020-1 Wyo. Code R. § 1-11

Current through April 27, 2019

Section 1-11 - Flow Conditions

(a) Numeric water quality standards shall be enforced at all times except during periods below low flow. Low flow can be determined by the following methods:

• (i) Using the 7Q10 (the minimum seven (7) consecutive day flow which has the probability of occurring once in ten (10) years);

• (ii) The EPA's biologically based flow method which determines a four (4) day, three (3) year low flow for chronic exposures and a one (1) day, three (3) year low flow for acute exposures (Technical Guidance Manual For Performing Waste Load Allocation, Book VI, Design Conditions: Chapter 1, Stream Design Flow for Steady-State Modeling, August 1986, US EPA); or

• (iii) Other defensible scientific methods.

  For all methods, application of the standards will conform to the magnitude, duration and frequency provisions described in these regulations.

(b) During periods when stream flows are less than the minimums described above, the department may, in consultation with the Wyoming Game and Fish Department and the affected discharger(s), require permittees to institute operational modifications as necessary to insure the protection of aquatic life. This section should not be interpreted as requiring the maintenance of any particular stream flow.

(c) The narrative water quality standards in Sections 14, 15, 16, 17, 28 and 29(b) of these regulations shall be enforced at all streamflow conditions.

020-1 Wyo. Code R. § 1-11

Amended, Eff. 4/24/2018.