United States National Exposure

Environmental Protection Research Laboratory

Agency Las Vegas, NV 89193-3478

Summary Report

Research and Development EPA/600/S-97/004 July 1997

The goal of this project was to directly observe and evaluate the subsurface movement and distribution of

selected volatile organic compounds,

particularly components of petroleum

fuels, through controlled laboratory experiments. Sand tank, column, and

batch-type laboratory experiments were

employed to measure the effect of specific variables associated with underground contamination events. The sand

tank experiments were carried out to

characterize leak sources and contaminant movement. Leak rate, petroleum

type, soil type, temperature, and backfill configuration were examined to determine which materials and methods

produced results that had the best application to field and regulatory situations. The spatial and temporal propagation of leaking fluids was measured

and recorded by several methods including gas chromatography and timelapse photography. The spatial and temporal measurements of vapor concentrations were mathematically modeled

using two-dimensional inverse methods. Diffusion parameters of Effective

Diffusion Coefficient, De, and Sorptioncorrected Porosity, A*, were determined, with De

 for gasoline generally

ranging from approximately 0.0024 cm2/

sec for clay to 4.4 cm2/sec for pea

gravel. Calculated diffusion parameters

were used to predict three-dimensional

propagation of vapors, and results were

compared with field and laboratory values. Additionally, the sand tanks were

used to measure the distribution of light

non-aqueous phase liquids around the

water table during conditions of vertiDetermination of Pollutant

Distribution and Movement by

Controlled Laboratory

Experiments

David K. Kreamer, David E. James and Katrina E. Varner

cal water table movement. Some of the

results from the research indicate that

the distribution of hydrocarbons in

these situations is more extreme than

previously recognized, and that entrapped diesel fuel in sands ranged

from 33 to 67 liters/cubic meter. Dimensional analysis as well as colordensity dye studies were also performed on the physical modeling.

In other work, plastic columns

equipped with fiber optic sensors were

used to measure diffusion parameters

from gasoline and diesel sources. Onedimensional mathematical modeling

was applied to observed concentration

values to calculate diffusion parameters. The data were compared with

the findings of other researchers, and

the reproducibility of results was evaluated. Generally, experimental reproducibility was quite good, and the fiber

optic probes showed a large dynamic

range to maximum responses of 22,000

to 35,000 ppmv for gasoline and 43,000

to 62,000 ppmv for diesel fuel. Field

operation of fiber optic devices was

also evaluated.

Sorption studies of selected organic

compounds on various soils were carried out in enclosed steel chambers.

The chambers allowed measurement of

sorption in soil media configured to

simulate actual field conditions. Soil

moisture content, temperature, soil

type, vapor pressure, and soil organic

content were incrementally varied.

Moisture content of an unsaturated soil

was generally the most important variable affecting sorption in vadose zone

materials. Partitioning coefficients were
2

found to be relatively independent of

the degree of saturation when gravimetric water contents exceeded 2-5%.

These findings correlate well with sorption-corrected porosity values obtained

from inverse mathematical modeling of

physical sand tank and column models. While some compounds displayed

sorption fitting a Freundlich isotherm,

dry soils typically exhibited nonlinear

isotherms and finite sorption kinetics.

Hydrogen-bonding compounds also

displayed nonlinear isotherms and finite sorption and desorption kinetics

in the presence of water. A recalcitrant

fraction was observed to be resistant

to desportion, especially with certain

compounds in clays.

Goals and Objectives of the

Research

The goal of this project was to directly

observe and evaluate the subsurface

movement and distribution of selected

volatile organic compounds, particularly

components of petroleum fuels, through

controlled laboratory experiments. Sand

tank, column, and batch-type laboratory

experiments were used to measure the

effect of specific variables associated with

underground contamination events. Many

of the studies centered on gaseous migration, and the variables examined included moisture content, soil type/grain

size, leak rate, temperature, and vapor

densities.

Objectives included: 1) establishing a

visual record through time-lapse photography of the movement of organic liquids

through unsaturated porous media, 2) augmentation of this visual record with quantitative measurements of vapor concentration and migration, 3) observation of

effect of the water table on the distribution

of non-aqueous phase liquids, and 4) the

quantitation of sorptive partitioning of the

gaseous phase organics onto and into

porous material and water. This work provided a video which has been extensively

used for educational purposes, publications in refereed journals, publications in

conference proceedings, and several

master’s theses.

