SITE INFORMATION AND CORRESPONDENCE

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In June 2009, ECM submitted a work plan to install two monitoring wells to provide additional measurement of induced drawdown and more accurate estimates of the capture zone for the IRAP system. In its letter dated November 3, 2009 RWQCB approved the workplan for these two additional wells. In December 2009, ECM installed monitoring wells M-50A and M-51A. The details of these well installation activities can be found in the well installation report submitted to RWQCB on April 15, 2010. On-Site Extraction System Hydraulic Capture Assessment On May 4, 2010, with the approval of Jim Brownell at the RWQCB, ECM shut down the On-Site extraction system for 72 hours to collect groundwater elevation data for the new and old monitoring wells and to estimate the hydraulic capture zone for extraction wells EU-3 and EU-4. ECM monitored the groundwater elevation in wells EU-3, EU-4, M-1A, M-113, M-46A, M-47A, M-48A, M-49A, M-50A, M-51A before, during, and after the 72- hour shutdown. Using the water elevation data collected and as presented in Table 2, during the 72-hour system shut-down, ECM developed the contours of induced drawdown through interpolation of the groundwater elevation data. Figure 2 presets an interpolated plot of the drawdown induced, and resulting capture zone, when the wells EU-3 and EU-4 are each pumping at 30 gpm. Figure 3 shows the particle tracking using flow model when both E-3 and EU-4 are pumping at 30 gpm. In comparison, the capture zone predicted by the numeric groundwater flow model and the field measured drawdown are similar. Nonetheless, the actual capture zone is slightly larger in size than the capture zone predicted by the groundwater flow model, suggesting that the numeric groundwater flow model represents a conservative estimate of the hydraulic capture actually provided by EU-3 and EU-4 under in-field pumping conditions. Current On-Site extraction System Sampling and Monitoring Data Sampling of groundwater monitoring wells and influent to the On-site treatment system is conducted according to the schedule outlined in the Monitoring Reduction Plan (MRP). The results of monitoring of COC influent concentrations at the Industrial Avenue system (Figure 1) indicate a 97% reduction in combined influent concentration (i.e. from both EU-3 and EU-4). Influent TCE concentrations have decreased from 920 pg/L in February 2008 to 29 pg/I in April 2010, the most recent system sampling date. TCE concentrations measured in groundwater from each individual well have also shown significant declines by over 97% since system startup, with TCE concentrations reported at 28 pg/L at EU-3 and 21 pg/L at EU-4 during the May 4, 2010 sampling event (Figure 1, Table 1). Proposed Changes to Operation of TRAP System It is unclear whether the rapid decline in TCE mass removal rate since February 2008 is due to mass removal, or whether the TCE mass removal rate may be influenced by the evolution of a relatively stable flow field, where a zone of relative stagnation or slow moving groundwater may exist between the extraction wells, hindering mass removal. To further explore this possibility, a maximum 60-day shutdown of extraction well EU-3 is proposed. The shutdown would allow for assessment of the possible stagnation zone 2