A2-other RAO_081418_SouthY_obj+alts (2)Table 1: Basin Remedial Action Objectives -DRAFTPrevent exposure to groundwater containing COCs exceeding acceptable risk levels•Provide an alternate water supply for the population served by existing wells affected by the plume of constituents of concern (COCs)•Establish institutional controls to restrict access to the contaminant plumeProtect uncontaminated groundwater and surface water for current and future use•Prevent contamination of existing wells that could be affected by the plume and in adjacent groundwater•Prevent or minimize further migration of groundwater containing COCs within the Basin (plume containment)Return groundwater to their expected beneficial uses wherever practicable (aquifer restoration)•Prevent or minimize further migration of contaminants from source area to groundwater (source control)•Reduce contaminant concentrations within the area of the plume to levels that are safe for drinkingProtect environmental receptors•Reduce contaminant concentrations in the plume to levels that are safe for biological receptors that may be affected at the groundwater discharge pointCleanup LevelRestore pre‐contamination media qualityArea of AttainmentGroundwater and surface water within the source area and limits of plume extentRestoration Time FrameUncertain since source control/removal has not yet been achieved. Depending on the extent of residual secondary source areas (e.g. fine‐grained formations to which contaminants may adsorb then back diffuse over time), minimum restoration time frame following source control/removal may be one pore volume of the plume (i.e. current modeled range of average travel time across the plume extent is estimated from 17 to 30 years), although it is likely that multiple pore volumes may be required.
Table 2: Interim Remedial Action Objectives -DRAFTCleanup LevelMaximum Contaminant LevelsArea of AttainmentPoint of compliance at water supply wellsRestoration Time FrameAs soon as can feasibly be implemented to support continued and uninterrupted water supplyInterim RAOsBasin RAOsPrevent exposure to groundwater containing COCs exceeding acceptable risk levelsProtect uncontaminated groundwater and surface water for current and future useReturn groundwater to its expected beneficial uses wherever practicableProtect environmental receptorsContinue to provide uninterrupted drinking water supply to consumers that meet safe consumption requirementsAchieve a concentration reduction to <50 ppb at drinking water wells to avoid “impaired source” designation, which would trigger DDW 97‐005 compliance requirementsDesign and implement remedies without increasing existing volume of groundwater impacted by COCs