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It began with the infamous Tea Party of 1773, and the citizens of Boston,
Massachusetts, have been pouring their waste into the sea ever since. Now
Boston Harbour, labelled ‘the dirtiest harbour in America’ during the 1988
presidential campaign, is due for a change. More than 1000 construction
workers are building what will be the US’s largest single sewage works.
Most large American cities spread sewage treatment around several sites,
but Boston is building a single massive plant that will serve 2 million
people in the metropolitan area. When completed in 1999, it will cover most
of the 84-hectare Deer Island in Boston Harbour.

Meanwhile, the island’s 24-year-old plant processes an average of 1.1
million cubic metres of sewage a day, and sends its effluent roaring into
the harbour in a veritable waterfall. A plant on Nut Island contributes
a further 570 000 cubic metres. The old Deer Island works will be demolished
once the first half of a new primary treatment works begins operating in
mid-1994. The second half will come on stream in mid-1995, as waste water
starts being piped through a 15-kilometre tunnel into the middle of Massachusetts
Bay (see Diagram 1). Planners hope the combination of better treatment,
and greater dilution in more open water, will ease the pollution.

Boston Harbour’s awful reputation derives from quirks of geography.
Enclosed by islands and the curve of the coastline, it has an area of 130
square kilometres and is fed by the Charles River, together with the smaller
Mystic, Chelsea and Neponset Rivers. Together they deliver an average of
18 cubic metres of water per second to the harbour. Thus the 20 cubic metres
per second from the two existing Massachusetts Water Resources Authority
(MWRA) sewage plants represents over half the ‘fresh water’ input to the
harbour. To make matters worse, the rivers drain urban and suburban areas,
and so are themselves somewhat polluted. The shallow harbour – on average
only 5.8 metres deep – is protected from coastal currents, leaving only
the 2.7-metre tide to flush it out. A single tidal cycle replaces about
17 per cent of the harbour water.

Engineers initially sought to take advantage of the harbour’s tidal
flushing when they built Boston’s sewer systems, between 1876 and 1904.
The sewers collected sewage and storm runoff and discharged it, untreated,
into the harbour at Deer Island, Nut Island and Moon Island. It was considered
a good system a century ago. The city won an international award for what
then seemed like a good idea – dumping sewage on the outgoing tide. But
much of it washed back on the next high tide.

STARTING THE TREATMENT

It was many years before the city began to treat its sewage. The Metropolitan
District Commission (MDC), which took over the sewers in 1919, began operating
primary treatment plants on Nut Island in 1952 and on Deer Island in 1968.
Such plants are supposed to remove heavier solids by letting them settle
as ‘sludge’ from raw sewage before the liquid is discharged. This is supposed
to remove sewage solids. However, Boston simply let the sludge sit while
bacteria decomposed some of the wastes, then discharged it into the harbour.
The result was not a great improvement.

The cash-strapped MDC had other problems, such as poor maintenance work
and the fact that storm water channelled into the sewers can easily overload
the sewage plants. Nut Island already handles on average one-third more
than the 420 000 cubic metres of sewage a day that it was designed for,
which reduces the settling time for sewage. The existing Deer Island plant
is running at 85 per cent of its capacity of 1.3 million cubic metres per
day. When storms overload the plants, sewage pours into the harbour with
little or no treatment.

All America’s big coastal cities have, at some time, faced similar problems.
Before the Clean Water Act of 1972, many American coastal cities, such as
Los Angeles, Miami and Seattle, dumped sewage into the ocean with little
or no treatment. But while they cleaned up, Boston dragged its feet. Neither
the public nor leading politicians seemed to care. It took a pair of lawsuits
– filed in 1982 and 1983, respectively by the city solicitor of Quincy,
Boston’s neighbour to the south, and the Conservation Law Foundation – to
force action.

The delay proved costly. The administration led by Ronald Reagan in
the early 1980s virtually eliminated the federal programmes that had financed
new sewage plants in many other cities. By the end of 1984, when the courts
pronounced judgment, it was clear that Boston would have to pay for the
cleanup itself. The courts forced the state of Massachusetts to create the
water resources authority to operate the water supply and sewers in the
Boston area. Unlike most goverment agencies, the MWRA can borrow money and
set water rates without reference to the state legislature.

