MitigationofLandMovement-FINAL(2)(2)

INTRODUCTION

This document, created in collaboration with Golder Associates Inc and the INGAA Foundation, outlines strategies for mitigating land movement affecting pipeline alignments and rights-of-way (ROWs) It draws on Golder's extensive experience in geotechnical and hydrotechnical engineering, particularly in supporting Williams Ohio Valley Midstream projects in northern West Virginia With over 30 years of expertise in managing landslide and erosion hazards in pipeline projects across the northwestern United States, Golder highlights the significant risk of landslides in the northern West Virginia region and the Appalachian Basin, as documented by Radbruch-Hall et al.

In West Virginia, the areas identified in red on the map (Figure 1-1) indicate a high susceptibility to landslides, as noted by Radbruch-Hall et al (1982) This significant risk underscores the necessity for heightened awareness of landslide hazards when designing, planning, and constructing pipelines in the region.

Figure 1-1: Landslide Incidence and susceptibility across the US (Radbruch-Hall, et al., 1982, USGS Professional Paper 1183)

West Virginia's unique mountainous terrain, characterized by its steep, rugged, and geologically diverse landscape, poses significant challenges for pipeline construction due to potential land movement threats To address these challenges, specific topographic conditions have been identified to inform typical construction scenarios, such as ridge tops and side slopes, along with corresponding mitigation measures These strategies not only aid in the design and planning phases of pipeline projects but can also be implemented during installation as varying conditions arise Furthermore, these mitigation efforts are applicable to other regions across the United States that share similar hydrologic, topographic, and geological characteristics.

Project Objective

This study aims to highlight essential considerations for planning and implementing effective mitigation strategies against land movement hazards, such as landslides and erosion, that pose a threat to pipelines.

Identifying landslide and erosion hazards is crucial for effective project design, planning, and construction While the science of recognizing and characterizing these hazards is not covered in this document, it is essential to incorporate this knowledge into mitigation strategies This approach ensures that potential risks are addressed proactively, enhancing the safety and sustainability of construction projects.

 The critical role of route selection in identifying and avoiding hazards that may impact pipelines and ROWs;

Incorporating site-specific mitigation measures into project planning is essential to effectively address threats to pipelines and the right-of-way (ROW) Ultimately, it is the responsibility of the owner/operator to determine the acceptable level of risk associated with each mitigation package.

The relationship between land movement and both surface and subsurface water is influenced by alterations in local ground conditions due to recent or historical geological changes and construction activities Consequently, it is essential to implement mitigation measures specifically designed to address these unique site conditions.

 Reducing ground disturbance through minimized ROW footprints, appropriately sized and applicable equipment, and planning construction during optimal seasonal conditions (i.e dry versus wet) can minimize mitigation requirements;

When planning for pipeline construction, it is essential to evaluate landslide and erosion processes, as well as the water sources affecting the right-of-way (ROW) Mitigation measures should focus on the disturbed ground from initial grading and construction activities, rather than solely on the final restored surface of the ROW.

Organizing mitigation options into a structured framework of Typical Scenarios and corresponding Typical Details ensures consistency with the construction of the right-of-way (ROW), such as ridge tops, planar slopes, and side slopes This approach facilitates the swift creation of site-specific mitigation plans during the project planning and design phases.

Designing strategies to address specific threats from land movement enables owners and operators to choose their desired level of risk mitigation This approach provides the necessary time for them to plan, evaluate, and make informed, risk-based decisions on the optimal management of their assets.

While this study focuses on specific aspects of pipeline projects, it does not cover critical elements such as geologic hazard identification, environmental assessments, permitting, land access and acquisition, detailed design, materials specifications, and safety considerations These topics are essential for comprehensive project planning and should be integrated into the overall pipeline development process.

Structure of the Study

This study is divided into Planning and Mitigation sections, with the Planning section outlining the routing process and key factors in selecting the optimal pipeline alignment Although Planning is not the main focus, it is crucial to address the key issues that inform mitigation recommendations This section provides a general overview of how planning identifies hazards related to land movement that may affect the pipeline and right-of-way (ROW) By pinpointing potential hazards, the planning and routing process enables the owner/operator to assess risks along the pipeline alignment, forming the foundation for effective hazard mitigation strategies.

The Mitigation section of this study emphasizes effective strategies for managing landslide and erosion hazards frequently encountered along Right-of-Way (ROW) alignments in OVM It is crucial to comprehend the underlying issues and identify the processes that drive these hazards to develop appropriate solutions.

In the April 2016 report on Land Movement Mitigation in Rugged and Steep Terrain, an effective approach is presented for selecting suitable mitigation responses through Typical Scenarios and supporting Typical Details This section offers a comprehensive overview of mitigation concepts, alongside detailed guidelines tailored for specific Typical Scenarios encountered along pipeline Rights-of-Way (ROW) Additionally, it includes descriptions of corresponding Typical Details, which outline individual mitigation measures The discussion also addresses the general cost implications and risk factors associated with mitigating land movement.

Limitations

The recommendations provided are based on extensive experience with the geological, geotechnical, and hydrotechnical conditions typical of the Williams OVM system in West Virginia These guidelines are specifically designed to address similar hazards observed in this region It is crucial that mitigation efforts involve technical experts who are knowledgeable about the identified hazards and can implement effective mitigation measures Additionally, any recommendations should incorporate thorough site-specific investigations, characterization, technical assessments, and engineering to support ongoing planning, design, and construction activities.

PLANNING

The planning phase of pipeline projects involves a variety of essential tasks, such as project needs analysis, modeling, and conducting an open season for FERC projects It includes project justification analysis, obtaining authorization and certification from regulatory agencies, and performing environmental and corridor reviews Additionally, it encompasses evaluating routing alternatives, negotiating and acquiring right-of-way (ROW), conducting surveys, and designing the pipeline and associated facilities.

2013) While this study focuses on mitigation efforts (Figure 2-1), it is important to understand where mitigation fits into the overall process for addressing hazards

The routing phase of pipeline project planning is essential as it determines the path the pipeline will take across the landscape This stage not only identifies the proposed route but also assesses potential hazards the pipeline may face Understanding these hazards is crucial, as it informs the necessary measures to mitigate risks during the design, construction, and operation of the pipeline.

The basic conceptual approach to address landslide and erosion-related hazards is shown in Figure 2-

Routing is a crucial early process that involves identifying hazards and conducting characterization and assessment studies These steps are essential for understanding the potential impacts and threats that identified hazards pose to specific pipeline alignments.

Figure 2-1: Conceptual Approach to Geologic Hazard Management

After identifying and characterizing hazards, effective mitigation strategies can be developed Continuous monitoring is essential to assess the performance of these mitigation measures If issues arise with existing mitigation or if new hazards emerge, the process involves re-evaluating and characterizing these hazards to determine necessary additional mitigation This iterative process typically unfolds in phases, with a more efficient flow when the steps are interconnected.

Understanding the Project Setting

Comprehending the unique geological characteristics of specific regions is essential for creating effective strategies to mitigate landslides and erosion This study focuses on northern West Virginia, situated in the northern un-glaciated plateau region, commonly referred to as the low plateau.

The Appalachian Basin, particularly in its eastern and southern regions, transitions into mountainous terrain characterized by a high plateau Our findings in the low plateau area suggest a significant risk of landslide and erosion hazards, highlighting the need for awareness and preparedness in these regions.

Land movement mitigation in rugged and steep terrain is crucial, particularly in areas like the Appalachian basin, with significant implications for West Virginia The red areas highlighted in Figure 1-1 indicate regions at risk, emphasizing the need for effective strategies to address potential land instability.

The Dunkard Group, found in northern West Virginia, is characterized by non-marine cyclic sequences of sedimentary units, including sandstone, claystone, siltstone, mudstone, shale, limestone, and coal This sedimentary rock formation is predominantly flat-lying, showcasing a diverse range of geological materials (Nicholson et al 2007).

The alternating layers of sedimentary bedrock exhibit differing physical properties that influence their weathering and erosion rates Geologic processes, including uplift and incision, create steeper faces in the more resilient limestone and sandstone compared to the flatter slopes formed by softer claystone, siltstone, shale, and coal This variation in erosion leads to a distinct stepped and benched terrain, as illustrated in Figure 2-2, which also shows a constructed pipeline right-of-way (ROW) following a local ridge-line through this unique topography.

The LiDAR hillshade illustration in Figure 2-2 showcases the stepped and benched topography of northern West Virginia, highlighting key features such as the pipeline right-of-way (ROW) that descends along the ridge Additionally, the image reflects disturbed terrain along and beneath the benches, which indicates potential landslide movement For further details on LiDAR technology, refer to Section 2.4 of the study (Williams 2015).

Benches are characterized by alternating layers of strong and weak sedimentary materials Over time, these layers can weather and erode, leading to more uniform planar slopes where the distinction between units is less pronounced This process often results in the formation of residual soils, or in some cases, the combination of weathering and sediment infilling can create backfilled benches.

Colluvium and residual soil from weathered sedimentary bedrock create sensitive ground conditions that can easily destabilize due to water saturation The sedimentary layering influences groundwater flow, resulting in flat pathways that often discharge at seeps and springs where bedrock units transition Additionally, the benches can intercept and direct surface water flows, which can be altered through surface disturbances These unique geological features significantly impact landslide and erosion hazards, forming the foundation for the mitigation strategies discussed in this study.

Challenges of Routing in West Virginia

Routing involves the strategic planning and decision-making necessary to determine the best alignment for a pipeline This process requires careful consideration of various factors, including challenging topography, environmental and cultural resources, wetlands, rivers, surface soils, subsurface geology, shallow bedrock, protected and developed areas, public properties, residential homes, wells, septic systems, existing rights-of-way, pipelines, roads, and mining activities.

In West Virginia's mountainous terrain, optimal pipeline routing typically follows ridge tops and valley bottoms, but these areas are often occupied by existing residential and commercial developments This situation forces pipeline corridors into more challenging alignments along sidehills and sloping terrain, complicating the search for the ideal "good ground" that balances project requirements with minimal length The established infrastructure in these regions has leveraged the stability of higher ridge tops, resulting in concentrated development of roads, homes, and businesses in these areas Consequently, the rugged landscape limits the availability of additional stable ground, pushing new infrastructure into more difficult terrains.

When planning pipeline alignments in areas susceptible to land movement, project lengths may be significantly increased—potentially doubled or tripled—to circumvent identified hazards However, attempting to avoid a single hazard can inadvertently lead to encountering additional risks Since it's impossible to avoid all hazards, the planning process must carefully consider the trade-offs between the costs associated with longer alignments and the expenses related to hazard mitigation Consequently, decisions are often made to incorporate hazard mitigation strategies during the design, construction, or operational phases of the project.

Routing – An Art and a Science

Initial Routing Considerations

Selecting a pipeline corridor involves analyzing supply locations and delivery markets to identify the most cost-effective route while considering regulatory, environmental, engineering, and operational factors Utilizing existing pipeline corridors can be beneficial, as they may already represent optimal routing choices However, even minor adjustments of a few feet can significantly impact route quality While micro-routing modifications can target specific sites, they may not adequately account for broader regional issues such as recurring landslide or erosion risks.

In areas with significant landslide and erosion hazards, combined with sensitive environmental resources and prominent topographic features such as rivers, lakes, and mountain ranges, routing options become severely restricted Additionally, localized landowner requirements for access can complicate alignments, often leading to less favorable routing scenarios When pipelines and right-of-ways encounter these hazards and other routing constraints, implementing mitigation strategies may be necessary to ensure safety and environmental protection.

Conceptual Routing Approach

Any routing study includes some aspect of the following basic steps:

 Preliminary Route identification relative to possible hazards, and review of option(s);

 Desktop assessment and review of routing option(s) and corresponding hazards;

 Field reconnaissance of routing option(s);

 Selection/evaluation of route(s) (note that review and assessment of options may include risk-based methods); and,

 Design and planning of targeted mitigation measures to address identified hazards

(addressed in subsequent sections of this study)

To effectively route a pipeline, it is advisable to position it along ridge tops or flat valley bottoms, while traversing straight down planar valley slopes when necessary Although ridge tops and flat valley bottoms generally present fewer landslide and erosion hazards, valley bottoms may still face risks such as stream crossings and bank erosion In contrast, landslide and erosion hazards are more prevalent on steep slopes and where the pipeline alignment intersects existing hazards Ground disturbance during construction can trigger new landslides or exacerbate existing ones, particularly in rugged terrain, underscoring the importance of thorough planning to identify high-risk areas Implementing targeted mitigation strategies during the project planning phase or construction can effectively address these hazards and ensure successful restoration efforts.

