Delineating the extent of brine contamination in shallow groundwater systems using piezometers
is costly and does not provide adequate data resolution. Direct-push (D-P) electrical conductivity
(EC) profiling enables rapid in situ measurements of bulk soil EC (ECa) at the cm scale. Previous
studies using D-P EC profiling to detect contaminant plumes have solely relied on ECa
measurements, and where attempts were made to isolate pore-water salinity variations from
changes in ECa they were accomplished using simple linear methods. In this study D-P EC
profiling was used to define groundwater salinity distributions using an established soil
conductance model and estimate the timing of groundwater contamination at a long-term potash
mine in south-central Saskatchewan, Canada. The site was dominated by fine-grained postglacial
and glacial sediments with known Na-K-Cl brine impacts resulting from mining activities.
Coreholes (n=22) were drilled to 7.6-12.2 m below ground (mbg) to obtain continuous cores for
detailed geologic descriptions and measurements of index parameters (n=522) below the water
table. Pore-water EC (ECw) and Cl- results from squeezed core samples (n=142) at 12 locations
were compared to ECa measurements collected using a D-P probe adjacent to each corehole.
Measured ECw and pore-water Cl- results ranged from 1.94-55.1 mS/cm and 87-20,700 mg/L,
respectively. In situ D-P EC values from logs collected adjacent to all 22 coreholes ranged from
2-8 mS/cm within the oxidized zone (5-6 mbg) and decreased to background values of
0.3-2 mS/cm within the underlying unoxidized zone. Significant linear ECa–ECw regressions
established for four lithological groups (r2=0.78-0.95) were used with porosity and dry density
measurements to generate high-resolution depth profiles of ECw from D-P EC measurements. A
significant linear ECw–Cl regression (r2=0.92) further enabled the generation of pore-water Cldepth
profiles from ECw predictions. Observed 1D vertical profiles of Cl-, ECw, and ECa at three
locations were modeled. Results suggested solute transport can be described as diffusion-dominated
below depths of 3-5 mbg and that groundwater contamination began shortly after the
onset of mining. Based on the results attained, this method can generate high-resolution depth
profiles of pore-water salinity that can be used to define the lateral and vertical extent of brine
contamination, dominant solute transport mechanisms, and timing of groundwater
contamination.
| Identifer | oai:union.ndltd.org:USASK/oai:ecommons.usask.ca:10388/ETD-2015-06-2016 |
| Date | 2015 June 1900 |
| Source Sets | University of Saskatchewan Library |
| Language | English |
| Detected Language | English |
| Type | text, thesis |
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