&EPA
Office of
United States	Ground Water and
Environmental Protection Agency	Drinking Water
CLASS V UIC STUDY FACT SHEET
EXPERIMENTAL WELLS
What is an experimental well?
What types of fluids are
injected into experimental
wells?
Do injectate constituents
exceed drinking water
standards at the point of
injection?
What are the characteristics
of the injection zone of an
experimental well?
Are there any contamination
incidents associated with
experimental wells?
Are experimental wells
vulnerable to spills or illicit
discharges?
How many experimental wells
exist in the United States?
Where are experimental wells
located within the United
States?
How are experimental wells
regulated in states with the
largest number of this type of
well?
Where can I obtain additional
information on experimental
wells?
Experimental wells are Class V underground injection control (UIC) wells used to test new or
unproven technologies. This well category includes: experimental "tracer study" wells and
aquifer thermal energy storage (ATES) systems. Experimental "tracer study" wells are used
to inject chemicals and evaluate hydrogeological parameters. ATES systems are used to store
thermal energy by injecting heated and/or cooled water into an aquifer.
Experimental tracer study wells inject many different types of substances, including organic
dyes, inert gases, short half-life radionuclides, rare earth metals, and inorganic or organic
compounds. ATES system wells inject heated or cooled process water, which may originate
from native ground water, surface water, or potable water.
Only one experimental tracer study well was reported for which injectate did not meet the
primary and secondary drinking water standards and health advisory levels (HALs). The
injectate for this tracer well exceeded drinking water standards for sulfates and chloride, and
contained arsenic and molybdenum at levels greater than HALs. Injectate data are not
available for ATES system wells.
The injection zone characteristics for experimental wells vary widely depending upon the
purpose of the well. Wells used for tracer studies may inject into contaminated aquifers,
sometimes including aquifers that serve as drinking water supplies.
Experimental ATES system wells inject water into the same formation from which it was
withdrawn.
No contamination incidents have been reported for experimental tracer study wells. While no
contamination incidents have been reported for ATES system wells, several reports mentioned
that the concentration of constituents in ground water receiving fluids from some ATES wells
were higher than background levels.
Experimental tracer study wells and ATES system wells are not vulnerable to spills or illicit
discharges because injectate quality is controlled by the conditions of the experiment being
conducted or by the conditions of the process operation.
There are 396 documented experimental tracer study wells in the United States. No operating
ATES system wells are believed to exist in the United States.
The documented experimental tracer study wells are located in six states: SC, CO, NV, ID,
TX, and WA. More than 97 percent of the documented tracer study wells exist in SC (207
wells or 52%) and NV (179 wells or 45%, although some of these wells are reportedly now
plugged and abandoned). Experimental tracer study wells are also believed to exist in MA,
FL, MS, and IL. ATES systems were recently operated in MN and NY.
Permit by rule: CO, TX, ID (for wells <18 ft. deep)
Individual permit SC, NV, WA, and ID (for wells >18 ft. deep)
For general information, contact the Safe Drinking Water Hotline, toll-free 800-426-4791.
The Safe Drinking Water Hotline is open Monday through Friday, excluding federal holidays,
from 9:00 a.m. to 5:30 p.m. Eastern Standard Time. For technical inquiries, contact Amber
Moreen, Underground Injection Control Program, Office of Ground Water and Drinking
Water (mail code 4606), EPA, 401 M Street, SW, Washington, D.C., 20460. Phone: 202-260-
4891. E-mail: moreen.amber(@epa.gov. The complete Class VUIC Study (EPA/816-R-99-
014, September 1999), which includes a volume addressing experimental wells (Volume 15),
can be found at http://www.epa.gov/OGWDW/uic/cl5study.html.

-------