Abstract

The eventual loss of the Retsof Salt Mine from flooding was initiated on March 12, 1994 with a magnitude 3.6 earthquake, the collapse of a small-pillar panel, an initial inrush of brine and gas to the mine and a sustained inflow of fresh water. An examination of closure data for two mine panels involved in the inflow suggested an anomalous buildup of fluid pressure above the panels in the period leading up to their collapse. The initial brine and gas inflow immediately following the collapse coincided with the apparent relief of the excess pressure. The potential existence of a pre-collapse, pressurized, brine and gas pool above the panels was investigated through an analysis of nineteenth century solution mining data, a review of recent salt mine data, and an interpretation of geologic and geophysical data from post-collapse investigations. Published reports from the nineteenth century reveal that natural brine and gas pools existed in the region prior to mining. Correlation of gamma ray logs with geologic logs from contemporary drill holes and core holes provided a mechanism for interpreting the distribution of those natural brine pools. Our investigation indicated that natural gas and brine pools existed within Unit D of the Syracuse Formation approximately 160 ft above the mining horizon. Such brine accumulation apparently formed from the circulation of meteoric water through vertical discontinuities that were connected to overlying fresh water aquifers long before mining began in the valley in the late nineteenth century.

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