INJECTION WELLS
An Introduction To Their
Use, Operation And Regulation
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Introduction
Public Awareness: The Key to
Protecting Drinking Water
Most Americans are surprised to learn that:
• 50 percent of this nation's drinking water comes from
ground water. . .water that is found underground in
rock, sand, or gravel.
• 75 percent of our cities derive all or part of their water
from underground sources.
• Rural America is 95 percent dependent upon ground
water.
• Daily use has increased from 34 billion gallons in
1950 to more than 90 billion gallons a day.
Simply put, ground water is essential to our public
water supply systems, economic growth, national
agricultural production and the quality of life we all
share whether or not we personally rely on it as drink-
ing water.
Estimates place the volume of nationally usable
ground water at 100 quadrillion gallons. However, a
problem exists. This problem is the potential for ground
water contamination. Once a ground water resource has
been contaminated, remediation is extremely difficult
and sometimes not feasible.
Ground water is extremely susceptible to contamina-
tion from a variety of everyday sources, including sep-
tic tanks, feed lots, fertilizer, highway de-icing-salts, in-
dustrial processes, landfills, underground storage tanks,
etc. Also of concern are the approximately 300,000 wells
in the United States which inject fluids underground.
Since the passage of legislation in the 1970s that
regulates waste disposal into the water, air and land-
fills, underground injection has grown in importance.
In the petroleum industry alone, at least 20 to 30 million
barrels of salt water are brought to the surface, along
with oil, and then reinjected deep underground each
day.
Even though there are federal, state or local regula-
tions affecting all these contaminant sources, each of
us should learn how our community might be affected
by any of them and if we are, what we can do about it.
Ground Water
Ground water is stored beneath our local communities
in formations of saturated rock, sand, gravel, and soil.
Unlike surface water, ground water does not flow in a
series of lakes and rivers. Instead, the precipitation that
seeps into our soil continues its downward journey and
eventually fills the pores of rock formations similar to
the way water fills a sponge.
Rock formations that contain enough usable amounts
of water to feed springs or wells are called aquifers. Two
factors determine the amount of water that aquifers can
provide: porosity and permeability. Porosity refers to
the ability to store or hold water, and permeability refers
to the ability to move ground water through rock pores
and cracks. Sandstone, a highly porous material, allows
water to seep through easily. Some rock formations, in-
cluding many shales and clays, are extremely non-
permeable and act as confining layers which make it
possible to dispose of liquids underground into porous
intervals while still being very protective of ground
water.
Ground water quality generally deteriorates with in-
creased depth. Waters of lesser salinities and mineral
content (fresh waters) are usually located nearer the
earth's surface. Deeper waters, into which liquid waste
disposal takes place, are waters of limited quality or use
with high dissolved mineral content. These waters with
high salinity are not considered to be potential sources
of drinking water.
Underground Injection Wells
The practice of underground injection has become
essential to many of today's industries including the
petroleum industry, chemical industry, food and pro-
duct manufacturing companies, geothermal energy
development, and many local small specialty plants and
retail establishments.
Within the past few decades, the realization that sub-
surface injection could contaminate ground water has
prompted several states to develop programs and
methods to protect underground sources of useable
water. Additionally, to increase ground water protec-
tion, a federal Underground Injection Control (UIC)
program has been established under the provisions of
the Safe Drinking Water Act (SDWA) of 1974. This
federal program establishes minimum requirements for
effective state UIC programs. Since ground water is a
major source of drinking water in the United States, the
UIC program requirements were designed to prevent
contamination of Underground Sources of Drinking
Water (USDW) resulting from the operation of injec-
tion wells. A USDW is defined as an "aquifer or its por-
tion which supplies any public water system or contains
a sufficient quantity of ground water to supply a public
water system, or contains less than 10,000 milligrams
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per liter total dissolved solids and is not an exempted
aquifer."
Since the passage of the Safe Drinking Water Act,
state and federal regulatory agencies have modified ex-
isting programs or developed new strategies to protect
ground water by establishing even more effective regula-
tions to control the permitting, construction, operation,
monitoring and closure of injection wells.
