August 5, 2009 1

Task Order No. 3003 – Task 2, Subtask d – Current Equipment Use 

Technical Directive No. 5

Summary for Current Equipment Use Analysis

This report summarizes the methodology and findings of the review of underground storage tank 

(UST) equipment currently in use for federally regulated USTs (hereafter referred to as “tanks”) 

in 23 states.

Methods

E

2

Inc. reviewed state UST databases obtained from a search of 56 state and territory UST Web

sites and direct contact with nine state UST agencies for information regarding tank construction,

pipe construction, and release detection type for federally regulated tanks. Databases were 

queried for specific information requested by OUST. Thirteen states provided data that indicated 

which tanks were federally regulated. For states that did not specify which tanks were federally 

regulated, rules based on tank volume and types of substances contained in the tanks were 

applied to the data to estimate which tanks were federally regulated. 

Complete results of this analysis can be found in the following appendices:

Appendix A: Tank Type - Currently In Use

Appendix B: Pipe Type - Currently In Use

Appendix C: Tank Leak Detection - Currently In Use

Appendix D: Pipe Leak Detection - Currently In Use

Appendix E: Other Characteristics - Currently In Use

Appendix F: Interstitial Monitoring - Currently In Use

Appendix G: Tank Type - Temporarily Out Of Service

Appendix H: Pipe Type - Temporarily Out Of Service

Appendix I: Tank Leak Detection - Temporarily Out Of Service

Appendix J: Pipe Leak Detection - Temporarily Out Of Service

Appendix K: Other Characteristics - Temporarily Out Of Service

Appendix L: Interstitial Monitoring - Temporarily Out Of Service

An overall summary of the data, including rules applied and data limitations, is contained in the 

Results and Data Limitations sections. Percent usage of the most commonly used equipment and 

materials was calculated for each category. Raw percentages within each category may not add 

up to 100 percent because they are based on the number of tanks in each state for which that 

particular type of equipment is possible. For example, some states have “NA” in place of a 

specific equipment type. In these instances, the total number of tanks for that state is not 

included in the total number of tanks in the denominator for that particular equipment type. The 

normalized percentage was calculated by dividing the un-normalized percentage by the total of 

the un-normalized percentages. Normalized percentages are presented in this report and may not 

add up to 100 percent, due to rounding. Results are organized by the following topics: tank type, 

pipe type, tank leak detection, pipe leak detection, other characteristics, and interstitial 

monitoring.
August 5, 2009 2

Results 

Tank Type

Of the 23 states researched, all but Hawaii had information available regarding whether tanks 

were single-walled or secondarily contained. Tanks at currently in-use facilities (hereafter 

referred to as “CIU”) totaled 318,544 tanks, while temporarily out of service facilities (hereafter 

referred to as “TOS”) totaled 19,713 tanks. Most tanks are single-walled (Table 1). 

 

Table 1. Percent of single versus secondarily contained tanks

Tank status Single-walled Secondarily Contained Unknown

CIU 69.89% 28.81% 1.30%

TOS 78.89% 9.13% 11.98%

Total 70.41% 27.67% 1.92%

Overall, 45.45 percent of tanks are made of steel, 36.16 percent are fiberglass, 13.64 percent are 

composite and 2.50 percent are jacketed (Table 2). Lined steel tanks make up 5.19 percent and 

cathodically protected steel tanks make up 36.53 percent of all tanks.

Table 2. Overall material of construction among single-walled and secondarily contained tanks

Tank status Steel Fiberglass Composite1 Steel 

jacketed Other2 Unknown

CIU 43.92% 37.17% 14.10% 2.60% 0.28% 1.93%

TOS 72.80% 18.06% 5.58% 0.56% 0.45% 2.55%

Total 45.45% 36.16% 13.64% 2.50% 0.29% 1.96%

1 Examples of “composite” include steel with fiberglass and urethane cladding.

2 An example of “other” is concrete.

Twenty-one states reported the type of construction used among all single-walled tanks. 

Wisconsin reported the number of single-walled versus secondarily contained tanks but did not 

specify type of construction. Most single-walled tanks are made of steel (Table 3). The second 

most common material used is fiberglass.

