British Columbia Mine Reclamation Symposia

Site investigations and remediation : Yankee Girl tailings site, Ymir, BC Tinholt, M. 2009

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SITE INVESTIGATIONS AND REMEDIATION YANKEE GIRL TAILINGS SITE, YMIR, BC   M. Tinholt, P.Eng.1    N. Sandstrom, P.Eng.1 J. Sevigny, Ph.D.2 G. Stewart, P. Geo3 G. Sinnett, P.Geo3  1 SNC Lavalin Environment/Morrow Environmental Consultants Inc. 385D Baker Street, Nelson, BC  V1L 4H6 112, 1212 – 1st Street SE, Calgary, AB  T2G 2H8  2 Iridium Consulting Inc. 812 Victoria Street Nelson, BC  V1l 4l5   3 Ministry of Agriculture and Lands, Crown Contaminated Sites Branch PO Box 9361, Stn Prov Govt Victoria, BC  V8W 9M2  ABSTRACT  The Yankee Girl Gold Mine near the community of Ymir, BC operated from 1935 to 1942.  As part of this historical mining activity, tailings were deposited adjacent the Salmo River and Wildhorse Creek. The Ymir townsite is located directly across the river from the site, resulting in the site being valued by the local community as a location for recreational activities.  Site assessment work was initiated in 2004 by the Ministry of Agriculture and Lands (MAL) to address an Inspector’s Direction issued by the Department of Fisheries and Oceans (DFO).   In 2005 through 2007, Morrow Environmental Consultants Inc. (Morrow) completed a supplemental detailed site investigation (DSI) and a refined Human Health and Ecological Risk Assessment (HHERA) to develop a comprehensive understanding of the extent, magnitude and significance of contamination at the site.  The assessment confirmed that unacceptable human health and/or ecological risk existed at the site as a result of erosion of tailings into the Salmo River, leaching of metals and acidity into a side channel, residual spilled concentrate in soil at the mill area, and exposed tailings.  Morrow then developed several conceptual options for site remediation. Several public meetings were held between 2004 and 2007 to present the assessment results and conceptual remedial options, and to consult with the stakeholders.  Site remediation commenced in 2007 and includes consolidating the tailing and soil with residual concentrate within a secure on-site containment cell with erosion/flood control and aquatic habitat enhancement in the riparian areas adjacent to the site.  Added value was found by incorporating the community’s desires for final land use into the remediation plan so that there will be ongoing beneficial use of the rejuvenated area and stewardship of the site.  INTRODUCTION  On behalf of the Ministry of Agriculture and Lands (MAL), Crown Contaminated Sites Branch (CCSB), Morrow Environmental Consultants Inc. (Morrow) and Iridium Consulting Inc. completed a supplemental Detailed Site Investigation (DSI), a Human Health and Ecological Risk Assessment (HHERA) and conceptual remediation plan for the Yankee Girl Tailings site, located at Ymir, B.C. Site Description and History  The subject site consists of the approximately 6 ha area bound by the Salmo River, Ymir Creek, Wild Horse Creek Road, and the south limit of a side channel to the Salmo River.  Figure 1-1 illustrates the key features of the site, which include the following: • Upper Tailings Area • Lower Tailings Area • East Lobe Lower Tailings Area • Old Mill Area • Side Channel • North of Upper Tailings Area • North of Wildhorse Creek (also referred to as Ymir Creek) • Slope between Site and Wild Horse Creek Road • Floodplain Southwest of the Site  Table A:  General Summary of Property and Project History  Date Subject Site History 1886–1899 Mineral claims were staked and mining began in the Ymir region.  In 1897, Quartz Creek town site was renamed “Ymir”, and surveyed lots were sold to prospectors and miners working in the area. 1896/99 Gold was discovered at the Dundee and Yankee Girl mines. 1899–1951 Intermittent mining in which ore was shipped primarily off-site for processing.  Mine production increased in 1935 following the construction of a 100 ton/day mineral processing mill located across from the town of Ymir and adjacent to the Salmo River (i.e., subject site). 1935–1942 Ore obtained from the Dundee/Yankee Girl workings was processed at the new mill and the concentrate smelted in Trail.  The tailings were stacked on the site until 1942 when the mill was shut down.  