[en] Practically all the water used in tree photosynthesis comes from the soil. In 1979 it became apparent that some of the tritium in groundwater from the Solid Waste Disposal Facility (a low-level radioactive waste burial ground) was being released to the environment through an outcrop to a surface stream. Because of inadequacies in historical stream and groundwater records in the vicinity of the outcrop, it was decided to investigate the tree ring tritium concentration in the forest which covers most of the area. Results of the comparison of analytical methods suggest that extraction of pure hollocellulose is not necessary, and that there may have been some increase in tritium activity as early as 1972. The tritium activity in the rings increases sharply in 1974 and has a pronounced upward trend through 1985; it then drops after 1985 and begins rising again in 1990. It appears that the tritium plume reached the surface outcrop between 1972 and 1974