May, 1980
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This document is intended to summarize the basis and purpose underlying the
underground injection control regulations promulgated in 40 CFR Part 146. It sets forth
generally the reasoning behind the Agency's regulatory choices and references data upon which
EPA relied.
This statement first discusses the categorization of wells. It then surveys the major
pathways which contaminants can take to enter underground sources of drinking water and the
requirements which these regulations impose to assure that movement of fluids resulting from
well injection does not contaminate underground sources of drinking water. Programmatic
requirements of Part 146, such as monitoring and reporting, are covered in the concluding
In general, the requirements of the regulation differ from those of the initial proposal of
this regulation (41 FR 36730. August 31, 1976) and the reproposal of this regulation (44 FR
36730) in that they furnish a greater degree of flexibility to State Directors in regulating well
injection. EPA has modified its earlier proposal in this way as it became more fully aware of
various well injection practices, the characteristics of substrata into which fluids are injected, and
the range of methods by which well injection is accomplished.
The regulations separate wells into distinct categories. This categorization is necessary to
assure that wells with common design and operating techniques will be required to meet
appropriate performance criteria.
In categorizing wells, EPA first looked to available literature regarding the injection
practices. It considered information on existing and abandoned injection well practices, well
construction technology, and on the variety of fluids injected into wells. It discussed with
regulatory agency personnel from many States their experience with then-existing well injection
regulatory practices and reviewed existing regulations in a number of States.1 After such review
and discussions, it commissioned a reputable consulting organization to provide assessments and
a report on types of wells and their typical operation.2 EPA then studied this information to
arrive at a consistent and comprehensive well classification scheme. As a result, EPA decided to
classify wells into the following five groups:
1	Interviews with State officials from Texas, Florida, Kansas, California and Michigan.
2	Preliminary Injection Well Practices, Geraghty and Miller, Inc., Tampa, Florida; 1977.
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Class I:	Wells used by generators of hazardous wastes or owners or operators of
hazardous waste management facilities to inject hazardous waste, other
than Class IV wells, other industrial and municipal disposal wells which
inject fluids beneath the lowermost formation containing, within one
quarter mile of the well bore, an underground source of drinking water.
Class II: Wells which inject fluids (1) which are brought to the surface in
connection with conventional oil or natural gas production (2) which are
used for enhanced recovery of oil or natural gas and (3) which are used for
storage of hydrocarbons which are liquid at standard temperature and
Class III: Wells which inject for e.xtraction of minerals or energy, including:
mining of sulfur by the Frasch process; solution mining of minerals; in-
situ combustion of fossil fuel, and recovery of geo thermal energy.
Class IV: Wells used by generators of hazardous wastes or of radioactive wastes, by
owners or operators of hazardous wasce management facilities or by
owners or operators of radioactive wastes disposal sites to dispose of
hazardous wastes into or above a formation which within one quarter mile
of the well contains an underground source of drinking water.
Class V: Injection wells not included in Classes I, II, III, or IV.
In formulating these classifications, EPA gave substantial weight to a number of
considerations. First the Agency concluded that wells which inject into strata nearest thd land
surface should, as a general matter, be classified separately from those which inject into strata at
greater depth. The method of injection which wells use is frequently dependent upon the
injection horizon into which they deposit fluids. Wells which inject into strata near the land
surface often inject by use of simple gravity, often crudely constructed, they can simply be holes
dug or bored into the ground, the sides of which may be stabilized by brick, stone, timber, or
other materials in the well. They can function as convenient dumping sites for wastes, or, in
other instances, can serve beneficial purposes, such as recharging groundwater supplies or
creating a subsurface barrier to saltwater intrusion.3
3 See Generally The Report to Congress. Waste Disposal Practices and Their Effects on
Ground Water. U.S. Environmental Protection Agency (January, 1977), Sections V, VIII, XIII
("Report to Congress"): A Manual of Laws. Regulations, and Institutions-for Control of
Groundwater Pollution. U.S. Environmental Protection Agency, (June, 1976), Chapter I
("Manual"). Underground Injection Control Regulations. Subpart F. Injection Well Practices.
Draft Final Report. Geraghty and Miller, Inc. and Temple, Barker and Sloane, Inc. March, 1978
("Subpart F"). Preliminary Evaluation of- Well Injection Practices. Geraghty and Miller,
("Preliminary Evaluation").
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Wells which inject into lower strata are usually constructed and operated differently from
wells which inject into strata near the land surface. Such wells are drilled rather than dug or
bored, and emplace fluids into the subsurface by use of more sophisticated technology, materials,
and equipment. Wells of this sort require the use of casing and cementing.4 Escape of injected
fluids into sources of drinking water is prevented by such casing, and by tubing and packer or
other methods. Injection is accomplished by either the force.of gravity or the application of
additional mechanical pressure to overcome the natural friction and hydrostatic,resistance of the
receiving formation.5
In addition, aquifers nearest the land surface most often supply water for domestic use.6
Consequently, wells which inject into or above these aquifers increase the risk of human
exposure to the injected contaminants.
