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KCUIVN/AL VVMI Cn DUMnv • � -"- •• •-•-,-ii <br /> PETITIONS FOR REVIEW OF %A' 'E DISCHARGE REQUIREMENTS <br /> ORDER NO. 135-2007-0036 (NPb1=S NO. CA0079154)AND <br /> TIME SCHEDULE ORDER NO. R5-2007-0037 <br /> CITY OF TRACY, WASTEWATER TREATMENT PLANT <br /> CSPA — CONTENTION K: The Order fails to include limits and monitoring for <br /> methylmercury. <br /> CSPA contends that an interim effluent limitation for methylmercury should be included in <br /> Order R5-2007-0036 and a reopener should be included to allow inclusion of mercury effluent <br /> limitations upon adoption of a mercury TMDL. The 303(d) listing of the Delta is for mercury. <br /> Although Regional Water Board staff is developing a methylmercury TMDL, the TMDL is still <br /> under development and has not been adopted by the Regional Water Board. Pursuant to <br /> Section 2.1.1. of the SIP, the Order contains an interim mass limitation on total mercury to <br /> maintain current loadings pending TMDL development. The Order also contains a reopener <br /> provision (Section VI.C.1.c.) to include effluent limitations for mercury (total or methylmercury) <br /> upon adoption of a TMDL. <br /> CSPA contends that monitoring for methylmercury should be included in the Order to support <br /> the mercury TMDL. Effluent and receiving water monitoring for total and methylmercury is <br /> included in the Order. The Regional Water Board added new influent, effluent, and receiving <br /> water monitoring for methylmercury in the agenda version of the Order due to comments by <br /> CSPA. There were no objections to these changes at the Board hearing by the Discharger or <br /> other interested persons. <br /> CSPA also contends that the method for determining compliance with the total mercury interim <br /> effluent limitation allows the Discharger to increase mercury loadings to Old River. CSPA <br /> asserts that the sum of peak mercury concentrations and the total monthly discharge flow <br /> should be used for the calculation. The conversion from concentration to mass is performed <br /> using the following equation: <br /> Concentration (mg/L) x Flow (million gal/mo.) x 8.34 (conversion factor) = Mass (lbs/mo.) <br /> The Order requires monthly mercury monitoring, so in most cases the total mass loading of <br /> mercury would be calculated using the concentration of a single sample and the total monthly <br /> flow. When more than one sample is collected during a month, averaging the constituent <br /> concentrations is appropriate for calculation of the total monthly loading, because it would <br /> represent the best estimation of mercury concentrations discharged for the month. If the <br /> constituent concentrations were summed, it would significantly overestimate the total monthly <br /> loading, due to the summing of concentrations prior to multiplication by the total discharge <br /> flow. <br />