FIELD DOCUMENTS AND WORK PLANS 1987

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Greg K. Vaughn • -2- 1 May 1987 treatment plant capacity) instead of 1. 31 mgd until completion of the second stage of the plant. At that time MCTC may apply for a revision their permit to accommodate the increase in their treatment plant capacity. The average flow value should also be revised to reflect the first stage treatment plant capacity. The other proposed revisions are acceptable and will be incorporated into the revised permit. Revision 3A. The water quality control plan (Basin Plan) for our region requires that waters designated for use as a domestic or municipal water supply not contain concentrations of chemical constituents in excess of the limits specified in the California Administrative Code, Title 22 , Article 4 , Section 64435. Title 22 provides a standard of 0. 05 mg/l for total chromium but does not provide standards for other forms of chromium (ie. CrVI or Cr III) . Therefore, the existing discharge specification (0 . 05 mg/1) for total chromium will remain in the revised permit until the Basin Plan or Title 22 is amended. Revision 3B. The inland surface water quality objectives established in the Basin Plan, state that the "pH shall not be depressed below 6 . 5 nor raised above 8 . 511 . Therefore, the existing pH limits will remain the same for the revised permit until the Basin Plan is amended. Revision 3C. See comment for Revision 2 . Revision 4 . In order to define the Calaveras River rather than the Stockton Diverting Canal (SDC) as the receiving water body for your discharge several Technical issues need to be considered. First, is your discharge toxic? To determine whether your discharge is toxic, we will be requiring that you perform biotoxicity tests in accordance with the procedures contained in the "Technical Support Document for Water Quality Based Toxics Control" , EPA Document 440/4-85-032 . I£ the tests confirm that your discharge is toxic, then the second issue that should be considered is whether the beneficial uses for the SDC should be protected. This issue must be resolved due to the fact that during low flow or dry periods the discharge will receive little or no dilution before entering the SDC and eventually the Calaveras River. The primary constituent of concern is copper because it is toxic to aquatic organisms at relatively low concentrations. Finally, we recognize that the Stockton Diverting Canal (SDC) is dry certain times of the year.