Framework Document for Monitored Natural Attenuation of Inorganic Contaminants in Ground Water

Transcription

1 Framework Document for Monitored Natural Attenuation of Inorganic Contaminants in Ground Water Long-Term Performance Monitoring of Metals and Radionuclides in the Subsurface: Strategies, Tools and Case Studies Bob Puls, Office of Research & Development, NRMRL, Project Lead Ron Wilhelm, Office of Radiation and Indoor Air, Co-Chair Radionuclides Ken Lovelace and Stuart Walker, Office of Solid Waste and Emergency Response, Co-Chairs 1

2 Technical Issues Natural Attenuation Definition: Naturally occurring processes in the environment that act without human intervention to reduce the mass, toicity, mobility*, volume or concentration of contaminants * Immobilization identified as primary process operative for contaminant metals and metalloids (SAB Review of EPA s Research Program for Monitored Natural Attenuation; EPA-SAB- EEC ) 2

3 OSWER Directive Definition for Monitored Natural Attenuation (EPA, OSWER Dir p, 1999) Reliance on natural attenuation processes to achieve site-specific remediation objectives within a time frame that is reasonable compared to that offered by other more active methods. 3

4 OSWER Directive Definition for Monitored Natural Attenuation (EPA, Dir p, 1999) In-situ processes include: biodegradation, dispersion, dilution, sorption, volatilization, radioactive decay, and chemical or biological stabilization, transformation, or destruction of contaminants. 4

5 Technical Issues Scientific foundation for assessment and acceptance: Timescale of attenuation process consistent with regulatory needs for site remediation Stability of immobilized contaminant sufficient to resist re-mobilization due to changes in site geochemistry Assessment of immobilization process employing technically feasible and scientifically defensible analytical methods Geochemical models can be employed to test feasibility of immobilization process 5

6 Scientific and Technical Needs Framework for screening candidate sites and assessing the technical requirements to demonstrate viability. Identification of contaminant- and site-specific immobilization processes Determination of site-specific rate and capacity of immobilization process Evaluation and codification of test methods to assess stability of immobilized contaminant Development and application guidance on geochemical models for site characterization 6

7 Framework Document Team USEPA ORD/NRMRL Robert Puls Robert Ford Rick Wilkin Steve Acree Ann Keeley Chunming Su OSWER/OSRTI Ken Lovelace Stuart Walker OAR Ron Wilhelm Region 1 Steve Mangion 7

8 Framework Document Team Non-EPA Institutions Jim Ammonette Pacific Northwest National Laboratory Paul Bertsch University of Georgia Craig Bethke University of Illinois Pat Brady Sandia National Laboratory Doug Kent U.S. Geological Survey 8

9 Framework Document Focus Radionuclide and Inorganic contaminants in GW Tiered approach for guiding decisions on use of MNA Focus on GW; unsaturated zone treated as source term Addresses both rad and non-rad elements 9

10 MNA Decision Analysis: Tiered Approach I. Actively demonstrate removal from ground water (site-specific data and theoretical basis) II. III. IV. Identify/confirm mechanism(s) of removal Demonstrate long-term capacity and stability Design monitoring program, define triggers for MNA failure, and establish contingency plan 10

11 Proposed Elements Radionuclides Americium Cesium Cobalt Iodine Plutonium Radium Radon Strontium Technetium Thorium Tritium Uranium 11

12 Proposed Elements Non - Radionuclides Arsenic Cadmium Chromium Copper Lead Mercury Nickel Nitrate Perchlorate Selenium Zinc 12

13 Two major parts: Document Structure Policy, scientific basis, and framework for technical assessment of inorganics MNA Element-specific assessment of feasibility based on current state of knowledge Strong emphasis placed on site characterization: Hydrology Biogeochemistry (solid and aqueous) 13

14 Document Structure Part 1 Basis for Assessment Section I - Conceptual Background for Natural Attenuation Section II - Scientific Basis for Natural Attenuation Section III - Site Characterization Section IV - Modeling and the Tiered Approach 14

15 Document Structure Part 2 Element Chapters Occurrence and Distribution Regulatory Aspects Geochemistry and Attenuation Processes Site Characterization Long-term Stability and Capacity Tiered Analysis 15

