Iterative High-Resolution Site Investigation and Remediation
Monday, December 4, 2017: 3:30 p.m.
Subsurface investigation and in situ remediation technologies have historically been linked. The limitations of conventional drilling technologies led to investigations yielding insufficient data density to characterize site heterogeneities, and remediation systems with insufficient numbers of delivery points accurately placed to overcome impediments to site remediation imposed by heterogeneity. The demand for cost-effective remedial strategies has spawned an expanding array of direct push technology (DPT) tools for both investigation and remediation. Geophysical and hydrogeologic measurement tools combined with discrete sampling allow geoscientists to collect high resolution site characterization (HRSC) data and develop an enhanced conceptual site model (CSM) that accurately reflects transport and storage properties of contaminants in soil and groundwater. Subsequent refinement of the CSM using high resolution data allows remediation geoscientists to target the contaminant mass adequately within the full array of porosity and permeability textures common in both naturally deposited and anthropogenic formations.
While a complete HRSC in advance of remediation is an appropriate goal and defines an environmental management paradigm shift, many legacy, abandoned, and underfunded sites do not offer the luxury of this approach. Iterative cycles of site characterization, CSM refinement and remediation become fruitful when implemented using high density data and DPT investigative tools.
An example site in Louisiana has been the subject of iterative investigations which identified a retail gas station as the source of a petroleum hydrocarbon plume in groundwater seeping into and impacting a down-gradient stream. A dense DPT grid of in-situ chemical oxidation (ISCO) injection points near the stream bank identified localized pockets and channels of non-aqueous phase hydrocarbons not easily discernable using a traditionally drilled network of monitoring wells. Pressure and flow monitoring allowed injection of large volumes of oxidant into heterogeneous sediments. Data collected throughout the remediation effort led to a revised CSM and a cost-effective remedial strategy.