Plan Would Cut Sewage Overflow By 75%

Liana Teixeira PhotoThirty-six million gallons of dirty water poured into the West River last year. That’s not as bad as engineers predicted—and they have a plan to do way better than that.

Officials from the Water Pollution Control Authority (WPCA) detailed that plan in a public meeting Thursday night at Truman School. The plan aims to reduce the amount of storm and waste water by 75 percent by filling sewer pipes to capacity.

The plan is part of a larger $450 million long-term plan to prepare for super storms and to send less sewage into the Quinnipiac, Mill, and West rivers and Long Island Sound. The long-term plan includes $50 million in upgrades to the East Shore water treatment plant.

The Discovery

At Thursday’s meeting, WPCA Engineering Director Tom Sgroi and two engineers from CH2MHill, Eric Muir and Dingfang Liu, detailed how they believe they can stop more yucky water from entering West River. That belief is based on a discovery that the sewers along West River at Whalley, Derby, Legion and Orange Avenues can handle much more sewage than they currently are.

The discovery is based on a recent study. The WPCA in 2012 installed flow meters at all of the places where storm and waste water—called “combined sewer overflow (CSO)”—enters the West River. The meters reported that 35.8 million gallons of CSO poured into the river in 2013. That’s far less than the 127 million gallons that had been predicted based on a 2008 model.

The estimate was far off base because the model officials used to predict the sewage flow was not very sophisticated, said Liu (pictured).

“The backbone of that model was constructed in early 2000s,” he said. The computers available back then came from the “dinosaur age” compared to the powerful computers available today.

The old model required extensive resources to keep a detailed and accurate record of geographic information, Liu continued. It meant people needed to go to hundreds – sometimes thousands – of manholes, pop them open and measure how deep each manhole was. That wasn’t always possible.

If not enough information was gathered, or there wasn’t a budget to measure them all, only a small sample was made available. Having an insufficient sample size can make all the difference, Liu said.

“Until 2012, we thought that was the reality because that’s all we had,” Sgroi said. Now, with the meters in, engineers can monitor CSOs in real time.

A New Plan

After discovering only a fraction of the predicted amount of sewage was actually reaching West River, Sgroi concluded that the pipes could take on much more storm and waste water before reaching capacity.

The WPCA hired consulting firm CH2MHill to prepare an abatement study of the Boulevard trunk sewer, at the intersection between Ella T. Grasso Boulevard and Orange Avenue, to see what modifications could be made to the existing infrastructure.

And then, everything fell into place. “It’s like we got that ‘aha’ moment,” Sgroi said.

By using the Sept. 28, 2012, storm as a model, the study determined that the pipes are able to handle more storm water than previously thought. They found that, during some storms, the pipes completely filled up and beyond the manholes, but didn’t create any sewer backups.

This means the weirs – barriers designed to redirect excess water to West River after reaching approximately 70 percent capacity – could be raised to 100 percent capacity. With higher barriers, more dirty water goes down the sewage pipe, and less dumps into the West River, said Sgroi.

Sgroi proposed raising the weirs at four spots along the West River so that more sewage stays in the pipes.

Muir said this could potentially result in a 75 percent reduction of CSO volume and 90 percent reduction in the number of times sewage flows into the West River. Until the new weirs can be installed and tested, however, these are simply projections.

To secure the $5 million needed to raise the weirs, the WPCA only needs approval from the state Department of Energy and Environmental Protection (DEEP). Half of the money would come from the DEEP and the other half from a 2 percent interest loan shared by the WPCA and the city. The WPCA would be responsible for paying 60 percent of that loan, and the city 40 percent.

Sgroi said the WPCA is still completing its study of West River; it should be done by the end of summer. After the formal request is made, the DEEP usually takes about six months to make a decision, Sgroi estimated. Then the WPCA would design the project and put it out to bid. If everything goes according to plan, construction should begin around 2016.

A confident Sgroi said he doesn’t foresee there being many problems with the DEEP request. “It’s on their priority list,” he said.

“We want to go forward and actually start constructing this so we can immediately have big gains and see big reductions in CSOs,” Sgroi said.

No More Salt In Parking Lots?

Liu also introduced some options of “green” infrastructure for the West River area that could further reduce CSO overflow.

Ideas included redirecting runoff storm water to tree pits, grass swales, wetlands and wetponds, and a green roof.

Liu also suggested porous pavement areas. When it rains on these lots, the water seeps into the soil, he said, leaving the pavement relatively dry at all times. City officials and attendees raised a skeptical eye to Liu’s additional claim that salt would no longer be needed in the winter to thaw away the multiple feet of ice and snow that typically accumulate in those lots.

Liu clarified that these projects can only work in areas that have good soil and groundwater suitability.

“Can we put it in here? We’ll have to find out,” he said. “If the condition is right, we can build it here.”

Liu’s model represents yet another push for “green” infrastructure around town this year. In January, the WPCA unveiled a $13 million green sewer project in East Rock. The project, slated to be completed by 2015, would add a mile of new storm water drainage pipes, 37 manholes and 24 new catch basins, 300 feet of pervious concrete sidewalk, and seven “bioswales,” or landscaped drainage courses.

Sgroi said the WPCA put in a $1 million request for green infrastructure on the next DEEP priority list, but isn’t sure how they will react since this is the first time the DEEP has reserved money specifically for green infrastructure projects.

Tags: , ,

Post a Comment

Commenting has closed for this entry


posted by: Interesting thought on June 10, 2014  1:42pm

And to think, people always fish on the banks of the West River! YUCK!