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(:V ASSOCIATES I N C . The CPT boring will be advanced to an estimated depth between 80 and 100 feet bgs. if no significant clay layer is encountered to a depth of 100 feet bgs, the CPT boring will be advanced further if subsurface conditions allow it. Once a significant clay layer has been discovered and the boring is advanced into another sand layer, a Geoprobe boring will be advanced adjacent to the CPT boring and a discrete groundwater sample will be collected from the deeper aquifer. After the sample has been collected, the boring will be grouted to the surface. Installation of Vapor Extraction and Monitorinz Wells Five soil borings will be advanced using a hollow stem auger equipped drill rig to depths of approximately 35 to 65 feet bgs. Soil samples will be collected at five-foot intervals or significant changes in lithology. Drilling will be conducted by a State licensed (C57) drilling company. A field geologist will be present to log all drill cuttings and soil samples. Each soil sample will be field screened with a Photoionization Detection (PID) meter or similar instrument and at least two samples from each of the five borings, based on field observations (i.e. odor, discoloration, PID readings), will be placed in a cooler with ice and submitted for laboratory analysis. Placement of Borings and Wells To evaluate the lateral extent of impacted groundwater, one boring will be located approximately 40 feet north of the former UST and one boring will be located near the southwest corner of the on-site building. These borings will be completed as groundwater monitoring wells. Three borings will be located in the immediate vicinity of the former UST and will be completed as three vapor extraction wells. Proposed boring locations are shown on Figure 2. Groundwater Monitoring Wells Construction Details The borings will be completed as groundwater monitoring wells or vapor extraction wells. The depth of the groundwater monitoring wells will be approximately 65 feet. Two vapor extraction wells will be completed at depths of 45 feet and one vapor extraction well will be completed at a depth of 35 feet. The wells will be constructed of 2-inch inside diameter schedule 40 PVC well screen and casing. A 0.020-inch well screen slot and #2112 mesh sand pack will be used. Neat cement will be used to seal the wells in accordance with California Well Standards (December 1981). To protect the integrity of the wells, locking, water-tight well plugs will be installed on each well and a water-tight wellhead labeled "monitoring well" will be concreted over each well. Proposed well construction details are shown on Figures 3 and 4. The top of casing of the new wellheads will be surveyed and tied into the existing groundwater monitoring well to assess groundwater gradient and flow direction. All drill cuttings will be stored on site in 55-gallon drums pending laboratory results. Sample Analysis w:1625771reportslwkpinVaMExts.doa 3