&EPA
United States
Environmental Protection
Agency
Solid Waste And
Emergency Response
5403W
EPA510-F-94-005
August 1994
UST Program Facts
Detecting Releases
Why have release detection?
The U. S. Environmental Protection Agency
designed part of the technical regulations for
underground storage tanks (USTs) to make sure
releases or "leaks" from USTs are discovered quickly
before contamination spreads from the UST site.
Owners and operators are responsible for detecting
leaks from their tanks and piping.
Who needs leak detection?
All USTs must now have leak detection. USTs
installed after December 22,1988 must have leak
detection when they are installed. USTs installed
before December 22,1988 had compliance deadlines
that varied with the age of the USTs. By December
22,1993, all of these "older" USTs had to be in
compliance with leak detection requirements.
What are the leak detection methods?
Owners and operators of petroleum USTs must use
at least one of the seven leak detection methods
below, or other methods approved by their state
agency.
1. Automatic tank gauging systems use monitors
permanently installed in the tank. These monitors
are linked electronically to a nearby control device to
provide information on product level and
temperature. During a test period of several hours
when nothing is put into or taken from the tank, the
gauging system automatically calculates the changes
in product volume that can indicate a leaking tank.
This method does not work on piping.
2. Groundwater monitoring senses the presence
of liquid product floating on the groundwater. This
method requires installation of monitoring wells at
strategic locations in the ground near the tank and
along the piping runs. To discover if leaked product
has reached groundwater, these wells can be checked
periodically by hand or continuously with
permanently installed equipment This method is
effective only at sites where groundwater is within
20 feet of the surface.
3. Vapor monitoring senses and measures product
vapor in the soil around the tank and piping to
determine the presence of a leak This method
requires installation of carefully placed monitoring
wells. Vapor monitoring can be performed
periodically using manual devices or continuously
using permanently installed equipment.
4. Secondary containment and interstitial
monitoring involves placing a barrier between the
UST and the environment. The barrier provides
"secondary" containment and can be a vault, liner,
or double-walled structure. Leaked product from the
UST is directed toward a monitor located in the
"interstitial" space between the UST and the outer
barrier. Interstitial monitoring methods range from a
simple dip stick to automated vapor or liquid sensors
permanently installed in the system. New USTs
holding hazardous substances must use this method.
5. Statistical inventory reconciliation uses
sophisticated computer software to determine
whether a tank system is leaking. The computer
conducts a statistical analysis of inventory, delivery,
and dispensing data collected over a period of time
and provided by the operator to a vendor.
6. Manual tank gauging can be used only on tanks
2,000 gallons or smaller. This method does NOT
work on tanks larger than 2,000 gallons or on
piping. This method requires taking the tank out of
service for at least 36 hours each week to take
measurements of the tank's contents. Tanks 1,000
gallons or less can use this method alone. Tanks
from 1,001-2,000 gallons can use this method only
when it is combined with periodic tank tightness
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testing and only for 10 years after installation or
upgrade of the UST. After 10 years, these USTs
must use one of the leak detection methods listed
above in 1-5.
The additional method below can be used
temporarily at all petroleum UST sites:
7. Tank tightness testing and inventory control
combines two methods. Tank tightness testing
requires periodic tests conducted by vendors who
temporarily install special equipment that tests the
soundness of the tank. Tank tightness testing must
be used in combination with inventory control.
Inventory control is an ongoing accounting system,
like a checkbook, kept by the UST owner or operator
to detect leaks. Inventory control requires taking
daily accurate measurements of the tank's contents
and performing monthly calculations to prove that
the system is not leaking. Tank tightness testing
and inventory control can be used only for 10
years after installation or upgrade of an UST.
After 10 years, these USTs must use one of the leak
detection methods listed above in 1-5.
What does piping need?
Pressurized piping needs automatic line leak
detectors (these can be automatic flow restrictors,
automatic flow shutofis, or continuous alarm
systems). Pressurized piping also needs one of the
following: groundwater monitoring, vapor
monitoring, secondary containment and interstitial
monitoring, or an annual tightness test of the piping.
Suction piping needs no leak detection if it meets
two design requirements: 1) piping slopes so that
the product drains back into the tank when suction is
released, and 2) piping has only one check valve
located closely beneath the pump in the dispensing
unit Suction piping not meeting these design
requirements must use one of the following:
tightness test of the piping every 3 years,
groundwater monitoring, vapor monitoring, or
secondary containment and interstitial monitoring.
Reporting and recordkeeping necessary?
UST owners and operators need to report to the
regulatory authority data about the UST, including
description of the leak detection method. If
operation of the leak detection method indicates a
possible leak, UST owners and operators need to
report the potential release to the regulatory
authority. UST owners and operators must keep
records on leak detection performance and upkeep.
These include the previous year's monitoring results,
the most recent tightness test results, performance
claims by the leak detection device's manufacturer,
and records of recent maintenance and repair.
"Detecting Releases" is one in a series of fact sheets
about underground storage tanks (USTs) and leaking
USTs. The series is designed to help EPA, other federal
officials, and state authorities answer the most frequently
asked questions about USTs with consistent, accurate
information in plain language. Keep the fact sheets
handy as a resource. This fact sheet addresses federal
regulations. You may need to refer to applicable state or
local regulations, as well. For more information on
UST publications, call the RCRA/Superfund Hotline at
800424-9346.
RtcyclMi/ftocyctabl*
Printed with Soy/C¬a Ink on paper that
contains at least 50% post-consumer recycled fiber
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