STATEMENT OF NEED: UTILITY LOCATING TECHNOLOGIES A Joint Project of the Federal Laboratory Consortium's State and Local Governments Committee, the Trenchless Technology Center and the Technology Transfer Information Center

About the Project


Introduction to the Statement of Need
Technology Requirement
Background: Problem and Impact of Solution


The Problem
Consequences of Third Party Utility Damage
Market Potential for New Technology

State-of-the-Art Technology

One Call Systems
Destructive Methods
Non-Destructive/Geophysical Methods

Technology Constraints and Specifications

Most Important Application Criteria
Current Industry Accuracy and Cost Parameters
Accuracy Levels of Information Provided From Industry Locates
Costs for Location Services

References and Bibliography

APPENDIX A: Types of Underground Utilities and Materials


Table 1: Types of Underground Utilities
Table 2: Common Materials for Underground Utilities



Cover Letter and Project Sponsors

ABOUT THE PROJECT

This Statement of Need (SON),Utility Locating Technologies, seeks technological solutions to the problem of effectively locating all types of underground utilities under the variety of site conditions found in urban areas. The SON addresses an issue of significant national importance-the current and increasing potential for damage to underground utility systems caused by other excavation and utility installation/repair activities.

The project seeks to identify emerging and uncommercialized technologies that meet the criteria defined within the SON. Deadline is Friday, August 27, 1999.

Have ideas on how to solve the needs? By August 27, send suggestions to Dr. Ray Sterling, Director, Trenchless Technology Center, Louisiana Tech University, P.O. Box 10348, Room 203, Engineering Annex, Arizona Street, Ruston, LA 71272-0046. Phone number is (318) 257-4072; fax (318) 257-2777; email sterling@coes.latech.edu. He will compile for industry a State-of-the-Art report that analyzes the potential technologies and recommends those that should be investigated further for possible commercialization and/or implementation.

INTRODUCTION

This Statement of Need (SON) is the result of a request from a member of the American Public Works Association to the Federal Laboratory Consortium's (FLC) State and Local Governments Committee. The SON addresses an issue of significant national importance--the current and increasing potential for damage to underground utility systems caused by other excavation and utility installation/repair activities. This SON seeks novel solutions to the problem of effective location of all types of underground utilities under the variety of site conditions found in urban areas.

TECHNOLOGY REQUIREMENT

The goal for improved utility location technology is to avoid third-party damage to existing underground utilities caused by the presence of unknown utilities or mis-located utilities. This goal requires radically improved location technologies and the integration of these technologies into the planning and execution of excavation work. The focus of this Statement of Need is on the location technologies themselves but, as discussed under technology constraints and specifications, technology advances that relate to other aspects of this problem also are of interest.

The required technology is a single multi-sensor system that accurately locates all underground utilities under the variety of site conditions found in urban areas. Ideally, the method(s) would operate from the ground surface and not require prior knowledge of the location of the utility or access to the utility to introduce special signals for detection. Novel approaches, sensors and/or a combination of technologies are needed to increase the reliability of utility detection in terms of the size, depth and utility materials that can be detected and that can operate in the presence of utility congestion and error-producing conditions that are present in urban rights-of-way.

BACKGROUND: PROBLEM AND IMPACT OF SOLUTION

The Problem

Overhead utility lines are becoming a thing of the past except in rural areas. The urban underground has become a spider's web of utility lines, including phones, electricity, gas, cable TV, fiber optics, traffic signals, street lighting circuits, drainage and flood control facilities, water mains and waste water pipes. In some locations, major oil and gas pipelines, national defense communication lines, mass transit, and rail and road tunnels also compete for space underground. The deregulation of utility services is adding to the problem as multiple service providers seek to place their networks underground.

Utility lines are all susceptible to being damaged as construction and renovation equipment excavate in their vicinity. Records are often poor with inaccurate utility positions and/or depths. Some live services do not even show on the utility plans. This means that the ability to physically determine on-site the location, nature and depth of underground utility services is critical to reducing the risk and consequences of inadvertent damage during construction.

