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INFORMATION SHEET • • 9 <br /> WASTE DISCHARGE REQUIRMENTS ORDER NO.R5-2002-XXXX <br /> MARLEY COOLING TOWER COMPANY <br /> STOCKTON, SAN JOAQUIN COUNTY <br /> Hexavalent Chromium <br /> Previous Order No. 93-221 included daily maximum and monthly average effluent limitations for <br /> hexavalent chromium based upon water quality objectives established by the California Inland <br /> Surface Waters Plan. Order No. 93-221 included a daily maximum limitation for hexavalent <br /> chromium of l lgg/L(ppb), and a monthly average limitation for hexavalent chromium of 11 gg/L <br /> (ppb). New limits for hexavalent chromium have been established in this new Order based upon <br /> the reasonable potential to exceed the chronic freshwater aquatic life criterion in the CTR(new <br /> information). Results of final effluent monitoring indicate maximum effluent concentrations <br /> (MEC's) of hexavalent chromium have been high as 17 gg/L(ppb) (9/15/00). Without regard to <br /> dilution, this MEC exceeds the acute aquatic life Criterion Maximum Concentration(CMC) and <br /> the chronic aquatic life Continuous Criterion Concentration(CCC) for hexavalent chromium (16 <br /> gg/L(ppb) and 11 gg/L (ppb) respectively). New water quality based effluent limitations have <br /> been calculated based upon methodologies in the SIP. <br /> Considering that the Stockton Diverting Canal may at times have little or no flow and provide little <br /> or no assimilative capacity for hexavalent chromium, final water quality based effluent limitations <br /> have been developed using the steady state model in the SIP,with no credit provided for dilution. <br /> The acute and chronic effluent concentration allowance's (ECA's) were set equal to the aquatic <br /> life criterion for hexavalent chromium, and the most limiting long-term average (LTA) discharge <br /> condition was determined using Table 1 of the SIP,using a default coefficient of variation of 0.6. <br /> The average monthly effluent limitation (AMEL) and maximum daily effluent limitation (NOEL) <br /> were then calculated using multipliers in Table 2 of the SIP as shown below: <br /> WATER QUALITY BASED EFFLUENT LIMITATIONS <br /> Hexavalent Chromium <br /> Number of Observations >20 <br /> Effluent Maximum P <br /> Dilution Credit <br /> ECA acute <br /> Percent of Observations Below Detection Coefficient of Variation efault Limitin LTA(acute)= ECA acute*Table 1 Acute Multi lier S lin Fre uenc n <br /> AMEL LTA*Table 2 AMEL Multiplier) 8.0 2 b <br /> MDEL(LTA*Table 2 MDEL Multi Tier) 16.0 /L b <br /> New final average monthly(8.0 gg/L(ppb)) and daily maximum(16 gg/L (ppb)) effluent <br /> limitations for hexavalent chromium have been established in this Order in accordance with <br /> Sections 1.3 and 1.4 of the SIP. With proper operation of the existing treatment facilities, the <br /> Discharger is capable of meeting these new limitations, therefore a time schedule for compliance is <br /> not included in this new Order. <br /> Total Chromium <br />