COMPLIANCE INFO_2024 FINAL SITE CHARACTERIZATION WORK PLAN

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4 Site Characterization Work Plan SWT Engineering Z:\PROJECTS\SiteLogIQ\Site Characterization Work Plan\Text\Riverbank_Site Charac. Work Plan (Feb 2024)_Final.doc Preliminary assumptions concerning the nature, extent, and potential threat to public health and safety environment are that the Riverbank City Dump is shallow (probably <15 feet deep), has limited extent, and poses a very low potential threat to public health and safety and the environment. Figures 2 and 3 show the estimated horizontal extent of the waste (i.e., waste limits) within the property boundary (approximately 0.8 acres). Assuming an average depth of 10 feet, the total estimated volume of waste in-place is approximately 13,000 cubic yards. The waste is likely to be mainly soil mixed with burn dump residue, with “de minimis” degradable materials that could generate landfill gas or leachate. Monitoring for landfill gases (i.e., methane and volatile organic compounds) will be conducted using field instruments during excavations and sampling (methane and/or organic vapor analyzers) as part of the Health and Safety Plan (Appendix C). 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 up to 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. Minimally invasive augur borings up to 3 - 4 feet are proposed to verify the limits of waste to Jacob Myers Park. Trenches are not proposed in order to minimize the impacts of material required by the LEA to be backhauled to a permitted disposal facility. The location and number of potholes/borings may change depending on conditions in the field. Because it is likely that large, resistant materials may be encountered, such as concrete slabs or asphalt, direct-push equipment are not suitable for the intrusive investigation. This intrusive field investigation (i.e., potholing) 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. Representative samples will be taken from each pothole. The thickness, soil type, and condition of any cover soil is part of the evaluation from the potholes and augur borings. 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, proper ty lines, structures, and other investigation information. A magnetometer (metal detector) or ground penetrating radar (GPR) sur vey was considered to further define the area of potholing. However, the small area and dense spacing of potholes/borings obviates the usefulness of geophysical survey methods. A utility line field survey will be conducted prior to excavation to preclude any excavation from impact to utility lines. The proposed pothole and augur boring locations are shown on Figure 3 and will be marked prior to implementation. Twenty-two (22) pothole and eight augur locations are proposed (approximately 50-foot spacing). The number and location of potholes and augur borings may be adjusted based on field conditions. 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