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Seepage Chemistry Manual RECLAMManagAingTWateIr iOn theNWest Report DSO-05-03 Seepage Chemistry Manual Dam Safety Technology Development Program U.S. Department of the Interior Bureau of Reclamation Technical Service Center Denver, Colorado December 2005 Form Approved REPORT DOCUMENTATION PAGE OMB No. 0704-0188 The 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 the collection of information. Send comments regarding this burden estimate or any other aspect of this collection of information, including suggestions for reducing the 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) 12-2005 Technical 4. TITLE AND SUBTITLE 5a. CONTRACT NUMBER Seepage Chemistry Manual 5b. GRANT NUMBER 5c. PROGRAM ELEMENT NUMBER 6. AUTHOR(S) 5d. PROJECT NUMBER Craft, Doug 5e. TASK NUMBER 5f. WORK UNIT NUMBER 7. PERFORMING ORGANIZATION NAME(S) AND ADDRESS(ES) 8. PERFORMING ORGANIZATION REPORT Bureau of Reclamation, Technical Service Center, D-8290, PO Box 25007, NUMBER Denver CO 80225 DSO-05-03 9. SPONSORING/MONITORING AGENCY NAME(S) AND ADDRESS(ES) 10. SPONSOR/MONITOR’S ACRONYM(S) Bureau of Reclamation Denver, Colorado 11. SPONSOR/MONITOR’S REPORT NUMBER(S) DSO-05-03 12. DISTRIBUTION/AVAILABILITY STATEMENT National Technical Information Service, 5285 Port Royal Road, Springfield, VA 22161 13. SUPPLEMENTARY NOTES 14. ABSTRACT Gypsum, anhydrite, calcite, dolomite, and halite are soluble minerals that are common in the western United States where the Bureau of Reclamation has constructed many dams. Dams sited on foundations and abutments containing soluble minerals have the potential to develop seepage problems that require monitoring by water resource managers. When mineral dissolution is suspected at a dam, seepage samples may be collected, analyzed and compared to reservoir water to help determine whether soluble minerals pose a structural safety problem. Seepage chemistry investigations are interdisciplinary and require collaboration among chemists, geologists, engineers, and geophysicists. This peer reviewed technical report summarizes the basic chemistry associated with mineral dissolution, weathering, biotic processes and mixing, all of which may contribute to changes in seepage chemistry during structural transit. This report also provides references and good practice procedures to guide seepage chemistry investigations, and includes examples from successful seepage investigations performed over the past 20 years by Bureau of Reclamation Dam Safety Program professionals. 15. SUBJECT TERMS dam safety, dam seepage chemistry, procedures, geochemistry, mineralogy, petrography, hydrology, groundwater, chemical equilibrium, kinetics, soluble minerals, solubility, dissolution, congruent dissolution, incongruent dissolution, weathering, limestone, gypsum, calcite, dolomite, anhydrite, karst, piezometer, wells, flow-weighted, mass wasting, void formation, mass balance, mass balance models, saturation index, chemical equilibrium models, MINTEQA2, undersaturation, oversaturation, Horsetooth Dam, Glen Canyon Dam, Lake Powell, Deer Flat Embankments, Lake Lowell 16. SECURITY CLASSIFICATION OF: 17. LIMITATION 18. NUMBER 19a. NAME OF RESPONSIBLE PERSON OF ABSTRACT OF PAGES SAR 164 a. REPORT b. ABSTRACT c. THIS PAGE 19b. TELEPHONE NUMBER (Include area code) U U U Standard Form 298 (Rev. 8/98) Prescribed by ANSI Std. Z39.18 BUREAU OF RECLAMATION Technical Service Center, Denver, Colorado Fisheries Applications Research Group, 86-68290 Report DSO-05-03 Seepage Chemistry Manual Dam Safety Technology Development Program Denver, Colorado Prepared: Doug Craft Research Chemist, Fisheries Applications Research Group, 86-68290 Peer Review: Doug Hurcomb Geologist, Materials Engineering and Research Laboratory, 86-68180 _____________ Peer Review: Margaret Lake Date Chemist, Construction Management, 86-68160 REVISIONS Date Description Prepared Checked Technical Approval Peer Review 7/28/05 First draft to peer reviewers X X 2/24/06 Final revisions X Mission Statements The mission of the Department of the Interior is to protect and provide access to our Nation’s natural and cultural heritage and honor our trust responsibilities to Indian Tribes and our commitments to island communities. The mission of the Bureau of Reclamation is to manage, develop, and protect water and related resources in an environmentally and economically sound manner in the interest of the American public. Acknowledgments This work was funded by the Bureau of Reclamation (Reclamation) Dam Safety Technology Development Program, managed by Nate Snorteland, and the Technical Service Center (TSC) Manuals and Standards Program. Case studies at Horsetooth Dam were supported by Reclamation’s Great Plains Region, Billings, Montana, and Gene Price, Eastern Colorado Area Office, Loveland, Colorado; at Deer Flat Embankments by the Pacific Northwest Regional Office, Boise, Idaho; and at Glen Canyon Dam by the Upper Colorado Regional Office, Salt Lake City, Utah. Special thanks to Margaret Lake and Doug Hurcomb, TSC, Denver, Colorado, for peer review and comments on this manuscript, and Lelon Lewis, TSC, for editing, document layout, and publication assistance. iii Contents Page Acknowledgments..................................................................................................iii Executive Summary................................................................................................ 1 Introduction............................................................................................................. 2 Dam Safety and the Bureau of Reclamation..................................................... 2 What Is Seepage?.............................................................................................. 2 What Is Mineral Dissolution? ........................................................................... 3 What Is Seepage Chemistry? ............................................................................ 4 Chemistry Concepts................................................................................................ 5 What Is Solubility? ........................................................................................... 5 Primary Variables Affecting Aqueous Solubility............................................. 6 pH—Hydrogen Ion Activity ....................................................................... 6 pE and Eh—Free Electron Activity ............................................................ 6 Other Variables Affecting Solubility................................................................ 7 Solubility Data and the Real World.................................................................. 8 The Equilibrium Concept and Solubility Classes ....................................... 8 Weathering and Geochemistry.............................................................................. 10 Weathering and Mineral Dissolution.............................................................. 10 Congruent Dissolution .............................................................................. 12 Incongruent Dissolution............................................................................ 13 Weathering and Water Quality ....................................................................... 14 The Major Ions.......................................................................................... 14 Trace and Ultratrace Constituents............................................................. 15 Describing Water Quality ......................................................................... 15 Other Processes Affecting Seepage Chemistry..................................................... 16 Biotic Processes .............................................................................................. 16 Metabolism and Respiration ..................................................................... 16 The Sequence of Bacterial Activity .......................................................... 18 Ion Exchange .................................................................................................. 20 Mixing and Hydrologic Factors ...................................................................... 21 Mixing with Another Groundwater Aquifer............................................. 21 Local Mixing along Seepage Flow Paths.................................................. 21 Changing Reservoir Water Quality and Delayed Flows........................... 22 A Note about Unchanging Concentrations ............................................... 24 Mineral Dissolution and Dam Seepage................................................................. 25 Seepage in a New Structure ............................................................................ 25 Seepage in Formations with Minimal Soluble Minerals................................. 25 Seepage in Karst and
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