How clean is clean? National policy on human health and ecological risk assessment has proceeded for some time on a precautionary approach to remediation requirements. Conservative assumptions on "safe" levels of exposure have created underlying assumptions of "clean up to background" levels of contamination as anything less would not guarantee safety for future residential use. These generic assumptions rather than more site-specific assessments predominated, in large part, due to scientific uncertainty in risk assessment and concern that site-specific analysis necessarily entailed more time and expense.

Scientific research on "natural attenuation" (recovery through natural processes) and a more generalized expansion of scientific knowledge has prompted site assessors, responsible parties for cleanup, state agencies, and federal agencies to question the validity of the traditional generic approach in a variety of different contexts. There is more disagreement in these groups over the definition of "bioavailability" than there appears to be in the scientific community as to its overall validity as a scientific precept and methodology for risk assessment. Whatever the precise definition, the essential concept of bioavailability is a site-specific assessment of the risk to human health and the environment from contamination, and remediation to the level necessary to return the site to its actual future use. Assuming sufficient information (a critical assumption), incorporation of bioavailability into the risk assessment process holds the promise of more accurate, cost-effective cleanups with no greater actual risk to human health or ecology than under the traditional generic approach.