Tunnel Vision

Wastewater agency’s sweeping CSO abatement project keeping Narragansett Bay cleaner
Tunnel Vision
Workers lower ventilation components into the Deep Rock Tunnel during construction. As the tunnel boring progressed, necessary utilities such as electricity and fresh air also had to be built forward.

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Combined sewer overflows were once a regular headache for the wastewater treatment operators and the residents living around Narragansett Bay in Rhode Island, but thanks to an aggressive program that combined capital investment and changes in procedure, they are becoming a thing of the past.

CSOs haven’t been eliminated entirely, but they’ve diminished considerably, says Ray Marshall, executive director of the Narragansett Bay Commission. There’s room for even more improvement, but the benefits have been readily apparent — fewer beach closings on the bay and fewer disruptions in the busy shellfishing industry in the waters to the south. Not to mention reduced threats to health and safety.

Marshall gives the credit to the commission’s Combined Sewer Overflow Abatement Plan that was begun in 2001 after a decade of planning. An ongoing monitoring program helps keep the effort sharp. And thanks to extensive communication going all the way back to the project’s planning stages, it’s enjoyed support from the people who count most — the ratepayers whose sewer bills bear the program’s cost.

“We enjoy a very positive reputation,” Marshall says. “Quite a few of the political figures in the state have made it a point to come down and see our facility.”


Urban utility

The Narragansett Bay Commission is a regional authority divided into two separate service districts, each served by its own treatment plant. The Field’s Point service district includes the City of Providence and the communities of Johnston and North Providence to the northwest of the bay as well as a small segment of the Town of Lincoln. The Bucklin Point district ranges north along the eastern shore of the bay, from East Providence up through Pawtucket and Central Falls and on to the rest of Lincoln and Cumberland.

Altogether the commission serves some 360,000 people, about one third of the state’s population of 1.1 million, and covers about a fifth of the state’s acreage — the urban and industrial portion, says Marshall. It controls about 110 miles of interceptor pipes and the associated control regulators. Some 1,200 or more miles of laterals owned by the communities the commission serves send sewage through the commission’s pipes and to its treatment plants.

But about 40 percent of the area the commission serves uses combined sanitary/storm sewer systems, Marshall says. Historically, heavy storms brought significant sewage overflows as the pipes normally conveying effluent filled with rainwater.

Those overflows regularly put the commission in violation of the federal Clean Water Act, and in recent years, Marshall notes, “the bar keeps getting raised higher and higher” as regulations become more stringent.


Shellfishing impact

Sewer overflows hold a special hazard for Narragansett Bay. The bay is a prime site for shellfishermen targeting hard-shell quahog and soft-shell steamer clams. Shellfishing is both a commercial industry and a pastime for local residents and tourists. After every overflow, however, fishing must be shut down until sampling tests establish that the water in the bay is clean again. That’s been as long as seven days at a stretch, says Marshall.

In the early 1990s, the commission agreed with the Rhode Island Department of Environmental Management to develop a comprehensive abatement plan for overflows. Separating all of the combined sewers — “the deepest pipe in any street” — would have created huge disruptions, especially in commercial districts, and so was ruled out. Instead, the agency planned to build a series of underground storage tanks and tunnels.

That plan evolved over subsequent years in response to changing federal rules, and in 1997, the commission narrowed a list of more than 16 options to three, presenting them to a stakeholders advisory group representing utility ratepayers, business owners, environmentalists, shellfishermen and the general public.

Besides the original plan, the advisors also considered a plan to build 19 smaller satellite treatment plants at overflow sites to intercept and immediately treat effluent that would otherwise be dumped in the lake. “That never won widespread support,” Marshall says; the additional plants would have required additional personnel — and no one wanted them built in their neighborhoods.


Three-phase project

The advisors favored a different alternative: constructing six miles of underground storage tunnels to serve as holding tanks for water that rapidly accumulates during storms, along with several other related projects.

“The Deep Rock Tunnel is the centerpiece of an entire three-phase program,” Marshall says.

Phase 1 of the Combined Sewer Overflow Abatement Plan includes the first tunnel, which serves the Field’s Point district, and related projects. Begun in 2001, the $350 million initial phase was completed and its components put into use in 2008. Phase 2, priced at $245 million, is now beginning. According to Bay Commission chief environmental engineer Phil Albert, this phase consists of another dozen contractors building long interceptor lines to connect overflow points with the tunnel. It also includes creation of a wetlands treatment system to treat overflow after screening and settling of effluent in one area, Marshall says, along with 12 sewer-separation projects in the City of Providence.

