This paper was written as part of the 2004 Alaska Ocean Sciences Bowl high school competition. The conclusions in this report are solely those of the student authors.
Tailings Disposal Options for the Kensington Mine at Berners Bay Near Juneau, Alaska
The Kensington Gold Mine, located 45 miles north of Juneau (Figure 1), Alaska, has been inoperative since 1937. Coeur Alaska, the sole owner and operator, has spent $25 million (Richins, pers. comm.) on environmental and biological research in regards to a planned re-opening in order to find the most environmentally and economically feasible plan of operation. The most recent environmental impact statement (EIS) which is pending completion, and will be available in January 2004, will concern the current plan of operations. In this paper we will examine the history, economics, and politics of the mine and discuss the marine science relevant to a submarine tailings disposal option in the Lynn Canal compared subaqueous disposal in Lower Slate Lake (LSL).
Berners Bay is also located approximately 45 miles north of downtown Juneau (Figure 2). Four rivers, the Antler, Gilkey, Lace, and Berners rivers, reach Lynn Canal at the bay and create a delta expanding seaward. The glacial terrain of Lion's Head Mountain and the valley below support a vast biological ecosystem of rich flora and fauna, and the accompanying waters of Berners Bay and the Lynn Canal (as well as numerous streams and lakes) provide ideal habitat for southeast Alaskan marine and aquatic species. Once covered by glacial ice, the area is continually isostatically rising and changing geologically. Still pristine, the Berners Bay area supports recreational activities such as hiking, fishing, and boating, and is important in the view of many southeast Alaskan residents.
The area also harbors a valuable deposit of gold ore. Historically mined by the deserted Jualin and Kensington mine sites (Figure 2), the mining corporation Coeur Alaska, Inc. (Coeur) now owns all of the mineral rights to the area and plans to re-open the Kensington Mine on current Forest Service land. The mine is planned to operate for approximately 12 years, potentially processing 2,400 tons of ore per day (Hall, pers. comm.). Under the currently proposed plan, mine tailings from the operation will be deposited in a natural glacial lake near the mining site. Mine tailings are the waste left after the ore minerals are extracted, consisting of finely ground waste and ore minerals. Roads and stream crossings will be built to and from the site of tailings deposition, and the necessary structures built in and around wetland areas. The necessary federal, state, and local permits for all of these concerns have been obtained twice by Coeur Alaska; currently, the disposal of the operation's mine tailings is the company's biggest issue. Therefore, the disposal of potentially toxic tailings will be the main concern of this paper.
Kensington Gold Project Details
The Kensington mine was in operation from 1887 until 1937. Coeur is the mining corporation that has owned a portion of the mine since 1987, and has been the sole owner/operator since 1995. Coeur was permitted to reopen the Kensington in 1992 and 1998, but at both those times the methods proposed to remove the gold were not economically feasible. Currently a new mining technique is being analyzed by environmental engineering consultants to obtain the necessary permits. Various plans have been proposed for the disposal of mine tailings including dry tailings disposal, submarine tailings disposal, and subaqueous tailings disposal. The most recent plan, for which an EIS is pending release, proposes the latter method.
The Kensington Gold Mine is currently under permit to operate as an underground mine, with a mining process that includes underground primary crushing, surface grinding, and conventional flotation. The mine would be capable of producing up to 2,400 tons of ore and 400 tons of waste rock daily (Hall, pers. comm.). The ore would be concentrated through a chemical and physical flotation process, and the flotation concentrate would be shipped off-site for further processing. Up to 25 percent (US Forest Service, 2002) of the mine tailings would be combined with cement to form a paste, then used to backfill the underground mine openings during operations. The remaining tailings would be trucked to the dry tailings facility (DTF). This facility would be built on 150 acres of wetlands. The DTF would consist of thoroughly dried stacks of tailings, covered in clay to minimize seepage. Seepage and runoff from the DTF would be collected in a sediment pond and discharged into Camp Creek. Approximately 170 employees, brought in by helicopter, would stay at the mine for 10 to 14 days. The total surface disturbance (or footprint) during operations would be 268 acres, including facilities for loading and unloading supplies at Comet Beach on the Lynn Canal (US Forest Service, 2003b).
