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to still contain elevated contaminants, then excavation will extend beyond the sample location. A partial excavation has the benefit of providing contaminant removal in a short period of time, which helps to minimize costs. Removing part of the source contaminants will help to reduce the time it takes to completely remediate the site. The length of time that a water treatment system would need to be employed could be lessened by up to half of the time, depending on the amount of contaminants that can be removed during excavation. Excavation in the source area will provide a benefit in removing TPH-gas and any residual BTEX. However, due to its high solubility, MTBE will preferentially partition out of gasoline and into the aqueous phase. Therefore, MTBE in residual fuel sources is rapidly depleted, and subsequent source reduction may not significantly accelerate the reduction of dissolved MTBE concentrations. Dissolved MTBE has been identified in many of the shallow wells on-site and has migrated to MW-9, approximately 140 ' to 150 ' west of the source area. Groundwater contamination should be addressed near the source area, near MW-3R. MW-2 or MW-21 . The EHD expressed concerns that "a pumping test immediately outside the plume impacted groundwater may have the unintended consequence of inducing plume migration into areas currently not impacted." Taking this into consideration, the aquifer pumping test and groundwater extraction proposed should be performed on either MW-3R or MW-21 . Either of these two wells is located relatively near the source area. If product identified in MW-21 is significant, then the aquifer test and groundwater pump and treat will be performed at MW-3R. Sheen droplets identified in MW-2 and free product in MW-21 have indicated that contaminant source removal is necessary. In addition to soil excavation and )n o y z Ida ' -r groundwater pump and treat, free product removal may be required. Before BEA can hi June determine a removal method, the amount of free product in each well must be ° UL 'r -Brea determined. At this point it seems that the sheen droplets in MW-2 could just be the partitioning of elevated dissolved TPH-gas in the well. The presence of sheen droplets does not indicate that a measurable amount of product is present in MW-2 . MW-21 identified a small amount of product that may be measurable. During the upcoming quarterly groundwater monitoring, an oil-water interphase probe will be used to determine the existence of measurable product in MW-2 and MW-21 . Past results indicate that it is likely that MW-2 contains no measurable product and Z MW-21 contains a small amount. If measurable product is identified, it will be removed using a disposable bailer and the amount will be measured later in the day to find an approximate recharge rate. With a small amount of product and slow recharge rate, passive skimmers may be recommended for free product removal . 2