16 Developing Framework Document Document Review Internal Program Offices, Regional (GW Forum) 2004 Eternal Peer Review Interstate Technology Regulatory Council 2004 Estimated Publication FY05 Working Document Revisions or updates warranted with increased: Understanding of element chemistry Eperience with technology application 16

17 Radionuclide Current MCL (pci/l) Proposed MCL (pci/l) Mass Equiv to MCL, Proposed MCL, or RBL (mg/l) Am E-09 Cs E-09 H-3 20, E-09 I E-06 Pu E-07 Ra E-09 17

18 Radionuclide Current MCL (pci/l) Proposed MCL (pci/l) Mass Equiv to MCL, Proposed MCL, or RBL (mg/l) Ra E-11 Sr E-11 Tc E-05 U (or 20 µg/l) 3.2E-06 U (or 20 µg/l) 6.0E-02 18

19 Element (EPA, 1999b) Cd Redo Sensitive Radionuclide Primary Species at ph7 and Oidizing Conditions Cationic Anionic Neutral Transport Through Soils at ph 7 Not Retarded Retarded Cs Cr Pb Pu 19

20 Element (EPA, 1999b) Redo Sensitive Radionuclide Primary Species at ph7 and Oidizing Conditions Cationic Anionic Neutral Transport Through Soils at ph 7 Not Retarded Retarded Rn Sr Th 3 H U 20

21 Element (EPA, 2004, Draft final) Redo Sensitive Radionuclide Primary Species at ph7 and Oidizing Conditions Cationic Anionic Neutral Transport Through Soils at ph 7 Not Retarded Retarded Am As X (limited) Cm I Np Ra (limited) (limited) Tc 21

22 Element (EPA, 1999b) Cd Cs Cr Important Aqueous- and Solid-Phase Parameters influencing Contaminant Sorption [Aluminum/Iron-Oide Mineral], [Calcium], Cation Echange Capacity, [Clay Mineral], [Magnesium], [Organic Matter], ph, Redo, [Sulfide] [Aluminum/Iron-Oide Mineral], [Ammonium], Cation Echange Capacity, [Clay Mineral], [Mica-Like Clays], ph, Potassium [Aluminum/Iron-Oide Mineral], [Organic Matter], ph, Redo Pb Pu Rn [Aluminum/Iron-Oide Mineral], [Carbonate, Fluoride, Sulfate, Phosphate], [Clay Mineral], [Organic Matter], ph, Redo [Aluminum/Iron-Oide Mineral], [Carbonate, Fluoride, Sulfate, Phosphate], [Clay Mineral], [Organic Matter], ph, Redo none 22

23 Element (EPA, 1999b) Sr Important Aqueous- and Solid-Phase Parameters influencing Contaminant Sorption Cation Echange Capacity, [Calcium], [Carbonate], ph, [Stable Strontium] Th [Aluminum/Iron-Oide Mineral], [Carbonate], [Organic Matter], ph 3 H none U [Aluminum/Iron-Oide Mineral], [Carbonate, Fluoride, Sulfate, Phosphate], [Clay Mineral], [Organic Matter], ph, Redo, [U] 23

24 MNA Performance Monitoring Categories (EPA OSWER Dir P, 1999) Assess background contaminant levels and ambient geochemical indicators Process monitoring to assure progress of chemical attenuation Monitoring to detect plume epansion 24

25 Performance Monitoring Objectives (EPA OSWER Dir P, 1999) Demonstrate natural attenuation is present Detect changes in environmental conditions Identify potentially toic and/or transformation products Verify plume non epanding Verify no unacceptable impact downgradient Detect new releases of contaminants to the environment that impact MNA Demonstrate efficacy of institutional controls in place to protect receptors Verify attainment of remediation objectives 25

26 References USEPA, 1999a. Use of Monitored Natural Attenuation at Superfund, RCRA Corrective Action, and Underground Storage Tank Sites. OSWER Directive p. USEPA, 1999b. Understanding Variation In Partition Coefficient, Kd, Values. ORIA, EPA402-R A&B. USEPA, Soil Screening Guidance for Radionuclides: User s Guide. ORIA/Superfund, EPA/540-R PB