Evaluation of the Fate, Transport, and Mass Flux/Discharge of Commingled Chlorinated Benzenes, Toluenes, and Xylene near a River

摘要

Background/Objectives. An evaluation of the fate, transport, and mass flux/discharge of commingled volatile organic compounds (VOCs) in groundwater is being performed at a former industrial site in the northeast United States. The primary VOCs in groundwater are chlorobenzene (up to 14 mg/L), 1,2-dichlorobenzene (up to 30.7 mg/L), 2-chlorotoluene (up to 48.4 mg/L), toluene (up to 15.4 mg/L), and xylenes (up to 1.1 mg/L). The water table is 7 to 10 feet below ground surface (ft bgs), and the site is underlain by the following stratigraphic layers: (1) urban fill and concrete structures; (2) homogenous gray silt of alluvial origin; (3) a heterogeneous mixture of gray sand, silt, clay, and gravel of glacial outwash origin; (4) relatively homogeneous fine sand and silty sand; (5) glacial till; and (6) competent sandstone bedrock (50 to 59 ft bgs). Groundwater migrates beneath a steel sheetpile bulkhead at a depth of 25 ft bgs, eventually discharging to a river adjacent to the site. The portion of the groundwater VOC plume with VOCs at concentrations above applicable regulatory criteria is approximately 2 acres in aerial extent, and extends over a depth interval of 7 to 42 feet below ground surface (ft bgs). A groundwater extraction and treatment system situated upgradient of the bulkhead to intercept the plume was operated between 1995 and 2010, yielding asymptotic mass removal rates towards the end of operation. The purpose of the current evaluation is to characterize mass flux discharge to the river and to evaluate alternative remedial approaches to address the completed exposure pathway.