Answer: Whether or not the roots of your tree will invade the drain field is really anybody's guess. Tree roots tend to remain in the top 18-24" of soil and radiate out about one and one-half times the diameter of the canopy of the tree. If you plant your Twisty Baby Locust, a variety of dwarf black locust, which grows up to 15 ft wide and tall about 15-20' away from the drain field, it should be fine. Best wishes with your garden!
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