A CRITICAL EVALUATION OF SLOPE STABILITY AND DRAINAGE OF SURFACE WATER AND GROUND WATER AT THE ELIZABETH MINE SITE

with Recommendations toward the Superfund Remediation of Metallic Compounds in Copperas Brook consistent with Historic Preservation of the Site

Richard W. McGaw, P.E.
Geotechnical Engineer January 2002

BACKGROUND

The Elizabeth Mine Site in South Strafford, Vermont has been determined to be an important and valuable artifact of an era of human endeavor that spanned a period from the early 19th Century to World War II and beyond (1809-1958). In the mining and processing of copperas (a copper compound), and finally of copper itself from the same ore body, the people who worked this site were supporting the development of a new and innovatively democratic country.

It is instructive to realize that the Elizabeth Mine was in active operation during the war of 1812, the building of canals and railroads in the 1830s, the California gold rush of 1849, the Civil War and the abolition of slavery, the settling of the West, the Spanish-American War, World War I, World War II, and the Korean War. Although not as extensive as modern copper-mining operations, the Elizabeth Mine represents an enduring application on a single site of individual enterprise and independent effort, human values that are important in American society, and particularly basic to the traditional culture of Vermont. If preserved, renewed where appropriate, and protected into the future, the mine site landscape of tailing piles and of foundations and buildings that housed specialized processes, will become an educational resource to remind and inform ourselves and future generations of a long period in U.S. history during which the country, New England, and Vermont were evolving into the "modern" communities we know today.

ABOUT THE AUTHOR

The writer is a geotechnical engineer who works as a consultant on engineering problems involving surface drainage, underground drainage, and the stability against failure of soil embankments, both natural and man-made. Not surprisingly, an assessment of slope stability always involves considerations of drainage inasmuch as natural soils gain (and lose) much of their strength from the physical and chemical interaction of water, soil grains, and gravity.

The writer holds a bachelor's degree in civil engineering from the University of Michigan, where he studied the strength of materials, hydraulics, hydrology, geology, and structures. Following three years in the U.S. Navy as a destroyer officer during the Korean War, he studied soil mechanics and foundation engineering at the Harvard Graduate School, under Arthur Casagrande. He was taught engineering geology by Karl Terzaghi. The writer holds a Master of Science degree and a Master of Engineering degree from Harvard in geotechnical engineering. He is a registered Professional Engineer. Following the school years he worked at the Cold Regions Research and Engineering Laboratory in Hanover as a soils engineer, performing independent research on the fundamental properties of soils as engineering materials, including the processes of freezing and thawing.

The writer is also experienced in the remediation (under Superfund) of hazardous waste sites, most especially those of waste asbestos on outdoor commercial and residential sites. As an engineering consultant to EPA from 1983 to 1991, he personally developed a method based on climatic exposure for remediating waste asbestos materials in regions subject to freezing and thawing. It is the method used today by the EPA in northern regions of the U.S.

In these applications the major health hazard is air quality, which complicates on-site human operations of remediation. Nevertheless, as with the mine tailings, the erosive actions of gravity, frost, wind, rain, surface water, and underground drainage are major factors that determine the long-term stability of asbestos waste piles. Containment was the major principle utilized here, with very little relocation of material, including regrading, because such action not only brings new material to the surface, but also destroys any natural cover that might have developed over a 30- to 50-year period. The natural growth and propagation of indigenous grasses, shrubs, and trees has been found to be a major consideration in achieving a cover that will increase its protective quality with time, thereby creating a positive potential for permanence and low maintenance.

The writer's expertise with the remediation of waste asbestos is important because many of the principles developed in reaching a permanent solution with this material are equally valid in the remediation of the mine waste piles at the Elizabeth Mine Site. Those principles also appear to be consistent with promoting the continuation of historic human concerns associated with the site.

top

PURPOSE

This report provides an assessment of specific engineering requirements in the final remediation of the Elizabeth Mine Site. The focus is on water quality in Copperas Brook as it affects the waters of the West Branch of the Oppompanusuc River. The first aim of the remediation is to reduce the natural levels of the major anionic constituents, iron, copper, and to a lesser degree aluminum in Copperas Brook, from its headwater in the upper tailing pile (TP-3) to below the lower tailing pile (TP-1) and on to its confluence with the West Branch.

These metallic anions occur as compounds in the ore and also in the waters of Copperas Brook. Reduction or removal involves the breakdown of the natural compounds through chemical means of one sort or another into stable soluble compounds or through the formation of chemical precipitates such that the targeted anions are removed from the water itself.

A byproduct of the chemical process, whether natural or induced, is usually an increase or a decrease in the hydrogen ion content of the effluent, resulting in an increase of acidity or alkalinity in the water. Increasing the acidity of the West Branch water apparently further endangers the invertebrate and fish populations; alkalinity seems not to. Thus the specter of "acid mine drainage" has been raised. But whether the ions themselves, or the acidity resulting from natural or man-induced processes, is the major problem in the water of the West Branch has not yet been determined, to the writer's knowledge.

Considering what has been presented above, it becomes clear that engineering requirements for any proposed remediation of the metallic content of Copperas Brook must take into account three major factors: the potential for the preservation of historic values of various kinds throughout the site; the total water chemistry of the brook and whatever is done to it; and the physical factors of the site (drainage and slope stability) as it stands at present and as it may be following a chosen form of remediation.

The engineering assessment performed by the writer, and the recommendations derived from it, were accomplished with these major requirements in mind.

Additionally, it should be mentioned that the costs of the particular form of remediation finally chosen, both initial and long-term, are of course an important consideration. Public funds will be expended for the clean-up itself and for the maintenance of the site, including the appurtenances brought about during the clean-up process (drainage courses, slopes, ground cover, treatment cells, etc.). Funds not utilized on this site are available to remediate other sites in Vermont and elsewhere; consequently, costs should be conservative to the extent possible.

However, as the Vermont Agency of Natural Resources has stated: funds are not unlimited, but within reasonable bounds, costs should not drive the decision on how to remediate; let the factors listed above determine the outcome. And further: the desires of the community are of paramount importance in regard to the mine site; it is for them to consider the role that the mine site will play in the future of the community and to make informed decisions on how that role is to be brought about.

Here, the key element is informed decision. The aim of the assessment presented here is to inform all those concerned as to what are reasonable alternatives in the remediation of the site, consistent with the stated goals.

ASSESSMENT OF THE MINE SITE

THE SOUTH CUT

Although this cut contains water, it appears to be the cleanest from the standpoint of metallic compounds of the entire mine site, as measured at the surface water sampling station H-5. The south cut drains into the watershed of Lord's Brook, which itself has very low background values. The cut and Lord's Brook are tributaries of the West Branch, entering downstream from the entrance of Copperas Brook.

Drainage and slope stability present no problems at this portion of the mine site. Ground cover is also not a factor, although a small tailing pile is located nearby, near the unmaintained (Class IV) road leading from TP-3. Runoff from this pile appears to enter the watershed of Copperas Brook; the pile is small and isolated, however, so that no problem is presented.

Recommendations

No remedial action is required. The cut is recommended as a potential source of quarried rock for rip-rap in lower portions of the mine site (TP-2, TP-1), if needed. Trucking of such material would not require traveling town roads other than a small section of Mine Road. There are also no year-around residences in the vicinity of the South Cut.

