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2.0 RATIONALE FOR ABANDONMENT As recommended by Parsons in the Ninth Quarterly (Q9) Groundwater Monitoring Report and Operable Unit 2 Closure Request (Parsons 2014), groundwater sampling was discontinued for the following reasons: • Limited mass of hydrocarbons remaining in Site groundwater(approximately 0.00458 pounds in the dissolved phase); • Historically decreasing concentration trends; • Limited extent of impact(conservatively estimated to be 34 foot by 20 foot by 5 foot in AOI 3); • Remaining TPH concentration meets the project cleanup goal (TPH<l00 µg/L); and • Impacts will likely remain onsite while they attenuate naturally(and will therefore not likely impact potential sensitive receptors). In a letter dated August 7, 2014, DTSC approved the permanent discontinuation of groundwater monitoring and granted a determination of "No Further Action" with respect to groundwater impacts at the Site. As recommended in the closure request, Parsons will abandon the wells, injection points, extraction points, and soil vapor monitoring points consistent with San Joaquin County Department of Environmental Health requirements to ensure that they cannot act as conduits for contaminant migration to the subsurface. The details of the abandonment methodology are provided below. 3.0 ABANDONMENT METHODOLOGY Prior to intrusive abandonment work,the following tasks will be completed: • Prior to field mobilization, well abandonment permits (as applicable) will be obtained from the San Joaquin County Department of Environmental Health (SJCDEH). • Underground Service Alert will be notified at least 48 hours prior to intrusive field activities. All potentially-affected utility companies will be required to mark in paint the locations of their respective utilities. In addition, a private utility locating contractor will determine the presence and locations of underground features and utilities in the vicinity of all wells to be abandoned. Geophysical methods for boring clearance will include a combination of the following methods: radio detection (conductive and inductive), magnetometer, and ground-penetrating radar. • Static water levels in all wells/extraction points will be gauged prior to intrusive activities and the well bottoms will be tagged. This will provide a final set of groundwater level data for well abandonment reporting and for the completion of State of California Department of Water Resources (DWR) well abandonment forms. • Surface completions (well boxes and concrete skirts) will be removed and disposed of as construction waste. 3