I've found and used the Impact Effects calculator with the following inputs:
Distance from Impact: 2.00 km = 1.24 miles
Projectile Diameter: 40.00 m = 131.20 ft = 0.02 miles
Projectile Density: 8000 kg/m3
Impact Velocity: 100.00 km/s = 62.10 miles/s
Impact Angle: 72 degrees
Target Density: 1000 kg/m3
Target Type: Liquid Water of depth 50.00 meters, over typical rock.
Gravity is roughly earthlike, but the atmosphere is substantially thinner. The area is very rich in various minerals, which is why there's a large mining base there. The impactor strikes a largish (two by ten kilometres), though heavily polluted, lake which is used for dumping waste from a nearby mine. The lake has a permanent layer of ice several meters thick, and the planet is quite dead so there's no soil.
Incidentally the impact velocity is deliberately higher than what is naturally possible. It's not actually an asteroid, but an artificial impactor launched by a competing mining company.
Here are my questions:
1. How long would it take for the debris to settle? E.g. for the dust and gravel to stop raining down.
2. How quickly would the crater cool down? Consider that it will quickly be flooded with cold water.
3. How quickly would the crater begin to collapse?
4. How easy would it be to find and identify a sample of the impactor?
5. If you got a sample would it be possible to roughly identify where the iron was refined? E.g. tell what kind of refining process, and possibly where it was refined, if it were in orbit or not. I have my own ideas here but I'd greatly appreciate any input.
If you need any figures that I haven't given already just plug in something that sounds reasonable, I'm not going to quote exact data in the story, but I do want things to be reasonable.