Read Doing Inventory Control Right for Underground Storage Tanks text version

United States Environmental Protection Agency

Solid Waste And Emergency Response 5403W

EPA 510-B-93-004 November 1993

Doing Inventory Control Right For Underground Storage Tanks

CONTENTS

Why You Should Read This Booklet If You Use Inventory Control . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1 How Does Inventory Control Work? . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2 Do You Have The Right Equipment? . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4 Step 1 -- Measure The Tank's Contents . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6 Step 2 -- Record The Amount Pumped . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7 Step 3 -- Record Fuel Deliverables . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8 Using Tank Charts Without 1/8-Inch Conversions . . . . . . . . . . . . . . . . . . . . . . . 9 Step 4 -- Calculate Daily Change In Inventory . . . . . . . . . . . . . . . . . . . . . . . . 10 Step 5 -- Calculate Monthly Changes In Inventory . . . . . . . . . . . . . . . . . . . . . 12

Why You Should Read This Booklet If You Use Inventory Control

Federal and state laws require underground storage tanks (USTs) to have leak detection. 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. If inventory control is part of your leak detection, then this booklet can help you make sure you do inventory control correctly. Inspections conducted nationwide indicate that most people who think they are doing inventory control are not doing it in a way that is likely to find leaks and meet the law's requirements for leak detection. So even if you are SURE you are doing inventory control right, read this booklet carefully--it could save you a lot of grief and money. 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.

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How Does Inventory Control Work?

This booklet helps you use inventory control to meet federal regulatory leak detection requirements by showing you how to do three important tasks: ! ! ! Good sticking Good math Good recordkeeping

Without these three, you may fail to meet the leak detection requirements. To do inventory control right, you have to spend time to make sure that you consistently measure the tank's contents correctly, that you don't let math errors creep into your daily and monthly calculations, and that you keep complete, easy-to-read records on file for at least a year. Basically, inventory control requires daily measurements of tank contents and math calculations that let you compare your "stick" inventory (what you've measured) to your "book" inventory (what your recordkeeping indicates you should have). Some people call this process "inventory reconciliation." If the difference between your "stick" and "book" inventory is too large, your tank may be leaking. Be sure you read about several important restrictions on the use of inventory control that are described on the next page.

To use INVENTORY CONTROL correctly, follow Steps 1--5 starting on page 6.

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Please note these important restrictions on the use of inventory control as leak detection:

! Inventory control can never be used alone. Inventory control must always be used in combination with tank tightness testing. Tanks must be tightness tested every 12 months if they do not have corrosion protection and spill/overfill devices. Tanks with corrosion protection and spill/overfill devices must be tested every 5 years. Inventory control is a TEMPORARY leak detection method. You can use inventory control 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. 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 can use inventory control only until December 1998, when these tanks must be upgraded or closed. (See "Straight Talk On Tanks.") ! The combined use of inventory control and tank tightness testing 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.

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Do You Have The Right Equipment?

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 nonsparking 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. Pastes For Finding Water Or Fuel You must check for water in the bottom of the tank at least once each month by smearing a water-finding paste along the bottom of the gauge stick. The paste changes color when it comes in contact with water. Many operators improve their stick readings by smearing a fuel-finding paste on about 6 inches of the stick where they expect the fuel level to be. Fuel-finding paste changes color when it comes in contact with fuel. Forms The instructions in this booklet are keyed to two forms: the "DAILY INVENTORY WORKSHEET" and the "MONTHLY INVENTORY RECORD." You will find filled-in sample copies of these forms on the last two pages of this booklet. These samples are on perforated pages, so tear them out and refer to them while you read through the directions that are keyed alphabetically to the sample forms. Also, near the back of the booklet, you will find "masters" you can copy repeatedly to provide forms for use in your recordkeeping. If these forms are filled out according to the instructions in this booklet, you will be in compliance with federal regulations for inventory control. You should find out if state or local requirements have limitations on the use of inventory control or have requirements that are different from those presented in this booklet. You can use other standard recordkeeping forms, as long as they are clear, consistent, and contain all the information required by the federal and state leak detection regulations.

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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 forms 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 9. Drop Tube The fill pipe through which the fuel is delivered into the tank must have a drop tube extending to within 1 foot of the bottom of the tank. Stick measurements should be made through a drop tube in the fill pipe or gauging port. If your fill pipe does not have a drop tube, call your petroleum equipment supplier to have one installed. Calibrated Dispensing Meters Meters must be calibrated according to local standards. Manifolded Tanks If you have manifolded tanks or dispensers that blend fuel, consider these tanks as one tank system if they share a common inventory of stored fuel. As you follow the directions on the following pages, you will need to combine your measurements and calculations for all the tanks manifolded into one system.

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Step 1--Measure The Tank's Contents

You must measure the tank every day that fuel is added or removed. You may take measurements using a gauge stick or a mechanical or electronic tank level monitor. No fuel can be added or removed from the tank while you are performing Step 1 or Step 2. Every day you measure the tank, you should fill out a "DAILY INVENTORY WORKSHEET." As you go through the following directions, refer to the sample DAILY INVENTORY WORKSHEET you will find on the last pages of this booklet. For easy reference, the sample is on a perforated page so you can tear it out and keep it handy as you read through the directions. Also, near the back of the booklet is a "master copy" on a perforated page you can tear out to make copies of the DAILY INVENTORY WORKSHEET for your recordkeeping. Fill in the identifying information at the top of the worksheet. Next to the "TANK IDENTIFICATION" box are empty vertical columns. Each column represents one tank--consistently enter all information on that one tank in the same vertical column. NOTE: Once you have filled in the tank identification boxes, make copies of the worksheet so you won't have to repeatedly enter the same information. USE GOOD STICKING PRACTICES: Slowly lower the gauge stick to the tank's bottom. Let the stick gently touch the bottom, then quickly bring it back up. Read the depth of fuel indicated by the wet mark to the closest c inch division on the stick. Use of fuel-finding paste will make your stick readings more accurate. Write your measurement in the box labeled "END STICK INCHES" for the tank you measured. NOTE: If your tank is equipped with an automatic tank gauge (ATG), you may record the inches of product and gallons of product directly from the ATG's printed tape or simply staple the tape with this information to the worksheet.

