United States	Office of Underground Storage
Environmental Protection Tanks
&EPA
General Guidance For Using
EPA's Standard Test Procedures
For Evaluating Release Detection
Methods
May 2019

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Acknowledgments
The U.S. Environmental Protection Agency's Office of Underground Storage Tanks contracted
with Battelle under Contract No. EP-C-10-001 to develop this document. It is based largely on
1990 documents written by Midwest Research Institute, Vista Research, and Radian. Individual
members of the National Work Group on Leak Detection Evaluations, as well as Ken Wilcox
and Associates, reviewed this document and provided technical assistance. A stakeholder
committee, comprised of approximately 50 representatives from release detection method
manufacturers and various industry associations, commented on this document.
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Contents
Section 1: Demonstration Of Performance Standards	1
1.1	EPA Standard Test Procedures	1
1.2	National Consensus Code Or Standard	2
1.3	Alternative Test Procedure Deemed Equivalent To EPA's Standard Test
Procedures	2
1.4	Purpose And Intended Use Of This Document	3
Section 2: EPA Standard Test Procedures	4
2.1	Regulatory Performance	4
2.2	Release Detection Methods	5
2.2.1	Automatic Tank Gauging Systems	7
2.2.2	Pipeline Release Detection	8
2.2.3	Statistical Inventory Reconciliation	8
2.2.4	Tank Tightness Testing	9
2.3	Release Detection Method Evaluation	11
2.3.1	TestDesigns	12
2.3.2	Statistical Analysis	13
2.3.3	Report Organization	15
2.4	Alternative Availability Of Release Detection Method Performance
Verification	16
Figures
Figure 1. Distribution Of Measurement Error On A Tight And Leaking Tank	14
Figure 2. Distribution Of Measurement Error On A Tight And Leaking Tank With A Positive
Bias	15
Tables
Table 1. Roles And Responsibilities	4
Table 2. Summary Of Release Detection Methods And Operating Principles	6
Table 3. Summary Of The Scope Of Each Standard Test Procedure	12
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List Of Acronyms And Abbreviations
ASTM International American Society for Testing and Materials International
ATGS
automatic tank gauging system
B
bias
CFR
Code of Federal Regulations
CITLDS
continuous in-tank leak detection system
EPA
U.S. Environmental Protection Agency
gal/hr
gallon per hour
NWGLDE
National Work Group on Leak Detection Evaluations
OUST
Office of Underground Storage Tanks
P(d)
probability of detecting a leak
P(fa)
probability of false alarm
R
leak rate
SIR
statistical inventory reconciliation
Th
threshold
TTT
tank tightness testing
UST
underground storage tank
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Section 1: Demonstration Of Performance Standards
The federal underground storage tanks (UST) regulation in 40 Code of Federal Regulations
(CFR) Part 280 specifies performance standards for release detection methods. UST owners and
operators must demonstrate that the release detection method they use meets the U.S.
Environmental Protection Agency's (EPA) regulatory performance standards. This guidance
provides an overview of the standard test procedures so UST owners and operators can evaluate
test procedures best suited to their facility; discusses ways owners and operators can determine
whether their release detection methods meet federal regulatory requirements; and describes a
process for using the standard test procedures to evaluate release detection methods. UST
implementing agencies may have additional requirements for approving the use of release
detection methods. Check with the UST implementing agency where your UST system is
located to ensure you meet all applicable requirements.
The large number of commercially available release detection methods makes it impossible for
EPA to test all methods or to review all performance claims. EPA does not test, certify, or
approve specific brands of commercial release detection methods. Rather, EPA describes how a
method should be tested to prove that it meets performance standards. Vendors, in conjunction
with evaluating organizations, are responsible for testing methods.
EPA recognizes three ways to prove that a release detection method meets the federal
performance standards:
•	Evaluate the method using EPA's standard test procedures for release detection methods
•	Evaluate the method using a national consensus code or standard developed by a
nationally-recognized association or independent testing laboratory
•	Evaluate the method using an alternative procedure deemed equivalent to an EPA
standard test procedure by a nationally-recognized association or independent testing
laboratory
The vendor should prove the release detection method meets the regulatory performance
standards using one of three ways described below. For regulatory enforcement purposes, each
way is equally satisfactory.
1.1 EPA Standard Test Procedures
In 1990, EPA developed a series of seven standard test procedures that covered the most
commonly used UST release detection methods. Over the years, new methods became available
and other fuels were being stored in and dispensed from USTs; therefore, in 2019 EPA updated
the standard test procedures and consolidated them into four main categories. They are:
•	Standard Test Procedures For Evaluating Release Detection Methods: Automatic Tank
Gauging Systems
•	Standard Test Procedures For Evaluating Release Detection Methods: Pipeline Release
Detection
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•	Standard Test Procedures For Evaluating Release Detection Methods: Statistical
Inventory Reconciliation
•	Standard Test Procedures For Evaluating Release Detection Methods: Tank Tightness
Testing - Volumetric And Non-volumetric
The standard test procedures provide an explanation of how to conduct the evaluation tests,
perform the required calculations, and report the results. The results from the standard test
procedures provide information tank owners and operators need to determine if their release
detection method meets the regulatory requirements.
