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The Abbotsford-Sumas aquifer is located within the Fraser and Nooksack River lowlands in southwest British Columbia and northern Washington State. The aquifer is mostly unconfined and is located on a broad outwash plain, which is elevated above the adjacent river floodplains. The outwash terrace slopes southward, and terminates in escarpments along the Nooksack River floodplain. Small streams drain area. The aquifer is highly productive, is bisected by the international boundary, and provides water supply for nearly 10,000 people in the US (towns of Sumas, Lynden, and farmlands) and 100,000 in Canada, mostly in City of Abbotsford, but also in township of Langley. |
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| The Abbotsford-Sumas aquifer is confined by bedrock outcrops at Sumas and Vedder Mountains along the Sumas Valley and hills to the south of Nooksack River near Bellingham. The bedrock surface is buried beneath thick Pleistocene sediment fill that masks most of the bedrock topography. The elevation of the bedrock surface beneath the Pleistocene deposits of the lowland varies considerably, indicating pre-glacial erosional topography with large relief. Near Abbotsford, there is about 300 to 500m of Pleistocene sediment, which thins out near Sumas Mountain. A digital bedrock topography map has been generated using deep borehole data, existing bedrock contour maps, valley wall profiles, and extrapolated cross-sections through the study area. |
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The glacial sediments are very complex in the Fraser Lowland. The lithostratigraphic units are approximately equivalent to the chronostratigraphic units as described in the Quaternary history of the area. Sumas Drift forms the unconfined Abbotsford-Sumas Aquifer. Sumas Drift consists of diamictons (lodgement and flow tills), thick and well-sorted glaciofluvial outwash sands and gravels (advance and recessional), glaciolacustrine sediments, and ice-contact sediments deposited during the Sumas Stade. It also contains lenses of till. The construction of cross-sections through the aquifer has proven to be a difficult task as layers are not easily identifiable. Shown to the left are colour coded well logs across Abbotsford. |
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| Shown to the right is the layered model constructed for the aquifer with lithologic units colour codes. Drak blue is glaciomarine clays, pale blue is recent floodplain deposits, green is glaciolacustrine silts, yellow is sand, and orange is gravelly sand of the Sumas Drift. This aquifer architecture or geologic model has been used a the framework for a three dimensional groundwater flow model that has been used to simulate potential impacts of future climate change and to simulate nitrate transport originating from berry cultivation throughout the region. |
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