Dissolved Organic Carbon Concentrations and Compositions, and Trihalomethane Formation Potentials in Waters from Agricultural Peat Soils, Sacramento-San Joaquin Delta, California: Implications for Drinking-Water Quality By Roger Fujii, Anthony J. Ranalli, George R. Aiken, and Brian A. Bergamaschi U.S. GEOLOGICAL SURVEY Water-Resources Investigations Report 98–4147 Prepared in cooperation with the California Department of Water Resources 6217-37 Sacramento, California 1998 U.S. DEPARTMENT OF THE INTERIOR BRUCE BABBITT, Secretary U.S. GEOLOGICAL SURVEY Thomas J. Casadevall, Acting, Director The use of firm, trade, and brand names in this report is for identification purposes only and does not constitute endorsement by the U.S. Geological Survey. For additional information write to: Copies of this report can be purchased from: District Chief U.S. Geological Survey U.S. Geological Survey Information Services Placer Hall, Suite 2012 Box 25286 6000 J Street Federal Center Sacramento, CA 95819-6129 Denver, CO 80225 CONTENTS Abstract.................................................................................................................................................................................. 1 Introduction ........................................................................................................................................................................... 2 Description of Study Site and Study Design ......................................................................................................................... 5 Hydrologic Framework for Study Design ................................................................................................................... 6 Sampling and Analytical Approach ............................................................................................................................. 8 Dissolved Organic Carbon Concentrations............................................................................................................................ 11 Upper Soil Zone........................................................................................................................................................... 11 Lower Soil Zone .......................................................................................................................................................... 12 Drainage Ditch............................................................................................................................................................. 15 Composition and Reactivity of Dissolved Organic Carbon................................................................................................... 16 Specific Ultraviolet Absorbance .................................................................................................................................. 16 Fractionation of Dissolved Organic Carbon into Hydrophobic and Hydrophilic Acids.............................................. 18 Trihalomethane Formation Potential ........................................................................................................................... 19 Upper and Lower Soil Zones....................................................................................................................................... 21 Trihalomethane Formation Potential of Isolated Fractions ......................................................................................... 24 Summary and Conclusions .................................................................................................................................................... 27 Conclusions ................................................................................................................................................................. 28 Summary of Supporting Observations......................................................................................................................... 28 Dissolved Organic Carbon Concentrations........................................................................................................ 28 Quality and Composition of Dissolved Organic Carbon................................................................................... 29 Trihalomethane Formation ................................................................................................................................ 29 Other Significant Observations.................................................................................................................................... 30 Implications of Study Results...................................................................................................................................... 30 References Cited.................................................................................................................................................................... 30 Appendix A: Field and Sample Collection Methods ............................................................................................................. 34 Installation of Samplers............................................................................................................................................... 34 Sample Collection and Field Measurements ............................................................................................................... 34 Appendix B: Dissolved Organic Carbon and Ultraviolet Absorption Measurements ........................................................... 45 Appendix C: Dissolved Organic Carbon Fractionation and Isolation ................................................................................... 49 Appendix D: U.S. Geological Survey Trihalomethane Methods .......................................................................................... 54 Background.................................................................................................................................................................. 54 The Chemistry of Disinfection Byproduct Formation................................................................................................. 54 Methods Employed by the U.S. Geological Survey Laboratory for Trihalomethane Formation Potential Analysis........................................................................................................................... 55 Appendix E: Carbon-13 Nuclear Magnetic Resonance Analyses ......................................................................................... 58 Introduction ................................................................................................................................................................. 58 Results ......................................................................................................................................................................... 58 Appendix F: Preliminary Data for Wetland-Habitat Ponds ................................................................................................... 70 FIGURES 1-2. Maps showing: 1. Location of the study area, Twitchell Island, Sacramento-San Joaquin Delta, California....................................... 3 2. Location of the lysimeters and piezometers in the agricultural field study site, Twitchell Island, California ......... 4 3-4. Schematics showing: 3. Typical installation of lysimeter and piezometer pairs for sampling soil water from the upper and lower soil zones ........................................................................................................................................................ 6 4. Simplified conceptual hydrologic model of the field studied................................................................................... 7 Contents III 5. Graph showing specific conductance of lysimeter samples, December 1995–January 1997......................................8 6. Schematic showing XAD isolation procedure...........................................................................................................10 7–24. Graphs showing: 7. Dissolved organic carbon concentrations for lysimeter samples, February 1996–January 1997 ...........................11 8. Dissolved oxygen concentrations for piezometer samples, August 1996–April 1997 ...........................................13 9. Redox potential measurements for piezometer samples, August 1996–April 1997...............................................13 10. Dissolved organic carbon concentrations for piezometer samples, February 1996–January 1997 ........................14 11. Specific conductance of piezometer samples, December 1995–January 1997.......................................................15 12. Dissolved organic carbon concentrations in samples from the drainage ditch, February 1996–January 1997 ......16 13. Specific ultraviolet absorbance for lysimeter, piezometer, and drainage ditch samples, February 1996–January 1997..................................................................................................................................17 14. Fractionation of dissolved organic carbon into hydrophobic and hydrophilic acids, for lysimeter, piezometer, and drainage ditch samples, February 1996–January 1997.................................................................19 15. Comparison of reactivity-based and dose-based trihalomethane formation potential measurements....................20 16. Relation between trihalomethane formation potential and dissolved