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Dioxins in Dredged Material

Testing for Dioxins/Furans in the DMMP


Contact the DMMO

Seattle District (CENWS)
Dredged Material Management Office
PO Box 3755
Seattle, WA 98124-3755


About Dioxins

Polychlorinated dibenzo-dioxins (PCDDs) and polychlorinated dibenzo-furans (PCDFs) are commonly referred to together as "dioxins."  Dioxins are a group of chlorinated organic compounds with similar chemical structures, called congeners. The most studied and most toxic dioxin congener is 2,3,7,8- tetrachlorodibenzo-p-dioxin (2,3,7,8-TCDD). 2,3,7,8-TCDD has been identified as a "known human carcinogen" (IARC 1997) and a probable human carcinogen by USEPA (Group B2 carcinogen). Other dioxins may cause cancer, disrupt the endocrine system, and cause reproduction and developmental effects (USEPA 2003; Dioxins are toxic to humans and other mammals at very low concentrations.

Dioxins are unintentionally produced by natural and industrial activities.  Natural activities include forest fires or volcanic activity. Industrial processes include incomplete combustion of materials in the presence of chloride, such as burning of fuels, municipal and domestic waste incineration, as well as chlorine bleaching of pulp and paper, and chlorinated pesticide manufacturing.

Although dioxins are produced at very low levels (e.g., parts per trillion or parts per quadrillion), the compounds exist throughout the environment. Due to their chemical and physical properties, they persist and have the potential to bioaccumulate in the tissue of humans and wildlife.

DMMP Evaluates Dioxins Depending on Disposal Site and Project Specifics

Disposal at Non-Dispersive Sites (Elliott Bay, Port Gardener, Anderson/Ketron and Commencement Bay sites)

Testing for dioxins proposed for disposal at non-dispersive sites is required on a case-by-case basis in areas where there is reason to suspect presence of these chemicals. Factors which can trigger testing include the following:

  • Location within an urban bay and having no historical information showing that dioxin is below interim guidelines
  • Proximity to current or historical point sources, such as outfalls
  • Proximity to chlor-oxide bleach process pulp mills, chlor-alkali or chlorinated solvent manufacturing plants, former wood treatment sites, phenoxy herbicide manufacture and/or use and handling areas
  • Proximity to areas with high polychlorinated biphenyl (PCB) concentrations
  • Proximity to former hog fuel burners/boilers and areas with previous fires or incineration sources
  • Proximity to areas previously sampled that showed elevated levels of dioxin
  • Dioxin testing will be required for all projects meeting one or more of the reason-to-believe factors described above. Deeper underlying sediments, which are confirmed as “native,” may be exempt from testing. Native material within the dredge prism, and lying directly under sediment that is being tested for dioxins, should be archived for possible dioxin analysis.

Disposal at Dispersive Sites (Port Angeles, Port Townsend and Rosario Strait)

Dredged material placed at dispersive sites does not stay on site, but is rapidly dispersed with the tides. Post-disposal monitoring is not possible. Therefore, only DMMUs meeting the Disposal Site Management Objective of 4 pptr TEQ may be placed at dispersive sites.

DMMP Dioxin Guidelines

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For non-dispersive disposal sites, the guidelines include definitions of both a Non-dispersive Disposal Site Management Objective and Non-dispersive Dredged Material Suitability Guidelines. 

Non-dispersive Disposal Site Management Objective:   Four pptr TEQ will be the objective for surface sediments within the boundary of a disposal site, to be achieved over time as the updated suitability guidelines are implemented.  This objective will aid in case-by-case decision-making (see next paragraph) on the suitability of material for disposal and assure protection of human and ecological health.  This objective is also based on an upper bound estimate of the distribution of dioxin in sediments from non-urban areas of Puget Sound[1]. Disposal site monitoring will provide the feedback necessary to determine whether the site management objective is being met.

