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Natural processes in aquatic ecosystmes tend to concentrate heavy metals, chlorinated hydrocarbons, pesticides, nutrients, and oil and grease compounds in bottom sediments. These contaminants are not very soluble in water under the conidtions that normally occur in oxygenated uncontaminated surface waters. Therefore, introducing high concentrations of these contaminants into aquatic ecosystems will generally result in an equilibrium condition where most of the contaminant will be sorbed (adsorbed and absorbed) by suspended particulate material and then deposited on the bottom when the suspended material settles. The time necessary to achieve the equilibrium condition depends upon the physicochemical conditions in the aquatic system and the quantity and duration of the contaminant introduction. Dredged Material Research Program (DMRP) reports and other literature indicate that dredging operations have the potential to temporarily mobilize or release some contaminants from the sediments. During disposal operations, the anaerobic sediments are mixed with aerated surface water, and a complex chemical interaction occurs. Heavy metals, such as cadmium, copper, chromium, lead, and zinc, are stabilized in the oxygen-free sediments as insoluble sulfides.
Natural processes in aquatic ecosystmes tend to concentrate heavy metals, chlorinated hydrocarbons, pesticides, nutrients, and oil and grease compounds in bottom sediments. These contaminants are not very soluble in water under the conidtions that normally occur in oxygenated uncontaminated surface waters. Therefore, introducing high concentrations of these contaminants into aquatic ecosystems will generally result in an equilibrium condition where most of the contaminant will be sorbed (adsorbed and absorbed) by suspended particulate material and then deposited on the bottom when the suspended material settles. The time necessary to achieve the equilibrium condition depends upon the physicochemical conditions in the aquatic system and the quantity and duration of the contaminant introduction. Dredged Material Research Program (DMRP) reports and other literature indicate that dredging operations have the potential to temporarily mobilize or release some contaminants from the sediments. During disposal operations, the anaerobic sediments are mixed with aerated surface water, and a complex chemical interaction occurs. Heavy metals, such as cadmium, copper, chromium, lead, and zinc, are stabilized in the oxygen-free sediments as insoluble sulfides.
Under the Dredged Material Research Program (DMRP), studies of the impact of dredged material disposal in open-water systems (Aquatic Disposal Field Investigations (ADFI)) were conducted at five locations: New York (Eatons Neck), Ohio (Ashtabula River), Texas (Galveston), Oregon (Columbia River), and Washington (Duwamish Waterway). The sites were representative of a variety of disposal practices, dredged materials, and aquatic habitats. Disposal did not occur during the course of the Eatons Neck ADFI but did at the other four sites. This report summarizes the findings of the investigations.
This report synthesizes data from the U.S. Army Engineer Waterways Experiment Station, Dredged Material Research Program (DMRP), Task 1E. Task 1E consisted of seven research projects (work units) that investigated the pollution properties of dredged material and procedures for determining their potential for effect on water quality and aquatic organisms. The short-term impact of dredged material on water quality and aquatic organisms is related to the concentration of chemically mobile, readily available contaminants rather than the total concentration. The elutriate Test, which measures concentrations of contaminants released from dredged material, can be used to evaluate short-term impacts on water quality. Longer term impacts of dredged material on water quality have generally been slight and can be evaluated by means of the Elutriate Test and analysis of the mobile forms of sediment contaminants. No significant long-term increase in water column contaminant concentrations has been observed at any aquatic disposal field site. The greatest hazard of dredged material disposal is the potential effect of the material on benthic organisms. Most dredged material has not proven particularly toxic. Some dredged material has not proven particularly toxic. Some dredged material, however, can be extremely toxic or of unknown toxicological character. Benthic bioassay procedures are now available which can identify this toxic dredged material.
The major goal of the Eatons Neck disposal site field investigation was to evaluate the effects of aquatic disposal of dredged material on organisms and water quality, including the significance of physical, chemical, and biological factors that influence the rate of disposal site recolonization by benthic animals. A comprehensive research program was planned and conducted at Eatons Neck in order to evaluate cause and effect relationships associated with the impacts of open-water disposal. This volume of the study presents the investigation of the hydraulic regime and the physical characteristics of bottom sedimentation. Acoustic-reflection profiles and mechanical analysis of core and grab samples of the bottom were used to define the sediment-type distribution of the area. Results were confirmed by penetrometer tests and bottom and profile photographs. The study concluded that there was no physical evidence of significant dispersion of dredged material from the Eatons Neck disposal site; no previously deposited material was detected outside the designated disposal area.
A multidisciplinary study was conducted offshore of the mouth of the Columbia River to characterize the baseline physical, chemical, and biological aspects of the nearshore zone and to investigate the effects of open-water disposal on the study area. Physical data analyzed during the study indicate that dredged material deposited in the nearshore zone off the mouth of the Columbia River maintains its identity relative to surrounding sediments for periods of years and that such material migrates towards the north at a rate of approximately 0.6 kilo-metre per year. Chemical data suggest that the release of dredged material at the experimental disposal area has no measurable effect on either ambient water quality or quality of the sediments. Dredged material removed from the Columbia River entrance channel can be characterized as fine to medium sand with insignificant levels of pollutants. Bottom sediments examined from the tidal delta in the region of disposal site B consistently showed higher levels of nutrients and metals than sediments from adjacent sampling sites. Biological studies indicate that the disposal of dredged material had a measurable effect on both the benthic macroinvertebrates and the demersal finfish at the experimental disposal area.
This report synthesizes data from the U.S. Army Corps of Engineers' Dredged Material Research Program, Task 1D. Task 1D consisted of six research projects (work units) that investigated the direct and indirect effects of dredging and disposal of dredged material on aquatic organisms. Determination of potential environmental effects of dredging and disposal, in spite of research conducted to date, is still in preliminary stages due to the multiplicity of variables involved. Bioavailability of sediment-sorbed heavy metals is low. Release of sediment-associated heavy metals and their uptake into organism tissues have been found to be the exception rather than the rule. Research results suggest that there is little or no correlation between the bulk sediment content of heavy metals and environmental impact. Oil and grease residues, like the heavy metals, seem tightly bound to sediment particles and accumulation of these residues by organisms is minimal. The diversity of variables that have the potential for direct and indirect effects on acquatic life argues for an integrated, whole-sediment bioassay, using sensitive test organisms. Such a procedure is currently under development by the Environmental Protection Agency and the Corps of Engineers and should uncover site-specific toxicity problems which can be addressed by appropriate chemical testing and biological evaluation of dredged material.