United States Office of Water EPA 816-R-01-007
Environmental Protection (4601) March 2001
Agency Washington, DC 20460 www.epa.gov/safewater
SEPA Class ' Underground Injection
Control Program: Study of the Risks
Associated with Class I Underground
Injection Wells
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Contents
Preface iii
Executive Summary ix
Class I Expert Panel xv
I. Introduction 1
LA Overview of Class I Wells 2
IB History of the UIC Program and Rulemakings Related to Class I Injection 5
The 1980 UIC Regulations 5
The RCRA Hazardous and Solid Waste Amendments 6
The Land Disposal Restrictions 7
Phase I Rulemaking 7
Phase n and m Rulemakings 8
Phase IV Rulemaking 9
II. Technology Summary 9
II. A Injection Well Technology 10
II.B Geologic Siting 12
II.C Class I Well Risks 13
Well Failure 13
Pathways for Fluid Movement in the Area of Review 13
II.D Introduction to Modeling 14
III. Options for Decharacterized Wastewaters 16
IV. Oversight of Class I Wells 17
IV. A Regulations and Criteria for Class I Wells 18
Siting Requirements 18
Construction Requirements 21
Operating Requirements 22
Monitoring and Testing Requirements 23
Reporting and Record Keeping Requirements 25
Closure Requirements 26
IV.B How EPA Administers the Class I UIC Program 27
EPA Headquarters' Management of the National Program 28
Regional Oversight of Primacy Programs 28
Direct Implementation of State Programs 30
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V. Risk Associated with Class I Wells 30
V.A Studies of the Effectiveness of the UIC Regulations 30
Underground Injection Practices Council and
General Accounting Office Studies 30
The OSWER Report 32
EPA Analysis of Class I MI Failures 33
V.B Qualitative Studies of Class I Wells 34
V.C Quantitative Studies of Risks Due to Phase IE Wastes 35
EPA OGWDW Draft Phase HILDRRIA 36
Comments by the Chemical Manufacturers Association on the
Phase HILDRRIA 37
EPA OGWDW Final RIA 37
Evaluation of Risks from Exceedance of the UTS 38
V.D Other Studies of Risk Due to Class I Wells 38
Revisions to GeoTrans' Modeling Assumptions 39
Probabilistic Risk Assessment of Class I Hazardous Wells 40
VI. Conclusions 41
VTI. Annotated Bibliography of Class I Documents 43
Appendix A: The Land Disposal Program Flexibility Act of 1996.
Appendix B: Supplemental Risk Analysis in Support of The Class 1 UIC Regulatory
Impact/Benefits Analysis For Phase 111 Wastes: Examination of Risks Associated
With East Gulf Coast/Abandoned Borehole Scenario And Variations in
Permeability Ratio Between The Injection Zone And The Confining Layer
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Preface
The Land Disposal Program Flexibility Act of 1996 (Public Law 104-119) requires the
United States Environmental Protection Agency (EPA) to complete a study of the risks to human
health and the environment associated with hazardous waste disposal practices and directly
related to decharacterized wastes managed by surface impoundments and Class I injection wells
regulated under the Underground Injection Control (UIC) program. EPA has been charged with
compiling information on these waste disposal activities and making a determination on whether
existing programs administered by the Agency or the states are adequately protective or new
regulations are needed to ensure safe management of these wastes.
Two offices within EPA are tasked with this response. The Office of Solid Waste and
Emergency Response, Office of Solid Waste (OSW) is preparing a study on surface
impoundments to be completed within 5 years of the enactment of this legislation. The Office of
Water, Office of Ground Water and Drinking Water (OGWDW) is conducting a study on Class I
inj ection wells in a similar timeframe. This Study of the Risks Associated with Class I
Underground Injection Wells is OGWDW's response to Congress' request.
Direction of the Class I Study
In the Act, Congress did not ask EPA to do an entirely new study regarding Class I UIC
wells that would have required a re-collection of the large amount of report data and information
already compiled. Nor did Congress require the states to contribute new field data or tabulations
of data already being reported.
EPA decided that the Class I study would describe the current Class I UIC Program,
document past compliance incidents involving Class I wells, and summarize studies of human
health risks associated with Class I injection conducted for past regulatory efforts and policy
documentation. This compilation would serve as the basis for the Agency's decision either to
promulgate new regulations, or determine that existing Class I controls are adequate. This study
would be submitted to appropriate members of Congress and their staffs and to fulfill the
Agency's commitment under the Act.
The Study Report
As stated above, this study is a compilation of existing information on the Class I UIC
injection program. Much program data has been gathered on Class I hazardous and
nonhazardous injection wells, and each type of well is regulated separately, but stringently. In
the study, the hazardous and nonhazardous Class I requirements are presented together to give a
complete picture of the UIC program. Many UIC Primacy states place requirements on Class I
nonhazardous waste disposal wells under their jurisdiction that are equivalent to, or stricter than,
the federal Class I hazardous well requirements. Moreover, the Agency believes, from
information collected in past studies and reports related to rulemaking, that substantial volumes
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of decharacterized wastewaters are being managed in Class I hazardous injection wells, thus
providing a significant degree of protection to human health and the environment. Any different
requirements between Class I non-hazardous and hazardous wells are described and compared to
give the reader a more complete perspective of the preventative aspects of the entire UIC Class I
program.
Based on the recommendations of expert reviewers, and to be consistent with the June
1998 memorandum from President Clinton to all federal agencies to take steps to improve the
clarity of government writing, this report is written in "plain English." In addition, the authors
assume that the audience is a mixture of educated non-scientists and people with a more
sophisticated understanding of geology, risk analysis, and other relevant sciences. As a result,
the report tries to educate the audience on the basic principles of geology, modeling, etc., and
some portions could be considered repetitive by more knowledgeable readers.
Data Needs and Initial Steps
The study relies on secondary data, that is, existing information such as studies, reports,
and background information documents prepared by EPA, the states, and others. By using
existing information, OGWDW becomes bound by certain limitations, such as data accuracy,
quality, soundness of methodology, and other pertinent technical data. However, EPA believes
that such data are usually very accurate given the finite universe of Class I wells and the history
of regulation of these wells by EPA and the states, among other things. EPA Regional Offices
and the states have collected operational and construction-related data for these wells for a fairly
long time, and such data are compiled and reviewed on a regular basis. Thus, the documents
upon which the study is based are reliable. While many of these documents have not been peer
reviewed, per se, they were subject to technical and policy review by informed individuals
including regional staff, state staff, and other technical stakeholders. In most cases, they were
developed to support Agency rulemakings and were therefore subject to public comment. A
large library of such documents existed in EPA files and dockets as of 1996.
As the initial step in conducting the study, in September 1996 EPA prepared a paper
titled Class I Underground Injection Control Program: Background Document and Assessment
of Risks Associated with Class I Underground Injection Wells. Prior to completion of this paper,
OGWDW decided to investigate and apply the Office of Water Peer Review Process to ensure
that the scientific and technical "underpinnings" of any decisions involving Class I UIC wells
meet two important criteria:
- They should be based on the best current knowledge from science, engineering, and
other domains of technical expertise.
- They should be judged credible by those who deal with the Agency.
Although the Background Document, which represented a compilation of existing
documents related to Class I UIC wells, was not judged to be a "major scientifically and
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technically based work product," OGWDW determined that it would benefit from some form of
technical review. Although the study addresses controversial issues, supports a policy decision,
and could have significant impact on the investment of Agency resources, other tempering
factors (i.e., it is not a new data collection but a compilation of existing studies and it represents
an "update" of progress in the UIC Class I program) suggest that it is not a candidate for bona
fide peer review.
Expert Panel Process
OGWDW chose to seek external review of the initial draft of the study document
primarily to ensure scientific and technical accuracy. To do this, EPA engaged a contractor to
convene a panel of experts in the scientific and technical subject matter. The panel was balanced
to encompass a multi-disciplinary group of experts in other disciplines who could contribute to
the full range of issues concerning Class I wells.
The five-member panel's experts have many years of experience with deep well injection
and related technology. Panel members represented a variety of perspectives on Class I wells,
including industry and consulting, state regulatory agencies, and academia. They have
experience with development and oversight of EPA and state UIC programs, as well as permit
preparation and review. Their technical expertise spans aquifer characterization, geohydrologic
model development, no-migration petition demonstrations, well siting and construction, and well
testing including mechanical integrity. The expert panel's primary goal is to serve as peer
reviewers and to further acknowledge that information and data collected is technically sound,
appropriate, and accurate.
OGWDW distributed the first draft of its work product on the Class I study to the expert
panel in April 1998. After initial review, the entire panel met in Alexandria, Virginia, in late
April 1998 to begin discussions. The panel provided substantial comment and recommended
several changes to the text of the report, including reordering the presentation, adding a
discussion on modeling methodology, and writing the report in plain English. EPA revised the
draft based on the expert panel members' comments and edits. A follow-up draft of the study
was prepared and sent to the members for review in December 1998. The panel then met for a
second time prior to a Ground Water Protection Council Meeting in New Orleans, Louisiana, in
January 1999. Additional edits and comments were compiled via teleconferences and electronic
mailings, and EPA prepared a third and final draft product in December 1999.
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Distribution of the Study Document
The Office of Water (OW) is providing the Class I study to Congress for its
consideration. OW is also making the study available to states and other stakeholders, including
the interested public through a number of mechanisms. As part of the communication strategy
for such studies, EPA will place it on a list of UIC documents on OGWDW's Web site, and
make it available to the general membership of the Ground Water Protection Council and the
National Drinking Water Council and via general Water Program announcements.
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Exhibits
Exhibit 1: Number of Class I Wells by State
Exhibit 2: Hazardous and Nonhazardous Class I Wells
Exhibit 3: A Typical Class I Injection Well
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Executive Summary
In 1996, Congress enacted the Land Disposal Program Flexibility Act, which exempted
Class I underground injection wells disposing of decharacterized hazardous wastes from the
provisions of the Resource Conservation and Recovery Act (RCRA) Land Disposal Restrictions
(LDRs). This legislation also required the U.S. Environmental Protection Agency (EPA) to
conduct a study of such wastes and disposal practices to determine whether Class I wells pose
risks to human health and the environment, and if current state or federal programs are adequate
to address any such risks. EPA must also determine whether such risks could be better
addressed under existing state or federal programs. Upon receipt of additional information or
upon completion of such study and as necessary to protect human health and the environment,
the Administrator may, but is not required to, impose additional requirements under existing
Federal laws, including subsection (m)(l), or rely on other state or federal programs or
authorities to address such risks.
EPA's Study of the Risks Associated with Class I Underground Injection Wells describes
the Class IUIC Program, injection well technology, the Land Disposal Restrictions, and the
1996 legislation; documents past failures of Class I wells; and summarizes studies of human
health risks associated with injection via Class I wells, including non-hazardous and hazardous
wells. The study also includes an updated risk analysis using Class I injection well data and an
annotated bibliography of literature on injection via Class I wells.
Class I wells inject industrial or municipal wastewater beneath the lowermost
underground source of drinking water (USDW).1 Class I wells are designated as hazardous or
nonhazardous, depending on the characteristics of the wastewaters injected. (Wastewaters are
considered to be hazardous wastes if they demonstrate a hazardous characteristic of ignitability,
corrosivity, reactivity, or toxicity, or are a listed waste as determined by EPA.) This designation
affects the stringency of the requirements imposed on operators of Class I wells. The wastewater
injected into Class I wells typically is associated with the chemical products, petroleum refining,
and metal products industries.
History: Early Concerns, EPA's Response
The practice of underground injection of wastewater began in the 1930s as oil companies
began disposing of oil field brines and other waste products into depleted reservoirs. In the mid
1960s and 1970s, injection began to increase sharply, growing at a rate of more than 20 new
wells per year. In 1974, responding to concerns about underground injection practices, including
failure of some wells, EPA issued a policy statement in which it opposed underground injection
EPA defines an underground source of drinking water as an aquifer or portion of an aquifer that supplies a public water
system (PWS) or contains enough water to supply a PWS; currently supplies drinking water for human consumption or contains
water with less than 10,000 milligrams/liter of total dissolved solids (IDS); and is not exempted by EPA or state authorities from
protection as a source of drinking water (40 CFR 144.3).
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without strict control and clear demonstration that the wastes will not adversely affect ground
water supplies. In December 1974, Congress enacted the Safe Drinking Water Act (SOWA),
which required EPA to set requirements for protecting USDWs; EPA passed its Underground
Injection Control (UIC) regulations in 1980.
In 1984, Congress enacted the Hazardous and Solid Waste Amendments (HSWA) to
RCRA, which banned the land disposal of hazardous waste, unless the hazardous waste is treated
to meet specific standards. EPA amended the UIC regulations in 1988 to address the Hazardous
and Solid Waste Amendments. Operators of Class I wells are exempt from the ban if they
demonstrate that the hazardous constituents of the wastewater will not migrate from the disposal
site for 10,000 years or as long as the wastewater remains hazardous. This demonstration is
known as a no-migration petition. HSWA also requires EPA to set dates to prohibit the land
disposal of all hazardous wastes: EPA has instituted the LDRs in a phased-in schedule. The
Phase m LDR rule implemented the Land Disposal Program Flexibility Act.
Class I Technology Ensures Safe Disposal
Class I fluids are injected into brine-saturated formations thousands of feet below the
land surface, where they are likely to remain confined for a long time. The geological formation
into which the wastewaters are injected, known as the injection zone, is sufficiently porous and
permeable so that the wastewater can enter the rock formation without an excessive build up of
pressure. The injection zone is overlain by a relatively nonpermeable layer of rock, known as the
confining zone, which will hold injected fluids in place and restrict them from moving vertically
toward a USDW.
EPA requires that Class I wells be located in geologically stable areas that are free of
transmissive fractures or faults through which injected fluids could travel to drinking water
sources. Well operators must also show that there are no wells or other artificial pathways
between the injection zone and USDWs through which fluids can travel. The site-specific
geologic properties of the subsurface around the well offer another safeguard against the
movement of injected wastewaters to a USDW.
All Class I wells are designed and constructed to prevent the movement of injected
wastewaters into USDWs. Their sophisticated multi-layer construction has many redundant
safety features. The well's casing prevents the borehole from caving in and contains the tubing,
or injection string. Constructed of a corrosion-resistant material such as steel or fiberglass-
reinforced plastic, the casing consists of an outer surface casing, which extends the entire depth
of the well; and an inner long string casing that extends from the surface to or through the
injection zone. The innermost layer of the well, the injection tubing, conducts injected
wastewater from the surface to the injection zone. All of the materials of which injection wells
are made are corrosion-resistant and compatible with the wastewater and the formation rocks and
fluids into which they come in contact. A constant pressure is maintained in the annular space
and is continuously monitored to verify the well's mechanical integrity and proper operational
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conditions. Trained operators are responsible for day-to-day injection well operation,
maintenance, monitoring, and testing.
EPA's Requirements Minimize Risk
There are two potential pathways through which injected fluids can migrate to USDWs.
First, wells could have a loss of waste confinement; second, improperly plugged or completed
wells or other pathways near the well can allow fluids to migrate to USDWs. EPA's extensive
technical requirements for Class I wells at 40 CFR 146 (for all Class I wells) and 148 (for
hazardous waste wells) are designed to prevent contamination of USDWs via these pathways.
The requirements for hazardous wells are more stringent than those for nonhazardous wells.
Class I wells must be sited so that wastewaters are injected into a formation that is below
the lowermost formation containing, within one-quarter mile of the well, a USDW. Class I well
operators must demonstrate via geologic and hydrogeologic studies that their proposed injection
will not endanger USDWs. Operators must identify all wells in the vicinity that penetrate the
injection or confining zone, determine whether they could serve as pathways for migration of
wastewaters, and take any corrective action necessary. In addition, Class I operators seeking to
inject hazardous wastewaters must demonstrate via a no-migration petition that the hazardous
constituents of their wastewaters will not migrate from the disposal site for as long as they
remain hazardous.
EPA requires that Class I wells be designed and constructed to prevent the movement of
injected wastewaters into USDWs. These requirements specify the multi-layer design of Class I
wells. Class I wells must be operated so that injection pressures will not initiate new fractures or
propagate existing fractures in the injection or confining zones. Class I hazardous wells must be
equipped with continuous monitoring and recording devices that automatically sound alarms and
shut down the well whenever operating parameters exceed permitted ranges.
Operators of Class I wells must continuously monitor the characteristics of the injected
wastewater, annular pressure, and containment of wastewater within the injection zone.
Operators also must periodically test the well's mechanical integrity.
Upon closing their wells, operators must flush the well with a non-reactive fluid, and tag
and test each cement plug for seal and stability before the closure is completed. Operators must
submit a plugging and abandonment report when closure is complete.
Studies Assess the Safety of Class I Practices
EPA and others have performed numerous studies to assess the risks associated with
disposal via Class I wells. Early studies of the effectiveness of the 1980 UIC regulations looked
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at ways in which Class I wells fail.2 Many of the failures documented in these studies were a
result of historic practices that are no longer acceptable under the UIC regulations.
Although studies emphasizing risk of injection practices have primarily focused on Class
I hazardous waste injection wells, EPA believes such studies to be very relevant to all Class I
wells, including those managing decharacterized wastewaters. The Agency believes that a
substantial volume of decharacterized wastewaters are, in fact, injected into Class I hazardous
waste wells, thus affording a particularly strong level of public health protection from these
activities.
Studies performed in anticipation of the 1988 updates to the UIC regulations assessed the
risks associated with disposal of hazardous wastewater via Class I wells. These include a two-
phase qualitative assessment of waste confinement potential in the Texas Gulf Coast geologic
setting given either a grout seal failure or the presence of an unplugged abandoned borehole. An
additional study assessed the difference in risk among various geologic settings.
In support of EPA's Phase m LDR rulemaking, the Office of Ground Water and Drinking
Water (OGWDW) prepared a draft Benefits Analysis estimating the risks associated with
injection of Phase m wastes into Class I hazardous wells; EPA revised the Benefits Analysis in
response to comments in 1995. To provide a quantifiable analysis in support of the de minimis
requirements in the proposed Phase m rule, EPA in 1996 analyzed cancer and noncancer risks of
varying the underlying hazardous constituent concentrations for five Phase HI LDR waste
constituents.
In the most recent studies of the risks posed by Class I wells, data on Class I wastewaters
have been used to refine models of well failure scenarios. And failure-tree scenarios have been
used to estimate quantitatively the risk that waste would no longer be contained based on the
probabilities that sequences of events leading to containment loss would occur.
Conclusions: Current Class I Regulations are Adequately Protective of
Human Health and the Environment
Since the early days of Class I injection, EPA has learned much about what makes Class
I wells safe and what practices are unacceptable. The UIC regulations are based on the concept
that injection into properly sited, constructed, and operated wells is a safe way to dispose of
wastewater.
Class I injection practices offer multiple safeguards against failure of Class I non-
hazardous and hazardous waste wells, or the migration of injected fluids. For example, EPA
requires operators to identify and address all improperly abandoned wells in the area of review
Failures are defined by two potential pathways through which injected fluids can migrate to USDWs: failure of the well
or improperly plugged or completed wells or other pathways near the well.
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(AoR) around the injection well, because studies show that an unplugged abandoned borehole
may contribute significantly to the migration of injected fluids from the injection zone. (Many
of the states that oversee a large proportion of the Class I well inventory have even more
stringent AoR requirements than does EPA.) In addition to the AoR requirement, Class I wells
are sited to minimize the potential for waste migration and designed to minimize the possibility
that the wells will fail. Inspections and well testing, along with passive monitoring systems, can
detect malfunctions before wastewaters escape the injection system. Several decades of well
operation bear this out: only four cases of significant wastewater migration from underground
injection wells have been documented (none of which affected a drinking water source).
Under EPA's UIC regulations, the probability of loss of waste confinement due to Class I
injection has been demonstrated to be low. The early problems with Class I wells were a result
of historic practices that are not permissible under the UIC regulations. Class I wells have
redundant safety systems and several protective layers to reduce the likelihood of failure. In the
unlikely event that a well should fail, the geology of the injection and confining zones serve as a
final check on movement of wastewaters to USDWs.
Through modeling and other studies of Class I injection, EPA has learned much about the
fate and behavior of hazardous wastewater in the subsurface. The 1988 UIC regulations
implementing the HSWA offer additional protection by requiring operators of Class I hazardous
wells to complete no-migration petitions to demonstrate that the hazardous constituents of their
wastewater will not migrate from the injection zone for 10,000 years, or that characteristic
hazardous wastewater will no longer be hazardous by the time it leaves the injection zone. EPA
believes that a substantial volume of decharacterized wastewaters are being injected into Class I
hazardous wells (which require a no-migration petition) because industrial, manufacturing, and
petrochemical facilities typically do not segregate waste streams. Therefore, an extremely high
level of protection, even above minimum federal requirements, is given by these practices. But,
even the disposal of decharacterized wastewaters into a typical Class I non-hazardous well
affords the public and the environment an extremely low level of risk from injection due to the
multiple levels of safety features outlined in this study.
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Class I Expert Panel
EPA prepared the Study of the Risks Associated with Class I Underground Injection
Wells in consultation with a panel of experts on Class I deep well injection practices. These
experts were selected because of their experience with deep well injection and related
technology; they represent industry and consulting, state regulatory agencies, and academia.
The experts attended two working sessions on drafts of the study report, discussed the
preliminary findings, and reviewed and offered comments on the technical accuracy of the study.
E. Scott Bair, Ohio State University, Department of Geological Sciences
Professor E. Scott Bair is chair of the Department of Geological Sciences at Ohio State
University. He teaches courses on quantitative groundwater flow modeling, hydrogeology, field
methods in hydrogeology, contaminant hydrogeology, science in the courtroom, and water
resources. He has worked with the U.S. Geological Survey and as a consultant on groundwater
monitoring and groundwater modeling issues. Dr. Bair has written or co-written more than 40
books, papers, and government-sponsored reports on groundwater monitoring, aquifer
investigations, groundwater flow modeling, aquifer management, and wellhead protection area
delineation. He was a 1998 fellow of the Geological Society of America and the 2000 Birdsall-
Dreiss Distinguished Lecturer sponsored by the society. He is a member of the American
Geophysical Union's Horton Scholarship Committee and an associate editor of the journal
Ground Water published by the National Ground Water Association. Dr. Bair earned his Ph.D.
and Master's degrees in Geology from the Pennsylvania State University and his Bachelor's
degree in Geology from the College of Wooster.
Larry Browning, P.E., Geological Engineering Specialties
A Principal with Geological Engineering Specialties, Larry Browning is an expert in every aspect
of the UIC program. As a consultant or an EPA employee, Mr. Browning has supported virtually
every UIC regulatory initiative since the program began and has in-depth knowledge of all
classes of UIC wells. He was appointed special technical advisor to EPA's landmark Class I
Regulatory Negotiation Committee. For EPA's Class I petition review process, Mr. Browning
developed training documents and performed technical reviews of important petitions. He
performed two analyses of Class I mechanical integrity failures, spanning 1988 through 1991 and
1991 through 1998. Since 1975, he has performed over 120 technical studies for EPA, including
a two-volume technical manual on wireline testing of Class II injection wells which is used in all
10 EPA regions. Mr. Browning worked with EPA Region 6 and supported writing of the
original UIC regulations. He has also performed ground water investigations, well testing, and
investigations of injection wells and hazardous waste disposal facilities. Mr. Browning earned a
Master's degree in Geology from the University of Texas at Austin and a Bachelor's degree in
Geology from Northern Kentucky University.
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James Clark, DuPont Engineering
James Clark has over 25 years' experience, including 18 years with DuPont working on
groundwater issues. As a senior leader for DuPont, he works on Class IUIC issues spanning
well construction, permitting, testing, and no-migration petitions. In this capacity, he has written
numerous publications on injection issues and regulatory requirements for Class I wells. For the
past 14 years, Mr. Clark has served as a technical representative to the Chemical Manufacturers
Association's UIC Group; in this capacity, he worked on an assessment of the risk associated
with Class I injection. Prior to joining DuPont, Mr. Clark worked as a geohydrologist with Law
Engineering Testing Co. where he gained 4 years' experience on suitability studies of salt domes
as repositories for nuclear waste. He also served as Chief Geologist for the Georgia Department
of Transportation. Mr. Clark has written over 20 publications on Class I injection, waste
confinement, aquifer monitoring, and groundwater flow. Mr. Clark has a Master's degree in
geophysical sciences from the Georgia Institute of Technology and a Bachelor's degree in
geology from Auburn University.
Ben Knape, TNRCC, UIC Permit Team
For over 20 years, Ben Knape has worked with the Texas Natural Resource Conservation
Commission (TNRCC) and its predecessors on regulation of Class I injection wells and oversight
of the state's UIC program. As a UIC Program geologist, Mr. Knape focuses on ground water
studies and the use of Class I wells for industrial waste disposal. As UIC program administrator,
he served as project coordinator on revising the commission's UIC program to reflect a
significant rulemaking, which included strengthening construction and performance standards for
Class I wells and interpreting and implementing the commission's program standards for Class I
well monitoring and inspections. Mr. Knape has served as co-chair of the Ground Water
Protection Council's Division I, representing Class I injection issues, and is a board member of
the Underground Injection Practices Research Foundation. He is leader of TNRCC's UIC
Permits Team for Class I and Class in wells. Mr. Knape holds degrees in Geology and Zoology
from the University of Texas at Austin.
David Ward, Michael Baker Jr., Inc.
David Ward recently joined Michael Baker Jr., Inc. as Director of the Technology Applications
Division. He has over 20 years of experience as a consultant, with expertise in hydrogeologic
modeling of groundwater flow and hazardous waste transport in porous and fractured media. He
has managed projects for EPA and industrial clients on deep well injection of hazardous wastes,
including well test interpretation, groundwater flow and waste confinement, and no-migration
petition preparation. Mr. Ward performed numerical simulations of well failures in a variety of
geologic settings. He has prepared applications of flow and transport codes for many
hydrogeologic models, including SWIFT and MODFLOW, including applications to
geochemical analyses and no-migration demonstrations. He has written more than 80
publications on groundwater flow, waste transport, and well failure simulations. Mr. Ward
holds a Master's degree in Water Resources from Princeton University and a Bachelor's degree
in Civil Engineering from Lehigh University.
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Abbreviations
ACC American Chemistry Council
AoR Area of Review
BDAT Best Demonstrated Available Technology
CFR Code of Federal Regulations
CMA Chemical Manufacturers Association
DI Direct Implementation
EPA U.S. Environmental Protection Agency
GAO General Accounting Office
GWPC Ground Water Protection Council
HSWA Hazardous and Solid Waste Amendments
FIWIR Hazardous Waste Identification Rule
LDR Land Disposal Restriction
MI Mechanical Integrity
MIT Mechanical Integrity Test
OAL Oxygen Activation Log
OGWDW Office of Ground Water and Drinking Water
OSWER Office of Solid Waste and Emergency Response
PWS Public Water System
RCRA Resource Conservation and Recovery Act
RIA Regulatory Impact Analysis
RTS Radioactive Tracer Survey
SDWA Safe Drinking Water Act
TDS Total Dissolved Solids
TRI Toxic Release Inventory
UHC Underlying Hazardous Constituent
UIC Underground Injection Control
UIPC Underground Injection Practices Council
USDW Underground Source of Drinking Water
UTS Universal Treatment Standards
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I. Introduction
The U.S. Environmental Protection Agency (EPA) regulates Class I underground
injection wells under the Safe Drinking Water Act (SDWA) and the Hazardous and Solid Waste
Amendments of the Resource Conservation and Recovery Act (RCRA). These regulations
establish siting, design, construction, and monitoring requirements for Class I injection wells to
ensure protection of underground sources of drinking water (USDWs) from injected wastewater.
HSWA prohibits injection of certain hazardous wastewater3 unless the well operator can prove
that the injected wastewater will not migrate out of the injection zone for as long as the
wastewater remains hazardous.
