Here's an interesting article I read today that may address your problem:
How to Get Rid of Ants Without Using a Pesticide - Associated Content
Summary:
1. cornmeal or grits -- ants can't completely digest it, starve to death
2. vinegar -- vinger/water solution keeps ants away
3. boric acid -- proven killer, nontoxic
4. pour boiling water on ant nest
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