HYDROSTRATIGRAPHIC ANALYSIS OF A QUADRA SAND AQUIFER, COMOX, BC

The hydrostratigraphy is assessed and modeled for the Comox-Merville aquifer as part of a Masters of Science research project. Situated within Vancouver Island's eastern coastal lowlands, the aquifer borders the Beaufort Mountain range to the west and the Georgia Strait to the east. The aquifer overlies Upper Cretaceous Nanaimo Group sedimentary bedrock and trends northwest-southeast, spanning approximately 150 square kilometers. Classified as moderately developed and having a low level of vulnerability to surface contamination, this aquifer is a primary groundwater supply for the local communities.

Previous mapping has established the Comox-Merville aquifer as Late Pleistocene Quadra Sand. This lithostratigraphic unit is widely spread throughout the Georgia Depression and Puget Lowland, and consists of horizontally and cross-stratified, well-sorted sand with minor silt and gravel. Previous provenance and paleocurrent studies have determined that the Quadra Sand was sourced from the Coast Mountains to the northeast and deposited in front of ice advancing south down the Georgia Depression. The unit is time-transgressive and has been dated as older than 29000 C-14 years in northern Georgia Strait and younger than 15000 C-14 years in southern Puget Sound.

Over 700 groundwater wells developed within this aquifer are being investigated for hydrostratigraphic information. The drilling logs are lithologically standardized and then mapped using a 2.5-D subsurface modeling software. In this manner, discreet units logged by each well are correlated to form surfaces marking the contact between two successive units. A spatial depiction of the aquifer's interpreted subsurface hydrostratigraphy is thus created. Field observations along the aquifer's coastal exposures are incorporated into the model in order to calibrate the well logs. Groundwater well yields and screened intervals are combined with field observations and local groundwater knowledge to further understand and model the hydrogeologic regime of the Comox-Merville aquifer in its entirety.