Hydrogeochemistry Of major And Trace Elements In Ground And Surface Water In The New Jersey Pine Barrens

Abstract

This study investigates major and trace element geochemistry of ground and surface water in the New Jersey Pine Barrens (around Wharton State Forest). The chemical composition of dissolved species of Cohansey Formation groundwater differs from that of the underlying Kirkwood Formation. The difference implies that groundwater from the two formations has different sources, geochemical processes and flow patterns and that cross-formational flow between them is minor. The source of iron in bog iron deposits in the New Jersey coastal plain is thus not from cross-formational flow from a deeper formation, but from within the Cohansey Formation. Chemistry of Cohansey groundwater is mainly controlled by precipitation (rain and snow) with limited water:rock reactions. Solutes in Kirkwood groundwater are mostly derived from water:rock reactions because Kirkwood groundwater is controlled by regional flows that have long residence time. The presence of clay and other confining layers contributes to the heterogeneity of groundwater composition, even over short distances. Most well waters did not show seasonal variations in composition because groundwater has residence time longer than a year. Stream water is similar to Cohansey groundwater in major element composition, which shows that stream and shallow groundwater are both dominated by precipitation composition and that there is extensive recharge interchange between them. The low pH values of surface water (average 4.5) and Cohansey groundwater (average pH = 5.3) appear to be affected by acid rain in this region. High pH of Kirkwood groundwater (average 8.3) is caused by water:rock reactions in the Kirkwood Formation. Na+/Cl- in the Cohansey groundwater has a ratio (0.577) close to that in seawater (0.55), indicating Na+ and Cl- are from marine aerosols. When pH is greater than 4.8, aluminum concentration is consistent with controls by gibbsite or/and kaolinite solubility. However, when pH is less than 4.8, Al is undersaturated with these minerals. At low pH, Al activity is controlled by saturation with organic aluminum phases having low Al/COOH ratios.