-------
An environmental protection publication in the solid waste management
series (SW-168). Mention of commercial products does not constitute
endorsement by the U.S. Government. Editing and technical content of
this report are the responsibility of the Systems Management Division
of the Office of Solid Waste Management Programs.
Single copies of this publication are available from Solid Waste
Information, U.S. Environmental Protection Agency, Cincinnati,
Ohio 45268.
-------
USE OF THE WATER BALANCE METHOD
FOR PREDICTING LEACHATE GENERATION
FROM SOLID WASTE DISPOSAL SITES
This report (SW-168) was written
for the Office of Solid Waste Management Programs
by DENNIS G. FENN, KEITH J. HANLEY, and TRUETT V- DeGEARE
U.S. ENVIRONMENTAL PROTECTION AGENCY
1975
-------
CONTENTS
INTRODUCTION
THE WATER BALANCE METHOD
Basic Concepts and Terminology 3
Water Balance Calculations for 8
a Sanitary Landfill
Leachate Generation 17
Other Considerations 23
CONCLUSIONS AND RECOMMENDATIONS 26
APPENDIX 28
Basic Calculations 28
Parameters and Procedures for 31
the Water Balance
Soil Moisture Retention Tables 35
REFERENCES 39
LIST OF FIGURES
No. Page
1 Soil Moisture Storage 5
2 Sanitary Landfill Water Balance 9
3 Water Balance for Cincinnati, Ohio 12
4 Water Balance for Orlando, Florida 14
5 Water Balance for Los Angeles, California 16
6 Time of First Appearance of Leachate 20
7 Annual Leachate Quantities After Time of 21
First Appearance
m
-------
LIST OF TABLES
No.
1 Characteristics of Leachate and Domestic 2
Waste Waters
2 Soil Moisture 6
3 Runoff Coefficients 8
4 Water Balance Data for Cincinnati, Ohio 11
5 Water Balance Data for Orlando, Florida 13
6 Water Balance Data for Los Angeles, California 15
7 Summary of Water Balance Calculations 18
8 Theoretical Leachate Quantities and Time of 23
First Appearance
9 Soil Moisture Retention Table - 100 mm 35
10 Soil Moisture Retention Table - 125 mm 37
11 Soil Moisture Retention Table - 150 mm 38
-------
INTRODUCTION
The land serves as the ultimate repository for over 90
percent of our Nation's solid waste. Incineration, shredding,
and resource recovery processes reduce the amount of solid waste
but produce residues requiring disposal. Because of the impor-
tance of land disposal to solid waste management systems, it
is imperative to thoroughly consider the potential environmental
impact of land disposal site selection and operation. Of parti-
cular concern in this report is potential contamination of ground
and surface waters by leachate.
Leachate is liquid which has percolated through solid waste
and has extracted dissolved or suspended materials from it.
Whenever water comes into direct contact with solid waste, it
will become contaminated. There are many materials in solid waste
which are readily soluble in water. Other water soluble materials
are generated as products of the biological degradation of the
solid waste. Still other materials become soluble through the
action of leachate upon them. Table 1 illustrates some of the
chemical and biological characteristics found in leachate and
compares fresh leachate to a typical domestic waste water.
Generally, the more water that flows through the solid
waste, the more pollutants will be leached out. Thus, proper
sanitary landfill site selection precludes tracts where ground
or surface waters would flow through the waste. Furthermore,
the proper sanitary landfill design and operational approach
is to eliminate or minimize percolation of moisture through the
solid waste. With the smaller amounts of percolation, the pol-
lutants tend to be more concentrated, but the rate at which
they are transmitted to the surrounding environment is not so
apt to exceed the capability of the natural surroundings to
accept and attenuate most of them to some degree.
Recognizing the importance of percolation in the environ-
mental assessment of a potential leachate problem at a land
disposal site, this paper analyzes the factors effecting per-
colation and its relationship to leachate generation and dis-
cusses a methodology to estimate leachate generation. This
methodology is based on the water balance method commonly used
in the soil and water conservation fields.
-------
TABLE 1
CHARACTERISTICS OF LEACHATE AND DOMESTIC WASTE WATERS
ro
Const! tuent
Chloride (Cl)
1 ron (Fe)
Manganese (Mn)
Zinc (Zn)
Magnesium (Mg)
Calcium (Ca)
Potassium (K)
Sodium (Na)
Phosphate (P)
Copper (Cu)
Lead (Pb)
Cadmium (Cd)
Sulfate (SCK)
Total N
Conductivity (/\mhos)
IDS
TSS
PH
Alk as CaCO,
Hardness tot.
300r
COD
Range*
(™g/0
3'i-2,800
0.2-5,500
.06-1 ,1)00
0-1,000
16.5-15,600
5-4,080
2.8-3,770
0-7,700
0-154
0-9-9
0-5.0
--
1-1,826
0-1,416
--
0-42,276
6-2,685
3.7-8.5
0-20,850
0-22,800
9-5*1,610
0-89,520
Range +
(mg/1)
100-2,400
200-1 ,700
--
1-135
--
--
--
100-3,800
5-130
--
--
--
25-500
20-500
--
—
--
4.0-8.5
--
200-5,250
--
100-51 ,000
RangeT
(mg/1)
600-800
210-32.5
75-125
10-30
160-250
900-1,700
295-310
450-500
--
0.5
1.6
0.4
400-650
--
6,000-9,000
10, 000- 14)000
100-700
5.2-6.4
800-4,000
3,500-5,000
7,500-10,000
16,000-22,000
Leachate?
Fresh
742
500
49.
45
277
2 , 1 36
--
--
7.35
0.5
--
--
—
989
9,200
12,620
327
5.2
—
—
14,950
22,650
old
197
1.5
--
0.16
81
254
--
--
4.96
0.1
--
--
--
7-51
1,400
1,144
266
7.3
--
—
--
81
Waste watei
50
0.1
0.1
--
30
50
--
--
10
--
—
—
—
40
700
—
200
8.0
--
—
200
500
r§ Ratio§
15
5,000
490
--
9
43
--
--
0.7
--
--
--
—
25
13
--
1.6
--
--
—
75
45
*0ffice of Solid Waste Management Programs, Hazardous Waste Management Division. An environmental
assessment of potential gas and leachate problems at land disposal sites. Environmental Protection
Publication SW-l10.of. [Cincinnati], U.S. Environmental Protection Agency, 1973. 33 p. [Open-file report,
restricted distribution.]
+Steiner, R. C., A. A. Fungaroli, R. J. Schoenberger, and P. W. Purdom. Criteria for sanitary landfill
development. Public Works, 102(3): 77-79, Mar. 1971.
£Gas and leachate from land disposal of municipal solid waste; summary report. Cincinnati, U.S.
Environmental Protection Agency, Municipal Environmental Research Laboratory, 1975. (In preparation.)
§Brunner, D. R., and R. A. Carnes. Characteristics of percolate of solid and hazardous waste deposits.
Presented at AWWA [American Water Works Association] <4th Annual Conference, June 17, 1974 Boston
Mass. 23 p.'
-------
THE WATER BALANCE METHOD
The infiltration fraction of precipitation is the principle
contributor to leachate generation from a sanitary landfill.*
The infiltration into the soil cover and any subsequent percolation
down to the solid waste will be determined by surface conditions
of the sanitary landfill and by the climatological characteristics
of the site's location.
Therefore, in order to assess the leachate problem for a
given area, a procedure that provides for a detailed analysis
of the existing surface and climatological conditions is needed.
The water balance method is presented as a satisfactory and
feasible procedure for performing the required task.
