Groundwater provides much of the water used for residential and agricultural purposes in rural parts of the region. It also moves nutrients to vegetation and provides flow to streams. Groundwater is stored in, and moves through, porous sand and gravel and porous or fractured bedrock (aquifers). Aquifers are recharged by the infiltration of rainwater or snowmelt from the ground surface. However, throughout much of the Ottawa valley, an impervious blanket (aquitard) of Champlain Sea silt and clay limits aquifer recharge. Excessive pumping of groundwater can deplete aquifers.
A simplified drawing of the groundwater system of the region.
Slow flow rates and long residence times in aquifers cause groundwater quality to be controlled by the chemical composition of the aquifer. Pyrite-bearing rocks yield water with a characteristic rotten-egg odour. Water from salt-rich Champlain Sea sediments can be saline. Calcium and magnesium, dissolved from limestone and dolostone, produce what is known as hard water.
Groundwater can be contaminated. Contaminant sources in urban areas include gas stations, dry cleaners, garbage dumps, snow-disposal dumps, and industrial sites. Municipal waste-disposal sites in Carp, Gloucester, and Aylmer have leaked and contaminated aquifers. In rural areas, livestock wastes, pesticides, and fertilizers have polluted groundwater.
Did you know? ...
In 1991, the improper disposal of dry-cleaning chemicals in Manotick contaminated about 100 household wells and required development of a water main for local residents at a cost of millions of dollars.