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Island County > Public Health > Environmental Health > Hydrogeology > Seawater Intrusion Source Monitoring

Seawater Intrusion Source Monitoring

Island County Code 8.09.099 (Seawater Intrusion Protection) is designed to help protect our aquifers / drinking water from issues related to seawater intrusion.  One of the tools incorporated into the code is the development of seawater intrusion risk ratings for areas of the county.  Areas are classified as being either 'low', 'medium', 'high', or 'very-high' risk fo​r seawater intrusion based on water level elevation and chloride concentration data from all wel​ls located within 1/2 mile of the point in question.  Public water system (3 or more connections) sources that are classified as having elevated seawater intrusion risk (medium, high, or very-high) are required (under ICC 8.09.099 C2A) to monitor water quality in those sources.  A map showing seawater intrusion risk ratings across the county can be found HERE.  A listing of all known public water systems sources, and their seawater intrusion risk ratings can be found HERE (last updated 03/23/2021).

When monitoring of a well is required, the well needs to be sampled twice per year, during the months of April and August.  Samples need to be submitted to a state-certified laboratory, and analyzed for chloride and electrical conductivity.  Samples are required to be collected from each source (that has elevated risk rating), not combined wellfield sources.  In order to get credit for the monitoring, samples should be labeled as 'compliance' and the water system ID (PwsID) and source number must be included. 

An SWI Rating of "ND" means there is insufficient data available to calculate a rating at this location.  Monitoring is not required in this situation (Monitoring Required = "No").  If however Monitoring Required = "No*" then based on available information, ICPH recommends that monitoring be conducted (although it is not required).​

​More information regarding seawater intrusion can be found in the Seawater Intrusion Topic Paper.