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a <br /> Port of Stockton - 3 - 6 September 2013 <br /> Rough and Ready Island <br /> Stockton, San Joaquin County <br /> away from Site 49, it is inappropriate for these wells (located 700 and 770 feet, <br /> respectively, from the source area at Site 49) to be used as data points to determine <br /> the effectiveness of reductive dechlorinization at Site 49. Historic data from these <br /> wells suggests they are part of separate VOC plumes from Site 49. <br /> Required Action: provide a trend analysis using wells specific to Site 49 located <br /> within a reasonable distance from the source area (no more than 100 feet). Account <br /> for any vertical gradient and how upward (or downward) migration of groundwater <br /> will affect reductive dechlorination. <br /> D. Concern: The water quality parameters presented in Table 13 are insufficient to <br /> evaluate the continuance of reductive dechlorinization at Site 49. There have been <br /> no measurements of dissolved oxygen, nitrate, nitrite, dissolved ferrous iron, sulfide, <br /> pH, or dissolved hydrogen to determine the past or current anaerobic state of <br /> groundwater in the source area. There has been no effort through on-going <br /> measurements of dissolved oxygen, methane, and sulfate to determine the <br /> geochemical environment within the plume to evaluate the presence of a <br /> methanogenic environment, which is required to reduce VC to carbon dioxide. <br /> Required Action: Conduct measurements of geochemical parameters (dissolved <br /> oxygen, methane, nitrate, nitrite, dissolved ferrous iron, sulfide, pH, or dissolved <br /> hydrogen). Prepare a SCM of the geochemical environment to document the <br /> presence of a methanogenic environment within the plume. <br /> E. Concern: Groundwater analysis indicates that petroleum hydrocarbons once <br /> present at Site 49, and a source of oxidants for the VOC plumes, has been <br /> depleted. Historic data also shows a continued source of VC is present at Building <br /> 816-D. <br /> Required Action: Evaluate the trend analysis data for VC in the source area <br /> (showing either increasing or stable trends) with regards to the possibility reductive <br /> dechlorination may be stalling at the source area. <br /> F. Well W-247, located at the border of Sites 8 and 43, west of Site 49 is included in <br /> the trend analysis for Site 49. Well W-247 contains cis-1,2- DCE at concentrations <br /> of 7 ug/L. This well was never included in the original plume boundary of Site 49, <br /> and does not show any decreasing trend. <br /> Required Action: Provide a rationale for why this well is included in the trend <br /> analysis of Site 49, or, if reductive dechlorination is still occurring within the plume. <br /> Explain why concentrations of cis-1,2- DCE have not decreased at this location. <br /> Well 247, located 770 feet from the source area, should have reduced to VC as the <br /> other wells in the vicinity have if reductive dechlorination was still an active process. <br /> G. Concern: Trend analysis was only conducted on three wells in the vicinity of the <br /> source area, varying from 30 to 40 feet away. The remainder of trend analysis was <br /> conducted on wells from 200 to 770 feet away. Of the three wells in the immediate <br /> vicinity of the source area, the trends for VC indicate no trend for two wells and one <br /> showing a decreasing trend. The data from the decreasing well is suspect, as the <br /> most recent data shows a spike in VC concentrations. (See comment E.) <br />