x=,EPA
United States
Environmental Protection
Agency
TRANSITION SUMP
SUBMERSIBLE
TURBINE PUMP (STP)
SUMP
TANK
DOUBLE-WALLED PIPING
INTERSTICE OF DOUBLE- _
WALLED PIPING IS OPEN
In-Depth Discussion:
Automated Interstitial Monitoring
Systems for Underground Pressurized
Piping on Emergency Power Generator
UST Systems
E P A-510-K-22-002
May 2022

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Contents
Purpose	1
Background	2
Section 1: Regulatory Allowance for AIM Systems and Overview of Meeting the Dual Release
Detection Requirements	4
Section 2: Description of AIM Systems	6
Section 3: Recognizing AIM System Capability to Meet Regulatory Requirements	13
Section 4: Examples of Category 1 and 2 Systems	17
Section 5: Example of a Basic Category 3 System	22
Section 6: Alternative System Configurations Used for Category 3 AIM Systems	32
Section 7: O&M Testing and Inspections Requirements At A Glance	35
Section 8: Basic Test Requirements (by System Component)	38
Section 9: Required Documentation from UST System Owners and Operators	41
Section 10: AIM Systems Inspection and Testing Checklists	45
Appendix	51

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Purpose
This document includes background and technical information on
the U.S. Environmental Protection Agency's (EPA's) recognition
of using automated interstitial monitoring (AIM) systems to meet
federal release detection requirements for underground pressurized
piping systems on emergency power generator (EPG) UST
systems. Owners and operators must obtain approval from their
UST implementing agency to use an AIM system. EPA has
provided a Certification of Compliance Form to assist owners and
operators with their approval request. State UST implementing
agencies might not allow these systems in their jurisdictions or
may require different or additional information to verify design
and installation criteria have been met
The intent of this document is to familiarize state UST
implementing agencies with the concept of AIM systems to
consider allowing use of these systems in their jurisdicti ons. This
document also can assist UST system installers, fuel system
designers, and other qualified professionals when installing or
modifying fuel storage systems to meet federal UST regulatory
requirements for underground pressurized piping systems. AIM
systems are optional, and state UST implementing agency
requirements may be different.
This is a companion document to these EPA publications:
•	Owner And Operator Introduction: Automated Interstitial
Monitoring Systems for Underground Pressurized Piping
on Emergency Power Generator UST systems. and
•	Requirements for Emergency Power Generator UST
Systems.

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Background
A wide variety of automatic line leak detectors, both electronic and
mechanical, are commercially available for most regulated UST
systems. They help meet the federal release detection requirement
for underground pressurized piping. Manufacturers, third-party
release detection equipment, and method evaluators have
categorically verified the circumstances under which these devices
are capable of meeting performance standards in the federal UST
regulation. Manufacturers and evaluators followed EPA's release
detection methods evaluation test procedures to verify performance
criteria.
The federal UST regulation relies on performance-based standards
for release detection equipment performance criteria to protect
human health and the environment. Owners and operators may use
non-traditional release detection methods or combinations of
methods to meet regulatory requirements, including to detect
releases from pressurized piping.
Regarding pressurized piping release detection, EPA specifically
stated in the preamble to the original 1988 federal UST regulation
(Federal Register Vol. 53, No 185, September, 23,1988, p. 37153):
"The Agency notes that one release detection method can
be used as the sole method if it can meet both the hourly
release detection requirement and the annual or monthly
release detection requirement. For example, double-walled
piping with interstitial monitoring that meets the
performance standard continues to be an acceptable option
for pressurized piping and would not require shutoffs,
restrictors, or tightness tests. The system must be equipped,
however, with an alarm that will indicate when a release
into the interstitial space has begun. "
In the preamble language above, the concept of continuous
interstitial monitoring, referenced herein, is described as an
automated interstitial monitoring system. ForEPG UST systems,
an AIM system can meet equivalent requirements for catastrophic
line leak detection (3 gallons per hour [gph] at 10 pounds per
square inch [psi] line pressure within 1 hour) and monthly
monitoring (0.2 gph) for pressurized piping systems.
While AIM systems may be technically feasible for use with
conventional UST systems such as at gasoline service stations,
EPA's recognition for use of these systems is recommended only
forEPGUST systems. In many jurisdictions, conventional UST
systems must meet fire code requirements that require installation
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of a listed (as defined below) leak detection device on the
discharge side of the pump at facilities that dispense motor fuel.
Thus, interstitial monitoring-based AIM systems cannot be used;
EPA does not recommend they be used as an alternative means of
meeting pressurized piping release detection when fire code
requirements must be met. Depending upon the jurisdiction, either
Chapter 23 (Motor Fuel-Dispensing Facilities and Repair Garages)
of the International Fire Code (IFC) or NFPA 3 OA, Code of Motor
Fuel Dispensing Facilities and Repair Garages, which is
published by the National Fire Protection Association, will be
applicable. Both codes cover motor fuel-dispensing facilities that
dispense liquid and gaseous motor fuels into fuel tanks of
automotive vehicles and marine craft.
IFC Section 2306.7.7.1 Leak detection
Where remote pumps are used to supply fuel dispensers,
each pump shall have installed, on the discharge side, a
listed detection device that will detect a leak in the piping
and provide an indication. A leak detection device is not
required if the piping from the pump discharge to under the
dispenser is above ground and visible.
NFPA 30A Section 5.4.4 Leak Detection.
On remote pressure pumping systems, each pump shall
have installed, on the discharge side, a listed leak detection
device that will provide an audible indication, a visible
indication, or will restrict or shut off the flow of product if
the piping and dispensing devices are not liquid-tight
IFC defines the term listed as equipment, materials, products or
services included in a list published by an organization acceptable
to the fire code official and concerned with the evaluation of
products or services that maintains periodic inspection of
production of listed equipment, materials or periodic evaluation of
services and whose listing states either that the equipment,
material, product or service meets identified standards or has been
tested and found suitable for a specified purpose.
NFPA defines the term listed as equipment, materials, or services
included in a list published by an organization that is acceptable to
the authority having jurisdiction and concerned with the evaluation
of products or services, that maintains periodic inspection of
production of listed equipment or materials or periodic evaluation
of services, and whose listing states that either the equipment,
material, or service meets appropriate designated standards or has
been tested and found suitable for a specified purpose.
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Section 1: Regulatory Allowance for AIM
Systems and Overview of Meeting the Dual
Release Detection Requirements
Note: To comply with Energy
Policy Act of2005
requirements, most state
USTimplementing agencies
established compliance
dates for their secondary
containment and interstitial
monitoring requirements
that pre date the federal
compliance date.
General Discussion about Using AIM Systems on
Pressurized Piping Systems
The federal UST regulation requires that UST system owners and
operators with underground pressurized piping equip their systems
with an automatic line leak detector that will alert the owner or
operator to the presence of a leak. The alert either restricts or shuts
off the flow of regulated substances through piping or triggers an
audible or visual alarm. In addition to the automatic line leak
detector, UST system owners and operators must have a second
release detection method by meeting one of these two
requirements, as applicable:
•	Pressurized piping installed on or before April 11, 2016,
must have an annual line tightness test conducted according
to 40 CFR § 280.44(b) or have monthly monitoring
conducted according to 40 CFR § 280.44(c).
•	Pressurized piping installed or replaced after April 11,
2016, must use monthly interstitial monitoring according to
40 CFR § 280.43(g).
This document uses the terms monthly or month and annually or
annual. These terms in the context of federal release detection
requirements mean at least once every 30 days and not to exceed
365 days, respectively.
For all pressurized piping systems associated with EPG UST
systems, regardless of the installation date of the piping system,
EPA recognizes the use of an AIM system, as described in this
document, as an option to meet both release detection requirements
for pressurized piping systems.
AIM systems are continuous interstitial monitoring systems
comprising multiple parts that rely on detection of breaches to the
interstice from the primary or secondary walls in category 1 or 2
systems. Category 3 systems rely on the detection of breeches from
the primary to the interstice. These qualitative release detection
methods are not expressed as pass or fail, which indicates a tight or
not-tight condition, respectively.

