Report says Potlatch proposal will not impact on streams or neighbouring wells

Derek Kilbourn

Sounder News

Tuesday, February 14 2017

The subdivision as proposed in the Potlatch Density Transfer application will not have a measurable impact on local streams and water licences, according to the report turned in to the Local Trust Committee (LTC) at this past week’s meeting.

R. Allan Dakin (P. Eng.) stated as much in both his written and verbal reports to the LTC.

The senior groundwater engineer said he has been consulting in the field for over 45 years and has done a number of projects on Gabriola.

“I was pleased to find the Trust and RDN had commissioned a number of studies to look at the whole island. That let me look at ‘the whole forest’ as it were.”

Dakin said his instructions were to study whether the proposed new wells would have an impact on existing groundwater users (the neighbours of the proposed subdivision area), and whether new wells would impact base surface streams and have other environmental impacts.

His recommendations to the LTC and the applicants were that if/when wells are put into the subdivision, they should be at least 30 metres apart, with the exception of proposed Lot 25 (the closest to the ocean) which he said should have it’s well 40m from the shoreline, and limit it’s pumping to less than three cubic metres per day.

In terms of whether a well is impacting a neighbour’s well, or even if a well is not producing water, Dakin said other information has to be taken into account when that happens.

“People say a well has gone dry - we ask people where is the pump set? Sometimes it turns out the pump is not set at the bottom or where the water comes in.

“Sometimes a pump has a very high capacity - it pumps five cubic metres per day very quickly - it will suck [the well] down to dry. But if [the well owner] had pumped at one fifth of that rate, they could have been drawing more water over a longer time and the pump would not have stalled.

“So there are other problems to be aware of with wells.” 

Dakin said while there are areas on Gabriola where wells may have measurable impacts on neighbouring wells, the proposed area “appears to be in surplus.”

He added that a difference might be if someone were putting in wells in a cluster of half-acre lots rather than in the case of the Potlatch application, where properties will be four or more acres in size.

Interestingly, as the Trustees pointed out, Dakin’s report did not include a recommendation to have the homes in the proposed subdivision utilize rainwater as a way to supplement their well usage.

He said the recharge during the winter would be enough to sustain the aquifer through the summers, as the proposed area sees a fluctuation of four metres between the summer and winter levels.

Dakin did suggest that for Lot 25, as well as other properties which may have a risk of salt water intrusion (if too much water is taken at once) - property owners would be wise to set up a storage cistern or pressure tank, so the property could slowly sip water from the well, but still have the water available for high usage times.

Asked why there were no pump tests done as part of the study, Dakin said it was not necessary, nor “required by any kind of guideline.”

“It’s an expensive thing to do - and if you run a pump test on one well, then you run one on all wells....if this was a subdivision where water supply was supplying the whole subdivision, then it would be mandatory - but then you’re talking about much higher pumping rates.”

Dakin’s summary and conclusions: 

1. A 30-year record of groundwater level trends and water quality shows that the development of wells in and around the Village area has not had a significant impact on either of these two parameters. 2. The fractured bedrock aquifer that extends beneath all of the proposed 25 lots is relatively productive and can easily provide sufficient water with, or without, imposed conservation measures. 3. Theoretical calculations and water level monitoring data in OBS Well 194 indicate that the inter-well impact from wells set 30m apart will be only a few centimetres. 4. The estimated pumpage from the proposed subdivision will not have a measurable impact on local streams and water licences. 5. The water pumped from wells constructed on each lot will likely meet the Canadian Drinking Water Quality standards for all parameters, with the possible exception of fluoride and iron.

Dakin’s recommendations:

1. New water wells should be set at least 30m from neighbouring wells, both on and surrounding the property. 2. Wells located on Lot 25 should be set at least 40m from the shoreline, and restricted to pumping less than 3m3/day. 3. The subdivision design and layout should incorporate measures to promote temporal detention of rainfall runoff from hard surfaces and/or ground infiltration. 

Also, while not justified for the project, the Ministry of Forests, Lands and Natural Resource Operations should be encouraged to reinstate a monitoring well in the local aquifer for long-term management of the valuable local aquifer.