Cumulative Environmental Effects of Oil and Gas Activities on Alaska's North Slope (2003) / Chapter Skim
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6. Effects on the Physical Environment
6. Effects on the Physical Environment
Pages 64-75
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From page 64... ...
The active layer contains and sustains the living tundra vegetation mat, which in turn sustains the region's diverse populations of land animals and influences landform processes like runoff, erosion, and soil Stowage. Below the active layer, the permafrost generally contains a substantial fraction of ice.
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From page 65... ...
and between many locations on the Arctic Coastal Plain and in the Brooks Range foothills. The most troublesome disturbances are those for which a thickening of the active layer is not self-arresting; that is the thawed increment from permafrost flows off as a slurry rather than remaining in place to augment the active layer' s insulation.
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From page 66... ...
Photograph by George Gryc. FIGURE 6-2 Intersection of three small ice wedges exposed in an undercut bank of Elson Lagoon, near Barrow.
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From page 67... ...
EFFECTS ON THE PHYSICAL ENVIRONMENT FIGURE 6-3 Upper portion of an ice wedge exposed in a riverbank on the Colville delta near Nuiqsut, Arctic Coastal Plain. Photograph by H
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From page 68... ...
Additionally, the continuous berms intercept natural drainage, creating ponds that collect solar radiation, thicken the active layer, and initiate thermokarst (Walker 1996~. Road dust also can perturb the thermal balance of the active layer and underlying permafrost.
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From page 69... ...
However, in the North Slope oil fields, fluids are injected into the wells in volumes comparable to those that are withdrawn; they too can have environmental consequences for the tundra surface and for subsurface water sources. Injection serves two purposes: It enhances production by restoring lost pressure in a waning reservoir, and it is used to dispose of drilling mud and other wastes by placing 69 them in previously undisturbed porous rock strata.
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From page 70... ...
, thawed chimneys did not coalesce and most of the permafrost remained intact and able to resist damaging settlement, especially if casings were insulated. However, wells are now being drilled so close together that, without additional mitigating measures, their thawed chimneys would coalesce to cause destructive differential settlement of the pads (see "Well Pads and Annular Thawing".
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From page 71... ...
The hazards associated with subsurface injection of these materials are discussed below. Annular Injection Annular disposal is the process of pumping drilling mud and cuttings from drilling operations down the annulus formed when another casing is cemented inside the surface casing.
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From page 72... ...
Rigorously measured total dissolved solids profiles should be routinely acquired, compiled, and used to identify patterns of freshwater distribution as a tool for planning and for evaluation and conservation of the groundwater if appropriate. ESCAPE OF INJECTED WASTE FLUIDS IN THE MARINE ENVIRONMENT One concern regarding the effects of industrial activities on the marine environment is that injected waste fluids might travel laterally through a disposal zone to intersect the ocean floor.
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From page 73... ...
FRESHWATER ENVIRONMENT Industrial activities on the North Slope have to some degree affected the chemistry, flow patterns, and drainage patterns of the area's fresh waters. Effects could accumulate as a result of withdrawal or redistribution of water for construction of ice roads and pads, gravel mining in rivers, and blockage of drainage caused by gravel roads.
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From page 74... ...
Only a few small spills have occurred in marine waters to date, but mechanical recovery the method allowed by current regulationsis not efficient and only removes a small fraction of the spilled oil, especially in broken ice. Concerns about conCUMULATIVE EFFECTS OF ALASKA NORTH SLOPE OIL AND GAS lamination of marine waters center primarily on the potential effects on marine organisms.
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From page 75... ...
The results of winter and summer measurements of temperature, salinity, dissolved oxygen, pH, total suspended solids, and total residual chlorine showed values that were within permitted ranges both within and outside of the mixing zone. Sediment monitoring at the Kuparuk STP outfall revealed no adverse effects of the discharge on sediment grain size.
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