British Columbia Mine Reclamation Symposium

Assessment of the Mount Polley Mine site for potential passive or semi-passive treatment options Simair, Monique; Martz, Rachel; Friesen, Vanessa; McMahen, Katie; Litke, Shauna; Hughes, Colleen; Moger, Luke; Anglin, Lyn 2018

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ASSESSMENT OF THE MOUNT POLLEY MINE SITE FOR POTENTIAL PASSIVE OR SEMI-PASSIVE TREATMENT OPTIONS   Monique Simair1, Rachel Martz1, Vanessa Friesen1, Katie McMahen2, Shauna Litke2, Colleen Hughes2, Luke Moger3, ‘Lyn Anglin3  1Contango, an AEG company, Saskatoon, Saskatchewan 2Mount Polley Mining Corporation, Likely, British Columbia 3Imperial Metals Corporation, Vancouver, British Columbia   Contango, an AEG Company Saskatoon, Saskatchewan, Canada.  ABSTRACT   Passive water treatment is often sought as a component of long-term mine closure management. Passive water treatment promotes relatively self-sustaining conditions for the management of mine impacted water, with outcomes often being low maintenance and operational costs. However, owing to the sensitive biogeochemical nature of these technologies, a site-specific phased approach is necessary for evaluating passive treatment as a component of mine closure management, and ultimately, its successful implementation. The Mount Polley Mine (the “Mine”) was evaluated for the viability of constructed wetland treatment systems (CWTSs) as part of their long-term water management plan. A site assessment was conducted, which identified potential plant species for use in a CWTS, and evaluated the water, substrates, and plants in the context of a CWTS. Genetic microbial community profiling was used to assess natural wetlands, and components of the water management infrastructure at the Mine, and was paired with traditional growth-based microbial characterization and quantification. This information was evaluated in the context of water chemistry, treatment objectives, and biogeochemical processes to assess the feasibility for semi-passively or passively treating Mine water. Upon assessment of the natural treatment capacity at the Mine, natural conditions and processes were identified that could potentially benefit water quality.   KEY WORDS   Passive water treatment, sustainability, biogeochemistry, microbial community profiling, constructed wetland treatment systems, mine closure management.   BACKGROUND AND INTRODUCTION  The Mount Polley Mine (the “Mine”), owned and operated by Mount Polley Mining Corporation (MPMC), is an active, open pit and underground copper/gold mining property located 8 kilometres (km) southwest of Likely, British Columbia . An updated reclamation and closure plan (RCP) was prepared for the Mine site in January 2017 (MPMC, 2017) that included a long-term water management strategy with a focus on, to the extent practicable, a transition into passive or semi-passive treatment of site contact waters, with treated waters being returned into multiple watersheds. Contango Strategies Ltd. (Contango) developed a Feasibility Assessment Report that outlines a detailed assessment and independent evaluation of the feasibility of constructed wetland treatment systems (CWTSs) at the Mine. Passive and/or semi-passive water treatment systems are being contemplated at the Mine site to address the constituents of potential concern (COPCs) in closure (Contango, 2017). This paper is a summary of these Feasibility Assessment Report findings.  For a CWTS to be efficient and effective, it must be designed, piloted, optimized, implemented, monitored, and maintained in a site-specific manner (Haakensen et al., 2015). A phased approach is often recommended for designing and optimizing these site-specific systems, and in the case of the Mine site, the following phases are currently being considered:  Phase 1a: Information gathering and feasibility assessment; Phase 1b: Conceptual design and sizing for closure; Phase 2: Off-site bench-scale testing and optimization; Phase 3a: Off-site pilot-scale testing and optimization; Phase 3b: On-site pilot-scale design, sizing, testing, and optimization; Phase 4: On-site demonstration-scale implementation and monitoring; and Phase 5: On-site full-scale implementation and maintenance.  