Current through September 24, 2024
Each method of leak detection for tanks used to meet the
requirements of § 280.41 must be conducted in accordance with the
following:
(a)
Inventory
control. Product inventory control (or another test of equivalent
performance) must be conducted monthly to detect a leak of at least 1.0 percent
of flow-through plus 130 gallons on a monthly basis in the following manner:
(1) Inventory volume measurements for
regulated substance inputs, withdrawals, and the amount still remaining in the
tank are recorded each operating day;
(2) The equipment used is capable of
measuring the level of product over the full range of the tank's height to the
nearest one-eighth of an inch;
(3)
The regulated substance inputs are reconciled with delivery receipts by
measurement of the tank inventory volume before and after delivery;
(4) Deliveries are made through a drop tube
that extends to within one foot of the tank bottom;
(5) Product dispensing is metered and
recorded within the local standards for meter calibration or an accuracy of 6
cubic inches for every 5 gallons of product withdrawn; and
(6) The measurement of any water level in the
bottom of the tank is made to the nearest one-eighth of an inch at least once a
month.
(b)
Manual
tank gauging. Manual tank gauging must meet the following
requirements:
(1) Tank liquid level
measurements are taken at the beginning and ending of a period using the
appropriate minimum duration of test value in the table below during which no
liquid is added to or removed from the tank;
(2) Level measurements are based on an
average of two consecutive stick readings at both the beginning and ending of
the period;
(3) The equipment used
is capable of measuring the level of product over the full range of the tank's
height to the nearest one-eighth of an inch;
(4) A leak is suspected and subject to the
requirements of Rule 2.5 if the variation between beginning and ending
measurements exceeds the weekly or monthly standards in the following table:
|
Nominal tank capacity |
Minimum Duration |
Weekly standard (one
test) |
Monthly standard (average of four
tests)
|
|
550 gallons or less |
36 hours |
10 gallons |
5 gallons. |
|
551-1,000 gallons
(when tank diameter is 64 inches) |
44 hours |
9 gallons |
|
551-1,000 gallons
(when tank diameter is 48 inches) |
58 hours |
12 gallons |
|
551-1,000 gallons |
36 hours |
13 gallons |
7 gallons. |
|
1,001-2,000 gallons |
36 hours |
26 gallons |
13 gallons. |
(5)
Only tanks of 550 gallons or less nominal capacity may use this as the sole
method of leak detection. Tanks of 551 to 2,000 gallons may use this method in
place of manual inventory control in § 280.43(a). Tanks of greater than
2,000 gallons nominal capacity may not use this method to meet the requirements
of this rule.
(c)
Tank tightness testing. Tank tightness testing (or another
test of equivalent performance) must be capable of detecting a 0.1 gallon per
hour leak rate from any portion of the tank that routinely contains product
while accounting for the effects of thermal expansion or contraction of the
product, vapor pockets, tank deformation, evaporation or condensation, and the
location of the water table.
(d)
Automatic tank gauging. Equipment for automatic tank gauging
that tests for the loss of product must meet the following requirements:
(1) The automatic product level monitor test
can detect a 0.2 gallon per hour leak rate from any portion of the tank that
routinely contains product. The equipment must be capable of visual or audible
alarms and the equipment must be capable of printing the completed 0.2 gallon
per hour leak rate test; and
(2)
The equipment is inspected for proper operation at least once every 12 months.
The inspection must be conducted in accordance with the manufacturer's periodic
maintenance specifications and any applicable code of practice listed in §
280.13.
(3) The test must be
performed with the system operating in one of the following modes:
(i) In-tank static testing conducted at least
once every 30 days; or
(ii)
Continuous in-tank leak detection operating on an uninterrupted basis or
operating within a process that allows the system to gather incremental
measurements to determine the leak status of the tank at least once every 30
days.
