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Delineation and Destruction Work Plan for Well B-1 2.4 Proposed Soil and Groundwater Sampling Sampling methods and procedures for soil and groundwater samples are outlined below. They are derived from the DTSC Guidelines for Planning and Implementing Groundwater Characterization of Contaminated Sites (DTSC 2012) for site characterization and other guidance documents referenced in the DTSC site characterization guidance. 2.4.1 Permitting and Utility Clearance Prior to the fieldwork,Dudek will obtain a permit for the borings,as required by the County EHD. Prior to the commencement of field activities, a private underground-utilities-locating company will perform a survey to determine whether underground utilities are present near the sample locations. In addition, Dudek will contact Underground Service Alert of Northern/Central California and Nevada(USA North 811) at least 2 days prior to subsurface work. 2.4.2 Sample Locations and Depths Three exploratory borings will be advanced using a hollow stem auger drilling rig. The borings will be located approximately 7 feet down-gradient of well B-1. To account for the possibility that the well may have been drilled at a slight angle (rather than vertically), the distance between well B-1 and the exploratory boreholes should be greater than 5 feet to avoid grazing or punching through the possibly non-vertical well casing. One boring will be located northeast of well B-1, toward the center of the site; this is the down-gradient direction when the treatment system is operating. Two borings will be located east and west-southwest of well B-1, which are the two typical down-gradient directions observed when the treatment system is not operating. Borings will be advanced to a target depth of 1 foot below the bottom of the well screen, approximately 56 feet bgs. In the event that refusal is encountered prior to reaching the target depth, a step-out location will be drilled approximately 7 feet from well B-1, approximately 3 feet from the original borehole (proceeding clockwise around the B-1 well box). Acetate cores of soil extracted from the boreholes will be split open and screened with a photoionization detector (PID), and observations regarding odor and any discoloration of the soil (e.g., dark, stained soil) will be recorded. If elevated PID readings (defined as greater than 5 parts per million) or significant petroleum odor or significant discoloration are observed in the soil collected near the target depth, the borehole may be advanced an additional 5 feet or until discoloration, petroleum odor, and elevated PID readings are not observed. Additionally, if elevated PID readings, significant petroleum odor, or significant discoloration are observed in the soil at any depth,an additional step-out borehole will be advanced no more than 3 feet farther from well B-1, at the same bearing from well B-1 as the initial borehole. 10886-7 DUDEK 5 January 2019