The routing process must encompass the identification and assessment of potential hazards along proposed corridors, while also evaluating the logistics of pipeline construction in various terrains The feasibility of a route is significantly influenced by the ability to construct the pipeline safely, economically, and practically Adequate temporary right-of-way (ROW) is essential for construction, especially in challenging terrains, alongside a corresponding permanent ROW for ongoing access When reviewing proposed or alternate alignments, it is crucial to consider construction feasibility in relation to the necessary temporary and permanent ROW widths The methods employed in constructing the ROW impact the stability of the disturbed area and subsequent restoration efforts, which in turn affects the risk of land movement.

Routing efforts typically begin with desktop analysis of publicly available data, followed by ground reconnaissance and aerial surveys using helicopters or fixed-wing aircraft to assess potential routes As route options advance through the review process, detailed site surveys and mapping efforts are conducted to gather further insights.

A generalized routing process consists of logical decision steps tailored to meet project objectives The Williams routing decision process, illustrated in Figure 2-3, integrates relevant information, evaluates conditions, and identifies potential impacts and hazards to the pipeline and right-of-way (ROW) This approach facilitates iterative reviews and the development of alternative solutions A concise summary of this process is provided below.

The following provides a summary of the conceptual routing approach steps from Figure 2-3:

Following the project kick-off, the first step involves conducting desktop reviews and feasibility studies for both preferred and alternative routes These feasibility studies incorporate geologic hazard assessments that utilize specialized mapping and data sets to identify potential risks such as landslides, subsidence, and erosion This thorough evaluation of various routing alternatives aids in selecting the most optimal route available.

After identifying a corridor and potential route options, preliminary access permission is obtained to evaluate on-site conditions This may involve conducting environmental, geotechnical, hydrotechnical, or geological studies to understand site-specific factors and assess constructability The process is iterative, combining technical and environmental evaluations with ground reviews to address planning considerations and facilitate ongoing project design, permitting, and construction As ground conditions become clearer, field evaluations and re-route assessments can be performed Continuous coordination with property owners is essential for land access and authorizations along both primary and alternate alignments.

When modifications to routing are necessary, it is essential to evaluate their feasibility This process may involve conducting additional studies and coordinating with technical experts and landowners to thoroughly assess potential re-route options.

After a route receives approval, the operator undertakes comprehensive civil and environmental surveys, finalizes maps and alignment sheets, secures necessary easements, and conducts thorough on-site inspections of the entire alignment.

After establishing the final project alignment, a comprehensive design review is conducted Any issues identified with the route that could affect final approval may lead to a re-evaluation and modification of the route.

 After completing the final route review, and no additional routing modifications are needed, then the route is finalized and issued for construction

This example of the routing process serves as a foundational framework, offering insights into the essential components needed for an effective approach It emphasizes that while this framework provides a starting point, specific details and steps must be tailored to each individual project to ensure successful outcomes.

Effective land movement mitigation in rugged and steep terrain requires collaboration and input from the project team, especially from regulatory and environmental subject matter experts (SMEs) This approach ensures that the anticipated regulatory planning and review processes are adequately addressed, aligning with the project's objectives.

Figure 2-3: Conceptual Williams Project Planning and Routing Approach (Williams 2015)

Land Movement Mitigation in Rugged and Steep Terrain - 11 - April 2016

New Tools for Routing and Monitoring

LiDAR

Airborne LiDAR is an active laser scanning technology that measures the time it takes for a laser signal to return from a target, allowing for the determination of elevations and the creation of digital elevation models (DEMs) of the Earth's surface This system is particularly effective for acquiring three-dimensional data that characterizes landform elevations along specific corridors or mapping areas The ability to remotely gather detailed information about ground conditions offers significant advantages for projects such as pipeline alignments, facilitating improved design, planning, and construction processes.

Figure 2-4: Airborne LiDAR data collection system schematic (Williams 2015)

LiDAR technology operates by sending numerous laser pulses across a designated area, allowing some of these pulses to bounce off various surfaces like vegetation, buildings, and power lines, while others reach the ground The data collected from these reflections can be analyzed to distinguish between different surface types and the underlying terrain.

LiDAR technology generates a "bare Earth model" by classifying data that represents the ground surface, enabling detailed visualization of topographic and geomorphic features This model is instrumental in identifying and assessing geologic hazards, such as landslides and erosion processes, by detecting subtle ground morphologies like scarps, settlement areas, and disrupted drainage Additionally, it supports ongoing engineering evaluations and the development of mitigation plans to address these potential threats effectively.

Figure 2-5: Multiple Returns from LiDAR Laser Pulses (Williams 2015)

Effective planning and design for LiDAR mapping data acquisition are essential, especially since laser pulses can be obstructed, diffused, or diminished by dense vegetation and rugged terrain Key specifications for LiDAR mapping often include various parameters that ensure optimal data collection and accuracy.

 On-ground Laser Beam Diameters;

 Aggregate Pulse Density (i.e “points per m 2 ”, or ppsm);

When acquiring LiDAR data, it is crucial to consider "leaf-on" versus "leaf-off" conditions, especially in areas with deciduous trees that can obstruct the ground view from the data acquisition platform, such as fixed-wing or helicopter aircraft The ideal time for data collection is during leaf-off conditions, typically occurring in late winter or early spring when the ground is snow-free This period is also advantageous for monitoring winter-related landslides and erosion Other suitable times for LiDAR acquisition include fall through early winter, after leaves have fallen and before snow cover appears Data collection can continue during winter months into spring until foliage begins to grow, which can create dense ground cover The specific leaf-off period varies by site and geographic region, and LiDAR specifications can be relaxed during this time due to improved laser pulse access to the ground surface.

LiDAR technology is evolving rapidly, enhancing both the hardware and software used for data acquisition and processing Effective planning for a LiDAR mapping mission requires coordination with an experienced mapping professional to align with the project's seasonal conditions and requirements A key parameter in this planning process is "aggregate Pulse Density," commonly expressed as "points per square meter" (ppsm), which provides essential guidance for project teams and mapping contractors Typical ppsm parameters are crucial for ensuring optimal data collection.

 Open country with low-level and sparse brush or ground cover: ~2-4 ppsm;

 Leaf-on rolling moderate terrain in light trees and brush: ~8-10+ ppsm;

 Leaf-off rugged terrain in trees and bush: ~10-15 ppsm; and,

 Leaf-on rugged terrain in trees and bush: ~15-20 ppsm.

LiDAR data processing is usually performed by specialized mapping contractors to create bare Earth Digital Elevation Models (DEMs) that remove vegetation and reveal the underlying terrain This refined data can then be utilized for routing and various project-related applications.

Figure 2-6: Example of LiDAR hillshade data presentation highlighting landslides across and adjacent to a pipeline alignment (Williams 2015)

LiDAR data enables the analysis of proposed routes and existing rights-of-way (ROWs) to identify potential landslide and erosion hazards An example is illustrated in Figure 2-6, which uses "hillshade" views from LiDAR Digital Elevation Model (DEM) data to assess a pipeline alignment for landslide risks The image highlights a landslide (1) that intersects the pipeline alignment, necessitating a review of its potential threat to the current pipeline For proposed alignments, this hazard would prompt consideration of appropriate mitigation measures.

(2), located away from the pipeline alignment, may have a lower threat potential and therefore not require further studies or mitigation

LiDAR data is valuable for the ongoing monitoring of landslide and erosion hazards along existing pipeline right-of-ways (ROWs) after construction By utilizing repeated LiDAR assessments, programs can effectively compare elevation changes, identifying potential land movements, landslides, erosion zones, or subsidence areas This approach creates a tool for delineating new hazards and tracking previously identified risks The sequential data can be visualized as a "heat map," highlighting changes in ground elevations that indicate possible landslide, erosion, or subsidence activity (Williams 2015) It is crucial to review these identified areas and conduct field verification to ascertain the actual conditions and underlying causes of the topographic changes.

Figures 2-7 to 2-9 illustrate the application of LiDAR technology in monitoring land changes at a pipeline site Figure 2-7 presents a hillshade view of the location with a valve set, captured before any land movement occurred In contrast, Figure 2-8, taken approximately one year later, highlights significant land movement along the outer slope of the constructed pad Finally, Figure 2-9 features a heat map that visualizes the elevation changes caused by the failure of the pad embankment.

Figure 2-7: Example of Pre-movement LiDAR derived hillshade (Williams 2015)

Figure 2-8: Example of Post-movement LiDAR derived hillshade (Williams 2015)

Figure 2-9: Example of “heat-map” showing comparison of successive data sets (Williams 2015)

The heat map, created by analyzing consecutive LiDAR mapping data sets, visually represents land changes, with green indicating the upslope depletion zone (loss of elevation) and red signifying the downslope depositional zone (gain of elevation) By acquiring successive datasets and reviewing the compiled heat map results, rapid assessments of potential land movement in pipeline systems can be effectively conducted.

InSAR

InSAR, or Interferometric Synthetic Aperture Radar, is a satellite-based radar technology that captures ground elevation data by measuring the phase of returned signals at an angle perpendicular to its travel direction This method enables the detection of ground deformation by comparing successive datasets, which are typically collected on a monthly basis from historical archives While InSAR is primarily utilized to monitor ground deformations associated with natural events such as earthquakes, volcanoes, and subsidence, it is not commonly employed for assessing routing or land movement hazards related to pipeline alignments.

The suitability of InSAR data for a specific site can be influenced by various factors, including changes in moisture content and vegetation height between datasets, which may be misinterpreted as ground movement Polar orbiting satellites typically have a "look direction" oriented east or west, making them more adept at detecting movement on slopes aligned with this direction, while being less effective on north-south slopes Additionally, monitoring steep slopes can pose challenges due to phenomena such as layover, foreshortening, and shadow effects caused by the satellite's incidence angle.

The use of corner reflectors, which are approximately one meter orthogonal metal structures anchored to immobile foundations, can help address certain challenges in InSAR applications However, their effectiveness relies on strategic placement at specific locations Depending on site conditions and the intended use of data for a project, InSAR may serve better as a historical monitoring tool for detecting ground elevation changes, rather than as a means for routing assessments in new projects Therefore, it is essential to evaluate the suitability of InSAR on a case-by-case basis to determine its feasibility for each specific application.

Typical Land Movement Processes

Hazard Classification

To effectively prioritize sites for investigation and management of landslide or erosion hazards, a tailored hazard classification scheme is essential This scheme should define the unique characteristics of the hazards associated with each pipeline system or specific site Typically qualitative, the classification considers factors such as the type, nature, proximity, magnitude, and activity level of the hazards, along with their potential impact on the pipeline.

A straightforward hazard classification system is essential to avoid complicating current and future efforts In many cases, a simple classification ranging from high to low hazard levels is adequate However, some situations may require a more intricate system that considers pipeline integrity alongside potential environmental threats While this topic is technically specialized and not the main focus of this study, it is crucial to invest the necessary time and effort in developing a comprehensive hazard classification scheme to effectively catalog hazards and assess their relative risks to pipelines.

Engaging a geosciences professional in the development of the classification system for a given project is recommended.

Hazards Database and GIS information

Creating a comprehensive inventory of landslide and erosion hazards within a pipeline system is essential for monitoring changes and formulating effective mitigation strategies As data accumulates, establishing a database becomes crucial for organizing and managing this information, facilitating efficient queries and enhancing decision-making processes.

A specialized database platform can be created to facilitate operations, maintenance, and emergency response related to landslides and erosion This database should encompass essential information such as site-specific data, geospatial details, pipeline integrity assessments, potential environmental impacts, field investigation reports, photographs, slope monitoring data, and documentation of mitigation and remedial construction efforts It can be implemented using various commercially available software solutions that align with the owner's information management and integrity operations needs.

To effectively represent identified sites, geospatial data must be created and stored using a geographic information system (GIS) platform LiDAR images serve as a foundational mapping dataset, illustrating topographic features and the size, shape, and location of landslides in relation to key elements like pipelines, easement boundaries, property lines, and construction limits, along with critical features such as roads, structures, and water bodies Additionally, site-specific surveys or publicly available mapping data can contribute to developing comprehensive baseline mapping information.

Geospatial data must encompass essential pipeline details, including the pipeline name, type of product transported (such as gas or liquids), diameter, and milepost or engineering stationing Additionally, GIS base maps should feature current or historical aerial imagery, geologic maps, and topographic maps, along with site-specific slope analysis maps created using GIS tools when relevant.

