Gregory G. Rucker Owner/Senior Advisory Engineer

Enthalpy Environmental Software & Consulting, LLC

gregrucker51@gmail.comMarch 16, 2015

Innovative Model Efficiently Estimates Less Restrictive Soil-To-Groundwater Cleanup Levels

EESC-2015-01

National Groundwater Association2015 Groundwater Summit

San Antonio, Texas

Model Provenance

EESC-2015-02

Vadose Zone Contaminant Migration Multi-Layered Model

(VZCOMML Model pronounced Vee-Zee-Com-M-L)

VZCOMML:• Is one dimensional

• Screens for NAPL (4-phase)• Simulates dispersive mixing in saturated zone

• Uses 3-phase equilibrium-partitioning algorithms• Uses a multi-layered user-defined soil column (5 layers)

First used at the Department of Energy’s Savannah River Site on May 26, 1999

Innovations in VZCOMML Model

EESC-2015-03

• Simultaneously evaluates all contaminants on the USEPA TAL/TCL List; 52 volatiles, 74 semi-volatiles, 26 pesticides/PCBs, 25 metals, 42 radionuclides; 219

contaminants in a single simulation

• Algorithms calculate less conservative soil clean-up levels

• Algorithms calculate groundwater concentration at receptor well

• Innovatively uses time as an SSL evaluation criteria

• Automatic evaluation of 3 SSL criteria to determine if there are soil-to-groundwater contaminants of concern (COCs)

• Capability to construct a heterogeneous soil column and assign hydraulic functions to soil layers!

• Uses pore-water velocity to measure travel time to the aquifer

• Capability to perform “What-If” analyses

• Consistent with USEPA guidance

Model Provenance

EECS-2015-04

Versions, Copyrights, Dates

Version Copyright Date1.0 TXu00891407 19982.0 TXu001101245 19993.0 TXu001300116 20054.0 TXu0011663361 2010

Model Provenance

EESC-2015-05

Model Experience

• 100’s of CERCLA, RCRA, D&D documents projects at the DOE Savannah River Site since 1999

• Used by Savannah River Site for research and special studies for radiological contaminants such as Reactor Seepage Basin

Plug-In RODS and Reactor Building RODs• Independent Consultant Recommended VZCOMML for

protecting water resources in New Zealand• Used by California Regional Water Quality Control Board

Central Valley to quantify retardation factors• Final Remedial Action Plan Taylor Yard Los Angeles, CA• Supplemental Feasibility Study Technology Screening at

Eastern Michaud Flats Superfund Site Idaho• Academic study at Calgary University Alberta

Model Provenance

EESC-2015-06

Department of Energy: Technology Transfer Company and Date

• VZCOMML was developed in a line organization (environmental remediation) rather than in a university or laboratory – this means it was designed with utility

for a broad range of user needs

• DOE’s Savannah River National Laboratory is responsible for transferring technologies developed in pursuit of its mission at the Savannah River Site to

the private sector so these technologies may have the collateral benefit of enhancing US economic competitiveness

Version Company Date License2.0 Penn Anderson ~2001 to 2006 Expired4.0 NAPLSoft.com 2014 to 2019 Current

About USEPA Soil Screening Levels (SSLs)

EESC-2015-07

• SSLs are threshold contaminant concentrations for soil below which there is no concern the contaminant will migrate to groundwater and exceed an

action level such as an MCL, RSL, PRG, RG, etc

• Infinite source and mass-limited SSLs (i.e., steady-state concentrations are maintained over the exposure period)

• Uniformly distributed contamination from the surface to the top of the aquifer

• Instantaneous and linear equilibrium soil/water partitioning

• Receptor drinking water well adjacent to the downgradient edge of the source zone and screened in the GW plume

USEPA Soil Screening Levels (SSLs con’d)

EESC-2015-08

• SSLs are back-calculated from a groundwater concentration such as a MCL, RSL, PRG, RG, or other action level

• There are two types of SSLs:1. Infinite source SSL

2. Mass-limited source SSL

• SSLs are back-calculated soil concentrations beginning with determination of the appropriate groundwater target concentration (the action level) and then

multiplying it by the Dilution Attenuation Factor (DAF)

• The DAF is a dimensionless factor which represents dilution of a contaminant concentration once it has reached the aquifer

