ESTCP 

Final Report 

ENVIRONMENTAL SECURITY 

TECHNOLOGY CERTIFICATION PROGRAM 

U.S. Department of Defense

Validation of the 

Low-Range Differential Pressure (LRDP) 

Leak Detection System 

 for Small Leaks in Bulk Fuel Tanks
ii

Executive Summary

The Naval Facilities Engineering Service Center (NFESC), Port Hueneme, California, and its industrial 

partners, Vista Research, Inc., and Vista Engineering Technologies, L.L.C., have demonstrated and validated 

(DEM/VAL) an innovative mass-based leak detection system for bulk underground storage tanks (USTs) 

containing petroleum fuels. The Low-Range Differential Pressure (LRDP) system is a computer-controlled 

system that can reliably detect small leaks in bulk USTs ranging in size from 50,000 gal to 12,500,000 gal. 

As part of this project, it has been evaluated for performance by an independent third party in a 122.5-ftdiameter, 2,100,000-gal tank following EPA’s standard test procedures. The LRDP meets the monthly 

monitoring and annual precision (tightness) test regulatory compliance guidelines established by California 

using either a 10-h (overnight) or 24-h test. This project was performed under the Environmental Security Technology Certification Program (ESTCP). The objective of the ESTCP is to demonstrate and validate innovative environmental technologies that are 

needed to address the environmental objectives of the Department of Defense (DoD), that are cost effective, 

and that will be ready for the development of commercial products and services at the completion of the 

DEM/VALs. All of the objectives of the project have been met, and the LRDP is ready for commercial use. 

Both (1) on-line, permanently installed monitoring systems and (2) tightness testing services using the LRDP 

can be obtained commercially through Vista Research, Inc. 

The LRDP system achieves a very high level of performance against small leaks because of its high precision 

(0.0002 in.) and its accurate methods of compensating for the thermal expansion and contraction of the fuel, 

the instrumentation, and the tank. Because of its innovative design, the LRDP achieves this high level of 

precision and accuracy with an off-the-shelf, industrial-grade differential pressure sensor. Thus, the LRDP 

not only delivers high performance, but it is also rugged and field-worthy. 

The LRDP system is fully automatic and is comprised of (1) an innovative in-tank level sensing unit, (2) an 

embedded remote test controller to collect and analyze the data from a test, and (3) a host computer to initiate, 

report, and archive the results of a test. A test can be initiated by an operator or can be automatically 

scheduled for a future date and time. The in-tank sensor can be installed through a standard 8-in.-daimeter 

opening without removing fuel from the tank. The electronics meet Class 1, Div. 1 standards. The LRDP 

system is compatible with the DoD Fuels Accounting System (FAS) and can be integrated with FAS to test 

the tanks in a fuel farm or a bulk storage facility. 

The in-tank sensor is comprised of (1) a vertical reference tube that spans the full usable height of the tank, 

(2) a sealed, bottom-mounted container that houses all of the level-measurement sensors, and (3) a special 

bellows-mounting system that is used to attach the system to the top of the tank. The reference tube is shaped 

so that it has a cross-sectional area that is proportional to the cross-sectional area of the tank as a function of 

depth. Except for 50,000-gal USTs and the 12,500,000-gal Red Hill tanks, all of the DoD’s bulk USTs have 

vertical walls, and therefore, the reference tube has a constant cross-sectional area. A valve at the bottom of 

this tube allows fuel from the tank to enter or leave. When the tank is to be tested for leaks, the valve is 

closed, thus isolating the fuel in the reference tube from that in the tank. As the level of liquid in the tank 

fluctuates, the level of liquid in the closed reference tube mimics it—except when the change in level is due to 

a leak. High precision is achieved because the dynamic range of the differential pressure sensor only needs to 

accommodate the differences in level between the reference tube and the tank and not the full height of the 

tank. The very small differences between the changes in level (pressure) in the tank and those in the tube are 

detected by a differential pressure sensor that is located in the sealed container at the bottom of the tube. 

Thus, the differential pressure sensor makes a direct measurement of the change in level that is due to a leak, 

if one is present. Because the differential pressure is housed at the bottom of the tank, where it is not subject 

to ambient air conditions, it avoids a common problem of other mass-based leak measurement systems—

thermally induced drift of the pressure sensor. In addition, the special bellows-mounting system removes any 

thermally induced vertical movement of the tank, the manway, or the in-tank sensor. The LRDP system is 

self-calibrating, and its performance and functionality can easily be checked between tests any time the valve 

is in the open position. 

The performance of the system was independently evaluated for a 10- and a 24-h test by Ken Wilcox 

Associates, Inc. (KWA), a nationally recognized third-party evaluator, using a variety of detection thresholds 

that were selected (1) to maintain a low probability of false alarm, (2) to optimize performance against certain 

target leak rates, and (3) to meet or exceed known regulatory requirements. The performance was determined 
iii

experimentally and was reported in accordance with the guidelines set forth in “Alternative Test Procedures 

for Evaluating Leak Detection Methods: Evaluation of Bulk Field-Constructed Tanks,” a standard test 

procedure for bulk underground tanks that is approved by the National Work Group on Leak Detection 

Evaluations (NWGLDE), an EPA-sponsored oversight group. A leak detection method cannot be used unless 

the evaluation has been approved by this group. The evaluation consisted of 12 tests conducted on a 122.5-ftdiameter, 2,100,000-gal bulk underground storage tank containing jet fuel and located at the Navy’s Point 

Loma Fueling Facility, San Diego, California. The tests were conducted over a wide range of temperature 

and induced leak conditions beginning on March 22, 2000 and ending on June 8, 2000. Neither the 

temperature conditions nor the leak rates were made available to NFESC until the test results had been 

generated and the evaluation report prepared. 

The LRDP is currently listed by the NWGLDE and is approved for use in California based on a third-party 

evaluation previously conducted at NAS North Island on an 88-ft-diameter tank. The results of the current 

ESTCP evaluation, conducted on the 122.5-ft-diameter tank at Point Loma, a much larger tank than the one 

used in the North Island evaluation, have been submitted to the NWGLDE for review and update of the 

previous listings. The results of the KWA evaluation (which are presented in this report) indicate that a single 

10-h test with the LRDP-10 can detect a leak of 1.14 gal/h with a probability of detection (PD) of 95% and a 

probability of false alarm (PFA) of 5% in a 122.5-ft diameter tank. The performance of the LRDP-10 scales 

with the product surface area of the tank and improves as the tank diameter decreases. The LRDP-10 can 

detect leaks as small as 0.2 gal/h in a single test in a 51-ft-diameter tank; by averaging four tests, a 0.2-gal/h 

leak can be detected in a 73-ft-diameter tank with the same probabilities of detection and false alarm. The 

performance improves with a 24-h test. The LRDP-24 can detect a leak of 0.69 gal/h with a PD of 95% and a 

PFA of 5% in a 122.5-ft diameter tank; when the 12 monthly tests are averaged together, the system has the 

capability for detecting leaks as small as 0.2-gal/h. The LRDP-24 can detect leaks as small as 0.2 gal/h with 

the same PD and PFA in a 66-ft-diameter tank with a single test and in a 93-ft-diameter tank by averaging four 

tests together. The LRDP-10 and the LRDP-24 are the only in-tank, on-line monitoring systems that can meet 

both Option 7 and Option 10 of the California regulatory guidelines for underground bulk storage tanks. 

A DEM/VAL of the LRDP system configured to test 50,000-gal underground storage tanks was performed at 

Hunter Army Airfield. For these tests, the reference tube was shaped to match the cylindrical cross-section of 

the tank as a function of depth. While a third-party evaluation was not performed, it was clear from the 

results of the DEM/VAL tests that the LRDP could meet the 0.2-gal/h monthly monitoring regulatory 

requirements with an 8-h test. 

Many important improvements to the LRDP previously evaluated at NAS North Island have been made under 

this ESTCP project. As a consequence of these improvements, the LRDP is ready for implementation 

throughout the DoD. Some of these improvements are: 

• The notebook computer and data acquisition system were replaced with field-worthy embedded 

controller, which collects data, evaluates data quality, analyzes test results, and stores the results. 

• The system was made fully automatic, and the software was made easy to use. The electronics are 

housed in an explosion proof container and meet Class 1, Div 1 Standards. 

• The system was originally approved as a portable system and can now also be used as a stand-alone 

system for on-line, real-time, in-tank monitoring. 

• The in-tank sensor unit was redesigned for easy installation and now fits into a standard 8-in. 

diameter opening and a tank of any diameter and any product depth. 

• The LRDP can be easily interfaced with base fueling operations, including the FAS, and can be 

used for both leak detection and inventory monitoring 

• The evaluated performance of the LRDP is 20% better than originally determined in the first 

evaluation, and the performance limitations (e.g., a 24-h waiting period) have been removed. 

• A leak detection test can be conducted with the LRDP using either a 10-h or a 24-h test. 

The LRDP has several significant cost advantages over other internal and external technologies. 

The cost advantages are realized because of the extremely high performance of the LRDP and 

the low probability of false alarm, the on-line monitoring capability of the LRDP when 

permanently installed in a tank, the capability of the system to conduct a short test (an overnight 
iv

test), and the low recurring costs associated with testing. For each tank brought into compliance, 

the LRDP can realize cost savings over other mass-based methods in terms of installation and 

testing of $250,000 or a factor of 3 over a 10-year period. The cost savings realized by the 

LRDP over an in-tank tracer method can be well over $1,000,000 or a factor of 12 over a 10-year 

period. This can result in savings of up to several tens of millions of dollars for each DoD fuel 

storage facility. The savings of the LRDP compared to other mass-based systems would result in 

a payback of less than three years. This payback is less than one year when compared to an intank tracer method. The cost of a tracer method is expensive because of the high recurring cost 

of testing. The costs of other mass-based methods are high because of lower performance and 

the inability to meet both the monthly monitoring and annual precision regulatory requirements 

with an on-line system. In addition to the installation and operational cost savings, the LRDP 

has the potential to save DoD many hundred of millions of dollars in terms of clean-up and tank 

replacement cost avoidance.
v

Table of Contents

Executive Summary....................................................................................................................... ii 

List of Figures............................................................................................................................. viii 

List of Tables ................................................................................................................................ xi 

Acronyms.................................................................................................................................... xiii 

Acknowledgments....................................................................................................................... xiv 

1.0 Introduction.............................................................................................................................. 1 

1.1 Problem..................................................................................................................................... 3 

1.2 Background............................................................................................................................... 4 

1.3 Objectives of the Demonstration .............................................................................................. 6 

1.4 Regulatory Requirements ......................................................................................................... 6 

1.5 Improvements to the LRDP Evaluated at NAS North Island ................................................... 8 

1.6 Report Organization................................................................................................................ 11 

2.0 Technology Description......................................................................................................... 12 

2.1 Description.............................................................................................................................. 12 

 2.2.1 Sources of Noise ............................................................................................................ 14 

 2.2.2 Reference Tube .............................................................................................................. 15 

 2.2.3 Measurements Sensors in a Bottom-Mounted Sealed Container................................... 17 

 2.2.4 Mounting of the In-Tank Sensor Unit............................................................................ 18 

 2.2.5 Remote Test Controller.................................................................................................. 19 

 2.2.6 Software ......................................................................................................................... 19 

 2.2.7 Conduct of a Test........................................................................................................... 20 

 2.2.8 Data Quality Indices ...................................................................................................... 21 

Page
vi 

Table of Contents (cont.)

 2.2.9 Summary ........................................................................................................................ 22 

2.2 Strengths, Advantages, and Weaknesses ................................................................................ 23 

2.3 Factors Influencing Cost and Performance............................................................................. 24 

3.0 Site/Facility Description ........................................................................................................ 25 

3.1 Background............................................................................................................................. 25 

3.2 Site/Facility Characteristics .................................................................................................... 25 

 3.2.1 DEM/VAL 1: Point Loma Fuel Terminal (Third-Party Evaluation in a Bulk UST).... 25 

 3.2.2 DEM/VAL 2: Hunter Army Airfield (50,000-gal UST) .............................................. 26 

4.0 Demonstration Approach....................................................................................................... 28 

4.1 Performance Objectives.......................................................................................................... 28 

4.2 DEM/VAL 1: Point Loma Fuel Terminal (Third-Party Evaluation in a Bulk UST)............. 28 

 4.2.1 Evaluation Procedure..................................................................................................... 28 

 4.2.2 Evaluation Tank............................................................................................................. 31 

 4.2.3 Evaluation Conditions and Test Results ........................................................................ 33 

 4.2.4 Comparison of the LRDP Evaluated at NAS North Island and the LRDP Evaluated 

Under ESTCP................................................................................................................ 34 

4.3 DEM/VAL 2: Hunter Army Airfield (50,000-gal UST)........................................................ 36 

4.4 Other Field Tests in Bulk USTs with the LRDP .................................................................... 39 

5.0 Performance Assessment ....................................................................................................... 40 

5.1 Results of the First LRDP Evaluation..................................................................................... 40 

5.2 Methods Evaluated ................................................................................................................. 42 

5.3 Results of the Leak Detection Tests at Point Loma................................................................ 43 

Page
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Table of Contents (cont.)

5.4 Performance Estimates for a Single Test (LRDP-10 and LRDP-24) ..................................... 46 

5.5 Performance Estimates for More than One Test (LRDP-10-n and LRDP-24-n).................... 47 

5.6 Formula to Compute the Threshold and Target Leak Rate as a Function of Tank Diameter for 

the LRDP-10 and LRDP-24.......................................................................................................... 49 

5.7 How to Use the LRDP System................................................................................................ 51 

5.8 Results of the DEM/VAL of the LRDP in a 50,000-gal UST ................................................ 52 

5.9 Results of the DEM/VAL of the LRDP in a 132.5-ft Diameter Bulk UST at San Pedro....... 55 

6.0 Cost Assessment .................................................................................................................... 57 

6.1 Cost Performance.................................................................................................................... 57 

6.2 Cost Comparison to Conventional and Other Technologies .................................................. 60 

6.3 Cost Avoidance....................................................................................................................... 62 

6.4 Cost of the Parts to Manufacture the LRDP ........................................................................... 64 

7.0 Regulatory Issues................................................................................................................... 65 

8.0 Technology Implementation .................................................................................................. 68 

8.1 DoD Need ............................................................................................................................... 68 

8.2 Transition ................................................................................................................................ 68 

9.0 Lessons Learned .................................................................................................................... 69 

10.0 Summary .............................................................................................................................. 71 

11.0 References............................................................................................................................ 72 

Appendix A: Points of Contact................................................................................................. A-1 

Appendix B: Listings Submitted to the NWGLDE for the LRDP-10 and the Update of the 

 LRDP-24 ...............................................................................................................B-1

Page
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Table of Contents (cont.)

Appendix C: Product Description and Product Specification Sheets.........................................C-1 

Appendix D: Software User Interface Screens .......................................................................... D-1

Appendix E: Performance Equations for Version a of the LRDP-10, LRDP-24, LRDP-10-n 

 and LRDP-24-n.......................................................................................................E-1 

Appendix F: Performance Equations for Versions 1.0a, 1.1a, and 1.2a of the LRDP-10, 

 LRDP-24, LRDP-10-n and LRDP-24-n .................................................................F-1 

Appendix G: Performance Estimates for the LRDP-10 for Versions 1.0a, 1.1a, and 1.2a as a 

 Function of TLR and Tank Diameter.................................................................... G-1 

Appendix H: Performance Estimates for the LRDP-24 for Versions 1.0a, 1.1a, and 1.2a as a 

 Function of TLR and Tank Diameter.................................................................... H-1 

Appendix I: Performance Estimates for the LRDP-10 as a Function of TLR and Tank Diameter 

 (Product Surface Area) for a Threshold Set to Yield a PD = 95% for the Selected 

 TLR...........................................................................................................................I-1 

Appendix J: Performance Estimates for the LRDP-24 as a Function of TLR and Tank Diameter 

 (Product Surface Area) for a Threshold Set to Yield a PD = 95% for the Selected 

 TLR..........................................................................................................................J-1

Page
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List of Figures

Figure 1. Low-Range Differential Pressure (LRDP) system for bulk USTs ............................1 

Figure 2. LRDP system with a tapered tube installed in a 12,500,000-gal Red Hill UST .......5 

Figure 3. Engineering Prototype of the LRDP system for bulk USTs .....................................5 

Figure 4. LRDP system used in the ESTCP bulk UST DEM/VALs......................................13 

Figure 5. In-tank portion of the LRDP system for a bulk UST with vertical walls................15 

Figure 6. Shaped reference tube used in a 50,000-gal UST ..................................................16 

Figure 7. Bottom container of the LRDP housing the sensor systems ...................................16 

Figure 8. A time series of the LRDP illustrating that the precision is 0.0002 in....................17 

Figure 9. Mounting system for a permanently installed LRDP in a bulk UST ......................18 

Figure 10. Remote Test Controller: (a) photograph and (b) schematic...................................19 

Figure 11. Example of the results of the data quality indices identifying that a pump was 

turned on during a test.............................................................................................22 

Figure 12. Example of the results of the data quality indices identifying a problem with the 

stability of the data trend.........................................................................................22 

Figure 13. Tank 175 at the Point Loma Fuel Terminal ............................................................26 

Figure 14. Tank 45 at the Hunter Army Airfield......................................................................26 

Figure 15. Installation of the LRDP in the Point Loma tank....................................................32 

Figure 16. Comparison of the LRDP data obtained with the engineering prototype of the 

LRDP and the LRDP evaluated in the ESTCP project ...........................................34 

Figure 17. Installation of the LRDP in the 50,000-gal UST.....................................................37 

Figure 18. Top of the being installed in an 8-in.opening in a 50,000-gal UST........................38 

Figure 19. Level data obtained with the LRDP-10 system for Test 10 ....................................44 

Figure 20. Level data obtained with the LRDP-24 system for Test 10 ....................................44 

Page
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List of Figures (cont.)

Figure 21. Level data obtained with the LRDP system over a 96-h period in a 132.5-ftdiameter tank at San Pedro......................................................................................44 

Figure 22. Least-squares lines fitted to the test results of the LRDP-10 and the LRDP-24.....44 

Figure 23. Difference between the induced leak rate and the volume rate measured with the 

LRDP-10 and the LRDP-24 ....................................................................................45 

Figure 24. Cumulative frequency distributions of the test results in a 122.5-ft-diameter bulk 

UST after the volume changes due to the induced leak were removed. .................45 

Figure 25. Height-to-volume calibration level data in a 50,000-gal UST................................53 

Figure 26. Volume data from a 24-h leak detection test with the LRDP-24 ............................53 

Figure 27. Volume data obtained from 74-h of measurements with the LRDP .......................53 

Figure 28. Estimate of Performance made for the LRDP in a 50,000-gal UST .......................54 

Figure D-1. LRDP Main Menu: display screen allowing the user to conduct a leak detection 

test or to review the results of previous leak detection tests. ............................... D-2 

Figure D-2. Enter New Test Parameters: display screen allowing the user to use the default 

testing option and test parameters shown on the screen or to enter new test 

parameters. ........................................................................................................... D-3 

Figure D-3. Test Initiation: display screen allowing the user to start the test immediately or to 

schedule the start of the test for a later time......................................................... D-4 

Figure D-4. Leak Detection Test Preparation: display screen reminding the user that valves 

need to be closed before a test can be conducted................................................. D-5 

Figure D-5. Leak Detection Test Setup/Monitor Screen: display screen allowing the user to 

monitor the level in real time ............................................................................... D-6 

Figure D-6. LRDP Test Results: display screen presenting the results of the leak detection to 

the user ................................................................................................................. D-7 

Figure D-7. Leak Detection Test Archives: display screen allowing the user to review previous 

test results and test data........................................................................................ D-8 

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List of Tables 

Table 1. California Testing Options for Bulk USTs................................................................8 

Table 2. Summary of the Four Methods of the LRDP System for Bulk Tanks ......................9 

Table 3. Illustration of the Magnitude of the Sources of Errors in a 122.5-ft-Diameter Bulk 

UST Containing 2,100,00 gal of Fuel .....................................................................14 

Table 4. Standard Test Schedule ...........................................................................................29 

Table 5. Summary of the Test Results and Induced Leak Rates for the LRDP Systems .....33 

Table 6. Summary of the Evaluation Temperature Conditions.............................................35

Table 7. Final Results for the Evaluation of the LRDP-10 at Point Loma............................36 

Table 8. Final Results for the Evaluation of the LRDP-24 at Point Loma............................36 

Table 9. Test Results for the LRDP in a 50,000-gal UST at Hunter Army Airfield.............38 

Table 10. Mean and Standard Deviation of the Difference between the Measured Leak Rates 

(Test Results) and Induced Leak Rates for the LRDP-10 and LRDP-24................45 

Table 11. Performance Estimates for the LRDP-10 and the LRDP-24 ..................................46 

Table 12. Performance Estimates for the LRDP-48 and the LRDP-24 against Larger Leaks 47 

Table 13. Mean and Standard Deviation of the Difference between the Measured Test 

Results and Induced Leak Rates for the LRDP-10-n and LRDP-24-n for n = 4, 6, 

and 12 .....................................................................................................................48 

Table 14. Performance Estimates Made for the LRDP-10-n and the LRDP-24-n Systems....48 

Table 15. Formula to Compute the Threshold and Target Leak Rate as a Function of Tank 

Diameter for the LRDP-10 .....................................................................................49 

Table 16. Formula to Compute the Threshold and Target Leak Rate as a Function of Tank 

Diameter for the LRDP-24 ......................................................................................50 

Table 17. Example of the MDLR in gal/h (PD = 95% and a PFA = 5%) as a Function of Tank 

Diameter .................................................................................................................50 

Table 18. Largest Diameter Tank in which a 0.20 gal/h Leak Rate Can Be Detected as a 

Function of the Number of Tests Averaged Together ............................................51 

Page
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List of Tables (cont.)

Table 19. Largest Diameter Tank in which Various Leaks Can Be Detected as a Function of 

Target Leak Rate .....................................................................................................51 

Table 20. Estimate of performance for the LRDP made for an 8-h and a 24-h test duration in 

a 50,000-gal UST ....................................................................................................54 

Table 21. Summary of the Results of Eight 24-h Tests with the LRDP in the San Pedro Tank 

after the Mean Flow Was Removed ........................................................................55 

Table 22. Summary of the Costs of the Two DEM/VALs of the LRDP System....................57 

Table 23. Compliance Monitoring Technology Costs for the LRDP on a Per Tank Basis.....59 

Table 24. Comparison of the Cost of Testing with Monthly Monitoring and an Annual 

Precision Test for Each Bulk UST for the First Year .............................................61 

Table 25. Comparison of the Cost of Testing with Monthly Monitoring and an Annual 

Precision Test for Each bulk UST Over 1, 3, 5 and 10 Years ................................62 

Table 26. Comparison of the Cost of Testing with Monthly Monitoring and an Annual 

Precision Test for 15 bulk USTs Over 1, 3, 5 and 10 Years ..................................62 

Table 27. Comparison of the Cost of Testing with Monthly Monitoring and an Annual 

Precision Test for 300 bulk USTs Over 1, 3, 5 and 10 Years ................................62 

Table 28. Parts List for the LRDP...........................................................................................64 

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xiii

Acronyms 

AST Aboveground storage tank 

CERF Civil Engineering Research Foundation 

CERL Construction Engineering Research Laboratory (Army) 

DESC Defense Energy Support Center (DESC) 

DoD Department of Defense 

EPA Environmental Protection Agency 

ESTCP Environmental Security Technology Certification Program 

EvTEC Environmental Technology Evaluation Center 

I/F Interface 

MDLR Minimum Detectable Leak Rate 

MODBUS Industrial Networking System that uses RS232 Serial Master-Slave 

Communications 

NAS Naval Air Station 

NFESC Naval Facilities Engineering Service Center 

NWGLDE National Work Group on Leak Detection Evaluations 

PD Probability of Detection 

PFA Probability of False Alarm 

PMD Probability of Missed Detect 

PLC Programmable Logic Controller 

PSA Product surface area 

RTD Resistance Temperature Device 

TLR Target Leak Rate 

UST Underground Storage Tank 

VR Volume Rate 

Page
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Acknowledgments 

 The LRDP team would like to acknowledge and thank the fuel farm directors and their 

staff at the Point Loma Fuel Terminal, the Hunter Army Airfield, the Defense Energy Office, 

Los Angeles (San Pedro), and the NAS North Island for making their facilities available for the 

DEM/VALs of the LRDP system, and for coordinating and supporting the DEM/VALs. We 

would also like to acknowledge the input and support of the Defense Energy Supply Center 

(DESC) and Endress+Enhauser Coggins Systems. Ken Wilcox Associates, Inc., performed the 

third-party evaluation of the LRDP. The LRDP was initially developed by NFESC and Vista 

Research with funding from the Pollution Abatement Ashore Program, which is sponsored by 

the Environmental Protection, Safety and Occupational Heath Division (N45) of the Chief of 

Naval Operations, and from Vista Research. The work described in this report was funded 

through the Environmental Security Technology Certification Program (ESTCP) and is entitled, 

“Validation of the Low Range Differential Pressure (LRDP) Leak Detection System for Small 

Leaks in Bulk Fuel Tanks.” A full list of contacts is included in Section 8 of this report. 

The LRDP team would like to especially thank Dr. Jeffrey Marqusee and Dr. Robert Holst for 

their support. 

 Project Manager: Leslie A. Karr, REM 

 NFESC 

 

 Project Engineers: William R. Major 

 NFESC 

 

 Dr. Vincent F. Hock 

 CERL 

 Technical Director: Dr. Joseph W. Maresca, Jr. 

 Vista Research, Inc. 

 Design/Field Engineers: James W. Starr, P.E. 

 Vista Research, Inc. 

 Gary A. Hayter 

 Vista Research, Inc. 

 
1

1.0 Introduction 

The Low Range Differential Pressure (LRDP) system is an innovative technology that was 

developed for the reliable detection of small fuel leaks in the bulk underground storage tanks 

(USTs) that are owned or operated by the Department of Defense [1-2]. If a tank is leaking, the 

LRDP quantitatively measures the leak rate in gallons per hour, the quantity of regulatory 

interest. The LRDP system can be used to test tanks ranging in capacity from 50,000 gallons to 

12.5 million gallons and will work for tanks with vertical and/or curved walls. The LRDP is a 

fully automatic, mass-based system, which is easy to install and use. The LRDP system can be 

permanently installed in a tank and used for on-line monitoring and precision (tightness) testing. 

It can also be used as a portable system for periodic testing of any tank in the fuel farm. The 

duration of a test can be either 10 or 24 h depending on the size of the tank and the performance 

required. 

The LRDP, which is shown 

in Figure 1, is the only intank system that has the 

performance to address both 

the monthly monitoring and 

annual precision test leakdetection regulatory 

requirements for bulk USTs 

[3-5] without requiring the 

installation, operation and 

cost of a second system. Not 

only is the LRDP the only 

system that can cost 

effectively meet both 

requirements, it can meet 

these requirements with a 

very low probability of false 

alarm. It is also the only 

system that can conduct an 

overnight test. The 

technology is not site-specific, and the performance of the technology is not affected by site 

geology or topographic factors. The system can be implemented in a bulk tank of any size and of 

any configuration. It can also be readily integrated into the DoD tank farm Fuel Accounting 

System (FAS) and other fuel management and handling systems. 

The LRDP technology also provides facility operators with valuable tank replacement and cleanup cost avoidance information, because the probability of a missed detection, the probability of a 

false alarm, and the confidence intervals on the measurement of the flow rate due to a leak are 

Figure 1. Low-Range Differential Pressure (LRDP) system for bulk USTs. 
2

known for the LRDP. With this information, an estimate of the life-cycle cost of the technology 

can be made. Significant cost savings can be realized, because the performance of the LRDP is 

high, and the recurring costs associated with operation of the system are low. 

As part of the Environmental Security Technology Certification Program (ESTCP), the LRDP 

technology was demonstrated and validated (DEM/VAL) in two 2,100,000-gal, field-erected, 

bulk USTs and in a 50,000-gal, shop-fabricated UST, all owned and operated by the DoD. One 

of the bulk USTs was located at the Point Loma Fuel Terminal, San Diego, California, and the 

other was located at the San Pedro Fuel Facility, Defense Energy Office, Los Angeles. The 

DEM/VAL conducted on the 50,000-gal UST was conducted at the Hunter Army Airfield (a subunit of Fort Stewart), Savannah, Georgia. These technology demonstrations were performed by 

the Naval Facilities Engineering Service Center (NFESC), Port Hueneme, California, the U. S. 

Army’s Construction Engineering Research Laboratory (CERL), Champaign, Illinois, and their 

industrial partners, Vista Research, Inc., Sunnyvale, California, and Vista Engineering 

Technologies, L.L.C., Kennewick, Washington. The ESTCP is a corporate DoD program that 

promotes innovative, cost effective environmental technologies through demonstration and 

validation at DoD sites. This project was performed as part of the Compliance ESTCP Thrust 

Area under Improved Leak Detection and Prevention Technologies for Underground Storage 

Tanks (USTs) and Underground Pipelines. The main points of contact for this project are listed 

in Appendix A. 

The objective of the DEM/VAL conducted at the Point Loma site was to obtain an independent 

third-party evaluation of the performance of the LRDP as an on-line monitoring and precision test 

leak-detection system. This evaluation was originally planned for the San Pedro site, but a small 

flow across the pipeline valve prevented the evaluation from being conducted at this site. 

However, the limited number of tests conducted at San Pedro indicated that the LRDP had the 

capability for meeting the regulatory requirements for precision testing and monthly monitoring. 

Before a method can be used, it must be evaluated for performance by an independent third party 

and listed by the National Work Group on Leak Detection Evaluations (NWGLDE). The 

evaluation was performed by Ken Wilcox Associates, Inc. (KWA) at the Point Loma site. The 

evaluation was conducted in a 122.5-ft-diameter bulk UST in accordance with a standard test 

procedure following EPA guidelines that was developed specifically for bulk storage tanks [6, 7]. 

This procedure was reviewed and approved by the NWGLDE, a national group of regulators, 

which is sponsored by the EPA, to simplify the certification of leak detection methods by the 

states. The NWGLDE reviews the third-party evaluations of leak detection methods for 

completeness and accuracy. If the evaluation is complete and accurate, the NWGLDE will list 

the method. This listing allows the states, which develops a list of approved methods that can be 

used for leak detection in their state, to approve methods without extensive review. If the method 

is not listed by the NWGLDE, the states will not approve or use the method. The listing gives a 

description of the method, its performance, and the limitations on its use. 

The results of this performance evaluation for an overnight test (10 h) and for a 24-h test have 

been submitted for review and update of the current LRDP listings by the NWGLDE so that the 

system can be used by the states to address their leak detection regulatory requirements [8-15]. A 

draft of the updated listing is presented in Appendix B. The performance of the system is 

presented in terms a probability of detection (PD) of a given target leak rate (TLR) in gallons per 
3

hour and a probability of false alarm (PFA), where the PD = 95% and the PFA < 5%. The TLR is 

usually specified by the regulatory requirements and may be different from state tot state. The 

TLRs are typical 1, 2, or 3 gal/h for monthly monitoring and 0.2 gal/h for precision testing. 

The objective of the DEM/VAL conducted at the Hunter Army Airfield site was to demonstrate 

the technology in a 50,000-gal UST with cylindrical walls. This DEM/VAL consisted of a 

limited number of tests showing that the system was capable of meeting the EPA’s regulatory 

requirements for monthly monitoring at 0.2-gal/h. A third-party evaluation was not performed for 

this type of UST. If the LRDP is to be used for testing cylindrical USTs, a third-party evaluation 

will be required. 

This technology has been successfully transferred to industry. Leak-detection products and 

services based on this technology are commercially available through Vista Research, Inc.; these 

products and services include (1) on-line, permanently installed monitoring systems and (2) 

tightness testing services. Product description and product specification sheets are included in 

Appendix C. 

1.1 Problem 

The DoD owns and operates over 300 bulk USTs. They range in size from 100,000 gal to over 

4,000,000 gal, and have diameters up to 135 ft. Over half of these bulk USTs are located in 

California. The DoD also owns twenty 12,500,000-gal USTs in Red Hill, Hawaii. In addition, 

the DoD owns and operates many thousands of large shop-fabricated USTs (e.g., 50,000-gal) 

throughout the country. Until recently, unlike the small USTs found at petroleum service 

stations, the bulk tanks had no regulatory requirements for periodic leak detection. The federal 

regulations deferred bulk USTs from the regular annual tightness test or monthly monitoring tests 

that other smaller USTs must undergo. However, various states have implemented regulations or 

testing guidelines, which have the strength of regulations, for bulk USTs. This presents a unique 

problem for DoD, because DoD is the only owner of bulk USTs. Because of increasing 

remediation and cleanup costs due to tank leakage and the implementation of regulatory 

guidelines and requirements, the DoD is in need of one or more leak detection systems to meet 

their environmental needs. 

Prior to the start of this ESTCP project, the only system that could meet the Federal UST 

regulatory requirements was a tracer method in which a unique tracer could be added to the fuel. 

However, the cost of using this technology is very expensive, even for a single annual tightness 

test, and is not cost effective for monthly monitoring. The use of other types of tracer methods, 

which use one or more constituent components of the fuel as tracers, do not work, because the 

background contamination results in too many false alarms. While acoustic systems have 

application for aboveground storage tanks (ASTs), they have not been used for bulk USTs and do 

not have the performance to meet regulatory guidelines for bulk USTs. Volumetric systems, 

comprised of level and temperature sensors like those used on the smaller USTs at petroleum 

service stations, cannot adequately compensate for the thermal expansion and contraction of the 

fuel to be considered. While statistical inventory reconciliation methods are approved and widely 

used at service stations, their performance, even for these small tanks, is suspect by the regulatory 

community. Regardless, of performance, the fuel farm UST systems are not adequately 
4

configured for leak detection, and it would be very expensive to retrofit the fuel farm to 

implement this approach. 

The technology of preference for DoD’s bulk UST owners and operators is an in-tank, massbased system. The performance of a conventional mass measurement system, however, is 

seriously limited by three factors and cannot be used to address the regulatory guidelines for both 

monthly monitoring and periodic precision testing unless these limitations are fully addressed. 

The first limitation is that a conventional system, which uses a differential pressure sensor with 

sufficient dynamic range to measure level changes over the full vertical extent of the tank, lacks 

the precision required to detect small leaks unless special-purpose, delicate and expensive sensors 

are used. The second limitation is that, in a tank with a variable cross-sectional area, thermal 

influences can cause large changes in volume, which are not compensated by a differential 

pressure sensor. The third limitation is the errors produced by the thermal expansion or 

contraction of both the instrumentation and mounting system. 

The LRDP system was developed to address these limitations. The reference tube addresses the 

first limitation, and a “shaped” tube addresses the second limitation; the bottom-mounted sensors 

and the special bellows mounting system used in the LRDP system described below address the 

third limitation. 

1.2 Background 

The LRDP system was developed to address the requirements for leak detection specified in the 

Navy’s Environmental Quality Research and Development Requirement No. 2.iii.2.a “Improved 

Leak Detection and Prevention Technologies for Underground Storage Tanks (USTs).” The 

LRDP system provides the DoD a method of leak detection for bulk USTs that 

• will be in compliance with local, state and federal regulatory requirements, 

• has with sufficient performance to detect a leak, if one were to occur, so that the 

environmental damage and the costs associated with cleanup and remediation could be 

minimized, 

• is reliable enough to be used, because it does not have false alarm problems and could be 

used without any significant impact to operations, and 

• is very cost effective, because it can be installed, operated, and maintained over time less 

expensively than other technologies, and could be effectively used to minimize the cost of 

cleanup and remediation by early detection of and quantification of the size of a leak. An 

estimate of the cost savings associated with the use of this technology is between $500 M 

and $1 B. 

All four of these objectives are based on the performance of the method, and the LRDP system 

has more than sufficient performance to meet the compliance, detection, operation, and cost 

objectives required of a leak detection technology needed to satisfy DoD’s environmental needs. 
5

The LRDP, shown in Figure 2, was originally developed for detection of leaks in the world’s 

largest USTs [2]. The 20 Red Hill tanks, which are owned and operated by the U. S. Navy, are 

buried over 100 ft deep in the hills above 

Honolulu, Hawaii and contain 12.5 

million gallons of fuel. Each tank is 100 

ft in diameter and 250 ft in height. In 

1996, an LRDP was installed in one of 

the Red Hill tanks (Tank 16) for 

demonstration purposes. (Another 

LRDP has recently been installed in 

Tank 9 (March 2001) and a third-party 

evaluation has been completed [16]). 