Under the Land Disposal Program Flexibility Act of 1996,4 Congress declared that
wastewaters considered hazardous only because they exhibit a hazardous characteristic
(ignitability, corrosivity, reactivity, or toxicity) are not prohibited from land disposal if they do
not exhibit the characteristic (i.e., decharacterized) at the point of disposal. Class I well
operators do not, therefore, have to identify and treat underlying hazardous constituents in these
decharacterized wastewaters prior to injection. This legislation effectively overturned the D.C.
Circuit Court's opinion in Chemical Waste Management v. EPA, 976 F. 2d 2 (D.C. Cir. 1992).
EPA had interpreted the D.C. Circuit Court's opinion to require that hazardous constituents in
characteristic wastes be removed, destroyed, or immobilized through treatment before the
wastewaters were available for land disposal.
In passing the Land Disposal Program Flexibility Act, Congress stated the following (see
Appendix A for the complete text of the Act):
Not later than 5 years after the date of enactment of this paragraph, the
Administrator shall complete a study of hazardous waste managed pursuant to
paragraph (7) or (9) to characterize the risks to human health or the environment
associated with such management. In conducting this study, the Administrator
shall evaluate the extent to which risks are adequately addressed under existing
state or federal programs and whether unaddressed risks could be better addressed
under such laws or programs. [PL 104-119 s 2 (10)]
In order for a waste to be a hazardous waste, it must not be excluded by EPA under 40 Code of Federal Regulations (CFR)
261.4(a) or through the delisting process under 40 CFR 260.22. There are two major categories of hazardous wastes: listed
wastes and characteristic hazardous wastes. The listed hazardous wastes are described in Subpart D of 40 CFR 261. The second
major category of hazardous wastes includes any wastewater that exhibits any or all of the four characteristics of hazardous waste
(i.e., ignitability, corrosivity, reactivity, and toxicity) described in Subpart C of 40 CFR 261. Characteristic wastes are identified
by sampling a wastewater, or using appropriate company records concerning the nature of the wastewater, to determine whether a
wastewater has the relevant properties.
4 Public Law 104-119, March26, 1996.
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Study of the Risks Associated with Class I UIC Wells
In response to Congress' requirement for such a study, EPA identified the need for a
document that synthesizes existing information on the Class I program, including documented
studies of the risks to human health or the environment posed by Class I injection wells. This
document presents this information by:
• Providing an overview and history of EPA's Class I Underground Injection
Control (UIC) program.
• Summarizing the geologic, engineering, and modeling sciences as they relate to
Class I injection and outlining the risks associated with Class I wells.
Describing the regulations designed to minimize the potential threat Class I wells
pose to human health or the environment, and reviewing the Land Disposal
Restrictions, the D.C. Circuit Court's opinion, and the 1996 legislation.
• Presenting studies that document Class I well failures, synthesizing various
studies of human health risks associated with Class I injection wells, and updating
a risk analysis using recent Class I injection well data.
• Providing an annotated bibliography of documents related to Class I injection
wells.
I.A Overview of Class I Wells
By definition, Class I wells inject industrial or municipal wastewater beneath the
lowermost USDW.5 An underground source of drinking water is an aquifer or portion of an
aquifer that supplies a public water system (PWS) or contains enough water to supply a PWS,
supplies drinking water for human consumption or contains water with less than 10,000 milli-
grams/liter of total dissolved solids (TDS), and is not exempted by EPA or state authorities from
protection as a source of drinking water.6 Class I wells are classified as hazardous or
nonhazardous, depending on the characteristics of the wastewaters injected.7 Class I wells
The UIC Program oversees four other classes of wells, in addition to Class I wells. Class II wells are used to dispose of
fluids which are brought to the surface in connection with oil or natural gas production, to inject fluids for enhanced recovery of
oil or natural gas, or to store hydrocarbons. Class III wells inject fluids for the extraction of minerals. Class IV wells inject
hazardous or radioactive waste into or above strata that contain a USDW (these wells are banned). Class V includes wells not
included in Classes I, II, III, or IV. Typical examples of Class V wells are agricultural drainage wells, storm water drainage
wells, industrial drainage wells, untreated sewage waste disposal wells, and cesspools.
6 40 CFR 144.3.
Hazardous wastes are defined at 40 CFR 261.
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Study of the Risks Associated with Class I UIC Wells
permitted to inject hazardous wastewater are referred to as hazardous wells; those that inject only
nonhazardous wastewater are known as nonhazardous wells. Class I wells used for disposal of
treated municipal sewage effluent are referred to as Class I municipal wells.
Many Class I wells inject wastewater associated with the chemical products, petroleum
refining, and metal products industries. Injected wastewaters vary significantly based on the
process from which they are derived. Some of the most common wastewaters are manufacturing
process wastewater, mining wastes, municipal effluent, and cooling tower and air scrubber
blowdown.
Class I municipal wells are found only in Florida, primarily due to a shortage of available
land for waste disposal, strict limitations on surface water discharges, the presence of highly
permeable injection zones, and cost considerations. Class I municipal wells inject sewage
effluent that has been subject to at least secondary treatment. These wells have been constructed
with well casings up to 30 inches in diameter to allow injection of large volumes of water (e.g.,
over 19 million gallons per day) at low pressures (e.g., about standard atmospheric pressure).
Class I municipal wells are not subject to the same strict requirements as other Class I wells.
This study does not address Class I municipal wells because they are not included in the Land
Disposal Program Flexibility Act's mandate to Study Class I injection.
Currently, there are 473 Class I wells in the United States, of which 123 are hazardous,
and 350 are nonhazardous or municipal wells. Most Class I wells are located in EPA Regions 6
(184 wells), 4 (134 wells), and 5 (53 wells). Texas has the greatest number of Class I hazardous
wells (64), followed by Louisiana (17). Florida has the greatest number of nonhazardous wells
(the majority of which are municipal wells), followed by Texas and Kansas. Exhibit 1 presents
the national distribution of hazardous and nonhazardous Class I wells; Exhibit 2 shows the
relative numbers of hazardous and nonhazardous Class I wells.
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Exhibit 1
Number of Class I Wells by State
I Primacy State *
I Direct Implementation State *
* See Section IV.B for explanation.
EPA Regions are outlined.
Number of wells in State denoted: Hazardous/Nonhazardous.
Source: EPA's Class I Well Inventory, 1999.
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Study of the Risks Associated with Class I UIC Wells
Exhibit 2
Hazardous and Nonhazardous Class I Wells
Hazardous
(123)
Nonhazardous
(350) *
I.B History of the UIC Program and Rulemakings Related to Class I Injection
Underground injection of wastewater began in the 1930s when oil companies began
disposing of oil field brines and other oil and gas waste products into depleted reservoirs. Most
of the early injection wells were oil production wells converted for wastewater disposal. In the
1950s, injection of hazardous chemical and steel industry wastes began. At that time, four Class I
wells were reported; by 1963, there were 30 wells. In the mid 1960s and 1970s, Class I injection
began to increase sharply, growing at a rate of more than 20 wells per year.
The 1980 UIC Regulations
Prior to EPA's regulation of Class I injection wells, several cases of well failures
occurred. The Hammermill Paper Company in Erie, PA, and the Velsicol Chemical Corporation
in Beaumont, TX, are two examples.
In April 1968, corrosion caused the casing of Hammermill Paper Company's
No. 1 well to rupture and spent pulping liquor to flow onto the land and enter
Lake Erie. Additionally, a noxious black liquid seeped from an abandoned gas
well at Presque Isle State Park, 5 miles away. The Pennsylvania Department of
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Study of the Risks Associated with Class I UIC Wells
Environmental Resources suspected (though never conclusively determined) that
wastewaters from Hammermiirs injection well migrated up the unplugged,
abandoned well bore.
• In 1974 and 1975 the Velsicol Chemical Company noted lower than normal
injection pressures in one of its two injection wells, which was designed without
tubing. In 1975, Velsicol shut down the well to determine the cause of the
decreased injection pressures, and an inspection revealed numerous leaks in the
well's casing. The company decided to plug the well and drill a new one. During
the course of the abandonment, Velsicol determined that contaminated
wastewater had leaked to a USDW. The wastewater was pumped from the
aquifer.
In 1974, responding to concerns about underground injection practices, EPA issued a
policy statement in which the Agency opposed underground injection "without strict control and
clear demonstration that such wastes will not interfere with present or potential use of subsurface
water supplies, contaminate interconnected surface waters or otherwise damage the
environment." In December 1974, Congress enacted the SDWA, which required EPA to set
requirements for protecting USDWs.
EPA promulgated the UIC regulations in 1980 based on the idea that, properly
constructed and operated, injection wells are a safe mechanism for disposing of liquid waste.
The SDWA provided a definition of an underground source of drinking water; the 1980 UIC
regulations categorized injection wells into five classes. The regulations established technical
requirements for siting, construction, operating, and closure of injection wells. These
regulations are described in section IVA.
The RCRA Hazardous and Solid Waste Amendments
In 1984, Congress enacted the Hazardous and Solid Waste Amendments (HSWA) to
RCRA, which banned the land disposal of hazardous waste, unless the hazardous waste is treated
to meet specific concentration-based or technology-based standards, or unless the hazardous
waste is injected into a land disposal unit that has an approved "no-migration" exemption.
Underground injection is included in the definition of land disposal methods that require
regulation at section 3004(k) of HSWA.
EPA amended the UIC regulations in 1988 to address the amendments to RCRA. The
1988 changes require operators of Class I hazardous wells to demonstrate through sophisticated
models that the hazardous constituents of the wastewater will not migrate from the disposal site
for 10,000 years, or as long as the wastewater remains hazardous. This demonstration is known
as a no-migration petition, which may be in the form of a fluid flow petition or a waste
transformation petition (see section IV. A for more on these demonstrations).
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Study of the Risks Associated with Class I UIC Wells
Once a no-migration petition is approved, an operator may inject only wastes that are
listed in the petition. Operators who do not successfully complete the petition process must
either treat their wastewater to acceptable levels, stop injecting, or implement pollution
prevention measures, as specified by EPA in the regulations. EPA's treatment standards are
based on the performance of the best demonstrated available technology (BDAT). EPA may also
set treatment standards as constituent concentration levels, and the operator may use any
technology not otherwise prohibited to treat the wastewater.
The Land Disposal Restrictions
HSWA also requires EPA to set dates to prohibit the land disposal of all hazardous
wastes (40 CFR 148 and 40 CFR 268). EPA was required to promulgate, by May 8, 1990, land
disposal prohibitions and treatment standards for all wastes that were either listed or identified as
hazardous at the time of the 1984 amendments. The Agency was also required to promulgate
prohibitions and standards for wastes listed or identified as hazardous after the 1984
amendments, within 6 months of the listing or identification of these wastes. EPA did not meet
all of these deadlines and, as a result, the Environmental Defense Fund (EDF) filed a lawsuit
which resulted in a consent decree outlining a schedule for adoption of prohibitions and
treatment standards for hazardous wastes (EDF v. Reilly, Cir. No. 89-0598, D.D.C). Various
wastes have been listed or identified as hazardous, and Congressionally mandated prohibitions
on land disposal of these wastes have been instituted in a phased-in schedule. Progress on each
phase of the Land Disposal Restriction (LDR) rulemakings is described below.
Phase I Rulemaking
Phase I included Congressionally mandated restrictions on spent solvents and dioxins,
hazardous wastes that were banned from land disposal by the State of California (known as
"California list" wastes), and an assessment of all the hazardous wastes listed in 40 CFR 261.
Since there were a large number of these wastes, this requirement was divided into three parts,
referred to as the first, second, and third-thirds wastes. The Third-Thirds rule, published in June
1990 (55 FR 22520, June 1, 1990), addressed regulation of characteristic wastes (i.e., wastes
considered hazardous because they exhibit a characteristic of ignitability, corrosivity, reactivity,
or toxicity). This rulemaking did not require treatment of underlying hazardous constituents
(UHCs) in these characteristic wastes, and it generally allowed for the use of dilution to remove
the characteristic in order to meet disposal standards.
In 1992, the D.C. Circuit court's opinion in Chemical Waste Management v. EPA, 976
F.2d 2 (D.C. Cir. 1992) essentially negated the 1990 Third-Thirds rule. In this decision, the
court made a number of rulings pertaining to treatment standards for characteristically hazardous
wastes. First, the court held that LDR requirements can continue to apply to characteristic
hazardous wastes even after they no longer exhibit a hazardous characteristic. Second, to satisfy
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Study of the Risks Associated with Class I UIC Wells
the requirements of RCRA section 3004(m) that address both short-term and long-term threats
posed by land disposal, the court held that it is not enough that short-term threats are addressed
(e.g., waste is rendered no longer corrosive). Instead, the court believed that long-term threats
posed by toxic underlying hazardous constituents contained in the characteristically hazardous
wastewater must be addressed. Third, the court held that dilution was not an acceptable means
of treating hazardous constituents because it did not remove, destroy, or immobilize hazardous
constituents.
This decision would have far-reaching implications for operators of Class I nonhazardous
wells because a large number of these wells inject decharacterized wastewaters (e.g.,
wastewaters rendered nonhazardous through treatment or commingling with other wastewaters).
These operators would have to reduce the UHCs to treatment standard levels through source
reduction and waste segregation and remove the characteristic which rendered the waste
hazardous.
Phase II and III Rulemakings
EPA published the Phase n LDR rule in September 1994. It established concentration-
based "universal treatment standards" (UTS) for 216 characteristic and listed wastes. The UTS
simplified treatment standards by setting uniform constituent concentration levels across all
types of wastes and replacing concentration standards, which could vary based on the type of
waste containing the constituents. These technology-based UTS may eventually be superseded,
or capped, by the proposed risk-based exit levels in the Hazardous Waste Identification Rule
(HWIR) (60 FR 66344, December 21, 1995).
In the Phase in Rule, as proposed in March 1995, the Agency suggested that Class I
operators could segregate their characteristically hazardous wastes and treat just that volume of
the wastewater to treatment standard levels in order to meet the treatment requirements.
However, a number of commenters on the proposed rule indicated segregation was both
technically and economically impractical due to the way wastewater is handled at Class I
facilities. Commenters also noted that segregation and treatment could pose greater human
health risks than underground injection. The other alternatives available to these operators were
to seek a no-migration variance, apply for a case-by-case capacity variance (in addition to an
existing national capacity variance), or reduce mass loadings of hazardous constituents by
instituting pollution prevention measures.
On March 26, 1996, President Clinton signed the Land Disposal Program Flexibility Act.
In effect, this legislation put back in place the approach adopted by EPA in the Third-Thirds rule
of 1990 on the disposal of decharacterized wastewater. The new legislation stated, in essence,
that hazardous wastes which are hazardous only because they exhibit a characteristic are not
prohibited from Class I nonhazardous well disposal if they no longer exhibit the characteristic at
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Study of the Risks Associated with Class I UIC Wells
the point of injection. The characteristic can be removed by any means, including dilution or
other deactivation through aggregation of different wastewaters. Operators of Class I
nonhazardous wells do not, therefore, have to identify and treat underlying hazardous
constituents. Nonhazardous Class I facilities injecting decharacterized wastewater would not be
reclassified as hazardous and would not have to make no-migration demonstrations or treat
underlying hazardous constituents in order to keep injecting these wastes. The legislation also
called for a study, to be completed within 5 years of the Act's passage, which would assess the
risks of land disposal and Class I underground injection of decharacterized wastes.
The final Phase m LDR rule, published in April 1996, implemented the Land Disposal
Program Flexibility Act by narrowing the applicability of UTS to decharacterized wastewaters
managed in Class I wells. The Phase m rule also addressed issues related to small quantity
generators by establishing a de minimis volume exclusion. Under this approach, Class I
operators could continue injecting small volumes of characteristically hazardous wastewaters
when mixed with a greater volume of nonhazardous waste. Class I facility wastewaters that meet
the de minimis standard must have hazardous waste constituent concentrations of less than 10
times the established UTS at the point of generation. In addition, the facility's hazardous
wastewater must account for less than 1 percent of the total flow at the point of injection and
after commingling with the nonhazardous streams. Finally, the total volume of the hazardous
streams must be no more than 10,000 gallons per day.
Phase IV Rulemaking
EPA published the Phase IV LDR rule on May 12, 1997 and May 26, 1998, establishing
treatment standards and land disposal restrictions for wood preserving, toxicity characteristic
metals, and mineral processing wastewaters. EPA estimated that the economic impact of
restricting these wastes from disposal in Class I wells is minimal. Although the annual volume
of Phase IV wastes is small, treatment capacity is not readily available or applicable because
Phase IV wastes are process wastes injected on-site. Meeting no-migration demonstrations or
other proposed management options may be difficult for most facilities at this time. A 2-year
capacity variance has been granted to deal with the lack of treatment capacity.
II. Technology Summary
Injection engineering technology, regional and local geologic characterization, and site-
specific mathematical modeling are combined to ensure that injected fluids from Class I wells
travel to their intended location safely away from USDWs, and remain there for as long as they
pose a risk to human health or the environment.
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Study of the Risks Associated with Class I UIC Wells
II.A Injection Well Technology
Class I wells are designed and constructed to prevent the movement of injected
wastewaters into USDWs. Wells typically consist of three or more concentric layers of pipe:
surface casing, long string casing, and injection tubing.8 Exhibit 3 shows the key construction
elements of a typical Class I well.
The well's casing prevents the borehole from caving in and contains the tubing. It
typically is constructed of a corrosion-resistant material such as steel or fiberglass-reinforced
plastic. Surface casing is the outermost of the three protective layers; it extends from the
surface to below the lowermost USDW. The long string casing extends from the surface to or
through the injection zone. The long string casing terminates in the injection zone with a
screened, perforated, or open-hole completion, where injected fluids exit the tubing and enter
the receiving formation. The well casing design and materials vary based on the physical and
chemical nature of injected and naturally occurring fluids in the rock formation, as well as the
formation's characteristics. The wastewater must be compatible with the well materials that
come into contact with it. Cement made of latex, mineral blends, or epoxy is used to seal and
support the casing.
The characteristics of the receiving formation determine the appropriate well completion
assembly—a perforated or screen assembly is appropriate for unconsolidated formations such as
sand and gravel, while an open-hole completion is used in wells that inject into consolidated
sandstones or limestone.
The innermost layer of the well, the injection tubing, conducts injected wastewater from
the surface to the injection zone. Because it is in continuous contact with wastewater, the tubing
is constructed of corrosion-resistant material (e.g., steel and high-nickel alloys, fiberglass-
reinforced plastic, coated or lined alloy steel, or more exotic elements such as zirconium,
tantalum, or titanium).
The annular space between the tubing and the long string casing, sealed at the bottom by
a packer and at the top by the wellhead, isolates the casing from injected wastewater and creates
a fluid-tight seal. The packer is a mechanical device set immediately above the injection zone
that seals the outside of the tubing to the inside of the long string casing. The packer may be a
simple mechanically set rubber device or a complex concentric seal assembly. Constant pressure
is maintained in the annular space; this pressure is continuously monitored to verify the well's
mechanical integrity and proper operational conditions.
All three layers are required of Class I hazardous wells [40 CFR 146.65(c)].
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Study of the Risks Associated with Class I UIC Wells
Exhibit 3
A Typical Class I Injection Well
Monitoring of
inject ion
flow
regulatory
compliant*.
of and
aquifers.
A pressurtzed
''amiulus"
is
continuously
to
itafcE.
Drinkmq Aquifer
Protective
continue to the
I poorly permeatote
confining layer
flow of wastes
in trie
myeh like millian-
ycnr-gld oil gas
deposits.
The packer seals
the to the
wastes convert
into harmful
substances.
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Study of the Risks Associated with Class I UIC Wells
II.B Geologic Siting
In addition to the multiple safeguards of the injection well design, the geologic properties
of the subsurface around the well offer a final safeguard against the movement of injected
wastewaters to a USDW. Class I wells are sited so that, should any of their components fail, the
injected fluids would be confined to the intended subsurface layer.
Class I wells inject into zones with the proper configuration of rock types to ensure that
they can safely receive injected fluids. The geological formation into which the wastewaters are
injected is known as the injection zone. Extensive pre-siting geological tests confirm that the
injection zone is of sufficient lateral extent and thickness and is sufficiently porous and
permeable so that the fluids injected through the well can enter the rock formation without an
excessive build up of pressure and possible displacement of injected fluids outside of the
intended zone. The injection zone is overlain by one or more layers of relatively impermeable
rock that will hold injected fluids in place and not allow them to move vertically toward a
USDW; this rock layer(s) defines the confining zone. Confining zones are typically composed
of shales, which are "plastic," meaning they are less likely to be fractured than more brittle
rocks, such as sandstones.
Class I fluids are injected deep into the earth into brine-saturated formations or non-
freshwater zones. The typical Class I well injects wastewaters into geologic formations
thousands of feet below the land surface. In the Great Lakes region, injection well depths
typically range from 1,700 to 6,000 feet; in the Gulf Coast, depths range from 2,200 to 12,000
feet or more. Fluids at these depths move very slowly, on the order of a few feet per hundred or
even thousand years, meaning that fluids injected into the deep subsurface are likely to remain
confined for a long time.
Class I hazardous wells are located in geologically stable areas. The operator of a well
must demonstrate that there are no transmissive fractures or faults9 in the confining rock layer(s)
through which injected fluids could travel to drinking water sources. Well operators also must
show that there are no wells or other artificial pathways between the injection zone and USDWs
through which fluids can travel. EPA regulations prevent Class I hazardous wells from being
sited in areas where earthquakes could occur and compromise the ability of the injection zone
and confining zone to contain injected fluids.
A transmissive fracture or fault is one that has sufficient permeability and vertical extent to allow movement of fluids
between formations.
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Study of the Risks Associated with Class I UIC Wells
II.C Class I Well Risks
There are two potential pathways through which injected fluids can migrate to USDWs:
(1) failure of the well or (2) improperly plugged or completed wells or other pathways near the
well. EPA's extensive technical requirements for Class I wells are designed to prevent
contamination of USDWs via these pathways.
Well Failure
Contamination due to well failure is caused by leaks in the well tubing and casing or
when injected fluid is forced upward between the well's outer casing and the well bore should
the well lose mechanical integrity (MI). Internal mechanical integrity is the absence of
significant leakage in the injection tubing, casing, or packer. An internal mechanical integrity
failure can result from corrosion or mechanical failure of the tubular and casing materials.
External mechanical integrity is the absence of significant flow along the outside of the casing.
Failure of the well's external mechanical integrity occurs when fluid moves up the outside of the
well due to failure or improper installation of the cement. To reduce the potential threat of well
failures, operators must demonstrate that there is no significant leak or fluid movement through
channels adjacent to the well bore before the well is issued a permit and allowed to operate. In
addition, operators must conduct appropriate mechanical integrity tests (MITs) every year (for
hazardous wells) and every 5 years (for nonhazardous wells) thereafter to ensure the wells have
internal and external MI and are fit for operation. It is important to note that failure of an MIT,
or even a loss of MI, does not necessarily mean that wastewater will escape the injection zone.
Class I wells have redundant safety systems to guard against loss of waste confinement (see
section m.A for further discussion).
Pathways for Fluid Movement in the Area of Review
The Area of Review (AoR) is the zone of endangering influence around the well, or the
radius at which pressure due to injection may cause the migration of the injectate and/or
formation fluid into a USDW. Improperly plugged or completed wells that penetrate the confin-
ing zone near the injection well can provide a pathway for fluids to travel from the injection zone
to USDWs. These potential pathways are most common in areas of oil and gas exploration. Be-
cause the geologic requirements for Class I hazardous injection activities are similar to those for
oil and gas exploration, these activities often take place in the same areas. EPA estimates that
there may be as many as 300,000 abandoned wells and 100,000 producing wells potentially in
the AoRs of Class I injection wells.
To protect against migration through this pathway, wells that penetrate the zone affected
by injection pressure must be properly constructed or plugged. Before injecting, operators must
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Study of the Risks Associated with Class I UIC Wells
identify all wells within the AoR that penetrate the injection or confining zone, and repair all
wells that are improperly completed or plugged before a permit is issued.
Fluids could potentially be forced upward from the injection zone through transmissive
faults or fractures in the confining beds which, like abandoned wells, can act as pathways for
waste migration to USDWs. Faults or fractures may have formed naturally prior to injection or
may be created by the waste dissolving the rocks of the confining zone. Artificial fractures may
also be created by injecting wastewater at excessive pressures. To reduce this risk, injection
wells are sited such that they inject below a confining bed that is free of known transmissive
faults or fractures. In addition, during well operation, operators must monitor injection pressures
to ensure that fractures are not propagated in the injection zone or initiated in the confining zone.
II.D Introduction to Modeling
Site-specific modeling of wastewater migration is the foundation of a no-migration
demonstration that hazardous wastewaters will remain in the injection zone for as long as they
remain hazardous. Models are also the basis on which the requirements for hazardous and
nonhazardous waste disposal were developed. A long-term analysis is the only way to know with
absolute certainty what will happen to injected fluids; however this is impractical, given the time
frames involved in movement of deep-injected fluids. The purpose of modeling is to provide
long-term prediction of the extent of injected wastewater migration at great depths and
demonstrate, using conservative assumptions, that the wastewater will remain contained or
rendered nonhazardous. Modeling is based on rigorous science, and models are well-established
scientific tools. All of the models on which studies and no-migration petitions are based are
accepted by the scientific and regulatory communities.
The modeling process has several components: the conceptual model, the mathematical
model or equations, and the numerical model or computer code used to solve the equations. In
general, modeling is a conceptual representation, using simplifying assumptions about the
injection well, the surrounding formation, and well operations. The mathematical model
involves equations to represent the conservation of mass and momentum. The equations
simulate fluid pressure and chemical or constituent concentration levels changes over time.
Because of the difficulty in measuring the slow movement of fluids over long time periods (i.e.,
10,000 years at great depths), the injection and emplacement of the wastewater is modeled
mathematically using complex computer simulations.
The conceptual model is a simplified representation of the geologic strata in the vicinity
of the injection well. It is envisioned that the well operations include wastewater injection
operations, based on both the actual operational history of the site and future injection
conditions. In addition, the model includes a post-operation period of 10,000 years in which the
wastewater will migrate from the point of emplacement in the injection zone. Several processes
are considered in the conceptual model, including pressure build-up, fluid displacement, mixing
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Study of the Risks Associated with Class I UIC Wells
or dispersion of the injected wastewater and the native formation fluids, and fluid density
differences.
Mathematical models are used to simulate the injection and migration of fluids within the
injection zone. These models include fluid flow and dissolved contaminant transport within
geologic materials using mathematical expressions based on the physical principles associated
with the geology and the native (in situ) and injected fluids. Within the model, the injection
zone and the confining zone are defined by subdividing the region into series of adjoining
"cells." The lateral extent of the model is often several miles wide. The cells or blocks are
defined in order to segment the region both vertically and laterally. Each cell within the
modeled region has defined geologic parameters and fluid properties including permeability,
porosity, compressibility, dispersivity, fluid density and viscosity. The mathematical models
solve for the fluid pressure and chemical concentration. Realistic modeling requires considerable
knowledge about the fluid properties of the injectate and the physical properties of the rock
formation, all of which serve as inputs to the model. It is also possible to mathematically
simulate chemical interactions between the injected fluids, the native fluids, and the geologic
formation. More complex models also include a representation of the complex geologic
structure through a series of surface and subsurface maps.
The models or computer codes are used to simulate the effects of injecting fluids at some
initial time into one or more of the cells and predict the flow and chemical concentration
transferred from cell to cell over an extended period of time. Many calculations take place in the
model. At each time step (i.e., from the start of the injection operations to 10,000 years), the
model must track the new amount of wastewater injected, the flow and chemical flux into
adjacent cells, and the subsequent flow and chemical flux from cell to cell. There may be
thousands of cells in a model, and the flow and chemical flux must be calculated for every side
of each cell. The model tracks the mass of the fluids, the fluid density and viscosity, chemical
concentrations, and temperature of rock and water within every cell at specified times.
Models are constructed based on field observations and measurements of downhole
pressure, surface injection pressure, geophysical logs, rock cores extracted from depth,
injectivity tests, pressure fall-off test, tracer surveys, injection chemical concentration, and fluid
density. The process of model calibration is a fitting of the input parameters in order to match
field conditions. For example, pressure fall-off tests may be analyzed using analytical tools for
injection zone permeability. The values for permeability are used as inputs from one fall-off test
and then compared with field observations from another test. The input parameters are then
adjusted to afford the best possible match with field conditions. Conservative assumptions are
embedded throughout the model construction, so that the model predicts the maximum extent of
wastewater migration.
