July 24, 2006 revision SC-05 – Interstitial Integrity Testing 1

Task Order No. 1010 – General Technical And Programmatic Support In Implementing The Energy Policy Act Of 2005

Task 1010-04 – Technical Research/Analysis And Summarize Information 

Subject 4 – Secondary Containment

Subtask SC-05 – States’ Periodic Interstitial Integrity Testing Requirements

E

2

Inc. researched all 50 states and the District of Columbia to identify: which states require periodic interstitial integrity testing (also 

known as secondary containment testing), the options for meeting those requirements, and the costs of those options. E2Inc. used 

state Web sites, online statutes and regulations, Internet searches, and phone calls to several states. Periodic interstitial integrity

testing recurs at regular intervals; it does not include testing during installation or episodic testing (for example, testing that is required 

if a leak is suspected). At the direction of OUST’s subject matter expert for secondary containment, Paul Miller, E2Inc. did not 

investigate state requirements for episodic interstitial integrity testing or interstitial integrity testing during installation. In addition, in 

general, E2Inc. did not investigate states where periodic interstitial integrity testing is one of several options because, by presenting 

options, these states are not requiring interstitial integrity testing. For all of the states that require periodic interstitial integrity testing, 

Table 1 presents information about the requirements and options for meeting the requirements.

There are three general methods of interstitial integrity testing: vacuum, pressure, and hydrostatic. All three methods can be 

conducted either continuously or periodically. The vacuum method involves drawing a vacuum on the interstitial space and 

monitoring for a decrease in the vacuum. The pressure method involves creating a very slight pressure in the interstitial space and 

monitoring for a decrease in the pressure. The hydrostatic method involves filling the interstitial space with a liquid and monitoring 

for a change in the level of liquid. The continuous hydrostatic method, which is used only for tanks (primarily fiberglass tanks), 

involves filling the tank’s interstice with liquid (for example, brine); the liquid level is then automatically monitored for an increase or 

decrease. The periodic hydrostatic method is performed by filling the interstice with liquid and then, after some time has passed, 

checking for a drop in the liquid’s level; the time elapsed can be 24 hours for a visual determination or 15-30 minutes using a more 

advanced technology that can discriminate smaller drops in liquid level than can the human eye (for example, Tanknology uses “the 

patented VPLT precision test system” to test containment sumps and dispenser pans “in as little as 15 minutes”). 

E

2

Inc. interviewed two Tanknology employees at two different locations. Tanknology is a company that performs periodic secondary

containment testing, among other tank services. Both employees interviewed stated that the predominant periodic secondary

containment testing methods used by their Tanknology locations are: vacuum testing for tanks, pressure testing for piping, and 
July 24, 2006 revision SC-05 – Interstitial Integrity Testing 2

hydrostatic testing for tank sumps and dispenser sumps. According to the company’s secondary containment brochures, these are the 

methods used at all Tanknology locations, both in California and elsewhere.1

E

2

Inc. obtained costs for periodic secondary containment testing from the two Tanknology locations; these are recurring costs 

incurred every time the test is performed. E2Inc. obtained from a Xerxes Corporation representative the cost to equip a double-walled 

fiberglass tank with brine for continuous hydrostatic monitoring; this is a one-time cost incurred at the UST’s purchase – there are no 

additional, recurring costs. The costs are presented in Table 2.

Table 1: States’ Periodic Interstitial Integrity Testing Requirements And Options

State Does The State Require

Periodic Interstitial Integrity Testing? Options

CA New USTs (installed after 1983, or farm fuel USTs installed after 1986 (§2611)):1

Secondary containment must be tested upon installation, 6 months after installation, 

and every 36 months thereafter (systems with continuous monitoring are exempt from 

periodic testing) (§2637); annual tightness testing required for underground pressurized 

piping and under-dispenser piping if certain conditions are not met (§2636(f)).