Following closure, responsibility for the site eventually reverted to the Crown. Sept. 2000 B.C. Ministry of Energy, Mines and Petroleum Resources collected water and tailing samples at the site. Nov. 2001 B.C. Ministry of Environment collected additional tailing samples May 2003 Department of Fisheries and Oceans issued a Directive to the Province requiring a site investigation and prevention of further erosion of tailings into the Salmo River. Nov. 2004 A detailed site investigation, preliminary risk assessment and remedial options evaluation were initiated. Nov. 2004 Public Meeting #1 July 2005 Technical review of remedial options completed. July 2005 Public Meeting #2 Oct. 2005 Public Meeting #3 (Open House):  Additional assessment work to confirm preferred remedial option initiated. Dec. 2005 Installation of interim erosion control barrier. May 2006 Erosion control barrier augmented where necessary due to 1:10 year river level event. Oct. 2006 Completion of additional site investigations and human health / ecological risk assessment. Nov. 2006 Public Meeting #4 (Open House) Feb. 2007 Public Meeting #5: Further clarification and input from the community regarding the preferred remedial option and post remediation land use plan. Apr. 2007 Final decision notice on remedial option made by CCSB. May 2007 Terrestrial site preparation work commenced in the area of the former mill. Photo 1:  Yankee Girl Tailings Site  (Credit:  Gerry Nellstjin) ASSESSMENT FINDINGS  Although preliminary site assessment work commenced in 2000, detailed data necessary to identify a preferred remedial solution was not obtained until 2005/2006.  Media assessed included the soil (surface and subsurface), tailings, groundwater, surface water, sediment and drinking water at and adjacent to the site.  The primary contaminants of concern were determined to be arsenic, cadmium, lead and zinc, as they are the elements that most frequently exceed provincial environment standards and are present at the greatest concentrations.  These metals are associated with minerals in the ore that was transported to the site for processing.  Cyanide was used in the ore milling process; however, concentrations in analyzed soil and water samples from the site do not exceed applicable comparison standards.  The key assessment findings are summarized below:  • In soil, metals concentrations exceed provincial environment standards across the site.  In general, metal concentrations are highest in the lower and upper tailings areas1  and around the former mill.  Concentrations of the primary metals of concern are also elevated in areas associated with remnant tailings deposits located northeast and northwest of Wild Horse Creek; however, these areas support a healthy ecosystem and are less accessible for human activities  • Groundwater and seepage water quality is poorest in the southeast lobe of the lower tailings area at the side channel and at the former mill site as a result of acid rock drainage and metal leaching (ARD/ML)2.  Groundwater quality beneath the upper tailings area was considered acceptable.  • Surface water sampling results indicate that the side channel is not suitable as aquatic habitat; however, the Salmo River water quality meets provincial guidelines with the exception of cadmium, which appears to be regionally elevated.  The total metal concentrations in the Salmo River water are similar upstream, adjacent and downstream the site.  • In sediment, the highest concentrations of primary metal contaminants are present within the side channel where deposits of tailings run-off and metal precipitate exist.  Within the Salmo River, concentrations of the primary metal contaminants in sediment at and downstream of the site are somewhat higher than upstream of the site, which is consistent with the fact that tailings eroded into the river until the erosion control barrier was installed in 2005.  Overall, the average Salmo River sediment concentrations are less than the conservative provincial environmental standards. Now that tailings erosion has been controlled, average sediment concentrations will likely decrease.   1  Historic information indicated that some of the tailings were processed twice, resulting in differing tailing chemistry (and appearance) between the upper and lower tailings. 2  During 2006, other potentially acid-generating materials located immediately adjacent the Salmo River area at the west side of the upper tailings area were excavated prior to the installation of the erosion control barrier and placed in a stockpile on the upper tailings area. • Water analyzed from the nearest drinking water well located downstream of the subject site are less than provincial drinking water standards for all four sampling events.  • A risk-based approach was utilized to prioritize remedial management options for the site, since removal of all areas with elevated metals is not physically possible. The key risk assessment results are outlined as follows:  Human Health Risk Assessment Results  o Residual concentrate in soil at the former mill area must be excavated to avoid potential human health risks. o The mine tailings must be covered to avoid potential human health risks via direct contact. o Rainbow trout from the Salmo River are safe to consume.  