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especially (a) hydrodynamic response and geotextile strains during release from a transport 

 platform, descent through the water column, and impact on the seafloor; and (b) responses of the 

 geotextile bags to physical, chemical, and biological degradation caused by the combination of 

 contained waste and abyssal environment. 



(4) An in-situ experiment using uncontaminated, organic-rich, fine-grained dredged material 

 would be needed to generate the data necessary for fiirther development and validation of models 

 to predict changes in physical, biological, and chemical environments of the abyssal seafloor 

 when perturbed by large-volume deposits of contaminated dredged material. Tracers should be 

 added to the material in the experiment to mimic potential contaminant bioaccumulation and 

 transport if such were to occur with implementation of the abyssal waste isolation option. 



(5) Development and refmement of techniques necessary for the safe handling, bagging, and 

 release of contaminated dredged material would be needed when, and if, environmental 

 acceptability of the abyssal isolation option is demonstrated. 



Advanced Research Projects Agency Project 



Scope and Approach - In June 1995, NRL was funded by the Advanced Research Projects 

 Agency (ARPA) to apply, to the extent possible, the concept of Simulation-Based Design to the 

 waste isolation problem, focusing entirely on the end-to-end concept of dredged material 

 isolation on the abyssal seafloor and the environmental impact, with the goal of optimizing the 

 dredging-to-isolation system. The project scope includes consideration of dredging techniques 

 and dredged material handling necessary to facilitate containment for transport and lowering 

 through the water column. Model improvements and developments programmed for simulating 

 the dredging-to-placement segment of the process include (1) modeling of improved 

 full-containment dredge design and transport ship loading system; (2) optimization of the surface 

 transporter through application of linear and, if merited, non-linear ship design models; (3) 

 optimization of the geotextile bag-hopper-release system design to reduce potential for bag 

 tearing on release; and (4) modeling of the hydrodynamics of waste-filled bags in free-fall to 

 understand and control the deviation from ideal free-fall path to the seafloor with the intent of 

 maximizing the concentration of bags from each transporter payload drop. To facilitate 

 improved understanding of the environmental impact of placing dredged material on the abyssal 

 seafloor, model improvements and development underway include (1) modeling of the plume 

 generated by filled bags impacting on the ocean bottom, and the subsequent advection, 

 dispersion, and settlement of the plume materials; (2) modeling of the geochemical processes 

 within individual dredged material-filled bags and sediments buried under bags; (3) modeling the 

 formation of methane hydrate within the deposit and assessing potential impact on isolation; and 

 (4) modeling the pathways for toxicant bioaccumulation. 



Participants and Progress - We are now at an early stage of the ARPA project. We have brought 

 all expected academic participants on board including one new participant, Robert Moorhead, 

 Mississippi State University, who will develop a visualization of simulation products. We are in 

 final contract negotiations with a contractor team of industrial and academic participants for 

 developing the dredging-to-seafloor placement portion of the modeling and simulation. We 



35-799 96-6 



