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Presenting: Common Questions on Leak Detection
Here's help in handling the most frequently asked
questions on leak detection!
Are you looking for a way to make sure your office is
providing accurate and consistent answers to leak de-
tection questions?
Are you spending too much time answering basic leak
detection questions?
Have you sometimes wondered how EPA Headquar-
ters answers certain leak detection questions?
If so, COMMON QUESTIONS ON LEAK
DETECTION can help you.
We've canvassed States and Regional Offices to compile a list of the
most commonly asked questions on leak detection and have pre-
pared answers that reflect the Federal requirements. These include:
© general leak detection
© automatic tank gauging systems
© tank tightness testing and inventory control
© manual tank gauging
© ground-water monitoring
© vapor monitoring
© secondary containment with interstitial monitoring
© piping
We've also included space to write in State/local answers or notes
that you and your staff can refer to as you answer calls.
COMMON QUESTIONS is a tool that can especially help State
and local officials answer questions on leak detection efficiently
and ensure that their answers are complete, accurate, and consis-
tent.
For more information, contact your EPA Regional Office or the EPA
Hotline at 1-800-424-9346.
Also available in our leak detection series:
® "Straight Talk on Tanks: Leak Detection Options" (2-
page summaries on the various methods allowed under
the Federal requirements)
© "Leak Lookout" (a brochure on external release detectors)
® "Detecting Leaks: Successful Methods Step-by-Step" (a
handbook describing the procedures of the Federally-
approved methods of leak detection)
® "Volumetric Tank Testing: An Overview" (an ORD
booklet summarizing the technical findings of an EPA
study on volumetric tank testing)
Office of Underground Storage Tanks, Washington, D.C. 20460
February 1990
Printed on Recycled Paper
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EPA 510-K-92-007
STRAIGHT TALK
ON TANKS
^HB^^^^^^^^Hi^^VI»^••^••^••Ml^^I^KWBM
A telephone tool for State underground storage tank program staff
Common Questions on L^ak Detection
This document presents answers to commonly asked questions concerning leak detec-
tion regulations for underground storage tanks (USTs). If you often need to answer
technical questions on leak detection, yo^ should find these "Q's & A's" useful in re-
sponding to public inquiries.
You will find the questions arranged primarily by leak detection method, but some
questions are general. Also, a list of additional sources of information appears after
the Index to Questions.
Please note the following two items before you start to use these questions and an-
swers.
• You wiU find a "Federal Answers" column on each page. Because State or local
requirements may be different from those presented in the Federal answer, we
have left space for you to enter any different requirements or additional
material in a "State/Local Answers" column.
• As you help people with UST questions, keep in mind EPA's "Straight Talk on
Tanks " series of 2-page flyers. Each flyer describes one of the approved leak
detection methods. You may want to suggest sending these flyers to the caller,
reserving detailed information, if possible, until the caller has read the flyers.
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Common Questions on Leak Detection
Index to Questions
Page
General
Do the Federal UST regulations for leak detection require me to replace my tank? 1
Are there any differences between choosing leak detection for an existing UST and
a new UST? , 1
Which leak detection methods are approved by EPA? 2
What is the "best" or 'least expensive" leak detection method? 2
What do the probabilities of detection and false alarm mean? What methods
do they apply to? 2
What do I do if I think I have a leak? 3
Ground-Water Monitoring
What information should I gather during a site assessment? 4-
What constitutes proper design and construction of ground-water
monitoring wells? 4
The Federal regulations require the detection of at least one-eighth inch
of free product. What does this mean and what kind of equipment do I need? 4
How many ground-water monitoring wells do I need? Where should they be placed? 5
Vapor Monitoring
What information should I gather during a site assessment? 6
What constitutes proper design and construction of vapor monitoring wells? 6
Can I use vapor monitoring at a site with background contamination? 6
Where should vapor monitoring wells be placed? How many wells do I need?
