Volume 3, Issue 6 (June 2006)
Reactive Material Options for In Situ Capping
Environmental dredging creates challenges in finding areas to construct confined disposal facilities and typically results in residual contamination. In situ capping (either in place of dredging or for capping residual contaminants) can be limited by concerns regarding navigation, uniform cap placement, biointrusion and geotechnical stability. A potential solution for many in situ capping concerns is the use of a reactive material cap. A reactive material cap could greatly reduce the thickness required for the cap compared to conventional sand caps. Various reactive materials (e.g., activated carbon, apatite, organoclay, zeolite, zero-valent iron) are used for removal of organics and metals in wastewater and groundwater treatment and may be applicable to in-situ capping. There are several ways that could be used for in-situ capping with reactive materials. A layer of reactive material could be placed in bulk using a clamshell or pumped through a tremie pipe. Another option is a reactive material filled geotextile mat. A reactive material mat would have several advantages over loose placement of reactive materials, including: (1) uniform and verifiable mass per area placement of reactive or adsorptive material; (2) ability to mix reactive or adsorptive materials in defined proportions; (3) geotextiles provide separation of the reactive material from the contaminated sediment and cover material; (4) geotextiles provide a barrier to biointrusion; (5) multiaxial strength of the geotextiles provides resistance to uplift and differential settlement; and (6) geosynthetic reinforcement provides stability on sloped areas. In the United States, a carbon-based geotextile mat was constructed and successfully deployed. A barge with a crane was used to deploy the material off shore. Other deployment methods have also been used for installing geosynthetics in waterways from shoreline and would be applicable to a reactive material mat.