Hazardous Substance Research Centers/South & Southwest

What Is In-Situ Capping?

In-situ capping involves the placement of a covering or cap over an established layer of contaminated sediment. This covering seals the sediments physically and chemically, preventing pollutants from migrating into the surrounding water. The cap is composed of one or more layers of sand, silt, rock, or geotextile fabric. Soil layers can be dredged from a nonpolluted underwater location or collected at a site on-land.

In-situ capping does not transform these pollutants into harmless substances; however, the act of isolating them gives natural forces more time to break down the pollutants. The thickness of the cap depends on a variety of environmental factors, but it is normally from two to five feet thick.

As a single-step technology that requires no sediment removal, transport, or pretreatment, in-situ capping promises a less complex and costly approach to remediation.