Dr. David Huntley
Professor Emeritus of Geological Sciences,
San Diego State University
The movement of light non-aqueous phase liquids – a risk perspective.
Part II - Practical Assessment
David Keith Todd Distinguished Lecture Series
Sponsored by GeoSyntec Consultants, Regenesis, and Luhdorff & Scalmanini, Consulting Engineers
$30 for members
$35 for non-members
$10 extra for walk-ins
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Natural attenuation of dissolved phase contaminants is widely recognized and consideration of it has become a standard part of assessing the risk of future contamination. Stabilization of the footprint of a dissolved phase plume as a result of natural attenuation is well understood. Much attention has turned to the source of many of the dissolved phase plumes, a non-aqueous phase liquid (NAPL) with significant soluble components. Both regulatory agencies and responsible parties want to know the velocity of the NAPL, whether the NAPL footprint is likely to expand, and, if so, the future extent of the NAPL. Remediation of a NAPL is directed at both decreasing the mass of the soluble components contributing to the dissolved phase plume and to limiting the potential expansion of the NAPL source. Significant lateral or downgradient expansion of the NAPL source can result in an expanded dissolved phase plume even under conditions where degradation rates are high. The success of s ource area remediation is often judged by the degree to which the mobility of the NAPL is reduced or eliminated.
Once the source of a NAPL (e.g. leaky tank, pipeline break, surface spill) is eliminated, there are several physical processes that limit the mobility of the NAPL. As the NAPL spreads, a fixed volume of NAPL moves into an increasingly large volume of rock or soil, thereby decreasing the saturation of the NAPL and, as a result, the mobility of the NAPL. At the trailing edge of the NAPL, water will displace NAPL, ultimately stabilizing the NAPL by reducing NAPL saturation to it's residual saturation. Movement at the leading edge of the NAPL source area will be limited by the need for NAPL to accumulate to a sufficient degree that the capillary entry pressure is exceeded. This talk will discuss the physical controls on the mobility of NAPLs (emphasizing LNAPLs), a variety of approaches to assess the mobility of NAPLs, and the typical time frames that should be considered when putting NAPL mobility into a risk context.
Dave Huntley is a Professor Emeritus of Geological Sciences at San Diego State University. He has taught graduate and undergraduate classes in groundwater hydrology for 31 years after obtaining his Ph.D. at Colorado School of Mines. His research focus is the distribution, mobility, and dissolution of non-aqueous phase liquids, the effects of geologic heterogeneity on dissolved phase solute transport, groundwater flow and solute transport in fractured rock, and the application of geophysics to groundwater hydrologic problems. He is currently Associate Editor of the journals Ground Water and Ground Water Monitoring and Remediation. In addition to his research and journal activities, he is a private consultant for both industry and regulatory agencies throughout the country.