Retsof salt mine collapse and aquifer dewatering, Genesee Valley, Livingston County, New York

Independent investigations by state and federal agencies have attributed the 1994 localized collapse and subsequent flooding at the Akzo Nobel Salt, Inc. (ANSI) salt mine near Cuylerville, New York, to collapse of bedrock and valley fill above an area of excessively wide yield-pillar panels. The 11.5-mi(2) room-and-pillar mine is located about 1100 ft beneath a glacially scoured valley. The mine filled with water in 21 months at a rate estimated to have been nearly 30,000,000 gal/day and drained ground water from overlying bedrock and glacial deposits. Surface subsidence is attributed to mine collapse, as well as to sediment compaction due to lowering of hydraulic head in unconsolidated valley-fill aquifers. Horizontal stresses, well documented in western New York, may have been responsible for loading the rock overburden to critical stress levels prior to mining. Regionally occurring high horizontal stress, combined with additional stress concentrated by the topography of the buried valley, may have created a broad valley anticline and fractures that are inferred to coincide with the axis of the buried valley. The collapsed panels were developed beneath the area where rock quality is inferred to have been affected by preexisting stress. The resulting stressed rock appears to have been mechanically incapable of providing the structural integrity required for the successful application of the yield-pillar mining method at the designed scale. This case history underscores the importance of geological and geomechanical exploration and characterization of rock and soil masses prior to engineering design.