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OCR for page 67
Shallow Lanct Burial of
Municipal Wastes
4
INTRODUCTION
KEROS CARTWRIGHT
lllinois State Geological Survey
AB STRACT
Environmental laws and regulations promulgated since the early 1960s have increased the use of the sanitary
landfill and changed its character. Total isolation of wastes from the environment is not possible; some
migration of leachate from wastes buried in the ground will always occur. Disposal sites should be judged
on a site-by-site basis rather than by rigid criteria for site selection and design. The performance should take
into account several factors: (1) the nature of the wastes; (2) the site hydrogeology, including a complete
water balance; (3) the attenuation of contaminants by geologic materials; and (4) the release rate of unattenuated
contaminants to surface waters or groundwaters.
In recent years there has been a trend away from numerous, small disposal sites toward fewer and larger
sites. Large disposal sites increase the environmental stress, since the attenuation capacity of the geologic
material has a finite, though generally not well-defined, limit. Fine-grained geologic materials, which have
low hydraulic conductivities and attenuating characteristics considered favorable for waste disposal, are
geologic conditions generally considered suitable for disposal of wastes. Landfill covers are, perhaps, the
least regulated engineered part of sanitary landfills, yet they are critical in controlling leachate migration and
the water balance. Also, the role of migration in the unsaturated zone is often overlooked, especially in humid
areas.
The environmental effects of land disposal are difficult to de-
termine because the subsurface is complex and we do not
understand it well enough to be able to describe it completely
and monitor it properly. Studies of the hydrologic systems in
fine-grained geologic materials into which current disposal
practices direct most wastes were almost nonexistent 20 years
ago. However, during the past two decades, studies of fine-
grained materials have developed methods to provide the data
required to study waste-disposal sites (e. g., Farquhar and Rov-
ers, 1975; Griffin et al., 1976, 1977; Cartwright et al., 1981).
Today, this is a highly active field of research, and it is nearly
impossible to keep up with all the scientific literature. Many
67
disposal sites have been studied that document the chemical
and physical changes that can occur in the earth materials as
a result of the burial of waste. Land disposal of solid wastes
domestic and industrial has been practiced for many years;
over the past 30 to 40 years the open burning dump has grad-
ually been replaced by the sanitary landfill. Garland and Mosher
(1975) estimated that in 1973 there were about 14,000 operating
sanitary landfills in the United States, and Clark (1975) esti-
mated that about 240 were operating in Illinois in 1973 (down
from the more than 2000 known disposal sites a decade earlier).
This reduction in the number of operating landfills typical
throughout the United States has effectively concentrated
increasing volumes of refuse at fewer sites, especially near the
urban center.
OCR for page 68
68
The ever-increasing volume of waste generated by humans
can be placed in the air, water, and land. The increasingly
strict regulations, passed in the 1960s and 1910s and governing
the discharge of pollutants to the air and surface water, placed
increased emphasis on land disposal. This was only natural
considering the public awareness of air and water pollution and
the very clear dangers if past practices continued. Since there
are interchanges between the three media, land disposal of
waste ultimately discharges some of the waste products back
to the water or air. It is interesting to note that the success of
land disposal is judged primarily by the rate of return of the
pollutants to the air or water. A thoughtful discussion of land
disposal of wastes was published by the American Society for
Testing and Materials (ASTM) Subcommittee D18.14 (19811.
One characteristic of the sanitary landfill is the potential for
production of large amounts of leachate and gas (Pohland, 1980~.
The environmental consequences of the leachate and gas pro-
duction have received considerable attention. This concern, in
turn, has led to a variety of developments for control and treat-
ment, including the concept of total isolation. The degree of
control and treatment required is a function of the environ-
mental sensitivity of the site and the degree of uncertainty
acceptable.
LEACHATE CHARACTERISTICS
In the case of most municipal landfills, leachate is produced
when infiltration from rainfall, surface drainage, and/or ground-
TABLE 4.1 Characteristics of Leachate and Domestic Waste Waters
KEROS CARTWRIGHT
water inflow combine with the moisture already in the waste
to exceed the liquid holding capacity (full capacity). In some
cases, the compaction processes used at landfills may squeeze
sufficient moisture from the refuse to exceed the liquid holding
capacity and cause leachate movement prior to infiltration of
moisture.
There are only limited data on sanitary landfill leachate char-
acteristics (Table 4.1~. There are three main variables control-
ling the leachate characteristics: (1) the variability of the waste
itself, (2) the climatic and hydrogeologic setting, and (3) time.
The available data show the variability of leachate character-
istics from site to site and from time to time. The recognition
of the variability of the characteristics with time offers potential
for innovative control measures and treatment practices.
