vvEPA
United States
Environmental Protection
Agency
Hazardous Waste Engineering
Research Laboratory
Cincinnati OH 45268
EPA/600/2-86/001
January 1986
Research and Development
Underground Tank
Leak Detection
Methods:
A State-of-the-Art
Review
-------
EPA/600/2-86/001
January 1986
UNDERGROUND TANK LEAK DETECTION METHODS:
A STATE-OF-THE-ART REVIEW
by
Shahzad Niaki and John A. Broscious
IT Corporation
Pittsburgh, Pennsylvania 15235
Contract No. 68-03-3069
Project Officer
John S. Farlow
Releases Control Branch
Hazardous Waste Engineering Research Laboratory
Edison, New Jersey 08837
HAZARDOUS WASTE ENGINEERING RESEARCH LABORATORY
OFFICE OF RESEARCH AND DEVELOPMENT
U.S. ENVIRONMENTAL PROTECTION AGENCY
CINCINNATI, OH 45268
Protection *••"<*
230 South Dearborn Street
Chicago, Illinois 60604
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DISCLAIMER
The information in this document has been funded wholly or in part
by the United States Environmental Protection Agency under Contract No.
68-03-3069 to IT Corporation. It has been subject to the Agency's peer
and administrative review, and it has been approved for publication as
an EPA document. Mention of trade names or commercial products does not
constitute an endorsement or recommendation for use.
U,S. Environmental Protection Agency
-------
FOREWORD
Today's rapidly developing and changing technologies and industrial
products and practices frequently carry with them the increased gener-
ation of solid and hazardous wastes. These materials, if improperly
dealt with, can threaten both public health and the environment.
Abandoned waste sites and accidental releases of toxic and hazardous
substances to the environment also have important environmental and
public health implications. The Hazardous Waste Engineering Research
Laboratory assists in providing an authoritative and defensible engi-
neering basis for assessing and solving these problems. Its products
support the policies, programs, and regulations of the Environmental
Protection Agency, the permitting and other responsibilities of State
and local governments, and the needs of both large and small businesses
in handling their wastes responsibly and economically.
This report describes both commercially available and developing
techniques for detecting leaks in underground storage tanks, and will be
useful to government officials, industry, and those members of the
public concerned with this aspect of preventing the pollution of ground
water.
For further information, please contact the Land Pollution Control
Division of the Hazardous Waste Engineering Research Laboratory.
David G. Stephan, Director
Hazardous Waste Engineering Research Laboratory
ill
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PREFACE
This report has been prepared by IT Corporation (IT) under contract
with the U.S. Environmental Protection Agency (EPA), to be used as a
state-of-the-art overview of available and developing leak detection
methods for testing underground tank, systems. The descriptions of
detection methods and the techniques to compensate for the effects of
the variables affecting detection methods have been reviewed by the man-
ufacturer, practitioner, or developer of the detection method. It is
expected that this report will result in further evaluation in detection
methods to compensate for variables affecting the accuracy of available
and developing detection methods.
The variables described in this report should be considered as
potential sources of error, especially in the application of volumetric
leak detection methods. The applicability and effectiveness of
detection methods identified must be determined on an individual test
situation basis. The applicability of a detection method will depend
upon numerous factors including hydrogeologic, economic, climatic, and
conditional considerations.
As an aid to identifying all of the available and developing leak
detection methods for underground tank testing, a list of the identified
detection methods was published by the Petroleum Equipment Institute
(PEI) in its Tulsa letter in August 1984 (together with the request that
IT be advised of any other detection methods). In addition, a limited
patent search was conducted to identify other leak detection methods for
testing underground tanks or tank systems.
iv
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ABSTRACT
This report is a state-of-the-art review of available and develop-
ing methods for finding small leaks in underground storage tanks used
primarily for gasoline and other liquid petroleum fuels. This review
describes (based on information provided by the manufacturers or practi-
tioners) a total of thirty-six volumetric, nonvolumetric, inventory mon-
itoring, and leak effects monitoring detection methods; provides general
engineering comments on each volumetric and nonvolumetric leak detection
method; and discusses variables which may affect the accuracy of
detection methods. The emphasis throughout is on volumetric and
nonvolumetric leak detection methods.
This report was submitted in fulfillment of Contract No. 68-03-3069
by IT Corporation under the sponsorship of the U.S. Environmental Pro-
tection Agency. This report covers a period from July 1984 to January
1985, and work was completed as of June 1985.
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CONTENTS
PAGE
DISCLAIMER ii
FOREWORD iii
PREFACE iv
ABSTRACT v
FIGURES xi
TABLES xii
ACKNOWLEDGEMENT xiii
SECTION 1 - INTRODUCTION 1
STATEMENT OF THE PROBLEM 1
REPORT OBJECTIVE 2
SECTION 2 - SUMMARY 3
SECTION 3 - CONCLUSIONS 26
SECTION 4 - RECOMMENDATIONS 27
SECTION 5 - VARIABLES AFFECTING LEAK DETECTION METHODS 28
VOLUMETRIC LEAK DETECTION TESTS 28
Temperature 35
Water Table 35
Tank Deformation 37
Vapor Pockets 42
Product Evaporation 42
Piping Leaks 42
Tank Geometry 42
Wind 44
Vibration 44
Noise 44
vii
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Equipment Accuracy 45
Operator Error 45
Type of Product 45
Power Variation 45
Instrumentation Limitation 45
Atmospheric Pressure 46
Tank Inclination 46
NONVOLUMETRIC LEAK TESTS 46
Temperature 46
Water Table 47
Tank Deformation 47
Vapor Pocket 48
Product Evaporation 48
Piping Leaks 48
Tank Geometry 48
Wind 48
Vibration 48
Noise 48
Equipment Accuracy 49
Operator Error 49
Type of Product 49
Power Variation 49
Instrumentation Limitation 49
Atmospheric Pressure 49
Tank Inclination 49
General Problems 49
INVENTORY CONTROL 50
LEAK EFFECTS MONITORING 50
SECTION 6 - LEAK DETECTION METHODS REVIEW 51
CLASSIFICATION 51
Volumetric (Quantitative) Leak Testing 52
Nonvolumetric (Qualitative) Leak Testing 52
viii
-------
Inventory Control 52
Leak Effects Monitoring 52
LEAK DETECTION TESTING METHODS 52
Volumetric (Quantitative) Leak Testing 52
Methods
1- Ainlay Tank Tegrity Testing (TTT) 52
2- ARCO HTC Underground Tank Leak Detector 56
3- Certi-Tec Testing 60
4- "Ethyl" Tank Sentry Testing 63
5- EZY-CHEK Leak Detector 66
6- Fluid-Static (Standpipe) Testing 71
7- Heath Petro Tite Tank and Line Testing 72
(Kent-Moore Testing)
8- Helium Differential Pressure Testing 76
9- Leak Lokator LD-2000 Test (Hunter- 77
Formerly Sunmark Leak Detection)
10- Mooney Tank Test Detector 82
11- PACE Leak Tester 84
12- PALD-2 Leak Detector 87
13- Pneumatic Testing 89
14- Tank Auditor 90
15- Two-Tube Laser Interferometer System 93
Nonvolumetric (Qualitative) Leak Testing 96
Methods
1- Acoustical Monitoring System (AMS) 96
2- Leybold-Heraeus Helium Detector, 97
Ultratest M2
3- Smith & Denison Helium Test 98
4- TRC Rapid Leak Detector for Underground 100
Tanks and Pipes
5- Ultrasonic Leak Detector, Ultrasound 100
6- VacuTect (Tanknology) 102
7- Varian Leak Detector (SP Y2000 or 938-41) 103
Inventory Monitoring 105
1- Gage Stick 105
ix
-------
2- MFP-414 TLG Leak Detector 105
3- TLS-150 Tank Level Sensor (Veeder-Root) 108
Leak Effects Monitoring 109
1- Collection Sumps 109
2- Dye Method 109
3- Ground Water or Soil Core Sampling 111
4- Interstitial Monitoring in Double- 111
Walled Tanks
5- LASP Monitoring System (Leakage Alarm 112
System for Pipe)
6- Observation Wells 112
7- Pollulert and Leak-X Detection Systems 114
8- Remote Infrared Sensing 114
9- Surface Geophysical Methods 114
10- U-Tubes 114
11- Vapor Wells 116
REFERENCES 118
APPENDIX - LEAK DETECTION METHODS - MANUFACTURER OR PRACTITIONER
PHONE NUMBERS
x
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FIGURES
FIGURE NO. TITLE PAGE
1 Temperature Stratification 29
2 Average Gasoline Temperature for All Test Stations 30
3 Mean Temperature Distribution as a Function of Depth 31
for Four Different 24-Hour Periods
4 Tank Temperature Stratification and Gradients for a 32
24-Hour Period After Tank Fill Up
5 Location of Temperature Sensors in the SRI Tank 33
6 Delivery Temperatures 34
7 Tank End Deflection 38
8 Change in Tank Volume Due to Tank End 39
Deflections - In Gallons
9 Examples of Three Common Vapor Pockets 43
10 Ainlay Tank Tegrity Testing Method 53
11 ARCO Underground Tank Leak Detector 57
12 Certi-Tec Tank Testing System 61
13 "Ethyl" Tank Sentry Kit 64
14 "Ethyl" Tank Sentry Installation 64
15 EZY-CHEK Leak Detector 67
16 EZY-CHEK Leak Detector Installation 68
17 EZY-CHEK Leak Detector Temperature Averaging Probe 68
18 Petro Tite Installation 73
19 Leak Lokator Installation 78
20 Two-Tube Laser Interferometer 94
21 MFP-414 TLG Leak Detector-Sensor Assembly 106
22 MFP-414 TLG Tank Level Gauge & Leak Detector 107
23 Typical Wells for Continuous Gas or Vapor Monitoring 110
24 Examples of Observation Wells 113
25 Example of a U-Tube Installation 115
xi
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TABLES
TABLE NO. TITLE PAGE
1 Volumetric Leak Detection Methods - General 5
Information
2 Nonvolumetric Leak Detection Methods - General 8
Information
3 Other Leak Detection Methods - General Information 10
4 Volumetric Leak Detection Methods - General
Capabilities 12
5 Nonvolumetric Leak Detection Methods - General 14
Capabilities
6 Other Leak Detection Methods - General Capabilities 15
7 Volumetric Leak Detection Methods - Compensation 16
for Effects of Variables
8 Nonvolumetric Leak Detection Methods - Compensation 22
for Effects of Variables
9 Other Leak Detection Methods - Compensation for 24
Effects of Variables
10 Thermal Expansion of Liquids 36
11 Pressure-Height Chart 40
12 Total Force on Tank Ends 40
13 Apparent Loss of Product Volume Due to Force on Tank 41
Ends - In Gallons
xii
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ACKNOWLEDGEMENT
This report was prepared by IT Corporation, Pittsburgh,
Pennsylvania. The authors wish to express their indebtedness to Mr.
John S. Farlow, the U.S. Environmental Protection Agency's (EPA) Project
Officer, for his constant cooperation which assisted in the preparation
of this report.
The authors wish to acknowledge the valuable contribution of many
people and organizations, including the American Petroleum Institute
(API), the Petroleum Equipment Institute (PEI), and the underground tank
leak detection manufacturers or developers which were contacted. In
particular, the authors would like to thank those individuals on the
Environmental Protection Agency Technical Review Committee, including
Mr. James H. Pirn, Suffolk County Department of Health Services; Mr.
Andres Talts, Department of Defense; Mr. William E. Blain and Mrs. Diane
English, New York Department of Environmental Conservation; Mr. Steven
Way, EPA Office of Solid Waste; and Mr. David Chin, EPA Region I, who
provided valuable comments and suggestions on the report outline and
text.
xiii
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SECTION 1
INTRODUCTION
STATEMENT OF THE PROBLEM
In recent years, the increase in leaks from underground gasoline
storage tanks has had a significant adverse environmental impact on the
United States. Current estimates from government and industry sources
are that between 1.5 to 3.5 million underground storage tanks exist in
the nation. Estimates of the number of leaking tanks range from 75,000
to 100,000; and 350,000 others may develop leaks within the next five
years (1). The 1983 National Petroleum News Factbook Issue forecasts
the existence of approximately 140,000 gasoline service stations in the
United States at the end of 1983. New York State estimates that 19
percent of its 83,000 active underground gasoline tanks are now leak-
ing. Maine estimates that 25 percent of its 1,600 retail gasoline
underground tanks are leaking approximately 11 million gallons yearly.
In Michigan 39 percent of ground water contamination incidents are
attributed to storage tanks.
One of the primary causes of tank leakage is corrosion of the stor-
age tanks. Product loss from leaking tanks may cause an adverse effect
on the environment, endanger lives, reduce income, and require the ex-
penditure of millions of dollars for cleanup. To prevent or reduce the
adverse effects of gasoline leakage, an accurate method must be used to
determine whether or not an underground tank is leaking.
The 1984 Resource Conservation and Recovery Act (RCRA) amendments
regulate underground storage tanks containing petroleum products and
substances defined in Comprehensive Environmental Response,
Compensation, and Liability Act (CERCLA). RCRA regulations specify
release detection, prevention, and corrections and require a leak
detection system, an inventory control system, and a tank testing (or
equivalent system). States are also passing legislation and writing
regulations requiring both staged replacement of existing underground
tanks and installation of monitoring wells to detect leaks. Performance
standards for new tanks will be specified under RCRA and included in
various state regulations.
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REPORT OBJECTIVE
The objective of this report is to identify existing and developing
techniques to detect leaks in underground fuel storage tanks. This
objective is accomplished by a review of the manufacturer's description
of each method, its capabilities, and its claimed precision and
accuracy.
The variables affecting leak detection methods are introduced in
Section 5. This information should give the reader an understanding of
the major variables and their effects on the accuracy of various leak
detection methods. Section 6 presents a description of each detection
method based on the available literature from the manufacturer (or
practitioner). The descriptions in Section 6 of the manufacturer's
techniques for offsetting the effects on each detection method of these
major variables are based on information from the manufacturer's liter-
ature, reports, and/or verbal communications between the authors and the
staff of the manufacturer. This information was reviewed for correct-
ness by most of the manufacturers, practitioners, or developers of the
detection methods (instruments). Independent engineering evaluations of
error sources for each detection method are provided by the authors.
Finally, Tables 1 through 9 in Section 2 summarize the capabilities of
the leak detection methods. Information in these tables is primarily
from each manufacturer's description and, where noted, from the engi-
neering comments in Section 6. The appendix at the end of this report
provides the phone number and contact name of the manufacturer/
practitioner for each manufactured leak detection method.
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SECTION 2
SUMMARY
Existing and developing leak detection methods were reviewed, and
techniques for offsetting the effects of variables which affect accuracy
were evaluated. In Tables 1 through 9, general information, general
operational capabilities, and compensation for effects of variables dis-
cussed in this text are summarized for volumetric, nonvolumetric, and
other leak detection methods for underground storage tanks. Wherever it
is appropriate, in these summary tables, the information furnished is
based on engineering comments and not the manufacturer's claim.
To conduct this survey, the American Petroleum Institute (API) and
the Petroleum Equipment Institute (PEI) were contacted for assistance in
developing a comprehensive list of available detection methods. A
limited patent search was performed to identify methods currently being
developed, but not yet available commercially. In all, fifteen volu-
metric leak testing, seven nonvolumetric leak testing, three inventory
monitoring, and eleven leak effects monitoring methods were found.
The information on the following pages (Tables 1 through 9) is
based almost entirely on information provided by the manufacturers and
practitioners of the detection methods.
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TABLE 1. VOLUMETRIC LEAK DETECTION METHODS - GENERAL INFORMATION
Method
Description
1. Ainlay Tank Tegrity
Testing
2. ARCO HTC Underground
Tank Leak Detector
3. Certi-Tec Testing
4. "Ethyl" Tank Sentry
5. EZY-CHEK Leak Detector
6. Fluid-Static (Stand-
pipe) Testing
Principle
• Pressure measurement by
a coil type manometer,
determine product level
change in a propane
bubbling system
• Level change measurement
by float and light sensing
system
• Monitors pressure changes
resulting from product
level changes
• Level change magnification
by a "J" tube manometer
Pressure measurement,
determine product level
change in an air bubbling
system
Pressurize a system by
a standpipe
Keep the level constant
by product addition or
removal
Measure rate of volume
change
Claimed Accuracy Calibration
(gal/hr) During Test
0.02
0.05
0.05
Sensitive to
0.02 inches
level change
Less than 0.01
Gross
Yes
Yes
No
No
Yes
No
Cost of
Testing*
$225/day + Exp.
3 tanks/day (8)
$300/tank (17)
$300/tank (19)
Low
Single Tank
Preparation
for Test
Fill a tank evening
before a test
Adjust the level at
66-76 percent
None
No deliveries 24
hours prior to a
test
Fill up four hours
prior to a test,
usually test at
night
Fill the tank prior
to a test
(continued)
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TABLE 1 (continued)
Method
Description
Principle
Claimed Accuracy Calibration Cost of
(gal/hr) During Test Testing*
Single Tank
Preparation
for Test
7.
Heath Petro Tite Tank
and Line Testing (Kent-
Moore)
8.
9.
Helium Differential
Pressure Testing
Leak Lokator Test
Hunter-Formerly
Sunmark Leak
Detection
• Pressurize a system by a
standpipe
• Keep the level constant
by product addition or
removal
• Measure volume change
• Product circulation by
pump
• Leak detection by differ-
ential pressure change in
an empty tank
• Leak rate estimation by
Bernoulli's equation
• "Principle of Buoyancy"
The apparent loss in
weight of any object
submerged in a liquid
is equal to the weight
of the displaced volume
of liquid
Less than 0.05
Yes
$75/1,000 gal (21)
Less than 0.05
0.05 even at
product
level at
the center
of a tank
No
Yes
$500/tank (25)
Fill the tank prior
to a test
Seal the ports to
the atmosphere,
empty the tank
Typically fill the
tank before testing
(if it is possible
to fill a tank by
the product)
10. Mooney Tank Test
•Detector
11. PACE Tank Tester
• Level change measurement 0.02
with a dip stick
• Magnification of pressure Less than
change in a sealed tank 0.05
by using a tube and based
on manometer principle
Yes
Yes
$250/tank (27)
Not Commercial
Fill the tank 12-14
hours prior to a
test
• Fill the tank 12
hours prior to a
test
• Seal all the ports
except fill pipe
(continued)
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TABLE 1 (continued)
Method
Description
Principle
Claimed Accuracy Calibration Cost of
(gal/hr) During Test Testing*
Single Tank
Preparation
for Test
12. PALD-2 Leak Detector
13. Pneumatic Testing
14. Tank Auditor
15. Two-Tube Laser Inter-
ferometer System
• Pressurize system with
nitrogen at three dif-
ferent pressures
• Level measurement by
an electro-optical
device
• Estimate leak rate
based on the size of
leak and pressure
difference across the
leak
• Pressurize system with
air or other gas
• Leak rate measurement
by change in pressure
• "Principle of Buoyancy"
Less than 0.05
No
Not commercial
Level change measurement
by laser beam and its
reflection
Gross
0.00001 in the
fill pipe
0.03 at the
center of a
10.5-foot-
diameter tank
Less than 0.05
No
Yes
Low
Yes
Fill the tank 24
hours prior to a
test. All ports
must be hermetic-
ally sealed
Seal the ports
$400/tank None
Not Commercial None
^Charges could be negotiated with manufacturer for different numbers of tank testing and different tank specifications.
( )See References.
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TABLE 2. NONVOLUMETRIC LEAK DETECTION METHODS - GENERAL INFORMATION
Method
Description
oo
1. Acoustical Monitoring
System (AMS)
2.
Leybold-Heraeus Helium
Detector, Ultratest M2
3.
Smith & Denison Helium
Test
4.
TRC Rapid Leak Detector
for Underground Tanks
and Pipes
Principle
• Sound detection of
vibration and elastic
waves generated by a
leak in a pressurized
system by nitrogen
• Triangulation tech-
nique to detect leak
location
• Rapid diffusivity of
helium
• Mix a tracer gas, with
products at the bottom
of the tank
• Detect helium by a
sniffer mass spec-
trometer
• Rapid diffusivity of
helium
• Differential pressure
measurement
• Helium detection out-
side a tank
• Rapid diffusion of
tracer gas
• Mix a tracer gas
with product
• Detect tracer gas
by a sniffer mass
spectrometer using
a vacuum pump
Claimed Accuracy
(gal/hr)
Does not provide
leak rate
Detect leak as
low as 0.01 gal-
lons per hour
Calibration
During Test
Cost of
Testing*
Does not apply Not commercial
Single Tank
Preparation
for Test
Seal all ports
prior to a test
Does not apply By contractor
• Does not provide
leak rate
• Helium could leak
through 0.005 inches
leak size(38)
Provide the maxi- Does not apply By contractor
mum possible leak
based on the size
of the leak (does
not provide leak
rate)
Helium could leak
through 0.005 inches
leak size
• Seal all ports
prior to a test
• Monitoring holes
• Seal all ports
• Monitoring holes
Does not provide
leak rate
Tracer gas could
leak through
0.005 inches leak
size (38)
Does not apply By contractor
Seal all ports
prior to a test
Monitoring holes
(continued)
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TABLE 2 (continued)
Method
Description
5. Ultrasonic Leak
Detector (Ultrasound)
6. VacuTect (Tanknology)
7. Varian Leak Detector
(SPY2000 or 938-41)
Principle
Vacuum the system
(5 psi)
Scanning entire tank
wall by Ultrasound
device
Note the sound due
to leak by head-
phones and register
on a meter
• Vacuum application at
higher than product
static head
• Detect bubbling noise
by hydrophone
• Estimate approximate
leak rate by experi-
ence
• Similar to Smith &
Denison
Claimed Accuracy
(gal/hr)
Does not provide
the leak rate
A leak as low as
0.001 gallons per
hour of air could
be detected
A leak through
0.005 inches
could be
detected
Provide approxi-
mate leak rate
Similar to Smith
& Denison
Calibration
During Test
Cost of
Testing*
Does not apply Not commercial
Single Tank
Preparation
for Test
Seal all ports
Empty the tank
Does not apply $500/tank (44)
Seal all ports
Does not apply By contractor
• Seal all ports
• Monitoring holes
Charges could be negotiated with manufacturer for different numbers of tank testing and different tank specifications.
( )See References.
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TABLE 3. OTHER LEAK DETECTION METHODS - GENERAL INFORMATION
Description
Method
Principle
Claimed
Accuracy
Calibration
During
Testing
Cost of
Testing*
Single Tank
Preparation
for Test
I-1
O
Inventory Monitoring
1. Gage Stick
2.
