This page of The Last of Us game guide contains information on where to find the training manuals and tools in the Tommy's Dam chapter. Those items are collectibles-secrets. Our walkthrough indicates the exact location of each artifact and pendant.
Bomb Containment 1
Description: Increases the range of the ground explosives.
After you bump into the sound trap, take several steps ahead, until you reach a destroyed bookshelf.
The manual is on the shelf.
You can find them in the pick-up truck to the left of the ice-cream truck.
Melee Manual 2
Description: Increases the durability of blades.
Close to the tools described above, there is a red-brick house.
Walk into the building and climb onto the first floor. Take a careful look at the ceiling. This way, you will find a manhole to the attic, which you can open (triangle).
Joel cannot get up there but he can give a boost to Ellie. The girl will find there the manual.