-------
southeastern United States) the growth of both summer and winter grasses will
extend the range of evapotranspiration and erosion resistance for cover soils
(Lutton et al., 1979).
A recent study of vegetative growth in landfill environs (Gilman et al.,
1979) ranked the relative tolerance of selected tree species to high cover
soil concentrations of C02 and methane, a typical landfill condition that
causes the displacement of oxygen from the root zones of growing plants. The
tree species included (in order of decreasing tolerance): Black Gum, Norway
Spruce, Gingko, Black Pine, Bayberry, Mixed Poplar, White Pine, Pin Oak,
Japanese Yew, American Basswood, American Sycamore, Red Maple, Sweet Gum,
Green Ash, and Honey Locust. The same study found that mounds of topsoil
underlain by clay gas-barriers, or trenches underlain with polyethylene
sheeting and vented with perforated PVC vent pipes (Figures 3-4, A and B)
effectively prevented the migration of landfill gases (products of anaerobic
decomposition) into the root zone of trees. A further discussion on gas
migration control can be found in Section 6.0. The Gilman study also con-
cluded that woody plant species are more likely to survive on a completed fill
if planted when small, generally less than three feet tall (Gilman, et al.,
1979).
Loamy topsoils--those with nearly equal percentages of clay, silt, and
sand-sized grainsare generally best suited for revegetation establishment.
They are easily seeded and allow easy root penetration.
Sandy soils may be productive when blended or mulched with organic matter
(Lutton et al., 1979).
3.3.3 Advantages and Disadvantages
A well-designed and properly implemented revegetation planwhether for
long-term reclamation or short-term remedial actionwill effectively
stabilize the surface of a covered disposal site, reducing erosion by wind and
water, and will prepare the site for possible reuse. Evapotranspiration and
interception of precipitation by vegetative cover will also control leachate
generation at landfills by drying out the water near surface layers of refuse
and soil (Molz et al., 1974). This effect, however, is more or less offset by
enhanced soil infiltration capacity due to the increased detention of surface
flow by the vegetation and to the effects of the root systems on the cover
soil (increases permeability). If subsurface liners of clay or synthetic
membranes are constructed, infiltration of water into buried wastes (and
subsequent leachate production) will virtually be eliminated. This illus-
trates the importance of a layered surface sealing system and properly graded
slopes, which, in combination with suitable vegetative cover, will isolate
buried wastes from surface hydro!ogic input.
61
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FIGURE 3-4A
CROSS SECTION END VIEW OF GAS BARRIER TRENCH
(Source: Gilman et al., 1979)
1' Topsoil
V Subsoil
Plastic Sheet
PVC Perforated
Vent Pipes
FIGURE 3-4B
CROSS SECTION END VIEW OF SOIL MOUND
(Source: Gilman et al., 1979)
II 1'Clay H
62
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The selection of suitable plant species, the use of appropriate mulches
and stabilizers, the application of required doses of lime and fertilizers,
and optimum timing in seeding will help ensure the establishment of an effec-
tive vegetative cover. However, unforeseen difficulties may compromise the
effectiveness of revegetation. Clays or synthetic barriers below supporting
topsoil in poorly drained areas may cause swamping of cover soil and sub-
sequent anaerobic conditions. Too thin a cover soil may dry excessively in
arid seasons and irrigation may be necessary. Improperly vented gases and
soluble phytotoxic waste components may kill or damage vegetation. The roots
of shrubs or trees may penetrate the waste cover and cause leaks of water
infiltration and gas exfiltration. Also, periodic maintenance of revegetated
areasliming, fertilizing, mowing, replanting, or regrading eroded slopes
will add to the costs associated with this remedial technique.
3.3.4 Costs
Table 3-8 presents various unit costs associated with revegetating
covered disposal sites. These data represent estimated 1980 costs for the
indicated revegetation activities.
The costs of revegetating a hypothetical 20-acre disposal site are
calculated from these unit costs.
Assume that a 20-acre disposal site has been capped and graded, and has
been prepared for revegetation (loam topsoil has been spread and tilled). The
entire site is to be hydroseeded in the spring with grass seed, lime, and
fertilizer. It is to be hay-mulched over 15 acres; 5 acres of the site are
relatively steep slope areas that require stapled jute mesh for erosion con-
trol. Assume that the site will require six grass mowings the first year and
one refertilizing operation. Assume that no other maintenance (e.g., sodding)
is required.
The site is to be planted with selected evergreens and shrub species in
the spring of the second year of revegetation. Assume that 1,000 30- to
36-inch-high evergreens and 1,000 2- to 3- feet-high shrubs are to be evenly
distributed over the site. Each plant requires handspread wood chip mulching
over 1 ft2 (.111 yd2) at its base.
63
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TABLE 3-8
UNIT COSTS ASSOCIATED WITH REVEGETATION OF COVERED DISPOSAL SITES
Description
Hydraulic spreading (hydroseeding),
lime, fertilizer, and seed
Mulching, hay
Loam topsoil, remove and stockpile
on-site; using 200 h.p. dozer,
6' deep, 200' haul
500' haul
Hauling loam on-site
Spreading loam, 4-6" deep
Plant bed preparation (unspecified),
18" deep, by machine
Hydraulic seeding and fertilization
of large areas, with wood fiber mulch
Mulch, hand spread 2" deep, wood
chips
Liming slope areas
Fertilizing, level
slope
Seeding, level
slope
Sodding, in East, 1" deep, level
slope
Maintenance:
Grass mowing, slopes
level areas
Refertilization
Weeding/pruning shrubs
Unit costs1
$470/acre
$143/acre
$ .76/yd3
$2.92/yd3
$1.86/yd3
$ .40 - .70/yd3
$6.2I/yd2
$ .33/yd2
$1.01/yd2
$220/acre
$200/acre
$270/acre
$325/acre
$395/acre
Jute mesh, stapled (erosion control) $ .65/yd2
$3.10/yd2
$3.42/yd2
$38/acre
$17/acre
$128/acre
$810/acre
Source
2
2
3
3
2
2
3
2
2
2
2
3
3
2
2
2
2
continued--
64
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TABLE 3-8 (Continued)
Description Unit costs1 Source
On-site planting
Trees, evergreens 30-36" $44 ea. 2
36-42" $56 ea. 2
42-48" $80 ea. 2
4-5' $100 ea. 2
5-6' $130 ea. 2
Black Pines 7-8' $130 ea. 3
Yews 2-2.5' $33 ea. 3
Junipers 4-5' $44 ea. 3
Shade trees (balled and burlapped)
6-8' $37 ea. 2
8-10' $52 ea. 2
1.5 - 2.5" diam. $140-$220 ea. 2
2.5 - 4.0" diam. $350-$500 ea. 2
Birch 8-10' $78 ea. 3
Oak 8-10' $84 ea. 3
Shrubs (balled and burlapped)
2-3' $18 ea. 2
3-4' $41 ea. 2
4-5' $50 ea. 2
Honeysuckle shrub 4-5' $29 ea. 3
1A11 costs include materials and installation (labor and equipment), unless
otherwise indicated. Note different units (acre; yd2; yd3; each).
2McMahon and Pereira, 1979.
3 Godfrey, 1979.
The site is to be further planted in its third year of reclamation with
selected species of 6- to 8- feet-high shade trees. Assume that 500 of these
trees are to be planted, and that no special maintenance (mulching, pruning)
will be required.
Site Revegetation Costs:
First Year
o Hydroseeding with seed, lime, and fertilizer: ($470/acre) (20 acres)
= $9,400
65
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Hay mulching over 15 acres: ($143/acre) (15 acres) = $2,145
Jute mesh over 5 acres: (5 acres) (4,840 yd2/acre) ($0.65/yd2) =
$15,730
Grass mowings, 6 times: (20 acres) ($38/acre) (6 mowings/year) =
$4,560/yr.
Refertilizing, 1 time: (20 acres) ($138/acre) = $2,760
TOTAL FIRST-YEAR COSTS = $34.600
Second Year
Evergreens: (1,000 plants) ($44/planting) = $44,000
Shrubs (balled and burlapped): (1,000 plants) ($18/planting) =
$18,000
Hand-spread wood chip mulching: (2,000 plants) (.111 yd2/plant)
($1.01/yd2) = $224
TOTAL SECOND-YEAR COSTS = $62.200
Third Year
Shade trees: (500 plants) ($37/planting) = $18.500
TOTAL REVEGETATION COSTS OVER 3 YEARS (including one year of maintenance)
= $115.300
3.4 SURFACE WATER DIVERSION AND COLLECTION
The construction of surface water diversion and collection structures may
provide short-term or permanent measures to hydrologically isolate waste
disposal sites from surface inputs. Surface runoff can be managed so that it
does not contribute to leachate generation or erosion of cover materials.
Conventional civil engineering techniques are used to control flooding,
surface water infiltration, and off-site erosive transport of possible con-
taminated sediments and debris.
Several well-established construction techniques are available for
diverting and handling surface water flow in critical areas. Those methods
most applicable as remedial measures at uncontrolled disposal sites are ad-
dressed below.
66
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3.4.1 Dikes and Berms
3.4.1.1 Description and Applications
Dikes and benns are well-compacted earthen ridges or ledges constructed
immediately upslope from or along the perimeter of disturbed areas (e.g.,
disposal sites). These structures are generally designed to provide short-
term protection of critical areas by intercepting storm run-off and diverting
the flow to natural or manmade drainage ways, to stabilized outlets, or to
sediment traps. The two terms, dikes and berms, are generally used inter-
changeably; however, dikes may also have applications as flood containment
levees (Section 3.4.6).
Dikes and berms may be used to prevent excessive erosion of newly con-
structed slopes until more permanent drainage structures are installed or
until the slope is stabilized with vegetation (EPA, 1976). Dikes and berms
will help provide temporary isolation of un-capped and unvegetated disposal
sites from surface run-off that may erode the cover and infiltrate the fill.
These temporary structures are designed to handle relatively small amounts of
runoff; they are not recommended for unsloped drainage areas larger than 5
acres (Virginia SWCC, 1974).
3.4.1.2 Design and Construction Considerations
Specific design and construction criteria for berms and dikes will depend
upon desired site-specific functions of the structures. An interceptor dike/
berm (Figure 3-5) may be used solely to shorten the length of exposed slopes
on or above a disposal site, thereby reducing erosion potential by inter-
cepting and diverting runoff. Diversion dikes/berms (Figure 3-6) may be in-
stalled at the top of the steeper side slopes of unvegetated disposal sites to
provide erosion protection by diverting runoff to stabilized channels or
outlets.
Dikes and berms ideally are constructed of erosion-resistant, low-perme-
ability, clayey soils. Compacted sands and gravel, however, may be suitable
for interceptor dikes and berms. The general design life of these structures
is on the order of one year maximum; seeding and mulching or chemical stabili-
zation of dikes and berms may extend their life expectancy. Stone stabiliza-
tion with gravel or stone rip-rap immediately upslope of diversion dikes will
also extend performance life.
67
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FIGURE 3-5
TEMPORARY INTERCEPTOR DIKE
(Source: Virginia SWCC, 1974)
Disturbed Right-of-Way
2:1 or Flatter Slopes
CROSS SECTION
R.O.W
Side Slopes
2; I or Flatter
mm
Upslope Toe
Outlet Onto Stabilized Area
PLAN VIEW
68
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FIGURE 3-6
TEMPORARY DIVERSION DIKE
(Source: U.S. EPA, 1976)
18" min
Cut or fill slope
Flow
Stone stabilization,
if required
2:1 slope or flatter
Existing ground
Cross-section
Positive drainage. (Grade
sufficient to dram.)
AA
AA
A A
A A
A A
Y V
Y
Plan view
'Cut or fill slope
69
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Common design and construction criteria for interceptor and diversion
dikes/berms include the following:
Drainage area: 5 acres maximum
Top width: 2 feet minimum
Height (compacted): 18 inch minimum
Side slopes: 2:1 or flatter
Grade: Dependent upon topography, but must have positive
drainage to the outlet; for interceptor dikes/berms,
1.0 to 1.5 percent.
Spacing (interceptor only):
Distance between dikes 150' 200' 300'
Maximum slope of area above dike >IQ% 5-10% <5%
All earthen dikes should be machine-compacted.
Diverted runoff should outlet directly onto stabilized areas, level
spreader, grassed channel, or chute/downpipe.
Periodic inspection and maintenance should be provided.
Diversion dikes must be seeded and mulched immediately after con-
struction.
3.4.1.3 Advantages and Disadvantages
The following advantages are afforded by properly designed and con-
structed dikes and berms:
Standard construction techniques are used; required excavation and
grading equipment may be available at disposal site.
Required earth fill may be available on-site.
Erosion of cover material from slopes of disposal site will be
controlled until further site stabilization is achieved (through
cover compaction, regrading, revegetation).
Diversion of storm runoff will decrease amount of water available
for infiltrating soil cover; therefore, leachate generation may be
reduced.
70
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Disadvantages associated with berms and dikes are generally due to main-
tenance requirements and the nonpennanent nature of the structures. These
problems include the following:
Periodic inspections and maintenance are required to ensure struc-
tural integrity and prevent upslope deposition of sediments.
Improperly installed dikes and berms may increase seepage, contrib-
uting to soil instability and leachate generation.
The structures are suitable only for relatively small drainage areas
( 5 acres).
Ultimate removal of the structures (after effective performance
life) entails additional costs.
3.4.1.4 Costs
The costs of installing and maintaining dikes and berms will vary with
the site conditions, depending on: number and size of structures required,
local availability of suitable soil and equipment, local climate and site
hydrology (intensity and volume of storm runoff to be diverted), amount of
maintenance required, design life of the structures, amount and type of sta-
bilization required (seeding, mulching, chemical soil additives, and unfore-
seen construction difficulties.
Unit costs associated with dike/berm construction and maintenance are
presented in Table 3-15 at the end of this chapter.
3.4.2 Ditches, Diversions, and Waterways
3.4.2.1 Description and Applications
Ditches (or swales) are excavated, temporary drainageways used above and
below disturbed areas to intercept and divert runoff. They may be constructed
along the upslope perimeter of disposal areas to intercept storm runoff and
carry it to natural drainage channels downslope of the site. As shown in
Figure 3-7, ditches may also be installed downslope of covered disposal sites
to collect and transport sediment-laden flow to sediment traps or basins.
Ditches should be left in place until the disposal site is sealed and sta-
bilized with cover vegetation.
Diversions are permanent or temporary shallow drainageways excavated
along the contour of graded slopes and having a supporting earthen ridge (dike
or berm) constructed along the downhill edge of the drainageway. Essentially,
71
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FIGURE 3-7
TYPICAL DRAINAGE DITCH AT BASE OF DISPOSAL SITE
(Source: ORB and Emcon Associates, 1980)
Final cover
Gross line for erosion
protection
a diversion is a combination of a ditch and a dike (EPA, 1976). Diversions
are used primarily to provide more permanent erosion control on long slopes
subject to heavy flow concentrations. They may be constructed across long
slopes to divide the slope into nonerosive segments. Diversions may also be
constructed at the top or at the base of long graded slopes at disposal sites
to intercept and carry flow at nonerosive velocities to natural or prepared
outlets. Diversions are recommended for use only in slopes of 15 percent or
less (EPA, 1976).
Grassed waterways (or channels) are graded drainageways that serve as
outlets for diversions or berms. Waterways are stabilized with suitable
vegetation and are generally designed to be wide and shallow in order to
convey runoff down slopes at nonerosive velocities. Waterways may be con-
structed along the perimeter of disposal sites located within natural slopes,
or they may be constructed as part of the final grading design for disposal
areas that have been capped and revegetated.
72
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3.4.2.2. Design and Construction Considerations
Ditches, diversions, and waterways are generally of V-shaped, trapezoidal
or parabolic cross-section design. The specific design will be dependent on
local drainage patterns, soil permeability, annual precipitation, area land
use, and other pertinent characteristics of the contributing watershed. In
general, such drainageways should be designed to accommodate flows resulting
from rainfall events (storms) of 10- or 25-year frequency. More importantly,
they should be designed and constructed to intercept and convey such flows at
non-erosive velocities.
Figure 3-8 depicts the effect of drainage channel shape on relative
velocity of conveyed flows. In general, the wider and shallower the channel
cross-section, the less the velocity of contained flow and therefore, the
less the potential for erosion of drainageway side slopes. Where local
conditions dictate the necessity of building narrower and deeper channels,
or where slopes are steep and flow velocities are excessive, the channel
'will require stabilization through seeding and mulching or the use of stone
riprap to line channel bottoms and break up flow.
Table 3-9, below, presents maximum permissible design velocities for
flow in ditches and grassed waterways, based on the channel grade and
stabilizing cover material.
Figure 3-9 shows the standard design for drainage ditches. These struc-
tures are designed for short-term application only, for upslope drainage areas
of less than 5 acres. A minimum grade of one percent, draining to a sta-
bilized outlet such as a grassed waterway or, where necessary, to a sediment
basin or trap, is recommended for temporary ditches. For channel slopes
greater than 5 percent, stabilization with grasses, mulches, sod, or stone
riprap will be necessary. As with all temporary structures, periodic inspec-
tion and maintenance are required to ensure structural integrity and effective
performance (EPA, 1976).
Figure 3-10 presents general design features of parabolic and trapezoidal
diversions. A formal design is not required for diversions used as temporary
water-handling structures. General design and construction criteria for
permanent diversions include the following: (EPA, 1976).
Diversion location is determined on the basis of outlet conditions,
topography, soil type, slope length and grade.
Constructed diversion shall have capacity to carry peak discharge
from 25-year design storm.
73
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FIGURE 3-8
EFFECT OF DRAINAGE DITCH ON VELOCITY
(Source: Lutton, et al., 1979)
1.00'
t.87'
18.01
V=1.00*
10.0'
15.0'
*V=RELATIVE VELOCITY
10.5'
7.0'
74
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The maximum grade of the diversion may be determined by using design
velocity of the flow based on stabilization by cover type (Table
3-9, above).
The diversion channel shall be parabolic or trapezoidal in shape,
with side slopes no steeper than 2:1.
The supporting ridge (dike or berm) shall have a minimum width of 4
ft.; freeboard shall be 0.3 ft. minimum over peak water level in
channel.
Each diversion shall have a stable outlet such as a natural water-
way, stabilized open channel, chute, or downpipe.
Stabilization: For design velocities 3.5 ft/sec, seeding and
mulching for vegetative establishment; for velocities 3.5 ft/sec,
stabilize with sod or with seeding protected by jute or excelsior
matting.
t For channels that carry flow during dry weather (base flow) due to
groundwater discharqe or delayed subsurface runoff the bottom should
be protected with a stone center as shown in Figure 3-11 for grassed
waterways; subsurface drainage with gravel/stone trenches may be re-
quired where the water table is at or near the surface of the channel
bottom.
Fills shall be compacted as needed to prevent unequal settlement.
All trees, bushes, stumps, and obstructions shall be cleared to pre-
vent improper functioning of the channel.
Figures 3-11 and 3-12 depict general design configurations for grassed
waterways. The design and construction criteria presented above for diver-
sions are applicable to grassed waterways also.
3.4.2.3 Advantages and Disadvantages
When they are carefully designed, constructed, and maintained, ditches,
diversions, and grassed waterways will control surface erosion and infiltra-
tion at disposal sites by intercepting and safely diverting storm runoff to
downslope or off-site outlets. When situated at the base of disposal site
slopes, they function to protect off-site habitat from possible contamination
by sediment-laden runoff. These structures are generally constructed of
readily available fill, by well-established techniques.
Temporary ditches and diversions, however, entail added costs because
they require inspections and maintenance. Grassed waterways must be periodi-
cally mowed to prevent excessive retardation of flow and subsequent ponding of
water. Also, periodic resodding, remulching, and fertilizing may be required
to maintain vegetated channels.
75
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TABLE 3-9
PERMISSIBLE DESIGN VELOCITIES FOR STABILIZED DIVERSIONS AND WATERWAYS
Cover
Vegetative
Bermuda grass
Reed canary grass;
Tall fescue;
Kentucky bluegrass
Grass-legume mix
Channel grade
0-5
5-10
10
0-5
5-10
10
Red fescue;
Redtop, sericea lespedeza
Annuals;
Small grain (rye, oats,
barley);
Ryegrass
0-5
5-10
0-5
0-5
Maximum design velocity
(ft/sec)
6
5
4
5
4
3
4
3
2.5
2.5
(Source: EPA, 1976)
If fertilization is used, an additional disadvantage is introduced, in
that nitrogen and phosphorus are added to drainage wastes, which then con-
tribute to the problem of accelerated eutrophication in receiving water
bodies.
also be necessary to install temporary straw-bale check dams,
ouu^u uuwn at 50- to 100-foot intervals, across ditches and waterways in
order to prevent gulley erosion and to allow vegetative establishment (Tour-
It may
staked down
76
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FIGURE 3-9
STANDARD DESIGN FOR DRAINAGE DITCHES
(Source: U.S. EPA, 1976)
' r*. ,*i
Flow
2:1 or flatter
1
r
i
min.
7' min.
level
Existing ground
Cross-section
1% or steeper, dependent on topography
Flow
Outlet as required.
See item 6 below.
Plan view
77
-------
FIGURE 3-10
GENERAL DESIGN FEATURES OF DIVERSIONS
(Source: U.S. EPA, 1976)
width
Trapezoidal cross-section
Parabolic cross-section
78
-------
FIGURE 3-11
GRASSED WATERWAYS WITH STONE CENTERS
(Source: U.S EPA, 1976)
Trapezoidal cross-section
Parabolic cross-section
bier and Westmacott, 1974). The installation and ultimate removal of these
check dams will add to the costs associated with diversions and waterways.
Permanent diversions and waterways are more cost-effective techniques
than temporary structures for controlling erosion and infiltration on a long-
term basis at inactive disposal sites.
79
-------
FIGURE 3-12
GRASSED WATERWAYS
(Source: U.S. EPA, 1976
D T.
Trapezoidal cross-section
Parabolic cross-section
3.4.2.4 Costs
As with all surface-water diversion structures, costs for ditches, diver-
sions, and waterways will be highly variable because of site-specific dif-
ferences in fill materials and equipment availability, design capacity and
life expectancy of the structure, etc. Unit costs associated with the con-
struction and maintenance of these structures are presented at the end of
this chapter in Table 3-15.
80
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3.4.3 Terraces and Benches
3.4.3.1 Description and Applications
Terraces and benches are relatively flat areas constructed along the
contour of very long or very steep slopes to slow down runoff and divert it
into ditches or diversions for off-site transport at nonerosive velocities.
These structures are also known as bench terraces or drainage benches.
Although benches and terraces are slope reduction devices, they are
generally constructed with reverse fall or natural fall (see Figure 3-13), to
divert water to stabilized drainageways. Benches and terraces may be used to
break up steeply graded slopes of covered disposal sites into less erodible
segments. Upslope of disposal sites, they act to slow and divert storm runoff
around the site. Downs!ope of landfill areas, they act to intercept and
divert sediment-laden runoff to traps or basins. Hence, they may function to
hydrologically isolate active disposal sites, to control erosion of cover
materials on completed fills, or to collect contaminated sediments eroded from
disposal areas. For disposal sites undergoing final grading (after capping
and prior to revegetation), construction of benches or terraces may be in-
cluded as part of the integrated site closure plan.
3.4.3.2 Design and Construction Considerations
Benches and terraces generally do not require a formal design plan.
Figure 3-14 presents the design for a typical drainage bench located on the
slope of a covered landfill. This particular bench is designed with a natural
fall. It is intended for long-term erosion protection as the associated
V-shaped channel is asphalt concrete-lined. Diversions and ditches included in
bench/terrace construction may be seeded and mulched, sodded, stabilized with
riprap or soil additives, or stabilized by any combination of these methods.
Lining the channels with concrete or grouted riprap is a more costly alterna-
tive.
The width and spacing between benches and terraces will depend on slope
steepness, soil type, and slope length. In general, the longer and steeper
the slope and the more erodible the cover soil, the less the distance between
drainage benches should be. This will maximize the erosion reduction afforded
by constructed benches. For slopes greater than 10 percent in steepness, the
maximum distance between drainage benches should be approximately 100 feet,
i.e., a bench every 10 feet of rise in elevation (EPA, 1976).
When the slope is greater than 20 percent, it has been recommended that
benches be placed every 20 feet of rise in elevation (EPA, 1979). Benches
81
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FIGURE 3-13A
BENCH TERRACES WITH RESERVE FALL
(Adapted from Tourbier and Westmacott, 1974)
Swale or Ditch
I
Swale or Ditch
FIGURE 3-13B
BENCH TERRACES WITH NATURAL FALL
Ditch
Ditch
or
Dike
82
-------
FIGURE 3-14
TYPICAL DRAINAGE BENCH
Final Soil Cover
D = 1.5
3" Min. Asphaltic Concrete Liner
should be of sufficient width and height to withstand a 24-hour, 25-year storm
(EPA, 1979).
Bench terraces do not necessarily have to be designed with diversions or
ditches to intercept flow. Reverse benches and slope benches (Figure 3-15)
may be constructed during final site grading on well-stabilized slopes (e.g.,
vegetated) to enhance erosion control by reducing slope length and steepness.
At sites where an effective cap (e.g., clay or synthetic liner) has been
constructed, or for sites located in arid regions, these nondrainage benches
will function to slow sheet runoff and allow greater infiltration rates, which
will aid in the establishment of a suitable vegetative cover. For most dis-
posal sites in wet climates, however, where leachate generation and cover
erosion are major problems, benches and terraces should be designed in asso-
ciation with drainage channels that intercept and transport heavy, concen-
trated surface flows safely off-site.
83
-------
FIGURE 3-15
SLOPE REDUCTION MEASURES
(Source: U.S. EPA, 1976)
84
-------
As with other earthen erosion control structures, benches and terraces
should be sufficiently compacted and stabilized with appropriate cover
(grasses, mulches, sod) to accommodate local topography and climate. They
should be inspected during or after major storms to ensure proper functioning
and structural integrity. If bench slopes become badly eroded or if their
surfaces become susceptible to ponding from differential settlement, regrading
and sodding may be necessary.
3.4.3.3. Advantages and Disadvantages
In areas of high precipitation, drainage benches and terraces are proven
effective in reducing velocity of storm runoff and thereby controlling
erosion. For excessively long and steep slopes above, on, or below disposal
sites, these structures are cost-effective methods for slowing and diverting
runoff. They may also be used to manage downs!ope washout of disposal site
sediments that may be contaminated with hazardous waste components. Terraces
and benches are easily incorporated into final grading schemes for disposal
sites, and do not require special equipment or materials for their con-
struction.
If improperly designed or constructed, bench terraces will not perform
efficiently and may entail excessive maintenance and repair costs. It is
important that these structures be stabilized with vegetation as soon as
possible after grading and compaction, or they may become badly eroded and
require future resodding or chemical stabilization. Benches and terraces also
require periodic inspections, especially after major rainfall events.
3.4.3.4 Costs
The costs of bench and terrace construction will depend on the amount of
fill required, the local availability of fill materials and grading equipment,
the size and type of diversion channels to be installed, and the local costs
of seeding, mulching, and other stabilizing materials. The frequency and
extent of required maintenance will add to these costs.
Unit costs for these construction and maintenance activities are pre-
sented in Table 3-15 at the end of this chapter.
85
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3.4.4 Chutes and Downpipes
3.4.4.1 Description and Applications
Chutes and downpipes are temporary structures used to carry concentrated
flows of surface runoff from one level to a lower level without erosive
damage. They generally extend downs!ope from earthen embankments (dikes or
berms) and convey water to stabilized outlets located at the base of terraced
slopes.
Chutes (or flumes) are open channels, normally lined with bituminous
concrete, Portland cement concrete, grouted riprap, or similar nonerodible
material. Temporary paved chutes are designed to handle concentrated surface
flows from drainage benches located near the base of the long, steep slopes at
disposal sites.
Downpipes (downdrains; pipe slope drains) are temporary structures con-
structed of rigid piping (such as corrugated metal) or flexible tubing of
heavy-duty fabric. They are installed with standard prefab-ricated entrance
sections and are designed to handle flow from drain-age areas of 5 acres or
less. Like paved chutes, downpipes discharge to stabilized outlets or sedi-
ment traps. Downpipes may be used to collect and transport runoff from long,
isolated outslopes or from small disposal areas located along steep slopes.
Temporary downpipes may also be constructed by joining half-round
sections of bituminous fiber or concrete pipe (Figure 3-16). These structures
may be quickly constructed for emergency situations when downs!ope ditches or
waterways overflow during severe storms and threaten to erode the base of
disposal fill areas.
3.4.4.2 Design and Construction Considerations
Chutes and downpipes are temporary structures that do not require formal
design. General design criteria are presented in Figures 3-17 (paved chute),
3-18 (rigid downpipe), and 3-19 (flexible downpipes).
Chutes are designed to handle flows based on two basic size groups. Paved
chutes of size group A have the following three qualifications:
Height (H) of dike at entrance = 1.5 feet minimum
Depth (D) of chute down the slope = 8 inches minimum
Length (L) of inlet/outlet sections = 5 feet minimum
86
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Similarly, chutes of size group B meet the following criteria:
H = 2 feet minimum
0 = 10 inches minimum
L = 6 feet minimum
FIGURE 3-16
HALF-ROUND BITUMINOUS FIBER PIPE USED FOR TEMPORARY HANDLING
OF CONCENTRATED FLOW
(Source: U.S. EPA, 1976)
87
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Table 3-10 below presents the bottom width and maximum drainage area for
designed chutes of the two size groups.
TABLE 3-10
BOTTOM WIDTHS AND MAXIMUM DRAINAGE AREAS FOR TEMPORARY CHUTES
Size
group
A- 2
A- 4
A-6
A-8
A- 10
Bottom
width, D
(ft.)1
2
4
6
8
10
Maximum
drainage
area (acres)
5
8
11
14
18
Size
group
B-4
B-6
B-8
B-10
B-12
Bottom
width, D
(ft.)1
4
6
8
10
12
Maximum
drainage
area (acres)
14
20
25
31
36
'Source: U.S. EPA, 1976.
If 75 percent or more of the drainage area has good vegetative cover
(established grasses and/or shrubs) throughout the design life of the chute,
the drainage areas listed in Table 3-10 may be increased by 50 percent. If 75
percent or more of the drained area has a mulch cover throughout the struc-
ture's life, the areas may be increased by 25 percent (EPA, 1976).
1976):
Paved chute construction considerations include the following (EPA,
The structure shall be placed on undisturbed soil or well-compacted
fill.
The lining shall be placed by beginning at the lower end and pro-
ceeding upslope; the lining shall be well-compacted, free of voids,
and reasonably smooth.
The cut-off walls at the entrance and at the end of the asphalted
discharge aprons shall be continuous with the lining.
An energy dissipator (riprap bed) shall be used to prevent erosion
at the outlet.
88
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FIGURE 3-17
PAVED CHUTE (OR FLUME)
(Source: U.S. EPA, 1976)
Top of earth dike &
top of lining
Slope varies, not
steeper than 1.5:1
& not flatter than
20:1
Undisturbed soil or
compacted fill
Dimen-
sion
Hmin
dmin
L-min
Size Group
A
1.5'
8"
5'
B
2.0'
10"
6'
Profile
mm.
Place 3" layer of sand J L 6"\ ]
imafiA tms-Jarmi + lA+'*r-ซซl<%Aiป * ' \
for drainage under outlet as show
for full width of structure
Riprap is 9" layer of
6" min. rock or rubble
r
Toe of slope
Plan view
2 1/2" min.
Section B-B.
89
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For downplpes (Figure 3-18 and 3-19), the maximum drainage area is deter-
mined from the diameter of the piping, as follows (EPA, 1976):
PIPE/TUBING DIAMETER, D (INCHES)
12
18
21
24
30
MAXIMUM DRAINAGE AREA (ACRES)
.5
1.5
2.5
3.5
5.0
General construction criteria for both rigid and flexible downdrains
include the following:
The inlet pipe shall have a slope of 3 percent or greater.
For the rigid downpipe, corrugated metal pipe with watertight con-
necting bands shall be used.
For the flexible downdrain, the inlet pipe shall be corrugated
metal; the flexible tubing shall be the same diameter as the inlet
pipe, securely fastened to the inlet with metal strapping or water-
tight connecting collars.
A riprap apron shall be provided at the outlet; this shall consist
of 6-inch diameter stone placed as shown in the figures.
The soil around and under the inlet pipe and entrance sections shall
be hand-tamped in 4-inch lifts to the top of the earth dike.
Follow-up inspection and any needed maintenance shall be performed
after each storm.
3.4.4.3 Advantages and Disadvantages
When properly designed and constructed, chutes and downpipes may be
cost-effective temporary grade-stabilization structures. The advantages and
disadvantages associated with their construction and maintenance are sum-
marized in Table 3-11.
3.4.4.4 Costs
Costs of chute and downpipe construction and maintenance will vary,
depending on the size (length, width, depth) of the structure and the type of
liner and pipe material used (corrugated metal, flexible drainpipe, bitumi-
90
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FIGURE 3-18
RIGID OOWNPIPE
(Source: U.S. EPA, 1976)
Discharge into a
stabilized watercourse
sediment trapping device
or onto stabilized area
Cutaway used
to show inlet
W*:M\
Length as necessary to go
thru dike
2:1
Diameter (D)
Profile
4' min.
@ less than 1% slope
Standard flared
entrance section
oo o0
I '! n
JY-l
-**" -
rp^cs
^/,^-S-ffolii
jL.fcy^.r?/ซ^^a
Riprap shall consist of 6"
diameter stone placed as shown.
Depth of apron shall equal the pipe
diameter and riprap shall be a min-
imum of 12" in thickness.
Riprap apron plan
91
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FIGURE 3-19
FLEXIBLE DOWNDRAIN
(Source: U.S. EPA, 1976)
Discharge into a
stabilized watercourse,
sediment trapping device,
or onto a stabilized area
NOTE: Size designation is:
PSD-Pipe Diam. (ex., PSD-
18=Pipe Slope Drain with
18" diameter pipe)
="- -'.^f:-:>
- -- =*ฃ<;. :
-- .--=- --'i'<
-------
TABLE 3-11
SUMMARY OF ADVANTAGES AND DISADVANTAGES OF CHUTES AND OOWNPIPES
Advantages
Construction methods are
inexpensive and quick; suitable
for emergency measures.
No special materials or
equipment are required.
Are effective in pre-
venting erosion on long,
steep slopes.
Can be used to channel
storm runoff to sediment
traps, drainage basins,
or stabilized waterways
for off-site transport.
Can be key element in
combined surface control
systems.
Disadvantages
Provide only temporary
erosion control while
slopes are stabilized
with vegetative growth.
Entail extra cost for
periodic inspections
and maintenance and
ultimate removal.
If improperly designed,
may overflow and cause
severe erosion in con-
concentrated areas.
Downpipes are suitable
for drainage areas 5
acres in size; limited
applications in
general.
nous fiber, PVC). Unit costs associated with these temporary structures are
presented at the end of the chapter in Table 3-15.
3.4.5 Levees
3.4.5.1 Description and Applications
Levees are earthen embankments that function as flood protection struc-
tures in areas subject to inundation from tidal flow or riverine flooding.
Levees create a barrier to confine floodwaters to a floodway and to protect
93
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structures behind the barrier. They are most suitable for installation in
flood fringe areas or areas subject to storm tide flooding, but not for areas
directly within open floodways (Tourbier and Westmacott, 1974).
Flood containment levees may be constructed as perimeter embankments
surrounding disposal sites located in floodplain fringe areas, or they may be
installed at the base of landfills along slope faces that are subject to
periodic inundation. Levees serve to protect land disposal sites from flood-
waters, which may erode cover materials and transport waste materials off-
site, or which may add water to waste materials and thus increase hazardous
leachate production.
Levees are generally constructed of compacted impervious fill. Special
drainage structures are often required to drain the area behind the embank-
ment. Levees are normally constructed for long-term flood protection, but
they require periodic inspection and maintenance to assure proper functioning.
They may be costly to build and maintain, but if properly designed on a site-
specific basis, levees will reduce flooding hazards at critical waste disposal
areas.
3.4.5.2 Design and Construction Considerations
To provide adequate flood protection, levees should be constructed to a
height capable of containing a design flood of 100-year magnitude. Levees
designed to protect disposal areas from maximum flood levels of lesser magni-
tude/greater frequency (e.g., 50-year flood) may not provide sufficient flood
protection, particularly for sites known to contain large quantities of haz-
ardous wastes. Elevation of 100-year base flood crests can be determined from
floodplain analyses typically performed by state or local flood control agen-
cies. A minimum levee elevation of 2 feet above the 100-year flood level is
recommended (JRB Associates and Emcon Associates, 1980).
Figure 3-20 presents design features of a typical levee constructed at
the toe of a landfill slope. This design is appropriate for new or uncom-
pleted disposal sites; filled wastes may eventually be placed on the inboard
slope of the levee. Where levee construction is impractical due to lack of
soil or limited space, perimeter protection of vulnerable landfill slopes may
be afforded by the design shown in Figure 3-21. A minimum top width of 10
feet is recommended for most levees; this will permit easy access for con-
struction and maintenance equipment (Linsley and Franzini, 1979).