(e)
Vapor monitoring. Testing or monitoring for vapors within the
soil gas of the excavation zone must meet the following requirements:
(1) The materials used as backfill are
sufficiently porous (e.g., gravel, sand, crushed rock) to readily allow
diffusion of vapors from releases into the excavation area;
(2) The stored regulated substance, or a
tracer compound placed in the tank system, is sufficiently volatile (e.g.,
gasoline) to result in a vapor level that is detectable by the monitoring
devices located in the excavation zone in the event of a release from the
tank;
(3) The measurement of vapors
by the monitoring device is not rendered inoperative by the ground water,
rainfall, or soil moisture or other known interferences so that a release could
go undetected for more than 30 days;
(4) The level of background contamination in
the excavation zone will not interfere with the method used to detect releases
from the tank;
(5) The vapor
monitors are designed and operated to detect any significant increase in
concentration above background of the regulated substance stored in the tank
system, a component or components of that substance, or a tracer compound
placed in the tank system;
(6) In
the UST excavation zone, the site is assessed to ensure compliance with the
requirements in paragraphs (e) (1) through (4) of this rule and to establish
the number and positioning of monitoring wells that will detect releases within
the excavation zone from any portion of the tank that routinely contains
product and
(7) Monitoring wells
are clearly marked and secured to avoid unauthorized access and
tampering.
(f)
Ground-water monitoring. Testing or monitoring for liquids on
the ground water must meet the following requirements:
(1) The regulated substance stored is
immiscible in water and has a specific gravity of less than one;
(2) Ground water is never more than 20 feet
from the ground surface and the hydraulic conductivity of the soil(s) between
the UST system and the monitoring wells or devices is not less than 0.01 cm/sec
(e.g., the soil should consist of gravels, coarse to medium sands, coarse silts
or other permeable materials);
(3)
The slotted portion of the monitoring well casing must be designed to prevent
migration of natural soils or filter pack into the well and to allow entry of
regulated substance on the water table into the well under both high and low
ground-water conditions;
(4)
Monitoring wells shall be sealed from the ground surface to the top of the
filter pack;
(5) Monitoring wells
or devices intercept the excavation zone or are as close to it as is
technically feasible;
(6) The
continuous monitoring devices or manual methods used can detect the presence of
at least one-eighth of an inch of free product on top of the ground water in
the monitoring wells;
(7) Within
and immediately below the UST system excavation zone, the site is assessed to
ensure compliance with the requirements in paragraphs (f) (1) through (5) of
this rule and to establish the number and positioning of monitoring wells or
devices that will detect releases from any portion of the tank that routinely
contains product; and
(8)
Monitoring wells are clearly marked and secured to avoid unauthorized access
and tampering.
(g)
Interstitial monitoring. Monitoring of the space between the
inner (primary) and the outer (secondary) tank walls may be used, but only if
the system is designed, constructed and installed to meet the following
requirements:
(1) The sampling or testing
method can detect a release from any portion of the tank that routinely
contains product;
(2) The sampling
or testing method can detect ingress of external fluids (groundwater or other
fluids not intended as monitoring fluids) into the interstice;
(3) Records must be maintained that show the
interstice has been checked at least every 30 days for evidence of a leak or
ingress of external fluids;
(i) If the
interstice is monitored continuously, records must document that the electronic
device monitoring the interstice is in communication with the control console
at least monthly;
(ii) If the
interstice is monitored continuously, records must document the alarm history
and provide the response action taken, appropriate reporting (if applicable)
and reconciliation of each alarm;
(iii) Any electronic device that monitors the
interstice must be tested at least once every 12 months for proper function.
The functionality test must simulate a leak and be in accordance with the
manufacturer's specifications and any applicable industry code or recommended
practice listed in § 280.13; and
(4) Any regulated substance that enters the
interstice must be removed within 24 hours of discovery or another time frame
determined by the MDEQ to be reasonable.
(h)
Other methods. Any other
type of leak detection method, or combination of methods, can be used if:
(1) It can detect a 0.2 gallon per hour leak
rate or a release of 150 gallons within a month with a probability of detection
of 0.95 and a probability of false alarm of 0.05; or
(2) The MDEQ may approve another method if
the owner and operator can demonstrate that the method can detect a release as
effectively as any of the methods allowed in paragraphs (c) through (h) of this
rule. In comparing methods, the MDEQ shall consider the size of leak that the
method can detect and the frequency and reliability with which it can be
detected. If the method is approved, the owner and operator must comply with
any conditions imposed by the MDEQ on its use to ensure the protection of human
health and the environment.
