2007-11-20_REVISION - M1982015 (14)

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' Petroleum impacts did spread laterally into the surrounding soils ranging from approximately 3 to 12 feet from the centerline of the SWE. Soil conditions were highly ' variable but generally consisted of silty and sandy clay from the ground surface to 6 to 8 feet bgs. Fine sands ranging to poorly sorted and gravel was present at depths ranging from 6 to 12 feet bgs. Much of the upper ground surface was frozen at the time of the excavation but this material was generally not impacted by gasoline. However, if surface ' material that was encountered appeared to be contaminated, it was removed for off-site disposal. ' The SWE was backfilled by using clean soil from the northern portion of the site within one week of completion of the excavation. The soil was compacted to 95% proctor in preparation of re-excavating the slurry wall trench to prevent caving. ' 4.2 Slurry Holding Trench Excavation - (February 13-20, 2007) Based on the initial sampling and laboratory analysis of the material in the "slurry holding ' trench" (SHT), this material was determined to be characteristically hazardous at that time. In the ICAP, E-21 proposed to handle this material as a characteristically hazardous waste. Based on meetings, teleconferences and email correspondence, the ' addition of cement as an absorbent was approved by the CDPHE to assist in stabilizing the slurry mud in-place in an effort to make it a consistency that was possible to safely handle and remove. This was performed from approximately January 11, 2007 to February 2, 2007. A photolog of site activities for work performed on February 2, 2007 is ' included in Appendix 3. After all the material in the SHT was handled, E-21 resampled the SHT material for ' waste characterization. Based on the lab results, none of the samples exceeded the benzene TCLP limit of 0.5 mg/I or 10 mg/Kg for benzene. The results of this sampling are summarized on Table 2B. The laboratory analytical report is included in Appendix 4. ' The analysis was submitted to CDPHE and excavation and disposal of this material was scheduled to begin on February 13, 2007 following conditional approval by CDPHE as discussed in the February 6, 2007 email. On February 13, 2007, E-21 and GeoCon personnel initiated excavation and disposal of the material in the SHT. As discussed in the original ICAP, the slurry and some impacted sidewall soils were stabilized using cement. Post-stabilization BTEX and TCLP ' analysis indicated that the material was not characteristically hazardous and was acceptable for disposal at a properly licensed solid waste landfill disposal facility. A photolog of excavation work during this period is included in Appendix 3. ' The soils were excavated using a track hoe operated by GeoCon personnel. Excavation of impacted material extended from station marker (sm) 19+00 to 22+90. As soil was excavated, the material in the track hoe bucket was screened for proper disposal ' determination using a calibrated PID to determine qualitative concentrations of petroleum hydrocarbons. Visual and olfactoral observations were also used to determine relative petroleum hydrocarbon impacts. Measurements were recorded in ' approximately 10 to 25-foot intervals along the length of the excavation. 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 under special waste manifest to the Allied Waste Landfill at 8480 Tower Road in Commerce City, Colorado. When soil was encountered that did not appear contaminated by hydrocarbons based on PID measurements or sight and smell 3