EPA letter - TP-1 stability 3-19-03

UNITED STATES ENVIRONMENTAL PROTECTION AGENCY
REGION I
ONE CONGRESS STREET SUITE 1100
BOSTON, MASSACHUSETTS 02114-2023
March 19, 2003
Elizabeth Mine Community Advisory Group
c/o Robert Walker, Chairperson
432 Ulman Rd.
Thetford Center, VT 05075
Dear EMCAG:

Recent work by the United State Environmental Protection Agency (EPA) indicates that there is the potential for the large tailing pile (a pile of processed rock often referred to as "TP-1") at the Elizabeth Mine Superfund Site to release a tailing flood wave (a large mudslide) that could threaten low lying areas of the West Branch of the Ompompanoosuc River. EPA has sent letters to notify those individuals living in homes that have been identified as being within the impact zone. EPA will be presenting more information regarding this matter at EMCAG meeting scheduled for Wednesday, April 9th at 7:00 p.m. at Barrett Hall in South Strafford.

I want to preface the following information with the fact that TP-1 has been abandoned and intact since 1958. While recent findings by EPA raise serious concerns regarding the stability and long-term integrity of TP-1, it is impossible to predict whether TP-1 will continue to remain intact as it has for 45 years. It is also impossible to predict when conditions will worsen resulting in the consequences described in this letter. It is quite possible that Site conditions will not deteriorate to the point that a failure of TP-1 occurs.

After careful consideration of the information available, including the possible consequences of a tailing dam failure, EPA and VTDEC believe that there is a need for immediate action to significantly reduce the potential for a slope failure and tailing flood wave. We have notified the local authorities of the situation and will be coordinating our efforts with them.

What is being done to minimize the hazard?

- EPA and VTDEC have begun monitoring the Site to identify any change in Site conditions and to provide notice to local authorities if conditions change.

- VTDEC will be installing debris racks to reduce the potential for material to enter and block the decant system (the decant system consists of concrete piping that currently drains surface water off the tailing pile).

- EPA will install pumps to reduce the water level on TP-1 in the event that the decant system were to become blocked or collapse.

- EPA will repair the internal dam erosion (piping) of material out of the tailing dam as soon as possible.

- EPA is seeking funds to install a temporary surface water diversion system to replace the need for the pumps and to install a more permanent surface water diversion system to divert surface water around TP-1.

With these measures, EPA and VTDEC will have implemented all reasonable precautions to minimize the chance of a tailing dam failure. EPA and VTDEC will also be working with local authorities to provide regular updates regarding Site conditions and to assist in the development of an emergency response plan.

I have attached additional information to better explain the circumstances at the Site and the basis for the concern expressed by EPA and VTDEC. Please read this information and feel free to come to the meeting or call and ask questions. For information about the emergency response plans associated with this situation, please contact your local Emergency Management Director or Selectboard.

You may also contact Ed Hathaway, US EPA at (617) 918-1372 or toll free: 1-888-372-7341 ext. 91372,email address: hathaway.ed@epa.gov or John Schmeltzer, VTDEC at (802) 241-2886 and email:johns@dec.anr.state.vt.us if you have any questions regarding the activities at the Site.

Sincerely,

Edward Hathaway, RPM
ME/VT/CT Superfund Section

Attachment 1

Information Relating to the Geotechnical/Stability Concerns at the Elizabeth Mine
March 2003

The information below provides a detailed explanation of the five factors which contribute to the identification of TP-1 as a significant hazard, and why EPA is concerned about the stability of TP-1.

The first is the nature of the material contained within both TP-1 and TP-2. The tailing material was generated during the copper mining of 1942 - 1958. The tailing material behaves like a silt material such that when saturated or exposed to water, it becomes suspended and flows with the water. The tailing slurry was deposited at the downstream edge of TP-1. This caused a physical separation of the tailing slurry. The more coarse-grained, better draining, material was retained along the outer edge of the tailing pile and the higher water content, less well draining material accumulated within the interior. The end result is that the outer well drained material forms the dam that holds back the other material. A breach in that outer dam portion of TP-1 would result in the release of the fine grained material and this material would flow with the water released from TP-1. TP-1 covers over 30 acres and contains approximately 2 million cubic yards of material, most of which is the fine grained weaker material.

The second factor is the deteriorating drainage system for TP-1. The entire 300-acre upper Copperas Brook watershed drains on to TP-1 and flows through a deteriorating drainage system designed and built in the 1940's and 1950's as a decant system for the tailing slurry deposition. Recent video inspection of the decant system revealed it to be in poor condition with cracks and partial blockage due to encrustation and debris. It is reasonable to assume that at some point in the future the decant system will cease to function and significant quantities of water will accumulate on top of TP-1.

