SITE INFORMATION AND CORRESPONDENCE_2004-2014

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Mr. Maurice Benson December 30, 2009 Page 2 Analytical groundwater data recorded TCE contamination as high as 1,600 pg/L at 45 feet below ground surface (bgs) and TCE in soil gas in excess of 8,300 parts per billion volume. Fieldwork characterization data confirmed that former site P-5A is a persistent source of TCE contamination to groundwater with approximately 270 pounds of contaminant mass remaining in the source area. Hydraulic fracturing and emplacement of the carbon coated zero valent iron substrate was selected as the preferred treatment technology for Site P-5A for the following reasons: ability to provide source of carbon necessary for biodegradation, of TCE; ability for a long-lasting reductive amendment; potential propagation into tighter formations from fracturing techniques for better diffusion to VOC locations; and, the variability of injection techniques based on site conditions and constraints. DTSC has reviewed the report and has the following comments: General Comments 1.) Hydraulic fracturing techniques used during this pilot study created preferential pathways that were non-uniform, non-repeatable, and followed coarse-grained channels similar to the South Balloon pilot study results with Potassium Permangante. 2.) Metals concentrations and total dissolved solids measured throughout the test showed moderate to significant increases above baseline and were specific to arsenic, manganese, barium, boron, iron, and strontium. The 12-month metals sampling event in the South Balloon demonstrated that much higher concentrations remained compared to the baseline results. 3.) TCE concentrations decreased in monitoring wells within the area of the EHC delivery with up to a 95 percent reduction in some locations. TCE concentrations during the pilot study did not reduce to the Aquifer Cleanup Level of 5 pg/L. The highest reduction in TCE concentrations were achieved at MW321B1 where TCE was reduced from 760 pg/L to 37 pg/L. Cis-1, 2-Dichloroethene (cis-1,2-DCE), a common degradation by-product from TCE increased within the pilot study timeframe and remained during the 12-month event. MW321B1 and MW322132 showed the most significant increases in breakdowns with 12-month concentrations of 320 pg/L and 180 pg/L, respectively, compared to baseline levels of 21 pg/L and 5 pg/L. It is uncertain whether the increases in cis-1,2-DCE are a result of a "stall' in the breakdown of TCE and additionally, if the by-product levels will decline back to near baseline numbers in the future.