MITIGATION OVERVIEW

In situations where routing efforts to avoid hazards in a project corridor have been fully explored yet some hazards persist, it is essential to implement mitigation strategies that are tailored to the specific conditions of the site These strategies should effectively balance the costs involved with the practicality of installation, operation, and risk mitigation Ultimately, the responsibility lies with the owner or operator to determine the acceptable level of risk associated with any chosen mitigation approach for identified hazards.

In the design and planning process of pipeline projects, it is essential to consider all reasonable mitigation options to effectively address potential hazards Experience with OVM indicates that land movement often correlates with surface and subsurface water, as well as changes in local ground conditions due to construction or geological factors Consequently, the mitigation strategies outlined in this report focus on managing water sources and enhancing local site conditions Effective options include re-grading the right-of-way (ROW) to alleviate soil loading, modifying drainage systems to minimize water discharge, and implementing sub-surface drainage solutions Additional measures may involve using engineered backfill materials, protecting ground surfaces with erosion control features, employing special pipeline coatings, and adjusting pipeline designs for increased durability These strategies are typically integrated rather than applied in isolation, ensuring a comprehensive approach to mitigating identified hazards at each site.

Structural measures are available to address unstable slopes, such as retaining walls, soldier piles, sheet piles, wire mesh systems, mechanically stabilized earth systems and other mechanical structures

While structural measures can be beneficial in certain situations, they are often not designed for pipeline applications and are typically intended for roads, bridges, and other infrastructure These measures can be expensive, necessitate custom designs, and require specialized equipment and construction techniques, which can be difficult to implement correctly Additionally, they may not adapt well to unforeseen site conditions, restrict future access or expansion in narrow right-of-way corridors, and impose specific long-term maintenance needs In contrast, this document proposes an approach that utilizes materials and methods commonly employed in pipeline construction, which do not need specialized equipment, can be adjusted on-site to accommodate varying conditions, and are easily adaptable for future expansions.

Landslides and erosion hazards typically arise from a combination of factors, making it essential to identify the key geologic hazards and the geotechnical and hydrotechnical engineering processes involved in their movement This understanding is crucial for the effective planning and design of mitigation strategies Implementing the approaches outlined in Section 2.0 and Figure 2-1 enhances the effectiveness of these strategies A successful mitigation plan must acknowledge the various factors influencing a site and may necessitate long-term performance monitoring to ensure complete mitigation is realized.

Mitigation strategies may not always aim for permanent hazard elimination; rather, they often focus on delaying or prolonging the engagement of potential threats to pipelines to an acceptable risk level For instance, employing deformable backfill and monitoring can help schedule stress relief excavations over time Therefore, it's essential to customize mitigation measures to address specific site conditions, assess the risk tolerance of the owner/operator, evaluate the costs and benefits of both long-term and short-term solutions, and integrate construction considerations.

Pipeline projects involve a distinct construction planning and execution process that follows a series of sequential steps to establish the right-of-way (ROW) and install the pipeline Effective mitigation efforts, whether implemented at an individual site or across a larger project, must seamlessly integrate with the overall construction process to ensure success.

Mitigation strategies should always account for overall construction considerations in the planning and design efforts

The following sections address these topics and outline general guidelines for mitigation.

Typical Construction Sequence

A typical construction sequence for building cross-country pipelines includes the following general steps:

 Welding, pipeline coating and weld inspection;

 Lowering the pipeline and backfilling;

The construction of pipelines involves a series of generalized sequential steps that are essential to the process Typically, a simplified graphical representation of these construction activities, like the one illustrated by Williams (Figure 3-1), is included in the planning and permitting documents during the initial phases of a pipeline project.

Mitigation efforts are crucial during the phases of right-of-way (ROW) clearing, grading, trenching, and restoration While construction typically assumes flat ROW conditions, rugged and steep terrains significantly complicate these processes, necessitating thorough planning for landslide and erosion mitigation In such challenging environments, temporary drainage improvements may be required early in the project to ensure the ROW remains usable However, these temporary measures can be damaged or need adjustments due to ongoing construction activities, leading to the installation of final drainage solutions during the ultimate restoration phase.

Effective pre-construction planning for pipeline projects in steep, rugged, mountainous terrain is essential to address landslide and erosion hazards This planning should also account for challenging weather conditions, such as wet or winter weather, which may interrupt construction and require temporary measures Designers must ensure that mitigation strategies are seamlessly integrated into the construction sequence to achieve efficient, functional, and cost-effective installations.

The following sections define and discuss general ROW construction scenarios that are consistent with the conceptual pipeline construction sequence

Figure 3-1: Williams Typical Construction Sequence (Williams 2015)

ROW Construction Scenarios

Valley Bottom ROW Construction

Building right-of-way (ROW) in flat valley bottom areas minimizes the risk of land movement hazards, as these regions are generally flat or gently sloped and less susceptible to landslides While surface erosion and challenges from existing infrastructure or nearby rivers may occur, the likelihood of earth or debris flows initiating in these areas is low compared to steeper terrains Although valley bottoms can experience depositional and run-out scenarios from such flows, they typically do not pose a significant threat to pipelines located in these zones.

Figure 3-3: Typical Valley Bottom ROW Construction (and inset showing conceptual location of the construction scenario referenced on Figure 3-2) (Williams 2015)

The construction of the pipeline right-of-way (ROW) involves a significant disturbance, as illustrated in Figure 3-3, which depicts the necessary cut and fill to remove topsoil and level the area for access Trenching in flat terrain generally does not require specialized planning or equipment for design or restoration However, valley bottom areas are particularly vulnerable to surface runoff from higher elevations, as they are located at the lowest points in ridge-valley landscapes Consequently, construction in these valley bottoms often involves navigating floodplains, rivers, streams, and various water bodies, including seeps, artesian conditions, lakes, and wetlands.

Planar Slope ROW Construction

Constructing a right-of-way (ROW) on planar slopes involves similar processes to building on flat terrain, but the steep incline necessitates more detailed construction planning due to an elevated risk of landslides and erosion The extent of ground disturbance required for pipeline ROW installation is illustrated in Figure 3-4, particularly in areas just ahead of the excavator This disturbance may increase to accommodate longitudinal variations in the ROW profile, particularly in benched topography or on slopes that alter in grade due to local geological conditions or other topographical changes.

Figure 3-4: Typical Planar Slope ROW Construction (and inset showing conceptual location of the construction scenario referenced on Figure 3-2) (Williams 2015)

Planar slopes aligned with the slope's fall line experience reduced upslope surface runoff, making them highly susceptible to the impacts of access roads and transportation points These structures can redirect surface and subsurface water back to the right-of-way (ROW) from adjacent upslope areas, which typically would not contribute runoff to the disturbed ROW This redirection can trigger erosion and landslide hazards due to the increased water accumulation in the pipeline trench or along the disturbed ROW surface To mitigate these risks, implementing trench breakers and slope breakers, also known as water bars, is essential as an initial defense strategy for both short- and long-term protection.

Ridge Top ROW Construction

Routing pipelines along ridge tops or steeply sloped ridges is ideal in rugged ridge-and-valley terrain This alignment offers the most stable ground due to minimal geological changes over time, significantly reducing the risk of landslides and erosion hazards.

Figure 3-5: Typical Ridge Top ROW Construction (and inset showing conceptual location of the construction scenario referenced on Figure 3-2) (Williams 2015)

The stability of the area is primarily attributed to the absence of drainage basin contributions to the disturbed right-of-way (ROW), as there are no slopes or basins directing water towards it The potential water sources that might necessitate mitigation are mainly limited to precipitation and the diminished likelihood of a seep or spring found along the ridge.

The construction of pipeline right-of-way (ROW) on ridge tops involves a general magnitude of disturbance illustrated in Figure 3-5, which is slightly greater than that required for valley bottom flat areas or planar slopes However, this disturbance remains relatively minor compared to other scenarios A key challenge in ridge top construction is effectively managing temporary construction spoils while minimizing their loss to the steep valley sides that slope away from the ridge.

Sidehill ROW Construction

Constructing a right-of-way (ROW) in sidehill conditions poses significant challenges for designing, planning, and mitigating landslide and erosion hazards The ideal alignment should run parallel to the slope contours, as shown in the conceptual figure However, issues can also arise when the ROW traverses the slope at oblique angles to the fall line The extent of disturbance required for the construction of the sidehill pipeline ROW is substantial and must be carefully considered.

Land movement mitigation in rugged and steep terrain involves significant excavation, as illustrated in Figure 3-6 This figure highlights that sidehill construction results in the highest volume of excavated materials and the most extensive disturbance area compared to other typical construction methods.

To create a temporary flat Right-of-Way (ROW) surface for pipeline access and installation, extensive additional excavations are necessary in the upslope direction, particularly in steep sidehill conditions This upslope excavation may require significant depth, leading to a wider ROW to accommodate work in challenging terrain Consequently, sidehill excavation produces an increased amount of spoils that must be properly managed.

Figure 3-6: Typical Sidehill ROW Construction (and inset showing conceptual location of the construction scenario referenced on Figure 3-2) (Williams 2015)

Deep excavation on the upslope side of the Right-of-Way (ROW) can capture seeps, springs, and surface runoff, directing this water onto the temporary ROW surface during construction The design of this temporary surface significantly influences how surface and subsurface water sources interact with the restored backfill as the ROW transitions into its operational phase If these water sources are not properly managed during construction and restoration, they may infiltrate the ROW backfill, leading to saturated and unstable conditions, which often contribute to land movement along the ROW after construction and restoration.

Mitigation strategies must consider the construction of the Right of Way (ROW), including its configuration, size, and the techniques employed to create the temporary ROW surface Additionally, these efforts should address the potential sources of water, particularly along the historical temporary ROW surface, which may significantly differ from the conditions of the restored ROW surface.

Temporary ROW Surface Intercepts Surface and Subsurface Water

The construction of the temporary Right-of-Way (ROW) surface significantly influences the interaction between surface and subsurface water sources and the restored construction backfill Seepage flows and springs, which typically follow the local geological bedding and benched topography, manifest at specific ground surface locations that reflect pre-construction conditions These surface seepages then flow downhill, guided by the original topography With the creation of the temporary ROW surface, these seepage flows are redirected along the new surface, where the excavation intercepts existing flow paths Consequently, the temporary ROW surface serves as a preferential flow path, directing water along the steep cut slope on the uphill side and across the flat bottom width of the ROW.

The backfill and restoration of the right-of-way (ROW) utilize spoil materials that fail to replicate the original geological conditions and seepage flow characteristics Even with compaction and contour matching, the backfill remains fundamentally different from the pre-disturbed state When exposed to water from surface or subsurface sources, the backfill tends to become saturated Following the restoration of the temporary ROW, the surface continues to intercept seepage flows from the steep cut slope and the backfill itself, acting as a preferential flow path Consequently, the new discharge point for seepage is located beneath the backfilled materials and further downslope from its original discharge location prior to the project.

Effective mitigation should be implemented at the intersection of seepage and the temporary excavated right-of-way (ROW) surface, rather than solely at observed seeps and springs This approach addresses the source of water flows and prevents further saturation of the backfill materials, which can lead to increased risks of landslides, erosion, and slope failure It is crucial to target areas where seepage accumulates on the flat portions of the temporary ROW surface and infiltrates into the pipeline trench, as well as locations where the surface geometry directs water towards the ROW backfill.

When pipeline trenches or rights-of-way (ROW) are left open for extended periods, it may be necessary to implement temporary drainage solutions to manage intercepted seeps and springs along the upslope surface or within the trench These measures should be initiated during the clearing, grading, and trenching phases, particularly in typical planar slope, ridge top, and sidehill scenarios Temporary mitigation may need to remain in place throughout the construction process and could require repairs or modifications due to ongoing construction activities For effective final restoration of the ROW, these measures must be installed at the source of water, rather than where water appears on the surface of the restored area.

Figure 3-7: Temporary ROW Surface Interaction with Seeps and Springs (Williams 2015)

Comparison of Relative ROW Disturbance in Sidehill Scenarios

Figure 3-8 illustrates a comparison of the disturbance areas associated with different Right-of-Way (ROW) construction scenarios, emphasizing the significant increase in excavation volume and footprint in the sidehill scenario It is crucial to identify these disturbed areas early in the project design and planning stages to minimize their impact as much as possible.

Operators should implement site-specific mitigation measures to effectively address potential water sources and stabilize the right-of-way (ROW) backfill materials when avoidance is not possible.

