structural geology, propagation mechanics and - Stanford School of ...

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