The United States Environmental Protection Agency
(LJSEPA) has delegated primary regulatory authority to
those state agencies that have demonstrated an ability
to implement UIC programs that meet USEPA re-
quirements promulgated under Section 1422 or 1425 of
the SDWA. These states are referred to as Primacy
Delegated Programs vs
EPA Implementation
Primacy
Programs
40
Number
of Programs
•Does not include Federal programs on Indian lands
Injection Well Classification Chart
Table 1
States. In many states more than one state agency has
primary regulatory authority for one or more classes of
injection wells. In states that have not received primacy,
the responsible regulatory agency is the USEPA. These
states are referred to as Direct Implementation States.
Some states share responsibility with the USEPA.
A well, as defined in Title 40 Part 144 of the Code
of Federal Regulations, "is either a dug hole or a bored,
drilled or driven shaft whose depth is greater than its
largest surface dimension." Injection is defined as the
subsurface emplacement of fluids in a well, where a fluid
is any material that flows or moves whether it is semi-
solid, liquid, sludge or gas.
Distribution of Active Injection Wells
Class II
45.1%
Class I
0.2%
Class 111
5.9%
Class V
48.8%
Class IV
(less than 0.006%)
USEPA
( 1 \sslHC\IION
< 1 AS> 1
< 1 \ss II
( 1 \ss III
CLASS l\
< 1 ASS \
IVIICIION «K1.I. IttM'KIPIHIN AcmiTNU.NlOin
icath the lowermost I Sl>\\
Wells ii industrial non-ha/ardous liquid wastes beneath the lowermost I s|>\\
^cli* i municipal »\ 'aieath the lowernu'M 1 M>\\
\\elK used i Mted with Ihc production or oil and natural eas.
WelU used to inject tluids tor enhanced oil
Wells used tor the Morajic ol hguid h.
Uells used to inject lluids lor ihe extraction ol minerals.
\\clK used to dispose ot ha/ardous or radioaclue \\aMes into 01 jhine .1 L Sl)\\
II 1' \ has banned the use lit these »rlls.|
Well- noi included in the other Jav-c-N used 10 generally inject non-ha/ardoi^ lluid into
M>\\
245
233
152
121,086
918
: 1.027-
2(1
173.159-
Located in 192 Facilities
Inventory from EPA Class V Report 10 Congress
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Injection Well Relationship to USDWs
Class II
EOR Well
Oil
Reservoir
Class 111
Uranium
Solution
Mining
T^".--..^:^-;..^-
W '/5^-rr- : ^^T^
•&? • -JZZmL
Water Table
USDWs
Minerali/ed
- Ore Body
Exempt
Aquifer
Base of the
lower-most
USDW
He// diameter enlarged
KI s/un\- detail.
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Class I Injection Wells
Injection Wells Related to Hazardous, Industrial Nonhazardous,
and Municipal Wastewater Disposal Below USDWs
Some waste is an unavoidable by-product of a myriad
of manufacturing processes that create thousands of the
products we use in the course of everyday living. While
industry continues to reduce waste by recycling and im-
proving manufacturing processes, there are still wastes
that require disposal. There are many environmentally
safe ways to do this job, including incineration,
biological or chemical treatment, landfilling in properly
located and constructed sites, and disposal through in-
jection wells. Injection wells penetrate many thousands
of feet below the earth's surface into rock formations
where the waste cannot contaminate underground
sources of drinking water.
The suitability of this disposal method depends on
the availability of appropriate underground rock for-
mations that have the natural ability to accept and con-
fine the wastes. It is this long-term confinement that
makes deep-well disposal an environmentally sound
waste disposal method. This same natural ability of sub-
surface rock formations to confine liquids is the \cry
characteristic that has permitted the entrapment and
containment of naturally occurring oil and gas deposits
for millions of years. These deposits have been held in
place, moving little, if at all, for eons.
Class I injection wells can be subdivided by the types
of waste injected: hazardous, nonhazardous, and
municipal.
Hazardous Class I Injection Wells
Hazardous wastes are those industrial wastes that
meet the definition in40CFR Part 261.3 under Section
3001, of Subtitle C of the Solid Waste Disposal Act,
as amended by the 1976 Resource Conservation and
Recovery Act. Class I hazardous waste wells are located
in 15 states. A high concentration of these wells is
located along the Texas-Louisiana Gulf Coast because
this area offers a combination of suitable injection zones
and large numbers of waste generators. The Great Lakes
region also has a high concentration of Class I hazar-
dous wells for the same basic reasons.
