Environmental Engineering Reference
In-Depth Information
contamination disasters. Love Canal was an abandoned canal partially
constructed to generate electricity by conveying water from upper Niagara
Falls in upstate New York. When Hooker Chemical Company took over the
abandoned canal section and adjacent land, they converted it to an uncon-
trolled disposal area for toxic chemicals. When this improvised and poorly
managed landfill reached capacity, it was covered with soil and conveyed
to the City of Niagara for a dollar. During the late 1950s, homes and a school
were built directly over the old disposal area, and then in the late 1970s,
the dam broke, so to speak. A record rainfall washed away the soil cover
exposing corroding waste-disposal drums and killing the vegetation. This
was followed by disturbingly high rates of birth defects, miscarriages, and
other adverse human health conditions, both chronic and acute (Beck 1979).
The U.S. EPA recognized that this was not an isolated case, similar occur-
rences would erupt throughout the country, and an immediate legislated
attack on the problem was critical, thus the passage of Superfund.
With this background and legitimate risk to human life and health, the
focus of Superfund was obviously not on the birds, bees, bunnies, and other
ecological resources. Also, because human health was the focus of early
hazardous waste site identification and cleanup, the activity tended to be in
developed areas where humans were at risk and ecological resources were
scarce. With human health as the initial focus of Superfund, the human
health risk assessment was one of the key tools enhanced for use at hazard-
ous waste sites to determine the threat and thus the need for remediation
(Doyle and Young 1993). The human health risk assessment tool evolved to
consist of four steps to characterize the baseline or existing risk to humans
from contamination (U.S. EPA 1989a):
r Data collection and evaluation, to determine where the contamina-
tion exists and at what concentrations
r Exposure assessment, to identify the pathways of exposure (e.g.,
ingestion, inhalation, dermal exposure), the population exposed,
and the degree of exposure
r Toxicity assessment, determination of safe levels (e.g., the mass of
dioxin that could be ingested without causing cancer) for each con-
taminant present at elevated concentrations
r Risk characterization, a comparison of the level of exposure and
safe levels to identify and quantify risk
As the most egregious sites that posed human health risk were investigated,
the nature of past hazardous waste practices and typical contamination migra-
tion patterns became apparent. One common factor that was revealed by this
increasing knowledge and understanding was that water flows downhill, and
when the water originates or passes through a hazardous waste site, it transports
the contaminants with the runoff. Thus the contaminated water and the eroded
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