Both of a B757's engines were damaged by FOD after landing at JAC on a runway clear of snow and ice. The runway clearing machine was removing the asphalt surface leaving pebbles to damage the aircraft's engines.

Narrative

We were landing at JAC and we were very light as we were ferrying the airplane. Approach speed was 128 KTS. I went 1 dot low on GS to insure touchdown in the first 1000 Feet. We touched down prior to 1000 FT or just slightly beyond. Touchdown was firm but not excessive. I used maximum automatic brakes as no passengers were aboard and I wanted to see how quickly the airplane would stop in the maximum setting. The braking was so effective that I never went to maximum reverse as it was evident that I was going to have to add power to make the midfield turnoff. The taxiways were snow packed but our parking spot was bare as it was covered with deice fluid so I shut down the #2 engine approaching the parking spot. On the walkaround my First Officer found nicks on the fan blades of the #2 engine and small pieces of rocks in the fan cowl. We advised Maintenance Control and changed aircraft to a B757 that also received FOD damage to its blade earlier that day but had been repaired (dressed). JAC does not use deice fluid on its runways. Instead it uses some fancy Norwegian sweepers to keep the runway clean. I suspect the sweepers are weakening the aggregate of the runway causing small stones to be ingested. Callback conversation with Reporter revealed the following information: The reporter stated that both of the aircraft's engines were damaged and required 93 fan blades to be repair. After this event; a vacuum street sweeper followed the runway ice chipper to remove the FOD that the process created. Runway deice fluid cannot be used on the airport's runways because it is in a national park boundary and the fluid is considered an environmental contaminant.