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City of Stockton -3- 14 August 1990 II (toxicity identification) , and phase III (toxicity confirmation) TIE work will commence and be completed, (ii ) dates when Regional Board and City staff and Consultants will meet to review data and discuss succeeding phases of the project. 2. Monthly written progress report should be submitted which summarize all the results obtained during the previous month and interpret them in light of all previously obtained data. In addition, the City should use the reports to request any workplan changes thought necessary to successfully complete the TIE/TRE goals. 3. A Final Report due i May 1991 should be submitted which contains: a) A list of the name(s) of the chemical (s) causing toxicity and a summary all the data supporting the conclusion. b) If the City elected the treatability option, the Report must precisely describe the treatment method and time schedule to be used to eliminate toxicity. c) If the City elects a) , above, then a time schedule must be submitted for developing and implementing a treatment strategy to insure that no further violations of the toxic provision of the permit occur with regard to the identified chemicals. II. CERIODAPHNIA TOXICITY A. Background Order No. 86-088 states, in part, that "The discharge shall not cause concentrations of any materials in the receiving waters which are deleterious to human, animal , aquatic or plant life. Order No. 86-088 also directs the City to conduct EPA's three species toxicity testing (EPA/500/4-85%014) of its effluent for a one year period and for Board staff to then analyze the data and develop effluent toxicity limits pursuant to EPA's Water Quality based Technical Support Document (EPA/440/4-85/032) . The purpose of the toxicity limits are to insure that the effluent produces no acute or chronic instream toxicity, using the three species test as a measurement of compliance. Initial City chronic testing demonstrated that too much acute toxicity to the invertebrate Ceriodaohnia was present in the effluent making chronic testing not meaningful . A 48-hour static acute test with Ceriodaphnia was used instead as a screening test. When the screening test showed acute toxicity was present in the effluent, staff decided it would be better to work with the City on a TIE/TRE to determine the cause and to develop corrective actions rather than to impose numerical permit limits which would place the City out of compliance. However, this decision was predicated upon the City of Stockton making a continued good faith effort to address toxicity problems. The initial TIE/TRE was completed in 1988 and the cause of invertebrate toxicity was determined to be the use of the pesticides Temephos and Fenthion to control midges in the City's oxidation ponds. The City now employs the bacteria Bacillus thurinaiencis