The results of the model are verified against actual data from the field (i.e., data from
pressure tests, drawdown or build-up tests). Typically, model verification does not address
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Study of the Risks Associated with Class I UIC Wells
concentration levels. Occasionally, new wells are constructed near existing injection wells, and
model verification of the existing wastewater plume can be performed. Because the model is
predictive over a long time scale and the geologic materials are naturally variable, a conservative
model is designed to address the issue of variability in the model parameters and fluid motion
within the injection zone through a series of analyses. Multiple simulations or computer runs
using differing input parameters are generally performed to assess variations in the predicted
outcome. Moreover, it is preferable for the models to use conservative assumptions to predict
worse-case scenarios and reflect the high degree of uncertainty in the no-migration
demonstrations (40 CFR 148.21). This worst-case scenario brackets the outer limits of the fluid
migration within the area of investigation.
When the modeling analysis is complete, the output is typically a series of graphs and
maps that depict the amount of fluid pressure increase and the concentration of the injected fluid
within the injection zone. Although the conditions at the final time step (10,000 years) are the
objective, it is possible to show the physical position of injected fluids at any specified time.
Numerous models or codes are based on work by the United States Geologic Survey,
EPA, U.S. Department of Defense, U.S. Army Corps of Engineers, many universities and
colleges, and the oil and gas industry. These are distributed commercially, and many are
available for free on the Internet. The models have evolved in their complexity and ability to
represent the real world, from simple displacement approaches to models incorporating
molecular diffusion and variable pressure responses.
III. Options for Decharacterized Wastewaters
Under RCRA, wastewaters that demonstrate the characteristic of ignitability, corrosivity,
reactivity, or toxicity are considered to be hazardous wastes.
Ignitable wastes are capable of causing fire through friction at standard
temperature or pressure. Ignitable wastes are produced by the organic chemical
production, laboratories and hospitals, paint manufacturing, cosmetics and
fragrances, pulp and paper, and construction industries.
Corrosive wastes are extremely acidic or alkaline (i.e., have a pH less than or
equal to 2 or greater than or equal to 12.5). The organic chemical production,
laboratories and hospitals, paint manufacturing, cosmetics and fragrances,
equipment cleaning, soaps and detergents, electronics manufacturing, iron and
steel, and pulp and paper industries produce corrosive wastes.
Reactive wastes are normally unstable wastes that react violently or form
potentially explosive mixtures with water. Examples of industries that produce
reactive wastes include organic chemical production and petroleum refining.
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Study of the Risks Associated with Class I UIC Wells
Toxic organic wastes contain toxic constituents in excess of a regulatory level.
They are produced by organic chemical production, petroleum refining, and waste
management and refuse systems.
Characteristic hazardous wastes are identified with waste codes D001 through D043. These
waste codes are used for record keeping, tracking off-site shipments, and determining the
applicability of the LDR program.
Prior to disposal in a Class I nonhazardous well, hazardous wastewaters must be
decharacterized (i.e., the hazardous characteristic must be removed) by any means including
treatment, dilution, or other deactivation through aggregation of different wastewaters, including
commingling with nonhazardous or exempt wastewaters. The Class I nonhazardous wells, into
which the decharacterized wastewater is injected, must conform with all federal and state UIC
regulations. The management of these wastewaters by Class I injection well operators provides a
low-risk option, as will be described in the next sections of this study.
In addition, from a general analysis of data from previous studies, including databases
specific to Class I nonhazardous and hazardous injection wells, EPA believes that a substantial
volume of decharacterized waste is being injected into Class I hazardous wells. Facilities using
Class I injection wells, including industrial, manufacturing, petrochemical, and refinery
operations, will generally use their Class I hazardous wells to dispose of wastewaters from their
process operations which may not be amenable to segregation. They can use their Class I
hazardous wells for disposal of any wastewaters allowed by their permits, and included in their
no-migration petition demonstration (permitting and no-migration petitions will also be
discussed later in this study). This practice affords an even greater (though not essential) level
of protection, as the Class I hazardous waste wells have additional operating, monitoring, and
other redundant safety requirements beyond the already protective requirements of the Class I
nonhazardous wells.
IV. Oversight of Class I Wells
This section describes how EPA oversees the Class I program. Section IV. A describes the
Agency's regulations for siting, constructing, operating, monitoring and testing, and closing
Class I wells. Section IV.B describes how EPA Headquarters and regions oversee Class I
injection practices.
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Study of the Risks Associated with Class I UIC Wells
IV.A Regulations and Criteria for Class I Wells
EPA's siting, construction, operating, monitoring, and closure requirements for Class I
wells provide multiple safeguards against well leakage or the movement of injected wastewaters
to USDWs. The following sections describe the Class I Program regulations (40 CFR 146 and
148).
Siting Requirements
Class I wells must be sited so that wastewaters are injected into a formation that is below
the lowermost formation containing, within one-quarter mile of the well, a USDW [40 CFR
146.12(a); 40 CFR 146.62(a)]. In siting Class I wells, operators must use geologic and
hydrogeologic studies and studies of artificial penetrations of the injection and confining zones
to demonstrate that their proposed injection will not endanger USDWs. In addition, Class I
operators seeking to inject hazardous wastewaters must demonstrate via a no-migration petition
that the hazardous constituents of wastewaters will not migrate from the disposal site for as long
as the wastewaters remain hazardous.
Additional siting requirements are imposed on Class I hazardous wells to ensure that they
are located in geologically stable (e.g., low risk of earthquakes) formations that are free of
natural or artificial pathways for fluid movement between the injection zone and USDWs.
Geologic Studies
Studies of the injection and confining zones are conducted to ensure that Class I wells are
sited in geologically suitable areas. Well permitting decisions are based on whether the
receiving formations are sufficiently permeable, porous, and thick to accept the injected fluids at
the proposed injection rate without requiring excessive pressure. The injection zone should be
homogeneous. It should also be of sufficient area! extent to minimize formation pressure
buildup and to prevent injected fluids from reaching aquifer recharge areas. The confining zone
should be of relatively low permeability to prevent upward movement of injected materials.
For Class I hazardous wells, additional structural studies must demonstrate that the
injection and confining formations in the area around the well are free of vertically transmissive
fissures or faults, and that the region is characterized by low seismicity and a low probability of
earthquakes. The operator must demonstrate that the proposed injection will not induce
earthquakes or increase the frequency of naturally occurring earthquakes.
Injected fluids must be geochemically compatible with the well materials and the rock
and fluids in the injection and confining zones. The injection zone must have no economic value
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Study of the Risks Associated with Class I UIC Wells
(i.e., be unfit for drinking or agricultural purposes and lack dissolved minerals in economically
valuable quantities).
Operators must demonstrate that the wastewater and its anticipated reaction products are
compatible with both the geologic material of the injection zone and any native (naturally
occurring) or previously injected fluids. Water analyses must be performed to characterize the
geochemistry of the native water to predict potential interactions, and to provide a baseline to
determine whether contamination has occurred.
Area of Review
The AoR, or the zone of endangering influence (the radius at which injection can affect a
USDW), must be determined by either a fixed radius or mathematical computation.10 When a
fixed radius is used, the AoR for Class I nonhazardous wells and municipal wells must be, at a
minimum, one-quarter mile [40 CFR 146.69(b)]; for hazardous wells, the AoR is extended to, at
a minimum, 2 miles [40 CFR 146.63]. It is important to note, however, that for many Class I
nonhazardous wells, the radius of the AoR studied was larger than the federally-required one-
quarter mile. Seventy-six percent of the wells studied by the Underground Injection Practices
Council (UIPC) had an area of review that exceeded one-quarter mile.11 Several states require an
AoR for all Class I wells that is larger than that required under the federal regulations. For
example, Texas requires a minimum 2/^-mile AoR; Louisiana requires a 2-mile AoR; and
Florida and Kansas regulations establish a 1-mile minimum. These four states collectively
account for nearly 70 percent of the Class I well inventory.
Operators must identify all wells within the AoR that penetrate the injection or confining
zone, and determine whether any of these wells are improperly completed or plugged and thus
could serve as pathways for migration of wastewaters. Along with the permit application, the
operator must submit a corrective action plan containing the necessary steps or modifications to
address improperly completed or plugged wells [40 CFR 144.55(a)]. The plan must take into
account the nature of native fluids or injection byproducts, potentially affected populations,
geology and hydrogeology, and the history of injection activities. Prior to commencing
injection, the operator must demonstrate that all potential pathways for migration have been
adequately addressed.
The zone of endangering influence may be determined via computations as specified at 40 CFR 146.6 for Class I
nonhazardous wells, or at 40 CFR 146.61(b) for Class I hazardous wells. For hazardous wells, the computations specified in 40
CFR 146.6 are superseded by the requirement for a 2-mile radius, at 40 CFR 146.63 (whichever is greater).
Underground Injection Practices Council. A Class I Injection Well Survey (Phase I Report): Survey of Selected Sites.
D19976.S1. Prepared by CH2M Hill, Gainesville, Florida. April 1986.
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Study of the Risks Associated with Class I UIC Wells
No-Migration Petition
In addition to geological and AoR studies, operators of Class I hazardous waste injection
wells must demonstrate with reasonable certainty that the hazardous components of their
wastewaters will not migrate from the injection zone [40 CFR 148.20].
To qualify for this exemption from the ban on disposal of certain wastes, EPA requires
operators to show that the wastewaters will remain in the injection zone for as long as they
remain hazardous, or that the wastes will decompose or otherwise be attenuated to nonhazardous
levels before they migrate from the injection zone. A detailed hydrogeological and geochemical
modeling study, known as a no-migration petition, may take one of the following forms:
A Fluid Flow Petition demonstrating that for at least 10,000 years12 no lateral
movement to a pathway to a USDW or vertical movement out of the injection
zone will occur. Petitioners must demonstrate that the strata in the injection zone
above the injection interval are free of transmissive faults or fractures and that a
confining zone is present above the injection interval.
A Waste Transformation Petition to demonstrate that attenuation,
transformation, or immobilization will render wastes nonhazardous before they
migrate from the injection zone. Petitioners must demonstrate that the zone
where transformation, attenuation, or immobilization will occur is free of
transmissive faults or fractures and that a confining zone is present above the
injection interval.
Each petition is a multi-volume complex technical analysis which describes the well
construction, the injected wastewater, and the local and regional geology and hydrogeology. It
relies on conservative mathematical models demonstrating that the hazardous wastewater will
not migrate from the injection zone into USDWs. Once a no-migration petition is approved, an
operator may inject only those wastes that are listed in the petition. (See section n.D for a
description of the modeling for no-migration petitions.)
Preparing a no-migration petition is a lengthy process which typically costs $300,000 and
requires up to 11,000 hours of technical work by engineers, computer modelers, geochemists,
geologists, and other scientists. Factoring in the cost of necessary geological testing and
modeling, no-migration petitions can cost in excess of $2 million.
The 10,000-year standard is considered sufficiently long to ensure that the no-migration standard would be met, and short
enough to be within the abilities of predictive models. [NRDC v EPA, 907 F.2d at 1158 .]
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Study of the Risks Associated with Class I UIC Wells
Summary of Siting Requirements13
Hazardous Wells
Nonhazardous Wells
2-mile AoR study performed.
No-migration petition
demonstration required.
Sited in demonstrated
geologically-stable areas.
Additional geologic structural
and seismicity studies
performed.
%-mile AoR study performed (a
larger AoR study may be
conducted if required by state
regulations).
Sited in demonstrated
geologically-stable areas.
Construction Requirements
EPA requires that Class I wells be designed and constructed to prevent the movement of
injected wastewaters into USDWs. Construction requirements for Class I nonhazardous wells
and municipal wells are set forth at 40 CFR 146.12; construction requirements for hazardous
wells are specified at 40 CFR 146.65 and 40 CFR 146.66. These requirements specify the multi-
layer design of Class I wells, as described in section n.A.
During the permit application process, the permitting authority reviews and approves
engineering schematics and subsurface construction details. The design of the casing, tubing,
and packer must be based on the depth of the well; the chemical and physical characteristics of
the injected fluids; injection and annular pressure; the rate, temperature, and volume of injected
fluid; the size of the well casing [40 CFR 146.12(c)(2)]; and cementing requirements (40 CFR
146.65). Any changes to the proposed design during construction must be approved before
being implemented.
During well construction, operators conduct deviation checks at sufficiently frequent
intervals to ensure that there are no diverging holes which would allow vertical migration of
fluids. Other logs and tests (e.g., resistivity or temperature logs) also may be required during
construction. EPA or the permitting authority may witness portions of construction activities.
13
Decharacterized waste is injected into Class I nonhazardous wells (although it may be injected into both hazardous and
nonhazardous wells). Requirements for both Class I hazardous and nonhazardous wells are presented in this report for
comparison and to provide a complete portrayal of the UIC Program. It should be noted that some states impose some of the
federal Class I hazardous well requirements on nonhazardous wells.
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Study of the Risks Associated with Class I UIC Wells
Summary of Construction Requirements
Hazardous Wells
Well is cased and cemented to
prevent movement of fluids into
USDWs.
Detailed requirements for
appropriate tubing and packer.
UIC Program director must approve
casing, cement, tubing and packer
design prior to construction.
Nonhazardous Wells
Well is cased and cemented to
prevent movement of fluids into
USDWs.
Constructed with tubing and packer
appropriate for injected wastewater.
Operating Requirements
EPA's operating requirements for Class I wells provide multiple safeguards to ensure that
injected wastewater is fully confined within the injection zone and the integrity of the confining
zone is never compromised. At a minimum, all Class I wells must be operated so that injection
pressures will not initiate new fractures or propagate existing fractures after initial stimulation of
the injection zone during well construction.
The annular space between the tubing and the long string casing must contain approved
fluids only and permitted pressures must be maintained.14 Class I hazardous wells are subject to
additional or more explicit permitting requirements and operating standards related to annular
monitoring parameters and continuous demonstration of mechanical integrity.15
Class I hazardous wells must be equipped with continuous monitoring and recording devices
that automatically sound alarms and shut-in the well whenever operating parameters related to
the injection pressure, flow rate, volume, temperature of the injected fluid, or annular pressure
exceed permitted ranges.16 When this occurs, the owner or operator must cease injection; notify
the Director within 24 hours; and identify, analyze, and correct the problem. Operators of Class
I wells are required to notify the UIC Program Director and obtain approval before performing
14
40CFR146.13(a).
40 CFR 146.67 (a) to (e).
40 CFR 146.67 (f), (g), and (j).
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Study of the Risks Associated with Class I UIC Wells
any workover or major maintenance on the well.17 The operator may resume injection only upon
approval of the Director.
Summary of Operating Requirements
Hazardous Wells
Continuously monitor injection
pressure, flow rate, and volume.
Install alarms and devices that shut-
in the well if approved injection
parameters are exceeded.
Maintain injection at pressures that
will not initiate new fractures or
propagate existing fractures.
Nonhazardous Wells
Continuously monitor injection
pressure, flow rate, and volume.
Maintain injection at pressures that
will not initiate new fractures or
propagate existing fractures.
Monitoring and Testing Requirements
Operators of Class I wells must monitor and test for mechanical integrity, containment
within the injection zone, and characteristics of the injected wastewater. They must also monitor
USDWs within the AoR for indications of fluid migration and pressure changes indicating a
potential for contamination.18
Class I well operators must continuously monitor injection pressure, flow rates and
volumes, and annular pressure.19 Monitoring requirements for Class I hazardous wells have
explicit procedures for reporting and correcting problems related to a lack of mechanical
integrity or evidence of wastewater injection into unauthorized zones. In addition to monitoring
the well operation, operators of hazardous wells are required to develop and follow a waste
analysis plan for monitoring the physical and chemical properties of the injected wastewater.20
The frequency of these analyses depends on the parameters being monitored. Complete analysis
of the injected wastewaters must be conducted at frequencies specified by the plan or when
process or operating changes affect the characteristics of the wastewater.
17 A
18
19
40 CFR 146.67 (j).
40CFR146.13(b)(4).
40 CFR 146.13 (b).
40 CFR 146.68 (a).
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Study of the Risks Associated with Class I UIC Wells
Operators of Class I hazardous wells must perform tests to demonstrate that the
wastewater's characteristics remain consistent and compatible with well materials with the
wastewater.21
Periodic testing of all Class I wells also is required.22 The operator must develop a
monitoring program that includes, at minimum, an annual pressure fall-off test in addition to an
internal MIT every year and an external MIT every 5 years. (Texas and Michigan require
external MITs every year.)
Class I operators must conduct tests to demonstrate that their wells have internal and
external mechanical integrity.23 Every year, operators of Class I hazardous wells must
demonstrate internal mechanical integrity by conducting an approved pressure test to inspect the
long string casing, injection tubing, and annular seal, as well as an approved radioactive tracer
survey (RTS) or Oxygen Activation Log (OAL)24 to examine the bottom hole cement. Operators
of Class I nonhazardous wells must demonstrate internal MI every 5 years. Every 5 years, all
Class I well operators must demonstrate external MI using noise, temperature, or other approved
logs to test for fluid movement along the borehole. Casing inspection logs or noise, temperature,
or other approved logs are also required when a well workover is conducted, or if the Director
believes that the long string casing lacks integrity.
An internal or external MI failure does not imply failure of the injection well or loss of
wastewater confinement. These are simply indicators that one of several protective layers in the
injection well system has malfunctioned. As long as the other protective elements are intact,
wastewaters would be contained within the injection system.
UIC regulations authorize the use of monitoring wells in the AoR to monitor fluids and
pressure. Monitoring wells can be used to supplement required injection and pressure
monitoring if needed. The location, target formation, and the types of monitoring wells should
21 40 CFR 146.68 (c).
22 40 CFR 146.13 (d) and 40 CFR 146.68 (e).
23 40 CFR 146.13 (b) and 146.68 (b).
The OAL has been approved as an alternative to the RTS to test for movement of fluids between the casing and the well
bore. Case studies by EPA Region 6 indicate that the RTS and the OAL are equally effective in identifying channels behind the
casing, which are in hydraulic communication with the injection zone. The OAL is a preferred method where channeling is not
in hydraulic communication with the injection interval. EPA Region 6 has also requested the use of the OAL to increase
confidence in MIT results.
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Study of the Risks Associated with Class I UIC Wells
be based on potential pathways of contaminant migration. Monitoring within the USDW can
provide geologic data or evidence of contamination.25
Summary of Monitoring and Testing Requirements
Hazardous Wells
Follow approved waste analysis
plan.
Conduct internal MIT every year
and external MIT every five
years.
Monitoring wells to supplement
required monitoring are
authorized.
Nonhazardous Wells
Conduct internal and external
MITs every 5 years.
Monitoring wells to supplement
required monitoring are
authorized.
Reporting and Record Keeping Requirements
All Class I well operators must report the results of required monitoring and testing to the
state or EPA UIC Director. Class I hazardous well operators must report quarterly on monitoring
results and annually on the results of radioactive tracer surveys, casing pressure tests, ambient
monitoring, and pressure fall-off tests. They must also report any changes to closure plans,
including updates to plugging and abandonment cost estimates.
All Class I operators must report on the physical, chemical, and other relevant
characteristics of injected fluids; monthly average, maximum, and minimum values for injection
pressure, flow rate, volume, and annular pressure; and monitoring results of USDWs in the
AoR.26 MIT results, other required tests, and any well workovers must be reported in the next
quarterly report following the tests or workovers.
Quarterly reports on Class I hazardous wells must also identify the maximum injection
pressure for the quarter, any event that exceeds permitted annular or injection pressure, any event
that triggers an alarm or shutdown from the continuous recording device, the total volume of
fluid injected, any change in the annular fluid volume, results from the waste analysis program,
and geochemical compatibility information.27
Warner, D. L. "Monitoring of Class I Injection Wells." In: Deep Injection Disposal of Hazardous and Industrial Waste:
Scientific and Engineering Aspects. John A. Apps and Chin-Fu Tsang, eds. San Diego, California: Academic Press. 1996.
26
40CFR146.13(c).
40 CFR 146.69.
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Study of the Risks Associated with Class I UIC Wells
In states where EPA administers the UIC program, the Regional Administrator may
require operators to submit additional information, if needed to determine if a well poses a
hazard to USDWs. Such information may include evidence of groundwater monitoring and
periodic reports of such monitoring, periodic reports on analysis of injected fluids, and a
description of the geologic strata through and into which injection is taking place.
In addition, all operators must notify the permitting authority of planned changes to the
facility, changes that may result in noncompliance, progress in meeting the milestones of a
compliance schedule, any loss of mechanical integrity or other indication of possible
endangerment of a USDW (within 24 hours), and any noncompliance with permit conditions.
Summary of Reporting and Record Keeping Requirements
Hazardous Wells
Nonhazardous Wells
Report quarterly on injection and
injected fluids and monitoring of
USDWs in the AoR; results from the
waste analysis program; and
geochemical compatibility.
Report on internal MIT every year and
external MIT every 5 years.
Report any changes to the facility,
progress in meeting the milestones of
a compliance schedule, loss of Ml, or
noncompliance with permit conditions.
Report quarterly on injection and
injected fluids and monitoring of
USDWs in the AoR.
Report every 5 years on internal and
external MITs.
Report any changes to the facility,
progress in meeting the milestones of
a compliance schedule, loss of Ml, or
noncompliance with permit conditions.
Closure Requirements
Upon closing their wells, operators must submit a plugging and abandonment report
indicating that the well was plugged in accordance with the plugging and abandonment plan
(submitted when the well was permitted). Plan requirements and subsequent closure reporting
requirements are specified in greater detail for hazardous wells than for nonhazardous wells.
Class I hazardous well operators must also conduct pressure fall-off and mechanical
integrity tests, and report the results in their closure reports. The well must be flushed with a
non-reactive fluid. Each cement plug must be tagged and tested for seal and stability before the
closure is completed.28 In addition, Class I hazardous well operators are required to continue and
complete outstanding clean-up actions, and continue groundwater monitoring until pressure in
/5 40 CFR 146.71.
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Study of the Risks Associated with Class I UIC Wells
the injection zone decays to the point where no potential for influencing the USDW exists. They
must also notify and provide appropriate information to local and state authorities regarding the
well, its location, and its zone of influence at closure.29
Summary of Closure Requirements
Hazardous Wells
Nonhazardous Wells
Flush well with a non-reactive fluid;
tag and test each cement plug.
Conduct pressure fall-off test and
MIT.
Submit plugging and abandonment
report.
Complete outstanding clean-up
actions; continue groundwater
monitoring until injection zone
pressure can not influence USDW.
Inform authorities of the well, its
location, and zone of influence.
Flush well with a non-reactive fluid;
tag and test each cement plug.
Submit plugging and abandonment
report.
IV.B How EPA Administers the Class I UIC Program
Class I wells are regulated under the SDWA to ensure protection of USDWs. Class I
hazardous wells also are regulated under RCRA and HSWA. They are subject to the ban on land
disposal of certain wastes, unless owners/operators of these wells demonstrate via a no-migration
petition that the wastewaters will not migrate from the injection zone for 10,000 years or as long
as they remain hazardous.
EPA authorizes state agencies to regulate Class I wells, provided that the state meets
requirements specified under section 1422 of the SDWA. States that receive primary regulatory
and enforcement responsibility are referred to as primacy states. EPA regional offices administer
the UIC program for tribes30 and in states that do not have primacy authority, commonly referred
to as direct implementation (DI) states.
29
40 CFR 146.72.
There are no Class I wells on Indian lands.
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Study of the Risks Associated with Class I UIC Wells
Operators in primacy states submit data to the primacy agency, and the primacy agencies
forward this information to the regions. Operators in DI states submit data directly to the EPA
region. The regions forward appropriate information to EPA Headquarters.
EPA Headquarters' Management of the National Program
EPA Headquarters is responsible for performing a variety of rulemaking activities, as
well as other analytical and oversight functions, for the UIC program. Headquarters UIC staff
coordinate with the EPA Office of Solid Waste on LDR rulemaking efforts. In connection with
these efforts, Headquarters staff conduct independent economic analyses and regulatory impact
analyses (RIAs) of the potential costs and benefits of proposed rules.
EPA Headquarters uses information from the regions to respond to information requests
and to perform analyses for EPA management, the Office of Management and Budget, Congress,
and the public. In addition, Headquarters uses information submitted by primacy agencies via
the UIC program's 7520 reporting forms to track, evaluate, and report on state performance.
Headquarters establishes and tracks performance targets and measures for EPA regional
programs. EPA Headquarters also assesses the effectiveness of existing regulatory requirements,
using state and regional information to justify future program modifications.
Headquarters compiles and analyzes Class I well information on a national basis, through
efforts such as the 1996 Class IUICWELLS database. This database contains detailed well-
specific data, such as geology, waste characteristics, and injection volumes. Headquarters uses
the database to analyze the potential impacts of proposed rules on the Class I community.
Regional Oversight of Primacy Programs
The regions develop operating budgets and program plans, allocate resources, track state-
by-state performance, and respond to inquiries. The regions are responsible for reviewing and
verifying information before forwarding it to EPA Headquarters.
EPA's regions oversee the primacy agencies using quarterly, semi-annual, and annual
reports submitted by the states. The information is used to track state progress against
commitments and to ensure that state programs can take timely and appropriate action in
response to threats to public health from contaminated USDWs.
Regions use well-specific information to track state enforcement actions against facilities
that are significant noncompliers—violators most likely to contaminate USDWs. Regions may
initiate federal enforcement action jointly with a primacy state, at the request of the state, or
where a state does not fulfill its enforcement responsibilities.
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Study of the Risks Associated with Class I UIC Wells
EPA's regions are also responsible for reviewing all no-migration petitions associated
with Class I hazardous wells. Each no-migration petition must be submitted to the Regional
Administrator.31 In reviewing no-migration petitions, EPA expects to gain valuable experience
and information which may affect future land disposal restrictions.
Regional staff work closely with well operators throughout the petition development
process. Several technical staff members may review a single petition and may take a year or
more to determine whether it should be approved. Each part of a petition is reviewed by a
specialist. For example:
• • An engineer or geologist reviews information about the construction, operation,
maintenance, and compliance history of the well; local and regional geology and
seismology; and the compatibility of the wastewater with the well materials and
the injection and confining zone rock and fluids.
A modeling expert evaluates the accuracy of the model's predictions compared to
actual conditions at the site. The modeler has to verify that the model takes into
account all significant processes that affect waste mobility and transformation, is
sensitive to subsurface processes, and has been properly validated and calibrated.
The petition is subject to public notice and comment. EPA publishes a draft notice of its
decision to approve or deny the petition, offers a public hearing, develops a fact sheet or
statement of basis, and responds to all comments. Notice of the final decision on a petition is
published in the Federal Register.
Direct Implementation of State Programs
In addition to their oversight responsibilities, EPA regional offices implement the UIC
program on tribal lands and in states without primacy. In these DI states, EPA regional offices
review permit applications to ensure that proposed wells are properly sited and designed.
Following permit approval and well completion, the regions use monitoring and testing reports
submitted by operators to determine if the well has mechanical integrity. EPA regions are also
responsible for reviewing no-migration petitions for Class I hazardous wells in DI states.
DI programs also use information submitted by operators to focus efforts on injection
wells that require enforcement action. Operators who have been out of compliance for at least
two consecutive quarters are identified and targeted for enforcement action.
31 40 CFR 268.6.
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Study of the Risks Associated with Class I UIC Wells
V. Risk Associated with Class I Wells
Early failures associated with Class I injection such as those at Hammermill Paper
Company and Velsicol Chemical Company (described in section IB), illustrated the potential
threats of wastewater injection and the need for and importance of the UIC regulations.
The 1980 UIC regulations address many of these risks. Since passage of the regulations,
EPA and other organizations have conducted numerous studies of hazardous and nonhazardous
Class I wells which demonstrate that such failures are unlikely to occur. The following sections
describe these studies. These reports are described in greater detail in the annotated
bibliography at the end of this study report.
