US Army Corps of Engineers

New England District

Elizabeth Mine Engineering Evaluation/Cost Analysis Comments and Technical Review Reports

Superfund Records Center SHE: £ ) r-*-.*' n .v BREAK: C t OHiER: I 4 r^ »-i

Prepared for:

U.S. Army Corps of Engineers New England District Concord, Massachusetts

22 January 2002

Arthur D. Little, Inc. Acorn Park Cambridge, Massachusetts 02140-2390 U.S.A.

Contract No. DACW33-00-D-0002

Reference No. 75986

12

345

67

Comments and Reports Provided by:

) Jim Gusek, Knight Piesold ) Bob Hedin, Hedin Environmental

) Don Runnells, Shepard Miller ) Phil Leonhardt, Shepard Miller ) Frank Bergstrom, Amerikanuak

) Bob Seal, USGS ) URS Corporation

x-w -f * Jrt ' - '"J* TComments Jim Giisekl

Knight Piesold

* . T 1

January 22, 2002

Mr. Scot A. Foster, Director Arthur D. Little, Inc. Acom Park EE_CA Review.ooc Cambridge, MA 02140-2390

Re: Elizabeth Mine, Vermont EE/CA Review

Dear Mr. Foster:

At the request of Arthur D. Little, Inc. (ADL), Knight Piesold and Co. (Knight Piesold) conducted a technical review of the information included in ADL's Draft Engineering Evaluation/Cost Analysis (EE/CA) of the Elizabeth Mine dated September 28, 2001. Our technical review assignment was to concentrate on the passive treatment and pollution prevention aspects of the cleanup approach with a secondary focus on geotechnical issues. The review is supported by the observations of James J. Gusek, P.E., who visited the Elizabeth Mine Site on October 10,2001.

The goal of this letter report is to summarize our professional evaluation of the design concepts and cost estimates provided in the Draft EE/CA, addressing the following specific questions:

• Is the overall technical approach reasonable? • Are the underlying assumptions for the passive approach reasonable? • Are the cost estimates reasonable, especially focussing on the frequency of system cleanout?

The report provides our brief background understanding of the Elizabeth Mine Site, a discussion of the bio-geochemical processes involved in passive treatment, followed by the findings of the technical review.

Background Understanding of the Elizabeth Mine Site

There are three mining/processing waste source areas at the Elizabeth Mine that generate acid rock drainage (ARD), designated by ADL as TP-1 through TP-3 (TP = Tailings Pile). The materials in the source areas range from typical hydrometallurgical mill tailings stored in the impoundments comprising TP-1 and TP-2, to mine wastes resulting from crude metallurgical processing techniques that included open roasting and subsequent leaching in TP-3.

The ARD streams being produced from these two waste types are similar in character but different enough to warrant slightly different treatment system designs. Both ARD streams are acidic and contain heavy metals as shown in the summary table below which is included for completeness. The flow rates of ARD from each site are different as well. The existing discharges from TP-1 and TP-2 are five groundwater seeps of relatively small flow rates that

Mr. Scot A. Foster January 22, 2002 Technical Evaluation - Draft EE/CA, Elizabeth Mine

respond to spring snowmelt. The TP-3 flow rate appears to vary significantly, especially i response to storm events and spring snowmelt.

Average Characteristics Elizabeth Mine ARD

TP-1 & 2 Parameter (5 Seeps) TP -3

Aluminum (mg/L) 0.5 61.5 Arsenic 0 0.4 Cadmium 0 0.4 Copper (mg/L) 0 46.3 Iron (mg/L) 462 88 Manganese (mg/L) 4 2.3 Nickel (mg/L) 0 0.3 Zinc (mg/L) 0.1 10.3 Acidity (mg/L) 700 (est) 1,300 Sulfate (mg/L) 2,000 1,520 pH (s.u.) 6 3.6 Flow (gpm) 5 to 10 40

The primary goals of the proposed remediation project at the Elizabeth Mine as expressed in the EE/CA appear to be three fold:

• To prevent or significantly hinder ARD formation by installing caps or covers on TP-1 and TP-2,

• To passively treat residual ARD from TP-1 and TP-2 collected from the toe of the TP-2 impoundment where groundwater breaches the surface in seeps or springs, and

• To passively treat ARD runoff from TP-3 that will be collected in a holding pond.

Passive Treatment Bio-Geochemical Processes The following is a general discussion partially excerpted from Gusek (2000) which is included as Attachment 1.

Many physical, chemical, and biological mechanisms are known to occur within passive treatment systems to reduce the metal concentrations and neutralize the acidity of problematic ARD. Notable mechanisms include:

• Sulfide and carbonate precipitation catalyzed by sulfate-reducing (SR) bacteria in anaerobic zones

• Hydroxide and oxide precipitation catalyzed by bacteria in aerobic zones

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Mr. Scot A. Foster January 22, 2002 Technical Evaluation - Draft EE/CA, Elizabeth Mine

• Dissolution of limestone • Filtering of suspended material and mineral precipitates • Metal uptake into live roots and leaves • Adsorption and exchange with plant, soil, and other biological materials.

Remarkably, some studies have shown that plant uptake does not contribute significantly to water quality improvements in passive treatment systems (Wildeman, et al., 1993). However, plants can replenish systems with organic material and add aesthetic appeal. In aerobic systems, plant-assisted reactions appear to aid overall metal-removal performance, perhaps by increasing oxygen and hydroxide concentrations in the surrounding water through photosynthesis-related reactions and respiration in the plant root zone. Plants also appear to provide attachment sites for oxidizing bacteria/algae. Research has shown that microbial processes are a dominant removal mechanism in passive treatment systems (Wildeman, et al., 1993). One anonymous researcher considered a passive treatment system as a "bioreactor with a green toupee," referring to the substrate where most of the bio-reactions occur and the collection of plants that grow on top of the treatment cells.

The decisions to use one particular kind of cell or cells in series will be influenced most by the ARD chemistry. As shown in the sketch below, there are two major geochemical zones found in natural wetland systems: an aerobic zone near the surface where oxidizing geochemical reactions occur and a deeper anaerobic, oxygen-depleted zone where reducing geochemistry predominates.

For convenience, these zone labels have been adopted to describe certain passive treatment cell types: anaerobic and aerobic. Most passive treatment cell types fall under these two general categories. Successive Alkalinity Producing Systems or SAPS are a type of anaerobic cell; so is an Anoxic Limestone Drain (ALD). A Sulfate Reducing Bioreactor or SRB cell is

DAM

TYPICAL WETLAND ECOSYSTEM another anaerobic cell type that fosters the activity of SR bacteria. Descriptions of the SAPS cell and an ALD are contained in the EE/CA; they will not be repeated

here. An SRB cell is typically comprised of a relatively homogeneous layer of organic material and crushed limestone (called substrate) placed above a drainage/collection layer as shown in cross section in the sketch below. This organic substrate layer is the "reaction zone" where the sulfate reducing bacteria function. Like a SAPS, the flow is vertically from the top of the substrate to the bottom. The substrate is totally saturated with ARD. The substrate surface can be either exposed to the elements, underwater, or even buried.

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Mr. Scot A. Foster January 22,2002 Technical Evaluation- Draft EE/CA, Elizabeth Mine

INFLOW

DISCHARGE

ORGANIC MATTER & LIMESTONE MIX

(SUBSTRATE)

DRAINAGE SYSTEM

ANAEROBIC SULFATE REDUCING BIOREACTOR

CROSS SECTION VIEW

NOTE: DRAWING IS NOT TO SCALE

In order to better support our technical comments on the EE/CA, a discussion of the appropriateness of applying anaerobic and aerobic cells follows.

Typical Conditions for Using Anaerobic Cells Anaerobic cells are most appropriate to remove heavy metals from low to neutral pH ARD. Aluminum concentration will dictate whether a SAPS or SRB is the more appropriate in some circumstances. Typically, anaerobic cells can raise pH, either as a result of limestone dissolution (SAPS and ALD's) or biologically produced bicarbonate ion (by SR bacteria). Dissolved metals can either be precipitated: 1) in the anaerobic cell itself in the case of an SRB (as a metal sulfide or carbonate) or 2) in a subsequent aerobic cell (as a hydroxide) in the cases of a SAPS or an ALD.

Both SAPS and SRB cells use the controlled decay of organic matter to achieve slightly different geochemical goals. In a SAPS, the decaying organic layer "de-aerates" the ARD and reduces ferric iron (Fe ) to ferrous iron (Fe ), converting a previously oxidized ARD to an anaerobic state. This is necessary to allow the anaerobic dissolution of limestone, which also occurs in an ALD. Exposing limestone to ferric iron in solution causes an armoring condition that quickly blinds the limestone surfaces and severely limits the dissolution rate. Thus it is important to reduce ferric iron to the ferrous state to prevent armoring in a SAPS unit.