Figure 3-8: Conceptual Comparison of Relative Disturbance Areas (Williams 2015)

Sequencing Mitigation with Construction

To effectively manage existing or potential landslide and erosion hazards, it is essential to implement mitigation measures that incorporate the temporary constructed right-of-way (ROW) surface Depending on the anticipated duration of the open ROW, the installation of drains may be necessary to manage intercepted seeps and springs along the upslope temporary ROW surface or within the pipeline trench These measures should be integrated during the clearing, grading, and trenching phases of work, particularly in typical planar slope, ridge top, and sidehill ROW scenarios It's important to note that these temporary mitigation measures may need to remain functional throughout the construction activities and may require adjustments, leading to the installation of final mitigation measures during the restoration phase.

The restoration phase of pipeline construction is crucial, involving final backfill, finish grading, and the installation of erosion control measures such as slope breakers and vegetation It is essential to implement final land movement mitigation strategies, which may include constructing new drains or re-establishing temporary drains from earlier phases For these mitigation measures to be effective, they must be installed at the source to prevent erosion and ensure site stability.

Effective land movement mitigation in rugged and steep terrain requires careful coordination of water management strategies, ensuring that water is directed away from the surface of the backfilled right-of-way (ROW) during pipeline construction phases.

General Guidance Using Typical Scenarios for Landslide Mitigation

General Approach for Mitigation of Land Movement using Typical Scenarios

The following outlines the general approach for mitigating land movement for Side Slope and Planar Slope Typical Scenarios (as outlined and discussed above):

1 The final configuration of any ROW restoration measures should be determined based on the conditions encountered at the time of construction, and may change or vary and require additional measures to mitigate hazardous landslide conditions that are identified during the work The volumes, grade, elevations and quantities will vary depending on the site conditions encountered

2 Landslides at any given site should be evaluated on a case-by-case basis and should incorporate the site-specific conditions Mitigation recommendations should be specific to each site and should incorporate appropriate site investigations and assessment, review, mapping, characterization and delineation of site-specific landslide features in order to understand the site-specific processes and dynamics of the landslide at that site

3 If possible, look to re-route and avoid the landslide site If re-routes are not possible, then consider additional mitigation measures

4 Investigate the landslide site to confirm depth to failure zone, extents and limits of the landslide mass, etc This may be accomplished by: site-specific sub-surface drilling; geophysical surveys; use of LiDAR to map surficial landslide features; digging test- pits; manual probes; or through excavations of the temporary ROW surface Although sub-surface investigations are often preferred, the timing, access or site conditions may not allow specialized equipment access, and it is common for investigation activities to include test-pit or other localized excavation methods (using rubber-tire or tracked excavators) to quickly map out landslide conditions and confirm depths of the active landslide zone and the corresponding depth to bedrock

5 If possible, install the pipeline trench in stable bedrock or unyielding and intact native soils

6 Where the depth to stable bedrock or stable native soils is too deep, or it is not feasible to install the pipeline at that depth, then the following measures should be considered: a Install a deformable backfill around the pipeline (PRCI 2009), which allows for improved drainage along the pipeline trench, and allows the backfill to deform around the pipeline in response to continued land movement and thereby attenuates for accumulated strain in the pipeline; b Install monitoring on the pipeline to track potential increases in strain in the pipeline (i.e strain gauges); c Install other monitoring at the site to track potential land movement (i.e geodetic monitoring, regular visual monitoring, inclinometers, piezometers, extensometers, etc.); d Install enhanced drainage measures in the trench to mitigate for subsurface flows and target identified sources of water that may be discharging to the site; e Modify surface water draining to the site to mitigate for discharges from streams, creeks, runs, gullies or other sources of surface run-off that may be contributing water to the site and exacerbating land movement; f Install trench breakers and slope breakers to mitigate for trench seepage and to divert intercepted trench flows along the surface to safe discharge points; g Reduce the loading on the site by removing and/or reducing the excess backfill materials to off-site locations Spoil placement should be carefully planned to avoid triggering land movement in other locations; h Compact backfill materials at the site to achieve optimal moisture content and to provide increased strength Added compaction can increase strength and stability of the backfill and reduce infiltration of water into the backfill, thereby further mitigating for potential for land movement; i Wet backfill materials may require drying the soils using special additives to allow the materials to be re-used and worked at the site Over-saturated materials may require extensive time and space to dry Use of lime-kiln dust or cement-kiln additives may be needed (pending environmental requirements); j Where local materials cannot be re-used, use of a small angular (i.e free-draining) rock backfill for ROW restoration (not in the pipeline trench) may be installed Rock materials allow for reconstruction of slopes and grades in wet conditions and can be placed to establish desired grading and re-contouring at the site Rock backfill can also be re-used and re-placed during future maintenance activities; and, k Where needed, install shear trenches in planar and oblique sidehill scenarios where continued land movement is expected and targeted relief of differential ground movement is possible

7 Complete an as-built survey to identify and map out the installed mitigation measures at the site, including documentation, drawings, and database information as discussed earlier

8 Develop a site monitoring plan to track potential changes at the site

Refer also to the corresponding Typical Scenario sheets in Appendix A-1.

General Approach for Mitigation of Land Movement using Typical Details

This section provides a general overview of mitigation efforts, focusing on key categories such as subsurface drainage, surface drainage, and grading For more comprehensive guidance and detailed discussions, please refer to Applied Guidance Section 4.0.

Effective subsurface water management is crucial for any site-specific plan It is essential to prioritize subsurface drainage enhancements that consider the construction of the right-of-way (ROW) and implement drainage systems that respond to alterations in subsurface flow and discharge patterns, rather than solely focusing on surface flow characteristics after restoration.

Site-specific drainage solutions must be adaptable to ensure effective integration into the construction process This flexibility may involve the use of temporary drainage systems during initial grading and trenching, transitioning to permanent drains once trenching is completed and pipelines are lowered Additionally, proper drainage management is crucial during the restoration phase of the project.

Examples of subsurface drainage measures include (but are not limited to):

 French drains that incorporate drain rock with perforated collection pipes to capture and convey water in the trench or other targeted areas;

Enhanced drainage systems utilize drain rock along with perforated collection and tightline conveyance pipes, allowing for targeted designs that boost water capture and conveyance efficiency These systems can be implemented in trenches or various locations to effectively manage and mitigate water accumulation.

Utilize targeted seep drains, incorporating drain rock, piping, and additional materials, to create collection and conveyance systems at specific water sources within the right-of-way cut or trench These drains are frequently integrated with existing drainage systems to effectively remove excess water.

Bleeder drains are essential features that create notches in the outboard trench wall at low spots or intervals in sloping trenches They effectively allow accumulated seepage from water sources to exit the right-of-way backfill, preventing pooling in the trench or backfill material Typically constructed with drain rock, these drains may also incorporate piping and trench breakers to enhance water flow Additional excavation may be necessary to establish a slope-to-drain grade through elevated areas.

Trench breakers are strategically designed to enhance drainage by addressing seepage along the trench line, and they are often integrated with surface drainage management solutions, such as slope breakers, to improve overall water management.

All these variations on drains allow for the collection and evacuation of subsurface seepage, and may be modified and/or combined to fit site conditions

3.4.2.2 Surface Drains, Runoff Improvements, and Channels

Surface water run-off can lead to both consistent incremental discharges and significant peak flows during storms While landslide and erosion failures frequently occur during storm events, the underlying cause is often the continuous small discharges, known as base flows Consequently, effective surface drainage plans must be designed to manage a variety of flow conditions.

Surface drainage measures may include (but are not limited to):

 Collection and diversion channels, ditches, brow ditches, berms, slope breakers

(discussed in more detail below), swales, etc that intercept and convey base flows and mitigate for saturation of the ROW backfill or other targeted landslide prone terrain at a site;

Improving runoff management involves grading the right-of-way (ROW) and the adjacent ground to effectively direct surface and subsurface water away from the site This can be achieved by altering slopes and adjusting cut-fill techniques to prevent the concentration of aggregate surface runoff Additionally, the implementation of slope breakers may be coordinated to enhance these efforts, ensuring better control and infiltration of water into the ROW backfill.

Armored channels equipped with drain pipes effectively manage high flow rates and prevent erosion during peak events The armoring protects the channel, while the drain pipes efficiently capture lower seepage base flows, preventing them from infiltrating oversized armor rock.

Armored channels on steep terrain effectively collect and convey surface runoff and point sources of water, such as seeps and springs, which are susceptible to erosion This armoring can involve the use of riprap materials, sack-crete lining, or the reconstruction of steep trenches and right-of-way backfill in bedrock conditions, while also incorporating local erosion-resistant geological units like bedrock into the channel design.

3.4.2.3 Grading, Backfill Improvements, and Surface Treatments

Any site-specific mitigation plan will include some form of grading and surface mitigation slope work Examples include:

 Grading to reduce the overburden on the site and thereby minimize or reduce driving forces on a potential landslide;

 Maintaining a stable outboard wedge of soil or bedrock material along the downslope side of ROW to maintain a stable trench;

 Compaction of backfill materials during ROW restoration;

 Drying, moisture conditioning, use of soil additives to soils during ROW backfill and restoration work to improve construction feasibility and stability of materials;

 Removing unsuitable soils when they cannot be used in the backfill or cannot be dried sufficiently;

Utilizing free-draining rock backfill, such as small to medium-sized angular riprap, effectively replaces unsuitable soil materials and reconstructs right-of-way (ROW) slopes This method accommodates various slope geometries, ensuring a stable backfill configuration for both low and high-angle slopes Additionally, this approach allows for the backfill to be reused during future maintenance and operational activities, enhancing sustainability and efficiency.

Utilizing sack-crete materials for reconstructing localized trench backfill, right-of-way (ROW) slopes, and transitions between soil and bedrock enhances stability and durability This approach can be effectively combined with drainage improvements to address both surface and subsurface water issues.

 Tracking or other surface erosion control treatments for disturbed final ground surfaces;

 Installing erosion control fabric, silt socks, silt logs, “coir” products, and/or other erosion control devices; and

Rock armoring, utilizing medium to large-sized riprap materials, is employed on steep or erosion-prone slopes to stabilize these areas and mitigate surface erosion This technique effectively integrates transitions between soil and bedrock units while also reconstructing localized over-steepened right-of-way slopes.

Incorporating trench and slope breakers into right-of-way (ROW) restoration is essential for effective restoration and mitigation strategies These elements should be regarded as a fundamental aspect of standard mitigation planning, design, and construction processes.

APPLIED MITIGATION GUIDANCE

This article offers practical mitigation strategies for various Typical Scenarios, along with discussions and guidance on relevant Typical Details, which are specific mitigation measures aimed at addressing landslide and erosion hazards (Williams 2015).

 Side Slopes, sub classified normal (Appendix A-1, Sheet 1110) and oblique (Appendix A-1, Sheet 1120) orientation to pipeline;

 Planar Slopes (Appendix A-1, Sheets 1150 and 1160);

 Areas of Fill Soil (Appendix A-1, Sheet 1600); and

Typical scenarios are essential for defining geotechnical and hydrotechnical engineering processes, as well as geological hazards associated with specific locations They offer a practical framework for identifying potential threats to pipelines, facilitating informed decision-making regarding conceptual design and the selection of appropriate mitigation measures tailored to each site.

Each Typical Scenario features a graphical representation, such as a cross-section or topographic view, along with a library of relevant Typical Details tailored to the scenario These Typical Detail sheets, resembling "fly-sheets" or "cut sheets," illustrate individual mitigation measures like silt fences, compaction techniques, or targeted drainage features This flexible approach facilitates the addition and updating of mitigation strategies while preserving a consistent framework for identifying and addressing potential hazards and threats to pipelines The goal is not to implement all Typical Details at every site, but to provide a range of solution options that can be chosen based on specific site conditions.

The Typical Scenario and Typical Details package aims to create a conceptual framework for identifying site-specific hazards and corresponding mitigation measures The selection of these measures, including their precise locations and extents, must be validated through thorough site observations and investigations, while also considering construction processes This information is often integrated with a topographic plan, such as contour or site survey data, to accurately determine the coordinates and dimensions of the mitigation measures in relation to the site's topography and cross-sections.

Side Slope Conditions

Engineering/construction recommendations for side slope normal

In a side-slope normal scenario, the pipeline trench features a flat or shallow gradient that follows the slope's contour, leading to potential issues with runoff and drainage This construction disturbance can result in accumulated seepage, causing saturation of the native soil or fill, which may destabilize the backfill and potentially trigger or reactivate nearby landslides Effective restoration measures must prioritize minimizing surface and near-surface flow to the trench and ensure efficient drainage of accumulated seepage from the backfill Additionally, these measures may need to extend beyond the right-of-way footprint to prevent broader slope instability.