Non-dispersive Dredged Material Suitability Guidelines:   Proposed revised suitability guidelines will be used in a case-by-case decision-making approach that is consistent with the narrative human health standard in the SMS rule.  The following Non-dispersive Screening Levels represent sediment concentrations of dioxin which the agencies believe can be safely disposed at non-dispersive, open-water sites.  A project-specific evaluation would be necessary to allow disposal of material with higher levels.   It is anticipated that this evaluation process will produce information and experience that will support the future adoption of specific suitability criteria by rule. The suitability guidelines will have three components: 

  1. Nondispersive Screening Levels.  DMMUs with dioxin concentrations below 10 pptr TEQ will be allowed for open-water disposal as long as the volume-weighted average concentration of dioxins in material from the entire dredging project does not exceed the Disposal Site Management Objective of 4 pptr TEQ.
  2. Case-by-Case Determinations:  As has been the case throughout the history of the DMMP program, case-by-case determinations may be made based on consideration of the individual aspects of dredging projects.  Case-by-case decisions to allow disposal of material not meeting the screening levels may be made by the DMMP Agencies based on the overall goal of meeting the Non-dispersive Disposal Site Management Objective.  Case-by-case considerations will include the following: (a) material placement sequencing; (b) consideration of the possible cumulative effects of other bioaccumulative compounds within the project sediments; and (c) the frequency of disposal site use.
  3. Small Business Considerations for Nondispersive Sites:  Public or Private enterprises defined as “Small Businesses” by Chapter 19.85 RCW [2], which are permit applicants for projects with total dredged volume less than 4,000 cubic yards, will be encouraged to submit applications for case-by-case consideration as long as all DMMU concentrations are less than 10 pptr TEQ dioxin.  These projects may not be required to meet the volume-weighted average guideline if DMMP review determines that the Disposal Site Management Objective of 4 pptr will likely be met on an annual average basis, based on knowledge of other anticipated use of the identified disposal site.  To clearly define what constitutes a project of less than 4,000 cubic yards, there are two key qualifiers. First, intentional partitioning of a dredging project to reduce or avoid testing requirements is not acceptable. Second, recognizing that multiple small discharges can cumulatively affect the disposal site, project volumes are defined in as large a context as possible. One example of this latter qualifier is recurring maintenance dredging of a small marina where "project volume" will be the projected dredging volume over 5 years. Another example is multiple-project dredging contracts where a single dredging contractor conducts dredging for several projects under a single contract or contract effort. Again, the "project volume" will be summed across all projects (as will any sampling and compositing efforts prior to testing). 

[1] Specifically, 4 pptr is the nonparametric estimation of the 90% upper confidence limit for the 90th percentile of the distribution of the background Puget Sound Main Basin data set, rounded up to the nearest whole digit.

[2] In Chapter 19.85 RCW "Small business" means any business entity, including a sole proprietorship, corporation, partnership, or other legal entity, that is owned and operated independently from all other businesses, and that has fifty or fewer employees.

For dispersive disposal sites, the revised guidelines include definitions of both a Dispersive Disposal Site Management Objective and a Dispersive Dredged Material Suitability Guideline. 

Dispersive Site Management Objective: 4 pptr (parts per trillion, dry-weight) 2,3,7,8-tetrachloro-p-dibenzodioxin toxicity-equivalents (TEQ) will be defined as the Site Management Objective for all dispersive disposal sites in Puget Sound.  This value is based on an upper bound estimate of the distribution of dioxin in sediments from non-urban areas of Puget Sound [1].

Dispersive Dredged Material Suitability Guideline:  The Dredged Material Suitability Guideline is the maximum dioxin concentration allowed in any single Dredged Material Management Unit (DMMU). For dispersive sites, this guideline is set equal to the Dispersive Site Management Objective of 4 pptr TEQ. Other dioxin concentrations can be approved on a case-by-case basis, if demonstrated to be consistent with the anti-degradation provisions in the Sediment Management Standards (SMS) rule[2].

