Boston Harbor Clean up

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Boston Harbor clean up

Like many harbors near cities along the eastern seaboard, the Boston Harbor in Massachusetts has been used for centuries as a receptacle for raw and partially treated sewage from the city of Boston and surrounding towns. In the late 1800s, Boston designed a sewage and stormwater collection system. This sewage system combined millions of gallons of untreated sewage from homes, schools, hospitals, factories, and other buildings with stormwater collected from streets during periods of moderate to heavy rainfall. The combined sewage and stormwater collected in the sewage system was discharged untreated to Boston Harbor on outgoing tides. Sewage from communities surrounding Boston was also piped to Boston's collection system and discharged to Boston Harbor and the major rivers leading to it: the Charles, Mystic, and Neponset Rivers. Many of the sewage pipes, tunnels, and other infrastructure built in the late 1800s and early 1900s are still in use today.

In the 1950s, the City of Boston was concerned with growing health risks of swimming in and eating shellfish harvested from Boston Harbor as well as odors and aesthetic concerns that resulted from discharging raw sewage into Harbor waters. The city built two advanced primary sewage treatment plants during the 1950s and 1960s on two islands located in Boston Harbor. The first sewage treatment plant was built on Nut Island; it treated approximately 110 million gal/per day (416 million l/per day). The second sewage treatment plant was built on Deer Island; it treated approximately 280 million gal/per day (1060 million l/per day). The two sewage treatment plants removed approximately half the total suspended solids and 25% of the biological oxygen demand found in raw sewage. The outgoing tide in Boston Harbor was still used to flush the treated wastewater and approximately 50 tons (46 metric tons) per day of sewage sludge (also called biosolids), which was produced as a byproduct of the advanced primary treatment process. The sewage sludge forms from solids in the sewage settling in the bottom of tanks.

During the 1960s, the resources devoted to maintaining the City's aging sewage system decreased. As a result, the sewage treatment plants, pipes, pump stations, tunnels, interceptors, and other key components of Boston's sewage infrastructure began to fall into disrepair. Equipment breakdowns, sewer line breaks, and other problems resulted in the discharge of raw and partially treated sewage to Boston Harbor and the rivers leading to it. During this time, the Metropolitan District Commission (MDC) was the agency responsible for sewage collection, treatment, and disposal.

In 1972, the United States Congress enacted the Clean Water Act . This was landmark legislation to improve the quality of our nation's waters. The Clean Water Act required that sewage discharged to United States waters must meet secondary treatment levels by 1977. Secondary treatment of sewage means that at least 85% of total suspended solids and 85% of biological oxygen demand is removed from sewage. Instead of working towards meeting this federal requirement, the MDC requested a waiver from this new obligation from the United States Environmental Protection Agency (EPA). In 1983, the EPA denied the waiver request. The MDC responded by modifying its waiver request to promise that the city would construct a 9.2 mi (14.8 km) outfall to achieve increased dilution of the sewage by discharging to deeper, more flushed waters. As part of its waiver, MDC also promised an end to discharging sewage sludge in the harbor and initiation of a combined sewer overflow abatement project to cease flow into Boston Harbor from 88 overflow pipes. In 1985, EPA denied the second waiver request.

During EPA's consideration of Boston's waiver request, in 1982, the City of Quincy filed a lawsuit against the MDC for violating the Clean Water Act. In 1983, the Conservation Law Foundation filed two lawsuits; one was against MDC for violating the Clean Water Act and the other was against EPA for not fully implementing the Clean Water Act by failing to get Boston to comply with the law. The Massachusetts legislature responded to these pressures by replacing the MDC with the Massachusetts Water Resources Authority (MWRA) in 1984. The MWRA was created as an independent agency with the authority to raise water and sewer rates to pay for upgrading and maintaining the collection and treatment of the region's sewage. The following year, the federal court ruled that the MWRA must come into compliance with the Clean Water Act. As a result of this ruling, the MWRA developed a list of sewage improvement projects that were necessary to upgrade the existing sewage treatment system and clean up Boston Harbor.

The Boston Harbor clean up consists of $3.4 billion worth of sewage treatment improvements that include the construction of a 1,270 million-gal/per day (4,800 million-l/per day) primary sewage treatment plant, a 1,080 million-gal/per day (4,080 million-l/per day) secondary sewage treatment plant, a dozen sewage sludge digesters, disinfection basins, a sewage screening facility, an underwater tunnel, a 9.5 mi-long (15.3 km) outfall pipe, 10 pumping stations, a sludge-to-fertilizer facility, and combined sewer overflow treatment facilities.

