- CLOGGING OF DRAINAGE MATERIAL
IN LEACHATE COLLECTION SYSTEMS 9' 9'
A Thesis Presented to The Faculty of the College of Engineering and Technology Ohio University Athens, Ohio
In Partial Fulfillment of the Requirements for the Degree Master of Science in Civil Engineering
BY V.K. Reddy Nandela) - .- June, 1992 This thesis has been approved for the Department of Civil Engineering and the College of Engineering and Technology
Dean of the College of Engineering and Technology ABSTRACT
Clogging of leachate collection systems could be a real possibility if one assumes that mechanisms such as those responsible for clogging of agricultural drainage tiles would be applicable in the landfill environment. An extensive laboratory testing program was undertaken to investigate the clogging mechanism of three types of drainage media typically utilized in the leachate collection system in the U.S. Two permeameters, 5 inches in diameter by 12 inches long, were fabricated, and flow of actual landfill leachate was maintained gravitationally without recirculation at 1 and 2% hydraulic gradients in a constant head permeability test environment to simulate landfill bottom drainage conditions. Flow rates were monitored, and influent and effluent leachate samples were collected for various physical and chemical characterizations. The study results indicated that the permeability of gravel, poorly graded sand and well-graded sand was reduced from lo0, lo-*, cm/sec, to approximately 10-~, crn/sec, respectively. ACKNOWLEDGMENT
I greatly appreciate the assistance and encouragement given to me by my advisor, Dr. Gayle F. Mitchell. I would like to express my gratitude to Dr. William B. Greer, for his guidance and numerous hours spent with me to initiate this project. I would like also to express my appreciation to Dr. Shad Sargand for his valuable comments and suggestions.
Special thanks to Dr. James Shirey for serving as a member of my thesis committee.
I would like to express my special gratitude for the help rendered by Mr. Teruhisa Masada. I appreciate Waste Management of North America, Inc. for providing partial support of my graduate research work. TABLE OF CONTENTS
Abstract ...... iii Acknowledgements ...... iv Table of Contents ...... v List of Tables ...... viii List of Figures ...... ix
Chapter 1
INTRODUCTION 1.1. GENERAL ...... 1 1.2. OBJECTIVES ...... 6 1.3. RESEARCH OUTLINE ...... 6
Chapter 2
LITERATURE REVIEW 2.1. LEACHATE COLLECTION SYSTEMS ...... 8 2.1.1. DESIGN ...... 10 2.1.1.1. DRAINAGE LAYER ...... 12 2.1.1.2. FILTER LAYER ...... 15 2.1.1.3. COLLECTION PIPES ...... 18 2.2. CLOGGING AND FAILURE OF LCS ...... 19 2.2.1. PHYSICAL MECHANISMS ...... 19 2.2.2. CHEMICAL MECHANISMS ...... 22 2.2.3. BIOCHEMICAL MECHANISMS ...... 24 2.2.4. BIOLOGICAL MECHANISMS ...... 27
Chapter 3
EXPERIMENTAL STUDY 3.1. CHARACTERIZATION AND PREPARATION OF MEDIA ...... 28 3.2. DESCRIPTION OF APPARATUS ...... 32 3.2.1. PERMEAMETER ...... 32 3.2.2. CYLINDERS ...... 37 3.3. LABORATORY EXPERIMENTAL SETUP ...... 37 3.4. DETERMINING BASELINE PERMEABILITY ...... 40 3.5. LEACHATE CHARACTERIZATION ...... 42
Chapter 4
DISCUSSION OF RESULTS 4.1. BASELINE PERMEABILITY TESTS ...... 45 4.1.1. GENERAL ...... 45 4.1.2. AASHTO #8 GRAVEL ...... 47 4.1.3. POORLY GRADED SAND ...... 47 4.1.4. WELL-GRADED SAND ...... 50 4.2. LEACHATE FLOW TEST RESULTS ...... 53 4.2.1. AASHTO #8 GRAVEL ...... 53 4.2.2. POORLY GRADED SAND ...... 54 4.2.3. WELL-GRADED SAND ...... 64 4.3. CHARACTERIZATION OF INFLUENT AND EFFLUENT LEACHATE ...... 64 4.3.1. SOLIDS ANALYSIS ...... 69 4.3.2. CHEMICAL ANALYSIS ...... 74 4.3.3. METAL ANALYSIS ...... 78 4.3.4. pH ANALYSIS ...... 97 4.3.5. ANALYSIS OF LEACHATE, AND RESIDUE DEPOSITED ON
MEDIA AT THE CONCLUSION OF EXPERIMENTS ...... 97
Chapter 5
CONCLUSIONS AND RECOMMENDATIONS 5.1. CONCLUSIONS ...... 101 5.2. RECOMMENDATIONS ...... 104
References ...... 105
Appendix A ...... 118 LIST OF TABLES
Chapter 2
Table 2.1. Particle size requirements for filters ...... 16
Chapter 4
Table 4.1. Baseline permeability test results ...... 46 Table 4.2. Metal analysis results for gravel (Test la) ...... 83 Table 4.3a. Suspended solids and metal analysis of contents of permeameter and cells at the completion of Tests la and lb (Gravel) ...... 98 Table 4.3b. Suspended solids and metal analysis of contents of permeameter and cells at the completion of Tests 4a and 4b (Poorly graded sand) ...... 99 Table 4.3~.Suspended solids and metal analysis of contents of permeameter and cells at the completion of Tests 5a and 5b (Well-graded sand) ...... 100 LIST OF FIGURES
Chapter 2
Figure 2.1. Leachate collection system layout
Chapter 3
Figure 3.la. Sieve arrangements for AASHTO #8 gravel Figure 3.lb. Sieve arrangements for poorly graded sand Figure 3.1~.Sieve arrangements for well-graded sand
Figure 3.2a. Grain size distribution curve for AASHTO #8 gravel Figure 3.2b. Grain size distribution curve for poorly graded sand Figure 3.2~.Grain size distribution curve for well-graded sand Figure 3.3. Overall experimental set-up of large scale constant head permeability and clogging test system Figure 3.4. Schematic of construction and dimensions of permeameter Figure 3.5. Schematic of construction and dimensions of Biological cell unit. Chapter 4
Figure Baseline permeability for gravel in the upper, the lower, and the overall sections of the media for Test lb. Figure Baseline permeability for poorly graded sand in the upper, the lower, and the overall sections of the media for Test 4a. Figure Baseline permeability for well-graded sand in the upper, the lower, and the overall sections of the media for Test 5b. Figure Permeability in the overall section of the media for 2.3% hydraulic gradient system in Test lb. Figure Permeability in the upper and the lower sections of the media for 2.3% hydraulic gradient system in Test lb. Figure Rate of flow curve for 2.3% hydraulic gradient system in Test lb. Figure Permeability in the overall section of the media for 1% hydraulic gradient system in Test 4a. Figure Permeability in the overall section of the media for 2.17% hydraulic gradient system in Test 4b. Figure Permeability in the upper and the lower sections of the media for 1% hydraulic gradient system in Test 4a. Figure Permeability in the upper and the lower sections of the media for 2.17% hydraulic gradient system in Test 4b. Figure Permeability in the overall section of the media for 1% hydraulic gradient system in Test 5a. Figure Permeability in the overall section of the media for 2% hydraulic gradient system in Test 5b. Figure Permeability in the upper and the lower sections
of the media for 1%hydraulic gradient system in
Test 5a. Figure Permeability in the upper and the lower sections of the media for 2% hydraulic gradient system in Test 5b. Figure Total suspended solids for the influent and effluent leachate samples of 0.75% hydraulic gradient system in Test la. Figure Total suspended solids for the influent and effluent leachate samples of 2.3% hydraulic gradient system in Test lb. Figure Total suspended solids for the influent and
effluent leachate samples of 1%hydraulic gradient system in Test 4a. Figure Total suspended solids for the influent and
effluent leachate samples of 2.17% hydraulic
gradient system in Test 4b. Figure Total suspended solids for the influent and
effluent leachate samples of 1%hydraulic gradient system in Test 5a.
Figure COD and alkalinity test results for the influent and effluent leachate samples of 0.75% hydraulic gradient system in Test la. Figure 4.21. COD and alkalinity test results for the influent and effluent leachate samples of 2.3% hydraulic gradient system in Test la. Figure 4.22. TOC test results for the influent and effluent
leachate samples of 1%hydraulic gradient system
in Test 4a. Figure 4.23. TOC test results for the influent and effluent leachate samples of 2.17% hydraulic gradient system in Test 4b. Figure 4.24. TOC test results for the influent and effluent
leachate samples of 1%hydraulic gradient system in Test 5a. Figure 4.25. TOC test results for the influent and effluent leachate samples of 2% hydraulic gradient system in Test 5b. Figure 4.26. Iron concentration in the influent and effluent leachate samples of 1.77% hydraulic gradient system in Test 3a.
Figure 4.27. Iron concentration in the influent and effluent
leachate samples of 2.32% hydraulic gradient system in Test 3b. Figure 4.28. Iron concentration in the influent and effluent
leachate samples of 1%hydraulic gradient system in Test 4a. Figure 4.29. Iron concentration in the influent and effluent
leachate samples of 2.17% hydraulic gradient system in Test 4b. Figure 4.30. Iron concentration in the influent and effluent
leachate samples of 1%hydraulic gradient system in Test 5a. Figure 4.31. Iron concentration in the influent and effluent
leachate samples of 2% hydraulic gradient
system in Test 5b. Figure 4.32. Calcium concentration in the influent and
effluent leachate samples of 1.77% hydraulic gradient system in Test 3a. Figure 4.33. Calcium concentration in the influent and effluent leachate samples of 2.32% hydraulic gradient system in Test 3b. Figure 4.34. Calcium concentration in the influent and
effluent leachate samples of 1%hydraulic
gradient system in Test 4a. Figure 4.35. Calcium concentration in the influent and effluent leachate samples of 2.17% hydraulic gradient system in Test 4b. Figure 4.36. Calcium concentration in the influent and
effluent leachate samples of 1%hydraulic gradient system in Test 5a. Figure 4.37. Calcium concentration in the influent and effluent leachate samples of 2% hydraulic gradient system in Test 5b. Chapter 1
INTRODUCTION
1.1 General
Concern over possible and actual pollution of groundwater supplies by landfills has increased greatly in the last few decades. As a result of this growing concern, numerous studies have been implemented to determine the sources, processes, and severity, as well as the prevention of this pollution.