GAS PRODUCTION
The principal gases produced by sanitary landfills (in addition
to the obnoxious odor) are potentially explosive mixtures of
methane (CH4) and acidification of the groundwater due to the
solution of carbon dioxide (COO. Methane is considered to be
the greatest problem since the acidification problem is gen-
erally easily overcome by the natural buffering capacity of most
geologic materials.
Farquhar and Rovers (1973) studied the pattern of gas gen-
eration of a "typical" sanitary landfill (Figure 4.1~. They iden-
tified four phases: Phase 1, aerobic; Phase 2, anaerobic non-
Constituent
Rangea Ranger Ranger
(mg/L) (mglL) (mg/L)
34-2,800
0.2-5,500
0. 06-1,400
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
Leachate
Fresh
Old Wastewatert
50
0.1
0.1
30
50
Ratio"
Chloride (Cl)
Iron (Fe)
Manganese (Mn)
Zinc (Zn)
Magnesium (Mg)
Calcium (Ca)
Potassium (K)
Sodium (Na)
Phosphate (P)
Copper (Cu)
Lead (Pb)
Cadmium (Cd)
Sulfate (S04)
Total N
Conductivity (limbos)
Total dissolved solids
Total suspended solids
pH
Alkalinity as CaCO3
Hardness total
Biological oxygen demand
Chemical oxygen demand
100-2,400
200-1,700
1-135
100-3,800
5-130
25-500
20-500
0-42,276
0-2,685
0.7-8.5
0-20,850
0-22,800
9-54,610
0-89,520
4.0-8.5
200-5,250
100-51,000
600-800
210-325
75-125
10-30
160-250
900-1,700
295-310
450-500
742
500
49
45
277
2,136
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
197
1.5
0.16
81
254
7.35
0.5
989
9,200
12,620
327
5.2
4.96
0.1
7.51
1,400
1,144
266
7.3
14,950
22,650 81
10
40
700
200
8.0
200
see
15
5,000
490
9
43
0.7
25
13
75
45
1.6
aU. S. Environmental Protection Agency (1973).
Stein et al. (1971~.
CU.S. Environmental Protection Agency (1975~.
Runner and Carnes (1974~.
OCR for page 69
Shallow Land Burial of Municipal Wastes
LANDFILL GAS PRODUCTION PATTERN
100
0 80
an
O LL
=~ 60
O ~
L) O
Or, 40
~ m
,, 20
z
PH A S E
I, ~ , m
1 1
1 !
1 1
l
,~
I
1
/ \ C He
O - ~ Hi
O TIME
FIGURE 4.1 Sanitary landfill gas production pattern (from Farquhar
and Rovers, 1973).
~ a=
methanogenic; Phase 3, anaerobic methanogenic, unsteady;
and Phase 4, anaerobic methanogenic, steady. The nonme-
thanogenic stage is initiated by hydrolytic processes by reduc-
ing complex organic matter to soluble components by means
of cellular enzymes. The microorganisms in the methanogenic
stage are generally considered common bacterial inhabitants
of soil and sewage.
The gas generation is controlled by refuse composition, mois-
ture, temperature, alkalinity, and plI (see Figure 4.2~. The
rate of gas production and the length of each of the initial three
phases vary considerably, depending on conditions. Most san-
itary landfills will reach stable CH4 production (Phase 4) in 180
to 500 days (Farquhar and Rovers, 1973~. The initial phases
may only be a few days to weeks in length.
FACTOR GROUP
a B
TEMPERATURE
r the /
/ ~ AERATION ~—~ _ ~
/ I ~ .~^tCTe 'DC ~ lentil TEATIME \
I I V me I vat" ~
// ~ CONTENT
GAS _ _ pH
\: ALKALINITY
\ NUTRITION
\- TOXIC
COMPO UN DS
, AIR TEMPERATURE
. ATMOSPHERIC
PRESSURE
, ~ ~
/ \~ ~ PLACEMENT AND
/ \\\ COVER ~
/ \ \ \~ PRECIPITATION
/ \ — TOPOG RAPH Y
H Y D RO G E O LOGY
RE FUSE 3~'
COMPOSITION
FACTORS OVER WHICH SOME CONTROL MAY BE
EXERTED DURING SANITARY LANDFILL DESIGN
AND OPERATION.
FIGURE 4.2 Factors affecting gas production in sanitary landfills
(from Farquhar and Rovers, 1973).
69
Conditions may be such as to allow gas generation, but there
may be nutritional deficiencies in the refuse, which impede
the microbial population and slow gas production rates. Also,
it is certain that there are many materials that are toxic or
inhibitory to gas-producing microorganisms, which could be
disposed of into sanitary landfills.
