On 08/18/2015 a sill failure in the 4260-135 occurred as a result of a fall of ground in the inactive 4200-135. A sill failure is not reportable, the ground fall did not occur in an active area and there were no injuries therefore a call was not immediately made to MSHA. On 11/16/2015 an order was issued for not reporting the event within 15 minutes.