MTBE

Hampton Bays, Suffolk County, NY

The Suffolk County Department of Health Services detected 54,000 ug/L of MTBE in a municipal well in Hampton Bays, Long Island. A site assessment procedure by a New York State Department of Environmental Conservation (NYSDEC) contractor suggested that a mixed fuel oxygenate plume including MTBE and its degradation product TBA extended over 2,500 feet from a leaking fuel tank to a sensitive surface water receptor, Tiana Bay. SSP&A was retained to model groundwater flow and the migration of MTBE and TBA to evaluate potential impacts on Tiana Bay and support the design and management of a pump-and-treat (P&T) remedy.

SSP&A allocated a spatially-variable additional recharge term weighted by property area and water usage data for residences in the study area, obtained by the state contractor. Transport modeling with the redefined recharge matched the plume well indicating that locally enhanced recharge caused deepening of the plume to three times the depth expected for typical conditions. The revised model was used to simulate conservative transport of MTBE, TBA, TAME and TAA. The model was later modified to simulate first-order decay of MTBE with accumulation of TBA, and recalibrated. Modeling indicated that degradation of MTBE to TBA is occurring at the site at a rate comparable to those calculated at other sites by a variety of investigators. This result was reinforced by a collaborative field study at the site that showed enriched d13C values in areas where TBA had accumulated. Recent data suggest the plume is shifting in response to changing pumping patterns at nearby Suffolk County supply wells. The model was also used to simulate the potential impacts of municipal well operations on plume migration.

The investigative and remedial approach adopted at the site was used as a demonstration site for a joint New York State Department of Environmental Conservation - Interstate Technology & Regulatory Council - Long Island Groundwater Research Institute workshop entitled MTBE and TBA Comprehensive Site Assessment and Successful Groundwater Remediation.  Dr. Matthew J. Tonkin was an invited instructor (December 2003). In September, 2004, the prime contractor on the Hampton Bays project, Environmental Assessment & Remediations (EAR) was the recipient of the 2004 NGWA Outstanding Groundwater Remediation Project Award, presented in December, 2004 at the NGWA national conference in Las Vegas. SSP&A was recognized as a project team member in this award.

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