Ground water monitoring
Secondary containment with interstitial monitoring
Automatic tank gauging systems
Tank tightness testing and inventory control
Manual tank gauging
Leak detection for underground suction piping
Leak detection for pressurized underground piping
Statistical inventory reconciliation
NOTE: Ground-water monitoring cannot be used at sites where ground water is more than 20 feet below the surface.
Will I be in compliance?
When installed and operated according to manufacturer's instructions, a ground-water monitoring system meets the Federal leak detection requirements for new and existing UST's. Operation of a ground-water monitoring system at least once each month fulfills the requirements for the life of the tank. Ground-water monitoring can also be used to detect leaks in piping (see the later sections on leak detection for piping).
You should find out if there are State or local limitations on the use of ground-water monitoring or requirements that are different from those presented below.
How does it work?
Ground-water monitoring involves the use of one or more permanent monitoring wells placed close to the UST. The wells are checked at least monthly for the presence of product that has leaked from the UST and is floating on the ground-water surface. The two main components of a groundwater monitoring system are the monitoring well (typically a well of 2-4 inches in diameter) and the monitoring device.
The number of wells and their placement is very important. Many state and local agencies have developed regulations for this, usually requiring somewhere between one and four monitoring wells per UST (additional ones may be required for piping). Before installation, a site assessment is necessary to determine the soil type, ground-water depth and flow direction, and the general geology of the site.
- Detection devices may be permanently installed in the well for automatic, continuous measurements of leaked product.
- Detection devices are also available in manual form. Manual devices range from a bailer (used to collect a liquid sample for visual inspection) to a device that can be inserted into the well to electronically indicate the presence of leaked product. Manual devices must be operated at least once a month.
What are the regulatory requirements?
- Ground-water monitoring can only be used if the stored substance does not easily mix with water and floats on top of water.
- If ground-water monitoring is to be the sole method of leak detection, the ground water must not be more than 20 feet below the surface, and the soil between the well and the UST must be sand, gravel or other coarse materials.
- Monitoring wells must be properly designed and sealed to keep them from becoming contaminated from outside sources. The wells must also be clearly marked and locked.
- Wells should be placed in, or very near to, the UST backfill so that they can detect a leak as quickly as possible.
- Product detection devices must be able to detect one-eighth inch or less of leaked product on top of the ground water.
Will it work at my site?
In general, ground-water monitoring works best at UST sites where:
- The ground-water surface extends beneath the tank;
- Monitoring wells are installed in the tank backfill;
- Ground water is between 2 and 10 feet from the surface; and
- There are no previous releases of product that would falsely indicate a current release.
A site assessment is critical for determining these site-specific conditions.
What other information do I need?
The proper design and construction of a monitoring well system is crucial to effective detection of leaked product and should be performed by an experienced contractor. Before construction begins, any specific State or local construction requirements should be identified.
Purchasing a ground-water monitoring system is similar to any other major purchase. You should "shop around," ask questions, get recommendations, and select a company that meets the needs of your UST site.
How much does it cost?
The capital costs for ground-water monitoring are generally much greater than the annual operating costs. The following cases illustrate the effect that different factors have on the cost of ground-water monitoring:
One tank - well in backfill - short piping runs - manual monitoring -
two wells installed:
Equipment Cost = $200-250
Installation Cost = $15-25/ft well depth
Annual Operating Cost = Under $100
One tank - well not in backfill - long piping runs - automated
monitoring - five wells installed:
Equipment Cost = $2,200-5,000
Installation Cost = $50-70/ft well depth; conduit to the central console = $500-2,000
Annual Operating Cost = Under $200