WordNet (r) 3.0 (2006):

garbage dump
    n 1: a piece of land where waste materials are dumped [syn:
         dump, garbage dump, trash dump, rubbish dump,
         wasteyard, waste-yard, dumpsite]

Moby Thesaurus II by Grady Ward, 1.0:

22 Moby Thesaurus words for "garbage dump":
   bog, cesspool, cloaca, cloaca maxima, colluvies, compost heap,
   drain, dump, dunghill, kitchen midden, manure pile, marsh, midden,
   mire, mixen, quagmire, refuse heap, septic tank, sewer, sink, sump,
   swamp