Research Approach

There were three components of the

research approach: sand tank experiments,

column experiments, and batch-type sorption experiments. As the work progressed,

the research approach underwent review,

at times partial revision, and augmentation to optimize results.

Sand tank experiments were carried out

to characterize leak sources and contaminant movement. Experiments were first

performed to vary the tank filling procedure to allow the best reproducibility possible in the experimentation. Leak rate,

petroleum type, soil type, temperature, and

backfill configuration were examined to

determine which materials and methods

produced results that had the best application to field and regulatory situations. In

another aspect of experimentation, it was

quickly discovered that the sand tank environment was inadequate to simulate vapor extraction remediation; gaseous advection on the small sand tank scale suffered boundary interferences which were

too severe to proceed using the smaller

volume tanks proposed in this work.

In vadose zone leak simulations performed in the sand tanks, liquid and vapor

measurements were made. The spatial

and temporal propagation of leaking fluids

was measured and recorded by several

methods including gas chromatography

and time lapse photography. Contour maps

of the distribution of leaked fluids were

constructed. The spatial and temporal

measurements of vapor concentrations

were mathematically modeled using twodimensional inverse methods. Diffusion

parameters of Effective Diffusion Coefficient, De, and Sorption-corrected Porosity,

A*, were determined. Calculated diffusion

parameters were used to predict threedimensional propagation of vapors, and

results were compared with field and laboratory values. Additionally, the sand tanks

were used to measure the distribution of

light non-aqueous phase liquids around

the water table during conditions of vertical water table movement.

Column experiments took on several

forms. Experiments were performed to

measure the flux of organic compounds

across the water table. A glass column

equipped with side ports was used to determine the feasibility of this approach.

Additionally, plastic columns equipped with

fiber optic sensors were used to measure

diffusion parameters from gasoline and

diesel sources. One-dimensional mathematical modeling was applied to observed

concentration values to calculate diffusion

parameters. The data were compared with

the findings of other researchers. The reproducibility of results was evaluated.

Sorption studies of selected organic

compounds on various soils were carried

out. Experiments in enclosed steel chambers were conducted. The chambers allowed measurement of sorption in soil

media configured to simulate actual field

conditions. Soil moisture content, temperature, soil type, vapor pressure, and soil

organic content could be controlled and

incrementally varied.

Summation of Individual Areas

of Research

Sand Tank Experiments

Through controlled laboratory experiments, the effect of specific variables associated with underground contamination

events was examined with time-lapse photography and quantitative measurements

of vapor concentration and migration. The

research approach had several subcomponent activities. Initial sand tank experiments examined the tank filling procedure

with the objective to allow the best reproducibility possible in the experimentation.

Although several procedures were used,

the most reproducible filling technique involved the gravity release of soil into a

tank through a overhead funnel equipped

with sieves. This methodology is visually

shown in a short video (available from

authors), and is described in James et al.

(1996a).

Another subcomponent of the sand tank

activities involved the measurement of liquid and gaseous propagation from a petroleum hydrocarbon leak. The goal of this

endeavor was to characterize leak propagation, hopefully in a way amenable to

mathematical modeling. This undertaking

was successful. The spatial and temporal

propagation of leaking fluids was measured and recorded by the methods discussed previously. Contour maps (in regards to the distribution of leaked fluids)

were constructed. Time-lapse movement

of liquid migration is shown in the video

tape. The spatial and temporal measurements of vapor concentrations were mathematically modeled to determine values

of coefficients and porosity. For example,

De for gasoline was generally found to

range from approximately 0.0024 cm2/sec

for clay to 4.4 cm2/sec for pea gravel.

Calculated diffusion parameters were used

to predict three-dimensional propagation

of vapors, and results were compared with

field and laboratory values. Mathematical

modeling of gaseous movement is detailed in Chaganti (1990), Johnson and

Kreamer (1994), Kreamer et al. (1996),

and Squire (1996). Calculated gaseous

diffusion parameters showed conformance

to the few values available in the literature. Optimal leak rates, petroleum types,

soil types, temperatures, and backfill configuration were examined to determine

those procedures allowing efficient and

safe experimental techniques, while retaining applicability to real field and regulatory situations.
3

In another aspect of experimentation,

the sand tanks were used to measure the

distribution of light non-aqueous phase liquids (LNAPLs) around the water table during conditions of vertical water table movement. This aspect of research is shown in

the video, and is reported in James et al.