TP-3 AND THE NORTH CUT

This area, entirely above Mine Road consists of mounds of roasted copperas byproducts and of un-roasted waste from the WWII operations. The mounds are of essentially coarse sands with various colors ranging from iridescent violet to rose to ochre (dark yellow). The north portion is of a yellow hue, indicating high sulfide content, consisting apparently of un-roasted low-grade ore. Seepage from this latter material following the infiltration of rain water may contain levels of metallic compounds (cuprous copper-based) different from those emanating from the roasted material, which would appear to be more nearly ferric iron-based.

All piles, including the walls and floor of the North Cut, are clearly stable against gravity and against the action of surface runoff of rain and melting snow. No major watercourses have been formed, although two or three rivulets converge to form the beginning of Copperas Brook.

The conclusion may be drawn from these observations that the majority of the material, especially in the piles of roasted waste or of rock, has a high permeability to infiltration. It may be predicted that almost an entire rainfall event becomes runoff within hours of the event (not days), carrying with it in the first hours all formerly retained water and its metallic contents. Following each rainfall event, the water retained should be no more than about 15% of the volume of the piles, held in the capillary state.

This is the site of all of the production activities involving copperas. Various foundations of mine buildings still remain. This area of the mine site has particular historic value because of the uniqueness of copperas production.

Recommendations

No remedial action relative to stability is required other than a simple re-directing of the rivulets (by minimal regrading between mounds) to one or two channels below the Class IV road. In this work, the potential for erosion should be addressed, perhaps by utilizing a rock-lined and bounded channel leading down to Mine Road.

It is recommended that individual measurements of surface water from the roasted and un-roasted piles be made. It may be that these areas will require different forms of treatment, indicating also that drainage from individual areas should be separated.

In particular, seepage of surface water from three potentially different sources of metallic compounds should be separated and measured for chemical content and load, prior to any treatment protocol proposed downstream: 1) the area of roasted copperas waste; 2) the area of un-roasted but processed waste; and 3) the area of unprocessed waste at the highest elevation. Presumably the waste "rock" is of granite, requiring no specific chemical assessment.

After the chemistry of the various pile materials has been well-established, it is recommended that in-situ treatment be considered such that the form and color of the piles are not compromised. Spraying with a stabilizing chemical or organic compound that penetrates to the interior and coats all of the particles may be an effective method.

It is further recommended that the flat area immediately adjacent to, and above, Mine Road be used for a permanent holding pool large enough to receive and retain volumes of brook water and watershed water up to and beyond the largest storm surge of record. If treatment cells, passive or otherwise, are utilized in Copperas Brook at this location or at locations downstream, a uniform flow of water will be required for them to be effective. The outlet of the holding pool could be arranged so that this requirement would be accommodated.

In summary, based upon its unique historical perspective and its physical stability, it is recommended in the strongest terms that the entire area of TP-3 be preserved in its present state except for the limited activities mentioned here. Adjustments to be made to accommodate future interpretive functions relative to the site would be left for those in a stewardship role to determine at a later time.

top

COPPERAS BROOK and TP-2

The portion of Copperas Brook leading from the Mine Road to TP-2 flows down a narrow vale, incorporating two or three sources of clean watershed water as it goes downhill on a grade averaging about 5%. At the time of this writing, the writer does not know what the monthly flow rates might be, although the A.D. Little report gives, at H3, a yearly mean of 2.8 cuft/sec, which calculates to be 168 cuft/min or 1,260 gal/min. Considering the minor flow rate observed by the writer at H3 (where Copperas Brook passes through the culvert under Mine Road) on the morning following three days of nearly continuous rain (Dec.1, 2001), as well as at other times following a day or night of rainfall, this mean figure seems unrepresentative of most daily stream flows.

Nevertheless, the brook gains a noticeable increase in flow as it approaches the head of the sloping floodplain on which TP-2 and TP-1 were deposited. Midway down to TP-2, several small dams of timber and rock have been constructed, presumably to limit the rates of flow during periods of snow-melting or intense rainfall. Many of the timbers in these dams or weirs are still present, the copper and iron content of the brook having acted as a preservative of this material; some of the timbers even give the impression of rock ledge covered with moss, seemingly in the early stages of petrification.

It is important that features such as these be preserved, to continue to perform the originally intended function. One of these dams, not necessarily the one lowest in elevation, has clearly been used to intercept at least a portion of the brook (perhaps all of it) with a 24-in. inside-diameter concrete conduit leading at a shallow slope (1%-2%) to the rear edge of the tailings now designated as TP-2. Passing through two "decant towers" (circular concrete catch basins open at the top, 8-10 ft high), each of which changed the direction of the flow by about 30-degrees and provided a drop in elevation of the flow of about 3 ft, the water of Copperas Brook proceeded through the TP-2 tailings, discharging near the former Cross-Valley Road. A 1939 air-photo clearly shows that this road had been "thrown up" by then, with two small branches of the brook flowing across the former right-of-way at its lowest level.

A portion of the concrete conduit has dropped several feet into what appears to have been part of the original streambed of Copperas Brook. Close inspection indicates that the brook had been dammed by a barrier some 10 feet high of vertical timbers and rock, so that the stream flowed through the conduit leading through the eastern portion of the tailings of TP-2, some 6 ft above the streambed. Before its failure sometime after the tailings had been deposited, the conduit appears to have exited down a dug ramp leading from one of the eastern frontal terraces of TP-2; the ramp is still visible, although it carries no water. If seems to have joined a natural stream that flowed toward the cross-valley road.

Upstream of the barrier, and against it apparently, a flat berm of compacted former road material had been built for the purpose of supporting the conduit. This material was gray in color, apparently being a sand that was impregnated with a blackish coating of some byproduct of petroleum (probably tar). Remains of this material may still be discerned at the base of TP-2 at the location of the former barrier. A thin stream of an apparently oily substance flows out of it at this point and rests as a film on the surface of the present Copperas Brook as it approaches and then flows out onto TP-1.

The writer does not know whether this oily film has been tested for its possible influence on the metallic content of Copperas Brook beyond the location of the broken conduit. This should be done.

Clearly the gray berm material was eventually carried away by the flow, the barrier of timber and rock failed, and the brook returned to one of its former channels, where it remains today. The other channel appears on a 1939 air photo to have been directly under the center of TP-2, crossing the former road on the same level as the present stream. The failure of the barrier and of the concrete conduit allowed the brook to erode completely through TP-2 at this location, forming a wide gully the full height of the tailings and more than 100 ft in length. There is evidence that the profile of the tailings at TP-2 originally extended horizontally across this impressive gully, to the easternmost edge of the tailings. The material eroded from the gully represents a large volume (perhaps 150,000 cubic ft) that now resides on the original surface of TP-1 somewhat beyond its southeastern corner. This volume of material would cover more than 3 acres to an average depth of one foot.

The sides of the gully are presently being further eroded by the action of rainfall, washing tailing material into the streambed, where it continues to be carried out onto TP-1. There is evidence that the bed itself is being eroded of the tailing material deposited into it.

It is important in any remediation scenario that erosion from the sides and bottom of this gully should be stopped, inasmuch as the eroded material is totally in contact with the rain water and would not have been previously oxidized by environmental influences. This material represents a major source of contamination into Copperas Brook.

top

The lower three terraces of tailings at TP-2 are also being eroded at a rapid rate. A 1990 photograph seems to indicate a somewhat smoother appearance to the surfaces here than there is currently, indicating that a significant portion of the erosion has occurred in the last 10 years. The most likely reason for this is a decrease in rainfall during the period, which would result in a drier condition in these frontal features, which clearly are of a coarser size of sand particle than is the higher part of the tailings at TP-2. It is likely that the frontal berms were terminated at lower levels then was the main tailing pile precisely because the coarse sand would not support a sufficiently high embankment. Unfortunately, the terracing of the tailings in this fashion encourages runoff from the front of a berm to collect at the rear of the berm immediately below, promoting the formation of a lateral stream that finally flows to lower levels through a vertical erosion channel. When a coarse sand such as this is even locally saturated by rainfall, stabilizing forces in the pore water set up by capillarity are lost, and the sand will flow like a viscous liquid. This is believed by the writer to be the process by which these terraces have been so deeply eroded.

