SITE INFORMATION AND CORRESPONDENCE_CASE 2

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REGIONAL WATER BOARD RESPONSE (SWRCB/OCC File A-I646(a) and ' 1846(b)) -23- PETITIONS FOR REVIEW OF V%�,w FE DISCHARGE REQUIREMENTS `/ ORDER NO. R5-2007-0036 (NPDES NO. CA0079154) AND TIME SCHEDULE ORDER NO. R5-2007-0037 CITY OF TRACY, WASTEWATER TREATMENT PLANT CSPA — CONTENTION O: Reasonable potential exists for Bis(2-ethyl-hexyl)phthalate and an effluent limitation is required. Based on four monitoring samples performed by the Discharger from January 2002 through December 1002, bis(2-ethylhexyl)phthalate was detected, but not quantified Wall four samples. The concentration was estimated in each case, with a maximum estimated concentration of 2 pg/L. The estimated concentration exceeds the NTR criterion for bis(2-ethyl hexyl)phthalate (1.8 pg/L). However, without quantifiable detections, it is unclear if the discharge has a reasonable potential to cause or contribute to an in-stream excursion of the NTR criterion. Also, because bis (2-ethylhexyl) phthalate is a common contaminant of sample containers, sampling apparatus, and analytical equipment, and sources of the detected bis (2-ethylhexyl) phthalate may be from plastics used for sampling or analytical equipment, the Regional Water Board is not establishing effluent limitations for bis (2- ethylhexyl) phthalate at this time. In accordance with Step 8 of Section 1.3 of the SIP, Order R5-2007-0036 requires monthly monitoring of bis(2-ethylhexyl)phthalate for one-year using improved sample collection and handling techniques and a method detection level below the NTR criterion. The Order may be reopened for the addition-of-new-effluent limitations for bis(2-ethyl hexyl)phthalate if there are detectable effluent concentrations exceeding the NTR criterion. CSPA — CONTENTION P: The Order allows the Receiving Water Limitation for turbidity to expire. Order R5-2007-0036 contains effluent and receiving water limitations for turbidity. The receiving water limitations are effective immediately, while the effluent limitations become effective 1 August 2008, which is when Title 22 disinfection requirements are required in the Order. The turbidity effluent limitations are required to meet Title 22 disinfection requirements, which will assure compliance with the Basin Plan water quality objective for turbidity. Therefore, at the time the effluent limitations for turbidity become effective, the receiving water limitations would no longer be necessary and the Order terminates the receiving water limitations. CSPA — CONTENTION Q: The Order allows 100% use of the assimilative capacity of the receiving stream without an adequate analysis of flow rates CSPA contends that the SIP requires receiving water flow monitoring for allowance of a human health dilution credit. The Regional Water Board agree that real-time flow monitoring may be necessary to develop protective dilution credits for acute and chronic aquatic toxicity criteria due to the short averaging periods (i.e. 1-hr, 4-day, and 30-day). However, water quality objectives to protect human health rely on a long averaging period, utilizing the harmonic mean flow of the receiving water. Therefore, the Regional Water Board concluded