Michael R. Shultz blogs that outcropping ancient river deposits illustrates the primary challenge to successful groundwater remediation ... stratigraphic heterogeneity. Encountering heterogeneity in the form of stratigraphic layering is common at every groundwater remediation site where sedimentary aquifers are impacted. Unfortunately, so too is the common practice of layer labeling and counting in which it is assumed that the first sand encountered when drilling (i.e., the A sand), is a homogeneous, isotropic layer, followed by the next layer, etc. This almost never the case, and in fact should be presumed not to be the case.
In the example discussed here, as a result of lateral shifting of the river channel through time, the sands are deposited not from the bottom up as commonly assumed, but from left to right as the channel migrated with time. The sand bodies are hydraulically separated from one another by thin clay units which appear as dark bands dipping from upper left to lower right. This shingled or laterally-offset stacking is a common feature of sedimentary deposits. The significance of this when addressing remediation of a contaminated aquifer, is that the three wells installed into the uppermost sand for the purpose of monitoring or remediation are really not in hydraulic communication with one another. If you and your remediation engineers were trying to inject or extract for remediation purposes, the outcome would not be what you hoped for.
Also of note is that high resolution subsurface data like HPT or CPT for these locations would look identical, and the lateral shingling would not be identified without knowledge of the environment and stratigraphy. Depositional models or facies models predict such heterogeneity and should be applied at groundwater remediation sites where sedimentary aquifers are impacted.
Original URL: https://www.linkedin.com/pulse/why-groundwater-remedies-fail-sand-michael-r-shultz
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