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LFR Inc. LFR has routinely monitored the performance of the system by measuring vacuums, flow rates, and VOC levels using a PID at the wellheads of SVE and soil-vapor monitoring wells. A typical iso-vacuum contour map generated using vacuum data measured at SVE and monitoring wellheads during operation of the SVETS is depicted on Figure 13. Figure 14 presents a time versus concentration graph of the SVE mass removal rate since start-up. This figure graphically displays the initial rapid Hazardous Substance removal rates (represented by PCE concentrations), which have declined asymptotically with time and which are currently at de minimis rates of generally less than approximately 0.2 pound per day. The mass removal rate of the SVETS increased temporarily upon activation of the Phase IV air sparging system in March 2007. This occurred as the Hazardous Substances present within groundwater were volatilized into the overlying vadose zone by sparging air into the underlying Hazardous Substance- affected groundwater. The sparged air and any Hazardous Substances within the air were captured and removed by the overlying SVE system. Operation of the sparging system initially consisted of sparging air(April to August 2007), with ozone being added in September 2007. 1.3 Phase IV IRA (Air and Ozone Sparging) The air and ozone sparging system was started up in May 2007 in accordance with the "Proposed Phase IV Interim Remedial Action Detailed Plan," dated July 3, 2006 (LFR 2006). System construction and start-up activities are summarized in LFR's "Construction Completion and System Startup Report, Phase IV Interim Remedial Action," dated October 5, 2007 (LFR 2007). Figure 15 is a histogram that graphically displays the concentration of Hazardous Substances in samples collected from groundwater monitoring wells located within the area of the sparge system. This figure shows the average Hazardous Substance concentrations before sparging was initiated (April 2007), and the rapid Hazardous Substance reductions over time to the present. In all cases, post-sparging values are at least one order of magnitude lower than the pre-sparging average; in many cases, the reduction is two orders of magnitude. These results showed that the system was effectively remediating Hazardous Substances in the Historical Source Area with only air. Ozone sparging was started on November 5, 2007, after the October 2007 sampling event, when the levels of Hazardous Substances in all wells were below 1,000 micrograms per liter (µg/L). The wells were most recently sampled in January 2009, and results indicate that all wells contained the lowest concentrations of Hazardous Substances detected since sparging began. PCE concentrations reported in treatment system wells during the most recent monitoring event ranged from not detected to 19 µg/L in well PT-8 (Figures 4 and 15). pla losu Phll_IV_IRA-Aug09-06750.dm:deh Pap 3