There’s too little information for a fully informed response, and here’s why:
1. It matters when the landfill was started, that is, under what rules, and how well it has been constructed and managed since then. Modern landfills are excavated and lined with impermeable clay first, and then that is topped with another layer to protect the clay itself. So in that case there’s no leaching of the landfill’s content into groundwater. Older landfills – and you can’t very well retrofit an existing landfill – were not “built” in this way; they were mostly just existing hollows or depressions in the local geography and far enough off the beaten path to be mostly unobjectionable.
2. Second, it matters where your drinking water comes from. Do you use an on-premises well? How deep is it? How often has the water been tested, and for what substances? If you use piped-in “city water” from a metropolitan water company which uses professional and high-quality management techniques, then that’s less of an issue.
3. Third, if you DO use a deep-water well, then are you geologically upstream or downstream from the landfill? That’s important for reasons that should be obvious.
4. You’re actually probably more at risk if you live close to actively managed farm fields. Fertilizer runoff (and to a far lesser extent, pesticides) are more likely, more widespread and in general more damaging if they get in your drinking water.
So the answer is… “it depends”.