structural geology, propagation mechanics and - Stanford School of ...
structural geology, propagation mechanics and - Stanford School of ...
structural geology, propagation mechanics and - Stanford School of ...
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anticipated sustainable pumping rate based on the results <strong>of</strong> simple slug tests <strong>and</strong> the<br />
assumption <strong>of</strong> homogeneous, isotropic permeability. Given any <strong>of</strong> the CB scenarios<br />
presented in Figures 7.12, 7.13 <strong>and</strong> 7.14, this approach would lead to misplaced wells,<br />
both in terms <strong>of</strong> their location relative to the effective contaminant transport direction <strong>and</strong><br />
the spacing needed for complete capture given elliptical drawdown patterns (Matthai et<br />
al., 1998). Failure to recognize the transport-distorting effects <strong>of</strong> CBs would also<br />
complicate efforts to locate the unknown source <strong>of</strong> a contaminant plume, <strong>and</strong>/or identify<br />
its extent based on limited well data.<br />
6. General discussion<br />
While the model simulation scenarios presented above in no way constitute a<br />
complete treatment <strong>of</strong> the flow <strong>and</strong> transport effects <strong>of</strong> CBs in the Aztec s<strong>and</strong>stone, the<br />
results do illustrate a clear potential for substantial impacts. Given the broad practical<br />
implications <strong>of</strong> these findings, a few key interpretations <strong>and</strong> assumptions underlying this<br />
work warrant further comment.<br />
Firstly, as acknowledged in the section on mapping, limitations <strong>of</strong> outcrop exposure,<br />
image resolution <strong>and</strong> map scale prevent the final CB map (Figure 7.3) from capturing the<br />
full abundance <strong>and</strong> detail <strong>of</strong> the b<strong>and</strong> array present in the field. The map does, however,<br />
accurately represent the relative abundance, distribution, orientation <strong>and</strong> connectivity <strong>of</strong><br />
the exposed pattern <strong>of</strong> oldest CBs that dominates the area <strong>and</strong>, as such, is adequate to the<br />
purpose <strong>of</strong> modeling flow <strong>and</strong> transport effects at relatively coarse scales <strong>of</strong> practical<br />
interest. In fact, ins<strong>of</strong>ar as the true abundance, distribution <strong>and</strong> connectivity <strong>of</strong> the b<strong>and</strong>s<br />
are under-represented in the map, the substantial flow <strong>and</strong> transport effects realized here<br />
can reasonably be considered as conservative, low-end estimates.<br />
Also, our 2-D approach to an undeniably 3-D problem is dictated by the nature <strong>of</strong> the<br />
outcrop exposure, which presents a roughly horizontal slice through the CB array to<br />
reveal the detailed pattern as mapped. Given accurate 3-D data <strong>and</strong> sufficient computing<br />
power, the full spatial effects <strong>of</strong> the entire CB array could be modeled. Nonetheless,<br />
abundant field observations throughout the upper 600 m <strong>of</strong> the Aztec s<strong>and</strong>stone,<br />
particularly in areas <strong>of</strong> topographic relief, attest to the vertical persistence <strong>of</strong> the overall<br />
CB array. We suggest therefore that, to a reasonable first approximation, the<br />
anastomosing pattern <strong>of</strong> b<strong>and</strong>s in Figure 7.3 can be assumed to extend hundreds <strong>of</strong> meters<br />
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