To initiate the phased approach, a site assessment (Phase 1a) was completed in November 2016, and was intended to: i) identify potential plant species for use in a CWTS, ii) conduct baseline characterization of water, substrates, and plants in the context of a CWTS, iii) assess the latent remediation potential of the site, and iv) develop recommendations and next steps. In summary, the feasibility assessment determined that passive treatment appears to be a feasible option at the Mine site, and identified natural treatment mechanisms that are occurring at the site. It also found that new wetlands forming adjacent to the Mine site host a diverse microbial population.    METHODS  A site visit was conducted at the Mine site between November 7, 2016 and November 10, 2016. Fourteen locations were selected for sample collection at the Mine site to evaluate the natural treatment capacity and assess the feasibility of passive or semi-passive water treatment (Figure 1; Table 1). Sampling locations were selected by Contango and MPMC based on the presence of potentially beneficial wetland plants, information from long-term water chemistry monitoring, in-situ water quality parameter measurements, and other visible features that suggested the location might inform strategies for water quality improvement by CWTSs.    Figure 1 – Mine site sample locations.  Table 1 — List of locations and samples collected. Type of Waterbody Samples or Measurements Taken  Full Name  Abbreviated Name Soil Redox 1 Water Soil Plant  Micro Seep   Junction Zone Ditch Weir JZD Weir Yes Yes NT C C South Seepage Pond SSP Yes Yes Yes T T Long Ditch-1 LD-1 Yes Yes NT M M Long Ditch-2 LD-2 Yes Yes NT M M Northeast Zone-1 NEZ 1 Yes Yes Yes NT Biofilm Southeast Rock Disposal Site 13 Wetland A2 SERD Wetland 13 A Yes Yes Yes S S Long Ditch-Lower Sump North LD-LS Yes Yes Yes T T Joe’s Creek Pipe Pond JCP Yes Yes Yes T T Pond Southeast Rock Disposal Site 13 Wetland B2 SERD Wetland 13 B Yes Yes Yes T T Hazeltine Pond N/A Yes Yes Yes T, C T, C Duck Pond N/A Yes Yes Yes T T Sedge Pond N/A Yes Yes Yes C C Orica N/A Yes Yes Yes T,  C aq. T,  C aq. Mount Polley Pond MP-Pond Yes Yes Yes T, C T Water samples and in-situ measurements were collected at all sites. In-situ measurements include temperature, dissolved oxygen (DO), conductivity, pH, and oxidation reduction potential (ORP). ‘Yes’ indicates sample collected or measurement taken, as appropriate; ‘C’ indicates C. utriculata; ‘C aq.’ indicates C. aquatilis; ‘T’ indicates T. latifolia; ‘M’ indicates aquatic moss; ‘S’ indicates S. tabernaemontani; ‘NT’ = Not Taken - indicates sample was not collected or no measurement taken, as appropriate. 1 Soil redox potential measurement  2 SERD Wetland 13 A was determined to be more representative of SERD Seep data, and SERD Wetland 13 B is potential ponded surface water.  Sample Collection As appropriate to the types of samples collected at a given location, water samples were collected, followed by microbiological samples, and finally, soil and vegetation samples. A total of 14 water samples, 11 soil samples, and 16 vegetation samples were collected for analytical testing (Table 1). A total of 16 microbiological samples were collected from the Mine site and analyzed for potentially beneficial microbes in the context of water remediation in a CWTS to identify latent potential for treatment associated with sampling locations.  Whole plants were harvested for future bench- and pilot-scale CWTS testing for the Mine site, and are being maintained in nursery systems at Contango. Explanatory parameters, which are quantifiable aspects of a CWTS environment (i.e.  dissolved oxygen, oxidation reduction potential, etc.), were collected as in-situ water and soil measurements, and tested along with laboratory parameters (i.e., chemical oxygen demand, hardness, total and dissolved metals, nutrients, etc.) (Contango, 2017).   