MFP-414 TLG Leak
Detector
3. TLS-150
0 Product level measur- Gross
ment with dip stick
during station's close
time
• Product weight monitor- Sensitive to 0.1
ing by pressure and percent of product
density measurement at height change
the top, middle, and
bottom of tank
• Electronic level
measurement device
• Programmed micro-
processor inventory
system
Leak Effect Monitoring
1. Collection Sumps •
2. Dye Method
Collection mechanism
of product in collec-
tion sump through
sloped floor under
the storage tank
• Hydrocarbon detection
through perforated
pipe by soluble dye
Sensitive to 0.1
inches level
change
Does not provide
leak rate
Does not provide
leak rate
No
No
No
3. Ground Water and • Water and soil sampling Does not provide
Soil Sampling leak rate
4. Interstitial
Monitoring in
Double-Walled
Tanks
5. L.A.S.P.
• Monitoring the inter-
stitial space between
the walls of double-
walled tanks using
vacuum or fluid
sensors
• Diffusion of gas and
vapor to a plastic
material
Does not provide
leak rate
Does not provide
leak rate
No
No
Does not
apply
No
Does not
apply
Minimal
$5,000-$6,000
(equipment
cost)
$5,000 (equip-
ment)
Provided by
contractor
Provided by
contractor
Provided by
contractor
By tank manu-
facturer
Provided by
contractor
None
None
None
None
None
None
None
None
(continued)
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TABLE 3 (continued)
Method
Description
6. Observation
Wells
7. Pollulert and
Leak-X
8. Remote Infrared
Sensing
9. Surface Geo-
physical Methods
10. U-Tubes
Principle
• Product sensing in
liquid through moni-
toring wells at areas
with high ground water
Claimed
Accuracy
Does not provide
leak rate
• Difference in thermal Does not provide
conductivity of water leak rate
and hydrocarbon through
monitoring wells
« Determine soil tempera- Does not provide
ture characteristic leak rate
change due to the
presence of hydrocar-
bons
11. Vapor Wells
• Hydrocarbon detection
by ground penetrating
radar, electromagnetic
induction, or resis-
tivity techniques
• Product sensing in
liquid
• Collection sump for
product directed
through a horizontal
pipe installed under
a tank
• Monitoring of vapor
through monitoring
well
Does not provide
Leak rate
Does not provide
leak rate
Does not provide
leak rate
Calibration
During
Testing
No
Does not
apply
Does not
apply
Does not
apply
No
No
Cost of
Testing*
Provided by
contractor
Provided by
contractor
Provided by
contractor
Provided by
contractor
Provided by
contractor
Provided by
contractor
Single Tank
Preparation
for Test
None
None
None
None
None
None
Charges could be negotiated with manufacturer for different numbers of tank and different tank
specifications.
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TABLE 4. VOLUMETRIC LEAK DETECTION METHODS - GENERAL CAPABILITIES
Description
Method
1. Ainlay Tank Tegrity
Testing
2. ARCO HTC Underground
Tank Leak Detector
3. Certi-Tec Testing
4. "Ethyl" Tank Sentry
Testing
5. EZY-CHEK Leak Detector
6. Fluid-Static (Stand-
pipe) Testing
7. Heath Petro Tite Tank
and Line Testing (Kent-
Moore Testing)
8. Helium Differential
Pressure Testing
9. Leak Lokator LD2000
Test (Hunter-Formerly
Sunmark Leak Detection)
Detects
Leak
In /Out
Both
Both
Both
Both
Both
Both
Both
Both
Both
Differentiates
Leak in Piping
or Tank
Yes
Yes
Yes
Tank Testing
Yes
Ho
Yes
No
Yes
Tests Single
or Multiple
Tanks
2
4
2
1
2
1
4
1
3
Has Potential
for Printed
Readout
No
Yes
Yes
No
Yes
No
No
Yes
Yes
Tests at
Pressure not
Greater than
5 PSIG
Yes
Yes
Yes
Yes
Yes
Yes
Sometimes No
Yes
Yes
Detects Leak
Only Below
Normal High
Fill Level
No
Yes
No
Yes
No
No
No
No
No
Total
Downtime
for Testing
10-12 hours (filled
a night before 1.5
hours testing)
4-6 hours
4-6« hours
Typically 10 hours
4-6a hours (2 hours
waiting after fill up,
1 hour test)
Several days
6-8 hours
Minimum 48 hours
3-4 hours
Requires
Empty/Full
Tank for Test
Full
No
Full
No
Full
Full
Full
Empty
Typically full
(continued)
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TABLE 4 (continued)
Description
Method
10. Mooney Tank Test
Detector
11. PACE Tank Tester
12. PALD-2 Leak Detector
13. Pneumatic Testing
14. Tank Auditor
15. Two-Tube Laser Inter-
ferometer System
Detects
Leak
In/Out
Both
Both
Both
Differentiates
Leak in Piping
or Tank
Yes
Tank Testing
No
Tests Single
or Multiple
Tanks
3
1
1
Has Potential
for Printed
Readout
No
No
Yes
Tests at
Pressure not
Greater than
5 PSIG
Yes
Yes
No
Detects Leak
Only Below
Normal High
Fill Level"
No
Yes
No
Total
Downtime
for Testing
14-16 hours (12-14
hours waiting after
fillup, 1-2 hour test)
14 hours
14 hours (preferably
Requires
Empty/Full
Tank for Test
Full
Full
Full
Both
Both
Both
No
Yes
Yes
No Try to keep below No
5 psi but some
times exceeds
5 psi
Yes Yes No
Yes Yes No
a day before, 1 hour
fill testing, include
sealing time)
Several hours
1.5-3 hours
4-5b hours
No
Typically full
No (at existing
level)
alncluding the time for tank end stabilization with testing with standpipe.
''Including 1 to 2 hours for reference tube temperature equilibrium.
-------
TABLE 5. NONVOLUMETRIC LEAK DETECTION METHODS - GENERAL CAPABILITIES
Method
Description
1. Acoustical Monitor-
ing System (AMS)
2. Leybold-Heraeus
Helium Detector,
Ultratest M2
3. Smith & Denison
Helium Test
4. TRC Rapid Leak
Detector for Under-
ground Tanks and
Pipes
5.
Ultrasonic Leak
Detector (Ultra-
sound)
6. VacuTect (Tank-
no logy)
7. Varian Leak Detector
(SPY200Q or 938-41)
Detects Leak
In/Out
Does not
differentiate
Does not
differentiate
In a 24-
hour test
Does not
differentiate
Does not
differentiate
Differentiates
In a 24-
hour test
Differentiates Tests Has Tests at Detects Leak
Leak in Single or Potential Pressure not Only Below
Piping Multiple For Printed Greater Normal High
or Tank Tanks Readout Than 5 PSIG Fill Area
No
Partially
Yes
Yes
Partially
Several
Partially 1
Partially Several
Several
Yes
Yes
Yes
Yes
Yes
Yes
Yes
Ho
Yes
Yes
Yes
Vacuum
Vacuum
Yes
Yes
No
No
No
No
No
No
Total
Downtime
for Testing
1-2 hours
Requires
Empty/Full
Tank for Test
No
None No
Few-24 hours (exclude Empty
sealing time)
None No
Few hours (including Empty
tank preparation and
20-minute test)
1 hour No
Few-24 hours (exclude Empty
sealing time)
-------
TABLE 6. OTHER LEAK DETECTION METHODS - GENERAL CAPABILITIES
Method Description
Inventory Monitoring
1. Gage Stick
2. MFP-414 TLG Leak
Detects Leak
In/Out
Both
Both
LieaK in
Piping
of Tank
No
No
aingie or
Multiple
Tanks
Single
6
rotentiai
for Printed
Readout
No
Yes
treasure not
Greater
than 5 PSIG
Yes
Yes
unty oe
Normal 1
Fill Ai
Yes
Yes
Detector
3. TLS-150
Tank Level Sensor
(Veeder-Root)
Both
No
Yes
Yes
Yes
Total
Requires
Downtime _ / /_ ,,
.. „ . Empty/Full
for Testing _ , .- _,
„ . ° Tank for Test
Testing
Variables No
None No
None
No
Leak Effect Monitoring
Out
No
Severalb
Yesc
Does not apply Does not apply
None
No
aAt the station's close of business and again at start of day.
Except Interstitial Monitoring in double-walled tank and U-Tubes which are used for single tank monitoring.
cExcept Dye Method.
-------
TABLE 7. VOLUMETRIC LEAK DETECTION METHODS - COMPENSATION FOR EFFECTS OF VARIABLES*
2.
3.
4.
5.
Variable
;hod
Ainlay Tank
Tegrity Testing
ARCO HTC Under-
ground Tank Leak
Detector
Certi-Tec Testing
"Ethyl" Tank
Sentry Testing
EZY-CHEK Leak
Detector
Temperature
• 3 temperature
sensors
• 0.01 °F
accuracy
Not affected
by temperature
change
• 5 or more
temperature
sensors
• 0.01°F
accuracy
Thermometer
measurement at
the beginning
and end of a
test
• Averaging
temperature
coi 1
• 0.001 °F
accuracy
Ground Water
Masking
May conduct
testing when the
leak is com-
pletely masked*
May conduct
testing when
the leak is
completely
masked*
Conduct test by
standpipe if
water table is
suspected
May conduct test
while the leak
is completely or
partially masked
by variations of
the tank1 s in-
ternal forces
due to tempera-
ture and pres-
sure changes
Conduct test by
standpipe if
water table is
suspected
Tank End
Deflection
• Overnight
waiting after
tank fill up
t If tank is
filled one
hour before
testing, the
tank deflec-
tion is recog-
nized by eval-
uation of
test results
• No effect
(since the
test is con-
ducted at
normal
conditions)
• Test contin-
ues to obtain
equal leak at
two consecu-
tive tests
Recognized by
test results
evaluation
No product
delivery 24
hours prior to
a test
Recognized by
test results
evaluation
Vapor
Pockets
If the vapor
pocket is recog-
nized, the tank
top will be
excavated and
the vapor is
removed by
drilling
Not applicable
• Not applicable,
when the test
is conducted
below the fill
pipe
• Using stand-
pipe to
stabilize
vapor pocket
Not applicable
• Could be re-
leased by a
float tube
• Using stand-
pipe to
stabilize
vapor
pocket
Product
Evaporation
• Use propane
gas to reduce
evaporation
• 20-minute
testing
(short test-
ing inter-
vals)
Saturate the
vapors on top
of product
before test
by circula-
tion of prod-
uct
No compensation
when the test
is performed
without the
standpipe
(long testing)
No compensation
during 10-hour
testing
• The testing
time is short
• Overnight
testing
(usually)
• Could use
standpipe to
reduce
evaporation
Wind
Not
cora-
pen-
sat-
ed+
Par-
tial-
ly
com-
pen-
sated*
Par-
tial-
ly
com-
pen-
sat-
ed+
Not
af-
fect-
ed
Par-
tial-
ly
com-
pen-
sated
by
print-
ed re-
sult
eval-
tion*
(continued)
16
-------
TABLE 7 (continued)
Vibra-
tion '
Not
conr
pen-
sat-
ed+
Par-
tial-
ly
com-
pen-
sated*
Par-
tial-
i n
ly
com-
pen-
sat-
ed+
Noise
Not
af-
fect-
ed
Not
af-
fect-
ed
Not
af-
ed
Tank
Geome-
try
• Not
corn-
pen
sated
for
temp-
era-
ture
com-
pensa-
tion
• Re-
duced
by cali-
bration*
Not af-
fected
Not com-
pensated
perature
compensa-
tion*
Instrumentation Operator
Limitation Error
Leak rate meas- Insignifi-
urement when cant
the volume
change is less
than 0.06 gal-
lons during
testing*
No limitation Insignifi-
for typical cant
tank testing
(4-inch fill
pipe)
No limitation Insignifi-
for typical cant
(4-inch fill
pipe)
Atmospheric Inclined
Pressure Tank
Not affected By cali-
bration
Not affected By cali-
bration
Not affected • Compen-
sated
when
tests
by
stand-
pipe
• Not com-
pensated
Power
Variation
Not affected
Not compen-
pensated
Not compen-
sated
when tests
below
fill pipe
Not
af-
fect-
ed
Par-
tial-
ly
corn-
pen
sated
by re-
sult
eval-
uation
and /or
by us-
ing
stand-
pipe*
Not
af-
fect-
ed
Not
af-
fect-
ed
Not com-
pensated
for leak
volume
calibra-
tion*
Not com-
pensated
for tem-
perature
compen-
sation*
• No limitation Insignifi-
for typical cant
tank testing
(4-inch fill
pipe)
f Minimum 20
inches of
product
No limitation Insignifi-
for typical cant
tank testing
(4-inch fill
pipe)
Not affected Not com-
pensated
Mot affected By cali-
bration
Not affected
Not affected
(continued)
17
-------
TABLE 7 (continued)
Variable
Method
6.
7.
8.
9.
10.
Fluid-Static
(Standpipe
Testing)
Heath Petro
Tite Tank and
Line Testing
(Kent-Moore
.Testing)
Helium Differ-
ential Pressure
Testing
Leak Lokator
LD2000 Test
(Hunter-
Former ly
Sunmark Leak
Detection)
Mooney Tank
Test Detector
Temperature
No compensation
• One tempera-
ture sensor
• 0.003 °F
accuracy
• Product cir-
culation
Use reference
tube
• One tempera-
ture sensor
at midvolume
• 0.001 °F
accuracy
• Three temper-
ature sensors
at unusual
conditions
• Five tempera-
ture sensors
• 0.001 °F
accuracy
Ground Water
Masking
Tests by stand-
pipe
Tests by stand-
pipe
May conduct test
while the leak
is completely or
partially masked
by variation of
the tank1 s
internal forces
due to pressure
changes
May conduct
testing when the
leak is com-
pletely masked*
May conduct
testing when
the leak is
completely
masked*
Tank End
Deflection
No compensation
Stops the end
deflection
within 2 hours
by test results
evaluation
Test is con-
ducted within
48 hour s
• The end
deflection
occurs imme-
diately after
fill up
• 1.5 hours
waiting for
temperature
adjustment
Tests 12 to 14
hours after
filling
Vapor
Pockets
No compensation
The presence of
vapor pockets is
recognized by
observing
bubbles in the
standpipe
Not applicable
• Compensate if
the pocket is
released
• Not affected
during in-
tank testing
No compensation
Product
Evaporation
Not compensated
The graduate
top is capped
Not applicable
Compensated by
a hollow
sensor filled
with product
Compensated by
using an evapo-
ration cup
Wind
Not
af-
fect-
ed
Not
af-
fect-
ed
Not
af-
fect-
ed
Par-
tial-
ly
com-
pen-
sat-
ed*
Not
com-
pen-
sat-
ed*
(continued)
18
-------
TABLE 7 (continued)
Vibra-
tion
Not
af-
fect-
ed
Not
af-
fect-
ed
Not
af-
fect-
ed
Noise
Not
af-
fect-
ed
Not
af-
fect-
ed
Not
af-
fect-
ed
Tank
Geome-
try
Not af-
fected
Not com-
pensated
for t em-
perature
compensa-
tion'1'
Not com-
pensated*
Instrumentation
Limitation
No limitation
for typical
tank testing
(4-inch fill
pipe)
No limitation
for typical
tank testing
(4-inch fill
pipe)
No limitation
for typical
tank testing
(4-inch fill
pipe)
Operator
Error
Insignifi-
cant
Insignifi-
cant
Signif icanl
potential
( inc ludtng
improper
sealing)*
Atmospheric Inclined Power
Pressure Tank Variation
Compensated
Not affected
Not af-
fected
By cali-
bration
Not affected Not af-
fected
Not affected
Not affected
Not compen-
sated
Par-
tial-
ly
com-
pen-
sat-
ed+
Not
af-
fect-
ed
Not com-
pensated
for tem-
perature
compensa-
tion*
Sometimes due
to tank inclin-
ation*
Insignifi-
cant
Compensated
By cali-
bration
No t compen-
sated
Not
com-
pen-
sat-
ed*
Not
af-
fect-
ed
Not com-
pensated
for tem-
perature
compensa-
tion*
No limitation
for typical
tank testing
(4-inch fill
pipe)
Insignifi-
cant
Not affected
By cali-
bration
Not affected
(continued)
19
-------
TABLE 7 (continued)
Variable
Method
Temperature
Ground Water
Masking
Tank End
Deflection
Vapor
Pockets
Product
Evaporation
Wind
11. PACE Tank
Tester
12. PALD-2 Leak
Detector
• Three
Thermo-
couples
• O.Ol'F
accuracy
Due to short
testing time
May conduct
testing when the
the leak is
completely
masked
Tests at least
at three dif-
ferent pres-
sures
Tests 12 hours
after filling
The effect is
minimized hy
short testing
time (15 min.)
Not applicable
Must be rele
at any cost
Compensated
in calculation
sed Not applicable
Not
com-
pen-
sat-
ed
Not
af-
fect-
ed
14.
15.
Pneumatic
Testing
Tank Auditor
Two-Tube Laser
Interferometer
System
No compensa- May conduct test
tion while the leak
is masked com-
pletely or par-
tially by varia-
tion of tank1 s
internal forces
due to tempera-
ture or pressure
changes
Use reference The test is
tube performed at two
different levels
Use reference If the test
tube shows no leak,
the complete
masking effect
could be checked
by changing the
product level
The effect is
reduced when
the testing
time is in-
creased
Test at normal
operating condi-
tions or 3 to
6 hours after
delivery
Test at normal
operating con-
ditions
Not applicable
• Not compen-
sated during
testing in a
filled tank
• Not applicable
during in-tank
testing
Not applicable
during in-tank
testing
Not applicable
Not
af-
fect-
ed
• Short testing Com-
• Compensated pen-
by tempera- sated*
ture probe
• Short testing Com-
• Compensated pen-
sated by sated
reference
tube
(continued)
20
-------
TABLE 7 (continued)
Vibra-
tion ,
Noise
Tank
Ge ome-
try
Not Not Compensa-
af- af- ted by
feet- feet- calibra-
ed ed tion
Instrumentation Operator Atmospheric Inclined
Limitation Error Pressure Tank
Thermocouple
accuracy
Insignifi- Compensated Not af-
cant fected
Power
Variation
Not affected
Not Not Not
com- af- af-
pen- feet- feet-
sated ed ed
Not Not Not
af- af- af-
fect- feet- fect-
ed ed ed
No limitation
for typical
tank testing
(4-inch fill
pipe)
No limitation
for typical
tank testing
(4-inch fill
pipe)
Significant
( inc luding
improper
sealing)*
Significant
(including
improper
sealing)*
Not affected Not compen-
sated
Not affected Not af-
fected
Not compen-
sated
Not affected
Not Not Cora-
corn- af-
pen- fect-
sated+ ed by
cal i-
pen-
sated
bration
Sometimes due
to tank in-
clination
Insigni f i-
cant
Not Affected By cali-
bration
Not compen-
sated
Com- No t
pen- af-
sated* feet-
ed
Corn-
pen-
sated
by
cali-
bration
Sometimes due
to tank in-
clination*
Insignifi-
cant
Compensated
Compen-
sated
Not compen-
sated
The type of liquid petroleum fuel does not affect any nonvolumetric leak detection method except
the accuracy of reading of tests using "Ethyl" Tank Sentry may or may not be affected by oxygenates
t a I "nV.nl ^
(alcohol).
+Based on the engineering comments.
21
-------
TABLE 8. NONVOLUMETR1C LEAK DETECTION METHODS - COMPENSATION FOR EFFECTS OF VARIABLES*
Variable
Method
_ Ground Water
Temperature .. . .
r Masking
Tank End Vapor
Deflection Pockets
Product
Evaporation
. ,
Acoustical Moni-
toring System
(AMS)
Not affected Compensated
Not affected Not appli-
cable
Not appli-
cable
Not af-
fected
2.
Leybold-Heraeus
Helium Detector,
Ultratest M2
Not affected
Compensated
if aware of
water table
Not affected Not appli-
cable
Not appli-
cable
Not af-
fected
3.
Smith & Denison
Helium Test
By using Compensated
reference tube if aware of
for leak rate water table
approximat ion
Not affected Not appli-
cable
Not appli-
cable
Not af-
fected
4.
TRC Rapid Leak
Detector for
Underground
Tanks and Pipes
Not affected
Compensated
if aware of
water table
Not affected Not appli-
cable
Not appli-
cable
Not af-
fected
5.
Ultrasonic Leak
Detector, Ultra-
Not affected
Compensated
by vacuum
Not affected Not appli-
cable
Not appli-
cable
Not af-
fected
6.
VacuTect (Tank-
nology)
Not affected
Compensated
by vacuum
Not affected Not appli-
cable
Not appli-
cable
Not af-
fected
7.
Varian Leak
Detector
(SPY 2000
or 938-41)
By using re-
ference tube
for leak rate
approximation
Compensated
if aware of
water table
Not affected
Not appli-
cable
Not appli-
cable
Not af-
fected
(continued)
22
-------
TABLE 8 (continued)
Vibration Noise
Not affected Not af-
fected
Not affected Not af-
fected
Not affected Not af-
fected
Not affected Not af-
fected
Not affected Not af-
fected
Not affected Not af-
fected
Not affected Not af-
fected
Tank
Geometry
Not af-
fected
Not af-
fected
Not af-
fected
Not af-
fected
Not af-
fected
Not af-
fected
Not af-
fected
Instrumen- _
tatlon
T . . at or
Limita- +
Error
tion
None Signifi-
cant (in-
cluding
improper
sealing)
None Signifi-
cant (in-
cluding
improper
sealing)
None Signifi-
cant (in-
c luding
improper
sealing)
None Signifi-
cant (in-
c luding
improper
sealing)
None Signifi-
cant (in-
cluding
improper
sealing)
None Signifi-
cant (in-
cluding
improper
sealing)
None Signifi-
cant (in-
c luding
improper
sealing)
Atmo-
spheric
Pres-
sure
Not af-
fected
Not af-
fected
Not af-
fected
Not af-
fected
Not af-
fected
Not af-
fected
Not af-
fected
Inc lined
Tank
Not af-
fected
Not af-
fected
Not af-
fected
Not af-
fected
Not af-
fected
Not af-
fected
Not af-
fected
Power
Variation
Not af-
fected
Not af-
fected
Not af-
fected
Not af-
fected
Not af-
fected
Not af-
fected
Not af-
fected
The type of a liquid petroleum fuel does not affect any nonvolumetric detection methods.
+Based on the engineering comments.
23
-------
TABLE 9. OTHER LEAK DETECTION METHODS - COMPENSATION FOR EFFECTS OF VARIABLES*
Variable
Method
Temperature
Ground Water
Masking
Tank End
Deflection
Vapor
Pockets
Product
Evaporation
Wind
Inventory Control:
1. Gage Stick
2. MFP-414 TLG
Leak Detector
Not comp-
sated
Not affec-
ted
Not com-
pensated
By perma-
nent moni-
toring
By permanent Not appli- Not corapen- Not corn-
monitoring cable sated pensated
By permanent Not appli- Not compen- Not af-
monitoring cable sated fected
3.
TLS-150 Tank
Level Sensor
(Veeder-Root)
One tempera-
ture sensor
By perma-
nent moni-
toring
By permanent Not appl-
monitoring cable
Not compen-
sated
Not af-
fected
Leak Effects Moni-
Not appli-
cable
Not appli-
cable
Not appli-
cable
Not appli-
cable
Not appli-
cable
Not ap-
plicable
(continued)
24
-------
TABLE 9 (continued)
Vibration
Instrumen-
Tank tation
Geometry Limita-
tion
Oper-
ator
Error
Atmo-
spheric
Pres-
sure
Inclined
Tank
Power
Variation
Insig-
nificant
Not af-
fected
Not com-
pensated
Not af-
fected
Not com-
pensated
Not com-
pensated
Not ap-
plicable
Not com-
pensated
Not corapen- Not ap- Not com- None
sated pi icable pensated
Not affected Not af- Not com- None
fee ted pensated
for tem-
perature
compensa-
tion"1"
Not affected Not af- Not com- None
fected pensated
for tem-
perature
compensa-
tion*
Not ap- Not ap- Not ap- Not appli- Not ap- Not ap- Not ap-
plicable plicable plicable cable plicable plicable p lie able
Not af-
fee ted
Not af-
fected
Not com-
pensated
Not com-
pensated
Not com-
pensated
*The type of a liquid petroleum fuel does not affect the detection methods.
on the engineering comments.
