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 4 of 5 The vapor extraction wells were drilled to depths of 11 to 18 feet depending on the ground surface elevation and anticipated depth to groundwater. A 5-foot or 10-foot screen (0.01 inch factory slotted) was installed on the bottom of the well and set in 10/20 clean silica sand followed by a hydrated bentonite seal to the ground surface. The vapor extraction wells were placed at 80 to 120 foot spacings and between the sparge wells. The well completion details are included in Appendix 1. No soil or groundwater samples were collected from the remediation wells. Response to CDPHE Comments There were several comments or requested modifications recommended in your letter dated July 16, 2007 which is included in Appendix 4. Our response to the comments is included below. 1. A schedule for implementation of the groundwater remediation system is included in Appendix 5. 2. Air emissions data has been collected and analyzed. An APEN will be submitted for review and approval on an expedited basis. It is expected the air emissions will exceed allowable limits for benzene and accordingly, a thermal oxidizer is planned for emissions treatment. ' 3. Monitoring wells MW-28 and MW-29 were installed generally northeast of MW-4R and MW- 5R. It appears the extent of groundwater plume is defined by MW-28 as this well is dry. Thus groundwater "pinches out" in this area and dissolved phase impacts are not present. However, the plume was not delineated by MW-29 and additional wells will be installed further ' to the east. 4. The well design was re-evaluated and we opted to not install nested wells. Air sparge wells ' are still spaced around 50 feet apart parallel to the slurry wall and the vapor extraction wells are at 100 foot spacings. All the wells will have individual control valves so that modifications can be made in the field to optimize the remediation well radius of influence. 5. The remediation program will concentrate on treating the eastern end of the plume first. 6. Two sparge wells and two vapor extraction wells were placed on the south side of the slurry wall near MW-18 and MW-19 to treat petroleum impacts in that area. It does not appear necessary to perform remediation to areas east of MW-19 on the south side of the slurry wall. In the event petroleum impacts are encountered in wells further to the east, additional remediation wells will be installed and added to the remediation system. 7. The slurry wall extends for approximately 1 mile to the northeast along the south shore of Big Lake. The slurry wall extends approximately 8 to 10 feet below the top of the bedrock for a total depth of approximately 30 feet below the ground surface. 8. MTBE was analyzed for in all samples collected during the August 11, 2007 sampling event. MTBE was not detected in any of the samples. Thus, it will not be analyzed for in future sampling events. 9. This report documents the activities you requested. 10. The items requested in this request will be submitted under separate cover.