The third factor is the potential problem that could arise once the drainage system is no longer functioning. If the decant system were to become blocked or to collapse due to deterioration, water would pond on the surface of TP-1 with three potential negative consequences.

1. An increase in the water level on TP-1 would result in additional infiltration into TP-1 with a resulting rise in amount of water stored within TP-1. A five to fourteen foot increase in the water table within TP-1 could cause internal instability that could result in a slope failure and massive release of tailing material.

2. There is currently internal erosion of the tailing dam. Internal erosion, also known as piping, occurs when fine material from within the pile is carried out with seepage and causes a sinkhole, which can collapse and cause failure of the dam. An increase in the water level within TP-1 will create more internal erosion, which increases the chance that the internal erosion will result in a slope failure and massive release of tailing material.

3. If the water on top of TP-1 were to increase to a level where the water overtopped TP-1, the resulting erosion could result in a slope failure and massive release of tailing material.

The fourth factor is the behavior of the tailing material once the tailing dam is breached through slope failure, internal dam erosion (piping), or overtopping. Based upon experiences at other similar sites and computer modeling results evaluating these types of events, a preliminary estimate of a tailing dam failure and release at the Elizabeth Mine suggest that between 500,000 and 1,000,000 cubic yards of tailing could be released depending on the actual breach geometry and the amount of water in the decant pond at the time of the failure. The resulting flood wave would be eight to nine feet high and travel at a velocity of 10 - 15 feet per second (7-10 miles per hour). The flood wave would travel a distance of one to five miles from the Site with a significant quantity of tailing material being transported from the confluence of Copperas Brook and the West Branch of the Ompompanoosuc River into the Connecticut River. The fifth and final factor (and most critical factor) in identifying the potential failure of the tailing dam at the Elizabeth Mine as a significant hazard is the potential impacts to human health and the environment. There is a serious concern that a tailing flood wave could overtop the West Branch of the Ompompanoosuc River in the low lying sections between Copperas Brook and Rices Mills. Many structures impacted by the flood wave would be seriously damaged, potentially threatening the lives of any occupants of those buildings. Ten to fifteen structures have been identified within the potential impact area of a tailing dam failure. The environmental impacts of the release would also be severe with the potential for a major fish kill and high metal/low pH conditions in the impacted stretch of water for an extended period of time (possibly tens of years). The environmental impacts would extend from Copperas Brook to the Connecticut River and possibly into the Connecticut River.

Attachment 2

Additional Technical Information and Definitions: This information was obtained from the website: http://www.antenna.nl/wise/uranium/mdas.html#WATERLEVELRISE and site specific facts were added as deemed appropriate.

Tailing: Tailing are the residue of the milling process that is used to extract metals of interest from mined ores. During this process, ores are first milled and finely ground, and then treated in a hydrometallurgical plant. Since the extracted metal represents only a small percentage of the whole ore mass, the vast majority of the material mined ends up as a fine slurry. The tailing contain all other constituents of the ore but the extracted metal, among them heavy metals and other toxic substances. Moreover, the tailings also contain the chemicals added during the milling process. In addition, as a result of the milling process, all these contaminants now are much better available for dispersion into the environment than in the original ore. The mechanical stability of the tailing mass is very poor, due to its small grain size and the usually high water contents.

Tailings impoundments: Most of the mill tailings mass produced worldwide is dumped in large surface impoundments ("tailings dams"). The embankments forming these impoundments are earthfill dams. Although water-retention type dams would be very suitable for tailings dams, they are not used for their high cost. Unlike water-retention type dams, tailings dams usually are not constructed initially to completion, but raised sequentially as the impoundment fills. At the Elizabeth Mine, TP-1 and TP-2 are tailing dams.

Upstream Tailing Dams: TP-1 and TP-2 were constructed as Upstream Tailing Dams: Upstream-type embankments are the most popular embankments for tailing dams; new parts of the embankment are built on top of the slurries impounded during the previous stage - the dam crest thus moving "upstream". For its low cost, the upstream embankment type is used with most tailings dams worldwide, but it bears the highest risk. Dam stability is of particular concern with this type of tailings embankments. Upstream dams are particularly susceptible to liquefaction under severe seismic ground motion. This motion may result from earthquakes, from nearby mine blasting, or even from nearby motion of heavy equipment, for example. Upstream dam stability is endangered if the raising rate of the dam is too high. Raising rates greater than 15 m/yr can be hazardous. They can produce excess pore pressure within the deposit, decreasing stability.

Phreatic Surface: ?The phreatic surface is critical for the dam stability. Dam failure can occur, if the beach width between the decant pond and the dam crest becomes too small - from flood inflow, or from improper mill operation, for example. While the determination of phreatic surface location is so important for upstream-type embankments, it is more complex by far for this embankment type than for any other type of tailings-retention structure.