1. Gregory G. Rucker
Owner/Senior Advisory Engineer
Enthalpy Environmental Software
& Consulting, LLC
gregrucker51@gmail.com
March 16, 2015
Innovative Model Efficiently Estimates Less Restrictive
Soil-To-Groundwater Cleanup Levels
EESC-2015-01
National Groundwater Association
2015 Groundwater Summit
San Antonio, Texas
2. 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
3. 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
5. 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
6. 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 License
2.0 Penn Anderson ~2001 to 2006 Expired
4.0 NAPLSoft.com 2014 to 2019 Current
7. 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
8. 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
10. Features in VZCOMML: Dilution Attenuation
Factor (DAF) and Mixing Zone
EESC-2015-10
Estimation of Mixing Zone:
= 0.0112 ∙ 0.5 + ∙ 1 −
− ∙
∙ ∙
Boundary Condition:
≤
Dilution Attenuation Factor (DAF) Calculation:
= 1 +
∙ ∙
∙
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
11. 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"Parameter
Ks (ft/yr)
EESC-2015-11
= ∙
Clapp and Hornberger Moisture Characteristic (1978)
Sand
Concrete
Low Ks Clay
I = Infiltration Rate
θw = Moisture content
nt = Total porosity
Ks = Saturated Hydraulic Conductivity
“b” = Moisture Characteristic
13. Features in VZCOMML: SSL Algorithms Use
Travel Time for First-Order Decay
EESC-2015-13
Retardation is spontaneously calculated in the Result Modules:
= 1 +
+
Mean Travel Time to Aquifer
=
∙
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]
14. 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
ReceptorDrinkIngWell
Δ
GW Flow
Source Zone L1
Vadose Zone L2
ReceptorDrinkIngWell
Vadose Zone L3
Vadose Zone L4
Vadose Zone L5
Saturated Zone
Δ
GW Flow
Tt
Mass Transfer
15. Features in VZCOMML: Algorithms Use Mass
Transfer in the Vadose Zone
EESC-2015-15
Mass transfer in the vadose zone:
= ∙ ∙ ∙
= ∙ ∙ ∙
= (because of conservation of mass)
∙ ∙ ∙ = ∙ ∙ ∙
= ∙
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]
16. Features in VZCOMML: NAPL Screening
with Soil Saturation Equation (Csat)
EESC-2015-16
Equation for NAPL Saturation in Soils:
= ∙ ∙ + + ∙
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
17. Tier II SSL Algorithms for Infinite Source with First-Order
Decay & Mass Transfer
EESC-2015-17
Infinite source equation for organics with vapor-phase:
/ = ∙ ∙ +
+ ∙
∙
1
∙
USEPA Default Term Decay Term Mass Transfer
Term
Mass-limited source equation:
/ = ∙ ∙
∙
∙
∙
1
USEPA Default Term Decay Term
Where:
SSLt1/2 = Time and mass adjusted SSL
MLSSLt1/2 = Time adjusted MLSSL
θa = 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]
18. Tier II Mass-Limit and Infinite Source Algorithms Using First-Order
Decay & Mass Transfer for Radionuclides
EESC-2015-18
Mass balanced equation:
/ = ∙ 0.001 ∙ ∙
∙
∙
∙
1 −
∙
1
Groundwater infinite source equation:
=
∙ 1000
+
+
∙
1 −
∙
1
∙
VZCOMML works equally as well with radionuclides as with conventional
contaminants
19. 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 !!!
