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DNR releases tundra travel validation Department: seismic work in 2004-05 under new standard resulted in no significant environmental change; monitoring continues Kristen Nelson Petroleum News Editor-in-Chief
The Alaska Department of Natural Resources said Dec. 23 that a study of the impact of seismic work done in the winter of 2004-05 shows its new standards for allowing exploration on frozen North Slope tundra are proving reliable in protecting the tundra.
The state’s new standard, developed as a result of work completed in October 2004, limits tundra travel to areas where the soil has reached minus 5 degrees Centigrade at a 12-inch depth, and there is six inches of snow cover in coastal areas and nine inches in the foothills. The standard was developed with support from the U.S. Department of Energy, Yale University’s School of Forestry, the Alaska Oil and Gas Association and oil and gas companies.
The verification study looked at areas where seismic exploration was done in 2004-05; the state is also continuing to monitor the experimental plots used for the original study.
The follow-up study was produced for DNR’s Division of Mining, Land and Water under contract by Harry Bader, project consultant, Betula Consulting of Alaska. Bader was formerly northern region land manager for the Division of Mining, Land and Water and headed up the original study which resulted in the 2004 change in how the dates for tundra openings are determined. Report: standard prevented significant environmental change The Betula Consulting report says the department’s new standard, “derived from the model prediction (developed in the study), resulted in preventing significant environmental change as a consequence of overland vehicle travel pursuant to hydrocarbon exploration under actual working conditions.”
The report also said “no delayed effects” were observed in the second year after treatment in the experimental plots.
The report notes that the department’s new standards for opening the tundra were generated in “an empirical study under controlled field conditions,” and the department validated the results in the winter of 2004-05, testing predictions “under routine activity as conducted by geotechnical companies in the normal course of actual seismic exploration.” The tundra disturbance from 2004-05 winter seismic work was evaluated in the summer of 2005, along with a continued evaluation of the original study plots. Validation study in collaboration with Veritas The department selected a validation study site in collaboration with Veritas, a Canada-based seismic exploration company. The site was approximately 11 miles south and nine miles west of the Deadhorse airport, close enough to the Dalton Highway that department staff could access it by snow machines, had topographic variability, proximity to University of Alaska ground temperature monitoring stations and was free of prior disturbance.
In exchange for confidentiality, Veritas provided coordinates of the survey where receiver and source lines crossed. The report said such intersection points are crossed once by a vibrator (a track vehicle containing a pedestal which vibrates against the ground) and twice by vehicles laying out and picking up receiver lines. A seismic operation typically creates more than 2,000 miles of combined source and receiver lines in a season.
The department sent staff to 12 intersection points selected from among the 1,000 provided by Veritas in advance of the seismic work, but the study areas were left unmarked “so as not to alert seismic crew of their location. Blowing wind and snow obscured all trace of the measure work by the time crews came in contact” with the study areas some 24 hours later. Department staff collected snow depth, snow slab thickness and ground hardness data in advance of the seismic work. Sites marked later Two months later department staff returned in a track vehicle and re-surveyed and marked the locations with metal rods pounded into the frozen ground. The report noted that the Haagland tracked vehicle used by the department represented an additional pass over the points, with the potential for greater disturbance than under exploration conditions.
In July 2005 the department flew to the sites by helicopter and measured depth of the active layer and soil moisture.
The department’s modeling study (completed in October 2004) “anticipated that a snow cover of 15 cm and a ground soil temperature of minus 5 degrees C throughout a 30 cm deep soil profile would ameliorate the effects of cross country travel over sedge dominated tundra by exploration equipment.”
Prior to exploration equipment traveling over the 2004-05 study areas, the department found an average snow depth of 19 centimeters and a ground temperature of minus 8 degrees C at the surface, minus 7.5 degrees C at a 15 centimeter depth and minus 7 degrees C at a 30 centimeter depth.
The report said when the department evaluated the area in the summer it found “no statistically significant differences” between areas where seismic vehicles passed and control areas with no vehicle passage. Long-term monitoring The report also evaluated summer 2005 measurements at the experimental plots evaluated for the 2004 study, with comparisons between the treatment and no treatment plots.
In its first (2004) report the department found statistically significant changes in soil moisture and depth of active layer between no treatment plots and plots traveled by a tractor when the ground temperature was warmer than minus 5 degrees C and snow depth less than 15 centimeters in wet sedge tundra and less than 23 centimeters in tussock tundra. The report said 2005 monitoring found “resiliency in these same plots” with the difference between the treatment and no treatment plots converging.
Differences between treatment and no treatment plots in 2005 were no longer statistically significant in the sedge tundra, the report said. While there were still statistically significant differences between depth of active layer and soil moisture in the tussock tundra tractor plots in the foothills, both “actual and relative differences in depth of active layer” between treatment and no treatment plots declined from 2004 to 2005.
The report said that based upon 2005 findings at the experimental plots, the department “is confident that no new manifestations of disturbance type or trend have developed in the study plots.” The department does not anticipate new disturbance indicators, but will continue to take monitoring measurements at the plots.
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