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May 28, 2008

Subsurface Utility Engineering (SUE)

Subsurface Utility Engineering (SUE) is an engineering process that has evolved considerably over

the past few decades. It has been used primarily by State transportation departments (DOTs),

local highway agencies, utility companies, and highway design consultants. The SUE process

combines civil engineering, surveying, and geophysics. It utilizes several technologies, includingvacuum excavation and surface geophysics. Its use has become a routine requirement on highway

projects in many states.

SUE began in the early 1980s. Traditional methods of dealing with subsurface utilities were not

working. It was common practice to design projects without consideration of any utilities and to

then deal with them during construction. This resulted in many unnecessary utility relocations,

construction delays, and unexpected encounters with subsurface utilities. It seemed possible that

two relatively new technologies, air/vacuum excavation and surface geophysics, could be

combined to gather data on the exact location of subsurface utilities early in the development of

projects.

Air/vacuum excavation. Highway engineers recognized that it was a good idea to exposesubsurface utilities before beginning any excavation. Unfortunately, the only known way to do this

in the early 1980s was to dig a trench with a backhoe. Far too often utilizing this method,

unknown and even known utilities were damaged, resulting not only in damage to the utilities, but

often in injuries, deaths, and property damage. Thus, the use of vacuum excavation to expose the

utilities was of much interest to many progressive highway people.

Surface geophysics. The first providers and users of SUE recognized that it would be very

difficult to find subsurface utilities using vacuum excavation alone. Since the records provided by

utility companies were more often than not inaccurate and incomplete, the use of emerging

surface geophysical equipment was introduced to help determine relatively precise horizontal

locations of subsurface utilities.

The terms "designating" and "locating" were developed to differentiate surface geophysics andair/vacuum excavation, respectively.

For more background see: http://www.fhwa.dot.gov/programadmin/history.cfm

Surgically Eliminating Subsurface Surprises

Minimally Invasive Vacuum Excavation Is Fast and Cost-EffectiveArticle originally appeared in the April 2008 issue of Utility Contractor Magazine. Reprinted with permission.

By Mike Twohig

Exposing underground utilities is like surgery. And there is an

inherent risk in peeling back layers. Risk and healing time in themedical world have been reduced by endoscopy, a minimally

invasive diagnostic procedure that involves inserting a tube into

the body through a small incision in order to assess the interior

surfaces of an organ. Non-destructive vacuum excavation is the

endoscopy of the subsurface utility engineering (SUE) profession.

The opening is small (1 sq ft), the suctioning of earth usually

swift (10 minutes or less) and the utility exposed in a safer

manner than using a backhoe, excavator or even hand digging.

Precise X, Y and Z locations can be captured, and in some cases,

the utility can be assessed for repair or maintenance. If air
http://www.fhwa.dot.gov/programadmin/history.cfmhttp://www.enewsbuilder.net/inthepipe/e_article001107320.cfm?x=b11,0,whttp://www.fhwa.dot.gov/programadmin/history.cfmhttp://www.enewsbuilder.net/inthepipe/e_article001107320.cfm?x=b11,0,w


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The Costs and Ripple Effects of a

Damaged Utility

Potential injury and death

Criminal investigations

vacuum excavation is used, as opposed to the hydro method,

then the removed materials (if free of contaminants) can be put

back in the hole practically eliminating healing time.

Theres a key difference in this analogy, though. Surgeons know

their way around a human body. Organs and arteries, bones,

joints and muscles are pretty much in the same place from person

to person, but we dont always know what or exactly where

utilities are located beneath the ground.

Out of SightThere are millions of miles of utilities in the United States

communication, gas/propane, petroleum, water, sewer, storm,

power and steam lines weaving a spidery network of veins and

arteries below the Earths surface. With advanced mapping

technologies such as GPS and GIS, utility locators are getting

better at knowing precise locations. But more often than not,

they dont know for sure, and not everyone knows how to

properly read those maps.

Despite the best intentions, utilities are often mis-marked. One wrong move with an excavator,

backhoe or even a hand shovel can be catast rophic for the workers, others in the vicinity, the

property/utility owners and sometimes entire communities. Lives, liability and litigation havebecome buzzwords on the tongues of project owners, as well as the engineers and contractors

hired to designate, expose, locate and perform work on utilities.

Case in point: Several years ago in Walnut Creek, Calif., workers digging a water main trench with

a backhoe struck a petroleum pipeline, triggering an explosion. The costs were catastrophic: five

dead, four seriously injured, property damage, project delays, criminal invest igations, litigation,

hundreds of thousands of dollars in fines and at least $6 million in settlements.

California safety investigators mainly blamed the pipeline owner for untrained employees who didnt

know how to read blueprints and failed to properly mark a bend in the high-pressure line. But the

contractor and engineering companies were also fined, as was the water main owner.

After the Walnut Creek explosion, California enacted a law establishing tougher safety practices for

excavation work conducted near high-risk utilities. Some of these practices include non-

destructive excavation, as well as certified training for anyone whose job is to mark utility

locations.

