Deep Aquifer Remediation Tools (DARTs): A new

technology for ground-water remediation

Potable ground-water supplies throughout

the world are contaminated or threatened

by advancing plumes containing radionuclides, metals, and organic compounds.

Currently (1999), the most widely used

method of ground-water remediation is a

combination of extraction, ex-situ

treatment, and discharge of the treated

water, commonly known as pump and

treat. Pump-and-treat methods are costly

and often ineffective in meeting long-term

protection standards (Travis and Doty,

1990; Gillham and Burris, 1992; National

Research Council, 1994). This fact sheet

describes a new and potentially costeffective technology for removal of

organic and inorganic contaminants from

ground water. The U.S. Geological Survey

(USGS) is currently exploring the

possibilities of obtaining a U.S. Patent for

this technology.

Instead of pumping water to the surface

for ex-situ treatment, a tool has been

developed to take advantage of the natural

ground-water gradient to channel ground

water into highly permeable reactive

material(s). These Deep Aquifer

Remediation Tools (DARTs) are used in

conjunction with non-pumping wells and

offer a low-cost and virtually maintenance-free alternative to ex-situ treatment

methods. As the ground water passes

through the permeable reactive material,

the contaminant is immobilized or

transformed to a non-toxic form by a

variety of chemical reactions depending

on the reactive material and contaminant

of concern.

The DARTs are deployed into an aquifer

and corresponding contaminant plume

through a series of non-pumping wells

(fig. 1). Wilson and Mackay (1997) have

found that ground water will converge to

arrays of unpumped wells in response to

the difference in hydraulic conductivity

between the well and aquifer. Numerical

simulations conducted during DART

development indicate that each well

typically intercepts ground water in the

upgradient part of the aquifer that is

approximately twice the inside diameter

of the well (fig. 1).

Trenching techniques are commonly used

to emplace permeable reactive barriers

(PRBs) for in-situ contaminant removal

in shallow aquifers (Manz and Quinn,

1997; Schmithorst and Vardy, 1997).

Trench emplacement of PRBs has a

number of disadvantages that include:

(1) limited to shallow treatment zones;

(2) requires specialized trenching equipment; (3) increased health and safety

concerns during installation; and (4)

replacement and disposal costs of reactive

material after breakthrough. Because

DARTs are deployed through non-pumping

wells, in-situ treatment of deeper contaminant plumes (greater than 100 feet

below land surface) that could not be

treated with currently available trenching

technologies is now possible. In addition,

DARTs allow for easy retrieval, replaceU.S.Department of the Interior

U.S. Geological Survey

USGS Fact Sheet 156-99

October 1999

Figure 1: Schematic diagram showing non-pumping wells containing DARTs and modeled contaminant capture zones,

Fry Canyon, Utah.

BZ1

BZ2

BZ3

Non-pumping well

designation

Inside diameter of

non-pumping well

Model capture zone for

each non-pumping well.

Capture zone width is two

times the well diameter
ment, and disposal of reactive material

after chemical breakthrough.

DARTs are designed to fit a variety of

well dimensions and plume geometrys. A

DART is composed of three basic

components (fig. 2): (1) a rigid PVC shell

with high-capacity flow channels to

contain the permeable reactive material;

(2) flexible wings to direct the flow of

ground water into the permeable reactive

material; and (3) passive samplers to

determine the quality of the treated water.

Multiple DARTs can be joined together

for the treatment of thicker contaminant

plumes. DARTs also allow for “vertical

stacking” of different reactive materials

for the treatment of chemically segregated

contaminant plumes.

Since 1997, several DART prototypes

have been field tested in non-pumping

wells for the removal of uranium (U) from

ground water at sites in Utah and Wyoming (fig. 3). The reactive material used

during these field tests consisted of a

mixture of bone charcoal and iron oxide

pellets. The probable mechanism for U

removal in this mixture is sorption or

precipitation of insoluble uranyl precipitates. Results from the latest DART field

test completed in July 1999 indicate an

order of magnitude reduction in U

concentrations compared to pre-treatment

water samples. Additional field tests of

the DARTs are currently (September

1999) in progress and include the testing

of an additional barrier material (zerovalent iron). Previous research with zerovalent iron (installed using trenching

techniques) has indicated greater than

99.9 percent U removal rates over

extended field operations (Naftz and

others, 1999).

For More Information

For information about licensing of this or

other USGS technologies, please contact:

Technology Enterprise Office

U.S. Geological Survey

12201 Sunrise Valley Drive, MS 211

Reston, VA 20192

Tel: (703) 648-4450

Fax: (703) 648-5068

Email: ttO@usgs.gov

For information about the technical

details of this technology, please contact

the inventors:

David L. Naftz

U.S. Geological Survey

2390 South 2300 West

West Valley City, UT 84119

Tel: (801) 975-3389

Email: dlnaftz@usgs.gov

James A. Davis

U.S. Geological Survey

345 Middlefield Rd., MS 465

Menlo Park, CA 94025

Tel: (650) 329-4484

Email: jadavis@usgs.gov

References

Gillham, R.W., and Burris, D.R., 1992,

Recent developments in permeable in

situ treatment walls for remediation

of contaminated groundwater:

Proceedings, Subsurface Restoration

Conference, June 21-24, 1992,

Dallas, Tex.

Manz, C., and Quinn, K., 1997, Permeable treatment wall design and cost

analysis: International Contaminant

Technology Conference Proceedings,

February 9-12, 1997, St. Petersburg,

Flor., p. 788-794.

Naftz, D.L., Davis, J.A., Fuller, C.C.,

Morrison, S.J., Freethey, G.W.,

Feltcorn, E.M., Wilhelm, R.G., Piana,

M.J., Joye, J.L., and Rowland, R.C.,

1999, Field demonstration of permeable reactive barriers to control

radionuclide and trace-element

contamination in ground water from

abandoned mine lands, in

Morganwalp, D.W., and Buxton,

H.T., eds., U.S. Geological Survey

Toxic Substances Hydrology Program—Proceedings of the Technical

Meeting, Charleston, South Carolina,

March 8-12, 1999—Volume 1 of 3—

Contamination from Hardrock

Mining: U.S. Geological Survey

Water-Resources Investigations

Report 99-4018A, p. 281-288.

National Research Council, 1994,

Alternatives for ground water

cleanup, National Academy Press,

Washington, D.C., 315 p.

Schmithorst, W.L., and Vardy, J.A., 1997,

RCRA corrective measures using a

permeable reactive iron wall, U.S.

Coast Guard Support Center, Elizabeth City, North Carolina: International Contaminant Technology

Conference Proceedings, February 9-

12, 1997, St. Petersburg, Flor., p.

794-813.

Travis, C.C., and Doty, C.B., 1990, Can

contaminated aquifers at Superfund

sites be remediated?: Environmental

Science and Technology, vol. 24, p.

1464-1466.

Wilson, R.D., and Mackay, D.M., 1997,

Arrays of unpumped wells: An

alternative to permeable walls for in

situ treatment: International Contaminant Technology Conference Proceedings, February 9-12, 1997, St.

Petersburg, Flor., p. 888-894.

Figure 2: Schematic diagram of Deep Aquifer Remediation

Tool (DART).

Non-pumping

well

Ground-water flow

Passive

Sampler

Rigid PVC shell

Reactive barrier material

Flexible wing

Figure 3: Deployment of DART prototype into non-pumping

well at Fry Canyon, Utah, during October 1998.