Use the sample "DAILY INVENTORY WORKSHEET" from the last two pages of the booklet to see where you put the information from letters "A" through "M" in the following directions.

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Step 2--Record The Amount Pumped

At the same time you measure the tank contents (Step 1), you must record on the DAILY INVENTORY WORKSHEET the amount of fuel pumped. No fuel can be added or removed from the tank while you are sticking the tank and recording the amount pumped. Locate the box labeled "AMOUNT PUMPED" on the left side of the worksheet. Copy the numbers from each dispenser's totalizer onto the worksheet. Be very careful that you write all the meter readings for a tank in the same column. You may have several dispensers and totalizers for one tank, so the worksheet provides boxes in which you can enter several readings in any order. Add up the totalizer meter readings in each column and write the result in the box labeled "TODAY'S SUM OF TOTALIZERS." Find the last DAILY INVENTORY WORKSHEET you completed. Copy "TODAY'S SUM OF TOTALIZERS" from that worksheet into the "Previous Day's Sum of Totalizers" box of the worksheet you are working on today. On today's worksheet, subtract "Previous Day's Sum of Totalizers" from "T ODAY' S SUM OF TOTALIZERS" and write the result in the box labeled "AMOUNT PUMPED TODAY." You may have an alternative to reading totalizers. If you have a selfservice fueling operation where the cashier can authorize fuel sales from inside the facility, you can probably print out a daily report that gives you the total sales for each type of fuel. NOTE: You can use the sales volumes from this report instead of reading your totalizer meters only if no fuel sales are made between the time you print the report from the cash register and the time you measure your tanks (Step 1). If you are using cash register reports to record the amount pumped, enter the amount of each type of fuel pumped in the box labeled "AMOUNT PUMPED TODAY" or staple the printout to the worksheet.

If you pumped fuel through a dispenser and back into a tank, for example during a test, subtract the number of gallons you pumped from "AMOUNT PUMPED TODAY."

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Step 3--Record Fuel Deliveries

You must check how much fuel has been delivered every time any amount of fuel is delivered to your tank. NOTE: You should not pump any fuel during the time it takes to do items "I" and "J" below. Before the delivery begins, the liquid level in the tank must be measured. Always use good sticking practices: slowly lower the gauge stick, gently touch the stick to the bottom of the tank, then quickly bring the stick back up. Read the depth of fuel indicated by the wet mark to the nearest c inch division on the stick. Write your measurement in the box labeled "Inches of Fuel Before Delivery" for each tank you measured. The delivery person can now deliver fuel into the tank. After the delivery, wait at least 5 minutes for the fuel level in the tank to stabilize, and then measure again as described above. Record fuel level in the box labeled "Inches of Fuel After Delivery." Using your tank chart with c inch readings, convert both delivery readings to the correct number of gallons. Record these numbers in the boxes labeled "Gallons of Fuel Before Delivery" and "Gallons of Fuel After Delivery." (If necessary, see page 9 on converting inches into gallons.) Subtract "Gallons of Fuel Before Delivery" from "Gallons of Fuel After Delivery." Record the result in the box labeled "GALLONS DELIVERED (STICK)." Now look at the delivery receipt and find the volume of each type of product that was delivered. If two volumes are given, one labeled "net" and the other "gross," use the gross gallons as the volume of product delivered. For each type of fuel delivered, copy the gross gallons delivered from the delivery receipt onto the worksheet in the box labeled "GROSS GALLONS DELIVERED (RECEIPT)." The gallons in items "L" and "M" should roughly match. If they don't, contact your supplier.

An automatic tank gauge (ATG) can usually print a delivery report. If your tank has an ATG that prints such a report, you may simply staple the ATG's delivery report to the DAILY INVENTORY WORKSHEET.

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Using Tank Conversions

Charts

Without

c

Inch

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 43d 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 44 inches: 3,585 gallons Chart reading at 43 inches: 3,480 gallons ----------------------------------------------------------------------------------Difference: 105 gallons 2. Dividing 105 by 8 will give you the number of gallons per c inch, which in this example is 13. (More exactly it is 13.125, but do round off the number to the nearest whole number.) Because your fraction is d, multiply 13 gallons by 3, which gives you 39 gallons as the volume represented by d inch. CAUTION: The gallons represented by each c inch will vary from top to bottom of the tank and must be calculated for each conversion. 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 43 inches: 3,480 gallons Gallons at d inch: + 39 gallons ----------------------------------------------------------------------------------Sum: 3,519 gallons Thus, your stick reading of 43d inches converts to 3,519 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.

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Step 4--Calculate Daily Changes In Inventory

In this step, you will copy information from the DAILY INVENTORY WORKSHEET onto the MONTHLY INVENTORY RECORD. You will then do some math to determine your daily inventory. You need one MONTHLY INVENTORY RECORD for each tank that you have. As you go through the following directions, refer to the sample MONTHLY INVENTORY RECORD you will find on the reverse side of the DAILY INVENTORY WORKSHEET sample you have already been using. For easy reference, the sample is on a perforated page so you can tear it out and keep it handy as you read through the directions. Also, near the back of the booklet is a "master copy" on a perforated page you can tear out to make copies of the MONTHLY INVENTORY RECORD for your recordkeeping. Fill in the identifying information at the top of the RECORD.

MONTHLY INVENTORY

Use the sample "MONTHLY INVENTORY RECORD" from the last two pages of the booklet to see where you put the information from letters "N" through "Z" in the following directions.