Moisture content is perhaps the most interesting controlling
factor. Moisture is critical to gas generation. Gas production
increases in sanitary landfills with moisture content up to sat-
uration. With saturation and a rise in the water table up through
the refuse, gas generation is reduced, especially the production
of CH4. This in part explains the lack of gas problems at many
older landfills in humid environments.
HYDROGEOLOGIC CRITERIA
Regulations governing the disposal of wastes including haz-
ardous wastes are designed to protect human health and en-
sure the quality of our water resources. It is unrealistic to
assume that rigid geologic and hydrogeologic criteria can be
applied over the entire United States or even to a single state.
Strict application of some criteria, such as the depth from the
bottom of the waste to the water table, can actually lead to the
selection of unsuitable sites. Regulations governing the disposal
of wastes should be applied on a site-by-site basis and should
provide performance standards that the disposal site must meet.
In evaluating a site, the possible effect on the environment is
the most important consideration. In addition, the specific
character of the wastes, the geologic materials at the proposed
site, and their interaction must be carefully examined.
Each regulatory agency has different rules, regulations, and
guidelines that categorize wastes and landfills according to the
type of wastes to be received, geologic setting, or engineering
specifications. For example, landfill sites in Illinois are divided
into five classes on the basis of geologic and groundwater con-
ditions. Illinois regulations require disposal of hazardous wastes
in class I and possibly class II sites. Class I sites require a
permeability barrier at the bottom and sides of the trenches
consisting of 10 ft of material with a hydraulic conductivity of
1 x 10-8 cm/see or less; class II sites require the same thick-
ness of material, but the material must have a hydraulic con-
ductivity of 5 x 10 - ~ cm/see or less. No standard specifications
are given for making this measurement, but ASTM (1970) does
have a suggested laboratory method. Laboratory measurement
of such low values is difficult; the error in measurement may
be quite large (see Figure 4.3>, possibly greater than the dif-
ference that distinguishes the classes of sites. Field measure-
ment is also difficult, time-consuming, and costly and may be
no more accurate than laboratory measurement. Current Illi-
nois Environmental Protection Agency (IEPA) guidelines re-
quire, in addition to the specified permeability barrier at the
bottom and sides of trenches, a minimum of 500 ft separating
the waste from the nearest water well or body of surface water.
These and other hydrogeologic requirements (such as re-
quired depth from the trenches to the water table) are sub-
jective; some are based on misconceptions rather than on sci-
entific principles. For example, there is little point in regulating
OCR for page 70
70
FIGURE 4.3 Comparison of field and lab-
oratory hydraulic conductivities at Wilson-
ville, Illinois (from Johnson et al., 1983).
the distance between a landfill and a water well unless other
factors critical to the protection of the well (such as well con-
struction, well depth, groundwater gradient, and the hydraulic
conductivity of the intervening earth materials) are also con-
sidered in the regulation.
A performance standard should stipulate the maximum ef-
fects disposal can have on surrounding land uses. For example,
a standard might be written to limit the volume and concen-
tration of the contaminant allowed to be discharged from the
landfill and specify the water-quality criteria as related to a
specific water use and/or the degree to which ambient water
quality can be altered. The performance standard can be a
KEROS CARTWRIGHT
Idealized stratigraphic column
Depth
(ft)
_ =_
. _
~ IN .
7y'>
At/
7M ~
'a\/\/
it/
,/~\~\'
'\/~\/
,/~/ aim
b/, -
,_ / '_ /
/~\/\'
'\/~\/
/~/,
/~-/
, ~ /\'
'\/~\/`
/~\~'
_/~_
'
~~/
,\/\,~
'
it\/
/~\/~1
/\/~/\/~
,_ / '_ /
At\/
10—
20—
30—
40—
50-
60 -
70
80 -
90 ~
Average
texture (%)
Material sand-silt-clay
Peoria Loess 5- 65- 30
Roxana Silt
Sangamon Soil
Vandalia Till
(ablation)
Hydraulic Hydraulic
conductivity (cm/s) conductivity (cm/s)
F ield Test1 Lab Test:
1.1 x 10-6
30-35-35 4.4x 10-7 1.6x 10-7
45-40-15 4.1 x 10-5 - 2.3 x 10-4 2.0 x 10-7
Vandalia Till
(basal)
fractured, few
sand lenses
41-40-19 2.0x 10-4 2.0x 10-7
Vandalia Till
(basal) 38-43-19 4.4x 10-7 4.1 x 10-9
few sand lenses
Ban(tell)Fm 10-50-40
Pennsylvanian
shale
'Water injection/recession curve tests by ISGS
2 Samples recompacted
general statement specifying drinking-water standards or des-
ignating specific-ion concentrations, or a combination of both.