Typical conceptual restoration measures used in side slope normal conditions may include:

1 Generally re-contour the restored ROW to re-establish pre-construction contours

(Appendix A-2, Sheet 2G), except where targeted site assessments recommend reducing backfill over unstable or landslide areas (Appendix A-2, Sheet 2H)

2 Grade the temporary ROW construction surface (Appendix A-2, Sheet 2A) so that it drains away from the inside of the cut The objective is to minimize the potential for infiltrated water to accumulate, or tend to move along the transition from the disturbed ROW areas and the undisturbed temporary ROW surface (i.e the native ground) An additional objective is to avoid a situation where the excavated colluvium and residual soils are stockpiled in a manner that traps water, causing the excavated soils to become saturated prior to backfilling the ROW Temporary construction surfaces need to be incorporated into the final site drainage configuration to limit potential for saturation of the backfill and native soils

3 Grade the temporary ROW surface and depth of the pipeline trench to allow for a stable outboard wedge of soils/rock material adjacent to the pipeline trench (to the out- slope side), see Appendix A-2, Sheet 2B This maintains a protective stable section of ground on the outboard slope side of the pipeline trench that mitigates for potential raveling, degradation, landslide or other slope instability or erosion processes that may impact the pipeline

4 Cut bleeder trenches (Appendix A-2, Sheet 1D) into the downslope side of the pipeline trench at an approximate 100-foot spacing, or to match the local topography

Bleeders should be excavated to the bottom of the pipeline trench and sloped to drain into native soil or rock, ensuring discharge occurs on stable ground Enhancing bleeders with geotextile-wrapped drain rock or drainage pipes, such as French drains, can improve their effectiveness The primary goal of bleeder trenches is to create regular drainage relief points, allowing accumulated seepage to exit the trench efficiently.

5 Install brow ditches (Appendix A-2, Sheet 6B) excavated into the ground, slope breakers (Appendix A-2, Sheets 5A and 5B), a combination of built-up and excavated water bars and armored channels with drain pipes (Appendix A-2, Sheets 1F, 1H and 1E) along the upslope side of the ROW to intercept and divert surface run-off to stable locations away from the side slope areas The need and layout of these depends on the topography, for instance if there is no stable location to discharge the intercepted water In this case, rely more on other measures

6 Where surface run-off from one or more slope breakers, or other surface or near surface water sources needs to be conveyed down steep slopes that may be subject to erosion, consider using armored channels with an apron at the discharge (Appendix A-2, Sheet 1F and 1E), or in steep terrain the armored channel and more robust drainage piping may be needed (Appendix A-2, Sheet 1H and 1E)

7 Compact the backfill (Appendix A-2, Sheet 2C) during side slope ROW reconstruction This adds strength to the backfill to make it more stable, and reduces infiltration of water Achieving compaction in steep and rugged terrain is difficult Recommended methods include use of sheep’s-foot rollers pulled behind a dozer, a self-propelled sheep’s-foot compactor or sheep’s-foot roller attached to an excavator arm

8 Where the local soils are not suitable for backfill and/or compaction, for example due to the sensitive nature of the local fine-grained soils or excessive moisture content, it may be necessary to haul the unsuitable material off the site These materials should not be stockpiled or spoiled in areas that may initiate or exacerbate landslides

(Appendix A-2, Sheet 2E) Replace with a free-draining, angular, clean, small sized

Rock backfill, typically ranging from 4 to 8 inches, is highly stable and can maintain steep angles without retaining water, making it adaptable to future site changes such as settlement or slip movement To achieve optimal moisture content in drying soils used as backfill, it is essential to spread the soil in windrows and actively work them under low humidity and warm temperatures Alternatively, incorporating lime or cement kiln dust into wet soils can enhance moisture conditions, following manufacturer guidelines for mixing This approach allows for effective work even in wetter environments, though mixing rates and methods should be tailored to specific site conditions and may require experimentation for the best results.

9 Install a French drain (Appendix A-2, Sheets 1A and 1E) along the inside catch of the constructed temporary ROW surface at the transition from disturbed soils (i.e where the backfill starts) and the undisturbed native soils Drains should discharge at stable locations downslope of the backfill areas so that it does not recharge the backfill

10 Install drains (Appendix A-2, Sheet 1C and 1E) where seeps or other subsurface water sources are identified during temporary ROW construction

11 Install slope breakers or other surface diversion berms to intercept surface run-off, or combine slope breakers/berms with armored channels to control run-off (Appendix A-

12 Special consideration is needed to construct and restore drainage measures for existing, permanent and temporary access roads on a site-specific basis Access roads may collect runoff from upslope areas, increasing the contributing basin area draining to any given site, and deliver water to the ROW, the pipeline trench or to other areas of concern Use drainage measures such as slope breakers, water bars, grading to improve drainage, French drains, enhanced drains, armoring, armored ditches with drain pipes, rock fill, etc (Appendix A-2, Sheet 5D) to manage and mitigate drainage issues

13 Cover disturbed area with erosion control fabric (Appendix A-2, Sheet 3C) or other functional erosion resistant ground covering to mitigate over the short-term until the local vegetation can take over and establish itself In especially unstable and steep slope conditions, erosion control products such as armor rock may be needed

14 Track disturbed slopes (Appendix A-2, Sheet 3A) and re-vegetate all disturbed areas to provide long-term surface stabilization (i.e replace the short-term erosion control fabric protection).

Engineering/construction recommendations for side slope oblique

In side-slope oblique scenarios, similar conditions to those found in normal side slope scenarios apply; however, intercepted seepage flows can be accelerated due to the trench's sloping gradient This increase in seepage velocities heightens the risk of instability and erosion, including both piping and surface erosion While the typical restoration measures for normal side slopes are applicable, additional strategies are necessary to effectively address the unique challenges posed by oblique conditions.

1 Drainage pipes in the pipeline trench are needed to mitigate for the increased gradient and seepage velocities resulting from the sloping trench (i.e due to the oblique orientation of the trench along the side slope) The bleeder trenches used in side slope normal scenarios may not provide enough drainage relief, and on sloped ground may actually discharge back into the trench Drainage pipes can be configured as

For effective drainage in normal or low flow conditions, French drains should be installed with discharge points located at the edge of the right-of-way (ROW) on stable ground, incorporating erosion pads In areas where excessive seepage may occur, the drainage system should be upgraded to include perforated drain pipes that gather water, directing it into solid, smooth-interior-walled tightline pipes for efficient conveyance away from the site.

2 Install trench breakers (Appendix A-2, Sheet 4A), preferably using sandbags, at spacing and locations corresponding to the trench slope (not necessarily the ground slope, which may be much steeper) Where foam materials are used for the trench breakers, there should be drainage measures incorporated into breakers that mitigate for accumulation of seepage on the upslope side of the breaker, allowing it to drain through the breaker

Modifications or alternatives to the above described measures that are feasible and maintain the function and intent as described and offer practical alternatives are encouraged.

Ridge Tops

Engineering/construction recommendations for ridge tops

In ridge top scenarios, backfill is less likely to become saturated, allowing for effective drainage to stable ground on either side of the ridge, which minimizes the risk of concentrated seepage flows Common restoration measures employed in these ridge top conditions include various techniques designed to enhance drainage and stability.

(Appendix A-2, Sheet 2G), except where site assessments recommend reducing backfill over unstable or landslide areas (Appendix A-2, Sheet 2H)

2 Grade the temporary ROW construction surface (Appendix A-2, Sheet 2A) so that it drains away from the inside of the cut The objective is to minimize the potential for infiltrated water to accumulate, or tend to move along the transition from the disturbed ROW areas and the undisturbed temporary ROW surface (i.e the native ground) An additional objective is to avoid a situation where the excavated colluvium and residual soils are stockpiled in a manner that traps water, causing the excavated soils to become saturated prior to backfilling the ROW Temporary construction surfaces need to be incorporated into the final site drainage configuration to limit potential for saturation of the backfill and native soils

3 Grade the temporary ROW surface and depth of the pipeline trench to allow for a stable outboard wedge of soils/rock material adjacent to the pipeline trench (to the out- slope side, Appendix A-2, Sheet 2B) This maintains a protective stable section of ground on the outboard slope side of the pipeline trench that mitigates for potential raveling, degradation, landslide, or other slope instability or erosion processes that may impact the pipeline On ridge tops, this may be on both sides of the pipeline trench

4 Drying soils (Appendix A-2, Sheet 2D) used as backfill materials can be achieved by spreading the soil in windrows and actively working the windrows until the soil achieves a suitable moisture content Low humidity and warm temperatures are needed to make this work An alternative is the use of lime or cement kiln dust, or a similar product, as an additive to wet soils to help facilitate more optimal moisture content Lime or cement kiln dust is added and mixed with targeted soils, following the manufacturers recommendations, until a suitable soil condition is achieved Use of lime or cement kiln dust allows for working in wetter conditions Mixing rates and methods need to be calibrated to site conditions and may require experimenting to find the right blend for implementation

5 Compact the backfill during side slope ROW reconstruction This adds strength to the backfill to make it more stable, and reduces infiltration of water

6 Where the local soils are not suitable for backfill and compaction, for example due to the sensitive nature of the local fine-grained soils or excessive moisture content, it may be necessary to haul that unsuitable material off the site These materials should not be stockpiled or spoiled in areas that may initiate or exacerbate landslides

(Appendix A-2, Sheet 2E) Replace with a free-draining, angular, clean, small-sized

Rock backfill, ranging from 4 to 8 inches in size, is highly effective for construction as it can maintain steep angles without water retention This type of backfill offers exceptional stability and adaptability to future ground condition changes, such as settlement and ongoing slip movement.

7 Special consideration is needed to construct and restore drainage measures for existing, permanent, and temporary access roads, on a site specific basis Access roads may collect runoff from upslope areas, thereby increasing the contributing basin area draining to any given site, and deliver water to the ROW, the pipeline trench, or to other areas of concern Use drainage measures, as described in this study, to manage and/or mitigate drainage issues, such as slope breakers, water bars, grading to improve drainage, French drains, enhanced drains, armoring, armored ditches with drain pipes, rock fill, etc (Appendix A-2, Sheet 5D)

8 Cover disturbed area with erosion control fabric (Appendix A-2, Sheet 3C), or other functional erosion resistant ground coverings to mitigate over the short-term until the local vegetation can take over and establish itself

9 Track disturbed slopes (Appendix A-2, Sheet 3A) and re-vegetate all disturbed areas to provide long-term surface stabilization (i.e replace the short-term erosion control fabric protection)

Inclined Ridges

Engineering/construction recommendations for inclined ridges

In inclined ridge top scenarios, the risk of backfill saturation is minimized, as water can effectively drain to stable ground on either side of the ridge, thereby reducing focused seepage flows Consequently, the same recommendations for ridge tops apply here However, the inclined gradient creates a need for additional measures to manage and slow seepage flows along the trench Common strategies for addressing seepage in these inclined ridge conditions include implementing effective drainage systems and utilizing barriers to control water movement.

(Appendix A-2, Sheet 2G), except where site assessment recommends reducing backfill over unstable or landslide areas (Appendix A-2, Sheet 2H)

2 Grade the temporary ROW construction surface (Appendix A-2, Sheet 2A) so that it drains away from the inside of the cut The objective is to minimize the potential for infiltrated water to accumulate or tend to move along the transition from the disturbed ROW areas and the undisturbed temporary ROW surface (i.e the native ground) An additional objective is to avoid a situation where the excavated colluvium and residual soils are stockpiled in a manner that traps water, causing the excavated soils to become saturated prior to backfilling the ROW Temporary construction surfaces need to be incorporated into the final site drainage configuration to limit the potential for saturation of the backfill and native soils

3 Grade the temporary ROW surface and depth of the pipeline trench to allow for a stable outboard wedge of soils/rock material adjacent to the pipeline trench (to the out- slope side, Appendix A-2, Sheet 2B) This maintains a protective stable section of ground on the outboard slope side of the pipeline trench that mitigates for potential raveling, degradation, landslide, or other slope instability or erosion processes that may impact the pipeline On ridge tops, this may be on both sides of the pipeline trench

5 Compact the backfill during side slope ROW reconstruction This adds strength to the backfill to make it more stable, and reduces infiltration of water

6 Where the local soils are not suitable for backfill and/or compaction, for example due to the sensitive nature of the local fine-grained soils or excessive moisture content, it may be necessary to haul that unsuitable material off the site These materials should not be stockpiled or spoiled in areas that may initiate or exacerbate landslides

(Appendix A-2, Sheet 2E) Replace with a free-draining, angular, clean, small-sized

Rock backfill measuring between 4 to 8 inches is highly effective for construction projects due to its ability to maintain steep angles without water retention This type of backfill offers exceptional stability and adaptability to changing ground conditions, including settlement and ongoing slip movement.