Phase 3 will be to build a second deep rock tunnel in the Bucklin Point district about the same size as the Field Point district tunnel.

“The whole thing should be done by 2021,” says Marshall.

The cost of the project is being financed through the Rhode Island Clean Water Finance Agency, which allows for a 33 percent discount on interest rates. Debt service costs are applied to ratepayers’ bills.


Concrete results

Since they came online in 2008, the first tunnel and other abatement measures have captured 3.5 billion gallons of sewer overflow. Of that, 90 percent has received full secondary treatment, and 10 percent has been treated in the commission’s wet-weather facilities — a treatment plant within the treatment plant — where it gets primary treatment plus chlorination.

“We’ve treated an extra 100 million gallons of flow per month since that tunnel has been online,” Marshall says.

Once the entire project is completed in the next decade, the commission expects the number of overflows to drop to four per year from about 30 per year before any of the work began. But already results are showing.

Before the abatement project, Marshall says, those 30 “rain events” per year led authorities to shut down shellfishing beds in the southern portion of the bay for as many as 200 days — more than half the year.

Now, closures of the shellfish beds have dropped to fewer than 10 over the two-year period of 2009-2010. And instead of lasting seven days at a time, the commission’s sampling has found the water to be clean enough after as few as four or five days. That has allowed the beds to be reopened sooner. In fact, the findings have led the state environmental and health departments to revise the criteria for halting shellfishing.

“Historically, once half an inch of rain falls they assume there have been overflows,” Marshall explains. The state would automatically order a 5,500-acre shellfish bed area closed. After another half-inch of rain — meaning an inch total — the state would shut down a second 4,500-acre area. Now the standard for when to shut down the beds has risen: the first area isn’t shut until there have been eight-tenths of an inch, and the second not until there’s been a total of 1.5 inches.

In the upper part of Narragansett Bay, the number of pollution-related beach closings was down 36 percent in 2010 (the most recent year available) compared with four years earlier, and the number of days lost to closures was down by 73 percent. The beach closest to a commission treatment plant — Conimicut Beach — was closed just eight days in 2010, compared with 45 days in 2006.

“The tunnel and the combined sewer overflow facilities overall are doing their job, and we’re able to document that by the water-quality monitoring that’s being done and by the results that we’re seeing,” Marshall says.


Monitoring and maintenance

Additional elements of the commission’s effort include monitoring and preventive maintenance, with commission employees handling general maintenance and outside contractors filling in on specialty tasks such as video inspections and cleanings. Meg Goulet, who manages the maintenance program for the agency, notes that some of the lines are a century old.

Working from a comprehensive set of inspection and maintenance data, Goulet and her staff are ranking the conditions of the entire network, scheduling maintenance and other projects, including lining sewers, reconfiguring manholes, and dig-and-replace repairs where necessary.

A regular program of monitoring water quality is overseen by Tom Uva, director of Planning, Policy, and Regulation for the Bay Commission. That includes sampling rivers upstream and downstream of combined sewer overflow points to see if blockages are creating overflows in dry weather. It also includes weekly trips around the bay itself in a 23-foot boat that samples water and conducts surface mapping. A pair of stationary water-quality sensors continually check for temperature, salinity, dissolved oxygen, pH, chlorophyll and water clarity as well. And when extreme weather hits, “we’re out there monitoring it,” Uva says.


Good business and goodwill

Besides simply being the right and necessary thing to ensure that treatment and collection systems are operating at peak efficiency, there’s self-interest in monitoring, Uva notes. With federal and state regulators requiring treatment operators to reduce nitrogen loadings in discharge, it’s important to get data that shows whether the treatment operation is actually the nitrogen source — or if it’s coming from elsewhere.

“The monitoring program like this really protects your ratepayers,” Uva says.

Altogether, the commission’s laboratory analyzes 110,000 samples per year, including 26,000 directly collected by the monitoring program. Urban rivers are sampled twice weekly for bacteria, for example.

Efforts like these have drawn industry recognition. Phase 1 of the CSO abatement project was awarded Project of the Year by the Underground Construction Association for 2009. Both the CSO abatement project and the water monitoring program were cited when the National Association of Clean Water Agencies gave the Bay Commission its Excellence in Management Recognition award in 2011 — the third time in 10 years the agency has received the designation.

Support remains strong close to home as well, Marshall says. “I think the stakeholders group that we had back in the mid- to late-90s is the reason why,” he says. “We let people take part — it wasn’t run by a bunch of engineers. People felt like they had some say.”

Well on its way to its goal of sharply reducing overflows, the Narragansett Bay Commission seems likely to maintain that goodwill — and keep earning kudos as well.


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