Groundwater vulnerability to potential contamination in the Annapolis Valley, Nova Scotia.

摘要

The Geological Survey of Canada, in conjunction with various partners, has been undertaking a groundwater characterization project in the Annapolis Valley, Nova Scotia for the past three years. This thesis contributes towards this project through the modelling of groundwater vulnerability in the Annapolis Valley region. The groundwater vulnerability modelling utilized the concept that the degree of potential vulnerability to contamination can be mapped as a function of selected hydrologic conditions. A regional view of the vulnerability to potential contamination of groundwater resources within the Annapolis Valley was modelled using the DRASTIC methodology. This index-overlay method included the seven hydrogeologic parameters of Depth to water, net Recharge, Aquifer media, Soil media, Topography, Impact of the vadose zone, and hydraulic Conductivity, and was programmed using object modelling available in ArcGIS.; Several groundwater vulnerability scenarios were determined to take into account issues with data quality, data quantity, and potential hydrogeologic conditions variability. The resulting groundwater vulnerability for both bedrock and surficial aquifers was examined for each scenario and compared. This exercise indicated that the vulnerability model produced by the DRASTIC method can be significantly altered by seemingly minor variations in data precision and accuracy for discreet parameters. Some of those parameters that have the highest impact in the results (net recharge, depth to water, and impact of the vadose zone) commonly exhibit low dataset precision and accuracy, which is an important consideration in the establishment of groundwater protection and monitoring programs. Vulnerability results vary according to, and within, each geological unit, although generally surficial units are significantly more vulnerable than bedrock units. The bedrock (Wolfville and Blomidon formations) and surficial (sand and gravel) units believed most promising in terms of aquifer quantity and quality were found to be the units potentially most vulnerable to contamination.