Utility companies, locator services, and contractors are searching for new locating equipment and methods, and ways to overcome unreliable utility locates. But they face huge obstacles. For instance, the conduits for these utilities range from steel, cast iron and ductile iron pipes to clay, polyethylene, polyvinyl chloride, and fiberglass reinforced plastic pipes. Cable may be copper or fiber optic. The conduits have different shapes, compositions, densities, and diameters, and their depths may be as little as 0 to 0.5 meter or in excess of 50 meters. Some lines (usually local telephone, electric and gas lines) may be stacked vertically in a common trench. Multiple lines may be grouped in a single conduit or duct bank. Multiple utilities may be grouped in common utility tunnels often called utilidors. Figures 1, 2 and 3 show some recommended utility layouts within public rights-of-way but standard layouts are an exception rather than the norm.

Figure 1 Example Utility Layout A (APWA/ASCE 1974)

Figure 2 Example Utility Layout B (APWA/ASCE 1974)

Figure 3 Example Utility Layout C (APWA/ASCE 1974)

Utility layouts grow as a city grows and must accommodate to what is already underground. In older cities and, especially at intersections of streets, underground utilities can become extremely congested (Figure 4).

Figure 4 Illustration of Subsurface Utilities at a
Downtown Intersection in San Francisco (APWA 1971)

Some underground utilities at shallow depths can be located with relative ease using inexpensive equipment but many types of utilities and especially smaller non-conducting utilities at greater depths are extremely difficult to locate. The complex signal records produced by some types of current locating equipment requires expert interpretation - raising costs and making underground utility location an art as well as a science. This lack of definition is problematic, however - informed guessing about the location of utility lines is not good enough. Mistakes bring down vital 911 emergency services, electric cash registers can't be opened, security alarms go down, online stock transactions are lost, bank records can't be accessed, and for people who work at home, business and many other comforts of home grind to a halt.

Consequences of Third Party Utility Damage

For some utilities, hits cause interruptions to daily life and commerce, for others they can cause physical danger to workers, bystanders and nearby buildings. They all result in expense that is borne by a combination of the contractor, the locating company, utility providers, insurance companies and the affected public and business owners. Individual incidents can have costs out of all proportion to the cost of the work being undertaken and the sum total of all utility damage costs are very significant and rising. Some incident examples and company statistics illustrate the magnitude of the problem:

• In 1998, Public Service Company of Colorado reported 300 primary feeder cable cuts in the state. A primary feeder carries power to 2,000 to 3,000 customers and hence 300 cuts affects 600,000 to 900,000 customers (Rocky Mountain News, 3/14/1999).
• The Public Service Company of Colorado also reported that a total of more than 3,000 underground lines were cut in 1998 - up by more than 1,000 over the previous year (Rocky Mountain News, 3/14/1999).
• Damage to the US West cable network can exceed 2000 hits in one month and averages over 1000 hits per month (Nelson and Daly 1998).
• A phone utility hit in Colorado in early March 1999 cut off service for 12,000 customers.
• A 36 fiber, fiber optic cable can carry up to 870,912 circuits, and can generate over $175,000 per minute in revenue (Milliken 1998).
• In 1993, there were more than 104,000 hits or third party damage to gas pipelines with a total cost exceeding $86 million (Doctor et al, 1995).
• A construction crew driving piles for a new garage accidentally crushed high-voltage underground electrical cable serving Newark airport's three passenger terminals. Several hundred passenger flights were canceled and the travel plans of tens of thousands of people were ruined (Mpls. Star Tribune Jan 10,1995).
• In 1997, Memphis Light, Gas and Water paid damages of $515,000 and collected damages of $793,000 for utility damage (Stinson, 1998).

Not all damage to utilities is reported or immediately detected. This makes assigning responsibility for damage costs difficult. It may also cause later service problems that are difficult to trace and unexpected severe safety consequences. For instance, a new gas line was inadvertently installed through a clay sewer service pipe using horizontal directional drilling. The sewer service pipe later plugged and the sewage backed up into a home. A sewer cleaning firm was called to clean out the sewer line - unknowingly rupturing the gas line in the process. Gas entered the house basement from the sewer and later caused a gas explosion that destroyed the house.