To support this contention, it may be noted that at the easternmost corner of the tailings at TP-2, the terraces are still smoothly rounded as apparently they were originally, with no serious erosion in the last 40 years. In fact, a persistent growth of greenish moss has developed on these surfaces. The major difference between this latter portion of the terraces and the eroded portions seems to be only that the latter are shaded by a grove of small aspens and birches, preventing desiccation by direct summer sunlight. Taller trees probably provided this shade in the past.

Continuing the description of TP-2, a prominent feature bisecting all of the frontal berms and terminating at the front face of the highest pile, is a deep "notch," representing a significant loss of material. It is important to find the cause of this apparent slope failure because it may indicate a potential for similar failures on the higher faces of TP-2 and on those of TP-1.

After careful inspection of this feature and a consideration of the conditions of the supporting subsoil, the writer does not believe it to be a condition general to the remaining faces of TP-2 and TP-1. On the contrary, it appears quite certain that it is a local, one-time slope failure brought about by an unusual coarseness of tailing material in this portion of the terrace together with a temporary high water table beneath it, owing to its location immediately above one of the two places where Copperas Brook formerly crossed the cross-valley road.

A 1990 air photo clearly shows that the notch resulting from this failure of material was made prior to that time. The photograph also indicates that the coarse, sandy, and essentially dry tailing material currently residing on the surface of TP-1 adjacent to the edge of the vegetated portion is directly on a line with the orientation of the notch. The writer believes that this is material that flowed rapidly from the location of the notch when material at its base underwent a temporary condition of liquefaction. Today, the visible lateral surfaces of the notch are found to contain similarly coarse sandy material that is gradually sloughing off owing to desiccation.

Inasmuch as the remnants of the cross-valley road are to the present time only a few feet below the surface of the erosional out-flow material at the toe of TP-2, it is at least possible that a similar sub-surface drainage condition in the future could again cause a slippage of this sort. A question arises as to whether such an event would trigger a landslide on the face of what may be considered the main tailing pile at TP-2. And if that is so, what about similar faces of TP-1?

In answer to these important questions, the writer finds no evidence to support either contention. The main part of the TP-2 tailings was already in place when the slippage occurred (we cannot tell exactly when that might have been); even so, the slippage stopped at the face of the main pile. Clearly, the stability against failure of this face was at a higher level even under the presumed high water-table condition at the time of the slippage. Furthermore, there is also no visible indication that the stability of the main face of TP-2 (or of the similar faces of TP-1) has been compromised in any way since the placement of the piles some 50 years ago. All the faces of TP-2 except those in the gully (as well as those of TP-1) are significantly stabilized by double rows of successively higher timber trestle supports that were purposely buried in the process of deposition; this reinforcing structure is some 10 ft in both height and width, runs parallel to the faces, and provides an unusual degree of slope support that should not be disturbed. The writer will return to this topic in connection with the assessment of TP-1.

Even the surfaces of TP-2 that face the gully through which Copperas Brook now flows, although deeply eroded by rain water and with the current stream at their toe, show no sign of a potential for deep-seated slope failure. Because these walls were formed after the piles had been deposited, there are no imbedded timbers here left over from the process under which deposition was accomplished. Owing to the lack of reinforcement, the walls of the gully are easily eroded and should be stabilized against further erosion.

Finally, another area of TP-2 not mentioned to this point is the upper surface. This surface slopes gently away from the main face of TP-2, and is an example of an effective confluence between the tailing piles and the natural environment. The groundcover here, where it has developed, is exemplary. A thin layer of moss in various stages of development is interspersed with small birch shrubs and even a few small birch trees. The development appears to have been naturally induced, although a small amount of organic soil seems to be present in places beneath the moss. Perhaps it was blown in, developed spontaneously, or may even have been placed there by someone. Whichever way the cover was actually developed, it is a good example of an esthetic and environmentally sound groundcover on the tailings. Effects of erosion from rain runoff or melting snow seem to be absent here. The absence of erosion, in addition to the retention of moisture within the surface, is key to the natural development of the cover observed.

There is a portion (perhaps 30%) of the sloping upper surface that is composed simply of clean, yellow tailing material. It is probable that this material as it stands is too coarse to hold sufficient surface moisture to support plant growth.

Recommendations

In summary, TP-2 exists as a transition area in Copperas Brook between TP-3 at its upper reaches and the lower part of the valley where TP-1 sits. Events at TP-2 have encroached severely upon TP-1, which lies below it in elevation. A large volume of tailing material has eroded from TP-2 and has flowed onto the surface of TP-1, changing its original grade. Moreover, Copperas Brook exits from TP-2 and now flows directly onto TP-1 over the erosional material from TP-2, carrying the combined load of metallic compounds from TP-3 and TP-2 directly to the pond on TP-1. From here, pond water will seep through the tailings of TP-1, adding further to its metallic load.

It is strongly recommended that Copperas Brook, as it flows from TP-2, be diverted from its encroachment onto TP-1. It is important that this be done prior to any other part of the remediative process. Such diversion would isolate the waters of TP-3/TP-2 from those of TP-1 so that their chemistry and possible treatment could be considered independently of TP-1; it would also restore an essentially unchanging condition to TP-1, facilitating its analysis and remediation as a separate entity.

The writer believes that a possible solution would be a standpipe/catch basin approximately at the centerline of the former cross-valley road, with a buried culvert leading along the old roadbed northwesterly to the narrow valley that has been formed between the edge of TP-1 and the former mine buildings. The catch basin would provide for the change of direction as well as a drop in elevation of the brook.

An alternative solution beyond the toe of TP-2, would be a surface channel, perhaps lined with limestone. However, the current erosion taking place in the terraces of the toe area must also be controlled in some way; a surface diversion channel could not be accomplished in a permanent way until the erosion work was done, and the channel would require annual maintenance. With an underground diversion channel in place, the erosion work could be done independently of it.

One might ask why the brook should not be diverted into a surface channel along the right-hand edge of TP-1, without a major change in direction. It would not then affect the material at the toe of TP-2. The answer is that the metal-laden water of Copperas Brook would still enter the tailings of TP-1. Along that edge, TP-1 is at the original ground surface, forming a feathered edge. Copperas Brook would mix with watershed surface water and seep under the edge into the depths of TP-1. In short, the brook would not be isolated from TP-1 unless a curtain wall to bedrock was built the entire length of the edge. This solution would be very costly. In addition, the current cleanliness of watershed water along this edge would be compromised. This course of action cannot be recommended.

