United States
Environmental Protection
Agency
Solid Waste And
Emergency Response
5403W
EPA510-B-93-005
November 1993
&EPA
Manual Tank Gauging
For Small Underground
Storage Tanks
Printed on Recycled Paper
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CONTENTS
Why You Should Read This Booklet 1
How Does Manual Tank Gauging Work? 2
Do You Have The Right Equipment? 4
Step 1 — Find The Right Testing Period 5
Step 2 — Measure The Tank's Contents 5
Step 3 — Do Some Math 6
Step 4 — Find The Right Test Standards 6
Step 5 — Compare Your Measurements
With Test Standards 7
Using Tank Charts Without 1/8-Inch Conversions 8
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Why You Should Read This Booklet
Federal and state laws require underground storage tanks (USTs)
to have leak detection. A lot of attention has been focused on large
gasoline tanks, but it is also important to detect leaks from tanks
2,000 gallons or smaller, which often contain used oil.
If your USTs do not have leak detection, you can be cited for
violations and fined. Leak detection violations can also keep you
from getting legally required insurance coverage and reimbursement
for cleanup costs. Without leak detection, you constantly risk
discovering a leak only after it becomes a major financial burden for
yourself and an environmental problem for everyone.
Manual tank gauging is a unique leak detection method that
can be used only on tanks 2,000 gallons or smaller. If this
method is appropriate for any of your USTs, this booklet can help
you make sure you do manual tank gauging correctly.
If you need information on federal leak detection requirements and
the various methods of leak detection available to you, see "Straight
Talk On Tanks." Call EPA's toll-free Hotline at 800 424-9346 and
order this free publication by number: EPA 530/UST-90/012.
SEPA Straight Talk On Tanks
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How Does Manual Tank Gauging Work?
This booklet helps you use manual tank gauging to meet federal
regulatory leak detection requirements by showing you how to do
three important tasks:
! Good sticking
! Good math
i
Good record keeping
Without these three, you may fail to meet the leak detection
requirements. Steps 1 through 5 on the following pages show you
how to perform manual tank gauging correctly.
Basically, manual tank gauging involves taking the tank out of
service every week for 36 hours or more while you measure the
tank's contents to see if changes in the tank's volume indicate a
possible leak.
Manual tank gauging can be used only on tanks 2,000 gallons
or smaller. Be sure you read about several important restrictions
on the use of manual tank gauging that are described on the next
page.
To use MANUAL TANK GAUGING correctly,
follow Steps 1—5 starting on page 5.
-2-
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Please note these important restrictions on the use of
manual tank gauging:
! Manual tank gauging can be used only on tanks 2,000 gallons or
smaller.
i
Tanks 1,000 gallons or smaller can use this method alone.
! Tanks from 1,001 to 2,000 gallons can use manual tank gauging
only when it is combined with periodic tank tightness testing.
The combined method of manual tank gauging and tank tight-
ness testing is a TEMPORARY leak detection method. You can
use the combined method only for 10 years after installing a new tank
that has corrosion protection and spill/overfill devices or for 10 years
after upgrading an old tank with corrosion protection and spill/overfill
devices. (However, tanks that are filled by transfers of no more than
25 gallons at one time are not required to have spill/overfill devices.)
During this 10-year period, tanks need tightness testing every 5 years.
After the 10-year period, you must use a monthly monitoring method,
such as groundwater monitoring or interstitial monitoring.
Tanks without corrosion protection and spill/overfill devices cannot
use this combined method after December 1998, when these tanks
must be upgraded or closed. Before December 1998, these tanks
need tightness testing every year. (See "Straight Talk On Tanks.")
! The use of manual tank gauging does not meet your tank
system's leak detection requirements for piping. Pressurized and
some suction piping must use other methods of leak detection, such
as interstitial monitoring. (See "Straight Talk On Tanks.")
If you don't pay careful attention to these restrictions,
you will fail to meet the leak detection requirements.
-3-
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Do You Have The Right Equipment?
Find out if state or
local requirements
have limitations on
the use of manual
tank gauging or have
requirements different
than those presented
here. You can also
use other standard
forms, if they show
the information that
state and federal
regulations require.
STICK
READING GALLONS
Gauge Stick Or Other Gauges
The gauge stick used to measure the depth of liquid in an underground
tank must be marked or notched to the c inch, starting with zero at the
bottom end. Check your stick to be sure the end has not been worn or
cut off and that the stick is not warped. The stick should be made of non-
sparking material, such as wood, and varnished to minimize the creeping
of fuel above the actual fuel level in the tank. Instead of using a gauge
stick, you may use a mechanical or electronic tank level monitor.
