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

CLASS V UIC STUDY FACT SHEET
AGRICULTURAL DRAINAGE WELLS
What is an agricultural
drainage well (ADW)?
ADWs are Class V underground injection control (UIC) wells that receive agricultural drainage.
This includes improved sinkholes, abandoned drinking water wells, and underground drain tiles
and cisterns.
What types of fluids are
injected into ADWs?
Excess surface and subsurface water from agricultural fields, including irrigation tailwaters and
natural drainage resulting from precipitation, snowmelt, floodwaters, etc. ADWs may also
receive animal yard runoff, feedlot runoff, dairy runoff, or runoff from any other agricultural
operation.
Do injectate constituents
exceed drinking water
standards at the point of
injection?
Available sampling data show that the primary constituent in ADW injectate that is likely to
exceed health-based standards is nitrate. The data also indicate that boron, sulfate, colifonns, and
certain pesticides (cyanazine, atrazine, alachlor, aldicarb, carbofuran, 1,2-dichloropropane, and
dibromochloropropane) in agricultural drainage have exceeded primary drinking water standards
or health advisory levels. Total dissolved solids (TDS) and chloride in some ADWs also have
been measured above secondary drinking water standards.
What are the
characteristics of the
injection zone of an ADW?
Suitable subsurface geologic formations for ADWs often include areas with shallow, fractured
bedrock formations, or limestone bedrock, particularly where affected by karst that provides
solution channels and sinkholes that allow rapid transmission of water.
Are there any
contamination incidents
associated with ADWs?
A number of studies and incidents have shown that ADWs have in fact contributed to or caused
ground water contamination. In particular, ten studies reviewed for The Class V UIC Study
document nitrate contamination of ground water in agricultural areas; six of these studies clearly
link the contamination to ADW use. In addition, there are two known contamination incidents in
IA involving direct discharges from septic tanks to ADWs. Other contamination incidents
include ground water and drinking water contamination linked to 15 drainage wells in Minidoka
County, ID and a community supply well in Dane, WI.
Are ADWs vulnerable to
spills or illicit discharges?
ADWs may be vulnerable to spills from manure lagoons, direct discharges from septic tanks, and
accidental releases of materials used in fanning operations (e.g., motor oils, pesticides).
How many ADWs exist in
the United States?
There are at least 1,069 documented ADWs and more than 2,842 ADWs estimated to exist in the
United States.
Where are ADWs located
within the United States?
Although believed to exist in at least 21 states, more than 95 percent of the documented wells are
in just five states: ID (303), IA (290), OH (>200), TX (135), and MN (92).
How are ADWs regulated
in states with the largest
number of this type of
well?
Individual permit: ID (for wells >18 deep) and TX
Permit by rule: OH, ID (for wells <18 feet deep)
Ban: MN (for "wells" that reach ground water)
/.I: all wells that existed before 2/18/98 must close or get a permit by 12/31/01; new wells
prohibited but may be permitted under strict conditions (unlikely to be permitted)
Where can I obtain
additional information on
ADWs?
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:
morccn.a mbe r Vv cpa.gov. The complete Class V UIC Study (EPA/816-R-99-014, September
1999), which includes a volume addressing ADWs (Volume 2), can be found at
http://www.epa.gov/OGWDW/uic/cl5study.html.

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