Interstitial spaces of tanks and piping of USTs installed on or after July 1, 2004 must 

be continuously monitored using vacuum, pressure, or interstitial liquid level 

measurements (HSC §25290.1(e))2

Pressure, vacuum, or hydrostatic

FL UST systems installed on or after July 13, 1998 (§62-761.200(70)) that have closed 

interstices must have the tank’s and piping’s interstices tested for a breach of integrity

at installation and every 5 years, unless the testing is continuous (breach of integrity

testing not required for piping sumps and dispenser liners) (§62-761.640(3)(a)(2))3

Continuous hydrostatic system approved by

DEP, continuous vacuum system approved by

DEP, liquid tightness test in accordance with 

manufacturer’s instructions, or other approved 

method (§62-761.640(3)(a)(2))

MD Only if the owner is claiming secondary containment as his release detection method, 

in which case tank and piping must be tested annually;

4

there are also sump testing 

requirements that could be considered interstitial testing (twice per year for high-risk 

ground water areas, annually for rest of state)

Hydrostatic (brine), vacuum, pressure

 

1

http://www.tanknology.com/pdf/SecCont%20NON%20California.pdf, http://www.tanknology.com/pdf/SecondaryContainment.pdf 
July 24, 2006 revision SC-05 – Interstitial Integrity Testing 3

State Does The State Require

Periodic Interstitial Integrity Testing? Options

OH Double-walled underground piping in hazardous substance UST systems and in 

sensitive areas must have annual interstitial tightness testing (1301:7-9-08(F)(5));5

double-walled underground pressure piping must have monthly or annual interstitial 

tightness testing (1301:7-9-08(F)(4)(b)); double-walled underground suction piping 

that does not meet certain requirements must have interstitial tightness testing every 36 

months (1301:7-9-08(F)(4)(c))

Follow manufacturer’s requirements

RI Existing double-walled UST systems must have interstitial tightness testing (for tank 

only)

6

beginning 20 years after installation, and every 2 years after that (§8.08(A)(3))7

Vacuum, pressure, brine level8

UT When a sump sensor is used as a leak detector, the secondary containment sump must 

be tested for tightness annually (R311-203.5(c));9no operators have chosen this option 

yet because it is less expensive to use line leak detectors10

Follow manufacturer’s guidelines or other 

method approved by the State11 (no methods 

have been approved yet)12

Table 2: Costs For Selected Interstitial Integrity Tests

Method Cost

Periodic Tests (recurring costs)

Vacuum (for tanks) $110–200 per tank

Pressure (for piping) $95–110 per line (3–8 lines per 

facility is typical)

Hydrostatic (for sumps)

 Tank sump $150 per sump

 Dispenser sump $150 per sump

 Spill bucket $95 each

Continuous Monitoring (one-time costs)
July 24, 2006 revision SC-05 – Interstitial Integrity Testing 4

Additional cost to equip 

double-walled UST with brine 

and reservoir for hydrostatic 

monitoring

 5,000 gallon UST $1,300

 10,000 gallon UST $1,800

 12,000 gallon UST $2,021
July 24, 2006 revision SC-05 – Interstitial Integrity Testing 5

Interviews Conducted:

States

 Kevin Gillen of Rhode Island’s Department of Environmental Management

 Herb Meade of Maryland’s Department of the Environment

 Tom Walter of Maryland’s Department of the Environment 

 David Wilson of Utah’s Department of Environmental Quality

Interstitial Testers

 Jerry Belloli of Tanknology in Sacramento, California

 Dave Grenier of Tanknology in Cherry Hill, New Jersey

Tank Manufacturers

 Rod Walsh, representative for Xerxes Corporation

 Jim Evans of Modern Welding Company of Georgia, Inc.

All interviews were conducted in June 2006.
July 24, 2006 revision SC-05 – Interstitial Integrity Testing 6

Appendix A: Selected Relevant Legal Language

California

www.calregs.com

BARCLAYS OFFICIAL CALIFORNIA CODE OF REGULATIONS

TITLE 23. WATERS

DIVISION 3. STATE WATER RESOURCES CONTROL BOARD AND REGIONAL 

WATER QUALITY

CONTROL BOARDS

CHAPTER 16. UNDERGROUND TANK REGULATIONS

ARTICLE 1. DEFINITION OF TERMS

This database is current through 04/21/06, Register 2006, No. 16. 

