LNAPL MIGRATION FROM UPLAND SOURCE ZONES TO SURFACE WATER

Sites with LNAPL-related impacts to adjoining surface water bodies often include seeps and sheens from one or more sources of varying product types and ages. Migration pathways are notoriously hard to find, and conceptual site models often involve LNAPL flow primarily along the groundwater table. Proprietary electrical resistivity imaging work has provided new insights regarding the interaction between LNAPL-related groundwater impacts and surface water. These data indicate that migration pathways are often small, below the groundwater table, and may be microbially controlled. Additionally, monitoring well data alone are normally insufficient to develop an effective conceptual model of these sites due to inadequate data density and depth of investigation that often stops just below the groundwater table. These findings indicate that common assumptions about LNAPL migration may be insufficient for understanding these sites. Case studies will be discussed to illustrate the general patterns observed and the resulting paradigm shift required to more effectively investigate and remediate these sites at lower cost.