Nonhazardous Industrial Class I Injec-
tion Wells
Nonhazardous wastes are any other industrial wastes
that do not meet the legal definition of hazardous
wastes. Texas and Kansas have the greatest number of
wells in this category because these states have specific
industries that generate large quantities of nonhazardous,
liquid wastes. Nonhazardous industrial Class 1 wells are
located in 19 states.
Municipal Class I Injection Wells
Municipal wastes, which are not specifically defined
in the federal regulations, are wastes associated with
sewage effluent that has received a minimum of second-
ary treatment. Disposal of municipal (treated sewage
effluent) waste through injection wells is currently prac-
ticed only in Florida. In Florida, this waste-disposal
practice is chosen more and more often due to a shortage
of available land, strict surface-water discharge limita-
tions, extremely permeable injection zones and cost
effectiveness.
States With Class I Injection Wells
Primacy States with Class I Injection Wells
Direct Implementation States with Class I Wells
States with no Class I Wells
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Site Selection and Distribution
Site selection for a Class I disposal well is dependent
upon geologic and hydrogeologic conditions, and only
certain areas are suitable. Most favorable locations are
generally in the mid-continent, gulf-coast, and great
lakes regions of the country.
The process of selecting a site for a Class I disposal
well involves evaluating many conditions. Paramount
in the consideration, is the determination that the
underground formations possess the natural ability to
contain and isolate the injected waste. An important
part of this determination is the evaluation of the history
of earthquake activity. A well would not be located in
an area of geologic instability. Also the existence of
abandoned wells, mineral resources and underground
sources of drinking water are identified and evaluated.
A detailed study is conducted to determine the
suitability of the underground formation for disposal.
The receiving formation must be far below any usable
ground waters and be separated from them by confin-
ing layers of rock, which prevent fluid migration into
the ground water. The injection zone in the receiving
formation must be of sufficient size and have sufficient
pore space to accept and maintain the injected wastes.
The region around the well must be geologically stable,
and the injection zone should not contain recoverable
mineral resources such as ores, oil, coal, or gas.
Abandoned wells of any type which penetrate the pro-
posed injection zone are investigated in an area of review
within a specified radius of the injection well to assure
that they were properly plugged to prevent escape of
injected materials.
Construction and Monitoring
Requirements
The primary concern in the construction of a Class
I injection well is the protection of ground water by
assuring containment of the injected wastes through a
multilayer protection system. A Class I injection well
is constructed in stages, the first stage being the drill-
ing of a hole to a depth below the lowermost USDW.
A steel casing or surface pipe is installed the full length
of the borehole and cement is placed outside of the
casing from the bottom to the top of the hole. This pro-
vides a barrier of steel and cement to protect drinking
water.
The second phase is to continue drilling below the sur-
face casing down to the intended injection zone. A se-
cond protective casing string is installed from the sur-
face down through the injection zone and again
cemented in place the entire length of the casing to seal
the space outside of the casing. A smaller pipe, called
injection tubing, is installed inside the protective cas-
ing string. The tubing is secured with a wellhead at the
surface and a packer at the bottom. The space between
the tubing and the protective casing is known as the an-
nulus and it is filled with a noncorrosive fluid. The fluid
in the annulus is monitored as a continuous check on
the mechanical integrity of the downhole system. Should
a leak develop, a change in the annulus pressure would
occur and the well could be shut down prior to con-
tamination of a USDW.
Class I injection wells are continuously monitored and
controlled with sophisticated equipment. Pressure re-
cording inside and outside of the injection tubing and
routine mechanical integrity testing of the components
of the well insure containment of the injected fluids.
Closure
When a Class I well is retired from service, the
borehole and casing must be securely plugged to pre-
vent any movement of the waste. A properly sealed well,
using cements and other materials, permanently con-
fines the waste within the injection zone as well as
prevents any movement of high salinity water into a
USDW. Thus, a Class I disposal well is secured — not
abandoned.
Properly located, designed, constructed, operated and
monitored — Class I wells have proven to be an en-
vironmentally and technically sound method for the
disposal of many liquid wastes which could not be safely
disposed of otherwise.
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Class II Injection Wells
Injection Wells Related to Oil and Gas Activity
Class 11 injection wells have been used in oil field
related activities since the 1930s. Today there are ap-
proximately 170,000 Class II injection wells located in
31 states. All class 11 injection wells are regulated by
either a state agency which has been granted regulatory
authority over the program or by the USEPA directly.
