Permafrost

Oil and gas pipelines in polar regions must cope with the special properties of permafrost and of a surface active layer that is subject to much freezing and thawing. Permafrost is ground that remains frozen year in and year out. A state of being perennially frozen is more probable at a considerable depth in the soil than it is near the surface. At a depth of 15 m there is no detectable seasonal temperature change. At this depth a steady mean annual temperature prevails, and when it is O⁰C or less, permafrost exists. If the temperature is very cold for much of the year, the permafrost layer will be close to the surface and the active layer will be quite shallow. Sometimes the depth of the permafrost layer varies a great deal.

Soils of cold regions are characterized by polygonal patterns of soil and rock, ice wedges, and pingos. A pingo is a hill 10 m or more high with an ice core.

When the active layer or the underlying permafrost is melted by the heat from a pipeline or in any other manner, the ground becomes soft, mushy, and unstable and pools of meltwater will form. Roads, houses, buildings, bridges, and pipelines must be isolated or insulated from the active surface layer and from the permafrost. Special construction techniques are required in the arctie. Roads and small buildings or homes must be built on a thick gravel mat and larger buildings must be placed on pilings sunk deep into the ground.

Pipelines in Canada

There are three major types of pipelines use to transport hydrocarbons, defined by throughput: crude oil pipelines, natural gas pipelines and product pipelines.

Crude Oil Pipelines

Approximately 421,300 cubic meters (2.65 million barrels of crude oil) of oil per day travel through Canada’s crude oil pipeline network which includes everything from small-diameter plastic gathering lines to steel conduits more than one metre in diameter. Small-diameter (five centimetres to 15 centimetres; two inches to six inches) gathering system pipelines in individual fields carry oil from wellheads to a central facility in the field called a battery. Larger lines (up to 20 centimetres (eight inches) in diameter) connect groups of batteries with local refineries or with still larger trunk lines (up to 120 centimetres (47 inches) in diameter) which feed refineries across the country.

Where gathering systems are not available, oil is trans- ported by truck to trunk lines. Crude oil and refined products are also transported by ship and by railway. The oil is moved along the pipelines by powerful centrifugal pumps spaced along the line at intervals depending upon pipeline size, capacity and topography. Different types of oil, heavy oil, bi- tumen and natural gas liquids travel in batches at between four and eight kilometres per hour.

Because the different batches in a pipeline move as a continuum at the same speed, there is no need to separate them. Mixing only occurs where two batches come in contact with each other and these small volumes, known as transmix, are reprocessed.

Major Crude Oil Pipelines

Enbridge Pipelines’ crude oil pipeline system stretches from Norman Wells in the Northwest Territories to northern Alberta and from Edmonton eastward to Sarnia, Toronto, Montreal and the central United States. The leg between Sarnia and Montreal, originally built to carry Western Canadian crude oil eastward, was reversed in 1999 so that it now brings imported and offshore Canadian oil production westward to Ontario refineries.

The Trans Mountain system, owned by Kinder Morgan, carries crude oil and refined products westward from Edmonton to Vancouver and into Washington State. Kinder Morgan also operates the Express Pipeline, which carries crude oil from Hardisty, Alberta, to Wyoming where it joins another Kinder Morgan pipeline, the Platte, to supply markets in the Midwestern United States. Other pipelines that transport crude oil south from Alberta to Montana include the Rangeland, Milk River and Bow River systems. The Wascana pipeline carries crude oil from Saskatchewan into Montana.

Pipeline systems operated by Enbridge, Kinder Morgan and other companies also transport synthetic crude oil, heavy oil and bitumen to refineries and marketing terminals in Alberta. The Cochin Pipeline carries natural gas liquids, such as propane and petrochemicals, such as ethylene from Alberta to Sarnia, and the Trans-Northern Pipeline supplies refined petroleum products in southern Ontario and Quebec. Canada’s Crude oil imports arrive by tankers at East Coast ports or at Portland, Maine, for shipment by pipeline to Montreal. There has also been some tanker transport of oil products on the Great Lakes.