The following presentation is based on the water balance
method as developed by C. W. Thornthwaite in the soil and water
conservation field. '7'8
Basic Concepts and Terminology
Before discussing the specific engineering application
of the water balance method to sanitary landfills, it is important
to first understand the basic concepts and terminology of the
method itself. The following is a brief discussion of the water
balance method—its basic concepts and terminology.
The water balance, as developed in the soil and water
conservation literature, is based upon the relationship among
precipitation, evapotranspiration, surface runoff, and soil
moisture storage. Precipitation represents that amount of
water added. Evapotranspiration, the combined evaporation
from the plant and soil surfaces and transpiration from plants,
represents the transport of water from the earth back to the
atmosphere, the reverse of precipitation. Surface runoff repre-
sents water which flows directly off the area of concern. The
soil moisture storage capacity represents water which can be
held in the soil.
* Other contributors include the water of decomposition, the
initial moisture content of the solid waste and infiltration of
ground water. All of these factors will be assumed negligible
for a properly sited and designed sanitary landfill, relative to
the infiltration fraction of precipitation.
-------
The water added by precipitation will either evaporate
directly back to the atmosphere from the soil surface, be
utilized by plants through transpiration, serve to recharge
a dried soil to field capacity,* or become downward percola-
tion or surface runoff. The relative amounts of each of these
depends in large measure on the relationship between precipi-
tation and evapotranspiration.
The water balance method centers around the amount of
free water present in the soil. Until the field capacity of
the soil is reached, the moisture in the soil is regarded as
being a balance between what enters it as a result of precipi-
tation and what leaves through evapotranspi ration. If the monthly"1"
moisture loss from the soil through evapotranspiration is compared
with the monthly precipitation, an accounting of the soil
moisture can be made by a simple bookkeeping procedure. The
moisture in the soil is analogous to a bank account where pre-
cipitation adds to the account, and evapotranspiration withdraws
from it.
Since the precipitation and evapotranspiration are governed
by different climatic factors, they are not often the same
either in amount or in distribution through the year. However,
almost all areas of the United States can be characterized by
two seasons during the one-year cycle—a wet season and a dry
season. During the wet months, precipitation will exceed evapo-
transpi ration and water recharge to the soil will occur. During
the dry months, there will be less precipitation and a high
evapotranspiration demand will cause a moisture deficit in
the soil. In most arid and semi-arid areas, moisture recharge
during the wet season theoretically will be too small to attain
field capacity, resulting in little or no water surplus. However,
the opposite is true in humid areas, resulting in a definite
downward percolation.
The three critical factors that must be considered in
the water balance method are the concepts of soil moisture
storage, evapotranspiration and surface water runoff.
* "Field capacity" is defined as the maximum moisture content
which a soil (or solid waste) can retain in a gravitational field
without producing continuous downward percolation.
+ The bookkeeping can be based on yearly, monthly, weekly, or
daily values with the latter providing the best estimate of perco-
lation. For the purposes of this paper, an accounting based on mean
monthly values provides an estimate within the desired accuracy.
-------
Soil Moisture Storage. One way in which the cover soil
of a sanitary landfill influences the amount of percolation
is through its capacity to store water. The amount of storage
mainly depends on the soil type, structure and its attendant
field capacity, as well as the depth of the soil layer itself.
- Field capacity
Available
water
Hygroscopic
water
- Wilting point
- Zero soil moisture
Figure 1. Soil Moisture Storage
As illustrated in Figure 1, the total amount of water
stored in the soil at field capacity consists of two components.
First is the "hygroscopic water" which ranges from zero moisture
content to the wilting point.* This amount of water is tightly
bound to the soil particles, is not available to the plants
for tanspiration, and will never be depleted from the soil. The
second component is the "available water" which ranges from the
wilting point to the field capacity. This water will undergo
capillary movement and is all subject to evapotranspiration losses,
In the water balance method we are concerned with the
available water component of the soil moisture storage. It
is this portion that varies, being depleted by evapotranspiration
losses and recharged by infiltration additions.
* Defined as the moisture content below which moisture
is unavailable for withdrawal by plants.
-------
The amount of available water that can be stored in a
given profile will depend on the depth of root zone and on
the soil type and structure. This amount can vary from a
few millimeters for a shallow rooted crop in a sandy soil to
several hundred millimeters for a fine textured soil with a
deep rooted crop. Approximate field capacities, wilting points
and amounts of available water for several different soil types
are given in Table 2. These values will be used in the water
balance calculations made later in the paper.
TABLE 2
SOIL MOISTURE
MILLIMETER WATER -PER METER SOIL
Type of soil Field capacity* Wilting point* Available water
Fine sand
Sandy loam
Silty loam
Clay loam
Clay
120
200
300
375
450
20
50
100
125
150
100
150
200
250
300
* Thornthwaite, C. W., and J. R. Mather. Instructions and
tables for computing potential evaportanspiration and the water
balance. Centerton, N. J., 1957. p. 185-311. (Drexel Institute
of Technology. Laboratory of Technology. Publications in
Climatology, v.10, no.3).
Evapotranspiration. The amount of available water present in
the soil that'is lost to the atmosphere from a given area depends on
the type of soil and vegetation. It is also closely related to
the climatic factors that affect the soil moisture content,
principally precipitation, temperature and humidity.
Evapotranspiration occurs as the result of evaporation from
the soil and transpiration by the vegetative cover. Of the two,
most of the soil moisture lost to the atmosphere is due to
transpiration.
-------
Actual measurements made in soil lysimeters have shown
that the rate of evapotranspiration drops as soil moisture
is depleted."''0 When the soil moisture is at or near field
capacity, evapotranspiration occurs at its maximum potential
rate. However, as the soil moisture content approaches the
wilting point the amount of available water begins to restrict
the rate of evapotranspiration, resulting in reduced actual
water losses. In the water balance method, this effect will
be taken into account.
The evapotranspiration values used in this paper are those
developed by C. W. Thornthwaite. His method for accounting
for the effect of soil moisture on evapotranspiration rates is
also used. This is done by application of his soil moisture reten-
tion tables as explained in the Appendix. Generally, Thornthwaite's
values show that for humid areas there is essentially no difference
between the potential and actual evapotranspiration rates during
the wet season when sufficient water is available in the soil.
However, the actual evapotranspiration rate drops off during
the growing season as the soil moisture becomes depleted.
It should be pointed out that Thornthwaite's method for
estimating evapotranspiration may not provide the best estimate
for all areas of the country. The literature presents several
methods, each tailored for different areas of the country.
Therefore, it is left to the discretion of the design engineer
to select the method best suited for his area.
Surface Runoff. Some fraction of the incident precipitation
will run off the site and be lost to overland flow before it
has a chance to infiltrate. The amount of surface runoff will
depend upon many factors, including the intensity and duration
of the storm, the antecedent soil moisture condition, the per-
meability and infiltration capacity of the cover soil, the slopes,
and the amount and type of vegetation cover.
In performing the water balance, one must select a method
for estimating the runoff fraction of the incident precipitation
during each month of the year. The approach used herein will
be to apply empirical runoff coefficients which are commonly used
to design surface water drainage systems. These coefficients will
provide a means of estimating surface runoff quantities for given
site conditions. Table 3 presents coefficients used in the
"Rational Formula" for various surface conditions. By applying
the coefficients to the mean monthly precipitation, an estimate
of "mean monthly surface runoff" can be calculated. Although
this method will in most cases underestimate surface runoff, it
was felt that ignoring the surface runoff totally would result
in a misleading assessment of the leachate generation potential.