(1996a, 1996b), Rajagopalan (1995), and

Sabapathi (1993). Results indicated that

the distribution of hydrocarbons in these

situations is more excessive than previously recognized, and that entrapped diesel fuel in sands ranged from 33 to 67

liters/cubic meter. Dimensional analysis

and color-density dye studies were also

performed on the physical modeling.

Column Studies

Column studies were undertaken to

measure the flux of organic compounds

across the water table and capillary fringe,

and to determine diffusion parameters from

gasoline and diesel sources. A glass column equipped with side ports was used to

determine the feasibility of vertical flux

measurements. This line of experimentation was basically unsuccessful. Slow diffusion in the aqueous phase (approximately 5 orders of magnitude slower than

gaseous diffusion), coupled with advection created by withdrawal of water and

vapor during sampling, created results with

little reproducibility. Spacing of the side

ports was also too wide, and the perturbation of the soil column created by syringe

sample withdrawal appeared to be largely

responsible for the lack of reproducible

results. To gain some understanding of

hydrocarbon movement and distribution

near the water table, studies of vertical

LNAPL distribution around moving water

tables were initiated in sand tanks as described earlier (James et al., 1996a, 1996b;

Rajagopalan, 1995; Sabapathi, 1993).

Additionally, plastic columns equipped

with fiber optic sensors were used to measure diffusion parameters from gasoline

and diesel sources (Kreamer et al., 1996).

One-dimensional mathematical modeling

was applied to observed concentration

values to calculate diffusion parameters.

The data were compared with the findings

of other researchers and the reproducibility of results was evaluated. Generally,

experimental reproducibility was quite

good, and the fiber optic probes showed a

large dynamic range to maximum responses of 22,000 to 35,000 ppmv for

gasoline and 43,000 to 62,000 ppmv for

diesel fuel. Field operation of fiber optic

devices was also evaluated (Kreamer et

al., 1996).

Sorption Batch Testing

Sorption studies of selected organic

compounds on various soils were carried

out in enclosed steel chambers (Fairley,

1993; Houston and Kreamer, 1989; Oja

and Kreamer, 1992; Kreamer et al., 1994;

Schmeltzer, 1993; Steinberg et al., 1994;

Steinberg and Kreamer, 1992, 1993). The

chambers allowed measurement of sorption in soil media configured to simulate

actual field conditions. Soil moisture content, temperature, soil type, vapor pressure, and soil organic content could be

controlled and incrementally varied.

Moisture content of an unsaturated soil

was generally the most important variable

affecting sorption in vadose zone materials. Partitioning coefficients were found to

be relatively independent of the degree of

saturation when gravimetric water content

exceeded 2 to 5%. These findings correlate well with sorption-corrected porosity

values obtained from inverse mathematical modeling of physical sand tank and

column models. While some compounds

displayed sorption fitting a Freundlich isotherm, dry soils typically exhibited nonlinear isotherms and finite sorption kinetics.

Hydrogen-bonding compounds also displayed nonlinear isotherms and finite sorption and desorption kinetics in the presence of water. A recalcitrant fraction was

observed to be resistant to desorption,

especially with certain compounds in clays.

Research Accomplishments

This research has contributed to many

publications, reports, master’s theses, a

widely distributed video, and provided supporting information for many workshops

and conferences.

Publications

Houston, S.L., Kreamer, D.K. and R.

Marwig, 1989. A Batch-Type Testing

Method for Determination of Adsorption of Gaseous Compounds on Partially Saturated Soils. Geotechnical

Testing Journal, ASTM, March 1989,

p.3-10.

Houston, S.L. and D.K. Kreamer, 1989.

Effect of Temperature on the Potential

for Gaseous Adsorption by Partially

Saturated Soils, Engineering Geology

and Geotechnical Engineering, Watters

(ed.) p.357-361. A.A. Balkema/

Rotterdam/Brook, Hardbound, ISBN 90

6191 878 2.