[1] Specifically, 4 pptr is the nonparametric estimation of the 90% upper confidence limit for the 90th percentile of the distribution of the background Puget Sound Main Basin data set, rounded up to the nearest whole digit.

[2] Case-by-case determinations will require the dredging proponent to submit a high level of supporting data on a regional scale to be reviewed by DMMP Agencies.

When the sediment dioxin concentration in a dredging unit exceeds the 10 pptr TEQ screening level and the dredging unit is found unacceptable for non-dispersive disposal under case-by-case decision-making, the dredging proponent will have the option of pursuing bioaccumulation testing to determine whether or not individual DMMUs could qualify for open-water disposal. This option will be based on a modified version of the Tier III testing procedures included in the existing DMMP User Manual.

A target tissue level (TTL) to be used in the bioaccumulation evaluation has not been determined for dioxins at this time. In the absence of a TTL, the dredging proponent who selects the option of bioaccumulation testing will be required to include exposure of test organisms to a suitable reference sediment as part of the bioaccumulation test. Concentrations in the project test-sediment tissue would be compared against concentrations in the reference-sediment tissue to determine the bioavailability of sediment dioxin and, thereby, the suitability of dredged material for open water disposal. Over time, a tissue database will be developed, which may allow for the adjustment of this protocol.

Please Note:  This information is no longer current.  These guidelines were in use for suitability determinations prior to November 2011.  Because some existing suitability determinations still refer to these guidelines, the information is provided here for reference purposes only.


For non-dispersive sites in Puget Sound:

  • Based on a comparison of dioxin in test sediments to disposal-site background.
  • "Background" is defined using disposal-site sediment dioxin data generated as part of DMMP site monitoring.
  • Dioxin concentrations in any given dredged material management unit may not exceed site maximum (see table below).
  • Average dioxin concentrations (weighted to the volume of each dredged material management unit) cannot exceed mean site concentration.



Non-Dispersive Disposal Site Sediment Dioxin Toxic Equivalence (ng/kg-dry wt)

Updated 11/14/2008 (changes in bold)

Disposal Site    



Port Gardner



Anderson Ketron



Bellingham Bay



Elliott Bay



Commencement Bay




For dispersive sites in Puget Sound:

  • Based on a comparison of dioxin in test sediments to reference background.
  • "Background" is defined using sediment dioxin data from nearest reference site.
  • The available reference site dioxin data are limited to Carr Inlet and Sequim Bay. It is the dredger's responsibility to sample nearest reference site if data are not available.
  • Bioaccumulation testing for dioxin is currently not used to determine suitability for either dispersive or non-dispersive sites in Puget Sound.

For more information please contact the DMMO office.

Although the underlying regulations referenced and described in this guidance document contain legally binding requirements, this guidance document does not substitute for those provisions or regulations, nor is it a regulation itself. In the event of a conflict between the discussion in this document and any statute or regulation, this document would not be controlling. Thus, it does not impose legally binding requirements on the DMMP agencies or the regulated community, and might not apply to a particular situation based upon the circumstances. The word "should" as used in the Guidance is intended solely to recommend or suggest, in contrast to "must" or "shall" which are used when restating regulatory requirements.  While the guidance document indicates the DMMP agencies’ anticipated approach to assure effective implementation of legal requirements, the preferential analytical framework is flexible, decisions made utilizing this framework are made on a project-specific basis through the application of best professional judgment, the framework encompasses alternative evaluation processes that may be applied at the election of the proponent, and DMMP agencies’ decision-makers retain the discretion to adopt approaches on a case-by-case basis that differ from the guidance where appropriate. Any decisions regarding a particular project will be made based on the statute and regulations.  Interested parties are free to raise questions and objections about the analytical approach reflected in the guidance and the appropriateness of the application of the guidance to a particular situation. The guidance is a living document and may be revised periodically through the SMARM process. The document will be revised, as necessary, to reflect any relevant future regulatory amendments. The DMMP agencies welcome public comments on the document at any time and will consider those comments in any future revision of the guidance document.