Microbial Analysis To evaluate the latent potential for water treatment at the Mine site, genetic- and growth-based analyses were performed to assess presence, abundance, identity, and diversity of bacteria naturally found at the site. Microbial communities were also tested for their ability to reduce sulphur compounds, nitrate, and selenium by the most probable number (MPN) growth-based method (Contango, 2017).   RESULTS AND DISCUSSION  Water Water quality models in the 2017 RCP update predict that contact water collected on the Mine site may be elevated in concentrations of some constituents, such as select metals. As described in the RCP update (MPMC, 2017), water quality targets (WQT) have been predicted for the constituents in closure, based on the most stringent of Effluent Discharge Objectives (EDOs), Metal Mining Effluent Regulations (MMER) limits, maximum British Columbia water quality guidelines (WQG), or alternative acute screening values for applicable receiving environments.    Laboratory Analysis Some locations had concentrations of total copper and selenium above WQT, while total zinc was only above WQT at NEZ-1, and antimony and iron were below WQT at all locations (Table 2). Generally, sulphate, nitrate, and total and dissolved selenium were at higher concentrations in seeps than ponds, while total and dissolved iron was higher in ponds compared to seeps. Nitrite was below the detection limit at all locations, except for LD-LS (0.0092 mg/L). Total phosphorus was below the detection limit for all locations, except for LD-1, SERD Wetland 13 B, LD-LS and Hazeltine Pond, although the detection limit is above the WQT for total phosphorus (0.015 mg/L). It should be noted that the WQT for phosphorus is only applicable to lakes. Total copper was elevated at all locations other than SERD Wetland 13 A, Duck Pond, and Orica, with copper concentrations of 0.00318 mg/L, 0.00319 mg/L, and 0.00313 mg/L, respectively. Although select COPCs are above the WQT at some locations that were sampled, the water chemistry analysis indicates that the water at the Mine site is relatively benign in the context of concentration of COPCs. Table 2 - Results of water laboratory analyses for constituents of potential concern. Location TSS SO4 NO3 NO2 Antimony Copper Iron Selenium Phosphorus Zinc T D T D T D T D T T D JCP <1.0 293 <0.025 <0.005 <0.00010 <0.00010 0.00480 0.00471 0.053 <0.030 0.00108 0.00103 <0.050 <0.0030 <0.0030 LD-1 <1.0 851 20.6 <0.01 0.00051 0.00045 0.0201 0.0192 <0.030 <0.030 0.0503 0.0535 0.06 0.0058 0.0056 LD-2 <1.0 849 20.5 <0.01 0.00051 0.00046 0.0174 0.0155 <0.030 <0.030 0.0476 0.0531 <0.10 <0.0060 <0.0030 NEZ 1 6.8 947 2.74 <0.01 0.00040 0.00036 1.10 0.408 <0.030 <0.030 0.148 0.159 <0.050 0.0573 0.0443 SERD Wetland 13 A 3.3 647 7.83 <0.005 0.00023 0.00016 0.00318 0.00276 0.035 <0.030 0.0118 0.0101 <0.050 <0.0030 <0.0030 SERD Wetland 13 B 36.9 128 <0.0050 <0.001 <0.00010 <0.00010 0.00433 0.00300 0.320 0.157 0.000265 0.000265 0.095 0.0035 <0.0030 LD-LS 202 322 4.59 0.0092 <0.00010 <0.00010 0.0134 0.00700 0.177 <0.030 0.00169 0.00191 0.13 0.0069 <0.0030 Hazeltine Pond 2.6 43.1 0.0093 <0.001 0.00015 0.00016 0.0596 0.0285 0.710 0.041 0.00114 0.00121 0.051 0.0037 <0.0030 Duck Pond 1.9 16.8 <0.0050 <0.001 <0.00010 <0.00010 0.00319 0.00205 0.117 <0.030 0.000229 0.000207 <0.050 <0.0030 <0.0030 Sedge Pond 4.0 66.1 <0.0050 <0.001 0.00010 <0.00010 0.00919 0.00652 0.607 0.207 0.000147 0.000109 <0.050 <0.0030 <0.0030 SSP <1.0 850 12.1 <0.01 0.00031 0.00026 0.0241 0.0227 <0.030 <0.030 0.140 0.123 <0.050 0.0067 0.0064 Orica 5.6 8.10 <0.0050 <0.001 0.00011 <0.00010 0.00313 0.00205 0.321 0.058 0.000096 <0.000050 <0.050 <0.0030 <0.0030 MP-Pond <1.0 43.4 <0.0050 <0.001 <0.00010 <0.00010 0.00431 0.00392 0.090 0.050 0.000104 0.000115 <0.050 <0.0030 <0.0030 JZD-Weir <1.0 545 9.47 <0.005 0.00012 <0.00010 0.00830 0.00740 0.031 <0.030 0.0260 0.0278 <0.050 <0.0030 <0.0030 WQT 15 218 3 0.02 0.0009 - 0.004 - 1 0.35 0.002 - 0.015 0.01 - All values reported as mg/L. Cells shaded in grey indicate they are greater than the WQTs, and bold indicates higher than MMER guidelines for maximum authorized concentration in a grab sample. NO3 and NO2 reported as N. The detection limits for total phosphorus (0.050 mg/L and 0.10 mg/L) are above the WQT for total phosphorus (0.015 mg/L).  