Design and analysis of a natural-gradient ground-water tracer test in a freshwater tidal wetland, West Branch Canal Creek, Aberdeen Proving Ground, Maryland

• DOI: 10.3133/sir20045190
• Publication Date: 2018-08-15T19:08:55Z
• Authors: Lisa D. Olsen; Frederick J. Tenbus
• Keywords: Piezometer; TRACER; Hydraulic head

A natural-gradient ground-water tracer test was designed and conducted in a tidal freshwater wetland at West Branch Canal Creek, Aberdeen Proving Ground, Maryland. The objectives of the were to characterize solute transport site, obtain data more accurately determine velocity upper sediments, compare conservative, ionic (bromide) volatile (sulfur hexafluoride) ascertain whether volatilization could be an important process attenuating organic compounds ground water. within peat unit layer sediments that also includes lower clayey unit; combined overlies aquifer. area selected for thought have above-average rate discharge based on head distributions near-surface detections measured previous studies. Because velocities expected slow compared underlying aquifer, small scale. Ninety-seven ?-inch-diameter inverted-screen stainless-steel piezometers installed cylindrical array approximately 25 cubic feet (2.3 meters) with vertically upward hydraulic gradient. Fluorescein dye used qualitatively evaluate hydrologic integrity before start test, including verifying absence short-circuiting due nonnatural vertical conduits potentially created during piezometer installation. Bromide sulfur hexafluoride tracers (0.139 liter solution containing 100,000 milligrams per bromide ion 23.3 co-injected monitored generate dataset three dimensions. Piezometers sampled 2 15 times each, from July 1998 through September 1999, assess background conditions monitor movement. During 644 samples analyzed fluorescein, 617 ion-selective electrode, 213 colorimetric methods, 603 hexafluoride, collected prior injection concentrations. Additional (96 samples) methane (37 distribution these contaminants extent methanogenic array; however, not analysis test. fluorescein dye, bromide, transported predominantly direction, although all moved outward directions point, it is likely some mass beyond lateral edges array. An tracer-test performed use breakthrough curves isoconcentration contour plots. Results show movement non-conservative tracer, retarded other two tracers, as result sorption onto sediments. Suspected loss along prevented straightforward quantitative sulfur-hexafluoride data. In addition, initial density bromide/sulfur (calculated 1.097 grams milli2 Ground-Water Tracer Test, MD liter) caused sink below point undergoing dilution moving back up into For reasons, this report largely qualitative method