One way pollution may occur is by percolation of leachate from the landfill to groundwater through the landfill bottom liner. Landfill leachate* is defined as "any liquid, including any suspended components in the liquid, that has percolated through or drained from solid waste" (Jeffrey, 1986) . Leachate is formed as precipitation infiltrates the landfill and contacts the buried waste during construction and after development of the cover. Another source of leachate is the water and other liquids contained in the solid waste.
* The term "leachate" in this thesis refers to landfill leachate. Due to the variety of types and combinations of waste's, the possible leachate constituents are limitless (Kaplovsky, 1976). Inorganics, organics, and microorganisms are the three major groups of contaminants. Common inorganic ions include chlorides, sulfates, calcium, magnesium, sodium, potassium, manganese, phosphorous, iron and nitrates. Heavy metals such as chromium, nickel, lead, copper, and zinc may also be present in leachate, depending on the types of soil cover and liner. Of the myriad organic pollutants in the landfill leachate, generally phenols are the most common. Microorganisms include bacteria and viruses.
A landfill experiences aerobic conditions during its active stage or operational period. Sufficient oxygen is available through the drainage pipes of the LCS or direct exposure of waste to the atmosphere. ~naerobic conditions occur in the post closure period. Organic matter, decomposing under aerobic conditions, produces carbon dioxide which, in turn, combines with the leaching water to form carbonic acid. This acid reacts with metals in the refuse and with calcarious materials in the soil and rocks to produce increased hardness in the water. Under such aerobic conditions, decomposition of organic matter is accomplished by bacterial action releasing amrnonia,which is oxidized to form nitrate. Where decomposition is accomplished by such bacterial action, the leachate has a high biochemical oxygen demand. Leachate may eventually migrate to the saturated zone and result in ground water pollution. At one time, it was assumed that a few feet of separation between refuse and underlying ground water is sufficient to prevent water quality problems. Although it is true that porous media remove many bacteria from the percolating leachate, concentrations of dissolved chemical contamin'ant s are often not significantly affected (Cartwright and Sherman, 1969) . Therefore, a separation of refuse and water table of only a few feet may be insufficient to prevent contamination of neighboring water systems.
Because of the inadequacy of natural filtration and biochemical processes to fully remove contaminants in leachate, it is necessary to prevent leachate from entering the groundwater if pollution is to be prevented. This prevention could be accomplished in two general ways: water can be excluded from the fill, and thereby prevent the formation of leachate, which is generally impractical; or the produced leachate can be intercepted prior to entering the ground water system. Remson (1968) found that most of the water which infiltrates a landfill will not appear as leachate until all the refuse layers have reached field capacity (Field capacity is "the amount of water held in soil after excess water has drained away and the rate of downward movement has materially decreased, which usually takes place within 2-3 days after a rain or irrigation in previous soils of uniform structure and texture.") . Thus, if infiltration can be maintained such that the refuse never
reaches field capacity, leachate production will be minimized. In practice, however, this goal can only be
approximated because liners used to cover deposited refuse inevitably permit some infiltration; also, some leachate is produced immediately after refuse burial by compaction of
initially wet refuse (Lane, 1968). During wet seasons, the uncovered portion of the landfill may initially exceed field capacity even before attempts at exclusion of infiltration. Therefore, because leachate production cannot be completely prevented, provision should be made to intercept and remove leachate by use of a leachate collection system (LCS) at the bottom of the landfill.
A typical landfill leachate collection system consists of a series of contiguous, alternating-direction sloping layers, constructed from material of low permeability, overlaid by a drainage layer of high permeability. Whatever
the quality and quantity of leachate, it will move gravitationally downgradient through the waste material to the base of the landfill where it encounters the leachate
collection system. Here the leachate passes into a high permeability drainage layer (generally gravel) , and flows to a perforated pipe system at the base of the drainage layer. Within the perforated pipe, its velocity is greatly increased as it travels to a sump area at the low elevation end of the landfill facility. The collected leachate is pumped from the sump into a temporary storage tank from which it is pumped either to an on-site treatment facility or to a larger volume storage tank.
The first leachate collection systems were installed in landfills in the early 1970's. Since then design and operation practices have changed significantly. As a result, experience with modern leachate collection system design performance is limited.
Although some guidelines on design and construction of leachate collection systems can be obtained from recent literature, little information is available on the performance of leachate collection systems. One way in which the performance of a LCS could be impaired is by clogging of the drainage blanket and/or the perforated pipe system. According to Bass (1986), some recent studies have concluded that clogging of LCS is a possibility, particularly if one assumes that mechanisms such as those responsible for clogging of agricultural tile drainage are operative in the landfill environment. Leachate collection systems can clog due to a variety of physical, chemical, biological and biochemical mechanisms. A system is considered to be clogged if it cannot maintain the leachate saturated depth over the liner at less than 30 cm as required by the Resource Conservation and Recovery Act (RCRA) standards (Bass, 198 6) . Most of the experience with drainage systems and drain clogging is in the area of agricultural drainage. Limited research has been conducted on the clogging of the drainage blanket in the leachate collection system. Laboratory and field investigations on this specific component of the leachate collection system are lacking. In order to fill this void, a study on clogging of drainage materi'al in leachate collection systems was undertaken.
1.2 Objectives
In initiating this study, the following objectives were established. These are:
1. to establish how the permeability of the drainage layer varies with type of material.
2. to study the variations in the permeability of the drainage layer due to clogging.
3. to investigate the mechanisms causing clogging of the drainage layer.
1.3 Research outline
To meet these objectives, three different media were selected for this study. These were gravel, poorly graded sand and well-graded sand with permeabilities of approximate- ly lo0, and cm/sec, respectively. Constant head permeability tests were conducted using landfill leachate on each media to determine the variation in permeability due to clogging. Leachate influent and effluent samples were collected and analyzed for various physical, chemical and biological parameters.
The contents of each chapter are briefly discussed below:
Chapter 2 discusses LCS design and clogging mechanisms.
Chapter 3 discusses about the experimental set-up and determining permeability.
Chapter 4 presents results of this study.
Chapter 5 presents conclusions and recommendations. Chapter 2
LITERATURE REVIEW
2.1 Leachate Collection Systems
The U.S. Environmental Protection Agency's minimum technological requirements for waste treatment, storage, and waste disposal facilities require the use of leachate collection systems (LCS) in new landfills (McEnroe et al., 1982) . The leachate collection system should be designed to collect and remove leachate from the drainage layer during the active life of the facility and post closure maintenance period.
Early regulations (before 1982) from the U.S. Environmental Protection Agency (EPA) specified only general guidelines for leachate collection system designs. The regulation stated that:
"A leachate detection, collection and removal system must be designed so that liquid will flow freely from the system to prevent the creation of pressure head within the collection system in excess of that necessary to cause the liquid to flow freely ." In other words, early regulations required that leachate collection systems should allow free flow of leachate without mounding, but did not make specific requirements about LCS design, performance, or maintenance (McEnroe, 1988) .
Current EPA regulations are more specific, requiring that new landfills have a leachate collection system "that is designed, constructed, maintained, and operated to collect and remove leachate from the landfill." The LCS is to be located immediately above the liner (a layer of low permeability such as a clay and/or synthetic material which is required at the base of the landfill) . The landfill (to include LCS) is to be designed and operated "to ensure that the leachate depth over the liner does not exceed 30 cms (1 foot) ." EPA regulations require that the LCS be:
(i) Constructed of materials that are:
(A) Chemically resistant to the waste managed in the landfill and the leachate expected to be generated; and
(B) Of sufficient strength and thickness to prevent collapse under the pressure exerted by overlying wastes, waste cover materials, and any equipment used at the landfill; (ii) Designed and operated to function without clogging through the scheduled closure of the landfill."
Experience with LCS clogging is not very extensive. Most of the experience with clogging mechanisms is from underground agricultural drainage systems, porous media wastewater treatment works, wastewater tile fields, water supply wells, and other subsurface liquid conveyance systems (Bass, 1986) . Young et .a1 (1982) reported that clogging in a
LCS may be similar to clogging in underground agricultural drainage systems. They also indicated that clogging which occurs in wastewater systems such as porous media filters (sand filters, trickling filters) is applicable to understanding physical and biological clogging mechanisms in leachate collection systems. The major types of clogging mechanisms in LCS are physical, chemical, biochemical, and biological. Each of these topics are discussed in later sections (2.2.1, 2.2.2, 2.2.3, 2.2.4) of this chapter.
2.1.1 Design
Two types of landfill designs evolved in the United States in the early 1970,s: the natural attenuation (NA) type and containment type. In the NA type landfill design, a clay liner is placed at the bottom of the landfill and leachate is allowed to percolate through the liner and eventually enter the groundwater system. The NA design ,relies upon natural processes in the liner and other soil to remove contaminants from the leachate before it reaches a groundwater supply. However, because contaminant removal in this manner is now
considered unreliable, the NA design is no longer permitted for new landfills in the United States.
The containment landfill design is the only design now permitted in the United States. The essential difference
between the NA and containment designs is that the later includes a leachate collection system immediately above the liner at the base of the landfill. Containment design may be further broken down into two subdesigns: one for hazardous
waste and one for the nonhazardous waste. The design for hazardous waste requires a secondary system for leachate collection below the primary one, and a means to detect
leakage from the primary system. EPA regulations (40 CFR
1991, July 1, 1991) require a leachate collection system to
have :
"(a) At least a 30 centimeter drainage layer with a
hydraulic conductivity not less than 1x10-' cm/sec and a
minimum slope of 2 percent;
(b) A graded granular or synthetic fabric filter above the drainage layer to prevent clogging, except in the case of secondary leachate detection, collection, and removal systems that are in direct contact with the primary synthetic liner.
(c) A drainage tile system of appropriate size and spacing and a sump pump or other means to efficiently remove leachate."
A schematic of a closed containment landfill for nonhazardous waste illustrating the leachate collection system is shown in Figure 2.1.
2.1.1.1 Drainage Layer
Leachate movement in the drainage layer is a function of liner slope, collection-pipe size and spacing, the size and number of perforat ions in the collection pipe, permeability of the drainage material, and rate of leachate generation (Moore, 1980) . The maximum rate of leachate generation must be estimated in order to design the components of the drainage layer (Bass, 1986). The rate of leachate generated from infiltrating precipitation can be estimated by performing a water balance on the landfill. One way to obtain the needed water balance and generation rate is by use of the HELP Computer Model (Schroeder et . al., 1984) . The HELP Model gives output on water movement through the system including percolation, drainage, evapotranspiration, runoff, and soil water storage. The results obtained with this model are a function of climatologic and soil conditi,ons for a particular waste disposal site.