While waiting for fuel to be added to 

Tank 16 at Red Hill, a second LRDP was 

built and installed in a 88-ft-diameter, 

600,000-gal UST at the NAS North 

Island Fuel Farm. The first 

implementation of this system, which is 

shown in Figure 3, was developed for 

cylindrical tanks with vertical walls and 

evaluated for performance by KWA in a 

600,00-gal UST at the NAS North Island 

Fuel Farm in 1998. The LRDP was 

listed by the NWGLDE for use as a 

precision leak-detection system for bulk 

USTs using either a 24- or 48-h test, a waiting period of 24 h, and an average of a set number of 

tests (1, 4 or 5 tests) [1, 5]. The performance estimates made in this third-party evaluation were 

contaminated by a small inflow (~0.1 gal/h) that occurred during the evaluation; this inflow 

introduced a small bias and degraded the performance of the system over what it should have 

been. Even so, the performance was excellent and more than sufficient to meet regulatory 

requirements for both monitoring and precision testing. The limitations and constraints imposed 

on the use of the LRDP by the 

NWGLDE as a result of this first 

evaluation were addressed and 

eliminated in the evaluation 

described in this report. 

The main difference between the 

LRDP system installed at NAS 

North Island and the one used in this 

evaluation is the size and location of 

the sealed container at the bottom of 

the reference tube. The 

measurement sensors in the sealed 

container were the same for both 

systems. Since the fuel in both 

Figure 2. LRDP system with a tapered tube installed in a 

12,500,000-gal Red Hill UST. 

Figure 3. Engineering Prototype of the LRDP system for bulk 

USTs 
6

versions of the reference tube extended from the bottom of the tank to the product surface and had 

an identical cross-sectional area, identical performance is expected and was verified by a side-byside comparison of the improved version of the LRDP system evaluated during the Point Loma 

DEM/VAL. 

1.3 Objectives of the Demonstration 

The objective of this ESTCP project was to demonstrate and validate (DEM/VAL) a reliable, 

cost-effective leak-detection system for monthly monitoring and periodic precision testing of the 

bulk underground storage tanks (USTs) with vertical walls that are owned and operated by the 

DoD. This project was an expansion of the previous testing and regulatory approval obtained in 

California for the LRDP on an 88-ft-diameter bulk UST at NAS North Island [1]. The present 

tests were designed to demonstrate the system on larger tanks and to obtain regulatory approval 

for use of the system as an on-line monitoring system and with a test duration of 24 h and a 

second test duration shorter than 24 h (i.e., 10 h). The output of the project is an alpha-prototype 

of the LRDP leak detection system (1) that is ready for pre-production testing by industry and (2) 

that has been evaluated for performance by an independent third party following a standard test 

procedure developed by the EPA and approved by the NWGLDE. The third-party evaluation 

will be submitted to the NWGLDE for review and inclusion on a national list of leak detection 

methods, which are ready for use by the states. An additional objective was to demonstrate that 

the LRDP system also can be used to test the smaller, 50,000-gal underground storage tanks with 

curved walls. 

Unlike many other environmental technologies, the approach to DEM/VAL is prescribed by the 

EPA. In 1988, the EPA developed a set of standard test procedures for estimating the 

performance of various types of leak detection methods. In 1996, a standard test procedure was 

prepared for mass-based or volumetric leak detection methods for bulk USTs [6]. The results are 

presented in terms of a volumetric target leak rate (TLR) in gallons per hour, a probability of 

detection (PD), and a probability of false alarm (PFA). The regulatory requirements of each state 

are specified in terms of PD, PFA, and TLR, where the state sets the TLR, and at a minimum, the 

PD must be equal to or better than 95% and the PFA must be less than or equal to 5%. The 

standard test procedure for mass-based systems allows for the scaling of performance for verticalwall USTs with surface areas up to 250% of the surface area of the UST used in the evaluation. 

The standard test procedure places a number of constraints on the scaling of performance. First, 

the performance of the method could not be scaled to a target leak rate less than 0.2 gal/h, and 

second, the smallest UST that the method is approved for use has a capacity of 50,000 gal. 

1.4 Regulatory Requirements 

The UST regulation, issued in 1988 by the EPA, deferred the requirements for testing bulk or 

field-erected USTs for leaks [3]. The main reason for the deferral of field-erected USTs was the 

lack of any technologies in 1988 that could reliably test these large tanks for leaks. Only the 

shop-constructed USTs, which are typically used at service stations and have capacities of 50,000 

gal or less, were strongly regulated. In contrast, the large field-erected USTs, which have 

capacities between 100,000 to 12,500,000 gal, did not need to meet the rigorous leak-detection 

performance standards for monthly monitoring or annual tightness testing established for small 

USTs [3]. 
7

The performance of a leak detection system with a PD = 95% for a specified TLR and a PFA = 5% 

is called the minimum detectable leak rate (MDLR), where the MDLR equals the specified TLR. 

This jargon should not be confused with the smallest leaks that can be detected. Leaks smaller 

than the TLR can be detected, but the PD may be less than 95% (even if the threshold is not 

changed) or the PFA may be less than 5% (by changing the threshold). While many leak detection 

systems are operated at this level of performance, the chief advantage of computing the MDLR 

for each method, even if they are not operated at this level, is that the performance of different 

methods can be easily and directly compared. 

The UST regulation, which was required to be implemented by the states, requires that all 

regulated USTs be tested for leaks on a monthly basis with a leak detection system capable of 

detecting a leak as small as 0.2 gal/h with a probability of detection (PD) of 95% or greater and a 

probability of false alarm (PFA) of at 5% or better. Between the issuance of the UST regulation 

on 22 December 1988 and the 10-year period that allowed for tank owners to meet the UST 

upgrading requirements (by 22 December 1998), tightness (or precision) tests of the USTs were 

allowed in lieu of the monthly monitoring. While the testing schedule prescribed by the EPA 

regulation allowed intervals of up to 5 years between tests, most states required annual tightness 

testing if this option was selected by the tank owner. To meet the regulatory requirements for a 

tightness test, a leak detection system capable had to be capable of detecting a leak as small as 0.1 

gal/h with a PD > 95% and a PFA < 5%. During this 10-year period, the states struggled with how 

to test bulk USTs and what performance standards should be required. Until the mid- to late1990s, bulk USTs were rarely tested for leaks; large inventory imbalances were the primary mode 

for identifying a leak. The volumetric systems that were typically used to meet the performance 

standards required for the small regulated USTs found at service stations could not meet these 

same standards on the bulk USTs. The LRDP, a mass-based system, was developed in response 

to the need for detection of leaks in bulk USTs owned by the Department of Defense (DoD). 

During the late 1990s, California, where the majority of all of DoD’s bulk tanks are located, 

developed regulatory guidelines for testing bulk tanks. Since the DoD owns almost all of the bulk 

USTs in the United States, the California guidelines were mainly prepared for DoD compliance. 

The basic option for testing USTs, regardless of size, is to meet the 0.2-gal/h monthly 

requirement in the EPA UST regulation. This option, included by California as Option 1, is 

overly stringent and does not have a low enough PFA for routine monitoring. As a consequence, 

California developed other options that included a precision test at 0.1 gal/h, which is not realistic 

for testing bulk USTs [4]. 

Two of the ten testing options (Options 7, 10) developed by California were based on the input 

from discussions from NFESC and Vista Research and the results of the first third-party 

evaluation of the LRDP [4] conducted at North Island. Both of these options required monthly 

monitoring and a periodic precision test. These performance guidelines are stringent, consistent 

with bulk operations, and achievable. These two guidelines are summarized in Table 1. The 

other options are variances of the UST leak detection performance standards issued for the small 

USTs found at service stations and are not generally consistent with the design and operation of 

bulk USTs. The State of California requires that each leak detection system be third-party 
8

evaluated, be approved and listed by the NWGLDE, and be approved and listed on the California 

list. 

As will be discussed in Section 5, the LRDP meets all of these standards. However, any leak 

detection system that can meet Option 1 can also meet Options 7 and 10, so Option 1 would not 

be the first choice by the fuel farm operator unless such level of protection is really needed or the 

standard can be met with a much lower PFA than 5%. Furthermore, the LRDP system is the only 

on-line monitoring mass-measurement system that can meet both the monthly monitoring and 

precision testing guidelines in Options 7 and 10 for all bulk USTs owned by DoD. 

Table 1. California Testing Options for Bulk USTs [4] 

California Testing Options Monthly Monitoring Test Precision (Tightness) Test 

Option 1 

Target Leak Rate – gal/h 0.2 gal/h 

PD - % > 95% 

PFA - % < 5% 

Testing Schedule – years 1 month 

 

Option 10 

Target Leak Rate – gal/h 0.3 to 1.0 gal/h 0.2 gal/h 

PD - % > 95% > 95% 

PFA - % < 5% < 5% 

Testing Schedule – years 1 month 1 year 

 

Option 7 

Target Leak Rate – gal/h 1.0 to 2.0 gal/h 0.2 gal/h 

PD - % > 95% > 95% 

PFA - % < 5% < 5% 

Testing Schedule – months 1 month 6 months 

Because of the particularly high performance achieved by the LRDP, the State of California 

would not allow the system to be used as designed (Version a in the NWGLDE listing), even 

though it met these performance guidelines. The State limited the target leak rate to twice the 

minimum detectable leak rate (MDLR) achieved by the system (Versions 1.1a or 1.2a). For most 

UST sizes, the PFA << 5% for the LRDP. 

1.5 Improvements to the LRDP Evaluated at NAS North Island 

The work was accomplished in the following four tasks: 

• Task 1 - Prepare and execute work plan 

• Task 2 - Design, assemble, integrate and checkout alpha prototype 

• Task 3 - Conduct system DEM/VAL and evaluation testing at selected DoD installations 

Task 4 - Prepare technology transfer package and implementation plan 
9

All four tasks were successfully completed; the technology has been transferred to industry and is 

being offered commercially to address DoD’s bulk UST environmental needs. 

Four testing methods of the LRDP system were evaluated for performance. For each method, one 

of four thresholds can be used to detect a specific target leak rate (TLR) or to operate with a 

specific PFA. The TLR is usually specified by the regulatory agency. The PD = 95% for all 

thresholds and all methods used by the LRDP. The list distinguishes each threshold by a unique 

version number. Table 2 summarizes the four methods. Two of the methods require only one 

test, and two of the methods require the averaging of up to 12 tests. The name of the method 

contains the duration of the test in hours and the number of tests to be averaged. The LRDP-10 is 

implemented with a 10-h test, and the LRDP-24 is implemented with a 24-h test. The LRDP-10-

n is a test that requires the averaging of “n” tests. The number of tests to be averaged depends on 

the required performance. This type of method is normally used to meet the 0.2-gal/h precision 

(tightness) test requirement for the larger tanks owned by DoD. Any or all four of these methods 

can be used in combination to address regulatory requirements. For example, the LRDP-10 might 

be used to address the monthly monitoring requirement, and the LRDP-24 might be used to 

address the precision test requirement. 

Table 2. Summary of the Four Methods of the LRDP System for Bulk Tanks 

Name of Test Method Type of Test Test Duration 

Number of Tests 

Averaged Together 

LRDP-10 Monitoring, Precision1 10 h 1 test 

LRDP-10-n Precision1 10 h 1 < n < 12 tests 

LRDP-24 Version A Monitoring, Precision1

 24 h 1 test 

LRDP-24-n Version A Precision1 24 h 1 < n < 12 tests 1

 Can be used to address the regulatory standards for a 0.20-gal precision test, when the monthly monitoring 

requirement is 2.0 gal/h or less. 

Many important improvements to the LRDP evaluated at NAS North Island have been made 

under ESTCP. As a result of these improvements, the LRDP is ready for implementation 

throughout the DoD. However, none of these improvements effected any changes to those parts 

of the system that control performance. For example, the same differential pressure sensor was 

used in both systems. Some of these improvements are: 

• The notebook computer and data acquisition system were replaced with a field-worthy 

remote test controller, which collects data, evaluates data quality, analyzes test results, 

and stores the results. 

• The system was made fully automatic, and the software user interface was made easy to 

use. 

• The system was originally approved as a portable system and can now also be used as a 

stand-alone system for on-line, real-time, in-tank monitoring. 

• A special set of data quality indices were developed and tested to insure the reliability of 

each test result. 

• The in-tank sensor unit was redesigned for easy installation and now fits into a standard 

8-in. diameter opening of a tank of any diameter and any product depth. 
10

• The LRDP can be easily interfaced with base fueling operations, including the FAS, and 

can be used for both leak detection and inventory monitoring 

• The evaluated performance of the LRDP is 20% better than originally determined in the 

first evaluation, and the performance limitations (e.g., a 24-h waiting period) have been 

removed. 

• The monthly monitoring regulatory guidelines can be met with the LRDP using a 10-h 

test, which is short enough to be conducted overnight. For many of DoD’s bulk USTs, 

the LRDP also be used to address the precision testing guidelines with a 10-h test. The 

LRDP can be used to address the precision testing guidelines for the remaining bulk 

USTs with a 24-h test. 

• The electronics are housed in an explosion proof container and meet Class 1, Div 1 

Standards. 

• With changes to the design of the reference tube, the LRDP was adapted for use in 

testing 50,000-gal USTs and other USTs with curved walls. 

The main attributes of the LRDP system are summarized below: 

• The LRDP is directly inserted into a standard 8-in.-diameter opening in the tank that is 

being tested or monitored. 

• The LRDP can be used to perform a leak detection test without removing fuel from the 

tank. 

• The LRDP can be used to test USTs with both vertical and curved walls. 

• The output of a leak detection test is easy to interpret, because it is a direct measurement 

of the leak rate in gallons per hour, the quantity of regulatory and engineering interest. 

• Because the LRDP system is a mass-based system, it inherently compensates for the 

thermal expansion or contraction of the fuel in the tank during a test. Furthermore, 

accurate tests can be initiated without a long pre-test waiting period that are needed by 

other systems to allow the horizontal temperature gradient to stabilize throughout the 

tank. 

• The special mounting system eliminates thermally induced movement of the reference 

tube during a test. 

• Thermally induced drift of the differential pressure sensor is virtually eliminated, 

because it is mounted in a sealed container at the bottom of the tank. 

• Because the differential pressure sensor used to measure level (volume) changes in the 

tank needs a dynamic range of only 1 in. (rather than the total height of the tank, like 

other mass-based systems), the LRDP has the precision (0.0002 in.) to detect very small 

leaks in large-diameter tanks. 

• The system is self-calibrating, and the performance and functionality of the LRDP can 

easily be checked between leak detection tests. 
11

1.6 Report Organization 

This report is organized following the ESTCP final report outline. Section 2 provides a 

description of the technology. Section 3 describes the sites/facilities where the DEM/VALs were 

conducted, and Section 4 describes the demonstration approach. Section 5 presents the results of 

the DEM/VALs and the performance of the LRDP. Section 6 presents a cost assessment of the 

technology. Section 7 describes the regulatory interactions. Section 8 describes how the 

technology can and is being implemented. Section 9 describes the lessons learned that might be 

useful for other demonstrations, and Section 10 briefly summarizes the results of the project. 
12

2.0 Technology Description

A description of the LRDP is presented below. 

2.1 Description

The LRDP system is a mass-based, leak-detection system for use in bulk USTs containing 

petroleum fuels. If a tank is leaking, the LRDP quantitatively measures the leak rate. The LRDP 

system can be used to test tanks ranging in capacity from 50,000 gallons to 12.5 million gallons 

and will work for tanks with vertical and/or curved walls. Its modular design makes it easy to 

install in a tank of any depth or diameter. It can be installed through a standard 8-in.-diameter 

opening without removing any fuel from the tank. The LRDP system can be permanently 

installed in a tank and used for on-line monitoring and precision (tightness) testing. It can also 

be used as a portable system and be moved from tank to tank for periodic testing of any tank in 

the fuel farm. The former is the preferred configuration, because of the regulatory requirements 

for monthly monitoring. A test can be completed in 10, 24, or 481 hours. Better performance is 

achieved as the duration of the test is increased. For almost all applications, a 10- or 24-h test is 

sufficient; a 48-h test can be used if enhanced performance is needed. 

The LRDP can be used to test all three types of large, regulated, fuel USTs owned by the DoD: 

(1) bulk, field-erected USTs with vertical walls, (2) very large bulk USTs like those at Red Hill, 

and (3) large, shop-constructed cylindrical USTs (e.g., 50,000-gal tanks). The largest bulk USTs 

owned by DoD have diameters of ~134 ft and capacities of 2,000,000 to 4,000,000 gal. The 

largest USTs are located in Red Hill and have a capacity of 12,500,000 gal; these tanks are 250 ft 

in height and 100 ft in diameter; the top and bottom 50 ft of the tank is dome shaped. The 

50,000-gal USTs are nominally 10.5 (to 12.0) ft in diameter and 77.2 (to 59.0) ft in length. 

The pre-production prototype of the LRDP system, developed in this ESTCP project and shown 

in Figure 4, is a fully automatic, computer-controlled system. It is comprised of (1) an in-tank 

level sensing unit, (2) a local embedded remote test controller to implement a test and to collect 

and analyze the data from a test, and (3) a host computer to initiate, display, report, and archive 

the results of a test. The level-measurement sensor is an industrial differential pressure (DP) 

sensor that is located in a sealed container at the bottom of the in-tank sensing unit. A test is 

initiated by an operator using the host computer. The remote test controller, located in close 

proximity to the tank, automatically operates the LRDP system. A test report is generated upon 

completion of the test. The LRDP system is compatible with the DoD Fuels Accounting System 

(FAS) and can be integrated with FAS to test the tanks in a fuel farm or bulk storage terminal. 

 

1

 A 48-h test was evaluated for performance at NAS North Island. The performance obtained for the 24-h test in the 

second evaluation conducted as part of this ESTCP project was better than that obtained for the 48-h test in the first 

evaluation. This result is a consequence of contamination of the first results with a small inflow that occurred 

during the evaluation. If a 48-h test were performed, it would have better performance than a 24-h test. It should 

only be used, however, if the results of the 24-h test are inconclusive and better performance is needed. Although 

better performance will be achieved with a 48-h test, the performance claim can be no better than the 24-h test, 

unless it is re-evaluated. 
13

The in-tank level sensing unit of the LRDP system that has been designed for tanks with vertical 

walls (that is, upright cylinders with flat bottoms) is comprised of the following: 

(1) a reference tube that extends from the top to the bottom of the tank 

(2) a valve, located near the bottom of the tank, with which to open and close the tube 

(3) a sealed container mounted at the bottom of the reference tube 

(4) a differential pressure sensor, mounted in a sealed container located at the bottom of 

the tank, that measures the difference between the level of liquid in the tank and that in 

the reference tube 

(5) two pressure sensors, mounted in the sealed container, that can be used to measure the 

level and specific gravity of the fuel in the tank 

(6) a temperature sensor, mounted on the differential pressure cell in the sealed container, 

that can be used to 

compensate the 

differential pressure 

sensor or the pressure 

sensors for 

temperature, and/or to 

measure the 

temperature of the fuel 

at the bottom of the 

tank 

(7) electrical wires (4-20 

ma contained in a 

sealed conduit) that 

connect the bottommounted sensors to the 

data acquisition 

system outside the 

tank, and 

(8) a special bellowsmechanical mounting

system to eliminate 

thermal movement of 

the reference tube and transducer enclosure. 

The fuel in the tank is allowed to enter or leave the reference tube through a valve located at the 

bottom of the tube. The valve is opened and closed electronically (a function that can also be 

done manually). Except for a test, the valve is left in the open position. This allows fuel from 

the tank to enter the reference tube until the level of liquid is the same in both. When the valve is 

open, i.e., when the level of liquid in the tube is identical to that in the tank, the precision and 

accuracy of the LRDP system can be checked. When the tank is to be tested, the valve is closed, 

isolating the fuel in the tube from the fuel in the rest of the tank. With the exception of a level 

change due to a leak, the level of the fuel in the reference tube mimics the level of the fuel in the 

tank. The DP sensor measures the difference in the levels of fuel between the reference tube and 

Figure 4. LRDP system used in the ESTCP bulk UST DEM/VALs.
14

the tank. If the rate of change of the level in the tank (which can be expressed in terms of 

gallons per hour based on a height-to-volume conversion from the tank’s strapping table) 

exceeds a pre-set detection threshold, the tank fails the test. 

 

 2.2.1 Sources of Noise 

Ambient noise—real and apparent volumetric changes not associated with a leak—may, unless 

compensated, mask the presence of a leak or look like a leak. The LRDP compensates for the 

important source of ambient noise. Since it is known that the reference tube is not leaking, and 

since level changes in the tube mimic those in the tank, the ambient noise is removed from the 

test result. Because the LRDP is a mass-based system, it compensates automatically for the 

greatest source of noise—the level (volume) changes produced by thermal expansion and 

contraction of the fuel. Note that this approach must be modified for tanks with curved walls 

(e.g., horizontal cylinders, or vertical cylinders with spherical tops and bottoms). To address this 

type of tank, the LRDP system incorporates a second design in which the constant-diameter 

reference tube is replaced by a variable-shaped tube that mimics the cross-sectional changes in 

the tank’s geometry [17]. Such a reference tube was used to test the 50,000-gal USTs during the 

Hunter Army Airfield DEM/VAL. 

High performance is achieved with the LRDP system, because the novel design of the in-tank 

sensing unit results in (1) a very high precision for making level measurements with an off-theshelf differential pressure sensor and (2) effective compensation of the thermally induced 

changes of the fuel, the sensors, the tank, and the mounting system. For bulk tanks, both high 

precision and effective compensation is required to meet regulatory guidelines. 

Table 3. Illustration of the Magnitude of the Sources of Errors in a 122.5-ft-Diameter Bulk UST Containing 

2,100,00 gal of Fuel 

 Level Change Temperature 

Change 

Volume 

Change 

over 24 h 

Volume Error 

24-h Test* MDLR** 

24-h Test 

 (in.) (oC/h) (gal) (gal/h) (gal/h) 

Precision 0.001 1.50 0.062 0.22 

Thermal Expansion or 

Contraction of Jet Fuel 

 0.01 504.00 21.00 75.39 

 6-in. of exposed manway by air 

temperature 

 0.10 22.04 0.92 3.30 

DP sensor by fuel temperature 0.01 17.63 0.73 2.64 

DP sensor/electronic equipment 

by air temperature 

 0.10 176.33 7.35 26.38 

Total without Thermal Expansion 

or Contraction 

 7.44 26.71 

Total 22.28 79.99 

* Assumes 24 degrees of freedom in regression line. ** TLR for a PD = 95% and a PFA = 5%. 

Table 3 illustrates, for the conditions given, the magnitude of the errors in a 122.5-ft diameter 

UST and the MDLR that would result if these errors were not compensated. These conditions 

are modest and do not represent extreme conditions. Unless these thermally induced sources of 

noise are compensated by the leak detection system, leaks as small as 0.2 or even 1.0 or 2.0 gal/h 

would be masked by these large volume changes and would not be detected. Conversely, unless 
15

these volume changes are not compensated, they might be confused with a leak and lead to false 

declarations (i.e., false alarms). It is the latter that tends to plague systems and results in a loss of 

confidence in the system and ultimately in not using the system by fuel farm operators. 

As can be seen in Table 3, any one of the errors, if not compensated, can be large enough to 

prevent the method from meeting the regulatory requirements. For example, if a method has a 

precision of 0.001 in., this results in a volume change of 1.50 gal over a 24-h period in a 122.5-

ft-diameter tank. This assumes that a regression line is fit to data in and that there are 24 degrees 

of freedom. Assuming this was the only error, the method would have a MDLR of 0.22 gal/h. 

In a tank with a capacity of 2,100,000 gal, a 0.01o

C/h change in temperature results in a 21.00 

gal/h volume change. If this thermally induced volume change is not compensated to within 

0.01oC/h, then the error would be too large to use this approach for leak detection. This is the 

main reason mass-based systems, rather than volumetric (level and temperature) systems, are 

used for bulk USTs. A mass-based system compensates this error directly as part of the 

measurement. Even if a volumetric system can compensate to 0.001oC/h, a performance of 7.54 

gal/h would result, which is also too large for routine use. 

Exposed parts of the tank upon which the leak detection system is mounted will change elevation 

by thermal expansion and contraction of the mounting system. Diurnal temperature swings of 

over 15 oC are not uncommon. An estimate of the thermally induced level change based on a 

temperature difference of 2.4o

C over a 24-h period (0.1oC/h) on an exposed section of manway 

of 6 in. results in 0.92 gal/h error. This error is quite common for improperly mounted systems 

and would prevent the reliable detection of leaks of 3.3 gal/h if there were no other errors. As 

shown in Table 3, the thermally induced changes in a differential pressure cell or it electronics 

can result in apparent height changes that are also very large if not compensated. 

All of these potential sources of error must be 

reduced or compensated to about a third of the target 

leak rate required for regulatory compliance. In 

California, this means that monitoring methods must 

compensate to within 0.3 gal/h to meet a monthly 

monitoring requirement of 1.0 gal/h and to within 

0.06 gal/h to meet a periodic (semi-annual or annual) 

precision test of 0.2 gal/h. The LRDP compensates 

for over 98% of all of the thermally induced changes 

listed in Table 3, and because of the reference tube, 

the LRDP can achieve a very high precision with a 

DP sensor (0.0002 in.). 

 2.2.2 Reference Tube 

The key components of the in-tank sensing unit are a 

reference tube that spans the full usable height of the 

tank and a sealed container at the bottom of the tube 

(and tank) that houses the measurement sensors. 

Unlike most other mass-based systems, the LRDP 

Figure 5. In-tank portion of the LRDP 

system for a bulk UST with vertical walls.
16

system does not require a high-precision 

DP sensor nor does it require special 

compensation for changes in the 

temperature of the pressure sensor itself. 

Instead, the precision of the LRDP is 

controlled by the reference tube. The 

reference tube, because it greatly reduces 

the dynamic range over which 

measurements must be made, increases the 

precision of the DP sensor significantly - 

100 to 3,000 times in comparison to 

systems without a reference tube. This 

allows the LRDP system to employ an offthe-shelf, inexpensive, and rugged DP 

sensor instead of a special purpose, 

expensive and delicate one. An industrial 

grade DP sensor, which is manufactured 

by Rosemount, is located in the sealed 

container and measures the change in level 

between the fuel inside the reference tube 

and in the tank. 

 

A straight, constant diameter tube is used to test tanks 

with vertical walls (Figure 5), and a geometrically 

shaped tube is used to test tanks with curve walls 

(Figure 6). For bulk tanks with straight walls, the 

reference tube has a diameter of 3.5 in. For tanks with 

curved walls, the tube is shaped so that the product 

surface area at any depth changes in the same 

proportion in the tube and in the tank [17]. A shaped 

reference tube is needed for 50,000-gal horizontal tanks 

and for the 12.5-M-gal tanks at Red Hill. If the tube is 

not shaped appropriately, the thermally induced volume 

changes of the fuel cannot be accurately compensated. 

This is true for both mass-based and volumetric 

systems. The errors can be large enough to prevent the 

system from meeting the regulatory guidelines. In the 

Red Hill tanks, for example, the tapered tube eliminates 

an error of 20 gal/h that would otherwise be present in 

the measurement. Such errors can occur even when the 

rate of change of temperature is extremely small (e.g., 

0.0023o

C/h, as it was in this estimate). 

The same shaped reference tube can be used for all 

tanks with the same diameter, regardless of capacity. 

For best accuracy, the design of the tube should change 

as the diameter of the tank changes. For 50,000-gal 

Figure 6. Shaped reference tube used in a 50,000-gal 

UST.

Figure 7. Bottom container of the LRDP 

housing the sensor systems. 
17

tanks two reference-tube designs would cover the range of tank diameters (generally 10.5 to 12.0 

ft) found in commercial and DoD tanks. 

 2.2.3 Measurement Sensors in a Bottom-Mounted Sealed Container 

 

All of the measurement sensors are located in a special sealed container at the bottom of the tank 

(Figure 7). This container is 18 in. in height and 6.8 in. in diameter. The sealed container is 

actually comprised of a cylinder within a cylinder. The inside cylinder is dry and contains a 

differential pressure sensor, one or two pressure sensors, and a temperature sensor attached to the 

differential pressure sensor. The annular space that exists between the inner and outer cylinder 

contains fuel and communicates with the fuel in the reference tube attached to the top of this 

bottom module. As an extension of the reference tube, the cross-sectional area of the annular 

space also changes in the same proportion as the product surface area in the tanks changes. If the 

tank has vertical walls, then the cross-sectional area of the annular space does not change. If the 

walls of the tank are curve, then a special spacer bar is inserted into the annular space whose 

volume changes with depth so that the cross-sectional area of the annular space changes 

appropriately with depth. A spacer bar, whose volume is constant with depth, can be used to 

reduce the cross sectional area in the annular space if a reference tube with a smaller diameter 

than 3.5-in. is used. These spacers are made of aluminum to reduce weight. To avoid the 

possibility of leakage, the bottom of the container is welded closed. 

The DP sensor is the main sensing element of the LRDP. It measures the difference in level of 

the fuel in the reference tube and in the tank. The DP sensor measures the change in level 

between the fuel inside the reference tube and in the tank. The two sensing ports of the DP 

sensor are at the same elevation. One of the ports communicates directly with the fuel in the 

tank. The other port communicates with the fuel in the annular space. As stated above, an 

industrial grade differential pressure sensor, which has a long-term demonstrated track record of 

performance, can be used in the system, 

because the measurement configuration 

only requires measurements to be made 

over the small differences in height that 

may occur in the reference tube and in the 

tank during a test. The differential pressure 

sensor is set to operate over a height range 

of +0.5 in. of fuel; the same dynamic range 

was used for the Red Hill tank. This 

configuration increases the precision of the 

differential pressure measurement by a 

factor of at least 150 over a system that 

does not use a reference tube. Because of 

the small dynamic range of the 

measurement, the precision of measuring 

level is 0.0002 in., where the precision is 

defined as the one-standard deviation of the 

measured level fluctuations (Figure 8). 

-0.0004

-0.0002

0.0000

0.0002

0.0004

0 20 40 60

Time - min

Level - in. Water

Figure 8. A time series of the LRDP illustrating that the 

precision is 0.0002 in. 
18

A temperature sensor (RTD) is attached to the body of the DP sensor. It can be used to 

compensate for any thermal changes of the sensor if they become large. None of the field 

demonstrations and evaluations conducted to date has required such compensation, because the 

sealed container housing the sensors is located in a nearly constant temperature bath (i.e., the fuel 

in the bottom of a tank). While 0.01oC/h changes in the fuel temperature are large enough to 

produce volume changes of the fuel that mask a leak, such temperature changes are too small to 

affect errors in the DP sensor measurement. Temperature changes of several degrees per hour or 

more are required to introduce errors that may impact the accuracy of the DP sensor 

measurements. The temperature sensor mounted on the DP sensor can also be used to obtain an 

estimate of the mean temperature of the fuel in the tank. 

One or two absolute pressure sensors may be located in the sealed container. If one pressure 

sensor is located in the container, then the level of the fuel in the tank can be measured and used 

for inventory control purposes. If two pressure sensors are installed in the container, then in 

addition to the level measurement, either the specific gravity of the fuel can be measured, or the 

level of any water at the bottom of the tank can be measured. The former measurement is made 

with the two sensors communicating with the fuel in the tank and separated by 16 in. The latter 

measurement is made by placing one of the sensors at a depth near the bottom of the tank, so that 

it is located in the water when water is present. 

 2.2.4 Mounting of the In-tank Sensor Unit 

 

The reference tube and its connection into the annular space extends from the bottom of the tank 

to a level that is higher than the maximum level at which the tank is to be tested. The top of the 

reference tube must be able to communicate 

freely with the vapor space. Many years of 

experience has indicated that any leak 

detection system with a level sensor needs to 

rest on the bottom of the tank. Thus, the 

reference tube should be installed such that it 

rests on the bottom of the tank. Suspending 

the reference tube (or a level sensor from the 

top of the tank) introduces errors due to the 

thermal expansion and contraction of the 

staff, chain or tube used to suspend the level 

sensor. Problems are also encountered when 

the system is rigidly attached to a manway 

plate at the top of the tank, because the 

manway plate can raise (or lower) the 

reference tube due to thermal expansion or 

contraction. As shown in Figure 9, the 

mounting system is comprised of a 4-in. 

diameter cap in the manway of the tank, a 

bellows to prevent thermal movement, and a 

motor to open and close the valve. The 

bellows mounting system eliminates the 

thermal movement of the tank or manway 

Figure 9. Mounting system for a permanently installed 

LRDP in a bulk UST.
19

subject to ambient air temperatures. While thermally induced level changes of several 

thousandths of an inch can introduce large test errors, the bellows system allows for level 

changes of many hundredths of an inch (0.03 to 0.06 in.) before any errors are introduced. 

 2.2.5 Remote Test Controller 

The remote test controller, shown in Figure 10, is located near each tank to be monitored and 

contains a microprocessor, a disk, a temperature sensor, and a stable resistor. The remote test 

controller can collect up to 8 channels of data, but more channels can be added, if required. 

Once a test is initiated from the host computer, the microprocessor collects, analyzes, outputs, 

and stores the data and the results. The analysis not only includes a computation of the measured 

volume rate, which is equal to the leak rate, if a leak is present, but also includes a 

comprehensive set of quantitative data quality indices (DQIs) that automatically assess the 

quality of the data before the data are used to complete a test. Up to 50 tests can be conducted 

and stored without downloading the data. The power supply and sensor electronics are also 

located in the controller unit. Because of the temperature 

sensitivity of the pressure sensors and the large swings 

that can occur in the ambient temperature during a test, a 

temperature sensor and a stable resistor are installed in 

the controller for compensation. Only one, either the 

stable resistor or the temperature 

sensor, is needed for compensation. However, both have been demonstrated as effective in this 

project. 

2.2.6 Software 

The host computer is used to initiate a test with its user-friendly Graphical User Interface (GUI) 

developed in a Windows 98 platform. Appendix D shows seven of the user screens. The first 

Figure 10a. Photograph of the remote test

controller.

Figure 10b. Schematic of the remote test controller.
20

screen (Figure D-1) allows the operator to conduct a leak detection or review the results of 

previous leak detection tests. 

The next screen (Figure D-2) asks what type of test will be conducted (a 10-, 24-, or 48-h test), 

the duration of the waiting period after the final tank operations have been terminated, the start 

of the test, and the threshold criterion. The current date and time is also given for information. 

The software is set up to operate using Version 1.1a of the LRDP system [8-15]. Once the tank 

diameter is specified and the type of the test is selected, the threshold criterion and the waiting 

period change accordingly. If a longer waiting period or a different threshold is desired, it can be 

entered directly. 

The screen shown in Figure D-3 can be used to initiate a test now or to schedule one for a later 

time. Before a test can be started, it is imperative that the tank is isolated from its associated 

piping. A special reminder screen (Figure D-4) is displayed before a test can be initiated to make 

sure that the operator has shut all of the valves necessary to perform a leak detection test. 

A test is initiated by clicking on the Start/Schedule Test button. One a test is initiated, no further 

action is required by the operator. Output of a time history of the data from any of the sensors 

can be displayed during the test. This screen also contains the relevant information about the test 

being conducted, including the start and stop time. 

The next screen (Figure D-6) shows an output report from a leak detection test. This report can 

be printed and is sufficient to address all of the typical reporting requirements of the state and 

local regulating agencies. 

The screen shown in Figure D-7 summarizes the results of previous tests and allows the user to 

obtain the test reports from any previous test. This screen is particularly useful when addressing 

the monthly monitoring requirement or when averaging data. 

 2.2.7 Conduct of a Test 

A test consists of a waiting period (between the last transfer into and out of the tank and the start 

of a test) and the test itself. The waiting period used in these evaluations was 2 h. This waiting 

period is not necessary from a performance stand point, but practically, it insures that the tank 

has been prepared for a test, i.e., all valves have been closed and any drainback or disturbance 

from pumps etc. have been minimized. The basic procedure for conducting a test is described 

below. 

• Specify what type of test will be conducted (i.e., the test duration) and what waiting 

period will be used. There are two standard tests: (1) the LRDP-10, comprised of a 2-h 

waiting period and a 10-h test, and the LRDP-24, comprised of a 2-h waiting period and a 

24-h test. 

• Specify the threshold to be used in determining whether or not the tank passes or fails the 

test 

• The valve at the bottom of the reference tube is automatically left open between tests and 

the level of the fuel in the tube should be at the same level as the fuel in the tank 
21

• If the LRDP is being inserted into the tank for a test, allow the reference tube to fill up 

with fuel so that the fuel in the tube and in the tank is at the same level 

• Close the valve to isolate the fuel in the reference tube from the fuel in the tank 

• Begin collecting data with the LRDP. The data collected during the waiting is not used 

in the analysis. The data collected following the waiting period is used in the analysis. 

• Generate a time series of the difference in the level changes in the tube and the tank using 

the pressure measurements obtained with the DP sensor. Level measurements are 

obtained by dividing the pressure measurements by the specific gravity of the fuel (e.g., 

0.82). 

• Convert the level time series to a volume time series using the height-to-volume 

conversion (HVC) factor for the tank. For a 122.5-ft-diameter tank, the HVC factor is 

7,347 gal/in. 

