Preliminary survey of ground-water resources for Island County, Washington

Increased ground-water withdrawals associated with the population increase in Island County have caused concern about ground-water availability and potential seawater intrusion. The most widespread and widely used aquifer lies near sea level. Locally, available data also indicate that one or more water-bearing zones lie above the sea-level aquifer. Pumpage in 1979 totaled about 1.67 billion gallons; about 90% was pumped from the sea-level aquifer. Most large producing wells in the county have pumping water levels near or below sea level, so that if pumping continued for a long enough time, seawater intrusion would result. Sampling of chloride concentrations in July 1978, April 1980, and August 1980 indicated problem areas mainly in northeastern and southern Camano Island and in central Whidbey Island. (USGS)