The production of acid rock drainage (ARD) from mine tailings is a significant environmental concern at various abandoned mine sites in Yukon. Leachate with low pH and high dissolved metals concentrations deriving from mine tailings impoundment areas can negatively impact various groundwater and surface water resources. The presence of both oxygen and water is required for ARD to develop. Therefore, the reduction of the oxygen and water sources from the mine tailings will limit ARD production. This is the basis of reclamation of the Arctic Gold and Silver (AGS) Tailings Site near Carcross, Yukon using a lowpermeability tailings cover which acts as an oxygen and water infiltration barrier. ARD processes have resulted in a significant contamination of the groundwater beneath the tailings impoundment at the AGS site with multiple dissolved metals showing elevated concentrations. The use of a low permeability cover to reduce ARD such as that used at the AGS site is one of the first such reclamation applications in Yukon. EBA Engineering Consultants Ltd. and partners initiated a performance assessment of the low permeability cover system in the fall of 2000 and continued the monitoring in 2001 as part of Mining Environment Research Group (MERG) funded studies. The results of these assessments suggested that the low-permeability cover functions as an oxygen and infiltration barrier; however, the limited data and short period of monitoring precluded any prediction of the long-term performance of the tailings cover. Further monitoring was recommended.

The effects of permafrost degradation in Yukon have serious negative implications for the structural integrity of vertical infrastructure. This is especially pertinent for critical buildings such as hospitals, schools, etc., in small communities that are situated on top of warm, ice-rich permafrost. Projections of mean annual air temperature over the next few decades, based on regional climatic models, indicate that air temperature will rise, hastening the thaw of permafrost. The combination of rising of air temperatures and buildings situated on warm permafrost has prompted this investigation into the vulnerability of Yukon Government vertical infrastructure. The application of DC resistivity and ground penetrating radar in conjunction with borehole drilling indicates that in Dawson there is warm ice-rich permafrost beneath the Palace Grand Theatre; the Old Territorial Administration building is underlain by primarily unfrozen sediment; and permafrost under the St. Andrew’s Church is characterized by high variability. A deep active layer was observed at Ross River School and geophysical surveys indicate that warm water drainage from the roof is contributing to the thaw of the underlying permafrost.

EBA Engineering Consultants Ltd. has prepared this report, based on literature review, to provide information to assist the Yukon mining industry in remediating environmental problems caused by acid rock drainage (ARD) with its associated heavy metals contamination. There are three main sections to this review. First, the history of ARD is presented. Second, the chemistry and microbiology of ARD and the treatments that are used worldwide, with emphasis on cold climate treatments, are reviewed. Finally, we present the most promising technologies developed in temperate regions, that could be tested under typical Yukon conditions. This is the main challenge given the short growing season and cold temperatures. Acid mine drainage is caused by oxidization of metal ores, containing sulphur and metal sulfides found in coal. There are three steps in this process. First, oxygenated water, from rain, for example, oxidizes metal sulfides producing acidic water and ferrous iron. When the water becomes moderately acidic, a number of bacteria can assist in further oxidization and increase the acidification of the drainage water. Finally, when the water reaches a pH of 3.5, an iron bacterium, Thiobacillus ferroxidans, can further dissolve metal sulfides, such as pyrite, producing ferric hydroxide, which can smother vegetation. Also, the sulphuric acid is acutely toxic. Heavy metals that are toxic, are also present in the ARD. Some common treatments for ARD identified by EBA including neutralizing the acidity of water using limestones, minimizing water contact with metal sulfides, or using organic amendments to bind with heavy metal contaminated waters. Important developments in using natural wetlands for ARD, have taken place in the late 1990s, which have identified that anaerobic (oxygen free conditions) are important in treating ARD. High sediment loads in streams have been found to limit neutralization by coating carbonates and decreasing microbial reduction of metal, as well as preventing metal uptake by vegetation.

