The Sheen Stops Here: How to Select a Remedial Technology that Won’t Pass the Buck



The Sheen Stops Here: How to Select a Remedial Technology that Won’t Pass the Buck

Presenter:  Todd Cridge (Arcadis US, Inc.)
Authors: Todd Cridge, Shannon Dunn and Barbara Orchard Aragon (Arcadis US, Inc.)


When non aqueous phase liquid (NAPL) seeps from soil and sediment to the surface of a water body and visible sheens occur, the Clean Water Act of 1972 (the “Sheen Rule”) can prompt the requirement that anthropogenic sheens be mitigated. The ability to predict the potential for NAPL seepage and resulting sheens, as well as their potential magnitude, requires a knowledge of NAPL mobility and natural depletion, hydrogeology, and groundwater-surface water hydrology. The scale and aggressiveness of mitigation measures should be connected to the existing and future potential for NAPL seepage to generate sheens, rather than assuming that all NAPL, both near the groundwater-surface water interface (GSI) and in the upland, will contribute to the generation of sheens. The NAPL seepage conceptual site models (CSM) includes delineation of mobile NAPL and identification of NAPL transport mechanisms. A well-developed NAPL seepage CSM will allow selection of the appropriate remedial technology. The selection of the remedial technology is based on the amount of mobile NAPL, the transport mechanism, and the mass flux of NAPL. Remedial technologies to control sheen can be categorized based on how they address sheen. By using the NAPL seepage CSM and the remedial technology categories, the remedial technology is selected that will best control the NAPL seepage at the site. This presentation will discuss the development of NAPL seepage CSM and the state of the art in NAPL seepage mitigation. The CSM should account for how NAPL migrates from soil and sediment to the GSI, mechanisms of NAPL seepage at the GSI, and how long upland NAPL flow will recharge NAPL at the GSI. The remedial technologies that can be used to address sheen, given the NAPL seepage CSM, will be presented, including innovative technologies.

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