Ideal construction of levees is with erosion-resistant, low-permeability
soils, preferably clay. Most levees are homogeneous embankments; but if
impermeable fill is lacking, or if seepage through and below the levee is a
problem, then construction of a compacted impervious core or sheet-pile cutoff
extending below the levee to bedrock (or other impervious stratum) may be
94
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FIGURE 3-20
TYPICAL LEVEE AT BASE OF DISPOSAL SITE
(Source: JRB Associates and Emcon Associates, 1980)
Final Soil Cover
Elevation: Minimum 2'
Above 100 Year Flood
^5-^
Compacted Impervious
Soil Levee
Equipment I
Width 10 1
"l_-li-- ^
k " ^>_ . i
-^ ^C
_i_^,_
i ; t
| 1 V Min. Stripping
j 1 Impervious Groundwater Cutoff Tre
. May Be Required in Certain Soils
_
.. "
Fill
rich
FIGURE 3-21
PERIMETER FLOOD PROTECTION STRUCTURE
(Source: JRB Associates and Emcon Associates, 1980)
Final Soil Cover
Existing Grade
Compacted Impervious Soil
Elevation: Minimum 2'
Above 100 Year Flood.
5
Slope 2%
V Key Into Impervious Soil
Verify Existing V Thick
Clay Cover Soil (Typ.)
95
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necessary. Figure 3-22 depicts these two special cases. Excess seepage
through the levees should be collected with gravel-filled trenches or tile
drains along the interior of the levee. After draining to sumps, the seepage
can be pumped out over the leeve. Levee bank slopes, especially those con-
structed of less desirable soils (silt, sands), should
erosion by sodding, planting of shrubs and trees, or
(Linsley and Franzini, 1979).
be protected against
use of stone riprap
FIGURE 3-22A
LEVEE WITH IMPERVIOUS CORE
3:1 Max
3:1 Max
_
Compacted
Impervious
Fill
Filter
VV.v^VV.V/lV/^v^ Rock or Impervious Stratum
FIGURE 3-22B
LEVEE WITH CUTOFF AND DRAIN
(Source: Tourbier and Westmacott, 1974)
Compacted Impervious Fill
Filter Drain
LOW PERMEABILITY
Blanket
Sheet Pile Cut Off
Impervious Stratum V\\ttV:A^l^vV'r-;V':^V.y'?V.Vป*'V:
96
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Fill material used in levee construction should be compacted in layers,
with the least pervious layer along the riverside of the levee. Because the
use of levees will reduce floodplain storage capacity, fill material should be
dredged from borrow pits within the floodplain to provide alternate storage
volume for floodwaters. This measure will help control rising floodpeaks and
prevent an increase in depth of downstream flood stage (Tourbier and West-
macott, 1974).
Storm runoff from precipitation falling on the drainage area behind the
levee may cause backwater flooding. To handle such interior drainage, upslope
interceptor ditches, diversions, or grassed waterways can be used to channel
runoff to downslope holding basins (for subsequent pumping) or to off-site
streams for natural gravity discharge. Another method to handle backwater
flow is the installation of pressure conduits (with upslope intake works) that
discharge beneath the levee. These conduits should be equipped with tidal
gates or backwater valves to prevent back-flow and regulate discharge.
Because of the relatively long, flat side slopes of levees, an embankment
of any considerable height requires a very large base width. For locations
with limited space and fill material, or excessive real estate costs, the use
of concrete floodwalls is preferred as an alternative to levee construction.
Floodwalls are designed to withstand the hydrostatic pressure exerted by water
at the design flood level. They are subject to flood loading on one side
only; consequently, they need to be well founded (Tourbier and Westmacott,
1974). Figure 3-23 presents typical floodwall sections. Like levees, flood-
walls may require sub-surface cutoffs and interior drainage structures to
handle excessive seepage or backwater flow.
3.4.5.3 Advantages and Disadvantages
The advantages and disadvantages associated with flood protection levees
at waste disposal sites are summarized in Table 3-12.
3.4.5.4 Costs
Costs associated with constructing and maintaining levees will depend on
site-specific design variables, availability of suitable embankment soil, and
the local frequency and magnitude of flooding. If backwater flooding or
seepage is a problem, then special structures must be included in the con-
struction plan. Regular annual inspection for evidence of bank caving, bank
sloughing, erosion, and foundation settlement will also increase associated
costs.
97
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FIGURE 3-23
SOME TYPICAL FLOODWALL SECTIONS
(Source: Linsley and Franzini, 1979)
rac^rrr^ /yf^wg?-
D
Simple cantilever and sheet pile
sAdequate foundation
Gravity
Earth
fill
t/
Cellular
Slab and buttress
Buttress
T-cantilever
Unit costs relating to levee construction and maintenance are included in
Table 3-15 in Section 3.4.8.
3.4.6 Seepage Basins and Ditches
3.4.6.1 General Description and Applications
Seepage or recharge basins are designed to intercept runoff and recharge
the water downgradient from the site so that groundwater contamination and
leachate problems are avoided or minimized.
3.4.6.2 Design and Construction Considerations
There is considerable flexibility in the design of seepage basins and
ditches. Figures 3-24 through 3-27 illustrate possible design variations.
98
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TABLE 3-12
SUMMARY OF EVALUATION OF LEVEES
Advantages
Can be built at relatively
low cost from materials
available at site
Will provide long-term flood
protection if properly
designed and constructed
Controls major erosive
losses of waste and cover
material; prevents massive
leachate production and
subsequent contamination
from riverine or tidal
flooding
Disadvantages
Flooding from storm runoff
behind levee may be a
problem
Loss of flow storage
capacity, with greater
potential of downstream
flooding
Levee failure during major
flood will require costly
emergency measures (emer-
gency embankments; sand
bags) and rebuilding of
structure
Require periodic main-
tenance and inspections
Special seepage cutoffs or
interior drainage struc-
tures (e.g., pressure con-
duits) will add to con-
struction costs
Where seepage basins are used (Figure 3-24), runoff will be intercepted
by a series of diversions, or the like, and passed to the basins. As illus-
trated, the recharge basin should consist of the actual basin, a sediment
trap, a by-pass for excess runoff, and an emergency overflow. A considerable
amount of recharge occurs through the sidewalls of the basin, and it is pre-
ferable that these be constructed of pervious material. Gabions are frequently
used to make sidewalls. An alternative design for a seepage basin is shown in
Figure 3-25. This is not designed for as intensive recharge as the previously
discussed system, and is usually used where the aquifer is shallow.
Dense turf on the side slopes of these basins will prevent erosion and
sloughing and will also allow a high infiltration rate. Prevention of scour
by the inlet is an important consideration since it can significantly reduce
99
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FIGURE 3-24
SEEPAGE BASIN; LARGE VOLUME, DEEP DEPTH TO GROUNDWATER
(SOURCE: Tourbier and Westmacott, 1974)
See Copyright Notice, Page 496
Seepage basin Overflow
t
Sediment
trap
Bypass
FIGURE 3-25
SEEPAGE BASIN; SHALLOW DEPTH TO GROUNDWATER
(Source: Tourbier and Westmacott, 1974)
Seepage
basin
Dense turf
Gravel filled
trench
maintenance requirements. This can be accomplished by a "hydraulic jump" or
an impact stilling basin before water flows into the recharge basin. Perco-
lation can be improved by construction of gravel-filled trenches along the
basin floor, as shown in Figure 3-24 (Tourbier and Westmacott, 1974).
100
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Use of seepage ditches (Figures 3-26 and 3-27) distributes water over a
larger area than can be achieved with basins. They can be used for all soil
where permeability exceeds about 0.9 in/day. Runoff is disposed of by a
system of drains set in ditches of gravel. Depth and spacing of drains
depends on soil permeability. A minimum depth of 48 inches is generally
recommended, and ditches are rarely less than 10 feet apart. The ditches are
backfilled with gravel, on which the distribution line is laid. Sediment is
removed prior to discharging runoff into the seepage ditches by use of a
sediment trap and distribution box. The efficiency of the seepage area can be
increased by interconnecting two trenches by a continuous 12-inch gravel bed,
as shown in Figure 3-27 (Tourbier and Westmacott, 1974).
FIGURE 3-26
SEEPAGE DITCH
(Source: Tourbier and Westmacott, 1974)
10' (min.)
Topsoil
2" hay or
12" min.
straw
Gravel
12" min.
18" min.
48" min.
18" (max.
101
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FIGURE 3-27
SEEPAGE DITCH WITH INCREASED SEEPAGE EFFICIENCY
(Source: Tourbier and Westmacott, 1974)
18" max.
1 10' min.
3.4.6.3 Advantages and Disadvantages
2" hay
or straw
N Tile,
perforated
bitumen
fiber or
p.v.c. pipe
3-13.
Advantages and disadvantages of drainage systems are listed in Table
TABLE 3-13
ADVANTAGES AND DISADVANTAGES OF GRAVITY DRAINAGE SYSTEMS
Advantages
Cost effective means of intercepting
runoff and allowing it to recharge
Systems can perform reliably if
well maintained
Disadvantages
Seepage basins and ditches are
susceptible to clogging
Deep basins or trenches can be
hazardous
Not effective in poorly permeable
soils
102
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3.4.7 Sedimentati on Basins/Ponds
3.4.7.1 General Description and Application
Sedimentation basins are used to control suspended solids entrained in
surface flows. A sedimentation basin is constructed by placing an earthen dam
across a waterway or natural depression, or by excavation, or by a combination
of both. The purpose of installing a sedimentation basin is to impede surface
runoff carrying solids, thus allowing sufficient time for the particulate
matter to settle. Sedimentation basins are usually the final step in control
of diverted surface runoff, prior to discharge into a receiving water body.
They are an essential part of any good surface flow control system and should
be included in the design of remedial actions at waste disposal sites.
3.4.7.2 Design and Construction Considerations
The removal of suspended solids from waterways is based on the concept of
gravitational settling of the suspended material.
The size of a sedimentation basin is determined from characteristics of
flow such as the particle size distribution for suspended solids, the inflow
concentration, and the volumetric flow rate. To calculate the area of the
sedimentation basin pond required for effective removal of suspended solids,
the following data on the flow characteristics are needed:
The inflow concentration of suspended solids.
The desired effluent concentration of suspended solids. The desired
effluent concentration is usually regulated by local and/or Federal
government authorities. For example, for coal mines, the proposed
EPA "Effluent Guidelines and Standard" limits are as follows: (1)
total suspended solids concentration maximum for any one day is to
70 mg/1, and (2) average daily values for 30 consecutive days shall
not exceed 35 mg/1.
The particle size distribution for suspended solids.
The water flow rate (Q) to the pond. For a pond receiving direct
runoff, the runoff volume over a certain period of time must be
determined. As an example, EPA has chosen the 10-year, 24-hour
precipitation event as a design criteria for the overflow rate
determination.
The steps in calculating the required area of the sedimentation basin are
as follows:
103
-------
(1) Calculate the removal efficiency of the pond by using the following
formula:
R(ซ solids removed) = 1 - 10 /Cl "1 x 100
106/C2 -1
where C, = solids concentration in influent (mg/1 )
C2 = solids concentration in effluent (mg/1)
(2) Determine the smallest size of particle that must be removed to achieve
the required removal efficiency. The size of the removed particle can be
graphically obtained from a particle size distribution for the suspended
solid in the influent to the pond. Figure 3-28 shows a typical "particle
size distribution" graph.
(3) Once the particle size is chosen, the settling velocity associated with
the selected particle size can then be calculated using Stoke's law:
Vq = -2-(S-l)D2
5 18y
where:
V = settling velocity (cm/sec)
g = gravitational acceleration (981 cm/sec2)
y = kinematic viscosity of the fluid (cm/sec2)
S = the specific gravity of the particle
D = diameter of the particle (cm), assumed on sphere
(4) With the obtained water flow rate to the pond and the settling velocity,
surface area of the pond can then be calculated as follows:
Vs
where:
A = required area of the pond (m2)
Q = the volumetric flow rate through the pond
(overflow rate) (m3/sec)
V = the critical settling velocity (m/sec)
(5) The final step is to multiply the required area of the pond by a safety
factor of 1.2 to account for non- ideal settling:
A A
adjusted = 1.2 required
A typical installation of a sedimentation basin embankment is illustrated
in Figure 3-29. As shown in this figure, the pond consists of a dike which
retains the polluted water flow. For water drawdown purposes, a principal
spillway is also needed.
104
-------
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The principal spillway consists of a vertical pipe or riser joined to a
pipe that extends through the dike and outlets beyond the water impoundment.
The riser is preferred to be topped by an antivortex device and trash rack.
The riser should be watertight and, except for the dewatering opening at the
top, it should not have any holes, leaks, or perforations. The riser base
should be attached to a watertight connection and have sufficient weight to
prevent flotation of the riser.
The water discharged from the sediment basin through the principal spill-
way should be conveyed in an erosion-free manner to an existing stable stream.
Thus, at the discharge end of the spillway pipe, an impact basin, riprap,
excavated plunge pools, and revetment should be constructed as protective
measures against scour.
Emergency spillways are also suggested in the design of a sediment basin.
They are provided to convey large flows safely past an earth embankment, and
they are usually open channels excavated in earth, rock, or reinforcement
concrete.
The efficiency of sedimentation ponds varies considerably as a function
of the overflow rate. Sedimentation ponds perform poorly during periods of
heavy rains and cannot be expected to remove the fine-grained suspended solids
(Rogoshewski, 1978). If the sedimentation pond is expected to remove sedi-
ments that may have been contaminated by waste materials, consideration should
be given to improving removal efficiencies by modifying basin or outlet
design. One such modification to the outlet structure is shown in Figure
3-30. It is essentially a dual media sand filter surrounding the riser pipe.
Other possible design modifications include the use of baffles, extra wide
inflow or outflow weirs, energy dissipators, and siphon drawdown riser pipes
(Rogoshewski, 1978). Alternatively, a two-pond system could be considered
that should significantly increase removal efficiencies.
The quantity of material to be stored is also an important consideration
in the construction of the sedimentation basin. The required storage capacity
can be calculated by multiplying the total area disturbed by a constant sedi-
ment yield rate. Table 3-14 shows the storage requirements for some states.
In some states, such as Maryland and West Virginia, there is a requirement to
clean the sedimentation basin when the sediment accumulation reaches a
specified limit imposed by the state. As an example, in West Virginia, the
law requires cleaning of the sedimentation pond when the level of accumulation
is 60 percent of the design capacity.
107
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TABLE 3-14
DESIGN STORAGE CAPACITY REQUIREMENTS FOR SEDIMENTATION BASINS
State Requirement
Maryland 0.5 inches/acre drained
0.2 inches/acre drained1
Kentucky 0.2 acre-ft/acre disturbed
West Virginia 0.125 acre-ft/acre disturbed
60 percent2
Pennsylvania V = (AIC) + (AIC/3)
v = volume (ft3)
A = area drained
I = rainfall/24 hours
C = runoff constant
1To be cleaned when storage capacity drops below 0.2 inches/acre
drained.
2To be cleaned when sediment accumulation approaches 60 percent
design capacity.
(Source: EPA, 1976)
3.4.7.3 Advantages and Disadvantages of Sedimentation Basins
The advantages of the sedimention basin in the control of water flow
contaminated with suspended solids can be listed as follows:
Easy to design and install
Requires low operational and maintenance effort
Very effective in the removal of suspended solids
The major disadvantage of this method can be identified as follows:
Other than the removal of suspended solids, it can not be used to
remove other contaminants such as organic or inorganic chemicals
Faulty design of the embankment or failure of the structure may result
in damages to properties and life as well as interruption of the use
of pub!ic utilities
108
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3.4.7.4 Cost
Table 3-15 lists costs for equipment, materials, and construction needed
for installation of sedimentation basins.
3.4.8 Summary
3.4.8.1 Combined Techniques
At any given disposal site, the most effective method for managing sur-
face flow may be a combination of two or more of the techniques discussed in
this chapter. An individual technique or structure may have limited applica-
tion in terms of permanence of function, versatility of performance, topo-
graphic/hydrologic limitations (e.g., only suitable for certain size drainage
area), and required capital. Where a single technique can not effectively
control a site-specific problem (erosion, infiltration or flooding), an inte-
grated system of several different techniques may be required.
Whenever several different structures are to be combined at a disposal
site to manage surface flow, a site-specific plan is necessary to ensure that
the individual techniques complement each other in terms of design, construc-
tion, and performance. The selection of individual techniques will depend on
the size and topography of the site, local climate and hydrology, and soil
characteristics. Specifically, the length and steepness of slopes, the fre-
quency and intensity of rainfall, and soil permeability, erodibility, and
fertility will all affect the choice of type and number of individual struc-
tures to be included at the site.
Figure 3-31 illustrates one possible combination of surface water inter-
ception and diversion techniques used to control surface flow in one area of a
critical site. An integrated system of surface flow management techniques may
include any combination of dikes, berms, diversions, waterways, bench ter-
races, chutes, downpipes, levees, drainage trenches, and sedimentation basins
or traps. The general function of surface water diversion and collection
structures is to intercept or detain and channel runoff at flow rates that
cause neither excessive erosion nor excessive infiltration. The water carried
by these structures must be discharged to stabilized outlets, holding ponds,
or natural waters. Accordingly, some of the surface flow management struc-
tures are designed and constructed only in combination with other structures.
For example, a grassed waterway may be constructed upslope of a disposal site
to channel runoff around the site to a sedimentation pond or seepage basin
locate offsite.
For very long or very steep slopes on critical sites, several diversions
or several drainage benches may be constructed along the contour with the
collected runoff being channeled to two grassed waterways draining downslope
110
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FIGURE 3-31
INTEGRATED SYSTEM OF INTERCEPTION AND DIVERSION TECHNIQUES
(Source: EPA, 1976)
Reverse
bench
Haul road
Vegetative
buffer area
along either side of the site. The waterways may outlet to level spreaders
stabilized with vegetation or riprap; the spreaders function to convert the
concentrated flow of the waterways to non-erosive sheet flow (Figure 3-32).
3.4.8.2 Costs
The costs of excavation, hauling, backfill, grading (spreading, com-
paction), vegetative stabilization, and maintenance are common to almost all
surface flow control techniques. Other costs associated with surface water
diversion/collection structures include those for ditch linings, riprap slope
protection, soil testing, corrugated metal pipe, sheet piling, backflow
valves, and sumps. Table 3-15 summarizes these unit costs, and the structure
construction they apply to.
Ill
-------
FIGURE 3-32
LEVEL SPREADER
(Source: EPA, 1976)
Last 20' of
diversion not to
exceed 1% grade
exceed 1% grade ^..^.'S^J*^*ฃ~?\^~
-&&'''' '&&?^^^---~-
-:^' '///^- -7"--'-*'-'::
Diversion-^-^^:^^^^1-',!-:-:-'--:'^
-:":"/^<-^ฃ^^"J^ i-^v^
Flow--" ' ...*- "
.3**'
"' Undisturbed outlet
Level Spreader _^
Stabilized slope
^
Channel grade 0%
All cost estimates should be determined on a site-specific basis, con-
sidering the specific structures to be installed, all associated earthwork,
and any special appurtenances that may be required. A general methodology for
estimating costs for construction of surface water diversion/collection struc-
tures will contain the following elements:
Determine source of required earth fill; on-site vs. off-site, and
hauling distances
Determine amount of fill required (yd3)
Determine type and quantity of other materials required (yd3of pipe,
ft2 of riprap, etc.)
112
-------
Determine costs of installation or placement of these materials
using unit costs
Determine costs of required stabilization for earthen structures
(levee, berms, etc.) based on area in yd2 to be stabilized; revege-
tation, riprap, or gravel stabilization
Determine required maintenance or repair costs for a given time
period based on reasonable assumptions; for example: assuming the
diversion requires rebuilding (new fill and compaction) two times/
year after major storms, then costs will be...
Add all calculated costs for total estimated construction and main-
tenance expenditures
Costs are derived simply by multiplying unit costs (shown in Table 3-15) by
required quantities of the material or service. These costs will give gross
estimates only; they are to be used as general guides for the decision-maker
in evaluating alternative remedial action strategies.
113
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TABLE 3-15
UNIT COSTS ASSOCIATED WITH SURFACE WATER DIVERSION AND COLLECTION STRUCTURES
Description
Excavation, hauling,
grading (spreading
and compaction)
Trench excavation;
Loam, sand, and loose
gravel
1 ' -6' deep, %:1 sides
6'-10' deep
Compacted gravel and
till
l'-6' deep, %:1 sides
6'-10' deep
Building embankments;
spreading, shaping,
compacting; material
delivered by scraper
material delivered by
back dump
Placement of ditch
liner pipe;
1/3 section, 15" radius
18" radius
24" radius
Catch basin sump,
3'x4'xl.5'
Corrugated galvanized
steel underdrain pipe,
asphalt-coated, per-
forated;
Applicable
structures1
All
Unit cost
Source of
cost data
See Tables 3-2 and 3-4
D/B; D/D/W; BT,
L; DT/B
All
D/D/W; drainage
benches; C/D
L; DT/B
DT/B
$.39-.67.yd3
$.39-52/yd3
$.39-.69/yd3
$.30-.49/yd3
$.19-.38/yd3
$.45-.63/yd3
i
$9.6/ft
$14.7/ft
$18.4/ft
$148 each
2
2
2
2
2
2
2
2
continued--
114
-------
TABLE 3-15 (Continued)
Description
12" diameter, 16 gage
18" diameter, 16 gage
Corrugated galvanized
metal pipe, with paved
invert
18" diameter, 14 gage
36" diameter, 12 gage
48" diameter, 12 gage
Steel sheet piling;
15' deep, 22 psf
20' deep, 27 psf
25' deep, 38 psf
Backflow preventer;
gate values, auto-
matic operation,
flanged, 10" diameter
Floating baffles
Sump pumps;
6"-12" centrifugal
pumps, operating 1
shift/day
Revegetation, mulch-
ing, maintenance
Loose gravel, exca-
vation, loading,
hauling 5 miles,
spread and com-
pacting
Applicable
structures1
C/C; SB
L (seepage
control )
L (drainage
control)
Unit cost
$12/ft
$17/ft
$19.75/ft
$50.4/ft
$66.8/ft
$8.15/ft2
$9.50/ft2
$12.20/ft2
$8,900 each
Source of
cost data
2
2
2
2
2
3
3
3
3
SB
L (backwater
drainage)
D/B; D/D/W;BT;
L
All (slope pro-
tection; drain-
age)
$20-50/ft
$165-240/day
See Table 3-8
$4-4.50/yd:
--continued
115
-------
TABLE 3-15 (Continued)
Description
Stone riprap; dumped
from trucks, machine-
placed
Soil testing;
liquid and plastic
limits
hydrometer analysis;
specific gravity
moisture content
permeability
Proctor compaction
shear tests, triaxial
direct shear
Temporary sediment
construction;
drainage area,
1-25 acres
50-75 acres
75-100 acres
100-125 acres
Sediment removal from
basins
Level spreader con-
struction
Applicable
structures1
Unit cost
Source of
cost data
All (slope
protection;
channel & out-
let stabilization)
All (preconstruc-
tion evaluation)
$16.65/yd:
SB
SB
Paved flume, installed C/D; SB
D/B; D/D/W;
BT; C/D
$35/test
$60/test
$ 8/test
$50/test
$40-45/test
$195-350/test
$75-225/test
$300-1600 each
$3000-5000
$5000-6400
$6400-8000
$3-7/yd3
$20-30/yd2
$2.50-5.00/
linear foot
3
3
3
3
3
3
5
5
5
5
Key: D/B, dikes and berms; D/D/W, ditches, diversions, and waterways; BT,
bench terraces; C/D, chutes and downpipes; L, levees; DT/B, drainage
trenches and basins; SB, sediment basins.
2McMahon and Pereira, 1979.
3 Godfrey, 1979.
"Environetics, Inc., 1980.
5Virginia Soil and Water Conservation Commission, 1974.
116
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REFERENCES
Brunner, D., and D. Keller. 1972. Sanitary landfill design and operation.
U.S. Environmental Protection Agency. Report SW-65
Environetics, Inc., Bridgeview, IL. 1980.-Personal communication with Carl
Klikas.
Fields, T. Jr., and A. W, Lindsey. 1975. Landfill disposal of hazardous
wastes: A review of literature and known approaches. U. S. Environ-
mental Protection Agency report, EPA/530/SW-165. Office of Solid
Waste Management Programs, Washington, D.C.
Fisher, G., DuPont de Nemours & Co., Inc. Wilmington, DE. February 1980.
Personal communication with G. Hunt.
Gilman, E., F. Flower, I. Leone, and J. Arthur. 1979. Vegetation growth
in landfill environs in municipal solid waste. In: Land Disposal Pro-
ceedings of the Fifth Annual Research Symposium. Wanielista, M. and J.
Taylor (eds.). Cincinnati, Ohio: Municipal Environmental Research
Laboratory, Office of Research and Development. EPA-600/9-79-023a.
Godfrey, R. (ed.). 1979. Building construction cost data, 1980. Kingston,
MA: Robert Snow Means Company, Inc.
Haseley, M., Haseley Trucking Company, New York, NY. February 1980. Personal
communication with D. Twedell.
JRB Associates, Inc., and Emcon Associates. 1980. Assessment of alternatives
for upgrading Navy solid waste disposal sites. Draft Final Report.
McLean, VA.
Linsley, R., and J. Franzini. 1979. Water resources engineering, 3d ed.
New York: McGraw-Hill Book Company.
Lutton, R. 1978. Selection of cover for solid waste in land disposal of
hazardous wastes. Proceedings of the Fourth Annual Research Symposium.
D. Shultz (ed.). Cincinnati, Ohio: Municipal Environmental Research
Laboratory, ORD. EPA-600/9-78-016.
Lutton, R., G. Regan, and L. Jones. 1979. Design and construction of covers
for solid waste landfills. Cincinnati, Ohio: Municipal Environmental
Research Laboratory, ORD. EPA-600/2-79-165.
McMahon, L., and P. Pereira. 1979. 1980 Dodge guide to public works and
heavy construction costs. New York: McGraw-Hill Information Systems.
Molz, F., S. Van Fleet, and V. Browning. 1974. Transpiration drying of
sanitary landfills. Groundwater 12(6): 394-398.
117
-------
Nawrocki M. 1976, Removal and separation of spilled hazardous materials
from impoundment bottoms. Cincinnati, Ohio. EPA-600/2-76-245.
Rogoshewski, P. 1978. Construction source sediment control. Washington,
O.C.: USEPA, Office of Research and Development.
Tolman, A., A. Ballestero, W. Beck, and G. Emrich. 1978. Guidance manual for
minimizing pollution from waste disposal sites. Cincinnati, OH: U.S.
Environmental Protection Agency. Cincinnati, OH. EPA-600/2-78-142.
Tourbier, J., and R. Westmacott. 1974. Water resources protection measures
in land developmenta handbook. Newark, Delaware: Water Resources
Center, University of Delaware.
U.S. Environmental Protection Agency. 1976. Erosion and sediment control,
surface mining in the eastern U.S., vol. 1: Planning; vol. 2: Design.
Washington, D.C.: EPA Technology Transfer. EPA-625/3-76-006.
U.S. Environmental Protection Agency. 1979. Hazardous waste: proposed
guidelines and regulations and proposal on identification and listing.
Federal Register 43(243): 59011. December 19, 1979.
Universal Linings, Inc., Philadelphia, PA. 1980. Personal communication be-
tween D. Small and P. Rogoshewski.
Virginia Soil and Water Conservation Commission. 1974. Virginia erosion and
sediment control handbook: standards, criteria and guidelines. Rich-
mond, Virginia: Virginia SWCC.
Wilson, D.G. (ed.). 1977. Handbook of solid waste management. New York:
Van Nostrand Reinhold Co.
118
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4.0 GROUNDWATER CONTROLS
Groundwater that has been contaminated by an uncontrolled waste disposal
site can be dealt with in a number of ways. Impermeable barriers constructed
of bentonite slurry, cement or chemical grouts, or sheet piling can be in-
stalled vertically to (1) prevent groundwater from migrating away from the
site; or (2) divert groundwater so that contact with waste materials is pre-
vented. Another potential method of dealing with contaminated groundwater is
to allow it to flow through permeable treatment beds (limestone and/or acti-
vated carbon) in which the contaminants would be removed as the groundwater
flowed through the bed. The above two treatment methods can be considered
passive groundwater control.
The pumping of groundwater with subsequent surface treatment is con-
sidered an active remedial measure. Pumping of groundwater can be speci-
fically designed to lower the groundwater table in the area of a disposal site
or it can be designed to contain a contaminated groundwater plume.
The above-mentioned methods for control of contaminated groundwater are
discussed in this chapter.
4.1 IMPERMEABLE BARRIERS
Impermeable barriers can be used to divert groundwater flow away from a
waste disposal site or to contain contaminated groundwater emanating from a
waste site. Various methods and materials that can be used to construct
impermeable groundwater barriers are discussed in the following sections.
Before selection of an impermeable barrier to control groundwater flow,
it should be recognized that impeded groundwater flow may cause an increase in
upgradient hydraulic head, with consequent associated effects on rates of
vertical movement of the water. The probable effects of a locally heightened
water table should be carefully considered before deciding to apply this
method of control.
119
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4.1.1 Slurry Walls
4.1.1.1 General Description
Slurry trenching is a method of constructing a subsurface barrier or
slurry wall to reduce or redirect the flow of groundwater. This technique was
pioneered in the United States in the mid-1940's using technology developed by
the oil industry (Boyes, 1975). Today, this practice covers a range of con-
struction techniques from the simple to the quite complex, and though it is
becoming more common, is still performed by only a few specialty contractors.
In recent years, engineers and contractors have become aware of the low cost
and nearly universal success of slurry trench cut-offs, and this technique has
largely replaced other methods such as grout curtain cut-offs and sheet piling
cut-offs (D'Appolonia, 1979).
In general, slurry trenching involves excavating a trench through or
under a slurry of bentonite clay and water, and then backfilling this trench
with the original soil with or without slurry mixed in. Most commonly, the
trench is excavated down to, and often into, an impervious layer in order to
shut off groundwater flow. This may not be the case when only a lowering of
the water table is required. The width of the trench can vary, but is typi-
cally from 2 to 5 feet (D'Appolonia, 1979). Depending on the depth of the
trench, light or heavy equipment is used for excavation.
The slurry used in this practice is essentially a 4 to 7 percent by
weight suspension of bentonite in water (Boyes, 1975). Bentonite is a clay of
the montmorillonite group of 2:1 expanding lattice clays. The silica and
alumina mineral lattice or layers of these clays can expand and contract
depending on the amount of water and the interlayer cations present. In
bentonite, the interlayer cations are primarily sodium, whose large hydration
radius causes maximum swelling of the clay layers (Baver et al., 1972).
Bentonite is mined in the western United States, principally in Wyoming, and
is often called Wyoming bentonite.
Excavation of a trench under a bentonite slurry causes two things to
happen. First, the slurry acts as shoring, supporting the trench walls to
prevent cave-ins and slumping during further excavation. Secondly, and most
importantly, the weight of the slurry forces bentonite into the soil matrix on
the trench walls and bottom. As more and more bentonite is forced into the
soil, a filter cake is formed, the thickness of which depends on the per-
meability of the soil and the weight of slurry. In essence, the trench be-
comes completely lined with a layer of soil and bentonite of extremely low
permeability.
When the trench has been excavated to the desired depth, backfilling is
begun. Often one section of trench is backfilled while a new section is being
120
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excavated. Backfilling is sometimes done with only the excavated soil mate-
rial, but most often with a soil and bentonite mixture. In some cases, addi-
tional soil or Portland cement is added to achieve the desired result. This
is discussed in more detail below. The end result of this procedure is a wall
that is impervious or of negligible permeability.
4.1.1.2 Applications
Slurry walls were first used to effect groundwater cut-off in conjunction
with large dam projects. In recent years, they have found use as both ground-
water and leachate barriers around hazardous waste disposal sites. Placement
of the wall depends on the direction and gradient of groundwater flow as well
as location of the wastes.
When placed on the upgradient side of a waste site, a slurry wall will
force the groundwater to flow around the wastes. In some instances, it may be
unnecessary to sink the wall down to an impervious stratum. A wall sunk far
enough into the water table upgradient from the wastes can reduce the head of
the groundwater flow, causing it to flow at greater depth beneath the wastes.
In either case, groundwater flow through the wastes is virtually eliminated
and the production of hazardous leachate is greatly reduced.
In certain settings, such as in tidal areas or along major rivers, the
direction of groundwater flow can periodically reverse. In this case, or when
an extreme hazard (posed by pollutants such as dioxin) requires total isola-
tion, a slurry wall can be installed to completely surround the wastes. The
slurry wall must come in contact not only with groundwater, but with chemical-
laden leachate as well. Tests have been conducted to determine the ability of
bentonite slurry walls to withstand the effects of certain pollutants, and the
results are encouraging. As can be seen in Table 4-1, of the chemicals test-
ed, only alcohols were found to completely destroy the slurry wall. To deter-
mine the probable effectiveness of a slurry wall for a particular site, how-
ever, tests should be conducted using the acutal leachate from the site.
In cases where the permeability of the bentonite is found to decrease in
the presence of leachate, the admixture of polymer compounds to the slurry may
prevent the breakdown of the retaining properties of the slurry wall.
4.1.1.3 Design and Construction Considerations
From the above factors, it should be evident that slurry trenching must
be preceded by thorough hydrogeologic and geotechnical investigations. A good
hydrogeologic study will tell the designers the depth, rate, and direction of
groundwater flow, and the chemical characteristics of the water. A geotechni-
cal investigation will provide information on soil characteristics such as
121
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TABLE 4-1
PERMEABILITY INCREASE DUE TO LEACHING WITH VARIOUS POLLUTANTS
SB backfill
(silty or clayey sand)
Pollutant Filter cake 30 to 40% fines
CA or Mg @ 1,000 PPM
CA or Mg G> 10,000 PPM
NH4N03 @ 10,000 PPM
HCL (155)
H2S04 (1%)
HCL (5%)
NaOH (1%)
CaOH (125)
NaOH (5%)
Sea Water
Brine (SG=1.2)
Acid Mine Drainage FeS04
++ (PH-3)
Lignin (in Ca solution)
Alcohol
N
M
M
N
M
M/H1
M
M
M
N/M
M
N
N
H (failure)
N
M
M
N
N
M/H1
M
M
M/H1
N/M
M
N
N
M/H
N - No significant effect; permeability increase by about a factor of 2 or
less at steady state.
M - Moderate effect; permeability increase by factor of 2 to 5 at steady
state.
H - Permeability increase by factor of 5 to 10.
Significant dissolution likely.
(Source: D'Appolonia, 1980)
permeability, amount of stratification, and depth to bedrock or an impervious
layer. In addition, it will tell the nature and condition of the bedrock.
When the slurry wall is intended to provide total water cut-off, rather than
just to lower the water table, particular attention must be paid to the soil/
rock interface. It may be necessary to excavate several feet into the bedrock
to ensure the integrity of the wall. Another method of ensuring this integ-
rity is to install the slurry wall as outlined above and to drill down through
it into rock, and then to inject a grout solution to seal all voids. Although
this is very effective, it is also quite costly. (See Section 4.1.2).
122
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The type of equipment used to excavate a slurry trench depends primarily
on the depth. Hydraulic backhoes can be used to excavate to around 55 feet.
Beyond that depth, a clam-shell shovel must be used. If it is necessary to
install the slurry wall into hard bedrock, drilling or blasting may have to be
used to excavate the rock. Special blasting techniques would be required to
maintain the integrity of the bedrock.
Backfilling of a trench is often accomplished with the equipment used to
excavate the trench. A bulldozer is used to mix the soil with the slurry
alongside the trench as well as to backfill the upper portion of the trench.
Care must be taken to ensure that no pockets of slurry are trapped during the
backfilling, as these can greatly reduce the wall's effectiveness and perma-
nence.
For maximum permeability reduction, the soil/bentonite mixture used for
backfilling should contain 20 to 25 percent fines (soil particles that will
pass a 200-mesh sieve). To ensure long-term permeability reduction, as much
as 40 to 45 percent fines may be required. In the event the on-site soils are
too coarse, imported fines or additional bentonite must be added (Shallard,
1980).
4.1.1.4 Advantages and Disadvantages
The process outlined above includes a number of variables that can affect
the long-term effectiveness of a slurry wall. The extent to which these
variables, such as groundwater, soil, and rock characteristics, can influence
the integrity of a wall, can usually be determined by a variety of precon-
struction tests. From the results of these field and laboratory tests, more
site deficiencies can be identifed and corrected prior to construction. A
properly designed and installed slurry wall can be expected to provide effec-
tive groundwater control for many decades with little or no maintenance.
4.1.1.5 Costs
Slurry wall construction is a relatively high-technology technique,
performed by only a few specialty firms. It is by no means inexpensive. The
following example provides an idea of the costs involved:
A slurry wall, 1,000 feet long and 3 feet wide, is to be placed down
to bedrock along the upgradient side of a hazardous waste disposal
site. Along this line, depth to hard bedrock averages 40 feet. In
all, 4,440 cubic yards of slurry wall must be installed. The costs
associated with construction of this wall are listed in Table 4-2.
123
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TABLE 4-2
COSTS ASSOCIATED WITH SLURRY WALL CONSTRUCTION1
Activity
Testinggeotechnical,
hydrologic, and lab
filter cake permeability
Equipment mobilization
hydraulic backhoe, bull-
dozer, slurry mixer, etc.
