This report was .prepared as an account of work sponsored by an agency of the United States Government. Neither the United States Government nor any agency thereof, nor any of their employees, make any warranty, express or implied, or assumes a n y legal liability or responsibility for the accuracy, completeness, or usefulness of any information, apparatus, product, or process disclosed, or represents that its use would not infringe privately owned rights. Reference herein to any specific commercial product, process, or service by trade name, trademark, manufacturer, or otherwise does not necessarily constitute or imply its endorsement, recommendation, or favoring by t h e United States Government or any agency thereof. The views and opinions of authors expressed herein do not necessarily state or reflect those of the United States Government or any agency thereof.

This report documents the range and the upper limit for background concentrations of radionuclides and radioactivity in soils and river sediments that occur as natural rock-forming minerals and worldwide fallout from atmospheric nuclear weapons tests. Documentation is based on the collection of soil and sediment in northern New Mexico and analyzed for 137 Cs, 238 Pu, 23a240 p U! 90 Sr. total uranium, gross gamma, and tritium. The data used to establish the statistical range and upper limit of background concentration cover a 9-or 13-year period ending in 1986. The knowledge of background levels is necessary to interpret soil and sediment data collected for the annual environmental surveillance report and other reports relating to radionuclides or radioactivity in soils and sediments.

Mesita del. Buey is used for the disposal of wastes contaminated by rudionuclides, of toxic or explosive chemicals, and of classified materials. These are buried in pits or shafts dug into the mesa surface. The mesa, covered by a clay-like soil, is underlain by a series of ashfalls of rhyolite tuff is from 240 to 5S0 ft thick. The tuffs are above the main aquifer of the Los Alamos area which lies at a depth of about 1,000 ft. Stream flow in adjacent canyons is intermittent. Water in the alluvium of the stream-connected aquifer in the canyon south of the mesa is recharged by storm runoff. The hydrologic characteristics and conditions of the soil, tuff, and seal material used to cover the wastes indicate no recharge to the stream-connocted aquifer or main aquifer through the soil, buried wastes, or tuff at Mesita del Buey.

The distribution of Pu, 241Am, and water in Bandelier Tuff beneath a former liquid waste disposal site at Los Alamos was investigated. The waste use history of the site was described, as well as the previous field and laboratory studies of radionuclide migration performed at this site. One of the absorption beds studied had 20.5 m of water added to it in 1961 in an aggressive attempt to change the distribution of radionuclides in the tuff beneath the bed. Plutonium and 241Am were detected to sampling depths of 30 m in this bed, but only found to depths of 6.5 to 13.41 m in an adjacent absorption bed (bed 2) not receiving additional water in 1961. After 17 yr of migration of the slug of water added to bed 1, 0.3 to 5.1% of the Pu inventory and 3.0 to 49.6% of the 241Am inventory was mobilized within the 30‐m sampling depth, as less than one column volume of water moved through the tuff profile under the bed. The results of similar lab and field studies performed since 1953 were compared with our 1978 data and site hydrologic data was used as a time marker to estimate how fast radionuclide migration occurred in the tuff beneath absorption bed 1. Most of the radionuclide migration appeared to have occurred within 1 yr of the 20.5‐m water leaching in 1961. The implications of our research results to nuclear waste management were also discussed.

Cover photo: An aerial view of Fenton Hill geothermal site, looking south toward Albuquerque. An Affirmative ActwnlEqual %tunity Employer 30 NOT M I C R O~I L~ COVER This report ums prepared as an account of work sponsored by an agency of the United Stafes Guvernment. Neither The Regents of the Unimity of California, the United States Government w any agency thereof, nor any of their employees, makes any warranty, express or implied, or assumes any legal liability or responsibilityfor the accuracy, completeness, OT usefulness of any information, apparatus, product, or process disclosed, or represents that its use mould not infringe primtely owned rights. Reference herein to any specific commercial product, process, or seroice by trade name, trademark, manufacturer, or otherwise, does not n e e y i i amstitute or imply its endorsement, recommendation, or fnwring by The Regents ofthe Unmemty of Gdijbmia, the United States Government or any agency thereof. The views and opinions of authors expressed herein do not necessarily state or refed those of The Regents of the University of Gdifornia, the United States Govenrment or any agency thereof.