MassDEP recommends that at sites relying on a sub slab depressurization system (SSDS) to prevent exposure to contaminants of concern, annual checks be conducted of fan operation status and for potential differential pressure drops. These annual checks should be conducted as part of site maintenance and monitoring activities, and are recommended even after the installation of remote monitoring (telemetry). 

This applies to SSDS systems at sites in Remedy Operation Status, and sites with a Temporary Solution or a Permanent Solution with Conditions. 

This is a reminder that the Responsible Party is advised to continue to verify the operation of the SSDS until such time that it is demonstrated the SSDS is no longer needed.

From VAPOR INTRUSION GUIDANCE: SITE ASSESSMENT, MITIGATION AND CLOSURE Policy #WSC-16-435, Table 3-1.