SITE INFORMATION AND CORRESPONDENCE_CASE 2

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REGIONAL WATER BOARD RESPONSE (SWRCB/OCC File A-1846(a) and " 1846(b)) -13- PETITIONS FOR REVIEW OF V� E DISCHARGE REQUIREMENTS IftO ORDER NO. R5-2007-0036 (NPDES NO. CA0079154) AND TIME SCHEDULE ORDER NO. R5-2007-0037 CITY OF TRACY, WASTEWATER TREATMENT PLANT not acceptable WVVI-P design parameters. Consequently, the flow limitations contained in the Order are not based on acceptable WWTP design parameters and therefore fail to comply with federal regulations. -CSPA s contention is based on the March 2006 tentative Order, not the adopted Order. The effluent flow limitations were changed based on CSPA's comments on the tentative Order. Therefore, this contention is not applicable to the adopted Order. CSPA - CONTENTION D: The limit for acute toxicity is inconsistent with Basin Plan and federal requirements. The Order acknowledges in detail that there is no assimilative capacity in the receiving stream for individual toxic pollutants. It further acknowledges that ambient waters are impaired for unknown toxicity. Allowing 30% mortality in acute toxicity tests allows that same level of mortality in the receiving stream, in violation of federal regulations. and contributes to exceedance of the Basin Plan's narrative water quality objective for toxicity. Accordingly, the Order should be revised to prohibit acute toxicity. Order R5-2007-0036 contains several mechanisms to ensure that the effluent discharge does not cause acute or chronic toxiciton the-receiving water. Receiving water limits proscribe the discharge from causing toxicity in the receiving water. For effluent limitations included for the protection of the aquatic life beneficial use, the Order includes end-of-pipe effluent limits that were developed based on aquatic life toxicity criteria. Furthermore, the Order requires whole effluent chronic toxicity testing, which identifies both acute and chronic effluent toxicity. If this testing shows that the discharge causes, has the reasonable potential to cause, or contributes to an in stream excursion of the water quality objective for toxicity, the Order requires the Discharger to investigate the causes of, and identify corrective actions to eliminate the toxicity. The acute whole effluent toxicity limits establish additional thresholds to control acute toxicity in the effluent: survival in one test no less than 70% and a median of no less than 90% survival in three consecutive tests. Some in-test mortality can occur by chance. To account for this, in the EPA acute toxicity test method, the test acceptability criteria allow ten percent mortality (requires 90% survival) in the control. Thus, the acute toxicity limits allow for some test variability, but impose ceilings for exceptional events (i.e., 30% mortality or more), and for repeat events (i.e., median of three events exceeding mortality of 10%). These effluent limitations are consistent with U.S. EPA guidance. In its document titled "Guidance for NPDES Permit Issuance", dated February 1994, it states the following beginning on page 14: "In the absence of specific numeric water quality objectives for acute and chronic toxicity, the narrative criterion 'no toxics in toxic amounts'applies. Achievement of the narrative criterion, as applied herein, means that ambient waters shall not demonstrate for acute toxicity: 1) less than 90% survival, 50% of the time, based on the monthly median, or 2) less than 70% survival, 10% of the time, based on any monthly median. For chronic toxicity, ambient waters shall not demonstrate a test result of greater than 1 TUc."