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Final Report (Posted 4/21) FINAL REPORT Compound Specific Isotope Analysis of Mineral-Mediated Abiotic Reduction of Nitro Compounds SERDP Project ER-2618 APRIL 2021 William A. Arnold Matthew J. Berens Yiran Tong Jennifer H. Strehlau University of Minnesota Thomas B. Hofstetter Bridget A. Ulrich Eawag, Swiss Federal Institute of Aquatic Science and Technology Distribution Statement A This report was prepared under contract to the Department of Defense Strategic Environmental Research and Development Program (SERDP). The publication of this report does not indicate endorsement by the Department of Defense, nor should the contents be construed as reflecting the official policy or position of the Department of Defense. Reference herein to any specific commercial product, process, or service by trade name, trademark, manufacturer, or otherwise, does not necessarily constitute or imply its endorsement, recommendation, or favoring by the Department of Defense. Form Approved REPORT DOCUMENTATION PAGE OMB No. 0704-0188 Public reporting burden for this collection of information is estimated to average 1 hour per response, including the time for reviewing instructions, searching existing data sources, gathering and maintaining the data needed, and completing and reviewing this collection of information. Send comments regarding this burden estimate or any other aspect of this collection of information, including suggestions for reducing this burden to Department of Defense, Washington Headquarters Services, Directorate for Information Operations and Reports (0704-0188), 1215 Jefferson Davis Highway, Suite 1204, Arlington, VA 22202- 4302. Respondents should be aware that notwithstanding any other provision of law, no person shall be subject to any penalty for failing to comply with a collection of information if it does not display a currently valid OMB control number. PLEASE DO NOT RETURN YOUR FORM TO THE ABOVE ADDRESS. 1. REPORT DATE (DD-MM-YYYY) 2. REPORT TYPE 3. DATES COVERED (From - To) 21-04-2021 SERDP Final Report June, 2016 – April 2021 4. TITLE AND SUBTITLE 5a. CONTRACT NUMBER WQ912HQ-16-C-0014 P00001 Compound Specific Isotope Analysis of Mineral-Mediated 5b. GRANT NUMBER Abiotic Reduction of Nitro Compounds 5c. PROGRAM ELEMENT NUMBER 6. AUTHOR(S) 5d. PROJECT NUMBER ER 2618 Matthew J. Berens, Yiran Tong, Bridget A. Ulrich, 5e. TASK NUMBER Jennifer H. Strehlau, Thomas B. Hofstetter, William A. Arnold 5f. WORK UNIT NUMBER 7. PERFORMING ORGANIZATION NAME(S) AND ADDRESS(ES) 8. PERFORMING ORGANIZATION REPORT NUMBER Department of Civil, Environmental, and Geo- Engineering University of Minnesota ER 2618 500 Pillsbury Dr. SE Minneapolis, MN 55455 9. SPONSORING / MONITORING AGENCY NAME(S) AND ADDRESS(ES) 10. SPONSOR/MONITOR’S ACRONYM(S) Strategic Environmental Research and Development Program SERDP (SERDP) 4800 Mark Center Drive, Suite 16F16 11. SPONSOR/MONITOR’S REPORT Alexandria, VA 22350-3605 NUMBER(S) ER 2618 12. DISTRIBUTION / AVAILABILITY STATEMENT Distribution Statement A: Approved for Public Release, Distribution is Unlimited 13. SUPPLEMENTARY NOTES ii 14. ABSTRACT Methods are needed to verify that abiotic attenuation of energetic compounds, such as trinitrotoluene (TNT) and hexahydro-1,3,5-trinitro-1,3,5-triazine (RDX), in groundwater is occurring, and it must also be possible to verify that strategies to enhance abiotic processes are having the desired effects. The overall objective of the project is to quantify the isotope fractionation factors of nitro compounds, including new components in insensitive munitions, during their abiotic reactions with iron bearing minerals. The central hypothesis is that abiotic attenuation processes will lead to specific fractionation of carbon (C) and nitrogen (N) contained with the pollutants. Specific objectives were to measure isotope enrichment factors during the abiotic reduction of nitroaromatic and nitramine explosives and assess how solution conditions and multiple reduction cycles influenced these values. Testing of the overall objective was met by accomplishing the following overall tasks 1) Mineral Synthesis and Characterization, 2) Kinetic Studies with Synthetic Minerals, 3) Compound Specific Isotope Analysis (CSIA) method development, 4) Kinetic Studies with Natural Materials, and 5) Testing of Regeneration/Enhancement of Reactivity. CSIA was performed on samples collected from batch and column reactors in tasks 2, 4, and 5. Reaction conditions (mineral identity, pH, presence of natural organic matter) influence reaction kinetics, but the isotope fractionation of N and C is unaffected by reaction conditions. Additionally, the fractionation measured with natural materials is similar to that with synthetic materials, and regeneration of reactivity with dithionite also leads to consistent isotope