2007-11-20_REVISION - M1982015 (14)

Home Browse Search

gallons was pumped from the excavation. The lab results and report from this sampling are in Appendix 4. C 0 1 1 Based on the high BTEX content, the water was removed from the site by ACI Services for treatment at the Raritan Centralized Waste Water Plant located in Englewood, Colorado. The waste disposal manifest is located in Appendix 6. 4.4 Post Excavation Slurry and Backfill Results The slurry wall construction work resumed on February 15, 2007 at about sm 14+50. During the slurry wall excavation and construction, gasoline odors were detected by GeoCon while digging in the area of sm 18+00. This is immediately west of the pipeline release point. Occasional product globules were observed in the slurry wall excavation mud and a slight odor was present. E-21 performed air monitoring and collected slurry mud and backfill samples over the next few weeks to assess the level of the gasoline contamination in the slurry. The source of the contamination was likely petroleum impacts in soils at or below the groundwater interface which was not excavated during the gross removal process as to not mix impacted soils with groundwater. Residual contamination was expected to be encountered near the east and west side of the pipeline right-of-way near the release point, however the amount was not expected to be substantial. The results of the sampling are summarized on Table 2D. The laboratory reports are included in Appendix 4. A photolog showing the slurry wall construction work is included in Appendix 3. Based on the lab results, high BTEX concentrations were detected in the slurry backfill from samples collected at 18+40 and 19+00. The slurry wall was completed around the pipeline and in the right-of-way immediately after pipeline repairs were made in November 2007. During the gross removal process, some of the most heavily contaminated soil was located immediately east of the pipeline (approximately 18+75 to 19+50. Low level residual impacts near or below the water table were likely excavated in the area immediately west of the pipeline right-of-way. Then, during resuming excavation at about 18+75, higher level residual impacted soil may have been excavated during the slurry wall excavation. This material was blended with cement and bentonite to make the slurry wall mixture. The mixture was then placed into the slurry wall excavation where it hardened and become impermeable. Thus, any BTEX contamination that may have been incorporated into the mixture will likely be immobilized and attenuate rapidly with the cement. 5.0 Surface Water Sampling Results During the course of this project, surface water bodies in the proximity of the release were repeatedly sampled including; the St. Vrain River, Sunset Lake (referred to as Quarry Pond #1), Big Lake (referred to as Quarry Pond #2), and the unnamed quarry pond located just east of the 1-25 frontage road and west of Sunset Lake. The sampling was performed to determine if petroleum impacts may have migrated through the subsurface to impact the surrounding water bodies and/ to verify pond water was free of BTEX compounds and acceptable to pump from the ponds to the St. Wain River for pond draining and construction purposes. The initial sampling of the quarry ponds and the St. Wain River was performed on December 18, 2006. Periodic sampling was performed until April 21, 2007. The sampling locations are shown on Figure 1. The summary of the sampling results is included in Table 3. The laboratory reports are included in Appendix 4. 6