The release of contaminants from solidified low-level waste forms is being studied in a field lysimeter facility at the Hanford Site in southeastern Washington State. The lysimeter facility, constructed in 1984, consists of ten 3-m-deep by 1.8-m-diameter steel caissons surrounding a 4-m-deep central instrument caisson. Each lysimeter contains one field-scale waste form (210-L barrel), obtained from a commercial power reactor. Solidification agents being tested include masonry cement, Portland III cement, Dow polymer, and bitumen.

Most of the precipitation at the Hanford Site arrives as winter snow; this contributes to a strong seasonal pattern in water storage and drainage observed in the lysimeters. This seasonal pattern in storage corresponds to an annual range in the volumetric soil water content of 11% in late winter to 7% in the late summer and early fall. Annual changes in drainage rates cause pore water velocities to vary by nearly two orders of magnitude, from approximately 4 cm/week in early spring to less than 0.01 cm/week in early fall.

Measurable quantities of tritium and cobalt-60 are being collected in lysimeter drainage water. Approximately 30% of the original tritium inventory has been leached from the only two waste forms containing tritium. Cobalt-60 is contained in all waste form samples and is consistently being leached from five lysimeters. Total cobalt-60 collected from each of the five lysimeters varies, but in each case is less than 0.1% of the original cobalt inventory of the waste sample.