| Summary: | The effects of coal bed methane (CBM) development on the quantity and quality of
groundwater in the vicinity of the City of Merritt, British Columbia were assessed
through a modeling study.
The impacts of coal seam dewatering for C B M at a pilot scale and at a regional scale are
assessed here using a series of groundwater flow models. Two potential pathways were
identified that could hydraulically connect a dewatered coal seam and the aquifer: faults
within the Tertiary rock and coal seam subcrops.
A pilot scale model included coal seam subcrops along the unconformity between the
Tertiary rocks and the Quaternary sediments and examined their potential response to
coal seam dewatering. Using estimates of hydraulic conductivity (K) and subcrop
exposure, the rate at which groundwater enters the subcrops ranges from approximately
7500 m³/ day for a high hydraulic conductivity scenario to approximately 70 m³/day for a
low hydraulic conductivity scenario. For the medium hydraulic conductivity scenario the
groundwater loss was 725 m³/day. Under a modified scenario where dewatering takes
place only in relatively continuous coal seams and relatively far from subcrops, the loss
was approximately 45 m³/day.
The regional scale model assessed the role of a fault that extends from the southwest to
the northeast through the region. For a thick, high hydraulic conductivity fault, the
estimated loss was approximately 1430 m³/day whereas for a narrow, medium hydraulic
conductivity fault the estimated loss was 83.2 m³/ day.
Based on the results of this study, if coal seam dewatering takes place in areas relatively
unaffected by faults, subcrops or other potentially high hydraulic conductivity features,
the risk towards the City of Merritt's groundwater supply are likely to be low. However,
as the city continues to develop and the groundwater demands increase, there is
inherently greater risk to the groundwater supply. === Science, Faculty of === Earth, Ocean and Atmospheric Sciences, Department of === Graduate
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