PlaceDossier / BC places / Aquifers
BC aquifer 186 · sand and gravel · 17 km² · Cowichan Valley
Aquifer 186: Lower Cowichan River A
Aquifer 186 (Lower Cowichan River A) is an unconfined sand and gravel (medium stream system) aquifer of 17 km² in the Cowichan Valley Regional District, mapped in 2020. The province rates its productivity high, its vulnerability to contamination from the surface high, and the demand on it high. 207 wells on record are linked to it; water-supply wells there are typically 16.8 m deep and tested at a median 379 L/min. It lies under North Cowichan (17%), Cowichan Valley, Electoral Area D (15%), Cowichan Valley, Electoral Area E (10%), Duncan (8%).
How the province rates it
Productivity high, vulnerability high, demand high.
| Rating | What it means | |
|---|---|---|
| Productivity how much water the aquifer gives up to wells, judged from well yields, the aquifer material and pumping tests | high | Wells here tend to yield well: the guide puts high productivity at coarse sand and gravel, or typical well yields over about 3 L/s (180 L/min). |
| Vulnerability how easily something spilled at the ground surface could reach the water, judged from what lies above the aquifer and how deep the water is | high (class A) | Little natural protection (the guide's class A): a shallow water table or sand and gravel above it lets surface water and spills soak down quickly. |
| Demand how much the aquifer is used now, judged from the number and density of wells and what they're used for | high | Heavily used: where homes rely on private wells, the guide's heavy band is over 20 domestic wells per km². |
| Level of development Inferred demand compared with productivity | Heavy or moderate (class I or II) | Read by us from the guide's table of demand against productivity; where it gives two classes the mapper chose with local knowledge. Heavy (I): new wells should be carefully assessed; moderate (II): given careful thought; light (III): more use is usually fine if the aquifer can supply it. |
Ratings are the province's, set when the aquifer was mapped (2020) from wells, geology and local studies. Vulnerability is about the ground, not what's built on it: a well-protected aquifer under a busy area can still be at more risk than an exposed one in the bush.
Sources: Ground Water Aquifers, Water Protection and Sustainability Branch, Province of BC and Groundwater Wells (GWELLS), Province of BC, as published on October 1, 2026 (Open Government Licence – British Columbia); ratings explained after Berardinucci and Ronneseth (2002), Guide to Using the BC Aquifer Classification Maps for the Protection and Management of Groundwater, BC Ministry of Water, Land and Air Protection. Summaries by PlaceDossier.
The wells in it
207 wells on record are linked to this aquifer.
| Wells linked | 207 (106 water-supply) |
|---|---|
| Water-supply well depth | median 16.8 m; middle half 10.1 m to 23 m (103 wells) |
| Tested yield | median 379 L/min; middle half 75.7 L/min to 3,785 L/min (77 wells tested) |
| Water level below ground | median 2.7 m when drilled (71 wells) |
| Drilled | 1950 to 2018 |
This aquifer's medianIts middle half of wellsAnother BC aquifer's median
Depths are how deep the driller finished the well; yields are the driller's test, often an hour or less, in litres per minute. A domestic well's yield is usually judged against the household's peak use; ask a driller what's enough for yours.
Where it is
Outline simplified by us from the provincial map; not for locating a lot.
| Kind | Unconfined sand and gravel aquifer - medium stream system |
|---|---|
| Geological unit | Salish Sediments |
| Location, as described | Duncan |
| Area | 17 km² |
| Water use | Several uses (for example household wells, water systems, irrigation or industry) |
| Mapped | 2020 |
Unconfined: nothing tight lies over it, so rain and surface water soak straight down to it; the water table rises and falls with the seasons. The province's page for this aquifer lists the studies behind it and its observation wells: GWELLS aquifer 186.
Sources: Ground Water Aquifers, Water Protection and Sustainability Branch, Province of BC and Groundwater Wells (GWELLS), Province of BC, as published on October 1, 2026 (Open Government Licence – British Columbia); ratings explained after Berardinucci and Ronneseth (2002), Guide to Using the BC Aquifer Classification Maps for the Protection and Management of Groundwater, BC Ministry of Water, Land and Air Protection. Summaries by PlaceDossier.
What this record doesn't cover
The province maps aquifers where wells and studies give enough to go on, mostly in settled valleys; most of BC isn't mapped, and a lot outside every outline can still have groundwater. Outlines are drawn from geology and well logs at the scale of the study, so an edge can be well off on the ground, and one aquifer can lie under another. Wells are linked to an aquifer by provincial staff from the driller's log: not every well inside an outline is linked, and well depths and yields are as the driller reported them, often from a short test.
These are mapped ratings and drillers' records, not a test of any one lot. Before you buy a property on a well, or plan to drill, ask a qualified hydrogeologist or a registered well driller what this aquifer gives where you are, and test the water.