Table 3. Material of construction among all single-walled tanks

Tank status Steel Fiberglass Composite1 Other2 Unknown

CIU 55.29% 30.94% 12.17% 0.35% 1.25%

TOS 76.89% 14.93% 5.07% 0.48% 2.63%

Total 56.73% 29.87% 11.70% 0.36% 1.34%

1 Examples of “composite” include steel with fiberglass and urethane cladding.

2 An example of “other” is concrete.

Table 4 summarizes the six types of construction among single-walled tanks made of steel. The 

most common classifications for tanks were “cathodic protection unknown” and “with general 

type of cathodic protection.” The following rules were applied to all tanks using steel:

 The category of “cathodic protection unknown” includes steel tanks with no type of 

cathodic protection marked. This category may include both tanks without cathodic 

protection and those that have cathodic protection, but it is not indicated in the state 

database.
August 5, 2009 3

 The category of “with general type of cathodic protection” included steel tanks with both 

impressed current and galvanic anode cathodic protection as well as steel tanks with an 

unspecified type of cathodic protection. In this instance, tanks were not counted in the 

“with impressed current cathodic protection” or “with galvanic anode cathodic 

protection” categories.

 Tanks marked as having “internal lining” and “galvanic anode cathodic protection” or 

“impressed current cathodic protection” were counted as “with internal lining and 

cathodic protection.” In this instance, tanks are not counted in the “with impressed 

current cathodic protection” or “with galvanic anode cathodic protection” categories.

Table 4. Type of construction among single-walled tanks using steel1

Tank status

Cathodic 

protection 

unknown

With 

impressed 

current 

cathodic 

protection

With 

galvanic 

anode 

cathodic 

protection

With general 

type of 

cathodic 

protection

With 

internal 

lining

With internal 

lining and 

cathodic 

protection

CIU 14.18% 19.86% 20.51% 31.86% 4.42% 9.17%

TOS 39.14% 12.82% 16.53% 25.45% 1.90% 4.16%

Total 16.46% 19.22% 20.13% 31.29% 4.19% 8.72%

The same 21 states that reported the type of construction used among all single-walled tanks also 

reported the type of construction used among all secondarily contained tanks. Most of the 

secondarily contained tanks were made of fiberglass (Table 5). Composite was the second most 

common material used.

Table 5. Material of construction among all secondarily contained tanks

Tank 

status Steel Fiberglass Composite1 Steel jacketed Other2 Unknown

CIU 16.34% 52.27% 18.77% 8.92% 0.12% 3.58%

TOS 37.44% 45.08% 10.02% 5.44% 0.15% 1.87%

Total 16.73% 52.15% 18.60% 8.85% 0.12% 3.54%

1 Examples of “composite” include steel with fiberglass and urethane cladding.

2 An example of “other” is concrete.

Table 6 summarizes the six types of construction among secondarily contained tanks using steel. 

The most common classification is “with galvanic anode cathodic protection.” The same rules 

that applied to single-walled tanks using steel described above were applied to secondarily 

contained tanks using steel.

 

1 The distribution of cathodic protection types among tanks and pipes were normalized based on the normalized 

percentage of all construction types. Those cathodic protection types that were not tracked in all state databases may 

be overstated, as the normalization applies the percentage calculated for tanks and pipes in states that track these 

cathodic protection types to tanks and pipes in states where it is not.
August 5, 2009 4

Table 6. Type of construction among secondarily contained tanks using steel

Tank status

Cathodic 

protection 

unknown

With 

impressed 

current 

cathodic 

protection

With 

galvanic 

anode 

cathodic 

protection

With general 

type of 

cathodic 

protection

With 

internal 

lining

With internal 

lining and 

cathodic 

protection

CIU 11.78% 4.56% 54.10% 28.72% 0.40% 0.44%

TOS 6.03% 4.16% 60.61% 28.22% 0.33% 0.65%

Total 11.56% 4.53% 54.25% 28.82% 0.39% 0.45%

Pipe Type

Of the 23 states researched, 20 states had information available regarding the type of pipes used. 

The Massachusetts, Ohio, and Wisconsin databases reported no information on piping. 

Currently in-use tanks with pipe totaled 274,022 while 18,870 tanks with pipes were reported as 

TOS. Most of the pipes reported are single walled (Table 7). The following rule was applied 

when counting the number and type of pipes:

 Missouri and Mississippi tracked multiple piping records for each tank and all of the 

multiple records were counted in pipe totals.

Table 7. Percentage of single-walled versus secondarily contained pipes

Tank status Single-walled Secondarily contained Unknown

CIU 61.63% 36.28% 2.09%

TOS 75.62% 10.06% 14.32%

Total 62.54% 34.59% 2.87%

Most pipes are made of fiberglass (Table 8). Steel is the second most common material for 

single-walled pipes and flexible plastic is the second most common material for secondarily

contained pipes.

