Need Help? Call Us Today!| (850) 558-0609

Fostering the Remediation & Redevelopment of
Manufactured Gas Plant Sites

Rick Beach


Presentation Title

Remediation of DNAPL Impacted Sediments –  “In the Eye of the Beholder?”

Rick Beach, Associate Principal & Vice President, GZA GeoEnvironmental, Inc.

Co-Authors: Meredith Hayes, Dan Amate, Michael Shaw, and John Oberer, GZA GeoEnvironmental, Inc.


The evaluation and remediation of contaminated sediments is a mature practice which incorporates advanced methods for investigations, feasibility studies, and remediation. Likewise, addressing upland MGP and other DNAPL impacted soils is a mature practice, however, many challenges still remain when addressing MGP (and analogous) DNAPLs in sediment. Applying upland approaches to the aquatic environment can be misleading at best or just plain wrong.

In part, remediation of DNAPL impacted sediments is currently driven by a strong “remove or stabilize” mentality that originates from the relatively straight-forward removal or stabilization of upland DNAPL impacted soils.  Risk at the majority of DNAPL sediment sites (with no/limited ebullition) results from PAHs from DNAPL that are bioavailable from the pore water pathway to the benthic community in the surficial bioactive zone (BAZ). However, often the most common investigative and remedial approaches are focused on the delineation of the DNAPL in sediments for removal or in-situ stabilization. As a result, the following mistakes have occurred:

  • No evaluation of bioavailable PAHs.
  • Limiting bioavailable assessments to solid phase partitioning instead of pore water evaluations, resulting in remedial footprints that have been 189% larger than needed.
  • Compositing the 4-6-inch BAZ into 1 or 2-foot sampling intervals, with the resulting overestimation of PAH concentrations 4-13 fold at some sites. 
  • Improper use of sediment dating.
  • Inadequate or no evaluation of DNAPL weathering, which can greatly impact DNAPL migration and the partitioning of PAHs into pore water.
  • Lack of PAH and supportive data over the complete sediment profile, without which technical impracticability and remedial cost effectiveness cannot be determined.  These are intrinsically “In the Eye of the Beholder.”

The presentation will include a primer on why sediments should not be treated as wet soils, and examples of key lessons learned when dealing with MGP (and analogous) DNAPLs in sediments as part of site redevelopment.


Rick is GZA’s National Sediments Practice Leader.  He has a BS in Marine Biology and a MS in Chemical Oceanography.  His 40-plus years of experience covers the range from investigations to feasibility studies, remedial designs, and project optimizations during remedial construction.  His approach to projects benefits from his interdisciplinary background in analytical chemistry, fate & transport studies, environmental research, research diving, remedial technologies, and is influenced by a healthy, albeit skeptical respect for site-specific “facts.” (in air-quotes)  In recent years, Rick’s projects have focused on evaluating upland sources of contamination, assessing potential contributions to Superfund river sites, and developing scientifically based advocacy positions for the allocation of liabilities.