Water Stewardship Information Sources

Citation Liggett, JE and Gilchrist, A. 2013. Technical summary of intrinsic vulnerability mapping methods in the Regional Districts of Nanaimo and Cowichan Vallye, British Columbia (2010). Geological Survey of Canada Open File 6168.
Organization NRCAN
URL http://wmsmir.cits.rncan.gc.ca/index.html/pub/geott/ess_pubs/287/287315/of_6168.pdf
Abstract/Description or Keywords 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.
Information Type report, mapping
Regional Watershed Vancouver Island South
Sub-watershed if known Cowichan, Nanaimo
Aquifer #
Project status complete
Contact Name
Contact Email