A Sediment Testing Reference Area Database for the Guam Deep Ocean Disposal Site (G-DODS)
- Background on Testing Sediment for G-DODS Disposal
- The Reference Area Database
- Cautions for Project Proponents about Using the Reference Area Database
- Tables of Physical, Chemical and Biological Data
Background on Testing Sediment for G-DODS Disposal
The Guam Deep Ocean Disposal Site (G-DODS) is the second deepest ocean dredged material disposal site in the United States. It is located off the Continental Shelf in approximately 8,800 feet (2,680 meters) of water, approximately 11.1 nautical miles (20.6 kilometers) offshore of Apra Harbor.
In order for U.S. Army Corps of Engineers (USACE) to authorize a permit for the disposal of dredged material at the G-DODS, sediment evaluations (as described in the national testing manual, the Ocean Testing Manual) must first be conducted on the dredged material proposed for ocean disposal. EPA and USACE can determine suitability of dredged material for ocean disposal by comparing the test results of the proposed dredged material against the test results of a designated reference sediment. EPA identifies reference sediments as substantially free of contaminants and as representative as possible of what conditions at the disposal site would be if no dredged material had ever been disposed there.
The reference area identified by EPA for the G-DODS is located in approximately 7,200 feet (2,200 meters) of water, at approximately 13°33.90' N and 144°37.32' E (NAD 83). This site is approximately 7 nautical miles (13 kilometers) from the G-DODS itself, and approximately 7 nautical miles (13 kilometers) from the closest coast of Guam.
Just as the G-DODS is one of the nation's deepest disposal sites, its reference area is one of the deepest as well. The great water depth and open-ocean location of the reference site make the collection of its sediment very expensive and logistically difficult. Weather and sea-state conditions can force costly delays in project sampling programs and, in extreme conditions, can present a concern for human safety. For these reasons, EPA believes it is appropriate to establish and maintain a reference area database of previously-collected sediment test results that may be used in lieu of collecting and testing the reference area's sediment directly. EPA anticipates that project proponents will typically elect to compare their test result against the appropriate values in the database when timing, cost or safety considerations present significant obstacles in collecting new reference site sediment.
The Reference Area Database
Several sets of sediment test data have been successfully collected from the G-DODS reference area since 2009. Physical, chemical and biological data from these studies are summarized in Tables 1 through 4.
- Table 1 depicts the range of bulk sediment chemistry values found at the reference site for all typical contaminants of concern.
- Table 2 shows solid phase acute toxicity bioassay results for three species of amphipods and one species of polychaete.
- Tissue chemistry results are provided for all typical bioaccumulative contaminants of concern, for one clam species in Table 3 and one polychaete species in Table 4.
(Suspended particulate phase bioassays are not included in the database, since results from these tests are compared against water quality criteria as opposed to reference sediments.) Thus, all types of reference sediment data necessary for full Tier III OTM evaluations are included in the database.
Cautions for Project Proponents about Using the Reference Area Database
If you choose to compare your dredged material test data against the G-DODS reference area database, you must use the same test species reflected in the database. You should use caution when comparing to the reference area database values, as this can result in disposal suitability determinations by EPA and the USACE that are slightly more conservative (more environmentally protective) than would be the case if the reference sediments were tested directly.
This is because, in this approach, you are directly (not statistically) comparing to the reference area database values. Therefore, when average amphipod mortality in a sediment sample is more than 20 percent above the overall average value in the reference area database, the test sediment is automatically considered unsuitable for ocean disposal. This will be true even if the test sediment and reference area sediment might not have been statistically different if they had been tested directly at the same time.
In the same manner, when polychaete mortality is more than 10 percent above the corresponding overall average value in the reference area database, it is considered unsuitable for ocean disposal.
Comparison of bioaccumulation test results to the reference area database also will be made directly, as opposed to statistically. For bioaccumulation data, EPA will evaluate test data generally against the range of tissue concentrations in the reference area database, as well as consider available published scientific information concerning tissue residue effects.
Before starting any sediment testing program that supports proposed ocean dumping at the G-DODS, you should work with the Region 9 EPA Dredging and Sediment Management Team to develop a draft Sampling and Analysis Plan. The Region 9 team must approve the Plan.
Tables of Physical, Chemical and Biological Data Collected from G-DODS Reference Area
- Table 1a. Sediment Chemistry for the G-DODS Reference Area: Conventionals
- Table 1b. Sediment Chemistry for the G-DODS Reference Area: Trace Metals
- Table 1c. Sediment Chemistry for the G-DODS Reference Area: Organics
- Table 1d. Sediment Chemistry for the G-DODS Reference Area: Chlorinated Organic Pesticides
- Table 1e. Sediment Chemistry for the G-DODS Reference Area: Dioxins and Furans
- Table 2. Percent Survival in Acute Toxicity Bioassays of G-DODS Reference Area Sediments
- Table 3a. Tissue Chemistry for the Clam Macoma nasuta Exposed to G-DODS Reference Area Sediments: Trace Metals
- Table 3b. Tissue Chemistry for the Clam Macoma nasuta Exposed to G-DODS Reference Area Sediments: Organics
- Table 3c. Tissue Chemistry for the Clam Macoma nasuta Exposed to G-DODS Reference Area Sediments: Chlorinated Organic Pesticides
- Table 3d. Tissue Chemistry for Clam Macoma nasuta Exposed to G-DODS Reference Area Sediments: Dioxins and Furans
- Table 4a. Tissue Chemistry for the Polychaete Nephtys caecoides Exposed to G-DODS Reference Area Sediments: Trace Metals
- Table 4b. Tissue Chemistry for the Polychaete Nephtys caecoides Exposed to G-DODS Reference Area Sediments: Organics
- Table 4c. Tissue Chemistry for the Polychaete Nephtys caecoides Exposed to G-DODS Reference Area Sediments: Chlorinated Organic Pesticides
- Table 4d. Tissue Chemistry for the Polychaete Nephtys caecoides Exposed to G-DODS Reference Area Sediments: Dioxins and Furans.
1. Calculated using ND = 0
- Calculated using the 2022 updated World Health Organization TEQs and using ND = 0
- Calculated using the 2022 updated World Health Organization TEQs and using ND = 1/2 Method Detection Limit
- Average calculated using ND = 0
- Average calculated using ND = 0
- Average calculated using ND = 1/2 MDL
- Average calculated using ND = 0
- Average calculated using ND = 0
- Average calculated using ND = 0
- Average calculated using ND = 1/2 MDL
- Average calculated using ND = 0