AUBURN — No, it’s not foggy. It’s just the city testing the sewers.

The Auburn Sewer District, with help from Weston & Sampson Engineers, is testing the sewer system for leaks weekdays from now through Aug. 9.

During the testing, white smoke will be introduced to the sewer system by a machine, causing it to vent from manhole covers in roads as well as plumbing vent pipes on or near building rooftops.

“This smoke is normal and should not cause alarm,” an Auburn news release stated Monday.

Auburn Water District Superintendent Sid Hazelton said Monday that the testing is designed to identify “clean” sources of water that are getting into the sanitary sewer system. He said water from roof drains, catch basins and other areas need to be removed because they increase sewer treatment costs, and can contribute to sewer overflows into the Androscoggin River during large rain events.

The news release states that the smoke should not enter buildings unless there is a dry drain trap, unused fixture or a plumbing defect present. If it does enter a building, the district said, occupants should not be alarmed — “the smoke is nontoxic, nonstaining and will dissipate quickly through open windows. If you have a lung ailment or respiratory condition such as asthma or emphysema, stay away from the smoke.”

If smoke enters the building, the release states, residents may want to pour two gallons of water down basement floor drains or unused plumbing fixtures to ensure that drain traps will be effective.

Smoke inside a structure should be reported immediately by calling the testing team directly at 603-570-8791.

Weston & Sampson Engineers will be in a marked vehicle and its personnel will be wearing clearly-marked Weston & Sampson shirts and safety vests and will have identification cards with them.

Homes and businesses within the testing zone have all received a notification sheet and will receive another sheet once the testing of their area has been completed. All questions regarding this project should be directed to the testing team or to the Auburn Water & Sewerage Districts at 784-6469.

According to an article in Water & Wastes Digest, a trade magazine, research has shown that approximately 65% of all extraneous storm water inflow enters the system from somewhere other than the main line.

“Smoke travels throughout the system, identifying problems in all connected lines,” the article states. “Even sections of line that were not known to exist or thought to be independent or unconnected.”

According to the report, smoke testing has been “used extensively” for more than 40 years, and is a vital ingredient of successful “inflow and infiltration” studies.

The firm began testing Monday in the area of Lake Auburn Avenue, Harvard Street and Broadview Avenue.