There are currently 16 refineries in Canada: two in British Columbia, three in Alberta, one in Saskatchewan, four in Ontario, three in Quebec and three in the Atlantic Provinces, all of which are connected to the pipelines system.

Natural Gas Pipelines

Approximately 484 million cubic meters (17,1 billion cubic feet) of natural gas per day travel through Canada’s natural gas pipeline network which, like oil pipelines, comprises everything from small-diameter plastic gathering lines to steel conduits more than a meter in diameter. Unlike crude oil, natural gas is generally delivered directly to the consumer by pipeline. However, it begins that journey in a manner similar to crude oil. Gas wells are connected to small-diameter (five centimeters to 15 centimeters; two inches to six inches) gathe- ring systems that take the gas to a gas processing facility. Gas processing facilities, usually referred to as gas plants, vary in size from small compression facilities that are mounted on moveable platforms and that remove impurities and water from the gas, to large gas plants that also remove sulphur and carbon dioxide. Some gas plants also extract ethane, propane, and butane, which are referred to as natural gas liquids or NGLs. The generally dry gas may then be compressed prior to moving into the transmission system which consists of steel pipe from 50 centimeters (20 inches) to more than a meter (39.4 inches) in diameter. Gas flows through the system from areas of high pressure to areas of low pressure through the use of compressors, turbines similar to jet engines that increase the pressure of the gas up to 10,300 kilopascals (1,500 pounds per square inch). Compressor stations are placed at regular intervals along the pipeline to increase line pressure which is reduced due to friction of the gas moving through the pipe- Transmission line compressors are most often driven by gas turbines with the necessary fuel being taken from the pipeline. Where electricity is preferable, electric motors may be used to drive compressors. Transmission systems move the gas across great distances to local distribution companies or gas utilities, where the pressure is reduced and the gas enters a distribution main for local delivery to service lines connected to individual homes or businesses.

Alaska Oil Pipeline. Environmental and Ecological Impacts

In 1968 geologic explorations proved the existence of a large oil field on the north coast of Alaska near Prudhoe Bay. As America approached oil shortages in the early 1970s, it became increasingly urgent to begin to move this oil out of the ground and deliver it to the lower 48 states. Because oil tankers can only reach Prudhoe Bay during the ice-free summer season

• a few months of the year - it was necessary to build the Trans-Alaska or Alyeska pipeline connecting Prudhoe Bay with the ice-free port of Valdez on the south coast of Alaska. From here the oil is shipped by tanker to West Coast ports in the United States»

In 1977, an oil pipeline of diameter 122 cm was completed; it runs 1300 km from Prudhoe Bay to Valdez. This pipeline is claimed to be the largest engineering project in human history undertaken by private industry. Its cost was $7 billion. It carries nearly 2 million barrels of oil per day to Valdez. When pumped out of the ground, the oil is at 80°C; and while it flows through the pipeline, it is between 60° and 65°C. When the oil cools to air temperature, it congeals and becomes a very sticky substance. Pumping stations lie along the route of the pipeline at frequent intervals. Each time the oil is compressed by the pumps and given a boost on its way along the pipeline, energy is added to it, so it maintains its warm temperature.

The Alyeska pipeline traverses a great variety of forest, swamp, mountain, and tundra terrain. At least three-quarters of the route from Prudhoe Bay to Valdez overlies permafrost,. A warm pipeline laid on or in the ground would thaw soil to a depth of 10 m during the first year of operation. The thawing would be highly variable, depending on permafrost and ice conditions, and the pipeline would settle into the ground in a highly irregular and uncertain manner. Considerable disruption of the pipeline would occur, each event carrying the poten- tial for breaks and serious oil spills into the ecosystem. Therefore, the pipeline had to be mounted aboveground on towers

for much of its route; and when placed in the ground, it had to be insulated. The southernmost section of the pipeline passes through a major earthquake zone. However, pipelines have often been built through earthquake-prone regions, such as in the Middle East, and the technology is well developed for making them highly resistant to seismic damage.

