HR: 0830h
AN: H41C-1021    [PDF]
TI: A Test of a Major-ion Toxicity Model to Predict the Toxicity of Coal Bed Methane Product Waters to Aquatic Biota
AU: * Forbes, M B
EM: mforbes@uwyo.edu
AF: University of Wyoming, Department of Zoology and Physiology, Laramie, WY 82071-3166 United States
AU: Meyer, J S
EM: meyerj@uwyo.edu
AF: University of Wyoming, Department of Zoology and Physiology, Laramie, WY 82071-3166 United States
AB: Coal bed methane (CBM) accounts for about 7.5% of the total natural gas production in the United States, and the Powder River Basin (PRB) in Montana and Wyoming has recently become a major production area. During CBM extraction, a coal seam is partially de-watered to relieve hydraulic pressure, thus causing methane gas to desorb. Some of this water (called product water) is discharged on the land surface and allowed to run into local drainages in the PRB. Due to the massive amounts of product water being discharged (rates up to 64,000 L/day per well), studies are needed to examine the potential effects on aquatic organisms. Additionally, models to predict such effects would be useful regulatory screening tools. To that end, we tested the ability of a multivariate logistic regression model of the toxicity of major inorganic ions (i.e., Na$^{+}$, K$^{+}$, Ca$^{2+}$, Mg$^{2+}$, Cl$^{-}$, HCO$_{3}$$^{-}$, SO$_{4}$$^{2-}$) to predict the acute toxicity of CBM-related waters to two aquatic invertebrates ({\it Ceriodaphnia dubia} and {\it Daphnia magna}) and fathead minnows ({\it Pimephales promelas}). First, we entered water chemistry data for several CBM product and receiving waters from the PRB into the major-ion model. Then we compared the model's predicted survival to the survival of the three species in toxicity tests we had previously conducted with those waters. For the majority of CBM product water and stream water samples in which CBM product water constituted the entire flow of the stream, the major-ion model consistently under-predicted survival by $>$50%. Therefore, from a regulatory standpoint, this model is conservative for detecting toxicity of CBM product waters (i.e., it over-predicts toxicity). Although the model appeared to be an excellent predictor of survival for receiving waters that contained no inputs from CBM processing (i.e., the difference between predicted and observed survival was $\leq$10%), the majority of those cases were inconclusive tests of the model because the predicted and observed survival were either both $>$90% or both $<$10%. In such cases, it was not possible to test the accuracy of the regression coefficients in the major-ion model.
DE: 1615 Biogeochemical processes (4805)
DE: 1831 Groundwater quality
DE: 1871 Surface water quality
SC: Hydrology [H]
MN: 2003 Fall Meeting