Contractor 2018-03-29 Trans Mountain Expansion Project Revision Geotechnical HDD Feasibility Contractor A Whitemud Creek at SSEID 005 KP 28.2 Revision Page 1 of 158 TMEP18-025 Trans Mountain Expansion Project Geotechnical HDD Feasibility Whitemud Creek at SSEID 005 KP 28.2 KMC Document #01-13283-S1-0000-PL-RPT-0035 RA Reviewed by Pages Rev No. Prepared by / Date Reviewed by / Date Approved by / Date Issued Type TMEP Revised Shannon Ashe Pete Quinn Alex Baumgard A Leo Moreno Issued for Review 2018-03-29 2018-03-29 2018-03-29 TRANS MOUNTAIN PIPELINE ULC TRANS MOUNTAIN EXPANSION PROJECT GEOTECHNICAL HDD FEASIBILITY ASSESSMENT WHITEMUD CREEK AT SSEID 005.5 KP 28.2 PROJECT NO.: 0095150-14 DATE: March 29, 2017 DOCUMENT NO.: TMEP18-025 Trans Mountain Pipeline ULC, Trans Mountain Expansion Project March 29, 2017 Geotechnical HDD Feasibility Assessment, Whitemud Creek at SSEID 005.5 KP 28.2 Project No.: 0095150-14 EXECUTIVE SUMMARY As part of the engineering design and assessment for the Trans Mountain Expansion Project (TMEP), BGC Engineering Inc. (BGC) has been retained to complete geotechnical feasibility assessments for trenchless crossings at select watercourse and overland crossings along the proposed pipeline corridor. This report provides a feasibility-level geotechnical assessment for a Horizontal Directional Drill (HDD) crossing of Whitemud Creek located at approximately Kilometer Post (KP) 28.2, in south Edmonton, Alberta. In June of 2013, Advisian Geophysics Group (a consulting division of WorleyParsons Group), under subcontract to BGC, completed geophysical surveys at the crossing along the proposed TMEP alignment. In June and July of 2014, BGC monitored the drilling of two geotechnical boreholes adjacent to the proposed TMEP alignment as part of an investigative program for four stream crossings identified by Universal Pegasus International (UPI). Initially, the proposed primary crossing method was planned as a conventional trench, with HDD identified as a contingency crossing method. A letter report (BGC 2015) provided geotechnical drilling data collected during the 2014 site investigation. HDD has recently been selected as the primary crossing method. The scope of work for this assessment included a desktop review of the relevant local and regional geological settings, existing available third-party data, examination of records of historic underground coal mining, 2013 and 2014 geophysical surveys and drilling, and compilation and interpretation of this data to provide, from a geotechnical perspective, an indication of the feasibility of the proposed 726 m long HDD crossing. The conclusions presented herein are based solely on the limited scope of the investigation undertaken at this time for the purpose of obtaining information for the feasibility study. Results of geotechnical drilling and the electrical resistivity tomography (ERT) survey indicate the subsurface soils at the proposed crossing consist of silty clays and silty sands/sandy silts that were very soft to firm at shallow depths, becoming very stiff below 10 m depth (on the west side of the crossing). The ERT survey results suggest the possible presence of buried channel fill, potentially including coarse gravel, cobbles and boulders, below the existing creek to a depth near the proposed borepath invert. A review of the location of the proposed HDD at the Whitemud Creek crossing relative to the inferred location of the mapped thalwegs of known nearby pre- glacial valleys (New Sarepta Ellerslie Valleys) suggests that they do not intersect. It may be possible that the ERT survey results indicate the presence of historic coal mines, rather than buried valley channel fill. Horseshoe Canyon Formation (HCF) Bedrock consisting of interbedded sandstone, claystone and siltstone was encountered at approximate depths of 3.4 mbgs and 15.4 mbgs in BH-BGC14-WM-01 and -02, respectively. While advancing through claystone and siltstone, thin layers of very stiff, light green, very high plasticity bentonite clay seams (plasticity index greater than 300%) were encountered at different depths, as noted in both boreholes. Coal 0095-150-14 HDD Geotechnical Feasibility Report - Whitemud Creek Page i BGC ENGINEERING INC. Trans Mountain Pipeline ULC, Trans Mountain Expansion Project March 29, 2017 Geotechnical HDD Feasibility Assessment, Whitemud Creek at SSEID 005.5 KP 28.2 Project No.: 0095150-14 seams containing black, shiny, heavily fractured coal were also encountered at different depths in the claystone and siltstone in both boreholes; a 1.5 m thick coal seam was observed at an elevation of 653.4 metres above sea level (masl) at BH-BGC14-WM-01, while a 1.1 m thick coal seam was observed at 651.4 masl at BH-BGC14-WM-02. Data from the online atlas of historic coal mines developed by Alberta Energy Regulator (AER 2017) indicates the approximate footprints of known mines, their years of operation, the target coal seam thickness, and the approximate depth of mining below ground surface. The proposed HDD alignment will pass through or along coal seams that have been targeted by known mines. Reported