There has been a growing trend to tighten stormwater regulations with the intent to improve the quality of our water resources. Advances in environmental sciences have made it possible to quantify and measure the impact of specific pollutants. While stormwater in Massachusetts has been treated to remove total suspended solids and oils for years now, nutrients, such as phosphorus, are the target of the latest regulations.
Phosphorus is a naturally occurring element in all living creatures, and it is found in our streams and rivers. Man-made products such as lawn fertilizers, pesticides, cleaners, oils, and auto exhaust contain high concentrations of the element. During rainstorms, these products end up in stormwater runoff and drain into nearby stormwater systems, and ultimately into our streams, rivers and lakes.
Excessive phosphorus in the Charles River has been attributed to large algae blooms, which can cause a number of water quality issues, such as eutrophication. Of particular concern are blue- green algae species, which can be toxic to humans and pets, thereby affecting the ability to use the River for recreational activities.
In compliance with the Clean Water Act (CWA), the Massachusetts Department of Environmental Protection (MADEP) has developed a list of impaired waters and determined the Total Maximum Daily Load (TMDL) of a pollutant that a water body can sustain. The TMDL outlines reduction goals of the targeted pollutant for individual communities. To achieve these goals, coordination is required with existing and proposed regulations and programs, such as the National Pollutant Discharge Elimination System (NPDES) permits program.
The Environmental Protection Agency (EPA) regulates point sources that discharge pollutants into waters of the United States through the NPDES permit program. Part of this program requires municipalities to submit applications for their stormwater discharges. To receive approval, these stormwater discharges must meet the requirements outlined in the EPA Municipal Separate Storm Sewer permit (MS4 Permit) for their specific area.
In February, 2010 the EPA issued a draft MS4 permit for the Lower Charles River with a key provision that requires all towns and cities tributary to the Lower Charles River to meet the goals to the TMDL within ten years. This requires municipalities in this area to lower their phosphorus discharges anywhere between 5.2– 65.5%. This will have a significant impact on how stormwater is collected, treated and discharged for municipalities located within areas that have higher pollutant reduction goals.
Towns and cities will have to retrofit existing stormwater management systems to meet this requirement. New development and redevelopment within these areas will be required to reduce their phosphorus discharges at a minimum to meet the goals of the TMDL. This will add cost and complexity to proposed projects.
As with most design elements, phosphorus mitigation is site-specific. Cost effective ways to treat for phosphorus include prohibiting the use of fertilizers containing phosphorus, infiltrating stormwater, and treating stormwater with rain gardens or constructed stormwater wetlands. Suburban and rural developments with adequate land area will likely be able to utilize these better management practices to treat for phosphorus. Significant additional cost may not be incurred if these strategies can be used since they are often required to meet the standards of the 2008 MADEP Stormwater Management Handbook
In the greater Boston area, where land is valuable and space is limited, a whole site – whole building design approach will be required. There is often little to no open space to treat or infiltrate stormwater prior to draining to a municipal system. When open space is available, challenges are often presented by the existing soils which frequently are comprised of urban fill and may not be suitable for infiltration. To meet the goals of the TMDL, civil engineers will have to team-up with landscape architects, mechanical and plumbing engineers, and architects to implement successful solutions. Collecting roof runoff and reusing it for irrigation, HVAC make-up water or toilet flushing can significantly reduce a site’s phosphorus discharge. Green roofs may also be a viable alternative for treatment, as well as the use of proprietary filter systems.
The EPA hasn’t stated when the MS4 permit for the Lower Charles River will be finalized. It was originally scheduled for issuance in 2010, but has been delayed due to significant public response. Some municipalities are taking a proactive approach and require new development and redevelopment projects to meet the goals of the TMDL now. When the permit is issued it will strongly alter the way we think, plan and design for stormwater management.
Elizabeth Clark is a Professional Engineer with nine years of industry experience. She works
for Beals and Thomas, Inc., where she is a project manager and lead engineer on a variety of
projects including mixed-use developments, medical and educational campus improvements,
and commercial and residential developments. She also serves as the reviewing engineer for
several Massachusetts municipalities.