-------
TABLE 3
RUNOFF COEFFICIENTS*
Surface conditions Runoff coefficient
Grass cover:
Sandy soil ,
Sandy soil ,
Sandy soil ,
Heavy soil ,
Heavy soil ,
Heavy soil ,
flat, 2%
average, 2-7%
steep, 7%
flat, 2%
average, 2-7%
steep, 7%
0.05
0.10
0.15
0.13
0.18
0.25
- 0.10
- 0.15
- 0.20
- 0.17
- 0.22
- 0.35
* Chow, V. T., ed. Handbook of applied hydrology; a
compendium of water resources technology. New York, McGraw-Hill,
[1964]. Iv. (various pagings).
Water Balance Calculations for a Sanitary Landfill
As shown in Figure 2, the water routing through a sanitary
landfill basically consists of two phases—routing through the
soil cover and routing through the compacted solid waste beneath.
The soil cover is that phase which interfaces directly with the
atmosphere and will determine the amount of infiltration into
the soil and percolation into the solid waste. The solid waste
phase and its attendant moisture storage capacity will determine
the quality and time of first appearance of the leachate.
Therefore, a water balance can be performed on the soil cover
phase to determine the amount of percolation. The solid waste
phase can then be analyzed in relation to the percolation amounts
to determine the extent of potential leachate problems.
Treating the moisture regime of the soil cover as a one
dimensional system, the water balance method can be used to
calculate the percolation of water into the solid waste. In
applying the method, the surface conditions of the sanitary
landfill site must be well defined. The type and thickness
of the cover soil, the presence or absence and type of vegeta-
tive cover, and the topographical features are the primary
surface conditions that will affect percolation.
8
-------
Actual
Evapotranspiration
(AET)'
S \ (
\ \-\\\\\\\\.\.\ vV
^ ^ ~"
Precipitation (P) Vegetative
Surface Runoff (R/0) I /1x- Cover
^-^ '
•\ N.
'x?rz Infi 11rat ion (II ^\<
*£J.'l*3y-A-'li-i-A^vZ-^v'-'*^>» V'--)^-*«"-Vv*^^*,.v .— *._.. v"- /o••,-•-*>-.''->--->••", '--^*-y; -_J-/vJ^^. ;'.'>%ta',4.».->»i,^J^j_^,-',';V^»i >•'. /*.•
' '''
Virgin Ground
Figure 2. Sanitary Landfill Water Balance
-------
To best illustrate the water balance of a sanitary landfill,
three case studies have been selected to reflect various climatic
and soil conditions. Cincinnati, Ohio, was selected to represent
a humid climate with a sandy type soil; Orlando, Florida, to
represent a humid climate with a sandy type soil; and Los Angeles,
California, to represent a dry climate with a fine grained soil.
Conditions will vary among sites and among the stages of
a given site's life. These conditions must be considered in
applying the water balance method. For illustrative purposes,
the water balance analysis was simplified by the following
basic assumptions:
1. The landfill has been completed with 0.6 meters (2 feet)
of final cover and graded with a 2 to 4 percent slope over most
of the surface area.
2. The solid waste, cover soil, and vegetative cover were
emplaced instantaneously at the beginning of the first month
of the computation initiation. Practically speaking, this
ignores any percolation that may occur prior to the placement
of the final cover soil.
3. The final use of the site is an open green area to be
used for recreation or pasture.
4. The surface is fully vegetated with a moderately deep-
rooted grass, the roots of which draw water directly from all
parts of the soil cover but not from the underlying solid waste.
5. The sole source of infiltration is precipitation falling
directly on the landfill's surface. All surface runoff from
adjacent drainage areas is diverted around the landfill surface.
All ground water infiltration is prevented through proper site
selection and design.
6. The hydraulic characteristics of the soil cover and
compacted solid waste are uniform in all directions.
7. The depth of the landfill is much less than its horizontal
extent. Thus, all water movement is vertically downward.
The water balances for the three case studies are presented
and depicted in Tables 4, 5, and 6 and Figures 3, 4, and 5 for
Cincinnati, Orlando, and Los Angeles respectively. In order to
fully understand the calculations and manipulations involved in
the water balance procedure, refer to the Appendix which presents
the basic calculations, a discussion of each of the parameters
and their manipulations, and copies of the three soil moisture
retention tables used in the calculations.
10
-------
TABLE 4
WATER BALANCE DATA FOR CINCINNATI, OHIO
f
Parameter k
PET
P
R/0
R/0
I
I-PET
SLNEG (I-PET)
ST (Table C)
AST
AET
PERC
J
0
80
0.17
14
66
+66
150
0
0
+66
F
2
76
0.17
13
63
+61
150
0
2
+61
M
17
89
0.17
15
75
+58
150
0
17
+57
A
50
82
0.17
14
68
+18
(0)
150
0
50
+18
M
102
100
0.17
17
83
-19
-19
131
-19
102
0
J
134
106
0.13
14
92
-42
-61
99
-32
124
0
J
155
97
0.13
13
84
-71
-132
61
-38
122
0
A
138
90
0.13
12
78
-60
-192
41
-20
98
0
s
97
73
0.13
9
64
-33
-225
33
-8
72
0
0
51
65
0.13
8
57
+6
39
+6
51
0
N
17
83
0.13
11
72
+55
94
+55
17
0
D
3
84
0.17
14
70
+67
150
+56
3
+11
Annual
766
1025
154
872
+106
658
213
The parameters are as follows: PET, potential evapotranspiration;
P, precipitation; CJ^/Q surface runoff coefficient; R/0, surface runoff;
I, infiltration; ST, soil moisture storage; A ST, change in storage; AET,
actual evapotranspiration; PERC, percolation. All values are in millimeters
(1 inch = 25.4 mm). See Appendix for discussion of parameters.
11
-------
nun
120.
100.
D
Figure 3. Water Balance for Cincinnati, Ohio
Percolation Q 0 Infiltration
==Soil Moisture Recharge &• A Actual Evapotranspi rat ion
/////Soil Moisture Utilization
12
-------
TABLE 5
WATER BALANCE DATA FOR ORLANDO, FLORIDA
Parameter *
PET
P
C
R/0
R/0
I
I-PET
S.NEG (I-PET)
SI (Table A)
AST
AET
PERC
J
33
50
.075
4
46
+13
100
+9
33
+4
F
39
56
.075
4
52
+13
100
0
39
13
M
59
91
.075
7
84
+25
(0)
100
0
59
25
A M
90 140
88 81
.075 .075
6 6
82 75
-8 -65
-8 -73
92 47
-8 -45
90 120
0 0
J
167
161
.075
13
148
-19
-92
39
-8
156
0
J
175
230
.075
17
213
+38
-25+
77
+38
175
0
A
173
180
.075
13
167
-6
-31
73
-4
171
0
S
142
200
.075
15
185
+43
100
+27
142
16
0
100
121
.075
9
112
+12
100
0
100
12
N
53
39
.075
3
36
-17
-17
84
-16
52
0
D
35
45
.075
3
42
+7
91
+7
35
0
Annual
1206
1342
100
1243
36
1172
70
* See footnote, Table 4.
The situation where a positive I-PET value occurs between two negative
values is a special case. Here, ST is found by direct addition of I-PET to the
preceding ST. The-S-NEG (I-PET) value is then found from the soil moisture
retention table for the ST value.
13
-------
210-
180.
