Atrium Lobby (Hyatt Regency Baltimore on the Inner Harbor)
The U.S. Geological Survey, in cooperation with the U.S. Environmental Protection Agency, Region III and the State of Delaware, is studying the water-quality and hydrogeologic properties of the surfical Columbia aquifer and semi-confined Potomac aquifer, and the extent of cross-aquifer contamination at the Standard Chlorine of Delaware, Inc. Superfund Site. Contaminants, including benzene, various dissolved and dense non-aqueous phase (DNAPL) chlorobenzenes, and hydrochloric acid, are frequently detected in shallow groundwater, and have been detected in the uppermost sand layer (Sand-A) of the Potomac formation, a regional drinking water supply. Conceptual site hydrology has been redefined since 2005, when long-term continuous water-level monitoring began. Strong local vertically downward gradients between the shallow and deep aquifers have been observed resulting from industrial pumping in multiple aquifer layers of the Potomac formation. Following several decades of continual pumping, a recent one-year cessation has changed local flow gradients. An aquifer test was performed by pumping Sand-A to evaluate local connections with the overlying contaminated Columbia aquifer. Observed head changes in the semi-confined system during the aquifer test show a hydraulically continuous Sand-A layer underlying the site. Vertically downward flows were induced in several Columbia wells located adjacent to Red Lion Creek, confirming the absence of an effective confining layer that would prevent downward contaminant migration in this area. Dissolved phase contamination detected in Sand-A to the north and west of the site corresponds to a mixed aquifer water signature reflected by the major ion chemistry, and suggests close proximity to areas where confining clays are absent and/or groundwater travel time has allowed sufficient mixing. Major ion chemistry in contaminated Sand-A to the southeast, however, does not reflect the same degree of aquifer mixing and suggests other mechanisms for contaminant transport, such as gravity driven DNAPL movement and subsequent dissolving.