It seems to the writer that the sandy, erosion-prone terraces at the toe area of TP-2 are fair game for regrading, or even for possible removal. In no way, however, should the stable, steeper slope of the main pile be disturbed during such work. It is important that the reinforcing, buried timber structures be retained intact as they currently stand. A careful engineering assessment indicates that any regrading of the high slope of the main pile at TP-2 would bring into play at least three major influences, all of which are detrimental to the permanence of the remediation: 1) the present top surface cover, which is stable under current environmental conditions and is naturally increasing in coverage gradually, would be destroyed and would require costly replacement and maintenance; 2) regrading to a shallower slope would increase the amount of surface area open to erosion, this new area being composed entirely of currently-buried material which would not have achieved chemical equilibrium under atmospheric conditions and would require the establishment of new cover; 3) the factor of safety of the slope against landslide-type failure would not be increased, but would be decreased to a range between 1.3 and 1.5 according to the analysis of the Corps of Engineers; except for the aberration of the notch area, their analysis shows the factor of safety at the present time to be greater than 1.5, conforming to their own guidelines for slope stability used throughout New England.

The sandy, terraced area of TP-2 to the left of the exit of Copperas Brook is erosion-prone, probably equaling the erosional potential of the open faces of the gully area. The toe material could be regraded into a single slope of tailings, resting against the face of what has been termed the main tailing pile. However, most of the disadvantages of large-volume regrading noted immediately above would be brought into play, requiring continuing vigilance and the expense of long-term maintenance.

The writer proposes the following alternative, which has the advantage of closing off the erosional potential of the gully faces as well. The alternative is to utilize the sandy terrace material to rebuild TP-2 across the gully through which Copperas Brook flows. Along the present streambed, an approximately 100-ft-long permanent culvert of steel or concrete appropriately sized to carry a 200-year storm volume of water, would be placed on a rock underlayment, possibly also with a pool structure at the inlet to protect against overtopping. The culvert would carry Copperas Brook through the gully without allowing further contact with the tailings, and would terminate at the catch basin previously mentioned at the former cross-valley road right-of-way. A rock fill would be placed around and above the culvert serving to support the toe of the gully faces from further undercutting by groundwater seepage and to increase their stability against slip failure. The rock fill would extend perhaps 8 to 10 ft above the culvert, completely filling the bottom of the gully. The actual height of rock would be determined by the total volume required to completely fill the gully to the original height of the main tailing pile of TP-2 by adding, above the rock, the terrace material from the toe of TP-2. This material would be lifted by crane, placed in layers and compacted, its final contours being those of the main tailing pile as it was originally.

top

The toe of the entire face of TP-2 would then be protected by a sloping rock fill placed to the same height as in the gully. The somewhat smoothed upper face of the tailing pile would be hydro-seeded to resist sheet erosion from rainfall, and an appropriate cover similar to that which has developed naturally would be placed on the top surface of the tailing pile where it is not currently established. Particular attention would be given to the newly placed material in the area of the gully, possibly providing some form of internal reinforcement at the front face.

A second alternative, which would not utilize a culvert, would be to provide a rock-lined channel through TP-2 at the same level as the present brook. The rock would extend as rip-rap 8-10 ft up on both sides, to stabilize the walls of the gully. The brook would again enter a catch basin to provide for a change in direction and a drop in elevation, proceeding through a buried channel as in the first scenario. The terraced area of TP-2 would require regrading (laterally) and a ground cover to control erosion; rock rip-rap could be provided over the lower portion depending upon the final slope. Smoothing and hydroseeding of the upper portions of the gully walls and of the front face would be applied, with treatment of the top surface as before.

Finally, a third alternative would provide a rock-lined surface channel for the entire length of the diversion, changing direction at a catch basin but providing only a few feet of drop in elevation. Treatment of the walls of the gully, the terraces, the front face of the main pile, and the top surface would be as in the second scenario. A surface channel might be less costly initially, but as a permanent feature would require considerably more long-term maintenance. Possibly it could be considered as a temporary means of separating Copperas Brook from TP-1 for a year or so, to be replaced by a buried channel during the final remediation phase.

In all three scenarios the terraces presently to the east of Copperas Brook would probably remain, because they appear to be stable against both failure and serious erosion except along the faces toward the brook. These faces would have been dealt with in the work described above.

TP-1 and LOWER COPPERAS BROOK

It has taken considerable space to this point to describe the area of TP-2, and to provide an assessment of its condition and recommendations relative to its remediation. This is because it stands at the foot of the steep portion of Copperas Brook, just at the point where the valley begins to broaden as the brook flows toward the West Branch past TP-1. In addition, as noted above, TP-2 represents a transition point in the progression of metallic pollutants in the brook. At the present time, pollutants arising from TP-3, together with pollutants arising from TP-2, flow onto TP-1 where they mix in an existing pond with pollutants from the surface of TP-1, and then finally mix with pollutants from within the tailings of TP-1 before exiting into lower Copperas Brook. This is the water which then flows into the West Branch.

With such a progression, the chemistry of water in lower Copperas Brook is complex, making any treatment proposed against chemical content of the water complex as well. As noted above in the discussion of TP-2, the writer proposes that the water (and the chemistry) of TP-1 be isolated from that of Copperas Brook above TP-1. Such action would clarify the effect of the tailings at TP-1 on brook water immediately below it, measured of course before the seepage from TP-1 reunites with brook water diverted at the location of TP-2.

It may be that the water chemistries are sufficiently different that differing treatment protocols would be called for. Another matter that could be settled is a question in the writer's mind relative to TP-1 of whether to allow clean (oxygenated) watershed water, which collects at its eastern periphery, to seep into the tailings along the contact of the tailings with the original ground. The question is also related to whether oxygenated rain water falling on the surface of TP-1 should be excluded or limited in some way, or should actually be encouraged to infiltrate. The writer needs (and perhaps others do as well) some clarification on this point before a firm recommendation relative to clean seepage water and infiltrating water can be made. Further mention of this matter is made later on.

As TP-1 stands today, however, an assessment of the following nature can be made. TP-1 has indeed been deposited in the broadest part of the valley, as evidenced by the almost triangular footprint of the tailings pile. Where TP-1 abuts TP-2, the two piles measure several hundred feet across the valley. The location is underlain by the former Cross-Valley Road, which prior to 1940 joined the present Mine Road higher up on each side of the valley. The former road lies today only a few feet below the surface, being evidenced by a horizontal stratum of black mud, probably having been tar originally. This layer is a remnant of a marshy area that extended along the former road, lateral to TP-2. Vestiges of the original extended marsh still protrude above several transecting flows of erosional material emanating from the notch and terraces of TP-2.

Just below the location where Copperas Brook exits TP-2, an existing marsh filled with tall reeds survives in spite of being overlain by a thin layer of moss-encrusted yellow tailings. Currently this existing marsh is skirted by Copperas Brook as it flows out onto TP-1; the marsh is fed by surface water flowing down the former road right-of-way from the east and by seepage from the eastern terraces of TP-2.

It appears that the existing marsh and the extended portions were a continuous feature which developed following the deposition of both TP-1 and TP-2. It is likely that both tailing piles terminated at the road but did not originally encroach upon it. What had been the road would have been the natural collection area for surface flow from the rear of TP-1 and for seepage from TP-2. In addition, Copperas Brook would have exited from the concrete conduit and flowed into this collection area, from the eastern terrace of TP-2.

It is important to realize that this linear marsh must have existed right up to the time that erosional flows from TP-2 began to overtop portions of it and thereby to change the direction of surface drainage toward TP-1. Prior to this time, the extended marsh would have acted as a barrier to surface flow from both directions, providing a continuously high water table in the toe area of TP-2 and the area of the previously mentioned notch. It is likely that the outlet of flow from the marsh, and from the pond that may have preceded it, would have been to the north as is proposed by the writer for the diversion of Copperas Brook.