150
120,
M
M
J J
MONTH
0
N
Figure k. Water Balance for Orlando, Florida
II I I|III Percolation 0 0 Infiltration
: Soi 1 Moisture Recharge A A Actual Evapotranspi rat ion
X/Xx/Soil Moisture Utilization
-------
TABLE 6
WATER BALANCE DATA FOR LOS ANGELES, CALIFORNIA
Parameter*
PET
P
C
R/0
R/0
I
I-PET
•£ NEC (I-PET)
ST (Table B)
A ST
AET
PERC
J
34
78
0.15
12
66
+32
52
+32
34
0
F
36
79
0.15
12
67
+31
83
+31
36
0
M
49
66
0.15
10
56
+7
-39
90
+7
49
0
A
59
27
0
0
27
-32
-71
70
-20
47
0
M
76
9
0
0
9
-67
.-138
40
-30
39
0
J
94
2
0
0
2
-92
-230
19
-21
23
0
J
117
0
0
0
0
-117
-347
7
-12
12
0
A
115
1
0
0
1
-114
-461
3
-4
5
0
S
96
5
0
0
5
-91
-552
1
-2
7
0
0
73
14
0
0
14
-59
-611
1
0
14
0
N
52
29
0
0
29
-23
-634
1
0
29
0
D
39
68
0.15
10
58
+19
20
+19
39
0
Annual
840
378
44
334
-506
334
0
See footnote, Table 4,
15
-------
10
M
J J
MONTH
0
N
D
Figure 5- Water Balance for Los Angeles, California
i1 Moisture Recharge 0 0 Infiltration
\\ Moisture Utilization & ^Actual Evapotranspi rat ion
16
-------
Table 7 presents a summary of the water balances for the
three case studies. As expected, the locations in the humid
areas experienced percolation while the dry location experienced
no significant percolation: It is interesting to note that all
three cases are characterized by at least one wet season and one
dry season during the one-year cycle. However, only in the humid
areas is the precipitation sufficiently greater than the evapo-
transpiration to exceed the soil moisture storage capacity and
produce percolation.
The fluctuating nature of percolation during the one-year
cycle is an interesting phenomena to analyze. For example,
examine the percolation in Cincinnati. During the dormant season
(December to April), little or no evapotranspiration occurs,
resulting in a high soil moisture content and significant amounts
of percolation. During the growing season (May to September),
the large evapotranspiration demand utilizes all of the infil-
tration moisture. The effect of the soil moisture storage is
clearly seen in the fall months of October and November when the
infiltration exceeds the potential evapotranspiration. This
excess infiltration recharges soil moisture storage, resulting
in no significant percolation until December. The fluctuating
nature of percolation will cause variations in leachate generation.
Leachate Generation
Knowing the amount of water that percolates through the
cover material (phase I), an analysis of the water routing
through the solid waste (phase II) can now be performed to
determine the magnitude and timing of leachate generation
(refer to Figure 2).
Like its cover material, the underlying solid waste cells
(including the relatively thin layers of daily cover material)
will exhibit a certain capacity to hold water. The field capacity
of solid waste has been determined by many investigators to vary
from 20 percent to as high as 35 percent by volume.3'12 In other
words, the field capacity would vary from about 200 mm water/meter
refuse (2.4 inches/foot) to about 350 mm water/meter refuse
(4.2 inches/foot). For present purposes, a value of 300 mm/meter
(3.6 inches/foot) will be used.
17
-------
TABLE 7
SUMMARY OF WATER BALANCE CALCULATIONS
Location
Parameters - mean annual (mm)
Precipitation Runoff Infiltration AET Percolation
Cincinnati,
Ohio
Orlando,
Florida
Los Angeles,
California
1025
1342
378
154
100
44
872
334
658
1243 1172
334
213
70
18
-------
The amount of water which can be added to the solid waste
before reaching field capacity depends also on its moisture
content when delivered to the landfill site. This value will
vary over a wide range depending on the composition of the waste
and the climate. Several analyses performed on municipal solid waste
show its moisture content to range anywhere from 10 to 20 percent
by volume, ''^'l3 A moisture content of 15 percent by volume
or about 150 mm/m (1.8 inches/foot) will be used here. Therefore,
with a field capacity of 300 mm/m and an initial moisture content
of 250 mm/m the compacted waste would have an adsorbtion capacity
of about 150 mm of water per meter of solid waste (1.8 inches/foot).
Theoretically, the water movement through a compacted solid
waste cell will act like water movement through a soil layer.
In other words, the field capacity of a given solid waste level
must be exceeded before any significant leachate to a lower level
will occur. For the examples, this means that 150 mm of percola-
tion would have to be applied to a municipal solid waste layer
one meter deep before any significant leachate would be generated
from the bottom of that layer. Practically speaking, due to the
heterogeneous nature of the solid waste, some channeling of water
will occur causing some leaching to occur prior to attainment of
field capacity. However, this amount should be small and certainly
not a continuous flow and will be assumed negligible.
Employing the above concepts, one can assess the extent of
the leachate problem for a given sanitary landfill site. The time
of first appearance of leachate would be influenced by the land-
fill's depth and the leachate quantities by the landfill surface
area (size). Figure 6 shows the relationship between annual
percolation amounts and time of first appearance of leachate for
various landfill depths. Figure 7 shows the relationship between
annual percolation amounts and leachate quantities for various
size landfills.
This methodology will be illustrated by application to the
three case studies. Equal amounts of solid waste will be
assumed for all three cases in determining the relative depths
and acreage requirements at the different locations.
Case I—Cincinnati, Ohio. The landfills in this location,
as in most of the northern part of the country, are generally
trench operations or area fills in small ravines. The depth
of these operations would be expected to range between 10 and
20 meters, with the surface area usually above 50 acres (ca.
2X1O^m^). A site will be assumed here with an average depth of
15 meters and a surface area of 202,000 m2 (50 acres). Therefore,
with an average annual percolation of slightly more than 200 mm
19
-------
Figure 6. Time of First Appearance of Leachate
Depth of Landfill (meters)
300 T
200 ' ' —1 —
O
O
O
100 -•
60
Based on a solid waste moisture absorption capacity of 150 mm/m.
Time zero is defined as that time when the field capacity of the
soil cover is first exceeded, producing the first amounts of percolation.
20
-------
figure 7. Annual Lcachatc Quantities
After Tine of Hrst Appearance
Area of Landfill
Surf ace (nrx 104)
300 •-
200 ••
o
o
100
50 ••
20 >*0 60 80
Leachate Quantity (liters/year x TO6)
100
120
21
-------
(Table 4), it would take close to 11 years (Figure 6) for signi-
ficant amounts of leachate to appear at the bottom of the fill,
at which time the average annual leachate quantity would be about
40 million liters (Figure 7).
Case 2—Orlando, Florida. The depth of landfills in this
location and most of the coastal United States are limited due
to proximity of the water table to the ground surface. The
regulations of most state agencies prohibit dumping of solid waste
directly into the ground water and, in fact, require a few feet
of undisturbed soil between the high ground water level and the
bottom of the landfill. With these restrictions, most landfills
will fill below ground only one or two meters and above ground
as high as availability of cover material will allow. Assuming
an average depth of 7.5 meters, only half the depth as Case 1,
the surface area required would be doubled to 100 acres (ca.
4xl0^m2). Therefore, if the average annual percolation is
70 mm (Table 5), it would take close to 15 years for signifi-
cant amounts of leachate to appear (Figure 6), at which time
the average leachate quantity would be about 30 million liters/
year (Figure 7).
