4.3 Interstitial Monitoring (IM)
Interstitial monitoring involves the use of secondary containment that can prevent a leak from reaching the environment.
There are two types of Commerce approved interstitial monitoring techniques. They are:
1. Secondary barrier in the excavation zone
2. Double-wall tanks and/or piping
Interstitial monitoring can only be used if the owner can ensure that the system is installed and maintained to detect a leak from any portion of the tank or piping that routinely contains product.