ARCHIVED REPORTS_REMOVAL ACTION COMPLETION REPORT

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Draft Removal Action Completion Report Neighborhood C, Mountain House,CA Page 17 8.0 FINAL GRADING AND PAVING OF GREAT VALLEY PARKWAY Upon completion of the impacted soil movement, the Site was graded and balanced using remaining soil. No imported fill soil was used, and all necessary soil used to balance the Site originated from previously evaluated areas of Neighborhood C. Final installation of asphalt paving of Great Valley Parkway was concluded on 9.0 CONCLUSIONS AND RECOMMENDATIONS 9.1 VARIANCE FROM THE RAW During the removal action, unexpected conditions necessitated implementation of modifications to soil removal activities as presented in the RAW. Field personnel notified the Site Manager when unexpected conditions warranted deviations from the RAW. DTSC was notified of the modifications immediately and the DTSC Project Manager was consulted before implementing the modifications. Modifications or variances to the approved RAW were documented in the field logbook and are described in the previous sections. A summary of notable variances from the RAW include: • Instead of analyzing the remaining three confirmation samples for each subparcel as described in the RAW, MHD elected to take a more conservative approach and remove additional soil from the entire subparcel until the cleanup goal was achieved. • The encapsulation trench was excavated significantly deeper than planned. A total of approximately 70,000 cubic yards of dieldrin-impacted soil was excavated from the removal area and placed in the entombment area. An additional engineering control, a fabric marker barrier, was emplaced over the dieldrin-containing soil in Great Valley Parkway. These variances are not considered to have significant impact on conditions anticipated in the RAW, on the ultimate disposition of waste soil, or the protectiveness of the waste soil encapsulation to public health or the environment. The addition of the warning fabric will enhance the protectiveness of the waste soil encapsulation. • Waste characterization samples were not included in the analyzed composite sample from the bottom six to eight feet of the encapsulation trench from 1,400 feet north of Grant Line Road to the north end of the trench. However, due to the fact that 10 of 14 encapsulation zones exceeded the action level for administrative controls, MHD will take the conservative approach that the entire waste encapsulation be subject to administrative controls. • Dieldrin fenceline air sampling was performed at a lower flow rate, at a different laboratory, using a slightly different analytical method, and with resultant different detection limits than those specified in the RAW. This was done in order to comply with the analytical method guidelines and to provide complete coverage during an entire work day. This is not considered a significant variance due to the dieldrin was not detected in the air sampling results, and because dust monitoring results rarely exceeded fenceline action levels. • Discrete depth sampling was performed outside of the scope of the RAW to provide guidance to MHD and DeSilva regarding excavation depth required to achieve the cleanup goal within the subparcels requiring additional excavation. The results of the discrete depth sampling were not used in lieu of confirmation sampling results and therefore this is not considered a significant variance from the RAW. • Additional sampling was required from the haul roads, transit road, and equipment parking area to confirm that the COC had not been spread outside of the removal or encapsulation areas.