The 122-cm diameter steel pipe of which the Alyeska pipeline is constructed has a wall thickness of only about 1 cm. The steel pipe is wrapped with insulation. Over much of the route, where the pipeline is elevated on vertical support members (known as VSMs), air passing beneath the pipe dissipates most of the heat and generally reduces the thermal impact on the active and permafrost layers. Problems of thermal construction and expansion of the pipe were overcome by allowing some pipe movement at the VSMs and by placing the pipeline in the trapezoidal zigzag as it traverses the landscape. In general, the pipe can move laterally through some 4 m, and in special situations more than this vertically-a scheme that also affords protection against earthquakes.

The original plan called for the Alyeska pipeline to pass under rivers. In fact, it does go 5 to 6 m beneath the Tonsina River. Here the pipeline was encased in 22 cm of concrete in order to weight it down. However, other large rivers are crossed by bridges to which the pipe is slung. Crossing the Tanana River requires a bridge and sling 360 m in length. Crossing rivers is particularly difficult because in the spring the Upper 2 to 3 m of the riverbeds are periodically removed by scouring and erosion by the spring floods. Where the pipeline has been buried, there is a difficult problem with the permafrost near the river banks, where it is more prone to thaw. Crossing the rivers requires not only avoiding the scour problems, but also the preservation of conditions suitable for fish populations. Building bridges and slinging the pipeline from them was the best solution to these problems.

The frequent passage of men and equipment near the pipeline inevitably damages vegetation and initiates a thawing of

the permafrost. Enormous quantities of gravel were laid down as pads about 1.5 m thick for work areas and for the road paralleling the pipeline. Often these were underlaid with a ure- thane plastic insulation. Gas and oil storage units at Prudhoe Bay and elsewhere were elevated on piles 2 to 2.5 m above the ground surface, wherever permafrost was present.

The eight pumping stations operating at intervals along the Alyeska pipeline have advanced gas turbines that power centrifugal pumps and complex valve systems. At several of the pumping stations, the foundations of the buildings have refri- geration systems to maintain the underlying soil in a frozen condition.

The Alaska pipeline and haul road cross the Arctic tundra of the North Slope and forested areas in the mountains and south of the Brooks Range. The ecosystems traversed are highly varied and the impacts on these are extremely different.

Tundra. Tundra is often viewed as easily disturbed or changed but it is quite stable and resilient to major environ- mental changes. It appears to be adapted to large, natural, often sudden environmental fluctuations. On the North Slope of Alaska, the coastal tundra undergoes various natural perturbations that are part of a thaw-lake cycle. Thousands of years are required for the cycle to return the ecosystem to its original alluvial state. The ion-exchange capacity of mosses and the nutrient uptake by all the plants and microorganisms removes the nutrients from snowmelt and runoff, thereby retaining nutrients in the soil surface.

In anticipation of the Alaska pipeline carrying hot oil, an experiment was conducted in which a wet meadow substrate was heated in situ. A 10°C soil temperature increase for one month at Barrow, Alaska increased the thaw depth, the decomposition rate, the nitrogen availability, the plant nutrient absorption rates, and the primary production. Many years later very little of the disturbance effect could be detected. When, instead of short-term heating, soils were heated for one year, the result was much increased thaw depth, melting of ice in the

permafrost, subsidence of the ground surface, and ponding of water. Rapid decomposition of organic matter depleted the oxygen concentration of the soil, and all the vegetation died within a year. Recolonization of the site did not occur over a year term. On the other hand, experimental heating of an ice- free soil in the interior of Alaska throughout the year caused no subsidence, no die-off of vegetation, and, in fact, increased primary productivity. Detrimental effects associated with soil heating seem to relate to a series of events associated with melting ice, soil subsidence, and changing chemical and physical conditions.

