Peer Re view Draft – March 2005 Do Not Cite Or Quote

Petroleum Releases At

Underground Storage Tank Facilities

In Florida

United States Environmental Protection Agency

Office Of Underground Storage Tanks

Peer Review Draft – March 2005
Peer Re view Draft – March 2005 Do Not Cite Or Quote

ICF Incorporated, L.L.C. provided support to develop

this document under Contract No. 68-W0-0065.

Lynn Depont

EPA Project Officer

U.S. Environmental Protection Agency

Washington, D.C. 20460
Peer Re view Draft – March 2005 Do Not Cite Or Quote

Contents

Executive Summary To Be Added...................................................................1

Introduction......................................................................................................2

Background ......................................................................................................2

Purpose Of The Study.......................................................................................3

Study Methodology...........................................................................................3

Valid Versus Invalid Data ........................................................................................................ 3

Type Of Data Collected............................................................................................................ 4

Data Collection.......................................................................................................................... 4

Developing And Applying Data Collection Forms................................................................. 4

Data Review And Quality Control .......................................................................................... 5

Summary And Analysis Of Release And Use Data................................................................ 5

Results...............................................................................................................6

Valid And Invalid Data ............................................................................................................ 6

Release Sources......................................................................................................................... 7

Release Causes........................................................................................................................... 7

Releases From Dispensers ........................................................................................................ 8

Releases From Piping.............................................................................................................. 10

Releases During Fuel Delivery ............................................................................................... 15

Releases From Tanks.............................................................................................................. 16

Pump (Turbine) Releases....................................................................................................... 20

Other Release Sources............................................................................................................ 21

Volume Of Releases................................................................................................................ 22

Environmental Media Affected By UST Releases................................................................ 23

Method Of Release Discovery ................................................................................................ 25

Performance Of Leak Detection Methods ............................................................................ 26

Discussion Of Results......................................................................................28

Appendix A - Data Collection Forms............................................................A-1

Appendix B - Statistical Methods.................................................................B-1

Appendix C – Data Summary Tables And Statistical Results......................C-1
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List Of Figures

Figure 1: Summary Of Reasons For Invalidating Data .................................................................. 6

Figure 2: Sources Of UST Releases................................................................................................ 7

Figure 3: Summary Of Known Causes For All Releases............................................................... 8

Figure 4: Known Causes Of Dispenser Releases............................................................................ 9

Figure 5: Known Causes Of Piping Releases ............................................................................... 10

Figure 6: Known Causes Of Fiberglass Piping Releases.............................................................. 11

Figure 7: Known Causes Of Steel Piping Releases ...................................................................... 12

Figure 8: Known Causes Of Approved Synthetic Material Piping Releases................................ 12

Figure 9: Piping Releases And Use Versus Piping Material Of Construction............................. 13

Figure 10: Known Causes Of Releases During Fuel Delivery ..................................................... 15

Figure 11: Known Causes Of Tank Releases............................................................................... 17

Figure 12: Summary Of Known Causes For Steel Tank Releases ............................................... 18

Figure 13: Summary Of Known Causes For Fiberglass Tank Releases....................................... 19

Figure 14: Tank Releases And Use Versus Tank Material Of Construction................................ 19

Figure 15: Known Causes For Pump (Turbine) Releases............................................................. 21

Figure 16: Known Causes For Other Releases ............................................................................. 22

Figure 17: Proportion Of Releases From Each Source Affecting Water...................................... 24

Figure 18: Total Number Of Releases Affecting Water By Source ............................................. 25

Figure 19: Method Of Release Discovery .................................................................................... 26

List Of Tables

Table 1: Dispenser Releases And Secondary Containment............................................................ 9

Table 2: Effect Of Secondary Containment On Piping Releases................................................. 14

Table 3: Piping Releases And Pump Type ................................................................................... 14

Table 4: Fuel Delivery Releases And Overfill Protection Methods ............................................. 16

Table 5: Effect Of Secondary Containment On Tank Releases.................................................... 20

Table 6: Release Volumes For The Different Sources ................................................................. 23

Table 7: Releases Affecting Groundwater And Surface Water By Source Of Release................ 23

Table 8: Proportions Of All Releases Identified And Not Identified By Tank Leak Detection 

Methods Compared To Frequency Of Use ........................................................................... 27

Table 9: Failures And Successes For Electronic And Mechanical Line Leak Detectors ............. 27
Peer Review Draft – March 2005 Do Not Cite Or Quote 1

Executive Summary To Be Added 
Peer Review Draft – March 2005 Do Not Cite Or Quote 2

Introduction

In this document, the U.S. Environmental Protection Agency (EPA) presents analyses of 

data related to liquid underground storage tank (UST) releases1 in Florida discovered and 

reported between January 1995 and April 2002. The following sections discuss the background 

and purpose of the study, the methodology used to gather and analyze the data, the study results 

(including data summary and statistical analyses), and a discussion of the results. The 

appendices contain the forms used to gather the data, an explanation of the statistical 

methodology used in the evaluation, and data tables and statistical analyses.

Background

In 1984, Congress responded to the increasing threat to groundwater posed by leaking 

underground storage tanks by adding Subtitle I to the Resource Conservation and Recovery Act. 

This legislation required EPA to develop a comprehensive regulatory program for USTs storing 

petroleum or certain hazardous substances in order to protect the environment and human health 

from releases. In 1988, EPA issued regulations for owners and operators of UST systems 

covering leak detection and prevention, including minimizing the potential for USTs to corrode. 

(The regulations also cover additional requirements, such as financial responsibility and 

corrective action, not discussed in this report.) The regulatory requirements were phased in over 

ten years; the final deadline was December 22, 1998. 

Federal and state regulations helped EPA achieve its mandate. As a result of these 

regulations, USTs are now significantly more protective of human health and the environment 

than those installed before the requirements were implemented. Today UST systems have leak 

detection, spill, overfill, and corrosion protection equipment. Some states have additional 

requirements, such as secondary containment. States are reporting fewer releases. In the early 

1990s, the average number of releases reported nationwide exceeded 50,000 per year. In the mid 

1990s, the national average was over 25,000; in 2004, the number of reported confirmed releases 

across the country was less than 8,000. Despite these improvements, however, releases from 

new and upgraded UST systems continue. To better understand where and why these releases 

are occurring, EPA’s Office of Underground Storage Tanks initiated an effort to evaluate the 

performance of new and upgraded UST systems. The specific objectives of the overall UST 

system evaluation effort are to: 

• Identify the most common sources and causes of releases.

• Determine how successful leak detection methods are at detecting releases. 

• Determine what, if any, improvements are needed in the UST program. 

This study is one piece of EPA’s overall effort to evaluate UST systems. For this study, 

EPA entered into a partnership with the Florida Department of Environmental Protection (FDEP)

 

1

Florida uses the term discharge to describe a release to the environment that cannot be quickly cleaned up. EPA 

will refer to these discharges as releases throughout this report.
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to assemble and analyze data on tank system incidents and releases in Florida.

2

 FDEP was an 

ideal partner because of their willingness to assist with the data collection effort, earlier 

compliance deadlines than the federal requirements, superior compliance records (including 

annual inspection records), and ability to provide the type of information needed for the study. 

Because FDEP manages both USTs and aboveground storage tanks in an integrated program, 

Florida gathered data for both types of tank systems. However, for purposes of this study, EPA

limited the analysis to releases from USTs only.

3

Purpose Of The Study

The purpose of this study is to quantify UST system performance by analyzing releases 

from UST systems in Florida.

4 The study provides information on the sources and causes of 

releases from UST systems. In addition, it examines how often leak detection methods are 

succeeding or failing to detect releases from UST systems. When tank or piping is the source of 

a release, the study evaluates the construction details of the tank or piping and compares the 

releases from different construction types to their frequency of use. The study also analyzes

UST system age when the release was reported, the volume of the release, environmental media 

affected, and secondary containment.

Study Methodology

This section provides a brief overview of the study methodology. The study methodology 

included the following steps:

• Specify criteria for including data.

• Determine the specific type of data to be collected.

• Determine how and where data would be collected.

• Develop and apply data collection instruments (forms).

• Collect, review, and compile the data.

• Compile corresponding baseline data on UST system equipment use.

• Develop data summaries and analyses.

Valid Versus Invalid Data

Florida requires owners and operators to report releases (of product to the environment 

that cannot be quickly cleaned up) and incidents (small releases that can be quickly cleaned up or 

that do not reach the environment and false alarms) when they occur. EPA and FDEP 

established criteria for determining which data would be included in the data gathering and 

analysis based on the study objectives of developing information on the sources and causes of 

 

2

 As used in this document, the terms release and incident refer to events that require preparation and submittal of a 

Discharge Report Form (#62-761-900(1)) or Incident Notification Form (#62-761-900(6)), respectively, to the 

Florida Department of Environmental Protection (FDEP).

3

 EPA may conduct additional analysis on the UST incident and AST release and incident data at a later date.

4

 This study analyzes liquid releases. Vapor releases are not included in this study.
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releases from new and upgraded UST systems. EPA and FDEP considered a data point invalid

under any of the following conditions:

• Unknown release source.

• Release occurred before July 1, 1992 (final compliance date for Florida UST upgrade

regulations). 

• Tank system was installed prior to September 1, 1984 (date the first Florida UST regulations 

went into effect) and the release was discovered during closure activities. 

• The component which was the release source did not meet regulatory requirements.

• The release source was a non-regulated tank system.

• The release source was not associated with a tank system or filling (delivery or fueling) 

activity.

• Multiple tank systems were present and it was not clear which one was the release source.

• No release to the environment occurred, nor was information available to identify the 

occurrence as an incident.

 

Type Of Data Collected

EPA and FDEP collected a range of information to describe the tank/piping systems and 

the release. For tank and piping systems, inspectors gathered various information, including the 

installation date, material of construction, corrosion protection information, type of overfill 

protection, type of leak detection and the presence and type of secondary containment. 

Inspectors also gathered information about releases, including the release discovery date, source, 

cause, method of discovery, media affected and release volume.

Data Collection

FDEP contracted with current and former county inspectors from nine of the largest 

counties in Florida (Brevard, Broward, Dade, Duval, Hillsborough, Orange, Palm Beach, 

Pinellas, and Sarasota) to collect the data. These counties represent over 60 percent of the more 

than 6,500 UST and AST releases reported to Florida between January 1995 and April 2002. 

The inspectors reviewed and collected information from the files of facilities identified by FDEP 

as having reported one or more releases since January 1, 1995.5 FDEP chose to have county

inspectors collect the data because the inspectors were familiar with the structure and content of 

FDEP files and able to find and interpret the information quickly and accurately.

Developing And Applying Data Collection Forms

EPA and FDEP developed release and incident data collection forms to facilitate data 

collection and to record information in a consistent format suitable for database entry and 

analysis (Appendix A contains these forms). To help ensure the inspectors interpreted and 

applied the forms consistently, EPA and FDEP also developed instructions that included 

decision-making rules and examples of how specific situations should be recorded. In order to 

 

5

 Prior to 1998, FDEP used one form to report both incidents and releases. Thus, some facilities identified as having 

a reported release between 1995 and July 1998 may in fact have reported an incident (based on the current FDEP 

definition, which is used in this study). In such situations, the inspectors who collected data for this study recorded 

the relevant information on an incident information form.
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effectively manage the large amounts of data being collected, EPA used a database to enter and 

analyze the data.

Data Review And Quality Control

EPA and FDEP implemented measures to ensure the quality of the data collected and 

analyzed in this study. Before data collection began, EPA and FDEP held conference calls with 

the Florida county inspectors (who would gather the data) to discuss written instructions and 

provide examples of possible incident and release scenarios. As data collection progressed, 

FDEP discussed lessons learned with inspectors. Inspectors reviewed files, completed data 

collection forms, and submitted files and forms electronically to FDEP and EPA. Both agencies

reviewed each data collection form for completeness and accuracy and, if necessary, supporting 

file information. If EPA or FDEP found a problem, it was corrected by getting additional 

information from the inspector or reviewing the supporting file information.

EPA performed two types of quality control checks after entering data into the database. 

First, an individual who was not involved in the original data entry process selected 10 percent of 

the data entry forms at random from each batch of forms. The individual verified that the 

information in the database was identical to the information on the selected data forms, including 

any corrections made during the agency review. Second, EPA queried the database to tabulate 

the data and then reviewed the tabulations for inconsistencies. EPA highlighted any anomalies, 

reviewed related documentation, and updated the database as necessary.

Summary And Analysis Of Release And Use Data

EPA summarized the data and then performed an analysis using a variety of parametric 

and nonparametric statistical methods. Appendix B provides a description of the statistical 

methods used. Appendix C presents a summary of the data and results of the statistical analyses.

EPA performed statistical analyses to determine whether the sources, causes, and 

methods of identification were significantly different, marginally different, or not different. In 

addition, EPA compared detailed release source information (e.g., the percent of tank releases 

from single-walled fiberglass tanks) to the corresponding use information (e.g., percent of tanks

that are single-walled fiberglass) to determine whether there were significant or marginal 

statistical differences. Comparing releases to use is necessary to determine whether or not the 

frequency of releases for a given source is simply a function of its frequency of use. For 

example, if a specific tank type is used 90 percent of the time but has only 10 percent of tank 

releases, then that tank type is performing well relative to its use. However, if a tank type is used 

10 percent and accounts for 90 percent of tank releases, then that tank type is performing poorly 

relative to its use. EPA also compared the volumes of releases from different release sources and 

the differences in media affected by releases from tanks and piping systems. Finally, EPA 

compared the age distribution of releases (the time from installation to release discovery) to the 

age distributions of tanks and piping systems in use.

EPA compiled data on the various UST system construction characteristics for the UST 

population in the nine counties included in the study. This use data came from two separate 

sources – the releases and incidents data set generated by this data-gathering effort (referred to as 

R&I data) and from the FDEP database containing information on all USTs in the nine counties 
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(referred to as FDEP data). EPA believes the R&I data generally represent tank and piping use 

over the period of the study and FDEP data represent tank and piping use as of January 2003. 

EPA used both data sets because some R&I data on the collection form was not complete; either 

there was no particular characteristic of interest on the form or there was no information 

available to the data collector. For example, the data collection forms did not provide unknown 

as a possible response in the section on tank secondary containment. Thus, a lack of information 

on secondary containment in the discharge or incident databases may indicate either that: the 

tank does not have secondary containment or the person completing the data collection form did 

not or could not determine whether secondary containment was present. In these situations, EPA 

also relied on the FDEP data for use information. To remove potential bias from the R&I data 

for tank and piping releases, EPA did not include tank use information from a data point where 

the tank was the source of the release. Likewise, piping use information does not include data 

points where piping was identified as the source of the release.

Results

Valid And Invalid Data

FDEP collected data on 2,280 releases, including 512 valid UST releases and 130 valid 

AST releases. EPA considered a data point invalid for purposes of this study for one or more of 

the reasons discussed in the Study Methodology section (see page 3). Figure 1 shows the 

relative frequency of reasons for invalidating data. The most common reason (57 percent) is that

the source of release was unknown (or not specified in the record). Other common reasons for 

invalidating data were that the release was discovered at closure and the system was installed 

before September 1984 (25 percent) and the facility was not in compliance with the UST 

regulations (10 percent).

6

Figure 1: Summary Of Reasons For Invalidating Data

57%

25%

10%

2%

7%

0%

20%

40%

60%

80%

Source

Unknown

Closure &

Install Before

9/84

Leaking

Component

Did Not Meet

Regulations

Release

Occurred

Before 7/92

Other

Reason For Being Invalid

Percent Of Invalid Data Points .

 

6

 EPA classified 1,693 records as invalid.
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The following sections discuss the results of data analysis for UST releases. As noted 

above, the statistical methods and the detailed results of the statistical analyses are provided in 

Appendices B and C, respectively.

Release Sources

Figure 2 summarizes the sources of releases for the data. A total of 524 releases were 

reported from 512 records (some records reported multiple sources). Dispensers, piping, and 

delivery problems account for 25 percent, 23 percent, and 19 percent of releases, respectively,

and are the three most frequent sources of releases. The remainder of releases came from tanks, 

turbine pumps, and other sources. People putting product or used oil in monitoring wells 

(intentional or accidental), personal vehicles, and fill pipes are the most common other sources.

Figure 2: Sources Of UST Releases

25%

23%

19%

12%

10% 11%

0%

10%

20%

30%

Dispenser Piping Fuel

Delivery

Tank Pump

(Turbine)

Other

Release Source

Percent Of Releases .

The proportions of releases from dispensers and piping are significantly greater than 

releases from all other individual sources. The proportion of releases associated with fuel 

delivery is significantly greater than the proportions of releases from tanks and turbine pumps. 

The difference between the number of piping and dispenser releases is not large enough to 

conclude that dispenser releases occur more frequently than piping releases.

Release Causes 

Releases from UST systems were attributed to a wide range of causes (Figure 3). Loose 

components accounted for the largest proportion of releases for any single known cause (23

percent), followed by physical/mechanical damage (16 percent), overfill (15 percent), and spills 

(14 percent). Together, spills and overfills were responsible for 29 percent of all releases. The 

cause was unknown for 17 percent of releases.
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Figure 3: Summary Of Known Causes For All Releases

(435 Known Causes Identified For 524 Releases)

23%

16% 15% 14%

9%

5% 4% 4%

11%

0%

10%

20%

30%

Loose

ComponentPhys/Mech

Damage

Overfill

Spill

Puncture

Vehicle

Accident

Corrosion

Improper

Install

Other

Release Cause

Percent Of All Releases

While there are significant differences among the frequencies of the different causes, the

relative frequencies of causes vary substantially for different sources of releases. These 

differences are discussed in the following sections. Fueling of tanks or vehicles (which can 

result in spills, overfills, and deliveries to monitoring wells) appears to be the most common 

class of causes. The proportion of releases due to improper installation may be underreported

because improper installation is hard to identify in the field after a release has occurred. 

Deliveries to monitoring wells were the most frequent other cause.

Releases From Dispensers 

Releases from dispensers were the most frequent source, accounting for 25 percent of all 

releases. Releases from dispensers include not only releases from inside the dispenser housing, 

but also releases from hoses and nozzles. The cause was unknown for 36 percent of dispenser 

releases. Figure 4 provides a breakout of known causes for dispenser releases.

The most common known causes of dispenser releases were loose components (41 

percent), vehicle accidents (17 percent), physical or mechanical damage (13 percent), and spills 

(12 percent). Releases due to loose components occur significantly more frequently than 

releases from any other known dispenser cause. Releases from dispensers due to vehicle 

accidents, physical/mechanical damage, and spills occur significantly more frequently than 

releases due to the less common causes (corrosion, puncture, and improper installation). 

Vandalism and human error were the two most common other causes. 
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Figure 4: Known Causes Of Dispenser Releases

(83 Total Known Dispenser Release Causes)

41%

17%

13% 12%

5%

2% 1%

8%

0%

10%

20%

30%

40%

50%

Loose

Component

Vehicle

Accident

Phys/Mech

Damage

Spill

Improper

Install

Puncture

Corrosion

Other

Cause

Percent Of Dispenser Releases

EPA evaluated the potential effectiveness of under-dispenser containment (UDC) on the 

frequency of dispenser releases. Table 1 shows release and use data for dispensers with and 

without UDC. Looking at the R&I use data, releases from dispensers without UDC were slightly 

less frequent (33 percent) than dispensers that use UDC (36 percent). This difference is not 

significant. While this analysis does not indicate any effect by UDC on the frequency of 

dispenser releases, these results are subject to potential reporting bias because the data collection 

form only prompted inspectors to indicate if UDC was present and did not provide a means for 

indicating no UDC or whether the presence of UDC was unknown. Thus, some of the facilities 

without dispenser releases characterized as not having UDC might be facilities where the 

presence or absence of UDC was not determined. Therefore, EPA also evaluated dispenser 

secondary containment using the FDEP data. Based on that data, EPA found the use of dispenser 

containment is much more common than indicated by the data collected in this study and 

dispenser releases occur significantly more frequently – approximately twice as often – when 

dispenser containment is not present. EPA believes the FDEP data is more accurate, indicating 

that UDC appreciably reduces the frequency of releases from dispensers.

