PlaceDossier / BC places / Aquifers
BC aquifer 206 · sand and gravel · 16 km² · Cowichan Valley
Aquifer 206: Mill Bay
Aquifer 206 (Mill Bay) is an unconfined sand and gravel (late glacial outwash) aquifer of 16 km² in the Cowichan Valley Regional District, mapped in 2019. The province rates its vulnerability to contamination from the surface high; its productivity and demand are not rated. 240 wells on record are linked to it; water-supply wells there are typically 24.1 m deep and tested at a median 37.9 L/min. It lies under Cowichan Valley, Electoral Area A (57%), Cowichan Valley, Electoral Area B (28%), Cowichan Valley, Electoral Area C (15%).
How the province rates it
Productivity not rated, vulnerability high, demand not rated.
| Rating | What it means | |
|---|---|---|
| Productivity how much water the aquifer gives up to wells, judged from well yields, the aquifer material and pumping tests | not rated | The province hasn't rated this for this aquifer. |
| 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 | not rated | The province hasn't rated this for this aquifer. |
| Level of development Inferred demand compared with productivity | unclear | Unclear: the province hasn't rated both demand and productivity. |
Ratings are the province's, set when the aquifer was mapped (2019) 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
240 wells on record are linked to this aquifer.
| Wells linked | 240 (142 water-supply) |
|---|---|
| Water-supply well depth | median 24.1 m; middle half 16.8 m to 42.4 m (141 wells) |
| Tested yield | median 37.9 L/min; middle half 22.7 L/min to 75.7 L/min (123 wells tested) |
| Water level below ground | median 14.5 m when drilled (100 wells) |
| Flowing (artesian) wells | 5: water rose to or above the ground when drilled |
| Drilled | 1950 to 2021 |
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 - late glacial outwash |
|---|---|
| Geological unit | Quadra Sand/ Dashwood Drift |
| Location, as described | Mill Bay and Cobble Hill |
| Area | 16 km² |
| Water quality concerns | Local: concerns documented across part of the aquifer |
| Mapped | 2019 |
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 206.
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.