A frequent issue raised early in the Remedial Investigation/Feasibility Study (“RI/FS”) process at CERCLA sites is whether chemicals of concern occur naturally at the site or are there due to a man-made. If it is a “naturally occurring substance,” no remediation obligation is triggered by its detection as provided by CERCLA § 104(a)(3)(A).
Chromium levels in groundwater at 1990 CERCLA sites were deemed naturally occurring if the concentrations in groundwater did not exceed the US EPA MCL for total chromium of 100 ppb (micrograms/liter). Many of the groundwater cleanup standards used for 1980s – 1990s CERCLA sites were based on MCLs that were established in the 1970s – 1980s. Now, US EPA and some states are in the process of updating their MCLs.
For example, in California the MCL for total chromium was 50 ppb, half of the federal MCL, because California uses more stringent levels. California is in the process of updating its MCL for chromium, which will now be set only for hexavalent chromium (Cr-6). California recently calculated a Public Health Goal for hexavalent chromium of 0.02 ppb, which is likely to become California’s new MCL.
If you were involved with a CERCLA site that conducted its RI/FS before 2008, your consultant probably does not have any hexavalent chromium data to establish naturally occurring levels. The expected changes to hexavalent chromium MCLs at the state and federal level will probably trigger an EPA demand to conduct a new background analysis of hexavalent chromium at sites not yet delisted from the National Priorities List.
As the MCLs for chromium, arsenic and other naturally-occurring chemicals are reset in the future at lower concentrations, your environmental team may need to respond to the potential applicability of the new standards to your unique site circumstances. Confirming that a chemical of concern is naturally-occurring could be well worth the effort to manage remediation costs and avoid EPA reopeners.