James, D. E, Kreamer, D.K., Sabapathi,

J. and V. Rajagopalan, 1996a. Effects

of Vertical Water Table Fluctuations on

LNAPL Distribution in Porous Media,

1. Effects of Varying Water Table Rise

Rates in Initially Dry Sand. J. of Contaminant Hydrology. Accepted 1995 for

Publication in 1996.

James, D. E, Kreamer, D.K., Rajagopalan,

V. and S.K. Steinberg, 1996b. Effects

of Vertical Water Table Fluctuations on

LNAPL Distribution in Porous Media,

2. Effects of Varying Grain Size in Initially Moist Sands. J. of Contaminant

Hydrology. Accepted 1995 for Publication in 1996.

Johnson, T.E. and D.K. Kreamer, 1994.

Physical and Mathematical Modeling of

Diesel Fuel Liquid and Vapor Movement in Porous Media. Ground Water,

Vol. 32, No. 4., p. 551-560.

Kreamer, D.K., Brown, C. and D. Sloop,

1996. Report on the Suitability of

PetroSense® Probes for Leak Detection at Contaminated Sites. Las Vegas,

NV, March 1996.

Kreamer, D.K., Oja K.J., Steinberg, S.M.,

and H. Phillips, 1994. Vapor Adsorption of a Solvent on Quartz Sands of

Varying Grain Size. Journal of Environmental Engineering, ASCE, Vol. 120,

No. 2, p. 348-358.

Kreamer, D.K., Starr, K., Cogent, S.,

Johnson, T. and H.A. Phillips, 1990.

Gasoline Vapor Compound Ratios as

a Tool to Locate Subsurface Fuel

Leaks; from Minimizing Risk to the Hydrologic Environment, Selected Papers

from the American Institute of Hydrology Conference, Las Vegas, Nevada,

March 13-15, 1990, p.243-249.

Softbound.

Kreamer, D.K. and K.J. Stetzenbach, 1990.

Development of a Standard, Pure-Compound Base Gasoline Mixture for Use

as a Reference in Field and Laboratory

Experiments. Ground Water Monitoring Review, Spring 1990, p.135-145.

Oja, K.J. and D.K. Kreamer, 1992. (Invited Paper). The Effect of Moisture on

Adsorption of Trichloroethylene Vapor

on Natural Soils. Proceedings of the

U.S. Environmental Protection Agency

and National Center for Ground Water

Research Symposium on Soil Venting,

April 29 - May 1, 1991, Houston, TX, p

13-28. Softbound.
4

Steinberg, S.M., Fairley, J. and D.K.

Kreamer, 1994. Slow Desorption of

Toluene from Several Ion-Exchanged

Montmorillonites. J.Soil Contamination

3(3):249-264.

Steinberg, S.M. and D.K. Kreamer, 1992.

Determination of Sorption Isotherms for

Volatile Organic Compounds on Soil

using Gas Chromatography. Structure,

Bonding, and Kinetics at Mineral Surfaces Symposium, American Chemical

Society, April 5-10, 1992, San Francisco.

Steinberg, S.M. and D.K. Kreamer, 1993.

Persistence of Several Volatile Organic

Compounds in a Low Organic Carbon,

Calcareous Soil from Southern Nevada.

Proceedings of the National Symposium on Measuring and Interpreting

VOCs in Soils: State of the Art and

Research Needs. U.S. Environmental

Protection Agency, Jan.12-14, Las Vegas, NV.

Steinberg, S.M. and D.K. Kreamer, 1994.

Determination of Sorption Isotherms for

Volatile Organic Compounds on Unsaturated Calcareous Soil from Southern Nevada Using Inverse Chromatography. Environmental Science and

Technology. Vol. 27, No. 5, 883-888.

Videos

Two short videos were produced: Physical Modeling of Subsurface Fuel Migration by Controlled Laboratory Tests (10

mins) and Effects of Vertical Water Table

Fluctuations on LNAPL Distribution (14

mins). These videos have been shown at

approximately 65 conferences and workshops. On request, they have been distributed to approximately 700 people.

Theses

Master’s theses supported are:

a) from the University of Nevada, Las

Vegas:

• Fairley, J., 1993. Desportion Hystoresis

in Five Ion Exchanged Montmorillonites. Master of Science Thesis. Water

Resources, Department of Geoscience, UNLV.

