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COLORADO ])EPARTMENT OF HEALTH, Water Quality Control Division <br />Rationale - Page 12. Permit No. CO-0032115. <br />VI. TERM;i AND CONDITIONS OF PERMIT <br />4. Discussion of Limitations: <br />a) Salinit CTotal Dissolved Solids): The Regu:Lation for <br />mp ementation o t e ors o Salinity Standards Through the: <br />Colorado Discharge Permit Program (3.10.0), addresses the <br />discharge of total dissolved solids (TDS) to the Colorado River <br />Basin. It is a requirement of this regulation that all <br />discharges into the Colorado River basin be monitored for TD:i on <br />a continual basis. Therefore, in compliance with this <br />regulation the permittee must monitor for TDS oa a quarterly <br />basis. <br />'i. Whole Effluent Toxicity (WET) Testing: For this facility, acute <br />WET testing is require at 005, 006, 009, and 011,. (See <br />Parts I.A and I.B of the permit. Monitoring shall be performed <br />commencing with the first full calendar quarter following the <br />permit effective date. <br />a) Purpose of WET Testing: Section 6.9.7 of the Regulationia for <br />the State Discharge Permit System (6.1.0), passed by the Water <br />Quality Control Commission (WQCC), has established the use of <br />WET testing as a method for identifying and controlling tox:Lc <br />discharges from wastewater treatment facilities. WET testing is <br />being utilized as a means to ensure that there are no discharges <br />"in amounts, concentrations or combinations which are harmful to <br />the beneficial uses or tonic to humans, animals, plants, of <br />aquatic life" as required by Section 3.1.11 (1)(d) of th.e Basic <br />Standards and Methodologies. <br />Chemical analysis of effluent has provided only a partial <br />evaluation of the potential impact a discharge could have on the <br />receiving stream. Also, chemical analysis cannot evaluate the <br />synergistic or antagonistic effect of compounds. There are also <br />compounds for which an accurate or reproducable method of <br />chemical analysis bas not yet been developed, as well a~a <br />compounds which are just beginning to be evaluated for toxf.c <br />effects. WET testing will provide a more comprehensive means of <br />evaluating the toxicity of a discharge than could otherwise <br />currently be accomplished. <br />b) Instream Waste Concentration (IWC): As a condition of the <br />permit, t e permittee will a required to conduct routine <br />monitoring for acute toxicity. Acute toxicity occurs when there <br />is a statistically significant difference in the mortality <br />observed, for Ceriodaphnia sp. (water flea) and fathead'. minnows, <br />between the contro an nay effluent concentration. Should <br />acute tonicity be detected in any effluent concentration less <br />than or equal to the Instream Waste Coacentraciaa (IWC) or <br />