Petroleum Soil Cleanup Guidelines

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Petroleum Soil Clean-up Guidelines

• Scenario
• Leaching to Groundwater

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Objective

• Determine the soil concentration limit that will
  protect groundwater, used as a drinking water
  supply, from leaching of the soil by rainwater

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Maine Conceptual Model(From Uddameri, 1998)
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Maximum ConcentrationPoint of Compliance Report
- Xylenes
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How its Done

• Dilution Attenuation factor (DAF ratio)
• Soil Conc. (source) / groundwater Conc.
  (receptor)
• Soil Cleanup Guideline (Leaching Scenario)
• Soil Guideline DAF x MEG (drinking water
  standard)

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Tetraethyldeath ExampleDAF Determination

• Source Concentration, soil
• 4 mg/kg (model input)
• Receptor Concentration, groundwater
• 0.02 mg/L (model output)
• DAF 4 (mg/kg) / 0.02 (mg/L) 200 (L/kg)
• C soil 200 x C groundwater

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Maine Conceptual Model(From Uddameri, 1998)
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Soil Guideline Determination Back Calculation
from the drinking water guideline (MEG)

• Csoil 200 x Cgroundwater
• MEG Tetraethyldeath 0.003 mg/L (3 ppb)
• Csoil 200 x 0.003 0.60 mg/kg
• Soil Guideline 0.60 mg/kg

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If you exceed the soil guideline,you will
exceed the MEG

• If soil concentration 0.61 mg/kg, the
  groundwater concentration will exceed the MEG
• Cwater 0.61 (Csoil) / 200 (DAF)
• Cwater .0031 and exceeds MEG

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Leaching to GroundwaterBack CalculationSummary

• Cs/Cgw DAF ratio (from the model)
• mg/kg/mg/L L/kg
• DAF x MEG Soil Guideline
• L/kg x mg/L mg/kg

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Model Output

• The maximum concentration at the point of
  compliance
• The receptor well

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Maximum ConcentrationPoint of Compliance Report
- Xylenes
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Selection of The Model
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Mathematical Models

• SESOIL
• Contaminant transport in soil above the water
  table.
• Bonazountas Wagner, 1984
• AT123D
• Analytical groundwater fate and transport model
  Yeh, 1981

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Why Select These Models?

• SESOIL
• Simulates seasonal climate variations
• Vadose zone flow system based on rigorous soil
  physics model by Peter Eagleson, Civil
  Engineering Dept. at MIT
• Created for EPA and is broadly used throughout
  the U.S.
• AT123D
• Analytical groundwater fate and transport model
  easily linked to SESOIL

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Other States Have Used the Model for Soil
Leaching Standards

• Include
• Oregon
• Colorado
• Wisconsin
• Massachusetts
• California
• New Hampshire
• New Mexico
• Hawaii

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MODEL DETAILS
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SESOIL COMPONENTS

• Hydrologic Cycle
• Pollutant Fate Cycle

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Hydrologic Cycle

• Rainfall Climate data
• Surface Runoff
• Infiltration
• Capillary Rise
• Evapotranspiration
• Soil Moisture Retention
• Groundwater Recharge

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Pollutant Fate Cycle

• Advection through soil and Recharge Rate
  controlled by soil parameters
• Volatilization
• Sorption related to organic carbon fraction of
  soil and the organic carbon partitioning
  coefficient of the chemical
• Biological Decay
• Diffusion

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Chemical Properties

• Water Solubility
• Henrys Law Constant
• Organic Carbon Partitioning Coefficient
• Biodegradation Rates
• Solid and Liquid phases
• Air Diffusion Coefficient
• Water Diffusion Coefficient

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Calibration of the Model

• Calibration to Groundwater Recharge Rates
• Attenuation and degradation of chemical
  contaminants is directly related to the volume of
  water that flows through the soil and the rate at
  which it flows
• It is more important to calibrate the hydrologic
  system to recharge than to perfectly match the
  individual parameters

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Recharge Rate Estimates

• Ground Water Recharge Rates for Maine Soils and
  Bedrock, Robert G. Gerber Charles S. Hebson,
  1996
• Geological Society of Maine Bulletin 4, Selected
  Papers on the Hydrogeology of Maine, edited by
  Marc Loiselle, Weddle, T.K. and White, C.
• Sand and Gravel Aquifer 55
• Kennebunk, Kennebunkport Wells Water District
• Till 20
• Little Androscoggin River Basin, So. Paris