Case 3--Los Angeles, California. The landfills in this
area are generally area fills in deep canyons with depths ranging
between 30 and 60 meters. Assuming an average depth of 40 meters,
the surface area required would only be about one-fourth that of
case 1, or 12 acres (ca. 5xl04m2). As noted in Table 6, percolation
is negligible and one can easily assess the leachate problem as
being insignificant for such a location.
A summary of the results for the three case studies is
presented in Table 8.
Analysis of the sanitary landfill water balance calculations
presented above points out some very interesting aspects of leachate
generation of importance to the design engineer. These aspects
should be considered in the overall assessment of the problem
and may enter into the selection and design of leachate control
measures.
First, in most cases leachate generation presents a potential
problem principally in humid (low AET and high precipitation) areas
of the country. Therefore, except for those sites where irrigation
is utilized (discussed later), leachate problems will be virtually
nonexistent at sanitary landfills in arid parts of the country.
22
-------
TABLE 8
THEORETICAL LEACHATE QUANTITIES
AND TIME OF FIRST APPEARANCE
Leachate
Time of first Average
Location appearance annual quantity
(years) (liters/year) x 10
Cincinnati , Ohio
Orlando, Florida
Los Angeles, California
11
15
40
30
0
Second, there may not be a continuous flow of leachate throughout
the year. Percolation and generation of leachate will most likely
follow a pattern similar to that of the precipitation. This will
result in the major portion of the leachate being produced during
those months of significant percolation, with much lower flows
occurring during the rest of the year.
Third, there will be a variation in the leachate generation
pattern and amounts from year to year. The water balance cal-
culations presented in this paper use mean monthly climatic values
determined over a 25-year period. However, a brief analysis of
precipitation data for any given location will indicate significant
variations from year to year. So, while the average year might
indicate a relatively minor leachate problem requiring little
or no leachate control measures, an above average year may result
in an entirely different assessment of the problem. Therefore,
the engineer may wish to base his design on monthly precipitation
values higher than the average values in order to provide a factor
of safety in the estimation of leachate flow.
Other Considerations
The above methodology is presented with the intention of
being a basic tool for engineers in assessing and designing
sanitary landfills. The presentation was purposely kept straight-
forward since the concern was more to develop a clear understanding
of the basic concepts and methods involved rather than a full
scale design manual that would assess leachate problems for all
conditions in all areas of the country.
23
-------
Consequently, in an effort to avoid complications and con-
fusion, special field conditions encountered at sanitary landfills
sites in various parts of the country were ignored. The following
discussion addresses three such special conditions and their
effects on the water balance of a sanitary landfill.
1. Shallower cover soil with no vegetation. During the
sanitary landfill's operating life, only completed parts of the
landfill will be provided with final cover (two feet in thickness)
and vegetated. The rest of the landfill surface might only have
one foot of cover soil (intermediate cover) with no vegetation.
The time to placement of final cover soil and vegetation will
vary with the type and size of operation. Two contrasting examples
are the deep quarry landfill in Montgomery County, Pennsylvania,
and the shallow ravine landfill in Kansas City, Kansas. In the
former case, no portion of the landfill surface will have final
cover and vegetation until the quarry is completely filled. However,
in the latter case the operation is completed in stages with no
part of the landfill surface remaining more than one year without
final cover and vegetation.14
Having different surface characteristics than the final
vegetated cover soil, the intermediate cover soil condition
will affect the results of the water balance. The shallower
depth reduces soil moisture storage, thereby allowing more
percolation to occur. The absence of vegetation will tend to
have a compensating effect by increasing surface runoff and
decreasing the evapotranspiration. Without vegetation, the
surface runoff may double or triple for a heavy-type soil and
experience only a slight increase for a sandy-type soil.
Evaporation from the bare soil surface is quite rapid when the
surface is wet but is greatly retarded when the top few milli-
meters become dry, and practically no evaporation occurs at
depths greater than about 200 mm. Because the surface moisture
condition is heavily dependent on the distribution of precipita-
tion, any estimate of monthly evaporation from bare soil must be
associated with the monthly precipitation. It is estimated that
the evaporation from bare soil is roughly half of the precipitation
for the heavy soils and about 30 percent of the precipitation for
a sandy soil.15
Coupled with the above effects, the operational inefficiencies
at a landfill, such as lack of adequate drainage, erosion, etc.,
will also tend to increase percolation. Therefore, it is safe
to say that for almost all cases significantly more percolation
will occur during the operating life of the landfill. This
being the case, it is very likely that leachate may appear sooner
and in larger quantities than was predicted by the earlier
calculations which considered the completed sanitary landfill
condition.
24
-------
For example, examine the Orlando case study (Table 7), but
assume a bare sandy soil. With the runoff doubled to about
22 mm, the infiltration would decrease to about 1150 mm. With
evapotranspiration (AET) reduced to about 400 mm (30 percent
of the precipitation), the percolation would be greatly increased
to about 750 mm per year, or slightly more than ten times as much
percolation than was predicted for the completed landfill surface.
This would cause leachate to occur in a short period of time
(about one year) and in larger quantities. A similar comparison
can be done for Cincinnati, with similar but somewhat less
severe end results.
2. Irrigation. If the final use of the landfill site is
a park or an agricultural area, irrigation is likely to be
practiced in semi-arid and arid areas. The amount of water
that would be applied to a surface would be equal to the potential
evapotranspiration requirements of the vegetative cover. In
addition, the irrigation necessary to supply heavy evapotrans-
piration demands of the growing season is never 100 percent
efficient. Some fraction—up to 40 percent—is never absorbed
from the soil and eventually percolation will depend on the soil
type and will generally be less in finer grained soils.
The effect of irrigation on the results of the water balance
is obvious. If the irrigation system is not carefully designed
to minimize inefficiencies, it is possible in a dry climate to
create a significant amount of leachate which would not have been
caused by precipitation alone.
For example, examine the Los Angeles case study. If the
final use is a park, irrigation will be required to maintain a
good grass cover. It is not uncommon to apply up to 700 mm
of water annually. If 25 percent of the irrigation is lost to
percolation (less than 40 percent due to the fine grained soil),
175 mm of water will reach the solid waste. Although this is
still a relatively minor amount in light of the landfill depth,
it should, nevertheless, be considered.
3. Frozen ground and snow accumulation. During the winter
months, the northern portion of the country will have frozen ground
conditions and snow accumulations. This will reduce the infil-
tration fraction of the precipitation that falls during the winter
months. This is due to the fact that the frozen ground will
virtually eliminate percolation during these months, and the
spring snow-melt will exhibit higher amounts of surface water
runoff than would normally have occurred in a warmer area.
Therefore, in general, the net effect on the water balance will
be to decrease the amount of percolation and consequently, the
amount of leachate generated.
25
-------
CONCLUSIONS AND RECOMMENDATIONS
The water balance method will serve as a useful engineering
tool in conducting environmental assessments of proposed or
existing sanitary landfill sites, specifically in regards to
leachate generation. However, it should be remembered that the
method as presented in this paper is intended only as a basic
tool for the engineer, and certain site specific assumptions
will be necessary to tailor the method for a particular location.
These assumptions will involve the choice of precipitation data
and proper methods for predicting evapotranspiration and surface
runoff; the accounting for bare soil conditions during the operating
life of the landfill; and the accounting for irrigation, frozen
ground and snow-melt conditions where applicable.
The water balance method points out the following charac-
teristics of leachate generation:
1. Leachate will be generated in humid areas, while no
significant amounts will be generated in dry areas.
2. Leachate generation is not likely to result in a constant
flow throughout the year or from year to year but will follow a
pattern somewhat similar to that of precipitation.