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Achieving the volume aspects of the federal UST release detection
requirements by category 1, 2, and 3 AIM systems is relatively
straightforward. These volume aspects are the 0.2 gph leak rate for
the monthly monitoring requirement and 3 gph at 10 psi line
pressure equivalent for the automatic line leak detector (ALLD)
performance standard. In addition, meeting the frequency
requirement of once per 30-days monitoring frequency associated
with the 0.2 gph leak standard is also relatively straightforward to
achieve for each category of AIM system. Each category of AIM
system is a continuous monitoring method. Continuous monitoring
of both the inner and outer walls by pressure, vacuum, or liquid-
filled piping interstitial spaces, performed by category 1 and 2
systems, respectively, and continuous monitoring for potential
breaches from the primary wall for category 3 systems, exceeds the
once per 30-day monitoring frequency. EPA also recognizes AIM
systems designed, installed, and tested as described in this
document as meeting federal UST regulatory probabilities of
detection and false alarm requirements for the ALLD performance
standard.
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Section 2: Description of AIM Systems
This section describes key features and use of AIM systems to
meet release detection requirements for pressurized piping on EPG
UST systems.
General Description
AIM systems are secondary containment systems that include
piping and all connected containment sumps, e.g., submersible
turbine pump, transition, collection, and detection containment
sumps. The piping and connected sumps have been specifically
designed and constaicted by the system manufacturer or installer
in accordance with a code of practice Underwriters' Laboratories
(UL) or other nationally recognized association) for containment
purposes and are compatible with fuels stored in the EPG UST
system.
The AIM system must meet the dual release detection
requirements, meaning the combined performance standards
required by:
•	40 CFR § 280.41 (b)( 1 )(i)(A) & 280.44(a) for an ALLD: 3
gph at 10 psi line pressure within 1 hour.
•	40 CFR § 280.43(g)(1) (in accordance with 280.44(c)) for
monthly, that is, every 30 days, interstitial monitoring for
double-walled piping.
The AIM system must be designed, constructed, and installed to
detect a leak from any portion of the piping that routinely
contains product. The sampling or testing method used in the
AIM system must be able to detect a leak through the inner wall in
any portion of the piping that routinely contains product.
Interstitial communication is a crucial part of an AIM system
because the federal UST regulation requires that the sampling or
testing method be able to detect a leak through the inner wall in
any portion of the piping that routinely contains product.
Interstitial communication relies on the integrity of the secondary
wall of an AIM system to ensure product leaked from an inner wall
breach is detected by the sampling or testing method. The
interstice is a critical component of the sampling or testing method.
The AIM system must provide facility notification in the event of a
suspected release at a minimum equivalent to the 3 gph at 10 psi
within a one-hour performance standard for in-line piping release
detection. The piping interstitial space is monitored continuously,
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and audible or visual alarms notify owners and operators of leaks.
UST system owners and operators must respond by taking
appropriate action according to requirements at 40 CFR Subpart
E—Release Reporting, Investigation, and Confirmation. For
purposes of AIM systems, EPA defines continuously monitored
and monitored on a continual basis as a method controlled by an
electronic or automated mechanism that performs leak detection on
an uninterrupted basis and provides an alarm within one hour of
the beginning of the leak. The method must communicate an alarm
condition to a specific individual or individuals, such as a
designated Class A, B, and C operator or petroleum or power
services contractor.
List of Key Components of AIM Systems
•	Double-walled piping with full interstitial communication
>	Piping that is a secondarily contained system. It is a
pipe within a pipe, or pipe encased in an outer
covering with an interstitial space between the outer
and inner piping walls. All components must be
compatible with the product stored.
•	Monitoring points: pressure, vacuum, or liquid reservoirs
(category 1 and 2 systems) or containment sumps
(primarily category 3 systems)
P Dedicated areas used to monitor piping for loss of
product or change in condition of pressure, vacuum,
or liquid level.
•	Sensors
P Pressure sensors or liquid-detecting sensors
(category 1 or category 2 systems, respectively)
S Sensors designed to respond to changes in
pressure (vacuum) or changes in liquid-
level within monitoring reservoir.
>	Liquid-detecting sensors (category 3 systems) using
various operating principles such as float-based,
optical, and hydrocarbon polymer sensitive.
•	Leak detection monitoring console with alarm system
(audible or visual)
sP* An automatic tank gauging system or other system
controller (i.e., console) that works in conjunction
with the pressure, vacuum, or liquid reservoirs, or
liquid-detecting sensors to determine potential
product loss from the AIM system. They contain an
audible or visual alarm component that is
configured to relay an alarm condition to an
appropriate alarm. The alarm condition must be
conveyed to the attention of specific individuals
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such as a designated Class A, B, or C operator or
petroleum or power services contractor within one
hour of the suspected release.
Note: Category 1 and 2
systems also will use
containment sumps and
liquid detecting sensors to
meet the piping interstitial
monitoring requirement
associated with secondary
containment areas. Unless
all piping components
within a sump are double
walled or otherwise
secondarily contained, the
underlying sump is the
secondary containment and
must be monitored for
releases. This is typically
accomplished using a liquid
detecting sensor.
The Three Categories of AIM Systems
There are three categories of AIM systems: category 1, category 2,
and category 3. An audible or visual alarm notifies a breach in any
of these systems.
•	Category 1 is a pressure or vacuum system that monitors
changes in pressure or vacuum levels within the interstice.
This system continually monitors the integrity of both the
inner and outer walls of double-walled piping.
•	Category 2 is a liquid-filled system that monitors changes
in the level of a liquid, such as brine or propylene glycol
solutions, within the reservoir holding the interstitial liquid
This system also continually monitors the integrity of both
the inner and outer walls of double-walled piping.
•	Category 3 is a dry interstice system. This system uses
float-based or other type sensors, typically located in
containment sumps to monitor dry interstitial spaces, that
are used for piping interstitial monitoring. Category 3 AIM
systems use liquid-detecting sensors to monitor for leaks
through the inner wall. A breach of product through the
primary wall is conveyed through the interstice to the
containment sump where it contacts the sensor.
Properly installed categories 1 and 2 AIM systems, with tight
secondary containment, can detect breaches at the 3 gph at 10 psi
performance standard and be set to automatically trigger an audible
or visual alarm well within the required period of 1 hour. For
category 3 systems to meet all aspects of this performance
standard, there are limitations to the distance between sensor
placement that are based on pipe type, the interstitial pipe volume,
uniform sloping, and pump pressure.
Categories 1, 2, and 3 AIM systems comprise the same
components, except that category 1 and 2 systems contain a
pressure or vacuum monitor, or liquid monitoring reservoir,
respectively, located at various places in the piping run. These two
categories of AIM systems also include containment sumps or
transition sumps at the end points or connection points for double-
walled piping; but monitoring pressure, vacuum, or liquid levels is
performed at the monitoring reservoir.
Category 3 systems do not contain a monitoring reservoir but
instead contain a single containment sump or multiple sumps used
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Note: Piping monitoring in
category 1 and 2 systems is
limited to the double walled
piping of the system. Unless
all piping components that
routinely contain product are
monitored by vacuum,
pressure, or liquid, as
applicable, by the monitoring
reservoir, the single walled
piping components that are
typically contained in the
containment sumps must also
meet aU monitoring
requirements. For more
information, see
Vmwwn page 10.
as monitoring areas by liquid-detecting sensors for breaches from
the inner wall. See Section 3 "Addressing the Key Concern with
Category 3 Systems.' for more details about EPA's concern with
category 3 systems meeting regulatory requirements.
Design Considerations for AIM Systems
Double-Walled Piping Construction
The piping must be double walled and meet federal secondary
containment requirements. For example, UL 971 -listed piping
meets this requirement. Piping installed within polyvinyl chloride
(PVC) pipe or within an access pipe or chase pipe does not meet
these requirements unless both the inner and outer walls are
evaluated and listed under UL 971. All components must be
compatible with the product stored.
Chase piping that was not manufactured or intended to be used as
secondary containment (for example, non-compatible corrugated
chase piping and PVC pipe) does not meet this requirement.
The piping and secondary containment system must be installed
according to an applicable nationally recognized code of practice,
such as Petroleum Equipment Institute or American Petroleum
Institute's recommended practices and manufacturer instructions.
Piping Integrity
For each category of AIM systems, the integrity of secondary
containment is critical for the system to work. The piping and a
small portion of the containment sump(s) are the line leak detector.
If there is no integrity, category 1 and 2 systems will almost
immediately identify loss of integrity.
Piping Communication
The interstice of the double-walled piping must be unobstructed
and:
•	allow pressure, vacuum, or liquid for category 1 and 2 systems
to reach each monitoring point; or
•	product for category 3 systems must flow unimpeded to each
moni toring point so notification of a suspected release can
occur within one hour.
Pressure, vacuum, liquid, or product must be demonstrated to flow
unimpeded during the testing of the piping integrity by air pressure
testing the secondaiy containment with a pressure gauge located at
the opposite end from where pressure is introduced.

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Piping Slope and Length
For category 3 systems, the slope of the pipe should not include
low points that allow product to pool and delay detection. For
double-walled piping of inconsistent slopes, significant changes of
direction, or for relatively long lengths, intermediate containment
sumps along the length of the piping may be necessary to detect
suspected releases within one hour. Additional evaluation and
verification may be required to assure the performance standard is
met in the above situations. Note that the interstice of double-
walled piping should be left open within each monitored
containment sump and not use jumper tubes to connect one piping
interstice to another to ensure the most efficient means of
interstitial communication. See the Monitoring Points section
below for a note regarding the use of containment sumps that are
considered part of piping secondary containment and may need to
be installed to meet piping interstice integrity testing requirements.
For all three categories, additional verification by the equipment
manufacturer, installer, or licensed professional engineer (PE)
might be required for use on AIM systems that are installed
through multiple story structures where an underground segment
cannot be isolated.
Monitoring Points
For category 1 and 2 systems, maintain reservoirs to monitor
pressure, vacuum, or liquid levels according to the manufacturer's
written instructions.
For all categories of AIM systems, maintain containment sumps
used as piping interstitial monitoring points and confirm they are
tight.
Regarding where containment sumps are typically used and must
be monitored as part of the federal piping interstitial monitoring
requirement:
• To meet the secondary containment requirement for piping,
all underground piping components must have secondary
containment. All piping components must be double-walled
or otherwise secondarily contained. This includes piping
tees, flex connectors, and other piping components that
connect the storage tank to the day tank or emergency
generator. Containment sumps are considered part of the
secondary containment system for single-wall piping or
piping components. These sumps are typically installed at
the end of piping runs. The double-walled piping interstice
is open within these sumps and in the event of inner wall
failure, product collects in the sump and may be monitored
by using a liquid-detecting sensor. Transition sumps are
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typically installed on piping runs transitioning between
underground and aboveground. All underground piping
installed within these transition sumps are considered
below ground or underground and are subject to the
secondary containment requirement. These transition
sumps serve as secondary containment for piping tees, flex
connectors, and other piping components that are typically
single walled. Therefore, these sumps must be monitored as
part of the piping interstitial monitoring requirement.
• To meet piping interstice integrity testing requirements,
both ends of the piping run must be accessible to perform a
test. Again, a containment sump is typically used at both
ends of double-walled piping runs. When installed, these
containment sumps become part of secondary containment
for the piping and, therefore, must be monitored as part of
the piping interstitial monitoring requirement.
Liquid-Detecting Sensors
Liquid-detecting sensors must be able to detect a liquid. They must
also alert the operator of a suspected release in conjunction with a
leak detection monitoring console. Liquid-detecting sensors should
be third-party certified to detect the targeted liquids. Some UST
implementing agencies require sensors and other release detection
equipment to be listed by the National Work Group on Leak
Detection Evaluations (NWGLDE).
Liquid-detecting sensors must be installed at the lowest point
within the containment sump, preferably in contact with the bottom
of the sump, unless prohibited by the manufacturer's instructions
or UST implementing agency requirements. This allows for the
earliest detection of any liquid in the sump.
Sensors must be included in all low-point sumps, including STP,
transition, or collection and detection containment areas.
The sensor should be tested for the type of liquid it is targeting.
Leak Detection Monitoring Console
Leak detection monitoring consoles, in conjunction with the
pressure, vacuum, or liquid reservoirs in category 1 and 2 systems,
or liquid-detecting sensors in category 3 systems, must be able to
alert specific individuals, such as a designated Class A, B, or C
operator or petroleum or power services contractor, to any
suspected release within one hour of a leak occurring. The system
must be set up to properly connect to cell phones or other relay
systems, as applicable, to alert specific individuals within one hour
of the occurrence of a leak.
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Alarm Systems
Automatic tank gauging systems and other systems controllers
containing audible or visual alarm components or that can be
configured to relay an alarm condition to an appropriate alarm may
be used at EPG UST systems. Many EPG I,\ST systems contain a
panel of sophisticated alarms in a control room that is not usually
associated with typical UST sites. Regardless of the type of alarm,
the alarm condition must be conveyed to the attention of specific
individuals, such as a designated Class A, B, or C operator or
petroleum or power services contractor, within one hour of the
suspected release incident. Conveying or notifying an alarm
condition applies to staffed and unstaffed locations.
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Section 3: Recognizing AIM System
Capability to Meet Regulatory
Requirements
The federal UST regulations establish the performance standard for
ALLDs to detect a leak of 3 gph at 10 psi line pressure within one
hour. This quantitative performance standard is stated for in-line
piping release detection methods that, by design, continuously
monitor the in-line piping fluid pressure. AIM systems
continuously monitor the piping secondary space for a leak from
the primary piping. AIM systems do not rely on direct indications
of fluid pressure or volume changes within the primary piping to
identify a potential leak. They also do not indicate quantitative
results as primary piping release detection methods do.
Category 1 and 2 AIM Systems
Category 1 and 2 systems' capability to meet the 3 gph at 10 psi
standard within one hour relies on the interstitial space having
integrity. EPA used the industry standard for secondary
containment piping integrity testing as a means of determining
whether these AIM system categories can meet the ALLD
performance standard. If tightness testing of secondary piping can
detect an air leak equivalent to a 3 gph at 10 psi fluid leak, then
equivalency of these AIM systems to the performance standard is
verified.
Petroleum Equipment Institute's (PEI) RP 1200, Recommended
Practices for the Testing and Verification of Spill Overfill, Leak
Detection and Secondary Containment Equipment at UST
Facilities. provides a procedure for piping secondary containment
integrity testing. This test procedure requires bringing the piping
interstitial space to a test pressure of 5 psi and observing for one
hour. The criteria for this test to meet and yield a passing result is
no loss in pressure during the duration of the one-hour test period.
EPA used an orifice, or hole, the size equivalent to a 3 gph at 10
psi fluid leak from a pressurized line to determine whether PEI RP
1200 can detect the air loss from this equivalent orifice size during
piping secondary containment integrity testing.
Theoretically, category 1 and 2 systems don't have an interstitial
volume limit. To determine whether PEI RP 1200 would detect an
equivalent orifice size leak of 3 gph at 10 psi line pressure in these
systems, EPA used a 750-gallon capacity interstitial air space for
this comparison. EPA reasoned that this capacity would address
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most EPG UST systems. Approximately 254 gallons of additional
air are needed to pressurize a 750 gal air space to 5 psi. Between
test pressures of 5 and 1 psi, the fl ow rate of air through the
equivalent 3 gph at 10 psi orifice is between approximately 851
gph (5 psi) and 425 gph (1 psi). As gauge pressure approaches 0
psi, the air leak rate through the orifice approaches 0 gph. With
only 254 gallons of additional air released during testing, an air
leak rate exceeding 425 gph in the pipe interstice would result in a
discernable drop in gauge pressure well within the standard one-
hour period of the piping secondary containment integrity test
period.
Analyzing the capability of PEIRP 1200's piping interstitial
integrity testing to detect a breach equivalent to an orifice size leak
of 3 gph at 10 psi shows that category 1 and 2 AIM systems can
detect a leak equivalent to the 3 gph at 10 psi line pressure loss.
The above analysis represents the upper limit of 750 gallons piping
interstitial volume to be allowed for use on category 1 and 2
systems. Category 1 and 2 systems, by design, continuously
monitor pressures in the piping interstitial space. However, Tables
1 and 2 identify several listings of equipment that have been third-
party evaluated. These equipment evaluations were not specifically
evaluated for use on or as AIM systems detailed in this document.
The equipment is potentially adaptable for use in category 1 and
category 2 AIM systems that could meet the design criteria for use
on EPG UST systems.
Category 1 and 2 systems are ideal systems to use. A potential
product loss is indicated by the system almost immediately
indicating a loss of pressure, vacuum, or liquid, as applicable, in
the interstice. The system alarm is triggered, and the facility can
quickly respond to this suspected release.
For more information on the analysis to determine the capability of
piping interstitial integrity testing to detect a breach equivalent to a
3 gph at 10 psi leak rate within one hour, see Appendix:
Comparison of Equivalent 3 sph Leaks -Formulas and Rationale.
Category 3 AIM Systems
Category 3 system's capability to meet the 3 gph at 10 psi standard
within one hour also relies on the interstitial space having integrity.
However, the operating principle of these systems presents a major
concern. This category of systems is designed for the secondary
containment to operate at atmospheric pressure. Based on using the
pump operating pressure to determine the equivalent volume of
fuel compared to 3 gph at 10 psi, the volume released in one hour
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is assumed to be that which will fill the pipe interstice and the
containment sump to the activation point of the liquid detecting
sensor. This makes the length of piping—that is, the total
interstitial volume of the double-walled piping—and distance to
sensors critical to category 3 systems in meeting the one-hour
response period. For category 3 systems, the length of piping and
placement of sumps containing the dry interstitial sensor, as
monitoring point, is dictated by the submersible pump operating
pressure used by the EPG UST system and the calculated fuel leak
rate through an equivalent 3 gph at 10 psi orifice.
The key concern with category 3 AIM systems to meet the ALLD
performance standard is ensuring that a leak equivalent of 3 gph at
10 psi line pressure is detected by this passive piping interstitial
monitoring system within 1 hour of occurrence of that size leak.
The worst-case scenario is detecting a breach in the primary wall
occurring at the furthest point from the sensor. This product leak
must be communicated or conveyed by the secondary wall and
detected by the sensor.
Addressing the Key Concern with Category 3 Systems
When using a category 3 system, it is considerably more difficult
to achieve and harder to verify within the period of 1-hour that a
leak through the inner wall in any portion of the piping that
routinely contains product has occurred. Category 3 systems
monitor dry interstitial spaces using a liquid-point or other type of
passive sensor to ensure that a leak through the inner wall is
detected. This operating principle vulnerability of category 3
systems increases the likelihood to miss potential product releases
within the required one-hour period. Category 3 systems may
appear to be functioning appropriately, despite product actively
escaping through a breach in the secondary wall. The release
detection system may not detect these product leaks in the time
frame required by the regulations. The release detection system
may never indicate a suspected release because product may never
reach the sensor. This inherent limitation with category 3 systems
must be addressed to ensure they can detect potential product
releases within the one-hour criteria for the ALLD performance
standard to indicate whether there is a suspected release of product.
Category 3 systems are characteristically vulnerable to missing
released product, and effective use of these systems is challenged
by the low product throughput and infrequently used nature of
EPG UST systems. These systems are typically only cycled
monthly or weekly for system testing.
As a result, distances between containment sumps containing
sensors used for dry interstitial monitoring of piping in category 3
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systems are notably shorter than distances allowed between
monitoring reservoirs for category 1 and 2 systems. For category I
and 2 systems, monitoring reservoirs are typically placed as far
apart as at the end points of piping runs when monitoring by
pressure or vacuum, or liquid-filled interstices using category 1
and 2 systems, respectively. In comparison, category 3 systems
typically rely upon sloped piping. Piping slope is not a requirement
for these systems but because of gravity, should speed the transport
of product leaks from the primary wall toward the sensor. See
Section 5: Example of Basic Category 3 System for more
information.
16

