Course:EOSC270/2022/Acid Mine Drainage from Britannia Mine

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Introduction to Howe Sound and Britannia Mine

Map of Howe Sound with Britannia Beach, the location of Britannia Mine at Britannia Beach (Circled in red, at 49°38′N, 123°12′W)

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Howe Sound is a temperate, coastal ecosystem with high productivity and species diversity. Metal mining beginning in the early 20th century has led to several creeks carrying toxic pollutants into the ecosystem. Britannia creek runs through the decommissioned Britannia Copper Mine, carrying low pH waters dense in toxic heavy metals, originating from a process known as Acid Mine Drainage (AMD)[1]. This pollution has had measurable impacts on the floral and faunal communities in the area, including on primary productivity and consumer mortality[2][3][4]. There are current measures to remediate environmental damage and prevent further damage, and clean up is ongoing. Clean up has ben successful to the point that organisms have been returning to areas near the mine that they had not been seen in over 80 years[5].

Howe Sound Ecosystem

Howe Sound is a shallow inlet located North of Vancouver, British Columbia, Canada. It is an estuarine system, as it receives fresh water from multiple rivers and creeks, with the Squamish River alone inputting as much as 7.5 billion cubic meters of waters annually [6]. The system becomes stratified on a seasonal basis, when the snowmelt season begins in early June, to the extent that there will be thin a layer of freshwater on the surface of the sound holding dissolved materials from the rivers and creeks.

As a temperate coastal inlet, Howe Sound experiences seasonal variation in primary productivity and nutrient availability throughout the year, due to variation in solar fluxes and river inputs[7]. Productivity is dominated by diatom species, and experiences a sharp increase in the spring. Macroalgae and marine plants such as eelgrass also contribute to the primary productivity in the sound. Marine copepods graze on the diatom bloom alongside numerous invertebrate suspension feeders.

The primary producers support a diverse food web of epipelagic marine invertebrates, such as crustacean larvae, amphipods and mussels[7]. These organisms in turn support a variety of fish species including flounders, gunnels, rockfish and cod. The Squamish River is a spawning zone for species of salmon such as Chum (Oncorhynchus keta) and Chinook (Oncorhynchus tshawytscha), who migrate into Howe Sound as juveniles, relying on zooplankton for nutrients[8]. The Salmon are of particular concern due to their contribution to the economy of British Columbia, cultural significance to the regional Squamish (Sḵwx̱wú7mesh Úxwumixw) First Nation, and recently declining stocks[1][9].

Britannia Mine

Britannia Mines Concentrator, currently serving as a museum

Britannia Mine was a Copper Mine in Britannia Beach, British Columbia approximately 50 kilometers north of Vancouver that opened in 1904 and was operational until 1974[1][2]. Ever since operations began, the runoff from nearby rivers and creeks have become sources of pollution into the near- surface ecosystem of Howe Sound. The freshwater plumes formed during the snowmelt season create a layer of low-salinity water at the ocean surface, which contains toxins from the mine at a higher concentration than the water below the pycnocline [7]. It has been a significant source of heavy-metal contamination to Howe Sound through a process called acid mine drainage (AMD)[1]. It deposits dozens of metals such as copper, aluminum and zinc at concentrations that exceed Canadian water quality guidelines and has been lethal to many local species, negatively impacting food web dynamics and reducing population counts[1]. A survey taken before preventative measures began estimated that 40 million liters of toxic-metal rich runoff went into the sound daily, making it one of the worst sources of heavy metal pollution in North America[2].

What is Acid Mine Drainage (AMD)?

Acid Mine Drainage is caused by exposed sulphide-bearing material in oxygen and water. The production of AMD usually occurs in iron sulphide-aggregated rocks[10]. The major source of AMD is the accelerated oxidation of iron pyrite (FeS2) and other sulphidic minerals. The reason of massive of sulphide materials leak during the mining is because that most of metals occurs as sulphide ores, like zinc in sphalerite, and pyrite is the most abundant sulphide mineral in the Earth[11].

The productions of AMD are not only occurred in mining industries, but also appear everywhere sulphide materials are exposed, such as highways, tunnel constructions, and other deep excavations[12], or galvanic processing and the scrubbing of flue gases at power plants[11]. AMD may occur naturally, by natural bacteria to break down sulphide materials. Most of AMD, however, are primarily caused by mine waste rocks, tailings, and mine structures, like pits and underground workings. In this case, it also referred as Acid Rock Drainage (ARD)[10].  

