United States
Environmental Protection
Agency
Office of
Research and Development
Washington, DC 20460
EPA/600/2-91/037
August 1991
&EPA
Chemicals Stored in USTs:
Characteristics and Leak
Detection
-------
-------
EPA/600/2-91/037
August 1991
CHEMICALS STORED IN USTs:
CHARACTERISTICS AND LEAK DETECTION
by
Joseph W. Maresca, Jr.
Vista Research, Inc.
Mountain View, California 94042
and
Robert W. Hillger
U.S. Environmental Protection Agency
Edison, New Jersey 08837
Contract No. 68-03-3409
Project Officer
Robert W. Hillger
Superfund Technology Demonstration Division
Risk Reduction Engineering Laboratory
Edison, New Jersey 08837
RISK REDUCTION ENGINEERING LABORATORY
OFFICE OF RESEARCH AND DEVELOPMENT
U.S. ENVIRONMENTAL PROTECTION AGENCY
CINCINNATI, OHIO 45268
Printed on Recycled Paper
-------
DISCLAIMER
This material has been funded wholly or in part by the United States Environmental
Protection Agency under Contract 68-03-3409 to CDM Federal Programs Corporation. It has
been subject to the Agency's review and it has been approved for publication as an EPA
document. Mention of trade names or commercial products does not constitute endorsement or
recommendation for use.
-------
FOREWORD
Today's rapidly developing and changing technologies and industrial products frequently
carry with them the increased generation of materials that, if improperly dealt with, can threaten
both public health and the environment. The U. S. Environmental Protection Agency is charged
by Congress with protecting the nation's land, air, and water resources. Under a mandate of
national environmental laws, the agency strives to formulate and implement actions leading to a
compatible balance between human activities and the ability of natural systems to support and
nurture life. These laws direct the EPA to perform research to define our environmental
problems, measure the impacts, and search for solutions.
The Risk Reduction Engineering Laboratory is responsible for planning, implementing,
and managing research, development, and demonstration programs to provide an authoritative,
defensible engineering basis in support of the policies, programs, and regulations of the EPA
with respect to drinking water, wastewater, pesticides, toxic substances, solid arid hazardous
wastes, and Superfund-related activities. This publication is one of the products of that research
and provides a vital communication link between the researcher and the user community.
This document presents an analysis of the characteristics of chemicals stored in
underground storage tanks (USTs) and how these characteristics affect the detection of leaks in
such tanks. The work reported in this document has application to the UST release detection
technical standards in CFR 280 Subpart D.
E. Timothy Oppelt, Director
Risk Reduction Engineering Laboratory
-------
ABSTRACT
The regulations issued by the United States Environmental Protection Agency (EPA) in
1988 require, with several exceptions, that the integrity of underground storage tank systems
containing petroleum fuels and hazardous chemicals be routinely tested. The regulatory
standards for leak detection in tanks containing hazardous chemicals are more stringent than
those for tanks containing petroleum motor fuels. This report describes (1) the regulatory
standards for leak detection in tanks containing hazardous chemicals, (2) the types of chemicals
being stored, (3) the characteristics of the tanks in which these chemicals are stored, (4) the
effectiveness of tank tightness tests and automatic tank gauging systems for detection of leaks in
tanks containing chemicals other than petroleum, and (5) the approaches to leak detection that
are being implemented by tank owners and operators.
This report was submitted in fulfillment of Contract No. 68-03-3409 by Vista Research,
Inc., under the sponsorship of the U.S. Environmental Protection Agency. This report covers a
period from 23 April 1990 to 11 January 1991, and work was completed as of 21 January 1991.
IV
-------
TABLE OF CONTENTS
Disclaimer jj
Foreword ;. jjj
Abstract .. iv
Acknowledgments vj
Section 1: Introduction 1
Objectives 2
Report Organization 2
Section?,: Conclusions ; . 4
Characteristics of Tanks Containing Non-Petroleum Chemicals 4
Analysis of the Applicability of Volumetric Leak Detection Systems to Tanks
Containing Hazardous Chemicals 4
Currently Used Approaches to Leak Detection 5
Section 3: Recommendations 7
References g
Appendix A: An Analysis of the Characteristics of Underground Storage Tanks
Containing Chemicals IQ
Appendix B: Volumetric Leak Detection in Underground Storage Tanks
Containing Chemicals 25
Appendix C: Industry Survey of the Leak Detection Practices Associated with
Underground Storage Tanks Containing Hazardous Chemicals 41
-------
ACKNOWLEDGMENTS
Robert W. Hillger was the Technical Program Monitor on the Work Assignment for
EPA/RREL. Anthony N. Tafuri and Robert W. Hillger of EPA/RREL gave technical assistance,
coordinated the collection of data from state regulators, contributed to the preparation of a
peer-reviewed journal article, and provided a technical review of the work. Mr. Hillger
formulated, actively supported, and contributed to the technical direction of the project and to the
work itself.
The authors would especially like to acknowledge the assistance and cooperation of the
many state underground storage tank programs that provided their databases on chemicals stored
in underground storage tanks for analysis. The states are listed below, along with the names of
those in each state who provided assistance.
Connecticut
Delaware
Florida
Illinois
Indiana
Maine
Minnesota
Mississippi
Missouri
New York
Ohio
Texas
Virginia
Wisconsin
Peter Zack
Regina Alford
Shawn Abbott
Jane Squires
Anne Black
Anne Lapoint
JoAnn C. Henry
John Harper
Gordon Ackley
Russell Braucksieck
Robert Ireson
Dale Lyne
Fred Cunningham
William Morrissey
This document was edited by Monique Seibel and prepared for publication by Pamela
Webster.
VI
-------
SECTION!
INTRODUCTION
On 23 September 1989, the United States Environmental Protection Agency (EPA) issued
technical standards and corrective action requirements for owners and operators of underground
storage tanks (USTs) that are used for petroleum products and hazardous chemical substances
[1]. (A hazardous chemical is any substance defined by the Comprehensive Environmental
Response, Compensation, and Liability Act (CERCLA) [2]). Section 280.42 of the regulation
presents the requirements for storing hazardous substances. There are five options for release
detection in new tank and pipeline systems used to store hazardous substances. Four of these
options require some form of secondary containment and periodic monitoring or leak detection
within the secondary containment. The fifth option allows for leak detection without secondary
containment safeguards providing that (1) the method or system is at least as effective as the
ones allowed for use in petroleum USTs in Section 280.43 (b) through (h) of the regulation,
(2) information is provided about the chemical and physical properties of the stored substance,
the health risks associated with the substance, the characteristics of the site, and corrective action
technologies that can be used in case of a release, and (3) approval from the implementing
agency is received before installation and operation of the UST system. Existing USTs do not
have to meet these requirements until 1998. Until that date, existing USTs need only meet the
requkements for petroleum UST systems given in Section 280.41. After 1998, all existing USTs
containing hazardous substances will be subject to the same requkements as new tanks.
Tank tightness test methods and automatic tank gauges (ATGs) are the two most
frequently used release detection systems for petroleum USTs. Either one/when used in
conjunction with monthly inventory reconciliation, is acceptable as the fifth option and thus will
satisfy the requkements delineated in the regulations. (This option should not be used, however,
if an accidental release cannot be envkonmentally tolerated even though detection may be
immediate). The release detection requkements for tank tightness tests and ATGs are given in
Section 280.43 (c) and (d) of the regulations. Tank tightness tests must be capable of detecting a
0.1-gal/h leak with a probability of detection of 0.95 and a probability of false alarm of 0.05, and
ATGs must be capable of detecting a leak of 0.2 gal/h with the same probabilities of detection
and false alarm as a tank tightness test. Because an ATG conducts tests more frequently, its
performance requkement is not as stringent as that of a tank tightness method.
-------
Over the next eight years, owners and operators of existing hazardous-substance USTs will
be using volumetric leak detection systems (for example, tank tightness tests) that were
developed primarily for use with petroleum products. As noted above, owners/operators may
continue to use these systems after 1998 if the requirements specified in the fifth option are met.
It is therefore critical to determine whether volumetric leak detection systems can be relied Upon
when used on tanks containing non-petroleum chemicals. The performance requirements that
were developed for tank tightness tests and ATGs were based on extensive measurements in
underground storage tanks containing petroleum motor fuels such as gasoline and diesel
[e.g., 3-14], Hazardous substances can differ from these fuels in density, coefficient of thermal
expansion, viscosity, and vapor pressure. Moreover, since the list of hazardous substances is
extensive, the variability of these properties is expected to extend over a broad range. The
effects of these properties on volumetric testing, and therefore on the performance of tank
tightness tests and ATGs, have not been fully assessed. Such assessment must be done if the
owners and operators of existing hazardous-substance USTs are to have any assurance that they
can depend on tank tightness tests and ATGs to guard against accidental releases.
Objectives
The objectives of this project were (1) to identify the chemicals being stored in
underground storage tanks and the characteristics of the tank systems used to store these
chemicals, (2) to assess the influence of the physical properties of the stored products on the
performance of volumetric leak detection systems, and (3) to identify and determine the
effectiveness of the approaches to release detection that owners and operators of tanks containing
hazardous chemicals are taking to achieve compliance with the regulations.
Report Organisation
The work that was done in fulfillment of these objectives is presented in the three technical
papers [15-17] included in this report as Appendices A, B, and C. Each paper addresses one of
the objectives of the project. The main conclusions and recommendations derived from this
work are summarized in Sections 2 and 3 of this report.
The paper included in Appendix A has been accepted for publication in a peer-reviewed
journal. This paper presents the results of an analysis of databases containing information on
non-petroleum chemicals stored in underground storage tanks. These databases, compiled by
14 states, include the types of chemicals stored in USTs and the characteristics of the USTs
themselves. This paper enlarges upon the work described in [18], which gave a comprehensive
-------
analysis of the data provided by New York, California, and the Chemical Manufacturers
Association (CMA). The important results presented in [18] are also discussed in the paper
included in Appendix A.
The paper included in Appendix B has been accepted for publication in the proceedings of
the Air & Waste Management Association's 84th annual meeting, held in June 1991. This paper
describes an analysis of the performance that could be achieved with volumetric test methods
developed for tanks containing motor fuels or hazardous chemicals.
The paper included in Appendix C was published in the proceedings of the 17th annual
research symposium sponsored by EPA's Risk Reduction Engineering Laboratory and held in
April 1991. This paper summarizes the important aspects of the entire work assignment,
including the chemical tank survey presented in Appendix A, the leak detection: analysis
presented in Appendix B, and the results of a survey of the leak detection practices of tank
owners and operators. ' : •
-------
SECTION!
CONCLUSIONS
The main conclusions derived from the surveys and analyses conducted as part of this
project are summarized below.
Characteristics of Tanks Containing Non-Petroleum Chemicals
A survey of the registered tanks containing chemicals other than petroleum was conducted
and reported in [15]; a copy of the referenced paper is included as Appendix A of this report.
The following states participated in the survey: California, Delaware, Florida, Illinois, Indiana,
Maine, Massachusetts, Minnesota, Missouri, Montana, New York, Ohio, Texas, Virginia, and
Wisconsin. The results of the survey suggest that chemical tanks, containing both hazardous and
non-hazardous chemicals, comprise up to 2% of the total national underground tank population.
Of the chemical tanks surveyed, approximately 50% were found to contain hazardous
substances, while the remaining 50% contained chemicals that are not regulated. The most
striking feature to emerge from the survey of chemical tanks is the wide variety of substances
that are stored. Analysis of these substances indicates, however, that roughly 80 to 90% of the
stored hazardous chemicals are organic solvents, and, of these, the most common are acetone,
toluene, xylene, methanol and methyl-ethyl ketone. These five chemicals account for
approximately 49% of the tanks containing hazardous materials.
Assessments were made not only of the most commonly stored substances but also of the
ranges of tank capacity, age, and construction materials. The average tank capacity was found to
be approximately 7,200 gallons, with over 27% of the tanks having capacities of 10,000 gallons
or more. The mean age of the tanks was roughly 18 years, and over 86% were fabricated from
steel. In view of survey's findings, it can be expected that substantial upgrading of tank
installations will occur over the next eight years.
Analysis of the Applicability of Volumetric Leak Detection Systems to Tanks Containing
Hazardous Chemicals
The performance of volumetric leak detection systems that could be used to meet the tank
tightness testing and the automatic tank gauge release detection option was analyzed [16]. The
results, presented here in Appendix B, show that (1) the performance of a volumetric leak
detection system is directly proportional to the coefficient of thermal expansion of the stored
-------
product, and (2) the waiting period required for the effects of structural deformation to subside is
essentially the same for all values of density (even though higher densities produce greater
deformation-induced volume changes immediately after any product-level change). When a leak
detection system is used with a chemical having a coefficient of thermal expansion lower than
that of the product used in the evaluation of the system, the system's performance will be better
than it was in the evaluation. Because gasoline has a higher coefficient of thermal expansion
than many chemicals, a system evaluated with a gasoline product can be used with such
chemicals and still maintain a similar levelof performance.
For a large portion of the tank population, internal leak detection methods! such as tank
tightness tests and ATGs are a viable approach to testing tank integrity. The physical properties
of the most commonly stored chemicals are generally similar to those of the unleaded gasoline
upon which the quantitative performance standards in the regulations are based, In addition, the
size and construction of a majority of chemical tanks closely approximate those from which the
data used to support the regulations were developed. Assuming, therefore, that practical details
of material compatibility and safety have been addressed, it would seem that only minimal
extrapolations of current knowledge are needed before volumetric leak detection systems can be
applied to storage tanks containing chemicals.
Currently Used Approaches to Leak Detection
An informal telephone survey of two types of organizations was conducted: those that
own and operate tank systems containing hazardous substances and those that provide tank
testing services to such organizations [17]. The object of the survey was to determine the type
and effectiveness of the leak detection systems and inventory control practices being used to test
tank systems. A copy of the referenced paper is included as Appendix C of this report.
Even though a diverse cross section of organizations was contacted, the responses obtained
during the telephone survey should not be interpreted quantitatively; the number of organizations
was very limited, and the survey was not statistically designed or statistically analyzed. As a
consequence, the results should be interpreted cautiously, and the temptation to generalize,
particularly about the status of regulatory compliance, should be avoided unless: additional data
are gathered. The following observations are noteworthy, however, either because the response
was overwhelming or because it was ambiguous.
5
-------
Based on the discussions conducted during the course of the survey, one would tend to
conclude that most owners and operators of chemical tanks are actively involved in upgrading
their tank systems to minimize the liability associated with any accidental releases. Most
organizations said that they were replacing their underground storage tanks with aboveground
tanks whenever possible. When this was not possible, tank and piping systems with secondary
containment, primarily double-wall tanks and piping, were being used; none of the organizations
contacted was considering the use of single-wall tanks or piping in conjunction with the release
detection option. What is not clear from the survey is how much time will be required for those
organizations currently upgrading their tank systems to complete the process. If the time
required for upgrading a tank system exceeds one year, the regulations require that the tank
system be tested in the interim by means of methods commonly used on tanks containing
petroleum.
