Articles
Go to Site Index See "Articles" main page
4th September 2023
EDITOR
Continued from Part 1

Whereas the ground surface in the vicinity of Cassidy and The Nanaimo Airport is essentially flat today, geological mapping of the top of the Cretaceous bedrock reveals a valley system which was eroded into it during and just after the last glacial period about 14,000 years ago.

Hydrogeology of the Cassidy aquifers

Hydrogeology refers to the movement of water within rocks and sediments.
The Cassidy area lies within the watershed of the Nanaimo River, which includes the Nanaimo River and its major tributaries such as Haslam Creek.

The majority of the watershed lies within the Nanaimo Regional District (NRD); the southernmost part of the watershed, including part of the Cassidy area, lies within the Cowichan Valley Regional District (CVRD).

Analysis of groundwater levels in observation wells provides some understanding of how water flows into and out of the various geologic units.

The Cretaceous bedrock of the area is an important aquifer to those living outside of the distribution of the fossil valley-fill sediments. The BC Provincial Aquifer database recognises two bedrock aquifers, numbered 162 and 964; the boundary between the two is roughly along a line continuing northwest parallel to the north shore of Ladysmith Harbour with 964 being west of this line and 162 east of it. Groundwater recharge for both aquifers is direct from rain, but due to the bedrock’s limited permeability and porosity it appears to be slow and care has to be taken not to over-produce from wells and running them dry. Fractures associated with faults in the bedrock appear to be an important factor in locally higher well production rates.

The water-bearing densely packed sands and gravels with moderate porosity and permeability of Valley-fill Unit 1 are numbered Aquifer 160 in the B.C. Provincial Aquifer database. There are relatively few well penetrations because it underlies a shallower good aquifer (Unit 3). Recharge occurs after a week’s lag following rainfall which indicates groundwater flows into it either from the underlying bedrock or via a slight connection to the overlying aquifer Unit 3. Aquifer 160 is termed a ‘confined’ aquifer due to its not being exposed at ground surface and because it is everywhere overlain by the impermeable claystone Unit 2. Only a few wells produce from aquifer 160; their low volume of production appears to have minimal effect as observation wells appear stable over time, the most recent data reviewed being from 2016.

The clay-rich ‘tight’ (ie non porous and impermeable) Unit 2 acts as a barrier to groundwater movement between Units 1 and 3 and is scientifically termed an ‘aquitard’.

Valley-fill Unit 3, numbered Aquifer 161 in the B.C. Provincial Aquifer database, is the most important aquifer in the area. Its high porosity and permeability sands and gravels provide good well flow rates. This aquifer is termed ‘unconfined’ due to its being exposed at the ground surface. While groundwater recharge is mainly direct from rainfall in the watershed, local recharge from streams has prompted its division into two connected aquifers (Figure 5iii) – Cassidy Aquifer 1 to the south which is locally recharged by Haslam Creek, and Cassidy Aquifer 2 in the north which is strongly influenced by the Nanaimo River. The strong recharge in the north from the Nanaimo River facilitates bulk water extraction for industrial purposes by Harmac. Data suggests that groundwater pumping significantly affects water levels in Aquifer 161. Proximity to recharge sources, such as the Nanaimo River, locally allows for a stable high rate extraction, but more work with up to date information for the southern Cassidy Aquifer 1 (most recent data seen by the author dates from 2016) is required for determination of how much water can be taken from this aquifer without long term decline in groundwater water levels occurring.

Except where locally overlain by the impermeable clay-rich Unit 4, the sands and gravels of Unit 3/Aquifer 161 are exposed at ground surface beneath a variable soil cover.

The regional map of groundwater elevations in wells in Aquifer 161 (Figure 7) indicates that, on average, groundwater flows from the uplands west of Cassidy and diverges from the central Cassidy area, northeastward towards the Nanaimo River and estuary, and southeastward toward Ladysmith Harbour. However, this regional picture may be locally modified by production from water wells – as extraction of water from a well reduces the pressure around that wellbore and prompts groundwater movement toward it. This can cause local ground water movement against the regional flow.
More detailed analysis of many wells in the area is required to determine whether this aquifer is being over-taxed by the current level of withdrawal from wells or not, and how surface contamination might travel within the aquifer.

Aquifer Vulnerability and Industrial Activity

Increased land development pressures in the early 2000s, coupled with industrial and agricultural land use activities that were considered to potentially threaten the quality of ground and surface water, prompted the CVRD to participate in a multi-year study which focussed on assessing the relative vulnerability of groundwater resources to surface contamination on Vancouver Island. This study was conducted jointly by the BC Ministry of Environment, Vancouver Island University, Natural Resources Canada, The Vancouver Island Health Authority and the Regional Districts on Vancouver Island. A rating system, called by the acronym ‘DRASTIC’ (relating to seven significant factors taken into account) was devised; each recognised aquifer was assigned a vulnerability rating of either Low, Moderate or High. A vulnerability map for surface aquifers on Vancouver Island was produced that shows high vulnerability in the Cassidy area

Of the Cassidy area aquifers:

Cretaceous bedrock aquifer 162 which outcrops over a wide area was considered of High Vulnerability to surface contamination entering via exposed high permeability fractures.

Although also recognised as possessing highly permeable fractured zones, Bedrock Aquifer 964 was rated of Moderate Vulnerability as it only locally outcrops at surface.