Vendors or an independent evaluator on behalf of the vendor may conduct EPA's standard test
procedures. Generally, regulatory authorities and UST owners and operators prefer that an
independent evaluator carry out the evaluation to prove compliance with the regulation.
Evaluations are more likely to be fair and objective if the evaluator is independent of the vendor.
Independent evaluators may include consulting firms, test laboratories, not-for-profit research
organizations, or educational institutions.
1.2	National Consensus Code Or Standard
Another way for a vendor to prove the performance of a release detection method is to evaluate
the method following a national voluntary consensus code or standard developed by a nationally
recognized association such as the American Society of Mechanical Engineers, American
National Standards Institute, or ASTM International. Throughout the development of the 2015
UST regulation, EPA relied on national voluntary consensus codes to help tank owners and
operators decide which methods and equipment are acceptable to meet various regulatory
requirements. You can find information for developing voluntary consensus codes in the U.S.
Department of Commerce Procedures for the Development of Voluntary Product Standards (15
CFR Part 10) and Federal Participation in the Development and Use of Voluntary Consensus
Standards and in Conformity Assessment Activities (Office of Management and Budget Circular
No. A-119).
1.3	Alternative Test Procedure Deemed Equivalent To EPA's Standard Test
Procedures
There may be instances where existing EPA standard test procedures or national voluntary
consensus codes or standards do not adequately cover a release detection method, particularly as
new fuels and the methods and equipment designed to function with those fuels come to market.
Additionally, vendors may have data that make it easier to evaluate the method another way.
Vendors who want their methods tested, or who have already tested their methods according to a
different procedure, must use a nationally-recognized association or independent laboratory such
as Factory Mutual, National Sanitation Foundation, Underwriters Laboratory to develop or
review that procedure. The association or laboratory's test conditions must be at least as
rigorous as EPA's standard test procedures and the accreditation of the association or laboratory
must be included in the evaluation.
These are the requirements for using an alternative test procedure:
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•	The evaluator tests the method both under a no-leak condition and an induced-leak
condition with an induced leak rate as close as possible to or smaller than the
performance standard. In the case of volumetric tank tightness testing (TTT), this will
mean testing under a minimum of 0.0 gal/hr, 0.05 gal/hr, and 0.1 gal/hr leak rates. In the
case of automatic tank gauging systems (ATGS), this will mean testing under a minimum
of 0.0 gal/hr, 0.05 gal/hr, and 0.2 gal/hr leak rates.
•	The evaluator must test the method under at least as many different environmental
conditions as the corresponding EPA standard test procedures.
•	The conditions under which the method is evaluated must be at least as rigorous as the
conditions specified in the corresponding EPA test procedures. For example, in the case
of volumetric TTT, the test must include a temperature difference between the delivered
product and that already present in the tank, as well as account for deformation caused by
filling the tank prior to testing. Additionally, when method performance is sensitive to
stored product viscosity, the method's most rigorous viscosity of listed products must be
evaluated.
•	The evaluation results must contain the same information and be presented in the same
format as EPA's reporting forms provided in the appendix of each EPA standard test
procedure.
•	The evaluation of the release detection method must include physical testing of a full-
sized version of the release detection method; full disclosure of the experimental
conditions under which the evaluation was performed, and the recommendation for use.
An evaluation based solely on theory or calculation is insufficient.
1.4 Purpose And Intended Use Of This Document
This 2019 general guidance document includes background information, updates, and
standardization of the original test procedures. This document:
•	Reduces unnecessary duplication of information presented in the test procedures
•	Provides general information applicable to all of the test procedures
•	Presents and explains standard terminology
•	Describes typical release detection methods and operating principles used by these
methods
•	Discusses common elements of the test procedures such as scope, test design, statistical
calculations, and how reports are organized
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Section 2: EPA Standard Test Procedures
This section briefly summarizes the overall design of the standard test procedures and provides
guidance for using the procedures. This section also follows the process for proving that a
release detection method meets the regulatory performance standards. Table 1 presents the
context for release detection methods and standard test procedures, basic steps required, and
identification of parties involved to prove regulatory compliance. The federal UST regulation
establishes what owners and operators must do to use release detection methods with a proven
level of performance.
