To visualize further, 60 barrels could contaminate one square mile of aquifer in ND, and 3500 barrels can contaminate 60 square miles.
While there's certainly some cleanup for the crew to do (the article says it's already 20% done) this is still a relatively small spill and probably pales in comparison to the contamination already created by gas stations in the region.
Please correct me if I misread, but I thought the article said 20% of the oil was recovered, not that cleanup and restoration was 20% complete. Full restoration is rarely possible, and cleanup can take decades as there is a very long tail of activities.
Help me visualize a square mile - in km if possible!
A little over 5km squared
About 1,6 km by 1,6 km. So 16 100 m run tracks or football pitches long sides. Albeit those can be 90 to 120 m for UK or 100 to 110 m for international...