SITE INFORMATION AND CORRESPONDENCE_1985-2004

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INFORMATION SHEET O NO. R5-2004-0028 • 11 CITY OF MANTECA, CITYOF LATHROP AND DUTRA FARMS WASTEWATER QUALITY CONTROL FACILITY SAN JOAQUINCOUNTY 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. The WQCF outfall is a side bank discharge to the San Joaquin River. The chlorine residual limitations required in this Order are protective of aquatic organisms in the undiluted discharge. Because of this, the Regional Board does not anticipate residual chlorine impacts to benthic organisms if compliance is maintained. 9.2 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/l as a recommended level, 1000 mg/1 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/1 as a long-tern average 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). Water Quality for Agriculture evaluates the impacts of salinity levels on crop tolerance and yield reduction, and establishes water quality goals that are protective of sensitive agricultural uses. 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) (water rights)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/l, a lowest monthly average of 540 mg/l, and a highest monthly average of 727 mg/1. These concentrations exceed the applicable objectives. Limited TDS data collected at receiving water sample location RI from January 2002 through December 2002 showed a TDS concentration range from 210 mg/1 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. These data indicate 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