Monitoring for Vapors in the Soil
How does the release detection method work?
This method samples for either: product vapors in the soil gas surrounding the UST (sometimes called passive monitoring) or presence of a tracer compound introduced into the UST system (sometimes called active monitoring). Leaked petroleum produces vapors that can be detected in the soil gas. Presence of a tracer compound outside of the UST system is an indication of a suspected release. The UST regulation describes several requirements for using this release detection method. For example, this method requires using porous soils in the backfill and locating the monitoring devices in these porous soils near the UST system.
Features of vapor monitoring systems are:
- Passive vapor monitoring senses or measures vapors from leaked product in the soil around the tank to determine if the tank is leaking.
- Active vapor monitoring senses or measures a tracer compound leaked in the soil around the tank to determine if the tank is leaking.
- Fully automated vapor monitoring systems have permanently installed equipment to continuously or periodically gather and analyze vapor samples and respond to a release with a visual or audible alarm.
- Manually operated vapor monitoring systems range from equipment that immediately analyzes a gathered vapor sample to devices that gather a sample that must be sent to a laboratory for analysis. Monitoring results from manual systems are generally less accurate than those from automated systems. Manual systems must be used at least once a month to monitor a site.
- All vapor monitoring devices should be periodically calibrated according to the manufacturer's instructions to ensure that they are properly responding.
- Before installation, a site assessment is necessary to determine the soil type, groundwater depth and flow direction, and the general geology of the site. This can only be done by a trained professional.
- The number of wells and their placement is very important. Only an experienced contractor can properly design and construct an effective monitoring well system. Vapor monitoring requires the installation of monitoring wells within the tank backfill. A minimum of two wells is recommended for a single tank excavation. Three or more wells are recommended for an excavation with two or more tanks. Some state and local agencies have developed regulations for monitoring well placement.
What are the regulatory requirements?
- The UST backfill must be sand, gravel or another material that will allow the vapors to easily move to the monitor.
- The backfill should be clean enough that previous contamination does not interfere with the detection of a current leak.
- The substance stored in the UST must vaporize easily so that the vapor monitor can detect a release.
- High ground water, excessive rain, or other sources of moisture must not interfere with the operation of vapor monitoring for more than 30 consecutive days.
- Monitoring wells must be secured and clearly marked.
- Beginning on [three years after effective date], you must keep records of a site assessment, for as long as you use this method, showing that the monitoring system is set properly. If you do not have a site assessment, you will need to have one conducted.
- Site assessments conducted after [effective date] must be signed by a licensed professional.
- Beginning on [three years after effective date], you must perform the following, as applicable, on your release detection equipment annually to make sure it is working properly:
For hand held non-electronic equipment:
- Check for operability and serviceability
- Keep records of these checks for one year
For other equipment:
- Verify the system configuration of the controller
- Test alarm operability and battery backup
- Inspect sensors for residual build-up
- Test manual electronic devices (such as photoionization detectors)
- Keep records of these tests for three years
Will it work at your site?
Before installing a vapor monitoring system, a site assessment must be done to determine whether vapor monitoring is appropriate at the site. A site assessment usually includes at least a determination of the groundwater level, background contamination, stored product type, and soil type. This assessment can only be done by a trained professional.
Will you be in compliance?
For USTs installed [on or before 180 days after effective date], owners and operators may use vapor monitoring as their primary method of release detection. When installed and operated according to the manufacturer's specifications and in accordance with the site assessment, vapor monitoring meets the federal release detection requirements. Vapor monitoring can also be used to detect leaks in piping. Operation of the vapor monitoring system at least once each month fulfills federal release detection requirements. USTs installed or replaced after [180 days after effective date] may no longer use vapor monitoring as the primary method of release detection. USTs must be secondarily contained and use interstitial monitoring.