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Risk Assessment evaluates the data
collected and provides the risk information necessary to assist in
decision-making at remedial sites. The risk assessment
provides the information necessary to justify action (or no action)
at a site and to select the best remedy for the site. The risk
assessment includes characterization of the contaminants, the
potential exposures, and the potentially exposed populations to
determine what risks need to be reduced or eliminated and what
exposures need to be prevented. A conceptual site model is
used to evaluate the potential contaminant transport pathways and
potential pathways by which humans could be exposed to site
contamination. A baseline
Human Health Risk Assessment (HHRA) is conducted to evaluate the
potential human health risks associated with the presence of
contaminants in surface and subsurface soil, surface water,
sediment, and groundwater at a site. The HHRA characterizes
current and potential future human health risks at a site if no
additional remediation were to be implemented. Health risks are
based on a conservative estimate of the potential carcinogenic
(cancer) risk or the potential to cause other health effects not
related to cancer (noncarcinogenic risk). A Hazard Quotient (HQ)
is calculated for a given constituent, and the total
noncarcinogenic risk is calculated as the sum of all HQs, and is
called a Hazard Index (HI).
Health risk levels, determined using USEPA guidance to ensure
that conservative estimates of potential health effects were
obtained, differ depending on the assumed land use. This is
because potential human exposure to contamination differs with
land use. A conservative estimate of risk is developed
incorporating potential exposure scenarios; construction
workers, maintenance workers, on-site recreational users,
full-time employees, adolescent trespassers, adult recreational
users, and future on-site residents who may be exposed to media
at the site.
An Ecological Risk Assessment (ERA) is used to evaluate
ecological risks associated with the presence of contaminants in
soil, surface water, sediment, and groundwater. As with a HHRA,
summary HQs are also used to evaluate ecological risks; below a
HQ of 1, adverse effects to ecological receptors are not
expected. Risks are evaluated for terrestrial habitats (in
relation to the surface) and for aquatic habitats (in the
surface water bodies) that may be impacted from discharges of
site-related contaminants. The ERA also considered the following
factors when evaluating and interpreting the risk results:
inorganic constituent concentrations in site soils compared to
those in reference samples; chemical bioavailability in
sediment; chemical distribution in site soil and sediment;
influence of grain size and total organic carbon (TOC) on
chemical distribution in sediment; potential chemical sources to
site drainage; and potential risks to ecological receptors.
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