Environmental Engineering Reference
In-Depth Information
for soil transfer and management. In practice, risks for man should be solved in the
year 2015 (a policy choice), which resulted in a very large reduction of the case load
for urgent action. Further, the techniques described in Hodson et al. (
Chapter 16
of
this topic) are being used to provide information from other lines of evidence to the
decision makers before, during or after a remediation is undertaken. Toxic pressure
assessment is one of the three approaches being used for this purpose.
14.14.5.5 Outcome Assessment
Outcome Assessments can focus on sites and on the national inventory list. As yet,
there are no published Outcome assessments focusing on toxic pressure reduction.
It is however clear that the remediation resulted in concentration decreases, since
that is the primary benchmark to follow the success of the remediation process.
14.14.6 A Contrasting Approach, the U.S. Superfund
Ecological Risk Assessments for contaminated sites in the United States (U.S.) are
performed in the framework of the contaminated sites law known as “Superfund”
(formally: CERCLA, the Comprehensive Environmental Response, Compensation
and Liability Act). Superfund focuses on a relatively small number of highly
contaminated sites.
In 2008, there were 1255 listed sites in the entire U.S., more than 75% of
which are remediated or have final cleanup plans. The process of assessing human
health and ecological risks at Superfund sites often requires several years, due to
the requirements for multiple stages of consultation, planning, and site-specific
sampling, analysis, and assessment.
Ecological Risk Assessments for Superfund sites are performed in two stages
(Sprenger and Charters
1997
; Suter et al.
2000
). First, a screening assessment
uses hazard quotients (
HQ
) which are quotients of an exposure concentration (
C
e
)
divided by a toxicological benchmark concentration (
C
b
). That is:
=
C
e
/
HQ
C
b
(14.1)
where
C
e
is a site concentration that is a conservative (i.e., high) estimate of the expo-
sure concentration, such as the maximum observed concentration, and
C
b
is a
conservative (i.e., low) estimate of the threshold for toxicity.
Ecological benchmark values for plants, soil invertebrates, mammals
and birds exposed to soil are presented at
http://www.epa.gov/oswer/
riskassessment/ecorisk/ecossl.htm
, including references to the origin and underpin-
ning of the
C
b
values in general (in the Guidance Document) and for the numerical
value of
C
b
for different contaminants. The
C
b
values for a suite of compounds are
based on extensive literature searches and evaluations. They are derived separately
for four groups of ecological receptors: plants, soil
invertebrates, birds, and
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