Aeration

Enriched leachates were stored under carbon dioxide and
also bubbled with air for 15 days. The phenol levels in the
air-aerated samples were significantly reduced when
compared with the levels in the carbon dioxide covered
samples except for nitrophenol, which showed little
reactivity.

The references listed below are reports and articles
submitted in partial fulfillment of Contract 68-03-0208 and
Grants R805731 and R803988 by the University of Arizona
under the sponsorship of the U.S. Environmental Protec-
tion Agency. The Principal Investigator was Dr. Wallace H.
Fuller of the University of Arizona, Tucson, AZ 85721.
Michael H. Roulier was the EPA Project Officer.

The EPA reports and symposium proceedings are avail-
able only from:

National Technical Information Service

5285 Port Royal Road

Springfield, VA 22161

Telephone: 703-487-4650

The NTIS order numbers are listed at the end of each
reference citation. The other references were published in
journals, as noted, and are available at many libraries.

References

1. Fuller, W. H. 1977. Movement of selected metals,
asbestos, and cyanide in soil: applications to disposal
problems. (EPA-600/2-77-020) U.S. Environmental Pro-
tection Agency, Cincinnati, OH 45268. NTIS No. PB
266 905.

2. Fuller, W. H. 1978. Investigation of landfill leachate
pollutant attenuation by soils. (EPA-600/2-78-158) U.S.
Environmental Protection Agency, Cincinnati, OH
45268. NTIS No. PB 286 995.

3. Fuller, W. H., B. A. Alesii, and G. E. Carter. 1979.
Behavior of municipal solid waste leachate. |. Compo-
sition variations. J. Environ. Sci. Health, A14(6): 461-
586.

United States
Environmental Protection
Agency

Information
Cincinnati OH 45268

10.

1.

12.

Center for Environmental Research

. Fuller, W. H., A. Amoozegar-Fard, £. E. Niebla, and M.

Boyle. 1980. Influence of leachate quality on soil atten-
uation of metals. p. 108-117. In David Schultz (ed.)
Proc. 6th Annual Res. Symposium, Chicago, IL, 17-20
Mar. 1980. (EPA 600/9-80-010). U. S. Environmental
Protection Agency, Cincinnati, OH 45268. NTIS No. PB
80-175-086.

. Fuller, W. H., and B. A. Alesii. 1979. Behavior of

municipal solid waste leachates. II. In soil. J. Environ.
Sci. Health, A14(7): 559-592.

. Korte, N. E., J. Skopp, W. H. Fuller, E. E. Niebla, and

B. A. Alesii. 1976. Trace element movement in soil:
influence of soil physical and chemical properties. Soil
Sci. 122:350-359.

. Boyle, M., and W. H. Fuller. 1987. Effect of municipal

solid waste leachate composition on zinc migration
through soils. J. Environ. Qual. 16(4):357-360.

. Turjoman, A. M., and W. H. Fuller. 1987. Behavior of

lead as a migrating pollutant in Saudi Arabian soils.
Arid Soil Research and Rehabilitation, 1°31-45.

. Alesii, B. A., and W. H. Fuller, and M. V. Boyle. 1980.

Effect of leachate flow rate on metal migration through
soil. J. Environ. Qual. 9:119-126.

Fuller, W. H. 1981. Liners of natural porous materials
to minimize pollutant migration. (EPA-600/2-81-122)
U.S. Environmental Protection Agency, Cincinnati, OH
45268. NTIS No. PB 81-221-863.

Amoozegar-Fard, A., A. W. Warrick, and W. H. Fuller.
1983. A simplified model for solute movement though
soils. Soil Sci. Soc. Am. J. 47:1047-1049.
Amoozegar-Fard, A., W. H. Fuller, and A. W. Warrick.
1984. An approach to predicting the movement of
selected polluting metals in soils. J. Environ. Qual.
13:290-297.

. Artiola-Fortuny, J., and W. H. Fuller. 1982a. Phenols in

municipal solid waste leachates and their attenuation
by clay soils. Soil Sci. 133:218-227.

. Artiola-Fortuny, J., and W. H. Fuller. 1982b. Adsorption

of some monchydroxybenzene derivatives by soils.
Soil Sci. 133:18-26.

