Whitefish has a chronic problem with groundwater seeping into its city sewer system, and it’s much worse after heavy rainstorms.

Following the late May storms that dumped several inches of rain on Whitefish, one manhole in the River Lakes development illustrated the problem perfectly.

“We were filling a 5-gallon bucket every 10 seconds,” said Jim Swain, owner of SuperTec Infrastructure Technologies, a Kalispell firm that has been hired to reinforce dozens of manholes throughout Whitefish. “It leaks something horrible.”

The city recently embarked on a $813,000 project to rehabilitate 36 manholes and reinforce 5,000 feet of sewer main.

It’s difficult, though, to pinpoint exactly how much stray groundwater is getting into the city sewer system, Whitefish Public Works Director Craig Workman said.

“One of the hardest things we do in the sewer collection realm is trying to quantify infiltration,” he said. “We know it’s a significant amount.”

As much as 4 million gallons of groundwater a day — a ballpark figure — seeps into the sewer system during a heavy rain event, Workman estimated.

Using a national industry standard of about $2 per 1,000 gallons to treat wastewater, that’s an extra $4,000 in treatment costs per day.

“My goal is to knock [the infiltration] down by 10 to 15 percent,” Workman said. “In round numbers the goal is to get rid of a half-million gallons [a day] during a heavy rain event.”

Swain’s crew is tackling manholes in three key areas — Birch Point, City Beach and River Lakes.

Birch Point and City Beach manholes and sewer lines are among the oldest parts of the city’s collection system. River Lakes was developed in the early 2000s, but the workmanship was substandard, Workman said.

“In River Lakes we’re dealing with infrastructure not that old, and infrastructure we shouldn’t have to be spending money on, but we’ve definitely seen some significant failures there,” he said. “We’re dealing with a point in city history where so much infrastructure was being built and the city was stretched so thin to inspect it properly.”

Swain started SuperTec Infrastructure Technologies 20 years ago and does manhole rehabilitation throughout the country and Canada.

The process begins by applying an epoxy resin on a custom-made laminated composite liner — a product invented in 1991 by Thain’s good friend, Ron McNeil, who holds several patents on the process and operates a liner manufacturing plant in Florida.

Air is pumped into the manhole to press the liner to the wall. The liner bonds with the inside of the manhole through a steam-curing process.

“It permanently seals off groundwater infiltration into the sewer system,” Thain explained. “It’s the very best possible product.”

The liners come with a 20-year warranty, and independent lab testing shows a lifespan of 50 to 100 years, he said.

SuperTec’s portion of the project is about $316,000. PEC Inc. of Helena will handle the pipeline rehabilitation later this year at a cost of about $497,000. State grants will pay for a portion of the work, and the city will take out a state revolving fund loan at 2.5 percent interest to pay the remainder of the cost, according to City Manager Chuck Stearns.

A study done 10 years ago showed 18,500 linear feet of sewer line in need of repair. Some rehabilitation work was done in 2011, but further analysis done in 2013 showed more work was needed.

“This is the third round of infiltration reduction over the last 15 years,” Workman said. “We have seen a significant reduction [in infiltration] this spring at the wastewater treatment plant.”

SuperTec began its manhole rehabilitation in April and is wrapping up the project.

Infiltration of groundwater is a fairly common problem for municipalities, but Whitefish’s high groundwater worsens the problem, Workman said.

“Some manholes are literally into the groundwater, so the constant inflow is what we’re trying to reduce,” he said.

Another culprit is illegal connections to the city sewer system such as sump pumps, roof drains and downspouts that direct water into the sewer instead of the ground or storm sewer, Workman added.

Features editor Lynnette Hintze may be reached at 758-4421 or by email at lhintze@dailyinterlake.com.