Sand Cover & Armored Caps

Sand cover and armored caps are two remediation methods used in addition to dredging, for addressing sediments containing PCBs. 

In June 2008, the U.S. EPA and Wisconsin DNR approved an optimized remedy, including sand cover and armored caps to address low PCB-concentrated sediment as part of the final phase of the Little Lake Butte des Morts cleanup project.

Specifically, the optimized remedy required dredging in shallow areas so that armored caps (layers of gravel and sand) are only placed where the final water depth will be no less than 6 feet.  It also required sand cover be used over certain areas with low levels of PCB-contaminated sediment as well as over some areas previously dredged, but with residual PCB concentrations.  Lastly, armored caps (gravel and sand layers) were placed over remaining sediments to be addressed by the cleanup effort.  These armored caps will keep sediment in place to ensure that it is not available to the biota (fish and invertebrates). 

The work under the optimized remedy began in mid-2008 through fall 2008, and resumed in mid-April 2009 and was completed in May 2009, thus ending all of the in-water work for the project.

This optimized remedy is an amendment to the EPA's Record of Decision and is consistent with the optimized remedy approved in early 2007 for the downstream segments of the Fox River.  EPA has determined that the optimized remedy is as protective as the dredging-only remedy.  Also, this optimized remedy allowed the project to achieve the goal of reducing fish exposure to PCBs in an accelerated timeframe and was more cost effective than the remedy set forth in the original Record of Decision.

For more information on capping and cover remediation methods, please visit
Click here to view a map of Little Lake Butte des Morts and the remediation areas addressed by the LLCT.
The map below shows the engineered cap locations for OU1.

Above is a graphic that shows how the armored caps were constructed on the floor of the lake to keep the low PCB-concentrated sediment in place permanently.
The model above was used at public meetings on the optimized remedy to demonstrate how the armored cap was constructed. Click on the photo for a larger view of the model.