23 CCR s 2611

Cal. Admin. Code tit. 23, s 2611

s 2611. Additional Definitions.

...

"Existing underground storage tank" means an underground storage tank installed prior to 

January 1, 1984. The term also includes an underground storage tank installed before

January 1, 1987 and which is located on a farm, has a capacity greater than 1,100 gallons, 

and stores motor vehicle fuel used primarily for agricultural purposes and not for resale.

...

"New underground storage tank" means an underground storage tank which is not an 

existing underground storage tank.

23 CCR s 2636

Cal. Admin. Code tit. 23, s 2636

s 2636. Design, Construction, Installation, Testing, and Monitoring Requirements 

for Piping.

...

(f) Underground piping with secondary containment, including under-dispenser piping 

with secondary containment, shall be equipped and monitored with monitoring systems 

as follows:

(1) All secondary containment, including under-dispenser containment, and underdispenser spill control or containment systems shall be equipped with a continuous 

monitoring system that either activates an audible and visual alarm or stops the flow of 

product at the dispenser when it detects a leak.

(2) Automatic line leak detectors shall be installed on underground pressurized piping 

and shall be capable of detecting a 3-gallon per hour leak rate at 10 psi within 1 hour with 
July 24, 2006 revision SC-05 – Interstitial Integrity Testing 7

a probability of detection of at least 95 percent and a probability of false alarm no greater 

than 5 percent, and shall restrict or shut off the flow of product through the piping when a 

leak is detected.

(3) Until November 9, 2004, other monitoring methods may be used in lieu of the 

requirement in subdivision (2) if it is demonstrated to the satisfaction of the local agency

that the alternate method is as effective as the methods otherwise required by this section. 

Continuous monitoring systems as described in subdivision (1), which shut down the 

pump in addition to either activating the audible and visual alarm or stopping the flow of 

product at the dispenser, satisfy the automatic line leak detector requirement of 

subdivision (2).

(4) Monitoring shall be conducted on all underground pressurized piping with secondary

containment at least annually at a pressure designated by the equipment manufacturer, 

provided that the method is capable of detecting a minimum release equivalent to 0.1 

gallon per hour defined at 150 percent of the normal operating pressure of the product 

piping system at the test pressure with at least a 95 percent probability of detection and 

not more than a 5 percent probability of false alarm.

(5) Continuous monitoring systems as described in subdivision (f)(1) satisfy the annual 

tightness testing requirement of subdivision (f)(4) if both of the following conditions are 

met:

(A) The monitoring system shuts down the pump or stops the flow of product at the 

dispenser when a leak is detected in the under- dispenser containment.

(B) The monitoring system for all product piping other than that contained in the underdispenser containment is fail safe, and shuts down the pump when a leak is detected.

(6) For emergency generator tank systems, continuous monitoring systems as described 

in subdivision (1), which activate an audible and visual alarm in the event of a leak or a 

malfunction of the monitoring system satisfy the automatic line leak detector requirement 

of subdivision (2), provided that the monitoring system is checked at least daily by either 

remote electronic access or on-site visual inspections. A log of daily checks shall be 

available for local agency review upon request.

23 CCR s 2637

Cal. Admin. Code tit. 23, s 2637

s 2637. Secondary Containment Testing.

(a) Secondary containment systems installed on or after January 1, 2001 shall be tested 

upon installation, 6 months after installation, and every 36 months thereafter. Secondary

containment systems installed prior to January 1, 2001 shall be tested by January 1, 2003 

and every 36 months thereafter.
July 24, 2006 revision SC-05 – Interstitial Integrity Testing 8

(b) By December 31, 2002, the owner or operator of any secondary containment system 

that the owner or operator determines cannot be tested in accordance with this section 

shall replace the secondary containment system with a system that can be tested in 

accordance with this section. As an alternative, the owner or operator may submit a 

proposal and workplan for enhanced leak detection to the local agency in accordance 

with subdivisions 2644.1(a)(1), (2), (4), and (5) by July 1, 2002; complete the program of 

enhanced leak detection by December 31, 2002; and replace the secondary containment 

system with a system that can be tested in accordance with this section by July 1, 2005. 