Whatever measuring device you use must be capable of measuring the
level of product over the full range of the tank's height to the nearest c
inch.
Forms
The instructions in this booklet are keyed to the "MANUAL TANK GAUGING
RECORD" form. You will find a filled-in sample of this form on the last
page of this booklet. This sample is on a perforated page, so tear it out
and refer to it while you read through the directions that are keyed
alphabetically to it. Also, near the back of the booklet, you will find
blank "masters" you can copy repeatedly to provide forms for use in
your recordkeeping. If the "MANUAL TANK GAUGING RECORD" is filled out
according to the instructions in this booklet, you will be in compliance with
federal regulations for manual tank gauging.
Tank Chart
A tank chart is a table that converts the number of inches of liquid in the
tank into the number of gallons. You need a tank chart that exactly
matches your storage tank (tank manufacturers usually provide charts for
their tanks). If you have more than one tank, you will need a chart for
each tank unless the tanks are identical. The tank chart must show
conversion to gallons for each c inch stick reading. If your tank chart
does not convert each c inch reading into gallons, contact the tank
manufacturer, or, if you have a steel tank, the Steel Tank Association
(708 438-8265) to get an appropriate chart.
You always need to convert inches into gallons in order to fill out the
form correctly and to do the necessary math. To convert inches into
gallons, find your stick's reading to the nearest c inch on the tank chart,
then simply read across to the gallons column to find the number of
gallons. If you cannot get a tank chart showing conversion to gallons for
each c inch reading, you must do the additional math explained on page
8.
-4-
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Step 1—Find The Right Testing Period
Once each week you must take your tank out of service for a testing period. The
length of the testing period depends on the size of your tank and whether you are
using manual tank gauging alone or in combination with tank tightness testing.
w Circle your tank size and test duration in the table so you will
know which you are using. To identify the appropriate testing period,
use the sample form found on the last page of this booklet and locate
your tank on the table in the upper left corner of the sample form (see
the section labeled "A"). You know which testing period you need to
use every week by looking at the number in the "Minimum Duration Of
Test" column next to the box that matches a description of your tank.
With tanks of 551 to 1,000 gallons, you can choose a shorter test time
(36 hours) with tightness testing or a longer test time (44 or 58 hours,
depending on tank diameter) without tightness testing.
During the test period the tank must remain out of service so that nothing
is put into the tank and nothing is taken out of it.
Step 2—Measure The Tank's Contents
Every week, you must take liquid level measurements twice before and twice
after each out-of-service testing period.
w Fill in the identifying information at the top of the "MANUAL TANK
GAUGING RECORD" form. You need a separate form for each tank using
manual tank gauging.
0 Take your first stick reading using "good sticking practices" noted in
the box on the right. Enter your reading in the column labeled "First
Initial Stick Reading."
Cr Wipe the stick dry with a rag and take a second stick reading as you
did before. Enter the second reading in the column labeled
"Second Initial Stick Reading."
After the readings are taken, the tank opening should be closed so that no
liquid can be added or removed from the tank.
w When the out-of-service testing period is over, take two more stick
readings in the same way you took the first two readings. Enter the
ending readings in the columns labeled "First and Second End
Stick Reading."
Use the sample
"MANUAL TANK
GAUGING RECORD" on
the last page of the
booklet to see where you
put the
information from
letters "A" through
"M" in the following
directions.
USE GOOD STICKING
PRACTICES: Slowly
lower the gauge stick,
let the stick gently
touch bottom, and
quickly bring it back
up. Read the depth of
the fuel indicated by
the wet mark on the
stick to the nearest
1/8 inch.
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Step 3—Do Some Math
Every week at the end of the test period, you must record some math calcula-
tions.
IP Average the two initial stick readings to the nearest c inch. Enter the
result in the "Average Initial Reading" column.
The average stick reading of the tank's contents will be in inches. You
always need to convert inches into gallons in order to fill out the form
completely and to calculate the change in the tank volume. Find your
stick's reading on the tank chart to the nearest c inch, then read
across to the gallons column to find the number of gallons. Enter the
result in the "Initial Gallons" column.
Your tank chart should have direct conversions from c inch stick
readings to gallons. If you cannot get a tank chart with c inch
conversions, do the additional math explained on page 8.
