best Management Practices Manual (Figure B-2). Although a number of states
and other jurisdictions had prepared BMP manuals, this was the first state man-
ual to aggressively advocate volume-reduction technologies, although not without
great discussion. An advisory committee was structured to assist Cahill Associates
and the PADEP in this brainstorming process, and although the final design cri-
teria were by no means embraced uniformly by all parties, the BMP manual did
represent the closest effort to structuring the concepts of low-impact development.
The most important recommendation to come out of this work was the design
criterion for volume control, expressed as follows:
All new development shall prevent any net increase in the volume of runoff
generated from a development site during the 2-year, 24-hour frequency
rainfall.
Multiple criteria were discussed and considered, and nonstructural measures
were strongly recommended, but again the subject of local government control
of the land development process influenced the final document. This manual has
served as the basis for inclusion in many local land development regulations, but
because of the rural nature of much of the state, has yet to find full adoption in
all of the 2,560 municipalities across the state.
The major urban centers, including Philadelphia and Pittsburgh, were
struggling with a multiplicity of land redevelopment issues, only one of which
was stormwater. In communities with combined sewers the impact was felt in
the uncontrolled overflow from combined sewer overflows (CSOs) to surface
waters, a much more direct water quality impact and health threat, especially to
communities situated downstream. For these urban environments, independent