Reno, NV, United States
Reno, NV, United States

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Wolfe S.A.,Geological Survey of Canada | Wolfe S.A.,Carleton University | Stevens C.W.,SRK Consulting U.S. Inc | Gaanderse A.J.,Carleton University | Oldenborger G.A.,Geological Survey of Canada
Geomorphology | Year: 2014

Lithalsas are permafrost mounds formed by ice segregation in mineral-rich soil that occur within the zone of discontinuous permafrost. Nearly 1800 lithalsas were mapped using archival aerial photographs within the Great Slave Lowland, Northwest Territories, Canada. These are up to 8. m high and several hundred meters in length and width. One lithalsa, examined by electrical resistivity and boreholes, rises 4 to 6. m above an adjacent peatland, shows clear evidence of ice-segregation at depth and ground heave of between 2.5 and 4.0. m, and is estimated to have formed within the past 700. years. Regionally, lithalsas are typically located adjacent to ponds and streams with mature forms vegetated by deciduous (birch) forest or mixed (birch and spruce) forest with a herb-shrub understory and include circular, crescentic and linear forms. They are abundant within the Lowland region, which contains widespread glaciolacustrine, lacustrine and alluvial fine-grained sediments. The lithalsas are most common within the first few tens of meters above the present level of Great Slave Lake, indicating that many are late Holocene, and some less than 1000. years, in age. A comparison with lithalsas in contemporary environments reveals that comparatively warm but extensive discontinuous permafrost, fine-grained sediments (alluvial, lacustrine, marine or glaciomarine), and available groundwater supply provide the climatic and hydro-geological parameters for the development of lithalsas in permafrost terrain. The identification of lithalsas in this region is important given their sensitivity to climate change and potential hazards to northern infrastructure upon thawing. © 2013 .

Stevens C.W.,SRK Consulting U.S. Inc. | Wolfe S.A.,Geological Survey of Canada | Wolfe S.A.,Carleton University
Permafrost and Periglacial Processes | Year: 2012

Surface hydrology is an important aspect of northern environments on account of the thermal influence of water on permafrost. In this study, we demonstrate the ability of light detection and ranging (LiDAR) to map wet terrain within an area of discontinuous permafrost adjacent to the Northwest Territories Highway 3, located west of Yellowknife, Canada. Wet terrain was identified from LiDAR intensity measurements beneath forest canopies and across vegetated surfaces, including peatlands, fens, flooded black spruce and birch forests, and terrain adjacent to the highway embankment. Surface water pathways representing hydrological connections between water bodies and wet terrain were also identified at locations otherwise indiscernible from optical imagery. Statistical separability between terrain types, and thus the ability to map them, was improved by integrating LiDAR all-return and bare-earth intensity with colour orthophotos. The average classification accuracy for wet terrain was 93 per cent. These results indicate that LiDAR intensity can be used for local-scale mapping of wet terrain, as required by northern engineers and scientists. Future integration of LiDAR intensity and elevation measurements may be used to assess changes in surface hydrological conditions impacting permafrost. © Her Majesty the Queen in Right of Canada 2012.

Wolfe S.A.,Geological Survey of Canada | Wolfe S.A.,Carleton University | Short N.H.,Canada Center For Remote Sensing | Morse P.D.,Geological Survey of Canada | And 2 more authors.
Canadian Journal of Remote Sensing | Year: 2014

Differential Interferometric Synthetic Aperture Radar (DInSAR) is an increasingly viable method for assessing permafrost terrain stability, but the accuracy and performance within discontinuous permafrost terrain has not been well studied. We used a RADARSAT-2 DInSAR data stack for a 120-day period in the summer of 2010 to map seasonal surface displacement in the discontinuous permafrost terrain of Yellowknife, Northwest Territories. Calculated displacement was compared to surficial geology and municipal land use zones. Displacement results reveal that glaciofluvial, glaciolacustrine, humanly modified, and organic terrain are increasingly unstable, in contrast to predominantly stable bedrock. Within municipal zones, increased proportional displacement is related to higher proportions of glaciolacustrine sediments and organic terrain. Organic terrain, associated with the highest proportion of the moderate downward displacement (−3.0 cm to −6.0 cm), occupies less than 6% of the total area. Widespread glaciolacustrine sediments (30% total area) are associated with most of the downward displacement in municipal zones. Semi-quantitative field and geotechnical validations indicate that most areas of moderate seasonal downward displacement in developed areas also represent areas of long-term subsidence. This work shows that even a short InSAR data stack and a simple stack processing method can yield information that is useful for municipal knowledge and planning. © Crown Copyright 2014.