Other states have similar laws: the Underground Utility Damage Prevention Act (Virginia), the

Underground Utility Fac ility Damage Prevention Ac t (Illinois) and the Underground Facility Damage

Prevention and Safety Act (Florida), to name a few.

Room for Improvement

Non-destructive methods that manually determine a utility are considered safe excavation

practices in 38 states, according to the Common Ground Alliance (CGA), a Virginia-based, non-

profit organization that advocates for safer digging practices. Every state has a call-before-you-dig hotline. Still, the CGA estimates there are between 500,000 and 750,000 accidental strikes of

underground utilities each year in the United States.

That number could be reduced to nearly zero. There are four SUE Quality Levels, with each level

providing an additional, more-detailed layer of due diligence and protection.

These Quality Levels, described in the Standard Guideline

for the Collection and Depiction of Existing Subsurface

Utility Data, were developed by the American Society of

Civil Engineers (ASCE). This National Consensus Standard

(NCS) follows the legal procedures for adoption not only as

an ASCE standard but also as an American National


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Environmental contamination

Project delays

Lost time and productivity

Financial liability

Redesign costs

Higher construction bids

Change orders

Extra work orders

Construction claims

Higher insurance costs Higher fi nancing costs

Detours

Bad publicity

An ounce of prevention really is worth a

pound of cure. A Purdue University studyfound that for every $1 spent on SUEmethods, $4.62 was saved. In that vein,North Carolinas DOT spent $10,000 butsaved an estimated $500,000 using vacuumexcavation for a p roject to locate a waterline.

Standard Institute (ANSI) standard. Courts and lawyers

use these standards to assist in both defining a

professionals standard of care and in assigning blame. The

Federal Highway Administration (FHWA) and many state

DOTs support these standards as best practices. The

Quality Levels are:

Quality Level D (QL-D) involves utility records

research and interviews with knowledgeable utility

personnel.Quality Level C (QL-C) involves surface survey,

identifying and recording aboveground features of

subsurface utilities such as manholes, valves and hydrants.

Quality Level B (QL-B) involves application of surface

geophysical methods such as electromagnetic-based locating instruments, ground penetrating

radar, radar tomography, metal detectors and optical instruments to gather and record

approximate horizontal (and, in some cases, vertical) positional data.

Quality Level A (QL-A) involves physical exposure via soft-digging (vacuum excavation or

hand digging) and provides precise horizontal and vertical positional data.

So, what does all of this mean? According to the FHWA,

the intent of this standard is to present a system ofclassifying the quality of the existing subsurface utility

data. Such a classification allows the project owner,

engineer and contractor to develop strategies to reduce

or, at a minimum, allocate risk.

It also means the engineer needs to know the appropriate

recommendations to make to the project owner and the

engineer will likely be held responsible for negligent errors

and/or omissions in the utility data at the certified Quality

Level. Ultimately, the project owner decides which Quality

Level he or she is willing to pay for a decision that also

carries liability. And contractors who dont precisely follow

maps, blueprints and procedures also could face penalties.

QL-B lists some pretty high-tech equipment to locate

utilities, but not all utilities can be located with these

devices because of their material (e.g., plastic pipes cant

be detected with metal detectors).

QL-A ensures absolute location identification. So why doesnt everyone take it to this level,

especially given the fac t that various safe-dig laws require non-destruct ive excavation when

digging within the tolerance zone of a designated utility? The answer lies in a perception problem:

QL-A, specifically vacuum excavation, is perceived as expensive.

Reality: Non-Destructive Vacuum Excavation Saves MoneyAn ounce of prevention is worth a pound of cure. A Purdue University study found that for every

$1 spent on SUE methods, $4.62 was saved.

The costs of obtaining QL-B and QL-A data, according to the Purdue study, were less than 0.5

percent of the total construction costs and resulted in a construction savings of 1.9 percent over

traditional QL-C and/or QL-D data.

North Carolinas DOT spent $10,000 but saved an estimated $500,000 using vacuum excavation for

a project to locate a water line.

In Boston, vacuum excavation was used to verify locations on a $30 million utility project, which


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Consider the size and cost of a typical

was part of a $14 billion Central Artery/Tunnel project. By spending $98,000, the contractors

sleeved and moved about 37,000 ft of pipes, mains and ducts without damage or delay and found

pipes that werent previously marked finishing the job five months ahead of schedule.

There are hundreds, if not thousands, of positive examples like these.

Consider the size and cost of a typical contractor test pit. Most are 50 to 100 sq ft, whereas air

vac test pits are 1 sq ft. In cities where a street opening permit costs $50-plus per square foot,

vacuum excavation offers significant savings not to mention that backhoes and excavators

often require a lot of manpower, closure of streets and are not as environmentally friendly.

In some cases, vacuum excavation is half the cost of exposing the utility with a backhoe or

excavator.

But what about hand digging? Well, if time is money, then hand digging isnt necessarily cost-

effective. And, there is the possibility that a shovel could hit and rupture or cut a utility. Air

vacuum excavation is fast and properly operated, it will not damage a utility or the utilitys

protective coating.

Why Dont We Know Whats in the Ground?

