MOBILITY OF MERCURY IN DISTURBED SOILS WITHIN THE NEW JERSEY COASTAL PLAIN

Despite low background levels (<0.010µg/L), mercury (Hg) exceeds the USEPA maximum contaminant level (2 µg/L) in water from about 700 domestic wells in the unconfined and acidic Kirkwood-Cohansey aquifer system in New Jersey’s Coastal Plain. This highly permeable system, composed of predominately quartz sands with lenses of silt and clay, is vulnerable to contamination, with a water table depth commonly less than 7 m below land surface. Past agricultural use of mercurial pesticides and atmospheric deposition from nearby industry are two likely sources of Hg to the aquifer. It is hypothesized that in this system, Hg sorbed to soils from either of these sources may be mobilized during residential development activities, and that subsequent land applications within these newly urban areas may further contribute to release and transport of Hg from disturbed sediments to shallow groundwater. Flow-through column experiments were used to test the effects of soil disturbance and anthropogenic inputs on the mobility of background and atmospheric Hg , in dissolved and particulate phase.

Soils cores were collected using direct push methods from an undeveloped forested area where Hg inputs are likely only from atmospheric deposition. Previous studies had indicated Hg is sorbed to iron (Fe) hydroxides in Coastal Plain subsoils; thus, B-horizon soils were separated, mixed thoroughly to simulate disturbance, and packed into 650 mm long by 15.5 mm diameter acrylic columns. The B horizon soils were analyzed for Hg by CVAFS and Fe by ICP-MS. Three column experiments were performed in duplicate, pumping solution through each column to simulate possible anthropogenic inputs of de-icing solutions (NaCl), fertilizer applications (20-20-20 fertilizer), and de-ionized water as a control. Four liters of solution were pumped upward through the columns at a rate of 6.5 milliliters per minute to simulate post-storm recharge. Composited effluent was subsampled and analyzed for dissolved and total Hg and Fe as above. With all three solutions, about 25-30 percent of Hg in the soil was removed, nearly all on particles. Large concentrations of particulate Fe also were removed, indicating likely mercury sorption to iron hydroxide particles, and suggesting a mechanism for mobilizing Hg from disturbed sediments after storm events.