LECTURE 13 MONITORED NATURAL ATTENUATION

Monitored Natural Attenuation As defined by U.S. EPA: reliance on natural processes to achieve site-specific remedial objectives

Source: Pope, D. F., and J. N. Jones, 1999. Monitored Natural Attenuation of Chlorinated Solvents. U.S. EPA Remedial Technology Fact Sheet. Report Number EPA/600/F-98/022. Office of Research and Development, U.S. Environmental Protection Agency, Washington, D.C. May 1999. (http://www.epa.gov/ada/download/fact/chl-solv.pdf).

Biodegradation

Sorption

Processes of NATURAL ATTENUATION of Petroleum Hydrocarbons Dispersion and Dilution

Volatilization (Evaporation) Chemical Reactions

Historical development of MNA Historical development • 1985 – Always a remedial alternative: EPA says it was used in Superfund as early as 1985 • 1988 – Guidance on Remedial Actions for Contaminated Ground Water at Superfund Sites discusses natural attenuation, but mostly as a comparison standard for active remediation. Natural attenuation is not encouraged • Began to be more commonplace with recognition of intractability of DNAPL cleanups and inadequacy of pump and treat technology • Simultaneously, there was increasing recognition that in situ processes were containing or cleaning up contamination • 1993-94 – Two key studies by National Research Council: • In Situ Bioremediation – When does it work? – 1993 study discusses intrinsic bioremediation • Alternatives for Ground Water Cleanup – 1994 • 1995 – Technical Protocol for Implementing Intrinsic Remediation with Long-Term Monitoring for Natural Attenuation of Fuel Contamination Dissolved in Groundwater • Prepared by Air Force Center for Environmental Excellence working with U.S. EPA research laboratory • Defines procedure to show intrinsic remediation is occurring • September 1996 – EPA Symposium on Natural Attenuation of Chlorinated Organics in Ground Water • November 1996 – Draft Technical Protocol for Evaluating Natural Attenuation of Chlorinated Solvents in Groundwater (Final in Sept. 1998) • December 1997 – OSWER Policy Directive: Use of Monitored Natural Attenuation at Superfund, RCRA Corrective Action, and Underground Storage Tank Sites • Sept.-Dec. 1998 – EPA Seminars on Monitored Natural Attenuation in nine cities around the US

1988 Guidance on Ground Water

1993 and 1994 – NRC Studies "In Situ Bioremediation. When does it work?" National Research Council.

"Alternatives for Ground Water Cleanup." National Research Council.

1995 – AFCEE Technical Protocol

Technical Protocol for Implementing Intrinsic Remediation with Long-Term Monitoring for Natural Attenuation of Fuel Contamination Dissolved in Groundwater Volume 1 By Todd Wiedemeier

Parsons Engineering Science, Inc. Denver, Colorado

John T. Wilson and Donald H. Kampbell

U.S. Environmental Protection Agency Robert S. Kerr Laboratory Ada, Oklahoma

Ross N. Miller and Jerry E. Hansen

Air Force Center for Environmental Excellence Technology Transfer Division Brooks AFB, San Antonio, Texas

Air Force Center for Environmental Excellence Technology Transfer Division Brooks AFB, San Antonio, Texas

1996 – EPA Symposium on Natural Attenuation

1996 – Draft Technical Protocol

Nov. 1996 – Draft Sept. 1998 - Final

1997 – MNA Policy Directive

1998 – MNA Seminars

Definition of MNA (continued) May be physical, chemical or biological Act without human intervention to reduce the mass, toxicity, mobility, volume, or concentration of contaminants in soil or ground water Processes include: biodegradation dispersion dilution sorption volatilization chemical or biological stabilization, transformation, or destruction Source: Pope, D. F., and J. N. Jones, 1999. Monitored Natural Attenuation of Chlorinated Solvents. U.S. EPA Remedial Technology Fact Sheet. Report Number EPA/600/F-98/022. Office of Research and Development, U.S. Environmental Protection Agency, Washington, D.C. May 1999. (http://www.epa.gov/ada/download/fact/chl-solv.pdf).

