UST
Vapor Monitoring FAQ
The purpose of this page is to provide you with information concerning VAPOR MONITORING, one of the available methods for meeting the leak detection requirements set forth for all regulated petroleum USTs.
What is Vapor Monitoring?Vapor monitoring is a stand-alone form of leak detection (not subject to periodic tank or line tightness testing) that uses monitoring wells as testing locations for leaking product. Tiny pores between individual grains of soil allow the petroleum products to become volatile and move through the soil (vaporize) in the excavation zone (UST pit). Vapor monitoring wells are placed in strategic locations so they can intercept any petroleum vapors that may be moving through the soil due to a leak. Vapor monitoring can detect leaks in tanks and piping.
It is the responsibility of the owner and operator to provide accurate semi-monthly (every 14 days) testing data for the compliance inspection. The inspector will be looking for the following information at your compliance inspection:
- The last 12 months of your leak detection records which show that the vapor wells were checked every 14 days. If vapor monitoring has not been carried out for 12 months, leak detection records from other methods must be reviewed for the balance of the year.
- To see if the proper notification procedures were followed if any vapor concentrations exceeded background concentrations during the past 12 months.
- The excavation zone assessment that states that vapor monitoring is an acceptable method for this site and that a qualified person has addressed all of the above requirements.
- The third-party certification for the vapor sensor (if applicable).
When using vapor monitoring as a monthly monitor, a leak should be suspected if any indication of hydrocarbon vapors is found during the semi- monthly testing. Your DWM Regional Office must be contacted within 24 hours of receiving information regarding a leak. A leak investigation, in accordance with 15A NCAC 2N .0603, must be conducted within seven days,
Assessment
for
Vapor
Monitoring must show:
*The backfill if sufficiently porous to allow diffusion of vapors
(e.g.,
gravel, sand, crushed rock);
The stored product is volatile enough to result in a vapor level that is detectable by the monitoring devices in the UST pit in case of a leak from the tank;
Groundwater, rainfall, soil moisture, or other interference's will not hinder detection of a leak, Background contamination on the UST pit will not interfere with the method used to detect leaks from the tank; and
The number and positioning of the monitoring wells are sufficient to detect leaks from any portion of the tank system.
Key Elements of a Vapor Monitoring System
Monitoring
Wells
The monitoring wells used for vapor monitoring must be constructed
according to state regulations 15A NCAC 2N .0504. They must be clearly
marked and locked to prevent tampering or unauthorized
access.
14
Day Testing
The monitoring wells must be checked every 1 days to determine if any
petroleum vapor is present indicating a leak in a tank or line. A vapor
detector is used in conjunction with
monitoring wells to detect the
presence
of petroleum vapors. Sensors cone in a variety of shapes and sizes.
Federal
and State regulations require a third-party
certification for each type
of sensor used. Choose one that best fits your leak detection needs.
Soil
Assessment
A qualified person* must conduct a soil assessment of the UST pit
before
employing a vapor monitoring system for leak detection. The
assessment
will determine if site conditions are suitable for vapor monitoring.
Certain
soil and groundwater characteristics must be identified before a
vapor
monitoring system can be utilized. The assessment also determines the
positioning
and the minimum number of monitoring wells or devices
that will detect
a leak from the UST system.
Disadvantages
You do not know about the leak until a great deal of soil (and
potentially
groundwater) has already been contaminated. This could lead
to
expensive
cleanup costs.
This method is very site-specific; it might not work at your facility due to soil and./or groundwater conditions. Therefore, a site assessment is required of the subject facility by a qualified person for this to be an applicable method
Common
Questions
I use vapor monitoring on a monthly basis. What records do I need for
a compliance inspection?
- You need at least the last 12 months of vapor monitoring well test results indicating that they were checked every 14 days;
- Third party evaluation for hydrocarbon sensor (contact sensor vendor if you need one).
- Assessment of excavation zone by a qualified person.
No, because vapor monitoring is a monthly monitoring for piping. (This holds true for suction piping as well.) Wells must be placed every 50 feet along the piping runs such that a leak from the piping can be detected. However, all pressurized piping systems must have an automatic line leak detector that must be tested annually.
When
do I have
a leak?
You have a suspected leak when there is an indication of petroleum
hydrocarbons in the vapor monitoring wells. Once a leak has been
identified,
follow the notification requirements described above.
Who
is a
"qualified person"?
A "qualified person" is one who, through training and experience, is
competent to evaluate the UST site. We recommend that this person be
a
registered Professional Engineer or a Licensed Geologist.
Additional
Policy Notes:
On April 24, 1995, the Division released a letter detailing the
applicability
of vapor monitoring systems started before the state regulations came
into
effect. If you are using vapor monitoring as a method of leak
detection,
it MUST comply with current requirements. This includes having
an
assessment
conducted to verify site conditions. For systems that do not meet all
of
the requirements set forth in 15A NCAC 2N, owner/operators have
two
options:
- Correct all deficiencies of the system (i.e., have a qualified person assess the site suitability, well construction and locations, etc.).
- Abandon on-site wells and begin another form of leak detection.
Contact your regional (DWM office (see map) OR
Contact the DWM Central Office at:
NCDENR
Division of Waste Management
UST Section
1637 Mail Service Center
Raleigh NC 27699-1637
(919) 733-8486
The purpose of this page is for general guidance. More specific information on UST regulations can be found in 15A NCAC 2N.
1646 Mail Service Center, Raleigh, NC 27699-1646
(919)508-8400
