Natural sources of mercury in the Kirkwood-Cohansey aquifer system of the New Jersey coastal plain

Mercury (Hg) deposits are fonned by low temperature and low pressure hydrothermal processes in tectonically active areas. Sandstone and limestone host many of the larger deposits. The large ionic radius of mercury precludes its incorporation into the crystal lattice of most common minerals. Glauconite, which is virtually absent from the Kirkwood-Cohansey aquifer system, is the only mineral known to contain mercury in the New Jersey Coastal Plain. Heavy minerals of the Kirkwood-Cohansey aquifer system may contain traces of natural mercury, although no site-specific, quantitative data are available. Partial data on the mercury concentration in rocks which were a source of the Kirkwood-Cohansey sediments and in soils overlying the Cohansey Sand suggest that the natural background concentration is approximately 10 nanograms Hg/g (ng Hg/g). The natural background concentration of aqueous mercury in New Jersey ground waters has not been determined. The standard cold-vapor atomic-absorption-spectrometry protocol is not sufficiently sensitive to measure aqueous mercury concentrations below the method detection limit of 0.1 micrograms per liter (ug/L). Pristine surface waters analyzed with more sensitive techniques have approximately l to 5 ng Hg/L. The low mercury concentrations in the sediments of the KirkwoodCohansey aquifer system, together with the low solubility and high particle reactivity of mercury, indicate that ground water in the aquifer system exceeding 10 ng Hg/L is probably contaminated.This series has at times has been entitled Geologic report series, Geologic report (Trenton, N.J.), and ultimately Geological survey report (Trenton, N.J.)