SITE INFORMATION AND CORRESPONDENCE_2005-CURRENT

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reasonable potential to cause or contribute to an instream excursion above Basin Plan objectives for each of the eight constituents identified in the City's petition. Although Water Code section 13241 identifies economic considerations and several other factors to be considered in establishing the water quality objectives in a water quality control plan, consideration of those factors is not required each time the Regional Board adopts effluent limitations to implement previously established objectives. (Hampton v. Superior Court(1977) 67 Cal.App.3d 472; State Board Orders WQ 2001-16, WQ 94-8, WQ 77-16, and WQ 73-4.) Of the numeric and narrative water quality objectives utilized by the Regional Board and the effluent limitations in the City's permit based on those objectives, the State Board believes that substantial issues exist only with respect to: (1) the effluent limitations that the Regional Board established for EC; (2) the relationship between total concentrations of pollutants and dissolved concentrations; and (3) the use of mixing zones and dilution credits. 2. Effluent Limitations Established Based on Water Quality Objectives for Electrical Conductivity (EC) The water quality objectives for EC applied by the Regional Board are set forth in Table 111-5 of the Basin Plan. The footnote to Table III-5 of the Basin Plan explains that the water quality objectives in the table were "taken from the State Water Board's Water Quality Control Plan for Salinity, May 1991." The document referred to in the Basin Plan is the"Water Quality Control Plan for Salinity, San Francisco Bay/Sacramento-San Joaquin Delta Estuary, 91-15 WR, May 1991." (1991 Delta Plan.) The 1991 Delta Plan is one in a series of documents that the State Board has prepared and adopted in its efforts to protect water quality in the Delta area through the coordinated exercise of the State Board's authority over water rights and water quality." Table 1-1 of the 1991 Delta Plan specifies water quality objectives for EC to protect agriculture in the area covered by the plan. The table includes water quality objectives for EC at the Vernalis gage station--and three southern Delta locations--of 0.7 millimhos per centimeter (mmhos/cm) from April 1 through August 31 and 1.0 mmhos/cm from September I " The State Board's water quality control plans for the Sacramento/San Joaquin Delta have been based, in part, upon recognition of the interrelationship between water rights and water quality in the complex Delta system. In addition to addressing the effect of water diversions from the Delta and upstream tributaries on water quality in the (Continued on next page) 6.