JOINT RUSSIAN-AMERICAN HYDROGEOLOGICAL-GEOCHEMICAL STUDIES OF THE KARACHAI-MISHELYAK SYSTEM, SOUTH URALS, RUSSIA

In September 1994, a Russian-American team conducted hydrogeological, geochemical, geophysical, and radiometric measurements in the territor y of the Mayak Production Association, Russia. The primary purpose of these operations was to examine the frontal area of a radioelement- an d nitrate-laden groundwater plume moving from the disposal site, Lake Karachai, toward the Mishelyak River. Activities encompassed (1) isola tion of hydrologic intervals in two wells and production of water from these intervals, to compare isolated versus open-well sampling method s and to determine hydraulic transmissivities of the aquifer(s); (2) s urface and soil-water sampling, accompanying radiometric measurements and subsequent chemical analyses; and (3) electrical resistivity profi ling in areas of expected contrasting resistivity. Preliminary results indicate that (1) Co-60, Cs-137, and Sr-90 are present in small conce ntrations (similar to 0.1% of permissible levels) in water of the Mish elyak River; (2) analyses of water samples collected by a downhole sam pler and of water produced from packed-off intervals agree within limi ts of laboratory accuracy, attesting to the efficacy of the sampling m ethods presently used by the Russian workers; (3) considerable differe nces in contaminant concentrations exist between nearby wells, support ing the concept that the plume from Lake Karachai toward the Mishelyak River is controlled by steeply dipping fractures and shear zones; and (4) strong contrasts occur between the electrical resistivities of so il and bedrock. Further collaborative work is strongly recommended and should include more detailed isolation of intervals in wells by multi -packer installations, to better determine the geochemical and hydrolo gical characteristics of the Karachai-Mishelyak system; deployment of a broader soil water and soil sampling array; a more detailed examinat ion of the distribution and concentration of radionuclides by high-res olution field gamma spectrometry; and a detailing of the area's electr ical resistivity setting, using a mobile electromagnetic measurement s ystem.