EPA designed the standard test procedures to use the leak rate specified in the appropriate
regulatory requirement. Vendors develop or improve on commercially available release
detection methods. Evaluators collect the data to estimate performance in terms of leak rate,
P(d), and P(fa) according to the method's abilities following the appropriate standard test
procedures; both no-leak and induced-leak conditions are tested. Evaluators may use other leak
rates, typically below but also above the regulatory standard. Once evaluators collect these data,
they are analyzed, reported and presented in Appendix B - Reporting Forms, of the associated
standard test procedure. For the volumetric and non-volumetric tank tightness testing
procedures, reporting forms for volumetric methods are presented in Appendix B and reporting
forms for non-volumetric methods are presented in Appendix C. These standard test procedures
provide owners and operators with results proving the method they maintain and operate meets
regulatory compliance.
Table 1. Roles And Responsibilities
Ac(i\ i(\
Slops And Piirlics ln\ol\od
UST Regulation
EPA's UST regulation sets release detection performance criteria to prevent
releases and protect the environment
Release Detection Methods
Vendors develop release detection methods
Standard Test Procedures
EPA provides test procedures for evaluating method performance level to meet
regulation
Testing
Evaluators collect data, perform statistical analyses, and prepare the reports
Method Listing (Optional)
National Work Group on Leak Detection Evaluations (NWGLDE) reviews the
reports
Release detection methods are listed as meeting regulatory performance
standards
2.1 Regulatory Performance
The evaluator determines the specifications of method performance under the range of conditions
the method was evaluated. The test procedures challenge the release detection method according
to its abilities.
Method performance, in most cases, requires a P(d) and P(fa) at a defined leak rate. The P(d), or
the probability of detecting a leak, is the number of times that a method would detect a leak of a
specified size if there were such a leak. Thus, a P(d) of 95 percent, which may also be written as
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0.95, suggests the method will correctly declare leaks of the specified size in 95 percent of
systems tested. Missed detections, also referred to as false negatives, occur if the method fails to
declare a leak when one is present; this occurs most frequently when the leak is small or
changing due to such factors as head pressure in a tank or pipeline pressure and thermal
expansion or contraction.
The P(fa), or probability of false alarm, is the proportion of tight, non-leaking UST systems that
would be declared leaking if all the UST systems tested were tight. Thus, a P(fa) of 5 percent
suggests the method will incorrectly declare leaks in 5 percent of the non-leaking systems tested.
The P(d), P(fa), method threshold (Th), and leak rates are all interrelated; changing one
parameter affects the value of one or more of the other parameters. The choice of parameters
affects the conclusions drawn from release detection tests, that is, the reliability of the test
results. Once Th has been selected for each set of data analyzed, the P(fa) is determined and
does not change, regardless of the leak rate to be detected. The P(d), however, does change with
leak rate if Th is kept constant for each set of data analyzed. The P(d) increases as the leak rate
increases, that is, there is a better chance of finding large leaks than small leaks. Th is usually
chosen in such a way that P(d) and P(fa) present an acceptable balance between economic and
environmental risks.
2.2 Release Detection Methods
Section 1.1 lists the four EPA standard test procedures for release detection methods. Table 2
presents the release detection categories and specific methods in each category. These methods
represent the most common methods and operating principles in each category. Release
detection methods are grouped as either volumetric or non-volumetric methods; in some cases, a
method may apply to both categories. Owners and operators may use either type to satisfy
requirements of 40 CFR 280 except when using statistical inventory control (SIR) methods. The
primary distinction between the two categories is that volumetric methods report quantitative
results, or a reported leak rate compared to Th, whereas non-volumetric methods report
qualitative results, or only whether there is evidence of a leak or not.
Volumetric methods quantitatively measure leak rate from an UST, based on changes in liquid
level in a tank. Various methods are available for measuring these changes, including floats,
load cells, and ultrasonic devices. They can be further categorized into methods that meet 40
CFR 280 requirements for precision testing; 0.1 gal/hr leak rate, for example tank or pipeline
tightness tests or a 0.2 gal/hr leak rate, for example ATGS or SIR respectively. Accurate use of
each volumetric method requires knowledge of certain storage conditions and fuel properties, so
you can adjust and compensate for other factors that might produce a change in liquid level. For
example, you must know the coefficient of thermal expansion to correct the volume based on
changes in the temperature of the stored product. Without this correction, a volume change that
occurs as the storage temperature drops could be interpreted as a fuel leak or the actual
calculated leak rate may be inaccurate. Other possible corrections include: fuel density based on
temperature and ethanol content, air density based on temperature above the stored liquid, or
groundwater level surrounding a tank.
Non-volumetric methods qualitatively identify when a leak is occurring in an UST. While you
cannot use these methods to determine an actual leak rate in an UST system, the signal from the
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methods indicates a tank might be leaking. Various non-volumetric methods include: acoustic
measurements, water sensing equipment, and interstitial sensors. Examples of how these
methods detect possible leaks are by detecting sounds made by fuel leaks through an opening in
the tank shell, water present at the bottom of a tank, or liquids in the interstitial space of a
double-walled tank. An indicator from one of these type methods cannot be used to calculate an
exact volume or leak rate, but observing an indicator clearly shows the tank operator that the
integrity of the tank shell may have been compromised. Other non-volumetric methods include
vapor and liquid out-of-tank monitoring in the excavated soil area or groundwater surrounding
an UST. Tracers can also be used to detect the presence of a leak.
