If 48 mm is the actual BB drop, and I think Scooper's method can be done accurately, then it is real high. But that's a common issue with small frames. If you have a short small (48 cm remember) frame, as the TT is made shorter the front wheel moves closer to the BB. If the head tube anlgle is not changed, the tire to downtube clearance can get too small for fenders. One part of mitigating this is to raise the BB and hence move the downtube. Another aspect of course is to lay back the head tube, and decrease rake to restore desired trail.
It's hard to directly compare small frames (<51 or 52 c-c, I think) to more standard sizes, like 56 cm. Unfortunately, Trek did not publish their geometry for all frame sizes. The usually only talked about the 22.5 inch, 56 cm sizes.
My 52 cm Woodrup, built originally for 27 inch wheels and fenders, has a 6.5 mm BB drop. It always feels a little teetery to ride.