Groundwater impacts associated with mining and coalbed methane

Situation: Norwest was part of a group hired by the U.S. Department of Interior, Bureau of Land Management (BLM) and the U.S. Department of Agriculture, Forest Service (FS) to develop the Environmental Impact Statement (EIS) and Planning Amendment for the Powder River Basin Oil and Gas Project. The proposed project included the drilling of nearly 40,000 new CBM wells over an area of approximately 8,000,000-acres during a ten year period. The preparation of an EIS is required under NEPA for any actions involving federal lands. Norwest’s role was to predict the impacts of the PowderRiver Basin groundwater systems from future coal bed methane (CBM) development. 

Solution: Norwest participated in the EIS scoping process and developed a plan for assessing the impacts of surface water and ground water resources. Norwest completed a detailed assessment of channel and pond conveyance losses within several representative drainage basins for the surface water impact assessment. These studies of pond seepage and channel conveyance loss were used to supplement studies completed by the USGS and the BLM to predict re-infiltration of CBM produced water. Norwest developed a 17-layer numeric model of the Powder River Basin to simulate the impacts of the groundwater systems on various development scenarios. The model incorporated recharge/discharge conditions, superimposed mining influences, and surface water interactions. The project involved the assimilation of an enormous amount of historic regional hydrologic data as well as performing site-specific field studies to supplement existing data, including conveyance loss (recharge) studies on several major tributaries of the Powder River.

Result: The model was successfully used to predict: 1) the volume and rate of produced water over the life of the development, 2) drawdown and recovery in the target coals and overlying units, and 3) the volume of recharge into the various sub watersheds from discharge water depending on the distribution of water management methods.