Tracer Study for Characterization of Groundwater Movement and Contaminant Transport in Fractured Dolomite

Abstract: The authors characterized and instrumented a small (125 x 75 ft) study site located in an active dolomite quarry in Door County, WI. The quarry floor was cleared of sediment and vertical fractures were mapped and digitized. Eighteen boreholes, including five coreholes, were drilled to a depth of 35 ft. Borehole geophysical logs revealed several laterally extDoor ensive horizontal fractures and dissolution zones. Flowmeter and short-interval packer testing identified which of these features were hydraulically important. The monitoring system, consisting of multi-level samplers installed in 11 of the boreholes, was designed to monitor four horizontal fractures and two dissolution zones. Data on the hydraulic conductivity of the fracture network were obtained from a multi-well pumping test conducted with eight 35-ft open boreholes, a second pumping test conducted after the multi-level samplers had been installed, and packer tests conducted with a 0.75-ft straddle interval. The distribution of hydraulic head was monitored in both open boreholes as well as in the discrete intervals of the multi-level samplers. Several controlled-gradient and one ‘ natural-gradient tracer tests completed at the site yielded horizontal and vertical groundwater velocities on the order of 10’s to 100’s of ft/day. A two-dimensional discrete fracture flow model was used to simulate one of the controlled-gradient tracer tests. Using measured data on fracture characteristics, the model reproduced data from the tracer experiment relatively well.

To develop a better understanding of the movement of groundwater and contaminants in shallow, fractured, carbonate aquifers. The study was designed to 1) provide a better understanding of the hydrogeology of fractured dolomite in terms of advective flow rates and hydraulic conductivity distributions; 2) generate a data set for use in evaluating existing fracture-flow computer codes; 3) help determine the scales at which it is appropriate to approximate fractured carbonate rock as an equivalent porous medium; and 4) test the effectiveness of monitoring wells in a fractured-rock setting.

Final report linked covers the work of two grants:  DNR-101/WR92R010 (July 1992 to June 1994) and WR94R016 (July 1994 to June 1996).