For more than a decade, responding to catastrophic fuel spills at forward operating areas in remote portions of Alaska has been an integral part of the 611th Civil Engineer Squadron (611 CES) mission. Several of these forward operating areas have bulk fuel tanks that exceed 1,000,000-G. The 611 CES spill response is uniquely designed to be completely air mobile and compartmentalized for rapid deployment. Spill-response equipment can be in transit within four hours of notification of a spill. The initial goal of the 611 CES spill response is to get on site, assess, control and begin containment and recovery of the spill.
The 611 CES conducts regular training exercises in conjunction with other agencies, including the U.S. Coast Guard, the U.S. Navy Supervisor of Salvage, the U.S. Environmental Protection Agency, the Alaska Department of Environmental Conservation and the Chadux Corp. Due to the widely variable geographic areas and weather conditions in Alaska, containment and recovery tactics must be adapted to address both of these issues.
Annual spill-response training is mandated by federal and state agencies that oversee environmental laws and regulations pertaining to Alaska. Additionally, the regular changes in military personnel staffing warrant the annual training for the squadron to efficiently perform spill-response tasks. Without annual training, actual spill response would be haphazard and unorganized. The potential for a larger spill and vastly greater environmental impact could be devastating both from an environmental and fiscal standpoint.
Cold-Weather Spill Response
As spill response has evolved, Ice Operations (IceOps) has grown from a subset of spill-response training to a standalone, large-scale exercise. The fact that the majority of the forward operating installations in Alaska experience winter conditions for nearly half the year dictates the necessity of planning and training for cold-weather spill response. IceOps in an annual exercise held during the winter months to prepare all participants for an oil spill on or in water under Arctic conditions. The goal of IceOps is to develop and practice recovery operations during winter conditions; one of the goals is the recovery of oil that lies beneath a solid sheet of ice. During the IceOps exercise in March 2008, an attempt was made to utilize the ground-penetrating radar (GPR) across the frozen surface of Six-Mile Lake on Elmendorf Air Force Base, Alaska.
GPR emits radio frequency energy pulses into the ground. The radar signal’s propagation through the underlying materials is directly related to signal velocity and electrical conductivity of underlying material. Changes in the electrical properties of the materials reflect portions of the signal and therefore indicate physical changes in the underlying material. Attenuation of the GPR signal is directly related to the amplitude of the original signal and the ability of the underlying material to efficiently transmit that signal. For example, attenuation of the GPR signal is negligible in ice but profound in clays and wet sediments.
The role of the GPR was to profile the ice sheet and provide real-time data as to thickness of the ice sheet at any point along a traverse. Because there are no data gaps as there would be between boreholes, the results of a GPR profile are more comprehensive than ice coring. GPR traces are processed to provide a 3D map of the ice sheet that accounts for relative ice thickness and variations in surface topography. Most importantly, the map locates the ice/water interface “elevation highs,” which would serve as natural oil traps in an actual oil recovery scenario.
The GPR unit consisted of a 500-MHz antenna mounted on a Noggin Smart Cart that included an odometer, battery pack and real-time LCD display. The survey was conducted over an area approximately 200-ft by 160- ft. Nine traverses were conducted roughly perpendicular to the shoreline, each measuring 160-ft in length long and spaced 25-ft apart. Three medial traverses measuring 200-ft in length and spaced 50-ft apart were run perpendicular to the nine traverses to ensure data correlation. The radar sections were then downloaded into mapping software that processed the traces and modified signal velocities and the signal gain to provide migrated and easily interpretable cross-sections.
Concurrent with the GPR observations, global positioning system (GPS) receivers were used to collect GPS positions along each GPR transit at 10-ft intervals. GPS utilizes satellite signals that are collected by ground-based observers: a known location (base station) and an independent observer (a rover). The rover data are corrected against the base data, allowing for data accuracies in cartographic and elevation coordinates of less than a half inch. Once collected, the GPS data, including the ice surface elevations of the lake, were exported to a format compatible with geographic information systems (GIS). The ice depths from the GPR corresponding to each survey location were integrated into a database, and invert elevations were calculated by subtracting ice thickness from the surface ice elevation. The tabular data were processed using a spatial analyst extension, which allowed for the creation of a continuous surface from tabular data and enabled users to cartographically manipulate results. The resultant profile of the underside of the ice sheet can be used by end users in incident planning and recovery activities.
Maximum elevation difference in the ice/water interface under the frozen surface of Six-Mile Lake in the study area was 0.68-ft. The elevation map of the ice/water interface shows two distinct linear trends representing elevation highs in the ice/water interface. These two linear trends would serve as natural accumulation areas for pooled oil under the ice; as such, they would be preferred locations to initiate oil recovery efforts. Under static condition—that is, minimal subsurface water currents—the two trends would further serve as long-term oil recovery zones due to the preference of fuel and oil, having lower specific gravity than water, to naturally flow to the higher elevation zones as oil is removed.
Utilization of GPR to locate natural pooling locations for fuel and petroleum products beneath the ice can allow spill response personnel to immediately begin entry and recovery operations where the potential for maximum recovery exists. Therefore, spill response personnel can not only recover the most potential oil, but man and equipment hours would be reduced in the search and recovery phases of spill response.
The timely use of the GPR in IceOps could determine ice thickness and consequent ice strength prior to the deployment of equipment and personnel. GPR profiling could also be utilized in determining potential flow directions for oil beneath the ice surface under non-static conditions.