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Mr. Scot A. Foster January 22, 2002 Technical Evaluation - Draft EE/CA, Elizabeth Mine

The ultimate goal of SAPS and ALD's is to add alkalinity so that the ARD is buffered against pH drops when the iron is ultimately hydrolyzed and precipitated as a hydroxide. The presence of aluminum in the ARD is problematic for SAPS and ALD's (Sterner, et al., 1997) because the geochemical conditions formed in them favor the formation of the mineral Gibbsite [Al (OH)3], which is a gelatinous solid. The Gibbsite sludge tends to fill the void spaces between the limestone rock used in a typical SAPS or ALD and becomes a major maintenance problem. Small amounts of aluminum in the ARD thus preclude the use of an ALD; aluminum can be tolerated in minor amounts by SAPS units, but periodic flushing of sludge from the unit (about once every several months) is required to maintain cell effectiveness.

An SRB cell also utilizes the organic matter to strip dissolved oxygen from the ARD and create anaerobic geochemical conditions. In addition, the SR bacteria use the organic matter as a nutrient source that supports their biological activity. The SR bacteria also require sulfate, which is typically found in ARD, as a nutrient. Sources of SR bacteria include mushroom compost, most sources of domesticated animal manure, and soils in the anaerobic zones of natural wetlands. Domestic sewage sludge is typically too sterile to be an effective source of SB bacteria. Organic matter sources include forestry waste (sawdust and wood chips), agricultural materials (alfalfa, native hay and straw); SR bacterial inoculum can also be a source of organic matter. Unfortunately, domestic sludge and composted yard waste are relatively poor long-term SR bacteria nutrient sources for anaerobic systems. The sewage digestion/composting processes consume much of the beneficial organic material needed to support the SR bacteria over the long term.

The processes by which SR bacteria remediate ARD do not involve the uptake of metals or acidity by the cells themselves. Remarkably, the by-products of cell metabolism are responsible for the improvements in ARD chemistry. The SR bacteria life-cycle reactions involve the generation of:

• Sulfide ion (S~2) or hydrogen sulfide (IfeS) gas, which combine with dissolved metals to precipitate sulfides, and

• Bicarbonate (HCOa") or carbon dioxide (CC>2), which raise the pH of the effluent.

The SR bacteria appear to facilitate the above through the following reaction:

(Equation 1) SO4"2 + 2 CH2O => S'

2 + 2 HCO3" + 2 H*

The dissolved sulfide ion combines with dissolved metals to precipitate those metals as sulfides, essentially reversing the reactions that occurred to produce ARD. For example, the following reaction occurs for dissolved zinc, forming amorphous zinc sulfide (ZnS):

(Equation 2) Zn"1"2 + S~2 => ZnS

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Mr. Scot A. Foster January 22,2002 Technical Evaluation - Draft EE/CA, Elizabeth Mine

The SR bacteria perform best in a pH of 5.0 or above, which they can self-maintain through the production of bicarbonate ion. For insurance, SRB cells typically include a crushed limestone component mixed in to protect the SR bacteria from acidity excursions in the ARD being treated.

While-the precise mechanisms have not been completely identified, the precipitation of Gibbsite is avoided in SRB cells. It is suspected that unidentified alternative aluminum compounds form in the SRB cells instead of Gibbsite, and these compounds are less prone to plugging. When aluminum is present, ponding the ARD on top of the SRB cell has been found to be best approach to preventing premature Gibbsite formation.

Anaerobic cells, particularly SRB cells, can operate in harsh weather conditions. Reisinger and Gusek (1999) reported on the operation of a pilot sized SRB cell at an elevation of 9,500 feet at an underground copper mine site in south central Wyoming. This cell functioned in sub-freezing conditions at water temperatures as low as 0.2 °C. While SR bacterial activity slowed during the winter monitoring period, it was still sufficient to provide effective treatment. The physical action of ice formation on the poorly insulated side of the test cell was more problematic than the modest reduction in bacterial activity. This problem was subsequently solved in a second pilot SRB cell that was completely buried; the 10 feet of snow at this site provided additional insulation during the winter months.

The longevity of a SAPS unit is limited by its "reservoirs" of organic material and limestone rock. Design lives of 15 to 25 years are typically realized (Skousen, et al., 1998). A similar design life is reasonable for an ALD. A minimum 24-hour [limestone] retention time in these cell types provides a quasi-safety factor in that the cells will not stop functioning completely when the retention time drops to slightly below the design value. Organic material may need to be replenished more frequently than the limestone in a SAPS, depending on the natural contributions of leaf litter and other sources.

The longevity of an SRB cell will be governed by the exhaustion of the "reservoir" of organic carbon that was installed when the cell was built. Two molecules of organic carbon are stoichiometrically required to reduce a molecule of sulfate (see Equation 1). We have found that SR bacteria can typically reduce sulfate (to sulfide) at a rate of 0.3 moles per day per cubic meter of cell volume. The rate decreases slightly during the winter. Typical cell designs have been based on carbon consumption rates estimated in pilot scale SRB cells. Cell longevity values on the order of 25 to 30 years have been estimated. But due to the relative novelty of the design concept (the oldest operating large scale SRB system in Missouri is only five years old), actual cell longevity on this order has not be directly observed. However, one volunteer passive treatment system outside an abandoned metal mine that has operated unattended since about 1889, over a century (Beining and Otte, 1997), has been identified in Ireland. This volunteer passive treatment system reportedly has 70 percent of its total metal removal capacity remaining.

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Mr. Scot A. Foster January 22, 2002 Technical Evaluation - Draft EE/CA, Elizabeth Mine

The goal of an SRB is to immobilize metals as sulfides. There may be a concern about metal accumulation in the substrate may cause the material to be classified as a hazardous waste. Limited experience has shown in several instances that SRB substrate is non-hazardous if it is allowed to "age" for several weeks after exhumation. If this was found to not be the case, the substrate materials could be leached in situ and the metals stripped out and recovered prior to exhumation to produce an non-hazardous material suitable for sanitary landfill disposal.

The reaction shown in Equation 1 shows the generation of sulfide ion (S~2) which can under certain geochemical situations produce hydrogen sulfide gas which is particularly odorous. Odor control is achieved by carefully balancing the metal loading and sulfate reduction rates (Equations 1 and 2) in the SRB cell so that excess hydrogen sulfide is minimized. We have also observed the colonization of SRB cell outfall areas by purple-sulfur bacteria that oxidize sulfide back into sulfate. While sulfate reduction rates may decline in the winter, typically metal loading rates decline as well.

The SR bacteria also produce excess alkalinity in accordance with Equation 1. This excess alkalinity is very beneficial in that it is available to neutralize ARD that may need to be diverted around the SRB cells in storm event situations that are outside the system design criteria.

It should be noted that the discharge from an anaerobic cell is typically devoid of dissolved oxygen and may contain dissolved organic matter that can further consume oxygen. Thus, anaerobic cell discharge is typically polished in an aerobic cell. These cell types are discussed below.

Typical Conditions for Using Aerobic Cells/Systems For slightly acidic (pH greater than 5.5) ARD without excessive dissolved iron and aluminum concentrations, hydroxide and oxide precipitation catalyzed by bacteria may be utilized as the dominant removal mechanism. Aerobic systems are similar to "natural" wetlands in that they typically have shallow depths to encourage oxygen exchange.

For the same level of treatment capacity, aerobic systems typically require larger areas than anaerobic systems. This can be an important design consideration if land availability is an operational constraint. In a telephone survey of state agencies conducted by Knight Pidsold in 1998, it was found that aerobic systems have been used to successfully treat iron- and manganese-containing coal mine ARD at over 600 sites throughout the US.

If the ARD is net alkaline, relatively diluted and contains manganese, aerobic cells may be appropriate to treat ARD containing heavy metals such as copper, lead and zinc. We believe that the primary removal mechanisms in this situation include adsorption on to biologically-deposited manganese oxide or iron hydroxide and/or adsorption on to organic residues from the decay of plants. We have documented moss harvested from a seep at an iron mine in Wyoming to contain 39 percent manganese by dry weight and 0.2 percent zinc. The seep water itself contained only

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Mr. Scot A. Foster January 22, 2002 Technical Evaluation - Draft EE/CA, Elizabeth Mine

trace amounts of these constituents. Microscopic examination of the moss revealed evidence of bacterial precipitation of manganese and iron (Robbins, 1998). If the ARD is strongly net-acidic, the removal of heavy metals in an aerobic cell is not efficient. Alkalinity can be added to mildly acidic water using SAPS and ALD's to increase iron removal efficiency, but this amount of alkalinity is usually insufficient to raise the pH high enough to precipitate metal oxides of heavy metals such as copper, lead and zinc.

Aerobic cell longevity is typically measured on the order of centuries, even considering the accumulations of bog iron and manganese oxide deposits. There are a number of "volunteer" aerobic type wetlands throughout the world that have functioned in removing metals (Sobolewski, 1997). Aerobic cells constructed by the Tennessee Valley Authority in the mid1980's have yet to require the cleaning out of iron precipitates (Brodie, 2001).

