AGE DATING GROUND WATER BY USE OF CHLOROFLUOROCARBONS (CC13F AND CC12F2), AND DISTRIBUTION OF CHLOROFLUOROCARBONS IN THE UNSATURATED ZONE, SNAKE RIVER PLAIN AQUIFER, IDAHO NATIONAL ENGINEERING LABORATORY, IDAHO by Eurybiades Busenberg, Edwin P. Weeks, L. Niel Plummer, and Roy C. Bartholomay U.S. GEOLOGICAL SURVEY Water-Resources Investigations Report 93-4054 Prepared in cooperation with the U.S. DEPARTMENT OF ENERGY Idaho Falls, Idaho April 1993 U.S. DEPARTMENT OF INTERIOR Bruce Babbitt, Secretary U.S. GEOLOGICAL SURVEY Dallas L. Peck, Director For additional information Copies of this report can be write to: purchased from: U.S. Geological Survey U.S. Geological Survey Idaho National Engineering Laboratory, MS 4148 Books and Open-File Reports Section P.O. Box 2230 Box 25425, Federal Center Idaho Falls, ID 83403 Denver, CO 80225 -11- CONTENTS Page Abstract..................................................................................................................................... 1 Introduction.............................................................................................................................. 2 Purpose and Scope .............................................................................................................. 3 Geohydrologic setting......................................................................................................... 3 Methods of study...................................................................................................................... 6 Collection and analysis of ground-water samples for nitrogen, oxygen, argon, and carbon dioxide.......................................................................................................... 6 Collection and analysis of ground-water and soil-gas samples for chlorofluorocarbons....................................................................................................... 6 Estimation of recharge-water temperature...................................................................... 7 Selected characteristics of ground water............................................................................... 10 Dissolved-gas content.......................................................................................................... 10 Chlorofluorocarbon content............................................................................................... 14 Age dating ground water by use of chlorofluorocarbons ..................................................... 18 Reconstruction of the chlorofluorocarbon concentrations in the atmosphere............. 18 Chlorofluorocarbon-model ages of recharge..................................................................... 21 Uncertainties in chlorofluorocarbon-model recharge ages of old and young ground water................................................................................................................... 22 Ground waters contaminated with chlorofluorocarbons................................................ 25 Age of recharge at the Idaho National Engineering Laboratory................................... 29 Distribution of chlorofluorocarbons in the unsaturated zone ............................................ 31 Radioactive Waste Management Complex........................................................................ 31 Test Area North................................................................................................................... 33 Summary and conclusions....................................................................................................... 40 References cited........................................................................................................................ 41 ILLUSTRATIONS Figure 1. Location of the Idaho National Engineering Laboratory and selected facilities.............................................................................................................. 5 2. Dissolved nitrogen and argon compositions of ground waters collected at and near Idaho National Engineering Laboratory....................................... 13 -111- Page 3. Concentrations of chlorofluorocarbon-11, and chlorofluorocarbon-12 in the atmosphere ................................................................................................. 20 4. Locations of selected wells and model chlorofluorocarbon-11 and chlorofluorocarbon-12 recharge dates, Idaho National Engineering Laboratory and vicinity ................................................................................... 27 5. Locations of selected wells and model chlorofluorocarbon-11 and chlorofluorocarbon-12 recharge dates, Test Reactors Area and Radioactive Waste Management Complex.......................................................................... 