I just checked out the run course and here is a basic description (sorry, no mileages):
The first section (.4mi) out and back is on concrete and flat. After that concrete as you head east along the river path. After you go under the Mill bridge, the path turns to hard packed pea gravel and continues all the way to the Rural Road bridge. A small concrete hill up to the bridge and then up and over the river. Now on the north side of the river and heading west, concrete path all the way until a hill to another gravel path. There is a steepish downhill with some loose gravel here so footing can be tricky if something is not modified here. Now you are heading east again on hardpack gravel along a small canal. When you get to College ave. you are again on pavement/concrete and it is a slight incline for probably two miles. This will not be easy! A few turns on the road get you back to the canal and the whole out and back on the canal is hardpack gravel again. Repeat at the turn around and the hard incline section is now downhill in your favor until the river path where is flattens out again (concrete). All in all, I think it is rather technical, no real long boring stretches of concrete, and rather slowish gravel for approx 40% of each loop. Nice views (if you care) and you may want to be prepared if you are a slower IM’er as it will be very dark in many spots at night time. Be prepared.