None of the organizations contacted used inventory control as a means of leak detection. It
also appears that this method of leak detection would be difficult to apply because of the lack of
metering devices or the lack of accuracy in the metering devices being used.
The tank testing firms contacted indicated that approximately 5% of their tests were
conducted on tanks containing hazardous chemicals, a figure that is slightly higher than the
estimated percentage of such tanks in existence in the U.S. This is inconsistent with the response
obtained from the 13 tank-owning organizations that responded to the survey. None of these
organizations indicated that they were using or planning to use such services; this inconsistency
is probably due to the small size of the survey.
-------
SECTION 3
RECOMMENDATIONS
Although the number and volume of underground storage tank systems containing
hazardous chemicals is small, it is important to ensure that good leak detection practices are
being used—in other words, practices that are in compliance with state and federal regulations.
No attempt was made in this project to assess the status of regulatory compliance by
owners and operators of underground storage tank systems containing hazardous chemicals.
The principal recommendation of this project is that a survey be conducted (1) to assess the
level of compliance on the part of owners and operators, and (2) to determine whether guidance
documents in support of compliance efforts are needed and would be effective.
-------
REFERENCES
1. U. S. Environmental Protection Agency. 40 CFR 280 — Technical Standards and
Corrective Action Requkements for Owners and Operators of Underground Storage Tanks.
Federal Register, Vol. 53 (23 September 1988).
2. U. S. Environmental Protection Agency. Part 302 -- Comprehensive Environmental
Response, Compensation, and Liability Act. Federal Register, Vol. 45 (11 December
1980).
3. U. S. Environmental Protection Agency. Evaluation of Volumetric Leak Detection
Methods for Underground Fuel Storage Tanks. Vol. I (EPA/600/2-88/068a) and Vol. II
(EPA/600/2-88/068b), Risk Reduction Engineering Laboratory, Edison, New Jersey
(December 1988).
4. J. W. Maresca, Jr., J. W. Starr, R. D. Roach, and J. S. Farlow. Evaluation of the Accuracy
of Volumetric Leak Detection Methods for Underground Storage Tanks Containing
Gasoline. Proceedings of the 1989 Oil Spill Conference, Oil Pollution Control, A
Cooperative Effort of the U.S. Coast Guard, American Petroleum Institute and U.S.
Environmental Protection Agency, San Antonio, Texas (March 1989).
5. J. W. Maresca, Jr., R. D. Roach, J. W. Starr, and J. S. Farlow. U.S. EPA Evaluation of
Volumetric UST Leak Detection Methods. Proceedings of the Thirteenth Annual
Research Symposium, EPA/600/0-87/015, Hazardous Waste Engineering Research
Laboratory, Office of Research and Development, U.S. Environmental Protection Agency,
Cincinnati, Ohio (July 1987).
6. R. D. Roach, J. W. Starr, C. P. Wilson, D. Naar, J. W. Maresca, Jr., and J. S. Farlow.
Discovery of a New Source of Error in Tightness Tests on an Overfilled Tank.
Proceedings of the Fourteenth Annual Research Symposium, EPA/600/9-88/021, Risk
Reduction Engineering Laboratory, Office of Research and Development, U.S.
Environmental Protection Agency, Cincinnati, Ohio (July 1988).
7. J. W. Maresca, Jr., J. W. Starr, R. D. Roach, J. S. Farlow, and R. W. Hillger. Summary of
the Results of EPA's Evaluation of Volumetric Leak Detection Methods. Proceedings of
the Fifteenth Annual Research Symposium, EPA/600/9-90/006, Risk Reduction
Engineering Laboratory, Office of Research and Development, U.S. Environmental
Protection Agency, Cincinnati, Ohio (February 1990).
8. J. W. Maresca, Jr., J. W. Starr, R. F. Wise, R. W. Hillger, and A. N. Tafuri. Evaluation of
Internal Leak Detection Technology for Large Underground Storage Tanks. Proceedings
of the Sixteenth Annual Research Symposium, EPA/600/9-90/037, Risk Reduction
Engineering Laboratory, U.S. Environmental Protection Agency, Cincinnati, Ohio (August
1990).
9. J. W. Maresca, Jr., J. W. Starr, R. F. Wise, R. W. Hillger, and A. N. Tafuri. Evaluation of
Volumetric Leak Detection Systems for Large Underground Storage Tanks. Submitted for
publication in/, of Hazardous Materials (March 1991).
10. J. W. Starr, R. F. Wise, J. W. Maresca, Jr. Volumetric Leak Detection Experiments on
190,000-Liter Underground Storage Tanks. Draft Final Report, Risk Reduction
Engineering Laboratory, Office of Research and Development, U.S. Environmental
Protection Agency, Cincinnati, Ohio (in press).
-------
11. J. W. Maresca, Jr., J. W. Starr, R. D. Roach, D. Naar, R. Smedfjeld, J. S. Farlow, and
R. W. Hillger. Evaluation of Volumetric Leak Detection Methods Used in Underground
Storage Tanks. /. of Hazardous Materials, Vol. 26 (1991).
12. U. S. Environmental Protection Agency. Underground Motor Fuel Storage Tanks: A
National Survey, Vols. I and n. Office of Pesticides and Toxic Substances, Washington
D.C. (May 1986).
13. J. W. Maresca, Jr., C. P. Wilson, and N. L. Chang, Jr. Detection Performance and
Detection Criteria Analysis of the Tank Test Data Collected on the U. S. Environmental
Protection Agency National Survey of Underground Tanks. Prepared for Midwest
Research Institute, Vista Research Project No. 2013, Vista Research, Inc.,, Palo Alto,
California (September 1985).
14. J. W. Maresca, Jr., N. L. Chang, Jr., and P. J. Gleckler. A Leak Detection: Performance
Evaluation of Automatic Tank Gauging Systems and Product Line Leak Detectors at Retail
Stations. Final Report, American Petroleum Institute, Vista Research Project No. 2022,
Vista Research Inc., Mountain View, California (January 1988).
15. R. W. Hillger, J. W. Starr, and M. P. MacArthur. Characteristics of Underground Storage
Tanks Containing Chemicals. Submitted for publication (April 1991).
16. J. W. Starr, R. F. Wise, J. W. Maresca, Jr., R. W. Hillger, and A. N. Tafuri. Volumetric
Leak Detection in Underground Storage Tanks Containing Chemicals. Accepted for
publication in Proceedings of the 84th Annual Meeting and Exhibition of the Air and
Waste Management Association, Vancouver, B.C., Canada (15-17 June 1991).
17. R. F. Wise, J. W. Starr, J. W. Maresca, Jr., R. W. Hillger, and A. N. Tafuii. Underground
Storage Tanks Containing Hazardous Chemicals. Proceedings of the Seventeenth Annual
Research Symposium, EPA/600/9-91/002, Risk Reduction Engineering Laboratory, Office
of Research and Development, U.S. Environmental Protection Agency, Cincinnati, Ohio
(3-5 April 1991).
18. I. Lysyj, R. W. Hillger, J. S. Farlow, and R. Field. A Preliminary Analysis of
Underground Storage Tanks Used for CERCLA Chemical Storage. Proceedings of the
Thirteenth Annual Research Symposium, EPA/600/9-87/015, Hazardous Waste
Engineering Research Laboratory, Office of Research and Development, U.S.
Environmental Protection Agency, Cincinnati, Ohio (July 1987).
-------
APPENDIX A
CHARACTERISTICS OF UNDERGROUND
STORAGE TANKS CONTAINING CHEMICALS
Robert W.Hfflger
Risk Reduction Engineering Laboratory
U. S. Environmental Protection Agency
Edison, New Jersey 08837
James W. Starr and Maria P. MacArthur
Vista Research, Inc.
Mountain View, California 94042
This paper was accepted for publication in a peer-reviewed journal.
10
-------
CHARACTERISTICS OF UNDERGROUND
STORAGE TANKS CONTAINING CHEMICALS
by
R. W. Hfflger1, J. W, Stan2, and M. P. MacArthur2
ABSTRACT
It is generally acknowledged that a small fraction of the total underground storage tank
population is used to store chemicals. The detailed characteristics of these tanks, however, are
not well understood. Additional information is, required if competent decisions are to be made
regarding leak detection, tank upgrading, and tank management practices. In older to obtain
more detailed information regarding these tanks, two surveys were conducted over the course of
several years. The first survey examined the chemical tank populations in two states, California
and New York, along with data from the Chemical Manufacturers Association. The second
survey focused ofi the chemical tank databases for 14 states covering a wide geographical area.
Data from these two surveys were then analyzed to determine the primary features of the
chemical tank population. The results of these analyses indicate that up to 2% of the total tank
population contains non-petroleum chemicals, with roughly half of these tanks, either by number
or tank volume, containing hazardous substances. Solvents were found to comparise the single
largest fraction of hazardous chemicals. Of these, acetone, toluene, methanol and methyl ethyl
ketone were found to be the most commonly stored chemical substances, comprising roughly
60% of hazardous materials stored in tanks, and 34% of all chemical tanks, which contain both
hazardous and non-hazardous substances, in the sampled states. Tank age was found to average
18 years, with over 85% of the tanks being fabricated from steel. Roughly 60% of the tanks in
the state databases had capacities between 1,000 and 10,000 gallons, with the average tank size
from all states being 7,205 gallons. These characteristics suggest that a strong potential exists
for corrosion-induced tank leakage, but that conventional tank integrity testing could be applied
to detect leakage from a large fraction of the chemical tank population, with no modifications to
the leak detection performance requirements.
1 U.S. Environmental Protection Agency, Releases Control Branch, Risk Reduction Engineering
Laboratory, Edison, NJ 08837
2 Vista Research, Inc., 100 View St., Mountain View, CA 94041
11
-------
Introduction
Federal underground storage tank regulations promulgated on 23 September 1988 (40 CFR
280,281) establish a broad range of minimum requirements for the design, installation, operation
and testing of a large fraction of tanks in the United States containing both petroleum fuels and
other hazardous chemicals (as defined by CERCLA, 40 CFR 302) [1,2]. These regulations are
designed to help the underground tank community control and minimize the adverse
environmental impact caused by leakage of product from the tank. Quantitative leak detection
performance standards are included in these regulations. These standards were developed
through an extensive theoretical and experimental test program conducted at the U.S. EPA's
Underground Storage Tank Test Apparatus in Edison, New Jersey, on 8,000-gal tanks containing
unleaded regular gasoline.
The federal regulations, as noted above, apply to petroleum substances as well as to a wide
variety of chemicals having a broad distribution of chemical and physical properties. Specific
information has not yet been assembled to characterize the features of the chemical tank
population, or potential impact of these features on leak detection performance. Technically,
since a large portion of the federal standards are based on data for a single, particular petroleum
product, the influence of varying chemical composition on the ability of leak detection methods
to satisfy the mandated performance standards needs to be addressed. The primary objective of
this study is to develop, in sufficient detail, the characteristics of the tank population in which
leak detection could be employed. With this information, a focused analysis of leak detection
practices in underground chemical tanks can be made, and areas of potential alteration or
improvement to the leak detection performance standards can be identified, if required. This
paper describes the results of two chemical tank surveys. The first survey, conducted in 1987,
was limited in scope, and relied on data from California, New York, and the Chemical
Manufacturers Association [3]. A second survey, conducted in 1990, utilized the information
from chemical tank databases in 14 states. Where possible, efforts were made to draw
comparisons between the two data sets in an effort to gain an understanding of the characteristics
of the chemical tank population.
Approach
As the first step in assessing the impact of underground chemical storage tanks on leak
detection practices and performance, the basic characteristics of the tank population were
identified. This was accomplished by means of two surveys conducted over the course of several
years. The first survey utilized data from the two most populous states, California and New
York, and on a national level, data from the Chemical Manufacturers Association (CMA). CMA
data were used because, at the time of the survey, the registration of tanks in compliance with the
Resource Conservation and Recovery Act (RCRA) amendments had not been fully implemented.
The second survey used the chemical tank databases compiled by 14 different states distributed
over a wide geographic area (Delaware, Florida, Illinois, Indiana, Maine, Massachusetts,
Minnesota, New York, Ohio, Texas, Virginia, and Wisconsin). Li selecting these states, efforts
were made to obtain representative national coverage while simultaneously examining the more
12
-------
populous industrial states, which might be expected to have large numbers of chemical tanks.
New York was again included in the second survey so that changes in its tank population since
the earlier survey might be identified. For each state, information regarding stored substances
was compiled. (This included CERCLA name and/or CAS number, tank capacity, material of
construction, and tank age.) The information collected from this second survey was based
primarily on the responses to the national underground tank registration requirements,' which
were instituted in 1984 as part of the amendments to the RCRA. The resulting data were then
organized and sorted so that the basic characteristics of the sample population could be
quantified. '
Chemical Distribution
Previous studies suggest that, of the total number of underground tanks installed in the
United States, approximately 95% are used to store petroleum products. The remaining 5%,
comprising non-petroleum tanks, are devoted to the storage of a vast array of hazardous and
non-hazardous chemicals. The initial survey of data from California, New York, and the
Chemical Manufacturers Association indicated that non-hazardous chemicals comprised
roughly 44 to 46% of the non-petroleum tank population. Of the remaining non-petroleum
tanks, 3,766 (2.25%) of a total population of 166,973 tanks in California were found to
contain CERCLA chemicals, while 792 (1.07%) of the 73,819 registered tanks in New York
were considered hazardous.
Based upon the more recent data obtained from the survey of 14 states, the proportion
of hazardous to non-hazardous tanks in the sampled non-petroleum tank population appears
to be similar to that in the earlier survey. These data are summarized by state in Table 1. As
would be expected, the relative proportion of hazardous and non-hazardous taniks in each of
the sampled states exhibits a degree of variability. However, compilation of the aggregate
proportions for all 14 states indicates that the hazardous fraction, by both number of tanks
and by tank volume, is approximately 51.1% and 53.1%, respectively, compared to the
earlier range of 44 to 46%.
Approximately half of the non-petroleum tanks are used to store hazardous chemicals as
defined by CERCLA. Since this group of substances poses a significant environmental hazard,
basic information regarding the primary characteristics of the tank population can be useful in
helping to guide leak detection strategies. In addition, classification of this group of tanks can
provide a useful means of comparing the data obtained from the tank surveys. This comparison
can then be used to help identify any trends that may be developing in the management of this
class of tanks.
