Smoke testing being conducted to check sewer flow, infiltration

By: Nick Mordowanec | Fraser - Clinton Township Chronicle | Published September 12, 2017

CLINTON TOWNSHIP — Smoke testing in Clinton Township sewers is estimated to begin the week of Sept. 18, lasting for a one- or two-week period.

Per an administrative consent order that began in 2000, Clinton Township officials and associated engineers continue to monitor flow data in various sewer districts. The ACO is being mandated by the Michigan Department of Environmental Quality.

Clinton Township Public Services Director Mary Bednar said the intent is to capture and analyze wet weather events closer or equal to 25-year, 24-hour events. She said the township has already spent approximately $24 million on related projects and studies.

Currently, phases one and two of District E sewers are operating as intended. The work was conducted within the timeframe described in the current ACO. Area-velocity meters remain installed at an upstream pipe tributary at 15 Mile Road and Little Mack Avenue — an outlet to the Macomb Interceptor Drain. 

Scott Chabot, senior project manager for the township’s engineering firm, Giffels Webster, said during the township’s Aug. 28 meeting that metered sub-districts have been identified that possess significant sources of inflow and infiltration.

Some of the wet weather flows are from footing drains, with incremental flows suggesting that flows may be coming from other sources, including broken private sanitary sewer leads, sewer manholes or illicit downspout connections.

A smoke test study was recommended to dissect and understand flow patterns in an approximate total of 44,275 lineal feet of sanitary sewers. ADS Environmental Services is conducting the work at an estimated cost of $37,508.

Sewers being investigated run in a square pattern in the township’s southern end, between Metropolitan Parkway and Glenwood Street and Harper and Gratiot avenues.

Smoke testing identifies direct inflow links, such as in catch basins, area drains, roof leaders and manholes, as well as infiltration sources — such as broken sewer lines, open joints and service laterals.

Work begins at a manhole and progresses either upstream or downstream from the project location. Basically, if leaks exist, smoke will exit the system showing where water may enter the system.

Chabot described the testing as being similar to smoke emitted from fog machines during the Halloween season. It is a dense gas that is odorless, nontoxic, can penetrate orifices and is harmless to humans and animals.

“Smoke tests are a fairly common used test in older communities to detect sources of extraneous inflows in the sewer collection system,” Chabot said. “The meter districts chosen were based on results of several years of metering. These are districts exhibiting high incremental flow rates — high flows per acre of area — on wet weather events when compared to other districts metered in the area.”

If smoke enters a resident’s home, Chabot said, the effects will subside in a period of five to 10 minutes.

Giffels Webster coordinated a meeting with ADS and public services beforehand, identifying the project scope, establishing lines of communication and setting the project schedule.

Clinton Township’s role included alerting residents via public broadcasts or media notices, as well as having initial contact with township police and fire departments and local businesses and institutions. ADS is expected to notify residents in the sewer district at least 48 hours prior to work being conducted.

 The sanitary sewer lines were said to be tested in groups of 1,500 lineal feet or less. During testing, crew personnel will look for any indication that observed smoke emission may be related to “inactive or abandoned” lines.

Also, the township is utilizing “laser meters” that, according to Chabot, shoot an array of lasers into the flow to measure speed. It also shoots a laser downward to measure level. Taking both measurements can accurately compute flow rate.

Bednar said the laser meters are separate from the smoke testing and will be implemented to prevent future catastrophes, such as the current interceptor collapse on 15 Mile Road.

Overall, Chabot said sewer work has been positive.

“Relief sewers constructed in (the) last few years are working as intended and have prevented sanitary sewer overflows from occurring,” he said. “Some additional studying — more flow metering, smoke testing, manhole inspections — is needed to identify any further sources of inflow in sewer collection system.

“All of our efforts have the primary goals of continued prevention of sewer flows from backing up into basements and to eliminate wet weather sewer discharges into the storm sewers that eventually flow into the Clinton River and Lake St. Clair.”