• Calculation of mass-limited SSLs requires site-specific data must be available such soil type, depth of contamination and source zone dimensions

• If the soil contaminant concentration is less than either the infinite source or mass-limited SSL, there is no concern for contamination of the aquifer

Features in VZCOMML: User-Defined Multi-Layer Soil Column

EESC-2015-09

Features in VZCOMML: Dilution Attenuation Factor (DAF) and Mixing Zone

EESC-2015-10

Estimation of Mixing Zone:

푑 = 0.0112 ∙ 퐿 0.5 + 푑 ∙ 1 − 푒−퐿 ∙ 퐼

퐾 ∙ 푖 ∙ 푑 푓푡

Boundary Condition:

푑 ≤ 푑 표푟 푑

Dilution Attenuation Factor (DAF) Calculation:

퐷퐴퐹 = 1 +퐾 ∙ 푖 ∙ 푑퐼 ∙ 퐿 푑푖푚푒푛푠푖표푛푙푒푠푠

Where:L = Length of source parallel to groundwater flow [ft]d = Mixing zone depth used in DAF calculation [ft]da = Measured depth of aquifer beneath source zone [ft]di = Calculated depth of mixing zone [ft]I = Infiltration rate [ft/yr]i = Aquifer hydraulic gradient [ft/ft]Ka = Aquifer hydraulic conductivity [ft/yr]

Mixing zone from MULTIMED model.

First term estimates depth of mixing due to vertical dispersivity; second term estimates the depth of mixing due to the downward velocity of infiltrating water

Features in VZCOMML: “b” Parameter Curve Fit for Moisture Content

y = 17.798x-0.188

R² = 1

0.00

10.00

20.00

30.00

40.00

50.00

60.00

70.00

0 1000 2000 3000 4000 5000 6000 7000

"b"

Para

met

er

Ks (ft/yr)

EESC-2015-11

휃 = 푛 ∙

Clapp and Hornberger Moisture Characteristic (1978)

Sand

Concrete

Low Ks Clay

I = Infiltration Rateθw = Moisture contentnt = Total porosityKs = Saturated Hydraulic Conductivity“b” = Moisture Characteristic

Features in VZCOMML: Soil Moisture Algorithm for a Wide Range of Soil Types

EESC-2015-12

Soil Type“K” Parameter

(ft/yr)“b” Parameter

(unitless)Total Porosity

(fraction) Effective Porosity

(fraction)

Sand 6004 3.47 0.430 0.383

Loamy Sand 1772 4.36 0.410 0.353

Sandy Loam 755 5.12 0.410 0.346

Silty Loam 394 5.79 0.450 0.383

Silt 51 8.50 0.456 0.425

Loam 197 6.59 0.430 0.352

Sandy Clay Loam 131 7.12 0.390 0.289

Silty Clay Loam 43 8.78 0.430 0.342

Clay Loam 66 8.10 0.410 0.315

Sandy Clay 33 9.22 0.380 0.281

Silty Clay 26 9.72 0.360 0.289

Clay 16 10.57 0.380 0.311

Low Permeability Clay 1.0 17.80 0.757 0.657Concrete 0.003 65.22 0.120 0.10

Data for Calculating Soil Moisture Content

Features in VZCOMML: SSL Algorithms Use Travel Time for First-Order Decay

EESC-2015-13

Retardation is spontaneously calculated in the Result Modules:

푅 = 1 +퐾 + 휌휃 푑푖푚푒푛푠푖표푛푙푒푠푠

Mean Travel Time to Aquifer

푇 =퐿 ∙ 푅푉

푓푡푦푟

Where:R = Retardation [dimensionless]Kd = Soil-water partition coefficient [L/kg]ρβ = Bulk density [kg/L]θe = Effective moisture content [decimal fraction]Lv = Vadose zone depth from bottom of source to aquifer [ft]Vs = Mean vertical non-retarded pore-water velocity [ft/yr]

Comparison of Conceptual Site Model for VZCOMML and Soil Screening Levels (SSLs)

