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Ms. Diane Hinson and Ms. Margaret Lagorio Page 3 ( August 27, 1995 quarterly for the parameters specified in CH2M HILL's SOP as part of the ongoing quarterly groundwater monitoring program at the Disco Site. In addition, data collected from monitoring well MW-1 and the existing piezometers for the air sparging and soil vapor extraction system may also provide useful information for the demonstration study. Table 1 MonitorinR Wells for Intrinsic Bioremediation Demonstration Monitoring Well Rationale for Well Selection MW-DIS-9 Located upgradient, back round well . MW-DIS-2 Located within dissolved plume; outside of air sparging/soil vapor extraction radius of influence MW-DIS-8S and 8D Located at downgradient frin a of plume MW-DIS-3 Located near fringe of plume After four quarters of data are collected for the demonstration study, CH2M HILL will evaluate the biodegradation activity at the Disco Site and the potential for biodegradation activity to limit or reverse the gasoline plume. Based on the results, CH2M HILL will provide recommendations for long term management and remediation of the gasoline plume. In the August 17, 1995 letter, PHS/EHD requested confirmation sampling in other areas of the groundwater contamination plume. CH2M HILL feels that confirmation sampling, may not be necessary due to the number of data points proposed for the demonstration study. However, this should be further discussed and evaluated after the four quarters of data is collected and if the data is inconclusive. PHS/EHD also requested information about the radius of influence of the existing soil vapor extraction (SVE) and air sparging (AS) system at the Disco Site. Based on data from the existing piezometers, the radius of influence of the SVE system is approximately 25 feet and the radius of influence of the AS system is approximately 10 to 25 feet. This information is further discussed in the recent quarterly monitoring report dated August 11, 1995. Schedule The schedule to implement the intrinsic bioremediation demonstration study is shown in Table 2. The quarterly monitoring activities for the demonstration study will occur concurrently with the ongoing quarterly groundwater monitoring program at the Disco Site.. Data from the demonstration study will be included with the quarterly groundwater monitoring reports for the Disco Site.