Official Business
Penalty for Private Use $300

EPA/600/M-89/023

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United States

Environmental Protection

Agency

Risk Reduction
Engineering Laboratory
Cincinnati OH 45268

Research and Development

EPA/600/M-89/023 Jan. 1990

“EPA

ENVIRONMENTAL

RESEARCH BRIEF

Predicting Movement of Selected Metals in So

Application to Disposal Problems

Hinton K. Howard”

Abstract

Data from laboratory column studies of movement of
selected metals in municipal solid waste (MSW) leachate
through soils from several parts of the United States were
used as a base for developing simple, field-oriented tools
for predicting pollutant movement. The metals studied
were arsenic, beryllium, cadmium, chromium, copper,
iron, mercury, nickel, lead, selenium, vanadium, and zinc.
Principal variables in the laboratory study and in the
models were 1. Physical/chemical properties of soil such
as clay content, pH, and iron/manganese hydrous oxide
content, and 2. Leachate properties such as total organic
carbon (TOC) and total salts.

The first model was based on the Lapidus and Amundson
(L-A) equation. A simpler, more adaptable mode! based
on the Error Function equation was also developed and
tested. Both models effectively predicted rates of metal
movement through soil in MSW leachates, but the L-A
method of developing the model was somewhat more
difficult in terms of the amount of input data and param-
eter estimation.

“Risk Reduction Engineering Laboratory, U S Environmental Protection
Agency, Cincinnati, OH 45268

Work was also conducted on movement in soil of the
natural phenolic fraction of MSW leachate and of six
monohydroxybenzene derivatives of phenol added to
MSW leachate. Movement rates and the soil and feachate
characteristics that influenced the rates were identified;
the results have not been incorporated into the model.

This Research Brief was developed by EPA's Risk
Reduction Engineering Laboratory, Cincinnati, OH, to
announce key findings of the research projects that are
fully documented in separate reports and journal articles.

Introduction

The composition of landfill leachate and the charac-
teristics/composition of the soil determine the rate at
which metals in the leachate migrate through the soil.
Having the capability to predict migration rates based on
a knowledge of the leachate and soil characteristics would
greatly aid in the design of landfills. The first section of
this Research Brief outlines the small-scale soil column
experiments that measured migration rates of various
materials through a variety of soils and the development
of equations for predicting leachate migration rates in
soils. The work builds on the results of a previous
literature survey (1) and laboratory soil column studies
with MSW leachate (2,3,4) by Dr. Wallace H. Fuller et al.,



at the University of Arizona. The second section presents
information concerning adsorption and movement in soils
of the phenolic fraction of MSW leachate.

No field data were available to test the equations for
predicting leachate migration rates. It is thought that
models based on laboratory soil column data are capable
of making qualitative predictions (relative migration rates,
etc.) but are much less accurate for quantitative pre-
dictions. The hydraulic characteristics of a laboratory soil
column may not be very representative of field conditions
because 1. removing a soil sample from the ground and
placing it in a column can alter the sample physically and
2. the sample(s) size or numbers may not be sufficient to
represent the total ground area of interest. The adsorptive
characteristics of a soil sample will, however, represent the
field characteristics unless the adsorptive process 1s slow
and the contact times (between leachate and soil) are
different in the laboratory than in the field

Models based on laboratory soil column data may not
quantitatively predict migration in field soils Nevertheless,
predictions of extremes based on laboratory data can
provide important perspective concerning pollutant migra-
tion in the field, e¢g., identifying contaminants or soil/
leachate conditions that will produce slow or rapid
migration.

Soil Column Procedure

The several experiments covered in this publication took
place during the period 1976-1982 The same general
procedures, as described below, were used for all
experiments, with variations introduced as required for
specific experiments.

Leachate was generated in 4000-L containers packed with
materials representative of those found in municipal waste
After packing, the containers were filled with water and the
resulting mix was allowed to age. Leachate was withdrawn
from the bottom of the tank anaerobically and stored under
a blanket of carbon dioxide. Leachate was spiked with the
metals of interest and applied to the 5-cm-diameter x 10-
cm-length packed columns using a constant head
apparatus that supplied a blanket of carbon dioxide to
prevent oxidation/precipitation of leachate components
Leaching through the soils was continued until one of three
conditions was met: breakthrough (effluent concentration
= influent concentration), steady state (unchanging or very
slowly changing effluent concentration); or continued
absence of a trace metal after extended leaching The
trace element content of the leachate was determined and
used to calculate a correlation matrix and a multiple
regression analysis of trace metal mobility versus soil
properties.

