An Analysis of the Boston Sewer System

At the turn of the century, Boston had one of the most advanced sewer systems in the country. Through decades of neglect and a failure to truly update the system until the 1980’s, the pollution in Boston Harbor became so bad that the harbor became a national embarrassment. The two sewer treatment plants in Boston Harbor were only equipped for primary treatment when most plants in the country were providing secondary if not tertiary treatment for their waste water. The waste from these plants was being dumped into the shallow waters of the Harbor, at the end of a relatively short outfall pipe.

Another eyesore for the Commonwealth were the eighty-one combined sewer overflows in the cities of Boston, Chelsea, Cambridge and Somerville. Combined Sewer Overflows occur when sewage flow in a combined sewer system backs up due to heavy rains or other precipitation. When the flow gets too heavy, these CSO’s act as release valves spilling excess sewage directly into Boston Harbor (MWRA website).

Not even the passage of the 1972 Clean Water Act prompted Massachusetts to clean up its act, so to speak. It was not until the city of Quincy and the Conservation Law Foundation filed law suits against Massachusetts for violations of the Clean Water Act, that the state decided to make updates to its system (Aubrey, Connor 62). The result of these lawsuits was the creation of the Massachusetts Water Resources Authority (MWRA) in late 1984. Once the MWRA took control of the sewer system changes began to be made.

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The MWRA oversaw the construction of new primary and secondary treatment plants of Deer Island, which removed the mandatory 85% of pollutants in the wastewater required by the Clean Water Act (MWRA website). They built a new 9.5 mile outfall tunnel which would dump effluent into the deep open ocean currents of Boston Harbor.

Because of these achievements, Boston Harbor began to lose its reputation as one of the most polluted harbors in the country, until it rained. When it rained, the excess sewage still spilled through the release valves, into nearby bodies of water. It was obvious that the CSO problem had to be taken care of in some form or another for the Boston Harbor cleanup project to be a success.

A little history on the Boston area sewer system is needed before getting into how the problem was and should be handled. Since the problems with Boston’s sewer system didn’t begin with the MWRA, it is necessary to look at the history of Boston’s sewer system. The system originated in 1876 when Massachusetts state legislators approved the construction of the Boston Main Drainage System (MWRA website). This drainage system was begun in 1877 and wasn’t operational until 1884. The system piped sewage from 18 cities and towns in and around Boston to Moon Island in Boston Harbor. The sewage was held in giant vats and released into the outgoing tide where it would be carried out into deeper water where it was assumed it would cause no problems.

In 1889 the Metropolitan Sewerage District (MSD) was formed (MWRA website). The purpose of this group was to oversee the construction of a regional sewer system. The system was built and continually expanded upon for years. It was looked upon as one of the best in the country since the sewage was released into the outgoing tide as opposed to just being continually dumped into the harbor like most cities at the time.

The Boston system offered no form of treatment for the sewage and as a result, by 1919, many of the areas shellfish beds were closed due to sewage pollution. In an attempt to remedy this situation, the Metropolitan District Commission (MDC) took control of the MSD. The MDC couldn’t stop the pollution and by 1933 all shellfish taken from Boston Harbor required some form of purification (MWRA website). It wasn’t until 1940 that state legislators recommended the construction of treatment plants at the three raw sewage discharge points: Moon Island, Nut Island and Deer Island.

The Nut Island Primary Wastewater Treatment Plant was the first of the plants to be built in Boston Harbor. It was completed in 1952 and treated the sewage collected from the southern Boston collection system. It was not until 1968 that Deer Islands sewage treatment plant was completed. Deer Island treated the sewage from the northern Boston collection system. With both treatment plants operational, the old holding tanks on Moon Island were to be used only in emergency situations.

With the passage of the Clean Water Act of 1972, Massachusetts found their sewer treatment plants to be sub-standard. According to the Clean Water Act, all municipal sewer systems must have primary and secondary treatment of wastewater. Moon Island, when used, had no treatment. Nut and Deer Islands had only primary treatment. Primary treatment is a settling process and secondary treatment is a microorganism facilitated process which removes more impurities by further settling (U.S. Water News Online).

