TECHNICAL MEMO Tetra Tech Canada Inc. 150, 1715 Dickson Avenue Kelowna, BC V1Y 9G6 CANADA Tel 250.862.4832 Fax 250.862.2941 ISSUED FOR USE To: Bill Eisbrenner, P.Eng. Ven Tabenero, P.Eng. Date: April 23, 2020 c: Alex Izett, P.Eng. Don Gillespie, P.Eng. Memo No.: 2020-001_FarrellCk Revision 01 From: James Barr, P.Geo File: 704-V13103415-03 Subject: Preliminary ARD-ML Classification for Bedrock Material at the Farrell Creek Bridge and Highway Realignment Construction Area, Highway 29 Realignment – Rev 01 1.0 INTRODUCTION As part of BC Hydro’s Site C Clean Energy Project, filling of the Site C Reservoir will require realignment of 32 km of Highway 29 and the construction of five new bridge crossings. R.F. Binnie & Associates Ltd. (Binnie) have been contracted as Coordinating Professional Engineers for the realignment of Highway 29 including these bridges. Tetra Tech Canada Inc. (Tetra Tech) has been retained by BC Hydro and Power Authority (BC Hydro) as part of the BC Hydro Owners Engineer team for the delivery of the Highway 29 Realignment Project, and to provide services to Binnie as part of the Farrell Creek Bridge design in respect to the management and mitigation of potential acid rock drainage (ARD) and metal leaching (ML) from bedrock material. The Farrell Creek Bridge project is located along the future Highway 29 alignment and is designed as a 6-span bridge approximately 400 m long. The bridge design requires excavation of bedrock materials for construction of the eastern bridge abutment, pile foundations (rock sockets) at both abutments and all piers, and some temporary excavation for Pier 5 pile cap construction. Additionally, disturbance of bedrock is possible during the preparation and construction of the Realigned Channel, and small volumes of bedrock may be exposed in several other unplanned locations related to the road and drainage construction activities. Bedrock underlying the Farrell Creek Bridge abutments is marine shale of the Shaftesbury Formation, part of the Fort St. John Group. Testing of Shaftesbury Formation shales at several locations along the Highway 29 realignment has confirmed the bedrock material has potential for ARD-ML. Occurrence of ARD is a result of the oxidation of sulphide minerals when exposed to oxygen and water resulting in acidification of run-off water. It is a naturally occurring process that can be exacerbated by rock disturbances, such as excavation. The occurrence of ML is the release of elemental (e.g., metal) constituents into solution as leachate from the rock mineral mass and can occur under acidic, neutral, or alkaline drainage conditions. In accordance with the Site C Clean Energy Project Construction Environmental Management Plan (CEMP) (BC Hydro, rev 6.1, December 12, 2019) Appendix E (rev. 5.2, July 26, 2016) and the Environmental Management Plan Site C Clean Energy Project Highway 29 Realignment (rev. 11, March 3, 2020) the project has adopted measures for management of potentially ARD-ML generating materials so that there is an insignificant change in pH, total metals, and dissolved metals downstream of construction as a result of project construction activities. This memo discusses the current site conditions at the proposed Farrell Creek Bridge, potential implications for management of ARD-ML based on the currently proposed development plan for the site, provides options for mitigating ARD-ML, and recommendations for management and monitoring activities. Engineering of geotechnical
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TECHNICAL MEMO
Tetra Tech Canada Inc. 150, 1715 Dickson Avenue
Kelowna, BC V1Y 9G6 CANADA Tel 250.862.4832 Fax 250.862.2941
ISSUED FOR USE
To: Bill Eisbrenner, P.Eng.
Ven Tabenero, P.Eng.
Date: April 23, 2020
c: Alex Izett, P.Eng.
Don Gillespie, P.Eng.
