[Code of Federal Regulations] [Title 40, Volume 18] [Revised as of July 1, 2002] From the U.S. Government Printing Office via GPO Access [CITE: 40CFR131.13] [Page 376] TITLE 40--PROTECTION OF ENVIRONMENT CHAPTER I--ENVIRONMENTAL PROTECTION AGENCY (CONTINUED) PART 131--WATER QUALITY STANDARDS--Table of Contents Subpart B--Establishment of Water Quality Standards Sec. 131.13 General policies. States may, at their discretion, include in their State standards, policies generally affecting their application and implementation, such as mixing zones, low flows and variances. Such policies are subject to EPA review and approval.