+Based on the engineering comments.
25
-------
SECTION 3
CONCLUSIONS
The conclusions listed below are based on the review of leak
detection methods described in this report.
1. Variables affect the testing results of available or developing
volumetric, nonvolumetric, and in-tank monitoring methods used
for leak detection of underground tank systems. These vari-
ables are potential sources of errors in using the detection
methods successfully. The importance of each variable may vary
due to the characteristics of the tank being tested and to such
test conditions as the temperature of additional product used
to fill a tank prior to testing, depth of the water table, tank
deformation, random variation of ambient temperature or pres-
sure, tank inclination, product vapor pressure, and tank age.
2. The 36 methods identified include 15 volumetric leak detection,
7 nonvolumetric leak detection, 3 in-tank monitoring, and 11
leak effects monitoring methods.
3. Detection methods attempt to compensate for variables affecting
accuracy in various ways.
4. Available data on the performance evaluation of the leak
detection methods reviewed were not adequate to determine their
relative accuracy.
26
-------
SECTION 4
RECOMMENDATIONS
The accuracy and precision of volumetric leak detection methods
(at least) should be determined in order to permit selection of the ones
appropriate to any specific need. A cost-effective procedure is to make
use of signal/noise theory and a high quality data base to estimate the
likely performance of each method under a variety of representative con-
ditions, and to verify performance by evaluating the method under a few,
selected, controlled conditions in a full-scale test apparatus.
27
-------
SECTION 5
VARIABLES AFFECTING LEAK DETECTION METHODS
The capability of leak detection methods to accurately measure
rates of leakage is affected by variables, as well as the detection
method itself. The principal variables and the way they affect accuracy
are discussed in this section. This discussion of variables precedes
the description of leak detection methods in Section 6 to provide back-
ground information important to an understanding of the detection
methods.
Principal variables which affect the accuracy of most of the avail-
able leak detection methods are:
Temperature Change
Water Table
Tank Deformation
Vapor Pockets
Product Evaporation
Piping Leaks
Tank Geometry
Wind
Vibration
Noise
Equipment Accuracy
Operator Error
Type of Product
Power Variation
Instrumentation Limitation.
Atmospheric Pressure
Tank Inclination
The effects attributable to variables upon the ability to conduct leak
detection tests for different detection methods are discussed in this
section. The current methods used to compensate for the variables are
discussed in Section 6 of this report.
VOLUMETRIC LEAK DETECTION TESTS
Volumetric leak detection tests identify the leak or determine leak
rate based on the measurement of properties associated with a change in
volume. Certain variables affect the volume change or the measurement
of the volume change.
28
-------
DRIVEWAY
MANHOLE FILL PIPE
LIQUID IN BOTTOM
>/2 OF TANK-590 .
LOAD ADDED-590 :
3 PM 10 PM
61V4° ROSE TO 64°
TEMPERATURE
VARIATIONS
AFTER FILL-UP
3000 GAL. TANK (64* DIA.) END VIEW
Figure 1. Temperature Stratification (4)
Ref: Heath Consultants, Inc. Petro Tite Tank Test Bulletin
29
-------
CM
e
TO-
•0-
40'•
10
_._> DAILY AMBIENT (SURFACE AIR TEMP)
...... UNDERGROUND TANK
. DISPENSED PRODUCT
JPUAUJJASOMO
MOUTHS
Figure 2. Average Gasoline Temperature For All Test Stations (5)
Ref: API Publication No. 4278
30
-------
8
7
6
£
20* 21* 22* 23* 24* 25*
TEMPERATURE - °C
26°
Figure 3. Mean Temperature Distribution As A Function Of Depth For Four
Different 24-Hour Periods (5)
Ref: SRI International, Project 7637, Conducted for API
Technical Report 1, June 1979
31
-------
Illlllllllltllllll
' iiiiiiiiiiiiiiim
u>
ro
75OOCALS
7OOOCALS
TEMPERATURE
SENSOR UKATIONS
MIOTANK
MIO VOLUME
e
TIME IN HOURS
Figure 4. Tank Temperature Stratification And Gradients For A- 24-Hour
Period After Tank Fill Up (5)
Ref: SRI International, Project 7637, Conducted for API
Technical Report, June 1979
-------
TO CHART
RECORDER
AMBIENT
GROUND LEVa
SRI UNDERGROUND TANK
113. 5 in
78.5 GASOLINE LEVEL H • 85.5 in
67.5
44.5
21.5
10.5
2.5
Figure 5. Location Of Temperature Sensors In The SRI Tank (5)
Ref: SRI International, Project 7637, Conducted for API
Technical Report 1, June 1979
33
-------
Temperature F
DELIVERY TEMPERATURES
Service Station No. 379 Houston
Montrose at West Alabama
Temperature of Product in Underground Tank
Figure 6. Delivery Temperatures
Ref: Heath Consultants, Inc., Petro Tite Tank Tester Bulletin
Figure 6 shows the graphed temperature recordings for an entire year by
combining the results of 52 weekly graphs (4). The vertical lines,
either down or up, show the immediate effect of the delivery on the tank
temperature and the curving lines show the gradual return to underground
temperatures.
The graph also shows a seasonal change of 30 degrees Fahrenheit in
underground temperatures occurring even in south Texas. Much greater
differences between summer and winter would exist further north and
particularly in those areas of the country noted for hot summers and
cold winters.
Ref: Heath Consultants, Inc., Petro Tite Tank Tester Bulletin
-------
Temperature
Changes in temperature cause expansion, or contraction, in the
product and in tank dimensions. Due to the insignificant thermal
coefficient of expansion for steel (fiberglass has a higher thermal
expansion than steel) and existence of external factors (e.g., water
table and fill material physical effects), the thermal variation of the
tank cannot be measured during the occurrence of a leak and small
temperature changes. The product volume change can be measured because
it is much more sensitive to temperature change. When liquid is added
to fill a tank for testing, several days may be required before the
liquid stabilizes to ground temperature; however, ground temperature is
also constantly changing (and thus prevents stabilization of the
system's temperature). The rate of temperature change in the first day
or two after addition of liquid will generally be in the range of 0.02
to 0.25 degrees Fahrenheit per hour (3). Temperature changes occur
because of the following conditions (Figures 1 through 6) (4,5):
Hot days
Cool nights
Sunshine
Clouds
Rain
Water table
Type and compaction of fill material.
Two important temperature effects should be considered: volume
change and stratification. Gasoline has an expansion coefficient of
0.00068 gallons per degree Fahrenheit (Table 10) (4). To detect leaks
as small as 0.05 gallons per hour, a change of 0.01 degrees Fahrenheit
per hour in a 10,000-gallon tank may cause a 0.068-gallon change in the
product volume per hour, thus offsetting or amplifying an observed leak
rate. This temperature effect could be eliminated by accurate
temperature measurement. However, the stratification normally present
in underground tanks should also be considered. Stratification is due
to the variation of product temperature from the top to the bottom of
the tank. The top layer temperature may be several degrees higher than
the bottom layer. The layer temperatures usually change at different
rates at different levels, which makes the temperature measurement more
complicated.
Water Table
Hydrostatic head and surface tension forces caused by ground water
outside an underground storage tank may mask tank leaks partially or
completely. Such leaks may take the form either of product leaving the
tank or of ground water entering. When the forces are equal at two
sides of a leak opening before or during the testing period, a complete
masking effect occurs. The chance of this situation occurring increases
35
-------
TABLE 10. THERMAL EXPANSION OF LIQUIDS (4)
Ref: Heath Consultants, Inc., Petro Tite Tank Tester Bulletin
poonnrT VOLUMETRIC COEFFICIENT
TYPE OF PRODUCT Qp EXpANSION pER DEGREE p
Benzol (benzene) 0.00071
Diesel fuel 0.00045
Ethyl alcohol 0.00062
Fuel oil #1 0.00049
Fuel oil #2 0.00046
Fuel oil #3 0.0004
Gasohol
0.10 Ethyl + 0.90 Gasoline 0.000674
0.10 Methyl + 0.90 Gasoline 0.000684
Gasoline 0.00068
Hexane 0.00072
Jet fuel (FP 4) 0.00056
Kerosene 0.00049
Methyl alcohol 0.00072
Stove oil 0.00049
Tuluol (toluene) 0.00063
Water at 68°F 0.000115
These are average values and may vary. If there is any
doubt, the product should be checked with a hydrometer.
36
-------
when the testing method is performed on a tank which is not completely
filled and especially when no product is added or removed for testing.
The level of ground water may vary seasonally or because of intensity
and duration of rainfall. To evaluate the masking effect, the relation-
ship between the product level inside the tank and the ground water
level outside the tank system must be known.
Tank Deformation
Changes or distortions of the tank due to significant changes in
pressure or temperature can cause an apparent volume change in the
product. This is called the tank deformation effect (Figures 7 and 8)
and may be affected by the wetness and nonhomogeneous properties of
backfill material around the tank (4), the material of tank
construction, the thickness of the tank shell, the age of the tank, and
forces due to ground water level exerted on the tank. The tank
deformation effect is uncontrollable and different for every tank.
The construction of steel tanks is such that distortion effects of
the flat ends are generally much greater than that of the cylindrical
sides (the reverse is generally true for fiberglass tanks). The
pressure within a tank will vary with the specific gravity of the liquid
and the liquid height above the bottom of the tank. These pressures can
be computed for any height of the tank from Table 11 (4). The total
change of the force, in tons, at various pressure changes on each end of
a typical steel tank is shown in Table 12 (4).
In some methods for testing tanks with large diameters, the
stabilization time for tank end deflection may be more than 36 hours.
The stabilization time for deflection of an underground tank is
important because the apparent product volume loss caused by tank end
deflection cannot be measured and may mask the occurrence of a leak.
For example, in a 96-inch-diameter steel tank, the apparent loss of
product volume is 1.957 gallons for 1/16-inch tank end deflection. If
this volume change occurs within one hour and if it occurs during the
test period, it will offset the testing accuracy and the tank will
appear to be leaking. The magnitude of apparent volume change for
various deflections of a given size steel tank, when it is filled, can
be found in Table 13 (4), Figure 8 (5), or can be calculated from the
following formula (4):
2
VT =[ f (r2+| )h][2]
*j
where V^, = total volume change due to tank end deflections, in. ,
r = tank radius, in., and
h = deflection of tank end, in.
37
-------
Standpipa
•Pressure of liquid proportionate to
height of liquid in tank or standpip«.
_Heod when tank it
"empty.
-Head is forced out
in proportion to
internal pressure
from liquid.
Figure 7. Tank End Deflection (4)
Ref: Heath Consultants, Inc. Petro Tite Tank Tester Bulletin
38
-------
0.60
Tank Diameters
64" 72" 76" 84" 96" 102"
NOTE:
Deflection figures for 64" diameter
tank were measured using hydro-
static pressure on an above-ground
tank. All other data from tank
manufacturers.
I
PROBABLE END DEFLECTIONS
AND CAPACITY WHEN FILLED
TO GROUND LEVEL
Capacity, Thousand Gallons
Figure 8. Change in Tank Volume Due To Tank End Deflections - In Gallons (5)
Ref: Hunter Environmental Services, Inc., Leak Lokator LD2000
39
-------
Re£:
TABLE 11. PRESSURE-HEIGHT CHART (4), LBS/SQ. IN.
Heath Consultants, Inc., Petro Tite Tank Tester Bulletin
PRESSURE - HEIGHT CHART
Height Gasoline Kerosene Fuel Oil Water
1 In.
2 In.
3 In.
4 In.
5 In.
6 In.
7 In.
8 In.
9 In.
10 In.
11 In.
1 Ft.
2 Ft.
3 Ft.
4 Ft.
5 Ft.
10 Ft.
15 Ft.
Water
Gasoline
Kerosene
Fuel Oil
.026
.053
.079
.105
.132
.158
.188
.211
.237
.264
.290
.316
.632
.949
1.265
1.581
3.162
4.744
Specific
1.00
.73
.81
.85
.029
.058
.088
.117
.146
.175
.209
.234
.263
.292
.322
.351
.702
1.053
1.404
1.754
3.509
5.263
Gravity
at62°F.
.031 .036
.061 .072
.092 .108
.123 .144
.153 .181
.184 .217
.219 .258
.245 289
.276 .325
.307 .361
.338 .397
.368 .433
.736 .866
1.105 1.300
1 .473 1 .733
1.841 2.166
3.682 4.332
5.523 6.498
API Gravity
Typical
62.3) gravity
43.2) readings
35.0) varV wit^
grade and
season.
TABLE 12. TOTAL FORCE ON TANK ENDS (4)
FORMULA: FORCE = (AREA) X (PRESSURE) (LBS/SQ. IN.)
TOTAL FORCE IN TONS AT:
Ref: Heath Consultants Inc.. Petro Tite Tank Tester Bulletin
Took Dio.
1 Pti. 2 Psi. 3 Psi. 4 Psi. 5 Psi.
48"
64"
72"
84"
96"
0.9
1.6
2.0
2.8
3.6
1.8
3.2
4.0
5.6
7.2
2.7
4.8
6.0
8.4
10.8
3.6
6.4
8.0
11.2
14.4
4.5
8.0
10.0
14.0
18.0
40
-------
TABLE 13. APPARENT LOSS OF PRODUCT VOLUME (4)
DUE TO FORCE ON TANK ENDS - IN GALLONS
Ref: Heath Consultants, Inc., Petro Tite Tank Tester Bulletin
APPARENT LOSS OF PRODUCT VOLUME DUE TO FORCE
OH TAMK ENDS - IN GALLONS
END DEFLECTION IN INCHES
'/..
41*
172
1 227
1 M
1 »17
121
•10»-
317
%
»•
1.74
24*
100
1*1
442
-* 12-
475
'*.
1 47
2*1
III
1M
410
J»7
**1
-» II-
1012
%
1 »i
V
14>
441
4*1
too
712
1*1 '
-1221-
1100
Vu
244
"A-
S"
111
.,,N
730
»77
ii at
-1510-
1611
%
2*1
I 22
**2
\'»
^
II 71
11.10
-II 1»-
20.1
Vu
^>
4I«
7.72
1*0
1010
1^7.
11.10
-21 40-
211
%
^
^
*.»7
1.12
*.ll
1200
ll.*l
U770
*v
-2410-
270
X-
\
%
E "1"
X
II 01
1227
1100
1*17
2220
-MM-
.1171
% 'A I 1% I'A ,.A
N
X
1*00
2110
2**0
401
"A"
"B"
x^
^s
Probable
Limit of
•21 00
2740
11 00
472
X
Limit of tank end deflection capacity
increase
Maximum tank end deflection capacity
increase
2400
si,*,
35 40"
140
X
1*10
s
"X
*07
X
4750
•/..'
1100
. Su.l
V."
»*-
102"
120"
12*"
Maximum Deflection Figures are Preliminary based on limited data
from Tank Manufacturers and completely fluid soil conditions
Measurements were made with air pressure above ground
-------
Vapor Pockets
Vapor pocket effects may offset the test results obtained via
methods which require the tank to be overfilled. This effect increases
when rapid changes in ambient pressure or temperature occur during the
test period. Basically, three types of vapor pockets are possible: one
that forms in the high end of a tank when the tank is not perfectly
level, one that is trapped in the top of the manway, and one that is
trapped at the top of a drop line (Figure 9) (5). The vapor pocket may
release due to a pressure decrease or temperature increase and lead to
inaccurate leak test results. Even if the vapor pocket is not released
during the test, a change in its temperature or pressure will cause a
change in its volume, thus leading to an inaccurate test result.
Therefore, vapor pockets should be minimized, without excavations, if
feasible. Within a short period of time, vapor pockets trapped in
abandoned lines will possibly have a significant effect, especially if
vapor pockets are close to grade and are subjected to ambient
temperature change. As an example, for a two-cubic-foot vapor pocket at
60 degrees Fahrenheit, a 2.5 degrees Fahrenheit temperature decrease
will cause a volume decrease of 0.05 gallons.
Product Evaporation
Evaporation causes a decrease in volume which, if not accounted
for, would be interpreted as a leak by the leak measurement device.
Awareness of this effect is particularly important in hot weather, dry
climates, and high altitudes. The evaporation rate may differ,
depending on whether the volume change of the product is measured in or
under the fill pipe. The evaporation rate also depends on the volume of
the empty space in the tank above the product level. The presence of
more empty space above the product level will provide more volume for
gasoline evaporation before the space is saturated. For example, in.a
dry climate at 70 degrees Fahrenheit ambient temperature, for a four-
inch fill pipe filled with gasoline, a rate of 0.014 gallons per hour
gasoline evaporation can be calculated by Pick's Law of mass transfer.
This is equivalent to an 0.3 inches per hour reduction of the gasoline
level in the fill pipe.
Piping Leaks
Leaks at tank vents, manholes, or other piping connections to the
tank will cause misleading results during the leak detection tests
(because in some leak testing methods, this type of leak cannot be
differentiated from leaks which occur in the tank).
Tank Geometry
Many of the volumetric leak detection methods are product-level
and/or temperature-sensitive. In either case, one or more tank
specifications (e.g., the product surface area at different elevations
42
-------
I
Figure 9. Examples Of Three Common Vapor Pockets (5)
Ref: Hunter Environmental Services, Inc., Leak Lokator LD2000
-------
of the tank or the volume of the tank) is used to calculate the overall
volume change and the total volume change due to the temperature change
during a test period. In either case, differences between the actual
tank specification and the nominal manufacturer's specification can
affect the accuracy of test result evaluations.
When a reference tube filled with product is used to measure the
representative level changes due to temperature variation, the cylin-
drical geometry of the tank affects the accuracy of the test results.
This effect is minimized when the product level is at 75 percent of a
tank diameter, and increased at higher product level (33).
Wind
When a leak detection method is sensitive to product level or
pressure changes and the fill pipe or the vents are kept open to the
atmosphere during testing, the test results can be affected by wind.
Wind, especially when it is strong, can disturb the testing and reduce
the data reading accuracy by creating a wave on the product free
surface, irregular fluctuation of the pressure exerted on the liquid, or
both. The effect is more pronounced when the product level is below the
fill pipe.
Vibration
In some leak detection methods, external influences such as ground
vibration, traffic, wind, and background noise may cause inaccurate test
results. The vibration effect decreases when the testing results are
recorded based on a continuous average detection; this can be provided
by using a microprocessor. The vibration effect in level measurement
increases as the free surface area of the product increases when the
test is conducted at product level under the fill pipe. The magnitude
of the vibration effect is very difficult to measure precisely. When
the test method is based on the product level measurement in the fill
pipe, the vibration may be enough to change the overall result from "not
leaking" to "leaking" (from slightly below 0.05 gallons per hour to
slightly above).
Noise
Noise can affect the testing accuracy of a product level- or sound-
sensitive detection method. None of the volumetric leak detection
methods are sound-sensitive. In product level-sensitive detection
methods, the vibration due to powerful noise such as an explosion or
thunderstorm or nearby reciprocating machinery can create waves and
reduce the accuracy of the product level measurement. Typical back-
ground noise has insignificant effect on the accuracy of nonsound-
sensitive detection methods.
44
-------
Equipment Accuracy
Because changes of variables during a test period are commonly mea-
sured, the equipment accuracies reported by most of the manufacturers
are the sensitivity of the equipment to respond to certain variation.
However, the equipment accuracy (the ratio, multiplied by 100 percent,
of error in measurement to actual value) is subject to change at
different operating conditions such as temperature, pressure, range of
the measurement, etc. If the variations are not compensated for during
testing, they can reduce or change the accuracy of the detection method.
Operator Error
The more complicated the testing procedure, the greater the
potential for operator error. Typically, this is minimized or reduced
by using trained and experienced operators to conduct the testing. In
some cases, when the testing requires extensive sealing of the system's
ports and openings, improper sealing also could be considered as
operator error.
Type of Product
The physical properties of the product (including effects of
possible contaminants) could affect the repeatability and/or
applicability of a detection method. However, in all the identified
leak detection methods in this report, the accuracies are reported to be
unaffected by the type of product with physical properties similar to
gasoline. These include jet fuel, diesel fuel, and kerosene.
Power Variation
Most of the detection methods require electric power for oper-
ation. In some methods, this power is provided by using batteries.
Usually, the batteries are replaced with new ones before each testing.
This reduces the testing inaccuracy due to power variation. However,
when a method uses a 110V AC electric source, the results can be
affected by power variations during a test period. This effect can be
reduced when both the test results and voltage measurements are printed
against a common time base and considered together during the final
interpretation.
Instrumentation Limitation
Some of the leak detection methods are applicable to be used and
operated under certain tank situations or operating conditions. This
can be due to the size and range of applicability of the instruments
used in a method. Size of a fill pipe, inclination of the fill pipe,
range of product level or pressure change are examples of variables
which can limit the applicability of a method. If an attempt is made to
use a method outside of its designed range, the accuracy of detection
will be decreased.
45
-------
Atmospheric Pressure
Barometric pressure change during a test period can affect leak
rate measurement. For example, in a 10,000-gallon tank filled with
gasoline at approximately 60 degrees Fahrenheit (assume constant
compressibility factor) with a vapor pocket size of four gallons, a
pressure change of 0.02 inches of mercury provides an approximate
apparent leak equal to 0.0035 gallons. However, about 80 percent of
this volume change is due to the presence of the vapor pocket (because
of the difference between the compressibilities of air and gasoline).
An apparent leak of approximately 0.01 gallons would result from a
change in barometric pressure of 0.07 inches of mercury.
Tank Inclination
When a product level-sensitive detection method is used to
determine leaks in an underground storage tank, tank inclination can
affect detection accuracy. In an inclined tank, the volume change per
unit of level change is different than in a horizontal tank. This is
due to the difference between cross sectional areas, at certain product
elevations, for inclined and vertical conditions. This effect is
corrected by measurement of level change due to a known product volume
change.
In some cases, significant inclination may cause the method to be
inapplicable.
NONVOLUMETRIC LEAK TESTS
The nonvolumetric leak detection test is used to determine the
presence of leaks by qualitative analysis, usually by using a second
material other than the product (tracer material). The performance of
testing may be affected by certain variables.
Temperature
If a tank must be emptied and then filled with a tracer material
(usually helium) prior to leak testing, the temperature effect can
change the pressure and the viscosity of the tracer material. The leak
rate of tracer material will increase with temperature increase. This
is the result of pressure increase and viscosity decrease of a tracer
material due to temperature increase, both of which tend to increase the
leak rate. However, because the typical tracer material is helium with
significant diffusivity, the temperature increase can only reduce the
detection time of the tracer slightly. Therefore, the accuracy of this
test is not significantly affected by temperature changes.
Some detection methods, in addition to detection of leaks by tracer
gas, attempt to provide an approximate leak rate by pressure monitoring
46
-------
during a test period. These methods must compensate for pressure change
due to temperature effect.
If testing is conducted with product at normal existing conditions
and leaks are detected by monitoring the sound due to leaks or detection
of tracer gas outside a tank, the change of the leak rates due to
temperature change will have slight effect on the detection time and no
effect on the testing accuracy.