Occurrence of AMD

AMD is strong acidic, rich in high concentration of dissolved ferrous and non-ferrous metal sulphates and salts[12]. These releases have low pH, high specific conductivity, high concentrations of iron (Fe), aluminum (Al) and manganese (Mg), and low concentrations of toxic heavy metals. Since pyrite is the most common sulphide mineral its oxidation could be best illustration of the reactions of acid generation. The first important reaction is the oxidation of the sulfide mineral into dissolved iron, sulphate and hydrogen[10][12]:

Pyrite cubic crystals on marl from Navajún, La Rioja, Spain
2FeS2 + 7O2 + 2H2O → 2Fe2+ + 4SO42− + 4H+ (1)

Depending on concentration of O2, pH value >3.5 and bacterial activity, most of ferrous iron will oxidize to ferric iron (Fe3+)[10][12]: 

4Fe2+ + O2 + 4H+ → 4Fe3+ + 2H2O (2)

At pH values between 2.3 ~ 3.5, ferric iron precipitates as Fe(OH)3 (a few of them becomes jarosite precipitation), leaving little Fe3+ in solution, reducing the pH value[10][12]: 

Fe3+ + 3H2O → Fe(OH)3 (solid) + 3H+ (3)

Fe3+ remains in solution if pH < 2, while it will be used for oxidation of additional pyrite as the following equation[10][12]: 

FeS2 + 14Fe3+ + 8H2O → 15Fe2+ + 2SO42− + 16H+ (4)

Combining the first 3 equations, the acid generation that produces iron which eventually precipitates as Fe(OH)3 may be as following[10][11][12]: 

4FeS2 + 15O2 + 14H2O → 4Fe(OH)3 + 8SO42− + 16H+ (5)

Although this equation is often quoted, it is not completed for the whole processes, since Fe3+ plays a more important role than O2[11]. In this case, the completed equation including ferric ion should be[10][12]: 

8FeS2 + 15O2 + 52Fe3+ + 34H2O → 60Fe2+ + 16SO42- + 68H+ (6)

The regeneration of ferric iron, which is reduced to ferrous on reaction with pyrite, is the key reaction in continuing of oxidation of the material[11].  When pH < 3, the oxidation of pyrite by ferric iron is about 10 ~ 100 times faster than by oxygen[12].   

General Impact of AMD

The situation of AMD is unique for every mine; therefore, each AMD for each mine should be specifically analyzed and solved, since there are no standardized methods for every mine. In this case, the owners of each mine have their duties to measuring and reducing the risk of AMD[10]. Due to its strong acidic characteristic, however, if left AMD untreated, the contamination of ground and surface water sources will damaging the health of plants, humans, wildlife, and aquatic species. Although AMD is considered as a looming problem that should be solved cost-effectively and sustainably as early as 1970s, the governments, NGOs and mining companies do not provide a feasible solution until now[12].  

Metal contamination and Impact

Metal contamination represents the situation that environmental conditions in a place are spoiled and polluted by metal composition. The pollutants are usually heavy metals, which are difficult for microbial degradation. The heavy metal defines those metals and metalloids whose density is greater than 4~5 g/cm3, or at least 5 times greater than water density[13]. The common heavy metals include copper (Cu), zinc (Zn), lead (Pd), mercury (Hg), etc.[14]

The mine sites are usually the main source of pollution since the act of mining always produces heavy metals. The spilling of heavy metals occurs during mining processes, as well as the resulting wastes. Since mine sites are always built beside rivers, it is easy for toxic wastes to pollute the water body, and then spoil into the sea through rivers. It makes the related water system hazardous, because of its excess metal content and high density. It also makes the water body acidic by ionic properties[15]. The indecomposable would also be absorbed by marine life, especially the basic microbial communities, leading to destruction of the marine food chain[16].

How has AMD from Britannia Mine impacted the local ecosystem?

The fresh AMD rich waters from Britannia Creek lay on top of the saltier sea water of Howe Sound. Phytoplankton and organisms that rely on them spend a majority of their time in this top layer and are at greater risk of AMD toxicity.

Acid Mine Drainage (AMD) from Britannia Mine flows into the local creeks and streams, most notably Britannia Creek, which flows all the way down to Howe Sound. For nearly a century, Britannia Creek was known for having seemingly clear pristine waters. However, upon closer inspection the creek owed its clarity to the toxic metals and acidic conditions caused by AMD, devoiding the creek of any life[17]. The environmental impact of this acid mine drainage also reaches Howe Sound, where the effects are mostly diluted by the ocean. The effects from AMD are most noticeable in estuaries where AMD first enters Howe Sound via several streams and creeks before significant dilution occurs.