coal seam thicknesses, and therefore room heights, are 1.1 to 1.5 m. The maximum depth to the base of the known mine workings varies from 22.9 to 43.9 m below ground surface. In 2016, Southwest Edmonton Connector Project of ATCO Pipelines (ATCO) installed a 51 cm (20 inch) pipeline beneath Whitemud Creek using an HDD crossing method. Due to the likelihood of the proposed HDD borepath intersecting the former underground coal mines, a jet grouting program was implemented to fill voids with low-strength cement grout. The grout was injected into more than a hundred drilled holes and was completed in early 2017. No investigative geotechnical report, including grouting technical information, geophysical testing, coring of the area, nor HDD construction records were available to BGC at the time of writing. The proposed TMEP HDD alignment across Whitemud Creek is designed to be constructed within the Edmonton transportation and utility corridor (TUC), parallel to the ATCO pipeline. The current TMEP HDD alignment is proposed to be approximately 10 m south of, and with a maximum depth of approximately 16 m above, the ATCO HDD. Given the above, and based on the desktop study, available public information and results of the geotechnical and geophysical site investigation, an HDD at this location may be considered feasible from a geotechnical perspective provided the following concerns are addressed during detailed design and construction: Possible hazards related to historical coal mines: ○ TMEP HDD may encounter voids, timbers, steel rails or loose/destressed rock in or near the boundaries of old mine workings. The portion of the pipeline installed above old coal mines may be exposed to future subsidence (i.e., vertical displacement of the ground over the footprint of the mine, and horizontal ground displacement). The rocks above the mine workings may be disturbed, loosened, or partially destressed due to previous displacements following mining. Discontinuous (i.e., non-uniform) displacement may also be expected due to future failure of the mine roof and localized subsidence of the overlying strata. ○ Although no geotechnical data was available regarding the ATCO HDD construction, it is known that several mitigation measures were taken, including a jet grouting program to improve conditions at the depth of the old coal mines prior to the installation of the pipeline, and it is also understood that considerable subsurface investigation was completed to support the design of mitigation. 0095-150-14 HDD Geotechnical Feasibility Report - Whitemud Creek Page ii BGC ENGINEERING INC. Trans Mountain Pipeline ULC, Trans Mountain Expansion Project March 29, 2017 Geotechnical HDD Feasibility Assessment, Whitemud Creek at SSEID 005.5 KP 28.2 Project No.: 0095150-14 ○ Additional subsurface investigations (i.e., geotechnical drilling targeting the area where the proposed HDD will intersect the coal seams in the footprint of the old coal mines) will allow the project to assess the intersection zone and determine whether a grouting program or other mitigation measures would be necessary. ○ A review and evaluation of any available geotechnical or construction reports for the ATCO HDD, including borehole logs, borehole photos, geophysics, grouting design, and HDD construction records, may reduce the needed efforts of further geotechnical investigation. Coarse clasts in buried channel fill: There is some chance the bore may encounter coarse channel fill below the existing creek, as suggested by the ERT survey. If encountered, the coarse clasts could cause challenges for borepath stability, deflect the HDD borepath and/or damage the carrier pipe when it is pulled into the borepath. Deepening the borepath by up to about 20 m to avoid the area where channel fill deposits are inferred may be considered as a means of reducing uncertainty and associated risk; alternatively, additional geotechnical investigation may be considered to determine whether buried channel fills are present. Steering difficulties and borepath stability: The rocks above old mine workings may be disturbed, loosened, or partially destressed due to prior displacements associated with collapse and subsidence of old mine workings. The permeability of this disturbed rock mass may be higher than rock outside the mine footprints, and there may also be increased steering issues compared to surrounding undisturbed rock. Bedrock in the 2014 site investigation was observed to be poorly lithified (soil-like) with extremely weak to very weak strength, which may also contribute to steering issues (i.e., bit skipping on the harder materials encountered at flat angles). Loss of drilling fluids: Drilling conditions in the vicinity of old mine workings may be poor and lost circulation zones may be more common, compared to areas outside the mine footprints. Loss of fluid in these formations was observed during the geotechnical drilling. 100% fluid loss was noted from 13.4 to 16.5 mbgs (653.6 to 650.5 masl) at BH-BGC14- WM-01, beginning just above the point where a 1.5 m thick coal seam was intersected (from 653.4 to 651.9 masl).