The change of the temperature would be based on ambient temperature
change, sunshine, clouds, rain, water table, and type and compaction of
backfill material.
Water Table
If a detection method indicates a leak by detection of tracer gas
outside of a tank, the presence of a high water table can prevent the
exit of the tracer gas from the tank. However, this can be overcome by
increasing the pressure of the tracer material inside the tank until it
exceeds the external pressure, in which case the tracer gas (helium)
will bubble up through the water to the surface. For certain pressure
of tracer material inside the tank, a higher water table will result in
a longer detection period.
Some detection methods, in addition to the detection of leaks by
sniffing tracer gas outside a tank, attempt to provide maximum possible
product leak rate by'pressure monitoring inside the tank. In this case,
a partial masking effect of the water table affects the testing accuracy
for leak rate evaluation.
When a method is applied to detect leaks by sound monitoring of the
leak under pressurized or vacuumed tank conditions, a lower partial
masking effect (lower water tables) can cause a more pronounced sound
for detection of a leak. In this case, due to the pressure differential
at two sides of a leak opening, a complete masking effect is avoided.
Tank Deformation
The nonvolumetric methods operate either by monitoring a tracer gas
outside a tank or monitoring the sound due to a leak inside a tank.
Therefore, tank deformation does not affect the detection accuracy.
(However, the effect of the tank deformation on the diameter of small-
size leaks should be studied.)
When a method provides the maximum possible leak rate of the
product by pressure monitoring inside a tank, the tank end deflection
effect on the leak rate will decrease for longer test periods.
47
-------
Vapor Pocket
In nonvolumetric detection methods it is necessary to test a tank
at emptied or normal existing product level condition. Therefore,
during these testings, vapor pockets cannot be created.
Product Evaporation
When testing is conducted on a completely empty tank, the product
evaporation effect is eliminated. If a nonvolumetric method indicates
leaks by detection of a tracer gas outside a tank or sound monitoring of
leaks inside a tank, in both cases at normal existing product level, the
product evaporation cannot affect testing performance.
Piping Leaks
In nonvolumetric tank leak testing with tracer gas, leaks at tank
vents, manholes, or other piping connections to the tank can cause
misleading results. This is because the tracer gas is very diffusive
and can diffuse through some pipe connections even after they are
tightened enough to contain liquids.
Tank Geometry
None of the nonvolumetric leak detection methods is product level-
sensitive. Therefore, tank geometry does not affect testing.
Wind
Based on the testing procedures for nonvolumetric detection
methods, all the ports of a tank should be sealed from the atmosphere
prior to testing to assure that the wind does not affect the testing
performance. However, in some detection methods where leak detection is
performed by sniffing a tracer gas at the ground level above a tank, in
windy conditions, small monitoring holes should be installed. This will
prevent the masking effect of wind for detection of tracer gas by direct
sniffing of gas through monitoring holes.
Vibration
None of the nonvolumetric detection methods are sensitive to the
level change of any fluid during a testing period. Therefore, the
testing performance is not affected by the vibration effect.
Noise
Noise can affect the testing accuracy of a sound-sensitive de-
tection method. Unless the background noise can be differentiated from
the sound due to leaks, the test cannot be successfully carried out.
48
-------
Equipment Accuracy
(See the description for volumetric leak detection methods.)
Operator Error
In all nonvolumetric methods, all tank ports must be sealed from
the atmosphere. Therefore, one of the major potentials for operator
error is the operator's ability to seal a tank completely prior to a
test. In sound-sensitive detection methods, the operator's level of
experience can reduce the time required to assure the certainty of
detecting leaks or the leak rate.
Type of Product
When testing is performed in an empty tank, the effect due to type
of the product will be completely eliminated. In acoustical leak
detection methods which are conducted in tanks containing product, the
product viscosity can affect the sound characteristics of leaks below
the product level. However, for products with properties similar to
liquid petroleum fuel, this effect is insignificant.
Power Variation
The nonvolumetric leak detection methods are based either on
detection of a tracer gas (helium) outside the tank or detection of the
leak sound inside a tank. In either case, the typical AC power
variation during the detection period cannot be enough to mask the
detection completely.
Instrumentation Limitation
(See the description for volumetric leak detection methods.)
Atmospheric Pressure
Because all the nonvolumetric detection methods are operated only
after the tank ports are sealed to the atmosphere, atmospheric pressure
(barometric pressure) change has no effect on the test results.
Tank Inclination
Because none of the nonvolumetric leak detection methods are
product-level sensitive, tank inclination does not affect testing.
General Problems
The principal problems inherent in nonvolumetric detection methods
are that they:
49
-------
• Cause or enhance a Leak during testing by exerting pressure
higher than normal tank operating pressure.
• Adversely affect product quality if a compound that is not inert
is used for testing in a tank containing product.
• Risk an explosion hazard when product is present in the tank
during testing.
• Usually cannot measure leak rate accurately, or at all.
• Require a long testing time for low leak rates when the type and
compaction of the backfill material around the storage tank is
varied. In some cases, the testing time could be up to 24
hours.
INVENTORY CONTROL
The problem of keeping records of product inventory is complicated
by the fact that gasoline is volatile and losses due to evaporation are,
to a degree, unavoidable. However, the inventory method could be used
as a first and most convenient method for gross leak monitoring. The
accuracy of this method is very much related to the manner in which
variable factors are compensated.
LEAK EFFECTS MONITORING
Problems associated with methods in this category are not discussed
in this section because these methods are not considered as existing or
developing in-tank, leak detection techniques, which are the focus of
the present study.
50
-------
SECTION 6
LEAK DETECTION METHODS REVIEW
All leak detection methods discussed are reviewed in this
section. The classifications of leak detection methods are presented
first, and then the methods themselves are described. Tables 1 through
9 (in Section 2) summarize the general information and operational
capabilities for each of the leak detection methods discussed in this
report.
Note that each "Manufacturer's Description of Method" is based on
the available literature from the manufacturer of that method. However,
the information regarding the "Manufacturer's Techniques to Compensate
for Effects of Variables" is a combination of the available information
in the manufacturer's literature, reports, and/or verbal communications
with the staff of the manufacturer.
The "Engineering Comments" herein are based on the authors' engi-
neering 'judgment . Therefore, it is possible an engineering judgment
would be different from the information or detection method capabilities
claimed by the manufacturer.
As used in this section, "testing" refers to those leak detection
methods that determine, at a point in time, whether a tank or tank
piping is tight or leaking. Testing is different than monitoring
techniques. Monitoring techniques provide continuous surveillance to
detect early leaks or area-wide surveillance to investigate the source
of a leak or spill. "Tank testing" refers to the detection of leaks in
tanks and tank piping systems.
CLASSIFICATION
The four general classes of methods to detect leaks in underground
storage tanks are:
• Volumetric (quantitative) leak testing, for leak indication and
leak rate measurement
• Nonvolumetric (qualitative) leak testing, for leak indication
• Inventory control
51
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• Leak effects monitoring. ^
These methods can be used individually or in combination.
Volumetric (Quantitative) Leak Testing
This classification of testing includes methods which test for
leaks based on the volume change. The change in volume can be deter-
mined by measuring parameters associated with volume change; including
changes in liquid level, temperature, pressure, and density.
Nonvolumetric (Qualitative) Leak Testing
This classification of testing includes methods which principally
determine the presence of a leak in an underground storage tank by
qualitative measurements. After identifying an underground tank leak by
this technique, a volumetric test can be used to measure the leak rate.
The main concerns about most qualitative testing methods are:
potential enhancement of leak, effect on product quality, explosion
hazard, inability to measure the leak rate, and required time for
testing.
Inventory Control
Advocates of inventory control claim it is the simplest and most
economical leak detection method. They contend that the technique has
not worked in the past only because recommended practices have not been
followed. Recommended practices for inventory control at service
stations can be found in the American Petroleum Institute's Publication
API 1621, Recommended Practice for Bulk Liquid Stock Control at Retail
Outlets (55).
Leak Effects Monitoring
This classification of leak detection methods identifies leaks by
monitoring the environmental effects of the leak inside or outside an
underground storage tank. These methods usually require drilling small
holes or wells, installing monitoring casings, and chemical analysis.
LEAK DETECTION TESTING METHODS
Volumetric (Quantitative) Leak Testing Methods
1- Ainlay Tank Tegrity Testing (TTT) (6,7)—
Manufacturer's Description of Method (6)—In this method, the level
change in a completely filled tank is measured by monitoring pressure
change through a bubbling system (Figure 10). The method is used to
measure and differentiate leaks in tank and piping. The tank is filled
into the fill pipe the evening before testing.
52
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Air and water chamber
wrapped around with
plastic tubing makes
a Manometer
Hose to bubble tube
Digital
Thermometer
Sensitive to
.005° F.
Bubble tube
Thermometer probes
Figure 10. Ainlay Tank Tegrity Testing Method
Ref: Schematic Drawing by Steel Tank Institute
53
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Propane gas bubbles are introduced one inch below the product level
through a 1/4-inch copper tube. The pressure required to introduce
bubbles varies with changes in product level, and is related to volume
changes. Pressure changes are monitored by a manometer type coil (slope
tube) with a colored water indicator. A slight drop in liquid in the
tank is exaggerated approximately 50 times when transmitted from bubble
tube to the slope tube. The temperature change during the test period
is measured. Based on data available at the site on tank volume, the
volume change due to temperature change during a test period is calcu-
lated. Finally, the volume change due to a leak is calculated by
subtracting the volume change due to temperature change from the total
volume change.
Ainlay TTT can be performed in one hour and can detect a leak as
small as 0.02 gallons per hour. The equipment used for setup and
operations is carried in a portable case and can be hand carried as
baggage on board an airplane.
Manufacturer's Techniques to Compensate for Effects of Variables
(7)—In the Ainlay TTT detection method, the following effects of
variables are compensated for as described below:
• Temperature—Temperature change is measured by three electronic
temperature probes at the center of each of three product layers
with 25 percent, 50 percent, and 25 percent, respectively, of
tank volume. Locations of the probes for tanks with various
diameters are provided on a table. When the three temperature
readings have stabilized, the temperature reading is recorded
and averaged on the report form. The temperature can be read on
a digital display with 0.01 degrees Fahrenheit accuracy.
The API gravity of the product is measured at the beginning.of
the test with a hydrometer. A table is included in the
instruction book. For testing a tank, this table will translate
the API gravity reading to coefficient of expansion. This table
covers all petroleum products from fuel oil to highest API
gasoline. Since the coefficient of expansion of chemical
solvents cannot be determined by hydrometer, another table is
included to cover 175 chemicals such as alcohol, acetones, etc.
If the tank tested has a drop tube (an insert in the fill pipe
which extends nearly to the bottom of the tank), it must be
removed before the test because the tube affects accuracy in the
detection of temperature shifts. In addition, filling and
allowing the tank to stand overnight stabilizes the temperature
in advance of the test.
• Water Table—The presence and amount of water in the tank is
determined with water-finding paste on the depth level stick at
the beginning and completion of the test. An increase or
54
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decrease in the water Level will indicate a Leak into or out of
the tank.
• Tank Deformation—This effect is minimized by filling the tank
the evening before testing (8). However, if the tank is topped
off one hour before the test, the end deflection effect is rec-
ognized when the calculated leak rates change in a decreasing
manner. As long as the end deflection is recognized and the
measured volume changes are not correlated with changes caused
by temperature change, the calculated leak rate is not con-
sidered as TTT's final result. Therefore, the overall testing
time will increase.
• Vapor Pockets—If vapor pockets are noticeable, the suspected
locations are excavated and the vapor pocket is released (8).
(For example, the vapor pocket at the end of the tank is
released by drilling a hole at that end.) As a second alterna-
tive, the test is conducted when the level of the product is 0.5
inches under the fill pipe.
• Product Evaporation—Propane gas is bubbled into the tank to
reduce the evaporation due to bubbling of gas in the product.
• Piping Leaks—A leak in the piping system can be detected by
lowering the product level to about one inch into the fill pipe,
or one inch above the top of the tank. This places the product
level below the piping level. If a leak is indicated at this
level, it must be in the tank as lines are not involved in the
test.
• Equipment Accuracy—Digital temperature probes register and read
out temperature shifts as small as 0.01 degrees Fahrenheit. The
volume change of approximately less than 0.01 gallons can be ob-
served on the manometer (slope tube).
• Operator Error—As operator skill increases, the temperature
reading can be as precise as 0.005 degrees Fahrenheit. In
addition, a better estimation of a portion of a 0.01-gallon
volume change can be provided.
• Type of Product—As long as a bubble can be generated in the
product, the accuracy of the TTT method does not change (8).
• Tank Inclination—This effect can be corrected by measuring the
exact product volume change in the coil-type manometer with
change in product level in the fill pipe. This is done by
addition/removal of the product, with known volume, to/from the
fill pipe until the product level in the slope tube reaches the
level when the test began.
55
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• Tank geometry, noise, power variation, and atmospheric pressure
do not have an effect on testing accuracy (8).
Engineering Comments—The Ainlay TTT's accuracy may be affected for
the following reasons:
• Differences between measured temperature changes and actual
temperature changes.
• Lack of compensation for masking effect on the leak rate caused
by hydrostatic pressure and surface tension.
• Presence of unidentified vapor pockets.
• Evaporation of product during a test.
• Difference between the obtained tank volume and the actual
volume.
• Strong wind.
* Strong vibration.
• Slope tube limitation to measure volume change more than 0.06
gallons during the test.
• Effect of barometric change on vapor pocket volume (if any).
In addition to the above, another disadvantage of this method is that a
printed readout is not provided for studying unusual events during a
test.
2- ARCO HTC Underground Tank Leak Detector (7,9,10,11,12)--
Manufacturer's Description of Method (7,12)—The ARCO underground
tank leak detector is an ultrasensitive device for measuring volume
changes in an underground storage tank caused by leaks through tank
walls under a product level, or product distribution lines (Figure
11). This method is substantially unaffected by temperature changes
that may occur in the tank during a test. However, a one-hour waiting
period is recommended to allow the equipment to stabilize and wave
action to diminish. To minimize fuel evaporation during the test
period, a saturated vapor condition is provided above the liquid
phase. This is done by circulating the fuel in the tank for an amount
of time, set by tank size.
The ARCO system consists of a float, a detector rod, and a strip
chart recorder. The float senses the liquid level in the tank, the
detector rod measures the relative position of the float with respect to
the rod, and the recorder makes a permanent record of the measurement.
Figure 11 illustrates the arrangement of testing equipment in a tank.
56
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• Height Adjustment
Tank Riser
3/8" Pipe
(Detector Rod)
DETECTION DEVICE
Linkage
Hollow Tube
Figure 11. ARCO Underground Tank Leak Detector (12)
Ref: ARCO Underground Tank Leak Detector Bulletin
57
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The float is assembled differently for different tank types. A
float shell is selected from a group of varying length shells suitable
for a variety of tank sizes. The float length and weight are chosen
based on the tank diameter, the liquid height in the tank, and the
liquid density. These measurements are taken at the site just prior to
starting the test.
The detector rod assembly consists of a photoelectric cell and a
float attachment hinge. The float movement forces an ink-type solution
into or out of the photocell. The change in light transmittance in the
photocell results in a voltage drop across the cell. The voltage
change, which is a function of the product level change, is measured by
a precalibrated voltage meter. Calibration and one-hour testing periods
are continued until two consecutive readings give the same calculated
result. The strip chart recorder has multiple input ranges. The ARCO
system can test four tanks simultaneously.
The test can be performed accurately when the tank level is between
66 and 76 percent of the tank diameter (9). Only leaks under the
product level may be detected.
The ARCO leak detector can be used with the tank at a normal opera-
ting level and pressure. The entire test procedure takes two to three
hours and leaks smaller than 0.05 gallons per hour can be detected;
however, longer test periods are possible. Operator attendance is not
required during each one-hour test interval.
Manufacturer's Techniques to Compensate for Effects of Variables
(7,12)—In the ARCO Tank Leak Detection testing methods, the following
effects of variables are compensated as described below:
• Temperature—The detector takes advantage of natural temperature
compensation by selecting a point in the tank (when the product
level in the tank is less than 76 percent of tank diameter)
where a floating object will be unaffected by temperature
variations in the liquid. A relationship exists between
temperature and three factors; namely, liquid density, liquid
buoyant forces (a function of density), and liquid volume. A
change in temperature, affecting liquid volume, can be exactly
offset by density (buoyancy) changes, providing the floating
object is at the point where the volumetric and density changes
caused by temperature variation have an equal, neutralizing
effect.
• Water Table—Water ingress will be detected as an upward float
movement, thus the ARCO system detects "leaks in" as well as
"leaks out."
• Tank Deformation—Because the tank is not overfilled during the
test, no provision needs to be made for this effect.
58
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• Vapor Pockets—Vapor pockets are not formed in this test
(because the tank is not filled).
• Evaporation—Based on field observation, this method reduces
product evaporation during the test period by providing a
saturated vapor condition above the liquid phase. This is done
by circulating the product in the tank for a required period
before conducting the test.
• Piping Leaks—When the tank testing is complete, the submerged
pump (which is part of the tank system) is turned on, and the
dispenser is kept in the off position; therefore, leaks in the
lines are measured with this method.
• Tank Geometry—In a horizontal cylindrical tank, the thermal
effect on level change is minimized when the product level is as
described in the test procedure (13).
• Equipment Accuracy—The system is calibrated for readout for
level change due to one liter volume change at the beginning of
each one-hour test.
• Operator Error—The operator error will be reduced with train-
ing, experience, and follow-up of the testing procedure (12).
• Type of Product—The method could be used with any type of
liquid as long as the float can move freely (12).
• Tank Inclination—The effect due to this variable is compensated
by using a calibration at the beginning of each one-hour test.
• Noise, power variation, and instrumentation limitation will not
affect the testing accuracy (12).
Engineering Comments—The accuracy of the testing may be affected
for the following reasons:
• Existence and change in the water level at the bottom of the
tank. This prevents a constant buoyancy force during the test
period. In addition, leak rate reduction or masking due to
ground water cannot be avoided.
• Occurrence of waves on the product's free surface due to wind
and vibration. However, this effect is partially corrected by
the chart results evaluation.
• Power variations.
• Atmospheric pressure change during the test period.
59
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In addition, one of the disadvantages of this method is that tank
leaks above the product Level will be undetected.
3- Certi-Tec Testing (10,14)—
Manufacturer's Description of Method (14,15)—The Certi-Tec test
monitors pressure changes resulting from product level changes (Figure
12). Product level changes are due to volume changes. The method is
capable of testing storage tanks filled either beyond or below
capacity.
The system uses a sensitive pressure transducer located below the
product surface. Five or more temperature sensors are used to measure
temperature at different levels. A microprocessor collects temperature
and pressure change data and determines the volume change of the mass
above the pressure transducer.
When it is possible to fill the tank, the test method uses a stand-
pipe. The standpipe is installed above the grade of the tank. The
pressure transducer is installed in the standpipe and the product level
change is measured. If a leak is detected, the product level is
decreased below the fill pipe and the pressure transducer installed in
the tank. The results of the tests at these conditions could determine
if the leak is in the tank or piping.
The system accuracy to measure leak rate is within that recommended
by NFPA (0.05 gallons per hour). The accuracy of the test is reduced
when a partially filled tank is tested. However, to achieve maximum
accuracy, the test must be performed over a longer period of time than
the test with the standpipe. The test can be performed in two- to four-
hour testing periods.
Manufacturer's Techniques to Compensate for Effects of Variables
(15)
—In the Certi-Tec Tank testing method, the effects of the following
variables are compensated as described below:
• Temperature—In this system, temperature sensors are suspended
at five or more levels. A microprocessor collects the tempera-
ture data to measure the volumetric average of product tempera-
ture during a test. The volume change of the mass above a
pressure transducer, which is used for leak detection, is
determined for the estimated temperature change (10,14).
• Water Table—A potential problem exists when the test is con-
ducted in a tank filled with less than capacity and the tank is
located in high ground water conditions. The ground water could
mask the leak. In this testing, the level of water in the tank
is measured by water-finding paste.
60
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h
I
•
c
r
DATA LOGGER
n
— | 1 1— 1 ^ TO 110 V POWER SUFFLJ
3
1 1 II '
PRESSURE TRANSDUCER POWER SUPPLY V\
LIQUID LEVEL ^
PRESSURE TRANSDUCER
j FILL PIPE
UNDERGROUND STORAGE TANK
Figure 12. Certi-Tec Tank Testing System (14)
Ref: Schematic Drawing by Fuel Recovery Co.
61
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• Tank Deformation—This effect is recognized when the measured
leak rate changes in a decreasing manner.
• Vapor Pockets—When a tank can be filled, a test is conducted
with standpipe. In this case, the head pressure induced by the
standpipe can reduce the vapor pocket volume (if any) and,
therefore, reduce the volume change due to vapor pocket
effect. When the test is conducted with product level under the
fill pipe, no vapor pocket exists to affect the testing accur-
acy; however, this reduces the pressure transducer sensitivity
and increases the time for testing.
• Equipment Accuracy—The temperature readout of smaller than 0.01
degrees Fahrenheit can be recorded. In addition, the pressure
transducer can provide ±0.25 percent accuracy and ±0.05 percent
repeatability.
• Operator Error—Operator error will be minimized if the testing
procedure is followed precisely.
• Type of Product—The system could be used with gasoline, jet
fuel, diesel fuel, and other liquid petroleum fuels.
• Instrument Limitation—The pressure transducer can only be used
from 0 to 3 pounds per square inch pressure range.
• Atmospheric Pressure—The system is designed to compensate for
atmospheric pressure change during the test period. This is
accomplished by measurement of the gage pressure.
• Noise and power variations will not affect the test results:
Engineering Comments—The accuracy of the Certi-Tec testing can be
affected by:
• Difference between measured temperature changes and actual
temperature changes.
• Lack of compensation for water table masking effect or reduction
of the leak rate.
t Vapor pockets, if the test is conducted using the standpipe.
• Product evaporation when the test is conducted without
standpipe.
t Difference of obtained tank volume with the actual volume.
62
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• Wind, especially when the test is conducted at product level
below the fill pipe. However, it is partially corrected by the
microprocessor, which continuously provides the average results
for every 15 seconds.
• Vibration, especially when the test is conducted at product
level below the fill pipe. However, it is partially corrected
with the same technique to compensate for wind.
• Equipment accuracy should be checked for each test by
calibration.
• Power variations.
• Effect of atmospheric pressure change on vapor pockets volume
(if any).
• When the test is conducted with a pressure transducer in the
fill pipe or tank, the tank inclination effect should be
compensated by calibration.
4-"Ethyl" Tank Sentry Testing (7,9,10,11,16) —
Manufacturer's Description of Method (16)—The "Ethyl" tank sentry
is used to detect and measure small changes in the liquid level of
underground fuel tanks. The heart of the detector is a "j" tube man-
ometer containing a special indicator fluid; the fluid is not miscible
with fuel. The long leg of the "J" tube connects with a larger diameter
fuel reservoir. A manually operated valve on the long leg of the "J"
tube is used to admit or drain fuel from the reservoir. A second valve
is installed in the short leg of the "j" tube to control the indicator
fluid. Both valves can be operated while the detector is in the tank.
Figures 13 and 14 illustrate the detector kit and the installation of
the detector in a tank (16).
