SITE INFORMATION AND CORRESPONDENCE_CASE 2

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Ms. Jeanine Townsend -2 - 4 March 2009 The Regional Water Board has initiated basin plan amendments to implement a Salinity Management Plan that will apply throughout the entire Central Valley including the Delta. This effort has been underway for two years and is expected to be brought to the Board for consideration in 2015. The amendments will establish beneficial uses and new or revised objectives for salts and nutrients. (hftp://www.waterboards.ca.gov/centraIvaIley/Water—issues/ salinity/index.shtml) The draft Order recognizes the dilemma faced by Tracy and the Regional Water Board. There is clearly Reasonable Potential for salinity, and the receiving water objectives are clear, but the City cannot comply with salinity effluent limitations now or in the foreseeable future. Modeling study results contained in the record demonstrate the salinity concentrations in the City's discharge contributes a relatively small impact to the receiving water, and that impact will decrease as the City increases its use of lower salinity water supplies. Limited water supply data indicates that the average water supply electrical conductivity (EC) of the combined water sources is 700 umhos/cm (-500 mg/L TDS), which is the effluent limitation for part of the year. Based solely on'water supply salinity and a common increase of 500 umhos/cm (-380 mg/L TDS) in salinity for domestic use of water, Tracy's discharge would exceed the Bay-Delta Plan's irrigation and non-irrigation season standards. Time schedules will allow the City to identify and control salinity discharges to the wastewater collection system, but there is no reasonable expectation that the City can achieve compliance with the salinity effluent limitations without treatment to remove salts. If the draft Order is not modified in accordance with the discussion above, we suggest a minor language change. The draft Order concludes at the top of page 10 that one solution is to increase the salt objectives through a site-specific objective or basin plan amendment. However, the Bay-Delta Plan "supersedes the regional water quality control plans to the extent of any conflict between this plan and the regional.water quality control plans." (Bay-Delta Plan, p. 3.) Therefore, we suggest the following clarification, at the top of page 10: "... site-specific water quality objectives;a or other basifl play amendment to the basin plan and/or Bay-Delta Plan; or, if the timing allows, the results of the State and Central Valley Water Boards' joint study and planning process regarding management of salt in the watershed (CV-SALTS. Central Valley Salinity Alternatives for Long-Term Sustainability)." Dilution Credits We agree that the Fact Sheet uses a "complete mixing" analysis for the human health mixing zone, and must be revised to include appropriate findings based on site-specific data and studies showing that the discharge completely mixes and is as small as practicable, and to specify the mixing zone boundaries. However, we believe the record already includes site- specific studies that satisfy the SIP's definition of a "mixing zone study" for purposes of the human health mixing zone in question. The draft Order states that the record does not include the appropriate studies to support a site-specific analysis based on the SIP methodology for incompletely mixed discharges. For the following reasons, we request several minor modifications to the draft Order to avoid the unintended consequence of requiring the Discharger to submit additional studies, if information already in the record can support appropriate findings. Very precise modeling is necessary to allow dilution credits for aquatic toxicity criteria, in order to ensure protection of the beneficial uses of the receiving water. This is because adverse ' Fact Sheet, at pp. F-22—F-23