These considerations influenced the categorization of wells in Classes I and II separately
from those in Classes IV and V. Classes I and II encompass wells which normally inject into
strata below underground sources of drinking water. Class I wells are further limited to those
which inject beneath formations which contain an USDW within 1/4 mile of the well site; other
wells are included in Class V. The agency chose this approach since individual formations may
be identifiable for hundreds of miles and a formation which is suitable in one area as a source of
drinking water may not be in other sections. This limitation prevents a well from being subjected
to Class I requirements simply because it injects under an aquifer which, miles away, contains
drinking water. Class IV wells (which by definition inject into or above strata containing
underground sources of drinking water) will generally inject into or above the aquifers nearest
the land surface. Class V for the most part comprises wells which inject non-hazardous materials
into those same aquifers.7
Also influencing this proposed well class-ification was the nature of injected fluids.
Wells which handle hazardous materials war-rant close regulatory scrutiny. This consideration
influenced EPA to create a separate category (Class I) for wells which dispose of industrial and
municipal wastes. Such wastes commonly contain chemicals or other substances which can be
fairly characterized as noxious and, as appropriate, require separate performance criteria.
Nuclear waste practices are currently being reviewed by the Administration and therefore EPA is
4	§§ 146.12(b); 146.22(b); 146.32(a)
5	See Generally Report to Congress. Section XL, XLLL; Manual. Chapter LC: Preliminary
Evaluation; Ground Water Pollution From Subsurface Excavations. U.S. Environmental Protection
Agency, 1973, Part 2, Section LL, Ground Water Pollution."
6	Report to Congress. Sections in, IV; Manual. Chapter I, pp. 1-10 — 1-50.
7	Report to Congress. Section VIII, IX, XIII: Manual. Chapter I; Subpart F; Preliminary
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not including wells which inject nuclear waste a USDW into a Class I at this time.8 Until a final
policy is developed, such wells are included in Class V.
Similarly, among those wells which inject into aquifers nearest the land surface, .Class IV
wells were separated from Class V because of the heightened risk which Class IV wells create.
Class IV wells may be the most harmful class of wells because of the hazardous nature of fluids
injected into them and the proximity of their injection zone to underground sources of drinking
water. Within wells categorized as Class IV, two general subcategories maybe defined: those
which inject hazardous waste directly into underground sources of drinking water, and those
which inject hazardous waste above underground sources of drinking water. It was felt that this
difference was sufficient to warrant-distinct treatment. Accordingly, Class IV wells which inject
into an underground source of drinking water are being banned under an "interim final" rule
within 6 months after a State UIC program becomes effective. A decision regarding Class IV
wells which inject above an underground source of drinking water is being reserved-at this time
pending further Agency consideration and public comment. The rational for this approach is
presented in more detail in a later discussion. Management of radioactive waste which is
injected into or above USDWs will follow this same regulatory scheme, i.e., such waste injected
into a underground source of drinking water will be banned within 6 months after a State UIC
program becomes effective, and decisions regarding such waste injected above USDWs are being
reserved. This applies to radioactive waste as defined by both RCRA and the Atomic Energy Act
of 1954.
An additional factor which influenced this reproposed classification of wells was the Safe
Drinking Water Act ("SDWA") itself. Sections 1421(b),(2) and 1422(c) of the SDWA state that
regulations for State underground-injection control programs may not prescribe requirements
which interfere with or impede underground injection in connection with oil and natural gas
production or the secondary or tertiary recovery of oil and gas production unless such
requirements are essential to assure that underground sources of drinking water will not be
endangered by such injection. House Report No. 93-1185 accompanying the Act takes care to
clarify this directive. At page 31, the Report characterizes the term "interferes with or impedes"
as referring to only those requirements which could "stop or substantially delay" oil or natural gas
production. Thus, the "test" of essentiality would only be relevant upon a demonstration that a
requirement would stop or substantially delay such production.
EPA has observed this statutory admonition by including all injection wells relating to oil
and natural gas production and hydrocarbon storage into a single category (Class II) with the
exception of gas storage wells. Gas storage wells have been included in Class V wells. Such a
grouping makes it possible to modify specific requirements and allow additional flexibility where
possible without endangering human health. It was felt that the economic incentive for
preventing leakage, and the relatively innocuous character (natural gas is not highly soluble)
8 Comprehensive Radioactive Waste Management Program Message from the President
Received during Recess. Congressional Record - Senate, February 18, 1980
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associated with gas storage wells warranted that these wells be studied further before subjecting
them to regulation equivalent to other Class II wells.
Class III, which includes special process wells (including those used for solution mining)
are classified separately from other wells because of their atypical injection practices. Special
process wells serve a variety of purposes, including the extraction of minerals or other materials
from the earth. Individual domestic injection wells used to generate heat and/or electricity,
although special process wells, have been included in Class V. The Agency chose to consider
these systems under Class V due to the limited impact on underground sources of drinking water
anticipated from these wells. It should be noted that domestic syst ems utilizing a closed loop in
conjunction with heat exchangers are not injection wells and consequently, are not covered under
these regulations.
