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Dye-tracer tests were done during 1985-92 to investigate the hydraulic connection between fractures in Pennsylvanian coal-bearing strata at a ridge-and-valley-wall site near Fishtrap Lake, Pike County, Ky. Fluorescent dye was injected into a core hole penetrating near-surface and mininginduced fractures near the crest of the ridge. The rate and direction of migration of dye in the subsurface were determined by measuring the relative concentration of dye in water samples collected from piezometers completed in conductive fracture zones and fractured coal beds at various stratigraphic horizons within the ridge. Dye-concentration data and water-level measurements for each piezometer were plotted as curves on dye-recovery hydrographs. The dye-recovery hydrographs were used to evaluate trends in the fluctuation of dye concentrations and hydraulic heads in order to identify geologic and hydrologic factors affecting the subsurface transport of dye. The principal factors affecting the transport of dye in the subsurface hydrologic system were determined to be (1) the distribution, interconnection, and hydraulic properties of fractures; (2) hydraulic-head conditions in the near-fracture zone at the time of dye injection; and (3) subsequent shortand long-term fluctuations in recharge to the hydrologic system. In most of the dye-tracer tests, dye-recovery hydrographs are characterized by complex, multipeaked dyeconcentration curves that are indicative of a splitting of dye flow as ground water moved through fractures. Intermittent dye pulses (distinct upward spikes in dye concentration) mark the arrivals of dye-labeled water to piezometers by way of discrete fracture-controlled flow paths that vary in length, complexity, and hydraulic conductivity. Dye injections made during relatively highor increasinghead conditions resulted in rapid transport of dye (within several days or weeks) from near-surf ace fractures to piezometers. Injections made during relatively lowor decreasing-head conditions resulted in dye being trapped in hydraulically dead zones in water-depleted fractures. Residual dye was remobilized from storage and transported (over periods ranging from several months to about 2 years) by increased recharge to the hydrologic system. Subsequent fluctuations in hydraulic gradients, resulting from increases or decreases in recharge to the hydrologic system, acted to speed or slow the transport of dye along the fracture-controlled flow paths. The dye-tracer tests also demonstrated that mining-related disturbances significantly altered the natural fracture-controlled flow paths of the hydrologic system over time. An abandoned underground mine and subsidence-related surface cracks extend to within 250 ft of the principal dyeinjection core hole. Results from two of the dye-tracer tests at the site indicate that the annular seal in the core hole was breached by subsurface propagation of the mining-induced fractures. This propagation of fractures resulted in hydraulic short-circuiting between the dye-injection zone in the core hole and two lower piezometer zones, and a partial disruption of the hydraulic connection between the injection core hole and downgradient piezometers on the ridge crest and valley wall. In addition, injected dye was detected in piezometers monitoring a flooded part of the abandoned underground mine. Dye was apparently transported into the mine through a hydraulic connection between the injection core hole and subsidence-related fractures. INTRODUCTION In summer 1985, the U.S. Geological Survey, in cooperation with the Kentucky Geological Survey and the U.S. Office of Surface Mining Reclamation and Enforcement, investigated ground-water flow in Pennsylvanian coal-bearing strata at a ridge-and-valley-wall site near Fishtrap Lake, Pike County, Ky. The investigation was designed to accomplish the following two main objectives: (1) to evaluate the importance of fractures to the circulation of ground water in a topographic and geologic setting typical of the Appalachian Plateaus Physiographic Province, and (2) to provide evidence to refute a previously held concept that the stratification of sedimentary rocks of relatively low primary porosity and permeability provides hydrogeologic isolation between ridgetops and valley-bottom aquifers in the Appalachian coal fields. Eight core holes were drilled to various depths along the ridge and valley wall to begin the investigation, and a series of down-hole pressure-injection tests were done to identify hydraulically conductive intervals in each core hole. The results of the pressure-injection tests indicated that the most hydraulically conductive intervals in each core hole were associated with fracture zones and coal beds (Davis, 1987). Multiple piezometers were installed in most core holes to monitor changes, over time, in hydraulic head in fracture zones and coal beds at various depths. A dye-tracer test was then done to determine the hydraulic interconnection between the various piezometer zones. The dye-tracer test was done by injecting