MERCURY IN GROUND WATER, SOILS, AND SEPTAGE, NEW JERSEY COASTAL PLAIN

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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)

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Our objectives information about--

• Occurrence of mercury (Hg) contamination in
  groundwater in southern New Jerseyan 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.

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OCCURRENCE
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The Problem

• Total Hg exceeds the MCL (2 mg/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 mg/L
• Concentrations of sodium, chloride and nitrate
  elevated in domestic-well water
• VOCs may be detected.
• Hg found in ground water in Delaware, too.

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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 lt0.01 mg/L in water
• Vulnerability to contamination from the land
  surface.

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SOURCES
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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

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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.

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Hg in soils and aquifer materials

• More Hg in undisturbed soils (up to 150 mg/kg)
  than in (1) disturbed residential soils (lt50
  mg/kg) and (2) most aquifer materials (lt50
  mg/kg)
• Hg higher in aquifer clay lenses (50-110 mg/kg)
• Hg in ground water above and below clay lenses at
  background levels.

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Hg in topsoils was associated with organic
materials, but, in subsoils, with iron and
aluminum hydroxides.
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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.
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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.

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Chemical characteristics of septage and
leach-field effluent were--

• Hg concentrations in septage ranging from lt 0.02
  to 0.06 mg/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.

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----Effluent------
------------Domestic wells----------------
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PROCESSES
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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 subsoils iron hydroxides,
• Iron and adsorbed Hg go into solution in the
  effluent.

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In leach-field effluent, Hg concentrations
increased with Fe concentrations.
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Hg concentrations decreased with dissolved
organic carbon (DOC) concentrations apparently,
DOC is not transporting Hg.
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Concentrations of Hg in effluent increased as pH
decreased. In ground water, the same relation
occurs.
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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.

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Differences in Hg in filtered and unfiltered
sample pairs from 16 domestic and production
wells
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Co-occurrence of Hg gt0.1 mg/L and VOCs was
examined for 6 Atlantic County Hg sites. o,
Non-significant at p0.10 Significant at or
above p0.1 , Significant at or above p0.05
Significant at or above p0.01 --,
Insufficient VOC data to test
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IMPORTANT ENVIRONMENTS
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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.

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Were 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_at_usgs.gov