In the course of public review, a number of commenters urged that Class III wells be
subcategorized. In response, the Agency commissioned a study to provide information on this
issue.9 Based on this study it does not appear that either current operating and construction
practice for existing State regulations governing such wells differentiate sufficiently to warrant
subcategorizing Class III wells. Consequently, the final regulations do not establish
subcategories for Class in wells.
As stated earlier, Class IV wells injecting into aUSDW are banned; decisions concerning
Class IV wells injecting above an USDW are being reserved. In order to afford some level of
protection before the final promulgation of regultions for Class IV wells and implementation of
State UIC programs, all injectors of hazardous waste must obtain "interim Status" under the
RCRA hazardous waste management program. The Agency decided to reserve final decisions
concerning Class IV wells which inject above USDW's for several reasons. Commenters pointed
out that injection wells which overlie deep or remote drinking water supplies would have little or
no potential for contaminating the aquifer and thereby endangering health. Moreover, portions of
some aquifers may be so deep or so remote that they may never serve as drinking water sources,
or may not be subject to contamination from injection practices.
A further reason for the proposed approach is that regulations under RCRA and SDWA overlap
at several points. Facilities under Class I and Class IV overlap the class of facilities designated
under RCRA as hazardous waste management facilities. It is, therefore, appropriate that
technical standards under RCRA and UIC be consistent, to the extent allowable under the
governing statutes, for facilities capable of causing a similar degree of risk.
EPA anticipates issuance of permitting standards for HWM facilities until fall 1980.
Adoption of UIC standards now for class IV wells could prove misleading to the States and the
public, because EPA might decide this fall to revise the standards to reflect policy decisions
9 Development of Procedures for Subclassification of Class III Injection Wells. Geraghty
and Miller, April 30, 1980.
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made in connection with RCRA standards. Accordingly, EPA has determined that the best
course is to defer the "technical standards for Class IV wells which inject above USDWs until
fall 1980.
Finally, Class V wells include all wells not covered by the preceding categories, and those
wells for which EPA currently lacks comprehensive information. With the exception of wells
injecting radioactive waste, which are covered under Class IV and V, the Agency has reason to
believe that Class V wells pose a significantly lesser environmental danger than do other
categories of wells. Some Class V wells can cause risks to public health, of course, but many of
them can be actually beneficial to groundwater. Due to incomplete data, EPA has classified
these remaining wells together and is proposing no immediate performance criteria for them at
this time. Instead, these wells are to be assessed and, based on that assessment, EPA will
formulate a regulatory program suitable, for them at a later time. In the meantime, if remedial
action appears necessary, an individual permit maybe required (§122.37) or the Director may
require remedial action or closure by order (§ 122.37(c)).
The regulations propose the use of a variety of measures to assure that injection wells will
not jeopardize underground sources of drinking water. This section addresses, the major
technical requirements by discussing each in conjunction with the particular problem it is
designed to prevent or remedy. The "problems" are basically six in number, and are described
here as "pathways of
contamination" - ways in which fluids can escape the well or injection horizon and enter
underground sources of drinking water. These "pathways" are the following:
1.	movement of fluids through a faulty injection well casing;
2.	movement of fluids through the annulus located between the casing and
well bore;
3.	movement of fluids from'an injection zone through the confining strata;
4.	vertical movement of fluids through improperly abandoned and improperly
completed wells;
5.	lateral movement of fluids from within an injection zone into a protected
portion of that stratum; and
6.	direct injection of fluids into or above an underground source of drinking
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The casing of a well can serve a variety of purposes. It supports the well bore to prevent
collapse of the hole and consequent loss of the well, serves as the conductor of injected fluids
from the land surface to the intended injection zone, and supports other components of the well.
If a well casing is defective, injected fluids may leak through it. Such migration can contaminate
an underground source of drinking water.10
To prevent migration of fluids in this manner, the promulgated regulations require that
wells in Class I use casing sufficient to prevent the movement of fluids into any underground
source of drinking water. Casing requirements for Class II and III wells are different and are
discussed in more detail below.11 The impact of this standard should vary on a well-by-well
basis. In some instances, injection wells would only need a minimal surface casing to prevent
migration of fluids into underground sources of drinking water. In other cases, multiple strings
of casing might be necessary. EPA is proposing this flexible, goal-related standard, rather than a
fixed requirement, in order to allow State Directors the discretion to vary the requirement, as
appropriate, in each instance. Allowing this discretion should lessen the cost of the requirement
while still accomplishing its preventive objective.12
The regulations also require wells to comply with certain operational requirements which
can serve to minimize migration of fluids through casing. Foremost among these are the
requirements to demonstrate mechanical integrity.13 A mechanical integrity test is used to verify,
as its name indicates, the "integrity" of a well, i.e., whether there is an absence of significant
The determination of what constitutes a significant leak is left to the Director. This
acknowledges the site-specific nature of the question and allows a case-by-case review of
important local phenomena that must be considered in establishing-"significance". The
regulations require operators of all new Class I-M wells (wells coming into operation after an
10	Report to Congress. Section XI, XIII; An Introduction to the Technology of
Subsurface Wastewater Injection. U.S. Environmental Protection Agency (December, 1977),
Chapter 7 ("Subsurface Wastewater Injection").
