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5 <br /> decreased, while concentrations of cis-1,2-DCE increased. This suggests the <br /> transformation from TCE to cis-1,2-DCE was likely occurring; however, complete <br /> transformation of the TCE to ethene was not observed during the short test. Table <br /> A.2-1 provides the details of these laboratory results and the changes observed in COCs <br /> and field parameters during the PPT in wells M1-A and M1-B <br /> 3.2 Metals COC Groundwater Sampling and Analysis <br /> Selenium concentrations increased from a baseline concentration (pre-test = 2.7 pg/L) to <br /> a high of 54 ug/L in a groundwater sample from well M-113; (Table A.2-2). The higher <br /> concentrations of selenium are interpreted as transient because values in subsequent <br /> samples from wells M-1 B and M-1A decreased to around pre-test values approximately <br /> 30 days after carbohydrate injection occurred. <br /> Baseline (pre-test) arsenic concentrations were 3.3 and 8.7 pg/L in groundwater <br /> samples from wells M-1A and MAB, respectively. Arsenic concentrations increased <br /> from baseline concentrations to maximum concentrations of 13 and 19 pg/L in samples <br /> from wells M-1A and M-113, respectively. Concentrations of arsenic in samples <br /> decreased to below background levels approximately 63 days (M-1A) and 99 days (M- <br /> 1B) after carbohydrate injection. This indicates that that effect of carbohydrate injection <br /> on arsenic concentrations was transient. However, if this technology is applied on a <br /> regular or continual basis, mobilization of arsenic may be an ongoing concern. <br /> The apparent increase in metals may be related to the reductive dissolution of ferric and <br /> manganic oxides and associated trace metals that are naturally occurring within site <br /> soils. These effects are expected to be transient and localized to the zone where <br /> carbohydrate is delivered. These processes were further evaluated through a program of <br /> post-test sampling conducted in the test wells and well ED-2, which is located <br /> approximately 40 feet downgradient and screened in the same interval as well M-1A <br /> (100 to 120 feet bgs). Effects of the carbohydrate injection were not observed in <br /> groundwater samples from well ED-2, as TOC, bromide, VOCs, and arsenic <br /> concentrations were similar to background concentrations observed in the sample from <br /> well M-1A. <br /> 3.3 Post-Test Groundwater Sampling and Analysis <br /> Environmental Cost Management, Inc. (ECM) completed post-test groundwater <br /> sampling in wells M-1A, M-1 B, and ED-2 (screened interval 100 to 120 feet bgs; located <br /> approximately 40 feet downgradient of well M-1A) on December 6, 2005. Additional <br /> post-test groundwater sampling was conducted on well MAB on January 11, 2006. <br /> Extraction well EW-1 resumed operation on December 6, 200510 <br /> 3.4 Soil Sampling and Analysis <br /> Soil samples were collected during the treatment zone delineation to further evaluate the <br /> potential for mobilization of arsenic during ISB (see Table A.2-3). Soil samples were <br /> collected from location CPT-11 between 31.5 to 33.5 feet bgs and 51 to 53 feet bgs. <br /> Soil samples were analyzed for iron, manganese, arsenic, bioavailable iron and <br /> manganese, and bioreleased arsenic. The amount of bioavailable iron and manganese <br /> or bio-released arsenic in the sample is the difference between the initial and final <br /> concentrations of the constituents extracted from the soil sample. The metals were <br /> extracted from the soil by mixing the sample with hydrochloric acid for 48 hours. <br />