A remedial investigation (RI) is ongoing at a site in New York State adjacent to the Hudson River. The focus of the investigation is a polychlorinated biphenyl (PCB) dense non-aqueous phase liquid (DNAPL) in the fractured shale bedrock near a former industrial outfall. The objective of the RI is to delineate the vertical and horizontal extent of the PCB DNAPL in the bedrock. Data collected during the RI will be used in the Feasibility Study to evaluate and select appropriate remedial alternatives for the DNAPL.
As with many investigations at contaminated fractured rock sites, characterization and evaluation of the hydrogeologic controls on the location of the DNAPL zones is particularly challenging. The spatial distribution of the DNAPL has been strongly influenced by the stratigraphy and structure of the shale, hydraulic gradients within the shale, as well as the physical and chemical properties of the DNAPL.
A number of investigative techniques were used to develop the conceptual model of the hydrogeologic framework and DNAPL distribution at this site. These techniques included: rock core examination, sampling and analysis; bedrock and outcrop fracture mapping; aerial photograph review; multi-level monitoring well installation; visual observations of DNAPL presence and accumulation; borehole geophysics; hydraulic testing, including packer pressure tests, slug tests, and step-drawdown tests; periodic water level monitoring; and groundwater, surface water and DNAPL sampling and chemical analysis.
This paper presents a summary of the data collection techniques used to delineate the extent of the DNAPL, as well as a conceptual model for the site.
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