The standard should clearly specify the area at which the cri-
teria for water quality are to be applied (such as at the property
line or the nearest aquifer or body of surface water). If a mixing
zone is acceptable (as in the case of a point-source discharge
into surface water), then the performance standard should spec-
ify the size of that zone. These specifications must be realistic;
specifying that there must be a "zero discharge" immediately
adjacent to the waste is not realistic.
The performance standard presumes that it can be demon-
strated in advance how fast and where the contaminants will
OCR for page 71
Shallow Land Burial of Municipal Wastes
travel and that both retardation and mobilization factors are
known. In fact, this is imperfectly known, and estimates are
all that is available. However, predictions can be verified through
the proper design ofthe monitoring system. Methods discussed
in many chapters of this volume deal directly with methods to
predict contaminant transport.
To promulgate guidelines or regulations using design cri-
teria, a regulatory agency must be sufficiently knowledgeable
in its field to ensure that the particular method or design spec-
ified is the only appropriate means of achieving the desired
result. In waste disposal, we generally do not have sufficient
knowledge to stipulate method or site characteristics that apply
consistently. Thus, where design criteria are stipulated, defi-
ciencies are generally present in regulations and guidelines.
Each site will be different and must be considered on a site-
by-site basis.
Unsaturated Flow
Unsaturated flow of groundwater has only recently been rec-
ognized as an important factor in contaminant transport by
geologists and engineers engaged in waste-disposal work. The
field of soil physics has made great progress in the past 20 yr;
however, little is known about this field by many practicing
hydrogeologists. This was shown by the design of French drains
for landfills, such as at Sheffield, Illinois (Dragonette et al.,
1979), where the principles of unsaturated groundwater flow
were not utilized, resulting in nonfunctioning drains.
We must also consider the vapor transport of contaminants
with the landfill gases. Such transport could be very rapid.
Johnson and Cartwright (1978, 1980) reported on studies of
sanitary landfills in the unsaturated zone. They show that the
same hydrologic and geochemical processes occurred as were
reported by Hughes et al. (1971) for sites below the top of the
zone of saturation. Also, there are reports of rapid movement
of contaminants in the unsaturated zone, which cannot be ex-
plained as vapor transport. Rapid fluid movement due to cap-
illary forces or gradients in the unsaturated zone must be oc-
curring. Contaminant transport velocities may be many times
greater (perhaps up to several orders of magnitude) than the
saturated flow velocity (Cartwright, 1982~. The following may
be an important factor in this regard. Consider the transport
of contaminants in saturated porous media; since the effective
porosity term appears in the denominator of the Darcy equa-
tion, the smaller the effective porosity the faster the transport.
While there is not a great deal of information about the effective
porosities of fine-grained sediments, there is general consensus
that it is a small percentage of the total porosity. As these
sediments become unsaturated they lose only a small per-
centage of their water, even at fairly high tensions. The water
lost is essentially equal to the effective porosity. Thus, as the
sediments lose moisture, the remaining effective porosity must
become increasingly small. If an analogy to saturation can be
made, the rate of contaminant transport may increase signifi-
cantly, perhaps by an order of magnitude. (The whole problem
is far more complex than this simple explanation; obviously
much research needs to be undertaken in this area.)
71
Site Size
In recent years there has been a trend from numerous, widely
dispersed, small disposal sites to fewer and larger sites (Clark,
1975; Garland and Mosher, 1975~. It seems that this strategy
should be used with some caution for several reasons. The
attenuation capacity of any geologic materials (its capacity to
remove contaminants from the water) has a limit, which if
exceeded by the volume of leachate that enters the material
will allow contaminants to pass through the material almost
unretarded. Unfortunately, we do not know enough about the
attenuation capacities of geologic materials for most leachate
constituents, so we cannot clearly define this limit. Tables 4.2
and 4.3 give the mobility and relative hazard of a few common
leachate constituents. Larger landfills are more likely than smaller
sites to exceed this limit; therefore, smaller, more widely dis-
persed sites may be less dangerous to the environment.
