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Certification
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Leak
rate of 0.1 gph with PD = 100% and PFA = 0%. Leak rate
of 0.005 gph with PD = 97% and PFA = 2.9%.
The US EPA has not set a minimum detectable leak
rate for aboveground storage tank systems at the time
of this evaluation.
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Leak
Threshold
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A
tank system should not be declared tight when tracer chemical
greater than the background level is detected outside
of the tank system.
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Applicability
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Gasoline,
diesel, aviation fuel, fuel oil #4, waste oil, crude oil.
Other fluids which are compatible and soluble with an
acceptable tracer chemical may be tested after consultation
with the manufacturer.
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Tank
Capacity
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Not
limited by capacity.
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Waiting
Time
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Ranges
from 7 to 30 days after tracer is added to tank without
support of on-site leak simulation.The waiting period
may be adjusted below this range when supported by on-site
leak simulations performed as described below.
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Leak
Simulations
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The
release of surrogate tracer into the soil beneath the
tank to evaluate the migration of a tracer and the sensitivity
of the test under on-site sub-surface conditions. Sub-surface
conditions throughout the test area must be at least as
favorable as those at the leak simulations location in
order to use the results. This requirement may be satisfied
by sampling the soil beneath the tank, and/or making flow/vacuum
measurements from the sampling probes.
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Tracer
Dosage
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Dosage
of tracer is based on tank size, product volume in tank,
and frequency and volume of tank refills according to
manufacturer's recommendations.
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Permeability
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Soil
permeability must readily allow tracer movement (greater
than 1 Darcy).The permeability of the soil beneath the
tank must be verified by the detection of a leak simulation
tracer in a sample collected at least 13 feet from the
release location.
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Probe
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Typical
probe radius during evaluation was 10 to 12 feet. All
tank surfaces must be within the zone of influence of
a sampling probe. Probes must be installed per manufacturer's
guidelines.Probe radius below an AST can be increased
beyond the 10 foot limit when supported by a leak simulation
as described above.
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Groundwater
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Depth
to groundwater must be at least 2 inches below bottom
of tank.Groundwater less than 2 inches below bottom of
tank may limit effectiveness of test method.
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Comments
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Tester
may determine that pre or post testing is needed to establish
the background level of tracer in the soil.The presence
of a layer of water saturated soil, or frozen soil, may
inhibit the effectiveness of the method by impeding the
transport of the tracer labeled product into the unsaturated
zone.The system should be installed and operated in accordance
with Praxair Services, Inc.'s “AST Testing Procedures”
document.
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