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RISK Poster
Session
Fecal
Contamination of Agricultural Soils, Ground Water, and
Surface Water Following Hurricane-Associated Flooding in
Eastern North Carolina
Michael J. Casteel,
Christine E. Stauber, Otto D. Simmons, III,
John S. Meschke, Greg L. Lovelace,
Ming Jing Wu, and Mark D. Sobsey,
University of North Carolina at Chapel Hill
Hurricane Floyd uH caused
widespread flooding of water and land in eastern North
Carolina in 1999. We analyzed agricultural soils, and
sentinel ground and surface waters, for microbial
indicators of fecal contamination. Ground and surface
waters also were analyzed for culturable human enteric
viruses (CEVs) and for Cryptosporidium oocysts
using standard methods developed by the USEPA. Grab
samples were collected from nine wells used as sources of
drinking water and from several rivers impacted by the
flooding. Fecal coliforms, Escherichia coli, Clostridium
perfringens spores, and Entercocci (EN) were
assayed using membrane filtration methods for water
samples, while mutliple-tube/dilution assays in liquid
media were used for soil samples. Male specific and
somatic coliphages also were assayed from 1-liter water
samples and from soil using an enrichment presence/absence
method. CEVs and Cryptosporidium oocysts were not
detected in the water samples analyzed. However, positive
results were obtained for indicator bacteria and
coliphages in soil and in both ground (well) and surface
water samples. Ground water samples showed higher and more
persistent contamination when compared with surface water.
Microbial indicators of fecal contamination also were
detected in soil samples collected several months after
the flooding had occurred. Temporal results suggested that
while surface water contamination by flood waters was
transient, groundwater contamination was more persistent
following the flood. These results suggest that persistent
enteric microbes in ground water and on the land may pose
health risks to humans and animals via ingestion of edible
plants grown in fecally contaminated soil, or from the
consumption of contaminated water. Persistent fecal
contamination of soil and ground water following flooding
may require additional or alternative measures to protect
crop growing areas and consumer drinking water supplies.
Such measures may include alternative drinking water
sources, continuous disinfection of contaminated ground
water sources, exclusion of crop growing areas from flood
plains, or destruction of crops exposed to fecally
contaminated flood waters.
Soil
and Groundwater to Indoor Pathway Evaluation for Risk
Assessment at Commercial/Industrial Properties: A
Comparison of Model Derived Risks with Soil Vapor
Concentrations
Eric M. Cherry, Kevin Wildman, Stephen Weldert and Bud
K. Tjandra, Hull & Associates, Inc.
The soil to indoor air (SIA) and groundwater to indoor
air (GIA) pathway has been evaluated for a number of well
characterized sites where VOC contamination is present in
soils and groundwater. The objective of this work was to
evaluate the applicability of SIA/GIA models for
calculating risk or establishing standards for commercial
and industrial properties. The geological settings include
silty clay till soils and silty clay tills over sand and
gravel. The long term variation of subsurface soil vapor
concentrations with respect to soil or groundwater
concentrations indicate that vapor concentrations have a
seasonal component and have a poor to moderate correlation
with the adjacent media. This suggests that the fate and
transport behavior of VOCs deviates from the estimates
based on simplified models.
Risk calculations were performed for soils, soil
vapors, and groundwater using a modified version of the
Johnson and Ettinger (1991) SIA and GIA models, as
developed on the basis of USEPA (1998), to evaluate
commercial and industrial scenarios. The models were
modified for slab on grade construction and air exchange
rates that comply with BOCA construction standards.
Sensitivity analysis indicates that these models are very
sensitive to variations in soil moisture and indoor/soil
pressure differential and ventilation rates. For
individual VOCs under various site-specific conditions the
indoor air/soil vapor attenuation factor was calculated to
range from 5x10-2 to 3x10-6. The
commercial/industrial scenario modifications allow for
more appropriate site-specific estimates of risk than the
default residential scenarios typically used in these
models. In many cases, saturation or free-phase limits in
soil and/or groundwater are calculated before risk based
standards are reached. Therefore, it is appropriate to
complete sufficient site characterization, including soil
vapor monitoring and soil determining soil properties
prior to establishing risk-based standards for the soil or
groundwater to indoor air pathway.
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