Flathead County and state officials are closely watching an increase in groundwater contamination at the county landfill to determine what kind of corrective action can best address the problem.

The contamination is primarily tetrachloroethylene, a carcinogenic chemical commonly used as a solvent in products such as dry-cleaning fluid, paint stripper and metal degreasers.

In the most affected groundwater monitoring well at the landfill, tetrachloroethylene concentrations currently are three times the limit allowed in public drinking water systems by the U.S. Environmental Protection Agency.

County Public Works Director Dave Prunty said the level of contamination — 16 parts per billion — is the equivalent of 16 blades of grass in an area the size of a football field.

Prunty advised county commissioners about the increased contamination last week, explaining potential solutions to curb the tetrachloroethylene level.

“We’ve kept DEQ [the Montana Department of Environmental Quality] in the loop,” Prunty said. “One of the things we’ll look at is there are bugs [bacterial microbes] that can be put into the well casing and they break down chemicals and clean the groundwater.”

Groundwater contamination at the landfill has been known and monitored since the 1990s when a plume of contamination was found on the eastern boundary of the landfill. That is the oldest portion of the landfill and was built in the 1970s without a liner and without leachate and landfill gas control systems.

Corrective actions to control but not eliminate the spread of contamination were approved by the state and completed by the Flathead County Solid Waste District in 2001, according to a report by Hydrometrics Inc., a Kalispell consulting firm.

Those corrective measures rely on the control of stormwater, shallow groundwater and landfill gas to reduce the spread of contamination and allow the natural degradation of chemicals within the groundwater.

During the early 2000s, groundwater contamination diminished, due largely to the corrective action, although lower-than-normal precipitation likely was a contributing factor, the Hydrometrics report noted.

Groundwater tetrachloroethylene concentrations began to increase in historically impacted monitoring wells in 2011 and current levels are similar to levels in the late 1990s before corrective measures were put in place.

In response to the rise in contaminant levels, corrective actions were re-evaluated in 2012-13 and improvements to some water-control systems were completed in 2013.

Prunty said it is anticipated the rise in contamination should slow or reverse itself in the not too distant future because of the corrective-action improvements made two years ago. The cyclic nature of precipitation could create drier conditions that also would lessen the contamination.

However, the report notes, current groundwater contamination near the landfill likely will spread and disperse to the southeast. If the plume behaves as it did in the early 2000s, it is likely that groundwater contamination will be detectable — although likely better than drinking water standards — at downgradient wells such as the ones on the First National Pawn and former Adanac Kennels properties within one to three years.

Even though existing corrective steps are believed to be working to control and limit the migration of contamination, a number of measures are planned this year, including more frequent monitoring of water supply wells downgradient of the plume, a more detailed review and monitoring of landfill gas conditions on the eastern side of the landfill, and stepped up communication with the state.

“This really is a partnership with DEQ,” Prunty said.

There’s also a work plan that may be put into this year’s budget cycle for further monitoring, such as the installation of additional monitoring wells, the biological degradation of chemicals and point-of-use treatment of off-site water supply wells using granulated activated carbon.

Currently the state requires semi-annual reports from the monitoring wells, but that could change to quarterly reports as part of the corrective-action plan, Prunty said.

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