Because of the current economics of gold mining and environmental concerns, Coeur has proposed modifications to the original plan of operations. Access to the project would be shifted from Comet Beach on Lynn Canal to Slate Creek Cove in Berners Bay and surface operation from the Sherman Creek drainage to the Johnson Creek drainage near Berners Bay. The new plan would also convert Lower Slate Lake (LSL) to a tailings storage facility, rather than using the dry tailings facility. A tunnel would be built connecting the Kensington workings to the Jualin Mine land holdings, through which the Kensington would be accessed. The new plan would reduce the overall disturbance footprint from 268 to less than 200 acres. Flotation concentrate would be shipped off-site for processing and mine drainage would be treated at Kensington facilities, as with the current plan of operations (US Forest Service, 2002).
In order to convert LSL to a tailings storage facility, a concrete-faced dam would be constructed before the outlet of the lake to ensure that, as the tailings cover and raise the lake bottom, they are covered by a constant minimum depth of 20 feet. LSL would grow to cover approximately 58 acres, 38 more than the current 20 acres that the lake covers (Richins, pers. comm.). The tailings storage facility would be sized to accommodate approximately 4.5 million tons of tailings (US Forest Service, 2003b), as well as to include adequate routing for the maximum flood (US Forest Service, 2002). The tailings would reach the lake as thickened slurry from the mill via a 3.5-mile gravity-fed pipeline. The pipeline would be less than 12 inches in diameter and run along a 20-foot-wide service road connecting the mill facilities with LSL (US Forest Service, 2002). Flow sensors would be installed to detect any blockages or breaks in the system.
The LSL would act as both a tailings storage facility (TSF) and a settling pond. The discharge from LSL to East Slate Creek would be made to mimic the existing hydrology of the stream system (US Forest Service, 2003a) and would be required to meet Alaska's water quality standards (US Forest Service, 2002). Water would be pumped from the pond near the back end of the TSF to the spillway inlet for discharge (US Forest Service, 2003b). Water from the TSF would also be recycled for use in the process facilities at an average rate of 150 gallons per minute. At the end of mine operations, LSL would be reclaimed. Reclamation objectives are to return to the land to a fresh water lake similar to that of pre-development. The lake is to be made capable of sustaining a habitat for Dolly Varden (Salvelinus malma). If necessary, the fish would be reintroduced from Upper Slate Lake (US Forest Service, 2003a).
The employee camp would be replaced by a method of ferrying employees daily between marine facilities in Slate Creek Cove and Cascade Point. The employees would take a bus between Cascade Point and Juneau. A small landing point at Slate Creek Cove and a 5-mile access road to the Jualin mine site are already present and would be simply upgraded to handle traffic. The Slate Creek Cove marine facilities would include an earthfill ramp and floating platform system designed for barges, which would deliver an average of seven times per week (Richins, pers. comm.). The Cascade Point facilities would be constructed on private lands (US Forest Service, 2002). The footprint of the mine wiould cover privately and publicly owned lands, as well as lands owned by the Forest Service.
Environmental damage due to stream crossings, watershed disturbance, road and ferry access, noise pollution, and visible mine structures are already sanctioned; the appropriate permits have already been approved by the Environmental Protection Agency (EPA), Department of Natural Resources (DNR), and Department of Environmental Conservation (DEC). The issue considered in this report is the method of tailings disposal.
