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RESPONSE TO WRITTEN COMMENTS -22- City Of Stockton -Regional Wastewater Control Facility NPDES No. CA0079138 26 April 2002 Board Meeting "downgradient". The requirements are inconsistent with the Basin Plan, Resolution No. 68-16, Water Code Section 13263, and permits issued to other dischargers. RWQCB Response: Groundwater.Limitation F.2. states, "Any-constituent concentration, when compared with background, shall not be incrementally increased beyond the current concentration in downgradient wells. "The limitation does not preclude all degradation downgradient, but requires that it not become incrementally increased from that which currently exists, pending completion of studies required by Provision G.10. The requirements are consistent with the Basin Plan, Resolution 68-16, and Water Code Section 13263. The Regional Board is not establishing a new water quality objective, rather, it is implementing the Porter-Cologne Act, the Basin Plan, and Resolution 68-16. Water Code section 13000 requires the state to "exercise its full power and jurisdiction to protect the quality of the waters in the state from degradation . . ." Resolution 68-16 requires the Regional Board to maintain the highest water quality unless certain findings and requirements are made. In this case, there is insufficient information to make a finding that further degradation should be allowed without determining the existing water quality. The Groundwater Limitation F.2 maintains the existing water quality until further information is received by the Regional Board. VI. Laboratory Monitoring Stockton Comment No. VLA (Effluent Monitorin¢)• The tentative permit stipulates that acute bioassay samples are to be run under Standard Methods, Fourth Edition. Currently, the operators of the RWCF can determine whether or not to discharge for a period of time should they feel this is in the best interest of the City, or to meet the requirements of the WDR. A decision of this nature can be made while the bioassay sample may be in the middle of the test. The City would recommend that the permit be rewritten to allow the bioassay to continue with a static-renewal with daily composite samples while the discharge is terminated. Additionally, the permit should provide that the bioassay test should not be invalidated unless the discharge is terminated for over 48 continuous hours during the test process. RWQCB Response: The acute bioassay protocol (EPA/600/4-901/027F, Fourth Edition, provides protocols for static, static renewal, and flow through bioassays. The intermittent operation of the tertiary plant may require that the City select a static or static renewal test method rather than a flow through bioassay. The protocol does not include a method for a hybrid flow through/static renewal test and cannot be approved. Additionally, because the protocol provides methods that provide acceptable test results for intermittent discharges, the City cannot be exempted from the requirement to provide results each time the discharge is terminated for over 48 hours. No changes were made as a result of the comment. Stockton Comment No. VLA (Effluent Monitoring)' Note (7) requires mercury to be sampled and tested by use of"clean technique" (EPA Method 1631). The City completed a full year of sampling under these requirements in 1995-96. However, note(2)requires the samples to be proportional composite samples. As the City determined during the previous sampling, this will not