Slurry trenching, excavation,
mixing, and backfilling
Overall
Unit costs
(where applicable)
N.A.
N.A.
$45 - $70 per
cubic yard
N.A.
Total costs
$20,000-$80,000
$20,000 - $80,000
Approximately
$200,000 - $310,000
$240,000 - $470,000
1Cost from a variety of industry sources (1980).
Note: These figures are for a 10-acre waste site located 150 miles from the
trenching contractor. The upgradient portion of the site is given a
thorough investigation; the downgradient portion, a cursory investiga-
tion; and the portion containing the wastes, no investigation.
4.1.2 Grout Curtains
4.1.2.1 General Description
Another method of groundwater control is the installation of a grout
curtain. Grouting is, in general, the pressure injection of one of a variety
of special fluids into a rock or soil body to seal and strengthen it. Once in
place, these fluids set or gel into the rock or soil voids, greatly reducing
the permeability of and imparting increased mechanical strength to the grouted
mass. When carried out in the proper pattern and sequence, this process can
result in a curtain or wall that can be a very effective groundwater barrier.
124
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Because a grout curtain can be three times as costly as a slurry wall, it is
rarely used when groundwater has to be controlled in soil or loose overburden.
The major use of curtain grouting is to seal voids in porous or fractured rock
where other methods of groundwater control are impractical.
The pressure injection of grout is as much an art as a science. The
number of U.S. firms engaging in this practice is quite limited. The injec-
tion process itself involves drilling holes to the desired depth and injecting
grout by the use of special equipment. In curtain grouting, a line of holes
is drilled in single, double, or sometimes triple staggered rows (depending on
site characteristics) and grouting is accomplished in descending stages with
increasing pressure (Bowen, 1975). The spacing of the injection holes is also
site-specific and is determined by the penetration radius of the grout out
from the holes. Ideally, the grout injected in adjacent holes should touch
between them (Figure 4-1). If this process is done properly, a continuous,
impervious barrier (curtain) will be formed.
4.1.2.2 Applications
In general, grouts can be divided into two main categoriessuspension
grouts and chemical grouts. Suspension grouts, as the names implies, contain
finely divided particulate matter suspended in water. Chemical grouts, on the
other hand, are true Newtonian fluids. Most of the grouting in the United
States is done with suspension grouts, while about half of the grouting in
Europe is done with chemicals (Kirk-Othmer, 1979). The principal grouts in
use today are briefly described below.
Suspension grouts are non-Newtonian fluids composed, for the most part,
of either Portland cement, bentonite, or a mixture of the two. Their primary
use is in sealing voids in materials with rather high permeabilities, and they
are often used as "pregrouts" with a second injection of a chemical grout used
to seal the fine voids. If a suspension grout is injected into too fine a
medium, filtration of the solids from the grout will occur, thus eliminating
its effectiveness.
Portland cement is an extremely popular construction material, and one of
the first to see use as a grout. When mixed with water, it will set up into a
crystal lattice in less than two hours. For grouting, a water-cement ratio of
0.6 or less is more effective (Bowen, 1975). The smallest voids that can be
effectively grouted are no smaller than three times the cement grain size.
For this, it is clear that a more finely ground cement makes a more water-
tight grout (Bowen, 1975). Portland cement is often used with a variety of
additives that modify its behavior. Among these are clays, sands, fly-ash,
and chemical grouts.
125
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Of the clay minerals used for grouting, bentonite is by far the most
common. Other locally available clays, especially those of marine or river
origin, may be used but must be extensively tested and often chemically modi-
fied (Bowen, 1975). Bentonite, however, because of its extremely small par-
ticle size (one micron or less), is the most injectable, and thus the best
suited for grouting (Tallard and Caron, 1977). Bentonite grouts can be in-
jected into materials with lower permeabilities than can other suspension
grouts. Medium- to fine-textured sands, with permeabilities of around 10"3
-10~4 cm/second, can be sealed with a bentonite grout (AFTES, 1975). Dry
bentonite is mixed with water on-site at a rate of 5 to 25 percent by dry
weight (Bowen, 1975; Tallard and Caron, 1977). In these ratios, bentonite
will absorb large amounts of water and, with time, form a gel. This gel,
although it imparts little if any structural strength, is an extremely effec-
tive water barrier.
Chemical grouts are a more recent development than suspension grouts.
With the exception of one, silicate grout, they have been developed since
World War II. Chemical grouts are true Newtonian fluids and can, depending on
their nature and concentration, have low to very high viscosities. Some have
viscosities approaching that of water and so can be injected virtually any-
where water can penetrate. Because of this, they can be used to waterproof
very fine rock and soil voids. They are often used in conjunction with Port-
land cement or bentonite, to seal both large and small voids. This versa-
tility can offset the high cost and complicated technology of injecting chemi-
cal grouts.
The oldest and still the most commonly used chemical grouts are silicate-
based. Today, they account for over 75 percent of the grouting performed for
waterproofing (Tallard and Caron, 1977). Silicate grouts are composed of a
sodium silicate base, a reactant, an accelerator, and water. The reactant is
typically an amide, an acid, or some polyvalent cation. A salt, such as
calcium chloride or sodium aluminate, is used to accelerate the set or gel of
the grout. The concentration of sodium silicate in the grout varies between
20 and 60 percent, and for waterproofing should be less than 30 percent (Tal-
lard and Caron, 1977). As with many other grouts, the lower the concentra-
tion, the lower the viscosity will be. The concentration of the grout used
will depend on the material into which it is to be injected, with the lower
limit of injectability being soil with greater than 20 percent sand (Bowen,
1975).
Lignochrome grouts consist of lignosulfonate or lignosulfite reacted with
a hexavalent chromium compound. Lignosulfonates and 1ignosulfites are by-
products of the wood pulp processing industry, and depending on the extraction
process used, can be salts of calcium, ammonium, or sodium. For grout use,
sodium lignosulfonates are too unstable, while calcium lignosulfonates provide
the best waterproofing and the most stability (Tallard and Caron, 1977).
Lignochrome grouts set up in an acid medium, where the highly toxic hexavalent
chromium is reduced to the less toxic trivalent form. The set time of the
grout is controlled by varying the concentrations of both the chromate and the
127
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accelerator (usually a metallic salt). Set times of from 10 minutes to 10
hours are possible (Tallard and Caron, 1977). Although grout viscosities low
enough to be injected into fairly fine soils (10"3 cm/sec minimum) are obtain-
able with lignochromes, the viscosity increases gradually until set is
achieved (AFTES, 1975). With most other grouts, the viscosity remains fairly
constant until they set abruptly.
The use of acrylamide grouts was pioneered during World War II by the
American Cyanamid Company. Their grout, AM-9, was the predominant acrylamid
grout until production ceased in 1978. Since that time, a Japanese grout of
slightly different formulation has been offered in this country as a replace-
ment for AM-9. In general, acrylamide grouts are composed of acrylamide
monomer; a cross-linking agent, methylene-bis-acrylamide; an accelerator,
usually ammonium persulfate; and a catalyst (Bowen, 1975). American Cyana-
mid's grout used dimethylamino proprionitrile as a catalyst, and toxicity
problems associated with it may well have led to its withdrawal from the
market. The new acrylamide grouts use as a catalyst much less toxic trietha-
nolamine (Avanti International, 1979). Still, because of the toxicity of the
acrylamide monomer, care must be taken in mixing and injecting these grouts.
Because of their low viscosities and rapid and controlled set times, these are
among the most versatile grouts. They_ can be effectively injected into silty
soils with permeabilities as low as 10 7 cm/sec (AFTES, 1975).
Phenoplasts are chemical grouts formed by the polycondensation of a
phenol and an aldehyde (Tallard and Caron, 1977). By far the most commonly
used phenoplast grout is resorcinol-formaldehyde. The reaction of these two
compounds to form the set grout is achieved by an increase in the pH, with
minimum set time obtained at a pH of 9.3 (Tallard and Caron, 1977). Set time
can also be controlled by varying the dilution of the grout, with more dilute
solutions taking longer to set (Tallard and Caron, 1977). Viscosities similar
to those of acrylamide are obtainable with resorcinol-formaldehyde; hence the
two types of grout have similar applications.
Aminoplasts are a class of grout that has seen little development and
application. The major grout in this class is urea-formaldehyde. It forms a
resin by a condensation reaction caused by heat in an acid medium. Because of
the requirement for heat and a low pH, and their high viscosity, urea-formal-
dehyde grouts have been used very little (Tallard and Caron, 1977).
Grout curtains, because of their relatively high cost, are not the method
of choice for groundwater control where a less expensive method, such as a
slurry wall, is practical. Grouts are, however, the most practical and effi-
cient method for sealing fissures, solution channels, and other voids in rock.
As noted in .Section 4.1.1, grouts can be very effective in insuring a water-
tight seal where a slurry wall is tied into bedrock or some other impermeable
layer. Where rock voids allow the passage of large volumes of water, a grout
can be formulated to set with sufficient speed to quickly shut off the flow.
In theory, it is possible to place a grout curtain upgradient or downgradient
from or beneath a hazardous waste site.
128
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As with slurry walls, placing a grout curtain up the groundwater gradient
from a waste site can redirect the flow so that groundwater no longer flows
through the wastes that are creating hazardous leachate. Given a normal range
of groundwater chemistry, most grouts could be expected to function well in
this capacity.
Placement of a grout curtain downgradient from or beneath a hazardous
waste site is quite another matter. Problems could be expected when attempt-
ing to grout in the presence of leachate or extreme groundwater chemistry. In
many instances it would be difficult or impossible to control the set time,
and consequently, to emplace a curtain of reliable integrity. Little informa-
tion was found in the literature on the resistance of grouts to chemical
attack. Should a case arise where grout must contact leachate or groundwater
of extreme chemical characteristics, extensive tests would be have to be
conducted. Additional problems occur in attempting to grout a horizontal
curtain or layer beneath a waste site. In order to inject grout in such a
case, injection holes must be drilled either directionally from the site
perimeter, or down through the wastes. The first situation would be very
expensive and the second could be very dangerous. In either case, it would be
very difficult to place an effective barrier and virtually impossible to
monitor its effectiveness.
4.1.2.3 Design and Construction Considerations
Pressure grouting is a high technology endeavor. As with slurry trench-
ing, extensive geotechnical and hydrologic testing must precede the placement
of a grout curtain. Boring, pumping, and laboratory tests will determine
whether or not a site is groutable and will provide the necessary groundwater,
rock, and soil information to allow for the choice of the best-suited grout or
grouts. They will further provide the designer with the information needed to
plan the pattern and procedure for injection. Other tests may be needed to
evaluate leachate resistance, effectiveness of the grouting, or other factors.
The equipment used in pressure grouting is for the most part sophisti-
cated special machinery. Much of this equipment is patented and/or proprie-
tary. This machinery includes pumps and specialty drills for the boring of
injection holes. Often, the pumps are connected to a manifold to allow
grouting of several holes at once. In nearly all cases, the pumps are
equipped with gages and meters to monitor grout pressures and volumes. Since
only a few contractors perform this type of work, it is likely that equipment
mobilization fees associated with grout curtain installation will be high.
4.1.2.4 Advantages and Disadvantages
When it becomes necessary to stop or reroute groundwater flowing in
porous rock, pressure injection of grout may well be the only means. Grouts
129
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can be formulated to set within a few seconds, so that even rapidly flowing
water can be shut off. Grout also can be used to control groundwater flow in
soils, but in most cases, a more cost-effective method is available.
The drawbacks to grout usage stem from the fact that grouting is con-
ducted by a limited number of firms in the United States and involves special
techniques and equipment. In most cases, a substantial equipment mobilization
fee must be paid. Equally important is the cost of pregrouting testing that
must be performed to insure effective grouting. A final consideration is the
cost of the grout itself. Approximate costs of the grouts discussed above are
found in Table 4-3.
TABLE 4-3
APPROXIMATE COST OF GROUT1
Approximate cost
Grout type $/ga11on of solution
Portland cement 0.95
Bentonite 1.25
Silicate - 20%ฑ 1.75
- 30% 2.10
- 40% 2.75
Lignochrome 1.55
Acrylamide 6.65
Urea formaldehyde 5.70
1 Costs taken from various industry sources (1980).
4.1.2.5 Costs
Some of the costs involved with grout curtain installation are illus-
strated by the following example: (Figure 4-2).
130
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A 5-acre hazardous waste site is having leachate generation prob-
lems, and it is determined that a grout curtain should be placed
upgradient from the wastes. The area chosen for the curtain is very
shallow, hard, fractured rock; therefore, other control methods are
not feasible (see Section 4.1.3). Site investigations show that an
800-foot-long wall, 20 feet deep, will solve the problem. The rock
is found to have a permeability of 1 x 10"3 cm/sec, and a porosity
of 30 percent. It is determined that injection holes will be placed
3 feet apart, and that a double row of holes is needed. The con-
tractor feels a 20-percent silicate grout will effectively stop the
groundwater flow. The porosity measurements show that for every
cubic yard of curtain, 0.3 cubic yards of grout will be needed. The
costs associated with installing this curtain are given in Table
4-4.
TABLE 4-4
COSTS ASSOCIATED WITH SILICATE GROUT CURTAIN PLACEMENT 1
Unit cost
Activity (where applicable) Total cost
Testinggeotechnical, N.A. $10,000-$40,000
hydro!ogic, site grout-
ability
Equipment mobilization N.A. $20,000 - $80,000
drills, mixers, pumps,
manifolds, etc.
Grout $145/yd3 $154,640
in place (1066.5/yd3)
Overall N.A. $185,640 - $247,640
1Based on parameters cited in example on page 128.
4.1.3 Sheet Piling Cut-off Walls
In addition to slurry wall and grout curtain cut-offs, sheet piling can
be used to form a continuous groundwater barrier. Sheets piles can be made of
131
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wood, precast concrete, or steel. Wood is an ineffective water barrier,
however, and concrete is used primarily where great strength is required.
Steel is the most effective in terms of groundwater cut-off and cost, and so
is discussed here.
4.1.3.1 General Description
The construction of a steel sheet piling cut-off wall involves driving
interlocking piles into the ground with a pneumatic or steamdriven pile
driver. In some cases, the piles are pushed into pre-dug trenches. Lengths
of the piles are commonly from 4 to 40 feet, although longer lengths are
available by special order (ARMCO, 1980). Nearly every manufacturer of steel
sheet piling offers its own shape of piling and often its own form of inter-
lock. Some of these are shown in Figure 4-3. Widths of sheet pile range from
15 to 20 inches (Ueguhardt, 1962).
4.1.3.2 Applications
In instances where wastes are deposited in contact with a permanent or
seasonal water table, generation of hazardous leachate can be controlled with
a sheet piling cut-off. As with slurry walls and grout curtains, sheet piling
cut-offs can form barriers that will redirect groundwater around or below the
deposited wastes.
4.1.3.3 Design and Construction Considerations
For construction of a sheet piling cut-off, the pilings are assembled at
their edge interlocks before they are driven into the ground. This is to
ensure that earth materials and added pressures will not prevent a good lock
between piles. The piles are then driven a few feet at a time over the entire
length of the wall. This process is repeated until the piles are all driven
to the desired depth.
The sheet piling is forced into place by a drop hammer or a pile driver.
Heavy equipment is desirable for fast driving and to prevent damage to the
piles. Light-weight equipment can distort the top edge of the pile and slow
the driving (ARMCO, 1980). Often, a cap block or driving head is placed on
the top edge to prevent the driving equipment from damaging the piles.
When first placed in the ground, sheet piling cut-offs are quite per-
meable. The edge interlocks, which are necessarily loose to facilitate place-
ment, allow water easy passage. With time, however, fine soil particles are
washed into the seams and water cut-off is effected. The time required for
this sealing to take place depends on the rate of groundwater flow and the
133
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FIGURE 4-3
SOME STEEL PILING SHAPES AND INTERLOCKS
(Source: (Jeguhardt, 1962)
Straight Web Type
Arch Web Type
Deep Arch
Web Type
Z-Type
Y-Fitting
134
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T-Fitting
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texture of the soil involved. In very coarse, sandy soils, the wall may never
seal. In such cases, it is possible to grout the piling seams, but this is a
costly procedure.
The performance life of a sheet piling wall can be between 7 and 40
years, depending on the condition of the soil in which the wall is installed.
Sheet piling walls have been installed in various types of soils ranging from
well-drained sand to impervious clay, with soil resistivities ranging from 300
ohm cm to 50,000 ohm cm, and with soil pH ranging from 2.3 to 8.6. Inspec-
tions of these installed walls did not reveal any significant deterioration of
the structure due to soil corrosion (EPA, 1978). Additional protection of the
sheet piling wall against corrosion can be achieved by using hot-dip galva-
nized or polymer-coated sheet. Cathodic protection has also been suggested
for submerged piling (EPA, 1978).
Steel sheet piles
Even if enough force
cobbles and boulders,
wall ineffective.
should not be considered for use in very rocky soils.
can be exerted to push the piles around or through
the damage to the piles would be likely to render the
4.1.3.4 Advantages and Disadvantages
The advantages and disadvantages of the sheet piling cut-off walls are
summarized in Table 4-5.
TABLE 4-5
ADVANTAGES AND DISADVANTAGES OF THE SHEET PILING WALL
Advantages
Easy to install and readily
available
Relatively inexpensive
Low maintenance requirements
Disadvantages
Cannot be used effectively
in rocky soils
The wall initially is not
waterproof
Corrosion of the wall may
occur if exotic chemical
substances exist in the
soil
135
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4.1.3.5 Costs
The unit costs of installing a sheet piling cut-off wall are summarized
in Table 4-6.
TABLE 4-6
UNIT COST FOR INSTALLATION OF A SHEET PILING WALL
Sheet Piling
Assumptions
Black steel
Costs
$l,!57/ton1
Hot dipped galvanized steel $l,3!7/ton1
(5 gage dimensions: 19.6 in.
laying width, 3.18 in. front
to back, and 20 ft. long)
Installation
$235/ton2
1 ARMCO, 1980; Material and transportation costs.
2McMahon and Pereira, 1979.
As an example, the total cost of installing a sheet piling cutoff wall 1,000
feet long and 20 feet deep made of 5-gage galvanized steel sheet can be cal-
culated as follows:
The total area of the wall is:
(1,000 ft) (20 ft) = 20,000 ft2
As a rule-of-thumb in the construction business, the adjusted area of the
sheet piling wall is calculated by multiplying the required area by a factor
of 1.6 to account for the area of the interlocking devices (Staples, 1980).
Adjusted = Required x ll6
(20,000 ft2)(1.6) = 32,000 ft2
136
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According to ARMCO, the weight of 5-gage galvanized ARMCO steel sheet per
unit of area is 11.6 Ibs/sq. ft. Thus the total tonnage of sheet piling
needed is:
(32,000 ft2)(11.6 lbs/ft2) = 371,000 Ibs or 186 tons
As shown in Table 4-6, the cost of 1 ton of sheet piling is $1,317;
therefore, the material cost of the wall amounts to:
(1,317/ton) (186/ton) = $245,000
The installation unit cost of the sheet piling wall is also shown in
Table 4-6. Therefore, the installation cost can be calculated as
fol1ows:
($235/ton)(186/ton) = $43,700
Therefore, the total cost of installing a sheet piling cutoff wall can
be calculated as follows:
(Materials Cost) + (Installation Cost) = Total Cost
$245,000 + $43,700 = $288,700
4.2 PERMEABLE TREATMENT BEDS
4.2.1 General Description
In many cases where a disposal site is located near the water table,
groundwater may be contaminated with leachate from the site. In many of these
cases, the groundwater is found at relatively shallow depths. Contaminated
groundwater can be contained by constructing a physical barrier to prevent its
flow, or it can be treated in place by constructing a permeable treatment bed
that can physically and chemically remove the contaminants. Permeable treat-
ment beds may become saturated or plugged in time, hence they may need re-
placement. They should, therefore, be considered as temporary rather than
permanent remedial actions.
This section discusses possible methods for treating contaminated ground-
water by using different types of permeable beds. These methods may have
considerable potential for reducing the quantities of contaminants present in
groundwater. The present state-of-the-art in this area of technology, how-
ever, is more or less conceptual.
137
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4.2.2 Applications
Relatively few materials can be feasibly employed in permeable beds to
control contaminated groundwater. These materials include:
Limestone or crushed shell
Activated carbon
Glauconitic greensands or zeolite
Synthetic ion exchange resins.
A limestone bed may be applied in cases where neutralization of acidic
groundwater flow is needed. Limestone beds have also been claimed to be
effective in removing certain metals such as cadmium, iron, and chromium (EPA,
1978). Crushed shell, which has the same chemical characteristics as lime-
stone, can also be used as a material for permeable treatment beds. In most
coastal regions where the availability of shells is good, crushed shell can
become a very useful material for permeable treatment beds, and may compete
with limestone in the control of acidic groundwater by this method.
In cases where the groundwater is contaminated with organic compounds,
activated carbon may be applicable; however, costs of this material may be
prohibitively high.
Glauconitic greensand deposits of the Atlantic Coastal Plain have been
reported to exhibit good adsorption properties for several heavy metals
(Spoljaric and Crawford, 1979). They are accessible as subsurface deposits in
extensive areas of New Jersey, Delaware, and Maryland. The locations of these
deposits suggest that permeable treatment beds using local greensand deposits
might provide an economical remedy for contaminated groundwater at disposal
sites in the Mid-Atlantic region.
Other materials that could be used for removing contaminants in ground-
water are zeolite and synthetic ion exchange resins. These materials are very
effective in the removal of heavy metal contaminants but are economically and
practically infeasible for permeable beds because of problems such as short
life, high cost, and re-activation difficulties. Therefore, these materials
are not recommended for use except where engineering and economic evaluations
prove their desirability in specific cases.
138
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4.2.3 Design and Construction Considerations
The construction of a permeable treatment bed is essentially the same for
all the above-mentioned materials. It consists of excavating a trench to
intercept the flow of the contaminated groundwater, filling the trench with
the appropriate materials, and capping the trench. Figure 4-4 shows a typical
permeable treatment bed installation.
An important consideration in the design of a permeable treatment bed is
the size and shape of the trench as it relates to the specific problem of
groundwater contamination. The trench should be long enough to contain the
plume of the contaminated flow and deep enough to stop the groundwater from
flowing underneath. For practical design purposes, the depth of the bed is
the distance between the ground surface and the bedrock or other impermeable
layer (such as a layer of clay). The width of the trench is determined by the
velocity of the groundwater flow, the permeability of the material used for
treatment, and the contact time required for effective treatment. Further
discussion on the determination of width for the trench is presented in later
sections.
Trench excavation will require the use of conventional shoring such as
sheet piling, and bracers and struts. Since the trench will intersect the
water table, dewatering will be required during excavation. Groundwater
pumped from the trench will likely be contaminated and therefore will probably
require treatment.
To properly design a permeable treatment bed, a working knowledge of the
mechanisms of groundwater flow is essential. The flow of water through ground
or its filtration through sand may be determined by using Darcy's law:
where _v is the approach velocity or the quantity of water through a unit
cross-sectional area (ft/sec), I is the gradient or loss of elevation head per
unit of length in the direction of the flow, J< is the coefficient of per-
meability or the proportionality constant of water at a given temperature
flowing through a given material, and ji is the effective porosity of the
material. Thus, by knowing the permeability coefficient of the soil through
which the groundwater flows and the difference in hydraulic head between two
points, one may be able to estimate the velocity of the flow or the volumetric
flow rate of groundwater. Darcy's law is applicable to a steady flow of
groundwater in a confined aquifer of uniform thickness, which is called a
steady one-directional flow. In most cases, this ideal situation does not
occur. However, Darcy's law can still be used to provide fair approximations
of groundwater flow rate in field applications.
139
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FIGURE 4-4
INSTALLATION OF A PERMEABLE TREATMENT BED
Permeable Treatment Bed
The thickness of the permeable treatment bed is a function of required
residence time and the flow velocity of the groundwater through the bed, as
expressed in the following equation:
140
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where w, is the width or thickness of the bed, v^ the velocity of groundwater
through the bed (ft/sec), and tc the contact time (sec). To determine the
thickness of the bed, groundwater flow velocity and contact time should be
known.
For conservatism, the highest groundwater velocity found in the immediate
area should be used as the design velocity of the flow through the bed. The
bed thickness can then be estimated, using the flow velocity of groundwater
through the bed and the optimum contact time (discussed below).
To insure that disturbance of the groundwater flow by the treatment bed
is minimized, flow velocities within the soil and within the bed should be
equal. Assuming that the hydraulic gradients in the bed and in the soil are
the same, the permeability of the bed must be the same as the permeability of
the soil. These permeabilities can be easily determined in the laboratory by
using a "falling-head pemeameter" (Fair et al., 1966; Johnson Division,
1975).
Residence time or contact time is a function of the level of contamina-
tion of groundwater and the treatment characteristics of the material used for
the decontamination process. The residence time of the contaminated ground-
water flow through the bed must be sufficient to insure optimum treatment
conditions. Thus the determination of the optimum contact time, tcm, requires
a knowledge of the chemstry of the contaminated groundwater and of its reac-
tion to treatment by the material that will be present in the bed.
To summarize, in the actual design of a treatment bed, the permeability
of the soil and the hydraulic gradients in the field must be studied in order
to estimate the actual velocities of the groundwater flow in the soil. Then
the highest groundwater flow velocity is chosen as the design velocity of the
flow through the bed, to insure optimum operational conditions. To obtain the
same velocity of groundwater through the bed as through the soil, the perme-
ability of the bed must be the same as the permeability of the soil. Con-
sequently, the particle size of the material used in the bed must be chosen to
achieve the desired permeability of the bed. This can be accomplished by
conducting a series of bench-scale permeability tests with bed materials of
different particle size. To design an effective treatment bed, an optimum
contact time must be determined on the the basis of expected rates of inter-
action between the groundwater and the bed material. When the velocity of the
flow through the bed and the optimum contact time are estimated, the bed
thickness can be determined.
141
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4.2.3.1 Limestone Bed
As previously discussed in Section 4.2.2, limestone may be used for the
neutralization of slightly acidic groundwater. To a certain extent, it also
may be used to remove metallic contaminants from groundwater.
Fuller and other researchers (EPA, 1978) have discussed the use of
crushed limestone as an effective low-cost landfill liner to aid in the atten-
uation of the migration of certain heavy metals from solid waste leachates.
According to the authors, dolomitic limestone (containing significant amounts
of magnesium carbonate) is less effective in removing ions than purer lime-
stone containing little magnesium carbonate. Therefore, in the design of a
limestone treatment bed, it is recommended that limestone with high calcium
content be used to remove heavy metals and to neutralize contaminated ground-
water.
The particle size of limestone used depends on the results of the analy-
sis of the type of soil in which groundwater flows and the level of ground-
water contamination. The grade of limestone can vary from "gravel size" to
"sand size." For practical design purposes, it is advisable to use a mixture
of "gravel size" and "sand size" limestone to minimize settling of the bed as
limestone dissolves. The smaller "sand size" particles help prevent excessive
channelling through the bed and also improve the contact between the contami-
nated flow and the bed.
Fuller (EPA, 1978) studied the neutralization effect on acidic water
flowing through a crushed limestone bed. The results, illustrated in Figure
4-5, show the relationship between changes in pH and the contact time. Thus,
as shown in extrapolating the data present in Figure 4-5, the contact time
needed to change 1 pH unit is in the range of 8 to 15 days.
Little information is presently available on determining the contact time
needed for optimum removal of heavy metals. According to Fuller (EPA, 1978),
the efficiency of limestone in removing heavy metals from leachate depends
heavily on (a) contact time, (b) leachate concentration and (c) leachate pH.
Limestone has been proved to be very effective in the attenuation of the
migration rate of chromate, but an explanation for the mechanism of removal of
this metallic is not available (EPA, 1978). Removal of metallic cations such
as Be, Cd, Ni, and Zn from leachate were also studied, but no conclusive
result was obtained. Thus more studies are needed to determine the effective-
ness of limestone in the removal of heavy metals from landfill leachate and to
determine the optimum contact time for the removal process.
142
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PH
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6.6-
6.4-
6.2-
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Changes in pH of Acidic Water in Contact with Crushed Limestone
14 15
143
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4.2.3.2 Activated Carbon
Activated carbon may be used to control organic contaminants present in
the groundwater flow. Nonpolar organic compounds such as PCB and CC1 are
removed by activated carbon by adsorption resulting from Van de Waals and
other chemical attractive forces. Polar organic compounds such as alcohols
and ketones may not be very effectively removed by activated carbon because of
their electrical charges. Activated carbon also can remove certain heavy
metals, but is not very practical for actual use in a metallic contaminants
removal system.
4.2.3.3 Glauconitic Greensands
Glauconitic greensand deposits of the Atlantic Coastal Plain have high
potential for the removal of a number of heavy metals from contaminated
waters. Glauconite is a hydrous aluminosilicate clay mineral, rich in ferric
iron and with significant amounts of potassium (Spoljaric and Crawford, 1979).
Glauconite occurs as dark, light, or yellowish-green pellets O.g-1 mm long, as
casts of fossil shells, as coatings on other grains, and as a clayey matrix in
coarser-grained sediments.
Studies by Spoljaric and Crawford (1979) indicate that glauconitic green-
sand had superior retention of heavy metal cations in bench-scale studies with
leachate from the Pigeon Point landfill in northern Delaware. Highest removal
efficiencies were reported for copper, mercury, nickel, arsenic, and cadmium,
as shown in Table 4-7. The authors reported increased efficiencies with
increased contact time. Contact time for bench scale testing was estimated at
2 minutes, suggesting that with contact times used in the field being in the
order of days, metal removal efficiencies may be extremely high for many of
the metals listed (Spoljaric, 1980). The glauconitic sand treatment was also
found to reduce odors, suggesting that adsorption of organics occurred as
well.
Only minute amounts of metal cations were released from the charged
greensand upon flushing with distilled water and solutions of pH 2 and pH 12
(Spoljaric and Crawford, 1979). The results of these experiments suggest that
greensands have a high capacity for heavy metal cation retention, and thus
seem very applicable as a material for permeable treatment beds (Spoljaric,
1980). Saturation points for heavy metal adsorption by glauconitic greensands
were not determined; thus, the sorptive capacity for glauconitic sands has yet
to be assessed through further experimentation. Also, the applicability of
greensands in treating higher concentrations of heavy metals has not been
determined. While they appear promising, more experimental work is required
before glauconitic greensands can be thoroughly assessed as a permeable treat-
ment bed material.
144
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TABLE 4-7
RESULTS OF CHEMICAL ANALYSES OF GREENSAND FILTRATION
OF PIGEON POINT LANDFILL LEACHATE1
Cation
Cation concentration (ppm)
Before After
filtration greensand
1F1ow rate: 100 ml/nrin.
2Parts per billion (yg/liter).
3Not detected.
Source: Spoljaric and Crawford, 1979.
Percent retained
by greensand
Aluminum
Arsenic (ppb)
Cadmium (ppb)2
Calcium
Chromium
Cobalt
Copper
Iron
Lead
Magnesium
Manganese 2
Mercury (ppb)
Nickel
Potassium
Silver (ppb)2
Na
Zinc
PH
0.68
2.2
6
129
0.03
0.015
0.38
8.1
0.13
62
4.1
8.7
0.074
122
1.4
275
0.49
7.65
0.17
0.2
1
48
0.01
0.003
n.d.3
1.1
n.d.3
20
0.48
n.d.3
0.003
74
0.7
175
0.16
6.29
75
91
83
63
66
80
100
86
100
67
88
100
96
39
50
36
67
4.2.4 Advantages and Disadvantages of the Use of Permeable Treatment Bed
The advantages and disadvantages of the use of limestone beds, activated
carbon beds, and glauconitic greensand beds are summarized in Tables 4-8, 4-9,
and 4-10 respectively.
145
-------
TABLE 4-8
ADVANTAGES AND DISADVANTAGES OF CRUSHED LIMESTONE TREATMENT BED
Advantages
Can be used to neutralize a
slightly acidic groundwater
stream
Applicable for the removal of
certain heavy metals contained
in groundwater
Good potential for successful
control for chrcmate anion
present in groundwater flow
Very cost effective to install
since limestone is inexpensive
and readily available
Disadvantages
Cementation or solidifica-
tion of the limestone bed
may occur, leading to plug-
ging of the flow
Not effective for the remov-
al of organic contaminants
Not effective for the remov-
al of organic contaminants
Solution-channelling through
bed may occur
TABLE 4-9
ADVANTAGES AND DISADVANTAGES OF ACTIVATED CARBON TREATMENT BED
Advantages
Very effective in the removal
of nonpolar organic compounds
from the groundwater flow
Readily available and easy to
handle and install
Disadvantages
Plugging of the bed may
occur
Not very effective for the
removal of polar organic
compounds
Presence of other chemicals
in the groundwater may de-
crease the effectiveness of
bed absorption
continued
146
-------
TABLE 4-9 (Continued)
Advantages Disadvantages
Desorption of the hazardous
absorbed materials to the
clean water flow may occur,
resulting in recontarnination
Removal and disposal of
spent activated carbon is
difficult and hazardous
Cost of the material is very
high
Competitive absorption with
large organic molecules may
decrease the removal effec-
tiveness of the bed
Life of the bed may be very
short in the presence of
complex organic compounds
such as hutnic compounds
4.2.5 Cost
The cost of installing a permeable treatment bed includes the cost of
trench excavation and dewatering, trench shoring, bed materials, and bed
installation. The unit costs for these operations are summarized in Table
4-11.
147
-------
TABLE 4-10
ADVANTAGES AND DISADVANTAGES OF GLAUCONITIC TREATMENT BED
Advantages
Apparent high effectiveness
in the removal of many heavy
metals
Good residence time characteristics
for efficient treatment; relatively
little material required for bed
Abundant in New Jersey, Delaware,
and Maryland
Good metal retention charac-
teristics
Good permeability
Disadvantages
Saturation characteristics
unknown
Area of application probably
limited by transportation
costs to Mid-Atlantic region
May require land purchase
since it does not seem to
be commercially mined
Reduction in permeability
and plugging of bed may
occur after a time
May reduce pH
Removal efficiencies of
metals at high concentra-
tions unknown
TABLE 4-11
UNIT COSTS FOR INSTALLATION OF A PERMEABLE TREATMENT BED
Trench excavation
Spreading
Well-point dewatering
Assumptions
20 ft deep, 4 ft wide,
by backhoe
Spread nearby to grade
trench and cover
500 ft header 8" diameter,
for one month
Costs
$l/cubic yard1
$0.66/cubic yard1
$75/linear foot1
continued
148
-------
TABLE 4-11 (Continued)
Sheet piling
Walers, connections,
struts
Limestone
Activated carbon
Assumptions
Pull and salvage
2/3 salvage
Mixed "gravel size" and
"sand size"
Installation
Total cost including
overhead and profit
Coarse size
Installation
Total cost including
overhead and profit
Costs
$5.70/square foot1
$105/ton2
$4.75 - $6.00/ton
or $6.75 -5$8.00/
cubic yard5
$1.90/cubic yard1
$10 - $11.5/cubic
yard1
$0.5/lb6 or
$l,180/cubic yard
$1.90/cubic yard1
$l,360/cubic yard1
1Godfrey, 1980; Costs are total, including contractor overhead and profit.
2Godfrey, 1980; Materials only.
3Milam, 1980; Assumed 50 percent installation cost.
Universal Linings, 1980.
5Germany Valley Limestone Co., West Virginia, 1980; materials only.
W.S. Frey Co., Virginia, 1980; materials only.
McDonough Bros., Inc., Texas, 1980; materials only.
6Calgon, 1980; materials only.
These costs are based on the following assumptions:
The trench dimensions are 20 ft deep, 4 ft wide, and 1,000 ft long.
Limestone used for the treatment bed is a mixture of "gravel size" and
"sand size" particles.
The average bulk density of the limestone mixture is 100 lb/ft3.
The average particle density of activated carbon is 1.4 g/cc or 87.4
lb/ft3 (EPA, 1978).
149
-------
Costs of glauconitic greensand would entail possible land purchase,
borrow excavation, and hauling to the disposal site. Costs for buying bulk
quantities of glauconitic greensand from a producer were not available at the
time of this writing. The cost of zeolite and synthetic ion exchange resins
is very expensive (about $5/1b), and thus might prove to be economically
infeasible.
As an example, the total cost of a permeable treatment bed 1,000 feet
long, 4 feet wide and 20 feet deep can be calculated as follows:
The total volume of the treatment bed is:
(1,000)(4 ft) (20 ft) = 80,000 ft3 or 3,000 cubic yard.
The surface area of the side of the trench is:
(1,000 ft)(20 ft) = 20,000 ft2
The unit costs for trench excavation and preparation are shown in
Table 4-11. The total cost of trench excavation and associated
works includes the following costs:
- Trench excavation cost:
($l/cubic yard)(3,000 cubic yard) = $3,000
Spreading cost:
($0.66/cubic yard)(3,000 cubic yard) = $1,980)
Well point dewatering cost:
Assuming that two 8"-diameter 500-ft headers are needed.
