The Science of Safely Disposing Dredged Sediment
The journey of dredged material from a murky river bottom to an approved ocean site is a remarkable feat of environmental stewardship.
Imagine a busy port slowly choking on its own success. Sediment accumulates, threatening the safe passage of ships that bring vital goods. Dredging—the process of excavating this underwater material—becomes essential. But what happens when this sediment, often laden with decades of industrial contaminants, needs to be disposed of in the ocean? The answer lies in a rigorous scientific evaluation process designed to protect marine life and human health. This is the critical, unseen environmental safeguard that allows commerce and ecology to coexist.
Sediments dredged from our nation's waterways are often more than just sand and mud. They can be a historical archive of chemical pollution, contaminated by past industrial activities 1 . If this contaminated material is dumped into the ocean without treatment, the consequences can ripple through the entire ecosystem.
The primary concerns are toxicity and bioaccumulation. When contaminants are biologically available, they can be ingested or absorbed by marine organisms 1 . This can cause immediate harm, such as death, or more insidious effects like the accumulation of pollutants in an organism's tissues 1 . This contamination then travels up the food web, ultimately exposing humans who consume contaminated seafood 1 . The goal of the evaluation process is to act as a gatekeeper, ensuring that only material that will not cause these adverse effects is permitted for ocean disposal.
Immediate harmful effects on marine organisms including mortality and reproductive issues.
Contaminants build up in organisms over time, concentrating in tissues and organs.
Contaminant concentrations increase at higher levels of the food chain.
People are exposed through consumption of contaminated seafood.
The entire process of ocean disposal of dredged material is governed by a robust federal framework. The Marine Protection, Research, and Sanctuaries Act (MPRSA), also known as the Ocean Dumping Act, makes it illegal to transport any material for the purpose of dumping it into ocean waters without a permit 1 . The U.S. Army Corps of Engineers (USACE) is the agency that issues these permits, but it must rely on the EPA's environmental criteria to do so .
Prohibits transportation of material for ocean dumping without a permit. Establishes environmental criteria for evaluation.
Provides national standardized guidance for sampling, testing, and analyzing dredged material for environmental acceptability 1 .
The cornerstone of this evaluation is the Ocean Testing Manual, often called the "Green Book," jointly published by the EPA and the USACE 1 . This manual provides the national, standardized guidance for sampling, testing, and analyzing dredged material to determine its environmental acceptability 1 . Furthermore, the EPA and USACE develop regional manuals that tailor the guidance to local conditions, such as identifying contaminants of particular concern for specific harbors and recommending local species to be used in testing 1 .
The evaluation of dredged material relies heavily on standardized bioassays, or tests using living organisms, to simulate how the sediment might impact the marine environment 1 . The process is meticulous and multi-staged.
Before a single sample is taken, project proponents must develop a detailed Sampling and Analysis Plan (SAP) 2 . This plan, which must be approved by relevant state and federal agencies, dictates where and how sediment cores will be collected, often using techniques like vibracoring and sonic drilling to retrieve samples from precise depths 2 . A recent study in Baltimore, for example, sampled 52 locations in a channel, with cores extending down to -52 feet 2 .
Once collected, the sediment is subjected to a battery of tests. The exact suite of tests can vary, but they are designed to answer two fundamental questions: Is the material toxic, and do pollutants from it accumulate in marine life?
The material is first characterized for its physical properties (like grain size) and chemically analyzed for a wide range of potential contaminants.
This is the core of the evaluation. Species like clams, worms, or shrimp are exposed to the sediment to measure effects.
The results of these tests are then interpreted according to established guidelines. For ocean disposal under the MPRSA, the material must meet the specific marine protection criteria to be eligible 2 . For other management options, like upland placement, material is often categorized. For instance, the Maryland Department of Environment uses a three-category system:
Suitable for unrestricted residential reuse.
Restricted to non-residential use.