Class II wells are subject to a regulatory process which
generally requires a technical review to assure adequate
protection of drinking water and an administrative
review defining operational guidelines.
Class II injection wells are categorized into three
subclasses. They are salt water disposal wells, enhanced
oil recovery (EOR) wells, and hydrocarbon storage
wells.
Salt Water Disposal Well
As oil and gas are brought to the surface they are
quite often mixed with salt water. On a national average,
approximately 10 barrels of salt water are produced with
States With Class II Injection Wells
Primacy States with Class II Injection Wells
Direct Implementation States with Class II Wells
States with no Class II Wells
every barrel of crude oil. Approved geologic formations
receive the produced waters that are reinjected through
disposal wells and EOR wells. One of the common
forms of liquid waste disposal by the oil and gas industry
is through injection into geologic formations that do not
contain hydrocarbons. These disposal wells have been
used extensively to return salt water associated svith oil
and gas production to the subsurface. Approximately
30 percent of salt water produced with oil and gas on-
shore in the United States is disposed of via salt water
disposal wells.
Enhanced Oil Recovery Wells
Enhanced Oil Recovery (EOR) injection wells are us-
ed to increase and prolong oil production from depleting
oil producing fields. SECONDARY RECOVERY is an
EOR process, commonly referred to as waterflooding.
In this process salt water co-produced with oil and gas
is reinjected into the oil producing formation to drive
oil into pumping wells, resulting in the recovery of ad-
ditional oil. TERTIARY RECOVERY is an EOR pro-
cess that is used after secondary recovery methods
become inefficient or uneconomical. Tertiary recovery
methods include the injection of gases, enhanced waters
and steam in order to maintain and extend oil produc-
tion. Approximately 60 percent of salt water produced
with oil and gas onshore in the United States is injected
into EOR wells.
Hydrocarbon Storage Wells
These wells are used for the underground storage of
crude oil, liquified petroleum gas (LPG), and other
liquid hydrocarbon products in naturally occurring rock
formations. The same wells are often designed for both
injection and removal of the stored hydrocarbons.
Construction Requirements
Construction of Class 11 injection wells is subject to
either State or Federal regulation. Construction design
must adequately confine injected fluids to the authorized
zone as well as prevent the migration of fluids into
USDWs. Through the permitting process, site specific
regulations can be imposed to meet any unusual
circumstances.
Injection wells are drilled and cased with steel pipe
which is cemented in place to prevent the migration of
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fluids into USDWs. Surface casing in conventionally
constructed wells is set and cemented back to surface,
preventing fluid movement. Cement is also placed
behind the production casing to confine injected fluids
to the authorized zone of injection. A typical salt water
disposal injection well also has an interior string of pipe
called tubing through which injection takes place. A
packer is commonly used to isolate the injection zone
from the annular space between the tubing and produc-
tion casing above the packer.
Operations
Typically, the oil, gas and salt water are separated
at the oil and gas production facilities. The salt water
is then either piped or trucked to the injection site for
disposal or EOR operations. There, the salt water is
transferred to holding tanks and pumped down the in-
jection well. For EOR, the salt water may be treated
or augmented by other fluids prior to injection. Fresh
\\ater or fresh water converted to steam is injected to
maximize oil recovery in some EOR operations.
Injection well operations must be directed in such a
manner as to prevent the contamination of USDWs and
to ensure fluid emplacement and confinement within the
authorized injection zone. Primacy states have adopted
regulations, which have been approved by the USEPA
as protective of USDWs, concerning Class II injection
well operations. These regulations address injection
pressures, mechanical integrity testing, pressure
monitoring and reporting. Direct Implementation states
must meet operational guidelines as set out by the
USEPA.
Closure of Class II injection wells must be conducted
in a manner as to protect USDWs. Although regulations
vary slightly from state to state, commonly a cement
plug is required to be placed in the wellbore across the
injection zone, with additional plugs set across the base
of the lowermost USDW and a final near surface plug.
Testing and Monitoring
After placing Class II injection wells in service,
ground water protection is accomplished by testing and
monitoring the wells. Injection pressures and volumes
are monitored as a valuable indicator of well perform-
ance. Effective monitoring is important since any
downhole problems can normally be recognized and cor-
rective action can be taken quickly to prevent endanger-
ment of USDWs.
