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in the region of interest. This then presents a picture of the changing dynamics of oxygen and BTEX in the entire system over time. As can be seen in Figure 1, the oxygen mass increased to a maximum in first 3-5 days and remained relatively constant for the next thirty days. At this point, the rate of oxygen consumption increased in response to an influx of BTEX through the barrier caused by the excavation of the source upgradient of the barrier (discussed below). Field measurements are indicating the ORC®Filter Socks will have a longevity of about six months under these conditions. A significant, correlative reduction of the BTEX plume was documented. A series of contour plots illustrate the reduction of the BTEX plume as a result of oxygen migrating from the ORC® barrier. There was clear evidence of enhanced oxygen dispersion into the formation of at least 20 feet downgradient from the monitoring well network, as detailed in Technical Bulletin IV.3a. As illustrated, in Figures 2a and 2b, there was a significant reduction in BTEX mass in the treatment zone and at a significant distance away from the barrier. Concentrations of total BTEX in samples from the most downgradient well, 120 feet from the barrier, declined to Non-Detect (ND). Also, at this well, assays of aerobic microbial degraders were two orders of magnitude higher than background indicating the presence of oxygen from the ORC installation was driving bioremediation. The gasoline spill was in an area approximately 30' X 45' and located at between 50 - and 100 feet behind the barrier. Groundwater velocity was 1-2 feet per day. Project timelines dictated that the excavation was to immediately precede barrier placement. This physical activity disturbed the equilibrium of groundwater interaction with sorbed material; rainfall into the open excavation may also have been a factor. The result was that a pulse of increased dissolved phase BTEX was created and carried into the barrier, where it was detected by day 47. This effect is also seen in the contour plots. The BTEX levels then decreased as further remediation began to bring the situation under control. An increase in the rate of oxygen consumption is noted as a result. Due to the presence of an overhead power line, a 4 well section of Oxygen Barrier was installed_in the Northeast corner of the site. Based on the direction of groundwater flow, it was not subject to the pulse of BTEX from the excavated area. Consequently,the area immediately downgradient was remediated. REG EN ES IS -------------------------------------------------------------------=--------------- Bioremediation ProduCts 27130A Paseo Espada, Ste 1407, San Juan Capistrano, CA 92675 Phone: 714-443-3136 Fax: 714-443-3140