AN AQUITARD INTEGRITY STUDY – PRELIMINARY FINDINGS FOR THE POTOMAC/ARUNDEL FORMATION CLAY AT A SITE IN DEEPWATER, NJ

The site is located east of the Fall Line on unconsolidated sediments in New Jersey along the eastern shore of the Delaware River. The environmental legacy of operating a manufacturing facility over 90 years has resulted in the presence of site-related constituents in groundwater in unconfined and semi-confined aquifers that consist of sequences of estuary interbedded and channelized sands, gravels, silts, clays, and peats of Holocene and Quaternary age. These units are separated from the underlying regional drinking water aquifer by an overconsolidated silt and clay (paleosol) aquitard that is thought to be equivalent to the regional Potomac (PA/NJ) or Arundel Formations (MD). For this investigation, it was assumed that the aquitard may have preferential pathways such as paleo rootholes, through which site-related constituents may be able to migrate into the underlying aquifer until results of an aquitard integrity study prove otherwise. The aquitard integrity study started in 2007, included examining recent literature, drilling at new locations to confirm the presence and thickness of the clay in different areas of the site, measuring physical properties (grain size, moisture, permeability), collection of cores to determine if microstructures (X-radiography) exists in the unit, and to characterize the concentration profile of site-related constituents in the top of clay using samples collected at close intervals. Physical measurement results of the clay indicated that it is present throughout the site-at a significant thickness, little to no microstructures were observed at different depths of the clay, a total organic carbon value of 0.281% was determined, a USCS CH classification was determined with an in-situ saturated moisture content of 25%, and an average permeability of 9.5 x 10-⁹ cm/sec was determined. Chemically a diffusion profile was observed in the top two feet of the clay, which is not indicative of advective transport that would be characteristic of transport through secondary pathways.