V.A Studies of the Effectiveness of the UIC Regulations
Early studies by EPA and other organizations looked at potential operational problems
for Class I wells. Many of the failures documented in these studies were the result of historic
practices that are no longer acceptable under the promulgated UIC regulations.
Underground Injection Practices Council and General Accounting Office
Studies
In the mid-1980s, UIPC, presently the Ground Water Protection Council (GWPC), and
the General Accounting Office (GAO) conducted studies which described past Class I well
malfunctions in the United States and discussed how current Class I regulations would minimize
the possibility of failures. In April 1986, UIPC published a study that provided comprehensive
data on the operation and performance characteristics of Class I injection wells.32 The study
included case histories of Class I well sites or facilities with reported histories of operational
problems. A 1987 GAO study focused on Class I failures resulting in aquifer contamination.33
GAO reviewed the cause of each incident to determine whether regulations in place would have
prevented it.
The UIPC study identified malfunctions at 26 facilities, involving 43 wells, suggesting an
overall well malfunction rate of approximately 9 percent of the 500 Class I wells reported to
exist at the time. Only six wells, or 2 percent of all Class I wells, experienced malfunctions
resulting in leakage into a USDW. The 1987 GAO study reported only two cases of drinking
32 Underground Injection Practices Council. A Class I Injection Well Survey (Phase I Report): Survey of Selected Sites.
D19976.S1. Prepared by CH2M Hill, Gainesville, Florida. April 1986.
U.S. General Accounting Office. Hazardous Waste—Controls Over Injection Well Disposal Operations. 1987.
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Study of the Risks Associated with Class I UIC Wells
water contamination from Class I wells, one case of suspected contamination, and eight
documented cases of non-drinking water aquifer contamination.34
At most of the facilities in the UIPC study where well malfunctions occurred and all of
the cases in the GAO study, failing wells had been constructed and injection had commenced
prior to the implementation of the 1980 UIC standards. Most of the malfunctions reported in the
UIPC study were related to design, construction, or operating practices that are no longer
allowed under UIC regulations. Examples of the various malfunction scenarios include the
following:
Leaks in the injection well casing caused movement of wastewaters into a USDW at
four facilities. The leaks were detected either through annular monitoring or separate
monitoring wells. These leakages were attributed to defects in well construction that
would not have been allowed under the 1980 UIC regulations.
Excessive injection pressure or hydraulic surges causing a blowout at the wellhead or
surface piping, leading to contamination at the surface, was documented in the UIPC
study. UIC requirements for siting wells to limit the need for excessive injection
pressures and pressure monitoring requirements would have prevented such incidents.
The presence of improperly abandoned wells was cited as a factor in contamination at
the surface in the UIPC study. Required AoR studies would have detected these
pathways and, under UIC regulations, they would have been plugged prior to any allowed
injection.
Leaking packer assemblies were the most likely cause of leakage into an unpermitted
non-drinking water zone. This was the most commonly documented malfunction in the
UIPC study, at 17 facilities involving 29 wells. Such leaks allow wastewater to come
into contact with the protective well casing, causing corrosion. Under current UIC
regulations, the packer design must meet EPA approval based on the chemical and
physical characteristics of the injected fluids, as well as the rate, temperature, and volume
of injected fluid.
Corrosion of the casing or tubing was suspected as the cause of leakage of injected fluids
documented in the GAO study. In one case, corrosion caused the tubing to separate,
resulting in a blowout and waste spillage at the surface. UIC requirements stipulate that
the well casing be constructed of a corrosion-resistant material and that the wastewater be
compatible with the well materials which come into contact with it.
The incidents described in the GAO report may also be included in the UIPC study; at least the two incidents of drinking
water contamination are described in both reports.
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Study of the Risks Associated with Class I UIC Wells
Injection directly through the casing, without packer and tubing, was the primary cause
of two cases of drinking water contamination from Class I wells. This practice is not
allowed under UIC regulations: current safety features include double casing and
cementing to below the base of the drinking water zone.
All of the wells in the UIPC study that experienced serious malfunctions were removed
from service and plugged, repaired, and returned to service, or repaired and converted to
monitoring wells as part of ongoing injection operations or to monitor water quality in the
USDW. Both studies reported that aquifer restoration was initiated at the facilities where a
USDW or non-drinking water aquifer was contaminated. Remedial activities included installa-
tion of monitoring wells, groundwater recovery systems, and excavation of contaminated soils.
The OSWER Report
The EPA Office of Solid Waste and Emergency Response (OSWER) prepared a study
which evaluated the relative risks posed by many waste management practices.35 The study
found that, based on acute and chronic health risks and other health risks (such as cancer risks),
groundwater sources affected, welfare effects, and ecological risks, Class I hazardous wells are
safer than virtually any other waste disposal practice.
EPA Analysis of Class I Ml Failures
EPA analyzed trends of all nonhazardous and hazardous Class I MI failures, in selected
states, from 1988 to 1991.36 This report assessed the number of these Class I injection failures
during the period, analyzed the causes of these MI failures, and identified EPA and state
responses to them. EPA studied more than 500 Class I nonhazardous and hazardous wells in 14
states and identified the following:
• From 1988 to 1991, 130 cases of internal MI failures (leakage in the injection
tubing that can result from corrosion or mechanical failure of the tubular
materials) were reported. All of these internal MI failures were detected during
well operation by the continuous annulus monitoring systems or by MITs. The
wells were shut-in until they were repaired. Of these MI failures, 42 percent
occurred in the tubing and 23 percent involved the long string casing.
U.S. EPA, Office of Solid Waste and Emergency Response. OSWER Comparative Risk Project: Executive Summary and
Overview. EPA/540/1-89/003. November 1989.
U.S. EPA, Office of Ground Water and Drinking Water, Underground Injection Control Branch. Class I Well Failure
Analysis: 1988-1991. March 1993.
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Study of the Risks Associated with Class I UIC Wells
One external MI failure (flow along the outside of the casing) occurred. It was
detected by a routine external MIT and did not involve wastewater migration.
• Only four cases of significant nonhazardous wastewater migration were detected.
Three of the cases were detected by monitoring wells. The fourth potential
wastewater migration case was discovered when a Class I well was drilled into the
same formation. None of these failures is known to have affected a USDW.
To provide as up-to-date information as possible for the Class I study, EPA performed a
second analysis, summarizing mechanical integrity failures in Class I nonhazardous and
hazardous wells between 1993 and 1998.37 This was the most recent time period for which the
Agency had complete information. EPA found that MI failures of all types dropped by half in
every state, except Texas. MI failures for all Class I wells in Texas increased two-fold during the
assessment's time period compared to the previous study period. In fact, a relatively high Class I
well mechanical integrity failure rate of 65 percent was indicated. However, Texas' UIC
primacy agency, the Texas Natural Resource Conservation Commission (TNRCC), reviewed that
assessment and refutes these numbers. Based on a review of the draft report against its records,
TNRCC cites a 37-percent failure rate for Class I wells in Texas from 1993 to 1998.
V.B Qualitative Studies of Class I Wells
Two studies were performed in anticipation of the 1988 updates to the UIC regulations to
assess the risks associated with disposal of hazardous wastewater via Class I wells. They were
conducted by GeoTrans, Inc., in two phases, and Industrial Economics, Inc. (ffic).
In 1987, GeoTrans, Inc. conducted a two-phase qualitative study of Class I injection.38
Phase I assessed the effects of certain variables on the performance of the Texas Gulf Coast
geologic setting in containing waste. The study produced findings about the relative impacts of
certain failure scenarios, including the presence of an abandoned unplugged borehole, fractured
deterioration of a grout seal, and the presence of fractures in the confining zone,39 along with
high rates of withdrawal from an aquifer above the confining unit.
37 ICF, Inc. Class I Mechanical Integrity Failure Analysis: 1993-1998. Prepared by ICF, Inc., Fairfax, Virginia, for U.S.
Environmental Protection Agency, Office of Ground Water and Drinking Water, Underground Injection Control Program.
September 1998.
GeoTrans, Inc. A Numerical Evaluation for Class I Injection Wells for Waste Confinement Performance, Final Report,
Volumes I and II. Prepared for U.S. Environmental Protection Agency, Office of Drinking Water, Underground Injection Control
Program. September 30,1987.
Grout seal failure occurs when the seal is not sufficiently impermeable to prevent migration of wastewater to a USDW, or
when the seal separates from the well casing or the borehole and loses integrity.
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Study of the Risks Associated with Class I UIC Wells
The Phase I study also modeled the extent of wastewater migration from the injection
zone due to containment failure. It assessed the effect of the hydraulic conductivity of the
potential failure pathway, the degree of containment loss, the injection fluid characteristics, and
the relative location of the failure pathway to the injection well. The conclusions of the Phase I
study include the following:
Waste confinement increases in scenarios where abandoned unplugged boreholes
are farthest from the injection zone.
• Under certain conditions, containment failure can result in migration of waste
from the injection zone. When contamination of overlying strata does occur,
waste migration appears to be localized to within a few hundred to a thousand feet
from where the failure occurred.
• The mode of failure (e.g., grout seal failure, presence of an abandoned borehole,
or fractures in the confining zone), is less significant than the degree of failure,
the injection fluid characteristics, and the location of the failure pathway relative
to the injection well.
• Pumpage in an overlying aquifer with failure pathways increases the amount of
waste escaping from the injection zone. (It should be noted that, if a USDW were
directly over a proposed injection zone, Class I regulations would not allow the
well to be constructed; this makes the addition of the pumping scenario to the
model overly conservative.)
The Phase II study by GeoTrans, Inc. focused on two of the failure scenarios studied in
Phase I—grout seal failure and the presence of an unplugged abandoned borehole—and three
ranges in the degree of failure for four hydrogeologic settings (East Gulf Coast, Great Lakes,
Kansas, and Texas). Some of the conclusions reached in the Phase n study were:
• To ensure waste confinement, the confining zone should be much less permeable
than the injection zone (by one-thousand fold). Where there is less contrast in
permeability, significant amounts of wastewater may migrate into the overlying
zone.
• Models should provide sufficient hydrogeological detail to account for rock layers
between the injection zone and the USDW that could attenuate some of the
wastewater that migrates upward through a failure pathway. Using simplified
zones for injection, confinement, and USDW in models may cause overestimation
of the potential extent of contamination in USDWs.
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Study of the Risks Associated with Class I UIC Wells
The additional stress on the systems related to pumpage in the USDW
significantly reduced waste containment in all settings.
Using the data from the GeoTrans modeling, ffic estimated the magnitude of human
health risks which might occur if underground injection of hazardous wastewaters results in
contamination of USDWs.40 ffic assessed the difference in risk among the four geologic settings
modeled by GeoTrans. Risk between the best and the worst setting may vary by over 20 orders
of magnitude depending on the type of failure. The study also estimated relative risks associated
with an abandoned, unplugged borehole and a grout seal failure along with the impact of
withdrawing water from the USDW.
V.C Quantitative Studies of Risks Due to Phase III Wastes
In 1995, in support of EPA's Phase III LDR rulemaking (see section IB), the EPA
Office of Ground Water and Drinking Water (OGWDW) prepared a draft Benefits Analysis (as
part of the Regulatory Impact Analysis [RIA] of the proposed Phase III LDR rule) to estimate
the risks associated with injection of Phase III wastes into Class I hazardous wells. The
Chemical Manufacturers Association (CMA), now the American Chemistry Council (ACC),
submitted comments on the Benefits Analysis in 1995, after which EPA revised the RIA. In
1996, EPA performed an analysis in support of the de minimis requirements that the underlying
hazardous constituent concentrations must be less than 10 times the universal treatment standard
(UTS).
EPA OGWDW Draft Phase III LDR RIA
In 1995, OGWDW performed a Benefits Analysis as part of the RIA of the proposed
Phase HI LDR rule. In the RIA, EPA modified the approach taken in the 1987 lEc study to
estimate human health risks from five Phase m waste constituents (benzene, carbon
tetrachloride, chloroform, phenol, and toluene).41 EPA estimated health risks, including cancer
risks and hazard indices,42 for each of the four geologic settings and two malfunction scenarios
(grout seal failure and abandoned, unplugged borehole). The study also assessed the effects of
varying drinking water well pumping rates. The results showed:
40
Industrial Economics, Inc. Risk Analyses for Underground Injection of'Hazardous Wastes. May 1987.
U.S. EPA, Office of Ground Water and Drinking Water. Draft Regulatory Impact Analysis of Proposed Hazardous
Waste Disposal Restrictions for Class I Injection of Phase III Wastes: Benefits Analysis. 1995.
A hazard index is used to compare the relat
an increased risk of non-carcinogenic health effects.
A hazard index is used to compare the relative risk posed by contaminants. A hazard index of greater than one indicates
35
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Study of the Risks Associated with Class I UIC Wells
• Only two of the estimated cancer risks for both malfunction scenarios slightly
exceed the one-in-ten-thousand to one-in-one-million risk range generally used by
EPA to regulate exposure to carcinogens.43 These were the cancer risks from
exposure to benzene and carbon tetrachloride, assuming an abandoned borehole
scenario in the East Gulf Coast region at the highest drinking water well pumping
rate.
All but one of the hazard indices for both malfunction scenarios are less than
EPA's level of concern for a hazard index of 1.55 (i.e., greater than the concern
level of 1). The exception is for exposure to carbon tetrachloride in the East Gulf
Coast setting with an abandoned borehole and the highest drinking water well
pumping rate.
Comments by the Chemical Manufacturers Association on the Phase III
LDR RIA
CMA submitted a critique of the Benefits Analysis in the Phase HI RIA as part of its
comments on the proposed Phase HI LDR rule.44 CMA claimed the analysis was overly
conservative, given that Class I regulations have made the occurrence of these failure scenarios
highly unlikely. CMA expressed concerns about the assumptions used, the placement of
receptors, and the modeling of the East Gulf Coast hydrogeologic setting. CMA also indicated
in its critique that the benefits analysis should have taken into account the probability of the
failure scenarios actually occurring, given Class I operational safeguards, and should have
weighed the risks of injecting Phase HI wastes against the risks of handling, storing, and
transporting them.
CMA also evaluated the qualitative risk assessment. Its critique emphasized that there
have not been any instances of USDW contamination at a facility in compliance with the current
UIC program regulations, and the malfunctions cited in the EPA study involved facilities that
had not yet been required to comply with the UIC program requirements. CMA further asserted
that underground injection of hazardous waste is particularly low risk compared to other waste
management practices,45 and the risks of handling, transporting, and treating segregated Phase m
wastes might actually be greater than the risks of injecting the waste.
43 U.S. EPA, Office of Solid Waste and Emergency Response. Role of the Baseline Risk Assessment in Superfund Remedy
Selection Decisions. OSWER Directive 9355.0-30. 1991.
Comments on Benefits Assessment of EPA's Draft Regulatory Impact Analysis. Prepared by Woodward-Clyde
Consultants for Chemical Manufacturers Association UIC Management Task Group. May 1995.
U.S. EPA, Office of Solid Waste and Emergency Response. OSWER Comparative Risk Project: Executive Summary
and Overview. EPA/540/1-89/003. November 1989.
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Study of the Risks Associated with Class I UIC Wells
EPA OGWDW Final RIA
The revised Phase in RIA46 addressed several of the concerns raised in the CMA critique
of the Phase in LDR Benefits Analysis. Specifically, waste receptors in the base of the USDW
were included in the analysis, and limitations on the results of the analysis were discussed.
Although a lack of data precluded a quantitative assessment of the probability of the failure
scenarios actually occurring, incident occurrences were discussed further. The conclusions
regarding human health risks did not change.
Evaluation of Risks from Exceedance of the UTS
To provide a quantifiable assessment in support of the de minimis requirements in the
proposed Phase HI rule, EPA analyzed the effects of varying the criteria that underlying
hazardous constituent concentrations must be less than 10 times UTS.47 Specifically, it outlined
how increasing permissible levels to 50 times UTS changes the estimated potential health risks
for several contaminants detected in the wastewaters of facilities affected by the Phase m LDR
rule. The analysis estimated cancer and noncancer risks based on the well failure scenario and
geologic setting that are associated with the greatest risk as depicted in the Benefits Analysis of
the Phase m LDR RIA. In this analysis, EPA again used the five Phase HI waste constituents
(benzene, carbon tetrachloride, chloroform, phenol, and toluene) that were evaluated in the
Phase m LDR RIA and Benefit Analysis.
Results of the analysis showed that, in general, carcinogenic risks were within the range
generally used by EPA to regulate exposure to carcinogens, and noncancer risks were less than
the hazard index of 1. The analysis concluded that a standard which would be more reflective of
the potential for health hazards could be satisfied by defining the de minimis criterion as a value
between 10 times and 50 times the UTS.
Using the same methodology, EPA conducted a brief analysis of the Hazardous Waste
Identification Rule exit levels for the five chemicals examined. For benzene, carbon
tetrachloride, and chloroform, the HWTR exit level concentrations were well below the UTS.
Since the risk analysis presented above showed acceptable risk levels for these three chemicals at
concentrations higher than the HWIR exit levels, no significant risk would be associated with the
HWTR exit levels. For toluene and phenol, however, the HWTR exit levels were significantly
U.S. EPA, Office of Ground Water and Drinking Water. Final Draft: Regulatory Impact Analysis of Proposed
Hazardous Waste Disposal Restrictions for Class I Injection of Phase III Wastes: Benefits Analysis. 1995.
U.S. EPA, Office of Ground Water and Drinking Water. Evaluation of Risks from Exceedance of the Universal
Waste-water Treatment Standards (UTS), Including Addendum on HWIR Concentrations. February 1996.
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Study of the Risks Associated with Class I UIC Wells
higher than 50 times the UTS. Neither chemical analyzed yielded a hazard index equal to or
greater than 1, indicating an acceptable level of risk.
V.D Other Studies of Risk Due to Class I Wells
More recently, GeoTrans conducted additional modeling of MI failure scenarios using
then current data on Class I wastewaters. In 1998, CMA quantitatively estimated the risk of
waste containment loss from a Class I well based on probabilities that sequences of events would
occur and result in a loss of containment.
Revisions to GeoTrans' Modeling Assumptions
At EPA's request, in response to CMA's 1995 comments on the Benefits Analysis and
using more recent data on the constituents of Class I wastewaters, GeoTrans revised certain
assumptions in its 1987 modeling of failure scenarios.48 In this study, additional modeling
focused on the scenario of an abandoned unplugged borehole 500 feet from the Class I well and
a high drinking water well pumping rate. In the models, the differences in permeability between
the injection zone and the layer just above the injection zone were increased by four orders of
magnitude (i.e., by 10,000 times).
Results from the analysis showed that the effect of the abandoned borehole overwhelms
the transport directly through the confining zone—with increasing permeability ratios, greater
amounts of fluid are transported upward through the borehole and into the USDW. In effect, the
reduced conductivity "squeezes" more of the waste fluids up the path of least resistance (the
borehole). This is consistent with the conclusions drawn in the 1987 study.
This increase in concentration, however, occurs only between the base case and the
revised scenarios. Comparison of the individual results for the revised scenarios shows that the
concentrations decrease as the permeability ratio increases. This could imply that the
"squeezing" effect does not hold true after a certain permeability contrast has been achieved, or
that possibly some small amount of leakage occurs through the confining zone. Thus, greater
permeability contrasts lead to lower contamination concentrations in the USDW. These
potential causes may be the subject of further research.
Human health risks were calculated using the results of the revised GeoTrans analysis.
(Appendix B to this report presents the complete revised human health risks analysis.) Recent
data from EPA's UICWELLS database were used to determine 90th-percentile concentrations
for benzene, carbon tetrachloride, and arsenic. The cancer risks for each chemical, based on
Revisions to GeoTrans' Modeling Assumptions, Analysis of New Data From 1996 Class I UICWELLS Database.
September 1996.
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Study of the Risks Associated with Class I UIC Wells
exposures to concentrations estimated at a receptor 500 feet from the injection well in an aquifer
below the USDW at higher permeability ratios, exceed the risk range generally used by EPA to
regulate exposures to carcinogens.49 Likewise, at the same receptor location, the hazard indices
estimated for each chemical are greater than EPA's level of concern for a hazard index greater
than 1. All other cancer risk and hazard index estimates are within regulatory levels.
These risk levels should, however, be assessed in the context of the low probability of
this failure scenario actually occurring given Class I AoR requirements. Although no
quantitative method to assess this probability currently exists, the small number of such failures
after promulgation of the existing UIC regulations, indicates that the probability is likely very
low.
A number of detailed human health risk analyses were conducted using actual Class I
waste constituent data to determine the potential for cancer and noncancer risks associated with
ingesting water from a USDW contaminated by a Class I well. The results showed that cancer
and noncancer risks exceed the acceptable risk range for three chemicals at one receptor located
adjacent to an abandoned unplugged borehole, 573 feet from the injection well, in an aquifer
below the USDW. This assumes an abandoned borehole is located 500 feet from the injection
well, and a drinking water well located 1,000 feet from the injection well is pumping 720,000
gallons per day from an overlying aquifer. Under current UIC regulations requiring AoR studies,
however, it is unlikely that an abandoned borehole would go undetected. Also, given the small
number of documented USDW contamination incidents (described in section V.A), the
probability of this scenario actually occurring is likely very low.
Probabilistic Risk Assessment of Class I Hazardous Wells
In 1998, Rish et al. quantitatively estimated the risk of waste containment loss as a result
of various sets of events associated with Class I hazardous wells.50 Through a series of "event
trees," the study estimated the probability that an initiating event will occur and be undiscovered,
followed by subsequent events that could ultimately result in a release of injected fluids to a
USDW.
The study assumed that, given the redundant safety systems in a typical Class I well, loss
of containment requires a string of improbable events to occur in sequence. For example, a leak
develops in the packer, followed by a drop in annulus pressure that is undetected due to a
U.S. EPA, Office of Solid Waste and Emergency Response. Role of the Baseline Risk Assessment in Superfund Remedy
Selection Decisions. OSWER Directive 9355.0-30. 1991.
Rish, W.A., T. Ijaz, and T.F. Long. A Probabilistic Risk Assessment of Class I Hazardous Waste Injection Wells. Draft.
1998.
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Study of the Risks Associated with Class I UIC Wells
simultaneous malfunction of the pressure monitoring system, followed by a leak in the long
string casing between the surface casing and the upper confining layer, resulting in a loss of
waste isolation.
The Rish study concluded that Class I hazardous injection wells which meet EPA's
minimum design and operating requirements (i.e., a completed no-migration study, two
confining zones between the injection zone and the lowermost USDW, completed long string
and surface casings, and redundant safety systems) pose risks that are well below acceptable
levels. According to the study, the probability of containment loss resulting from each of the
scenarios examined ranges from one-in-one-million to one-in-ten-quadrillion. The risks for each
are ranked as follows (from most probable to least probable): cement microannulus leak,
inadvertent extraction from the injection zone, major injection tube failure, major packer failure,
breach of the confining zone(s), leak in the packer, and leak in the injection tubing.
This low risk is attributed to the use of engineered systems and geologic knowledge to
provide multiple barriers to the release of wastewater to USDWs. And although this risk
analysis was primarily concerned with Class I hazardous wells, many of the well design and
construction requirements pertain to Class I nonhazardous wells also. Therefore, the findings of
a relative low risk in operation of the wells investigated in the Rish study can be extrapolated to
the typical Class I well which may be managing only decharacterized wastewaters.
VI. Conclusions
EPA's UIC requirements and current operational practices for all Class I wells reflect
years of experience and insight into what makes Class I wells safe and what practices are
unacceptable. From the early failures of Class I wells, EPA learned that migration of injected
wastewater can result from failure of injection wells due to faulty design, construction, operating
practices, or the presence of pathways for migration near the injection zone.
Recognizing this, EPA passed its UIC regulations for Class I nonhazardous and
hazardous wells in 1980 based on the idea that injection into properly constructed and operated
wells is a safe means to dispose of wastewater. EPA's geologic siting, well engineering, and
operating requirements for Class I wells offer multiple safeguards against failure of the well or
migration of injected fluids.
Because the presence of an unplugged abandoned borehole can be a significant potential
contributing factor to migration of injected fluids from the injection zone, EPA requires
operators to identify and address all improperly abandoned wells in the AoR. Several states that
account for the majority of all Class I wells require an AoR that is even larger than that required
by federal regulations. These unplugged wells, if found, must be properly addressed before UIC
permitting authorities will allow operators to begin injection.
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Study of the Risks Associated with Class I UIC Wells
In addition to the AoR requirement, Class I wells are sited to minimize the potential for
waste migration. Pre-construction studies by operators must demonstrate that the rock
formations which make up the injection and confining zones and the local geologic structure are
amenable to safe injection and confinement of wastewaters. Wells are constructed using well
materials that are suitable to the injection of wastewaters at the intended pressure, rate, and
volume.
Inspections and well testing, along with passive monitoring systems such as continuous
annulus monitoring systems, can detect malfunctions before wastewaters could escape the
injection system. Periodic MTTs are an additional means of ensuring the integrity of the well
components. An internal or external MI failure does not imply failure of the injection well or
loss of wastewater confinement. Rather, they indicate that one of the several protective elements
may have malfunctioned.
The probability of Class I well failures, both nonhazardous and hazardous, has been
demonstrated to be low. Many early Class I failures were a result of historic practices that are
no longer permissible under the UIC regulations. Class I wells have redundant safety systems
and several protective layers; an injection well would fail only when multiple systems fail in
sequence without detection. In the unlikely event that a well would fail, the geology of the
injection and confining zones serves as a final safety net against movement of wastewaters to
USDWs. Injection well operators invest millions of dollars in the permitting, construction, and
operation of wells, and even in the absence of UIC regulations would carefully monitor the
integrity of the injection operation to safeguard their investments.
Indeed, failures of Class I wells are rare. Most failures of MI are internal failures, detect-
ed by continuous annulus monitoring systems or MITs, and the wells are shut-in until they are
repaired. EPA's study of more than 500 Class I nonhazardous and hazardous wells showed that
loss of MI contributed to only 4 cases of significant wastewater migration (none of which
affected a drinking water source) over several decades of operation. Even as injection wells are
entering "middle age," their MI remains intact. This can be attributed to the rigorous
requirements for monitoring and for ensuring that the well materials are compatible with the
wastewater injected.
The 1988 UIC regulations implementing the HSWA offer additional protection by
requiring operators of Class I hazardous wells to complete a no-migration petition to demonstrate
that the hazardous constituents of the wastewater will not migrate from the injection zone for
10,000 years, or as long as the wastewater remains hazardous. Although operators are not
required to place decharacterized wastes in wells subject to no migration requirements, the fact
that these wastes are being injected into Class I hazardous wells offers additional protection by
this practice.
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Study of the Risks Associated with Class I UIC Wells
From an assessment of information collected on Class I wells, both nonhazardous and
hazardous, EPA believes that a substantial volume of decharacterized wastes are still being
disposed via Class I hazardous wells, particularly where the facility may not segregate waste
streams. Thus, public health and the environment is being afforded an additional level of
protection by this injection practice, because the additional controls on hazardous wells are in
place. No migration petitions account for all volumes of waste injected into a Class I hazardous
well to ascertain the size, shape, and directional drift of the waste plume.
In addition, states with a proportionally large number of the national total for Class I
injection wells have stricter regulatory requirements than the minimum federal standards for their
Class I nonhazardous wells. As such, a substantial number of Class I nonhazardous wells
managing decharacterized wastes are extremely protective. The EPA has no reason but to
conclude that existing Class I UIC regulatory controls are strong, adequately protective, and
provide an extremely low-risk option in managing the wastewaters of concern.
VII. Annotated Bibliography of Class I Documents
The sections below provide an annotated bibliography of documents related to Class I
injection wells. The bibliography is organized by type of document as follows: general
information on Class I injection; descriptions of computer modeling; studies of mechanical
integrity testing; program histories, overviews, and evaluations; Class I research; risk analyses;
and technical and instructional documents.
General Information on Class I Injection
The American Association of Petroleum Geologists. "Underground Waste Management and
Environmental Implications." Memoir 18 in T.D. Cook, ed., Proceedings of the Symposium on
Underground Waste Management and Environmental Implications Houston, Texas, December
6-9, 1971. AAPG. 1972.