Memo No.: 2020-001_FarrellCk
Revision 01
From: James Barr, P.Geo File: 704-V13103415-03
Subject: Preliminary ARD-ML Classification for Bedrock Material
at the Farrell Creek Bridge and Highway Realignment
Construction Area, Highway 29 Realignment – Rev 01
1.0 INTRODUCTION
As part of BC Hydro’s Site C Clean Energy Project, filling of the Site C Reservoir will require realignment of 32 km
of Highway 29 and the construction of five new bridge crossings. R.F. Binnie & Associates Ltd. (Binnie) have been
contracted as Coordinating Professional Engineers for the realignment of Highway 29 including these bridges. Tetra
Tech Canada Inc. (Tetra Tech) has been retained by BC Hydro and Power Authority (BC Hydro) as part of the BC
Hydro Owners Engineer team for the delivery of the Highway 29 Realignment Project, and to provide services to
Binnie as part of the Farrell Creek Bridge design in respect to the management and mitigation of potential acid rock
drainage (ARD) and metal leaching (ML) from bedrock material.
The Farrell Creek Bridge project is located along the future Highway 29 alignment and is designed as a 6-span
bridge approximately 400 m long. The bridge design requires excavation of bedrock materials for construction of
the eastern bridge abutment, pile foundations (rock sockets) at both abutments and all piers, and some temporary
excavation for Pier 5 pile cap construction. Additionally, disturbance of bedrock is possible during the preparation
and construction of the Realigned Channel, and small volumes of bedrock may be exposed in several other
unplanned locations related to the road and drainage construction activities. Bedrock underlying the Farrell Creek
Bridge abutments is marine shale of the Shaftesbury Formation, part of the Fort St. John Group. Testing of
Shaftesbury Formation shales at several locations along the Highway 29 realignment has confirmed the bedrock
material has potential for ARD-ML.
Occurrence of ARD is a result of the oxidation of sulphide minerals when exposed to oxygen and water resulting in
acidification of run-off water. It is a naturally occurring process that can be exacerbated by rock disturbances, such
as excavation. The occurrence of ML is the release of elemental (e.g., metal) constituents into solution as leachate
from the rock mineral mass and can occur under acidic, neutral, or alkaline drainage conditions.
In accordance with the Site C Clean Energy Project Construction Environmental Management Plan (CEMP)
(BC Hydro, rev 6.1, December 12, 2019) Appendix E (rev. 5.2, July 26, 2016) and the Environmental Management
Plan Site C Clean Energy Project Highway 29 Realignment (rev. 11, March 3, 2020) the project has adopted
measures for management of potentially ARD-ML generating materials so that there is an insignificant change in
pH, total metals, and dissolved metals downstream of construction as a result of project construction activities.
This memo discusses the current site conditions at the proposed Farrell Creek Bridge, potential implications for
management of ARD-ML based on the currently proposed development plan for the site, provides options for
mitigating ARD-ML, and recommendations for management and monitoring activities. Engineering of geotechnical
HIGHWAY 29 REALIGNMENT, FARRELL CREEK ARD-ML MITIGATION
FILE: 704-V13103415-03 | APRIL 23, 2020 | ISSUED FOR USE
The bedrock was logged by Wood to be shale interbedded with siltstone and minor sandstone, weak, with bedding
planes typically horizontal, and grey to dark grey in colour. Description of in situ rock weathering characteristics in
the geotechnical logs is limited, and the degree of weathering is based on the presence of orange or brown iron
oxide deposits in fractures, rock strength, and intensity of visible fracturing. Sample descriptions are included in
Table 2.