The soils used in the experiments, obtained from different
regions of the United States, exhibited a wide range of
composition and characteristics (Table 1). Before being
packed into 5-cm-diameter x 10-cm- length columns, the
souls were air dried and passed through 0 S-mm screens.
Soil columns were perfused with either constant head or
constant flux, depending upon the specific experimental
objectives.

Metals Migration

The metals used in the soil properties study (5,6) were
arsenic, beryllium, cadmium, chromium, copper, mercury,

nickel, lead, selenium, vanadium, and zinc. This study
investigated the effect of soil properties, leachate proper-
ties, and leachate flow rates on Metal Migration

Soil Properties

There were 11 different soils from 7 orders in the Soil
Taxonomy classification system. The best correlation with
mobility was obtained for the percent clay in a soil,
followed in order by the surface area and the percentage
of free iron oxides. The researchers concluded that, even
though the mobilities of trace metals differed significantly,
qualitatively predicting mobility on the basis of these soil
properties should be possible.

Leachate Properties

The leachate properties studies (4,5,7,8) examined the
movement of salts of cadmium, tron, nickel, and zinc
through six soils (see Table 1). The leachate composition
vaniables were total organic carbon (TOC), total inorganic
salts (SALT), and iron (Fe)

Leachate was displaced through the soil under saturated
anaerobic conditions at constant flux rates. Influent and
effluent analysis at set time intervals provided the basis for
conclusions concerning the influence of the various
parameters on metal migration.

For each of the four metals in all of the soils it was found
that the rate of migration was higher when the con-
centration of any of the three parameters (TOC, SALT, Fe)
was higher. The quantitative results from these studies
were used to develop equations for predicting metals
migration.

Leachate Flow Rate

In the leachate flow rate studies (9,10), leachates were
individually enriched with salts of arsenic, beryllium,
cadmium, chromium, tron, nickel, and zinc and displaced
through soils under anaerobic saturated conditions with
controlled flow rates from 12 to 18 cm/day. Nine soils
were used. Effluent collected at hourly intervals was
analyzed for the metal tons of interest. Solution
displacements continued until the concentration of the
metal in the effluent equaled that of the influent.

In general, the results showed that the slower the flux,
the lower the concentration of metals in the effluent at a
given number of pore volume displacements. The
magnitude of the effect was large for arsenic, beryllium,
chromium, and iron ions; and small for cadmium, nickel
and zinc ions.

Prediction Equations

The general method to develop prediction equations
(11,12) was regression analysis with the use of movement
rates for Ni, Cd, and Zn from the soil column studies Soil
and leachate properties were used to obtain coefficients
for the prediction equation.

The predictive equation developed from the error function
model was:

CiCo = 0.5 erfc [(Rz-vt)(4DAt)? §} in)

where C is the solute concentration in soil water at time t
and depth z, Co is the solute concentration in the input


Table 1. Soil Properties*
Iron
Soll Clay Surface Dominant Texture
Oxide
Senes (%)  (%) (M2%/g) Clay Minerals (USDA)
Davidson 7 52 51 Kaolin. + Cl.
Molokai 23 52 67 Kaolin., Gibbs. Cl.
Nicholson 56 49 120 Vermic. Si. Cl.
Fanno 3.7 46 122 = Mont., mica cl.
Mohave (Ca) 25 40 128 = Mica, Mont. Cl. loam
Chalmers 3100 31 96 Mont, Vermic. Si Ci loam
Ava 4 31 62 Vermic., Kaolin. Si Cl loam
Anthony 18 15 20 = =Mont., mica Sandy loam
Mohave Wo 38 © Mica, Kaolin. Cl. loam
Wagram 06 4 8 Kaolin., Chior. Loamy sand
Kalkaska 1.8 5 9 Chlor., Kaolin. Sand

“Most common values cited in the references at the end of this

Research Brief.

