These standards are intended to describe required levels of performance rather than detailed requirements. Wherever possible, operators and designers will be permitted flexibility in meeting the objectives set by the standards. Where the term “adequate” or the phrase “as approved by the enforcement agency” is used, the operator will usually propose a method, physical improvement, or other appropriate means to comply with a standard. The enforcement agency may thereupon accept, modify, reject, or replace the operator's proposal, and shall incorporate the means of compliance into the operator's permit, if applicable and appropriate.