As introduced in the discussion of anaerobic cells, aerobic cells are required to polish anaerobic cell discharge. In the case of a SAPS or ALD, this step is necessary to oxidize ferrous iron to ferric and subsequently hydrolize the ferric iron to ferric hydroxide, a solid. Thus, the aerobic cell needs to have features to introduce oxygen and provide settling/retention time. In the case of an SRB cell, re-oxygenation alone is needed, especially at startup when heavy concentrations of organic matter in the cell effluent result in commensurate biochemical oxygen demand or BOD. This is a temporary condition that can be remedied with mechanical aeration as needed. Once BOD levels drop to less than about 10 mg/L (usually in several months), the re-oxygenation process can occur in a cascading open channel or in an aerobic "wetland" cell populated with plants and algae. These cells can also polish for heavy metals that may not have been removed in upstream cells, especially if manganese is present in the anaerobic cell discharge.

The operation of aerobic cells in the winter may be problematic due to ice formation. If the water can be kept moving, complete freeze-up is unlikely. As the primary function of these cells is aeration, ice formation will slow oxygenation. This can be overcome by including frequent cascades in the cell design, an easily accomplished task since most mining sites are located in hilly to mountainous terrain.

Metal oxide residues generated in aerobic cells are not typically characterized as hazardous waste; iron oxide residues from some sites have reportedly been marketed and sold to paint manufacturers (Hedin, 1998).

Design Flow Chart Figure 1, attached, attempts to simplify the above discussions into a decision tree that might be applied to a number of ARD situations, including the Elizabeth Mine Site. It is an enhanced modification of a decision tree introduced by the former US Bureau of Mines for addressing coal mine ARD in the early 1990's.

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9 Mr. Scot A. Foster January 22,2002 Technical Evaluation- Draft EE/CA, Elizabeth Mine

Comments regarding the appropriateness of the technical approaches presented in the Draft EE/CA to fulfilling the above goals follow.

Draft EE/CA Comments The comments are organized in the following order, beginning with a discussion on the design the proposed passive treatment system at the upper-most site (TP-3), progressing downhill to the proposed passive treatment system at TP-1 and TP-2, and concluding with comments on the cap designs and other ARD prevention issues.

TP-3 Passive Treatment System The proposed passive treatment system for TP-3 includes a holding pond and a Successive Alkalinity Producing System (SAPS). We agree that a holding pond is required to normalize the ARD feed rate to the treatment cells by minimizing peaks (both in flow and ARD geochemistry) that result from storm events or spring snowmelt. The size, general location and layout of the holding pond appears to be adequate for the proposed application. As noted in the EE/CA, because the TP-3 runoff contains significant amounts of aluminum, the planned SAPS unit is likely to have plugging problems with Gibbsite. Frequent flushing may be required and may not even solve the problem.

Construction of a SRB, another type of anaerobic cell like the SAPS, is more appropriate for the TP-3 geochemistry not only because it solves the aluminum clogging problem, but the other heavy metals are effectively removed as well. As stated earlier, a SAPS is more appropriate for iron removal using the alkalinity added from the limestone dissolution as a buffering agent when the iron hydrolyzes.

An SRB cell for a flow rate of 40 gpm and the chemical parameters listed on page 2 of this document would cover about two acres; the substrate would be about 3 feet deep. The capital cost of this unit would be on the order of $670,000. The cell would last from 20 to 25 years before the substrate would need to be replaced; the substrate comprises about 40 percent of the cell capital cost. The SRB system would actually be comprised of two cells, plumbed in parallel. Thus, while maintenance was being performed on one cell, the other cell could continue treatment. The discharge from the SRB cells would pass through an aerobic cell less than 0.25 acres in size. This cell would actually be a cascading channel leading down to the TP-1 and 2 site. The cost of this cell would be about $50,000 and periodic maintenance costs are negligible.

If the acreage for the SRB cells described above is not available or not deemed feasible, "semipassive" pre-treatment of the TP-3 effluent might be considered to reduce the total size and capital cost of the SRB cells. Pre-treatment would be accomplished with a "water-wheel" powered lime dosing feeder; this commercially-available unit would be installed just upstream of the holding pond. Most of the units have been installed in Appalachia but one was being tested at the Summitville Mine Superfund Site in southwestern Colorado (Campbell 2000). Key features of the unit/technology, marketed by Aquafix, Inc. of Kingwood, WV, include a water

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Mr. Scot A. Foster January 22, 2002 Technical Evaluation - Draft EE/CA, Elizabeth Mine

wheel connected to the ARD source, a bin to hold from 500 pounds to 100 tons of pebble lime and a screw feeder. A mixing channel for aeration and settling pond for precipitates is typically included in the design.

As the' units typically feed in lime pebbles, zero flow rates become problematic because the lime has a tendency to cake up and seize up the screw feed mechanism. A minimal flow is therefore required so some reagent consumption is unavoidable. Because solid materials are involved, the unit is not subject to the effects of sub-freezing weather. Stainless steel construction is available. Plugging of the outlet if the system sits idle is probably the biggest maintenance headache.

At the TP-3 Site, the iron precipitate formed would settle out in the holding pond along with the suspended solids load. The auto lime dosing unit is available commercially but is considered a "semi-passive" technology because the lime bin needs to be refilled perhaps every several months. However, since the sediment collected in the holding pond would need removal almost on the same schedule, a maintenance presence on the site is already committed.

In summary, there are other technologies better suited to passively treating the TP-3 ARD runoff than the proposed SAPS unit. The capital costs of these technologies are similar to those cited in the EE/CA. The 25 year maintenance cost for retrofitting the SRB cells is 40% of capital or $268,000 or about $10,720 per year. The net present value of this maintenance effort is significantly less than the amount cited in the EE/CA. Therefore, the EE/CA amount should be considered conservative.

TP-1 & 2 Passive Treatment System The proposed passive treatment system for TP-1 and TP-2 includes a ground water collection gallery, holding pond and a SAPS. Due to the low aluminum concentration, a SAPS cell would work at this site, but so would an SRB cell. Due to the low flow, we think that the holding pond can be omitted from the design if an SRB cell were constructed. SRB cells tolerate low flows as long as the substrate can remain saturated. With the constant ground water flow assumed to be five gpm, this would be an ideal situation for an SRB cell.

Construction of an SRB cell for a flow rate of 10 gpm (double the estimate) and the chemical parameters listed on page 2 of this document would cover about 0.5 acres; the substrate would be about 4 feet deep. The capital cost of this unit would be on the order of $140,000. As with the SRB recommended for TP-3, the cell would last from 20 to 25 years before the substrate would need to be replaced. The discharge from the SRB cell would pass through an aerobic cell less than 0.1 acres in size. The cost of this cell would be about $7,000 and periodic maintenance costs are negligible. In our experience, at a flow rate of 10 gpm, this treatment unit would be considered pilot scale. The engineering required would be straightforward. The combined cost of this treatment system, at twice the required capacity, is about $150,000.

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11 Mr. Scot A. Foster January 22, 2002 Technical Evaluation - Draft EE/CA, Elizabeth Mine

In summary, either the SAPS technology or the SRB technology would work to remediate the flow from the seeps at TP-1 and TP-2. The estimated capital cost of the SRB technology (at double the design capacity) is about $100,00 less than the SAPS technology cost cited in the EE/CA. The 25 year maintenance cost for retrofitting the SRB cell is 40% of capital or $56,000 or about $2,250 per year. The net present value of this maintenance effort is significantly less than the amount cited in the EE/CA. Therefore, the EE/CA amount should be considered inflated, but conservative.

TP-1 & 2 Cap Design and OtherARD Prevention Issues The capping of ARD-generating mine waste to mitigate ARD is a technology accepted around the world. The geotechnical approaches presented in the Draft EE/CA appear to be appropriate for the site conditions.

During the site visit, the diversion of runoff from TP-3 into the open cut was discussed. This low-cost alternative might decrease the loading to the TP-3 treatment system but would add metal loading to the groundwater system connected to the open cut. The additional metal loading to the mine pool is probably negligible compared to the total metal load provided by the local stratigraphy.

The upper cut was also included in the site tour. This location appears to offer several opportunities for ARD control:

• Backfilling the pit with ARD-prone waste from a nearby waste rock dump. Permanent submergence of the waste rock would be required to mitigate ARD formation;

• Placement of passive treatment in the floor of the exit zone of the upper cut to polish effluent water leaving the site. The passive treatment system could be constructed on top of the backfilled waste. Some temporary active treatment of the pit effluent might be required during and after backfilling. The chemistry of the pit water would dictate whether an anaerobic or aerobic system would be more appropriate.

References Cited (INCOMPLETE)

Beining, B.A., and M.L. Otte, 1997. "Retention of Metals and Longevity of a Wetland Receiving Mine Leachate," presented at the 1997 National Meeting of the American Society for Surface Mining and Reclamation, Austin, Texas, May 10-16.

Brodie, Gregory, 2001. Personal communication.

Campbell, Angus, 2000. Personal communication.