T = Total; D = Dissolved; SO4 = Sulfate; NO3 = Nitrate; NO2 = Nitrite. Soils  Sulphate concentrations are important to consider in terms of metals such as antimony, copper, and zinc which could be treated from water by precipitation as a metal sulphide. The action of producing sulphide in a CWTS is biological (i.e., by sulphide-producing bacteria “SPB”), can be affected by temperature, and may have difficulty in directly accommodating large increases of metals concentrations instantaneously. Fortunately, when excess sulphides are generated by SPB, they can be stored in sediments as acid volatile sulphides (AVS) for future use in metals treatment in an on-demand manner. AVS are a sulphide with iron (FeS) where the mineral is newly formed (e.g., biogenically) and its amorphous structure allows for the sulphide to preferentially exchange iron for heavy metals (e.g., copper and zinc) which are then more stably bound. This can be tested for by a method that assays both the AVS and simultaneously extracted metals (SEM; cadmium, copper, lead, mercury, nickel, zinc). If a soil has a molar ratio of ∑SEM:AVS < 1, then it is considered to be theoretically capable of exchanging iron for SEM-type elements, circumventing influences of temperature and biological reaction rates on treatment of elements being removed as sulphide minerals. Moreover, when ∑SEM:AVS < 1, the AVS can serve as a buffer to oxidation should the soils of a reducing (sulphide-producing) passive treatment system be exposed to oxygen (e.g., briefly drying out), thereby making sequestered metals less likely to resolubilize.  The field investigation found that, of the eleven sample locations tested, five locations had AVS (JCP, SERD Wetland 13 A, SERD Wetland 13 B, Sedge Pond and MP-Pond), and six locations did not (NEZ-1, LD-LS, Hazeltine Pond, Duck Pond, SSP, and Orica). Of the five locations that did have AVS, all were found to be well-suited to sustainable metals treatment (e.g., antimony, copper, and zinc), with an ∑SEM:AVS < 1. Total organic carbon, iron, and soil redox did not explain the differences seen between locations with and without AVS. Generally, the assumption is the AVS is being produced during warmer months when reducing conditions exist in these locations and is being stored through the colder conditions under which the feasibility assessment was conducted.   At all locations where AVS was found, copper and selenium were also both found to be in greatest abundance in reduced form in the soils (confirmed by sequential Tessier extractions; data not shown). This suggests reducing conditions exist in these areas for at least parts of the year, and the AVS is serving as a buffer from re-oxidation in shoulder seasons when reducing conditions might not be consistently maintained.   Plants Five plant species at the Mine site were identified for potential use in treatment wetlands, including Carex aquatilis (commonly known as aquatic sedge), Carex utriculata (commonly known as common beaked sedge), Typha latifolia (commonly known as cattails), Schoenoplectus tabernaemontani (commonly known as bulrush), and an aquatic bryophyte (aquatic moss) (Figure 2). These plant species are natural to the Mine site and are therefore capable of withstanding the climatic and chemistry fluctuations experienced in the watersheds of the area. T. latifolia and C. utriculata were the most abundant emergent macrophyte species at the Mine site and therefore would be the best candidates for long-term establishment of a CWTS. S. tabernaemontani and C. aquatilus were only found at one location each, and were therefore given lower priority for potential use as they may be replaced by the more strongly colonizing T. latifolia and C. utriculata in the area. Most sample locations were exclusively colonized by either T. latifolia or C. utriculata, although some contained both key species. While these plants can co-exist, a CWTS would be planted with only a single species in any given treatment cell to avoid transition of treatment conditions with the change in plant population.  