Review Comments: "A Critical Evaluation of Slope Stability and Drainage of Surface Water and Groundwater at the Elizabeth Mine Site," by Richard W. McGaw, P.E.

I am not a geotechnical engineer; I will leave those aspects of Mr. McGaw's report to Dr. Richard Downer, P.E., the other C.A.G. consultant. I have reviewed McGaw's report in the context of pertinent water quality aspects. Mr. McGaw should be commended for his interest in this project and for his report, which contains an interesting and useful physical description of the site. His comments on slope stability and drainage may also be useful and reflect well on his expertise as a geotechnical engineer. Unfortunately, some of his other comments and suggestions either miss or minimize the main problem at hand. All of the many people involved in this project are involved because the site as it now exists is a source of very significant water pollution, and a very significant part of that contaminated seepage would continue even if all of Mr. McGaw's suggestions were implemented. He has also, erroneously, minimized the effectiveness of the EPA proposals with his comment "Considering that this protection involves no more than a reduction of metallic compounds in a small brook flowing into the West Branch, the justification for those large scale activities was not given." The justification has been clearly given, the purpose of the project is to eliminate the sources of pollution and to satisfy federal and State water quality standards. However, Mr. McGaw offers no feasible alternatives, apparently he believes that if the slopes are stable the pollution in the "small brook" and the West Branch are then of little consequence.

His experiences with remediation of waste asbestos sites are unfortunately not really relevant to the Elizabeth Mine site. The main issue at asbestos sites is movement of the asbestos fibers. Seepage of metallic pollutants and acidic substances is not usually an issue. Any seepage at an asbestos site is typically innocuous if the fibers are filtered and retained by the soil. Mr. McGaw's expertise on the freeze thaw of soils was usefully applied, by the EPA, to be sure that freeze thaw cycles, at northern sites, did not move and expose asbestos through the soil cover after remediation. Infiltration into these sites, and seepage are not typically issues of concern. However, these aspects are the main issues of concern at the Elizabeth Mine, and that is why the EPA has proposed diversion of surface runoff and elimination of precipitation infiltration into the tailings piles by capping them with an impermeable barrier. Mr. McGaw also proposes diversion of surface runoff, but this has already been a feature of the EPA plans from the beginning.

Mr. McGaw also recommends, "...in the strongest terms that the entire area of TP-3 be preserved in its present state except for the limited activities mentioned here (eg: in his report)." His "limited activities" would include diversion of surface runoff (already suggested by the EPA) and a chemical spray to coat "all of the particles" in the tailings piles. The source, and long term effectiveness of such an unproven spray is unknown. In a rational, and conservative design, it must be assumed that the tailings piles will continue to discharge significant water pollutants as a result of infiltration of rainfall and snow melt even after surface runoff is diverted. Mr. Robert Hedin, the EPA's expert consultant on acid mine drainage has indicated that the present seepage from TP 3 would be very difficult and expensive to treat due to the presence of aluminum and the high acidic content (See my report # 3 on the Elizabeth Mine Web site for details). Mr. Hedin would recommend complete removal of all the pollution sources at TP 3. In recognition of community interests, the EPA has suggested intermediate options where the worst of the pollution sources would be removed and a significant area preserved for historical purposes. Preservation of the entire TP 3 site as suggested by Mr. McGaw would then require construction of a very complex treatment system and very high operation and maintenance costs by the State of Vermont, and these maintenance activities (including significant truck traffic) and costs could persist for generations.

Mr. Hedin, and the other EPA experts believe that the seepage from TP 1 and 2 can be treated cost effectively because it contains little aluminum and lower acidity. Adjacent surface runoff would again be diverted and the purpose of the cap would be to significantly reduce the amount of precipitation infiltration. With both of these measures in place, the amount of seepage to be treated would, over time, be reduced to a very low level and the operation and maintenance requirements by the State of Vermont reduced to a minimum.

It is true that capping of TP 1 would destroy the existing surface vegetation on TP 1. Mr. McGaw suggests that "...the presence of the mature vegetation over three-fourths of the surface area also severely limits the amount of rain water that actually enters the surface..." This suggestion is not correct. The presence of such vegetation does serve to reduce surface erosion, but typically it serves to increase surface infiltration of rainfall. EPA proposes to revegetate the site, as part of the remedial effort, to again limit erosion. Such vegetation also does limit seepage and runoff through evapotranspiration (ET). In an arid climate such evapotranspiration might remove almost all of the precipitation. In this part of Vermont, evapotranspiration might account for up to 56 percent of the annual precipitation, with most of that occurring in the warm summer months.

Mr. McGaw provides an estimate of the retention time of the infiltrated rainfall in the TP 1 tailings before appearing as seepage. Such information is interesting, but not critical to the issue at hand, since the seepage is contaminated and apparently has been for many, many years. The annual average precipitation in this part of Vermont is about 35 inches per year, and the evapotranspiration about 19.8 inches per year. That leaves about 15.6 inches per year to either infiltrate or runoff. That is equivalent to about 420,000 gallons of water per acre per year. Assuming, in the worst case, that most of that infiltrates TP 1, there has been at least 130 million gallons of rainfall moving through TP 1 in the past 50 years and the seepage is still contaminated! It is impossible to predict how many more years and millions and millions of gallons would have to move through the tailings before the pollutants are all leached out.

In summary, it can be concluded that Mr. McGaw's report provides some useful insights on slope stability and drainage at the Elizabeth Mine site but it does not significantly address the main problem, or offer a meaningful alternative to the EPA proposals.

Sherwood C. Reed, P.E.
Principal, E.E.C.

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