Ecological Risk Assessment Results  o The tailing deposit must be covered to provide a physical barrier as well as a growth medium for vegetation (in addition to protecting human health). o Toxicity testing, fish analyses, and food web modelling show that the aquatic ecosystem is not being significantly impacted.  There are, however, localized effects on benthic organisms due to the erosion of tailings into the sediment, and non-functionality of the side channel. o Food web modelling and small mammal analyses (deer mouse and shrew) show that the terrestrial ecosystem adjacent to the tailing deposit has not been unacceptably impacted, with the exception of possible localized effects to soil organisms and plants.  CONCEPTUAL REMEDIATION PLAN  The unacceptable risk issues at the site that were identified for remediation are summarized in Table B, along with the preferred remedial solution, which involves a combination of excavation, impoundment, covering and habitat restoration.  The preferred remediation solutions are illustrated in the Conceptual Remediation Plan, Figure 130692-Fig C. Table B:  Preferred Solutions to Address Unacceptable Risk Issues at the Site  Unacceptable Risk Issue Conceptual Remediation Plan Erosion of tailings into/by Salmo River and Ymir Creek.  Extend erosion control along Ymir Creek. Construct the main erosion control barrier to withstand the 1:200 year flood event. Ensure that west side (town side) of the Salmo River bank is not compromised in terms of flood control. Leaching of metals and acidity into the existing side channel from lower tailings area. Excavate lower tailings area and consolidate into containment cell within the upper tailing area. Existing side channel currently not functioning as habitat or flood relief.  Create new side channel by excavating material and placing into old side channel.  Enhance new side channel habitat under no-net loss principles. Spilled concentrates in surface soil at mill area present potential human health risk and ability to leach into groundwater. Excavate the surface soil and place into the upper tailings area containment cell. Exposed upper tailings area is eroding through surface runoff, and presents potential human health risk. Place engineered cover over the upper tailings area following containment of the excavated materials.  Post-Remediation Land Use  The Government’s remedial actions are being undertaken to ensure protection of human health and the environment.  The community desired to use the property for the future, and it was recognized that there would be added value by incorporating the community’s desires for final land use into the remediation plan so that there will be ongoing beneficial use of the rejuvenated area and stewardship of the site. However, the community’s choice for post-remediation land use must be compatible with the remedial option implemented.  The integrity of the engineered cover over the upper tailings area must be maintained over the long term, and, as such, some factors that will govern post-remediation land use include: • control of motorized vehicle access; • continued access to groundwater wells for future monitoring and testing; • establishment of vegetative cover established—but deep-rooting trees must be excluded on the capped tailings area (trees can be established in the backfilled lower tailings area and backfilled side channel areas); and • ongoing care and maintenance to ensure erosion barrier and engineered cover are not damaged.  Based on feedback from the community at the public meetings, a park-like setting that is accessible by foot (including a potential footbridge) was generally desired as a final land use for the site.  Controlled vehicle access is also desired to allow set-up for special events.  The covered tailing area could accommodate a stage or amphitheatre, and/or the lower tailings/former side channel could accommodate other desired recreational uses, such as disk golf or even a skateboard park.  Compatibility with protection of ecological values, primarily riparian habitat, was also desired.  Based on these concepts, Drawing REM-FIG-1 provides a conceptual representation of a potential post-remediation site configuration that is compatible with the preferred remediation plan and our understanding of the community’s desires. FIGURES  Figure 1-1:  Areas of Environmental Concern (AEC)   130692-Fig C:  Conceptual Remediation Plan  130692 – REM-FIG-1:  Potential Post Remediation Site Configuration


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