The ability to raise money was essential. As well as a water and sewer
system, the new authority inherited lawsuits on water quality. By the end
of 1985, it had a court-imposed schedule for cleaning up the harbour. The
details have changed, but the overall approach is still to improve existing
systems while building new primary and secondary treatment plants. By the
year 2000, the bill will total about $4 billion, most of it coming from
the MWRA’s customers. Average annual bills for a family of four have nearly
quadrupled since 1985 to $535 now.

The first step was to stop discharging the scum – grease, plastics and
other floating debris – from the primary treatment tanks into the harbour.
In December 1988, the MWRA began mixing scum from Deer Island with cement
dust and sending it to a landfill; scum from Nut Island followed in 1989.
Both plants were overhauled. Work began on limiting discharges of raw sewage
caused by storm water overloads. Checks of the system found many illegal
(though often not intentionally so) connections of sewers to storm drains.

The MWRA began an aggressive campaign to keep toxic wastes out of sewers,
both by seeking the cooperation of industry and by enforcing state and federal
regulations. This cut discharges of nine heavy metals (specifically cadmium,
copper, chromium, lead, mercury, molybdenum, nickel, silver and zinc) from
1369 kilograms per day in 1984 to 312 kilograms per day in 1992, most of
the decrease coming through industrial controls.

TOXIC WASTE DOWN THE KITCHEN SINK

In 1992 the authority also collected nearly half a million dollars in
fines. But households remain one of the hardest sources to control. The
MWRA estimates that households now produce between 25 and 30 per cent of
the copper, zinc and petroleum hydrocarbons in sewage, 25 per cent of surfactants
(from detergents and soaps) and 30 to 50 per cent of lead.

Meanwhile, construction work was beginning. The first big project was
a plant on the site of an old shipyard at Quincy to dry sludge. Heating
sludge for 30 minutes at 380 °C kills pathogens and produces three-millimetre
pellets that meet federal and state standards for fertilising arable land,
though it contains too much molybdenum to be used on grazing land in Massachusetts.
On completion of the first stage of the Quincy plant last December, the
MWRA was able to stop dumping sludge into the harbour.

The new Deer Island primary treatment plant will use conventional settling
tanks built in pairs, one on top of the other, to make the most of the land
available. As well as the wastes that were previously pumped to the old
Deer Island plant, they will receive sewage from Nut Island through a 3.4-metre,
8-kilometre tunnel to be bored under Boston Harbour. Work on the secondary
treatment plant begins in January. Part of it will be built on the site
of the existing Deer Island works, so construction of this part of the secondary
plant cannot start until after 1994, when the new primary plant is operating
and the old one is demolished.

The scale of the new plant troubles some observers. Its daily capacity
of up to 4.9 million cubic metres makes it the largest in the US. This is
dictated not by the size of population being served, but by the large amounts
of storm runoff and ground water carried by local sewers. Sewage engineers
usually allow for about 0.4 cubic metres of waste from each resident. But
in Boston, the additional flow from storm drains and ground-water leakage
means that the MWRA’s 2 million customers generate an average daily flow
of 1.7 million cubic metres rather than the 0.8 million cubic metres the
rule of thumb suggests. The new plant has a capacity of nearly three times
the average in order to handle the peak extra flow during storms.

ENGINEERING ON A GIANT SCALE

But rather than trying to handle such large volumes of sewage, wouldn’t
it be better to keep ground water and storm water out of the sewage? Anne
Blackburn of the Charles River Watershed Association, a conservation group
based in Newton, on the western edge of Boston, suggests that the Boston
Water and Sewer Commission should improve sewer maintenance and crack down
on illegal sewer connections.

Diverting storm runoff that now mixes with sewage could also make smaller
plants feasible. Blackburn suggests that the MWRA may be building the Deer
Island works because it is more secure with old-time giant-scale engineering.
However, Mike Connor, the MWRA’s director of environmental quality, says
rebuilding the sewer system would be impractically expensive in densely
developed older parts of Boston.

In mid-October contractors started drilling the outfall pipe, a 7.3-metre
concrete-lined tunnel that will stretch through 15 kilometres of solid rock
from Deer Island into Massachusetts Bay. The $279 million project (of which
$77 million is for the diffusers through which sewage will enter the sea)
is the largest of its kind in the US. Its design reflects a traditional
assumption of sewer engineers – that dilution can solve pollution problems.
By that reasoning, if Boston Harbour can’t absorb Boston’s sewage, it should
be pumped further out, into the deeper waters of Massachusetts Bay.