How deep should they be? 7
Can I use vapor monitoring at a diesel site? 7
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Secondary Containment with Interstitial Monitoring
8
What does secondary containment mean? . . ! ; •
Does the whole tank have to be surrounded by 'the secondary containment? 8
Why is proper installation especially crucial to1 the effectiveness of g
secondary containment?
9
"What is interstitial monitoring?
Automatic Tank Gauging System
How does an ATGS work?
Why does an ATGS have two different modes of operation? 10
JHbwo/ie/idoIhavetousetiieATGS? . . . ,
Vfhatproduct level in the tank is necessary to run the leak test mode on an ATGS? . ... .11
Do I have to dig up my tank to install an ATGS?
Tank Tightness Testing and Inventory Control
How good is tightness testing? Can Hie results be trusted? 12
13
How often do I have to do a tightness test? . . . . .
1 Q
Whatkind of tightness tests are available? ;.......
How can I increase the accuracy of daily inventory control? 1
What are the reporting requirements for inventory control?
I
Manual Tank Gauging
What is the difference between periodic manual tank gauging and i g
inventory control? • • • •
' 1A
For what size of tank can manual tank gauging be used?
Suction Piping
1 7
Does the rule require me to install suction piping?.
Pressurized Piping
What does the Federal regulations' requirement for an "automatic line leak
defector" mean?
11
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How to Get More Information
The following people can provide more information:
• State and local agencies that regulate USTs
• Local fire department
• Trade association representative
• State petroleum marketers association
• Contractor, jobber, or equipment supplier
• Leak Detection Technology Association (202) 835-2355/828-1000
• National Leak Prevention Association (800) 543-1838
• EPA's RCRA Hotline (for Federal requirements only) (800) 424-9346
Other sources of information are:
• EPA's "Straight Talk on Tanks" series of 2-page flyers
• EPA's handbook, Detecting Leaks: Successful Methods Step-by-Step
• EPA's booklet, Leak Lookout — Using External Leak Detectors to Prevent Petroleum
Contamination from Underground Storage Tanks
• EPA's booklet, Oh No! Petroleum Leaks and Spills: What Do You Do?
• EPA's booklet, Volumetric Tank Testing: An Overview
• '^Underground Storage Tanks; Technical Requirements and State Program Approval";
Final Rules 40 CFR Parts 280 & 281 (Federal Register Part II 9/23/88)
Order these from: U.S. Environmental Protection Agency
Office of Underground Storage Tanks
P.O. Box 6044
Rockville,MD 20850
• Cleanup of Releases from Petroleum USTs: Selected Technologies
Stock No. 055-000-00272-0 $7.50
• Petroleum Tank Releases Under Control: A Compendium of Current Practices
for State UST Inspectors
Stock No. 055-000-00295-9 $8.50
• Processes Affecting Subsurface Transport of Leaking Underground Tank Fluids
Stock No. 055-000-00269-0 $3.25
• Survey of Vendors of External Petroleum Leak Monitoring Devices for Use with USTs
Stock No. 055-000-00277-1 - $4.25
Order these from: Superintendent of Documents
U.S. Government Printing Office
Washington, D.C. 20402
(202) 783-3238
iii
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-------
General
Questions
Federal
Answers
State/Local
Answers
Q. Do the Federal UST regula-
tions for leak detection re-
quire me to replace my tank?
No, but you must install leak detection
at your UST site according to the follow-
ing schedule:
.COMPLIANCE SCHEDULE
It must have leak
If tank was detection by
installed... December of...
before 1965 or unknown 1989
1965-1969 1990
1970-1974 1991
1975-1979 1992
1980 - Dec. 1988 1993
Suction piping as above
Pressurized piping 1990
You should remember, however, that
your existing UST must also meet the
requirements for corrosion protection
and spill/overfill prevention by
December 1998.
* [see FR 37201/37146]
Q. Are there any differences
between choosing leak de-
tection for an existing UST
and a new UST?
