1

In-Situ Treatment of Groundwater with Non-aqueous Phase Liquids

December 10-12, 2002, Chicago, IL

Scott G. Huling, Ph.D., P.E.USEPA Robert S. Kerr Environmental

Research Center, Ada OK

In-Situ Fenton Oxidation: A Critical AnalysisFundamental ChemistryBench-scale Treatability StudiesField-scale Applications (pilot- or full-scale)Fate and Transport Issues

1

2

Fenton and Related ReactionsH2O2 + Fe+2 Fe+3 + OH- + ·OH (1)

H2O2 + Fe+3 Fe+2 + ·O2- + 2 H+ (2)

·O2- + Fe+3 Fe+2 + O2 (3)

·OH + Contaminant Products (CO2, Cl-, etc.) (4)Scavenging reactions n

i=1 ki

·OH + ni=1 Si products of scavenging rxn (5)

Nonproductive reactions2 H2O2 + reactants O2 + 2 H2O (6)

Miscellaneous optimum pH 3-4; metals mobility;

exothermic; stabilizers

3

Potential Limitations of Fenton Oxidation

1. Non-productive reactions2. Scavenging3. Low reaction rates4. Insufficient Fe5. pH adjustment 6. Oxidant, iron, acid, stabilizer transport7. O2(g) production8. Undesirable reaction byproducts9. Enhanced volatilization and transport

10. Unreactive target compounds

4

Cross-section of hazardous waste spill/release

5

6

Bench-scale Treatability Study Objectives

High Priority1. Proof of concept – quantify extent of

oxidation given potential limitations2. Determine reaction byproducts3. Metals mobility

7

Bench-scale Study Guidelines

1. Components: soil, ground water, reagents 2. Capture and quantify losses from the reactor3. pH change4. Monitoring parameters: target, byproducts,

metals 5. Control6. Establish pre-, post-oxidation concentrations 7. Perform pre-, post-oxidation mass balance

8

Field-Scale Application Guidelines

1. Injectate volume vs. pore volume target area 2. H2O2 concentration 3. pH adjustment4. Pulse injection of Fe(II) and H2O2

5. Injection strategy

9

H2O2 Reaction, Subsurface Transport[H2O2(t)] / [H2O2]O = exp(–KH2O2 R2 π Z η / Q)

(After, Clayton, 1998)

Flow, well spacing, pH

0

0.2

0.4

0.6

0.8

1

1.2

0 0.2 0.4 0.6 0.8 1 1.2

Radial Distance (m)

C (t

) / C

0

12 L/min

4 L/min

kH2O2 = -0.91/hr

10

Other Chemical Reagents

Reactions/interactions

Fe(II) - precipitation, complexation, oxidationAcid - consumed by acid neutralizing capacity Stabilizers (H2O2, Fe(II)) - precipitation,

complexation, oxidation

11

12

13

K = 100 ft/day

K = .0001 ft/day

K = 0.1 ft/day

Diffusion

Advection

Avg. K = 10 ft/day

K = .01 ft/day

14

Non-ideal Conditions Need to be Considered

Preferential pathways - greater rate of transport and oxidant delivery occurs through high conductive zones

Lower permeability zones - diffusion dominated transport << H2O2 reaction

Multiple applications

15

Transport Issues

Representative volume Heat and O2(g) released - impact

Pneumatic transport of ground water Decreased DNAPL visc., increased mobilityDNAPL evaporationVolatilization of DNAPL componentsThermal desorption from the solid phaseEnhanced H2O2 decomposition

16

17

18

Ground waterflow

19

20

SVE is a Complimentary Technology to Fenton Oxidation

Capture/treat/dispose volatiles SVE may already be part of the remedyMinimize the transport/uncontrolled lossMinimize potential exposure pathwaysVent wells for deeper systems

21

Performance Monitoring

Preferred monitoring parameters:target compound - aqueous (rebound: long

term vs. immediate), solidreaction byproducts - aqueousMetals - aqueousH2O2 - aqueous

Off-gas, soil gas samplesEstablish sentry wells

22

… performance monitoringGround water monitoring

Low priority - limited value for performance evaluation

CO2

DOTOC CODConductivityORPTemperature

23

Effects of ISFO on Natural Attenuation?

1. H2O2 - antiseptic, heat 2. Heterogeneity - microniches, preferential pathways3. Improvement in post-oxidation biodegradation4. Microbial sensitivity5. Population changes6. Toxicity response

24

Health and Safety

Heat released O2(g) released + Flammable vaporsEnhanced volatilization Accumulation of vapors (buildings, utilities)

25

Conclusions

Hydroxyl radical – strong oxidantPotential limitationsNumerous parameters influence success/failureMonitoring parameters/approach – key to successful

performance evaluationEnhanced transport processesRecognize/capture volatile emissions

25

26

Scavenging Analysis

Target contaminant oxidation reaction: k OH + C reaction byproducts

Scavenger oxidation reaction: ki

OH + Si reaction byproducts

Reaction rate equations: D[C]/dt = k OH [C] D[Si]/dt = iki OH [Si]

27

Relative Reaction Rates

Relative rate of reaction (RR) between OH and Si, and OH and C

RR = (iki [OH] [Si]) / (k [OH] [C])

28

Example 1

[TCE ] = 450 g/L (3.42×10-6 M); k = 4.2×109 L/mol-s [Cl-] = 1250 mg/L (3.52×10-2 M); k = 4.3×109 L/mol-

s[CO3

2- ] = 150 mg/L (2.5×10-3 M); k = 3.9×108 L/mol-s[·OH] assume 10-15 M

RR = 10,600

29

Example 2

[PCE ] = 4.15 mg/L (2.5×10-5M); k = 2.6×109 L/mol-s [Cl-] = 45 mg/L (1.27×10-3M); k = 4.3×109 L/mol-s[H2O2]= 50% , 500,000 mg/L (1.47×101M); k = 2.7×107 L/mol-s[·OH] assume 10-15 mol/L

RR = 6,180