If this is the very first day of your inventory recordkeeping, convert the "END STICK INCHES" from the DAILY WORKSHEET into gallons and enter on the MONTHLY RECORD under "END STICK INVENTORY (GALLONS)" for that starting date. (If necessary, see page 9 on converting inches into gallons.) This is all you can do today. Starting tomorrow, follow all of the instructions listed below. Find the line in the left column on the MONTHLY RECORD with today's date listed. Copy the previous day's "END STICK INVENTORY (GALLONS)" number into the box for today's "START STICK INVENTORY (GALLONS)." Enter the amount of fuel delivered from the DAILY INVENTORY WORKSHEET. If you were NOT pumping fuel during the time when the delivery was taking place, then use the "GALLONS DELIVERED (STICK)" number. However, if you had to pump fuel while the delivery was taking place, then use the "GROSS GALLONS DELIVERED (RECEIPT)" number as your delivery amount. Copy the "AMOUNT PUMPED TODAY" number from the DAILY INVENTORY WORKSHEET into the "GALLONS PUMPED" column of the MONTHLY INVENTORY RECORD.

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Add the "START STICK INVENTORY (GALLONS)" and the "GALLONS DELIVERED" columns; then subtract the "GALLONS PUMPED" column. Enter the result in the column labeled "BOOK INVENTORY (GALLONS)." Copy the "END STICK INCHES" number from the DAILY WORKSHEET into the column labeled "END STICK INVENTORY (INCHES)" on the MONTHLY RECORD. Convert inches into gallons and enter the result in the column on the MONTHLY RECORD labeled "END STICK INVENTORY (GALLONS)." (If necessary, see page 9 on converting inches into gallons.) Subtract the "BOOK INVENTORY (GALLONS)" from the "END STICK INVENTORY (GALLONS)." Enter the difference into today's "DAILY OVER OR SHORT" box. This number will usually be a positive or negative number (only rarely will it be zero). Enter your initials to show who entered today's information. At least once each month, you must also measure for water in the tank. Smear water-finding paste on the bottom few inches of the gauge stick. Open the fill pipe and slowly lower the stick to the tank's bottom. Hold the stick on the bottom for 10 seconds for gasoline (30 seconds for diesel). Then remove the stick. If there is water in the bottom of the tank, the water-finding paste will change color. Read the depth of water indicated by the line where the waterfinding paste has changed color to the closest c inch division on the stick. Do not use this stick reading to measure the amount of fuel in the tank, because the fuel will creep up the stick and will give you an inaccurate reading. If you checked the tank for water today, enter the number of inches of water in the tank on the line under "Facility Name" at the top of the monthly record. If there is no water present, enter a zero to indicate that you in fact checked for water but found none. If you find more than 1 inch of water, you should arrange for its immediate removal, notify the product supplier, and conduct further tests to ensure that the tank is not leaking.

GOOD ADVICE: If you are "over" for 5 days in a row (or "under" for 5 days in a row), you should check for problems with your math and your UST.

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Step 5--Calculate Inventory

Monthly

Changes

In

At the end of each month, follow the directions below to see if the difference between "stick" and "book" inventory indicates a possible leak. Add all of the month's "GALLONS PUMPED" numbers and write this total at the bottom of the column in the box labeled "TOTAL GALLONS PUMPED." Add all the month's "DAILY OVER OR SHORT" numbers: pay careful attention to positive and negative numbers to get an accurate total. For example, adding +4 and +3 and -2 should equal +5. Enter the total at the bottom of the column in the box labeled "TOTAL GALLONS OVER OR SHORT." Fill out the "LEAK CHECK" line at the bottom of the RECORD as follows: ! !

MONTHLY INVENTORY

Take the "TOTAL GALLONS PUMPED" number and drop the last two digits to get 1% (for example: 6594 becomes 65). Add 130 (for example: 65 + 130 = 195).

Enter the result of this calculation at the end of the "LEAK CHECK" line. This number is the maximum change in inventory allowed by federal regulations (1% of throughput plus 130 gallons). At the bottom of the MONTHLY INVENTORY RECORD, circle "YES" or "NO" to show whether your "TOTAL GALLONS OVER OR SHORT" number is LARGER than the "LEAK CHECK" number you identified in the previous item. Even if your "TOTAL GALLONS OVER OR SHORT" is a negative number, treat it as a positive number for the purpose of this comparison. For example, -74 would become +74. If you circle "YES" for 2 months in a row, you must notify your regulatory agency as soon as possible (usually within 24 hours) that your tank may be leaking.

NOTE: Keep your inventory control records on file for at least 1 year. Your state, however, may have different rules about when you have to report a leak or how long you must keep the inventory records. Be sure you know the rules that apply to you.

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DAILY INVENTORY WORKSHEET

FACILITY NAME: _________________________________________ YOUR NAME: _________________________________________ DATE: _________________________________________

TANK IDENTIFICATION

Type of Fuel Tank Size in Gallons

END STICK INCHES AMOUNT PUMPED

Totalizer Reading Totalizer Reading Totalizer Reading Totalizer Reading Totalizer Reading Totalizer Reading Totalizer Reading Totalizer Reading TODAY'S SUM OF TOTALIZERS Previous Day's Sum of Totalizers AMOUNT PUMPED TODAY

9

9

9

9

9

DELIVERY RECORD

Inches of Fuel Before Delivery Gallons of Fuel Before Delivery

(from tank chart)

9

9

9

9

9

Inches of Fuel After Delivery Gallons of Fuel After Delivery

(from tank chart)

GALLONS DELIVERED (STICK)

[Gallons "After" ! Gallons "Before"]

GROSS GALLONS DELIVERED (RECEIPT)

MONTHLY INVENTORY RECORD

TANK IDENTIFICATION & TYPE OF FUEL: ____________________________________ MONTH/YEAR :_______/______ FACILITY NAME: ___________________________________________________________ DATE OF WATER CHECK: ___________

START STICK INVENTORY (GALLONS) BOOK INVENTOR Y (GALLONS)

LEVEL OF WATER (INCHES):_________

DAILY OVER (+) OR SHORT (!) ! ["End" ! "Book"]

DATE

GALLONS DELIVERED

GALLONS PUMPED

END STICK INVENTORY _________________________ ___ (INCHES) ' (GALLONS)

INITIALS

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31

(+) (+) (+) (+) (+) (+) (+) (+) (+) (+) (+) (+) (+) (+) (+) (+) (+) (+) (+) (+) (+) (+) (+) (+) (+) (+) (+) (+) (+) (+) (+)

(!) (!) (!) (!) (!) (!) (!) (!) (!) (!) (!) (!) (!) (!) (!) (!) (!) (!) (!) (!) (!) (!) (!) (!) (!) (!) (!) (!) (!) (!) (!)

