No discussions about development in Hudson, Rigaud and St. Lazare should exclude the impact on the water table supplying our drinking water.
A study released in June 2015 found that precipitation falling on Rigaud Mountain and the Hudson and St. Lazare plateaus represents 41% of the total replenishment of the Vaudreuil-Soulanges aquifer, the water table supplying drinking water to more than 100,000 Vaudreuil-Soulanges residents. (FYI, St. Lazare is the largest municipality in Quebec entirely dependent on well water.)
The chief concern expressed in the Programme d’acquisition de connaissances sur les eaux souterraines (PACES) report is that the zones with the highest replenishment rate — Mont Rigaud, Hudson and St. Lazare — also happen to be the most vulnerable to contamination.
The study was carried out over a two-year period by a multidisciplinary team from the Université du Québec à Montréal, École Polytechnique and GéoMont, the agency mandated to map the Montérégie using satellite data. Their methodology and models are well explained and accessible to anyone with a scientific bent.
Here’s the PACES final report (en français seulement): rapport_final_paces_vaudreuil-soulanges
My English summary:
– About 105,000 Vaudreuil-Soulanges residents living in 18 municipalities get their drinking water from artesian wells. (The other 35,000 get their water from the Ottawa or St. Lawrence rivers.)
– Those 18 municipalities suck 11.2 million cubic metres of water a year from the underground water table, equivalent to a sheet of water 14 millimetres deep covering the entire 814-square-kilometre Vaudreuil-Soulanges MRC.
– St. Lazare is far and away the biggest consumer, averaging 2.8 million cubic metres a year, followed by Vaudreuil-Dorion at 2.1 million (VD draws most of its drinking water from the Ottawa River) and Rigaud, at 1.7 million.
– Hudson’s 5,400 residents come a surprising fourth, consuming 1,123,024 cubic metres a year.
– Our region consumes 20% more water than the Quebec average, with 56% going to residential, 33% for industrial/institutional and 11% for agriculture, most of that to grow sweet corn, a notoriously thirsty crop. (That 33% residential/industrial usage is misleading; this sector draws only 58 percent of its total consumption from public water networks because many have their own wells pulling from the same aquifer.)
– The aquifer is replenished by precipitation averaging just under 1,000 millimetres a year.
Two aspects of the study should be of particular interest to those concerned about water quality and quantity:
The PACES team found total dissolved mineral content in samples from more than 50 testing sites throughout Vaudreuil-Soulanges to be far higher than provincial norms (58.5%). Calcium is 34.8% higher; iron, 31% and sodium, 25%. But it’s the manganese level (30% higher than approved levels) that causes the team the most concern, so much so that it rates a mention in the introduction. The report quotes a 2011 Quebec study which linked higher manganese levels with lower IQs among young children. This was the reason behind Quebec’s decision to approve Hudson’s water filtration plant as part of the 2008 waterworks upgrade — so that manganese could be precipitated out of the water supply. On a positive note, our water has nitrate levels well below provincial norms.
The second aspect of the study deals with the rate at which the aquifer is being replenished, and from where. The aquifer beneath the southern half of the county lies beneath a thick layer of impermeable clay, making it what is classified as captive or semi-captive, relatively protected from contamination but slow to replenish. They get a sizeable percentage of their replenishment from the Glengarry hills of southeastern Ontario.
The researchers discovered the marshes, bogs, swamps and fens found in Hudson, Rigaud and St. Lazare are far more efficient in replenishing the aquifer, with 41 square kilometres of wetland and forested areas supplying 41 per cent of the Vaudreuil-Soulanges aquifer’s total replenishment. But because they’re better connected to the water table, any contamination is also more likely to find its way into the aquifer.
The PACES study went unnoticed when it was released last year, because there is no agency in Quebec with a clear mandate to protect underground water sources. Vaudreuil-Soulanges, like most regions of Quebec, has its Conseil de bassins versants (Rigaud’s Mayor Gruenwald is a former COBAVER-VS president and currently sits on the board) but the COBAVERs have no teeth.
In 2014 the provincial government adopted its Reglement sur le prélevement des eaux et leur protection, setting threshold levels for the risks of contamination of underground water sources, but there’s no indication the Ministry of Sustainable Development, Environment and the Battle Against Climate Change (I kid you not) is making our most precious resource a protection priority.
Call me madcap, but I’m thinking the three municipalities in Vaudreuil-Soulanges with the most to lose from contaminated water should make it a factor.