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9 0 SWMU 21 . Soil samples will be collected from approximately 4 to 6 inches below the surface using hand tools (e.g., slide hammer) depending on the site conditions. The soil samples will be analyzed for TPH-d and TPH-mo. CE also proposes to collect soil samples at 5' intervals beginning at 15' bgs in the monitoring well installation borings. Logs of soil penetrated by the borings will be compiled from samples collected from the borings using the Unified Soil Classification System. The locations of the proposed borings are presented on the site map. See Figure 3. 3.4 Additional Monitoring Wells (MW-9 and MW-10) Two (2) monitoring wells (MW) are proposed for construction south of existing well MW-8 to an estimated depth of 70-80 ft bgs. Drilling Methodology Based on the past drilling experience onsite and in consulting various drillers, drilling will be performed by a high torque hollow stem auger. In the case of repeated refusal, a change to mud rotary may be required, but is not thought to be likely. MW-9 will be drilled with a continuous core that will be logged by the onsite geologist, and the cores that are not used for chemical analyses, will be boxed and preserved for future reference. The logs of the borehole and well construction, similar to those of the past wells (included in the reports) will be included in the subsequent report. Well Completion A two-inch diameter Schedule 40 polyvinyl chloride (PVC) plastic, with sufficient screen (0.010-inch slot) to span the groundwater-bearing zone will be installed in each boring. A filter pack (sand) will be installed from the total depth of the boring to 2-ft above the top of the well screen. 2.5 feet of hydrated bentonite pellets will be installed above the filter pack. The well will then be grouted using concrete slurry to local grade level. Following the grouting of the well a metal Christie box, will be installed at the well head. A lockable water tight cap will be secured to the top of the 2" PVC well casing. The installation of the MW will be in accord with applicable regulatory requirements, i.e. permits, inspections, etc. The minimum of 24 hours will elapse between MW installation and MW development. An oil/water interface probe will be used to determine the depth to water and the depth to the bottom of the well casing. Monitoring wells will be developed using a rod and surge block assembly. After initial pH, conductivity and temperature parameters are recorded, the surge block will be installed. The rod and block assembly will be forced through the water column and then raised. Typically a well will be surged 25 times then two volumes of water will be extracted from the well casing. The parameters will again be collected and the complete cycle repeated three additional times. Parameters will be collected and the well purged once again for two additional volumes of water. CE Project No.99R-4041 Additional Investigation Work Plan 4