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Calibration Process

• Select Hydraulic Conductivity and convert to
  Intrinsic Permeability
• Select Effective Porosity
• Adjust Soil Pore Disconnectedness Index
• Start Over

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Soil Pore Disconnectedness Index a complex
parameter

• Eagleson water balance dynamics theory
• Defines Relative Permeability in the soil
  water/air system
• Related to soil type pore system geometry

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Basis for Hydrologic Cycle

• Peter Eaglesons annual water balance dynamics
  theory in soils, a very detailed analytical
  model.
• Title Climate, Soil and Vegetation
• Published October 1978, Water Resources Research
  - a series of 7 papers, 72 pages.

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Groundwater RechargeEagleson Equation

• Uniform flow rate to water table
• Downward flow of infiltrating rain water minus
  upward capillary flow.
• R K(1) soc - w n, K(1), Z
• Bonazountas Wagner, 1984

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Downward flow component

• K(S) K(1)Sc
• Relative Permeability equation
• c soil pore disconnectedness index
• S of pore filled with water
• K(1) Intrinsic permeability

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Eaglesons Explanation for the Saddle

• For large values of K(1) we note a saddle in
  RgA/PA as c increases, particularly for Santa
  Paula. This results from the behavior of soc,
  where so is less than one and increases with c.

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Lets think about this

• As pores become more disconnectedK decreases and
  recharge decreases
• At the same time more water is held in the
  disconnected pores
• Water saturation increases and when it reaches
  high levels (80-90) relative K increases and
  recharge increases
• Where the disconnectedness index is high this
  effect is small but noticeable

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Hydrologic Cycle CalibrationSand Gravel

• Calibrated to Recharge Estimation
• Sand Gravel Aquifer, Branch Brook Aquifer,
  Kennebunk and Wells
• Gerber and Hebson, 1996, Ground Water Recharge
  Rates for Maine Soils and Bedrock
• Average Annual Recharge Rate
• 55 of Precipitation

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Calibrated Soil Parameters

• Porosity 37
• Hydraulic Conductivity 1 x 10-3 cm/sec
• Intrinsic Permeability 1 x 10-8 cm2
• Bulk Density 1.5 g/cm3
• Soil Pore Disconnectedness Index 5.5
• Organic Carbon Content 0.20
• Freundlich Exponent 1.0

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Sand Gravel Aquifer Hydrologic Cycle
Report(units inches)
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Hydrologic Cycle CalibrationTill

• Calibrated to Recharge Estimation
• Sandy Till, Little Androscoggin River, North of
  South Paris, Maine, study by Dan Morrisey, 1983
• from Gerber and Hebson, 1996, Ground Water
  Recharge Rates for Maine Soils and Bedrock
• Average Annual Recharge Rate
• 20 of Precipitation

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Calibrated Soil ParametersGlacial Till

• Porosity 20
• Hydraulic Conductivity 3 x 10-5 cm/sec
• Intrinsic Permeability 3 x 10-10 cm2
• Bulk Density 1.5 g/cm3
• Soil Pore Disconnectedness Index 11.0
• Organic Carbon Content 0.20
• Freundlich Exponent 1.0

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Till Hydrologic Cycle Report(units inches)
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Pollutant Cycle

• Fate and Transport

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Application Data

• 4 Layer Model
• Top Layer, 6 ft. Clean
• Bottom 3 layers, fully contaminated to
  groundwater table at 15 ft
• Volatilization Factor 1.0
• Contaminant Load Area 750,000 cm2
• Based on cross section area of 15,000 gal. tank
  halo 1.5 x tank dimensions
• 94 of registered gasoline tanks lt 15,000 gal.

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Chemical Property Data

• Obtained from Environmental Chemistry Databases
• Most variable among databases
• Organic Carbon Adsorption Coefficient
• Henrys Law Constant
• Biodegradation Rate
• I used the data mostly from the Massachusetts
  database
• Solid Phase Biodegradation Rate 0 except for
  Benzene, C9-C10 aromatics, C11-C22 aromatics

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SESOIL Pollutant Cycle Output
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Soil Leaching Guideline ExamplesSand Gravel vs
Till comparison (Units in mg/kg)
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Soil Leaching Guidelinesin Context (units mg/kg)