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In 2009, to support an evaluation of the feasibility of reopening the Pearce Creek Dredge Material Containment Area (DMCA) in Cecil County, Maryland, for dredge-spoil disposal, the U.S. Geological Survey (USGS) began to implement a comprehensive study designed to improve the understanding of the hydrogeologic framework, hydrology, and water quality of shallow aquifers underlying the DMCA and adjacent communities, to determine whether or not the DMCA affected groundwater quality, and to assess whether or not groundwater samples contained chemical constituents at levels greater than maximum allowable or recommended levels established by the U.S. Environmental Protection Agency Safe Drinking Water Act. The study, conducted in 2010–11 by USGS in cooperation with the U.S. Army Corps of Engineers, included installation of observation wells in areas where data gaps led earlier studies to be inconclusive. The data from new wells and existing monitoring locations were interpreted and show the DMCA influences the groundwater flow and quality. Groundwater flow in the two primary aquifers used for local supplies—the Magothy aquifer and upper Patapsco aquifer (shallow water-bearing zone)—is radially outward from the DMCA toward discharge areas, including West View Shores, the Elk River, and Pearce Creek Lake. In addition to horizontal flow outward from the DMCA, vertical gradients primarily are downward in most of the study area, and upward near the Elk River on the north side of the DMCA property, and the western part of West View Shores. Integrating groundwater geochemistry data in the analysis, the influence of the DMCA is not only a source of elevated concentrations of dissolved solids but also a geochemical driver of redox processes that enhances the mobilization and transport of redox-sensitive metals and nutrients. Groundwater affected by the DMCA is in the Magothy aquifer and upper Patapsco aquifer (shallow water-bearing zone). Based on minimal data, the water quality in the upper Patapsco aquifer deep water-bearing zone does not seem to have been impacted by the DMCA. Introduction The U.S. Army Corps of Engineers (USACE), Philadelphia District’s mission includes managing the water resources of the Delaware River basin. The agency is responsible for maintaining a navigable channel for large ocean-going and smaller vessels along the Chesapeake and Delaware Canal (C&D Canal) (fig. 1). The C&D Canal allows shipping vessels to go from the Delaware River to the Chesapeake Bay, and ultimately to the Port of Baltimore, thereby reducing the 300-mi (mile) trip south along the Atlantic Coast of Delaware, Maryland, and Virginia to the mouth of the Chesapeake Bay, and from there north in the bay to the Port of Baltimore. The C&D Canal became navigable in 1829, albeit the canal was much narrower than it is today. To maintain navigability, the C&D Canal periodically (generally annually or biennially) needs to be dredged, and the dredged material disposed. Dredging and disposal of this dredged material is the responsibility of the USACE. The USACE acquired a total of 996 acres of land, which is referred to in this report as the Pearce Creek Dredge Material Containment Area (DMCA) property, in 1937 as part of new (then) dredging work to deepen the C&D Canal (T. Kelly, USACE, written commun., 2012). In 1937, perimeter dikes were built around an area of approximately 260 acres, which is referred to in this report as the DMCA (bermed area), and a sluice was constructed that would allow water to leave the bermed area and flow into Pearce Creek. Subsequently, an additional sluice was constructed near the mouth of Pearce Creek, which limited the discharge from Pearce Creek to the Elk River and created what is referred to in this report as Pearce Creek Lake. Dredge materials were placed in the DMCA bermed area at the site in 1937 and 1938, and then again from the 1960s until the last placement of materials in 1993 (T. Kelly, USACE, written commun., 2012). In 1989, the dikes at the DMCA were raised to their current (2010–11) elevation, approximately 35 to 40 ft (feet) relative to the North American Vertical Datum of 1988 (NAVD 88), by bulldozing sediment within the DMCA bermed area to build the higher dikes (T. Kelly, USACE, written commun., 2012). It is estimated that 4.0 million cubic Hydrogeologic Framework, Hydrology, and Water Quality in the Pearce Creek Dredge Material Containment Area and Vicinity, Cecil County, Maryland, 2010–11 By Cheryl A. Dieter, Michael T. Koterba, Otto S. Zapecza, Charles W. Walker, and Donald E. Rice 2 Hydrogeologic Framework, Hydrology, and Water Quality in the Pearce Creek Dredge Material Containment Area yards of material was placed at the DMCA during this time (T. Kelly, USACE, written commun., 2012). Since 1993, the USACE has placed dredge materials at open-water sites, such as Pooles Island, located 18 mi to the southwest of the DMCA, in the Chesapeake Bay. In preparation for the closure of all open-water disposal sites in the Chesapeake Bay by the State of Maryland on December 31, 2010, the USACE began looking for alternative disposal locations. Pearce Creek DMCA is the preferred option for the USACE because of its available capacity and proximity to the C&D Canal, which will result in lower dredging, transport, and placement costs than alternatives such as Court House Point or Poplar Island, 7 mi to the northeast and 50 mi to the south of the DMCA, respectively (D. Sirkis, USACE, written commun., 2009). The USACE asked the U.S. Geological Survey (USGS) to conduct a study of the Pearce Creek DMCA and vicinity (fig. 2), to define the hydrogeologic framework, and to determine groundwater flow directions both laterally and vertically in the shallow groundwater flow system. The USACE also asked the USGS to determine whether or not chemical constituents in groundwater were greater than maximum allowable and (or) recommended U.S. Environmental Protection Agency (USEPA) Safe Drinking Water Act (SDWA) standards in (1) shallow private domestic wells adjacent to the DMCA, (2) shallow groundwater between the DMCA and Elk River, and (3) shallow groundwater upgradient of the DMCA. The final task was to determine whether or not the DMCA has affected groundwater quality adjacent to the site. In 2010, the USGS began an investigation of the Pearce Creek DMCA and vicinity. The results of the investigation are presented in this report. Purpose and Scope The purpose of this report is twofold: first, to present the results of the USGS study to describe the hydrogeologic framework, hydrology, and quality of groundwater in the USACE Pearce Creek DMCA and vicinity; and second, to assess whether or not the DMCA has affected the quality of groundwater for domestic drinking-water supplies in the vicinity of the DMCA. Understanding the interrelations among the hydrogeologic setting, groundwater flow, and groundwater quality are critical to understanding and illustrating the effect of the DMCA on drinking-water supplies in the study area. Thus, this report includes a description of the hydrogeology, Figure 1. Location of the Pearce Creek Dredge Material Containment Area, Cecil County, Maryland. Ch es ter Riv er Uicorn r. Elk Riv er Little lk r. ig lk r.

scientific investigations report

Hydrogeologic framework, hydrology, and water quality in the Pearce Creek Dredge Material Containment Area and vicinity, Cecil County, Maryland, 2010-11