4. A federal employee who fails to file a tranfer application within the election period under section 3 or who began to receive a benefit under the Public Service Superannuation Act (R.S.C. 1985, c. P-36) is deemed to have elected to participate in the provincial pension plan retroactively to 1 January 1992 where he is an employee referred to in paragraph 1 of section 2, or to 1 July 1992 where he is an employee referred to in paragraph 2 of that section. Any contributions made by him since that date shall be adjusted accordingly and any overpayment shall be refunded to him with interest at the rate of 4% compounded annually and calculated from the date on which he began to contribute to this plan.