The local agency shall review the proposed program of enhanced leak detection within 45 

days of submittal or re-submittal.

(c) Periodic testing of secondary containment systems shall be conducted using a test 

procedure that demonstrates that the system performs at least as well as it did upon 

installation. For example, if the secondary containment system was tested upon 

installation by using a test method that applied a pressure of 5 psi, then the periodic test 

must be conducted using a method that tests the system at an equivalent pressure. These 

tests shall be performed in accordance with manufacturer's guidelines or standards. If 

there are no manufacturer's guidelines or standards, secondary containment systems must 

be tested using an applicable method specified in an industry code or engineering 

standard. If there are no applicable manufacturers guidelines, industry codes, or 

engineering standards a test method approved by a state registered professional engineer 

shall be used.

(d) Secondary containment testing shall be performed by either a service technician or a 

licensed tank tester, both of which must meet the requirements of section 2715, 

subdivision (i).

(e) Underground storage tank owners and operators shall submit a copy of the test report 

to the local agency within 30 days of the completion of the test.

(f) Owners and operators of underground storage tanks must notify the local agency at 

least 48 hours prior to conducting the test, unless this notification requirement is waived 

by the local agency.

(g) Secondary containment systems where the continuous monitoring automatically

monitors both primary and secondary containment, such as systems that are 

hydrostatically monitored or under constant vacuum, are exempt from periodic secondary

containment testing.

http://www.waterboards.ca.gov/ust/regulatory/ab2481_status.html

25290.1. 

...

 (e) The interstitial space of the underground storage tank shall be maintained under 

constant vacuum or pressure such that a breach in the primary or secondary containment 

is detected before the liquid- or vapor-phase of the hazardous substance stored in the 
July 24, 2006 revision SC-05 – Interstitial Integrity Testing 9

underground storage tank is released into the environment. The use of interstitial liquid 

level measurement methods satisfies the requirements of this subdivision.

http://www.waterboards.ca.gov/ust/regulatory/ab1702_enacted.html

The Governor signed Assembly Bill (AB) 1702 (Statutes 2003, Chapter 42) into law on 

July 7, 2003. As an urgency bill, the requirements of AB 1702 are effective immediately. 

Among other things, AB 1702 extends the July 1, 2003 deadline for TWO requirements 

of AB 2481 (Statutes 2002, Chapter 999). Specifically, AB 1702 extended the deadline 

until July 1, 2004 for: (1) the continuous monitoring of the interstitial spaces of tank and 

piping using vacuum, pressure, or interstitial liquid level measurements and (2) the use of 

vapor sensors. Please note that all other AB 2481 requirements for new systems installed 

on or after July 1, 2003 are not affected by AB 1702.

http://www.waterboards.ca.gov/ust/leak_prevention/lgs/162_1.pdf

In accordance with H&S Code, Section 25290.1(e), which components of USTs installed 

on or after July 1, 2004 must be continuously monitored using vacuum, pressure, or 

interstitial liquid level measurement methods?

The interstitial space of the tank and product piping (including fill, vent, and vapor 

recovery piping), that are beneath the surface of the ground must be maintained under 

constant vacuum or pressure. Statute also requires that a breach in the primary or 

secondary containment be detected before the liquid or vapor of the stored substance is 

released to the environment. Continuous vacuum, pressure, or interstitial liquid level 

measurement methods can be used to satisfy these requirements. As with all leak 

detection equipment used to monitor the UST system, these methods must be third party 

certified and should be listed in Local Guidance (LG) Letter 113.
July 24, 2006 revision SC-05 – Interstitial Integrity Testing 10

Florida

http://www.dep.state.fl.us/waste/quick_topics/rules/documents/62-761.pdf

62-761.200 Definitions.

...

(70) “UST Category-C system” means a system that was installed on or after July 13, 

1998. USTs that are removed and relocated on or after July 13, 1998 are considered 

Category-C systems.

62-761.640 Performance Standards for Release Detection Methods.

...

(3) Internal release detection methods.

(a) Interstitial monitoring for UST systems.