Mechanical integrity tests (MITs) are required prior
to initial injection and at a minimum of once every five
years thereafter. Variations of acceptable tests and fre-
quencies greater than once per five years are determined
on a test by test basis and are rigorously reviewed by
the USEPA. These tests evaluate the operational integri-
ty of the well so that USDWs will not be endangered.
A TYPICAL
CLASS II INJECTION
PRESSURE
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Class III Injection Wells
Injection Wells Related to Mineral Extraction
Class III injection wells are located in 16 states. Every
Class 111 injection well, whether located in a primacy
or a direct implementation state, is subject to a permit-
ting requirement through the authorized regulatory
agency. The operating permit will require the well to
meet any regulations the state has adopted to assure the
protection of USDWs. The permits may include specific
well construction, monitoring, mechanical integrity
testing, maximum allowable injection pressure, and
reporting requirements. Proper closure or plugging of
all Class 111 injection wells must be conducted in a man-
ner to protect USDWs from potential contamination.
The techniques these wells use for mineral extraction
may be divided into two basic categories: solution min-
ing of salts and sulfur; and in situ (in place) leaching
for various minerals such as uranium, gold or copper.
Solution Mining
Solution mining techniques are used primarily for the
extraction of salts and sulfur. For common salt, the
States With Class III Injection Wells
Primacy States with Class 111 Injection Wells
] Direct Implementation States with Class III Wells
] States with no Class III Wells
solution mining process involves injecting water, which
dissolves the underground salt formation. The resulting
brine is pumped to the surface either through the tubing-
casing annulus of the injection well or through produc-
tion wells.
The technique for solution mining of sulfur is known
as the Frasch process. This process consists of injecting
superheated water down the tubing-casing annulus of
the injection well and into the sulfur-bearing formations
to melt the sulfur. The molten sulfur is extracted from
the subsurface through tubing within the injection well
with the aid of compressed air, which mixes with the
liquid sulfur and airlifts it to the surface.
In Situ Leaching
In situ leaching is commonly used to extract uranium,
gold, and copper. Uranium is the predominate mineral
extracted by this technique. The uranium in situ leaching
process involves injection of a neutral ground \\ater
solution containing non-toxic chemicals (e.g. oxygen
and carbon dioxide) down injection wells. This fortified
water is circulated through an underground ore body
or mineral zone to dissolve or leach the uranium par-
ticles that coat the sand grains of the ore body. The
resulting uranium-rich solution is then pumped to the
surface where the uranium is extracted from the solu-
tion, and the leaching solution is recycled back into the
ore body through the injection wells. This same general
technology is employed for in situ leaching of other
minerals, with the only difference being the type of fluid
used for injection.
The typical life of an in situ leaching well is less than
five years. At the end of the in situ leaching operations,
U1C regulations require restoration of the mined aquifer
to its original quality.
Construction and Testing
Requirements
Construction standards for Class III injection wells
are designed to confine injected fluids to the authoriz-
ed injection zone and prevent migration of these fluids
into USDWs. Class III injection wells are drilled into
mineralized rock formations and are cased with pipe
which is cemented in place to prevent fluid migration
into USDWs. Construction materials and techniques
vary and depend upon the mineral extracted and the
nature of the injected fluids.
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Typical Salt Solution Well Completion
Typical In Situ Leaching Well
Completion
XXX XXXXXXXXX
xxxxxxx xxxx
xxxxxxxxxxx*
xxxxxxxxxxx.
xxxxxxxx
xxxx
X X X X X
xxxxxxxxxx
Mechanical integrity tests are required prior to initial
operation of Class III injection wells. Several different
tests have been approved, however, in each case the tests
are required to determine that there are no leaks in the
tubing, casing or packer (if used) and there is no signifi-
.-^H Cement [- — •
'. • - ; | Casing
•\J Centralizer
~-=\ Cement basket h="-"=-~
'''' •'•.*.•*.
Plug (drilled out t >;:.';'-•
Slotted screen or pipe
,»•: | Mineralized zone [|.•'.'
•J cap [>'>',,>.• 7-.
cant fluid movement into a USDW. In situ leaching
wells also require that the ore body be surrounded by
monitoring wells to detect horizontal migration of the
mining solutions. Additionally, overlying and underly-
ing aquifers must be monitored to detect any vertical
migration of these same fluids.
