SITE INFORMATION AND CORRESPONDENCE

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Kennedy/Jenks Consultants A preliminary site assessment was performed .in November 1992. The work included a review of available agency records, installation of five groundwater monitoring wells, and analysis of soil and groundwater samples from each well. Static depth to water was established at approximately 30.5 feet below the ground surface, with a groundwater-gra- dient toward the northeast. Soil analysis again detected petroleum hydrocarbons at depths of 25 and 30 feet in four of the five well borings. No petroleum hydrocarbons were detected in any of the borings at depths of 15 to 20 feet. Trace concentrations of hydrocarbons and/or BTEX were detected in four of the five groundwater monitoring wells. Quarterly sampling of the on-site monitoring wells was performed in June, September, and December of 1993. Water levels rose four feet from a depth of approximately 30.5 to 26.5 feet between November of 1992 and June of 1993, saturating most of the previ- ously impacted soil on the site. Petroleum hydrocarbon and particularly benzene concen- trations in groundwater increased. Groundwater gradients were consistently toward the northeast at slopes ranging from approximately 31 to 42 feet per mile. In October 1993, an evaluation of.remedial alternatives for petroleum impacted soil on the site was performed. The scope included eight additional soil borings and one pilot soil vapor extraction well. The results of the soil sampling showed detectable concentrations of petroleum hydrocarbons in the soil at a depth of 23 to 28 feet across the site. 3. PROPOSED WORKPLAN Collection of Soil Vapor Samples Soil vapor samples will be collected from seven sampling locations as illustrated on Figure 1 , at depths of 16, 21, and 26 feet below the ground surface (bgs). Samples will be collected by simultaneously driving a 231$-inch diameter drive casing and a 1518-inch diameter soil core tube into the soil. The soil core tube will be removed after every 3-foot advance so that lithology can be identified. Discrete soil samples from the targeted depths of 16, 21 and 26 feet bgs will also be collected, preserved, and stored onsite pending the results of the onsite mobile -lab's soil vapor analyses. If in the judgment of the field engi- neer, the results of the soil vapor analysis are inconclusive, these soil samples may be analyzed. As the drive casing reaches depths of 13, 18, and 23 feet, the soil core tube will be removed and replaced by a 1-inch diameter soil vapor sampling tube. The sampling tube with expendable steel drive points will be driven 3 feet into the undisturbed soil beneath the outer drive casing. When the required sampling depth is reached, the probe will be pulled up to expose the probe to the desired sampling interval. The top of the vapor probe will than be coupled to a Tedlar® bag within a sealed vacuum box using 1/4"-diameter Teflon® tubing. The vacuum box will be evacuated with an elec- tric or hand vacuum pump, allowing the sample bag to fill with soil vapor from the sample .interval. A minimum of one probe volume (approximately 6 cubic inches per vertical foot of probe) will be purged from the probe before a sample is collected. Once the sample is collected, soil vapor probes-will be removed from the ground with the sampling rig, and the soil core tube is reattached to the sampling rig and advanced to the next sampling depth in three-foot intervals. g:l obs1840549%swkp1en.doc 2