Requires placement in a contained facility with a protective cap 2 .
| Tool/Reagent | Function in the Experiment |
|---|---|
| Test Organisms | Species like clams, worms, or shrimp are exposed to the sediment to measure acute toxicity (death) or sub-lethal effects. Regional manuals often specify local species 1 . |
| Control Sediment | A sample of clean, reference sediment used as a baseline to compare against the test results from the dredged material, ensuring any effects are due to contamination. |
| Whole Sediment | The unaltered dredged material sample, used in tests to expose organisms directly to the sediment-water interface, mimicking bottom-dwelling conditions. |
| Elutriate | A liquid created by mixing the sediment with water and then centrifuging it. This tests the potential for contaminants to leach into the water column during disposal. |
| Bioaccumulation Chambers | Enclosed systems where organisms are held in contact with the sediment for an extended period to measure how much pollutant accumulates in their tissues 1 . |
A recent project in Maryland provides a perfect real-world example of this science in action. The Sparrows Point Container Terminal conducted an extensive, independent study to characterize over 2.55 million cubic yards of sediment from its channel 2 .
The study followed an approved SAP, using vibracoring and sonic drilling to collect samples 2 . After rigorous testing, the findings were revealing:
| Category | Description | Volume Percentage |
|---|---|---|
| Category 1 | Residential unrestricted use soil and fill material | Part of 89% total |
| Category 2 | Non-residential restricted use soil and fill material | Part of 89% total |
| Category 3 | Material requiring placement and capping | 11% |
| Data derived from the independent North and South Channel studies 2 . | ||
These results allowed the project to propose a "balanced placement approach," a nuanced and environmentally sound management plan. Instead of a single disposal method, the dredged material was routed to different locations based on its characteristics. Crucially, the study found that 1.57 million cubic yards from the South Channel met the strict MPRSA criteria for ocean placement at the Norfolk Ocean Disposal Site 2 .
| Disposal Location | Material Type | Volume (Cubic Yards) |
|---|---|---|
| Ocean Placement (Norfolk Site) | Material passing MPRSA criteria | Up to 1,570,000 |
| Onsite Upland Placement (DMCFs) | Category 1, 2, and 3 material | Up to 2,000,000 |
| Offsite Placement (MPA Facilities) | Category 1, 2, and 3 material | Up to 1,250,000 |
| DMCF: Dredged Material Containment Facility. Plan based on proposed project data 2 . | ||
The scientific testing is just one part of a comprehensive permitting process that can take six to 18 months to complete . This process is built on checks and balances. Before applying, developers are encouraged to consult with the USACE and EPA . The EPA then has a 45-day period (with a possible 45-day extension) to review the application and can concur, concur with conditions, or decline to concur (non-concur) . If the EPA non-concurs, the USACE is prohibited from issuing the permit, giving the EPA a powerful veto to enforce environmental standards .
Public engagement is also a key component, with the USACE required to issue a public notice and consider all public comments as part of its "public interest review" .
Developers consult with USACE and EPA to understand requirements.
Comprehensive application with all required studies and documentation.
EPA evaluates application and can concur, concur with conditions, or non-concur.
USACE issues public notice and considers public comments.
USACE conducts comprehensive review considering all factors.
USACE issues or denies the permit based on complete evaluation.
The complex journey of dredged material—from the bottom of a creek to a scientifically vetted resource—showcases a critical commitment to environmental protection. It is a process where advanced science, strict regulation, and transparent public process intersect. Through meticulous sampling, sophisticated biological testing, and a multi-layered approval system, we can ensure that the necessary work of maintaining our vital waterways does not come at the expense of our precious ocean ecosystems. This unseen work below the waterline is what allows our ports to thrive above it, in harmony with the natural world.
Advanced testing methods ensure environmental safety
Comprehensive laws and guidelines protect ecosystems
Commerce and environmental protection working together
For further information on the national testing standards and permitting process, you can visit the official U.S. EPA website pages on Dredged Material Testing and MPRSA Permits 1 .