If it's actually coolant (make sure), you need to trace it up from the puddle to the highest point you see it. There are several potential sources for leaks on that side. Bypass hoses, water pump gasket, water pump weep hole, heater hoses, etc. We can't tell you what it is, you have to find it.

Rule out Head Gaskets. We've seen one or two POSSIBLE head gasket failures with 9000 members over almost 6 years here.