Major Applicable Rules and Regulations
The State of Alaska Department of Environmental Conservation (DEC) and the federal Environmental Protection Agency (EPA) introduce standards and regulations that will affect the how and when of the Kensington re-opening. DEC water quality standards state that lake waters may not exceed 5 nephelometric turbidity units (ntu) above natural conditions, and all other freshwater bodies supporting aquaculture may not exceed 25 ntu (DEC Water Quality Standards, 2003). The EPA prohibits submarine tailings disposal (George, pers. comm.). Because of this, under most circumstances submarine tailings disposal is never an option for mining operations to consider. However, the feasibility of submarine tailings disposal is almost entirely dependent on specific cases (Tomich Kent, pers. comm.), and in the case of the AJ Mine Project in Juneau, AK, the EPA granted an exemption to the Echo Bay Mining Co. and agreed to extensive studies and research that could lead to approved submarine tailings disposal (US EPA, 1996). In this instance, for EPA consideration it had to be shown that submarine tailings disposal is the most environmentally sound option through extensive analysis including physical, chemical, and geological oceanography and sedimentation information of the area in question (Echo Bay Mines, 1995).
A corporation such as Coeur must also obtain a National Pollutant Discharge Elimination System (NPDES) permit from the EPA prior to operation. Coeur Alaska has already obtained an NPDES permit, but modifications must be made according to the new plan of operations (George, pers. comm.). The company must also modify their official plan of operations; release a supplemental Forest Service EIS; amend the Large Mine Permit, DEC Solid Waste Permit, and permits involving water discharge pipes from LSL; and obtain DEC certifications for the zone of tailings deposition (Coeur Alaska Group, 1998).
Economic History and Future
Coeur Alaska has already spent over $150 million on the Kensington Project (Richins, pers. comm.). The re-opening of the Kensington Mine will be a great boost to southeast Alaska's economy, as it will employ about 225 permanent workers (Alaska Department of Natural Resources, 2003), along with many additional support sector employment opportunities: approximately 180 additional indirect jobs will be created (USFS/McDowell Group, 1990; Richins, pers. comm.).
Four hundred two state jobs will be lost under Governor Murkowski's 2003 budget plan (Inklebarger, 2003) and mine-related employment can help to offset the losses as a promised 95% of the work force will be Alaskan citizens (Bigsby, 2003) averaging a wage of $50,000 a year. The payroll of the proposed project will be an annual $16 million (Richins, pers. comm.) The jobs created would increase basic industry employment in Juneau from between 1.9% and 5.7% (US Forest Service/McDowell Group, 1990). In 1992, the Kensington Gold Mine project record of decision was approved with the estimated project cost at $210 million, and an operating cost of $282/oz of gold (ADNR, 2003).
The newly proposed project will save the company around $60 million; the cost of operation will be about $155 million (Richins, pers. comm.). It will last at least 12 years: 2 years for construction and startup, 8 years for gold recovery, and two years for active reclamation (Richins, pers. comm.). The corporation will spend at least $7.5 million for direct local purchases during construction and $13.5 million during operation.
The cost of gold in 1988 was $500/oz, whereas in 1998 it was $220/oz (Richins, pers. comm.). This drop was so drastic that it compromised the feasibility of the mine; Coeur was not able to operate efficiently enough to profit under the on-land disposal plan of operations that had been permitted. But with a rise in price to $300/oz in 2000, the mine was again proposed–with a few changes. Production would be lowered from 4,000 tons per day to 2,400 tons per day (Hohensee, pers. comm.) to render the mine less dependent on gold prices (current prices are around $400/oz), and instead of storing dry tailings in a facility on land (as the previously permitted plan had required), subaqueous tailings disposal in LSL was proposed. Both submarine and subaqueous tailings disposal cost $0.10 per ton of waste, thus both disposal systems are equally economically preferable to on-land disposal systems of any sort.
Other Alaskan corporations establish a background for the Coeur d'Alene mining operations in southeast Alaska. The Cape Fox Land Adjustment Act of 2002, Senate Bill (SB) 2222 proposed by Alaska senator Frank Murkowski, proposes a land-swap that would "consolidate Cape Fox, Sealaska and Tongass National Forest surface and substrate estates and simplify Forest Service boundaries." (Richins, 2002) Currently, the surface of the land in question is owned by the Forest Service, while the mining rights to the subsurface area is privately owned by Coeur.