Initially nothing was done to bring the plants up to speed, but in the early 1980’s when Boston Harbor was at its worst, all that changed. After the city of Quincy and the Conservation Law Foundation (CLF) both filed lawsuits against Massachusetts for violations in the Clean Water Act, the state decided to act (Aubrey, Connor 62). The Massachusetts Water Resources Authority (MWRA) was created in late 1984. The MWRA assumed control of the sewer system from the MDC in 1985.

With the creation of the MWRA came the new treatment plants and the new outfall pipe and a plan on how to deal with the CSO’s. CSO’s plague all cities with an old sewer system and Boston has one of the oldest. Parts of the sewer system in Boston, Chelsea, Cambridge and Somerville collect stormwater runoff in the same pipes that carry sewage, hence the name combined sewer. A combined sewer system is fine in dry weather when the flow can be handled by the sewer lines and sent to Deer Island for treatment.

In times of unusually high rainfall, the excess water entering the sewer from storm drains can overload the system and necessitate its release through the CSO’s into one of the following bodies of water: the Charles, Mystic, or Neponset Rivers or directly into Boston Harbor itself. As bad as these CSO’s are, they are necessary because without them in times of unusually high rainfall the sewers would back up into homes and businesses.

CSO’s are such a problem because they pollute the body of water into which they are released. CSO’s also violate various federal and state water quality stardards. The most frequent reason why Boston area beaches are closed is because of CSO discharges. Boston is not the only area hampered by CSO problems, in all there are one thousand communities in the United States trying to figure out how to solve their CSO problems in a successful and cost effective manner.

After the more immediate task of solving Boston’s main sewer treatment problems by building the new Deer Island plant, the MWRA could move on to solving the CSO dilemma. The MWRA met with the effected communities of Boston, Chelsea, Cambridge and Somerville to discuss possible solutions. In 1990 the MWRA came up with a possible solution. This solution called for the creation of huge underground storage tunnels in the bedrock under the city which would store the excess sewage until drier times when the overflow could be piped to Deer Island for treatment (CSO factsheet). This plan had worked for other communities, but the cost and complexity of such a project worried the MWRA and the citizens who would have to pay much higher rates for their sewer use to offset the estimated 1.3 billion dollar cost of the project (MWRA website).

The MWRA decided that 1.3 billion dollars was too much of a commitment to make so soon after the one billion dollars spent on the Boston Harbor plan already. In 1994 the MWRA and the four effected communities came up with another plan. This new plan would build upon present means of dealing with CSO’s and cost only 370 million dollars, only one quarter of the cost of the original plan. The 370 million dollars would cover the cost of design, construction and operation.

Under this new plan 28 different projects would be undertaken which would focus on improving the water quality in five areas in and around Boston by reducing or treating the excess sewage released by the CSO’s. The areas that would be cleaned up would be Dorchester Bay, the Neponset River, Constitution Beach in East Boston, the Charles River as well as Boston Harbor itself (CSO factsheet). These areas were chosen due to the fact that they have extensive shellfish beds or are popular recreational areas, as well as the fact that in order to clean Boston Harbor you must keep the tributaries flowing into it clean as well.

At one point there were 81 active CSO’s. Today 12 have been closed, this leaves 69 active CSO’s in the cities of Boston, Cambridge, Chelsea and Somerville (MWRA website). This means that in times of heavy rain, Boston Harbor, and the Mystic, Neponset and Charles Rivers are subject to sewer overflows.

CSO’s are clearly a major problem for the MWRA to deal with. In 1988 they unveiled a three phase plan to deal with the CSO problem. Phase I began in 1988 and was concluded in 1992. The first stage of Phase I was to improve the CSO treatment facilities, so that when sewage was released in an overflow situation it would receive at least some treatment. The second stage of Phase I was to increase Deer Island’s ability to pump sewage into the facility from surrounding sewers, so that backups would become less frequent. By 1992 there was a 55% reduction in the volume of CSO’s over the 1988 levels. Of the remaining CSO’s half of them received treatment of some sort.

Phase II began in 1992, as soon as Phase I was completed. The first part of this phase was to make low cost alterations to the CSO facilities to improve their ability to treat overflow sewage. The second part of this phase was to continue to increase Deer Island’s ability to handle larger than usual flows. The results of this phase were basically improvements over the results of Phase I. CSO volume was down another 15%, and 60% of CSO’s now received treatment.