Average the two end stick readings to the nearest c inch. Enter the
result in the "Average End Reading" column.
Convert the average stick reading from inches into gallons (as you did
in item "G" above) and enter the result in the "End Gallons" column.
Subtract the "End Gallons" column from the "Initial Gallons" column.
Enter the result in the column labeled "Change In Tank Volume."
Step 4—Find The Right Test Standards
The weekly and monthly test standards depend on tank size and
whether you are using manual tank gauging alone or in combination
with tank tightness testing. To find your tank's weekly and monthly test
standards, locate your tank on the table in the upper left corner of the
sample MANUAL TANK GAUGING RECORD (see the section labeled "K").
You know which test standards apply to your tank by looking at the
gallon numbers in the "Weekly Standard" and "Monthly Standard"
columns next to your tank.
Circle the weekly and monthly test standards in the table that
apply to your tank so you will know which standards your tank
must meet.
-6-
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Step 5—Compare Your Measurements With
Test Standards
You must compare your calculation of "Change In Tank Volume" to the weekly
and monthly test standards for your tank.
™ Every week, compare your "Change In Tank Volume" number to the
weekly test standard. For the purpose of this comparison, consider all
numbers to be positive (for example, a -16 would become a +16). If
your "Change In Tank Volume" number is not larger than the weekly
test standard, circle YES in the "Tank Passes Test" column. If your
"Change In Tank Volume" number is larger than the weekly test
standard, circle NO. If you circle NO, you must also call your
regulatory agency to report a suspected leak as soon as possible.
Once a month, add up the 4 weekly "Change In Tank Volume"
numbers: this time pay careful attention to positive and negative
numbers to get an accurate total. For example, adding +4 and +3 and
-2 and -1 should equal +4. After you have the sum of the 4 weekly
tests, divide by 4 to get the monthly test average. Enter the result at
the bottom of the "Change In Tank Volume" column.
Compare your monthly test average to the monthly test standard for
your tank. For the purpose of this comparison, again consider all
numbers to be positive (for example, a -16 would become a +16). If
your "Change In Tank Volume" number is not larger than the monthly
test standard, circle YES in the "Tank Passes Test" column. If your
monthly average "Change In Tank Volume" is larger than the monthly
test standard, circle NO. If you circle NO, you must also call your
regulatory agency to report a suspected leak as soon as possible.
Keep your manual
tank gauging records
on file for at least 1
year. Also, keep a
record of the last
tank tightness test, if
you use the method
that combines
manual tank gauging
with periodic tank
tightness testing.
-7 -
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Using Tank Charts Without c Inch Conver-
sions
If your tank chart does not list direct conversions from inches to gallons for every
c inch, then you must do the additional math described below every time you
stick your tank.
The easiest way to explain this procedure is with an example. Let's say you have
a stick reading of 23d inches and you need to figure how many gallons are in
your tank.
1.
Look on your tank chart and find the inch measurements that are just
above and below your stick reading and write down the number of gallons
for these inch readings. Subtract the gallon readings to find the
difference between the two readings:
Chart reading at 24 inches:
Chart reading at 23 inches:
325 gallons
293 gallons
Difference:
32 gallons
2.
Dividing 32 by 8 will give you the number of gallons for each c inch,
which is 4 gallons. (Round off the number to the nearest whole number.)
Because your fraction is d, multiply 4 gallons by 3, which gives you 12
gallons as the volume represented by d inch.
CAUTION: The gallons represented by each
top to bottom of the tank and must be
conversion.
c inch will vary from
calculated for each
3. Take the number of gallons you have just calculated and add it to the inch
reading just below your actual stick reading:
Chart reading at 23 inches:
Gallons at d inch:
293 gallons
+ 12 gallons
Sum: 305 gallons
Thus, your stick reading of 23d inches converts to 305 gallons.
NOTE: If your tank chart is in half or quarter inches, you must still use this
procedure so that your gallon readings are accurate to c inch.
After all of this math, you can see why it pays to have the correct tank chart
that indicates gallons for each c inch.
