SITE INFORMATION AND CORRESPONDENCE

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substantial disruption of streets, businesses, sewers and other utilities while producing little or no benefit to current or anticipated beneficial uses of the minimal area of groundwater not meeting Basin Plan objectives. Furthermore, if complete removal of detectable traces of petroleum constituents becomes the standard for UST corrective actions, the statewide technical and economic implications will be enormous. For example, disposal of soils from comparable areas of excavation throughout the state would greatly impact already Iimited landfill space. In light of the minimal if any benefit to be gained, the evidence of continuing attenuation of residual petroleum concentrations, and the precedent that would be set by requiring additional excavation at this site, attaining background water quality in this limited area is not feasible. While it is impossible to determine the precise level of water quality that will be attained given the residual petroleum constituents that remain at the site, in light of all the factors discussed above, a level of water quality will be attained that is consistent with the maximum benefit to the people of the state., The final step in determining whether cleanup to a level of water quality less stringent than background is appropriate for this site requires a determination that the alternative level of water quality will not result in water quality less than that prescribed in the relevant Basin Plan. Pursuant to SWRCB Resolution No. 92-49, a site may be closed if the Basin Plan requirements will be met within a reasonable time frame. In this particular case, as discussed above, TPH-g and BTEX in the shallow groundwater in immediate contact with the limited residual petroleum hydrocarbon constituents adsorbed to soils will likely remain above, and thus violate, the Basin Plan's objectives in a localized volume of surrounding groundwater for a significant period of time. This time period could be anywhere from a few decades for BTEX to degrade below MCLS to hundreds of years for that limited s In approving an alternative level of water quality less stringent than background,the SWRCB has also considered the factors contained in California Code of Regulations, title 23,section 2550.4,subdivision(d). As discussed earlier, the adverse effect on shallow groundwater will be minimal and localized,and there will be no adverse effect on the groundwater contained in deeper aquifers,given the physical and chemical characteristics of petroleum constituents; the hydrogeological characteristics of the site and surrounding land: and the quantity of the groundwater and direction of the groundwater flow. in addition,the potential for adverse effects on beneficial uses of groundwater is low, in light of the proximity of groundwater supply wells; the current and potential future uses of groundwater in the area;the existing quality of groundwater; the potential for health risks caused by human exposure: the potential damage to wildlife,crops, vegetation, and physical structures: and the persistence and permanence of potential effects. Finally, a level of water quality less stringent than background isunlikely to have any impact on surface water quality, in light of the volume and physical and chemical characteristics of petroleum constituents; the hydrogeological characteristics of the site and surrounding land;the quantity and quality of groundwater and the direction of groundwater flow; the patterns of precipitation in the region,and the proximity of residual petroleum to surface waters. 12