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Section 4: Examples of Category 1 and 2
Systems
NWGLDE Listed Potentially Adaptable Systems
Tables 1 and 2 provide information presented on the NWGLDE
website. There are several listings of equipment that have been
third-party evaluated. These equipment evaluations are not specific
for use on or as AIM systems detailed in this document. The
equipment is potentially adaptable for use in category 1 and
category 2 AIM systems designed for EPG UST systems.
Owners and operators who want to use these systems need to
evaluate their EPG UST sites based on the capabilities of the
individual system and how the listed equipment operates to
determine whether that system is acceptabl e for use. Some of the
vacuum methods listed, for example, rely on the turbine pump to
continuously maintain a partial vacuum within the interstitial space
of the double-walled piping. Given the infrequency of pump
runtime for EPG UST systems, for example, an alternative vacuum
generating source may be necessary to allow proper equipment
function. The methods may require further evaluation regarding
applicability to meet design criteria and potential system
limitations described in this document.
The equipment listed in Table 1 applies to category 1 systems;
equipment listed in Table 2 applies to category 2 systems.
Reference NWGLDE's website for current information.
17

-------
Table 1 - NWGLDE Listings for Continuous Interstitial Line
Monitoring Method (Pressure/Vacuum)
Table 1
Vendor
Equipment
Name
(Release Detection Capability)
Operating Principle/Max Pipeline
Length
Link to NWGLDE
Listing
Core
Engineered
Solutions
Safesite Vacuum
Interstitial
Monitoring
System
0.1 gph / 95.0% probability of detection (PD) /
<5.0% probability of false alarm (PFA). System
uses a vacuum generated by a vacuum pump or
submersible pump to continuously maintain a
partial vacuum of 7.5 pounds per square inch in
gauge (psig), equivalent to 207.6-inch water
column for 60 minutes and maintain vacuum for
30 seconds prior to testing. System is designed to
activate a visual and acoustic alarm, and optional
submersible pump shutdown before stored
product can escape to the enviromnent. System
was evaluated for detecting breaches within the
interstitial space of Ys inch or greater of a double-
walled tank or double-walled piping. The volume
of monitored interstitial space must not exceed
270 gallons or 5,690 feet of piping.
httt>://nwglde.org/evals/c
ore engineered a. html
SGB
(Sicherungsge
ratebau
GmbH)
Overpressure
Leak Detection
System Model
DLR-G
Not determined / System uses pressurized
nitrogen gas to continuously maintain an
overpressure within the interstitial space of
double-walled piping. System is designed to
activate a visual and acoustic alarm before stored
product can escape to the enviromnent. System is
capable of detecting breaches in both the inner
and outer walls of double-walled piping (Method
not limited by pipe length.)
httt>://nwglde.org/evals/s
gb a. html
Veeder-Root
Secondary
Contaimnent Leak
Detection (SCLD)
TLS-450Plus and
TLS-
3 50/ProMax/EM
C Console with
Vacuum Sensors
857280-100, 200,
30x, or Assembly
332175-001
Not Determined / System uses vacuum generated
by the turbine pump to continuously maintain a
partial vacuum within the interstitial space of
double-walled tanks and double-walled piping.
System is designed to activate a visual and
acoustic alarm, and optional turbine pump
shutdown before stored product can escape to the
enviromnent. System is capable of detecting
breaches in both the inner and outer walls of
double-walled tanks and double-walled piping. /
(Method not limited by pipe length)
http://nwglde.Org/evals/v
eeder root zu.html
18

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Table 2 - NWGLDE Listings for Continuous Interstitial Monitoring
Method (Liquid Filled)
Table 2
Vendor
Equipment
Name
(Release Detection Capability)
Operating Principle/Max Pipeline
Length
NWGLDE Web
Listing
Ameron
International
Dualoy 3000/LCX
and MCX Pipe
Monitoring System
Liquid Filled
Interstitial Space
An applicable liquid is used to fill the Ameron
Dualoy 3000/LCX and MCX fiberglass double-
wall pipe interstice.
A reservoir at the high point of the system
contains a dual-point level sensor that will alarm
if the liquid level is too high or too low. / 344 feet
htft>://nwglde.org/evals/a
meron a.html

Dualoy 3000/LCX
and MCX Pipe
Monitoring System
Liquid Filled
Pressurized
Interstitial Space
An applicable liquid is used to fill the Ameron
Dualoy 3000/LCX and MCX fiberglass double-
wall pipe interstice, which is pressurized using an
air compressor or gas bottle.
A reservoir contains a dual-point level sensor that
will alarm if the liquid level is too high or too
low. / 344 feet
htft>://nwglde.org/evals/a
meron b.html
Western
Fiberglass,
Inc.
Co-Flow Hydraulic
Interstitial
Monitoring System
Propylene glycol is used to fill the Western
Fiberglass, Inc., double-walled/coaxial flexible
pipeline interstice.
Two reservoirs are used to contain the liquid, one
at each end of the system. / 200 feet
http://nwglde.org/evals/
western fiberglass a.ht
M

Co-Flow Hydraulic
Interstitial
Monitoring System
Propylene Glycol
Filled Pressurized
Interstitial Space
Propylene glycol is used to fill the Western
Fiberglass, Inc., double-walled/coaxial flexible
pipe interstice.
A pressurized cylinder is used to maintain
pressure in the reservoir. / 200 feet
htft>://nwglde.org/evals/
western fiberglass b.ht
M

Liquid-Filled
Reservoir for
Double-Wall Sumps
with Liquid Sensor
Models WF-3 and
WF-750
Propylene glycol is used to fill the Western
Fiberglass double-walled sump or under
dispenser contaimnent sump interstice. / Not
applicable.
htft>://nwglde.org/evals/
western fiberglass c.ht
M
19

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Category 1 Systems: Continuous Monitoring using
Pressure or Vacuum-Based Methods
Example 1.1 (Pressure)
Example 1.2 (Vacuum)
20

-------
Category 2 Systems: Continuous Monitoring using
Liquid-Filled Piping Interstice Methods
Example 2.1 (Liquid-Filled)
21

