title: Effects of Flow Regime on Metal Concentrations and the Attainment of Water Quality Standards in a Remediated Stream Reach, Butte, Montana.
abstract: Low-flow synoptic sampling campaigns are often used as the primary tool to characterize watersheds affected by mining. Although such campaigns are an invaluable part of site characterization, investigations which focus solely on low-flow conditions may yield misleading results. The objective of this paper is to demonstrate this point and elucidate the mechanisms responsible for the release of metals during rainfall runoff. This objective is addressed using data from diel and synoptic sampling campaigns conducted over a two-day period. Low-flow synoptic sampling results indicate that concentrations of most constituents meet aquatic standards. This finding is in contrast to findings from a diel sampling campaign that captured dramatic increases in concentrations during rainfall runoff. Concentrations during the rising limb of the hydrograph were 2-23 times concentrations observed during synoptic sampling (most increases were >10-fold), remaining elevated during the receding limb of the hydrograph to produce a clockwise hysteresis loop. Hydrologic mechanisms responsible for the release of metals include increased transport due to resuspension of streambed solids, erosion of alluvial tailings, and overland flow. Rainfall also elevated the alluvial groundwater table and increased infiltration through the vadose zone, likely resulting in dissolution from alluvial tailings that were dry prior to the event.
authors.affiliation: U.S. Geological Survey , 3215 Marine Street, Suite E127, Boulder, Colorado 80305, United States.
authors.forename: Robert L
authors.initials: RL
authors.lastname: Runkel
authors.affiliation: U.S. Geological Survey , 2329 W Orton Circle, West Valley City, Utah 84119, United States.
authors.forename: Briant A
authors.initials: BA
authors.lastname: Kimball
authors.affiliation: U.S. Geological Survey , 3162 Bozeman Ave., Helena, Montana 59601, United States.
authors.forename: David A
authors.initials: DA
authors.lastname: Nimick
authors.affiliation: U.S. Geological Survey , Mail Stop 415, Denver Federal Center, Denver, Colorado 80225, United States.
authors.forename: Katherine
authors.initials: K
authors.lastname: Walton-Day
mesh_terms: D004784:Environmental Monitoring; D060587:Groundwater; D008670:Metals; D009009:Montana; D045483:Rivers; D014874:Water Pollutants, Chemical; D060753:Water Quality
chemical_list: D008670:Metals; D014874:Water Pollutants, Chemical