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Sustainable, Low-Profile Investigation Technique Finds Numerous Contaminant Sources: Bronx Borough, New York City Example

A cost-effective and non-intrusive technique was implemented to characterize a multi-acre area within New York City as part of an Urban Renewal Area program in order to identify areas where contamination is present in soil, groundwater, and/or soil vapor, and to accurately guide further site investigation activities. The New York City Department of Health (NYCDOH) and the U.S. Environmental Protection Agency (USEPA) chose a passive soil gas (PSG) investigation technique to cover approximately 150 acres in a mixed residential and light industrial neighborhood. Using a state-of-the-art sampling system in both sampler design and sample analysis, a broad range of volatile and semi-volatile organic compounds can be identified, including chlorinated solvents and petroleum hydrocarbons.

The samplers were installed via a small diameter (2cm) hole advanced to a depth of approximately 90 cm using a hand-held rotary hammer drill. The samplers were deployed in a grid/transect-pattern along public right-of-ways to cover the area while virtually eliminating underground utility concerns and generating no waste from soil cuttings. Three-hundred and twenty-four (324) samplers were installed and left in the subsurface for seven days, after which time they were shipped back to the laboratory. The samplers were analyzed following EPA Method 8260C utilizing advanced thermal desorption-gas chromatography/mass spectrometry (TD-GC/MS) instrumentation, which does not generate any solvent waste. The resulting analytical data was computerized into compound-specific data files that contained 49 compounds. The spatial distributions of numerous compounds of interest were examined by contour maps that enabled a depiction of the mass changes across the area.

The resulting data from the survey revealed several previously unknown potential sources of petroleum hydrocarbon and chlorinated solvents in the mature urban neighborhood, which present at a minimum the potential for future on-site vapor intrusion issues. As an example of the information available from the survey, tetrachloroethylene (PCE) was recorded at 173 locations with eleven separate/distinct areas of elevated measurements. A statistical evaluation of eight compounds revealed the detections generally followed a Frechet probability distribution. The discovery of these source areas while only sampling in public right-of-ways (e.g., through sidewalks and ornamental tree boxes with no need for property access permissions), with a relatively non-obtrusive technology, provided NYCDOH and the USEPA a powerful tool for potential enforcement follow-up and an invaluable site-management tool.