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12 Mr. Scot A. Foster January 22, 2002 Technical Evaluation - Draft EE/CA, Elizabeth Mine

Gusek, JJ., 2000. "Reality Check: Passive Treatment of Mine Drainage An Emerging Technology or Proven Methodology", Presented at the Society for Mining, Metallurgy and Exploration Annual Meeting, Salt Lake City, Utah, February 28-March 1, Preprint No. 00-43.

Hedin, Robert, 1998. "Recovery of A Marketable Iron Product From Coal Mine Drainage". Proceedings of the West Virginia Surface Mine Drainage Task Force, Morgantown WV, April, 1998.

Robbins, Elenora, 1998. Personal communication.

Reisinger, R. and J. Gusek, 1999

Skousen, et al., 1998

Sobolewski, Andre, 1997. "The Capacity of Natural Wetlands to Ameliorate Water Quality:A Review of Case Studies". Proceedings of 4th ICARD, Vancouver, B.C., 1997., p 1549.

Sterner, et al., 1997

Wildeman, T. R., G. A. Brodie, and J. J. Gusek, 1993. Wetland Design for Mining Operations. BiTech Publishing Co., Vancouver, B.C. Canada.

Closing Remarks

In summary, the overall technical approach that ADL considered for the passive treatment system for TP-1 and TP-2 is appropriate, but a similar approach, an SRB cell, may function better and cost less to construct and maintain. The SAPS unit proposed for TP-3 will be problematic due to aluminum plugging. An SRB cell followed by an aerobic cell, costing about the same to construct as a SAPS, would be a more appropriate technology, would not be prone to aluminum plugging and would be designed to last longer than 12 to 15 years before requiring a major retrofit.

In light of the presumed 12 to 15 year maintenance cycle which may be extended to 25 years, the capital and long term maintenance costs presented in the EE/CA appear to be conservative.

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Mr. Scot A. Foster January 22, 2002 Technical Evaluation - Draft EE/CA, Elizabeth Mine

We appreciate the opportunity to support ADL in its work with the US Army Corps of Engineers at the Elizabeth Mine. If you require clarification of any aspect of our technical review, please contact us.

Sincerely, Knight Piesold and Co.

James J. Gusek, P.E. Donald R. East, P.E. Senior Project Manager President

Attachments

Gusek, J. 2000

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Mr. Scot A. Foster January 22,2002 Technical Evaluation - Draft EE/CA, Elizabeth Mine

DETERMINE FLOW RATE ANALYZE WATER CHEMISTRY

CALCULATE LOADINGS

Relatively 1 NET MJCMJNE NTT ACIDIC Bad

Water WOEP

Relatively Relatively *

WJER

DETERMINE 00, Good Fair Ferric Iron. Al Water Water

i PO

i = 1 flpEN UUESTONE CHANNEL

AEROBIC , POLISH FOR DC. UW6WESE, BOD 5AP3 i ft FECM. COUFOHUS (startup only WETLAND SETTUNG i

POND AERATION AND SETTLING POND

MEETE •RJUENT HO rRE- EVA! jlftTESMNO C£SK ;N i

S1M4MRD5?

YES 1 T

DISCHARGE

Figure 1 Flow Chart for Passive Treatment Cell Type Selection

(this figure will be cleaned up in the final draft)

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.";-;»

*.Bob Hedin Hedin Environmental

195 Castle Shannon Blvd. Pittsburgh, PA 15228 Phone (412)571 -2204 Fax (412) 571 -2208

E-mail bhedin@hedinenv.com

November 14, 2001

Scot Foster Arthur D. Little, Inc. 20 Acorn Park Cambridge, MA 02140

Dear Scot;

This letter/report is my review of the Draft EE/CA for the Elizabeth Mine in Strafford Vermont. My opinions are based on my review of the document, water chemistry data provided by yourself and USGS, and my November 7, 2001 visit to the site. I have focused on the passive treatment proposals. My expertise on passive treatment results from six years studying the technology with the US Department of Interior (1988-1994) and seven years of recent experience in the design and construction of passive systems.

Passive Treatment Concepts

All treatment plans for polluted mine drainage must consider the neutralization of acidity and the precipitation of contaminant metals. In passive systems acidity is neutralized by bicarbonate alkalinity generated by carbonate dissolution, typically limestone, and bacterial processes, principally sulfate reduction. Metals are removed by adsorption/chelation processes, by plant uptake, and by precipitation as oxides, hydroxides, sulfides and carbonates. The design of the system influences the importance of each of the geochemical processes. A variety of passive treatment techniques are available and, often, a contaminant problem can be corrected through several technologies. The most appropriate technological solution is determined by water chemistry, flow variation, the targeted effluent conditions, site conditions, materials cost, predicted O&M requirements, and the particular expertise/experience of the system designer.

Passive Treatment of TP1/TP2 Seeps

Contaminated water flows from several seeps at the base of the TP1 pile. The water source for the seeps appears to be infiltration of precipitation and Copperas Brook. Data for the TP1 seeps were obtained from AD Little and verified by USGS. The seeps have pH 5-6 and are contaminated with ferrous iron. Concentrations of iron vary for seeps

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between 50 and 750 mg/L. Because of the acidic properties of iron, the seeps are net acidic. Manganese concentrations are 2-6 mg/L. Aluminum concentrations are generally less than 1 mg/L. No other metals are known to be present at levels of concern. The recommended treatment in all the EE/CA alternatives is an Anoxic Limestone Drain (ALD), followed by a holding pond, followed by two SAPS ponds, followed by a constructed wetland. This design is conceptually sound. The seepage water is well suited for treatment with an ALD because it has low concentrations of Al and ferric iron. The ALD will likely discharge water with 150-300 mg/L alkalinity. Aeration of the ALD effluent in the holding pond will cause the precipitation of 75-150 mg/L Fe. Flow through the two SAPS ponds will generate additional alkalinity and precipitate iron. Based on the flows observed on November 7 and the chemistry provided by AD Little, collection of the seeps will result in a flow containing approximately 300 mg/L Fe and 450 mg/L acidity. Properly designed SAPS ponds generally generate 150-200 mg/L of net alkalinity. Thus the ALD and two SAPS ponds should generate 450-700 mg/L alkalinity - enough to neutralize the current acidity. Iron will be removed in the holding pond, the SAPS, and the wetland. A sedimentation pond should be considered between the SAPS ponds to promote iron precipitation and lessen plugging of the second SAPS with iron oxide.

The final design of the passive system should be based on the actual flow and chemistry of the TP1 seeps. Both of these parameters are uncertain because the proposed stream diversion, surface water diversion, and surface capping will lessen flow through the pile. Chemical loading should also be lessened by removal of the substantial acid input from Copperas Brook infiltration. Rough calculations suggest that the removal of Copperas Brook, alone, should decrease acidity loadings by 33-50%. This calculation is based on an assumption that 50-75% of the average TP3 acidity loading (-60,000 g/day1) contributes directly to the current TP1 acidity loading of the seeps (-110,000 g/day2). Thus, the quality of the TP1 seeps is likely to improve, making the prognosis for the proposed passive treatment system even better.

Until these remedial actions occur, the flow and chemistry of the TP1 discharges should be monitored on a regular basis. Flow measuring devices should be installed as close to the discharges as possible and samples should be collected directly from the discharge points. Flows and chemistry should be measured on a monthly basis, or more frequently. Using these data, the characteristics of a single combined flow can be calculated. It would also be useful to establish stations in Copperas Brook above TP2 and below TP1 so that infiltration of the stream can be estimated and compared to the summed TP1 seeps.

Confidence in the performance of the passive system would be increased by an accurate estimate of the amount of alkalinity that the ALD will generate. A reliable way to predict the performance of the ALD is to measure the alkalinity produced after incubating the

1 estimate based on 15 gpm of flow (estimated infiltration of 15 acres of precipitation) at 785 mg/L of acidity (ADL reported average value) 2 estimate based on 43 gpm of flow (November 7,2001) and 462 mg/L acidity (average of calculated acidities for ADL TP1 seep data)

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seepage water with limestone aggregate in an anoxic environmental for 4-12 hours. A "cubitainer" incubation method was described in a paper by Watzlaf and Hedin. (The paper is attached.) I have developed improved procedures for predicting alkalinity for and AID that I would be glad to discuss at a later date.

Operation, Maintenance, and Replacement of the TP1 Passive System

Lang-term performance of the proposed treatment system will require operation, maintenance, and replacement (O&M&R). The system should be inspected monthly to assure that the AID discharge pipe(s) are flowing freely, that all channels are free of obstructions, and that the pond and wetland berms are competent. Samples should be collected for analysis on a schedule determined by the State. Every few years more substantial maintenance should be anticipated. Iron oxide accumulations my require the cleaning of a ditch or part of a pond (likely, with a backhoe). Animal problems (muskrats, beavers) may need to be resolved. If a seep develops outside of the collection system, it will need to be collected and piped into the system.

