The purpose of this rulemaking is to add the term, "semi-impervious" to the environmental resource permit rules and portions of the Environmental Resource Permitting Manual Part B, Basis of Review, which set forth permitting exemptions, limitations or requirements that are based upon the amount of impervious surface proposed for a project. The effect will be to clarify that semi-impervious material is to be included in requirements relating to impervious material. Historically, impervious and semi- impervious materials have been treated the same in District rules. However, recent rulemaking involving adoption of a separate definition of "semi-impervious" made the continued inclusion of semi-impervious materials in calculations relating to impervious material unclear.