High Resolution Mobile NAPL Interval Identification and Transmissivity Calculations for DNAPL
High Resolution Mobile NAPL Interval Identification
and Transmissivity Calculations for DNAPL
Lisa Reyenga P.E. and Michael Hawthorne, P.G. (GEI Consultants, Inc.)
Lisa Reyenga, P.E.
Lisa Reyenga is a Senior Engineer with GEI Consultants, Inc. She has ten years of experience in the field of characterization and remediation of NAPL contaminated sites. Lisa’s particular specialty is in the quantification of NAPL recoverability under complex hydrogeologic conditions. She earned in BS from Tufts University and MS from the Massachusetts Institute of Technology.
Dense Non-Aqueous Phase Liquid (DNAPL) can be persistent in the saturated zone, and complex in terms of its distribution with multiple mobile NAPL intervals separated by lenses of lower permeability soils. These multiple MNIs can result in perched DNAPL that yields exaggerated thicknesses of DNAPL in wells relative to the actual MNI thicknesses in the formation. To date, no method has satisfactorily accounted for these complexities in the measurement of DNAPL transmissivity, thus yielding artificially low DNAPL transmissivity values due to falsely large assumed drawdowns. The authors have developed patent pending procedures to identify each individual MNI across a given well screened interval, and to accurately calculate DNAPL transmissivity values for each MNI and for the well in the aggregate. The resulting information provides precise determination of the elevation and thickness of each MNI as well as the associated DNAPL transmissivity value for each MNI. This information can be used in a variety of ways to augment the conceptual site model (CSM) to better quantify potential DNAPL migration risk and pathway identification and design improved remedies. Perhaps more importantly, this information can be used to justify cessation of DNAPL recovery and site closure where no other risk driver exists and DNAPL recovery is the only driver for continued work.