Methane levels at closed landfill considered risk

City, state evaluating remediation measures
Alexis Barker
NLJ Reporter
 
Methane in one of the wells surrounding Newcastle’s landfill No. 1 has reached levels that are considered a health and safety risk, according to Caroline Brewer, project geologist with Trihydro Corp. 
Brewer, who met with the Newcastle City Council on Feb. 4, said that Trihydro discovered during monitoring that one of the perimeter wells had a measurable amount of methane in it. 
“The only well with measurable methane was well MMW-3 and it was at 100 percent LEL (lower explosive limit) and 21 percent CH4 (methane),” Brewer said. “This is a health and safety risk at the sportsman’s club.” 
The well, she said, is adjacent to the Weston County Sportsman’s Club. 
“This was not unanticipated; we recognized the problem in the past,” Brewer said. “This is a serious concern. The well is way above the limits and is a potential explosive hazard, may introduce methane into a close structure and you also have asphyxiation. These are the things you have to think about when you have methane concerns.” 
The Wyoming Department of Environmental Quality was also represented at the meeting. Trihydro is a Laramie-based engineering and environmental consulting company hired by the state to work on landfill remediations across the state.
The landfill, which was operated from sometime before 1945 until its closure in 1989, covers 38 acres of land near the Weston County Sportsman’s Club and contains an estimated 700,000 cubic yards of waste. 
Trihydro’s scope of work at the landfill includes methane monitoring, groundwater monitoring, statistical analysis, evolution of remedial alternative (the current task at hand), preliminary design, cost estimates and reporting for the city and the state. 
Brewer said that fluid levels are also collected during the surveys, measuring where water is in respect to the surface and how the water is flowing. Water at the old landfill flows from south to north, corresponding well with the land’s topography, with levels ranging from 33 feet in the north part of the landfill to as shallow as 3 feet in the south. 
“Something else we did was collect samples for groundwater quality testing,” Brewer said. 
She explained that water samples showed that oxidation reduction is potential, indicating that there is some potential for chemical reactions. 
“This is important because we believe there is a problem,” Brewer said. The reports are telling them there is a reaction taking place in the water, she said. 
Councilman Roger Hespe asked if this was common in landfills.
“Not necessarily,” Brewer said. 
Marge Bedessem, senior environmental engineer with Trihydro, said that most of what was found in the water was solvents. 
“They are not exceeding groundwater standards, but there are some inorganic compounds,” Bedessem said. 
After her report to the council, Brewer said that the task now consists of an “evaluation of remediation alternatives” based on the specifics of the landfill. 
“We are looking to identify a series of alternatives,” Brewer said. “Part of the process is meeting with the city to request additional information or receive additional information and to verify that the goals and alternatives selected address and satisfy all stakeholder’s concerns.” 
Those goals and objectives, she said, are methane control to reduce health and safety risks and addressing the impacted groundwater and seep control. 
Brewer told the council that it is important to make sure the methane isn’t moving from the landfill and entering the building located at the sportsman’s club. 
“There are a couple of alternatives,” Brewer said. “One we have listed here would have to occur at that building that is not part of the landfill.” 
She explained that this would be a sub-slab depressurization system at the building and that the other option would be a passive venting system at the landfill boundary. 
Craig McOmie, manager of DEQ’s Municipal Landfill Cease and Transfer Program, said that the city decides on the best solution. Bedessem said that the city has a liability to protect the community. 
“We are more interested in potential solutions that take care of you for the long term,” Bedessem said. “You have to look at public acceptance and decide what route you want to go.” 
The other issue identified by Brewer was the impact to groundwater near the landfill and seeps coming out below the landfill. She said that other landfills look at alternatives involving better caps to prevent water from leaking through. 
“That is not really the situation here,” Brewer said. “It is not necessarily rain water, it is groundwater going through the waste.”
Some solutions to the problem, Brewer said, include cutoff walls, hydraulic control, interceptor trench and combinations of multiple alternatives. 
“Notice none of these options are for a more elaborate capping system like what is done at other landfills,” Brewer said. “This is an unusual situation.” 
Brewer said that evaluating the alternatives include feasibility, technical engineering, costs and the level of protection. 
“Some may be overkill for the level of concern, but others may only give assurance for 20 years,” Brewer said. 
The group will continue to look at the alternatives before coming back to Newcastle
in March for another discussion, with the plan to have the final reports done in April, Brewer said.