(=) (=) (=) (=) (=) (=) (=) (=) (=) (=) (=) (=) (=) (=) (=) (=) (=) (=) (=) (=) (=) (=) (=) (=) (=) (=) (=) (=) (=) (=) (=) TOTAL GALLONS OVER OR SHORT >

TOTAL GALLONS PUMPED >

DROP THE LAST 2 DIGITS from the TOTAL GALLONS PUMPED number and enter on the line below

Compare these

numbers

LEAK CHECK:

_____________

+

130

=

____________ gallons (circle one)

Is "TOTAL GALLONS OVER OR SHORT" LARGER than "LEAK CHECK" result? YES NO

If answer is "YES" for 2 MONTHS IN A ROW, notify regulatory agency as soon as possible.

KEEP THIS PIECE OF PAPER ON FILE FOR AT LEAST 1 YEAR

>>>Copy and post this reminder where employees who measure tanks can see it!<<<

GET GOOD INVENTORY CONTROL MEASUREMENTS!

! Measure each tank every operating day ! Use gauge sticks that are T marked to the c inch T not cut off or worn off at the "0" end T varnished and not warped ! Measure through the same drop tube each time ! Use good sticking practices T SLOWLY lower stick T GENTLY touch stick on tank bottom T QUICKLY pull stick out ! Measure just before each delivery ! Wait at least 5 minutes after delivery, then measure again ! Read and record totalizer meters carefully ! Check for water at least once a month using water-finding paste

Developed in cooperation with...

United States Environmental Protection Agency

Solid Waste And Emergency Response 5403W

EPA 510-B-95-009 September 1995

Introduction To Statistical Inventory Reconciliation

For Underground Storage Tanks

Printed on Recycled Paper

Contents

Why You Should Read This Booklet ......................................................1 How Does SIR Work?...............................................................................2 Necessary Equipment..............................................................................3

Gauge Stick Or Other Gauges..................................................................................3 Pastes For Finding Fuel Or Water ............................................................................3 Tank Chart ...............................................................................................................3 Calibrated Dispensing Meters ...................................................................................4 Forms.......................................................................................................................4

SIR Reporting And Recordkeeping.........................................................4

What You Should Provide To The Vendor ................................................................4 What The Vendor Should Provide To You ................................................................4 What You Should Keep On File................................................................................5 What To Do When You Get A `FAIL'..........................................................................7 What To Do When You Get An `INCONCLUSIVE' .........................................................7

Answers To Frequently Asked Questions .............................................8

"Can SIR be used on manifolded tanks?"..................................................................8 "Can SIR be used as an annual tightness test?"........................................................8 "Why did a SIR vendor fail my tank for a leak under 0.2 gph?" .................................8 "What is the difference between `qualitative' and `quantitative' SIR methods?"....................................................9 "What is this `estimated leak rate,' `threshold,' and `MDL' stuff all about?".................9 "Can SIR be used as a monthly test of my piping, too?".......................................... 10 "How much does SIR cost?" ................................................................................... 10 "There are so many vendors. How do I choose?" .................................................... 10

Publications And Videos About USTs ............................................................11 State UST Program Office Numbers..................................... inside back cover

Why You Should Read This Booklet

Federal and state laws require underground storage tank systems (USTs) to have leak detection. One of the available leak detection methods is Statistical Inventory Reconciliation (SIR). In this method, a trained professional uses sophisticated computer software to conduct a statistical analysis of inventory, delivery, and dispensing data. SIR can allow the owner or operator of an UST facility to meet leak detection requirements without an extensive outlay of capital, using only the equipment that most facilities have readily at hand--a tank stick and a tank chart used for inventory control. The SIR analysis itself is usually provided as a service by vendors who charge a monthly fee based on the number of tanks. This booklet provides basic information on the method--what it is, how it works, factors that impact data quality--to assist you in determining if SIR is appropriate to your needs. If you need information on federal leak detection requirements and the various methods of leak detection available to you, see Straight Talk on Tanks. For a free copy, call the U.S. Environmental Protection Agency's (EPA's) toll-free Hotline at 800 424-9346 and ask for publication EPA 510-K-95-003.

Introduction To SIR 1

How Does SIR Work?

On the face of it, SIR looks very similar to old-fashioned inventory control--the owner or operator, using simple equipment, tracks tank volumes, deliveries, and sales. However, the similarity ends there. Simple inventory control is relatively imprecise. Depending on your system throughput, you could be losing hundreds of gallons every month without realizing anything is wrong! By contrast, SIR analysis can be very sensitive and accurate. A SIR vendor can take the same inventory data and analyze them for releases so small that many would go unnoticed with inventory control. By using a month's worth of good tank data, it is possible for SIR methods to detect a release of just over 1½ pints per hour (that's about 145 gallons per month) from a tank or its product lines 95 times out of a hundred. The mechanics of how SIR works are beyond the scope of this booklet. SIR vendors actually use a variety of statistical tools to evaluate inventory data, and no two vendors' methods are exactly alike--the information they collect and the results they provide can vary. Still, for fundamental release detection purposes, there are only three possible bottom-line responses for any SIR test: PASS, FAIL, or INCONCLUSIVE. These bottom-line responses are described below and on the following pages. PASS--According to the analyzed data, the UST system tests tight. A `FAIL' does not necessarily mean your system is leaking, but you must still notify your local UST agency. FAIL--Analyzed data indicate a loss of product from the system or an influx of groundwater. However, a FAIL does not necessarily indicate that your system is leaking. A FAIL may indicate miscalibrated dispensers, inaccurately metered deliveries, or stolen product. There is also a chance that a FAIL is a false alarm. If you receive a FAIL, you must first notify your local UST regulatory agency. Then, you should explore possible reasons for the FAIL (see page 7). Keep your local UST agency informed as to your findings. INCONCLUSIVE--Analyzed data cannot make the call. There is a chance that the information provided to the SIR vendor is so bad that it is not possible to make a determination. This often can be traced back to poor tank sticking or bookkeeping practices (for example, a new hire who has received inadequate training). Whatever the reason, an INCONCLUSIVE result means, in effect, that you have failed to perform leak detection on the UST in question for that month. You are in violation of federal leak detection requirements. Contact your state UST program office to find out local policy on how INCONCLUSIVE results are handled. See page 7 for additional information.