Table 2: Lithology and Description of Bedrock at Farrell Creek
Hole
ID
Sample
ID
From
(m)
To
(m)
Sample Description
(Wood)
TH18-FC-002 ARDFC-1 4.3 17.1 Fresh SHALE, interbedded with minor sandstone, very weak to medium strong, dark grey
TH18-FC-002 ARDFC-2 17.1 25.1 Fresh SHALE, interbedded with minor sandstone, very weak to medium strong, dark grey
TH18-FC-003 ARDFC-3 2.7 10.7 Fresh SHALE, interbedded with minor sandstone, very weak to medium strong, dark grey
TH18-FC-015 ARDFC-4 7.6 15.6 Slightly to moderately weathered SHALE interbedded with minor sandstone, very weak to weak, dark grey (7.6-9.1m); Fresh SHALE,
interbedded with minor sandstone, very weak to medium strong, dark grey (9.1-15.6 m)
TH19-FC-001 ARDFC-5 4.6 12.6 Fresh SHALE, massive, weak to medium strong, dark grey (4.6-7.7 m); Fresh SHALE, massive to interbedded with minor
siltstone and sandstone, weak to strong, dark grey (7.7-12.6 m)
4.3 Acid Base Accounting
The analytical results for the ABA analysis of five samples collected from Farrell Creek characterize all samples as
PAG with some small variation to the material mineralogical composition.
ABA analysis includes whole rock paste pH, total sulphur by LECO furnace with IR detection, sulphide sulphur
determined by Sobek 1:7 Nitric Acid and ICP finish, sulphate sulphur by 25% HCl Leach with ICP finish, total
inorganic carbon by LECO furnace with IR detection, neutralization potential (NP) by Modified Sobek method, and
fizz rating. Sulphide sulphur was used to calculate acid potential (AP); a value for maximum potential acidity (MPA)
calculated by total sulphur was not reported by SGS and was calculated by Tetra Tech using the reported total
sulphur concentration.
The Modified Sobek neutralization potential ratio (M.Sobek NPR) is the ratio of neutralization potential to the
maximum potential acidity (Sobek NP:MPA). Carbonate NP is calculated from carbonate carbon (CO2%) and used
to calculate a Carbonate NPR value (Carbonate NP:MPA).
The NPR value is used for material classification in accordance with the MEND Guidelines (Price 2009). The
guidelines state that a sample with an NPR value of less than one is classified as potentially acid generating (PAG)
and as non-acid generating (NAG) if the NPR is greater than two. Material characterized by an NPR of between
one and two is classified as “Uncertain” and may require additional information to determine the acid rock drainage
potential.
HIGHWAY 29 REALIGNMENT, FARRELL CREEK ARD-ML MITIGATION
FILE: 704-V13103415-03 | APRIL 23, 2020 | ISSUED FOR USE
Screening completed on BCAWQG-FST and CCME guideline values. 1 BC Ministry of Environment, Water Protection & Sustainability Branch (2019). British Columbia Approved Water Quality Guidelines (BCAWQG): Aquatic Life, Wildlife & Agriculture Summary Report. 36 pp. 2 CCME - Canadian Council of Ministers of the Environment Canadian Environmental Quality Guidelines (2018). 3 Guideline is pH dependant. 4 Guideline is hardness dependant. NG - No Guideline. Shaded Light Grey: Exceeds BCAWQG-FST and/or CCME guideline value. BOLD and shaded dark grey: Exceeds BCAWQG-FST and/or CCME guideline value by more than one magnitude.
A copy of the shake flask extraction analytical results is attached.
4.6 Quantitative X-Ray Diffraction
All five samples were analyzed by quantitative x-ray diffraction (XRD) by Rietveld Refinement at SGS Minerals in
Burnaby, BC (Project Number/LIMS No. 14094-01B/MI4513-JUL19). The minerals identified in variable wt. % are
Effort to minimize disturbance of the native soils is recommended to reduce erosion and scouring potential of the
creek bed. It is recommended a minimum of 0.50 m cover of compacted native creek bed material is maintained
over bedrock. Where bedrock is exposed during excavation, sub-excavation and removal of the material may be
required to accommodate placement of the 0.50 m cover. The excavated bedrock will be transported and placed in
the PAG disposal facility. A volume is estimated to be approximately 2,000 m³ as the amount of bedrock potentially
required for excavation along the channel from station 2020+100 to the southern termination should 0.50 m of
bedrock be removed by sub-excavation. This volume should be confirmed and used for cost-risk planning.
