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OBSERVATIONS FROM CONTAMINANT PLUMES ON LONG ISLAND
Citation:
Weaver, J W. OBSERVATIONS FROM CONTAMINANT PLUMES ON LONG ISLAND. Presented at American Geophysical Union Fall Meeting, San Francisco, CA, December 15-19, 2000.
Impact/Purpose:
The primary objective of the research program is to develop, test, and apply a multimedia, multi-pathway, multi-receptor exposure and risk assessment modeling system (the 3MRA) and accompanying methodologies to assess uncertainty and to support regulatory-based applications.
Description:
The aquifers of Long Island serve as a sole source drinking water supply for the entire
local population of about three million people. Where the shallow Upper Glacial Aquifer has been contaminated with petroleum hydrocarbons and methyl tert-butyl ether (MTBE), intensive site investigations have established the vertical and horizontal distribution of contaminants. Plumes and contaminant pulses are the presumed consequences of source emplacement in fairly homogeneous aquifer materials, high recharge and leaching rates through the sources, high ground water velocity, plume diving in the aquifer, and low rates of biodegradation. Detailed vertical characterization of the plumes has revealed orders-of-magnitude variation in concentration in adjacent sample points. Two types of variations have been explored with borehole flowmeter studies. The first type is apparent plume diving associated with changes in
the amount of pervious cover at these locations. The flowmeter studies have show that concentration discontinuities are not associated with observable changes in hydraulic conductivity. Thus the presumed reason for plume diving is enhanced recharge. Additional evidence is supplied by models of vertical flow that confirm the magnitude of vertical displacements caused by infiltrating water. The second type of variation shows concentration discontinuities that are not associated with land use changes. These have been shown not to be associated with observable changes in hydraulic conductivity. Through repeated observations of the plumes the gross motion of the contaminants and some measure of projected contaminant distributions have been determined. Processes controlling fine scale or boundary processes have not been incorporated into site assessments, however, even though in some cases these may have a dominant affect on even the gross features of the contaminant plumes.