.,, 9. Test Reactor Area, Idaho National Engineering Laboratory (S.I.C. 28) At the Test Reactor Area of the Idaho National Engineering Laboratory ponds are used to dispose of low-level radioactive wastes, chemical wastes, and sanitary wastes. Se epage from three radioactive waste ponds since 1952 and from the chemi al waste pond has resulted in discrete, relativel,y small bodies of shallow perched ground water in the surface alluvium, at _depths of about 50 ft. Downward migration has created a second perched-water zone, at about 150 ft., in fineg rained water sediments within. the basalts. This deeper perched groundwater body has been formed by the combined seepage frolll above; it is centered under the area of the disposal ponds and was about 6,000 ft. long and 2,500 ft. wide in 1972. Some of the perched .water percolates downward through openings j.n the basalts and interbedded sedimentary layers to the Snake 'River Plain aquifer~ at depths of about 450 ft. Average dis.charge to the radioactive waste ponds has been about 200 million gallons per year from 1952 to 1973 . The total content of radionuclides averaged 1, 700 Ci (curies). per. year during the period 1971 to 1973. The majority of these has a short half-life and is. of little consequence. Chromium-51, however, was determined in a water sample from the main perched-water zone in 1972, indicating relatively.rapid seepage from the ponds. Other radionuclides were present in.the following concentrations: Tritium Cobalt~60 Strontium-90 353 pCi/ml (picocuries per millilitre) 6.4 pCi/ml 0.817 pCi/ml
The concentration of these radioactive constituents in the perched water varies relatively rapidly, according to the nature of the wastes that are being discharged to the ponds. With the exception of strontium-90, concentrations generally meet established standards for drinking water. Cesium~l37 has never been detected in water samples from the perched-water zone, although it is being discharged to the waste ponds in quantities exceeding those of strontium-90; apparently cesium is strongly adsorbed by clays and other minerals during seepage from. ~the ponds. Similarly, strontium is being adsorbed during its downward passage to the Snake River Plain aquifer, .and water samples from well. s tapping the aquifer in the rest Reactor Area have not contained detectable strontium. Evidence of seepage from the radioactive7waste ponds to the regional aquifer is found, however, in relatively high concentrations o.f tritium in water from deep wells in the area. A plume of high tritium content, slightly in excess of 150 pCi/ml, extends southward from the disposal ponds. A disposal pond for chemical (non-radioactive) wastes has been in use ,.. in the test Reactor Area since 1962. The discharg.ed waters, about 50 million gallons per year, co.nsist largely of sulfate and sodium, with minor amounts of sulfite, phosphate, and chloride. High specific conductance in water samples from .the main perched-water zone, in excess of 3,000 micromhos/cm, is indicative of increased total dissolved ~olids, largely due to seepage from the hemical waste pond. Relat;i.v.ely high specific conductance values determined in samples from the Snake River Plain.aquifer may be due to seepage from the disposal pond. It is more likely, however, that they reflect the injection of non-radioactive wastes directly into the aquifer through a deep well in the Test Reactor Area. The degree of contamination and the movement of contaminants in the .perched and regional ground-water bodies are being monitored in the I.N.E.L. area.