3. In humid areas where leachate will be generated, the
hydrogeology of the site will be carefully evaluated to determine
its inherent capability to naturally attenuate leachate
contaminants. Where it is determined that water pollution would
result, leachate collection and treatment facilities should be
employed.
4. Leachate generation can be minimized by proper and
efficient covering operations, careful contouring and drainage
design of the final surface, proper selection of a vegetative
cover, and in some cases the final use selected for the site.
5. Leachate generation will eventually cease if the final
use of the landfill prevents percolation.
From the above statements, it is obvious that leachate will
be generated for a long period of time unless percolation is
prevented by site operating and completion procedures. If
percolation is prevented in the final site use, leachate generation
will cease shortly after the landfill is completed.
26
-------
1. The water balance technique should be applied to all
existing and proposed sites.
2. If it is determined that leachate generation is signi-
ficant enough to cause a problem (i.e., the site's hydrogeology does
not have the inherent capability to naturally attenuate leachate),
then leachate collection and treatment facilities should be provided
3. Recommended operating practices should be followed
so as to minimize infiltration, thereby reducing leachate generation
during the operating life of the landfill.
4. The final surface of the landfill should be designed to
minimize percolation into the solid waste. For example, if the
final use is an open green area, an impermeable membrane or
clay layer can be placed under the top soil. If the final use
is a parking lot, the surface material should by its very nature
prevent infiltration. In all cases, surface drainage from
adjacent areas should be diverted from the landfill.
27
-------
APPENDIX
Basic Calculations
Case J, - Cincinnati, Ohio - Table H and Figure 3
a) Soil Moisture Storage at Field Capacity -
For a clay-loam and moderately deep-rooted grass,
available water = 250 mm/m (Table 2)
root zone = . 6 m (limited by depth of soil)
Therefore,
soil moisture storage = 250 x .6 = 150 mm at field
capacity
Use Soil Moisture Retention Table n
b) Surface Runoff Coefficient - C - (Table 3)
R/0
Grass and heavy soil at 2% slope
C = .17 for wet season
R/O
=.13 for dry season
(Note: higher coefficient during wet season to reflect
the effect of higher antecedent moisture condition of
soil.)
28
-------
Case 2 - Orlando, Florida - Table 5 and Figure H
a) Soil Moisture Storage at Field Capacity -
For a sandy-loam and moderately deep-rooted grass,
available water =150 mm/m (Table 2)
root zone = . 6 m (limited by depth of soil)
Therefore,
soil moisture storage = 150 x .6 = 90 mm at field
capacity
Since there is no soil moisture retention table for
90 mm, use Soil Moisture Retention Table 9.
b) Surface Runoff Coefficient - C - (Table 3)
R/O
Grass and sandy soil at 2% slope
C = .075 for all months
R/O
Case 3 - Los Angeles, California - Table 6 and Figure 5
a) Soil Moisture Storage at Field Capacity -
For a silty loam and moderately deep-rooted grass
available water = 200 mm/m (Table 2)
root zone = . 6 m (limited by depth of soil)
Therefore,
29
-------
Soil moisture storage = 200 x .6 = 120 mm at field
capacity
Since there is no soil moisture retention table for
120 mm, use Soil Moisture Retention Table 10.
b) Surface Runoff Coefficient - (Table 3)
Grass and silty soil at 2% slope
C =.15 for only those months where P > PET
R/0
(Note: Surface runoff is assumed to be negligible for
the dry months in an arid climate.)
30
-------
Parameters and Procedures for the Water Balance
1. Basic equation: PERC = P R/0 - A ST - AET.
2. Potential Evapotranspiration (PET) - Mean monthly
value based on the 25 year period, 1920 to 1944, were used.
The values are derived from Thornthwaite's PET equation
(Reference 7) and associated tabular data.
3. Precipitation (P) - Mean monthly values based on
the 25 year period, 1920 to 1944, were used. These data are
available from the U. S. Weather Bureau for any location in
the United States.
4. Surface Runoff Coefficients (C R/Q) ~ Based on the
runoff coefficients for use in the rational runoff
calculation method. As strictly defined, the runoff
coefficient is the ratio between the maximum rate of runoff
from the area and the average rate of rainfall on the area.
5. Surface Runoff (R/O) - The selected runoff
coefficient is applied to the mean monthly precipitation to
obtain the mean monthly surface runoff value. This
represents the amount of precipitation that runs off the
landfill surface before it can infiltrate into the cover
soil.
6. Infiltration (I) - Represents the amount of
precipitation that enters the surface of the cover soil. It
is simply the difference between the precipitation and the
surface runoff (1= P - R/O).
7. Infiltration minus potential evapotranspiration
(I - PET) - To determine periods of moisture excess and
deficiency in the soil it is necessary to obtain the
difference between infiltration and potential
evapotranspiration. A negative value of I-PET indicates the
amount by which the infiltration fails to supply the
potential water need of a vegetated area. A positive value
of I-PET indicates the amount of excess water which is
31
-------
available during certain periods of the year for soil
moisture recharge and percolation.
In most locations there is only one so called "wet"
season and one "dry" season per year. Thus, there will be
only one set of consecutive negative and one set of positive
differences. Note that Orlando is an exception to this
statement. Cincinnati and Orlando are examples of locations
where excess precipitation (positive I-PET) during the year
will be greater than the potential water loss (negative I-
PET), while Los Angeles is an example of a location where
the reverse is true. This latter situation will occur in
dry areas where precipitation is not sufficient to bring the
soil moisture back up to its maximum value of water holding
capacity at any time during the year. At locations with
positive annual values of I-PETr the soil moisture at the
end of the wet period is always at the maximum value of
water holding capacity.
8. Accumulated Potential Water Loss [£ NEG (I-PET)] -
The negative values of I-PETr representing the potential
water loss, are summed month by month. In most humid areas
(defined as areas where the sum of all the I-PET values is
positive), the value of accumulated potential water loss [Z
NEG (I-PET) ] with which to start accumulating the negative
values of I-PET is O (see examples for Cincinnati and
Orlando). This value of O is assigned to the last month
having a positive value of I-PET. The reason for this is
that the soil moisture at the end of the wet season is at
field capacity. However, for dry areas (defined as areas
where the annual total I-PET is negative) such as
Los Angeles, soil moisture at the end of the wet season is
below field capacity. Therefore, it is necessary to find an
initial value of E NEG (I-PET) with which to start
accumulating the negative values of I-PET. This is done by
utilizing Thornthwaite1s method of successive approximations
(reference 7) .
9. Soil Moisture Storage (ST) - This factor represents
the soil moisture, or the moisture retained in the soil
32
-------
after a given amount of accumulated potential water loss or
gain has occurred. As shown in the sample calculations for
Cincinnati and Orlando (humid areas), the initial value is
calculated at field capacity by multiplying available water
per unit depth of soil (Table 2) by root zone depth. This
initial value of ST is assigned to the last month having a
positive value of I-PET, i.e., the last month of the wet
season. In dry areas such as Los Angeles, soil moisture at
the end of the wet season is below field capacity. Thus,
the initial, as well as subsequent, ST values must be
determined from the appropriate soil moisture retention
table utilizing the values of I NEG (I-PET) calculated per
item 8, above.
To determine the soil moisture retained each month,
Thornthwaite has developed soil moisture retention tables
for various water holding capacities. Tables 9, 10, and 11 at
the end of this Appendix are the appropriate soil moisture
retention tables for Orlando, Los Angeles and Cincinnatir
respectively. After the soil moisture storage for each of
the months with negative values of I-PET has been found from
the table, the positive values of I-PET, representing
additions of moisture to the soil, must be added to the
previous month1s ST value. No ST value can exceed soil
moisture storage at field capacity. Thus, any excess of I-
PET above this maximum ST value becomes percolation.