Table 2. Summary Of Release Detection Methods And Operating Principles
Method
Principle Of Operation
Volumetric-Based Method Type
Automatic Tank Gauge Systems (ATGS)
Magnetostrictive
Probes
Wire sensor inside a shaft detects presence of magnetic field, which indicates height of float.
Ultrasonic or
Acoustic Methods
(speed)
Sensor detects changes in fluid levels detecting a sound wave echo reflected from the interface
of water and fuel or fuel and air; it calculates level based on speed of sound in the product.
Capacitance
Probes
Detection is based on dielectric property of the stored liquid.
Mass Buoyancy
And Measurement
Systems
Buoyancy of probe is detected on a load cell and compared to tank geometry to calculate liquid
level.
Statistical Inventory Reconciliation (SIR) Methods
Traditional SIR
SIR vendor performs analysis of liquid level data for evidence of tank tightness. Data are
collected by taking daily manual liquid level readings or using an ATGS.
Continuous SIR
SIR vendor software performs temperature compensation and leak-test calculations on data
collected from designated input devices during tank quiet times. Also called continuous in
tank leak detection system (CITLDS or CITLD).
Tank Tightness Testing
Overfill
Product is added to tanks past levels of overfill prevention equipment typical settings.
Non-Volumetric Based Method Type
Pipeline Methods (Piping)
Pressure Decay
Measures the change in pressure between the atmosphere and the pressurized product in the
line over time.
Constant Pressure
Sensors monitor change in volume at constant pressure.
Electronic Line
Leak Detectors
Usually incorporate a microprocessor and feature precisely calibrated sensors that allow more
sensitive tests on piping as compared to mechanical devices. Its detection element feeds data
to a control panel that can trigger audible and visible alarms and even shut off a pump. The
standard 3.0 gph test is performed after each dispensing activity.
Mechanical Line
Leak Detectors
Pressure-operated valves typically installed on the head of the submersible pump. They
perform a test of the piping each time the pump is turned on. Conducts leak tests every time
the pump engages.
Tank Tightness Testing: Out of Tank Liquid and Vapor Monitoring Methods
Fuel Sensitive
Polymers
Fiber optic cable is coated with a polymer that interacts with fuel. When fuel is present, the
light or current passing through the cable is affected.
Tracers
Chemical markers or tracers are added to the product and the surrounding soil is monitored for
the tracers.
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Method
Principle Of Operation
Acoustic Precision
Test
Detected sounds are used to identify potential leaks; an orifice is used to simulate the sound
produced as liquid or air leaks out of a system. This uses acoustic sensors and microphones, as
well as ultrasonic sensors and hydrophones.
Vacuum And
Pressure Decay
Test
Determine tank tightness by the decay rate of the vacuum or pressure established by the
method.
Tank Tightness Testing: Dry Interstitial Integrity Monitoring Methods
Vacuum And
Pressure Decay
Monitoring
Method uses an integral vacuum pump or pressurized system to continuously maintain a partial
vacuum or pressure within the interstitial space of double-walled tanks and double-walled
piping. Method is capable of detecting breaches in both the inner and outer walls of double-
walled tanks or double-walled piping.
Tank Tightness Testing: Wet Interstitial Integrity Monitoring Methods
Liquid Filled
A liquid solution fills the tank or piping interstice. The dual-point level sensor system
monitors the liquid level in the interstitial reservoir and sounds an alarm if the liquid level is
either too high, which indicates ingress of liquid, or too low, which indicates egress of liquid.
Method is capable of detecting breaches in both the inner and outer walls of double-walled
tanks or double-walled piping.
Sensor - liquid
ingress
Varies depending on the type of sensor; comes in multiple forms. Most examples include use
of refractive index or float switch.
Tank Tightness Testing: Water Detection Methods (and ATGS component)
Water Float
Buoyancy of float allows the magnetic field or capacitance signal generated to coincide with
the top of the liquid layer; it is based on the liquid density in comparison to the float density.
These floats are specifically designed for water detection and the density difference between
water and the fuel product.
Density Float
Buoyancy of a float signals changes in product; it compares density data changes over time to
assess the change in product quality due to water ingress. This float is sensitive to the aqueous
phase detection found in ethanol-blended fuels.
Conductivity
Water Probe
The probe detects water by measuring current flow when water contacts the probe; used with
certain acoustic methods.