Another old unpaved road ran from the location of the marsh northerly, through the woods to Bailey's Corner on Route 132 near the bridge at Tucker Hill Road in Thetford. Today this road lies at the eastern edge of the tailings of TP-1, on a contour elevation of close to 1,000 feet at the marsh end and near the pond, rising to about 1,100 feet where it leaves TP-1 at the northeastern corner. Parts of this road may still be found just within the edge of the present tree line.

Along this edge of TP-1 the tailings lie on the original surface of the ground, forming a swale along the old road between the tailings and the ground sloping downward from the east. Watershed runoff and seepage continuously collect here even today, which has caused a permanent wetland 20-30 ft wide to develop along the entire eastern edge of the tailings. Plant growth indicates an essentially aerobic condition in this wetland over the tailings.

According to a 1939 air photo, land uphill from the road, i.e. to the east, was then a meadow essentially free of trees; the area now encompassed by TP-1 was forested down to the floodplain of Copperas Brook, the floodplain being quite narrow where Copperas Brook crossed the cross-valley road in two small streams, widening to perhaps 100 ft at one point still within the TP-1 area, before narrowing again in a steeper section of the valley downstream from the front (northeasterly) face of TP-1. From above, the original floodplain runs diagonally under the TP-1 tailings from the marsh mentioned above to the present stream course immediately below the highest part of the front face, which is several hundred feet easterly from the northwestern corner of TP-1.

Water from the wetland has formed a pond over the tailings at the lowest point of the old road. This pond, somewhat over an acre in area at periods of high water table, collects surface drainage from TP-1 and Copperas Brook, as well as water from the wetland. The pond water has overridden a ground area not cleared of trees indicating a general rise in water level.

top

It is important to understand that the ground surface, between the original floodplain of the brook and the eastern edge of the TP-1 tailings, slopes almost uniformly downhill toward the lower terminus of Copperas Brook (under the high part of the front face). The trees are gone of course, having been cut prior to the deposition of TP-1, but one may be sure that seepage water still flows slowly along the contact zone between the bottom of the tailings and the original glacial till.

This contact zone has a gradient of about 10%, or approximately one foot of vertical drop in 10 horizontal feet, and extends almost precisely from the pond now situated on TP-1 to the above-mentioned terminus below the front face. On a surface, the gradient is the steepest slope at any point, the direction of which is perpendicular to the surface contours of elevation at that point.

Using the known value of permeability of coarse sandy soils, 1 x 10 -3 cm/sec, it may be calculated that the velocity of the seepage along the ground is approximately 1 x 10 -4 cm/sec = 0.4 cm/hr = 10 cm/day = 1/3 ft/day = 10 ft/month. Considering that the pond is some 900 feet horizontally from the terminus and some 100 feet higher in elevation, it can be seen that it takes about 90 days (3 months) for seepage water to traverse from the first location (the pond) to the other. This figure represents the retention time that seepage water from the pond is in contact with the buried tailing material of TP-1. This is also the period in which the seepage water is gaining metallic pollutants (or perhaps losing them, depending upon the specific water chemistry that is operative within the buried material.)

What is this seepage composed of? Because of the changes in surface elevation of TP-1 brought about by the erosional flows emanating from TP-2, almost all surface runoff water on TP-1, including Copperas Brook, now flows toward the pond. At present the pond water and the seepage from it are composed of watershed water and pollutants from TP-3 and TP-2, of surface runoff from TP-1, and of clean water from the watershed east of TP-1. The amount of watershed water entering the pond and the seepage zone is especially critical during periods of high water table following storm events.

It may be seen that a diversion of Copperas Brook prior to its encroachment upon TP-1 would leave only TP-1 surface runoff and clean watershed water in the pond and in the seepage zone, greatly simplifying the analysis and treatment of seepage water passing through the tailings of TP-1.

Another source of water in TP-1 is of course water infiltrating the tailings vertically downward during rainstorms and during snow melting (after the surface is thawed). The capping proposed by EPA is intended to cut off this source of water into the tailings. The effectiveness of this operation in reducing the level of polluting chemicals in the seeps at the bottom of TP-1 depends upon several factors: 1) the percentage of rainfall that actually infiltrates the present cover; a large percentage of rainfall will be accounted for by surface runoff toward the pond, evaporation into dry or heated air, and transpiration through the roots and leaves of existing grasses, shrubs, and trees; 2) the volume of infiltration water compared to the volume of water seeping from the pond and from the watershed into the ground below the tailing pile; and 3) the retention times of the infiltration water and of seepage water within the tailings.

As has been shown, the retention time is equal to the time it takes to flow from one location in the pile to the terminus of the seeps (the lowest point of the valley at the northern face of TP-1) or to one of the other seeps to the east or west of this location. Because every profile (or vertical plane) passed through the tailing pile is essentially triangular, seepage times are proportional to the distance from the terminus; infiltration times are proportional to the vertical distance from the surface to the water table, measured along the triangular profile at the same point.

Although appearing to be technical, the result of this line of analysis is actually simple. Directly above the terminus area, infiltrating rain water or snowmelt will take only one day to reach the bottom of the pile (seepage time here is zero). However, halfway up the floodplain, diagonally toward the marsh at the lower corner of TP-2, infiltration time is only one-half day, but the seepage time to reach the terminus is 75 days. Again, halfway toward the pond area (which is closer), infiltration time is also one-half day, but the seepage time is 45 days.

The effect may be summarized in the following way: immediately above the terminus, and only in the near vicinity of the front face, is infiltration time plus seepage time in the order of several days. Everywhere else within the tailings of TP-1, the combined time to reach the terminus is in the order of weeks or months, whereas infiltration time to reach the water table at the same location is always less than one day.

Only the additional factor of a downward-sloping high water table within the tailings would decrease these retention times, but probably only by a small degree. Nevertheless, there does not appear to be much of a water table within the tailings, judging from the fact that seepages are almost entirely from the very bottom of the front face (apparently none from the side face). Only once has the writer personally seen seeps some 10 ft directly above the terminus area, immediately following a rain. These temporary seeps appeared to have no erosive effect on the material from which they flowed; quite likely they were from a layer of vitrious slag that had been produced by the smelting process and placed at the lowest level of the floodplain prior to the deposition of the tailings.

Thus it appears from the analysis that clean groundwater seepage from the eastern edge of TP-1, together with contaminated seepage from the pond area, accounts for the major portion of the water retained within the tailings of TP-1. Considering that small episodic events of infiltrating water join the general seepage quickly following a rainstorm, but then slow to the same rate as the general seepage flow, these events do not appear to have a major effect on the amount of water retained at any given time, or on the rate of flow of that water out of the tailings.

It may be noted here that over the last two years the rate of flow from the seeps emanating from TP-1 has been measured to be very nearly constant, which is consistent with the preceding analysis.

On the upper surface of TP-1, approximately three-fourths of the total area of 20 or so acres is currently covered by a mature ground cover consisting of mosses, grasses, saplings, and small trees. These latter are poplars, white and yellow birches, aspens, and quaking aspens, in ages ranging from one to approximately 20 years. At the corner near the northern end of the former cross-valley road is a large pile of tree stumps that has been covered over by soil (and possibly tailing material) and planted with grass. Nearby is a pile of old trees that has not been covered. Runoff from these piles may be different from that of the covered areas, and should be assessed.

top

Within the covered area but nearer the northernmost corner of TP-1 are two areas covered only in prairie grass; no trees or saplings are growing within these grassy areas, for reasons unknown to the writer. From the contour elevations that have been published for the upper surface of TP-1, there is some indication that these areas may receive and retain surface runoff to a greater extent than do the areas with growing trees. Because they are directly above the former floodplain and near the terminus area, these grassy plots may be an important source of infiltration into the seeps of TP-1. If so, they should be built up, perhaps gradually, to a level sufficient to direct runoff into the general flow toward the area of the existing pond.

