Executive Summaries

  1. Stormwater Monitoring Program
  2. Management Plan for Stormwater
Executive Summary
San Juan County recently implemented a three-year pilot stormwater monitoring program to identify sources of water pollution to local freshwater and marine resources. Results of Year 1 monitoring provide an initial characterization of stormwater in creeks and waterways in six focus areas on San Juan, Lopez, and Orcas islands. Review of water quality data collected in Year 1 suggests that stormwater is generally supportive of designated beneficial uses with respect to water temperature, dissolved oxygen, pH, and turbidity. However, additional data are needed to characterize existing conditions for dissolved oxygen, as much of the Year 1 dissolved oxygen data were flagged for quality assurance review issues. Several common stormwater constituents were present at low levels or were non-detectable, including total and dissolved metals (arsenic, cadmium, lead, zinc), total petroleum hydrocarbons (TPHs), and 3 herbicides / pesticides commonly used on the islands (permethrin, MGK-264, and glyphosate). Total arsenic, cadmium, lead, and zinc are relatively low in San Juan County stormwater compared with reported values for typical urban stormwater runoff and Puget Sound Puget Sound Phase 3 monitoring. Total copper may be somewhat elevated at particular sites when compared with other San Juan County sites, but overall, Year 1 median total copper values were generally similar to recently reported median values for Puget Sound Phase 3 monitoring. All dissolved metals were below available Washington State Department of Ecology (WSDOE) acute and chronic numeric criteria for aquatic life toxicity, suggesting a low toxicity potential in San Juan County stormwater with respect to metals. Anionic surfactants measured during Year 1 were similar to previous measurements reported for multiple sites across the San Juan Islands and are far below available U.S. Environmental Protection Agency (USEPA) criteria for drinking water sources. Nutrient concentrations were low to moderate compared with values measured in Puget Sound Phase 3 monitoring and reported in three national databases of monitored stormwater concentrations. In contrast to other stormwater constituents, bacteria data (i.e., fecal coliform, Escherichia coli) collected during Year 1 monitoring suggest that levels of this constituent may be generally elevated in stormwater in San Juan County.

Determination of how runoff water quality differs among the six focus areas and how it affects nearshore areas in San Juan County is somewhat challenging given the relatively small number of samples collected during Year 1 and the lack of receiving water data. A preliminary analysis indicates that Garrison Bay, False Bay and Westcott Bay focus areas exhibit relatively lower bacteria and nutrient concentrations, while Mud Bay, Fisherman Bay and Eastsound focus areas exhibit relatively higher concentrations. Additional data collected during Years 2 and 3 should allow for more a definitive comparison between focus areas and may allow for identification of specific sources of nutrients and/or pathogens within the five priority basins. Further, monitoring of receiving waters and receiving water sediments during Years 2 and 3 of the pilot program will help to determine whether stormwater constituents are present at levels sufficient to affect water and sediment quality in the bays and channels that surround the islands. Based on the results of Year 1, several adaptive management recommendations for future years of the San Juan County pilot stormwater monitoring program are included in this report.