Table 1: Dispenser Releases And Secondary Containment

R&I Data FDEP Data Dispenser 

Secondary 

Containment

Number Of

Dispenser

Releases

Percent Of 

Dispenser 

Releases

Records With 

Non-Dispenser

Releases Percent Of Use UST Systems Percent Of Use

Present 43 33% 202 36% 12,362 81%

Not Present 87 67% 365 64% 2,833 19%

Total 130 100% 567 100% 15,195 100%
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Releases From Piping

Causes Of Releases. Piping was the source for 23 percent of UST releases. Figure 5

shows the relative frequency of known piping causes. The cause was unknown for 21 percent of 

piping releases. Of known causes, the more common were physical/mechanical damage (28

percent), loose components (26 percent), and puncture (20 percent). Other less common causes

each accounted for eight percent or less of piping releases. All of the more common piping 

release causes noted above occur significantly more frequently than the less common causes.

Figure 5: Known Causes Of Piping Releases*

(97 Total Known Piping Release Causes)

28%

26%

20%

8%

6% 6%

8%

0%

10%

20%

30%

Phys/Mech

Damage

Loose

Component

Puncture Corrosion Improper

Install

Vehicle

Accident

Other

Cause

Percent Of Piping Releases * Includes 111 releases from piping, plus 10 releases reported from both dispenser and piping and one 

release reported from both piping and tank, but excludes 26 piping releases of unknown cause.

Material Of Construction. Releases from fiberglass piping represent 77 percent of all 

piping releases. Figure 6 shows a summary of known causes for fiberglass piping releases. The 

cause was unknown for 24 percent of fiberglass piping releases. Loose component, puncture, 

and physical/mechanical damage are the most common causes for fiberglass piping. These three 

causes occur significantly more often than any of the other known causes for fiberglass piping.

Note that corrosion was identified as the cause of 4 percent of fiberglass piping releases. 

However, fiberglass itself doesn’t corrode – what corrodes are the metal connectors that may be 

included as part of the fiberglass piping system. Releases from the metal connectors attached to 

fiberglass piping are included in the releases attributed to fiberglass piping. This applies equally 

to metal and approved synthetic material piping releases. EPA includes metal connectors in the 

releases by piping construction because the data collection form did not specifically include 
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metal connectors as a source of release. Some data forms indicated the specific location of the 

release in the comments area. There may be other cases where the metal connector was the 

source of release but that information was not recorded. Therefore, EPA could not be sure that 

all cases where the release occurred from the metal connector were identified.

Figure 6: Known Causes Of Fiberglass Piping Releases

(71 Total Known Fiberglass Piping Release Causes)

28%

25% 25%

6%

4% 4%

0%

10%

20%

30%

Loose

Component

Phys/Mech

Damage

Puncture Improper

Install

Corrosion Other

Cause

Percent Of Fiberglass Piping Releases

Releases from steel piping represent 14 percent of all piping releases. Figure 7 shows a 

summary of known causes for steel piping releases. The cause was unknown for 13 percent of 

steel piping releases. Corrosion occurs more frequently than any other cause. However, the 

statistical analysis does not show that corrosion occurs significantly more often than any of the 

other causes. EPA looked at the type of cathodic protection (impressed current or galvanic 

anodes) used when corrosion was the cause of a steel piping release. However, there were 

insufficient data to perform any analysis. 

Releases from piping made of approved synthetic material7 represent nine percent of all 

piping releases. Figure 8 shows a summary of known causes of releases for piping made of 

approved synthetic material. The cause was unknown for 18 percent of releases for piping made 

of approved synthetic material. Physical/mechanical damage occurs more frequently than any 

other cause.

 

7

 According to FDEP, approved synthetic material is flexible plastic piping. 
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Figure 7: Known Causes Of Steel Piping Releases

(15 Total Known Steel Piping Release Causes)

33%

20% 20%

7% 7%

13%

0%

10%

20%

30%

40%

Corrosion Phys/Mech

Damage

Loose

Component

Vehicle

Accident

Improper

Install

Other

Cause

Percent Of Steel Piping Releases

Figure 8: Known Causes Of Approved Synthetic Material Piping Releases

(9 Total Known Approved Synthetic Material Piping Release Causes)

67%

22%

11%

0%

10%

20%

30%

40%

50%

60%

70%

80%

Phys/Mech Damage Loose Component Puncture

Cause

Percent Of Approved Synthetic Material Piping 

Releases
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Figure 9 shows a comparison of piping releases and use by material of construction. The 

proportion of releases from fiberglass piping (77 percent) was not significantly different than the 

proportion of USTs using fiberglass piping, based on both the R&I data (71 percent) and the 

FDEP data (77 percent). Similarly, the proportion of releases from approved synthetic piping 

was not significantly different than the proportion of systems that used this type of piping. For 

steel piping, the data indicate the difference between the proportion of steel piping releases (14 

percent) and the proportion of steel piping systems (21 percent) is marginally significant based 

on the R&I data. However, a significant and opposite relationship appears based on comparison 

with the FDEP data that indicates 8 percent of piping is steel. EPA believes the FDEP data is an

accurate reflection of steel pipe use in January 2003, while the R&I data is more indicative of 

steel pipe use over the period of the study. Overall, the data suggest the material of construction 

does not strongly affect frequency of releases from piping when comparing piping release and 

use data.

Figure 9: Piping Releases And Use Versus Piping Material Of Construction*

77%

14%

9%

0%

71%

21%

7%

1%

77%

8%

14%

2%

0%

10%

20%

30%

40%

50%

60%

70%

80%

90%

Fiberglass Steel Approved Synthetic

Material

Other FDEP Approved

Material

Piping Construction

Percent

Piping Releases Piping Use (R&I) Piping Use (FDEP)

 * Excludes two releases where the material of construction was unknown or not reported.

Secondary Containment. The release data showthat 43 percent of piping releases were

from secondarily-contained piping (Table 2). This proportion is the same as the proportion of 

piping using secondary containment in the R&I data. These results are subject to potential 

reporting bias, however, because the data collection form only prompted inspectors who 

completed the form to indicate if secondary containment was present and did not provide a 

means for indicating no secondary containment or unknown. Therefore, the use of piping 

secondary containment may be underreported in the R&I data. EPA believes the FDEP data 

better reflects the use of secondarily-contained piping. Based on this data, the use of piping 

secondary containment is much more common (60 percent compared to 43 percent) and the 

difference in the frequency of releases and use from secondarily-contained piping is significant. 

Therefore, these analyses suggest piping secondary containment is effective in reducing the 
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frequency of piping releases. Further statistical analyses using the FDEP data shows that singlewalled piping is nearly twice as likely to have a release to the environment as secondarilycontained piping (see the statistical analysis on page C-11).

Table 2: Effect Of Secondary Containment On Piping Releases

R&I Data FDEP Data Piping 

Secondary 

Containment Number Of

Piping Releases

Percent Of 

Piping

Releases

Records With 

Non-Piping

Releases

Percent Of 

Use

UST 

Systems 

Percent Of 

Use

Present 53 43% 214 43% 9,101 60%

Not Present 69 57% 286 57% 6,026 40%

Total 122 100% 500 100% 15,127 100%

Pressure Versus Suction Pumps. Most USTs were identified as having pressure pumps

(88 percent) with the remainder of USTs using suction pumps (12 percent). As shown in Table 

3, the proportions of releases from piping at USTs with pressure and suction pumps closely 

matched the R&I use data. The differences in proportions of piping releases versus piping use

are not significant for either pump type. Thus, the data do not suggest a disproportionate 

probability of piping releases associated with either pressure or suction pumps.

Table 3: Piping Releases And Pump Type

R&I Data

Pump Type For Piping 

Releases 

Number Of

Piping Releases

Percent Of 

Releases

Records With NonPiping ReleasesPercent Of 

Use

Pressure Pump 100 90% 409 88%

Suction Pump 11 10% 54 12%

Total 111 100% 463 100%

Comparison Between Age Of Piping In Use And Time To Piping Releases (UseRelease Analysis). All of the comparisons to this point between frequency of releases and use

have been made without consideration of piping age. Analyses that examine the relationship 

between age and release frequency can help address the relative performance over time of 

different piping configurations and materials of construction. EPA examined the relationship 

between the age distribution of piping in use and the age distribution of piping with releases in 

three ways – average age comparison, young versus old piping comparison, and cumulative age 

distributions. In these analyses, EPA used FDEP data as the source of the age distribution of 

piping in use. EPA determined the FDEP data to be a more appropriate source of information on 

the age of the piping in use because the age of piping in the R&I data is artificially limited by the 

date when an USTrelease occurred.

First, EPA performed a use versus release comparison by material of construction and by 

type of product delivery system for average piping age. This analysis shows the average release 

age for fiberglass, steel, and pressurized piping is significantly lower than the average use age for 

that type of piping. The average release age for approved synthetic piping and suction piping 

was also lower than the average use age; however, these differences were not statistically 

significant.

Second, EPA compared releases to use for young and old piping. Young is defined as 

piping under a specified age and old is piping greater than that age. EPA analyzed four different 
Peer Review Draft – March 2005 Do Not Cite Or Quote 15

age groupings: less than 5 years old, less than 10 years old, less than 15 years old, and less than 

20 years old. For piping less than 5 years old, steel and fiberglass piping releases were 

marginally greater than corresponding use. For approved synthetic piping under 5 years old, 

releases were significantly lower than use. For piping less than 10 years old, fiberglass piping 

releases were significantly greater than corresponding use, steel piping releases were marginally 

greater than use, and approved synthetic piping releases were significantly lower than use. For 

piping less than 15 years old and piping less than 20 years old, there were no significant 

differences between releases and use with one exception – approved synthetic piping releases

were marginally lower than corresponding use for synthetic piping less than 15 years old. 

Third, EPA compared cumulative age distributions of piping in use to those of piping 

with releases. This statistical test looks at the difference between releases and use at each 5 year 

age increment by analyzing the overall shape of the age curve. The differences were significant 

for all piping combined, for fiberglass piping and for piping associated with pressure pump 

systems. Specifically, releases are not distributed uniformly over the life of these piping 

systems; rather, they occur more frequently when the systems are less than 15 years old. It is not 

surprising to find the same for all piping, fiberglass piping, and piping associated with pressure 

pump systems because, as noted above, most piping is fiberglass, most pump systems are 

pressurized systems, and most releases were from fiberglass and pressurized piping systems.

Releases During Fuel Delivery 

As indicated in Figure 2, 19 percent of releases occurred during fuel delivery. Overfills 

and spills were identified as the cause of 50 percent and 43 percent of these releases, respectively 

(Figure 10). Loose components were associated with 3 percent of releases. All other causes were 

fuel deliveries to monitoring wells. There were no unknown causes for fuel delivery releases. 

Figure 10: Known Causes Of Releases During Fuel Delivery

(101 Total Known Fuel Delivery Release Causes)

50%

43%

3% 4%

0%

10%

20%

30%

40%

50%

60%

Overfill Spill Loose Component Other

Cause

Percent Of Fuel Delivery Releases
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To analyze the impact of overfill protection on releases, EPA compared the overfill 

protection used when a fuel delivery release occurred with the general use of overfill protection 

in both the R&I data and the FDEP data (Table 4). EPA could not evaluate the effectiveness of 

spill buckets because the UST systems without spill buckets were reported as being out of 

compliance and, thus, were not classified as valid data points for the purposes of this study. In 

addition, the condition of spill buckets was not recorded. 

Table 4: Fuel Delivery Releases And Overfill Protection Methods*

R&I Data FDEP Data

Overfill Protection 

Method

Number Of 

Delivery 

Releases

Percent Of 

Delivery 

Releases

Records With NonDelivery ReleasesPercent Of 

Use

UST 

Systems

Percent Of 

Use

Ball Check Valve 36 77% 473 81% 11,122 67%

Flow Shutoff 11 23% 105 18% 5,593 33%

Total 47 100% 578 100% 16,715 100%

* Excludes high level alarms because an anomaly on the data collection form is likely to have resulted in 

underreporting of high level alarm use.

The proportion of total releases occurring at USTs with ball check valves (77 percent) is 

slightly lower than USTs using ball check valves in the R&I data (81 percent), but the difference 

is not statistically significant. Similarly, the proportion of releases at USTs with flow shutoff (23 

percent) is not significantly different from USTs using this technology (18 percent). In addition, 

comparison of the frequency of release with the frequency of use based on the FDEP data also 

indicates no significant difference for either overfill protection method. Thus, the data suggest 

the type of overfill protection used does not affect the likelihood of UST releases.

Releases From Tanks 

Causes Of Releases. Tank releases represent 12 percent of all UST releases in the data. 

Figure 11 shows the known causes for tank releases. The cause was unknown for 14 percent of 

tank releases. Puncture was the most common cause, identified in 31 percent of releases. 

Physical or mechanical damage (26 percent) and corrosion (19 percent) were also common 

causes of releases. Less common causes (loose components, overfill, or improper installation) 

collectively accounted for 13 percent of all tank releases. Eleven percent of tank release causes 

were listed as other and were primarily due to damage during removal and damage during 

delivery. The more common causes of tank releases occur significantly more frequently than all 

of the less common causes. The comparatively high frequency of puncture and physical or 

mechanical damage as the cause of release is not surprising given, as discussed below, that the 

majority of tank releases were from fiberglass tanks.
Peer Review Draft – March 2005 Do Not Cite Or Quote 17

Figure 11: Known Causes Of Tank Releases

(54 Total Known Tank Release Causes)*

31%

26%

19%

9%

2% 2%

11%

0%

10%

20%

30%

40%

Puncture Phys/Mech

Damage

Corrosion Loose

Component

Overfill Improper

Install

Other

Cause

Percent Of Tank Releases

* Includes 61 releases from tanks plus one release reported from both dispenser and a tank and one release from 

both piping and a tank.

Material Of Construction. Releases from steel tanks8 represent 30 percent of all tank 

releases. Figure 12 shows a summary of known causes for steel tank releases. The cause was 

unknown for 12 percent of steel tank releases. Corrosion is the most frequent known cause 

representing 59 percent of steel tank releases. Corrosion occurs significantly more frequently 

than any other known cause for steel tanks. EPA looked at the type of corrosion protection 

(internal lining, impressed current, or galvanic anodes) used when corrosion was the cause of a 

steel tank release. For the ten steel tank releases due to corrosion, four came from tanks with 

impressed current and three each from tanks with galvanic anodes and from internally lined 

tanks. There were not enough data to support statistical analyses by corrosion protection type.

 

8

 Fiberglass-clad steel tanks are considered as a separate category in this study and are not included when analyzing 

steel tanks.
Peer Review Draft – March 2005 Do Not Cite Or Quote 18

Figure 12: Summary Of Known Causes For Steel Tank Releases

(17 Total Known Steel Tank Release Causes)

59%

18%

12%

6% 6%

0%

10%

20%

30%

40%

50%

60%

70%

Corrosion Phys/Mech

Damage

Loose

Component

Puncture Improper Install

Cause

Percent Of Steel Tank Releases

Releases from fiberglass tanks represent 65 percent of all tank releases. Figure 13 shows 

a summary of known causes for fiberglass tank releases. The cause was unknown for 17 percent 

of fiberglass tank releases. Puncture and physical/mechanical damage are the two most frequent 

causes of releases for fiberglass tanks. Punctures occurred significantly more often than all other 

causes except physical/mechanical damage for which it was marginally greater. Physical or 

mechanical damage occurred significantly more often than loose components and overfills.

Fiberglass-clad steel, polyethylene (jacketed steel), and concrete tanks each had one 

release. There were insufficient data to analyze the causes of release for these tank types.

As was done for piping releases, EPA compared tank releases and use by material of 

construction (Figure 14). The proportion of releases from fiberglass tanks (65 percent) was not 

significantly different than fiberglass tank use, based on both the R&I data and the FDEP data. 

Similarly, the analysis indicates steel tank releases (30 percent) were not significantly different 

than the steel tank use (27 percent), based on the R&I data. In contrast with the R&I data for 

steel tanks, the FDEP data show steel tanks are used less often (18 percent), resulting in steel 

tank releases being significantly greater than steel tank use for the FDEP data. Thus, the data do 

not suggest a clear conclusion regarding the frequency of release relative to use for steel tanks. 

In contrast, the data do clearly suggest that releases from fiberglass-clad steel tanks (2 percent) 

are significantly less than the fiberglass-clad steel tank use for both data sets (18 percent and 23 

percent).
Peer Review Draft – March 2005 Do Not Cite Or Quote 19

Figure 13: Summary Of Known Causes For Fiberglass Tank Releases

(35 Total Known Fiberglass Tank Release Causes)

46%

31%

3% 3%

17%

0%

10%

20%

30%

40%

50%

60%

Puncture Phys/Mech

Damage

Loose

Component

Overfill Other

Cause

Percent Of Fiberglass Tank Releases

Figure 14: Tank Releases And Use Versus Tank Material Of Construction

65%

30%

2% 2% 2%

55%

27%

18%

0% 0%

59%

18%

23%

0% 0%

0%

10%

20%

30%

40%

50%

60%

70%

Fiberglass Steel Fiberglass-Clad Steel Polyethylene Concrete

Tank Construction

Percent

Tank Releases Tank Use (R&I) Tank Use (FDEP)
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Secondary Containment. To analyze the impact of secondary containment on releases, 

EPA compared releases from secondarily-contained tanks to both the R&I use data and FDEP 

use data (Table 5). When examining the R&I use data, the proportion of releases from tanks 

with secondary containment (6 percent) is much lower than the proportion of tanks with 

secondary containment (23 percent). The difference is significant, to the extent that the chance 

of a release from a tank without secondary containment is approximately four times greater than 

from a tank with secondary containment (see the statistical analysis on page C-10).

Table 5: Effect Of Secondary Containment On Tank Releases

R&I Data FDEP Data

Tank Secondary 

Containment

Number Of 

Tank 

Releases

Percent Of 

Tank Releases

Records With 

Non-Tank 

Releases

Percent Of 

Use UST Systems

Percent Of 

Use

Present 4 6% 144 23% 6317 42%

Not Present 59 94% 484 77% 8878 58%

Total 63 100% 628 100% 15195 100%

As with the piping analysis, EPA believes the R&I data undercount tank systems with 

secondary containment and the FDEP data better reflects the use of these systems. When the 

FDEP data on tank use and releases are compared, the difference between use and releases from

secondarily-contained tanks is even greater. The difference between the proportion of releases 

from tanks with secondary containment (6 percent) and the use of tanks with secondary 

containment (42 percent) is significant, resulting in the relative risk of a release from a tank 

without secondary containment being more than 10 times greater than from a tank with 

secondary containment (see the statistical analysis on page C-10). Thus, the data strongly 

support that the presence of tank secondary containment results in fewer releases to the 

environment from tanks.

Comparison Between Age Of Tanks And Time To Tank Releases. EPA examined the 

relationship between the age distribution of tanks in use and the age distribution of releases from 

tanks in a similar manner as described above for releases from piping. The differences in the

average ages of tank releases to the average age of tanks in use were not significant for any tank 

construction. Also, the cumulative age distributions of all tanks and for steel and fiberglass tanks 

in use were not significantly different than the distributions of tank age at the time of release. 

EPA did not perform comparisons for fiberglass-clad steel tanks because the study data include 

so few releases from this type of tank.

Pump (Turbine) Releases

Figure 15 shows the known causes of releases from turbine pumps9. The cause was 

unknown for 12 percent of turbine pump releases. Of known causes, loose component was the 

most common cause of release (48 percent), followed by physical and mechanical damage (30 

percent). A less common cause was improper installation (11 percent). The most common other 

release causes for turbine pumps were all related to human error. Pump releases caused by loose 

components were significantly more frequent than releases from any of the other known causes. 