Despite the mine's closure, there are still elevated levels of copper, zinc, and cadmium present, primarily in the surface waters of estuaries[18]. This has negatively impacted the local marine life as seen by the clear reduced abundance of invertebrate species that salmon fry prey on, reduced coverage of algae and lower phytoplankton levels compared to other estuaries that are not affected by AMD[3][19].

Salmonid Species

Creeks that flow from Britannia Mine contain very high levels of dissolved copper, zinc and cadmium; with copper generally regarded as the main explanation for toxic effects observed in local species[17][19]. The effects of copper on salmonids, which are native to Howe Sound and Britannia Creek, are well studied. Reduced abundances of salmon species are found near the mouth of Britannia Creek where copper concentrations are the highest[19]. There are many factors involved in the reduced abundances but the main reason is due to the effects that copper has on the gills of fish[4]. Copper ions enter the gills of fish, which interferes with breathing when the copper binds to proteins that maintain the function of the gills[4].

A simplified overview of the food chain in Howe Sound. The phytoplankton in this food chain act as the major primary producer to create all the biomass that makes up the entire upper trophic levels. Salmon, and other carnivorous fish rely on the phytoplankton to feed smaller organisms like zooplankton, which salmon fry feed on to grow.
An overview of prevention methods used to prevent pollution.

AMD runoff contains high levels of toxic metals as well as sulfuric acid, making the water very acidic. Unfortunately, copper toxicity is greatly enhanced by the acidic conditions as it allows copper to more easily dissolve in water and affect organic life[7][20]. AMD contamination results in a decreased pH of less than 6 in the estuaries of Howe Sound, which is well below typical Marine pH levels of ~8[4]. Along with enhancing copper toxicity, low pH directly results in the death of fish through impairment of gill electrolyte homeostasis, morphological changes/damage to gills, impairment of growth, among other factors[20]. Because salmon fry reside in the upper layers of the water column that are rich in AMD, many individuals die from a combination of the low pH and toxic copper[4][7].

Estuary Food Web

Reduced population sizes of salmonid species in Howe Sound can also be attributed to AMD’s effect on primary producers, and thus the entire food web. Increased levels of copper in the water column is associated with decreased levels of chlorophyll a in phytoplankton, and reduced growth of key algal species[2][3]. Regions of Howe Sound within 100m of AMD polluted creeks were found to have reduced populations of several key invertebrate species that normally serve as prey for growing salmon[19]. This observation is most likely explained by the extremely high copper concentration and acidic pH, as these conditions prevent the growth of most invertebrate species[19]. This clear reduction of primary producers and prey species along estuaries of Howe Sound significantly affects salmon populations as salmon fry typically hunt for prey within these contaminated estuaries.

Given the impact, what are the solutions?

Current State

Since 2016, the majority of mine water and contaminated groundwater has  been captured, treated, and discharged to Howe Sound at a depth of 50 metres. These methods are known to work because species such as pink salmon, mussels and rockweed are now in areas around Britannia Creek where they had not been seen for about 80 years.[5] In addition, the water is now potable and all pollution flowing into Britannia Creek has ceased[21]. Unfortunately, while there were improvements in surface water, it was found that the quality of groundwater had not. Unsurprisingly, samples show that areas with higher groundwater metal concentrations show lower intertidal species diversity. However, areas with greater salinity have denser population which indicates that the salinity is unlikely the reason for low population numbers[22]

Prevention

In 2001, researchers from the Department of Mining at the University of British Columbia plugged the tunnel, named 2200L, from which a considerable portion of mine drainage was excreted. This was done with a new endurable barrier named the ‘Millenium Plug’.[23]

Another method of prevention implemented was to divert surface water around the mine in order to prevent contamination. In addition, it will reduce the volume of water the treatment plant would have to treat. The construction of these diversions consists of an intake and a pipe to discharge the water.[24]

Remediation

In 2006, the 30 million dollar water treatment plant began to process acid mine drainage. The Millenium Plug which blocked the 2200L tunnel diverted water to a different tunnel. From there, the water is transported to the water treatment plant. In the treatment plant, the water’s pH level is raised from 3.8 to 9.3.[23] This is done by adding a lime slurry to the water. The lime slurry precipitates out the metals in the solution forming larger metal particles which then sink to the bottom of the tank.[24]