Table 8. Material of construction among single-walled and secondarily contained pipes

Tank status Steel Fiberglass Flexible plastic Other1 Unknown

All single-walled and secondarily contained pipes

CIU 18.08% 58.13% 13.37% 2.16% 8.25%

TOS 47.78% 39.40% 3.73% 1.19% 7.89%

Total 19.78% 57.05% 12.82% 2.11% 8.23%

Single-walled

CIU 26.65% 62.72% 4.32% 1.97% 4.34%

TOS 51.81% 38.15% 1.20% 1.05% 7.79%

Total 28.62% 60.80% 4.07% 1.90% 4.61%

Secondarily contained

CIU 3.53% 50.32% 28.76% 2.49% 14.91%

TOS 17.49% 48.79% 22.78% 2.29% 8.65%

Total 3.79% 50.29% 28.64% 2.49% 14.79%

1 Examples of “other” include copper, pvc and iron.

Overall, 19.78 percent of pipes are made of steel, 57.05 percent are fiberglass, and 12.82 percent 

are flexible plastic.
August 5, 2009 5

Of all single-walled and secondarily-contained pipes using steel, most do not have cathodic 

protection indicated in the databases (Table 9). However, in cases where impressed current 

cathodic protection is used for the tank, the same method of cathodic protection may be used for 

the piping. Of single-walled and secondarily contained pipes that do have cathodic protection,

most are classified as “with general type of cathodic protection.” The following rule was applied 

to pipes using steel:

 The category of “with general type of cathodic protection” included steel pipes with both 

impressed current and galvanic anode cathodic protection as well as steel pipes with an 

unspecified type of cathodic protection. 

Table 9. Type of construction among single-walled and secondarily contained pipes using steel

Tank status

Cathodic 

protection 

unknown

With impressed 

current cathodic 

protection

With galvanic 

anode cathodic 

protection

With general type 

of cathodic 

protection

Single-walled

CIU 34.02% 26.55% 11.54% 27.89%

TOS 61.78% 14.65% 6.56% 17.01%

Total 37.97% 24.86% 10.82% 26.35%

Secondarily contained

CIU 50.92% 2.39% 8.89% 37.79%

TOS 64.39% 3.18% 2.07% 30.36%

Total 52.06% 2.46% 8.30% 37.18%

Nine of the 23 states did not provide information regarding piping product delivery system type. 

Of the 14 states that did provide information, most pipes used a pressure delivery system (Table 

10). Tanks with unknown product delivery types were removed and assumed to have the same 

distribution of pressurized, suction, and other types as was found in those where the type was 

known: 81.21 percent, 17.30 percent, and 1.50 percent respectively. The following rules were 

applied to piping product delivery system types:

 Delivery systems marked as “no valve – suction,” “valve – suction,” “safe suction,” 

“unsafe suction,” and “u.s. suction” were included under the suction category. Delivery

systems marked as “gravity” or “manifold” were included under the “other” category. 

The unknown category includes delivery systems reporting multiple methods of delivery

as well as “unknown,” “bulk product system,” and blank cells. 

Table 10. Piping product delivery system type

Tank status Pressure Suction Other

CIU 82.23% 16.36% 1.41%

TOS 60.37% 36.53% 3.10%

Total 81.21% 17.30% 1.50%

Tank Leak Detection

Of the 23 states queried, 17 states provided information regarding leak detection methods for 

tanks. A total of 348,017 tank leak detection instances were identified. Currently in-use tanks 
August 5, 2009 6

accounted for 94 percent of these instances. Automatic tank gauging was the most common leak 

detection method (Table 11). The following rules were applied to the data:

 For tanks using more than one method of leak detection, all methods were counted;

 Tanks marked as “tank tightness testing,” “inventory control,” or “other” were recorded 

as “other;” and

 When none of the specific leak types were selected, they were counted towards 

“unknown.”

