Environmental Analysis Tools - Environmental Impact Analysis: Process and Methods - page 281

However, in many cases the screening-level benchmarks represent concen-
trations lower than necessary to protect receptors or the designated measure-
ment endpoint. In such cases, site-specific benchmarks can be identified or
developed that represent the endpoint species, lifecycle stages of concern, and
site specific conditions rather than the broad-based and conservative bench-
marks used in the screening assessment. For example, if there is no salmonid
(e.g., trout) habitat associated with the site because the natural water tempera-
tures are too high, water-quality benchmarks for warm water fisheries (which
are usually higher concentrations) may be more appropriate. Similarly, since
juvenile forms of most animals are typically more sensitive to contamination
than adults, a higher-effect concentration might be appropriate for sites where
there is no potential for breeding or rearing of receptor species.
The effects characterization can also take into account site-specific condi-
tions. For example, the hardness and other natural characteristics of surface
waters can affect the concentrations of contaminants that cause toxic effects.
In recognition of the phenomena, procedures have been developed to adjust
water-quality criteria based on site-specific conditions (U.S. EPA 1994). Also
evaluation of the ingestion pathway for a large carnivorous receptor should
take into account that they may only derive a portion of their food from the
site, because they forage over a large area, thus the effect concentration of
on-site prey items would have to be adjusted by the size of the site relative to
their forage area (Boucher 1993).
The effects characterization often identifies more than one concentration or
dose to represent different degrees of exposure or levels of risk. For example,
water-quality concentrations associated with both acute and chronic effects
(U.S. EPA 2013) are frequently included in the effects characterization. Thus,
if a receptor will only be exposed for short durations, such as swimming by a
discharge point, the acute criteria might be the appropriate effects concentra-
tion. But if the receptors are subject to long-term exposure, such as within a
reach of stream, the chronic criteria will be more appropriate.
The product of the effects characterization is a listing and documentation
of concentrations, doses, or other levels of stress that result in various levels
of risk. There should be an effects level for comparison to each measurement
endpoint and for every media identified in an exposure pathway. Some of
these levels will be standard and may even be the same benchmarks used in
the screening-level assessment. Others will be adjusted to site conditions and
still others will be developed specifically for the site through toxicity testing
and other ecological investigations (Table 7.3).

7.2.8 Risk Characterization and Input to Remediation Decisions

Risk characterization is the final technical step in the ecological risk assessment,
and because it provides direct input to remediation decisions, it can be consid-
ered the most important. However, in concept it is the most simple. At the base