SITE INFORMATION AND CORRESPONDENCE_CASE 2

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Response to Written Comments -28- 24 April 2007 City of Tracy WWTP San Joaquin County SOUTH DELTA WATER AGENCY (SDWA) COMMENTS SDWA — NPDES COMMENT #1: The SDWA argues that the tentative Order presented by Staff is insufficient to protect the agricultural beneficial uses of the receiving water into which the City of Tracy discharges its treated effluent, because the proposed Order does not include any real limitation on salinity. The tentative Order only requires studies regarding what might be done to decrease the salinity of the Tracy discharge. The SDWA claims that effluent limitations based on the south Delta salinity standards are necessary to protect the agricultural beneficial uses. RESPONSE: It is unclear if effluent limitations based on the south Delta salinity standards are necessary to protect the agricultural beneficial uses of the south Delta waterways. However, it is certain that effluent limitations based on these standards would require operation of a large-scale reverse osmosis treatment plant. The State Water Board has ruled in WQO 2005-005 (for the City of Manteca), the following, "...the State Board takes official notice (pursuant to Title 23 of California Code of Regulations, Section 648.2)of the fact that operation of a large-scale reverse osmosis treatment plant would result in production of highly saline brine for which an acceptable method of disposal would have to be developed. Consequently, any decision that would require use of reverse osmosis to treat the City's municipal wastewater effluent on a large scale should involve thorough consideration of the expected environmental effects." The State Water Board further states, "Although the ultimate solutions to southern Delta salinity problems have not yet been determined, previous actions establish that the State Board intended for permit limitations to play a limited role with respect to achieving compliance with the EC water quality objectives in the southern Delta." The State Water Board also states that, "Construction and operation of reverse osmosis facilities to treat discharges...prior to implementation of other measures to reduce the salt load in the southern Delta, would not be a reasonable approach." A stakeholder group that included representatives from the SDWA, City of Tracy, Mountain House Community Services District (MHCSD), California Sportfishing Protection Alliance, the Department of Water Resources, and the Regional Water Board developed appropriate scenarios for running the Delta Simulation Model II (DSM2 model) to evaluate the salinity impacts of the Tracy and MHCSD wastewater discharges to the south Delta. The DSM2 modeling showed that under reasonable worst-case conditions the salinity impacts caused by the Tracy discharge are minimal. Therefore, the Regional Water Board finds in the proposed Order that imposing effluent limitations for salinity that require the construction and operation of reverse osmosis facilities to treat discharges prior to implementation of other measures to reduce the salt loading in the Tracy discharge is not a reasonable approach. This is consistent with the ruling by the State Water Board. The Tracy discharge is one of many contributors to the Regional Water Quality Control Board, Central Valley Region Board Meeting—3/4 May 2007 Item*17