In order to facilitate the analysis, the hazardous chemicals from the initial survey were
classified into organic and inorganic compounds, and particular emphasis was then placed on
characterizing the organic tank population. The organics were found to comprise approximately
81% of the CERCLA tanks in the databases. Organic compounds were classified as solvents,
monomers, or miscellaneous compounds. Solvents include ketones/aldehydes, alcohols,
13
-------
Table 1. Percentage of Hazardous vs. Non-Hazardous Chemicals Stored in Registered Non-Petroleum Tanks
State
% by Number of Tanks
Number % Haz % Non-Haz
% by Volume
% Haz % Non-Haz
Delaware
Florida
Illinois
Indiana
Massachusetts
Maine
Minnesota
Missouri
Montana
New York
Ohio
Texas
Virginia
Wisconsin
18
404
2862
506
66
667
406
734
76
936
795
692
896
598
78.9
28.2
72.0
100.0
49.0
28.8
24.9
33.0
100.0
100.0
35.6
57.4
34.2
44.8
21.1
71.8
28.0
*
51.0
71.2
75.1
67.0
*
*
64.4
42.6
65.8
55.2
97.0
30.4
68.1
100.0
54.8
22.6
28.9
47.4
100.0
100.0
43.6
57:1
42.7
49.5
3.0
69.6
31.9
*
45.2
77.4
71.1
52.6
*
*
56.4
42.9
57,3
50.5
* An asterisk denotes that only hazardous, non-petroleum chemicals were reported in the database for that state.
aromatic hydrocarbons, esters/ethers, chlorinated hydrocarbons, and aliphatic hydrocarbons.
Monomers include intermediates important to many manufacturing processes, including styrene,
acrolein, vinyl esters, and ethylene and propylene oxides. Miscellaneous chemicals include
various amines, organic acids, anhydrides, phenols, and other less common substances. The
results of this classification of the data from California, New York, and CMA are shown in
Table2.
Table 2. Summary of Organic CERCLA Substances Stored in Underground Tanks (source: [3])
California Data
Chemical
Groups
Solvents
Monomers
Miscellaneous
Pesticides
%by
Tank
Number*
87.1
3.6
7.4
1.4
%by
Tank
Volume*
81.9
6.2
7.0
4.2
New York Data
%by
Tank
Number*
91.4
2.8
6.0
-.
%by
Tank
Volume*
90.0
1.6
8.0
—
CMA Data
%by
Tank
Number*
78.3
13.3
8.8
-
%by
Tank
Volume*
72.3
22.2
5.0
-
Due to rounding, the total percentages may not sum to 100.
14
-------
Inspection of these data indicates that, in terms of both capacity and number of tanks,
solvents comprise the largest single fraction of the CERCLA tank population. Based upon this
finding, additional sorting and classification was performed to characterize the solvent tank
population, and to identify the most commonly stored substances. The results of this analysis are
summarized in Table 3. While the CMA database suggested that the number of tanks containing
acrolein, ethylene oxide, and styrene was fairly large (approxmately 2.5%), these chemicals were
not included in Table 3, because their contributions to the New York and California databases
were very small.
Table 3. Summary of the Most Commonly Stored Organic CERCLA Solvents (source: [3])
California Data
Chemical
Acetone
Toluene
Xylene
Methanol
Methyl- Ethyl
Ketone
Methylene
Chloride
TOTALS
%by
Tank
Number*
22.8
13.3
8.1
6.6
10.3
2.8
63.9
%by
Tank
Volume*
18.0
14.2
6.3
5.5
9.6
2.1
55.7
New
%by
Tank
Number*
12.0
22.4
15.5
11.5
9.0
1.4
71.8
York Data
%by
Tank
Volume*
18.3
21.1
11.7
8.5
7.0
0.7
67.3
CMA Data
• ' % by
Tank
Number*
17.8
13.1
5.6
15.8
3,.8
8,,5
64.6
% by
Tank
Volume*
19.1
16.9
3.4
14.9
1.6
7.6
63.5
* Percentages apply only to the CERCLA chemical tank populations in the initial survey.
These data suggest that a large fraction of the CERCLA organic chemical tank population
is comprised of only a few predominant substances. In all three databases, the most commonly
stored substances were found to be the same in four of five cases. The only difference that was
found was in the case of methylene chloride and methyl-ethyl ketone; the former was more
prevalent in the CMA data, while the latter was more common in the two state databases.
In order to provide a comparison with the more recent data collected from the 14 state
databases, a similar analysis was made to identify the most commonly stored chemicals. The
results of this analysis are given in Table 4. .
In examining these data, two characteristics are notable. First, except for methanol and
methyl ethyl ketone, the most commonly stored chemicals are the same in both surveys. The
relative ranking of the most common chemicals by number of tanks or by storage capacity is
slightly different in the two surveys. These differences depend upon the data siurvey analyzed, or
15
-------
Table 4. Summary of the Most Commonly Stored Chemical Substances Based on Data from 14 States
Chemical
Toluene
Acetone
Methanol
Methyl-
Ethyl
Ketone
Mineral
Spirits
Xylene
%by
Tank
Number*
5.6
3.9
3.8
3.7
3.1
—
% by
Tank
Volume*
9.2
4.2
3.3
2.9
2.5
TOTALS
. 20.1
22.1
* The data are reported as a traction of the total number (or volume) of all hazardous and non-hazardous tanks.
whether the classification is based upon the number of tanks or on the storage capacity.
Regardless of the data set examined, acetone, toluene, methanol, xylene, and methyl ethyl ketone
are found to be prevalent in each survey.
Second, considering the broad range of chemicals, both hazardous and non-hazardous, the
five most common chemicals comprise a significant fraction of the total chemical tank
population. The initial survey indicated that as much as 81% of the chemicals stored in
hazardous tanks was devoted to organic substances. Of that organic portion, 60% was comprised
of the five most common substances. After the fraction of inorganic tanks has been accounted
for, the five most common organics are estimated to comprise 49% of the total population of
CERCLA (i.e., hazardous) tanks. The more recent survey of 14 states, extrapolated to the
national level, suggests that this dominance is diminishing slightly. The results of this later
survey indicate that only 40% of the hazardous chemical tank population is accounted for by the
five most common solvents.
Tank Distribution
The initial survey indicated that tank capacities ranged from as little as 2,000 gallons to
more than 20,000 gallons. The mean tank capacity in both the California and New York data
was 6,000 gallons, while in the CMA data it was 15,000 gallons.
16
-------
The range of tank sizes in the second survey, as well as the number of tanks in different
size ranges, are summarized in Table 5. To generate this table, five different ranges for tank
capacity were developed and the data then sorted by tank capacity. The resultis indicate that the
average tank size in all surveyed states for which data were available ranged between 3,409 and
12,400 gallons. The aggregate average tank size was found to be 7,205 gallons. The largest size
reported for an individual tank (found in Delaware) was 430,000 gallons.
Table 5. Summary of Tank Size Distributions Compiled from the 14 State Databases and Expressed as a
Fraction of the Number of Tanks in Each State
State
Delaware
Florida ,
Illinois
Indiana*
Maine
Massachusetts
Minnesota
Missouri
Montana*
New York*
Ohio
Texas
Virginia
Wisconsin
TOTAL
< 1,000
5.6
27.7
7.1
4.3
6.2
15.5
15.3
10.1
44.7
12.8
6.6
11.3,
15.8
8.4
11.3
1,000-
<4,000
16.7
39.9
29.2
16.0
26.2
32.1
34.5
28.7
23.7
22.3
33.8
28.0
29.4
30.4
29.6
Range of Tank
4,000-
<10,000
27.8
22.0
33.6
26.5
36.9
28.7
23.9
31.9
19.7
30.8
37.9
28.9
28.7
37.6
31.9
Capacities (Gallons)
10,000-
<20,000
22.2
7.4
19.8
19.8
24.6
19.7
18.2
21.0
3.9
23.5
18.1
19.7
17.0
19.7
19.6
>20,i900
27.8
0.5
5.9
29.6
6.2
4.0
7.1
8.3
7.9
10.6
3.6
6.8
6.9
3.8
7.6
Average
Volume
101293
3409
6826
11525
8226
6132
6211
9144
12400
8957
5546
6952
6534
6350
7205
* Totals for New York, Indiana, and Montana are based on CERCLA chemicals only.
It is clear from these data that the majority of the tanks exhibit capacities of 20,000 gallons
or less. In addition, over 70% of the tanks have capacities less than or equal to 10,000 gallons,
with the two largest groups comprising the range between 1,000 and 10,000 gallons. With the
exception of Delaware, the average tank volume for most states was generally found to be
17
-------
between 6,000 and 9,000 gallons. The data for Delaware are comprised of only 18 tanks, four of
which have capacities of 430,000 gallons each, resulting in an extremely biased average tank
volume.
The implication of this tank size distribution for leak detection should be carefully
considered. Based upon the experimental data used to support the development of the national
regulations, it is expected that, qualitatively, as the tank capacity is increased beyond 10,000
gallons, it will become increasingly more challenging to conduct precision tests. Fortunately, the
majority of tanks in the surveyed states have capacities of 10,000 gallons or less. This
characteristic, coupled with the chemical and physical properties of the most commonly stored
chemicals, suggests that a significant portion of the hazardous chemicals may be addressed by
volumetric tests, which have performed satisfactorily in detecting leaks of petroleum motor fuels.
As a consequence, the impact of tank size on the feasibility of conducting internal (i.e.,
volumetric) tests of these tanks should be minimal. For larger tank capacities, issues associated
with appropriate scaling of volumetric leak detection performance would need to be addressed
before employing this type of test. For the near term, however, volumetric testing would
probably be a preferred leak detection approach, since interstitial monitoring, which could be
used to detect product leakage through the primary tank wall, would be limited to the small
fraction of installed double-walled tanks. The suitability of exterior monitoring for the current
tank population cannot be assessed from the current data.
Tank Construction
Data from both surveys indicate that the primary material of construction for underground
tanks containing hazardous substances is carbon steel. In the initial survey, summarized in
Table 6, New York and CMA data indicated that the fraction of steel tanks in the entire
population was 86.4% and 87.7%, respectively. Painting was the predominant method of
corrosion protection for these tanks. The majority of these tanks utilized single-walled
construction, with New York reporting that 54.9% and CMA that 38.4% of tanks were painted
for corrosion resistance. Of particular note in this survey was the large number of tanks in which
corrosion protection was not employed or the type of protection was unknown. In New York,
41.3% of the tanks exhibited this characteristic, while for the CMA, the fraction was 42.9%.
Table 6. Summary of Tank Construction Materials (source: [3])
Construction
New York Data
% by Tank Number
CMA Data
% by Tank Number
Steel
Fiberglass/Plastic
Other
90.3
3.4
6.3
93.7
0.7
5.6.
18
-------
In the more recent survey, summarized in Table 7, the distribution of steel tanks was found
to support these earlier findings. In addition, significant portions of the installed tanks in some
of the states are of unknown construction, with as many as 22.3% of the tanks in Florida fitting
this category.
Table 7. Summary of Tank Construction Materials Compiled from 14 State Databases
State
Delaware
Florida
Illinois
Indiana*
Maine
Massachusetts
Minnesota*
Missouri
Montana
New York
Ohio
Texas*
Virginia
Wisconsin
TOTAL
Steel
77.8
62.9
89.4
— -
72.7
90.3
—
83.4
85.5
83.9
94.1
—
86.5
79.3
86.1
Fiberglass
Reinforced
Plastic
0.0
9.2
4.2
—
15.2
5.4
—
7.2
—
12.3
2.1
—
5.9
9.4
6.2
Other
5.5
5.7
2.6
—
10.6
3.0
—
6.1
—
3.8
1.5
—
5.1
7.2
3.9
Unknown
16.7
22.3
3.8
1.5
1,3
—
3.3
—
0.0
2.3
—
2.6
4.2
3.8
* Materials were not reported for Indiana, Minnesota, and Texas. Only steel tanks were reported for Montana.
Values reported are percentages of the total tank populations in each state.
Age Distribution
Inspection of the tank age distribution derived from the two surveys can yield some
insights into the likelihood of potential problems, as well as an early indication of developing
trends in tank construction practices. Data from the original survey suggest that, while the tank
ages ranged from new to 60 years old, the mean tank age for both New York and the CMA
(national) data was approximately 18 years. While no information was developed regarding the
distribution of ages in this survey, the average age, coupled with the large fraction of marginally
protected (if at all) steel tanks, suggest that there exists strong potential for tank leakage due to
19
-------
corrosion. The extent of this potential threat is somewhat site-specific and dependent upon
numerous other factors, including tank maintenance practices, electrical properties of the local
backfill, and local water-table levels.
The more recent study of the 14 sampled states yields a tank age distribution summarized
in Table 8. As can be seen in this table, the mean age of all tanks containing chemical
substances is 18.3 years, with nearly 40% of the tanks being over 20 years old. According to this
survey, the average age of those tanks in New York whose age was known was 17.9 years in
1990. This suggests that, in spite of the upgrading requirements in the federal underground tank
regulations, large scale improvements to the chemical tank population have not yet been widely
implemented.
Table 8. Summary of Tank Age Distributions Compiled from 14 State Databases and Expressed as a Percentage of
the Number of Chemical Tanks in Each State
State
Delaware
Florida
Illinois
Indiana
Maine
Massachusetts
Minnesota
Missouri
Montana
New York
Ohio
Texas
Virginia
Wisconsin
Oto4
22.2
3.5
2.6
6.9
9.1
1.8
3.0
3.3
2.7
14.8
1.5
6.2
2.1
4.3
5 to 9
5.6
31.4
12.1
15.2
14.1
14.0
23.0
20.9
4.0
15.2
15.8
21.3
19.1
13.8
Range of Tank
10 to 14
5.6
18.7
22.9
20.6
13.9
43.9
22.2
23.0
4.0
20.0
20.4
26.1
21.6
24.9
Age (Years)
15 to 19
0.0
11.0
18.2
16.8
16.2
17.5
10.0
16.0
2.7
14.2
21.5
17.9
21.1
25.6
>=20
66.7
35.4
44.2
40.5
46.7
22.8
41.8
36.8
86.7
35.8
40.8
28.4
36.0
31.5
AVERAGE
4.9
16.2
21.6
17.6
39.7
20
-------
Conclusions
Based upon the currently available information, the chemical tank population, although
comprising only 1 to 2% of the total national underground tank population, appears to pose a
substantial environmental hazard. Of the chemical tanks surveyed, approximately 50% were
found to contain hazardous chemicals, while the remaining 50% contain chemicals that are not
regulated.
The most striking feature of the surveyed chemical tank population is the wide variety of
substances that are stored. Analysis of these substances indicates that roughly 80 to 90% of the
hazardous chemicals are organic solvents. Of these, the most common constituents are acetone,
toluene, methanol and methyl ethyl ketone, comprising between 44 to 49% of the number of
surveyed CERCLA tanks.