Wastes should be segregated where possible. This may be
possible to accomplish by designating sites for particular types
of waste disposal. Segregation of wastes allows for better pre-
diction of attenuation characteristics of the geologic material
using geochemically similar waste materials in an aqueous so-
lution. This is a simpler procedure than predicting attenuation
characteristics for mixed wastes. Segregation also prevents in-
teraction among incompatible wastes. Chemical reactions be-
tween some wastes may enhance the mobility of certain toxic
constituents. For example, the mobility of most heavy metals
is directly related to the pH of the solution "generally, the
TABLE 4.2 Ranking of Chemical Constituents in Municipal
Leachate According to Their Relative Mobility through Clay
Mineral Columns by Mean Attenuation Number (ATNja
Mean
Chemical Attenuation
Constituent Number
Qualitative
Grouping
Pb
Zn
Cd
Hg
NH4
Mg
COD
Na
C1
R
Mn
Ca
99.8
97.2
97.0
96.8
58.4
54.7
38.2
37.1
29.3
21.3
15.4
10.7
-11.8
-95.4
- 656.7
High
Moderate
Low
Negative
(elusion)
aThe negative ATN indicates greater concentration emerging from the
columns than in the influent leachate, probably the result of ion ex-
change.
OCR for page 72
72
TABLE 4.3 Increase in Salinity of an Aquifer or Small Stream from Landfill Leachatea
KEROS CARTWRIGHT
Hydraulic
Conductivity Increase in Increase in
of Liner Gradient Aquifer Salinity Stream Salinity
(cm/see) (cm/cm) (ppm) (ppm)
1 x 10-8 1/1 0.8 0.002
1 x 10-6 1/10 7.7 0.02
1 x 10-4 1/100 77.0 0.2
1 x 10-2 1/1000 769.0 ~ n
The salinity of the leachate, using the following assumptions, is low, typical of 20-yr-old sites, not fresh" refuse: (l) hydraulic conductivity of the
aquifer is 1 x 10-0 cm/see, and its gradient is 1/1000 cm/cm; (2) there is 104 m2 of refuse; (3) aquifer is 30 m thick; (4) leachate salinity is 2000
ppm (Hughes et al., 1971); and (5) stream discharge is 1 m3/sec.
more acid the solution, the more mobile the heavy metals
(Griffin et al., 1976, 1977~], and organic toxicants such as PCBs,
which are nearly immobile in aqueous solution, become highly
mobile in organic solvents such as carbon tetrachloride (Griffin
and Chou, 1981~. The present practice of segregating wastes
into acids, bases, and organics is woefully inadequate.
The nature and rate of degradation of wastes must also be
considered; the waste may change, by some natural process,
from its present form to a less complex chemical compound
and less noxious form. Categorization into degradable and non-
degradable wastes is desirable for all types of wastes because
a time factor is added to geologic and geochemical considera-
tions. The decay/decomposition process may result from ra-
dioactive decay, organic decomposition, or other processes.
Wastes that require a long decay/decomposition period (thou-
sands of years) probably should, from a practical hydrogeologic
point of view, be considered nondegradable. These wastes must
be diluted to bring the levels of contaminants to acceptable
levels (Table 4.4~.
Water Balance
The proper balance between water entering and leaving the
disposal sites is critical. Wastes are buried in trenches dug in
natural clay materials or in trenches having artificial or clay
liners of low hydraulic conductivity that will contain the wastes
and thereby protect groundwater resources. This approach can
create problems in humid climates where the amount of water
infiltrating naturally from the surface is greater than the amount
leaving the excavation through the surrounding natural ma-
terial or liner. When this excess infiltration occurs, the disposal
trench fills with leachate and overflows, spilling out the sides
as springs. This phenomenon is known as the bathtub effect.
The bathtub eject is partly attributable to the fact that most
wastes have much higher hydraulic conductivities than the
natural material into which they are placed; they also have very
different unsaturated soil-moisture characteristics. The hy-
draulic conductivity of some wastes can be reduced by com-
paction. Municipal landfill wastes are crushed by heavy equip-
TABLE 4.4 Chemical Constituents in Leachate from a Landfill in Du Page County, Illinois, Ranged by Pollution Hazard Indexa
-
Chemical Effective Concentration Toxicity Mobility Hazard
Constituent Drinking Water Standard Index Index Index
NH4 862/0.5 1724.0 62.9 108,440.0
B (29.9 + 3.5)/1.0 33.4 111.8 3734.0
COD 1340/50 26.8 78.7 2109.0
Hg 0. 87/0.002 435.0 3.2 1392.0
C1 3484/250 13.9 89.3 1241.0
Ca (46.8 + 307.3)/2506 1.42 756.7 1072.0
Cd 1.95/0.01 195.0 3.0 585.0
Fe 4.2/0.3 14.0 41.6 582.0
Na 748/270 2.77 84.6 234.0
Mn (0.02 + 0.02)/0.05 0.78 195.4 153.0
K 501/250 2.00 61.8 123.0
Mg 233/250 0.93 70.7 65.7
Pb 4.46/0.05 89.2 0.2 17.8
Zn 18.8/5.0 3.76 2.8 10.5
Si 14.9/250 0.06 45.3 2.7
aSee Griffin et al. (1976) for the definition and derivation of each term
Actual value not established by EPA; therefore assumed to be the same as chloride.
