COMPLIANCE INFO_2024 DRAFT REVISED SITE CHARACTERIZATION WORK PLAN

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4 Site Characterization Work Plan SWT Engineering Z:\PROJECTS\SiteLogIQ\Site Characterization Work Plan\Text\sdwrev 2-4-2024 Riverbank_Site Charac. Work Plan (Rev Feb 2024).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. Aerial photographs included in Appendix A do not indicate a timeframe as to when disposal activities may have occurred or indicate changes in site use and vegetation. The WWTP is present in the 1957 aerial photograph and 1953 topographic map (both pre-disposal), and by 1963 (during disposal) had expanded. Topographic maps indicate a variable shallow slope area with little change in relief (up to 10-15 feet) over time. Topographic maps from 1916 and 1953 (both pre-disposal) show a north-northeast trending trench, which is most likely a former irrigation canal at the west end of the site from 10-15 feet deep that is not present in 1957 (pre-disposal). It is likely that the former canal was filled between 1953 and 1957 (pre-disposal). This former canal appears to be the area of waste fill and is located where the 565-kW ballasted ground mount array is to be placed on the old landfill area. The former canal area extends to the outside limits of the WWTP operations to Jacob Myers Park, which is within the parcel boundary and owned by the City of Riverbank. Figure 3 shows the approximate limits of waste of the disposal site with respect to the proposed Solar array. 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. Figure 2 shows the approximate horizontal extent of the waste (i.e., waste limits) within the property boundary (approximately 0.76 acres). Assuming an average 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 up to 10-15 feet deep are determined to be the most suitable intrusive field investigation method and are being DRAFT