Cluster Wastewater Treatment Systems A Flexible Alternative

By BRIAN H. KEHRL
In the spectrum of wastewater treatment systems, neighborhood-size facilities are tough to generalize.
They can cost less than individual nitrogen-removing systems but can present legal and regulatory obstacles. They can remove at least 20 percent more nitrogen pollution from the environment than standard Title V systems but cost about 50 percent more.
Homeowners may like them better than having a facility in their back yard, but they can be a pain for developers.
The state Department of Environmental Protection requires a special “shared system” permit for them, but they do not require the more onerous groundwater discharge permit required of larger systems.
They have their ups and downs was the conclusion of a pair of presentations on “cluster systems” at Waquoit Bay National Estuarine Research Reserve this week.
The presentations, by Michael D. Giggey, a senior vice president at the engineering firm Wright-Pierce, and Brian A. Dudley, a wastewater specialist with DEP, covered the basics of when cluster systems should be considered and what obstacles need to be overcome for them to be built.
The Mashpee Sewer Commission is considering cluster-size systems as part of its townwide plan, including at least one scenario made up entirely of these neighborhood-size systems.
Preliminary cost projections show that the cluster approach may be considerably less expensive than using a more conventional centralized approach, but before cost is considered, the commission must establish that the proposals will remove enough nitrogen pollution from the groundwater to comply with the federal Clean Water Act and state standards. The engineering figures for all the scenarios that the sewer commission is reviewing are being tested by a third-party consultant.
No one from the sewer commission or other town departments attended the information session at WBNERR on Wednesday morning. Officials from Falmouth, Sandwich, Barnstable, and other towns were among the 40 or so people in attendance.
Mr. Giggey covered the basics of the systems, ticking off a variety of examples, from Norwell to Mashpee to Eastham.
According to figures provided by Mr. Giggey, the cluster system in Mashpee, at Main Street Village, was built by the same engineering consultant that is developing a cluster scenario for the town. In about two years of operation the Main Street Village system, as well as another system built by the same contractor in Eastham, have been recording nitrogen levels better than all other cluster system technology and as low as any centralized system.
In nitrogen-sensitive areas, which includes nearly all of Mashpee, Mr. Giggey said the largest advantage cluster systems have over individual ones is that they cut down on operations and maintenance costs by nearly half over the life of the systems.
Mr. Giggey estimated that cluster systems cost on average $17,500 per household, while individual nitrogen-removing systems cost about $22,000, and the standard Title V systems that most homeowners currently use cost about $13,500.
However, due to economies of scale, he estimated that as the systems get larger and larger, from single households up to centralized plants serving entire swaths of a town, they become less and less expensive per homeowner.
He said cluster systems should be considered based on whether an economic analysis proves them to be the most efficient, if the degree of nitrogen removal can be reached, and if the land is available.
Cluster systems can later be linked into larger sewer systems, he said.
Mashpee in many ways meets what Mr. Giggey described as the best case scenario, in which a comprehensive planning effort should be able to coordinate different parties with efficiency and cost in mind.
However, most of the town is already developed, which can present a separate, unwieldy set of issues, including more complicated cost projections and obtaining easements. Generalizing about pre-existing development is difficult because the conditions can vary widely.
Whether the development is already there or not, Mr. Giggey said the need to coordinate different property owners on financial, ownership, and responsibility matters can also present issues.
Mr. Dudley said the state requires information on all legal and financial issues, including who owns the facility, who is responsible for its regular maintenance, and how any large-scale renovations would be paid for, as well as detailed plans and an explanation of why a shared system is preferable.
A common approach is a sort of homeowners’ association formed by all the property owners, he said.
The Mashpee Sewer Commission is scheduled to meet next on August 19, at 7 PM, at Mashpee Town Hall.