Disturbance of frozen ground, through placer mining activities, may lead to slope failure. A stockpile of frozen overburden has recently begun eroding from the formation of a runoff channel. A large cut, approximately 300 metres long and up to 50 metres deep has been created adjacent to Gold Run Creek, a heavily mined area southeast of Dawson City. This stockpiled overburden has been in place for several years and has revegetated with several species of mature willows (age dated to 15 years). Either due to heavy rainfall or climate change, melting has commenced in the stockpile resulting in the formation of a runoff channel. This has increased in size and slope failure continues to enlarge the cut. Laberge Environmental Services conducted a reconnaissance survey of the site in July 2003, to assess the site with the purpose of exploring ways of halting the slope failure and stabilizing the disturbed section of overburden. Several bioengineering techniques have been suggested to assist in controlling the erosion.

A reconnaissance-level study of post-mining hydrogeochemical conditions was carried out at the Brewery Creek gold deposit within the Tintina Gold Province. The deposit is characterized byepizonal mineralization with a consistent arsenic-gold-mercury-antimony geochemical signature. Surface discharges and seeps in the area are naturally alkaline (pH=7.6-8.2), Ca-HCO3 ¯-SO4²¯ waters. Upstream from the recognized mineralization, waters contain <3 ¿g/L As and <1 ¿g/L Sb. Water samples immediately downstream from the ore bodies show maximum concentrations of 18 ¿g/L dissolved and 47 ¿g/L total arsenic, and 18 ¿g/L dissolved and 21 ¿g/L total antimony. Two kilometres below the mineralization, on lower Laura Creek, arsenic concentrations are diluted to background levels of <3 ¿g/L, and antimony levels are still slightly elevated at 9-10 ¿g/L. Comparison with hydrogeochemical data from Donlin Creek, an undeveloped epizonal deposit in Alaska, indicates that elevated concentrations of a few tens of ¿g/L arsenic and antimony are typical of waters draining such gold systems, regardless of their state of development. In addition to their usefulness for the construction of geoenvironmental models, these data also provide information for establishing exploration programs utilizing water sampling.

An Integrated Regulatory Regime for Yukon Placer Mining was the final report of the Yukon Placer Implementation Steering Committee, submitted to the Minister of Fisheries in 2005. Under a proposed new management regime, the Yukon's placer mining industry will be managed through an adaptive management framework, with the aim of striking a balance between maintaining a viable placer industry and the protection and conservation of aquatic ecosystem integrity and fish populations. The effectiveness of the regime at achieving this balance will be monitored and assessed with appropriate adjustments to the requirements as required. The report recommended that a number of protocols be prepared and implemented in order to monitor the effectiveness of the new management system and among these is one with the primary objective of assessing and monitoring watershed health. A draft Watershed Health Monitoring protocol was completed July 1, 2006, and is currently being reviewed and considered by first nation, territorial and federal government agencies, industry and conservation organizations, and the general public. The draft protocol aims to provide for a process to help assess how effective the new management regime is for maintaining watershed health and to generate monitoring results that will be used to guide the adaptive management framework assessment and adjustment phases. After consideration of a number of methods, the Reference Condition Approach (RCA) was selected for assessing and monitoring watershed health under the draft protocol. There were a number of reasons for this choice: - It is the most robust of many biomonitoring methods - It is the basis of regional programs in Canada (it is an accepted design under the federal Environmental Effects Monitoring program), and programs in other countries, several USEPA programs in the United States, national programs in Australia and the United Kingdom, and has been adopted under the European Water Directive. - An RCA program has been underway in the Yukon for a number of years that could be immediately applied to the placer mining areas and augmented by future fieldwork. When the draft protocol was in preparation in the spring of 2006, meetings were held among those already conducting some type of stream sampling program associated with the Yukon placer mining industry. This included The University of Western Ontario, the federal Department of Fisheries & Oceans, and Environment Yukon Fisheries section. These three groups agreed to collaborate and carry out RCA sampling in 2006 in a manner consistent with that provided for in the draft Watershed Health Monitoring Protocol in order to "test drive" the methodology and assess its effectiveness at achieving the new management regime's objectives. Follow-up Geographical Information System March, 2007 3 (GIS) data collection and data analysis were also carried out as provided for in the draft protocol. In addition, reference sites were subjected to simulated impacts and then the RCA models were applied to these impacted sites in order to demonstrate the ability of the RCA models to detect a known degree of disturbance in streams.