Physical or mechanical damage was a significantly more frequent cause than any of the other 

 

9

 Pump (turbine) releases include releases from line leak detectors.
Peer Review Draft – March 2005 Do Not Cite Or Quote 21

causes except loose components. Releases due to improper installation were significantly more 

frequent than releases due to puncture.

Figure 15: Known Causes For Pump (Turbine) Releases

(46 Total Known Pump Release Causes)

48%

30%

11%

2%

9%

0%

10%

20%

30%

40%

50%

Loose

Component

Phys/Mech

Damage

Improper Install Puncture Other

Cause

Percent Of Pump (Turbine) Releases

Other Release Sources 

Other release sources are those identified as not fitting into one of the major categories 

previously discussed. Other sources primarily include releases from fill pipes, vapor recovery 

lines, vent lines (other than those releases occurring during delivery), and releases associated 

with personal vehicles. Figure 16 shows the distribution of known causes for other releases. 

Four percent of other release source causes were unknown. Overfills, loose components, and 

spills are the major known causes of other releases. Most of the other release causes were due to

either intentional or unintentional deliveries to monitoring wells. These deliveries are not 

associated with fueling, but rather putting fuel or used oil into a monitoring well by hand. 

Among the other sources, overfills were marginally greater than loose components and

significantly greater than releases from the other identified causes. Releases due to loose

components were significantly more frequent than other identified causes except spills. Spills 

were significantly greater than all other less frequent causes.
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Figure 16: Known Causes For Other Releases

(53 Total Known Other Release Causes)

26%

17%

13%

4% 4%

2%

35%

0%

10%

20%

30%

40%

Overfill Loose

Component

Spill Phys/Mech

Damage

Puncture Improper

Install

Other

Release Cause

Percent Of Other Releases

Volume Of Releases

The sizes (volumes) of releases were reported for 31 percent of releases. Limited data on the 

distribution of release volumes are available for the most common sources (Table 6). The 

average volume released ranges from just ove r 1,150 gallons for piping to 33 gallons for turbine 

pumps. Omitted from the table are releases attributed to multiples sources – one from piping and 

dispenser (85 gallons) and one from tank and piping (10 gallons). Median releases are much 

smaller than the averages because of the skewed nature of the volume distributions. Most 

releases are small, but the averages are strongly affected by a few very large releases. Because 

the data are not normally distributed, confidence limits on the average releases were calculated 

using non-parametric bootstrap sampling.

Of the known sources, piping and tanks have the highest average release volumes – 1,152 

and 696 gallons per release, respectively. The average volume for piping is strongly influenced 

by one very large release (25,000 gallons), without which the mean release would be about 525 

gallons. The average release volume for dispenser releases is 260 gallons, less than for tanks and 

piping, but more than twice as high as the averages for all other specified sources. These data 

suggest that tanks, piping, and dispensers are more likely to have a large release, though the 

median release size across release sources was relatively similar.
Peer Review Draft – March 2005 Do Not Cite Or Quote 23

Table 6: Release Volumes For The Different Sources

Release Source

Number Of 

Releases Of 

Known 

Volume

Average 

Release 

(Gallons)

Median 

Release 

(Gallons)

Minimum 

Release 

(Gallons)

Maximum 

Release 

(Gallons)

Lower 95% 

Confidence 

Limit Of 

Mean 

(Gallons)*

Upper 95% 

Confidence 

Limit Of 

Mean 

(Gallons)

Piping 39 1,152 50 2 25,000 202 2,701

Tank 17 696 50 5 3,500 228 1,283

Other 23 408 25 2 5,000 66 939

Dispenser 30 260 25 3 3,400 64 543

Fuel Delivery 43 126 50 1 1,250 64 208

Fill Pipe 3 93 55 25 200 -- --

Pump 

(Turbine) 6 33 23 10 75 15 54

Overall 161 491 40 1 25,000 231 878

* Confidence limits were calculated by resampling (bootstrap) analyses of the data (10,000 iterations for each 

source).

Environmental Media Affected By UST Releases

Releases can affect both soil and water. However, because releases to water are of 

greatest concern, this section focuses on the extent to which releases from different sources 

impact groundwater or surface water. Summary data show that more than 60 percent of all 

releases impacted water (Table 7). Note that Florida has a high groundwater table. Therefore, 

the impacts to groundwater in this study may be higher than in states with lower groundwater 

tables. However, the relative likelihood of different release sources reaching groundwater should 

be independent of groundwater depth.

Table 7: Releases Affecting Groundwater And Surface Water By Source Of Release

Impacting 

Groundwater

Impacting Surface

Water

Total Impacting 

Water

Source

Number 

Of 

Releases

Number Percent Number Percent Number Percent

Percent Of 

Each Sources’

Contribution 

To Total Water 

Impacts

Fuel 

Delivery 101 64 63% 2 2% 66 65% 21%

Dispenser 130 53 41% 4 3% 57 44% 18%

Piping 122 71 58% 3 3% 71 58% 22%

Pump 

(Turbine) 52 32 62% 0 0% 32 62% 10%

Tank 63 54 86% 1 2% 54 86% 17%

Other 56 35 63% 4 7% 39 70% 12%

Total Media 

Affected 524 309 59% 14 3% 319* 61%

* Total does not sum because four releases affected both groundwater and surface water

Figure 17 shows the proportion of releases from each source affecting water. The

proportion of tank releases that impact groundwater or surface water (called water) is larger (86 

percent) than for any other release source, while dispensers have the lowest proportion of 

releases from a given source impacting water (44 percent). 
Peer Review Draft – March 2005 Do Not Cite Or Quote 24

Figure 17: Proportion Of Releases From Each Source Affecting Water

86%

65% 62% 58%

44%

70%

0%

10%

20%

30%

40%

50%

60%

70%

80%

90%

100%

Tank Fuel Delivery Pump

(Turbine)

Piping Dispenser Other

Release Source

Percent Releases From Each Source 

Impacting Water .

Figure 18 shows a breakdown of the proportions of total releases affecting water from 

each source, reflecting both release volume and release frequency. The most frequent sources of 

releases to water are piping (22 percent) and fuel delivery mishaps (21 percent). Dispensers and 

tanks are the next frequent sources of releases to water at 18 percent and 17 percent, respectively. 

The proportions of releases to water from the four most common sources – piping, fuel delivery, 

dispensers, and tanks – are significantly more frequent than releases from the less common 

sources. Although the data in Figure 17 indicate a tank release is about twice as likely as a 

dispenser release to affect water, dispenser releases are about twice as common as tank releases, 

with the result that the overall frequency with which these two sources affect water is about the 

same (as shown in Figure 18).
Peer Review Draft – March 2005 Do Not Cite Or Quote 25

Figure 18: Total Number Of Releases Affecting Water By Source

22% 21%

18% 17%

10%

12%

0%

10%

20%

30%

Piping Fuel Delivery Dispenser Tank Pump

(Turbine)

Other

Release Source

Percent Contribution To Total Water 

Impacts .

Method Of Release Discovery

The method of release discovery was reported for 99 percent of all releases. Of releases with a 

known method of discovery, 26 percent were discovered by leak detection methods (Figure 19). 

The most common method of discovery was visual and/or olfactory (38 percent), i.e., by seeing 

or smelling the release. Closure, defined as releases identified through closure in place or 

removal, accounted for 15 percent of releases discovered. Nearly one-half of the releases in the 

other category, or 7 percent of all releases, were identified through compliance or maintenance 

inspections. Tank tightness testing or line tightness testing performed for reasons other than leak

detection10 was reported as the method of release discovery in only a small proportion of releases

(5 percent). These data are notable in that the majority of releases are identified by a means 

other than leak detection. However, most of the leak detection technologies evaluated in this 

study are designed to only detect releases from tanks and piping, and the majority of releases 

(about 65 percent) come from non-tank and non-piping sources. The high proportion of releases 

that are first detected simply by seeing or smelling the release is noteworthy. This proportion is 

significantly greater than the proportions discovered by any other method.

 

10 Tank tightness testing or line tightness testing for leak detection are included in the leak detection count, but 

tightness testing used for other purposes (e.g., to investigate a suspected release) was separated into its own 

category.
Peer Review Draft – March 2005 Do Not Cite Or Quote 26

Figure 19: Method Of Release Discovery

(505 Total Releases With A Method Of Discovery Identified)

38%

26%

15%

5%

16%

0%

10%

20%

30%

40%

Visual/Olfactory Leak Detection Closure TTT Or LTT

Performed For

Other Reasons

Other

Method Of Discovery

Percent Of Releases

Performance Of Leak Detection Methods

EPA gathered information on the proportions of releases where specific leak detection 

methods failed or succeeded in detecting releases. Leak detection was identified as failing to 

detect 23 percent of releases and succeeded in detecting 26 percent of releases. For the other 51 

percent, EPA could either not make a determination or the leak detection device did not have an 

opportunity to detect the release.

Table 8 compares the frequencies with which specific technologies were identified as 

succeeding or failing to detect releases with their frequencies of use in the R&I data. Several 

leak detection technologies are identified as failing or succeeding significantly more or less 

frequently than their corresponding use. Groundwater monitoring, the most frequently used 

technology (52 percent of facilities), is reported to have both failed and succeeded in detecting 

releases significantly more frequently than it is used. Conversely, secondary containment/

interstitial monitoring, manual tank gauging, and automatic gauging are identified as succeeding 

and failing less often than they are used. Given these results, EPA could not make any 

determinations of whether one leak detection method is better than another in terms of both 

succeeding and not failing to detect a release.
Peer Review Draft – March 2005 Do Not Cite Or Quote 27

Table 8: Proportions Of All Releases Identified And Not Identified By Tank Leak 

Detection Methods Compared To Frequency Of Use

Leak Detection 

Method

Number 

Identified 

As Failed

Percent Of 

Identified 

Failures*

Number 

Identified

As 

Succeeding 

Percent Of 

Identified 

Successes *

Number Used 

(R&I Data)**

Percent Use 

(R&I Data)**

 Groundwater Monitoring 70 73% 84 73% 396 52%

 Automatic Tank Gauging 1 1% 0 0% 106 14%

 Secondary/Interstitial 11 11% 8 7% 97 13%

 IC/TTT*** 9 9% 11 10% 54 7%

 Manual Tank Gauging 1 1% 1 1% 39 5%

 Line Tightness Testing 0 0% 9 8% 33 4%

 SIR*** 3 3% 2 2% 31 4%

 Vapor Monitoring 1 1% 0 0% 8 1%

 Total 96 100% 115 100% 764 100%

* Dark shading = significantly different from use; light shading = marginally different.

** Excludes incidents involving false or faulty leak detection alarms.

*** IC/TTT = inventory control/tank tightness testing; SIR = statistical inventory reconciliation.

EPA also compared the frequencies of success and failure for electronic and mechanical 

line leak detectors (LLDs) with their corresponding use in the R&I data. The results of that 

analysis are shown in Table 9. The frequencies at which electronic and mechanical LLDs

succeed or fail to detect releases are not significantly different from their frequencies of use. 

Thus, the data do not indicate either method is more or less effective than the other.

Table 9: Failures And Successes For Electronic And Mechanical Line Leak Detectors

Leak Detection 

Method

Number 

Identified 

As Failed

Percent Of 

Identified

Failures

Number 

Identified As 

Succeeding 

Percent Of 

Identified

Successes

Number Used 

(R&I Data)*

Percent Use 

(R&I Data)*

Electronic LLD 4 17% 21% 4 63 18%

Mechanical LLD 19 83% 79% 15 280 82%

Total 23 100% 100% 19 343 100%

* Excludes incidents involving false or faulty leak detection alarms.
Peer Review Draft – March 2005 Do Not Cite Or Quote 28

Discussion Of Results

EPA and FDEP reviewed data from 2,280 releases or incidents in nine Florida counties. 

From these, 512 sites were identified with releases from new or upgraded UST systems and had

sufficient and appropriate data to include in this study. EPA analyzed the data for sources, 

causes, component-specific characteristics (such as material of construction and secondary 

containment), method of release discovery, media affected, and release extent. Data for UST 

incidents and AST releases and incidents were not included in this report, but may be analyzed 

for future reports. 

Releases And Causes

Dispensers, piping, and fuel delivery were the three most frequent sources of releases. 

Tanks and turbine pumps were also common sources, but releases from these sources occurred 

significantly less frequently than the three most frequent sources. Piping has been a frequent

source of UST system releases since the inception of the program, as has fuel delivery. These 

sources persist despite release prevention requirements aimed at reducing these releases. 

Dispensers, however, have emerged as a frequent source of releases. Neither EPA nor most 

states have release prevention requirements for dispensers. Tanks are a much less frequent 

source of release than dispensers, piping, and fuel delivery. This may indicate success in 

regulatory requirements aimed at reducing releases from tanks. Turbine pumps, including the 

attached line leak detectors, are typically not subject to release prevention requirements, unless 

they are in contact with soil.

Loose components are the most frequent known cause of releases at 23 percent, occurring 

significantly more often than any other release cause. Physical or mechanical damage, overfills, 

and spills each occurred about 15 percent of the time. The most common class of known causes 

is associated with deliveries or vehicle fueling and includes spills, overfills, and deliveries to 

monitoring wells. The frequency of different known causes varies substantially by source and is 

discussed further below. Please also note the proportion of releases due to improper installation 

is likely underreported because improper installation is hard to identify in the field after a release 

has occurred. Thus this study does not allow EPA to say with certainty the extent improper 

installation leads to UST system releases. Another important consideration is that while loose 

components and physical/mechanical damage are significant causes of releases, EPA generally 

could not pinpoint the specific causes for the loose component or damage – be they poor 

materials, improper installation, or improper or insufficient operation and maintenance.

Dispensers

Dispensers were the most common source of releases at 25 percent, occurring 

significantly more frequently than all other release sources except piping. Loose components

were the most common known cause of dispenser releases at 41 percent, occurring significantly 

more frequently than any other known cause. Dispensers contain many different components, so 

there are many opportunities for connections to become loose. Vehicle accidents, physical or 

mechanical damage, and spills were also common causes of releases at dispensers. The high 

occurrence of dispenser releases is an important finding because EPA and most states do not 

have any release prevention requirements for dispensers. Looking at UDC, the presence of UDC 

significantly reduced the likelihood of a release from a dispenser when compared to FDEP data,
Peer Review Draft – March 2005 Do Not Cite Or Quote 29

with dispenser releases occurring about twice as often at dispensers without UDC than at those 

with UDC.

Piping

Piping was the second most frequent source of releases, representing 23 percent of 

releases in the data. Piping releases occurred significantly more frequently than all other release 

sources except dispensers. Physical/mechanical damage, loose components, and puncture were 

the three most frequent known causes of piping releases. The relatively large percentage of 

releases due to puncture was somewhat surprising, and highlights the need to more carefully 

consider tank and piping location while performing construction work at an UST site. It is 

important to note, however, that the causes of releases varied significantly by material of 

construction.

Fiberglass piping (including any associated metal connectors) is the most commonly used 

piping and is the most frequent source of piping releases. Loose component, physical or 

mechanical damage, and punctures were the predominant known causes of fiberglass piping 

releases. Corrosion was identified as the cause of four percent of fiberglass piping releases. 

However, fiberglass itself doesn’t corrode – what corrodes are the metal connectors that are 

typically included at the ends of the fiberglass piping. Releases from the metal connectors 

attached to fiberglass piping are included in the releases attributed to fiberglass piping. EPA

could not separate these releases because the number of fiberglass piping releases from the metal 

portion of the piping run could not be identified.

Corrosion was the primary known cause of releases from steel piping. However, due to 

the limited number of steel piping releases (14), EPA was not able to make statistically valid 

claims as to the relative frequency of the different causes. As with fiberglass piping, steel piping 

may have had metal connectors and any releases that occurred in those connectors was attributed 

to a release from the steel piping.

For approved synthetic piping (flexible plastic piping), physical or mechanical damage 

was the primary known cause of releases. As with the other piping constructions, any releases 

that occurred at metal connectors associated with the approved synthetic piping run were 

attributed to the synthetic piping.

None of the three primary materials of construction appeared to be any more or less 

likely to have a release, relative to their use. In other words, none of the three materials 

performed significantly better or worse than the other materials. Similarly, no distinction was 

observed between the performance of pressurized and suction piping systems.

EPA compared releases to use for single-walled and secondarily-contained piping. 

Secondarily-contained piping performed at least as well as single-walled piping with the R&I use 

data and significantly better than single-walled piping when compared to the FDEP use data. 

EPA believes that, because of the way data could be entered on the form for the R&I data, the 

piping secondary containment captured in the R&I data would be the absolute minimum use of 

secondarily-contained piping and very likely undercounts the use of secondarily-contained 

piping. Therefore, FDEP data is a more accurate represent ation of the use of secondarilycontained piping. Using the FDEP use data for single-walled piping versus secondarily-
Peer Review Draft – March 2005 Do Not Cite Or Quote 30

contained piping, single-walled piping was significantly more likely to have a release. In fact, 

single-walled piping was approximately twice as likely to have a release, relative to its use. 

Therefore, secondarily-contained piping is more effective than single-walled piping at reducing 

the frequency of piping releases to the environment.

EPA also analyzed the relationship between piping age and release frequency by material 

of construction and by type of product delivery system using three approaches – average age 

comparison, young versus old piping comparison, and cumulative age distributions. The 

comparison of average ages showed the average age to release was lower than the average age of 

piping in the ground for all piping constructions. The difference was statistically significant for 

fiberglass, steel, and pressurized piping. The comparison of release to use for young and old 

piping showed releases from fiberglass piping less than 10 years old is significantly higher than 

use of fiberglass piping of the same age. Similarly, releases from steel piping were marginally 

higher than use of steel piping of the same age. In contrast, releases from approved synthetic 

piping less than 10 years old were significantly lower than use for approved synthetic piping of 

the same age. The cumulative age distributions found a significant relationship between 

fiberglass piping age and the likelihood of a release. Specifically, fiberglass piping less than 15 

years old is more likely to have a release than older fiberglass piping. This relationship also held 

true for all piping and for pressurized piping systems. However, since fiberglass piping 

represented the majority of all piping releases and use, the relationship for all piping is likely 

influenced by the large number of fiberglass piping systems.

Fuel Delivery

Fuel delivery was another frequent source of releases at 19 percent, occurring 

significantly more frequently than all other sources except dispensers and piping. Nearly all fuel 

delivery releases were caused by spills or overfills at the time of delivery. Loose components 

and deliveries to monitoring wells collectively contributed to seven percent of these releases. 

The large percentage of spills and overfills raises questions about the reliability of current 

spill and overfill prevention systems. EPA was not able to record and analyze the relative 

performance of different spill bucket sizes, materials of construction, and general condition in 

the field because that data was not available in FDEP files. EPA was also not able to determine 

how many releases were due to poor, improper, or damaged equipment; improper or insufficient 

operation and maintenance; or delivery driver accident or negligence. EPA analyzed how ball 

float valve and automatic shutoff overfill protection technologies performed, but neither method 

stood out as more or less effective than the other.

Tanks

Tanks represented 12 percent of all releases. Releases from tanks occurred significantly

less frequently than releases from dispensers, piping, and fuel deliveries. Puncture and physical 

or mechanical damage were the most frequent known causes of tank releases, followed by 

corrosion. However, the known causes of tank releases varied significantly by material of 

construction.

Releases from steel tanks represented 30 percent of all tank releases. Corrosion (at 59 

percent) was by far the most frequent known cause of releases from steel tanks. Unfortunately, 
Peer Review Draft – March 2005 Do Not Cite Or Quote 31

there was insufficient data to analyze the differences between steel tanks protected by impressed 

current systems and galvanic systems.

Puncture and physical/mechanical damage were the most frequent known causes of 

releases from fiberglass tanks, representing nearly all of the known causes. Fiberglass-clad steel, 

polyethylene (jacketed steel), and concrete tanks did not have enough releases to compare their 

respective release causes.

