The sidebar next to the Excavation Site suggests that players may be ready to level up after this encounter. This is strictly true, providing the players have hit every encounter, received no XP bonuses from quests or roleplaying, and have incomprehensibly backtracked after the Torture Chamber in order to see the encounters in the order they are presented in the module.
Levelling up in 4th Edition is an odd experience. On face value, it's never been easier. Page 29 of the Player's Handbook has everything you need to gain your new level bonuses. All classes need the same amount of experience to level, and they all level in the same way.
On the other hand, 4th Edition persistently uses the concept of "half your level"; you add this number to your skill totals, your defences, your initiative, some of your attacks but not others, and in certain situations to your ability modifiers. Mechanically, this is a good way of ensuring that characters scale up appropriately, but in practice it means that every second level you'll be re-writing nearly half of your character sheet.
The problem with the half-level mechanic is that it's not consistent. If you simply added it to every roll, you could note it once on your character sheet and just play through. But it doesn't follow such clear-cut rules. You add it to your defences, but not your saves. You add it to your initiative, but not your speed. You add it to attack rolls, but not to damage. These distinctions aren't hard to remember with some practice but they're neither intutive nor clear.
Still, it's a huge improvement on previous editions.
 Keep on the Shadowfell has its own little twist on levelling up. It suggests that rather than players levelling immediately upon hitting their XP target, they should instead only level after taking an extended rest. This not only contradicts the Player's Handbook, but also runs counter to the 4th Edition philosophy of discouraging rest-related downtime. I understand why you might not want characters to pause combat in order to level up, but why is a short (five-minute) rest not a good time?