Concluded

7. (Concluded).

U.S. Army Engineer Waterways Experiment Station

3909 Halls Ferry Road, Vicksburg, MS 39180-6199;

U.S. Army Engineer District, New England

696 Virginia Road, Concord, MA 01742-2751;

Texas A&M University, College Station, TX 77843

13. (Concluded).

The main body of this report describes specific procedures for all aspects of capping project evaluation and design. A

recommended sequence of design activities is presented, and specific design steps are organized into flowcharts as necessary.

A number of appendixes are also included in this report that provide detailed information on specific testing procedures,

predictive models, etc.

A capping operation must be treated as an engineered project with carefully considered design, construction, and moni-

toring to ensure that the design is adequate. There is a strong interdependence between all components of the design for a

capping project. By following an efficient sequence of activities for design, unnecessary data collection and evaluations can

be avoided, and a fully integrated design is obtained. The major components of the project design and evaluation process

include site selection, equipment and placement techniques, geotechnical considerations, mixing and dispersion during

placement, required capping sediment thickness, material spread and mounding during placement, cap stability, and moni-

toring. Processes influencing the cap design include bioturbation, consolidation, erosion, and potential for advection or

diffusion of contaminants. The basic criterion for a successful capping operation is simply that the cap thickness required to

isolate the contaminated material from the environment be successfully placed and maintained.

The cost of capping is generally lower than alternatives involving confined (diked) disposal facilities. The geochemical

environment for subaqueous capping favors long-term stability of contaminants as compared with the upland environment

where geochemical changes may favor increased mobility of contaminants. Capping is therefore an attractive alternative for

disposal of contaminated sediments from both economic and environmental standpoints.