11	§146.12(b). For a full discussion of the requirements for Class II, and III wells, see pages
11-12 below.
12	Subsurface Wastewater Injection. Chapter 7.
13	§146.08.
14	See generally, Mechanical Integrity Testing of Injection Wells. Geraghty and Miller,
Inc., April 30, 1980.
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applicable UIC program becomes effective in the State) to conduct mechanical inte§rity tests and
provide the results to the Director. If a test indicated that a well did not have mechanical
integrity, i.e., it leaked injected fluids, the well would not be authorized for injection. For
existing-wells, the regulations require that mechanical integrity be demonstrated before
continued operation.of the well can be authorized.
The selection of a mechanical integrity test as a requirement of these regulations is
uniquely appropriate because normally wells cannot be inspected directly. Well integrity can be
demonstrated by the absence of a significant leak in the casing, tubing or packer and the absence
of significant fluid movement into an underground source of drinking water. The regulations
specify a choice of two tests to detect leaks, and two others to detect fluid movement.15 The
regulations specify monitoring of annulus pressure or pressure tests'with a liquid or gas for
detecting leaks, and use of noise or temperature logs for detecting fluid movement. Existing
Class II wells may use well records as proof of adequate cement to prevent fluid movement.
These tests are commonplace in the well injection, industry, and are considered reliable
indicators of mechanical integrity.16
The regulations also would allow the-use of mechanical text.17 To integrity tests not
specifically listed in the t use any of these tests, a Director would have to demonstrate its
suitability for the intended, purpose and secure EPA approval prior to its use. Once approved by
EPA, the test would be eligible for use by all persons unless specifically restricted. EPA allows
this flexibility because it recognizes that there may be mechanical integrity tests which, although
unspecified in the regulations, are fully adequate to detect well defects. Moreover, tests which
might be acceptable may be developed in the future.
The regulations further require that operators of wells which have been authorized for
injection under this program perform, additional,mechanical integrity testing at least once every
five years of operation for most wells.18 However, additional mechanical integrity tests for Class
III wells will only be required for those wells which are used for relatively long periods, such-as
salt solution and geothermal wells. Other Class III wells, which have a shorter life span, will not
be required to perform periodic mechanical integrity tests. In addition, Class II wells mayuse
well records to demonstrate the presence of adequate cement to prevent significant fluid
movement. As part of an evaluation, a statistically valid random sample of wells will be tested
with either noise or temperature logs to assess the adequacy of well records as a measurement of
mechanical integrity.
15	§ 146.08(b),(c).
16	see generally. Mechanical Integrity Testing of Injection Wells.
17	§ 146.08(d).
18	§§146.13(b),(3), 146.23(b),(3), 146.33(b),(3).
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The Agency decided on the five year frequency period after long consideration and
consultation with state officials. EPA staff determined that the requirement for a mechanical
integrity test at least every five years during operation of the well would provide satisfactory
assurance of continued well soundness and in addition would be reasonable from a cost
perspective. Moreover, the five-year review schedule facilitates Agency efforts to combine the
several permit programs under its charge.
A second protective feature of these regulations is the requirement for a tubing and
packer, fluid seal, or an alternative approved by the director for Class I wells. The Agency
applied this requirement to Class I wells due to the potentially corrosive nature associated with
Class I wastes. This requirement does not apply to municipal, wells injecting non-corrosive
fluids. The reproposal specified only tubing and packer or alternative. As a result of public
comment, the Agency included the use of a fluid seal in the final regulations. Fluid seals are
used extensively and have proved effective. Tubing and packer can best be described as a
removable liner device within a well which isolates the casing of the well from injected fluids.
By preventing this contact between casing and injected fluids, the possibility of movement of
contaminants through leaks in the casing is greatly diminished. For the same reason, tubing and
packer or equivalent also lessens the chances of corrosion of the casing. Tubing and packer
offers two further advantages. It isolates the annulus (between the tubing and casing) from the
injection zone, facilitating detection of any leaks in the tubing. It also allows for visual
inspection for deterioration of the tubing during routine maintenance.19
The regulations make the use of tubing and packer or an acceptable substitute mandatory
for Class I well S,20 except for municipal wells injecting only non-corrosive wastes. EPA expects
that Class I wells will be injecting highly corrosive material more frequently than Class II or III
wells,21 hence, routine use of tubing and packer or an acceptable substitute becomes appropriate
(For Class II and III wells, the requirement to use tubing and packer is discretionary with the
Director because the inflexible use of the requirement for Class II and III wells would likely
interfere with production from many of these wells without any significant benefit to protecting
USDW).22 Even though a tubing and packer requirement is not mandatory for wells in Classes II
and III, Directors should require its use when appropriate to prevent fluid migration into
underground sources of drinking water.)
