United States
                          Environmental Protection
                          Solid Waste And
                          Emergency Response
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

    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

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
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