Today, approximately 370 million gallons/per day (1,400 million l/per day) of sewage effluent from over 2.5 million residents and businesses is discharged to Boston Harbor. Almost half the total flow is stormwater runoff from streets and groundwater infiltrating into cracked sewer pipes. The combined sewage and stormwater is moved through 5,400 mi (8,700 km) of pipes by gravity and with the help of pumps. Five of the 10 pumps have already been replaced. At least two of the pumping stations that were replaced as part of the clean up effort dated back to 1895. The sewage is pumped to Nut Island where more than 10,000 gal/per day (37,800 l/per day) of floatable pollution such as grease, oil, and plastic debris are now removed by its new sewage screening facility. The facility also removes any grit, sand, gravel, or large objects. A 4.8-mi (7.7-km) long deep-rock tunnel will be used to transport screened wastewater to Deer Island for further treatment.

One of the most significant changes that has occurred as part of the Boston Harbor clean up project is the reconstruction of Deer Island. Prior to 1989, Deer Island had prison buildings, World War II army bunkers, and an aging sewage treatment plant. All the old buildings and structures have been removed and the island has been reshaped to accommodate 12 massive sewage sludge digesters, 60 acres (24.2 ha) of a new primary sewage treatment plant, and a new secondary treatment facility. The primary sewage treatment plant has reduced the amount of suspended solids discharged to Boston Harbor from 13857 tons per day (12652 metric tons).

The secondary sewage treatment plant on Deer Island is still under construction. It will use settling tanks, as are found in primary sewage treatment plants, as well as microorganisms , which will consume organic matter in the sewage thereby increasing treatment levels. Secondary treatment of Boston's sewage will result in an increase in removal of total suspended solids from 5090% and biological oxygen demand from 2590%. The first phase of the secondary treatment plant construction was completed by the end of 1997.

After the sewage is treated and disinfected to remove any remaining pathogens (disease-causing organisms), the effluent is discharged through a 9.5 mi (15.3 km) long outfall tunnel into the waters of Massachusetts Bay. Massive tunnel boring machines were used to drill the tunnel below the ocean floor. The outfall has 55 diffuser pipes connected at right angles to it along the last 1.25 mi (2.01 km) of the outfall. The diffuser pipes will increase dispersion of the treated sewage in the receiving waters. The tunnel was opened in September of 2000.

The outfall has been a source of controversy for many residents of Cape Cod and for the users of Massachusetts Bay and the Gulf of Maine. There is concern about the long-term impact of contaminants from the treated sewage on the area, which is used for transportation , recreation , fishing, and tourism. Some alternatives to the sewage treatment plant and the 9.5-mi (15.3-km) long outfall pipe were developed by civil engineers at the Massachusetts Institute of Technology. The alternatives included modifications to the advanced primary treatment facility and a smaller secondary treatment facility with the effluent discharged to Boston Harbor. Because there was not enough evidence to convince EPA that water quality standards would always be met in the harbor, EPA rejected the alternatives.

As part of the Boston Harbor clean up, sewage sludge is no longer discharged to the harbor. Twelve sewage sludge digesters in Deer Island were constructed in 1991. The digesters break down the sewage sludge by using microorganisms such as bacteria. Different types of microorganisms are used in the sewage sludge digestion process than in the secondary treatment process. As the microorganisms consume the sewage sludge, methane gas is produced which is used for heat and power. Prior to 1991, all the sewage sludge was discharged to Boston Harbor. Since 1991, the sewage sludge has been shipped to a facility that converts the digested sewage sludge into fertilizer .

The sludge-to-fertilizer facility dewaters the sludge and uses rotating, high temperature dryers that produce fertilizer pellets with 60% organic matter, and important nutrients such as nitrogen , phosphorus , calcium, sulfur, and iron. The fertilizer is marketed in bulk and also sold as Bay State Organic, which is sold locally for use on golf courses and landscape.

This massive undertaking to clean up the harbor by upgrading its sewage treatment facilities is one of the world's largest public works projects. Over 80% of the Boston Harbor clean up is completed. These changes have resulted in measurable improvements to Boston Harbor. The harbor sustains a $10 million lobster fishery annually as well as flounder, striped bass, cod, bluefish, and smelt recreational fisheries.

[Marci L. Bortman Ph.D. ]



National Research Council. Managing Wastewater in Coastal Urban Areas. Washington DC: National Academy Press, 1993.


Aubrey, D. G., and M. S. Connor. "Boston Harbor Fallout Over the Outfall." Oceanus 36:1, (Spring 1993).

Levy, P. F. "Sewer Infrastructure: An Orphan of Our Times." Oceanus 36:1, (Spring 1993).

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Boston Harbor Clean up

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