2007-11-20_REVISION - M1982015 (13)

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Bayshore Pipeline Release - Spill Incident No.2006-1029 August 2007 Groundwater Monitoring and Remediation Progress Report Page 3 of 5 Groundwater Laboratory Analysis and Extent of Dissolved Phase Petroleum Impacts The groundwater samples were submitted to Origins for analysis of BTEX, TVPH and MTBE by EPA Method 82608. Based on the results, dissolved phase petroleum impacts are still present in all the wells generally north of the slurry wall and in wells MW-18, MW-19 and MW-20 on the south side of the slurry wall. MTBE was not detected in any of the 28 water samples analyzed during this sampling event. The groundwater laboratory results are summarized on Table 3. The laboratory reports are included in Appendix 3. Please note that monitoring well MW-29 was installed on August 15, 2007 and sampled on August 20, 2007. Monitoring wells MW-2R was inadvertently not sampled and MW- 28 was dry. Based on the laboratory results, the extent of the dissolved phase plume is defined to the north side of the slurry wall and west of the spill area by MW-26 and MW-27. However, the extent of the plume is not defined to the east of the pipeline as indicated by elevated BTEX concentrations in MW-25 and MW-29. Dissolved phase impacts found in MW-25 are likely the result of migration of contaminants to the northeast by the prevailing groundwater flow that was documented during the spill and prior to completion of the slurry wall. Dissolved phase impacts in MW-29 are likely the result of migration of contaminants northeast of the spill area that are now following the prevailing flow parallel to the slurry wall. Two additional wells will be installed to the east-northeast of the MW-29 to confirm the extent of the dissolved phase plume. Dissolved phase impacts remain present on the south side of the slurry wall as indicated by MW-18, MW-19 and MW-20 with the highest concentrations in the immediate proximity of the spill area. Neither of the samples collected from the St. Wain River contained any detectable petroleum compounds. The sample collected from a pool of water remaining in Quarry Pond #1 near the staff gauge did not contain any detectable petroleum compounds. The surface water laboratory results are summarized in Table 4. The laboratory report is included in Appendix 3. Remediation Well Installations Twenty one new 2" diameter air-sparge (S-2 to S-22) and eleven new 4" diameter vapor extraction (V- 2 to V-12) wells were installed between August 10 and 17, 2007 in preparation for the air-sparge / soil vapor extraction (AS/SVE) remediation program. All the wells were constructed using Schedule 40 ' PVC well materials. The well locations are shown on Figure 1A. In general, the sparge wells were drilled one foot into or below the top of the shale bedrock. A 2-foot ' screen (0.01 inch factory slotted screen) was installed on the bottom of the well and set in 10/20 clean silica sand. The sand pack was set approximately one foot above the top of the well screen followed by a bentonite seal that was hydrated in lifts using tap water. ' Sparge wells were concentrated along the north side of the slurry wall at 50 foot spacings parallel to the wall and 60 to 80 foot spacings perpendicular to the wall. Based on the petroleum concentrations in MW-29, additional remediation wells may need to be installed further to the east-northeast of the ' existing sparge well array. However, it is expected once remediation is started, increase oxygen produced by the sparge wells combined with the removal of vapor phase petroleum impacts in overlying soils will quickly reduce downgradient petroleum impacts and additional wells may not be needed.