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Subtidal (Offshore) Sediment Chemistry
The current subtidal (offshore) marine sediment monitoring program was established in 2007 to characterize sediment within the County’s borders, though some sites have been sampled since 1985. We currently monitor sediments at 14 sites. Every 2 years we sample eight sites in Elliott Bay and every 5 years we collect samples from three deep sites in the mainstem of the Central Basin as well as in three smaller embayments.
The top 2 centimeters of sediment is collected for chemistry analysis by a dual van Veen grab sampler. These samples are collected along with another grab sample used to assess the benthos (organisms living within the sediment). Next, the King County Environmental Lab analyzes the samples for physical and chemical parameters, including total solids, total organic carbon, grain size, metals, and a group of organic compounds. We analyze the 47 chemicals of concern listed in Washington State’s Marine Sediment Management Standards (SMS) (Chapter 173–204 WAC) as well as additional metals and organic chemicals.
More Information
The goals of this monitoring are to:
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Identify differences in sediment chemistry between sampling locations, including those outside of King County.
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Track changes in sediment chemistry between sampling years.
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Compare chemical concentrations to current marine sediment quality standards.
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Evaluate the relationship between environmental parameters and benthic invertebrates.
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Support coordinated regional monitoring efforts and inform management decisions.
| Parameter Type | Parameter | Method* |
|---|---|---|
| Conventionals | Total solids | SM 2540-G |
| Particle size distribution | ASTM D422 | |
| Total organic carbon | EPA 9060 (SW-846); PSEP, 1996 | |
| Metals | Mercury | EPA 7471B (SW-846) |
| SMS metals (arsenic, cadmium, chromium, copper, lead, mercury, silver, zinc) | EPA 3050B/6010D (SW8-846) | |
| Aluminum, iron, nickel, manganese, selenium | EPA 3050B/6010D (SW8-846) | |
| Organics | PAHs | EPA 3550C /8270D (SW8-846) |
| Phthalates | EPA 3550C /8270D (SW8-846) | |
| PCB Aroclors | EPA 8082A (SW8-846) | |
| SMS chlorinated semi-volatile organics | EPA 3550C /8270D (SW8-846) | |
| SMS misc. non-polar organics | EPA 3550C /8270D (SW8-846) | |
| SMS polar organics | EPA 3550C /8270D (SW8-846) | |
| PBDE congeners (types or forms) | EPA 3550C /8270D (SW8-846) |
*For more details on methods and detection limits refer to the most recent sampling and analysis plans.
SMS = sediment management standard
Download Data
Download data from our online database.
Note: some data may be provisional. Contact MarineWQ@kingcounty.gov for information about the most recent quality control of data.
Documentation
Learn more about our program by reading documents such as the latest sampling and analysis plan and read relevant reports and presentations.
Contact us with any questions or access additional resources in the Science Section Library.