A. Yes. The main difference results from
the difficulties of installing leak detec-
tion at existing UST sites. For example,
it can be difficult and expensive to pro-
vide an existing tank with a secondary
containment system. Also, it is impor-
tant to identify the location of the exist-
ing UST and its piping before installing
the monitoring wells used in vapor and
ground-water monitoring. Otherwise,
you run the risk of puncturing the exist-
ing tank and piping during the installa-
tion of monitoring wells. It is also gen-
erally easier to install and properly lo-
cate monitoring wells when the tank is
being installed rather than after instal-
lation.
* The FR numbers appearing in brackets in this document refer to corresponding pages in the Federal Register
(40 CFR Parte 280 and 281; September 23,1988). The number before the slash mark refers to the Rule; the number
after the slash mark refers to discussion in the Preamble.
-1-
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General \
Questions;
Federal
Answers
Q. Which leak detection meth-
ods are approved by EPA?
The Federal regulations allow the fol-
lowing leak detection methods for tanks:
i
• Ground-water monitoring
• Vapor monitoring
• Secondary containment with intersti-
tial monitoring
• Automatic tank gauging
• Tank tightness testing and inventory
control
• Manual tank gauging
• Other methods, if approved
Most of these methods can also be used
for detecting.leaks from piping (only
manual and automatic tank gauging
cannot be used). In addition, pressur-
ized piping requires automatic line leak
detectors, which must be in place by
December 1990.
NOTE: These Federally approved meth-
ods for detecting leaks from tanks and
piping are described in EPA's "Straight
Talk on Tanks" flyers. See these flyers
for details and restrictions on the use of
each method.
[see FR 37202-203/32157-166]
State/Local
Answers
Q. What is the "best" or 'least ex-
pensive" leak detection
method?
There is no one leak detection method
that is best suited for an individual site
or that will always be the least expen-
sive choice. Choosing the best, most
cost-effective leak detection depends on
your tanks, site conditions, business
schedule, and many other factors.
Q. What do the probabilities of
detection and false alarm
mean? What methods do
they apply to?
These probabilities refer to how often a
method makes a mistake in detecting a
leak. Tightness testing, automatic tank
gauging, and! automatic line leak detec-
tors must meet the Federal require-
ments for "probabilities" by December
1990. (The probability of detection is 95
percent and the probability of false
alarm is 5 percent.)
[see FR 37201/37145]
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General
Questions
Federal
Answers
State/Local
Answers
Q. What do I do if I think I have
a leak?
An EPA booklet called "Oh No!
Petroleum Leaks and Spills: What Do
You Do?" is available on this subject. It
gives you details on what to do and
what to consider when you have a leak.
But in short, if you think you have a
leak you need to quickly confirm if the
leak is real. What first appears to be a
leak may be the result of faulty equip-
ment (for example, fittings on top of the
tank) that is part of your UST system or
its leak detection system. Double check
this equipment carefully for failures.
You may simply need to repair or re-
place equipment that is not working.
If repair or replacement of faulty equip-
ment does not solve the problem, then
you must report this finding to the regu-
latory authority and test the entire UST
system to confirm the leak. You must
report confirmed leaks to your regulato-
ry authority.
[see FR 37204/37169-172]
3-
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Groiund-Waier
Monitoring Questions
Q. What information should I
gather during a site assess-
ment?
Federal
Answers
A. Before installing a ground-water moni-
toring system, a preliminary site assess-
ment should supply the following infor-
mation:,
« Locationof the tanks and piping;
• Type of backfill and its permeability;
• Contamination level of backfill;
• Location of [the ground water;
• The ground water's direction of flow,
flow gradient, and level of fluc-
tuation;
• The stored product's compatibility
with the monitoring device; and
• The stored product's specific gravity
and solubility.
[see PR 37203/37162-163]
State/Local
Answers
Q. What consitutes proper de-
sign and construction of
ground-water monitoring
wells?