Under SB 2222, Sealaska, the regional native corporation for southeast, would trade the 8,200 acres on Prince of Wales Island received under the original Alaska Native Claims Settlement Act for approximately 9,300 in the Berners Bay area. Cape Fox, the regional native corporation for Saxman would give up 2,900 acres of marginally logged land near Ketchikan for 2,700 acres of area near Berners Bay (Alaska Journal of Commerce, 2003). If the proposed SB 2222 is passed, Coeur will pay land lease payments to the native corporations, as opposed to the federal government.
The Ore Body and Tailings
The gold deposit in question occurs within a structurally sheared portion of rock. The body has low sulfide content and is thus net neutralizing (not acid generating); the material does not pose a significant risk of Acid Rock Draining (ARD). Gold occurs in quartz veins in four states: in the mineral calaverite, as native gold, as inclusions in pyrite, and along microfractures (Robinson, pers. comm.). Studies have detected trace amounts of tellurite (TeO2), coloradite, (Ag3AuTe2) and altaite (PbTe) (Dave Cox, pers. comm.).
Tailings consist of about 40% quartz, 20% plagioclase, 12% muscovite, 8% chlorite, 6% potassium feldspar, 6% calcite, and 8% minor constituents (Kline, pers. comm.). The most concentrated elemental components are silicon, aluminum, calcium, iron, sodium, carbon, potassium, and magnesium; tailing mineralogy is similar to natural Lynn Canal and LSL sediment (Figure 4), and is similar or lower in trace element content (Kline, Richins, pers. comm.). The more toxic components of ore are liberated in the milling process when organic, degradable reagents potassium amyl xanthate and methyl isobutyl carbinol are added to produce the ore concentrate for off-site shipment (Kline, pers. comm.).
Ecological Assessment: Lower Slate Lake; Subaqueous Tailings Disposal
According to the Forest Service's Ecological Risk Assessment of Aqueous Tailings Disposal at the Kensington Mine, the only chemicals of potential ecological concern (COPEC) to consider for the Berners Bay tailings disposal plan are chromium, aluminum, pH and total suspended solids (TSS) or turbidity (Tetra Tech Inc., 2003). In aqueous conditions, the toxicity of aluminum depends on the pH of the water. Aluminum and chromium, as bioaccumulative metals, can travel through the food chain and cause disease and death to fish as well as other predators when accumulated in the tissues of fish and other prey. Aluminum is found naturally in sediment, while chromium is introduced when chromium steel equipment is worn from use (Robinson, pers. comm.). Natural lake sediments have similar to greater amounts of aluminum, so post-operational recovery from aluminum-containing sediment is of little concern. Leach tests indicate that there is essentially no mobility of metals to water (US Forest Service, 2003a).
Acid rock drainage (ARD) is not an environmental hazard in the Kensington Mine situation because the proposed Kensington ore body has insignificant ARD potential–the rock in the area is very low in sulfides (Hohensee, pers. com.), the only sulfides being in traces of pyrite (Connor, pers. comm.). The deposition of tailings in LSL will raise the pH of the lake to an estimated 7.8, well within the range deemed acceptable by the Forest Service of 6.0-9.8 (Tetra Tech, 2003). The possibility of heavy metals leaching from discharged tailings in any body of water, LSL or the Lynn Canal, is negligible as the tailings placed deep underwater lack the oxygen contact that aids in liberating metals from ore in terrestrial evironments.
Total suspended solids is an unavoidable issue concerning sub-aqueous tailings disposal. Under the current plan, tailings slurry deposited in Slate Lake will raise the turbidity of the lake past the DEC water quality standards during the time which the mine is in operation. However, at the point of outlet, the water in Slate Creek, and thus the water flowing from Slate Lake into Berners Bay, does meet DEC standards due to settling and dilution.
