Stormwater Design Options
STACKING FUNCTIONS
Combining the water quality volume,
channel protection volume, and flood
protection volume in one cell, i.e. stacking
functions, is allowed by MSD with certain
limitations. The BMP Toolbox website,
www.stlmsd.com/engineering/planreview/bm
ptoolbox, specifies these allowances and
contains more details.
SITE-SPECIFIC MODELING
Site-specific modeling - in lieu of using
standard equations - is allowed by MSD as
long as performance criteria are met. It
should be noted that while modeling may
require a larger investment for initial
engineering costs, it may render significant
cost savings in the construction phase. MSD
does provide standard equation
spreadsheets, but these are offered as a tool
for developers and engineers who decide
that they do not wish to fully model their
project.
UPDATED PRE-CONSTRUCTION
RUNOFF CALCULATIONS
In order to ensure that pre-construction
runoff calculations are flexible enough to
reflect actual conditions, MSD will soon
release a new amendment and update its
standard equation spreadsheets to reflect
new runoff calculations. These amendments
and updates will be available at
http://www.stlmsd.com/engineering/planrevi
ew/bmptoolbox/calctools. MSD took this
action to provide standards that reflect local
conditions and that provide more flexibility
than the standard guidance information
provided by the EPA.
SOIL TESTING FLEXIBILITY
Different soil types affect infiltration
performance and the calculations for
determining pre- and post-construction
runoff. Soil testing determines a site’s soil
conditions and the infiltration rate expected.
The Maryland Manual requires one
infiltration test and one test pit per 200
square feet of subgrade area. MSD will
accept either this approach, or another
combination of infiltration testing and soil
testing, as outlined at
http://www.stlmsd.com/engineering/planrevi
ew/bmptoolbox/bioretention/designdetails.
MSD strongly recommends designers
discuss soil testing with MSD prior to
performing field investigations. MSD also
allows designers the opportunity to use its
‘conceptual review process’ to negotiate a
site-specific soil investigation workplan.
INERT SOILS
MSD does not require use of
inert/irradiated/‘weed free’ soils, but soil is
required to be mixed to certain
specifications to ensure basins drain in 48
hours or less. While there are vendors that
currently sell soil mixed to the proper
specifications, sites are not required to
purchase soil from these vendors. Soil may
be mixed onsite provided it meets MSD’s
requirements.
Stormwater Design Tips
BMPs ARE AMENITIES
When conceptualizing stormwater, consider
that BMPs have the potential to be amenities
that add value to the community and
minimize maintenance.
COMMUNICATION
In order to maximize the effectiveness of
your stormwater infrastructure, MSD and
the PFT encourage everyone to work with
MSD staff throughout the planning process
and take advantage of the references
provided, such as the BMP Toolbox and
other online features. MSD is committed to
keeping its internal communication
effective, in order to provide everyone
consistent direction on how to comply with
its version of the Maryland Manual. And,
MSD is always willing to help engineers
find new and flexible means of compliance.
Likewise, MSD and the PFT are committed
to working together to provide education
and updates to the development community.
For more informaiton on upcoming
opportunities, contact your PFT
representative.
Stormwater Resources
MSD BMP Toolbox website:
www.stlmsd.com/engineering/planreview/bm
ptoolbox
Missouri DNR Stormwater Information
Clearinghouse:
www.dnr.mo.gov/env/wpp/stormwater/index.html
EPA Green Infrastructure Design and
Implementation Resources:
http://water.epa.gov/infrastructure/greeninfrastr
ucture/gi_design.cfm
EPA National Menu of Stormwater Best
Management Practices:
http://cfpub.epa.gov/npdes/stormwater/menuofbmps/
American Society of Civil Engineers
Environmental and Water Resources Institute:
www.asce.org/ewri/
THE PARTNERSHIP
FOR TOMORROW
The Partnership for Tomorrow, a coalition
of the construction and development
industries, is comprised of the following
organizations: the Associated General
Contractors of St. Louis, the Home Builders
Association of St. Louis and Eastern
Missouri, the Missouri Growth Association,
the St. Louis Association of REALTORS®,
the St. Louis Regional Chamber and Growth
Association, and the St. Louis Council of
Construction Consumers. The mission of the
Partnership for Tomorrow is to stimulate job
growth, attract and retain residents, and
promote new businesses within the St. Louis
region through balanced policy relating to
construction and development.
Industry Update:
Stormwater Regulations
American Society of Landscape Architects:
www.asla.org
Center for Watershed Protection:
www.cwp.org
International BMP Database:
www.bmpdatabase.org
The Engineer’s Club of St. Louis:
www.engineersclub.net
May 2012