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of threatened and endangered species. The Regional Board also noted numerous flaws and areas of uncertainty regarding the reliability of the dilution studies, including, but not limited to the lack of real-time flow data for the San Joaquin River near the discharge during dry-year conditions. The burden was squarely upon the Petitioner to prove that dilution existed, and the Regional Board's finding that the Petitioner did not meet that burden is supported by substantial evidence.' Contention: The Regional Board acted arbitrarily and unreasonably in calculating the effluent limitations for chloroform and dichloromethane, and did not comply with section 13241 of the Water Code. Finding: We have previously held that when a Regional Board includes permit limits more stringent than limits that would be based on an applicable numerical objective in the relevant basin plan or the California Toxics Rule(CTR), the Regional Board must address the section 13241 factors in the permit findings. (See e.g., State Board Order WQO 2002-15,p. 35.) Neither the CTR nor the Basin Plan contains numerical objectives for chloroform. Instead, the limitations were based on narrative water quality objectives in the Basin Plan. Accordingly, the Regional Board's adoption of effluent limitations for chloroform need not consider the section 13241 factors. A construction of Water Code section 13263 that requires a section 13241 analysis every time a numerical effluent limitation is derived from a narrative water quality objective, that itself was established pursuant to section 13241, would render such objectives illusory. Moreover, it would multiply the burden imposed on the regional boards because each discharger would be entitled to an individualized consideration of the section 13241 factors in order to establish effluent limitations that implement water quality standards appropriate for each discharger. We have declined to accept this construction in the past, and decline again to do so here. The CTR, however, does contain a numerical criterion for dichloromethane (identified as methylene-chloride). (40 C.F.R. § 131.38(b)(1)#36.) The Regional Board contends that this effluent limitation was calculated in accordance with SIP using applicable CTR criteria, and is therefore not subject to Water Code sections 13241 and 13263. According ' The Petitioner's related request for a hearing before the State Board is hereby denied. 4.