Market Potential for New Technology

STATE-OF-THE-ART TECHNOLOGY

The following discussion is intended to provide an overview of the current state-of-the art in technologies used for utility location detection and other subsurface site investigation. The description provides the general principles involved in the methods rather than the specifics of any particular methods.

One Call Systems

"One Call" systems are mandated in most areas of the country as a partial solution to the utility damage problem. They serve as a single point of contact for excavators to determine which utilities are present in the area in which they will be digging. The One Call system notifies the utility companies with utilities in the vicinity of the dig area and the utility company provides a physical locating/marking service prior to the excavation.

There are several inadequacies of current one call systems and the way that they are used in the industry. These include:

• Not all utilities are participants in all one call systems.
• One call systems will only identify and notify utilities that show a utility in the affected area. If a utility is not recorded, the company may not be contacted to provide a "locate."
• Depth information is not provided by companies when marking their utilities.
• Problems occur with demand for locates and timing of locates relative to actual construction.
• Many contractors do not use the one call system.
• Even when the one call system is used and utilities are marked, hits still occur due to mis-locates and poor excavation practices (56 percent of damage in 1995 for gas pipelines was caused when the one-call system was used; 25 percent of hits on located facilities were due to mis-locates).

Destructive methods

Soil borings are the traditional method of determining the zonation and properties of subsurface materials. Since a soil boring will damage underground utilities if the boring strikes the facility, borings must be used carefully in the vicinity of existing utilities. The hole created by the boring operation can be used for other non-destructive site investigation methods (described below).

Test pits can be excavated by a combination of machine and hand excavation methods. They create a large enough hole for the direct physical examination of the in-place soil materials and any exposed utilities. Care must be taken not to damage utilities during the excavation process and the cost of a test pit rises rapidly as the hole becomes deeper, the soil becomes weaker or the excavation extends below the water table.

Hand excavation is normally used when excavating near existing utilities. However, even shovels can easily damage unprotected cables and many cases of damage occur because the utility is not in the expected location and before the contractor switches to hand excavation.

Vacuum excavation (potholing) is used to create 0.3 to 0.5 m diameter holes to physically confirm the position and depth of an underground utility. A hole is first cut in the road pavement using a rotary core drill and then the excavation is advanced using compressed air jets and/or high pressure water jets in conjunction with a vacuum excavator wand. The excavation process will not normally damage an existing utility and the hole in the street pavement is kept to a minimum and is easily repaired. This procedure can only be used to confirm the position of known utilities or previously located utilities.

Non-destructive/geophysical methods

Geophysical methods of locating objects underground typically utilize a wave/signal that is introduced into the ground and/or a physical property of the object that is to be located that is different from the surrounding ground. An instrument is then used to measure the ground response and from this response, information about the position of the object below ground and/or soil properties is inferred. Many of the methods can be used in several different arrangements that vary in terms of what can be detected, depths of penetration, sizes and types of objects that can be resolved and cost of implementation.

Listed below are some of the basic types of waves or field properties that are used:

Seismic waves are ground vibrations that travel through soil and rock. They can be introduced into the ground using explosives, hammers or vibrating elements. Seismic waves travel at different velocities in different materials and also will be reflected at discontinuities below ground, e.g. embedded objects and geological layers. Different types of seismic waves are used for different purposes: compression waves (p-waves), shear waves (s-waves) and surface waves (Rayleigh waves and Love waves).

Ground penetrating radar (GPR) uses radio frequency signals to penetrate the ground. These signals are introduced to the ground using antennas. The design of the antenna typically controls the frequency of the wave introduced. The signals are reflected (re-radiated) at interfaces of dissimilar materials as with seismic waves.

Magnetic field variations can be used to determine the position of magnetic materials below ground or cables/pipes that either create or can be induced to create their own electromagnetic field.

Electrical field properties are also used by measuring the AC resistivity between different points within the soil or on the surface of the ground. Either electric dipoles or magnetic dipoles may be used. The variation of resistivity seen between different points reflects the nature of the materials along the path of current flow between the points.