The major maintenance issue for the SAPS ponds will be losses of substrate permeability due to the accumulation of iron solids. Accumulation of iron oxide on the substrate surface may eventually result in a "hardpan" layer that acts as a barrier to vertical flow of water. The problem can be corrected by scarifying the substrate surface with an excavator. This activity may be necessary every five years. Eventually, the system will require major maintenance due to the consumption of limestone in both the AID and SAPS and also due to the accumulation of iron oxide sludge. The ALD will need new limestone. The SAPS ponds will need new organic substrate and limestone. The sedimentation ponds will require removal of iron sludge. The assumed frequency of these major activities is currently every 12 years. This period is reasonable. Depending on the scale of the installed system relative to the actual contaminant loading, the frequency of major maintenance for the ALD and sedimentation ponds may be as long as 20-25 years.

Passive Treatment of TP3 Seeps

Seepage was observed flowing from near the base of TP3 and into a stream channel that flowed onto TP1. Chemical data provided by AD Little indicated that the seepage is highly contaminated. The seepage has pH 2-3 and contains 500-1100 rag/acidity, 30-130 mg/L Al, 60-130 mg/L Fe, 20-100 mg/L Cu, 5-15 mg/L Zn and 1-5 mg/L Mn. TP3 seepage differs from TP1 seepage by: 1) its unsuitability for treatment with an anoxic limestone drain due to high Al concentrations; 2) the presence of elevated concentrations of copper and zinc; and 3) the highly variable flows and loadings. The current remediation plans assume that TP3 will not be reclaimed and that all surface water, which is highly contaminated, will be collected and treated.

I am unaware of any passive treatment system that currently treats AMD similar to that existing at TP3. While the proposed treatment plans are reasonable extrapolations of

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existing technologies, they should be considered extrapolations. Problems may develop that can not be anticipated from the current knowledge of passive treatment. My personal experience with the treatment of waters contaminated with Zn and Cu is limited to coal mine drainage containing 500-2000 ug/L Zn and up to 500 ug/L Cu. At these concentrations, SAPS systems and constructed wetlands are very effective at lowering moderate concentrations of Zn and Cu to 50-100 ug/L. However, Cu concentrations for TP3 average 46,300 ug/L - well outside the range of my experience.

The current treatment plan includes the construction of a holding pond, two SAPS ponds, and a wetland. The system would generate alkalinity through a combination of limestone dissolution and bacterial sulfate reduction. Metals would be retained in the SAPS and wetland. The current conceptual design is sound (given my reservations expressed above). A sedimentation pond should be placed above the constructed wetland that would be used for the accumulation of solids flushed from the SAPS ponds. The system should be plumbed to allow the SAPS ponds to be used in a parallel arrangement.

The holding pond is intended primarily to store storm flows and secondarily to provide some solids removal. At pH values less than 3, very little metal removal should be expected in this pond. Both ferrous and ferric iron are highly soluble at pH values less than 3. In order to retain metals in this pond, alkalinity will need to be added. A waterwheel device might be installed that would meter in fine limestone or hydrated lime. This addition of alkalinity would promote precipitation of Fe and Al. While this would protect the downstream SAPS ponds from high accumulations of Fe and Al, the solids that precipitated in the pond would need to be periodically removed. If alkalinity addition is considered for the pond, the design should consider the need to prevent solids from being washed from the pond to the SAPS units.

The SAPS ponds should very effectively remove all of the Al and most of the Fe. Much of this removal will probably occur within the limestone aggregate. The SAPS ponds should be designed with plumbing to facilitate the periodic flushing of solids from the limestone aggregate. In Pennsylvania, a wide variety of plumbing designs are being used in SAPS systems. A review of these designs and their effectiveness should be done before the final design for the TP3 is developed. George Watzlaf, US Department of Energy in Pittsburgh, is currently assessing the effectiveness of SAPS flushing systems in Pennsylvania.

As noted above, my limited experience with Zn and Cu indicates that SAPS systems are effective for the removal of low concentrations of these metals. I suspect that the removal occurs in the organic substrate, where sulfate reduction occurs, and thus the metal solids would not be readily flushed out. For the system to provide long-term removal of Cu and Zn, I expect that sustained sulfate reduction must occur. Experiments with low pH highly oxidized mine waters has shown that even alkaline substrates are gradually acidified by very low pH AMD. Once the substrate is acidified, little bacterial activity and metal removal occurs. To delay this as long as possible, the organic substrate used in the SAPS should be amended with limestone or a similar alkaline material.

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Wetlands constructed with a compost substrate are effective at polishing discharges from SAPS ponds. The addition of organic substrate to the wetland increases the significance of anaerobic microbial processes that can remove Cu and Zn. In order to better polish the TP3 water, the wetland should be constructed with 12 inches of an alkaline organic substrate.

Other Passive Treatment Technologies for TP3

Because of the high concentrations of Cu and Zn at TP3, a treatment approach with a higher reliance on sulfate reducing bacteria (SRB) may be preferable over the current SAPS design. Jim Gusek is a proponent of the SRB approach and has reported success at several sites in the US. To my knowledge, none of the sites combine TPS's flow variation, high Cu and Zn concentrations, high Al and Fe concentrations, very low pH, and cold winter temperatures. I am particularly concerned that the precipitation of high loads of Al and Fe within the SRB bed might quickly compromise its permeability. Consideration might be given to placing an SRB system downstream of a SAPS pond. The SAPS pond would remove most of the Al and Fe, while the SRB system would remove the Cu and Zn.

Operation, Maintenance, and Replacement of the TP3 Passive System

The TP3 passive system will have much larger O&M&R requirements than the TP1 passive system. As outlined above, a substantial portion of TP1 acidity and metal contamination (Fe) can be treated with an ALD and sedimentation pond. This arrangement separates the alkalinity-generating process (limestone dissolution) from the metal precipitation process (iron oxide precipitation), which lessens concerns about substrate permeability. The technologies used for TP3 treatment, either a SAPS or SRB approach, will unavoidably combine alkalinity generation and metal precipitation. Solids accumulation will decrease the permeability of the alkaline substrate and eventually result in a plugging problem that will decrease treatment efficiency. In SAPS systems the plugging problem has been addressed through the incorporation of flushing systems in the limestone aggregate. As noted above, these flushing systems will not remove metals from the organic substrate - where a majority of the Zn and Cu is expected to accumulate. To my knowledge, no non-destructive methods have been developed to remove metal solids from organic substrate. As a consequence, I believe that the O&M&R schedule for the TP3 system should be more vigorous than that for the TP1 system. Specifically, I recommend that major maintenance of SAPS ponds be anticipated on a 5-10 year cycle for the TP3 system. The major maintenance would involve replacement of organic substrate that was responsible for supporting beneficial bacterial processes. At the same time, the limestone aggregate would be inspected and replaced on an as-needed basis.

If alkalinity addition occurs in the holding pond, then sludge removal would be periodically required for the basin. The use of limestone would result in a dense sludge that would likely need to be removed every 5-10 years. The use of hydrated lime, which

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will provide more effective pre-treatment, would result in a less dense sludge and require removal every 2-5 years.

Disposal of Sludge and Substrate Wastes

Substrates and sludge removed from the treatment systems will require disposal. Sludge removed from the TP1 holding pond will consist primarily of Fe hydroxides. Sludge removed from the TP3 holding pond (assuming alkalinity addition occurs) would consist primarily of Fe and Al hydroxides. Solids flushed from the TP3 SAPS would consist primarily of Al hydroxides. Organic substrate removed from the TP1 SAPS will contain Fe hydroxides and sulfides. These Fe and Al solids are not considered hazardous and, in Pennsylvania, are legally disposed of through on-site burial. Organic substrate removed from the TP3 SAPS will contain Cu, and Zn. Because of the presence these metals, the material may require special handling and disposal. Vermont and EPA's standing on sludge disposal should be determined so that the final O&M costs fully account for this significant activity.

Miscellaneous Comments

A tenet of AMD remediation is to attempt source reduction before settling on treatment. In many cases, the generation of AMD can be substantially lessened through reclamation, special handling of acidic materials, and hydrologic manipulations. Source reduction is planned for TP1 and will lessen long-term costs and increase the probability of treatment success. Little source reduction is currently planned for TP3, despite the likelihood that major reductions in AMD generation can be achieved. Specifically, the acidic materials should be isolated from surface and ground water flows. Well-established methodologies exist for the special handling and on-site disposal of acidic mine wastes. The site should then be reclaimed and revegetated so that surface water flows off the site with minimal contamination. I suspect that a well conceived reclamation plan could eliminate toxic aspects of the site, while restoring some of the attributes of the site that give it an historical context. In the absence of source reduction at TP3,1 am skeptical that the passive treatment system will provide continuous and long-term compliance with the effluent targets unless the State is committed to a vigorous O&M&R program.

Please contact me with questions about this report.

