ARCHIVED REPORTS_REMOVAL ACTION COMPLETION REPORT

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Draft Removal Action Completion Report Neighborhood C, Mountain House,CA Page 9 3.6.3 Dust Control Plan During all phases of the removal action, appropriate dust control measures were implemented to minimize fugitive dust from the Site and ensure public and worker safety. Air monitoring action levels were used to determine whether dust control measures being employed were sufficient. Spray-applied water was the primary method of dust control on Site. Prior to commencement of excavation activities, excavation areas were sprayed with enough water to minimize dust generation as necessary. Water trucks equipped with spray attachments(or appropriate alternatives)were on-Site during soil movement activities. When the dust control methods described above were not sufficient to perform the removal action, additional water trucks were brought in to apply water to the soil as it was being picked up into the scrapers. No additional methods were necessary or implemented. As discussed in Section 3.6.1.1, the Air Monitoring Officer enforced dust action levels by informing the MHD representative onsite, who then informed the DeSilva foreman and equipment operators when dust concentrations were nearing action levels and ensuring that appropriate mitigation measures were taken if the action levels were exceeded. 4.0 SAMPLING PROCEDURES 4.1 CONFIRMATION SAMPLING The area to be excavated was divided into 41 approximately one-acre subparcels. The contractor staked the subparcel boundaries and confirmation sampling locations using GPS. The RAW specified that confirmation samples would be collected at a frequency of four samples per subparcel from the excavated area(40.6 acres), for a total of 164 samples, 41 primary analyses, and that four duplicate samples would be collected from the same location as their primary counterparts and analyzed for the same constituent. Confirmation sampling was conducted in general accordance with the QAPP included in the Appendix G of the RAW. Variances from the RAW were necessary because the vertical extent of the dieldrin exceeding the cleanup goal was greater than anticipated in the RAW. A total of 127 primary and 7 duplicate confirmation samples were ultimately collected and analyzed. The actual ratio of primary samples to duplicate samples was 18:1, which was greater than the 10:1 ratio included in the RAW but nearly double the number anticipated in the RAW. Confirmation and duplicate samples were collected by inserting laboratory-supplied glass jars directly into the soil. A stainless steel spoon or trowel was not used to place loose soil into the laboratory-supplied glass jars. Directly filling the jars eliminated the potential for cross-contamination and the need to decontaminate any tools. Each jar was labeled for sample identification, placed in chilled coolers, and delivered under chain-of-custody procedures to McCampbell Analytical Inc. (MAI) of Pittsburg, California. No equipment blank samples were necessary because no sampling equipment was used to collect confirmation samples. For each set of four samples per subparcel,one sample was initially analyzed for dieldrin by EPA Method 8081A. In variance to the RAW, the project team agreed that the sampling and analysis plan should be modified. Instead of analyzing the remaining three confirmation samples for each subparcel, additional excavation was conducted on the entire subparcel and confirmation sampling was repeated at the same location as before after removal. To help constrain additional excavation depth, discrete depth sampling was conducted as described in Section 4.2. From each subparcel where additional excavation was conducted, the contractor re-staked the confirmation sampling location and an additional confirmation sample was collected. Confirmation sample locations and final laboratory results are indicated on Figure 4,Appendix A.