Subsurface Utility Engineering
A Technology-Driven Process that Results in Increased Safety, Fewer Claims, and Lower Costs

A lack of reliable information on the location of underground utilities can result in costly conflicts, damages, delays, service disruptions, redesigns, claims, and even injuries and lost lives during construction activities. While the location of subsurface utilities might be found on plans and records, experience has often shown that the utility locations are not exactly as recorded or the records do not fully account for the buried utility systems. This may be especially true of our nation’s aged roadway infrastructure.

An engineering process known as Subsurface Utility Engineering (SUE) has proven to be a welcome solution to providing this much-needed utility information. Combining civil engineering, surveying, geophysics, nondestructive excavation, and other technologies, SUE provides accurate mapping of existing underground utilities in three dimensions during the early design phase, which avoids unnecessary utility relocations and related downtime, eliminates unexpected conflicts with utilities, and enhances safety during construction. The use of SUE services has become a routine requirement on highway and bridge design projects, and is strongly advocated by the Federal Highway Administration and many State Departments of Transportation.

INTRODUCTION

n engineering process known as Subsurface Utility Engineering (SUE) helps locate underground utilities prior to or during construction or renovation activities. The process combines civil engineering, surveying, geophysics, nondestructive excavation, and other technologies. It provides accurate mapping of existing underground utilities in three dimensions, which avoids unnecessary utility relocations and related downtime, eliminates unexpected conflicts with utilities, and enhances safety during construction. The use of SUE services has become a routine requirement on highway and bridge design projects, and is strongly advocated by the Federal Highway Administration (FHWA) and many State Transportation Departments (DOTs).

A Purdue University study of 71 DOT projects in four states -- Texas, North Carolina, Ohio, and Virginia -- quantified a significant return on investment of $4.62 for every $1 spent on SUE services. Similar economic benefits, in addition to increased safety to workers and the public, are available to those involved with roadway or other construction projects that may encounter subsurface utilities.

PROCESS

A lack of reliable information on the location of underground utilities can result in costly conflicts, damages, delays, service disruptions, redesigns, claims, and even injuries and lost lives during construction activities. While the location of subsurface utilities might be found on plans and records, experience has shown that the utility locations are often not exactly as recorded or the records do not fully account for the buried utility systems. In the past there was no good solution to these problems. It was a given situation that had to be endured. Now there is a proven solution – Subsurface Utility Engineering.

SUE is an engineering process that takes advantage of some of the oldest and newest of technologies to accurately identify the quality of subsurface utility information needed for highway plans, and for acquiring and managing that level of information during the development of a highway project. A new national standard further defines SUE as a branch of engineering practice that involves managing certain risks associated with utility mapping at appropriate quality levels, utility coordination, utility relocation design and coordination, utility condition assessment, communication of utility data to concerned parties, utility relocation cost estimates, implementation of utility accommodation policies, and utility design. These activities, combined with traditional records research and site surveys, and utilizing new technologies such as surface geophysical methods and non-destructive vacuum excavation, provide "qual­ity levels" of information.

QUALITY LEVELS

The question of “how much subsurface utility information is really needed” to adequately map underground utilities for construction of a project is ultimately a question as to the degree of risk that the project owner, utility owner, and contractor are willing to accept. Within the SUE process, this issue is addressed by an established set of four quality levels that represent different combinations of traditional records research, site surveys, and the application of new technologies.

all quality levels of information, including the highest accuracy level at points along a utility’s path where conflicts may occur. In contrast, a lower quality level may be adequate in those areas where little to no utility conflict is anticipated.

The four quality levels are described below.

• Quality Level D. Quality Level D (QL-D) is the most basic level of information. It comes solely from existing utility records. These records are often inaccurate, unreliable, and/or out-of-date. Even so, this level of information provides a general overview of utility congestion and is appropriate to support decisions made early in the project planning process.

• Quality Level C. Quality Level C (QL-C) has traditionally been the most commonly used level of information for engineering projects. It involves supplementing QL-D information with a visual ground survey of existing utility features, such as manholes and valve boxes. When using this information, it is not unusual to find that many underground utilities have either been omitted or erroneously plotted. Its usefulness, therefore, should be confined to rural projects where utilities are not prevalent, or are not too expensive to repair or relocate.

