| Class I wells are technologically
sophisticated and inject hazardous and non-hazardous wastes below
the lowermost underground source of drinking water
(USDW). Injection occurs
into deep, isolated rock formations that are separated from the lowermost
USDW by layers of impermeable clay and rock.
Class II wells are oil and gas production
brine disposal and other related wells. Operators of these wells
inject fluids associated with oil and natural gas production. Most
of the injected fluid is brine that is produced when oil and gas
are extracted from the earth (about 10 barrels of brine for every
barrel of oil).
Class III wells are wells that inject
super-heated steam, water, or other fluids into formations in order
to extract minerals. The injected fluids are then pumped to
the surface and the minerals in solution are extracted. Generally,
the fluid is treated and re-injected into the same formation. More
than 50 percent of the salt and 80 percent of the uranium extraction
in the U.S. is produced this way.
Class IV wells inject hazardous or
radioactive wastes into or above underground sources of drinking
water. These wells are banned under the UIC program because
they directly threaten public health.
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In general, owners and operators of most new Class
I, II and III injection wells are required to:
- Site the wells in a location that is free of faults and other
adverse geological features;
- Drill to a depth that allows the injection into formations that
do not contain water that can potentially be used as a source
of drinking water. These injection zones are confined from any
formation that may contain water that may potentially be used
as a source of drinking water;
- Build to inject through an internal pipe (tubing) that is located
inside another pipe (casing). This outer pipe has cement on the
outside to fill any voids occurring between the outside pipe and
the hole that was bored for the well (borehole). This allows for
multiple layers of containment of the potentially contaminating
injection fluids;
- Test for integrity at the time of completion and every five
years thereafter (more frequently for hazardous waste wells, §146.68(d));
- Monitor continuously to assure the integrity of the well.
Operators of Class I wells injecting hazardous waste are required
to demonstrate that the waste will never return to the surface or
impact an underground source of drinking water (for 10,000 years).
These wells inject at 4,000 feet below the surface or more. Over
9 billion gallons of hazardous waste is injected into wells each
year in the US.
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| Class V wells are injection
wells that are not included in the other classes. Some Class
V wells are technologically advanced wastewater disposal systems used
by industry, but most are "low-tech" wells, such as septic systems
and cesspools. Generally, they are shallow and depend upon gravity
to drain or "inject" liquid waste into the ground above or into underground
sources of drinking water. Their simple construction provides little
or no protection against possible ground water contamination, so it
is important to control what goes into them. |
The largest number of injection wells are shallow
wells that inject non-hazardous fluids into very shallow aquifers
that are or can be used as sources of drinking water. Some of the
wells in this category are:
- Drainage wells in industrial setting that can receive surface
runoff contaminated with a variety of pollutants;
- Septic tank systems and dry-wells used in automotive shops that
receive fluids from repair and maintenance bays;
- Cesspools that receive sewage from a community;
- Agricultural drainage wells that may receive water contaminated
with pesticides and fertilizers.
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