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Abdelwahed Facility, Ultran%an"Site No. 13792 %..d May 5, 2012 Stockton California Work Plan Well for DPE Well Installation and Soil Gas Investigation A soil vapor extraction system (VES) has operated at the site since October 5, 2007. The VES is set up to extract vapors from wells VW -1 through VW -5, MW -1 and MW -3. Vapor extraction wells VW -3, VW -4 and VW -5 are the only vapor wells not currently flooded by groundwater. An air sparge (AS) system is connected to sparge wells SW -1 and SW -2 and is operated in conjunction with the VES. The locations of remediation system compound and underground piping are shown on Figure 4. As of March 6, 2012 the VES has removed approximately 40,297 pounds of otal petroleum hydrocarbons as gasoline (TPHg) including 28.4 pounds of benzene. The VES has operated on a pulsing schedule since February 2011 to evaluate the effect on influent hydrocarbon concentrations. Influent TPHg concentrations and the influent hydrocarbon extraction rate are both decreasing with time. The latest hydrocarbon concentration data and distribution in groundwater indicate persistent and elevated hydrocarbon concentrations in the well MW -1 area located immediately east of the former southern dispenser island. The well MW -1 screen (35 to 55 feet bsg) is approximately 2 feet below the current water table. Groundwater analytical results from nearby well MW -9 (screen 83 to 88 feet bsg) indicate vertical delineation. Soil analytical data indicate hydrocarbon impacts in the former southern dispenser island area extend to approximately 65 feet bsg. The recalcitrant concentrations detected in well MW -1 are thought to be caused, in part, by hydrocarbon fouling of the well filter pack and casing by conditions encountered at the time of well installation and during the ensuing time since well installation. This condition persists despite air sparging into nearby wells SWA and SW -2 and concurrent vapor extraction from well MW -1 from October 2007 through February 2008. The tasks proposed in this work plan include: drilling out well MW -1 and backfilling the boring; drilling a new boring at the location and installation of a replacement monitoring well that would potentially be suitable for conducting a DPE remedial action; conduct a DPE remedial action if data from the replacement well indicates that it is necessary; conduct a soil gas investigation to provide data on which to evaluate the potential health risks posed to workers inside existing and future site buildings. All fieldwork shall be conducted according to the appropriate Horizon Field Methods and Procedures attached to this work plan. Proposed MW -1 Destruction Well MW -1 construction details are shown on the attached boring/well log. The proposed drill out shall consist of the following tasks: Task 1 Select and schedule a C-57 licensed drilling contractor to provide hollow - stem auger drilling and well abandonment services; obtain required well permit from the .EBD; and prepare a Site Health and Safety Plan. 1792 DPI;' Well WP Project No. 1792.26 2 HORIZON ENVIRONMENTAL INC.