Cold joint gap between basement foundation walls – GreenBuildingAdvisor

I’m in the process of building an addition to my existing house, which includes a new foundation/basement wall abutted to the existing basement/foundation wall. The two walls were tied together with rebar epoxied into the existing. The new wall was poured about 18months ago. It appears the new foundation has settled over the course of the first 9 months or so, such that a gap of 1/2” appeared at the top of the joint. It is much smaller at the bottom, which indicates a bit of wall rotation due to settlement. I have not observed any additional settlement in the last 6months. 

The back of the wall is waterproofed, drained and backfilled with course gravel. No water is getting through, which tells me the waterproofing has stretched and is holding. However, it makes me a bit uneasy. How would you treat this condition? Dig up the exterior and add some type of extra robust cap sheet? Fill the gap from the inside with something? If so, with what (backer rod and sealant? Hydraulic cement? Some type of injection?) see photo attached.