Please Note:  Effective June 20, 2005 - The Island County Seawater Intrusion Policy has been replaced by a new section in Island County Code 8.09.099, Seawater Intrusion Protection.

---

Under ICC 8.09.099, all areas of the Island County have a seawater intrusion risk rating based on a combination of aquifer water level elevations and chloride concentrations as described in the following table:  

Table 1.  Seawater Intrusion Risk Categories

Risk Category	Water Level Elevation 1	Chloride Concentration 2
Low	Greater than 8.4 feet	Any 3
Medium	Less than or Equal to 8.4 feet	Less than 100
High	Less than or Equal to 8.4 feet	Between 100 and 250
Very-High	Less than or Equal to 8.4 feet	Greater than 250

¹ Water Level Elevation in feet (Vertical Datum = NAVD 88). 

² Chloride Concentration in Milligrams per Liter (mg/l)

³ Where water level elevations are greater than 8.4 feet, chloride concentrations are irrelevant

 

The above matrix results in a seawater intrusion risk rating map, which can be viewed by clicking this link:  Circle Map

 

 

Project proposals are evaluated for seawater intrusion risk analysis based upon the risk category and the scope of the proposed activity.  Table 2 defines which projects are subject to review under each risk category:

 

Table 2. Projects subject to Seawater Intrusion Risk Analysis

Risk Category	Land Subdivision	New or Expanding Public Water Systems	Individual Water System
Low	N/A	N/A	N/A
Medium	More than 6 lots	More than 6 connections	N/A
High	All	More than 1 connection	< 1.5 acre lot size
Very-High	All	All	< 5 acre lot size

Related Links

• View Seawater Intrusion "Circle Map" 

• Back to Island County Groundwater Resource Program

• Aquifer Testing Protocol

• For more information pertaining to seawater intrusion, and the development of these policy changes, please see the Island County Water Resources Advisory Committee (WRAC) Topic paper on Seawater Intrusion

• Island County Code 8.09.099, Seawater Intrusion Protection.