Can garbage be sent into the (near-)center of the world? I've been thinking about how difficult it is to eliminate toxic chemical waste -- it usually needs high temperatures and pressures. So: would it be feasible (and maybe cheaper) to send it into the mantle or core of the world? 
I thought about grinding &amp; liquifying our junk and pumping it into a subduction zone off the California coast. But I don't know if that would work; after a million years it might pop up in a California hot springs.
Edit: Instead of pumping junk into a subduction zone, why not just drop the junk onto the sea floor at a subduction zone? It would have to be resistant to ocean water, but other than that it would gradually be pulled below the crust. And presumably be neutralized by the hot high pressure.
No. In fact, I don't know why David Hammen didn't say that instead of commenting.
The deepest hole that mankind ever dug was barely a scratch on the Earth's surface when you look at its size. They didn't even reach the mantle. The hole is only 12km deep, took about 20 years to create, and is still only 1/3 of the way to the mantle! Also, the hole is nothing through which you could dump garbage. It's only NINE inches in diameter.
Have you wondered what it means to dump trash into the Earth? Trash takes up space. There are no known voids in the deep Earth. It is very dense. To make room for trash, first you would have to dig the IMMENSELY expensive hole. Doing this also wastes energy. Then, you would need to invent technology to dig out a massive space, working from inside a nine-inch hole that goes over 7 miles into the Earth's surface. How expensive would that be? Is it even possible to carve out a space in the Earth under that much pressure without it collapsing? Given that scientists have only managed to keep open a nine-inch hole, you can bet we currently don't have available technology to build any kind of void for trash, let alone a void big enough to hold enough trash to make more room on the surface.