($75/lin. ft)(500 ft)(2) = $75,000
Sheet piling cost:
As a rule-of-thumb in the construction business, the total area of sheet
piling needed can be estimated by multiplying the side areas of the trench by
a factor of 1.6 to account for the allowance area for the interlocking devices
(Staples, G., JRB Associates , 1980). Thus the total area of sheet piling
required is:
(2)(20,000 at2)(1.6) = 64,000 ft2
According to ARMCO, The average weight of sheet piling per square foot of wall
is 10 Ibs. Thus the total tonnage of the sheet piling can be calculated as
follows:
150
-------
(64,000 ft2)(10 lbs/ft2) = 640,000 Ibs or 290 metric tons.
The cost of the sheet piling can then be calculated as follows:
(64,000 ft2)($5.70/ft2) = $365,000
Waler, connection, and strut costs:
As a rule-of-thumb in the construction business, the total tonnage of
walers, connections, and struts are 20 percent of the weight of sheet piling
(Staples, 1980). Therefore, the tonnage required for walers and struts is:
(290 tons)(0.2) = 58 tons
The cost for walers and struts is:
($105/ton)(58 ton) = $6,100
Total cost of trench construction:
$3,000 + $1,980 + $75,000 + $365,000 + $6,100 = $451,000
The total cost of a permeable treatment bed includes trench construction and
the costs of materials and their installation. Unit costs for the materials
and their installation are given in Table 4-11.
In the case of a limestone treatment bed, materials and their installa-
tion costs are:
($11.5/cubic yard)(3,000 cubic yard) = $34,500
The total cost of the limestone bed is:
(Trench construction cost) + (Materials and installation cost) =
Total Cost
$451,000 + $34,500 = $485,500
The total cost of the installation of an activated carbon bed can be estimated
as follows:
Materials and installation cost:
($l,360/cubic yard)(3,000 cubic yard) = $4,080,000
Therefore the total cost of the activated carbon bed is:
$451,000 + $4,080,000 = $4,531,000
151
-------
4.3 GROUNDWATER PUMPING
This section describes several applications of groundwater pumping to
control contaminated groundwater beneath a disposal site. These approaches
emphasize the active diversion of groundwater as compared to passive ap-
proaches of installing either impermeable barriers or permeable treatment
beds. Three applications are described:
Pumping to lower a water table
Pumping to contain a plume
Groundwater treatment systems
4.3.1 Water Table Adjustment
4.3.1.1 General Description
Groundwater pumping can be used to lower the water table in a particular
area. By placing wells close together, the combined cones of depressions of
each well can result in a depression network, in which the effective elevation
of the groundwater has been lowered. Pumping to cause a change in groundwater
elevation has a number of applications, which are discussed below.
4.3.1.2 Applications
Groundwater pumping to lower the water table may be a suitable remedial
action for contaminated groundwater under several conditions. Specific appli-
cations include:
Lowering an unconfined aquifer sufficiently so that contaminated
groundwater does not discharge to a receiving stream that is hydrau-
1ically connected
Lowering the water table so that it is not in direct contact with
the waste site
Lowering the water table to prevent leaky aquifers from contami-
nating other aquifers
These three applications are illustrated in Figures 4-6 through 4-8. A
groundwater treatment system will frequently be needed to treat the water
after pumping. (See Section 4.3.3.)
152
-------
FIGURE 4-6
LOWERING A WATER TABLE TO PREVENT STREAM DISCHARGE OF CONTAMINATED WATER
Before Pumping
Water Bearing Sands
Grฐ"ndwater Flow ~~ ~
After Pumping
Water Bearing Sands
153
-------
FIGURE 4-7
LOWERING THE WATER TABLE TO ELIMINATE CONTACT WITH A DISPOSAL SITE
Before Pumping
Groundwater Flow
After Pumping
154
-------
FIGURE 4-8
LOWERING WATER TABLE TO PREVENT CONTAMINATION OF AN UNDERLYING AQUIFER
Before Pumping
Contaminated Aquifer
ifer X
After Pumping
155
-------
4.3.1.3 Design and Construction Considerations
The water table can be lowered by using a well point dewatering system or
by using deep wells--a method discussed later in this section. Figure 4-9
shows a well point system.
FIGURE 4-9
SCHEMATIC OF A WELL POINT DEWATERING SYSTEM
(Source: Johnson, 1975)
The system consists of a group of closely spaced wells, usually connected
by a header pipe and pumped by suction centrifugal pumps, submersible pumps,
or jet ejector pumps, depending on the depth of pumping and the volume to be
dewatered. A pump may be connected to one well point, or a central pump may
be used for the entire well point system, depending upon the depth, volume,
and permeability of the affected materials.
Lowering the groundwater level over the site involves creating a com-
posite cone of depression by pumping from the well point system. The indi-
vidual cones of depression must be close enough together so that they overlap
and thus pull the water table down several feet at intermediate points between
pairs of wells (Johnson Division, 1975).
156
-------
The proper design and construction of wells and well points involves an
understanding of the particulars of well hydraulics.
Darcy's Law tells us that flow in a porous medium varies directly with
the characteristics of the medium and the hydraulic gradient. The expression
for these relationships, taking into account the effects of porosity, is:
v =M.
n
Where: k = Hydraulic conductivity (ft/day)
I = Hydraulic gradient (dimensionless)
V = Apparent velocity (ft/day)
n = Effective porosity (percent)
The hydraulic gradient (I) is the difference in hydraulic head divided by
distance along the flow path in fluid flow. With increasing velocity, the
hydraulic gradient increases as the flow converges towards a well. As a re-
sult, the lowered water surface develops a continually steeper slope towards
the well. The form of this surface resembles a cone-shaped depression. The
distance from the center of the well to the limit of this cone of depression
is called the radius of influence. The hydraulic conductivity is measured
using the meinzer unit, defined as the flow of water in gallons per day
through a cross-sectional area of 1 square foot under a hydraulic gradient of
1 at a temperature of 60ฐ F. The value of K depends upon the size and ar-
rangement of the particles in an unconsolidated formation and the size and
characteristics of the surfaces of crevices, fractures, or solution openings
in a consolidated formation. Figure 4-10 shows typical hydraulic conductivi-
ties for various soil and rock types. Darcy's Law remains valid only under
conditions of laminar flow, involving fluids with a density not significantly
higher than pure water.
Two other factors, transmissivity (T) and storativity (S), also affect
the rate of flow. The coefficient of transmissivity indicates how much water
will move through a formation and is equivalent to the permeability times the
saturation thickness of the aquifer. The coefficient of storativity indicates
how much water can be removed by pumping and draining and is defined as the
volume of water released from or taken into storage per unit area of aquifer
per unit change in hydraulic head normal to the surface.
The usual procedure during the initial exploration of an aquifer is to
drill a number of wells with one or more observational piezometers and then to
conduct pumping tests to determine the values of transmissivity and stora-
tivity.
Once the aquifer properties of transmissivity (T) and storativity (S),
have been determined, it is possible to predict the drawdown in hydraulic head
157
-------
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158
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in a confined aquifer at a distance, r, from the well and at a time, t, for a
given pimping rate (Q). Thus, by determining the drawdown at various radii
from the well, one can determine the radius of influence for a given pumping
rate.
For a given aquifer, the cone of depression initially increases in depth
and extent with increasing pumping time until eventually it levels off.
Drawdown at any point at a given time is directly proportional to the pumping
rate and inversely proportional to aquifer transmissitivity and storativity.
(Freeze and Cherry, 1979).
The Theis equation, used to estimate drawdown, is expressed as follows:
s = -9- W(u)
4irT
Where:
s = Drawdown (ft)
Q = Pumping rate (gal/day)
W(u) = Well function; dimensionless
u =
r =
T =
S =
r2S
4Tt
Radius from well (ft)
Transmissivity (gal/day/ft)
Storativity (dimensionless)
For a specific value of u, W(u) can be calculated from values shown in
Table 4-12. As time approaches infinity, the value of W(u) levels off.
Figure 4-11 expresses the drawdown in potentimetric surface from a con-
fined aquifer being pumped by two wells with equal flow.
For a system of n wells pumping at rates Q,, Q2 -- Qn, drawdown at
radius, r, from each well can be calculated as follows:
s =
W(uJ
_
4-rrT
W(u2)
irT
W(un)
159
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FIGURE 4-11
DRAWDOWN IN POTENTIOMETRIC SURFACE OF A CONFINED
AQUIFER BEING PUMPED BY TWO WELLS
(Source: Freeze, 1979)
See Copyright Notice, Page 496
Drowdown due to Qg Drawdown due to 0)
Total drawdown
Theis's equation for drawdown estimates is based on an ideal aquifer, or
one that is homogeneous and isotropic. In an isotropic aquifer, the trans-
missivity is independent of the direction of measurement.
In reality, drawdown at a given point and the total radius of influence
for a well are determined by the following factors:
(1) Rate of pumpage
(2) Permeability and thickness of the water-bearing strata
(3) The manner in which groundwater is replenished
(4) Presence of boundaries that limit the extent of the aquifer
(5) Length of time that pumping continues (Johnson Division, 1975)
161
-------
The Theis equation cannot account for factors 3 and 4 listed above, and
numerous equations have been developed to predict drawdown considering these
factors.
A basic assumption of Theis's equation, that geological formations over-
lying a confined aquifer are impermeable, is seldom true. As would be ex-
pected, drawdown in leaky aquifers is less than that in completely confined
aquifers, and predictions based on the Theis equation therefore provide a
conservative estimate; i.e., the equation overpredicts the drawdown. Esti-
mates of drawdown in a leaky aquifer can be determined using a solution de-
rived by Hantush (1960) and Neuman and Witherspoon (1969a, 1969b) . The reader
should refer to these papers for solutions to drawdown problems for leaky
aquifers. Aquifers generally do not conform to the basic assumption of the
theis equation that the aquifer extends infinitely in all directions. Defi-
nite geologic and hydraulic boundaries generally limit the aquifer. When an
expanding cone of depression strikes an impervious boundary on one side of a
pumped well, no additional water can be supplied from that direction. The
cone inst expand and deepen more rapidly in all directions to maintain the
yield of the well .
The Theis equation is only applicable for drawdown estimates from a
confined aquifer; estimates for an unconfined aquifer are complicated by the
fact that, in addition to the horizontal components of flow found in a con-
fined aquifer, there is also a vertical component of flow. Hydraulic gra-
dients induced by pumpage create a drawdown cone in the water table itself and
thus cause vertical components of flow. A solution to estimating drawdown
from an unconfined aquifer was developed by Neuman (1972, 1973, 1975) and
accounts for the effect of gravity drainage. The equation is similar to the
Theis equations:
w(v v N)
where W (ua, u^, N)is the unconfined well function and N is the square of the
radius over the square of the initial saturated thickness of the aquifer. W
(u,, u^, N) can be determined from theoretical curves developed by Neuman
(1975). This approach is similar to Boulton's method.
From the above equations, the drawdown at various distances from the well
can be determined and a distance-drawdown diagram can be drawn. The well's
radius of influence can be determined directly from these diagrams.
Designs of well point dewatering systems vary considerably, depending on
the depth to which dewatering is required, the transmissivity and storativity
of the aquifer, the size of the landfill, and the depth of the water-bearing
formation.
162
-------
Depth, Spacing, and Sizing of Pipes
Depth for well points will be governed by the depth to which the water
table must be lowered. This, in turn, influences the type of pump that can be
used and the diameter of the well points and riser pipes. The maximum draw-
down that can be maintained in the formation adjacent to each well is the
depth of the vacumm or suction head, in feet, developed by the pumping equip-
ment minus the distance from the center of the pump to the static water level
and minus the head loss in the piping and well points themselves.
Where the landfill is situated in the water table, or where the depth to
water-bearing sands is shallow, a well point system with a centrifugal suction
pump located in the center of the header may be suitable. Theoretically, the
maximum suction lift obtainable with suction pumps is about 20 to 25 feet, but
friction losses reduce this to about 15 to 18 feet (Johnson Division, 1975).
Therefore, a dewatering system using suction pumping should not be expected to
pump more than 15 feet (Johnson Division, 1975; U.S. Department of Interior,
1977). Since the height of the landfill often is less around the periphery,
considerable advantage would be gained by situating the well system along the
periphery of the site to take advantage of the suction lift available. One
potential problem with this approach is that the composite cones of depression
may not encompass the center of the landfill. In this case, it may be neces-
sary to include a few deep, high-capacity wells equipped with jet injector or
submersible pumps in the center of the site.
Pipe size for well points is generally determined from experience and
verified in the field for specific sites. For silt or other fine-grained
materials, well points with a diameter of about 1.5 inches are generally
satisfactory when centrifugal suction pumps are used, but the diameter re-
quired can be as much as 6 inches, depending upon the permeability of the
soil. One-inch-diameter riser pipes are suitable for small-diameter well
points; this size should be increased to 2.0 to 2.5 inches for well points
with a diameter of 3.5 inches. (Johnson Division, 1975; U.S. Department of
Interior, 1977.)
The length of well screens depends on the thickness of the aquifer and on
the stratigraphic properties of the aquifer.
Where the depths to water-bearing sands are greater than 10 feet or so,
where water-bearing sands must be dewatered to depths greater than 10 to 15
feet, or where several layers of stratified material must be penetrated, deep
well point systems will probably be needed and submersible or jet ejector-
based pumps should be used. Jet ejector pumps can lift water from 100 feet or
more when connected to individual riser pipes. However, this type of system
requires an additional header system to bring operating water to each pump.
This results in higher operating costs. Submersible pumps have almost un-
limited capacities, but are more costly. Although operation and maintenance
163
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costs for jet ejector pumps and submersible pumps are higher than for suction
lift pumps, they will function effectively in deep wells (Johnson Division,
1975). Required piping diameter is larger for well-point dewatering systems
pumped with jet ejector or submersible pumps. The diameter of well points may
reach 6 inches for a jet ejector pump system with riser pipes of 3.5 inches or
larger in order to permit installation of the jet ejector pump.
Well point spacing is based on the radius of influence of each well and
the composite radii of influence needed to lower the water table. Once
storativity and transmissivity have been determined, the equations discussed
previously can be used to determine drawdown and area of influence. In prac-
tice, spacing for a few well points would be determined and then field-tested;
any necessary adjustments would then be made to account for the fact that
wells do not always meet the idealized conditions assumed in equations to
estimate drawdown.
When centrifugal suction pumps are used, well points are usually spaced
from 2 to 6 feet apart, depending on the permeability of the water-bearing
materials and the depth to which the water table must be lowered. In silt and
fine sands, 2.0 to 2.5 feet is the usual spacing. Where deep well points are
required, and a jet ejector pump is used, spacing of 4 to 10 feet is common.
No generalizations can be made for submersible pumps, since pumping capacities
vary so widely (Johnson Division, 1975; U.S. Department of Interior, 1977).
Installation
Well points are made to be driven in place, to be jetted down, or to be
installed in open holes. The most common practice is to jet the well points
down to the desired depth, to flush out the fines, leaving the coarser frac-
tion of material to collect in the bottom of the hole, and then to drive the
point into the coarser materials.
A method used in some unstable material consists of jetting down or
otherwise sinking temporary casing into which the well point and riser pipe
are installed. As the casing is pulled, gravel may be placed around the well
point.
Special Cases
In several instances, design modifications will be required or at least
various methods should be compared for cost-effectiveness.
Fine silts and other slowly permeable materials cannot be readily
drained by well point systems alone. However, soils can be
partially drained and stabilized by vacuum wells or well point
164
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systems that create negative pore pressure or tension in the soil.
The well points should be gravel-packed from the bottom of the hole
to within a few feet from the surface of the poorly permeable
material. The remainder of the hole should be sealed with bentonite
or other impermeable materials. If a vacuum is maintained in the
well screen or pack, flow towards the well points is increased.
Such a system usually requires closely spaced well points, and
pumping capacity is reduced. Vacuum booster pumps may be required
on the headers or individual wells for effective operation (Johnson
Division, 1975).
Vertical sand drains may be used in conjunction with well points to
facilitate drainage in stratified soils. The drains, usually 16 to
20 inches in diameter, are installed on 6- to 10-foot centers
through the impermeable layers that need to be dewatered and are
extended to underlying permeable layers where well points are
placed.
Two or more well point systems may be required when two or more
strata of water-bearing sand are separated by impermeable barriers.
The depth for dewatering will be different for each system, and
consequently pipe lengths and diameters and pumping requirements
will be determined independently.
4.3.1.4 Advantages and Disadvantages
Advantages and disadvantages of well point pumping to adjust the water
table are listed in Table 4-13.
4.3.1.5 Costs
Costs for equipment and construction of well point dewatering systems are
listed in Table 4-14. Costs for pumping will vary widely with site conditions
and pumping requirements. Costs shown in Table 4-14 should be considered only
as examples. These unit costs have been used for cost estimates of a hypo-
thetical site where dewatering was needed to lower a water table. It is
assumed that the water table is to be lowered 12 feet along the perimeter of
the site and that 2,500 feet of header pipe will be required.
Field testing and theoretical determinations using the Theis equation
specified well point placement at 6-foot intervals. The system will require a
centrifugal suction pump with a lift of 15 feet, 2-inch-diameter well points,
and a 6-inch-diameter header. The well points will be placed around the
periphery of the site. However, in order to obtain a composite cone of
depression under the entire site, two high capacity wells were found to be
needed within the site. These wells will be 30 feet deep and will require
4-inch submersible pumps and 6-inch well casing. Three monitoring wells will
165
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TABLE 4-13
ADVANTAGES AND DISADVANTAGES OF WELL POINT SYSTEMS FOR WATER TABLE ADJUSTMENTS
Advantages
High design flexibility
Good on-site flexibility
since the system can be
easily dismantled
Construction costs may be
lower than for construction
of artificial groundwater
barriers
Good reliability when
properly monitored
Disadvantages
May not adequately
drain fine silty soils,
and flexibility is re-
duced in this medium
Higher operation and
maintenance costs than
for artificial ground-
water barriers
also be required around the periphery of the site to determine the height of
the water table. The total cost of equipment, construction, and installation
was calculated to be $240,100. The calculations for these estimates are
detailed below:
2,500 feet of 6-inch header pipe
(2,500 feet) ($35/linear foot)
2" -15' well points installed every 6'
(416 well po1nts)(!5')($22.6/ft.)
(416 well points)($15 for fittings)
Centrifugal suction pump
(1 pump) ($284/pump)
2 High capacity wells
($2.50 per inch diameter per foot)(6 inches)
(30 feet) (2 wells)
--(two 4-inch submersible pumps)($l,175)
6-inch PVC well casing
($6.50/ft.)(30 ft.)(2 wells)
= $ 87,500
$141,000
6,200
284
900
2,350
390
166
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3 monitoring wells to depths of 15 feet
($2.50 per inch diameter per foot)(4 inches)
(15 feet)(3 wells) = 450
3 centrifugal pumps x $284/pump = 852
Casing
--(15 feet)(3 wells)($4.50/ft.) 203
$240,129
4.3.2 Plume Containment
4.3.2.1 General Description
This section considers three applications of pumping in order to contain
a plume:
1. Use of a series of extraction and injection wells that will allow
water within the plume to be pumped, treated, and pumped back into
the aquifer
2. Low rates of pumping to contain a plume with JTO subsequent recharge
to the aquifer
3. Pumping and treatment of the plume followed by recharge using re-
charge basins
167
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TABLE 4-14
UNIT COSTS FOR EQUIPMENT USED IN WELL POINT DEWATERING
Unit
2-inch well point
Header pipe - 6 inches
Cost
$22.6/ft. + $15 for
fittings
$35/ft.
Source
1
2
4-inch well point
Header pipe - 8 inches
$30/ft. + $28 for
fittings
$46/ft.
Centrifugal suction pump $284
15-ft. lift; 4-5 GPM
Jet ejector pump - $530
120 ft. lift;
5GPM; 3/4 H.P.
4-inch submersible pump- $1,175
180 ft. lift;
23 GPM
Monitoring Wells
4-inch PVC casing
6-inch PVC casing
$2.00 - 2.50 per inch
diameter per foot of
depth (without casing)
$4.50/ft.
$6.50/ft.
1Davis, 1980
2Godfrey, 1980
3Jacuzzi Pumps, 1980
4U.S. Department of Interior, 1977
5Leazer Pumps and Wells, 1980
168
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Figures 4-12, 4-13, and 4-14 illustrate these systems.
FIGURE 4-12
USE OF EXTRACTION/INJECTION WELLS FOR PLUME CONTAINMENT
Water Table
Ground water Flow
I I I I I I I
T
' ' . '
1 ' . ' I 1
'
TT'
..... ... 1........
i i i i i i i i i i Bedrock ] ' ' ' ' ' ' ' ' '
pearocK
I I I I I I i i
I
' . ' . ' . '
'
'
r
T
r
i 71. r ~r i i
. .
' . '
' ' '
i ป
.
i i i i
Before Pumping
Injection Well
\
,.r::::;; Plume ::-^:>^
1 I I I I
I I T 1 T 1
I 1 I T
' .1.1
I I I I
I
' ' 1 ' 1 1 I I
i i T i ' ' T '
l.l.i.i.i.i.i.i,
i i i i i i i i
RoHrr.r-1-
Bedrock
. ' . ' I . ' . ' . ' I T~l
T^. I I I I I I I I ~T~
' ' ' ' ' ' T
i i i i
_L
i . i . i i
i i i ~r ~r
After Pumping
169
-------
FIGURE 4-13
GROUNDWATER PUMPING TO CONTAIN A PLUME (NO RECHARGE)
Water Table f'::-\.-^:-.^^
ฃ>::ป" Plume ;:H:-:x:".^Urx
Groundwater Flow
iiii
I
i i . i r i T II
T
i I I I I 77 I I I I
.
l.l.l.l.l.l.l.l.l-'' ', i . i . i i i i i i i i i
,1,1,1,1,1,1,1,1,1 Bedrock i i i i i i I I I l~
i i i i i i i i i ..... l i i i i i i l i
i
' . ' . i . i . i i ' i i . i i . i i i
i i
'
i
. . .
i i i i i i i i i
Before Pumping
Groundwater to
Discharge
Groundwater to
Discharge
i i i i ' ' ' ' i ' i i i i i i
I I 1 I I I . I I I I 1 I I I ~T "I 1 I I I
I I I I I I I I I ' ' ' I I I I I I ' .
i i i i i i i..J i i TT Bedrock i i i i i i i i
' ' ' i ' ' i ' '
i i i i
i . i
i . i i i . \ r ~r
i i T ~r ~r~i .'.'.'.'.''. '
After Pumping
170
... . .
i iiiii
-------
FIGURE 4-14
USE OF EXTRACTION WFLLS FOR PLUME CONTAINMENT
FOLLOWED 8Y SUBSEQUENT RECHARGE THROUGH SEEPAGE BASINS
Water Table
r;:x:":;:: Plume ::::::::::::"::".>~^r~ .
Groundwater Flow
i i i i i i . '
'
i i "I
T
TIII
. . . . . . ...
i i i i i i i i i i i i i i i i i i i i i i i
1 ' - ' ''''-' Bedroc'k ' ' ' ' ' ' ' ' ' ' '
i i i i i
i i
i i i i i i i i i
i . i
j_
i . i r T r i i
i.i.i
i
I . I . I . I . I . I . I . I . I t I l I lll I l I l I l I l I I I I I I 1
Before Pumping
Recharge Basin
\
Recharge
Boundary
i i i i i i i i ' Jill
' ' ' ' ' '
i ' ' '
' ' ' ' ' .....
i i i i i i i i i i
~r r i
i i i i i i i i i
' ' ' i i i i ' i . ' i
'i
After Pumping
171
-------
4.3.2.2 Applications
Plume containment by pumping is an effective means of preventing the
eventual contamination of drinking water wells or the pollution of streams or
confined aquifers that are hydraulically connected to the contaminated ground-
water. The technique may be particularly useful for surface impoundments.
Pumping without subsequent recharge may be an acceptable approach when
small quantities of groundwater are involved. However, when large groundwater
flows are involved or when residents are dependent on groundwater for a drink-
ing water source, recharge will be necessary. Pumping large volumes without
subsequent recharge may lead to changes in the potentiometric surface or
direction of flow within a confined aquifer.
4.3.2.3 Design and Construction Considerations
Extraction/Injection Wells
The theory behind containing a plume by pumping is based on incorporating
the plume within the radius of influence of an extraction well. Such a system
would require careful monitoring to determine the extent of the plume and any
changes that may occur in the plume as pumping continues.
In order to design an effective extraction/injection well system, the
effect of the injection wells on the drawdown and radius of influence of the
extraction wells must be understood. Figure 4-15 illustrates how the injec-
tion well affects the drawdown and radius of influence. As the cone of de-
pression expands and eventually encounters the cone of impression from the
recharge well, both the rate of expansion of the cone and the rate of drawdown
are slowed. With continued pumping, the cone of depression expands more
slowly until the rate of recharge equals the rate of extraction and the draw-
down stabilizes. Thus, the effect of the injection well is to narrow the
radius of influence and to decrease the drawdown with increasing distance from
the well (Freeze and Cherry, 1979; U.S. Department of Interior, 1977).
In order to predict drawdown and radius of influence in such a system,
the principle of superposition of solutions is applied. The summation of the
cone of depression from the extraction well and the cone of impression from
the injection well leads to the following expression for drawdown in a con-
fined aquifer:
172
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s = -- W(u) - W(u.)
2
where: u = re S
4Tt
4Tt
The distance between the discharge well and a piezometer is called reand
the distance between the recharge well and the piezometer is called r,(Freeze
and Cherry, 1979). All other parameters are the same as defined for the Theis
equation in Section 4.3.
For a groundwater plume that is contained in the original radius of
influence of the extraction well, the injection well would have the following
effects:
It may reduce the radius of the influence of the extraction well to
the point where the entire plume may not be contained within the
radius of influence.
The increased pressure from the injection system will tend to move the
plume towards the extraction well, thereby partly negating the effect
of the decreased radius of influence.
Because of these complications, the extraction/injection well system
should be designed so that the radii of influence do not overlap. Another
important reason for placing the wells distant enough so that their radii of
influence do not overlap is that any changes that must be made in pumping as a
result of changes in the plume due to age of the landfill, quantity of pre-
cipitation and physical changes in the size, such as compaction or excavation,
would be complicated by the effect of the overlap of the areas of influence.
In some instances site limitations may require that the extraction and
injection wells are placed so close together that the radii of influence
overlap. It may be desirable in these situations to place an impermeable
barrier between the extraction and injection wells to avoid recontamination of
recharge water. The impermeable barrier will need to be placed to the depth
of the first impermeable layer to avoid mixing of contaminated and noncon-
taminated water.
A system of extraction/injection of wells is currently being used in Palo
Alto, California, to prevent salt water intrusion. The system designed for
173
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t/o
UJ
a:
o.
UJ
O
u.
o
o
CJ
LD I
rI
^f O
UJ _l
o: _i
ro LU
-------
Palo Alto used a series of nine well pairs, with a total punping capacity of
2.0 MGD. This corresponds to an average pumping rate of 150 gpm. Pumping is
conducted in an aquifer 45 feet deep, with a tra_nsmissivity of 8,700 gpd/ft
and a coefficient of storativity equal to 3.6 x 10" . Optimum spacing between
well pairs was determined to be 1,000 feet (Shealan, 1977).
Groundwater Pumping System Without Recharge
Applying the principles of radius of influence, it is possible to contain
a plume by extraction alone. There are both advantages and disadvantages to
this system as compared to the extraction/injection system. The withdrawal
system does not incur the added pumping and maintenance costs for an injection
system, but also does not have the advantage of replenishing the groundwater
supply. Use of an extraction system alone would be best suited to sites where
low rates of pumping are required or where the aquifer water supply is not
needed as a drinking water source.
The design of an extraction system is considerably less complicated than
the previously mentioned extraction/injection well systems, since the effects
of the cone of impression from the injection wells do not need to be con-
sidered in determining the radius of influence needed to contain a plume.
However, effective use of this system will still depend on the accurate and
frequent monitoring of the plume and on a flexible design that can be adjusted
as the plume changes.
Groundwater Pumping with Recharge Through Seepage Basins
As a less costly alternative to recharging water through injection wells,
seepage basins or recharge basins can be used. Since seepage basins require a
high degree of maintenance to insure that porosity is not reduced, they would
not be practical where several basins are required for recharge of large
volumes of water or where adequate maintenance staff is not available.
As is the case for extraction/injection well systems, the effects of
recharge on the cone of depression must be accounted for in designing a system
that will contain the plume. Ideally, the recharge basins should be located
outside the area of influence of the extraction wells.
The dimensions of a recharge basin vary considerably. The basin should
be designed to include an emergency overflow and a sediment trap for runoff
from rainwater. The side walls of the basin should be pervious since con-
siderable recharge can occur through the walls (Tourbier and Westmacott,
1974).
175
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Well Systems for Plume Containment
Well point systems will be suitable for extracting a plume in some cases;
these systems are more flexible and can be readily adjusted to account for
changes in the plume. Well point systems are discussed in Section 4.3.1.
However, in most instances, high capacity wells will be needed.
In choosing the size of the well casing, the controlling factor will be
the size of the pump expected to be required for the yield of the well needed
to incorporate the plume. The diameter of the well casing should be larger
than the nominal diameter of the pump. Generally, a 4-inch submersible pump
will be used for extraction volumes of less than lOOgpm, and a 6-inch pump for
yield requirements of 150-400 gpm. A low pumping rate will be required in
many instances, and a jet ejector pump may be used.
The number of pumps needed to contain the plume will be determined by
applying the equations for composite radius of influence, or for superposition
of solutions if the radii of influence of the extraction and injection systems
overlap.
In many instances it will be desirable to pack the wells with gravel. An
artificially gravel-packed well usually costs more to construct, but is
favored for such geologic conditions as:
- Fine uniform soils where use of gravel packing would allow larger slot
openings in the well screen
- Thick artesian aquifers so that the entire aquifer could be screened
- Loosely cemented sandstone where small-slot well screens would other-
wise be required
- Thinly bedded formations where it would otherwise be very difficult to
choose the length of screen and slot sizes without knowing the thick-
ness and nature of each stratum (Johnson .Division, 1975).
The optimum length of the well screen is chosen with relation to the
thickness of the plume, and the required drawdown. It will be necessary to
install the well screen or wells to the first impermeable layer in order to
contain the plume.
An example of an effective system for plume containment is currently
operating at the Rocky Mountain Arsenal, and this system is undergoing design
for expansion. Groundwater is extracted, treated, and recharged through
injection wells to the other side of an impermeable barrier. The completed
system will handle a flow of 443 gpm and will extend for 5,200 feet. The
176
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system will consist of about 33 extraction wells, most of which are 8 inches
in diameter, and approximately 40 injection wells with a diameter of 16 to 18
inches. The extraction and injection systems are separated by an impermeable
barrier to prevent mixing of contaminated and uncontaminated water. (U.S.
Army Toxic and Hazardous Materials Agency, 1979.)
4.3.2.4 Advantages and Disadvantages
The advantages and disadvantages of the systems proposed for plume con-
tainment are listed in Table 4-15.
TABLE 4-15
ADVANTAGES AND DISADVANTAGES OF GROUNDWATER PUMPING TO CONTAIN A PLUME
Advantages
System may be less costly than
construction of an impermeable
barrier
High degree of design flexibility
Moderate to high operational
flexibility, which will allow the
system to meet increased or
decreased pumping demands
Disadvantages
Plume volume and character-
tics will vary with time,
climatic conditions, and
changes in the site. This
will result in costly and
frequently monitoring
System failures could lead
to contamination of drink-
ing water
0 & M costs are higher than
for artificial barriers
4.3.2.5 Cost for Well Construction and Pumping
Table 4-16 lists unit costs for well construction and installation suit-
able for containing groundwater plumes. Well point systems may also be used,
and costs for these have been presented in Section 4.3.1.5.
177
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TABLE 4-16
COSTS FOR WELL CONSTRUCTION AND INSTALLATION
Unit
Wells; construction and
installation without
casing
Casing
4 inch PVC
6 inch PVC
8 inch PVC
4 inch Submersible Pump-
180 feet; 23gpm
Recharge basins
Excavating costs
using a backhoe
Hauling; assume one
mile round trip
Retaining wall using
stone filled gabions
Sand liner (including
transportation costs)
Costs
$2-2.5 per inch diameter
per foot of depth
$4.50/ft
$6.50/ft
$10.50/ft
$1,175
$1.5/yd3
$1.8/yd3
$76/linear foot
$7/yd3
Source
3
3
3
3
1U.S. Department of Interior, 1977
2Leazer Pumps and Wells, 1980
36odfrey, 1980
The following example
injection well system:
illustrates the actual costs for an extraction/
A plume has contaminated an aquifer to a depth of 35 feet. The
dimensions of the plume are 2,000 feet by 750 feet by 35 feet. In order
to contain the plume, a series of extraction wells will be installed.
The contaminated waste will also be treated (see Appendix B and Section
4.3.3), and recharge to the aquifer through a series of injection wells.
The extraction system will consist of seven wells which will be pumped to
a depth of 35 feet with 4-inch submersible pumps. The injection well
system will be similarly designed, except that there will be four addi-
tional backup wells in case of clogging. In addition to the extraction/
178
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injection wells, four Tionitoring wells will be installed to monitor the
pi time.
A network of 8-inch diameter pipe will carry the water from the
extraction system to the treatment system, and finally to the injection
wells. The distance between the extraction wells and injection wells
will be 1,000 feet to avoid overlap of the radius of influence of the
extraction and injection systems. Four thousand feet of piping will also
be required to carry the water to and from the individual wells. De-
tailed costs are shown below.
22 wells for extraction/injection & monitoring
~ ($2.5/inch diameter; foot) (6 inches) (35 feet)
(22 wells) = $11,550
- ($6.5/foot casing) (35 feet) (22 wells) = 5,000
4-inch submersible pumps for each well = 25,850
~ ($l,175/pump) (22 pumps)
8-inch steel piping = 230.000
($46/linear foot) (5,000 feet)
Total = $272,400
4.3.3 Contaminated Water Treatment
4.3.3.1 General Description
Groundwater pumping systems can be coupled with treatment systems
designed for specific groundwater contamination problems. There is consider-
able flexibility in the design of treatment systems. The system described in
this section and illustrated in Figure 4-16 is based on a modular treatment
unit designed by TACION for industrial wastewater treatment and is intended to
remove organics and inorganics at tertiary treatment efficiences (TACION,
Inc., 1979). Appendix 3 discusses wastewater treatment modules in some
detail, and the reader is referred to that section for additional information
on available treatment options.
4.3.3.2 Applications
Groundwater treatment systems should be used in conjunction with pumping
to lower a water table or to contain a contaminated plume. In the case of
lowering the water table, it may be necessary to treat the contaminated water
before disposing of it. Pumping to contain a plume will require accompanying
groundwater treatment if the water is to be recharged to the aquifer or
released to surface discharge. Groundwater treatment systems can renew
drinking water supplies and prevent contamination of streams or aquifers that
are hydraulically connected.
179
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FIGURE 4-16
FLOW SCHEME OF TACION APPARATUS FOR INDUSTRIAL APPLICATIONS
(Source: TACION, 1979)
Purified Water for Reuse
^V
t I
Rinse Water Circulating
Tank Pump
1
Filtration
t-
~~>
1
Adsorption
L
t
t
Ion Exchange
180
-------
4.3.3.3 Design and Construction Considerations
A pipeline network from the discharge wells is needed to deliver the
effluent to the rinse water tank. From there it should be pumped at a con-
trolled rate to a dual-media filter for removal of suspended solids. In
dual-media filters used for tertiary treatment, a combination of sand and
graded coal are often used. The usual rate of water application is about 6
gpm/f t2.
Dual-media filters can tolerate suspended solid loads of about 120 mg/1
for filter runs of 1 to 3 days at 6 gpm/f t3 before backwashing is required.
At this loading, then, backwash will be needed every 1 to 3 days (Linsley and
Franzini, 1979).
After removal of suspended solids, water is pumped under pressure to
carbon adsorption units. Carbon is very effective in treating certain classes
of organics. Activated carbon will effectively remove pesticides and PCB's,
and in general its treatment capabilities can be summarized as follows:
Molecules low in polarity and solubility tend to be preferentially
adsorbed. Polar groups with a high affinity for water usually
diminish adsorption from aqueous solutions.
Strongly ionized materials are poorly adsorbed.
Unless the carbon pores become physically blocked, large molecules
will adsorb more easily than small molecules (Ford, 1977).
Adsorbate removal kinetics can be conducted in batch assays to determine the
effectiveness of carbon for specific organics and mixtures of organics.
General criteria used for carbon adsorption where no biological treatment
is included are (Gulp, 1973):
Contact time 10 - 50 minutes
Hydraulic loadings 2-10 gpm/ft
Backwash rate 15 - 20 gpm/ft2
Load 500 - 1,800 Ib carbon/106 gal
The final step in the treatment system is a series of ion exchange units for
removal of inorganics. The design for the ion exchange system depends on the
nature of the inorganics present, since it is possible to use several combina-
tions of various cation and anion exchange resins. The least selective method
for removing toxic metals is to use a column of strong acid cation exchange in
either the acid or sodium cycles. Another method involves the ability of
181
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certain weakly basic resins to form complexes with the transition metals and
with the metals immediately following the transition element (Gulp, 1978).
Chelating resins are selective for removing metal capable of forming coordi-
nating complexes. Copper, nickel, lead, and zinc can readily be removed with
chelating resins (Dow Chemical, 1976).
