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Port of Stockton - 2 - 6 September 2013 <br /> Rough and Ready Island <br /> Stockton, San Joaquin County <br /> The Revised RI/FS also includes an evaluation of remedial alternatives from the standpoint of <br /> effectiveness, ease of implementation and cost. The remedial alternatives ERS has considered <br /> are: <br /> • "No Action" <br /> • "Land Use Restrictions-Institutional Controls" <br /> • "Monitored Natural Attenuation (MNA)" <br /> • "Enhanced In-Situ Bioremediation" <br /> • "In-Situ Chemical Oxidation (ISCO)" <br /> The following observations and comments regarding the Revised RI/FS are offered. <br /> 1. Based primarily upon trend analysis and historical groundwater monitoring results, ERS <br /> has concluded that reductive dechlorination has decreased the concentration and plume <br /> size of total cis-1,2- DCE and VC at Site 49, and that the natural anaerobic environment in <br /> groundwater beneath Site 49 will continue to be effective in reducing volatile organic <br /> compound (VOC) concentrations to MCLs in a reasonable period of time (refer to comment <br /> item #4). <br /> Although Central Valley Water Board and DTSC staff concur with the observation of <br /> decreased plume size and concentrations of the VOCs at Site 49, and that this is the result <br /> of reductive dechlorination, there are a number of concerns not being addressed by ERS <br /> regarding the continuing efficacy of intrinsic biodegradation. These concerns and required <br /> actions are presented below. <br /> A. Concern: The Site Conceptual Model presented in the Revised RI/FS does not <br /> contain detailed information regarding the hydrogeologic regime of Site 49 and how <br /> the global hydrogeologic regime across Rough and Ready Island affects Site 49, or <br /> the other sites in the Rough and Ready portfolio. Understanding the flow of <br /> groundwater through Site 49 from other parts of Rough and Ready Island is <br /> imperative to understanding the status of the groundwater chemistry and ultimately <br /> the status of continuing natural biodegradation at Site 49 and other sites as well. <br /> Required Action: ERS needs to provide a potentiometric map of Rough and Ready <br /> Island to exhibit the global groundwater regime present. <br /> B. Concern: ERS has stated that an upward vertical migration of groundwater between <br /> the water bearing zones at Site 49 is highly likely, yet no calculations of a vertical <br /> gradient have been provided. <br /> Required Action: ERS needs to provide calculations to determine the presence of a <br /> vertical gradient, in part to assess the hydrogeologic regime at Site 49, and in part <br /> because ERS has used the presence of this vertical gradient as a rationale for why <br /> contamination of a lower aquifer is not possible. <br /> C. Concern: ERS has stated that to the east of Site 49 there exists a "very steep <br /> gradient directed to the southeast in the vicinity of Davis and Ellsberg Drive". Two <br /> wells (W-124 and W-127) within this steep gradient are being used as data points in <br /> the ERS trend analysis (Table 11) for Site 49. If groundwater flow at this location is <br />