| Summary: | <p>Four techniques for obtaining δ<sup>18</sup>O and δ<sup>2</sup>H values in clay-rich geologic media were
compared and evaluated. The results of this evaluation were then applied to a hydrogeologic
investigation of a complex clay-rich aquitard system. The four techniques included mechanical
squeezing, centrifugation, azeotropic distillation, and a direct soil-water equilibration technique.
Direct CO<sub>2</sub>-core equilibration yielded sufficiently accurate and reproducible δ<sup>18</sup>O results of pore
water in clay-rich tills. Mechanical squeezing and centrifugation produced results similar to
direct equilibration. Azeotropic distillation produced a high level of discrepancy in δ<sup>18</sup>O and
δ<sup>2</sup>H results compared to the other methods. The results of this study suggested that direct
equilibration is the best method for determining detailed δ<sup>2</sup>H and δ<sup>18</sup>O values of pore water in
clay-rich aquitard systems.</p>
<p>The aquitard system investigated in this study consisted of a thick Quaternary till
overlying an intertill aquifer. A detailed vertical profile of pore water δ<sup>18</sup>O through the aquitard
suggested that the till unit was divisible into three distinct hydrogeochemical zones: an upper
zone (0 - 10.5 m), an intermediate (10.5 - 30m) zone, and a lower zone (30 - 62.5 m). A
comparison of laboratory and field hydraulic conductivity (K) values suggested that the K in the
upper 30 m of till is higher than the underlying till due to a system of interconnected fractures
and sand layers. In contrast, results suggested that the lower zone (35 - 62.5 m) was not
fractured but contained sand lenses or streaks. Results of K measurements supported the
presence of three distinct zones suggested by the δ<sup>18</sup>O data. Bulk K was estimated to range
from 3.2x10<sup>-9</sup> to 3.4x10<sup>-8</sup> m/s and 1x10<sup>-11</sup> to 1x10<sup>-10</sup> m/s in the upper/intermediate and lower
zone, respectively. Measured values of hydraulic head in the aquitard supported the contention
that the lower zone had a significantly lower K than the overlying till. Although K in the upper
and intermediate zones is high, these data suggest that active groundwater flow is limited to
shallow localised zones. This investigation also shows that a three-dimensional study of
groundwater flow at the site is warranted.</p>
<p>Note:</p><p>Page 61 is missing.</p>
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