Elements of Natural Attenuation MNA is not: No-action alternative Presumptive or default remedy

MNA must be: Evaluated along with other alternatives Selected only is it meets remediation objectives Work in reasonable time frame (30 years) Used very cautiously as sole remedy

Components of MNA Required components of MNA: Source control Performance monitoring

Prerequisite for MNA: Site-specific characterization data and analysis

Demonstrating efficacy of MNA 1. Historical chemical data showing clear trend of decreasing mass or concentration. 2. Hydrogeologic or geochemical data that indirectly demonstrate natural attenuation processes 3. Field or microcosm studies that directly demonstrate natural attenuation processes

Aerobic biodegradation of fuel hydrocarbons Oxygen used as electron acceptor 2C6H6 + 15O2 → 12CO2 + 6H2O Indicators of biodegradation: Reduction in dissolved oxygen (3 mg DO needed to metabolize 1 mg of benzene) Reduction in hydrocarbon concentration

Biodegradation sequence Order of aerobic biodegradation: Ethyl benzene Toluene Benzene Xylene

Denitrification Nitrate is electron acceptor 6NO3– + 6H+ + C6H6 → 6CO2↑ + 6H2O + 3N2 ↑ Actually occurs in multiple steps mediated by different bacteria: NO3 – → NO2– → NO → N2O → NH4+ → N2

Denitrification Indicators of biodegradation: Reduction in nitrate Reduction in hydrocarbon concentration Presence of denitrifying bacteria Reducing conditions (dissolved oxygen < 1 mg/L)

Iron reduction Insoluble iron(III) (ferric iron) is electron acceptor Reduced to soluble iron(II) (ferrous iron) 60H+ + 30Fe(OH)3 + C6H6 → 6CO2 + 30Fe2+ + 78H2O

Iron reduction Indicators of iron biodegradation: Increase in dissolved iron Reduction in hydrocarbon concentration Low or no dissolved oxygen

Sulfate reduction Sulfate is electron acceptor Sulfate reduction to sulfide 30H+ + 15SO42- + 4C6H6 → 24CO2 + 15H2S + 12H2O

Methanogenesis (Methane fermentation) Not a redox reaction – fermentation reaction Occurs only in highly anaerobic conditions 4C6H6 + 18H2O → 9CO2 + 15CH4

Methanogenesis Indicators of methanogenesis: Increase in methane and carbon dioxide Reduction in hydrocarbon concentration Very low or no dissolved oxygen Presence of methanogenic bacteria

Carbon dioxide neutralization All hydrocarbon degradation processes create CO2 CO2 + H2O → H2CO3 (carbonic acid) H2CO3 + CaCO3 → Ca2+ + 2HCO3CO2 neutralization increases alkalinity 8 mg alk produced per mg benzene degraded

Analytical protocol Ground water: Total hydrocarbons – confirm HC decrease Aromatic hydrocarbons – confirm BTEX decrease Oxygen – confirm utilization, redox state Nitrate – confirm utilization Iron(II) – confirm production Sulfate – confirm utilization Methane – confirm methanogenesis

Analytical protocol Ground water: Alkalinity – confirm CO2 production and neutralization Oxidation-reduction potential – confirm geochemical environment pH, temperature, conductivity, chloride – confirmation of single ground-water system

Analytical protocol Biological: Field dehydrogenase test – confirm presence of aerobic bacteria Volatile fatty acids – biodegradation byproduct of complex organic compounds Microcosm studies – confirm biodegradation is occurring

Average Relative Contribution of BTEX Biodegradation Processes in Site Ground Water at 42 sites Methanogenesis 16%

Aerobic Oxidation Nitrate Reduction 3% 3% Iron (III) Reduction 4%

Sulfate Reduction 74%

Source: http://www.afcee.brooks.af.mil/er/ert/download/natattenfuels.ppt

Average Relative Contribution of BTEX Biodegradation Processes in Site Ground Water at 42 sites (Excluding five sites with >200 mg/L Sulfate Reduction Capacity) Aerobic Oxidation 8% Methanogenesis 45%

Denitrification 7% Iron (III) Reduction 12%

Sulfate Reduction 28%

Treatability Study Results (continued) BTEX assimilative capacity averaged 64 mg/L Field-scale biodegradation half-lives: Range = 9 days to 9.5 years Mean = 1 year.