A. To answer this question definitively,
you should have your State send a
schematic of a monitoring well that
meets State specifications.
Q. The Federal regulations re-
" quire the detection of at
least one-eighth inch of free
product. What does this
mean and what kind of
equipment do I need?
"Free product" refers to liquid that has
leaked from the UST and is found float-
ing on the ground water. (The liquid
must float on the water table when re-
leased.) The monitoring device you use
must be able to detect the presence of a
one-eighth inch layer of liquid on the
ground water. The monitoring equip-
ment used fo!r this can be as simple as a
clear bailer bucket that you use manu-
ally on at least a monthly basis, or a
permanently installed device that oper-
ates automatically on a continuous
basis.
[see FR 37203/37162-163]
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Ground-Water)
Monitoring Questions
Federal
Answers
State/Local
Answers
Q. How many ground-water
monitoring wells do I need?
Where should they be
placed?
A general rule recommended by profes-
sionals is the placement of at least one
monitoring well on each side or corner
of the tank field. In some cases, the in-
stallation of a well upgradient of the
UST system might be beneficial if there
are off-site petroleum UST systems lo-
cated near your site — this will help
identify whether a leak is from your
tank or one of the neighboring UST
sites.
In general, the use of a single monitor-
ing well will be adequate for UST sites
with only one tank. If the site consists
of multiple tanks, more than one moni-
toring well should be provided. The
exact number of wells should be based
on the site hydrogeology and the UST
system configuration, especially the ex-
tent and location of piping runs.
Monitoring wells should be placed as
close to the tank excavation as possible.
Care needs to be taken when selecting a
monitoring well site to ensure that the
installation of the well will not interfere
with any subsurface structures such as
utilities or UST system piping.
Monitoring wells should be marked and
closed to outside unauthorized access so
that they are not inadvertently contami-
nated by activities from the surface.
[see FR 37203/37162-163]
-5
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Vapor Monitoring
i Questions
Federal
Answers
State/Local
Answers
Q. What information should I
gather during a site assess-
ment?
A. Before installing a vapor monitoring
system, a preliminary site assessment
should supply the following information:
• Location of the tanks and piping;
• Type of backfill and its permeability;
• Contamination level of backfill;
• Location of the ground water;
• The stoied product's compatibility
with the monitoring device; and
• The stored product's volatility.
[see FR 37202/37161-162]
Q. What constitutes proper de-
sign and construction of
vapor monitoring wells?
To answer this question definitively,
you should have your State send a
schematic of a monitoring well that
meets State specifications.
Q. Can I use vapor monitoring
at a site with background
contamination?
Yes, under certain conditions. Vapor
monitors may respond to vapors re-
maining from previous spills or leaks,
falsely indicating a current leak.
However, vapor monitors work effective-
ly as long as the background contamina-
tion levels are low enough not to inter-
fere with the monitoring system. Use of
a vapor monitoring system is not recom-
mended, without further investigation,
at sites with high background concen-
trations (for example, above 1,500 ppm
of total hydrocarbons for gasoline). The
level of background contamination that
may preclude the use of a particular
vapor sensor should be discussed with
the vendor of the sensor.
[see FR 37202/37161-1621
6-
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Vapor Monitoring
Questions
Federal
Answers
State/Local
Answers
Q. Where should vapor monitor-
ing wells be placed? How
many wells do I need? How
deep should they be?
The Federal UST regulations require
that vapor sensors be placed in wells
that are installed in the UST excavation
backfill. In addition, vapor wells are
normally placed as close to the tank as
is technically feasible. Sometimes this
is accomplished by installing the wells
at a slant instead of vertically.
Although EPA's research and field expe-
rience indicates that at least one well
every 40 feet should be sufficient for
gasoline tanks in a clean dry backfill,
some State and local requirements spec-
ify that wells be separated by no more
than 20 to 35 feet.
