Vertical variation in groundwater chemistry inferred from fluid specific-conductance well logging of the Snake River Plain Basalt aquifer, Idaho National Engineering Laboratory, southeastern Idaho

Well logging of electrical fluid specific conductance (Cs) shows that permeable zones yielding ground water to intrawell flows and the water columns in some wells at INEL have highly different chemistry, with as much as a two-fold variation in Cs. This suggests that dedicated-pump sampling of ground water in the aquifer may not be representative of the chemistry of the waste plumes migrating southwest of the nuclear facilities. Natural background Cs in basalt-aquifer ground water of this part of the Snake River Plain aquifer is less than 325μS/cm (microSiemans/cm), and total dissolved solids in mg/L units, (TDS) ∼ 0.6Cs. This relationship underestimates TDS for waters with chemical waste, when Cs is above 800 μS/cm. At well 59 near the ICPP water of 1115 μS/cm (∼6570+ mg/L TDS) enters the well from a permeable zone between 521 and 537 ft depth; the zone being 60 ft below the water level and water of 550 μS/cm. At the time of logging (9/14/93) the 1115/μS/cm water was flowing down the well, mixing with less concentrated waters and exciting at 600 or 624-ft depth. Waste water disposed of down the injection well at ICPP until 1984 was estimated to have a C5 of 1140 μS/cm, identical to the water detected in logging. 29 refs., 8 figs., 1 tab