BIOSCREEN

Microsoft Excel Worksheet

BIOSCREEN BIOSCREEN Natural Natural Attenuation Attenuation Decision Decision Support Support System System

Hill Hill AFB AFB

Air Air Force Force Center Center for for Environmental Environmental Excellence Excellence

Version Version 1.3 1.3

UST UST Site Site 870 870 Run Run Name Name

1. 1. HYDROGEOLOGY HYDROGEOLOGY Seepage Seepage Velocity* Velocity* or or Hydraulic Hydraulic Conductivity Conductivity Hydraulic Hydraulic Gradient Gradient Porosity Porosity

5. 5. GENERAL GENERAL Modeled Modeled Area Area Length* Length* Modeled Modeled Area Area Width* Width* Simulation Simulation Time* Time*

2. 2. DISPERSION DISPERSION Longitudinal Longitudinal Dispersivity* Dispersivity* Transverse Transverse Dispersivity* Dispersivity* Vertical Vertical Dispersivity* Dispersivity* or or Estimated Estimated Plume Plume Length Length 3. 3. ADSORPTION ADSORPTION Retardation Retardation Factor* Factor* or or Soil Soil Bulk Bulk Density Density Partition Partition Coefficient Coefficient FractionOrganicCarbon FractionOrganicCarbon

Vs Vs

1609.1 1609.1 (ft/yr) (ft/yr)

KK ii nn

8.1E-03 (cm/sec) 8.1E-03 (cm/sec) 0.048 0.048 (ft/ft) (ft/ft) 0.25 0.25 (-) (-)

or or

alpha alpha xx alpha alpha yy alpha alpha zz

28.5 28.5 2.9 2.9 0.0 0.0

Lp Lp

1450 1450

(ft) (ft)

1.2 1.2

(-) (-)

(ft) (ft) (ft) (ft) (ft) (ft)

or or

R R

or or or or

rho rho Koc Koc foc foc

4. 4. BIODEGRADATION BIODEGRADATION lambda 1st lambda 1st Order Order Decay Decay Coeff* Coeff* or or Solute t-half Solute Half-Life Half-Life t-half or or Instantaneous Instantaneous Reaction Reaction Model Model Delta DO Delta Oxygen* Oxygen* DO Delta NO3 Delta Nitrate* Nitrate* NO3 Observed Fe2+ Observed Ferrous Ferrous Iron* Iron* Fe2+ Delta SO4 Delta Sulfate* Sulfate* SO4 Observed CH4 Observed Methane* Methane* CH4

1.7 (kg/l) 1.7 (kg/l) 38 (L/kg) 38 (L/kg) 8.00E-04 8.00E-04 (-) (-)

1450 1450 320 320 55

6. 6. SOURCE SOURCE DATA DATA Source Source Thickness Thickness in in Sat.Zone* Sat.Zone* Source Source Zones: Zones: Width* Width* (ft) (ft) Conc. Conc. (mg/L)* (mg/L)* 50 0.07 50 0.07 11 11 25 2.8 25 2.8 22 100 99 100 33 25 2.8 25 2.8 44 50 0.07 50 0.07 55 Source (see Help): Help): Source Decay Decay (see SourceHalflife* Infinite SourceHalflife* Infinite (yr) (yr) Soluble Soluble Mass Mass In In NAPL, NAPL, Soil Soil

LL

(ft) (ft) (ft) W (ft) W (yr) (yr) 10 10 (ft) (ft)

Data Data Input Input Instructions: Instructions: 115 1. 115 1. Enter Enter value value directly....or directly....or 2. or 2. Calculate Calculate by by filling filling in in grey grey or cells 0.02 cells below. below. (To (To restore restore 0.02 formulas, formulas, hit hit button button below). below). Variable* Data Variable* in model. model. Data used used directly directly in 20 Value 20 model. Value calculated calculated by by model. (Don't (Don't enter enter any any data). data).

