Drilling onshore by Ocean Drilling Program (ODP) Legs 150X (Island Beach and Atlantic City, New Jersey [Miller et al., 1994], Cape May, New Jersey [Miller et al., 1996a]) and 174AX (Bass River, New Jersey [Miller et al., 1998], Ancora, New Jersey [Miller, Sugarman, Browning, et al., 1999, 2000], Oceanview, New Jersey [Miller, Sugarman, Pekar, Browning, et al., 2001], and Bethany Beach, Delaware [Miller, McLaughlin, Browning, et al., 2003]) (Fig. F1) has focused to date on global sea level and regional tectonic changes. The mid-Atlantic U.S. coastal plain that encompasses New Jersey and Delaware is a natural laboratory for teasing out the influences of global sea level (Miller et al., 1996b, 1997), regional tectonic, and sediment supply changes (Browning et al., submitted [N1]). This region is also inhabited by over 10 million people (2 million in southern New Jersey, 0.8 million in Delaware [0.5 million depend on groundwater], and 8 million in Maryland and northern Virginia), many of whom rely on groundwater for their day-to-day sustenance. Because of this, drilling at Bass River, Ancora, and Oceanview, New Jersey, was partially funded by the New Jersey Geological Survey (NJGS). Similarly, drilling at Bethany Beach, Delaware, was partially funded by the Delaware Geological Survey (DGS). Both the NJGS and the DGS have endeavored to understand the relationship among groundwater resources (aquifers), their confining units, and sequence stratigraphy.
Sequence stratigraphy was pioneered by Exxon Production Research Company in their quest to understand the geological controls on oil-bearing units (e.g., Vail et al., 1977; Posamentier et al., 1988). Sequences are unconformity-bounded units that provide a predictable pattern for not only oil but also water-bearing beds (aquifers). In the New Jersey and Delaware coastal plains, marine sequences consist of basal unconformities, thin lower TST sands, thick medial lower HST silty clays and silts, and thick upper HST sands (Sugarman et al., 1993). Lowstand systems tracts are largely missing in the onshore coastal plain. The upper HST sands generally compose aquifers, whereas the silty lower HST units compose confining units (Sugarman and Miller, 1997). Understanding the sequence stratigraphy of the coastal plain provides a predictability for the distribution of groundwater resources.
With this in mind, the NJGS funded drilling targeting aquifers in the southern part of the state, namely Salem and Cumberland Counties (Fig. F1). This region currently derives nearly all of its drinking water supplies from groundwater (Cauller et al., 1999). This is especially true for southwestern Cumberland County, where surface water supply is nonexistent. Critical issues face water resource planners in this area, as in many areas of New Jersey, where the demand for water is projected to increase significantly over the next 20 yr. The Salem/Cumberland area is projected to be one of the five fastest growing areas in New Jersey, highlighting the need for additional water resources and intelligent water resource planning. Continuous coring of sequences in this region is needed to help determine the areal distribution of aquifers to allow efficient use of water resources.
In addition to water use, planners must consider saltwater intrusion and regulatory issues. One of the major aquifers in this region, the PRM aquifer system (Fig. F2), is susceptible to saltwater intrusion because of proximity to the Delaware estuary and heavy pumping in surrounding areas. Regulatory issues include the existence of water supply Critical Area No. 2 in northern Gloucester, Camden, and Burlington Counties, where pumpage is regulated, and its proximity to the Pinelands, a protected region. The resulting scenario is one of numerous restrictions coupled with vulnerable aquifers. These concerns have resulted in the initiation of a Water Supply Action Plan for the Salem/Gloucester/Cumberland area calling for a focus on evaluating the effect of proposed PRM withdrawals. The PRM is the major aquifer of focus because other regional confined aquifers, including the Wenonah–Mount Laurel and the Piney Point, have relatively low yields based on aquifer testing and are therefore inadequate to satisfy anticipated future demands in Salem and Gloucester Counties (note: the PRM is too deep to presently be considered in Cumberland County).
Planning and regulation of aquifers in this region are additionally complicated by the fact that New Jersey shares the PRM aquifer system with Delaware. Current and future PRM withdrawals in Delaware may have significant potential effects on the quantity and quality of the PRM aquifer system in New Jersey and vice versa. A coordinated study of the hydrogeology of the PRM between New Jersey and Delaware is needed to develop strategies to protect and restore the PRM and to help ensure the availability of freshwater to meet future needs in the Lower Delaware Basin.
One of the primary objectives of NJGS-funded coastal plain drilling is to evaluate the geologic framework of Salem and Cumberland Counties, with a main emphasis on the PRM aquifer system. To this end, two stratigraphic control coreholes were proposed by the NJGS. The first, at scenic Fort Mott State Park on the Delaware River (Fig. F1), was completed in October 2001 and was the eighth continuously cored borehole drilled in New Jersey as part of the New Jersey Coastal Plain Drilling Project. The second was drilled in 2002 at Millville, New Jersey (Fig. F1), and will be reported in a subsequent site report. The Fort Mott corehole was drilled to a depth of 820 ft (249.94 m) and provides a continuously sampled borehole to investigate the water resource potential of two critical water-bearing units (aquifers) within the Magothy and Potomac Formations. These are two of the primary aquifers in the New Jersey coastal plain in a belt that parallels the Delaware River from Monmouth through Salem Counties. These units are made up of clay-silt and interbedded sands deposited in riverine and nearshore paleoenvironments (Fig. F3) during the middle part of the Cretaceous, ~125–84 m.y. ago. Our understanding of the distribution of these clays and sands is critical for prediction of water resources and pollution remediation in the southern part of the state, but it is limited by lateral facies changes and poor sampling of the formations in both outcrop and discontinuously sampled water wells. Continuous geological samples obtained at Fort Mott provide new insights into the complex environments of deposition, especially in the Potomac Formation (e.g., Fig. F3), and their impact on the distribution of water resources.
Drilling and study of the Fort Mott borehole was a collaborative project: the NJGS provided scientific personnel and funds to drill the borehole; the DGS provided scientific personnel and downhole logging support; Rutgers, The State University of New Jersey, provided science personnel and logistical support; the U.S. Geological Survey (USGS) drilled the hole; and ODP provided publications support. The Fort Mott site is the most updip location drilled to date by this team. Recovery was good (78%), with 639 of 820 ft (194.77 of 249.94 m) recovered. A full suite of wireline logs was obtained to 800 ft (243.84 m). The on-site scientific team provided preliminary descriptions of sedimentary texture, structure, color, and fossil content and identified lithostratigraphic units, lithologic contacts, and sequences.