The operating principle during the test is that a change in the
indicator fluid level occurs due to a change in the liquid level of a
partially filled tank. Any change in tank level is magnified by a
factor of approximately five in the manometer. The difference in height
of the indicator fluid in the manometer legs is read and recorded. By
referring to tank tables and applying certain factors, the loss or gain
in fuel volume is calculated. A level change as small as 0.02 inches
can be detected. For a one-hour test with the product level in the
middle of a typical, cylindrical 8,000-gallon tank (eight-foot
diameter), a change of 0.02 inches per hour reflects a leak rate of 2.12
gallons per hour. Because the accuracy in measuring and detecting leaks
is a function of the time span of the test, the probability of detection
can be increased by extending the test time or by averaging two or more
replicated tests. As an example, a level change of 0.02 inches within a
ten-hour span (instead of a one-hour span) calculates to a 0.212 gallons
63
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Figure 13. "Ethyl" Tank Sentry Kit (16)
* Ethyl Corporation Bulletin
WATER TRAP
Figure 14. «Ethyl» Tank
Ref: Ethyl Corporation Bulletin
64
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per hour leak rate. The test requires that the test period must span
several hours.
Manufacturer's Techniques to Compensate for Effects of Variables
(17)
—In the "Ethyl" Tank. Sentry testing, the following effects of variables
are compensated as described below:
• Temperature—The temperature is measured by a temperature probe
(thermometer). This is done before and after the tests and is
used to calculate the volume change due to temperature effect.
Equipment instructions state that a one degree Fahrenheit change
in product temperature during the test will negate the results;
tests should not .be conducted within 24 hours after product
delivery. After this time, the product temperature usually
varies less than one degree Fahrenheit for the test period. In
addition, careful adherence to the test procedure reduces
possible effects of temperature variables (16).
• Tank Deformation—This effect is eliminated during the testing
period. This is due to the test requirement that the tank be
idle and no deliveries be made to the tank during the preceding
24 hours. In addition, careful adherence to the test procedure
reduces possible effects of tank end deflection variable (16).
• Vapor Pockets—Because the testing requires product level under
the fill pipe, this effect is eliminated
• Noise—Not applicable.
• Equipment Accuracy—Any change in tank level is magnified in the
manometer, making it possible to detect level changes as small
as 0.02 inches.
• Operator Error—This can be minimized by carefully following the
testing procedure.
• Type of Product—The testing accuracy would be unaffected by the
product type as long as the viscosities and vapor pressures of
products are not too high. However, "Ethyl" Tank Sentry may or
may not give accurate readings with gasolines that contain any
oxygenates (alcohol).
• Power Variation—Not applicable.
• Instrumentation Limitation—The method is used to measure leaks
in underground fuel tanks having a three-inch or larger fill
pipe diameter and containing at least 20 inches of fuel (16).
65
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• Atmospheric Pressure—The manometer eliminates the effect of
barometric changes during the testing period.
Engineering Comments—The "Ethyl" tank sentry testing accuracy may
be reduced due to the following reasons:
• Difference between measured temperature changes and actual
temperature changes.
• Lack of compensation for water table level on the leak rate. In
addition, it is not capable of preventing masking effect due to
the water table. However, the effect is reduced when a test is
conducted for a longer period of time.
• Product evaporation during the test period due to the tempera-
ture and/or pressure change.
• Piping leaks.
• Difference in the calculated surface area and volume of the pro-
duct, based on the available tank's data, and the actual values
to estimate the overall volume change and thermal volume change
during a test period.
• Tank inclination is not considered or compensated by
calibration.
In addition, the system disadvantages include:
• The data are not recorded continuously. They are only recorded
at the beginning and end of the test period.
• The leaks are not detected above the product level in the
storage tank.
• Long testing period is required to differentiate between tank
leaks and piping leaks. Therefore, usually another method of
leak detection is required for pipe testing.
5- EZY-CHEK Leak Detector (5,7,10,11,18,19)—
Manufacturer's Description of Method (5,18,19)—In this method, the
level change is measured by monitoring the pressure change through a
bubbling system. The storage tank is typically overfilled into the fill
pipe. However, the testing can be taken at any level in the standpipe
above the highest point in the tank, in the fill pipe, or in the tank.
The system consists of a standpipe, an averaging temperature probe,
an air supply tank and chart recorder. The liquid level change is
monitored with a sensitive pressure gage. The pressure recorder has a
66
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Figure 15. Ezy-CHEK Leak Detector (18)
Ref: Horner Creative Metals Bulletin
67
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Figure 16. EZY-CHEK Leak Detector Installation (18)'
Reft Horner Creative Metals Bulletin
EXTEND OR
CONTRACT TO
MONITOR TEMP
CHANGE FROM
TO BOTTOM
OF TANK
Figure 17. EZY-CHEK Leak Detector Temperature Averaging Probe (18)
Ref: Horner Creative.Metals Bulletin
68
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full range of approximately one ounce of pressure. The air supply
forces a small flow of low pressure air into the top 1/2 inch of liquid
in the tank, through a 1/4-inch tube clamped to the fill pipe. The
recorder measures the pressure necessary to cause the bubbling action.
If the recorder charts a straight line, the liquid level is not chang-
ing. The temperature change is monitored with an averaging temperature
probe to compensate for the volume change due to the temperature vari-
ation during the testing period. Figures 15 through 17 illustrate the
equipment and the installation of the EZY-CHEK system (18).
Complete tank testing includes at least four 15-minute testing
periods and could usually be performed with 0.01 gallons per hour leak
detection accuracy within four hours after the tank is topped off.
Manufacturer's Techniques to Compensate for Effects of Variables
(5,18,19)—In the EZY-CHEK testing method, the following effects of
variables are compensated as described below:
• Temperature—Temperature change is monitored by an electronic
temperature averaging probe which is installed in the tank. The
probe consists of platinum sensing wires encased in a "coil
spring" of special plastic tubing. The probe is formed with
more coils at the center of its length than at its ends, thus
proportioning the length of sensing wire to the volume of the
tank. When the weighted probe is dropped into any tank ranging
from 2 to 20 feet in diameter, it stretches to match the tank
diameter. The digital readout display temperature changes to
0.001 degrees Fahrenheit. It can monitor up to four tanks
simultaneously. Currently, the above temperature measurement
system is used instead of the system with "stoddard solvent,"
which was used in the past.
• Water Table—When a high water table is suspected, a standpipe
device can provide the necessary head pressure to prevent the
masking effect. In this situation, the volume change is
measured in the standpipe.
• Tank Deformation—If it is necessary to stabilize tank end de-
flections, a standpipe device can provide the necessary head
pressure to eliminate this effect. Also, if the tank is filled
up into the fill pipe the night before or at least four hours
prior to the test, this will allow tank ends to stabilize.
• Vapor Pockets—When it is necessary to stabilize entrapped vapor
pockets, a standpipe device can provide the necessary head
pressure to reduce vapor pocket effect. Vapor pocket volume is
reduced by pressurization of the standpipe with regulated
pressure.
69
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To eliminate the vapor pocket effect after a tank is filled up,
if the standpipe device is not used, the vapor pockets are
released by a "float tube" device designed for this purpose.
The opening of the tube is connected to a float. Therefore, it
is always situated at the top of the product in a tank (20).
• Evaporation—Since the test is usually conducted overnight, not
in the heat of the day, evaporation effect is reduced especially
when a test is conducted with the standpipe (20).
• Piping Leaks—If a leak is detected by EZY-CHEK tank testing,
the EZY-CHEK line testor is used to detect the leak in the
lines.
• Wind—If the weather is windy, the vent pipe is covered with a
cap (20).
• Vibration—To minimize vibration effects, vehicles with con-
siderable vibration effects are not allowed in the testing area
or a test is conducted with standpipe (20).
• Noise—The effect of this variable on testing accuracy is
insignificant (20).
• Equipment Accuracy—The recorder can easily detect a change of
0.005 inches in the liquid level. The temperature readout could
be performed with 0.001 degrees Fahrenheit accuracy (5,18).
• Operator Error—This will be minimized by training and careful
consideration of testing procedure (20).
• Type of Product—Testing could be performed with any type of
product as long as air could be bubbled through the product and
evaporation effect is insignificant (20).
• Power Variation—Recorder motor is spring wound and no
electricity required. The temperature monitoring system is
supplied with a 12-volt battery pack.
• Instrumentation Limitation—The detection method can be used for
any type of liquid petroleum fuel storage tank (20).
• Atmospheric Pressure—The same barometric pressure is exerted on
the liquid and the recorder's bellows; therefore, this variable
does not affect test results (5,18).
• Tank Inclination—This effect is eliminated by recorder cali-
bration by known volume at the beginning of a test (5,18).
70
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Engineering Comments—In the EZY-CHEK testing method, the Leak
detection accuracy may be affected due to the following reasons:
• Difference between measured temperature change and the actual
temperature change in the tank during a test period.
• Leak rate reduction due to the water table level.
• Unidentified vapor pockets. This is because the efficiency of
the float tube has not been experimented thoroughly enough to
assure that it could release all the existing vapor pockets in a
tank.
• Product evaporation, when testing is performed on hot nights.
• Occurrence of wave due to wind and vibration. However, this
effect is partially corrected by the chart results evaluation.
• Difference of theoretical tank volume and actual tank volume.
• Effect of atmospheric pressure change on vapor pocket volume (if
any).
6- Fluid-Static (Standpipe) Testing (7,9,10,11)—
Description of Method (9,10)*—This detection method is known as
"Hydrostatic Testing."However, hydrostatic terms refer to testing with
water, but in underground tank testing the test is conducted with the
product in the tank which is being tested. Therefore, in this text,
"fluid-static" is used as a correct term for hydrostatic testing.
A standpipe is filled to pressurize a completely filled tank. The
pumps in the siphon systems are removed from service and the manifold
vent lines are disconnected. The pressure exerted by the fluid in the
standpipe is generally enough to provide five psi pressure at the bottom
of the tank. The volume change is calculated from the level change in
the standpipe.
This method is not a manufactured system and can be used without
special training by the gasoline service station operators. However,
the method is not adequate for detecting slow leaks nor for determining
tank system tightness and has an unspecified accuracy. Because the
volume change due to a leak is accumulative, the accuracy of the test
will increase if a long testing period is used and the system is near
temperature and mechanical equilibrium.
*Reported
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Techniques to Compensate for Effects of Variables—This method does
not compensate for the volume changes due to temperature changes, tank
deformation, vapor pockets, and for evaporation for testing. However,
when the testing time is increased, the effects of tank end deflection
and other variables could be reduced in the final testing result.
Special precaution should be taken so that pumps in the siphon
systems are taken out of service and that manifold vent lines are
disconnected.
Engineering Comments—Due to the lack of compensation for major
variables which affect the testing accuracy (unless a long testing
period is used) this method is not adequate as a precision testing
method to detect small leaks. An apparent loss of product is observed
due to the expansion of the tank volume from tank end deflection and
temperature changes. The magnitude of this apparent loss can be sub-
stantial. To detect a leak in this system, the leak must be greater
than the volume variation resulting from tank end deflection and
temperature changes. These effects could be minimized by using a long
time period and permitting deflection equilibrium conditions.
The standpipe test method does not require specialized equipment or
personnel. The testing is time consuming and the accuracy is unspeci-
fied. However, fluid-static testing is more sensitive than the pneumatic
testing (9).
7- Heath Petro Tite Tank and Line Testing (Kent-Moore Testing)
(4,5,7,9,10,11)—
Manufacturer's Description of Method (4)—This test is essentially
a fluid-static (standpipe) test. The tank and standpipe (installed in
the tank opening) are completely filled. A loss can be observed and
measured to 0.01 gallons. A one-gallon graduate is used to measure the
exact amount of gasoline added to or drained from the standpipe to main-
tain a constant level. The constant level results in a uniform tank
pressure.
A circulating pump draws gasoline from at least six inches below
the tank top through a suction tube; if necessary, the tube is
lengthened by a hose extension. The gasoline is discharged under
approximately 25 pounds per square inch pressure through a discharge
hose into sections of tubing which have been coupled together to form an
outlet jet at the bottom of the tank. This jet is adjusted to be above
any water in the tank bottom and is adjusted to be below any drop
tube. The jet is directed 45 degrees upward from the center line of the
long tank axis. These suction and jet systems create a vortex-like
swirling motion in the tank and attempt to produce a uniform temperature
throughout the tank. Figure 18 illustrates the Petro-Tite testing
method.
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GRADUATED CONTAINER
STAND PIPE
AIR SEAL-*
THERMISTOR
DISCHARGE NOZZLE-
PUMP
INLET
/ V-
THERMAL SENSOR
S.
PIPE 110V 1 PHASE
STORAGE TANK
Figure 18. Petro Tite Installation (4)
Ref: Heath Consultants Inc., Petro Tite Tank Tester Bulletin
73
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The uniform temperature obtained by circulation is electrically
measured by a thermistor in the bottom of the suction tube. The
thermistor is located approximately 6 inches below the top of the
tank. Temperature changes are constantly measured. Volume changes are
calculated from the temperature changes. The calculated volumes are
subtracted from the volume change measured by the graduate. Measured
volume changes are due to tank end deflection or leakage. Any dif-
ference between the calculated and measured volumes in the 15 to 30
minutes after tank end deflections cease, (approximately two hours), is
considered to be leakage if it is equal to or more than 0.05 gallons per
hour.
The minimum time to perform the test is 2.5 hours. The entire test
can usually be completed in one working day (10).
Manufacturer's Techniques to Compensate for Effects of Variables
(4)—In the Petro Tite testing method, the following effects of vari-
ables are compensated as described below:
• Temperature—This is done by using a thermal sensor and a
temperature monitoring system. During the test, the product is
constantly circulated to attain an average temperature.
Circulation time is five to eight minutes per 1,000 gallons;
five minutes for lighter liquids (gasoline) and eight minutes
for heavier liquids (fuel oil). The thermal sensor is attached
to a semiconductor thermistor probe in the tank and is capable
of discerning 0.003 degrees Fahrenheit changes. By passing a
small electric current through the thermistor, the average
temperature is measured at the point of withdrawal six inches or
more below the tank top. However, due to the overall accuracy
and repeatability of the thermal system, the exact fraction of a
degree Fahrenheit (i.e., 0.003 degrees Fahrenheit) varies
slightly at different temperatures, which may cause some in-
accuracy in the measurement of actual temperature changes. A
chart gives the fraction for any temperature. Because the test
takes several hours, accurate temperature monitoring can be
accomplished.
• Water Table—The leak masking effect due to a water table is
eliminated by inducing a constant pressure gradient on a leak.
In addition, in areas with a water table and when there is no
data available on the water level, the data should be obtained
by drilling a monitoring well, prior to a test. The water level
is used to determine the product level in the standpipe for
testing.
• Tank Deformation—Apparent volume changes are compared with a
chart to recognize the occurrence of tank end deflection.
Volume changes are observed in equal time intervals and recorded
on the Tank Test Data Chart. The manufacturer reports
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diminishing apparent losses in equal time intervals as end
deflection occurs.
A technique has been developed to quickly eliminate these
apparent losses due to tank end deflection. A high level, and
therefore a greater pressure, is maintained at the beginning of
the test in the standpipe. When recorded data indicate steadily
decreasing losses, the product level, and therefore the pres-
sure, is lowered, and tank end deflection usually disappears
within two hours.
• Vapor Pockets—The presence of vapor pockets in the tank is
recognized by direct observation of the bubbles in the stand-
pipe. This is due to product circulation for temperature
monitoring which carries some of the air to the fill pipe.
• Evaporation—Product loss by evaporation is minimized by using a
cap to cover the graduate's top.
• Piping Leaks—For storage systems with submerged pumping,
separate tests must be run on the tank and piping by the tank
tester and line tester units. On suction delivery tank systems,
the test checks the entire system simultaneously.
• Equipment Accuracy—The product volume change in the standpipe
(tank) can be measured by using a one-gallon graduated
cylinder. Volumes less than 0.01 gallons can be read on this
cylinder (21). The temperature changes are constantly measured
with 0.003 degrees Fahrenheit accuracy.
• Operator Error—This is minimized by using a skilled technician.
• Type of Product—As long as the product is of low enough
viscosity to be free flowing, the method can be used to detect
small leaks (21).
• Tank geometry, wind, vibration, noise, power variation, and
instrumentation limitation do not appear to have significant
effects on the applicability and accuracy of the detection
method.
Engineering Comments—In the Petro-Tite method, the testing
accuracy to measure leak rate may be affected due to the following
reasons:
• Difference of measured temperature change with the actual
temperature change in the tank.
• Water table level changing the leak rate.
75
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• Leak rate measurement higher than the leak rate of normal tank
operations. This is due to the use of fluid-static head greater
than normal operating conditions.
• Unidentified vapor pockets.
• Difference between the theoretical tank volume and actual tank
volume.
• Effects of atmospheric pressure change on vapor pockets volume
(if any).
8- Helium Differential Pressure Testing (22)—
Manufacturer's Description of Method (22)—This test is an inert
gas pressure test and is used to determine whether an underground tank
is leaking and, if so, at what rate.
The tank is pressurized with helium after capping off all product
and closing all vent lines connected to the tank. The tank pressure is
compared to the pressure of a reference probe inserted in the tank. The
tank pressure, differential pressure, and ambient temperature are
measured at half-hour intervals for a minimum of 48 hours. The data
provided by these measurements are sufficient to calculate whether any
observed changes in tank pressure are due to leakage from the tank or
are caused by the diurnal variation in ambient temperature. A leak rate
less than 0.05 gallons per hour can be detected by this procedure. The
equivalent volume of product lost during the test is computed from
Bernoulli's equation for flow through an orifice.
Manufacturer's Techniques to Compensate for Effects of Variables
(22)
—In this testing method, the following effects of variables are compen-
sated as described below:
• Temperature—The pressure change due to the temperature change
is compensated by using a reference tube inserted in the tank.
• Tank Deformation—The effect of tank end deflections is reduced
by the 48-hour testing period (23).
• Type of Product—The type of product stored in the tank is
compensated by including the product molecular weight in
computation of gas density. Computed gas density is used in the
leak rate computation.
• Vapor pockets, evaporation, tank geometry, wind, vibration,
noise, power variation, instrumentation limitation, atmospheric
pressure, and tank inclination are not applicable in this method
of testing (23).
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Engineering Comments—In this method, testing accuracy may be
affected by the following reasons:
• Difference between the compensated (calculated) pressure change
and the actual pressure change due to the temperature effect.
• The masking effect and leak, rate reduction due to a water table
level cannot be avoided.
• Differences between the actual tank geometry and the given
geometry by tank manufacturer which is used for leak rate
estimation.
• Piping leaks cannot be differentiated from tank leaks.
• The error in the measurement of differential pressure is reduced
by installing the measurement device inside the tank. In this
situation, the measurement will not be affected by ambient
temperature change.
• The operator efficiency to tighten and seal the accessible ports
and flanges. In addition, operator experience is necessary to
use the appropriate printed differential pressure result to
obtain the final leak rate.
9- Leak Lokator LD-2000 Test (Huntef-Formerly Sunmark Leak Detection)
(5,7,10,11,24)--
Manufacturer's Description of Method (5,24)—This method operates
on the Archimedes Principle of Buoyancy which states, "The apparent loss
in weight of any object submerged in a liquid is equal to the weight of
the displaced volume of the liquid."
The Leak Lokator consists of a hollow cylinder which is sealed at
the bottom, an analytical balance (weighing scale), electronic
transmitting circuitry, and a strip chart recorder. A sensor, suspended
from the analytical balance, is placed in the tank liquid. The weight
of the sensor is equal to its actual weight minus the buoyancy force
from the liquid in the tank. Any change in liquid level will change the
buoyancy force on the sensor and hence, the weight of the sensor. The
weight change is monitored by the analytical balance which
electronically transmits a "signal" to the recorder. The chart recorder
graphically shows volume changes versus time. The angle and length of
the line drawn by the recorder is directly correlated to the quantity
and rate of leakage. Figure 19 illustrates the Leak Lokator testing
method.
77
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00
ANALYTICAL BALANCE
IQUID LEVEL
ENSOR
Figure 19. -Leak Lokator Installation (24)
Ref: Hunter Environmental Services, Inc., Leak Lokator LD2000 Bulletin
-------
The chart recorder notes the lapsed time in minutes versus volume
change in cubic centimeters of the product displaced either into or out
of the tank. A vertical line shows no change in volume, while lines
with positive or negative slopes indicate decrease and increase,
respectively, in the product volume. The system is calibrated at least
six times during each test. This is performed by quickly adding or
removing a calibration rod of precise known volume to the test system.
Typically, the time for equipment set up and temperature adjustment
is 1.5 hours. A complete testing on one tank can usually be performed
in 3 to 4 hours, and on four tanks in 8 to 10 hours. After the
equipment is set up, the test to determine a volume change typically
takes less than one hour. This time will increase to at least two hours
for in-tank testing. The least sensitivity occurs when the product
level is near the center line of the tank. However, even at this level,
volume changes of 0.05 gallons per hour can be detected by adjusting
test time and the electronic signal. The greatest sensitivity for
detecting a small leak is achieved if the testing is conducted with the
liquid in a riser above grade.
Manufacturer's Techniques to Compensate for Effects of Variables
(5,24)—In the Leak Lokator testing method, the following effects of
variables are compensated as described below:
• Temperature—This test compensates for temperature variation by
lowering a thermistor to the center (midvolume) of the tank and
measuring temperature change continuously during the test. The
product temperature is stratified at various levels throughout
the tank; however, it has been researched and proven to the
satisfaction of this manufacturer that the midvolume location is
a proper location to measure the average rate of temperature
change for the entire volume as long as the strata are undis-
turbed, and the tank is buried and not subjected to ambient or
unusual external effects. If a tank system is uncovered for any
reason and subjected to ambient temperatures, or if the system
is subjected to some other external source of temperature
change, testing is conducted using three probes equally volume-
spaced, and the average rate of temperature change is the
volumetric average of the three probes. The signal from the
probe(s) is electronically transmitted to a strip chart recorder
and displayed on a digital meter with a resolution of 0.001
degrees Fahrenheit. The x-axis full-scale strip chart is
typically set at one degree Fahrenheit (0.01 degrees Fahrenheit
per division).
In addition, to enhance the accuracy of the temperature compen-
sation technique, a precise measurement of the product API
specific gravity is made, on site, by taking a sample of the
liquid being tested. The API gravity and observed temperature
are then related to the coefficient of volumetric expansion
using ASTM data.
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Water Table—If the water table level is known, the proper
product level is used to overcome the forces of water outside
the tank. When the water level is unknown, the test level is
set assuming the water table is above the tank top. In addi-
tion, the level changes due to temperature changes during a test
period virtually prevent the condition for a leak to be
masked. This is due to the differences between the forces
inside and outside a tank whenever the level changes.
Tank Deformation—In this method of testing, because the pres-
sure exerted by a fully charged system is only about one pound
per square inch, the tank end deflection is minimized. In addi-
tion, because the most significant effect of deflection occurs
almost immediately after a system is topped off, end deflection
is typically not a problem. If for some reason fill pipe
product levels must be raised higher than normal for testing,
charts are provided by the manufacturer to compensate for
related volume changes. If tank end deflection is significant,
the test slope will be erratic and inconsistent, thereby indi-
cating the need to compensate by raising and lowering the level.