• Quality Level B. Quality Level B (QL-B) is the first level of information where the “designating” activity is introduced into the SUE process. Designating provides two-dimensional horizontal mapping information along the entire length of utility lines. Various types of surface geophysical techniques are typically used for this purpose, including electromagnetic, magnetic, and elastic wave methods. This level addresses problems caused by inaccurate utility records, abandoned or unrecorded facilities, and lost references. It is particularly useful very early in the design phase of a project because slight adjustments in the design can still be made, producing substantial time and cost savings by avoiding the need to relocate many utilities.

• Quality Level A. Quality Level A (QL-A) utilizes the “locating” activity and provides the highest level of informational accuracy available for final design decisions. Locating provides a precise three-dimensional mapping of underground utilities and related structures. It involves the use of nondestructive digging equipment to physically expose underground utilities at critical points along their path. B y knowing exactly where utilities are positioned in three dimensions, designers can often make small adjustments in elevations or horizontal locations and avoid conflicts with utilities. Additional information such as utility material, condition, size, soil contamination, and paving thickness also assist designers and utility owners in their decisions.
  

EXAMPLES OF USE

Although Subsurface Utility Engineering came into use in the early 1980’s, the name “Subsurface Utility Engineering” was not used until 1989 when the process was introduced as such at the first National Highway/Utility Conference in Cleveland, Ohio. A detailed history of SUE may be found on the FHWA’s SUE website.

Today, through the efforts of pioneering providers and the FHWA, more than 30 State DOTs are using SUE on their highway projects. Possible applications include, but are not limited to, the following:

• Construction or renovation of roadways and runways. An example is the successful application by several DOTs of the SUE process at the design phase to avoid costly utility conflicts, damage, delays, service disruptions, redesigns, claims, and injuries.
• Testing, rehabilitation, or replacement of fuel transmission systems. Whether for O&M purposes or in response to pending tank regulations, the need often exists to locate and visually observe pipe conditions without the use of destructive excavation methods.
• Location of underground storage tanks and septic systems. Just as with utility lines, the SUE process is effective in precisely locating underground tanks, even to the point of exactly locating the dimensions of the tank in those sensitive areas where highly controlled excavation is required.
• Location and characterization of abandoned/out of service utility corridors. This can be an important component of environmental investigations, because the materials used for backfilling utility trenches are typically more porous than the surrounding soils and consequently provide preferential pathways for contaminant migration.
• Clearance of areas in support of new utility corridors. Whether the new utility systems are in support of environmental remediation projects or overall facility upgrades, the SUE process can be an important component. A typical example could include a new pipeline that is needed to connect an off-site groundwater extraction system to an on-site treatment system
• Performance of routine operation and maintenance activities. These activities often involve excavation work in areas where existing utilities represent potential design and construction constraints, as well as elevated safety concerns.
• Facility-wide updating of “as builts” or other types of utility mapping. This is a viable option for those installations being renovated under the expectation of an extended operational life.

RISK ALLOCATION

The fact that readily available information on utility locations is often incomplete and inaccurate has been a given among project owners, engineers, and contractors for decades. One can easily presume that the following scenario has been played out on many projects, in response to this informational uncertainty and the associated risks.

• The project owner would initially assign responsibility for utility mapping to the design engineer by including general language in the scope of work. Typically, standard practice for the design engineer would be to compile utility information from the utility owners, local public works files, and other readily available sources of such data, and then to correlate this information with the site plan for the project.
• Recognizing the likelihood that utilities would either be missed or erroneously located through this process, the design engineer would include a disclaimer on the plans. In essence, the disclaimer would pass responsibility for utilities onto the contractor. Such disclaimers would rarely be challenged by either the project owner or the contractor. Thus, the design engineer would incur minimal risk for any errors related to utility designation and location.
• Facing a bid competition, and recognizing that project owners are typically held responsible for delays and costs associated with unknown or differing site conditions, contractors would have no option other than to assume that utility locations on the plans were complete and accurate.
• In the meantime, “one call” statutes would often result in utility owners coming into the field and marking expected utility locations during construction. These locations may or may not have coincided with the engineering plans.
• Consequently, the project owner would often face a situation in which:

• Initial construction bids would likely have a contingency built-in, to account for the informational uncertainty and likelihood that claims would have to be developed and negotiated
• The contractor would secure a preferable position, since any additional work would be negotiated and performed outside of a bid situation
• The financial risk would be magnified by the potential costs of construction downtime, schedule delays, redesign, and utility relocation
• A worst-case scenario could develop that may involve utility damage, consequential damages, and injury to workers and the public.