1. Interstitial monitoring for double-walled tanks, double-walled integral piping, 

dispenser liners, piping sumps, and other secondary containment systems, shall be 

designed and constructed to allow monitoring of the space between the primary and

secondary containment. One or more of the following methods of interstitial monitoring 

shall be used:

a. Manual sampling of, or visual monitoring for, liquids;

b. Continuous electronic sensing equipment;

c. Hydrostatic monitoring systems; or

d. Vacuum monitoring.

2. Breach of integrity tests for Category-C systems. A test shall be performed for a breach 

of integrity of the interstice for double-walled USTs and for double-walled integral 

piping that is in contact with the soil and that is connected to USTs. Piping sumps and 

dispenser liners are not required to perform a breach of integrity test. The test shall be 

performed to determine the integrity of the inner and outer wall, is required only for tanks 

and integral piping with closed interstices, and does not apply to open-interstice systems 

with liners. The test shall be performed at the time of installation, and every five years 

from the date of installation, unless the test is a continuous test. If a UST is totally

submerged in groundwater, monthly monitoring of the interstice for the presence of water 

shall be conducted. The breach of integrity test may be performed by using at least one of 

the following methods:

a. A continuous hydrostatic system approved by the Department in accordance with 

subsection 62-761.850(2), F.A.C.;

b. A continuous vacuum system, pursuant to paragraph 62-761.640(3)(a), F.A.C., that is 

approved by the Department in accordance with subsection 62-761.850(2), F.A.C.;

c. Testing of the interstice for liquid tightness in accordance with manufacturer’s 

installation instructions; or

d. Another method in accordance with subsection 62-761.850(2), F.A.C.

3. Vacuum monitoring of the interstice shall meet the following requirements:

a. Liquid-filled gauges and air-filled gauges shall be calibrated in accordance with the 

National Institute of Standards and Technology. The gauges shall be operational at all 

times.
July 24, 2006 revision SC-05 – Interstitial Integrity Testing 11

b. Vacuum monitoring may be used as a continuous method of release detection provided 

that the vacuum system is equipped with an audible or visual alarm. The alarm shall 

indicate when the minimum vacuum level allowed is reached as provided in the

equipment approval granted in accordance subsection 62-761.850(2), F.A.C.

c. Vacuum readings shall be recorded monthly. Upon discovery of any significant 

vacuum level decrease, or any loss of vacuum exceeding 20% of the initial level, or any

loss in excess of the levels established in the test protocols provided in the third party 

certification for the test method, the tank manufacturer shall be contacted and the vacuum 

refreshed in accordance with the storage tank system’s equipment approval in subsection 

62-761.850(2), F.A.C. If the loss of vacuum persists, an investigation shall be initiated 

and an incident reported in accordance with subsection 62-761.450(2), F.A.C. The source 

of the loss shall be repaired in accordance with Rule 62-761.700, F.A.C.
July 24, 2006 revision SC-05 – Interstitial Integrity Testing 12

Ohio

http://www.com.state.oh.us/sfm/pub/bust_1301_7-9.pdf

1301:7-9-07 Release detection requirements and methods for UST systems.

...

(F) Testing methods for UST systems.

...

(2) Tightness testing for piping.

...

(c) Tightness testing of the interstice of double wall piping shall follow the manufacturers

testing requirements.

...

1301:7-9-08 Operating requirements for UST systems.

...

(F) Operation of release detection components.

All owners and operators shall maintain and operate release detection equipment in 

accordance with paragraph (F) of this rule and shall document their actions on a form 

prescribed by the fire marshal in accordance with paragraph (G)(1) of this rule.

...

(4) All release detection methods for piping and containment systems described in rule 

1301:7-9-07 of the Administrative Code shall be inspected to confirm proper operation in 

accordance with the following:

...

(b) Underground piping that conveys regulated substances under pressure shall meet one 

of the following:

(i) Have an annual tightness test conducted in compliance with paragraph (F)(2) of rule

1301:7-9-07 of the Administrative Code; or

(ii) Have a monthly tightness test conducted by the on-site electronic line testing unit

provided that the unit can detect a two-tenth of a gallon per hour leak rate at operating

pressure.