The 1998 Kensington Mine proposal called for onsite gold extraction, a process that could introduce cyanide into the surrounding environment. However, the revised proposal of 2002 includes off-site shipment of concentrated material containing gold ore for processing at facilities outside of Southeast Alaska. This eliminates the issue of unnatural amounts of cyanide in the Berners Bay area due to mining activity.
The LSL area provides a rich and pristine habitat for a wide variety of southeast Alaskan species. Predators include black bear (Ursus americanus), gray wolf (Canis lupus), river otter (Lutra canadensis), and mink (Mustela vison); raptors include bald eagles (Haliaeetus leucocephalus) and red-tailed hawks (Buteo jamaicensis); herbivores include moose (Alces alces), Sitka black-tailed deer (Odocoileus hemionus sitkensis), beaver (Castor canadensis), red squirrel (Tamiascirus hudsonicus), and snowshoe hare (Lepus americanus) (Tetra Tech, 2003). Benthic invertebrates include members of families Chironomidae (insect) and Sphareriidae (molluscan) taxons Amphipoda, Nematoda, Diptera, Coloptera, and Tricoptera; plankton in LSL include copepods, cladocerans, rotifers, and protozoans (Kline, 2001). Fish species in Lower Slate Creek (below fish barrier keeping fish from LSL) include 800 to 1,000 (Richins, Kline, pers. comm.) Dolly Varden, sculpin (Cottus spp.), trout (Oncorhynchus clarki and mykiss) and salmon (Oncorhynchus gorbusha and kisutch). With such a rich and complete food chain involved, any activity detrimental to a particular species can cause problems up the food chain.
The eulachon (hooligan) run that occurs within Berners Bay each spring in late April and early May is a major issue concerning the disposal of mine tailings. The eulachon are small fish with over 20% body fat, and the Berners Bay run of 10 to 20 million fish (Hall, pers comm.) provides predators with needed energy to begin the mating season. An estimated 300 to 600 sea lions utilize a haulout within ten miles of the bay, and 1,000 more within forty miles north (Hall, pers. comm.), and before breeding the animals gather in Berners Bay to feed. Approximately 1,000 sea lions, 40,000 gulls, 600 eagles (Hudson, 2003) and numerous other species gather for each eulachon run, and any actions detrimental to the run would have dire consequences on such a vast amount of predators. The east fork of Slate Creek runs from LSL into Berners Bay, and while water out of LSL would meet DEC water quality standards, any material leaving the lake through the creek would empty into the shallow area of the delta used by small fish, including the eulachon.
Approximately 20 acres of wetland area will be affected under this proposal. There will be a net gain of aquatic habitat; LSL will increase from 20 to 58 acres, forming a larger, shallower lake. This change will be beneficial to aquatic systems in the area, as at present much of the lake is too deep for light to penetrate and is an unproductive habitat (Richins, pers. comm.). No permanent habitat loss to fisheries are anticipated to be suffered (Kline, pers. comm.), however areas of wetland will be used for construction, and acres will be submerged as the lake expands.
Ecological Assessment: Lynn Canal (Submarine Tailings Disposal)
The possible submarine tailings disposal system will deposit tailings in Lynn Canal. The canal occupies a 93-mile flooded glacial fjord with maximum width of 12 miles. The substrate is soft at depths greater than 36 ft. and flat, with a bottom depth of 650-980 ft. Tides, freshwater sources, and wind primarily control water circulation in the canal, varying depending on relative location along the canal. Freshwater input is due to rivers, streams, and precipitation, which at its highest input during the summer and fall creates great estuarine circulation. Tidal amplitudes near the proposed site range up to 24.6 ft., and there is a constant general movement of fresh surface water away from shore and deeper waters toward shore (Coeur Alaska Inc., 1998). The substrate has similar elemental components to the tailings; composition of tailings vs. marine sediment is shown in Figure 6.