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Section 5: Example of a Basic Category 3
System
When using category 3 AIM
systems, do not exceed
distances for maximum
piping length (in feet)
Between Sensors noted on
either Table 3 or 4, as
applicable. Under conditions
identified below, the
distances noted in Tables 3
and 4 represent the
maximum extent of sensor
placements that ensure a
potential product release
from the primary wall can be
identified to meet the
catastrophic, 3 gph at 10 psi
within one hour regulatory
performance standard
associated with ALLDs.
Depending on factors such as
the size of the sump, sensor
threshold placement, and
sensor type, maximum piping
lengths shown on the tables
may not be achieved.
Suggested system
improvements are provided
below to assist in enhancing
systems to achieve noted
maximum piping lengths.
Category 3 Systems: Liquid-Detecting Sensor in
Containment Sump Monitoring Interstice of Double-
Walled Pipe
Example 3.1 (Liquid Detecting Sensors-Sump Monitoring to
Sensor Activation Point)
A basic category 3 AIM system design depicted below highlights
two key system components of this standard design: double-walled
piping, that is, total interstitial volume of the double-walled piping,
and the sumps being monitored by diy interstitial sensors. The one-
hour period for alarm system notification involves the combination
of the time it takes for product leaked into the piping interstice
from a breach in the primary wall to flow through the piping
interstice and accumulate within the sump to where it acti vates the
sensor at the sensor threshold.
Table 3 and Table 4 show maximum lengths of double-walled
piping that can be used in category 3 AIM systems, under
conditions identified below. Table 3 provides examples of
commercially available pipe with their corresponding interstitial
volumes. Table 4 provides general reference standards based on set
interstitial volumes of double-walled piping.
Piping types indicated in this document are not a complete list of
pipe and pipe manufacturers that may be available on the market.
Following design criteria specified in this document, other piping
may be used on AIM systems.
The federal UST regulatory performance standard that ALLDs
must achieve is marked on each table in yellow highlight. This
22

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standard is associated at a pump pressure of 10 psi. Determine the
operating pressure of the pump on the EPG UST system or planned
purchase of a suitable pump and use the information on the pump
pressure posted by the manufacturer to determine maximum piping
lengths—that is, interstitial volume—allowed between sensor
placements, for category 3 systems. Interstitial volumes vary
among manufacturers' products and manufacturers. Generally, the
smaller the interstitial volume of the piping, which facilitates faster
communication and transport of product, the farther apart sensors
may be placed
Conditions
•	The EPG UST system is operating under normal
conditions: either during routine system test periods of a
minimum one-hour duration or when in use for its designed
purpose of supplying power.
Rationale And Assumptions
•	Assumption warranted with the understanding that if the
pipe secondary containment is tight, per PEI RP 1200
standard or equivalent, any loss of fuel from the primary
wall will appropriately make its way to the low-point
collection area, such as the sump. The time to fill the
interstice to 100 percent capacity should decrease with
adequate pipe slope, based on site conditions. Piping must
be installed according to industry codes and the
manufacturer's specifications.
•	The product volume in piping interstice and quantity
necessary to accumulate in sump to trigger the sensor
equals the total volume equivalent of the 3 gph at 10 psi
line pressure loss to meet monitoring system notification
within one hour.
•	Ensure sensor threshold is reached. Sensor response times
are assumed to begin at a level of 1 inch of liquid
accumulation in the sump. This level may vary
significantly based on sensor placement and sensor design
specifications.
o Assumption is warranted given the typical product
throughput and sizes of these systems are relatively
small in scope compared to typical UST facilities.
•	Containment sumps have a diameter of 36 inches or less,
based on sensor activation threshold at 1 inch. All piping
routinely containing product, including single-wall
components within the sump, must meet the ALLD
requirement. Coverage to point of sensor activation is
23

-------
required. Maximum sump diameter will vary based on
sensor activation threshold.
Step-By-Step Design of a Basic Category 3 AIM System
Step 1: Determine operating pressure, or psi, of the pressurized
piping. This is the pressure in the line with full fuel flow through
the day tank or with a generator running during normal operation
status.
Example: Operating pressure of piping is 25 psi.
Step 2: Reference Table 3 to determine the equivalent 3 gph at 10
psi leak rate based on the piping operating pressure determined in
Step 1.
Example: From Table 3, the Equivalent Leak Rate Volume
at a line pressure of 25 psi for the piping segment is 4.7
gph.
Step 3: Determine the surface area of the largest containment
sump or collection point in inches squared by using the applicable
formula below.
Circle
Rectangle
Square
Area of Circle
A = surface area (in2)
7i = pi (3.141592653)
r = radius of circle (in)
Area of Rectangle
A = surface area (in2)
1 = length (in)
w = width (in)
Area of Square
A = surface area (in2)
s = length of side (in)
Example: The surface area of a 3-foot circular sump is
determined by using the formula A 7cr2; A = 3.14 (x) (18
inches)2. The surface area of the sump is 1,017 in2.
Step 4: Determine the activation point of the sensor in inches, such
as Vi inch, Vi inch, 3A inch, and 1 inch. This is the sensor threshold.
Use the manufacturer's stated threshold if the sensor is installed at
24

-------
the lowest point of the sump. If the sensor is raised from the lowest
point, then add the level that the sensor is raised to the
manufacturer's stated threshold.
Example: The sensor is raised from the manufacturer's
stated threshold to 1 inch (this is the sensor threshold).
Step 5: Multiply surface area (in2) by sensor threshold (in) to yield
cubic inches (in3).
Example: The surface area of the sump (1,017 in2) (x)
sensor threshold (1 in)equals 1,017 in3.
Step 6: Convert inches cubed (in3) to gallons by dividing by 231
in3/gallon to obtain the number of gallons required to reach the
activation point of the sensor within the containment sump.
Example: 1,017 in3 divided by 231 inVgallon equals 4.4
gallons.
Evaluate:
•	If the number of gallons calculated in Step 6 exceeds
the number of gallons referenced in Step 2, the
containment sump and or sensor threshold is too large.
This means there is no amount of piping that can be
attached to the sump. Modification and or correction is
required. See tips below.
•	If the number of gallons calculated in Step 6 is less than
the number of gallons referenced in Step 2, proceed to
Step 7.
Example: Since the number of gallons calculated in Step 6
is 4.4 gallons, which is less than 4.7 gallons referenced in
Step 2, proceed to Step 7.
Step 7: Subtract the number of gallons obtained in Step 6 from the
number of gallons referenced in Step 2. The result or difference is
the maximum number of gallons allowable for the double-walled
piping interstitial space.
Example: The difference between the number of gallons
referenced in Step 2 of 4.7 gallons minus the number of
gallons obtained in Step 6 of 4.4 gallons equals 0.3 gallons.
This is the maximum number of gallons allowed or that can
be contained in the interstitial space of the double-walled
piping and still meet the release detection requirement.
Step 8: Reference Table 4, to determine the volume in gallons per
foot for the piping interstitial space chosen. Select either a specific
25

-------
Note: Some sumps do not
have a flat bottom, and
there is a low point
collection area where the
sensor should be
positioned. This may
make it extremely
difficult to calculate but
could be experimentally
derived. The system
installer, for example,
could position the sensor
and then add measured
amounts of water until
the sensor is activated.
This value could then be
used in lieu of the
calculated volume
derived in Step 5 above,
needed to trigger the
sensor.
manufacturer's piping (e.g., APT or UPP) or base selection on the
interstitial volume of an unspecified pipe product with that
interstitial volume.
Example: If purchasing Ameron Dualoy 3000/L 2" piping,
use Table 4, which lists the interstitial volume of this
piping as 0.0133 gallons/foot.
Step 9: Divide the volume or gallons calculated in Step 7 by the
number of gallons per foot for the piping interstitial space
referenced in Step 8. The result is the maximum length of piping
allowed for the piping segment to meet the required 1-hour
detection time.
Example: Divide the volume calculated in Step 7 of 0.3
gallons by 0.0133 gallons per foot referenced in Step 8 for
the Ameron Dualoy 3000/L 2-inch piping selected. The
maximum length of piping allowed to meet the required 1-
hour detection time for this AIM system is 22.5 feet.
This means, for this example, installing Ameron Dualoy 3000/L 2-
inch piping with a length up to 22.5 feet between sensor
placements on a basic category 3 AIM system is sufficient since
piping pressure is 25 psi; surface area of sump is 1,017 in2; and
sensor threshold is 1 inch. In other words, installing a length of
Ameron Dualoy 3000/L 2" piping up to 22.5 feet between an STP
sump and transition sump with diameters that do not exceed 3 feet
is sufficient, since piping pressure is 25 psi and the sensor in each
sump is set to activate at their sensor thresholds of 1 inch.
Suggested System Improvements to Basic Category 3
Systems
•	Select a submersible pump with a higher operating
pressure. This increases the number of gallons applicable to
Step 2.
•	Select and install a sensor with a smaller activation
threshold or sensor threshold. This decreases the number of
gallons required to activate the sensor.
•	If the length of piping exceeds the calculated maximum
allowable pipe length calculated in Step 9, measure that
distance from the STP sump along the pipe. That is where
you install another collection point. Repeat the previous
steps based on this newly installed collection point,
working towards the generator. Determine the number of
26

-------
additional containment sumps needed and distribute
appropriately.
• Calculate and recalculate, as necessary and appropriate.
Modifying any of the variables that are part of the general
design stated above impacts the results.
An alternative design that involves using a concentrated collection
point that can be located inside the larger sump is discussed in
Section 6: Alternative System Configurations Used for Category 3
AIM Systems. The setup creates a sump within a sump that
separates monitoring of components within the sump from the
double-walled piping run into the sump. Using that design, the
calculations for pipe maximum allowable pipe length would then
be based on the surface area of the smaller collection point and will
increase the length of pipe, based on its interstitial volume, you
may install.
27

-------
Table 3 (Part 1) - Maximum Lengths of Double-Walled Piping for Category 3 AIM Systems (Examples of Commercially Available Pipe)
Leak Rate Equivalency to 3.0 gph at 10
psi

Example Commercially Available Pipe: Manufacturer and Product
Ameron
APT
Dualoy
3000/L 3 in.
Over 2 in.
Dualoy
3000/L 4
in. Over 3
in.
Dualoy
3000/L 6
in. Over 4
in.
Dualoy
3000/L 2
in.
Dualoy
3000/L 3
in.
Dualoy
3000/L 4
in.
0.5 in.
Double
Wall
0.75 in.
Double
Wall
1.00 in.
Double
Wall
1.5 in.
Double
Wall
1.75 in.
Double
Wall
2 in.
Double
Wall
2.5 in.
Double
Wall
Interstitial Volume (gal/ft)
Line
Pressure
(psi)
3.0 gal/hr
Equivalent
Vol
(miymin)
Equivalent
Leak Rate
Vol (gph)
0.2186
0.2652
0.8398
0.0133
0.0196
0.0252
0.0031
0.0042
0.0119
0.0052
0.0182
0.0218
0.0104
Maximum Piping Length (ft) Between Sensors
10
189
3.0

13.7
11.3
3.6
225.3
152.9
118.9
966.5
713.3
251.8
576.2
164.6
137.4
288.1
15
232
3.7

16.8
13.9
4.4
276.5
187.6
145.9
1186.3
875.6
309.0
707.2
202.1
168.7
353.6
18
254
4.0
18.4
15.2
4.8
302.7
205.4
159.8
1298.8
958.7
338.4
774.3
221.2
184.7
387.2
19
261
4.1
18.9
15.6
4.9
311.1
211.1
164.2
1334.6
985.1
347.7
795.7
227.3
189.8
397.8
20
268
4.2
19.4
16.0
5.1
319.4
216.8
168.6
1370.4
1011.5
357.0
817.0
233.4
194.9
408.5
21
274
4.3
19.9
16.4
5.2
326.6
221.6
172.4
1401.1
1034.2
365.0
835.3
238.7
199.2
417.6
22
281
4.5
20.4
16.8
5.3
334.9
227.3
176.8
1436.9
1060.6
374.3
856.6
244.7
204.3
428.3
23
287
4.5
20.8
17.2
5.4
342.1
232.1
180.5
1467.6
1083.2
382.3
874.9
250.0
208.7
437.5
24
293
4.6
21.2
17.5
5.5
349.2
237.0
184.3
1498.3
1105.9
390.3
893.2
255.2
213.1
446.6
25
299
4.7
21.7
17.9
5.6
356.4
241.8
188.1
1529.0
1128.5
398.3
911.5
260.4
217.4
455.7
26
305
4.8
22.1
18.2
5.8
363.5
246.7
191.9
1559.6
1151.2
406.3
929.8
265.7
221.8
464.9
27
311
4.9
22.6
18.6
5.9
370.7
251.5
195.6
1590.3
1173.8
414.3
948.1
270.9
226.1
474.0
28
317
5.0
23.0
18.9
6.0
377.8
256.4
199.4
1621.0
1196.5
422.3
966.4
276.1
230.5
483.2
29
322
5.1
23.4
19.2
6.1
383.8
260.4
202.6
1646.6
1215.3
428.9
981.6
280.5
234.1
490.8
30
328
5.2
23.8
19.6
6.2
390.9
265.3
206.3
1677.2
1238.0
436.9
999.9
285.7
238.5
499.9
28