(c) Underground piping that conveys regulated substances under suction shall meet one 

of the following:

(i) Have a tightness test conducted every thirty-six month period in compliance with

paragraph (F)(2) of rule 1301:7-9-07 of the Administrative Code; or

(ii) Demonstrate compliance with paragraph (B)(3)(b) of rule 1301:7-9-07 of the

Administrative Code.

...

(5) All release detection methods for hazardous substance UST systems and UST systems 

located in sensitive areas as described in paragraph (C) of rule 1301:7-9-07 of the 

Administrative Code shall be inspected annually to confirm proper operation in 

accordance with the following:

...

(c) All underground piping that routinely contains regulated substances shall have an 

annual tightness test pursuant to paragraph (F)(2) of rule 1301:7-9-07 of the 

Administrative Code
July 24, 2006 revision SC-05 – Interstitial Integrity Testing 13

Rhode Island

http://www.dem.ri.gov/pubs/regs/regs/waste/ustreg05.pdf

8.08 Leak Detection for Existing Tanks: Except as provided in Rule 8.01 above, 

owners/operators of all existing facilities shall comply with the applicable leak detection 

requirements:

(A) Double-Walled USTs: The following requirements apply to all double-walled USTs 

except those used for emergency generators and waste oil. These two exemptions are 

required to comply with either 8.08 (D) or 8.08 (E).

(1) Install and operate a continuous interstitial space electronic monitoring system 

consistent with the requirements in Rules 9.15 and 9.17, and

(2) Perform daily and monthly inventory control and record keeping consistent with Rule

11.03, and maintain inventory records in accordance with Rule 11.02(B).

(3) Perform a test for tightness on the interstitial space between the tanks walls when the 

tank has been installed for a period of twenty years, and once every 2 years thereafter.
July 24, 2006 revision SC-05 – Interstitial Integrity Testing 14

Utah

http://www.rules.utah.gov/publicat/code/r311/r311-203.htm

R311-203-5. UST Testing Requirements.

...

(c) Containment sump testing. When a sump sensor is used as a leak detector, the 

secondary containment sump shall be tested for tightness annually according to the 

manufacturer's guidelines or standards, or by another method approved by the Executive 

Secretary.
July 24, 2006 revision SC-05 – Interstitial Integrity Testing 15

 

1 Unless otherwise noted, all information for California is from 

http://www.swrcb.ca.gov/cwphome/ust/regulatory/docs/ccr_title23div3chapt16.pdf. See also: 

http://www.waterboards.ca.gov/ust/regulatory/ab2481_status.html;

http://www.waterboards.ca.gov/ust/regulatory/ab1702_enacted.html;

http://www.waterboards.ca.gov/ust/leak_prevention/lgs/160.html;

http://www.waterboards.ca.gov/ust/leak_prevention/lg113/Misc_Files/topics_lg113_vph_methods_8_13_0

4.html

2

http://www.waterboards.ca.gov/ust/leak_prevention/lgs/162_1.pdf

3 Unless otherwise noted, all information for Florida is from 

http://www.dep.state.fl.us/waste/quick_topics/rules/documents/62-761.pdf

4 Unless otherwise noted, all information for Maryland is from a June 22, 2006 phone call with Herb 

Meade of MDE. See also: 

http://www.mde.state.md.us/assets/document/OilControl/Oil_Pollution_Tank%20Man_Reg26.10.pdf; 

http://www.dsd.state.md.us/comar/subtitle_chapters/26_Chapters.htm

5 Unless otherwise noted, all information for Ohio is from 

http://www.com.state.oh.us/sfm/fire_laws.aspx#1301_7_9

6

June 22, 2006 phone call with Kevin Gillen of RIDEM.

7

http://www.dem.ri.gov/pubs/regs/regs/waste/ustreg05.pdf

8

June 22, 2006 phone call with Kevin Gillen of RIDEM.

9

http://www.rules.utah.gov/publicat/code/r311/r311.htm

10 June 22, 2006 phone call with David Wilson of UDEQ.

11 http://www.rules.utah.gov/publicat/code/r311/r311.htm

12 June 22, 2006 phone call with David Wilson of UDEQ.