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EVALUATION OF THE NATURAL RECOVERY
AND ATTENUATION POTENTIAL OF NEAR-SURFACE SOILS
CONTAMINATED BY VOLATILE ORGANICS AND HEAVY METALS
DURING FLOODING & PROLONGED INUNDATION USING SOIL AIR
METHODOLOGY
Research by Dr. Douglas E. Wyatt, Jr.
Department of Biology and Geology
 Recent
flooding in the New Orleans area caused floodwaters to
mingle with a variety of contaminates. The inundation of
low-lying neighborhoods caused surface waters to
saturate the underlying soils, possibly leaving behind
contaminants.
University of South Carolina researchers set out to
establish profiles using surface soil air samples,
backed by soil sediment samples of varying depth, to
indicate whether natural attenuation is probable. Their
theory was that repeated samples at predefined and
coincident locations would allow them to make a time
comparison for volatile organics and metals in the
sediments. Further, they believed that the establishment
of a vertical profile, and a comparison of changes
between sampling events, would allow them to estimate
attenuation with time.
Researchers began their investigation with three key
questions: 1) Are detectable analytes present in surface
soil vapor samples? 2) Are detectable contaminates
present at varying depths? 3) Do the concentrations of
analytes change over time spatially and by depth?
Researchers understood that the answers to these
questions could either allow them to estimate the rate
of natural attenuation or could suggest that it is not a
viable mechanism.
In order to investigate the potential for sediments to
recover from organic volatile and heavy metal
contamination, USC researchers first had to measure the
presence and vertical distribution. Their first course
of action was to establish sample sites in areas where
people are likely to return. Researchers visited these
sites on three separate dates. Based on lithology, they
made soil vapor measurements, obtained sediment core to
a depth of two meters, and sampled four depth-discrete
intervals. They also made measurements repeatedly at the
same location and depths over sufficient time intervals
to allow natural processes to act.
Researchers expected that access to areas for sampling
might be restricted and that oversight was probable.
They reported that the number of military checkpoints,
ID and credential checks, and the requirements for a
vehicle placard, were interesting conditions for
academic research. What they didn’t expect was the loss
of several sample sites to FEMA trailer construction.
While researchers knew that FEMA was considering using
their sample area “after the holidays,” they thought
FEMA meant after the New Year. Political realities and
human need accelerated the FEMA process, requiring the
team to modify its research. Fortunately, FEMA had 10
centimeters of soil removed before trailers were
installed.
On the first visit, sediments were saturated below 60
centimeters depth. The vertical change in sediment type
and character was abrupt, from loamy, silty soils often
containing shells to gray-blue fat clays. The
researchers observed very little vertical gradation in
the sediment core; however, a few thin beds in the clays
contained higher levels of silty sand. The researchers
also noted an organic vapor odor in the core and could
feel the cooling effect of evaporation, presumably from
volatile organics, through their gloves.
The soil air methodology generated mixed results.
Researchers discovered that only methylene chloride was
consistently measured, with single hits of other
analytes. Light hydrocarbons demonstrated atmospheric
methane levels. Researchers extracted soil air directly
from three sediment core tubes on the third visit with
similar results to the vapor traps. Assuming 35 percent
soil porosity for the upper 60 centimeters and near-zero
porosity for the underlying clays, researchers concluded
that there might have been insufficient soil air volume
for adequate vapor measurements.
The researchers’ sediment analysis revealed detectable
levels of metals and organics in the soil at each depth
interval. Generally, in all surface sediments, including
local USEPA samples, all eight RCRA metals, except
selenium, diminished over time, as did the ketones,
benzenes, and carbon disulfide. Researchers found that
for the sample depth 50–60 centimeters, all analytes
decreased except acetone, selenium, and arsenic. For the
120-130 centimeter sample depth, all analytes decreased
except selenium, cadmium, acetone, and 2-butanone, while
benzene remained constant. Finally, for the 180-190
centimeter sample depth, all analytes increased or
remained constant except ethylbenzene, m & p xylene,
chromium, and arsenic. By depth, metals generally
decrease with time and depth, while organics increase
with time. Researchers are continuing their analysis.
 This
research is unique in that it approaches
flooding-related soil contamination with depth and time
rather than just as a surface soil contamination
problem. Other researchers might choose to follow up on
this approach to discover potential future health
effects resulting from deeper possible contamination.
USC researchers strongly suggest the collection of soils
data in an area before potential hurricane flooding to
establish clear pre-flooding conditions.
Although prolonged flooding from levee failure is unique
to New Orleans, USC researchers believe that the
potential hurricane-related lowland flooding with waters
containing metal and organic contaminants is possible
along the entire Southeastern coastline. This study
might add benefit to the understanding of soils
contamination from this type of natural hazard.
The results from this research are being readied for
publication as a journal paper. Additionally, the data,
results, and conclusions will be provided to officials
in St. Bernard Parish and posted to websites available
to the public.
On a personal note, the researchers said they witnessed
incredible devastation in both physical and human terms.
While in the field, they gave more gloves, masks, and
water to people returning to their homes than they used
in conjunction with their research.
Biography
Dr. Douglas Wyatt is a research associate professor
at the University of South Carolina-Aiken, and a
consulting scientist with Washington Group International
where he works in clean-energy development and
environmental assessment. Until recently, Wyatt was a
senior scientist and technical advisor to the Department
of Energy at the National Energy Technology Laboratory,
working in energy assurance and supply. Before that, he
spent 13 years at the Savannah River Site as fellow
scientist working in regional geology and geophysics,
non-proliferation, and environmental geosciences. Before
Savannah River, he worked 10 years in oil and gas
exploration. Research Team/Collaborators:
Two undergraduate students, Kurtis Drake, a senior,
and Benjamin Morris, a sophomore, supported the field
research and soil core sampling. Both are majors in
biology at USCA. Drake will use this research program
and data to support his senior research project. Morris
is using the research to help guide his specific
direction of study.
As research progressed, Dr. Michele Harmon, assistant
professor in biology and geology at USCA, began using
the soils data to conduct bioaccumulation and toxicity
studies, an added benefit to the research program. Her
research might suggest the possibility of secondary or
future toxicity from flooded sediments. |
