Monitored Natural Attenuation of Metals and Radionuclide-Contaminated Sites

Pat Brady Sandia National LaboratoriesMike Truex Pacific Northwest National LaboratoryChuck Newell GSIKaren Vangelas Savannah River National LaboratoryMiles Denham Savannah River National Laboratory

Sponsored by: DOE EM-22 Attenuation-Based Remedies for Metals and Radionuclide Project (Leads: M. Denham and K. Vangelas, Savannah River National Laboratory)

Sandia National Laboratories is a multi-program laboratory managed and operated by Sandia Corporation, a wholly owned subsidiary of Lockheed Martin Corporation, for the U.S. Department of Energy’s National Nuclear Security Administration under contract DE-AC04-94AL85000.

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http://www.epa.gov/ada/download/reports/600R07139/600R07139-01.pdf

http://www.epa.gov/ada/download/reports/600R07140/600R07140.pdf

Volume 3Assessment for RadionuclidesIncluding Isotopes of Cesium, Iodine, Neptunium, Plutonium, Strontium, Technetium, and Uranium

In Preparation

Recent EPA Guidance for MNA of Metals and Radionuclides

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The Scenarios Approach

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Scenarios

Contaminant

Scenario 1 low redox high CEC

Scenario 2 low redox low CEC

Scenario 3 high redox high CEC high Fe

Scenario 4 high redox high CEC

low Fe

Scenario 5 high redox, low CEC high Fe

Scenario 6 high redox, low CEC low Fe

Cr(III) ↓S ↓S

Cr(VI) reduced to Cr(III)

reduced to Cr(III)

99Tc(IV) ↓S ↓S Likely oxidized

to Tc(VII) Likely oxidized

to Tc(VII) Likely oxidized

to Tc(VII) Likely oxidized

to Tc(VII)

99Tc(VII) reduced to Tc(IV)

reduced to Tc(IV)

Pu

U

Pb ↓S ↓S

Cd ↓S ↓S

Zn ↓S ↓S

Ni ↓S ↓S

Cu ↓S ↓S

As ↓S ↓S

Se

90Sr ↑TDS ↑TDS ↑TDS

Nitrate can degrade can degrade

Perchlorate can degrade can degrade

129I

HIGH Mobility

Mobility increases above and below pH7 S Increasing sulfur

decreases mobility

MEDIUM Mobility

Mobility increases above pH7 TDS Increasing TDS

increases mobility

LOW Mobility

Mobility decreases above pH7 and increases below pH7

Transformed to other valence state

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Mechanisms

Sorption Solubility

Microbial Processes

Dilution DegradationDecay

Groundwater Condition

Impact on Sorption

Impact on Solubility

Redox Low: Most uranium compounds are relatively insoluble under low redox conditions High: uranium is generally soluble. U(IV) reoxidizes to U(VI).

CEC Fe Iron oxides are major

sorption sites for uranium

pH Sorption may decrease with decreasing or increasing pH compared to neutral. Clay and iron mineral dissolution and precipitation of amorphous phases changes sorption sites

Changes U complexation and impacts solubility

Sulfur TDS Blank indicates “no major impact”

Example: Uranium

Mechanisms

Sorption Solubility

Microbial Processes

Dilution DegradationDecay

Groundwater Condition

Impact on Sorption

Impact on Solubility

Redox Low: Dissolution of iron oxides can release arsenic into the groundwater As(III) (reduced form) sorption is somewhat lower than As(V) sorption

Low: Generally no insoluble solids except for arsenic sulfides

CEC High CEC may increase sorption

Fe Iron oxide dissolution may be important (see redox discussion)

pH Sorption may decrease with decreasing pH

Possible increases in solubility with decreasing pH

Sulfur Under low redox conditions sulfide compounds result in low solubility

TDS Phosphate or silicate can inhibit sorption

Blank indicates “no major impact”

Example: Arsenic

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Table 9 Remediation Technologies Matrix for Metals in Soils and Groundwater (GWRTAC, 1997)

Remediation Technology Metals Treated Cost Long-term

effectiveness Applicability to

High Metals Concentration

Toxicity Reduction

Mobility Reduction

Volume Reduction

Capping 1-3

Subsurface Barriers 1-3,5

S/S (Ex-situ) 1-3, 5

S/S (In-situ) 1,2,4,6

Vitrification (Ex-situ) 1-3, 5

Vitrification (In-situ) 1-3, 7

Chemical Treatment 2 -- --

Permeable Treatment Walls 2 -- --

Biological Treatment 1-5

Physical Separation 1-6

Soil Washing 1-3, 5-7

Pyrometallurgical Extraction 1-5, 7

Soil Flushing (In-situ) 1,2,7

Electrokinetic Treatment 1-6 Metals: 1-Lead, 2-Chromium, 3-Arsenic, 4-Zinc, 5-Cadmium, 6-Copper, 7-Mercury Abbreviations: S/S – solidification/stabilization Symbols: ( ) – Good, ( ) – Average, ( ) – Marginal, (--) – Insufficient information

Enhanced Attenuation

Figure 15. Segments of the source and plume system and type of enhancers that can be implemented for the purpose of EA (Adapted from DOE 2006a)

Table 8 Cost Estimates and Applicability of Metals Remediation Technologies (USEPA 1997; Mulligan et al.; 2001; ESTCP 2008)

Remedial Technology Applicability Cost Range

EA Source Control $/ton(1) $/cu yd(2)

Physical Treatment Containment ● 10-90 14-122 Encapsulation ● 60-290 81-392 Vitrification ● 400-870 540-1175 Subsurface Barriers ● ● 3-10(3) - Ex-situ Treatment Soil Washing ● 25-300 34-405 Physical Separation ● 60-245 81-331 Pyrometallurgical ● 200-1000 270-1350 In-situ Treatment Reactive barriers ● 60-245 81-331 Soil Flushing ● 60-200 81-270 Phytoremediation ● 25-100 34-135 Potential Technologies Enhanced Bioremediation (Electron Donor Delivery)

● ● 27-152 37-206

Reactive barriers (ZVI) ● 4500(4) - Reactive barriers (mulch) ● 400(4) - (●) symbol indicates the treatment technology is applicable to the strategy (1) Costs do not include pretreatment, site preparation, regulatory compliance costs, costs for additional treatment

of process residuals, or profit (2) Density of soil assumed: 100 lb/ft3 (3) Cost for subsurface barriers is for slurry walls; cost is $ per square foot (4) Cost for ZVI and mulch reactive barriers reported as $ per linear foot