The Canadian Appalachians cover about 309 000 km2 in the eastern part of the country. In this region, three hydrogeological contexts are defined on the basis of distinctive bedrock and/or surficial geology features: 1) Appalachian uplands with sparse glaciofluvial sediments and localized
glaciolacustrine submergence, 2) Appalachian piedmont with localized Late Quaternary marine sediment cover, and 3) Maritimes Basin. In the first two contexts, bedrock is extensively deformed, faulted and fractured and is mainly composed of low-permeability sandstones, mudstones, carbonates and
volcanics that have been affected by low-grade metamorphism. The Maritimes Basin is mostly composed of a sequence of moderately to highly permeable sandstone, conglomerate, siltstone and shale. Surficial sediments consist primarily of glacial sediments and minor glaciofluvial sediments. In uplands
and high tablelands of the region, the Quaternary sediment cover is generally thin and discontinuous, while in lowlands, such as in the Maritimes Basin, it is more continuous and generally thicker. The Appalachian region is one of the wettest in Canada, with precipitation on the order of 1150 mm/y.
Between 34 and 100% of the population relies on groundwater for its water supply, and most wells are completed into bedrock. However, rocks of the first two contexts typically provide fairly low yields. The most important bedrock aquifers are hosted by sedimentary rocks of the Maritimes Basin. There
are also good granular aquifers, such as eskers and sand and gravel units in river valleys, but their extent is rather limited in all three contexts. Groundwater flow is generally topography driven. Nonetheless, groundwater levels in the Appalachian region vary from artesian conditions to depths
reaching as much as 50 m below the ground surface. In spite of the wide range of conditions, groundwater level typically lies within about 7 m from the surface, and is usually deeper in high relief areas. The proportion of groundwater discharge to rivers represents from 60% to 70% of annual stream
flow. Recharge is highly variable, ranging on average from 5 to 30% depending on the local context. Although its permeability is variable, recharge occurs mainly through the till cover, due to its widespread occurrence. Groundwater quality is generally excellent.