Variations in gravitational field can be used to locate objects or voids that exhibit substantial density variations from the surrounding material. Since the changes in gravitational field are very small, the method is usually referred to as a microgravity method.

Temperature field variations are used to identify objects that disturb the normal ground temperature field - either because of the function of the object (e.g. steam pipe) or because the object has different thermal characteristics than the surrounding ground. Changes in solar radiation input to the ground surface or surface air temperature variations may provide sufficient changes in the thermal field for shallow buried objects.

Nuclear methods typically introduce a form of radiation into the ground and measure the response of the ground with appropriate detectors. Common forms of radiation used are gamma rays and neutron rays. Naturally occurring radiation such as cosmic radiation has also been used to detect underground voids.

Gas detection may be used to locate objects such as plastics that outgas during their lifetime. The gas diffuses through the ground and, if in detectable concentrations, can indicate the presence and approximate location of the object. Such methods are used to detect plastic mines. Also, sewers may be pressurized with smoke and visual observation of smoke escaping from the ground used to identify locations of leaks in sewers.

Most of the above methods can be applied in several configurations or types of applications that are described below:

Airborne methods allow wide area coverage at low cost. They are typically used for magnetic surveys, infrared surface temperature surveys and photographic observation of surface features that provide evidence of subsurface conditions.

Surface methods may be truck or cart mounted or be small enough to be carried by an individual. No excavation is necessary but, in street rights-of-way, there may be interference with normal traffic flow. In utility applications, the method used must be capable of working through the discontinuities and material properties provided by the surface pavement layers. Surface methods may use a single location for both emitter and receiver or may use multiple locations for both emitters and receivers.

Downhole (well logging) methods use a borehole created by drilling to insert signal emitters and sensors that provide information about the ground conditions or objects in the vicinity of the borehole. This may allow retrieval of information about conditions at much greater depth than the equivalent surface method but only near to the borehole. Downhole methods rely on local material properties or reflected/re-emitted signals.

Surface/downhole methods combine emitters at the surface with receivers at depth in a borehole (or vice versa). These methods allow direct path information to be collected.

Cross-hole methods use two or more different boreholes with emitters and/or sensors. Direct path information between pairs of boreholes can be collected.

Reflection/back scatter methods rely on reflection or re-emission of signals at interfaces of dissimilar materials. Since reflections may be weak and the total path length is twice the distance to the object to be detected, signal attenuation is more important than in direct path methods.

Direct path methods use information on field properties, or travel time between two points to infer the presence of objects along the travel path or variations in subsurface layering. Attenuation is less of a problem than with reflected signal methods but creating information from multiple signal paths is usually required. For example, seismic refraction uses seismic wave travel time between varying spacings of surface emitters and receivers to distinguish geological layering. AC resistivity methods use the resistivity information between different surface and/or borehole locations to detect the position and nature of inhomogeneities in the subsurface.

Normal-operation signal emission methods use the normal operating conditions of a cable or pipe for detection. For example, an electric cable can be located by its electromagnetic field and this is made easier by the known frequency of the signal. A steam pipe may be located by the disturbance to the ground temperature field.

Direct-induced signal emission methods introduce signals into pipes, cables or fluids with pipes that are then radiated from the utility to aid in its detection and location. For example, a metal pipe may be used to complete an AC circuit and the resulting electromagnetic field used to locate the pipe or compression waves introduced into a water-filled pipe for seismic position detection. These methods require that the utility be known about in advance and that the utility is accessible at various locations so that the signals can be introduced into the line.

Portable direct-signal emission methods use signal generators that can be moved along a pipeline for location purposes. For example, radio frequency emitters (sondes) can be towed along a plastic pipeline generating a signal that can be interpreted for location at the ground surface. These methods require that the utility be known about in advance, that the utility is accessible for the introduction and retrieval of the emitter, and that the pipe is sufficiently unblocked to allow the passage of the emitter.

Surface-induced signal emission methods generate signals at the surface that will induce a response in the cable, pipe or tracer wire underground. For example, the creation of a fluctuating electromagnetic field in the ground will induce a current in a metal pipe and the field due to the induced current can be used to locate the pipe. Unknown pipes can be identified using this technique and no direct connection to the pipe is required. Signal strengths are, however, lower than in the case of direct signals.