When the use of a packer in Class I wells is inappropriate, the regulations allow for use of
alternative means to accomplish the'saime objective provided that the Director approves such
19	Subsurface Wastewater Injection. Chapter 7.
20	§U6.12Cc).
21	Report to Congress. Section XIII; Ground-Water Pollution. Part 2. Section II.
22	Subsurface Wastewater Injection. Chapter 7.
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methods.23 In fact, based upon the type of well involved, it is possible that an alternative to
tubing and packer or fluid seal might actually provide a greater degree of protection.24 When
other effective methods are proposed, EPA.does not oppose their use. Prior to use, however, EPA
reserves the right of review and approval.
The final provision by which the regulations propose to eliminate contamination through
this first pathway is to require that Class I and Class III wells-which in ect corrosive fluids be
constructed of corrosion'-resistant materials.25 This standard is intended to prolong the operating
life and continued viability of wells.
A second way by which contaminants can reach underground sources of drinking water is
by migrating upward through the annulus located between the drilled hole and the casing. Under
usual injection conditions, injected fluids, upon leaving the well in the injection zone, enter a
stratum which to some degree resists the entry of the fluids. Resistance results from friction
created by extremely small openings in the materials which comprise the injection zone.
Because fluids tend to take the path of least resistance unless properly contained, they may travel
upward through this annulus. If sufficient injection pressure exists, the fluids could migrate into
an overlying source of drinking water.
The measures taken in the regulations to prevent contamination by this pathway are
parallel to those already mentioned concerning Pathway 1. In this case, well injectors must
demonstrate to the satisfaction of the Director that there is no significant fluid movement into
underground sources of drinking water through this annulus. Mechanical integrity tests can be
conducted to provide information on contamination by this route.26 As with Pathway 1, and for
the same reasons, mechanical integrity must be demonstrated at least every five years.
For Class I and III wells, the annulus between the hole and casing must also be filled with
cement adequate to prevent the flow of fluids into an overlying drinking water source.27
Depending upon the complexity of the well, this cementing can be accomplished in different
23	§146.12(c)(1).
24	Subsurface Wastewater Injection. Chapter 7; See also Cook, T.D. Underground Waste
Management and Environmental Implications. American Association of Petroleum Geologists
(Tulsa, Okla., 1972).
25	§146.12(c).
26	§146.08
27	§§146.12(b); 146.32(a).
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ways. A well with a single casing, for example, may need cementing at only one interval (e.g..
through the confining stratum which separates the injection zone from the source of drinking
water). Other wells, which penetrate to greater depths or which involve more than one casing,
may need a more elaborate cementing procedure. Because of this range, EPA is proposing the
cementing requirement in general terms and intends to leave decision making to Directors'
discretion. Directors are instructed in the regulations to take a variety-of factors into account
when determining specific cementing requirements for individual wells.28
All new Class II wells will be subject to requirements outlined above. Existing and
converted Class II wells need nut meet these requirements if they were subject to regulatory
controls at the time they were drilled and they are in compliance with those controls, and
injection will not result in the migration of fluids into an underground source of drinking water
so as to create a significant risk to the health of persons using the source as drinking water.
Similarly, new (newly drilled) wells in existing fields must meet casing and cementing
requirements applicable to the field, and cannot allow movement of fluids into an underground
source of drinking water if such movement will create a significant risk to health of persons.29
For Class III wells, all new wells must comply with the requirements discussed above.
Existing wells which have long lives, such as salt solution and geothermal wells, must
demonstrate mechanical integrity; however, they are not required to meet other casing and
cementing requirements. Various considerations underlie this modified approach.
As mentioned in the preamble to these regulations, costs played arole: EPA data
indicates that compliance for Class II wells equivalent to casing and cementing requirements for
Class I wells could generate cos ts to the oil industry of more than $20 billion over 5 years.30,31
Imposing regulatory requirements of this financial magnitude in EPA's view, would interfere
with injection of brines or other fluids which are brought to the surface in connection with Oil
and natural gas production and with injection for secondary or tertiary recovery of oil or natural
gas without being essential to assure that underground sources of drinking water will not be
endangered by such injection. Moreover, the imposition of this casing and cementing
requirement could be an unnecessary disruption of state UIC programs currently in effect and
being enforced in a substantial number of states.
28	§§ 146.12(b),(l)-(7); 146.22(b),(l)-(7); 146.32(a),(l)-(7).
29	§ 146.22(b).
30	Estimated after discussions with consultants. See generally Cost of Compliance Proposed
Underground Injection Control Programs. Oil and Gas Wells. Arthur D. Little, Inc. (June, 1979)
("Oil and Gas Wells").
31	See generally Underground Injection Control Program Class II Well Incremental
Compliance Cost Refinements. Booz, Allen and Hamilton Inc., and Geraghty and Miller, Inc.,
April 30, 1980.
