INNOVATION March-April 2012

f ea t u r e s

the methane:ethane (C1:C2) ratio is a good indicator of the ther- mogenic (C1/C2 < 50) or biogenic (C1/C2 > 100) origin of the gases, however this ratio alone is inadequate for identification involved with dispute resolution because subsurface migration of hydrocarbon gases may allow methane oxidation thus compro- mising the ratio. Consequently, a simple scan of inorganics, C1 and C2, as used in Pennsylvania, is inadequate for identification associ- ated with dispute resolution. A more conclusive approach to assess the origin of hydrocarbon gases is the carbon and hydro- gen isotope analysis of methane. As shown in Figure 2, this analysis reveals discrete domains that point to the origin of the methane, ie, biogenic gas common in Quaternary bedrock valley aquifers (eg, Alliston, Ontario) or deep reservoir gas of thermogenic origin. Additionally, radiocarbon (14C) measure- ments can distinguish between methane from Quaternary organic sources (ie, biogenic) and from thermogenic sources associated with Paleozoic or Mesozoic hydrocarbon reservoirs. Aquifers of Northeast BC Fifty-five shallow freshwater aquifers have been mapped to date by Lowen Hydrogeology Consulting in the Peace River area of North- eastern British Columbia. (Their locations can be viewed at the Min- istry of Environment’s BC Water Resources Atlas website www.env. gov.bc.ca/wsd/data_searches/wrbc/index). These unconsolidated and Golder Associates, one of the most respected ground engineering and environmental services teams in the world, has immediate openings in its Santiago office. As a career springboard, this is an extraordinary opportunity. You’ll work on world-class mining projects and live in one of South America’s most vibrant and modern cities, enjoying a comfortable lifestyle and access to Chile’s famed natural wealth. I urge you to contact me if you have experience in mining or mine-waste and you fit one of these two profiles: n Proven technical and problem-solving experience, along with strong analysis, design and writing skills n Strong communication skills and an ability to lead large projects with multidisciplinary engineering and science teams As part of the global Golder team, you’ll have access to employee- ownership, our strong values and a culture that recognises excellence and rewards innovation. While Spanish would be an asset, it is not essential. Rediscover Geotechnical Engineering in Chile

bedrock aquifers have been identified mainly on the basis of water well records from domestic, municipal, agricultural and industrial wells that range from 10 to 250 m in depth. Only developed (ie, cur- rently used) aquifers are mapped. Freshwater aquifers exist through- out Northeastern BC and the blank areas where no aquifers have been mapped simply mean that no data (primarily from water well records) were available at the time of mapping. Deep bedrock aquifers (> 250 m below surface) often containing non-potable saline groundwater have also been identified through oil and gas drilling activities. Aquifer Type Two categories of freshwater aquifers are reported, namely (a) uncon- solidated aquifers (32 of 55) and (b) bedrock aquifers (23 of 55). Unconsolidated aquifers are composed of sand and gravel, deposited before, during and after the last major glaciation that affected the region during the Quaternary Period (the last 2.5 mil- lion years). These deposits overlie bedrock and in some instances are hydraulically connected with bedrock aquifers. The majority of the unconsolidated aquifers identified are located along the main river valleys (Peace, Pine and Halfway Rivers). Many are hydrauli- cally connected in part to adjoining surface waters. In these areas, large capacity water supply wells have been completed in glacioflu- vial deposits for the communities at Tumbler Ridge, Fort St John, west of Taylor and Pouce Coupe. Aquifers found in preglacial and interglacial valleys are of special significance in the region. These incised bedrock-channel systems comprise valleys that existed prior to glaciation (pregla- cial valleys) and those that were cut into bedrock during the Pleis- tocene Epoch (glacial or interglacial valleys). Both types of buried valleys occur in the region and may be partly or completely filled with glacial sediments. Some contain sand and gravel aquifers, hence they are important targets for groundwater exploration. Groundwater flow systems within unconsolidated aquifers can be readily monitored with a limited number of observation wells that measure water levels (hydraulic head) and water quality. Bedrock aquifers include various bedrock formations that contain water within primary (intergranular) and secondary (fracture, solution channel and bedding plane) porosity. Region- ally, the main bedrock aquifers include permeable zones within the Dunvegan Formation of Upper Cretaceous age and overlying formations dominated by competent sandstone strata such as the Kaskapau Formation. The Dunvegan and Kaskapau contain zones of potable groundwater unlike deeper saline aquifers. Coal and fractured shale beds in some areas may also produce water. Groundwater flow systems in the bedrock are more complex and require detailed stratigraphic information and multi-level hydraulic head determinations with depth and over larger areas to be fully understood. This has special significance for abandoned oil and gas wells that may not have been properly plugged and The BC Ministry of Environment classifies both unconsolidated and bedrock aquifers according to: (a) their level of development or use, from heavy (I) to moderate (II) to light (III); and (b) their intrinsic vulnerability to contamination from potential sources of pollutants discharged to the land, from high (A) to moderate (B) to low (C). This results in the possibility of nine aquifer classes ranging from, sealed, ie, “legacy wells.” Aquifer Classification

To learn more, e-mail Björn Weeks at: bweeks@golder.com www.golder.com/careers

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