Fiberglass tanks were both the most commonly used tanks and the tanks with the most 

releases. In comparing use to releases, fiberglass tanks did not appear to release significantly 

more or less frequently than would be expected given their frequency of use. Steel tanks 

appeared more likely to release using the FDEP data, but no more likely to have a release using 

the R&I data. Since EPA cannot identify one use data set as more appropriate in this case, the

Agency could not draw a clear conclusion as to the relative likelihood of a release from a steel 

tank. Fiberglass-clad steel tanks, however, performed quite well relative to their use. They 

represent approximately 20 percent of tanks in use, but account for only one of the 63 tank 

releases (less than two percent). 

Secondary containment significantly reduced the likelihood of a tank release when 

compared to tank use. Using the R&I data, single-walled tanks were four times more likely to 

have a release than secondarily-contained tanks. Using the FDEP data, which EPA believes to 

be more representative of secondarily-contained tank use, single-walled tanks were ten times 

more likely to have a release. Thus, the data strongly support that the presence of tank secondary 

containment results in fewer releases from tanks to the environment.

EPA also examined the relationship between tank age and likelihood of tank releases. 

There were no significant differences between use and releases, either for tanks in general or for 

any specific material of construction.

Pumps (Turbines)

Releases from turbine pumps (including line leak detectors) represented 10 percent of 

releases in the data. Loose components were the most frequent known cause of releases for 

turbine pumps. Physical/mechanical damage was the second most frequent known cause, 

followed by improper installation. Interestingly, improper installation was identified more 

frequently for pumps (as a percentage of total causes) than for either tanks or piping. This may 

be because pumps are typically not buried and are more readily inspected, making improper 

installation easier to determine.

Release Volumes And Environmental Impacts

Release size was not available for 69 percent of releases (release volume can be difficult 

to determine). Most identified releases were fairly small. The median release size was 40

gallons and no more than 55 gallons for any individual source. The release volume data shows 

that large releases are more likely to come from tanks and piping, followed by dispensers. The 

largest recorded release (25,000 gallons) came from piping. These large releases lead to average 

release sizes of more than 1,000 gallons for piping, nearly 700 gallons for tanks, and more than 

250 gallons for dispensers.
Peer Review Draft – March 2005 Do Not Cite Or Quote 32

While size can be a strong indicator of a release’s likelihood of having significant 

environmental or human health impacts, impacts to water (groundwater or surface water) is 

probably even more important. More than 85 percent of releases from tanks impacted water, 

compared with only 44 percent of dispenser releases. Releases from fuel deliveries, pumps, and 

piping reached water approximately 60 percent of the time. Florida has relatively high 

groundwater, so the water impact rates identified in this study may be higher than normal, but the 

relative likelihood of impacting water across sources should be similar for areas with lower 

groundwater. Coupling release frequency with likelihood of impacting groundwater, the data 

show piping and fuel delivery releases as having the most water impacts, followed by dispensers 

and tanks.

Method Of Detection And Leak Detection Performance

Seeing or smelling a release was the most common method of release discovery, 

occurring at 38 percent of releases. This number may even be undercounted because many

releases discovered during an inspection were attributed to the other release discovery category. 

Releases found at closure represented 15 percent of release discoveries.

Leak detection successfully detected 26 percent of all releases. Conversely, leak 

detection was specifically identified as failing to detect 23 percent of releases. For the remaining

releases, the success or failure of leak detection could not be determined because either the data 

could not determine whether leak detection failed or the leak detection device did not have an 

opportunity to detect the release. While only a relatively small percentage of releases were 

discovered by leak detection, two important factors to be considered are: most leak detection 

devices are not designed to detect releases from some of the more frequent sources of releases 

(such as fuel deliveries or dispensers) and some release rates may be too small for the leak 

detection method to detect. It is also important to point out that when a leak detection method 

was identified as failing, EPA could not determine the exact reason for the leak detection method 

failure – whether it was faulty equipment; improper installation, operation or maintenance; or 

insufficient performance standards. Nonetheless, since leak detection identified only one-quarter 

of releases raises questions about the effectiveness of the current approach to leak detection.

EPA also compared specific leak detection methods. However, EPA could not determine

that any one leak detection method was better than others in terms of both successfully detecting

and not failing to detect a release.
Peer Review Draft – March 2005 Do Not Cite Or Quote A-1

Appendix A – Data Collection Forms

Appendix A contains Florida’s two data collection forms used by the inspectors:

• Storage Tank System Release Investigation Information Form

• DEP Storage Tank System Incident Investigation Information Form






Peer Review Draft – March 2005 Do Not Cite Or Quote B-1

Appendix B - Statistical Methods

EPA used a number of statistical tests to evaluate the data related to releases from 

underground storage tanks in Florida (Table B-1). These tests include parametric and nonparametric procedures selected based on the nature of the comparisons being made and the 

data being evaluated, as discussed in the following sections.

Table B-1: Statistical Tests Used In The Analysis Of Florida UST Release Data

Data Evaluated Statistical Tests 

Used

Nature Of Comparisons

Releases by source z-test proportions of releases from individual sources

Causes of release 

by source

z-test proportions of all releases and releases from each source

z-test proportions of releases by cause from steel and fiberglass tanks, 

proportions of total releases from tanks made of different materials

Tanks materials 

and causes

Fisher's exact test proportions of releases by cause from steel tanks (small numbers)

z-test proportions of releases by cause from steel, fiberglass, approved 

synthetic piping, proportions of total releases from piping made of 

different materials

Piping materials 

and causes

Fisher's exact test proportions of releases by cause from steel, approved synthetic liners 

(small numbers)

z-test proportions of releases from tanks, piping, dispensers with and without 

secondary containment (R&I data only), proportions of releases versus 

type of tank spill containment

Secondary 

containment and 

overfill protection

Odds ratio and 

confidence limits

frequencies of release with frequencies of use (separate analyses with 

use data from R&I, FDEP data sets)

Release 

identification

z-test proportions of releases detected by different methods

Leak detection z-test proportions of successes and failures to detect releases versus use by 

individual type of leak detection technologies and for electronic and 

mechanical line leak detectors

Contamination by 

source, media

z-test proportions of releases from different sources affecting groundwater 

and/or surface water, proportions of releases from systems with pressure 

or suction pumps affecting groundwater and/or surface water

Release volumes non-parametric 

bootstrap

nonparametric confidence limits on release volumes from different 

sources

Tanks, piping use, 

release

z-test proportions of releases versus use data (separate comparisons using R&I 

data, FDEP data), for steel, fiberglass, fiberglass-clad steel tanks, 

fiberglass, steel, and approved synthetic piping; binary comparisons of 

use versus release proportions for tanks, piping secondary containment, 

releases from pressure, suction piping 

t-test average age of tanks, piping systems versus average age at release 

discovery (age data from FDEP)

z-test and Fisher’s 

exact test

proportions of releases versus use data (FDEP data) for tanks and piping 

by material of construction and age

Age at release 

discovery versus 

population age

KolmorgorovSmirnov testcomparisons of profiles of release age versus tank/piping age 
Peer Review Draft – March 2005 Do Not Cite Or Quote B-2

B-1. The z-Test For Difference Of Proportions

The z-test for difference of proportions tests the hypothesis that two independent 

proportions, p1 and p2, are equal. The statistic (z) is calculated as (Sheskin, p. 379): 

(B-1)

(B-2)

Where: n1, n2 = number of observations (e.g., tank systems or records) in the sample

X1, X2 = number of successes (e.g., number of releases) in the sample

p1, p2 = sample proportions = X1/n1, X2/n2 

P = weighted average of the sample proportions

Using a two-sided test, the hypothesis that the proportions are equal can be discarded 

with 95 percent certainty (or p = 0.05) if z is greater than or equal to the critical value of

1.96. This value corresponds to the point on the normal (Gaussian) distribution which

excludes five percent of the total probability density (2.5 percent on each end). The 

difference in proportions is characterized as marginally significant (0.05 < p = 0.10) if z = 

1.65 and z < 1.96. The z value indicating a 90 percent certainty is 1.65. The two-tailed test 

is used in non-directional situations where there is no reason to believe that either p1 or p2 is 

greater or less than the other; it is more demanding (less likely to identify a difference in 

proportions as significant) than the one-tailed test.

In some cases, the proportions being compared are both drawn from the same set of 

observations (all records). In that case, the z-calculation is:

(B-3)

(B-4)

where: N is the total number of observations (records)

P is the average of the sample proportions

The underlying assumption of the z-test is that the two proportions are independent of 

one another and are the result of sets of Bernoulli trials having a constant probability of 

success. The z-test is less reliable when the ns and Xs are relatively small. Where relatively 

few observations are available (see Section B-2), the Fisher’s Exact Test was used to 

evaluate differences in proportions.

z ( p p ) P P N

P X X N

= − −

= +

1 2 1

1 2 2

/ ( ) /

( ) /

z (p p ) P P n P P n

P X X n n

= − − + −

= + +

1 2 1 1 1 2

1 2 1 2

/ ( ) / ( ) /

( ) / ( )
Peer Review Draft – March 2005 Do Not Cite Or Quote B-3

B-2. Fisher’s Exact Test

When the number of observations is small, the non-parametric Fisher’s Exact Test is 

considered to be superior to the z-test for judging the difference in frequencies of outcomes. 

Sheskin (p. 368) states that most sources recommend that parametric tests (Chi-squared, ztest) not be used when the total number of observations (N, or n1 + n2 as defined in equations 

B-1 through B-4) is less than approximately 20. In the analysis of the data, EPA used the 

Fisher’s Exact Test to evaluate the significance of the difference in proportions of tank and 

piping releases associated with different causes (corrosion, puncture, etc.) where the numbers 

of observations was less than 20. 

This non-parametric (distribution-independent) procedure tests the hypothesis that 

two sets of results (successes) in a number of observations (trials) are equal. Put another 

way, the procedure provides an estimate of the probability that the observed difference in 

proportions could have arisen by chance, assuming both samples came from the same 

population. A low p-value indicates that the proportions being compared are significantly 

different. 

Calculation of the test statistic (p-value) is computationally intensive, involving exact 

evaluations of the probability that the specific permutations of results (n1 successes in X1

trials, n2 successes in X2 trials) could have arisen by chance, relative to all other 

permutations. (See Sheskin, pp. 371-376). In this analysis, EPA calculated p-values using 

the Fisher’s Exact Test algorithm in the STATISTICA® Version 5.0 package and the SAS®

version 8 package. EPA characterized p-values less than or equal to 0.05 as indications that 

two proportions were significantly different from one another. EPA characterized p-values 

greater than 0.05 and less than or equal to 0.10 as marginally different from one another.

B-3. Yates-Corrected Chi-Squared

Fisher’s Exact Test is theoretically valid for large samples. However, because the test 

involves factorials, beyond a certain number of observations the calculation exceeds the 

precision achievable with a personal computer. Thus for large n (greater than about 200 per 

cell), EPA employed either the z-test described above, or the Yates-Corrected chi-squared 

test for the difference of proportions. In the analysis, EPA used the Yates-Corrected chisquared test to test the differences in raw rates (e.g., numbers of releases divided by the 

numbers of tank systems from the FDEP data) across different materials of construction.

 The chi-squared procedure is a standard method for evaluating the distribution of 2 

by 2 tables, that is, for comparing two groups of observations that differ in frequency of a 

binary outcome according to whether they receive a certain treatment. The Yates correction 

is a marginal adjustment to the values in the cells that improves the reliability of the test by 

accounting for continuity of the outcome variables.
Peer Review Draft – March 2005 Do Not Cite Or Quote B-4

The Yates-corrected chi-squared statistic (?2) is calculated as:

 

(B-5)

Where i and j refer to the two groups being compared, and where O and E are 

analogous to the numbers of successes (e.g, releases, etc.) observed in one group versus the 

other. In a large sample from a homogeneous distribution, O and E would be equal, so the 

value of ?2 would be zero. The calculated ?2 value is compared to a table of critical values, 

and again, the difference in proportions is considered significant if the p-value is less than or 

equal to 0.05 and marginally significant if the p-value was greater than 0.05 and less than or 

equal to 0.10. EPA calculated the Yates-Corrected Chi-Squared values using

STATISTICA®. Detailed summaries of the STATISTICA® outputs are provided in 

Appendix C.

B-4. t-test For Differences Of Means 

The Student’s t-test is the standard parametric (distribution-dependent) test used to 

test for the difference of means of two or more samples. The t-statistic is calculated as:

t x x n n (n n )( ) / (s / s/ )

1 2 2

1 2

1

2

1 2

2

+ − 2

= − + (B-6)

where: x 1 , x 2 = Means of group 1, group 2

s1

2

, s2

2

 = Sample standard deviations of groups 1, 2

n1, n2 = Number of observations in groups 1, 2

As shown in the equation, the t-statistic has (n1 + n2 -2) degrees of freedom. 

Differences in means are characterized as significant if the t-value with the appropriate 

degrees of freedom exceeds tabulated critical values for p = 0.05, and marginally significant 

if the t-value exceeds the critical value for p = 0.10 but does not exceed the critical values for 

p = 0.05. EPA used the STATISTICA® software package for all t-tests.

B-5. Odds Ratio

EPA also estimated the degree to which releases were associated with the use or 

absence of secondary containment for tanks, piping, and dispensers. An ideal measure would 

be relative risk, the ratios of the numbers of releases per tank system with and without 

secondary containment. However, this measure was not directly accessible due to the nature 

of the data available (data related to releases and use came from different tank systems.) 

Therefore, EPA calculated odds ratios for the presence/absence of secondary containment, as 

a surrogate measure of secondary containment performance. Sample data used in the 

calculation of odds ratios are shown in Table B-2.

( )

c

2

2

05

=

− −





















∑ ∑

O E

E

ij ij

i j ij

.
Peer Review Draft – March 2005 Do Not Cite Or Quote B-5

Table B-2: Sample Of Data Used In The Calculation Of Odds Ratios

Tank Secondary 

Containment

Releases (R&I 

Tank Releases)

Use (R&I Data, Tank 

Systems With No 

Tank Releases)

Present 4 144

Not Present 59 484

The odds ratio for the presence or absence of secondary containment versus releases 

can be calculated as the ratio of the products of diagonal elements of the table (Sheskin, p. 

405). That is, odds ratio = (144 * 59) / (4 * 484) = 4.39. This result can be interpreted as the 

data indicate that the odds of finding secondary containment on a tank with no release is 4.39 

times higher than the odds of finding secondary containment on a tank that has had a release. 

An odds ratio of 1.0 would imply no difference in the frequency of secondary containment at 

tanks with releases. Where the values of releases are low compared to use, the numerical 

value of relative risk will be close to the numerical value for the odds ratio but, as noted 

above, it is not possible to directly estimate relative risk (the relative probability of release 

given the presence or absence of secondary containment) from these data.

It can be shown that the natural log of the odds ratio is normally distributed. A 

normal z-value for the odds ratio (OR) can be calculated as:

z = ln (OR) / SE (B-7)

Where the standard error (SE) of the odds ratio is given by:

SE = 1/n1 + 1/n2 + 1/n3 + 1/n4(B-8)

Where n1 through n4 are the numbers of observations in the four cells of the table. 

Using these formulas, SE = 0.53, and z = 4.55. Thus, the odds ratio in this example is 

significantly greater than 1.0 (since the p-value associated with z = 4.55 is less than 0.001). 

Confidence limits on the odds ratio were also calculated using the standard error.
Peer Review Draft – March 2005 Do Not Cite Or Quote B-6

B-6. Kolmorgorov-Smirnov Test

The Kolmorgorov-Smirnov (K-S) test evaluates the probability that two cumulative 

distributions (such as cumulative numbers of releases over time) might have arisen by 

chance, rather than as a result of a real difference in the distributions. EPA used the K-S test 

in the analysis to compare the time distributions of releases from tanks and piping with the 

distribution of ages of tank systems with the same characteristics. A significant K-S statistic 

indicates that the distributions are different over time, but does not indicate the nature of the 

difference. For example, in the UST analysis for piping, all of the significant K-S test 

statistics are found where the average age of piping releases from the R&I data are 

significantly less that the average age of tank systems in the FDEP data, that is, releases seem 

to occur at higher frequencies from piping at younger tank systems.

The K-S test is simple and robust, even when there are relatively few observations. 

The test statistic for the K-S test is simply the largest vertical distance between two 

cumulative distributions. The calculation of the statistic can be illustrated using the data in 

Table B-3 that compares the distribution of the age of all of the tanks in the FDEP data with 

the age distribution of releases from these types of tanks.

Table B-3: Age Distribution Of All Tanks And Releases

Age Distribution

Cumulative 

Age Distributions Cumulative Proportions

Use Releases Use Releases Use Releases

Difference 

(M)

0-<5.0 2,044 3 2,044 3 0.132 0.070 (0.062)

5-<10 1,785 9 3,829 12 0.247 0.279 0.032

10-<15 4,650 13 8,479 25 0.547 0.581 0.034

15-<20 4,549 10 13,028 35 0.841 0.814 0.027

20-<25 1,439 5 14,467 40 0.933 0.930 0.003

25-<30 419 1 14,886 41 0.960 0.953 0.007

30-<35 411 2 15,297 43 0.987 1.000 0.013

35-<40 125 0 15,422 43 0.995 1.000 0.005

40-<49 78 0 15,500 43 1.000 1.000 0.000

Total 15,500 43 15,500 43 1.000 1.000 --

The left-hand columns of the table show the numbers of tanks in the data set in 

specified tank system age groups (use), and the numbers of releases tanks in the same age 

groups (releases). The numbers of tanks and releases are then re-expressed in cumulative 

form and are converted to cumulative probability distributions (proportions), starting at zero 

(no tanks, no releases) and ending at 1.0 (all tanks, all releases). 

The next step is to find the maximum difference between the proportions of tanks and 

proportion of releases at any point in the age distribution. It can be seen in the final column 

of the table that the maximum difference occurs at 0-5 years, which corresponds to about 13 

percent on the use distribution, but only about 7 percent on the release distribution. This 

difference (0.062) is M, the value that is used in the probability calculation. 
Peer Review Draft – March 2005 Do Not Cite Or Quote B-7

The p-values associated with different values of M for given degrees of freedom are 

tabulated in statistics texts. However, when the number of observations is large enough, the 

p-value can also be estimated using the Chi-Squared Approximation, as follows:1

 (B-9)

Where: ?

2

= Chi-squared value (two degrees of freedom)

M = Maximum vertical distance from K-S test

n1, n2 = number of observations (tanks, releases)

The p-value can thus be calculated using the CHIDIST function in Excel®, and two 

distributions are characterized as significantly different if the resulting p-value is less than or 

equal to 0.05 and marginally different if the p-value was greater than 0.05 and less than or 

equal to 0.10. For the example data set, the chi-squared value corresponding to M = 0.062 is 

0.66, and the corresponding p-value is 0.72. Thus, the two distributions are not significantly 

different.

B-7. Bootstrap Confidence Limits

Limited data were available concerning the amounts of product released from various 

sources. The release volume data were found to be irregularly distributed and often skewed 

(many low values, a few very high values). For the analysis, EPA used nonparametric 

bootstrap methods to derive robust (distribution-independent) estimates of upper and lower 

confidence limits on the mean volumes released. 

Briefly stated, the bootstrap method involved taking random samples from the raw 

release data, and evaluating the distribution of the resulting mean values. For example, if 

there were 16 releases from a source, we took 10,000 samples of 16 values (with 

replacement) from those data. The distributions of the mean values from these random 

samples can be shown to have a Student’s t-distribution with a standard error that can be 

estimated based on the sampling results. The Studentized upper and lower 95 percent 

confidence limits on the mean can then be easily calculated. (Davison and Hinkley, pp 191, 

ff) The bootstrap sampling was performed using the Visual Basic for Applications (VBA) 

capability of Excel. 