Erosion is conspicuously absent in the large area encompassed by this varied ground cover, indicating that the cover is, and has been for some time, compatible with the underlying tailing material and with the environment. In the writer's experience and judgment, no better cover for the protection of the tailing piles could have been achieved. From the historical perspective, it should clearly be retained as an integral part of the enduring mine landscape.

The area of TP-1 that does not contain the cover described above represents perhaps 5 acres of the total area. It includes the existing pond of about one acre in area at average water depth of 1 to 2 ft; the remainder contains only open tailing material which is coarse dry sand in a band adjoining the covered area, becoming finer-grained and increasingly moist toward the pond.

Originally, this area would have sloped gently toward TP-2. As previously mentioned, erosional flows of tailing material from TP-2 have reversed the slope, which is now toward the pond. Copperas Brook flows over this material, eroding and depositing material in succession as it meanders. Because of the additional material deposited within it, the pond now encloses what was once a stand of trees adjacent to its eastern edge. This stand is now represented by a considerable number of dead tree trunks protruding from the pond.

Recommendations

The writer recommends, as have others including the hydrologist Lori Barg, that the pond be drained. Even though the water there would be cleaner following a diversion of Copperas Brook from TP-1, the pond is a natural receptacle for surface runoff from most of the remaining area of TP-1; present surface contours demonstrate that surface drainage is generally toward the area of the pond, as it is in a major portion of the watershed to the east. Drainage could be effected quickly and efficiently on a continuous basis by utilizing the decant tower (or towers) close to the pond and the associated concrete conduits leading to the H1 sampling point at the northeasterly corner.

The writer has found that the decant tower immediately adjacent to the pond will drop inlet water 2 ft to a conduit leading 250 ft to a second decant tower on TP-1, which in turn provides a drop of 3 ft to another 250-ft conduit leading to H1, the northeasterly corner of TP-1. There is approximately an 8 ft drop in elevation in each length of conduit, for a total of approximately 21 ft below the pond level. With an inside diameter of 24 in., this system can carry a considerable volume of water. The writer can personally attest that the system is open and will carry water for its entire length.

The writer recommends that the pond be drained, but he also recommends that the area of the pond be retained as a collection point for surface runoff, with provision for nearly continuous draining. It is possible that under the pond area a constructed hardpan layer of limestone, or perhaps a geomembrane, would positively prevent entrance of future pond water into the tailings. This work could be accomplished with no disruption of the present ground cover if no more than the open area without current ground cover were involved.

On the other hand, the pond presently appears to be underlain by a considerable amount of clay derived from the tailings. The depth of this clay and its relative permeability should be determined, including the rate of seepage from the pond as a whole.

As for the current ground cover on TP-1, it is very strongly recommended that it not be graded except to construct shallow drainage swales perhaps 5 ft wide to enhance the conduction of surface runoff down-gradient toward the pond area. The possibility of excess retention of surface runoff of rain and melt water by the stump area and the grassy areas should be assessed; if found, local measures to correct the condition should be taken, followed by replacement of the cover. In general, the present condition of the cover should be protected from damage, maintained, and enhanced as an integral and important part of the historic landscape of the Mine Site.

In relation to the front face of TP-2, it was previously explained that the imbedded timber supports for the sluicing pipe that was used to deposit the tailing material help to cause the face to be sufficiently stable to exceed the Corps of Engineers requirements that the factor of safety be no less than 1.5. Upon careful inspection this condition is judged to be true also for the frontal and lateral faces of TP-1. There is no evidence whatever of a potential for incipient slip failure; such evidence would be the appearance of a series of open cracks on the upper surface, running parallel to the face some 10-20 ft back from the top of the slope. The writer finds no visible evidence of such cracks, or of any settlement of the upper surface. Furthermore, there are no lumps or humps of tailing material in the creek bed that would indicate past slip failures. Judging from the evidence, these tailing faces have stood for nearly 50 years at the same slope at which they were deposited.

Regrading of the frontal and lateral faces of TP-1, as has been proposed by the EPA, should not be accomplished. Destruction of the system of continuous reinforcing provided by the timbers remaining from the trestle structure would not significantly increase the stability against slip failure of the current face, and it probably would decrease the factor of safety. Because of the manner in which the tailings were deposited, the material is progressively finer the farther it is from the present face; this condition will be true at every depth. Consequently, no matter how well the regrading was done, or to what slope, the brow of the new face would be composed of finer-grained material than at present, with a higher water content and a lower shear strength; the timber reinforcement would of course be gone. Perhaps more important, a new potential slip surface would have been moved farther into the tailing mass, passing through material which is even finer than the material at the brow. Shear strength, which provides resistance to slip failure, would be reduced accordingly. The length of the slip surface would be longer, tending to provide more resistance to failure, but the total effect of these changes cannot be determined at the present time.

Unlike the current condition, in which the faces are composed of uniformly-graded material having a uniform negative pore pressure, the new faces would be composed of truncated layers of tailing material which would become successively coarser toward the bottom of the slope. Pore pressures would vary with position on the slope and would be unknown. On the other hand, all of the material would be newly exposed to the external environment.

To reiterate, regrading of the frontal or lateral faces of TP-1 to any slope different from the present condition would be ineffective and detrimental from the engineering and the historical standpoints. Such proposed action cannot be warned against strongly enough.

The only evidence of erosion on the high faces of TP-1, both frontal and lateral, are vertical surface erosion features that are related to the impingement and downward flow of rainfall. The timbers protruding from the surface, assuming that they were trimmed flush with the original surface, indicate an average surface erosion of approximately 1.5 ft in the last 40 years. It is recommended that these erosional features be smoothed out without disturbing the timbers, and stabilized by means of hydroseeding with a resistant cover.

It may be noted that a localized terrace structure about 200 ft in length extends downstream a short distance beyond the front face, and in the deepest part of the Copperas Brook floodplain below TP-1.This terrace shows no evidence of erosion or of deep-seated instability. The writer has not confirmed it, but it may be composed of slag. This terrace is an important stabilizing feature, as it evidently was intended to be, and should be retained intact.

It is recommended that a permanent rock fill be constructed across the entire toe of the front face of TP-1 to carry a roadway wide enough to accommodate trucks and heavy equipment such as a crane. A sloping zone of rock rip-rap could then be placed against the face to a height of an additional 15 or 20 ft. The rock fill and the rip-rap would serve to protect the toe of the front face against further erosion that might have a destabilizing effect. A similar rip-rap should be utilized for the lateral face of TP-1.

As recommended above, the faces of TP-1 would be smoothed from below prior to the placement of rip-rap, and hydro-seeded above the rip-rap to prevent future erosion by rainfall.

top

PASSIVE TREATMENT CELLS and POOLS

Clearly, some form of treatment facilities to remove polluting compounds from the waters of Copperas Brook, and hence from the waters of the West Branch, are indicated. Passive systems have been recommended by other consultants, and the writer supports these recommendations as being consistent with the goals of the remediation, both physical and historical. As for their number, size, and placement locations, the recommendations provided here relative to drainage and slope stability, if implemented, would have a mitigating effect on the requirements for sizing, on long-term maintenance, and on the cost of such treatment appurtenances.

