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_ _ _ <br /> intended to protect human health from carcinogenic effects, the arithmetic mean of <br /> observed ambient water concentrations. Ambient background concentrations are the <br /> observed maximum detected water column concentrations for aquatic life protection. <br /> Because the receiving waters for discharges from the facilities covered under this Order <br /> are varied,receiving water background concentrations were not considered for this RPA. <br /> d. Reasonable Potential Determination for Priority Pollutants <br /> The MECs and the most stringent applicable WQC used in the RPA are presented in the <br /> following table, along with the RPA results (yes or no) for each pollutant. Reasonable <br /> Potential was not determined for all pollutants because there are not applicable WQC for <br /> all pollutants, or monitoring data are not available for others. Based on a review of the <br /> effluent data, the pollutants that demonstrate reasonable potential by Trigger 1 are <br /> benzene,bromoform, chlorodibromomethane, 1,2-dichloroethane, l,l-dichloroethylene, <br /> methylene chloride,trichloroethylene,vinyl chloride, and bis(2-ethylhexyl)phthalate. <br /> The Regional Water Board has also determined that Reasonable Potential exists to <br /> exceed water quality objectives,by Trigger 3, for the organic pollutants that have been <br /> identified as pollutants that are commonly present in VOC and fuel-contaminated <br /> groundwater(i.e., those pollutants for which TBELs have been established.) As these <br /> TBELs limitations are achievable dependent on the proper design and operation of <br /> treatment systems, there is Reasonable Potential for excursions above applicable water <br /> quality criteria for these pollutants if the system is not designed or operated correctly. <br /> Total residual chlorine is also identified as a pollutant with Reasonable Potential to <br /> exceed the Basin Plan narrative toxicity objective, as deternlined by Trigger 3. The <br /> Regional Water Board has identified that chlorine may be used in conjunction with air <br /> stripping and/or activated carbon treatment systems to control biological growth, and <br /> therefore Reasonable Potential exists for total residual chlorine for those facilities that <br /> use it. <br /> Table F-5. Summar of RPA Results � <br /> Goveming Applicable Criteria(µg/L) <br /> MEC or <br /> CTR# Priori Pollutants Minimum A uatic Life Human Health RPA Results <br /> �y DL un=� �3� <br /> Basin <br /> �µ�-� (Most Plan <br /> stringent of CTR Water Title CTR <br /> salt and fresh + 22 Organisms <br /> water) Or anisms MCLs Onl <br /> 1 Antimon 21 --- 14 6 4300 Ud <br /> 2 Arsenic 140 36 --- 10 --- Ud <br /> 3 Be llium 0.00053 --- --- 4 --- Ud <br /> 4 Cadmium 036 1.1 --- 5 --- Ud <br /> Sa Chromium III) NA 207 --- 50 --- Ud <br /> Sb Chromium(VI) 14 11 --- --- --- Ud <br /> 6 Co er 24 4.7�"� --- ]000 --- Ud <br /> Attachment F—Fact Sheet F-20 <br /> For VOC and Fuel General NPDES Permit No.CAG912002 <br />