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WASTE DISCHARGE REQUOMENTS ORDER NO. R5-2004-002i* -20- CITY OF MANTECA, CITY OF LATHROP AND DUTRA FARMS WASTEWATER QUALITY CONTROL FACILITY SAN JOAQUIN COUNTY Electrical conductivity(EC) shows reasonable potential to exceed water quality objectives in both the effluent and in the receiving water. A review of the Discharger's monitoring reports from January 1998 through December 2002 shows the annual average effluent EC is 1099 umhos/cm,the lowest monthly average is 819 umhos/cm, and the highest monthly average is 1300 umhos/cm. These levels exceed the applicable objectives. EC data collected at receiving water sample location Rl from January 2002 through December 2002 show that the conductivity in the receiving water ranged from 380 umhos/cm to 1100 umhos/cm and averaged 686 umhos/cm in 12 sampling events. Hourly EC data collected at the Department of Water Resources (DWR) Mossdale monitoring station(RSAN087) from December 2000 through September 2002 show that the conductivity in the San Joaquin River ranged from 299 umhos/cm to 1131 umhos/cm and averaged 721 umhos/cm. San Joaquin River monitoring for electrical conductivity at Vemalis between 1985 and 1998 showed frequent exceedances of the EC water quality objectives (Reference Figure 1-3, Total Maximum Daily Load for Salinity and Boron in the Lower San Joaquin River(January 2002)). These data show that the receiving water frequently has no assimilative capacity for EC. An Effluent Limitation for electrical conductivity is included in this Order and is based on the Basin Plan water quality objective for electrical conductivity in the South Delta. The TDS, chloride, and electrical conductivity objectives and recommended levels are all measures of the salt content of the water. Compliance with the Effluent Limitations for electrical conductivity based on the Basin Plan seasonal water quality objectives of 700 umhos/cm and 1000 umhos/cm will be protective of the chloride and TDS recommended levels; therefore,no limitations are included for chloride and TDS. 46. Aluminum: Aluminum concentrations in the effluent were detected in the range of 70 ug/L to 350 ug/L in 12 samples collected between January 2002 and December 2002. Aluminum was detected in the receiving water (R-1)in the range of 420 ug/L to 2200 ug/L in 12 samples collected between January 2002 and December 2002. Dissolved concentrations of aluminum in the effluent and the receiving water were significantly less than the totals listed above. The Basin Plan's chemical constituents water quality objective prohibits chemical constituents in concentrations that exceed state MCLS or that adversely affect beneficial uses. MUN is a beneficial use of the San Joaquin River. The Primary and Secondary MCLs for aluminum are 1000 ug/1 and 200 ug/1 respectively. The Basin Plan contains a narrative toxicity objective. Consistent with 40 CFR 122.44(d), USEPA's ambient Water Quality Criteria for protection of freshwater aquatic life for aluminum expressed as total recoverable are 750 ug/1(1-hour average) and 87 ug/1(4-day average), and are appropriate to implement the narrative toxicity objective. Since both the receiving water and the effluent exceed USEPA's ambient water quality criteria and the secondary MCL, no dilution can be granted. The effluent has reasonable potential to cause or contribute to an in-stream excursion above water quality objectives for aluminum. Therefore, this Order includes an effluent limitation for aluminum of 7lug/1 as a monthly average and 143 ug/1 as the daily maximum. 47. Iron: Iron concentrations in the effluent ranged from 170 ug/l to 730 ug/l while background concentrations in the San Joaquin River ranged from 780 ug/1 to 2800 ug/I based on results from