In addition to assessments of the most commonly stored substances, assessments were
made of the range of tank capacities, ages, and materials of construction. Based upon these
analyses, the mean tank age was found to be roughly 18 years, with over 86% of the tanks
fabricated from steel. The average tank capacity was found to be roughly 7200 gallons, with
over 60% of the tanks having capacities between 1,000 to 10,000 gallons. In view of these
findings, substantial upgrading of tank installations can be expected to occur over the next
8 years, as tank owners comply with the national regulations.
Internal leak detection appears to offer one viable approach to testing the integrity of a
large fraction of the tank population. The physical properties of the most commonly stored
chemicals are generally similar to those of the unleaded gasoline upon which the quantitative
performance standards in the regulations are based. In addition, the size and construction of a
majority of the chemical tanks closely approximate those from which supporting data for the
regulations were developed. As a consequence, assuming practical details of material
compatibility and safety have been addressed, only minimal extrapolations of current knowledge
should be needed in order to conduct tank integrity tests.
References
U.S. Environmental Protection Agency. "Part 280 - Technical Standards and Corrective
Action Requirements for Owners and Operators of Underground Storage Tanks." Federal ,
Register, Vol. 53 (23 September 1988).
U.S. Environmental Protection Agency. "Part 302 - Comprehensive Environmental
Response, Compensation, and Liability Act." Federal Register, Vol. 45 (11 December
1980).
!• Lysyj, R. W. Hillger, J. S. Farlow, and R. Field. "A Preliminary Analysis of Underground
Storage Tanks Used for CERCLA Chemical Storage." Proceedings of the Thirteenth
Annual Research Symposium, Hazardous Waste Engineering Research Laboratory, Office
of Research and Development, U.S. Environmental Protection Agency, Cincinnati, Ohio
(July 1987).
1.'
2.
3.
21
-------
Appendix
PARTIAL LIST OF CHEMICALS STORED IN UST
22
-------
Partial List of Chemicals Stored in UST
CERCLA
Ketones/Aldehydes
Alcohols
Esters/Ethers/Glycols
Aromatic Hydrocarbons
Chlorinated Hydrocarbons
Monomers
Miscellaneous Chemicals
Acetone
Methyl ethyl ketone
Methyl iso butyl ketone
Cyclohexanone
Fonnaldehyde
Methanol
n-Butanol
iso-Butanol
Ethyl acetate
n-Butyl acetate
iso-Butyl acetate
Dioctyl phthalate
Ethyl ether
Benzene
Toluene
Xylene
Methyl chloride
Methylene chloride
1,1,1, Trichloromethane
Carbon tetrachloride
Ethylene dichloride
Stryrene
Propylene oxide
Vinyl acetate
Methyl methacrylate
Ethyl acrylate
Acetic acid
Propionic acid
Adipic acid
Phenol
Tetrahydrofuran
Furfural
Hydrazine
Monomelhyl amine
Toluene di-iso cyanide
Acetic anhydride
Allyl chloride
Phosgene
Carbon disulfide
NON-CERLA
Ethanol
n-Propanol
iso-Propanol
Tridecyl alcohol
2-Ethyl hexanol
2-Methoxy ethiuiol
2-Ethoxy ethanol
Methyl amyl alcohol
Strearyl alcohol
Ethylhexyl acetate
n-Propyl acetate
Trioctyl phthalate
Cellosolve acetate
Sodium octyl acetate
Sodium phenyl acetate
Methly ether
Propylene glycol-methyl ether
Ethylene glycol:
Propylene glycol
1-Propyl toluene
Trichloromonofluoromethane
Butyl acrylate
Methyl cellosolve
Ethyl cellosolve
Butyl cellosolve;.
Naphthol
Perchloroethylene-hydroflouric acid
Hexyl cellosolve
Sodium silicate
1-Nitropropane
(continued)
23
-------
Partial List of Chemicals Stored in UST (continued)
CERCLA
NON-CERLA
Inorganic Chemicals
Sodium hydroxide
Potassium hydroxide
Hydrochloric acid
Sodium hypochlorite
Sodium cyanide
Ammonium thiosulfate
Ferric chloride
Ferrous chloride
Chromic acid
Chlorine
Zinc
Chromium
Phosphorus
Ammonium hydroxide
Nitric acid
Sulfuric acid
Phosphoric acid
Ammonium sulfide
Ferrous sulfate
Hydrogen cyanide
Potassium fluoride
Calcium mitrate
24
-------
APPENDIX B
VOLUMETRIC LEAK DETECTION
IN UNDERGROUND STORAGE TANKS CONTAINING CHEMICALS
James W. Starr, Richard F. Wise, and Joseph W. Maresca, Jr.
Vista Research, Inc.
Mountain View, California 94042
Robert W. Hillger and Anthony N. Tafuri
Risk Reduction Engineering Laboratory
U. S. Environmental Protection Agency
Edison, New Jersey 08837
This paper was accepted for publication in the Proceedings of the
84th Annual Meeting and Exhibition of the Air and Waste
Management Association held by the Air and Waste Management
Association. The paper was presented at the meeting held in
Vancouver, B.C., Canada, on 15-17 June 1991.
25
-------
Volumetric Leak Detection
in Underground Storage Tanks Containing Chemicals
James W. Starr, Richard F. Wise, and Joseph W. Maresca, Jr.
Vista Research, Inc.
Mountain View, California 94042
Robert W. Hillger and Anthony N. Tafuri
Risk Reduction Engineering Laboratory
U. S. Environmental Protection Agency
Edison, New Jersey 08837
Abstract
Volumetric tank tightness test methods are most commonly used to detect
small leaks in underground storage tanks containing petroleum products. The
performance of most of these leak detection systems has been evaluated on 30,000-
or 38,000-L (8,000- or 10,000-gal) tanks containing gasoline or diesel products.
These same systems can be used to test underground storage tanks containing other
chemicals provided that the equipment is not damaged by the chemicals contained in
the tank. The performance achieved by these testing systems depends on the
chemical properties of the product in the tank. Two analyses based on mathematical
models of volumetric leak detection systems were done. The purpose was to
determine if significant differences in performance should be expected when such
systems are used to test tanks containing liquids other than petroleum. The first
analysis, covering the range of chemicals stored in underground tanks, addressed
errors in temperature compensation as a function of the coefficient of thermal
expansion. The second analysis dealt with the waiting period required for the
volume changes due to structural deformation of the tank to subside, and examined
this waiting period as a function of the density of the stored product. It was assumed
in both analyses that the hypothetical volumetric leak detection system used an array
of five equally spaced thermistors each having a precision better than 0.001 °C/h
(0.002*F/h), and a level sensor having a precision better than 40 ml/h (0.01 gal/h).
For the purpose of the analysis, the tank was partitioned into five layers of equal
thickness, each layer centered on a thermistor; the thermally induced volume
changes in each layer were then summed, giving an estimate of the thermally
induced volume changes in the tank as a whole. The analyses suggest that the
performance of a volumetric leak detection system is directly proportional to the
coefficient of thermal expansion of the stored product and that the waiting period
required for the effects of deformation to become neglible is nearly independent of
the chemical stored in the tank. Because gasoline has a higher coefficient of thermal
expansion than many chemicals, most volumetric leak detection systems designed to
test tanks containing gasoline products can also be used to test tanks containing the
most commonly stored chemical products, without sacrificing performance.
1 Introduction
Only a small fraction of the total underground storage tank population is used to store
chemicals. An analysis of a database of chemical storage tanks in 14 states indicates that
26
-------
approximately 2% of the total tank population contains non-petroleum chemicals, with roughly
half of these tanks, either by number or tank volume, containing hazardous substances [1].
Solvents were found to comprise the single largest fraction of hazardous chemicals. Of these,
acetone, toluene, methanol and methyl-ethyl ketone were found to be the most commonly stored
chemical substances, comprising roughly 60% of the hazardous materials stored in tanks and
34% of all chemical tanks in the sampled states. Tank age was found to average 18 years, with
over 85% of the tanks being fabricated from steel. Roughly 60% of the tanks in the state
databases had capacities between 3,800 and 38,000 L (1,000 arid 10,000 gal), with the average
tank size from all states being 27,275 L (7,205 gal). These characteristics, wliich are more
thoroughly described in [1], suggest that a strong potential exists for corrosion-induced tank
leakage.
Detection of leakage from underground chemical tanks poses many of the same challenges
encountered in testing petroleum storage tanks. Many of the procedural requirements identified
in previous work for testing petroleum tanks can be expected to be applicable to chemical tanks
as well [2-10]. Currently available data suggest that a large fraction of the chemical tank
population utilizes single-walled steel construction. The release detection standards in the
federal regulations for tanks containing hazardous chemicals are more stringent than for tanks
containing petroleum products and require that all existing tanks be upgraded to meet these
standards by 22 December 1998 [11]; all new tanks must also meet these standards. While the
regulations strongly encourage the replacement of single-wall tanks with tanks that are
secondarily contained, the regulations permit the use of single-wall tanks with leak detection
provided that approval from the regulatory agency is obtained. Until upgrading is fully
implemented, however, volumetric tank tightness testing can be expected to play an important
role in the detection of leaks from chemical tanks. While permitted by regulation, the role of
volumetric testing after 1998 is expected to be small, because most tanks will be secondarily
contained and methods applicable to the "interstitial" space will be used.
The volumetric leak detection systems developed to test underground storage tanks
containing petroleum products should be applicable to tanks containing other chemicals provided
that the chemicals in question do not damage the equipment. Most of these s)rstems were
designed to meet the EPA regulatory standards [11], which means that they must be able to
detect leaks as small as 380 ml/h (0.1 gal/h) with a probability of detection (Pro) of 0.95 (95%) or
better and to keep the probability of false alarm (PFA) less than or equal to 0.05 (5%). The
performance achieved by these systems depends on the chemical properties of the product in the
tank. Performance has, in most cases, been determined through an evaluation based on a single,
specific, stored product. Volumetric leak detection systems were developed specifically to test
27
-------
storage tanks containing petroleum fuels, and any estimates of their performance, therefore, have
been based on this class of liquids. Most performance evaluations of such systems have been
conducted in 30,000- or 38,000-L (8,000- or 10,000-gal) tanks containing either gasoline or
diesel fuels. If the tank contains a chemical that differs, in density, viscosity, or coefficient of
thermal expansion, from the product used in the evaluation of a given leak detection system, the
performance of that system on the chemical tank will be different from what it was on the
petroleum tank.
The chemical properties of the stored product affect the magnitude of the ambient noise
field and thus the performance of the leak detection system. Among the more important sources
of ambient noise are the volume changes produced by fluctuations in product temperature and by
the structural deformation of the tank-backfill-soil system. Both types of volume changes can be
affected by the kinematic viscosity, surface tension, density, and coefficient of thermal
expansion of the product. Kinematic viscosity (dynamic viscosity divided by density) and
surface tension affect the rate of flow through a hole at a given pressure head even if the leak is
as small as 380 ml/h. However, since the signal is reported in terms of flow rate and not hole
size, the influence of viscosity on the magnitude of the signal does not enter into the performance
calculations. The density affects the pressure differential between the product in the tank and the
backfill and soil system supporting the tank walls, and, as a consequence, is an important factor
in determining how long it takes for the time-dependent volume changes due to structural
deformation to subside. The coefficient of thermal expansion of the product affects the
magnitude of the thermally induced volume changes and therefore the accuracy of temperature
compensation. When a tank is partially filled, the product may exists in two states, liquid and ,
vapor. In a test conducted on such a tank, the vapor pressure affects the magnitude of the
volume changes due to evaporation or condensation at the vapor/liquid or vapor/wall interface.
When a test is conducted on an overfilled tank, the vapor pressure affects the volume changes
due to the expansion or contraction of any pockets of trapped vapor.
This paper investigates the influence of the viscosity, density, and coefficient of thermal
expansion of the stored product on the performance of volumetric leak detection systems used to
test tanks containing the chemicals identified in [1]. The signal and noise models developed for
petroleum-based testing systems are used to investigate (1) the effect of the coefficient of
thermal expansion on the magnitude of the thermally induced volume changes and (2) the effect
of density on the magnitude of the deformation-induced volume changes. Aspects of the vapor
pressure are not discussed in this paper.
28
-------
2 Chemical Properties of the Stored Product
A wide variety of chemicals are stored in underground tanks. Table 1 lists some of the
most commonly stored hazardous chemicals and presents baseline values for those properties of
the listed chemicals that affect volumetric tests (i.e., density, coefficient of thermal expansion,
and dynamic viscosity). To expand the range of baseline values, ethylene glycol and carbon
tetrachloride, which have higher densities (and in the case of the former, a higher viscosity as
well), have been added to the list in Table 1. Also included are typical values for water and the
two most common petroleum fuels, gasoline and diesel. The chemical properties of the
petroleum fuels provide a basis for comparison and a reference point for material discussed later
in this paper.
Table 1. Summary of the Physical Properties of Selected Chemical Substances at a Temperature of 20°C. (Typical
properties of diesel and unleaded gasoline at 20°C are included for comparison.)
Stored Product
Acetone
Toluene
Xylene
Methanol
Ethylene Glycol
Carbon Tetrachloride
Water
Diesel
Gasoline
Density
(g/ml)
0.790
0.867
0.880
0.791
1.120
1.595
1.000
0.800
0.743
Coefficient of
Expansion
(/°Q
0.001423
0.00109
0.000968
0.00120
0.00065
0.00118
0.0001
0.000792
0.001251
Viscosity
(cp)
0.32
0.59
0.81
0.60
19.9
0.969
0.44
2.50
0.63
3 Temperature Compensation
In volumetric testing, the most important physical property to be considered is the
coefficient of thermal expansion (Ce) of the stored fluid. Temperature fluctuations in the fluid
cause it to expand and contract, a phenomenon that is manifested as apparent changes in volume.
Virtually all volumetric leak detection systems attempt to compensate for these changes by
estimating what portion of the total volume change is due to thermal activity and then subtracting
this portion from the total in order to obtain the actual volume change (the change due to the leak
alone). Therefore, the coefficient of thermal expansion is of direct importance to the accuracy of
the test.
29
-------
The performance of a leak detection system is expressed in terms of the PFA and the PD
against a specific leak rate [2-7]. Estimates of performance are made from the histogram of the
noise and the signal-plus-noise. The noise is compiled from a large number of tests on one or
more nonleaking tanks over a wide range of ambient temperature conditions. In the present
study, the temperature database that had been compiled from the wide range of temperature
conditions generated in the 30,000-L (8,000-gal) steel and fiberglass tanks at EPA's UST Test
Apparatus in previous studies [2-7] was used to estimate the performance of the model leak
detection system with different stored chemicals. This database, even though it is based on
unleaded gasoline (the product in the EPA tanks at the time of the previous work), was the only
option because it is the only one of its kind in existence; there are no similar temperature
databases for other chemicals. Unleaded gasoline has a coefficient of thermal expansion of
0.00125/*C, and it was assumed in the performance estimates made as part of the present study
that all the liquids examined exhibit temperature changes identical to those seen in gasoline.