To many people, SIR may seem like magic. But it's based on sound mathematical principles.

Introduction To SIR 2

Necessary Equipment

One of the major attractions of SIR for UST owners and operators is that it does not require a large, up-front investment of capital--the primary cost is subscribing to the SIR vendor's services. The equipment needed to use the method is usually already found on-site at most UST facilities. Gauge Stick Or Other Gauges A gauge stick, made of wood or other non-sparking material, is used to measure the depth of liquid in the UST. Typically, such sticks are marked or notched in 1/8-inch increments starting with the bottom of the stick. It is important that the stick be in good condition. Sticks that have worn ends, cutoff ends, worn-off numbers, or worn-off varnish coatings are not acceptable and should be replaced. Other forms of gauges can also be used if they are available and in good operating condition. Automatic tank gauges, for instance, can simplify measuring tank volumes. (Keep in mind, of course, that some automatic tank gauging systems can serve as acceptable monthly tank leak detection methods by themselves.) Whatever form of gauge you choose to use, you must follow the SIR vendor's instructions carefully to gather useful data. For instance, many providers of SIR services require that the tank measurements are made to the nearest 1/8-inch. If you fail to follow the vendor's instructions, you may end up with inconclusive test results. Pastes For Finding Fuel Or Water If you use a gauge stick, you can improve the quality of your readings if you use a fuel-sensitive paste smeared over about six inches of the stick where you expect the fuel level to be. The paste changes color where it comes into contact with the fuel. Similarly, you can use a water-sensitive paste on the end of the stick to monitor for the presence of water in the bottom of the tank. While water in the tank can come with your deliveries or as a result of condensation of moisture inside the tank, it can also come from groundwater leaking in through holes or through loose fittings high in your tank. Tank Chart The strapping chart used to convert stick measurements into gallons must be the right one for the tank. The chart should have stick measurements listed to 1/8 of an inch to minimize math errors that occur when using charts marked off to the nearest inch. SIR vendors can quickly determine if the chart is inappropriate to your tank, and will often generate a proper one for your tank.

Good sticking practices are essential to good SIR analyses.

Introduction To SIR 3

Calibrated Dispensing Meters A poorly calibrated totalizer can produce bad data that may be mistaken for some types of releases. While many SIR vendors can identify this pattern as a possible cause of a FAIL, it is wise to avoid the problem entirely. Keep your dispensers in good operating condition and have them periodically recalibrated as recommended by your equipment manufacturer and as required by state and local weights and measures agencies. Forms The SIR vendor typically provides forms on which daily stick readings, sales, and deliveries are recorded. These forms often resemble the inventory sheets usually maintained at UST facilities. In some instances, SIR vendors may allow submission of the data on a facility's own inventory sheets. Some vendors may also permit submission of data in electronic format, such as computer spreadsheets.

SIR Reporting And Recordkeeping

What You Should Provide To The Vendor Although SIR vendors may ask for a variety of information, some of the more common elements include:

n n n n n n n n n

Tank size (capacity, diameter, and length). Tank type, material of construction, and manufacturer. Product type. Date each stick measurement was taken. Daily opening stick measurement and volume. Daily closing stick measurement and volume. Daily sales volume. Gross deliveries over the course of the month. Thirty days of observations.

What The Vendor Should Provide To You Vendors supply different levels of service to their clients. You will need to consult with individual vendors to find the collection of features you desire. However, there is a core of reporting elements that should be common to all SIR analyses (see sample on page 6). These include:

Introduction To SIR 4

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Clear and timely reporting of results in terms of PASS, FAIL, or INCONCLUSIVE. Complete and annotated copies of inventory records used in the analysis, showing such problems as errors in delivery records or bad measurements tossed out by the test. Suggestions as to the likely cause of any test failure or inconclusive result. Instructions on follow-up actions to be taken in the event of a FAIL or INCONCLUSIVE (for example: "Notify your local UST agency of a failed test result within 24 hours").

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[ Pass

Fail Inconclusive

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Also, in the case of quantitative testing methods, the form should report the calculated leak rate in gallons per hour and the leak threshold at which a leak would be declared based on the data provided for each tank. The minimum detectable leak rate (MDL) for your data may also be provided by some vendors. (See page 9. ) Your SIR vendor may also supply you with other useful information and services beyond the basics itemized above. SIR vendors may further provide:

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Off-site storage of leak detection records. Potential reasons for a FAIL other than a release of product: F Apparent product theft F Missed product delivery entry F Suspected totalizer miscalibration Potential reasons and possible solutions for any INCONCLUSIVE results. Possible location of leak within the system. Assessment of tank sticking practices. Special tank-specific strapping charts for those tanks needing them (such as tilted tanks and odd-sized tanks).

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What You Should Keep On File The minimal recordkeeping requirements for facilities using SIR are the same as for other release detection methods:

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All written performance claims pertaining to the SIR method used and the manner in which those claims were justified or tested by the vendor (such as a third-party evaluation of the method) must be kept on file for five years from the date you started using the method at the facility. The monthly SIR reports, along with the results of any other sampling, testing, or monitoring, must be kept for at least one year.

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Introduction To SIR 5

Introduction To SIR 6

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Records of equipment calibration and maintenance must be kept for at least one year. Any schedules of required calibration and maintenance provided by the SIR vendor must be kept for five years from the date you began using the method at the facility.