+Cl #-Clay; Si #-Silty; Mont. #-Montmorilionite; Kaolin.-Kaolnite;
Gibbs.-Gibbsite; Chior.-Chiorite, Vermic.-Vermiculite

solution; z is the depth; t is the time; v is the pore water
velocity; R is the retardation factor (dimensionless); D ts
the diffusion coefficient (units 12/t); and erfc is the
complementary error function. The user obtains values
for D and R from regression equations [2] of the form:

V = CIP1 + C2p2 + C3P3 + .. [2]

where V is the value for D or R to be used in equation [1];
C1, C2, C3, etc., are coefficients that were developed
from regression analysis of the soil column data, and P1,
P2, P3, etc., are soil and leachate properties such as clay
content, TOC, etc., supplied by the user. One set of
coefficients (C1, C2, C3, etc.) was developed for each
metal when it is the only solute of interest in the leachate,
and another set is to be used when one or more other
competing metals are present in the leachate.

The predictive equations developed from the L-A model
(3) are of the form:

V# =(v/25)[C1P1 +C2P2 + C3P3 + ...] {3]

where V.# is the velocity of the relative solute
concentration (C/Co), e.g. # = 0.1, 0.2, 0.3, etc.; v 1s the
pore water velocity (seepage velocity); C1, C2, C3, etc.,
are regression coefficients calculated from the soil
column data; and P1, P2, P3, etc., are properties such as
clay and iron oxide content in soil and TOC and salt
concentration in leachate. There is one set of the
regression coefficients for each metal and for each of 10
relative concentrations (0.1, 0.2,...0.8, 0.9). Additionally, a
second set of coefficients was developed for use when
one or more competing metals are present in the
leachate along with the metal of interest

The results provide a simple set of equations that can be
quickly calculated without the aid of a computer. Although
no field test has been conducted to date, it should be
Noted that the equations were based on soils with a great

variety of chemical and physical properties. This
suggests that the results will be broadly applicable,
particularly where exact values are not of interest (as in
screening studies).

Phenols Migration/Adsorption

Phenols are water contaminants both because of their
toxicity and because they may, at low concentrations,
render drinking water unpotable due to their strong
taste and odor. Simple phenols (monohydroxybenzene
derivatives) are found in soil as a result of the
decomposition and disposal of organic wastes,
biological synthesis, and the breakdown of aromatic
pesticides. Lakes and lagoons used by paper mill
industries for disposal of large amounts of delignified
wood wastes contain abundant natural phenols. Oil
refineries and coke plants also separate and dispose of
large amounts of phenols from coal tar wastes.
Industries dealing in the manufacturing and use of
medicinals, dyes, resins, perfumes, explosives,
disinfectants, and photodevelopers use and dispose of
sizable quantities of phenols of both natural and
synthetic origin.

in the phenol studies (13, 14), the parameters
investigated were phenol concentration in MSW
leachates versus leachate age, effect of soil
composition on attenuation, and the effect of aeration.

Adsorption

Six different monohydroxybenzene derivatives
(phenols) at concentrations from 5 to 200 ppm in water
were mixed with small amounts of five different soil
samples with which contact was maintained for up to
14 days. The amount of the various phenols adsorbed
on each soil was measured, and the results were
correlated with soil properties. The characteristics that
correlated most highly were, in order, level of free iron
oxide, pH, and percent clay.

Concentration versus Age

The natural phenol levels in Carbon dioxide-blanketed
leachates ranging from 1 to 7 yr old were monitored
over a 12-mo period. The phenol concentration
dropped considerably in the 1-year-old (initially)
leachate but remained relatively constant in 5-yr-old
and 7-yr-old leachate. Even in the older leachates, the
level remained at 40 to 90 times higher than that of
drinking water standards, leading to the conclusion that
MSW landfill leachates retained large quantities of
natural phenols in solution, whether they are young or
old.

Soil Composition

Anaerobic constant flux soil column experiments were
run using the natural leachate as well as leachates
enriched with specific phenols. The overall results
showed that soils with higher iron levels were more
effective at attenuating phenol migration. Also, high
TOC levels and low pH in leachates correlate with low
retention of phenols by soils.