Class IV Injection Wells
Injection Wells Related to Hazardous and Radioactive
Wastewater Disposal Into or Above USDWs
These wells have been identified by the EPA as a
threat to human health and environment. The EPA has
banned the use of these wells. As these wells are iden-
tified by State and Federal UIC regulatory agencies they
are subject to corrective action which may include
remediation as well as permanent closure.
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Class V Injection Wells
Injection Wells not Included in the Other Classes
Class V - Simple to Complex
If a well does not fit into the first four classes of in-
jection wells and still meets the definition of an injec-
tion well, it is considered a Class V well. Class V injec-
tion practices recognized by the USEPA include 30 in-
dividual types of wells, which range in complexity from
simple cesspools that are barely deeper than they are
wide, to sophisticated geothermal reinjection wells that
may be thousands of feet deep.
It should be noted that not all Class V wells are used
for disposal. Examples of Class V practices which are
not disposal related include: Aquifer Recharge, Fossil
Fuel Recovery and Mineral Recovery wells. Table 2
describes all of the subclasses of Class V wells, the
potential contaminants, and the ground water con-
States With Class V Injection Wells
I | Primacy States with Class V Injection Wells
] Direct Implementation States with Class V Wells
States with no Class V Wells
lamination potential.
As seen in Table 2, the Class V injection well category
is very large and diverse. Class V injection practices can
be divided into two general categories, "high-tech" and
"low-tech." "Low-tech" wells generally have simple
casing designs and surface equipment and inject into
shallow formations by gravity flow or low volume
pumps. In contrast, "high-tech" wells typically have
multiple casing strings, sophisticated well head equip-
ment to control and measure pressure and inject fluids
into deep saline formations that are separated from
aquifers by impermeable confining layers or rock.
Class V Injection Systems and Your
Drinking Water
Class V wells injecting below the lowermost USDW
have the least potential for contaminating ground water.
Class V injection directly into USDWs is potentially
more harmful to the water quality than discharges above
the water table. This is because some contaminants can
be removed from the waste by attenuation, adsorption
and degradation as they move through shallow soils and
some rock formations.
Based on inventories conducted by the states, it is
estimated that there are approximately 170,000 Class
V wells in the United States and its Territories and
Possessions. This number is only an estimate and the
actual number is considerably higher. There are seven
major categories of Class V injection wells, which com-
prise 30 individual well types. About 83 percent of all
Class V wells belong to two categories: drainage wells
(57 percent) and sewage related wells (26 percent).
The USEPA is currently developing a strategy for
dealing with Class V injection wells. State and local
government, as well as public involvement is essential.
Many states have already adopted regulations and or-
dinances for oversight of certain Class V wells. The
USEPA is looking closely at Class V wells which pose
the greatest environmental risks as candidates for federal
regulation and enforcement. Two groups of particular
interest are the industrial disposal wells (5W20) and
automobile service station disposal wells (5X28) as
discussed in Table 2.
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Class V Injection Well Subclasses
Table 2
Name of Well Type and Description
DRAINAGE WELLS (a.k.a. DRY WELLS)
Agricultural Drainage Wells — receive irrigation tailwaters, other field
drainage, animal yard, feedlot, or dairy runoff, etc.
Storm Water Drainage Wells — receive storm water runoff from paved
areas, including parking lots, streets, residential subdivisions, building
roofs, highways, etc.
Improved Sinkholes — receive storm water runoff from developments
located in karst topographic areas.
Industrial Drainage Wells — wells located in industrial areas which
primarily receive storm water runoff but are susceptible to spills, leaks,
or other chemical discharge.
Special Drainage Wells — used for disposing water from sources other
than direct precipitation. Four types were reported: landslide control
drainage wells (Montana), potable water tank overflow drainage wells
(Idaho), swimming pool drainage wells (Florida), and lake level control
drainage wells (Florida)
GEOTHERMAL REINJECTION WELLS
Electric Power Reinjection Wells — reinject geothermal fluids used to
generate electric power — deep wells.
Direct Heat Reinjection Wells — reinject geothermal fluids used to
provide heat for large buildings or developments — deep wells.
Heat Pump/Air Conditioning Return Flow Wells — reinject groundwater
used to heat or cool a building in a heat pump system — shallow wells.
Groundwater Aquaculture Return Flow Wells — reinject groundwater
or geothermal fluids used to support aquaculture. Non-geothermal
aquaculture disposal wells are also included in this category (e.g. Marine
aquariums in Hawaii use relatively cool sea water).