Another important consideration in designing the drainage layer is the maximum height to which leachate rises in the drainage layer. Harr (1962) presented the following equation which may be used to estimate leachate depth above the base (which is assumed to be horizontal and impermeable) of a drainage layer:
where :
D = leachate depth above the liner, cm
L = distance between adjacent drains, cm
N1 = rate of leachate input into the drainage layer, cm/sec
Kd = horizontal permeability of the drainage layer, cm/sec.
The above equation can be used when the base of the drainage system is horizontal. However, according to recent regulations ( July lst, 1991), at least a 2% slope should be provided in the liner forming the base of the drainage layer.
Moore (1980) presented an equation to calculate leachate depth which accounts for slope of the liner: where :
'ma x = maximum height of leachate over the liner, (cm)
L = length of spacing between drainage pipes, (cm)
e = quantity of leachate seeping into drainage layer, (cm/sec)
k = permeability of drainage layer, (cm/sec)
s = slope of liner The above equation may be used to select combinations of
values for L, sf and k which will maintain an hmax of 30 cm or less for a given value of e.
2.1.1.2 Filter Layer
Generally two kinds of filter layers are used in landfills: granular filters and geotextile filters. Granular filters are soil layers with coarse gradation. Geotextile filters are cloth-like sheets made of synthetic fibers (Hoare, 1982) . Filter layers are provided above the drainage layer to trap fines, prevent waste material from entering the drainage layer and to transmit leachate to the drainage layer. Generally, filter design depends on the particle-si;e distribution of the overlying waste material. Particle size distribution of soil is the relative proportion of each particle size on a dry-weight basis (Bass, 1986) . Peck et .all (1974) recommended that the particle size curve representing the filter material should have a smooth shape. They also presented the following design criteria:
D, of filter R, = ....,...... E q. 2.3 D, of overlying soil '
where :
Rn = the filter ratio for the n percent size
Dn = particle size which n percent of the soil particles are smaller than The following table from Peck et al. (1974) summarizes particle size requirements for three different types of filter materials.
Table 2.1: Particle size requirements for filters (Peck et al. (1974))
Grading of Filter Material R50 R15
Uniform 5 to 10 No requirements Nonuniform, sub rounded particles 12 to 58 12 to 40 Nonuniform, angular particles 9 to 30 6 to 40 In Table 2.1 filter material is considered to be nonuniform if the coefficient of uniformity is greater than 4 (Coefficient of uniformity is an indication of the spread (or range) of grain sizes).
The approach for the selection of geotextile consists of comparing the soil particle size characteristics with the apparent opening size of the geotextile (Bagchi, 1989) . Chen et. al. (1981) presented the following criteria for geotextiles :
P95 the geotextile < 2...... Eq. 2.4 of the overlying soil
Criterion 2:
Pg5 of the geotextile 2 2...... Eq. 2.5 D15 of he overlying soil where :
Pg5 = pore diameter of the geotextile which 95% of the pores are smaller than Dn is as,defined above.
The first criterion is to prevent overlying soil passing through the filter, and the second criterion is to provide sufficient permeability and to prevent clogging. Carroll
(1983) suggested that the permeability of the geotextile should be 10 times greater than the permeability of the overlying soil.
As Chen et al. (1981) considered pore size of the geotextile, Koerner (1986) considered the weight of particles that pass through the no. 200 sieve. Koerner (1986) recommends the following criteria for geotextiles:
For soils in which 508 or less of the particles can pass through a 0.074 mm sieve (P200), the apparent opening size of the geotextile should be greater than or equal to 0.59 mrn (US
No. 30 sieve) .
2.1.1.3 Collection Pipes
Collection pipes in the leachate collection system collect and transport leachate in the drainage layer to a sump without allowing leachate buildup in the drainage layer. The factors that must be considered in designing pipe networks are pipe perforations, slope of the pipe, layout of the pipe network etc. Bass (1986) recommends that the following factors should be considered in determining the strength specifications for the pipe: a. vertical loading
b. perforations c. deflection d. buckling e. compressive strength f. backfill compaction and
g. loading during construction
2.2 Clogging and Failure of LCS
Clogging is defined as the physical buildup of material in the collection pipe, drainage layer, or filter layer, to the extent that leachate flow is significantly restricted. Clogging may be caused by the buildup of deposited soil particles, biological organisms, chemical and biochemical precipitates, or the combination of all three (Bass, 1984). The major types of clogging mechanisms are physical, chemical, biochemical and biological mechanisms.
2.2.1 Physical Mechanisms
In general, physical mechanisms are probably the predominate cause of failure in drainage systems. ~ccording to the Bureau of Reclamation (Young, et al., 1982), LCS drainage system failures are usually associated with unstable soil conditions which cause shifts in pipe alignment which can result in blockage or reduction in pipe flow. Crushing of pipe due to equipment loads and migration of very fine grain soils into and through the drainage filter envelop surrounding the pipe are some other physical failure mechanisms in leachate collection systems.
Clogging of drainage systems by soil sediment deposits is a common problem in agricultural drainage systems and has occured in leachate collection systems (Young et. all 1982) that has been reported in the literature. In studies of agricultural drainage systems, Grass et.a1.(1979) reported that soil sediment deposites ranged widely to include sand, loamy sand, sandy loam, loam, silt, silt loam, clay loam, and silty clay loam. They also concluded that both the drainage envelop and the surrounding soil are the source of the sediment deposits in many cases. Patterson (1978) and Young
et. a1 (1982) have noted in agricultural and LCS drainage systems, respectively, that a wide range of particle sizes may be eroded from adjacent soils. These studies indicate that although significant amounts of very fine particulates are removed by lateral flow in the pipes, coarser material and great amounts of clay settle in the drainage layer.
The effects of undesirable soil types which may be adjacent to LCS can be minimized by (1) the proper selection of the filter and drainage layer soil particle size gradation to exclude the smaller particle sizes; and (2) adapting adequate facilities for cleanout of the system if it becomes necessary (Young et . al., 1982) .
Another major factor related to clogging is the quantity of leachate. The leachate production rate will influence the buildup of hydrostatic head which should not be more than 30 cm (EPA, 1982). The buildup of hydrostatic head in the drain or filter layer of the collection system should be integrated
into the LCS design as discussed in the EPA technical
resource document (TRD) SW-869 (Moore, 1980) .
Koerner (1989) found that increasing the volume of
leachate will increase the potential for clogging of geotextiles. Demery (1980) conducted a constant head test on a geotextile with a head of 30 cm and reported that the permeability decreased by an order of magnitude over a period of -1000 hours. In that test the rate of flow decreased from
300 ml/hour to less than 100 ml/hour. Demery concluded that
increasing the volume of leachate will increase the deposition of clogging agents such as bacteria, slimes, silt etc.
Clogging of drainage systems can be affected by design of the system, materials used for construction, and installation procedures. When the perforated pipe network is placed in the drainage layer, no unplugged ends should be allowed and the drainage layer materials in contact with the pipes must be coarse enough to be excluded from joints, holes, or slots (Cedegren, 1967).
The US Army Corps of Engineers (1955) has provided criteria for drainage material with respect to pipe openings as follows:
For slots:
De5 filter material = 1.2 ...... Eq. 2.6 slot width
For ci,rcular holes :
DB5 filter material = 1.0 ...... Eq. 2.7 hole diameter
Cadergren (1967) reported that the above equations give satisfactory results.
2.2.2 Chemical Mechanisms
Factors contributing to chemical precipitation are high concentrations of calcium or magnesium and bicarbonate ions
and relatively high pH (Pelleg, 1978). Temperature is also a factor since the solubility of calcium carbonate precipitate decreases with an increase in temperature. The chemical equation for this reaction is
High calcium and bicarbonate concentrations, high pH, or high temperature causes the equilibrium illustrated in the above equation to shift to the left. The first two factors are established by the chemical quality of the leachate; the third factor is affected by system layout and climatic conditions (Hills et al., 1989) .
Calcium carbonate precipitates have been found to cause clogging problems around well screens and in drainage layers. In wells, pressure changes accelerate the conversion of the bicarbonate ion to the carbonate ion by permitting escape of carbon dioxide from the liquid (Shuckrow, 1981) . Investigators have formulated the following expression to determine the likelihood of forming calcium precipitates in terms of Incrustation Potential Ratio (I.P .R) (Bass, 1986) as :
(Total Alkalinity) X (Hardness) 1.P.R = ...... ~q.2.9 10 -3 X 10'll-pH' where, total alkalinity and Hardness are expressed in ppm CaC03. If the 1.P.R ratio is less than one,, then no calcium carbonate precipitate problem should exist. If the 1.P.R is greater than one, calcium carbonate precipitates may occur
(The approximate 1.P.R value of the leachate used for this study is 27.2 as the average alkalinity of the leachate is 660 ppm as CaC03, the average hardness is 535 ppm as CaC03, and the average pH is 7.9). Experiences with calcium carbonate clogging in irrigation systems indicated that the above phenomenon is usually limited to arid regions with waters rich in calcium carbonates and bicarbonates (Pelleg,
1974).
Chemical precipitates of manganese (manganese carbonates) also cause problem of clogging. Manganese can form carbonates, sulfides, and silicates (Young et. al,
1982). Precipitation occurs when the pH increases and when sufficient quantities of carbonate are present.
2.2.3 Biochemical Mechanisms
A predominant phenomenon in clogging of agricultural drainage systems is formation of iron deposits. Grass (1969), reported that the underground drainage systems in agricultural areas of the Imperial Valley failed because of ferric oxide and manganese dioxide. Ford (1979), reported that the formation,of iron deposits occur when oxygen is available. He also reported that reduced soluble forms of iron and manganese are metabolized by aerobic iron bacteria as an energy source producing large quantities of ferric and manganese hydroxides which biologically precipitate within and at the water entry openings of drains. Weers (1979) reported that biological precipitates (ochre) form in the presence of iron bacteria as follows:
4Fe (HC03)2 + O2 + 2H20 -+ 4Fe (OH)34 + 8c02T + energy ...Eq. 2.10
MnC03 + 2H20 + O +M~o(oH)~J+ H20 + ~0~7'+ energy.. ...Eq. 2.11
2Fe (OH) + H20 + 0 + 2Fe (OH) 3J + energy ...... Eq. 2.12
The iron bacteria proliferate at pH conditions of 7.4 to
9.5 and between the temperatures of 20° and 30° C. Although iron bacteria are found to grow in waters with low oxygen content, these bacteria need readily available oxygen (Weers,
1967). Barbic (1975) reported that ochre sedimentation will occur in the presence of water soluble forms of iron and iron-precipitating bacteria, when the following conditions for iron concentration, pH, and redox potential are fulfilled:
~e"= 0.2 up to 0.5 mg/l...... Eq. 2.13 rH2 = 14.5 + or - 1 ...... Eq. 2.14
Eh = -10 + or - 20 mV ...... Eq. 2.15 where : rH2 = Eh/0.029 + 2pH
Eh = redox potential
Iron(I1) entering drain pipes may depends on anaerobic sulfate reducing bacteria, hydrogen sulfide, and the existence of iron-organic acid complexes that flow in the soil solution (Bass,1986). The following reaction shows the role of sulfate reducing bacteria in forming iron sulfide precipitates :
The sulfate reducing bacteria proliferate at pH 4 to 8 and at temperatures between 20° and 40O~(Sherard, 1972) . The iron sulfide deposits can adhere to the soil and form a thin film between the soil particles and cause clogging (Ford, 1974).
