a) No later than April 1 of each year, a public utility offering natural gas service shall file an annual mercury compliance report with the Chief Clerk of the Commission. The report shall contain the following information for the previous calendar year:

1. 1) The number of locations that required a mercury vapor air sample test; and
2. 2) An identification of the number of locations that contained confirmed readings in excess of the allowed levels and the concentration of mercury vapor detected by the public utility at each location as set forth in Section 535.200(c).

c) A public utility’s exemption from the reporting requirements in this Section ends in the event that:

1. 1) The public utility discovers a mercury-containing regulator or manometer used in providing natural gas service within its system; or
2. 2) The public utility merges with another Illinois natural gas utility or acquires Illinois service territory from another public utility that has not met the requirements of subsection (b).