ARCHIVED REPORTS_REMOVAL ACTION COMPLETION REPORT

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Draft Removal Action Completion Report Neighborhood C, Mountain House,CA Page 5 northern section of the trench was placed as fill in sections of Neighborhood C outside of the removal area.Once the waste soil encapsulation area was prepared,paddle-wheel scrapers began moving the waste soil from the removal areas to the encapsulation area. The southern section of Great Valley Parkway that is within the soil removal area (from Grant Line Road to 1,200 feet northward) was excavated after the upper 1.5 feet of soil was first removed, then entombed in the northern section of Great Valley Parkway, and confirmation sampling results were received that verified that the cleanup goal had been achieved. Concurrence was requested from the DTSC that the cleanup goal had been achieved in the Hill group and Area 1 and that cut and fill could proceed in a letter dated November 2, 2013. Concurrence and authorization to proceed was received the same day in email correspondence (Appendix F). Excavation of the southern section of the entombment area began after DTSC authorization had been received. Soil removed from the southern section of the trench was placed as fill on Area 1 after DTSC concurrence that all subparcels of Area 1 had met the cleanup goal. 3.4 SOIL REMOVAL Excavation equipment used for soil removal included graders and bulldozers to form windrows of soil and fine-cut excavation areas, and paddle-wheel scrapers to transport the soil from the removal area to the entombment area. Once the scrapers were filled, they proceeded to the Great Valley Parkway excavated roadway (entombment area) and deposited payloads. Excavation areas were controlled to avoid dust generation using water trucks with spray nozzles according to the Dust Control Plan and Air Monitoring Plan in the RAW. The entire soil removal area was excavated to a depth of 0.5 feet. Initial confirmation sampling results indicated that additional soil removal would be required to achieve the cleanup goal. To assist with constraining depth of additional excavation within subparcels, discrete depth sampling was conducted (Section 4.1). Analytical results were requested on a 24-hour turnaround time. A variance from the RAW to increase the depth of excavation in the majority of subparcels was necessary based on the laboratory results of the first round of confirmation sampling. As a more conservative measure than was described in the RAW, instead of analyzing the remaining three confirmation samples within each subparcel, MHD elected to strip the entire subparcel in most areas until the cleanup goal was achieved. Additional dieldrin soil removal re-commenced in Area 1 to various depths within the subparcels (Figure 4,Appendix A).Next,the section of Great Valley Parkway that is within the removal area,the hill group, an additional 1.0 feet of soil was removed and entombed in the pre-excavated northern sections of Great Valley Parkway. Excavation continued in the remainder of Area 2. Depths of excavation were increased for each subparcel, then additional confirmation samples were collected. The process was repeated in an iterative manner until the soil with dieldrin concentrations greater than the cleanup goal of 0.035 milligrams per kilogram(mg/kg)dieldrin had been removed and placed in to the entombment trench. The depth of soil removed from individual subparcels ranged from 0.5 feet to two feet (24 inches) below original grade. Approximately 33,000 in-place cubic yards of waste soil were anticipated to be excavated and deposited in the encapsulation area.Additional soil volumes were excavated in consultation with DTSC after receipt of confirmation sampling results that indicated that excavation to depths of up to 24 inches below original site grade were necessary. The actual volume of soil removed and placed in the entombment area was approximately 70,000 cubic yards. 3.4.1 Temporary Storage Operations Temporary storage was not anticipated or required as part of this removal action.