Phase III began in 1996, while Phase II was winding down. Phase III calls for the separation of some of the combined sewers in some of the areas of heavier flow to reduce the risk of overflows during heavy rains. Two new treatment facilities will be built. The first treatment facility will be for screening and disinfection of overflows.

The other facility will be for the holding of overflow sewage until it can be given primary and secondary treatment. In addition to the two new facilities, some of the CSO facilities will be upgraded to handle the flow they receive during wet weather (MWRA website). The goals of Phase III will be accomplished by 2001. These goals will include: the closing of thirty of the eighty-one CSO’s, twelve of which have already been closed, the reduction of CSO volume by 84%, the treatment of 95% of the remaining overflow, and to reduce CSO situations to a maximum of four times per year per CSO.

So in summary of the MWRA’s CSO correction plan, by the year 2001, thirty of the eighty-one CSO’s will be closed, eleven will discharge primary treated sewage, and the remaining forty CSO’s will be reduced to less than four discharges per year (CSO factsheet). Despite the fact that CSO volume will be reduced by 84% over 1988 volumes and 95% of the remaining flow will receive some treatment, there are still problems with the Boston area CSO’s. The main problem stems from the fact that even if each of the forty remaining CSO’s only discharge once each year, that’s still forty times per year when raw sewage is released into one of the aforementioned rivers or Boston Harbor itself. Forty discharges is at the low end of the spectrum of what’s been deemed acceptable by the MWRA.

This is the main problem which has yet to be dealt with by the MWRA or anyone else. Concerning the discharge of untreated sewage from the forty operating CSO’s, I propose that instead of just releasing them into the body of water directly they should be rerouted to a form of septic tank and leaching field wherever such an action would be possible. Overflow would pass through a large underground septic tank which would remove floatables and let the heavier pollutants settle out.

The pretreated sewage would then be allowed to pass through a leaching field where it would be allowed to be naturally decontaminated and then eventually seep back into the river where it would have been dumped anyway, at least this way it could receive some sort of treatment. The CSO’s in areas where a large scale leaching field would not be plausible should at least have large underground storage tanks where the overflow could be held until it could be sent to Deer Island for treatment.

If this plan were put into effect all remaining CSO’s would receive some form of treatment, at least primary treatment. Ideally there should be no CSO’s but short of digging up and separating all 5,000 plus miles of combined sewers under the streets of Boston this would be almost impossible. Separating the sewer lines is something that will have to be done eventually due to the degradation of these sewer lines, many of which have been in place for almost a century. This would be a larger scale project than anything that the MWRA has ever attempted and would cost too much at this point in time, given the vast amounts of money that have already been spent of the Boston Harbor clean- up plan.

In detail the leaching field plan would work like this: the CSO would be rerouted to a park or forested area or even a large vacant lot where the MWRA could oversee the construction of large scale septic tanks and leaching fields. Ideally the leaching field should be near a river so that the treated overflow could seep back into the river without having to cross too many populated areas. This would achieve roughly the same amount of treatment that the CSO’s with their own primary treatment facilities would receive. In fact a leaching field would probably be better for the environment since it disinfects the wastewater naturally instead of using concentrated chlorine which ends up being dumped into the river with the overflow sewage.

In areas that are too densely populated to install leaching fields nearby, large storage tanks could be used to hold the overflow. These tanks would be double walled fiberglass with sensors installed in them to detect any leaks that may occur. When the volume of flow in the sewer lines has decreased the tanks would pump out the sewage so that it could be sent to Deer Island for sewage treatment.

Given that there are forty operational CSO’s which receive no treatment at all, this plan would have to be instituted over a span of several years. The more active CSO’s would be the first to be dealt with. By the end of the process the CSO’s that rarely discharge could be taken care of as well.

This plan is not without its flaws. It would take a lot of convincing for the towns to allow large leaching fields to be built under their feet, but in the long run it would be better that having raw sewage dumped into their rivers several times each year. The other problem facing this plan, and even the CSO’s that receive treatment is that it receives at best primary treatment followed by disinfection. It is still a violation of the Clean Water Act in principle. The Clean Water Act calls for all discharged sewage to have secondary treatment. While this plan has its faults it is still a realistic alternative to separating the 5,400 miles of combined sewers under the streets of Boston, or building many secondary treatment plants to treat the overflow at the CSO sites.