Confining Unit Effects on Water Quality in the New Jersey Coastal Plain

Abstract

AbstractSediment and pore‐water samples from Tertiary and Cretaceous strata in the New Jersey Coastal Plain were collected from cores from Freehold Township, Monmouth County; Howell Township, Monmouth County; and from Clayton Township, Gloucester County. These strata form a multilayered aquifer system in which upper units are marine origin and lower units are predominantly nonmarine.Concentrations of major constituents in pore‐water samples from confining units and aquifers were highly variable: calcium (1.7–660 mg/I), magnesium (0.3–140 mg/l), sulfate (1.52200 mg/l), and dissolved inorganic carbon (9–290 mg/l); with large differences between marine confining units and aquifers. Where the aquifers are unconfined and oxic, well waters in the Potomac‐Raritan‐Magothy aquifer system in the northern Coastal Plain have higher concentrations of nitrate, chloride, and dissolved oxygen. In areas where the aquifer system is confined and anoxic, there are higher concentrations of sulfate and bicarbonate. Differences in bicarbonate concentrations between two wells (12 and 67 mg/l) along a regional flow path can be caused by mixing of water in a nonmarine aquifer with leached sulfate‐enriched, marine confining‐unit water, and subsequent reduction of sulfate.Bacterially mediated organic carbon oxidation, iron reduction, and sulfate reduction, and ion‐exchange reactions may explain constituent variations. Bacteriological assays of core sections from the Howell and Clayton Township coreholes showed viable sulfate‐reducing bacteria as deep as 558 feet below land surface. Sediments from a depth of 210 feet showed populations of sulfate‐reducing bacteria of 103–l06 organisms per gram of soil.