Failure modes and effects analysis for Ely Mine

Challenge

The Ely Mine is an abandoned copper mine near Vershire, Orange County, Vermont. Ely Mine lies in the Ely Brook valley north of Schoolhouse Brook, a tributary of the Ompompanoosuc River. The mine was exploited from 1853 to the early 1900’s and again sporadically during World Wars I and II.

Ely Mine was an underground hardrock mine with shafts, stopes, and adits. The main shaft of the mine extends to a depth of approximately 1,400 ft. below ground surface (bgs). Successive owners and/or operators of the mine developed plans to better follow the ore body and extract the richest ore resulting in a maze of underground workings.

The first layout and associated cross sections of the underground workings were developed in 1944 by the U.S. Geological Survey (USGS) in a report including a detailed description of the geology of the area and complemented by numerous follow-on investigations. The USGS identified the adits and shafts and noted that there are two networks of underground workings believed not to be connected.

Solution

SLR toured the site and collected the information relevant to the Failure Modes and Effects Analysis (FMEA) including:

• Layout of the underground workings;
• Geology of Ely Mine;
• Groundwater regimes as understood in 2016; and
• Proposed remediation.

SLR identified the potential failure modes associated with the underground workings considering triggering events such as earthquakes, extreme weather, and disturbances induced during the performance of additional investigations and during construction.

The FMEA was casted in a probabilistic framework through a measure of the likelihood (probability) of occurrence of each failure mode and a measure of the consequence of each failure mode. The results were combined in a colour-coded risk characterisation matrix, as shown in the figure above.

Impact

The following conclusions were drawn from FMEA conducted at the underground workings of Ely Mine:

• The risk of catastrophic failure and associated release of mine impacted water is low.
• Conditions near the portal should be investigated further.