Environmental Engineering FOURTH EDITION

Assessing Environmental Impact 23

Table 2-4.

Item Project PIU After project EQI x PIU = EIU

Appearance of water 1 0.33 x 1 = 0.33

Odor 1 0.5 x 1 = 0.5

Suspended solids 2 0.01 x 2 = 0.02

Aquatic life 5 0.2 x 5 = 1.0
Dissolved oxygen 1 0.88 x 1 = 0.88

Total 10 2.73

Multiattribute utility analysis, a more sophisticated ranking and weighting method,
has been developed by Keeney (Keeney and Raiffa 1993; Bell et al. 1989) and is now
used by many federal agencies. The details of the method are unfortunately beyond
the scope of this text.

Evaluation

The final part of the environmental impact assessment, which is reflected in the record
of decision, is the evaluation of the results of the preceding studies. Qpically the
evaluation phase is out of the hands of the engineers and scientists responsible for the
inventory and assessment phases. The responsible governmental agency ultimately
uses the environmental assessment to justify the record of decision.

USE OF RISK ANALYSIS IN ENVIRONMENTAL ASSESSMENT

The rationale for including risk analysis in environmental impact assessment is
threefold:

Risk analysis provides a method for comparing low-probability, high-

consequence impacts with high-probability, low-consequence impacts.

Risk analysis allows assessment of future uncertain impacts, and incorporates

uncertainty into the assessment.

The United States and international agencies concerned with regulating environ-

mental impact are adopting risk-based standards in place of consequence-based

standards.

The following example incorporates risk analysis into environmental impact
assessment: In 1985, the U.S. EPA promulgated a regulation for radioactive waste
disposal which allowed a 10% probability of a small release of radioactive material,
and a 0.1 % probability of release of ten times that amount (USEPA 1985). This standard
is shown in the stair-step of the diagram of Fig. 2-2.