Vapor Pockets—Due to the short duration of the test, vapor
pockets compensation is rarely required because vapor pockets
only affect test results when ambient barometric pressure or
temperature changes significantly during a test period. If the
pocket size is four gallons or less, and if the barometric
pressure change is less than 0.02 inches Hg per hour, no cor-
rections are needed. Tables are provided to compensate for
changes greater than 0.02 inches Hg per hour. In addition, if
vapor pockets are present and affected by temperature or pres-
sure, the test slope will be erratic and inconsistent, thereby
indicating the need to compensate and/or eliminate the pockets
until conclusive results can be obtained.
Product Evaporation—In this method, a hollow sensor is used to
compensate for product evaporation. This sensor is sealed at
the bottom, filled with the product, and suspended for testing
to a point a few inches higher than the product level in the
tank. The inside diameter at the top of the sensor is slightly
larger than where the sensor enters the product so that the
surface area inside the tube is the same as the surface area
occupied by the tube in the product. For this reason, evapora-
tion takes place from the surface area of the sensor at the same
rate as from the surface area of the product measured. As
evaporation occurs from the hollow tube, the sensor becomes
lighter. However, the buoyancy force exerted on the sensor by
the product in the tank decreases at the same rate due to
evaporation, thus entirely compensating for evaporation effects.
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• Piping Leaks—If a leak is found during the full system test,
with the product level raised so that all buried piping is being
tested, the level is then lowered to tank top (within one to six
inches) and another test is conducted to check leaks in only the
tank.
• Vibration—Vibration factors, such as traffic may cause the leak
rate slope to fluctuate; however, the rate of change is easily
determined by drawing a slope through the fluctuations. The
most significant effects of vibration occur during in-tank
testing.
• Equipment Accuracy—The reading accuracy for volume change is
calculated by chart calibration with addition or removal of
product to optimize the chart deflection per calibration. The
electronic voltage signal is also optimized to minimize the
volume calibration per division. The temperature readout is
provided at 0.001 degrees Fahrenheit accuracy on a digital
display. Both temperature and volume change are continuously
recorded.
• Operator Error—The operator error is minimized by using a crew
of trained operators (25). All testing services are provided by
Hunter employees.
• Type of Product—The method can be performed effectively on any
products or mixture of products where the sensor can be freely
suspended.
• Instrumentation Limitation—The test can be conducted in any
size underground tank system with two-inch or larger opening.
However, for in-tank testing, a minimum opening of four inches
is required.
• Atmospheric Pressure—It has been determined that a barometric
pressure increase during the test period would have to exceed
0.07 inches Hg in one hour to effect an apparent leak of 0.01
gallons per .hour. Because a pressure increase is generally
slower than a pressure decrease and therefore would not occur
during the short test period, it is normally not necessary to
compensate; however, charts are provided in the operator's
manual if this unusual circumstance occurs.
• Tank Inclination—The effect of tank inclination is eliminated
by testing calibrations (25).
Engineering Comments—In the Leak Lokator testing, the accuracy may
be affected due to the following reasons:
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• Difference between measured apparent temperature change and
actual temperature change.
• Leak rate change due to the water table effect; therefore, the
water table masking effect cannot be avoided.
• Tank end deflection, if it is unidentified.
• Vapor pockets. When the volume of the vapor pocket is unidenti-
fied, there is no way to measure its volume changes due to
temperature and barometric pressure changes during a test
period.
• Occurrence of wave due to wind and vibration. However, this
effect is partially corrected by the chart results evaluation.
• Difference between theoretical tank volume and actual tank
volume.
• Power variations due to the use of 110V AC power source.
• In some cases, the fill pipe is at such an angle from vertical
that the sensor could not be installed in the tank without
touching the wall. Therefore, tank testing is not possible by
this method.
10- Mooney Tank Test Detector (5,7,10,26)—
Manufacturer's Description of Method (5,26)—In this method, an
underground storage tank is filled with product into the fill pipe. The
test starts 12 to 14 hours after product delivery. The product level
and the temperature of the liquid within the tank are monitored over a
one-hour period with 20-minute testing intervals. A leak as small as
0.02 gallons per hour can be detected (27). If the elevation of the
liquid in the fill pipe changes from the level caused by expansion or
contraction due to temperature changes, and by evaporation loss, this
indicates a leak in the tank.
In the past, level changes were monitored by either a mechanical
float device or an electronic capacitance probe (27). The electronic
type could provide a digital readout of 0.01 inches of level change. At
the present time, a dip stick graduated at 0.05-inch divisions is used
to measure the level. One side of the dip stick is covered with gaso-
line or water indicator paste and inserted into a tank. To increase the
level measurement accuracy, the dip stick is connected to a leveling
device which sits on the opening of the fill pipe. The instrument box
is capable of testing three tanks at the same time.
Manufacturer's Techniques to Compensate for Effects of Variables
(5,26)—In the Mooney Leak Detection testing method, the following
effects of variables are compensated as described below:
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• Temperature—The average temperature of the tank is measured by
monitoring the temperature at the center of each of five Layers
with equal volumes. The device includes an electronic tempera-
ture differential measuring system consisting of five electronic
sensors and digital readout. The anticipated accuracy for
temperature measurement is in a range of 0.001 to 0.006 degrees
Fahrenheit.
• Tank Deformation—In this method, the significance of the tank
end deflection effect is minimized by filling the tank up into
the fill pipe 12 to 14 hours before the test period.
• Evaporation—This system uses an evaporation cup as a measuring
device. The cup is filled and installed in the fill pipe. The
height of product which evaporates from the cup during the test
period is measured. This height is equal to the height of the
liquid evaporated from the fill pipe and will be considered as
the final resultant evaporation.
• Piping Leaks—If a leak is detected, the level of the product is
lowered in the fill pipe to below the top of the tank, and a
complete set of testing is performed (27). This test will
identify if a leak is in the piping.
• Equipment Accuracy—The level measurement device "dip stick" is
divided to 0.05-inch divisions. The temperature readout could
be provided with 0.001 degrees Fahrenheit accuracy on a digital
display.
• Type of Product—The type of the product will not affect the
testing accuracy as long as the level change of liquid can be
determined on the product indicator paste (27).
• Tank Inclination—This effect is compensated by calibration for
level reading at the beginning of each testing period.
• Instrumentation limitation and power variations have insigni-
ficant effects on the detection method (27).
Engineering Comments—In the Mooney Tank testing method, the
accuracy of the results may be affected due to the following reasons:
• Difference between the measured temperature change and the
actual temperature change during the test period.
• Leak rate changes or masking due to water table effect.
• Unidentified vapor pocket(s).
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• Difference between theoretical tank volume and actual tank
volume.
• Error in level reading due to vibration by wind and traffic.
• Operator accuracy in reading the product level changes from the
dip stick.
• Rapid change in barometric pressure.
11- PACE Leak Tester (28)--
Manufacturer's Description of Method (28)—In testing with the PACE
Leak Tester a tank is nominally filled, at a product level several
inches below the top of the fill pipe, about 12 hours before testing is
started to allow the temperature to stabilize. The tank's vent and feed
pipes are sealed except for one which is fitted with a "dip tube."
Measurements of the liquid level in the dip tube are taken during the
course of the testing.
The system consists of a small-diameter tube (dip tube) as the test
tube, a wooden ruler to measure the product level in the dip tube, three
thermocouples to read product temperature, and a barometer to read atmo-
spheric pressure. The dip tube is welded into a cap that is then
threaded onto the testing tank's fill pipe in such a way that the dip
tube extends above the fill pipe. It is possible to gain access to the
stored product through this open-ended pipe. During the tank testing,
this pipe is the only access point to the product. The presence of the
void above the product level in the tank converts the dip tube into one
arm of a manometer that measures the difference in pressure between the
gas in the void and the atmosphere outside the tank. The product levels
within the tube and the tank will both change in response to a leak or
to a temperature change. The change of the void pressure due to a leak
is magnified in the dip tube. The recommended procedure is to install
thermocouples at three specific locations at the top, middle, and bottom
of the tank.
Four consecutive measurements of product level in the dip tube, and
temperature measurements are made at approximately half-hour intervals
spanning a 1.5-hour period. In addition, the atmospheric pressure is
measured at the beginning and end of the testing. The results are ana-
lyzed and leak rates are derived using a simplified calculation.
The computed leak rates can also be assessed statistically. The
statistical analysis performed can also be calculated on the three
estimated leak rates to produce an overall average and corresponding
standard error. If this overall average is not greater than the largest
of the four leak volume error values, then the experiment indicates that
a leak (if present) is less than the intrinsic error of the experi-
ment. If the overall average is greater than the largest error, but is
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not more than eight ounces per hour greater than the largest error, then
the experiment has not detected a Leak greater than the NFPA leak
detection limit of eight ounces per hour (0.05 gallons per hour).
The PACE Tank Testing is in principle a simple, accurate, and
practical test, which has been theoretically and experimentally tested
in a program conducted for the Petroleum Association for Conservation of
the Canadian Environment. This method is not commercially available.
Manufacturer's Techniques to Compensate for Effects of Variables
(28)—In testing with the PACE Tank Tester, the following effects of
variables are compensated as described below:
• Temperature—When a tank is filled with product, the test will
be conducted after a 12-hour temperature stabilization period.
Based on statistical evaluation, it is found that three thermo-
couples are satisfactory to measure the product temperature at
the top, middle, and bottom of the testing tank. The accuracy
of each thermocouple is 0.01 degrees Fahrenheit. After the
initial temperature measurements, the measurements will be
repeated at three equal intervals of a half-hour. These
measurements are used to compute the mean value of the expansion
effect and its standard error. In some experiments (during the
summer) this statistical error is the factor limiting the
accuracy of the measured leak rate.
The measurements for three test repetitions also allow for a
statistical estimate of the overall error in measuring the leak
rate.
The thermal expansion of the liquid gasoline is the largest
perturbation in this method and is always significant. It is
imperative that thermal expansion be compensated.
• Tank Deformation—The fill/empty cycles during the normal oper-
ation of a tank should compact the backfill material adjacent to
the tank ends. This results in a void between the ends and the
limit of the deflections. If the movement of the ends is unres-
trained, the deflection will occur immediately after filling.
In addition, a 12-hour temperature stabilization period also
ensures that/ the end deflection is not a significant factor.
• Product Evaporation—It is calculated that the effect of product
evaporation due to the increase of the void volume by a small
leak is negligible.
The evaporation effect due to change of product vapor pressure
by temperature change is compensated by obtaining the vapor
pressure from the Reid Chart and is based on the top thermo-
couple temperature reading.
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• Tank Geometry—The effect of the tank geometry on the void
volume above the product level is minimized by initial cali-
bration. The initial depth of the product from the top of the
dip tube is measured with a ruler. Finally, a measured volume
of product, about 0.05 gallons, is removed from the tank with a
syringe inserted into the dip tube. This creates an artificial
leak and the new depth of the product in the dip tube is
measured. Since these all take place within about one minute,
the temperature and atmospheric pressure are considered constant
and hence the artificial leak without expansion effect is
measured.
• Vibration—In this method, due to the magnification of the
product level change in the dip tube, the vibrations due to such
things as vehicle traffic do not have a significant impact on
the results.
• Equipment Accuracy—The accuracy of this method is especially
affected due to temperature variation. In a 5,000-imperial-
gallon tank, the intrinsic error in the temperature measurement
(0.005 degrees Fahrenheit) corresponds to an expansion effect of
2.5 ounces (0.015 gallons). The accuracy is increased during
the winter period. It is estimated that in this method
accuracies of 0.125 inches, 0.01 degrees Fahrenheit, and 0.1
inches of mercury for ruler, thermocouples, and barometer,
respectively, are sufficient.
• Operator Error—This method is invented to provide a method with
little or no requirement for operator training.
• Instrumentation Limitation—Since the temperature is only
measureable to the nearest 0.01 degrees Fahrenheit, this
limitation may be more important than the statistical error
value.
• Atmospheric Pressure—The main effect of a change in atmospheric
pressure is on the level in the dip tube. Other effects such as
a change in volume of the tank and the liquid within it are
bound to be negligible for the small changes of pressure ex-
perienced as the weather changes. In addition, the steel tank
and its product contents are effectively incompressible. The
atmospheric pressure could be measured with a barometer at an
accuracy of 0.1 inches of mercury. However, under normal
conditions the change in atmospheric pressure over the short
period of the test (1.5 hours) will not significantly affect the
results and hence this measurement can normally be eliminated.
Engineering Comments—If the void space above the product level
behaves as an ideal gas, the testing results with the PACE Tank Tester
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will be theoretically acceptable. However, any deviation of the void
space from ideal gas behavior will affect the accuracy of the testing.
This method is a developing method with limited experimental trials on
steel underground storage tanks and none on fiberglass tanks. There-
fore, there is not sufficient data and evidence available to conclude
that the void space behaves as an ideal gas.
In this testing method, the detection accuracy may be affected due
to the following reasons:
• Lack of proper technique to measure the representative
temperature of the product and the void space. These will
affect compensation for evaporation due to inadequate
estimations of product vapor pressure.
• Water table effect on the leak rate cannot be prevented. In
some cases, the leak may be completely masked due to the water
table effect.
• Vapor pocket effect may be insignificant, due to short period of
testing.
• Product evaporation due to the dip tube with an end open to the
atmosphere.
• Piping leaks into the tank.
• Wind effect on product evaporation rate due to the presence of
the dip tube with an open end to the atmosphere.
• Noise will not affect the detection accuracy.
• Type of product will affect the vapor pressure and the rate of
the evaporation.
• The power variation effect can be minimized by using a new
battery for each tank testing, since the digital thermocouples
in this method are the only electrical components.
• Since the product level is measured in a dip tube with 1.5-inch-
diameter, the tank inclination effect on the detection accuracy
will be insignificant.
• The precision of the method is overstated (the entire
statistical analysis should be carefully reviewed).
12- PALD-2 Leak Detector (10,29)--
Manufacturer's Description of Method (29)—In this method, a
completely filled underground storage tank is pressurized with nitrogen
to allow the level to rise within a sensing column to a viewing window
above ground level. The tank is pressurized to at least three different
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pressures during the course of testing. All ports and vents to the
atmosphere must be closed and/or sealed.
The system consists of a nitrogen cylinder, a pressure measuring
device, a series of electro-optical level sensors, a microprocessor, and
a printer. The level changes are detected through electro-optical
sensors. The microprocessor determines the validity of the readings and
sends the calculated leak rate to the printer. The leak rate is cal-
culated based on the size of the leak and on the pressure difference
across the leak. The testing depends on the requirement to rapidly
settle the tank after each pressure change. This is accomplished by
raising the gas pressure above the test pressure for a short duration.
Care must be taken not to go beyond the equilibrium point. The
sensitivity of the system is high (less than 0.05 gallons per hour) and
monitoring time short (less than 15 minutes).
Manufacturer's Techniques to Compensate for Effects of Variables
(29)
—In the PALD-2 testing method, the following effects of variables are
compensated as described below:
• Temperature—The temperature effect is minimized by the short
duration of the testing in an equalized condition.
• Tank Deformation—The effect due to this variable is minimized
by the short duration of the testing in an equalized condition.
• Vapor Pockets—Presence of entrapped air has a serious negative
effect on the test quality and it should be removed prior to
testing, at all cost.
• Instrumentation Limitation—Care must be taken not to go beyond
the equilibrium point. If this occurs, the tank will contract
during the measurement and a negative volume change will be
indicated. In this case, the test may be abandoned and repeated
at a later time or the microprocessor may be reprogrammed to
repeat the test at a slightly higher pressure.
• Other sources of error are: ground water table, ground motion
introduced by external sources, oscillations within the tank
system, and atmospheric pressure changes. However, the method
to reduce most of these errors is to allow ample time for the
tank to settle.
Engineering Comments—In this testing method, the detection
accuracy may be affected due to the following reasons:
• Temperature effect on volume change may be significant, as com-
pared to the measured volume change during a short testing
period.
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• Leak rate change by the water table effect and leak rate
enhancement due to the application of pressure greater than the
normal operating condition.
• Piping leaks.
• Equipment accuracy.
t Power variations.
• Product evaporation, tank geometry, wind, operator accuracy,
type of product (with similar vapor pressure), and tank
inclination do not appear to affect the quality of the test.
In addition, in this testing method, the following disadvantages
are noticeable:
• Due to the use of pressure greater than the normal operating
pressure, the leak rate increases during the course of testing.
• There is a risk that tanks weakened by corrosion will be
ruptured by pressurization.
13- Pneumatic Testing (7,9,10,11)—
Description of Method (9,10)*—In this method, which is not a manu-
factured system, the storage tank and the piping systems are pressurized
with air or another gas. The pressure change depends on the change of
gas volume in the tank and piping. However, this method does not com-
pensate for any variable changes during the testing period. The method
is not sensitive to small leaks and is not likely to detect leaks below
the liquid level in the tank. In addition, the piping and tank leaks
could not be differentiated from each other.
Techniques to Compensate for Effects of Variables (9,10)*—The tank
end deflection effect could be reduced during the testing period. How-
ever, this method will not compensate for other variables which may
affect the testing results. Greater accuracy can be achieved, when the
tank is full or nearly full.
Engineering Comments—In the pneumatic testing method, the follow-
ing problems could be noticed:
• Air pressure and vapor pressure of the stored liquid in the tank
vary greatly with temperature. The temperature effect can be
measured, but this method does not compensate for pressure
changes resulting from temperature variation and tank end
deflections.
*Reported
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• Water table changes in or masking of the leak rate cannot be
avoided.
• The method does not compensate for pressure changes due to tank
end deflections.
• If the pressure exceeds the tank's normal operating pressure,
there is a risk of tank rupture, especially if the tank is badly
corroded. The more product in the tank, the more the risk of
overpressurization should be considered.
• A faulty or inaccurate gage may allow overpressurization and
lead to a tank explosion or rupture. This should not happen if
equipment is properly calibrated.
• Potential increase in leak rate during the test period (and,
possibly, after).
• Testing with air in tanks containing flammable and/or com-
bustible liquids is extremely hazardous (3).
• Due to the exertion of additional pressure on the tested tank,
product may be forced out of the tank at leaks during the test
period.
• The method is time consuming and the accuracy is unspecified.
14- Tank Auditor (30)—
Manufacturer's Description of Method (30)—This is an electro-
mechanical system for detecting leaks in underground piping and tank
systems. The method operates on the Archimedes Principle of Buoyancy,
The major component of this system consists of a product height
deviation transducer, a temperature probe height deviation transducer, a
temperature probe, and a recorder. A force deflection transducer sup-
ports a negatively buoyant member within the liquid-filled fill pipe.
Buoyancy forces are changed due to product level change and create a
linear deflection of the force transducer that is sensed by a noncontact
electronic probe with a voltage output proportionate to the deflection
of the force transducer. The temperature probe, consisting of a thin-
walled hollow cylinder closed at the bottom and opened at the top, is
placed into the fill pipe. The length of this probe is equal to or
greater than the tank diameter. The probe is filled with product. A
force transducer, similar to the product height deviation transducer, is
used to sense height deviations within the probe. A recorder receives
the output voltage from the transducers and the results are printed on a
strip chart. At the end of a 15-minute test, the recording is
stopped. The total volume change due to a leak is calculated. At the
beginning and end of each test, both transducers are calibrated by
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addition and/or removal of known volumes of the product from the
temperature probe and the tank.
If the tank is filled prior to a test, the test is conducted at
least three to four hours after tank fillup (31). The average time
required to test a single tank, including setup and dismantling, is one
hour. Typically, an additional hour of testing is required due to
unusual situations such as piping leaks, tank leaks, presence of an air
pocket, syphon systems, and common vents. The detection method has an
accuracy of 0.05 milliliters (0.00001 gallons) gross volume change in a
four-inch fill pipe and 129 milliliters (0.03 gallons) gross volume
change in a half-full, 10.5-foot-diameter tank. Therefore, the tank
could be tested even when it is partially full.
Manufacturer's Techniques to Compensate for the Effects of
Variables (31)—In the tank auditor detection method, the following
variables are compensated as described below:
• Temperature—A thin hollow copper tube, filled with product, is
used for temperature compensation. This probe can be used when
the fill pipe diameter is larger than three inches.
• Water Table—The complete masking effect of ground water is
eliminated by performing tests at the bottom and the top of the
fill pipe. Because the static head changes, a leak cannot be
completely masked.
• Tank Deformation—If the system is filled prior to a test, major
tank deflection occurs immediately after tank fillup. Further
effects will be reduced or eliminated by three to four hours
waiting period before a test.
• Vapor Pockets—If the presence of vapor pocket is recognized,
the level of the product will be lowered below the tank top and
the test performed. However, piping leaks will not be deter-
mined and the time for testing will be increased.
• Product Evaporation—Because the product level changes due to
product evaporation in the fill pipe (or fill tube) and in the
temperature probe are equal, the effect is compensated for
simultaneously with compensation for temperature change.
• Piping Leaks—Piping leaks are determined by performing tests at
the bottom and the top of the fill pipe. If a leak is
identified, the elevation of the leak will be determined by
adjusting the product level.
• Tank Geometry—When the tank is partially filled, this effect is
eliminated by the testing calibration.
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• Wind—Wind effect is minimized or eliminated by electronic
dampening and performing the testing under a tent.
• Vibration—This method is relatively insensitive to vibration
due to mounting on the tank fill pipe.
• Equipment Accuracy—A level change due to 0.05 milliliters
(0.00001 gallons) volume change in a four-inch fill pipe and 129
milliliters (0.03 gallons) volume change in a half-full 10.5-
foot-diameter tank can be measured by the product deviation
transducer. The sensitivity of the temperature measurement
probe is to 0.015 degrees Fahrenheit.
• Operator Error—This is minimized by defined testing procedures
and operation by trained personnel.
• Type of Product—The detection method could be used for any
product as long as the probes can sink.
• Instrumentation Limitation—The fill pipe must be vertical to
the extent that a plumb bob can be hung four inches into the
liquid from the top of the fill pipe at any point on the
circumference of the pipe without touching the side of the fill
pipe at the lower end. The probe must hang vertically into the
product from the fill line, vent, or manhole. Some fill pipes
are at such angles from vertical that testing is not possible.
A piping and tank 'system test is always possible. In addition,
the temperature probe can be used when the fill pipe diameter is
larger than three inches.
• Tank Inclination—As long as tank inclination does not prevent
the equipment utilization, its effect is eliminated by
calibration of the chart at the beginning and end of a test.
• Noise, power variations, and atmospheric pressure do not
generally affect the detection method accuracy.
Engineering Comments—In the Tank Auditor detecting method, testing
accuracy may be affected by:
• Difference between the product level changes in the tank and the
reference tube due to temperature change.
• Leak rate changes due to the water table effect cannot be
avoided.
• Volume changes due to an unidentified tank end deflection three
to four hours after tank fillup, during a testing period.
• Unidentified vapor pockets in a completely filled tank.
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• Power variations.
• Effect of atmospheric pressure change on vapor pocket volume (if
any in a completely filled tank).
15- Two-Tube Laser Interferometer System (9,10,29,32,33)—
Manufacturer's Description of Method (29)—The Two-Tube Laser
Interferometer System simultaneously measures the difference in the
height of the product in an open tube and a closed tube initially filled
to the same level. The height changes in the open tube caused by the
principal noise sources that could hide a small leak in a partially
filled gasoline storage tank (e.g., thermally induced volume changes and
evaporation/condensation) are removed (i.e., compensated for) by
subtracting the height changes in the closed tube.
