SITE INFORMATION AND CORRESPONDENCE

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Finding: The interim effluent limit of 0.1 µg/I is appropriate. According to the Fact Sheet, Table 12-1, the Regional Board used the DFG recommended criteria guidance and applied procedures that are consistent with the SIP to calculate an Average Monthly Effluent Limit of 0.047 µg/1 and a Maximum Daily Effluent Limit of 0.061 99/1 for diazinon. The Regional Board's explanation and evidence are provided in the permit Finding 31 and Fact Sheet Section 12 and Table 12. The Petitioner alleges neither facts nor authority for the suggestion that use of the DFG criteria guidance was not appropriate. Absent some such demonstration, the explanation in the Fact Sheet is adequate. The Permit Effluent Limitation B.1 for diazinon, however, was set at 0.1 µg/1. An explanation for the final permit limit is not provided in the permit, however, the Fact Sheet, Table 12 also used USEPA Technical Support Document statistical procedures to calculate an Estimated Maximum Concentration of 0.10 µg/1 diazinon. It appears the Regional Board may have intended to adopt a performance based interim limit of 0.1 µg/1 for diazinon, but mistakenly placed the limit in the permit as a final limitation. If so,the Regional Board should correct the WDRs and adopt a final effluent limitation for diazinon. (33 U.S.C. § 1311; 40 C.F.R. § 122.44(d).) III. CONCLUSION Based on the above discussion, the State Board concludes that: 1. The Regional Board's determination in this matter not to employ outside consultants was not inappropriate or improper. 2. The Regional Board's determination not to grant dilutions credits or a mixing zone for ammonia was appropriate and proper. 3. The effluent limitation for chloroform,based on the unadopted CTR criterion of 5.7 µg/1 is inappropriate for the reasons set forth in State Board Order WQO 2002-15. 4. The effluent limitation for dichloromethane was inappropriately derived without compliance with Water Code section 13241. 5. The Regional Board did not act inappropriately in basing the diazinon effluent limitation upon DFG criteria guidance; however, the Regional Board must clarify the WDRs to 6.