(This may not be true if the thermal diffusivity of a chemical differs sufficiently from that of
gasoline.) The effect of the coefficient of thermal expansion was determined directly from this
database and a model of a volumetric leak detection system having sufficient performance to
meet the EPA regulatory standard for a tightness test.
The performance estimate made in this study was derived according to the following
procedure.
• It was assumed that the volumetric leak detection system used five evenly spaced,
volumetrically weighted thermistors for temperature compensation and that the
pressure head remained nearly constant during a leak detection test.
• A test conducted with this leak detection system was initiated 12 h after product
had been added (whether in the form of a delivery or topping). For the tanks at the
UST Test Apparatus, this waiting period was sufficiently long that deformation had
become negligible and that the performance of the system was controlled mainly by
the accuracy of the temperature compensation.
• The length of this test was 1 h.
• The precision of both the thermistors and the level sensor was more than sufficient
to keep the total instrumentation uncertainty less than 40 ml/h (0.01 gal/h); each
thermistor had a precision better than 0.001 °C (0.002°F).
• Temperature data from each thermistor wer.e sampled once per minute; data from
the level sensor were sampled once per second and averaged to one sample per
minute.
• The tank was partitioned into five layers of equal thickness, each layer centered
about a thermistor, and the thermally induced volume changes in each layer were
calculated and summed to obtain the thermally induced volume change in the tank
as a whole.
30
-------
• The temperature-compensated-volume time series was generated by subtracting the
thermally induced volume changes measured by the thermistor array from the
volume changes measured by a level sensor.
• The temperature-compensated volume rate was estimated by fitting a least-squares
line to the temperature-compensated-volume time series.
The effect of the coefficient on the cumulative frequency distribution of the noise can be
seen in Table 2 and Figure 1. Each cumulative frequency distribution was compiled from the
temperature-compensated-volume rates from 321 tests simulated with the leak detection system
described above. Given the variety of chemicals found in underground storage tanks, there can
be a wide range of values for the coefficient of thermal expansion. Three values of the
coefficient were selected here in an attempt to encompass as much of this range as possible. The
middle curve in Figure 1 shows the cumulative frequency distribution of the test results when the
product was gasoline (0.00125/°C). As can be seen in Table 2, increasing the value of the
coefficient of thermal expansion from half that of gasoline to twice that of gasoline results in a
corresponding increase in the standard deviation of the temperature-compensated-volume-rate
histogram. Thus, the performance of a volumetric system is directly proportional to the value of
the coefficient. The impact of this increase can best be appreciated if we calculate its effect on
the detectable leak rate at a PD of 0.95 and a PFA of 0.05. The results of these calculations are
given in Table 2. It should be noted that the detectable rates given in Table 2 assume that
thermal expansion is the only noise source present, and that performance has not been degraded
by insufficient sensor resolution or by improper test procedures.
Table 2. Variation in Detectable Leak Rate for Selected Coefficients of Thermal Expansion (It is assumed that the
compensated-volume-rate histogram has a normal distribution.)
Coefficient
(/°C)
0.00062
0.00125
0.00250
Standard
Deviation
(ml/h)
34
68
136
Threshold
(ml/h)
-55
-112
-223
Probability of
False Alarm
0.05
0.05
0.05
Probability of
Detection
0.95
0.95
0.95
Leak Rate
(ml/h)
111
223
446
It is evident from Table 2 that, as the coefficient of thermal expansion increases, the
detectable leak rate at a given value of PD increases by the same amount. This occurs because
the nonnal model used to characterize the histograms of the noise and signal-plus-noise is
completely described by the standard deviation (i.e., there is no bias and the mean of the noise
histogram is 0 ml/h), and the relationship between the coefficient and the standard deviation of
the compensated-volume-rate histogram is linear, Based upon this observation, we can expect
31
-------
-600 -400 -200 0 200
VOLUME RATE - ml/h
400
600
Figure 1. Cumulative frequency distributions for three coefficients of thermal expansion generated from
temperature-compensated-volume-rate histograms, given a leak detection system employing five volumetrically
weighted, evenly spaced thermistors. Curves A, B, and C show coefficients of 0.00062/°C, 0.00125/°C, and
0.0025/*C, respectively.
that the performance of a given volumetric leak detection system will be proportional to the
coefficient of thermal expansion of the stored product. As a result, appropriate adjustments to
the threshold value (the basis for declaring a leak) will be necessary if a system's performance is
to be maintained at levels comparable to those obtained when that system was evaluated.
A typical example of the need for such threshold adjustments can be seen if we examine
the threshold required to maintain a PFA of 0.05 in the case of a volumetric leak detection system
that was evaluated on a tank containing gasoline (Ce=0.001251 /°C) but is now used on tanks
containing other chemical products. When the coefficient is half that of gasoline, using a
threshold of 112 ml/h results in a PFAof 0.0005, much better than what is required to meet the
minimum EPA performance requirements; but when the coefficient increases by a factor of 2
over what it is for gasoline, the PFAcan be as high as 0.21. Thus, when the coefficient is greater
than that of the product used in the evaluation, it may be necessary to increase the threshold to
satisfy the performance requirements specified in the EPA regulation; such an adjustment will
not be possible if the performance just barely meets the EPA standards.
Similar behavior can be expected in the case of the probability of detection and the
detectable leak rate. In this case, using a fixed threshold while the coefficient increases beyond
that of gasoline will increase the detectable leak rate while maintaining a constant PD.
Conversely, maintaining the detectable leak rate at a fixed value yields a lesser PD as the
coefficient increases.
32
-------
It is clear from the data shown in Table 2 that a leak detection system cannot be applied
indiscriminately to a fluid other than that used in the performance evaluation of that system.
Such an application should be undertaken with appropriate caution if regulatory standards are to
be maintained. This is particulary true when the coefficients are greater by a factor of 2 or more
than those in the evaluation, for example, when a system evaluated with diesel fuel (Ce =
0.000792/°C) is to be used with another petroleum fuel such as gasoline (Ce = 0.00125/°C) or
with a chemical product such as acetone (Ce = 0.00142/°C).
The most commonly used leak detection threshold is 0.05 gal/h. Table 3 presents the PD
and PFA against a 380-ml/h (0.1-gal/h) leak; a normal model is used to estimate performance. A
normal model usually does not describe the tails of the cumulative frequency distributions well,
and it generally results in better performance estimates than the leak detection system would
realize in actual operation. Estimates of performance using the empirically derived cumulative
frequency distributions are presented in Table 4. In the case of the two smaller coefficients, the
performance estimates made with the normal model suggest better performance than would
actually be achieved. This is important because very few chemicals have a coefficient as high as
gasoline (the second coefficient shown in Table 4). In the case of the highest coeffficient, the
performance estimates made with the normal model are about the same as those made with the
empirical model.
Table 3. Estimates, Made with a Normal Model, of the PFA and the PD against a Leak Rate of 380 ml/h (0.1 gal/h)
Using a Threshold of 190 ml/h (0.05 gal/h)
Model
Normal
Normal
Normal
Coefficient
(/°C)
0.00062
0.00125
0.00250
Standard
Deviation
(ml/h)
34
68
136
Threshold
(ml/h)
-190
-190
-190
Probability of
False Alarm
< 0.0000001
0.0026
0.080
Probability of
Detection
> 0.9999999
0.9974
0.920
Leak Rate
(ml/h)
380
380
380
Table 4. Estimates, Made with the Empirically Determined Cumulative Frequency Distribution, of the PFA and the
PD against a Leak Rate of 380 ml/h (0.1 gal/h) Using a Threshold of 190 ml/h (0.05 gal/h)
Model
DataCFD
DataCFD
Data CFD
Coefficient
(/°C)
0.00062
0.00125
0.00250
Standard
Deviation
(ml/h)
33.7
67.8
135.6
Threshold
(ml/h)
190
190
190
Probability of
False Alarm
« 0.003
0.015
0.074
Probability of
Detection
» 0.997
0.994
0.949
Leak Rate
(ml/h)
380
380
. 380
33
-------
4 Structural Deformation
In the temperature-compensated histogram in Section 3, the bias of the leak detection
system was equal to 0.0 ml/h. Under actual conditions, this may not be the case. One of the
primary sources of bias in a test result is the residual structural deformation of the tank in
response to a change in product level. Previous work conducted in support of the initial EPA
evaluation of volumetric test methods [2-10] identified the basic exponential characteristics of
this phenomenon, and recommended that a waiting period be adopted as part of a leak detection
system's test protocol. This waiting period minimizes the detrimental effect of structural
deformation on a system's performance. In the EPA work, unleaded gasoline was the fluid used
in evaluating leak detection systems. In the present study, therefore, an assessment was made as
to whether varying the density of the product would have a significant effect on the response of
the tank in terms of structural deformation.
Any time that the level of the product in the tank is raised or lowered, the potential exists
for the tank to expand or contract due to the concomitant pressure change. A comprehensive
discussion of the volume changes produced by tank deformation is presented in [2,6,8]. In the
works cited, models were developed, and validated through experiments, to predict the
magnitude of the volume changes produced by two different measurement methods: (1) when
the product is maintained at a constant pressure head and the volume changes are measured
directly and (2) when the product level is allowed to change freely during a test and volume
changes are measured in a 10-cm (4-in.) -diameter fill tube. These models showed that the latter
method can lead to highly erroneous measurements of the volume changes, whether these
changes are produced by the leak or whether they are produced by any one or more of the
sources of noise.
Since deformation is primarily pressure-driven (hydrostatic pressure changes cause the
tank's end walls to deflect until a new state of equilibrium is attained), calculations were made to
examine the effects of different fluid densities on the deformation response of the tank. In each
of these calculations, three different densities were used: 0.743,1.00, and 1.20 g/ml. The
smallest of these values is representative of a typical gasoline and approximates the values of a
large number of organic chemicals. The other two values expand the range of gravities that may
be encountered and cover a large fraction of the substances identified in the chemical tank survey
[1]. The deformation response of the tank to an instantaneous level change of 100 cm was
calculated for each density and for both measurement methods described in the preceding
paragraph. The elasticity constant and the time constant used in the analysis were those of the
34
-------
steel tank at the EPA's UST Test Apparatus (120 cm2 and 3 h, respectively). Choosing these
three values, even though they result in a high degree of deformation, afforded direct
comparisons to the earlier work [2-10].
It was assumed in the calculations that there was a leak of -380 ml/h and that a level
change of 100 cm took place. Figure 2 shows the results of these calculations when product
level (in a 10-cm (4-in.) -diameter fill tube) was allowed to vary, and Figure 3 when a constant
product level was maintained. Figures 4 and 5 show the results of the same calculations, but
with two differences. First, part (a) of both figures shows, for comparison purposes, a leak of
0 ml/h, and part (b) shows the -380-ml/h leak; second, in both part (a) and part (b) the data
collection begins at a point 4 h after the level change. This is done not only to show the curves
in more detail but also because most leak detection systems, in order to minimize the effects of
temperature inhomogeneities when product is added to or removed from the tank, specify a
waiting period before the test is begun. Most systems wait at least 4 to 6 h after any delivery of
product and at least 3 h after topping, regardless of the magnitude of the deformation changes.
CO
a
CO
o
UI
LU
-2 -
-4
-6 -
0.743 g/ml
1.0 g/ml
1.2 g/ml
—i—
2
—i—
4
—r——i
8
TIME - h
—i—
10
—i—
12
14
Figure 2. Typical deformation behavior for a non-constant-level volumetric test of a tank with a -380 ml/h leak. It
is assumed that the structural properties of the tank are the same as those of the steel tank at the UST Test
Apparatus.
Figure 2 indicates that, as fluid density increases, an increase of 100 cm iin product level at
the beginning of a test results in an initially larger rate of change in volume in cases when
product level is allowed to vary. This is due to greater pressures induced by the greater fluid
densities. Because the fluid is not maintained at a constant level, these early rapid volume
changes create height changes that are sufficiently large to reduce the rate of change of volume.
35
-------
OT
Q
I
W
-2-
.4 -
-en
0.743 g/ml
1.0 g/m!
1.2g/m!
6 8
TIME - h
10
12
IT"
14
Figure 3. Typical deformation behavior for a constant-level volumetric test of a tank with a -380 ml/h leak. It is
assumed that the structural properties of the tank are the same as those of the steel tank at the UST Test Apparatus.
This results in a volume-rate crossover approximately 2 h after the initial change in product
level. After this time, the rate of change of volume is higher than it would have been in a
constant-level test, even when the fluid is less dense, until a state of equilibrium is reached and
all rates of change approach a common value. As was the case in earlier studies of this
phenomenon [2,6,8], when there is a leak (or any other volume change not associated with
deformation), the measured volume change will be only a fraction of the true volume change
unless the product is maintained at a constant level. The magnitude of this error varies according
to the density of the fluid, with higher densities tending to result in greater errors. This is best
illustrated in Figure 4b. The error in measuring the leak rate ranges from 49% for the least dense
fluid to 61% for the most dense fluid.
In volumetric testing the preferred practice is to maintain a constant product level
throughout the duration of a test and measure the volume of product that must be added or
removed at periodic intervals to keep the level constant. Figure 3 shows the rate of change of
volume when the product is maintained at a constant level. When the level is constant, fluid
density has no effect on the test if the waiting period is sufficiently long for the volume changes
due to deformation to subside. Although the tank generally behaves similarly whether product
level is allowed to vary or whether it is kept constant, there is one major difference, which occurs
after the initial step change in product level. A higher fluid density results in a corresponding
increase in the rate of change of the volume of the tank itself, without any tendency for the rates
to cross over as in non-constant-level tests. In addition, the equilibrium volume rates (attained
36
-------
after approximately 5 time constants of the tank) approach the true volume rates, rather than only
a fraction of those rates, as happens in non-constant-level tests. While this simplifies the
interpretation of the volumetric measurements, it does not obviate the need for a waiting period
appropriate to minimize the bias. As shown in Figure 5b, after 15 h, the rate of change of
volume approaches -380 ml/h, the flow rate due to the leak. If a test is begun before the
deformation has subsided, large errors in measuring the leak rate will occur, and the higher the
density of the product, the greater these errors will be.
0.743 g/ml
1.0g/ml
1.2 g/ml
LU
-300
-100
-200
-300 -
-400 -
14
TIME - h
-500
0.743 g/ml
1.0 g/ml
1.2 g/ml
6
—i 1—
10
TIME - h
—i—
12
—i—
14
Figure 4. Typical deformation behavior during a non-constant-level volumetric test of (a) a nonleaking tank (top)
and (b) a tank that has a leak of 380 ml/h (bottom). It is assumed that the structural properties of the tank are the
same as those of the steel tank at the UST Test Apparatus.