2.2.1 Automatic Tank Gauging Systems
ATGS are volumetric release detection methods. An ATGS relies on physical properties of the
storage system to generate an electronic signal that can be converted into a value representing the
volume in a tank. Manual tank gauging typically consists of sticking a long pole containing
graduated length markings into an UST. An ATGS consists of a probe or sensor located inside
the UST and a controller or console mounted in an indoor location. The probe or sensor generate
the electronic signal that is subsequently processed in the console and calculates volume changes
or leak rate. The electronic signal is generated in one of several ways, including:
•	A float mounted to a probe; this is a liquid level method
•	A set of acoustic sensors to detect sound in the liquid or the air space above the liquid;
this is a sound transmission or reception method similar to sonar or radar
•	A load cell suspended in the liquid product; this is a buoyancy method
•	A set of sensors to determine the electrical properties of a liquid; this is an electric
conductance or capacitance method
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Regardless of the method employed, the signal generated by any of these methods is combined
with a specific set of other data, which are recorded by the ATGS, and processed to calculate a
volume of liquid in the UST. The console contains a processor that compares calculated
volumes at different times, when the UST is not dispensing or receiving fuel, to determine if a
difference is due to a leak or some other factor.
Depending on the ATGS, its data processor must correct the calculated volume for other method
conditions. For example, the volume derived from the liquid height of a float system, electrical
property, or acoustic sensor must be adjusted for liquid expansion or contraction produced by
changes in temperature of the stored liquid. Similarly, to accurately calculate volume, the result
obtained from a pressure, buoyancy, or sound velocity reading must incorporate a liquid or air
density factor, which also varies with temperature. Given the proper inputs, the ATGS will yield
information on volume of stored fuel and on calculated leak rates during a leak test. Most probes
for ATGSs are also equipped with a water detection float.
2.2.2	Pipeline Release Detection
Pipeline release detection methods can be volumetric or non-volumetric methods. Both use
similar operating principles and can be applied to testing both large pipelines such as those
located at airport hydrant fueling systems and piping at typical UST facilities to meet, for
example, the annual line tightness test requirement. These methods use fluid flow
instrumentation to monitor flow rate of fluid moving through the underground piping of an UST
system at one or more locations or the static pressure in a sealed pipe system. Flow
measurement devices are usually based on pressure; however, these devices could also use a
displacement piston or graduated cylinder instead of a pressure-based measurement device. The
liquid within the piping is non-compressible and, therefore, a single flow measurement or a
comparison of the flows at different locations will indicate if a leak has occurred along the
piping. By necessity, several properties of the fluid must be known to correctly convert the
measurement into a flow rate. Most non-compressible flow monitoring systems need critical
parameters such as fluid density and viscosity. Even without these parameters, comparison of
the pressures at different monitoring points can indicate the presence of a leak. Before
confirming a leak, friction losses in high-volume or long piping sections may need to be
calculated. Static pressure devices installed on a non-leaking pipe section should show the
pressure is maintained over the duration of the test. Temperature correction may be needed if the
product temperature is susceptible to change during the test; product expansion or contraction
changes the static pressure.
2.2.3	Statistical Inventory Reconciliation
There are two types of SIR release detection methods: traditional and continuous. Traditional
SIR takes daily manual liquid level readings of the product in the tank or uses an ATGS and
reconciles product readings in the tank with the amounts of dispensed and delivered product.
Continuous SIR performs the same product reconciliation as traditional; however, it can
differentiate between line and tank leaks and can compensate for temperature variations with a
continuous in-tank leak detection system (CITLDS). For continuous SIR, data are gathered from
all designated input devices during tank quiet times when there are no sales and no deliveries.
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When enough data are recorded, the SIR vendor software programs perform leak-test
calculations. Most CITLDS methods use an ATGS to gather product-level data; this is
considered a hybrid SIR method. Other CITLDS methods gather product-level data from input
devices such as dispenser totalizers and point-of-sale records. CITLDS are well suited to
facilities that are open 24 hours a day, 7 days a week, as long as the volume of the product sold
from USTs does not exceed the throughput limit of the CITLDS method and there is enough
quiet time to collect adequate data. For more information on test procedures for evaluating these
types of release detection methods, refer to Evaluation Protocol for Continuous In-Tank Leak
Detection Systems protocol revised on January 7, 2000 by Dr. Jairus D. Flora, Jr. More recent
versions of this protocol may be used if listed as acceptable by the National Work Group on
Leak Detection Evaluations (NWGLDE).
The SIR methods then use these inventory records to perform a statistical analysis of inventory
discrepancies. CITLDS methods, in comparison to periodic measurements, provide a larger
quantity of data, which compensate for temperature and typically provide better data for SIR
analysis. Various components that might contribute to these discrepancies are generally isolated
before a leak rate is estimated. Although a qualitative SIR evaluation option was previously
allowed, EPA no longer allows this type SIR method. The federal UST regulation only allows
quantitative methods.