The ideal depth of a vapor well, as indi-
cated by industry recommendations, is 1
to 2 feet deeper than the base of the
tank. The less permeable the backfill is,
the closer the vapor well should be to
the recommended ideal depth.
[see FR 37202/37161-162]
Q. Can I use vapor monitoring A.
at a diesel site?
Yes. Although diesel does not evaporate
as easily as gasoline, vapor monitoring
is still appropriate in most cases. You
should check with the equipment's ven-
dor to be sure that the system responds
to diesel vapor. However, additional
monitoring wells may be necessary.
Also, at old diesel sites, diesel vapors
may be masked by contamination in the
soil and it would be best to introduce a
tracer into the fuel. A tracer is simply a
component that easily evaporates and
makes identification of leaked product
easier. The monitoring device must be
sensitive to the tracer; the tracer and
the stored substance must be capable of
being mixed; and the tracer must not in-
terfere with the normal use of the
stored substance.
[•ee FR 37202/37161-162]
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Secondary Containment
with Interstitial Monitoring
Federal
Answers
State/Local
Answers
Q. What does secondary con-
tainment mean?
A. Secondary containment is any barrier
immediately around or beneath a
tank that is designed and installed
to detect a leak. Although double-
walled tapks are perhaps the most com-
mon typeiof secondary containment cur-
rently available, numerous other types
of secondary containment include
"trays" beneath the tank, flexible plastic
liners that cover the bottom and sides of
the excavation hole, partial double
walls, loo^e flexible "jackets" that close-
ly surround the tank, and flexible tank
membranes that can be placed inside
rigid outer tanks. Some secondary con-
tainment techniques can also be used to
meet the leak detection requirements
for piping.
[see FR 37203/37164-165]
Q. Does the whole tank have to
be surrounded by the sec-
ondary containment?
A. For petroleum UST systems, secondary
containment does not have to complete-
ly surround the tank IF all leaks will
contact the containment and be directed
towards a monitor that can detect the
leaks. The design must also consider
site conditions, such as presence of
water or product contamination from
old spills or leaks. If there is a lot of
water or contamination, full contain-
ment should be considered. The con-
tainment material must be imperme-
able and thick enough that leaked prod-
uct won't pass through it.
[see FR 37203/37164-165]
Q. Why is proper installation
especially crucial to the ef-
fectiveness of secondary con-
tainment?
A. Although proper installation is crucial
to the effectiveness of any leak detection
method, [secondary containment is espe-
cially vulnerable to any mistakes made
during installation. Double-walled
tanks can be cracked if not installed
precisely according to instructions.
Liners can leak at the seams if they are
not sealed correctly. Trays can be posi-
tioned incorrectly relative to the tank.
Because!of the varieties of containment
available, the wide variety of site condi-
tions, arid the importance of proper se-
lection, design, and installation, the use
of secondary containment requires expe-
rienced and trained professionals.
I [see FR 37203/37164-165]
-8-
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Secondary Containment
with Interstitial Monitoring
Federal
Answers
State/Locaf
Answers
Q. What is interstitial monitor-
ing?
Interstitial monitoring is any method
that checks for leaks in the space
between the tank and its secondary
barrier: for example, between the inner
and outer walls of a double-walled tank.
There is a wide variety of interstitial
monitors. Some monitors indicate the
physical presence of leaked product by
checking for liquid or vapors. Other
monitors check for a change in condition
that indicates a hole in the tank, such
as a loss of pressure or vacuum in the
interstitial space or a change in the
level of water between the walls of a
double-walled tank.
Interstitial monitors can be very simple,
such as a dip stick that is manually in-
serted into the space between the barri-
er and the tank to check for accumulat-
ed liquid. Monitors can also be sophisti-
cated automated systems that continu-
ously check the condition of the intersti-
tial space and sound an alarm when a
leak is discovered.