However, Ford (1976) indicated that ~e+~less than 7 ppm, total sulfides less than 2 ppm and pH of about 6, will minimize the formation of flocculating FeS and ochre. 2.2.4. Biological Mechanisms
Biological clogging is operative for wastewater tile fields, porous media wastewater treatment, and agricultural drainage and irrigation systems. In low volume irrigation systems, a filamentous slime forming organism and soil bacteria, which act as clogging agents in the absence of iron, were found in a number of studies (Ford, 1976) . Investigations by Kobayashi (1982) indicated that many microorganisms have the ability to mobilize various waste compounds.
Biological clogging of wastewater filtration systems, including trickling filters and sand filters, can result from buildup of various microbial populations (fungi, bacteria
etc.) . An example of a biological formation which occurs in porous media wastewater treatment works is the biological film growing on trickling filter media (Metcalf, 1991). Chapter 3
Experimental Study
This chapter describes the preparation of the porous media used in the study, the experimental setup for constant head permeability test, the method for calculating permeability based on test results, and the analysis used to characterize the leachate.
3.1 Preparation and Characterization of Media
Three media were used in the study: a gravel and two
sands. The gravel was obtained from Slater Builders Supply,
The Plains, Ohio. It was smooth-surface river-bed gravel conforming to specifications for AASHTO #8 aggregate.
The two sand media were a poorly graded sand and a well- graded sand. The poorly graded sand was obtained from Central Silica, Zanesville, Ohio. The well-graded sand was prepared from the poorly graded sand by sieving.
The media was prepared according to AASHTO T87-70. Sieve analysis of the test sample was made by ASTM D421-58 and D422-63 test procedures. First the soil was washed by placing the test sample on sieve no.50 for the gravel and on sieve no.200 for the poorly graded and well- graded sands. The material was washed through the sieve using tap water till the water was clear. The sample was washed carefully without losing any soil. The washed soil was then placed in a large container and allowed to air-dry for 36 hours. Then, the dried sample was run through a stack of sieves varying from large sizes to small sizes. Each time a small amount of sample was placed on the top sieve, and the stack of sieves was placed in a mechanical sieve shaker and sieved for 7 to 8 minutes. The stack of sieves was removed from the shaker, and the weight of material remaining on each sieve was obtained.
The percent retained on each sieve was computed by dividing the weight retained on each sieve by the original
sample weight. The percent finer was computed by starting with 100 percent and subtracting the percent retained on each sieve as a cumulative procedure.
A semi-log plot of grain size versus percent finer was made for each sample as shown in Figures 3.la, b and c for gravel, poorly graded sand and well-graded sand respectively.
As shown in Figure 3.1af gravel is within the bounds of AASHTO#8 specifications. From Figure 3.1bf it can be calculated that the coefficient of uniformity and coefficient Fig 3.la: Grain size distribution curve for gravel
- ,A AASHTO #8 Upper limit
----.t------.t-- Gravel used for test - AASETO #8 Lower limit
0 2 4 6 8 10 12 14
Grain size (mm) Fig 3.lb: Grain size distribution curve (Poorly graded sand)
loe2 lo-' Grain size (in) of gradation are 2.67 and 1.33, respectively for poorly graded sand. According to the specifications for poorly graded sand the coefficient of uniformity should be less than 6 and coefficient of gradation should be between 1 and 3. From Figure 3.1~~for well-graded sand the coefficient of uniformity is 6.67 and the coefficient of gradation is 1.33. These values are also within the limits of specifications as coefficient of uniformity is more than 6 and coefficient of gradation is between 1 and 3.
3.2 Description of apparatus
In this study the constant head permeability test was used. The overall experimental set-up of the constant head permeability test is shown in Figure 3.2. The system consists of an upper reservoir, a lower reservoir, a source tank and a recyclable leachate tank, a permeameter, and a set of eight cylinders. In this section each apparatus used in the constant head permeability test is described.
3.2.1 Permeameter
The permeameter was designed according to the ASTM D 2432-68 standards (according to ASTM D 2434-68, the permeameter should have a minimum diameter of approximately 8 Fig 3.1~: Grain size distribution curve (Well-graded sand)
Grain size (in) or 12 times the maximum particle size). The permeameter is a thick clear acrylic cylinder with an inner diameter of 5 inches and a thickness of 0.5 inches. It is covered on top and bottom by two acrylic plates of 8 inches diameter and a thickness of one inch (Figure 3.3) . The acrylic plates have openings of 0.25 NPT, two at the top and one at the bottom.
An acrylic plate of 5" diameter with 1/8" diameter holes is provided at the bottom of the permeameter to support the screen. '0' rings are placed at the top and bottom of the permeameter between the acrylic plates and cylinder wall, as shown in Figure 3.3, to prevent leakage from the top and bottom of the permeameter. The bottom opening of the permeameter is connected to the lower head tank. One of the top openings of the permeameter, which is at the center of the plate is connected to the upper reservoir. The other opening is connected to the bleed valve.
The permeameter is equipped with three manometers at the top, bottom, and at the center. The manometers are Tygon tubes of 3/8 inch diameter attached to a wooden plate. A precision rule with 0.01 inch subdivisions is mounted parallel to each manometer tube. Using these manometers the gradients in the top, and the bottom sections of the permeameter were monitored. The manometer set up is shown in Figure 3.2. Another unit that is a duplicate to the one described was also fabricated, but without the cylinders described in the next section. Leachate Inflow
A
-lll-,,,tl11-11-11 1 10"
v
FIGURE 3.3: SCHEMATIC OF CONSTRUCTION AND DIMENSIONS OF 5 INCH - ID PERMEAMETER (COMPONENT A) 3.2.2 Cylinders
Eight acrylic cylinders, each 14 inches in height and with an inner diameter of 1.5 inches, were operated in parallel to one permeameter. These are attached to a 3'x2'6" wooden stand as shown in Figure 3.4. Each cylinder is 0.25 inch thick and with a diameter of 2 inches. The top of the cylinder is attached to a 0.75 inch thick acrylic plate with
an 'Of ring surrounding it to prevent leakage. The top plate has a 0.25 inch opening. The top opening of each cell is connected to a common reservoir, 2.5 feet long, and has the same diameter as the cell. The common reservoir is connected to an upper reservoir. The bottom openings of each cell are connected to a lower reservoir. All cylinders have the same hydraulic situation as one of the permeameters.
3.3 Laboratory Experimental Setup
The large scale constant head permeability test was set up in 032 Lab.,Stocker Center, Ohio University. The setup is as shown in Figure 3.2. The overall set-up consists of a source reservoir, an upper reservoir, a lower reservoir, a permeameter with manometers, a set of eight cylinders, a recyclable, overflow, fresh-leachate collection tank, effluent leachate collection tank and a pump. Leachate Inflow From Upper Constant Head Tank
2" O.D. -1/4" Wall Clear Acrylic Cylinder Sand
Scr
2" 05.- 114" Wall Clear Acrylic Cylinders
Leachate Outflow To Lower Constant Head Tank
FIGURE 3.4: SCHEMATIC OF CONSTRUCTION AND DIMENSIONS OF CELL UNIT (COMPONENT B) The upper and lower reservoirs consist of over flow pipes to maintain constant hydraulic heads. Manometers are connected to these reservoirs to monitor upper and lower heads of the permeameter. The upper reservoir is connected to a source tank which supplies fluid to the upper reservoir. Discharge tubes are connected to lower reservoirs to monitor volume of flow and to collect the samples for leachate characterization. The permeameter and small cylinders were covered with thick black paper to block out the light.
Initially, the fluid is pumped to the source reservoir from where it is allowed to flow to the upper reservoir.
Valve 'Af is used to control the overflow fluid in the upper reservoir to the least possible flow. The fluid overflowing through the overflow tube in the upper reservoir is collected in the recyclable, overflowed, fresh-leachate or water tank. The purpose of the overflow tube is to maintain a constant head in the upper reservoir. The fluid from the upper reservoir flows through the small diameter cells and the permeameter (valves 'B' and 'C' were closed when discharge through the permeameter is measured). The discharge from the permeameter and cells flows to the lower head tank. The fluid which overflows through the overflow tube in the lower reservoir is collected in an effluent fluid collection tank. 3.4 Determining Baseline Permeability
Soil obtained from the sieve analysis was mixed thoroughly using a mixer. Then, the sample was placed in the permeameter in uniform thin layers of approximately equal thickness (after compaction), and the soil in the permeameter was compacted thoroughly by giving twenty five tamping blows, uniformly distributed over the surface of the layer. The surface of each layer was scratched before placing the next layer. The total 12 inches height of sample was placed in 5 layers of approximately equal thickness. The above procedure was followed for the small diameter cells also.
The soil was then saturated using a vacuum pump by evacuating the specimen for 15 minutes to remove air adhering to soil particles and from the voids. The evacuation was followed by a slow saturation of the specimen from the bottom upward under full vacuum in order to free any remaining air in the specimen.
After the specimen had been saturated and the permeameter was filled with water, the bottom valve on the outlet tube was closed and the vacuum was disconnected. Special care was taken to ensure that the permeability flow system and manometers were free of air and that they worked satisfactorily. The inlet tube was then filled with water from an upper reservoir by slightly opening the tank valve. The inlet tube was then connected to the top of the permeameter, and opened slightly. The permeameter was thus free of air. The inlet valve was then closed, and the outlet valve opened slightly to allow water in the manometer tubes to reach their stable water level under zero head. After this step, the upper reservoir was adjusted to the hydraulic gradient required for the test.
The volume of fluid passing through the soil in a known time, temperature of the fluid, and manometer readings were measured. Since the permeability depends on viscosity of the fluid; it was standardized to 20°c. The permeability was determined using the following equations.