According to Cost Savings on Highway Projects Utilizing Subsurface Utility Engineering,

Purdue University, existing records of underground site conditions are usually incorrect,

incomplete or otherwise inadequate because: They were not accurate in the first place. Design drawings are not as-built or

installations were field-runand no record was ever made of actual locations.

Multiple parties have been involved over the years. On old sites, there have usually

been several

utility owners, architects/engineers and contractors installing facilities and burying

objects for decades. Seldom are the records placed in a single fi le, and they are often

lost. There is almost never a composite.

References are frequently lost. Records show that an object is a certain distance from

a building that is no longer there, or an object is a certain distance from the edge of a

two-lane road that is now four lanes or is part of a parking lot.

Records are often insuffi ciently maintained. Lines, pipes and tanks are removed from

the ground but arent removed from the drawings.

Air vs. Hydro

Vacuum excavation technology has been around in some shape or form since the 1950s. Today,

there are two main forms of vacuum excavation: air and hydro.

A variety of factors influence which method is right for a given situation.

Air vacuum excavators use compressed air to loosen the soil and positive displacement blowers to

vacuum the spoils into a tank. Hydro vacuum excavators use high-pressure water to loosen soils,

and the residual slurry spoils are easily extracted into the debris tank.

Air vacuum excavator systems are generally used in drysands, gravel and other loose materials, using little if any

water. Hydro vacuum excavator systems work better on

the clays and heavy, dense soils typically found in the

Southern and Midwestern states, although there are some

very powerful air vacs now on the market as well as

combo vacs that offer air and hydro from the same unit.

The biggest mechanical difference between the hydro and

air is filtration. Hydro requires very little filtration as few

airborne particles pass through the debris tank and into

the blowers. Air vacuum excavator systems, however,


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contractor test pit most are 50 to 100 sqft, whereas air vac test pits are 1 sq ft notto me ntion that backhoes and e xcavatorsoften require a lot of ma npower, closure ofstreets and are not as environmentallyfriendly.

have significant amounts of small particles traveling

through the tank into the filter cartridges. All of the

airborne particles need to be extracted from the airflow

before going through the blower system. The buildup of

this dust on the filter media will begin to starve the blower

of air. This creates heat and potential for damage to the system if the airflow cannot be

maintained. Purchase, rental and maintenance costs for air vacs are typically more than for hydro.

While hydro vacuum excavators may appear to be less complicated and less expensive, there are

other factors to consider. Hydro vacuum excavations often require hundreds of gallons of water for

a days work. This greatly increases the size and weight of the truck or trailer, which could be aproblem when working on soft or sloped terrain or in a tight area. The spoils from hydro vacuum

excavators cannot be placed back in the hole and the surface cannot be restored quickly. Most

significant, if the soil is contaminated, the increased volume from water may increase the handling

and disposal costs of the spoils.

Air vacuum excavators weigh far less, and the dry material can be replaced in the hole and

compacted using tampers. Disposal issues of contaminated spoils are also mitigated as no water or

chemicals have been introduced into the soil.

There are additional economical and safety advantages of air vs. water. Water is a non-

compressible fluid, so it will try to cut whatever it encounters. Air is compressible, so if it hits

something hard, it will compress and flow around it, avoiding any damage. Air is also non-conductive, so it is safer for operators.

After the utility is exposed, the following information is typically recorded: utility, material, size,

depth, condition, location (X, Y, Z), orientation, roadway section materials and depths, soil type

and water table.

Air vacuum excavation can also be used at proposed boring locations to excavate below the utility

window, which is usually about 8 ft. This is very useful where the mandated setbacks to utilities

cannot be maintained or the location of certain utilities is in question.

Vacuum excavation is especially useful in applications where, in the middle of a big site, there are

hidden underground utilities. Its also great for checking for environmental contamination withoutexposing a large area.

If vacuum excavation is the endoscopy of the SUE world, then Mother Earth is our patient. We

should treat her and her people right.

Mike Twohig is a subsurface utility engineer with Woolpert Inc. based in Orlando, Fla.

SUE Best Practices, Including Non-destructive Vacuum Excavation, Save Money

By:

Reducing unforeseen utility conflicts and relocations

Reducing project delays due to utility relocates

Reducing claims and change orders

Reducing delays due to utility cuts Reducing project contingency fees

Lowering project bids

Reducing costs caused by confl ict redesign

Reducing the cost of project design

Reducing travel delays during construction to the motoring public

Improving contractor productivity and quality

Reducing utility companies costs to repair damaged facilities

Minimizing utility customers loss of service

Minimizing damage to existing pavements

Minimizing traffi c disruption and increasing DOT public credibility

Improving working relationships between DOT and utilities


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Increasing efficiency of surveying activities by elimination of duplicate surveys

Fac ilitating electronic mapping accuracy

Minimizing the chance of environmental damage

Inducing savings in risk management and insurance

Introducing the concept of a comprehensive SUE process

Reducing right-of-way acquisition costs

Source: Cost Savings on Highway Projects Utilizing Subsurface Utility Engineering, Purdue

University

Published by Association of Oil Pipe LinesCopyright 2013 Association of O il Pipe Lines. All rights reserved.

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