Development and Placement of a Sorbent-Amended Thin Layer Sediment Cap in the Anacostia River

Abstract

Incorporating materials into sediment caps that can sequester contaminants will greatly improve their ability to isolate contaminants in the underlying sediments from the rest of the aquatic environment. For highly sorptive media a thin layer (cm) may be sufficient, but accurately placing a thin layer (cm) of material over submerged contaminated sediment is difficult. A reactive core mat (RCM) was designed to accurately place a 1.25 cm thick sorbent (coke) layer in an engineered sediment cap. In April 2004, twelve 3.1 m × 31 m sections of RCM were placed in the Anacostia River, Washington, D.C., and overlain with a 15 cm layer of sand to secure it and provide a habitat for benthic organisms to colonize without compromising the integrity of the cap. Placement of the RCM did not cause significant sediment re-suspension or impact site hydrology. The RCM is an inexpensive and effective method to accurately deliver thin layers of difficult to place, high value, sorptive media into sediment caps. The approach can also be used to place granular reactive media that can degrade or mineralize contaminants.

Keywords:

• Sediment remediation
• sediment capping
• in-situ sediment management
• innovative remediation technologies
• remediation technologies
• aquatic habitat restoration

Notes

^a Planned but not yet installed.

^a Source: Horne Engineering Services, Inc., 2004.

^b Water sample was taken after the silt curtain was placed in the river but before any capping installation work began.

^c Average and standard deviation of two samples taken at different times during placement.