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i 5 I . I TECHNICAL APPROACH SUMMARY The objectives of this proposed scope of work include further defining the lateral and vertical extent of impacted soil and the lateral extent of impacted groundwater, and removing the source of continuing impact to groundwater beneath the site. To achieve these objectives, five soil borings will be advanced for soil and groundwater-grab samples using a Geoprobe and heavily impacted soil in the vicinity of the former 4,000-gallon UST will be excavated. To further define the extent of impacted soil and groundwater beneath the site, five soil borings will be drilled with a Geoprobe. Three of the borings will be located north of the former UST within the State Highway 99 right-of-way. One of these three borings will be angled under the highway road surface. The fourth soil boring will be positioned approximately 40 feet east of MW-1 to delineate the boundary of the plume of impacted groundwater to the east. The fifth soil boring will be advanced in close proximity to the former UST to define the vertical extent of impacted soil in the source area. From each of the five soil borings, soil samples will be i collected at five-foot intervals for field screening and possible laboratory analysis and a groundwater-grab sample will be collected for laboratory analysis. All soil and groundwater samples will be analyzed for TPH-as-diesel, TPH-as-gasoline, BTEX and MTBE by Modified EPA Methods 8015 and 8020. To remove the source of continuing impact to groundwater, heavily impacted soil in the vicinity of the former UST will be excavated. The limits of the excavation will ultimately be based on field O observation and confirmatory soil sample analyses. The estimated excavation limits would be approximately 40 feet by 40 feet by approximately 15 to 20 feet deep. Anticipating-groundwater recharge, the excavation pit will be de-watered during the excavation operation. This will facilitate the excavation of saturated soil and increase petroleum hydrocarbon mass remov .Z` Arm-yrs Following excavation, a total of eight excavation side-wall soil samples and two excavation floor samples will be collected for laboratory analysis. The decision to terminate excavation activities will be based on confirmation soil sample results. Following the completion of the excavation, the saturated soil and standing groundwater at the v-)ti�S base of the excavation will be bridged with %-inch rock. To support microbial activity and the .- ��; enhanced biodegradation of residual petroleum hydrocarbon mass, approximately 200 pounds of bulk Oxygen Release Compound (ORC) will be mixed with the rock at the base of the excavation. The remaining excavation pit will be filled with clean imported fill. —uwwel) The excavated impacted soil will be stockpiled on site and sampled for proper disposition. The water purged from the excavation will be stored in a rented water tank and treated on site using granular activated carbon. Once treated, the water will be discharged to the sanitary sewer. The results of the site investigation and source removal activities will be published in a report for regulatory submittal. Concurrently, the three existing groundwater wells will be monitored and sampled on a quarterly basis for a period of at least one year. !I i