THE OCCURRENCE AND DOMINANT CONTROLS OF ARSENIC IN THE NEWARK AND GETTYSBURG BASINS

Groundwater often contains a wide range and higher than average concentration of arsenic, due to its direct interaction with aquifer rocks (Smedley and Kinniburgh, 2002). Arsenic is a ubiquitous element throughout the Earth’s crust, but has been found heterogeneously distributed at concentrations above the crustal average of 1.7 mg/kg in crystalline environments such as the Northern Appalachian Mountains (Peters, 2008) and in sedimentary environments such as the Newark and Gettysburg rift basins of New Jersey and Pennsylvania. In addition, groundwaters in both crystalline and sedimentary aquifers have arsenic concentrations above the maximum contaminant level of 10μg/L, however, the Newark Basin has a greater percentage of water samples above the MCL than the Gettysburg Basin. Little research has been done on the relationship between arsenic concentrations in groundwater and the surrounding rocks in the Newark and Gettysburg rift basins. Prior research shows that arsenic in groundwater has a relationship with pH, alkalinity, and iron concentration as well as physical properties of rocks such as grain size. By sorting the rock types in each basin to five bins; fine-grained, sandstone/siltstone, conglomerate, igneous intrusion, and metamorphic, the dominant controls on arsenic desorption in these basins is assessed.