LESSON'S LEARNED FROM TWO DECADES OF DETAILED CHARACTERIZATION OF CHLORINATED SOLVENT SOURCE AREAS IN FRACTURED META-SEDIMENTARY BEDROCK SETTINGS IN MAINE

This presentation explores lessons learned and observations gained over two decades of acquiring and interpreting structural, geochemical and geophysical data from chlorinated solvent sites in fractured metamorphic sedimentary bedrock. The presentation will compare characterization and data reduction approaches we used in the mid-1990s to those used currently as a metric to measure progress in improving fractured bedrock characterization. Data from multi-level and discrete interval sampling devices (Westbay, FLUTe, straddle packer systems, and vertically paired wells) will also be compared to consider potential strengths and weaknesses of these tools in specific monitoring applications.

The presentation will draw from older characterization data which delineated approximately 235 acres of chlorinated solvent and jet fuel contamination in pellitic limestone (Carys Mills Formation) at Loring Air Force Base in northern Maine. Investigations there included 449 bedrock wells and borings completed between 1986 and 1997. Borehole geophysical investigations began in 1990 using early generation acoustic velocity logging tools, (later known as Acoustic Televiewer (ATV)). After 1993, Heat Pulse Flow Meter (HPFM), and Borehole Image Processing Systems (BIPS) were added to target groundwater sample intervals using low flow straddle packer methods, and to complete base wide and contaminant source area structural interpretations. Fracture flow models and methanol extracted rock chip sample data supported Technical Impracticability evaluations for matrix diffusion and DNAPL dominated source areas. From 1999 through 2006, these investigation methods were improved for characterization of DNAPL sources in fractured sedimentary bedrock (Waterville Formation) underlying the Eastland Woolen Mill Superfund Site in Corinna, Maine. Interpretative improvements included 3-D data visualization of oriented fracture data, groundwater, rock matrix, and tracer analytical results, in addition to HPFM, and borehole geophysical and tomographic data.