No abstract

The placement of a sediment cap was the remedial alternative selected in the Record of Decision for the containment of PAH-contaminated sediments near the Wyckoff/Eagle Harbor Superfund site shoreline, a former log rafting area at this closed wood treatment site. Soft sediments with substantial quantities of nonaqueous phase liquid (NAPL) occurred in this area, which raised a concern that there would be environmental releases or potential cap failure in this area of the site. As part of the investigations to guide cap design, a laboratory bench study was devised to evaluate consolidation-driven NAPL and dissolved phase PAH permeation of the cap. Sediment cores collected from the site were extruded side-by-side into 20 cm diameter, 120 cm high acrylic columns to maintain sediment stratification. Synthetic seawater was added until approximately 60 cm of water covered the site sediment. The simulated cap material was added to each column in such a manner as to fall through the overlying water at a uniform rate to simulate settling velocities expected during a barge wash-off placement event. Vertical loads were applied incrementally to the cap/sediment columns until the total consolidation stress was equivalent to a 90-cm cap. Each column was extruded, inspected visually for the migration of NAPL, and sectioned into three layers with each analyzed for total petroleum hydrocarbons and PAHs. In all three test cylinders, there was no indication of impact to the top 10 cm of the cap (the biologically active zone). The results suggest that the chemicals detected at high concentrations in the native sediments would stay in place and not migrate through a overlying cap via consolidation-induced advection.

No abstract

Preoperational baseline characterizations and postoperational monitoring strategies associated with dredged material disposal in the coastal zone commonly document changes in sediment and benthic invertebrate communities inhabiting those sediments. The U.S. Army Engineer Waterways Experiment Station is developing and field-testing a technique that uses benthic invertebrate community data to make quantitative statements about the feeding habitat value to fish of natural bottoms and bottoms modified by dredged material disposal or other activities influencing substrate quality. The technique, called Benthic Resources Assessment Technique (BRAT), employs two different types of information from a project area.A list of the bottom-feeding fishes inhabiting a project area is used to select the benthic resources important to an impact assessment. As the first step, observations and measurements of the morphology of specimens of these species are carried through a data reduction and analysis sequence that assigns each fish to a feeding strategy class or guild that appears to correlate with potential prey size and a prey's location (depth) below the sediment surface. The second step involves the analysis of information from benthic macroinfaunal invertebrate compdmity survey. The BRAT then classifies the'invertebrate taxa according to their size and the distribution of their biomass relative to the sediment surface. Estimates of standing crop complement this classification scheme. When combined, the two types of information provide estimate of the potential prey biomss (grams/ meter squared) or energy (kilocalories/meter squared) available to the fish in a particular feeding guild.a an This technique facilitates the development of a quantitative impact statement using data on changes in the benthos related to project activities. Additionally it allows quantitative comparison to be made between areas being considered for disposal and/or other modification during project planning and uses a measure with social significance (i.e., the potential productivity of the demersal fishery) .