-8-
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MANUAL TANK GAUGING RECORD
Circle your tank size, test duration, and weekly/monthly standards in the table below:
Month _
Tank Identification
Year
Tank Size
up to 550 gallons
551 -1,000 gallons
(when tank diameter is 64")
551 -1,000 gallons
(when tank diameter is 48")
551-1,000 gallons (also requires
periodic tank tightness testing)
1,001-2,000 gallons (also requires
periodic tank tightness testing)
Minimum
Duration
Of Test
36 hours
44 hours
58 hours
36 hours
36 hours
Weekly
Standard
(1 test)
10 gallons
9 gallons
12 gallons
13 gallons
26 gallons
Monthly Standard
(4-test average)
5 gallons
4 gallons
6 gallons
7 gallons
13 gallons
Person Completing Form
Facility Name
Compare your weekly readings and the monthly average of the 4 weekly
readings with the standards shown in the table on the left.
If the calculated change exceeds the weekly standard, the LIST may be leaking.
Also, the monthly average of the 4 weekly test results must be compared to
the monthly standard in the same way.
If either the weekly or monthly standards have been exceeded, the LIST may be
leaking. As soon as possible, call your implementing agency to report the
suspected leak and get further instructions.
Start Test
(month, day,
and time)
Date:
Time: AM/PM
Date:
Time: AM/PM
Date:
Time: AM/PM
Date:
Time: AM/PM
First
Initial
Stick
Reading
Second
Initial
Stick
Reading
Average
Initial
Reading
Initial
Gallons
(convert
inches to
gallons)
[a]
End Test
(month, day, and
time)
Date:
Time: AM/PM
Date:
Time: AM/PM
Date:
Time: AM/PM
Date:
Time: AM/PM
First
End
Stick
Reading
KEEP THIS PIECE OF PAPER ON FILE FOR AT LEAST 1 YEAR
Second
End
Stick
Read-
ing
Average
End
Reading
End
Gallons
(convert
inches to
gallons)
[b]
To see how close you are to the
monthly standard, divide the sum of
the 4 weekly readings by 4 and en-
ter result here >
Change
In Tank
Volume
In Gal-
lons
+ or (-)
[a-b]
Tank
Passes
Test
(circle
YES or
NO)
Y N
Y N
Y N
Y N
Y N
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MANUAL TANK GAUGING RECORD
Circle your tank size, test duration, and weekly/monthly standards in the table below:
Month
Tank Identification
Year
Tank Size
up to 550 gallons
551-1,000 gallons
(when tank diameter is 64")
551-1,000 gallons
(when tank diameter is 48")
551-1,000 gallons (also requires
periodic tank tightness testing)
1,001-2,000 gallons (also requires
periodic tank tightness testing)
Minimum
Duration
Of Test
36 hours
44 hours
58 hours
36 hours
36 hours
Weekly
Standard
(1 test)
10 gallons
9 gallons
12 gallons
13 gallons
26 gallons
Monthly Standard
(4-test average)
5 gallons
4 gallons
6 gallons
7 gallons
13 gallons
Person Completing Form
Facility Name
Compare your weekly readings and the monthly average of the 4 weekly
readings with the standards shown in the table on the left.
If the calculated change exceeds the weekly standard, the LIST may be leaking.
Also, the monthly average of the 4 weekly test results must be compared to
the monthly standard in the same way.
If either the weekly or monthly standards have been exceeded, the LIST may be
leaking. As soon as possible, call your implementing agency to report the
suspected leak and get further instructions.
Start Test
(month, day,
and time)
Date:
Time: AM/PM
Date:
Time: AM/PM
Date:
Time: AM/PM
Date:
Time: AM/PM
First
Initial
Stick
Reading
Second
Initial
Stick
Reading
Average
Initial
Reading
Initial
Gallons
(convert
inches to
gallons)
[a]
End Test
(month, day, and
time)
Date:
Time: AM/PM
Date:
Time: AM/PM
Date:
Time: AM/PM
Date:
Time: AM/PM
First
End
Stick
Reading
KEEP THIS PIECE OF PAPER ON FILE FOR AT LEAST 1 YEAR
Second
End
Stick
Reading
Average
End
Reading
End
Gallons
(convert
inches to
gallons)
[b]
To see how close you are to the monthly
standard, divide the sum of the 4 weekly
readings by 4 and enter result here >
Change
In Tank
Volume
In Gallons
+ or (-)
[a-b]
Tank
Passes
Test
(circle
YES or NO)
Y N
Y N
Y N
Y N
Y N
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MANUAL TANK GAUGING RECORD
Circle your tank size, test duration, and weekly/monthly standards in the table below:
Month
Tank Identification
Year
Tank Size
up to 550 gallons
551-1,000 gallons
(when tank diameter is 64")
551-1,000 gallons
(when tank diameter is 48")
551-1,000 gallons (also requires
periodic tank tightness testing)
1,001-2,000 gallons (also requires
periodic tank tightness testing)
Minimum
Duration
Of Test
36 hours
44 hours
58 hours
36 hours
36 hours
Weekly
Standard
(1 test)
10 gallons
9 gallons
12 gallons
13 gallons
26 gallons
Monthly Standard
(4-test average)
5 gallons
4 gallons
6 gallons
7 gallons
13 gallons
Person Completing Form
Facility Name
Compare your weekly readings and the monthly average of the 4 weekly
readings with the standards shown in the table on the left.
