You are here:
COMPARATIVE EVALUATION OF MTBE SITES ON LONG ISLAND
Citation:
Weaver*, J W., J. E. Haas, AND C. B. Sosik. COMPARATIVE EVALUATION OF MTBE SITES ON LONG ISLAND. Presented at US Environmental Protection Agency Methyl Tert-Butyl Ether (MTBE) Biodegradation Workshop, Cincinnati, OH, February 1-3, 2000.
Impact/Purpose:
To assist decision-making by improving approaches to subsurface contaminant transport modeling based on evaluation of field observations and subsequent development of appropriate modeling approaches and tools.
Description:
The aquifers of Long Island serve as the sole-source drinking water supply for approximately 3 million people. About 20 percent of this population obtains drinking water directly from the water table aquifer (Upper Glacial) whereas the remainder obtain their drinking water from deeper aquifers (Mahothy and Lloyd). High population density assures a large number of gasoline stations and numerous fuel releases which directly impact the water table aquifer. Thin surface soils (less than 2 feet) overlie the coarse sands and gravels of the Upper Glacial aquifer through this area, leaving the aquifer particularly vulnerable to contamination. This paper summarizes observations from four gasoline release cases investigated by the New York State Department of Environmental Conservation. Since all the sites are on Long Island, they share some common general characteristics, namely similar climate and geology. Differences in the geometry of the observed plumes result from the differences in timing and volume of the releases, prior release history and the chemical properties of benzene, toluene, ethylbenzene and the xylenes (BTEX) and methyl tert-butyl ether (MTBE), rather than dramatic hydrogeologic variation among the sites. At the East Patchogue and Riverhead sites, the MTBE plume is moving as a detached pulse ahead of the benzene and other plumes. This appears largely due to high ground water velocity and high recharge rate causing relatively rapid dissolution of MTBE from the gasoline at East Patchogue. One of the two plumes at Riverhead had extensive source removal, but the distribution of MTBE suggests that the majority of MTBE leaching had already occurred when the excavation was done. In contrast, at Uniondale and Lindenhurst, the MTBE plume is continuous with the source. Although the ground water velocity and recharge at Uniondale and Lindenhurst are also high, the releases are positively dated to a later time than those at East Patchogue and Riverhead. Thus these plumes have had less time to evolve. The sites also have less disturbance and remain paved, reducing any flushing of the source area by rainfall. For each of four sites, however, the highest MTBE concentrations were observed in the downgradient portion of the plumes.