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WASTE DISCHARGE REQ MENTS ORDER NO. R5=2004-00210 -21- CITY OF MANTECA, CITY�ATHROP AND DUTRA FARMS WASTEWATER QUALITY CONTROL FACILITY SAN JOAQUIN COUNTY 12 samples collected between January 2002 and December 2002. The Basin Plan chemical constituent objective includes a receiving water objective in Table III-1 for iron of 300 ug/1 in the Delta, and the secondary MCL for iron of 300 ug/l. Both the receiving water and the effluent exceed the Basin Plan numeric objective and the secondary MCL. Therefore, effluent limitations are included in this Order based on the Basin Plan chemical constituents objective. 48. Manganese: Manganese concentrations in the effluent ranged from 13 ug/1 to 120 ug/1 while background concentrations in the San Joaquin River ranged from 82 ug/1 to 220 ug/1 based on results from 11 samples collected between January 2002 and December 2002. The Basin Plan chemical constituent objective includes a receiving water objective in Table III-1 for manganese of 50 ug/1 in the Delta, and the secondary MCL for manganese of 50 ug/l. Both the receiving water and the effluent exceed the Basin Plan numeric objective and the secondary MCL. Therefore, effluent limitations are included in this Order based on the Basin Plan chemical constituents objective. 49. Chlorine: The Discharger currently uses chlorine for disinfection and has reported that it uses sodium hypochlorite for maintenance. Chlorine is extremely toxic to aquatic organisms. The Discharger uses a sulfur dioxide process to dechlorinate the effluent, but will discontinue this with the installation of the UV disinfection system. Because of the existing chlorine use and the future use of hypochlorite solutions without effluent dechlorination, there is reasonable potential for chlorine to be discharged at toxic concentrations. The Basin Plan contains a narrative toxicity objective. Consistent with 40 CFR 122.44(d), it is appropriate to use the USEPA ambient water quality criteria for chlorine for protection of freshwater aquatic life of 11 ug/1 as a 4-day average (chronic) concentration, and 19 ug/1 as a 1-hour average (acute) concentration to implement the narrative toxicity objective. Therefore, this Order includes water quality based effluent limitations for chlorine based on the USEPA ambient criteria to protect freshwater aquatic life. 50. Methylene blue active substances (MBAS): The effluent contains MBAS at levels that may cause or contribute to exceedances in the receiving waters of water quality objectives in the Basin Plan. The Basin Plan includes the "Chemical Constituents"objective that incorporates state MCLS applicable to waters designated MUN. MUN is a designated beneficial use of the San Joaquin River. The Secondary MCL Consumer Acceptance Limit is 500 ug/1 for foaming agents (MBAS). The Basin Plan also includes water quality objectives that water not contain floating material or taste- or odor-producing substances in concentrations that causes nuisance or adversely affect beneficial uses. The Basin Plan identifies non-contact water recreation,which includes aesthetic enjoyment, as a beneficial use of the San Joaquin River. MBAS concentrations in excess of the Secondary MCL-Consumer Acceptance Limit produce aesthetically undesirable froth, taste, and odor. Foam has been observed on the surface of the discharge plume from the WQCF. The maximum observed effluent MBAS concentration is 1800 ug/l. The maximum observed upstream receiving water MBAS concentration is less than 20 ug/l. An Effluent Limitation for MBAS is included in this Order based on of the Basin Plan water quality objectives for chemical constituents, floating material, and tastes and odors. 51. Molybdenum: The recommended agricultural water quality goal for molybdenum, that would implement the narrative "Chemical Constituent'objective, is 10 ug/l based on Water Quality for