Okla. Admin. Code § 252:628-9-6
Applicants shall submit to DEQ three (3) copies and receive approval of the engineering report for proposed new construction or modifications to IPR SWTPs prior to the submittal of plans and specifications. All engineering reports submitted to DEQ shall be signed and sealed by an engineer licensed by the State of Oklahoma. The engineering report, including the results of any pilot studies, shall address the project pursuant to the approved feasibility study. Applicants shall also submit a letter in which the applicant endorses the contents of each engineering report submitted to DEQ. Engineering reports shall include the requirements as described in OAC 252:656-3-4, as well as addressing the design requirements of this Chapter.
Okla. Admin. Code § 252:628-9-6