Can Orisa’s ‘Halt State’ be unlocked with environmental kills

Shoot the ground directly in front of the opponent. Since its a scatter effect it will work best against big targets. It's a little tricky to do, as the idea is that the arrow will impact the ground so close to the opponent that all the scattered arrows don't have a chance to go into anywhere else. I would recommend loading up the training grounds and trying it on the training dummies to get a feel for how it works.

Edit: Here's a crude drawing of what you're trying to do. The red line is the scatter arrow. It's like you're firing a shotgun shell at the point of impact so the closer the impact point, the more effective it is.

It would appear as though the amount of ultimate charge is granted based on the current health of the target when the kill is registered by the death-zone at the bottom of the pit.

Test case 1: Winston (500HP) Environmental

Test case 2: Winston (~240HP) Damage+Environmental

Test case 3: Winston (500HP) Full Damage

Test case 4: Winston Primal Rage (1000HP) Environmental

Test case 5: Tracer (150HP) Environmental

Test case 6: Tracer (120HP) Punch+Suicide

We can see from these clips that, negating the over time ultimate gain, the amount of charge gained is consistent with the total damage dealt, not including any measure of overkill.

For reference: For every 15 points of damage dealt by or as a result of Pharah's actions, 1% ultimate charge is granted. This means 33.3% charge for Winston, 10% for Tracer (consistent with what we see above).