Pore Water Concentration Measurement in Boreholes in Low Permeability Cohesive Geological Media for Depth Discrete High Resolution Concentration Profiles

Date

2019-08-09

Authors

Martin, Gregory

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Journal ISSN

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Publisher

University of Guelph

Abstract

One of the major factors in building a Conceptual Site Model (CSM) is understanding the contaminant mass in the subsurface. A key factor is the contaminant mass within the pore water as this is its common mode of transportation. Given the heterogeneity frequently found in the subsurface, it is important to sample and analyze the pore water in a high resolution fashion to properly assess the contaminant’s subsurface distribution for the CSM. In this thesis, a high resolution sampling device to measure organic analyte pore water concentrations in low permeability cohesive geological media was developed and tested called the G-360 pore water sampling device (G-360 PSD). Laboratory soil column experiments simulating field conditions showed that the sampling device and subsequent analytical methodology is capable of accurately measuring the concentration of a variety of organic analytes within 14 days of placement. The device was then field tested in both ex-situ and in-situ applications. The ex-situ application involved pushing the samplers into a removed clay core and allowing it to equilibrate for a period of time with the core sample. The organic analyte’s pore water concentrations determined from using the G-360 PSD were strongly correlated with the pore water concentrations calculated from the soil core analysis: an R2 of 0.83 to 0.94 for all organic analytes tested. In the in-situ field application, multiple G-360 PSDs were suspended down a borehole using a metal line and pushed against the borehole wall using a FLUTe™ liner. Using a stepwise linear regression model with MLS concentration data and data from four other geophysical parameters led to an R2 of 0.85 when fitted against the G-360 PSD concentration data. In summary, this research represents a number of firsts, including: sampling pore water using a peeper device in a bore hole at depths greater than a few meters, sampling at the sub-meter scale, and sampling for a wide variety of organic analytes. The information collected at each site using this sampling device led to a different but more complete understanding of the CSM in comparison to traditional methods.

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Keywords

Pore Water, Peeper, Borehole, Chlorobenzenes, Trichloroethylene, Tetrachloroethylene, Toluene, Gas Chromatography, Mass Spectrometry, Isotope Dilution, Groundwater Sampling Device

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