Environmental Analysis Tools - Environmental Impact Analysis: Process and Methods - page 264

contaminated soil particles migrated to water bodies and wetlands. Although
the human health risk, except for drinking water supplies, was less in streams,
rivers, and wetlands than in developed areas, generally the most sensitive and
vulnerable ecological resources are located in wetlands and water bodies. As a
result, the biologists and ecologists within regulatory and natural resource agen-
cies became increasingly concerned about long-term and significant impacts
to sensitive and critical ecological attributes from the migration of hazardous
waste from uncontrolled disposal sites to sensitive ecological resources.
In order to assess the magnitude of the potential threat to ecological resources
from contamination, EPA surveyed 250 hazardous waste sites (U.S. EPA 1989b
and 1989e). None of the sites surveyed were placed on the Superfund prior-
ity list (i.e., the sites with highest priority for investigation and remediation)
due to ecological concerns because, prior to about 1989 there was no real con-
sideration of ecological resources in the listing process. Hence there was no
ecological information available on approximately 75% of the sites and only
limited information on the remaining 25% of the sites surveyed. Based on
the limited information that was available, the survey concluded that there
were severe ecological threats at 10% of the sites and moderate threats at an
additional 80% of the sites. Because water does flow downhill, wetlands and
freshwater ecological resources were found to be the most common ecological
resources threatened at the sites identified as posing an ecological risk.
With this information in hand, EPA launched a program, first within the
Superfund divisions and then agency wide, to address ecological risk at
Superfund sites. The agency's attention to the matter resulted in requirements
and initial guidance for ecological risk assessment (U.S. EPA 1989f and U.S. EPA
1992). This new emphasis on ecological aspects of hazardous waste investiga-
tion and cleanup also prompted a series of peer-reviewed articles and two early
text/reference topic (Maughan 1993 and Suter 1993) on the newly formed eco-
logical risk assessment tool and process. After a decade of experience, research,
academic study, and numerous draft versions and associated public comments,
the practice of ecological risk assessment matured, and EPA and other federal
agencies issued a final guidance (U.S. EPA 1992 and 1997).

7.2.2 Process and Approach

As referenced above, the ecological risk assessment tool grew out of a com-
bination of the well-established human health risk assessment and environ-
mental impact analysis procedures. As a result, elements of each exist in the
ecological risk assessment framework. However, ecological risk assessment
differs from the other two procedures in significant ways:

r Human health risk assessment compared with ecological risk
assessment:
- Only one receptor is considered as opposed to multiple species,

ecological processes, and habitats.