In many applications, a toxic ion will be present in small amounts to-
gether with large amounts of a relatively innocuous ion of the same or higher
valence. Specific ion exchangers have been developed for removal of specific
ions in solution, and these should be considered in order to avoid needlessly
high regeneration costs.
The costs of regeneration of carbon and ion exchange resins on-site may
be prohibitively high, especially when the site is remote. It may be desir-
able to use a system with replacement modules so that the carbon and resins
can be regenerated off-site. TACION has such a system on the market; the
system uses replacement and returnable modules, and no in-plant regeneration
is necessary. The system consists of filtration, carbon adsorption, and ion
exchange, and can be tailored for specific wastewater problems.
4.3.3.4 Advantages and Disadvantages
The advantages and disadvantages of physical-chemical treatment of con-
taminated groundwater are listed in Table 4-17.
4.3.3.5 Costs
Table 4-18 lists costs for the modular treatment system for a range of
volumes of groundwater. Costs for individual treatment modules are presented
in Appendix B.
4.4 INTERCEPTOR TRENCHES
The use of interceptor trenches or ditches can be very effective, de-
pending on the geohydrology of the site, in lowering the local water table and
in controlling the direction of groundwater flow at a site. The design and
application of interceptor trenches is discussed in detail in Section 5.2,
Drainage Ditches, and therefore is not discussed further here.
182
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TABLE 4-17
ADVANTAGES AND DISADVANTAGES OF THE GROUNDWATER TREATMENT SYSTEM
Advantages
Achieves tertiary treatment
of groundwater
High design flexibility
Permits water to be pumped
back into aquifer with little
change in potentiometric surface
Good reliability
Disadvantages
Large quantities of
costly adsorption and
ion exchange material
are required
Costs for regeneration
of carbon and resins
are high
Potential for clogging
of adsorption and ion
exchange material
TABLE 4-18
COSTS FOR PHYSICALCHEMICAL TREATMENT SYSTEMS1
Treatment
"TACION" Modular Treatment System
w/filtration, carbon adsorption
and ion exchange.
0.04 MGD
Costs
Reference
0.06 MGD
0.18 MGD
$5.3995 for equipment
and material
$1,100 for 3 months
regeneration
$84,995 for equipment
and material; $2,975
for 3 months regeneration
TACION, 1979
TACION, 1979
$225,995 for equipment TACION, 1979
and materials; $9,380
for 3 months regeneration.
1Pumping costs not included.
183
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4.5 BIORECLAMATION
4.5.1 General Description
As previously described, in cases where a disposal site is located near a
water table, groundwater flow can become contaminated with hazardous materials
due to the leaching of toxic substances from the refuse site. Contaminated
groundwater can be controlled by installing impermeable barriers or permeable
treatment beds, by groundwater pumping, or by a bioreclamation process, if the
contaminants are biodegradable. The last method is discussed in this section.
Bioreclamation is an in-place groundwater treatment technique based on
the concept of utilizing microbial organisms combined with aeration and addi-
tion of nutrients to accelerate the biodegradation rate of the groundwater
contaminants. Bioreclamation is a newly developed technique that has great
potential for controlling contaminated groundwater flow.
4.5.2 Applications
Bioreclamation has been previously demonstrated to be an effective method
of controlling groundwater contamination from underground hydrocarbon spills.
The method may also be applied to a clean-up operation of groundwater contami-
nated by organic hazardous waste from landfills.
According to Suntech, Inc., a pioneering firm in the field of biorecla-
mation, the technique can be effectively used to clean up underground hydro-
carbon plumes that contaminate the groundwater. However, certain organic
substances, such as chlorinated solvents, cannot be very effectively con-
trolled (A.M. Kirby, 1980).
4.5.3 Design and Construction Considerations
Microbiological research has identified several species of microorganisms
that have the capability of degrading hydrocarbons and certain organic com-
pounds to carbon dioxide, water, and other basic molecules. The microorga-
nisms that degrade hydrocarbons are tentatively identified as bacteria be-
longing to the genera Pseudomonas and Arthrobacter (Raymond et al., 1976).
Results from a pilot study to determine the growth rate of indigenous microb-
ial flora have shown that the small, natural microbial population could be
increased a thousandfold by adding air, inorganic nitrogen, and phosphate
salts to the groundwater (Jamison et al., 1975). Utilization of the hydro-
carbon substances by microbial activities was also found to be proportional to
the growth rate of the microbial population.
184
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Application of the bioreclamation method to control of contaminated
groundwater from waste disposal sites may require slight modifications to the
currently employed method. Groundwater contaminated with materials that
leached from a disposal site may contain a great variety of hazardous sub-
stances besides hydrocarbon compounds. Therefore, when the bioreclamation
technique that was originally developed for the "in-situ" clean-up of ground-
water contaminated with hydrocarbons is used, it is necessary to adjust cer-
tain factors of the process to accommodate the removal of contaminants that
may comprise a wide range of toxic materials.
It is recommended that the contaminated groundwater be studied to deter-
mine the chemical constitutents to be removed. Once the contaminants are
identified, appropriate bacteria can be chosen to accomplish the desired
degradation process.
The general method of treating contaminated groundwater with the bio-
reclamation method is illustrated in Figure 4-17. First, wells are placed at
strategic locations with respect to the contaminant plume. Then the chosen
microorganisms are injected into the groundwater along with oxygen and nu-
trients. Prior to the injection, the bacteria should be acclimated to the
wastes they are intended to treat. To promote microbial action, a proper
balance of oxygen and nutrients is maintained by continuous pumping, makeup,
and reinjection into the groundwater.
Proper aeration can be obtained by purging oxygen into wells by the use
of diffusers attached to paint-sprayer-type compressors that can deliver
oxygen at a constant volumetric flow rate. The compressors are equipped with
pressure gages and relief valves to aid in determining that each diffuser is
operating properly (Raymond et al., 1976).
The addition of nutrients can be achieved by using conventional pumps.
For actual design practices, Suntech, Inc. has recommended that the following
preliminary information be obtained:
Identification of the chemical constituents of the contaminated
groundwater
The type of bacteria most appropriate for the degradation of these
contaminants
The size of the contaminated groundwater plume
Geological information on the site proposed for treatment, including
type of subsurface material and permeability
The volumetric flow rate of the groundwater flow and the level of
contamination.
185
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o
LU
LU
a;
o
ป i
CO
Q
Z
13
O
OL
O
Q
LU
-------
After the treatment process has started, is is advisable to monitor the
treated groundwater flow to ensure the adequacy of the treatment system.
4.5.4 Advantages and Disadvantages
The advantages and disadvantages of the bioreclamation method are summa-
rized in Table 4-19.
TABLE 4-19
ADVANTAGES AND DISADVANTAGES OF THE BIORECLAMATION TECHNIQUE
Advantages
Good for removal of hydrocarbons
and a limited amount of organic
material from contaminated groundwater
Environmentally sound
Fast, safe and economical
Inexpensive materials used
Good for short-term treatment
of contaminated groundwater
Disadvantages
Does not remove
chlorinated solvents or
heavy metals
Introduction of nutri-
ents containing phos-
phate and nitrogen may
have adverse effects on
the surface water
stream located near the
treatment site
Excessive breakdown of
equipment such as
pumps, compressors, and
diffusers may occur,
resulting in higher
maintenance and opera-
tional cost
Long-term effectiveness
of this method is
unknown
187
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4.5.5 Cost
It is difficult to present a detailed estimate of the cost of treating
contaminated groundwater using the bioreclamation method, since it involves a
large number of variables. According to A.M. Kirby of Suntech, the cost of
treating a 5-acre area contaminated with petroleum crude would be approxi-
mately $50,000 based on a 6-inonth clean-up period. But this cost is only
applied to a clean-up of petroleum waste. Treatment cost for groundwater
contaminated with other hazardous waste materials could run up to several
million dollars, depending upon the size of the contaminated groundwater
plume, the level of contamination, the geology of the soil, and the length of
time needed for complete removal.
188
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ARMCO, Inc., Baltimore, MD. April 1980. Personal communication with P. Le.
AFTES (Association Francaise des Travaux en Souterrain). 1975. Recommenda-
tions for the use of grouting in underground construction, trans. G. W.
Clough.
Avanti International. 1979. AV-100 chemical grout safe operating practices
program. Houston, TX.
Baver, L.O., W.H. Gardner, and W.R. Gardner. 1972. Soil physics. New York:
John Wiley & Sons, Inc.
Bowen, R. N. C. 1975. Grouting in engineering practice. New York: Halsted
Press.
Boyes, R. G. H. 1975. Structural and cut-off diaphragm walls. London:
Applied Science Publishers, Ltd.
Calgon Company, Pittsburgh, PA. 1980. Personal communication with P. Rogo-
shewski.
Culp, R. L. et al. 1978. Handbook of advanced wastewater treatment. New
York: Van Nostrand Reinhold Environmental Engineering Series.
D' Appolonia, D. J. 1980. Soil bentonite slurry trench cut-offs. Journal of
the Geotechnical Engineering Div., ASCE 106(4):399-717.
Davis, T., Johnson Divison, UOP. April 1980. Personal communication with
K. Wagner.
Dow Chemical. 1977. A basic reference on ion exchange. Form No. 1976-194-77.
Fair, G. M., J.C. Geyer, and D.A. Okun. 1966. Water and wastewater engi-
neering, vol. 1. New York: John Wiley & Sons, Inc.
Ford, D. L. 1977. Putting activated carbon in perspective. Reprint Engi-
neering Science, Inc., Austin, TX.
Freeze, R. A., and J. A. Cherry. 1979. Groundwater. Englewood Cliffs, NJ:
Prentice-Hall, Inc.
Frey Co., W. S., Virginia. April 1980. Personal communication to P. Le.
Germany Valley Limestone Co., WV. April 1980. Personal communication to
P. Le.
Godfrey, R. (ed.). 1979. Building construction cost data, 1980. Kingston,
MA: Robert Snow Means Co., Inc.
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Hantush, M.S. 1960. Modification of the theory of leaky aquifers. Journal
of Geophysics Research 65(11) :3713-3725.
Jacuzzi Pumps, Standard Supply, Inc., Gaithersburg, MD. April 1980. Per-
sonal communication with K. Wagner.
Jamison, V. W., R.L. Raymond, and J.O. Hudson, Jr. 1975. Biodegradation of
high-octane gasoline in groundwater. Development in Industrial Micro-
biology, vol. 16. Washington, D.C.: American Institute of Biological
Sciences, pp. 305-312.
Johnson Division, UOP, Inc. 1975. Groundwater and wells. Edward F. Johnson,
Inc., Saint Paul, Minnesota.
Kirby, A. M., Suntech, Inc., April 1980. Personal communication to P. Le.
Kirk-Othmer, 1979.
Leazer Pumps and Wells, Remington, VA. April 1980. Personal communication
with K. Wagner.
Linsley, R., and J. Franzini. 1979. Water resources engineering, 3d ed.
New York: McGraw-Hill Book Co.
McDonough Bros. Inc., Texas; personal communication to P. Le, April 4, 1980.
McMahon, L., and P. Pereira. 1979. 1980 Dodge guide to public works and
heavy construction costs. New York: McGraw-Hill Information Systems Co.
Mi lam, 1980.
Neuman, S. P. 1972. Theory of flow in unconfined aquifer considering delayed
response to the water table. Water Resources Research 8:1030-45.
Neuman, S. P. 1973. Supplementary comments on theory of flow in unconfined
aquifers considering delayed response to the water table. Water Re-
sources Research 9:1102-03.
Neuman, S. P. 1975. Analysis of pumping test data from aniostrophic uncon-
fined aquifers considering delayed gravity response. Water Resources
Research 11(2):329-345.
Neuman, S. P., and P. A. Witherspoon. 1969a. Theory of flow in a confined
two-aquifer system. Water Resources Research 5:803-816.
Neuman, S. P., and P. A. Witherspoon. 1969b. Applicability of current
theories of flow in leaky aquifer. Water Resources Research 5:8817-29.
Raymond, R. L., V.W. Jamison, J.O. Hudson, Jr. 1976. Beneficial stimulation
of bacterial activity in groundwaters containing petroleum products. AlCh
Symposium series, vol. 73, no. 166, pp. 390-404.
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Shallard, S. G., Engineered Construction International, Inc., Pittsburgh, PA.
1980. Personal communication with P. Spooner.
Shealan, N. T. 1977. Injection/Extraction well system - A unique seawater
intrusion barrier. Groundwater 15: 1.
Spoljaric, N., Delaware Geological Survey, Newark, Delaware. June 1980. Per-
sonal communication with P. Rogoshewski.
Spoljaric, N, and W. Crawford. 1979. Removal of contaminants from landfill
leachates by filtration through glauconitic greensands. Environmental
Geology 2(6):359-363.
Staples, G., ORB Associates, Inc., McLean, VA. April 1980. Personal com-
munication with P. Le.
TACION. 1979. Tacion systems for industrial pollution control. Tacion water
purification system product literature.
Tallard, G.R., and G. Caron. 1977. Chemical grouts for soils, vol. 1: Avail-
able Materials. Federal Highway Administration Report, FHWA-RD-77-50.
Tourbier, J., and R. Westmacott. 1974. Water resources protection measures
in land development. U.S. Department of Interior. Office of Water
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Universal Linings, Inc., Philadelphia, PA. 1980. Personal communication be-
tween D. Small and P. Rogoshewski.
Ueguhardt, L. C. et al. 1962. Civil engineering handbook. New York:
McGraw-Hill Book Co.
U.S. Army Toxic and Hazardous Materials Agency, 1979. Environmental impact
statement on groundwater treatment system for the Rocky Mountain arsenal.
Draft Report.
U.S. Department of Interior. 1977. Groundwater manual - a water resources
technical publication, Washington, D.C.: U.S. Government Printing
Office.
U.S. Environmental Protection Agency. 1978. Guidance manual for minimizing
pollution from waste disposal sites. Cincinnati, OH. EPA-600/2-78-142.
U.S. Environmental Protection Agency. 1978. Proceedings of the fourth annual
research symposium held at San Antonio, TX, March 6-8. pp. 282-298.
EPA-600/9-78-016.
Wenzel, L. K. 1942. Methods of determining permeability of water-bearing
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191
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5.0 LEACHATE COLLECTION AND TREATMENT
Leachate is defined as the contaminated liquid discharged from a waste
disposal site to either surface or subsurface receptors. Water percolating
through the surface of a landfill eventually saturates the waste to its field
capacity moisture content. At that stage, moisture may percolate to the
ground below or seep from the side of the landfill. A leachate collection
system is designed to intercept the leachate before it becomes a problem by
contaminating groundwater or surface waters. The water is subsequently
treated or discharged depending on the extent of contamination.
Leachate collection systems consist of a series of drains that intercept
the leachate and channel it to a sump, wetwell, or appropriate surface dis-
charge point. The drains may consist of open ditches or trenches that may or
may not include pipes or tile drains. The sump, wetwell, or other collection
basin is also part of the collection system and from here the water is pumped
to treatment or an appropriate discharge point. Leachate treatment will be
highly variable depending on the composition and strength of the leachate.
Liners may also serve as a passive interceptor for leachate. Although
liners have widespread application for leachate collection in new landfill
sites, technical and economic factors markedly restrict their use for existing
sites.
Leachate collection systems are applicable to control of surface seeps
and seepage of leachate to groundwater. Leachate seeps on slopes are caused
when surface water infiltrates the cover soil, migrates downward until it
encounters a less permeable intermediate soil layer or refuse layer, and then
moves laterally until it seeps through the soil cover. Groundwater contamina-
tion by leachate results from water percolating through the site as well as
from lateral groundwater inflow through the fill material.
In many cases, disposal sites are placed in low-lying areas, mined-out
areas, or valleys. All these situations are natural pathways for drainage
flows or streams. These streams must be protected from contamination and from
entering the disposal site and increasing leachate generation. It may be
necessary to divert these natural flows or to collect them in separate drain-
age systems.
192
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Prior to system design, detailed studies must be undertaken. These
should include delineations of the site's topographic and geographic setting,
waste characterization, leachate characterization, and leachate treatability
studies.
5.1 SUBSURFACE DRAINS
5.1.1 General Description
Subsurface drains consist of underground, gravel-filled trenches gener-
ally lined with tile or perforated pipe. The drains intercept leachate or
infiltrating water that is destined to become leachate and transport it away
from the site.
5.1.2 Applications
Subsurface drains can be used to intercept leachate or infiltrating water
in any clay or silty clay soil where the permeability is not adequate to
maintain sufficient flow and at sites where the leachate is not too viscous or
gummy to prevent flow to the drains. Other conditions, such as a deep frost
zone, may also restrict the use of underdrains in certain soils. Subsurface
leachate collection systems have been proposed or constructed at several
existing landfills. Examples include Love Canal (Glaubinger et al., 1979),
and the Rossman's Landfill in Oregon City (Solid Waste Management, 1979). The
layout for the collection system at Love Canal and at the Rossman's Landfill
is considered in more detail in Section 5.1.3.
5.1.3 Design and Construction Consideration
The objective of this section is to provide the user with both theoreti-
cal and practical aspects for the design and construction of leachate collec-
tion systems.
Design of a suitable leachate collection system requires that the quan-
tity of leachate produced .can be reasonably estimated. The water balance
equation is generally used as a basis for predicting leachate production and
is generally expressed in inches per month or per year (EPA, 1979).
Percolation = P - R - AET - S
where: P = precipitation (inches)
R = runoff (inches)
AET = actual evapotranspiration (inches)
S = gain in moisture storage within the soil (inches)
193
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Moisture storage is a function of pore characteristics and thickness of the
layer and is determined by obtaining the best estimate of available water
content, based largely on soil type, and then adjusting the estimate to ac-
count for the thickness of the root zone (EPA, 1979).
The water balance equation can be conducted on several levels of detail
depending upon the need. It can be integrated for any desired length of time
and over any chosen number of time steps. The necessary tables and procedures
for estimating the water balance can be obtained from a paper by Thornthwaite
and Mather (1957).
The quantity of leachate produced, as predicted by the water balance
equation, can then be used in estimating drainage requirements, i.e. size and
spacing.
Aside from precipitation, there are a number of other sources of leach-
ate. In some situations, groundwater flow through the site may contribute
significantly to the generation of leachate. This is particularly true of
unlined disposal sites. This factor should be considered in estimating drain-
age requirements for all sites. Estimates of the volume and velocity of
groundwater flow can be obtained through observations and computations dis-
cussed in Section 4.3.1.3. Other possible sources of leachate at the disposal
site are the production of liquids from biodegradation of some organic com-
pounds and the dumping of liquids at the site. These should also be con-
sidered when estimating drainage requirements.
Once the quantity of leachate has been estimated, the design of the col-
lection system is undertaken. The collection system will consist of a sump,
basin, or wetwell for final collection and a series of drains and/or wells
located within, directly beneath, or in the immediate proximity of the land-
fill so as to maximize collection of leachate and minimize collection of clean
water.
Subsurface leachate collection systems have been proposed or constructed
at several existing landfills. The drainage systems are generally constructed
by excavating a trench and laying tile or piping end to end in strings along
the bottom. The trench is then backfilled with gravel or other envelope
material to a designated thickness and then the rest of the trench is back-
filled with soil. Often the gravel is lapped with fabric to prevent fine soil
from entering the gravel and clogging the drain. The front-view of a sub-
surface leachate collection system is illustrated in Figure 5-1.
In some instances, gravel-packed wetwells may be used. Wells are con-
structed similarly to trenches.
194
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FIGURE 5-1
SUBSURFACE LEACHATE COLLECTION DRAIN
(Source: EPA, 1979)
10"
f/ Clay or /
'/ Top Soil />
Pipe Drain
and Gravel
or Sand
Filter
Cover
An impermeable liner may be required on the down-gradient end of the
subsurface drain to prevent the flowthrough of intercepted and contaminated
groundwater if the surrounding materials have a moderately high to high perme-
ability.
The flow path of water from the ground surface to the drainage system
consists of four phases: (1) flow from the ground surface through the fill
and to the saturated water level; (2) flow to the sides and bottom of the
trench; (3) flow through the backfill and envelop material through the tube
joints of perforations; (4) flow into the tube itself (Van Schlifgaarde,
1974).
The major design problem for subsurface drains is to determine the opti-
mum spacing, depth and hydraulic capacity. Determination of these criteria is
usually based on practical experience, experimental data, and calculations
using drainage formula. Spacing between drain lines and wetwells depends upon
the depth of the drain below the surface, the hydraulic conductivity of the
soil, the amount of subsoil to be drained, and the potential for constructing
underdrains beneath the landfill.
Where depth and spacing are determined experimentally, they are usually
determined from such properties as soil texture, hygroscopic moisture, and
specific surface of soil particles as well as from the depth of fill material.
(Van Schlifgaarde, 1974).
195
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Design equations that have been developed for flow to a drainage pipe
indicate that a greater depth allows for wider spacing. These formulae are
considered in this section in relation to spacing. This will be an important
consideration when designing a collection system for waste disposal sites;
while it is necessary to intercept all leachate beneath the site, it is fre-
quently undesirable or hazardous to excavate through the waste material. In
positioning drains at the Love Canal site, seismic tests were used to estab-
lish the boundaries of the waste material so that the drains could be posi-
tioned outside of these boundaries and yet still intercept all leachate
(Glaubinger et al., 1979). For practical and economic reasons, however, the
depth of tube drains cannot always be chosen freely. Limiting factors include
impermeable layers and operational limits of trenching machinery. It will be
technically feasible to excavate the trench to almost any desired depth, but
the economics of doing so may be prohibitively high. Hydraulic backhoes can
excavate to depths of 55 feet, and if the depth of fill exceeds 55 feet, a
crane and clam-shell arrangement can be used. The minimum depth of the drains
is determined by the strength of a drain to withstand expected loads and by
the risk of damage caused by frost.
The flow of groundwater to a drain pipe or ditch is governed by the same
factors that control flow to a well (see Chapter 4.3). Both ditches and
drains create a water table like that shown in Figure 5-2.
FIGURE 5-2
DIAGRAM OF HOOGHOUDT'S DRAIN-SPACING FORMULA
(Source: Baver et al., 1972)
Rainfall rate ป-(cm/sec in./hr)
i I I 1 1 I I I I I I
Soil surface
Impermeable layer
196
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The cone of depression observed around a well becomes a trough along the
line of the drain (Linsley and Franzini, 1979). The spacing of the drains
must be such that the water table at its highest point between drains inter-
cepts all leachate-generating wastes, and does not interfere with plant growth
or zone of aeration, if these factors play a part in proper operation of the
fill.
In actual practice, spacing of underdrains may be restricted by the
boundaries of the wastes in such a way that the composite cones of depression
of the drains do not completely overlap and some leachate escapes the collec-
tion system. This may occur where ideal spacing requires that underdrains be
constructed beneath a waste site. While horizontal boring techniques are
available, the logistics of installing a gravel-filled trench beneath the site
may be prohibitive. Since the drain spacing is influenced by depth and
hydraulic conductivity, it may be possible to increase spacing and still
intercept all leachate by increasing drain depth and by adjusting envelope
thickness to increase hydraulic conductivity so that underdrains beneath the
site are not necessary.
The simplest formula for estimating drain spacing assumes homogeneous
soils and one-dimensional flow. Drain spacing can be estimated from
Hooghoudt's formula as follows (Baver et al., 1972) (see Figure 5-2).
s = 4k [(D + H)2 - (D + h)2]
where S = drain spacing (feet)
k = hydraulic conductivity (feet/day)
Q = design flow to the drain (ft3 flow/day/
ft of ditch)
D = depth of flow layer beneath the drains (feet)
H = height of groundwater table above the plane
through the drains and midway between two
drains (feet)
h = height of water level in the drain (feet)
This equation has been widely used to calculate drain spacing from perme-
ability, flux, and desired water level, despite the fact that actual flow to a
drain is not one-dimensional. Hooghoudt's equation is based solely on Darcy's
law, discussed previously in Chapter 4.3. However, since flow is seldom
one-dimensional, the solution to many drainage problems is based on the La-
place equation, which combines the concepts of Darcy's Law and the equation of
continuity to determine drain spacing and flow in a two-dimensional and three-
dimensional system. Laplace's equation for two-dimensional flow is repre-
sented by:
197
-------
dy
- 0
* u
where x and y are direction of flow in a two-dimensional system and H equals
the height of groundwater table above the plane through the drains and midway
between two drains. An infinite number of solutions of this equation exist
and the problem is to find the solution that matches the specific boundary
conditions. A large number of solutions of the Laplace equation have been
published to date. The solution to drainage problems using the Laplace equa-
tion frequently requires use of an analog or digital computer program (Freeze
and Cherry, 1979). Further consideration of the Laplace equation is outside
the scope of this project.
In designing tube-drain systems for capacity, the size of the drainage
pipe is determined by design flow, slope and roughness (Van Schlifgaarde,
1974). Manning's formula is generally used:
A/n
2/3 1/2
Q = R ' S '
where: Q = discharge (ft3/sec)
R = diameter/4 (feet)
S = slope (ft/ft)
A = cross sectional area (ft2)
n = roughness coefficient
The minimum recommended roughness coefficients (n) for various conduit mate-
rials are:
Clay tile
Concrete tile and perforate pipe
Vitrified clay pipe
Perforated corrugated metal pipe
Corrugated plastic tubing
(Source: Van Schlifgaarde, 1974)
0.011
0.011
0.011
0.021
0.017
Fired clay generally has better resistance to corrosive or high strength
chemical wastes than do plastic tubing or metal pipe.
The design flow will be based on the water balance equation and on the
required drain spacing.
Minimum grade or slope is determined on the basis of site conditions and
size of the drains. Some designers wish to specify a minimum velocity rather
198
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than a minimum grade. It is generally desirable to have a slight slope in
order to obtain a velocity sufficient to clean the drain during discharge and
to speed up emptying of a drain after a discharge period (Van Schlifgaarde,
1974). Minimum recommended grades for subsurface drainage are as follows:
Drain Tube Size
cm
10.2
12.7
15.2
in
4
5
6
Grade, %
0.10
0.07
0.05
Slopes of about 0.1 percent can be obtained with present trench digging equip-
ment accurate to within 1 cm of the prescribed depth (Van Schlifgaarde, 1974).
Drains have a relatively small area of inflow, causing an entrance re-
sistance. Total flow resistance, including the entrance resistance, depends
on:
Hydraulic conductivity of the material surrounding the drain
Geometric characteristics of flow
Geometric characteristics and distribution of the inflow openings in
the tube wall
It has been found that failures of tube drains are often due to the high
resistance of approach of the envelope material and soil and that the type of
tube is usually less critical to performance than the envelope material and
soil. Application of the proper envelope material in sufficient quantities
can significantly reduce the effect of resistance (Van Schlifgaarde, 1974).
The most commonly used envelope materials include sand and fine gravel, and to
a lesser extent straw, woodchips, and fiberglass.
Where the envelope and base material are more or less uniformly graded,
the Soil Conservation Service recommends the following as a generally safe
envelope stability ratio:
particle diameter of 15% (by wt.
particle diameter of 85% (by wt.
of the envelope material
of the base soil material
<5
For placement around perforated tubing, the 85 percent (by weight) over-
lap particle size should be no smaller than one-half the perforation diameter
(Van Schlifgaarde, 1974).
Recommendations for drain envelope thickness have been made by various
agencies. The Bureau of Reclamation recommends a minimum thickness of 10 cm
199
-------
around the pipe, and SCS recommends a minimum of 8 cm for agricultural drains.
In actual practice, much thicker envelopes may be used to increase hydraulic
conductivity. An 8-inch-diameter perforated pipe used for leachate collection
at Love Canal is surrounded with about 2 feet of gravel (Glaubinger et al.,
1979).
After the trench is backfilled with the
material, it may be desirable to wrap the
clogging of the gravel and drains with soil
Typlar, a strongly woven fabric that allows
vents soil from getting into the pipeline
appropriate thickness of envelope
gravel with a fabric to prevent
One such available material is
liquids to pass through but pre-
(Solid Waste Management, 1979).
The design and construction of leachate collection systems can be exem-
plified by the Love Canal and Rossman's Landfill collection systems. Figures
5-3 and 5-4 illustrate the leachate collection system designed for Love Canal.
FIGURE 5-3
DESIGN PLAN FOR LEACHATE COLLECTION SYSTEM AT LOVE CANAL
(Source: Glaubinger et al., 1979)
See Copyright Notice, Page 496
Leachate Storage
Treatment Plant
Gravity and force mains
Barrier Drains
Lateral
Manholes
(6) Wetwells
200
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FIGURE 5-4
LEACHATE COLLECTION SYSTEM FOR LOVE CANAL - TRAVERSE VIEW
(Source: Glaubinger et al., 1979)
See Copyright Notice, Page 496
Love Canal
Fill composition (original depth)
and depth
unknown
Clay cap, 3 ft thick (permeability 10 7 cm/s)
97th St
J&SSSZS^S^^Permeability = 10~3
Ground level
18-25 ft
4 0-5 5 ft
80 ft
z-i-=225iS;55iS^* 23 0 ft
The heart of the collection system at Love Canal is a series of drains
with 6 to 8 inch-diameter perforated, vitrified clay pipe backfilled with
about 2 feet of gravel envelope. The ditches run roughly parallel along the
north and south borders of the canal, as shown in Figure 5-3. The trenches
are approximately 12 feet below grade, dropping to a maximum of 15 feet. With
a gradient of 0.5 percent, they empty leachate into precast concrete wetwells.
Leachate is pumped from wetwells by vertical submersible pumps to an 8-inch-
diameter gravity main, from which it descends into concrete holding tanks.
Drains of different elevations are connected by manholes. To hasten de-
watering from the canal, lateral trenches have also been dug between the canal
boundaries and the main drainage system (Glaubinger et al., 1979).
An interesting modification of the Love Canal collection system is being
designed for the Rossman's Landfill in Oregon City (Solid Waste Management,
1979). This landfill contains only municipal wastes. The system is, again,
an unlined gravity-fed leachate collection system. The collection system
consists of four 48-inch manholes connected to 8-inch perforated PVC pipes
that run in a north-south and east-west direction to two pumps. The perforate
pipes will be surrounded by about 1-1/2 inches of gravel and wrapped in a
membrane of Typlar. Pumpage requirements are anticipated to be about 50 gpm,
although flow may reach 100 gpm during record rainfalls. Leachate will flow
by gravity to the pump station, where it will be pumped to a series of dis-
201
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posal fields similar to septic tank adsorption fields for treatment. Current
plans are to recirculate the leachate back through the landfill (Solid Waste
Management, 1979).
5.1.4 Advantages and Disadvantages
5-1.
Advantages and disadvantages of subsurface drains are summarized in Table
5.1.5 Costs for Materials and Construction
The costs for materials and construction of underdrains are presented in
Table 5-4 at the end of this chapter.
TABLE 5-1
ADVANTAGES AND DISADVANTAGES OF SUBSURFACE DRAINS
Advantages
Operation costs are relatively cheap
since flow to underdrains is by
gravity
Provides a means of collecting
leachate without the use of
impervious liners
Considerable flexibility is avail-
able for design of underdrains;
spacing can be altered to some
extent by adjusting depth or
modifying envelope material
Systems fairly reliable,
providing there is continuous
monitoring
Disadvantages
Not well suited
meable soils
to poorly per-
In most instances it will not be
be feasible to situate underdrains
beneath the site
System requires continuous and
careful monitoring to assure
adequate leachate collection
202
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5.2 DRAINAGE DITCHES
5.2.1 General Description and Applications
Drainage ditches can be an integral part of a leachate collection system
in that they may be used as collectors for surface water runoff, collectors
leading from subsurface drains, or as interceptor drains.
Surface drainage may be essential for flat or gently rolling landfills
underlain by impermeable soils where subsurface drainage may be impractical or
uneconomical. Open drainage ditches have been included as part of the leach-
ate collection system for an impoundment operated by Union Carbide (SIover,
1976). The impoundment has a clay floor and a subsurface drainage system to
prevent ponding. Open ditches are included around the periphery of the site
to carry off impoundment surface waters and peripheral waters that may con-
tribute to ponding and leachate formation.
Open ditches may be used as interceptor drains to collect lateral surface
seepage from the landfill, thus preventing it from percolating into ground-
water or flowing laterally to an area that should be protected. The choice
between using an open drain or subsurface drain depends upon the slope of the
flow. For steep slope, open drains are generally more desirable.
Finally, an open ditch may be used in certain instances to intercept
subsurface collectors and carry the leachate to its ultimate disposal.
5.2.2 Design and Construction Considerations
Open ditches are on the order of 6 to 12 feet deep. When they are con-
nected to subsurface drains, they must be deep enough to intercept the under-
drains (Van Schlifgaarde, 1974).
The water level in a ditch is determined by the purpose the ditch has to
serve. Surface drains require sufficient freeboard when running at full
capacity. The flow velocity should be kept within certain limits in view of
scouring of the bed and side slopes and of sediment deposition. Important
factors governing the desired flow velocity are soil type, type of channel,
well roughness, and sediment load (Van Schlifgaarde, 1974). The size of ditch
necessary to carry the estimated quantity of water can be determined from the
Manning Velocity equation and is dependent upon the slope, depth, and shape of
its cross-section.
203
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The selection of side slopes is based on stability of soil and on the
hazard of scour, taking into account possible groundwater pressures and vege-
tative cover. The stability of side slopes may be improved by tamping or
rolling. Trapezoidal cross sections are generally most efficient. In fine-
grained soils such as heavy clays, 1/2 to 1 slopes (0.5 ft to 1 ft vertical)
and 1-1/2 to 1 are common. In coarser textured soils, 1 to 1 or 2 to 1 may be
advisable (Van Schlifgaarde, 1974).
Ditch bottoms at junctions should be at the same elevation to avoid drops
that may cause scour. Right angle junctions encourage local scour of the bank
opposite the tributary ditch, and the smaller ditch should be designed to
enter the larger at an angle of about 30 degrees. Scour will also occur at
sharp changes in ditch alignment so long radius curves should be used where
change is necessary (Linsley and Franzini, 1979).
An open ditch can be kept in efficient working condition by careful
maintenance. A drain allowed to become obstructed by brush, weed growth, or
sediment can no longer be efficient; it should be cleaned to its original
depth when efficiency is curtailed.
5.2.3 Advantages and Disadvantages of Drainage Ditches
The advantages and disadvantages of drainage ditches are summarized in
Table 5-2.
TABLE 5-2
ADVANTAGES AND DISADVANTAGES OF DRAINAGE DITCHES
Advantages Disadvantages
Low construction and operating cost Require extensive maintenance to
maintain operating efficiency
Useful for intercepting landfill
side seepage and runoff Generally not suited for deep
disposal sites or impoundments
Useful for collecting leachate in
poorly permeable soils where sub- May interfere with use of land
surface drains cannot be used
May introduce need for additional
Large welted perimeter allows safety/security measures
for high rates of flow
204
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5.2.4 Costs
Costs of materials and construction for open ditches are included in
Table 5-4, later in this chapter.
5.3 LINERS
5.3.1. General nescrijJtion and Applications
Liners for control of leachate are impermeable barriers situated beneath
the landfill and that intercept the leachate before it reaches the groundwater
supply. Use of subsurface liners at existing sites is limited by the logis-
tics of placing the liner beneath the wastes. Although prefabricated liners
have widespread use as bottom sealant for new sites, it is not technically
feasible to use prefabricated liners for existing disposal sites. However,
slurries and grouts may be injected to form a bottom seal under certain
limited conditions. Possibilities for bottom seals at existing sites include:
Formation of a bottom seal by the use of pressure-injected grouts
Use of a bentonite slurry that would be allowed to settle to the
bottom of a lagoon, thereby forming a seal
5.3.2. Design and Construction Considerations
A bottom seal could be created by pumping or pressure injecting grout
under an existing landfill. The grout, selected for its compatibility with
the wastes, would be injected through tubes placed along a predetermined grid
pattern. This grid pattern would be determined by drilling exploratory bore-
holes to determine both vertical and horizontal limits of the sites. Grouts
would be pumped to a thickness of 4 to 6 feet and would be situated about 5
feet below the site to allow for irregularities in the site bottom. Leachate
collection would need to be implemented so as not to exceed capacity of the
bowl (EPA, 1978).
Consideration of this method of bottom sealing should be accompanied by a
great deal of caution and testing. As indicated under advantages and disad-
vantages of liners in Table 5-3, the method is costly and has severe technical
1 imitations.
Another method of bottom sealing which may have limited applicability is
use of a sodium bentonite slurry. American Colloid Company manufacturers a
granular bentonite, which when premixed with water can be pumped into a con-
taminated lagoon and allowed to settle. American Colloid recommends an appli-
205
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cation rate of 2.5 - 10 lb/ft2 of Saline Seal 100, a sodium bentom'te formu-
lation for industrial landfills or lagoons (American Colloid, 1981). This
bentom'te is formulated for resistance to strong concentrations of dissolved
salts, acids, and alkali (Misrock, 1979). It has been used successfully to
seal an oily waste treatment lagoon. This method is best suited to plugging
up leaks in a lagoon bottom.
Top liners, or caps, may be used to reduce or to eliminate surface infil-
tration through the waste facility, and therefore to reduce the amount of
leachate that is generated. Such top liners may be installed at existing
sites. Various types of plastic membranes are used as top liners. A covering
of soil is emplaced over the membrane to hold it in place and to protect it.
Such top liners are chemically very stable and, if sufficiently protected from
surface traffic, may resist breakage ,or puncture for years.