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Table 3 (Part 2) - Maximum Lengths of Double-Walled Piping for Category 3 AIM Systems (Examples of Commercially Available Pipe)
Leak Rate Equivalency to 3.0 gph at
10 psi

Example Commercially Available Pipe: Manufacturer and Product
Environ
NUPI
GeoFlex Piping
0.75 in. Dia.
(GFP-2075)
GeoFlex
Piping 1.0 in.
Dia. (GFP-
2100)
GeoFlex
Piping 1.5 in.
Dia. (GFP-
2150)
GeoFlex
Piping 2.0 in.
Dia. (GFP-
2200)
GeoFlex
Piping 3.0 in.
Dia. (GFP-
2300)
2 in. Over 1.5
in. Piping
(2.48 in. OD x
1.969 in. OD)
3 in. Over 2
in. Piping
(2.953 in. OD
x 2.480 in.
OD)
5 in. Over 3
in. Piping
(4.921 in. OD
x 3.543 in.
OD)
4 in. Over 2
in. Piping (4.3
in. OD x2.48
in. OD)
Interstitial Volume (
gal/ft)
Line
Pressure
(psi)
3.0 gph
Equivalent
Vol
(mL/min)
Equivalent
Leak Rate
Vol (gph)
0.0028
0.0039
0.0060
0.0060
0.0164
0.0546
0.0518
0.3299
0.4010
Maximum Piping Length (ft) Between Sensors
10
189
3.0

1070.0
768.2
499.3
499.3
182.7
54.9
57.8
9.1
7.5
15
232
3.7

1313.5
943.0
612.9
612.9
224.2
67.4
71.0
11.1
9.2
18
254
4.0
1438.0
1032.4
671.1
671.1
245.5
73.7
77.7
12.2
10.0
19
261
4.1
1477.6
1060.9
689.6
689.6
252.3
75.8
79.9
12.5
10.3
20
268
4.2
1517.3
1089.3
708.1
708.1
259.0
77.8
82.0
12.9
10.6
21
274
4.3
1551.2
1113.7
723.9
723.9
264.8
79.6
83.9
13.2
10.8
22
281
4.5
1590.9
1142.2
742.4
742.4
271.6
81.6
86.0
13.5
11.1
23
287
4.5
1624.8
1166.5
758.3
758.3
277.4
83.3
87.8
13.8
11.3
24
293
4.6
1658.8
1190.9
774.1
774.1
283.2
85.1
89.7
14.1
11.6
25
299
4.7
1692.8
1215.3
790.0
790.0
289.0
86.8
91.5
14.4
11.8
26
305
4.8
1726.7
1239.7
805.8
805.8
294.8
88.6
93.3
14.7
12.1
27
311
4.9
1760.7
1264.1
821.7
821.7
300.6
90.3
95.2
14.9
12.3
28
317
5.0
1794.7
1288.5
837.5
837.5
306.4
92.0
97.0
15.2
12.5
29
322
5.1
1823.0
1308.8
850.7
850.7
311.2
93.5
98.5
15.5
12.7
30
328
5.2
1857.0
1333.2
866.6
866.6
317.0
95.2
100.4
15.8
13.0
29

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Table 3 (Part 3) - Maximum Lengths of Double-Walled Piping for Category 3 AIM Systems (Examples of Commercially Available Pipe)
Leak Rate Equivalency to 3.0 gph at
10 psi
Line
Pressure
(psi)
3.0 gph
Equivalent
Vol
(mL/min)
Equivalent
Leak Rate
Vol (gph)
10
189
3.0
15
232
3.7
20
268
4.2
21
274
4.3
22
281
4.5
23
287
4.5
24
293
4.6
25
299
4.7
26
305
4.8
27
311
4.9
28
317
5.0
29
322
5.1
30
328
5.2
Example Commercia
My Available Pipe: Manufacturer and Product
Smith
Total Containment
UPP
Western
Fiberglass
3 in. Over
2 in.
4 in. Over
3 in.
6 in. Over
4 in.
OmniFlex
1.5 in.
OmniFlex
2.5 in.
63/75
Piping
90/160
Piping
CoFlex
1.5 in.
CoFlex
2 in.
Fiberglass
Fiberglass
Fiberglass
(CP1503)
(CP2503)
Piping
Piping
Interstitial Volume (gal/ft
)
0.2300
0.2760
0.8230
0.0052
0.0079
0.0762
0.9824
0.0077
0.0094
Maximum Piping Length (ft) Between Sensors
13.0
10.9
3.6
576.2
379.2
39.3
3.0
389.1
318.7
16.0
13.3
4.5
707.2
465.5
48.3
3.7
477.6
391.2
18.5
15.4
5.2
817.0
537.8
55.8
4.3
551.7
452.0
18.9
15.7
5.3
835.3
549.8
57.0
4.4
564.1
462.1
19.4
16.1
5.4
856.6
563.9
58.5
4.5
578.5
473.9
19.8
16.5
5.5
874.9
575.9
59.7
4.6
590.8
484.0
20.2
16.8
5.6
893.2
587.9
61.0
4.7
603.2
494.1
20.6
17.2
5.8
911.5
600.0
62.2
4.8
615.6
504.2
21.0
17.5
5.9
929.8
612.0
63.4
4.9
627.9
514.3
21.4
17.9
6.0
948.1
624.0
64.7
5.0
640.3
524.5
21.8
18.2
6.1
966.4
636.1
65.9
5.1
652.6
534.6
22.2
18.5
6.2
981.6
646.1
67.0
5.2
662.9
543.0
22.6
18.8
6.3
999.9
658.2
68.2
5.3
675.3
553.1
Interstitial volumes for Table 3, Parts 1-3 were obtained from Veeder-Root's Secondary Containment Volumes by Manufacturer
http://docs.veeder.com/gold/download.cfm7doc id=8533
30

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Table 4 - Maximum Lengths of Double-Walled Piping for Category 3 AIM Systems (General Reference Standards)
Leak Rate Equivalency to 3.0 gph at
10 psi
Line
Pressure
(psi)
3.0 gph
Equivalent
Volume
(mL/min)
Equivalent
Leak Rate
Volume
(gph)
10
189
3.0
15
232
3.7
16
239
3.8
17
247
3.9
18
254
4.0
19
261
4.1
20
268
4.2
21
274
4.3
22
281
4.5
23
287
4.5
24
293
4.6
25
299
4.7
26
305
4.8
27
311
4.9
28
317
5.0
29
322
5.1
30
328
5.2
General Reference Standards
Interstitial Volume (gal/ft)
0.0100
0.0200
0.0300
0.0400
0.0500
0.0600
0.0700
0.0800
0.0900
0.1000
0.2000
0.3000
Maximum Piping Length (ft) Between Sensors
299.6
149.8
99.9
74.9
59.9
49.9
42.8
37.5
33.3
30.0
15.0
10.0
367.8
183.9
122.6
91.9
73.6
61.3
52.5
46.0
40.9
36.8
18.4
12.3
378.9
189.4
126.3
94.7
75.8
63.1
54.1
47.4
42.1
37.9
18.9
12.6
391.5
195.8
130.5
97.9
78.3
65.3
55.9
48.9
43.5
39.2
19.6
13.1
402.6
201.3
134.2
100.7
80.5
67.1
57.5
50.3
44.7
40.3
20.1
13.4
413.7
206.9
137.9
103.4
82.7
69.0
59.1
51.7
46.0
41.4
20.7
13.8
424.8
212.4
141.6
106.2
85.0
70.8
60.7
53.1
47.2
42.5
21.2
14.2
434.3
217.2
144.8
108.6
86.9
72.4
62.0
54.3
48.3
43.4
21.7
14.5
445.4
222.7
148.5
111.4
89.1
74.2
63.6
55.7
49.5
44.5
22.3
14.8
455.0
227.5
151.7
113.7
91.0
75.8
65.0
56.9
50.6
45.5
22.7
15.2
464.5
232.2
154.8
116.1
92.9
77.4
66.4
58.1
51.6
46.4
23.2
15.5
474.0
237.0
158.0
118.5
94.8
79.0
67.7
59.2
52.7
47.4
23.7
15.8
483.5
241.7
161.2
120.9
96.7
80.6
69.1
60.4
53.7
48.3
24.2
16.1
493.0
246.5
164.3
123.2
98.6
82.2
70.4
61.6
54.8
49.3
24.6
16.4
502.5
251.3
167.5
125.6
100.5
83.8
71.8
62.8
55.8
50.3
25.1
16.8
510.4
255.2
170.1
127.6
102.1
85.1
72.9
63.8
56.7
51.0
25.5
17.0
519.9
260.0
173.3
130.0
104.0
86.7
74.3
65.0
57.8
52.0
26.0
17.3
31

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Section 6. Alternative System
Configurations Used for Category
3 AIM Systems
Note: Proper interstitial
space monitoring
requires at least two
sensors: one for the
larger containment sump
and one for the smaller
collection point installed
within it Keep in mind,
double walled piping
typically includes
collection points at both
ends but may only be
open at one end of the
lowest point of the
piping.
Calculate the maximum
length of allowable
piping based on the
collection point with the
largest surface area
where the pipe
interstitial space is open.
There are several variations of the basic AIM system design for
category 3 systems (Example 3.1), that use a liquid-detecting
sensor placed in the containment sump or sumps for monitoring the
interstice of double-walled pipe. Figures 6.2 below shows use of a
small containment vessel attached directly to the piping interstice
as a concentrated collection point instead of a larger containment
sump. It uses a smaller collection point that is installed within the
larger containment sump to concentrate the collection of fuel
flowing from the interstice of the double-walled piping.
Monitoring a Concentrated Collection Point
The one-hour period for alarm system notification in the category 3
system basic design discussed above involves the combination of
time it takes for product leaked into the piping interstice from a
breach in the primary wall to flow through the piping interstice and
accumulate within the sump to where it activates the sensor at the
sensor threshold. An alternative to this design involves using a
concentrated collection point that can be located inside the larger
sump.
This setup creates a sump within a sump that separates monitoring
of components within the sump from the double-walled piping run
into the sump. The calculations for pipe maximum allowable pipe
length will now be based on the surface area of the smaller
collection point and will increase the length of pipe, based on its
interstitial volume, you may install.
This example shows apparatus that provides for low-point sensor
placement and very minimal liquid to activate. (See Figure 6 1
below of apparatus during fabrication and Figure 6.2 installation
complete). This illustration depicts an oil burner system, not a
generator system, and is provided for illustrative purposes only.
•	Double-walled product pipe should have
consistent slope toward low point inside
building.
•	UL 971, for example double-walled piping,
converts to schedule 40 steel aboveground
32