EESC-2015-14

USEPA SSL CSM VZCOMML SSL CSM

Source Zone

Saturated Zone

Re

ce

pt

or

Dr

in

kI

ng

We

ll

Δ

GW Flow

Source Zone L1

Vadose Zone L2

Re

ce

pt

or

Dr

in

kI

ng

We

ll

Vadose Zone L3

Vadose Zone L4

Vadose Zone L5

Saturated Zone

Δ

GW Flow

Tt

Mass Transfer

Features in VZCOMML: Algorithms Use Mass Transfer in the Vadose Zone

EESC-2015-15

Mass transfer in the vadose zone:

푀 = 퐶 ∙ 휌 ∙ 퐴 ∙ 푑 푚푔

푀 = 퐶 ∙ 휌 ∙ 퐴 ∙ 푇 푚푔

푀 = 푀 (because of conservation of mass)

퐶 ∙ 휌 ∙ 퐴 ∙ 푑 = 퐶 ∙ 휌 ∙ 퐴 ∙ 푇

퐶 = 퐶 ∙ 푚푔

Where:Mtsz = Contaminant mass in source zone [mg]Ctsz = Concentration in source zone [mg/kg]As = Area of source zone [ft2]ds = Source depth [ft]

Mtvz = Contaminant mass in vadose zone [mg]Ctvz = Concentration in vadose zone [mg/kg]As = Area of vadose zone [ft2]Tc = Total depth of soil column [ft]

Features in VZCOMML: NAPL Screening with Soil Saturation Equation (Csat)

EESC-2015-16

Equation for NAPL Saturation in Soils:

퐶 =푆휌 ∙ 퐾 ∙ 휌 + 휃 + 휃 ∙ 퐻

푚푔푘푔

Where:Csat = Concentration in soil at which the absorptive limit of the soil

particles, the solubility limit in pore-water, and the saturation of soil pore-air have been reached. This is the soil NAPL threshold saturation limit.

Above this concentration, the contaminant may be present in free-phase (NAPL)

S = Pure phase aqueous solubility [mg/L]

*Csat is calculated and screened for all organic chemicals in VZCOMML by clicking the “Run Tier I Screening” command button on the “Result”

modules

Tier II SSL Algorithms for Infinite Source with First-Order Decay & Mass Transfer

EESC-2015-17

Infinite source equation for organics with vapor-phase:

푆푆퐿 / = 퐶 푀퐶퐿 ∙ 퐷퐴퐹 ∙ 퐾 +휃 + 휃 ∙ 퐻

휌 ∙1

푒∙푇푑

푚푔푘푔

USEPA Default Term Decay Term Mass TransferTerm

Mass-limited source equation:

푀퐿푆푆퐿 / = 퐶 푀퐶퐿 ∙ 퐷퐴퐹 ∙퐼 ∙ 퐸퐷휌 ∙ 푑

∙1

푒푚푔푘푔

USEPA Default Term Decay TermWhere:SSLt1/2 = Time and mass adjusted SSLMLSSLt1/2 = Time adjusted MLSSLθa = Air-filled soil porosity [fraction]ρβ = Soil bulk density [kg/L]H = Henry’s Law Constant [unitless]λ = Rate constant ( )

/[yr-1]

ED = Exposure Duration [70 years]TMean = Mean Travel Time to Aquifer (calculated) [yr]Tc = Total depth of soil column [ft]ds = Source depth [ft]

Tier II Mass-Limit and Infinite Source Algorithms Using First-Order Decay & Mass Transfer for Radionuclides

EESC-2015-18

Mass balanced equation:

푀퐿푆푆퐿 / = 퐶 푀퐶퐿 ∙ 0.001 ∙ 퐷퐴퐹 ∙퐼 ∙ 퐸퐷휌 ∙ 푑 ∙

휆푡1 − 푒

∙1

푒푝퐶푖푔

Groundwater infinite source equation:

퐶 =

퐶 ∙ 1000 푔푘푔

퐷퐴퐹

퐾 + 휃 + 퐻휌

∙휆푡

1 − 푒∙푒

1 ∙푑푇

푝퐶푖퐿

VZCOMML works equally as well with radionuclides as with conventional contaminants

Screening Criteria Used in VZCOMML

EESC-2015-19

Screening Tests Imbedded in Result Modules

1. Is the groundwater concentration “greater than or equal to” the MCL? In operator form: Cgw>=MCL

2. Is the mean travel time “less than or equal to” the evaluation time (Te)? In operator form: TMean=<Te

3. Is the waste site soil concentration “greater than or equal to” the MLSSLt1/2? In operator form: Ct>=MLSSLt1/2

The partial code form of the compound logic argument would look like this:

IF(AND)(Cw>=MCL, TMean=<Te, Ct>=MLSSLt1/2, value if true, value if false)

VZCOMML CALCULATES LESS CONSERVATIVE, BUT STILL PROTECTIVE, CLEAN-UP THRESHOLDS !!!