.._ _~. . . ~~.~—— ~` ~_~4 ~ - ~ 111.
OCR for page 73
Shallow Land Burial of Municipal Wastes
ment or are processed and compacted with soils from the site
to achieve greater and lesser hydraulic conductivity, respec-
tively. If a similar procedure could be followed with toxic waste,
fewer problems with the bathtub effect might occur; however,
many wastes may be too dangerous to handle in this manner,
and different engineering techniques may have to be used to
achieve similar results.
The bathtub effect occurs primarily because more moisture
enters the landfill area than would infiltrate under normal,
undisturbed conditions. Trench covers are generally much more
permeable than the natural material or liners below the waste,
and both cover and liner play an important role in controlling
moisture movement through the waste.
Trench Covers
Trench covers, which are critical to minimizing moisture move-
ment through the waste, were almost ignored until a few years
ago, although careful attention has been given to landfill liners
for some time. The assumption was that trench covers could
be constructed to achieve a desired low hydraulic conductivity
and to limit infiltration for the required period of containment
or until stabilization of the wastes. However, costly, long-term
programs are required to maintain most trench covers. The
covers must withstand attack by vegetation, weather (freeze/
thaw, wet/dry cycles), erosion, and strain caused by consoli-
dation within the trench. Wastes buried in round barrels are
especially hard to deal with since it is very difficult to backfill
completely between round barrels, and the voids left even-
tually cause problems. Trench covers should be designed to
utilize hydrogeologic concepts of saturated and unsaturated
flow systems and to allow for unexpected consolidation. Re-
search is now under way to design and construct a cover that
will control and divert infiltration and will not lose its integrity
under moderate compaction of the wastes (see Herzog et al.
(1981) for a review of the problem). Properly buried and cov-
ered, the wastes would be unaffected by surface effects and
could meet the containment requirements with minimal mon-
itoring and maintenance.
Trench Liners
Assuming that we can construct a trench cover to match the
liner, the question arises as to which type of plastic membrane
or clay should be used and, if clay is used, what type clay it
should be. (Clay is the name of a large group of minerals all
having, among other common characteristics, extremely small,
plate-like crystals.) Clay liners can be compacted so that their
hydraulic conductivities are very low; plastic membranes can
have even lower hydraulic conductivities. Membranes are cur-
rently in vogue and are being used in liners and covers; how-
ever, little information seems to be available on the longevity
of the membranes even though we are considering the iso-
lation of the waste for perhaps hundreds of years. Some concern
has been expressed as to whether these membranes can with-
stand attack by the array of chemicals buried especially the
organic solvents.
Because of these concerns, clay liners have for many years
73
been considered best suited for use in burial of wastes; the
expandable and chemically very active montmorillonites were
usually considered the best material for liners. This type of
clay was known to be subject to attack by acids, however, and
recent research has shown that some organic liquids can cause
cracking in the clay. Other types of clays, even though they
provide less attenuation and cannot be compacted to as low a
permeability as the montmorillonites, may be more stable. Also
burying the wastes in a solid rather than a liquid form might
solve this problem. Water leachates of the various chemicals
probably would not have nearly so destructive an effect on the
clay liners as would "pure" liquid chemicals.
Many of these questions could be solved if expertise from
the clay and chemical industry would be brought to bear on
them. I still favor the use of some mixture of natural earth
materials that allow very slow leakage of leachate from the site
and provide attenuation of many of the leachate constituents.
Many landfills especially the hazardous-waste sites now
have leachate collection systems designed such that the leach-
ate can be intercepted and removed if the cover leaks. This
trend to engineered sites with leachate collection systems seems
to be a temporary measure, particularly when used for slowly
degradable or nondegradable wastes; the leachate collected will
have to be disposed of at a final disposal site, perhaps at great
expense. Such engineered sites may be suitable for the disposal
of degradable wastes where isolation of wastes from the envi-
ronment is not necessary for long periods of time. Engineered
sites may be used to reduce the volume of wastes that must
be transferred for final disposal. Treatment to destroy the haz-
ardous leachate components may be difficult, and processing
the leachate in a standard waste-treatment plant may only di-
lute the hazardous substances, possibly causing the sludge from
the treatment plant to become hazardous. The idea of collecting
leachate from one site and redisposing of it elsewhere resem-
bles "perpetual motion" and can only cause increased difficul-
ties later.
In addition, many of the designs that I have seen for col-
lecting leachate do not correctly apply the basic principles of
soil physics (the study of the movement of water in partly
saturated soils and rocks). Many collection systems would allow
leachate to bypass the collection system if the soil were not
saturated and would only intercept leachate when a massive
failure of the cover occurs. The collection system thus provides
a false sense of security.
