SITE INFORMATION AND CORRESPONDENCE_FILE 2

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• i. CLEANUP AND A13AV16-_NT ORDER NO. 92-707 -2- AMENDING CLEANUP AND ABATEMENT ORDER NO. 91-720 FOR SOUTHERN PACIFIC TRANSPORTATION COMPANY, TRACY YARD, SAN JOAQUIN COUNTY toluene; xylene; ethylbenzene; polynuclear aromatic hydrocarbons; naphthalene; hexane; styrene; and tetraethyl lead. {I `i 9. In the vicinity of the impoundment covered by the Toxic Pits Cleanup Act (TPCA impoundment), pollutants in soils exist at relatively high concentrations from the !� surface to, and likely below, the current water table. A significant free petroleum product phase has been, measured at the water table. This information indicates ' j that on-site soils lack the ability to impede the migration of pollutants to a degree sufficient to protect ground water quality. ' 10. On 18 June 1992, the State Water Resources Control Board adopted Resolution No. 92-49, Policies and Procedures for Investigation and Cleanup and Abatement of �I Discharges Under Water Code Section 13304 ' This policy for water quality control 4! requires that cleanup standards be consistent with the antidegradation policy of ii State Water Board Resolution No. 68-16 and with the requirements of Section 2550.4 of Title 23 of the California Code of Regulations (CCR). 3 11. Section 2550.4 of Title 23 of the CCR states in part: "(c) For a corrective action program, the, regional board shall establish a '. i; concentration limit' for a constituent of concern that is greater than the t i background value of that constituent only if the regional board finds that it is technologically or economically infeasible"to achieve the background value for that constituent and that the constituent will not pose a substantial present or ;I potential hazard to human health or 'the environment as long as the concentration limit greater than background is not exceeded." "(e) In no event shall a concentration limit greater than background established under this section for a constituent of concern exceed the lowest concentration that the discharger demonstrates and the regional board finds is technologically EI and economically achievable. No provision of this section shall be taken to ' allow a concentration limit greater than background, for a constituent of ! concern, to exceed the maximum concentration that would be allowed under !I other applicable statutes or regulations... a ' "(g) Proposals 'for concentration limits greater than background shall include a t; demonstration that the aggregate of hazardous constituents in the environment '! will not result in excessive_ exposure to a sensitive biological receptor. In the absence of scientifically 'alid data to the contrary; theoretical risks from chemicals associated with the release from the waste management unit shall be considered additive across all media of exposure, and shall be considered .; 'I additive for all chemicals having similar toxicological effects or having II carcinogenic effects." ii i!