Confidential Third-party Subject Matter Expert

NAPL Mobility in Sediment in an Urban Waterway


  • Confidential


  • New Jersey

Key Elements

  • NAPL Mobility in Sediment
  • Urban waterway
  • Former MGP
  • Commingled Plumes
  • Subaqueous Capping
  • Litigation Support

GEI was retained as a confidential third-party subject matter expert (SME) to provide strategic and technical oversight of investigation and remediation for a former MGP Site adjacent to an urban waterway. The Site includes both upland and sediment NAPL impacts, and the sediment is also impacted by NAPL and other constituents of concern from other contaminated sites.

GEI works in a team with the client, internal and external counsel, and other SME consultants to aid in the management of the remediation program. This includes review of technical documents produced by the local consultant as well as work conducted by
other parties impacting the waterway. GEI also provides strategic guidance to ensure that the scope of investigations will meet the future needs of the Site and the client is well positioned for ongoing litigation.

Recent work at the Site has included oversight of the activities related to investigation and remediation of impacted sediments. GEI reviewed a third-party design plan for subaqueous capping and the on-site consultant’s investigation plan for improved NAPL

GEI identified that the existing plan for subaqueous capping did not include plans or cost estimates to address potentially migrating NAPL. Likewise, the existing investigation plan only addressed the presence/absence of NAPL and would not provide information on the potential for the NAPL to migrate to the surface water body. This discrepancy left the client open to unknown, but potentially significant, costs demanded by the third party to modify the remedy design to address potentially migrating NAPL.

GEI provided guidance to the client for modifications to the investigation workplan to be able to determine the potential for migration from the NAPL. GEI also provided cost estimates for potential modifications to the existing design plan for subaqueous capping to address potentially migrating NAPL. The estimates included multiple potential technologies as well as multiple scenarios for mobility (e.g. if all, none, or a portion of the total delineated area is assumed to have the potential to migrate).

This work allowed the client to make an informed decision on the benefits and costs for the scope of additions to the field investigation as well as to position themselves both strategically and financially for ongoing litigation with the third-party.

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