Clay or clayey soils may also be used to cap existing sites and to reduce
infiltration. Capping soils must be carefully chosen for their low perme-
ability characteristics and emplaced so as to provide continuous gradients
away from the site. Such materials are usually rolled or otherwise compacted
and may be covered by other soils to provide better trafficability in wet
weather.
5.3.3 Advantages and Disadvantages of Liners as a Remedial Action for
Existing Sites
Advantages and disadvantages of using liners at existing sites are summa-
rized in Table 5.3.
5.3.4 Costs
To provide an indication of the overall costs associated with leachate
collection the following example is presented, with reference to unit costs
given in Table 5-4.
A disposal site has the approximate dimensions of 1,200 feet by 300 feet,
and wastes have been disposed of to a depth of 12 feet below the surface.
In order to collect leachate, generated at peak rates of 50 gpm, sub-
surface gravity drains will be run along the perimeter of the site at a depth
of approximately 18 feet. The drains will have a slight slope (^Q.2%) in
order that they can flow by gravity to two wetwells. Pipe placed in the
drains is 8-inch perforated vitrified clay pipe, which will be imbedded in
about 2 feet of gravel. In order to increase flow to the main subsurface
drains, a series of 15 lateral drains (average length of 20 feet) will be
206
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TABLE 5-3
ADVANTAGES AND DISADVANTAGES OF LINERS AT EXISTING SITES
Advantages
Can assure control of leachate
migration from certain sites
Disadvantages
Use of prefabricated liners
technically infeasible
is
Although use of a bentonite
slurry will be suitable for
sealing leaks from certain sur-
face impoundments, it is not ap-
plicable for landfills and not
well suited to impoundments that
are permeable along the entire
site bottom
Construction costs
injected grouts is
for pressure
very high
There may be difficulty or haz-
ards involved in drilling through
sites to inject grout
In using pressure-injected grout
there is no available method to
determine if all voids between
injection points have been filled
placed at horizontal runs from the site to the main drains. The laterals will
be 6-inch perforated pipe with 2 feet of gravel envelope. Four manholes have
been included in the collection system to connect drains at different depths.
Leachate flowing to
ible pump to a leachate
collection system.
the wetwells will be carried by a vertical submers-
holding tank. Figure 5-5 depicts schematically the
207
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TABLE 5-4
UNIT COSTS FOR A LEACHATE COLLECTION SYSTEM
Item
Excavation;
20 ft. deep, 4 ft. wide;
hydraulic backhoe
Crushed stone; 3/4 inch
Cost to buy, load, haul
2 miles, place, and spread.
Tile Drainage
Vitrified clay (Standard bell
and spigot)
4" perforated
6" perforated
8" perforated
Precast concrete manholes
48" x 3'
48" x 4'
Concrete wetwells
Sewer piping;
Concrete; nonreinforced;
extra strength
6" diameter
8" diameter
Bituminous fiber
4" diameter
Sewer piping; PVC
4"
6"
8"
Backfilling:
Spread dumped material
by dozer
Unit cost
$1.00 yd3
5.30 yd3
Source
$2.15 LF installed
$2.63 LF installed
$4.33 LF installed
$180.59
$215.73
$6,500.00
$3.94 LF
$4.31 LF
$2.04 LF
$1.74 LF
$2.89 LF
$4.61 LF
$.66 yd
--continued
208
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TABLE 5-4 (Continued)
Item Unit cost Source
4" Submersible pumps $1,700 1
installed; to 180 ft.
2 HP; 840-14406PH $2,375
5 HP; 1302 - 1494 GPH;
Holding tank;
Horizontal cylindrical glass
fiber reinforcement phthalic
resin tanks
10,000 gal $6,354 installed 4
20,000 gal $14,164.50 4
installed
Portland cement grout 0.95/gallon 3
Bentonite grout 1.25/gallon
'Godfrey, 1979
2McMahon and Pereira, 1980
Industrial sources, 1980
4Richardson Engineering Services, 1980
The total volume of trenching required for the main subsurface drains is:
(18 ft) (2.67 ft) (3,000 ft) = 144,200 ft3
5,334 yd3
Volume of trenching required for the laterals:
(18 ft) (2.5 ft) (20 ft) (15 drains) = 13,500 ft3
500 yd3
Trench excavation costs are as follows:
5,334 yd3 + 500 yd3 x $l/yd3 = $5,834
The volume of gravel required for 2 feet of envelope material is estimated as
follows:
209
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FIGURE 5-5
LEACHATE COLLECTION COSTING EXAMPLE
300
ft.
1200ft.
Wetwells
Main Drainage System
Lateral Trenches
Manholes
Holding
Tank
Main subsurface drains
[(4 ft2) - (.56 ft2)](3,000 ft)
Laterals
[(4 ft2) - (.38 ft2)](300 ft)
Total cost of 3/4 inch gravel envelope is:
[(381 yd3) + (169 yd3)]($8.301yd3)
= 10,320 ft3
or 381 yd 3
456 ft3
or 169 yd 3
= $4,565
A total length of 3,000 feet of 8-inch perforated vitrified clay pipe is re-
quired. The total is:
(3,000 ft) ($4.33/ft)
= $13,000
210
-------
A total of 300 ft of 6-inch perforated pipe is required for the laterals:
(300 ft) ($2.63/ft) = $789
The total costs for four precast concrete manholes is estimated as follows:
(4) ($215.73) = $862.93
The total cost for two concrete wetwells is:
(2) ($6,500) = $13,000
Figure 5-5 shows that 300 feet of sewer piping is required to carry the leach-
ate to the holding tank:
(300 ft) ($3.94/ft) = $1,182.00
Two submersible pumps that can pump to 25 gpm:
(2) ($1,700) = $3,400
Total costs for materials and labor:
$5,834 + $4,565 + $13,000 + $789 + $863 + $13,000 + $1,182 + $3,400 = $42,633
5.4 LEACHATE TREATMENT
5.4.1 Leachate Treatment Modules
A leachate treatment system can be defined as a treatment module or group
of modules designed to meet suitable treatment levels for stream discharge,
groundwater recharge, discharge to municipal treatment systems, or recycle
through a landfill.
Leachate composition and strength vary widely from landfill to landfill
and within a given landfill, depending upon the nature of the waste, the age
of the fill, the amount of precipitation, and the porosity, permeability and
adsorption characteristics of the soil. Because of the wide variability from
site to site, each treatment system must be designed on a case-by-case basis
after completion of an extensive monitoring program. From a systems design
standpoint, changes in leachate composition with age are problematic because a
system that may be adequate now may not be suitable as the landfill ages.
From an operations standpoint, fluctuations in leachate quantity and strength
can cause serious problems in trying to automate chemical additions and main-
tain an active biomass for biological treatment. These fluctuations can be
dampened to some extent by equalization, but it is evident that design and
operation of an effective leachate treatment system will require a continuous
211
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monitoring program and flexibility to adjust treatment to meet changing leach-
ate strength.
An example of the wide variability in leachate composition from site to
site is presented in Table 5-5. Results of analysis from thirteen municipal
sites indicate that the COD's and BOD's can vary by several orders of magni-
tude from one site to the next. TOC and total solids vary somewhat less,
though the range of values is considerable. Extensive sampling of municipal
landfills has enabled researchers to make some generalizations regarding
leachate composition and age of fill; ratios of COD/TOC, BOD/COD, VS/TS, and
S04/CL have been shown to reflect the age of the fill. Figure 5-6 shows that
these ratios decrease as the landfill stabilizes, reflecting a decrease in
biodegradability, an increase in washout of inorganics, and increasingly
anaerobic conditions that reduce sulfates to sulfides and cause them to pre-
cipitate out as the metal sulfide (EPA, 1977a). These trends in leachate
composition with age provide a useful though not infallible tool for deter-
mining changes in leachate treatment needs as a municipal landfill ages. Such
trends may occur to varying extents in industrial landfills as well, depending
largely on the biodegradability of the wastes. In general, industrial land-
fills can be expected to exhibit a lower ratio of BOD/COD where organics are
part of the fill material.
Table 5-6 presents an overview of the treatment modules or unit processes
which have potential for treatment of leachates of various strengths and
compositions. Each unit process is summarized with regards to its applicabil-
ity, major design considerations, environmental effects, technology status,
and reliability. The unit processes are considered in further detail in
Appendix B. Since detailed design and construction factors for these pro-
cesses are well published, no attempt was made to give a comprehensive review
of each process module. Rather, the objective of Appendix B is to provide
sufficient information for the reader to determine feasible treatment tech-
nologies for a leachate with a particular strength and compositon. Final
selection of a treatment scheme and the corrresponding design of that scheme
will require thorough site investigations along with detailed engineering
design and cost considerations.
Table 5-7 summarizes the relative costs and energy requirement of the
various modules. In estimating costs it was assumed that low volumes of
leachate would be treated at any particular site (0.1-0.3 mgd). Some of the
unit processes are more cost effective for higher volumes of leachate. Costs
curves are included in Appendix B and are based on 1976 dollars unless other-
wise noted.
Shuckrow et al. (EPA, 1980) have also prepared a comprehensive study of
unit processes suitable for hazardous waste treatment and are currently in-
volved in studies of process train selection.
212
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223
-------
TABLE 5-7
COST COMPARISON FOR TREATMENT MODULES (0.1 AND 0.3 mgd)
Process
Activated sludge (with clarifier)
Ammonia stripping (no recovery)
Anaerobic/facultative lagoons
Biological seeding (used with
conventional or pure oxygen-
activated sludge)
Carbon adsorption (no regeneration)
Chlorination
Equalization
Ion exchange
Liquid ion exchange
Precipitation/floc/sedimentation
Pure oxygen-activated sludge
(including clarifier)
Rotating biological disc (including
clarifier)
Trickling filter
Wet air oxidation
Capital
Cost1
High
Low/
moderate
High
High
Moderate
Low
Low
Generally
high but
very var-
iable
Generally
high but
very var-
iable
Low
Moderate/
high
Moderate/
high
Moderate
High
O&M1
Low
High
Low
Low to
moderate
Moderate
to high
Low
Low
Moderate
to high,
variable
Moderate
to high,
variable
Moderate
Moderate
Moderate
Low
High
Relative
Energy Use1
Moderate
High
Low
Moderate
to high
Low
High
High
Low
Low
Low
Moderate
Moderate
Low
High
1See legend on next page.
Source: EPA, 1978; DeRenzo, 1978; EPA, 1979
224
-------
Capital Costs
TABLE 5-7 (Continued)
Legend Explaining Relative Cost Comparisons
(Based on 1978-79 costs)
Low: <$75,000 for 0.1 mgd;
<$100,000 for 0.3 mgd
Moderate: $75,000 - $110,000 for 0.1 mgd;
$100,000 - $200,000 for 0.3 mgd
High: <$110,000 for 0.1 mgd;
<$200,000 for 0.3 mgd
O&M Costs
Low: <$7,500 for 0.1 mgd;
<$1,300 for 0.3 mgd
Moderate: $7,500 to $20,000 for 0.1 mgd;
$1,300 to $25,000 for 0.3 mgd
High: <$20,000 for 0.1 mgd;
<$25,000 for 0.3 mgd
Energy
Low: <7% of O&M
Moderate: 7-15% of O&M
High: <15% of O&M
5.4.2 Leachate Treatment System Cost Example
Although the costs associated with individual treatment modules have been
provided in Appendix B, it is evident that leachate treatment will require a
series of several modules in order to meet treatment objectives in most cases.
225
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This section provides treatment costs for a leachate treatment system designed
for a municipal landfill. Although the treatment system is typical of what
one might expect for the wastes specified, the wastes (and treatment com-
ponents) are not representative of all landfills. Each site will be unique in
terms of its treatment needs.
The cost example for the municipal leachate treatment system is based on
the leachate characteristics of the GROWS Landfill in Bucks County, Pennsyl-
vania, and on the basic design for that treatment system (EPA, 1977b). Cost
curves presented throughout Appendix B are used as the basis for cost esti-
mates, rather than actual costs incurred by construction of the GROWS treat-
ment system.
The GROWS Landfill is an active municipal landfill that generated a
maximum leachate flow of about 0.31 mgd during an operating period when in-
fluent and effluent had the characteristics shown in Table 5-8.
The treatment system is illustrated in Figure 5-7 and consists of lime
addition, sedimentation, air stripping, neutralization, and activated sludge
treatment.
FIGURE 5-7
SCHEMATIC OF LEACHATE TREATMENT SYSTEM AT GROWS LANDFILL
(Source: EPA, 1977)
Sludge
Holding
Waste Sludge
Pump \ /
/T
Lime'
Lagoon
Aeration
Chamber
Aeration
Chamber
/
- Settling
Chlorine
Contact
To River or Landfill
Sludge
H2S04
H3P04
226
-------
TABLE 5-8
TREATMENT PERFORMANCE AFTER ACCLIMATION OF ACTIVATED SLUDGE
Concentration
Item
Suspended solids
Dissolved solids
COD
BOD
Alkalinity
Hardness
Magnesium
Calcium
Chloride
Sulfate
Phosphate
Ammonia-N
Kjeldahl-N
Sodium
Potassium
Cadmium
Chromium
Copper
Iron
Nickel
Lead
Zinc
Mercury
Influent
445
10849
9689
4993
3718
4647
495
819
3172
197
1.62
510
539
992
823
0.049
0.105
.313
205
.52
.545
3.64
.015
Effluent
126
5369
576
60.5
388
1629
109
472
2925
1333
17.8
46.5
141
724
505
0.014
.075
.078
.96
.27
.12
.44
.004
Percentage removal
71
50
94
98.8
89.6
64.9
78.0
42.4
7.8
90.9
73.8
49.
38.
71.4
28.
75.
99.
48.
78.0
87.9
73.3
.6
.1
,5
,1
Source: EPA, 1977
Treatment design criteria are as follows:
Lime Clarification
The primary circular clarifier is designed for an overflow rate of 800
gal/d/ft2. Costs include sludge pumps. Lime storage and feed equipment are
based on the use of hydrated lime at dosages of 440 - 6000 mg/ฃ which are
required to raise the pH above 10 for ammonia stripping.
227
-------
Ammonia Stripping
Although the GROWS landfill uses an ammonia stripping lagoon, cost esti-
mates have been made for a packed tower. Ammonia recovery was not included;
although the ammonia concentrations are high, flow is relatively low. Con-
struction costs include a 20-foot-high packed tower, packed with 1/2-inch
diameter PVC pipe at 3 inch centers. Hydraulic loading to the tower is 1.0
gal/min/ft2 and the air/water ratio is 400 ft3/gal.
Neutralization
Prior to discharging to activated sludge treatment, the effluent from
ammonia stripping is adjusted to neutral pH with H2S04; pH adjustment requires
0.69 gal H2S04/1000 gal.
Activated Sludge
Biological treatment consists of two aeration units and two secondary
clarifiers in sequence. Experience at the GROWS landfill indicated that it
was necessary to maintain a MLVSS concentration of 3000-8000 mg/ฃ, in order to
obtain 90 percent BOD reduction for the high strength leachate. This high
MLVSS concentration was maintained by return sludge pumps capable of de-
livering a return sludge flow equal to 200 percent of the influent flow.
Units could operate as conventional sludge or extended aeration units. Ex-
tended aeration was chosen for costing purposes and included a chlorine con-
tact chamber. It was also their experience at GROWS that the sludge required
additional phosphorous as a nutrient supplement. Phosphoric acid was added at
a rate of 0.085 gal/1000 gallons. Separation of treated wastewater from the
MLVSS was achieved by gravity sedimentation in secondary clarifiers.
Costs for this system are summarized in Table 5-9.
5.4.3 Leachate Recycle
Leachate recycle involves the recirculation of leachate back through the
refuse pile for purposes of accelerating the rate of biological stabilization
and in order to remove readily degradable pollutants from the leachate.
Leachate concentrations are reduced by anaerobic degradation.
Leachate recycling is applicable to leachate with a high readily degrad-
able organic content. The ratio of BOD to COD should be high for successful
recycling. The process is not well suited to most industrial waste fills.
228
-------
TABLE 5-9
COSTS FOR MUNICIPAL LEACHATE TREATMENT SYSTEM
Item
Primary clarifier
Lime storage and feed
Lime: (? $1.20/1000 gal*
Ammonia stripping tower
Neutralization with
H2SO ; @ 64
-------
FIGURE 5-8
BIOCHEMICAL OXYGEN DEMAND OF LEACHATE
(Source: EPA, 1975)
Control
Leachate Recycle
(j E Leachate Recycle and pH Adjustment
oO Leachate Recycle, pH Adjustment and
Initial Sludge Addition
"60 120 180 240 300 360 420 48O ab^OOMO 720 780840 8OO 960 1020 1080 1140
Time Since Leachate Production Began, days
through 5-10, BOD, COD, and TOC all exhibit the same pattern: low residuals
were obtained in a short time relative to the system without leachate recycle.
Recycling promotes a more rapid development of anaerobic activity and methane
fermentation, and it increases the rate and predictability of biological
stabilization of readily available organics. Control of pH and initial sludge
seeding can further enhance these effects. Optimum pH for stabilization of an
anaerobic culture is 6.8 to 7.2, since it is in this pH range that methane-
forming bacteria are most active.
concentrations of most heavy metals in the leachate were low at the
the project. However, the results generally indicated that there may
increase in the levels of metals. Initially, the fill is
reduced and metals are precipitated as the sulfide. With
volatile acids, the environment becomes less reducing, the
dized, and the metals are released.
The
start of
be an initial
an increase in
sulfides are oxi-
230
-------
FIGURE 5-9
TOTAL ORGANIC CARBON CONCENTRATION OF LEACHATE
(Source: EPA, 1975)
6000
Control
Leachate Recycle
00 Leachate Recycle and pH Adjustment
oo Leachate Recycle, pH Adjustment and
Initial Sludge Addition
60 120180240300360420480540600660720780840000960 1020 1080 1140
Time Since Leachate Production Began, days
Recirelation rates and nutrient requirements will need to be determined
on a case-by-case basis. The demonstration project discussed above used
recirculation rates on the order of 0.5-2.0 gal/ft2/day for a municipal refuse
that was manually compacted to a density of 537 Ib/yd3.
231
-------
FIGURE 5-10
CHEMICAL OXYGEN DEMAND OF LEACHATE
(Source: EPA, 1975)
Control
Leachate Recycle
Da Leachate Recycle and pH Adjustment
oo Leachate Recycle, pH Adjustment and
Initial Sludge Addition
120 180 240 300 360 420 480 540 600 660 720 780 840 900 060 K>2O 1O80 1140
Time Since Leachate Production Began, days
232
-------
REFERENCES
American Colloid Co. 1981. Volclay product information. Skokie, IL.
Baver, L. D. et al. 1972. Soil physics. New York: John Wiley and Sons,
Inc.
Bern, J. 1976. Living with Leachate. In: Proceedings of the fourth national
congress. Waste management technology and resources and energy recovery.
Atlanta. November 12-14, 1975.
De Renzo, D.J. 1978. Unit operations for treatment of hazardous industrial
wastes. Noyes Data Corp., Park Ridge, N.J.
Freeze, R.A., and J.A. Cherry. 1979. Groundwater. Englewood Cliffs, NJ:
Prentice-Hall.
Godfrey, R. (ed.) 1979 Building construction cost data, 1980. Kingston, MA:
R. S. Means Company, Inc.
Glaubinger, R. S. et al. 1979. Love canal aftermath. Chemical Engineering.
Volume 86. No. 23, 86-92.
Hammer, M. J. 1975. Water and wastewater technology. New York: John Wiley
& Sons, Inc.
Linsley, R., and J. Franzini. 1979. Water resources engineering, 3d ed.
New York: McGraw-Hill Book Company.
Liptak, B. G., ed. 1974. Environmental engineers' handbook, vol. 1: Water
pollution. Radnor, PA: Chilton Book Company.
McMahon, L., and P. Pereira. 1979. 1980 Dodge guide to public works and
heavy construction costs. New York: McGraw-Hill Information Systems Co.
Misrock, A. Atlas-Misrock Co., Inc. May 1980. Personal communication with
K. Wagner.
Pohland, T.G. 1979. Pilot scale investigation of accelerated landfill sta-
bilization with leachate recycle. Proceedings of the Fifth Annual Re-
search Symposium - Municipal Solid Waste Land Disposal. EPA-600/
9-79-023a.
Richardson Engineering Services. 1980. Richardson rapid construction cost
estimating system, vol. 4: Process plant construction estimating stan-
dards.
Slover, E. 1976. A case history: Implementing a chemical waste landfill.
IN: Proceedings of the fourth national congress, waste management tech-
nology and resource and energy recovery, Atlanta, 12-14 November 1975.
233
-------
Solid Waste Management. 1979. Oregon landfill seeks to control leachate
under difficult conditions, Solid Waste Management 9:21.
Thornthwaite, C.W., and J.R. Mather. 1957. Instructions and tables for com-
puting potential evapotransperation and the water balance. Drexel Insti-
tute Publications in Climatology 10(3):185-311.
U.S. Environmental Protection Agency. 1977. Demonstration of a leachate
treatment plant. Office of Solid Waste. Washington, D.C. PB-269-502.
U.S. Environmental Protection Agency. 1977a. Evaluation of leachate treat-
ment. E.S. Chian and F.B. Dewalle for Municipal Environmental Research
Laboratory. Cincinnati, OH. EPA-600/2-77-186a+b.
U.S. Environmental Protection Agency. 1978. Innovative and alternative tech-
nology assessment manual. Office of Water Program Activities. Washing-
ton, D.C. EPA -430/9-78-009.
U.S. Environmental Protection Agency. 1978. State-of-art study of land im-
poundment techniques. W.S. Stewart, Exon Research and Engineering Co.
for Municipal Environmental Research Laboratory. Cincinnati, OH. EPA-
600/2-78-196.
U.S. Environmental Protection Agency. 1979. Design and construction of
covers for solid waste landfills. R.J. Lutton et al. for U.S. Army
Engineering Experimental Station and Municipal Environmental Research
Laboratory. Cincinnati, OH. EPA-600/2-279-165.
U.S. Environmental Protection Agency. 1979. Estimated waste treatment costs,
vol. 3: Cost curves applicable to 2500 gpd. to 1.0 mgd. treatment
plants. Municipal Environmental Research Laboratory. Cincinnati, OH.
EPA-600/2-79-162C.
U.S. Environmental Protection Agency. 1980. Management of hazardous waste
leachate. R.J. Shuckrow et al., for Municipal Environmental Research
Laboratory. Cincinnati, OH. SW-871.
Van Schlifgaarde, 0. 1974. Drainage for agriculture. American Society of
Agronomy. Agronomy 17. Madison, VII.
234
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6.0 GAS MIGRATION CONTROL
Approaches to control of gas from landfilled materials can be grouped
into two categories: control of methane, and control of volatile toxics.
Control of methane gas is important at sites where biodegradable organics
are present. Anaerobic decomposition of organics produces methane gas, which
forms an ignitable mixture with air at concentrations of from 5 to 15 percent
(Moore and Rai, 1977). Methane diffuses readily along paths of least resis-
tance and may travel laterally and collect in underground structures, thus
presenting an imminent hazard. Methane is not usually an explosion hazard in
the soil, since its concentration is usually much greater than the upper
explosive limit. Approaches to the control of methane migration are aimed
principally at stopping lateral subsurface migration rather than controlling
emissions to the atmosphere.
Control of volatile toxic compounds, on the other hand, is concurrently
aimed at limiting both the lateral movement and atmospheric emissions of toxic
vapors. Gas collection and emission control treatment are mandatory for
volatile toxics, while their use in sites generating methane is primarily for
fuel recovery.
Before gas migration controls can be properly installed at a hazardous
waste site, it is important to determine the type of wastes present, the depth
of fill, and the subsurface geology of the site and adjacent areas. Also,
field measurements to determine gas concentrations, positive or negative
pressures, and soil permeabilities should be used to establish optimum design
of vent systems.
6.1 PIPE VENTS
6.1.1 General Description
Pipe vents consist of vertical or lateral perforated pipe installed in
the landfill for collecting gases or vapors. They may be installed in and
around the landfill alone, or in combination with trench vents (see Section
6.3) for the control of lateral gas migration. Pipe vents are usually sur-
235
-------
rounded by a layer of coarse gravel to prevent clogging by solids or water.
They may discharge directly to the atmosphere or be connected to a negative
pressure collection system (see Section 6.4). Various configurations of pipe
vents are shown in Figure 6-1.
6.1.2 Application
Pipe vents can be employed to control lateral and vertical migration for
both methane and volatile toxics. The basic configurations in Figure 6-1
cover, or can be modified to cover, most of these applications. Atmospheric
vents, both mushroom and "U" type, are used for venting methane at points
where gas is collecting and building up pressure. Atmospheric vents can be
placed at strategic locations where sampling (with gas probe) has detected an
area of gas collection. Methane will be vented to the atmosphere when the
absolute pressure adjacent to the gas vent is higher than the barometric
pressure. The maximum pressure differential is expected to be only a fraction
of an inch of water. The use of atmospheric vertical pipe vents, without
other measures to control methane gas, is limited to sites where lateral
migration is restricted by impermeable strata, and where gases are collecting
in a centralized area such as the crown of a landfill. Control of lateral
migration of methane by an array of atmospheric pipe vents surrounding a
landfill is believed to have little success unless vents are located very
close together (Moore, 1976). Such a situation approaches a trench vent, to
be discussed later in Section 6.2.
Methane migration control can be more effectively accomplished by in-
stalling forced-ventilation systems in which a vacuum pump or blower is con-
nected to the discharge end of the vent pipe. A drawdown with a radius of
influence of 150 feet is accomplished with a pumping rate of 50 ft3/min (Carl-
son, 1977). Such a system is applicable for controlling both vertical and
lateral movement of methane in the landfill, by installing vents inside and
along the perimeter of the site. The collected methane can be vented to the
atmosphere, flared, or recovered as a low-grade fuel gas.
In landfills containing volatile toxics, a closed forced-ventilation
system is required to prevent any toxic vapors' from migrating laterally or
vertically through the cover material to the atmosphere. Drawing (d) in
Figure 6-1 depicts a series of pipe vents connected to a manifold that leads
to a blower and finally to gas treatment. Such a configuration can be used to
prevent emission of toxics to the atmosphere across the entire area of the
site.
6.1.3 Design and Construction Considerations
When designing installations of atmospheric pipe vents for methane con-
trol, proper placement is the chief consideration. Preliminary sampling
236
-------
to
LU
OH
rs
CJ3
co
CL.
>I
Q-
U.
O
O
o
O
CO
LU
o
237
-------
should be conducted to determine gas collection points for proper vent place-
ment. Figures 6-2 and 6-3 show methane contours for two landfills. It is
apparent that methane concentrations vary widely depending on the specific
landfill configuration. The highest methane concentration (70 percent is the
theoretical limit) is expected in the most anaerobic section of the filled
material. In many cases, this is at the bottom (as in Figure 6-2), but not
necessarily (Figure 6-3). Optimum effectiveness will be obtained if vents are
placed at maximum concentration and/or pressure contours. To ensure proper
ventilation, vent depth should extend to the bottom of the fill material.
Proper spacing of vents is important to ensure adequate ventilation of
large areas where methane is concentrated. Distance between vents will depend
on soil permeability; however, this distance can be estimated for a typical
soil. Moore (1976) has derived predictions of methane reduction resulting
from a series of atmospheric pipe vents installed to control lateral migration
around a hypothetical municipal landfill in a permeable strata with a porosity
of 0.4. If the radius of influence of a pipe vent is assumed to extend to the
elbow of the concentration reduction ratio curve, as shown in Figure 6-4, the
radius of influence of the vent can be calculated from the value r/rf where:
r.p = the radius of landfill is 160 m. The radius of influence, r, then would
be:
r = 0.125 x 160 m = 20 m (66 ft).
This calculation suggests that a general rule to ensure adequate venti-
lation would be to locate wells 50 feet apart. As mentioned earlier, atmos-
pheric vent wells are not recommended for control of lateral migration of gas.
Forced ventilation is a more effective means of controlling the lateral
and vertical migration of methane or toxic vapors. The flow rate for venting
should be high enough to collect all gases being generated, i.e., it should be
at least equal to the gas generation rate. Also, the flow rate should be high
enough to ensure a fairly large radius of influence, so as to minimize the
number of wells needed to vent the area. When venting methane for recovery,
the flow rate must also be low enough so that no excess air is drawn into the
system. Excessive in-flow could (1) reduce the 8TU value of the gas; (2)
cause the landfill to become aerobic, thus inhibiting generation of methane;
and (3) cause spontaneous combustion due to the introduction of oxygen.
Studies of gas production rates at three municipal landfills in Cali-
fornia indicated' a range of from 22 to 45 ml/kg of refuse per day (Constable
et al., 1979). Assuming a bulk density of 250 kg/m3 for ground domestic
garbage (Liptak, 1974), these values convert to a range of 5.5 to 11.25
liters/ m3/day. If the average anaerobic layer of the fill is assumed to be
10 meters, then one can expect 55 to 113 liters of methane per day per square
meter of fill area. This translates to a ventilation requirement of at least
6 to 11 cubic feet per minute per acre. In an actual demonstration for re-
238
-------
covering methane from a municipal landfill, a steady state flow was obtained
at 50 ft3/min with the radius of influence at about 130 feet. This translates
to a ventilation rate of 107 ft3/ min/acre, which means a substantial portion
of excess air was introduced into the system (Carlson, 1977). However, it was
determined that methane production was not inhibited by this amount of air,
and maximum oxygen levels in the gas were only 4 percent.
Diffusion rates of volatile toxics should be calculated to determine
requirements for ventilation of hazardous waste landfills. Some research has
been done on predicting vapor flux through soils. Farmer et al., (1978)
developed an equation for predicting vapor flux through soil based on diffus-
ivity, as shown below.
J = DQ(Pa 1ฐ/3/P2,) (C2 CJ/L
where J = vapor flux from soil surface (ng/cm2/day)
DQ = vapor diffusion coefficient in air (cm2'day )
P = soil air-filled porosity (cm3/cm3)
P^ = total soil porosity (cm3/cm3)
C2 = concentration of the volatilizing material at the
surface of the soil
(ug/1)
C = concentration of the volatilizing material at the
s bottom of the soil
(yg/D
L = soil depth (cm)
The concentration of vapor at the bottom of the soil layer can be deter-
mined from the vapor pressure of the volatile substance, as follows (Fanner et
al., 1978):
Cs = pM/RT
where p = vapor pressure (mmHg)
M = molecular weight of compound (g/mole)
R = molar gas constant (mmHg/ฐK mole)
T = absolute temperature (ฐK)
239
-------
a
z.
et
t/1
u
8
-8
-s
S o
oc
H
0)
o
8
0)
'5.
a
o
g
CO
(Q
o
o
o
s
.o
*
a
o
I
m
a = Ud) nปo
240
-------
FIGURE 6-3
NON-UNIFORM DISTRIBUTION OF METHANE GAS IN LANDFILL
(Source: Constable et al., 1979)
Gas Withdrawal Well,
0.6 m Frozen
Layer
* 13.5m
Suit
Vertical-! 120
HofitonUl-1:240
Piezometers
FIGURE 6-4
VARIATION OF EFFECTIVENESS OF VENTS
(Source: Moore, 1976)
2.5
241
-------
Vapor pressures are available for most organic substances. Diffusion coeffi-
cients are available for a very limited number of substances, and may be
estimated from a known vapor diffusion coefficient from another substance by
the following formula (Farmer et al . , 1978).
wh(jre D - diffusion coefficient of substance A
A
My\ = molecular weight of substance A
DB = diffusion coefficient of substance B
Nig = molecular weight of substance B
The diffusion coefficient increases with temperature according to the
following operation (Farmer et al . , 1978).
D2 = D, (T2/T1)J'2
where T = absolute temperature (ฐK)
Mass flux rates through soil have been determined for a few organic sub-
stances, such as chloroform and hexachlorobenzene (Shen and Tofflemire, 1980).
A rough approximation of flux rates for other volatiles under similar soil
conditions can be calculated as follows (Shen and Tofflemire, 1980).
E = p x (M)2 x E
Pi x (M^2
where E = mass flux
p = vapor pressure
M = molecular weight
i = refers to data for chemicals for which flux
rate is available
As mentioned with the case of methane, the ventilation rate should exceed
the mass flux rate of the vapor for proper control. Ventilation rates for
venting toxics should not be so high as to dilute the vapor stream unneces-
sarily, thereby raising pumping and gas treatment costs.
242
-------
Some information has been developed with respect to withdrawal rates from
vents and head loss (Carlson, 1977). Figure 6-5 shows head versus withdrawal
rates for a gas vent withdrawing at the bottom of a landfill of compacted
refuse. Figure 6-6 shows head loss as a function of distance from wells.
Carlson defines the radius of influence as the distance where the head is -0.1
FIGURE 6-5
DISCHARGE RATING CURVE
(Source: Carlson, 1977)
60
50
General Formula
Hw = 0.00039Q (Q + 133)
Experimental Points
40
Head = H
w
(- Inches of
Water)
30
20
10
100 200
Withdrawal Rate = Q (Ft3/Min)
300
243
-------
FIGURE 6-6
HEAD LOSS CURVE
(Source: Carlson, 1977)
1.0
0.9
0.8
0.7
0.6
0.5
0.4
0.3
0.2
0.1
Head loss curve along the bottom of the landfill
when extracting gas from the bottom of the
landfill
General Formula:
then 77- = 12.5/R1-^ for R > 14
H
1.25.
w
and TT- = 1 - R/25 for 0 < R < 14
where
_h is the head along the bottom of the landfill
at some point distant from the well.
Hw is the head at the well
R is the distance from the well
0.600
0.296
0.178
0.124
0.094
0.075
0.062
h/Hw
0.052
0.045
0.040
0.030
0.024
0.017
0.013
0.010
50 100 200
Distance from Well (Ft.) = R
300
244
-------
inches of water, which is the point at which changes in atmospheric pressure
would predominate. These figures are related to a specific landfill and
should not be interpreted as applying to all sites. However, they should
prove useful in determining rough approximations of well spacing. To deter-
mine vent spacing at a particular site, one should first conduct a series of
test drawdowns at various flow rates while measuring head loss as a function
of distance from the vent.
Pipe wells are usually constructed of 4- or 6-inch PVC perforated pipe.
Other material, such as galvanized iron, may be required if PVC is not compat-
ible with the waste materials. A surrounding layer of gravel pack should be
installed to prevent clogging. The pipe vent should be sealed off from the
atmosphere with a cement or cement/soil grout so that excess air is not intro-
duced into the system, and methane or volatile toxics cannot leak out. Pipe
vents may be installed through' a clay cap, as shown in Figure 6-1, to prevent
emissions of gases or vapors to the atmosphere. Vent wells may also be in-
stalled in a continuous layer of sand overlying the fill, which serves as a
permeable channel for the transportation of gases, as shown in drawing (d) of
Figure 6-1.
6.1.4 Advantages and Disadvantages
Atmospheric vents are an effective means of control when used in situa-
tions where gases freely migrate to a collection point and there is little or
no lateral migration. They are not an effective means of controlling lateral
migration. Forced ventilation is by far the more effective method for con-
trolling migration. If forced ventilation is used, the flow rate can be
increased or decreased as the gas generation or vapor flux rate increases or
decreases. This offers a great deal of flexibility of control inherent in the
system. At a hazardous waste site where volatile toxics are present, the mass
flux rate will decrease with time as the volatiles are dissipated. Thus,
ventilation rates can be reduced with time and operating costs will decrease.
It is expected that gas vents from forced ventilation are more apt to clog
after time, and will need to be replaced. Also, it is expected that more
maintenance will be required for forced ventilation than for passive atmo-
spheric vent systems.
6.1.5 Costs
The cost of installing pipe vents is similar to that of groundwater
monitoring wells, because the same construction materials are used. Installed
costs range from $2.00 to $2.50 per inch diameter per foot of depth for small
diameter vent wells, excluding casing costs (U.S. Department of Interior,
1977). Casing costs for PVC range from $4.50 to $6.50 for 4 inch and 6 inch
casings, respectively (Leazer Pumps and Wells, 1980). Mushroom tops for
ventilation were quoted at $25 each (McCaffray Company, 1980). Costs for
elbows to fabricate a u-shaped top can be found in Table 6-5 in Section 6.4.5.
245
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Also, the cost for a small fan applicable to one pipe vent is given in Table
6-5. The maximum cost for a single forced ventilation pipe vent of 4 inches
diameter, and 30 feet deep, would then be as follows:
Installed cost (max) = ^Ift x 4 in x 30 ft = $ 300
Cost of casing (max) = Iii50 x 30 ft = $ 195
Fan = $ 615
Total Installed Cost =$1,110
6.2 TRENCH VENTS
6.2.1 General Description
Trench vents are constructed by excavating a deep, narrow trench sur-
rounding the waste site or spanning a section of the area perimeter. The
trench is backfilled with gravel, forming a path of least resistance through
which gases migrate upward to the atmosphere or to a collection manifold. By
diverting flow in this manner, the trench vents form a barrier against lateral
migration of methane or toxic vapors. Trench vents are used in combination
with liners to form an effective barrier against gas migration. Trenches can
be open or capped with clay and fitted with collection laterals and riser
pipes venting to the atmosphere or connected to a negative pressure fan or
blower. Also, air can be injected into trench vents to form a blanket that
controls gaseous migration. Various configurations of trench vents are shown
in Figure 6-7.
