Abstract:
The Powder River basin (PRB) in Wyoming has seen a rapid increase in coalbed methane (CBM) production over the past decade. Product water from the ~20,000 active CBM wells is mostly released in surface ponds. The product water may be high in total dissolved solids (TDS), be sodium dominated, and may contain trace elements that are toxic to humans, livestock, and wildlife. To date, about 4,000 such ponds have been permitted. The ponds can be either on-channel or off-channel. The fate of the pond water is generally unknown. Infiltration of pond water could lead to the contamination of shallow groundwater and surface water. Concentration of pond water due to evaporation could lead to unacceptable high trace element concentrations. Recent reports suggest that pond water infiltration reduces with time because of soil dispersion related to the high sodium content of the CBM water. We propose to examine the relationship between soil type, CBM water quality, and infiltration rate for a variety of unlined ponds across the PRB. We are particularly interested in determining the time frame over which the infiltration rate reduces as compared to the total lifetime of the ponds. This type of information is currently lacking for the PRB and would greatly benefit pond operators, landowners, and agencies in assessing the environmental impact of the ponds (i.e. groundwater contamination versus concentration of pond water constituents). Infiltration experiments conducted in the laboratory will be supplemented with numerical modeling of subsurface water flow and solute transport to assess the practical implications of the measured infiltration rates.