Over the last 15 years, four events began to change this scenario. One was the advent of technologies that were developed, partially as a result of the widespread use of geophysics in the burgeoning environmental business. These technologies could aid in the designation and location of utilities at an early stage of project development, without substantial cost investment. Second, competition in the marketplace allowed project owners to shift more responsibility and liability to the design engineers and contractors. This is especially true at federal facilities, where contract reform among federal agencies began to pass on liability to operation and management contractors, and in turn to design engineers and contractors. Third was the overall growth in litigation, and the associated increase in risk to all parties involved in design and construction projects. And fourth was the aforementioned birth of Subsurface Utility Engineering as a distinct service in the 1980s.

The subsurface utility engineer became the individual with the appropriate expertise and tools to allow construction activities to be designed away from high risk utilities when possible. This type of engineer also became the person that would characterize the nature of utility conflicts before work began in the field, coordinate utility relocations and easements, and develop utility “as builts” that were complete and accurate.

Related to the latter issue is the court-supported recognition in 1989 that SUE services are professional services rather than contractor services. This occurred as the result of a challenge to a state agency’s decision to procure SUE services on the basis of price rather than qualifications. The courts recognized that information placed on plans and relied upon by the public clearly fell into the professional services category. It was further recognized that the professional practices of geology, engineering, and land surveying all potentially involved the collection and interpretation of data supplied by subsurface utility engineers.

The overall issue of risk allocation among project owners, design engineers, and contractors, as it relates to underground utility information, was recently addressed by a subcommittee of the American Society of Civil Engineers in the development of a national consensus standard. This standard includes the four quality levels discussed above. Any utility depicted or described in a plan document will have a “quality level” assigned to it. The ultimate decision to contractually specify the utility quality level will be the responsibility of the utility owner. The design engineer can be expected to have input into this decision, due to the likely trade-off between the benefits of enhanced informational quality and the additional cost of progressively moving up to Quality Levels C, B, and A. Such standards of care will help project owners, design engineers, and contractors develop risk management plans and protect their own interests if others do not perform.

CONCLUSION

The technology is now available to achieve a complete and precise three-dimensional mapping of subsurface utilities prior to or at the construction phase of a project. If Quality Level A information is collected through the full use of the SUE process, the project owner, design engineer, and contractor can proceed with confidence that utilities have been identified and categorized as to their horizontal location, depth, elevation, width, composition, and condition. The use of the SUE process will continue to grow as project owners request higher quality levels of utility information to reduce and better manage their risks. Related standards that will better define the allocation of risk among the parties are being developed. In the end, the use of Subsurface Utility Engineering will tend to shift the risk of bad information to the party most capable of handling that risk — the subsurface utility engineer.

Related cost analyses have shown that the use of the SUE process provides a significant return on investment. As a rule of thumb, the cost of incorporating the SUE process is about 10 percent of the total preliminary engineering cost, or about 1 percent of the total project cost. These costs are small when compared to the overall savings on projects where the SUE process is used. Information compiled by Purdue University for the FHWA indicates $4.62 in total project costs is saved for every $1 spent on the SUE process.

In this era of partnerships, the SUE process provides an excellent opportunity to advance communication, cooperation, and coordination among all parties involved in engineering and construction projects. SUE represents a new way of doing business, in which the past adversarial relationship among project owners, design engineers, and contractors has been replaced by a cooperative effort to reach an appropriate balance between the risk of informational uncertainty and the associated cost of reducing that risk. Utility “owners,” whether they be a public or private utility company or an on-site utility department, are also brought into the cooperative partnership by the resultant reduction in utility conflicts and damage, as well as the ultimate enhancement of system knowledge and mapping. The shared goals are to work smart, to minimize utility conflicts, to deliver projects on time, to reduce or eliminate cost growth, and to enhance worker and public safety.

Credits
Author(s)
Nicholas Zembillas

Publication(s)
Not Published
Presented at ASCE International Pipeline Conference
July 2003