September 8, 2008
6:00 - 7:30 pm
State Technical Community College
10915 Hardin Valley Road, Knoxville
J.L. Goins Administration Building, Cafeteria Annex
a Complex TCE Plume, Eliminating Suspected Source Areas, and
Reducing Investigation Costs for a RCRA Facility Investigation at
Shaw Air Force Base, South Carolina
(Presenter: Mark Maki)
Shaw Environmental & Infrastructure, Inc.
The Triad approach was used successfully to complete a RCRA Facility Investigation (RFI) in a complex geologic setting with highly sensitive land use. Low concentrations of TCE were discovered in a deep drinking water aquifer beneath the active airfield during investigation of a fuel leak in the water table aquifer at Shaw AFB. An RFI was initiated to identify sources and to define the extent of contamination in the lower drinking water aquifer. The Triad approach ensured a timely and efficient investigation, providing identification and characterization of sources, as well as flexible and robust plume delineation.
Systematic planning meetings included South Carolina DHEC, USAF Air Combat Command, USACE Omaha District, Shaw Environmental and Infrastructure, and Stone Environmental. An open, cooperative effort yielded consensus on the use of Triad, team members, and industrial reuse criteria. The Triad team developed an initial conceptual site model (CSM), project and data quality objectives (DQOs), and dynamic decision logic. Real-time measurement technologies and data visualization tools were used during field work to rapidly obtain and communicate data to the Triad team and to reach consensus at critical decision points using established decision logic. The Triad team interacted effectively with Shaw AFB airfield managers to mitigate safety concerns while working on the active flight line. The dynamic work strategy included vertical groundwater profiling to establish distributions of relative hydraulic conductivity and contaminant concentrations. On-site analysis of VOCs provided defensible, quality data for near-real-time selection of subsequent sampling locations. Suspected source-area soils were sampled for confirmation. The plume was adaptively tracked to its actual source and delineated to its downgradient extent. Daily electronic data deliverables and hydrostratigraphic data were uploaded into ArcView IMS and posted on a project web-portal, allowing timely three-dimensional interactive views of the developing TCE plume by all stakeholders. Frequent Triad team teleconferences addressed findings, next steps, and site conclusions. In a three-phase, single-mobilization field effort over a nine-month period, the team successfully identified the source area, delineated the vertical and lateral extent of the TCE plume in two separate aquifers, and revealed that six suspected source areas were benign. Based on this delineation, eight shallow and 24 deep monitoring wells were installed. Field analytical quality, team cooperation, and well managed uncertainty resulted in an estimated savings of up to $1.5 million in investigation costs. This savings was largely realized by a dynamic work strategy and sampling methods that allowed rapid plume delineation and an agreed upon decision logic and DQOs for determining when delineation was complete and for sitting the monitoring well network, eliminating the need for subsequent investigation phases.
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