| (III) Monthly deviation--The variation between the
level measurements taken at the beginning and the end of one gauging
30-day period, converted to and expressed as gallons.
(ii) Any measuring equipment (whether operated manually
or automatically) shall be capable of measuring the level of a stored
substance over the full range of the tank's height to the nearest
1/8 inch.
(iii) Separate liquid level measurements in the tank
shall be taken at least once every 30 days at the beginning and the
ending of the gauging period, and the monthly deviation shall be determined
from such level measurements.
(iv) For the purposes of the 30-day tank gauging method
of release detection, a release shall be indicated when the monthly
deviation exceeds the maximum allowable standards indicated in the
following subclauses:
(I) for a tank with a capacity of 550 gallons or less:
monthly standard = five gallons;
(II) for a tank with a capacity of 551 gallons to 1,000
gallons: monthly standard = seven gallons;
(III) for a tank with a capacity of 1,001 gallons to
2,000 gallons: monthly standard = 13 gallons; and
(IV) for a tank with a capacity greater than 2,000
gallons: monthly standard = 1.0% of the total tank capacity.
(v) When the monthly standard is exceeded and a suspected
release is thereby indicated, the owner or operator shall comply with
the applicable release reporting, investigation, and corrective action
requirements of Subchapter D of this chapter.
(4) Automatic tank gauging in combination with inventory
control.
(A) A combination of automatic tank gauging and inventory
control may be used as a tank release detection method, subject to
the following requirements.
(i) Inventory control procedures shall be in compliance
with paragraph (1)(B) of this subsection.
(ii) The automatic tank gauging equipment shall be
capable of:
(I) automatically monitoring the in-tank liquid levels,
conducting automatic tests for substance loss, and collecting data
for inventory control purposes; and
(II) performing an automatic test for substance loss
that can detect a release of 0.2 gallon per hour from any portion
of the tank which contains regulated substances.
(iii) The automatic tank gauge testing 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.
(B) For emergency generator tanks and used oil tanks
only, automatic tank gauging may be used as a tank release detection
method without inventory control, provided that the automatic tank
gauging equipment shall be capable of:
(i) automatically monitoring the in-tank liquid levels;
(ii) conducting continuous automatic tests for substance
loss during the periods when the emergency generator engine is not
in operation;
(iii) performing an automatic test for substance loss
that can detect a release of 0.2 gallon per hour from any portion
of the tank which contains regulated substances; and
(iv) measuring the water level at the bottom of the
tank to the nearest 1/8 of an inch at least once every 30 days.
(5) Vapor monitoring. Equipment and procedures designed
to test or monitor for the presence of vapors from the regulated substance
(or from a related tracer substance) in the soil gas of the backfilled
excavation zone may be used, subject to the following limitations
and requirements.
(A) The bedding and backfill materials in the excavation
zone shall be sufficiently porous to allow vapors from any released
regulated substance (or related tracer substance) to rapidly diffuse
through the excavation zone (e.g., gravel, sand, crushed rock).
(B) The stored regulated substance, or any tracer substance
placed in the tank system, shall be sufficiently volatile so that,
in the event of a substance release from the UST system, vapors will
develop to a level that can be readily detected by the monitoring
devices located in the excavation zone.
(C) The capability of the monitoring device to detect
vapors from the stored regulated substance shall not be adversely
affected by the presence of any groundwater, rainfall, and/or soil
moisture in a manner that would allow a release to remain undetected
for more than 30 days.
(D) Any preexisting background contamination in the
excavation zone shall not interfere with the capability of the vapor
monitoring equipment to detect releases from the UST system.
(E) The vapor monitoring equipment shall be designed
to detect vapors from either the stored regulated substance, a component
or components of the stored substance, or a tracer substance placed
in the UST system, and shall be capable of detecting any significant
increase in vapor concentration above preexisting background levels.
(F) Prior to installation of any vapor monitoring equipment,
the site of the UST system (within the excavation zone) shall be assessed
by qualified personnel to:
(i) ensure that the requirements in subparagraphs (A)
- (D) of this paragraph have been met; and
(ii) determine the appropriate number and positioning
of any monitoring wells and/or observation wells, so that releases
into the excavation zone from any part of the UST system can be detected
within 30 days.
(G) All monitoring wells and observation wells shall
be designed and installed in accordance with the requirements of §334.46(g)
of this title.
(6) Groundwater monitoring. Equipment or procedures
designed to test or monitor for the presence of regulated substances
floating on, or dissolved in, the groundwater in the excavation zone
may be used, subject to the following limitations and requirements.
(A) The stored regulated substance shall be immiscible
in water and shall have a specific gravity of less than one.
(B) The natural groundwater level shall never be more
than 20 feet (vertically) from the ground surface, and the hydraulic
conductivity of the soils or backfill between all parts of the UST
system and the monitoring points shall not be less than 0.01 centimeters
per second (i.e., the soils or backfill shall consist of gravels,
coarse to medium sands, or other similarly permeable material).
(C) Any automatic monitoring devices that are employed
shall be capable of detecting the presence of at least 1/8 inch of
free product on top of the groundwater in the monitoring well or observation
well. Any manual monitoring method shall be capable of detecting a
visible sheen or other accumulation of regulated substances in, or
on, the groundwater in the monitoring well or observation well.
(D) Any preexisting background contamination in the
monitored zone shall not interfere with the capability of the groundwater
monitoring equipment or methodology to detect releases from the UST
system, and the groundwater monitoring equipment or methodology shall
be capable of detecting any significant increase above preexisting
background levels in the amount of regulated substance floating on,
or dissolved in, the groundwater.
(E) Prior to installation of any groundwater monitoring
equipment, the site of the UST system (within and immediately below
the excavation zone) shall be assessed by qualified personnel to:
(i) ensure compliance with the requirements of subparagraphs
(A) and (B) of this paragraph; and
(ii) determine the appropriate number and positioning
of any monitoring wells and/or observation wells, so that releases
from any part of the UST system can be detected within 30 days.
(F) All monitoring wells and observation wells shall
be designed, installed, and maintained in accordance with the requirements
in §334.46(g) of this title.
(7) Interstitial monitoring for double-wall or jacketed
UST systems. Equipment designed to test or monitor for the presence
of regulated substance vapors or liquids in the interstitial space
between the inner (primary) and outer (secondary) walls of a double-wall
or jacketed UST system may be used, subject to the following conditions
and requirements.
(A) Any double-wall UST system using this method of
release detection shall be designed, constructed, and installed in
accordance with the applicable technical and installation requirements
in §334.45(d) and §334.46(f) of this title.
(B) The sampling, testing, or monitoring method shall
be capable of detecting any release of stored regulated substances
from any portion of the primary tank or piping within 30 days of the
release.
Cont'd... |
