The US Environmental Protection Agency defines wetlands as lands where saturation with water is the dominant factor determining the nature of soil development and the types of plant and animal communities living in the soil and on its surface. Wetlands are found from the tundra to the tropics on every continent except Antarctica and include swamps, marshes, bogs and similar areas.

The prevalence of wetland terrain means that pipeline engineers, environmental consultants, construction contractors, and product and service providers operating anywhere around the world could be bidding for work on a pipeline which traverses wetland terrain. Knowing the challenges unique to these environments could be the key in securing a competitive tender.

Getting equipped

Choosing the right equipment is essential to avoid getting bogged down when installing pipelines in marsh, swamp and wetland terrain. Three manufacturers and distributors of amphibious equipment in North America explain the benefits of amphibious equipment.

Remote access vehicle manufacturer PFM Manufacturing supplies Land Tamer amphibious vehicles to pipeline construction companies in North America and around the world. PFM’s Patrick Miller Jr says that the main advantage of using amphibious vehicles for marsh or swamp terrain is their low ground pressure design. “They can cross over bogland, mud or swamp without leaving deep tracks and because of the low ground pressure, are much more environmentally friendly than other vehicles.

“Most amphibious equipment can float in water and this is the major advantage over non-amphibious vehicles. An amphibious vehicle needs to be able to make the transition from hard ground to swamp muskeg, to open water and get you back to your destination safely with minimal problems and minimal hassle,” says Mr Miller Jr.

US-based amphibious vehicle manufacturer Hydratrek’s Craig Simonton agrees that amphibious equipment has a range of benefits saying “There are many applications and reason to use amphibious equipment in marshes, swamps, and wetland areas. First, the machines are made from 100 per cent aluminium, which provides added durability, ruggedness, and safety over conventional all-terrain vehicles. Second, most equipment is built standard with rubber over-the-tyre tracks that can be used for multiple terrains and surfaces. The tracks lower the ground pressure significantly and allow the vehicles to handle heavy mud, excessive vegetation and debris with relative ease.

“Due to the rubber track system, the environmental impact is reduced significantly. Most equipment that is used in the industry is very large and weighs several tonnes. Utilising tracks instead of tyres will reduce the ground pressure, keeping the equipment from uprooting the vegetation and allowing the area to recover more quickly. Also, the diesel engines are very clean burning and fuel efficient compared to gasoline engines,” says Mr. Simonton.

Several small and large companies such as Tennessee Valley Authority, Georgia Power, Texas Gas Transmission, Hydro One, Atco Electric and Xcel Energy are using Hydratrek amphibious equipment on a daily basis for utility and gas projects all across North America. Applications range from right-of-way (RoW) survey and management, new line construction, vegetation control, auxiliary transport vehicle, and wildfire suppression.

Sunland Construction has completed two major 42 inch pipeline spreads for Cheniere Pipeline's Creaole Trail Pipeline in Louisiana, totalling 68 km, with the help of Sunland-Kori amphibious undercarriages. Sunland Construction also used Sunland-Kori amphibious undercarriages while working on 27 km of 42 inch pipeline for the Golden Pass Pipeline in Texas.

Sunland Construction Gulf Coast Division Manager Louis Ledet Jr says that during those projects amphibious equipment allowed excavators to manoeuvre in marsh and swamp areas without disturbing the terrain. “This is an important characteristic as contractors today are responsible for complying with strict environmental standards.”

Being versatile is key when working in swampland, and amphibious equipment manufacturers offer a variety of ‘boom-and-stick’ options, buckets, and other attachments to meet the demands of any operation.

“Many upper attachments are interchangeable and mounting can be done in a few hours. Other accessories, such as tree cutters, are designed to be quickly switched with the bucket. In addition to excavators, other heavy equipment can be mounted on amphibious undercarriages. Some examples of options include draglines, backhoes, geophysical drills, and personnel/cargo carriers,” says Mr Ledet Jr.

Developing construction methods to protect Russia’s wetlands

A section of Sakhalin Energy’s Sakhalin-2 Pipeline passes across significant areas of wetland habitat between Piltun and the LNG plant at Prigorodnoye in Aniva Bay, located in far-eastern Russia.

To address the challenges of constructing pipeline through wetland terrain, the company included a chapter dedicated to pipeline construction in wetlands in its Environmental Impact Assessment Addendum (EIAA) in 2005, which included a general discussion of the nature of wetland habitat, the specific types of wetlands encountered along the pipeline route, the construction methodology to be employed in crossing these areas and proposed mitigation and monitoring measures.