2.2.4 Tank Tightness Testing
Out Of Tank Vapor And Liquid Release Detection
Vapor-phase out-of-tank product detectors are non-volumetric methods that employ instruments
designed to detect hydrocarbon product vapors in the vadose zone or backfill area around an
UST. The detector relies on the high volatility of some chemical components of gasoline and the
ability to measure them at low concentrations. Thus, sampling the soil gas surrounding an UST
or within the tank top sump for gasoline components, such as benzene or toluene, can be used to
detect UST system leaks. However, you cannot quantify the fuel leak rate using this method.
A variation of this method is an external tracer. In this method, a volatile tracer compound is
added to the product stored in an UST and the tank backfill around the UST is monitored for this
tracer. The tracer must completely mix into the product yet be volatile enough to separate from
the fuel after a release from the tank. The tracer then migrates through the tank backfill to a
monitoring location where it is collected and later analyzed in a laboratory by gas
chromatography - mass spectrometry.
Liquid-phase out-of-tank product detectors are non-volumetric methods that employ instruments
designed to detect a free-product layer on the water table in an observation well near an UST or
on water collected in a dispenser sump. Free-product detectors are commonly used in site
remediation monitoring wells and rely on the immiscibility of petroleum products and water.
Gasoline that leaks from an UST and intercepts the water table will rise to the top of the water
column in an observation well and be detectable as a layer of product on top of the water.
Although leaks can be detected using these detectors, the leak rate cannot be determined.
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Acoustical methods, which are different from the ultrasonic ATGS, make use of an acoustic
sensor to detect the sound of fuel leaking out of an UST or water or air leaking into a tank. By
placing a tank under a slight negative pressure test condition, the airflow leak can be introduced
into the tank. To use this method, interfering sounds must be eliminated and only qualitative
leak determinations are possible. In addition, if the groundwater level is above the bottom of an
UST, water may enter the tank without an audible sound. Therefore, these methods include a
water detection component. One type is based on conductivity and referred to as a conductivity
water probe. A gauge measures current flow when water ingress contacts a probe while under
vacuum. In ethanol-blended gasoline, it is difficult to determine water ingress due to minimal
conductivity of the transition zone between low ethanol-blend gasoline and phase separation; it
will not work in high ethanol-blends due to the high conductivity of the high ethanol blend.
Interstitial Integrity Monitoring
Interstitial integrity monitoring is a method used on secondarily contained tanks and piping. Dry
interstitial monitoring is performed in one of two ways: a vacuum or pressure is induced in the
interstitial space and the pressure differential is monitored in the space; or a sump or reservoir is
connected to the interstitial space to allow liquid leaking into the space to collect and be detected
by liquid detection methods. Wet interstitial monitoring is performed with the interstice full of
liquid, usually brine, with a change in liquid level indicating a release into or out of the interstice.
These options can be performed continuously or intermittently; no other parameters must be
monitored to make adjustments based on the observations.
Water Detection
Traditional water detection methods make use of the insolubility of water in non-ethanol blend
gasoline, which is immiscible; these methods are specifically calibrated to detect the density of
water. The unexplained presence of water in a tank indicates a potential leak that must be
investigated.
A water float is located on the bottom of the tank where water may collect as a denser phase than
the fuel. As the water or water phase, which is a water-ethanol mixture, height increases, the
float rises and transmits an electronic signal proportional to the level of the denser phase in the
bottom of the tank. The inventory measurement also registers an increase in volume given water
ingress, although the quantified amount may not be accurate depending on the water solubility of
the fuel and proportion of a bio-component in the fuel, such as ethanol. Because these methods
must function in a wide range of fuel densities, a traditional water float is too dense to float on
the interface layer between the aqueous phase and ethanol-blended fuel.
Aqueous phase density floats are water detection methods that are calibrated for aqueous phase
detection; they are density-based methods that address concerns with ethanol-blended fuel and its
ability to absorb water. When enough water is absorbed, the ethanol and water separate from the
hydrocarbon phase and settle to the tank bottom. The density of this water-ethanol bottom is less
than that of water alone. As a result, traditional water floats do not consistently detect this
aqueous phase. These newly developed methods employ either a float with a density sensitive to
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ethanol-water mixtures or a sensor to directly measure the density or conductivity of the ethanol-
water mixture at the bottom of a tank.
2.3 Release Detection Method Evaluation
The evaluator follows EPA standard test procedures to evaluate release detection methods. The
goal is to establish regulatory performance criteria so a similar approach is taken in the test
parameters and designs, statistical analyses, and reporting. The release detection methods are
usually installed on an UST system for a particular test or permanently and can be made up of
many components that offer different release detection modes. All release detection modes must
be evaluated and the entire system evaluated against the regulatory performance level. That
means additional test procedures are included in the standard test procedures for system
components, such as water ingress detection modes and sensors used in various places of an UST
system. Of EPA's four main standard test procedures, the ATGS and the volumetric and non-
volumetric tank tightness test methods include additional test procedures for testing these
components individually. Table 3 summarizes the scope of EPA's four standard test procedures.