The unconsolidated confined Aquifer 160 (valley-fill Unit 1) is considered to have Low Vulnerability to contamination from surface sources as it does not outcrop at surface and is everywhere overlain by the aquitard Unit 2.

Aquifer 161 (valley-fill Unit 3), the porous and permeable sands and gravels of which are at ground surface over much of the Cassidy area, is considered of High Vulnerability to surface contamination.
The quoted vulnerability study also provided an example of appropriate hydrogeological assessment for development permit applications situated on various aquifer types. If Schnitzer’s Cassidy activities, which are located on top of High Vulnerability Aquifer 161, are considered as a commercial ‘junk yard’ and of moderate hazard for surface contamination, the following were deemed required for assessment of an application to conduct these activities at that location:
• a detailed groundwater site investigation including an ongoing monitoring program
• specifics of the potential contaminants (toxicity, quantity, transport behaviour),
• details on the protection design factors (natural attenuation, physical barriers, etc.)
• A detailed emergency response plan
• An assessment of the financial capacity of the responsible party to enact the plan.

However, if Schnitzer’s activities are considered as an industrial activity posing a high risk of surface contamination to the aquifer, the possibility of complete prohibition of those activities is cited.

What the Neighbours Think

The southern portion of Aquifer 161 straddles the boundary between the regional districts of Nanaimo and the Cowichan Valley, with Schnitzer’s activities being located immediately adjacent to the boundary on the CVRD side. Given the high permeability of Aquifer 161 and its deemed High Vulnerability to surface contaminants, it seems reasonable to assume that the Regional District of Nanaimo (RDN) is interested in what the CVRD decides regarding Schnitzer’s rezoning application. ‘Actions and Best Practices’ cited from a 2010 RDN “Groundwater Assessment and Vulnerability Study” by GW Solutions Inc. indicates that industrial activities in a high vulnerability aquifer zone are not recommended and that auto-wreck yards are not allowed in such zones.

Thank you to Dr. Quentin Goodbody for this explanation of how aquifers work.

Information Sources for Cassidy Aquifers

Barroso, S., R. Ormond, and P. Lapcevic (2016). Groundwater quality survey of aquifers in South Wellington, Cassidy and North Oyster, Vancouver Island. Prov. B.C., Victoria B.C., Water Science Series 2016‐05.

CVRD April 11th 2018: CVRD Bylaw No. 4194 – Electoral Area H – North Oyster/Diamond Official Community Plan Amendment Bylaw (13271 Simpson Road), 2018.

CVRD April 11th 2018: CVRD Bylaw No. 4195 – Electoral Area H – North Oyster/Diamond Zoning Amendment Bylaw (13271 Simpson Road), 2018

CVRD: May 3rd 2023: Staff Report to Electoral Area Services Committee Meeting from Community Planning Division, Land Use Services Department re: Application No. 03-H-16 S (PID. 008-903-603/Schnitzer Steel) plus attachment A: Draft Covenant and Schnitzer Steel Canada Ltd. Cassidy Facility Stormwater Maintenance Plan for Equipment maintenance and ELV Concrete Slab.

CVRD: May 3rd 2023: Electoral Area Services Committee Meeting Agenda and Minutes

CVRD: May 10th 2023: Minutes of the Regular meeting of the Board of the Cowichan Valley Regional District held in the Board Room, located at 175 Ingram Street, Duncan BC, on Wednesday, May 10, 2023 at 1:32 PM.

CVRD: July 19th 2023: Agenda of The Electoral Area Services Committee Meeting of July 19th 2023: Item 7: Information: Public Meeting Minutes Re: Application No. 03-H-16RS (Schnitzer Steel) – June 19, 2023.

Government of British Columbia: Ground Water Wells and Aquifers
https://apps.nrs.gov.bc.ca/gwells/aquifers

GW Solutions Inc. August 2017. STATE OF OUR AQUIFERS. Regional District of Nanaimo Aquifer 160. Report prepared for The Regional District of Nanaimo

GW Solutions Inc. August 2017. STATE OF OUR AQUIFERS. Regional District of Nanaimo Aquifer 161. Report prepared for The Regional District of Nanaimo

Liggett, J., Gilchrist, A. 2010: Technical Summary of Intrinsic Vulnerability Mapping Methods in the Regional Districts of Nanaimo and Cowichan Valley, Geological Survey of Canada, Open File 6168, 64 p.
Liggett, J., Lapcevik, P., Miller, K. 2011. A Guide to the Use of Intrinsic Aquifer Vulnerability Mapping. Report to the CVRD on the work of the Vancouver Island Water Resources Vulnerability Mapping Project., 60 p.

Take5 June 2023: 5 Minute Read: Cassidy Aquifer: https://issuu.com/take5publications/docs/online_take5_june_23.indd/s/25414243

Thurber Engineering Ltd: 2007. City of Nanaimo Engineering & Public Works Department Cassidy Aquifer Water Balance Study Completion Report.
Town of Ladysmith 2023: https://www.ladysmith.ca/sustainability-green-living/sustainability-program/watershed-protection

Waterline Resources Inc. 2013: Phase 1 Water Budget Project: RDN Phase 1 (Vancouver Island) submitted to the Drinking Water and Watershed Protection Technical Advisory Committee pages 160-190: Water Region # 6 – Nanaimo River

https://www.ladysmithhistoricalsociety.ca/?s=Cassidy+Aquifer