The United States Geological Survey and The American Association of Petroleum
Geologists undertook joint sponsorship of the Symposium on Underground Waste
Management and Environmental Implications. Their goal was to document the facts,
clearly and objectively review the state of the art, and highlight segments of the
underground waste disposal problems that need further study. The organizing
committees arranged a program which touched on all aspects of underground waste
management and its environmental implications. They called upon a panel of
distinguished authors and practitioners to discuss various segments of the problem. Their
data are presented in this document.
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Study of the Risks Associated with Class I UIC Wells
The American Association of Petroleum Geologists. "Underground Waste Management and
Environmental Implications." Jules Braunstein, ed. Papers Presented at the Second
International Symposium on Underground Waste Management and Artificial Recharge New
Orleans, Louisiana, September 26-30, 1973. Vol. 1 and Vol. 2, AAPG. 1973.
The two volumes in this publication represent the third in a continuing series of AAPG
publications devoted to the subject of underground waste management. They were
preceded by Memoir 10, Subsurface Disposal in Geologic Basins, and Memoir 18, the
proceedings of the First Symposium on Underground Waste Management and
Environmental Implications.
Brown, Michael. "The Lower Depths: Underground Injection of Hazardous Wastes." The
Amicus Journal. Winter 1986.
The premise of this article is that deep injection of industrial waste has become extensive
in America and a way for corporations to rid themselves of toxic residues without
encountering rigid governmental restrictions and the public clamor associated with the
more visible landfills. During the previous two decades (especially during the period in
which the Clean Water Act was implemented), use of such wells had grown to the point
where more hazardous liquids are injected deep underground than are poured into metal
drums and buried in standard dumpsites. At the same time that the Chemical
Manufacturers Association describes deep well injection as "a technically sound and
costly practice," a small but growing band of critics contends that, quite to the contrary, it
is both cheap and dangerous. Several cases of groundwater and air pollution resulting
from injection wells are provided. The author asserts that problems with UIC programs
include insufficient regulation and noncompliance with existing regulations. The author
also claims that some of the weaknesses of the UIC program are its failure to set testing
requirements to prevent adverse interactions between waste and formation; the lack of
requirements for financial responsibility after well abandonment; lack of monitoring
requirements; lack of requirements for post-closure care; and infrequent mechanical
integrity testing.
Carter, L.M.H., ed. Energy and the Environment—Application ofGeosciences to Decision-
Making. U.S. Geological Survey Circular 1108. February 13-16, 1995.
Sessions of the Tenth V.E. McKelvey Forum on Mineral and Energy Resources included
an introduction to energy and the environment, availability and quality of energy
resources, environmental effects of natural energy occurrence, and environmental effects
of energy extraction and utilization. This document contains the program and a list of
short papers from the event.
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Study of the Risks Associated with Class I UIC Wells
Chemical Manufacturers Association. Class I Underground Injection Wells: Responsible
Management of Chemical Wastes (Pamphlet). 1994.
This pamphlet highlights many of the successful efforts by Chemical Manufacturers
Association members to minimize wastes sent to deep injection wells.
Chemical Manufacturers Association. Deep Well Injection: An Option for Responsible
Management of Chemical Wastes (Pamphlet). 1994.
The suitability of deep well injection as a disposal method depends upon the local
geology and hydrology and the nature and volume of wastes. This pamphlet by the
Chemical Manufacturers Association provides an introduction to deep well injection of
chemical wastes.
Clark, James E. "Environmental Scoring Without Risk Assessment." Presented at CLEAN
TEXAS 2000 - Environmental Trade Fair, Underground Injection Control Workshop, Austin,
Texas. April 14, 1994.
Many environmental ranking systems continue to rely heavily on the U.S. EPA Toxic
Release Inventory (TRI) regarding releases of toxic chemicals to the environment. The
author believes that the current system of TRI reporting does not accurately measure
exposure or risk to human health and the environment and can overstate the risks
associated with underground injection.
E.I. DuPont de Nemours & Co., DuPont Deepwell Training Committee. An Introduction to
Deepwell Disposal. Injection Well Operator Training Series, Vol. 1. Beaumont, Texas: Tele-
Con Productions (Videocassette). 1989.
E.I. DuPont de Nemours & Co., DuPont Deepwell Training Committee. Well Operations and
Diagnostic Procedures. Injection Well Operator Training Series, Vol. 2. Beaumont, Texas:
Tele-Con Productions (Videocassette). 1989.
Ground Water Protection Council. Injection Well Bibliography. Third Edition. Oklahoma City,
Oklahoma: Ground Water Protection Council. August 1995.
This is the most comprehensive bibliography published to date on injection wells in the
United States. It is an update of the editions published by the Underground Injection
Practices Council in 1989 and 1993. The project was designed by the Ground Water
Protection Council as a primary reference tool for persons interested in the operation,
construction, and regulation of various types of injection wells. The bibliography is
divided into sections based upon well classification and associated topics for easier and
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Study of the Risks Associated with Class I UIC Wells
more accurate searching. The bibliography includes four sections on Class I injection
wells: "General," "Hazardous Waste Wells," "Non-Hazardous, Industrial Wells," and
"Non-Hazardous, Municipal Wells."
Hickey, John J., and John Vecchioli. "Subsurface Injection of Liquid Waste with Emphasis on
Injection Practices in Florida." U.S. Geological Survey Water-Supply Paper 2281. 1984.
Subsurface injection of waste is not well understood by many state and local
governmental officials and environmentally concerned citizens who make decisions about
waste disposal. This report serves as an elementary guide to subsurface injection and
presents subsurface injection practices in Florida as an example of how one state is
managing injection.
Lehr, Jay H. "Underground Injection: A Positive Advocate." Proceedings of the International
Symposium on Subsurface Injection of Liquid Waste. New Orleans, Louisiana, March 3-5, 1986.
Dublin, Ohio: National Water Well Association. 1986.
EPA has focused most of its public attention on the more prevalent brine reinjection
wells known as Class U wells. Concurrently EPA oversees in situ mining wells (Class
HI), outlaws the disposal of hazardous wastes into or above potable aquifers (Class IV),
and intends to offer general guidelines for all other injection wells from salt-water
intrusion barrier wells to geothermal energy wells (Class V). Since the passage of
SDWA, the least attention was focused on wells disposing of hazardous waste below and
separated from current or potential underground sources of drinking water (Class I).
Moffett, Tola B., Philip E. LaMoreaux, Janet Y. Smith, and M. Ben Dismukes. Management of
Hazardous Wastes by Deep-Well Disposal. Open File Report No. 11. Tuscaloosa, Alabama:
University of Alabama, Environmental Institute for Waste Management Studies. 1987.
This report provides an assessment of the deep-well injection of hazardous waste for
technically trained audiences and the general public. Chapter 2, "Relevant Issues,"
describes the complex factors that affect deep-well injection. Chapters 3 through 8
provide basic information concerning the history of deep-well injection, its methodology,
and its current status. These chapters also provide a basis for determining benefits and
risks of deep-well injection and for analyzing its potential role in hazardous waste
management.
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National Water Well Association. Proceedings of the International Symposium on Subsurface
Injection of Liquid Waste. New Orleans, Louisiana, March 3-5, 1986. Dublin, Ohio: National
Water Well Association. 1986.
The International Symposium on Subsurface Injection of Liquid Wastes was held in New
Orleans, Louisiana, March 3-5, 1986. Government officials, industry representatives,
consulting engineers, and geologists, researchers, and other interested persons met to
learn about and discuss state-of-the-art techniques employed and variables to consider in
the operation of underground injection facilities. The conference papers addressed a
wide variety of topics including a point/counterpoint on the practice of underground
injection, well construction and testing methods, case studies on the operation of selected
facilities, and a discussion of the fate and transport of injected wastes. This conference
provided a forum for all who attended to communicate and share experiences about the
practice of subsurface disposal and to learn about the implications of future regulation in
this area.
Russian-American Center for Contaminant Transport Studies. Summary Report (1993-1994).
1994.
This report summarizes the activities of the Russian-American Center for Contaminant
Transport Studies at the Lawrence Berkeley National Laboratory in 1993-1994. It
presents the publications and workshops sponsored by the Center, including the
International Symposium on Scientific and Engineering Aspects of Deep Injection
Disposal of Hazardous and Industrial Waste (May 10-13, 1994). Co-sponsored by EPA's
Office of Ground Water and Drinking Water and the Department of Energy's Office of
Environmental Management, the symposium provided an avenue to compare experiences
and ideas for improving deep well injection technology.
Smith, R. E. EPA Mission Research in Support of Hazardous Waste Injection 1986-1994. In:
Deep Injection Disposal of Hazardous and Industrial Waste: Scientific and Engineering Aspects.
John A. Apps and Chin-Fu Tsang, eds. San Diego, California: Academic Press. 1996. p. 9-24.
The central focus of the UIC Class I research program has been to determine under what
conditions (if any) injection of hazardous wastes is protective of human health and the
environment. Geological and hydrogeological research helped EPA set minimum siting
criteria for Class I wells and determine the appropriateness of specific areas for injection.
Geophysical research has helped delineate underground reservoirs, find abandoned wells
for Area of Review studies, and determine whether injection could contribute to
earthquake risk. Geochemical research has provided some additional information on
transformation of injected waste. Several studies have suggested new methods for well
siting, testing, and monitoring. Computer models have been required since the 1988
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Land Ban Regulations. A new area of study in modeling is diffusion, which can cause
minor upward vertical movement of injected wastes.
Strycker, Arden, and A. Gene Collins. State-of-the-Art Report: Injection of Hazardous Wastes
Into Deep Wells. Prepared by National Institute for Petroleum and Energy Research for U.S.
Department of Energy and U.S. Environmental Protection Agency, Robert S. Kerr
Environmental Research Laboratory. December 15, 1986.
A survey of the literature shows that some information is available on nearly all of the
potential chemical and biological transformation processes of hazardous wastes. This
survey also indicates that additional research is needed in all areas of abiotic and biotic
waste interactions before definitive explanations can be given on their long-term fate.
Thornton, Joe. A Shot in the Dark: Underground Injection of Hazardous Waste. A Greenpeace
Report. July 1990.
Deep well disposal of hazardous wastes has contaminated groundwater resources, caused
earthquakes, damaged geological formations, and contaminated soils and surface water
near wellheads. Because of loopholes in federal laws governing hazardous waste
disposal, deep well injection is the cheapest and one of the most poorly regulated of all
disposal methods.
Underground Injection Practices Council. Injection Wells: An Introduction to Their Use,
Operation, and Regulation. Undated.
This document is an outreach brochure designed to disseminate general information
about all classes of underground injection wells (including Class I).
Underground Injection Practices Council. An Introduction to the Underground Injection Control
Program. May 1990.
This manual is written to inform interested persons about the basic concepts, elements,
and procedures of the UIC program. Its purpose is to present a comprehensive overview
of the UIC program so those working with a single program element will have an
appreciation of the whole program and so elected officials and administrators will be able
to understand the operation and needs of a successful UIC program. This manual has
been written from the standpoint of experience gained operating and administering state
regulatory programs.
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U.S. EPA, Office of Water. Class I Injection Wells and Your Drinking Water. EPA 813-F-94-
002. July 1994.
This document is an EPA outreach brochure designed to disseminate general information
about Class I underground injection wells.
U.S. EPA, Office of Water. Underground Injection Wells and Your Drinking Water. EPA 813-
F-94-001. July 1994.
This document is an EPA outreach brochure designed to disseminate general information
about all classes of underground injection wells (including Class I wells).
Computer Modeling
Javandel, Iraj, Chin Fu Tsang, and Paul A. Witherspoon. Hydrologic Detection of Abandoned
Wells. Prepared by Lawrence Berkeley Laboratory for U.S. Environmental Protection Agency,
Office of Drinking Water. June 1986.
Thorough characterization of injection zones and confining beds is essential to ensuring
that no pathways exist for movement of injected wastes to USDWs. This paper presents
an analytical model for detecting improperly abandoned wells. The analytic solution
calculates the amount of leakage from an abandoned well and the corresponding
drawdown at monitoring wells. This paper also proposes a method for detecting deep
abandoned wells in the area of influence of proposed deep injection wells in a multiple
aquifer system.
Kazmann, Raphael G. "Deep Well Injection: Models, Reality, and How to Do It Right."
Ground Water. November/December 1988.
Deep well disposal, when properly done, is the safest method that can be devised for
removing hazardous wastes from the biosphere. The critical point is the wellhead where
injection takes place. The fate of the waste should be of no concern, if the geology has
been interpreted correctly and the other mechanical criteria that have been established are
met. The article asserts that mathematical modeling does not improve the safety of the
procedure and that, in the interest of saving time and money, EPA should abandon the
requirement that mathematical models be prepared as part of the application for a permit
for deep well disposal of hazardous wastes. The safely of the procedure depends on the
ability and integrity of the hydrogeologist who interprets the field data and the engineer
who designs and tests the injection well.
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LaMoreaux, P. E. Synopsis of Use of Mathematical Models to Evaluate Sites for Injection Wells
for Disposal of Hazardous Wastes. Preliminary Draft. Environmental Institute for Waste
Management Studies. December 1986.
Mathematical models are representations of physical systems or processes. Models, both
flow and geochemical, range from simple to complicated. There are three methods of
simulating injection of wastewater into reservoirs: analytical, semi-analytical, and
numerical.
Larkin, R. G., J. E. Clark, and P. W. Papadeas. "Modeling the Effect of Injectate-Density
Changes on Disposal Well Plumes." In: Deep Injection Disposal of Hazardous and Industrial
Waste: Scientific and Engineering Aspects. John A. Apps and Chin-Fu Tsang, eds. San Diego,
California: Academic Press. 1996. p. 381-402.
This paper compares the waste plumes generated by a model using two different
calculations for injectate density. Models of such plumes are required in some no-
migration petitions. Injectate that is of lower density than the native fluid in the injection
zone can cause the plume to float upward, while injectate with densities higher than those
of native fluids can cause the plume to sink. One run of the model was performed using
the average of densities recorded over time at an actual well. Another run was performed
using varying daily densities at the same well. In addition, equivalent runs were done
using randomly generated density data. No significant difference in the plume extent
existed between runs using an average and runs using fluctuating daily data.
Miller, C, T.A. Fischer II, I.E. Clark, W.M. Porter, C.H. Hales, and J.R. Tilton. "Flow and
Containment of Injected Wastes." Ground Water Monitor ing Review. Summer 1986.
This article examines several analytical models for predicting waste movement and
pressure increases within the injection zone and describing upward permeation of wastes
through confining layers. Models attempted to account for density differences between
the waste and native formation brine and permeability variation within the injection zone.
Initial results indicate that faults and fractures are not likely to provide conductive
pathways for contaminant migration in Gulf Coast settings, and that site-specific
evaluations are required to assess the impact of abandoned wells.
Milly, P.C.D. Obstacles Associated with Transport Modeling of Hazardous Waste Injected
Underground. 1987.
Mathematical modeling is one of the few alternatives available for assessing the risk of
future USDW contamination resulting from subsurface waste injection; alternatives are
extensive monitoring or comprehensive prohibitions of injection. This report describes
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Study of the Risks Associated with Class I UIC Wells
some of the more serious problems associated with using models to predict waste
transport. The discussion is general and not limited to any particular mathematical
model; most remarks apply to most of the models currently in use.
Morganwalp, David W., and Robert E. Smith. Modeling of Representative Injection Sites.
1987.
There are three main objectives to this study. The first is to find key parameters that
control the transport of hazardous waste at representative injection well sites. The
second is to investigate the role of molecular diffusion in hazardous waste injection well
settings. The third objective is to show by example that hazardous waste injection can be
modeled. The objectives were achieved by modeling idealized representations of actual
hazardous waste injection wells.
Papadeas, P. W. "Field Testing for Model Confirmation: Case Histories from Du Pont." In:
Deep Injection Disposal of Hazardous and Industrial Waste: Scientific and Engineering Aspects.
John A. Apps and Chin-Fu Tsang, eds. San Diego, California: Academic Press. 1996. p. 325-
348.
As part of hazardous and nonhazardous waste injection at Class I injection wells,
detailed, site-specific models are employed to predict and track waste injectate over time.
Flow and containment of this injected waste in the subsurface can be demonstrated to
regulators with a reasonable degree of certainty exclusively through the use of modeling
techniques; however, only direct field testing can corroborate the model results. Case
histories covering over 40 years of injection well operations corroborate the findings of
models and active disposal systems.
Thornhill, J.T., T.E. Short, and L. Silka. "Application of the Area of Review Concept." Ground
Water. Vol. 20, No. 1. January/February 1982.
Analytical equations can be used to calculate pressure buildup in injection zones. In
areas of review characterized by numerous injection wells, care must be taken to account
for the effect of every injection well on pressure buildup to prevent the migration of
fluids to USDWs.
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Study of the Risks Associated with Class I UIC Wells
Mechanical Integrity Testing
The Cadmus Group, Inc. External Mechanical Integrity Log Interpretations for Class I Wells in
Texas (DRAFT). Prepared for U.S. Environmental Protection Agency, Region 6, Underground
Injection Control Section. September 30, 1993.
This report presents a summary and analysis of the geophysical log interpretations
performed for Class I hazardous waste (HW) disposal wells in Texas. This task was part
of a larger Cadmus study of Class I HW file reviews undertaken for EPA Region 6, as
part of the oversight efforts required for primacy states under the UIC Program. The
report explains the technology, including radioactive tracer tests and cement bond logs,
used to assess mechanical integrity for 61 Class I wells. Analysis of the data indicate that
most radioactive tracer surveys were not conducted according to Texas Natural
Resources Conservation Commission guidelines, 29 percent of the wells had no cement
bond logs (CBLs) on file, and most wells that did have logs showed insufficient cement
casing (even though their permit applications state that cement extends to the surface).
Of the wells that did have CBLs, many had logs so poorly calibrated that interpretation
could not be considered reliable. Recommendations included minimum standards for
cement bond logs, performance standards for cementing Class I hazardous wells, use of
oxygen activation logs instead of radioactive tracer tests in some cases, and supplemental
training of MI reviewers at primacy agencies.
Engineering Enterprises, Inc. Analysis of Mechanical Integrity Tests and Permit File Reviews.
Prepared for U.S. Environmental Protection Agency, Office of Drinking Water, Groundwater
Protection Branch. September 1986.
This report analyzes the mechanical integrity testing programs for Direct Implementation
states. It discusses the applicability and effectiveness of various types of mechanical
integrity tests and comments on significant variances in failure rates. The report
evaluates the adequacy of file review procedures and provides recommendations for
standardizing reporting forms, for follow-up actions for MIT failures and call-in
procedures, and for file reviews of well operations.
Geraghty & Miller, Inc. Mechanical Integrity Testing of Injection Wells. Prepared for U.S.
Environmental Protection Agency, Office of Drinking Water. April 30, 1980.
The various logging techniques used in determining mechanical integrity are widely
employed and were developed for this purpose. They are an indirect measurement and
are indicators of a condition. They measure something electronically: temperature, sound
velocity, noise levels, etc. Thus, data interpretation is subjective and depends on the
skills and experience of the operator, in contrast to a pressure test, which is a more direct,
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Study of the Risks Associated with Class I UIC Wells
readily observable indicator of a condition. But surveys such as noise, temperature, and
tracer logs can be substituted for pressure testing. While the pressure tests yield more
positive results, it may be more economical for the operator to substitute the appropriate
log or logs. The evidence will be less direct, but the burden of proof should be on the
operator to demonstrate conclusively that the well possesses the required integrity.
Jarrell, Malcolm D. "Integrity Testing of Class I Hazardous Injection Wells—Related
Experience in the Great Lakes Region." Proceedings of the International Symposium on
Subsurface Injection of Liquid Waste. New Orleans, Louisiana, March 3-5, 1986. Dublin, Ohio:
National Water Well Association. 1986.
This paper discusses mechanical integrity testing of Class I hazardous waste disposal
wells in EPA Region 5. It addresses test procedure development, implementation, and
interpretation. The test procedures are based on site-specific well construction,
operation, and geological considerations. Testing methods include the radioactive tracer
survey and annular pressure testing. The interpretation of test results are discussed as
related to U.S. EPA's criteria for acceptance. The principles applied could prove helpful
in establishing regional standards for mechanical integrity testing.
Whiteside, Robert F., and Stuart F. Raef "Mechanical Integrity of Class I Injection Wells."
Proceedings of the International Symposium on Subsurface Injection of Liquid Waste. (New
Orleans, Louisiana, March 3-5, 1986). Dublin, Ohio: National Water Well Association. 1986.
This paper reviews the siting, construction, and testing of Class I disposal wells and how
these are designed to ensure mechanical integrity. Periodic mechanical integrity testing
is discussed, including pressure testing and logging, as are the advantages and limitations
of each technique. Advantages and disadvantages of packer-annulus versus packerless
well completions are discussed as they pertain to annulus monitoring.
Program Histories, Overviews, and Evaluations
Brower, Ross D., Ivan G. Krapac, Bruce R. Hensel, Adrian P. Visocky, Gary R. Peyton, John
Stephen Nealon, and Mark Guthrie. Evaluation of Current Underground Injection of Industrial
Waste in Illinois. Final Draft Report. Savoy, Illinois: Illinois Department of Energy and Natural
Resources, Hazardous Waste Research and Information Center. March 1986.
The objectives of this assessment were to determine whether underground injection is an
appropriate method of waste disposal in Illinois and to provide recommendations to the
Legislature, Legislative Council, the Governor's Office, and state agencies concerning
this disposal practice. The final report presents the results of the study mandated by
legislation. The following topics are addressed in the report: (1) The current state
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Study of the Risks Associated with Class I UIC Wells
regulations and regulatory practices of the Illinois Class I UIC program; (2) An historical
evaluation of the operation and maintenance of underground injection facilities in
Illinois, including a review of the types of wastes and potential problems associated with
underground waste disposal; (3) A review of the Class I UIC programs in other states and
comparison with the program in Illinois, including current issues and trends in deep well
injection; (4) A summary of geologic information in Illinois to identify areas and geologic
formations that are being used and might be targeted for future injection; (5) An
identification of alternative waste disposal management options, along with treatment
requirements, treatment technologies, associated costs for selected waste management
options, and potential environmental impacts; and (6) Conclusions and recommendations.
The authors conclude that deep well injection is a viable means of disposal when carried
out within the requirements of the UIC regulations. The regulations are sufficient,
although updates are needed for waste sampling protocol and chemical analysis of
samples in order to keep up with technological advances. Additions recommended for
Illinois' UIC program include analysis of the injection waste, which should be required at
the time of permitting and annually thereafter. Pretreatment of injection waste to remove
hazardous components could increase operating costs 3 to 40 times, depending on the
industry, and could have more serious environmental impacts than injection without
treatment. More research is needed on interaction between wastes, pore water, and
formations. A monitoring strategy should be developed.
The Cadmus Group, Inc. Responses to questions 2, 5c, and 9b of Congressman John D.
Dingell's letter to William K. Reilly, dated October 22, 1992, regarding disposal of hazardous
wastes, deep injection, and underground wells at 42 U.S.C. section 6924 (F) - (G). Prepared for
U.S. Environmental Protection Agency, Office of Ground Water and Drinking Water,
Underground Injection Control Branch. January 29, 1993 (for responses to 2 and 5c) and
February 24, 1993 (for response 9b).
Questions 2, 5c, and 9b of Congressman Dingell's letter request a list of wells for which
EPA has granted no-migration petitions, the education and background of staff who
review no-migration petitions, and reviews of compliance with groundwater monitoring
requirements associated with injection wells. This information is provided in the
response document.
Chemical Manufacturers Association, Underground Injection Control Program. Operational
Status of Class IHW Wells: 1984-1991. Washington, DC: Bryan, Cave, McPheeters &
McRoberts. February 1991.
This study was conducted to determine the impact of the Hazardous and Solid Waste
Amendments of 1984 on Class I hazardous waste injection well practices. The data
includes only those facilities that were in existence prior to 1984. The conclusions are
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Study of the Risks Associated with Class I UIC Wells
based on available documentation, including EPA's 1985 Report to Congress on the
Injection of Hazardous Waste, EPA's February 1988 Federal Underground Injection
Control Reporting System Class I wells printout, and individual facility reports.
Davis, Ken E., and T. Lawrence Hineline. "Two Decades of Successful Hazardous Waste
Disposal Well Operation—A Compilation of Case Flistories." Proceedings of the International
Symposium on Subsurface Injection of Liquid Waste. New Orleans, Louisiana, March 3-5, 1986.
Dublin, Ohio: National Water Well Association. 1986.
The monitoring systems and mechanical integrity programs required by the federal and
state UIC programs have an excellent record of detecting problem areas prior to any
deleterious effects on the environment. Most alleged MI failures are due merely to the
improper operation of monitoring equipment and do not result in any environmental
hazard. This article presents case histories on how operation problems were identified
and successfully eliminated, how monitoring systems identified potential problems, and
how wells were repaired.
Dingell, John D., Chairman, U.S. House of Representatives, Subcommittee on Oversight and
Investigations of the Committee on Energy and Commerce. Letter to William K. Reilly,
Administrator, U.S. Environmental Protection Agency, regarding disposal of hazardous wastes,
deep injection, and underground wells at 42 U.S.C. section 6924 (F) - (G). October 22, 1992.
Citing public concern about EPA's implementation of the HSWA Amendments,
Congressman Dingell requested information on injection wells, including no-migration
petitions, Class I well failures, inspection requirements, and other information.
Elsevier Science Inc. "RCRA Land Disposal Restrictions: A Guide to Compliance—1996
Edition." The Hazardous Waste Consultant. June/July 1996.
The most recent revisions to the Land Disposal Restrictions program were promulgated
in the Phase HJ LDR rule in early April 1996. The primary focus of this regulation is
implementation of H.R. 2036, the Land Disposal Program Flexibility Act. All of the
rules issued under Phases I, II, and HJ are discussed in this guide.
Gordon, Wendy, and Jane Bloom. "Deeper Problems: Limits to Underground Injection as a
Hazardous Waste Disposal Method." New York: Natural Resources Defense Council, Inc.
1986.
The injection of hazardous waste into subsurface rock formations is the predominant
form of liquid hazardous waste disposal in the United States and one of the least
understood. Despite the considerable reliance on underground injection for disposing of
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Study of the Risks Associated with Class I UIC Wells
hazardous wastes, neither the effective injection of fluids nor their safe containment can
presently be ensured. This article analyzes the practice of underground injection as a
hazardous waste disposal method and evaluates the limits to its use and the degree of
protection against groundwater contamination current injection methods can ensure. It
identifies specific research needs necessary to determine the technical and environmental
constraints associated with underground injection and its potential for ensuring complete
containment of waste. Also examined is the adequacy of the UIC program in preventing
groundwater contamination and other environmental damage due to migration of
hazardous wastes. The article recommends specific regulatory changes that could result
in more protective underground injection operations.
ICF, Inc. Class I Mechanical Integrity Failure Analysis: 1993-1998. Prepared by ICF, Inc.,
Fairfax, Virginia, for U.S. Environmental Protection Agency, Office of Ground Water and
Drinking Water, Underground Injection Control Program. September 1998.
This report summarizes mechanical integrity failures in Class I wells between 1993 and
1998, including the number of Class I injection failures during the period, the causes of
these MI failures, and EPA and state responses to them. It is a follow up to a similar
study of the period from 1988 to 1991. EPA found that between the last study and this
one, MI failures of all types dropped by half in every state, except Texas, where MI
failures increased two-fold. (The results of the study are described in greater detail in
Section V. A.)
Michigan Department of Natural Resources. Deep Well Injection of Hazardous Waste In
Michigan. May 1986.
The State of Michigan convened an advisory committee to determine whether deep well
injection in Michigan should be banned or allowed to continue under existing or revised
regulations. The committee concluded that deep well injection should be allowed to
continue, provided that the state's regulatory program is improved. Key
recommendations included specifying construction, closure, and mechanical integrity
testing requirements; banning the injection of highly toxic, persistent halogenated
organics; requiring shallow groundwater monitoring; requiring regular reassessments of
alternative technologies; and improving the compliance and enforcement program.
