Browsing by Author "Dalgleish, Janet B"

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    Dye Tracing Through Thick Unsaturated Zones
    (Proceedings of the 5th International Symposium on Underground Water Tracing. The Institute of Geology and Mineral Exploration, Athens, Greece, 1986. Edited by A. Morfis, P. Paraskevopoulou. Reprinted from Proceedings p.p. 181-188, 1986) Alexander Jr., E. Calvin; Davis, Marsha A; Dalgleish, Janet B
    Using the fluorescent dye Rhodamine WT, a field fluorometer, and direct samples of water collected from springs, wells, cave drips, and pools we have conducted two successful dye traces through thick unsaturated zones in karst regions. The first dye trace was of a proposed expansion site for a landfill in Winona County, southeastern Minnesota. The site sits on top of a narrow ridge about 150 meters above the adjacent valleys. The second trace was at Jewel Cave National Monument in the southern Black Hills of South Dakota. This trace was initiated to evaluate the impact of tourist facilities on the underlying cave. A visitor center was constructed on the surface, 50 to 100 meters directly above the cave. In both traces, small, irregular pulses of dye began to appear (in springs and wells at the Winona Landfill site and in cave drips and pools at Jewel Cave) within days of the dye injection, and the pulses continued to emerge for months. The pulses were typically a day or less in duration and a very small (10s to 100s of parts per trillion, 10- 12 g/g). The pulses are more frequent after major precipitation/runoff events but appear to be moving through both unsaturated zones in a very irregular, stochastic fashion. The very low levels of dye detected in many of the pulses required so.me type of confirmation analysis. We have successfully used the large negative temperature coefficient of Rhodamine WT's fluorescence to discriminate between low levels of Rhodamine WT and fluorescence due to background materials.
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    Sinkhole Distribution in Winona County, Minnesota
    (Proceedings of the First Multidisciplinary Conference on Sinkholes. Orlando, Florida 15-17 October 1984. "Sinkholes: Their Geology, Engineering and Environmental Impact. Edited by Barry F. Beck of the Florida Sinkhole Research Institute, University of Central Florida, Orlando. Page 311 - 318. Taylor & Francis, London, UK. Offprint., 1984-10-17) Dalgleish, Janet B; Alexander Jr., E Calvin
    Winona County, located in southeastern Minnesota, is part of a karst region in the upper Mississippi Valley. The karst is developing in flat-lying dolomitic Ordovician rocks. As part of a Minnesota Geological Survey county atlas program, we have systematically field located sinkholes, and prepared a 1 to 100,000 scale map showing sinkhole locations and sinkhole probability. We located 535 sinkholes in Winona County (~1600 [sq-km]). Most of these relatively small, geomorphically young sinkholes are not included in the USGS 7.5 minute topographic maps and cannot be readily detected on air photos. The sinkhole density, while low compared to many karst regions was much greater than local, regional, and state land use planners anticipated. New bedrock, surficial and hydrogeology maps of Winona County were used for correlation with the geographic distribution of the sinkholes. The primary control on the distribution of sinkholes appears to be the bedrock stratigraphy. The secondary controls, not necessarily in order of importance include slope of the land surface, and composition of surficial materials. The depth to the water table does not appear to have an important [effect] on sinkhole development. Age data indicate that the rate of sinkhole formation has [significantly] increased in recent years.