 

1 When (n1 and n2) are suitably large, the quantity of the right-hand side equation B-9 is known to 

have a chi-squared distribution with two degrees of freedom (Sheskin, p 326). Above n1 = n2 = 25, 

the K-S test critical values can be approximated by well-behaved functions that are consistent with 

the Chi-squared distribution to approximately one percent accuracy. (Sheskin, Table A-23). 

c

2 2 1 2

1 2

= 4

+











M 

n n

n n

*
Peer Review Draft – March 2005 Do Not Cite Or Quote B-8

References:

Davidson, A.C., Hinkley, D.V., Bootstrap Methods and Their Application, Cambridge 

University Press, 1997.

Sheskin, D. J., Handbook of Parametric and Nonparametric Statistical Procedures, Second 

Edition, Chapman and Hall, 2000.

Mason, Robert D. Statistical Techniques in Business and Economics, Fourth Edition, 

Richard D. Irwin, 1978
Peer Review Draft – March 2005 Do Not Cite Or Quote C-1

Appendix C – Data Summary Tables And Statistical Results

Appendix C contains release and use data summary tables and the results of the statistical 

analysis of that data. Appendix C contains the following:

Summary Of Releases By Source ................................................................... C-2

Causes Of Releases From Each Source ...................................................... C-3

Tank Materials And Release Causes .......................................................... C-7

Piping Materials And Release Causes .............................................................. C-8

Summary Of Statistical Tests For Secondary Containment (Tanks, Piping,

 Dispensers) And Overfill Protection ............................................................ C-10

Methods Of Release Identification ............................................................ C-14

Analysis Of Leak Detection Frequency Of Success, Failure, And Use .................. C-15

Contamination Of Groundwater And Surface Water By Source Of Release ............ C-16

Release Volumes ................................................................................. C-17

Analysis Of Tank And Piping Use Versus Releases ....................................... C-18

Tank And Piping Age Distributions ........................................................... C-21

t-Test For Mean Ages ........................................................................... C-22

Fisher’s Exact And Z-Tests For Piping Ages ................................................ C-23

K-S Test For Tank Ages ........................................................................ C-25

K-S Test For Piping Ages ...................................................................... C-26
Peer Review Draft - March 2005

Summary Of Releases By Source

Source Number Of Releases

Percentage Of 

Releases

Percentage Of 

Records

Piping 122 23.3% 23.8%

Dispenser 130 24.8% 25.4%

Fuel Delivery 101 19.3% 19.7%

Tank 63 12.0% 12.3%

Pump (Turbine) 

(Includes Line Leak Detector) 52 9.9% 10.2%

Others* 56 10.7% 10.9%

Total Releases 524 100.0%

Number Of Records** 512

** There were 512 records in the data set; 12 records identified two sources each.

Calculation of z-statistics: z = (p1 - p2) / sqrt (P * (1-P) * (1 / N))

Source 1 Source 2 p1 p2 p1-p2 P 1-P 1/N z p-value

Piping Versus Dispenser 0.23 0.25 -0.02 0.24 0.76 0.002 -0.82 0.413

Fuel Delivery 0.23 0.19 0.04 0.21 0.79 0.002 2.24 0.025

Tank 0.23 0.12 0.11 0.18 0.82 0.002 6.76 0.000

Pump (Turbine) 

(Includes Line Leak Detector) 0.23 0.10 0.13 0.17 0.83 0.002 8.22 0.000

Dispenser Versus Fuel Delivery 0.25 0.19 0.06 0.22 0.78 0.002 3.06 0.002

Tank 0.25 0.12 0.13 0.18 0.82 0.002 7.55 0.000

Pump (Turbine) 

(Includes Line Leak Detector) 0.25 0.10 0.15 0.17 0.83 0.002 8.99 0.000

Fuel Delivery Tank 0.19 0.12 0.07 0.16 0.84 0.002 4.57 0.000

Pump (Turbine) 

(Includes Line Leak Detector) 0.19 0.10 0.09 0.15 0.85 0.002 6.06 0.000

Tank

Pump (Turbine) 

(Includes Line Leak Detector) 0.12 0.10 0.02 0.11 0.89 0.002 1.54 0.124

Shading: = significant (p = 0.05)

 = marginally significant (0.05 < p = 0.10)

* Other releases include: 16 people putting product or used oil into monitoiring wells (intentional or accidental), 13 personal vehicles, 

11 fill pipes, 6 people spilling during deposits of waste oil, 2 components leaking due to damage during removal, 2 vent lines, 2 stage 

II vapor recovery lines, 1 airplane, 1 day tank, 1 fitting, and 1 pump riser.

Appendix C C-2
Peer Review Draft - March 2005

Causes Of Releases From Each Source

Source

Number Of 

Releases*

Percent Of 

Releases Loose Component

Vehicle 

Accident Spill

Phys/Mech 

Damage

Improper 

Install Puncture Corrosion Overfill Other

Number Of 

Known Causes1 

Number Of 

Unknown 

Causes

Unknowns As Percentage Of 

Total Causes

Piping 122 23.3% 25 6 0 27 6 19 8 0 6 97 26 21.3%

Dispenser 130 24.8% 34 14 10 11 4 2 1 0 7 83 47 36.2%

Fuel Delivery 101 19.3% 3 0 43 0 0 0 0 51 4 101 0 0.0%

Tank 63 12.0% 5 0 0 14 1 17 10 1 6 54 9 14.3%

Pump (Turbine) 

(Includes Line Leak Detector) 52 9.9% 22 0 0 14 5 1 0 0 4 46 6 11.5%

Others** 56 10.7% 9 0 7 2 1 2 0 14 19 54 2 3.6%

Total Releases 524 100.0% 98 20 60 68 17 41 19 66 46 435 90 17.2%

Percentage Of All Releases With Known Causes 22.5% 4.6% 13.8% 15.6% 3.9% 9.4% 4.4% 15.2% 10.6%

Calculation of z-statistics: z = (p1 - p2) / sqrt (P * (1-P) * (1 / N))

p1 p2 p1-p2 P 1-P 1/N z p-value

Loose Component Versus Vehicle Accident 0.225 0.046 0.179 0.136 0.864 0.002 10.922 0.000

Spill 0.225 0.138 0.087 0.182 0.818 0.002 4.726 0.000

Phys/Mech 0.225 0.156 0.069 0.191 0.809 0.002 3.661 0.000

Improper Install 0.225 0.039 0.186 0.132 0.868 0.002 11.467 0.000

Puncture 0.225 0.094 0.131 0.160 0.840 0.002 7.459 0.000

Corrosion 0.225 0.044 0.182 0.134 0.866 0.002 11.102 0.000

Overfill 0.225 0.152 0.074 0.189 0.811 0.002 3.923 0.000

Vehicle Accident Versus Spill 0.046 0.138 -0.092 0.092 0.908 0.002 -6.637 0.000

Phys/Mech 0.046 0.156 -0.110 0.101 0.899 0.002 -7.633 0.000

Improper Install 0.046 0.039 0.007 0.043 0.957 0.002 0.713 0.476

Puncture 0.046 0.094 -0.048 0.070 0.930 0.002 -3.943 0.000 Shading: = significant (p = 0.05)

Corrosion 0.046 0.044 0.002 0.045 0.955 0.002 0.232 0.817 = marginally significant (0.05 < p = 0.10)

Overfill 0.046 0.152 -0.106 0.099 0.901 0.002 -7.390 0.000

Spill Versus Phys/Mech 0.138 0.156 -0.018 0.147 0.853 0.002 -1.083 0.279

Improper Install 0.138 0.039 0.099 0.089 0.911 0.002 7.259 0.000

Puncture 0.138 0.094 0.044 0.116 0.884 0.002 2.844 0.004

Corrosion 0.138 0.044 0.094 0.091 0.909 0.002 6.842 0.000

Overfill 0.138 0.152 -0.014 0.145 0.855 0.002 -0.817 0.414

Phys/Mech. Versus Improper Install 0.156 0.039 0.117 0.098 0.902 0.002 8.236 0.000

Puncture 0.156 0.094 0.062 0.125 0.875 0.002 3.911 0.000

Corrosion 0.156 0.044 0.113 0.100 0.900 0.002 7.831 0.000

Overfill 0.156 0.152 0.005 0.154 0.846 0.002 0.266 0.791

Improper Install Versus Puncture 0.039 0.094 -0.055 0.067 0.933 0.002 -4.613 0.000

Corrosion 0.039 0.044 -0.005 0.041 0.959 0.002 -0.481 0.630

Overfill 0.039 0.152 -0.113 0.095 0.905 0.002 -7.997 0.000

Puncture Versus Corrosion 0.094 0.044 0.051 0.069 0.931 0.002 4.163 0.000

Overfill 0.094 0.152 -0.057 0.123 0.877 0.002 -3.650 0.000

Corrosion Versus Overfill 0.044 0.152 -0.108 0.098 0.902 0.002 -7.590 0.000

* The total number of causes is greater than the number of releases because one release had two causes.

All Releases

** Other causes include: 20 deliveries to monitoring wells, 7 improper removals, 6 human errors, 5 vandalisms, 3 contractor errors, 2 customer driveoffs, 2 damage during delivery, and 1 leaking filter. 

Appendix C C-3
Peer Review Draft - March 2005

Piping

Loose Component Versus Vehicle Accident 0.26 0.06 0.20 0.16 0.84 0.010 5.26 0.000

Spill 0.26 0.00 0.26 0.13 0.87 0.010 7.58 0.000

Phys/Mech 0.26 0.28 -0.02 0.27 0.73 0.010 -0.46 0.647

Improper Install 0.26 0.06 0.20 0.16 0.84 0.010 5.26 0.000

Puncture 0.26 0.20 0.06 0.23 0.77 0.010 1.45 0.146

Corrosion 0.26 0.08 0.18 0.17 0.83 0.010 4.59 0.000

Overfill 0.26 0.00 0.26 0.13 0.87 0.010 7.58 0.000

Vehicle Accident Versus Spill 0.06 0.00 0.06 0.03 0.97 0.010 3.52 0.000

Phys/Mech 0.06 0.28 -0.22 0.17 0.83 0.010 -5.67 0.000

Improper Install 0.06 0.06 0.00 0.06 0.94 0.010 0.00 1.000

Puncture 0.06 0.20 -0.13 0.13 0.87 0.010 -3.94 0.000

Corrosion 0.06 0.08 -0.02 0.07 0.93 0.010 -0.78 0.433

Overfill 0.06 0.00 0.06 0.03 0.97 0.010 3.52 0.000

Spill Versus Phys/Mech 0.00 0.28 -0.28 0.14 0.86 0.010 -7.92 0.000

Improper Install 0.00 0.06 -0.06 0.03 0.97 0.010 -3.52 0.000

Puncture 0.00 0.20 -0.20 0.10 0.90 0.010 -6.49 0.000

Corrosion 0.00 0.08 -0.08 0.04 0.96 0.010 -4.09 0.000

Overfill 0.00 0.00 0.00 0.00 1.00 0.010 N/A N/A

Phys/Mech. Versus Improper Install 0.28 0.06 0.22 0.17 0.83 0.010 5.67 0.000

Puncture 0.28 0.20 0.08 0.24 0.76 0.010 1.91 0.056

Corrosion 0.28 0.08 0.20 0.18 0.82 0.010 5.02 0.000

Overfill 0.28 0.00 0.28 0.14 0.86 0.010 7.92 0.000 Shading: = significant (p = 0.05)

Improper Install Versus Puncture 0.06 0.20 -0.13 0.13 0.87 0.010 -3.94 0.000 = marginally significant (0.05 < p = 0.10)

Corrosion 0.06 0.08 -0.02 0.07 0.93 0.010 -0.78 0.433

Overfill 0.06 0.00 0.06 0.03 0.97 0.010 3.52 0.000

Puncture Versus Corrosion 0.20 0.08 0.11 0.14 0.86 0.010 3.23 0.001

Overfill 0.20 0.00 0.20 0.10 0.90 0.010 6.49 0.000

Corrosion Versus Overfill 0.08 0.00 0.08 0.04 0.96 0.010 4.09 0.000

Dispenser

Loose Component Versus Vehicle Accident 0.41 0.17 0.24 0.29 0.71 0.012 4.84 0.000

Spill 0.41 0.12 0.29 0.27 0.73 0.012 5.97 0.000

Phys/Mech 0.41 0.13 0.28 0.27 0.73 0.012 5.68 0.000

Improper Install 0.41 0.05 0.36 0.23 0.77 0.012 7.84 0.000

Puncture 0.41 0.02 0.39 0.22 0.78 0.012 8.52 0.000

Corrosion 0.41 0.01 0.40 0.21 0.79 0.012 8.88 0.000

Overfill 0.41 0.00 0.41 0.20 0.80 0.012 9.25 0.000

Vehicle Accident Versus Spill 0.17 0.12 0.05 0.14 0.86 0.012 1.25 0.212

Phys/Mech 0.17 0.13 0.04 0.15 0.85 0.012 0.92 0.357

Improper Install 0.17 0.05 0.12 0.11 0.89 0.012 3.53 0.000

Puncture 0.17 0.02 0.14 0.10 0.90 0.012 4.46 0.000

Corrosion 0.17 0.01 0.16 0.09 0.91 0.012 4.98 0.000

Overfill 0.17 0.00 0.17 0.08 0.92 0.012 5.53 0.000

Spill Versus Phys/Mech 0.12 0.13 -0.01 0.13 0.87 0.012 -0.33 0.741

Improper Install 0.12 0.05 0.07 0.08 0.92 0.012 2.37 0.018

Puncture 0.12 0.02 0.10 0.07 0.93 0.012 3.39 0.001

Corrosion 0.12 0.01 0.11 0.07 0.93 0.012 3.97 0.000

Overfill 0.12 0.00 0.12 0.06 0.94 0.012 4.61 0.000

Phys/Mech. Versus Improper Install 0.13 0.05 0.08 0.09 0.91 0.012 2.68 0.007

Puncture 0.13 0.02 0.11 0.08 0.92 0.012 3.68 0.000

Corrosion 0.13 0.01 0.12 0.07 0.93 0.012 4.24 0.000

Overfill 0.13 0.00 0.13 0.07 0.93 0.012 4.85 0.000

Improper Install Versus Puncture 0.05 0.02 0.02 0.04 0.96 0.012 1.18 0.240

Corrosion 0.05 0.01 0.04 0.03 0.97 0.012 1.93 0.054

Overfill 0.05 0.00 0.05 0.02 0.98 0.012 2.86 0.004

Puncture Versus Corrosion 0.02 0.01 0.01 0.02 0.98 0.012 0.82 0.410

Overfill 0.02 0.00 0.02 0.01 0.99 0.012 2.01 0.044

Corrosion Versus Overfill 0.01 0.00 0.01 0.01 0.99 0.012 1.42 0.156

Appendix C C-4
Peer Review Draft - March 2005

Fuel Delivery

Loose Component Versus Vehicle Accident 0.03 0.00 0.03 0.01 0.99 0.010 2.47 0.014

Spill 0.03 0.43 -0.40 0.23 0.77 0.010 -9.49 0.000

Phys/Mech 0.03 0.00 0.03 0.01 0.99 0.010 2.47 0.014

Improper Install 0.03 0.00 0.03 0.01 0.99 0.010 2.47 0.014

Puncture 0.03 0.00 0.03 0.01 0.99 0.010 2.47 0.014

Corrosion 0.03 0.00 0.03 0.01 0.99 0.010 2.47 0.014

Overfill 0.03 0.50 -0.48 0.27 0.73 0.010 -10.79 0.000

Vehicle Accident Versus Spill 0.00 0.43 -0.43 0.21 0.79 0.010 -10.45 0.000

Phys/Mech 0.00 0.00 0.00 0.00 1.00 0.010 N/A N/A

Improper Install 0.00 0.00 0.00 0.00 1.00 0.010 N/A N/A

Puncture 0.00 0.00 0.00 0.00 1.00 0.010 N/A N/A

Corrosion 0.00 0.00 0.00 0.00 1.00 0.010 N/A N/A

Overfill 0.00 0.50 -0.50 0.25 0.75 0.010 -11.68 0.000

Spill Versus Phys/Mech 0.43 0.00 0.43 0.21 0.79 0.010 10.45 0.000

Improper Install 0.43 0.00 0.43 0.21 0.79 0.010 10.45 0.000

Puncture 0.43 0.00 0.43 0.21 0.79 0.010 10.45 0.000

Corrosion 0.43 0.00 0.43 0.21 0.79 0.010 10.45 0.000

Overfill 0.43 0.50 -0.08 0.47 0.53 0.010 -1.60 0.111

Phys/Mech. Versus Improper Install 0.00 0.00 0.00 0.00 1.00 0.010 N/A N/A

Puncture 0.00 0.00 0.00 0.00 1.00 0.010 N/A N/A

Corrosion 0.00 0.00 0.00 0.00 1.00 0.010 N/A N/A

Overfill 0.00 0.50 -0.50 0.25 0.75 0.010 -11.68 0.000

Improper Install Versus Puncture 0.00 0.00 0.00 0.00 1.00 0.010 N/A N/A

Corrosion 0.00 0.00 0.00 0.00 1.00 0.010 N/A N/A

Overfill 0.00 0.50 -0.50 0.25 0.75 0.010 -11.68 0.000

Puncture Versus Corrosion 0.00 0.00 0.00 0.00 1.00 0.010 N/A N/A

Overfill 0.00 0.50 -0.50 0.25 0.75 0.010 -11.68 0.000

Corrosion Versus Overfill 0.00 0.50 -0.50 0.25 0.75 0.010 -11.68 0.000

Tank

Loose Component Versus Vehicle Accident 0.09 0.00 0.09 0.05 0.95 0.019 3.24 0.001

Spill 0.09 0.00 0.09 0.05 0.95 0.019 3.24 0.001

Phys/Mech 0.09 0.26 -0.17 0.18 0.82 0.019 -3.22 0.001 Shading: = significant (p = 0.05)

Improper Install 0.09 0.02 0.07 0.06 0.94 0.019 2.38 0.017 = marginally significant (0.05 < p = 0.10)

Puncture 0.09 0.31 -0.22 0.20 0.80 0.019 -4.05 0.000

Corrosion 0.09 0.19 -0.09 0.14 0.86 0.019 -1.97 0.049

Overfill 0.09 0.02 0.07 0.06 0.94 0.019 2.38 0.017

Vehicle Accident Versus Spill 0.00 0.00 0.00 0.00 1.00 0.019 N/A N/A

Phys/Mech 0.00 0.26 -0.26 0.13 0.87 0.019 -5.67 0.000

Improper Install 0.00 0.02 -0.02 0.01 0.99 0.019 -1.42 0.155

Puncture 0.00 0.31 -0.31 0.16 0.84 0.019 -6.35 0.000

Corrosion 0.00 0.19 -0.19 0.09 0.91 0.019 -4.69 0.000

Overfill 0.00 0.02 -0.02 0.01 0.99 0.019 -1.42 0.155

Spill Versus Phys/Mech 0.00 0.26 -0.26 0.13 0.87 0.019 -5.67 0.000

Improper Install 0.00 0.02 -0.02 0.01 0.99 0.019 -1.42 0.155

Puncture 0.00 0.31 -0.31 0.16 0.84 0.019 -6.35 0.000

Corrosion 0.00 0.19 -0.19 0.09 0.91 0.019 -4.69 0.000

Overfill 0.00 0.02 -0.02 0.01 0.99 0.019 -1.42 0.155

Phys/Mech. Versus Improper Install 0.26 0.02 0.24 0.14 0.86 0.019 5.12 0.000

Puncture 0.26 0.31 -0.06 0.29 0.71 0.019 -0.90 0.367

Corrosion 0.26 0.19 0.07 0.22 0.78 0.019 1.31 0.190

Overfill 0.26 0.02 0.24 0.14 0.86 0.019 5.12 0.000

Improper Install Versus Puncture 0.02 0.31 -0.30 0.17 0.83 0.019 -5.84 0.000

Corrosion 0.02 0.19 -0.17 0.10 0.90 0.019 -4.05 0.000

Overfill 0.02 0.02 0.00 0.02 0.98 0.019 0.00 1.000

Puncture Versus Corrosion 0.31 0.19 0.13 0.25 0.75 0.019 2.20 0.028

Overfill 0.31 0.02 0.30 0.17 0.83 0.019 5.84 0.000

Corrosion Versus Overfill 0.19 0.02 0.17 0.10 0.90 0.019 4.05 0.000

Appendix C C-5
Peer Review Draft - March 2005

Pump (Turbine) (Includes Line Leak Detector)