DOMESTIC WASTEWATER DISPOSAL WELLS
Untreated Sewage Waste Disposal Wells — receive raw sewage wastes
from pumping trucks or other vehicles which collect such wastes from
single or multiple sources. (No treatment)
Cesspools — including multiple dwelling, community, or regional
cesspools, or other devices that receive wastes and which must have
an open bottom and sometimes have perforated sides. Must serve
greater than 20 persons per day if receiving solely sanitary wastes.
(Settling of solids)
Septic Systems (Undifferentiated Disposal Method) — used to inject the
waste or effluent from a multiple dwelling, business establishment, com-
munity, or regional business establishment septic tank. Must serve
greater than 20 persons per day if receiving solely sanitary wastes.
(Primary Treatment)
Septic Systems (Well Disposal Method) — examples of wells include
actual wells, seepage pits, cavitettes, etc. The largest surface dimen-
sion is less than or equal to the depth dimension. Must serve greater
than 20 pesons per day if receiving solely sanitary wastes. (Less treat-
ment per square area than 5W32)
Septic System (Drainfield Disposal Method) — examples of drainfields
include drain or tile lines, and trenches. Must serve more than 20 per-
sons per day if receiving solely sanitary wastes. (More treatment per
square area than 5W31)
Domestic Wastewater Treatment Plant Effluent Disposal Wells — dispose
of treated sewage or domestic effluent from small package plants up
to large municipal treatment plants. (Secondary or further treatment)
MINERAL AND FOSSIL FUEL RECOVERY RELATED WELLS
Mining, Sand, or Other Backfill Wells — used to inject a mixture of
water and sand, mill tailings, and other solids into mined out portions
of subsurface mines whether what is injected is a radioactive waste or
not. Also includes special wells used to control mine fires and acid mine
drainage wells.
Solution Mining Wells — used for in-situ solution mining in conven-
tional mines, such as slopes leaching.
In-situ Fossil Fuel Recovery Wells — used for in-situ recovery of coal,
lignite, oil shale, and tar sands.
Spent-Brine Return Flow Wells — used to reinject spent brine into the
same formation from which it was withdrawn after extraction of
halogens or their salts.
Ground Water
Contamination
Potential
High
Moderate
High-Moderate
High-Moderate
Moderate-Low
Moderate
Moderate
Low
Moderate
High
High
High-Low
High-Low
High-Low
High-Low
Moderate
Moderate-Low
Moderate
Low
Potential Contaminants
Pesticides, nutrients, pathogens, metals transported by
sediments, salts.
Heavy metals (Cu, Pb, Zn) organics, high levels of coliform
bacteria. Contaminants from streets, roofs, landscaped areas,
Herbicides, Pesticides.
Variable: pesticides, nutrients, coliform bacteria.
Usually organic solvents, acids, pesticides, and various other
industrial waste constituents. Similar to storm drainage wells
but usually higher concentrations.
Chlorinated and treated water, pH imbalance, algaecides,
fungicides, muriatic acid.
pH imbalance, minerals and metals in solution. (As, Bo, Se),
sulfates.
Hot geothermal brines with TDS between 2,000 to 325,000
mg/1. Co,, CaSCX, Sr and Ba, As.
Potable water with temperatures ranging from 90° to 1 10°
F., may have scale or corrosion inhibitors.
Used geothermal waters which may be highly mineralized &
include traces of arsenic, boron, fluoride, dissolved &
suspended solids, animal detritus, perished animals and
bacteria.
Soluble organic & inorganic compounds including household
chemicals. Raw sewage with 99.9% water and .03% sus-
pended solid. May contain pathogenic bacteria & viruses,
nitrates, ammonia.
Soluble organic & inorganic compounds including household
chemicals. Raw sewage with 99.9% water and .03% sus-
pended solid. May contain pathogenic bacteria & viruses,
nitrates, ammonia.
Varies with type of system: fluids typically 99.9% water (by
weight) and .03% suspended solids: major constituents in-
clude nitrates, chlorides, sulfates, sodium, calcium, and fecal
coliform.
Varies with type of system: fluids typically 99.9% water (by
weight) and .03% suspended solids: major constituents in-
clude nitrates, chlorides, sulfates, sodium, calcium, and fecal
coliform.
