Hydrology of the National Reactor Testing Station, Idaho, 1966

This annual report describes studies by the U. S. Geological Survey, sponsored by the U. S. Atomic Energy Commission, to determine the hydrologic effects of disposal of radioactive waste to the ground at the National Reactor Testing Station. The project has involved the collection and analyses of ground-and surface-water samples for radiometric and chemical changes. Results have been evaluated and mapped. Ground-water levels have also been mapped over the station. The net ground-water consumption after pumpage and waste injection has been determined. Two billion gallons of water were pumped during 1966 of which 40 percent was metered and returned to the Snake Plain aquifer.

A record runoff of the Big Lost River during 1965 and 1966 induced a large amount of recharge to the Snake Plain aquifer. The recharge caused water levels to rise as much as six feet, but apparently did not have a great effect on the concentrations of waste products in the ground water. Pressure transmission, or mass transfer effects from the recharge, were observed as far as 50 miles southwest of the river.

Tritium is the primary radioactive waste product discharged to the subsurface. Several aspects of tritium disposal have been studied in detail at the TRA (Test Reactor Area) and the ICPP (Idaho Chemical Processing Plant) areas. The distribution of waste tritium in the Snake Plain aquifer has been mapped, and background levels were determined to range from 0.05 to 0.1 pCi/m1 (picocuries per milliliter). Waste tritium in water from the Snake Plain aquifer has been detected 4-1/2 miles south of the ICPP. An estimated mass balance of total tritium remaining in the Snake Plain aquifer is presented for the TRA and ICPP areas. About 21,500 Ci (curies) of tritium at the ICPP and about 3,700 Ci at the TRA have been disposed from 1952 through 1966. About 14,000 Ci and 2,700 Ci of tritium, respectively, should remain after radioactive decay. Similar amounts are indicated to be present in the ground water. Waste tritium has been used as a tracer in studies of the complex flow characteristics of the aquifer in the ICPP area.

Dissolved chromium has been used to trace TRA pond waste water in perched ground-water bodies and downgradient 2-1/2 miles in the Snake Plain aquifer. Concentrations of hexavalent chromium ranged as high as 1.7 ppm (parts per million) in the perched water and 0.4 ppm in the water from the Snake Plain aquifer. Chromium serves as a good tracer of TRA wastes because it does not occur in nearby ICPP wastes, is not usually present in natural waters, and can be determined in very low concentrations.

Natural fluoride in the water of the Snake Plain aquifer has been used to trace the ground-water flow downgradient from the northeast end of the Snake River Plain. The fluoride, which is dissolved from certain rocks, indicates recharge areas and flow paths in the aquifer.

A project to test the feasibility of disposing radioactive gases into the ground is presently underway. A seismic survey was used to map surface sediment thickness, and two test wells were cored to evaluate potential injection-well sites.

A "breathing" well has been instrumented to study flow rates, temperature, humidity, and other aspects of vertical flow of air in the well. Results of the continuing study are presented.

Studies made on several wells which had vertically flowing borehole water indicated that the physical and chemical properties of the water are influenced by the flow. One well with downward flow had a head difference of 0.01 to 0.07 foot between two permeable zones throughout the year.