The plaintiffs' case rests on a number of circumstantial inferences, not on hard proof. They allege that TCE found in Wells G and H caused leukemia, yet half of the leukemia cases in Woburn were in areas NOT served by these wells. They allege that Wells G and H were contaminated by chemicals dumped by Grace that traveled through the groundwater, but half of the water from the wells came not from the groundwater but directly from the Aberjona River, which has been contaminated from many sources over many years. Taken together, these facts indicated that the plaintiffs' argument is no more than unsubstantiated speculation.