1. A. A person may elect to remediate to a background concentration for a contaminant.

2. B. A person who conducts a remediation to a background concentration for a contaminant shall establish the background concentration using all of the following factors:

   1. 1. Site-specific historical information concerning land use.
   2. 2. Site-specific sampling of soils unaffected by a release, but having characteristics similar to those of the soils affected by the release.
   3. 3. Statistical analysis of background concentrations using the 95th percentile upper confidence limit.

Historical Note

Adopted by emergency action effective March 29, 1996, pursuant to A.R.S. § 41-1026 and Laws 1995, Ch. 232, § 5; in effect until permanent rules are adopted and in place no later than August 1, 1997, pursuant to A.R.S. § 49-152 and Laws 1995, Ch. 232, § 5 (Supp. 96-1). Historical note revised to clarify exemptions of emergency adoption (Supp. 97-1). Interim emergency amendment reinstated at the request of the Department (see Supp. 97-1); historical note from Supp. 97-3 stating emergency expired removed for clarity. Section R18-7-204 adopted permanently effective December 4, 1997, replacing emergency rule (Supp. 97-4). Amended by final rulemaking at 13 A.A.R. 971, effective May 5, 2007 (Supp. 07-1).