Aquatic mosses are also species of interest due to their capability to remove COPCs from water through sorption. It is well known that moss has a high uptake rate of cations (such as copper and selenium) and is also a relatively benign sink for these elements (i.e., is not a food source for invertebrates or higher animals and as such does not contribute greatly to bioaccumulation (Haines & Renwick, 2009; Longton, 1997; Suren & Winterbourn, 1991). This was also confirmed in the feasibility assessment, which produced data indicating that moss at the Mine site has a high uptake of elements such as copper, and could therefore be an effective means of removing elements from seepage through uptake. Therefore, while metal and metalloid uptake by emergent macrophytes such as T. latifolia, C. utriculata, and C. aquatilis may not be desirable treatment mechanisms, sorption of these constituents to bryophytes (aquatic mosses) is a desired and targeted treatment pathway in scientifically designed treatment wetlands.      Figure 2 - Clockwise from top left: Bryophyte (aquatic moss) at LD-1; C. utriculata at Sedge Pond;  S. tabernaemontani at SERD Wetland 13 A; T. latifolia at SERD Wetland 13 B. No picture of C. aquatilis was available for this paper. Microorganisms Latent Potential for Treatment The latent potential for natural treatment at the Mine site was investigated in the context of passive treatment mechanisms for COPCs. Genetic testing identified a high diversity of bacteria, with over 1,100 different types in each sample. Natural microorganisms potentially beneficial to treatment of Mine-influenced waters were present in association with all plant species of interest for use in CWTSs (i.e., T. latifolia, C. aquatilis, and S. tabernaemontani) as well as aquatic mosses.   Beneficial microorganisms included several different types of bacteria involved in sulphide production, which is the desired targeted pathway for removal of various metals and metalloids in anaerobic treatment systems. All locations tested also had a high abundance of selenium- and nitrate-reducing bacteria, selenium and nitrate being key constituents to target for treatment at the Mine site. Beneficial microorganisms included those that are naturally psychrotolerant, meaning they can grow in cold temperatures, and those involved in the reduction of selenium, sulphate, and nitrate, all of which could be used to promote treatment of water in a CWTS at the Mine site. This information will be used in the CWTS design considerations, as systems can be designed to provide suitable habitat for specific types of microorganisms to target a desired function.  There were no major notable differences between C. utriculata and T. latifolia in terms of hosting beneficial microorganisms (Figure 3, Figure 4, and Figure 5). All three tested plant types (i.e., including S. tabernaemontani) host comparable inferred abundances of SPB (beneficial for treatment of antimony, copper, and zinc), as well as selenium- and nitrate-reducing bacteria (Figure 3). In consideration of proportions, inferred abundance, and diversity of beneficial organisms, the best sources for anaerobic treatment systems are C. utriculata from Hazeltine Pond or Sedge Pond, or T. latifolia from most of the tested locations except Orica or MP-Pond. S. tabernaemontani at SERD Wetland 13 A is also compatible for an anaerobic treatment system.  Comparing Hazeltine Pond to MP-Pond, it was found that the two locations were similar in the number of types of bacteria, as well as overall diversity (based on total number of operational taxonomic units, as well as Simpson’s index; data not shown). Although Hazeltine Pond is a newly established wetland in the “Polley Flats” (an area adjacent to the Mine site which was impacted by the release of tailings resulting from the foundational failure of the Mine’s Tailings Storage Facility in 2014), it hosts a similar quantity and overall proportion of beneficial microbes as MP Pond and other older more established wetland locations.Figure 3 - Top: Percentage of each type of SPB in the community is provided on the y-axis. Bottom: Inferred abundance of SPB as the MPN/cm3 (plants) or MPN/g (moss and biofilm) of sample. SPB are beneficial for anaerobic treatment systems for removal of metals and metalloids. HP=Hazeltine Pond, SP=Sedge Pond, JZD-W=JZD-Weir, SERD 13B=SERD Wetland 13 B, DP=Duck Pond, MPP=MP-Pond, SERD 13 A=SERD Wetland 13 A.      