Within 30 days of the effective date hereof, each company shall advise this commission, by a letter signed by a responsible official of the company, of the extent and circumstances under which it adds supplement and/or substitute gas to the gas usually distributed. If, at any time subsequent to said filing with this commission, a company proposes new or additional sources of supplement and/or substitute gas at existing or new locations, said company shall amend its filing, by a letter signed by a responsible official of the company, to advise this commission of the proposed sources of gas at least 90 days prior to the effective date of said change except that, in instances of sudden emergency where such prior notice of the proposed sources of gas proves impossible, such notice of the proposed sources of gas shall be given to this commission, by a telegram over the name of a responsible official of the company, at the earliest possible date.