20. Hydrogeological Input for Calculating Less
Restrictive SSLs
EESC-2015-20
DAF = 1.0 (the lowest DAF possible)
21. 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 Unitless
Toluene 2.30E+02 4.60E-01 6.00E-02 2.70E-01
trans-1,2-Dichloroethene 4.00E+01 8.00E-02 5.00E-01 1.70E-01
trans-1,3-Dichloropropene 7.20E+01 1.44E-01 3.10E-02 5.33E-02
Trichloroethylene 6.10E+01 1.22E-01 1.00E+01 4.00E-01
Trichlorofluromethane 4.40E+01 8.80E-02 1.00E+00 2.39E+00
Acetophenone 5.20E+01 1.04E-01 1.67E-01 4.25E-04
Anthracene 1.64E+04 3.28E+01 1.26E+00 2.27E-03
Atrazine 1.22E+02 2.44E-01 1.09E+00 9.65E-08
Benzaldehyde 1.10E+01 2.20E-02 5.48E-02 1.09E-03
Benzidine 1.20E+03 2.40E+00 2.20E-02 2.88E-09
Chlordane 3.40E+04 6.80E+01 3.80E+00 1.99E-03
Heptachlor 4.10E+04 8.20E+01 1.50E-02 1.20E-02
Heptachlor epoxide 1.00E+04 2.00E+01 1.51E+00 8.59E-04
Lindane (gamma-BHC) 2.80E+03 5.60E+00 6.58E-01 2.10E-04
Methoxychlor 2.70E+04 5.40E+01 1.00E+00 8.30E-06
Aluminum NA 1.50E+03 Infinite NA
Antimony (metallic) NA 4.50E+01 Infinite NA
Arsenic, Inorganic NA 2.90E+01 Infinite NA
Barium NA 4.10E+01 Infinite NA
Beryllium and compounds NA 7.90E+02 Infinite NA
Strontium-90 NA 3.50E+01 2.86E+01 NA
Technetium-99 NA 1.00E-01 2.17E+05 NA
Uranium-233/234 NA 4.50E+02 2.45E+05 NA
Uranium-235 NA 4.50E+02 7.04E+08 NA
Uranium-238 NA 4.50E+02 4.47E+09 NA
22. 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-01
trans-1,2-Dichloroethene 1.00E+02 1.58E+00 1.55E+01 Infinite Infinite 4.68E-01 2.6E-02 2.6E-02
trans-1,3-Dichloropropene NA 2.06E+00 2.02E+01 NA NA NA NA NA
Trichloroethylene 5.00E+00 1.90E+00 1.86E+01 3.04E-02 8.50E-02 2.34E-02 1.7E-03 1.7E-03
Trichlorofluromethane 1.30E+03 1.65E+00 1.62E+01 2.58E+05 4.46E+05 6.08E+00 7.0E-01 7.0E-01
Acetophenone 1.90E+03 1.77E+00 1.73E+01 Infinite Infinite 8.88E+00 5.1E-01 5.8E-01
Anthracene 1.80E+03 2.43E+02 2.38E+03 Infinite Infinite 8.42E+00 5.9E+01 5.8E+01
Atrazine 3.00E+00 2.80E+00 2.74E+01 2.31E+05 5.30E+05 1.40E-02 1.8E-03 1.9E-03
Benzaldehyde 1.90E+03 1.16E+00 1.14E+01 Infinite Infinite 8.88E+00 3.5E-01 4.3E-01
Benzidine 1.10E-04 1.87E+01 1.83E+02 Infinite Infinite 5.14E-07 2.8E-07 2.7E-07
Chlordane 2.00E+00 5.03E+02 4.93E+03 Infinite 3.27E+03 9.35E-03 1.4E-01 1.4E-01
Heptachlor 4.00E-01 6.06E+02 5.94E+03 Infinite Infinite 1.87E-03 3.3E-02 3.3E-02
Heptachlor epoxide 2.00E-01 1.49E+02 1.46E+03 Infinite Infinite 9.35E-04 4.0E-03 4.1E-03
Lindane 2.00E-01 4.23E+01 4.15E+02 Infinite Infinite 9.35E-04 1.2E-03 1.2E-03
Methoxychlor 4.00E+01 3.99E+02 3.91E+03 Infinite Infinite 1.87E-01 2.2E+00 2.2E+00
Aluminum 2.00E+04 1.11E+04 1.08E+05 1.50E+05 NC 9.35E+01 3.0E+04 3.0E+04
Antimony (metallic) 6.00E+00 3.33E+02 3.26E+03 1.36E+00 NC 2.81E-02 2.7E-01 2.7E-01
Arsenic, Inorganic 1.00E+01 2.15E+02 2.11E+03 1.46E+00 NC 4.68E-02 2.9E-01 2.9E-01
Barium 2.00E+03 3.03E+02 2.97E+03 4.12E+02 NC 9.35E+00 8.2E+01 8.2E+01
Berylliumandcompounds 4.00E+00 5.83E+03 5.71E+04 1.58E+01 NC 1.87E-02 3.2E+00 3.2E+00
Strontium-90* 8.00E+00 2.59E+02 2.54E+03 Infinite 2.87E-01 5.26E-02 4.0E-01 4.0E-01
Technetium-99* 9.00E+02 1.74E+00 1.70E+01 1.19E+00 4.21E+00 4.21E+00 2.4E-01 2.4E-01
Uranium-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+00
Uranium-235* 5.00E-01 3.32E+03 3.25E+04 1.13E+00 2.34E-03 2.34E-03 2.3E-01 2.3E-01
Uranium-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/g
NC = Not Calculated
NA = Not Available
Eliminated as a contaminant of concern because of time criteria in VZCOMML
Eliminated as a contaminant of concern based on enhanced Tier II infinite source algorithmin VZCOMML
Eliminated as a contaminant of concern based on enhanced Tier II mass-limited source algorithmin VZCOMML
“Infinite” indicates result was greater thanunity or >1,000,000 mg/kg or 1.0E+ 12 pCi/g
23. 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