• Rajagopalan, V., 1995. Influence of Grain

Size of a Porous Medium on the

Movement of Diesel Fuel Due to

Water Table Fluctuations. Master of

Science thesis. Water Resources, Department of Geoscience, UNLV.

• Sabapathi, J., 1993. Effect of Water

Table Fluctuations on Petroleum

Contamination Distribution. Master of

Science Thesis. Water Resources,

Department of Geoscience, UNLV.

• Schmeltzer, J., 1993. Effects of Soil

Moisture, Soil Carbonate and Organic

Matter Content on Vapor Phase Sorption of Volatile Organic Compounds

Using Inverse Gas Chromatography.

Master of Science Thesis. Water Resources, Department of Geoscience,

UNLV.

• Squire, J., 1996. Effect of Unsaturated

Zone Soil Moisture Content on Vapor

Phase Pollutant Propagation in Controlled Laboratory Experiments. Master of Science Thesis. Water Resources, Department of Geoscience,

UNLV.

• Starr, K., 1993. Sand Tank Modeling

of Hydrocarbon Migration Design,

Construction, and Testing. Master of

Science Thesis. Water Resources,

Department of Geoscience, UNLV.

b) from Arizona State University

• Chaganti, S., 1990. Vapor Transport

Modeling in Simulated Leaking Underground Storage Tank Environments. Master of Science Thesis. Department of Civil Engineering, ASU.

• Johnson, T., 1991. Modeling Diesel

Vapor Transport In a Simulated Underground Environment. Master of

Science Thesis. Department of Civil

Engineering, ASU.

Instruction/Technology

Transfer

Conferences, lecture series, training,

and workshops where information from

this research has been presented include:

• Superfund University Training Institute (SUTI) - approximately 6 courses,

U.S. EPA

• DNAPL National Workshop Series -

10 courses, U.S. EPA

• Monitoring Well Design National Series - 10 courses, U.S. EPA

• Landfills RCRA Subtitle D National

and International Series - 15 courses,

U.S. EPA

• U.S. Bureau of Land Management

Hazardous Waste Training - 5

courses. U.S. BLM

• Pesticide Managers Training, UC

Davis Extension - 5 courses, U.S.

EPA

• National Educational courses - 25

courses, National Ground Water Association and Environmental Education Enterprises

• Many National and International Conferences

Project Conclusions and

Recommendations

This work supports the contention that

vapor monitoring around underground storage tanks is beneficial to leak detection

efforts. Problems with the even, radially

outward propagation of gases can exist.

For example, this research has shown

that dry materials tend to sorb vapors,

and a recalcitrant fraction, resistant to desorption, can be formed. Organic materials in soils tested did not demonstrate

sorptive capacities that would make them

effective barriers to vapor migration. Fiber

optic probes showed some promise as

monitoring devices in varying degrees of

vapor saturation.

In sand tank models, colorimetric analysis of dyes, added to leaked fuels, showed

correlation to measured hydrocarbon concentrations, but the disparity is generally

too great between dye color and hydrocarbon concentration to rely on for quantitative work in scientific studies. In experiments run with air-dried porous material

overlying a LNAPL pool floating on a water table, unexpected isolation of product

occurred in situations where the water

table was raised. The distribution of entrapped hydrocarbon was observed to be

much more irregular than similar situations where the vadose zone was originally moist. This suggests the potential for

unusual hydrocarbon entrapment when the

water table rises in conditions where vapor extraction (enhanced volatilization)

techniques have been conducted in an

overlying vadose zone. This situation may

occur with remediation techniques that involve the combination of dewatering and

vapor extraction. Little is known about the

physics of interfacial interactions in soils

of varying moisture content, and a recommendation from this work is that this be

investigated further.

Acknowledgments

The Principal Investigators, David K.

Kreamer and David E. James, would like

to extend our appreciation to our students,

without whose efforts the research would

not be complete. We also extend our gratitude to the University of Nevada, LV for

funding distribution of the research videos.
5

• •

United States

Environmental Protection Agency

Center for Environmental Research Information (G-72)

Cincinnati, OH 45268

EPA/600/S-97/004

Official Business

Penalty for Private Use $300

BULK RATE

POSTAGE & FEES PAID

EPA

PERMIT No. G-35