• Apply a set of Data Quality Indices (DQIs) to the volume time series to determine if the 

data collected is of sufficient quality to be used in a test. If a data quality problem is 

encountered during the first half of a test, the test is automatically extended by a time 

interval equal to half the test duration. If a problem is encountered during the second half 

of the test, the test is automatically repeated. The test operator can abort the test at any 

time if there is not enough time to complete the tests before normal operations begin. 

Thus, the test may be extended either 12 or 24 h for a 24-h test, or 5 or 10 h for a 10-h 

test, depending on which half of the test data is of poor quality. If the test is extended, at 

present, the software only allows an extension equal to the duration of the test. If the 

extended test data fail the DQI tests, then another test can be initiated immediately or at a 

later time. 

• If the data fail the DQI tests, then the output of the test is Inconclusive and must be 

repeated. 

• If the data pass the DQI tests, then the rate of change of volume is computed by fitting a 

regression line to the volume time series data 

• The measured volume rate is compared to the detection threshold to determine whether 

the test is a Pass or a Fail. The tank passes the test if the measured volume rate is less 

than or equal to the threshold. If the tank fails the test, the tank and the test data should 

be checked for problems, and then the tank should be re-tested. A leak rate is only 

printed out if the tank fails the test. 

 

 2.2.8 Data Quality Indices 

Before a test is begun, the operator should verify that the valves required to isolate the tank from 

its associated piping are closed and that the level of the fuel in the tank is below the top of the 

reference tube (which is usually above the maximum safe operating level of the fuel for the 

tank). 

A number of data quality tests were developed and incorporated into the data acquisition and 

analysis software to identify potential problems that might occur during a test. These data 

quality problems were identified using previous data collected with the LRDP. One of the data 

quality tests is designed to determine if a pump is turned on during a test (Figure 11). Two pump 

signatures are shown in Figure 11. A test should not be conducted if product is being removed 

or added to the tank. 
22

Another data quality test is 

designed to determine if there is a 

step discontinuity in the data 

(Figure 11). Such discontinuities 

might occur, for example, if a 

product sample is obtained during 

the test, or if the tank is opened 

during a test. 

Another data quality test is 

designed to determine if there are 

any data dropouts or wild points in 

the data set (Figure 11). Still another data quality test is designed to determine if the fluctuations 

in the level are too large for analysis. Strong winds, internal waves, and other physical factors 

might produce such fluctuations. A data quality test is also designed to determine if there are 

any inflows during a test. 

Another data quality test is also 

used to determine if the data set 

is sufficiently stable to draw a 

conclusion. A non-stationary 

leak, structural deformation of 

the tank, evaporation or 

condensation, or a particularly 

strong thermal affect might 

produce an unstable data set. 

All of these data quality indices 

are set at the time the LRDP is 

installed and should not be 

changed unless the number of 

inconclusive tests is too high. Figure 12 shows a data set with stability problem in which the 

trend for the first half of the test is different than for the second half of the test. 

During the evaluation, the data quality indices were set sufficiently high so that all of the data 

would be of sufficient quality to use except for very extreme problems. This was required to 

minimize the time required to complete the evaluation. It was justified because many of the 

problems that might be encountered operationally would not be encountered during a controlled 

evaluation (e.g., a transfer during the middle of a test). 

 

 2.2.9 Summary 

In summary, the LRDP is designed to easily and accurately compensate for the major sources of 

noise that might occur during a leak detection test. Accurate compensation is obtained because 

the LRDP is specifically designed to compensate for each source of noise without the need for 

arrays of temperature sensors or delicate and expensive level sensors. As a consequence, all of 

the sensors are off-the-shelf, commercially available sensors that have a proven track record of 

-30.00000

-25.00000

-20.00000

-15.00000

-10.00000

-5.00000

0.00000

5.00000

10.00000

15.00000

20.00000

25.00000

0 2 4 6 8 10 12 14 16 18 20 22 24

Time - hour

Volume -gal

Figure 12. Example of the results of the data quality indices identifying 

a problem with the stability of the data trend. 

-45

-40

-35

-30

-25

-20

-15

-10

-5

0

5

10

15

20

25

30

0 2 4 6 8 10 12 14 16 18 20 22 24

Time - min

Volume -gal

Figure 11. Example of the results of the data quality indices 

identifying that a pump was turned on during a test. 
23

performance. The reference tube, the bellows mounting stand, and the bottom-mounted sensors 

are the key elements that lead to high performance. Other mass-based systems do not work as 

well because the sensors are mounted at the top of the tank and are subject to large diurnal 

swings in the ambient air temperature, are very delicate and expensive to achieve the level of 

precision required to conduct a test, and may require the use of nitrogen gas. 

2.2 Strengths, Advantages, and Weaknesses

The LRDP system is ready for Full-Scale Implementation. It has the following advantages over 

other technologies that might be used for leak detection in large tanks: 

• The LRDP is a mass-based technology, which is a preferred technology of the owners 

and operators of DoD bulk USTs. 

• The LRDP can be used to perform a leak detection test without removing fuel from the 

tank. 

• The LRDP system can be installed through a standard 8-in.-diameter opening in the tank. 

• The LRDP can be used to test USTs with both vertical and curved walls. The 

DEM/VALs were conducted in a bulk UST with vertical walls and a 50,000-gal UST 

with curved walls. In another evaluation, the LRDP was used to test bulk USTs with 

both vertical and curved walls. For tanks with curved walls, a special shaped reference 

tube needs to be constructed. 

• The LRDP has the best performance and the shortest test time (10 h) of any mass-based 

technology. It is the only system that conduct a test in less than 24 h. 

• The output of a leak detection test is easy to interpret, because it is a direct measurement 

of the leak rate in gallons per hour, the quantity of regulatory and engineering interest. 

• The system is constructed of off-the-shelf sensors and components that have a proven 

track record of high performance, excellent reliability, and low maintenance. 

• The LRDP can be used as a portable system for performing a precision test as part of a 

leak detection testing service or permanently installed in the tank for automatic tank 

gauging operations including monthly monitoring and precision testing. 

• The LRDP system has been successfully demonstrated in a variety of operational DoD 

tanks. 

• The LRDP system has been evaluated for performance and is listed with the National 

Work Group on Leak Detection Evaluations, a nationally recognized, regulatory group 

that allows the local and state regulatory agencies to select methods for their use. 

• The LRDP system is the only mass-based system that can meet both the monthly 

monitoring and the semi-annual or annual precision test regulatory guidelines in 

California. 

• The LRDP system is approved for use in California. 

• The recurring cost of using and maintaining the LRDP are significantly lower than tracer 

methods and other mass-measurement methods. Because the LRDP system is a mass-
24

based system, it inherently compensates for the thermal expansion or contraction of the 

fuel in the tank during a test. Furthermore, accurate tests can be initiated without a long 

pre-test waiting period. 

• The mounting system eliminates thermally induced movement of the reference tube 

during a test. 

• Thermally induced drift of the differential pressure sensor is virtually eliminated, because 

it is mounted in a sealed container at the bottom of the tank. 

• Because the differential pressure sensor used to measure level (volume) changes in the 

tank needs a dynamic range of only 1 in. (rather than the total height of the tank, like 

other mass-based systems), the LRDP has the precision (0.0002 in.) to detect very small 

leaks in large-diameter tanks. 

• The system is self-calibrating, and the performance and functionality of the LRDP can 

easily be checked between leak detection tests. 

• The sensors used to measure differential pressure, pressure, and temperature are robust 

and have been used commercially in the pipeline leak detection systems that Vista 

Research has been selling for many years. 

• The LRDP system can be modified for testing aboveground storage tanks (ASTs). 

The main limitation of the method is that all of the valves in the fuel facility that isolate the tank 

from its associated piping must seal completely; if these valves do not completely seal, the 

LRDP system will detect this flow. This is not usually a problem for monitoring, because the 

monitoring standards are high enough to accommodate small flows across the valve. For 

precision tests, however, the valves must seal completely. If the tank fails a test (either a 

monitoring or precision test), a detailed inspection of the tank and pipe valves is performed next 

assuming this is the reason for the failed test, and if necessary, valve blinds are installed to 

complete the test. In many instances, closing the valves tighter is all that is needed. The 

magnitude of this problem is not known for bulk tanks, but it is the same problem encountered 

and successfully addressed for routine monitoring of underground storage tanks at service 

stations. 

2.3 Factors Influencing Cost and Performance

Unlike remediation technologies, the performance of an LRDP is essentially independent of the 

site and the facility, because through the third-party evaluation, the performance is estimated 

over a range of conditions that the system will operate. While these conditions may not include 

the extremes, they are sufficient to identify performance problems that might be encountered 

under more challenging conditions. The main factor influencing the performance of the LRDP 

system (and other mass-based systems) is the size of the tank. The performance of the LRDP 

scales with the product surface area (tank diameter squared) in a prescribed way as determined 

by the third-party evaluation [6]. 

 

The main sources of problems during a test are operational ones. It is important that the tank is 

completely isolated from the associated piping, i.e., all valves are completely sealed, before a test 
25

is initiated. It is also important that any drainback of fuel into the tank has ceased before a test is 

initiated. 

 

The LRDP is designed to fit into a standard 8-in.-diameter opening in a tank. The initial 

purchase cost, the installation cost, and the cost of operational use and maintenance are not 

affected by site parameters or site geology. This assumes that electrical power is available at 

each tank and that communication cable has already been installed between each tank and the 

building where the host computer is located. This assumption is valid, because systems used to 

acquire inventory level data are currently being used at each site. The cost differential between 

an LRDP in a bulk UST with a small height (e.g., 13 ft) versus a large height (e.g., 25 ft) is 

insignificant and is attributed to the cost of a longer reference tube. 
25

3. Site/Facility Description 

An overview of the sites/facilities used in the two demonstration and validation (DEM/VAL) 

tests are described below. For more details, please see the ESTCP Demonstration Plan [18]. 

3.1 Background 

Two types of DEM/VALs were planned. The first, and most important, was to evaluate the 

performance of the LRDP in a large diameter bulk UST with vertical walls following a 

nationally accepted standard test procedure [6]. Since the leak detection system is not affected 

by soil conditions and site geology, and the evaluation procedure only requires that a tank that 

which is not leaking, the most important criterion in selecting a DEM/VAL site is to select a site 

with a suitable tank that can be used in the evaluation. Two criteria were used in selecting a site. 

 First, it was desired to perform the DEM/VAL in a tank with a large enough diameter to address 

all of the tanks used by DoD. Second, it was desired that no inflow or outflow due to leaking 

valves or drainback from piping occur during the evaluation. Both problems interfered and 

degraded the results of the North Island evaluation, and the estimate of system performance from 

the evaluation did not reflect the true performance of the system. If there were no inflows, the 

evaluated performance would have been at least a factor of two better than determined from the 

evaluation. Initially, a bulk UST at the San Pedro Fuel Farm was selected for the DEM/VAL. 

After a series of tests in the tank, it was found that a small uncontrolled outflow existed due to a 

faulty valve. Because this outflow could not be measured independently, the DEM/VAL was 

moved to the Point Loma site, because it met the site selection criteria and the facility expressed 

an interest in using the system. 

The second DEM/VAL was to demonstrate that the LRDP could be used for leak detection in a 

50,000-gal horizontal tank with curve walls. While not considered a bulk UST, these large tanks 

are usually found at bulk fueling facilities and are used for storage of fuel before transfer into a 

hydrant pit or a loading rack. These tanks are found at almost every military facility. The 

Hunter Army Airfield site was selected for the DEM/VAL because this is typically the largest 

tank found at Army sites and there was on-site support and interest in fielding a DEM/VAL. 

3.2 Site/Facility Characteristics

Brief descriptions of the Point Loma and Hunter Army Airfield DEM/VAL sites are given 

below. 

 

 3.2.1 DEM/VAL 1: Point Loma Fuel Terminal (Third-Party Evaluation in a Bulk UST) 

The Point Loma Fuel Terminal stores and supplies fuel to other facilities in the area (e.g., the 

NAS North Island). The facility is located in San Diego, California, and has over 30 bulk USTs. 
26

 The evaluation was conducted in Tank 175, because it was one of the largest field-erected bulk 

USTs owned or operated by DoD and the valves isolating the tanks had just been replaced and 

were expected to seal tightly. Also, the configuration of the tanks and their associated piping 

was easy to verify whether or not the valves sealed. Finally, the configuration afforded several 

ways to insure that the tanks were isolated from the piping. 

Figure 13 shows the location of 

Tank 175. This tank is located in 

a hillside and stores 2,100,000 gal 

of JP-5 fuel. Fuel is pumped into 

the tank to fill it and the removal 

of fuel from the tank is 

accomplished by gravity. The 

tank is 122.5 ft in diameter and 

23.5 ft in height. The tank is 

buried about 5 ft below the 

surface of the ground. The 

product surface area (PSA) of the 

tank is 11,786 ft2

. Level changes 

in this tank are converted to 

volume changes using a heightto-volume conversion (HVC) 

factor of 7,347 gal/in. 

 3.2.2 DEM/VAL 2: Hunter Army Airfield (50,000-gal UST) 

 

There are 30 shop-fabricated 50,000-gal USTs at the Hunter Army Airfield (a sub-unit of Fort 

Stewart). Each of these tanks are nominally 10.5 ft in diameter, 80 ft in length, and are made of 

3/8-inch thick welded steel. The tanks originally had a cut-back asphalt coating and, in 1986-87, 

were lined inside with a 10-mil 

thick epoxy coating. Impressed 

current cathodic protection systems 

were installed at the tank batteries in 

1978. Figure 14 shows the location 

of Tank 45, the 50,000-gal UST 

used in the DEM/VAL. 

The thirty 50,000 gal USTs are 

arranged in three batteries of ten 

tanks each, at Pumping Stations #3, 

 #4, and #5. The pumping stations 

are located in the Helicopter 

Landing and Parking Area. The 

tank batteries are about 1500 feet 

west of the Base Operations 

Building #1252 and are identified as 

structures #8080, #8082, and #8084. These tanks were installed in the 1952-53 time period. 

Figure 13. Tank 175 at the Point Loma Fuel Terminal. 

Figure 14. Tank 45 at the Hunter Army Airfield. 
27

Until 1996, the tanks were used to store JP5. In 1996, the facility converted to JP8. Neither the 

tanks nor the piping have ever had a discovered leak. Each 10-tank battery has a 6-inch diameter 

manifold connected supply pipeline and a 12-inch diameter discharge piping system running to 

the aircraft fueling area. An internal inspection, in 1997, of three selected tanks revealed the 

interior coating to be intact, with no signs of deterioration or significant corrosion. 
28

4.0 Demonstration Approach 

As stated above, two types of demonstrations were conducted. The first and most important was 

an evaluation of the performance of the technology following a standard test procedure used and 

approved by the regulating community for bulk USTs [6]. The second was a demonstration of 

the system on a 50,000-gal tank commonly found at bulk fueling facilities. This second 

demonstration consisted of a few tests to demonstrate that the system had the performance 

capability to meet the 0.2-gal/h monthly monitoring regulatory standard. For more details, please 

see the ESTCP Demonstration Plan [18]. 

4.1 Performance Objectives 

The performance objectives of the DEM/VALs are established by the regulatory guidelines for 

detection of leaks in bulk USTs. Since there are no national regulatory compliance standards for 

bulk USTs, the California regulatory guidelines were adopted as the basis for the performance 

objectives of this project, because they are practical and the most stringent standards. These 

guidelines indicate that the leak detection system must be evaluated for performance by an 

independent third-party following a standard test procedure [6]. The results of this evaluation 

must be reported in terms of a PD of the target leak rate (TLR) and a PFA. As stated above, the 

TLR is specified by the regulatory agency and at a minimum the PD must be equal to or better 

than 95% and the PFA must be less than or equal to 5%. The DEM/VAL at the Point Loma Fuel 

Terminal followed this standard test procedure. The performance objective of the DEM/VAL 

conducted on the 50,000-gal USTs at Hunter Army Airfield was to show that the results of 

several tests had the capability for detecting leaks of 0.2-gal/h, the regulatory standards for these 

tanks. This was accomplished by conducting a few tests and showing the results were not 

statistically different than the evaluation results. The evaluation results indicated that the LRDP 

would be able to detect a TLR = 0.2 gal/h with a PD = 95% and a PFA = 5%. 

4.2 DEM/VAL 1: Point Loma Fuel Terminal (Third-Party Evaluation in a Bulk UST) 

A third-party evaluation of the LRDP was conducted by Ken Wilcox Associates, Inc. (KWA). 

The output of the evaluation is the TLR that can be detected with a PD = 95% and a PFA, which 

must be less than or equal to 5% for the system to be used. The LRDP leak detection system was 

designed for use in petroleum fuel tanks, but can be used for other hazardous substances. This 

section describes the sampling/data-collection procedure used in the evaluation, the physical setup and operation of the facilities and equipment needed to conduct the evaluation, the conditions 

in the evaluation, and the output from each test conducted. 

 4.2.1 Evaluation Procedure 

The LRDP was evaluated in accordance with the protocol described in the report “Alternative 

Test Procedures for Evaluating Leak Detection Methods: Evaluation of Bulk Field-Constructed 
29

Tanks” [6]. This 1996 protocol was updated in 1999 for mass-based bulk leak detection systems 

and adheres to the guidelines specified in EPA’s standard test procedures for determining and 

reporting the performance of leak detection systems. The update allows the performance results 

to scale with the product surface area of the tank and averaging of the test results to improve 

performance. This protocol has been approved by the NWGLDE, and has been accepted by 

federal, state and local regulatory agencies as the means for demonstrating the performance of 

bulk tank leak detection systems. This protocol is also in accordance with the evaluation 

protocol and reporting procedures specified in the ASTM standard practice (E-1526-93) [7]. 

The UST regulation for USTs requires that the performance of any leak detection that is used for 

testing a tank be evaluated for performance following a standard test procedure. The states, 

which implement the regulation, require an independent third party to perform the evaluation. 

The leak detection systems used for the small USTs found at petroleum service stations are 

evaluated in testing facilities owned and/or operated by the third-party evaluator. For systems 

used in bulk USTs, an operational facility must be used because no bulk test facilities exist. 

When an evaluation is completed, it is submitted to the NWGLDE for review and certification 

that it has been properly evaluated. Properly evaluated leak detection systems are then added to 

a list for use by the states when approving leak detection methods for use in their states. For 

most of the states, if a method is listed, it can be directly approved. For a limited number of 

states, like California and Florida, a more detailed review may be required. 

As shown in Table 4, the evaluation protocol requires that 12 tests be conducted at four different 

leak rates and under variable fuel temperatures. The tank is emptied to 50% of capacity and 

refilled back to approximately 95% to produce (1) temperature conditions typical of 

Table 4. Standard Test Schedule 

Test Prep Test 

No. 

Pair 

No. 

Set 

No. 

Nominal 

Leak Rate 

Nominal 

Temp Diff 

Trial run - - - 0.00 0 

 

Empty to 50% 1 1 1 LR1 T1 

then refill to 95% 2 1 1 LR2 T1 

Empty to 50% 3 2 1 LR4 T2 

then refill to 95% 4 2 1 LR3 T2 

Empty to 50% 5 3 2 LR1 T3 

then refill to 95% 6 3 2 LR4 T3 

Empty to 50% 7 4 2 LR2 T4 

then refill to 95% 8 4 2 LR3 T4 

Empty to 50% 9 5 3 LR4 T5 

then refill to 95% 10 5 3 LR1 T5 

Empty to 50% 11 6 3 LR3 T6 

then refill to 95% 12 6 3 LR2 T6 

operational conditions during fuel deliveries and transfers and (2) the type of wall deformation 

that might occur as a result of a level change. Typically, the rate of change of temperature 

depends on the temperature difference between the fuel in the tank and the backfill and soil 
30

around it. For the purposes of the evaluation, a temperature condition, as reported on a given 

test, is equal to the difference in temperature between (a) the fuel in the tank and (b) the fuel 

brought into the tank during filling operations. (It is assumed that the temperature of the fuel in 

the tank before such a transfer is approximately the same as that of the backfill and surrounding 

soil.) For each test, the third-party evaluator induces leaks of a pre-determined size, all unknown

to the testing party. At the end of the 12-test sequence, the testing party submits its estimates of 

the leak rates, and the testing party’s data are analyzed in accordance with statistical guidelines 

provided in the evaluation protocol [6]. 

Neither the LRDP or any of the equipment used in the evaluation produce any contaminants. 

The product removed from the tank to simulate a leak flows through clean tubing into a clean 

barrel. Since the fuel is not contaminated, it is normally returned to the tank after the test. Thus, 

there is no test process waste, other than that resulting from final cleaning of the tube and barrel. 

The test results will qualify the system for use in bulk USTs with any commercial petroleum 

product of grade number 2 or lighter. For other liquids, some component materials may need to 

be changed for chemical compatibility. 

The evaluation protocol requires that performance be presented in terms of the leak detection 

system’s PFA and its PD against a specified TLR. The performance is estimated directly from the 

histogram of the noise and the histogram of the signal-plus-noise. In general, the noise 

histogram is estimated from a statistical compilation of the results of many leak detection tests 

on a non-leaking tank. These tests are conducted over a wide range of ambient thermal 

conditions and induced-leak conditions such as might be expected during routine testing. For 

mass-based systems, where the signal (volume changes) produced by the leak are additive with 

the noise, the signal-plus-noise is then a shifted replica of the noise histogram. The shift (or 

mean) of the signal-plus-noise histogram is equal to the TLR. The histograms are generally 

displayed in terms of their cumulative frequency distributions (CFDs). 

The performance of the LRDP system was estimated using a student-t probability model for the 

histograms. More detailed descriptions on how to estimate performance can be found in the 

standard test procedure [6]. Because mass-based systems test at a constant pressure, the signalplus-noise histogram can be generated directly from the noise histogram by adding the leak rate 

of interest to the test results. This is possible, because the volume changes due to a leak are 

additive with those due to noise. 

This is not true of all leak detection systems. With non-mass-based (and non-volumetric) 

systems, for example, the signal-plus-noise histogram must be generated experimentally for each 

and every leak rate for which the probability of detection is desired. 

Unlike remediation methods, once a leak detection method is evaluated in a tank, similar 

performance can be expected in other tanks provided that they are not too big and the main 

source of noise, thermal expansion and contraction of the fuel, is not too much larger than the 

conditions used in the evaluation. For in-tank volumetric methods, mainly used to test the small 

USTs found at service stations, at least two constraints were placed on the use of the system. 

First, the system could not be used to test a tank that was any larger than 150% of its volume. 

Second, the system could not be used to test a tank when the difference in the temperature of the 

fuel and the ground was greater than 150% of the average temperature condition used in the 
31

evaluation. The only performance that could be claimed by the manufacturer of the system was 

the one that was evaluated, regardless of the size of the tank or temperature conditions under 

which it would be used. If a larger tank was to be tested, then another third-party evaluation had 

to be performed. 

For bulk USTs using a mass-based system, these constraints were modified to accommodate the 

differences between mass and volumetric methods. The temperature constraint was eliminated, 

because it does not affect the performance of a mass-based system. The tank-size limitation was 

modified, because the performance of a mass-based system does not scale with the volume of the 

fuel in the tank; it scales with the product surface area. Because of the limited number of bulk 

USTs and the wide range of tank sizes, the NWGLDE increased the multiplier from 150% to 

250%. If the evaluation tank was properly selected, than once evaluated, it could be used to test 

any tank within the DoD. The use of the 150% constraint would have meant that at least three or 

four evaluations would have had to be conducted to cover all of the tanks. Because of the large 

range of tanks to be tested, the NWGLDE required that the performance of the method be scaled 

by the product surface area. Thus, for tanks larger than the one used in the evaluation, the 

performance of the method would be worse than that achieved in the evaluation, and for tanks 

smaller than the one used in the evaluation, the performance would be better. The NWGLDE 

also limited the TLR to no less than 0.2 gal/h, regardless of scaling. This scaling can be 

technically justified and has been experimentally verified for mass-based systems, but not for 

volumetric methods. 

KWA conducted its third-party evaluation of the LRDP system at the Point Loma Fuel Terminal, 

on a 122.5-ft-diameter, 2,100,000-gal bulk UST. This tank was selected because it was one of 

the largest diameter tanks owned and operated by the DoD, and the valves that are used to isolate 

the tank from its associated piping were new, double-block valves that sealed tightly. The tank 

contained jet fuel with a specific gravity of approximately 0.82. The tank was approximately 

23.8 ft in height. The tests were conducted between 87 and 90% of capacity, the maximum safe 

operating level for the tank. Several additional tests were conducted at 50% capacity to 

demonstrate that the performance does not vary with product depth. 

The evaluation was done in accordance with the EPA guidelines described above. With a massbased system like the LRDP, there is no real need to induce leaks during an evaluation, because, 

as stated above, volume changes due to a leak are simply additive with those due to noise (for 

example, thermal expansion or contraction of the fuel). Induced leaks are included in the 

evaluation, because they are required by the protocol to create a blind testing situation and to 

ensure that the system actually responds to a leak. 

 4.2.2 Evaluation Tank 

The evaluation was conducted at the Point Loma Fuel Facility over a three-month period 

beginning on March 22, 2000 and ending on June 8, 2000. The tank used in the evaluation is 

located on a hillside and stores JP-5 fuel. The fuel is pumped into the tank to fill it and the 

removal of fuel from the tank is accomplished by gravity. 

The evaluation was performed in an operational 2,100,000-gal steel-lined concrete tank 

containing jet fuel. The tank was 122.5 ft in diameter and 23 ft-5 in. in height. Figure 13 showed 

the location of the tank in the side of a hill. 
32

The LRDP was installed in the tank and 

checked out on 15-17 February 2000. 

Representatives from NFESC, KWA, Vista 

Research, and Vista Engineering were present. A 

two-person team is needed to install the system. 

The total installation time is less than 4 h. The 

LRDP was installed in an 8-in. opening (Figure 

15). The LRDP used at North Island and KWA’s 

level gauge and RTD array were installed in a 22-

in.-diameter manway located about 10 ft away 

from the 8-in. opening. The peristaltic pump used 

to induce leaks in the tank was also located in this 

manway. 

Level changes in this tank can be 

converted to volume changes using a height-tovolume conversion factor of 7,347 gal/in. Testing 

during the evaluation was accomplished by KWA 

personnel following the LRDP testing procedures 

specified by NFESC and Vista Research. Leak 

simulations and fuel deliveries were also defined 

by KWA. The LRDP data were collected by 

KWA. The output of each test was automatically 

output from the system. The results from additional test durations were also output from a 

worksheet used by KWA using the same analysis procedure as used in the system. The 

evaluation was interrupted, as required by fuel farm personnel, to support military and fuel 

operations. Delays of one or more days to a week or more sometimes occurred in executing the 

evaluation protocol. 

For comparison purposes, the LRDP evaluated in an 88-ft-diameter tank at NAS North Island 

(Figure 3), was also installed in the tank through a 22-in.-diameter manway near the 8-in. 

opening. This was done to demonstrate that the performance of the modified version of the 

system developed under this ESTCP project was no different than the system evaluated 

previously. The level data obtained with both systems, as expected, were nearly identical. 

Leaks were induced by KWA through the manway. For each test, the volume rate measured by 

the LRDP system was compared to the leak rate induced by KWA. Twelve tests were 

conducted. There was a total of six fuel transfers. Fuel was transferred from other tanks in the 

fuel farm. The temperature of the received fuel and the fuel in the tank was measured for each 

test. Tests were conducted with the tank at approximately 90% full with additional tests 

conducted at 50% full. The induced leaks were monitored by KWA throughout the three-month 

evaluation. 

The induced leaks were produced by pumping fuel out of the tank with a peristaltic pump. 

Nominal leak rates of 0.4, 0.8, and 2.0 gal/h were randomly induced during the evaluation. 

Neither the nominal nor actual leak rate was made known to NFESC or Vista until many months 

after the evaluation had been completed and the final evaluation report was prepared. Leak rates 

were calculated from the total mass of fuel removed from the tank during the test and the density 

of the fuel that was measured with an analytical balance in a laboratory. The mass of the fuel 

Figure 15. Installation of the LRDP in the Point 

Loma tank.
33

removed from the tank was measured by pumping the fuel into a barrel hanging from a load cell. 

 The uncertainty in the induced leak rates was less than 0.01 gal/h. During each test, KWA also 

verified the magnitude of the induced leak rate by measuring the pump rate with a graduated 

cylinder and a stop watch. 

Fuel levels and fuel temperatures were electronically monitored by KWA throughout the 

evaluation using a level gauge and an RTD array. This allowed KWA to record and document 

the exact times and temperatures of the fuel deliveries. The temperature array consisted of RTDs 

located in the bottom 50% of the tank. 

 4.2.3 Evaluation Conditions and Test Results 

The test conditions and results obtained during the evaluation are summarized in Table 5. 

Column 1 gives the test number, and column 2 gives the date and time that each test was started. 

 The level change due to the delivery of fuel to the tank prior to the start of the test is shown in 

column 3, and the temperature condition (the difference in temperature of the fuel in the tank and 

Table 5. Summary of the Test Results and Induced Leak Rates for the LRDP Systems 

Test 

No. 

Test Start 

(d/m/y (hhmm) 

Level Change due

to Delivery

 (in.) 

Temperature 

Condition1 

(

o

F) 

Fuel 

Depth 

(%) 

KWA 

Nominal Induced 

 Leak Rate2

(gal/h) 

KWA 

Actual Induced 

 Leak Rate2

(gal/h) 

1 

2 

3 

4 

03/22/00 1539 

03/23/00 1736 

03/27/00 1519 

03/28/00 1728 

116.0 

N/A 

113.4 

N/A 

 0.2 

 N/A 

 -0.2 

 N/A 

 

90 

90 

89 

89 

 -0.3 

 0.0 

 -0.4 

 -0.8 

 -0.327 

 0.000 

 -0.444 

 -0.824 

5 

6 

7 

8 

04/05/00 1715 

04/06/00 1919 

04/18/00 1614 

04/19/00 1740 

106.0 

N/A 

111.3 

N/A 

 -0.6 

 N/A 

 -0.2 

 N/A 

87 

87 

89 

89 

 -1.0 

 0.0 

 -0.8 

 -0.2 

 -1.040 

 0.000 

 -0.765 

 -0.170 

9 

10 

11 

12 

04/27/00 1308 

05/11/00 1500 

05/12/00 1731 

06/07/00 1557 

63.6 

N/A 

110.3 

109.4 

 1.43

 N/A 

 -0.5 

 -0.2 

90 

88 

88 

88 

 -2.0 

 -2.0 

 0.0 

 -2.0 

 -1.934 

 -1.820 

 0.000 

 -1.845 

1 A negative temperature condition means that the fuel in the tank was colder than the fuel in the tank and the 

surrounding ground. 

2 A negative value indicates a leak out of the tank. 

3 Test 9 was initiated 70.6 h after the transfer was completed so it was not used in the temperature differential 

 calculations. A test was not conducted before Test 9. 

the fuel delivered to the tank) is shown in column 4. The depth of fuel in the tank during the 

test, the nominal induced leak rate, and the actual leak induced by KWA as part of the evaluation 

are shown in columns 5 through 7, respectively. As shown in Table 5, the temperature 

conditions ranged from –0.6o F to +1.4o F. Fuel deliveries ranged from 463,662 gal (a level 

change of 63.6 in.) to over 845259 gal (a level change of 260 in.). The leaks induced by KWA, 
34

nominally 0, [0.2, 0.3, 0.4], [0.8, 1.0], and 2.0 gal/h, ranged from 0.0 gal/h to 1.94 gal/h. 

A more detailed summary of the test conditions and the results are presented in Tables 6-8. 

Tables 7 and 8 show the volumetric errors for both the LRDP-10 and LRDP-24. 

 4.2.4 Comparison of the LRDP Evaluated at NAS North Island and the LRDP Evaluated 

Under ESTCP 

To show that the 

performance of the system 

was unaffected by the 

changes to the LRDP 

system under ESTCP, leak 

detection data were 

simultaneously obtained 

using the LRDP tested at 

North Island and the LRDP 

used in the ESTCP 

evaluation. Figure 16 

shows a comparison of the 

two data sets offset by a 

constant of 0.002 in. for 

display purposes. The 

estimated volume rate 

determined by each LRDP 

is different by 0.01 gal/h. 

y = -2.2728x + 187.95

R2 = 0.9829

y = -2.2726x + 197.45

R2

 = 0.9656

75

100

125

150

175

12 16 20 24 28 32 36 40

Time - h

Volume - gal

LRDP-1 (1.428049) DLvl LRDP-1 Cal Linear (DLvl) Linear (LRDP-1 (1.428049))

Figure 16. Comparison of the LRDP data obtained with the engineering prototype 

of the LRDP and the LRDP evaluated in the ESTCP project. 
35

Table 6. Summary of the Evaluation Temperature Conditions

 Before Fill After Fill Before Fill After Fill Start End 

Test Delivery Delivery Delivery Level (50%) Level Volume (50%) Volume Temp Temp 

No. Start Time End Time Fill Time (inches)* (inches) (gallons) (gallons) (deg F) (deg F) 

1 3/22/2000 11:30 3/22/2000 15:31 1/0/1900 4:01 144.0 260.0 1,049,354 1,894,613 64.4 64.2 

3 3/27/2000 11:00 3/27/2000 15:18 1/0/1900 4:18 144.0 257.4 1,049,354 1,875,455 64.4 64.5 5 4/5/2001 8:22 4/5/2001 17:15 1/0/1900 8:53 144.0 250.0 1,049,354 1,821,852 64.6 65.1 7 4/18/2000 11:00 4/18/2000 15:30 1/0/1900 4:30 144.0 255.3 1,049,354 1,860,590 65.4 65.5 9 4/25/2000 12:59 4/25/2000 14:29 1/0/1900 1:30 196.5 260.1 1,431,905 1,895,567 65.8 65.4 

11 5/11/2000 10:34 5/11/2000 14:53 1/0/1900 4:19 144.0 254.3 1,049,354 1,853,303 65.8 66.2 12 6/7/2000 12:08 6/7/2000 15:54 1/0/1900 3:46 144.0 253.4 1,049,354 1,846,380 68.0 68.2 

(1) Height-to-volume = 7,287 gal/in. (2) Tank Capacity = 2,098,708 gal. (3) Tank Height = 288 in. 

* Tank operator stated that the level was dropped to 50% operational level before each delivery.
36

Table 7. Final Results for the Evaluation of the LRDP-10 at Point Loma 

Test 

No. 

New LRDP Filename Transfer

Prior to 

Test 

Nominal 

Leak Rate

Induced 

Leak Rate

Waiting 

Period 

EVR Actual VR VR Error

 (gal/h) (gal/h) (h) (gal/h) (gal/h) (gal/h) 

1 Tnk175_3_22_2000_15_39.dat -0.327 1.87 -0.179 -0.327 -0.148 

2 Tnk175_3_23_2000_17_36.dat Yes 0.3 0.000 0.00 0.470 0.000 -0.470 

3 Tnk175_3_27_2000_15_19.dat 0.0 -0.444 2.00 -1.142 -0.444 0.698 

4 Tnk175_3_28_2000_17_28.dat Yes 0.4 -0.824 0.00 -0.908 -0.824 0.0838 

5 Tnk175_4_5_2000_17_15.dat 0.8 -1.040 10.00 -0.724 -1.040 -0.316 

6 Tnk175_4_6_2000_19_19.dat Yes 1.0 0.000 0.00 -0.059 0.000 0.059 

7 Tnk175_4_18_2000_16_14.dat 0.0 -0.765 10.00 -1.014 -0.765 0.249 

8 Tnk175_4_19_2000_17_40.dat Yes 0.8 -0.170 0.00 -0.566 -0.170 0.395 

9 Tnk175_4_27_2000_13_8.dat 0.2 -1.934 3.00 -2.194 -1.934 0.260 

10 Tnk175_5_11_2000_15_0.dat 2.0 -1.820 1.95 -1.797 -1.820 -0.023 

11 Tnk175_5_12_2000_17_31.dat Yes 2.0 0.000 2.00 -0.238 0.000 0.238 

12 Tnk175_6_7_2000_15_57.dat Yes 0.0 -1.845 2.00 -1.786 -1.845 -0.060 

 Mean = 2.24 Mean = 0.080 gal/h

 Median = 1.98 Standard Deviation = 0.317 gal/h

 N = 12 

 dof = 11 

 MDLR = 1.140 gal/h

 n needed for 0.2 

gal/h =

32.5 

 tB = 0.878 

Table 8. Final Results for the Evaluation of the LRDP-24 at Point Loma 

Test 

No. 