WATERING DOWN WASTE

The existing Deer and Nut Island plants pump sewage into harbour water
just 3 metres deep, diluting the effluent by only 10 to 1. Engineers expect
that by going further out to sea and spreading diffusers over a large area,
they will get 200 to 1 dilution, and that the stronger ocean currents will
diffuse the wastes better than the quiet harbour waters.

However, critics are uneasy about the tunnel. ‘Trying to put something
further away does not solve the problem. Remember smokestacks,’ says Mary
Loebig, head of the Stop the Outfall Pipe (STOP) campaign, based on Cape
Cod, the tip of which is some 60 kilometres to the southeast of the outfall.
The US Environmental Protection Agency rejected a similar scheme proposed
by the old MDC in 1979 because it would have carried sewage that had only
received primary treatment at Deer and Nut Islands. The MWRA concedes it
is looking at alternatives to building the second half of the secondary
treatment plant, and critics remain worried that the MWRA may try to avoid
secondary treatment, or may not be able to afford it.

It was concern about effects of the outfall in Massachusetts Bay and
in Cape Cod Bay to the south that prompted the formation of STOP. The protest
group wants the MWRA to finish its secondary treatment plants before starting
discharges into the bay. ‘Why waste the money on transporting pollution
elsewhere, when that money can better be spent on treatment and source reduction?’
asks Loebig.

MWRA officials are confident that sewage from the new outfall pipe will
not foul Cape Cod beaches. However, STOP is far more concerned about more
subtle effects of the effluent, including the addition of sewage nutrients
to the ocean and possible toxic contamination. Both STOP and the MWRA have
sponsored scientific studies, but important uncertainties and disagreements
remain. Little is known about the ecology that supports the endangered whales
which use the bay as a seasonal feeding ground, and there are concerns that
nutrients from the outfall pipe might encourage blooms of toxic algae. There
is also the possibility that the nutrients might prompt algae and bacteria
to grow so much that they use up the oxygen which marine animals need to
survive .

Removing nutrients after secondary treatment is therefore desirable,
but it is not easy. Many cities use tertiary treatment to remove phosphorus
from effluent discharged to fresh water. But the nitrogen that poses a problem
in marine waters is harder to remove. Methods designed to remove 65 to 75
per cent of it from effluent are being tested at two plants discharging
into Long Island Sound, northeast of New York City, where oxygen depletion
is already a problem, but the results are not yet in.

Despite uncertainties about the effects of effluent on Boston Harbour
or of its possible effects on Massachusetts Bay, some environmentalists
are keen for the Deer Island project to go ahead. ‘We can’t wait forever,’
says Robert Buchsbaum, a coastal ecologist for the Massachusetts Audubon
Society. ‘Someone had to make a reasonable decision about Boston Harbour
based on existing technical understanding.’ Stopping sludge dumping has
already improved the appearance of the harbour, and bacteria counts are
down. Connor says that a few more years are needed to assess any resulting
changes on the seabed. Two severe storms in autumn 1991 have left their
mark, and the lack of historical data on water quality in the harbour makes
comparisons hard.

Those in favour of the Deer Island project include Peter Shelley of
the Conservation Law Foundation in Boston, the body which helped push the
legal action that led to the harbour project. He sees the complaints coming
from all sides as signs of a viable compromise. ‘I think it’s a good project,’
he says, ‘and it’s going to work.’

* * *

1: Three steps to sewage treatment

Initial screening removes large objects such as branches of trees; they
are taken for landfill.

Primary treatment involves physical processes to remove solids. In the
grit chamber, sand and grit settle out and are removed for landfill. In
the sedimentation tank, waste water sits for about an hour. Solids settle
to the bottom as sludge; grease and plastics float in a scum that can be
skimmed off and sent for landfill. Sludge, which contains a lot of water,
is removed to the digester. Liquid effluent goes to secondary treatment
(though at present it goes straight into Boston Harbour).

Primary treatment removes about 60 per cent of solids, up to 40 per
cent of toxic substances, and reduces the amount of organic matter – and
hence biochemical oxygen demand – by 35 per cent.