Vertical Vertical Plane Plane Source: Source: Look Look at at Plume Plume Cross-Section Cross-Section and and Input Input Concentrations Concentrations && Widths Widths for for Zones Zones 1, 1, 2, 2, and and 33

View View of of Plume Plume Looking Looking Down Down

or or

Infinite Infinite

(Kg) (Kg)

Observed Observed Centerline Centerline Concentrations Concentrations at at Monitoring Monitoring Wells Wells IfIf No No Data Data Leave Leave Blank Blank or or Enter Enter "0" "0"

7. 7. FIELD FIELD DATA DATA FOR FOR COMPARISON COMPARISON Concentration 9.0 Concentration (mg/L) (mg/L) 9.0 Dist. 00 145 Dist. from from Source Source (ft) (ft) 145

8.0

290 290

1.0 1.0

435 435

580 580

725 725

870 870

.02 .02

.005 .005

1015 1015 1160 1160 1305 1305 1450 1450

6.9E+0 6.9E+0 (per (per yr) yr)

8. 8. CHOOSE CHOOSE TYPE TYPE OF OF OUTPUT OUTPUT TO TO SEE: SEE:

or or

0.10 0.10

(year) (year)

5.78 5.78 17 17 11.3 11.3 100 100 0.414 0.414

(mg/L) (mg/L) (mg/L) (mg/L) (mg/L) (mg/L) (mg/L) (mg/L) (mg/L) (mg/L)

RUN RUN CENTERLINE CENTERLINE

RUN RUN ARRAY ARRAY

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Anaerobic transformation of carbon tetrachloride CCl4 → CHCl3 → CH2Cl2 → CH3Cl ↓ CO2 + H2O + Cl– Redox conditions: Denitrification CCl4 → CHCl3 Sulfate reduction CCl4 → CO2 + H2O + Cl–

Abiotic degradation of TCA CH3CCl3 → CH2CCl2 + CH3COOH → CO2 + H2O + Cl– 1,1,1-TCA → 1,1-DCE + Acetic acid → mineralization

Redox conditions: All redox conditions

Anaerobic dechlorination of TCA CH3CCl3 → CH3CHCl2 → CH3CH2Cl → CO2 + H2O + Cl– 1,1,1-TCA → 1,1-DCA → Chloroethane → mineralization

Redox conditions: Sulfate reduction 1,1,1-TCA → 1,1-DCA Methanogenesis 1,1,1-TCA → mineralization

Anaerobic degradation of PCE & TCE CCl2=CCl2 → CHCl=CCl2 → CHCl=CHCl → CH2=CHCl → CH2CH2 → CH3CH3 PCE

→

TCE → cis-1,2-DCE → vinyl chloride → ethene → ethane?

Redox conditions: Sulfate reduction PCE → DCE, TCE → DCE Methanogenesis PCE → ethene, TCE → ethene

Analytical protocol Ground water: Same as for hydrocarbons, plus: Methane – to confirm methanogenesis Chlorinated VOCs – materials degraded and degradation products Distinguish cis-1,2-DCE and trans-1,2-DCE

Degradation byproducts: CO2, ethane, ethene, chloride

Analytical protocols Ground water: Dissolved hydrogen – distinguishes strength of dechlorination and redox state: Electron acceptor Denitrification Iron reduction Sulfate reduction Reductive dechlorination

H2 concentration (ng/L) < 0.1 0.2 to 0.8 1 to 4 >1

Methanogenesis

5 to 20

Extent of Chlorinated Solvents and BTEX

BTEX and Electron Acceptors Total BTEX

4,000 - 6,000 µg/L 2,000 - 4,000 µg/L 0 - 2,000 µg/L

Nitrate

Dissolved Oxygen 5 - 10 mg/L 1 - 5 mg/L < 1 mg/L

Sulfate 2 - 4 mg/L 0.05 - 2 mg/L < 0.05 mg/L

10 - 20 mg/L 0.05 - 10 mg/L < 0.05 mg/L

BTEX and Metabolic Byproducts Total BTEX 4,000 - 6,000 µg/L 2,000 - 4,000 µg/L 0 - 2,000 µg/L

