You are here:
SURFACE AND GROUNDWATER INTERACTIONS AND EFFECTS ON SODIUM ADSORPTION RATIOS IN COALBED METHANE EXTRACTION AREAS
Impact/Purpose:
The Powder River Basin (PRB) of Wyoming and Montana are experiecing extensive coalbed methane (CBM) exploration and extraction. In order to extract coalbed methane, groundwater must be pumped to depressurize the reservoir and allow desorption of methane from the coal. High soil erosion rates, poor water quality and the depletion and/or contamination of shallow aquifers used for domestic or stock water are some of the major concerns of the people affected by CBM development. The produced water is either discharged into streams or discharged on the soil surface, flooding local areas that are used as rangeland. Results from other studies have shown that high dissolved solids, high sodium levels, high specific conductance, and high sodium adsorption ratios (SAR) typically characterize these waters. The hypothesis of this study is that there are sufficient ground and surface water interactions to lower the SAR that is being observed in these CBM waters. Six discharge streams to the Powder River will be assessed for these surface-ground water interactions. Three discharge streams will be sampled that have relatively short (or fast) travel time to the Powder River, and three streams will be sampled that have longer flow paths or slower travel times to the Powder River. Water quality samples will be collected from surface waters and ground waters will be collected from nested piezometers at three points on each discharge stream. The hypothesis is that the surface water discharge will have sufficient time to interact with the soils, particularly the calcareous soils to allow dissolution of divalent salts to decrease the sodium adsorption ratio and improve CBM discharge water quality.
The objectives of this project will be to determine if surface water and ground water interactions can lower the sodium adsorption ratio (SAR) of coalbed methane discharge waters. This will be tested by sampling discharge points for CBM wells and by sampling surface water and shallow groundwater, along the discharge stream. These samples will be tested for Ca, Mg, and Na in order to calculate the SAR of these waters. In-field analysis will include temperature, discharge rate, pH, and specific conductance for each water quality sample.
Description:
This project will be conducted in the Powder River Basin area of northeastern Wyoming. Sampling will start in May, and repeat sampling will be done monthly. To examine the interactions of the production water with the soil and the subsequent effects on SAR, 6 CBM water discharge locations will be used. To quantify the surface water/groundwater exchange, an in-stream tracer test using potassium bromide will be performed. The resulting data will be statistically analyzed for concentrations of Ca, Mg, Na, and the SAR of the sampling areas. The data obtained from this study will be compared to the data from the Powder River using Tukey's Honestly Significant Difference (HSD) method and using the Ryan, Einot, Gabriel, and Welsh (REGWQ) method. Both of these methods control both the Maximum Experiment wise Error Rate (MEER) and the Experiment wise Error Rate under Complete Null Hypothesis (EERC). Objective: The objectives of this project will be to determine if surface water and ground water interactions can lower the sodium adsorption ratio (SAR) of coalbed methane discharge waters.