Lower Nanaimo Group

Hydrostratigraphic Unit

Project
Nanaimo Lowlands

Update:2016-02-03

Physiography
The Lower Nanaimo Group is a terrestrial to marine succession formed within a basin during the orogenic development of the Canadian Cordillera in Jurassic-Cretaceous time. It is up to 4 km thick and consists of 11 interfingering sandstone-dominated and shale-dominated formations. In the study area, only the lower 8 formations are present. The dominant bedrock units are the Comox and Haslam formations, which are regarded as aquifer of moderate and low capacity. The Comox Formation sandstone/conglomerate is commonly between 100-150 m thick, and is overlain by Haslam Formation shale that is 100-150 m thick.
Hydrogeological region	Cordillera
Hydrogeological context
Relief	The regional topography ranges from sea level at the coast, up to 1819 m (Mount Arrowsmith). The coastal plain terrain is sub-horizontal with slopes lower than 6% except along incised rivers valleys (up to 20%).
Area	380.00 km2
Lithology
Description	In the study zone, the unit consists of 8 interfingering sandstone-dominated and shale-dominated formations.
Source
Aquifer
Aquifers

Bedrock aquifer media


Typical value:	porous
Description	sedimentary bedrock

Confinement

Typical value:	confined

Groundwater storage

Description	Specific stockage: 3.3E-6 (1/m)

Hydrogeological unit thickness
4000 m

Well depth
Range: [21.3 to 93.9] m

Groundwater depth


Bedrock hydraulic conductivity
Range: [1e-10 to 0.0005] m/s
Source	Compendium of Re-evaluated Pumping Tests in the Regional District of Nanaimo, British Columbia

Regional precipitation

Description	The total precipitation is typically up to 5000mm in the mountains (Mount Arrowsmith) (Waterline, 2013).
Source	Regional District of Nanaimo Phase One Water Budget Project

Regional recharge

Description	Recharge of the unit: 30 mm/yr

Regional discharge

Description	The regional analysis of the water budget reveals that 71% of the groundwater is discharging to surface water bodies, whereas the remaining 29% discharges along the coast of the Strait of Georgia. The groundwater in bedrock essentially drains toward the coast.

Hydrogeological unit potential

Typical value:	medium - low

Aquifer vulnerability

Typical value:	low

Threats

Description	saltwater intrusion caused by pumping