Seawater intrusion

Seawater intrusion is the movement of seawater into freshwater aquifers. Seawater intrusion can result from natural processes (such as sea level rise) and is made worse from human activities by lowering water levels in aquifers. Some wells in coastal Washington are now unusable because of seawater intrusion and its negative impacts on health, aesthetics, agriculture, and environmental quality.

Water rights and seawater intrusion

Many water rights issued along the Washington coastline contain provisions to monitor chlorides, conductivity, static water levels, and other parameters that can indicate seawater intrusion. Some water rights holders are required to report these measurements to Ecology so that we can better manage freshwater aquifers.

What is a monitoring provision?

We provision some water rights with requirements to collect and report seawater intrusion indicators – like chlorides, conductivity, and water levels – on a regular basis. These requirements differ from Washington State Department of Health or County water testing requirements and must be reported directly to Ecology.

Water right provisions to monitor seawater intrusion indicators are developed on a case-by-case basis. They are included alongside other provisions and generally look like this:

  • "By January 31 of each year, the following information shall be submitted in writing to the Department of Ecology. April and September measurements from the subject well(s) of: 1) Chloride and conductivity (the chemical analysis shall be performed by a state-accredited laboratory) 2) Depth to static water level (with pump off long enough to allow for stabilization). The chloride/conductivity sampling and the static water level measurement shall be conducted concurrently." 

For more about the fundamentals for the use and management of state waters, see RCW 90.54.020. To read the state’s water quality standards and antidegradation policy, see WAC 173-200-030.

Why does seawater intrusion matter?

Fresh water is essential for drinking, irrigation and healthy ecosystems. When seawater intrusion begins, the salt it contains can negatively affect farmlands, ecosystems, lives and livelihoods. Some coastal wells in Washington are now unusable because of seawater intrusion. This is particularly true in coastal areas where high population growth has placed increased demands on groundwater supplies. Seawater intrusion can potentially render large portions of Washington’s coastal aquifers unusable through degradation of water quality.

What can I do to prevent or limit seawater intrusion?

Seawater intrusion often occurs due to over-pumping of wells located near saltwater coastlines that draw water from aquifers at or below sea level. Over-pumping reduces aquifer levels and allows seawater to inch landward which can eventually contaminate wells.

We recommend that you inform yourself by regularly monitoring your well’s water levels, recognizing declining water level trends that exceed seasonal fluctuations, and regularly testing chloride and conductivity levels.

If seawater intrusion is indicated, a variety of preventative actions should be pursued. These include:

  • Reducing the pumping rate
  • Reducing the annual volume of water pumped
  • Limiting the number of service connections
  • Reducing outdoor watering
  • Scheduling pumping to coincide with low tides
  • Raising the pump intake
  • Moving your well or adding wells to spread impacts (both require that you contact Ecology)

Please contact us and your county planning department immediately if you are concerned about seawater intrusion.

What regulations authorize us to require seawater intrusion monitoring?

It is in the public interest to limit or prevent groundwater use that can lead to seawater intrusion. When making water rights decisions, we are authorized (RCW 90.54.020 and WAC 173-200-030) to protect aquifers from seawater intrusion which is a type of pollution. We may apply monitoring and prevention provisions as necessary.



Local Resources

Island County seawater intrusion policies and regulation

Jefferson County seawater intrusion policy