In addition, the specific chemistry between rain water and various portions of the tailings, as well as between the water of Copperas Brook at the location of a proposed treatment cell and the material in the cell, is of paramount importance for effective remediation. The separation of flows from differing waste materials at TP-3 is recommended, with measurement of the contents of the effluents prior to their mixture into Copperas Brook and prior to the choice of treatment cells and their locations. Likewise, the effect of diverting Copperas Brook from its current impingement upon, and its passage through, TP-1 should be measured and evaluated prior to the choice and location of appropriate treatment facilities. It is further recommended that these actions be taken in the earliest stages of the remediation of Copperas Brook.

The principle behind these recommendations is simple. Inasmuch as the contamination of the water of Copperas Brook is derived from at least three major sources, it is a complex mixture of ions, some metallic and some not. It makes sense to separate and measure these sources independently. As the brook flows progressively down-slope from one source to another, adding new compounds to all those gained upstream, perhaps it could be treated progressively. Beginning with the headwaters at TP-3, selected toxic ions could be reduced prior to the effluent reaching the next lower source. The final stage, of water flowing into the West Branch, would be simplified and its potential effectiveness maximized.

The three major sources of metallic and non-metallic compounds in Copperas Brook may be classified as follows: 1) infiltration into and runoff from the rock and piles of roasted and un-roasted sand at TP-3; 2) surface erosion from the terraces and the open sides of the gully at TP-2; and 3) seepage water in the lower reaches of the tailings of TP-1, which is retained for extended periods of time.

The source listed at TP-3 may be found to be two sources, inasmuch as the source material was placed many decades apart, and underwent different processes in the handling of the ore. In particular, the yellow sulfide-bearing piles at the northern edge represent an individual source, in all probability.

The sources listed at TP-2 and TP-1 may appear to be exactly similar, inasmuch as the tailing material at both locations underwent similar processes and was deposited at about the same time. They have been listed as two distinct source areas, however, for the following reasons: a) seepage from within the tailings at TP-2 appears to be virtually absent, whereas surface erosion by the action of rainfall is evident almost everywhere; runoff from these tailings is in contact with the tailings for only short periods of time, and remains aerobic; b) in contrast, water within the tailings of TP-1 has been shown by the writer to be in contact with the tailings for long periods of time, periods sufficiently long for it to lose its oxygen content; the chemical content of this water will not be the same as for effluent from the slopes of TP-2.

It will be noted that infiltration of rain water into the tailings, and its contamination prior to its eventual entrance into Copperas Brook, has not been listed above as a major source except in the case of TP-3. The reason is that, in the writer's judgment, infiltration per se is a contributing factor but not a major one. This position is in direct contrast to an early premise by the EPA that has led to their proposal to cap all of the tailings with an impermeable membrane.

The question here is one of scale. In the local area, natural cover is estimated by hydrologists to account (through evapotranspiration) for up to 85% of surface water from rainfall; only the remainder is available for infiltration. Has it been established that infiltration of rain water through the natural cover at TP-2 and TP-1 is a sufficiently significant source of contamination to justify the cost and disruption imposed by capping with an impermeable membrane? After a careful study of the site, of available data on flow rates in the brook and from the seeps, together with an estimate of the relative volumes and flow rates of infiltration water and seepage water, the writer does not believe so. Simpler means of limiting the amount of actual infiltration should be seriously considered and implemented.

It is strongly recommended that the influence of the major and contributing sources of contamination to Copperas Brook be measured and evaluated in the early stages of remediation, to aid in the design of treatment facilities. Perhaps the writer's current perceptions of the role of rainfall relative to the contaminating sources would be of assistance in the design; these are subject to change following actual measurements:

For TP-3, surface runoff is probably non-existent; daily infiltration and outflow are nearly equal to rainfall; except in the summer when evaporation controls, the volume of water retained is nearly constant and is the predominant source of contamination; retention time is approximately equal to the period between rainfall events.

For TP-2, surface runoff is nearly equal to rainfall, and is the predominant source of contamination through erosion of the frontal terraces and the open gully faces; retention time is only slightly longer than the rainfall event, except in the deepest part of the tailings, where infiltration through the uncovered portion of the top surface will join seepage water from the collection area at the upstream edge of the tailings; exiting is at the base of the terraces as buried seeps.

For TP-1, except in the spring over frozen ground, surface runoff is slow and non-erosive; the remainder of rainfall is probably retained for short periods within the vegetative cover and is dissipated through evaporation and transpiration; infiltration is a small percentage of rainfall, except possibly in the areas of open grass and stump deposition; infiltration water proceeds quickly to the seepage zone at the base of the tailings, from which it exits as part of the seeps; watershed water from the eastern edge and pond water make up the largest portion of the seeps, and are the predominant sources of contamination; retention time is in the order of weeks and months.

top

SUMMARY and EVALUATION

The descriptions and engineering assessments presented in this report are intended to provide information to private citizens of the community, to their boards and other groups representing their interests; to engineers, attorneys, and other professionals engaged in various portions of interest; and to governmental officials responsible for planning and directing the remediation of the Elizabeth Mine Site. It is hoped that possibilities of remediation consistent with the interests and goals of these various factions have been arrived at, and that they will be scrutinized and evaluated fairly.

The writer further hopes that this report that will facilitate the process of reaching consensus on the remediation of the Elizabeth Mine Site. The writer has striven to arrive in an impartial manner at the recommendations given here. Where these recommendations differ from previous proposals by others, those proposals have been afforded full credence until the findings have seemed to point in another direction.

The writer believes that the goals are the same in the remediation of the Elizabeth Mine Site as of any other hazardous waste site where byproducts of human activity adversely affect human health directly, or adversely affect the ecology of an area close to human habitation. These goals are to maximize environmental protection and historical preservation, limiting disruption to local residents and communities, and striving in the process to minimize the expenditure of public funds. These of course are the goals of Congress in enacting the Superfund legislation in 1980, and of the EPA in carrying out the tenets of that legislation.

The EPA has informed the community that it is at a point where it must finalize an official milestone of that process, the Engineering Evaluation and Cost Analysis (EE/CA), sometime in February 2002, followed by a Proposed Plan of Action. This Plan will determine the direction and major activities of an early removal phase of the remediation, but essentially it will represent a choice of one of the options already proposed by the EPA. The community may officially comment as to whatever option they prefer, but they have been informed that they cannot change those options in any major way.

There is a problem here. Many in the community regard the Mine Site as an important historic resource that should be "preserved to the greatest extent possible," consistent with remediation of the brook. The Vermont Agency of Natural Resources and the State Historic Preservation Office have concurred. And yet every option put forth by the EPA for the public to comment on includes two features that together would permanently alter historic landscape that gives character and value to the Site, and gives evidence of the human endeavor that produced it.

These features are included in all options offered at the present time:

1) Removal of all natural surface cover already established on TP-1 and TP-2, so that a geomembrane may be placed over the entire top surfaces for the purpose of intercepting the infiltration into the tailings of all rain water and snow melt; new soil would be brought in and placed over the membrane to support the growth of grass or other ground cover yet to be determined.

2) Regrading of the main faces of TP-1 and TP-2 (possibly the complete removal of TP-2) to a shallower slope, for the purpose of increasing the resistance to slip failure and erosion; material removed from the faces to develop new slope angles would be placed on top of the piles prior to the placement of the geomembrane. If TP-2 is removed, it also would be placed on top of TP-1, beneath the membrane.

