Stormwater Credit Trading
Stormwater has become a topic of increasing importance in the planning and
development of urban areas. Traditional “grey” infrastructure (drains and pipes)
has proven to be insufficient when dealing with stormwater runoff, causing floods
and water degradation. The increased flow of urban pollutants that gets carried to
rivers, ponds, lakes, and other bodies of water has caused toxic water conditions,
harmful algal blooms, depleted dissolved oxygen levels in the water, reductions in
aquatic plant life, increased temperatures, and hazardous conditions for aquatic
animals.
To deal with these problems, the EPA, the City of Boise, Garden City, the Ada
County Highway District, the Idaho Transportation Department and Boise State
University have begun to require and implement “Best Management Practices”
(BMPs) around the Boise area. BMPs are “green” methods and structures meant to
reduce water pollution. These include but are not limited to bioswales, retention
ponds, wetlands, and permeable pavers. In general, BMPs are a man-made imitation
of nature that traps, retains, and filters stormwater runoff. They are typically made
up of a rock base, a layer of sand, filtration fabric, a layer of soil, and vegetation
(permeable payers don’t have any vegetation). The EPA has determined that the
installation of BMPs effectively improves water quality, in some cases reducing
pollutants by 90%.
The installation and maintenance of BMPs isn’t always cheap, however.
Depending on the type of BMP and the specific conditions of each site, implementing
“green” infrastructure may not be affordable. In light of this, the City of Boise is
developing a “stormwater-credit-trading” program. Much like emissions trading,
this system utilizes market forces to achieve water quality goals in a cost-effective
manner. Each new development and redevelopment site is subject to retention
requirements (as of right now the requirement is full retention of a 90th-percintile
storm event). Landowners and developers are encouraged to go above and beyond
their requirements. If they do so, they will generate “stormwater credits”, which
represent the additional retention (or pollution reduction) achieved by the site.
These credits can then be sold to landowners and developers who cannot, for
whatever reason, achieve their retention requirements on-site. The additional
retention (or pollution reduction) on the credit-generating site offsets the
insufficient retention (or pollution reduction) on the credit-buying site, thus
meeting the overall requirements for the community as a whole.
Stormwater credit-trading in an urban area is a relatively new idea. In 2013
Washington, D.C. pioneered a program that, thus far, has been effective. Flooding
has been mitigated, and pollutant discharges into the Potomac River have been
markedly reduced. The City of Boise is looking towards the D.C. program and other
pollution trading programs around the country for guidance as they develop the
new stormwater management system. The implementation of BMPs coupled with a
credit-trading program may be the key to achieving Boise’s water quality goals.
For more information, please visit the EPA website at:
http://water.epa.gov/polwaste/npdes/stormwater/index.cfm
http://water.epa.gov/type/watersheds/trading.cfm
Bibliography
Ackerman, D., & Stein, E. (2008). Evaluating the Effectiveness of Best Management
Practices Using Dynamic Modeling. Journal of Environmental Engineering,
134(8), 628-639. doi:10.1061/
District Department of the Environment. (2013). Stormwater Management
Guidebook. Retrieved from
http://green.dc.gov/sites/default/files/dc/sites/ddoe/page_content/attach
ments/FinalGuidebook_changes%20accepted_Chapters%2017_07_29_2013_compressed.pdf
The United States Environmental Protection Agency. (2003). After the Storm.
Retrieved from http://www.epa.gov/npdes/pubs/after_the_storm.pdf