INTRINSIC SENSITIVITY AND AQUIFER VULNERABILITY IN THE COLD LAKE-BEAVER RIVER BASIN, ALBERTA, CANADA. Tony Lemay, Energy and Utilities Board Alberta Geological Survey, Edmonton, Alberta, Canada ABSTRACT The Alberta Geological Survey (AGS) recently completed both an assessment of the natural suitability of the geological setting of Alberta for waste management, and a compilation of potential sources of contamination within the Cold Lake Beaver River Basin (CLBRB). The natural suitability map can be used as an analogue of intrinsic sensitivity of aquifers within the CLBRB while the location of potential sources of contamination can pinpoint areas where aquifers are more vulnerable to contamination within the Basin. In plotting the location of potential sources of contamination, it becomes apparent that certain portions of the CLBRB are vulnerable to multiple potential sources of contamination. This assessment of intrinsic sensitivity and vulnerability of aquifers in the area could help to understand potential contamination risks as well as assist in the creation of management plans that can help avoid or address such risks. RÉSUMÉ Le Alberta Geological Survey (AGS) a récemment complété une enquête évaluative provinciale sure l appropriation naturelle des matériaux géologiques pour le contrôle des déchets. Le AGS vient aussi d achever une compilation de sources potentielles de contamination dans la région du Basin du Lac Cold Rivière Beaver (BLCRB). La carte de l appropriation naturelle peut être utilisée comme analogue d une sensibilité intrinsèque des aquifères dans la région; alors que la localisation des sources potentielles de contamination peut indiquer des endroits ou les aquifères sont le plus vulnérable à la contamination ans cette région. En traçant les endroits des sources potentielles de contamination, il c est avéré que certaines portions du site BLCRB sont vulnérables à plusieurs types potentiels de contamination. Cette évaluation de la sensibilité intrinsèque et de la vulnérabilité des aquifères dans la région peut apporter une meilleure compréhension des risques potentiels de contamination et peut aider dans la création de plans de gérance pour adresser ces risques et les contrôler. 1. INTRODUCTION groundwater contamination through anthropogenic means. The Cold Lake-Beaver River Basin (CLBRB) in Alberta is located in east-central Alberta, Canada (Figure 1). It extends from approximately 54 o North Latitude to 55.5 o North Latitude and from 110 o West Longitude to 113 o West Longitude. In Canadian National Topographic System coordinates, it occupies most of the 73L 1:250,000 map sheet, with parts overflowing into the 73M map sheet and in a more minor way, into adjoining sheets. In the Canadian Dominion Land Survey coordinates, the southeast corner of the Basin is at approximately Township 56 Range 1 W4 and extends northward as far as Township 78 and westward as far as Range 19 W4. Groundwater is used in the CLBRB for household, agricultural, municipal and industrial purposes. A number of chemical constituents of concern have been documented in groundwater within the Basin, including arsenic and phenols. These constituents could be naturally occurring based upon the chemical composition of aquifer and aquitard materials within the Basin, but can also be released as a result of anthropogenic activities. The area economy and population are growing and with this continued growth comes increased demand on the existing groundwater resource. A possible consequence from continued activity in the area is the increased risk of Figure 1. Study area. 1301
The combination of naturally occurring constituents of concern along with the possibility of anthropogenic impacts on groundwater suggests that management of groundwater from a quality perspective will be challenging. In order to develop such a management plan, the Alberta Geological Survey in conjunction with Alberta Environment undertook an assessment of groundwater quality as well as an initial assessment of intrinsic sensitivity and aquifer vulnerability within the CLBRB (Lemay, 2004). A subsequent Provincial assessment of natural suitability of the geological setting for waste management (Andriashek and Waters, 2005) offers an opportunity to reassess the intrinsic sensitivity and aquifer vulnerability in the area in light of this new information. sensitivity and vulnerability and is well suited for a preliminary assessment. 2. METHODOLOGY Focazio et al. (2002) define intrinsic sensitivity as, a measure of the ease with which water enters and moves through an aquifer; it is a characteristic of the aquifer and overlying material and hydrologic conditions, and is independent of the chemical characteristics of the contaminant and its sources. Whereas aquifer vulnerability as defined by Focazio et al. (2002) is a function not only of the properties of the groundwater flow system, but also of the proximity of contaminant sources, characteristics of the contaminant, and other factors that could potentially increase loads of specified contaminants to the aquifer and (or) their eventual delivery to a groundwater resource. Based on these definitions, the determinations of intrinsic sensitivity and vulnerability