1. For determination of permeability in the Upper section of the permeameter (Kupper1 :
- QLI -"It Kupper - cm/sec ...... Eq. 3.1 T (RI-R~) "I20
For determination of permeability in the lower section
(Klower):
- QL2 rlt K~'ower- X- cm/sec ...... Eq. 3.2 T (R2-R3) A r]20 For determination of the permeability in the overall section
(Koverall):
- Q(Ll+L2) qt Koverall - X- cm/sec ...... Eq. 3.3 T(RI-R~)A 7720
Where
Q = Volume of fluid drained from the permeameter (ml)
T = Time taken for collecting \Qf volume of fluid (sec)
Ll, L2 = Length of upper half and lower half sections of sample (inch)
R1, R2, R3 = Upper, center, and lower manometer readings (inch)
A = Cross-sectional area of material inside the permeameter (sq.cm) qtr q20 = Kinematic viscosity of water at temperatures at t and 20'~.
3.5 Leachate Characterization
Leachate samples were collected from influent and effluent lines of each system. In tests la and lb samples were tested for selected metals, solids, COD, alkalinity, and pH. In tests 2a to Sb, selected metals, solids, TOC, pH, COD and dissolved oxygen were determined. Samples were collected for microbial tests to count viable bacteria.
Solids analysis were performed to calculate total suspended solids (TSS), total dissolved solids (TDS), total solids (TS), total volatile solids (TVS), and total fixed solids (TFS) . All these solids tests were conducted according to the procedure specified in Standard Methods for Water and Wastewater Treatment (1985) . The volume of sample taken for TS, TVS, and TFS was 100 mL; whereas for TDS and TSS, it was 50 ml. The filter used for the suspended solids was 47 mm diameter and 0.45 micrometer pore size.
TOC was measured by a DC-80 Series modular unit by injecting 0.25 ml of sample into the reactor. The DC-80
Series modular manual was followed in measuring the TOC.
Dissolved oxygen was measured using a YSI Model 58 Dissolved Oxygen Meter by inserting a YSI 5700 Series probe into the leachate sample.
The COD test was performed using a Hach Model 16500 COD Reactor. The manufacturer's specifications were followed in performing the test. In this test a small amount of sample (2 ml) is pipetted into a vial containing the premeasured reagents, including catalysts and chloride compensator. The vials are incubated at 150~~for about two hours, and then cooled to room temperature. Then, COD determination is made by titration.
The concentration of metals was measured by the perkin- Elmer Model 2380 Atomic Absorption Spectrophotometer. Iron, calcium, magnesium, manganese, and copper were measured. CHAPTER 4
DISCUSSION RESULTS
4.1 Baseline Permeability Tests
4.1.1 General
The constant head permeability tests were performed with tap water or distilled water to achieve the baseline coefficient of permeability before introducing the leachate
into the system. For Tests la and lb on the AASHTO #8 gravel and for Tests 2a and 2b on the poorly graded sand, tap water
was used as a permeant, while distilled water was used for Tests 3a, 3b, 4a, and 4b on the poorly graded sand and Tests 5a and 5b on the well-graded sand. In each test (except for Test la) the hydraulic head loss was monitored in the upper one half and the lower one half sections of the permeameter
using the center manometer, and the coefficient of
permeability was computed for the overall, the upper, and the lower zones of the drainage media. In Test la hydraulic gradient was monitored in the overall section of the media.
In this chapter, notations of KO, k,, and kl are used to indicate the overall coefficient of permeability and the coefficients of permeability for the upper 6 inch and the
lower 6 inch sections. Table 4.1 summarizes the results for baseline permeability. The following sections present results
and observations made from each baseline permeability test. Table 4.1: Baseline permeability results
Test No. Typy of Baseline permeability Hydraulic media ( cm/s Gradient (%I Upper Lower Overall section section section la AASHTO - - 0.76 1.0 #8 lb Gravel 0.63 0.78 0.70 2.0 2a 0.028 0.025 0.026 2.0
3a poorly . Oeo21 0.015 0.017 2.0 3b graded 0.008 0.010 0.010 2.0 sand 4a 0.017 0.012 0.014 1.0 4b 0.014 0.012 0.013 2.0 5a well- 0.020 0.024 0.022 1.0 ' graded ' 5b 0.017 0.023 0.020 2.0 b sand 4.1.2. AASHTO #8 Gravel
The baseline permeability test on gravel (Test la) was started at 11 A.M. on December 15, 1990. The hydraulic gradient for Test la was set at 1%.It took about 21 hours for the system to reach steady state, and the test was continued for 46 hours. The KO (overall permeability) under the steady state conditions was 0.76 cm/sec as shown in
Figure A1 in Appendix A. Test lb was started at 9.20 p.m on January 6, 1991, under the hydraulic gradient of 2%. ~uring this test initial ku, kl, and ko values were 0.58 cm/sec, 0.67 cm/sec, and 0.63cm/sec, and the final Ku, kl, and ko values were 0.63 cm/sec, 0.78 cm/sec, and 0.70 cm/sec, as
shown in Figure 4.1. All the permeability coefficients
increased gradually after about 48 hours. This may be because of fines in the gravel being washed out. After about 72 hours, the system came to a steady state. To ensure the steady state, the test was conducted up to 118 hours.
4.1.3. Poorly Graded Sand
A total of six baseline permeability tests were performed on the poorly graded sand. Test 2a and test 2b were started simultaneously at 2 P.M. on August 2, 1991. Test 2a was conducted for 129 hours. The ku, kl, and ko values started at 0.027 cm/sec, 0.024 cm/sec, and 0.025 cm/sec Fig 4.1 Baseline permeability (Gravel, Test lb] D ';
o Upper permeability o Lower permeability o Overall Permeabilih
-U Q)
5E * 0- >* D. .-4d- .-n 0
IE a.Q)
I I I I 0 24 48 72 96 120 Elapsed time (Hours) 2.0% Hydraulic gradient system respectively as shown in Figure A2 in Appendix A. Then, all the permeability values dropped to 0.021 cm/sec after 5 hours. The permeability values in the upper and the lower sections switched to 0.024 cm/sec and 0.027 cm/sec, respectively, while the overall permeability stayed constant. The permeability values reached steady state at about 110 hours. The system for Test 2a was operated up to 129 hours to ensure steady state.
Tests 3a and 3b were operated at 2% hydraulic gradient. They were started at 4.30 P.M on September 6, 1991. The ku, kl, and ko values in Test 3a were reduced from 0.022 cm/sec to approximately 0.015 cm/sec for the first 76 hours and then separated (Figure A3 in Appendix A). They reached a steady state at 95 hours with permeability values of 0.021 c~/s~c, 0.014 cm/sec, and 0.017 cm/sec respectively, in the upper, the lower, and the overall section of the media. In Test 3b the permeability values started at 0.019 cm/sec and dropped down to 0.01 cm/sec after 25 hours. The system became steady at 88 hours with permeability values of 0.008, 0.01, 0.009 cm/sec in upper, lower, and overall sections of media (Figure
A4 in Appendix A). Both systems were operated up to 124 hours to ensure steady state conditions.
Tests 4a and 4b were started at 2.00 P.M. on October 21, 1991. Test 4a was operated at a 1%hydraulic gradient while Test#4b was at 2%. Test 4a started with permeability values of 0.013, 0.027, and 0.017 cm/sec respectively for the upper, lower, and overall sections of t.he media as shown in Figure
4.2. After about 15 hours the permeability values increased
by a factor 2. At about 48 hours, they became the same (0.015 cm/sec). The system achieved a steady state at 76 hours. The k,, kll and ko values of the media in Test 4b started at 0.021, 0.015, and 0.018 cm/sec. The system reached a steady state at 76 hours with the ku, kl, and ko values of 0.0142, 0.0118, and 0.0129 cm/sec, respectively (Figure A5 in
Appendix A). Both systems were operated up to 99 hours to ensure steady state.
4.1.4 Well-Graded Sand
Test 5a was started at a 1%hydraulic gradient, while Test 5b was initiated at a 2% hydraulic gradient. Both tests were
started at 2:00 P.M on the 23rd November, 1991. In Test 5a, th.e permeabilities in the upper, lower and overall sections
of the media tended to be separated initially and then merge
(Figure A6 in Appendix A). The final ku, kl, and ko values of Test 5a were 0.0197, 0.024, 0.0217 cm/sec, respectively. The permeability in Test 5b did not change significantly (Figure 4.3). The final permeabilities of Test 5b were 0.0168, .0238, 0.0197 cm/sec in the upper, lower and overall sections of the permeameter . Fig 4.2: Baseline permeability (Poorly graded sand, Test 4a)
Elapsed time (hours) 1.0% Hydraulic gradient system Fig 4.3: Baseline permeability (Well-graded sand, Test 5b) no o Upper permeability o Lower permeability I o Overall permeability
0 55 30 45 60 75 Elapsed time (hours) 2.0% Hydraulic gradient system 4.2 Leachate Flow Test Results
After the baseline permeability coefficient was established for a given test specimen, the tap water or distilled water was removed from the tanks, and leachate was introduced into the system by filling the upper, lower and source tanks with leachate. The permeability test was then restarted using leachate as the paramount.
4.2.1 AASHTO #8 Gravel
Test la at 1%hydraulic gradient (0.75% average gradient was operated for 2160 hours. The permeability of the media for this system was reduced by about a half from its baseline value upon introduction of leachate. As leachate flowed continuously through the system, the ko value decreased to about 90% of the baseline value at about 600 hours as shown in Figure A7 in Appendix A. After 600 hours the ko value fluctuated between 0.31 and 0.015 cm/sec with an average of 0.15cm/sec. An average reduction of 82% was observed from 1400 elapsed hours to the end of the test. Significant reduction in lower permeability (about 87%) was observed in about 220 hours. Thereafter, the permeability oscillated between 0.15 cm/sec and 0.0075 cm/sec till the end of the test. The upper permeability of the system fluctuated for the first 1700 hours with an average value of 0.11 cm/sec as shown in figure A8 in appendix A. A plot of the observed flow rate in Test la is presented in Figure A9. The hydraulic gradients fluctuated in the upper and lower sections of the media whereas the overall hydraulic gradient stayed at an average of 0.75% as shown in the Figure A10.
In Test lb, with an average hydraulic gradient 2.3%, the permeability decreased gradually from 0.70 cm/sec to 0.04
cm/sec (about 94% reduction), as shown in Figure 4.4. In this system, the lower permeability decreased gradually as the rate of flow as shown in Figures 4.5 and 4.6. The permeability in the upper section fluctuated between 0.48 and
0.1 cm/sec up to 620 elapsed hours, and thereafter it stayed at an average value of 0.1 cm/sec. The fluctuations in the
hydraulic gradients are shown in Figure All.
