# Presentation: 429838

## 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.

## OCCURRENCE

## 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.

## SOURCES

## 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 (50-110 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.

## 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:

- 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--

- 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------

## PROCESSES

## 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 | PCE | 1,1,1-TCA | TCE | Tolu-ene |
| --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- |
| 1 | -- |  o | -- | ** |  -- |  -- | -- | -- | -- | -- | -- |
| 2 | -- |  o | -- |  o |  *** |  ** | o | o | o | o | o |
| 4 | o | ** | ** | ** | -- | -- | o | -- | -- | -- | -- |
| 7 | -- | o | o | * | * | * | o | o | o | -- | -- |
| 18 | -- | -- | o | o | -- | -- | -- | -- | -- | -- | -- |
| 31 | * | o | -- | o | -- | -- | -- | -- | -- | -- | -- |

## IMPORTANT ENVIRONMENTS

## 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: jbarring@usgs.gov