Sewer Planning Scenarios Show Varied Results

By: Brian Kehrl
Published: 11/20/09

A first glance at the five basic scenarios that the town might use to develop a comprehensive wastewater treatment plan has found that the option projected to cost the least also provides the most effective treatment.

The scenario based on building 16 smaller wastewater plants around town, known as “clusters,” and using a patented technology known as Nitrex, which preliminary estimates projected to cost less than half the $500 million price tag of a more conventional approach, was the only one of the scenarios that met all four of the benchmarks used by scientists to measure whether the scenarios would remove enough nitrogen in Popponesset Bay to meet federal clean water guidelines.

The long-awaited presentation of the scenarios by Eduard M. Eichner, of the School for Marine Science and Technology at University of Massachusetts Dartmouth, came at the Mashpee Sewer Commission meeting Tuesday night. The scenarios were developed by two consultants—Stearns and Wheler, which is overseeing the whole wastewater planning project and oversaw four of the scenarios, and Lombardo Associates, which was subcontracted to oversee just the Nitrex model.

“What I take away from it is that at least based on the assumptions that were made, the Nitrex scenario proved itself,” said F. Thomas Fudala, chairman of the sewer commission.

The report only provides a partial picture of the scenarios, though, as it covered just Popponesset Bay and not East Waquoit Bay, the other large bay that the town is required to clean up.

Brian L. Howes, a Mashpee resident and scientist at UMass Dartmouth who is leading the statewide program to study nutrient loading in coastal waters, is scheduled to present the East Waquoit Bay scenarios and a summary of the two at the sewer commission’s next meeting, on December 15.

The presentation was not without a small controversy, with commissioners, particularly Mr. Fudala, expressing frustration that there were different basic assumptions used by the two consultants that may have benefited the cluster, Nitrex scenario.

While Stearns and Wheler in at least one of the scenarios assumed that the existing wastewater treatment plants reduce nitrogen levels down to 10 parts per million—the maximum allowed under state permits—Lombardo Associates assumed a nitrogen level of 3.75 parts per million—the established figure that modern, high-end treatment facilities are thought to be able to achieve.

“We just have to keep that in mind, because we are comparing five scenarios but some of them have different assumptions,” Mr. Fudala said, adding that he would have liked to see the scenarios use the historical data collected by the town about the performance of each wastewater treatment plant here.

Matthew T. Berrelli, sewer commissioner, said, “We have spent a lot of time and money trying to get a unified database for these, and now it is not really consistent.”

“It’s unified, we just need to make sure we use consistent assumptions,” Mr. Fudala said.

“Next time we need to make sure they are consistent,” Mr. Berrelli said.

Mr. Eichner said the assumptions that went into the scenarios were based on the information provided by each consulting group. “So what you see is the wishes of both firms,” he said.

The report comes in the context of a long-running planning process, one that still has considerable ground to cover before it is complete. There were several scenarios studied by the university before these, for example, that found using advanced onsite septic systems throughout town would not meet the nitrogen-removal targets and that using bogs and oysters to remove nitrogen can help to lighten some of the load from wastewater treatment.

Likewise, there are more scenarios to come. The next step in the process, after the preliminary East Waquoit Bay scenarios are presented next month, will be for the sewer commission to work with the consultants to pare the five basic scenarios to two more refined versions. Those two scenarios will then be run through similar tests before a final approach has been winnowed down.

The final approach will also need approval from Town Meeting, as well as county and state environmental regulators.

Mr. Fudala, emphasizing that he is speaking only as a single commissioner and not for the entire group, said he expects the two refined scenarios and even the final plan to be a combination of the ideas presented this week—with large and mid-sized wastewater treatment plants as well as some onsite systems.

“I suspect, and I have said this before, is the logical thing we are going to end up with is a mix of things, given the way the town is laid out, sort of all scattered around,” Mr. Fudala said.

The five scenarios cover a wide range of options for the town, from building a single, massive wastewater treatment plant to service nearly all of the town to upgrading the eight existing wastewater treatment plants in town to the cluster approach.

The cluster approach is widely considered to be somewhat non-traditional, as in the past the tendency has been toward fewer and larger rather than more and smaller systems.

The Nitrex technology, too, is not fully permitted by the state Department of Environmental Protection. It is only allowed to be installed in 50 locations throughout the state, until more data can be accumulated to prove its effectiveness. So far there are fewer than 10 installations in the state, though there are many more throughout the rest of the country.

In one location in Mashpee, however, it has proven to remove as much nitrogen as high-end wastewater treatment plants.

The university scientists tested each of the scenarios to see whether they would remove enough nitrogen to meet the clean water regulations for the main body of Popponesset Bay, as well as the “subembayments” of the Mashpee River, Shoestring Bay, and Ockway Bay.

The Nitrex cluster scenario was the only one to meet the limits in all four areas, and only Nitrex met the threshold for the Mashpee River.

“The Mashpee River looks like a tough nut to crack,” said Thomas C. Cambareri, water resources program manager for the Cape Cod Commission.

Mr. Cambareri said the commission could chose to send treated wastewater out of the Mashpee River area, to prevent even the low levels of nitrogen from treated water from entering the river. “But that will be something major to mull over,” he said.

“Absolutely, the Mashpee River is why we are here,” Mr. Fudala said.

Another issue that will need to be weighed is whether it is worth piping the wastewater to be discharged all the way down to the southern end of town, where the groundwater seeps out into Nantucket Sound rather than either of the two bays, Mr. Fudala said.

In response to questions from Burton Kaplan, who represents the Mashpee Board of Health on a citizens advisory panel formed to comment on the sewer planning process, Mr. Fudala said the town has appropriated about $475,000 for the study and has spent a little more than half of that so far.

“There is an end in sight,” Mr. Fudala said.

Also listed as co-authors of the report are John Ramsey and Sean Kelley, of the private, Mashpee-based firm Applied Coastal Research and Engineering. Mr. Ramsey developed the computer model with Dr. Howes and works with the university on each of the wastewater planning projects.

Related document

Cluster scenario preliminary map (.pdf, 3.1 MB)
A map from the sewer planning scenarios shows the proposed, preliminary locations and sizes for “cluster” wastewater treatment facilities scattered around town.