37
-------
0.742 g/ml
1.0g/ml
1.2 g/ml
-0.4-
c/T -0.6 -
o
1
t-
ui
Ul
-0.8-
-1 -
-1.2-
-1.4-
-1.6-
-1.8 -
-2
14
10
TIME - h
12
14
Figure 5. Typical deformation behavior during a constant-level volumetric test of (a) a nonleaking tank (top) and
(b) a tank that has a leak of 380 ml/h (bottom). It is assumed that the structural properties of the tank are the same as
those of the steel tank at the UST Test Apparatus.
Although density affects the rate of the volume change due to deformation in both
constant-level and non-constant-level tests, it does not have a significant effect on the
performance of a properly executed volumetric test. By this we mean one that includes a waiting
period that is sufficient to allow the rate of change to reach a state of equilibrium. If such a
waiting period is observed, the effect of the volume changes is so small that it is completely
negligible, especially in the case of a constant-level test. Initial work suggests that, for tanks
38
-------
similar to those at the UST Test Apparatus, the bias due to deformation can be reduced if a
waiting period of at least 12 to 18 h is observed after any change in product level preparatory to a
constant-level test. As reported in [2,6,8], variable-level tests lead to erroneous results and
should not be used unless the cross-sectional area of the container in which the level
measurements are made is very much larger than that of the fill tube, for example, in the case of
a tank that is partially filled.
5 Summary
The analyses reported here show that (1) the performance of a volumetric leak detection
system is directly proportional to the coefficient of thermal expansion of the product in the tank
and (2) the waiting period required for the effects of structural deformation to subside is
essentially the same for all values of density (even though higher densities produce greater
deformation-induced volume changes immediately after any product-level change). When a leak
detection system is used with a chemical product having a coefficient of thermal expansion
higher than that of the product used in the evaluation of the system, the system's performance
will be lower than it was in the evaluation. If the performance achieved in the evaluation barely
meets the minimum standards established by the EPA, it is possible that the leak detection
system will not be in compliance when used with chemicals having higher coefficients of
thermal expansion. Even if the leak detection system exceeds the minimum performance
standards, it is possible that it will not meet the PFA or PD requirement; however, if a system has
achieved high performance during the evaluation, judiciously changing the detection threshold
can make it possible for the leak detection system to meet the requirements Because gasoline
has a higher coefficient of thermal expansion than many other chemicals, a system evaluated
with a gasoline product can be used with such chemicals and still maintain a similar level of
performance. Nevertheless, even if the system was evaluated with a diesel product (which has
an even higher coefficient than gasoline) care must be exercised when applying the system to a
chemical product.
These analyses did not examine volume changes due to evaporation and condensation, or
those due to trapped vapor; the former may be an important source of error in tests conducted on
underfilled tanks, and the latter an important source of error in tests conducted on overfilled
tanks.
1.
References
R. W. Hfflger, J. W. Starr, and M. P. MacArthur, "Characteristics of Underground Storage
Tanks Containing Chemicals," to be submitted for publication (April 1991).
39
-------
2. R. D. Roach, J. W. Starr, and J. W. Maresca, Jr., "Evaluation of Volumetric Leak
Detection Methods for Underground Fuel Storage Tanks," Vol. I (EPA/600/2-88/068a) and
Vol. n (EPA/600/2-88/068b), Risk Reduction Engineering Laboratory, U. S.
Environmental Protection Agency, Edison, New Jersey (December 1988).
3. J. W. Maresca, Jr., "Volumetric Tank Testing: An Overview," Technology Transfer
Report No. EPA/625/9-89/009, Center for Environmental Research Information, Office of
Research and Development, U. S. Environmental Protection Agency, Edison, New Jersey
(December 1988).
4. J. W. Maresca, Jr., J. W. Starr, R. D. Roach, and J. S. Farlow, "Evaluation of the Accuracy
of Volumetric Leak Detection Methods for Underground Storage Tanks Containing
Gasoline," Proceedings of the 1989 Oil Spill Conference, Oil Pollution Control, A
Cooperative Effort of the U.S. Coast Guard, American Petroleum Institute and U.S.
Environmental Protection Agency, San Antonio, Texas (March 1989).
5. J. W. Maresca, Jr., J. W. Starr, R. D. Roach, J. S. Farlow, and R. W. Hillger, "Summary of
the Results of EPA's Evaluation of Volumetric Leak Detection Methods," Proceedings of
the Fifteenth Annual Research Symposium, Risk Reduction Engineering Laboratory, Office
of Research and Development, U.S. Environmental Protection Agency, Cincinnati, Ohio
(February 1990).
6. J. W. Maresca, Jr., J. W. Starr, R. D. Roach, D. Naar, R. Smedfjeld, J. S. Farlow, and R.
W. Hillger, "Evaluation of Volumetric Leak Detection Methods Used in Underground
Storage Tanks," /. of Hazardous Materials (in press).
7. J. W. Maresca, Jr., R. D. Roach, J. W. Starr, and J. S. Farlow, "U.S. EPA Evaluation of
Volumetric UST Leak Detection Methods," Proceedings of the Thirteenth Annual
Research Symposium, Hazardous Waste Engineering Research Laboratory, Office of
Research and Development, U.S. Environmental Protection Agency, Cincinnati, Ohio
(July 1987).
8. R. D. Roach, J. W. Starr, C. P. Wilson, D. Naar, J. W. Maresca, Jr., and J. S. Farlow,
"Discovery of a New Source of Error in Tightness Tests on an Overfilled Tank,"
Proceedings of the Fourteenth Annual Research Symposium, Risk Reduction Engineering
Laboratory, Office of Research and Development, U.S. Environmental Protection Agency,
Cincinnati, Ohio (July 1988).
9. J. W. Maresca, Jr., J. W. Starr, R. F. Wise, R. W. Hillger, and A. N. Tafuri, "Evaluation of
Internal Leak Detection Technology for Large Underground Storage Tanks," Proceedings
of the Sixteenth Annual Research Symposium, Risk Reduction Engineering Laboratory,
U.S. Environmental Protection Agency, Cincinnati, Ohio (in press).
10. J. W. Maresca, Jr., C. P. Wilson, N. L. Chang, Jr., and H. Guthart, "Preliminary
Experiments on the Ambient Noise Sources in Underground Tank Testing," Technical
Report, Vista Research Project 2014, Vista Research, Inc., Palo Alto, California
(September 1985).
11. U. S. Environmental Protection Agency, "40 CFR 280 -- Technical Standards and
Corrective Action Requirements for Owners and Operators of Underground Storage
Tanks," Federal Register, Vol. 53, No. 185 (23 September 1988).
40
-------
APPENDIX C
INDUSTRY SURVEY OF THE LEAK DETECTION PRACTICES
ASSOCIATED WITH UNDERGROUND STORAGE TANKS
CONTAINING HAZARDOUS CHEMICALS
Richard F. Wise, James W. Starr, and Joseph W. Maresca, Jr.
Vista Research, Inc.
Mountain View, California 94042
Robert W. Hillger and Anthony N. Tafuri
Risk Reduction Engineering Laboratory
U. S. Environmental Protection Agency
Edison, New Jersey 08&37
The paper in this appendix was published under the title
"Underground Storage Tanks Containing Hazardous Chemieajs" in
the Proceedings of the Seventeenth Annual Research Symposium
held by the Risk Reduction Engineering Laboratory, Office of
Research and Development, U. S. Environmental Protection
Agency, This paper was presented under the same title at the
meeting held in Cincinnati, Ohio, on 3-5 April 1991.
41
-------
UNDERGROUND STORAGE TANKS
CONTAINING HAZARDOUS CHEMICALS
Richard F. Wise, James W. Starr, and Joseph W. Maresca, Jr.
Vista Research, Inc.
Mountain View, California 94042
Robert W. Hillger and Anthony N. Tafuri
Risk Reduction Engineering Laboratory
U. S. Environmental Protection Agency
Edison, New Jersey 08837
ABSTRACT
The regulations issued by the United States Environmental Protection Agency
(EPA) in 1988 require, with several exceptions, that underground storage tank
systems containing petroleum fuels and hazardous chemicals be routinely tested for
releases. This paper summarizes the release detection regulations for tank systems
containing chemicals and gives a preliminary assessment of the approaches to
release detection currently being used. To make this assessment, detailed
discussions were conducted with providers and manufacturers of leak detection
equipment and testing services, owners or operators of different types of chemical
storage tank systems, and state and local regulators. While these discussions were
limited to a small percentage of each type of organization; certain observations are
sufficiently distinctive and important mat they are reported for further investigation
and evaluation. To make it clearer why certain approaches are being used, this paper
also summarizes the types of chemicals being stored, the effectiveness of several
leak detection testing systems, and the number and characteristics of the tank
systems being used to store these products.
This paper has been reviewed in accordance with the U. S. Environmental
Protection Agency's peer and administrative review policies and approved for
presentation and publication.
INTRODUCTION
Federal underground storage tank regulations promulgated on September 23,1988,
establish a broad range of minimum requirements for the design, installation, operation and
testing of a large fraction of tank systems in the United States. These regulations cover tank
systems containing petroleum fuels as well as those containing other hazardous chemicals [1,2].
They are designed to help the underground storage tank community control and minimize the
adverse environmental impact caused by leakage of product from a tank or. its associated piping.
The regulatory standards for leak detection in tank systems containing hazardous chemicals are
more stringent than for those containing petroleum motor fuels. This paper describes (1) the
regulatory standards for leak detection in tank systems containing hazardous chemicals, (2) the
42
-------
types of chemicals being stored, (3) the types of containers in which these chemicals are stored,
(4) the effectiveness of tank tightness tests and automatic tank gauging systems for detection of
leaks in tanks containing chemicals other than petroleum, and (5) the approaches to leak
detection being implemented by tank owners and operators. Items (2) through (4) have been
described in detail elsewhere [3-5]. The data used to develop the conclusions for items (2) and
(3) are tabulated differently in this paper than in [4]. The main focus of this paper is on the fifth
item, specifically, the results of a preliminary survey of manufacturers of leak detection
equipment for chemical tank systems, owners and operators of these systems, and state and
federal regulators.
REGULATORY STANDARDS
The federal regulatory standards for release detection in underground storage tanks issued
by the EPA on September 23,1988 [1] require that tank systems containing petroleum products
and hazardous chemicals be tested periodically for releases. (A hazardous chemical is any
substance defined by the Comprehensive Environmental Response, Compensation, and Liability
Act (CERCLA) [2].) The regulations for testing underground storage tanks containing
hazardous substances are similar to those for tank systems containing petroleum products.
During the first 10 years after the issuance of the regulations, all existing tank m& pipeline
systems containing hazardous substances must meet the requirements specified for tank systems
containing petroleum products. After 10 years, all existing tank and pipeline systems must be
upgraded, if necessary, to meet a more stringent set of requirements. These requirements
emphasize the use of either double-wall tanks and piping or tanks and piping with secondary
containment, both with interstitial monitoring to detect a leak in the inner wall of the system.
These options are described in Section 280.42 (a) - (d) of the regulations [1]. If the tank system
is new or has been upgraded, single-wall tanks and piping are permitted provided that owners
and operators meet the following three criteria.
• Use any one of the release detection methods for tanks specified in Sections 280.43
(b) - (h) of the regulations or demonstrate to the implementing agency that an
alternative method is at least as stringent. These include internal methods such as tank
tightness testing systems, automatic tank gauging systems, and manual tank gauging
for tanks 7,600 L (2,000 gal) or less, as well as external methods such as groundwater-
and vapor-monitoring systems.
• Provide information to the implementing agency about health risks, effectiveness of
corrective action, properties of the stored substance and characteristics of the site. If
the health risks associated with the release of the chemical substance being stored are
no higher than those associated with the release of a petroleum product, and there exist
effective methods to clean up a release, then a single-wall tank system with release
detection would be appropriate.
43
-------
• Obtain approval from the implementing agency.
Although for some types of stored chemicals the single-wall tank system may be a highly
effective way to satisfy the regulations, this option is treated as a variance. The onus is on the
owner or operator to demonstrate to the implementing agency that the chemical substance will
not be any worse than petroleum if accidentally released.
During the 10-year period between 1988 and 1998, the EPA regulations allow tank
owners/operators to use either internal or external systems to test for releases. All systems
attached to or inserted into the tank, piping, or interstitial space of double-wall tanks or piping
are considered internal systems. Internal systems must meet a specific performance standard:
they must have a capability to detect a leak of specific size with a probability of detection (PD) of
95% and a probability of false alarm (PFA) of 5%. No performance standards are speckled for
external systems, but specific requirements about conducting tests with such systems are given.
During this 10-year period, the regulations allow three general approaches to release
detection, any of which might be practically pursued. The first two approaches use internal
release detection systems and the third uses external monitoring systems. The first and most
popular approach is to conduct an annual tank or line tightness test to detect small releases and to
use more frequent monitoring by another method to detect large releases. All tank and line
tightness tests must be performed at least once per year and must be able to detect leaks of
0.38 L/h (0.1 gal/h). In all cases where annual tightness tests are used, the regulations require an
additional form of leak detection in which tests on tanks are conducted at least monthly and those
on pressurized lines at least hourly; this ensures the detection of excessively large releases. For
tanks, daily inventory records must be reconciled monthly. For pressurized lines, leaks of
11.4 L/h (3 gal/h) must be reliably detected; this is usually accomplished by means of a
mechanical line leak detector. The second approach is to install an automatic tank gauge or
automatic line leak detector that is capable of detecting leaks of 0.76 L/h (0.2 gal/h); all
monitoring tests must be done at least once per month. As with the tank and line tightness
testing approach, this option also requires that there be a system for detecting large leaks. The
tank gauge can be used to satisfy the inventory control requirements, and most automatic line
leak detectors are designed so as to be able to satisfy the 11.4-L/h (3-gal/h) hourly test for
pressurized piping. Interestingly, if the tank gauge is used to satisfy the Other option in the EPA
regulations rather than the Automatic Tank Gauge option, inventory control is not required;
however, owners or operators who use this option do so because of the potential for better and
more accurate control of inventory. The third approach is to install an external monitoring
system that can detect the presence of the stored chemical in or on the groundwater or in the
44
-------
backfill and soil surrounding the tank system. Among other things, the success of external
systems depends on the sensitivity of the sensor, the ability of the sensor to distinguish the stored
chemical from other chemicals (i.e., its specificity), the ambient background noise level of the
stored chemical, the migration properties of the chemical, and the samplinglietwork. In many
instances both internal and external methods are used in conjunction as a way to increase the
probability of detection.
STORAGE OF HAZARDOUS CHEMICALS
Two surveys were conducted to estimate (1) the number of tanks storing; hazardous
chemicals, (2) the types of stored chemicals by tank number and capacity, and (3) the
characteristics of the tanks by capacity, construction material, and age. A detailed description of
these surveys can be found in [3,4].
