Comfort letters are written by regulatory agencies to clear a given property from financial liability for cleanup of contamination from an off-site source. The Small Business Administration (SBA) requires these letters in order to approve financing of contaminated Property. In the past the RWQCB has issued these letters. The process was formal and it involved detailed review of a Phase 1 Environmental Site Assessment (ESA).

In addition to the ESA report, a written request would be made by an environmental consultant that would usually expedite the process. In some cases, Phase 2 subsurface groundwater information was required by the RWQCB. In other cases the RWQCB would not issue a comfort letter, even with Phase 2 data. Their refusal was usually for sites in known plume areas where the site history was not or could not be sufficiently documented.

Comfort letters are issued almost exclusively for solvent leak cases. In cases where a Property was contaminated by a fuel leak, it has not been possible to obtain a comfort letter from the local agency (usually a health department such as San Mateo County Department of Environmental Health).

ERAS has also been recently involved with obtaining a comfort letter from the Environmental Protection Agency (listed on NPL list) for a site in Mountain View. ERAS has also discussed these letters with representatives of the Department of Toxic Substances Control (DTSC).