fractionation. Experiments in column reactors and samples from a field site reveal that transport processes make the interpretation of isotope fractionation more difficult, but ancillary data (including the presence of reaction products) allow assessment as to whether reduction of nitroaromatic and nitramine explosives is occurring. This project has developed the tools necessary to assess if abiotic reduction is occurring in groundwater in situations where natural attenuation or an active remediation technology is being applied. While ancillary data is helpful in making the assessment, CSIA measurements are able to provide information as to 1) whether degradation is occurring, 2) the process responsible for the degradation, and 3) the extent of degradation versus dilution/non-degradative processes leading to concentration decreases. The methodologies will allow more robust information to be collected for evaluation of remediation success by responsible parties, practitioners, and stakeholders. 15. SUBJECT TERMS Nitro explosives, groundwater, reduction, natural attenuation, remediation, compound specific isotope analysis 16. SECURITY CLASSIFICATION OF: 17. LIMITATION 18. NUMBER 19a. NAME OF RESPONSIBLE PERSON OF ABSTRACT OF PAGES Dr. William Arnold a. REPORT b. ABSTRACT c. THIS PAGE UNCLASS 164 19b. TELEPHONE NUMBER (include area U U U code) NCLASS NCLASS NCLASS 612-625-8582 Standard Form 298 (Rev. 8-98) Prescribed by ANSI Std. Z39.18 iii 1 TABLE OF CONTENTS 1 Table of Contents .................................................................................................................. iv 2 List of Tables ......................................................................................................................... vi 3 List of Figures ..................................................................................................................... viii 4 List of Acronyms................................................................................................................ xvii 5 Abstract .................................................................................................................................. 1 6 Executive Summary ............................................................................................................... 2 7 Objectives ............................................................................................................................. 11 8 Background .......................................................................................................................... 13 8.1 Energetic compounds as contaminants .......................................................................... 13 8.2 Compound specific isotope analysis (CSIA) .................................................................. 14 8.3 Insensitive munitions ...................................................................................................... 16 8.4 RDX ................................................................................................................................ 18 8.5 Summary ......................................................................................................................... 19 9 Materials and Methods ....................................................................................................... 21 9.1 Chemicals and Materials ............................................................................................... 21 9.2 Mineral synthesis and characterization methods ........................................................... 21 9.2.1 Iron (oxyhydr)oxides .............................................................................................. 21 9.2.2 Green rust ................................................................................................................ 21 9.2.3 Chemically reduced smectites ................................................................................. 21 9.2.4 Characterization of synthetic minerals .................................................................... 23 9.3 Synthesis of RDX ............................................................................................................ 23 9.4 Batch experiments with synthetic minerals .................................................................... 23 9.5 Analytical methods and kinetics calculations ................................................................ 24 9.6 Natural Materials ........................................................................................................... 25 9.6.1 Collection of Natural Materials. ............................................................................. 25 9.6.2 Characterization of natural materials. ....................................................................
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