All Service was retained to investigate the issue of media loss. It was apparent a failure occurred to the underdrain system, which was of a nozzle type. Upon completion of the media removal a broken nozzle was found.
This failure allowed media to get down into the plenum area. The plenum area had no access to gain entry to remove the media. All Service had to cut four access points due to the plenum design.
All Service fabricated (4) 304 stainless steel man-ways to put in place where the access points were made. Each man-way had to have nozzles placed into the proper position so as not to affect the mal-distribution.