Sincerely,

Robert S. Hedin

RSH/kml

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SHEPHERD MILLER, INC. Environmental and Engineering Consultants

T E C H N I C A L M E M O R A N D U M

DATE: November 13,2001 SMI# 180910

TO: Scot Foster

FROM: Donald D. Runnells

SUBJECT: Observations, Comments, and Recommendations on Elizabeth Mine Reclamation Plans and Draft EE/CA

COPY: Phil Leonhardt

The following observations and comments are based on the meetings and visit to the Elizabeth

Mine site by Phil Leonhardt and myself on November 6 and 7, 2001. The meetings and visit were

very informative, and I hope the following observations, comments, and recommendations will be

helpful to you. I should mention that Phil Leonhardt and I have deliberately developed our reports

independently of each other.

OBSERVATIONS AND COMMENTS

(1) With the exception of TP-3, there is nothing unusual or surprising about the majority of the

Elizabeth Mine site. The physical and chemical characteristics of tailings ponds TP-2 and TP-1

are typical of base-metal tailings impoundments at numerous other sites in the U.S. However,

the presence of TP-3 is unusual and worrisome, as discussed below.

(2) There are two main types of rock wastes at TP-3. One type consists mainly of the residues from

historic roasting and leaching to yield the chemical reagent copperas. To the eye, this material

appears to be chemically stable and relatively benign. The other type of waste consists mainly

of sulfide-rich waste rock that was hand-cobbed during early stages of copper mining. The

mine waste rock is rich in sulfides and is actively generating acid and releasing metals, and it

poses an environmental and economic hazard.

(3) The plan to build a sedimentation pond and two S APs downgradient form TP-3 and upgradient

from TP-2 appears to me to be problematic. The amount of space that is available at the c.-Vrem user foUeiVoae?vct_759S6_i

Technical Memorandum Scot Foster November 13, 2001 Page 2

probable locations seems marginal. I also believe that the O&M costs of maintaining the

sedimentation pond will be distressingly high.

(4) I was surprised to see the large amount of volunteer vegetation that has developed on the thin

layer of native soil on a portion of the surface of TP-1. It is obvious that revegetation of the site

will be an easy task, regardless of the reclamation plan that is adopted. I was even more

impressed by the healthy population of volunteer vegetation that has developed on a small

section of the embankment of TP-1 where the embankment is protected from mechanical

erosion by waste stumps and logs that were dumped over the edge.

(5) Based on conversations with Jane Hammarstrom, the oxidized surfaces of TP-1 and TP-2 are

moderately acidic. This means that EE/CA Alternative 3D, involving the development of a

reactive, self-healing chemical hardpan, is technically feasible.

(6) Like many other historic tailings impoundments, the embankment of TP-1 is steep and, except

for gulleying, it is mechanically stable in its present configuration. I did not see any evidence of

slippage, mechanical failure, or mass movement anywhere on the embankment. Of course,

flooding or earthquake activity could cause a loss of stability. In my experience, the

embankments of base-metal tailings impoundments become more stable with age, and are

capable of standing at very steep angles. I believe this stability is the result of dewatering of the

tailings, and of chemical changes that result from weathering, producing cementation of the

tailings grains. Mechanical failures of tailings ponds with which I am familiar involve modem

ponds in which the hydrostatic head was not property controlled, or overtopping of meteoric

water occurred. In historic tailings impoundments, the only slope failures that I have personally

observed have resulted from undercutting by adjacent streams. People here at Shepherd Miller

who are more familiar with the engineering of tailings impoundments agree with my

observations on this issue.

(7) Based on the photographs taken by Jane Hammerstrom of the tailings in trenches, the interior of

TP-1 is in a reducing state. This is entirely consistent with the chemistry of the water that

emanates from the toe seeps, which is high in calcium, magnesium, sulfate, and ferrous iron,

but low in trace metals. The interior of TP-1 acts as a treatment system (or an "entombment

system") for immobilizing metals in a strongly reducing environment. This is in contrast to the f.-Vrom *serfoUtiYostei^acr_759KJatiO?romjnmti_nauit{s_2.

Technical Memorandum Scot Foster November 13, 2001 PageS

oxygen-rich, acidic, metal-rich waters that emanate from TP-3. If innovative technologies were

to be included in the remedy, some consideration could be given to routing the leachates from

TP-3 into the reducing interior of TP-1 to immobilize the metals and possibly neutralize the

acidity. Laboratory column tests could be used to determine whether or not this would be a

viable treatment system.

(8) Chemical analyses of the seepage water from the toe of TP-1 contain enough manganese to be

problematic in attaining aquatic stream standards downgradient from the proposed S APs and/or

anoxic drains. Manganese is very difficult to remove in engineered wetlands. Also, the high

concentrations of sulfate in water from the seeps may cause armoring by gypsum and loss of

reactivity of the limestone in anoxic limestone drains.

RECOMMENDATIONS

Based upon the observations and comments listed above, the following recommendations are

offered for your consideration:

(1) The sulfide-rich mine waste at TP-3 should be removed or covered. It poses a long-lasting

environmental and economic hazard. The sulfide-rich waste rocks will continue to generate

acid and release metals into the foreseeable future, and they will continue to be mechanically

eroded and carried downgradient during precipitation events. The O&M costs associated with

leaving the sulfide-rich mine rock in place at TP-3 will be large over the long term. In

contrast, the historic residues from the copperas operations seem to be relatively inert and

probably pose little environmental or economic hazard for the future. I cannot visualize a truly

successful and economically sensible remedy for the site as long as the sulfide-rich wastes are

exposed at TP-3.

(2) I recommend that serious consideration be given to moving the locations of the upper

sedimentation basin and SAPs from their present location between TP-3 and TP-2 down onto

the surface of TP-1. I cannot see anything that would prevent lined basins from being

constructed and operated in a safe manner on the surface of TP-2. If the sedimentation basin

and SAPs were constructed on the surface of TP-1, all aspects of maintenance, accessibility,

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Technical Memorandum Scot Foster November 13, 2001 Page 4

and replacement would be simplified, and future O&M costs would probably be reduced in

comparison to the presently proposed upgradient site.

(3) I recommend that, at a minimum, a test plot be established to investigate the viability of

generating a reactive, self-healing hardpan on the surface of TP-1 over the next year or so. A

test plot of about 100 square feet (10 feet by 10 feet) should be adequate. The paste pH values

of the surface tailings should be measured within the test area to make sure they are at least

moderately acidic (pH less than about 5). The initial permeability of the tailings within the test

area should be measured with a double-ring infiltrometer, prior to laying down a layer of

limestone granules. The limestone granules should be minus-3/8" in diameter, and spread on

the surface so the grains are generally in contact with each other. The goal is to cause a thin

layer of gypsum and metal hydroxides to form under and between the granules of limestone. A

small amount of lime could be mixed into the limestone to hasten the hardpan reactions. The

layer of granules should not be greater than about one-half inch in thickness, so that the

reactions and cementation products can be observed visually. Over a period of a few weeks to

a few months, the layer should be inspected and photographed. At the end of the test, the

infiltrometer measurements should be repeated to determine the new permeability through the

incipient hardpan.

(4) Although it is not my technical field, I personally cannot see any reason to cover the

embankment of TP-1 with a synthetic membrane. The footprint of the embankment itself is

very small relative to the size of TP-1, and infiltration of water due to direct fall-on of

precipitation is small relative to the flat surfaces on top of TP-1 and TP-2. It is obvious that

the embankment can be further stabilized, and infiltration of water reduced, simply by the

development of a healthy cover of vegetation. Vegetation will flourish on the embankment if

the surface can be temporarily protected from surface erosion until vegetation can be

established. The surface of the embankment could be smoothed, amended with lime (and

possibly fertilizer), and revegetated in place. It might be necessary to put down some burlap or

other porous retaining material to temporarily protect the surface from erosion until the

vegetation takes hold. After the vegetation has become established, the embankments will be

visually attractive and should be essentially free of maintenance.

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(5) The existing slopes on the tailings embankment already appear to be mechanically stable,

except for erosion by surface runoff. The current stability of the steep slopes is the result of

weathering reactions that have caused incipient cementation of the grains within the

embankments, by a mixture of gypsum and metal-bearing hydroxides and/or metal-bearing

siilfates, in much the same manner as would occur in an induced reactive hardpan. Although it

may be desirable to reduce the embankment slopes to produce a margin of safety, perhaps from

seismic events, I cannot imagine that it would be necessary to go to less than 2:1. The

geotechnical testing that will be done should recognize and take into account the fact that the

tailings on the embankment naturally tend toward a stable, steep slope as the grains weather

and become cemented together. The benefits of the inherent stabilizing properties of the

historic tailings could be exploited.

(6) The concept of a rock buttress against the downstream face of TP-1 seems to me to be

problematic. Phil Leonhardt has stated that it would require a very large volume of rock, and

that such a buttress would extend far downstream if emplaced at a low angle. If a buttress

were to be constructed, the toe seeps would be covered by a large rock buttress, thus requiring

an extensive system of surface and subsurface drains.

(7) Pilot studies of the proposed passive treatment systems are essential. All of the seepage waters

contain high concentrations of sulfate, which may lead to armoring and loss of reactivity of

limestone in anoxic drains even at neutral or elevated pH. The elevated concentrations of

manganese are also problematic because manganese is notoriously difficult to remove in

engineered wetlands. In Colorado we have a historic mine site at which it was necessary to

construct an active treatment plant primarily to remove manganese from the drainage water

because the aquatic standards for manganese in the receiving stream water are so low.

