Spill buckets: A dry interstice is not permitted because it does not always allow monitoring of the outer wall. An interstice monitored by a sensor only, must contain brine solution. – I have checked with suppliers and other industry personnel and have been unable to locate a spill bucket with a 'brine' solution.  Double walled spill buckets are either dry with no sensor or dry with an interstitial sensor. 

. . . If the sump is capable of being used for interstitial monitoring then it must be tested, unless the tank owner/operator can clearly demonstrate that they are not using the sump for interstitial monitoring. Regardless of whether other methods are also being performed, if interstitial monitoring is being used, these sumps must be tested.  – I am concerned about how field personnel will interpret this guidance.  I interpret as . . . you originally registered using IM, however changed to annual line and leak detector testing b/c you didn’t want to complete secondary containment testing. 

I'm concerned that if sensors are installed w/ DWL pipe, regardless of install date, some personnel may 'require' interstitial monitoring/secondary containment testing.  It is highly probable that multiple sites have sensors installed at locations with install dates prior to 9/15/2010.  Will it be necessary to remove sump/UDC sensors to ensure secondary containment testing will not be required?