Return to Retsof – Surface Geophysics Strikes Back
The Retsof salt mine experienced roof failure in 1994 that resulted in groundwater inflow from the basal unconsolidated aquifer and upper bedrock zones through two bedrock rubble ‘chimneys’. The mine subsequently filled with saturated brine due to solutioning of residual salt pillars in the mine cavity. Since the early 2000s, except for a period of remedial pumping in 2006 to 2013, high-salinity water has migrated upward through the rubble chimneys into the basal part the aquifer system. The extent of saline-water migration within the basal aquifer system had not been evaluated since the end of remedial pumping when all the monitoring wells were grouted and abandoned. An investigation of the current extent of saline water in the aquifer system began in the fall 2016 and the fall of 2017 by the U.S. Geological Survey in cooperation with the New York State Department of Environmental Conservation. During the two data collection periods, USGS collected time-domain electromagnetic and passive seismic soundings at 105 sites along 13 cross-valley transects north and south of the mine-collapse area, east of Piffard, New York, and further north on the Fowlerville Moraine in the Genesee River valley. An integrated analysis of the time-domain electromagnetic soundings with the passive seismic depth-to-bedrock estimates, well logs, and past chloride-monitoring data suggests the presence of a zone of high electrical conductivity associated with saline water in the confined basal valley-fill aquifer system that extends from the mine-collapse area northward for more than 2.5 miles. Saline water flowing upward through the bedrock-rubble chimneys mixes with northward groundwater flow in the thalweg of the bedrock valley where the basal confined aquifer is located. The northern extent of the high-conductivity zone is unclear because of the presence of what appears to be highly saline water that was delineated by time-domain electromagnetic soundings in the basal confined aquifer and uppermost bedrock in the area east of the hamlet of Piffard. This additional source of high conductivity water is probably associated with historic salt-solution wells in Piffard, or possibly sourced from natural brine pools, or from the upward migration of pressurized brine at the northern extent of the former salt mine within the Genesee Valley