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pipe. The interstice transitions continuously
inside larger black pipe sleeve and
terminates at the concentrated collection
point or detection containment vessel.
• Liquid sensor is positioned inside base of "j"
fabricated assembly to contain and detect
leaks from the primary pipe system
Figure 6.2. Another notable variation for the
design of a category 3 system involves a
liquid-detecting cable run within the length of
the piping interstice.
33

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Figure 6.3. TraceTek TT5000 Fuel Sensing cable.
Courtesy of Ravtech Group Systems.
13 mm (0.52 in)
Drawing not to scale
Cable construction
Figure 6.4. Schematic of cable. Courtesy of
Ravtech Group Systems.
Fluoropolymer braid
Red/white/black
Conductive polymer jacket
Continuity wire (red)
Spacer wire (white)
Signal wire (yellow)
Sensing wires (black)
Using Liquid-Detecting Cable Run within the Length of
the Piping Interstice
This example shows components that provide multiple liquid
contact points installed within secondary containment areas, for
example the containment sump, or a pipe chase surrounding
secondary piping. This equipment is available commercially and is
used in UST applications. This cable sensor is not reusable and
must be replaced once it contacts product.
34

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Section 7. O&M Testing and
Inspections Requirements at a
Glance
Type of AIM System,
Components, and Required
Actions
(As Applicable)
Required
Testing
Frequency
Regulatory
Citation
Comments
Categories 1 & 2 Systems
Monitoring console
^ Verify system configuration
S Test alarm
^ Test battery backup
Annual
280.40(a)(3)(i)
This can be an ATG or another controller
Sensors
^ Test alarm operability for
communication with controller
Annual
280.40(a)(3)(ii)
For all sensors, pressure/vacuum and liquid
detecting sensors
Sensors
^ Inspect for residual buildup
Annual
280.40(a)(3)(ii)
For liquid detecting sensors
ALLD
Test and inspect:
S DW piping
S Monitoring reservoir(s)
^ Containment sumps at end points
Annual
280.40(a)(3)(iii)
¦	The piping interstitial space and the
pressure, vacuum, or liquid monitoring
reservoir(s) and sensors (pressure,
vacuum, or stand-alone liquid detecting
sensor, as applicable), and contaimnent
sumps at end points, together are the
automatic line leak detector.
¦	Testing of monitoring reservoir and
sensors follows vacuum pumps and
pressure gauge testing, as noted on
table.
¦	Owners and operators must test their
DW piping to verify tightness of the
interstitial space. This can be done with
a system check.
¦	Verification of the integrity of the
contaimnent sumps at end points is
required annually. This could be by
testing of the sump or if the sump is
DW, proving that the interstitial space
of the contaimnent sump has integrity.
¦	Annual integrity testing of contaimnent
sumps at end points that varies from that
in 280.35(a)(l)(ii) may be used to test
the full area of sumps(s) or area of
sump(s) to the point of each sensor's
activation threshold if equipped with
liquid detecting sensor(s).
35

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Type of AIM System,
Components, and Required
Actions
(As Applicable)
Required
Testing
Frequency
Regulatory
Citation
Comments
Categories 1 & 2 Systems (Continued)
Monitoring Points (reservoirs and sumps)
Monitoring reservoir
¦S Ensure proper communication of
vacuum pumps and pressure
gauges with sensors and
controllers
Annual
280.40(a)(3)(iv)
Verily that the pressure, vacuum, or liquid
detecting sensor triggers the alarm at the
appropriate threshold and communicates that
to the monitoring console.
Containment sumps at end points of
category 1 or 2 systems (see example
1.1, 1.2or2.1)
^ Test contaimnent sumps used for
piping interstitial monitoring.
Note: If DW containment sump with
periodic monitoring of the integrity of
both walls of the sump, sump testing to
comply with 280.35(a)(l)(ii) is not
required.
Every three
years
280.35(a)(l)(ii)
¦ As a component of the ALLD, as noted
on the table, integrity/functionality of
contaimnent sumps at end points must
be verified annually. Owners and
operators testing annually using a
recognized low-level sump testing
procedure would meet the regulatory
requirement. If the owner and operator
use an annual test that varies from what
is allowed under 280.35 (a)(l)(ii), then
once every three years a test must be
completed that complies with
280.35(a)(l)(ii).
Category 3 System
Monitoring console (e.g., ATG or
another controller)
^ Verify system configuration
S Test alarm
^ Test battery backup
Annual
280.40(a)(3)(i)

Sensors
^ Test alarm operability for
communication with controller
Annual
280.40(a)(3)(ii)
For liquid detecting sensors
Sensors
^ Inspect for residual buildup
Annual
280.40(a)(3)(ii)
For liquid detecting sensors
36

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Type of AIM System,
Components, and Required
Actions
(As Applicable)
Required
Testing
Frequency
Regulatory
Citation
Comments
Category 3 System (continued)
ALLD
Test and inspect:
S DW piping
^ Area of containment sump(s) to
the activation point(s) of the
sensor(s)
Note: If DW containment sump with
periodic monitoring of the integrity of
both walls of the sump, sump testing is
not required.
Annual
280.40(a)(3)(iii)
¦	The piping interstitial space and the area
of the sump(s) used for interstitial
monitoring (to the point of each sensor's
activation threshold) and liquid
detecting sensors together are the
automatic line leak detector.
¦	Owners and operators must test their
DW piping (by air test) to verify
tightness of the interstitial space.
¦	Verification of the integrity of the
contaimnent sump is required annually.
This could be by testing the sump or if
the sump is DW, proving that the
interstitial space of the contaimnent
sump has integrity.
¦	Annual integrity test of contaimnent
sump that varies from that in
280.35(a)(l)(ii) may be used to test area
of sump(s) to the point of each sensor's
activation point.
Containment sump
^ Test contaimnent sumps used for
interstitial monitoring to ensure
liquid tight using vacuum,
pressure, or liquid testing.
Every three
years
280.35(a)(l)(ii)
¦ As a component of the ALLD,
integrity/functionality of contaimnent
sump(s) must be verified annually.
Owners and operators testing annually
using a recognized low-level sump
testing procedure would meet the
regulatory requirement. If the owner and
operator use an annual test that varies
from 280.35 (a)(l)(ii) then once every
three years a test must be completed that
complies with 280.35(a)(l)(ii).
For more information on low-level sump testing see the Spill Buckets, Under Dispenser
Containment Sumps, Containment Sumps section on EPA's Underground Storage Tank (LIST)
Technical Compendium about the 2015 UST Regulation webpage.
37

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Section 8. Basic Test Requirements (by
System Component)
General
AIM systems have multiple components. To ensure proper
function, evaluate each component as part of the system.
Components may be evaluated separately.
EPA recommends inspecting and replacing equipment according to
industry-standard code of practice or manufacturer's
specifications.
The components listed below, at minimum, must be tested for
proper operation, in accordance with one of the following:
manufacturer's instructions; a code of practice developed by a
nationally recognized association or independent testing
laboratory; or requirements determined by the implementing
agency to be no less protective of human health and the
environment that the preceding two options.
Key Components Tested (Annually, Unless Otherwise
Noted)
•	Monitoring Console
•	Sensors
•	Double-walled Piping
•	Monitoring Points
o Monitoring reservoirs category 1 and 2 systems:
Pressure, vacuum, or liquid reservoirs
o Containment sumps category 1, 2, and 3 systems
Monitoring Console
Verify system configuration has not changed since the initial
piping length and interstitial volume calculations were performed
upon system installation. Unless something changed, there is no
need to re-calculate pipe length or interstitial volumes. Reference
40 CFR § 280.40(a)(3)(i).
Verify that cell phone and other relay systems, as applicable,
respond within the appropriate time. Reference 40 CFR §
280.40(a)(3)(i).
38

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Note: PEIRP1200
Section 5, "Piping
Secondary Containment
Integrity Testing," or
piping manufacturer
interstice integrity
testing instructions may
be used to meet the
automatic line leak
detector requirements.
Test audible or visual alarm, or both if console has both, for
operability and communication with the monitoring console.
Reference 40 CFR § 280.40(a)(3)(i).
Ensure the battery backup system, as applicable, works properly.
Reference 40 CFR § 280.40(a)(3)(i).
Sensors
Test all sensors, including pressure, vacuum, and liquid detecting
sensors that are part of the monitoring reservoir and standalone
liquid detecting sensors in containment sumps for alarm operability
and communication with the monitoring console. Reference 40
CFR § 280.40(a)(3)(ii).
Inspect all liquid detecting sensors for residual buildup. Reference
40 CFR § 280.40(a)(3)(ii).
Double-Walled Piping
For category 3 AIM systems, perform an integrity test (by air test)
of the secondary walls of all double-walled piping of the system, to
prove tightness of the interstitial space, at least once every year
after installation. This subsequent testing verifies proper piping
interstitial communication for the system's capability to meet
automatic line leak detector requirements. Reference 40 CFR §
280.40(a)(3)(iii).
For category 1 and 2 AIM systems, integrity testing of the
interstitial space is not required by air test. Testing of the
secondary walls of DW piping associated with these systems to
verify tightness involves a full system check to ensure vacuum
pumps and pressure gauges are operating within the
manufacturer's specifications.
Monitoring Points
For Monitoring Reservoirs
Calibrate and maintain reservoirs, according to frequencies, per
manufacturer's instructions. Reference 40 CFR § 280.40(a)(2).
Ensure proper communication of vacuum pumps and pressure
gauges, as applicable, with sensors and a monitoring console. This
includes verifying that sensors trigger alarm(s) at the appropriate
39

-------
Note: Owners and
operators testing their
containment sumps
annually using a
recognized low level sump
testing procedure would
meet the regulatory
requirements under §
280.35(a)(1)(H) and §
280.40(a)(3)(iii).
threshold and communicate the alarm condition to the monitoring
console. Reference 40 CFR § 280.40(a)(3)(iv).
For Containment Sumps
Confirm integrity/functionality by testing the containment sumps,
including those at end points of category 1 and 2 systems, to meet
the ALLD annual testing requirement. The minimum area of
testing must encompass containment area bottom and sidewalls up
to sensor activation point. Reference 40 CFR § 280.40(a)(3)(iii).
Test containment sumps used for interstitial monitoring of piping
every three years to ensure liquid tight using vacuum, pressure, or
liquid testing. Reference 40 CFR § 280.35 (a)(l)(ii).
If the containment sump is double-walled with periodic monitoring
of the integrity of both walls of the sump, then sump testing to
comply with § 280.35(a)(l)(ii) is not required.
Records Maintenance
The results of the annual operations test conducted in accordance
with § 280.40(a)(3) must be maintained for three years. At a
minimum, the results must list each component tested, indicate
whether each component tested meets criteria in § 280.40(a)(3) or
needs to have action taken to correct an issue. Reference 40 CFR §
280.45(b)(1).
Written documentation of all calibration, maintenance, and repair
of release detection equipment permanently located onsite must be
maintained for at least one year after the servicing work is
completed, or for another reasonable time period determined by the
implementing agency. Any schedules of required calibration and
maintenance provided by the release detection equipment
manufacturer must be retained for five years from the date of
installation. Reference 40 CFR § 280.45(C).
Maintain records of operation and maintenance walkthrough
inspections per 40 CFR § 280.36(b), for one year. Records must
include a list of each area checked was acceptable or needed action
taken, a description of actions taken to correct an issue.
40