MONITORING
The extent of groundwater contamination can sometimes be
determined through a groundwater-monitoring program. Re-
liance on regional groundwater-quality-monitoring programs to
identify the contamination problems will not likely be suc-
cessful since the density of such monitoring would have to be
so fine as to be prohibitively expensive. The occurrence of a
contaminated well in a regional monitoring network indicates
that either (1) the well is located at a point not representative
of regional water quality (i.e., an isolated contaminated point
in the aquifer, which is not representative of water quality in
OCR for page 74
74
the aquifer) or (2) water-quality deterioration in the aquifer is
so extensive that it probably is too late for any reasonable action.
The detection of groundwater contamination is a process by
which it is determined that the groundwater quality has been
altered by the activities of man. Groundwater monitoring is a
process by which the extent of contamination is evaluated and
the necessity of remedial action is determined. Further, mon-
itoring should provide information as to what type of action, if
any, is feasible. As a matter of practicality, detection and mon-
itoring form a continuum and cannot be separated. Detection
of groundwater contamination can be approached by system-
atically searching for sources of contamination and generating
new data, by reviewing all existing data and information sources,
or by chance encounters. Unfortunately, the last method is the
most common.
The hydrogeologic monitoring conducted at waste-disposal
sites should address the purpose of monitoring as well as the
geology of the site to be monitored. This is seldom done, and
thus much of the monitoring that is done may have little tech-
nical merit. Thought must be given to the purpose for the
monitoring. This purpose may be (a) to verify predictions of
contaminant migration; (b) to detect contaminants in drinking-
water supplies and thus protect public health; (c) to activate a
contingency plan, such as a program for leachate collection; (d)
to protect the operator; or (e) a cosmetic procedure to reassure
the public. Each of these purposes will require a somewhat
different array of monitoring points and a somewhat different
sampling program. A proper monitoring system is impossible
to design without a specific purpose, or purposes, in mind.
The position of the monitoring points in the contaminant
flow path must be determined. To do this the contaminant flow
path must be clearly defined in three dimensions. Monitoring
points placed in particular parts of the contaminant plume at
known distances downgradient from the landfill can be used
to estimate contaminant attenuation versus distance and time.
This is necessary to measure the highest level of contamination,
to judge the effectiveness of the site design, or to predict the
future effects of contaminant migration from the site.
Monitoring programs should always be associated with con-
tingency plans. A program designed to detect a potential con-
tamination problem must be accompanied by a program to deal
with that problem if it becomes apparent. Contingency plans
may, at the one extreme, consist merely of abandoning a water
well and, at the other extreme, complete collection and treat-
ment of all contaminants produced by the waste-disposal site.
Most contingency plans should require the monitoring program
to verify predictions of expected contaminant levels at selected
points in the flow system at particular times and should require
that critical contaminant levels be specified that require a re-
sponse. A measure of our understanding of hydrogeologic and
geochemical systems associated with a disposal site is the de-
gree to which we can predict the response of those systems to
the waste.
Monitoring Methodology
A monitoring methodology is an organized approach to eval-
uating groundwater quality and specific groundwater contam-
KEROS CARTWRIGHT
ination problems, thus providing a framework for the planning
and development of a technological step necessary to arrive at
valid conclusions. Several methodologies exist at the site-spe-
cific level, while monitoring "strategies" are being developed
at the national and state levels. This discussion follows that of
Naymik (1982~.
A number of proposed methodologies for monitoring ground-
water currently exist. No one particular methodology is the
best. While some are quite general, most are tailored to a
specific site, because of the differences in goals for the moni-
toring programs. At the national and state levels, strategies are
being developed that will be very general because of the large
variation in groundwater problems. At particular sites, meth-
odologies become very specific.
At the national and state levels the word strategy is normally
used, rather than methodology, to describe the framework for
planning monitoring programs. A strategy is a general approach
that is more of an administrative matter, whereas a method-
ology is more specific and technological in nature. National and
state strategies have not, as yet, been completed. At present,
they are being developed within the guidelines of federal di-
rectives.
Todd et al. (1976) and Tinlin (1981) suggested methodologies
consisting of a general framework for an approach to a site-
specific monitoring program (Table 4.5~. They must be modi-
f~ed according to the specific situation, such as contamination
source, hydrogeologic situation, and political considerations.
Persons involved in a monitoring program will be required to
exercise professional judgment in order to apply these or any
other methodology to a specific site.
Verification of Contamination
Any report of groundwater contamination will have to be ver-
ified by sampling and analysis. Water samples have to be drawn
from springs or wells. To date, there have been no sampling
protocols established for springs, and none may be appropriate.