New LRDP Filename Transfer 

Prior to 

Nominal 

Leak Rate

Induced 

Leak Rate

Waiting 

Period 

EVR Actual VR VR Error

 (gal/h) (gal/h) (h) (gal/h) (gal/h) (gal/h) 

1 Tnk175_3_22_2000_15_39.dat Yes 0.3 -0.327 1.87 -0.327 -0.327 0.000 

2 Tnk175_3_23_2000_17_36.dat 0.0 0.000 0.00 0.232 0.000 -0.232 

3 Tnk175_3_27_2000_15_19.dat Yes 0.4 -0.444 2.00 -0.726 -0.444 0.282 

4 Tnk175_3_28_2000_17_28.dat 0.8 -0.824 0.00 -1.072 -0.824 0.248 

5 Tnk175_4_5_2000_17_15.dat Yes 1.0 -1.040 2.00 -0.832 -1.040 -0.208 

6 Tnk175_4_6_2000_19_19.dat 0.0 0.000 0.00 0.081 0.000 -0.081 

7 Tnk175_4_18_2000_16_14.dat Yes 0.8 -0.765 12.00 -1.053 -0.765 0.288 

8 Tnk175_4_19_2000_17_40.dat 0.2 -0.170 0.00 -0.453 -0.170 0.283 

9 Tnk175_4_27_2000_13_8.dat 2.0 -1.934 3.00 -2.162 -1.934 0.228 

10 Tnk175_5_11_2000_15_0.dat Yes 2.0 -1.820 1.95 -1.834 -1.820 0.014 

11 Tnk175_5_12_2000_17_31.dat 0.0 0.000 2.00 -0.190 0.000 0.190 

12 Tnk175_6_7_2000_15_57.dat Yes 2.0 -1.845 2.00 -1.997 -1.845 0.152 

 Mean = 2.24 Mean = 0.097 gal/h

 Median = 1.98 Standard Deviation = 0.192 gal/h

 N = 12 

 dof = 11 

 MDL

R =

0.690 gal/h

 n needed for 0.2 gal/h = 11.9 

 tB 1.750 
37

4.3 DEM/VAL 2: Hunter Army Airfield (50,000-gal UST) 

 

A DEM/VAL of the LRDP was conducted on a 50,000-gal UST at the Hunter Army Airfield, 

Savannah, GA (part of Fort Stewart). The specific objectives of the DEM/VAL, the physical setup and operation, and the sampling/data-collection procedure are described below. 

The primary objective of the test was to demonstrate that the system could be used to test 

horizontal tanks for leaks. A special reference tube, whose cross-sectional area changed as a 

function of depth was used instead of a constant-diameter tube. Other objectives of the 

DEM/VAL were to 

• demonstrate that the LRDP could measure the level of the fuel in the tank to the nearest 

1/8 in. for inventory control and reconciliation, 

• validate the deployment procedure that was developed to insure that all air was adequately 

bled from the tubing in the sensor system, and 

• demonstrate that the LRDP could be used as a portable system for performing an annual 

precision test of the tank. 

In a vertical right regular cylinder, the free surface area of the fuel is constant regardless of level. 

 In a tank with curved walls, however (e.g., a horizontal cylinder, or a vertical cylinder with a 

spherical top and bottom), the free surface area varies as a function of level. In this type of tank, 

a DP sensor will not completely 

compensate for the thermal expansion or 

contraction of the fuel. To address this 

type of tank, the LRDP system incorporates 

a second design in which the cylindrical 

reference tube is replaced by a variableshaped tube that mimics the cross-sectional 

changes in the tank’s geometry as a 

function of depth [17]. This shaped 

reference tube, which is shown in Figure 

was used instead of the constant-diameter 

tube used for bulk USTs. 

The DEM/VAL was conducted between 29 

November and 2 December 1999. The tank 

contained 38,100 gal (74% of capacity) for 

these tests. Figures 17 and 18 show the 

LRDP being installed in the tank through 

the standard 8-in.opening in the tank. The 

LRDP can be installed in less than four 

hours by a single person. 

Three types of tests were conducted to meet 

the objectives stated above. The first was 

to demonstrate that the level of the fuel in 

the tank could be measured and used for 

Figure 17. inventory purposes. The second was to Installation of the LRDP in the 50,000-gal UST. 
38

show that the system would 

respond if a known volume of 

product were to be removed or 

added to the tank. The third 

was to demonstrate that the 

LRDP had sufficient 

performance to meet the 0.2-

gal/h monthly monitoring 

regulatory standard. 

A 24-h test was conducted on 

November 19, 1999 to 

determine whether or not the 

tank was leaking. Having 

determined that the tank was 

tight, a demonstration of the 

system was conducted for site 

personnel on November 20, 

1999. After the demonstration, additional data were collected with the LRDP; a total of 74 h of 

data were collected. Analyses were then performed to make an estimate of performance of the 

LRDP for use in 50,000-gal USTs using test durations of 8 h and 24 h. 

To satisfy the 0.2-gal/h monthly monitoring regulatory standard, the LRDP would have to be able 

to detect a leak of 0.2 gal/h with a PD = 95% and a PFA < 5%. This performance is achieved if the 

standard deviation of the error in the tests used in an evaluation is less than or equal to 0.06 gal/h. 

 If only a single test was conducted, the error in this test would have to be less than 0.10 gal/h, as 

determined by a hypothesis test using a student’s t distribution at a level of significance of 0.05. 

 Table 9. Summary of the Test Results for the LRDP Systems in a 50,000-gal UST at Hunter Army Airfield 

Test No. Test Start 

(mm/dd/yy hhmm) 

Induced Leak 

Rate 

8-h Test 

VR* 

8-h Test 

VR Error 

24-h 

VR* 

24-h Test 

VR Error 

 (gal/h) (gal/h) (gal/h) (gal/h) (gal/h) 

1a 11/19/99 1155 0.000 -0.087 -0.087 0.014 0.014 

1b 11/19/00 1939 0.000 0.027 0.027 

1c 11/20/99 0339 0.000 0.123 0.123 

2a 11/20/99 1604 0.000 -0.049 -0.049 0.010 0.010 

2b 11/21/99 0004 0.000 0.051 0.051 0.010 0.010 

2c 11/21/99 0804 0.000 0.042 0.042 -0.008 -0.008 

2d 11/21/99 1604 0.000 -0.037 -0.037 

2e 11/22/99 0004 0.000 0.013 0.013 

2f 11/22/99 0804 0.000 0.014 0.014 

2g 11/22/99 1604 0.000 -0.080 -0.080 

2h 11/23/99 0004 0.000 0.010 0.010 

2I 11/23/99 0804 0.000 -0.025 -0.025 

2j 11/23/99 1604 0.000 0.066 0.066 

* VR = Volume Rate 

The 98 h of data collected during the November 19, 1999 and November 20, 1999 tests were 

grouped, and as shown in Table 9, the data were analyzed in 8 h and 24 h segments to make an 

estimate of performance.

Figure 18. Top of the being installed in an 8-in.opening in a 50,000-gal 

UST.
39

A full-scale evaluation was not performed, because the scaled results of the bulk UST evaluation 

indicates that this level of performance would easily be achieved by the LRDP in a 50,000-gal 

UST. As a consequence, only a few tests were performed and a statistical comparison was made. 

 If the LRDP were to be used to test these USTs, it would have to undergo a complete third-party 

evaluation. 

4.4 Other Field Tests in Bulk USTs with the LRDP 

It was originally intended to verify that the system was functional and then to evaluate the 

performance of the LRDP in a 132.5-ft-diameter, 2,100,000-gal bulk UST at the DEO-LA San 

Pedro Fuel Farm. The first objective was addressed, but the second objective could not be 

addressed because of a valve or valves that did not completely seal. 

The San Pedro fuel farm is located about 1.5 miles NW of the West Basin of Los Angeles Harbor. 

 Tank #5, which was been selected for the demonstration tests, contained jet fuel and was 20 ft in 

depth. It had extensive leak testing within the past two years and does not have any known leaks. 

The LRDP was installed in the tank on January 1999, and an extensive set of field measurements 

were made until May 1999. A small flow across the valve (outflow) of approximately 0.1 gal/h 

was observed that was believed to be due to valve leakage. The specific source of this small flow 

could not be identified, and it was determined that the evaluation should be performed on another 

tank in which the valves were known to be tight, as required by the evaluation protocol. Such a 

problem existed during the first evaluation of the LRDP at North Island and led to artificial 

constraints being placed upon the operational use and performance of the system by the 

NWGLDE. Additional discussion can be found in Section 9. 
40

5.0 Performance Assessment

The performance of the LRDP system was assessed for its suitability for both monthly monitoring 

and for annual or semi-annual precision (tightness) testing. The results of the third-party 

evaluation conducted by KWA on the Point Loma bulk UST are presented and discussed below. 

Section 5.1 summarizes the results of the previous evaluation, and why a second third-party 

evaluation was conducted. Section 5.2 describes the various methods evaluated. Section 5.4 

describe the data measured with the LRDP system and summarizes statistically the individual test 

results tabulated in Table 7 for the LRDP-10 and Table 8 for the LRDP-24. Estimates of the 

performance of the LRDP-10 and LRDP-24 are presented in Sections 5.4 for a single test. The 

enhanced performance achieved when two or more tests are averaged together is presented in 

Section 5.5 for the LRDP-10-n and the LRDP-24-n, where n is the number of tests averaged 

together. Section 5.6 summarizes the results for different thresholds and PFAs (Versions 1.0a, 

1.1a, and 1.2a). The applicability of the results and how to use the LRDP is meeting regulatory 

requirements are presented in Sections 5.7 through 5.10. Section 5.10 describes the results of the 

DEM/VAL at Hunter Army Airfield on a 50,000-gal UST. 

The only difference in the test protocol between the LRDP-10 and the LRDP-24 is the duration of 

the test. The 10-h test duration required by the LRDP-10 allows for monitoring tests to be 

conducted during an overnight period. The same type of monitoring test can be accomplished 

with the LRDP-24 using a 24-h test, but with a significantly better probability of false alarm 

against the same target leak rate, or a significantly better capability for detecting smaller leaks for 

the same probability of false alarm. As predicted by theory, the performance of the LRDP-24 in 

terms of detectable leak rate is 70% better than the performance of the LRDP-10. As shown 

below, however, both systems have sufficient performance to meet the regulatory standards for 

testing bulk tanks. 

5.1 Results of the First LRDP Evaluation

The performance of the LRDP system depends on the diameter of the tank, the duration of the 

test, and the number of tests averaged together. The LRDP was previously evaluated for 

performance by Ken Wilcox Associates. This evaluation was performed in an 88-ft-diameter 

UST at the NAS North Island Fuel Farm. Some degradation of performance occurred because of 

fuel drainback into the tank during the evaluation. Such degradation is not representative of the 

method, but rather the evaluation conditions. A data quality index was used to identify the 

presence of drainback (inflow) and to determine when it was small enough to begin a test. The 

average waiting time required to wait until the drainback was small was 24 h. Thus, a waiting 

period of 24 h was specified by the NWGLDE. Even though the drainback was small after 24 h 

(less than 0.1 gal/h), it degraded the performance by at least a factor of two over what should have 

been the outcome of the evaluation. This assessment could be made because of several back-toback tests with and without leaks in which the volume rate difference between these tests was 

equal to the induced leak to within 0.03 gal/h. 
41

Even with this degradation, the LRDP still achieved excellent performance. The performance 

achieved with the LRDP for a 24- and a 48-h test indicated that with a single test the LRDP could 

detect leaks as small as 0.46 and 0.38 gal/h, respectively, with a probability of detection of 95% 

and a probability of false alarm of 5%. By averaging 4 or 5 tests together, the performance 

improved by a factor of 2 or more for both methods. 

The main problem with this evaluation was the limitations placed on the LRDP that were 

technically unnecessary. These limitations included a 24-h waiting period (when none is actually 

required) and the inclusion of a 0.1-gal/h bias (due to the inflow and not the system) in the use of 

a threshold for conducting a precision test at 0.2 gal/h. While this bias does not impact a 

monitoring test at 1, 2 or 3 gal/h, it would impact a precision test. In addition, the inflow 

prevented the evaluation of the LRDP for a test duration shorter than 24 h. 

Since the LRDP did not automatically report the test result at the conclusion of a test, the system 

was not approved for stand-alone monitoring. Instead, the analysis was automatically performed 

in a spreadsheet at the completion of a test. This latter constraint is not significant, because all the 

criteria could be met for monitoring provided that an operator start and stop a test, and then 

imported the data into a spreadsheet for analysis. 

The LRDP was re-evaluated for performance during this ESTCP project to 

• eliminate the unnecessarily long waiting period imposed by the regulators, 

• obtain approval to operate the system as an automatic monitoring system, 

• obtain a more accurate estimate of performance that was not degraded by uncontrolled, 

nonleak-related inflows and outflows during the test, and 

• obtain approval for a test that could be conducted in less than 24 h (i.e., overnight). 

All of these objectives were met in the second evaluation conducted under ESTCP. 

The LRDP was operated in a fully automatic monitoring mode and was evaluated for test 

durations of 10 h and 24 h. A waiting period of 2-h was used just be sure that all operations had 

ceased before a test was begin. 

The results of the first evaluation were listed by the NWGLDE for test durations of 24 and 48 h 

[19-26]. The new results are being submitted for approval for a 10- and 24-h test [8-15]. There 

are presently 12 approved ways to implement a leak detection test with the LRDP system that 

change only in terms of test duration, testing frequency (monitoring or tightness regulatory 

requirements), number of tests averaged together, and probability of false alarm [5]. The 

performance and operation of the system were designed to meet the California regulatory 

guidelines for bulk tanks [5], but have general application for all states. The system is currently 

approved by the NWGLDE for 

• use as a portable system with a 24- and 48-h test (LRDP-24 or LRDP-48) [19-22], 

• averaging multiple tests together (e.g., 4 or 5 tests) for increased reliability and/or 

increased detection sensitivity LRDP-24-5 or LRDP-48-4) [23-26], 
42

• a variety of monthly monitoring (0.3-1.0, 1.0-2.0, and 2.0-3.0 gal/h) and precision testing 

(0.2 gal/h) regulatory options, and 

• all vertical-walled tanks with capacities greater than 50,000 gal and diameters less than 

140 ft. 

When the results of the third-party evaluations performed under ESTCP are listed by the 

NWGLDE, the LRDP system will be approved for 

• use as a stand-alone, in-tank monitoring system or as a portable system with a 10- and 24-

h test (LRDP-10 or LRDP-24) [8-11], 

• averaging multiple tests together (e.g., where the number of tests is less than 12) for 

increased reliability and/or increased detection sensitivity LRDP-10-n or LRDP-24-n) [12-

15], 

• a variety of monthly monitoring (0.3-1.0-2.0, 2.0, and 2.0-3.0 gal/h) and precision testing 

(0.2 gal/h) regulatory options, and 

• all vertical-walled tanks with capacities greater than 50,000 gal and diameters less than 

194 ft. 

5.2 Methods Evaluated

As described in Table 1, four LRDP test methods were evaluated: (1) LRDP-24, (2) LRDP-24-n, 

(3) LRDP-10, (4) LRDP-10-n. Methods (3) and (4) allow individual test results from up to 12 

tests to be averaged together before applying a threshold. As done in the first evaluation, for each 

of these test methods, the performance was estimated for four thresholds. As a consequence, for 

each method, there are four “versions” of the KWA evaluation report and four versions of the 

method. An “a” in the version number is used to differentiate the LRDP-24 evaluated at North 

Island from the LRDP-24 evaluated at Point Loma. The Point Loma results will replace the 

previous results for the LRDP-24. The LRDP-10 is a new method. Although this is a new 

method, a version number of “a” is also used to indicate it was evaluated at Point Loma. 

The performance was estimated for four thresholds to allow the method to be used as needed to 

satisfy regulatory and operational requirements and for direct comparison of the performance to 

other methods. The basic version, called Version a, sets the threshold to insure that the PD = 95% 

against the target leak rate and that the PFA is as small as possible and less than or equal to 5%. In 

this case, the TLR and PD (= 95%) can be the same for any tank diameter. However, if the 

threshold is selected in this way, the PFA will be different for each tank diameter, which is 

acceptable provided that the PFA < 5%. This method is used for the small regulated USTs found 

in petroleum service stations and is how the LRDP was intended to be used. However, the 

NWGLDE would not let us use this approach for a number of reasons. First, the performance of 

the LRDP was too good, and the NWGLDE, comprised of regulators from states with bulk USTs, 

were concerned that leaks smaller than the threshold would go undetected, because they knew that 

the method had the performance to detect them using a smaller threshold. Second, they did not 

want the PFA to be different for every tank tested, because they thought it would be confusing to 

tank owners. They wanted the PD and PFA to be the same for every tank and to allow the TLR to 
43

change. 

Version 1.0a, which was reported previously to the NWGLDE for a 2.0 and 3.0 gal/h leak as 

Version 1.0, is reported here for leaks of 1.65 and 2.40 gal/h for the 24-h test and leaks of 1.90 

and 2.40 for the 10-h test. These TLRs were selected because it allowed the LRDP to address the 

0.3-1.0-, the 1.0-2.0-, and 2.0-3.0-gal/h monthly monitoring standards for all tank sizes. In this 

method, the NWGLDE required that a TLR be selected for the evaluation tank. This TLR would 

then be scaled for the tank being tested, keeping the PD and PFA the same for tanks of different 

product surface areas. This method is different than “Version a,” because the selected TLR 

changes with tank diameter, but the PFA remains the same. In Version a, the TLR can be the same 

for all tank diameters. 

Version 1.1a is intended for use in California. For this version, the TLR for the evaluation tank 

was selected so that it is less than or equal to twice the MDLR. For the LRDP-24, a TLR of 0.95 

gal/h was selected, and for the LRDP-10 a TLR of 1.65 gal/h was selected. Both TLRs are less 

than 2 * MDLR1

. These TLRs are less than 2 * MDLR and were selected, because this choice of 

TLRs allows the LRDP to be used to address Option 7 or 10 of the California regulatory 

guidelines for monthly monitoring. 

In Version 1.2a, the threshold was selected to give the MDLR, the smallest leak rate that could be 

detected in a given tank and still insure a PD = 95% and a PFA = 5%. The MDLR is useful, 

because it is a simple way to compare the performance of different methods. 

Ken Wilcox Associates, Inc., has prepared four evaluation reports (LRDP-24, LRDP-24-n, 

LRDP-10, LRDP-10-n) [8-11]. These reports include Version a of the standard EPA Results 

Form. The performance that corresponds to the other three threshold selections are presented in 

four more KWA reports that include only the Results Forms and the Method Description Forms 

for versions V1.0a, V1.1a, and V1.2a [12-15]. As state above, these performance results are 

reported identically to the results determined from the North Island evaluation. This was done 

purposefully so that it should be straightforward for the NWGLDE to review and approve these 

updated results. 

 

The performance results scales with the square root of the number of tests, n, averaged together, 

and linearly the product surface area (PSA), which can also be expressed in terms of tank 

diameter (D). The formula used to compute the threshold and TLR for a particular tank size are 

presented in Appendix E for Version a and Appendix F for the other three versions. Examples of 

the results for all four versions are presented in Appendices G – J. 

5.3 Results of the Leak Detection Tests

An example of the level data measured with the LRDP in Test 10 for a 10-h test and a 24-h test is 

shown in Figures 19 and 20, respectively. The tests of the LRDP-10 were initiated at the same 

time as those of the LRDP-24. The induced leak rate was 1.82 gal/h, and the leak rate measured 

by the LRDP-10 was 1.80 gal/h and the LRDP-24 was 1.83 gal/h. 

 

1

 A TLR = 2 * MDLR for the LRDP-24 would equal 1.38 gal/h (2 * 0.69 gal/h), and a TLR = 2 * MDLR for the 

LRDP-10 would equal 2.28 gal/h (2 * 1.139 gal/h). 
44

The waiting period was initiated at 1500 on 11 May 2000, and the test started 2 h later at 1700. 

The precision of the data (i.e., the standard deviation of the data about a regression line fit to the 

data) is less than 0.0003 in. The data do not exhibit any evidence of ambient diurnal temperature 

effects on the differential pressure sensor or the reference tube mounting system. The linearity of 

the 24-h data in Figure 20 suggests that the volume rate estimated with these data should be about 

the same for both the 10-h and 24-h test periods. 

A 1-h periodicity is observed in the level data 

obtained for this test and several other tests. In 

some tests this periodicity was 2 to 3 h. This 

periodicity is consistent with the presence of 

internal waves in the tank. This periodicity was 

not observed in the San Pedro data shown in 

Figure 21. It is likely that the geometry of this 

specific tank is such that a resonance condition is 

sometimes established. The amplitude of these 

fluctuations observed during the other 11 tests 

ranged from a factor of three higher and lower. 

These fluctuations do not affect the results of 

either the 10- or 24-h tests. The main effect is that 

a test must include 3 to 5 cycles to achieve a stable 

performance. If the evaluation had been 

completed in the tank at San Pedro, it is likely that 

a 4- to 8-h test would have been evaluated. 

The results of the leak detection tests for 

the LRDP-10 and the LRDP-24 were 

tabulated in Tables 7 and 8. These test 

results are presented graphically in Figures 

22 and 23 for the LRDP-10 and the LRDP24. Each test result is plotted against the 

leak induced for that test. In Figure 22, the 

test results measured by the LRDP systems 

appear on the y-axis, while the KWAinduced leak rates appear on the x-axis. A 

least-squares line has been fitted to the 

results of the tests with each LRDP system. 

The slope of the line is nearly 1.0 (1.039 

for the LRDP-10 and 0.979 for the LRDPy = 1.0389x - 0.0673

R2 = 0.9434

y = 0.979x - 0.0966

R2

 = 0.8415

-2.500

-2.250

-2.000

-1.750

-1.500

-1.250

-1.000

-0.750

-0.500

-0.250

0.000

0.250

0.500

-2.250 -2.000 -1.750 -1.500 -1.250 -1.000 -0.750 -0.500 -0.250 0.000

Induced Leak Rate - gal/h

Measured Volume Rate - gal/h

LRDP-10 LRDP-24 Linear (LRDP-24) Linear (LRDP-10)

Figure 22. Least-squares lines fitted to the test results of 

the LRDP-10 and the LRDP-24. 

-60

-50

-40

-30

-20

-10

0

10

20

0 2 4 6 8 10 12 14 16 18 20 22 24

Time - h

Volume - gal

Figure 20. Level data obtained with the LRDP-24 

system for Test 10. 

-25

-20

-15

-10

-5

0

5

10

15

0 1 2 3 4 5 6 7 8 9 10

Time - h

Volume - gal

Figure 19. Level data obtained with the LRDP-10 

system for Test 10. 

0.565

0.567

0.569

0.571

0.573

0.575

0 50 100 150 200

Elapsed Time (hours)

Differential Level (inches)

0

20

40

60

80

100

120

Temperature (deg F)

Level BoxTemp

Figure 21. Level data obtained with the LRDP 

system over a 96-h period in a 132.5-ft-diameter tank 

at San Pedro. 
45

24); this indicates that the volume changes due to the induced leaks are additive with any other 

volume changes in the tank. The intercepts for the LRDP-10 and the LRDP-24 systems, -0.097 

and -0.067 gal/h, respectively. A statistical hypothesis test at a level of significance of 0.05 

shows that the intercepts are not different from zero. 

This is more easily seen in the error plot 

shown in Figure 23. The error plotted on 

the y-axis is the difference between the 

induced leak rate and the leak rate 

measured by the LRDP system for both 

test durations. The mean and standard 

deviation of the test results for each 

system, after the induced leak has been 

subtracted out, are summarized in Table 

10. The standard deviation of the 10-h 

test is nearly 70% larger than the 

standard deviation of the 24-h test, which 

is consistent with expectation. 

 

Table 10. Mean and Standard Deviation of the Difference between the Measured Leak Rates (Test Results) and 

Induced Leak Rates for the LRDP-10 and LRDP-24 

Type of 

LRDP System 

Number of Tests Mean Volume Rate 

(gal/h) 

Standard Deviation 

(gal/h) 

LRDP-10 12 0.080 0.318 

LRDP-24 12 0.097 0.192 

A two-sided statistical hypothesis test, as required by the evaluation protocol, was performed to 

determine if the mean was statistically different from zero. The results of a two-sided Student-t 

test conducted at a level of significance of 0.05 was that the mean could not be distinguished from 

zero. The critical Student-t statistic is 2.20 and the computed statistics for the LRDP-10 and the 

LRDP-24 were 0.878 and 1.750, respectively. This means that the mean computed in the 

evaluation does not have to be included in the threshold as a system bias. This is significant, 

because the mean was shown to be statistically significant in the first evaluation. Even though the 

NWGLDE recognized that this non-zero mean 

was produced by nonleak-related inflows and 

was not a bias of the method, they were 

requiring that the threshold include the mean, 

which when used would have resulted in an 

unacceptably high probability of false alarm. 

The present evaluation shows that the bias 

computed in the first evaluation was not real. 

Figure 24 shows the cumulative frequency 

distributions (CFDs) of the test results, with the 

dashed line denoting the LRDP-10 and the solid 

line denoting the LRDP-24. These CFDs were 

generated after the induced leak rate and the 

0.000

0.200

0.400

0.600

0.800

1.000

-0.750 -0.500 -0.250 0.000 0.250 0.500 0.750

Volume Rate - gal/h

Cumulative Frequency

LRDP-10 LRDP-24

Figure 24. Cumulative frequency distributions of the 

test results in a 122.5-ft-diameter bulk UST after the 

volume changes due to the induced leak were removed. 

-0.750

-0.500

-0.250

0.000

0.250

0.500

0.750

-2.250 -2.000 -1.750 -1.500 -1.250 -1.000 -0.750 -0.500 -0.250 0.000

Induced Leak Rate - gal/h

Measured Volume Rate - gal/h

LRDP-10 LRDP-24

Figure 23. Difference between the induced leak rate and the 

volume rate measured with the LRDP-10 and the LRDP-24.
46

mean inflow had been subtracted. Based on the CDF of the LRDP-10 and the LRDP-24, a 

threshold set at volume rates greater than –0.5 and –0.25 gal/h, respectively, would have resulted 

in no false alarms during the evaluation. 

The difference in performance between the LRDP-10 and the LRDP-24 can be attributed to one 

or two of the evaluation tests. If the LRDP-10 measured the same result as the LRDP-24 for 

Tests 2 and 3, the mean and standard deviation of the LRDP-10 would be 0.066 gal/h and 0.226 

gal/h, respectively, which means the performance of the LRDP-10 is similar to the LRDP-24 for 

most tests. Although its quoted performance is not nearly is good, in operation, it will give 

similar results for 80% of the tests conducted. 

The LRDP was also evaluated for an 18-h test with a 6-h waiting period. The mean and standard 

deviation was 0.080 gal/h and 0.198 gal/h, respectively. The performance of the LRDP using this 

test protocol is nearly the same as LRDP using a 24-h test with a 2-h waiting period and would 

result in a MDLR of 0.713 gal/h, as compared to an MDLR of 0.690 gal/h for the 24-h test. 

While the difference between the LRDP-24 and the LRDP-18 was only 0.02 gal/h, a 12-test 

average would not quite meet the 0.20-gal/h precision test standard with the LRDP-18 for the 

evaluation tank. For this reason and because the total test time for both methods is about the same 

and a 24-h test has already been approved by the regulators, only the 10-h and 24-h test protocols 

were evaluated. 

 

5.4 Performance Estimates for a Single Test (LRDP-10 and LRDP-24)

Estimates of the performance of the LRDP-10 and the LRDP-24, in terms of PD and PFA, were 

generated for the evaluation tank from the standard deviation of the test results given in Table 10. 

The formula for computing performance is presented in Appendix E. In Table 11, the thresholds 

used for detection were selected so as to maintain a PD of 95% and a PFA of 5%. As stated above, 

for such a threshold, the resulting leak rate is called the minimum detectable leak rate (MDLR). 

Table 11. Performance Estimates for the LRDP-10 and the LRDP-24 

Type of 

LRDP System 

Threshold 

(gal/h) 

Leak Rate 

(gal/h) 

Probability of 

False Alarm 

(%) 

Probability of 

Detection 

(%) 

LRDP-10 0.570 1.14* 5.0% 95.0% 

LRDP-24 0.345 0.69* 5.0% 95.0% 

* For these thresholds, the leak rate is also referred to as the minimum detectable leak rate (MDLR). 

The performance of these two systems against larger leaks in the evaluation tank is shown in 

Table 12. The thresholds set for these performance estimates were selected so as to maintain a PD

of 95% and to make the PFA as small as possible. In order for the LRDP-10 to maintain a PD = 

95% against a leak rate that is larger than 1.14 gal/h and still have a PFA < 5%, the threshold 

should be less than the leak rate by 0.57 gal/h or more and no smaller than 0.57 gal/h. In this 

case, a threshold anywhere from 0.57 to 1.43 gal/h could be used if the leak rate is 2.0 gal/h. 

Similarly, in order for the LRDP-24 to maintain a PD = 95% against a leak rate that is larger than 

0.69 gal/h and still have a PFA < 5%, the threshold should be less than the leak rate by 0.345 gal/h 

or more and no smaller than 0.345 gal/h. In this case, a threshold anywhere from 0.345 to 0.655 

gal/h could be used if the leak rate is 1.0 gal/h.; a threshold anywhere from 0.345 to 1.655 gal/h 
47

could be used if the leak rate is 2.0 gal/h. Because the evaluation is based on only 12 tests, the 

PFA is reported as very much less than 1% (<< 1%) if the calculated PFA is a factor of ten or more 

smaller than 1.0%. Additional performance results as a function of TLR and tank diameter are 

presented in Appendices I and J. 

Table 12. Performance Estimates for the LRDP-48 and the LRDP-24 against Larger Leaks

Type of 

LRDP System 

Threshold 

(gal/h) 

Leak Rate 

(gal/h) 

Probability of 

False Alarm 

(%) 

Probability of 

Detection 

(%) 

LRDP-10 1.43 2.0 <<1.0% 95.0% 

LRDP-10 0.93 1.5 0.7% 95.0% 

LRDP-24 1.655 2.0 <<1.0% 95.0% 

LRDP-24 1.155 1.5 <<1.0% 95.0% 

LRDP-24 0.655 1.0 <1.0% 95.0% 

The smallest leak rate that is detectable in the evaluation tank with a 24-h test with a PD = 95% 

and a PFA = 5% was 0.69 gal/h This scales to a detectable leak rate of 0.36 gal/h in an 88-ftdiameter tank, the diameter of the bulk UST used in the first evaluation at North Island. In the 

previous evaluation, the MDLR for a 24- and a 48-h test was 0.45 gal/h and 0.38 gal/h 

respectively. Thus, once the inflow problems experienced during the first evaluation are 

eliminated, the LRDP-24 performs slightly better than the LRDP-48 evaluated at North Island. 

5.5 Performance Estimates for More than One Test (LRDP-10-n and LRDP-24-n)

The performance of the LRDP-10 and the LRDP-24 (or any leak detection system) can be 

improved significantly by combining the results of two or more tests. Averaging two or more test 

results before applying the threshold will improve both the probability of detection and the 

probability of false alarm over that obtained for a single test. Performance improves as the 

number of tests averaged together increases. The performance will depend on the test duration 

and the number of tests, n, averaged together. For example, the performance of the LRDP-10-4 is 

a factor of 2.0 (square root of 4) times better than a single 10-h test with the LRDP-10; the LRDP10-4 uses a test duration of 10 h and averages four 10-h tests together. 

The performance of the LRDP-10-n and LRDP-24-n systems, where n is the number of 

independent tests averaged together, is obtained using the standard deviation of the mean test 

result, Sm, of the LRDP-10 and LRDP-24 systems. The standard deviation of the mean test result 

can be determined from the standard deviation of the single-test results, S, computed in the thirdparty evaluation. Once the standard deviation of the mean test result is known, the performance 

of the mean (average) test result (in terms of PD and PFA) can be computed using the same 

methods as for the single test results. 

For independent tests, Sm of the LRDP-10 and LRDP-24 is obtained from S and the number of 

tests, n, averaged together. The standard deviation of the mean, Sm, is given by 

Sm = S /(n)0.5 .
48

For the LRDP-10 and the LRDP-24, values of n that yield an MDLR of 0.2 gal/h or less were 

purposely selected. This equates to a system capable of detecting a 0.2-gal/h leak with a PD = 

95% and a PFA < 5%. In this way, the LRDP-10 and the LRDP-24 could meet the annual testing 

requirements for bulk tanks established by the state of California. Table 13 summarizes the mean 

and standard deviation of the mean test result for the LRDP-10-n and the LRDP-24-n for different 

values of n in the evaluation tank. Table 14 summarizes the performance in terms of the MDLR. 

Table 13. Mean and Standard Deviation of the Difference between the Measured Test Results and Induced Leak 

Rates for the LRDP-10-n and LRDP-24-n for n = 4, 6, and 12 

Type of 

LRDP System

Number of Tests 

Averaged Together 

Mean Volume Rate 

(gal/h) 

Standard Deviation 

of the Mean 

(gal/h 

LRDP-10-1 1 -0.080 0.3175 

LRDP-10-4 4 -0.080 0.1588 

LRDP-10-6 6 -0.080 0.1296 

LRDP-10-12 12 -0.080 0.0917 

LRDP-24-1 1 -0.097 0.192 

LRDP-24-4 4 -0.097 0.096 

LRDP-24-6 6 -0.097 0.0784 

LRDP-24-12 12 -0.097 0.0055 

Table 14. Performance Estimates Made for the LRDP-10-n and the LRDP-24-n Systems 

Type of 

LRDP System 

Threshold 

(gal/h) 

Leak Rate 

(gal/h) 

Probability of 

False Alarm 

(%) 

Probability of 

Detection 

(%) 

LRDP-10-1 0.57 1.14 5.0% 95.0% 

LRDP-10-4 0.285 057 5.0% 95.0% 

LRDP-10-6 0.233 0.465 5.0% 95.0% 

LRDP-10-12 0.165 0.329 5.0% 95.0% 

LRDP-24-1 0.345 0.690 5.0% 95.0% 

LRDP-24-4 0.173 0.345 5.0% 95.0% 

LRDP-24-6 0.141 0.282 5.0% 95.0% 

LRDP-24-12 0.100 0.199 5.0% 95.0% 

The average test result is important because it allows the same in-tank leak detection system to 

meet both the 0.3-1.0 or 1.0-2.0-gal/h monthly monitoring and the 0.2-gal/h annual leak testing 

requirements established by the state of California for bulk tanks. All of the LRDP systems can 

easily meet the monthly testing requirements with a very low probability of false alarm (<1%). 
49

With averaging, all of the bulk USTs owned or operated by the DoD can also meet the precision 

test requirements. 

5.6 Formula to Compute the Threshold and Target Leak Rate as a Function of Tank 

Diameter for the LRDP-10 and LRDP-24

The performance of a leak detection system can be affected by the size and geometry of the tank. 

This relationship is not quantitatively understood for volumetric methods, but is predictable for 

mass-based systems. For most mass-based technologies, performance is related to the surface 

area of the fuel in the tank (but not the volume of fuel in the tank). 

The evaluation protocol specifies that the threshold for declaring a leak must be adjusted when 

testing tanks that are smaller or larger than the tank used in the evaluation. For a mass-based 

system, the threshold and the TLR are obtained from the ratio of the surface area of the tank being 

tested and the surface area of the tank used in the evaluation. 

According to the evaluation protocol [6], the maximum tank size to which a mass-based method 

may be applied is determined by the surface area of the tank and is limited to two and one-half 

times the surface area of the tank used in the evaluation. Since the surface area of the 122.5-ft 

diameter, 2,100,000-gal tank used in this evaluation is 11,756 ft2, the LRDP-10 and the LRDP-24 

can be used to test tanks with diameters up to 193.4 ft. The maximum tank capacity (in terms of 

volume of fuel in the tank) that can be tested with the LRDP systems is not constrained by the 

evaluation and will depend on the height of the tank.

 

As discussed previously in this report, the NWGLDE would not list the LRDP using a threshold 

established to maintain a PD = 95% against the target leak rate. Instead, thresholds were selected 

against two leak rates using a set PFA and a PD = 95% (Version 1.0a), a TLR less than or equal to 2 

* MDLR using a set PFA and a PD = 95% (Version 1.1a) , and the MDLR (Version 1.2a). Tables 

15 and 16 present the formula for computing the thresholds and target leak rate as a function of 

tank diameter, D, (or product surface area) and number of tests, n, averaged for the LRDP-10 and 

LRDP-24, respectively. The tables also gives the largest tank diameter for which the MDLR is 

0.2 gal/h or less. The formula are based on a product surface area for the 122.5-ft-diameter 

evaluation tank of 11,786 ft2

. A more complete set of formula for these versions are presented in 

Appendix F. 

