Environmental Analysis Tools - Environmental Impact Analysis: Process and Methods - page 276

appropriate. The table also presents quotients for both the mean and maxi-
mum site concentrations. This provides additional information so that the
risk assessor can make an informed judgment regarding need for more inves-
tigation based on site knowledge and extent of available data. Following the
ecological resource and contaminant screening, the areas of ecological con-
cerns can be narrowed and the risk assessment can proceed to the next step
of detailed investigation focused on the critical endpoints potentially at risk.

7.2.5 Final Problem Formulation and Detailed Ecological Investigation

With the refinement of the endpoints, pathways, contaminants, habitats, and
receptors of concern accomplished through the screening-level ecological
risk assessment, the detailed assessment can focus on the areas of greatest or
unknown level of risk. Often this detailed assessment is termed a baseline eco-
logical risk assessment or BERA because the purpose is to define and quantify
the level of risk that currently exists before any remediation or additional
natural attenuation has occurred. The first activity is to fine tune the prob-
lem formulation and associated conceptual site model. The screening assess-
ment has almost always eliminated at least some pathways and receptors of
concern and the revised model should reflect the findings. In many cases,
the final model can include some degree of quantification or at least rela-
tive importance to identify the exposure and migration pathways of greatest
concern. Similarly, the initial endpoints identified can be revisited to be more
site specific, such as identifying individual species (e.g., osprey) rather than
general categories of receptors (e.g., piscivorous birds).
The final problem formulation and conceptual site model is the key tool for
identifying what additional studies are necessary to fully characterize the
risk and address the final measurement endpoints. A typical goal of the addi-
tional investigations is to quantify the extent of ecological damage that has or
continues to occur. Another is to relate media concentrations to the extent of
damage so an acceptable cleanup level can be established. Each study should
address a risk hypothesis related to a measurement endpoint such as:

r Ospreys feeding at the site ingest lead in quantities that impair
reproduction.
r DDT levels in soil inhibit microbial remineralization of essential
plant nutrients.
r Polycyclic aromatic hydrocarbons in sediments are toxic to benthic
invertebrates to the extent there is no sufficient food in the system to
support higher trophic levels.
r Eroded soil particles from contaminated areas following a rain event
accumulate in stream sediments to toxic levels.
r Volatile organic compounds in soils create air concentration in fox
dens acutely toxic to fox cubs.