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Final AOC 65 Interim Removal Action Report
Section 3 - Response Actions
3.1 - Building 90 Interim Removal Actions
The purpose of the IRA was to remove or significantly reduce the levels of VOCs present in the shallow soil material in and around Building 90. The removal activities conducted for Building 90 included the characterization of contaminants present in the soil zone and removal of impacted soil material from specific areas west of the building. This removal included impacted soils along a drain line and a drainage ditch west of Building 90 which exhibited high levels of VOCs. A soil vapor extraction (SVE) system was installed inside Building 90 to evaluate subslab ventilation as a removal option for contaminants underlying the building and that is, inaccessible to excavation.
3.1.1 Interim Removal Actions at Building 90
The exact location and extent of excavations performed at AOC-65 were determined from results of the exterior soil borings. Asphalt and soil were excavated along the abandoned drainpipe and the drainage ditch near the drainpipe outfall. The surface area exposed during the excavation was 6,033 ft2, which included portions of the asphalt driveway and the drainage ditch. The area of excavation is outlined in Figure 3-1. Photographs of the IRA activities are provided in Appendix D.
The total volume of excavated media was approximately 1,255 yds3. This volume included a significant portion of concrete from the drainage culverts in the ditch and asphalt from the paved surface. The asphalt was approximately six inches thick throughout the paved portion of the excavation whereas the average depth of the excavation was two feet below grade.
Six gutters from Building 90 were piped underneath the asphalt drive west of Building 90 and discharged into the drainage ditch. Portions of the gutter system inside the excavation area were excavated as part of the IRA. The remaining gutters were plugged with concrete slurry. The remaining roof drainage gutter network was modified to discharge southwest of Building 90.
The excavated material was handled and disposed of based on waste characterization testing. Sampling methodology and quality control are described in the SAP addenda is this document truly still draft (AOC-65 Treatability Study Sampling and Analysis Plan Addendum, Parsons, April 2002). Waste manifests for the excavated material are presented in Appendix C and the letter that was sent to CSSA, summarizing the waste characterization analytical data and generator information and containing the laboratory data reports for characterization samples provided to the landfill operator, is provided in Appendix E. All excavated material from AOC-65 was categorized as Class 2 nonhazardous waste as determined by waste characterization testing.
3.2 - Post-Excavation Confirmation Sampling
Confirmation samples were collected from the drainpipe excavation and from the drainage ditch excavation. A minimum of two samples were required to represent each excavated segment of pipe or ditch, or one sample for each 500 ft2 exposed area by the project specific data quality objectives (DQOs). A total of 8 confirmation soil samples were collected from the excavated area at AOC-65 (Figure 3-1).
Based on the estimated total square footage of the excavated areas (6,033 ft2), the number of confirmation samples collected was not sufficient to meet the project DQOs requirement (Project DQOs, TO0058). The correct number of confirmation samples was not collected in the field due to an error in calculating the area of the asphalt driveway excavation and erroneously excluding the drainage ditch excavation area from the total area tally. However, sufficient data to support this DQO may exist since two additional soil boring samples were collected in the ditch (SB-25 and SB-22) and two soil samples were collected from near-surface borings inside the excavation area (SB-19 and SB-20). These samples had no detectable levels of VOC contamination, although
SB-20 did contain low levels (less than 1.0 mg/kg) of PCBs.
The analyte concentrations detected in the confirmation samples are provided in Table 3-1. All VOC detections were below reporting limits (RLs). Of the metals constituents detected, cadmium, chromium, zinc, copper, and lead were present at concentrations above background levels.
Sample CS-AOC65-SS-02 had a lead concentration of 765.55 mg/kg that exceeded the background lead level of 84.5 mg/kg for CSSA soils and was the highest lead level observed. Sample CS-AOC65-SS-02 also had chromium (77.51 mg/kg) and zinc (187.11 mg/kg) concentrations greater than their respective background levels. The highest zinc concentration of 196.38 mg/kg occurred in sample CS‑AOC65-SS-04, exceeding the background zinc level of 73.2 mg/kg for CSSA soils. This sample also displayed elevated levels of lead, cadmium, and copper at 393.09 mg/kg, 17.49 mg/kg, and 64.3 mg/kg, respectively. Closure of the site under RRS1 is not possible at this time based on the concentrations of lead, zinc, chromium, copper, and cadmium found above background levels.
Backfill and Asphalt Resurfacing
Following excavation of the drain line and ditch, these areas were backfilled with clean soil and graded. The areas were then resurfaced with asphalt and concrete to facilitate drainage away from Building 90. Construction was completed by Total Remediation and Excavation Technologies, Inc. (TRET) and construction quality assurance and oversight was provided by Parsons personnel. As-built engineering drawings documenting post-remediation construction details are presented in Figure 3.2 and Figure 3.3.
The ground surface was restored to match the surrounding area in the vicinity of the excavation. Replacement of the asphalt pavement patch included a 2-inch surface course and a 4-inch base course. The replacement asphalt was overlain on approximately 8 inches of flexible sub-base compacted to 95% standard Proctor density.
During the course of the restoration activities, numerous site improvements were made to improve drainage on the site. The drainage improvements were implemented to reduce the amount of surface water infiltration through VOC impacted media around Building 90 during and after rainfall events. Drainage from the building gutters was rerouted after completion of the IRA so that drainage from the gutters was diverted from potential VOC source areas.
The existing drainage ditch was re-graded so that the highest point of the ditch is in the northwestern corner. In terms of drainage this effectively split the ditch into a northern portion, which flows to the east, and a western portion, which flows to the south. The entire drainage ditch was lined with concrete. The concrete was rolled against the rock face when an exposed rock face was present, effectively tying the drainage ditch into the rock wall allowing it to collect water from transient seepage. The asphalt from the existing roadway was extended to abut the concrete drainage ditch for much of its length.
In the western portion of the drainage ditch, the two preexisting culverts were removed. Where the southern culvert was removed, the alignment of the drainage ditch was altered slightly to allow it to follow the natural topography. This caused the drainage ditch to bend towards the west before continuing to the south. The land around the bend in the drainage ditch was re-graded as necessary to ensure that the topography sloped toward the ditch, allowing the ditch to capture surface runoff from the paved areas and field west of Building 90. The western portion of the drainage ditch was lined with concrete to approximately 150 feet south of Building 90 and terminates on the southern side of a series of faults located south of Building 90. The terminus of the drainage ditch was flared slightly and several large boulders were placed in and downstream of the concrete to dissipate the flow velocity and minimize soil erosion.
In the northern portion of the drainage ditch, the concrete was extended to the eastern edge of the rock wall. At the edge of the rock wall a drain box was installed to collect flow from the drainage ditch and a natural swale that flanks the rock wall and extends to the north. The swale receives a significant amount of runoff from the parking lot and driveway adjacent to the guardhouse. A concrete apron, which tied into the drainage ditch and wrapped around the rock wall, was constructed to direct runoff from the swale into the drain box. Downstream of the apron the soil was compacted and dressed with compacted stone to minimize erosion. A 12-inch PVC pipe exits the bottom of the drain box and slopes to the east, where it enters another newly installed drain box.
The second drain box was installed to collect runoff from the roadway and parking lot of Building 98. A concrete apron was poured to direct the runoff into the drain box. The concrete apron extends approximately 100 feet to the north and replaces the degraded and eroded asphalt that existed previously. A 12-inch PVC pipe conveys flow to the east, underneath the roadway, into the large ditch paralleling the abandoned railroad tracks. Several large boulders were placed at the pipes outfall, to help reduce the water�s velocity and minimize washout and erosion.