Table 15. Formula to Compute the Threshold and Target Leak Rate as a Function of Tank Diameter for the LRDP-10 

Method Tank Diameter Target Leak Rate

(Probability of detection of 

95% with a probability of 

false alarm of 5%) 

Version 1.2a 

For tank diameters less than 51.3 ft 

For tank diameters (D in ft) up to 193.7 ft 

For tank diameters D = [2,635.0*(n)0.5]

0.5

 (LRDP-10-n) 

0.20 gal/h 

(3.14*(D*0.5)2

/11,786)*1.139 gal/h 

0.20 gal/h (average of 1 < n < 12 tests) 

(Probability of detection of 

95% with a probability of 

false alarm of 0.29%) 

Version 1.1a 

For tank diameters (D in ft) up to 193.7 ft 

For tank diameters D = [1,817.3*(n)0.5]

0.5

 (LRDP-10-n) 

(3.14*(D*0.5)2

/11,786)*1.653 gal/h 

0.20 gal/h (average of 1 < n < 12 tests) 

(Probability of detection of 

95% with a probability of 

false alarm of <0.15%) 

Version 1.0a 

 For tank diameters (D in ft) up to 193.4 ft 

For tank diameters (D in ft) up to 193.4 ft 

(3.14*(D*0.5)2

/11,786)*(2.0-0.569) gal/h 

(3.14*(D*0.5)2/11,786)*(3.0-0.569) gal/h 
50

Table 16. Formula to Compute the Threshold and Target Leak Rate as a Function of Tank Diameter for the LRDP-10 

Method Tank Diameter Target Leak Rate

(Probability of detection of 

95% with a probability of 

false alarm of 5%) 

Version 1.2a 

For tank diameters less than 66.0 ft 

For tank diameters (D in ft) up to 193.7 ft 

For tank diameters D = [4,349.7*(n)0.5]

0.5

 (LRDP-24-n) 

0.20 gal/h 

(3.14*(D*0.5)2

/11,786)*0.69 gal/h 

0.20 gal/h (average of 1 < n < 12 tests) 

(Probability of detection of 

95% with a probability of 

false alarm of 0.48%) 

Version 1.1a 

For tank diameters (D in ft) up to 193.7 ft 

For tank diameters D = [3,172.4*(n)0.5]

0.5

 (LRDP-24-n) 

(3.14*(D*0.5)2/11,786)*0.946 gal/h 

0.20 gal/h (average of 1 < n < 12 tests) 

(Probability of detection of 

95% with a probability of 

false alarm of <0.003%) 

Version 1.0a 

 For tank diameters (D in ft) up to 193.4 ft 

For tank diameters (D in ft) up to 193.4 ft 

(3.14*(D*0.5)2

/11,786)*(2.0-0.345) gal/h 

(3.14*(D*0.5)2

/11,786)*(3.0-0.345) gal/h 

Tables 17-19 further summarize the results of the evaluation. Table 17 gives the MDLR for n = 

1, 4, 6, and 12 for three tank sizes. This table also presents the results from the previous 

evaluation for comparison. A more complete presentation of the results for these versions are 

presented in Appendices G and H. 

Table 18 gives the largest 

tanks in which the LRDP10, LRDP-10-n, LRDP24, and LRDP-24-n can 

meet the precision test 

TLR requirement of 0.20 

gal/h with two different 

PFAs. Table 19 gives the 

largest tank diameters in 

which the LRDP-10 and 

the LRDP-24 can meet 

the monthly monitoring 

standards of 0.3-1.0, 1.0-

2.0, and 2.0-3.0 gal/h. 

Also, Table 18 shows that 

an annual precision test 

can be conducted in any 

tank with a diameter of 

less than 51 ft with a PFA

= 5%, which covers over 50% of the bulk USTs. The LRDP-10 can also be used to meet the 

precision requirement using a single test at a PFA = 0.3% for all tanks with diameters less than 43 

ft. Table 19 shows that the LRDP-10 can be used to address the 0.3-1.0-gal/h and the 1.0-2.0-

gal/h monthly monitoring requirement for tanks with diameters up to 95 and 135 ft. respectively, 

with a very low PFA (0.3%). This covers the full range of bulk USTs owned or operated by the 

DoD. 

Table 17. Example of the MDLR in gal/h (PD = 95% and a PFA = 5%) as a 

Function of Tank Diameter 

Method PD-% PFA-% Target Leak Rate - gal/h 

 for tank diameters of 122.5 ft 88 ft 60 ft 

LRDP-10 95% 5% 1.14 0.59 0.27 

LRDP-10-4 95% 5% 0.57 0.29 0.14* 

LRDP-10-6 95% 5% 0.46 0.24 0.11* 

LRDP-10-12 95% 5% 0.33 0.17* 0.08* 

LRDP-24 95% 5% 0.69 0.36 0.17* 

LRDP-24-4 95% 5% 0.35 0.18* 0.09* 

LRDP-24-6 95% 5% 0.28 0.15* 0.07* 

LRDP-24-12 95% 5% 0.20 0.10* 0.05* 

LRDP-24* 95% 5% 0.89 0.46 0.21 

LRDP-48* 95% 5% 0.74 0.38 0.18* 

* Although the computed MDLR is less than 0.20 gal/h, the performance of the 

system must be reported and the system operated at 0.20 gal/h. 
51

As shown in Table 19, with 

the LRDP-24, the 0.3 – 1.0-

gal/h monthly monitoring 

requirements can be 

addressed for all but a few 

of the largest bulk USTs 

owned by DoD. The 

advantage of using the 0.3 – 

1.0-gal/h criterion is that 

only a single precision test 

at 0.2 gal/h is required each 

year. Table 19 shows that 

the LRDP-24 can be used to 

address the 0.3 – 1.0-gal/h and the 1.0 – 2.0-gal/h monthly monitoring requirement for tanks with 

diameters up to 126 and 178 ft. respectively, with a low PFA (0.5%). This covers the full range of 

bulk USTs owned or operated by the DoD. Also, Table 18 shows that an annual precision test 

can be conducted in any tank 

with a diameter of 66 ft with a 

PFA = 5%, which covers over 

50% of the bulk USTs. If a 

precision test is conducted 

with the LRDP-24, then all of 

the 88-ft-diameter tanks at the 

North Island fuel farm can be 

tested in compliance with 

California regulations by 

conducting a precision test 

four times a year. 

5.7 How to Use the LRDP System

The LRDP system gives the tank owner or operator great flexibility in developing a testing 

strategy for meeting the monthly monitoring and the precision test regulatory requirements. The 

overnight testing capability of the LRDP-10, the high performance of the LRDP-24, and the 

capability for averaging tests together allow a testing strategy to be developed that includes both 

methods. A testing strategy, which is both cost effective and minimizes disruption to operations, 

can be developed. Tables 18 and 19 suggest how the system may be used; also see Appendices G 

- J for more detail. The detailed calculations can be made using the formula in Tables 15 and 16; 

Appendices E and F give additional detail. 

Appendices G and H present the results for the LRDP-10 and the LRDP-24, respectively, for all 

four versions of each method (a, 1.0a, 1.1a, and 1.2a) for a sufficient number of TLRs to design a 

testing strategy without using the equations in Appendices E and F. The four tables in each 

appendix present the target leak rate, threshold, standard deviation, PD and PFA for specific target 

leak rates of interest and specific tank diameters of interest. These results will indicate which size 

tanks can be tested with the LRDP-10 and the LRDP-24 to meet the 0.2, 0.3-1.0, 1.0-2.0, and 2.0-

Table 18. Largest Diameter Tank in which a 0.20 gal/h Leak Rate Can Be 

Detected as a Function of the Number of Tests Averaged Together* 

Method PD PFA TLR-gal/h 

 For Tank Diameters < 

 n=1 n=4 n=6 n=12

LRDP-10-n 95% 5.0% 0.20 51 ft 73 ft 80 ft 96 ft 

LRDP-10-n 95% 0.3% 0.20 43 ft 60 ft 67 ft 79 ft 

LRDP-24-n 95% 5.0% 0.20 66 ft 93 ft 103 ft 123 ft 

LRDP-24-n 95% 0.5% 0.20 56 ft 80 ft 88 ft 105 ft 

*PD = 95% and a PFA < 5% for the LRDP-10, LRDP-10-n, LRDP-24, and 

LRDP-24-n as a Function of Tank Diameter and Averaging (n = 1, 4, 6, 12) 

Table 19. Largest Diameter Tank in which Various Leaks Can Be 

Detected as a Function of Target Leak Rate* 

Method PD PFA Tank Diameters 

 for TLRs in gal/h 

 for TLR in gal/h = 0.30 1.0 2.0 3.0 

LRDP-10 95% 0.3% 52 ft 95 ft 135 ft 165 ft

 for TLR in gal/h of 0.30 1.0 2.0 3.0 

LRDP-24 95% 0.5% 69 ft 126 ft 178 ft 218 ft 

*PD = 95% and a PFA < 5% for the LRDP-10 and the LRDP-24 
52

3.0 gal/h precision and monthly monitoring standards. The table also indicates how many tests 

need to be averaged to detect 0.2 gal/h. The standard deviation, which is used to estimate the 

performance, is also shown. Appendices I and J present the results for the LRDP-10 and the 

LRDP-24, respectively, for Version a, as a function of tank size, for the TLRs of interest (0.2, 0.3, 

1.0, 2.0, and 3.0). 

The guiding principle that should be used when developing a testing strategy is to minimize the 

probability of a false alarm. Any PFA that is less than 1% will suffice, but it is highly desirable to 

have the PFA < 0.1%. Experience shows that the PFA computed using a normal distribution, as 

required by the EPA standard test procedures, is reasonably accurate for estimating the PFA at 5% 

but results in a lower than observed PFA for PFAs < 1%. A PFA of about 0.01% really results in a 

PFA of about 0.1%. 

The performance of the 10-h test is sufficiently good that almost all of the monthly monitoring 

tests, regardless of tank size, can be conducted using a 10-h test. For tanks with diameters less 

than 51 ft, the 10-h test could also meet the 0.2-gal/h precision testing criterion established by the 

State of California. By averaging 4 tests together tanks as large as 73 ft in diameter could be test. 

When the LRDP was used for monitoring at 1.0, 2.0 or 3.0 gal/h, both tests had a PFA < 0.3% for 

all tanks owned or operated by DoD. 

All three of the testing options described in Table 1 can be used. As indicated by Tables 18 and 

19, for the smaller bulk USTs, the LRDP-10 or LRDP-24 to meet the 0.2-gal/h monthly 

monitoring requirement outright. However, it is probably more cost efficient and less disruptive 

to operations for 12 monthly tests to be performed using the 0.3 – 1.0-gal/h monthly monitoring 

option and one annual test at 0.2 gal/h than 12 monthly tests at 0.2 gal/h. This latter approach 

minimizes the potential for false alarms and provides excellent environmental protection well 

within the regulatory standards. If this latter approach is used, small valve weeps would not 

interfere with the monthly monitoring testing. For the largest DoD bulk USTs, the only available 

strategy may be to use the LRDP-24 and test at 0.2 gal/h. 

The exact option to select for the tank owner/operator to use will depend on the size of bulk USTs 

at the facility. The provider of the LRDP can help the tank owner/operator design a testing 

program that is best for the facility. The first step in the design process is to determine which 

LRDP system can be used for monitoring and which LRDP system can be used for precision 

testing with the fewest tests to be averaged and the lowest PFA that can be used. Once this is 

completed, a test protocol which is uses the minimum number of testing combinations (methods 

and versions) should be selected. The added time required to design the testing program in the 

beginning will have great benefits once it is implemented. 

5.8 Results of the DEM/VAL of the LRDP in a 50,000-gal UST 

The LRDP was successfully demonstrated at the Hunter Army Airfield in a 50,000-gal UST. All 

of the DEM/VAL objectives were met. First, it was demonstrated that the LRDP can be used as a 

portable leak detection system. The system was unpacked, pressure tested, installed and bled in 

less than a day. Also, the system was removed from the tank and packed up in less than a day. 

Though there were two people on-site at all times, for this size of system, a single person could 

easily install, bleed and remove the system. 
53

Second, upon installation, the level of the 

product in the tank was measured with the 

LRDP. The level measured with the LRDP 

was within 0.1 in. of the level measured with a 

tape measure. This is within the 1/8 in. (0.125 

in.) regulatory requirement for inventory level 

measurements. 

Third, a calibration check was performed next 

to verify that the height-to-volume conversion 

factor to use for the testing. This was 

accomplished by adding a gallon of fuel and measuring the level change with the LRDP. As 

shown in Figure 25, this addition was easily measured by the LRDP. At 74 % capacity, a one 

gallon volume change is equivalent to approximately a 0.002 in. level change. 

Fourth, four 24-h leak 

detection tests were conducted. 

The first two tests showed an 

inflow of ~ 0.25 gal/h. Upon 

further investigation, it was 

found that the system had not 

been properly bled. When this 

problem was corrected, the 

tank was tested with the LRDP 

for leaks using a target leak 

criterion of 0.1 gal/h. The test 

result was a PASS, because the 

measured volume rate of 0.014 

gal/h was less than a threshold of 0.05 gal/h. The final leak detection test was the demonstration 

of the system for the Hunter personnel. A 74-h data set was obtained (Figure 27). The data in 

Figures 26 and 27 were post 

analyzed to evaluate the 

performance of the system using 

shorter test periods. The results are 

tabulated in Table 9 for test 

durations of 8 h and 24 h. These 

preliminary results show that a leak 

rate criterion of 0.2-gal/h should be 

achievable in 50,000-gal tanks with 

only an 8-h test period. The results 

are presented graphically in Figure 

28, and the statistics are summarized 

in Table 20 for both test durations. 

-2.000

-1.500

-1.000

-0.500

0.000

0.500

1.000

1.500

2.000

0 2 4 6 8 10 12 14 16 18 20 22 24

Time - h

Volume - gal

c

Figure 26. Volume data from a 24-h leak detection test with the LRDP-24. 

0.36

0.361

0.362

0.363

0.364

0.365

0.366

12.6 12.8 13 13.2

Time (hours)

Diff. Level (inches)

One Gallon Added to Tank

Figure 25. Height-to-volume calibration level data in a 

50,000-gal UST.

41.4

41.6

41.8

42

42.2

42.4

42.6

42.8

43

43.2

43.4

12 36 60 84

Time - h

Level Change - gal

Figure 27. Volume data obtained from 74-h of measurements with 

the LRDP.
54

This demonstration provided an 

opportunity to learn additional 

information regarding the 

deployment of the LRDP. First, 

the importance of properly 

"bleeding" the system was 

demonstrated. Bleeding the 

system refers to the act of 

purging any air-bubbles that may 

be trapped in the LRDP tubing 

and which may contribute to 

erroneous level measurements. 

Originally, it was thought that 

adequate purging would take 

place if the system was installed 

in a near-full tank with the 

reference tube valve closed. 

When the LRDP is resting on the 

bottom, with the reference tube 

empty, the valve is then opened 

so that the fuel will rush through 

the plumbing and fill the tube. 

The head of fuel in a near-full 

tank was thought to be adequate 

to flush out any air bubbles. 

Two subsequent 24-h tests 

showed substantial level trends 

on the order of +0.4 gal/h and 

+0.2 gal/h, respectively. 

Because the tank was completely 

isolated from the fuel lines and a 

test for water infiltration was negative, we knew that the tank had no actual inflow and that the 

system results were erroneous. 

To address this problem, the system was repurged. The procedure was to close the valve, fill the 

reference tube to the top, pull the system up through the riser just to the point where the valve is 

still below the fuel surface, and open the valve so the fuel column in the reference tube will rush 

back through the plumbing until the DP cell reading is within 0.5 inches. Next, the valve is 

closed and the system is lowered to rest on the bottom. The valve is then opened to allow the fuel 

to rush back into the plumbing to fill the reference tube. This procedure was performed twice, 

and the volume rate obtained in a subsequent 24-h test was 0.014 gal/h. 

The need to perform extensive bleeding of the LRDP is a key finding of this DEM/VAL. The 

current design for the LRDP maintains the reference tube isolation valve in the open position 

when a test is not being conducted. It is possible that air bubbles may have gotten into the system 

when the tank was drained and the system was not effectively bled during the subsequent fill. A 

-0.2

-0.15

-0.1

-0.05

0

0.05

0.1

0.15

0.2

0 20 40 60 80 100

Time - h

Test Result - gal/h

8 h 24 h

Figure 28. Estimate of performance made for the LRDP in a 50,000-

gal UST. 

Table 20. Estimate of performance for the LRDP made for an 8-h and a 

24-h test duration on a 50,000-gal UST. 

Performance Parameters 

 8 h 24 h 

November 19-20, 1999 Data 

Test Duration – h 

Mean – gal/h 0.000 0.006 

Standard Deviation – gal/h 0.047 0.010 

Count 13 4 

Threshold – gal/h 0.084 0.023 

MDLR –gal/h 0.168 0.047 

 

Precision Test MDLR – gal/h 0.200 0.200 

Precision Test Threshold –gal/h 0.116 0.177 

Precision Test PFA 1.5% < 0.001% 
55

standard procedure for bleeding the system, including valve control logic changes, was 

implemented prior to the installation at Pt. Loma. 

We also found that not having the system mounted permanently made it susceptible to a noise 

level of a factor of 2 to 3 times higher than expected. This was due to two factors: (1) the system 

"rocked" a bit due to the curved bottom of the tank, and (2) any motion of the conduit due to 

wind/bumping/etc. induced this rocking motion. We showed that this problem existed by 

"jiggling" the conduit manual and then noting that the LRDP did not return to the exact previous 

position (before rocking), resulting in a step of 0.001 inch, or 0.5 gallons. This problem can be 

alleviated by shaping the bottom of the LRDP to better fit the bottom of the tank. 

An oscillation with a 2 to 3 h period is also present in the data collected during the first week of 

the installation (Figure 26). The peak-to-peak amplitude of this oscillation is about 0.001 inches 

or about 2 to 3 times the amplitude of the random background noise. While the source of this 

oscillation is unknown, this periodicity is consistent with those of internal waves. The oscillation 

was not present in later data sets, such as the 74-h data set. In addition, there is a small diurnal 

component to the signal that does not get compensated, on the order of 0.001 in. This may be due 

to thermal effects on the conduit that cause the LRDP to "rock", as discussed previously. 

5.9 Results of the DEM/VAL of the LRDP in a 132.5-ft Diameter Bulk UST at San Pedro 

Figure 21 showed a 74-h data set obtained in a 132.5-ft diameter bulk UST at San Pedro. 

Superimposed on the level data is the temperature of the electronic package located in the 

embedded controller. This figure illustrates a number of important characteristics of the LRDP 

system. First, the diurnal temperature changes observed in the embedded controlled are not 

present in the compensated level data. This indicates that the compensation algorithm is 

effective. Second, the random fluctuations about the mean level change is representative of the 

system noise and the random background noise. For these data, the fluctuation level is 0.005 in., 

which is somewhat higher than the precision of the level measurement capability of the system. 

Third, the mean trend suggests an outflow from the system of 0.1 gal/h, which is most probably 

associated with a valve that did not fully close. The tank is located at the top of a hill and product 

transfers are made under gravity flow from the tank. 

 

A preliminary estimate of performance was made using the data obtained during the system 

checkout (Table 21). The performance estimate was made eight 24-h tests and assuming that the 

valve flow leakage was zero. The performance obtained indicated that the LRDP could be used to 

Table 21. Summary of the Results of Eight 24-h Tests with the LRDP in the San Pedro Tank after the Mean Flow 

Was Removed. 

Test 

Duration 

(h) 

Tank 

Diameter 

(ft) 

Number 

 of Tests 

Leak Rate 

(gal/h) 

Probability of 

False Alarm 

(%) 

Probability of 

Detection 

(%) 

12 132.5 18 0.46 5.0% 95.0% 

24 132.5 8 0.26 5.0% 95.0% 

12 88 18 0.133 5.0% 95.0% 

24 88 8 0.069 5.0% 95.0% 
56

test the largest diameter bulk USTs owned and operated by the DoD. The performance obtained, 

when scaled for comparison of the previous evaluation results in an 88-ft-diameter tank, was over 

twice as good as obtained in the first evaluation. The results also suggested that a test duration 

that was shorter than 24 h would be possible. The MDLR determined from a sample of eight 24-h 

tests was 0.26 gal/h in the 132.5-ft diameter tank and 0.15 in the 88-ft-diameter tank. The tests 

conducted at San Pedro were a precursor to the Point Loma evaluation, and the results of the 

measurements made at San Pedro justified switching sites to complete the evaluation. 
57

6.0 Cost Assessment 

This section summarizes the cost and cost savings achievable with the LRDP for testing bulk 

USTs. This section also compares the cost of the LRDP to other in-tank mass-based systems and 

external systems such as tracer-based systems. The cost advantages of the LRDP are realized 

because of the extremely high performance of the LRDP, the on-line, monitoring capability of the 

LRDP when permanently installed in a tank, the capability of the system to conduct a short test 

(an overnight test), and the low recurring costs associated with routine testing to address 

regulatory requirements. 

Two DEM/VALs of the technology were conducted. The cost of these DEM/VALs are 

summarized in Table 22. The first DEM/VAL was to install an LRDP system in a 2,100,000-gal 

bulk UST (Tank 175) at the Point Loma Fuel Terminal, San Diego, California, and to conduct a 

third-party evaluation to determine performance. The second DEM/VAL was to conduct a series 

of tests with the LRDP in a 50,000-gal shop-fabricated UST (Tank 45) at Hunter Army Airfield, 

Savannah, Georgia. With the exception of the reference tube, the same LRDP system was used 

for both DEM/VALs. The DEM/VAL costs include an initial site visit, installation, checkout, and 

removal of the equipment, and conduct of the DEM/VAL (data collection, analysis, and briefing 

of the results). The DEM/VAL at Point Loma required the collection of data over a 2-month 

period to check out the system and over a 3-month period to conduct the third-party evaluation. 

The DEM/VAL at Hunter was only a demonstration of the technology and was completed in less 

than two weeks. 

 Table 22. Summary of the Costs of the Two DEM/VALs of the LRDP System 

DEM/VAL Cost of the 

DEM/VAL 

Cost of the Third-Party 

Evaluation 

Total 

Point Loma Fuel Facility $75,000 $45,000 $120,000 

Hunter Army Airfield $25,000 N/A $25,000 

 

Total $100,000 $45,000 $145,000 

Section 6.1 summarizes the estimated cost of the LRDP, and Section 6.2 compares the 

approximately cost of other in-tank mass-based methods and tracer-based methods to the LRDP 

system. Section 6.3 discusses the potential cost avoidance savings associated with the use of a 

reliable leak detection system like the LRDP. Finally, Section 6.4 summarizes the approximate 

cost of the parts used to manufacture the LRDP. 

 

6.1 Cost Performance 

The total life-cycle cost of leak detection includes the following items: 

• Cost of Regulatory Compliance: Purchase, installation, and operation of a leak detection 

system (direct and recurring costs)
58

− Purchase price of the leak detection system (direct cost) 

− Installation of the system (direct cost) 

− Training (direct and recurring cost) 

− Maintenance (recurring cost) 

− Cost of testing in meeting regulatory compliance requirements (recurring cost) 

− Cost of shutting down operations for testing (recurring cost) 

− Cost of false alarms (recurring cost) 

− Cost of missed detections (recurring cost)

• Cost Avoidance 

− Fines and Shutdown of Operations: Costs associated with fines for not being in 

compliance and the cost impact on operations and operational readiness. (direct cost) 

− Tank Replacement Cost Avoidance: Pre-mature replacement of tanks (direct cost) 

− Remediation/Cleanup Cost Avoidance: Clean-up costs due to lack of testing or 

testing mistakes (direct cost) 

• Commercialization and Technology Transfer Cost: Commercialization of the preproduction system (direct cost) 

It is possible to make an estimate of all of these costs, because the performance of the leak 

detection system is known through the third-party evaluation. The PD and PFA allow estimates of 

the cost of testing mistakes, remediation, and tank replacement to be made. The cost of 

regulatory compliance is described below; the costs associated with cost avoidance and 

commercialization and technology transfer is described in Section 6.3. 

Regulatory compliance will include the costs associated with the purchase, installation, and use of 

a leak detection system. It is estimated that the DoD owns or operates approximately 300 bulk 

UST with capacities greater than 100,000 gal. The life-cycle cost of a leak detection technology 

is comprised of the elements in Table 23. The Startup costs are fixed costs associated with the 

purchase, installation, and operator training. The Operational and Maintenance costs are also 

fixed and are small for the LRDP. The recurring costs associated with Compliance Testing and 

Test Mistakes are very small. Once the LRDP is permanently installed, a test can be initiated by 

pressing a start button. 

In general, it is not the direct costs that control the price of a leak detection system. Rather, the 

recurring costs of monthly monitoring and annual precision testing tend to control. For poor 

performing systems with a higher than desired PFA, the cost of testing increases, because 

• additional tests with the same system or another system will have to be conducted to 

distinguish false alarms from leaks, 

• site investigation may be required in terms of monitoring wells or uncovering of 

buried tanks to determine whether or not the tank is actually leaking, 
59

• such false declarations may have to be reported to regulatory authorities with all the 

ramifications of such a report, and 

• the activities required to determine whether or not a failed test is a false alarm will 

shutdown facility operations until the false alarm can be resolved. 

If the PFA is unacceptably too high, operational experience indicates that fuel farm personnel often 

do not operate or trust the equipment, and thus, leaks may go undetected. This can be very costly 

because of the remediation costs associated with undetected leaks. 

Table 23. Compliance Monitoring Technology Costs for the LRDP on a Per Tank Basis 

Direct Environmental Costs Recurring or Variable Environmental Costs

Startup Operation & 

Maintenance

Compliance Testing Testing Mistakes

Equipment Cost $40,000 Equipment 

Cost 

$40,000 Equipment 

Cost 

$40,000 FA Mitigation 

Remediation 

$40,000 

$750,000 

Activity % Activity % Activity % Activity % 

Facility 

preparation, 

mobilization 

 $4,000 

(10%) 

Labor to 

operate 

equipment 

$4000 

(10%) 

Monthly 

monitoring $400 

(1%) 

False alarms 

(PFA =< 0.1%) 

$40 

(0.1%) 

Equipment Design $4,000 

(10%) 

Utilities $800 

(2%) 

Annual 

precision 

testing 

$400 

(1%) 

Missed 

detections* 

$938 

(0.125%) 

Equipment 

purchase 

$40,000 

(100%) 

Consumable 

and supplies 

$400 

(1%) 

Facility 

shutdown costs 

for testing 

$1,200 

(3%) 

 

Installation $8,000 

(20%) 

Equipment 

maintenance 

$2,000 

(5%) 

Training of 

Operators 

$2,000 

(5%) 

Training of 

operators 

$800 

(2%) 

Total $58,000 

(145%) 

Total $8,000 

(20%) 

Total $2,000 

(5%) 

Total $978 

* It is assumed that the PD = 95% against a TLR = 0.2 gal/h and the number of leaking tanks is 10% of the 300 bulk 

USTs owned by the DoD. It is further assumed that all of the tanks are tested at a TLR of 0.2 gal/h, and as a 

consequence of testing at such a small leak rate, the remediation average remediation costs are assumed to be 25% of 

the average remediation costs.

Table 23 summarizes the costs associated with regulatory compliance with the LRDP. A Parts 

List for the LRDP is presented in Section 6.3. The purchase price of an LRDP assumed for this 

estimate is based on the purchase of 10 to 20 in-tank sensor units. Table 23 presents the cost 

model in terms of a percentage (%) of the equipment purchase price. The costs of false alarms 

and missed detections are based on an assumed price for additional testing ($500) and an average 

remediation cost ($750,000 per incident). The average remediation cost is based on 890 

remediation jobs performed by the Navy. These two costs are indicated in the table heading. It is 
60

assumed that the PFA is less than 0.1%, and that the probability of a missed detection is PMD = 1- 

PD = 5% for a target leak rate of 0.2 gal/h. It is further assumed for this computation that 10% of 

all of the bulk USTs owned by the military are leaking. Because small leaks can be detected with 

the LRDP, the large average cost of remediation can be greatly reduced; for this calculation, it is 

assumed that the cost of remediation is 25% of the average cost. 

An important cost is the cost of shutdown associated with testing and testing mistakes (false alarm 

investigations). Since the military is not selling fuel commercially, any short-term or permanent 

shutdown of fueling operations is difficult to quantify in terms of dollars. However, it is 

unacceptable to shutdown military operations, or to seriously impact operational readiness. An 

estimate of $40,000 for a False Alarm mitigation was used in Table 23, resulting in a $40 per tank 

cost at a PFA of 0.1%. The total cost per tank is $69,000. A cost comparison of the LRDP and 

tracer and other mass-measurement systems is given in Section 6.2. 

6.2 Cost Comparison to Conventional and Other Technologies 

The LRDP has several significant cost advantages over other technologies. The cost advantages 

are realized because of the extremely high performance of the LRDP, the on-line monitoring 

capability of the LRDP when permanently installed in a tank, the capability of the system to 

conduct a short test (an overnight test), and the low maintenance and recurring costs associated 

with the system and the testing. The monthly monitoring and precision testing requirements in 

California, for example, indicate that at least 12 and more likely 13 tests need to be conducted 

each year just for regulatory compliance, and one of these tests must be conducted at 0.2 gal/h. 

Only a permanently installed system can cost-effectively address such regulatory monitoring 

requirements. A number of the in-tank mass-based systems that are commercially available 

cannot be permanently installed in a tank and used for monitoring. The number of tests to be 

conducted each year will be increased (1) if the leak detection system is susceptible to false 

alarms, or (2) if tests need to be repeated, because they are too long and must be prematurely 

terminated or because they interfere with operations. 

An estimate of the cost savings realized by the LRDP over two other methodologies is shown in 

Tables 24 through 27. Method 1 represents a tracer method with a high recurring cost of 

Compliance Testing. Method 1 assumes that a tracer must be added to the tank; no cost estimate 

is provided for tracer methods that use constituents in the fuel as tracers, because their 

performance has been found to be unacceptable. Method 2 is an in-tank mass-based method with 

the capability to only meet the monthly monitoring requirements. No other permanently installed 

in-tank, mass-based system besides the LRDP has the capability to meet the annual 0.2-gal/h 

performance standard. No specific commercial methods are identified by brand name here, but 

the cost savings achieved with the LRDP over a tracer method is due to the small recurring cost of 

testing with the LRDP and over the other permanently installed in-tank methods is due to the fact 

that the LRDP can be used to meet the annual precision test as well as the monthly monitoring 

tests. The best way to interpret the tables is to examine the relative cost savings between the 

LRDP and the other methods. The calculation uses the fixed Start-up costs and the recurring 

Compliance Testing costs from Table 23 for the LRDP. 
61

The cost comparison calculation is done as follows. First, it was assumed that the Startup and 

O&M costs are the same for all methods. Established price lists for bulk leak detection systems 

are not generally available, because most product sales or testing jobs are performed under a 

unique contract bid. In many instances, the purchase price of the equipment or of the testing depends on 

the number of tanks that need to be tested. Therefore, it is difficult to make an estimate of the cost of other 

methods besides the LRDP. Historically, because the price of leak detection equipment and testing with 

the equipment tends to be market driven rather than cost driven, it is safe to assume that the price of all 

methods will be similar. This computation assumes $75,000, which is higher than anticipated for 

the LRDP and is probably lower than anticipated for Methods 1 and 2. This estimate includes the 

one-time purchase of the equipment for $40,000 (same as for the LRDP), as well as the operation 

and maintenance cost, the cost of testing and testing mistakes. The one-time purchase of 

equipment can be as high as $75,000 for mass-based systems. Second, the real cost savings of the 

testing tends to be controlled by the recurring cost of testing or the cost of additional testing 

because of lack of capability of the method to satisfy both the monthly monitoring and the annual 

precision test. The estimate assumes that 12 monthly tests and one annual precision at 0.2 gal/h 

are conducted each year. Third, there are significant cost savings associated with cost avoidance 

and remediation/cleanup because accurate and reliable leak detection is being performed. It is 

safe to say that the DoD would realize significant cost savings (many hundreds of millions of 

dollar) if any leak detection system was installed and used. If a reliable and accurate leak 

detection system is used, these savings can be a factor of 2 to 5 greater. These latter cost savings 

are not included in this calculation. Fourth, this cost comparison does not include the costs of 

Testing Mistakes. The number of tests to be conducted each year will be increased (1) if the leak 

detection system is susceptible to false alarms, or (2) if tests need to be repeated, because they are 

too long and must be prematurely terminated or because they interfere with operations. 

Table 24 summarizes the cost of the initial purchase and installation of the leak detection system, 

the cost of performing 12 monthly tests, and the cost of performing an annual precision test. It is 

assumed that Methods 1 and 2 have the capability for performing the monthly monitoring test, but 

only Method 1 also has the capability for performing the annual test. It is assumed that Method 2 

must use Method 1 to perform the annual precision test. It is also assumed that the recurring cost 

of testing is high for Method 1 as compared to the LRDP and that the recurring cost of testing is 

the same as the LRDP for Method 2. Table 25 summarizes the total cost of meeting the regulatory 

Table 24. Comparison of the Cost of Testing in Dollars ($) with Monthly Monitoring and an Annual Precision Test 

for Each Bulk UST for the First Year 

Purchase of 

System Monthly Monitoring Precision Test Total 

Initial Purchase 

for One UST 

Conduct of 

a Single 

Test 

Cost of 12 

Monthly 

Tests 

Cost of Monthly 

Monitoring for 

First Year 

Annual Cost of 

Precision Test 

Cost of Compliance 

for Year 1 

Method 1 75,000 10,000 120,000 195,000 195,000 

Method 2 75,000 240 2,880 77,880 25,000 102,880 

LRDP 75,000 240 2,880 77,880 77,880 

Method 1/LRDP 2.5 

Method 2/LRDP 1.3 
62

requirements for a single bulk UST for all three methods. Clearly, the recurring cost of Method 1 

dominates the cost of testing. Table 26 summarizes the cost for a fuel farm containing 15 bulk 

USTs, and Table 27 summarizes the cost for all 300 tanks throughout the DoD complex. 

The ratio of the cost of each method relative to the LRDP are given in the tables. The savings of 

the LRDP compared to Method 1 would result in a payback period of less than one year, and the 

savings compared to Method 2 would result in a payback period of approximately three years, 

even without including the savings due to fewer tank replacements and lower remediation costs. 

Table 22 summarizes the total cost of meeting the regulatory requirements for a single bulk UST 

for all three methods. Clearly, the recurring cost of Method 1 dominates the cost of testing. 

Table 23 summarizes the cost for a fuel farm containing 15 bulk USTs, and Table 23 summarizes 

the cost for 300 bulk USTs. When Methods 1 and 2 are compared to the LRDP, the cost of the 

other methods is a factor of 3 to 12 higher than the LRDP. 

Table 25. Comparison of the Cost of Testing in Dollars ($) with Monthly Monitoring 

and an Annual Precision Test for Each Bulk UST Over 1, 3, 5 and 10 Years 

Testing Method Total Cost of Compliance for 

First Year Three Years Five Years Ten Years 

Method 1 195,000 435,000 675,000 1,275,000 

Method 2 102,880 158,640 214,400 353,800 

LRDP 77,880 83,640 89,400 103,800 

Method 1/LRDP 2.5 5.2 7.6 12.3 

Method 2/LRDP 1.3 1.9 2.4 3.4 

Table 26. Comparison of the Cost of Testing in Dollars ($) with Monthly Monitoring 

and an Annual Precision Test for 15 Bulk USTs Over 1, 3, 5 and 10 Years 

Testing Method Total Cost of Compliance for 

First Year Three Years Five Years Ten Years 

Method 1 2,925,000 6,525,000 10,125,000 19,125,000 

Method 2 1,543,200 2,379,600 3,216,000 5,307,000 

LRDP 1,168,200 1,254,600 1,341,000 1,557,000 

Method 1/LRDP 2.5 5.2 7.6 12.3 

Method 2/LRDP 1.3 1.9 2.4 3.4 

Table 27. Comparison of the Cost of Testing in Dollars ($) with Monthly Monitoring 

and an Annual Precision Test for 300 bulk USTs Over 1, 3, 5 and 10 Years 

Testing Method Total Cost of Compliance for 

First Year Three Years Five Years Ten Years 

Method 1 58,500,000 130,500,000 202,500,000 382,500,000 

Method 2 30,864,000 47,592,000 64,320,000 106,140,000 

LRDP 23,364,000 25,092,000 26,820,000 31,140,000 

Method 1/LRDP 2.5 5.2 7.6 12.3 

Method 2/LRDP 1.3 1.9 2.4 3.4 

6.3 Cost Avoidance 
63

The magnitude of the cost savings that can be realized by minimizing testing mistakes, managing 

tank replacement efforts and minimizing remediation/cleanup efforts through early detection of a 

release is a direct function of the use and performance of the leak detection system. If the 

equipment is used frequently and the performance is high (i.e., the probabilities of false alarm and 

missed detection are low), then the integrity of the tanks can be verified periodically and do not 

need to be routinely replaced. They can continue to be used with confidence that they are not 

leaking, and if a leak develops, that it will be quickly detected. This reduces the volume of fuel 

released into the ground and the scope and cost of the cleanup. The high performance of the 

LRDP means that the number of false alarms and missed detections will be much smaller than 

other technologies. Furthermore, the high performance of the LRDP allows the probability of 

false alarm of the system to be set to a very low level without sacrificing the detection of small 

leaks. The other mass-based systems and some tracer-based approaches do not have the 

performance to operate with a low probability of false alarm. In addition, other mass-based 

methods must operate at a higher target leak rate. The total cost savings that can be realized by 

implementing a reliable leak detection program can be $500 million to $1 billion dollars. These 

cost savings are described below. 

