By Leslie Martin and Courtney deVries
Located outside Fairbanks in central Alaska, Eielson AFB is home to the 354th Fighter Wing, the northernmost U.S. fighter wing and part of Pacific Air Forces. The installation, which was built in 1943, has been listed as a Superfund site since November 1989 under the Comprehensive Environmental Response, Compensation, and Liability Act. Among the environmental concerns facing Eielson are unexploded munitions still present from historical military training activities.
A light detection and ranging/orthophotography (LiDAR) survey of the base performed in 2013 identified a potential Munitions Response Site with a large berm feature. After this investigation was conducted, it was determined that the berm contained exposed 2,000-lb and 500-lb bomb tail fin assemblies. The area that the berm was situated in had been used previously as a munitions storage facility.
An investigation was conducted in accordance with the second step of the Military Munitions Response Program, with the goal to determine the nature and extent of contamination within the site. However, in order to overcome the unique challenges of remediating the berm, an innovative solution utilizing an excavator outfitted with tele-remote control equipment would be required.
A CHALLENGING REMEDIATION
The berm was covered in vegetation and was approximately 25-ft high, 260-ft long, and 85-ft wide. Based on the ground scarring visible in the LiDAR survey data, it was speculated the berm was created by pushing tail fin assemblies and the surrounding soil into a berm feature. Ground reconnaissance or visual surveys were subsequently performed as part of the Comprehensive Site Evaluation Phase II, and a large pile of partially buried tail fin assemblies associated with AN-M66A2 2,000-lb and AN-M64A1 500-lb bombs were found protruding from the western side. No record of the berm’s existence or contents was found in Eielson’s archives or through anecdotal evidence, so it was unknown what was inside besides what was observed on the surface.
Investigating the berm posed an unusual challenge from a safety standpoint. Earthmoving machinery is commonly utilized to excavate and spread out berm material so unexploded ordnance personnel can sweep it with metal detectors in order to locate any munitions or explosives of concern. Machinery can be used to assist excavations of anomalies by digging within 12-in of a suspected item, or be armored to provide the measures needed to protect the operator from the fragmentation of an unintentional detonation.
In this instance, however, excavating within 12-in of suspected items was impractical because of the unknown nature and locations of the anomalies in the berm. Additionally, typical armoring methods could not be used because the size of suspected munitions (2000-lb or 500-lb bombs) meant that it was impossible to provide adequate safety measures to mitigate fragmentation and blast over pressure should an unintentional detonation occur.
Project leadership determined that a robotic excavator would be the safest approach for investigating the berm. To carry out this plan, an antenna and multiple remote cameras were installed on the excavator along with “tele-remote” control equipment and sensors. The antenna emitted a wireless signal that was read by a communications sled stationed at the work site. The communications sled was tethered by routed fiber optics to a control station with operator controls and screens, located approximately 4,500-ft from the berm, well outside the minimum safe distance for unintentional detonations.
The operator used the remote excavator to first clear the berm of large trees and vegetation before removing the soil in various sized lifts. The material was deposited adjacent to the work area where personnel swept it with metal detectors. This process was continued until the entire berm material had been excavated and cleared of any potential explosive hazards. No munitions and explosives of concern or materially potentially presenting and explosives hazard were found within the berm. Then, after the berm had been completely dismantled, the cleared material was graded back into the surrounding area. A challenge with this arrangement was that line of sight was always required between the sled and the antenna mounted on the excavator. Obstructions between the sled and antenna caused a loss of signal and halted operations. Due to the wooded and hilly nature of the work site, the sled was mounted at a higher elevation to the excavator in order to minimize disruptions to the wireless signal. Even at a higher elevation, the sled had to be kept within 100-ft to 150-ft to the excavator, which was significantly less than the wireless capability of the equipment at 1,000-ft with no obstructions.
SAFETY AND LOGISTICAL BENEFITS
The potential benefits for using tele-remote controlled equipment on other munition response or Superfund sites are many. Although the initial operator training is more intensive, the approach allows challenging work to be performed safely and efficiently up to several miles from the site under controlled conditions. Tele-remote technology could be applied to remediation projects at similar locations containing an unknown use or hazardous contaminants. In addition, tele-remote controlled equipment could facilitate work on sites with adverse weather conditions by reducing the amount of time personnel are exposed to the elements.
A possible limiting factor for the tele-remote equipment is related to line of sight. If obstructions exist between the antenna and communications sled, operation of the equipment can experience disruptions. However, these obstructions can be mitigated by vegetation clearance and/or the careful positioning of the sled. Ultimately, the tele-remote controlled equipment can be utilized on future remediation projects to efficiently clean up contaminated sites that could not previously be cleared for reuse due to safety, weather, or logistical concerns.
Leslie Martin is Environmental Scientist, and Courtney deVries is MEC Quality Manager, GSI Pacific Inc. They can be reached at firstname.lastname@example.org; and email@example.com.
[This article first published in the July-August 2021 issue of The Military Engineer.]