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Study of the Risks Associated with Class I UIC Wells
Reeder, Louis R., James H. Cobbs, John W. Field, Jr., William D. Finley, Steven C. Vokurka,
and Bernard N. Rolfe. Review and Assessment of Deep-Well Injection of Hazardous Waste
(Volumes I-IV). Prepared by Louis R. Reeder and Associates for U.S. Environmental Protection
Agency, Office of Research and Development, Municipal Environmental Research Laboratory.
June 1977.
Geologic and engineering data are generally available to locate, design, and operate a
deep injection well. In contrast, little information exists on salaquifer chemistry as well
as waste interactions with the receiving salaquifer. Problems occur when there is a
failure to use available geologic information and proven engineering practices in design
and completion. For more effective oversight of deep well injection, standardization of
state regulations is necessary.
Temple, Barker & Sloane, Inc. "Findings on Class I Hazardous Wells Affected by the Land Ban
Rules." Memorandum from Annette Hulse, Elaine Haemisegger, Marc Blaustein, Laurie
Remmers, and Hollie Maheney (TBS) to John Atecheson, Dave Morganwalp, and Mario Salazar,
U.S. Environmental Protection Agency. December 15, 1987.
This report summarizes the findings of a study on (1) wells affected by the land ban rules,
(2) available alternative commercial treatment, and (3) available transportation capacity
(truck and rail) to move the banned wastes from the current point of disposal to the point
of alternative treatment. The report concludes that, in the short-term after the land ban
would take effect, there would likely be a shortage of transport capacity given the great
increase in liquid hazardous waste to be transported. The report predicts that, after 2
years, the combination of reduced volumes of wastes to be transported and increased
transportation capacity should allow for safe movement of banned wastes.
Texas Department of Water Resources. Underground Injection Operations in Texas: A
Classification and Assessment of Underground Injection Activities. Compiled by Ben Knape.
Report 291. Texas Department of Water Resources, Austin, Texas. December 1984.
Underground injection operations in Texas are regulated by the Texas Department of
Water Resources (succeeded by the Texas Natural Resource Conservation Commission)
and the Railroad Commission of Texas. This report presents the history of regulatory
program development for underground injection operations in Texas. It describes the
construction features, operating practices, nature and volume of injected fluids, relative
pollution potentials, legal and jurisdictional considerations, and regulatory
recommendations for the various types of injection wells that exist in the state.
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Underground Injection Practices Council. A Class I Injection Well Survey (Phase I Report):
Survey of Selected Sites. D19976.S1. Prepared by CH2M Hill, Gainesville, Florida. April
1986.
This two-phase study provides a comprehensive data base and an objective summary of
the performance and operation of Class I injection wells. Phase I of study consisted of a
survey of the operational history of 45 Class I well sites representing 106 individual
wells. The selection of these 45 sites was based upon published reports and input from
UIC Program directors that identified injection well facilities with some history of or
alleged operation problems. This report provides a factual summary of the events
surrounding alleged operational problems at 45 Class I injection well facilities. (The
results of the study are described in greater detail in Section V.A.)
Underground Injection Practices Council. A Class I Injection Well Survey (Phase II Report):
Survey of Operations. December 1987.
In this nationwide study of Class I injection wells, files were reviewed and information
collected on 539 operational, previously operational, or planned wells. Phase n of the
study consisted of a survey of approximately 250 Class I injection well sites. Phase n
included development of a comprehensive data base for each of these sites and an
assessment of the performance characteristics of Class I injection wells. Ninety-nine of
these wells were eliminated from the data base because they could not be classified as
Class I wells by the type of waste injected, they were never constructed, or were under
construction when the study was conducted. Construction, operation, and permit data for
the remaining 440 wells as of January 1, 1985, were collected and reviewed to evaluate
the suitability and reliability of these wells as a waste disposal method. The primary
sources of information on Class I wells were the state or federal agencies responsible for
permitting the Class I wells in each state. The study concludes that Class I wells are a
viable method for disposal of wastewaters, where suitable hydrogeologic conditions exist.
Underground Injection Practices Council. Class I Injection Well Survey. Prepared by Golder
Associates, Inc., Houston, Texas. April 1990 (updated from April 1986).
This nationwide survey of Class I injection wells was conducted by Golder Associates to
evaluate the changes in geographic distribution and usage patterns and to identify the
major concerns of Class I injection operators. The collection of data for this survey
occurred from January 1 to March 31, 1990. As concluded in the previous Class I
Injection Well Survey (UIPC, 1987), this type of injection, as presently regulated, is a
cost-effective yet environmentally sound method of liquid waste disposal when suitable
hydrogeologic conditions exist.
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Study of the Risks Associated with Class I UIC Wells
U.S. EPA. Land Disposal Restrictions: Court Decision on Characteristic Hazardous Wastes.
Briefing for Administrator Carol Browner. March 1993.
This decisional briefing provides an overview of the RCRA Land Disposal Restrictions
Program, discusses the Third Third Rule, and highlights key aspects of the DC Circuit
Court's 1992 opinion on characteristic wastes and aspects of the Court's decision that
EPA must address.
U.S. EPA, Office of Drinking Water. Report to Congress on Injection of Hazardous Waste.
EPA 570/9-85-003. May 1985 (Second Printing, July 1985).
This report was prepared to meet the requirement of section 701 of the Hazardous and
Solid Waste Amendments of 1984. The report summarizes the collected raw data and
provides general information about disposal of waste by underground injection wells.
The report also covers aspects of engineering, hydrogeology, waste characteristics, and
regulatory controls.
U.S. EPA, Office of Drinking Water. Site Visit Report; (Facilities Visited as Part of the Data
Gathering Effort for the Preparation of the Report to Congress on the Injection of Hazardous
Waste). May 1985.
This document represents working papers used in preparation of the final Report to
Congress on the Injection of Hazardous Waste. It is a compilation of field reports on the
geology, well design and operation, and regulatory controls based on visits to 20 facilities
representing various hydrogeologic, regulatory, and other circumstances.
U.S. EPA, Office of Ground Water and Drinking Water. Underground Injection Control
Program: Information Collection Request. Prepared by the Cadmus Group, Inc. June 1998.
This document estimates the burden and cost to operators, states, and EPA associated
with implementing the UIC requirements. It outlines required activities associated with
siting, constructing, operating, and closing Class I hazardous and nonhazardous injection
wells based on the federal requirements at 40 CFR 146 and estimates cost associated with
all required activities, including no-migration petitions.
U.S. EPA, Office of Ground Water and Drinking Water. Analysis of the Effects of EPA
Restrictions on the Deep Injection of Hazardous Waste. EPA 570/9-91 -031. October 1991.
This report describes how EPA regulations, including the no-migration petition
requirement, prevent Class I hazardous wells from endangering USDWs. It also
documents changes in the Class I hazardous well population and Class I hazardous waste
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Study of the Risks Associated with Class I UIC Wells
management practices that have occurred since the regulations were promulgated. The
report concludes that Class I hazardous wells are subject to strict technical requirements
and are rigorously evaluated to ensure that they do not endanger USDWs.
U.S. EPA, Office of Ground Water and Drinking Water, Underground Injection Control Branch.
Class I Well Failure Analysis: 1988-1991. Prepared in response to Question 4 in Congressman
John D. Dingell's letter to William K. Reilly, dated October 22, 1992, regarding disposal of
hazardous wastes, deep injection, and underground wells at 42 U.S.C. section 6924 (F) - (G).
March 5, 1993.
This study focuses on the records of over 500 Class I wells in 14 states for the period
January 1988 to January 1993. Findings include 130 internal mechanical integrity (MI)
failures, 1 external MI failure, and 4 cases of significant waste migration. None of the
failures is known to have affected a USDW. The 130 internal MI failures were detected
during operation by the continuous annulus monitoring system, and the wells were
automatically shut-in until operators could make repairs. The single external MI failure
did not involve waste migration from the injection zone or flow into a USDW, and was
detected by routine periodic external MIT. Three of the 4 cases of nonhazardous waste
migration occurred in areas of Florida known to have small-scale natural fracturing and
were detected by deep monitoring wells installed for that purpose. The mechanism of
migration of the other case (Aristech, Ironton OH) is unclear, but is believed to be small-
scale natural fracturing. The need for deep monitoring wells at every Class I facility is
precluded by geologic conditions at most sites, but the option is available to directors if
local conditions warrant their use. (The results of the study are described in greater detail
in Section V.A.)
U.S. EPA, Office of Water Supply. The Report to Congress. Waste Disposal Practices and
Their Effects on Ground Water. January 1977.
This report to Congress examines the impact of waste disposal practices, including
injection, on groundwater quality in the United States. It discusses the severity of
contamination, sources of contaminants, and the regions of the nation where
contamination is most prevalent. The report recommended additional legislation for
groundwater protection. It also encouraged data collection on potential sources of
contamination and more careful siting of new land disposal facilities.
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Study of the Risks Associated with Class I UIC Wells
U.S. General Accounting Office. Hazardous Waste—Controls Over Injection Well Disposal
Operations. Report to the Chairman, Environment, Energy, and Natural Resources
Subcommittee, Committee on Government Operations, House of Representatives. GAO/RCED-
87-170. August 1987.
At the request of the Chairman of the Environment, Energy, and Natural Resources
Subcommittee, House Committee on Government Operations, GAO assessed the controls
that monitor the operations of underground injection wells. It evaluated whether and to
what extent there is evidence that hazardous waste from underground wells has
contaminated underground sources of drinking water. GAO also assessed EPA and state
oversight of underground injection of hazardous waste and determined what program
changes are expected from an upcoming ban on the underground injection of hazardous
waste. (The results of the study are described in greater detail in Section V.A.)
U.S. General Accounting Office. Information on EPA 's Underground Injection Control
Program. GAO/RCED-95-21. Report to The Honorable John D. Dingell, Chairman,
Subcommittee on Oversight and Investigations, Committee on Energy and Commerce, House of
Representatives. December 5, 1994.
This report reviews certain aspects of EPA's program governing deep-well injection.
Specifically, these include (1) results of EPA's efforts to implement the 1984
amendments to ban underground injection of hazardous wastes, (2) accuracy of EPA's
inspection and enforcement data to ensure reliable program oversight, and (3)
implementation of recommendations to improve the UIC program made in earlier reports.
The report concludes that EPA has either implemented or is in the process of
implementing most of the recommendations contained in GAO's prior two reports,
including strengthening its oversight of each region's underground injection control
program. EPA is currently reviewing proposed changes to the oil and gas waste injection
well program. One of the proposed changes would require all well operators to search
for and plug any improperly plugged wells in the immediate vicinity of their wells, as
GAO recommended.
Van Voorhees, Robert F., Kenneth M. Kastner, and Barton D. Day. New RCRA Land Disposal
Restrictions Will Radically Change Regulation of Characteristic Hazardous Waste. Prepared by
Bryan Cave. 1994.
This report is an update on the status of the RCRA LDR rules imposed by EPA in
response to the "Third Third" court decision. The report also summarizes the key
changes that occurred to the LDR program and EPA's rulemaking schedule.
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Visocky, Adrian P., Gary R. Peyton, and John S. Nealon. "Study of Current Underground
Injection Control Regulations and Practices in Illinois." Proceedings of the International
Symposium on Subsurface Injection of Liquid Waste. New Orleans, Louisiana, March 3-5, 1986.
Dublin, Ohio: National Water Well Association. 1986.
The regulatory structure for Class I injection wells is generally adequate in concept and
scope to ensure containment of injected wastes and to safeguard underground sources of
drinking water in Illinois. There is a need to update and strengthen selected portions of
the regulatory practices in the areas of waste sampling protocol, chemical analysis of
collected waste samples, and evaluation of well testing and monitoring data.
Class I Research
Collins, A. Gene and M.E. Crocker. Laboratory Protocol for Determining Fate of Waste
Disposed in Deep Wells: Project Summary. EPA/600/S8-88/008. Ada, Oklahoma: U.S.
Environmental Protection Agency, Robert S. Kerr Environmental Research Laboratory. April
1988.
The objective of this research investigation was to develop a laboratory protocol for use
in determining degradation, interaction, and fate of organic wastes disposed of in deep
subsurface reservoirs via disposal wells. Knowledge of the ultimate fate of such wastes is
important because provisions of the Resource Conservation and Recovery Act (RCRA)
require that by August 1988, EPA must show that the disposal of specified wastes by
deep-well injection is safe to human health and the environment, or the practice must be
stopped. The National Institute for Petroleum and Energy Research (NIPER) developed
this protocol primarily by transferring some of its expertise and knowledge of laboratory
protocol relevant to improved recovery of petroleum; for example, (1) core analysis, (2)
brine analysis, (3) oil analysis, (4) dynamic fluid flow systems, which simulate subsurface
reservoir conditions, and (5) appropriately trained personnel. This study was designed to
investigate the adsorption properties of a specific reservoir rock which is representative
of porous sedimentary geologic formations used as repositories for hazardous organic
wastes. Phenol is the principal hazardous waste product that has been injected into the
Frio formation; therefore, a decision was made to use phenol and sedimentary rock from
the Frio formation for a series of laboratory experiments to demonstrate the protocol.
The developed protocol can be used to evaluate mobility, adsorption, and degradation of
an organic hazardous waste under simulated subsurface reservoir conditions.
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Goolsby, Donald A. Geochemical Effects and Movement of Injected Industrial Waste in a
Limestone Aquifer. April 1972.
This paper presents a case history and the hydraulic and geochemical effects of an
industrial injection well system near Pensacola, Florida. Geochemical effects of the
injection, which were first detected at a monitoring well 10 months after injection
commenced, included increases in calcium ion concentration, total alkalinity, and
nitrogen and methane gas generation. Tests made in 1968 indicated that rapid
denitrification and neutralization of the waste occurred near the wells.
Grula, M.M., and E.A. Grula. Feasibility ofMicrobial Decomposition of Organic Wastes Under
Conditions Existing in Deep Wells. Final Report. U.S. Bureau of Mines. December 31, 1975.
The objective of this work was to determine the feasibility of inoculation of underground
injected wastes with bacteria which would decompose toxic substances underground
through metabolic processes. If such a technique could be developed, the toxicity of the
injected wastes could eventually be neutralized and thus eliminate a possible, although
remote, hazard that would result if the injected wastes found a conducting path to the
surface at some future date. Several new aspects of microbe growth under conditions of
elevated temperature and pressure were discovered. However, the general conclusion
drawn from this work is that biodegradation of organic compounds will be very limited,
or entirely absent, under the conditions existing in deep geologic formations.
Ffickey, John J., and William E. Wilson. Results of Deep-Well Injection Testing at Mulberry,
Florida. USGS/WRI 81-75. PB82-193004. Tallahassee, Florida: U.S. Geological Survey,
Water Resources Division. February 1982.
At the Kaiser Aluminum and Chemical Corporation plant, Mulberry, Florida, high-
chloride, acidic liquid wastes are injected into a dolomite section at depths below about
4,000 feet. Sonar caliper logs made in April 1976 revealed a solution chamber that is
about 100 feet in height and has a maximum diameter of 23 feet in the injection zone.
Results from two injection tests in 1972 were inconclusive because of complex
conditions and the lack of an observation well that was open to the injection zone. In
1975, a satellite monitor well was drilled 2,291 feet from the injection well and open to
the injection zone. In April 1975 and September 1976, a series of three injection tests
were performed. Based on an evaluation of the factors that affect hydraulic response,
water-level data suitable for interpretation of hydraulic characteristics of the injection
zone were identified to occur from 200 to 1,000 minutes during the test. Test results
indicate that leakage through confining beds is occurring. It appears that the overlying
beds are probably relatively impermeable and significantly retard the vertical movement
of neutralized waste effluent.
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Horvath, Edward. Interactions of Aquifer Flora and Industrial Waste in a Model Deep Well
Disposal System. Ph.D. Thesis, Department of Microbiology, North Carolina State University at
Raleigh. 1977.
A model system was developed to study the biological compatibility of aqueous industrial
waste and subterranean disposal zones for injected waste. The model design
incorporated devices for anaerobic, aseptic compositing of effluent samples (for chemical
and biological analysis); collection of gases generated in the model elements; isolation of
model elements against downstream contamination; and imposition of a normally
distributed waste concentration profile in the feed stream. The model demonstrated that
degradation of waste constituents was dependent on the addition of inorganic nutrients,
even in diluted wastes. The model was also used to study the mutual effects of
formaldehyde-free waste and aquifer flora. In effluent samples, formic acid in the waste
was completely degraded in 2 months; this degradation is related to reduction of sulfate
and nitrate in aquifer flora.
Jafvert, Chad T. and N. Lee Wolfe. Degradation of Selected Halogenated Ethanes in Anoxic
Sediment-Water Systems. Undated.
This paper presents the results of a study on degradation of selected halogenated ethanes
in anoxic sediment-water suspensions. This study was undertaken to investigate factors
that influence the rates of reductive transformations of halogenated hydrocarbons in
environmental systems. The study examined both environmental variables and inherent
chemical properties of substituted compounds. Eh measurements indicated reduced
environmental conditions. Hexachloroethane, 1,1,2,2-tetrachloroethane, 1,2-
diiodoethane and 1,2-dibromoethane degraded within minutes to days; 1,2-dichloroethane
remained in the systems for at least 35 days (the length of the experiment).
Johnston, Orville C., and Ben K. Knape. Pressure Effects of the Static Mud Column in
Abandoned Wells. LP86-06. Texas Water Commission, Austin, Texas. September 1986.
This study evaluated historical drilling practices and the safety of injection operations as
they relate to possible inter-formational fluid movement through abandoned boreholes,
gel strength of wellbore muds, and the effects of geologic and geographic variation on
natural borehole closure. It was based on literature and file research and interviews with
knowledgeable staff. The study found that wells plugged with mud only resist vertical
fluid movement to some extent, that abandoned uncased wells may remain stable for up
to decades, mud gel strengths increase with time and temperature, and some abandoned
uncased wells close on themselves due to unstable geology.
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Kreitier, Charles W. "Hydrogeology of Sedimentary Basins as it Relates to Deep-Well Injection
of Chemical Wastes." Preprint of a paper presented at the International Symposium on
Subsurface Injection of Liquid Waste. New Orleans, Louisiana. March 3-5, 1986.
This paper describes and compares the hydrogeology of three sedimentary basins in
Texas (the Gulf of Mexico, East Texas, and Palo Duro basins). Sedimentary basin
hydrogeology is important to hazardous waste injection because regional hydrogeology
controls the fate, transport, and confinement of chemical wastes injected into deep saline
sections of sedimentary basins. Factors that control and describe basin hydrogeology
include geologic history, flow mechanisms, potential energy distributions, permeability,
the occurrence of faults and fractures, and the origin and age of saline waters.
Leenheer, R.L. Malcolm and W.R. White. Physical, Chemical, and Biological Aspects of
Subsurface Organic Waste Injection Near Wilmington, North Carolina. U.S. Geological Survey
Professional Paper 987. 1976.
This is a case study of injection of an industrial organic waste into a sand, gravel, and
limestone aquifer near Wilmington, North Carolina. Field and laboratory data pertaining
to the physical, chemical, and biological effects of waste injection at the site are also
presented. The report discusses a conceptual model of the various stages of injectate
reactivity and its subsurface movement. Problems with injection well pressure build-up
and migration of wastes into shallower aquifers are attributed to reactions between
certain organic wastes and aquifer components.
Schwarzenbach, Rene P., and Walter Giger. Behavior and Fate of Halogenated Hydrocarbons
in Ground Water. Undated.
Groundwater contamination by halogenated hydrocarbons has been reported on
numerous occasions, and these compounds present human health concerns. This paper
summarizes the results of laboratory and field studies on the behavior and fate of
halogenated hydrocarbons in ground water and during groundwater infiltration. For
example, many halogenated hydrocarbons are very mobile and are quite resistant to
chemical transformations. Little is known about biotransformation, however. The paper
focuses on sorption behavior and mobility of halogenated hydrocarbons in aquifers. The
chemical and biological transformations of individual chemicals are discussed as well.
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Scrivner, N.C., K.E. Bennett, R.A. Pease, A. Kopatsis, SJ. Sanders, D.M. Clark, and M. Rafal.
"Chemical Fate of Injected Wastes." Proceedings of the International Symposium on Subsurface
Injection of Liquid Waste. New Orleans, Louisiana, March 3-5, 1986. Dublin, Ohio: National
Water Well Association. 1986.
The chemical fate of wastes put into disposal wells can be determined using standard
chemical engineering techniques. The concentration of hazardous constituents is
typically reduced by reactions within the waste itself or by reactions with the injection
zone material, thus reducing any potential impact on the environment. Such reactions
include neutralization, hydrolysis, ion exchange, adsorption, precipitation, co-
precipitation, and microbial degradation. Extensive research was done to quantify these
phenomena, so they could be used in a predictive model.
Vecchioli, John, D.J. McKenzie, C.A. Pascale, and W.E. Wilson. Active Waste-Injection
Systems in Florida, 1976. Open-File Report 79-1296. U.S. Department of the Interior,
Geological Survey. 1979.
By the end of 1976, seven systems were injecting liquid wastes into Florida's subsurface
environment at a combined average rate of 15 million gallons per day. This report
presents information for each of these systems on the kind and amount of waste injected
and type of pre-treatment, construction characteristics of the injection and monitor wells,
type of test and monitoring data available, and briefly discusses any operational problems
experienced.
Walter, Bill. "Remediation of Ground-Water Contamination Resulting From the Failure of a
Class I Injection Well: A Case History." Proceedings of the International Symposium on
Subsurface Injection of Liquid Waste. New Orleans, Louisiana, March 3-5, 1986. Dublin, Ohio:
National Water Well Association. 1986.
The purpose of this paper is to describe the sequence of events leading to the
contamination of a USDW and the ongoing cleanup process at an oil refinery industrial
waste disposal well in the New Orleans, Louisiana area. The case history is unique in
that the chronology covers a period of time which includes both pre- and post-regulatory
compliance with respect to permitting, monitoring, reporting, inspection and testing of
injection wells. Contaminated ground water near the injection zone has not been shown
to pose a hazard to any water wells in the area. Furthermore, future ground water
contamination being caused by the injection method used is unlikely because injection
wells currently permitted in Louisiana are equipped with injection tubing and continuous
monitoring of the annular space.
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Risk Analyses
Chemical Manufacturers Association UIC Management Task Group. Comments on Benefits
Assessment of EPA 's Draft Regulatory Impact Analysis. Prepared by Woodward-Clyde
Consultants. May 1995.
This critique of the Benefits Analysis in the Phase HI RIA evaluated the qualitative risk
assessment in the RIA. It emphasized that there have not been any instances of USDW
contamination at a facility in compliance with the current UIC program regulations, and
the malfunctions cited in the RIA involved facilities that had not yet been required to
comply with the UIC program requirements. The comments assert that injection of
hazardous waste is particularly low risk compared to other waste management practices,
and the risks of handling, transporting, and treating segregated Phase HI wastes might
actually be greater than the risks of injecting the waste. (The results of the study are
described in greater detail in Section V.C.)
GeoTrans, Inc. A Numerical Evaluation for Class I Injection Wells for Waste Confinement
Performance, Final Report, Volumes I and II. Prepared for U.S. Environmental Protection
Agency, Office of Drinking Water, Underground Injection Control Program. September 30,
1987.
The objective of this study was to evaluate the hydrogeologic response of injection well
systems to potential migration pathways in order to assess their impact on waste
containment performance. The scope of work assumed that these pathways may exist,
allowing waste to migrate from the injection interval into the containment and/or other
hydrogeologic strata in the vicinity of injection wells. The study relied on numerical
models of groundwater flow and chemical waste transport. Among the findings were the
following: under certain conditions, failure can result in escape of significant waste
volumes from the injection zone within a localized area; confinement performance
increases with distance between the injection well and the failure pathway; and the effect
of pumpage on overlying strata increases the volume of waste escaping in the presence of
a failure pathway. (The results of the study are described in greater detail in Section
V.B.)
Industrial Economics, Inc. Risk Analyses for Underground Injection of Hazardous Wastes.
Prepared for U.S. EPA, Office of Drinking Water. May 1987.
This report estimates the magnitude of human health risks posed if underground injection
of hazardous wastes resulted in contamination of USDWs. Risk estimates are presented
for four geologic settings (East Gulf Coast, Great Lakes, Texas, and Kansas) and various
failure modes and barrier thickness between the injection zone and the USDW. The risk
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analysis concludes that risk varies substantially (over 20 orders of magnitude) among the
geologic settings studied. Also, the risks associated with an abandoned, unplugged
borehole are significantly greater than those associated with grout seal failure. Lastly, the
report concludes that estimated health risks rise significantly when water is withdrawn
from a USDW in the abandoned borehole failure scenario. (The results of the study are
described in greater detail in Section V.B.)
Rish, W.A., T. Ijaz, and T.F. Long. A Probabilistic Risk Assessment of Class I Hazardous Waste
Injection Wells. Draft. 1998.
This study quantitatively estimates the risk of waste containment loss as a result of
various sets of events associated with Class I hazardous wells. Through a series of "event
trees," the study estimated the probability that an initiating event will occur and be
undiscovered, followed by subsequent events that could ultimately result in a release of
injected fluids to a USDW. It concluded that Class I hazardous injection wells which
meet EPA's minimum design and operating requirements (i.e., a completed no-migration
study, two confining zones between the injection zone and the lowermost USDW,
completed long string and surface casings, and redundant safety systems) pose risks that
are well below acceptable levels. (The results of the risk assessment are described in
greater detail in Section V.D.)
U.S. EPA, Office of Ground Water and Drinking Water. Final Draft: Regulatory Impact
Analysis of Proposed Hazardous Waste Disposal Restrictions for Class I Injection of Phase III
Wastes: Benefits Analysis. 1995.
This Benefits Analysis of the proposed Phase m LDR rule estimated human health risks
from five Phase HI waste constituents (benzene, carbon tetrachloride, chloroform, phenol,
and toluene). EPA estimated health risks, including cancer risks and hazard indices, for
four geologic settings and two malfunction scenarios (grout seal failure and abandoned,
unplugged borehole) at varying drinking water well pumping rates. The results showed
that only two of the estimated cancer risks for both malfunction scenarios slightly exceed
the risk range generally used by EPA to regulate exposure to carcinogens. The analysis
also showed that all but one of the hazard indices for both malfunction scenarios are less
than EPA's level of concern for a hazard index of 1.55. (The results of the benefits
analysis are described in greater detail in Section V.C.)
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U.S. EPA, Office of Ground Water and Drinking Water. Evaluation of Risks from Exceedance of
the Universal Wastewater Treatment Standards (UTS), Including Addendum onHWIR
Concentrations. February 1996.
To support the de minimis requirements in the proposed Phase m rule, EPA analyzed the
effects of varying the criteria that underlying hazardous constituent concentrations must
be less than 10 times UTS. Results of the analysis showed that, in general, carcinogenic
risks were within the range generally used by EPA to regulate exposure to carcinogens,
and noncancer risks were less than the hazard index of 1. The analysis concluded that a
standard which would be more reflective of the potential for health hazards could be
satisfied by defining the de minimis criterion as a value between 10 times and 50 times
the UTS. (The results of the risk evaluation are described in greater detail in Section
V.C.)
U.S. EPA, Office of Solid Waste and Remedial Response. OSWER Comparative Risk Project:
Executive Summary and Overview. EPA/540/1-89/003. November 1989.
In this study, several workgroups explored the comparative risks posed by various waste
management practices regulated by or under OSWER purview. The study determined
that injection wells generally posed medium or low risk for the types of effects examined.
The workgroups found Class I hazardous wells to be of comparatively low risk for non-
acute heath effects. Injection wells were ranked medium in terms of risk for acute health
effects, medium-low for ecological effects, and of low risk for welfare effects. (The
results of the study are described in greater detail in Section V.A.)
Ward, D.S., D.R. Buss, T.D. Wadsworth, J. Rosenblum, and S.T. Shaw. Numerical Simulation
for Waste Injection in Deep Wells: Phase 1 — Potential Failure Scenarios, Texas Gulf Coast.