Fines and Shutdown of Operations. The cost of testing more than offsets the cost of the fines 

that may be levied if the tanks are not tested within the specified regulatory guidelines and are out 

of compliance. Fines may be $25,000 per day per facility, or more. Ultimately, if the bulk USTs 

are not in compliance, fuel operations can be shut down. Since the military is not selling fuel, any 

permanent or short-term shutdown of fueling operations is difficult to quantify in terms of dollars. 

However, it is unacceptable to shutdown military operations, or to seriously impact operational 

readiness. Because the LRDP has the performance to perform both the monthly monitoring and 

the annual precision test, it is the most cost effective way to be in compliance. Because in many 

instances, an LRDP test can be performed in 10 h rather than the 48 or 72 h required by other 

methods, the impact on shutdown is significant. 

 

Tank Replacement Cost Avoidance. Most bulk USTs are expensive to replace; the costs per tank 

can be tens of millions of dollars. Replacement costs can be minimized, avoided, or delayed by 

using accurate and reliable leak detection. There are two types of tank replacement programs. 

First, the DoD has considered simply replacing all of the bulk USTs with bulk ASTs. The costs 

associated with such an approach would be well over $400,000,000. Such an approach can be 

avoided or minimized. It assumes that there are no accurate or reliable methods of leak detection, 

which is not true. Second, the DoD will need to replace or retrofit tanks as required for safe 

storage. The use of accurate and reliable leak detection can justifiably and safely avoid premature 

replacement of tanks. The cost savings associated with the use of leak detection is very large. 

For example, the U. S. Army has estimated that it would cost over $10,000,000 just to replace the 

50,000-gal USTs at the Hunter Army Airfield (without testing equipment or testing services) as 

opposed to $3,100,000 for implementation of a testing program with the LRDP over a 10-year 

period. For our calculations, we assumed that the cost of replacement is $5 per gallon of stored 

fuel. 

Remediation/Cleanup Cost Avoidance. The cost of remediation and cleanup are by the largest 

costs associated with leaking tanks and clean-up cost avoidance can be the most significant cost 

savings realized with the purchase, installation and use of reliable leak detection. It is difficult to 

estimate the portion of the costs associated with clean-up that can be avoided, but it is significant. 
64

The Navy has 659 future LUFT sites to clean up and has estimated that the total cost will be 

$890,000,000. Early detection of leaks can significantly reduce the total cost of cleanup because 

the concentration and areal extent of the plume is smaller than it would be if the leak was not 

detected early. 

Commercialization and Technology Transfer. The costs associated with technology transfer and 

commercialization have been minimized for the LRDP, because the third-party evaluation has 

already been completed and submitted to the NWGLDE for review and approval, and one 

company, Vista Research, has already commercialized the pre-production system. The former is 

a significant barrier (both in cost and time) for entry into the marketplace, and the later can take 

many years for industry to commit the resources needed for commercialization. 

6.4 Cost of the Parts to Manufacture the LRDP 

Table 28 summarizes the cost of the parts to assemble an LRDP. 

Table 28. Parts List for the LRDP

System Item Specification Vendor Price/ea Qty Total Price 

In-Tank 

 Differential Pressure Sensor Rosemount $1,568 1 $1,568

 Pressure Sensors Pressure Sys. $680 2 $1,360

 Indelas Electrical Actuator Flow Soln. $252 1 $252

 RTD and Transmitter Omega $173 1 $173

 Bellows (1) $86 1 $86

 Bellows (2) $181 1 $181

 SS Tubing (1) Peterson&Marsh $273 1 $273

 SS Tubing (2) Peterson&Marsh $635 1 $635

 Flanges, Ring, Cover Premier Tool $1,410 1 $1,410

 Valve RS Crum $130 1 $130

 Subtotal: $6,068

Above-Tank 

 DM6430X PC104 DAQ -40 to 85 deg C RTD $845 1 $845

 SKH486DX100 PC104 CPU Ext. Temp. RTD $1,296 1 $1,296

 72Mbyte Disk-On-Chip (M-systems) Normal Temp. AtOnce $683 1 $683

 Explosion Proof Box N/A Appleton $580 2 $1,160

 24 Volt Power Supply (chg to 25V) -10 to 71 deg C Acopian $205 1 $205

 ASTEC DC-DC (AA258024L0505) -25 to 70 deg C Bell Industries $83 1 $83

 RTD and Transmitter Omega $173 1 $173

 Voltage Reference (AD586) 0 to 70 deg C Newark $13 1 $13

 Red LED (XP) Miller Wholesale $69 1 $69

 Green LED (XP) Miller Wholesale $85 1 $85

 XP Barrier R. Stahl $153 4 $612

 Battery (Gell Cell) Newark $10 2 $21

 Labor to Drill Holes in XP boxes Danco Machine $300 1 $300

 Subtotal: $5,545

Misc. Electrical $644

Misc. Mechanical $2,692

 

 Total Parts: $14,951
65

7.0 Regulatory Compliance 

The DoD owns and/or operates almost all of the bulk USTs in the United States. While the leak 

detection requirements for bulk USTs (i.e., field erected USTs) were deferred in EPA’s UST 

regulation issued on 22 September 1988, many of the states have or are in the process of requiring 

testing of such tanks. California is a major example, but the bulk USTs in New York, Michigan, 

Maine, and Florida also require that these tanks be tested routinely for leaks. It is not surprising 

that the members of the NWGLDE for bulk USTs are comprised of senior and active regulators 

from each of these states. The NFESC team has had major interactions, meetings, and 

discussions with the members of the NWGLDE, both as work group representatives and as 

regulators. The process for obtaining approval of the LRDP-24 and the LRDP-48, based on the 

LRDP evaluated North Island, took over 18 months of frequent interactions. A number of 

important issues were derived from these interactions. The NFESC team took a lead role in these 

discussions and was responsible for many of the major regulatory changes that took place and 

allowed for DoD tanks to be in compliance. 

A new evaluation protocol was developed for mass-based leak detection systems, because of real 

differences between volumetric leak detection systems and mass-based leak detection systems. 

The NFESC team, in conjunction with KWA, took a lead role in developing and technically 

supporting these changes. The basic evaluation procedure comprised of conducting 12 blind tests 

did not change. Nor did the evaluation conditions change. What did change was how to report 

and apply the results of the evaluation. The new evaluation procedure 

• increased the range of tank sizes (diameters) for which the results of the evaluation 

would apply, 

• acknowledged the concept that mass-measurement systems compensate for the thermal 

expansion and contraction of the fuel in the tank and the performance and 

• acknowledged that the performance of mass-measurement systems scale with the 

surface area of the product in the tank and not the volume of the product in the tank, 

• allowed the performance to scale with tank size (more specifically, the surface area of 

the product in the tank), 

• limited the scaled performance of the method to no less than 0.2 gal/h, 

• allowed two or more tests to be averaged together to improve performance, and 

• limited how the threshold used to declare a leak could be set. 

The new evaluation procedure increased the ranged of USTs for which the evaluation was valid 

from 150% of the surface area of the product in the tank to 250% of the product surface area of 

the tank. This had significant positive ramifications. This meant that if an evaluation was 

performed in a tank with a diameter of 88 ft or greater, the leak detection system could be used to 
66

test all of the tanks owned and operated by DoD without having to be reevaluated. Before this 

change, the same system would have had to be evaluated a total of three times to cover the range 

of bulk USTs owned by DoD. Since the number of tanks is limited to 300, vendors would not 

have found it cost effective to have the evaluations conducted and a large number of DoD tanks 

would go untested and be out of regulatory compliance. The NFESC team provided analysis and 

technical arguments to support this increase to 250%. 

The new evaluation procedure acknowledged that the volume of product in the tank does not 

affect the result of a leak detection test with a mass-measurement system. Rather, the 

performance was affected by the surface area of the product in the tank. This was important, 

because, previously, the applicability of the evaluation was determined from the volume of 

product in the tank. This was also important, because, at the time, the NWGLDE was considering 

the option of scaling the performance of the evaluated method so that it could be used to test 

smaller and larger tanks than the one used in the evaluation. The NFESC team was the first group 

to make this argument with the regulators and provided experiment evidence, theory, and analyses 

to support this premise. 

The new evaluation procedure allowed the performance of the evaluated method to scale with the 

product surface area of the tank, provided that the target leak rate of the scaled performance was 

not less than 0.2 gal/h. Thus, any tank that had a product surface area that resulted in a scaled 

target leak rate less than 0.2 gal/h would be tested at 0.2 gal/h. There was no upper bound on 

performance except that the largest tank for which the evaluation was applicable was set at 250% 

of the product surface area of the tank used in the evaluation. The NFESC team provided 

experiment evidence, theory, and analyses to support this performance scaling. 

The new evaluation procedure acknowledged that averaging test results would increase 

performance for methods whose results were random, additive, and independent, and accepted the 

approach for computing the performance without having to be reevaluated. The NFESC team 

played the primary role in advancing this methodology. Its acceptance meant that a mass-based 

measurement system could be used for both monthly monitoring and annual precision testing for 

high performing systems, even if the tank being tested is too large for the method to meet the 0.2-

gal/h target leak rate criterion in a single test. 

The new evaluation procedure also established limitations on how some of the methods could be 

used. For small USTs found at service stations, the threshold of the leak detection system was 

selected to operate with at the MDLR = 0.2 gal/h (i.e., PD = 95% for a TLR = 0.2 gal/h and a PFA

= 5%), or with a threshold that was set so that the PD = 95% for a TLR = 0.2 gal/h and the PFA < 

5%. The performance of the LRDP was deemed to be too good by the NWGLDE to operate in 

this latter manner, because the threshold that would be used to detect a leak rate of 2 gal/h with a 

PD = 95% would be 1.9 gal/h. The regulators were afraid that smaller leaks would go undetected 

using such a threshold and limited the target leak rate to no larger than twice the MDLR. 

Practically, this prevented the LRDP from using the 3 gal/h monitoring standard in California, 

because its performance was too good, but allowed poor or marginal methods to use this standard. 

This NWGLDE-imposed usage limitation is unfortunate because it did not allow the LRDP to be 

operated as it was originally intended. It is also the reason that Versions 1.0, 1.1, and 1.2 exist. 

The performance of the LRDP is sufficiently good, however, that this regulatory limit does not 
67

impact its use. The NWGLDE also felt that the use of this approach for selecting a threshold 

would be confusing to tank owners because the PFA would change for every tank size tested 

(even though the PFA was always less than 5%). They agreed that a threshold could be selected 

that was less than 5% provided that the target leak rate would scale with tank size. The 

NWGLDE developed a table to show examples of the performance of the method when testing 

different size tanks. This table was added to the standard results form of the third-party 

evaluation. 

In addition to the changes to the evaluation protocol, the NFESC team helped developed two 

California leak detection standards for bulk USTs. In 1998, California developed a number of 

regulatory leak detection guidelines for the owners and operators of bulk USTs. The original 

guidelines were based on the target leak rates (0.1 and 0.2 gal/h) being used for 10,000-gal USTs 

at service stations. For monthly monitoring purposes, California developed a target leak rate of 1 

to 2 gal/h and 2 to 3 gal/h to accommodate the performance of the one evaluated mass-based leak 

detection system, provided that a 0.1-gal/h precision (tightness) test be conducted annually or biannually by another method. There were several problems with this approach. First, the 

guidelines do not acknowledge the differences between the small USTs found at service stations 

and the large infrastructure USTs found at bulk fueling facilities. Second, the emphasis on the 

use of a target leak rate of 0.1-gal/h was misguided, because even at service stations, this standard 

is difficult to meet. The NFESC team proposed that several guidelines be developed that replace 

the annual precision test at 0.1 gal/h with an annual precision test at 0.2 gal/h. This is significant, 

because a high performance mass-based leak detection system, like the LRDP, can be operated at 

0.2-gal/h. The two guidelines presented in Table 1 (options 7 and 10) were the result of the 

interactions. 

 

Finally, before the first evaluation was conducted, the NFESC team had several meeting with the 

NWGLDE and the California regulators to inform them of the evaluation procedure and to insure 

that the procedure being followed was acceptable. The evaluation procedure and reporting 

procedure followed at Point Loma is identical to that approved by the NWGLDE and various state 

regulatory agencies for the first evaluation. 

The NFESC team has worked closely with the NWGLDE and the state regulators to insure that 

the DEM/VALs conducted to evaluate the performance of the LRDP would be acceptable. This 

interaction has also played a very significant role in the acceptance of the LRDP, development of 

new ways to use bulk UST leak detection systems, development of better ways of evaluating and 

reporting the results of a third-party evaluation, and development of regulatory guidelines. 
68

8.0 Technology Implementation 

8.1 DoD Need

As stated in the introduction, the DoD owns and/or operates almost all of the bulk USTs in the 

United States. While the leak detection requirements for bulk USTs (i.e., field erected USTs) 

were deferred in EPA’s UST regulation issued on 22 September 1988, many of the states have or 

are in the process of requiring testing of such tanks. California has developed a set of regulatory 

guidelines for testing bulk USTs. Other states, like New York, Michigan, Maine, and Florida also 

require bulk USTs to be tested. The requirement for testing may cost many tens to hundreds of 

millions of dollars, depending on the testing approach used. The use of the LRDP, because of its 

ability to address the monthly monitoring and the annual precision testing with the same system, 

can realize significant cost savings for the DoD. 

8.2 Transition

The LRDP is ready for commercialization. The drawings, specifications, and software screens 

are described in Appendices C and D. A workshop was conducted by the Environmental 

Technology Evaluation Center (EvTEC) of the Civil Engineering Research Foundation (CERF) 

with representatives present from the petroleum industry, the Defense Energy Support Center 

(DESC), the U. S. Air Force, Army, and Navy, and technical experts to introduce the technology 

and to describe the advantages of the system for regulatory compliance [27]. The LRDP was also 

submitted for an R&D 100 award. 

The LRDP already has regulatory approval, and the evaluation conducted as a DEM/VAL at Point 

Loma has been submitted for approval by the NWGLDE in April 2001. Since this submittal 

parallels the previous submittal, no significant technical acceptance problems are anticipated. As 

of this publication date, the third-party evaluation is still under review by the NWGLDE. If the 

LRDP is used to test 50,000-gal USTs or tanks with curved walls for regulatory compliance, 

another third-party evaluation will have to be conducted. 

Vista Research has commercialized the LRDP. Product description and specification sheets are 

included in Appendix C. Immediate commercialization of this technology has been possible, 

because industry was involved during the demonstrations and the bulk storage tank facilities had a 

real need to be in regulatory compliance. 
69

9.0 Lessons Learned

Generally, the demonstrations of the LRDP at the three sites went smoothly. It is 

important that the site selected for the demonstration will be adequate for demonstration 

and validation and that the owners and/or operators of the site are interested in 

participating in and the outcome of the demonstration, because of the time and effort 

required to conduct a DEM/VAL. The LRDP teams received excellent support at all 

three sites. 

One problem was encountered during the demonstrations that is specific to the 

performance evaluations of in-tank leak detection systems. The third-party evaluation 

was originally scheduled to be conducted at the San Pedro Fuel Farm. The valves on the 

bulk UST selected for the evaluation at the San Pedro fuel farm did not completely seal. 

This allowed a very small flow (~ 0.1 gal/h) to occur. Such flows are too small to 

interfere with monthly monitoring tests that might be conducted on a tank, because the 

monitoring standards require that the threshold be set to detect the much larger leaks of 1 

or 2 gal/h, and the performance of the LRDP is easily capable of detecting such leaks. 

However, this problem could have had significant impact on the conduct of a precision 

test in which the leak to be detected is of similar magnitude. For the conduct of the 

annual precision test, the valves might need to be sealed more tightly or replaced with 

new valves, or valve blinds may need to be installed. 

The EPA standard test procedures require that the tank used in the evaluation be free of 

leaks and that no inflows or outflows occur during the evaluation. Unfortunately, the 

LRDP is the only system that could identify such small flows. The problem was 

identified and verified after a few tests during the checkout of the LRDP at San Pedro, 

but the problem could not be corrected in a timely manner. As a consequence, the 

evaluation was performed on a bulk UST at the Point Loma Fuel Terminal. New double 

block and bleed valve, which sealed tightly, had just been installed on the tanks in the 

fuel farm. 

It was important to conduct the evaluation on a tight tank, because in the previous 

evaluation conducted at North Island, small inflows were present, but even though they 

were identified and quantified, the NWGLDE imposed unrealistic constraints on the use 

of the method in their listing [5]. These constraints included requiring a much longer 

waiting period (24 h vice 2 h) and the suggestion of a system bias (due to a non-zero 

mean) even though none existed. The former was due to a data quality index preventing 

the start of the test until in the inflow, which took about 24 h to become small enough to 

be negligible, ceased. The latter had the potential for increasing the threshold, which 

would have result in declaring a leak when none was present during the conduct of an 

annual precision test at 0.2 gal/h. 
70

The magnitude of this valve problem is not known for bulk tanks, but it is the same 

problem encountered and successfully addressed for routine monitoring of underground 

storage tanks at service stations. 

Unlike many other environmental technologies, the LRDP and the DEM/VAL procedure 

is not site specific or geology dependent. The EPA evaluation procedure is designed to 

accommodate a wide range of conditions that might be encountered during actual leak 

detection tests at or other bulk fuel farms. The procedure places a constraint on the use of 

the equipment based on the conditions used in the evaluation. These constraints involve 

temperature conditions and tank size. Fifteen years of experience indicates that once a 

leak detection method is evaluated following an EPA standard test procedure, it can be 

used to test any tank. 
71

10.0 Summary

A reliable, flexible, easy-to-use, and cost-effective system for leak detection and 

inventory control has been demonstrated and validated for bulk USTs. The novel design 

of the LRDP allows off-the-shelf, commercially available process-control pressure 

sensors, which have a long-term demonstrated track record of performance, to be used. 

Delicate, expensive, one-of-a-kind, or special sensors are not required. The LRDP is a 

fully automatic, computer-controlled system that can easily integrated with FAS or other 

fuel management systems. The LRDP has been evaluated for performance for bulk USTs 

with vertical walls following the standard test procedures developed by the EPA and 

approved by the National Work Group on Leak Detection Evaluations. The performance 

of the LRDP exceeds regulatory requirements for leak detection and is currently on the 

listing of the National Work Group for Leak Detection Evaluations. The results obtained 

on this ESTCP project have been submitted as an update to these results. Precision leak 

detection tests at 0.2-gal/h can be completed in 10 h for tanks with diameters less than 90 

ft and in 24 h for larger tanks. Monthly monitoring tests at 1 or 2 gal/h can be 

accomplished with 10-h tests. 

The DEM/VAL conducted in a 50,000-gal UST indicates that the LRDP has the 

performance to meet the 0.2-gal/h monthly monitoring requirements in EPA’s UST 

regulations. If the LRDP is used to test these USTs, then a third-party evaluation will 

have to be conducted. 

With some simple modifications, the LRDP should be able to test aboveground storage 

tanks for leaks with a performance that is similar to that obtained for bulk USTs. These 

modifications must address the effect of the large diurnal swings in ambient air 

temperature that occurs during a test. 

The LRDP is ready for commercial use as a permanently installed system for monitoring, 

or a portable system for use in a testing service. Vista Research, Inc., has 

commercialized the system. 

 
72

11.0 References

1. J. W. Maresca, Jr. and J. W. Starr. “The LRDP System for Detection of Leaks in Bulk 

Storage Tanks.” Final Report, prepared for the Naval Facilities Engineering Service 

Center, 110023rd Avenue, Port Hueneme, CA 93043-4370, prepared by Vista 

Research, Inc., 100 View Street, Mountain View, CA 94042, 25 March 1998. 

2. W. Major, L. Karr, G. Warren, and J. Norbutas. “Red Hill Fuel Tank Leak Detection.” 

Proceedings of the Seventh (1997) International Offshore and Polar Engineering 

Conference, Honolulu, Hawaii, Naval Facilities Engineering Service Center, Port 

Hueneme, California, 25-30 May 1997. 

3. U.S. Environmental Protection Agency. “40 CFR 280 - Technical Standards and 

Corrective Action Requirements for Owners and Operators of Underground Storage 

Tanks.” Federal Register, Vol. 53, No. 185, 23 September 1988. 

4. California Water Resources Control Board. “Local Guidance Letters LG 151-2.” 22 

October 1999. 

5. National Work Group on Evaluation of Leak Detection Methods. “List of Leak 

Detection Evaluations for Underground Storage Tank Systems.” Office of 

Underground Storage Tanks, U.S. Environmental Protection Agency, 7th Edition, April 

2000. 

6. U.S. Environmental Protection Agency. “Alternative Test Procedures for Evaluating 

Leak Detection Methods: Evaluation of Bulk Field Constructed Tanks.” Region VII, 

Memorandum, March 1996. 

7. American Society of Testing Materials. “Standard Practice for Evaluating the 

Performance of Release Detection Systems for Underground Storage Tank Systems 

(ASTM E 1526 - 93).” in Annual Book of ASTM Standards (Philadelphia: American 

Society of Testing and Materials, May 1993. 

8. J. K. Wilcox. “Evaluation of the LRDP-10 on Bulk Field-Constructed Tanks: Final 

Report.” Third-Party Evaluation Report, prepared for the Naval Facilities Engineering 

Service Center and Vista Research, Inc., prepared by Ken Wilcox Associates, Inc., 

1125 Valley Ridge Drive, Grain Valley, MO 64029, 4 December 2000. 

9. J. K. Wilcox. “Evaluation of the LRDP-10 on Bulk Field-Constructed Tanks: EPA 

Forms.” Third-Party Evaluation EPA Forms, prepared for the Naval Facilities 

Engineering Service Center and Vista Research, Inc., prepared by Ken Wilcox 

Associates, Inc., 1125 Valley Ridge Drive, Grain Valley, MO 64029, 4 December 

2000. 
73

10. J. K. Wilcox. “Evaluation Update of the LRDP-24 on Bulk Field-Constructed Tanks: 

Final Report.” Third-Party Evaluation Report, prepared for the Naval Facilities 

Engineering Service Center and Vista Research, Inc., prepared by Ken Wilcox 

Associates, Inc., 1125 Valley Ridge Drive, Grain Valley, MO 64029, 4 December 

2000. 

11. J. K. Wilcox. “Evaluation Update of the LRDP-24 on Bulk Field-Constructed Tanks: 

EPA Forms.” Third-Party Evaluation EPA Forms, prepared for the Naval Facilities 

Engineering Service Center and Vista Research, Inc., prepared by Ken Wilcox 

Associates, Inc., 1125 Valley Ridge Drive, Grain Valley, MO 64029, 4 December 

2000. 

12. J. K. Wilcox. “Evaluation of the LRDP-10-n Bulk Field-Constructed Tanks: Final 

Report.” Third-Party Evaluation Report, prepared for the Naval Facilities Engineering 

Service Center and Vista Research, Inc., prepared by Ken Wilcox Associates, Inc., 

1125 Valley Ridge Drive, Grain Valley, MO 64029, 4 December 2000. 

13. J. K. Wilcox. “Evaluation of the LRDP-10-n Bulk Field-Constructed Tanks: EPA 

Forms.” Third-Party Evaluation EPA Forms, prepared for the Naval Facilities 

Engineering Service Center and Vista Research, Inc., prepared by Ken Wilcox 

Associates, Inc., 1125 Valley Ridge Drive, Grain Valley, MO 64029, 4 December 

2000. 

14. J. K. Wilcox. “Evaluation Update of the LRDP-24-n on Bulk Field-Constructed 

Tanks: Final Report.” Third-Party Evaluation Report, prepared for the Naval Facilities 

Engineering Service Center and Vista Research, Inc., prepared by Ken Wilcox 

Associates, Inc., 1125 Valley Ridge Drive, Grain Valley, MO 64029, 4 December 

2000. 

15. J. K. Wilcox. “Evaluation Update of the LRDP-24-n on Bulk Field-Constructed 

Tanks: EPA Forms.” Third-Party Evaluation EPA Forms, prepared for the Naval 

Facilities Engineering Service Center and Vista Research, Inc., prepared by Ken 

Wilcox Associates, Inc., 1125 Valley Ridge Drive, Grain Valley, MO 64029, 4 

December 2000. 

16. L. A. Karr, W. R. Major, J. W. Maresca, Jr., M. J. Talhami, J. W. Starr, and R. F. 

Wise. “Pre-Production Initiative: Low Range Differential Pressure (LRDP) Leak 

Detection System - Red Hill Test Results.” Final Report. Naval Facilities Engineering 

Service Center, 1100 23rd Avenue, Port Hueneme, California 93043-4370 and Vista 

Engineering Technologies, L.L.C., 8203 W. Quinault, Kennewick, Washington 

99336, 31 July 2001. 

17. J. W. Maresca, Jr., “System and Method for Leak Detection in Liquid Storage Tanks.” 

U. S. Patent No. 4,646,560, Vista Research, Inc., Palo Alto, California, 3 March 1987. 
74

18. W. R. Major, L. A. Karr, G. A. Hayter, and J. W. Maresca, Jr. “ESTCP Technology 

Demonstration Plan: Validation of the Low Range Differential Pressure (LRDP) Leak 

Detection System for Small Leaks in Bulk Fuel Tanks.” Naval Facilities Engineering 

Service Center, Port Hueneme, California, 18 July 1988. 

19. J. K. Wilcox. “Evaluation of the LRDP-24 on Bulk Field-Constructed Tanks: Final 

Report.” Third-Party Evaluation Report, prepared for the Naval Facilities Engineering 

Service Center and Vista Research, Inc., prepared by Ken Wilcox Associates, Inc., 

1125 Valley Ridge Drive, Grain Valley, MO 64029, 29 January 1998. 

20. J. K. Wilcox. “Evaluation of the LRDP-24 on Bulk Field-Constructed Tanks: EPA 

Forms.” Third-Party Evaluation EPA Forms, prepared for the Naval Facilities 

Engineering Service Center and Vista Research, Inc., prepared by Ken Wilcox 

Associates, Inc., 1125 Valley Ridge Drive, Grain Valley, MO 64029, 29 January 1998. 

21. J. K. Wilcox. “Evaluation of the LRDP-48 on Bulk Field-Constructed Tanks: Final 

Report.” Third-Party Evaluation Report, prepared for the Naval Facilities Engineering 

Service Center and Vista Research, Inc., prepared by Ken Wilcox Associates, Inc., 

1125 Valley Ridge Drive, Grain Valley, MO 64029, 29 January 1998. 

22. J. K. Wilcox. “Evaluation of the LRDP-48 on Bulk Field-Constructed Tanks: EPA 

Forms.” Third-Party Evaluation EPA Forms, prepared for the Naval Facilities 

Engineering Service Center and Vista Research, Inc., prepared by Ken Wilcox 

Associates, Inc., 1125 Valley Ridge Drive, Grain Valley, MO 64029,29 January 1998. 

23. J. K. Wilcox. “Evaluation of the LRDP-24-5 on Bulk Field-Constructed Tanks: Final 

Report.” Third-Party Evaluation Report, prepared for the Naval Facilities Engineering 

Service Center and Vista Research, Inc., prepared by Ken Wilcox Associates, Inc., 

1125 Valley Ridge Drive, Grain Valley, MO 64029, 29 January 1998. 

24. J. K. Wilcox. “Evaluation of the LRDP-24-5 on Bulk Field-Constructed Tanks: EPA 

Forms.” Third-Party Evaluation EPA Forms, prepared for the Naval Facilities 

Engineering Service Center and Vista Research, Inc., prepared by Ken Wilcox 

Associates, Inc., 1125 Valley Ridge Drive, Grain Valley, MO 64029, 29 January 1998. 

25. J. K. Wilcox. “Evaluation of the LRDP-48-4 on Bulk Field-Constructed Tanks: Final 

Report.” Third-Party Evaluation Report, prepared for the Naval Facilities Engineering 

Service Center and Vista Research, Inc., prepared by Ken Wilcox Associates, Inc., 

1125 Valley Ridge Drive, Grain Valley, MO 64029, 29 January 1998. 

26. J. K. Wilcox. “Evaluation of the LRDP-48-4 on Bulk Field-Constructed Tanks: EPA 

Forms.” Third-Party Evaluation EPA Forms, prepared for the Naval Facilities 

Engineering Service Center and Vista Research, Inc., prepared by Ken Wilcox 

Associates, Inc., 1125 Valley Ridge Drive, Grain Valley, MO 64029, 29 January 1998. 

27. Environmental Technology Evaluation Center (EvTEC). “Low Range Differential 

Pressure (LRDP) Leak Detection System Workshop Report.” Workshop Report. 
75

Environmental Technology Evaluation Center (EvTEC), 1015 15th Street, Suite 600, 

Washington D.C. 20005-2605, June 2000. 
A-1

Appendix A

Points of Contact 

Point of Contact Organization Phone/Fax/Email Role in Project 

Leslie A. Karr, REM 

Program Manager 

Naval Facilities Engineering 

Service Center (NFESC) 

1100 23rd Avenue 

Port Hueneme, CA 93043-4370 

voice: (805) 982-1618 

fax: (805) 982-4304 

e-mail: karrla@nfesc.navy.mil 

Project Manager 

William R. Major 

Project Engineer 

Naval Facilities Engineering 

Service Center (NFESC) 

1100 23rd Avenue 

Port Hueneme, CA 93043-4370 

voice: (805) 982-1808 

fax: (805) 982-4304 

e-mail: majorwr@nfesc.navy.mil 

Project Engineer 

Dr. Vincent F. Hock 

Program Manager 

U. S. Army Corps of Engineers 

Construction Engineering Research 

Laboratory (CERL) 

2902 Nemark Drive 

Champaign, Illinois 61826 

Voice: (217)373-6753 

fax: (217)373-6732 

e-mail: v-hock@cecer.army.mil 

Project Engineer 

Dr. Joseph W. Maresca, Jr. 

Vice President 

Vista Research, Inc. 

755 North Mary Avenue 

Sunnyvale, California 94086

voice: (408) 830-3306 

fax: (408) 830-3399 

e-mail: maresca@vrinc.com

Technical 

Director, Industry 

Partner

James W. Starr, P. E. 

Staff Engineer 

Vista Research, Inc. 

139 Glendale Avenue 

Edison, New Jersey 08817

Voice: (732) 777-2100 

Fax: (732) 777-9495 

e-mail: jstarr@vrinc.com

Project Engineer 

Gary A. Hayter 

Sr. Research Engr

Vista Research, Inc. 

755 North Mary Avenue 

Sunnyvale, California 94086

voice: (408) 830-3300; 

fax: (408) 830-3399 

e-mail: ghayter@vrinc.com

Project Engineer 

Dr. H. Kendall Wilcox 

President

Ken Wilcox Associates, Inc. 

1125 Valley Ridge Drive 

Grain Valley, MO 64029, USA

voice: (816) 443-2494 

fax: (816) 443-2495 

e-mail: kwilcox@kwaleak.com

Third-Party 

Evaluator

Col Patrick L. Fink 

U. S. Air Force 

Randolph Air Force Base 

San Antonio, TX

voice: (210) 652-6375 DEM/VAL 

Liaison 

George E. Cook, III 

Director, Fuel Farm

Supply Department Code 199, 

Building 426 

NAS North Island 

P. O. Box 357039 

San Diego, CA 92135-7039

Voice: (619) 545-8841 

fax: (619) 545-8841

DEM/VAL 

Liaison

Clarence Wilson 

Director, Fuel Farm

Defense Energy Office, Los 

Angeles 

3171 North Gaffey Street 

San Pedro, CA 90731-1099

voice: (310) 335-3090 ext. 404 

fax: (310) 335-

DEM/VAL 

Liaison

LCDR R. C. Griffin, SC, 

USN 

Point Loma Site Director

FISC San Diego 

Point Loma Fuel Terminal 

937 N. Harbor Drive, STE 480 

San Diego, CA 92132-0480

voice: (619) 553-1312 

fax: (619) 553-4877 

e-mail: 

Rowdy_Griffin@sd.fisc.navy.mil

DEM/VAL 

Liaison

Stephen L. Frey 

Fuels Terminal Director

FISC San Diego 

Point Loma Fuel Terminal 

937 N. Harbor Drive, STE 480, 

Code 701 

San Diego, CA 92132-0480

voice: (619) 553-1314 

fax: (619) 553-4877 

e-mail: 

Stephen_L_Frey@sd.fisc.navy.mil

DEM/VAL 

Liaison 

Dale Kiefer 

Environmental Division 

Head

Hunter Army Airfield 

Ft Stewart, GA 31314

voice: 912-767-2010 DEM/VAL 

Liaison 

Terry Nierenhausen Hunter Army Air Field 

98 South Middleground Road, 

Building 1216 

Savannah, GA 31409

voice: (912) 352-5535 DEM/VAL 

Liaison 
A-2

William Middleton Defense Energy Office – Los 

Angeles 

Defense Energy Supply Center 

(DESC) 

John J. Kingman Road, Suite 4950 

Fort Belvoir, VA22060-6222

voice: (702) 767-8313 

fax: (703) 767-8331 

e-mail: wmiddleton@desc.dla.mil 

DEM/VAL 

Liaison 

Brian Rustia EvTEC 

1015 15th Street, NW, Suite 600 

Washington D.C. 20005-2605 

voice: (202) 842-0555 

fax: (202) 842-2605 

CERF Workshop 

Heather Warkentien EvTEC 

1015 15th Street, NW, Suite 600 

Washington D.C. 20005-2605 

voice: (202) 842-0555 

fax: (202) 842-2605 

CERF Workshop 

Russ Brauksieck 

New York DEC

New York State Department of 

Environmental Conservation 

50 Wolf Road, Room 360 

Albany, NY 12233-3750

voice: (518) 457-4351 

fax: (518) 457-4332 

e-mail: 

rxbrauks@gw.dec.state.ny.us

NWGLDE, 

Chairman Bulk 

USTs, 

New York 

Regulator 

Beth DeHaas 

Maine DEP

Maine Department of 

Environmental Protection 

Statehouse Station No. 17 

Augusta, ME 04333

voice: (207) 287-2651 

fax: (207) 287-7826 

e-mail: beth.dehaas@state.me.us

NWGLDE, Bulk 

USTs, 

Maine Regulator 

Shahla Farahnak 

California SWRCB

California State Water Resource 

Board 

Division of Clean Water Program 

P. O. Box 944212 

Sacramento, CA 94244-2120

voice: (916) 227-4320 

fax: (916) 227-4349 

e-mail: 

farahnas@gwgate.swrcb.epa.gov

NWGLDE, Bulk 

USTs, 

California 

Regulator 

John Reeder 

Florida DEP

Florida Department of 

Environmental Protection 

3804 Coconut Palm Drive 

Tampa, FL 33619-8318

voice: (813) 744-6100 ext. 472 

fax: (813) 744-6125 

e-mail: jon.reeder@dep.state.fl.us

NWGLDE, 

Florida Regulator 

John Kneece 

South Carolina DHEC

South Carolina Department of 

Health and Environmental Control 

2600 Bull Street 

Columbia, SC 29201

voice: (803) 898-4364 

fax: (803) 898-4330 

e-mail: 

kneeceje@colum26.dhec.state.sc.us 

NWGLDE, South 

Carolina Regulator

Curt D. Johnson 

Alabama DEM

Alabama Department of 

Environmental Management 

P. O. Box 301463 

Montgomery, AL 36130-1463

voice: (334) 271-7986 

fax: (334) 270-5631 

e-mail: cdj@adem.state.al.us

NWGLDE, 

Chairman, 

Alabama 

Regulator
Appendix B 

 Listings for the LRDP-10 and 

the Update for the LRDP-24 

Submitted to the 

National Work Group on 

Leak Detection Evaluations (NWGLDE)
B-2

Revision Date: December 4, 2000

Vista Research, Inc. and Naval Facilities Engineering Service Center 

LRDP-24 (V1.0a.1.65,V1.0a.2.40) 

BULK FIELD-CONSTRUCTED AUTOMATIC TANK GAUGE MONITORING 

AND TIGHTNESS TEST LEAK DETECTION METHOD 

Certification: Leak rate is proportional to product surface area (PSA). 

 For tanks with PSA of 11,786 ft2, leak rate is 1.65 or 2.40 gph with PD = 95% and PFA = 0.0015% or PFA < 

0.001%, respectively. Choose one to determine the scaled leak rate and scaled leak threshold for the tank 

being monitored. 

 For other tank sizes, scaled leak rate equals [(PSA in ft2 ÷ 11,786 ft2) x (leak rate in gph)]. 