You should check with your local UST agency to determine if there are any additional recordkeeping requirements. What To Do When You Get A `FAIL' When your UST system fails a SIR monthly analysis, you must report the incident to your local UST program agency within 24 hours or whatever time period your local agency requires. At the same time, you need to begin to investigate the cause of the failed test. Within seven days, you must determine the cause of the FAIL and report back to your local agency. Your SIR vendor may, on the basis of the test results, be able to provide you with areas to examine, such as a miscalibrated totalizer. You must have any defective equipment repaired or replaced immediately. If the FAIL cannot be linked to equipment problems, you must have the system tightness tested or the site checked for evidence of a release (such as sampling in the excavation zone). You must report the results to the local agency. If a release is confirmed, the agency will provide instructions for any necessary cleanup action. What To Do When You Get An `INCONCLUSIVE' An INCONCLUSIVE means you have failed to meet leak detection requirements. However, the steps you must take upon getting an INCONCLUSIVE depend on the requirements of your local UST agency. In some instances, you may be required to perform a system tightness test to be sure the UST is not leaking. In others, you may be given an additional month to come into compliance. Be sure to know what is required locally. A list of UST agency phone numbers can be found in the back of this booklet. An INCONCLUSIVE should in no way be taken as demonstrating the failings of a given vendor's method--it is inherent to all methods. Even if vendors use terms other than "inconclusive," they represent the same condition. In all cases, you will want to double check your operating procedures to see what caused the INCONCLUSIVE and prevent its recurrence. Your SIR vendor will provide assistance in locating the problem and offer suggestions to improve your data collection.

An `INCONCLUSIVE' means that you effectively have no leak detection for that month.

Introduction To SIR 7

Answers To Frequently Asked Questions

"Can SIR be used on manifolded tanks?" SIR methods can be used on tank systems that have multiple tanks linked together by siphon bars. This generally requires that each tank in the manifolded system be individually stuck for inventory measurements. As with single tank systems, no product deliveries or sales should be made during the time the sticking and totalizer readings are taking place. Check with your local UST agency to determine if it permits use of SIR on manifolded systems or has additional requirements. "Can SIR be used as an annual tightness test?" For facilities that are still using inventory control with tightness testing as their means of leak detection, it is possible to use SIR in place of more traditional tightness tests such as an overfill test. The performance requirements for a tightness test are more stringent than for monthly monitoring methods, however, so be sure to check that your SIR vendor can meet those requirements. Tanks must be tested for releases of 0.1 gph with a probability of detection (PD) of 95% and a probability of false alarm (PFA) of 5%. To act as a replacement for piping tightness testing, the requirements are even more rigorous--the SIR method must be able to detect releases of 0.08 gph with a PD of 95% and a PFA of 5%. To find releases of this magnitude, SIR vendors often need several months of good data. Be sure to contact your local UST agency to see if it allows use of SIR as an annual test. Also, remember that inventory control with tightness testing can only be used for a limited time. You may want to consider moving now to an approved method of monthly monitoring, such as automatic tank gauge systems, monitoring wells, or monthly SIR analyses. "Why did a SIR vendor fail my tank for a leak under 0.2 gph?" There is no such thing as an "acceptable" leak. Any leak will cost you in the long run and should be fixed. First of all, it is a misconception that any leakage into the environment is acceptable. Even small leaks over long periods of time can result in extensive contamination that can cost you substantial time and money for soil and groundwater clean up. Secondly, the performance standard by which leak detection methods (including SIR) are measured says that leaks of 0.2 gph must be detected in 95 out of 100 times. Further, false alarms should not happen more than five times in a hundred. What this means is that the SIR vendor looks at the estimated leak rate determined for a tank--say 0.15 gph--and asks the question "What is the likelihood that the true leak rate is actually 0.2 gph?" On the basis of a statistical analysis of the data you provide the vendor, the SIR vendor can make the call as to whether your system tests tight or not.

Introduction To SIR 8

Typically, a FAIL will be called for apparent releases of around 0.1 gph. See the question on page 10 on `estimated leak,' `threshold,' and `MDL' for additional information. "What is the difference between `qualitative' and `quantitative' SIR methods?" Although there are many methods that are employed by vendors performing SIR analyses, they break down into two major classifications: qualitative and quantitative. Qualitative methods do not provide estimated leak rates. When a vendor's qualitative method is evaluated to demonstrate its capability of meeting the EPA performance standard, it simply reports results in terms of PASS, FAIL, or INCONCLUSIVE. These results are compared with the evaluator's knowledge of which tanks are leaking in a test set of tank records. Quantitative methods also categorize results in terms of PASS, FAIL, or INCONCLUSIVE, but they go further by actually providing a numerical estimate of the leak rate, typically in gallons per hour. In evaluating the performance of the method, the evaluator compares the method's estimates with the actual leak rates imposed on the test set of tank records. "What is this `estimated leak rate,' `threshold,' and `MDL' stuff all about?" These are rather technical statistical terms often used by quantitative SIR vendors to provide their clients with more detailed information on their analyses. They provide insight beyond the simple PASS, FAIL, and INCONCLUSIVE, including just how bad a leak appears to be (estimated leak rate) and how good the data are that you have been providing to the vendor for analysis (MDL). The estimated leak rate is the number a quantitative SIR method comes up with for the amount of product your tank appears to be losing. The number is usually expressed in gallons per hour since the EPA regulations use those units. This estimated leak rate is rarely, if ever, zero. All tanks, whether leaking or tight, will generally show a leak rate. The question is, is this leak rate significant? This is where the threshold comes in. The threshold is basically an action level leak rate. That is, if the estimated leak rate exceeds the threshold leak rate, the SIR vendor declares a FAIL. It is important to note that the threshold is not a fixed number, such as 0.1 gph. Instead, it is typically the value associated with a fixed percentage set to the probability of false alarms (that is, declaring a leak on a system that is actually tight) the SIR vendor is willing to accept. EPA's regulations allow no more than 5% of analyses to turn out to be false alarms. However, many SIR vendors consider one failure in twenty analyses to be too high and set their thresholds to a 1% probability of false alarm. NOTE: EPA neither certifies nor approves any leak detection vendor or method. Method evaluations are generally done by third-party testing organizations.

SIR vendors offer a diverse number of supplemental reporting options. Look over what each has to offer and choose the one that best meets your needs.