Once the various signals have been collected, the information must be processed or inspected to infer the position and/or nature of the buried object or subsurface inhomogeneity. This is done in a variety of ways, including:

Interpretation of pattern in plots of reflected signal data. For example, in either seismic reflection methods or surface GPR surveys, the plots showing signal traces versus horizontal position indicate reflections from surface interfaces as lines on the plot and reflections from localized objects as inverted hyperbolae. Spatial location and orientation can be inferred and the approximate depth estimated if the speed of travel of the wave in the subsurface material is known. Complex underground conditions and local interference sources can make interpretation of the plots very difficult.

Interpretation of dispersion curves for direct path signals. Dispersion curves indicate the change of a property with the wavelength of the emitted signal. For example, in the spectral analysis of seismic waves (SASW) method, the apparent wave velocity between two points on a surface usually changes with the wavelength of the signal. This change reflects the fact that the higher frequency waves depend more heavily on near surface layers due to the attenuation of the higher frequencies at greater depths. The dispersion curves can be interpreted by computer analysis to infer the actual layering of soils and pavement.

The use of tomography that has been highly developed in medical imaging allows the recreation of 3-D images of objects from spatially correlated sensor data.

The use of inverse methods of analysis. These are computational analysis methods that allow the spatial and property data of an object to be inferred from the field measurements taken. These are computationally intensive and may not have unique solutions.

Data filtering and other data processing or image enhancement techniques that improve the ability to interpret field data. For example, when looking for electric cables, signals at frequencies at other than 60 Hertz may be filtered to enhance the signal-to-noise ratio for cable detection.

Neural networks and other pattern matching methods may be used to interpret raw or processed field measurements. Expert systems may also be used to reduce the need for a trained expert in interpretation of results.

TECHNOLOGY CONSTRAINTS AND SPECIFICATIONS

All the methods described above as the current state-of-the-art have problems in one or more of the following areas:

• They cannot locate all types of utilities
• They can't be used in all types of soils
• They are affected by interference from nearby objects
• They cannot penetrate to the required depths
• They cannot resolve smaller utilities at the required depths
• They use hazardous materials that increase cost and risk
• They have a cost when used in normal practice that exceeds what the market is willing to pay.

The goal for improved utility location technology is to avoid third-party damage to existing underground utilities. This has several facets, and significant improvements in any area of location technology or in the linking of investigation data to field information or warnings, will assist in meeting that goal. The objective for the location technologies themselves is to make location of utilities foolproof in all types of soil and site conditions and for all types of utilities at all depths of interest. Utility location sensors may be used as part of a site investigation process prior to excavation and/or they may be used during the excavation process attached to a backhoe excavation bucket or drill bit. Although it addresses only part of the total problem, methods of manufacturing new non-metallic pipes/cable so that they are easily locatable and methods of adding foolproof marking systems to existing pipes and cables also are important in improving future location abilities. The objective for the total system is the combination of the locating data with existing utility records and the provision of a real-time information/warning transfer to the equipment operator that is planning to excavate or already in the process of excavation. Improvement is possible in many different areas but critical improvements that would significantly reduce the damage hazards experienced today are:

• Novel or improved methods of locating non-metallic pipes and cables, e.g. plastic and clay pipes and fiber optic cables
• Novel or improved methods of marking new or existing utilities so that they can be easily located in the future
• Novel or improved methods of detection/warning systems on excavation/drilling equipment that respond to the presence of other utilities before contact is made
• Multi-sensor technologies that compensate for weaknesses or potential interference with any individual locating method
• Improved analysis methods that allow resolution of objects at greater depth or in the presence of higher levels of interference
• Data management methods that allow a rapid interface between a field crew and a multi-utility database including

- Easy updating of utility records with new locating information


- Field alerts as to discrepancies between expected positions of utilities and field measurements


- Graphical displays of utility layouts in field based on most current information

Most Important Application Criteria

Although the eventual goal may be foolproof locating and elimination of third-party utility damage due to poor utility location information under all conditions, this is likely unattainable in the foreseeable future. The main constraints and application criteria for novel or improved methods are listed below:

• Methods must be applicable in urban right-of-way settings as well as being able to find a utility in an open-ground, uniform soil condition. Any new technology should

- Operate through asphalt or reinforced concrete road pavements


- Tolerate interference from metallic objects nearby


- Provide useful information in crowded utility settings


- Occupy small areas of the street on a short-term basis so as to not interfere significantly with traffic flows on major routes

• Methods should be readily portable, rugged enough for field use, and able to be powered by generators or batteries as appropriate:

- Truck mounted units, units on wheeled carts, and units that can be carried in a walkover mode all have applicability for different survey conditions


- Exposed sensor suites must be capable of operating effectively under normal exterior temperature, moisture, dust and other urban environmental conditions


- Equipment must withstand long-term use in field conditions


- Equipment and sensors to be used in boreholes and/or utility pipes must be able to withstand immersion in water and the potentially corrosive fluids/gases that may be present

• Methods should be able to be operated by a technician. The extent of training would depend on the comprehensiveness of the equipment.
• Methods ideally should be able to identify utilities with a depth to diameter ratio of 30:1 or better, i.e. a 25 mm pipe or cable at 0.75 m depth or a 1 m diameter pipe at 30 m depth.
• Methods ideally should be able to resolve depth and horizontal position of utilities to within a depth to accuracy ratio of 20:1 or better, i.e. an error in depth or horizontal position of 50 mm at 1 m depth or 1 m at 20 m depth.
• Methods or combinations of methods are more desirable if they are able to improve detection of all kinds of pipe or cable in all soil conditions but the cost of multi-sensor technologies must remain realistic
• Methods capable of greater depths are better but the following depth ranges are most important

- Cables: up to 2 m (larger depths becoming more important as trenchless technologies are more widely used)


- Pipes: up to 5 m most common, up to 10 m important, over 10 m uncommon

CURRENT INDUSTRY ACCURACY AND COST PARAMETERS

Accuracy Levels of Information Provided From Utility Locates

Although many existing methods can give more precise information under favorable conditions, the following information is considered the normal precision of utility location information (not including mis-locates):

Typical Surface-only Utility "Locates"

Horizontal location within 24 inches either side of location markings

Vertical location not provided

Typical Surface Survey with Vacuum Excavation Potholes for confirmation (Subsurface Utility Engineering (SUE) provider

Horizontal location within 0.5 ft.

Vertical location within 0.05 ft.

Costs for Location Services (Milliken 1998)

The cost range for typical current practice for utility location is shown below.

• Zero to $50 for one-call notification and "locates" at an excavation location
• $150 to $500 for SUE service at an excavation location
• $0.20 to $2.00 per foot for utility designation service (may include records research, paint markings, traffic control, field sketches, surveying, CAD mapping, signing and sealing by a professional engineer or professional land surveyor).

REFERENCES AND BIBLIOGRAPHY

APWA, 1971. Feasibility of Utility Tunnels in Urban Areas, Special Report No. 39, Feb. 1971, American Public Works Association, Chicago.

APWA/ASCE, 1974. Accommodation of Utility Plant within Rights-of-Way of Urban Streets and Highways: Manual of Improved Practice, American Public Works Association, Chicago.

Anspach, J.H., 1996. "Subsurface utility engineering," Proc. Symp. on the Application of Geophysics to Engineering and Environmental Problems (SAGEEP '96), Apr. 28-May 2, 1996, Keystone, CO, Environmental and Engineering Geophysical Soc., Wheat Ridge, CO., pp 443-450.

Barrow, B., N. Khadr, R. DiMarco and H.H. Nelson, 1996. "The combined use of magnetic and elctromagnetic sensors for detection and characterization of UXO," Proc. Symp. on the Application of Geophysics to Engineering and Environmental Problems (SAGEEP '96), Apr. 28-May 2, 1996, Keystone, CO, Environmental and Engineering Geophysical Soc., Wheat Ridge, CO., pp 4469-478.