[see FR 37203/37164-165]
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Autornatfc Tank Gauging
System Questions
Federal
Answers
Q. How does an ATGS work?
A. An ATGS is permanently installed in
the tank through a pipe other than the
fill pipe. An ATGS is an automatic
system 'that takes product level and
temperature readings nearly continu-
ously, with very little involvement from
the on-site staff. The ATGS is con-
trolled by a computer programmed at
installation by the vendor.
[see FR 37202/37160-161]
State/Local
Answers
Q. Why does an ATGS have two
different modes of operation?
In the inventory mode, the ATGS op-
erates in place of manually gauging the
tank to determine how much product is
in the tank. The ATGS collects invento-
ry data While the tank is in operation.
The ATGS's computer compares this in-
ventory data to the inputs and with-
drawals; from the tank to see if what is
actually in the tank agrees with the
record of what should be in the tank.
The leak test mode is a periodic opera-
tion. Although product data are collect-
ed in the same way as in the inventory
mode, during a leak test the tank is
closed down for several hours (usually
at night) to make sure nothing is added
to or taken from the tank. The ATGS's
computer uses this data to determine if
there is a meaningful decrease in vol-
ume over time that might indicate a
leak.
[see FR 37202/37160-161]
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Automatic Tank Gauging
System Questions
Federal
Answers
State/Local
Answers
Q. How often do I have to use
the ATGS?
The leak test mode must be used at
least once every month. Because the
system is completely automated, it is
very easy to perform a leak test, and
many owners and operators run tests
every night or every weekend. The tank
must be out of operation during the test
for 1 to 6 hours, depending on how often
the test is run each month.
IF the ATGS can detect a leak at least
as small as 0.2 gal/h with the probabili-
ties of detection and false alarm re-
quired in the Federal regulations, then
inventory control is not a regulatory re-
quirement. However, it is sound busi-
ness practice to perform inventory con-
trol regardless of the regulatory require-
ments, and the ATGS makes gathering
the inventory data very easy.
Therefore, it is still recommended that
the inventory mode of the ATGS be
used.
[see FR 37202/37160-161]
Q. What product level in the
tank is necessary to run the
leak test mode on an ATGS?
The manufacturer of the ATGS may re-
quire a certain product level, but the
Federal regulations do not require a
specific product level. A leak test con-
ducted with an ATGS each month will
usually, over time, test the tank at a va-
riety of product levels covering the nor-
mal range of levels stored in the tank.
[see FR 37202/37160-161]
Q. Do I have to dig up my tank
to install an ATGS?
No, although you may have to partially
uncover your tank. A probe must be in-
serted through a riser on top of each
tank, which must be separate from the
fill pipe or gauge port. Most tanks have
extra openings on the top to which the
riser can be attached and the probe in-
serted into the tank. If an extra open-
ing is not available on the part of the
tank that is normally uncovered, some
digging may be required to uncover
more of the top until a suitable opening
is found.
[see FR 37202/37160-161]
•11
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Tank Tightness,Testing
and Inventory Control
Federal
Answers
State/Local
Answers
REMEMBER: Tank tightness testing must be combined with monthly inventory
control. Also, this combined leak detection method can only be used for 10 years
following UST installation or upgrade (then you must use one of the monthly moni-
toring methods).
Q. How good is tightness test-
ing? Can the results be
trusted?
The tank tightness testing methods
studied by EPA generally met sensitivi-
ty and precision specifications, but the
Agency found that the procedures and
protocols of the test methods needed to
be improved. Procedures are easy to fix,
and most tightness testing companies
are already revising their protocols to
include the elements necessary for a
good tightness test. The primary ele-
ments oiF good procedure and protocol
are:
• Adequate product temperature mea-
surement (using at least 3 measure-
ments' at different levels or some
means of "homogenizing" the product
and its temperature);
• Adequate waiting period between
adding product to the tank and be-
ginning actual data collection (at
least 6 hours for large fills and 3
hours for small fills);
• Recognizing and removing vapor
pockets, for methods that fill the
tank with product all the way to the
top;
• A method for determining if water is
around the tank and compensating
for its presence; and
• The number of tests to be conducted
before making a leak determination
needs to be fixed in the protocol and
not at the discretion of the tester.