Prepared by Engineering Enterprises, Inc. Prepared for U.S. Environmental Protection Agency,
Office of Drinking Water. Herndon, Virginia: GeoTrans, Inc. January 1986.
This report presents the results of the first phase of a three-part study on well failures.
The purpose of Phase 1 was to assess the effect of undetected characteristics (the
presence of an abandoned unplugged borehole, fractured discontinuities in the confining
zone, failure of a grout seal, and high rates of ground water withdrawal in the aquifer
above the confining layer) on the hydrologic performance of an injection zone.
Preliminary results include the following findings: under certain conditions, failure can
result in escape of significant waste volumes from the injection zone; potential
contaminations can vary from waste concentrations that are below detection levels to
nearly the same as that of the injectate; and potential contamination occurs within a
localized area. These results will be used to formulate recommendations in later phases
of the study.
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Ward, D.S., T.D. Wadsworth, D.R. Buss, and J.W. Mercer. "Analysis of Potential Failure
Mechanisms Pertaining to Hazardous Waste Injection in the Texas Gulf Coast Region."
International Symposium on Subsurface Injection of Liquid Wastes New Orleans, Louisiana.
March 3-5, 1986.
Three failure scenarios are presented and simulated to assess the effect of undetected
characteristics of the Texas Gulf Coast hydrologic system in containing waste. The
scenarios are failure of a grout seal, the presence of an abandoned unplugged borehole,
and fractured discontinuities in the confining zone. A three-dimensional, finite-
difference model is used to simulate these three failure scenarios. Results from the
simulations are presented as time series plots of concentrations for various locations in
the injection zone and the USDW. These simulations assist in determining the degree of
safety inherent in hazardous waste injection.
Ward, David S., David R. Buss, David W. Morganwalp, and Terry D. Wadsworth. "Waste
Confinement Performance of Deep Injection Wells." Proceedings from Solving Ground Water
Problems With Models. Denver, Colorado. February 10-12, 1987.
A numerical flow and transport model is used to simulate the potential migration of waste
over the operational life of an injection well and to evaluate the hydraulic response to
hypothetical undetected pathways in the confining formations. Three potential pathways
are considered in this analysis: annular grout seal deterioration (cement between casing
and formation); presence of an unplugged, abandoned borehole; and plane of fractures or
conductive faults in the confining unit. The study includes findings on the impact of
migration pathways in four hydrogeologic settings studied (East Gulf Coast, Great Lakes,
Texas, and Kansas), and the waste confinement potential within each setting.
Technical and Instructional Documents
Apps, John A., and Chin-Fu Tsang, eds. Deep Injection Disposal of Hazardous and Industrial
Waste: Scientific and Engineering Aspects. San Diego, California: Academic Press. 1996.
This book is divided into eight sections that address the major subject areas pertinent to
deep injection disposal. The first section concerns some topics from the regulatory
perspective. It is followed by an introductory section covering the general aspects of
deep-well injection disposal. The focus of this section is on principles and criteria
affecting the optimal siting and operation of disposal wells. Section HJ includes papers
on the engineering aspects of well design and emplacement. Following in Section IV is a
collection of papers dealing with the important issues of well testing and model
development. Section V addresses some of the attendant problems of well performance
monitoring. Section VI, consisting of 10 chapters, addresses various aspects of the
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chemical processes affecting the fate of the waste in the subsurface environment.
Consideration is given here to reactions, such as acid neutralization, between the waste
and the geologic medium and to reactions that take place within the wastewater itself,
leading to the destruction of hazardous organic compounds. All aspects of this subject
are covered, including experimentation, field observation, theoretical modeling, and
prediction. Section VII provides a unique perspective on the philosophy and
implementation of radioactive waste disposal practices in the former Soviet Union.
Section Vin brings together four chapters that discuss novel technologies concerned with
the disposal of hazardous waste slurries by deep well injection.
Booz, Allen and Hamilton, Inc. Development of Procedures and Costs for Proper Abandonment
and Plugging of Injection Wells. Prepared by Booz, Allen and Hamilton Inc. under the direction
of Geraghty & Miller, Inc. for U.S. Environmental Protection Agency, Office of Drinking Water.
April 30, 1980.
This report summarizes the data analysis and findings on proper abandonment and
plugging. The objective was to assist EPA in resolving issues raised in public comments
on the proposed abandonment regulations and in completing the rule making. Five major
topic areas are discussed: (1) procedures for proper abandonment; (2) feasibility of
aquifer restoration; (3) abandonment costs; (4) financial responsibility; and (5) timing of
abandonment. Based on the public comments, literature review, and interviews, several
recommendations were made. The authors recommended retaining the proposed mud
weight equalization requirement for the well preparation phase of abandonment. On the
issue of aquifer restoration, they recommended that EPA issue guidance for restoration
and allow states to adopt requirements if desired; they concluded it was not feasible to
restore all degraded aquifers to baseline levels. The data indicate that costs of new
abandonment regulation will be low, since most states already require proper
abandonment. The authors suggest that EPA not require immediate abandonment but
determine a reasonable deadline beyond which wells must be properly abandoned or put
back into operation.
Clark, J. E., P. W. Papadeas, D. K. Sparks, and R. R. McGowen. "Gulf Coast Borehole Closure
Test Well: Orangefield, Texas." In: Proceeding of the Underground Injection Practices
Council, 1991 Winter and Summer Meetings. Point Clear, Alabama, February 24-27, 1991 and
Reno, Nevada. July 28-31, 1991.
This paper describes a borehole closure protocol for a Gulf Coast site near Orangefield,
Texas, developed by Du Pont. The procedures, based largely upon recommendations
provided by EPA Region 6, created a test to demonstrate that, under a worst case
scenario, any artificial penetration will seal naturally. The test successfully demonstrated
natural sealing. Within 1 week of setting the screen, tubing, and pressure transducers in
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Study of the Risks Associated with Class I UIC Wells
the borehole, testing confirmed the absence of upward movement of fluid from the test
sand. The absence of upward movement is documented by a Schlumberger Water Flow
Log and the absence of pressure response on the upper transducer located outside the
tubing and inside the casing. Testing was conducted in accordance with specified
procedures, with pressure testing conducted at even higher pressures to allow an added
margin of confidence. The borehole closure test provides a significant additional margin
of confidence that there will be no migration of hazardous constituents from the injection
zone for as long as the waste remains hazardous.
Creech, John R. "Class I Injection Well Design Considerations." Proceedings of the
International Symposium on Subsurface Injection of Liquid Waste. New Orleans, Louisiana,
March 3-5, 1986. Dublin, Ohio: National Water Well Association. 1986.
No single material is available that is universally resistant to all types of waste fluids. It
is important to match well materials to the injection stream for each injection well
application. For some wastes, the ferrous and nonferrous metals or Portland cements
commonly used in deep well construction may not offer the desired corrosion resistance.
This paper discusses two materials, fiber-reinforced thermoset plastics (FRP) and epoxy
resin cement, which have been particularly useful in solving these corrosion resistance
problems. The report concludes that when proper materials are used to minimize
corrosion, less maintenance and repairs are required and well operations are more
reliable.
Davis, Ken E. Factors Affecting the Area of Review for Hazardous Waste Disposal Wells.
1986.
This paper presents a method for calculating the area of review for hazardous waste
wells. It focuses on artificial pathways such as abandoned test holes or oil and gas wells.
These pathways are sealed with cement plugs and drilling mud; the mud provides
resistance to upward flow. Flow in an improperly abandoned well bore is initiated when
the pressure in an injection zone exceeds the sum of the static mud pressure and the mud
gel strength pressure. If the sum of these values is not exceeded, no potential for USDW
contamination exists. This paper presents a simplified approach for calculating the area
affected by the injection pressures.
Engineering Enterprises, Inc. Assessment of Treatment Technologies Available to Attain
Acceptable Levels for Hazardous Waste in Deep Injection Wells. Prepared for U.S.
Environmental Protection Agency, Underground Injection Control Branch. October 1987.
The potential for restrictions on land-disposal of hazardous waste into deep injection
wells under the Hazardous and Solid Waste Amendments of 1984 stimulated the need to
71
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Study of the Risks Associated with Class I UIC Wells
evaluate the ability of treatment technologies to reduce the likelihood of migration of
hazardous waste constituents from the injection zone. Physical/chemical and biological
(both above ground and in situ) pre-treatment technologies were assessed with respect to
their potential applicability in minimizing the mobility of injected hazardous constituents
via adsorption, precipitation, or transformation. The study shows that pretreatment
applications to minimize the mobility of contaminants in the injection zone could pose
operational problems for deep well injection systems. The extent to which specific
contaminants may be removed is unknown and may be complicated by interference with
nonhazardous components of the wastestream and by varying composition and
concentrations of many wastestreams. One important consideration is that many
pretreatment technologies result in the generation of sludge residue, requiring further
treatment or disposal.
Geraghty & Miller, Inc. Technical Manual: Injection Well Abandonment. Final. Prepared for
U.S. Environmental Protection Agency, Office of Drinking Water. 1983.
The purpose of this document is to provide technical guidance to assist the regulator in
reviewing proposed well abandonment plans. Emphasizing that proper abandonment
consists of more than cement plug placement, the document discusses all aspects of well
abandonment. Many procedures and materials are available for well abandonment; their
selection is influenced by a number of factors and depends on the specifics of the
situation. Frequently, there is no single best method. The approach taken in this
document is to identify and discuss the considerations needed to plug and abandon wells
of Classes I, n, or HI. This approach will enable the regulator to make decisions
regarding a specific abandonment plan. In this document, four major chapters follow the
introduction in Chapter 1. Chapter 2 considers injection well construction, general
considerations important to abandonment, and special Class in abandonment
considerations. Chapter 3 discusses the preparation of the well prior to plugging.
Procedures for plugging are covered in Chapter 4. Chapter 5 concludes the report with
an analysis of abandonment costs.
Geraghty & Miller, Inc., and Booz, Allen & Hamilton, Inc. Injection Well Construction
Practices and Technology. Prepared for U.S. Environmental Protection Agency, Office of
Drinking Water. October 1982.
This document describes construction practices and technologies related to Class I, Class
n, and selected Class in and Class V injection wells as defined by EPA. Topics covered
include siting, drilling, completion, equipment and materials, corrosion control, well
evaluation/logging, and formation testing. This document is not intended to be a
comprehensive "how-to" treatment of injection well construction; rather, it is a reference
that describes the different aspects of design and construction of injection wells.
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Study of the Risks Associated with Class I UIC Wells
Kazmann, Raphael G. "A Closer Look at Deep Well Disposal of Wastes." Ground Water.
May/June 1981.
This discussion is directed to conditions in the area away from the injection well: within
the quarter-mile to half-mile radius required by the EPA and the various state agencies.
The wells and abandoned test holes in this area are seen as potential pathways for the
movement of dangerous aqueous wastes from the storage aquifer to the biosphere. The
concern here is primarily with conditions in the Gulf Coast area, where the underlying
formations are either unconsolidated or semiconsolidated.
Keckler, K. P. "BP Chemicals Lima No-Migration Petition Demonstration Based on
Stratigraphic Test-Well and Site-Specific Data." In: Deep Injection Disposal of Hazardous and
Industrial Waste: Scientific and Engineering Aspects. John A. Apps and Chin-Fu Tsang, eds.
San Diego, California: Academic Press. 1996. p. 287-314.
To demonstrate containment of injected wastewater and to calibrate a site-specific
reservoir model, BP Chemicals drilled a Stratigraphic test well at a Lima, Ohio, facility
where it has injected wastewater from acrylonitrile production since 1968. This paper
presents the results of the extensive geologic testing and transport modeling. Sampling
from the waste plume at a test well approximately 1,700 feet from the nearest injection
well indicated significant degradation of most of the nitriles in the injected waste. In
addition, BP developed an extensive database which included core mechanical
properties; in situ stress test, transient pressure test, and minifrac test data; and a
summary of the facility's 20-year operating history.
Ken E. Davis Associates. Annulus Pressure Monitoring Systems for Class I Wells. Prepared by
Ken E. Davis Associates, Houston, Texas, for U.S. Environmental Protection Agency, Office of
Drinking Water. October 1986.
This report presents specific information concerning equipment and procedures currently
in use or available for detecting leakage from the annulus between the injection tubing
and the protection casing in injection wells. In current operating practice, this annulus
space is filled with nonhazardous, nonreactive fluid and maintained at a predetermined
pressure. The annulus pressure is monitored because a leak will result in a change in the
annulus pressure. However, the minimum rate of leakage or the amount of leakage that
can be detected by pressure-monitoring systems is not known. In addition, information is
also needed on alternative means of detecting leaks in disposal wells. This report is
therefore not confined to reporting on equipment and systems in use, but also on systems
73
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Study of the Risks Associated with Class I UIC Wells
that have the potential for such use. This report includes a review and inventory of
equipment that is, has, or could be used to detect leaks into or out of the annulus space in
injection wells. In addition, the review compares the leak detection capability of wells
completed with packers, seal assemblies, and fluid seals.
Mankin, Charles J., Tola B. Moffett, and Laura E. Whitaker. Evaluation of Certain Crucial
Issues Regarding the Use of Hazardous Waste Injection Wells. Prepared by the University of
Alabama Environmental Institute for Waste Management Studies for U.S. Environmental
Protection Agency, Office of Drinking Water. August 1988.
This report contains an evaluation of specific methodologies for siting, testing, and
monitoring of Class I injection wells. The evaluation of potential locations for hazardous
waste injection wells is a site-specific process which is analogous to that performed in the
siting of oil and gas wells. Seismic surveys and pressure testing, both of which are used
in the petroleum industry, are recommended. Regional studies and standard well logs are
considered insufficient. Hydrogeologic models of the site should be developed and
updated through the drilling and testing of the injection well. Recommendations for the
monitoring and testing of industrial waste injection wells are discussed.
SMC Martin, Inc., and The Underground Injection Control Quality Assurance Workgroup.
Technical Assistance Document: Corrosion, Its Detection and Control in Injection Wells.
Prepared for U.S. Environmental Protection Agency, Office of Drinking Water. August 1987.
This report summarizes available information on the occurrence, detection, and control of
corrosion in injection wells. Corrosion of the metallic materials and degradation of
nonmetallic materials are possible causes of leaks in injection wells. General corrosion,
the uniform or near-uniform thinning of metal, may be addressed by building a corrosion
allowance into the design thickness of the well casing. Localized corrosion, such as
pitting and cracking, is problematic because it can lead to premature failure of the well.
Tsang, C. F. "Some Hydrologic Factors Affecting the Safety of Deep Injection Disposal of
Liquid Wastes." In: Deep Injection Disposal of Hazardous and Industrial Waste: Scientific and
Engineering Aspects. John A. Apps and Chin-Fu Tsang, eds. San Diego, California: Academic
Press. 1996. p. 35-45.
Factors such as the presence of faults, formation fracturing pressures, and hydrology as
they relate to monitoring systems are important considerations in the planning of deep
injection wells. This paper reviews three phenomena that could affect estimates of waste
plume movement within the injection zone. They are formation heterogeneity; sloping of
the injection zone, which can cause a plume to flow by gravity; and fractures that can
form in the injection zone if the injection pressure is too high. The paper concludes that
74
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Study of the Risks Associated with Class I UIC Wells
the issues presented should be considered in determining optimal designs for monitoring
deep well injection.
U.S. EPA, Office of Drinking Water, State Programs Division. Technical Assistance Document:
The Application and Calibration of Pressure Instruments, Flowmeters, and Flow Control
Devices as Applied to Injection Wells. EPA 570/9-87-003. September 1987.
This report discusses the various devices that are used to measure the pressures and the
flow rates of injection wells, particularly those instruments used by regulatory agencies
and operators for assessing well operations. This report introduces the basic concepts of
flow and pressure metering in injection wells to EPA regional office staffers, state
regulators, and the regulated community.
U.S. EPA, Office of Ground Water and Drinking Water, and U.S. Department of Energy,
Environmental Management, Office of Technology Development. Scientific and Engineering
Aspects of Deep Injection Disposal of Hazardous and Industrial Wastes: An International
Symposium. Lawrence Berkeley Laboratory, Berkeley, California. May 10-13, 1994.
This document contains abstracts of papers presented at an international symposium on
the scientific and engineering aspects of the deep injection of hazardous and industrial
wastes. The symposium covered general aspects of deep well injection, engineering
aspects of well emplacement, well testing, monitoring, and model development.
U.S. EPA, Office of Research and Development. Assessing the Geochemical Fate ofDeep-Well-
InjectedHazardous Waste: A Reference Guide. EPA/625/6-89/025a. June 1990.
This reference guide presents state-of-the-art information on the geochemical fate of
injected wastes to address issues related to no-migration petitions and determination of
the compatibility of injected wastes with the injection zone formation. The seven
chapters in the guide provide an overview of injection practices in the United States,
processes affecting the geochemical fate of wastes, environmental factors affecting
geochemical processes, geochemical characteristics of hazardous wastes, methods and
models for predicting the geochemical fate of injected wastes, field sampling and
laboratory procedures, and case studies of deep-well injection of hazardous wastes.
Warner, D. L. "Monitoring of Class I Injection Wells." In: Deep Injection Disposal of
Hazardous and Industrial Waste: Scientific and Engineering Aspects. John A. Apps and Chin-
FuTsang, eds. San Diego, California: Academic Press. 1996. p. 421-431.
Class I injection wells have historically been monitored by observing well operating
parameters and by testing and logging to verify the mechanical integrity of the well.
75
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Study of the Risks Associated with Class I UIC Wells
Engineering and geologic reasoning support such limited monitoring as the most
appropriate, since most possible vertical pathways for escape of fluids from the injection
zone are concentrated in or immediately around the injection well. Such pathways can be
detected or inferred by monitoring and testing of the injection well. This paper discusses
ways to determine the necessity of monitoring wells, and how wells should be selected
and positioned.
Warner, Don L., and Jay H. Lehr. An Introduction to the Technology of Subsurface Wastewater
Injection. Prepared for U.S. Environmental Protection Agency, Office of Research and
Development, Robert S. Kerr Environmental Research Laboratory. December 1977.
This report provides an introduction to the proper siting, construction, testing, operation,
and abandonment of injection wells. Prior to construction, the local geologic and
hydrologic setting must be determined to assess compatibility with injected wastes. If
necessary, the waste may be treated to ensure physical, biological, and chemical
compatibility with the injection zone. Once the well begins operation, it should be
monitored for changes in injection conditions which may lead to system failure.
(Reprinted as: Warner, Don L, and Jay H. Lehr. Subsurface Wastewater Injection: The
Technology of Injecting Wastewater into Deep Wells for Disposal. Berkeley, California:
Premier Press. 1981.)
Whiteside, R. F., T. P. Roth, and J. R. Creech. "Applications of Corrosion-Resistant Materials
and Cement in the Design and Construction of Class I Injection Wells." In: Deep Injection
Disposal of Hazardous and Industrial Waste: Scientific and Engineering Aspects. John A. Apps
and Chin-Fu Tsang, eds. San Diego, California: Academic Press. 1996. p. 145-164.
Although numerous alternative candidate materials have been available, the typical
problems encountered with corrosion-resistant injection well designs prior to the mid to
late 1970s were due mainly to the inherent difficulties in adapting various alloy metals,
fiberglass, elastomers, resins, plastics, etc., from surface to subsurface applications.
Refinements over the past 15 to 20 years in the fabrication and machining of these
materials and well designs have dramatically improved the integration of specialized
corrosion-resistant materials into the design of Class I wells. This article describes these
materials and how they are tested by manufacturers.
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APPENDIX A
Land Disposal Program Flexibility Act of 1996
Public Law 104-119, March 26,1996
-------
PUBLIC LAW 104-119—MAR. 26, 1996
LAND DISPOSAL PROGRAM FLEXIBILITY ACT
OF 1996
-------
110 STAT. 830
PUBLIC LAW 104-119—MAR. 26, 1996
Public Law 104-119
104th Congress
An Act
Mar. 26, 1996
[H.R. 2036]
Land Disposal
Program
Flexibility
Act of 1996.
Environmental
protection.
42 USC 6901
note.
42 USC 6924.
To amend the Solid Waste Disposal Act to make certain adjustments in the land
disposal program to provide needed flexibility, and for other purposes.
Be it enacted by the Senate and House of Representatives of
the United States of America in Congress assembled,
SECTION 1. SHORT TITLE.
This Act may be cited as the "Land Disposal Program Flexibility
Act of 1996".
SEC. 2. LAND DISPOSAL RESTRICTIONS.
Section 3004 (g) of the Solid Waste Disposal Act is amended
by adding after paragraph (6) the following:
"(7) Solid waste identified as hazardous based solely on
one or more characteristics shall not be subject to this sub-
section, any prohibitions under subsection (d), (e), or (f), or
any requirement promulgated under subsection (m) (other than
any applicable specific methods of treatment, as provided in
paragraph (8)) if the waste—
"(A) is treated in a treatment system that subsequently
discharges to waters of the United States pursuant to
a permit issued under section 402 of the Federal Water
Pollution Control Act (commonly known as the "Clean
Water Act") (33 U.S.C. 1342), treated for the purposes
of the pretreatment requirements of section 307 of the
Clean Water Act (33 U.S.C. 1317), or treated in a zero
discharge system that, prior to any permanent land dis-
posal, engages in treatment that is equivalent to treatment
required under section 402 of the Clean Water Act (33
U.S.C. 1342) for discharges to waters of the United States,
as determined by the Administrator; and
"(B) no longer exhibits a hazardous characteristic prior
to management in any land-based solid waste management
unit.
"(8) Solid waste that otherwise qualifies under paragraph
(7) shall nevertheless be required to meet any applicable specific
methods of treatment specified for such waste by the Adminis-
trator under subsection (m), including those specified in the
rule promulgated by the Administrator June 1, 1990, prior
to management in a land-based unit as part of a treatment
system specified in paragraph (7)(A). No solid waste may qualify
under paragraph (7) that would generate toxic gases, vapors,
or fumes due to the presence of cyanide when exposed to
pH conditions between 2.0 and 12.5.
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PUBLIC LAW 104-119—MAR. 26, 1996 110 STAT. 831
"(9) Solid waste identified as hazardous based on one or
more characteristics alone shall not be subject to this sub-
section, any prohibitions under subsection (d), (e), or (f), or
any requirement promulgated under subsection (m) if the waste
no longer exhibits a hazardous characteristic at the point of
injection in any Class I injection well permitted under section
1422 of title XIV of the Public Health Service Act (42 U.S.C.
SOOh-1).
"(10) Not later than five years after the date of enactment
of this paragraph, the Administrator shall complete a study
of hazardous waste managed pursuant to paragraph (7) or
(9) to characterize the risks to human health or the environ-
ment associated with such management. In conducting this
study, the Administrator shall evaluate the extent to which
risks are adequately addressed under existing State or Federal
programs and whether unaddressed risks could be better
addressed under such laws or programs. Upon receipt of addi-
tional information or upon completion of such study and as
necessary to protect human health and the environment, the
Administrator may impose additional requirements under exist-
ing Federal laws, including subsection (m)(l), or rely on other
State or Federal programs or authorities to address such risks.
In promulgating any treatment standards pursuant to sub-
section (m)(l) under the previous sentence, the Administrator
shall take into account the extent to which treatment is occur-
ring in land-based units as part of a treatment system specified
in paragraph (7)(A).
"(11) Nothing in paragraph (7) or (9) shall be interpreted
or applied to restrict any inspection or enforcement authority
under the provisions of this Act.".
SEC. 3. GROUND WATER MONITORING.
(a) AMENDMENT OF SOLID WASTE DISPOSAL ACT.—Section
4010(c) of the Solid Waste Disposal Act (42 U.S.C. 6949a(c)) is
amended as follows:
(1) By striking "CRITERIA.—Not later" and inserting the
following: "CRITERIA.—
"(1) IN GENERAL.—Not later".
(2) By adding at the end the following new paragraphs:
"(2) ADDITIONAL REVISIONS.—Subject to paragraph (3), the
requirements of the criteria described in paragraph (1) relating
to ground water monitoring shall not apply to an owner or
operator of a new municipal solid waste landfill unit, an existing
municipal solid waste landfill unit, or a lateral expansion of
a municipal solid waste landfill unit, that disposes of less
than 20 tons of municipal solid waste daily, based on an annual
average, if—
"(A) there is no evidence of ground water contamination
from the municipal solid waste landfill unit or expansion;
and
"(B) the municipal solid waste landfill unit or expan-
sion serves—
"(i) a community that experiences an annual
interruption of at least 3 consecutive months of surface
transportation that prevents access to a regional waste
management facility; or
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110 STAT. 832 PUBLIC LAW 104-119—MAR. 26, 1996
"(ii) a community that has no practicable waste
management alternative and the landfill unit is located
in an area that annually receives less than or equal
to 25 inches of precipitation.
"(3) PROTECTION OF GROUND WATER RESOURCES.—
"(A) MONITORING REQUIREMENT.—A State may require
ground water monitoring of a solid waste landfill unit
that would otherwise be exempt under paragraph (2) if
necessary to protect ground water resources and ensure
compliance with a State ground water protection plan,
where applicable.
"(B) METHODS.—If a State requires ground water mon-
itoring of a solid waste landfill unit under subparagraph
(A), the State may allow the use of a method other than
the use of ground water monitoring wells to detect a release
of contamination from the unit.
"(C) CORRECTIVE ACTION.—If a State finds a release
from a solid waste landfill unit, the State shall require
corrective action as appropriate.
"(4) NO-MIGRATION EXEMPTION.—
"(A) IN GENERAL.—Ground water monitoring require-
ments may be suspended by the Director of an approved
State for a landfill operator if the operator demonstrates
that there is no potential for migration of hazardous
constituents from the unit to the uppermost aquifer during
the active life of the unit and the post-closure care period.
"(B) CERTIFICATION.—A demonstration under subpara-
graph (A) shall be certified by a qualified ground-water
scientist and approved by the Director of an approved
State.
"(C) GUIDANCE.—Not later than 6 months after the
date of enactment of this paragraph, the Administrator
shall issue a guidance document to facilitate small commu-
nity use of the no migration exemption under this para-
graph.
"(5) ALASKA NATIVE VILLAGES.—Upon certification by the
Governor of the State of Alaska that application of the require-
ments described in paragraph (1) to a solid waste landfill unit
of a Native village (as defined in section 3 of the Alaska
Native Claims Settlement Act (16 U.S.C. 1602)) or unit that
is located in or near a small, remote Alaska village would
be infeasible, or would not be cost-effective, or is otherwise
inappropriate because of the remote location of the unit, the
State may exempt the unit from some or all of those require-
ments. This paragraph shall apply only to solid waste landfill
units that dispose of less than 20 tons of municipal solid waste
daily, based on an annual average.
"(6) FURTHER REVISIONS OF GUIDELINES AND CRITERIA.—
Recognizing the unique circumstances of small communities,
the Administrator shall, not later than two years after enact-
ment of this provision promulgate revisions to the guidelines
and criteria promulgated under this subtitle to provide addi-
tional flexibility to approved States to allow landfills that
receive 20 tons or less of municipal solid waste per day, based
on an annual average, to use alternative frequencies of daily
cover application, frequencies of methane gas monitoring,
infiltration layers for final cover, and means for demonstrating
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PUBLIC LAW 104-119—MAR. 26, 1996 110 STAT. 833
financial assurance: Provided, That such alternative require-
ments take into account climatic and hydrogeologic conditions
and are protective of human health and environment.".
(b) REINSTATEMENT OF REGULATORY EXEMPTION.—It is the 42 use 6949a
intent of section 4010(c)(2) of the Solid Waste Disposal Act, as note.
added by subsection (a), to immediately reinstate subpart E of
part 258 of title 40, Code of Federal Regulations, as added by
the final rule published at 56 Federal Register 50798 on October
9, 1991.
SEC. 4. TECHNICAL CORRECTIONS TO SOLID WASTE DISPOSAL ACT.
The Solid Waste Disposal Act is amended as follows:
(1) In section 3001(d)(5) by striking "under section 3001" 42USC6921.
and inserting "under this section".
(2) By inserting a semicolon at the end of section
3004(q)(l)(C). 42 USC 6924.