Bradford, J., M. Ramaswamy, and C. Peddy, 1996. "Imaging PVC gas pipes using ground-penetrating radar," Proc. Symp. on the Application of Geophysics to Engineering and Environmental Problems (SAGEEP '96), Apr. 28-May 2, 1996, Keystone, CO, Environmental and Engineering Geophysical Soc., Wheat Ridge, CO., pp 519-524.

Butler, D., 1996. "The probability of magnetic or electromagnetic detection of a 55-gallon drum as a function of line and station spacing," Proc. Symp. on the Application of Geophysics to Engineering and Environmental Problems (SAGEEP '96), Apr. 28-May 2, 1996, Keystone, CO, Environmental and Engineering Geophysical Soc., Wheat Ridge, CO., pp 465-468.

Carver, C., 1998. Examine hidden costs of utility hits when allocating damage prevention dollars," Underground Focus Magazine, Jan/Feb 1998.

Doctor, R.H., N.A. Dunker and N.M. Santee, 1995. Third-party Damage Prevention Systems, Final Report for Gas Research Institute Contract No. 5094-810-2870, Oct. 1995, by Nicor Technologies, Naperville IL.

Gucunski, N. V. Ganji and M.H. Maher, 1996. "SASW test in location of buried objects," Proc. Symp. on the Application of Geophysics to Engineering and Environmental Problems (SAGEEP '96), Apr. 28-May 2, 1996, Keystone, CO, Environmental and Engineering Geophysical Soc., Wheat Ridge, CO., pp 481-486.

Hague, P.R. and E. Bogatyrev, 1996. "Recent improvements in ground penetrating radar antenna design," Proc. Symp. on the Application of Geophysics to Engineering and Environmental Problems (SAGEEP '96), Apr. 28-May 2, 1996, Keystone, CO, Environmental and Engineering Geophysical Soc., Wheat Ridge, CO., pp 535-544.

Imazaki, T. and T. Kurahashi, 1996. "Imaging and characterizing fractures ahead of tunnel face using in-tunnel HSP method," Proc. Symp. on the Application of Geophysics to Engineering and Environmental Problems (SAGEEP '96), Apr. 28-May 2, 1996, Keystone, CO, Environmental and Engineering Geophysical Soc., Wheat Ridge, CO., pp 597-604.

Kramer, S.R., W.J. McDonald and J.C. Thompson, 1992. An Introduction to Trenchless Technology, Van Nostrand Reinhold, NY.

Lockwood, G.J., R.A. Normann, L.B. Bishop, M.M Selph, and C.V. Williams, __. Environmental measurement-while-drilling system for real-time screening of contaminants," Project Summary, Department of Energy Contract No. DE-AC04-94AL85000, Sandia National Laboratories, Albuquerque, NM.

McDonald, J.R. and R. Robertson, 1996. "Sensor evaluation study for use with towed arrays for UXO site characterization," Proc. Symp. on the Application of Geophysics to Engineering and Environmental Problems (SAGEEP '96), Apr. 28-May 2, 1996, Keystone, CO, Environmental and Engineering Geophysical Soc., Wheat Ridge, CO., pp 451-464.

Milliken, Bob, 1998. "How accurate are locates?" Session handout, Session C5, Damage Prevention Convention, Atlanta GA, Dec 2-4, 1998.

Nelson, R. and M. Daly, 1998. "Creating a major emphasis on damage prevention," Session handout, Session F5, Damage Prevention Convention, Atlanta GA, Dec 2-4, 1998.

Nozaki, K. and R. Kanemori, 1996. "Microgravity survey for shallow subsurface investigations," Proc. Symp. on the Application of Geophysics to Engineering and Environmental Problems (SAGEEP '96), Apr. 28-May 2, 1996, Keystone, CO, Environmental and Engineering Geophysical Soc., Wheat Ridge, CO., pp 951-960.

Powers, M.H., and G.R. Olhoeft, 1996. Modeling the GPR Response of leaking buried pipes," Proc. Symp. on the Application of Geophysics to Engineering and Environmental Problems (SAGEEP '96), Apr. 28-May 2, 1996, Keystone, CO, Environmental and Engineering Geophysical Soc., Wheat Ridge, CO., pp 525-534.