While it is improbable that tailings will reenter the water column because of their density and the lack of sufficient current in the deeper parts of the Lynn Canal (Scott W. Johnson, pers. comm.), it is not impossible, as in the case of the Island Copper Mine in Vancouver, British Columbia. After being deposited in the ocean through an submarine tailings disposal system, tailings reentered the water column, becoming visible from shore and even washing up on the beach due to seasonal upwelling events (Moore, 2002). Shallow productive coastlines and areas with strong currents are therefore unacceptable deposition locations, as the risk of tailings re-circulating into the water column is increased (Ellis, 1982). Along the Lion's head mountain shoreline, the Lynn Canal reaches a depth of 600 ft. within approximately 4,000 feet of shore. The Echo Bay Mines company proposed depositing tailings in a fjord at a depth of 600 to 700 ft. (Johnson, pers. comm.), a depth reached easily from the Kensington Mine site by a gravity-fed pipeline.
Numerous fish species in the area include Pacific herring (Acanthogobiu flavimanus), Pacific halibut (Hippoglossus stenolepus), sole species, and eulachon (Thaleichstys pacificus); Chinook, coho, pink, and chum salmon (Oncorhynchus tshawyatscha, kisutch, gorbuscha, and keta) ; and dolly varden char (Sebastes caurinus). Mammals include harbor (Phocoena phocoena) and Dall's porpoises (Phocoenoides dalli), Steller sea lion (Eumetopias jubatus), otter (Enhydra lutris), and killer (Orcinus orca) and humpback whales (Megaptera novaeanglia) (Coeur Alaska Inc., 1998).
Lynn Canal substrate harbors a plentiful benthic community,
the level of creatures that would be most effected by an SUBMARINE TAILINGS
DISPOSAL system at Kensington. The most prevalent danger to the benthic
community under an SUBMARINE TAILINGS DISPOSAL system is the smothering
of organisms living within the sea-bottom sediment. Benthic fauna burrow
into and feed off of marine sediment, and form the primary food source
for many other bottom-dwelling organisms, such as the commercially important
king crab. Benthos in areas receiving high rates of tailings deposition
can be eliminated or displaced (Kline, 1998) as they cannot adapt to constant
and heavy sediment deposit. However, Kline (1996, 1999) showed that the
recolonization of sediment by benthic fauna and marine invertebrates (respectively)
would not be influenced by the presence of deposited gold mine tailings;
figure 5 illustrates their comparable benthic habitabilities.
Other bottom-dwelling organisms with potential to be directly affected by submarine tailings disposal are Pacific halibut (Hippoglossus stenolepis) and yellowfin sole (Pleuronectes asper) (S.W. Johnson et. al., 1998). These flatfish are both commercially important and sensitive to seas floor changes, as they burrow into and ingest soft sediment (Moles, pers. comm.). A 1998 study by S.W. Johnson, S.D. Rice, and Dr. Adam Moles showed that the preference of yellowfin sole of natural marine substrate over fresh and weathered gold mine tailings was behavioral; tailings material became so compact in the ocean environment that benthos were unable to burrow into them, thus forcing them to choose a softer substrate. Some tailings form a concrete-like layer in the ocean, but some do not; the probable density of the substance post-deposition can be changed pre-deposition by laboratory methods (Scott W. Johnson, pers. comm.). The 1998 study also showed that the fish preferred equally the natural sediment and tailings sediment that had been covered by as little as 2 cm of natural deposit; this suggests that the natural burial of tailings in an area of high sedimentation would lessen any temporary effect. An area such as this could be found at the mouth of one or several large rivers, such as the rivers in Berners Bay contributing to the expanding delta.