There are also some tightness testing
methods that measure properties that
are independent of temperature, tank
distortion, vapor, etc. If a test method
does not include the elements listed
above, ite sure to get an explanation of
why it does not. For whatever tightness
test method you select, the vendor must
supply!documentation of the perfor-
mance claims (minimum detectable leak
rate and probabilities of detection and
false alarm).
; [see FR 37202/37157-160]
MORE
-12
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Tank Tightness Testing
and Inventory Control
Federal
Answers
State/Local
Answers
Q. How often do I have to do a
tightness test?
Tank tightness tests must be performed
periodically as shown in the following
table:
New tanks
Existing tanks,
upgraded
Existing tanks,
not upgraded
Every 5 years for
10 years following
installation
Every 5 years for
10 years following
upgrade
Every year until 1998
("Upgraded" tanks have corrosion protection
and spill/overfill prevention devices.)
REMEMBER: After the applicable
time period listed above, you must have
a monthly monitoring method. The
"Straight Talk on Tanks" flyers describe
allowable monthly monitoring options.
[see FR 37202/37157-160]
Q. What kind of tightness tests
are available?
A. There are many kinds of tightness
tests already available and more are
being developed.
Underfill and Overfill Methods
Underfill methods cannot test the
whole tank surface or piping, because
the level of the product is below the top
of the tank. No additional pressure is
applied to the walls of the tank, and the
equipment that measures product level
must be more sensitive than that used
in overfill methods.
Overfill methods test the whole tank
surface, since the product level must be
at least to the fill pipe and often must
be raised above the level of the ground
using risers attached to the fill pipe. If
the product level is above the ground,
above normal operating pressure will be
applied to the bottom and walls of the
tank. Depending on the method and the
amount and condition of the piping, an
overfill method may also test the piping.
-13-
-------
Tank Tightness Testing
andlnventory Control
Federal
Answers
State/Local
Answers
Volumetric and Nonvolumetric
Methods
Volumetric methods measure and
monitor the volume of the product in
the tank over time. At the end of a vol-
umetric test, the tester calculates a leak
rate in gal/h and determines if the rate
is large enough to indicate a leak.
Nonvolumetric methods test for
leaks but cannot determine specific leak
rates. There are several approaches to
nonvolumetric testing, two of which are
described here. One approach uses
acoustic sensors to listen for the sound
of product bubbling out of the tank or
water bubbling mto the tank. Another
approach places a tracer material not
found in petroleum products into the
tank and checks for its presence outside
the tank. •
Whatever method is selected, it must
meet the minimum performance stan-
dards in the Federal regulations.
Vendors must supply documentation
of their performance claims.
[see FR 37202/37157-160]
Q. How can I increase the accu-
racy of daily inventory con-
trol?
The best; way to improve daily inventory
control is to take careful gauge stick
readings. Keep the stick as close to ver-
tical as possible and always insert it in
the same tank opening. Take two con-
secutive measurements, one immediate-
ly after the other, every time the tank is
gauged. Be sure to wipe off the gauge
stick between the consecutive measure-
ments. 'The average of the two mea-
surements should be used as the repre-
sentative gauging number. Also, you
can apply product-finding paste to the
gauge stick to make it easier to identify
the exact; level of product.
[see FR 37202/37157-160]
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Tank Tightness Testing
and Inventory Control
Federal
Answers
State/Local
Answers
Q. What are the reporting re-
quirements for inventory
control?
The Federal regulations require you to
report a suspected leak to the local im-
plementing agency when monthly recon-
ciliation for two consecutive months in-
dicates there may be a leak. A leak is
suspected when the cumulative monthly
overage or shortage is equal to at least
1.0 percent of total flow-through for the
month plus 130 gallons. The total flow-
through volume can be either the sum of
the monthly pump readings or the total
amount of product delivered in a month.