rhodamine WT (a red fluorescent dye) into a 61-ft-deep core hole drilled near the crest of the ridge. This core hole penetrates numerous near-surface and (as determined later) mining-induced fractures. The rate and direction of flow of dye to piezometers downgradient from the injection site was determined by collecting water samples and analyzing for the presence of dye. Within 14 days, rhodamine WT was detected in water samples collected from all the piezometers. This result demonstrated not only the hydraulic interconnection of the fracture zones and coal beds within the ridge, but also the rapidity with which dye (in ground water) could migrate through fractures from the ridgetop to the valley floor (estimated at an average velocity of about 36 ft/d by Davis (1987)). In an effort to confirm and refine the results of the initial dye-tracer test, five additional dye-tracer tests were done at the site during 1987-92. Preliminary evaluations of the data from these subsequent dye-tracer tests indicated that the apparent rate and pattern of dye migration to piezometer zones varied from one test to another and differed significantly from the first tracer test. This variation indicates that the subsurface transport of dyes injected into the ridge was affected by hydrologic properties not present or recognized during the initial dye-tracer test. Because these factors may be of significance to other studies of ground-water hydrology associated with coal-bearing strata in the Appalachian Plateaus Physiographic Province, the collective results of the dye-tracer tests at the site were examined in more detail. Purpose and Scope This report presents a summary and interpretation of dye-tracer tests done at the Fishtrap Lake study site during 1985-92, and it identifies and examines the geologic and hydrologic factors that affected the transport of fluorescent dye tracers through fracture zones at the study site. These factors are also expected to control the movement of ground-water contaminants through the type of hydrologic system associated with steep-sided ridge-and-valley topographic settings in the Appalachian Plateaus Physiographic Province. This information should be useful to the refinement of conceptual models of ground-water flow and will aid the development of ground-water monitoring programs needed to assess the effects of coal-mining and other land-use activities on the Appalachian region's ground-water resources. Description of Study Site The study site is delineated by the locations of core holes drilled along the crest and west valley wall of a ridge on the north shore of Fishtrap Lake, a U.S. Army Corps of Engineers impoundment on the Levisa Fork of the Big Sandy River in central Pike County, Ky. (fig. 1). The north-south-trending ridge is the topographic drainage divide between the Left Fork of Grapevine Creek to the east and an unnamed intermittent stream to the west. The site is on the Lick Creek topographic quadrangle (1:24,000) in the Kanawha Section of the Appalachian Plateaus Physiographic Province (Fenneman, 1938). This area is characterized by considerable topographic relief between narrow ridgetops and steep-sided valleys. The rugged topography is mostly the result of extensive stream dissection and downcutting of sedimentary rocks that are variably resistant to erosion. Near Fishtrap Lake, land-surface elevations range from more than 1,800 ft on ridgetops to about 700 ft along the valley floors. Land-surface elevations at the core holes at the site range from about 1,360 to 890 ft. The ridge rises to an elevation of more than 1,700 ft above (north of) the uppermost core hole. Underground mining has occurred beneath much of the ridge, and parts of an abandoned underground mine extend to within several hundred feet of the core holes at the site (fig. 1). Geologic Setting The eight core holes drilled at the site extend to various depths in strata of the Breathitt Formation of Lower and Middle Pennsylvanian age (McKay and Alvord, 1969). The Breathitt Formation consists mostly of interbedded and intergradational shale, siltstone, sandstone, and coal deposited in a former fluvial-marine environment similar to that of the modem-day Mississippi River delta complex. The stratigraphy of the Breathitt Formation is characterized by complex intertonguing, lensing, and pinching-out of beds. Stratigraphic correlations are difficult at local and intermediate scales, owing to rapid lateral and vertical changes in sedimentary facies within the formation. Determinations of Stratigraphic position within the Breathitt Formation must generally be made on the basis of distinctive fossiliferous strata and coal zones. Lithologic descriptions of rock cores retrieved during core-hole drilling (Davis, 1986) were used to prepare two geologic sections of the study site (pi. 1). Much of the strata at the site consist of interbedded shale (

water-resources investigations report

Summary and interpretation of dye-tracer tests to investigate the hydraulic connection of fractures at a ridge-and-valley-wall site, near Fishtrap Lake, Pike County, Kentucky