Problem - Roof collapses in the Retsof salt mine near Geneseo N.Y. in March and April of 1994 propagated upward through overlying bedrock, forming a 600-ft-long rubble zone or chimney that connected the mine to a glacial aquifer system and created sinkholes at land surface. Fresh water from the glacial aquifers flowed downward into the mine until the mine was completely flooded in January 1996. The mine opening is predicted to slowly close over a period of several hundred years, with most of the subsidence occurring before 2070. As the mine opening closes, about 40 percent of the brine will be displaced from the mine and migrate upward through the rubble chimney. Continuing monitoring of chloride concentrations indicates that upward migration of saline water through the rubble chimney represents a continuing source of contamination in the lower glacial aquifer. While not presently used as a public water supply, this aquifer represents a significant source of potable water that could be utilized in the future.
Objectives - The objectives of the study are to (1) estimate the migration rate of saline water and brine through the rubble chimney, (2) assess the impact of pumping brine from this complicated flow system and (3) determine the area of the lower aquifer that could be contaminated by saline water emanating from the rubble chimney. A further objective is to identify potential chemical reactions that could occur in repsonse to mixing of halite brine with saline and fresh waters, and to estimate the volume of rock materials affected. A three-dimensional, variable-density solute-transport model will be developed to simulate the movement of saline water and brine in the collapse area above the flooded Retsof mine and within the lower glacial aquifer. The geochemical reactions will be identified through geochemical modeling by using PHREEQC.
Benefits - Model simulations will provide estimates of the hydraulic properties of both the rubble chimney and water-bearing zones in the collapse area. This information, together with the site-scale model, will be valuable in designing the appropriate placement and production rates of pumps used to intercept saline water in the rubble chimney. The regional model will delineate the extent of the area potentially affected by intrusion prior to commencement of pumping, and could be used to identify suitable locations for monitoring water quality in the lower glacial aquifer. Information derived from the aqueous geochemical models may be useful in designing the pumping system to minimize the potential adverse effects of chemical reactions that may arise as a result of mixing the different source waters. This analysis, together with simulations of pumping using the site-scale model, could aid in the selection of pumping horizons and rates that result in mixing proportions that produce water of acceptable quality for desalination. Estimates of the materials removed through dissolution could be used to assess whether long term pumping is likely to significantly increase void formation in the rubble chimney and destabilize the collapse area.
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“Perspective three-dimensional views - Retsof salt mine”