Loose Component Versus Vehicle Accident 0.48 0.00 0.48 0.24 0.76 0.022 7.60 0.000

Spill 0.48 0.00 0.48 0.24 0.76 0.022 7.60 0.000

Phys/Mech 0.48 0.30 0.17 0.39 0.61 0.022 2.42 0.016

Improper Install 0.48 0.11 0.37 0.29 0.71 0.022 5.50 0.000

Puncture 0.48 0.02 0.46 0.25 0.75 0.022 7.15 0.000

Corrosion 0.48 0.00 0.48 0.24 0.76 0.022 7.60 0.000

Overfill 0.48 0.00 0.48 0.24 0.76 0.022 7.60 0.000

Vehicle Accident Versus Spill 0.00 0.00 0.00 0.00 1.00 0.022 N/A N/A

Phys/Mech 0.00 0.30 -0.30 0.15 0.85 0.022 -5.75 0.000

Improper Install 0.00 0.11 -0.11 0.05 0.95 0.022 -3.25 0.001

Puncture 0.00 0.02 -0.02 0.01 0.99 0.022 N/A N/A

Corrosion 0.00 0.00 0.00 0.00 1.00 0.022 N/A N/A

Overfill 0.00 0.00 0.00 0.00 1.00 0.022 N/A N/A

Spill Versus Phys/Mech 0.00 0.30 -0.30 0.15 0.85 0.022 -5.75 0.000

Improper Install 0.00 0.11 -0.11 0.05 0.95 0.022 -3.25 0.001

Puncture 0.00 0.02 -0.02 0.01 0.99 0.022 N/A N/A

Corrosion 0.00 0.00 0.00 0.00 1.00 0.022 N/A N/A

Overfill 0.00 0.00 0.00 0.00 1.00 0.022 N/A N/A

Phys/Mech. Versus Improper Install 0.30 0.11 0.20 0.21 0.79 0.022 3.28 0.001

Puncture 0.30 0.02 0.28 0.16 0.84 0.022 5.19 0.000

Corrosion 0.30 0.00 0.30 0.15 0.85 0.022 5.75 0.000

Overfill 0.30 0.00 0.30 0.15 0.85 0.022 5.75 0.000

Improper Install Versus Puncture 0.11 0.02 0.09 0.07 0.93 0.022 2.39 0.017

Corrosion 0.11 0.00 0.11 0.05 0.95 0.022 3.25 0.001

Overfill 0.11 0.00 0.11 0.05 0.95 0.022 3.25 0.001

Puncture Versus Corrosion 0.02 0.00 0.02 0.01 0.99 0.022 N/A N/A

Overfill 0.02 0.00 0.02 0.01 0.99 0.022 N/A N/A

Corrosion Versus Overfill 0.00 0.00 0.00 0.00 1.00 0.022 N/A N/A

Others

Loose Component Versus Vehicle Accident 0.17 0.00 0.17 0.08 0.92 0.019 4.43 0.000

Spill 0.17 0.13 0.04 0.15 0.85 0.019 0.77 0.444

Phys/Mech 0.17 0.04 0.13 0.10 0.90 0.019 3.15 0.002

Improper Install 0.17 0.02 0.15 0.09 0.91 0.019 3.76 0.000

Puncture 0.17 0.04 0.13 0.10 0.90 0.019 3.15 0.002

Corrosion 0.17 0.00 0.17 0.08 0.92 0.019 4.43 0.000 Shading: = significant (p = 0.05)

Overfill 0.17 0.26 -0.09 0.21 0.79 0.019 -1.66 0.097 = marginally significant (0.05 < p = 0.10)

Vehicle Accident Versus Spill 0.00 0.13 -0.13 0.06 0.94 0.019 -3.87 0.000

Phys/Mech 0.00 0.04 -0.04 0.02 0.98 0.019 -2.02 0.044

Improper Install 0.00 0.02 -0.02 0.01 0.99 0.019 -1.42 0.155

Puncture 0.00 0.04 -0.04 0.02 0.98 0.019 -2.02 0.044

Corrosion 0.00 0.00 0.00 0.00 1.00 0.019 N/A N/A

Overfill 0.00 0.26 -0.26 0.13 0.87 0.019 -5.67 0.000

Spill Versus Phys/Mech 0.13 0.04 0.09 0.08 0.92 0.019 2.46 0.014

Improper Install 0.13 0.02 0.11 0.07 0.93 0.019 3.12 0.002

Puncture 0.13 0.04 0.09 0.08 0.92 0.019 2.46 0.014

Corrosion 0.13 0.00 0.13 0.06 0.94 0.019 3.87 0.000

Overfill 0.13 0.26 -0.13 0.19 0.81 0.019 -2.41 0.016

Phys/Mech. Versus Improper Install 0.04 0.02 0.02 0.03 0.97 0.019 0.83 0.408

Puncture 0.04 0.04 0.00 0.04 0.96 0.019 0.00 1.000

Corrosion 0.04 0.00 0.04 0.02 0.98 0.019 2.02 0.044

Overfill 0.04 0.26 -0.22 0.15 0.85 0.019 -4.60 0.000

Improper Install Versus Puncture 0.02 0.04 -0.02 0.03 0.97 0.019 -0.83 0.408

Corrosion 0.02 0.00 0.02 0.01 0.99 0.019 1.42 0.155

Overfill 0.02 0.26 -0.24 0.14 0.86 0.019 -5.12 0.000

Puncture Versus Corrosion 0.04 0.00 0.04 0.02 0.98 0.019 2.02 0.044

Overfill 0.04 0.26 -0.22 0.15 0.85 0.019 -4.60 0.000

Corrosion Versus Overfill 0.00 0.26 -0.26 0.13 0.87 0.019 -5.67 0.000

Appendix C C-6
Peer Review Draft - March 2005

Tank Materials And Release Causes

Material Total Releases

Total Known 

Causes Corrosion Phys/Mech Damage Puncture

Loose 

Component Overfill

Improper 

Install Other Unknown

Steel 19 17 10 3 1 2 0 1 0 2

Fiberglass 41 35 0 11 16 1 1 0 6 6

Clad Steel (Composite) 1 1 0 0 0 1 0 0 0 0

Concrete 1 0 0 0 0 0 0 0 0 1

Polyethylene 1 1 0 0 0 1 0 0 0 0

Total 63 54 10 14 17 5 1 1 6 9

Calculation of z-statistics: z = (p1 - p2) / sqrt (P * (1-P) * (1 / N))

Cause Comparison By Material Of Construction

p1 p2 p1-p2 P 1-P 1/N z p-value

Corrosion Versus Phys/Mech Damage 0.59 0.18 0.41 0.38 0.62 0.059 3.49 0.000

Puncture 0.59 0.06 0.53 0.32 0.68 0.059 4.67 0.000

Loose Component 0.59 0.12 0.47 0.35 0.65 0.059 4.06 0.000

Improper Install 0.59 0.06 0.53 0.32 0.68 0.059 4.67 0.000

Phys/Mech Damage Versus Puncture 0.18 0.06 0.12 0.12 0.88 0.059 1.51 0.132

Loose Component 0.18 0.12 0.06 0.15 0.85 0.059 0.68 0.493

Improper Install 0.18 0.06 0.12 0.12 0.88 0.059 1.51 0.132

Puncture Versus Loose Component 0.06 0.12 -0.06 0.09 0.91 0.059 0.86 0.392

Improper Install 0.06 0.06 0.00 0.06 0.94 0.059 0.00 1.000

Loose Component Versus Improper Install 0.12 0.06 0.06 0.09 0.91 0.059 0.86 0.392

Phys/Mech Damage Versus Puncture 0.31 0.46 -0.14 0.39 0.61 0.029 1.74 0.083

Loose Component 0.31 0.03 0.29 0.17 0.83 0.029 4.48 0.000

Overfill 0.31 0.03 0.29 0.17 0.83 0.029 4.48 0.000

Puncture Versus Loose Component 0.46 0.03 0.43 0.24 0.76 0.029 5.91 0.000

Overfill 0.46 0.03 0.43 0.24 0.76 0.029 5.91 0.000

Loose Component Versus Overfill 0.03 0.03 0.00 0.03 0.97 0.029 0.00 1.000

Fisher's Exact Test - Selected Steel Comparisons

Comparison Yes No Comparison Yes No

Corrosion 10 7 Corrosion 10 7

Phys/Mech Damage 3 14 Puncture 1 16

0.032 0.002

Comparison Yes No Comparison Yes No

Corrosion 10 7 Corrosion 10 7

Loose Component 2 15 Improper Install 1 16

0.010 0.002

Material Of Construction

p1 p2 p1-p2 P 1-P 1/N z p-value

Steel Versus Fiberglass 0.30 0.65 -0.35 0.48 0.52 0.019 5.14 0.000

Composite 0.30 0.02 0.29 0.16 0.84 0.019 5.75 0.000

Concrete 0.30 0.02 0.29 0.16 0.84 0.019 5.75 0.000

Polyethylene 0.30 0.02 0.29 0.16 0.84 0.019 5.75 0.000

Fiberglass Versus Composite 0.65 0.02 0.63 0.33 0.67 0.019 9.90 0.000

Concrete 0.65 0.02 0.63 0.33 0.67 0.019 9.90 0.000

Polyethylene 0.65 0.02 0.63 0.33 0.67 0.019 9.90 0.000

Composite Versus Concrete 0.02 0.02 0.00 0.02 0.98 0.019 0.00 1.000

Polyethylene 0.02 0.02 0.00 0.02 0.98 0.019 0.00 1.000

Concrete Versus Polyethylene 0.02 0.02 0.00 0.02 0.98 0.019 0.00 1.000

Shading: = significant (p = 0.05)

 = marginally significant (0.05 < p = 0.10)

Material Of Construction Comparisons

Steel

Fiberglass

Fisher's Exact Test p-value: 

Fisher's Exact Test p-value: 

Appendix C C-7
Peer Review Draft - March 2005

Piping Materials And Release Causes

Material Total Releases

Total Known 

Causes Corrosion

Phys/Mech 

Damage Puncture

Loose 

Component Vehicle Accident

Improper 

Install Other Unknown

Steel 17 15 5 3 0 3 1 1 2 2

Fiberglass 92 71 3 18 18 20 5 4 3 22

Approved Synthetic Material 11 9 0 6 1 2 0 0 0 2

Total Of Known Materials And 

Causes 120 95 8 27 19 25 6 5 5 26

Unknown 2 2 0 0 0 0 0 1 1 0

Calculation of z-statistics: z = (p1 - p2) / sqrt (P * (1-P) * (1 / N))

Cause Comparison By Material

p1 p2 p1-p2 P 1-P 1/N z p-value

Corrosion Versus Phys/Mech Damage 0.33 0.20 0.13 0.27 0.73 0.067 1.17 0.243

Puncture 0.33 0.00 0.33 0.17 0.83 0.067 3.46 0.001

Loose Component 0.33 0.20 0.13 0.27 0.73 0.067 1.17 0.243

Vehicle Accident 0.33 0.07 0.27 0.20 0.80 0.067 2.58 0.010

Improper Install 0.33 0.07 0.27 0.20 0.80 0.067 2.58 0.010

Phys/Mech Damage Versus Puncture 0.20 0.00 0.20 0.10 0.90 0.067 2.58 0.010

Loose Component 0.20 0.20 0.00 0.20 0.80 0.067 0.00 1.000

Vehicle Accident 0.20 0.07 0.13 0.13 0.87 0.067 1.52 0.129

Improper Install 0.20 0.07 0.13 0.13 0.87 0.067 1.52 0.129

Puncture Versus Loose Component 0.00 0.20 -0.20 0.10 0.90 0.067 2.58 0.010

Vehicle Accident 0.00 0.07 -0.07 0.03 0.97 0.067 1.44 0.150

Improper Install 0.00 0.07 -0.07 0.03 0.97 0.067 1.44 0.150

Loose Component Versus Vehicle Accident 0.20 0.07 0.13 0.13 0.87 0.067 1.52 0.129

Improper Install 0.20 0.07 0.13 0.13 0.87 0.067 1.52 0.129

Vehicle Accident Versus Improper Install 0.07 0.07 0.00 0.07 0.93 0.067 0.00 1.000

Corrosion Versus Phys/Mech Damage 0.04 0.25 -0.21 0.15 0.85 0.014 5.01 0.000

Puncture 0.04 0.25 -0.21 0.15 0.85 0.014 5.01 0.000

Loose Component 0.04 0.28 -0.24 0.16 0.84 0.014 5.48 0.000

Vehicle Accident 0.04 0.07 -0.03 0.06 0.94 0.014 1.03 0.303

Improper Install 0.04 0.06 -0.01 0.05 0.95 0.014 0.55 0.584

Phys/Mech Damage Versus Puncture 0.25 0.25 0.00 0.25 0.75 0.014 0.00 1.000

Loose Component 0.25 0.28 -0.03 0.27 0.73 0.014 0.54 0.592

Vehicle Accident 0.25 0.07 0.18 0.16 0.84 0.014 4.19 0.000

Improper Install 0.25 0.06 0.20 0.15 0.85 0.014 4.59 0.000

Puncture Versus Loose Component 0.25 0.28 -0.03 0.27 0.73 0.014 0.54 0.592

Vehicle Accident 0.25 0.07 0.18 0.16 0.84 0.014 4.19 0.000

Improper Install 0.25 0.06 0.20 0.15 0.85 0.014 4.59 0.000

Loose Component Versus Vehicle Accident 0.28 0.07 0.21 0.18 0.82 0.067 2.15 0.032

Improper Install 0.28 0.06 0.23 0.17 0.83 0.067 2.33 0.020

Vehicle Accident Versus Improper Install 0.07 0.06 0.01 0.06 0.94 0.014 0.49 0.626

Corrosion Versus Phys/Mech Damage 0.00 0.67 -0.67 0.33 0.67 0.111 4.24 0.000

Puncture 0.00 0.11 -0.11 0.06 0.94 0.111 1.46 0.146

Loose Component 0.00 0.22 -0.22 0.11 0.89 0.111 2.12 0.034

Vehicle Accident 0.00 0.00 0.00 0.00 1.00 0.111 N/A N/A

Improper Install 0.00 0.00 0.00 0.00 1.00 0.111 N/A N/A

Phys/Mech Damage Versus Puncture 0.67 0.11 0.56 0.39 0.61 0.111 3.42 0.001

Loose Component 0.67 0.22 0.44 0.44 0.56 0.111 2.68 0.007

Vehicle Accident 0.67 0.00 0.67 0.33 0.67 0.111 4.24 0.000

Improper Install 0.67 0.00 0.67 0.33 0.67 0.111 4.24 0.000

Puncture Versus Loose Component 0.11 0.22 -0.11 0.17 0.83 0.111 0.89 0.371

Vehicle Accident 0.11 0.00 0.11 0.06 0.94 0.111 1.46 0.146

Improper Install 0.11 0.00 0.11 0.06 0.94 0.111 1.46 0.146

Loose Component Versus Vehicle Accident 0.22 0.00 0.22 0.11 0.89 0.067 2.74 0.006

Improper Install 0.22 0.00 0.22 0.11 0.89 0.067 2.74 0.006

Vehicle Accident Improper Install 0.00 0.00 0.00 0.00 1.00 0.111 N/A N/A

Shading: = significant (p = 0.05)

 = marginally significant (0.05 < p = 0.10)

Steel

Fiberglass

Approved Synthetic Material

Appendix C C-8
Peer Review Draft - March 2005

Fisher's Exact Test - Selected Steel Comparisons

Comparison Yes No Comparison Yes No Comparison Yes No

Corrosion 5 10 Phys/Mech 3 12 Puncture 0 15

Puncture 0 15 Puncture 0 15 Loose Comp 3 12

0.042 0.224 0.224

Comparison Yes No Comparison Yes No

Corrosion 5 10 Corrosion 5 10

Vehicle Accident 1 14 Improper Install 1 14

0.169 0.169

Fisher's Exact Test - Selected Approved Synthetic Material Comparisons

Comparison Yes No Comparison Yes No Comparison Yes No

Corrosion 0 9 Corrosion 0 9 Phys/Mech 6 3

Phys/Mech 6 3 Loose Component 2 7 Vehicle Accident 0 9

0.009 0.471 0.009

Comparison Yes No Comparison Yes No Comparison Yes No

Phys/Mech 6 3 Phys/Mech 6 3 Phys/Mech 6 3

Puncture 1 8 Loose Comp 2 7 Improper Install 0 9

0.050 0.153 0.009

Comparison Yes No Comparison Yes No

Loose Component 2 7 Loose Component 2 7

Vehicle Accident 0 9 Improper Install 0 9

0.471 0.471

Material Of Construction Comparison

Material Of Construction p1 p2 p1-p2 P 1-P 1/N z p-value

Steel Versus Fiberglass 0.14 0.77 -0.63 0.45 0.55 0.008 13.75 0.000

Approved Synthetic Material 0.14 0.09 0.05 0.12 0.88 0.008 1.71 0.088

Fiberglass Versus Approved Synthetic Material 0.77 0.09 0.68 0.43 0.57 0.008 14.94 0.000

Shading: = significant (p = 0.05)

 = marginally significant (0.05 < p = 0.10)

Fisher's Exact Test p-value: 

Fisher's Exact Test p-value: 

Fisher's Exact Test p-value: 

Fisher's Exact Test p-value:

Fisher's Exact Test p-value: 

Appendix C C-9
Peer Review Draft - March 2005

Summary Of Statistical Tests For Secondary Containment (Tanks, Piping, Dispensers) And Overfill Protection

Tanks

Number Of 

Releases

Percent 

Releases

Records With 

Non-Tank 

Releases Percent Use

Number Of 

UST Systems Percent Use

With Secondary Containment 4 6.3% 144 22.9% 6317 41.6%

Without Secondary Containment 59 93.7% 484 77.1% 8878 58.4%

Total 63 100% 628 100% 15195 100%

Calculation of z-statistics: z = (p1 - p2) / sqrt (P * (1-P) * (1 / N)) where 1/N = 1/n1+1/n2 if proportions are independent

Tanks With Secondary Containment -- Z-statistic

Significance Calculation

p1 

(Releases)

p2 

(Use) p1-p2 P 1-P 1/n1 + 1/n2 z p-value

Releases Versus R&I Data 0.063 0.229 -0.166 0.214 0.786 0.0175 -3.06 0.002

Releases Versus FDEP Data 0.063 0.416 -0.352 0.414 0.586 0.0159 -5.66 0.000

Odds Ratio Standard Deviation

Confidence 

Limits p-value

R&I Data 4.39 0.53 3.4 - 12.3 0.0024

FDEP Data 10.50 0.52 9.5 - 28.9 0.0000

Shading: = significant (p = 0.05)

 = marginally significant (0.05 < p = 0.10)

Tank Secondary Containment

Releases And Incident Data (R&I) FDEP Data

Odds Ratio Information For Tanks With Secondary Containment (Releases Versus Use)

Appendix C C-10
Peer Review Draft - March 2005

Piping 

Number Of 

Releases

Percent 

Releases

Records With 

Non-Piping 

Releases Percent Use

Number Of 

UST Systems Percent Use

Present 53 43.4% 214 42.8% 9101 60.2%

Not Present 69 56.6% 286 57.2% 6026 39.8%

Total 122 100% 500 100% 15127 100%

Calculation of z-statistics: z = (p1 - p2) / sqrt (P * (1-P) * (1 / N)) where 1/N = 1/n1+1/n2 if proportions are independent