Whichever method is chosen should be
used consistently. After reporting a
suspected leak, you need to take steps
to confirm the leak and keep the imple-
menting agency informed of your ac-
tions.
[see FR 37202/37157-160]
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Manual Tank Gauging
Questions
Federal
Answers
State/Local
Answers
Q. What ,is the difference be-
tween periodic manual tank
gauging and inventory con-
trol?
Although both tests use gauge sticks to
measure the volume of product found in
an UST, manual tank gauging is a
lengthy periodic test and inventory
control is generally a quick daily test.
Manual tank gauging takes measure-
ments at the beginning and end of at
least a 36-hour period during which the
tank operation has been shut down. By
contrast, inventory control takes mea-
surements during each day of normal
tank operation.
[see FR 37202/37158]
Q. For what size of tank can
manual tank gauging be
used?
Manual tank gauging may be used as
the sole method of leak detection only
for tanks with a capacity of 550 gallons
or less, for the life of the tank.
Tanks with a capacity of 551 - 2000 gal-
lons can temporarily use manual tank
gauging in combination with tightness
testing [(see the "Straight Talk on
Tanks" flyer on tank tightness testing).
Periodic tightness testing must follow
the schedule below:
MINIMUM TIGHTNESS TESTING
FREQUENCY
New tanks
Existing tanks,
upgraded
Existing tanks,
not upgraded
Every 5 years for
10 years following
installation
Every 5 years for
10 years following
upgrade
Every year until 1998
("Upgraded" tanks have corrosion protection
and spill/overfill prevention devices.)
REMEMBER: After the applicable time
period listed above, you must have a
monthly monitoring method. The
"Straight Talk on Tanks" flyers describe
allowable monthly monitoring options.
Tanks greater than 2000 gallons in ca-
pacity may not use this method to
meet the requirements for leak detec-
tion.
[see FR 37202/37158]
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Suction Piping
Questions
Federal
Answers
State/Local
Answers
Q. Does the rule require me to
install suction piping?
You do not have to install suction pip-
ing. However, if you install suction pip-
ing that meets the design requirements
listed below, no leak detection for the
piping is required:
• It operates at less than atmospheric
.pressure;
• It is sloped so that the product will
drain back into the tank should the
suction be broken;
• There is only one check valve, which
is located directly below and as close
as possible to the suction pump; and
• There is some way to check that the
above features are in fact in place.
If your suction system does not have the
design features described above, you
must use one of the following leak detec-
tion methods:
• Line tightness tests every 3 years; or
" Monthly vapor, ground-water, or in-
terstitial monitoring.
[see FR 37201/37154]
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Pressurized piping
: Questions
Federal
Answers
State/Local
Answers
Q. What does the Federal regu-
lations1 requirement for an
"automatic line leak defec-
tor" mean?
Pressurized piping must have an auto-
matic line leak detector (LLD). There
are three types of LLDs:
Automatic flow restrictor
If a leak occurs, a flow restrictor will
keep the flow of product in the line at
3 gal/h. This flow rate, much below
the usual flow rate through a pres-
surized line, interrupts service, which
signals that there is a leak in the
line.
Automatic flow shutoff
This device completely stops the flow
of product through a pipe when a leak
is detected.
Continuous alarm system
This system continuously monitors
the piping and triggers an audible or
visual alarm when a possible leak is
detected. For example, secondary
containment with interstitial moni-
toring is a continuous alarm system.
Whichever device you choose, the manu-
facturer must supply documentation
that the device meets the performance
standard bf detecting a leak at least as
small as 3 gal/h at 10 psi within 1 hour.
REMEMBER: In addition to the LLD,
pressurized piping must also use one of
the following leak detection methods:
• Annual line tightness tests; or
• At least monthly line tests at 0.2
gal/hr rate; or
• Monthly vapor, ground-water, or in-
terstitial monitoring.
[see FR 37201/37153-154]
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