Office of
CDA United States Ground Water and
^1 Environmental Protection Agency Drinking Water

CLASS V UIC STUDY FACT SHEET
AQUIFER REMEDIATION WELLS
What is an aquifer
remediation well (ARW)?
ARWs are used to clean up, treat, or prevent contamination of ground water. These wells may be
associated with RCRA or Superfund cleanup projects.
What types of fluids are
injected into ARWs?
Treated ground water (from pump and treat systems), bioremediation agents, or other contaminant
recovery enhancement materials.
Do injectate constituents
exceed drinking water
standards at the point of
injection?
For many reagents and nutrients injected into ARWs, the concentration in the injectate likely
exceeds drinking water standards or health advisory levels because high concentrations of
such reagents and nutrients are needed for them to serve their intended purposes. The data
available for these wells are insufficient to establish meaningful comparisons between
concentrations of injected reagents or nutrients in ground water monitoring wells, located
downgradient from the ARW where they were injected, and the corresponding drinking
water standards and health advisory levels.
What are the characteristics
of the injection zone of an
ARW?
ARWs typically release fluids into a contaminated aquifer where constituents of concern
exceed drinking water standards. In some cases, re-injection of treated ground water from
an onsite pump-and-treat system may occur into a different formation than that which is
being remediated, with the objective of recharging the aquifer. In these cases, the receiving
formation may be an underground source of drinking water (USDW) and the injectate is
monitored to ensure that constituents present in the injectate do not exceed drinking water
standards.
Are there any contamination
incidents associated with
ARWs?
One contamination incident associated with an ARW has been reported. The incident
occurred at the Hassayampa Landfill Superfund Site in Arizona. A failure in an automatic
cut-off valve in a pump-and-treat system concurrent with a failure in the treatment unit,
resulted in the accidental injection of untreated contaminated ground water into a clean
USDW. The extent of the impact on the USDW or to drinking water wells was not reported.
Are ARWs vulnerable to
spills or illicit discharges?
Notwithstanding the accidental release scenario described above, ARWs are not likely to be
vulnerable to spills or illicit discharges because injectate quality is controlled by the
conditions of the operations being conducted.
How many ARWs exist in the
United States?
There are 10,222 documented ARWs and 10,756 ARWs estimated to exist in the United
States. However, the actual number of ARWs could be between 12,000 and 14,000, due to
the number of wells reported as "under construction" at the time of the survey.
Where are ARWs located
within the United States?
The documented ARWs are located in 39 states and territories. A significant fraction (65
percent) of the total is concentrated in SC (3,409), TX (1,177), OH (1,170), and KS (936).
How are ARWs regulated in
states with the largest
number of this type of well?
Permit by rule: TX
Individual permit. KS, OH, SC
Where can I obtain
additional information on
ARWs?
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: mo re e n. a mb e r Vv c pa. go v. The complete Class VUIC Study
(EPA/816-R-99-014, September 1999), which includes a volume addressing ARWs (Volume
16), can be found at http://www.epa.gov/OGWDW/uic/cl5study.html.

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