EVIDENCE FOR A REGIONAL GROUNDWATER FLOW SYSTEM IN THE COAL-BEARING FRUITLAND FORMATION IN THE NORTHERN SAN JUAN BASIN, COLORADO—A NEW LOOK USING GEOLOGIC AND HYDROLOGIC DATA

The San Juan Basin (SJB) is the most productive source of coalbed methane (CBM) in North America with production developed from the coal-bearing Upper Cretaceous Fruitland Formation. Groundwater is produced from the Fruitland Formation and the adjacent Pictured Cliffs Sandstone in conjunction with CBM production. As part of an evaluation of possible depletive effects due to CBM production on surface water flow in the SJB, geologic and hydrologic data have been compiled in a new look at the coal-bearing stratigraphic sequence in the northern portion of the basin. The Fruitland-Pictured Cliffs stratigraphic sequence does not fit the typical definition of an aquifer, yet groundwater flow pathways do exist within the coalbed cleat systems and fractures in adjoining clastic sediments. Evidence exists in potentiometric surface levels, water quality conditions, and CBM well water production that points to a regional groundwater flow system around the margin and well into the interior of the SJB.