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State & Municipal Government
Delaware Department of Natural Resources and Environmental Control
Site Investigation and Restoration Branch
Sussex County, Millsboro, Delaware
Detection of trichloroethene (TCE) during routine water sampling at a local Boys and Girls Club in October 2005 was traced to the Millsboro, Delaware Township wells where TCE was detected at levels greater than the Maximum Contaminant Level. Since the Township of more than 2,500 residents relies solely on these wells for water, it was important that a thorough and aggressive site assessment be conducted to support decisions regarding immediate and long-term aquifer restoration and human health protection actions.
Immediacy of the situation required a flexible and adaptive decision process for selection of sample locations in the field based on real-time or next day data results. TRIAD methodology and principles were employed for rapid source identification and three dimensional delineation of TCE contamination. Use of direct-push vertical soil and groundwater profiling, fixed laboratory screening, and in-field decision process resulted in the collection of more than 300 vertical profile groundwater samples at 124 locations in approximately 6 months around and within the source area. Approximately 120 soil samples were collected within the source area. The direct-push sampling program that began at the well field tracked the TCE plume in three dimensions back to the actual source (a former poultry vaccine manufacturing facility) nearly a quarter mile southwest of the well field. The plume was defined in detail utilizing the direct-push analytical results and well installation results with Environmental Visualization Software. The possibility of intrusion of soil vapor into nearby structures was predicted using the Johnson and Ettinger model. Surface geophysics georeferenced to former building layout and aerial photographs optimized source area sample locations and subsequent interim removal actions.
The comprehensive sampling program was completed at a significant cost and time savings compared to a more traditional drilling and sampling program. Source removal interim actions were completed in less than 9 months after the initial discovery of TCE contamination, and a feasibility study was completed within 12 months of initial TCE discovery.
The Environmental Visualization Software model assisited in determining Membrane Interface Probe locations to further delineate the source of contamination for the completion of a Pilot Study Program at the source. An Insitu-Chemical Oxidation (Modified Fentons Reagent) Pilot Study, including monitoring (groundwater and soil sampling via direct push, groundwater sampling of onsite wells, and subsequent Membrane Interface Probe investigation), is currently in progress. A Pilot Study Report will be completed with recommendations and approach for full-scale Insitu-Chemical Oxidation remediation.