Iron (II) 10 - 11 mg/L 5 - 10 mg/L 0.05 - 5 mg/L

pe

Methane

4-7 2-4 0.5 mg/L 0.3 - 0.5 mg/L 0 - 0.3 mg/L

00

1,800 1,800 Fee Fee tt

Chlorinated Solvents and Byproducts Total BTEX

Trichloroethene

4,000 4,000 -- 6,000 6,000 µg/L µg/L 2,000 2,000 -- 4,000 4,000 µg/L µg/L 00 -- 2,000 2,000 µg/L µg/L

Vinyl Chloride >> 1,000 1,000 µg/L µg/L 500 500 -- 1,000 1,000 µg/L µg/L ND ND -- 500 500 µg/L µg/L

Dichloroethene 5,000 µg/L µg/L >> 5,000 1,000 -- 5,000 5,000 µg/L µg/L 1,000 1,000 µg/L µg/L 00 -- 1,000

>> 10,000 10,000 µg/L µg/L 1,000 1,000 -- 10,000 10,000 µg/L µg/L 00 -- 1,000 1,000 µg/L µg/L

Ethene

Chloride >> 500 500 µg/L µg/L 100 100 -- 500 500 µg/L µg/L ND ND -- 100 100 µg/L µg/L

>> 100 100 mg/L mg/L 50 50 -- 100 100 mg/L mg/L ND ND -- 50 50 mg/L mg/L

Plot of TCE, DCE, VC, and Ethene versus Distance Downgradient

Plume Classification

A

LNAPL Plume

B

N

C D

E F

A

Primary Monitoring Well

Dissolved BTEX-CAH Plume (1996)

0

500 1000 1500 2000

Adapted from: Carey, G. R., P. J. V. Geel, T. H. Wiedemeier, and E. A. McBean. "A Modified Radial Diagram Approach for Evaluating Natural Attenuation Trends for Chlorinated Solvents and Inorganic Redox Indicators." Ground Water Monitoring & Remediation 23, no. 4 (Fall 2003): 75-84.

Nitrate (NO3)

Manganese (Mn(II)) 0.0

10

1

0.1

1 1

Oxygen (O2)

10

0.1 10

8

6

4

2

0

1 0.1

Methane (CH4)

0.0

1

10 0

100

10

1

0.1

Iron (Fe(II))

10 20 30 40 50

Sulfate (SO4)

NO3

Mn(II) Fe(II)

O2 CH4

SO4

Aerobic

Methanogenic

Nitrate-Reducing

Sulfate-Reducing

Aerobic Background Concentrations

Manganogenic

Ferrogenic

Anaerobic Plume Concentrations

BIOCHLOR

Microsoft Excel Worksheet

Cape Data Input Input Instructions: Instructions: Cape Canaveral Canaveral Data 115 1. Fire Training Area 115 1. Enter Enter value value directly....or directly....or Fire Training Area

BIOCHLOR BIOCHLOR Natural Natural Attenuation Attenuation Decision Decision Support Support System System TYPE TYPE OF OF CHLORINATED CHLORINATED SOLVENT: SOLVENT:

Ethenes Ethenes Ethanes Ethanes

Version Version 1.1 1.1 for for Excel Excel 7.0/ 7.0/ '95 '95 5. 5. GENERAL GENERAL Simulation Simulation Time* Time* Modeled Modeled Area Area Width* Width* (ft/yr) Modeled (ft/yr) Modeled Area Area Length* Length* Zone Zone 11 Length* Length* (cm/sec) (cm/sec) Zone Zone 22 Length* Length*

