Wyo. Stat. § 35-11-1608 (2026)

attenuation.

     (a) If the department determines that no further
remediation is required on a site, the department shall, upon
request, provide the owner or prospective purchaser a no further
action letter, subject to reopener or termination as provided in
W.S. 35-11-1610. The department may only issue a no further
action letter upon a finding by the department that the site
does not require engineering or institutional controls or use
restrictions to meet the standards specified in W.S.
35-11-1605(a)(ii).

     (b) When the department has determined that monitored
natural attenuation over a reasonable period of time is
appropriate and that no exposure to contaminated media is
reasonably expected during the period of natural attenuation,
the department shall, upon request, provide the owner or
prospective purchaser a no further action letter. The no
further action letter may require that the current use of the
property continue during the period of natural attenuation and
also may require that testing be conducted to confirm that
standards are met.