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City of San Marcos TPDES Permit No. WQOO 1 0273002 CHRONIC BIOMONITORlNG REQUIREMENTS: FRESHWATER The provisions of this Section apply to Outfall 001 for whole effluent toxicity testing (biomonitoring). 1. Scope. Frequency and Methodology a. The permittee shall test the effluent for toxicity in accordance with the provisions below. Such testing will determine if an appropriately dilute effluent sample adversely affects the survival, reproduction, or growth of the test organisms. b. The permittee shall conduct the following toxicity tests utilizing the test organisms, procedures and quality assurance requirements specified in this Part ofthe permit and in accordance with "Short-Term Methods for Estimating the Chronic Toxicity of Effluents and Receiving Waters to Freshwater Organisms, Fourth Edition" (EPA-82l-R-02-013), or the most recent update: 1) Chronic static renewal survival and reproduction test using the water flea (Ceriodaphnia dubia) (Method 1002.0 or the most recent update). This test should be terminated when 60% of the surviving adults in the control produce three broods or at the end of eight days, whichever comes first. This test shall be conducted once per quarter. 2) Chronic static renewal 7-day larval surviyal and growth test using the fathead minnow (Pimephales promelas) (Method 1000.0 or the most recent update). A minimum of five replicates with eight organisms per replicate shall be used in the control and in each dilution. This test shall be conducted once quarter. The permittee must perform and report a valid test for each test species during the prescribed reporting period. An invalid test must be repeated during the same reporting period. An invalid test is herein defined as any test failing to satisfy the test acceptability criteria, including Percent Minimmn Significant Difference (PMSD) boundary requirements, procedures, and quality assurance requirements specified in the test methods and permit. All test results, valid or invalid, must be submitted as described below. c. The permittee shall use fiye effluent dilution concentrations and a control in each toxicity test. These additional effluent concentrations are 8%, 11 %, 14%, 19%, and 25% effluent. The critical dilution, defined as 19% effluent, is the effluent concentration representative of the proportion of effluent in the receiving water during critical low flow or critical mixing conditions. d. This permit may be amended to require a Whole Effluent Toxicity (WET) limit, Chemical-Specific (CS) effluent limits, a Best Management Practice (BMP), additional toxicity testing, and/or other appropriate actions to address toxicity. The permittee may be required to conduct additional biomonitoring tests and/or a Toxicity Reduction Evaluation (TRE) if biomonitoring data indicate multiple numbers of unconfirmed toxicity events. e. Testing Frequency Reduction I) If none of the first four consecutive quarterly fathead minnow tests demonstrates significant lethal or sub-lethal effects, the permittee may submit this information in writing and, upon approval from the Water Quality Standards Team, reduce the testing frequency to once per year. 2) If one or more of the first four consecutive quarterly fathead minnow tests demonstrates significant sub- lethal effects, the permittee shall continue quarterly testing until four consecutive quarterly tests Page 24