Preservation of all samples will be required using the protocol
established for well waters. In addition to normal careful pro-
cedures for handling samples to assure correct data, legal chain-
of-custody procedures are often called for in such circumstan-
ces.
According to Gibb et al. (1981), collecting "representative"
water samples from monitoring wells is not a straightforward
or easily accomplished task. Each well and surrounding envi-
ronment has its own individual hydrologic and chemical char-
acter. The selection of the type of sampling or pumping device;
sample preparation, preservation, and storage; and sampling
procedure must be tailored to the size and accessibility of the
individual well, its hydrologic and chemical character, the
chemical constituents of interest, the time of year, and the
purpose for monitoring.
The collection of representative samples was recognized early
as a problem in sampling monitoring wells at waste-disposal
sites, and several investigators have attempted to establish sam-
pling routines. Hughes et al. (1968) noted the need for flushing
monitoring wells and recommended that two well volumes be
pumped. (A well volume constitutes the initial volume of water
OCR for page 75
Shallow Land Burial of Municipal Wastes
TABLE 4.5 Major Sources and Causes of Groundwater Pollution and Methods of Waste Disposala
75
Category
Source
Common Method of Disposal
Surface Seepage Dry Injec-
Percolation Spreading and Pits and Stream Disposal tion
Point Line Diffuse Pond Irrigation Trenches Beds Landfills Wells Wells
Municipal
Sewer Leakage x x NA" NA NA NA NA NA N
Sewage Effluent x x x x x x x
Sewage Sludge x x x x x
Urban Runoff x x x x x x x
Solid wastes x x x
Lawn fertilizers x x
Agricultural
Evapotranspiration
and leaching
(return flow) x x
Fertilizers x x
Soil amendments x x
Pesticides and
herbicides x x
Animal wastes
(feedlots and
dairies) x x x x x x
Stockpiles x NA NA NA NA NA NA NA
Industrial
Cooling water x x x x
Process waters x x x x
Storm runoff x x x x x x
Boiler blowdown x x x
Stockpiles x NA NA NA NA NA NA NA
Water treatment
plant effluent x x x x
Hydrocarbons x x x x
Tanks and
pipeline leaks x x NA NA NA NA NA NA NA
Oilfield wastes
Brines
Hydrocarbons
Mining Wastes
x
x
x
x x
x x
x
x
x
Miscellaneous
Polluted
precipitation
and surface water x x NA NA
Septic tanks and
cesspools
Highway de-icing
Seawater intrusion
x NA x
x NA NA
x NA NA
aFrom Todd et al. (1976).
GINA, not applicable.
in the well casing prior to pumping.) He also recommends, as
did Mooij and Rovers (1975), that wells installed in materials
of low hydraulic conductivity be pumped dry and allowed to
recover before sampling. Mooij and Rovers (1975) also rec-
ommended pumping five well volumes, and Fenn et al. (1977)
recommended three to five well volumes before sampling.
Gilkeson et al. (1977) demonstrated changes in Pb, Fe, Zn,
x x x
NA
x
NA
NA
X X
X X X X
NA NA
x
NA NA
NA NA
NA NA
NA NA
NA NA
Cd, Cu. and Cr concentration in samples from an industrial
waste site with the number of well volumes pumped.
Pumping methods or mechanisms also have been shown to
affect the quality of groundwater samples. Most operating water
wells are sampled using the pumping system in place in the
well. The bailer has been used to sample monitoring wells,
and Hughes et al. (1968) and Mooij and Rovers (1975) suggested
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76
that this was the preferred method of sampling. Air or gas lifts
have also long been used for sampling monitoring wells (Hughes
et al., 1968; Trescott and Finder, 1970; Sommerfeldt and
Campbell, 1975~. However, several groups have cautioned against
the exposure of groundwater to the air during sampling as it
may cause chemical changes, especially in pH, alkalinity, and
iron (Wood, 1970; Wallich (1977~. In recent years small-di-
ameter downhole pumps have been developed that may solve
many of the problems encountered with other pumping mech-
anisms.
CONCLUSIONS
The problems discussed in this paper do not have easy answers.
In most cases we must make tradeoffs between various com-
peting solutions. One thing is certain: there will always be a
need for land disposal of waste. Even if "complete" recycling
were to occur, the sludges and residue from recycling plants
and furnaces would then have to be disposed of. I believe that
land burial of waste is a safe method to use with most wastes,
provided that the disposal site is properly located and engi-
neered, using the best technology available and a good measure
of common sense. Each land-disposal site must be considered
as unique and the disposal operation engineered specifically
for that site.
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Representative terms from entire chapter:
disposal sites
