Not cool. Ethylene glycol is highly toxic. Animals and small children love the stuff because it smells and tastes pleasant. You might wanna give weapons grade plutonium or "yellow cake" uranium oxide a try as a weed killer, too.
I was under the impression that glycol "rapidly biodegrades". wouldn't that mean it biodegrades before hitting the ground water?
Not all states have laws requiring embittering so a lot of antifreeze still tastes and smells sweet.
Somehow my 6 years of training as a chemist and environmental scientist tell me something a little different. If it's like sugar then why don't you just drink it? Methanol and Ethanol are both alcohols with just one carbon different but methanol will make you blind whereas ethanol will make you drunk. Look up malathion and parathion, they are a couple of other chemicals that are similar except one will kill humans quite easily and the other is relatively harmless. You might want to read up on solubility and biodegradation a little. Glycol and water do not readily separate and they sure won't separate by just dumping them in the ground. True chemicals like glycol can be degraded by putting them on soil but it isn't as simple as just dumping them out on the ground. The nitrates and nitrites commonly found in coolants can cause methemoglobinemia or blue baby syndrome in infants under 6 months old. This happens when they ingest water that contains these chemicals that "probably don't cause trouble".