 Example: For a tank with PSA = 10,000 ft2, leak rate = 1.65 gph; scaled leak rate = [(10,000 ft2 ÷ 11,786 

ft2) x 1.65 gph] = 1.40 gph. 

 Calculated minimum detectable leak rate is 0.690 gph with PD = 95% and PFA = 5%. 

Leak rate may not be scaled below 0.2 gph.

 

Leak Threshold: Leak threshold is proportional to product surface area (PSA). 

 For tanks with PSA of 11,786 ft2 and leak rate of 1.65 or 2.40 gph, leak threshold is 1.31 or 2.06 gph 

respectively. 

 For other tank sizes, scaled leak threshold equals [(PSA in ft2 ÷ 11,786 ft2) x (leak rate in gph - 0.345 gph)]. 

 Example: For a tank with PSA = 10,000 ft2, leak rate = 1.65 gph; scaled leak threshold = [(10,000 ft2 ÷ 

11,786 ft2) x (1.65 gph - 0.345 gph)] = 1.40 gph. 

 A tank system should not be declared tight if the test result indicates a loss or gain that equals or exceeds the 

calculated leak threshold. 

Applicability: Gasoline, diesel, aviation fuel. 

Other liquids may be tested after consultation with the manufacturer. 

Tank Capacity: Use limited to single field-constructed vertical tanks larger than 50,000 gallons. 

 Maximum product surface area (PSA) is 29,465 ft2 (approximately 193.7 ft. diameter). 

 Performance not sensitive to product level. 

Waiting Time: Minimum of 2 hours after delivery or dispensing. 

Valve leaks and pump drain-back may mask a leak. Allow sufficient waiting time to minimize these effects. 

 Waiting times during evaluation ranged from 0 to 3 hours. 

Test Period: Minimum of 24 hours. 

 There must be no dispensing or delivery during test. 

Temperature: Measurement not required by this system. 

Water Sensor: None. Water leaks are measured as increase in mass inside tank. 

Calibration: Differential pressure sensor must be checked regularly in accordance with manufacturer's instructions. 

Comments: Tests only portion of tank containing product. 

 As product level is lowered, leak rate in a leaking tank decreases (due to lower head pressure). Consistent 

testing at low levels could allow a leak to remain undetected. 

 Evaluated in a nominal 2,100,000 gallon, vertical underground tank with product surface area (PSA) of 

11,786 ft2. 

 Evaluated as a stand-alone system. 

 Performance of the system can be improved by combining results of 2 or more tests. If this option is used, it 

is important to determine the number of tests, their timing and the number of passing results necessary to 

confirm a tank is tight. The LRDP-24-n (V1.0a, V1.1a, V1.2a) combines the results of n tests, where n < 12 

and is one evaluated option to improve the performance of this system. 

Vista Research, Inc. Evaluator: Ken Wilcox Associates 

100 View St. Tel: (816) 443-2494 

Mountain View, CA 94042 Date of Evaluation: 01/29/99 

Tel: (650) 966-1171 
B-3

Revision Date: December 4, 2000

Vista Research, Inc. and Naval Facilities Engineering Service Center 

LRDP-10 (V1.0a.1.90,V1.0a.2.40) 

BULK FIELD-CONSTRUCTED AUTOMATIC TANK GAUGE MONITORING 

AND TIGHTNESS TEST LEAK DETECTION METHOD 

Certification: Leak rate is proportional to product surface area (PSA). 

 For tanks with PSA of 11,786 ft2, leak rate is 1.90 or 2.40 gph with PD = 95% and PFA = 0.075% or 0.006%, 

respectively. Choose one to determine the scaled leak rate and scaled leak threshold for the tank being 

monitored. 

 For other tank sizes, scaled leak rate equals [(PSA in ft2 ÷ 11,786 ft2) x (leak rate in gph)]. 

 Example: For a tank with PSA = 10,000 ft2, leak rate = 1.90 gph; scaled leak rate = [(10,000 ft2 ÷ 11,786 

ft2) x 1.90 gph] = 1.61 gph. 

 Calculated minimum detectable leak rate is 1.14 gph with PD = 95% and PFA = 5%. 

Leak rate may not be scaled below 0.2 gph.

 

Leak Threshold: Leak threshold is proportional to product surface area (PSA). 

 For tanks with PSA of 11,786 ft2 and leak rate of 1.90 or 2.40 gph, leak threshold is 1.33 or 1.83 gph 

respectively. 

 For other tank sizes, scaled leak threshold equals [(PSA in ft2 ÷ 11,786 ft2) x (leak rate in gph - 0.569 gph)]. 

 Example: For a tank with PSA = 10,000 ft2, leak rate = 1.90 gph; scaled leak threshold = [(10,000 ft2 ÷ 

11,786 ft2) x (1.90 gph - 0.569 gph)] = 1.13 gph. 

 A tank system should not be declared tight if the test result indicates a loss or gain that equals or exceeds the 

calculated leak threshold. 

Applicability: Gasoline, diesel, aviation fuel. 

Other liquids may be tested after consultation with the manufacturer. 

Tank Capacity: Use limited to single field-constructed vertical tanks larger than 50,000 gallons. 

 Maximum product surface area (PSA) is 29,465 ft2 (approximately 193.7 ft. diameter). 

 Performance not sensitive to product level. 

Waiting Time: Minimum of 2 hours after delivery or dispensing. 

Valve leaks and pump drain-back may mask a leak. Allow sufficient waiting time to minimize these effects. 

 Waiting times during evaluation ranged from 0 to 3 hours, with one at 7 hours and another at 10 hours. 

Test Period: Minimum of 10 hours. 

 There must be no dispensing or delivery during test. 

Temperature: Measurement not required by this system. 

Water Sensor: None. Water leaks are measured as increase in mass inside tank. 

Calibration: Differential pressure sensor must be checked regularly in accordance with manufacturer's instructions. 

Comments: Tests only portion of tank containing product. 

 As product level is lowered, leak rate in a leaking tank decreases (due to lower head pressure). Consistent 

testing at low levels could allow a leak to remain undetected. 

 Evaluated in a nominal 2,100,000 gallon, vertical underground tank with product surface area (PSA) of 

11,786 ft2. 

 Evaluated as a stand-alone system. 

 Performance of the system can be improved by combining results of 2 or more tests. If this option is used, it 

is important to determine the number of tests, their timing and the number of passing results necessary to 

confirm a tank is tight. The LRDP-10-n (V1.0a, V1.1a, V1.2a) combines the results of n tests, where n < 12 

and is one evaluated option to improve the performance of this system. 

Vista Research, Inc. Evaluator: Ken Wilcox Associates 

755 North Mary Avenue Tel: (816) 443-2494 

Sunnyvale, CA 94085 Date of Evaluation: 06/07/00 

Tel: (408) 830-3300 
B-4

Revision Date: December 4, 2000

Vista Research, Inc. and Naval Facilities Engineering Service Center 

LRDP-24 (V1.1a) 

BULK FIELD-CONSTRUCTED AUTOMATIC TANK GAUGE MONITORING 

AND TIGHTNESS TEST LEAK DETECTION METHOD 

Certification: Leak rate is proportional to product surface area (PSA). 

 For tanks with PSA of 11,786 ft2, leak rate is 0.95 gph with PD = 95% and PFA =0.48%. 

 For other tank sizes, leak rate equals [(PSA in ft2 ÷ 11,786 ft2) x 0.95 gph]. 

 Example: For a tank with PSA = 10,000 ft2; leak rate = [(10,000 ft2 ÷ 11,786 ft2) x 0.95 gph] = 

 0.81 gph. 

 Calculated minimum detectable leak rate is 0.690 gph with PD = 95% and PFA = 5%. 

Leak rate may not be scaled below 0.2 gph.

 

Leak Threshold: Leak threshold is proportional to product surface area (PSA). 

 For tanks with PSA of 11,786 ft2, leak threshold is 0.60 gph. 

 For other tank sizes, leak threshold equals [(PSA in ft2 ÷ 11,786 ft2) x 0.60 gph]. 

 Example: For a tank with PSA = 10,000 ft2; leak threshold = [(10,000 ft2 ÷ 11,786 ft2) x 0.60 gph] = 0.51 gph. 

 A tank system should not be declared tight if the test result indicates a loss or gain that equals or exceeds the 

calculated leak threshold. 

Applicability: Gasoline, diesel, aviation fuel. 

Other liquids may be tested after consultation with the manufacturer. 

Tank Capacity: Use limited to single field-constructed vertical tanks larger than 50,000 gallons. 

 Maximum product surface area (PSA) is 29,465 ft2 (approximately 193.7 ft. diameter). 

 Performance not sensitive to product level. 

Waiting Time: Minimum of 2 hours after delivery or dispensing. 

Valve leaks and pump drain-back may mask a leak. Allow sufficient waiting time to minimize these effects. 

 Waiting times during evaluation ranged from 0 to 3 hours. 

Test Period: Minimum of 24 hours. 

 There must be no dispensing or delivery during test. 

Temperature: Measurement not required by this system. 

Water Sensor: None. Water leaks are measured as increase in mass inside tank. 

Calibration: Differential pressure sensor must be checked regularly in accordance with manufacturer's instructions. 

Comments: Tests only portion of tank containing product. 

 As product level is lowered, leak rate in a leaking tank decreases (due to lower head pressure). Consistent 

testing at low levels could allow a leak to remain undetected. 

 Evaluated in a nominal 2,100,000 gallon, vertical underground tank with product surface area (PSA) of 

11,786 ft2. 

 Evaluated as a stand-alone system. 

 Performance of the system can be improved by combining results of 2 or more tests. If this option is used, it is 

important to determine the number of tests, their timing and the number of passing results necessary to 

confirm a tank is tight. The LRDP-24-n (V1.0a, V1.1a, V1.2a) combines the results of n tests, where n < 12 

and is one evaluated option to improve the performance of this system. 

Vista Research, Inc. Evaluator: Ken Wilcox Associates 

755 North Mary Avenue Tel: (816) 443-2494 

Sunnyvale, CA 94085 Date of Evaluation: 06/07/00 

Tel: (408) 830-3300 
B-5

Revision Date: December 4, 2000

Vista Research, Inc. and Naval Facilities Engineering Service Center 

LRDP-10 (V1.1a) 

BULK FIELD-CONSTRUCTED AUTOMATIC TANK GAUGE MONITORING 

AND TIGHTNESS TEST LEAK DETECTION METHOD 

Certification: Leak rate is proportional to product surface area (PSA). 

 For tanks with PSA of 11,786 ft2, leak rate is 1.65 gph with PD = 95% and PFA =0.29%. 

 For other tank sizes, leak rate equals [(PSA in ft2 ÷ 11,786 ft2) x 1.65 gph]. 

 Example: For a tank with PSA = 10,000 ft2; leak rate = [(10,000 ft2 ÷ 11,786 ft2) x 1.65 gph] = 

 1.40 gph. 

 Calculated minimum detectable leak rate is 0.690 gph with PD = 95% and PFA = 5%. 

Leak rate may not be scaled below 0.2 gph.

 

Leak Threshold: Leak threshold is proportional to product surface area (PSA). 

 For tanks with PSA of 11,786 ft2, leak threshold is 1.08 gph. 

 For other tank sizes, leak threshold equals [(PSA in ft2 ÷ 11,786 ft2) x 1.08 gph]. 

 Example: For a tank with PSA = 10,000 ft2; leak threshold = [(10,000 ft2 ÷ 11,786 ft2) x 1.08 gph] = 0.92 gph. 

 A tank system should not be declared tight if the test result indicates a loss or gain that equals or exceeds the 

calculated leak threshold. 

Applicability: Gasoline, diesel, aviation fuel. 

Other liquids may be tested after consultation with the manufacturer. 

Tank Capacity: Use limited to single field-constructed vertical tanks larger than 50,000 gallons. 

 Maximum product surface area (PSA) is 29,465 ft2 (approximately 193.7 ft. diameter). 

 Performance not sensitive to product level. 

Waiting Time: Minimum of 2 hours after delivery or dispensing. 

Valve leaks and pump drain-back may mask a leak. Allow sufficient waiting time to minimize these effects. 

 Waiting times during evaluation ranged from 0 to 3 hours, with one at 7 hours and another at 10 hours. 

Test Period: Minimum of 10 hours. 

 There must be no dispensing or delivery during test. 

Temperature: Measurement not required by this system. 

Water Sensor: None. Water leaks are measured as increase in mass inside tank. 

Calibration: Differential pressure sensor must be checked regularly in accordance with manufacturer's instructions. 

Comments: Tests only portion of tank containing product. 

 As product level is lowered, leak rate in a leaking tank decreases (due to lower head pressure). Consistent 

testing at low levels could allow a leak to remain undetected. 

 Evaluated in a nominal 2,100,000 gallon, vertical underground tank with product surface area (PSA) of 

11,786 ft2. 

 Evaluated as a stand-alone system. 

Performance of the system can be improved by combining results of 2 or more tests. If this option is used, it is 

important to determine the number of tests, their timing and the number of passing results necessary to confirm 

a tank is tight. The LRDP-10-n (V1.0a, V1.1a, V1.2a) combines the results of n tests, where n < 12 and is one 

evaluated option to improve the performance of this system. 

Vista Research, Inc. Evaluator: Ken Wilcox Associates 

755 North Mary Avenue Tel: (816) 443-2494 

Sunnyvale, CA 94085 Date of Evaluation: 06/07/00 

Tel: (408) 830-3300 
Appendix C 

Product Description and 

Product Specification Sheets 
VISTA RESEARCH, INC.  755 North Mary Avenue  Sunnyvale, CA 94085  (408) 830-3300

Dimensions 

Diameter of Base Sensor Cylinder 

Height of Base Sensor Cylinder 

Diameter of reference tube 

Height of constant diameter reference tube 

Height of shaped reference tube 

Embedded controller (2 connected units) 

7 13/16 in. (19.9 cm) 

16.0 in. (45.7 cm) 

3 1⁄2 in. (8.9 cm) 

0 to 50 ft (15.2 m) 

0-12 ft (3.7 m); 0-50 ft (15.2 m) 

12 in. x 12 in. x 8 in. (ea. unit) 

(30.5 cm x 45.7 cm x 10.2 cm) 

Weight 

Base Sensor Cylinder (Empty) 

Constant diameter reference tube, 

including conduit 

Shaped reference tube, including conduit 

Embedded controller (2 units) 

35 lbs (16 kg) 

5 lbs/ft (2.3 kg) 

5 lbs/ft (2.3 kg) 

60 lbs (27.3 kg) 

Detectable Leak Rate 

(Probability of detection of 95% 

with a probability of false alarm of 

5%) 

For tank diameters less than 51.3 ft 

For tank diameters (D in ft) up to 193.7 ft 

For tank diameters D = [2,635.0*(n)0.5]

0.5

 (LRDP-10-n) 

0.20 gal/h 

(3.14*(D*0.5)2

/11,786)*1.139 gal/h 

0.20 gal/h (average of 1 < n < 12 tests) 

(Probability of detection of 95% 

with a probability of false alarm of 

0.29%) 

For tank diameters (D in ft) up to 193.7 ft 

For tank diameters D = [1,817.3*(n)0.5]

0.5

 (LRDP-10-n) 

(3.14*(D*0.5)2

/11,786)*1.653 gal/h 

0.20 gal/h (average of 1 < n < 12 tests) 

(Probability of detection of 95% 

with a probability of false alarm of 

<0.15%) 

 For tank diameters (D in ft) up to 193.4 ft 

For tank diameters (D in ft) up to 193.4 ft 

(3.14*(D*0.5)2

/11,786)*(2.0-0.569) gal/h 

(3.14*(D*0.5)2

/11,786)*(3.0-0.569) gal/h 

Power 

In-tank sensor unit, embedded controller, 

interface computer 

Single-phase 120 VAC 60 Hz

Temperature 

Operating -20 o to 100 o F (-29 o to 38o

 C) 

User Interface 

System monitor Vista GUI software 

Windows 95 or FAS software

LRDP-10 

Low Range Differential Pressure System 

Product Data Sheet and 

System Specification 
VISTA RESEARCH, INC.  755 North Mary Avenue  Sunnyvale, CA 94085  (408) 830-3300

Dimensions 

Diameter of Base Sensor Cylinder 

Height of Base Sensor Cylinder 

Diameter of reference tube 

Height of constant diameter reference tube 

Height of shaped reference tube 

Embedded controller (2 connected units) 

7 13/16 in. (19.9 cm) 

16.0 in. (45.7 cm) 

3 1⁄2 in. (8.9 cm) 

0 to 50 ft (15.2 m) 

0-12 ft (3.7 m); 0-50 ft (15.2 m) 

12 in. x 12 in. x 8 in. (ea. unit) 

(30.5 cm x 45.7 cm x 10.2 cm) 

Weight 

Base Sensor Cylinder (Empty) 

Constant diameter reference tube, 

including conduit 

Shaped reference tube, including conduit 

Embedded controller (2 units) 

35 lbs (16 kg) 

5 lbs/ft (2.3 kg) 

5 lbs/ft (2.3 kg) 

60 lbs (27.3 kg) 

Detectable Leak Rate 

(Probability of detection of 95% 

with a probability of false alarm of 

5%) 

For tank diameters less than 66.0 ft 

For tank diameters (D in ft) up to 193.7 ft 

For tank diameters D = [4,349.7*(n)0.5]

0.5

 (LRDP-24-n) 

0.20 gal/h 

(3.14*(D*0.5)2

/11,786)*0.69 gal/h 

0.20 gal/h (average of 1 < n < 12 tests) 

(Probability of detection of 95% 

with a probability of false alarm of 

0.48%) 

For tank diameters (D in ft) up to 193.7 ft 

For tank diameters D = [3,172.4*(n)0.5]

0.5

 (LRDP-24-n) 

(3.14*(D*0.5)2

/11,786)*0.946 gal/h 

0.20 gal/h (average of 1 < n < 12 tests) 

(Probability of detection of 95% 

with a probability of false alarm of 

<0.003%) 

 For tank diameters (D in ft) up to 193.4 ft 

For tank diameters (D in ft) up to 193.4 ft 

(3.14*(D*0.5)2

/11,786)*(2.0-0.345) gal/h 

(3.14*(D*0.5)2

/11,786)*(3.0-0.345) gal/h 

Power 

In-tank sensor unit, embedded controller, 

interface computer 

Single-phase 120 VAC 60 Hz

Temperature 

Operating -20 o to 100 o F (-29 o to 38o

 C) 

User Interface 

System monitor Vista GUI software 

Windows 95 or FAS software

LRDP-24 

Low Range Differential Pressure System 

Product Data Sheet and 

System Specification 
Appendix D 

Software User Interface Screens
D-2

Figure D-1. LRDP Main Menu: display screen allowing the user to conduct a leak 

detection test or to review the results of previous leak detection tests 

Figure D-2. Enter New Test Parameters: display screen allowing the user to use the default testing 

option and test parameters shown on the screen or to enter new test parameters. 
D-3

Figure D-3. Test Initiation: display screen allowing the user to start the test immediately or to 

schedule the start of the test for a later time. 

Figure D-4. Leak Detection Test Preparation: display screen reminding the user that valves need to be 

closed before a test can be conducted. 
D-4

Figure D-5. Leak Detection Test Setup/Monitor Screen: display screen allowing the user to monitor the level 

in real time.

Figure D-6. LRDP Test Results: display screen presenting the results of the leak detection to the user. 
D-5

Figure D-7. Leak Detection Test Archives: display screen allowing the user to review previous test results 

and test data.
Appendix E 

Performance Equations for Version a 

of the LRDP-10, LRDP-24, LRDP-10-n and LRDP-24-n 
E-2

Operation of the Evaluated System 

Version a 

Mass Based Systems (with scaling included) 

Test Threshold *,

** 

Set PD = 95% against a Target Leak Rate > MDL 

to insure PFA < 5% 

Target Leak Rate, 

TLR – gal/h 

TLR > [MDL (A2/A1)] > 0.2 

or 0.2 for 

[(MDL (A2/A1)] < 0.2 

Threshold, 

C – gal/h 

[TLR - CMDL (A2/A1)] > 0.1 or 0.1 for 

[TLR - CMDL (A2/A1)] < 0.1 

PD – % 95% 

PFA - % < 5% 

*There may be more than one threshold specification for system operation; TLR = target leak rate. 

**Define MDL and CMDL = MDL/2 for A1; S for A1; and A1

 Operation of the Evaluated System 

Version a 

Mass Based Systems (with scaling and averaging included) 

Test Threshold *,

** 

Set PD = 95% against a Target Leak Rate > MDL 

To insure PFA < 5% 

Target Leak Rate, 

TLR – gal/h 

[(MDL/n0.5) (A2/A1)] = 0.2 

 such that 1 < n < 12 

or 0.2 for 

[(MDL (A2/A1)] < 0.2 

Threshold, 

C – gal/h 

[TLR-(CMDL/n0.5) (A2/A1)] > 0.1 

such that 1 < n < 12 

or 0.1 for 

[TLR- (CMDL/n0.5) (A2/A1)] < 0.1 

PD – % 95% 

PFA - % < 5% 

*There may be more than one threshold specification for system operation; TLR = target leak rate. 

**Define MDL and CMDL = MDL/2 for A1; S for A1; and A1; 1 < n < 12 
E-3

LRDP-24 Version a 

Test Threshold 1*,

** 

Set PD = 95% against a Target Leak Rate > MDL to insure PFA < 5% 

Target Leak Rate, TLR – 

gal/h 

[0.69 (A2/11,786)] > 0.2 

or 0.2 for 

[0.69 (A2/11,786)] < 0.2 

Threshold, 

C – gal/h 

[TLR – (0.345) (A2/11,786)] > 0.1 

or 0.1 for 

[TLR – (0.345) (A2/A1)] < 0.1 

PD – % 95% 

PFA - % <5% 

*There may be more than one threshold specification for system operation; TLR = target leak rate. 

**MDL = 0.69 gal/h; S = 0.192 gal/h; and A1 = 11,786 ft2

.

LRDP-24-n Version a 

Test Threshold 1*,

** 

Set PD = 95% against a Target Leak Rate > MDL to insure PFA < 5% 

Target Leak Rate, TLR – 

gal/h 

[(0.69/n0.5) (A2/11,786] = 0.2 

 such that 1 < n < 12 

or 

0.2 for 

 [(0.69/n0.5) (A2/11,786)] < 0.2 

Threshold, 

C – gal/h 

[TLR-((0.345)/n0.5) (A2/11,786] > 0.1 

such that 1 < n < 12 

and 0.1 for 

[TLR-((0.345)/n0.5) (A2/11,786] < 0.1 

PD – % 95% 

PFA - % < 5% 

*There may be more than one threshold specification for system operation; TLR = target leak rate. 

**MDL = 0.69 gal/h; S = 0.192 gal/h; and A1 = 11,786 ft2

; 1 < n < 12.
E-4

LRDP-10 Version a 

Test Threshold 1*,

** 

Set PD = 95% against a Target Leak Rate > MDL to insure PFA < 5% 

Target Leak Rate, 

TLR – gal/h 

[(1.139) (A2/11,786)] > 0.2 

or 0.2 for 

 [(1.139) (A2/11,786)] < 0.2 

Threshold, 

C – gal/h 

[TLR – (0.569) (A2/11,786)] > 0.1 

 or 0.1 for 

 [TLR – (0.569) (A2/11,786)] < 0.1 

PD – % 95% 

PFA - % < 5% 

*There may be more than one threshold specification for system operation; TLR = target leak rate. 

**MDL = 1.14 gal/h; S = 0.317 gal/h; and A1 = 11,786 ft2

.

LRDP-10-n Version a 

Test Threshold 1*,

** 

Set PD = 95% against a Target Leak Rate > MDL to insure PFA < 5% 

Target Leak Rate, 

TLR – gal/h 

[(1.139/n0.5) (A2/11,786] = 0.2 

 such that 1 < n < 12 or 

0.2 for [(1.139/n0.5) (A2/11,786)] < 0.2 

Threshold, 

C – gal/h 

 [TLR-((0.569)/n0.5) (A2/11,786] > 0.1 such that 1 < n < 12 

or 0.1 for 

 [TLR-((0.569)/n0.5) (A2/11,786] < 0.1 

PD – % 95% 

PFA - % < 5% 

*There may be more than one threshold specification for system operation; TLR = target leak rate. 

** MDL = 1.14 gal/h; S = 0.317 gal/h; and A1 = 11,786 ft2

; 1 < n < 12 .
Appendix F 

Performance Equations for Versions 1.0a, 1.1a, and 1.2a 

of the LRDP-10, LRDP-24, LRDP-10-n and LRDP-24-n 
F-2

Operation of the Evaluated System as Designed 

LRDP-24 

Mass Based Systems (with scaling included) 

Version 1.0a 

Test Threshold *,

** 

Set PD = 95% against a Target Leak 

Rate > MDL 

to insure PFA < 5% 

Version 1.1a 

Test Threshold 2** 

Set PFA < 5% and set 

PD > 95% such that the Target Leak 

Rate < 2 scaled-MDL 

Version 1.2a 

Test Threshold 3** 

Operate at the MDL (Set 

PD = 95% and set PFA = 5%) 

Target Leak Rate, 

TLR – gal/h 

TLR > [MDL (A2/A1)] > 0.2 

or 0.2 for 

[(MDL (A2/A1)] < 0.2 

[α MDL (A2/A1)] > 0.2 

or 0.2 for 

[(α MDL (A2/A1)] < 0.2 

such that α < 2 

[MDL (A2/A1)] > 0.2 

or 0.2 for 

[(MDL (A2/A1)] < 0.2 

Threshold, 

C – gal/h 

[TLR - CMDL (A2/A1)] > 0.1 or 0.1 

for 

[TLR – CMDL (A2/A1)] < 0.1 

[β MDL (A2/A1)] > 0.1 

or 0.1 for 

[(β MDL (A2/A1)] < 0.1 

such that α < 2 

[(CMDL = MDL/2) (A2/A1)] > 0.1 

or 0.1 for 

[(MDL/2) (A2/A1)] < 0.1 

PD – % 95% > 95% 95% 

PFA - % < 5% < 5% 5% 

*There may be more than one threshold specification for system operation; TLR = target leak rate. 

**Define MDL and CMDL = MDL/2 for A1; S for A1; and A1; α < 2 and β is a constant multiplier on MDL 

Operation of the Evaluated System as Designed 

LRDP-24-n 

Mass Based Systems (with scaling and averaging included) 

Version 1.0a 

Test Threshold 1*,

** 

Set PD = 95% against a Target 

Leak Rate > MDL 

To insure PFA < 5% 

Version 1.1a 

Test Threshold 2** 

Set PFA < 5% and set 

PD > 95% such that the Target Leak 

Rate < 2 scaled-MDL 

Version 1.2a 

Test Threshold 3** 

Operate at the MDL (Set 

PD = 95% and set PFA = 5%) 

Target Leak 

Rate, 

TLR – gal/h 

[(MDL/n0.5) (A2/A1)] = 0.2 

 such that 1 < n < 12 

or 0.2 for 

[(MDL (A2/A1)] < 0.2 

[(α MDL//n0.5) (A2/A1)] > 0.2 

or 0.2 for 

[(α MDL//n0.5) (A2/A1)] < 0.2 

such that α < 2 

[(MDL/n0.5) (A2/A1)] > 0.2 

or 0.2 for 

[(MDL//n0.5) (A2/A1)] < 0.2 

Threshold, 

C – gal/h 

[TLR-(CMDL/n0.5) (A2/A1)] > 0.1 

such that 1 < n < 12 

or 0.1 for 

[TLR- (CMDL/n0.5) (A2/A1)] < 0.1 

[(β MDL/n0.5) (A2/A1)] )] > 0.1 

or 0.1 for 

[(β MDL//n0.5) (A2/A1)] < 0.1 

such that α < 2 

[(0.5 MDL/n0.5) (A2/A1)] )] > 0.1 

or 0.1 for 

[(0.5 MDL//n0.5) (A2/A1)] < 0.1 

PD – % 95% > 95% 95% 

PFA - % < 5% < 5% 5% 

*There may be more than one threshold specification for system operation; TLR = target leak rate. 

**Define MDL and CMDL = MDL/2 for A1; S for A1; and A1; α < 2 and β is a constant multiplier on MDL; 1 < n < 12 
F-3

LRDP-24 

Version 1.0a 

Test Threshold 1*,

** 

Set PD = 95% against a Target Leak 

Rate > MDL to insure PFA < 5% 

Version1.1a 

Test Threshold 2** 

Set PFA < 5% and set 

PD = 95% such that the 

Target Leak Rate < 2 scaled-MDL 

Version 1.2a 

Test Threshold 3** 

Operate at the MDL (Set 

PD = 95% and set PFA = 5%)

Target Leak Rate, 

TLR – gal/h 

[0.69 (A2/11,786)] > 0.2 

or 0.2 for 

[0.69 (A2/11,786)] < 0.2 

[1.3711 (0.69) (A2/11,786)] > 0.2 or 

0.2 for 

 [(1.3711 (0.69) (A2/11,786] < 0.2 

such that α < 2 

[0.69 (A2/11,786)] > 0.2 

or 0.2 for 

[(MDL (A2/A1)] < 0.2 

Threshold, 

C – gal/h 

[TLR – (0.345) (A2/11,786)] > 0.1 

or 0.1 for 

[TLR – (0.345) (A2/A1)] < 0.1 

[0.8711) (0.69) (A2/11,786)] > 0.1 

or 0.1 for 

[(0.8711) (0.69) (A2/11,786)] < 0.1 

such that α < 2 

[0.345 (A2/11,786)] > 0.1 

or 0.1 for 

[(0.345 (A2/11,786)] < 0.1 

PD – % 95% 95% 95% 

PFA - % <5% 0.48% 5% 

*There may be more than one threshold specification for system operation; TLR = target leak rate. 

**MDL = 0.69 gal/h; S = 0.192 gal/h; and A1 = 11,786 ft2

; α = 1.3711; β = 0.8711.

LRDP-24-n 

Version 1.0a 

Test Threshold 1*,

** 

Set PD = 95% against a Target Leak 

Rate > MDL to insure PFA < 5% 

Version 1.1a 

Test Threshold 2** 

Set PFA < 5% and set 

 PD = 95% such that the 

Target Leak Rate < 2 scaled-MDL 

Version 1.2a 

Test Threshold 3** 

Operate at the MDL (Set 

PD = 95% and set PFA = 5%) 

Target Leak Rate, 

TLR – gal/h 

[(0.69/n0.5) (A2/11,786] = 0.2 

 such that 1 < n < 12 

or 

0.2 for 

 [(0.69/n0.5) (A2/11,786)] < 0.2 

[(1.3711 (0.69)//n0.5) (A2/11,786)] > 0.2 

or 0.2 for 

 [(1.3711 (0.69)//n0.5) (A2/11,786)] < 0.2 

such that α < 2 

[(0.69/n0.5) (A2/11,786)] > 0.2 

or 0.2 for 

 [(0.69//n0.5) (A2/11,786)] < 0.2 

Threshold, 

C – gal/h 

[TLR-((0.345)/n0.5) (A2/11,786] > 0.1 

such that 1 < n < 12 

and 0.1 for 

[TLR-((0.345)/n0.5) (A2/11,786] < 0.1 

[0.8711) (0.69)/n0.5) (A2/11,786)] > 0.1 

 or 0.1 for 

 [(0.8711) (0.69)//n0.5) (A2/11,786)] < 0.1 

such that α < 2 

 [(0.345/n0.5)} (A2/11,786)] )] > 0.1 

or 0.1 for 

 [(0.345/n0.5) (A2/11,786)] < 0.1 

PD – % 95% 95% 95% 

PFA - % < 5% 0.48% 5% 

*There may be more than one threshold specification for system operation; TLR = target leak rate. 

**MDL = 0.69 gal/h; S = 0.192 gal/h; and A1 = 11,786 ft2

; α = 1.3711; β = 0.8711; 1 < n < 12.
F-4

LRDP-10 

Version 1.0a 

Test Threshold 1*,

** 

Set PD = 95% against a Target 

Leak Rate > MDL to insure PFA <

5% 

Version 1.1a 

Test Threshold 2** 

Set PFA < 5% and set 

PD = 95% such that the 

Target Leak Rate < 2 scaled-MDL 

Version 1.2a 

Test Threshold 3** 

Operate at the MDL (Set 

PD = 95% and set PFA = 

5%) 

Target Leak Rate, 

TLR – gal/h 

[(1.139) (A2/11,786)] > 0.2 

or 0.2 for 

 [(1.139) (A2/11,786)] < 0.2 

[(1.4514) (1.139) (A2/11,786)] > 0.2 

or 0.2 for 

 [(1.4514) (A2/11,786)] < 0.2 

such that α < 2 

[1.139 (A2/11,786)] > 0.2 

or 0.2 for 

 [(1.139) (A2/11,786] < 0.2 

Threshold, 

C – gal/h 

[TLR – (0.569) (A2/11,786)] > 0.1 

 or 0.1 for 

 [TLR – (0.569) (A2/11,786)] < 0.1 

[0.9514) (1.139) (A2/11,786)] > 0.1 

 or 0.1 for 

 [(0.9514) (1.139) (A2/11,786)] < 0.1 

such that α < 2 

[(0.569) (A2/11,786)] > 0.1 

 or 0.1 for 

 [(0.569) (A2/11,786)] < 0.1 

PD – % 95% 95% 95% 

PFA - % < 5% 0.29% 5% 

*There may be more than one threshold specification for system operation; TLR = target leak rate. 

**MDL = 1.14 gal/h; S = 0.317 gal/h; and A1 = 11,786 ft2

; α = 1.4514; β = 0.9514.

LRDP-10-n 

Version 1.0a 

Test Threshold 1*,

** 

Set PD = 95% against a Target Leak 

Rate > MDL to insure PFA < 5% 

Version 1.1a 

Test Threshold 2** 

Set PFA < 5% and set 

PD = 95% such that the 

Target Leak Rate < 2 scaled-MDL 

Version 1.2a 

Test Threshold 3** 

Operate at the MDL (Set 

PD = 95% and set PFA = 5%) 

Target Leak Rate, 

TLR – gal/h 

[(1.139/n0.5) (A2/11,786] = 0.2 

 such that 1 < n < 12 

or 0.2 for 

 [(1.139/n0.5) (A2/11,786)] < 0.2 

[(1.4514) (1.139)//n0.5) (A2/11,786)] > 0.2 

or 0.2 for 

 [(1.4514 (1.139)//n0.5) (A2/11,786)] < 0.2 

such that α < 2 

 [(1.139/n0.5) (A2/11,786)] > 0.2 

or 0.2 for 

 [(1.139//n0.5) (A2/11,786)] < 0.2 

Threshold, 

C – gal/h 

 [TLR-((0.569)/n0.5) (A2/11,786] > 0.1 

such that 1 < n < 12 

or 0.1 for 

 [TLR-((0.569)/n0.5) (A2/11,786] < 0.1 

 [0.9514) (1.139)/n0.5) (A2/11,786)] > 0.1 

or 0.1 for 

 [(0.9514) (1.139)//n0.5) (A2/11,786)] < 

0.1 

such that α < 2 

 

[(0.569/n0.5)} (A2/11,786)] )] > 0.1 

or 0.1 for 

 [(0.569/n0.5) (A2/11,786)] < 0.1 

PD – % 95% 95% 95% 

PFA - % < 5% 0.29% 5% 

*There may be more than one threshold specification for system operation; TLR = target leak rate. 