(3) In section 3004 (g), by striking "subparagraph (A)
through (C)" in paragraph (5) and inserting "subparagraphs
(A) through (C)".
(4) In section 3004 (r) (2) (C), by striking "pertroleum-
derived" and inserting "petroleum-derived".
(5) In section 3004(r)(3) by inserting after "Standard" the
word "Industrial".
(6) In section 3005(a), by striking "polycholorinated" and 42 USC 6925.
inserting "polychlorinated".
(7) In section 3005(e)(l), by inserting a comma at the
end of subparagraph (C).
(8) In section 4007(a), by striking "4003" in paragraphs 42 USC 6947.
(1) and (2)(A) and inserting "4003(a)".
Approved March 26, 1996.
LEGISLATIVE HISTORY—H.R. 2036:
HOUSE REPORTS: No. 104-454 (Comm. on Commerce).
CONGRESSIONAL RECORD, Vol. 142 (1996):
Jan. 30, 31, considered and passed House.
Feb. 20, considered and passed Senate, amended.
Mar. 7, House concurred in Senate amendments.
WEEKLY COMPILATION OF PRESIDENTIAL DOCUMENTS, Vol. 32 (1996):
Mar. 26, Presidential statement.
o
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APPENDIX B
Supplemental Risk Analysis in Support of The Class I UIC
Regulatory Impact/Benefits Analysis For Phase III Wastes:
Examination of Risks Associated With East Gulf
Coast/Abandoned Borehole Scenario And Variations in
Permeability Ratio Between The Injection Zone And The
Confining Layer
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Supplemental Risk Analysis in Support of The Class I UIC Regulatory
Impact/Benefits Analysis For Phase III Wastes:
Examination of Risks Associated With East Gulf Coast/Abandoned
Borehole Scenario And Variations in Permeability Ratio Between The
Injection Zone And The Confining Layer
Introduction
This study further explores the results of the quantitative risk analysis conducted in the
benefits assessment for the Class I well injection of Phase III wastes described in the revised
Phase III RIA.1 In that analysis, EPA estimated health risks associated with five Phase III waste
constituents under two malfunction scenarios (grout seal failure and abandoned unplugged
borehole) in four geologic settings. The study also assessed the effects of varying drinking water
well pumping rates. The analysis showed that the only cases of elevated cancer and non-cancer
risks estimated were associated with exposure to benzene or carbon tetrachloride via migration
of injected Class I waste through an abandoned borehole into a USDW, with a drinking water
well pumping from an overlying aquifer at a rate of 720,000 gallons per day (gpd). The slightly
elevated risks were observed only when the above scenarios was assumed to be located in a
hydrogeologic situation comparable to the East Gulf Coast.
In the GeoTrans2 study, the model of the East Gulf Coast hydrogeology was designed to
examine the effect of highly permeable confining zones. Specifically, GeoTrans set the ratio of
the hydraulic conductivity between adjacent formations to be less than 100:1. That is, the
injection zone was less than 100 times more permeable than the confining layer.
The purpose of this analysis is to supplement the GeoTrans3 original risk assessment of
the above scenario by assuming five different permeability ratios of 1:1,000; 1:10,000;
1:100,000; 1:1,000,000; and, 1:10,000,000. GeoTrans varied the permeability ratio by reducing
the hydraulic conductivity of the lowest hydrogeologic zone (aquitard 6) just above the injection
zone.
U.S. EPA, Office of Ground Water and Drinking Water. Draft Regulatory Impact Analysis of Proposed Hazardous Waste
Disposal Restrictions for Class I Injection of Phase III Wastes: Benefits Analysis. 1995.
GeoTrans, Inc. Numerical Simulations of Deep Injection Wells in Support of EPA's UIC, Office of Ground Water and
Drinking Water. August 21, 1995.
GeoTrans, Inc. Numerical Simulations of Deep Injection Wells in Support of EPA's UIC, Office of Ground Water and
Drinking Water. September 17, 1996.
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Other aquifer and aquitard properties from the former analysis were unchanged in this
analysis. Specifically:
• The same hydrogeologic scenario is used: the East Gulf Coast hydrogeology, with an
abandoned borehole, and a high rate of pumping from the overlying aquifer.
The same quantitative risk methodology as described previously and based on the
Industrial Economics, Inc. (lEc) methodology is used.4 The current version of
SWIFT/486 was used to model these scenarios.
• The chemicals of concern for this risk assessment were selected via a procedure
consistent with that in the original risk analysis. Carbon tetrachloride and benzene, two
organic contaminants reported in Class I facilities, were selected as the chemicals of
concern. (The present risk analysis also includes arsenic, an inorganic contaminant
reported in Class I facilities.)
• The present analysis also uses the methods described in the previous studies to determine
the normalized injectate concentrations, to provide a range of concentrations achieved,
and to examine the ultimate effect on the risk estimates at different locations relative to
the injection well and USDW.
To assess the cancer and non-cancer risks from exposure to each of these three
contaminants, EPA used the 90th percentile concentration data for each contaminant as reported
in the Class I facility-specific data from OGWDW's 1996 Class IUICWELLS database. The
waste stream concentrations ("initial concentrations") of Phase III contaminants were obtained
from recent information provided by Class I facilities on concentrations of contaminants in their
waste streams.
The following section describes the normalized injectate concentrations modeled by
GeoTrans5 assuming the variations in permeability ratio as noted above and assuming three
different receptors. Concentrations at these receptors are upper-bound estimates.
Quantitative Risk Assessment
EPA used the results of GeoTrans' fate and transport modeling of drinking water
contamination from a nearby unplugged borehole to estimate the concentrations of certain Phase
III contaminants at three selected receptor locations within or below the USDW. The three
receptors are located: 500 feet from the injection well in an aquifer below the USDW (receptor
Industrial Economics, Inc. Risk Analyses for Underground Injection of'Hazardous Wastes. May 1987.
5 GeoTrans, Inc. 1996.
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B2); 500 feet from the injection well in the USDW (receptor A2); and approximately 2,000 feet
from the injection well in the USDW (receptor A4).
The concentrations at each receptor were used to estimate the risk to human health from
the hypothetical occurrence of these failures. Exhibits 1 and 2 present the normalized injectate
concentrations at the designated receptors assuming permeability ratios of 1:1,000 and
1:10,000,000, respectively.
Exhibit 1
Normalized Injectate Concentrations in the USDW Based on East Gulf Coast
Hydrogeology/Abandoned Borehole Failure Scenario With Pumping at 720,000
GPD and 1:1,000 Permeability Ratio1
Geographic
Location
East Gulf
Coast
Abandoned Unplugged Borehole:
Concentration (mg/L) 500 feet
away from the injection well in
the USDW plus a well pumping
drinking water at 720,000 gpd
(and time of occurrence in
years) 2
2.52E-04 (22.2 years)
Abandoned Unplugged Borehole:
Concentration (mg/L) 500 feet
away from the injection well in
an aquifer below the USDW plus
a well pumping drinking water at
720,000 gpd (and time of
occurrence in years) 3
3. 34E-02 (22.2 years)
Abandoned Unplugged Borehole:
Concentration (mg/L) 2,000 feet
away from the injection well in the
USDW plus a well pumping
drinking water at 720,000 gpd
(and time of occurrence in years) 4
4.83E-10 (22.2 years)
1 Source: GeoTrans, Inc. September 13,1996. Numerical Simulation of Deep Injection Wells in Support of EPA's UIC,
Office of Ground Water and Drinking Water.
2 The concentration noted is based on the concentration at receptor A2, located 500 feet away from the injection well in the
USDW.
3 The concentration noted is based on the concentration at receptor B2, located adjacent to an abandoned unplugged borehole
that is 573 feet away from the injection well in an aquifer below the USDW.
4 The concentration noted is based on the concentration at receptor A4, located 2,000 feet away from the injection well in the
USDW.
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Exhibit 2
Normalized Injectate Concentrations in the USDW
Based on East Gulf Coast Hydrogeology/Abandoned Borehole Failure Scenario
With Pumping at 720,000 GPD and 1:10,000,000 Permeability Ratio1
Geographic
Location
East Gulf
Coast
Abandoned Unplugged Borehole:
Concentration (mg/L) 500 feet
away from the injection well in
the USDW plus a well pumping
drinking water at 720,000 gpd
(and time of occurrence in
years) 2
1.68E-04 (22.2 years)
Abandoned Unplugged Borehole:
Concentration (mg/L) 500 feet
away from the injection well in
an aquifer below the USDW plus
a well pumping drinking water at
720,000 gpd (and time of
occurrence in years) 3
2. 10E-02 (22.2 years)
Abandoned Unplugged Borehole:
Concentration (mg/L) 2,000 feet
away from the injection well in the
USDW plus a well pumping
drinking water at 720,000 gpd
(and time of occurrence in years) 4
3. 06E-10 (22.2 years)
1 Source: GeoTrans, Inc. September 13,1996. Numerical Simulation of Deep Injection Wells in Support of EPA's UIC,
Office of Ground Water and Drinking Water.
2 The concentration noted is based on the concentration at receptor A2, located 500 feet away from the injection well in the
USDW.
3 The concentration noted is based on the concentration at receptor B2, located adjacent to an abandoned unplugged borehole
that is 573 feet away from the injection well in an aquifer below the USDW.
4 The concentration noted is based on the concentration at receptor A4, located 2,000 feet away from the injection well in the
USDW.
Exhibit 3 presents toxicity factors and concentration data for benzene, carbon
tetrachloride, and arsenic. Information presented includes the Cancer Slope Factor, Reference
Dose, and initial concentrations for each contaminant.
Exhibit 3
Toxicity and Concentration Data for Hazardous Phase III Contaminants
Chemical Abstract Services (CAS) Number
Cancer Slope Factor* (mg/kg/day)"1
Reference Dose (RiD)** (mg/kg/day)
Initial Concentration*** (mg/L)
Benzene
71-43-2
2.9 xlO'2
NA
47
Carbon Tetrachloride
56-23-5
1.3x10-'
7xlO'4
2.23
Arsenic
7440-38-2
1.5x10°
3.4 xlO'4
2.6
Source: U.S. EPA. January 11, 1995. Integrated Risk Information System (IRIS). Arsenic CSF is from IRIS. 1993.
** Source: U.S. EPA. January 11, 1995. IRIS. Arsenic RfD is from IRIS. 1993.
*** Based on the 90th percentile concentration from USEPA OGWDW. 1996. UICWELLS database.
NA = Not Available
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Methodology for Estimating Health Risks
The risk to human health was estimated separately for benzene, carbon tetrachloride, and
arsenic. The risk calculations were based on several assumptions about the average individual.
These include an average body weight of 70 kilograms and the ingestion of 2 liters of
contaminated water per day. The calculations also assumed that the affected person's body
retains 100 percent of the contaminants in the water.
The calculation of carcinogenic risk was based on the Cancer Slope Factor (CSF)
developed for individual carcinogens by EPA's Carcinogen Assessment Group. The Cancer
Slope Factor, an upper-bound estimate of the probability of an individual developing cancer as a
result of a lifetime of exposure to a particular level of a potential carcinogen, is calculated as
follows:
• The actual chemical concentration in the drinking water, expressed as milligrams per
liter, is calculated by multiplying the unit concentration from the dispersion modeling by
the contaminant concentration in the waste stream.
• Using the above assumptions about consumption of drinking water, the concentration
figure is converted to a dose expressed in milligrams of contaminant consumed per
kilogram of body weight per day (mg/kg/day).
• The dose is multiplied by the cancer unit risk factor, resulting in an upper-bound estimate
of the increased likelihood of developing cancer. The CSFs for benzene, carbon
tetrachloride, and arsenic are presented in Exhibit 3.
To calculate noncarcinogenic health effects, the chronic daily intake (GDI), in mg/kg/day,
of each contaminant is estimated. The GDI is based on a 70-year lifetime exposure. The GDI is
then compared to the toxicity factor for non-cancer effects, known as the Reference Dose (RfD).
The RfD is an estimate of a daily exposure level for the human population, including sensitive
subpopulations, that is likely to be without an appreciable risk of adverse effects during a
lifetime of exposure. The RfD represents EPA's preferred toxicity value for evaluating non-
cancer effects.6 Exhibit 3 presents the RfD for carbon tetrachloride and arsenic. Benzene does
not have an RfD.
The ratio of the GDI to the RfD represents the hazard index, which is used to compare the
relative risk posed by contaminants. A hazard index of greater than one indicates an increased
risk of non-carcinogenic health effects.
Results of Applying Methodologies
U.S. EPA. Risk Assessment Guidance for Superfund. Volume I. Human Health Evaluation Manual. EPA/540/1-89/002.
1989.
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Exhibit 4 summarizes the cancer risks and hazard indices for each chemical of concern
given the malfunction scenario and assuming 1:1,000 and 1:10,000,000 permeability
conductivity ratios. Exhibits 5 to 8 present specific input parameters used in the calculations of
cancer risks and hazard indices for benzene, carbon tetrachloride, and arsenic under the scenario
of concern. The quantitative risk assessment for the East Gulf Coast/abandoned borehole
scenario shows the following results:
• Cancer risks at receptors in the USDW are lower than those from the aquifer below the
USDW. The cancer risks were higher for the 1:1,000 permeability ratio than for the
1:10,000,000 permeability ratio.
• The risk assessment shows that cancer risks are the lowest at the receptor 2,000
feet from the well for either permeability ratio. These risks are extremely low: on
the order of four- to 120-in-one-trillion.
• Cancer risks are higher at the receptor located 500 feet from the injection well in
the aquifer below the USDW. These cancer risks range from on the order of 1.4-
in-one-million to 1.8-in-one-hundred-thousand.
• The cancer risks associated with exposures to concentrations estimated at receptor
B2, 500 feet from the injection well in an aquifer below the USDW, consistently
exceed the one-in-ten-thousand to one-in-one-million risk range generally used by
EPA to regulate exposures to carcinogens.7 All other cancer risk estimates are
within regulatory levels.
• The hazard indices for each contaminant were lowest at the receptor 2,000 feet from the
well, higher at the receptor 500 feet from the well, and the highest in the aquifer below
the USDW. For both carbon tetrachloride and arsenic, hazard indices were higher for the
1:1,000 permeability ratio than for the 1:10,000,000 permeability ratio.
Similar to the results for the cancer risk estimates, all of the hazard indices estimated at
the receptor in the aquifer below the USDW at both permeability ratios are greater than
EPA's level of concern for a hazard index of greater than 1. All other hazard index
estimates are within regulatory levels.
Thus, the cancer risks and hazard indices in all cases are higher assuming the
permeability ratio of 1:1,000 versus 1:10,000,000. The cancer and non-cancer risks associated
with exposure to contaminant concentrations at receptor B2, 500 feet from the injection well in
an aquifer below the USDW are, in all cases, above the level recommended by EPA as being
acceptable for human health exposures.
U.S. EPA. Office of Solid Waste and Emergency Response. Role of the Baseline Risk Assessment in Supetfund Remedy
Selection Decisions. OSWER Directive 9355.0-30. 1991.
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It should be noted that, given the existing UIC regulations, a failure scenario such as that
described in this analysis occurring is highly unlikely. Current regulations require that an area of
review (AoR) surrounding injection wells be identified, and abandoned boreholes within this
area be located. Therefore, a borehole within 500 feet of the well would be identified and
properly plugged before any injection would be permitted.
Exhibit 4
Cancer Risks and Hazard Indices for Contaminants of Concern
Based on East Gulf Coast/Abandoned Borehole Scenario With Pumping at 720,000
GPD and 1:1,000 and 1:10,000,000 Permeability Ratio '
Chemical/
Receptor Location
Benzene:
- 500 feet from well in base of USDW plus pumping
- 500 feet from well in aquifer below USDW plus pumping
- 2,000 feet from well in base of USDW plus pumping
Carbon Tetrachloride:
- 500 feet from well in base of USDW plus pumping
- 500 feet from well in aquifer below USDW plus pumping
- 2,000 feet from well in base of USDW plus pumping
Arsenic:
- 500 feet from well in base of USDW plus pumping
- 500 feet from well in aquifer below USDW plus pumping
- 2,000 feet from well in base of USDW plus pumping
Cancer
Risk/1: 1,000
Permeability
Ratio
9.82E-06
1.30E-03
1.88E-11
2.09E-06
2.77E-04
4.00E-12
2.81E-05
3.73E-03
5.39E-11
Hazard Index/
1:1,000
Permeability
Ratio
NA
NA
NA
2.30E-02
3.04E+00
4.40E-08
6.25E-02
8.28E+00
1.20E-07
Cancer Risk/
1:10,000,000
Permeability
Ratio
6.55E-06
8.19E-04
1.19E-11
1.39E-06
1.74E-04
2.54E-12
1.87E-05
2.34E-03
3.41E-11
Hazard Index/
1:10,000,000
Permeability
Ratio
NA
NA
NA
1.53E-02
1.91E+00
2.79E-08
4.16E-02
5.21E+00
7.58E-08
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Exhibit 5
CANCER RISKS ASSOCIATED WITH BENZENE, CARBON TETRACHLORIDE, AND ARSENIC
ASSUMING EAST GULF COAST WITH AN ABANDONED BOREHOLE SCENARIO AND WITH PUMPING AT 720,000 GPD AND A
PERMEABILITY RATIO OF 1:1,000 BETWEEN THE INJECTION ZONE AND THE CONFINING LAYER
Initial Normalized Drinking Water Ingestion Unit Cancer Slope
Chemical/ Constituent Injectate Concentration Conversion Dose Factor
Receptor Location Concentrations Concentrations (mg/l) Factor (mg/kg/day) (mg/kg/day)"1 4
(ma/I) 1 (ma/I) 2 (l/ka/dav) 3
Benzene:
- 500 feet from well in base of USDW plus pumping 5' 6
- 500 feet from well in aquifer below USDW plus pumping 7
- 2,000 feet from well in base of USDW plus pumping 8
Carbon Tetrachloride:
- 500 feet from well in base of USDW plus pumping 5' 6
- 500 feet from well in aquifer below USDW plus pumping 7
- 2,000 feet from well in base of USDW plus pumping 8
Arsenic:
- 500 feet from well in base of USDW plus pumping 5| 6
- 500 feet from well in aquifer below USDW plus pumping 7
- 2,000 feet from well in base of USDW plus pumping 8
1 Concentration set at 90th percentile concentration reported from
47.00 2.250E-04
47.00 3.340E-02
47.00 4.830E-10
2.23 2.250E-04
2.23 3.340E-02
2.23 4.830E-10
2.60 2.250E-04
2.60 3.340E-02
2.60 4.830E-10
1.18E-02 0.0286 3.39E-04 2.90E-02
1.57E+00 0.0286 4.49E-02 2.90E-02
2.27E-08 0.0286 6.49E-10 2.90E-02
5.62E-04 0.0286 1.61E-05 1.30E-01
7.45E-02 0.0286 2.13E-03 1.30E-01
1.08E-09 0.0286 3.08E-11 1.30E-01
6.55E-04 0.0286 1.87E-05 1.50E+00
8.68E-02 0.0286 2.48E-03 1.50E+00
1.26E-09 0.0286 3.59E-11 1.50E+00
Individual
Cancer
Risk
9.82E-06
1.30E-03
1.88E-11
2.09E-06
2.77E-04
4.00E-12
2.81 E-05
3.73E-03
5.39E-1 1
hazardous and nonhazardous Class I facilities.
2 Based on information provided in GeoTrans, Inc., September 13, 1996 report titled " Numerical Simulation of Deep Injection Wells in Support of UIC OGWDW."
3 IEC, Inc., 1987.
4 IRIS. January 11, 1995.
5 Assume pumping rate of 720,000 gallons per day.
6 The concentration measured at receptor A2 located in the base
of the USDW as modeled in
GeoTrans, Inc., 1995.
7 The concentration measured at receptor B2 located in an aquifer below the USDW as modeled in GeoTrans, Inc., 1995.
8 The concentration measured at receptor A4 located in the base
of the USDW as modeled in
GeoTrans, Inc., 1995.
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Exhibit 6
CANCER RISKS ASSOCIATED WITH BENZENE, CARBON TETRACHLORIDE, AND ARSENIC
ASSUMING EAST GULF COAST WITH AN ABANDONED BOREHOLE SCENARIO AND WITH PUMPING AT 720,000 GPD AND A
PERMEABILITY RATIO OF 1:10,000,000 BETWEEN THE INJECTION ZONE AND THE CONFINING LAYER
Chemical/
Receptor Location
Benzene:
- 500 feet from well in base of USDW plus pumping 5' 6
- 500 feet from well in aquifer below USDW plus pumping 7
- 2,000 feet from well in base of USDW plus pumping 8
Carbon Tetrachloride:
- 500 feet from well in base of USDW plus pumping 5° 6
- 500 feet from well in aquifer below USDW plus pumping 7
- 2,000 feet from well in base of USDW plus pumping 8
Arsenic:
- 500 feet from well in base of USDW plus pumping 5' 6
- 500 feet from well in aquifer below USDW plus pumping 7
- 2,000 feet from well in base of USDW plus pumping 8
Initial
Constituent
Concentrations
(ma/I) 1
47.00
47.00
47.00
2.23
2.23
2.23
2.60
2.60
2.60
Normalized Drinking Water
Injectate Concentration
Concentrations (mg/l)
(ma/I) 2
1.680E-04
2.100E-02
3.060E-10
1 .680E-04
2.100E-02
3.060E-10
1.680E-04
2.100E-02
3.060E-10
7.90E-03
9.87E-01
1 .44E-08
3.75E-04
4.68E-02
6.82E-10
4.37E-04
5.46E-02
7.96E-10
Ingestion
Conversion
Factor
(l/ka/dav) 3
0.0286
0.0286
0.0286
0.0286
0.0286
0.0286
0.0286
0.0286
0.0286
Unit
Dose
(mg/kg/day)
2.26E-04
2.82E-02
4.11E-10
1 .07E-05
1 .34E-03
1.95E-11
1.25E-05
1 .56E-03
2.28E-11
Cancer Slope
Factor
(mg/kg/day)-1 4
2.90E-02
2.90E-02
2.90E-02
1 .30E-01
1 .30E-01
1.30E-01
1.50E+00
1 .50E+00
1 .50E+00
Individual
Cancer
Risk
6.55E-06
8.19E-04
1.19E-11
1 .39E-06
1.74E-04
2.54E-12
1.87E-05
2.34E-03
3.41 E-11
1 Concentration set at 90th percentile concentration reported from hazardous and nonhazardous Class I facilities.
2 Based on information provided in GeoTrans, Inc., September 13, 1996 report titled " Numerical Simulation of Deep
3 IEC, Inc., 1987.
4 IRIS. January 11, 1995.
5 Assume pumping rate of 720,000 gallons per day.
6 The concentration measured at receptor A2 located
7 The concentration measured at receptor B2 located
8 The concentration measured at receptor A4 located
in the base of the USDW as modeled in
in an aquifer below the
GeoTrans, Inc., 1995.
Injection Wells
in Support of UICOGWDW."
USDW as modeled in GeoTrans, Inc., 1995.
in the base of the USDW as modeled in
GeoTrans, Inc., 1995.
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Exhibit 7
HAZARD INDEX - CARBON TETRACHLORIDE AND ARSENIC
ASSUMING EAST GULF COAST WITH AN ABANDONED BOREHOLE SCENARIO AND WITH PUMPING AT 720,000 GPD AND A
PERMEABILITY RATIO OF 1:1,000 BETWEEN THE INJECTION ZONE AND THE CONFINING LAYER
Initial Normalized
Chemical/ Constituent Injectate
Receptor Location Concentrations Concentrations
(ma/I) 1 (ma/I) 2
Carbon Tetrachloride:
- 500 feet from well in base of USDW plus pumping 5' 6
- 500 feet from well in aquifer below USDW plus pumping 7
- 2,000 feet from well in base of USDW plus pumping 8
Arsenic:
- 500 feet from well in base of USDW plus pumping 5' 6
- 500 feet from well in aquifer below USDW plus pumping 7
- 2,000 feet from well in base of USDW plus pumping 8
1 Concentration set at 90th percentile concentration reported from
2.23 2.520E-04
2.23 3.340E-02
2.23 4.830E-10
2.60 2.520E-04
2.60 3.340E-02
2.60 4.830E-10
Drinking Ingestion Unit Reference
Water Conversion Dose Dose (RfD)
Concentration Factor (mg/kg/day) (mg/kg/day) 4
(ma/I) (l/ka/dav)3
5.62E-04 0.0286 1.61E-05 7.00E-04
7.45E-02 0.0286 2.13E-03 7.00E-04
1.08E-09 0.0286 3.08E-11 7.00E-04
6.55E-04 0.0286 1.87E-05 3.00E-04
8.68E-02 0.0286 2.48E-03 3.00E-04
1.26E-09 0.0286 3.59E-11 3.00E-04
Hazard
Index
2.30E-02
3.04E+00
4.40E-08
6.25E-02
8.28E+00
1.20E-07
hazardous and nonhazardous Class I facilities.
2 Based on information provided in GeoTrans, Inc., September 13, 1996 report titled " Numerical
3 IEC, Inc., 1987.
4 IRIS. January 11, 1995.
5 Assume pumping rate of 720,000 gallons per day.
6 The concentration measured at receptor A2 located in the base
Simulation of Deep Injection Wells in Support of UIC OGWDW."
of the USDW as modeled in GeoTrans, Inc., 1995.
7 The concentration measured at receptor B2 located in an aquifer below the USDW as modeled
8 The concentration measured at receptor A4 located in the base
in GeoTrans, Inc., 1995.
of the USDW as modeled in GeoTrans, Inc., 1995.
10
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Exhibit 8
HAZARD INDEX - CARBON TETRACHLORIDE AND ARSENIC
ASSUMING EAST GULF COAST WITH AN ABANDONED BOREHOLE SCENARIO AND WITH PUMPING AT 720,000 GPD AND A
PERMEABILITY RATIO OF 1:10,000,000 BETWEEN THE INJECTION ZONE AND THE CONFINING LAYER
Initial Normalized
Chemical/ Constituent Injectate
Receptor Location Concentrations Concentrations
(ma/I) 1 (ma/I) 2
Carbon Tetrachloride:
- 500 feet from well in base of USDW plus pumping 5' 6
- 500 feet from well in aquifer below USDW plus pumping 7
- 2,000 feet from well in base of USDW plus pumping 8
Arsenic:
- 500 feet from well in base of USDW plus pumping 5' 6
- 500 feet from well in aquifer below USDW plus pumping 7
- 2,000 feet from well in base of USDW plus pumping 8
1 Concentration set at 90th percentile concentration reported from
2.23 1.680E-04
2.23 2.100E-02
2.23 3.060E-10
2.60 1 .680E-04
2.60 2.100E-02
2.60 3.060E-10
Drinking Ingestion Unit Reference
Water Conversion Dose Dose (RfD)
Concentration Factor (mg/kg/day) (mg/kg/day) 4
(ma/I) (l/ka/dav)3
3.75E-04 0.0286 1.07E-05 7.00E-04
4.68E-02 0.0286 1.34E-03 7.00E-04
6.82E-10 0.0286 1.95E-11 7.00E-04
4.37E-04 0.0286 1.25E-05 3.00E-04
5.46E-02 0.0286 1.56E-03 3.00E-04
7.96E-10 0.0286 2.28E-11 3.00E-04
Hazard
Index
1.53E-02
1.91E+00
2.79E-08
4.16E-02
5.21 E+00
7.58E-08
hazardous and nonhazardous Class I facilities.
2 Based on information provided in GeoTrans, Inc., September 13, 1996 report titled " Numerical
3 IEC, Inc., 1987.
4 IRIS. January 11, 1995.
5 Assume pumping rate of 720,000 gallons per day.
6 The concentration measured at receptor A2 located in the base
Simulation of Deep Injection Wells in Support of UIC OGWDW."
of the USDW as modeled in GeoTrans, Inc., 1995.
7 The concentration measured at receptor B2 located in an aquifer below the USDW as modeled
8 The concentration measured at receptor A4 located in the base
in GeoTrans, Inc., 1995.
of the USDW as modeled in GeoTrans, Inc., 1995.
11
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