Hydrogeological Input for Calculating Less Restrictive SSLs

EESC-2015-20

DAF = 1.0 (the lowest DAF possible)

Chemical Property Inputs for Calculating Less Restrictive SSLs

EESC-2015-21

Additional Inputs:

foc = 0.002 [fraction]Dry bulk density = 1.50 [kg/L]Koc, foc, bulk density, H’ set to USEPA default values for RSLs

(These are the same parameters as used in USEPA

default SSL calculations)

Evaluation Time = 1,000 [yr]

Analyte Koc Kd T1/2 H'

L/Kg L/Kg Years UnitlessToluene 2.30E+02 4.60E-01 6.00E-02 2.70E-01trans-1,2-Dichloroethene 4.00E+01 8.00E-02 5.00E-01 1.70E-01trans-1,3-Dichloropropene 7.20E+01 1.44E-01 3.10E-02 5.33E-02Trichloroethylene 6.10E+01 1.22E-01 1.00E+01 4.00E-01Trichlorofluromethane 4.40E+01 8.80E-02 1.00E+00 2.39E+00Acetophenone 5.20E+01 1.04E-01 1.67E-01 4.25E-04Anthracene 1.64E+04 3.28E+01 1.26E+00 2.27E-03Atrazine 1.22E+02 2.44E-01 1.09E+00 9.65E-08Benzaldehyde 1.10E+01 2.20E-02 5.48E-02 1.09E-03Benzidine 1.20E+03 2.40E+00 2.20E-02 2.88E-09Chlordane 3.40E+04 6.80E+01 3.80E+00 1.99E-03Heptachlor 4.10E+04 8.20E+01 1.50E-02 1.20E-02Heptachlor epoxide 1.00E+04 2.00E+01 1.51E+00 8.59E-04Lindane (gamma-BHC) 2.80E+03 5.60E+00 6.58E-01 2.10E-04Methoxychlor 2.70E+04 5.40E+01 1.00E+00 8.30E-06Aluminum NA 1.50E+03 Infinite NAAntimony (metallic) NA 4.50E+01 Infinite NAArsenic, Inorganic NA 2.90E+01 Infinite NABarium NA 4.10E+01 Infinite NABeryllium and compounds NA 7.90E+02 Infinite NAStrontium-90 NA 3.50E+01 2.86E+01 NATechnetium-99 NA 1.00E-01 2.17E+05 NAUranium-233/234 NA 4.50E+02 2.45E+05 NAUranium-235 NA 4.50E+02 7.04E+08 NAUranium-238 NA 4.50E+02 4.47E+09 NA

Results of VZCOMML Simulation

EESC-2015-22

Mean Tier II Tier II Tier I Tier I Risk/MCL Action Level Retardation Travel Time Infinite Source Mass-Limit Mass-Limit Infinite Source Based

Analyte MCL or RSL R TMean T1/2-SSL T1/2-MLSSL MLSSL SSL RSL/SSL(mg/L)/(pCi/L) (Unitless) (years) (mg/kg)/(pCi/g) (mg/kg)/(pCi/g) (mg/kg)/(pCi/g) (mg/kg)/(pCi/g) (mg/kg)/(pCi/g)

