Groundwater flow model of the Merritt region and potential response to coal seam dewatering

• Main Author: Barclay, Jordin Alexander
• Language: English
• Published: University of British Columbia 2009
• Online Access: http://hdl.handle.net/2429/5619

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.