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ST. FRANCOIS CONFINING UNIT |
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Carbonate and shale rock core samples from the St. Francois confining unit
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| If lead-zinc mining is permitted in the new exploration area, the upper
part of the Bonneterre Formation near mine tunnels and shafts would be dewatered. There is concern that mine dewatering could lower
ground-water levels in the overlying Ozark aquifer and decrease the flow of springs and streams that receive ground water from the Ozark
aquifer. The USGS with the cooperation of the Missouri Department of Natural Resources; Geological Survey and Resource Assessment Division
(formerly known as Division of Geology and Land Survey) is evaluating the the vertical hydraulic conductivity of the St. Francois
confining unit to determine if mine dewatering in the St. Francois aquifer would be likely to lower water levels in the Ozark aquifer. The
investigation includes laboratory measurements of the vertical hydraulic conductivity of rock core samples from the St. Francois
confining unit collected from exploration boreholes by mining companies, as well as mapping of the thickness, altitude of top, and
shale content of the St. Francois confining unit (Kleeschulte and Seeger, 2000; Kleeschulte and
Seeger, 2001). The estimated vertical hydraulic conductivity of 10-12 to 10-14 ft/sec (foot per second)
determined for carbonate and shale rocks that form the St. Francois confining unit suggests that the unit forms an effective barrier to
ground-water flow. However, the investigation does not include an assessment of the occurrence or hydraulic properties of vertical
fractures that may extend through the St. Francois confining unit. A pilot study is being conducted to investigate the value of using
audio magneto-telluric surveys to determine the presence of vertical
fractures in the confining unit. |
Previous Studies
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[Dye-Trace Studies] [St. Francois confining unit] [Stream Seepage]
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For more information contact:
Michael J. Kleeschulte, Hydrologist
U.S. Geological Survey
Missouri Water Science Center
1400 Independence Rd., MS 100
Rolla, MO 65401
Telephone: (573) 308-3675
Fax:(573) 308-3645
U.S. Department of the Interior, U.S. Geological Survey
Maintainer: Rita Choate, Webmaster
Updated: August 25, 2003
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