SITE INFORMATION AND CORRESPONDENCE_1985-2004

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Staff Report • • - 2 - City 2 -City of Manteca and City of Lathrop Wastewater Quality Control Facility restricted to two of the allowable test species, fathead minnows and golden shiners. When testing with fathead minnows or golden shiners, the new EPA procedure requires the use of these species in the larval stage(0 to 14 days old) instead of the previous method of using juveniles (15 to 30 days old). Larvae are much more sensitive to ammonia levels than the juvenile species. The City of Manteca did not operate their treatment plant to nitrify and therefore high ammonia levels were passed through their plant and discharged in their effluent. The Board, on 24 July 1998, adopted Cease and Desist Order No. 98-169 which directed the City of Manteca and the City of Lathrop to implement a permit compliance workplan. The plan included identification and implementation of changes required at the wastewater treatment plant to ensure reliable compliance with Waste Discharge Requirements Order No. 97-115. The plan was to include evaluation of treatment options and any other measures which would ensure compliance, including, but not limited to, changes in test species to include rainbow trout in addition to the permitted fathead minnow, and consideration of effects of the acutely toxic discharge on ambient waters and beneficial uses. The above stated plan included a time schedule with full continuous compliance with Order 97-115 by 1 December 1998. The Discharger proceeded with the necessary work to comply with Order 98-169 and the time schedule. In 1999, the Discharger investigated using rainbow trout as an alternative species to the permitted fathead minnows in the 96-hour bioassay test. The bioassay test results showed fathead minnow could not tolerate total ammonia concentrations greater than 10 mg/1 while rainbow trout could not tolerate ammonia concentrations above 20 mg/l. The Discharger has also found that while operating the plant in a partial nitrification mode, it was possible to maintain a constant effluent ammonia concentration of less than 20 mg/l,but extremely difficult to maintain a constant effluent ammonia concentration of less than 10 mg/l. Furthermore, U.S.E.P.A. stated that they do not support the proposed change in test species to rainbow trout, a less sensitive species. The Discharger has now withdrawn its request to use rainbow trout in the 96 hour bioassay. On 30 April 1999, the Regional Board adopted Cease and Desist Order(CDO)No. 99-051 to investigate and implement methods to bring the discharge into compliance with effluent limitation C.5 (acute toxicity). The CDO required the Discharger to identify and implement changes at the wastewater treatment plant to ensure reliable compliance with the Waste Discharge Requirements contained in Order 97-115 forthwith, but in no event later than the date provided in the following schedule: • Submit results of receiving water study, 1 March 2000; • Complete Plans and Specifications for treatment plant expansion, 1 March 2000; • Begin construction of Treatment Plant Expansion to reduce ammonia levels, 1 July 2000; • Complete Treatment Plant Expansion, 1 December 2001; • Achieve full compliance with Order 97-115 by 1 July 2002. A finding in the CDO acknowledged that the Discharger proposed to evaluate the effects of the current discharge and to determine the extent of the mixing zone currently affected by the acute