Toluene 1.00E+03 4.45E+00 4.36E+01 Infinite Infinite 4.68E+00 6.7E-01 6.7E-01trans-1,2-Dichloroethene 1.00E+02 1.58E+00 1.55E+01 Infinite Infinite 4.68E-01 2.6E-02 2.6E-02trans-1,3-Dichloropropene NA 2.06E+00 2.02E+01 NA NA NA NA NATrichloroethylene 5.00E+00 1.90E+00 1.86E+01 3.04E-02 8.50E-02 2.34E-02 1.7E-03 1.7E-03Trichlorofluromethane 1.30E+03 1.65E+00 1.62E+01 2.58E+05 4.46E+05 6.08E+00 7.0E-01 7.0E-01Acetophenone 1.90E+03 1.77E+00 1.73E+01 Infinite Infinite 8.88E+00 5.1E-01 5.8E-01Anthracene 1.80E+03 2.43E+02 2.38E+03 Infinite Infinite 8.42E+00 5.9E+01 5.8E+01Atrazine 3.00E+00 2.80E+00 2.74E+01 2.31E+05 5.30E+05 1.40E-02 1.8E-03 1.9E-03Benzaldehyde 1.90E+03 1.16E+00 1.14E+01 Infinite Infinite 8.88E+00 3.5E-01 4.3E-01Benzidine 1.10E-04 1.87E+01 1.83E+02 Infinite Infinite 5.14E-07 2.8E-07 2.7E-07Chlordane 2.00E+00 5.03E+02 4.93E+03 Infinite 3.27E+03 9.35E-03 1.4E-01 1.4E-01Heptachlor 4.00E-01 6.06E+02 5.94E+03 Infinite Infinite 1.87E-03 3.3E-02 3.3E-02Heptachlor epoxide 2.00E-01 1.49E+02 1.46E+03 Infinite Infinite 9.35E-04 4.0E-03 4.1E-03Lindane 2.00E-01 4.23E+01 4.15E+02 Infinite Infinite 9.35E-04 1.2E-03 1.2E-03Methoxychlor 4.00E+01 3.99E+02 3.91E+03 Infinite Infinite 1.87E-01 2.2E+00 2.2E+00Aluminum 2.00E+04 1.11E+04 1.08E+05 1.50E+05 NC 9.35E+01 3.0E+04 3.0E+04Antimony (metallic) 6.00E+00 3.33E+02 3.26E+03 1.36E+00 NC 2.81E-02 2.7E-01 2.7E-01Arsenic, Inorganic 1.00E+01 2.15E+02 2.11E+03 1.46E+00 NC 4.68E-02 2.9E-01 2.9E-01Barium 2.00E+03 3.03E+02 2.97E+03 4.12E+02 NC 9.35E+00 8.2E+01 8.2E+01Beryllium and compounds 4.00E+00 5.83E+03 5.71E+04 1.58E+01 NC 1.87E-02 3.2E+00 3.2E+00Strontium-90* 8.00E+00 2.59E+02 2.54E+03 Infinite 2.87E-01 5.26E-02 4.0E-01 4.0E-01Technetium-99* 9.00E+02 1.74E+00 1.70E+01 1.19E+00 4.21E+00 4.21E+00 2.4E-01 2.4E-01Uranium-233/234* 1.00E+01 3.32E+03 3.25E+04 2.47E+01 4.68E-02 4.68E-02 4.5E+00 4.5E+00Uranium-235* 5.00E-01 3.32E+03 3.25E+04 1.13E+00 2.34E-03 2.34E-03 2.3E-01 2.3E-01Uranium-238* 1.00E+01 3.32E+03 3.25E+04 2.26E+01 4.68E-02 4.68E-02 4.5E+00 4.5E+00*pCi/gNC = Not CalculatedNA = Not Available

Eliminated as a contaminant of concern because of time criteria in VZCOMMLEliminated as a contaminant of concern based on enhanced Tier II infinite source algorithm in VZCOMMLEliminated as a contaminant of concern based on enhanced Tier II mass-limited source algorithm in VZCOMML

“Infinite” indicates result was greater than unity or >1,000,000 mg/kg or 1.0E+ 12 pCi/g

Less Restrictive Clean Up Levels

EESC-2016-23

• The use of a user-defined soil column allows site-specific hydrogeological parameters to be incorporated into modeling

• A user-defined soil column allows the software to quantify travel times in the vadose zone and use time to calculate both biodegradation and

radiological first-order decay• 14 of 24 contaminants were eliminated based on exceeding a time limit

of 1,000 years• 15 of 24 contaminants based upon the enhanced Tier II Mass-Limited

SSL algorithm were higher than the default SSL• 24 of 24 contaminants based upon the Tier II Infinite Source SSL

algorithm were higher than the default SSL• SSLs calculated by the software were a minimum of 5X higher than the

default SSL• 12 SSLs were calculated at an “Infinite” level