Page 12 of 20

In addition, the imposition of the "full" casing and cementing requirement on Class II
wells in existing injection fields would not yield significant environmental benefit. If past
injection was performed in an unsafe way, nearby water resources will likely be too contaminated
for consumption as drinking water. Imposing casing and cementing in this instance would not be
helpful to the environment. On the other hand, if the injection has been performed historically in
a way which is protective of underground drinking water, it is reasonable to believe that the
injection method will continue to protect underground sources of drinking water. These facts are
particularly applicable to Class II wells because they are relatively older than wells in other
categories32 and are normally found in groups the members of which are similarly constructed.33
Older wells, with longer histories of operation; are more likely to have contaminated drinking
water, if at all, by this time, than are newer wells. Moreover, the similar construction of wells in
specific fields increases the chances that, if contamination has occurred, it is already extensive.
Lastly, the need for the "full" casing and cementing of Class II wells is generally less
because-brine and other fluids associated with oil and natural gas production pose less threat to
human health than fluids which Class I and some Class III wells often inject.
The third way by which fluids can enter an underground source of drinking water is from an
injection zone through the confining strata. Upon entry into an injection zone, fluids injected
under pressure will normally travel away from the well laterally and through the receiving
formation. In most cases, this expected occurrence gives rise to no concern, but, if the confining
stratum which separates the injection zone from an overlying or underlying underground
source of drinking water is either fractured or permeable, the fluids can migrate out of the
receiving formation and into the protected region.
For obvious reasons, there are no well construction standards which can address this
problem of migration of fluids through this pathway. Consequently, the regulations propose two
provisions to assure that fluids do not travel this pathway into underground drinking water. First,
the regulations require that, prior to the issuance of a permit, the geologic characteristics of the
injection zone and confining strata be reviewed.34 Data already available to states can assist
Directors in making these reviews. A permit should only be issued upon the Director's finding
that the underground formations are sufficiently sound to contain fluids in the injection zone.
Second, the regulations require that well injection pressure be controlled to prevent
opening fractures in the confining strata or otherwise causing the rise of fluids into an overlying
32	Report to Congress. Section XI.
33	Id.
34	§§146.14(a)(1); 146.24(a)(1); 146.34(a)(1).
Page 13 of 20

protected zone.35 Using this mechanism, injection pressures can be restricted to provide
conservative protection even in the face of less than ideal geologic characteristics. For example,
if a confining stratus is known to be fractured or permeable, injection might be permissible if
done at predetermined pressure levels which under no circumstances could cause arise of fluid
to the height at which it would enter a drinking water source.
One of the common ways by which fluids can enter an underground source of drinking
water is by migration through improperly abandoned and improperly completed wells. This
would occur if fluids moving laterally within an injection zone encountered an improperly
abandoned or completed well, and, following the path of least resistance, flowed upward within
the well until entering an overlying underground source of drinking water or overflowing onto
the land surface. Because of the large number of wells drilled in the past, and because well
operation and abandonment have not always benefitted from close regulatory scrutiny,
contamination by this route can present a significant risk to public health. It is estimated that
there are about 17,000 improperly abandoned or improperly completed wells which could cause
this problem.36
To prevent this contamination, the regulations require Directors to determine an "area of
review" for injection wells. This is the area around the injection well through which the
incremental pressure of injection can cause vertical migration. Operators of Class I, III, and new
Class II wells (operators of existing and converted Class II wells are treated differently, see
below) must locate other wells within the "area of review" and correct any problems related to
improperly abandoned or improperly completed wells before beginning injection.37 Under this
approach, well injectors would have the affirmative responsibility to demonstrate that the
proposed injection operation would not cause contamination by this route.
Directors could choose either of two methods to determine the area of review, the first
method would be to require use of mathematical formulae to determine, on a case by case basis,
the lateral impact which an injection operation could cause. The formula would indicate the
distance outward from the well which this particular injection would or could affect. The
Regulations provide one formula which can be used for this purpose. It takes into account a
range of factors, including hydraulic conductivity, thickness of the injection zone, time of
injection, storage coefficient, injection rate, hydrostatic head and specific gravity. EPA is
proposing this particular formula because it is based on an equation which has been in common
use for years and, in that time has demonstrated satisfactory results; however, other suitable
35	§ 146.06
36	Oil and Gas Wells; Chapter VIII-D.
37	§ 122.44(a).
Page 14 of 20

formulae are acceptable.38
If a suitable formula indicates that no problem exists, injection could commence without
any obligation to repair faulty wells found within the area of review. If it did indicate a problem,
however, the well operator would be expected to correct it. Correcting the problem could mean
that the well operator would have to plug a faulty well at his/her expense. In other cases, the
operator might simply have to modify injection pressure to assure that the rise of fluids caused
would not cause fluids to enter an underground source of drinking water.
The use of a formula to determine the area of review may not always be feasible. In some
instances, necessary information maybe lacking. Such formulae also do not have universal
applicability: Mathematical formulae, because they are based on ideal conditions (that aquifers
are homogeneous, isotropic, and infinite in extent, for example), may not always reflect actual
subsurface conditions. Moreover, they assume radial flow in all directions and, in some cases,
will not yield a finite distance measurement for well review purposes.