Bedrock exposed in cuts to accommodate toe or rip-rap protection should be mitigated with use of native creek bed
material in voids of the 250 kg rip-rap for lower 0.50 m, subject to geotechnical and hydrotechnical suitability.
Table 7: Depth to Bedrock Estimate under the Realigned Channel
Hole ID
Collar
Elevation
(m)
Depth to
Bedrock
(m)
Bedrock
Elevation
(m)
Location Description
TH18-FC-003 442.31 1.3 441.01 Under the proposed bridge alignment and approximately within the proposed Creek Diversion alignment
TH18-FC-004 444.92 3.8 441.12 To east of Realigned Channel and north of bridge alignment, near toe of eastern abutment slope
TH18-FC-005 445.39 5.3 440.09 East of the Realigned Channel and along the bridge alignment, within flood plain
TH18-FC-006 445.47 5.2 440.27 East of Realigned Channel and south of bridge alignment, within flood plain
5.1.5 Treatment Considerations for Chance Find Bedrock Exposure in Ditches and Roads
It is anticipated that unplanned exposure or excavation of PAG material will occur during the on-site construction
activities. In accordance with the CEMP, these occurrences must be evaluated and treated to minimize potential
negative downstream effects.
As each situation may be unique and influenced by various conditions such as depth, volume or surface area, slope
inclination, proximity to streams or sensitive areas, access to materials, etc., a single prescription will not be suitable
for all instances. It is recommended that “Chance Find” procedures are incorporated into all contractor EPPs to
include procedures such as temporary stoppage of work while the situation is assessed, and immediate
communication be initiated with a representative of BC Hydro and the onsite MoTI Representative to discuss
alternate treatment proposed by the contractor.
At the design stage, planned exposure or excavation of PAG in ditches with less than a 5% grade could be treated
with MoTI specified materials for accessibility and ease future ditch maintenance. If natural soils are not able to be
immediately replaced on the PAG material to a minimum thickness of 500 mm, a cover consisting of 250 mm
compacted high fines surfacing aggregate, covered with 150 mm of coarser surfacing material, then covered with
a rip-rap if specified for hydraulic engineering could be considered. This would require additional sub-excavation
(min. 400 mm) in the ditches and may not meet the design requirements, in which case an alternate solution will be
required.
It is noted that any PAG material that is required to be excavated to permit space for a cover will need to be transported and disposed of in an approved facility or in a manner approved by a BC Hydro representative.
HIGHWAY 29 REALIGNMENT, FARRELL CREEK ARD-ML MITIGATION
FILE: 704-V13103415-03 | APRIL 23, 2020 | ISSUED FOR USE
Prepared by: James Barr, P.Geo. Team Lead – Mining Geology Mining Group Direct Line: 778.940.1233 [email protected]
Reviewed by: Lara Reggin, P.Geo. Principal Consultant Mining Group Direct Line: 778.945.5889 [email protected]
/bi Enclosures: Limitations on the Use of This Document – Geoenvironmental
Tabulated SGS Results of Acid Base Accounting Tabulated SGS Results of Trace Element Analysis Tabulated SGS Results of Shake Flask Extraction Analysis Tabulated SGS Results of XRD Mineralogy Analysis
HIGHWAY 29 REALIGNMENT, FARRELL CREEK ARD-ML MITIGATION
FILE: 704-V13103415-03 | APRIL 23, 2020 | ISSUED FOR USE
BC Hydro. (2015). Appendix E: Acid Rock Drainage and Metal Leachate Management Plan, rev5.2, February 26,
2015, in Site C Clean Energy Project Construction Environmental Management Plan, rev04, July 26,
2016.
BC Hydro. (2016). Site C Clean Energy Project Construction Environmental Management Plan, rev04, July 26,
2016. BC Ministry of Transportation and Infrastructure. (MoTI, 2013). Technical Circular T-04/13:
Evaluating the Potential for Acid Rock Drainage and Metal Leaching at Quarries, Rock Cut Sites and from
Stockpiled Rock or Talus Materials used by the MoTI. September 15, 2013.
