COMPLIANCE INFO_7/2023 SITE CHARACTERIZATION PLAN + REV 11/2023

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4 Site Characterization Work Plan SWT Engineering Z:\PROJECTS\SiteLogIQ\Site Characterization Work Plan\Text \Riverbank_Site Charac. Work Plan (Nov 2023).doc depth of 12 feet, the total estimated volume of waste in-place is approximately 14,800 cubic yards. The waste is likely to be mainly inert debris and land clearing materials (soil and vegetation) associated with WWTP construction activities, with “de minimis” degradable materials that could generate landfill gas or leachate. The LEA Site Identification Form (dated June 20, 2011, see Appendix A) ranked the threat posed by the Site as “C”, which is a low threat to public health and safety and the environment with minimal action needed to prevent human contact with waste. Current land use is non-irrigated open space and storage and staging activities associated with WWTP operations. 4.0 SITE CHARACTERIZATION WORK PLAN Based on the available information, potholes and/or trenches 10-15 feet deep are determined to be the most suitable intrusive field investigation method and are being proposed to determine the vertical and horizontal extents of waste fill. The amount of potholes and/or trenches may change depending on conditions in the field. Because it is likely that large, resistant materials will be encountered, such as concrete slabs or asphalt, drilling or direct-push equipment are not suitable for the intrusive investigation. This intrusive field investigation (i.e., potholing and trenching) will be performed by sampling and analysis. The sampling and analysis is intended to document the procedural and analytical requirements for collection and analysis of the potentially contaminated soil hazardous materials. Samples will be taken of all four sides and bottom of each pothole and trench. A Sampling and Analysis Plan is provided in Appendix B. Results of exploration will be documented on a topographic drawing for the disposal area which will depict the waste boundary, property lines, structures, and other investigation information. A magnetometer (metal detector) or ground penetrating radar (GPR) sur vey may be conducted to further define the area of potholing and trenching. The proposed excavation locations are shown on Figure 3 and will be marked prior to implementation. The location of pothole test pits and trenches, as shown on Figure 3, may be adjusted based on field conditions. The approximate limits of waste are shown on Figures 2 and 3. For decades, the LEA has visited and visually surveyed the site during routine quarterly inspections of the closed landfill. As part of the proposed potholing, an additional geophysical visual survey of the disposal site area will be conducted. In addition to the assessment of historical aerial photograph analysis and topographic maps already included in this Work Plan (Appendix A), the suspected boundary will be further assessed, as needed, using photograph analysis and topographic maps. The most effective methods for determining horizontal and areal extent based on site conditions, e.g., physical properties of geology, development and the fill area, are part of the intrusive investigation/field work activities outlined in this section. Once limits of waste are better defined during this intrusive field work, the estimated volume of waste in-place will be updated from the information provided in Section 3.0. The types and relative quantities of materials excavated will be characterized by using the authoritative sampling method, as discussed in Sampling and Analysis Plan (see Appendix B) . The LEA will be notified when excavation activities (potholing and trenching) occur to allow them to observe the materials. Soil sampling will occur at each pothole and trench location as discussed in the Sampling and Analysis Plan is provided in Appendix B. If burn ash is encountered during potholing and trenching, soil/ash samples be collected and