The Need for Subsurface Utility Engineering
When undertaking a design and construction project on a military installation, there may be many uncertainties hiding beneath the surface that need to be understood and located before it's too late.
By Erek Dorman, M.SAME
The proliferation of underground infrastructure including communication, fiber optic and buried power lines in just the last 20 years alone has been staggering. Subsurface utility engineering (SUE) is a discipline that has emerged out of the need to define the collection and reporting of data on underground utilities. Having timely and accurate data on location, depth and condition of utilities becomes critical during the design and construction phases of any project. Incorporating an SUE plan into the programming, design and construction phases of a project is essential to ensure that all subsurface challenges are addressed in a comprehensive manner.
The subsurface challenges, and obstacles associated with construction on Department of Defense (DOD) installations can be met, and overcome, with the proper foresight and planning by incorporating a comprehensive SUE plan into the project program. Timely identification of subsurface utilities and other underground obstructions within installations is critical to proactively addressing unseen issues that can pose a risk to project safety, schedule and budget. Most states require surface marking of known underground utilities in advance of any excavations utilizing One-Call Centers, such as Miss Utility in Virginia, in an effort to avoid damaging buried public infrastructure. While these marking services provide some level of data for project planning, there are limitations to the service. These must be considered during the programming and design process.
For instance, the One-Call services will not mark private utility locations and in many instances will not work within DOD installations since federal property is frequently exempt from many state and local laws and regulations regarding construction activities. In addition, these marking services are usually performed immediately prior to construction for the contractor and do not determine the specific utility location or depth through test pitting.
UNCOVERING UNIQUE SITUATIONS
Military sites, particularly older DOD installations, also may encounter some very unique subsurface conditions that local communities do not experience.
Some of the buried obstructions that may exist on DOD installations include unexploded ordinance , hazardous materials, buried or abandoned infrastructure and equipment, which, depending on the age or nature of the installation and its history, present unique challenges to the design and construction process.Since many types of materials and objects may have been buried with little or no documentation over the years, it is critically important that SUE investigations be performed as part of the programming and design process.
Unexploded Ordnance. At installations where live-fire training has occurred in the past, unexploded ordnance poses a major concern. Given the age of some military posts, live-fire ranges may date back to the Civil War and have been long since abandoned. Generally, the removal of these materials is handled by military explosives ordnance disposal units; however, when a specific site proposed for improvements has identified unexploded ordnance considerations, sufficient time must be allowed in the project timeline for the coordination of the various resources (DOD teams or private contractors) to ensure the site is safe prior to any SUE investigations. In some cases, such as an investigation that was performed at Joint-Base Andrews, Md., SUE technicians were escorted by a military explosives ordnance disposal team that cleared each section of the project site immediately prior to the planned vacuum excavations.
Hazardous Materials. Nearly every military installation will have, at some time, stored, used or disposed of hazardous materials. These materials may include fuels such as gasoline or diesel; oils and other lubricants; cleaning chemicals; propellants; and even chemical weapons, such as those discovered in a Washington D.C. neighborhood that was once a military post during World War I. Some hazardous materials may have been buried in storage tanks or drums. Excavating in these areas always brings with it the risk of encountering contaminated soil. If buried hazardous materials are suspected at the site, appropriate subsurface testing should be scheduled to identify the extent of the contamination so that proper handling, removal and disposal can occur. SUE investigations performed during the programming and design phase of a project should be scoped to provide an adequate coverage of the area. This will further ensure that evidence of past hazardous materials disposal is discovered in a timely manner utilizing available technologies such as ground-penetrating radar.
The subsurface challenges, and obstacles associated with construction on Department of Defense (DOD) installations can be met, and overcome, with the proper foresight and planning by incorporating a comprehensive SUE plan into the project program.
