From The Grand Junction Daily Sentinel (Dennis Webb):
A woman living south of Silt urged Garfield County commissioners Tuesday to continue groundwater sampling there despite new tests finding no clear evidence of a link between methane and benzene in test wells and natural gas development. Lisa Bracken made her plea after representatives of the firm Tetra Tech presented the county with results from the third phase of a nine-year groundwater study in the area. It was conducted after the 2004 discovery of natural gas and benzene in West Divide Creek. The state blamed a faulty Encana well.
The latest tests involved three pairs of groundwater monitoring wells installed by the county, with each pair drilled to depths of about 400 and 600 feet deep in the Wasatch geological formation. The study found that methane in the shallower wells was biogenic, meaning from microbial sources, whereas methane in the deeper wells was thermogenic, resulting from geological heat and pressure. Thermogenic gas is what energy companies target for drilling.
The Tetra Tech consultants believe all the gas in the test wells is likely naturally occurring rather than a result of oil and gas development. Geoffrey Thyne, a longtime consulting geologist for the county, agrees that the research demonstrates that there is naturally occurring Wasatch formation methane that helps explain at least some of the methane being found in a number of domestic water wells.
But Bracken, who lives near the seep area, believes 600 feet is a suspiciously shallow level to be finding thermogenic gas. She said she also found “astonishing” the widespread detection of benzene, a carcinogen, in test well samples. Those detections were within safe drinking water standards in all but one case, and Tetra Tech theorizes the benzene also is naturally occurring.
County commissioners plan to seek a meeting with Thyne, and state oil and gas and health officials, before determining whether the county should undertake any more research.
Resident Marion Wells of Rulison said after Tuesday’s meeting that the latest research relies on several assumptions, including that carbon dioxide is present to allow for the kind of biogenic process believed to account for methane in the shallower test wells.