There has been a long history of oil exploration across the arctic tundra of Alaska. Vehicle tracks are seen across the arctic tundra in many directions, some of which were created during World War II. The severity of vehicle impact upon tundra seems to depend very much on the nature of the plant community and the character of the underlying soil. The vehicle tracks may crush the vegetation, compact the surface, and result in water impoundment in deepening troughs through partial ice melting. Striking vegetation changes may occur along an old vehicle track within a few years. Vehicle damage is greater in the shrub tundra than it is in the meadow tundra because of greater breakage of shrub stems. Sites with low ice content are less susceptible to vehicular damage than are those containing more ice. When the soil surface is compressed below the shallow water table, particularly in poorly drained meadow soils, standing water develops and decreases the access to sunlight. The standing water absorbs more sunlight, raises the underlying soil temperature, and accelerates the thawing of permafrost. These changes result in increased nutrient availability and increased primary productivity. When vehicle tracks cross ice wedges, deep permanent ponds may form. When there is much slope to the surface, very deep erosion of the soil will occur. Recovery from some of these impacts may take hundreds or even thousands of years.

Alaskan crude oil is toxic to most vegetation. Vegetation growth may accelerate because of the warmer condition resulting from the oil spill, despite some toxicity to the plant leaves. When water fills the site, the oil is not as likely to penetrate the soil and the more toxic volatile fractions may have time to evaporate. On the other hand, it is known that oil mdy remain in the active layer of the tundra for as long as 30 years or more. These hydrocarbons in the soil may increase some microbial activity, thereby causing an increased demand for nutrients so that the nutrients become less available to vascular plants. Oil kills some mycorhizal fungi, thereby further decreasing the ability of plants to assimilate nutrients. Oil is hydrophobic; therefore, once it penetrates the soil, it reduces water movement and reduces nutrient transport and availability to plants.

To test the sensitivity of tundra vegetation to oil spills, Walker Co.(1978) established a series of test plots within which crude oil or diesel fuel were spilled. The changes in the vege- tation within these plots were observed and compared with control plots nearby. These experiments were done in the tund­ra at Prudhoe Bay. One year following a simulated crude oil spill, most plant species were dead. On dry sites almost all plant species (including Dryas integrifolia, the most important vascular species) and all lichens were killed. In more mesic (wetter) sites, many moss species and nearly all herbaceous di- cotyledonous species were killed. A few plant species recovered a year after the spill. On a plot with standing water, total recovery of the vegetation occurred one year after the spill. The dry plots recovered very poorly, with the exception of willows (Salix) and sedge (Carex rupestris), which recovered well. The experiments using diesel fuel rather than crude oil on both wet and dry sites showed all species except an aquatic moss to be killed» Apparently, contact between diesel fuel and the plant leaves was sufficient to kill the plant and direct contact with the roots was not necessary. From these studies, augmented by other information, Walker Co.(1978) composed a sensitivity

map of the tundra vegetation in the vicinity of Franklin Bluffs, where an 1800-barrel crude oil spill occurred on 20 July 1977. The spill created a gradient of oil that radiated out from a broken valve of the Alaska pipeline. The oil apparently squirted vertically for 35 m and a strong north wind fanned it out over an area approximately 100 m long downwind. The soil was totally saturated with a thick layer of oil. Approximately 1400 barrels of oil were removed by cleanup procedures used on the area of heaviest impact. This left other areas covered with oil. About 400 barrels of oil remained on 8.3 ha. Of this, about 1.8 ha received a heavy oiling; a situation that was similar to the test plots at Prudhoe Bay. The Franklin Bluffs observations indicated that the dry areas away from the coast are more resilient than dry areas at the coast. It was also discovered that if the spilled oil is allowed to flow, it will tend to go to the wetter areas, where recovery is more probable. The oil may be more easily skimmed off a lake or off standing pools than off the land. A threat to waterfowl could exist, however, unless a means for frightening them can be devised.

Pipeline Construction

Pipeline Construction is usually divided into three phases: pre-construction, construction and post-construction.

Pre-construction