Piping With Secondary Containment -- Z-statistic

Significance Calculation

p1 

(Releases)

p2 

(Use) p1-p2 P 1-P 1/n1 + 1/n2 z p-value

Releases Versus R&I Data 0.434 0.428 0.006 0.429 0.571 0.0102 0.13 0.898

Releases Versus FDEP Data 0.434 0.602 -0.167 0.600 0.400 0.0083 -3.76 0.000

Odds Ratio Standard Deviation

Confidence 

Limits p-value

FDEP Data 1.97 0.18 1.6 - 2.8 0.0001

Shading: = significant (p = 0.05)

 = marginally significant (0.05 < p = 0.10)

Odds Ratio Information For Piping With Secondary Containment (Releases Versus Use)

Piping Secondary Containment

Releases And Incident Data (R&I) FDEP Data

Appendix C C-11
Peer Review Draft - March 2005

Dispensers

Number Of 

Releases

Percent 

Releases

Records With 

Non-Piping 

Releases Percent Use

Number Of 

UST Systems Percent Use

Present 43 33% 202 36% 12362 81%

Not Present 87 67% 365 64% 2833 19%

Total 130 100% 567 100% 15195 100%

Calculation of z-statistics: z = (p1 - p2) / sqrt (P * (1-P) * (1 / N)) where 1/N = 1/n1+1/n2 if proportions are independent

Dispensers With Secondary Containment -- Z-statistic

Significance Calculation

p1

(Releases)

p2

(Use) p1-p2 P 1-P 1/n1+1/n2 z p-value

Releases Versus R&I Data 0.331 0.356 -0.025 0.352 0.648 0.0095 -0.55 0.583

Releases Versus FDEP Data 0.331 0.814 -0.483 0.809 0.191 0.0078 -13.96 0.000

Odds Ratio Standard Deviation

Confidence 

Limits p-value

FDEP Data 8.83 0.19 8.5 - 12.8 0.0000

Shading: = significant (p = 0.05)

 = marginally significant (0.05 < p = 0.10)

Odds Ratio Information For Dispensers With Secondary Containment (Releases Versus Use)

FDEP Data

Dispenser Secondary Containment

Releases And Incident Data (R&I)

Appendix C C-12
Peer Review Draft - March 2005

Overfill Protection

Number Of 

Releases

Percent 

Releases

Records With 

Non-Piping 

Releases Percent Use

Number Of 

UST Systems Percent Use

Ball Check Valve 36 77% 473 82% 11122 67%

Flow-Shutoff 11 23% 105 18% 5593 33%

Total 47 100% 578 100% 16715 100%

Calculation of z-statistics: z = (p1 - p2) / sqrt (P * (1-P) * (1 / N)) where 1/N = 1/n1+1/n2 if proportions are independent

Overfill Protection

Significance Calculation

p1

(Releases)

p2

(Use) p1-p2 P 1-P 1/n1+1/n2 z p-value

Ball Check Valve Versus R&I Data 0.766 0.818 -0.052 0.814 0.186 0.0230 -0.89 0.374

Ball Check Valve Versus FDEP Data 0.766 0.665 0.101 0.666 0.334 0.0213 1.46 0.144

Flow Shut Off Versus R&I Data 0.234 0.182 0.052 0.186 0.814 0.0230 0.89 0.374

Flow Shut Off Versus FDEP Data 0.234 0.335 -0.101 0.334 0.666 0.0213 -1.46 0.144

Shading: = significant (p = 0.05)

 = marginally significant (0.05 < p = 0.10)

Overfill Protection Method

Releases And Incident Data (R&I) FDEP Data

Appendix C C-13
Peer Review Draft - March 2005

Methods Of Release Identification

Method Of Identification Number Of Releases Percent

Leak Detection 131 25.9%

Visual/Olfactory 193 38.2%

TTT Or LTT (Not Leak Detection) 24 4.8%

Closure * 76 15.0%

Other ** 81 16.0%

Total Known Methods Of ID 505

Unknown 7

* Includes 9 releases identified through close in place and 67 identified through removal.

** Includes 10 releases identified through water in tank and 71 identified by other means.

Calculation of z-statistics: z = (p1 - p2) / sqrt (P * (1-P) * (1 / N))

Method (1) Method (2) p1 p2 p1-p2 P 1-P 1/N z p-value

Leak Detection Versus Visual/Olfactory 0.259 0.382 -0.123 0.153 0.847 0.002 -7.65 0.000

TTT Or LTT (Not Leak Detection) 0.259 0.048 0.212 0.205 0.795 0.002 11.80 0.000

Closure 0.259 0.150 0.109 0.215 0.785 0.002 5.96 0.000

Visual/Olfactory Versus TTT Or LTT (Not Leak Detection) 0.382 0.048 0.335 0.266 0.734 0.002 17.01 0.000

Closure 0.382 0.150 0.232 0.099 0.901 0.002 17.43 0.000

TTT Or LTT (Not Leak Detection) Versus Closure 0.048 0.150 -0.103 0.099 0.901 0.002 -7.75 0.000

Shading: = significant (p = 0.05)

 = marginally significant (0.05 < p = 0.10)

Appendix C C-14
Peer Review Draft - March 2005

Analysis Of Leak Detection Frequency Of Success, Failure, And Use

Calculation of z-statistics: z = (p1 - p2) / sqrt (P * (1-P) * (1 / N)) where 1/N = 1/n1+1/n2 if proportions are independent

Leak Detection Method That 

Detected Release 

Number Of 

Releases Percent Releases

R& I 

Records Percent Use p1-p2 P 1-p 1/n1 +1/n2 z p-value

Groundwater Monitoring 84 73% 396 52% 21% 0.55 0.45 0.0100 4.26 0.000

TTT/IC* 11 10% 54 7% 2% 0.07 0.93 0.0100 0.95 0.340

Line Tightness Test 9 8% 33 4% 4% 0.05 0.95 0.0100 1.64 0.100

Secondary/Interstitial 8 7% 97 13% -6% 0.12 0.88 0.0100 -1.77 0.077

SIR 2 2% 31 4% -2% 0.04 0.96 0.0100 -1.22 0.223

Manual Tank Gauging 1 1% 39 5% -4% 0.05 0.95 0.0100 -2.03 0.042

ATG 0 0% 106 14% -14% 0.12 0.88 0.0100 -4.26 0.000

Vapor monitoring 0 0% 8 1% -1% 0.01 0.99 0.0100 -1.10 0.270

Total 115 100% 764 100%

Leak Detection Method Failed 

To Detect Release (For All 

Releases) Number Of 

Releases Percent Releases

R& I 

Records Percent Use p1-p2 P 1-p 1/n1 +1/n2 z p-value

Groundwater Monitoring 70 73% 396 52% 21% 0.54 0.46 0.0117 3.91 0.000

Secondary/Interstitial 11 11% 97 13% -1% 0.13 0.87 0.0117 -0.35 0.730

TTT/IC* 9 9% 54 7% 2% 0.07 0.93 0.0117 0.82 0.414

SIR 3 3% 31 4% -1% 0.04 0.96 0.0117 -0.44 0.659

ATG 1 1% 106 14% -13% 0.12 0.88 0.0117 -3.59 0.000

Manual Tank Gauging 1 1% 39 5% -4% 0.05 0.95 0.0117 -1.78 0.075

Vapor Monitoring 1 1% 8 1% 0% 0.01 0.99 0.0117 NA NA

Line Tightness Test 0 0% 33 4% -4% 0.04 0.96 0.0117 -2.08 0.038

Total 96 100% 764 100%

Leak Detection Method Appearances In 

Records

Use (Frequency Of 

Appearance In 

Records)1

Identified As 

Failed

Proportion Of 

Failures To Detect 

Release

Identified As 

Succeeding 

Proportion Of 

Successful 

Release 

Detection

Groundwater Monitoring 396 52% 70 73% 84 73%

ATG 106 14% 1 1% 0 0%

Secondary/ Interstitial 97 13% 11 11% 8 7%

TTT/IC 54 7% 9 9% 11 10%

Manual Tank Gauging 39 5% 1 1% 1 1%

Line Tightness Testing 33 4% 0 0% 9 8%

SIR 31 4% 3 3% 2 2%

Vapor monitoring 8 1% 1 1% 0 0%

Total 764 100% 96 100% 115 100%

1. Except for results of false or faulty alarms

LLD Detected Release (For All 

Releases)

Number Of 

Releases Percent Releases

R& I 

Records Percent Use p1-p2 P 1-p 1/n1 +1/n2 z p-value

Electronic LLD 4 21% 63 18% 3% 0.19 0.81 0.0555 0.29 0.769

Mechanical LLD 15 79% 280 82% -3% 0.81 0.19 0.0555 -0.29 0.769

Total 19 100% 343 100%

LLD Failed To Detect Release 

(For All Releases) Number Of 

Releases Percent Releases

R& I 

Records Percent Use p1-p2 P 1-p 1/n1 +1/n2 z p-value

ELectronic LLD 4 17% 63 18% -1% 0.18 0.82 0.0464 -0.12 0.907

Mechanical LLD 19 83% 280 82% 1% 0.82 0.18 0.0464 0.12 0.907

Total 23 100% 343 100%

Leak Line Detection Appearances In 

Records

Percent Use 

(Frequency Of 

Appearance In 

Records)1

Identified As 

Failed

Percent Of 

Failures To Detect 

Release

Identified As 

Succeeding 

Percent 

Successful 

Release 

Detection

Electronic LLD 63 18% 4 17% 4 21%

Mechanical LLD 280 82% 19 83% 15 79%

Total 343 100% 23 100% 19 100%

1. Except for results of false or faulty alarms

Shading: = significant (p = 0.05)

 = marginally significant (0.05 < p = 0.10)

* Tank Tightness Testing / Inventory Control

* Tank Tightness Testing / Inventory Control

Appendix C C-15
Peer Review Draft - March 2005

Contamination Of Groundwater And Surface Water By Source Of Release

Number Percent Number Percent Number Percent

Fuel Delivery 101 64 63.4% 2 2.0% 66 65.3%

Dispenser 130 53 40.8% 4 3.1% 57 43.8%

Piping 122 71 58.2% 3 2.5% 71 58.2%

Pump (Turbine)** 52 32 61.5% 0 0.0% 32 61.5%

Tank 63 54 85.7% 1 1.6% 54 85.7%

Other*** 56 35 62.5% 4 7.1% 39 69.6%

Total Media Affected 524 309 59.0% 14 2.7% 319 60.9%

* Total does not sum because four releases impacted both surface and groundwater

** Includes six LLD releases

*** Other includes seven fill pipe and one vent line release not included in the fuel delivery category

Calculation of z-statistics: z = (p1 - p2) / sqrt (P * (1-P) * (1 / N)) where 1/N = 1/n1+1/n2 if proportions are independent

Differences In Proportions Between Each Sources Contribution To Total Water Impacts

Releases (1) Releases (2) p1 p2 p1-p2 P 1-P 1/N z

2-tailed 

p-value

Dispenser 0.207 0.179 0.028 0.193 0.807 0.00313 1.28 0.201

Piping 0.207 0.223 -0.016 0.215 0.785 0.00313 -0.68 0.495

Pump (Turbine) 0.207 0.100 0.107 0.154 0.846 0.00313 5.28 0.000

Tank 0.207 0.169 0.038 0.188 0.812 0.00313 1.72 0.086

Piping 0.179 0.223 -0.044 0.201 0.799 0.00313 -1.96 0.050

Pump (Turbine) 0.179 0.100 0.078 0.139 0.861 0.00313 4.04 0.000

Tank 0.179 0.169 0.009 0.174 0.826 0.00313 0.44 0.658

Pump (Turbine) 0.223 0.100 0.122 0.161 0.839 0.00313 5.93 0.000

Tank 0.223 0.169 0.053 0.196 0.804 0.00313 2.40 0.016

Pump (turbine) Versus Tank 0.100 0.169 -0.069 0.135 0.865 0.00313 -3.61 0.000

Differences In Proportions Of The Likelihood Of Each Source Impacting Water

Releases (1) Releases (2) p1 p2 p1-p2 P 1-P 1/n1+1/n2 z p-value

Dispenser 0.653 0.438 0.215 0.532 0.468 0.01759 3.25 0.001

Piping 0.653 0.582 0.071 0.614 0.386 0.01810 1.09 0.275

Pump (Turbine) 0.653 0.615 0.038 0.641 0.359 0.02913 0.46 0.642

Tank 0.653 0.857 -0.204 0.732 0.268 0.02577 -2.86 0.004

Piping 0.438 0.582 -0.144 0.508 0.492 0.01589 -2.28 0.023

Pump (Turbine) 0.438 0.615 -0.177 0.489 0.511 0.02692 -2.16 0.031

Tank 0.438 0.857 -0.419 0.575 0.425 0.02357 -5.52 0.000

Pump (Turbine) 0.582 0.615 -0.033 0.592 0.408 0.02743 -0.41 0.681

Tank 0.582 0.857 -0.275 0.676 0.324 0.02407 -3.79 0.000

Pump (Turbine) Versus Tank 0.615 0.857 -0.242 0.748 0.252 0.03510 -2.97 0.003

Contamination Of Groundwater And Surface Water By Pressure And Suction Pumps

Source

Number Of 

Releases Number Percent Number Percent Number Percent

Pressure 100 58 58.0% 2 2.0% 58 58.0%

Suction 11 5 45.5% 1 9.1% 5 45.5%

Total Media Affected* 111 63 56.8% 3 2.7% 63 56.8%

* Does not include 11 releases where type of pump system was not reported.

Differences In Proportions Of Releases From Each Pump Type Impacting Groundwater And/Or Surface Water

Releases (1) Releases (2) p1 p2 p1-p2 P 1-P 1/N z p-value

Pressure Suction 0.921 0.079 0.841 0.500 0.500 0.01587 13.35 0.000

Differences In Proportions Of Releases From Each Pump Type Impacting Groundwater And/Or Surface Water

Releases (1) Releases (2) p1 p2 p1-p2 P 1-P 1/n1+1/n2 z p-value

Pressure Suction 0.580 0.455 0.125 0.568 0.432 0.10091 0.80 0.425

Shading: = significant (p = 0.05)

 = marginally significant (0.05 < p = 0.10)

Source

Number Of 

Releases

Percent Of Each 

Sources' 

Contribution To 

Total Water 

Impacts

16.9%

Impacting Groundwater

Impacting Surface 

Water

Total Impacting 

Water *

20.7%

17.9%

22.3%

10.0%

Impacting Groundwater

Impacting Surface 

Water

Total Impacting 

Water

12.2%

Fuel Delivery Versus

Dispenser Versus

Piping Versus

Piping Versus

Dispenser Versus

Fuel Delivery Versus

Appendix C C-16
Peer Review Draft - March 2005

Release Volumes

Number Of Releases By Source And Number Of Gallons Discharged

Release Source 0 To 10 10 To 50 50 To 100 100 To 500 500 To 1000 1000 To 5000 > 5000 Unknown Total

Fuel Delivery 7 16 9 9 1 1 0 58 101

Dispenser 7 12 4 4 0 3 0 89 119

Fill Pipe 0 1 1 1 0 0 0 8 11

Other 5 10 0 5 1 2 0 20 43

Piping 4 17 5 5 4 2 2 72 111

Piping And 

Dispenser 0 0 1 0 0 0 0 9 10

Pump 

(Turbine) 2 2 2 0 0 0 0 46 52

Tank 3 7 1 1 1 4 0 44 61

Tank And 

Piping 1 0 0 0 0 0 0 0 1

Tank And 

Dispenser 0 0 0 0 0 0 0 1 1

Vent Line 0 0 0 0 0 0 0 2 2

29 65 23 25 7 12 2 349 512

Release Source

Total Gallons 

Discharged Average Median Minimum Maximum

Lower 95% 

Confidence Limit 

Of Mean

Upper 95% 

Confidence 

Limit Of Mean

Fuel Delivery 5,416 126 50 1 1,250 64 208

Dispenser 7,798 260 25 3 3,400 64 543

Fill Pipe 280 93 55 25 200 -- --

Other 9,387 408 25 2 5,000 66 939

Piping 44,947 1,152 50 2 25,000 202 2,701

Piping And 

Dispenser 85 85 85 85 85 -- --

Pump 

(Turbine) 200 33 23 10 75 15 54

Tank 11,831 696 50 5 3,500 228 1,283

Tank And 

Piping 10 10 10 10 10 -- --

Overall 79,954 491 40 1 25,000 231 878

Number Of Gallons

Amounts Released And Bootstrap Confidence Limits On Average Release Volumes*

* Bootstrap confidence intervals are derived by "resampling" the input data for each release source (10,000 iterations) to determine the distribution of mean values 

Appendix C C-17
Peer Review Draft - March 2005

Analysis Of Tank And Piping Use Versus Releases

Tank Construction Materials

Material

Number Of 

Releases Percent Releases

Records With 

Non-Tank 

Releases* Percent Use

Number Of 

UST Systems Percent Use

Concrete 1 1.6% 1 0.2% 1 0.0%

Fiberglass 41 65.1% 336 54.5% 8819 59.3%

Clad Steel 1 1.6% 110 17.9% 3373 22.7%

Polyethylene 1 1.6% 0 0.0% 6 0.0%

Other FDEP-Approved Material 0 0.0% 1 0.2% 7 0.0%

Steel 19 30.2% 168 27.3% 2657 17.9%

Total 63 100.0% 616 100.0% 14863 100.0%

Blank 0 7 262

Unknown 0 5 70

* Excludes records with tank releases

Calculation of z-statistics: z = (p1 - p2) / sqrt (P * (1-P) * (1 / N)) where 1/N = 1/n1+1/n2 if proportions are independent

Differences In Proportions Of Releases Compared To Use Based On R&I Data

p1 

(Releases)

p2 

(Use) p1-p2 P 1-P 1/n1 + 1/n2 z p-value

Fiberglass 0.651 0.545 0.105 0.56 0.445 0.017 1.60 0.109

Clad Steel 0.016 0.179 -0.163 0.163 0.837 0.017 -3.33 0.001

Steel 0.302 0.273 0.029 0.275 0.725 0.017 0.49 0.625

Differences In Proportions Of Releases Compared To Use Based On FDEP Data

p1 

(Releases)

p2 

(Use) p1-p2 P 1-P 1/n1 + 1/n2 z p-value

Fiberglass 0.651 0.593 0.057 0.59 0.41 0.016 0.93 0.354

Clad Steel 0.016 0.227 -0.211 0.23 0.77 0.016 -4.00 0.000

Steel 0.302 0.179 0.123 0.18 0.82 0.016 2.54 0.011

Comparison Of Steel Tank Releases And Use By Corrosion Protection Method Where Cause Is Corrosion

Corrosion Protection 

(Steel Tanks)

Number Of 

Releases Percent Releases

R& I Records 

(Non-Tank) Percent Use p1-p2 P 1-P 1/n1 + 1/n2 z p-value

Impressed Current 4 40% 43 30.5% 9.5% 0.31 0.69 0.107 0.63 0.531

Sacrificial Anode 3 30% 74 52.5% -22.5% 0.51 0.49 0.107 -1.37 0.169

Lining 3 30% 24 17.0% 13.0% 0.18 0.82 0.107 1.03 0.301

Total 10 100% 141 100%

Shading: = significant (p = 0.05)

 = marginally significant (0.05 < p = 0.10)

Piping Use And Construction Material

Releases And Incident Data (R&I) FDEP Data

Releases And Incident Data (R&I) FDEP Data

Appendix C C-18
Peer Review Draft - March 2005

Materials

Number of 

Releases Percent Releases

Records with NonTank Releases* Percent UseNumber Of 

UST Systems Percent Use

Approved Synthetic Material 11 9.2% 36 6.7% 2053 14.1%

Other FDEP Approved Material 0 0.0% 4 0.7% 217 1.5%

Fiberglass 92 76.7% 386 71.3% 11131 76.5%

Steel/Galvanized Metal 17 14.2% 115 21.3% 1147 7.9%

Total Known Materials 120 100.0% 541 100.0% 14548 100.0%

Blank 1 26 486

Unknown 1 5 93

* Excludes records with piping releases

Calculation of z-statistics: z = (p1 - p2) / sqrt (P * (1-P) * (1 / N)) where 1/N = 1/n1+1/n2 if proportions are independent