6.2.2 Application
Trench vents are used primarily to attenuate lateral gas or vapor migra-
tion. They are most successfully applied to sites where the depth of gas
migration is limited by groundwater or an impervious formation. If the trench
can be excavated to this depth, trench vents can offer full containment and
control of gases and vapors.
As with pipe vents, the applicability of different trench vent systems
depends on whether methane generation is occurring or whether the problem at
the site is limited to the control of toxic vapors. Passive open trenches
(drawings (a) and (b) in Figure 6-7) may be applicable to the control of toxic
vapors in an emergency situation where immediate relief is required. They
also can be employed as a permanent control for methane migration; however,
their efficiency is expected to be low (Stone, 1978a). An impervious liner
246
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can be added to the outside of the trench to increase control efficiency (see
Section 6.4). Open trenches are more suitable for sparsely populated areas
where they will not be accidentally covered, planted over, or otherwise
plugged by outsiders (Bowerman, 1980).
Trench vents may be covered over by clay or other impervious materials
and vented either to the atmosphere or to a collection system. Such a system
insures adequate ventilation and prevents infiltration of rainfall into the
vent. Also, an impervious clay layer can be used as an effective seal against
the escape of toxic vapors. Figure 6-3 shows a closed trench with perforated
lateral and riser pipes venting to the atmosphere. Drawing (d) in Figure 6-1
depicts a closed trench with pipe vents installed at intervals and connected
to a negative pressure system. Another type of forced ventilation in a trench
for methane migration control is air injection; in this method, air injected
into the trench by a blower forces the gas or vapor back. This system should
work well in conjunction with pipe vents installed close to the landfill and
inside the circumference of the trench.
6.2.3 Design and Construction
Some important considerations are involved in the proper design and
construction of trench vents.
Open vents are subject to infiltration by rainfall runoff and could
become clogged by solids. Hence, they should not be located in an area of low
relief. It is probably advisable to construct a slope with some of the exca-
vated soil to direct runoff away from the trench as in drawings (a) and (b) of
Figure 6-7. Also, if possible, open trenches should be constructed within
controlled areas to prevent any safety or vandalism problems.
It is important to ensure that the gravel pack in the trench will be
permeable enough, relative to the surrounding strata, to transport the gas
adequately. Also, in areas of relatively high permeability or wherever safe-
guards are needed, a liner should be installed on the outside of the trench to
prevent bypass (see Section 6.3).
In passive closed trench vents, one can ensure good ventilation by proper
design of laterals and risers. One design consisted of 12-inch perforated
corrugated lateral pipe with 8-foot corrugated risers spread at 50-foot inter-
vals (Constable et al., 1979).
In closed trench vents with forced ventilation, one can apply the equa-
tion and design criteria discussed in Section 6.2.3 for the control of methane
and toxic vapors, since gaseous diffusion is omnidirectional. Acreages should
be converted to smaller areal units, which can be applied to the face area at
247
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FIGURE 6-7
DESIGN CONFIGURATIONS OF TRENCH VENTS
Gravel pack
(a) Open Trench
(b) Open Trench with Liner
Gravel pack
Side View Front View
(c) Closed Trench with Lateral and Risers
(d) Induced Draft
(e) Air Injection
248
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the trench. Pipes for trench ventilation can probably be placed at greater
distances, since the trench fill is composed of very permeable material. If a
liner is used, the pipe vents can probably be placed farther apart, since the
normal radial influence of the vents will be channeled even farther along the
trench.
It is important that trenches extend to form a continuous impermeable
seal with the groundwater or an unfractured impervious stratum. If the trench
is not bottom-sealed in this way, gases may migrate under, and completely
bypass, the trench.
6.2.4 Advantages and Disadvantages
Trench vents with passive ventilation have not been found to offer very
effective control of migrating gases. Passive trenches with an impermeable
liner may offer the required degree of effectiveness; however, the installa-
tion of a liner will generally be economical only if the required depth is 10
feet or less (Stone, 1978b). Also, since a liner is subject to tearing or
cracking, a substantial risk of failure is involved, so passive trench vents
with liners are not recommended if the methane problem is substantial. Also,
trench vents may become plugged by soil particles with time, thereby reducing
their long-term effectiveness.
Induced draft systems are by far the most effective and controllable
technology to remedy gas migration problems at waste sites. As they are more
easily maintainable than trench vents with liners, their long-term effective-
ness is expected to be greater.
6.2.5 Costs
The costs of installing trench vents include those for trench excavation
and dewatering, gravel backfill and liners, laterals, and risers, if appli-
cable. Unit costs for most of these items are given in Table 6-1. A trench
vent 20 feet deep, 4 feet wide, and 500 feet long with laterals, risers, and a
synthetic liner is costed as follows:
The total volume of the trench is:
(500 ft)(4 ft)(20 ft) = 40,000 ft3 or 1500 yd3
The surface area of the side of the trench is:
(500 ft)(20 ft) = 10,000 ft2
249
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TABLE 6-1
UNIT COSTS FOR INSTALLATION OF TRENCH UNITS
Trench excavation
Spread excavated
material
Well point
dewatering
Gravel
Sheet piling
Walers, connections,
struts
Lateral with risers
Liner
Assumptions
20'deep, 4' wide, by backhoe
Spread nearby and grade
and cover trench
500' header, 8" diameter,
for one month
Buy and haul from pit 2
miles, backfill with dozer
Pull and salvage
2/3 salvage
12" corrugated polyethy-
lene lateral, 6" PVC
risers, 15' long every 50'
500' lateral
Hypalon (36 mil)
Bracketed with heavy-
weight geotextile fabric
4" gunite layer with mesh
Costs
$l/cubic yard1
$.66/cubic yard1
$75/1inear foot1
$7.60/cubic yard1
$5.70/square foot1
$105/ton2
$6.50/linear foot1
$2.10 - $2.65/
square foot
$4.62 - $8.40/
square foot1
1Godfrey, 1979; Costs are total including contractor overhead and profit.
2Godfrey, 1979; Materials only.
3Camwell Corp., 1980; Assumed 50% installation cost.
"Universal Linings, 1980.
250
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The total cost of trench excavation is as follows:
Trench excavation cost
($l/cubic yard)(1500 cubic yards) = $1500
Spreading cost
($0.66/cubic yard)(1500 cubic yards) = $990
Well point dewataring cost:
Assume installation time of one month
($75/linear feet)(500 feet) = $37,500
Sheet piling cost.
As a rule-of-thumb in the construction business, the total area of sheet
piling needed can be estimated by multiplying the side (2) areas of trench by
a factor of 1.6 to account for the allowance area for the interlocking devices
(Staples, 1980). Thus the total area of sheet piling required is:
(2)(10,000 ft2)(1.6) = 32,000 ft2.
According to ARMCO, the average weight of sheet piling per square foot of wall
is 10 Ibs. (ARMCO, 1980). Thus the total tonnage of the sheet piling can be
calculated as follows:
(32,000 ft2)(10 lbs/ft2) = 320,000 Ibs or 145 tons.
The cost of the sheet piling can then be calculated as follows:
(32,000 ft2)($5.70/ft2) = $182,500
Waler, connection, and strut costs:
As a rule-of-thumb in the construction business, the total
tonnage of walers, connections and struts are 20 percent of the
weight of sheet piling (Staples, 1980). Therefore, the tonnage
required for walers and struts is:
(145 tons)(0.2) = 29 tons.
Therefore, the cost for walers and struts is:
($105/ton)(29 ton) = $3,050
Therefore, the total cost of trench excavation is:
$1500 + $990 + $37,500 + $182,500 + $3,050 = $225,540
251
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In addition to trench excavation costs, costs for the gravel fill, the
lateral and rise pipe, and the liner must be added:
Cost of gravel
(1500 cubic yards)($7.60/cubic yard) = $11,400
Cost of laterals and risers
(500 feet)($6.50/linear feet) = $3,250
Cost of liner (average)
- Hypalon liner bracket with geotextile fabric
Total area = wall area of trench, plus additional area needed
for anchoring.
Wall area of trench = 10,000 ft2
Additional area = (4 ft. x 4 ft) x 500 ft = 4,000 ft2
Total area = 14,000 ft2
Cost = (14,000 ft2)($2.38/ft2) = $33,320
The total cost of the trench vent described above would then be as
follows:
$225,540 + $11,400 + $3,250 + $33,320 = $273,510
It is obvious that costs for an effective trench vent system can be quite
substantial.
6.3 GAS BARRIERS
6.3.1 General Description
Barriers against the migration of gases and vapors are employed in a
number of ways at waste disposal sites, usually in conjunction with other
remedial measures. An effective barrier against gas flow must consist of a
material with low gas permeability. Materials found to prevent gas migration
include compacted clay, concrete slurry walls, gunite, and synthetic liners.
6.3.2 Application
Compacted clay used as a cap to prevent infiltration into waste disposal
sites has also been found to inhibit the vertical migration of methane gas
252
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(Stone, 1978a). This material can then be purposely used for vertical gas
migration control; however, it does not form an ideal barrier because it may
crack upon drying (Thibodeaux, 1979). It may be most applicable for con-
taining methane prior to gas recovery rather than as a remedial measure, since
more stringent control is desirable. Compacted clay is not recommended for
the control of vertical migration of toxic vapors, where a highly impermeable
barrier is required. Effectiveness of a clay barrier for gas and vapor con-
trol may be improved by using it in conjunction with a permeable sand sublayer
and forced ventilation, as shown earlier in Figure 6-l(d). Also, a cover of
topsoil and vegetation may serve to trap moisture and prevent clay layers from
drying out.
Other remedial actions not intended for gas control may incidentally form
effective gas barriers. Grout- curtains and concrete slurry walls, which are
used for groundwater containment, fall under this category. However, no data
were available on gas permeability of these materials, so their potential
effectiveness as gas barriers could not be determined.
Synthetic liners also have been used to prevent the migration of gases
and vapors. As described earlier, they can be used vertically in combination
with trench vents to form an effective barrier (see Section 6.3). They also
can be installed as a top cover the landfill for vertical gas control as well
as infiltration control (see Section 3.1). When installed in trench vents,
liners must extend to form a continuous bottom seal, either with groundwater
or impermeable bedrock. Their applicability is limited to areas where the
depth to groundwater or bedrock is less than the maximum digging depth of a
backhoe, approximately 50 feet (with clamshell attachment).
Synthetic liners used alone to prevent gas migration have not performed
well (Stone, 1978b). Gunite has also been used to form a vertical gas barrier
(Bowerman, 1980). However, its use is restricted to areas where it can be
applied easily, such as in trenches less than 10 feet deep.
6.3.3 Design and Construction Considerations
Two important considerations in constructing gas barriers are selection
of materials impermeable to gases, and maintenance of barrier integrity during
installation. Two synthetic materials exhibit low permeability to gases:
Hypalon, a chlorosulfonated polyethylene; and Neoprene, a well-known synthetic
elastomer. Hypalon's moderate cost and high seam strength make it more desir-
able than high-cost neoprene liners, which must be bound with epoxy and which
form a seal of lower strength (Universal Linings, 1980). Usually a reinforced
liner is recommended, in which one or more layers of nylon or dacron fiber
scrim are added to increase strength.
253
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To maintain liner integrity during installation in trench vents, the
liner must be protected against perforation by stones in the earth wall and by
the gravel fill. For this reason, it is recommended that the liner be sand-
wiched between two layers of heavy weight jute backing, known as geotextile.
When installing liners to control toxic vapors, consideration must be
given to the liners' compatibility with the vapors it may contact. Table 6-2
gives the chemical resistances of Hypalon and Neoprene with various gases and
vapors. It can be seen that many toxic organic chemicals may be incompatible
with these synthetic liners, and other materials may be required for toxic
vapor control.
One possibility for organic vapor control is the installation of a
Teflon-coated fiberglass liner. Such a liner would withstand attack from
almost all chemicals. However, available liner material is only 10 mil thick,
which may prove too light for this application. Also, this type of liner has
never been tested in the field, and since it is available only in 38-inch-wide
sheets, field bonding may present some problems. Finally, this liner is very
expensive.
Liners must be properly anchored when installed. Figure 6-8 shows a
recommended anchoring technique (B. F. Goodrich), a minimum of 3 1/2 feet of
border is required for proper liner anchoring in this technique.
Gunite, a form of sprayed concrete and admixed materials, such as asphal-
tic concrete, may also be suitable for the control of organic vapors. How-
ever, they have higher permeability than the synthetics (if compatible), and
tend to crack under conditions of differential settlement and weathering (JRB;
EMCOM, 1980).
6.3.4 Advantages and Disadvantages
Gas barriers afford fair containment of gases and vapors from landfills,
but must be used in conjunction with other gas control technologies to be
effective. Hypalon synthetic liners are good barriers for use in trench
vents, but are not compatible with many organic vapors. Gunite and asphaltic
concrete may be successful liner materials; however, they are subject to
cracking because of differential settlement and weathering. The cost of
installation of gunite seems prohibitive. For control of vertical migration,
compacted clay offers an economical and effective seal but will crack unless
kept moist. Clay may be an effective barrier for use in combination with
trench vents. Teflon liners, although impermeable and resistant to almost
everything, are expensive and have not been field-tested.
254
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TABLE 6-2
CHEMICAL RESISTANCE CHART (DUPONT)
Vapor type Hypalon* Neoprene1'
Acetic acid (glacial)
Acetone
Benzene
Butane
Butyraldehyde
Carbon tetrachloride
Cyclohexane
Dioctyl phthalate
Ethyl acetate
Ethyl alcohol A
Formic acid
Gasoline
Hydrochloric acid (Cone.)
Hydrocyanic acid
Hydrogen sulfide
Kerosene
Methyl alcohol A
Methyl ene chloride
Methyl Ethyl ketone
Naphtha
Perch! oroethyl ene
Toluene
Trichl oroethyl ene
Xylene
*Cured Sheet
A - Chemical has little or no effect.
B - Chemical has minor to moderate effect.
C - Chemical has severe effect.
X - No data - not likely to be compatible.
X
T
C
A
X
C
C
C
C
(158ฐF)
A
B
-
B
B
X
(158ฐF)
C
C
B
X
C
C
C
C
B
C
A
C
C
C
C
C
A (158ฐF)
A
B
-
A
A
B
A (158ฐF)
C (100ฐF)
C
C
C
C
C
C
Unless otherwise noted, concentrations of aqueous solutions are
saturated.
All ratings are at room temperature, unless specified.
255
-------
FIGURE 6-8
DESIGN OF ANCHOR TRENCH
256
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6.3.5 Costs
The costs for installing different types of liners include those for
materials and installation in the field. For trench vents, two layers of
geotextile backing should be used to protect synthetic liners from holes
caused by rocks and other protuberances. When determining cost estimates for
liners, at least 3 1/2 feet should be added to liner width to allow for proper
surface anchoring. Also, the area required to line the bottom of the trench
should be added to the total area of the liner. Determining liner installa-
tion costs is addressed in Section 6.2.5.
6.4 GAS COLLECTION SYSTEMS
6.4.1 General Description
As discussed earlier, gas vents are frequently connected to a fan or
blower, or to a manifold (with other vents) with a centralized fan or blower.
The fan may then discharge into a gas treatment system, such as a flare or
carbon unit, or into a gas recovery unit. The section between the vent(s) and
the gas treatment or recovery system has been termed the "collection" system.
The components of a collection system include piping (ductwork), fittings,
fans (or blowers), and any flow adjustment or measuring device located between
the vent(s) and the treatment or recovery system.
6.4.2 Application
Gas collection systems are employed whenever forced ventilation of pipe
or trench vents is designated. In their simplest form, they may consist of a
single pipe vent connected to a fan and directly discharging to the atmosphere
or to a treatment device. Such a simple system may be used at a small dis-
posal area. Since the radius of influence of a single forced ventilation pipe
has been found to be as high as 200 to 300 feet, it is conceivable that a
simple vent and fan system could be used on areas as large as 5 to 6 acres
(Carlson, 1977). A simple vent and fan collection system may also be appli-
cable to areas where different wastes have been partitioned, and where it is
undesirable to mix vented gases or vapors, either because of incompatibility
or because of separate treatment requirements. Also, separate fans may be
installed on individual pipe vents in the event of an emergency situation
requiring immediate action; fans can be installed more quickly than a manifold
collection system.
The more commonly specified collection system will consist of a manifold
system in which several pipe vents connect to an exhaust header, which in turn
may be one of several header branches leading into a larger manifold and
ultimately to a large centrifugal fan. Each branch take-off may be supplied
258
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with a butterfly valve for balancing, and a flow meter for checking flow rate.
These more complicated collection systems are applicable to larger disposal
areas (greater than 5 acres) and in situations where methane is to be col-
lected for burnoff in a centralized flare or recovered as a fuel gas, or where
toxics are collected for treatment, as in a well-controlled centralized treat-
ment facility. Gas collection systems are often underground, with access ports
built to valves, moisture traps, and other frequently adjusted features.
6.4.3 Design and Construetion Considerations
The primary consideration in designing a collection system for a single
pipe vent is the proper selection of a fan. As a rough guide in determining
static pressure and flow rates required for disposal site ventilation. Figures
6-5 and 6-6 can be used. As mentioned earlier, a flow rate of 50 ft3/nrin and
a static pressure of 3 inches of water were found to draw gas at a radius of
130 feet in compacted refuse (Carlson, 1977). A small-diameter blower is
required to pull 3 inches of pressure at such low flow rates; however, the
drive unit may require a substantial power rating, due to inefficiency of such
units. One unit found to be applicable had a drive rated at 1/3 horsepower
(Britton, 1980). Since the blower is outside, it should be fully enclosed.
If explosive gases are expected to be present, an explosive-proof motor
housing may be specified. Also, coating the internal blades is required if
corrosive materials, such as hydrogen sulfide, may be present. For proper
selection of a fan, one must use manufacturer's design charts as shown in
Figure 6-9. The flow rate moving through the fan is charted against the total
static pressure of the fan. This static pressure can be related to the static
pressure at the fan inlet by the following equation (Trane Company, 1965):
Fan
Ps '
- P
- P.
t(o) rt(i) - rv(o)
where P<;
P:
P
Static pressure of fan, inches of water
Total pressure of outlet, inches of water
Total pressure at inlet, inches of water
Velocity pressure at outlet, inches of water
Static pressure + velocity pressure
Velocity pressure can be calculated by the equation:
1.2 x 10'
where V
d
P
v
Velocity feet/min
Gas density, lb/ft
Velocity pressure,
inches of water
259
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The velocity at the fan outlet is found on fan charts as shown in Figure
6-9. In the low velocities found in landfill ventilation systems, Pv is
negligible and total inlet pressure is essentially all static pressure. In
situations where the fan is discharging to the atmosphere, static pressure
(gage) of the outlet would be equal to zero.
Besides fan selection, the design of manifold collection systems involves
duct sizing and providing for flow rating and flow balancing in the system.
Normally, noise level is the chief consideration in selection of the design
flow rate near the fan. In a disposal site ventilation system, the design
flow rate near the fan will be specified by the sum of the flow rates of each
vent in the system. The flow rate per vent, along with the required static
pressure for ventilation, must be determined by preliminary ventilation
testing in the area, as described earlier. Because a manifold is involved,
the friction loss in the piping is an important consideration; the designer
must select pipe diameters that enable the fan to handle both the static
pressure required at the vent, and the head loss from friction of the piping
system.
Friction loss is expressed in inches of water per length of pipe; it is
directly related to flow rate and inversely related to pipe diameter. In
other words, as pipe diameter increases and flow rate decreases, the head loss
due to friction decreases, and vice versa. Figure 6-10 provides a method of
solving frictional loss ("pressure drop" in the figure) if one knows the flow
rate, the ambient temperature, the molecular weight of the gas, and the pipe
diameter. Other charts are available; however, they do not take into consid-
eration the ambient temperature, which is important in an outside system.
Besides the friction loss from flow through the pipe, an additional
frictional head loss is incurred whenever the flow is disturbed, such as when
an elbow, tee, valve, constriction, enlargement, or anything other than the
normal pipe wall is encountered. In many cases, the frictional loss from
these fittings can be related to an equivalent length of pipe. For gases
similar to air, the following equation can be used to approximate an equiva-
lent pipe length, where K is a constant depending on the type of fitting.
Values for K can be found in Table 6-4.
}r=55K
Where Le = equivalent length, inches
D = inside pipe diameter, inches
Figure 6-11 provides a direct means of determining head loss (in inches of
water) for elbows and branch connections.
260
-------
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261
-------
I
VD
UJ
D_
ht
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C/0
UJ
D.
ii
*
> aj
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o a>
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cy
^ ^J OOOO O O O O
J....I.. . . 1.1.1.1. I 11 . 1 . I , I
262
-------
TABLE 6-4
K VALUES FOR FITTINGS AND VALVES
Type of fitting or valve
Additional friction loss,
Equivalent number of velocity heads,
45ฐ
45ฐ
90ฐ
ell, standard
ell, long radius
ell, standard
Long radius
Square or mite
180ฐ bend, close return
Tee, standard, along run, branch blanked on
Used as ell, entering run
Used as ell, entering branch
Branching bow
Coupling
Union
Gate valve, open
3/4 open
1/2 open
1/4 open
Diaphragm valve, open
3/4 open
1/2 open
1/4 open
Globe valve, bevel seat, open
1/2 open
Composition seat, open
1/2 open
Plug disk, open
3/4 open
1/2 open
1/4 open
Angle valve, open
Y or blowod valve, open
Plug cock = 5ฐ
10ฐ
20ฐ
40ฐ
60ฐ
Check valve, swing
Disk
Bail
Foot valve
0.35
0.2
0.75
0.45
1.3
1.5
0.4
1.0
1.0
1
0.04
0.04
0.17
0.9
4.5
24.0
2.3
2.6
4.3
21.0
6.0
9.5
6.0
3.5
9.0
13.0
36.0
112.0
2.0
3.0
0.05
0.29
1.36
17.3
118.0
2.0
10.0
70.0
15.0
continued
263
-------
TABLE 6-4 (Continued)
Type of fitting or valve
Water meter, disk
Piston
Rotary (star-shaped disk)
Turbine wheel
Additional friction loss,
equivalent number of velocity heads, K
7.0
15.0
10.0
5.0
Source: Perry, 1973
See Copyright Notice, Page 496.
When piping is sized, the total head loss must be compatible with the
selection of a fan. For example, if the static pressure required at each vent
is 3 inches of water, and a fan is found to pull the required flow rate at a
static pressure of 6 inches of water, then 3 inches of head can be lost as
friction along the length of the manifold. Incidentally, it should be pos-
sible to vary the static pressure of the fan and still be in proximity of the
maximum efficiency line, as shown in Figure 6-9. The longest fan-to-vent
distance in the system should be used to determine the allowable friction loss
per unit vent, keeping in mind that take-offs and other fittings will con-
tribute somewhat to the total head loss.
Once the unit friction loss has been specified, the designer or cost
estimator can work backwards from the fan to the first branch, and then to
succeeding branches, using the unit friction losses and calculated flow rates
to determine pipe diameters (from Figure 6-10).
The following simplified design problem illustrates the calculation
method. Assume a collection system must be designed in which a fan is con-
nected to four pipe vents. Previous testing indicated that a flow rate of 50
ft3/min at 3 inches of static head would have a radius of influence of 130
feet. For sufficient overlap, it was determined that the vent spacing should
be 200 feet. Therefore, a total of 600 feet was required between the first
vent and the fan. The system is pictured in Figure 6-12. An additional 20
feet was added from the last vent to the fan for a total maximum distance of
620 feet.
264
-------
NIW 03d JJ-AJ.IOOT3A HDNVUS
to
UJ
to
LU-
LU
o
LU
-------
FIGURE 6-12
EXAMPLE OF COLLECTION SYSTEM
200'
200'
200'
20'
1
50 ft.3/min
3" H20
50ft.3/min 50ft.3/m
4
50 ft.3/m
The fan size must handle 200 ft3/min at a static pressure of 3 inches of
water, plus the head loss. From Figure 6-9, a size 9 fan can handle about 218
ft3/min at about 6" SP with a power requirement of about 0.36 HP. If we
assume that 1 inch of static pressure is required at the fan discharge (to
push gas through a treatment system), then 2 inches of water is allowable for
head loss. Using the maximum length of pipe, the design friction loss is
0.003 inches of water per foot of pipe. If the ambient temperature is 30ฐC,
and the molecular weight of the gas is assumed to be approximately equal to
air, then Figure 6-10 can be used to determine appropriate pipe diameters as a
function of flow rate. At the section between the fan and the fourth vent,
there will be a total flow rate of 200 ft3/min or 900 Ib/hr, if the gas is
assumed to be air. Thus, from Figure 6-10, a 6-inch pipe would be required.
In the next section, 150 ft3/min, or 675 Ib/hr, would be flowing, and the
recommended pipe diameter also would be about 6 inches. In the next section,
450 Ib/hr would be flowing, and a 5-inch pipe would be required. Finally, in
the last section, 225 Ib/hr of gas would be flowing, and about a 4-inch pipe
would be required. It is important to be conservative and always scale up to
the larger pipe size when between sizes. The above example does not include
friction loss from take-offs and fittings, so in the actual design, the pipe
diameters may be slightly larger, or it may be more economical to have the fan
operate faster, and at a higher power requirement, to pull more static pres-
sure. The system will have to be balanced, since the design basis is uniform
fraction drop rather than insurance of the same static pressure at each branch
take-off (SMACNA, 1967). Balancing the system can be accomplished with the
use of butterfly valves in all vents except the one farthest from the fan.
As gases may be corrosive, it is important to consider the construction
materials. Plastic pipe, such as polyethylene or PVC, is recommended for use
with gases that may contain inorganic corrosives such as hydrogen sulfide or
hydrochloric acid vapors. Galvanized iron may be more suitable for organics,
since plastic pipe may not be compatible with certain organic chemicals.
Another alternative is the use of asbestos cement-bonded pipe, or ABS pipe.
Also, it may be desirable to design the collection system underground. In
this case, such design considerations as corrosion protection, compressive
266
-------
strength of material, and access for system adjustments and monitoring become
important.
6.4.4 Advantages and Disadvantages
The major advantages of a simple single-fan/vent collection system are
its low cost and low maintenance requirement. Its major disadvantage is that
it can be applied only to sites smaller than 5 or 6 acres. Manifolded collec-
tion systems are more costly, more complex in design and construction, and
require more maintenance, such as replacement of balancing valves and periodic
rechecks of balancing.
6.4.5 Costs
Some unit costs have been developed from a consideration of typical
construction materials and sizes found in other landfill ventilation systems.
They are presented in Table 6-5.
The previous above-ground example collection system, as shown in Figure
6-12, has been costed and calculations follow:
Cost of Fan
Fan size must handle 200 ft3/min at a static head of 6 inches. The
second fan listed in Table 6-5 is applicable. Capital and operating
costs can be assumed to be proportional to the flow rate. There-
fore, the following costs have been calculated from the given cost
ranges:
Total installed cost = $1410
Annual operating cost $ 20
Pipe and Fittings
As shown in Figure 6-12, about 620 feet of pipe will be re-
quired for a PVC collection system for four pipe vents. In
addition, four tees will be required to connect the vents.
Also, four balancing valves will be required in the system. To
simplify calculations, it will be assumed that all manifold
components are sized for 6-inch piping diameters:
- Pipe
(620 feet) ($17.15/foot) = $10,630
- Tees
(4) ($52.12/each) = $ 210
- Butterfly valves
(4)($240/each) = $ 960
267
-------
TABLE 6-5
UNIT COSTS OF COMPONENTS FOR GAS COLLECTION SYSTEMS
Fans
Flow rate (cfm)
0-136 @ 3" H20
135-600 @ 8" H20
500-2000 @ 8" H20
1900-6000 9 8" H20
Manhole
Total installed
cost ($)
6152
1400-14653
1900-20503
4175-4665 3
4905
Total installed costs ($/ft)
Annual operating
cost ($)
154
11-69
11-230
34-690
Pipe
PVC5
Asbestos Bonded6
Galvanized Iron5
El bows
PVC7
Galvanized iron5
ABS5'6
Tees
PVC7
Galvanized iron5
ABS5'6
Butterfly valves
Cast Iron5
PVC8
Flow meters5
4"
12.35
1.33
17.90
19.85
31.00
15.50
28.00
48.80
15.50
265.00
145.00
810.00
6"
17.15
1.78
35.00
41.90
70.70
24.86
52.20
111.30
24.86
390.00
240.00
1020.00
8"
2.73
46.00
73.50
130.40
31.50
106.70
217.70
34.50
590.00
380.00
1175.00
10"
4.16
61.00
146.00
190.30
75.87
214.00
366.70
75.70
845.00
500.00
1Belt-driven, utility mount, weather cover, and corrosion-resistant coating
2Britton Company, 1980
3McCaffray Company, 1980
"Cost = Fan Brake HP x 0.746 KW 8.760 hr $0.007
"Godfrey, 1979
6McMahon and Pereira, 1979
7Camwell Corp., 1980
8Plastic Piping Systems, 1980
HP
KW-hr
268
-------
- Flow meter
(1) ($1020) = $ 1,020
The total installed cost for the collection system would be as follows:
Total installed cost = $1410 + $10,630 + $210 +
$960 + $1020 = $14,230
Annual operating costs are made up of power costs, as previously discussed,
plus maintenance costs. It is assumed that costs for maintenance are 4 per-
cent of total installed costs, therefore:
Maintenance costs = (0.4) ($14,230) = $570
Total annual operating costs = $570 + $20 = $590
6.5 GAS TREATMENT SYSTEMS
6.5.1 Gen e ra1 De s cri p t i on
Gases from waste disposal sites frequently contain malodorous and toxic
substances, and thus require treatment before release to the atmosphere.
Several basic types of gas treatment are applicable: adsorption by
carbon; thermal oxidation; and ranking. Carbon adsorption systems are either
non-regenerative or regenerative. Thermal oxidation systems include the use
of a flare or afterburner, depending on the desired control requirements.
Tankers have been used successfully to remove specific types of constituents,
especially as required for gas recovery systems (see next section).
Carbon adsorption systems are composed of a drum, tank, or other con-
tainer that supports a bed of activated carbon. Contaminated gases flow
through the carbon and are adsorbed on the carbon surface due to Van der Waals
attraction and chemical bonding. The adsorbate can be removed or desorbed
from the carbon by raising the temperature, and the carbon can then be regen-
erated. In the actual process, steam is used as the heat source for the
desorption process. The activated carbon can be either regenerated on-site,
by a regeneration system attached to the process, or it can be removed from
the contaminant and be regenerated off-site.
Thermal oxidation systems include flares and afterburners. A flare is
basically an ignition chamber in which an ignitable gas is allowed to combust
in a controlled air environment. The vent gases are ignited by use of a pilot
burner. Smokeless flares have steam added, which converts any unburned heavy
hydrocarbon to carbon dioxide and hydrogen (Liptak, 1974). Smokeless flares
are usually not required for treating vent gases in waste disposal sites,
269
-------
since flares are used mainly for treatment of municipal landfill gases, which
do not contain any hydrocarbons that generate smoke during combustion.
Afterburners are incinerators for gases and vapors in which fuel is
burned to maintain a temperature of up to 1,600ฐF. Gases and vapors passing
through the afterburner decompose in the presence of oxygen to carbon dioxide
and water. Afterburners may incorporate the use of a catalyst, which facili-
tates oxidation at lower temperatures.
The above types of gas treatment systems will be discussed in the sec-
tions that follow.
6.5.2 Application
The specification of a particular type of gas treatment system depends on
three site criteria: (1) type of contaminant; (2) its concentration in the
overall gas stream; and (3) the total amount of gas being vented from the
waste site.
The origin of the gas, and the components it contains, are essential
criteria for the proper selection of a treatment. Gases from municipal land-
fills will be composed essentially of methane, hydrogen sulfide, hydrogen, and
odorous volatiles such as butyric and proprionic acids. Methane is not consi-
dered a pollutant; however, it is vented to prevent lateral underground move-
ment. Many times the accompanying gases and vapors are objectionable, and it
is recommended that the gases be flared off (assuming they are not recovered
as fuel gas). Flaring uses methane as fuel, and thus requires no auxiliary
fuel input. Flaring can be applied to vent gases that are at, or above, the
flammable concentration range. Gases with organic components that are present
below flammability limits, or are not considered flammable, can be incinerated
using fuel to generate the required temperatures. The device used for incin-
eration of gases is usually referred to as an afterburner. Afterburners, if
well designed and properly maintained, can achieve 98 percent destruction of
pollutants (Liptak, 1974). Afterburners should only be used to treat gases
and vapors that can be oxidized at temperatures of 1,600ฐF or less. In cer-
tain cases, where the contaminant is a relatively unstable chemical, a cata-
lytic afterburner can be used with lower oxidation temperatures (1,000ฐF -
1,600ฐF). Generally, these thermal oxidation techniques should be restricted
to those pollutants that will not produce objectionable oxidation products,
such as chloride or fluoride generated from the oxidation of certain pesti-
cides and freons.
Generally, flares and afterburners can be designed to handle a wide range
of gas flow rates. Afterburners are more economical than the other techniques
for gas treatment at high flow rates, or where high concentrations of combust-
ibles are present in the gas stream.
270
-------
Carbon adsorption systems are applicable to the treatment of vent gases
containing large molecular weight organic components. Non-polar organic
compounds are adsorbed best. Some high molecular weight organics are diffi-
cult to desorb from carbon, hence they exclude the use of regenerative sys-
tems. Carbon adsorption is also chosen when very toxic chemicals are present
and the required removal efficiencies are greater than those obtainable with
thermal oxidation. Carbon adsorption systems become expensive when they are
used to control large gas volumes and high organic concentrations.
Carbon acts as a catalyst to oxidize hydrogen sulfide gas in municipal
landfills. The efficiency of hydrogen sulfide adsorption can be increased by
using activated carbon impregnated with metal oxides (Calgon, 1975).
6.5.3 Design and Construction Considerations
In the case of gas treatment systems, the actual design and construction
is generally determined from specifications set by the equipment manufacturer.
However, there are a number of important design and construction considera-
tions with which the engineer working in remedial action technology should be
familiar, to ensure that the equipment is properly suited for its application
at the site, and for cost estimation.
With respect to treatment using air-activated carbon systems, an impor-
tant decision must be made as to whether the systems will be non-regenerative
or regenerative. If carbon is to be regenerated, a further decision must be
made as to whether it is to be regenerated on- or off-site. Non-regenerative
systems should be selected in cases where smaller gas volumes or low organic
concentrations are involved, since the cost of disposal or incineration of
spent carbon can be high. Also, if very toxic chemicals are present, such as
dioxins, it may be best to use the non-regenerative system and dispose of (or
incinerate) the spent carbon, rather than risk using inferior regenerated
carbon with lower removal efficiencies (Liptak, 1974).
Regenerative systems may be more economical when treating larger gas
streams. However, if the pollutant concentration is below 0.1 percent by
volume, carbon regeneration is not economical and a non-regenerative system
should be utilized (Rogoshewski et al., 1978). A regenerative system can in-
corporate the use of an off-site carbon regeneration unit, or regeneration may
be part of the on-site installation. Usually, the off-site regeneration can
be contracted to a vendor dealing with activated carbon (Calgon, 1980). A
higher-quality regenerated carbon can be obtained by using off-site vendor-
controlled regeneration rather than the less efficient on-site combined ad-
sorption/regeneration process.
271
-------
The maximum time period that a carbon bed may operate without a loss of
efficiency can be calculated by using the following equation (Liptak, 1974).
t= SW
MQCV/RT
where t = duration of adsorber, sec
S = fractional retentivity of adsorbent, mass
adsorbate/mass adsorbent
W = mass of adsorbent in the bed, kg
M = molecular weight of adsorbate, kg/gmol
Q = volumetric flowrate of total gas, liters/sec
R = gas constant, 0.082 l-atm/gmolฐK
T = temperature, ฐK
C = volume fraction of vapor in total gas
As shown above, there are a number of factors that affect the maximum oper-
ating time of a carbon adsorption bed. One of these factors, retentivity of
adsorbent, is dependent on the type of substance being adsorbed. Thus, oper-
ating times are expected to be different for different pollutants, all other
factors being constant. Table 6-6 lists several organic compounds with their
retentivities before and after regeneration. Notice that retentivities are
greatly reduced after regeneration, which confirms that regenerative adsorp-
tion systems are less efficient than non-regenerative beds. Also, in Table
6-6 the theoretical saturation rate is given for a number of compounds. In a
carbon adsorption treatment system, solvent breakthrough occurs at a very low
adsorbate/ adsorbent ratio. Thus, an equipment vendor usually uses a conserv-
ative adsorbate/ adsorbent ratio for design purposes. A typical design satu-
ration fraction is about 15 percent (Calgon, 1980).
The above equation and the design saturation fraction can be used to
determine the frequency of bed replacement, and also the amount of carbon that
must be disposed or incinerated. Costs of operating a carbon adsorption
treatment system can thus be determined.
The design of flare and afterburner systems 'is again primarily a function
of the equipment vendor specifications. Flares for landfill gas will usually
be the small ground flare type. Multiple flares connected in series can
handle a large spectrum of gas flow rates. This is important to note, since
gas generation rates will vary according to seasonal temperature, and proper
generation of flares is limited to a narrow range of flow rates (Varec, Inc.,
1980). Flares should be limited to low toxic gases, such as landfill methane.