Buried Infrastructure and Equipment. The military has in many instances in the past buried abandoned infrastructure or equipment in-place to facilitate operational needs. In addition to marking and locating active subsurface utilities, SUE investigations also should identify any additional buried or abandoned facilities that may include duct banks, conduits, pipes, foundations, burned building remnants, and old equipment. Unique equipment buried beneath the surface can include building materials, vehicles, aircraft, weapons components such as artillery pieces and armor. In some instances, Cultural Resource Management considerations come into play when excavating at a site that has historical significance. Archaeological assets that are discovered can pre-date European settlement of America and even reach back to pre-historic times. While SUE technicians generally excavate in locations that have been previously disturbed, it is not unusual to turn up bayonets, old coins, spent munitions, even bones. Research into the history of a site is prudent during project programming along with the identification of a resource for archaeological consulting, as may be necessary. Because of the myriad of possible subsurface conditions that could be discovered on a site, it is imperative that early scoping and coordination efforts of the subsurface investigations be established during project programming and design. This includes a collaborative effort with the facility engineer so that appropriate resources can be readily available when subsurface conditions warrant.
Aging infrastructure. Military installations face challenges associated with aging subsurface infrastructure since sites could predate the Civil War. SUE investigations utilizing electromagnetic-based locating equipment requires that there be some kind of conductive material in the utility or conduits. Today, many concrete or PVC conduits have tracer wires installed to aid in their detection with surface locators. However, if these conduits were installed prior to 1975 the chances of having any kind of tracer wire or conductive material decrease exponentially. Consequently, in many cases, vacuum excavation is usually the primary method utilized to determine the depth and condition of the utility. Vacuum excavation, a process that involves a high-pressure air lance to loosen the subsurface strata while the soils are removed by a generator driven vacuum tube, is the safest method to expose the facility without damaging it.
ONGOING OPERATIONAL CONSIDERATIONS
A key consideration during the programming and planning of a project is the safety and security of the personnel performing the subsurface utility investigation on the site. Working within the confines of an active military installation requires that all personnel who are given access to the site have appropriate security clearances and are properly instructed in necessary safety protocols associated with working in the area.
In many cases, SUE investigations are performed in the early stages of a project when no other contractors are in the area, further magnifying the need for appropriate safety and security protocols that recognize the ongoing operational considerations of the facility.
Since surface markings alone, as provided by contract locators, do not provide the accuracy necessary for detailed programming and design, the early utilization of an SUE provider is critical to securing the accuracy needed to properly address these issues in a timely manner. Surveyed locations of marked utilities and obstructions along with the use of vacuum-excavated test pits and other equipment will provide accurate information in the timeframe needed to address project programming and design requirements. SUE service providers include highly skilled technicians and field crews that understand the process required—and have the necessary certifications, training and experience to work efficiently and safely.
U.S. Army installation Fort Belvoir in Virginia typifies the type of challenges SUE service providers can assist with. The base has undergone substantial construction in recent years as a result of the Base Realignment and Closure program along with regular maintenance and upgrades. Part of the infrastructure improvements have included replacing water mains throughout the installation. Picture above, a vacuum excavation crew attempts to locate one of the mains in a residential section of the base. These particular water mains were installed when the neighborhood was constructed in the early 1980s. They are PVC mains without tracer wires, making them very difficult to locate. Without anything to return a signal with a conventional electromagnetic locator, the only option is to dig. The new water mains are PVC also, but contain dual tracer wires. Locating the water mains was further complicated by the fact that the movement of earth over several decades of construction and improvements caused their depth to vary between 4-ft and 7-ft in places.
Originally established in World War I, Fort Belvoir has been home to numerous defense agencies during its lifetime. The post was established on the former site of a colonial-era plantation dating to the early 18th Century. Subsurface congestion at sites like Fort Belvoir can include a stunning array of utilities, structures, equipment, artifacts and even ordnance. Understanding the risks and challenges with subsurface utility infrastructure going in to a design and construction project is critical to ensuring the health and safety of workers and occupants.