(8) If substantial regrading of the tailings pond embankment is undertaken, the current reducing

condition in the interior of TP-1 will be disrupted. This will result in rapid oxidation of the

interior sulfides, with the potential for release of slugs of acid and metals to the drainage water.

Liming and/or other protective measures must be undertaken concurrently with regrading to

avoid negative impacts to the receiving waters.

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(9) If it were possible to use innovative technologies, the development of unlined wetlands on the

surface of TP-1 could be very attractive. Some of the water from the wetlands would slowly

infiltrate through the underlying tailings, thus entering the interior "treatment system" that

likely exists in the strongly reducing interior of the tailings impoundment. Excess surface

water could be routed through attractive, meandering rock channels to an engineered

discharge; this has been done at two other mountainous mine sites with which I am familiar.

The potential for overtopping and erosion of the embankment during high-water events could

be eliminated by means of properly engineered retention ponds and a spillway.

SPECIFIC COMMENTS ON THE EE/CA

I do not have many specific comments on the EE/CA. I think it is well written and sufficiently

comprehensive to allow a reader to understand the site and the remedial alternatives. There are a

few typos, but those will doubtless by corrected in the final version. I offer the following

observations and comments:

(1) I was surprised by the paucity of information on the ground water hydrology and water balance

at the site. All of the remedial alternatives depend on an understanding of the ground water

hydrology and the water balance, but I found these to be inadequately described in the EE/CA.

The assumption of 5 gpm of ground water flow is not adequately supported.

(2) I would have benefited from a table of data in which the various surface-water standards that

were applied were compared to the range of values observed in waters at the site. Such a

comparison would have allowed me to understand, for example, why the specific six metals

were determined to be COCs.

(3) On page 1-24 of the EE/CA, a very brief discussion is given of the goals of the remedial action.

This discussion seems inadequate to me. I would have preferred to see a list of specific goals,

perhaps with sub-goals, followed by a discussion. As an example, exactly what is meant by

"...quality of surface water..." What surface water quality goals are we trying to achieve?

Similarly, a secondary goal is described as: "...addressing community concerns...," but what

are the specific community concerns?

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Technical Memorandum Scot Foster November 13, 2001 Page?

(4) On page 2-10, it is stated that the tailings pass the TCLP test. How many samples were tested,

and did they represent both the oxidized and reduced portions of the tailings sites?

(5) I think it is very important to emphasize, at several locations in the document, that various

bench-scale and pilot-scale tests will be performed prior to implementation of any alternative.

The document certainly does contain such statements (e.g., p. 3-7), but I don't think that they

are adequate. The same could be said for the required (and planned) geotechnical testing.

(6) In general, the documentation and references to outside literature are weak. For example, the

experience on SAPs at Howe Bridge, Pennsylvania, is mentioned several times, but I never

found a formal reference to the publications or reports.

(7) I do not have access to the water analyses, but there appears to be an error in the value of acidity

given at the top of page 3-16 for the toe seeps at TP-1. The value of acidity is given as 1300

mg/L. I thought the toe seeps at TP-1 were, in fact, alkaline.

(8) I recognize that the concept of roller compacted concrete has been abandoned, and I am glad to

know that I suspect that many types of concrete would be destroyed fairly rapidly by the high

dissolved sulfate concentrations in the tailings waters. The same is true for some types of rocks

that may come in direct contact with tailings materials as part of a remedial design. Standard

ASTM testing should be conducted on all synthetic and natural materials that may be placed in

direct contact with the tailings or waste rock. A good place to insert this discussion would be

on a revised page 3-17, where various materials are discussed.

(9) Although it is mentioned once or twice in the EE/CA, the concept of protection of the tailings

from oxygen is not adequately emphasized in the text. All of the remedial alternatives are

designed, and described, in terms of control of water. That is appropriate, but the same designs

will also control, to a greater or lesser degree, ingress of oxygen into the tailings piles. Just for

completeness, I suggest that the concept of control of oxygen be mentioned at several places in

the text. For example, a GCL layer is highly effective in controlling diffusion of oxygen into

the underlying materials if the degree of water saturation exceeds about 80 percent. Emphasis

on control of oxygen also opens other avenues of remedial action, such as using wood chips or

other organic materials as an integral part of the protective covers.

3801 Automation Way, Suite 100,Fort Collins, Colorado 80525 • Telephone (970) 223-9600 Fax (970) 223-7171

Technical Memorandum Scot Foster November 13, 2001 PageS

(10) On page 3-18, a discussion is given of the possible use of soil nailing. The possibility of

corrosion is included in the discussion, but I wonder if the possibility of anoxic corrosion of

steel by hydrogen sulfide gas in the interior of TP-1 has been considered?

(11) My name is mispelled on page 3-21 and elsewhere in the discussion of Alternative 3D.

(12) • On page 3-27, in the first line, I believe that the word "oxides" should be replaced with

"sulfides."

(13) Just a typo — on page 3-29, in the first line, replace the word "further" with 'farther."

(14) On page 3-35, the discussion of the enhanced entry of oxygen due to barometric pumping is

correct. An additional factor that might be mentioned is the consumption of oxygen in air by

sulfide-rich tailings, causing a decrease in the volume of the interstitial gas. The decrease in

volume of the interstitial gas may cause a pressure gradient to develop between atmospheric air

at the surface of the tailings and the oxygen-depleted gas phase at depth. The pressure gradient

can cause additional air to move downward into the tailings.

(15) On pages 3-38 through 3-40, in the discussion of Alternative 3D, I have four comments.

First, six inches of limestone is probably too much. I think three inches would be adequate, but

that can only be determined from a test plot. Second, the limestone should not be tilled into the

upper portion of the tailings; it should be placed in a layer directly on the tailings to allow a

hardpan layer to develop at the contact. Third, it is not necessary to use high-quality limestone

to form the reactive hardpan. All that is required is a source of calcium carbonate to react with

the sulfuric acid in the tailings. Fourth, Alternative 3D is potentially the least disruptive of the

various engineered covers. This is because the reactive, self-sealing hardpan requires only that

the limestone granules be spread on the surface in a reasonably uniform manner. The resulting

barrier is not sensitive to reasonable changes in the surface gradient or the grain size of the

tailings.

That concludes my remarks and suggestions. I hope they will be helpful to you. Please don't

hesitate to call me if you have any comments or questions.

f.Vrom l

380J Automation Way, Suite 100,Fort Collins, Colorado 80525 • Telephone (970) 223-9600 Fax (970) 223-7171

Phil Leonhardt : '• SST ,-, •, »« IDC ; * < Shepard Miller

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SHEPHERD MILLER, INC. Environmental and Engineering Consultants

TECHNICAL MEMORANDUM

DATE: November 16,2001 SMI# 180910

TO: Scot Foster

FROM: Phil Leonhardt

SUBJECT: Results of EE/CA Draft Report Analysis for Elizabeth Mine

COPY:

INTRODUCTION

This memo provides the results of a review by Phil Leonhardt of Shepherd Miller of the Draft report, Engineering Evaluation/Cost Analysis (EE/CA), Elizabeth Mine, Strafford and Thetford, Vermont.

As requested, this review focuses on the cap/cover design concepts in the EE/CA and specifically addresses whether the alternative technical approaches and cost estimates are reasonable. I have also provided general comments to the EE/CA. In addition to the document review, my comments are based on a visit to the Elizabeth Mine on November 7, 2001, and meetings at White River Junction, Vermont, on November 6 and 7, 2001 with personnel of A.D. Little, EPA, COE, USGS, and others. During these meetings, I was informed that the roller compacted concrete as steep embankment slope stabilization (described in Section 3.3.2.2 of the EE/CA) had been dropped from further consideration.

ALTERNATIVE TECHNICAL APPROACHES

The alternative technical approaches for the cap/cover are reasonable (with the exception of Alternative 3c). The general strategy for reclamation of TP-1 and TP-2, as described in the EE/CA, is consistent with tailings reclamation conducted at the California Gulch Superfund Site, Leadville, Colorado and other tailing reclamation sites with which I am familiar.

In my opinion, the 6-inch thick topsoil cover specified in Alternative 3c is not adequate, since a 6-inch thick cover may not be sufficient to sustain plant growth over the long term. Without adequate plant growth on the soil cover, it would not be erosionally stable and may present a risk of exposure and release of tailings during an extreme precipitation event.

3801 Automation Way,Suite 100, Fort Collins, Colorado 80525 • Telephone (970) 223-9600/FAX (970) 23-7171

Technical Memorandum Scott Foster November 16, 2001 Page 2

An alternative should be presented in the EE/CA that utilizes a rock cover as a replacement for the topsoil/soil layers specified in alternatives 2b and 2c. The rock could be sized to provide erosional stability and could potentially be obtained adjacent to or near the site. A rock cover could significantly decrease the cost of the alternative as compared to the soil cover alternatives and also reduce the truck traffic to the site during construction.