If the calculated change exceeds the weekly standard, the LIST may be leaking.
Also, the monthly average of the 4 weekly test results must be compared to
the monthly standard in the same way.
If either the weekly or monthly standards have been exceeded, the LIST may be
leaking. As soon as possible, call your implementing agency to report the
suspected leak and get further instructions.
Start Test
(month, day,
and time)
Date:
Time: AM/PM
Date:
Time: AM/PM
Date:
Time: AM/PM
Date:
Time: AM/PM
First
Initial
Stick
Reading
Second
Initial
Stick
Reading
Average
Initial
Reading
Initial
Gallons
(convert
inches to
gallons)
[a]
End Test
(month, day, and
time)
Date:
Time: AM/PM
Date:
Time: AM/PM
Date:
Time: AM/PM
Date:
Time: AM/PM
First
End
Stick
Reading
KEEP THIS PIECE OF PAPER ON FILE FOR AT LEAST 1 YEAR
Second
End
Stick
Reading
Average
End
Reading
End
Gallons
(convert
inches to
gallons)
[b]
To see how close you are to the monthly
standard, divide the sum of the 4 weekly
readings by 4 and enter result here >
Change
In Tank
Volume
In Gallons
+ or (-)
[a-b]
Tank
Passes
Test
(circle
YES or NO)
Y N
Y N
Y N
Y N
Y N
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MANUAL TANK GAUGING RECORD
i Month
Year
Tank Identification UC££>
Person Completing Form
Circle your tank size, test duration, and weekly/monthly standards in the table below: Facility Name M-fr
Tank Size ^
up to 550 gallons
551 -1,000 gallons
(when tank diameter is 64")
551 -1.000 gallons
(when tank diameter is 48")
551-1,000 gallons (also requires
_^_ periodic tank tightness tasting)
1,001-2,000 gallons (also requires
periodic tank tightness testing)
Minimum
Duration
Of Test
36 hours
44 hours
58 hours
36 hours
36 hours
Weekly ^
Standard §
(1 test)
1 0 gallons
9 gallons
1 2 gallons
13 gallons
26 gallons
^Monthly Standard
9 (4-test average)
5 gallons
4 gallons
6 gallons
7 gallons
1 3 gallons
C
r
I
/
t
I
I
s
— •
Compare your weekly readings and the monthly average of the 4 weekly
readings with the standards shown In the table on the left.
If the calculated change exceeds the weekly standard, the UST may be leaking.
Also, the monthly average of the 4 weekly test results must be compared to
the monthly standard in the same way.
If either the weekly or monthly standards have been exceeded, the UST may be
leaking. As soon as possible, call your Implementing agency to report the
suspected leak and get further instructions.
SAMPLE
Start Test
(month, day,
and time)
First
Initial
Stick
Reading
Second
Initial
Stick
Reading
Average
Initial
Reading
Initial
Gallons
(convert
inches to
gallons)
End Test
(month, day, and
time)
First
End
Stick
Reading
Second
End
Stick
Reading
Average
End
Reading
End
Gallons
(convert
inches to
gallons)
[b]
Change
In Tank
Volume
In Gallons
+ or(-)
[a-b]
Tank
Passes
Test
(circle
YES or
NO)
Date: 1>Y
Time:
not
Date:
Time:
If/9
-f/f
Date: <)/ U
Time: & Mt
Date:
Time:
6
N
Date:
Time:
W
W
10
Date:
Time:
to'/r
to
O
Date: 4 /7T
Time: AN
KEEP THIS PIECE OF PAPER ON FILE FOR AT LEAST 1 YEAR
To see how dose you are to the
monthly standard, divide the sum of
the 4 weekly readings by 4 and
enter result here >
N
N
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