ID. Change in Soil Moisture Storage (AST) - Represents
the change in soil moisture from month to month.
11. Actual Evapotranspiration (AET) - Represents the
actual amount of water loss during a given month. As soil
moisture is depleted, the rate of evapotranspiration
decreases below its potential rate, thereby resulting in an
AET value less than the corresponding PET value. For those
months where I-PET is positive, the rate of
evapotranspiration is not limited by moisture availability,
and AET is equal to PET. For those months where I-PET is
negative, the rate of evapotranspiration is limited by soil
moisture availability, and AET =PET + [(I-PET) - AST].
33
-------
12. Percolation (PERC) - After the soil moisture
storage reaches its maximum, any excess infiltration becomes
percolation through the cover soil and into the underlying
solid waste. Therefore, significant percolation will occur
only during those months when I exceeds PET (I-PET is
positive) and the soil moisture exceeds its maximum. For
most humid areas, this will occur during the wet season (see
examples for Orlando and Cincinnati). For dry areas,
significant percolation may never occur (see example for
Los Angeles).
34
-------
TABLE 9
SOIL MOISTURE RETENTION TABLE - 100 MM
SOIL MOISTURE RETAINED AFTER DIFFERENT AMOUNTS OF POTENTIAL EVAPOTRANSPIRATION
HAVE OCCURRED. SOIL MOISTURE STORAGE AT FIELD CAPACITY IS 100 MM.
JNEG(I-PET)
i
345
Umn fcmica it Sou
6
9
0
10
20
30
40
50
60
70
eo
90
100
no
120
130
140
150
160
170
180
190
200
210
220
230
240
250
260
270
280
2SO
300
310
320
330
340
350
350
370
380
390
400
410
420
430
440
450
460
470
480
490
500
100
90
61
74
65
60
54
49
44
40
35
32
29
25
24
22
19
18
16
14
13
12
10
9
8
8
7
6
6
5
5
4
4
3
3
3
2
2
2
2
2
2
1
1
1
1
1
1
1
1
1
99
89
81
73
66
59
53
43
44
39
35
32
29
26
24
21
19
17
16
14
13
11
10
9
8
8
7
6
6
5
5
4
4
3
3
3
2
2
2
2
2
2
1
1
1
1
1
1
1
1
1
98
63
80
72
65
59
53
48
43
39
35
32
29
26
23
21
19
17
15
14
12
11
10
9
8
8
7
6
6
5
4
4
4
3
3
3
2
2
2
2
2
2
1
97
83
79
71
64
58
52
47
43
38
35
31
28
26
23
21
19
17
15
14
12
11
10
9
8
7
7
6
6
5
4
4
4
3
3
3
2
2
2
2
2
2
1
96
87
78
70
64
58
52
47
42
38
34
31
26
25
23
21
19
17
15
14
12
11
10
9
S
7
7
6
6
5
4
4
4
3
3
3
2
2
2
2
2
2
1
1
1
1
1
t
1
1
1
95
66
77
70
63
57
51
46
42
33
34
31
28
25
23
20
18
17
15
14
12
11
10
9
8
7
7
6
5
5
4
4
4
3
3
3
2
2
2
2
2
1
1
1
94
85
77
69
62
56
51
46
41
37
34
30
27
25
22
20
18
16
15
13
12
11
10
9
8
7
6
6
5
5
4
4
4
3
3
3
2
2
2
2
2
1
1
1
1
1
t
1
1
1
1
93
84
76
68
62
56
50
45
41
37
33
30
27
24
22
20
18
16
15
13
12
11
10
9
8
7
6
6
5
5
4
4
4
3
3
3
2
2
2
2
2
1
1
1
32
83
75
63
61
65
50
45
40
36
33
30
27
24
22
20
18
16
14
13
12
11
10
9
8
7
6
6
5
5
4
4
4
3
3
3
2
2
2
2
2
1
1
1
91
82
74
67
60
54
49
44
40
36
33
33
27
24
22
20
18
16
14
13
12
11
10
9
8
7
6
6
5
5
4
4
4
3
3
2
2
2
2
2
2
1
1
-------
SOU KJJSrjSE ttimiOX TA2LE - 150 wi
(CCITIIU(O)
Z(I-PET) 0
UlTfX faTAIKfB II $011
450
460
470
4S3
4 S3
500
510
520
530
540
550
550
570
580
590
600
610
620
630
640
650
660
670
660
690
TOO
710
720
730
740
7
7
5
5
5
5
5
4
4
4
4
3
3
3
3
3
2
2
2
2
2
2
2
2
1
1
1
1
1
1
7
7
6
S
5
5
5
4
4
4
4
3
3
3
3
3
2
2
2
2
2
2
2
2
1
1
1
1
1
1
7
7
6
6
5
5
5
4
4
4
4
3
3
3
3
3
2
2
2
2
2
2
2
1
1
1
1
1
1
1
7
7
6
6
5
5
5
4
4
4
4
3
3
3
3
3
2
2
2
2
2
2
2
1
1
1
1
1
1
1
7
6
6
6
5
5
5
4
4
4
4
y
3
3
3
3
2
2
2
2
2
2
2
t
1
7
6
6
6
5
5
5
4
4
4
4
3
3
3
3
2
2
2
2
2
2
2
2
1
1
1
1
1
1
1
7
6
6
6
5
5
5
4
4
4
4
3
3
3
3
2
2
2
2
2
2
2
2
1
1
t
1
1
1
1
7
6
6
6
5
5
5
4
4
4
3
3
3
3
3
2
2
2
2
2
2
2
2
1
1
t
1
1
1
1
7
6
6
5
5
5
4
4
4
4
3
3
3
3
3
2
2
2
2
2
2
2
2
1
1
1
1
1
1
1
7
6
6
5
5
6
4
4
4
4
3
3
3
3
3
2
2
2
2
2
2
2
2
1
1
1
1
1
1
1
750
780
770
760
790
600
810
620
630
640
36
-------
TABLE 10
SOIL MOISTURE RETENTION TABLE - 125 MM
SOIL MOISTURE RETAINED AFTER DIFFERENT AMOUNTS OF POTENTIAL EVAPOTRANSPIRATION
HAVE OCCURRED. SOIL MOISTURE STORAGE OF FIELD CAPACITY IS 125 MM.