7 Install drains (Appendix A-2, Sheets 1C and 1E) where seeps or other subsurface water sources are identified during the temporary ROW construction

8 Where surface run-off from one or more slope breakers or other water sources needs to be conveyed down steep slopes that may be subject to erosion, consider using armored channels with an apron at the discharge (Appendix A-2, Sheet 1F and 1E)

For steep terrain the armored channel and more robust drainage piping may be needed (Appendix A-2, Sheet 1H and 1E)

9 Drainage pipes in the pipeline trench are needed to mitigate for the increased gradient and seepage velocities resulting from the sloping ridge top Drainage pipes can be configured as French drains (Appendix A-2, Sheets 1A and 1E) in low seepage flow conditions, with discharge points at the edge of the ROW on stable ground and/or with erosion pads Where excessive seepage along the trench may be a problem, then the piping configuration should be modified to include perforated pipes that collect water and feed into solid-smooth-interior-walled tightline pipes that convey it away (i.e enhanced drains, Appendix A-2, Sheets 1B and 1E)

10 Install Slope breakers (a.k.a water bars) along the ROW at spacing and orientations that intercept and direct surface run-off to stable and (preferably) vegetated areas along and off the ROW Slope breaker spacing is typically governed by slope angle and/or the presence of trench breakers (Appendix A-2, Sheet 5A) In steep slope conditions, a slope breaker should be placed just below a trench breaker, so that seepage that is pushed to the surface by the trench breaker is then captured by the slope breaker and diverted off the ROW Final spacing and placement of breakers should incorporate site specific information Where excessive run-off may need to be mitigated, then slope breakers can be discharged to an armored ditch or diversion channel (Appendix A-2, Sheets 5C, 6D, 1F and 1E)

11 Install trench breakers (Appendix A-2, Sheet 4A), preferably using sandbags, at spacing and locations corresponding to the trench slope (not necessarily the ground slope, which may be much steeper) Where foam materials are used for the breakers, there should be drainage measures incorporated into breakers that mitigate for accumulation of seepage on the upslope side of the breaker, allowing it to drain through the breaker

12 Install sack-crete breakers (Appendix A-2, Sheet 4C) in areas where the trench and slopes are steep and the breaker is needed to retain and/or stabilize the trench backfill These structures may be configured to provide a foundation for imported backfill, retain backfill in the trench itself on steep terrain, or to stabilize larger portions

To mitigate land movement in rugged and steep terrain, it is essential to install a sleeve interface, such as geotextile fabric or rock-shield, between the pipeline and large structures or trench backfill areas This interface provides slip separation, preventing the transfer of loading from the trench backfill to the pipeline, ensuring the integrity of the pipeline system.

13 Where the pipeline alignment passes through benched terrain, mitigate for complex backfill and drainage conditions by using rock fill, sack-crete breakers, enhanced drainage, or other measures, as needed (Appendix A-2, Sheet 10A) Benched topography can be very complex and may require site specific review to develop a practical and constructible mitigation and restoration package

14 Special consideration is needed to construct and/or restore drainage measures for existing, permanent, and temporary access roads, on a site specific basis Access roads may collect runoff from upslope areas, thereby increasing the contributing basin area draining to any given site, and deliver water to the ROW, the pipeline trench, or to other areas of concern Use drainage measures, as described in this study, to manage and/or mitigate drainage issues, such as slope breakers, water bars, grading to improve drainage, French drains, enhanced drains, armoring, armored ditches with drain pipes, rock fill, etc (Appendix A-2, Sheet 5D)

15 Cover disturbed area with erosion control fabric (Appendix A-2, Sheet 3C), or other functional erosion resistant ground coverings to mitigate over the short-term until the local vegetation can take over and establish itself

16 Track disturbed slopes (Appendix A-2, Sheet 3A) and re-vegetate all disturbed areas to provide long-term surface stabilization (i.e replace the short-term erosion control fabric protection)

Planar Slopes

Engineering/construction recommendations for planar slopes

Installing pipelines on planar slopes connects ridge tops to lower flat terrain, often involving long sections of right-of-way (ROW) with steep gradients While construction is common, it typically limits clearing and grading to vegetation and topsoil removal, maintaining a continuous vertical profile without significant lateral cuts In cases where lateral excavations are necessary, recommendations for side slope scenarios should be applied The presence of bedrock steps and benches along planar slopes often requires cutting through these features to establish the ROW and excavate the trench, necessitating site-specific plans These conditions pose unique challenges for both short and long-term restoration, with typical restoration measures tailored to planar slope environments.

2 Grade the temporary ROW construction surface (Appendix A-2, Sheet 2A) so that it drains positively away from the inside of the cut The objective is to minimize the potential for infiltrated water to accumulate, or tend to move along the transition from the disturbed ROW areas and the undisturbed temporary ROW surface (i.e the native ground) An additional objective is to avoid a situation where the excavated colluvium and residual soils are stockpiled in a manner that traps water, causing the excavated soils to become saturated prior to backfilling the ROW Temporary construction surfaces need to be incorporated into the final site drainage configuration to limit potential for saturation of the backfill and/or native soils

3 Compact the backfill (Appendix A-2, Sheet 2C) during side slope ROW reconstruction This adds strength to the backfill to make it more stable, and reduces infiltration of water Achieving compaction in steep and rugged terrain is difficult Recommended methods include use of sheep’s-foot rollers pulled behind a dozer, a self-propelled sheep’s-foot compactor, or sheep’s-foot roller attached to an excavator arm

5 Where deeper excavations along the planar slope are required to construct the temporary ROW, resulting in cut slopes and lowered grades that cannot drain to an outboard natural slope (i.e laterally confined drainage areas), then install armored channels with drains in shallow excavation areas (Appendix A-2, Sheet 1F or 1H in steep ground), or install French drains (Appendix A-2, Sheet 1A) in deeper excavation areas

In steep terrain the armored channel and more robust drainage piping may be needed (Appendix A-2, Sheet 1H and 1E)

7 Where the local soils are not suitable for backfill and/or compaction, for example due to the sensitive nature of the local fine-grained soils or excessive moisture content, it may be necessary to haul that unsuitable material off the site These materials should not be stockpiled or spoiled in areas that may initiate or exacerbate landslides

(Appendix A-2, Sheet 2E) Replace with a free-draining, angular, clean, small sized

Rock backfill measuring between 4 to 8 inches is highly effective for construction projects due to its ability to maintain steep angles and prevent water retention This type of backfill offers exceptional stability and can adapt to future ground condition changes, such as settlement and ongoing slip movement.

8 Drying soils used as backfill materials can be achieved by spreading the soil in windrows and actively working the windrows until the soil achieves a suitable moisture content (Appendix A-2, Sheet 2D) Low humidity and warm temperatures are needed to make this work An alternative is the use of lime or cement kiln dust, or a similar product, as an additive to wet soils to help facilitate more optimal moisture content

Lime or cement kiln dust is mixed with specific soils according to manufacturer guidelines to improve soil conditions, enabling work in wetter environments It is essential to adjust mixing rates and methods based on site conditions, which may involve experimentation to identify the optimal blend for effective implementation.

9 In cases where bedrock steps or benches (Appendix A-2, Sheet 10A) have been blasted or ripped to build the ROW and the trench, these spoil materials may be used, crushed, or re-processed to provide a more suitable backfill rock material that can be handled and placed as needed to rebuild and restore the ROW Restoring rock benches to re-create the pre-project bench geometry may not be possible, and is typically very difficult to achieve Backfill through rock benches should use angular rock materials to create safe slopes and provide the required cover over the pipeline trench Use of fine-grained soils in rock cuts should be avoided, and would require additional special drainage measures and possible engineered stabilization of the soil backfill Use of angular rock fill eliminates these requirements

10 Drainage pipes in the pipeline trench are needed to mitigate for the increased gradient and seepage velocities resulting from the sloping trench (i.e due to the oblique orientation of the trench along the side slope) Drainage pipes can be configured as

French drains are essential in managing low seepage flows and mitigating issues in temporary right-of-way (ROW) constructed surfaces, particularly in areas prone to excessive seepage on steep slopes To enhance drainage efficiency, the configuration should incorporate perforated corrugated pipes that collect water and direct it into solid, smooth-interior-walled tightline pipes for effective conveyance It is crucial that drainage pipes discharge at the edge of the ROW onto stable ground or utilize erosion pads to prevent soil erosion and maintain stability.

11 Install Slope breakers (a.k.a water bars) along the ROW at spacing and orientations that intercept and direct surface run-off to stable and (preferably) vegetated areas along and off the ROW, away from sensitive areas such as landslides Slope breaker spacing is typically governed by slope angle and/or the presence of trench breakers

In steep slope conditions, it is essential to position a slope breaker below a trench breaker to effectively capture and divert seepage away from the right-of-way (ROW) and sensitive areas like landslides The final placement and spacing of these breakers should be tailored to site-specific conditions Additionally, in cases where excessive runoff needs to be managed, slope breakers may be directed to an armored ditch or diversion channel for better control and protection.

12 Install trench breakers (Appendix A-2, Sheet 4A), preferably using sandbags, at a spacing and location corresponding to the trench slope (not necessarily the ground slope, which may be much steeper) Where foam materials are used for the breakers, there should be drainage measures incorporated into breakers that mitigate for accumulation of seepage on the upslope side of the breaker, allowing it to drain through the breaker

Convergent Topography

Engineering/construction recommendations for convergent topography

Typical conceptual restoration measures in these areas are the same as those described for side slope (Appendix A-1, Sheet 1110 and 1120) and planar slope (Appendix A-1, Sheet 1150 and 1160) conditions.

Shallow Bedrock

Engineering/construction recommendations for Shallow Bedrock

Typical conceptual restoration measures used in shallow bedrock conditions may include (but is not limited to):

1 Typical bedrock trench conditions in generally flat terrain may have challenges generating enough material for padding/bedding and for backfill, where the spoils are large and angular resulting from the blasting, ripping or chipping excavations Rock guard materials may be needed to provide additional protection around the pipeline to allow for irregularities in the trench bottom and oversized materials in the backfill

2 In typical ground conditions, install trench breakers (Appendix A-2, Sheet 4A), preferably using sandbags, at a spacing and location corresponding to the trench slope (not necessarily the ground slope, which may be much steeper) Sandbag breakers allow normal seepage to slowly migrate through the breaker Where needed, piping may be added to allow this slow movement of trench seepage water, and avoid excessive accumulations of seepage water on the upslope side of breakers Where foam materials are used for the breakers, there should be drainage measures incorporated into breakers that mitigates for accumulation of seepage on the upslope side of the breaker, allowing it to drain through the breaker

3 In steep rock trench conditions, the backfill may become unstable due to locally over- steepened slopes and/or the contribution of seepage water to the trench In these conditions, sandbag (Appendix A-2, Sheet 4A) or sack-crete (Appendix A-2, Sheet 4C) trench breakers are effective at retaining trench backfill and stabilizing ROW backfill The use of sack materials allows for building contour forming structures that have the mass and geotechnical properties to retain backfill soils or rock materials in steep conditions Use of foam breaker materials is not recommended in steep conditions Drainage piping should be added to breakers in steep conditions to collect and convey and evacuate accumulated seepage flows

4 Trench breakers in steep rock trench conditions should have a sleeved interface, such as a geotextile fabric or rock shield material, between the breaker and the pipeline that breaks the bond that may develop between the breaker material and the pipeline

(Appendix A-2, Sheet 4D) Where a tight and bonded connection between the pipeline and breaker occurs, the load from the backfill may be transferred to the pipeline, resulting in increased stress conditions

5 Drainage pipes in the pipeline trench are needed to mitigate for the increased gradient and seepage velocities resulting from the sloping trench (i.e due to the oblique orientation of the trench along the side slope) Drainage pipes can be configured as

French drains (Appendix A-2, Sheets 1A and 1E) where seepage flows are low, with discharge points at the edge of the ROW on stable ground and/or with erosion pads

To address issues of excessive seepage along trenches, it is essential to modify the piping configuration by incorporating perforated corrugated pipes These pipes effectively collect water and channel it into solid, smooth-walled tightline pipes, which then transport the water away, enhancing drainage efficiency.

