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Boston, MA

Boston’s Overflowing Problem

Problem:

Massachusetts receives about 45 inches of precipitation annually (Charles River Watershed Association). For a better perspective of volume (storm water generated), a one-acre parking lot will generate 27,000 gallons of storm water after one inch of rain (EPA). A naturally functioning ecosystem typically filters half of the local rainfall in the ground, while the other half turns into water vapor (Charles River Watershed Associated). Boston, well over half of all precipitation becomes polluted storm water leading to many combined sewer and sanitary systems over flowing directly into local water bodies (Charles River Watershed Association). The volume of storm water entering Boston’s combined sewer and sanitary systems is more than the system was intended to process during major storm events. With peak volume control methods that highlight water retention, evaporation, and infiltration, Boston can construct an environment that mimics a naturally functioning ecosystem.

Associated Risk:

The ‘superbug’ MRSA is now being found in U.S. wastewater treatment plants (Public Works). A University of Maryland study was conducted at two Mid-Atlantic and two Mid-Western WWTPs. Studies confirmed that MRSA was present in 83% of the influent (raw sewage) at all plants. Having these and other pathogens entering the waterways through the overflow of untreated sewage leads to increased public health risks. In addition to the public health risks, the Coastal Zoning Management Act identifies Urban Runoff as one of the five major types of non-point source pollution contributing to environmental risks (EPA). Urban waste-water run off pollution includes:

  • Sediment
  • Oil, grease and toxic chemicals from motor vehicles
  • Pesticides and nutrients from lawns and gardens
  • Viruses, bacteria and nutrients from pet waste and septic systems
  • Road salts
  • Heavy metals from roof shingles, motor vehicles and other sources
  • Thermal pollution from dark impervious surfaces such as streets and rooftops

A Possible Boston Mitigation Solution: Gravel Wetlands

Gravel wetlands are structurally refined by a thin layer of wetland soil that supports a thick vegetative cover. The supportive layer of gravel below functions as a median where algae and microbes grow. Gravel Wetlands are productive on a biological, chemical, and physical level. The forebay with in the Gravel Wetland design is required to remove at least 50% of the total suspended solids, aiding in a physical reduction of pollutants prior to even entering the gravel wetland, where further filtration occurs (NJ Storm Water Management). Vegetation concentrates unwanted chemicals that are absorbed from the passing water, while supporting a biologically rich wetland habitat.

Design Criteria for Gravel Wetlands
Wetland Design Feature Size
Minimum wetland soil depth 8 inches
Minimum pea gravel depth 3 inches
Minimum crushed stone depth 24 inches
Minimum distance flow length in gravel substrate cell 15 ft (for each cell)
Drain time of wetlands cells 30 to 48 hours
Forebay Volume 10% of WQV
Temporary Wetlands Volume (Per Cell) 50% of WQV
Distance of outlet invert above bottom of wetland soil  4 inches

(NJ Storm Water)

Mitigation Effectiveness

High pollutant removal efficiencies are one of the major benefits of constructed storm water subsurface gravel wetlands. Properly designed gravel wetlands can be very effective at eliminating many pollutants that are of concern in the Charles River watershed:

– Total Suspended Solids: 98% – 100%

– Total Phosphorus: 32% – 88%

– Gravel wetlands reduce peak flows by 77% – 85%

As stated previously, peak flow is the largest contributing factor to our waste-water treatment plants overflowing. Boston is desperately seeking solutions to slow down peak rates by methods of retention and infiltration. While both methods are most effectively used in coordination, retention will specifically aid in reducing peak flows immediately after storms.

NJDEP

from NJDEP

 

 

 

 

 

 

 

 

 

 

 

 

 

Sources:

1) Public Works “UMD-led study identifies ‘Superbug’ MRSA in U.S. wastewater treatment plants .” Public Works 12 Nov. 2012: 1-4. Print.

2) “Charles River Watershed Association.” Charles River Watershed Association. Web. 17 Apr. 2013. Stable URL: http://www.crwa.org

3) “Coastal Zone Management Act (CZMA) | Agriculture | US EPA.” US Environmental Protection Agency. Web. 17 April. 2013. Stable URL: http://www.epa.gov/oecaagct/lzma.html

4) ” Home | City of Johnson City, TN.” Home | City of Johnson City, TN. Web. 18 Apr. 2013. Stable URL: http://www.johnsoncitytn.org/

5) “NJDEP New Jersey Department of Environmental Protection.” NJDEP New Jersey Department of Environmental Protection. Web. 18 Apr. 2013. Stable URL: http://www.njstormwater.org

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