Crews Seek Sources of Sewer Infiltration Late at Night

February 23, 2024

The Bedford Department of Public Works has embarked on a new tactic to identify sources of groundwater infiltration in the sanitary sewer lines.

Specialists from the engineering and environmental firm Weston & Sampson and Inland Waters, a pipeline company, have begun overnight flow isolation work throughout the town. The investigations began on Jan. 21 and is scheduled to continue until April 26, between 11 p.m. and 6 a.m., weather permitting.  

“The purpose of the project is to identify problem areas of the sewer system that are in need of rehabilitation and/or repair in an effort to prevent infiltration from entering into the pipes,” said DPW Director David Manugian.

When groundwater enters the sewer system through defective pipes and structures, it “takes up capacity that would normally be available for wastewater,” Manugian explained. “It can cause pipes and service connections to back up and potentially overflow during extreme wet weather conditions.”

He added that sewer ratepayers are charged for infiltration as well as wastewater since they’re both pumped through the Massachusetts Water Resources Authority system for disposal.

“Flow isolation is a method of quantifying the amount of infiltration in a sanitary sewer system,” Manugian said. “Flows in the system are measured during off-peak times. Normally people are sleeping during those times, and if there is flow in the sewer it can be assumed to be largely infiltration.”

The work consists of opening and entering sewer manhole covers with shovels, tripods, and harnesses. Each location takes about 20 minutes to complete. There are no loud noises and lighting is kept to a minimum. 

Persons performing these inspections are in clearly-marked trucks, Manugian said, and the town’s consultants and contractors wear yellow reflective vests with identification.

“Some of the inspections are being conducted in town sewer easements through neighboring yards of residential properties,” Manugian said. “If your property has a town sewer easement, a separate notification will be delivered and a police detail will be scheduled on site.”

Additional information about town easements and this project can be found on the town’s mapping system at

Read more about the sanitary sewer system at

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