Paper No. 5
Presentation Time: 2:10 PM


HEILWEIL, Victor M., Utah Water Science Center, U.S. Geological Survey, 2329 Orton Circle, Salt Lake City, UT 84119, SOLOMON, D. Kip, Geology and Geophysics, University of Utah, Frederick Albert Sutton Building, 115 S. 1460 E. Rm 383, Salt Lake City, UT 84112, DARRAH, Thomas H., School of Earth Sciences, Ohio State University, 125 South Oval Mall, Columbus, OH 43210, RISSER, Dennis W., Pennsylvania Water Science Center, US Geological Survey, 215 Linekiln Road, New Cumberland, PA 17070, HYNEK, Scott A., Geosciences, Penn State University, 302 Hosler Building, University Park, PA 16802 and GRIEVE, Paul, Geosciences, Penn State, 236 Deike, State College, PA 16802,

The baseflow of gaining streams can provide an integrated chemical signal for groundwater systems. It may be possible to evaluate impacts from natural gas drilling and hydraulic fracturing to regional aquifers by sampling such streams. The stream-reach methane (CH4) mass balance method is one approach for establishing baseline groundwater quality prior to natural gas development and detecting subsequent contamination. This method has the advantage of using stream-integrated chemistry to indirectly monitor groundwater quality at the watershed scale, rather than relying on point values from monitoring wells. A tracer injection experiment in Nine-Mile Creek, a moderate-gradient stream in the Colorado Plateau Province of Utah, showed the downstream persistence of CH4 for over 1.5 km downstream and yielded an “apparent” gas transfer velocity of 4.5 m/d. The “apparent” gas transfer velocity primarily describes CH4 loss to the atmosphere, but may include microbial degradation. To evaluate the stream methane method in other climatic settings, a second experiment was conducted along West Bear Creek, a low-gradient stream in the Piedmont Province of North Carolina. The injected CH4 persisted for more than 2.5 km downstream. A noble gas (krypton) was also injected in order to separate atmospheric CH4 loss from any microbial degradation. Comparison of the gas transfer velocities determined from CH4 and Kr will indicate whether microbial degradation is a significant process (work is in progress). These methods are now being applied through pilot-scale studies in the Marcellus shale-gas play of Pennsylvania by the USGS and Pennsylvania State University. Preliminary reconnaissance sampling has yielded stream methane concentrations of up 20 ppb (1300 nMol/L). Follow-up work along a gaining reach of Sugar Run using an un-calibrated stream-reach mass balance (with 1-D advective transport modeling) indicated inflowing groundwater with CH4 concentrations of about 300 ppb (20,000 nMol/L); a gaining reach of Tunkhannock Creek showed a trend of 13C-CH4 enrichment (from -55 to -39 permil), indicating a possible thermogenic source. Future work in both streams includes CH4 isotopic fingerprinting to evaluate sources (biogenic or thermogenic) and tracer injections for quantifying gas transfer velocities.