TAXIING TFC IN NIGHT OP; A 727 FREIGHTER HITS L WING AGAINST SNOW BERM THAT WAS INFRINGING UPON THE TXWY.

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WHILE TAXIING WBOUND ON TXWY E ENRTE TO RWY 13 AT MDT (HARRISBURG INTL ARPT) THE L WING OF OUR B-727 CONTACTED THE UPPER PORTIONS OF A SNOW BANK THAT HAD NOT BEEN PROPERLY CLRED AWAY FROM THE TAXI AREA. CONDITIONS (WX) WERE NIGHT TIME AND WX BETTER THAN 5000 FT AND WHILE TAXIING FROM THE CARGO RAMP TO RWY 13 AT MDT I NOTICED THAT THERE WAS VERY LITTLE SNOW AT THE BEGINNING OF TXWY E. AS WE PROGRESSED ABOUT ANOTHER MI DOWN THE TXWY ON THE TXWY CTRLINE; I NOTICED THAT A SNOW BANK WAS AHEAD AND THAT A SIGNIFICANT PORTION OF THIS SNOW BANK PROTRUDED INTO TXWY E. TRAVELING WBOUND; FROM THE TXWY CTRLINE SOUTHWARD IT APPEARED THAT STAYING STRICTLY ON THE TXWY CTRLINE WOULD PLACE US UNCOMFORTABLY CLOSE TO THIS UNCLRED SNOW BANK. I THEREFORE ADJUSTED MY PATH 15 FT TO THE R (N) TO ALLOW EXTRA CLRNC. THE AREA TO THE R OF THE TXWY CTRLINE IS DARK; UNLIT; AND UNMARKED (BLACK TOP). 15 FT R OF CTRLINE IS AS FAR AS I FELT COMFORTABLE BEING DISPLACED FROM THE CTRLINE. THIS ADDITIONAL DISPLACEMENT WAS NOT ENOUGH AS OUR L WING IMPACTED THE SNOW/ICE BANK DAMAGING #1 AND #2 LEADING EDGE DEVICES. THE ACFT WAS RETURNED TO THE GATE FOR INSPECTION WITHOUT FURTHER INCIDENT. THIS MISHAP OCCURRED BECAUSE THE HARRISBURG INTL (MDT) AUTH DID NOT CLR THE TXWY SUFFICIENTLY OF SNOW AND ICE SUCH THAT NORMAL TAXI WOULD BE SAFE OR POSSIBLE.