The states participating in the program provided databases from their underground storage
tank registration programs1 for compilation and analysis; a total of 16 state databases were used
in the analysis. The first survey, conducted in 1987, used data from the two largest states in
terms of population, California and New York [3]. In the second survey, conducted in 1990,
chemical tank data from New York and 13 other states were analyzed [4], In selecting these
states, efforts were made to obtain representative national coverage while simultaneously
examining the more populous industrial states, which might be expected to have large numbers
of chemical tanks. The 14 states included in the 1990 survey were Delaware, Florida, Illinois,
Indiana, Maine, Massachusetts, Minnesota, New York, Missouri, Montana, Ohio, Texas,
Virginia, and Wisconsin. New York was included in the second survey so that changes in its
tank population since the earlier survey might be identified. Tables 1 through 5 summarize the
results of the survey.
TYPES OF CHEMICALS STORED
Solvents were found to comprise the single largest fraction of hazardous chemicals,
comprising over 85% of the total. Table 1 presents the distribution of the most commonly stored
chemicals by the number of tanks storing the chemical and by the total volume; of product being
stored. The 1987 data from New York and California are based only on the population of tanks
containing hazardous chemicals, while the 1990 data from the 14 state databases are based on
the population of all chemical tanks; the 1990 tabulation includes tanks containing both
1 In 1984, as part of the amendments to the Resources Conservation and Recovery Act (RCRA), each state was
required to register all underground storage tanks.
45
-------
hazardous and nonhazardous chemicals. As illustrated in Table 1, acetone, toluene, xylene,
methanol and methyl-ethyl ketone were found to be the most commonly stored chemical
substances. The 1987 survey indicated that these five substances accounted for as much as 60%
of all stored organic chemicals. After the fraction of tanks containing nonhazardous chemicals is
removed from the 1990 databases, it can be shown that the five most common organics comprise
49% of all tanks containing hazardous chemicals, a figure that is slightly less than the estimate
made from the survey of the two large states in 1987.
TABLE 1. SUMMARY OF THE MOST COMMONLY STORED ORGANIC CERCLA SOLVENTS
1987 California Data
Chemical
Acetone
Toluene
Xylene
Methanol
Methyl-
Ethyl
Ketone
TOTALS
%by
Tank
Number
22.8
13.3
8.1
6.6
10.3
61.1
%by
Tank
Volume
18.0
14.2
6.3
5.5
9.6
53.6
1987 New York Data
%by
Tank
Number
12.0
22.4
15.5
11.5
9.0
70.4
%by
Tank
Volume
18.3
21.1
11.7
8.5
7.0
66.6
1990 Data (14 States)
%by
Tank
Number
3.9
5.6
—
3.8
3.7
17.0
%by
Tank
Volume
4.2
9.2
2.5
3.3
2.9
22.1
CHARACTERISTICS OF THE TANKS STORING CHEMICALS
Tables 2 through 5 give information about the characteristics of the tanks used to store
chemicals. The characteristics tabulated are the number of tanks, the capacities of the tanks, the
construction materials, and the ages of the tanks. Table 2 presents the total number of tanks
compiled in the 1990 survey that contain hazardous substances. The 5,529 tanks containing
hazardous chemicals represent approximately 57% of the 9,656 registered tanks containing
products other than petroleum. The remaining statistics in the table (i.e., minimum, maximum,
mean, and standard deviation) are based on a tabulation of the number of hazardous-substance
tanks registered in each state. The mean number of tanks containing hazardous substances in
each state is 395. The large standard deviation, the large difference between the mean and the
median value, and the large spread between the states with the minimum and maximum number
of tanks indicate that the number of tanks per state is quite variable. In comparison to the
number of petroleum tanks, the number of tanks containing hazardous chemicals is only a very
small fraction of the total underground storage tank population. Based on these data, the number
of tanks containing hazardous materials throughout the United States should be between 1 to 2%
46
-------
of the total tank population, whether calculated by number or by tank volume. The tabulation
indicates that Illinois has more than twice the number of hazardous-substance tanks than any of
the other states surveyed [4].
TABLE 2. SUMMARY OF THE NUMBER OF TANKS CONTAINING HAZARDOUS CHEMICALS
COMPILED FROM 14 STATE DATABASES*
Statistics
Total for 14 States
Minimum
Maximum
Median
Mean per State
Standard Deviation
Number of Tanks
5,529
14
2,060
255
395
516
*The total number of registered tanks containing non-petroleum chemicals was 9,656.
Table 3 summarizes the capacities of the storage tanks containing hazardous substances,
including the average volume of product. The percentage of tanks in each category (denoted in
the first row across in Table 3) is based on the entire population of tanks containing hazardous
chemicals. The statistics in the remaining rows, both percentages and average volumes, were
computed from the average percentages and average volumes reported for each state. It is
interesting to note that the states having the minimum, maximum, and median values vary
considerably with tank capacity. Roughly 60% of the tanks in the state databases had capacities
between 3,800 and 38,000 L (1,000 and 10,000 gal), with the average size of a tank (based on
data from all states) being 7,205 gallons. Over 27% of the tanks are larger than 38,000 L
(10,000 gal).
TABLE 3. SUMMARY OF TANK SIZE DISTRIBUTIONS COMPILED FROM THE 14 STATE
DATABASES AND EXPRESSED AS A PERCENTAGE OF THE NUMBER OF TANKS IN EACH STATE
Range of Tank Capacities (Gallons)
Statistical
Parameters
Total*
Minimum
Maximum
Median
Mean*
Standard Deviation
< 1,000
11.3
4.3
44.7
12.2
13.7
10.8
1,000-
<4,000
29.6
16.0
39.9
29.0
27.9
6.6
4,000-
<10,000
31.9
19.7
37.6
28.8
29.6
5.6
10,000-
<20,000
19.6
3.9
24.6
19.7
18.2
5.7
>2<},000
7.6
0.5
29.6
7.0
9.2
8.6
Average
Volume
7,205**
3,409
101,293
6,889
7,555"
2,460
Totals for New York, Indiana, and Montana are based on CERCLA chemicals only.
Does not include the Delaware data because one of the tanks in that state has a capacity of 430,000 gal, and
inclusion of these data would result in a misleading statistical estimate.
47
-------
Table 4 summarizes the types of materials from which chemical tanks are constructed; the
total is broken down according to the percentage of tanks constructed from steel,
fiberglass-reinforced plastic, and "other" materials. As was the case for tank size (Table 3), the
percentage of tanks in each category (denoted in the the first row across in Table 4) is based on
the entire population of tanks. The data indicate that 86% of the tanks are fabricated from steel
and approximately 6% from fiberglass; about 4% are constructed of material(s) other than steel
or fiberglass, and for another 4%, the construction material is not known.
TABLE 4. SUMMARY OF TANK CONSTRUCTION MATERIALS COMPILED FROM LISTING OF
REGISTERED TANKS IN THE 14 STATE DATABASES AND EXPRESSED AS A PERCENTAGE OF
THE NUMBER OF TANKS IN EACH STATE*
Type of Construction Material*
Statistical
Parameters
Total
Minimum
Maximum
Median
Mean
Standard Deviation
Steel
86.1
62.9
94.1
83.9
82.4
8.9
Fiberglass
6.2
0.0
15.2
6.6
7.1
4.6
Other
3.9
1.5
10.6
5.6
5.1
2.6
Unknown
3.8
0.0
22.3
2.6
6.4
7.6
* Materials were not reported for Indiana, Minnesota, and Texas. Only steel tanks were reported for Montana.
Values reported are percentages of the total tank populations in each state.
Table 5 summarizes the age of the tanks. The average percentages are based on the entke
tank population. The remaining statistics are based upon the percentages reported for each state.
Tank age was found to average 18 years, with approximately 40% of the tanks being more than
20 years old.
TABLE 5. SUMMARY OF TANK AGE DISTRIBUTIONS COMPILED FROM 14 STATE DATABASES AND
EXPRESSED AS A PERCENTAGE OF THE NUMBER OF CHEMICAL TANKS IN EACH STATE
Range of Tank Age (Years)
Statistical
Parameters
Average
Minimum
Maximum
Median
Mean
Standard Deviation
Oto4
4.9
1.5
22.2
3.4
6.0
5.9
5to9
16.2
4.0
23.0
15.2
16.1
7.0
• 10 to 14
21.6
4.0
26.1
21.1
20.6
9.4
15 to 19
17.6
0.0
25.6
17.1
14.9
7.0
^20
39.7
22.8
86.7
38.7
42.4
16.3
48
-------
CONSEQUENCES FOR RELEASE DETECTION
The results of these tabulations suggest that there is a strong potential for leakage from
tanks containing hazardous substances. The statistics suggest that the tanks are generally old,
made of steel, and fairly large. One would speculate that because the average age of these steel
tanks is 18 years, many are unprotected by rust-resistant coatings and are highly susceptible to
corrosion. As noted in the next section, the analysis performed in [5] suggests that most tank
tightness and automatic tank gauging systems (which are internal leak detection systems) should
be able to test these tanks effectively. Most of these leak detection systems were evaluated on
30,000- or 38,000-L (8,000- or 10,000-gal) tanks, which is consistent with the average capacity
of tanks containing hazardous chemicals. Successful testing of chemical tanks should be
possible, especially because their number is relatively small, approximately 1 to 2% of the total
underground storage tank population. Moreover, a very small number of chemicals (five)
accounts for roughly half of the hazardous substances being stored. External methods of leak
detection can also be used provided that the leak detection system in question has the necessary
specificity.
VOLUMETRIC TANK TIGHTNESS TESTING
The same types of leak detection and monitoring systems used for testing; tanks and
pipeline systems containing petroleum products should be applicable to those containing
non-petroleum chemicals provided that the sensors and equipment are compatible with the
particular stored chemical and can be installed and used safely. The performance of these leak
detection systems has, in most cases, been determined through an evaluation baised on a single,
specific, stored product. Volumetric leak detection systems, such as tank tightness testing
systems and automatic tank gauges, were developed specifically to test storage tanks containing
petroleum fuels, and any estimates of their performance, therefore, have been based on this class
of liquids. Most performance evaluations of such systems have been conducted in 30,000- or
38,000-L (8,000- or 10,000-gal) tanks containing either gasoline or diesel fuels,, If the tank
contains a chemical that differs, in density, viscosity, or coefficient of thermal expansion, from
the product used in the evaluation of a given leak detection system, the performance of that
system when used to test a tank containing a non-petroleum product will be different from what
it was on the petroleum tank.
An analysis was made of the performance of tank tightness systems (and tank gauging
systems) when applied to tanks containing chemicals other than petroleum fuels; [5]. Since
petroleum was the stored product in most evaluations of tightness testing systems, the analysis
49
-------
attempted to determine the impact of liquids with viscosities, densities, and thermal properties
different from petroleum products. The influence of the viscosity, the density, and the
coefficient of thermal expansion on performance was investigated for the range of chemicals
identified in the 14 state databases. The analysis examined the two most important sources of
noise: thermal expansion or contraction of the product stored in the tank and the structural
deformation of the tank resulting from any level or pressure changes before or during a test.
Methods of compensating for thermal expansion/contraction and structural deformation were
also investigated.
The analysis showed that (1) the performance of a volumetric leak detection system is
directly proportional to the coefficient of thermal expansion of the product in the tank and (2) the
waiting period requked for the effects of structural deformation to subside is essentially the same
for all values of density (even though higher densities produce greater deformation-induced
volume changes immediately after any product-level change). When a leak detection system is
used with a chemical product having a coefficient of thermal expansion higher than that of the
product used in the evaluation of the system, the system's performance will be lower than it was
in the evaluation. If the performance achieved in the evaluation barely meets the minimum
standards established by the EPA, it is possible that the leak detection system will not meet the
standard when used with chemicals having higher coefficients of thermal expansion. Even if the
leak detection system exceeds the minimum performance standards, it is possible that it will not
meet the PFA or PD requirement; however, if a system has achieved high performance during the
evaluation, judiciously changing the detection threshold can make it possible for the leak
detection system to meet the requirements. Because gasoline has a higher coefficient of thermal
expansion than many other chemicals, a system evaluated with a gasoline product can be used
with such chemicals and still maintain a similar level of performance.
This analysis did not examine volume changes due to evaporation and condensation, or
those due to trapped vapor; the former may be an important source of error in tests conducted on
underfilled tanks, and the latter an important source of error in tests conducted on overfilled
tanks.
CURRENTLY USED APPROACHES TO LEAK DETECTION
An informal survey of the owners and operators of chemical tanks, manufacturers of tank
tightness testing and automatic tank gauging systems, and state and local environmental
regulators was conducted by telephone to determine
50
-------
• what methods of leak detection are being used for underground storage tanks
(i.e., tanks and associated pipelines) storing hazardous substances,
• the basic characteristics of the chemical tank population to which these methods are
applicable, and
• what inventory practices are being followed by owners/operators of underground
storage tanks containing hazardous substances.
A questionnaire was prepared as a guideline to stimulate discussion. The questionnaire, included
in the appendix, was designed to shed some light on what methods of leak detection are being
applied to single-wall tanks between 1988 and 1998. The responses were given in confidence,
and, as a result, the organizations discussing their environmental programs will not be disclosed
by name. They are identified only by size and by a general description of the type of business
they conduct. The organizations contacted ranged from small enterprises to large, well-known,
Fortune 500 companies. The organizations that were interviewed were located, in New York,
California and Illinois.
Two surveys were planned, one to address leak detection practices and the other to address
inventory practices. In the initial survey, tank tightness testers and organizations that store
chemicals were contacted to determine (1) which methods of leak detection are; being used and
(2) user perceptions as to the effectiveness of these methods. The second survey was designed to
address the inventory practices of tank owners/operators and to collect 30 to 90 days of inventory
records for analysis. As a check on the owners' responses, a brief discussion of inventory
practices in the chemical industry was held with a major inventory/statistical inventory
management service.
After the survey taker had contacted only a few organizations using tanks to store
chemicals, it became clear that these organizations were either in the process of or had completed
upgrading their systems to meet the regulatory standards required by 1998. As a consequence,
the emphasis of the questions shifted from the technical details of the types of leak detection
methods being used and the procedures followed for inventory reconciliation in-"single-wall
tanks, and turned instead to the upgrading approaches. Instead of two separate surveys, only one
was actually conducted.
RESULTS OF DISCUSSIONS WITH TANK TESTERS
Three tank tightness testing services that are well known in the leak detection industry
were asked whether they were capable of testing tanks containing chemicals other than
petroleum and whether they had actually tested such tanks. At the time of the survey, all three
companies had systems that conducted tests on overfilled tanks, and one had the ability to test
partially filled tanks. (At present, all three firms have the capability to test partially filled tanks.)
