A Citizen’s Guide to

Vertical Engineered Barriers

What Are Vertical Engineered Barriers?

A vertical engineered barrier, or “VEB,” is a wall built 

below ground to control the flow of groundwater. VEBs 

may be used to divert the direction of contaminated 

groundwater flow to keep it from reaching drinking water 

wells, wetlands, or streams. They also may be used to 

contain and isolate contaminated soil and groundwater 

to keep them from mixing with clean groundwater. 

VEBs differ from permeable reactive barriers in that 

they do not clean up contaminated groundwater. (See 

A Citizens Guide to Permeable Reactive Barriers [EPA 

542-F-12-015].) However, cleanup methods often are 

used together with VEBs to treat the isolated soil or 

groundwater.

How Do They Work?

VEBs are made of impermeable or slightly permeable 

materials, which means they prevent or minimize 

the flow of water and contaminants through the wall. 

A slurry wall is the most common type of VEB. It is 

constructed by digging a narrow trench, usually 2 to 4 

feet wide with a backhoe or long-reach excavator. The 

trench is filled with slurry, which consists of soil mixed 

with water and clay. A type of clay called “bentonite” is 

used most often because it expands when wet to fill 

gaps or holes in the VEB. Cement may be added to 

make the slurry wall stronger.

A VEB also can be constructed using sheet pilings 

made of steel, vinyl, or other materials. Sheet pilings 

are large sheets linked together at their edges to form 

a wall. Equipment is used to hammer or vibrate the 

sheets into the ground.

Where possible, the bottom of the VEB is “keyed 

into” a low-permeability layer of soil or bedrock. This 

means the bottom of the wall extends several inches 

into the soil or to the top of the bedrock, which helps 

to keep groundwater from seeping beneath the wall. A 

protective cap may be installed atop the VEB to prevent 

damage from vehicle traffic or other activities. A larger 

impermeable cap often is placed over the entire 

contaminated area enclosed by the VEB to prevent rain 

water and snow melt from entering it. (See A Citizen’s 

Guide to Capping [EPA 542-F-12-004].)

Even when surrounded by a VEB and cap, contaminated 

groundwater may build up in the isolated area or move 

outward through small openings in the VEB toward 

clean areas. To prevent this, wells may be drilled 

within the isolated area to pump out groundwater. 

Contaminated groundwater that has been pumped to 

the ground surface usually will require treatment.

The VEB, cap, and pumping wells are maintained and 

monitored to ensure the contaminated area remains 

isolated and that contaminated groundwater does not 

spread to clean areas.

How Long Will It Take?

Building a VEB may take anywhere from several days 

to several months. Construction of a VEB may take 

longer where:

• The contaminated area is large or deep.

• Soil is hard or rocky.

• The VEB is wide.

These factors vary from site to site. Some VEBs may 

stay in place permanently. Illustration of a VEB containment system around a contaminated area
United States Office of Solid Waste and EPA 542-F-12-022

Environmental Protection Emergency Response September 2012

Agency (5102G) www.epa.gov/superfund/sites

www.cluin.org

Example

Spills of wood-treating 

chemicals contaminated the soil 

and groundwater at the Taylor 

Lumber and Treating Superfund 

site in Oregon. A 2,040-foot 

long, 21⁄2-foot wide, VEB 

was constructed of bentonite 

and soil to isolate a plume of 

contaminated groundwater. The 

VEB encloses a 6-acre area 

and extends 14 to 16 feet below 

ground where it is keyed into 

bedrock. A protective asphalt 

cap installed over the VEB and 

contaminated area protect the 

VEB from heavy equipment 

traffic and prevent rainwater 

from soaking into the area it 

encloses. 

As part of the long-term 

operation and maintenance 

of the VEB, groundwater is 

pumped from four wells in the 

contaminated area to keep 

contaminants and groundwater 

from seeping outside the wall. 

Groundwater outside the VEB 

is regularly sampled to make 

sure contaminants remain in the 

enclosed area and do not pose 

a threat to human health or the 

environment.

For More Information

For more information about 

this and other technologies in 

the Citizen’s Guide Series, 

visit:

www.cluin.org/remediation

www.cluin.org/products/

citguide

NOTE: This fact sheet is intended solely as general information to the public. It is not intended, nor can it be relied upon, to create any 

rights enforceable by any party in litigation with the United States, or to endorse the use of products or services provided by specific 

vendors. The Agency also reserves the right to change this fact sheet at any time without public notice.

Are Vertical Engineered Barriers Safe?

The materials used to construct a VEB generally pose little risk to people or the 

environment. VEBs are effective at keeping contaminated groundwater from 

flowing toward clean areas. A VEB will continue to be protective as long as it is 

properly inspected and maintained. VEBs and the groundwater are monitored 

to make sure that there is no damage to the wall and contaminants are not 

moving to other areas. 

How Might It Affect Me?

Residents near the site may see increased truck traffic as materials are brought 

to the site. Construction of the VEB may involve backhoes, pile drivers, or 

other noisy machines. If sheet pilings are hammered or vibrated into place, 

nearby residents also may feel the vibrations. If buildings or people are nearby, 

monitoring can be conducted to make sure noise and vibration levels do not 

exceed limits. Workers often use equipment that cause as little noise and 

vibration as possible. Workers will need to access the area for VEB maintenance 

and repairs or to collect groundwater samples to ensure the VEB is working. At 

sites where groundwater is being removed and treated, workers may be present 

for longer periods of time. 

Why Use Vertical Engineered Barriers? 

VEBs may be selected at sites where cleanup of contaminated groundwater 

is difficult and expensive, or cannot be completed before contamination 

spreads to areas where people and wildlife can come in contact with it. VEBs 

are also helpful in cases where cleanup methods could push contaminants to 

uncontaminated areas. VEBs typically are less expensive to build and maintain 

than other types of technologies, especially in large contaminated areas. VEBs 

have been selected or are being used at dozens Superfund sites across the 

United States.

Installation of sheet piling Excavation of a slurry wall trench