require a good understanding of; 1) the geology of the study area, 2) the hydrologic conditions within the study area; and 3) the potential sources of contamination within the study area. The assessment of intrinsic sensitivity and aquifer vulnerability for the study area begins with a characterization of the geological conditions within the area. The most recent assessment of the geological material properties of the area was completed by Andriashek and Waters (2005). They compiled and used information on surficial geology, drift thickness, the presence of buried channels in the subsurface, and bedrock geology to assess the natural suitability of the geological setting of Alberta for waste management. The modified process is described in the following diagram (Figure 2).This assessment was designed to examine the geological setting only and so does not fully meet all of the necessary information requirements proposed by Focazio et al. (2002) to determine intrinsic sensitivity. Despite this fact, the information provided by Andriashek and Waters (2005) is used in this paper as the basis for describing intrinsic sensitivity. It is proposed, that the determination of intrinsic sensitivity based on geology alone generates a more conservative estimate of Figure 2. Decision tree for determining suitability of geological setting for waste management (modified from Andriashek and Waters, 2005) Aquifer vulnerability was determined by combining the intrinsic sensitivity map with the locations of potential sources of contamination. These sources of contamination were compiled from various governmental bodies and industrial sectors. For discussion purposes, the following possible sources of contamination are used as examples: urban development; agricultural land use; and certain oil and gas development activities. 3. RESULTS 3.1 Aquifer sensitivity The result of the process outlined in Figure 2 is presented in Figure 3. The most sensitive areas are the areas in dark grey. These areas are generally located in the vicinity of river channels, but are also located where geologic processes have deposited coarser-grained materials at or near the land surface, where thin glacial drift is present above permeable bedrock, and in the vicinity of buried channel deposits. The areas in light gray represent the areas where the geological characteristics of the surface and subsurface materials suggest that they are relatively impermeable and are therefore the least intrinsically sensitive. This is the dominant sensitivity category within the Basin. 1302
Figure 3. Intrinsic sensitivity within the study area based on geological suitability criteria. 1303
3.2 Aquifer vulnerability Aquifers will be vulnerable to contamination where the aquifer is considered sensitive and a potential source of contamination is present. There are a number of potential sources of contamination within the Basin. By overlaying the aquifer intrinsic sensitivity map with the locations of urban infrastructure (Figure 4), actual or potential agricultural land use areas (Figure 5) and certain types of oil and gas development (Figure 6), an assessment of aquifer vulnerability can be determined. Upon closer examination the potential exists for aquifers to be vulnerable to multiple types of potential contamination as areas of urban development, agricultural land use, confined feeding operations, oil and gas facilities, and pipelines are located in some of the same sensitive areas of the intrinsic sensitivity map. 4. CONCLUSIONS The collection of information on the geological material in the Basin allowed for the assessment of aquifer intrinsic sensitivity to contamination. Information compiled on agricultural land use, industrial activity, and urban development can be combined with the above sensitivity analysis to develop aquifer vulnerability maps that can be used to guide decisions regarding monitoring requirements, site construction requirements, and the future development options for certain portions of the Basin. The locations of potential sources of contamination indicate that many of the sensitive areas may be vulnerable to multiple potential sources of contamination and suggest that management of these areas will require careful consideration of this fact. References Andriashek, L.D. and Waters, E.J. 2005. Natural suitability of geological setting for waste management, Alberta Energy and Utilities Board, Map 330. Focazio, M.J., Reilly, T.E., Rupert, M.G., and Helsel, D.R. 2002. Assessing ground-water vulnerability to contamination: providing scientifically defensible information for decision makers, United States Geological Survey, Circular 1224. Lemay, T.G. 2004. Regional groundwater quality appraisal, Cold Lake Beaver River Drainage Basin, Alberta, Alberta Energy and Utilities Board, Special Report 73. 1304
Sea to Sky Geotechnique 2006 Figure 4. Aquifer vulnerability to potential contamination from urban development. 1305
Sea to Sky Geotechnique 2006 Figure 5. Aquifer vulnerability to potential contamination from actual or potential agricultural land use. 1306
Sea to Sky Geotechnique 2006 Figure 6. Aquifer vulnerability to potential contamination from oil and gas facilities, batteries or pipelines. 1307