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Section 9: Required Documentation from
UST System Owners and Operators
Certification of Compliance Form
Owner and Operator Verification to UST Implementing
Agency
According to 40 CFR § 280.40(a)(4), UST system owners and
operators must provide a method, or combination of methods, of
release detection that meets the release detection performance
requirements with any performance claims and their manner of
determination described in writing by the equipment manufacturer
or installer.
There are many variations among individual UST site conditions and system configurations
across the United States. This is especially applicable to EPGUST systems. Because of
these variations a complete AIM system would have to be manufactured and installed
onsite as a unit to meet the release detection method requirements. AIM systems are
comprised of several components. No one component manufacturer can verify that
applicable regulatory performance requirements can be met for the entire system.
UST system owners and operators can use the Certification of
Compliance Form on page 43 to verify that their AIM systems
meet design and installation criteria. The form must be signed by
the equipment installer, a licensed PE, or other professional
required by the applicable UST implementing agency. EPG UST
system owners and operators in Indian Country, where the federal
UST regulation (40 CFR part 280) applies, may submit this form to
the applicable EPA regional office. EPA's UST website lists the
EPA Regional UST contacts .
UST system owners and operators in other jurisdictions should
contact their UST implementing agency to determine whether the
agency allows the use of an AIM system to meet its regulatory
requirements and whether this sample form meets the agency's
documentation requirements. Note that many state UST
implementing agencies require UST system installers to be
licensed. EPA's UST website lists state UST contacts .
The checklist below covers testing requirements applicable to AIM
systems. This checklist helps owners and operators identify and
comply with key operation and maintenance testing requirements
associated with AIM systems. This checklist does not include all
41

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testing requirements that owners and operators of EPG UST
systems must meet. For additional information on meeting federal
UST requirements applicable to other equipment and components
of EPG UST systems see EPA's Requirements for Emergency
Power Generator UST systems at
https://www.epa.gov/ust/publications-related-under ground-storage-
tanks.
42

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Certification of Compliance Form: Use of AIM System for EPG UST Facility (Page 1 of 2)
Facility Name
Facility ID #
Physical Address
City
County
State
UST Owner
Installer or PE's Signature
Printed Name of Installer or PE
Description
Line #/ Product
Line #/ Product
Line #/ Product
Line #/ Product
Line Number / Product




Piping Manufacturer




Piping Model




Pipe Diameter / Length of Pipe
/
/
/
/
Approximate Pipe Interstice
Volume (Gallons)




Type of AIM System (Category #)
~ 1 ~ 2 ~ 3
~ 1 ~ 2 ~ 3
~ 1 ~ 2 ~ 3
~ 1 ~ 2 ~ 3
Pressure (P) / Vacuum (V) / Liquid
Reservoir Manufacturer
Category 1 or Category 2 Aim Systems
P / V / Liquid Reservoir Model
Note: Some category 1 and 2 systems may also have contaimnent sumps with liquid-detecting sensors like those used in
category 3 systems. These sumps may not be monitored by the pressure, vaccum, or liquid reservoirs. These sumps may be
needed to monitor single-walled piping components inside the sump. As a contaimnent sump used for interstitial monitoring of
piping, these sumps must be tested for integrity once every three years.
Note: Contaimnent sump testing is not required if the contaimnent is double-walled and uses periodic interstitial monitoring
that monitors the integrity of both walls of the sump.
Comments
43

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Certification of Compliance Form: Use of AIM System for EPG UST Facility (Page 2 of 2)
Category 3 Aim Systems
Sump Sensor Manufacturer
Sump Sensor Model
Secondary Pipe Open to Secondary
Contaimnent Sumps or Collection
Point?
~ Yes ~ No
~ Yes ~ No
~ Yes ~ No
~ Yes ~ No
Secondary Containment Sumps
Contaimnent Sump Manufacturer
Contaimnent Sump Model
Automatic Tank Gauge or Monitoring Console
Monitoring Console Manufacturer
Monitoring Console Model
With Alarm
~ Yes ~ No
~ Yes ~ No
~ Yes ~ No
~ Yes ~ No
Alarm
Alarm Manufacturer
Alarm Model
Comments
Attach relevant site diagrams, pictures, as-built drawings, and other supporting documentation, as
required by UST implementing agency.
44

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Section 10: AIM Systems Inspection and
Testing Checklists

-------
AIM System Inspection and Testing Checklist: Category 1 or 2
UST Facility
Person Completing Checklist
Facility Name
Facility ID #
Name
Physical Address
Company
City
County
State
City
State
UST Owner
Signature
Date Completed
Description
Line 1
Line 2
Line 3
Line 4
Type of AIM System (Category #)
~ i Q
~ l Q
~ 1 Q
~ l Q
Attach a copy of the Certification Form for detailed system description.
Walkthrough Inspections [280.36]
Annual
• Visually check contaimnent sumps at
endpoints for damage and leaks to the
contaimnent area or releases to the
enviromnent. Remove water and
debris.
~
~
~
~
• For double-walled sumps with
interstitial monitoring, check for a
leak in the interstitial area.
~
~
~
~
Every 30 Days
• Check that system is operating with
no alarms or unusual operating
conditions.
~
~
~
~
• Ensure records of system component
testing listed below are reviewed and
current
~	Pass
~	Fail
~	Pass
~	Fail
~	Pass
~	Fail
~	Pass
~	Fail
Note: The items below are not required to be performed every 30-days as part of the walkthrough inspection. Most
items must be performed annually, unless otherwise noted. Use this checklist to verify that each step has been
performed within one year (i.e., 365 days) of the previous test, unless otherwise noted. If No is checked for any of the
steps, the AIM system fails. Provide copies of all relevant test forms upon request to the UST implementing agency.
Testing (Required Annually -
Unless Otherwise Noted)

Monitoring Console 280.40(a)(3)(i)
• Verify system configuration.
~ Yes ~ No
~ Yes ~ No
~ Yes ~ No
~ Yes ~ No
• Test alarm
~ Yes ~ No
~ Yes ~ No
~ Yes ~ No
~ Yes ~ No
• Test battery backup
~ Yes ~ No
~ Yes ~ No
~ Yes ~ No
~ Yes ~ No
Date Last Test




Test Results
~	Pass
~	Fail
~	Pass
~	Fail
~	Pass
~	Fail
~	Pass
~	Fail
Sensors 280.40(a)(3)(ii)
• Test alarm operability for
communication with
controller/monitoring console.
~ Yes ~ No
~ Yes ~ No
~ Yes ~ No
~ Yes ~ No
46

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AIM System Inspection and Testing Checklist: Category 1 or 2
Testing (Continued)
Description
Line 1
Line 2
Line 3
Line 4
• Inspect for residual buildup.
~ Yes ~ No
~ Yes ~ No
~ Yes ~ No
~ Yes ~ No
Date Last Test




Test Results
~	Pass
~	Fail
~	Pass
~	Fail
~	Pass
~	Fail
~	Pass
~	Fail
ALLD 280.40(a)(3)(iii)
• DW piping.
Verify integrity of interstitial space by air
testing piping. Ensure vacuum pumps and
pressure gauges are operating within
manufacturer's specifications.
~ Yes ~ No
~ Yes ~ No
~ Yes ~ No
~ Yes ~ No
• Monitoring reservoir.
Note: Testing of this component covered
below. Listed to show as part of ALLD.
~ Yes ~ No
~ Yes ~ No
~ Yes ~ No
~ Yes ~ No
• Contaimnent sumps at end points.
Note: Verification of integrity could be by
testing of the sump or if the sump is DW,
proving that the interstitial space of the
contaimnent sump has integrity. Annual
integrity testing of contaimnent sumps at
endpoints that varies from that in
280.35(a)(l)(ii) may be used to test full
area of sumps(s) or area of sump(s) to the
point of each sensor's activation threshold,
if equipped with liquid detecting sensor(s).
~ Yes ~ No
~ Yes ~ No
~ Yes ~ No
~ Yes ~ No
Date Last Test




Test Results
~	Pass
~	Fail
~	Pass
~	Fail
~	Pass
~	Fail
~	Pass
~	Fail
Monitoring Points 280.40(a)(3)(iv)
• Monitoring Reservoir (P / V / Liquid)
¦S Ensure proper communication of
vacuum pumps and pressure gauges
with sensors and controllers, as
applicable. Verify that the pressure,
vacuum, or liquid detecting sensor
triggers the alarm at the appropriate
threshold and communicates that to
the monitoring console.
~ Yes ~ No
~ Yes ~ No
~ Yes ~ No
~ Yes ~ No
S P / V System Calibrated Per
Manufacturer's Instructions.
280.40(a)(2)
~ Yes ~ No
~ Yes ~ No
~ Yes ~ No
~ Yes ~ No
Describe calibration completed and frequency:
47

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AIM System Inspection and Testing Checklist: Category 1 or 2
Description
Testing (Continued)
Line 1	Line 2
Line 3
Line 4
Containment Sumps at End Points 280.35(a)(l)(ii) - Required Once Every Three Years
Test containment sumps used for
piping interstitial monitoring to ensure
liquid tight by using vacuum,
pressure, or liquid testing.	
~ Yes ~ No
~ Yes ~ No
~ Yes ~ No
~ Yes ~ No
Notes: If DW contaimnent sump with periodic monitoring of both walls of the sump, sump testing to comply with
280.35(a)(l)(ii) is not required.	
Owners and operators testing annually using a recognized low-level sump testing procedure would meet the regulatory
requirement. If the owner and operator use an annual test that varies from what is allowed under 280.35 (a)(l)(ii), then a
test that complies with 280.35(a)(l)(ii) must be completed every three years..
Date Last Test
Test Results
~
~
Pass
Fail
~
~
Pass
Fail
~
~
Pass
Fail
~
~
Pass
Fail
Comments
48

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AIM System Inspection and Testing Checklist: Category 3
UST Facility


Person Completing Checklist

Facility Name
Facility ID #
Name
Physical Address
Company
City
County
State
City
State
UST Owner
Signature
Date Completed
Description	Line 1	Line 2	Line 3	Line 4
Attach a copy of the Certification Form for detailed system description.
Walkthrough Inspections [280.36]
Annual
• Visually check contaimnent sumps at
endpoints for damage, leaks to the
contaimnent area, or releases to the
enviromnent. Remove water and
debris.
~
~
~
~
• For double-walled sumps with
interstitial monitoring, check for a
leak in the interstitial area.
~
~
~
~
Every 30 Days
• Check that system is operating with
no alarms or unusual operating
conditions.
~
~
~
~
• Ensure records of system component
testing listed below are reviewed and
current - Date of the last test is not
beyond 1-year (i.e., 365 days) from
the previous test.
~	Pass
~	Fail
~	Pass
~	Fail
~	Pass
~	Fail
~	Pass
~	Fail
Note: If any of the items below are marked as No. then the AIM system fails. Provide copies of all relevant test forms upon
request to the UST implementing agency.
Testing (Required Annually - Unless Otherwise Noted)
Monitoring Console 280.40(a)(3)(i)
• Verily system configuration.
~ Yes ~ No
~ Yes ~ No
~ Yes ~ No
~ Yes ~ No
• Test alarm
~ Yes ~ No
~ Yes ~ No
~ Yes ~ No
~ Yes ~ No
• Test battery backup
~ Yes ~ No
~ Yes ~ No
~ Yes ~ No
~ Yes ~ No
Date of Last Test




Test Results
~	Pass
~	Fail
~	Pass
~	Fail
~	Pass
~	Fail
~	Pass
~	Fail
Sensors 280.40(a)(3)(ii)
• Test alarm operability for
communication with
controller/monitoring console.
~ Yes ~ No
~ Yes ~ No
~ Yes ~ No
~ Yes ~ No
• Inspect for residual buildup.
~ Yes ~ No
~ Yes ~ No
~ Yes ~ No
~ Yes ~ No
49

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IM System Inspection and Testing Checklist: Category 3
Testing (Continued)
Description
Line 1
Line 2
Line 3
Line 4
Date of Last Test




Test Results
~	Pass
~	Fail
~	Pass
~	Fail
~	Pass
~	Fail
~	Pass
~	Fail
ALLD 280.40(a)(3)(iii)
• DW piping.
Test by air test to prove tightness of the
interstitial space.
~ Yes ~ No
~ Yes ~ No
~ Yes ~ No
~ Yes ~ No
• Area of containment sump(s) to the
activation point of the sensor.
~ Yes ~ No
~ Yes ~ No
~ Yes ~ No
~ Yes ~ No
Note: Integrity could be verified by
testing the sump or if the sump is DW, by
proving that the interstitial space of the
contaimnent sump has integrity. Annual
integrity testing of contaimnent sumps at
end points that varies from that in
280.35(a)(l)(ii) may be used to test full
area of sumps(s) or area of sump(s) to the
point of each sensor's activation
threshold, if equipped with liquid
detecting sensor(s).




