Water Stewardship Information Sources
| Citation | Newton, P and Gilchrist, A. 2010. Technical summary of intrinsit vulnerability mapping methods for Vancouver Island: Wancouver Island Water Resources Vulnerability Mapping Project - Phase 2. Vancouver Island University. |
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| Organization | Vancouver Island University |
| URL | https://web.viu.ca/groundwater/PDF/VI_DRASTIC_Summary_Phase2_2010.pdf |
| Abstract/Description or Keywords | The Vancouver Island Water Resources Vulnerability Mapping Project (VMP) was initiated in 2006 by the Vancouver Island Watershed Protection Steering Committee, with a goal of improving landuse decision-making tools concerning the preservation of groundwater quality. The VMP is a collaborative project between the BC Ministry of Environment, Vancouver Island University, Natural Resources Canada, and the Vancouver Island Health Authority. It was determined that intrinsic vulnerability maps would be developed to characterize the vulnerability of aquifers to contamination. Effective tools for decision-makers, these vulnerability maps identify where aquifers are vulnerable to contamination from various high risk land-use activities. The DRASTIC methodology developed by the U.S. Environmental Protection Agency was used in the pilot study to complete intrinsic groundwater vulnerability mapping for two of the seven regional districts on Vancouver Island – Nanaimo (RDN) and Cowichan Valley (CVRD). This methodology identifies seven parameters that influence groundwater vulnerability, each represented by a letter in the DRASTIC acronym: D – Depth to water, R – net Recharge, A – Aquifer medium, S – Soil medium, T – Topography, I – Impact of the vadose zone, and C – hydraulic Conductivity. All parameters are combined using an equation to determine areas of high, moderate, and low aquifer vulnerability. The pilot study was completed in 2009, and work began on phase 2 of the VMP with two primary objectives. The study area was expanded to derive intrinsic vulnerability maps for all regional districts of Vancouver Island, and many of the manual processes used to complete the pilot study analysis were automated. Although the specific processes varied, the methodology used to complete the phase 2 analysis was similar to the pilot study. Two notable exceptions include the use of terrain mapping in place of soil surveys, and the assumption that the upper-most surficial aquifers on Vancouver Island aquifers may not be truly confined. Phase 2 of the VMP used many of the same datasets as the pilot study to complete the intrinsic vulnerability analysis. Again, key datasets included the BC WELLS database, and aquifer maps provided by the BC Ministry of Environment. Terrain mapping was also an essential dataset, as digital soils mapping was not available for the entire island. As with the pilot study, the phase 2 analysis was completed on a regional scale, for all seven of the Vancouver Island regional districts. Results of the phase 2 intrinsic vulnerability analysis indicate that surficial aquifers represent moderate to high intrinsic vulnerability due to the lack of consistent confining layers and the resulting increased permeability of the vadose zone, in addition to higher aquifer media and hydraulic conductivity ratings, and the relatively shallow depth to water. Bedrock aquifers generally have low intrinsic vulnerability, due to their low aquifer media, vadose zone and hydraulic conductivity ratings, and their greater depth to water. This document details the methodology used to produce intrinsic vulnerability mapping for all regional districts of Vancouver Island. However, because the phase 2 analysis was largely based on methods used to complete the pilot study, this document focuses on the differences used to complete the phase 2 assessment. It should be used in conjunction with the pilot study report (Liggett and Gilchrist, 2010), to update the vulnerability maps in the future. |
| Information Type | report |
| Regional Watershed | Vancouver Island North, Vancouver Island South |
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| Project status | complete |
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