51
-------
All three said that they did test tanks containing chemicals. The only constraint on testing was
that the temperature and level (volume) measurement systems inserted into the tank had to be
compatible with the stored chemical. In general, such equipment was constructed of stainless
steel and Teflon. All three firms indicated that up to 5% of their services involved testing tanks
containing products other than petroleum. They all indicated that the performance of their
systems was the same regardless of whether a tank contained petroleum or other chemicals. This
response is consistent with our estimate of the number of tanks containing chemicals and our
previous knowledge of this industry. None of the organizations manufacturing automatic tank
gauges was contacted directly as part of this survey because, based on previous discussions with
several automatic tank gauge manufacturers, it was expected that they would give the same
general response as the tank tightness testing services. Automatic tank gauges are particularly
suited for meeting regulatory requirements in tanks containing chemicals because tests can be
conducted routinely and automatically without adding product to the tank.
RESULTS OF DISCUSSIONS WITH TANK OWNERS AND OPERATORS
The survey taker contacted a total of 19 organizations that use chemicals in their
operations and that own the tanks in which these chemicals are stored. He obtained responses
from 13. The level of response varied considerably, as shown in Table 6, which summarizes the
important aspects of the survey. Six of the firms, which are denoted by an asterisk, responded in
sufficient detail to address all the questions prepared for the survey. A triple dash means that the
organization did not respond to the question or did not know how to respond to the question.
In general, most firms had fewer than 50 tanks containing chemicals, and the median age
of these tanks was approximately 20 years. Two of the firms did not indicate the number or age
of their tanks because they were in the process of replacing all their single-wall tanks with
aboveground tanks, double-wall tanks, or tanks with secondary containment. In all cases the
tanks were used to store chemicals used in company operations. About half of the firms
responded to the question of removal and disposal of the chemicals after the process had been
completed. Waste chemicals were either reclaimed or stored in drums for removal.
None of the firms contacted indicated that they have had their tanks tested with a
volumetric tank tightness testing system; one firm had its tanks tested with an air test, but this
method was discontinued because of inaccuracy and other problems. (Air tests are no longer
recommended, nor are they commonly used.) None of the companies contacted were using or
planning to use automatic tank gauges for monitoring or inventory control purposes.
52
-------
TABLE 6. SUMMARY OF IMPORTANT RESPONSES TO THE SURVEY
Company Company
Product Size
Finishing*
Adhesives/Glues*
General
Chemicals*
Adhesives/Glues*
Printing*
Computers*
Chemicals
Cleaning
Chemicals
Adhesives
General
Chemicals
Tank Farm
Finishes/Paints
Computers
Small
Medium
Large
Large
Medium
Large
Small
Medium
Medium
Large
Medium
Medium
Large
No. of
Tanks
23
21
17
53
24
—
11
21
24
13
19
215
—
Was
inventory
Mean control
Age used?
25+
20
20
15-40
10
—
15-
20
25+
—
—
...
Yes
No
Yes
No
Yes
No
No
No
...
—
—
No
Were
tanks
being
replaced?
Yes
Yes
Yes
Yes
Yes
Yes
Yes
Yes
Yes
Yes
Yes
Yes
Yes
Were Were
double-wall aboveground
tanks being tanks being
used? useid?
Yes
Yes
Yes When
Possible
Yes When
Possible
Yes
When
Possible
— Yes
—
When
Possible
Yes
When
Possible
Yes
Yes
Were
single-wall
tanks with
secondary
containment
being used?
...
—
—
—
—
Single-wall/
vaulted
—
—
__-
—
...
—
...
* Firms that answered all survey questions in detail.
Only three of the firms indicated that they kept inventory records, but these were for
accounting and scheduling purposes only. These firms did not use inventory control data for
leak detection. Based on the discussions with these three organizations, it was determined that
the data being routinely obtained could not be used for inventory reconciliation either because
there was no meter used to indicate the volume of material removed from the storage tank or the
accuracy of this meter was inadequate for such an application.
All of the organizations contacted were replacing or planning to replace their single-wall
tanks with either aboveground tanks or double-wall tanks with interstitial monitors. It was clear
that the use of aboveground tanks was overwhelmingly preferred. The use of aboveground tanks
permits visual inspection for leaks and facilitates maintenance; aboveground tainks also minimize
the cleanup costs associated with an accidental leak.
53
-------
SUMMARY
Even though a diverse cross section of organizations was contacted, the responses obtained
during the telephone survey should not be interpreted quantitatively; the number of organizations
was very limited, and the survey was not statistically designed or statistically analyzed. As a
consequence, the results should be interpreted cautiously, and the temptation to generalize,
particularly about the status of regulatory compliance, should be avoided unless additional data
are gathered. The following observations are noteworthy, however, either because the response
was overwhelming or because it was ambiguous.
First, there is a strong tendency for owners/operators of tank systems to be planning ways
to comply with the "upgraded standards" specified for 1998. There appears to be an emphasis on
replacement of single-wall tank systems with (1) double-wall tanks and pipes equipped with
interstitial monitors (and in some cases combined with external monitors also) or (2) tank
systems mounted completely above ground so that visual inspection is possible. This emphasis
on meeting the upgraded standards has occurred, we believe, because of the potential for serious
environmental damage, the high clean-up costs, and the large liability associated with chemical
contamination of the soil and groundwater. Concern may also stem from the fact that tanks
containing chemicals are old (averaging 18 years) and constructed of steel (86%). What is not
clear from the survey is how much time will be required for those organizations currently
upgrading their tank systems to complete the process. If the time required for upgrading a tank
system exceeds one year, the regulations require that the tank system be tested by means of
methods commonly used on tanks containing petroleum.
Second, none of the organizations contacted used inventory control as a means of leak
detection. It also appears that this method of leak detection would be difficult to apply because
of the lack of metering devices or the lack of accuracy in the metering devices being used. This
observation was independently verified by a company that is heavily involved in analyzing
inventory control data for owners or operators of chemical and petroleum tank systems.
Third, the tank testing firms contacted indicated that approximately 5% of their tests were
conducted on tanks containing hazardous chemicals, a figure that is slightly higher than the
estimated percentage of such tanks in existence in the U.S. This is inconsistent with the response
obtained from the 13 tank-owning organizations that responded to the survey. None of these
organizations indicated that they used such services. In addition, the tank testing firms did not
know whether the owners and operators of the tanks they tested employed monthly inventory
reconciliation. (Inventory reconciliation is required by the regulations when the only form of
leak detection is an annual tightness test.) The contradictory responses offered by the testing
54
-------
firms and the owners and operators of tank systems containing chemicals sugg;est that the
owners/operators who responded to the survey may not be representative of the entire chemical
tank community.
Fourth, additional information is required before any assessment can be made of release
detection practices in effect now and during the next eight years (the time allowed for
owners/operators of chemical storage tanks to upgrade their systems in anticipation of the 1998
EPA deadline).
4.
5.
REFERENCES
U.S. Environmental Protection Agency. 40 CFR 280 -- Technical Standards and
Corrective Action Requirements for Owners and Operators of Undergroimd Storage Tanks.
Federal Register, Vol.53, 23 September 1988.
U.S. Environmental Protection Agency. Part 302 - Comprehensive Environmental
Response, Compensation, and Liability Act. Federal Register, Vol.45, II December
1980.
I. Lysyj, R. W. Hillger, J. S. Farlow, and R. Field. A Preliminary Analysis of
Underground Storage Tanks Used for CERCLA Chemical Storage. Proceedings of the
Thirteenth Annual Research Symposium, Hazardous Waste Engineering Research
Laboratory, Office of Research and Development, U.S. Environmental Protection Agency,
Cincinnati, Ohio, July 1987.
R. W. Hillger, J. W. Starr, and M. P. MacArthur. Characteristics of Underground Storage
Tanks Containing Chemicals. To be submitted for publication in April 1991.
J. W. Starr, R. F. Wise, J. W. Maresca, Jr., R. W. Hillger, and A. N. Tafuri. Volumetric
Leak Detection in Underground Storage Tanks Containing Chemicals. Accepted for
publication in Proceedings of the 84th Annual Meeting and Exhibition of the Air and
Waste Management Association, to be held in Vancouver, B. C., Canada in June 1991.
55
-------
Appendix
QUESTIONNAIRES
USED TO ASSESS LEAK DETECTION PRACTICES
IN UNDERGROUND STORAGE TANKS
CONTAINING HAZARDOUS CHEMICALS
(1) EPA Chemical Tank Leak Detection and Inventory Control
Practices Questionnaire
(2) Leak Detection Manufacturer Questionnaire
56
-------
EPA Chemical Tank Leak Detection and
Inventory Control Practices Questionnaire
Company Name:
Address:
Contact:
Telephone:
FAX:
Leak Detection
1.
2.
What types of leak detection practices are currently employed by your company on
underground tanks containing chemicals? Please check the appropriate response(s).
( ) Tank tightness tests
( ) Automatic tank gauges
( ) Interstitial monitors (for double-wall tanks only)
( ) External monitoring wells
( ) Inventory record analysis
( ) Other (Specify)
( ) None
What type of construction is employed on your underground chemical tanks?
( ) Single-wall steel
( ) Double-wall steel
( ) Single-wall reinforced plastic
( ) Double-wall reinforced plastic
( ) Other (Specify) ;
3 a. What type of construction is employed on the underground piping connected to the
underground tanks?
( ) Single-wall steel
( ) Single-wall steel
( ) Double-wall steel
( ) Single-wall reinforced plastic
( ) Double-wall reinforced plastic
( ) Other (Specify)
57
-------
3b. What is the average length (approximate) of the pipeline from the tank to the metering
point?
4. Are all of your chemical tanks subjected to leak testing? If not, which ones are excluded?
Why?
5. Are any special precautions or procedures required in order to conduct a test? Please
describe them briefly.
6. Which test methods or procedures have been utilized in the past for testing underground
chemical tanks?
Inventory Control
1. Are inventory records maintained for each underground chemical tank?
2. How many tank measurements are made each day?
( ) One
( ) Two
( ) More than two (Specify number)
( ) One per shift
( ) Other (Specify)
3. Is a standard procedure (such as API Publication 1621) followed in implementing inventory
control? Describe the procedure, or identify its source.
58
-------
4. How long are inventory records saved?
5. How are product levels measured in the tanks?
( ) Manually via stick measurements
( ) Automatically via automatic tank gages
( ) Other (Specify)
6. Are product levels measured after additions and withdrawals?
7. How are the product levels in the tank converted to volumes?
( ) Tank Chart
( ) Calibration Volume
( ) Other (Specify)
8. What is the source of product deliveries to the underground tanks?
( ) Truck
( ) RaU Car
( ) Pipeline
( ) Manufacturing Process on Site
( ) Other
9. Are flow meters used to measure product additions and withdrawals? If yes, what is the
accuracy of the meters?
10. How frequently are the inventory records reconciled?
( ) Daily
( ) Weekly
( ) Monthly
( ) Other (specify)
11. Have any leaks identified by the reconciliation procedure been confirmed by an independent
precision test or by excavation?
59
-------
Leak Detection Manufacturer Questionnaire
Note: These questions are intended to obtain basic background information from
manufacturers of leak detection test methods for underground storage tanks containing
chemicals, i.e., fluids other than petroleum motor fuels.
Company Name:
Address: ' !
Contact:
Telephone:
FAX:
1. What stored fluid(s) was the test method designed for?
2. What are the primary measurements made during the test? (Example: pressure, level,
temperature, etc.)
3. What tank level must be established in order 'to conduct a test?
4. Can double-wall tanks be successfully tested with the method?
5. Has a performance evaluation been prepared for the test method? If yes, which organization
conducted it?
6. What fluid was used to conduct the performance evaluation?
60
-------
7. Does the leak detection performnnce of the test method change for different stored
chemicals? If yes, how much?
8. Are there any chemicals or classes of chemicals for which tests cannot be (conducted?
Which ones?
9. How many chemical tanks have been tested with the method?
10. Are any special precautions or procedures required to test tanks containing chemicals?
Please describe them briefly.
61
-------
TECHNICAL REPORT DATA
(Please read Instructions on the reverse before completing)
1. REPORT NO. 2.
EPA/600/2-91/037
4. TITLE AND SUBTITLE
Chemicals Stored in USTs: Characteristics and
Leak Detection
7. AUTHOR(S)
Joseph W. Maresca, Jr., Vista Research, Mt.View.CA 94042
Robert W. Hillger, US EPA,RCB,STDD,RREL, Edison, NJ 08837
9. PERFORMING ORGANIZATION NAME AND ADDRESS
CDM federal Programs Corporation
13135 Lee Jackson Memorial Highway - Suite 200
Fairfax, Virginia 22033
12. SPONSORING AGENCY NAME AND ADDRESS
Risk Reduction Engineering Laboratory — Gin. , OH
Office of Research and Development
US Environmental Protection Agency
Cincinnati, Ohio 45268
3. RECIPIENT'S ACCESSION-NO.
5. REPORT DATE
August 1991
6. PERFORMING ORGANIZATION CODE
8. PERFORMING ORGANIZATION REPO
10. PROGRAM ELEMENT NO.
11. CONTRACT/GRANT NO.
68-03-3409
13. TYPE OF REPORT AND PERIOD CO
Project Report
14. SPONSORING AGENCY CODE
EPA/600/14
15. SUPPLEMENTARY NOTES
Project Officer: Robert W. Hillger (FTS) 340-6639 Comm: (908) 321-6639
16. ABSTRACT
The regulations issued by the United States Environmental Protection Agency (EPA)
in 1988 require, with several exceptions, that the integrity of underground storage
tank systems containing petroleum fuels and hazardous chemicals be routinely tested.
The regulatory standards for leak detection in tanks containing hazardous chemicals
are more stringent .than for those containing petroleum motor fuels. This report
describes (1) the regulatory standards for leak detection in tanks containing hazardous|
chemicals, (2) the types of chemicals being stored, (3) the characteristics of the
tanks in which these chemicals are stored, (4) the effectiveness of tank tightness
tests and automatic tank gauging systems for detection of leaks in tanks containing
chemicals other than petroleum, and (5) the approaches to leak detection that are
being Implemented by tank owners and operators.
t7.
KEY WORDS AND DOCUMENT ANALYSIS
a.
DESCRIPTORS
b.lDENTIFIERS/OPEN ENDED TERMS C. COSATI Field/Group
18. DISTRIBUTION STATEMENT
Release to Public
J'STs. Chemicals, Leak
Detection, Tank Character-
istics, Chemical USTs
19. SECURITY CLASS (ThisReport}
Unclassified
20. SECURITY CLASS (This page)
Unclassified
21. NO. OF PAGES
68
22. PRICE
EPA Form 2220-1 {9-73}
•&U.S. GOVERNMENT PRINTING OFFICE: 1991 - S48-I87/405«
-------
-------
* 3
D =t:
Q) O
Ill
2 o
r1 «r
.o 3
o ol
O :
O)
CO
m
9
co
01
ml
------- |