In Wednesday’s post, I mentioned the benefits of monitoring to help explain the reasons why green infrastructure facilities are being employed in their neighborhoods and specifically their effectiveness in improving water quality in our rivers and stream for which we all depend.
The City of Portland has done a great job at monitoring their green streets and other green infrastructure facilities. They provide this information on the Bureau of Environmental Services’ (BES) website. Their 2008 evaluation of their green street facilities have shown that for a 25-year storm event ( 25-yr, 6-hr) that peak flows were reduced by 80% or more. For CSO compliance events, their studies were shown to capture 60% or more of the storm volume.
It appears less has been published by the City on the pollutant removal capabilities for green streets. However, as mentioned in the article, studies conducted across the country have shown bioretention areas, the main stormwater management component of a green street, have been shown to be very effective. EPA’s fact sheet on bioretention shows the following removal rates:
- Total Phosphorous: 70%-83%
- Metals (Copper, Zinc, Lead): 93%-98%
- Total Kjehldahl Nitrogen (TKN): 68%-80%
- Total Suspended Solids: 90%
- Organics: 90%
- Bacteria: 90%
These number continue to be supported through researched conducted over the last decade. The concern that the accumulation of these pollutants, particularly metals will pose health risk have been unsubstantiated. A four-year study by Philip Jones (student) and Dr. Allan Davis (advisor) at the University of Maryland, showed the level of pollutants that accumulated within a bioretention cell on campus to exceed soil background levels but were far below EPA cleanup standards.
It is important to remember that currently, most conventional stormwater devices have no capacity to address pollutant removal. Portland is at the forefront in implementing green infrastructure practices and will be well positioned as Federal standards continue to be strengthened over the coming decade. More importantly, they are improving the water quality of their rivers for future citizens.
If fact, the EPA recently announced they are conducting stakeholder input in an effort to initiate a national rulemaking that would establish a comprehensive program to reduce stormwater discharges from new development and redevelopment and make other regulatory improvements to strengthen its stormwater program. At a minimum the EPA intends to propose a rule to control stormwater from newly developed and redeveloped sites, and to take final action no later than November 2012.