PNNL

Aerial photo of the Prototype Hanford Barrier in August 1995, shortly after construction in 1994.

A decades-long study of a surface cover for isolating underlying waste from intrusion and reducing or stopping the movement of precipitation into the waste has shown promise for use at the Department of Energy Hanford Site and beyond.

Known as the Prototype Hanford Barrier (PHB), the surface cover consists of the following main components:

a silt loam evapotranspiration layer with an underlying capillary break and a layer to prevent intrusion (termed the evapotranspiration-capillary [ETC] barrier) in the middle an asphalt concrete barrier and compacted soil layer at the bottom a gentle gravel slope and a steep basalt riprap slope

The ETC barrier is the centerpiece of the PHB and sits directly above the waste zone. It stores precipitation, releases stored water into atmosphere, and deters intrusion by plants, animals, and humans. The asphalt concrete barrier is redundant with the ETC barrier to divert drainage and to hinder intrusion. The two side slopes protect the barrier from damage or intrusion.

Cross-section view of the Prototype Hanford Barrier overlying the 216-B-57 waste crib at the Hanford Site. Enlarge Image

The PHB was built between 1993 and 1994 over an underground waste crib beneath the Hanford Site’s Central Plateau, and has been monitored ever since.

Under federal regulations, the barrier must last for at least 1,000 years. To demonstrate that the PHB can do this, researchers subjected it to a variety of possible conditions, including three years of simulated heavy (three times the average) precipitation, a simulated extreme rainstorm (known as a 24-hour, 1,000-year return rainstorm), and a controlled fire that burned the vegetation from half of the barrier surface.

The results of the study will soon be released by DOE in a report prepared by PNNL. The report indicates that the PHB will very likely perform for at least the remainder of its 1,000-year design life. Construction, monitoring, and the reporting on the PHB are the result of the efforts of many individuals from several organizations over the years, including the Department of Energy, PNNL, Bechtel National, Inc., CH2M Hill, and Westinghouse Hanford Company.