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r %6.01 DRAFT background water quality or the best water quality which is reasonable if background water quality cannot be restored (SWRCB Resolution No. 92-49, III.G). Any alternative level of water quality less stringent than background must be consistent with the maximum benefit to the people of the state, not unreasonably affect current and anticipated beneficial use of water, and not result in water quality less than that prescribed in the water quality control plan for the basin within which the site is located (hereafter Basin Plan). (Ibid.) Resolution No. 92-49 does not require, however, that the requisite level of water quality be met at the time of site closure. Even if the requisite level of water quality has not yet been attained, a site may be closed if the level will be attained within a reasonable period (SWRCB Resolution No. 92-49, III.A). The Central Valley RWQCB's Basin Plan designates existing and potential beneficial uses of groundwater in the San Joaquin Valley groundwater basin as municipal and domestic supply(Mid, agricultural supply (AGR), industrial service supply(IND), and industrial process supply(PRO) Central Valley Regional Water Quality Control Board& SWRCB, Water Quality Control Plan, Central Valley Region(1994) at p.II-3). The Basin Plan specifies a narrative taste and odor water quality objective as follows: "Ground waters shall not contain taste or odor-producing substances in concentrations that cause nuisance or adversely affect beneficial uses." (Id. at p. III-10). The Basin Plan also contains the following narrative water quality objective for organic chemicals: "...ground waters designated for use as domestic or municipal supply (MUN) shall not contain concentrations of chemical constituents in excess of maximum contaminant levels (MCLS) specified in...Title 22 of the California Code of Regulations..." (Id. at III-9). With regard to the water quality objectives for organic chemicals, the State Department of Health Services (DHS) has set MCLs for benzene, toluene, ethylbenzene, and xylene (BTEX) in drinking water of 1 ppb, 100 ppb, 680 ppb, and 1,750 ppb, respectively. (Cal. Code of Regs., tit. 22, § 64444). Although DHS has not yet set an MCL for methyl-tertiary-butyl-ether (MTBE), DHS has set an interim action level of 35 ppb (DHS Memorandum from Joseph P. Brown,Ph.D., Acting Chief, Water Toxicology Unit to Alexis M. Milea,P.E., Acting Supervisor, Standards and Technology Unit, Office of Drinking Water(February 19, 1991) at p_ 2). DHS has adopted a 5 ppb MTBE concentration as a secondary drinking water standard for taste and odor. The threshold odor concentration of commercial gasoline (measured as total petroleum hydrocarbon 3