Because of these possibilities, the regulations offer a second method for determining the
area of review. Directors may use (in lieu of a case by case formula) a fixed radius of one-
quarter mile or greater. The Agency selected this minimum radius after consideration of current
state practices and after applying it to a randomly selected population of well fields representing
various geologic conditions. EPA had considered use of more extensive review requirements,
particularly the use of one-half mile radius for area of review computation, but decided-against
them because the less rigorous requirement is more cost-effective, and the one-fourth mile radius
proved satisfactory in actual applications.39 In many cases, use of a larger fixed radius would
result in duplicative review of the same wells.
Moreover, the quarter-mile radius is compatible with coverage practiced in most states.
Generally, states impose review requirements on we'll operators in a range of 1000 feet from the
injection site up to two miles. EPA's selection of the quarter-mile distance represents its
assessment of the effectiveness of these varying requirements in the state programs.40
EPA has modified the area of review requirement for Class II wells.41 Unlike the
proposal for wells in Classes I and III, the regulations require that only new Class II wells
observe area of review requirements. Class II is characterized by large numbers of wells
clustered in oil fields. Because new injection wells are interspersed with existing Class II wells,
imposing the area of review requirements on new Class II wells should still result in discovery
38	§ 146.06(a).
39	See generally Oil and Gas wells. Chapter VIII.
40	Preliminary Evaluation of Well Injection Practices.
41	§ 146.24(a),(2).
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and correction of all faulty wells within the existing well fields, although over a more extended
time frame.42 The Agency opted for this approach because it deemed it to be effective, both.from
an environmental and cost perspective, and because it considers placing expenses on new, rather
than existing, well operators to be a preferable regulatory approach.43
With respect to corrective action itself, the regulations impose a flexible standard.
Corrective action required for each well will be fashioned by the Director on a case by case basis
after considering a variety of site specific criteria.44 EPA prefers this approach because of the
variety of problems or conditions which can trigger the need for corrective action. In one
instance, the only corrective action which maybe needed to prevent the migration of fluids into
an underground source of drinking water through a faulty well might be a reduction of the
pressure at which fluids are injected. In other instances, monitoring of nearby wells coupled with
a contingency plan to remedy any problems which result from the injection operation might be
feasible. In still other cases, it might be necessary to correct the wells. This range of
possibilities, as well as the significant costs which corrective action can generate; have
encouraged the Agency to adopt the more flexible approach.
In the most cases, the injection zone of a particular well will be physically segregated
from underground sources of drinking water by impermeable materials. In some instances,
however, well injectors,may inject into an unprotected portion of an aquifer which in another
area will be designated for drinking water purposes. In this event, there maybe no impermeable
layer or other-barrier to prevent migration of fluids into underground drinking water.
Injection into unprotected portions of aquifers which contain drinking water in other areas
must be done with great care. The regulations control this potentially dangerous activity by
according the Director a range of construction and operating controls which can be imposed at
his/her discretion.45 Notwithstanding the discretionaiy controls afforded the Director, specific
information must be considered by him prior to allowing injection into such an aquifer. The
Director must consider such factors as the injection pressure, the nature of the fluid injected,
specific geologic and hydrogeologic conditions, groundwater use patterns and other factors.
Usually, Directors can allow injections of this type if the predominant flow of the aquifer is such
that injected fluids will tend to move away from, rather than toward, the protected part of the
aquifer. Even if that is not the case, however, Directors could still allow the injection if any of a
42	See generally Oil and Gas Wells. Chapter VIII.
43	Id.
44	§§146.07, 146.14.
45	§146.12; 146.22; 146.32.
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variety of operational conditions were satisfied. For example, the Director might allow an
injection upon a determination that the rate of flow or the volume or pressure of injection was
sufficiently small to assure that fluids would not enter.the prote-cted region.
The last pathway of contamination of groundwater is potentially the most worrisome. The
injection of fluids into or above underground sources of drinking water can present the most
immediate risk to public health because it can directly degrade groundwater especially if the
injected fluids do not benefit from any natural attenuation from contact with soil, as they might
during movement through an aquifer or separating stratum.
The regulations prohibit injection of contaminants directly into an underground source of
drinking water for wells in Classes I to III;46 Class IV wells, which inject directly into
underground drinking water are to be banned as soon as possible but in no event later than six
months after a State underground injection control program becomes effective. Class IV wells
which inject above an underground drinking water source are to be studied further. Accordingly,
EPA has decided to defer issuance of permitting and technical standards for Class IV wells until
this fall. Class V wells, of which little is known, will be assessed before regulations for their
operation are proposed47 (for a fuller discussion of the regulatory approach proposed for Class IV
and V wells, see the preamble to the regulations).
	ABANDONMENT - the regulations also require that well injectors abandon their
injection wells in a way which will prevent the contamination of underground sources of
drinking water.48,49 As indicated earlier, abandoned wells can act as conduits for contaminants to
enter protected aquifers. To assure that currently used and future wells do not create problems of
this type, the regulations require plugging of wells after termination of operation. Again, the
exact means of accomplishing an effective abandonment are left to the judgment of the Director
to be exercised on a case by case basis. In addition, §146.10(d) requires the operator of a Class
III well to subinit a plan of abandonment which must demonstrate that no movement from the
mining zone into underground sources of drinking water will occur after abandonment.