This study investigated background levels and uptake rates of organophilic metals, particularly selenium, in ten streams draining portions of the Yukon-Tanana Terrane and Cassiar Platform between Ross River and Watson Lake, Yukon. The study area is suspected to have elevated background metals concentrations and is of interest for mineral exploration and development due to high mineralization. Information on natural metals levels is lacking for this region and for the Yukon in general. Water, sediments, benthic invertebrates and fish (slimy sculpin; Cottus cognatus) were sampled and analyzed for metals concentrations. Benthic invertebrates were identified to genus and percent composition of each species in each stream was calculated. The lack of anthropogenic activity in the area indicates that selenium concentrations found in all sample media and natural, background concentrations. Of all the sample media, concentrations of selenium were highest in sediment; however, sediment selenium concentrations were found to be in a range similar to levels documented at the Kudz Ze Kayah and Viceroy Brewery Creek mines in other regions of the Yukon. Selenium concentrations in water generally exceeded CCME guidelines, but also fell within a range similar to the Kudz Ze Kayah and Viceroy Brewery Creek mines. These findings with respect to selenium levels in water and stream sediments highlight the importance of developing site-specific selenium guidelines for management of aquatic systems. The rate of uptake of selenium in benthic invertebrate and fish tissues was greater than that of the other organophilic metals investigated. Selenium concentrations were generally higher in benthic invertebrates than in fish, likely owing to the detritus-feeding and bottom-dwelling life history of these invertebrates. Weak positive trends were noted in the relationship between selenium concentrations in fish and benthic invertebrates, and between fish and the water column. A significant positive relationship was noted between selenium concentrations in fish and stream sediments. These findings are consistent with past studies documenting dietary sources as the most common uptake pathways for selenium, with water comprising a secondary source. Examination of benthic invertebrate community composition revealed commonly abundant species and species typical of fast-flowing streams with high water quality, which is characteristic of the streams in the study area. The findings of this study provide valuable baseline information on background concentrations of metals, particularly selenium, as well as documentation of benthic invertebrate community composition, in an aquatic system that may experience resource development in the future.

Reclamation testing was carried out on 3 mineral exploration sites in Yukon: an alpine site at the Red Ridge property in the Whitehorse area, and 2 subalpine sites, a boreal forest site at the Nucleus property in the Carmacks area, and a site in moist permafrost at the Hawk propeerty int he Dawson City area.

The presence and proper classification of permafrost is essential to mine planning, operation, and abandonment in the Yukon Territory. This paper discusses the current state of practice regarding permafrost delineation and classification, presents information regarding design and monitoring of structures on permafrost (with particular reference to mining), and includes examples of Yukon and other northern mines where permafrost has affected operations. Permafrost in the Yukon is particularly sensitive to disturbance, as it is generally ¿warm¿ and discontinuous. It is therefore extremely critical that planning for new mines include provisions for the proper classification of permafrost on the mine property, as it will directly affect operations and abandonment of the site, with corresponding financial implications.

Results of surficial geology investigations in Wellesley basin and the Nisling Range can be summarized into four main highlights, which have implications for exploration, development and infrastructure in the region: 1) in contrast to previous glacial-limit mapping for the St. Elias Mountains lobe, no evidence for the late Pliocene/early Pleistocene pre-Reid glacial limits was found in the study area; 2) placer potential was identified along the Reid glacial limit where a significant drainage diversion occurred for Grayling Creek; 3) widespread permafrost was encountered in the study area including near-continuous veneers of sheet-wash; and 4) a monitoring program was initiated at a recently active landslide which has potential to develop into a catastrophic failure that could damage the White River bridge on the Alaska Highway.