COPA - PCBs and Superfund in Bloomington, Indiana

Lemon Lane Final Report
June, 2001

6.0 PREPARATION OF INTERIM CAP SURFACE

6.1 General Description of RCRA Cap Construction

As part of the closure of the LL Landfill, waste material that met the SOW criteria could be consolidated on site. Approximately 37,200 cy of waste, consisting mainly of ash and soils, met the SOW requirements for PCB content and were consolidated on site. This waste was contoured and graded to meet the slope requirements specified in the Lemon Lane Final Cap Design Report issued on October 18, 2000. The waste was consolidated and graded forming a high point at the east central area of the consolidation. Actual final slopes established flowing away from this peak ranged from 5.5% to 14% and are shown in Figure 9. The graded surface of the waste was proof-rolled prior to placement of one foot of cushion soil. The cushion soil was compacted and tested to insure that adequate compaction was achieved. On top of the cushion soil a geosynthetic clay liner (GCL) was installed. Once the GCL was installed it was immediately covered with a 40 mil very flexible polyethylene (VFPE) geomembrane. A geosynthetic drainage layer was installed over the goemembrane. A 24 inch protective cover soil layer was then placed over the drainage layer.

Figure 7 is an aerial photo showing most of these components being installed. The technical specifications for materials and installation of the RCRA cap components are contained in Appendix G of the Final Cap Design Report. The following sections provide a brief description of the steps identified above. For a more detailed description that includes the associated field documentation, refer to Golder Certification Report and the PSARA Technology Certification Report in Appendix G of this report.

6.2 Proof Rolling and Inspection of the Waste Surfac

e Once the final grading of the waste was completed in the consolidation area, the surface of the waste was compacted and the surface proof rolled prior to placement of the 1 foot of cushion soil. There was no target density requirement for the waste. Proof rolling consisted of several passes of an empty off-road Volvo A25C dump truck over the waste with no signs of excessive pumping, movement or sloughing of the waste. Two areas showed signs of waste material pumping when proof rolled. One was in the northwest and the other along the south slope. In both cases the waste material was reworked to promote drying and eventually the PSARA Technology inspector accepted the proof rolling. Once the waste surface was accepted after the proof rolling, the finished surface elevations of the waste surface were surveyed at selected locations. Smith Neubecker & Associates, Inc. (SNA) surveyed as-built elevations of the waste on a 50 ft. by 50 ft. grid system over the entire cap and at break points of the slope. This data served as a reference to verify the required thickness of the subsequent soil layers was achieved. Figure 9 shows the survey point locations and numbers. The table included on the drawing lists the initial waste elevation and thickness for subsequent soil layers.

6.3 Placement and Compaction of the Cushion Soil

The proof rolled compacted waste surface became the subgrade for one foot of cushion soil. This cushion soil then became a uniform bedding layer for the geosynthetic materials used to construct the RCRA cap.

The cushion soil was obtained from several sources. These sources include the stockpiled bedding material from beneath the previous Hypalon cover, from the on site borrow area and purchased soil supplied by Hanna Trucking. All these sources of soil were sampled and analyzed to insure that they met the quality control requirements in the technical specifications. It should be noted that in general anytime that borrow clay was used it was placed directly on the waste about 6 to 9 inches thick. Either the Hypalon bedding material or purchase cushion material was placed over the borrow material to obtain the total of twelve inches of cushion soil. Placing bedding or purchased cushion soil over the clay insured that a very consistent quality of material was in place as a subgrade for the GCL. The cushion soil was compacted as it was placed. Prior to the placement of the geosynthetic clay layer, the cushion soil was proof rolled to identify any soft areas over the surface of the consolidation materials. The proof rolling was done using a smooth drum roller. Once the area was proof rolled the surface was inspected by representatives from Envirocon, the geosynthetic installer and Colder Associates, responsible for onsite CQA (construction quality assurance). Occasionally during inspection rocks that were greater than one inch were found and removed. In general the cushion soil surface was substantially free from particles larger than 1 inch.

The detailed documentation is provided in Appendix G for the compaction test performed on the cushion soil and for the inspection of the cushion soil surface. The cushion soil compaction requirement of 90% of the maximum standard proctor dry density was met at all locations tested. Thelen Associates, Inc., 2140 Watcross Road, Cincinnati, Ohio, performed all compaction testing required for this project. In a few cases cushion soils had to be reworked and recompacted before the material passed compaction testing. Inspection forms were prepared and signed by both Colder and Envirocon representatives to document acceptance of the cushion soil surface prior to placement of the GCL. A detailed discussion of the cushion soil surface inspection and the inspection report is contained in Appendix G.

Once compacted, the thickness of one foot of the cushion soil was confirmed by survey. Any areas that were less than 1 foot thick were covered with additional soil to obtain the required thickness. Documentation for the cushion soil thickness is contained on the table included in Figure 9.

6.4 Installation of Piezometers

A total of six piezometers were installed after the cushion soil was placed and compacted. One piezometer (PZ-AS) was installed at the deepest part of the fill-soil horizon in the southern sink and one piezometer (PZ-AD) was installed in the deepest bedrock location under the cap in the southern sink. Also a pair of piezometers, one at the deepest fill-soil horizon (PZ-BS) and one at the deepest bedrock location under the cap (PZ-BD) were placed in the north sinkhole. PZ-AS is approximately 30 feet southwest of where PZ-1A was located prior to excavation and PZ-BS is at the approximate location where PZ-2A was located prior to excavation. These piezometers were installed within the LOO to monitor water levels at the fill-soil interface and the soil-bedrock interface in the deepest point of the two sinkholes. The deep PZ was screened across the soil-bedrock interface and the shallow PZ screened across the fill-soil interface. Two additional piezometers were installed on the west edge of the landfill just outside the LOC but within the limits of the RCRA cap materials. These were PZ-C and PZ-D. Both of these were installed with screens located in a recovery zone constructed of pea gravel at the top of bedrock. Based on the PCB levels measured, these locations may be used as recovery wells.

The locations of each of these piezometers are shown on Figure 9, with the surveyed coordinates for each provided on the table included on this figure. Also provided on this table are the elevations and screen depths. (Note: At the time of demobilization from the site the piezometers were not completed at the surface. Therefore the exact surface elevation was not available. This information will be provided at a later date.) Details of construction for the piezometers are provided in the installation logs contained in Appendix D.

All drilling and installation work for the six piezometers was performed by American Drilling Services of Indianapolis, Indiana, with oversight provided by Viacom. The holes for the piezometer casings were drilled by the hollow stem auger method. Each piezometer casing installation was finished at the surface by placing bentonite grout between the riser pipe and the wall of the borehole. In all cases the bentonite seal was carried through at least the full thickness of the cushion soil layer. Booting of the PVC riser pipe was completed as shown on Final Cap Design Drawing 11. The concrete pad was not installed due to poor weather conditions. This pad will be completed in early spring 2001 when weather and site surface conditions permit. Following completion of the installation a Record of Water Well Installation Logs will be prepared and submitted to the Indiana Department of Natural Resources, Division of Water.