You can use it as a guide for determining the most appropriate test procedure to use in an
evaluation.
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Table 3. Summary Of The Scope Of Each Standard Test Procedure
Standard Test
Procedures Method
Category
Scope
Performance Parameter
ATGS
• Quantitative ATGS release detection
o Optional lowest product level tests
• P(d) of 95% with P(fa) of 5% at
0.2 gal/lir for monthly monitoring
•	In-tank water ingress detection
•	Change in liquid level or wet interstitial
monitoring
•	Minimum detectable water level
•	Minimum water level change
Pipeline
•	Quantitative piping release detection
systems
•	Qualitative piping release detection
systems
•	Bulk piping release detection systems
o > 50,000 gallons
•	Optional trapped vapor tests
•	P(d) of 95% with P(fa) of 5% for
3 gal/lir at 10 psi for hourly
testing
•	P(d) of 95% with P(fa) of 5% at
0.2 gal/lir for monthly monitoring
•	P(d) of 95% with P(fa) of 5% at
0.1 gal/lir for annual TTT
•	Monitoring bulk piping is
dependent on the test section
volume and summarized in Table
1 in the standard test procedures
SIR
• Quantitative SIR release detection
o Single or syphoned USTs
• P(d) of 95% with P(fa) of 5% at
0.2 gal/lir for monthly monitoring
Tank Tightness Testing:
Volumetric and Non-
Volumetric
•	Quantitative or volumetric release
detection systems
•	Qualitative or non-volumetric release
detection systems
o Acoustical methods
•	Tracer methods
•	Sensors
o Discriminating and non-
discriminating liquid phase
o Product vapor phase
•	Vacuum decay
•	P(d) of 95% with P(fa) of 5% at 0.1
gal/lir for annual TTT
As applicable for device capabilities:
•	Average detection time
•	Liquid activation height
•	Accuracy
•	Precision
•	Specificity
•	Average recovery time
2.3.1 Test Designs
The approach to evaluating a release detection method is specific to the release detection method
category; however, the evaluator must test the methods following the same basic approach to all
method categories for both quantitative and qualitative method results. When the release
detection method can quantify the leak rate yielding volumetric results, fewer tests are needed to
establish the needed P(d) and P(fa). The basic test design includes varying the test conditions
with a minimum of 24 test results: leak rates (4 total, including a no leak condition), fill heights
(2 or 3), and temperature differentials (3). You may add optional tests to this basic design to
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demonstrate other method capabilities. When a method determines a leak against a threshold
and gives a qualitative or non-volumetric result, the number of tests increases to at least 42. This
second test design uses the same conditions but may be modified according to operating
principle. For example, temperature may or may not be a factor; therefore, it may not need to be
included in the test design. Depending on the performance standard, the targeted leak rates used
during testing will vary. The individual standard test procedures establish which specific test
design to follow based on the release detection method capabilities.
EPA's standard test procedures were written with a focus on the most common motor fuel
products stored in USTs as of the time of publication. These fuels include non-alcohol blended
gasoline, alcohol blended gasoline, and diesel. EPA anticipates there will be many fuels
introduced to the nation's fuel supply over time. The test procedures may be used to verify
release detection equipment performance in similar as well as dissimilar fuels to those listed.
Several test procedures indicate this allowance in specific sections. Evaluators should at
minimum, analyze the operating principle of the release detection method against target fuel
properties that include, but are not limited to: coefficient of thermal expansion, concentration of
or lack of petroleum, dielectric constant, electrical conductivity, and viscosity. The evaluator
must provide this analysis on the appropriate reporting form to verify decisions to include other
fuels as comparably performing, with or without limitations, as a tested fuel.
2.3.2 Statistical Analysis
The statistical calculations are similar across all test procedures. The performance of a release
detection method is expressed in terms of the P(fa) and P(d(R)), where R is the leak rate.
Generally, the volumetric release detection method - either a precision tank test or the leak test
function of an ATGS - or SIR estimates a leak rate. This calculated rate is compared to a
vendor-stated Th. If the calculated rate is in excess of Th, the tank is declared leaking;
otherwise, the tank is called tight. For non-volumetric release detection methods, the rate is not
quantified: however, the P(fa) and P(d(R)) are calculated using pass or fail results at the tested
leak rates. The calculations are similar; but the number of tests in the test design is larger to
evaluate non-volumetric results at the regulatory performance standard.
Figure 2 represents the process of determining whether a tank is leaking. The curve on the left
represents the inherent variability of the measured leak rate on a tight tank with zero leak rate. If
the measured leak rate exceeds Th, the tank is declared to leak, which is a false alarm. The
chance of this happening is represented by the shaded area under the curve to the right of Th,
denoted alpha (a).