The major components of the system consist of the laser inter-
ferometer measurement system, two equal length two-inch-diameter tubes
extending to the bottom of the tank, an aluminum float (for each tube)
containing a cube-corner reflector, and a data acquisition system. The
laser system consists of a laser head, laser display unit, a beam
splitter, and two interferometers mounted on a solid cast aluminum
stand. The laser head generates a safe, low-power (200 yW) beam which
is divided into two beams for the height measurements in each tube.
Because the interferometer is not attached to the laser head, motion of
the laser head does not' affect the measurement. The data acquisition
system receives the laser interferometer height measurements made at a
200 Hz sample rate, averages the data over a 42-second period, and
generates a time series at one-minute intervals for the leak detection
analysis. Figure 20 schematically illustrates the system.
The laser interferometer measurement system itself measures height
changes to one micro-inch (0.000001 inch). The accuracy of the Two-Tube
Laser Interferometer System to measure a known product level change is
60 micro-inches? this was determined by making repeated measurements of
the height changes in an 8,000-gallon storage tank produced by inserting
and removing several different solid aluminum bars of known volumes.
The accuracy of the system for detecting small leaks in an under-
ground storage tank was estimated from the analysis of data collected
during many field experiments (29). The analysis showed that a leak
rate of 0.041 gallons per hour could be detected with a probability of
detection of 95 percent and a probability of false alarm of 0.1 percent
assuming the tank was 75 percent full. The time period of the tank test
to achieve this performance is two hours.
The system was used in an experimental program conducted for the
American Petroleum Institute (29,32,33) and is not available on the com-
mercial market.
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BEAM SPLITTER
INTERFEROMETER 8
LASER
INTERFEROMETER A
GRODNO
OPTICAL GLASS-
GASOLINE SURFACE
FLOATS4
CUBE-CORNER
REFLECTORS
GASOLINE
NEEDLE VALVE
TWO BRASS
TUBES
Figure 20. Two-Tube Laser Interferometer (32)
Ref: Underground Tank Testing Symposium, Petroleum Association for
Conservation of Canadian Environment (PACE), May 25, 26, 1982
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Manufacturer's Techniques to Compensate for Effects of Variables
(34)
—In the Two-Tube Laser Interferometer System testing method, the
following effects of variables are compensated as described below:
• Temperature—Because the method uses two tubes (one closed and
one open end tube), the temperature effect is compensated
automatically (29,32,33).
• Water Table—If the first testing result indicates a nonleaking
tank, the water table masking effect could be checked by con-
ducting the test at levels lower or higher than the level in the
first test (or by measuring the depth of the water table).
• Tank Deformation—The effect of this variable is eliminated
because the test is performed at normal operating conditions.
• Vapor Pockets—Vapor pockets are not a problem because the
testing procedure does not require the tank to be full.
• Product Evaporation—Since the level changes due to product
evaporation in the open and closed (reference) tubes are equal,
this effect is compensated for simultaneously with the compensa-
tion for temperature changes.
• Tank Geometry—This does not affect the result because the
system is calibrated for level changes due to a known volume
change, before the test.
• Vibration—Waves in the tank due to the vibration effect is not
a problem because the raw laser height data is averaged over a
time period which is long compared to the wave period. In
addition, vibration of the ground is not a problem because these
effects are small and are removed by the two-tube measurement.
Also, vibration of the laser head is not a problem because the
laser is separated from the interferometer.
• Equipment Accuracy—The resolution of the Two-Tube Laser
Interferometer measurement systems used in field tests is
1 micro inch. The data acquisition system is used to store the
data after rounding off the data to the nearest 10 micro
inches. The system's reported accuracy is within ±60 micro
inches. The height change associated with a 0.05-gallons-per-
hour leak in a 3/4-full, 8,000-gallon, 8-foot-diameter tank is
530 micro inches.
• Type of Product—The type of product will not affect the testing
accuracy.
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• Tank Inclination—The effect due to this variable could be mini-
mized by calibration of the system on site.
Other potential sources of error in the height measurement were
investigated: thermal expansion or contraction of the laser equipment
and mounting stand, thermally induced changes in the tubes' diameter,
vertical alignment of the beam, changes in the refractive index of the
light between the interferometer and the corner-cube reflectors, settle-
ment of the mounting stand, and expansion or contraction of the ground
relative to the gasoline storage tank. Each of these errors were theor-
etically estimated, quantified experimentally, and rejected because they
were small.
Engineering Comments—In the Two-Tube Laser Interferometer testing
method, testing accuracy may be affected by the following:
• Differences between product level changes in the tank and the
reference tube due to temperature change.
• Leak rate change due to the water table effect cannot be
avoided.
• Vibration, strong enough to produce long waves which masks
height changes due to a leak.
• Operator skill to set up the test equipment.
• Power variations.
Nonvolumetric (Qualitative) Leak Testing Methods
1- Acoustical Monitoring System (AMS) (35)—
Manufacturer's Description of Method (35)—The acoustical monitor-
ing system can be used for detection of leaks in an underground storage
tank. This system includes the development of advanced instrumentation
for signal detection and processing, the development of signal interpre-
tation methodology, and the use of the triangulation technique for
locating leaks. Acoustic signals, generated when pressurized liquids
escape through a metal boundary, are detected by piezoelectric trans-
ducers attached to the surface of the pressure boundary. Nitrogen is
used to pressurize the tank. In this measurement, accelerometers
(resonant at 27 kHz) are used in conjunction with a wave guide mounted
acoustic emission sensor (resonant at 250 kHz). With this combination
of sensors, the range of frequencies of flow-induced vibrations and
elastic waves due to a leak can be monitored.
In an actual field test, the AMS system was able to detect leaks,
as indicated by the Petro-Tite system, of 0.01 gallons per hour. This
method is not commercially available and is subject to more experimental
studies.
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Manufacturer's Techniques to Compensatefor Effects of Variables—
The major variables considered for volumetric testing systems are not
applicable to this method. In addition, other variables are not
identified by the manufacturer which can affect the testing accuracy.
Engineering Comments—For the AMS detection method, the following
are noted:
• Does not provide leak rate.
• If the nitrogen pressure exceeds the tank's normal operating
pressure, there is a risk of tank rupture, especially if the
tank is badly corroded.
• Potential increase in leak rate during the test period (and,
possibly, after).
• The testing method on tanks containing flammable and/or
combustible liquids is extremely hazardous (3).
One of the advantages of the AMS method is the capability of
determining the leak's location in the tank.
2- Leybold-Heraeus Helium Detector, Ultratest M2 (5,7,10,36)—
Manufacturer's Description of Method (5,36)—In this method, helium
is used as a tracer gas for leak detection. With the vent line plugged,
the tank is pressurized with helium gas to four pounds per square
inch. The gas is fed at the bottom of the tank so that it mixes
thoroughly with the product in the tank.
To detect helium, five small holes must be drilled and located over
the corners and center of the tank. The sniffer probe of the detection
system samples the gas in each hole and the helium is detected using
mass spectrometric techniques.
Manufacturer's Techniques to Compensate for Effects of Variables
(5,36)—The testing method can detect leaks only by detection of helium
through the monitoring holes outside the tank and is thus not affected
by the variables discussed for other methods.
Engineering Comments—The method cannot measure leak rate. In
addition, due to the presence of product in the tank, ground water, and
ground characteristics (especially for tanks with clay backfill), test-
ing may require a long period of time before a small leak is detected.
One other reason which reduces the detection speed is that helium does
not flow freely through liquid (37). However, the method does not
require the tank or pipes to be removed from service during the testing.
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The five holes may provide an approximation of the location of the
leak (if further tracing of the leak is required).
3- Smith & Denison Helium Test (7,37)--
Manufacturer's Description of Method (37)—This method of leak
detection is based on differential pressure loss in the tank being
tested relative to a reference steel chamber equipped with a differ-
ential pressure manometer or gage. Excess pressure (over ambient
pressure) is induced by inserting helium gas into an empty tank and the
reference chamber. The pressure loss with time is monitored to indicate
leaks in the system. In addition to pressure loss, gas escaping from a
leaky system is detected, at ground level, by sampling the gas in the
soil pore space and measuring the concentrations of helium by a mass
spectrometer. This requires drilling small holes into the soil around
the tank or pipe. Testing is performed in two steps—one step with the
product in the tank (no level change prior to the test) to verify the
tank and piping are sealed above the product level (this test can
usually be performed in less than four hours while the tank is in ser-
vice) and one step when the tank is completely empty. The pressure
change in the test tank resulting from temperature change during the
test period is compensated for by the pressure change of the reference
chamber. The reference chamber can be in thermal equilibrium with the
helium gas in the tank one hour after the testing is started (38).
Leaks from tanks usually are detected very quickly. A search for helium
gas around the tank is conducted soon after differential pressure
equilibration. In some cases where the tank is protected by a clay
backfill, it may be necessary to continue the test for 24 hours before
helium gas is detected at the soil surface. If the concentration of the
helium in the soil gas is more than five ppm (helium concentration in
the air), the system is leaking. In this method, the size of the leak
opening and therefore the maximum possible fuel leak rate could be
calculated. The manufacturer's literature did not quantify a leak rate
(38) because it depends on the location of the leak in the testing tank,
but did describe the relationship between the size of an opening and the
overall measured helium loss during the testing.
Manufacturer's Techniques to Compensate for Effects of Variables
(37)
—In this testing method, the following effects of variables are compen-
sated as described below:
• Temperature—A reference steel chamber is used to compensate for
pressure change due to temperature change, which is done by
measuring the differential pressure of the tank and the
reference chamber during a test period. The reference chamber
can be in thermal equilibrium with the helium gas in the tank
one hour after the testing is started (38).
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• Water Table—The presence of a high water table surrounding the
tank prevents the exit of helium from the tank. However, this
can be overcome by increasing the helium pressure until it
exceeds the ambient pressure and can then bubble up through the
liquid to the surface.
• Tank Deformation—This effect will be eliminated by evaluation
of the printed record on pressure differential of the tank which
is conducted for at least four hours (38).
• Piping Leaks—These leaks could be identified during the first
step of testing, when the test is conducted with product in the
tank, and/or during the second test by the detection of high
concentrations of helium around piping.
• Equipment Accuracy—Differential pressure is measured by a
manometer or an electronic differential pressure gage, installed
inside the tank, with 0.01 or 0.1 inches of water reading
accuracy (37). The sensitivity of the helium leak detection
method is sufficient to indicate leak size which would result in
a gasoline leaks as small as 0.005 gallons per hour. However,
because the leak rate is dependent on the location of the leak,
this method cannot provide the actual leak rate (38). Modern
helium mass spectrometers can detect helium concentrations as
Ipw as 0.1 parts per million.
• Operator Error—Prior to conducting the test, all the ports are
sealed by the testing operator. However, a potential source of
error is helium leakage through these ports even after they are
tightened by the operator. However, this method is capable of
identifying these types of leaks.
• Atmospheric Pressure—The effect of barometric pressure change
is eliminated by using a device to measure differential
pressure.
• Vapor pockets, product evaporation, tank geometry, wind,
vibration, noise, type of product, power variation, instrument
limitation, and tank inclination are not applicable to this
testing method (38). One of the disadvantages of this method is
that helium does not flow freely in a liquid; therefore, the
tank should be completely empty prior to testing.
Engineering Comments—In this method, the following points may
affect testing accuracy:
• Differential temperature response of the reference chamber to
actual temperature changes in the tank.
• Pressure change due to unidentified tank end deflection.
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• Leakage due to piping and flanges.
In addition, this test cannot provide an actual leak rate under
normal conditions, especially when there is a high water table around
the tank.
4- TRC Rapid Leak Detector for Underground Tanks and Pipes (39)—
Manufacturer's Description of Method (39)—This method, which is
not commercially available, uses volatile and environmentally safe
tracers. One to three liters of tracer gas are added to the liquid
product. The tracer compound moves from the leaking tank or pipeline
through any leak. High-volume pumping in the backfill surrounding the
tank draws the tracer from the leak point to a monitoring pipe where the
soil gas is sampled and subjected to field chromatographic analysis.
The tracer plume is then probed upgradient to locate the leak point.
This method allows remedial measures to be implemented before
significant environmental damage has occurred. If more than one system
is suspected, different tracers can be used to test several systems at
once.
Manufacturer's Techniques to Compensate for Effects of Variables
(39)—The testing method can detect leaks only by detection of the
tracer gas outside a tank. High-volume pumping is used to speed the
tracer gas transfer to the detection points.
Engineering Comments—The TRC Rapid Leak Detector cannot measure
leak rate. In addition, due to the presence of product in the tank,
ground water, and ground physical characteristics (especially for tanks
with clay backfill), the testing may take a long period of time before a
small leak can be detected. One of the reasons is that the tracer gas
does not flow freely through the liquid (37). However, the method does
not require the tank or pipes to be removed from service during the
testing.
5- Ultrasonic Leak Detector, Ultrasound (40,41,42,43)—.
Manufacturer's Description of Method (40)—Utilization of ultra-
sound to detect leakage in underground storage tanks is a possibility.
For the past 15 years, portable ultrasonic sensors have been utilized to
locate pressure and vacuum leakage in a variety of systems such as power
plants and chemical plants. The detection probes sense ultrasonic
emissions produced by a pressure or vacuum leak. At present, an ultra-
sound system has not been used for tank leak detection; however, it is a
very promising method. Following is a description of the expected
system performance.
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By plugging all gas vents and draining the fluid from the tank, a
vacuum can be produced. The negative gage pressure will draw air into
the tank from the soils surrounding the tank wall through the leak
site. The entire tank wall can be scanned in seconds because the
detection head is directionally sensitive and can be rotated to detect
the maximum signal. Piping leaks can be detected at the same time, and
leaks can be pinpointed within a spread of 15 degrees from the apex of
the transducer. A leak will be noted through headphones worn by the
operator as well as being registered on a meter.
The ultrasound detection method requires a compact field unit with
headphones and meter. In addition, the system is designed to record
test results and the location of a leak. A relatively simple method of
airborne ultrasonic leak detection from existing commercially available
technology can be adapted to locate in-ground leakage in storage tanks
easily and rapidly.
Monitoring equipment setup for this system will be very simple.
Once set up, only 20 minutes is required to test a tank. Also, several
tanks can be tested simultaneously. The detection system can be
designed with sufficient sensitivity to measure a leak rate of 0.001
gallons per hour or greater of air (44). A leak of 0.005 inches in
diameter with a pressure differential of five pounds per square inch can
be detected over 30 feet away. Therefore, the task of detecting a leak
rate lower than 0.05 gallons per hour is straightforward.
Manufacturer's Techniques to Compensate for Effects of Variables
(40)
—For the Ultrasound System, the following variables are compensated for
as described below:
• Water Table—If the water table surrounds the leak hole, it will
be detected because the the tank chamber will be in a vacuum
state so that the pressure differential between the tank
environment and the ingress ing water droplets will cause the
water droplets to expand and, due to a low surface tension,
burst. This burst will produce a detectable ultrasound (between
20 kHz and 100 kHz).
• Piping Leaks—Because the detection head can be rotated to
detect maximum signal location, piping leaks will be detected.
• Noise—Because the detection sensor is mounted in a closed
system (the tank being tested), background noise in the
ultrasonic ranges would not affect the results. In addition,
the wave length of ultrasound is relatively short; therefore, it
is easily pinpointed in the presence of ambient, audible sounds.
• Equipment Accuracy—Ultrasound can be designed to sense a leak
at a rate of 0.001 gallons per hour or greater of air (44). A
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leak of 0.005 inch in diameter with a pressure differential of
five pounds per square inch can be detected.
• Operator Error—The system will be equipped with a meter to
register test results; this will minimize or eliminate
inaccuracy due to operator error (44).
• Power Variations—This will not affect system accuracy because
it will be powered by batteries.
• Instrumentation Limitation—The system can be capable of detect-
ing a leak of greater than or equal to 0.005 inches in diameter
with a pressure differential of five pounds per square inch at a
distance of 30 feet from the detector.
• Temperature, tank end deflections, vapor pockets, product
evaporation, tank geometry, wind, vibration, type of product,
atmospheric pressure, and tank inclination do not affect testing
accuracy (44).
Engineering Comments—For Ultrasonic leak detecting method, the
following are noted:
• No experimental or field testing has been conducted using this
system for tank testing. However, the method is a possibility.
• It will not provide an exact leak rate.
• It does not consider the effect of ground water level on the
leak rate.
6- VacuTect (Tanknology) (7,10,45)—
Manufacturer's Description of Method (45)—The air pressure above
the liquid in the tank is reduced to offset the pressure head of the
liquid in the tank. As air is drawn into the tank through a leak,
bubble sounds are detected by a hydrophone worn by the operator.
Characteristics of the sound permit identification of the leak. The
approximate size of the leak can be estimated from the characteristics
of the sound.
After sealing the ports from the atmosphere, this method can
normally be performed in less than one hour and no waiting time is
required before testing.
Manufacturer's Techniques to Compensate for Effects of Variables
(46)
—In this testing method, the following effects of variables are compen-
sated for as described below:
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• Water Table—When tanks are situated in areas of high water
table or the soil around the tank is saturated with water,
bubbles will not form or will persist for only a short time.
This situation is addressed by auxiliary sensors which detect
and measure the ingress of water and indicate water level
changes during the test.
• Piping Leaks—In most cases, piping leaks can be identified when
the product level is lower than the piping and a "hissing" sound
is detected by hydrophone during the test.
• Noise—The system is capable of compensating for background
noise during a test. However, potential noise sources should be
minimized in the test tank area during the test.
• Type of Product—As long as gas bubbles can be created in the
product, the testing method could be used effectively.
• Operator Error—The test can determine leaks by a skilled and
experienced operator, even in the presence of a water table
around the tank.
• Temperature, tank end deflection, vapor pocket, product evapora-
tion, tank geometry, wind, vibration, power variation,
atmospheric pressure, and tank inclination should not affect
test accuracy.
Engineering Comments—In the VacuTect testing method, the following
points are noticeable:
• Operator experience may affect the accuracy of determining a
leak rate.
• When a tank is old or corroded, tank damage or leak enhancement
due to a vacuum should be considered.
7- Varian Leak Detector (SPY 2000 or 938-41) (5,7,10,47)—
Manufacturer's Description of Method (5,47)—This method is based
upon the rapid diffusivity of helium gas through a leak, surrounding
soil, and even concrete and asphalt. An instrument using mass spectro-
metric techniques monitors helium concentration, which is introduced as
a tracer into the tank under 1 pound per square inch pressure. Normal
equilibrium time is one hour. If a very small leak is suspected, or if
the tank is surrounded by clay, it is recommended that the helium pres-
sure be raised to five pounds per square inch pressure and allowed to
equilibrate (dwell) overnight. Helium, due to its small molecular size
and surface tension, flows through a given leak more than 50 times
faster than gasoline. The method can detect a leak through which a
0.005 gallons per hour of gasoline would leak.
103
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The test is accomplished in two subtests. The first subtest is
conducted when the tank is at its normal level; this ascertains whether
the tank top, piping, and penetrations are leak free. The second sub-
test is conducted when the tank is completely empty.
Under most conditions, the test can be performed by moving the gas
detector probe over the surface above the tank. If the day is windy or
a shorter than one-hour dwell time is desirable, small holes must be
drilled through the material above the tank at about six-foot intervals
and the probe held in the holes.
As a check of the entire system, in the second subtest, a sensitive
differential-pressure gage is manifolded to the tank to determine if
there is a pressure loss during the dwell time. A pressure loss of
about 0.011 pounds per square inch in 24 hours is equivalent to a leak
that would allow a flow of about 0.05 gallons per hour in an average-
sized tank.
Manufacturer's Techniques to Compensate for Effects of Variables
(5,47)—In this method, the following effects of variables are com-
pensated for as described below:
• Temperature—The method is not significantly affected by
temperature change.
• Tank Deformation—The method is not significantly affected by
end deflection.
• Piping Leaks—Testing can accurately determine the location and
can estimate the depth of the leak before excavation begins.
Therefore, piping leaks outside the tank can be identified.
• Wind—If the day is windy, small holes must be drilled through
the material above the tank at about six-foot intervals and the
probe held in the holes.
• Equipment Accuracy—The helium detector is capable of measuring
concentrations as low as one part per million. Pressure differ-
ences as low as 0.001 pounds per square inch can be determined.
•
• Vapor pockets, product evaporation, tank geometry, vibration,
noise, operator error, type of product, power variation, atmos-
pheric pressure, and tank inclination do not affect testing
capability (48).
Engineering Comments—In the Varian Helium testing method, the fol-
lowing are noted:
• The pressure change due to temperature change is not used to
evaluate the leak rate.
104
-------
• The masking or Leak rate reduction effects of the water table
cannot be avoided.
• If the surface above the tank is frozen, small holes should be
dug to detect helium.
In addition, the system can only provide the maximum leak rate
without consideration of the location of the leak in the tank.
Inventory Monitoring
1- Gage Stick (49)—
A simple check is to record product depth with a gage stick at the
station's close of business and again at start of day. The longer this
period, such as weekends or pump repair servicing, the more accurate the
test. Gage sticks currently in use can be read to the accuracy of 1/8
inch. Since gage stick readings will fluctuate slightly because of the
angle of the stick when dipped into the tank, the condition of the tank
bottom and product creep, gaging of the stick into smaller increments
would not increase accuracy. Therefore, the gallonage represented by
1/8 inch is the possible error which will be recorded in the inventory
records whenever tanks are gaged. This may result in approximately 12
gallons per 1/8 inch measuring range error for a 10,000-gallon tank
(49a).
2- MFP-414 TLG Leak Detector (50)—
The MFP-414 TLG is basically used as an inventory monitoring sys-
tem. A sensor head is placed at the bottom of the tank (Figures 21 and
22). The sensor is connected via a shielded twisted pair of wires to
the Control Unit. The Control Unit is located in a nonhazardous area
inside the service station office. The sensor head consists cf three
pressure transducers referenced to the pressure at the top of the tank;
the bottom and middle transducers are used for water detection while the
top and middle transducers are used for product density measurement.
The absolute pressure at the middle transducer and the density measure-
ment are used to calculate the height of the product.
The electronic Control Unit can be used for monitoring up to six
tanks and can be installed more than 1,000 feet from any given tank.
The manufacturer indicates that the temperature effect is corrected by
density measurement. Accuracies of ±0.25 percent and sensitivity of 0.1
percent of product height in the measurement of the product height are
claimed. Also, for the most accurate overall results, for the total
volume of product, it is recommended that each tank be calibrated in
place to account for any deformities in the tank that may have occurred
during installation.
105
-------
SENSOR ASSEMBLY
STANDARD 3/4"
ELECTRICAL AND
PLASTIC CONDUIT
SERVICE LOOP
STANDARD 4" FILL
TUBE CAP
DIAPHRAGM FOR
MEASUREMENT OF
SPECIFIC GRAVITY
DIAPHRAGM FOR WATER
DETECTION
DIAPHRAGM FOR BOTTOM
PRESSURE, SPECIFIC
GRAVITY, AND WATER
DETECTION
Figure 21. MFP-414 TLG Leak Detector-Sensor Assembly (50)
Ref: Transitron Controls
106
-------
TAMK LEVEL GAUGE & LEAK DETECTOR
BASIC FUNCTIONS
-MEASURES LEVEL/VOLUME
-DETECTS LEAKS
-DETECTS WATER
• IMOTI COMMUNICATION
VI* TlklfNOn* UNO
DIGIT LED DISPLAY SHOWS
SEALED SWITCHES FOR TANK
-LINEARIZES HORIZONTAL TANKS
(FROM STRAPPING TABLES
OR EQUATIONS)
-ACCEPTS UP TO SIX(6) TANK
SIGNALS
-ACCEPTS UP TO SIX OTHER
SIGNALS
(FLOW DATA FROM PUMPS)
-ALARMS-HI /LO ,H|20, LEAK
-AC/DC POWER (2* VDC)
-OPTIONS:
o PRINTER
o LIGHTS, HORNS, BUZZERS, ETC.
