Modelling potential impacts of coalbed methane development on stream water quality in an American watershed

摘要

Coalbed methane (CBM) development raises serious environmental concerns and concerted efforts have been made to collect chemistry, salinity, and sodicity data on CBM produced water. A model is sorely needed to make use of this data to quantify potential changes in stream water quality resulting from directly and/or indirectly receiving CBM produced water, on which little information is available in the literature. However, the application of existing hydrodynamic and water quality models such as CE-QUAL-W2 is not straightforward because the number of outfalls is usually large and the channels poorly defined for intermittent streams in semiarid areas such as the Powder River watershed, located in the states of Wyoming and Montana. Hence, the objectives of this study were to: (I) develop a CBM produced water routing (CBMPRO) model, and (2) apply the new CBMPRO model, along with a CE-QUAL-W2 model, to examine potential changes in stream water quality due to CBM development in the Powder River watershed. The CBMPRO model was developed and used to chart the CBM discharge and the transport of its associated constituents (e.g. total dissolved solids and alkalinity) from an outfall to its inclusive subwatershed outlet. In turn, the outputs from the CBMPRO model were applied as inputs into the CE-QUAL-W2 model to predict changes in the water quantity and quality along the Powder River mainstem. The results indicate that discharges from CBM developments adversely affect the stream water quality. Compared with the baseline conditions, the developments would increase the stream flows as well as make the stream water warmer and more saline. In addition, the impacts were predicted to undergo seasonal and spatial variations and to become smaller with time, as expected.