28 6. Measured and simulated concentrations of chlorofluorocarbon-11 and chlorofluorocarbon-12 with depth in the unsaturated zone at an instal­ lation near Test Area North at Idaho National Engineering Laboratory.. 39 TABLES Table 1. Dissolved-gas compositions of ground waters............................................... 11 2. Well construction and water levels at the time of sampling, Idaho National Engineering Laboratory, Idaho....................................................................... 12 3. Concentrations of dissolved chlorofluorocarbon-11 and chlorofluoro­ carbon-12 in ground waters from Idaho National Engineering Laboratory, Idaho.................................................................................................................. 15 4. Yearly average concentrations of chlorofluorocarbon-11 and chlorofluoro­ carbon-12 in the atmosphere........................................................................... 19 5. The effects recharge of temperature on the model chlorofluorocarbon dates................................................................................................................... 23 6. The effects of elevation on the model chlorofluorocarbon dates................. 24 7. Concentrations of chlorofluorocarbon-11 and chlorofluorocarbon-12 in the unsaturated zone at Idaho National Engineering Laboratory, Idaho.................................................................................................................. 32 8. Molecular diffusion constant for the diffusion of gas A into gas B (DAB), liquid partitioning coefficients (Kw), and sorptivity to geologic materials (Kg) of chlorofluorocarbon-11 and chlorofluorocarbon-12........................... 36 9. The total porosity Op), the gas filled porosity (#D), and the tortuosity factor for the added resistance imposed by the structure of the porous medium (T), given as a function of depth and geologic material................................. 37 -IV- CONVERSION FACTORS, VERTICAL DATUM, AND ABBREVIATED WATER-QUALITY UNITS Multiply By To obtain millimeter (mm) 3.937 X10-2 incn centimeter (cm) 3.937 X 1(H inch meter (m) 3.281 X10° foot kilometer (km) 6.214 X10-1 mile square centimeter (cm2) 1.550 X 10-1 square inch square kilometer (km2) 3.861 X 10-1 square mile cubic centimeter (cm3) 6.102 X 10-2 cubic inch cubic meter (m3) 3.531 X 10 1 cubic foot milliliter (mL) 6.102 X 10-2 cubic inch liter (L) 2.642 X10-1 gallon picogram (pg) 3.527 X10-14 ounce gram (g) 2.205 X10-3 pound kilogram (kg) 2.205 XIQO pound kilopascal (kPa) 6.895 X 10° pound per square inch Temperature is given in degrees Celsius (°C), which can be converted to degrees Fahrenheit (°F) by use of the following equation: °F = 1.8(°C) + 32 Sea level: In this report "sea level" refers to the National Geodetic Vertical Datum of 1929--a geodetic datum derived from a general adjustment of the first-order level nets of the United States and Canada, formerly called Sea Level Datum of 1929. Abbreviated water-quality units used in this report: Chemical concentrations of con­ stituents dissolved in water are given in milligrams per liter (mg/L) or micrograms per liter 0<g/L). Specific conductance of water is expressed in microsiemens per centimeter at 25 degrees Celsius (/<S/cm). -v- AGE DATING GROUND WATER BY USE OF CHLOROFLUOROCARBONS (CC13F AND CC12F2), AND DISTRIBUTION OF CHLOROFLUOROCAR­ BONS IN THE UNSATURATED ZONE, SNAKE RIVER PLAIN AQUIFER, IDAHO NATIONAL ENGINEERING LABORATORY, IDAHO by Eurybiades Busenberg, Edwin P. Weeks, L. Niel Plummer, and Roy C. Bartholomay ABSTRACT Detectable concentrations of chlorofluorocarbons (CFC's) were observed in ground water and unsaturated-zone air at the Idaho National Engineering Laboratory (INEL) and vicinity. The recharge ages of waters were determined to be from 4 to more than 50 years on the basis of CFC concentrations and other environmental data; most ground waters have ages of 14 to 30 years. These results indicate that young ground water was added at various locations to the older regional ground water (greater than 50 years) within and outside the INEL boundaries. The wells drilled into the Snake River Plain aquifer at INEL sampled mainly this local recharge. The Big Lost River, Birch Creek, the Little Lost River, and the Mud Lake-Terreton area appear to be major sources of recharge of the Snake River Plain aquifer at INEL. An average recharge temperature of 9.7±1.3°C (degrees Celsius) was calculated from dissolved nitrogen and argon concentrations in the ground waters, a temperature that is similar to the mean annual soil temperature of 9°C measured at INEL. This similarity indicates that the aquifer was recharged at INEL and not at higher elevations that would have cooler soil