Presentation on theme: "MERCURY IN GROUND WATER, SOILS, AND SEPTAGE, NEW JERSEY COASTAL PLAIN Julia L. Barringer and Zoltan Szabo U.S. Geological Survey, West Trenton, NJ In cooperation."— Presentation transcript:
MERCURY IN GROUND WATER, SOILS, AND SEPTAGE, NEW JERSEY COASTAL PLAIN Julia L. Barringer and Zoltan Szabo U.S. Geological Survey, West Trenton, NJ In cooperation with the New Jersey Department of Environmental Protection (NJDEP)
Our objectives: information about-- ► Occurrence of mercury (Hg) contamination in groundwater in southern New Jersey—an ongoing problem (rarely studied elsewhere); ► Likely and unlikely Hg sources; ► Processes that are believed to lead to the contamination; ► The environments that seem conducive to causing the contamination.
The Problem: ► Total Hg exceeds the MCL (2 g/L) in water from a major NJ aquifer system. ► More than 600 domestic wells in more than 70 residential areas in 8 counties affected; ► Hg concentrations as high as 72 g/L; ► Concentrations of sodium, chloride and nitrate elevated in domestic-well water; ► VOCs may be detected. ► Hg found in ground water in Delaware, too.
The aquifer and affected residential areas are shown below. Aquifer characteristics are ► Quartz-rich sand and gravel; scattered clay lenses; ► Acidic ground water (pH ~ 4.5 – 6.0) ► Background Hg concentrations <0.01 g/L in water ► Vulnerability to contamination from the land surface.
None of the potential point sources (below) of Hg investigated by USGS and NJDEP could be conclusively linked to the Hg-contaminated ground water in the residential areas. ► Landfills ► Industrial sites ► Commercial operations ► Dentists’ offices ► Military Installations ► Cemeteries ► Hospital septic systems ► Laboratories
Likely Hg sources to land surface: ► Atmospheric deposition; ► Mercurial pesticides used on crops and turf (most residential areas were built on former agricultural land); ► Fertilizers containing Hg.
Hg in soils and aquifer materials: ► More Hg in undisturbed soils (up to 150 g/kg) than in (1) disturbed residential soils (<50 g/kg) and (2) most aquifer materials (<50 g/kg); ► Hg higher in aquifer clay lenses ( g/kg); ► Hg in ground water above and below clay lenses at background levels.
Hg in topsoils was associated with organic materials, but, in subsoils, with iron and aluminum hydroxides. Hg in topsoils was associated with organic materials, but, in subsoils, with iron and aluminum hydroxides.
We studied Hg in several residential septic systems to discover whether they were sources of Hg to ground water, or part of the process of Hg mobilization, or both.
At an unsewered residential area, evidence of septic-system effects on domestic-well water were: At an unsewered residential area, evidence of septic-system effects on domestic-well water were: ► Presence of detergents; ► High concentrations of ammonia, boron, chloride, nitrate, and sodium; ► Undetectable sulfate and detected sulfide, which indicate likely presence of sulfate-reducing bacteria that methylate Hg.
Chemical characteristics of septage and leach-field effluent were-- Chemical characteristics of septage and leach-field effluent were-- ► Hg concentrations in septage ranging from < 0.02 to 0.06 g/L; ► No dilution of Hg concentrations from septage to effluent, but dilution of other constituents; ► Concentrations of chloride (Cl) and sodium (Na) in domestic-well water overlapping those in leach-field effluent.
Domestic wells Effluent------
Potential processes for mobilizing mercury are-- ► Soil disturbance moves Hg from topsoil to subsoil; ► Hg adsorbs to iron hydroxides in subsoils; ► Effluent removes Hg from subsoils as it moves downgradient from the septic tank, ► Effluent reduces the subsoil’s iron hydroxides, ► Iron and adsorbed Hg go into solution in the effluent.
In leach-field effluent, Hg concentrations increased with Fe concentrations.
Hg concentrations decreased with dissolved organic carbon (DOC) concentrations; apparently, DOC is not transporting Hg.
Concentrations of Hg in effluent increased as pH decreased. In ground water, the same relation occurs.
The USGS and NJDEP also collected both unfiltered and filtered ground-water samples for Hg analysis; ► In some cases, the filtered sample contained less Hg than the corresponding unfiltered sample. ► A likely explanation for this observation is that some of the Hg is bound to particles that are removed by filtering.
Differences in Hg in filtered and unfiltered sample pairs from 16 domestic and production wells
Co-occurrence of Hg >0.1 g/L and VOCs was examined for 6 Atlantic County Hg sites. o, Non- significant at p=0.10; *Significant at or above p=0.1; **, Significant at or above p=0.05; ***; Significant at or above p=0.01; --, Insufficient VOC data to test Site number Other VOC Total VOC Ben- zene Chloro- form 1,1- DCA 1,1- DCE 1,2- DCE PCE1,1,1- TCA TCETolu- ene 1-- o ** -- 2 o o *** ** ooooo 4o -- o 7 oo *** ooo 18-- oo 31 * o--o
Some important components of the environment where Hg is mobilized may be: ► Disturbed soils ► Leach-field effluent ► Localized anoxic zones where iron reduction (also sulfate reduction and Hg methylation?) can occur; ► Particles to transport Hg.
We’re still trying to find out: ► Whether VOCs affect Hg mobility; ► Whether methyl Hg in ground water poses a problem; ► How Hg accumulates to high levels in the aquifer; ► Will the problem occur elsewhere in similar land-use, geologic, and biogeochemical settings? Contact: