Water quality in the Potomac-Raritan-Magothy aquifer system in the region of Greenwich Township, Gloucester County, New Jersey

Abstract

Results of water-quality analyses of ground water from 185 wells were used to describe regional variations in water chemistry in the PotomacRaritan-Magothy aquifer system, the sole-source aquifer in northern Gloucester County, New Jersey. The effects of industrial and other urban land uses on the quality of potable-water supplies were evaluated. The chemistry of water in shallow parts of the upper and middle aquifers is affected by the quality of precipitation, recharge from overlying wetlands (some of which are filled with dredge spoils from the Delaware River) and from the Delaware River estuary, chemical reactions with aquifer materials, and contamination from industrial and landfill sites. Although local variations in ground-water chemistry are great, pH, specific conductance, and concentrations of dissolved solids generally are low in the ambient ground water. The predominant dissolved cation generally is calcium or sodium and the predominant anion is sulfate or bicarbonate. Dissolved sodium and bicarbonate predominate and pH, specific conductance, and concentrations of dissolved solids generally are higher in the confined part of the aquifer system downgradient from the recharge area than in the shallow part, near the recharge area. These characteristics reflect continued chemical reactions with aquifer materials (including mineral dissolution, oxidation-reduction reactions, cation exchange, and oxidation of lignite) and the quality of water leaking from overlying marine deposits. Concentrations of sodium and chloride are greater in the southern part of the region than in the northern part, most likely as a result of mixing with saline water from deep parts of the aquifer system in southern Gloucester County. Water in most of the confined lower aquifer is slightly saline, probably as a result of limited recharge through the overlying confining unit; however, water in the northeastern part of the region, near the area in which the hydrologic units crop out in Pennsylvania, is more dilute because it receives more recharge. The presence of contaminated ground water at 34 industrial and landfill sites in the region was identified and investigated by the U.S. Environmental Protection Agency (USEPA) and the New Jersey Department of Environmental Protection. In general, ground water at or near all of these sites was potable but had a lower pH, a higher specific conductance, a lower concentration of dissolved oxygen, and higher concentrations of chloride, sulfate, calcium, magnesium, iron, manganese, nitrate, ammonium, and dissolved organic carbon than did ground water regionally. In addition, trace elements designated priority pollutants by the USEPA frequently were detected at concentrations greater than USEPA drinking-water regulations, and purgeable organic compounds were detected most frequently in groundwater samples from these sites or nearby areas. Ground-water chemistry at these sites is affected by addition of chemicals through leaks, spills, and disposal practices and by chemical reactions with aquifer materials. Recharge of slightly to moderately saline water from the estuary during drought can contribute to elevated concentrations of major ions in ground water at these sites. Detection of halogenated aliphatic compounds, decreases in pH, and increases in iron and sulfate concentrations in samples from public-supply wells in the region through time suggest that the water quality has degraded, possibly as a result of migration of contaminated ground water from industrial areas upgradient from the wells. Additional investigations are needed to identify specific sources of these constituents.