2007-11-20_REVISION - M1982015 (14)

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' the distance, direction, and location of these wells across the St. Vrain River from the release area, it is unlikely the wells would be impacted by the pipeline release. ' A driveby survey was performed of properties in the area south of the St. Vrain River. There were no observable wells other then the ones noted above. There was no water wells observed on the Bayshore property located along the north side of the St. Vrain ' River. 4.0 Summary of Soil Excavation and Waste Disposal Activities ' 4.1 Slurry Wall Excavation (February 7-10. 2007) E-21 and GeoCon personnel conducted the excavation and disposal of petroleum- impacted soil and slurry material that was backfilled in the "slurry wall excavation" (SWE) soon after the pipeline release. The excavation activities were conducted from February 7 to 10, 2007. Due to icy, muddy and snowy conditions, construction or maintenance of ' temporary roads and loading pads were completed by GeoCon prior to each day of soil excavation and loading. Soils were then excavated using a track hoe operated by GeoCon personnel. Excavation of impacted material was started at station marker (sm) ' 15+50 which was determined to be the western limit of petroleum impacts based on the results of the test pit sampling in January 2007 and reported in the Integrated Corrective Action Plan (ICAP) prepared by E-21 in January 2007. As soils were excavated, the material in the trackhoe bucket was screened for disposal determination using a ' calibrated photo-ionization detector (PID) to determine qualitative concentrations of petroleum hydrocarbons. Visual and olfactoral observations were also used to determine petroleum hydrocarbon impacts. Measurements were recorded in 10 to 20 foot intervals along the slurry wall excavation. A photolog showing the excavation work is included in Appendix 3. ' In general, if PID measurements exceeded 100 parts per million (ppm) and/or petroleum impacts were evident by sight or smell, the soil was loaded directly into dump trucks for transport to the Allied Waste Landfill at 8480 Tower Road in Commerce City, Colorado. When soil was encountered that did not appear impacted by hydrocarbons based on PID measurements and visual / olfactoral indications, the material was placed in a portion of the excavation that was completed and excavation in that particular area discontinued. Confirmation soil samples were placed in 4-ounce laboratory supplied glass jars and ' submitted to Origins Laboratory in Denver, Colorado for analysis. The samples were analyzed for benzene, toluene, ethyl benzene and total xylenes (BTEX) by EPA Method 82608. Confirmation soil samples were submitted for analysis as lateral excavation ' neared station markers in 50 foot intervals. The excavation ranged in depth from 3 to 10 feet below the ground surface (bgs). The excavation ranged from approximately 6 to 20 feet in width. The soil laboratory results are shown on Table 2A. The extent of the excavation and sample locations are presented on Figures 3 and 4. The laboratory ' reports are included in Appendix 4. The excavation extended from sm 15+50 to sm 18+25. Excavating was not performed ' generally deeper than 10 feet due to sidewall caving, and to avoid mixing of contaminants with groundwater which at the time was approximately 10-12 feet bgs. Approximately 1,445 cubic yards of soil was excavated from this area. The excavation ' was discontinued at the west edge of the pipeline right-of-way as required by Rocky Mountain Pipeline (RMP) and as a safety measure. Also, most of the soil in the pipeline release area that was impacted in the right-of-way soon after the release appears to have been removed by RMP. 2