CHARACTERIZATION OF THE B-BX-BY WASTE MANAGEMENT AREA, HANFORD SITE, WASHINGTON

The purpose of the 200 Areas Vadose Zone Characterization Project is to detect and quantify naturally occurring and man-made gamma-emitting radionuclides in the vadose zone by logging existing boreholes at the Hanford Site.

High-resolution spectral gamma log data have been acquired in more than 260 vadose zone boreholes and groundwater monitoring wells located in and near the B-BX-BY Waste Management Area (WMA). In addition to three tank farms (underground waste storage), this area includes several major radioactive liquid waste disposal sites. Man-made uranium was detected only in the vadose zone northeast of tank BX-102 (BX Tank Farm) and in one borehole near the 216-B-7B Crib.

A subsurface plume of man-made uranium contamination has been identified. This uranium originates near tank BX-102 and appears to intercept groundwater at a depth of approximately 250 ft and a lateral distance of 400 ft northeast from its presumed source. Geophysical log data indicate that this contamination reached this point between 1991 and 1997. Uranium migration may be following a stratigraphic dip northeast. Groundwater monitoring data collected by Pacific Northwest National Laboratory indicate that uranium was first detected in groundwater in January 1994 northeast of tank BX-102. Since 1994, the uranium plume in the groundwater appears to have migrated to the northwest.

Results of the 200 Areas Vadose Zone Characterization Project are posted on the Internet at: http://www.gjo.doe.gov/programs/hanf/HTFVZ.html.