Date Last Test




Test Results
~	Pass
~	Fail
~	Pass
~	Fail
~	Pass
~	Fail
~	Pass
~	Fail
Monitoring Points 280.40(a)(3)(iv)
Containment Sumps Used for Piping Interstitial Monitoring
280.35(a)(l)(ii) - Required Once Every Three Years
• Test contaimnent sumps used for
piping interstitial monitoring to
ensure liquid tight by using vacuum,
pressure, or liquid testing.
~ Yes ~ No
~ Yes ~ No
~ Yes ~ No
~ Yes ~ No
Notes: If DW contaimnent sump with periodic monitoring of both walls of the sump, sump testing to comply with
280.35(a)(l)(ii) is not required.
Owners and operators testing annually using a recognized low-level sump testing procedure would meet the regulatory
requirement. If the owner and operator use an annual test that varies from what is allowed under 280.35 (a)(l)(ii), then once
every three years a test must be completed that complies with 280.35(a)(l)(ii).
Date Last Test




Test Results
~	Pass
~	Fail
~	Pass
~	Fail
~	Pass
~	Fail
~	Pass
~	Fail
Comments
50

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Appendix
Comparison of Equivalent 3 gph Leaks—Formulas and Rationale
Constants used for Orifice Size
Calculation
Cd=	0.61 Sharp Edge
SG gas = 0.68 at 60 degrees Fahrenheit
Ph, std = 0.0361 density of water standard
Reference for Equation used to Determine Orifice Size:
https ://www. lmnoeng. com/Flo w/LeakRate .php
Flow Rate (gph) of Air at Constant Pressure through Orifice	Volume of Air Discharged at Constant Pressure





Specific




Test



Pressure
Gravity




Pressure
Diameter
Area
Cd
Differential
(SG)
Air Flow
Air Flow
Air Flow
Air Flow
psi
inches
in2

in WC
Air
ft3 / hr.
ft3/min
gph
gpm
10
0.11868
0.0111
0.61
277.08
1.68
143.73
2.40
1075.21
17.92
5
0.11868
0.0111
0.61
138.54
1.34
113.80
1.90
851.30
14.19
4
0.11868
0.0111
0.61
110.83
1.272
104.47
1.74
781.51
13.03
3
0.11868
0.0111
0.61
83.12
1.204
92.99
1.55
695.66
11.59
2
0.11868
0.0111
0.61
55.42
1.136
78.17
1.30
584.76
9.75
1
0.11868
0.0111
0.61
27.71
1.068
57.00
0.95
426.45
7.11
0
0.11868
0.0111
0.61
0.00
1
0.00
0.00
0.00
0.00
Comments
•	A pressure drop of 10 psi = approximately 300" water column.
•	SG air at 10 psi and 70 degrees F = 1.68 (see The Effect Of Air Pressure On Air on page 20 in the reference Eclipse Combustion
Engineering Guide (mathscinotes.com) table).
•	SG air at 5 psi and 70 degrees F = 1.34.
Orifice Size for 3 gph at 10 psi Equivalent for Gasoline
Pressure
Diameter
Area
Flow rate
Flow Rate
psi
inches
in2
in3 / sec
gph
10
0.11868
0.0111
0.19261129
3.001734336
51

-------
Reference for Air Flow Equivalent
Source: Eclipse Combustion Engineering Guide (mathscinotes.com)
Application of Boyles Law	P1V1 = P2V2
How much compressed air will a 100 ft3 pipe interstitial volume hold at 5 psi?
PI = 1 atm =	14.69	psi
VI = 134.04	ft3	Volume prior to compression (interstitial volume + ambient air needed)
P2 = 1 atm + 5	19.69	psi
V2 = 100.00	ft3	Volume after compression (interstitial space volume)
34.04	ft3	Volume ambient air added required to reach 5 psi
Explanation: Pipe interstice volume of 134 ft3 would compress down to 100 ft3 at 5 psi test pressure.
The difference, 34.04 ft3, is the volume of air required to bring the pipe pressure up to 5 psi.
34.04 ft3 is the volume of air necessary to bleed off to bring pipe interstice back to 0 psi atmospheric pressure.
52

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Time Required for PEI Air Test
The volume of loss per loss of 1 psi pressure is consistently 50.9 gallons of air.
This only applies to a volume of 100 ft3. In other words, it takes 50.9 gallons of air to be compressed to pressurize 100 ft3 for each psi.
Smaller pipe volumes would require less air loss per psi.
That is because of the relationship due to gas Equation P1V1 = P2V2.
A Closer Look at Time of Decay for 100 ft3 Pipe Interstice
Initial Atmospheric (At)	. „ „	Cumulative Volume of Air per psi Test .. ,
Test	„	At Test Pressure	„	Air Loss
Pressure	Pressure
Pressure
PI
VI
P2
Ml
Added
Lost
Per psi
psig
psia
ft3
gallons
psig
ft3
gallons
ft3
gallons
ft3
gallons
gallons
10.0
14.7
168.1
1257.4
24.7
100.0
748.1
68.1
509.3
0
0

9.0
14.7
161.3
1206.4
23.7
100.0
748.1
61.3
458.3
6.8
50.9

8.0
14.7
154.5
1155.5
22.7
100.0
748.1
54.5
407.4
13.6
101.9

7.0
14.7
147.7
1104.6
21.7
100.0
748.1
47.7
356.5
20.4
152.8

6.0
14.7
140.8
1053.7
20.7
100.0
748.1
40.8
305.6
27.2
203.7
50.9
5.0
14.7
134.0
1002.7
19.7
100.0
748.1
34.0
254.6
34.0
254.6
50.9
4.0
14.7
127.2
951.8
18.7
100.0
748.1
27.2
203.7
40.8
305.6
50.9
3.0
14.7
120.4
900.9
17.7
100.0
748.1
20.4
152.8
47.7
356.5
50.9
2.0
14.7
113.6
850.0
16.7
100.0
748.1
13.6
101.9
54.5
407.4
50.9
1.0
14.7
106.8
799.0
15.7
100.0
748.1
6.8
50.9
61.3
458.3
50.9
0.0
14.7
100.0
748.1
14.7
100.0
748.1
0.0
0.0
68.1
509.3
50.9
53

-------
Time Required for PEI Air Test (continued)
The volume of loss per loss of 1 psi pressure is consistently 50.9 gallons of air.
This only applies to a volume of 100 ft3. In other words, it takes 50.9 gallons of air to be compressed to pressurize 100 ft3 for each psi.
Smaller pipe volumes would require less air loss per psi.
That is because of the relationship due to gas Equation P1V1 = P2V2.
A Closer Look at Time of Decay for 100 ft3 Pipe Interstice
Initial Atmospheric (At)
Pressure
At Test Pressure
Cumulative Volume of Air per psi Test Pressure Air Loss
Pressure
PI
VI
P2
\
J2
Added
Lost
Per psi
psig
psia
ft3
gallons
psig
ft3
gallons
ft3
gallons
ft3
gallons
gallons
10.0
14.7
168.1
1257.4
24.7
100.0
748.1
68.1
509.3
0
0

9.0
14.7
161.3
1206.4
23.7
100.0
748.1
61.3
458.3
6.8
50.9

8.0
14.7
154.5
1155.5
22.7
100.0
748.1
54.5
407.4
13.6
101.9

7.0
14.7
147.7
1104.6
21.7
100.0
748.1
47.7
356.5
20.4
152.8

6.0
14.7
140.8
1053.7
20.7
100.0
748.1
40.8
305.6
27.2
203.7
50.9
5.0
14.7
134.0
1002.7
19.7
100.0
748.1
34.0
254.6
34.0
254.6
50.9
4.0
14.7
127.2
951.8
18.7
100.0
748.1
27.2
203.7
40.8
305.6
50.9
3.0
14.7
120.4
900.9
17.7
100.0
748.1
20.4
152.8
47.7
356.5
50.9
2.0
14.7
113.6
850.0
16.7
100.0
748.1
13.6
101.9
54.5
407.4
50.9
1.0
14.7
106.8
799.0
15.7
100.0
748.1
6.8
50.9
61.3
458.3
50.9
0.0
14.7
100.0
748.1
14.7
100.0
748.1
0.0
0.0
68.1
509.3
50.9
54

-------
AIM Systems Exceed the 3 gph at 10 psi Equivalent Performance Standard
3 gph standard
2 gph standard
1 gph standard
0.5 gph standard
0.2 gph standard
Air LR
Time
Air LR
Time
Air LR
Time
Air LR
Time
Air LR
Time
GPM
MIN
GPM
MIN
GPM
MIN
GPM
MIN
GPM
MIN
14.19
3.59
9.45
5.38
4.73
10.77
2.36
21.53
0.95
53.82
13.03
3.91
8.68
5.87
4.34
11.73
2.17
23.46
0.87
58.63
11.59
4.39
7.73
6.59
3.86
13.18
1.93
26.35
0.77
65.86
9.75
5.22
6.49
7.84
3.25
15.67
1.62
31.35
0.65
78.36
7.11
7.16
4.74
10.75
2.37
21.49
1.18
42.99
0.47
107.44
0
0
0
0
0
0
0
0
0
0
Sum
24.27

36.43

72.84

145.68

364.12
Sum is the total time required for test pressure to drop from 5 psi to 0 psi.
Air leak rate came from calibrated orifices on previous sheets. Same logic. 3 gph at 10 psi gas leak, these would be 2 gph at 10 psi
leak equivalent, etc.
This indicates:
For an interstitial space volume of 100 ft3, the PEIRP 1200 test would easily detect down to a 1 gph standard.
It would drop from 5 psi to 1 psi within 1 hour on the gauge.
0.5 gph and 0.2 gph calculations here are not equivalent to what we traditionally think of as a 0.5 or 0.2 gph leak rate, respectively.
Figures are based on a hole sized 0.2 gph at 10 psi, which will not be the same as the traditional set 0.2 gph leak rate. Should be a
smaller hole size depicted here because of the 10-psi pressure.
For the 0.5 and 0.2 gph leak rate, gauge reliability is extremely important.
For example, for the 0.5 gph leak rate, the test pressure would drop from 5 psi to near 2.5 psi.
For the 0.2 gph leak rate, the best-case scenario is an observer would see the gauge drop from 5 psi to 4 psi within 1 hour.
Selecting a lower maximum pipe volume (instead of 100 ft3) would produce better results here, but keep in mind these are based
on 0.2 gph at 10 psi in-line pipe pressure.
Picking a maximum pipe volume of 500 gallons, for example, would notably improve the results for 0.5 and somewhat enhance
0.2 results, but likely won't result in a significant drop in pressure within 1 hour. Reducing it further would improve 0.2.
55

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