Preservation of Water Quality near a Surface Coal Mine, NW Colorado

The Colowyo Coal Mine has operated as a surface coal mine in northwestern Colorado since the 1960s, with multiple seams of coal removed from the upper portions of the Cretaceous Williams Fork Formation.  Water quality and quantity parameters were obtained by the USGS and the operator from 1974 until the present.  Environmental protection regulations required by the Colorado Division of Reclamation, Mining, and Safety have been adhered to by the mine operators.  Bedrock groundwater is present in localized, discontinuous pockets within the Williams Fork Formation and over a wide area within the underlying Trout Creek Sandstone.   Unconfined groundwater is present in valley fill (alluvium and colluvium) along streams.  Surface water is present in several streams and in isolated stock ponds and springs. 

To monitor impacts from mining, water quality and quantity parameters have been monitored by the operators at key locations near mine impacts continuously since at least 1989.  A review of these revealed no statistically-significant trends in water quality or quantity at any sampling location.  Downstream surface water parameters plotted against time had coefficients of determination (r²) less than 0.16; this was similar to the r² of upstream surface water parameters.  Downstream valley-fill aquifer water parameters plotted against time displayed an increasing trend in water elevation, TDS, conductivity, and some ions; this may be due to localized effects raising the groundwater table into vadose soils with an abundance of salts rather than caused by mining impacts.  The r² values for these trends ranged from 0.41 for conductivity to 0.72 for TDS, indicating a weak correlation.  Upstream valley-fill groundwater did not have any trends over the study period.  These data indicate that the current regulations governing surface mining as applied at the Colowyo Mine protect human health and the environment from potential impacts caused by mining.