As is often the case with releases to the environment, initial estimates are much lower than the actual amount. In my recent post "Bugs on the Run in the Merrimack", I mentioned estimates of released plastic disks numbering in the tens of thousands. According to this article which appeared Wednesday in Seacoastonline.com, those estimates were understated. Current estimates for the number of released plastic disks (aka Biofilm Chip M media) are now at 4 to 8 million. This represents 10 to 20% of the 39 million disks employed at the facility. The disks are washing up on more and more shorelines between Salem, Massachusetts and the coast of New Hampshire. I've yet to hear of any floating disks being seen by boaters and wonder if the disks might be more easily recovered from the water's surface with nets. Sure would fill a lot of kayaks!
There are many questions as to exactly what happened at the Hooksett Wastewater Facility. Is it true that there was no high tank level alarm? Are reports stating that no personnel checked the facility on the Sunday in question, despite the combination of heavy rain and snowmelt, correct? What about the manufacturers "media retention sieves"? Were they in place? If so, was the hydraulic force strong enough to overcome the retention sieves?
Working in the field of wastewater treatment, I've seen a situation where media escaped past a retention system. Perhaps media retention is an area where a backup system or screen would not be redundant. Just as with double-walled fuel tanks and double-hulled fuel tankers, an ounce of prevention can be worth a pound of cure.