Abbotsford–Sumas Aquifer

The Abbotsford–Sumas Aquifer (also known as the Abbotsford Aquifer) is a shallow and largely unconfined aquifer lying between the U.S. state of Washington (a portion known as the Sumas–Blaine Aquifer) and the Canadian province of British Columbia. The aquifer underlies largely agricultural areas of the Fraser Valley and northern Whatcom County, Washington, including the communities of Lynden, Everson, Nooksack, and Sumas, as well as urban portions of Abbotsford, British Columbia. It contributes significantly to the overlying Sumas River (a tributary of the Fraser) and Nooksack River. The aquifer is a major source of water for the overlying communities, which includes one of the most agriculturally productive regions of Canada. However, surveys since the 1990s have indicated unsafe nitrate levels at some wells in the region contributed to by agricultural runoff from fertilizer and manure.

The aquifer consists of glaciofluval sand and gravel, alongside smaller amounts of glacial till and clayey silt. It is up to 70 m (230 ft) thick in its deepest portions, although generally ranges between 15 and 25 m (50 and 80 ft). The water table is deeper in the center of the aquifer, at most 30 m (98 ft) from the surface, but this can be as little as 2 m (6.6 ft) in the outlying portions. Due to seasonal fluctuations, the level of the water table varies by 2 or 3 m (7 or 10 ft) per year. Precipitation, the primary source of groundwater recharge, is high from October to March, but low for much of the growing season.