The propensity for contamination of groundwater by
methane gas was recognized as a valid concern.
In 1991 this issue was addressed in the preparation of a joint BLM/USFS
(United States Forest Service) Environmental Impact Statement (EIS) for the
proposed 64-well coalbed methane (CBM) drilling project in the HD Mountains
east of Bayfield, Colorado. In this
newly developed area, all wells were to be CBM wells. The potential problem of adversely affecting older conventional
well bores, often characterized by incomplete isolation of the Fruitland
Formation, was irrelevant due to the lack of conventional wells in this
area. All CBM well bores were approved
for primary annular cement placement spanning the entire vertical distance from
the producing horizon to the land surface.
Initial baseline sampling of groundwater to establish a benchmark of
water quality was proposed, and a BLM commitment was made to periodically
evaluate water quality in subsequent years.
Sixty–five to seventy water wells, largely on the periphery of the
sparsely inhabited interior of the HD EIS study area, have been monitored in
1993 and 1996 in an effort to provide early warning of any discernable gas
production-induced groundwater contamination.
So far virtually no adverse water quality impacts have been documented,
although concerns have arisen off the northwestern flank of the study area where
high levels of thermogenic methane with isotopic signatures similar to
Mesaverde gas have been documented in monitoring on private lands.