August 11, 2017

Gary Wealthall Published in Groundwater Monitoring & Remediation Journal

Gary Wealthall, Ph.D. (Guelph) has co-authored a paper, entitled "Integrity of Clay Till Aquitards to DNAPL Migration: Assessment Using Current and Emerging Characterization Tools," published in the journal Groundwater Monitoring & Remediation on July 17, 2017.

The paper is the second of a paired set of papers from the same site in Denmark, where Geosyntec partnered with COWI, NIRAS, the Danish Technical University (DTU), and the Capital Region of Denmark.

Gary's co-authors were Annika S. Fjordbøge, Gry S. Janniche, Torben H. Jørgensen, Bernt Grosen, Anders G. Christensen, Henriette Kerrn-Jespersen, Mette M. Broholm.

The first paper was published last year, was entitled "Integrity of Clay Till Aquitards to DNAPL Migration: Assessment Using Current and Emerging Characterization Tools," and was published in the Journal of Contaminant Hydrology in Volume 189, pages 68-85 in June 2016.

Gary's co-authors on the first paper were Mette M. Broholm, Gry S. Janniche, Klaus Mosthaf, Annika S. Fjordbøge, Philip J. Binning, Anders G. Christensen, Bernt Grosen, Torben H. Jørgensen, Carl Keller, Henriette Kerrn-Jespersen.

Abstracts

Part 2
Integrity of Clay Till Aquitards to DNAPL Migration: Assessment Using Current and Emerging Characterization Tools

Field investigations were carried out to determine the occurrence of tetrachloroethene (PCE) dense nonaqueous phase liquid (DNAPL), the source zone architecture and the aquitard integrity at a 30- to 50-year old DNAPL release site. The DNAPL source zone is located in the clay till unit overlying a limestone aquifer. The DNAPL source zone architecture was investigated through a multiple-lines-of-evidence approach using various characterization tools; the most favorable combination of tools for the DNAPL characterization was geophysical investigations, membrane interface probe, core subsampling with quantification of chlorinated solvents, hydrophobic dye test with Sudan IV, and Flexible Liner Underground Technologies (FLUTe) NAPL liners with activated carbon felt (FACT). While the occurrence of DNAPL was best determined by quantification of chlorinated solvents in soil samples supported by the hydrophobic dye tests (Sudan IV and NAPL FLUTe), the conceptual understanding of source zone architecture was greatly assisted by the indirect continuous characterization tools. Although mobile or high residual DNAPL (S t > 1%) only occurred in 11% of the source zone samples (intact cores), they comprised 86% of the total PCE mass. The dataset, and associated data analysis, supported vertical migration of DNAPL through fractures in the upper part of the clay till, horizontal migration along high permeability features around the redox boundary in the clay till, and to some extent vertical migration through the fractures in the reduced part of the clay till aquitard to the underlying limestone aquifer. The aquitard integrity to DNAPL migration was found to be compromised at a thickness of reduced clay till of less than 2 m.

Part 1
Integrity of Clay Till Aquitards to DNAPL Migration: Assessment Using Current and Emerging Characterization Tools

Characterization of dense non-aqueous phase liquid (DNAPL) source zones in limestone aquifers/bedrock is essential to develop accurate site-specific conceptual models and perform risk assessment. Here innovative field methods were combined to improve determination of source zone architecture, hydrogeology and contaminant distribution. The FACT™ is a new technology and it was applied and tested at a contaminated site with a limestone aquifer, together with a number of existing methods including wire-line coring with core subsampling, FLUTe® transmissivity profiling and multilevel water sampling. Laboratory sorption studies were combined with a model of contaminant uptake on the FACT™ for data interpretation. Limestone aquifers were found particularly difficult to sample with existing methods because of core loss, particularly from soft zones in contact with chert beds. Water FLUTe™ multilevel groundwater sampling (under two flow conditions) and FACT™ sampling and analysis combined with FLUTe® transmissivity profiling and modeling were used to provide a line of evidence for the presence of DNAPL, dissolved and sorbed phase contamination in the limestone fractures and matrix. The combined methods were able to provide detailed vertical profiles of DNAPL and contaminant distributions, water flows and fracture zones in the aquifer and are therefore a powerful tool for site investigation. For the limestone aquifer the results indicate horizontal spreading in the upper crushed zone, vertical migration through fractures in the bryozoan limestone down to about 16–18 m depth with some horizontal migrations along horizontal fractures within the limestone. Documentation of the DNAPL source in the limestone aquifer was significantly improved by the use of FACT™ and Water FLUTe™ data.

More Information

For more information regarding the second paper, visit: Goundwater Monitoring & Remediation
For more information regarding the first paper, visit: Journal of Contaminant Hydrology
For more information on Clay Till Aquitards and DNAPL Migration, contact Gary Wealthall at This email address is being protected from spambots. You need JavaScript enabled to view it..
To learn more about Gary see his profile at: https://www.geosyntec.com/people/gary-wealthall

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