The newly cleaned water is then expelled into the creek. Water is removed from the bottom sludge and the metal is used to create a cap around open pits which will reduce the amount of water flowing through the fractured rock. The reason this newly formed metal will not contribute to acid mine drainage is because it is in the form of a sulphide after being precipitated out by the lime slurry.[23]

In addition to the water treatment plant, improvements were also made to both surface and shallow groundwater drainage. Improvements consisted of a system of lined surface swales, catch pits, sediment traps, pipework, and a storm water interceptor sewer. [24]The purpose of these improvements is to collect contaminated runoff water from the mine.

A way to further improve the treatment of water would be to exchange the current lime treatment operation with a biological plant instead. In Cornwall, this change was estimated to reduce annual discharge by  >600kg iron,  >9900 kg zinc, >120 kg copper and various other metals.[25] The plant in Britannia can expect to reduce its discharge by a significant amount as well.

References

  1. ↑ 1.0 1.1 1.2 1.3 1.4 Alava, Juan Jose; Bodtker, Karin (2017). "Metal contamination from the Britannia Mine site: lingering problems, ongoing remediation" (PDF). Ocean Watch Átl’ḵa7tsem/Txwnéwu7ts/Howe Sound Edition 2020. 2017 Edition: 144–155 – via Ocean Wise Research Institute.
  2. ↑ 2.0 2.1 2.2 2.3 Levings, C. D., Varela, D. E., Mehlenbacher, N. M., Barry, K. L., Piercey, G. E., Guo, M., & Harrison, P. J. (2005). Effect of an acid mine drainage effluent on phytoplankton biomass and primary production at Britannia Beach, Howe Sound, British Columbia. Marine Pollution Bulletin, 50(12), 1585–1594. https://doi.org/10.1016/j.marpolbul.2005.06.032
  3. ↑ 3.0 3.1 3.2 Marsden, A. D. (n.d.). The effects of acid mine drainage at Britannia Beach, B.C., on Fucus Gardneri and associated intertidal algae [Master's thesis]. https://open.library.ubc.ca/soa/cIRcle/collections/ubctheses/831/items/1.0099345?o=0
  4. ↑ 4.0 4.1 4.2 4.3 4.4 Barry, K. L., Grout, J. A., Levings, C. D., Nidle, B. H., & Piercey, G. E. (2000). Impacts of acid mine drainage on juvenile salmonids in an Estuary near Britannia beach in Howe sound, British Columbia. Canadian Journal of Fisheries and Aquatic Sciences, 57(10), 2032-2043. https://doi.org/10.1139/f00-157
  5. ↑ 5.0 5.1 Alava, J. J. (2017, February). Metal contamination from the Britannia Mine site: lingering problems, ongoing remediation. https://oceanwatch.ca/howesound/wp-content/uploads/sites/2/2016/12/OceanWatch-HoweSoundReport-BritanniaMine.pdf
  6. ↑ Chandler, Peter (2020). "Ocean Warming: what's heating up the Sound?" (PDF). Ocean Watch Átl’ḵa7tsem/Txwnéwu7ts/Howe Sound. Edition 2020: 75–83 – via Ocean Wise Research Institute.
  7. ↑ 7.0 7.1 7.2 7.3 7.4 Levings, C., Barry, K., Grout, J., Piercey, G., Marsden, D., Coombs, A., & Mossop, B. (2004). Effects of Acid Mine Drainage on the Estuarine Food Web, Britannia Beach, Howe Sound, British Columbia, Canada. Hydrobiologia, 525, 185–202. https://doi.org/10.1023/B:HYDR.0000038866.20304.3d
  8. ↑ Levings, C.D., Riddell, B.E., (1992). Salmonids and their habitats in Howe Sound: status of knowledge. In: Levings, C.D., Turner, R.B., Ricketts, B. (Eds.), Proceedings of the Howe Sound Environmental Science Workshop, Canadian Technical Report of Fisheries and Aquatic Sciences 1879: 65–81.
  9. ↑ Price, M. H. H., English, K. K., Rosenberger, A. G., MacDuffee, M., & Reynolds, J. D. (2017). Canada’s Wild Salmon Policy: An assessment of conservation progress in British Columbia. Canadian Journal of Fisheries and Aquatic Sciences, 74(10), 1507–1518. https://doi.org/10.1139/cjfas-2017-0127