Introduction To SIR 9

Finally, the MDL is the Minimum Detectable Leak. The MDL is the smallest leak rate the vendor can determine for the data provided with a PD of 95% or better. The MDL is tied to the threshold and is usually twice the threshold leak rate. The MDL must be less than or equal to the EPA performance standard rate of 0.2 gph at a PD of 95% and a PFA of 5% in order to make a PASS/FAIL call. If the MDL exceeds the performance standard, your system cannot be given a PASS--an INCONCLUSIVE is the best you can get. Fortunately, most vendors who provide this level of detail often provide a "plain English" translation as well. "Can SIR be used as a monthly test of my piping, too?" NOTE: State programs may require a different form of testing for lines. Check with your local UST agency. Yes. SIR is a test of the entire UST system. Losses are reported regardless of their origins. So, whether you are losing product as a result of a tank leak, a line leak, miscalibrated equipment, or theft, a FAIL will result if the estimated leak rate exceeds the threshold for calling a leak. Remember, though, that if you are using pressurized lines, you will also need to have an automatic flow restrictor, shutoff device, or continuous alarm in place to fully meet piping leak detection requirements. "How much does SIR cost?" Unlike most other methods, SIR has no installation costs and equipment costs are minimal--a well-calibrated dispensing meter and a good stick are about all you need. While vendor costs will vary, monthly monitoring for a facility with three USTs costs about $800 to $1200 per year. SIR used as an annual tightness test costs about $200 to $600. (These figures are based on estimates in 1995.) "There are so many vendors. How do I choose?" Whether you have decided to invest in SIR services or other leak detection methods, the basic steps are similar:

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Request information from the vendors you are interested in. Compare their services, option packages, and prices to see which vendors best meet your needs. Ask for references and check them. Contact your local UST agency to see if it has a certification program for leak detection vendors. Consult the agency's list of certified service providers. Contact the Better Business Bureau to see if there have been any complaints lodged against the vendor.

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Introduction To SIR 10

Publications And Videos About USTs

PUBLICATIONS

TITLE

Musts For USTs: A Summary Of The Federal Regulations For Underground Storage Tank Systems Booklet clearly summarizes federal UST requirements for installation, release detection, spill, overfill, and corrosion protection, corrective action, closure, reporting and recordkeeping. (About 40 pages.) Normas Y Procedimientos Para T.S.A. Spanish translation of Musts For USTs. (About 40 pages.) Straight Talk On Tanks: Leak Detection Methods For Petroleum Underground Storage Tanks Booklet explains federal regulatory requirements for leak detection and briefly describes allowable leak detection methods. (About 30 pages.) Doing Inventory Control Right: For Underground Storage Tanks Booklet describes how owners and operators of USTs can use inventory control and periodic tightness testing to meet federal leak detection requirements. Contains reporting forms. (About 16 pages.) Manual Tank Gauging: For Small Underground Storage Tanks Booklet provides simple, step-by-step directions for conducting manual tank gauging for tanks 2,000 gallons or smaller. Contains reporting forms. (About 12 pages.) Don't Wait Until 1998: Spill, Overfill, And Corrosion Protection For Underground Storage Tanks Information to help owners and operators of USTs meet the 1998 deadline for compliance with requirements to upgrade, replace, or close USTs installed before December 1988. (About 16 pages.) Dollars And Sense: Financial Responsibility Requirements For Underground Storage Tanks Booklet clearly summarizes the "financial responsibility" required of UST owners and operators by federal UST regulations. (About 16 pages.) An Overview Of Underground Storage Tank Remediation Options Fact sheets provide information about technologies that can be used to remediate petroleum contamination in soil and groundwater. (About 26 pages.) Controlling UST Cleanup Costs Fact sheet series on the cleanup process includes: Hiring a Contractor, Negotiating the Contract, Interpreting the Bill, Managing the Process, and Understanding Contractor Code Words. (About 10 pages.) Federal Register Reprints Not simple summaries, these reprints are extensive records of the rulemaking process including technical information, explanatory preambles, and the rules as they appear in the Code of Federal Regulations. Reprints dated 9/23/88; 10/26/88; 11/9/89; 5/2/90; and 2/18/93. Over 300 pages.

AVAILABLE FREE FROM

You can call EPA's toll-free RCRA/Superfund Hotline at 800 424-9346 and order free copies. Just identify the titles you want. Or you can write and ask for titles by addressing your requests to: NCEPI Box 42419 Cincinnati, OH 45242 Or you can fax your order to NCEPI at 513 891-6685.

Introduction To SIR 11

Publications And Videos About USTs

PUBLICATIONS

TITLE

Doing It Right Illustrates proper installation of underground tanks and piping for installation crews. Part 1: Tanks (24 minutes); Part 2: Piping (16 minutes). Cost: $25 Doing It Right II: Installing Required UST Equipment Illustrates installation of spill and overfill equipment, observation wells, and piping leak detection (23 minutes). Cost: $60 Doing It Right and Doing it Right II Set Cost: $75

AVAILABLE FROM

Environmental Media Center Box 30212 Bethesda, MD 20814 301 654-7141 800 522-0362 Visa and MasterCard accepted

Keeping It Clean: Making Safe And Spill-Free Motor Fuel Deliveries Making pollution-free deliveries to USTs. Includes Stage 1 vapor recovery, overfill prevention and spill containment. For fuel tanker drivers and UST owner/operators (25 minutes). Cost: $60 Petroleum Leaks Underground How liquids and vapors move in the subsurface and why early response to leaked petroleum is so important. Part 1: How Liquids Move (14 minutes); Part 2: How Vapors Move (15 minutes). Cost: $75 Straight Talk On Leak Detection Overview of the leak detection methods available for complying with federal regulations. Part 1: Straight Talk From Tank Owners (owners address the problems of UST compliance [5 minutes]); Part 2: Straight Talk On Leak Detection (30 minutes). Cost: $40

