The largest garbage dump in the world is roughly twice the size of the  
continental U.S.

The Great Pacific Garbage Patch is a continent-sized constellation of  
discarded shoes, bottles, bags, pacifiers, plastic wrappers,  
toothbrushes and every other type of trash imaginable, floating in the  
Pacific Ocean about halfway between Hawaii and San Francisco. The  
ocean's swirling currents have pushed the piles of debris, accumulated  
detritus of sea vessels and decades of under-the-radar ocean dumping,  
together in loose configurations just below the water's surface.

cont'd....

http://www.forbes.com/business/2008/12/02/garbage-waste-landfills-biz-logistics-cx_wp_1202dumps.html