British Columbia Approved Water Quality Guidelines (BCAWQG-FST). Water Protection & Sustainability Branch,
Ministry of Environment & Climate Change Strategy, August 2019.
Canadian Council of Ministers of the Environment (CCME) Canadian Environmental Quality Guidelines (CEQG),
for the protection of freshwater aquatic life (PAL) (Accessed online July 2018).
Klohn Crippen Berger Ltd. and SNC Lavalin Inc. (Klohn and SNC), 2014, Site C Clean Energy Project, Definition
Design, Geochemical Characterization – Status at the End of 2013, BKS-03-104, November 2014.
Northwest Hydraulic Consultants Ltd. (NHC) (2020). Site C Hydro Project, Highway No. 29 Realignment and
Associated Roads, Hydraulic Design Report, Farrell Creek Bridge, 100% Submission – Final Report,
Revision 1, January 29, 2020.
Price, W.A. and J. Errington. 1997. Guidelines for Metal Leaching and Acid Rock Drainage at Minesites in British
Columbia, British Columbia Ministry of Employment and Investment (currently BC MEMPR)
Price WA. 2009. MEND Report 1.20.1: Prediction Manual for Drainage Chemistry from Sulphidic Geologic
Materials.
R.F. Binnie & Associates Ltd. – Drawings: British Columbia Ministry of Transportation and Infrastructure Bridge
Project No. 37501-0000, Highway No. 29, Farrell Creek, 100% Detailed Design, Jan. 31, 2020 (issued as
Draft for Review).
Wood, (2020). Geotechnical Data Report, Farrell Creek Segment, Highway 29, British Columbia, Project
#KX052807.31 issued to R.F. Binnie and Associates Ltd., by Wood Environmental and Infrastructure
Solutions, January 13, 2020.
LIMITATIONS ON USE OF THIS DOCUMENT
1
GEOENVIRONMENTAL 1.1 USE OF DOCUMENT AND OWNERSHIP
This document pertains to a specific site, a specific development, and a specific scope of work. The document may include plans, drawings, profiles and other supporting documents that collectively constitute the document (the “Professional Document”). The Professional Document is intended for the sole use of TETRA TECH’s Client (the “Client”) as specifically identified in the TETRA TECH Services Agreement or other Contractual Agreement entered into with the Client (either of which is termed the “Contract” herein). TETRA TECH does not accept any responsibility for the accuracy of any of the data, analyses, recommendations or other contents of the Professional Document when it is used or relied upon by any party other than the Client, unless authorized in writing by TETRA TECH. Any unauthorized use of the Professional Document is at the sole risk of the user. TETRA TECH accepts no responsibility whatsoever for any loss or damage where such loss or damage is alleged to be or, is in fact, caused by the unauthorized use of the Professional Document. Where TETRA TECH has expressly authorized the use of the Professional Document by a third party (an “Authorized Party”), consideration for such authorization is the Authorized Party’s acceptance of these Limitations on Use of this Document as well as any limitations on liability contained in the Contract with the Client (all of which is collectively termed the “Limitations on Liability”). The Authorized Party should carefully review both these Limitations on Use of this Document and the Contract prior to making any use of the Professional Document. Any use made of the Professional Document by an Authorized Party constitutes the Authorized Party’s express acceptance of, and agreement to, the Limitations on Liability. The Professional Document and any other form or type of data or documents generated by TETRA TECH during the performance of the work are TETRA TECH’s professional work product and shall remain the copyright property of TETRA TECH. The Professional Document is subject to copyright and shall not be reproduced either wholly or in part without the prior, written permission of TETRA TECH. Additional copies of the Document, if required, may be obtained upon request. 1.2 ALTERNATIVE DOCUMENT FORMAT
