Development of CBM in the CRB is dispersed over 350,000 acres. In 2008, there were over 2,900 active CBM wells. The average water production per CBM well was less than 3.3 gpm, and cumulative annual production was about 15,200 acre-ft. The annual water production from CBM is less than 0.05% of the estimated water-in-place, which is upwards of 36 million acre-feet (12 trillion gallons).
Due to very low vertical hydraulic conductivity of the Raton and Vermejo Formations and the depth of the target coals, the interaction between CBM pumping and surface water is minimal. The target coals thin, discrete lenses and comprise less than 6% of the overall. The majority of the target formations are comprised of low permeability shales and siltstones, which govern the vertical connectivity of the CRB. The baseflow from the groundwater system to the Purgatoire River is relatively small at 2.5 cfs, with the large majority of baseflow derived from the shallow groundwater system.
The numeric model incorporated recharge, formation hydraulic conductivity, the vertical igneous intrusive dikes, evapotranspiration, and discharge to rivers. The model was calibrated to potentiometric heads and groundwater flux. The area of nontributary groundwater was determined by multiple model simulations, with each simulation stressing the calibrated model for 100 years to determine surface water depletions.
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