I can count that damage roll for both instances ok?

If so the purple worm looks to be clinging to life and with all that's happened since the siege of the Goblin Horde you can surmise (without an investigation check) that this monster, much like the black dragon and later dracolich, were or are being controlled by some greater entity.

Pepin activates his force cannon as a BA:

To hit 22 for 9dmg
He than casts booming blade and hit with his warhammer:

To ht 11 for 15dmg

Luckily the force cannon happens to be enough to slay the purple worm. It's death is somewhat anti-climatic as it's last roar fades into a low, groaning death rattle and then it's bulky corpse is just laying there.

(This combat is over.)

Tempe dismisses his spell.

Randall:

”Is everyone okay?” Randall asks with concern.  Noting that the party members all appear to have survived, he backtracks the purple worm’s path of destruction to find any survivors who may be in need of healing.

Once the dust has settled and the wounded are seen to, Zenodor starts to examine the corpse of the beast.

"I never heard of such a monster near a city. I believe they live in deserts. This must have travelled far, and I cannot imagine it did so unprompted. Someone or something must have surely guided or ordered it to come here to attack us."

He examined the corpse, looking for signs of control like perhaps chains or manacles, or a magic item, or perhaps traces of a control spell.

Investigation 18

Arcana  14

(the desert planet of Arrakis seems a long way. I think we need to find out who sent this thing)

(lol, I was waiting for a Dune reference.)

Tempe looks upon the destruction, follows the worms path, not from where it came from, but where it was going too. He looks at the building it was about to destroy, wondering if this is some kind of power struggle. (Maybe, it's the spice 💩. )

Tempe suggests to Randle, while he follows the trail, "Maybe, you should gut the poor creature to find out where it's been, by, what it's ate. I think it's poison may be valuable, too."

Randall:

”Of course, good idea,” says Randall.  He guts the worm first to let out anything inside its stomach, then starts working carefully on the stinger tail.

Survival:  23

"Thanks to your healing I am" Pepin answers Randall After which he helps Randall with his tasks of both healing and taking care of the worm.

(I'm not sure if you're only supposed to get one dose or more but since it's near the end of the game I'm going to say you harvest 2 doses of purple worm poison.)

Quote from Touschka_ >>

He examined the corpse, looking for signs of control like perhaps chains or manacles, or a magic item, or perhaps traces of a control spell.

Investigation 24

Arcana  7

Quote from Stormbringer4729 >>

Tempe suggests to Randle, while he follows the trail, "Maybe, you should gut the poor creature to find out where it's been, by, what it's ate. I think it's poison may be valuable, too."

(Did we find out any hints about where it came from or what it was after?)

The tunnel leads back to join up with several cross-sections of other tunnels it used to move around underground. The only thing that makes any sense is that it was controlled but as for by who or what there are no clues.

Quote from Stormbringer4729 >>

Tempe looks upon the destruction, follows the worms path, not from where it came from, but where it was going too. He looks at the building it was about to destroy, wondering if this is some kind of power struggle. (Maybe, it's the spice 💩. )

Zenodor: "We could try to follow the tunnels back to where they came from. But maybe we should consult with the city and army leadership first. Perhaps they know what is going on"

"Yes let's have a talk if they heard any rumours."

Once their investigations of the worm and its tunnel are complete, Z, Pepin and the others head to the city leadership to speak to the General and the other leaders.

"This worm seems most unusual. Luckily we managed to dispatch it before it was able to do much damage. Has one like it ever been seen near the city before? Have you obtained any intelligence or rumour of who to what might be behind it?"

The military leadership has never defended the city from any giant worms before. They actually explain that until the siege of the Goblin Horde they can't remember when the city has faced such troubles and tribulations. Finally, they relay they're in the same boat waiting for the wizards to find and supply more information on the matter.

They expect to get something worthwhile in less than 24 hours.