6 Cut bleeder trenches (Appendix A-2, Sheet 1D) into the downslope side of the pipeline trench at an approximate 100-foot spacing, or to match the local topography Bleeders should be cut down to the bottom of the pipe trench excavation, and then slope to drain out through native soil or rock (i.e not in fill) and discharge on stable ground Bleeders can be enhanced by adding geotextile wrapped drain rock, and/or drainage pipeline (i.e French drains) The objective of bleeder trenches is to provide drainage relief points at regular intervals, so that as seepage accumulates, it finds an outlet from the trench

7 Install slope breakers (a.k.a water bars) along the ROW at spacing and orientations that intercept and direct surface run-off to stable and (preferably) vegetated areas along and off the ROW Slope breaker spacing is typically governed by slope angle and the presence of trench breakers (Appendix A-2, Sheets 4A and 4C) In steep slope conditions, a slope breaker should be placed just below a trench breaker, so that seepage that is pushed to the surface by the trench breaker is then captured by the slope breaker and diverted off the ROW Final spacing and placement of breakers should incorporate site specific information Where slope breakers are not possible, then consider using armored ditches with a drain pipe in the bottom to collect and convey surface run-off (Appendix A-2, Sheets 1F and 1E)

9 Special consideration is needed to construct and/or restore drainage measures for existing, permanent, and temporary access roads, on a site specific basis Access roads may collect runoff from upslope areas, thereby increasing the contributing basin area draining to any given site, and deliver water to the ROW, the pipeline trench or to other areas of concern Use drainage measures, as described in this report, to manage and mitigate drainage issues, such as slope breakers, water bars, grading to improve drainage, French drains, enhanced drains, armoring, armored ditches with drain pipes, rock fill, etc (Appendix A-2, Sheet 5D)

10 Where the pipeline alignment passes through benched terrain, mitigate for complex backfill and drainage conditions by using rock fill, sack-crete breakers, enhanced drainage or other measures, as needed (Appendix A-2, Sheet 10A) Bench topography can be very complex and may require site specific review to develop a practical and constructible mitigation and restoration package

Modifications or alternatives to the above described measures that are feasible and maintain the function and intent as described and offer practical alternatives are encouraged

Areas of Fill Soils

Engineering/construction recommendations for Areas of Fill Soils

Mitigating fill areas requires site-specific information and conditions, making it essential to address each case individually Expert input is crucial for understanding the type and nature of the fill, necessitating thorough investigations, analyses, and specialized engineering solutions While fill areas pose significant hazards, this article provides only a general overview of the issue.

Landslides

General Engineering/construction recommendations for Landslides

Landslides identified along a proposed pipeline route must be thoroughly characterized and assessed for potential hazards It is essential to evaluate the constructability of the pipeline in areas affected by these landslides In certain situations, tailored mitigation recommendations may be necessary, informed by site-specific assessments and investigations.

The following provides a brief summary of typical conceptual mitigation measures that may be employed at a landslide site, recognizing that any recommendations should incorporate site specific information:

1 Backfill around the pipeline using select “deformable” materials that allow for some movement of the backfill relative to the pipeline as the ground around it moves, before the movement begins to impact the pipeline, thereby attenuating accumulation of strain in the pipeline resulting from differential ground movement Deformable backfill is typically a loose granular sand material with little or no fines The deformable backfill is placed in a sloped wall trench all around the pipeline, allowing for more material along the direction and orientation (i.e horizontal and vertical) of landslide movement relative to the pipeline Typical dimensions for deformable backfill relative to the pipeline should match the expected horizontal and/or vertical ground displacement A filter fabric layer should be included around the backfill to limit the migration of local fine-grained soils into the imported backfill materials (Appendix A-2, Sheet 12B) The properties of the select backfill also have enhanced drainage performance, which can further mitigate landslide hazards, addressed in the following points

3 Cut bleeder trenches (drains) (Appendix A-2, Sheet 1D) into the downslope side of the pipeline trench at approximately 100-foot spacing, or to match the local topography

Bleeders must be excavated to the base of the pipeline trench and sloped to facilitate drainage through native soil or rock, ensuring discharge occurs on stable ground Enhancements such as geotextile-wrapped drain rock or drainage pipelines, like French drains, can improve their effectiveness The primary goal of bleeder trenches is to create regular drainage relief points, allowing accumulated seepage to exit the trench efficiently.

4 Install brow ditches (Appendix A-2, Sheet 6B) excavated into the ground, slope breakers (Appendix A-2, Sheets 5A and 5B), a combination of built-up and excavated water bars and/or armored channels with drain pipes (Appendix A-2, Sheets 1F, 1H - in steep terrain and 1E) along the upslope side of the ROW to intercept and divert surface run-off to stable locations away from the side slope areas The need and layout of these depends on the topography If there is no stable location to discharge the intercepted water, then rely more on other measures

In steep terrain the armored channel and more robust drainage piping may be needed (Appendix A-2, Sheet 1H and 1E)

6 Grade the temporary ROW construction surface (Appendix A-2, Sheet 2A) so that it drains away from the inside of the cut The objective is to minimize the potential for infiltrated water to accumulate, or tend to move along the transition from the disturbed ROW areas and the undisturbed temporary ROW surface (i.e the native ground) An additional objective is to avoid a situation where the excavated colluvium and residual soils are stockpiled in a manner that traps water, causing the excavated soils to become saturated prior to backfilling the ROW Temporary construction surfaces need to be incorporated into the final site drainage configuration to limit potential for saturation of the backfill and/or native soils

7 Grade the temporary ROW surface and depth of the pipeline trench to allow for a stable outboard wedge of soils/rock material adjacent to the pipeline trench (to the out- slope side, Appendix A-2, Sheet 2B) This maintains a protective stable section of ground on the outboard slope side of the pipeline trench that mitigates for potential raveling, degradation, landslide, or other slope instability or erosion processes that may impact the pipeline

8 Compact the backfill (Appendix A-2, Sheet 2C) during side slope ROW reconstruction This adds strength to the backfill to make it more stable, and reduces infiltration of water Achieving compaction in steep and rugged terrain is difficult Recommended methods include use of sheep’s-foot rollers pulled behind a dozer, a self-propelled sheep’s-foot compactor, or sheep’s-foot roller attached to an excavator arm

10 Haul materials off-site where the local soils are not suitable for backfill and compaction due to the sensitive nature of the local fine-grained soils or excessive moisture content These materials should not be stockpiled or spoiled in areas that may initiate or exacerbate landslides (Appendix A-2, Sheet 2E) Replace with a free-draining, angular, clean, small sized (i.e min 4 to 8 inch) rock backfill (Appendix A-2, Sheets 2F

Land movement mitigation in rugged and steep terrain can be effectively achieved using specialized rock backfill This material is designed to maintain stability at steep angles, prevent water retention, and adapt to future ground condition changes such as settlement and ongoing slip movement.

11 Final grading and ROW restoration in the area of the landslide should minimize cover depth over the pipeline (Appendix A-2, Sheet 2H) For instance, replacing deep fill soils over the pipeline in the post-landslide restoration condition may further exacerbate the problem Cover depth over the deformable backfill should be minimized to the greatest extent possible, to further reduce soil backfill loading on the landslide area This may require hauling excess spoils away from the site

12 Drainage pipes in the pipeline trench collect and discharge seepage and near-surface flows within the trench excavation depth Drainage pipes can be configured as French drains (Appendix A-2, Sheets 1A and 1E) running along the pipeline for low seepage flow conditions, or in specific locations to collect seepage trapped by grading of the temporary ROW or targeted seeps Where excessive seepage along the trench may be a problem, then the piping configuration should be modified to include perforated corrugated pipes that collect water and feed into solid-smooth-interior-walled tightline pipes that convey it away (i.e enhanced drains, Appendix A-2, Sheet 1B) Drainage piping can be configured to collect and convey seepage in targeted areas of the landslide, to make for more efficient discharge of flows or even to provide monitoring of specific areas (i.e isolating piping from targeted areas to track corresponding flows from those areas) Discharge points should be located at the edge of the ROW on stable ground and/or with erosion pads (Appendix A-2, Sheet 1E)

13 Drains may be needed at specific locations to address localized seepage, springs, wet areas, or ponded water areas that influence a landslide (Appendix A-2, Sheet 1C)

French drains or alternative configurations utilizing perforated and solid-wall pipes, combined with sandbags and geotextile-wrapped drain rock, can be customized to effectively manage specific site conditions.

When planning pipe placement near landslide areas, it is crucial to consider potential site changes and their impact on the pipes For instance, positioning collection or conveyance pipes perpendicular to a landslide shear boundary that may shift over time can lead to pipe damage and the risk of water discharge back into the landslide Ideally, pipes should be situated outside the landslide boundaries If this is not feasible, they should be aligned parallel to the landslide geometries and positioned to cross the landslide footprint at the downstream side, ensuring that any disruption allows water to flow away from the site.

14 Where landslides are located on sloping ground, trench breakers (Appendix A-2,

UNCERTAINTY IN FUTURE MITIGATION AND REPAIR COSTS

This article examines the uncertainties surrounding future mitigation and repair costs, drawing on findings from the Williams OVM system in northern West Virginia, specifically focusing on land movement mitigation efforts that have been completed.

Between 2012 and 2015, a probabilistic risk-based assessment was conducted to evaluate actual costs associated with landslide and erosion hazard mitigation at various sites This assessment included expenses related to equipment, materials, labor, access, permitting, design, and environmental operations Additionally, it considered potential future repair costs and long-term maintenance expenses, such as drainage improvements and stress relief excavations It is important to note that even after mitigation efforts, recurring landslide and erosion hazards may still affect the pipeline and right-of-way (ROW).

This article highlights the significance of employing a risk-based evaluation of landslide and erosion hazards in pipeline systems, akin to the methodologies used in OVM By utilizing relevant data and analyses, the discussion emphasizes how this approach can enhance operation and maintenance efforts, ultimately focusing on the mitigation costs associated with pre-emptive measures to minimize the likelihood of such hazards.

“failure”) is generally an order of magnitude lower than the un-mitigated cost risk (i.e cost to correct post

This article discusses the landslide and erosion hazards that pose risks to pipelines and right-of-way (ROW) areas The findings presented illustrate the types of hazards encountered and the mitigation efforts undertaken in the OVM region While detailed cost information is not included, these results serve as a basis for discussion and planning, and should not be relied upon for final cost estimations.

Costs associated with landslide and erosion hazards in the OVM are categorized based on their potential threat to pipeline integrity and right-of-way (ROW) For clarity, these hazards are classified into low-hazard sites and a combined moderate to high-hazard classification, as outlined in Table 5-1 This classification highlights the cost risk differences between maintenance activities at low-hazard sites, which pose a lower threat to integrity, and scenarios involving moderate to high-hazard sites that necessitate more rigorous review and management decisions for operational and maintenance actions.

Table 5-1: General Pipeline Integrity Hazard Description

Pipelines that traverse areas with active landslides or erosion hazards face significant stress, increasing the risk of damage from further land movement Observations or measurements indicating an active hazard can suggest that the pipeline is under stress and may necessitate mitigation measures to ensure safety and integrity.

Shallow landslides or limited erosion hazards can occur on or near the right-of-way (ROW) and may intersect the pipeline alignment However, the pipeline is typically situated in stable ground or trench, remaining below the landslide failure surface or the extent of erosion.

Continued hazard activity or possible lateral expansion/retrogression across the pipeline may occur in the future, but will likely not affect the pipeline

A risk-based evaluation of potential costs for additional sites, utilizing existing costing information and assessments from subject matter experts, was performed The findings, illustrated in Figure 5-1, indicate that the estimated mitigation costs for low-hazard landslide and erosion hazard sites range from approximately $40,000 to $160,000, corresponding to the 20th and 80th percentiles, respectively, based on data from 2014.

The estimated mitigation costs for landslide and erosion hazards that could jeopardize pipeline integrity range from approximately $180,000 to $600,000, reflecting the 20th to 80th percentiles based on 2014 USD values.

The cost risk was quantified without any mitigation efforts, focusing on un-mitigated risk factors The assessment evaluated various variables, including the likelihood of geologic hazards such as landslides and erosion, while acknowledging but excluding risks from pipeline material defects and construction accidents Key considerations encompassed the type, size, and proximity of hazard sites, construction costs for repairing land movement affecting the pipeline, expenses for damage repair and rerouting, potential rupture risks, staffing and overhead costs, loss of revenue from ruptures, remediation costs for hydrocarbon releases, and possible environmental impacts.