Where TETRA TECH submits electronic file and/or hard copy versions of the Professional Document or any drawings or other project-related documents and deliverables (collectively termed TETRA TECH’s “Instruments of Professional Service”), only the signed and/or sealed versions shall be considered final. The original signed and/or sealed electronic file and/or hard copy version archived by TETRA TECH shall be deemed to be the original. TETRA TECH will archive a protected digital copy of the original signed and/or sealed version for a period of 10 years. Both electronic file and/or hard copy versions of TETRA TECH’s Instruments of Professional Service shall not, under any circumstances, be altered by any party except TETRA TECH. TETRA TECH’s Instruments of Professional Service will be used only and exactly as submitted by TETRA TECH. Electronic files submitted by TETRA TECH have been prepared and submitted using specific software and hardware systems. TETRA TECH makes no representation about the compatibility of these files with the Client’s current or future software and hardware systems. 1.3 STANDARD OF CARE
Services performed by TETRA TECH for the Professional Document have been conducted in accordance with the Contract, in a manner
consistent with the level of skill ordinarily exercised by members of the profession currently practicing under similar conditions in the jurisdiction in which the services are provided. Professional judgment has been applied in developing the conclusions and/or recommendations provided in this Professional Document. No warranty or guarantee, express or implied, is made concerning the test results, comments, recommendations, or any other portion of the Professional Document. If any error or omission is detected by the Client or an Authorized Party, the error or omission must be immediately brought to the attention of TETRA TECH. 1.4 DISCLOSURE OF INFORMATION BY CLIENT
The Client acknowledges that it has fully cooperated with TETRA TECH with respect to the provision of all available information on the past, present, and proposed conditions on the site, including historical information respecting the use of the site. The Client further acknowledges that in order for TETRA TECH to properly provide the services contracted for in the Contract, TETRA TECH has relied upon the Client with respect to both the full disclosure and accuracy of any such information. 1.5 INFORMATION PROVIDED TO TETRA TECH BY OTHERS
During the performance of the work and the preparation of this Professional Document, TETRA TECH may have relied on information provided by persons other than the Client. While TETRA TECH endeavours to verify the accuracy of such information, TETRA TECH accepts no responsibility for the accuracy or the reliability of such information even where inaccurate or unreliable information impacts any recommendations, design or other deliverables and causes the Client or an Authorized Party loss or damage. 1.6 GENERAL LIMITATIONS OF DOCUMENT
This Professional Document is based solely on the conditions presented and the data available to TETRA TECH at the time the data were collected in the field or gathered from available databases. The Client, and any Authorized Party, acknowledges that the Professional Document is based on limited data and that the conclusions, opinions, and recommendations contained in the Professional Document are the result of the application of professional judgment to such limited data. The Professional Document is not applicable to any other sites, nor should it be relied upon for types of development other than those to which it refers. Any variation from the site conditions present, or variation in assumed conditions which might form the basis of design or recommendations as outlined in this report, at or on the development proposed as of the date of the Professional Document requires a supplementary investigation and assessment. TETRA TECH is neither qualified to, nor is it making, any recommendations with respect to the purchase, sale, investment or development of the property, the decisions on which are the sole responsibility of the Client. 1.7 NOTIFICATION OF AUTHORITIES
In certain instances, the discovery of hazardous substances or conditions and materials may require that regulatory agencies and other persons be informed and the client agrees that notification to such bodies or persons as required may be done by TETRA TECH in its reasonably exercised discretion.
HIGHWAY 29 REALIGNMENT, FARRELL CREEK ARD-ML MITIGATION
FILE: 704-V13103415-03 | APRIL 2020 | ISSUED FOR USE
CLIENT : Wood PLC
PROJECT : Farrell Creek
SGS Project # : 1923
Test : Modified Acid-Base Accounting
Date : July 15, 2019
Sample ID Paste TIC CaCO3 S(T) S(SO4) S(S-2) Insoluble S AP NP Net Fizz Test