Poonam Kulkarni and GSI Colleagues Publish Open Access Article on Natural Source Zone Depletion (NSZD) at an LNAPL Site

Poonam Kulkarni, Charles Newell, David King, and Lisa Molofsky at GSI, and Sanjay Garg at Shell Global Solutions (US), recently published a peer-reviewed, open access article titled “Application of Four Measurement Techniques to Understand Natural Source Zone Depletion Processes at an LNAPL Site” in Groundwater Monitoring and Remediation.

In this study, four different NSZD measurement methods (Gradient Method, Carbon Traps, Dynamic Closed Chambers [DCC LI-COR], and Thermal NSZD monitoring), as well as LNAPL composition and dissolved gas sampling, were applied at a site in Southern California. These techniques were used to evaluate key questions such as:
·         how do different NSZD rate measurement methods compare, and what causes variability in NSZD results?;
·         to what extent NSZD processes are occurring in LNAPL within the saturated zone?; and
·         how is NSZD related to LNAPL composi­tion change over time?

Key conclusions include:
·         Carbon Traps and Thermal NSZD monitoring measurement methods provided the most consistent NSZD data at this geologically heterogeneous site, with two location average NSZD rates of 540 and 480 gal/acre/year, respectively.
·         Overall, comparisons of NSZD rates between methods were challenging due to different measurement timeframes, significant temporal and spatial heterogeneity, and operational challenges with two of the NSZD methods.
·         Dissolved gas sampling provided direct evidence that CH4 and CO2 are being gener­ated at high rates in the saturated zone at LNAPL-impacted locations as compared to the background location. Sampling with the IsoFlask (closed-system sample collection) as com­pared to standard sampling methods (open-system sample collection) provided greater confidence of the dissolved gas concentrations. Stripping of inert gases such as N2 and Ar confirmed the presence of vigorous ebullition processes in LNAPL-impacted groundwater zones.
·         Finally, samples of subsurface LNAPL were collected for analysis in 2007 and 2016; results indicated that diesel-range constituents were already very degraded and anaerobic degradation of gasoline-range constituents was ongoing.
 
Click the following link to download a copy of the open access article: https://ngwa.onlinelibrary.wiley.com/doi/full/10.1111/gwmr.12398 

For more information, please contact Poonam Kulkarni (This email address is being protected from spambots. You need JavaScript enabled to view it.) or Chuck Newell (This email address is being protected from spambots. You need JavaScript enabled to view it.)