** MDL = 1.14 gal/h; S = 0.317 gal/h; and A1 = 11,786 ft2

; α = 1.4514; β = 0.9514; 1 < n < 12 .
Appendix G 

Performance Estimates for the LRDP-10 

for Versions 1.0a, 1.1a, and 1.2a 

as a Function of TLR and Tank Diameter 
G-2

Table G-1. LRDP-10. The threshold is set to give the MDLR (i.e., a system with a PD = 95% and a PFA = 5%) by 

selecting a threshold that gives a PD = 95% and a PFA = 5%. (Version 1.2a) 

Index Volume Ht Dia Area MDLR Std Dev Threshold PFA PD n for 

LR=0.2 

gal/h 

 (gal) (ft) (ft) (ft2) (gal/h) (gal/h) (gal/h) (%) (%) 

Eval 2,063,044 23.4 122.50 11,786 1.14 0.317 0.569 5.0% 95.0% 

1 204,093 13.2 51.30 2,067 0.20 0.056 0.100 5.0% 95.0% 1.0

2 433,533 14.0 72.60 4,140 0.40 0.111 0.200 5.0% 95.0% 4.0

3 500,687 13.2 80.35 5,071 0.49 0.136 0.245 5.0% 95.0% 6.0

4 1,255,054 23.4 95.55 7,170 0.69 0.193 0.346 5.0% 95.0% 2 12.0

5 306,341 13.2 62.85 3,102 0.30 0.083 0.150 5.0% 95.0% 2.2

6 1,548,582 20.0 114.80 10,351 1.00 0.278 0.500 5.0% 95.0% 

7 3,097,099 20.0 162.35 20,701 2.00 0.557 1.000 5.0% 95.0% 

8 4,643,904 20.0 198.80 31,040 3.00 0.835 1.499 5.0% 95.0% 

9 600,565 13.2 88.00 6,082 0.59 0.164 0.294 5.0% 95.0% 8.6

10 2,125,666 20 134.50 14,208 1.37 0.382 0.686 5.0% 95.0% 

11 2,274,866 20 134.50 15,205 1.47 0.409 0.734 5.0% 95.0% 

12 5,157,611 23.4 193.69 29,465 2.85 0.793 1.423 5.0% 95.0% 

Table G-2. LRDP-10. The threshold is set to give a specific PFA < 5% and a specific PD > 95%. The largest tank 

needs to be below the regulatory standard (e.g., 2 gal/h). This is accomplished by selecting a threshold that gives 

the PD and PFA of interest. The target leak rate is less or equal to twice the MDLR. (Version 1.1a)

Index Volume Ht Dia Area TLR Std Dev Threshold PFA PD n for 

LR=0.2 

gal/h 

 (gal) (ft) (ft) (ft2) (gal/h) (gal/h) (gal/h) (%) (%) 

Eval 2,063,044 23.4 122.50 11,786 1.65 0.317 1.083 0.288% 95.0% 

1 140,739 13.2 42.60 1,425 0.20 0.038 0.131 0.288% 95.0% 1.0 

2 281,987 13.2 60.30 2,856 0.40 0.077 0.262 0.288% 95.0% 4.0 

3 344,504 13.2 66.65 3,489 0.49 0.094 0.321 0.288% 95.0% 6.0 

4 864,695 23.4 79.31 4,940 0.69 0.133 0.454 0.288% 95.0% 12.0 

5 211,479 13.2 52.22 2,142 0.30 0.058 0.197 0.288% 95.0% 2.3 

6 1,067,177 20.0 95.30 7,133 1.00 0.192 0.656 0.288% 95.0% 

7 2,133,576 20.0 134.75 14,261 2.00 0.384 1.311 0.288% 95.0% 

8 3,200,970 20.0 165.05 21,395 3.00 0.575 1.967 0.288% 95.0% 

9 600,565 13.2 88.00 6,082 0.85 0.164 0.559 0.288% 95.0% 

10 2,125,666 20.0 134.50 14,208 1.99 0.382 1.306 0.288% 95.0% 

11 2,274,866 20.0 139.14 15,205 2.13 0.409 1.398 0.288% 95.0% 

12 5,157,611 23.4 193.69 29,465 4.13 0.793 2.708 0.288% 95.0% 
G-3

Table G-3. LRDP-10. The threshold is set to give a specific PFA < 5% and a specific PD > 95%. The largest tank 

needs to be below the regulatory standard (e.g., 2 gal/h). This is accomplished by selecting a threshold that gives the 

PD and PFA of interest. The TLR = 1.90 gal/h for the evaluation tank. (Version 1.0a TLR = 1.9 gal/h)

Index Volume Ht Dia Area TLR Std Dev Threshold PFA PD n for 

LR=0.2 

gal/h 

 (gal) (ft) (ft) (ft2) (gal/h) (gal/h) (gal/h) (%) (%) 

Eval 2,063,044 23.4 122.50 11,786 1.90 0.317 1.330 0.075% 95.0% 

1 122,537 13.2 39.75 1,241 0.20 0.033 0.140 0.075% 95.0% 1.0 

2 245,119 13.2 56.22 2,482 0.40 0.067 0.280 0.075% 95.0% 4.0 

3 300,037 13.2 62.20 3,039 0.49 0.082 0.343 0.075% 95.0% 6.0 

4 752,723 23.4 73.99 4,300 0.69 0.116 0.485 0.075% 95.0% 12.0 

5 183,930 13.2 48.70 1,863 0.30 0.050 0.210 0.075% 95.0% 2.3 

6 612,912 13.2 88.90 6,207 1.00 0.167 0.700 0.075% 95.0% 

7 1,856,612 20.0 125.70 12,410 2.00 0.334 1.400 0.075% 95.0% 

8 2,784,902 20.0 153.95 18,614 3.00 0.501 2.100 0.075% 95.0% 

9 600,565 13.2 88.00 6,082 0.98 0.164 0.686 0.075% 95.0% 

10 2,125,666 20.0 134.50 14,208 2.29 0.382 1.603 0.075% 95.0% 

11 2,274,866 20.0 139.14 15,205 2.45 0.409 1.715 0.075% 95.0% 

12 5,157,611 23.4 193.69 29,465 4.75 0.793 3.324 0.075% 95.0% 

Table G-4. LRDP-10. The threshold is set to give a specific PD > 95% and the PFA, which needs to be less than or 

equal to 5%, is computed for this PD. The TLR = 2.40 gal/h for the evaluation tank. (Version 1.0a TLR = 2.4 gal/h)

Index Volume Ht Dia Area TLR Std Dev Threshold PFA PD n for 

LR=0.2 

gal/h 

 (gal) (ft) (ft) (ft2) (gal/h) (gal/h) (gal/h) (%) (%) 

Eval 2,063,044 23.4 122.50 11,786 2.40 0.317 1.831 0.00619% 95.0% 

1 96,911 13.2 35.35 981 0.20 0.026 0.152 0.00619% 95.0% 1.0 

2 193,881 13.2 50.00 1,963 0.40 0.053 0.305 0.00619% 95.0% 4.0 

3 237,505 13.2 55.34 2,405 0.49 0.065 0.374 0.00619% 95.0% 6.0 

4 595,429 23.4 65.81 3,402 0.69 0.091 0.528 0.00619% 95.0% 12.0 

5 145,402 13.2 43.30 1,473 0.30 0.040 0.229 0.00619% 95.0% 2.2 

6 734,453 20.0 79.06 4,909 1.00 0.132 0.763 0.00619% 95.0% 

7 1,469,492 20.0 111.83 9,822 2.00 0.264 1.526 0.00619% 95.0% 

8 2,203,812 20.0 136.95 14,730 3.00 0.396 2.288 0.00619% 95.0% 

9 600,565 13.2 88.00 6,082 1.24 0.164 0.945 0.00619% 95.0% 

10 2,125,666 20.0 134.50 14,208 2.89 0.382 2.207 0.00619% 95.0% 

11 2,274,866 20.0 139.14 15,205 3.10 0.409 2.362 0.00619% 95.0% 

12 5,157,611 23.4 193.69 29,465 6.00 0.793 4.577 0.00619% 95.0% 
H-1

Appendix H 

Performance Estimates for the LRDP-24 

for Versions 1.0a, 1.1a, and 1.2a 

as a Function of TLR and Tank Diameter 
H-2

Table H-1. LRDP-24. The threshold is set to give the MDLR (i.e., a system with a PD = 95% and a PFA = 

5%) by selecting a threshold that gives a PD = 95% and a PFA = 5%. (Version 1.2a)

Index Volume Ht Dia Area MDLR Std Dev Threshold PFA PD n for 

LR=0.2 

gal/h 

 (gal) (ft) (ft) (ft2) (gal/h) (gal/h) (gal/h) (%) (%) 

Eval 2,063,044 23.4 122.50 11,786 0.69 0.192 0.345 5.0% 95.0% 11.9 

1 337,306 13.2 65.95 3,416 0.20 0.056 0.100 5.0% 95.0% 1.0 

2 1,022,854 20.0 93.30 6,837 0.40 0.111 0.200 5.0% 95.0% 4.0 

3 1,252,653 20.0 103.25 8,373 0.49 0.136 0.245 5.0% 95.0% 6.0 

4 2,072,501 23.4 122.78 11,840 0.69 0.193 0.346 5.0% 95.0% 12.0 

5 767,138 20.0 80.80 5,128 0.30 0.084 0.150 5.0% 95.0% 2.3 

6 2,555,394 20.0 147.47 17,080 1.00 0.278 0.500 5.0% 95.0% 

7 5,113,039 20.0 208.60 34,176 2.00 0.557 1.000 5.0% 95.0% 

8 7,670,653 20.0 255.50 51,271 3.00 0.835 1.500 5.0% 95.0% 

9 600,565 13.2 88.00 6,082 0.36 0.099 0.178 5.0% 95.0% 3.2 

10 2,125,666 20 134.50 14,208 0.83 0.231 0.416 5.0% 95.0% 

11 2,274,866 20.0 139.14 15,205 0.89 0.248 0.445 5.0% 95.0% 

12 5,157,611 23.4 193.69 29,465 1.72 0.480 0.862 5.0% 95.0% 

Table H-2. LRDP-24. The threshold is set to give a specific PFA < 5% and a specific PD > 95%. The largest tank 

needs to be below the regulatory standard (e.g., 2 gal/h). This is accomplished by selecting a threshold that gives the 

PD and PFA of interest. The target leak rate is less or equal to twice the MDLR. (Version 1.1a)

Index Volume Ht Dia Area TLR Std Dev Threshold PFA PD n for 

LR=0.2 

gal/h 

 (gal) (ft) (ft) (ft2) (gal/h) (gal/h) (gal/h) (%) (%) 

Eval 2,063,044 23.4 122.50 11,786 0.95 0.192 0.601 0.480% 95.0% 

1 262,577 14.1 56.30 2,489 0.20 0.041 0.127 0.480% 95.0% 1.0 

2 492,619 13.2 79.70 4,989 0.40 0.081 0.254 0.480% 95.0% 4.0 

3 602,887 13.2 88.17 6,106 0.49 0.099 0.311 0.480% 95.0% 6.0 

4 1,511,447 23.4 104.85 8,635 0.69 0.141 0.440 0.480% 95.0% 12.0 

5 369,226 13.2 69.00 3,739 0.30 0.061 0.191 0.480% 95.0% 2.2 

6 1,865,484 20.0 126.00 12,469 1.00 0.203 0.636 0.480% 95.0% 

7 3,729,256 20.0 178.15 24,927 2.00 0.406 1.270 0.480% 95.0% 

8 5,594,483 20.0 218.20 37,394 3.00 0.609 1.906 0.480% 95.0% 

9 600,565 13.2 88.00 6,082 0.49 0.099 0.310 0.480% 95.0% 6.0 

10 2,125,666 20.0 134.50 14,208 1.14 0.231 0.724 0.480% 95.0% 

11 2,274,866 20.0 139.14 15,205 1.22 0.248 0.775 0.480% 95.0% 

12 5,157,611 23.4 193.69 29,465 2.36 0.480 1.502 0.480% 95.0% 
H-3

Table H-3. LRDP-24. The threshold is set to give a specific PD > 95% and the PFA, which needs to be less than or 

equal to 5%, is computed for this PD. The TLR = 1.65 gal/h for the evaluation tank. (Version 1.0a TLR = 1.65 gal/h) 

Index Volume Ht Dia Area TLR Std Dev Threshold PFA PD n for 

LR=0.2 

gal/h 

 (gal) (ft) (ft) (ft2) (gal/h) (gal/h) (gal/h) (%) (%) 

Eval 2,063,044 23.4 122.50 11,786 1.65 0.192 1.305 0.00148% 95.0% 

1 141,069 13.2 42.65 1,429 0.20 0.023 0.158 0.00148% 95.0% 1.0 

2 281,987 13.2 60.30 2,856 0.40 0.047 0.316 0.00148% 95.0% 4.0 

3 345,539 13.2 66.75 3,499 0.49 0.057 0.388 0.00148% 95.0% 6.0 

4 866,271 23.4 79.38 4,949 0.69 0.081 0.548 0.00148% 95.0% 12.0 

5 211,317 13.2 52.20 2,140 0.30 0.035 0.237 0.00148% 95.0% 2.2 

6 705,076 13.2 95.35 7,141 1.00 0.116 0.791 0.00148% 95.0% 

7 2,136,744 20.0 134.85 14,282 2.00 0.233 1.582 0.00148% 95.0% 

8 3,202,909 20.0 165.10 21,408 3.00 0.349 2.371 0.00148% 95.0% 

9 600,565 13.2 88.00 6,082 0.85 0.099 0.674 0.00148% 95.0% 

10 2,125,666 20.0 134.50 14,208 1.99 0.231 1.573 0.00148% 95.0% 

11 2,274,866 20.0 139.14 15,205 2.13 0.248 1.684 0.00148% 95.0% 

12 5,157,611 23.4 193.69 29,465 4.13 0.480 3.263 0.00148% 326.3% 2 0.9 

Table H-4. LRDP-24. The threshold is set to give a specific PD > 95% and the PFA, which needs to be less than or 

equal to 5%, is computed for this PD. The TLR = 2.40 gal/h for the evaluation tank. (Version 1.0a TLR = 2.40 gal/h) 

Index Volume Ht Dia Area TLR Std Dev Threshold PFA PD n for 

LR=0.2 

gal/h 

 (gal) (ft) (ft) (ft2) (gal/h) (gal/h) (gal/h) (%) (%) 

Eval 2,063,044 23.4 122.50 11,786 2.40 0.192 2.055 0.000019% 95.0% 

1 96,911 13.2 35.35 981 0.20 0.016 0.171 0.000019% 95.0% 1.0 

2 193,881 13.2 50.00 1,963 0.40 0.032 0.342 0.000019% 95.0% 4.0 

3 253,699 14.1 55.34 2,405 0.49 0.039 0.419 0.000019% 95.0% 6.0 

4 595,429 23.4 65.81 3,402 0.69 0.055 0.593 0.000019% 95.0% 12.0 

5 145,402 13.2 43.30 1,473 0.30 0.024 0.257 0.000019% 95.0% 2.2 

6 484,739 13.2 79.06 4,909 1.00 0.080 0.856 0.000019% 95.0% 

7 1,469,492 20.0 111.83 9,822 2.00 0.160 1.713 0.000019% 95.0% 

8 2,578,460 23.4 136.95 14,730 3.00 0.240 2.569 0.000019% 95.0% 

9 600,565 13.2 88.00 6,082 1.24 0.099 1.061 0.000019% 95.0% 

10 2,125,666 20.0 134.50 14,208 2.89 0.231 2.478 0.000019% 95.0% 

11 2,274,866 20.0 139.14 15,205 3.10 0.248 2.651 0.000019% 95.0% 

12 5,157,611 23.4 193.69 29,465 6.00 0.480 5.138 0.000019% 95.0% 
Appendix I 

Performance Estimates for the LRDP-10 

as a Function of TLR and Tank Diameter (Product Surface Area) 

for a Threshold Set to Yield a PD = 95% for the Selected TLR 

 
I-2

Table I-1. LRDP-10. The threshold is set to give a PD = 95% against a specific TLR given that the PFA < 5%. The 

PFA will change with tank size, because the TLR is the same for all tank sizes. The TLR = 0.20 gal/h. (Version a)

Index Volume Ht Dia Area TLR Std Dev Threshold PFA PD n tests 

averaged 

 (gal) (ft) (ft) (ft2) (gal/h) (gal/h) (gal/h) (%) (%) 

Eval 2,063,044 23.4 122.5 11,786 0.200 0.055 0.101 2.295% 95.0% 33.0 

1 48,470 13.2 25.0 491 0.200 0.013 0.176 0.000001% 95.0% 1.0 

2 69,797 13.2 30.0 707 0.200 0.019 0.166 0.000069% 95.0% 1.0 

3 124,084 13.2 40.0 1,257 0.200 0.034 0.139 0.041125% 95.0% 1.0 

4 193,881 13.2 50.0 1,963 0.200 0.053 0.105 1.742% 95.0% 1.0 

5 279,188 13.2 60.0 2,827 0.200 0.054 0.103 1.956% 95.0% 2.0 

6 337,306 13.2 65.950 3,416 0.200 0.053 0.105 1.793% 95.0% 3.0 

7 380,006 13.2 70.0 3,848 0.200 0.052 0.107 1.526% 95.0% 4.0 

8 496,334 13.2 80.0 5,027 0.200 0.055 0.101 2.298% 95.0% 6.0 

9 506,273 13.2 80.8 5,127 0.200 0.052 0.106 1.599% 95.0% 7.0 

10 628,173 13.2 90.0 6,362 0.200 0.054 0.103 2.034% 95.0% 10.0 

11 1,175,034 20 100.0 7,854 0.200 0.055 0.102 2.137% 95.0% 15.0 

12 1,421,791 20 110.0 9,503 0.200 0.054 0.102 2.126% 95.0% 22.0 

13 1,692,049 20 120.0 11,310 0.200 0.056 0.100 2.386% 95.0% 30.0 

14 1,985,808 20 130.0 13,273 0.200 0.055 0.101 2.271% 95.0% 42.0 

15 250,591 14.1 55.0 2,376 0.200 0.045 0.119 0.567% 95.0% 2.0 

16 600,565 13.2 88.0 6,082 0.200 0.055 0.102 2.134% 95.0% 9.0 

17 2,125,666 20 134.5 14,208 0.200 0.055 0.101 2.289% 95.0% 48.0 

18 2,273,551 20 139.1 15,197 0.200 0.056 0.100 2.408% 95.0% 54.0 

Table I-2. LRDP-10. The threshold is set to give a PD = 95% against a specific TLR given that the PFA < 5%. The 

PFA will change with tank size, because the TLR is the same for all tank sizes. The TLR = 0.30 gal/h. (Version a)

Index Volume Ht Dia Area MDLR Std Dev Threshold PFA PD n for 

LR=0.2 

gal/h 

 (gal) (ft) (ft) (ft2) (gal/h) (gal/h) (gal/h) (%) (%) 

Eval 48,470 13.2 25.00 491 0.30 0.013 0.276 0.000000% 95.0% 2.3 

1 69,797 13.2 30.00 707 0.30 0.019 0.266 0.000001% 95.0% 2.3 

2 124,084 13.2 40.00 1,257 0.30 0.034 0.239 0.001023% 95.0% 2.3 

3 193,881 13.2 50.00 1,963 0.30 0.053 0.205 0.127% 95.0% 2.3 

4 204,093 13.2 51.30 2,067 0.30 0.056 0.200 0.208% 95.0% 2.3 

5 279,188 13.2 60.00 2,827 0.30 0.076 0.163 2.7% 95.0% 2.3 

6 306,633 13.2 62.88 3,105 0.30 0.084 0.150 5.0% 95.0% 2.3 

7 250,591 14.1 55.00 2,376 0.30 0.064 0.185 0.7% 95.0% 2.3 

8 600,565 13.2 88.00 6,082 0.30 0.164 0.006 48.5% 95.0% 2.3 
I-3

Table I-3. LRDP-10. The threshold is set to give a PD = 95% against a specific TLR given that the PFA < 5%. The 

PFA will change with tank size, because the TLR is the same for all tank sizes. The TLR = 1.00 gal/h. (Version a)

Index Volume Ht Dia Area TLR Std Dev Threshold PFA PD n for 

LR=0.2 

gal/h 

 (gal) (ft) (ft) (ft2) (gal/h) (gal/h) (gal/h) (%) (%) 

Eval 2,063,044 23.4 122.50 11,786 1.00 0.317 0.431 10.1% 95.0% 

1 48,470 13.2 25.00 491 1.00 0.013 0.976 0.000000% 95.0% 

2 69,797 13.2 30.00 707 1.00 0.019 0.966 0.000000% 95.0% 

3 124,084 13.2 40.00 1,257 1.00 0.034 0.939 0.000000% 95.0% 

4 193,881 13.2 50.00 1,963 1.00 0.053 0.905 0.000000% 95.0% 

5 204,093 13.2 51.30 2,067 1.00 0.056 0.900 0.000000% 95.0% 

6 279,188 13.2 60.00 2,827 1.00 0.076 0.863 0.000010% 95.0% 

7 380,006 13.2 70.00 3,848 1.00 0.104 0.814 0.000384% 95.0% 

8 496,334 13.2 80.00 5,027 1.00 0.135 0.757 0.008007% 95.0% 

9 628,173 13.2 90.00 6,362 1.00 0.171 0.693 0.096% 95.0% 

10 1,175,034 20 100.00 7,854 1.00 0.211 0.621 0.675% 95.0% 

11 1,421,791 20 110.00 9,503 1.00 0.256 0.541 2.9% 95.0% 

12 1,548,659 20 114.80 10,351 1.00 0.278 0.500 5.0% 95.0% 

13 250,591 14.1 55.00 2,376 1.00 0.064 0.885 0.000001% 95.0% 

14 600,565 13.2 88.00 6,082 1.00 0.164 0.706 0.061037% 95.0% 

15 2,125,666 20 134.50 14,208 1.00 0.382 0.314 21.5% 95.0% 

16 2,273,551 20 139.10 15,197 1.00 0.409 0.266 26.4% 95.0% 

Table I-4. LRDP-10. The threshold is set to give a PD = 95% against a specific TLR given that the PFA < 5%. The 

PFA will change with tank size, because the TLR is the same for all tank sizes. The TLR = 2.00 gal/h. (Version a)

Index Volume Ht Dia Area TLR Std Dev Threshold PFA PD n for 

LR=0.2 

gal/h 

 (gal) (ft) (ft) (ft2) (gal/h) (gal/h) (gal/h) (%) (%) 

Eval 2,063,044 23.4 122.50 11,786 2.00 0.317 1.431 0.044% 95.0% 

1 48,470 13.2 25.00 491 2.00 0.013 1.976 0.000000% 95.0% 

2 69,797 13.2 30.00 707 2.00 0.019 1.966 0.000000% 95.0% 

3 124,084 13.2 40.00 1,257 2.00 0.034 1.939 0.000000% 95.0% 

4 193,881 13.2 50.00 1,963 2.00 0.053 1.905 0.000000% 95.0% 

5 204,093 13.2 51.30 2,067 2.00 0.056 1.900 0.000000% 95.0% 

6 279,188 13.2 60.00 2,827 2.00 0.076 1.863 0.000000% 95.0% 

7 380,006 13.2 70.00 3,848 2.00 0.104 1.814 0.000000% 95.0% 

8 496,334 13.2 80.00 5,027 2.00 0.135 1.757 0.000003% 95.0% 

9 628,173 13.2 90.00 6,362 2.00 0.171 1.693 0.000041% 95.0% 

10 1,175,034 20 100.00 7,854 2.00 0.211 1.621 0.000485% 95.0% 

11 1,421,791 20 110.00 9,503 2.00 0.256 1.541 0.004284% 95.0% 

12 1,692,049 20 120.00 11,310 2.00 0.304 1.454 0.029% 95.0% 

13 1,985,808 20 130.00 13,273 2.00 0.357 1.359 0.146% 95.0% 

14 250,591 14.1 55.00 2,376 2.00 0.064 1.885 0.000000% 95.0% 

15 600,565 13.2 88.00 6,082 2.00 0.164 1.706 0.000024% 95.0% 

16 2,125,666 20 134.50 14,208 2.00 0.382 1.314 0.146% 95.0% 

17 2,273,551 20 139.10 15,197 2.00 0.409 1.266 0.146% 95.0% 

18 2,044,211 13.2 162.36 20,702 2.00 0.557 1.000 5.0% 95.0% 
I-4

Table I-5. LRDP-10. The threshold is set to give a PD = 95% against a specific TLR given that the PFA < 5%. The 

PFA will change with tank size, because the TLR is the same for all tank sizes. The TLR = 3.00 gal/h. (Version a)

Index Volume Ht Dia Area TLR Std Dev Threshold PFA PD n for 

LR=0.2 

gal/h 

 (gal) (ft) (ft) (ft2) (gal/h) (gal/h) (gal/h) (%) (%) 

Eval 2,063,044 23.4 122.50 11,786 3.00 0.317 2.431 0.000488% 95.0% 

1 48,470 13.2 25.00 491 3.00 0.013 2.976 0.000000% 95.0% 

2 69,797 13.2 30.00 707 3.00 0.019 2.966 0.000000% 95.0% 

3 124,084 13.2 40.00 1,257 3.00 0.034 2.939 0.000000% 95.0% 

4 193,881 13.2 50.00 1,963 3.00 0.053 2.905 0.000000% 95.0% 

5 204,093 13.2 51.30 2,067 3.00 0.056 2.900 0.000000% 95.0% 

6 279,188 13.2 60.00 2,827 3.00 0.076 2.863 0.000000% 95.0% 

7 380,006 13.2 70.00 3,848 3.00 0.104 2.814 0.000000% 95.0% 

8 496,334 13.2 80.00 5,027 3.00 0.135 2.757 0.000000% 95.0% 

9 628,173 13.2 90.00 6,362 3.00 0.171 2.693 0.000000% 95.0% 

10 1,175,034 20 100.00 7,854 3.00 0.211 2.621 0.000004% 95.0% 

11 1,421,791 20 110.00 9,503 3.00 0.256 2.541 0.000039% 95.0% 

12 1,692,049 20 120.00 11,310 3.00 0.304 2.454 0.000302% 95.0% 

13 1,985,808 20 130.00 13,273 3.00 0.357 2.359 0.001913% 95.0% 

14 250,591 14.1 55.00 2,376 3.00 0.064 2.885 0.000000% 95.0% 

15 600,565 13.2 88.00 6,082 3.00 0.164 2.706 0.000000% 95.0% 

16 2,125,666 20 134.50 14,208 3.00 0.382 2.314 0.004128% 95.0% 

17 2,273,551 20 139.10 15,197 3.00 0.409 2.266 0.008718% 95.0% 

18 5,157,611 23.4 193.69 29,465 3.00 0.793 1.577 3.603773% 95.0% 

19 3,066,365 13.2 198.85 31,054 3.00 0.835 1.500 5.0% 95.0% 
Appendix J 

Performance Estimates for the LRDP-24 

as a Function of TLR and Tank Diameter (Product Surface Area) 

for a Threshold Set to Yield a PD = 95% for the Selected TLR 
J-2

Table J-1. LRDP-24. The threshold is set to give a PD = 95% against a specific TLR given that the PFA < 5%. The 

PFA will change with tank size, because the TLR is the same for all tank sizes. The TLR = 0.20 gal/h. (Version a)

Index Volume Ht Dia Area TLR Std Dev Threshold PFA PD n tests 

averaged

 (gal) (ft) (ft) (ft2) (gal/h) (gal/h) (gal/h) (%) (%) 

Eval 2,063,044 23.4 122.5 11,786 0.200 0.055 0.100 4.863% 95.0% 12.0 

1 48,470 13.2 25.0 491 0.200 0.008 0.186 0.000000% 95.0% 1.0 

2 69,797 13.2 30.0 707 0.200 0.012 0.179 0.000000% 95.0% 1.0 

3 124,084 13.2 40.0 1,257 0.200 0.020 0.163 0.000337% 95.0% 1.0 

4 193,881 13.2 50.0 1,963 0.200 0.032 0.143 0.048% 95.0% 1.0 

5 279,188 13.2 60.0 2,827 0.200 0.046 0.117 1.359% 95.0% 1.0 

6 337,306 13.2 65.950 3,416 0.200 0.056 0.100 4.982% 95.0% 1.0 

7 380,006 13.2 70.0 3,848 0.200 0.044 0.120 1.004% 95.0% 2.0 

8 496,334 13.2 80.0 5,027 0.200 0.047 0.115 1.657% 95.0% 3.0 

9 506,273 13.2 80.8 5,127 0.200 0.048 0.113 1.919% 95.0% 3.0 

10 628,173 13.2 90.0 6,362 0.200 0.052 0.107 3.173% 95.0% 4.0 

11 1,175,034 20 100.0 7,854 0.200 0.052 0.106 3.345% 95.0% 6.0 

12 1,421,791 20 110.0 9,503 0.200 0.055 0.102 4.505% 95.0% 8.0 

13 1,692,049 20 120.0 11,310 0.200 0.056 0.100 4.930% 95.0% 11.0 

14 1,985,808 20 130.0 13,273 0.200 0.054 0.103 4.170% 95.0% 16.0 

15 250,591 14.1 55.0 2,376 0.200 0.039 0.130 0.312% 95.0% 1.0 

16 600,565 13.2 88.0 6,082 0.200 0.050 0.111 2.330% 95.0% 4.0 

17 2,125,666 20 134.5 14,208 0.200 0.055 0.102 4.415% 95.0% 18.0 

18 2,273,551 20 139.1 15,197 0.200 0.055 0.101 4.826% 95.0% 20.0 

Table J-2. LRDP-24. The threshold is set to give a PD = 95% against a specific TLR given that the PFA < 5%. The 

PFA will change with tank size, because the TLR is the same for all tank sizes. The TLR = 0.30 gal/h. (Version a)

Index Volume Ht Dia Area MDLR Std Dev Threshold PFA PD n for 

LR=0.2 

gal/h 

 (gal) (ft) (ft) (ft2) (gal/h) (gal/h) (gal/h) (%) (%) 

Eval 48,470 13.2 25.00 491 0.30 0.008 0.286 0.000000% 95.0% 2.3 

1 69,797 13.2 30.00 707 0.30 0.012 0.279 0.000000% 95.0% 2.3 

2 124,084 13.2 40.00 1,257 0.30 0.020 0.263 0.000003% 95.0% 2.3 

3 193,881 13.2 50.00 1,963 0.30 0.032 0.243 0.000541% 95.0% 2.3 

4 279,188 13.2 60.00 2,827 0.30 0.046 0.217 0.031613% 95.0% 2.3 

5 597,952 23.4 65.95 3,416 0.30 0.056 0.200 0.210% 95.0% 2.3 

6 380,006 13.2 70.00 3,848 0.30 0.063 0.187 0.616% 95.0% 2.3 

7 496,334 13.2 80.00 5,027 0.30 0.082 0.153 4.4% 95.0% 2.3 

8 506,273 13.2 80.80 5,127 0.30 0.084 0.150 5.0% 95.0% 2.3 

9 600,565 13.2 88.00 6,082 0.30 0.099 0.122 12.2% 95.0% 2.3 
J-3

Table J-3. LRDP-24. The threshold is set to give a PD = 95% against a specific TLR given that the PFA < 5%. The 

PFA will change with tank size, because the TLR is the same for all tank sizes. The TLR = 1.00 gal/h. (Version a)

Index Volume Ht Dia Area TLR Std Dev Threshold PFA PD n for 

LR=0.2 

gal/h 

 (gal) (ft) (ft) (ft2) (gal/h) (gal/h) (gal/h) (%) (%) 

Eval 2,063,044 23.4 122.50 11,786 1.00 0.192 0.655 0.290% 95.0% 

1 48,470 13.2 25.00 491 1.00 0.008 0.986 0.000000% 95.0% 

2 69,797 13.2 30.00 707 1.00 0.012 0.979 0.000000% 95.0% 

3 124,084 13.2 40.00 1,257 1.00 0.020 0.963 0.000000% 95.0% 

4 193,881 13.2 50.00 1,963 1.00 0.032 0.943 0.000000% 95.0% 

5 279,188 13.2 60.00 2,827 1.00 0.046 0.917 0.000000% 95.0% 

6 597,952 23.4 65.95 3,416 1.00 0.056 0.900 0.000000% 

7 380,006 13.2 70.00 3,848 1.00 0.063 0.887 0.000001% 95.0% 

8 496,334 13.2 80.00 5,027 1.00 0.082 0.853 0.000025% 95.0% 

9 628,173 13.2 90.00 6,362 1.00 0.104 0.814 0.000389% 95.0% 

10 1,175,034 20 100.00 7,854 1.00 0.128 0.770 0.004338% 95.0% 

11 1,421,791 20 110.00 9,503 1.00 0.155 0.722 0.034494% 95.0% 

12 1,692,049 20 120.00 11,310 1.00 0.184 0.669 0.197% 95.0% 

13 1,985,808 20 130.00 13,273 1.00 0.216 0.612 0.820% 95.0% 

14 250,591 14.1 55.00 2,376 1.00 0.039 0.930 0.000% 95.0% 

15 600,565 13.2 88.00 6,082 1.00 0.099 0.822 0.000% 95.0% 

16 2,125,666 20 134.50 14,208 1.00 0.231 0.584 1.4% 95.0% 

17 2,273,551 20 139.10 15,197 1.00 0.248 0.555 2.3% 95.0% 

18 1,687,589 13.2 147.52 17,091 1.00 0.278 0.500 5.0% 95.0% 

Table J-4. LRDP-24. The threshold is set to give a PD = 95% against a specific TLR given that the PFA < 5%. The 

PFA will change with tank size, because the TLR is the same for all tank sizes. The TLR = 2.00 gal/h. (Version a)

Index Volume Ht Dia Area TLR Std Dev Threshold PFA PD n for 

LR=0.2 

gal/h 

 (gal) (ft) (ft) (ft2) (gal/h) (gal/h) (gal/h) (%) (%) 

Eval 2,063,044 23.4 122.50 11,786 2.00 0.192 1.655 0.000159% 95.0% 

1 48,470 13.2 25.00 491 2.00 0.008 1.986 0.000000% 95.0% 

2 69,797 13.2 30.00 707 2.00 0.012 1.979 0.000000% 95.0% 

3 124,084 13.2 40.00 1,257 2.00 0.020 1.963 0.000000% 95.0% 

4 193,881 13.2 50.00 1,963 2.00 0.032 1.943 0.000000% 95.0% 

5 279,188 13.2 60.00 2,827 2.00 0.046 1.917 0.000000% 95.0% 

6 597,952 23.4 65.95 3,416 2.00 0.056 1.900 0.000000% 

7 380,006 13.2 70.00 3,848 2.00 0.063 1.887 0.000000% 95.0% 

8 496,334 13.2 80.00 5,027 2.00 0.082 1.853 0.000000% 95.0% 

9 628,173 13.2 90.00 6,362 2.00 0.104 1.814 0.000000% 95.0% 

10 1,175,034 20 100.00 7,854 2.00 0.128 1.770 0.000001% 95.0% 

11 1,421,791 20 110.00 9,503 2.00 0.155 1.722 0.000013% 95.0% 

12 1,692,049 20 120.00 11,310 2.00 0.184 1.669 0.000098% 95.0% 

13 1,985,808 20 130.00 13,273 2.00 0.216 1.612 0.000636% 95.0% 

14 250,591 14.1 55.00 2,376 2.00 0.039 1.930 0.000000% 95.0% 

15 600,565 13.2 88.00 6,082 2.00 0.099 1.822 0.000000% 95.0% 

16 2,125,666 20 134.50 14,208 2.00 0.231 1.584 0.001391% 95.0% 

17 2,273,551 20 139.10 15,197 2.00 0.248 1.555 0.002989% 95.0% 

18 5,157,611 23.4 193.69 29,465 2.00 0.480 1.138 1.855026% 113.8% 0.9 

19 3,375,098 13.2 208.62 34,181 2.00 0.557 1.000 5.0% 95.0% 
J-4

Table J-5. LRDP-24. The threshold is set to give a PD = 95% against a specific TLR given that the PFA < 5%. The 

PFA will change with tank size, because the TLR is the same for all tank sizes. The TLR = 3.00 gal/h. (Version a)

Index Volume Ht Dia Area TLR Std Dev Threshold PFA PD n for 

LR=0.2 

gal/h 

 (gal) (ft) (ft) (ft2) (gal/h) (gal/h) (gal/h) (%) (%) 

Eval 2,063,044 23.4 122.50 11,786 3.00 0.192 2.655 0.000001% 95.0% 

1 48,470 13.2 25.00 491 3.00 0.008 2.986 0.000000% 95.0% 

2 69,797 13.2 30.00 707 3.00 0.012 2.979 0.000000% 95.0% 

3 124,084 13.2 40.00 1,257 3.00 0.020 2.963 0.000000% 95.0% 

4 193,881 13.2 50.00 1,963 3.00 0.032 2.943 0.000000% 95.0% 

5 279,188 13.2 60.00 2,827 3.00 0.046 2.917 0.000000% 95.0% 

6 597,952 23.4 65.95 3,416 3.00 0.056 2.900 0.000000% 

7 380,006 13.2 70.00 3,848 3.00 0.063 2.887 0.000000% 95.0% 

8 496,334 13.2 80.00 5,027 3.00 0.082 2.853 0.000000% 95.0% 

9 628,173 13.2 90.00 6,362 3.00 0.104 2.814 0.000000% 95.0% 

10 1,175,034 20 100.00 7,854 3.00 0.128 2.770 0.000000% 95.0% 

11 1,421,791 20 110.00 9,503 3.00 0.155 2.722 0.000000% 95.0% 

12 1,692,049 20 120.00 11,310 3.00 0.184 2.669 0.000001% 95.0% 

13 1,985,808 20 130.00 13,273 3.00 0.216 2.612 0.000005% 95.0% 

14 250,591 14.1 55.00 2,376 3.00 0.039 2.930 0.000000% 95.0% 

15 600,565 13.2 88.00 6,082 3.00 0.099 2.822 0.000000% 95.0% 

16 2,125,666 20 134.50 14,208 3.00 0.231 2.584 0.000012% 95.0% 

17 2,273,551 20 139.10 15,197 3.00 0.248 2.555 0.000027% 95.0% 

18 5,157,611 23.4 193.69 29,465 3.00 0.480 2.138 0.048603% 95.0% 

19 5,062,631 13.2 255.50 51,271 3.00 0.835 1.500 5.0% 95.0%