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concentrations obtained by the two agencies for many important waste
constituents. Further, the correlation was not improved by sending
samples to different laboratories. Unfortunately, insufficient data were
obtained to determine the exact cause of the poor correlation.
An important step in any cleanup program is to determine when
cleanup is complete. This includes determining the acceptable level
of residual contaminants. Acceptable levels are typically determined
by comparing the contaminant levels to the standards for "clean" water
or to levels that existed prior to the release. These levels are normally
site-specific and are determined by negotiation with the appropriate
regulatory agencies (Cooper and Hanson, 1990). Determining cleanup
levels may require risk assessment studies to be conducted.
Because of the statistical variability in any data and possible prob-
lems with sampling and analysis, identifying when a particular stand-
ard has been achieved can be difficult. Remediation to where the
applicable standard is met with a 90% confidence limit is often used,
although the actual level required is normally determined through
negotiation with applicable regulatory agencies on a case-by-case basis
(Hoffman, 1993).
In determining whether further remediation is required, political and
institutional pressures that have no relevance to protecting human
health or the environment often exist. Too often these pressures are
not based on accurate scientific information and can result in additional
remediation costs with little benefit to the environment. This problem
is further compounded by the disagreement on what scientific stand-
ards should be used. Even the relatively simple question of whether
cleanup should be based on the level of total petroleum hydrocarbons
or the levels of individual hydrocarbon compounds has not been
resolved. In some cases, the actual risk to the environment often
depends more on the composition of a contaminant than on its total
amount, particularly when only trace quantities are present. The
importance of accurate scientific information is evidenced in the
conflicting stories about the environmental impact related to the Exxon
Valdez spill (Maki et al., 1993).

8.2 REMEDIATION PROCESSES

A number of remediation processes are available to clean up con-
taminated sites (Sims, 1990). Some are suitable for cleaning up