Implementation of In Situ Activated Carbon
Remedies at Contaminated Sediment Sites



CONSTRUCTION

REACTIVE CAP MATS

Permeable composite mats of GAC (or other reactive amendments) placed within geotextiles are referred to as Reactive Cap Mats (RCM) or Reactive Core Mats. RCMs are especially useful at sites where a thin cap is required that also affords erosion resistance, groundwater upwelling reduction, chemical isolation, and/or slope stability (USEPA 2013, ITRC 2014). RCMs are frequently placed on the contaminated sediment, and then secured with a layer of sand and/or larger rock for hydraulic stability or habitat requirements.

RCMs are commercially available and have a demonstrated history of use at multiple contaminated sediment sites. A list of contaminated sediment sites that have included RCMs as part of the overall remedy are provided in the table below.

Site

Contaminant

Project Description

Delivery Methods

Project Web Link

Naval Air Station, Cottonwood Bay, Dallas TX

PCBs, PAHs, chromium, lead

Small-scale pilot project that tested RCM  with 0.28 lb/ft2 activated carbon, 0.23 lb/ft2 apatite, 0.28 lb/ft2  organoclay in AOS 80 geotextile.

Prototype reactive mats rolled up and deployed from a john-boat by divers.  Divers secured the mats in the shallow bay with anchors, anchor screws, and blocks.  Some of the treatments were further covered with sand.

SERDP ER-1493

NAVFAC TR-2366-ENV Technical Report

St. Louis River Superfund Site 
Styker Bay
Duluth, MN

NAPL/PAHs

11 acres of cap that included a reactive core mat with GAC to absorb advected PAH-porewater during consolidation. The cross section of the cap was 0.5 ft (15 cm) sand/activated carbon mat/2.5 ft (75 cm) sand.

Reactive mats attached to outer sheet-pile wall and unrolled toward shore from a moveable barge.  Overlapping RCMs stapled and allowed to sink, followed by sand placement

ITRC 2014

CETCO Stryker Bay Fact Sheet

Zidell Marine Cleanup Site
Portland, OR

NAPL/PAHs/PCBs

The majority of the cap (12 acres) is a sand cap, consisting of material obtained from the Columbia River that was tested and determined to be clean. A low-profile cap was placed over a 1 acre area that consisted of a reactive core mat (RCM) with activated carbon and apatite to limit contaminant movement.  The RCM was covered with armored with rock to protect it from erosion

Construction of the low profile cap was completed by a dive team working in concert with a crane derrick to first lower RCM panels into place, and subsequently adjust the placement to meet overlap requirements.

ODEQ Zidell Site Report

CETCO Zidell Cleanup Fact Sheet

Anacostia River, Washington, DC

PCBs, PAHs, chromium, lead

1100 m2 area was capped with a coke-filled RCM and covered with 15 cm of sand.

Twelve 3.1 m x 31 m coke-filled RCMs were placed  with a 0.3 m overlap using a crane with a clamshell.A diver followed the unrolling mat to insure proper placement.  A sand layer (~15 cm)
was then placed above the RCM by particle broadcasting to secure it in place and provide a
habitat for benthic organisms to colonize.

McDonough et al, 2006

ITRC 2014



One of the earliest demonstrations for the use of activated carbon as part of an RCM occurred as part of the 2004 Anacostia River Active Capping demonstration project (McDonough et al, 2006). An 1,100 m2 area of PCB-contaminated sediment was capped with a coke-filled RCM and covered with 15 cm layer of sand. Subsequent analysis for PAHs above the coke breeze mat-amended cap demonstrated that the cap was effective in isolating the contaminants (USEPA 2013).

A reactive cap mat development and demonstration project was undertaken at Naval Air Station, Cottonwood Bay, TX for SERDP Project ER-1493. The project incorporated site-specific testing of for materials to be incorporated into a RCM that would sequester both HOCs and metals.

  

The results of bench-scaled testing lead to development and deployment of a RCM with 0.28 lb/ft2 activated carbon, 0.23 lb/ft2 apatite, 0.28 lb/ft2 organoclay in a geotextile on a small pilot project. Prototype reactive mats rolled up and deployed from a john-boat by divers in Cottonwood Bay, and were secured in the shallow bay with anchors, anchor screws, and blocks. Some of the treatments were further covered with sand. The sand cover proved to be crucial as the mats not secured with sand filled with methane released from the sediments and were raised off the bay floor.



A GAC-filled RCM was deployed as part of the St. Louis River Interlake/Duluth Tar Site Superfund Sediment Operable Unit at Duluth, MN. Approximately 500,000 ft2 of the RCM was placed by attaching the RCM to an outer sheet-pile wall and unrolled toward shore from a moveable barge. The overlapping RCMs were stapled and allowed to sink, followed by a sand cover.



At the former Zidell Marine Cleanup on the Lower Willamette River in Portland, OR, a RCM with activated carbon and apatite was placed over a 1-acre area. Construction of the cap was completed by a dive team working in concert with a crane derrick to first lower RCM panels into place, and subsequently adjust the placement to meet overlap requirements. The RCM was covered with armored with rock to protect it from erosion.