The variability of the measured leak rates for a tank that is actually leaking at the R is
represented by the curve on the right in Figure 1. Again, a leak is declared if the measured rate
exceeds Th. The probability the leaking tank is correctly identified as leaking is the area under
the right-hand curve to the right of Th. The probability of mistakenly declaring the leaking tank
tight is denoted by beta (P), the area to the left of Th under the leaking tank curve.
Changing Th changes both a and P for a fixed R. If R is increased, the curve on the right will
shift further to the right, decreasing P and increasing the P(d(R)) for a fixed Th. If the precision
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of a method is increased, the curve becomes taller and narrower, decreasing both a and P,
resulting in improved performance.
A bias (B) is a consistent error in one direction; see Figure 2. In it, both curves have been shifted
to the right by an amount of B. In this illustration, B indicates a greater R than is actually
present; B is positive in this case. This has the effect of increasing the P(fa), while reducing the
probability of failing to detect a leak. That is, the P(d(R)) of the size of R is increased, but so is
the chance of a false alarm. B toward underestimating R would have the opposite effect. That
is, it would decrease both the P(fa) and the P(d(R)).
Tight Tank	Leaking Tank
Th = Threshold for declaring a leak; a leak is declared if the measured
rate exceeds Th
a = Probability of false alarm, P(fa)
(3 = Probability of not detecting a leak rate, R
I - (3 = Probability of detecting a leak rate R, P(d(R))
R = Leak rate
Figure 1. Distribution Of Measurement Error On A Tight And Leaking Tank
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Tight Tank	Leaking Tank
Th
Threshold for declaring a leak;

a leak is declared if the measured rate exceeds Th
a
Probability of false alarm, P(fa)
P
Probability of not detecting a leak rate, R
I-P
Probability of detecting a leak rate R, P(d(R))
R
Leak rate
B
Bias
Figure 2. Distribution Of Measurement Error On A Tight And Leaking
Tank With A Positive Bias
2.3.3 Report Organization
The evaluator must report the results of release detection method evaluations in a similar fashion
regardless of the type of method evaluated. Appendix B of each standard test procedure provides
the evaluator with instructions and standard forms to collect and report the data. The test
procedure for volumetric and non-volumetric tank tightness testing also has reporting forms
presented in Appendix B for volumetric methods and Appendix C for non-volumetric methods.
Appendix B has several main parts. The number of parts vary depending on the specific test
procedure. Each of the main parts are preceded by instructions for their completion. Appendix
B includes a form for each of the main parts. Once the forms are completed and compiled, they
constitute the report. Here is an example, of typical forms contained in Appendix B:
•	Parti: Results of EPA standard evaluation form. This standard evaluation form
summarizes the overall findings and conclusions from the testing. UST owners and
operators use this form as an executive summary to verify the performance of their
chosen release detection method. The standard evaluation form is structured so the
results can be easily understood and is required in the report.
•	Part 2: Method description form. This release detection method description form is
included in Appendix B of each test procedure. The evaluator, assisted by the vendor,
should complete it.
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•	Part 3: Reporting form. This reporting form for leak rate data is described in Appendix
B of each test procedure. The form summarizes test results and contains information
about starting dates and times, test duration, and leak rate results.
•	Part 4 (optional): Individual test logs. Individual test logs record raw data collected
during testing; the test logs document the quality of the data used to evaluate the
performance estimates of the release detection method. These test logs are not mandatory
for the report and the evaluator must maintain them.
With various methods, Appendix B also includes additional forms for data collection and
additional room on the reporting forms for tests conducted in addition to the basic test design.
There may be a section of the report summarizing the raw data collected for demonstrating
additional capabilities of the release detection method, for example water detection or trapped
vapor. The individual test logs containing raw data are not mandatory for the report and must be
maintained by the evaluator. The conclusions from the optional tests may be reported on the
designated places within the standard evaluation form or reporting form.
2.4 Alternative Availability Of Release Detection Method Performance Verification
The federal UST regulation requires that UST owners and operators obtain and keep on file
release detection method performance claims and their manner of determination described in
writing by the vendor or installer (40 CFR 280.40 (a)(3)). Evaluators, such as consulting firms
or test laboratories without organizational conflict of interest, typically prepare release detection
reports. The reports and data are available to all interested parties, including UST owners and
operators. In addition, release detection method evaluation reports are typically submitted by
vendors to NWGLDE for review. If the review determines that the evaluation results are
acceptable, the release detection method is added to the NWGLDE list, available at
www.nwglde.org. This list provides quality reference information about the release detection
methods; that information can be useful to the regulated community and regulatory authorities.
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United States	Land And	EPA 510-B-19-006
Environmental	Emergency Management	May 2019
Protection Agency	5401R	www.epa.gov/ust

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