Table 11. Percentage of leak detection types among tanks with leak protection

Leak Detection Type CIU TOS Total

Deferred 1.06% 0.95% 1.06%

Inventory control and 

tank tightness testing 6.49% 8.44% 6.58%

Manual tank gauging 3.14% 3.32% 3.15%

Automatic tank gauging 34.82% 14.72% 33.66%

Interstitial monitoring 20.63% 5.18% 19.76%

Ground water 

monitoring 5.47% 6.03% 5.51%

Vapor monitoring 4.80% 8.44% 5.00%

Statistical inventory 

reconciliation 12.90% 13.73% 12.96%

Other 5.25% 8.54% 5.44%

Unknown 5.43% 30.65% 6.88%

Pipe Leak Detection

Of the 23 states queried, 16 states provided information regarding pipe leak detection for CIU 

pipes and 15 states provided that information for TOS pipes. A total of 437,490 pipe leak 

detection instances were identified. Currently in-use pipes accounted for 94 percent of these 

instances. For piping using line leak detectors (LLDs), 5.38 percent of piping indicated using 

electronic LLDs and 10.72 percent indicated using mechanical LLDs (Table 12). Most state 

databases did not indicate the type of LLD used. The following rules were applied to pipes with 

automatic line leak detection:

 Pipes not marked as “pressurized piping product delivery” were included in automatic 

line leak detection totals when they specified electronic or mechanical line leak detection. 

This applied to data from 10 states.

 When pipes were marked as “pressurized” but not as having automatic line leak 

detection, they were included in the “unknown” category. Pipes marked as 

“autolineleak” and “auto line leak detection” were similarly categorized. This applied to 

data from 11 states.

Table 12. Type of leak detection among pipes with automatic line leak detection

Tank status Electronic Mechanical Unknown

CIU 5.53% 11.08% 83.39%

TOS 1.29% 0.58% 98.12%

Total 5.38% 10.72% 83.90%
August 5, 2009 7

For periodic leak detection, most pipes use the line tightness testing method (Table 13). 

Interstitial monitoring is the second most common leak detection method among pipes.

Table 13. Type of leak detection among pipes with non-automatic line leak detection

Tank 

status Deferred

Line 

tightness 

testing

Interstitial 

monitoring

Ground 

water 

monitoring

Vapor 

monitoring

Statistical 

inventory 

reconciliation

Other Unknown

CIU 4.74% 37.79% 19.52% 3.48% 5.08% 13.70% 4.65% 11.04%

TOS 3.73% 20.26% 2.89% 2.83% 5.44% 10.86% 14.96% 39.02%

Total 4.69% 36.51% 18.30% 3.43% 5.12% 13.49% 5.28% 13.19%

Other Characteristics

Of the 23 states queried, only Utah reported information regarding other characteristics of 

containment. Utah reported whether or not tanks had under dispenser containment and 

submersible turbine pump containment. Currently in-use and TOS Utah tanks represent less than 

one percent of all tanks queried. Table 14 shows the percentage of under dispenser containment 

versus submersible turbine pump containment for tanks in Utah.

Table 14. Other characteristics of containment among tanks in Utah

Tank status Under dispenser containment Submersible turbine pump 

containment

CIU 57.10% 59.19%

TOS 22.01% 23.92%

Total 55.35% 57.43%

Interstitial Monitoring

Of the 23 states queried, 17 states provided information regarding interstitial monitoring among 

tanks, piping, or both tanks and piping. Table 15 shows the prevalence of interstitial monitoring 

among tanks and piping.

Table 15. Use of interstitial monitoring among tanks and pipes

Tank status

Secondarily contained 

tanks using interstitial 

monitoring

Tanks with secondarily 

contained piping using 

interstitial monitoring

Systems with both 

secondarily contained 

tanks and secondarily 

contained piping using 

interstitial monitoring

CIU 77.05% 49.32% 54.93%

TOS 56.79% 29.06% 34.38%

Total 76.64% 48.94% 54.60%

Data Limitations

The universe of USTs analyzed includes approximately 53 percent of the national total of active 

USTs. All ten regions are represented as well as small, medium, and large states. Due to the 

lack of data available for Florida and California, secondary containment totals may be 

underestimated if results are extrapolated to the nation as a whole. Utah is the only state 

analyzed that tracks information on under dispenser containment and submersible turbine pump 
August 5, 2009 8

containment, so it is probably not appropriate to extrapolate these totals to the national universe 

of tanks.

Due to varying database structures among the states, it was not possible to report a number of 

construction types in some states (e.g., in twelve of the 23 states analyzed, a secondarily

contained tank assignment precluded the assignment of impressed current cathodic protection), 

so those types may be underreported. To compensate, percentages reported for each type are 

calculated as a percentage of the total tanks in only those states where it is possible to report a 

particular type of construction.