MODELING OF STREAM CHANNEL INFILTRATION OF COALBED METHANE CO-PRODUCED WATER AND THE EFFECT ON THE SHALLOW AQUIFER

Rapid coalbed methane development in the Powder River Basin, Wyoming, has resulted in a dramatic increase in the number of producing wells, with as many as 40,000 new wells projected to drilled during the next decade. CBM development involves the co-production of large volumes of coalbed water, which is most commonly discharged to impoundments. Little is known about the potentially significant effects that this co-produced water may have on shallow aquifers and water budgets. Since many of the impoundments in the Powder River Basin are in-channel and supplement surface water flow, it is important to understand what factors influence stream channel infiltration. Modeling of cross-sectional infiltration in a stream channel was undertaken using the U. S. Geological Survey’s SUTRA finite-element code, simulating fluid movement from the stream channel, through the unsaturated zone, and into the shallow aquifer. Soil type, saturated hydraulic conductivity, and degree of anisotropy within the soil layer were analyzed to better understand the effects that each have on channel infiltration. At a small study site containing two in-channel infiltration impoundments in the Beaver Creek drainage (a tributary to the Powder River), water budgets have been determined from late July, 2003 to the present (excluding the winter months). Model simulations were compared to physically determined infiltration rates and water levels at this site to determine their correlation.