46	§ 122.34(a)(1).
47	§ 146.52(b)(1).
48	§146.10.
49	See Generally. Development of Procedures and Costs for Proper Abandonment and
Plugging of Injection Wells. Booz Allen and Hamilton Inc., and Geraghty and Miller, April 30,
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§146.10(b) specifies that the dump bailer method, the balance method, or.the two plug method be
used to plug a well. These practices represent existing methods employed that have proved
effective in a wide range of application.50
With respect to Class IV wells, traditional methods of abandonment, such as plugging,
may be inappropriate due to the crude construction of the well. In such a case, the only
abandonment requirements might simply be closure of the well.
The regulations also require various kinds of monitoring.51 Monitoring can provide an
early warning of potential serious degradation of underground sources of drinking water.
Wells in Classes I, II, and HI share common monitoring requirements. Injection fluids
must be tested with sufficient frequency to field data representative of fluid characteristics.
Information of this sort is essential for the Director to understand the operation of a particular
well. Such information serves the important function of providing basic knowledge of enabling
Directors to analyze reasons for well failures, to establish appropriate remedies to correct them
and to assess any endangerment the failures might cause.
The regulations also require monitoring of operating characteristics of wells in Classes I,
II, and III. Class I and III wells must have continuous recording devices to monitor injection
pressure, flow rate, and volume of injection fluids.52 Continuous monitoring is appropriate
because fluids injected by Class I and III wells are usually more corrosive and hazardous than are
fluids injected by others. These fluid properties increase the risk of serious well leaks or failures.
Continuous monitoring, furthermore, is a common practice for these wells, in part because they
often inject fluids in uninterrupted streams.
Class I wells must comply with the additional requirement of continuously monitoring the
pressure in the annulus of the well between the tubing and the long string. The "long string" is
the casing which extends from the ground surface to the injection zone. Wells in Class III which
may require the use of the annulus for injection, need not meet this requirement since, when the
annulus is employed for injection, pressure measurements reflect injection pressure.
50	Development of Procedures and Costs for Proper Abandonment and Plugging of
Injection Wells.
51	§§146.13; 146.23; and 146.33.
52	§§146.13(b)(2); and 146.33(b)(2).
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Class II injection well monitoring provisions aze less stringent than those for Classes I
and III.53 Continuous monitoring is not required for Class II; rather, depending on the actual
injection operation, monitoring frequency varies from daily to monthly. A stricter approach is
not essential for Class II wells because of the lesser toxicity and corrosivity of fluids which Class
II wells handle and because the total cost of imposing continuous monitoring on Class II wells
would have been inordinately burdensome in EPA's view.54
Class III wells are also required to monitor, on a quarterly basis, water supply wells
adjacent to the injection site to detect any excursions from the injection site.55 This monitoring is
commonly practiced by operators of Class III wells.56 EPA is promulgating this requirement for
Class III wells (and not for Class I wells) because Class III wells are often designed to inject into
shallower strata, thereby increasing the possibility of contamination of aquifers nearest the land
This added risk has prompted the Agency to require monitoring wells at each project site,
located to maximize the probability of detecting any horizontal or vertical fluid excursion from
the injection zone. Weekly monitoring of the fluid levels in these monitoring wells and of
parameters appropriate to determine if any excursions of injected fluids are entering underground
sources of drinking water, is also required. This requirement, although involving additional
expense, was considered necessary to assure that any migration of these potentially harmful
injected fluids into underground sources of drinking water, which are often located quite close to
the injection zones, would be discovered and rectified promptly. Class III wells may be
monitored on a field or project basis rather than an individual well basis by manifold monitoring
e.g. using a common header with individual well points. This approach may be used with
facilities that consist of more than one injection well if the owner or operator can demonstrate
that manifold monitoring is comparable to individual well monitoring.57
No monitoring requirements are proposed for Class V wells. These wells will be
assessed under the proposed regulatory scheme. The assessment should produce a substantial
amount of data upon which an entire regulatory approach, including monitoring, can be used.
53	§ 146.23(b).
54	Oil and Gas Wells. Chapter V-B, C.
55	§ 146.33(b)(5).
56	Comments of Freeport Sulfur Co., Jan. 14, 1977; Statement byTexas Gulf Co., Oct.
13, 1976.
57	§ 146.33(b)(6).
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The regulations also impose reporting requirement on well injectors.58 Owners and
operators of wells regulated under Classes I and III must report the results of monitoring and any
other significant operational information at least quarterly, while Class II well owners and
operators need only report to the director annually. The reasons underlying these proposals
parallel those for the monitoring requirements. Owners and operators of wells which inject
fluids of greater potential hazard must report more often than those which do not. Class V wells
need not submit monitoring or reporting data because the assessment planned for this category
will supply EPA with a substantial amount of data in its own right.
58 §§ 146.13; 146.23; and 146.33.
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