As Wilton Nears Sewer Flow Limits, Town Officials Consider $350,000 Plan to Investigate Sources of Excess Flow

Wilton’s Water Pollution Control Authority (WPCA) is going with the flow — trying to determine what is contributing to higher sewage flow that is pushing the limits of what Wilton can send to Norwalk for treatment under the Town’s current contractual agreement.

The WPCA is chaired by Lynne Vanderslice, with membership that currently includes each member of the Board of Selectmen (Josh Cole, Kim Healy, Bas Nabulsi and Ross Tartell), as well as former selectwoman Lori Bufano.

At its Sept. 13 meeting, the WPCA learned the results of a recent “inflow and infiltration” (I/I) study, which quantified the excess flow in Wilton’s sewer system.

Based on the findings, additional steps are now needed to determine where and how the excess flow is entering the system. To make those determinations, the WPCA is considering a proposal for a three-phase plan, at a cost of $350,000 — and the cost of any future remedies is still unknown.

But as the WPCA learned, the alternative — paying more for more capacity — could be much costlier.

The study presentation has been posted on the Town website.

Some Background

In Wilton, “sewers” refer to sanitary sewers, not the catch-basins that lead stormwater runoff away.

The Town of Wilton has a contractual agreement with Norwalk, for a limit of 0.65 million gallons per day of sewer flow.

Over the past 30 years, the trend line of annual flow has slowly inched higher, reaching a new high in 2018 and coming within 10% of the contractual limit for average daily flow.

More recently, the WPCA hired environmental engineering firm Wright-Pierce, which specializes in wastewater and related infrastructure, to conduct the I/I study in Wilton.

Inflow generally refers to rainwater that is misdirected to sanitary sewers, while infiltration occurs with underground issues such as defective manholes, cracked pipes, and improper connections from private properties.

Inflow and infiltration are both considered negative impacts when it comes to managing sewer flow. For that reason, they are often studied together.

I/I Results

Two Wright-Pierce engineers — Christine Kurtz and Lindsey Sylvester — attended the WPCA meeting to present the I/I results.

Kurtz explained the flow monitoring methodology, which used meters at key points in the system to collect data that was analyzed along with wet and dry weather patterns.

Sylvester explained the key findings and conclusions from the study:

• One sewer area (labelled “E” in the study) representing the area of South Wilton along lower Danbury Rd., was found to have excessive infiltration, based on industry standard measures.

• That same area also had the highest proportion of inflow which, at 51% of the total inflow, is also considered excessive.

• All areas had some degree of inflow, which ideally should all be eliminated.

“The next step after finding out the fact that you have excess flow is [to] start looking for where… where is the excess flow, what’s it coming from?” Kurtz said.

The recommended plan is a Sanitary Sewer Evaluation Survey (SSES) which includes three phases and employs a number of methods to identify the specific issues causing infiltration in the South Wilton sewer area and inflow in all areas. The three phases can run concurrently starting as soon as mid-October, with costs of $100,00, $115,000 and $135,000 respectively.

Based on the SSES findings, a fourth phase would include a rehabilitation plan, with a cost still to be determined. According to DPW Director/Town Engineer Frank Smeriglio, the plan could include solutions such as a number of manhole repairs, or adding lining to certain sections of pipe to prevent leaks, for example.

But until the SSES is completed, no one really knows what’s causing the excess flow. Smeriglio noted it’s possible that a single large commercial building in South Wilton could be the sole issue in that area. He also described manhole leaks that could add flow comparable to a 50-bedroom apartment building.

Short-term Fixes, Longterm Maintenance

Sylvester noted that the proposed SSES would identify immediate areas to improve, but a strategic perspective is also important — and often difficult when it comes to a topic like sewage.

“Our underground infrastructure [and] sanitary pipes are not the popular infrastructure topic, and they’re not often taken care of,” Sylvester said. “This [SSES] is a good step to finding those immediate defects [but] an ongoing program is something else to discuss so that the Town can keep track of this aging infrastructure.” 

Smeriglio wants to be proactive, especially in light of new development currently in progress in South Wilton and other development likely to come in the future.

“With the proposed developments that are coming down the pike, I think we should be aggressive,” Smeriglio said. “If we only had one development, we would only maybe do one phase now, second phase in 2024, but I think we should be aggressive with this work.”

Vanderslice concurred, noting that the alternative — buying more capacity — could cost a lot more.

“I agree with you Frank. I think we need to be aggressive as possible,” she said, adding that the SSES cost could be paid out of the budget reserve.

“If you need additional capacity, you’re buying it,” Vanderslice continued. “It costs real money to do that. So to the extent that you fix your problems, then you’re either not buying capacity or buying less capacity.”

The WPCA authorized Smeriglio to negotiate the details for the proposed SSES and present a contract to the Board of Selectmen for approval.