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Evaluation of a bedrock aquitard for regional- and local-scale groundwater flow Kenneth R. Bradbury, Madeline B. Gotko

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Evaluation of a bedrock aquitard for regional- and local-scale groundwater flow Kenneth R. Bradbury, Madeline B. Gotko

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    2. Demonstrate the importance of a thin aquitard in a regional flow system Show how regional and local characterizations differ Purpose of this talk…

    4. Units in the “sandstone” aquifer

    6. Eau Claire aquitard is not the same as Eau Claire Formation

    8. Aquitard presence indicated by gamma signature and head drop

    9. Is the aquitard continuous?

    10. Thickness of “shale” facies ranges from 50 meters to absent in Dane County

    11. Hydraulic conductivity Kh= 6 x 10-5 m/day (packer/slug tests) Kv = 2.2x10-4 m/day (regional model calibration)

    12. Eau Claire aquitard

    13. Pumping has caused significant drawdown in the deep sandstone aquifer and steep vertical hydraulic gradients across the aquitard

    15. Regional conclusion Eau Claire is a “good” aquitard, and is a key part of the regional groundwater system In general, water beneath the aquitard should be quite old (100’s-1000’s of years)

    16. Profiles of head in the interior of aquitards are critical for understanding and evaluation Hydrostratigraphy often does not match “classic” rock stratigraphy Hydraulic properties not always apparent from lithology Aquitards are rarely monolithic or uniform

    17. Packer results – aquitard interval

    18. Aquitard characterization:

    19. Locally, viruses detected in deep groundwater in two city wells

    21. Human enteric viruses were detected in two wells cased below the aquitard

    23. Implications Describing the three-dimensional spatial distribution and hydrogeologic properties of aquitards at all scales is essential for proper understanding and predictive simulation of groundwater systems. Aquitards should receive the same attention as aquifers in groundwater investigations Regional- and local-scale properties may differ The roles of heterogeneities, fractures, and well construction should not be ignored

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