| Aquifers with significant water-supply development near estuaries may have induced surface-water recharge. Danger from saltwater intrusion exists, especially during drought conditions. Potential sea-level rise, possibly in conjunction with drought conditions, constitutes a significant threat for the future of potable ground-water supplies hydraulically interconnected with estuaries. Understanding aquifer-estuary interaction and development of a quantitative technique to evaluate the vulnerability of an estuary-proximal ground-water supply to saltwater intrusion is vital. The Delaware River and underlying Potomac-Raritan-Magothy aquifer system in the vicinity of the Camden, New Jersey, metropolitan area provides an opportune case study to investigate aquifer-estuary interaction and to determine relative vulnerability to saltwater intrusion. The threat of seawater encroachment from the Delaware River and intrusion into the Potomac-Raritan-Magothy aquifer system was validated in November 1964, during significant drought conditions. Future seawater encroachment events in the Delaware River seem inevitable under the circumstances of sea-level rise.;An approach using a three-dimensional ground-water flow model in conjunction with particle-tracking analysis and a one-dimensional solute transport model can quantitatively evaluate river-aquifer interaction and provide an evaluation of vulnerability to saltwater intrusion. Approximately 30 percent of the Camden metropolitan area's ground-water supply pumpage is within the influence of river leakage. A dissolved chloride concentration of 260 to 500 milligrams per liter, in the river, under steady-state conditions will degrade the quality of ground water to nonpotable levels. A single encroachment event, having a duration of 30 days, perhaps coinciding with a drought episode, requires half-strength seawater or greater in the river, to approach non-potability conditions. A 30-day encroachment event with a return period of one to five years, perhaps coinciding with normal low freshwater discharge and river-dissolved chloride concentrations of 2,000 to 4,000 milligrams per liter, will have a significant potability impact. The methodology used for the case study, including conceptualization of ground-water flow and aquifer-estuary interaction, development of a ground-water flow model and analysis of solute transport is transferable to other locales. |
