TRANS MOUNTAIN PIPELINE ULC TRANSMOUNTAIN EXPANSION PROJECT PRELIMINARY GEOTECHNICAL HDD FEASIBILITY ASSESSMENT COQUIHALLA RIVER AT RK 1043.2 PROJECT NO.: 0095-150-14 DISTRIBUTION: DATE: Apr 04, 2014 RECIPIENT: 2 copies DOCUMENT NO.: 0095150-04-CQ BGC: 2 copies OTHER: 1 copy Trans Mountain Pipeline ULC Apr 04, 2014 Coquihalla River at RK 1043.2 Project No.: 0095-150-14 EXECUTIVE SUMMARY As part of the engineering design and assessment for the Trans Mountain Expansion Project, BGC Engineering Inc. (BGC) have been retained to complete geotechnical feasibility assessments for horizontal directional drilling (HDD) at select stream crossings along the proposed pipeline corridor. In August 2013, BGC supervised the drilling of two boreholes adjacent to the proposed HDD alignment at the Coquihalla River in Hope BC. WorleyParsons, under subcontract to BGC, completed geophysical surveys at the same site in July 2013. Results from the scour analysis estimate a maximum scour depth of approximately 2.5 m below the thawleg during a 200-year flood event. Given this result, the depth of cover above the proposed HDD borepath remains adequate for the entire HDD length. The HDD exit point on the right (north) bank is inside the 200-year floodplain limit and is therefore at risk of inundation should a large scale flood event occur during construction. However, because the exit point remains on the inside of the channel meander, incident energy is low therefore bank erosion is not anticipated to be significant. Further to this, based on a review of historical air photo imagery and a walk-over of the site, no significant bank instability was observed adjacent to the proposed HDD alignment. Consequently, it is not anticipated that channel migration caused by bank erosion would be sufficient to impact upon the proposed HDD alignment. However, overbank flows could result in localized scour. Therefore, additional design measures should be considered for the short section of the pipeline that lies within the mapped floodplain to the east of the HDD exit point. In general, soils encountered during investigative drilling appear to be stable with no caving observed in either borehole with the exception of the uppermost approximately 12-13 m of the overlying fluvial deposit where borehole stability observations are not available due to the use of casing advancement. Within this region borehole instabilities may need to be addressed during construction through the use of casing. One isolated zone of complete drilling mud circulation loss was encountered in very coarse material at a depth between 21.0 m and 21.5 m. Thus, given the geological origin of the material in the vicinity of the HDD crossing, and the complete loss of circulation experienced during the investigative drilling, intermittent losses in circulation may be encountered along the HDD borepath, and will have to be addressed through the use of the appropriate drilling fluids, casing or by other techniques. The minimum separation depth between the proposed HDD borepath and the river bed is 26 m. Comparing this separation distance and the elevation change from the HDD entry point to the deepest point of the borepath (approximately 28 m), the risk of loss of drilling fluids into the river is anticipated to be low based on anticipated overburden resistance due to weight of the overlying strata. However, given the nature of the fluvial soil deposits observed during investigative drilling, this risk should be calculated and confirmed by the HDD design team using the borepath geometry for frictional losses and the HDD rig and pumping characteristics. 0095-150-04 HDD Geotechnical Feasibility Report - Coquihalla River Page i BGC ENGINEERING INC. Trans Mountain Pipeline ULC Apr 04, 2014 Coquihalla River at RK 1043.2 Project No.: 0095-150-14 Based on the observations from two boreholes and the geophysics, an HDD crossing at this location can be considered feasible from a geotechnical perspective. The conclusions presented herein are based solely on the limited scope of the investigation undertaken at this time for the purpose of obtaining preliminary information, and additional investigation should be considered as part of detailed design. 0095-150-04 HDD Geotechnical Feasibility Report - Coquihalla River Page ii BGC ENGINEERING INC. Trans Mountain Pipeline ULC Apr 04, 2014 Coquihalla River at RK 1043.2 Project No.: 0095-150-14 TABLE OF CONTENTS EXECUTIVE SUMMARY ...................................................................................................... i TABLE OF CONTENTS ...................................................................................................... iii LIST OF APPENDICES ...................................................................................................... iii LIST OF DRAWINGS.......................................................................................................... iv LIMITATIONS ...................................................................................................................... v 1.0 PROJECT DESCRIPTION ........................................................................................ 1 2.0 SCOPE OF WORK .................................................................................................... 3 3.0 SITE GEOLOGY AND HYDROTECHNICAL ASSESSMENT................................... 4 3.1. Overview .................................................................................................................. 4 3.2. Surficial Geology .................................................................................................... 5 3.3. Bedrock Geology .................................................................................................... 5 3.4. Hydrotechnical Assessment ................................................................................. 5 Flood Frequency Analysis .............................................................................. 5 Scour .............................................................................................................. 6 Bank Erosion .................................................................................................. 7 Avulsion .......................................................................................................... 9 4.0 SITE INVESTIGATION ............................................................................................ 10 4.1. Geotechnical Drilling Data ................................................................................... 10 4.2. Geophysical Survey Data .................................................................................... 11 5.0 INFERRED GEOTECHNICAL CONDITIONS ALONG HDD DRILL PATH ............ 13 5.1. Left Bank and River .............................................................................................. 13 5.2. Right Bank ............................................................................................................. 14 6.0 PRELIMINARY GEOTECHNICAL FEASIBILITY ASSESSMENT .......................... 15 6.1. General Considerations ....................................................................................... 15 6.2. Borepath Stability ................................................................................................. 15 6.3. Circulation & Potential for Loss of Fluids .......................................................... 15 7.0 CLOSURE ............................................................................................................... 17 REFERENCES ................................................................................................................... 1 8 LIST OF APPENDICES APPENDIX A HYDROTECHNICAL INVESTIGATION AND ANALYSIS METHODOLOGY APPENDIX B BOREHOLE LOGS APPENDIX C LABORATORY TEST RESULTS 0095-150-04 HDD Geotechnical Feasibility Report - Coquihalla River Page iii BGC ENGINEERING INC. Trans Mountain Pipeline ULC Apr 04, 2014 Coquihalla River at RK 1043.2 Project No.: 0095-150-14 LIST OF DRAWINGS DRAWING 1 Bank Erosion & Avulsion Review DRAWING 2 Interpreted Geological Section DRAWING 3 Geophysics Results DRAWING 4 Field Photo’s 0095-150-04 HDD Geotechnical Feasibility Report - Coquihalla River Page iv BGC ENGINEERING INC. Trans Mountain Pipeline ULC Apr 04, 2014 Coquihalla River at RK 1043.2 Project No.: 0095-150-14 LIMITATIONS BGC Engineering Inc. (BGC) prepared this document for Trans Mountain Pipeline ULC (Trans Mountain). The material in this report reflects the judgment of BGC staff based upon the information made available to BGC at the time of preparation of the report, including that information provided to it by Trans Mountain. Any use which a third party makes of this report or any reliance on decisions to be based on it is the responsibility of such third parties. BGC accepts no responsibility whatsoever for damages, loss, expenses, loss of profit or revenues, if any, suffered by any third party as a result of decisions made or actions based on this report. As a mutual protection to our client, the public and BGC, the report, and its drawings are submitted to Trans Mountain as confidential information for a specific project. Authorization for any use and/or publication of the report or any data, statements, conclusions or abstracts from or regarding the report and its drawings, through any form of print or electronic media, including without limitation, posting or reproductions of same on any website, is reserved by BGC, and is subject to BGC's prior written approval. Provided