Varies with type of system: fluids typically 99.9% water (by
weight) and .03% suspended solids: major constituents in-
clude nitrates, chlorides, sulfates, sodium, calcium, and fecal
coliform.
Lower levels of organics and bacteria than other septic
systems and cesspools.
Acidic waters
2.4% sulfuric acid, pH less than 2 for copper & ferric cyanide
solution for gold or silver.
Steam, air, solvents, igniting agents.
Variable
EPA
Well
Code
5F1
5D2
5D3
5D4
5G30
5A5
5A6
5A7
5A8
5W9
5W10
5W11
5W31
5W32
5W12
5X13
5X14
5X15
5X16
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Table 2 (continued)
Name of Well Type and Description
INDUSTRIAL/COMMERCIAL/UTILITY DISPOSAL WELLS
Cooling Water Return Flow Wells — used to inject water which was
used in a cooling process, both open and closed loop processes.
Industrial Process Water and Water Disposal Wells — used to dispose
of a wide variety of wastes and wastewaters from industrial, commer-
cial, or utility processes. Industries include refineries, chemical plants,
smelters, pharmaceutical plants, laundromats and dry cleaners, tan-
neries, carwashes, laboratories, etc. Industry and waste stream must
'te specified (e.g. Petroleum Storage Facility— storage tank condensa-
tion water; Electric Power Generation Plant— mixed waste stream of
aboratory drainage, fireside water, and boiler blowdown; Car Wash-
Mixed waste stream of detergent, oil and grease, and paved area
washdown; Electroplating Industry— spent solvent wastes; etc.).
Automobile Service Station Disposal Well — repair bay drains connected
to a disposal well. Suspected of disposal of dangerous or toxic wastes.
RECHARGE WELLS
Aquifer Recharge Wells — used to recharge depleted aquifers and may
inject fluids from a variety of sources such as lakes, streams, domestic
wastewater treatment plants, other aquifers, etc.
Saline Water Intrusion Barrier Wells — used to inject water into fresh
water aquifers to prevent intrusion of salt water into fresh water aquifers.
Subsidence Control Wells — used to inject fluids into a non-oil or gas
producing zone to reduce or eliminate subsidence associated with over-
draft of fresh water and not used for the purpose of oil or natural gas
production.
MISCELLANEOUS WELLS
Radioactive Waste Disposal Wells — all radioactive waste disposal wells
other than Class IV wells.
Experimental Technology Wells — wells used in experimental or un-
proven technologies such as pilot scale in-situ solution mining wells in
previously unmined areas.
Aquifer Remediation Related Wells — wells used to prevent, control,
or remediate aquifer pollution, including but not limited to Sueprfund
sites.
Abandoned Drinking Water Wells — used for disposal of waste.
Other Wells — any other unspecified Class V wells: Well type/purpose
and injected fluids must be specified.
Ground Water
Contamination
Potential
Low-Moderate
High
High
High-Low
Low
Low
Unknown
Low-Moderate
Unknown
Moderate
Unknown
Potential Contaminants
Anti-sealing additives, thermal pollution, potential for in-
dustrial spills reaching ground water.
Potentially any fluid disposed by various industries,
suspended solids, alkalinity, sulfate volatile organic
compounds.
Heavy metals, solvents, cleaners, used oil and fluids,
detergents, organic compounds.
Variable: water is generally of good quality
Varies: advanced treated sewage, surface urban and
agricultural runoff, and imported surface waters.
No specific type of injected fluid noted, similar to aquifer
recharge wells.
Low-level radioactive wastes.
Varies depending on project.
Nutrients used in Biodegradation of organics, oil/grease,
phenols, toluene.
Potentially any kind of fluid, particularly brackish or saline
water, hazardous chemcials and sewage.
Variable
Well
Code
5A19
5W20
5X28
5R21
5B22
5S23
5N24
5X25
5X26
5X29
5X27
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Protecting
Drinking Water
The UIC program addresses only a part of the overall
threat to underground sources of drinking water. State,
federal and local UIC programs integrated with careful
planning, good management and other ground water
protection initiatives can significantly reduce the threat
of contamination to our drinking water supplies from
all classes of injection well activities.
For additional information contact the USEPA,
Office of Drinking Water at (202) 382-5530 or the
Underground Injection Practices Council at (405)
525-6146.
This brochure has been published by:
The Underground Injection Practices Council
in cooperation with
The United States Environmental Protection Agency
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