THE USE OF GEOCHEMICAL MASS-BALANCE AND MIXING MODELS TO DETERMINE GROUNDWATER SOURCES

The groundwater recharge system in the vicinity of the Idaho National Engineering Laboratory is complex, with potential recharge from horizo ntal regional flow from the NE, horizontal how originating in drainage basins N and NW of the site, streambed infiltration and infiltration of direct precipitation. Groundwater chemistry, tritium, delta D/delta (18)O, delta(34)S, delta(13)C and C-14 were measured at 9 wells along 2 groundwater flow paths at the Idaho National Engineering Laboratory. Geochemical mass balance and mixing models were used to determine gro undwater sources along the flow paths. Groundwater from the most dista l well, NPR-W01, was found to be a mixture of groundwater flow from th e NW, groundwater how from the NE and water from the Big Lost River. T he difference between measured and calculated C-14 concentrations at t his well indicate that the source waters are modern, which is consiste nt with the rapid horizontal how velocities of groundwater in the East ern Snake River Plain aquifer. Copyright (C) 1996 Published by Elsevie r Science Ltd