Evin G.,SRK Consulting U.S. Inc. | Henriquez F.,SRK Consulting U.S. Inc. | Ugorets V.,SRK Consulting U.S. Inc.
Proceedings of the 24th International Mining Congress of Turkey, IMCET 2015 | Year: 2015

With the variability of commodity prices and the constant increase of mining costs, it has become increasingly important to optimize pit slopes of mines, taking into consideration the complexity and the uncertainties presented by ground conditions. The variables in slope stability, geology, rock mass strength, structural defects, inherent and induced stresses, rock weathering, alterations, and groundwater, are well known, as are their impacts on slope performance. Most variables cannot be changed to optimize slopes. However, groundwater is one variable that can be managed during pit excavation, to reduce the effect of pore pressure on slope stability. Hydrogeologists and rock mechanics engineers combine their efforts in order to quantify, simulate, and control the effect of groundwater pressures on pit slope performance. Based on comprehensive field hydrogeological data collection and interactive numerical groundwater and geotechnical modeling, it is possible to evaluate the water pore pressure effect on the pit slope, to provide an efficient depressurization strategy to meet the geotechnical engineering targets, and thus to develop cost-effective mine plans. This paper discusses how proper management of groundwater conditions can contribute to mine planning and operations, through pit slope optimization. We show a complete approach from collection of hydrogeological data in the early stages of a project to design of an appropriate depressurization plan, taking into account the rock mass conditions, the mining plan, and the time to achieve an optimal pit slope.

Banta M.D.,SRK Consulting U.S. Inc.
Transactions - Geothermal Resources Council | Year: 2014

The U.S. Department of Energy (DOE) has been on the forefront of the development of geothermal resources in the United States, but interaction between the DOE and the hard rock mining industry has been minimal. In early 2010, SRK Consulting U.S. Inc. (SRK) was contracted to conduct a cooperative investigation of hydrogeologic and geothermal resources at a site in the Black Rock Desert of northern Nevada for the purpose of future mineral development. The hydrogeologic data collected for aquifer characterization and the methods used to collect these data were also used to characterize the geothermal resources within the project area. Initial characterization studies of the geothermal resources were conducted concurrently with mineral resource exploration under an approved mining exploration plan of operations issued through the U.S. Bureau of Land Management (BLM). Characterization and hydraulic testing of structures identified to be influencing or contributing to the hydrothermal regime of the project area were conducted using exploration core drill rigs. Hydraulic testing occurred in HQ (3.75-inch OD) size core holes at depths ranging between 700 and 2,770 feet below ground surface and in temperatures ranging between 110° and 196° Fahrenheit (F). Presently, the acknowledged limit of conventional retrievable packer systems is approximately 175°F. The Standard Wireline Packer System (SWiPS®) manufactured by Inflatable Packers, Inc. was modified with guidance from SRK to provide zonal isolation for hydraulic testing across a series of structures that had corrosive properties, water temperatures near 200°F, and moderate to high differential pressures during testing. Level TROLL® 700 Instrument pressure transducers, manufactured by In-Situ Inc., were utilized as the actual data collection mechanism within the SWiPS. Isolation of specific testing zones using the SWiPS allowed for quality characterization of the hydraulic conductivity, transmissivity, temperature, and chemistry of the water representing a relatively shallow geothermal system. The findings of this case study documented that the collection of hydraulic data across geothermal systems, utilizing low cost core drilling methods and the SWiPS, proved to be an effective means to significantly reduce the cost of traditional geothermal exploration drilling and data collection for preliminary geothermal resource characterization, evaluation, and development. Additionally, this case study identified that combining geothermal exploration permitting with conventional mineral exploration permitting could be advantageous in the collection of geothermal data due to the short permit turnaround period associated with a smaller disturbance area. Copyright © (2014) by the Geothermal Resources Council.

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