Don't put them in the trash. Actually illegal in most places.
If you have a place take the ammo out and bury it. BTW any of the shells that were in a box and out of the water should be ok. An inch and a half is only 2 rows of shells in a box. Pitch the bottom rows and try shooting the rest. As a test I once loaded a couple of boxes of 12 ga and put them in boxes. Put them outside in rain snow sleet sun for more than 2 years. Some were ugly but every shell fired and broke the clay target I was shooting at. Every shell also ejected from the 1100 I was using them in.
