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Chapter S CLEANUP LEVEL DETERMINATION AND CONTAMINATED SITE MITIGATION One of the most crucial determinations made in the cleanup of a contaminated site is what concentrations of contaminants can safely remain without the need for further remedial action, in other words, "how clean is clean?". These concentrations are often called "cleanup levels". Ideally,all contaminants should be removed and the site returned to "background" conditions;however,removing every molecule of a.contaminant is often technologically infeasible and may not be the best use of economic resources. A method for determining what is safe to leave at a site is, therefore, necessary. It is important at the outset of cleanup to establish goals for the mitigation effort. Ground water should be cleaned to the level where beneficial uses are restored (i.e., water quality goals are not exceeded). Soils should be removed or mitigation provided such that the remaining contaminants do not pose a threat to water quality,or to human health or the environment through direct or indirect pathways. If naturally occurring concentrations of constituents in waters or soils at the site ("background") exceed these cleanup criteria, the background levels should guide the cleanup effort. If background levels are lower than cleanup criteria, cleanup to background levels may also be appropriate if technologically and economically feasible(see the discussion of the State Water Resources Control Board- Resolution No. 65-16, "Statement of Policy With Respect to Maintaining High Quality of Waters in California" in Section 3.2 above). Under the Health and Safety Code,§25356.1, DHS and the Regional Water Boards share the responsibility for remedial action at sites contaminated with toxic and hazardous substances. Subsection (c) of that section lists six factors that must be considered in the - T development_of a remedial action plan _(RAP)for-such sites.These factors are: - --- -1)=health°and=safety risks=at the-site;= - - t 2) the effect of contamination or pollution levels upon present, future and probable beneficial uses of contaminated,polluted,or threatened resources; 3) the effect of alternative remedial action measures on the reasonable availability of L ground water resources for present,future, and probable beneficial uses; site specific characteristics;—� # 5) cost effectiveness; and 6) potential environmental impacts. LThe terms "present,future, and probable beneficial uses"clearly reflect wording of the Porter-Cologne Water Quality Control Act(Water Code,Division 7) and mandate the direct involvement of the Regional Water Boards in the cleanup and/or prevention of water quality impacts from contaminated sites. ' Designated Level Methodology Page 45