The data presented in Figure 5-2 indicates that potential unmitigated cost risks for low-hazard landslide and erosion sites can reach up to around $800,000, as identified in Table 5-1, representing the 80th percentile in 2014 USD Furthermore, there is minimal to no cost risk linked to low-hazard sites below this threshold.

The analysis indicates that the cost to mitigate low-hazard sites at OVM is likely higher than repairing a failure, suggesting a reduced response level may be appropriate In contrast, moderate to high-hazard sites pose a significant risk to pipeline integrity, necessitating a more robust response The potential un-mitigated cost risk for these sites ranges from approximately $0.5 million to $7 million, reflecting the 20th to 80th percentile in 2014 USD This broader cost risk range underscores the varying adverse impacts associated with higher-hazard sites.

Figure 5-2: Un-mitigated Cost Risk

The cost risk findings must be evaluated in light of the available data, which reflects the shallow translational landslides and erosion hazards common in northern West Virginia, as discussed in this study These findings, along with the assessments from subject matter experts involved in the risk evaluations, reveal a significant difference in the cost risks associated with mitigated versus unmitigated landslide and erosion hazards.

Mitigation efforts cannot completely eliminate land movement, landslides, or erosion hazards; however, a thorough proactive mitigation program can greatly lower the risks for pipeline operators and owners Implementing a comprehensive system-wide approach not only enhances safety but also yields cumulative benefits over time.

CONCLUSIONS

Identifying and characterizing landslide and erosion hazards along a proposed pipeline alignment is crucial at every project phase While careful planning and routing can help avoid these threats, mitigation strategies may be necessary when hazards cannot be circumvented Often, these measures aim to reduce risks to an acceptable level rather than completely eliminate them, such as using deformable backfill and scheduling stress relief excavations Therefore, mitigation should align with the risk tolerance of the owner/operator, weigh the costs and benefits of both long-term and short-term solutions, and integrate construction considerations into the planning and design processes.

Experience with OVM indicates that land movement in this region is often linked to surface and subsurface water, alongside recent or historical geological changes and construction activities This frequent combination of factors led to the creation of Typical Scenarios and Typical Details, facilitating the development of site-specific mitigation designs Throughout this process, several critical considerations for mitigating land movement on pipeline rights-of-way (ROWs) were identified.

Identifying landslide and erosion hazards is crucial for effective project design, planning, and construction Mitigation strategies must be customized to suit specific site conditions while balancing costs with the practicality of installation and risk management Although the science of identifying and characterizing these hazards is not covered in detail here, this document emphasizes the importance of implementing tailored mitigation efforts to address such risks effectively.

Effective route selection is essential for identifying and mitigating hazards that could affect pipelines and right-of-ways (ROWs) Prioritizing careful planning and routing helps to prevent or reduce risks associated with landslides and erosion However, when these hazards are unavoidable, implementing mitigation strategies becomes necessary to ensure the safety and integrity of the infrastructure.

Incorporating site-specific mitigation measures into project planning is essential for addressing pipeline threats and right-of-way (ROW) challenges Landslides and erosion hazards often arise from multiple contributing factors, making it crucial to identify the primary geologic hazards and the relevant geotechnical and hydrotechnical engineering processes involved in land movement This understanding supports the effective selection, planning, and design of a mitigation plan Ultimately, the owner or operator must determine the acceptable level of risk associated with the chosen mitigation strategy.

The relationship between land movement and both surface and subsurface water is influenced by changes in local ground conditions due to recent or historical geological shifts and construction activities Effective mitigation strategies include re-grading the right-of-way (ROW) surface, enhancing local drainage systems, and utilizing engineered backfill materials Additional measures involve the removal of unstable soil, implementing erosion protection, and employing slope and trench breakers Special pipeline coatings, protective sleeve-wraps, and tailored ROW configurations are also crucial These strategies are often combined to create a comprehensive approach for managing site-specific hazards.

To tackle unstable slopes, various structural measures can be employed, including retaining walls, soldier piles, sheet piles, wire mesh systems, and mechanically stabilized earth systems While these solutions can effectively enhance slope stability, they often come with high costs, necessitate specialized equipment for installation in steep conditions, and may restrict future access or expansion in limited right-of-way corridors Additionally, these structures may require ongoing maintenance to ensure their long-term effectiveness.

 Reducing ground disturbance through minimized ROW footprints, appropriately sized and applicable equipment, and planning construction during optimal seasonal conditions (i.e dry versus wet) can minimize mitigation requirements;

When addressing landslide and erosion processes, it's crucial to evaluate the water sources in relation to the constructed pipeline right-of-way (ROW) Mitigation measures must take into account the temporarily disturbed ground surface resulting from the initial grading and construction activities, rather than focusing solely on the final restored ROW surface.

Organizing mitigation options into a structured framework of Typical Scenarios and corresponding Typical Details, aligned with the construction of the right-of-way (ROW) such as ridge tops, planar slopes, and side slopes, facilitates the swift creation of conceptual, site-specific mitigation plans during the project planning and design phases.

Designing strategies to address specific threats from land movement enables owners and operators to choose their desired level of risk mitigation This approach provides them with the necessary time to evaluate and make informed, risk-based decisions on effectively managing their assets.

Effective mitigation strategies require an understanding of the various factors influencing a site and may involve long-term performance monitoring for complete risk reduction In some cases, the goal of mitigation is not to permanently eliminate hazards but to reduce risks to an acceptable level along the pipeline right-of-way (ROW) Therefore, mitigation measures must be customized to address specific site conditions, account for the risk tolerance of the owner/operator, evaluate the costs and benefits of both long-term and short-term solutions, and incorporate construction considerations into the planning and design phases, ensuring seamless integration with the construction process.

Although mitigation efforts cannot entirely eliminate landslides or erosion hazards, a comparison of costs between mitigated and un-mitigated scenarios indicates that a robust, proactive mitigation program implemented across the entire system can greatly lower overall risks in pipeline systems and yield cumulative benefits over time.

DEFINITIONS

This article offers concise definitions of key terminology relevant to the discussed topics, aimed at enhancing understanding and facilitating further exploration Readers are encouraged to delve deeper into any definition for additional details or specific information The definitions provided are drawn from our extensive experience in the oil and gas industry, as well as other pipeline-related expertise.

Armoring involves the installation of small diameter, angular riprap materials, geotextiles, biodegradable materials, or vegetation to prevent soil erosion on temporary or restored right-of-way (ROW) surfaces This method is commonly used alongside surface flow conveyance in designated channels and serves to protect steep slopes from erosion caused by runoff.

A bleeder drain is an effective drainage mitigation method designed to manage seepage flows in pipeline trenches It involves creating a gravity drainage pathway at the lowest point of the trench, often utilizing drain rock backfill wrapped in filter fabric, similar to a French drain This system is particularly beneficial in sidehill conditions where the pipeline gradient is flat, ensuring that excess water is effectively conveyed away from the trench.

Cost risk refers to the uncertain expenses arising from potential landslide or erosion failures, including emergency response costs, environmental clean-up, fines, lost revenue, and expenses related to planning, design, engineering, and construction to address these failures Unmitigated cost risk pertains to the financial impacts associated with sites that have not undergone mitigation efforts to lessen the likelihood or consequences of such failures In contrast, mitigation costs are the expenses incurred to reduce the hazards, thereby lowering both the probability of failure and the associated unmitigated cost risk.

Cover depth – the measurement from top of a pipeline to ground level along the ROW

Convergent topography features U-shaped or closed drainage basins characterized by steep slopes that direct surface runoff to a specific area at the valley's bottom or the slope's toe This process enhances and concentrates both surface and near-subsurface water flows, creating significant sources of water in these regions.

Cut and Fill – the cut down high ground and/or fill in low ground to achieve a uniform or design grade

Deformable backfill is a specialized material used around pipelines to accommodate movement caused by land shifts, such as landslides This backfill consists of loose granular sand with minimal fines, allowing it to deform and relieve stress on the pipeline as it adjusts to displacement It is strategically placed in a sloped wall trench that matches the anticipated movement dimensions, ensuring that the material is oriented appropriately to mitigate the effects of horizontal or vertical landslide forces By using deformable backfill, the risk of pipeline damage due to land movement is significantly reduced.

Easement – a right that one individual or company has to access land typically representing the ROW footprint; may be differentiated by temporary construction related easements versus permanent ownership

Enhanced drain is an effective drainage mitigation method that combines perforated pipes for collecting seepage and sub-surface water with solid-wall pipes for transporting the collected water away The perforated pipe segments, usually ranging from 50 to 100 feet in length, are encased in free-draining gravel or sand and protected by geotextile filter fabric Meanwhile, the conveyance pipes can be backfilled with native soils and are typically equipped with an erosion pad at the discharge point.

Erosion – grain-by-grain movement of soil and/or rock resulting from gravity or flowing water

A French drain is an effective drainage solution that consists of a perforated pipe encased in free-draining gravel or sand, along with a geotextile filter fabric This system is designed to capture and transport groundwater seepage, particularly in shallow subsurface environments.

Geology – the science that deals with the dynamics and physical history of the Earth’s materials, and the processes that act on it, and that change it

Geodetic monitoring involves surveying specific points over time to observe and track changes in their positions This technique is particularly useful at landslide sites, where it helps in monitoring alterations in ground position and elevation.

Geotechnical Engineering – the science and engineering addressing the Earth’s materials with a focus on geotechnics, soil and rock mechanics, slope stability, subsurface conditions, soil interactions, etc

Grading is essential for creating a smooth and even work area that allows for the efficient movement of equipment along the Right of Way (ROW) This process involves cutting and filling the native ground to establish a temporary surface that supports construction activities.

Hazard – in the context of this document; includes geologic, geotechnical, or hydrotechnical processes and conditions that can threaten the pipeline or ROW

Hydrotechnical Engineering is a specialized field that combines science and engineering to study and manage the earth's materials, emphasizing key areas such as hydrotechnics, hydrology, and hydraulics This discipline also explores fluvial geomorphology, erosion, scour, and the interactions between surface and near-subsurface water and soil.

Inclinometer – a monitoring instrument used to measure and monitor changes in horizontal displacements along a borehole resulting from subsurface ground movement, particularly associated with landslide activity

Land movement – generally describes horizontal and/or vertical changes in ground conditions resulting from landslide and/or erosion processes

Landslide – mass movement of soil and/or rock down a slope from the effects of gravity

Mitigation – in the context of this document; the planning, design, engineering, or construction efforts that are implemented or intended to reduce risk associated with an identified hazard

Normal – orientation of a pipeline alignment that generally follows sidehill with the contours and perpendicular (i.e normal) to the fall-line (i.e alignment straight down) of the slope

Oblique pipeline alignment refers to positioning a pipeline at an angle to the fall-line, which is the direct path straight down a slope This alignment can occur as the pipeline traverses down planar surfaces or runs alongside sidehill slopes.

Padding – screened or sifted soils placed in a trench to prevent the pipeline from damage caused by rocky or coarse grained trench backfill,

Piezometer – a monitoring instrument installed in a well or casing to track and monitor subsurface ground water levels

Pipeline – a system of connected lengths of pipe, usually buried, that is used for transporting liquid or gaseous products The pipeline can be used as a conveyor or a temporary storage container

Planar slopes refer to the construction of pipeline alignments and rights-of-way (ROW) in sloping terrain that appears generally flat when viewed down the slope While there may be some vertical variation, the alignment typically transitions through localized flatter or steeper segments as it moves up or down the slope In this context, the catchment area, which is the basin that captures rainfall, is usually confined to the disturbed ROW itself However, this area can expand if the pipeline ROW runs at an angle to the slope's fall-line.

The construction of pipeline right-of-way (ROW) along ridge tops, which are the highest elevation areas, effectively minimizes the catchment area that drains into the disturbed ROW This approach reduces the basin area capable of capturing rainfall In steeper ridge top regions, these areas are identified as 'inclined ridge tops.'

Right-of-Way (ROW) refers to the legal entitlement to pass through public land and privately owned property, encompassing the area designated for this purpose The width of a ROW typically ranges from 50 to 150 feet, depending on specific contract agreements and individual easements.

Routing – the planning and decision making process for selecting a pipeline alignment

Tiêu đề	Mitigation of Land Movement in Steep and Rugged Terrain for Pipeline Projects: Lessons Learned from Constructing Pipelines in West Virginia
Tác giả	Golder Associates, Inc.
Trường học	The INGAA Foundation, Inc.
Chuyên ngành	Geotechnical Engineering
Thể loại	final report
Năm xuất bản	2016
Thành phố	West Virginia

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Số trang	134
Dung lượng	8,62 MB