1. 1. ADVECTION ADVECTION Seepage Vs 111.7 Seepage Velocity* Velocity* Vs 111.7 or or or or KK 1.8E-02 Hydraulic 1.8E-02 Hydraulic Conductivity Conductivity Hydraulic ii 0.0012 (ft/ft) Hydraulic Gradient Gradient 0.0012 (ft/ft) Effective nn 0.2 (-) Effective Porosity Porosity 0.2 (-) 2. 2. DISPERSION DISPERSION Alpha 40 Alpha xx Calc. Calc. Method Method 40 (ft) (ft) Change Change Alpha Alpha xx (Alpha 0.1 (Alpha y) y) // (Alpha (Alpha x) x) 0.1 (-) (-) Calc. Method Calc. Method (Alpha 1.E-99 (Alpha z) z) // (Alpha (Alpha x) x) 1.E-99 (-) (-) 3. 3. ADSORPTION ADSORPTION Retardation R Retardation Factor* Factor* R or or Soil 1.6 (kg/L) Soil Bulk Bulk Density, Density, rho rho 1.6 (kg/L) 1.8E-3 (-) FractionOrganicCarbon, 1.8E-3 (-) FractionOrganicCarbon, foc foc Partition Koc Partition Coefficient Coefficient Koc 426 7.1 (-) PCE 426 (L/kg) (L/kg) 7.1 (-) PCE 130 (L/kg) 2.9 (-) TCE 130 (L/kg) 2.9 (-) TCE 125 2.8 (-) DCE 125 (L/kg) (L/kg) 2.8 (-) DCE 30 (L/kg) 1.4 (-) VC 30 (L/kg) 1.4 (-) VC 302 5.3 (-) ETH 302 (L/kg) (L/kg) 5.3 (-) ETH 2.9 Common (used in in model)* model)* == 2.9 Common R R (used -1st 4. -1st Order Order Decay DecayCoef* Coef* 4. BIOTRANSFORMATION BIOTRANSFORMATION λ (1/yr) Zone 1 half-life λ (1/yr) Zone 1 half-life (yrs) (yrs) Yield* Yield* PCE TCE 2.00 0.79 PCE TCE 2.00 0.79 0.74 TCE DCE 1.00 0.74 TCE DCE 1.00 0.64 DCE VC 0.70 0.64 DCE VC 0.70 VC ETH 0.40 0.45 VC ETH 0.40 0.45 λλ (1/yr) Zone half-life (1/yr) Zone 22 half-life (yrs) (yrs) PCE TCE 0.00 PCE TCE 0.00 TCE DCE 0.00 TCE DCE 0.00 DCE VC 0.00 DCE VC 0.00 VC ETH 0.00 VC ETH 0.00 ETH Ethane ETH Ethane

6. 6. SOURCE SOURCE DATA DATA Source Source Options Options

Run RunName Name

33 33 700 700 1085 1085 1085 1085 00

Conc. Conc. (mg/L)* (mg/L)* PCE PCE TCE TCE DCE DCE VC VC ETH ETH

LL (yr) (yr) (ft) (ft) W W (ft) (ft) (ft) (ft) Zone 2= 2= (ft) (ft) Zone LL -- Zone Zone 11

56 56

2. 2. Calculate Calculate by by filling filling in in gray gray

Variable* Data Variable* Data used used directly directly in in model. model. Test Test ifif Natural Natural Attenuation Attenuation Biotransformation Biotransformation Screening Protocol Screening Protocol is Occurring is Occurring Vertical Vertical Plane Plane Source: Source: Determine Determine Source Source Well Well Location Location and and Input Input Solvent Solvent Concentrations Concentrations

TYPE: TYPE: Single Single Planar Planar

Source Source Thickness Thickness in in Sat. Sat. Zone* Zone* Width* (ft) Width* (ft)

or or

cells. 0.02 cells. Press Press Enter, Enter, then then C 0.02 C (To (To restore restore formulas, formulas, hit hit "Restore "Restore Formulas" Formulas" button button ))

(ft) (ft)

105 105 C1 C1 .056 .056 15.8 15.8 98.5 98.5 3.08 3.08 .03 .03

View View of of Plume Plume Looking Looking Down Down Observed Observed Centerline Centerline Conc. Conc. at at Monitoring Monitoring Wells Wells

