Quantifying non-aqueous phase liquid (NAPL) mobility in sediments is critical when evaluating remedial alternatives and remediation engineering design. NAPL mobility in sediments cannot readily be evaluated using methods that are typically effective at upland sites. Little standardized guidance exists to evaluate NAPL mobility in sediment (currently in development with ASTM); therefore programs must be developed on a site-specific basis and negotiated with regulatory agencies with jurisdiction.
This case study presents a regulatory-approved risk-based approach to categorize NAPL in sediment as residual (immobile), mobile, or potentially migrating based on field observations and sediment core analysis. The approach is designed in a logical and progressive step-wise fashion with “off-ramps” after each step if the NAPL mobility is defined at that point. Thus, it is not necessary to complete the entire process, but only to conduct sufficient analysis to define the NAPL mobility potential. If NAPL in sediment is determined to be residual (immobile), then isolation and containment may be appropriate remedial actions. If NAPL is determined to be mobile or migrating, then additional remedial actions may be necessary to eliminate the potential for NAPL to migrate beyond its existing extent.

Primary Author / Conference Presenter:
Thomas Daigle
Project Manager
GEI Consultants, Inc.
Denver, Colorado, USA

J. Michael Hawthorne, GEI Consultants, Denver, CO
Camille Carter, GEI Consultants, Denver, CO
Lisa Reyenga, GEI Consultants, Denver, CO
Bjorn Bjorkman, GEI Consultants, Denver, CO