  10. ↑ 10.0 10.1 10.2 10.3 10.4 10.5 10.6 10.7 10.8 Akcil, Ata (28 April 2005). "Acid Mine Drainage (AMD): causes, treatment and case studies". Journal of cleaner production. 14(12-13): 1139–1145.
  11. ↑ 11.0 11.1 11.2 11.3 11.4 Johnson, D. Barrie (26 October 2004). "Acid mine drainage remediation options: a review". Science of The Total Environment. 338(1-2): 3–14.
  12. ↑ 12.0 12.1 12.2 12.3 12.4 12.5 12.6 12.7 12.8 12.9 Simate, Geoffery S. (22 July 2014). "Acid mine drainage: Challenges and opportunities". Journal of Environmental Chemical Engineering. 2(3): 1785–1803.
  13. ↑ Onakpa, Michael Monday (31 Aug 2018). "A Review of Heavy Metal Contamination of Food Crops in Nigeria". Annals of Global Health. 84(3): pp.488–494.CS1 maint: extra text (link)
  14. ↑ Li, Fang (08 Oct 2018). "Impact of the Coal Mining on the Spatial Distribution of Potentially Toxic Metals in Farmland Tillage Soil". Scientific Reports. 8. Check date values in: |date= (help)
  15. ↑ Yalçın, Sibel (08 August 2012). "Characterization and lead(II), cadmium(II), nickel(II) biosorption of dried marine brown macro algae Cystoseira barbata". Environmental Science and Pollution Research. 19: 3118–3125. Check date values in: |date= (help)
  16. ↑ Yin, Xuebin (25 July 2008). "Animal excrement: A potential biomonitor of heavy metal contamination in the marine environment". Science of The Total Environment. 399: 179–185.
  17. ↑ 17.0 17.1 Britannia Creek | A story of recovery and renewal. (n.d.). World Rivers Day – Millions of people in more than 100 countries participate in World Rivers Day. https://worldriversday.com/britannia-creek/
  18. ↑ Kay, B. H. (1989). Pollutants in British Columbia's marine environment: A status report. Conservation and Protection, Environmental Protection, Pacific and Yukon Region, 1989.
  19. ↑ 19.0 19.1 19.2 19.3 19.4 Levings, C. D., Barry, K. L., Grout, J. A., Piercey, G. E., Marsden, A. D., Coombs, A. P., & Mossop, B. (2004). Effects of acid mine drainage on the estuarine food web, Britannia beach, Howe sound, British Columbia, Canada. Hydrobiologia, 525(1-3), 185-202. https://doi.org/10.1023/b:hydr.0000038866.20304.3d
  20. ↑ 20.0 20.1 Reid, S. D. (1995). Chapter 11 adaptation to and effects of acid water on The Fish Gill. Biochemistry and Molecular Biology of Fishes, 213-227. https://doi.org/10.1016/s1873-0140(06)80037-8
  21. ↑ Meech, J. A., McPhie, M., Clausen, K., Simpson, Y., Lang, B., Campbell, E., Johnstone, S., & Condon, P. (2006). Transformation of a derelict mine site into a sustainable community: The Britannia project. Journal of Cleaner Production, 14(3-4), 349-365. https://doi.org/10.1016/j.jclepro.2004.08.009
  22. ↑ Zis, T., Ronningen, V., & Scrosati, R. (2004). Minor improvement for intertidal seaweeds and invertebrates after acid mine drainage diversion at Britannia beach, Pacific Canada. Marine Pollution Bulletin, 48(11-12), 1040-1047. https://doi.org/10.1016/j.marpolbul.2003.12.007
  23. ↑ 23.0 23.1 23.2 Smitheringale, W. (Bill). (2011). Great Mining Camps of Canada 5. Britannia Mines, British Columbia. Geoscience Canada, 38(3). Retrieved from https://journals.lib.unb.ca/index.php/GC/article/view/18783
  24. ↑ 24.0 24.1 24.2 O'Hara, G. (2007). Water management aspects of the Britannia mine remediation project, British Columbia, Canada. Mine Water and the Environment, 26(1), 46-54. https://doi.org/10.1007/s10230-007-0148-4
  25. ↑ Kaksonen, A. H., & Puhakka, J. A. (2007). Sulfate reduction based Bioprocesses for the treatment of acid mine drainage and the recovery of metals. Engineering in Life Sciences, 7(6), 541-564. https://doi.org/10.1002/elsc.200720216
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