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.

You can measure water levels in your well by following these instructions. Note: if you live in Island County, the Island County Health Department has an e-tape available for water users to borrow. Please contact them to determine availability.

For those with private wells this publication contains important general information; Private Wells: Information for Owners

Please keep in mind: You may want to perform your own research into options for safely and accurately measuring water levels in your well. Please contact your regional Ecology contact (listed below) to confirm suitability of your selected method.

Test your well for seawater intrusion parameters by first finding an accredited laboratory from our list. The laboratory should be able to provide you with all the information needed to collect a sample of your well water and understand the results of the tests.

*For those without water right requirements, if you have a well located near a saltwater coastline that draws water from near or below sea level, it may be advisable for you to voluntarily monitor these same indicators for the protection of your water source.

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

Contact information

Northwest Region
Island, King, Kitsap, San Juan, Skagit, Snohomish, and Whatcom counties

Jess Yates
Environmental Specialist
Northwest Region Office - Water Resources Program
jess.yates@ecy.wa.gov
206-594-0208

Mailing address:

Department of Ecology Northwest Region Office
Water Resources Program
PO Box 330316
Shoreline, WA 98133-9716

Southwest Region
Clallam, Clark, Cowlitz, Grays Harbor, Jefferson, Mason, Lewis, Pacific, Pierce, Skamania, Thurston, and Wahkiakum counties

Arlene Harris
Environmental Specialist
arlene.harris@ecy.wa.gov
360-280-7645