I am looking to the thread and posts for a while.. I looked to the ASCE 7-16 and try to see the applicable items and copied and pasted below;
-15.7.6 Ground-Supported Storage Tanks for Liquids
-15.7.6.1.3 Equipment and Attached Piping
-15.7.6.1.4 Internal Elements.
-15.7.7 Water Storage and Water Treatment Tanks and
Vessels
-15.7.7.3 Reinforced and Prestressed Concrete. Reinforced
and prestressed concrete tanks shall be designed in accordance
with the seismic requirements of AWWA D110, AWWA D115.........
The conservative approach will be, to check the performance of walkways, bridge mechanism , central column .... Apparently, your concern is The system is likely to fail regardless during a seismic event..Is this concern based on a performance calculation ?
The code item 15.7.7 is for Water Storage and Water Treatment Tanks .. and IMO, Water treatment is for potable water treatment rather than Sewage treatment plant.
I will suggest you to look ;
..and apparently , the sewage treatment plant and related units are not a lifeline item....
IMO, the owner / operator should decide for the exemption .