According to Sakhalin Energy “The construction of pipelines through wetland areas requires a combination of techniques and methods that are used as standard along the rest of the pipeline route and that are specifically designed to minimise impact within these hydrologically and ecologically sensitive areas.”

RoW clearance and operation

RoW clearance and operation, temporary sediment control and trench dewatering should all be undertaken with the addition of special measures to protect wetlands and marsh areas and to minimise the impact to the environment.

As outlined in Sakhalin Energy’s EIAA, constructors should limit construction equipment operating in wetland areas to that required for RoW clearing, trenching, installation of the pipeline, backfill of the trench and RoW reinstatement.

Vegetation should be cut just above ground level so that the plants’ existing root systems are left in place. Any cut vegetation should then be removed from the wetland for disposal.

It is also important that the pulling of tree stumps and grading activities are limited to the area directly over the trench line. When clearing the RoW, workers should not grade or remove stumps or root systems from the rest of the construction RoW, unless an environmental inspector has determined that safety-related construction constraints require grading or the removal of tree stumps from those areas.

The EIAA also directs constructors to refrain from using rock or soil imported from outside the wetland, and from using tree stumps or brush riprap to support equipment on the construction RoW.

According to Sakhalin Energy “If standing water or saturated soils are present, or if construction equipment causes ruts or mixing of the topsoil and subsoil in wetlands, constructors should use low ground-weight construction equipment, or operate normal equipment on timber riprap, prefabricated equipment mats, or terra mats.”

Temporary sediment control

Another consideration for contractors constructing pipelines through wetland, swamp or marsh environments is temporary sediment control. Sakhalin Energy’s EIAA recommends that sediment barriers are installed across the entire construction RoW at all wetland crossings, where necessary, to prevent sediment flow into the wetland. “Removable sediment barriers can be removed during actual construction, but must be re-installed after construction has stopped for the day and/or when heavy precipitation is imminent.

“Where wetlands are adjacent to the construction RoW and the RoW slopes toward the wetland, install sediment barriers along the edge of the RoW as necessary to contain spoil and prevent sediment flow into the wetland. These sediment barriers should be removed during the RoW cleanup following pipeline installation.”

Trench dewatering

Finally the EIAA suggest that contractors should dewater the trench (either on or off the construction RoW) in a manner that does not cause erosion and does not result in heavily silt-laden water flowing into any wetland. The Addendum states “Remove the dewatering structures as soon as possible after the completion of dewatering activities.”

North America’s marshlands

In 2009 Wilco Pipeline Contractors completed two projects in Louisiana, USA, which involved construction through marshland. The first project was completed for the US Army Corps of Engineers and involved a 6 km, 30 inch diameter steel pipeline near Hackberry.

The second project was completed for Denbury Resources and involved a 24 inch diameter steel pipeline approximately 21 km in length in the Atchafalaya Basin near Lottie.

Wilco Managing Member John Wilson Jr says “When there is access from existing public roads a ‘push site’ is established. Depending on the pipe diameter, the overall site size would be 18 to 30 m wide by 183 to 244 m long. Mats would be staged to provide firm foundation for the equipment and pipe racks. If land access is not available, then several barges would be used tethered together to provide similar area.

“Once the ‘push site’ is established, rollers are strategically placed to accommodate random pipe lengths. Various stations are established to accommodate initial and final welding, quality control inspection, repairs, coating application and float placement,” says Mr Wilson Jr.

Mr Wilson Jr says that access is a major concern when water is encountered as conventional equipment typically would not be able to manoeuvre in the extreme conditions encountered. Specialised equipment like the soft terrain vehicle or ‘buggy’ exerts low ground pressure and is available for rent and purchase. Also depending on the overall size of the pontoons, the buggy can float in up to 2.4 m of water and still be able to excavate the pipe ditch.

With modern coating systems and quality control, any potential for corrosion can be mitigated. Mr Wilson Jr says that original coating system and application is critical, while sacrificial anodes and rectifier systems can mitigate corrosive environments.

Other than routine safety measures like eye and hearing protection, lifting devices, electrical shock and individual strains, additional safety procedures are implemented to identify plants and insects that may be prevalent in the region. Mr Wilson Jr also notes “Employees are also cautioned concerning snakes, alligators and other wildlife in the region. Depending on the remoteness of the project, additional provisions may be implemented for use of helicopter equipment in the event that an individual requires emergency evacuation.”