ARCHIVED REPORTS_2021 SITE INVESTIGATION WORK PLAN

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09 December 2021 Project No. 14-3002 Page 4 of 9 (AOC2). The surface elevation of the former power plant area is approximately 3.5 to 5.0 feet higher than the surrounding area. Based on groundwater data collected from Site monitoring wells in April 2021, depth to groundwater was measured between approximately 10.5 and 11.5 feet bsg and groundwater elevations ranged between 4.32 feet and 5.01 feet above the North American Vertical Datum (NAVD88). Groundwater was inferred to be flowing to the southwest at an average hydraulic gradient of 0.001 foot per foot (ft/ft) across the Site (Figure 25). Depth to water and groundwater elevations are summarized in Table 11. 3.0. SCOPE OF WORK The scope of work was developed based on data collected during the previous investigations and monthly discussions with USEPA, CVRWQCB and EHD staff. AGI proposes the following scope of work: 1) collection of surface samples in the locations of proposed trenches at the Site to assess surficial PCB impact; 2) excavation of approximately 28 trenches throughout the undeveloped areas at the subject property to locate and identify existing buried waste and to define the limits of the waste if encountered; 3) advancement of approximately 70 soil borings within and around the former power plant area to delineate the extent of buried waste and define COC-impacted soil and groundwater; and 4) collection of concrete samples in the former transformer area in the southwestern portion of the former power plant to evaluate a potential PCB source area. For this investigation, the proposed scope of work includes the following tasks:  Permitting and pre-field work activities.  Surface sample collection.  Trenching excavation and sampling.  Soil boring advancement and sample collection.  Sample analyses.  Concrete sample collection.  Boring abandonment.  Report preparation. Each of these tasks is described in greater detail below.