Is seawater intrusion affecting ground water on Lopez Island, Washington?

Abstract

Lopez Island lies among the San Juan Islands, an archipelago in the coastal waters of Washington State, just offshore of Seattle and of Vancouver, British Columbia. Its scenic views and relatively little precipitation have made it one of Washington's premier places to live and play. So its population has been burgeoning, and its interior and shorelines have been under development. The Island's main freshwater source is ground water. Local surface water cannot be developed to meet increasing needs for freshwater because the Island lacks lakes and continuously flowing streams. But Islanders are concerned that pumping more ground water will affect its availability and quality. Because many wells are near the shores and the recharge rates to the aquifers are low, there is a great potential for seawater intrusion. In 1997, the U.S. Geological Survey (USGS), in cooperation with the San Juan County Conservation District, studied the possibilities of seawater intrusion on the Island and found that 46 percent of 185 freshwater samples had chloride concentrations indicating seawater intrusion.