4.2.2 Poorly Graded Sand
Test 2a for the poorly graded sand was stopped at 46.5
hours because of an odor control problem. At that time, the overall permeability had decreased by about 92% from the
baseline value. The ku and kl values decreased to 95% and 85%
of baseline, respectively. The overall permeability of the system is plotted in Figure A12, and similar plots are shown
for the upper and lower permeabilities in Figure A13. A plot of the observed flow rate for the test is shown in Figure
A14, appendix A.The overall hydraulic gradient of this system Elapsed time (Hours) 23% Hydraulic gradient system Fig 4.5: Upper, Lower Peneobility (Gravel, Test Ib] 4
Elapsed time (Hours) 2.3% Hydraulic gradient system Elapsed time (Hours) 2.3% Hydraulic gradient system was increased from 1.2% to approximately 2.0% at 6 hours. The hydraulic gradient in the upper section of the medium increased while that in the lower section decreased at 30 hours as shown in Figure A15.
Tests 3a and 3b were started simultaneously at 2% hydraulic gradient. The overall permeability in Test 3a (Figure A16) increased from 0.017 to 0.031 cm/sec upon introduction of leachate, while the permeability in the upper section stayed constant at 0.022 cm/sec. The lower
permeability increased by a factor of 4 (See Figure A17). The upper permeability lowered gradually to 0.001 cm/sec within 35 hours of the start of the test, and it stayed at an average value of 0.0009 cm/sec for the rest of the testing period. The lower permeability decreased to 0.025 cm/sec
after 40 hours. It fluctuated between 0.03 cm/sec and 0.006 cm/sec from 40 hours to 250 hours. The rate of flow curve for Test 3a is shown in Figure A18, and the gradient cu'rves in
Figure A19. It was very difficult to maintain the system at
2% gradient and the actual overall gradient averaged 1.7%.
Upon increasing the hydraulic gradient from 1.7% to 4% at 330 hours (Figure A19) , permeabilities increased (See Figures A16 and A17), but within 20 hours the permeability returned to previous or lower values.
The permeability in Test 3b was reduced by 60% within 30 hours of the start of leachate flow, as shown in Figures A20 and A21 in Appendix A. The corresponding flow curve is shown in Figure A22. The hydraulic gradients of the system are
shown in Figure A23. The overall gradient averaged 2.3%. At 330 hours the gradient was increased to 6%. The lower hydraulic gradient decreased to 1.5% as the leachate flow continued, while the upper gradient increased to about 10%. Upon increasing the gradient, the permeability also increased (See Figures A20 and A21), but a decline was noted soon after. The upper permeability controlled the-decrease.
Tests 4a and 4b were started simultaneously at 1%and 2%
(2.17% average) hydraulic gradients. As shown in Figures 4.7
and 4.8, the 2.17% hydraulic gradient system clogged about
80% within 100 hours, while the 1%hydraulic gradient system took more than 200 hours to come to the same percent reduction. The plots for upper and lower permeabilities for Tests 4a and 4b are shown in Figures 4.9 and 4.10, respectively. The rate of flow curve for Test 4a is presented in Figure A24. The hydraulic gradients of the permeameters were increased from 1%and 2% to 2% and 3% for Tests 4a and 4b at 452.5 hours, as shown in Figures A25 and A27, respectively. Upon increasing the hydraulic gradient, the ku,
klr ko values increased, but within 25 hours, the values returned to the previous values. (See also flow rate curves in Figures A24 and A26.) Fig 4.7: Overall Permeability (Poorly graded sand, Test 40)
o Overall permeability
0 100 200 300 4al 500 Elapsed time (hours) 1.0% Hydraulic gradient system Fig 4.8: Overall permeability (Poorly graded sond, Test 4b)
0 100 200 300 400 500 Elapsed time (hours) 2.17% Hydraulic gradient system Fig 4.9: Upper, lower permeability (Poorly graded sand, Test la) no1 o Upper permeability 1 o Lower permeability
Elapsed time (hours) 1.0% Hydraulic gradient system Fig 4.10: Upper, lower permeability (Poorly graded sand, Test 4b)
o Upper permeability o Lower permeability
Elapsed time (hours) 2.17% Hygraulic gradient system 4.2.3 Well-graded Sand
As shown in Figures 4.11, 4.12, 4.13 and 4.14, the ko, ku, kl values for the well-graded sand (Tests 5a and 5b) were initially higher than corresponding values of the poorly graded sand (Tests 4a and 4b), but clogging occurred in less time i e., 150 hours versus 250 hours) . In the well-graded sand tests also, it can be observed that the upper permeability and the flow rate curves followed the same pattern, as shown in Figures A28 and A30. During the well- graded sand test, the upper section of the media clogged more than the lower section, which was similar to the observation made during the poorly graded sand test. In Tests 5a and Sb, the hydraulic gradients were increased to 2% and 4%, respectively, at 180 hours. The permeabilities increased upon increasing the hydraulic gradients (Figures A29 and A31), but returned to the previous values within 18 hours.
4.3 Characterization of Influent and Effluent Leachate
Leachate samples were collected from the influent and effluent lines of each system, and various physical, chemical and metal analyses were performed. The following sections present the analytical results for the leachate. Fig 4.11: Overall permeability (Well-graded sand, Test 5a)
0 50 100 t50 200 250 Elapsed time (Hours) 1.0% Hydraulic gradient system Fig 4.12: Overall permeability (Well-graded sand, Test 5b)
Elapsed time (Hours) 2.0% Hydraulic gradient system Fig 4.13: Upper, lower permeability (Well-graded sand, Test 50) mo
o Upper permeability o Lower permeability 0; - cnz \ ,,-z i? -V % .---r .-n u ,-I 4) € I a.4)
m5 I I I I 0 50 100 150 200 250 Elapsed time (Hours) 1.0% Hydraulic gradient system Fig 4.14: Upper, lower permeability (well-graded sand, Test 5b)
o Upper permeability o Lower permeability
Elapsed time (Hours) 2.0% Hydraulic gradient system 4.3.1 Solids Analysis
A total of five types of solids tests (Total Solids (TS), Total Dissolved Solids (TDS), Total Suspended Solids (TSS), Total Volatile Solids (TVS), and Total Fixed Solids
(TFS)) were conducted on influent and effluent samples for the AASHTO #8 gravel, while TSS test was performed for the poorly graded and well-graded sand.
Figures A32 and A33 in Appendix A show the data for solids of Test la for influent and effluent, respectively. The data show an average reduction of 5% in TVS and 3% in TDS occurred during 2160 hours of leachate flow. About 30 to 35% suspended solids reduction can be observed from Figure 4.15. Similar results were observed from Test lb, which shows from
Figure A34 and A35 in Appendix A that a 5 to 7% reduction in total volatile suspended solids occurred. From Figure 4.16, only a 15% reduction in suspended solids can be observed. This might be because of higher flow velocities in the permeameter as it was at 2% hydraulic gradient. The concentrations of TS, TDS, TFS were not changed significantly for both the systems.
TSS in the poorly graded sand study did not change significantly for Tests 2a, Tests 3a, and Test 3b, while a significant change was observed for Tests 4a and 4b, as shown in Figures 4.17 and 4.18, respectively. Figure 4.17 shows Fig 4.15: Total suspended solids (Gravel, Test la]
o Total influent suspended solids o Total Effluent suspended solids
Elapsed time (Hours) 0.75% Hydraulic gradient system Fig 4.16: Total suspended solids (Gravel, Test Ib) a00
o Total effluent suspended solids 160
-A Fa V C .-0 #E' C, 5 ID
0z
0 0 320 640 960 1280 l600 Elapsed time (Hours) 2.3% Hydraulic gradient system Fig 4.17: Total suspended solids (Poorly graded sandJestla] DO
0 100 200 300 400 500 Elapsed Time (Hours) 1.0% Hydraulic gradient system Fig 4.18: Total suspended solids (Poorly graded sandJest4b)
o Total effluent suspended solids
-Y ,y
Elapsed Time (Hours) 2.17% Hydraulic gradient system that a large amount of deposition of suspended solids occurred in the voids of the media between 150 hours and 250 hours for Test 4a. Figure 4.18 also shows a considerable
reduction in TSS between the influent to the effluent.
A reduction of about 30% in TSS appeared to have occurred within the first 70 hours of operation of Test 5a,
as shown in Figure 4.19. A considerable accumulation of TSS happened from 75 hours to 160 hours in Test 5a. Figure A36 in Appendix A shows that about 50% of TSS reduction occurred in the first half of the testing period for Test 5b, and
thereafter, on an average, the TSS concentrations in the influent and the effluent samples appeared to be the same.
4.3.2 Chemical Analysis
Figures 4.20 and 4.21 present the data for COD and alkalinity for the influent and the effluent samples of 0.75% and 2.3% hydraulic gradient systems for the AASHTO #8 gravel.
About 36% reduction in COD was observed for Test la and
about 28% reduction in COD was observed in Test lb. In Test la, influent average alkalinity was 680 mg/L, while effluent alkalinity averaged at 520 mg/L. This corresponds to about 20% reduction. About 13% reduction in alkalinity was noted from the influent to the effluent from Test lb. Fig 4.19: Total suspended solids (Well-graded sand, Test 5a) - o Total influent suspended solids 0 Total effluent suspended solids
I I I 1
Elapsed time (Hours) 1.0% Hydraulic gradient system Fig 4.20: COD, Alkalinity (Gravel, Test la)
Elapsed time (Hours) 0.75% Hydraulic gradient system Fig 4.21: COD, Alkalinity (Gravel, Test Ib)
I 1 o Influent COD o Mluent alkalinity x Effluent COD o Effluent alkalinity
Elapsed time (Hours) 2.3% Hydraulic gradient system A considerable (30 to 40%) reduction in COD was observed in Test 3a and 3bf as shown in Figures A37 and A38 in
Appendix A. The TOC test was conducted on the influent and the effluent leachate samples for Tests 4a, 4b, 5a, and 5b.
In all these tests TOC of the effluent was much lower in the first 50 hours of the testing period, and, thereafter, the reduction averaged about 5%. Figures 4.22 through 4.25 illustrate the results of these tests. However, during part of this period it should be noted that the leachate was diluted some by the distilled water in the system, since the theoretical detention time of flow through the system was about 24 hours.