Figure 4 - Abundance of selenium-reducing organisms per sample.  Number of organisms per cm3 (plants, left plot) or per gram (moss and biofilm, right plot) of sample provided in log-scale, based on MPN analyses for selenite [Se(IV)] and selenate [Se(VI)] reduction to elemental selenium. Y-axis is adjusted to expand plot. HP=Hazeltine Pond, SP=Sedge Pond, JZD-W=JZD-Weir, SERD 13B=SERD Wetland 13 B, DP=Duck Pond, MPP=MP-Pond, SERD 13A=SERD Wetland 13 A.                   Figure 5 - Abundance of nitrate-reducing organisms per sample. Number of organisms per cm3 (plants, left plot) or per gram (moss and biofilm), right plot of sample provided in log-scale, based on MPN analyses for nitrate reduction. Y-axis is adjusted to expand plot. HP=Hazeltine Pond, SP=Sedge Pond, JZD-W=JZD-Weir, SERD 13B=SERD Wetland 13 B, DP=Duck Pond, MPP=MP-Pond, SERD 13A=SERD Wetland 13 A. CONCLUSION  The Mine site has several natural ponds, wetlands, and creeks, typically in the lower valley regions, that support aquatic vegetation. T. latifolia and C. utriculata were identified as the primary emergent macrophytes of interest for use in a CWTS, as they are most abundant and natural to the Mine site and are therefore capable of withstanding the climatic and chemical fluctuations experienced in the watersheds of the area. Aquatic mosses are also of interest due to their capability to remove COPCs from water through sorption. Analysis of soil, plants, and microorganisms identified beneficial microbial communities at multiple locations at the Mine site for use in a CWTS. These microbial communities facilitate biogeochemical processes at the Mine site (e.g., microbially-catalyzed sulphide production) which can remove metals, such as copper, from water as sulphide minerals. Additionally, selenium- and nitrate-reducing microorganisms were found to be abundant in numerous samples from the Mine site. These natural and beneficial processes can be further enhanced through guided design of passive water treatment strategies to improve water quality in closure.   The vegetation in these areas, as well as naturally associated beneficial microbes and soil chemistries, suggest that there are many naturally beneficial water treatment pathways present at the Mine site. These treatment pathways can be optimized through site-specific design and implementation of treatment wetlands for COPCs. Analysis of water during the feasibility assessment determined that the water chemistry at the Mine site is generally benign in terms of the concentration of COPCs, and constituents would be readily treatable by CWTSs or other biogeochemical treatment systems such as in-pit treatment or bioreactors.    REFERENCES  Contango Strategies Ltd. (2017). Mount Polley CWTS Feasibility Assessment Report. Document # 035_0317_02B.  Haakensen M, Pittet V, Spacil MM, Castle JW, Rodgers JH Jr. (2015). Key aspects for successful design and implementation of passive water treatment systems. J. Environ. Sol. Oil Gas Mining 1(1):59-81.  Haines, W. P. and Renwick, J. A. A. (2009). Bryophytes as food: comparative consumption and utilization of mosses by a generalist insect herbivore. Entomologia Experimentalis et Applicata 133: 296-306.   Longton, E.R. (1997). The role of bryophytes and lichens in polar ecosystems. In: Ecology of Arctic Environments, Blackwell Science. Woodin, S.J., and Marquiss, M (eds).  Mount Polley Mining Corporation (2017). Mine Reclamation and Closure Plan Update January 2017.  Suren, A. M. and Winterbourn, M. J. (1991). Consumption of aquatic bryophytes by alpine stream invertebrates in New Zealand. New Zealand Journal of Marine and Freshwater Research 25: 331-343.  


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