Groundwater contamination worsening at landfill
Flathead County Public Works Director Dave Prunty recently advised county commissioners about increased groundwater contamination at the county’s solid waste landfill on U.S. 93 between Kalispell and Whitefish.
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. County and state officials are closely watching the situation to determine the best corrective action to the problem.
In the most severely 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.
Prunty explained potential solutions to county commissioners.
“We’ve kept the Montana Department of Environmental Quality in the loop,” he said. “One of the things we’ll look at are there are 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 after a plume of contamination was found on the eastern boundary of the landfill. The oldest section of the landfill was built on the east side in the 1970s — without a liner and without leachate and landfill gas control systems.
The state approved corrective measures to control but not eliminate the spread of contamination, and the work was completed by the Flathead County Solid Waste District in 2001. The measures focused on control of stormwater, shallow groundwater and landfill gas to reduce the spread of contamination and to allow the natural degradation of chemicals in the groundwater.
Groundwater contamination diminished during the 2000s, largely due to the corrective action, although lower-than-normal precipitation likely was a contributing factor, according to a 2001 report by Kalispell-based Hydrometrics Inc.
Tetrachloroethylene concentrations began to increase in historically impacted monitoring wells in 2011, and current levels have reached similar levels from the late 1990s, before corrective measures were put in place. In response, corrective actions were re-evaluated in 2012 through 2013, and improvements to some water-control systems were completed in 2013.
Prunty said the contamination rise is anticipated to slow or reverse itself in the not too distant future because of corrective actions made two years ago. The cyclic nature of precipitation also could create drier conditions that would lessen the contamination.
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, groundwater contamination likely will be detectable at downgradient wells, such as the ones on the First National Pawn and former Adanac Kennels properties, within one to three years. But the level of contamination is expected to be better than drinking water standards
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.
A work plan may be included in this year’s county 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.