Sounds like you got yourself in a conversation with a super-edjumacated-professional-citified-county-office-worker who's more comfortable at a desk indoors (with bug repellent on and wearing sunscreen) than outside enjoying God's creation!!!!!!!
Have they ever grown a garden?
Eeks!! And on the subject of poo, you probably ought not ever plant a garden, because there could possibly be bird, deer, mouse, chicken, earthworm, bug, bee, microbial and other poo bits that might get on your plants! Safer bet altogether to just buy your veggies, because everything they sell at the grocery store is safe. It NEVER has e coli on it. You betcha!!
Anyway, while I could possibly maybe very faintly agree with not putting your 6 foot long carrot roots into the top of your septic tank, I feel that other areas of one's yard (like uphill from the septic, maybe - like - DUH!) seems like a fairly safe bet to me.
We've been doing fine here, even though we have a septic tank on our property.
We are buying a house with private well and septic. Yesterday, the County Health Dept told me that I should never grow root vegetables on the property (not just over the septic field) because of risk of E Coli. Really?! She said a raised garden would be okay, but that it wouldn't need to have a barrier. This makes no sense to me, but I'd love to hear your thoughts...