PRESSURE SENSORS
- INHERENT TEMPERATURE COMPENSATION
- COMPENSATE FOR DIFFERENCES IN SPECIFIC
GRAVITY OF PRODUCT
Figure 22. MFP-414 TLG Tank Level Gauge & Leak Detector (50)
Ref: Transitron Controls
107
-------
The system is equipped with a six-digit display that allows an
operator to view the total volume or weight of product in each tank in
any desired unit of measure. A switch on the display also allows for
entering a "SLEEP" mode whereby the tank is monitored for product gain
(fill) or loss (theft or leakage). An RS-232C port is provided for
connection to a printer, to the station computer/register, or to a
modem. The built-in modem support allows for automatic dialing and
reporting of alarm conditions (water, leakage, theft) when equipped with
an optional modem. This feature also provides a means of remote readout
of product inventory from a remote location.
3- TLS-150 Tank Level Sensor (Veeder-Root) (10,51)—
The TLS-150 tank level sensor is a system designed to improve in-
ventory management of nonconductive fluids such as gasoline and diesel
fuel in underground tanks. It can monitor up to four tanks to identify
inventory losses and accurately reconcile inventories of fuel with
dispensing and deliveries.
This system consists of a computerized inventory monitoring with a
digital electronic sensing probe for each tank monitored. The system
analyzes signals for liquid temperature, liquid depth, and water
level. An integral dot matrix printer provides hard-copy documentation.
The TLS system has three modes of operation: leak detection, tank
inventory, and automatic delivery reporting. When the leak monitor mode
is activated, the system continuously monitors fuel levels in each
tank. Also, an hourly report on each tank shows temperature-compensated
inventory changes to 0.1 gallons. When a loss of 25 gallons occurs
during a one-hour period, an inventory loss alarm initiates a signal.
An optional telecommunications interface allows remote polling of a
TLS system from a central management location through a computer or
teletype device.
In evaluating TLS system results, a measurement accuracy of ±1.5
degrees Fahrenheit for temperature and ±0.1 inches for level should be
assumed. These ranges of accuracies, with tank end deflection, may
preclude low leak rate detection with the TLS system.
Techniques to Compensate for Effects of Variables In Inventory
Control Leak Detection Tests—To minimize error when using this method
to identify a leaking storage tank and to determine the approximate leak
rate for major leaks, the following approaches are recommended:
1. American Petroleum Institute publication API 1621, "Recommended
Practice for Bulk Liquid Stock Control at Retail Outlets."
2. Inventory records on a daily basis. Failure to do so is often
considered by a Fire Marshall sufficient reason to order tests
108
-------
for leakage. NFPA 30, the Flammable and Combustible Liquids
Code, contains an inventory control requirement. This code has
been adopted by the Occupational Safety and Health
Administration (OSHA) and by 35 states.
3. The National Conference on Weights and Measures allows a legal
tolerance of 0.5 percent on gasoline meters. The total of all
such unavoidable losses should not exceed one-half of one per-
cent, or five gallons per 1,000 gallons delivered.
4. The system of inventory control should detect discrepancies.
5. Where remote gages are used, accuracy can be verified peri-
odically by checking the tank with stick gages.
6. All tanks must be measured for water levels, especially before
and after deliveries. Water gaging is accomplished by applying
a water-finding paste to the gage stick.
Leak Effects Monitoring
This class of leak detection methods provides an indirect indi-
cation of leakage by evaluating resulting environmental impact. It may
be difficult to determine which tank is leaking when there is more than
one tank. These methods are likely to be more conclusive than the
quantitative testing methods, if no interfering substances are present.
1- Collection Sumps (49)—
Collection sumps can be used in dry hole installations as a
collection mechanism which aids in leak detection.
In this type of system, the floor of the storage excavation (or
secondary containment liner) is sloped at a rate greater than or equal
to 1/8 inch per foot to a collection sump. The sump should be at least
two feet deep and be extended to grade via, at a minimum, a four-inch-
diameter (Schedule 40) polyvinyl chloride (PVC) pipe and topped with a
waterproof cap. This extension is essentially an observation well
screened in the region of the sump. The sump should be equipped with a
removable leak detection sensor capable of detecting 1/8 inches of
standing product, which activates a strategically located aboveground
alarm when that product is present. If constructed as described above
and shown in Figure 23, the sump and well can also be used for leak
sampling and for the recovery of leaked or spilled product.
2- Dye Method (10)—
In this method, a perforated pipe is installed around the perimeter
of the underground tank storage area. A bag of dye is connected to the
low point of the pipe. The dye is soluble in hydrocarbon and completely
109
-------
P.V.C. PIPE
PERFORATED P.V.C. PIPE
COVERED WITH
FIBERGLASS
CLOTH
CAP
BOREHOLE ANNULU8
WATER TABLE
IMPERMEABLE PLUQ8
PEA GRAVEL
BOREHOLE CUTTINGS
Source: Leak-X Corp., 560 Sylvan Ave., Englewood Cliffs, N.Y
Figure 23. Typical Wells For Continuous Gas Or Vapor Monitoring (49)
Ref: Recommended Practices for Underground Storage of Petroleum,
New York Department of Environmental Conservation
110
-------
unaffected by water. The bag is usually checked every day to see if any
of the dye has been dissolved.
The installation of the perforated pipe and the length of time to
detect small leaks are the drawbacks of this system. In addition, small
leaks most likely will not be detected.
3- Ground Water or Soil Core Sampling (10)—
The presence of trace organics can be detected by soil core or
water sampling in the vicinity of underground tanks. In both cases,
small holes or wells should be drilled. A portable gas chromatograph
could be used to analyze samples at the site. When a more precise
determination is required, the sample should be analyzed in a labora-
tory. If a series of wells are drilled at proper locations, the source
of the leak may be determined. However, this method cannot distinguish
between tank leaks and small spills in the area (usually from poor
housekeeping practices).
4- Interstitial Monitoring in Double-Walled Tanks (49)—
Systems which monitor the interstitial space between the walls of
double-walled tanks using either vacuum sensors or fluid sensors repre-
sent the best mode of continuous leak surveillance available. In such
systems, a leak can be detected due to failure of only one of the two
walls of the tank. Thus, the operator can be made aware of the leak
before stored product has left the tank and entered the environment.
In interstitial leak monitoring system, sensors would be used to
monitor tanks that have a vacuum drawn in the space between the tank
walls. Failure of either the inner or outer wall is detected by loss of
vacuum. Such systems are applicable in either wet or dry hole
installations.
Fluid sensors, on the other hand, would be located between the tank
walls to detect the presence of liquid due to failure of the inner wall
(detecting an outflow of product) or the outer wall (detecting an inflow
of water). Such systems are more applicable in wet hole installations
where failure of the outer wall will result in the presence of a fluid
in the interstitial space. Because failure of the outer wall can go
undetected if fluid sensors are used in dry hole installations, such an
application is not recommended if pressure sensors can be used instead.
In the case of either type of interstitial monitoring system, it is
important that the tank be constructed to allow for free movement of
fluids or gases in the space between the tank walls so that a leak any-
where in the tank can activate strategically located sensors.
Ill
-------
5- LASP Monitoring System (Leakage Alarm System for Pipe) (52)—
The wall-diffusion effect is the basis for the Leakage Alarm System
for Pipe (LASP) system. A one-half-inch-diameter sensor tube is made of
a plastic material that allows rapid wall diffusion. The LASP system
consists of three components: a flexible sensor tube, a pump, and a
detector. The sensor tube can be moved to strategic locations around
the tank. The vapors of a leaked product coming in contact with the
LASP tube will diffuse into the tube and be captured. At regular
intervals (e.g., every 24 hours), a stream of air followed by an injec-
tion of a detectable vapor is pumped through the LASP tube. The
detector at the end of the LASP tube will register on a line recorder
any leakages carried by the air stream, and the regular injection of a
detectable vapor will show as an end peak.
6- Observation Wells (49)—
Observation wells are used to monitor for leaks from underground
tank installations in areas of high ground water. In this instance,
ground water will be present in the excavation for most or all of the
year. A diagram of an observation well installation is shown in Figure
24.
An observation well, or liquid product sensing well, consists of,
at a minimum, a four-inch-diameter (Schedule 40) PVC pipe placed in the
tank excavation. The wells are constructed with a well screen long
enough to provide a length of five feet or more above the water table',
or to the well cap, and extending a minimum of five feet into the ground
water or two feet below the tank bottom, whichever is greater. Well
screens typically have a slot size of 0.02 inches. The connecting well
pipe is extended to grade and covered with a waterproof cap which is
capable of being sealed.
As is true of the vertical section of the U-tube, if observation
wells are constructed as described above and shown in Figure 24, they
can be used for leak sensing, direct sampling, and product (and con-
taminated ground water) recovery. When leak sensors are used, they must
be capable of detecting a 1/8-inch layer of the stored product on the
ground water surface, and they must activate a strategically located
aboveground alarm when that product is detected.
The selection of the number and location of the observation wells
in a particular storage system is dependent upon the local hydrogeology,
including parameters such as the ground water flow direction. It is
recommended that any installation using observation wells employ at
least two wells in each excavation.
Existing sites may have observation wells drilled to ground water,
provided the location and orientation of the tanks and piping is known.
112
-------
EACH WELL CONSISTS OF 4* PERFORATED PVC PIPE, DRIVEN AT
LEAST 2 FEET BELOW THE BOTTOM OF THE TANK OR AT LEAST
5 FEET INTO THE QROUNDWATER
WATERPROOF
CAPS CAPABLE OF
BEING SEALED
\
OVERFILL PREVENTION MANWAY- ALLOW ENTRY
DEVICE WITH EXTRACTABLE |NTO THE TANK- EXTENSION
TEE TO GRADE FITTING TO GRADE (OPTIONAL) FITTING
FINISHED GRADE
QROUNDWATER
T&
>-TCJ
ONCRETE KNOCKOUT
SECTION (OPTIONAL)
SPACING AND FILL TO
BE IN ACCORDANCE TO
TANK MANUFACTURER
SPECIFICATIONS
6'MIN.
i—f i unuunuTTA i en — i
' J7* - V * ZIr-
Source. James Pirn Suffolk County Dept. of Health Services
T
-V
Figure 24. Examples Of Observation Wells (49)
Ref: Recommended Practices for Underground Storage of Petroleum,
New York Department of Environmental Conservation
113
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7- Pollulert and Leak-X Detection Systems (11,53,54)—
Both detection systems use the significant difference between the
thermal conductivity of hydrocarbons and of water to detect leaks. The
system's solid-state electronic sensors are placed in a well near the
storage tank. The bottom of the well should be at least 10 feet below
the bottom of the storage tank. A programmed microprocessor contin-
uously monitors the presence of water or hydrocarbons in the monitoring
well. If the sensors detect any hydrocarbons, an alarm sounds. The
unit can be wired to automatically summon personnel by telephone.
The major drawbacks of this method are the installation and expense
of the monitoring well. However, once the well is installed, if a tank
begins to leak, the leak is detected before major damage occurs (unless
the leak goes straight down, as happens when ground water is low).
8- Remote Infrared Sensing (10)—
This method depends on the difference in soil temperature due to
the presence of hydrocarbons. An infrared sensing device (either an
infrared camera or a video system) remotely senses temperatures in the
storage tank area. This is usually done from an aircraft rather than at
ground level.
This method is usually only a part of a survey for leak detection;
additional ground or subsurface information is required to complete the
survey. The ability of this method to detect small leaks is doubtful.
9- Surface Geophysical Methods (10)—
The presence of hydrocarbons in the ground could be determined by
using a geophysical method such as ground penetrating radar, electromag-
netic induction, or resistivity techniques. These methods are not the
primary subject of this text; therefore, they will not be discussed in
further detail.
10- U-Tubes (49)—
A U-tube consists of a four-inch-diameter (Schedule 40) PVC pipe
installed as shown in Figure 25. The horizontal segment of the pipe is
half-slotted (typical slot size, 0.06 inches), wrapped with a mesh cloth
to prevent backfill infiltration, and sloped (pitched) toward the sump
with a slope on the order of 1/4 inch per foot. At the higher end of
the pipe, there is a 90-degree sweep to a vertical pipe that is extended
to grade. At the lower end of the horizontal pipe, there is a tee
connection with a vertical pipe. Above the tee this vertical section is
extended up to grade, and below the tee it is extended down two feet to
act as a collection sump. All vertical pipe sections are unperforated,
and the bottom of the sump is sealed to be leakproof. All openings to
grade are provided with watertight caps capable of being sealed. It is
114
-------
FINISHED
GRADE -
OVERFILL
PREVENTION
DEVICE WITH
EXTRACTABLE
TEE TO GRADE
OBSERVATION WELLS: WATERPROOF CAPS
CAPABLE OF BEING
SEALED
EXTENSION OF
MANWAY TO GRADE
(OPTIONAL)
NOTE:ALL PIPING
TO BE 4'
SCHEDULE
40 PVC
4' TEE
SEALED
CAP -
90* SWEEP
4* DIAMETER HALF SLOTTED PIPE
WRAPPED WITH FILTER MATERIAL - I/4"PER
FOOT PITCH TOWARDS SUMP.
SLOT SIZE .060
-SPACING AND FILL TO BE IN ACCORDANCE TO
TANK MANUFACTURER SPECIFICATIONS
Source: James Pirn, Suffolk County Dept. of Health Services
Figure 25. Example Of A U-Tube Installation (49)
Ref: Recommended Practices for Underground Storage of Petroleum,
New York Department of Environmental Conservation
-------
imperative that these tubes be secured so that products cannot be
accidentally delivered into them.
These tubes may be installed under each tank in an excavation, or
centrally located in the excavation. In either case, the excavation
bottom must be sloped slightly (a minimum of 1/4 inch per foot) toward
the U-tube to permit collection of any leaked material.
The collection sump of the U-tube should be equipped with a
removable sensing device which is capable of detecting 1/8 inch of
standing product or a 1/8-inch layer of product on water. This sensing
device is installed so as to activate an alarm which is strategically
located aboveground.
If the vertical section of the U-tube is designed as described
above and shown in Figure 25, leaked or spilled product can be readily
recovered from the collection sump using standard equipment such as a
3-3/8-inch submersible pump. Construction of the vertical section in
this manner also permits easy sampling of leaked material to pinpoint
the source of a leak. This may be necessary in situations where two or
more similar products are stored, such as in an excavation housing both
leaded and unleaded gasoline.
U-tubes can be used only in situations where the excavation is
above the high level mark of the ground water table (dry hole
installations), the excavation has been provided with an impervious
secondary containment layer on its floor, and the installation is
covered with a waterproof cap. In such cases, any leaked material will
eventually find its way to the U-tube's collection sump where it can be
detected without water interference.
11- Vapor Wells (49)--
A vapor well is similar to an observation well except that it is
intended for monitoring vapors or odors from underground storage systems
instead of liquids. Such a well consists of a four-inch-diameter PVC
pipe (Schedule 40) installed in the excavation within five feet of the
tank. In dry installations, these wells extend to the containment liner
on the floor of the excavation. In wet installations, they extend into
the ground water.
The well screens in vapor wells should have a slot size of 0.02
inches. In dry hole installations, the screened opening should extend
from the containment volume floor to a height of at least five feet. In
wet hole installations, the well screen must be long enough to provide a
length of five feet or more above the water table and should extend a
minimum of five feet into the water table or two feet below the tank
bottom, whichever is greater.
116
-------
Vapor wells can be used only at uncontaminated sites. Once product
vapors have entered the well, they will remain there until both their
source has been removed (the leak has been pinpointed and repaired) and
the well has been purged free of residual vapors. If the well cannot be
purged, the vapor well must be either retrofitted with an alternate
means of sensing leaked product or abandoned. Figure 23 is a diagram of
a typical, dry hole, vapor well.
117
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1. Conference Report on H.R. 2867 Hazardous and Solid Waste Amendments
of 1984, Congressional Record-House, H11140, October 3, 1984.
2. National Petroleum News, January 1979, pp. 64.
3. National Fire Protection Association, Underground Leakage of Flam-
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Association, Batterymarch Park, Quincy, MA 02269, 1983.
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Consultants, Inc., Stoughton, MA.
5. Tightness-Testing Systems for Underground Tanks Symposium,
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13. Verbal Communication with Gary L. Everett, ARCO Petroleum Products,
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118
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16. "Ethyl" Tank Sentry Testing Bulletin, Ethyl Corporation, Petroleum
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119
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32. Maresca, J. W. and P. C. Evans, "Measurement of Leaks in
Underground Storage Tanks Using Laser Interferometry," Technical
Report No. 1,
SRI Project 7637, SRI International, Menlo Park, CA, June 1979.
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Using Laser Interferometry," Final Report, SRI Project 7637, SRI
International, Menlo Park, CA, Sept. 1981.
34. Verbal Communication with Joseph W. Maresca, Vista Research, Inc.,
Palo Alto, CA.
35. Oh, C.B., Acoustical Monitoring System (AMS), Description Letter,
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38. Verbal Communication with William Burkhart, Smith & Denison,
Hayward, CA.
39. TRC Leak Detection, Tracer Research Corporation, Tucson, AZ.
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Elmsford, NY.
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42. Plant Engineering, April 3, 1980, pp. 103-106.
43. Hydrocarbon Processing, Jan, 1983, pp. 93-94.
44. Verbal Communication with Mark A. Goodman, Ue Syscems, Inc.,
Elmsford, NY.
45. Tanknology Bulletin, Tanknology, Edmonton, Alberta.
46. Verbal Communication with Edward Smith, Tanknology, Edmonton,
Alberta.
47. Varian Helium Leak Detectors 938-41 and SPY 2000 Bulletin, Varian,
Vacuum Products Division, Lexington, MA.
48. Verbal Communication with Ert Shivert, Varian, Vacuum Products
Division, Lexington, MA.
120
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49. Recommended Practices for Underground Storage of Petroleum, New
York Department of Environmental Conservation, Albany, NY, May
1984.
49a. Comments on "More About Leaking Underground Storage Tanks: A
Background Booklet to Accompany the Chemical Advisory," Report,
Holland & Knight, Washington, D.C., September 1984.
50. MFP-414 Leak Detector Bulletin, Transitron Controls, Easton, MA.
51. TLS-150 Tank Level Sensor, Bulletin, VEEDER-Root, Petroleum
Products, Hartford, CT.
52. Leakage Alarm System for Pipe (LASP) Bulletin, Teledyne Geotech,
Garland, TX.
53. Pollulert Fluid Detection Systems Bulletin, Mallory, Electrical/
Electronic Group of Emhart, Indianapolis, IN.
54. Leak-X Bulletin, Leak-X Corp, Englewood Cliffs, New Jersey.
55. Recommended Practice for Bulk Liquid Stock Control at Retail
Outlets, Publication 1621, American Petroleum Institute,
Washington, DC, 1977.
121
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APPENDIX
LEAK DETECTION METHODS
MANUFACTURER OR PRACTITIONER PHONE NUMBERS
LEAK DETECTION TESTING METHODS
PHONE NUMBER
CONTACT NAME
Volumetric (Quantitative) Leak
Testing Methods
1 - Ainlay Tank Tegrity Testing
(TTT)
2 - ARCO HTC Underground Tank
Leak Detector
3 - Certi-Tec Testing
4 - "Ethyl" Tank Sentry Testing
5 - EZY-CHEK Leak Detector
6 - Fluid-Static (Standpipe)
Testing
7 - Heath Petro Tite Tank and
Line Testing (Kent-Moore
Testing)
8 - Helium Differential Pressure
Testing
9 - Leak Lokator Test (Hunter-
Sunmark Leak Detection)
10 - Mooney Tank Test Detector
11 - *PACE Tank Tester
12 - *PALD-2 Leak Detector
13 - Pneumatic Testing
14 - Tank Auditor
15 - *Two-Tube Laser
Interferometer System
(312) 328-6119 Mr. John Ainlay
(312) 333-3000 Mr. Gary L. Everett
(612) 487-1484 Mr. Jonathan Nedved
(609) 452-8600 Mr. A. V. Morschauser
(517) 684-7180 Mr. John Homer
Method is used by different contractors
(617).344-1400 Mr. Jack Stillwagon
(415) 228-8400 Mr. John Schweizer
(215) 296-7380 Mrs. Donna Hymes
(504) 241-0453
(416) 443-7032
Mr. Joseph Mooney
Mr. Jack Witherspoon
(Not Available) Mr. Werner Grundmann
3425 West 30th Ave.
Vancouver, B.C.,
V6S1W3 CANADA
Method is used by different contractors
(617) 740-1717 Mr. William E. Baird
(415) 424-1251 Mr. Joseph W. Maresca
Not commercially available.
A-l
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LEAK DETECTION TESTING METHODS
PHONE NUMBER
CONTACT NAME
Nonvolumetrie (Qualitative) Leak
Testing Methods
1 - *Acoustical Monitoring
System (AMS)
2 - Leybold-Heraeus Helium
Detector, Ultratest M2
3 - Smith & Denison Helium Test
4 - TRC Rapid Leak Detector for
Underground Tanks and Pipes
5 - *Ultrasonic Leak Detector,
Ultrasound
6 - VacuTect (Tanknology)
7 - Varian Leak Detector
Inventory Monitoring
1 - Gage Stick
2 - MFP-414 Leak Detector
3 - TLS-150 Tank Level Sensor
(Veeder-Root)
Leak Effects Monitoring
1 - Collection Sumps
2 - Dye Method
3 - Ground Water or Soil Core
Sampling
4 - Interstitial Monitoring in
Double-Walled Tanks
5 - L.A.S.P. Monitoring System
6 - Observation Wells
7 - Pollulert and Leak-X
Detection Systems
(615) 966-4773 Mr. Charles B. Oh
(412) 327-5700
(415) 782-9788
(602) 623-0200
Mr. William C.
Worthington
Mr. William H.
Burkhart
Mr. Glenn Thompson
(914) 592-1220 Mr. Mark A. Goodman
(403) 483-3506 Mr. Edward Adams
(617) 935-5185 Mr. Roger Schneider
Method is used by different contractors
(617) 238-6911 Mr. Stanley Hayes
(203) 527-7201 Mr. Tony Spera
Method is used by different contractors
Method is used by different contractors
Method is used by different contractors
Method is used by different contractors
(214) 271-2561 Industrial System Mar-
keting
Method is used by different contractors
(317) 856-3857 Mr. Dale McClain (Pol-
lulert)
(212) 822-6767 Mr. John Gelles
(Leak-X)
Not commercially available.
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LEAK DETECTION TESTING METHODS
PHONE NUMBER
CONTACT NAME
8 - Remote Infrared Sensing
9 - Surface Geophysical Methods
10 - U-Tubes
11 - Vapor Wells
Method is used by different contractors
Method is used by different contractors
Method is used by different contractors
Method is used by different contractors
*Not commercially available
A-3
ft US GOVERNMENT PRINTING OFFICE 1986 - 646-116/20741
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