|Résumé||(Sommaire disponible en anglais seulement)|
The Vancouver Island Region Watershed Protection Steering Committee initiated a collaborative project beginning in 2006 between the BC Ministry of
Environment, Vancouver Island University, Natural Resources Canada, Vancouver Island Health Authority and Regional Districts on Vancouver Island to assess the relative vulnerability of the groundwater resources to contamination from surface sources.
The need for this type of assessment was highlighted by increased development pressures coupled with industrial and agricultural land use activities that may threaten the quality of ground and surface water supplies. The vulnerability of aquifers to
contamination needed to be characterized in order to be considered alongside other social, economic and environmental priorities for Vancouver Island and the province, as part of the comprehensive land use planning process.
The project team
decided to develop "intrinsic aquifer vulnerability maps" as an initial phase of the project since this type of mapping has proven to be an efficient tool for assisting in decision-making by prioritizing regions of concern with respect to
groundwater. Local governments, planners, and policy makers can use these maps to enable land-use decisions that take into consideration the sensitivity of the groundwater resources, encourage sustainable development, identify sensitive areas, plan
monitoring strategies, and focus remediation efforts. An existing aquifer vulnerability methodology developed by the US Environmental Protection Agency, known as DRASTIC, was employed in the assessment. DRASTIC is an acronym for the seven parameters
that can influence the vulnerability of a groundwater resource: D - Depth to water, R - (net) Recharge, A - Aquifer medium, S - Soil medium, T - Topography (slope), I - Impact of vadose zone and C - (hydraulic) Conductivity. These parameters are
combined in an equation that is used to produce the resultant map that identifies areas of relative (higher and lower) vulnerability.
Several information sources were analyzed to create the aquifer vulnerability maps. Key datasets include the
British Columbia Ministry of Environment's application (WELLS) that comprises a database of water-well construction records and mapped aquifer delineations. Other important information sources include soil surveys, precipitation data, a digital
elevation model and terrain classification. To address issues such as scope and consistent data coverage, the project team divided the Island by regional district boundaries to complete the intrinsic aquifer vulnerability assessment. Assessments for
the regional districts of Nanaimo (RDN) and Cowichan Valley (CVRD) were completed and are discussed in this report. The assessments for these two regional districts also allowed the project team to fine-tune the assessment to the characteristics of
Vancouver Island before the methodology is applied to the remainder of Vancouver Island. To ensure that the outputs of this project were relevant to decision-makers, staff from both the RDN and CVRD were involved in all stages of the project.
Results of the intrinsic aquifer vulnerability assessment for RDN and CVRD indicate that confined unconsolidated aquifers represent moderate to low intrinsic vulnerability due to the presence of a confining layer with low vadose zone
permeability, combined with a slightly deeper depth to water. Unconfined, unconsolidated aquifers have a higher intrinsic vulnerability due to their relatively shallow depth to water, and permeable vadose zone and aquifer medium (reflected in the A
and C parameters). Consolidated (i.e. bedrock) aquifers have a generally moderate to low intrinsic vulnerability due to their deeper depth to water, low permeability aquifer medium, conductivity, and vadose zone ratings.
This document details the
methods used to produce intrinsic aquifer vulnerability maps for the RDN and CVRD study area, and may be used to update these maps in the future or guide the application of these methods to other areas of Vancouver Island.
The project and this
document were completed in 2009 but formally published at a later date. The contents of the report have not been altered since 2009.