Stinson, W., 1998. "Preventing damage to unlocatable infrastructure," Session handout, Session A5, Damage Prevention Convention, Atlanta GA, Dec 2-4, 1998.

Valle, S. and L. Zanzi, 1996. "Radar tomography for cavities detection," Proc. Symp. on the Application fo Geophysics to Engineering and Environmental Problems (SAGEEP '96), Apr. 28-May 2, 1996, Keystone, CO, Environmental and Engineering Geophysical Soc., Wheat Ridge, CO., pp 535-544.

Waddington, B.S. and M. Maxwell, 1996. "Delineation of pipeline river crossing using cable and pipe locator with real-time differential GPS," Proc. Symp. on the Application of Geophysics to Engineering and Environmental Problems (SAGEEP '96), Apr. 28-May 2, 1996, Keystone, CO, Environmental and Engineering Geophysical Soc., Wheat Ridge, CO., pp 479-480.

APPENDIX A

TYPES OF UNDERGROUND UTILITIES AND MATERIALS

Table 1 provides a listing of the major types of underground utilities that may be present in the shallow underground and particularly in public rights-of-way. In Table 1, the utilities are divided by the type of utility and its function as a long-distance transmission, distribution or service connection line. The table is intended to provide a general reference to the types and functions of utilities that may be present and the likelihood of encountering specific utilities in different sett ings. Of course, many specific utility arrangements may not be well represented in this summary table. A distinction is made in most cases between urban, suburban and rural locations (see table notes for the usage of these terms in the table). The focus of the table is on utilities located in or adjacent to public rights-of-way and it is noted whether a particular type of utility is likely to be located underground. Typical general positions and depths within the right-of-way are given with a normal range of diameters for the individual cables or pipes that constitute the utility service. Cables may also be bundled together or laid adjacent to each other in conduit or duct banks. The smaller end of the range of diameters given will be the most difficult to locate for any particular material, soil type or depth. Finally, an indication of the relative severity of consequences associated with third party damage to each utility type is given both in terms of safety to excavators and/or the surrounding community and in terms of the economic consequences to all parties affected by the damage. Not included in the table are utilities that are not usually in a public right-of-way such as irrigation pipes and septic field lines. Also left out are ancillary structures to underground utility systems (e.g. manholes, junction chambers, storage tanks, catch basins, etc.) as well as underground struc tures that form buildings or parts of buildings (basements, parking garages) and tunnels for road and rail transportation systems.

Table 2 provides a listing of the most common materials used in underground utility systems and features that either make the utilities easier or more difficult to locate. Most older utility systems were laid in an open trench and were then backfilled with select material or with the soil removed. In either case, the presence of the trench and the different properties of the backfill within the trench provide a potential identification of the presence of utilities. Deeper and larger utilities may have been installed using tunnel construction techniques. These tunnels may have a variety of materials used in their supporting structures but are relatively large compared to most utilities. More recent smaller utilities may have been installed by what are termed "trenchless technologies" such as horizontal directional drilling (HDD), pipe jacking, microtunneling, etc. These techniques, as the name implies do not require a continuous trench for the installation of utilities but use small-scale drilling or pipe jacking/tunneling techniques to install utilities. These methods can be installed at greater depths without increasing costs as significantly as in trenched construction. They also have no trench to aid in location and, in the case of HDD, usually follow curved paths vertically and/or horizontally.

Definitions and Notes

1. Interstates may have continuous underground data transmission lines in rural areas, most roads will either not have a need for this service or it will be provided in overhead lines.
2. Routing will often be outside public rights-of-way
3. Depth may be large at major crossings, e.g. rivers and other natural/environmentally sensitive areas
4. Distribution and service may occur around major industrial plants
5. May be an issue in areas with major defense facilities and/or federal government installations
6. Environmental damage may be costly
7. Systems are rare but abandoned services may exist in older large cities
8. Systems have been proposed for capsule freight transport in pipelines in both rural and urban areas
9. Only in extended sewer districts
10. Only on major roads
11. Where old creeks have been built over
12. Usually aboveground except in areas of natural beauty or environmental preservation
13. May be aboveground in pipeline, canal or aqueduct