7. 7. FIELD FIELD DATA DATA FOR FOR COMPARISON COMPARISON PCE .056 PCE Conc. Conc. (mg/L) (mg/L) .056 TCE 15.8 .22 TCE Conc. Conc. (mg/L) (mg/L) 15.8 .22 DCE 98.5 DCE Conc. Conc. (mg/L) (mg/L) 98.5 3.48 3.48 VC 3.08 VC Conc. Conc. (mg/L) (mg/L) 3.08 3.08 3.08 ETH .03 .188 ETH Conc. Conc. (mg/L) (mg/L) .03 .188 Dist. 00 560 Dist. from from Source Source (ft) (ft) 560

.017 .017 .776 .776 .797 .797 650 650

.024 .024 1.2 1.2 2.52 2.52 .107 .107 930 930

.019 .019 .556 .556 5.024 5.024 .15 .15 1085 1085

8. 8. CHOOSE CHOOSE TYPE TYPE OF OF OUTPUT OUTPUT TO TO SEE: SEE:

RUN RUN CENTERLINE CENTERLINE

RUN RUN ARRAY ARRAY

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Diffusive disappearance Parker, B. L., R. W. Gillham and J. A. Cherry, 1994. "Diffusive Disappearance of Immiscible-Phase Organic Liquids in Fractured Geologic Media." Ground Water, Vol. 32, No. 5, Pp. 805-820. September/October 1994.

See Figure 1 of: Parker, B. L., R. W. Gillham and J. A. Cherry, 1994. "Diffusive Disappearance of Immiscible-Phase Organic Liquids in Fractured Geologic Media." Ground Water, Vol. 32, No. 5, Pp. 805-820. September/October 1994.

FRACTURE APERTURE 2b NAPL

JD = -nDe

MATRIX

¶C ¶x

POROSITY, n EFFECTIVE DIFFUSION, De

z

1.0 Relative Concentration

x

Distance (x-)

t4

t3

y

Distance (x+)

t2

t1

Dissolved

Sorbed

∂C JD = −nDe ∂x ∂C D e ∂ 2C = R ∂x 2 ∂t Assume C(x = 0, t ) = S w and C(x, t = 0 ) = 0

⎛ RD e ⎞ ⎟⎟ JD (0, t) = −nS W ⎜⎜ ⎝ πt ⎠

1/2

Integrate over time to get mass leaving fracture : M t = nS w

(

)

4 1/2 RD e t π

Equivalent Fx Aperture (m m)

1,000 100 10

Type Clay

f = 35%

R = 5.2

Type Shale

f = 10%

R = 3.2

Type Granite

f = 0.6%

R = 1.0

1 0.1

1

10

100

1,000

10,000

Time (days) Comparison of TCE mass loss rates for three geologic media expressed in terms of equivalent immiscible-phase fracture aperture and time for NAPL disappearance: type-clay R= 5.2, type-sandstone/shale R = 3.2, and type-granite R= 1. Parameter values provided in the next slide.

Image adapted from: Parker, B. L., R. W. Gillhamand J. A. Cherry, 1994. "Diffusive Disappearance of Immiscible-Phase Organic Liquids in Fractured Geologic Media." Ground Water, Vol. 32, No. 5. Pp. 805-820. September/October 1994.

Geologic media parameters for three type-fractured geologic media used for comparison of TCE mass loss rates due to diffusion and sorption to matrix solids presented in figure: type-clay, type-shale/sandstone, and type-granite.

Parameter Porosity: f Bulk density: r b (g/cm3) Fraction organic carbon: foc Apparent tortuosity: t

Clay 0.35 1.6 0.01 0.33

Type-geologic media Shale/sandstone 0.10 2.4 0.002 0.10

Granite 0.006 2.63 0 0.06

Combined parameters: TCE & geologic media Effective diffusion coefficient: De (cm2/s) Retardation factor: R

3.3E-06 5.2

1.0E-06 3.2

6.0E-06 1

Image adapted from: Parker, B. L., R. W. Gillhamand J. A. Cherry, 1994. "Diffusive Disappearance of Immiscible-Phase Organic Liquids in Fractured Geologic Media." Ground Water, Vol. 32, No. 5. Pp. 805-820. September/October 1994.