COST ESTIMATES

Cost estimates appear to be reasonable. However, I was only provided the cost summaries in the text of the report; therefore, I have not reviewed any unit rates, material quantities, or labor estimates. I can do so if provided with the necessary information.

Annual operation and maintenance (O+M) costs for all of the alternatives are approximately the same ($28,236 except for Alternative 2b, which has O+M costs of $26,544). This appears inconsistent since the cost would be based largely on the operation and maintenance of the passive treatment system. O+M cost is likely to vary in proportion to the amount of flow that the treatment system would be handling. The estimated flows to be treated for the alternatives vary from 5 gpm to 60 gpm (inconsistent seepage rates are listed in the EE/CA for alternatives 3b [30 gpm, page 3-32, and 15 gpm, page 4-22] and 3c [60 gpm, page 3-35 and 22 gpm, page 4-27]).

GENERAL COMMENTS

Additional Information

Additional information is needed in the following areas to effectively evaluate the alternatives:

• Investigation of soil and rock borrow materials in the immediate vicinity of the site.

• Investigation of the geotechnical characteristics of the tailings impoundment.

Borrow Material Investigation

A borrow material investigation of adjacent properties to determine available soil and rock characteristics and quantities would allow a more accurate evaluation of the cost and feasibility of the alternatives. A nearby borrow source would help alleviate truck traffic in the nearby towns during construction and may also decrease the cost of the alternative. As discussed above, it would be worthwhile to evaluate an alternative that utilizes a rock cover, with the rock obtained nearby.

Technical Memorandum Scott Foster November 16, 2001 PageS

Geotechnical Investigation

A geotechnical investigation of the tailings impoundment and underlying foundation would allow a more realistic cost analysis of the alternatives by reducing unknowns concerning regrading and slope stabilization approaches.

Currently, the impoundment has an embankment slope slightly flatter than lh:lv and a top surface slope of approximately 1 percent. All of the alternatives prescribe a 3h:lv embankment slope and a 2 to 3 percent slope on the top of the impoundment. Tailings impoundment grading modifications are typically achieved by (1) adding fill obtained away from the impoundment, or (2) by regrading the tailings using a balanced cut and fill of tailings. This second approach, as described in the EE/CA, would consist of laying back the existing embankment to 3h:lv and placing excavated tailings on the impoundment surface to achieve the desired contours. A geotechnical investigation would provide the data needed to evaluate the feasibility of these two regrading approaches and calculate the slope stability of the proposed final regraded slope.

The first approach, adding fill, is the most conservative or safest approach but also likely to be the more expensive of the two approaches. Regrading the embankment by buttressing (adding fill to the existing embankment) can be accomplished with little risk of slope failure or encountering low-strength tailings (specifically the saturated clays and silts [or slimes]). Also there is less risk of contaminant release since exposure of unoxidized tailings would be minimized. However, buttressing the embankment would require a large amount of imported soil or rock - roughly 250,000 cubic yards (cy).

The tailings embankment appears to be amenable to regrading using the second approach listed above based on the following: (1) the impoundment was constructed in an upstream manner such that the coarsest tailings settled in the embankment area, enhancing the slope stability in that area, (2) information from borings in the impoundment did not indicate slime layers, (3) tailings visible on the impoundment surface appear to be predominantly fine-grained sands and silts, and (4) there is no evidence of slope instability on the embankment.

Remediation Sequence

Remediation of TP-1 and TP-2 prior to understanding the long-term status of TP-3 is not recommended. In general, mine waste remediation should proceed from the top down (upgradient locations cleaned up before downgradient locations) to minimize the chance of recontamination of clean areas. Also, TP-1 and TP-2 would be the best location to dispose of any contaminated material from TP-3 (or other areas), if this option was to be implemented.

Technical Memorandum Scott Foster November 16, 2001 Page 4

EE/CA Goals and Objectives

Given the approaches in the EE/CA, Vermont water quality standards may not be achievable in the passive treatment effluent (page 3-7) or in Copperas Brook. It may be prudent to be somewhat less specific with the stated goals and objectives in the EE/CA concerning water quality. Water quality objectives stated in the EE/CA (page 2-1) may not be achievable without addressing discharges from the air vent, which is not in the scope of this EE/CA. A realistic goal for the site-wide feasibility study would be to achieve water quality standards in the WBOR allowing for a mixing zone that may not meet standards.

Perimeter Diversion Channels/Groundwater Collection

Construction of diversion channels to also collect groundwater may not be feasible. Deepening the diversion channel enough to capture groundwater would likely result in an overly wide channel (that would not be cost effective). Lining one side of the channel to limit recharge while still achieving groundwater collection does not seem feasible. If recharge through the channel is believed to be significant, then lining the entire channel with a geomembrane should be considered. Groundwater may not be encountered through much of the length of the channels, since the channels would likely be constructed largely in the glacial till that is not very transmissive. Upgradient groundwater collection drains (French drains) that empty into the diversion channels should be installed in areas where groundwater flow is observed or suspected.

North Cut Backfill

Backfilling of the North Cut with TP-3 material by pushing or end-dumping the material into place from the top of the North Cut was discussed during the site visit. This action may eliminate potential safety hazards associated with the North Cut's steep sides and isolate TP-3 material. The feasibility of this approach may be poor. Backfilling the North Cut by pushing or end-dumping the material into place would result in very loosely placed material subject to settling. Proper compaction of the material may be expensive and present safety hazards. Also, seeps evident in the east-facing sidewall of the North Cut may create the potential for long-term groundwater contamination as a result of the backfilling. If disposal of TP-3 material is desired, TP-1 and TP-2 are suitable locations. The safety hazards presented by both the North Cut and South Cut could be greatly minimized by fencing.

South Cut Water Quality

Disposal options for South Cut pit water were discussed during the site visit. Potential stratification of the pit water (with more saline water at depth) should be considered.

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From: Frank Bergstrom [mailto:aki@montana.com] Sent: Thursday, November 15, 200110:42 AM To: Acone, Scott E NAE Subject: RE: Elizabeth Mines, South Strafford, VT

Scott,

It was a pleasure to meet you and see the site. The Elizabeth mine is a very similar project to the site we are completing here in Montana. I Express mailed a letter report on Tuesday, so it should arrive in your office today. Although it is stated in our report, I cannot overstress my caution regarding cutting into TP-1 without adequate information. The photos contained in my report should exemplify that concern.

Although you obviously have solicited considerable expertise on water treatment methodologies, it is clear source control would be far preferable to runoff treatment for TP-3. Historical aspects aside, given your highly seasonal runoff regime, treatment via biological means will be - at least - problematic, expensive, and NOT passive. We prefer to refer to such systems as proposed as "biological" rather than passive. Operating costs and labor may be different (possibly less) than inorganic systems, but biological systems for metal mine drainage treatment are sensitive to flow rate and freezing conditions, such as ice cover. Our system here at Mineral Hill treats a very consistent 2.5 gallons per minute in buried vaults at constant temperature, yet the bacteria are quite sensitive, and their establishment has been less than straight forward. Fortunately, you will not have the cyanide toxicity issues, which have been very problematic at several Montana sites, including ours. I found it interesting that SRB bacteria appeared to be considered a separate treatment methodology by some attendees. To our way of thinking, SRB could constitute a PROCESS, not a method. The treatment proposals consider anaerobic wetlands, which would include SRB as a component process. I was unclear as to why some of the discussion appeared anti-SRB, when SRB would be an integral part of the systems proposed. If I was mistaken in this regard - my apologies.

We have also had variable success with anoxic limestone drains. First, anoxic conditions are essential, and if it is your proposal to use an anoxic limestone drain to treat surface runoff, I am unclear as to how anoxic conditions will be achieved. Second, the alkalinity that can be imparted to the water is limited. I did not review the water quality data, and thus will refrain from further comment.

Amerikanuak is very interested in continued involvement in the Elizabeth Mine project. Please consider our company as you move forward.

Best Regards, Frank Bergstrom Amerikanuak, Inc. aki @ montana.com 406/848-7421 ext. 214 406/848-7935 fax 406/223-0667 mobile

http:montana.commailto:mailto:aki@montana.com

Mr. Scott Acone November 13, 2001 Page 3

Figure 2. North (downstream) face of TP-1 embankment A reduction to; say, 3:1 would expose a large area of unsampled tailings.

• TP-1 is staled to have a thin rind of oxidized surface material overlying anoxic reduced tailings. Gray tails and a distinctive hydrogen sulfide odor, observed in one seep during our tour, evidence these anoxic conditions. We are experienced with such situations, and have encountered two major problems. First, any excavation of the tailings would expose these anoxic materials to air. Our experience suggests iron concentrations in seepage from such materials can increase by up to one order of magnitude once disturbed, replaced, and compacted (Figure 3). Second, due to the reduced state of these materials, we would also suspect high moisture content, wHch could preclude the effective use of scrapers, and inabilit