Sewer Commission Will Now Reconcile Results Of Five Different Scenarios
By: Brian Kehrl
The results were flipped this time in the second round of analysis of the townwide wastewater treatment scenarios prepared for the Mashpee Sewer Commission.
The first report of whether different sewer models would remove enough nitrogen from Popponesset Bay to meet environmental regulations, which were first presented last month, showed that only an alternative approach using mostly small wastewater treatment plants scattered around town would meet all of the benchmarks.
But the second report, unveiled at the sewer commission meeting on Tuesday, for the same scenarios showed that the cluster approach did not meet any of the benchmarks in Waquoit Bay, while a more traditional model came closest to meeting them.
The new figures, though they complicate any conclusions on which approach is the most effective, were reassuring to sewer commission Chairman F. Thomas Fudala. “The good news is that for all the watersheds at least one of the scenarios meets the targets,” he said. “So if we mash them together in the right way, we know we can make it.”
The nitrogen-removal targets are set by state and federal clean water regulations to restore the bay ecosystems to a condition in which they can support eelgrass and organisms that live in the sediment. Mashpee and most other towns on Cape Cod are required to lower nitrogen levels, a process that will be driven primarily by expanding wastewater treatment beyond the septic systems that most properties currently use.
The analysis, presented Tuesday evening by representatives of the School of Marine Science and Technology at the University of Massachusetts Dartmouth, reviewed five total scenarios proposed by the town’s two private engineering consultants, Lombardo Associates and Stearns & Wheler.
Stearns & Wheler pitched the more traditional models, while Lombardo Associates put together the cluster model.
According to preliminary cost projections, the cluster approach is expected to cost less than half of the $500 million expense for more traditional models.
The results set the stage for the sewer commission’s next task: to select from among the five scenarios the best parts of each and piece them into two more models, from which the final plan will be chosen. The five initial scenarios are basic, relying on single approaches, like expanding the existing treatment plants in town as much as possible; building a single large treatment plant to serve the whole town; leaving the existing plants as they are and building several other facilities; a “fair share” model, where each Mashpee’s neighboring towns would be responsible for its own wastewater; as well as using small, neighborhood-sized cluster systems.
Mr. Fudala said the next scenarios, and the final plan, will likely be some combination of these approaches.
The synthesis may prove to be a political challenge for the sewer commission as well as a technical one, as the three different consultants seem to hold little trust in each other.
Brian L. Howes, director of the University of Massachusetts Dartmouth Coastal Systems Program and a Mashpee resident, said some of the scenarios remove more nitrogen from certain parts of town than is necessary under the regulations, so the next task will also include paring down the treatment in certain areas.
Mr. Fudala said the commission will begin the next step at its next meeting, scheduled for January 21.
The results for the three sections of Waquoit Bay that Mashpee is responsible for managing—Jehu Pond, Hamblin Pond, and the Quashnet River—show that the cluster approach misses the targets by a fairly wide margin.
In Jehu Pond, for example, while the other four scenarios were well under the 0.446 milligrams of nitrogen per liter of water threshold, the cluster model achieved 0.472 milligrams per liter.
None of the scenarios met the 0.52 milligrams per liter target for the Quashnet River, but the fair share approach was only 0.003 off.
Dr. Howes said a figure that close would likely be acceptable to state regulators.
There was little information in the 20-minute presentation to the sewer commission by Eduard M. Eichner, a UMass Dartmouth scientist, about why some scenarios performed better than others, and why there was such a marked difference between the Popponesset and Waquoit results.
Mr. Fudala said some of the difference can be attributed to assumptions that went into the models. For example, Stearns & Wheler assumed that the wastewater generated in Falmouth is pumped up to the Massachusetts Military Reservation, while Lombardo Associates assumed a need to treat the wastewater in Falmouth within the Waquoit watershed, Mr. Fudala said.
Likewise, Mr. Fudala said Stearns & Wheler assumed that the existing wastewater treatment plants only remove nitrogen down to 10 parts per million, even though historical data show that they perform considerably better. That assumption would benefit the figures in the centralized scenario, he said.
Lombardo Associates, in turn, assumes that certain small cluster systems will achieve 3.75 parts per million nitrogen concentrations, though it is unclear whether state regulators will credit the small treatment plants for that low a level.
In a memorandum to the sewer commission sent after the meeting Tuesday, Pio S. Lombardo, of Lombardo Associates, made his case for why the cluster scenario did not meet the targets. He argued that a few small tweaks to the discharge areas for Hamblin Pond would meet the threshold there.
In Jehu Pond, he questioned how the cluster approach could not meet the targets when the others did, as all of the wastewater is removed from the area.
“The LAI [Lombardo Associates Inc.] Scenario removed more nitrogen than the other Scenarios so the results that the other Scenarios achieved TMDL compliance are very puzzling. Something is off. The LAI Scenario removed 100% of the wastewater nitrogen,” he wrote.
He estimated that changes needed to comply would cost about $8 million, a small fraction compared to the overall cost of the project. Mr. Lombardo also urged the commission to request access to the computer model the university uses to estimate the nitrogen loads, a subject that has repeatedly come up across Cape Cod as towns are facing hundreds of millions of dollars in capital costs based on a technical computer model that they cannot independently verify.
Mr. Eichner, in his presentation, also stressed the need for the sewer commission to consider the possibility of other alternative approaches, like creating man-made ponds or using the abandoned bogs south of Santuit Pond to remove nitrogen from the watersheds. However, Mr. Eichner said it is unclear how much credit the state Department of Environmental Protection will give such projects when evaluating whether the town’s nitrogen-removal plan is sufficient.
The commission could not hold a formal meeting on Tuesday night due to a lack of a quorum. Mr. Fudala said commission member Donald R. Desmarais called in sick and Matthew T. Berrelli e-mailed to say he could not attend, leaving only one member of the three-member commission present at the meeting.
There was a small handful of residents in the audience, including a few members of the Mashpee Community Advisory Committee, a group of citizens and representatives of various agencies designed to help guide the wastewater planning process.
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