Section 307. System revenues; adjustment of surcharge

All surcharge monies
  remitted to the municipality by a service supplier and all other  monies
  dedicated to the payment of system costs from whatever source derived or
  received  by  the municipality shall be expended only upon authorization
  of the board and only for payment of system costs as permitted  by  this
  article. The municipality shall separately account for and keep adequate
  books  and  records of the amount and source of all such revenues and of
  the amount and object or purpose of all expenditures thereof. If at  the
  end of any fiscal year the total amount of all such revenues exceeds the
  amount  necessary  for payment of system costs in such fiscal year, such
  excess shall be reserved and carried over  for  the  payment  of  system
  costs in the following fiscal year. However, if at the end of any fiscal
  year  such  E911  reserved  fund balance exceeds an amount equal to five
  percent of that necessary for the payment of system costs in such fiscal
  year, the board  shall  by  local  law  reduce  the  surcharge  for  the
  following  fiscal  year  to  a  level which more adequately reflects the
  system cost requirements of its E911 system. The board may also by local
  law reestablish or increase such surcharge, subject to the provisions of
  section three hundred three of this article, if the  revenues  generated
  by  such  surcharge  and by any other source are not adequate to pay for
  system costs.