Secondary treatment follows. In the aeration tank, oxygen is added to
the waste water for about two hours to encourage growth of microorganisms
which consume dissolved wastes. In the sedimentation tank, water from the
aeration tank sits long enough for microbes and solids to settle as sludge.
Some of the sludge is recycled to the aeration tank; the rest is sent to
sludge digesters, where chemicals are added to thicken it, after which it
is pumped into tanks and left for 10 to 22 days.

Anaerobic bacteria decompose the solids, compacting them by up to 45
per cent and reducing counts of bacteria that caused odour and disease.
The process produces methane, which can be burnt as fuel. After digestion,
the sludge is dewatered by being forced through filters which capture
the solids, and the liquid is pressed out, leaving ‘sludge cake’. This
is dried in an oven at 380 °C, producing pellets that can be used as
fertiliser.

Together, primary and secondary treatment remove about 90 per cent of
solids, 50 to 85 per cent of toxic materials and reduce biochemical oxygen
demand by 90 per cent. During disinfection, effluent from the sedimentation
tank is dosed with disinfectant to kill any harmful organisms. Chlorine
and sodium hypochlorite are common disinfectants, but in some areas chlorine
must be removed before the wastes are discharged. An alternative disinfectant
is a combination of ozone and ultraviolet light.

Tertiary treatment removes nutrients such as phosphates and nitrogen
compounds, which remain after secondary treatment and can promote excessive
growth of algae and plants. Phosphates are typically removed chemically
when sewage is released to sensitive fresh water. Processes for nitrogen
removal are still at the experimental stage. Neither process is planned
for the Boston Harbour project.

* * *

2: Feeding the ocean to death

Just as excess phosphates can cause problems in fresh water, excess
nitrogen can overstimulate the growth of algae and marine plants. Decay
of dead algae and plant matter then can deplete the water of oxygen, turning
it into a putrid green or brown broth devoid of oxygen-consuming animals.
This problem, called eutrophication, is best known in polluted ponds and
slow-moving streams. The fate of nitrogen compounds entering Boston Harbour
is unclear. In a study for the pressure group Stop The Outfall Pipe, John
Christensen of Oceanic Associates in Brunswick, Maine, found that in the
harbour, sediments may remove half to three-quarters of the nitrogen compounds
in sewage before the water escapes into Massachusetts Bay. If he is right,
the outfall pipe would dramatically increase the amount of nitrogen delivered
to the bay. However, in a study sponsored by the Massachusetts Water Resources
Authority, Anne Giblin of the Marine Biological Laboratory in Woods Hole
found that no more than 15 per cent of the nitrogen entering the harbour
was released as gas. This implies, she says, that most of the nitrogen compounds
released in the harbour already reach the bay, so the outfall pipe will
not make much difference.

The distribution of nutrients is also an issue. Sewage nutrients do
increase algal growth in Boston Harbour, but tidal mixing of the shallow
water keeps oxygen levels high, Christensen says. In contrast, the deeper
waters of Massachusetts Bay are stratified, making lower layers more vulnerable
to oxygen depletion as they receive little oxygen input from the air.

Opponents of the outfall worry that oxygen depletion or toxic wastes
could threaten the rich Stellwagen Bank north of Cape Cod, which was declared
a National Marine Sanctuary on 6 November, and the adjacent Stellwagen Basin.
Stellwagen Bank is a favourite feeding ground for whales: right whales,
humpbacks and fin whales are among the seven endangered species which inhabit
the bay for part of the year. Cape Cod Bay is a winter courting ground and
feeding area for the North Atlantic right whales, of which only about 350
remain. They feed on plankton, but too few details are known to predict
how the outfall might affect them, says Charles Mayo of the Center for Coastal
Studies in Provincetown, Massachusetts. He urges that discharges into the
bay should not start until the ecosystem is better understood.

Another uncertainty is the effect of the outfall on ‘red tide’ blooms
of toxic algae. Shellfish that have eaten the algae cause paralytic poisoning
when eaten by humans. Red tides are becoming more common along the Massachusetts
coast. The algae appear to be carried to Massachusetts Bay from northern
waters, by currents which pass near the region where the outfall is located.
Don Anderson of the Woods Hole Oceanographic Institution says that nutrients
might enhance growth of the toxic organisms – but adds that no one really
knows for sure.