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|Title:||Interim guidance for predicting the quality of effluent discharged from confined dredged material disposal areas|
|Authors:||Long-Term Effects of Dredging Operations Program (U.S.)|
Palermo, Michael R.
|Keywords:||Confined disposal facilities|
|Publisher:||Environmental Laboratory (U.S.)|
Engineer Research and Development Center (U.S.)
Abstract: The quality of effluent from confined dredged material disposal sites (water discharged during active disposal operations) is an environmental concern when the sediments to be dredged are contaminated. Dredged material placed in a confined disposal area settles, while the clarified supernatant waters with some residual colloidal solids are discharged from the site as effluent. The effluent may contain concentrations of both dissolved and particle-associated (adsorbed or attached by ion exchange) contaminants. A large portion of the total contaminant concentration is, however, particle associated. A modified elutriate test procedure to estimate both the dissolved and particle-associated concentrations of contaminants in confined disposal area effluents is discussed. The laboratory test simulates contaminant release under conditions prevalent in confined disposal areas and reflects sedimentation behavior of dredged material, retention time of the containment, and physicochemical environment in ponded water during active disposal. In the test, sediment and water from the dredging site are mixed to a slurry concentration equal to the expected influent concentration under field conditions. The mixed slurry is aerated in a 4-l cylinder for 1 hr to ensure oxidizing conditions will be present in the supernatant water. Following aeration, the slurry is allowed to settle under quiescent conditions for a period equal to the expected mean field retention time, up to a maximum of 24 hr. A sample is then extracted from the supernatant water and analyzed for total suspended solids, and for dissolved and total concentrations of contaminants of interest. The contaminant fractions of the total suspended solids may then be calculated. Column settling tests, similar to those used for design of disposal areas for effective settling, are used to define the concentration of suspended solids in the effluent for a given .operational condition, i.e. ponded area, depth, and inflow rate. Using results from both of these analyses, a prediction of the total concentration of contaminants can be made. The acceptability of the proposed confined disposal operation can be evaluated by comparing the predicted contaminant concentrations with applicable water quality standards while considering an appropriate mixing zone and the quality of the receiving water body.
|Appears in Collections:||Miscellaneous Paper|