Tank Closure Without Tears: An Inspector's Safety Guide Focuses on explosive vapors and safe tank removal (30 minutes). Video and Booklet Cost: $35; Booklet: $5 What Do We Have Here?: An Inspector's Guide To Site Assessment At Tank Closure Inspecting sites for contamination where tanks have been removed. Part 1: Site Assessment Overview (30 minutes); Part 2: Field Testing Instruments At A Glance (14 minutes); Part 3: Soil And Water Sampling At A Glance (7 minutes). Video and Booklet Cost: $45; Booklet: $5 Searching For The Honest Tank: A Guide To UST Facility Compliance Inspection Covers major steps of UST inspections from protocols and equipment to enforcement and followup; from cathodic protection to leak detection. Directed at inspectors, yet also helpful to owners and operators (30 minutes). Video and Booklet Cost: $40; Booklet: $5

New England Interstate Environmental Training Center ATTN:VIDEOS 2 Fort Road South Portland, ME 04106 207 767-2539

Introduction To SIR 12

State UST Program Office Numbers

Alabama Dept. of Env. Management 334 271-7986 Alaska Dept. of Env. Conservation 907 465-5203 Arizona Dept. of Env. Quality 602 207-4324 Arkansas Dept. of Pollution Control & Ecology 501 570-2801 California State Water Resources Control Board 916 227-4313 Colorado State Oil Inspection Office 303 620-4300 Connecticut Dept. of Env. Protection 203 424-3374 DC Env. Regulatory Administration 202 645-6080 Delaware Dept. of Natural Resources & Env. Control 302 323-4588 Florida Dept. of Env. Regulation 904 488-3935 Georgia Dept. of Natural Resources 404 362-2687 Hawaii Dept. of Health 808 586-4226 Idaho Dept. of Health & Welfare 208 334-0542 Illinois Office of State Fire Marshall 217 785-5878 Indiana Dept. of Env. Mgt. 317 233-6418 Iowa Dept. of Natural Resources 515 281-8135 Kansas Dept. of Health & Env. 913 296-1678 Kentucky Div. of Waste Mgt. 502 564-6716 Louisiana Dept. of Env. Quality 504 765-0243 Maine Dept. of Env. Protection 207 287-2651 Maryland Dept. of Env. 410 631-3442 Massachusetts Dept. of Public Safety 617 351-6000 Michigan Dept. of Natural Resources 517 373-8168 Minnesota Pollution Control Agency 612 297-8609 Mississippi Dept. of Env. Quality 601 961-5171 Missouri Dept. of Natural Resources 314 751-7428 Montana Dept. of Health & Env. Sciences 406 444-5970 Nebraska State Fire Marshal 402 471-9465 Nevada Dept. of Conserv. &Natural Resources 702 687-5872 New Hampshire Dept. of Env. Services 603 271-3644 New Jersey Dept. of Env. Protection 609 984-3156 New Mexico Env. Dept. 505 827-0188 New York Dept. of Env. Conservation 518 457-4351 North Carolina Pollution Control Branch 919 733-8486 Utah Dept. of Env. Quality 801 536-4100 Vermont Dept. of Natural Resources 802 244-8702 Virginia Dept. Env. Quality 804 527-5189 Virginia Dept. Env. Quality 804 527-5189

Washington Dept. of Ecology North Dakota Div. of Waste 206 407-7211 Mgt. West Virginia Div. of Env. 701 328-5166 Protection 304 558-6371 Ohio Dept. of Commerce 614 752-7938 Wisconsin Dept. of Industry, Labor & Human Oklahoma Corporation Relations Commission 608 267-7605 405 521-3107 Oregon Dept. of Env. Quality 503 229-5774 Oregon Dept. of Env. Quality 503 229-6642 Pennsylvania Dept. of Env. Resources 717 772-5599 Rhode Island Dept. of Env. Mgt. 401 277-2234 South Carolina Dept. of Health and Env.Control 803 734-5335 Wisconsin Dept. of Natural Resources 608 267-7560 Wyoming Dept. of Env. Quality 307 777-7096

U.S. TERRITORIES American Samoa Env. Protection Agency 684 633-2304 Commonwealth of Northern Mariana Islands Div. of Env. Quality 607 234-6984

South Dakota Dept. of Env. Guam Env. Protection & Nat. Resources 605 773-3296 Agency 671 646-8863 Tennessee Dept. of Env. & Puerto Rico Env. Quality Conservation Board 615 532-0945 809 767-8109 Texas Natural Resources Virgin Islands Div. of Env. Conservation Comm. Protection 512 239-2000 809 774-3320

United States Environmental Protection Agency

Solid Waste And Emergency Response 5403W

EPA 510-B-93-005 November 1993

Manual Tank Gauging For Small Underground Storage Tanks

Printed on Recycled Paper

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

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.

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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 Good recordkeeping

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.

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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. 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 tightness 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.

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Do You Have The Right Equipment?

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 nonsparking 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

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.

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.

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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. 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.

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.

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. 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. 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." 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. 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 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 calculations. 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.

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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-

Using Tank Charts Without c Inch Conversions

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: 325 gallons Chart reading at 23 inches: 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 c inch will vary from top to bottom of the tank and must be calculated for each conversion. 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: 293 gallons Gallons at d inch: + 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-

MANUAL TANK GAUGING RECORD

Circle your tank size, test duration, and weekly/monthly standards in the table below: Tank Size 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)

Month _______________ Year _________ Tank Identification _____________________________ 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 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.

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)

5 gallons 4 gallons 6 gallons 7 gallons 13 gallons

Start Test (month, day, and time)

First Initial Stick Reading

Second Initial Stick Reading

Average Initial Reading

Initial Gallons (convert inches to gallons) [a]

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: Time: Date: Time: Date: Time: Date: Time:

AM/PM

Date: Time: Date: Time: Date: Time: Date: Time:

Y

AM/PM

N

Y

AM/PM

N

AM/PM

Y

AM/PM

N

AM/PM

Y

AM/PM

N

AM/PM

KEEP THIS PIECE OF PAPER ON FILE FOR AT LEAST 1 YEAR

To see how close you are to the monthly standard, divide the sum of the 4 weekly readings by 4 and enter result here >

Y

N

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Doing Inventory Control Right for Underground Storage Tanks

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Introduction To Statistical Inventory Reconciliation For Underground Storage Tanks
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