SITE INFORMATION AND CORRESPONDENCE_1985-2004

Home Browse Search

INFORMATION SHEET ORDER NO. 97-115 (revised) -2- CITY OF MANTECA AND CITY OF LATHROP SAN JOAQUIN COUNTY 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 ammonia concentrations in their discharge. The study's objectives included: 1) defining what range of effluent concentrations are acutely toxic in accordance with the 96 hour static bioassay, 2) what range of concentrations are acutely toxic in the first hour of toxicity testing, 3) defining the zone of initial dilution in the receiving water to the extent ammonia concentrations are acutely toxic to the 1 hour exposure level, 4) define the zone of initial dilution in the receiving water to the extent ammonia concentrations are no longer toxic, using bioassay protocol, 5) determine the zone in the receiving water which exceeds the EPA Water Quality criteria for various river flows and pH, and 6) the extent of the zone of measurable ammonia downstream to a point where ammonia concentration do not exceed upstream. The CDO allowed time for the Discharger to conduct necessary bioassay and stream studies and to construct the treatment plant expansion to meet ammonia toxicity requirements. Based on the above receiving water study, on 9 July 1999, the Discharger requested modification of the effluent toxicity requirements in Order No. 97-115 to allow the utilization of a mixing zone in the receiving water. A mixing zone would allow dilution of the toxic effects of the ammonia contained in their treated effluent, thereby eliminating the violation of their permit and achieving compliance with their CDO. The Discharger submitted additional information documenting their request on 22 July 1999, 23 November 1999, 3 December 1999, 11 January 2000 and 14 January 2000. The Discharger proposes to mitigate the toxic effects of the effluent by constructing an effluent discharge diffuser in the River to enhance mixing and to minimize toxicity to benthic.organisms; and by utilizing existing of holding ponds during critical San Joaquin River flow conditions. The diffuser will be designed to prevent plume contact with the River bottom and channel side banks. The existing wastewater holding ponds will hold up to two days of treated effluent while maintaining two feet of freeboard. Revisions to this permit are limited to effluent acute toxicity requirements and effluent monitoring in the monitoring and reporting program.