A drinking well water test showing chloride concentration values of 100 milligrams per liter (mg/L) or greater indicates a potential threat of seawater intrusion.
Seawater intrusion in the San Juan Islands.
In the San Juan Islands where many wells are near the shoreline and the recharge rates to aquifers are low, there is an increased risk of seawater intrusion.
This is especially true on Lopez Island where the 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. There is growing concern that pumping more ground water will adversely affect the whole Island’s freshwater system.
A 1997 joint study by the U.S. Geological Survey (USGS) and the San Juan County Conservation District found that 40 percent of 185 freshwater samples on Lopez Island had chloride concentrations indicating saltwater intrusion. (View full report.) When chloride levels reach 160 mg/L in a well, the local governing body has the authority to monitor and implement practices at the land owner’s expense to counteract any further increase in chlorides.
The maximum contaminant level for chloride as a health standard is 250 mg/L. At this level, the health jurisdiction has the authority to decommission a private land owner well in order to protect the water aquifer resource from further degradation.
Current and future island dwellers, both on the interior and shoreline, face a serious water crisis.
What can be done to solve the problem?
Water conservation and judicious well operation practices can help reduce seawater intrusion. But that alone can’t solve the problem. San Juan County’s growing population will continue to put increased demand on the archipelago’s limited and fragile freshwater resources.
Watec offers another solution by tapping the most abundant water resource in the region—the ocean. Our customized residential and commercial seawater desalination plants use reverse osmosis technology to create abundant and sustainable freshwater supplies.
Economical, efficient and eco-friendly, today’s advanced desalination technology can supply water to the region while keeping our ground and surface water resources from becoming depleted or diverted from their other important environmental uses.