Section 120-B. Supervision of sewage system

If the public works herein
  provided be  constructed  and  operated  by  the  municipalities  acting
  jointly,  the  local  authorities  of  the contracting municipalities or
  districts  having  charge  of  sewage  shall   jointly   supervise   the
  construction  and  operation  of such sewage system, or they may jointly
  engage or employ a competent sanitary engineer for  such  purpose.  They
  shall  jointly  elect or appoint all necessary employees at the disposal
  plant and for the care of the trunk line sewer,  and  severally  appoint
  such  employees  as  they  may  be authorized so to do by the respective
  governing bodies to work  on  the  system  within  the  bounds  of  such
  municipality.