POTENTIAL CONFLICT GND. UNAUTH TKOF FROM CLOSED RWY.

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WITH A SNOWPLOW ON THE RWY WE TAXIED INTO POS. WHEN THE PLOW REACHED THE FAR END OF THE RWY IT APPEARED THAT THE PLOW EXITED THE RWY. AFTER REPEATED ATTEMPTS AT CONTACTING THE PLOW ON UNICOM WE PROCEEDED TO TKOF; UPON REACHING APPROX 65 KTS. THE PLOW RE-ENTERED THE RWY. (5000 FT RWY.) WE PROCEEDED TO TKOF AND SIDE STEP AROUND. (NOT CLOSE.) UPON CONTACTING ZSE AIRBORNE WE WERE ADVISED THAT THE RWY WAS CLOSED. AWOS DIDN'T INFORM US PRIOR TO TKOF AND THE PLOW WASN'T USING A RADIO! DURING THIS TIME; 1 ACFT LANDED AFTER APCH AND 3 OTHERS DEPARTED. ALSO; UNICOM DID NOT ADVISE ANYONE OF THE PLOW. CALLBACK CONVERSATION WITH RPTR REVEALED THE FOLLOWING INFO: RPTR STATED THAT; TO HIS KNOWLEDGE; THERE WAS NO NOTAM ISSUED FOR THE TIME THAT HE WAS DEPARTING EAT; WA. HE HAD RECEIVED HIS PLT BRIEFING FROM SEA FSS WHICH IS THE DESIGNATED FSS FOR EAT AND THEY HAD NOT MENTIONED THE RWY CLOSURE. RPTR WAS ASKED HOW THE CTR CTLR KNEW OF THE CLOSURE AND HE GUESSED THAT THE ONLY WAY HE COULD HAVE KNOWN WOULD HAVE BEEN BY A NOTAM BEING ISSUED. THE OTHER TFC ARRIVING AND DEPARTING HAD NOT RECEIVED NOTAM INFO EITHER. RPTR WAS ASKED IF HE HAD FELT ANY SCHEDULE PRESSURE AND HE SAID NO; AS THIS WAS A FERRY FLT AND THERE WEREN'T ANY TIME CONSIDERATIONS DRIVING THIS DEP. HE HAD NOT CONTACTED THE ARPT MGR AS THIS WAS A SATURDAY. HE TRIED TO CALL THE UNICOM BY PHONE BUT THEY DIDN'T ANSWER HIM. HE ADDED; THAT TO HIS KNOWLEDGE; HE HAD NEVER HEARD OF AWOS ADVISORIES ON CLOSED RWYS AND HAD JUST ADDED THAT NOTE TO HIS RPT. HIS CONCERN WAS THAT UNICOM; FSS AND THE VEHICLE DRIVER ALL SEEMED TO BE OUT OF THE LOOP AND HE WONDERED WHY. HE THINKS THE ARPT MGR SHOULD BE ALERTED TO THIS EVENT.