Characterizing a Complex TCE Groundwater Plume, Eliminating Suspected Source Areas, and Reducing Investigation Costs for a RCRA RFI at Shaw AFB, SC
Jonathan Shireman, PG, Shaw Environmental & Infrastructure, Inc., (Presenter). Paper authors also include Randal L. Rogers, Jr., Gas Environmental Services, and Jody Edwards, PG, Stone Environmental, Inc.
The Triad Approach was successfully used 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 a flexible and robust plume delineation, and identification and characterization of sources.
Systematic planning meetings included South Carolina DHEC, USAF Air Combat Command, USACE Omaha District, Shaw E&I, and Stone Environmental. An open, cooperative effort yielded consensus on the use of Triad, 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 the fieldwork to rapidly obtain and communicate data to the Triad Team, and reach consensus on 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 performed vertical groundwater profiling to establish distributions of relative hydraulic conductivity (Ik) and contaminant concentrations. Onsite analysis of VOCs provided defensible quality data for near real-time decisions on 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 (EDDs) and profiling hydrostratigraphic data were uploaded into ArcView IMS and posted on a project web-portal; providing timely 3-dimensional interactive viewing of the developing TCE plume to all stakeholders. Frequent Triad Team teleconferences addressed findings, next steps and site conclusions
In a three-phase, single mobilization field effort over a 9-month period, the team successfully identified the actual 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 then installed.
Field analytical quality, team cooperation and well-managed uncertainty resulted in an estimated savings of up to $1.5M in investigations cost. 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 siting the monitoring well network, eliminating the need for subsequent investigation phases.
Using Environmental Visualization System (EVS) Modeling to Develop Remediation Alternatives
Kym Takasaki, USACE, Seattle District
The Well 12A Superfund site in Tacoma, WA encompasses the source of contamination at the property of the former Time Oil Company and the City of Tacoma's production Well 12A. The contaminants of concern in soil and ground water are tetrachloroethane (PCA), tetrachloroethene (PCE), trichloroethene (TCE), trans-1,2-dichloroethene (DCE), and other VOCs. In addition, residual NAPL and soil concentrations exceeding human health standards also remain in place. Several remedial actions have been implemented since 1988, including groundwater extraction and treatment, excavation, and soil vapor extraction. However, no detailed conceptual site model had been constructed to evaluate the effectiveness of the remedies. This case study serves as an example of how 3-D analysis of existing data sets can be used during long-term systems optimization. To aid in review of the remedy, a conceptual site model was developed using geostatistical 3-D data analysis/visualization (EVS) to help visualize present site conditions. These visualizations were then used during systematic planning sessions to identify both specific contaminant areas requiring additional treatment and site conditions that will impact treatment choices. These activities resulted in a clearly communicated proposed plan that will lead to additional treatment at the site and development of explicit remedial action objectives.