4.3.3 Metal Analysis
Selected metals (manganese, calcium, iron, magnesium, zinc, and copper) were analyzed by atomic absorption spectroscopy for the influent and the effluent leachate samples of Test la. Table 4.2 presents the concentrations of metals in the influent and the effluent samples. It can be observed from the table that metal concentrations between the influent to the effluent decreased for all metals analyzed.
About 80 to 90% reduction in iron was observed in all poorly graded sand and well-graded sand tests in the first half of the testing period. Figures 4.26 through 4.31 present the results of Tests 3a, 3b, 4a, 4b, 5a, and 5b for the Elapsed Time (Hours) 1.0% Hydraulic gradient system Fig 4.23: TOC (Pooriy graded sand, Test ilb)
o Influent TOC o Effluent TOC
- d
I I I 1
Elapsed Time (Hours) 2.17% Hydraulic gradient system Fig 4.24: TOC (Well-groded sand, Test 54)
o Influent TOC o Effluent TOC
50 100 rn 200 250 Elapsed time (Hours) 1.0% Hydraulic gradient system Fig 4.25: TOC (Well-graded sand, Test 5b) - o Influent TOC o Effluent TOC
I I 1 1
Elapsed time (Hours) 2.0% Hydraulic gradient system Table 4.2: Metal analysis results for gravel (Test la)
Elapsed concentration (mg/L) of Sample Time (Hours) Cu Zn Mn Fe Ca Mg Effluent 2 12 0.008 0.281 0.309 4.75 69.03 413.80 Influent 236 0.023 0.392 0.391 6.15 76.65 410.65 Effluent 236 0.020 0.354 0.346 5.55 55.20 405.15 - - - - Influent 260 0.010 0.351 0.437 5.95 50.50 406.60 Effluent 260 0.017 0.311 0.378 4.05 40.95 381.10 Influent 380 - - 0.407 7.95 65.00 520.00 Effluent 380 - - 0.178 4.90 57.10 440.00 Influent 408 - - - 9.00 76.30 526.30 Effluent 408 - - - 5.50 52.90 500.00 Fig 4.26: Iron contentrotion (Poorly graded sand, Test 30) Fig 4.27: Iron concentrution (Poorly Graded Sand, Test
0 rX) 200 300 400 Elapsed Time (Hours) 2.32% Hydraulic gradient system Fig 4.28: Iron concentration (Poorly graded sand, Test 4a) 40
o Influent iron o Effluent iron
0 100 200 300 400 500 Elapsed Time (Hours) 1.0% Hydraulic gradient system 0 100 200 300 400 500 Elapsed Time (Hours) 2.17% Hydraulic gradient system Fig 4.30: Iron coocentrotion (Well-graded sand, Test 50)
Elapsed Time (Hours) 2.0% Hydraulic gradient system influent and the effluent leachate samples. In Tests 3a, 3b, 4a, and 4b, in the second half of the testing period, the influent and the effluent concentrations fluctuated, and the average percent reduction was about 10%. In well-graded sand tests (Test 5a and 5b), iron was reduced considerably (average 80%) throughout the test period.
Similar results to that of iron were noted for calcium as shown in Figures 4 -32 through 4.37 for the influent and the effluent metal analysis for the poorly graded and the well-graded sands. A slight reduction of about 15% (average) appeared in Tests 4a and 4b, while about 50% reduction was observed for the well-graded sand tests (Tests 5a and 5b). NO significant change was observed in Tests 3a and 3b as the influent and the effluent concentrations were fluctuating.
Magnesium and manganese concentrations were not significantly different from the influent to the effluent samples of the poorly graded sand (except for initial samples), as shown in Figures A39 through A50. In Tests 5a and 5b on the well-graded sand, concentrations of manganese and magnesium were reduced by about 40% and to about 35%, respectively. Fig 4.32: Calcium concentration (Poorly Graded SandJest 3a)
I o Influent Calcium 1
0 100 m 300 400 500 Elapsed Time (Hours) 1.77% Hydraulic gradient system Fig 4.33: Calcium concentration (Pooriy Graded SondJest 3b) 350 * o lnfluerrt Calcium P n Effluent Calcium
Elapsed Time (Hours) 2.32% Hydraulic gradient system Fig 4.34: Calcium concentration (Poorly Graded Sand,lest 40)
Elapsed Time (Hours) 1.0% Hydraulic gradient system Fig 4.35: Calcium concentration (Poorly Graded Sand Jest 4b]
o Influent Calcium o Effluent Calcium
Elapsed Time (Hours) 2.17% Hydraulic gradient system Fig 4.36: Calcium concentrution (Well-graded sand, Test 50)
XY)
80 - 1 F a V c .-0 -CIz -C, 44 5 0
20
0 50 TX) 150 200 250 Elapsed Time (Hours) 1.0% Hydraulic gradient system Fig 4.37: Calcium concentration (Well-graded sand, Test
0 50 m Ed 200 250 Elapsed Time (Hours) 2.0% Hydraulic gradient system 4.3.4 pH Analysis
The pH of the influent and the effluent samples remained fairly consistent for all the tests. For Test la and lb the
influent and the effluent pH values averaged 7.3 and 8.0. For Tests 3a and 3b the influent and the effluent pH values averaged 7.6 and 8.1, respectively, while for Tests 4a, 4b, 5a and 5b, the influent and the effluent values averaged to
8.0 and 8.4, respectively.
4.3.5 Analysis of Leachate and Residue Deposited on Media at Conclusion of Experiments
After completion of the permeability studies, the liquid in the media was removed. The residue on the aggregate was removed by washing each of the cell contents with one liter of distilled water, and for the media in the permeameter 3.5
liters of distilled water was used. Tables 4.3a, 4.3b, 4.3~
summarize the results obtained from the suspended solids and metal analysis. It can be observed from the tables that the maximum deposition of suspended solids and metals occurred on gravel media. Table 4.3a: Suspended solids and metal analysis of contents of permeameters and cells at completion of the Tests la and lb (Gravel).
Suspended solids Iron Calcium concentration concentration Concentration (mg/L) (mg/L) (mg/L) Liquid Washed Liquid Washed Liquid Washed in the media in the media in the media permea- permea- permea- meter meter meter or or or cell cell cell P-1 128 963 13.3 158.1 13.9 221.0 P-2 92 1372 554.0 244.8 148.0 297.8 Cell #1 ------Cell #2 ------Cell #3 156 1348 - - - - Cell #4 172 1126 - - - - Cell #5 118 12 2 8 6.2 24.4 20.9 15.6 Cell #6 92 1476 5.8 38.3 29.4 30.3 Cell #7 98 1124 69.0 132.0 148.8 152.2 Cell #8 106 984 69.1 68.9 138.8 126.0
Note: P-1 represents the permeameter in Test la P-2 represents the permeameter in Test lb Table 4.3b: Suspended solids and metal analysis of contents of permeameters and cells at completion of the Tests 4a and 4b (Poorly graded sand).
Suspended solids Iron Calcium concentration concentration Concentration (mg/L) (mg/L) (mg/L) Liquid Washed Liquid Washed Liquid Washed in the media in the media in the media permea- permea- permea- meter meter meter or or or cell cell cell P-1 61 44 0.00 0.28 22.9 10.4 P-2 58 61 0.06 0.15 17.5 12.2 Cell #1 33 63 0.25 0.00 46.6 14.4 Cell #2 38 98 0.02 0.27 38.7 9.4 Cell #3 27 43 0.27 0.08 47.8 8.4 Cell #4 32 45 0.11 0.44 50.5 10.1 Cell #5 24 32 0.17 0.00 47.2 10.5 Cell #6 41 56 0.23 0.08 48.4 6.9 Cell #7 45 69 0.05 0.19 38.9 10.3 Cell #8 40 58 0.00 0.07 45.5 9.3 Note: P-1 represents the permeameter in Test 4a P-2 represents the permeameter in Test 4b Table 4.3~:Suspended solids and metal analysis of contents of permeameters and cells at completion of the Tests 5a and 5b (Well-graded sand) .
Suspended solids Iron Calcium concentration concentration Concentration (mg/L) (mg/L) (mg/L) Liquid Washed Liquid Washed Liquid Washed in the media in the media in the media permea- permea- permea- meter meter meter or or or cell cell cell P-1 32 68 0.00 10.63 48.7 20.1 P-2 12 132 0.46 11.37 46.6 5.7 Cell #1 18 48 0.40 9.80 32.0 3.1 Cell #2 17 63 0.23 11.68 35.2 4.8 Cell #3 24 68 1.29 12.40 32.2 2.7 Cell #4 21 52 0.76 11.10 30.6 3.0 Cell #5 11 114 0.21 11.11 31.4 4.8 Cell #6 16 67 0.29 11.08 35.3 6.7 Cell #7 41 74 2.22 8.58 41.4 14.8 Cell #8 18 52 0.54 9.98 34.5 12.1
Note: P-1 represents the permeameter in Test 5a P-2 represents the permeameter in Test 5b CHAPTER 5
CONCLUSIONS AND RECOMMENDATIONS
5.1 Conclusions
The following conclusions can be drawn based on the results and observations made in this study:
(1) Regardless of the type of drainage media (AASHTO #8 gravel, well-graded sand, or poorly graded sand) or the level of hydraulic gradient (1 or 2%the leachate flow always caused clogging.
(2) Clogging or reduction in permeability occurred more rapidly in the systems with a 2% average gradient than in system with a 1% gradient. This indicates that clogging increases as the volumetric flow rate of leachate through the medium increases.
(3) A proportionality was observed between the rate of reduction in the permeability and the concentrations of suspended solids, iron and calcium in the leachate.
(4) In the poorly graded and well-graded sand tests, the permeability in the upper section was reduced more than the permeability in the lower section. The opposite was observed in the test with gravel.
(5) The well-graded sand clogged in less time than the poorly graded sand for tests with the same gradient. Higher deposition of suspended solids, iron and calcium occurred in the well-graded sand compared to the other soils.
(6) Suspended solids were deposited in all media used in the tests. In the gravel 17% to 35% of the influent suspended solids were deposited, while the solid depositions in the poorly grzded and the well-graded sands were 25% to 40% and 34% to 50%, respectively.
(7) In all the experiments conducted on different media, the test at 1% gradient showed a consistently higher percent reduction in suspended solids, than the tests at 2% gradient. However, the tests at 2% hydraulic gradient clogged more quickly than similar tests at 1% hydraulic gradient.The increased percent reduction at the smaller gradient is perhaps due to the decreased fluid driving force (represented by the gradient) on the suspended particles, resulting in fewer suspended solids being forced through the medium. The faster clogging at the higher gradient may occur because the higher rate at which suspended solids enter the porous medium at the higher gradient more than compensates for the reduced efficiency in their removal.
