More study of methane in Silt water, resident urges [subscribers only]
By Dennis Webb
A resident representative to Garfield County’s Energy Advisory Board says a recent study finding no apparent link between oil and gas development and methane in groundwater south of Silt shouldn’t be the last word on the subject.
“I’d like for there to be another study,” said Scott Brynildson, who lives south of Rifle, speaking Thursday night after the study results were presented at a board’s meeting.
He said it sounded as if the county’s consultants were guessing as to some of their conclusions.
But David Bohmann, an engineer with Tetra Tech, said that while the consultants aren’t saying they’re 100 percent certain about their conclusions, no study makes such a claim.
“I don’t think there’s a (new) study needed,” he said …
To recap, in the Phase III study there are three pairs of nested wells, one about 400 feet deep and the other about 600 feet deep. The Currie well, a nearby residential water well, was also sampled. Domestic water wells are typically 200 feet deep. Tetra Tech collected water samples from each well in January 2011, May 2011, August 2012, and December 2012. Even though the initial water samples showed significant levels of chloride, methane, and benzene, for reasons unknown they did not increase the sampling.
The three-year study concluded that the chloride, methane, and benzene detected in the water samples was naturally occurring (biogenic) and in many instances – but not all – the concentrations were declining.
.. One uncertainty for Tetra Tech involves high chloride levels found in the test wells. Produced water from oil and gas development is typically high in chloride.
Tetra Tech hydrogeologist Chris Gutmann said the chloride levels in the test wells appear to increase with depth and are consistent with concentrations in nearby domestic wells.
“We’re still not exactly sure what’s going on there,” he said.
Lisa Bracken, who lives near the West Divide seep area, also has called for continued study. Garfield County commissioners are awaiting a review of the latest study by an independent geological consultant.
The Tetra Tech consultants agreed with residents at this week’s meeting that even if the methane and benzene are naturally occurring, they are of concern. The consultants recommended that homeowners have their water wells tested, and said water can be treated accordingly if needed.
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