Use of Single-Well Tracer Dilution Tests to Evaluate LNAPL Flux at Seven Field Sites
Article first published online: 28 DEC 2011
© 2011, The Author(s). Ground Water © 2011, National Ground Water Association
Volume 50, Issue 6, pages 851–860, November/December 2012
How to Cite
Mahler, N., Sale, T., Smith, T. and Lyverse, M. (2012), Use of Single-Well Tracer Dilution Tests to Evaluate LNAPL Flux at Seven Field Sites. Groundwater, 50: 851–860. doi: 10.1111/j.1745-6584.2011.00902.x
- Issue published online: 6 NOV 2012
- Article first published online: 28 DEC 2011
- Received February 2011, accepted November 2011.
Petroleum liquids, referred to as light non-aqueous phase liquids (LNAPLs), are commonly found beneath petroleum facilities. Concerns with LNAPLs include migration into clean soils, migration beyond property boundaries, and discharges to surface water. Single-well tracer dilution techniques were used to measure LNAPL fluxes through 50 wells at 7 field sites. A hydrophobic tracer was mixed into LNAPL in a well. Intensities of fluorescence associated with the tracer were measured over time using a spectrometer and a fiber optic cable. LNAPL fluxes were estimated using observed changes in the tracer concentrations over time. Measured LNAPL fluxes range from 0.006 to 2.6 m/year with a mean and median of 0.15 and 0.064 m/year, respectively. Measured LNAPL fluxes are two to four orders of magnitude smaller than a common groundwater flux of 30 m/year. Relationships between LNAPL fluxes and possible governing parameters were evaluated. Observed LNAPL fluxes are largely independent of LNAPL thickness in wells. Natural losses of LNAPL through dissolution, evaporation, and subsequent biodegradation, were estimated using a simple mass balance, measured LNAPL fluxes in wells, and an assumed stable LNAPL extent. The mean and median of the calculated loss rates were found to be 24.0 and 5.0 m3/ha/year, respectively. Mean and median losses are similar to values reported by others. Coupling observed LNAPL fluxes to observed rates of natural LNAPL depletion suggests that natural losses of LNAPL may be an important parameter controlling the overall extent of LNAPL bodies.