It's not clear how you are grading from the hill and bridge to elevation 482. Assuming you have some sort of footprint to start from, and a given slope parameter that targets the 482 elevation, I would proceed as follows:
Create a single element at elevation 482 that spans between the hill and the bridge. Then using the slope element tool, project at 0% slope to EG on either side of the element. That will create elements that intersect the EG at the 482 contour. Add these slope elements to an object to create a flat surface at elevation 482. You will use this surface as a target for the gradings from the hill and the bridge, so extend it far enough beyond the hill and the bridge to ensure those gradings will be able find a target.
Next, create slope elements from the footprints for the hill and bridge by targeting the 482 surface using the required slope parameters. If you make the footprints wide enough, these slope elements will intersect the slope elements you created for the elevation 482 object.
Lastly, trim all the slope elements where they intersect each other and join them into a single chain element. This element will represent the planar surface between the bridge and the hill (of course the elements will lose all the modeler attributes when you trim and join them, but I'm assuming you only need a static solution). Lastly use this chain to create an element at elevation 482 and add it to your finished ground object along with the footprints for the hill and bridge.
There are other ways to do this but I think this approach is the most straight forward.