(8) About 36% reduction in COD was observed for the gravel during Test la (at a 1% gradient), while COD reduction was 20% for Test lb (at a 2% gradient).
(9) Average reductions in TOC of 13% and 7%, respectively were observed in 1% and 2% gradient tests of the poorly graded sand. In the well-graded sand, the reductions were 17% and 15%, respectively for the 1%and 2% gradient tests.
(10) The pH analysis on all influent and effluent samples indicated that the effluent samples had slightly higher pH values than the influent samples. For the gravel, The pH values averaged 7.3 and 8.0 for the influent and the effluent samples, respectively. The pH increased on the average by 4% from influent to effluent samples for the poorly graded and well-graded sands.
(11) In all the tests on all types of media, about 80 to 95% of the iron was removed in the medium during the first one- third to one-half of the test with somewhat less removal toward the end. Calcium precipitation was about 20 to 50%. Considerably less precipitation (5 to 40%) was observed for magnesium and manganese. 104 5.2 Recommendations
Based on the findings of the current study, the following recommendations can be made for future research work on clogging of drainage media:
(1) In this study, leachate samples from' only one landfill were utilized to monitor clogging rate of the drainage media.
A similar study is needed with leachate samples from different landfills to develop a more genera.lized data base.
(2) In this study, performance of the leachate collection drainage media was monitored for a maximum of three months. A similar study is recommended for longer durations of time.
(3) Biological clogging mechanisms must be investigated in detail for landfill leachate drainage media.
(4) In this study, leachate flowed through the drainage media continuously under a fixed hydraulic gradient. However, within the landfill leachate flow is generally discontinuous and under varied hydraulic gradient. Efforts should be made in future studies to simulate leachate flow conditions more realistically. REFERENCES
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Publication 933. Published by ASTM, Philadelphia, PA, USA, page 208-225. May, 1985. Appendix A Fig Al: Baseline permeability (Gravel, Test la) nl.
o Overall permeability
-u a sE 25*a. 0- .--c., .-13 0, - - - 0 E aI 0,
P-' I I I I 0 10 20 30 40 50 Elapsed time (Hours) 1.0% Hydraulic gradient system Fig A2: Baseline permeability (Poorty graded sand, Test 20) Fig A3: Baseline permeability (Poorly graded sand, Test 3a)
Elapsed Time (Hours) 2.0% Hydraulic gradient system Fig A4: Baseline permeability (Poorty Graded Sand, Test 3b) ao7 o Upper permeability o Lower permeability o Overall permeability
cnQ, '2;. E -U .-C a- 0 Q, E a-?, 0,
tlJ 1 I I I 0 X1 60 90 l20 t50 Elapsed Time (Hours) 2.0% Hydraulic gradient system Fig A5: Baseline permeability (Poorly graded sand, Test 4b)
Elapsed time (hours) 2.0% Hydraulic gradient system Fig A6: Baseline permeability (Well-graded sand, Test 50)
o Upper permeability o Lower permeability o Overall permeability
Elapsed time (hours) 1.0% Hydraulic gradient system Fig A7: Overall permeability (Gravel, Test la) 4 '"Io Overall permeabilify
Elapsed time (Hours) 0.75% Hydraulic gradient system Fig A8: Upper, lower permeability (Gravel, Test la]
0 440 880 1320 l760 2200 Elapsed time (Hours) 0.75% Hydraulic gradient system Fig A9: Flow rate (Gravel, Test la)
I ; ,I I , 1 0 44 880 1320 l760 my) Elapsed time (Hours) 0.75% Hydraulic gradient system Fig AM: Hydraulic gradients (Gravel, Test la)
0 440 830 1320 I760 2200 Elapsed time (Hours) 0.75% Hydraulic gradient system Fig All: Hydraulic gradients (Gravel, Test Ib]
Elapsed time (Hours) 2.3% Hydraulic gradient system Fig A12: Overoll pemeobility (Poorly graded sand, Test 20)
Elapsed Time (Hours) 2.0% Hydraulic gradient system Test 2a)
0 10 20 30 40 50 Elapsed Time (Hours) 2.0% Hydraulic gradient system Fig A14: Flow rate (Poorly graded sand, Test 2a)
o Rate of flow
cC
D-~ 1 1 I I 0 10 20 30 40 50 Elapsed Time (Hours) 2.0% Hydraulic gradient system Fig A15: Hydraulic gradients (Poody graded sand, Test 20) 5
4
3
2
1
0 0 0 10 20 30 40 50 Elapsed Time (Hours) 2.0% Hydraulic gradient system Elapsed Time (Hours) 1.77% Hydraulic gradient system Fig A17: Upper, lower permeability (Poorly graded sand, Test 3a)
o Upper permeability I . o Lower permeability
Elapsed Time (Hours) 1.77% Hydraulic gradient system Fig A18: Rate of flow (Poorly graded sand, Test 3a) - I o Rate of flow 1
0 XX) 200 300 400 500 Elapsed Time (Hours) 1.77% Hydraulic gradient system Fig A19: Hydraulic gradients (Poorly graded sand, Test 3a) X1
Elapsed Time (Hours) 1.77% Hydraulic gradient system Fig A20: Overall permeability (Poorly Graded Sand, Test 3b]
Elapsed Time (Hours) 2.32% Hydraulic gradient system Fig 1121: Upper, lower permeability (Poorly graded sand, Test 3b)
o Upper permeability o Lower permeability
0 100 200 300 400 500 Elapsed Time (Hours) 2.32% Hydraulic gradient system Elapsed Time (Hours) 2.32% Hydraulic gradient system Fig A23: Hydraulic gradients (Poorly Graded Sand, Test
Elapsed Time (Hours) 2.32% Hydraulic gradient system Fig 124: Rate of flow (Poorly graded sand, Test 4a) Fig A25: Hydraulic gradients (Poorly graded sand, Test 4a) 5
Elapsed Time (Hours) 1.0% Hydraulic gradient system Fig A26: Rate of flow (Poorly graded sand, Test 4b)
o4 I I I 1 0 100 200 300 400 500 Elapsed Time (Hours) 2.17% Hydraulic gradient system Fig A27: Hydraulic gradient (Poorly graded sand, Test 4b) 5
Elapsed Time (Hours) 2.17% Hydraulic gradient system
Fig A29: Hydraulic gradients (Well-graded sand, Test 50)
Elapsed time (Hours) 1.0% Hydraulic gradient system Fig AJO: Rate of flow (Well-graded sand, Test 5b)
0 50 100 150 200 250 Elapsed time (Hours) 2.0% Hydraulic gradient system Fig A31: Hydraulic gradients (Well-graded sand, Test 5b)
Elapsed time (Hours) 2.0% Hydraulic gradient system Fig A32: Influent solids (Gravel, Test la)
o Total dissolved solids x Total volatile solids 0 Total fixed solids
Elapsed time (Hours) 0.75% Hydraulic gradient system Fig A33: Effluent solids (Gravel, Test la)
o Total solids o Total dissohled solids x Total volatile solids 6 Total fixed solids 0
Elapsed time (Hours) 0.75% Hydraulic gradient system Fig 134: Influent solids (Gmel, Test Ib)
32al
-A \ -p2wo c .-0 CIz -CIz#ao cU 0 0
$3 - o Total dissoked solids x Total volatile solids o Total fixed solids
0 1 I I I 0 320 640 960 1280 1600 Elapsed time (Hours) 2.3% Hydraulic gradient system Fig A35: Effluent solids (Gravel, Test Ib)
o Total solids o Total dissolved soli js x Total volatile solids 6 Total Fixed solids 1 I I I
Elapsed time (Hours) 2.3% Hydraulic gradient system Fig 1136: Total suspended solids (Well-graded sand, Test 5b)
0 50 100 150 Zoo 250 Elapsed time (Hours) 2.0% Hydraulic gradient system Fig A37: COD (Poorly Graded Sand, Test 30)
o Influent COD
I I I I 0 40 80 l20 160 200 Elapsed Time (Hours) 1.77% Hydraulic gradient system Fig A38: COD (Poorly Graded Sand, Test 3b)
o Influent COD o Effluent COD : :
Elapsed Time (Hours) 2.32% Hydraulic gradient system Fig A39: Magnesium concentration (Poorly Graded Sand,Test3a)
Elapsed Time (Hours) 1.77% Hydraulic gradient system Fig A40: Magnesium concentration (Poorly Graded Sand,TestJb]
0 100 200 300 400 500 Elapsed Time (Hours) 2.32% Hydraulic gradient system Fig All: Magnesium concentration (Poorly Graded SandJest4a) m - o Influent Magnesium
I I I I
Elapsed Time (Hours) 1.0% Hydraulic gradient system Fig A42: Magnesium concentration (Poorly Graded SandJest4b)
o Influent Magnesium o Effluent Magnesium
I I I I
Elapsed Time (Hours) 2.17% Hydraulic gradient system Fig A43: Magnesium concentrotion (Well-graded Sand, Test 5a)
o Influent Magnesium
a Effluent Magnesium
I I I I
Elapsed Time (Hours) 1.0% Hydraulic gradient system Fig A44: Magnesium concentration (Well-graded Sand, Test 5b) 350 -
280 -
-A 1 g' 20 - c .-0 *z .c1 -g wo C 0 o Influent Magnesium 0 o Effluent Magnesium 70 -
0, I 1 I I 0 50 100 150 200 250 Elapsed Time (Hours) 2.0% Hydraulic gradient system Fig A45: Mongonese concentrotion (Poorly Graded SondJestJa) 5
0 100 200 300 400 500 Elapsed Time (Hours) 1.77% Hydraulic gradient system Fig A46: Manganese concentrution (Poorly graded sandfest3b)
0 100 2cQ 300 400 500 Elapsed Time (Hours) 2.32% Hydraulic gradient system Fig A47: Mongonese concentration (Poork Graded SondJest4o)
Elapsed Time (Hours) 1.0% Hydraulic gradient system Fig A48: Manganese concentration (Poorly Graded SandJest4b)
Elapsed Time (Hours) 2.17% Hydraulic gradient system Fig A49: Manganese concentration (Well-graded sand, Test 50) 213
16
-A 1 -F tJ c 0 .-u 0 I u dd 5 0
0.4
OD 0 50 rlo I50 200 250 Elapsed Time (Hours) 1.0% Hydraulic gradient system Fig A50: Manganese concentration (Well-graded Sand, Test 5b)
0 50 100 150 200 250 Elapsed Time (Hours) 2.0% Hydraulic gradient system