POSSIBLE EFFECTS OF PORE WATER FROM CONFINING UNITS ON GEOCHEMISTRY OF WATER IN THE PINEY POINT AQUIFER IN NEW JERSEY

Pore water from the silt-clay confining units enclosing the Piney Point aquifer was collected from core material recovered at Millville, New Jersey, by the U.S. Geological Survey in cooperation with Rutgers University and the New Jersey Geological Survey as part of the New Jersey Coastal Plain Drilling Project. The fine- to coarse-grained glauconitic quartzose sand composing the Piney Point aquifer pinches out or is beveled in the subsurface; therefore, recharge is limited primarily to vertical leakage. A water-level decline of 40 feet or more in the aquifer near Millville has been documented. Projected increases in the demand for water from the Piney Point aquifer likely will cause water levels to decline further, increasing leakage. To determine the possible effects of pore water from the confining units on the quality of water in the aquifer, pore-water chemistry was analyzed. Water chemistry of samples from 27 public-supply and other wells in the Piney Point aquifer throughout southern New Jersey was also examined. Glauconite was abundant in the core samples from both the confining units and the aquifer (maximum, 70 percent) and likely undergoes ion exchange. High concentrations of sodium (median, 1.74 mmol/L (millimole per liter); maximum, 5.87 mmol/L) and potassium (median, 0.13 mmol/L; maximum, 0.26 mmol/L) relative to those of chloride (median, 0.10 mmol/L; maximum, 2.03 mmol/L) in water from the aquifer indicate that ion-exchange reactions are important determinants of the water chemistry. Because concentrations of chloride and sulfate in the nine pore-water samples analyzed to date (2002) (maximum of 7.7 and 9.5 mmol/L, respectively) are higher than those in aquifer water, leakage from the confining units likely will affect the quality of water in the aquifer.