Other organisms potentially affected by tailings sediment are king and Tanner crabs, which, similar to flat fishes, ingest sediment while feeding. Tanner crabs (Chionoecetes bairdi) inhabit deep water up to 500 feet and are harvested by personal use and commercial fisheries. In a 1997 study by R.P. Stone and S.W. Johnson, Tanner crabs held for 500+ days on weathered tailings showed no differences in survival or growth than those held on reference material, and the metal burden of each tissue sample was similar. However, this test refers to old mine tailings; fresh tailings may leach metals, especially if deposited in an area with available oxygen. The area of the Lynn Canal in close proximity to the proposed mine site accommodates commercially harvested king and Dungeness crab (Focht, pers. comm.) that could be affected.
Important commercial fish in and around Berners Bay such as pink and chum salmon inhabit the higher zones of the ocean, and while they would not be affected directly by the tailings if they were to remain on the ocean floor, circulation of tailings could affect commercial fishing harvests in the area. Salmon and other fish are unlikely to be contaminated directly by mine tailings, as tailings will presumably be confined to a specific area of the Lynn Canal, and juveniles going to sea will not be exposed for long periods of time to any tailings (Focht, pers. comm.). A potential problem would arise if tailings were to settle near a salmon spawning or hatching area, or drift far into Berners Bay and contaminate the eulachon population. The average annual net value of the Lynn Canal alone between 1991 and 1997 was $3.62 million (Coeur Alaska Inc., 1998)–an indispensable economic resource. Possibly more dangerous to the commercial fishing industry than the physical threat of contamination are the marketing implications (Focht, pers. comm.). Alaskan-caught fish are marketed as 100% natural, and in the consumer's eye the quality of the product could decrease significantly with the introduction of mine tailings to the population.
Under a SUBMARINE TAILINGS DISPOSAL plan, less wetland habitat will be affected than under the LSL tailings storage plan (Richins, pers. comm.). Kensington tailings have been proven inert and very close in elemental and mineral composition to natural Lynn Canal sediment (Figure 4 ) (Kline, Richins, pers. comm.); in conclusion, toxins are of insignificant concern.
Conclusions and Recommendations
We conclude that the currently proposed plan of operations is not the most environmentally sound procedure; with accordance to further research, we recommend that the main mine waste product, the mine tailings themselves, be deposited in the ocean through a submarine tailings disposal system.
According to a study conducted by the U.S. Bureau of Mines, the right combination of conditions can render the environmental impacts of submarine tailings disposal minimal. These conditions include that: the percentage of sulfide minerals in the ore is low; no easily dissolvable toxic substances occur within the ore body; non-toxic reagents are used in the mill; milling does not generate secondary toxic products introduced into an environment; slurry is deposited with minimal amounts of water to reduce submarine transportation; tailings are deaerated (mixed with air and seawater to suspend tailings fines, to be released, and to minimize density differences between slurry and seawater) before entering the ocean; the density of liquid in tailings is equal to water density at the depth of disposal; tailings outfall is effectively placed; and the environment in which tailings are deposited is stable (Baer et al., 1995).
Past research shows that the Kensington Mine area has exceptional opportunity to undertake a submarine tailings disposal system with minimal impact to the environment. We believe submarine tailings disposal is a favorable option to subaqueous tailings disposal in LSL. Concerning the proposed Kensington area, and according to the above standards, we can justify Lynn Canal disposal because: (1) The Kensington ore body has an extremely low level of sulfides and sulfide compounds that contribute to toxicity and ARD potential; (2) the only potentially toxic COPECs are chromium and aluminum, both of which occur in very small amounts, and, if properly placed, will pose no risk to organisms above benthic level, a proven small or negligible risk to crabs and flatfish, and have no observed effect on benthic recolonization of the sediment; (3) no toxic reagents will be employed at the Kensington site, as ore will be shipped elsewhere for processing; (4) the topography of the Lynn Canal lends itself to deep submersion of tailings, therefore minimizing the possibility of tailings spreading on the ocean floor or reentering the water column; (5) all tailings slurry conditions discussed above can be feasibly induced on-site.