-PET)
0
10
20
30
40
SO
60
70
80
SO
100
110
120
130
140
150
160
170
180
190
200
210
220
230
240
250
260
270
280
290
300
310
320
330
340
350
360
370
360
390
400
410
420
430
440
0
125
115
105
S3
90
83
76
70
65
60
55
51
47
43
40
37
34
31
29
26
24
22
21
19
18
16
15
14
13
12
11
10
9
8
8
0
7
7
6
6
5
5
4
4
4
3
1
124
114
105
97
89
62
76
70
64
59
55
51
47
43
40
37
34
31
29
26
24
22
21
19
18
16
15
14
13
12
11
10
9
8
8
6
7
6
6
5
5
S
4
4
4
3
2
123
113
104
SS
88
.82
75
69
64
59
54
50
46
42
39
36
33
31
29
26
24
22
21
19
17
16
15
14
13
12
11
10
9
8
8
3
wmx-ft
122
112
103
95
87
81
74
69
63
58
54
50
46
42
39
36
33
30
29
26
24
22
21
19
17
16
15
14
13
12
11
10
9
8
8
450
460
470
480
490
500
510
520
530
540
4
:rn»to
121
111
102
S4
86
80
74
68
63
58
53
49
45
41
39
36
33
30
28
26
24
22
20
19
17
16
15
14
13
12
11
10
9
8
8
0
3
3
3
2
2
2
2
2
2
•*
5
ii SOIL
120
110
102
94
85
83
73
68
62
57
53
49
45
41
38
35
32
30
28
25
23
22
.20
13
17
15
14
13
12
11
10
10
9
8
7
5
3
3
3
2
2
2
2
2
2
1
6
119
109
101
93
85
79
73
67
62
57
53
49
45
41
38
35
32
30
28
25
23
22
20
18
17
16
14
13
12
11
10
10
9
8
7
7
113
103
100
32
64
79
72
67
61
56
52
48
44
41
38
35
32
30
27
25
23
21
20
13
17
16
14
13
12
11
10
10
9
8
7
550
560
570
580
590
600
610
620
630
640
117
107
99
SI
84
78
72
66
61
56
52
48
44
40
38
35
32
30
27
25
23
21
20
18
17
15
14
13
12
11
10
9
9
8
7
116
106
99
00
83
77
71
65
60
55
51
47
43
40
37
34
31
29
27
25
23
21
20
13
17
15
14
13
12
11
10
9
9
8
7
-------
TABLE 11
SOIL MOISTURE RETENTION TABLE - 150 MM
SOIL MOISTURE RETAINED AFTER DIFFERENT AMOUNTS OF POTENTIAL EVAPOTRANSPIRATION
HAVE OCCURRED. SOIL MOISTURE STORAGE AT FIELD CAPACITY IS 150 MM.
-PET)
0
10
20
30
40
50
60
70
eo
so
100
110
120
130
140
150
160
170
180
HO
200
210
220
230
240
250
260
270
280
290
300
310
320
330
340
350
360
370
380
390
400
410
420
430
440
0
150
140
131
122
114
107
100
S3
87
82
76
71
66
62
53
54
51
47
44
41
39
38
34
32
30
28
26
24
22
21
20
15
17
V6
15
14
13
12
11
11
10
9
9
8
a
1
149
139
133
122
113
106
99
92
85
81
75
71
6S
(?2
58
53
51
47
44
41
38
35
34
31
29
27
26
24
22
21
19
18
17
16
15
14
13
12
11
11
10
9
9
8
8
2
148
133
129
121
113
105
S3,
92
86
S1
75
70
65
61
57
53
50
47
44
41
38
35
33
31
29
27
25
24
22
21
19
18
17
16
15
14
13
12
11
11
10
9
9
8
8
3
WiTCl
147
137
128
120
112
105
97
91
85
80
75
70
65
51
57
53
50
46
43
40
38
35
33
31
29
27
25
23
22
20
19
18
17
15
15
14
13
12
11
10
10
9
8
8
7
4
BEM.I18
146
136
127
119
111
104
,•97
SO
84
73
74
69
65
SO
56
52
50
45
43
40
37
35
33
31
29
27
25
23
22
20
19
18
17
16
15
14
13
12
11
10
10
9
8
6
7
38
5
ii Sen
145
135
127
118
111
103
97
90
84
79
74
69
64
60
56
52
49
46
43
40
37
35
33
31
29
27
25
23
22
20
19
18
17
16
15
14
13
12
11
10
10
9
8
8
7
6
144
124
126
117
110
103
SS
69
84
73
73
68
64
60
55
52
49
45
42
40
37
35
33
30
28
26
25
23
22
20
19
18
17
16
14
14
13
12
11
10
10
9
8
8
7
7
143
133
125
115
109
102
95
89
83
77
72
68
63
59
55
52
48
45
42
39
37
34
32
30
23
26
24
23
22
20
19
17
16
15
14
13
12
12
11
10
10
9
8
8
7
8
142
132
124
115
108-
101
94
88
83
77
72
67
63
59
54
51
43
45
42
39
36
34
32
30
28
26
24
23
21
20
18
17
16
15
14
13
12
11
11
10
9
9
8
8
7
9
141
131
123
114
107
100
93
67
82
76
71
67
62
58
54
51
47
44
41
39
36
34
32
30
28
26
24
23
21
20
18
17
16
15
14
13
12
11
ft
10
9
9
8
8
7
-------
REFERENCES
1. Sinister, K. A. Leachate damage assessment; interim report.
[Washington], U.S. Environmental Protection Agency, 1975.
27 p., app. (Unpublished report.)
2. Report on the investigation of leaching of a sanitary landfill.
Publication No. 10. Sacramento, California State Water Pollution
Control Board, 1954. [92 p.]
3. Fungaroli, A. A. Pollution of subsurface water by sanitary landfills.
v.l. Washington, U.S. Government Printing Office, 1971. [200 p.]
4. Walker, W. H. Illinois ground water pollution. American Water
Works Association Journal. 61(1):31-40, Jan. 1969.
5. Salvato, J. A., W. G. Wilkie, and B. E. Mead. Sanitary landfill-
leaching prevention and control. Water Pollution Control Federation
Journal. 43(10):2084-2100, Oct. 1971.
6. Thornthwaite, C. W., and J. R. Mather. The water balance. Centerton,
N.J., 1955. 104 p. (Drexel Institute of Technology. Laboratory
of Climatology. Publications in Climatology, v.8, no.l.)
7. Thornthwaite, C. W., and J. R. Mather. Instructions and tables for
computing potential evapotranspiration and the water balance.
Centerton, N.J., 1957. p.185-311. (Drexel Institute of Technology.
Laboratory of Technology. Publications in Climatology, v.10, no.3.)
8. Average climatic water balance data of the continents, pt. 7.
United States. Centerton, N.J., 1964. p.419-615. (C. W.
Thornthwaite Associates. Laboratory of Climatology. Publications
in Climatology, v.l7, no.3.)
9. Mustonen, S. E., and J. L. McGuinness. Estimating evapotranspiration
in a humid region. Agriculture Research Service Technical Bulletin
No. 1389. Washington, U.S. Government Printing Office, July 1968.
123 p.
10. McGuinness, J. L., and E. F. Bordne. Comparison of lysimeter-derived
potential evapotranspiration with computed values. Agricultural
Research Service Technical Bulletin No. 1452. Washington, U.S.
Government Printing Office, Mar. 1972. 71 p.
11. Chow, V. T., ed. Handbook of applied hydrology; a compendium of
water resources technology. New York, McGraw-Hill, [1964]. Iv.
(various pagings).
39
-------
12. Merz, R. C., and R. Stone. Special studies of a sanitary landfill.
U.S. Department of Health, Education, and Welfare, 1970. [222 p.]
(Distributed by National Technical Information Service, Springfield,
Va., as PB-196 148.)
13. Gas and leachate from land disposal of municipal solid waste; summary
report. Cincinnati, U.S. Environmental Protection Agency, Municipal
Environmental Research Laboratory, 1975. (In preparation.)
14. Fenn, D. G., and N. Artz. Establishing a regional sanitary landfill
in Kansas City metropolitan area. Environmental Protection
Publication SW-43d. [Cincinnati], U.S. Environmental Protection
Agency, 1972. 13 p. [Open-file report, restricted distribution.]
15. Effects of refuse dumps on ground water quality. Publication No. 24.
Sacramento, California State Water Pollution Control Board, 1961.
107 p.
Order No. 483
40
t U. S. GOVERNMENT PRINTING OFFICE : 1380 260-229/4066
------- |