Abstract: Soil Remediation at Natural Gas Mercury Meter Stations in Montana and Northwestern Wyoming

Guy J. Larango

The Montana Power Company initiated voluntary soil assessment and remediation at natural gas meter stations reported to have contained a mercury manometer at some time during facility operation. Remedial sites were selected according to criteria developed from data collected during a Phase I Assessment of approximately 400 facilities. The Montana Power Company and the Montana Department of Environmental Quality agreed upon a soil cleanup action level of 23 parts per million Total Mercury. Remedial field work included an initial assessment with a mercury vapor analyzer to determine the areal extent of impact at each site, excavation of soil until laboratory analyses of confirmation samples met the cleanup action level, and disposal of the excavated soil.

The mercury meters were typically housed in small sheds measuring less than 10 feet by 10 feet. Generally, the spilled mercury was confined to areas beneath or adjacent to the meters; but in some cases, mercury was detected in other areas inside and outside the sheds. Approximately 355 cubic yards of soil at 103 sites were excavated primarily by hand and occasionally with a backhoe, and placed in one-yard soil bags for disposal. Composite soil samples were collected from each soil bag and analyzed by the Toxicity Characteristic Leaching Procedure for mercury to characterize the material as hazardous or non-hazardous. Bags characterized as non-hazardous were transported to an industrial landfill in Montana, while bags characterized as hazardous were transported to a facility in Tenness e where the mercury was recovered through a recycling process.

AAPG Search and Discovery Article #90952©1996 AAPG Rocky Mountain Section Meeting, Billings, Montana