The writer agrees fully with those who view the Mine Site as a prime candidate for historical preservation. He also wishes to see environmental protection maximized, as stated in the goals of remediation. But the proposed actions of "capping" and "regrading" do not appear to be compatible with either of these goals. They destroy a large part of the natural environment and replace it with materials that may prove to be less sound environmentally, in the process destroying the historic profile of the tailings that are in themselves integral to the site. Meanwhile, the extensive earthmoving and the transportation of materials through the community would be disruptive and expensive.

One would expect that the Engineering Evaluation document (the EE/CA) would address these questions in reaching a cost analysis. But when the writer inquired as to the engineering studies entered into and the conclusions found, he was informed that the options being proposed were conceptual only, and that an engineering design study would be conducted after an option was chosen for implementation.

The writer understands the course of events that has brought the EPA to the position of proposing remediative procedures that may not be fully supportable by the community. In fact, the personnel of EPA have been fully cooperative with local citizen's groups, and have considerably extended periods for comments and questions. In addition, they have made concerted efforts to minimize costs that would accrue to the State of Vermont and to the community through their taxes. They are to be commended for their efforts to satisfy the desires and attitudes of a broad range of constituents, while attempting to carry out regulations pertaining to the remediation.

But, in the writer's experience, the procedure that has evolved is backwards. There was no engineering design because there had not been an engineering study. There has been no engineering justification specific to this site for the capping and regrading, other than that they are procedures commonly utilized in the remediation of solid-waste landfills, and of mine waste toxic to humans. Solid-waste landfills are a random mixture of many diverse kinds of waste; the effluent resulting from the infiltration of rainfall in many cases is toxic to humans if it enters the water table or an aquifer. Moreover, a shallow slope to faces is called for when the material enclosed has no intrinsic strength. Toxic mine wastes may indeed require capping and grading when near human habitats.

But the mine tailings of TP-1, TP-2, and TP-3 are not typical landfill material, and the associated toxicity has not been found to be harmful to humans. This site is important from so many aspects that it deserves specific studies and engineering procedures in the determination of a design appropriate to the special features of the site and to its historical legacy.

It seemed to the writer that the public had no truly informed way to comment on the proposed actions. They had not been educated by personnel of the EPA on the engineering necessity of these procedures intended to maximize environmental protection to the community. Considering that this protection involved no more than a reduction of metallic compounds in a small brook flowing into the West Branch, the justification for these large-scale activities was not given, beyond the goal of eliminating infiltration into the tailings.

For this reason, the writer embarked on an engineering study of his own to determine, if possible, whether capping and regrading were necessary parts of a considered approach to reduction of metallic compounds in Copperas Brook and the West Branch. He had been involved in the study from the beginning, and had made suggestions from the floor relative to the measurement of the pollutants in Copperas Brook and the watershed in general, and relative to the effects in the West Branch. But he had not been authorized to personally visit the site until October of 2001, at which time he began a critical study of his own following procedures and lines of reasoning he had developed in the similar remediation of asbestos waste sites in New Hampshire and Illinois, all of which closely affected nearby residences and communities. Prior to this time he did not have sufficient knowledge of the site to evaluate or comment on the proposals put forth by the EPA.

Much really fine data has been obtained by professionals and by volunteers over the past two years. Excellent, informative reports have been written by Arthur D. Little, Inc. for EPA, by the Thayer School of Engineering, by the Gaia Institute, and by the professional consultants of the Elizabeth Mine Study Group. The writer has reviewed these studies, together with historical evidence pertaining to the site as it was originally, including air photo evidence of the watershed and the floodplain of Copperas Brook. He has walked the site, many times immediately after rainstorms, to observe the brook, seepage from the tailings and the watershed, drainage from the pond and from the watershed, and the effect on the cover and the faces of the tailing piles.

The resulting engineering assessment has been the subject of this report. Specific conclusions and the reasons for them have been set forth. Specific recommendations have also been laid out in accordance with those conclusions, to which the reader is referred. A brief summary of the conclusions and recommendations is presented here, in an evaluation of the study and of the site as a whole.

Stability: The piles at TP-3 are stable against slip failure or erosional failure. Regrading to any contour other than the present one would not improve the resistance to failure from either influence. From the historical standpoint, they should not be removed or disturbed.

The frontal terraces of TP-2 are of a coarser sand and clearly are erosion-prone under the influence of rainfall. The terraces and the walls of the gully are found to be a major source of contamination into Copperas Brook. They should be carefully regraded laterally to the high face of TP-2, which is stable in its present condition and should not be disturbed. Or alternatively, the terrace material could be used to refill the erosional gully at TP-2 through which Copperas Brook now flows; this approach would restore the contours and profile of the main tailing pile at TP-2 to the original configuration.

It is found that the steep faces of the tailing piles TP-1 and TP-2 are sufficiently stable against large-scale slip failure. The imbedded timber structure remaining from the process of deposition provides a high degree of reinforcement, and should not be disturbed by regrading to any slope different from that which the material formed at the beginning, and at which it stands now. This type of embankment is similar to that used in the Netherlands to build levees against the sea.

Drainage: Drainage on the site is the result of precipitation falling both on the piles and on the surrounding watershed. Watershed water collects along the eastern edge of TP-1, and is a major source of seepage water at the bottom of TP-1. The seepage water is retained for up to 5 months before it exits as a seep into lower Copperas Brook. Water infiltrating through the cover material already in place is judged to be a small part of the total flow; because it occurs episodically its chemical effect on the tailings might possibly be beneficial, consisting of an oxidized coating on the upper particles, as on an external surface.

Drainage at TP-2 is a problem, in that Copperas Brook gains contaminants in its passage through the gully and then flows onto TP-1 and into the pond. Seepage from the pond carries these contaminants to the seepage zone at the bottom of TP-1. It is recommended that Copperas Brook be diverted as it exits TP-2, so that it no longer flows onto TP-1. This diversion would be to the north by means of a buried channel; a temporary channel could be on the surface. The pond on TP-1 should be drained, but retained as a natural collection point for runoff from the surface of TP-1. Provision should be made for continuous draining of the pond through the existing decant-tower/conduit system. Possible seepage from the pond should be eliminated by means of a constructed hardpan or a membrane beneath the pond and the surrounding open tailings.

Drainage from the piles at TP-3 should be separated and contamination levels measured individually for the areas of rock, low-grade ore, and roasted or un-roasted tailings; the diversion system shown for Option 2 of a remediation plan for TP-3 could be used, with the addition of a channel immediately below the pile having high sulfide content. However, the removal part of that option should not be carried out.

Cover: The surface cover presently in place on TP-1 and TP-2 is mature and sound; is comprised of indigenous grasses, saplings, and trees, and is compatible with external environmental conditions as well as with the pH of the tailing material. It is judged to provide long-term and low-maintenance protection for the historical profile and the erosional stability of the tailing piles, and should be retained and enhanced. Capping operations proposed by the EPA would destroy the natural cover and the profile, and should not be entered into; alternative means of limiting infiltration of rain water into the tailings should be sought and developed.

Treatment Cells: The design, size and location of treatment cells depends upon the determination of specific sources of contaminants to Copperas Brook. Separation of drainage courses at TP-3, and diversion of Copperas Brook from TP-1 will assist in these determinations, and should be accomplished early in the remediation process.

-------------------

The writer wishes to thank all those who for the past 2 years have measured and assembled artifacts and data of many kinds to assist those of us who engage in analysis and design; your work is invaluable. And sincere appreciation to Guy Denechaud and John Freitag for their considerable assistance with this report.

top