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WASTE DISCHARGE REQU&MENTS ORDER NO. R5-2004-002* -19- CITY OF MANTECA, CITYATHROP AND DUTRA FARMS WASTEWATER QUALITY CONTROL FACILITY SAN JOAQUIN COUNTY 45. Salinity: The discharge contains total dissolved solids (TDS), chloride and electrical conductivity. These are water quality parameters that are typically indicative of the salinity of the water. Their presence in water can be growth limiting to certain agricultural crops and can affect the taste of the water for human consumption. There are no USEPA water quality criteria for protection of aquatic organisms for these constituents. The Basin Plan"Chemical Constituent"objective incorporates state MCLs, contains a narrative objective, and contains numeric water quality objectives for electrical conductivity. The secondary California maximum contaminant level (MCL) for TDS is 500 mg/1 as a recommended level, 1000 mg/l as an upper level, and 1500 mg/l as a short-term maximum. The recommended agricultural water quality goal for TDS, that would implement the narrative "Chemical Constituent"objective, is 450 mg/l as a long-term average based on Water Qualityfor Agriculture, Food and Agriculture Organization of the United Nations—Irrigation and Drainage Paper No. 29,Rev. 1 (R.S. Ayers and D.W. Westcot, Rome, 1985). The recommended agricultural water quality goal for chloride, that would implement the narrative "Chemical Constituent"objective, is 106 mg/1 based on Water Quality for Agriculture, Food and Agriculture Organization of the United Nations—Irrigation and Drainage Paper No. 29, Rev. 1 (R.S. Ayers and D.W. Westcot, Rome, 1985). The Basin Plan water quality objectives for electrical conductivity for the South Delta are 700 umhos/cm (from 1 April to 31 August) and 1000 umhos/cm (from 1 September to 31 March). State Board Decision 1641 (D-1641) requires that the 1000 umhos/cm objective be met year round until 1 April 2005 at which time the seasonal objectives will be effective. A review of the Discharger's monitoring reports from January 1998 through December 2002 indicates an annual average TDS effluent concentration of 634 mg/1, a lowest monthly average of 540 mg/l, and a highest monthly average of 727 mg/l. These concentrations exceed the applicable objectives. Limited TDS data collected at receiving water sample location Rl from January 2002 through December 2002 showed a TDS concentration range from 210 mg/I to 1300 mg/1 with an average of 500 mg/I in 12 sampling events. The Regional Board report Total Maximum Daily Load for Salinity and Boron in the Lower San Joaquin River (January 2002) presented monthly average TDS data for the San Joaquin River at Vernalis from October 1976 through September 1997. The Vernalis data showed a maximum monthly average TDS of 1024 mg/1 with 57 of 252 months having monthly averages greater than 500 mg/l. This data indicates that the receiving water frequently exceeds water quality objectives to protect its beneficial uses and lacks assimilative capacity for TDS. As water exported from the Delta by the State Water Project is, in part,mixed with Colorado River water to provide municipal water supply with an acceptable TDS, any increase in salt concentration effectively reduces the available water supply in Southern California(Metropolitan Water District of Southern California, Salinity Management Study, 1998). Chloride concentrations in the effluent ranged from 100-230 mg/1 with an average of 138 mg/l based on 16 samples collected during 2002. Background concentrations in the San Joaquin River ranged from 51-170 mg/l with an average of 98 mg/l based on results from eleven samples collected during 2002. Both the receiving water and the effluent exceed the water quality objective of 106 mg/l based on the narrative objective.