Differences In Proportions Of Releases Compared To Use Based On R&I Data

p1 

(Releases)

p2 

(Use) p1-p2 P 1-P 1/n1 + 1/n2 z p-value

Fiberglass 0.767 0.713 0.053 0.72 0.277 0.010 1.18 0.239

Steel 0.142 0.213 -0.071 0.20 0.800 0.010 -1.76 0.079

Approved Synthetic Material 0.092 0.067 0.025 0.07 0.929 0.010 0.97 0.333

Differences In Proportions Of Releases Compared To Use Based On FDEP Data

p1 

(Releases)

p2 

(Use) p1-p2 P 1-P 1/n1 + 1/n2 z p-value

Fiberglass 0.767 0.765 0.002 0.77 0.235 0.008 0.04 0.968

Steel 0.142 0.079 0.063 0.08 0.921 0.008 2.54 0.011

Approved Synthetic Material 0.092 0.141 -0.049 0.14 0.859 0.008 -1.55 0.121

Comparison Of Metal Pipe Releases And Use By Corrosion Protection Method Where Cause Is Corrosion

Corrosion Protection 

(Steel Piping)

Number Of 

Releases Percent Releases

R& I Records 

(Non-Tank) Percent Use p1-p2 P 1-P 1/n1 + 1/n2 z p-value

Impressed Current 3 60% 23 32% 28.5% 0.33 0.67 0.214 1.31 0.191

Sacrificial Anode 2 40% 50 68% -28.5% 0.67 0.33 0.214 -1.31 0.191

Total 5 100% 73 100%

Shading: = significant (p = 0.05)

 = marginally significant (0.05 < p = 0.10)

Pressure Versus Suction 

Pumps

Piping Releases With Pressure Versus 

Suction Pumps

Number Of 

Releases Percent Releases

Records With NonTank Releases* Percent UseNumber Of 

UST Systems Percent Use

Pressure Pump 100 90.1% 409 88.3% 11482 91.5%

Suction Pump 11 9.9% 54 11.7% 1061 8.5%

Total 111 100.0% 463 100% 12543 100%

Blank 11 110 2626

* Excludes records with piping releases, where pump type is specified

Releases And Incident Data (R&I) FDEP Data

Appendix C C-19
Peer Review Draft - March 2005

Calculation of z-statistics: z = (p1 - p2) / sqrt (P * (1-P) * (1 / N)) where 1/N = 1/n1+1/n2 if proportions are independent

Differences In Proportions Of Releases

p1 p2 p1-p2 P 1-P 1/n z p-value

Pressure Versus Suction 0.901 0.099 0.802 0.500 0.500 0.00901 16.90 0.000

Differences In Proportions Of Releases Compared To Use Based On R&I Data

p1 

(Releases)

p2 

(Use) p1-p2 P 1-P 1/n1 + 1/n2 z p-value

Pressure 0.901 0.883 0.018 0.89 0.113 0.011 0.523 0.601

Suction 0.099 0.117 -0.018 0.11 0.887 0.011 -0.523 0.601

Differences In Proportions Of Releases Compared To Use Based On FDEP Data

p1 

(Releases)

p2 

(Use) p1-p2 P 1-P 1/n1 + 1/n2 z p-value

Pressure 0.901 0.915 -0.015 0.92 0.085 0.009 -0.547 0.585

Suction 0.099 0.085 0.015 0.08 0.915 0.009 0.547 0.585

Shading: = significant (p = 0.05)

 = marginally significant (0.05 < p = 0.10)

Appendix C C-20
Peer Review Draft - March 2005

Tank And Piping Age Distributions

FDEP Tank Age Distributions (Numbers Of USTs) FDEP Piping Age Distributions (Numbers Of USTs)

Age All* Fiberglass Steel Clad Steel Age All* Fiberglass Steel/Galv.** Approv. Synth. Suction Pressure

0-<5.0 2044 1141 332 555 0-<5.0 1911 972 36 791 86 1601

5-<10 1785 947 196 538 5-<10 1722 1143 41 364 104 1390

10-<15 4650 2804 327 1297 10-<15 4506 3713 239 282 378 3143

15-<20 4549 2684 685 880 15-<20 4440 3351 379 372 237 3356

20-<25 1439 910 395 58 20-<25 1367 986 159 125 76 1034

25-<30 419 152 224 2 25-<30 410 272 70 33 39 306

30-<35 411 126 196 9 30-<35 394 282 61 26 48 264

35-<40 125 0 91 7 35-<40 125 78 38 0 13 84

40-<50 78 1 52 5 40-<50 78 54 7 0 7 44

Total 15501 8765 2498 3351 Total 14953 10851 1031 1993 988 11222

Time In Use Time In Use

Mean 14.30 13.78 18.32 11.76 Mean 14.37 14.77 18.74 9.72 15.22 14.08

Std. Dev. 7.39 6.34 9.89 5.53 Std. Dev. 7.36 6.85 7.47 7.41 7.67 7.36

Median 14.42 14.33 18.17 13.08 Median 14.42 14.50 17.50 6.58 14.04 14.33

*total, average, std. dev., and median statistics include one tank with age >50 **total, average, std. dev., and median statistics for steel/galvanized tanks include one tank with age >50

Numbers Of Tank Releases Versus Age Numbers Of Piping Releases Versus Age

Age All Tanks Fiberglass Steel Age All Piping Fiberglass Steel/Galv. Approv. Synth. Suction Pressure

0-<5.0 3 1 1 0-<5.0 20 15 2 3 2 18

5-<10 9 6 2 5-<10 28 24 1 3 2 24

10-<15 13 11 2 10-<15 24 19 3 2 4 20

15-<20 10 6 4 15-<20 11 9 2 0 0 11

20-<25 5 5 0 20-<25 0 0 0 0 0 0

25-<30 1 0 1 25-<30 2 1 1 0 1 0

30-<35 2 0 2 30-<35 0 0 0 0 0 0

35-<40 0 0 0 35-<40 0 0 0 0 0 0

40-<50 0 0 0 40-<50 0 0 0 0 0 0

Total 43 29 12 Total 85 68 9 8 9 73

Time To Release

Mean 14.40 13.95 17.07 Mean 9.7 9.7 12.1 6.29 11.3 9.3

Std. Dev. 7.06 5.41 9.53 Std. Dev. 5.7 5.4 8.20 3.73 7.6 5.2

Median 13.20 13.20 16.02 Median 8.9 8.9 12.3 6.53 10.1 8.8

Time To Release

* All >(fiberglass + steel + clad steel) because material of construction is not known 

for some tanks

*All > (fiberglass + steel + approv synth) because material of construction is not known 

for some piping

Appendix C C-21
Peer Review Draft - March 2005

t-Test For Mean Ages

FDEP Tank Age Versus R&I Tank Releases

Tank Configuration FDEP Tank 

Age R&I Releases t-Value Degrees Of Freedom p

All Tanks 14.30 14.40 -0.08 15,542 0.935

Fiberglass Tanks 13.78 13.95 -0.15 8,792 0.884

Steel Tanks 18.32 17.07 0.44 2,508 0.661

FDEP Piping Age Versus R&I Piping Releases

Piping Configuration FDEP Piping 

Age R&I Releases t-Value Degrees Of Freedom p

All Piping 14.37 9.65 5.90 15,036 0.000

Fiberglass Piping 14.77 9.73 6.05 10,917 0.000

Steel/Galvanized Piping 18.74 12.07 2.66 1,038 0.008

Approved Synth. Piping 9.72 6.29 1.31 1,999 0.191

Suction Piping 15.22 11.26 1.54 995 0.124

Pressure Piping 14.08 9.25 5.59 11,293 0.000

Shading: = significant (p = 0.05)

 = marginally significant (0.05 < p = 0.10)

Mean (Years)

Mean (Years)

Appendix C C-22
Peer Review Draft - March 2005

Fisher's Exact And Z-Tests For Piping Ages

ICF: Of piping whose age is less than the specified age, compare percent use and percent releases:

Material

FDEP Use 

Data Percent Use

Number Of 

Releases

Percent 

Releases

Fiberglass 972 54.0% 15 75.0%

Steel/Galvanized 36 2.0% 2 10.0%

Approved Synthetic Material 791 44.0% 3 15.0%

Total <5 Years Old 1799 20

Fiberglass 9879 81.8% 53 81.5%

Steel/Galvanized 994 8.2% 7 10.8%

Approved Synthetic Material 1202 10.0% 5 7.7%

Total >5 Years Old 12075 65

Calculation of z-statistics: z = (p1 - p2) / sqrt (P * (1-P) * (1 / n)) where 1/n = 1/n1+1/n2 if proportions are independent

p1 (Use) p2 (Releases) p1-p2 P 1-P 1/n z p - value Fisher's Exact p-value

Fiberglass 54.0% 75.0% -20.97% 54.26% 45.74% 0.051 1.87 0.06 0.07

Steel/Galvanized 2.0% 10.0% -8.00% 2.09% 97.91% 0.051 2.49 0.01 0.06

Approved Synthetic Material 44.0% 15.0% 28.97% 43.65% 56.35% 0.051 2.60 0.01 0.01

Material

FDEP Use 

Data Percent Use

Number Of 

Releases

Percent 

Releases

Fiberglass 2115 63.2% 39 81.3%

Steel/Galvanized 77 2.3% 3 6.3%

Approved Synthetic Material 1155 34.5% 6 12.5%

Total <10 Years Old 3347 48

Fiberglass 8736 83.0% 29 78.4%

Steel/Galvanized 953 9.1% 6 16.2%

Approved Synthetic Material 838 8.0% 2 5.4%

Total >10 Years Old 10527 37

p1 (Use) p2 (Releases) p1-p2 P 1-P 1/n z p - value Fisher's Exact p-value

Fiberglass 63.2% 81.3% -18.06% 63.45% 36.55% 0.02 2.58 0.01 0.01

Steel/Galvanized 2.3% 6.3% -3.95% 2.36% 97.64% 0.02 1.79 0.07 0.10

Approved Synthetic Material 34.5% 12.5% 22.01% 34.20% 65.80% 0.02 3.19 0.00 0.00

Piping <10 Years Old

significant = 

Piping <5 Years Old

marginally significant = 

Piping <5 years old

Piping >5 years old

Piping <10 years old

Piping >10 years old

Appendix C C-23
Peer Review Draft - March 2005

Material

FDEP Use 

Data Percent Use

Number Of 

Releases

Percent 

Releases

Fiberglass 5828 76.9% 58 80.6%

Steel/Galvanized 316 4.2% 6 8.3%

Approved Synthetic Material 1437 19.0% 8 11.1%

Total <15 Years Old 7581 72

Fiberglass 5023 79.8% 10 76.9%

Steel/Galvanized 714 11.3% 3 23.1%

Approved Synthetic Material 556 8.8% 0 0.0%

Total >15 Years Old 6293 13

p1 (Use) p2 (Releases) p1-p2 P 1-P 1/n z p - value Fisher's Exact p-value

Fiberglass 76.9% 80.6% -3.68% 76.91% 23.09% 0.014 0.74 0.46 0.57

Steel/Galvanized 4.2% 8.3% -4.17% 4.21% 95.79% 0.014 1.75 0.08 0.13

Approved Synthetic Material 19.0% 11.1% 7.84% 18.88% 81.12% 0.014 1.69 0.09 0.097

Material

FDEP Use 

Data Percent Use

Number Of 

Releases

Percent 

Releases

Fiberglass 9179 78.6% 67 80.7%

Steel/Galvanized 695 5.9% 8 9.6%

Approved Synthetic Material 1809 15.5% 8 9.6%

Total <20 Years Old 11683 83

Fiberglass 1672 76.3% 1 50.0%

Steel/Galvanized 335 15.3% 1 50.0%

Approved Synthetic Material 184 8.4% 0 0.0%

Total >20 Years Old 2191 2

p1 (Use) p2 (Releases) p1-p2 P 1-P 1/n z p - value Fisher's Exact p-value

Fiberglass 78.6% 80.7% -2.16% 78.58% 21.42% 0.012 0.48 0.63 0.69

Steel/Galvanized 5.9% 9.6% -3.69% 5.97% 94.03% 0.012 1.41 0.16 0.16

Approved Synthetic Material 15.5% 9.6% 5.85% 15.44% 84.56% 0.012 1.47 0.14 0.17

Piping >20 years old

Piping <20 Years Old

Piping <15 years old

Piping <20 years old

Piping >15 years old

Piping <15 Years Old

Appendix C C-24
Peer Review Draft - March 2005

K-S Test For Tank Ages

FDEP Tank Age Distributions (Numbers Of Tanks) Cumulative Distributions (Tank Age)

Age All* Fiberglass Steel Clad Steel Age All Fiberglass Steel Clad Steel

0-<5.0 2,044 1,141 332 555 0-<5.0 0.132 0.130 0.133 0.166

5-<10 1,785 947 196 538 5-<10 0.247 0.238 0.211 0.326

10-<15 4,650 2,804 327 1,297 10-<15 0.547 0.558 0.342 0.713

15-<20 4,549 2,684 685 880 15-<20 0.840 0.864 0.616 0.976

20-<25 1,439 910 395 58 20-<25 0.933 0.968 0.775 0.993

25-<30 419 152 224 2 25-<30 0.960 0.986 0.864 0.994

30-<35 411 126 196 9 30-<35 0.987 1.000 0.943 0.996

35-<40 125 0 91 7 35-<40 0.995 1.000 0.979 0.999

40-<49 78 1 52 5 40-<49 0.999935488 1 1 1

Total 15,501 8,765 2,498 3,351

Average 14.30 13.78 18.32 11.76

Std. Dev. 7.39 6.34 9.89 5.53

Median 14.42 14.33 18.17 13.08

**total, average, std. dev., and median statistics include one tank with age >50

Number Of Tank Releases Versus Age Cumulative Distribution (Tank Releases)

Age All Tanks Fiberglass Steel Age All Tanks Fiberglass Steel

0-<5.0 3 1 1 0-<5.0 0.070 0.034 0.083

5-<10 9 6 2 5-<10 0.279 0.241 0.250

10-<15 13 11 2 10-<15 0.581 0.621 0.417

15-<20 10 6 4 15-<20 0.814 0.828 0.750

20-<25 5 5 0 20-<25 0.930 1 0.750

25-<30 1 0 1 25-<30 0.953 1 0.833

30-<35 2 0 2 30-<35 1 1 1

35-<40 0 0 0 35-<40 1 1 1

40-<49 0 0 0 40-<49 1 1 1

Total 43 29 12

Average 14.40 13.95 17.07

Std. Dev. 7.06 5.41 9.53

Median 13.20 13.20 16.02

Age All Tanks Fiberglass Steel

0-<5.0 0.062 0.096 0.050

5-<10 0.032 0.003 0.039

10-<15 0.034 0.063 0.074

Shading: = significant (p = 0.05) 15-<20 0.027 0.037 0.134

 = marginally significant (0.05 < p = 0.10) 20-<25 0.003 0.032 0.025

25-<30 0.007 0.014 0.031

30-<35 0.013 0.000 0.057

35-<40 0.005 0.000 0.021

40-<49 0.000 0.000 0.000

M 0.062 0.096 0.134

Chi-squared 0.66 1.06 0.85

p-value 0.72 0.59 0.65

Time In Use

Time To Release

Differences In Cumulative Distributions, KolmorgorovSmirnov Test Results

Appendix C C-25
Peer Review Draft - March 2005

K-S Test For Piping Ages

FDEP Piping Age Distributions (Numbers Of Installations) Cumulative Distribution (Piping Ages)

Age All* Fiberglass Steel/Galv.** Approv. Synth. Suction Pressure Age All Fiberglass Steel/Galv. Approv. Synth. Suction Pressure

0-<5.0 1911 972 36 791 86 1601 0-<5.0 0.128 0.090 0.035 0.397 0.087 0.143

5-<10 1722 1143 41 364 104 1390 5-<10 0.243 0.195 0.075 0.580 0.192 0.267

10-<15 4506 3713 239 282 378 3143 10-<15 0.544 0.537 0.306 0.721 0.575 0.547

15-<20 4440 3351 379 372 237 3356 15-<20 0.841 0.846 0.674 0.908 0.815 0.846

20-<25 1367 986 159 125 76 1034 20-<25 0.933 0.937 0.828 0.970 0.892 0.938

25-<30 410 272 70 33 39 306 25-<30 0.960 0.962 0.896 0.987 0.931 0.965

30-<35 394 282 61 26 48 264 30-<35 0.986 0.988 0.955 1.000 0.980 0.989

35-<40 125 78 38 0 13 84 35-<40 0.995 0.995 0.992 1.000 0.993 0.996

40-<50 78 54 7 0 7 44 40-<50 1 1 0.999 1.000 1 1

Total 14953 10851 1031 1993 988 11222

Time in Use

Average 14.37 14.77 18.74 9.72 15.22 14.08

Std. Dev. 7.36 6.85 7.47 7.41 7.67 7.36

Median 14.42 14.50 17.50 6.58 14.04 14.33

*All > (fiberglass + steel + approv synth) because material of construction is not know for some piping

**total, average, std. dev., and median statistics for steel/galvanized tanks include one tank with age >50

Number Of Piping Releases Versus Age Cumulative Distribution (Piping Releases)

Age All Piping Fiberglass Steel/Galv. Approv. Synth. Suction Pressure Age All Fiberglass Steel/Galv. Approv. Synth. Suction Pressure

0-<5.0 20 15 2 3 2 18 0-<5.0 0.235 0.221 0.222 0.375 0.222 0.247

5-<10 28 24 1 3 2 24 5-<10 0.565 0.574 0.333 0.750 0.444 0.575

10-<15 24 19 3 2 4 20 10-<15 0.847 0.853 0.667 1 0.889 0.849

15-<20 11 9 2 0 0 11 15-<20 0.976 0.985 0.889 1 0.889 1

20-<25 0 0 0 0 0 0 20-<25 0.976 0.985 0.889 1 0.889 1

25-<30 2 1 1 0 1 0 25-<30 1 1 1 1 1 1

30-<35 0 0 0 0 0 0 30-<35 1 1 1 1 1 1

35-<40 0 0 0 0 0 0 35-<40 1 1 1 1 1 1

40-<50 0 0 0 0 0 0 40-<50 1 1 1 1 1 1

Total 85 68 9 8 9 73

Time To Release

Average 9.7 9.7 12.1 6.29 11.3 9.3

Std. Dev. 5.7 5.4 8.20 3.73 7.6 5.2

Median 8.9 8.9 12.3 6.53 10.1 8.8

Age All Piping Fiberglass Steel/Galv. Approv. Synth. Suction Pressure

0-<5.0 0.107 0.131 0.187 0.022 0.135 0.104

5-<10 0.322 0.379 0.259 0.170 0.252 0.309

10-<15 0.303 0.316 0.360 0.279 0.314 0.303

Shading: = significant (p = 0.05) 15-<20 0.135 0.139 0.215 0.092 0.074 0.154

 = marginally significant (0.05 < p = 0.10) 20-<25 0.044 0.049 0.061 0.030 0.003 0.062

25-<30 0.040 0.038 0.104 0.013 0.069 0.035

30-<35 0.014 0.012 0.045 0.000 0.020 0.011

35-<40 0.005 0.005 0.008 0.000 0.007 0.004

40-<50 0.000 0.000 0.001 0.000 0.000 0.000

M 0.322 0.379 0.360 0.279 0.314 0.309

Chi-squared 8.75 9.69 1.16 0.62 0.88 6.92

p-value 0.013 0.008 0.561 0.733 0.64 0.031

Differences In Cumulative Distributions, Kolmorgorov-Smirnov Test Results

Appendix C C-26