Characterizing a 1,4-Dioxane Groundwater Plume Upwelling into Wetlands Using the Triad Approach
Jackson Kiker, ECC, 33 Boston Post Road West, Suite 340, Marlborough, MA, 01752, US, Tel: 508-229-2270, Fax: 508-229-7737, Email:  jkiker@ecc.net
Al Easterday, ECC 33 Boston Post Road West, Suite 340, Marlborough, MA, 01752, US, Tel: 508-229-2270, Fax: 508-229-7737, Email: aeasterday@ecc.net
Jeff Donovan, ECC, 33 Boston Post Road West, Suite 340, Marlborough, MA, 01752, US, Tel: 508-229-2270, Fax: 508-229-7737, Email: jdonovan@ecc.net
Michael Rossi, Stone Environmental, 535 Stone Cutters Way, Montpelier, VT, 05602, US, Tel: 802-229-2194, Fax: 802-229-5417, Email: mrossi@stone-env.com
David Crosby, Stone Environmental, 535 Stone Cutters Way, Montpelier, VT, 05602, US, Tel: 802-229-2194, Fax: 802-229-5417, Email: dcrosby@stone-env.com

Awareness of 1,4-dioxane as an emerging contaminant of concern associated with chlorinated VOC (CVOC) plumes has raised public and regulatory concerns over past releases and potential future exposure.  Due to 1,4-dioxane’s hydrophilic properties and low soil-partitioning it results in 1,4-dioxane migration ahead of CVOCs plume, a plume previously defined by CVOC extent required timely re-characterization to determine the extent of 1,4-dioxane within and potentially beyond the previously established downgradient plume extent.

This 1,4-dioxane assessment was focused within an area of the plume where discharge of the plume into two surface water bodies was likely to be occurring.  In addition to the surface water bodies, the area included a large area of floodplain and wetlands.  Limited access to the floodplain, schedule constraints, and project economics required installing piezometers using a Geoprobe^® methods to intercept 1,4-dioxane during a single mobilization.  Original proposed investigation plan was based on a conventional approach with long equipment down-times waiting for off-site analytical results at a costly premium for quick turnaround time.

The geology within the wetland and floodplain is comprised of sand/silt layers atop a marine clay unit, which overlies an undulating bedrock surface.  Atop of the clay layer, a deep transmissive sand layer (called the lower sand unit) is the preferential contaminant pathway for the CVOC and 1,4-dioxane plume.  Within the wetland and floodplain area, the bedrock, clay, and sand/silt layers rise sharply towards the surface forcing the groundwater to upwell and discharge to the surface water(s) of the wetlands area.

Utilizing an innovative technique like Headspace Solid Phase Micro-Extraction with Gas Chromatography/Mass Spectrometry (HS/SPME/GC/MS), allowed for characterization of the extent of 1,4-dioxane using a Triad dynamic work strategy. 

A sampling approach utilized the HS/SPME/GC/MS real-time field characterization method, which provided a cost-effective plume characterization that was completed during a single field mobilization.

Relationship between Hydrocarbon Residuals and Groundwater Concentrations Downgradient in the Borden Aquifer
Student Presenter
Tianxiao Yang, Department of Earth and Environmental Science, University of Waterloo, 200 University Avenue West, Waterloo, Ontario, Canada N2L 3G1, Fax: 519-746-7484, Email: t8yang@sciborg.uwaterloo.ca
Jennifer Lambert, Department of Earth and Environmental Science, University of Waterloo , 200 University Avenue West , Waterloo , Ontario , Canada N2L 3G1 , Tel: (519) 888 - 4567 x 37287 Email: lambert_j_m@yahoo.com
James F. Barker, Department of Earth and Environmental Science, University of Waterloo, 200 University Avenue West, Waterloo, Ontario, Canada N2L 3G1, Tel: 519-888-4567 x 32103, Fax: 519-746–7484,  Email: jfbarker@sciborg.uwaterloo.ca  

Residual NAPL (non-aqueous phase liquid) serves as a contaminant source that may persist for decades. Identification of the distribution of the NAPL residuals is of significance in selecting appropriate remediation alternatives. The major objective of this research is to delineate the residual gasoline distribution in two source zones at Canadian Forces Base Borden Aquifer Facility and identify the relationship between residuals and the groundwater plume. The GMT (90% API 94-01 gasoline mixture with 9.8% methyl-tert-butyl-ether (MTBE) and 0.2% tert-butyl alcohol (TBA) by volume) source zone and the E10 (90% API 94-01 gasoline mixture with 10% ethanol by volume) source zone were created below the water table in 2004. Soil cores were collected from the center of the source zone, from the upgradient side and 4.5 m downgradient. Subsamples were extracted for chemical analysis (including BTEX, trimethylbenzenes and naphthalene). The presence of residuals was inferred following the method of Feenstra et al. (1991). Gasoline residuals were inferred in cores from the source zones but no residuals were detected in the downgradient and upgradient cores. Little buoyant rise during injection is evident. The groundwater contaminant concentrations in monitoring row shows good spatial correspondence to the soil extract contaminant concentrations in the source zone. This suggests that residual NAPL in a source zone may be usefully inferred from groundwater concentrations immediately downgradent, at least in hydraulically simple aquifers.

Top