We recommend that the EPA grant Coeur an exemption, as they considered in the case of the Alaska-Juneau Mine, so that they might utilize a submarine tailings disposal system as opposed to the subaqueous tailings disposal plan currently proposed. We suggest intense research concerning topography and current circulation in the Lynn Canal in order to find a deep, fairly contained area in which to deposit tailings through a gravity-fed pipeline leading from slurry storage on-site at the mine to the chosen deposition site underwater. Natural sedimentation deposition should also be considered, as constant and relatively heavy natural deposition hastens the recolonization of deposited tailings. Necessary structures for an SUBMARINE TAILINGS DISPOSAL system would include a gravity-fed pipeline from the mill down Lion's Head Mountain directly to a depth of at least 600 ft. (and well below photic zone) in a chosen submarine area; and a deaeration, or mixing, chamber near the shore pre-deposition. Remaining processing water should first be drained from tailings; then tailings may be transported by gravity through pipeline over land to the mixing tank. Water for these mixing tanks may be taken in from pipes on the ocean floor past 36 ft. from shore where rocky substrate turns to soft sediment. In determining deposit placement area and method, engineers should take into consideration submarine topography, current rates, fauna concentration, amount and velocity of discharge, and waste density.
It must be especially noted that according to intensive scientific study, Kensington tailings can be considered inert (Kline, pers. comm.). In the Lynn Canal area, submarine tailings disposal will only temporarily affect a uniform and widely spread marine habitat (Kline, 1998). Multiple studies have shown that tailings "may be disposed of in the ocean" (Kline, 1998)–Coeur Alaska's Kensington Gold Project represents a realistic opportunity to utilize submarine tailings disposal as the most environmentally and economically feasible option in a sound plan.
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*Connor, Cathy. Associate Professor of Geology at University of Alaska–Southeast Department of Natural Science Program. 11120 Glacier Hwy Juneau Alaska 99801. Phone: 465-6293.
*Cox, David. Hydrologist. US Forest Service, Tongass Minerals Group, Juneau Ranger District. 8465 Old Dairy Road, Juneau Alaska 99801. Phone: (907) 790-7454.
*Focht, Rick. Director of Research & Evaluation. Douglas Island Pink and Chum, Inc. 2697 Channel Drive, Juneau Alaska 99801. Phone: (907) 463-5114.
*George, Kenwyn P., P.E. Environmental Engineer. Department of Environmental Conservation, Division of Air and Water Quality, Wastewater Discharge Program. State of Alaska. 410 Willoughby Avenue, Suite 303, Juneau Alaska 99801. Phone: (907) 465-5313.
*Hall, Kat. Water Quality/Mining Organizer. Southeast Alaskan Conservation Council. 419 6th Street #200, Juneau Alaska 99801. Phone: (907) 586-6942.
*Hohensee, Steve. Geologist. US Forest Service, Tongass Minerals Group, Juneau Ranger District. 8465 Old Dairy Road, Juneau Alaska 99801. Phone: (907) 426-9104.
*Johnson, Scott W. Fisheries Biologist. National Marine Fisheries Service. 11305 Glacier Highway, Juneau Alaska 99801. Phone: (907) 789-6063.
*Kline, Edward R. Principle, Kline Environmental Research, LLC. 1731 50th Street, Somerset Wisconsin 54025. Phone: (715) 247-4466.
*Moles, Adam, PhD. NOAA Auke Bay Laboratory. 11305 Glacier Highway, Juneau Alaska 99801. (907) 789-6023.
*Richins, Robert. Vice President of Environmental and Government Affairs. Coeur d'Alene Mining Corporation. Boise, Idaho.
*Robinson, Robert. Geologist. Red Dog Mine, Teck Cominco. Kotzebue, Alaska. (907) 426-9104.
*Tomich Kent, Lynn J. Water Quality Programs Manager. Department of Environmental Conservation, Division of Air and Water Quality. State of Alaska. 410 Willoughby Avenue, Suite 303, Juneau Alaska 99801. Phone: (907) 465-5312.
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