Afterburners should be used when more toxic gases or vapors are encoun-
tered. It is important that the remedial action engineer consult suppliers
about the suitability of gases not specifically recommended for their equip-
ment. In some cases where corrosive oxidation products are formed, special
272
-------
TABLE 6-6
RETENTIVITY BY ACTIVATED CARBON
Adsorbate
Benzene
Cabron tetrachloride
Gasoline
Methyl alcohol
Isopropyl alcohol
Ethyl acetate
Acetone
Acetic acid
Saturation
weight
factor1
0.45-0.55
0.8-1.1
0.1-0.2
0.5
0.5
0.58
0.51
0.70
Approximate
retentivity,
weight fraction2
0.25
0.45
0.07
0.18
0.20
0.10
0.30
Retentivity
after
regeneration3
0.06
0.20
0.02
0.01
0.01
0.05
0.03
0.03
1Weight of adsorbate per weight of dry carbon.
2Weight of adsorbate per wieght of carbon retained in dry air stream at 20ฐC.
Regeneration with steam at 150ฐC for 1 hour.
(Source: Liptak, 1974)
See Copyright Notice, Page 496.
construction materials may be required, such as Monel* or Hastalloy* alloys.
It is important to confirm that the contaminants in the gas stream can be
oxidized at temperatures of 1600ฐF or less, and at retention times of 0.5 to
1 second, which represent operating ranges of afterburners. It is also im-
portant to consider the cost of fuel needed to maintain proper temperatures
before this treatment plan is selected.
6.5.4 Advantages and Disadvantages
Tables 6-7, 6-8, and 6-9 give a summary of advantages and disadvantages
of carbon adsorption, flares, and afterburners, respectively.
6.5.5 Costs
The capital and operating costs for carbon adsorption, flares, and after-
burners are presented in the following tables and graphs. Capital and oper-
ating costs for non-regenerative carbon adsorption treatment systems were
*These are trademark names.
273
-------
TABLE 6-7
ADVANTAGES AND DISADVANTAGES OF CARBON ADSORPTION GAS TREATMENT SYSTEMS
Advantages
Removes most organic compounds
from gas streams
Very high removal efficiencies
Able to oxidize hydrogen sulfide
Applicable to large gas streams
with low organic concentration
Disadvantages
Will not remove polar
organics efficiently
Not compatible with methyl ethyl
ketone
Requires constant monitoring
system
Not applicable to municipal
landfill gases since methane
is not adsorbed
Does not remove light organics
effectively
Requires either regeneration
or bed replacement
Requires disposal of spent
carbon or desorbed material
TABLE 6-8
ADVANTAGES AND DISADVANTAGES OF FLARE SYSTEMS
Advantages
Applicable to combustible gases
at, or above, the flammability
threshold
Low capital and operating cost
Most applicable to flaring of
low toxicity gases or vapors,
such as those from municipal
landfills
Disadvantages
Not applicable to dilute gas
streams below flammability
threshold
Not as efficient as inciner-
ation or carbon adsorption
Narrow range of flow rates
results in requirement for
more than one flare
274
-------
TABLE 6-9
ADVANTAGES AND DISADVANTAGES OF AFTERBURNERS
Advantages
High removal efficiency
Able to destroy almost all
organics
Disadvantages
Large fuel cost
Expensive for small gas
streams
May not be able to destroy
organics that will not oxi-
dize in less than 1 second
at temperatures below 1600ฐF
May form corrosive oxidation
products and may, therefore,
require expensive construction
materials
May generate smoke if heavy
unsaturated hydrocarbons are
present
developed from vendor information on four different flow rates, and are pre-
sented in Figure 6-13. Capital and operating costs were based on treating a
stream containing 50 ppm trichloroethylene. The operating costs in Figure
6-13 include costs for equipment maintenance, power, make-up carbon, and
hauling and incineration of spent-carbon. Maintenance costs were assumed to
be 4 percent of capital equipment costs (Perry, 1973). Power costs were
assumed to be 7 cents per kilowatt-hour. The costs for make-up carbon were
assumed to be $1.20 per Ib (Calgon, 1980). Disposal costs were based on a 20
percent adsorbate pick-up ratio, hauling a distance of 400 miles, and disposal
by incineration at $0.25 per pound (Rollins Environmental Services, 1980).
Figure 6-13 can only be used as a rough approximation for treatment of a
vent gas, since the information was developed for a stream having a specific
pollutant at a specific concentration. It will be necessary to work with
vendors to determine the design and costs of a non-regenerative carbon unit
for a particular application.
275
-------
FIGURE 6-13
CAPITAL AND OPERATING COSTS FOR NON-REGENERATIVE CARBON ADSORPTION SYSTEMS
TREATING VENT GAS CONTAINING 50 ppm TRICHLORETHYLENE
(Source: Calgon, 1980)
90-
_ 80"
In
jo
2 70H
&
I 60-
| 50-
8 40-
1
ง 30-
o 20-
10-
Total
Installed
Annual
Operating
rIOOO
-900
-800
-700
-600
-500
400
300
-200
Moo
C
0)
j+
(Q
O
8
sr
o
I
a.
C/3
O
g.
5T
01 2345678
Flow Rate (Thousand Cubic Feet Per Minute)
10
276
-------
Capital costs for regenerative carbon systems are higher. The installed
cost for a 1,700 ft3/nin unit was quoted at approximately $140,000 (Baron-
Blakeslee, 1980). This high cost is due to the extra equipment needed to
regenerate the carbon, plus special construction materials needed to prevent
corrosion at regeneration temperatures. Operating costs will be much less
than non-regenerative systems, since the high cost of carbon make-up and
disposal is not involved. Annual operating costs have been estimated to be
roughly $12,000 per year for the 1,700 ft3/min unit (Baron-Blakeslee, 1980).
Costs for flare systems have also been developed for a number of flow
rates. Total costs are given in Figure 6-14, and include material costs, plus
25 percent for installation, contractor overhead, and profit. Operating costs
are assumed to be negligible.
Installed costs for afterburning vary widely, and are presently estimated
to range from $5 to $20 per standard cubic foot per minute (Liptak, 1974).
The high end of the range is more applicable to the treatment of vent gases
from waste disposal sites, since the contaminants in the vent gas are likely
to be corrosive, thus requiring special construction materials. Annual oper-
ating costs for an afterburner with heat recovery, have been estimated to
range from $10 to $40 per cubic foot per minute (Combustion Engineering,
1980). Catalytic incinerators are usually associated with lower costs for
operation as they are able to use the vent gas as a fuel source.
6.6 GAS RECOVERY
As mentioned earlier, it may be possible to recover methane gas and
possibly other gases from landfills. Gas recovery is not a remedial action,
per se, but it may be included as part of a gas migration control plan, and
may partially offset the initial capital investment for gas control in the
long term. It is most applicable to landfills with a minimum depth of 30 to
40 feet. Otherwise, withdrawal rates must be limited to prevent air infiltra-
tion, and the economics of recovery may suffer (James and Rhyne, 1979).
Landfill gas from municipal disposal sites has been reported to have a
heating value of 450 to 500 BTU per standard cubic foot as compared to 1,000
BTU per standard cubic foot for natural gas. If the gas is to be recovered to
the point of pipeline quality, noxious components and non-combustibles must be
removed, that is, the gas must be sweetened and upgraded. Alternatively, the
gas can be used as is as a low grade fuel, or it can be blended with natural
gas to form a product of slightly lower quality.
The Palos Verde Gas Recovery Project, sponsored by Reserve Synthetic
Fuels, used a molecular sieve treatment facility to sweeten and upgrade and
landfill gas from 500 to 1000 BTU per standard cubic foot (James and Rhyne,
1979). It was reported that severe corrosion occurred in the recovery system
277
-------
(A
JS
"5
Q
T3
I
O
.c
v>
O
O
CD
1
|
FIGURE 6-14
TOTAL INSTALLED COST FOR SMALL GROUND FLARES
(Source: Varec, Inc., 1980)
5.0
4.5
4.0
3.5
3.0
2.5
2.0
1.5
1.0
.5
0
10
15
20 25 30 35 40
Gas Flow Rate
(Thousands of Cubic Feet per Hour)
278
-------
due to the presence of chlorinated hydrocarbons. This was corrected by using
corrosion-resistant nickel alloys and pretreating with a material to selec-
tively adsorb the corrosives.
Various upgrading schemes are available, from simple dehydration to a
combined dehydration, carbon dioxide, and nitrogen removal system. The more
contaminants removed, the greater the heating value of the recovered gas and
the greater the production cost. Another gas recovery project at the muni-
cipal landfill at Mountain View, California, plans to upgrade gas from 450
BTU/scf to 700 BTU/scf and blend this with pipeline natural gas (James and
Rhyne, 1979). In the process, dehydration, carbon dioxide removal, and molec-
ular sieves will be used. Costs for a 1-million cubic foot per day recovery
plant have been estimated, based on an overall efficiency of 70 percent, 12
percent cost of capital, a 10-year life, and a salvage value of 30 percent
(James and Rhyne, 1979). These costs are presented in Table 6-10, which also
include costs for the gas venting and collection system.
TABLE 6-10
COSTS FOR LANDFILL GAS RECOVERY AT MOUNTAIN VIEW, CALIFORNIA1
Molecular sieves
Compression
Wells and gathering system
Total installed cost
Equipment
cost
$245,000
200,000
Installed
Cost
$368,000
350,000
70,000
$788,000
Yearly costs
Maintenance
Manpower
Fixed charges
Feedstock costs
Total
Energy output, MMBTU/yr
Energy costs, $/MMBTU
$/Year
25,000
30,000
195,000
22,320
272,320
97,650
$2.79
1 Based on a flow of 1 million ft3/day
(Source: James and Rhyne, 1979)
279
-------
REFERENCES
Aladdin Heating Corporation. 1980. Industrial Tans Series 2000. San Leandro,
CA. Bulletin 462-C
ARMCO, Inc., Baltimore, MD. April 1980. Personal communication with P. Le.
Baron-Blakeslee Corp., Bayshore, NY. April 1980. Personal communication with
P. Rogoshewski.
B.F. Goodrich, Inc. 1980. Information Bulletin EL-1.5-775. B.F. Goodrich
Environmental Products.
Bowerman, F. Engineering Science, Inc. Arcadia, CA. March 1980. Personal
communication with P. Rogoshewski.
Britton Company, Norfolk, VA. April 1980. Personal communication with P.
Rogoshewski.
Bureau of Reclamation. 1977. Groundwater manual. U.S. Department of Inte-
rior, Denver, CO.
Calgon Corp. 1975. Air purification with granular activated carbon. Pitts-
burgh, PA.
Calgon Corp., Pittsburgh, PA. March 1980. Personal communication with P.
Rogoshewski.
Camwell Corp., Baltimore, MD. April 1980. Personal communication with P.
Rogoshewski.
Carlson, J. 1977. Recovery of landfill gas at Mountain View: Engineering
site study. U.S. Environmental Protection Agency, Washington, D.C.
EPA/530/SW-587d.
Combustion Engineering, Wellsville, NY. April 1980. Personal communication
with P. Rogoshewski.
Constable, T., G. Farquhar, and B.N. Clement. 1979. Gas migration and model-
ing- In: Proceedings of the 5th annual research symposium on municipal
solid waste: land disposal. U.S. Environmental Protection Agency,
Washington, D.C. EPA-600-9-79-023a.
DuPont de Nemours & Co., Inc. 1980. Flexible membranes for pond and reser-
voir liners and covers. Wilmington, DE.
Farmer, W., M. Yang, and J. Lefey. 1978. Land disposal of hexachlorobenzene
wastes: controlling vapor movement in soils. Land disposal of hazardous
wastes. Municipal Environmental Research Laboratory. Cincinnati, OH.
EPA-600/9-78-016.
280
-------
Godfrey, R. (ed.) 1979. Building construction cost data, 1980. Kingston, MA:
Robert Snow Means Company, Inc.
James, C., and C. Rhyne. 1979. Methane production, recovery, and utilization
from landfills. Recovery, Processing, and Utilization of Gas from Sani-
tary Landfills. U.S. Environmental Protection Agency, Cincinnati, OH.
EPA-600-2-79-001.
JRB Associates, and EMCON Associates. 1980. Assessment of alternatives for
upgrading Navy solid waste disposal sites: draft final report. McLean,
VA.
Leazer Pumps and Wells, Remington, VA. April 1980. Personal communication
with K. Wagner.
Liptak, B.G. (ed.) 1974. Environmental engineers' handbook. Vol. 1: Air
pollution; vol. 3: Land Pollution. Radnor, PA: Chilton Book Co.
Lutton, R., G. Regan, and L. Jones. 1979. Design and construction of covers
for solid waste landfills. U.S. Environmental Protection Agency, Cin-
cinnati, OH, EPA-600/2-79-165.
McCaffray Company, Batimore, MD. April 1980. Personal communication with
P. Rogoshewski.
McMahon, L., and P. Pereira (eds.). 1979. 1980 Dodge guide to public works
and heavy construction costs. New York: McGraw-Hill Information Systems.
Moore, C.A. 1976. Theoretical approach to gas movement through soils. Gas
and leachate from landfills, formation, collection. U.S. Environmental
Protection Agency, Cincinnati, OH. EPA-600-19-76-004.
Moore, C.O., and I. Rai. 1977. Design criteria for gas migration control
devices. Mangement of gas and leachate in landfills. U.S. Environ-
mental Protection Agency, Cincinnati, OH. EPA-600/9-77-026.
Perry, R., and C. Chilton. 1973. Chemical engineer's handbook, 5th ed.
New York: McGraw-Hill, Inc.
Plastic Piping Systems, Inc., Columbia, MD. April 1980. Personal communica-
tion with P. Rogoshewski.
Rogoshewski, P., P. Koester, C. Koralek, R. Wetzel, and K. Shields. 1978.
Standards of practice manual for the solvent refined coal liquefaction
process. U.S. Environmental Protection Agency, Washington, D.C. EPA-
600-7-78-091.
Rollins Environmental Services, Bridgeport, NJ. April 1980. Personal com-
munication with P. Rogoshewski.
281
-------
Shen, T., and T. Tofflemire. 1980. Air pollution aspects of land disposal of
toxic waste. Hazardous materials risk assessment, disposal and manage-
ment. Journal of Environmental Engineering Division, ASCE 106(EEI):
211-226.
SMACNA. 1967. Manual for the balancing and adjustment of air distribution
systems. Sheet Metal and Air Conditioning Contractors National Associa-
tion, Inc., Vienna, VA.
Staples, G., JRB Associates, McLean, VA. April 1980. Personal communication
with P. Le.
Stone, R. 1978a. Preventing the underground movement of methane from sanitary
landfills. Civil Engineering. January.
Stone, R. 1978b. Reclamation of landfill methane and control of off-site mi-
gration hazards. Solid wastes management/refuse removal journal. July.
Thibodeaux, L. 1979. Estimating the air emissions of chemicals from hazardous
waste landfills. American Institute of Chemical Engineers annual meet-
ing, San Francisco, CA.
Trane Company. 1965. Trane air conditioning manual. LaCrosse, WI.
Universal Linings, Inc., Philadelphia, PA. 1980. Personal communication be-
tween D. Small and P. Rogoshewski.
U.S. Department of Interior. 1977. Groundwater manual. Bureau of Reclama-
tion. Denver, CO.
Varec, Inc., Cherry Hill, NJ. April 1980. Personal communication with P.
Rogoshewski.
282
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7.0 DIRECT TREATMENT METHODS
This chapter discusses the direct treatment of hazardous wastes for
purposes of alleviating environmental or health risks associated with these
wastes. The single most important advantage of direct treatment methods as
compared to other methods discussed in this document is that direct treatment
affords removal of pollution at the source, while other methods simply con-
tain. In most cases, these techniques can be considered long-term permanent
solutions. Direct treatment of hazardous wastes involves one or more of the
following approaches:
Physical removal of the wastes to a better engineered or environmen-
tally less sensitive area (excavation, hydraulic dredging, and land
disposal);
Physical removal followed by waste stabilization (solidification and
encapsulation);
Waste destruction (incineration, wet air oxidation, molten salt,
macrowave plasma detoxification, and microbial degradation);
Chemical waste treatment within the site (neutralization and solution
mining).
Many of these direct treatment methods are not fully developed and the
applications and process reliability are not well demonstrated. Use of these
techniques for waste treatment will require considerable pilot plant work.
Others, such as excavation and land disposal, are widely used, although Re-
source Conservation and Recovery Act (RCRA) requirements will require signifi-
cantly greater degrees of monitoring and controls for land disposal tech-
niques. In addition, the combined costs of excavation (or dredging) with
subsequent treatment can be exorbitant if a large volume of wastes is in-
volved.
This chapter addresses the current state of technology and applicability
of each of the direct treatment methods.
283
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7.1 EXCAVATION
7.1.1 General Description and Applications
Excavation is a common technique used in earth-moving projects. It is
widely used to move solid and thickened sludge materials; however, it is not
well suited for removal of material with a low solids content. Where off-site
treatment methods are to be used for landfilled wastes, excavation and trans-
portation of the waste material will be required.
7.1.2 Design and Construction Considerations
Important factors that should be considered before excavation of a refuse
site can begin are listed below.
1. The density of solid waste in a landfill. This is dependent on the
composition of the waste and the degree of compaction achieved.
Average densities of landfilled wastes are reported to be from 800
to 1,000 lb/yd3 with moderate compaction (Brunner and Keller, 1972).
2. The settlement of the fil 1. As a result of decomposition of the
waste and the addition of new waste material, settling of fine
particles into voids between solid matter can occur.
3. The bearing capacity of the fill. The bearing capacity is defined
as the ability to support foundations (and heavy equipment). Al-
though the bearing capacity of the fill can vary from one refuse
site to another, average values ranging from 500 to 800 lb/ft2 have
been reported (EPA, 1978).
4. Decomposition rate of the waste. Most of the materials present in a
refuse site will decompose. Decomposition of organic waste under
anaerobic conditions predominantly occurs at the base of the site,
and can generate highly corrosive organic acids and toxic gases such
as methane or hydrogen sulfide.
5. Packaging of the waste. Packaging of waste in barrels and tanks may
present additional removal problems.
Excavation can be achieved by mechanical means. Typical excavation
equipment includes draglines and backhoes. This equipment is discussed below.
284
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7.1.2.1 The Dragline
A dragline excavator is a crane unit with a drag bucket connected by
cable to the boom. The bucket is filled by scraping it along the top layer of
soil toward the machine by a drag cable. The dragline can operate below and
beyond the end of the boom. Figure 7-1 shows a dragline unit. The various
working dimensions of draglines for various bucket sizes are shown in Table
7-1.
Maximum digging depth of a dragline is approximately equal to half the
length of the boom, while digging reach is slightly greater than the length of
the boom (EPA, 1978). Drag buckets come in light, medium, and heavy weight.
The use of a specific weight of bucket depends on the type of material to be
excavated.
The maximum practical digging depths for various lengths of boom are
shown in Figure 7-2. As shown in this figure, the recommended slope for
dragline is 45ฐ. With a 70 foot boom, the maximum digging depth is approxi-
mately 60 feet. Draglines are very suitable for excavating large land areas
with loosely compacted soil. Excavation with draglines of landfill sites
containing explosive materials or very toxic chemicals is unsafe.
The theoretical hourly production rate in cubic yards for operating in
different types of soil with various bucket sizes is shown in Table 7-2. The
figure presented in this table is estimated on the basis of 83 percent job
efficiency, 100 percent operator efficiency, 90 percent swing of boom, and 50
working minutes per hour (Godfrey, 1976). The actual production is estimated
at 50 percent of the theoretical values. As shown in this table, the optimum
digging depth of any size bucket is less than 14 feet.
Advantages, disadvantages and costs for this excavation method are given
in Section 7.1.3. and 7.1.4.
7.1.2.2 The Backhoe
The backhoe unit is a boom or dipper stick with a hoe dipper attached to
the outer end. The unit may be mounted on either crane-type or tractor equip-
ment. Figure 7-3 shows a typical design of a backhoe.
The digging dimensions of a backhoe are shown in Figure 7-4. The maximum
reach and depth for various sized hoes is shown in Table 7-3. As shown in
this figure, the largest backhoe will dig to a maximum depth of about 30 feet.
Deeper digging depth can be achieved by attaching long arms to one-piece
booms, or by adjusting the boom angle on two piece booms (EPA, 1978).
285
-------
FIGURE 7-1
A DRAGLINE
(Source: EPA, 1978)
286
-------
TABLE 7-1
TYPICAL DRAGLINE EXCAVATOR DIMENSIONS
Bucket size in cubic yards (CY)
Item
Dumping radius, ft
Dumping height, ft
Maximum digging depth, ft
Digging reach, ft
Boom Length, ft
Bucket length, ft
3/4
30
17
12
40
35
11.5
1
35
17
16
45
40
14.
1-1/4
36
17
19
46
40
67 11.83
1-3/4
45
25
24
57
50
13.08
2
53
28
30
68
60
14
Note that these values apply to operation of the oxcavator with its boom
at a 40ฐ angle to the horizon.
Source: EPA, 1978
Another hydraulic backhoe called the Gradall can be used to excavate,
backfill, and grade. It has an extensional boom which can be extended up to
100 feet or retracted for close work.
The theoretical hourly production rate for a backhoe for a 15 foot-deep
cut in different types of soil with various bucket sizes is shown in Table
7-4. The bases for these estimates are the same as those presented for the
dragline production.
To achieve deeper digger depth (i.e., deeper than 30 feet), clamshell
equipment must be used. A clamshell bucket is attached to a crane by cables.
A clamshell excavator can reach a digging depth of 50 feet or more. Figure
7-5 illustrates a clamshell bucket.
Regardless of the type of excavation equipment used, safety considera-
tions must be taken into account when the excavated sites contain toxic sub-
stances or explosive materials. The safety measures are discussed in Appendix
A.
287
-------
FIGURE 7-2
TYPICAL WORKING RANGES FOR CRANES AND DRAGLINES
(Source: Stubbs, 1959)
See Copyright Notice, Page 496
Adjustable ]ibs for
light lifts only.
Max. lengths shown
Standard crane boom.
Lengths available
\Droqline
range
Clamshell bucket
5 /stockpile widths
\]\// Allow 10' to 15' clam
S^ height above pile
XI 'XI l\
Recommended boomS
length for draglines
of sizes indicated, p
'x'S'o- fsMOVsO^Stockpile dia.
30 I 40 I 50 | 60 | 70 80 | 90
Distance from t rotation in feet
Max. practical dragline depth
with 30 boom at low angle
288
-------
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290
-------
FIGURE 7-4
HOE DIGGING RANGES
(Source: Stubbs, 1959)
See Copyright Notice, Page 496
291
-------
TABLE 7-3
MAXIMUM REACH AND DEPTH FOR VARIOUS SIZED HOES
(MAXIMUM DIGGING ANGLE OF 45ฐ)
Hoe size
(CY)
1
1-1/2
2
3-1/2
Source: EPA, 1
THEORETICAL
Moist loam,
sandy clay
Sand and
gravel
Common earth
Clay, hard
dense
Max. reach
of boom
(ft)
35
42
49
70
978
TABLE 7-4
HOURLY PRODUCTION OF A
Bucket
1 1-1/2 2 2-1
85 125 175 220
80 120 160 205
70 105 150 190
65 100 130 170
Max. depth
excav.
(ft)
22
25
30
45
HYDRAULIC BACKHOE
size (CY)
12 3 3-1/2
275 330
260 310
240 280
210 255
4
380
365
330
300
Source: EPA, 1978
292
-------
FIGURE 7-5
THE CLAMSHELL BUCKET
(Source: Carson, 1961)
See Copyright Notice, Page 497
Closing Line
7.1.3 Advantages and Disadvantages
Advantages and disadvantages of the excavation technique using dragline
and backhoe are shown in Table 7-5.
7.1.4 Costs
Unit costs for excavation techniques are shown in Table 7-6.
293
-------
TABLE 7-5
ADVANTAGES AND DISADVANTAGES OF DIFFERENT TYPES OF EXCAVATORS
Advantages
Dragline
Readily available
Applicable for excavation of
large area
Easy to operate
Disadvantages
Backhoe
Readily available
Easy to control the bucket
and thus control width and
depth of excavation
Can excavate hard and com-
pacted material
More powerful digging action
than dragline
Can be used to landfill and
compact
Difficult to spot
bucket for scraping
and dumping
Cannot backfill or
compact
Not applicable for
digging depth more
than 30 ft
Not applicable for dig-
ging depth over 30 ft
Cannot reach further
than 100 ft
The excavation cost of a refuse site can be estimated as follows, assum-
ing that the dimensions of the site are 30 feet deep, 1,000 feet long, and 750
feet wide, then the total volume of waste excavated would be:
(30 ft) (1000 ft)(750 ft) = 2.25 x 107 ft3 or 8.3 x 105 yd3
Using a dragline equipped with a 1.5 yd3 bucket, it would cost
$1.39/yd3 (Table 7-6). Thus the excavation cost amounts to:
(8.3 x 105 yd3)($1.39/yd3) = $1,160,000
294
-------
Using a backhoe equipped with a 1.5 yd3 bucket, the total
excavation cost would be:
(8.3 x TO5 yd3)($1.51/yd3) = $1,250,000
Using a clamshell unit with a 1 yd bucket, it would cost:
(8.3 x 10s yd) ($2.32/yd3) = $1,930,000
7.2 HYDRAULIC DREDGING
7.2.1 Description and Applications
For unlined surface impoundments containing hazardous wastes in liquid,
slurry, or semi-solid (sludge) form, it may be necessary to remove the wastes
by dredging. Several types of dredges are commonly used, including hydraulic,
pneumatic, and mechanical dredges (the latter of which include clamshells,
backhoes, and buckets, previously described in Section 7.1). This section
addresses hydraulic dredges.
The dredged wastes can be pumped to special treatment facilities or
transported to acceptable land disposal sites located nearby. The dredged
impoundment can be bottom-lined and, if necessary, reconstructed to make it
suitable for accepting industrial hazardous wastes. If the impoundment is
located in a totally unacceptable area (e.g., wetlands or floodplain), it may
be filled in and never reused.
Surface impoundments for which hydraulic dredging may be prescribed
include industrial storage, treatment, and disposal ponds -- holding ponds,
settling ponds, aeration lagoons, sludge or slurry pits, dewatering basins,
etc. These surface impoundments may be natural depressions, artificial exca-
vations, or diked containment areas. If the impoundments are outlined or if
the liner is ruptured or torn, and the contained wastes are hazardous in
nature, the potential of groundwater contamination by hazardous leachate may
exist. Available techniques for hydraulic dredging of surface impoundments
include centrifugal pumping systems and portable hydraulic pipeline dredges.
Hydraulic dredging serves the same basic function as mechanical excavation:
removal of hazardous waste materials from improperly constructed and improp-
erly sited disposal sites for offsite treatment or disposal.
Centrifugal pumping systems utilize specially designed centrifugal pumps
that chop and cut heavy, viscous materials as pump suction occurs. The
special chopper-impeller devices within these pumps allow high-volume handling
of heavy sludges and other solids mixtures without the use of separate augers
or cutters (Vaughan, 1980). These submersible pumps are installed on
floating, winch-driven platforms that can quickly and economically dredge
295
-------
TABLE 7-6
UNIT COST FOR EXCAVATION1
Excavation using
dragline
Excavation using
backhoe
Excavating using
clamshell
Assumption
3/4 yd3 bucket, 90ฐ swing,
rating 35/hr
1.5 yd3 bucket, 90ฐ swing,
rating 65 yd3/yr
hydraulic, crawler mounted
- 1 yd3 bucket, rating 45 yd3/hr
Cost
$2.06/yd3
$1.39/yd3
$1.78/yd:
- i jru UU<~NCI, laumy tJ _yu /nr .pi. / o/jru
- 1.5 yd3 bucket, rating 60 yd3/hr $1.51/yd3
- 2 yd3 bucket, rating 75 yd3/hr $1.59/yd3
- 3.5 yd3 bucket, rating 150 yd3/hr $1.16/yd3
wheel mounted
- 0.5 yd3 bucket, rating 20 yd3/hr $3.24/yd3
- 0.75 yd3 bucket, rating 30 yd3/hr $2.48/yd3
0.5 yd3 bucket, rating 20 yd3/hr
1 yd3 bucket, rating 35 yd3/hr
$3.47/yd3
$2.32/yd3
'Godfrey, 1979.
small pits, ponds, or lagoons. The Vaughan Company's "Lagoon Pumper" (Figure
7-6) is 8 feet wide, 14 feet long, approximately 7 feet high, and weighs about
3 tons; its 100-horsepower motor can pump up to 1,200 gpm of 15 to 20 percent
solids from depths up to 15 feet (Vaughan, 1980).
National Car Rental systems manufactures a similar unit, the Mud Cat
model SP-810, that utilizes a submerged pump mounted directly behind a hori-
zontal auger to handle highly viscous chemical sludges or thick, muddy sedi-
ments. The SP-810's centrifugal pump is hydraulically driven, has a variable
speed capability, and can pump from a maximum depth of 10 feet at reates up to
1,000 gpm. As with the Vaughan unit, the pump can be physically buried into
homogeneous settled sludges for high solids/low dilution pumping. The Mud Cat
unit also has a detachable mud shield for greater suction efficiency and
turbidity control. It is equipped with a depth gage to monitor cutting depth,
and is driven along a cable by a reversible winch (National Car Rental System,
Inc., 1980).
296
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FIGURE 7-6
PORTABLE CENTRIFUGAL PUMP SYSTEM FOR LAGOON DREDGING
(Source: Vaughan, 1980)
s'' >'~~~. ^ปป.'!*%r*r '
297
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These centrifugal pumping systems are relatively small, portable units
that may be ideal for small impoundment dredging where depths are less than 15
feet, where highly viscous materials such as consolidated chemical sludges are
present, and where direct truck loading of dredged material without dewatering
is desirable. For larger impoundments that require greater operational
depths, higher volume removal, higher pumping rates, and greater pumping
distances, larger (but still portable) dredge vessels are required.
Cutterhead pipeline dredges are widely used in the United States; they
are the basic tool of the private dredging industry (Gren, 1976). Cutterhead
dredges loosen and pick up bottom material and water, and discharge the mix-
ture through a float-supported spoil pipeline to off-site treatment or dis-
posal areas. Portable cutterhead pipeline dredges are those small enough and
light enough to be easily assembled and dismantled, and economically trans-
ported to inland dredging sites such as surface impoundments. They are gen-
erally from 25 to 60 feet in length, with pump discharge diameters from 6 to
20 inches. There are two basic types of portable cutterhead dredges: the
larger dredges that operate by swinging about on stern-mounted spuds and use
standard basket cutters (Figure 7-7); and the smaller specialty dredges that
use a horizontal auger assembly and move only by cable and winch.
For dredging surface impoundments greater than 20 feet deep, the standard
cutterhead dredge (Figure 7-8) is required. This type of dredge moves forward
by pivoting about on two rear-mounted spuds (heavy vertical posts), which are
alternately anchored and raised. The swing is controlled by winches pulling
on cables anchored forward of the dredge (Figure 7-9). The rotating cutter on
the end of the dredge ladder physically excavates material ranging from light
silts to consolidated sediments or sludge, cutting a channel of variable width
(depending on ladder length) as the dredge advances. For deep surface im-
poundments containing only soft, unconsolidated bottom materials, a variation
of the standard cutterhead dredgethe suction pipeline dredgecan be used to
dredge the impoundment. Suction dredges are not equipped with cutterheads, or
they simply operate without cutterhead rotation; they merely suck the material
and dilution water off the bottom and, like most dredges, discharge the mix-
ture through a stern-mounted pipeline leading to a spoil disposal area.
Ellicott Machine Corporation and the Dixie Dredge Corporation manufacture
a diverse line of portable cutterhead dredges that can pump as much as 1,000
cubic yards per hour of solids (based on 10 to 20 percent solids by volume).
Ellicott's "Dragon" series of portable dredges operate at digging depths from
17 to 33 feet, with ladder lengths variable from 23 to 42.5 feet (Ellicott
Machine Corporation, 1969).
For hydraulic dredging of surface impoundments less than 20 feet deep,
where access for the larger portable cutterhead dredges may be difficult, and
where turbidity (material re-suspension) is a problem, small cutterhead d
redges with horizontal auger cutters may be effective. National Car Rental's
Mud Cat MC-915 (Figure 7-10) can remove sediment in a 9-foot-wide swath, 18
298
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FIGURE 7-7A
STANDARD CUTTER ASSEMBLY: SPIRAL BASKET CUTTER
(Source: Huston, 1976)
Ladder Head
Cutter
*
"T^wssss?^
Ladder
Dredged Bottom
FIGURE 7-?B
STANDARD CUTTER ASSEMBLY: SPIRAL BASKET CUTTER
(Source: Linsley and Franzini, 1979
See Copyright Notice, Page 497
299
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Stern connection
Floating Imev^
FIGURE 7-8
THE STANDARD CUTTERHEAD DREDGE VESSEL
(Source: Huston, 1976)
-Gantry
Engine house
A frame
Main
I Mam engine -*f'
Pontoon -s l [
Spud well -^
Spud-
Hull
Dredged bottom
Ladder'
ฅ
FIGURE 7-9
STANDARD CUTTERHEAD DREDGE OPERATION
(Source: Linsley and Franzini. 1979)
See Copyright Notice, Page 497
Anchor
Spud up
xv^/ r~ Spud down for
first cut
Spoil line
Cutter
Anchor
Cable ^ ^ ^- Second cut
Floats '=.
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inches deep, at depths as great as 15 feet and as shallow as 21 inches. The
horizontal auger assembly can be tilted left and right to a 45 degree angle to
accommodate sloping sides of impoundments. With an auger wheel attachment,
the Mud Cat can dredge in lined impoundments without damaging the liner. Two
people are required to operate the 30-foot-long machine, which moves by winch-
ing itself in either direction along a taut, fixed cable at average operating
speeds of 8 to 12 feet per minute. The Mud Cat has a retractable mud shield,
which surrounds the cutter head, entrapping suspended material, increasing
suction efficiency, and minimizing turbidity. The Mud Cat can discharge
approximately 1,500 gpm of slurry with 10 to 30 percent solids through an
8-inch pipeline, although greater flow rates may be achieved for loosely
compacted materials. Depending on site-specific conditions, the Mud Cat can
remove up to 120 cubic yards per hour of solids (National Car Rental System,
Inc., 1980). Vaughan-Maitlen Industries (VMI) manufactures a line of similar
"mini dredges" that can remove up to 133 cubic yards of sedimentary material
per hour with discharge diameters from 6 to 10 inches, at cutting depths as
great as 20 feet (Vaughn-Maitlen Industries, 1980).
There are several other dredges that may be applicable to surface im-
poundment work. Waterless Dredging Company is presently field-testing a newly
developed system in which the cutter and a submerged centrifugal pump are
enclosed within a half-cylindrical shroud. The cutting blades remove the
material near the front of the cutterhead with minimal water pick-up. The
system has a reported capability of pumping industrial sludges with solids
contents of 30 to 50 percent by weight with little turbidity generated
(Barnard, 1978).
The Delta Dredge and Pump Corporation has also developed a small portable
unit that has high solids capabilities. The system uses a submerged 12-inch
pump coupled with two counter-rotating, low speed, reversible cutters.
Ellicott Machine Corporation has recently developed a bucket wheel cutter
head, which can efficiently excavate highly consolidated material.
Many of these dredges also result in minimal turbidity; therefore, they
are useful for dredging sediments in lakes, streams, and rivers.
7.2.2 Design and Construction Considerations
The selection of hydraulic dredging equipment or pumping systems for
surface impoundment operations will depend largely on manufacturer specifica-
tions for a given dredge vessel or pump system. Important selection criteria
that will vary from site to site include the following:
Maximum depth of the impoundment
302
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Surface area of impoundment
Physical nature of material being dredged - e.g., consolidated sludge
or hard clay vs. loose sand and gravel
Chemical nature of dredged material - may dictate special handling
procedures; special pipeline for corrosives
Total volume of material to be dredged
Distance over which material is to be pumped - proximity of spoil
disposal site or treatment facilities
Terminal elevation of discharge pipeline - contributes to total head
to be overcome by pumping; may necessitate use of booster pumps
Type and amount of aquatic vegetation or overgrowth in impoundment -
tree stumps may require special excavation; special cutting
attachments for heavy weed growth
Presence of bottom liner in impoundment
Power source for dredge or pump systems; availability of electric
current
Ease of access to impoundment
Maximum size and weight limits for overland transportation
Cost consideration - see Section 7.2.4.
All these criteria must be considered before selection of a pumping system or
dredge vessel of the appropriate size, efficiency, and overall capabilities
can be made. Figure 7-11 presents a schematic diagram of important distances
used in the selection of a dredge vessel and pipeline equipment for a given
dredging site. It should be noted that the depth capability of a unit may be
increased by lowering the water level of the impoundment.
The centrifugal pumps used in pumping systems or dredge vessels have a
rated discharge capacity based on maximum pump speed (in revolutions per
minute, rpm) and a given head against which they are pumping. The total head
against which pumps must work is affected by the depth of dredging, the dis-
tance over which the material is pumped, and the terminal elevation of the
discharge pipeline in relation to the water level within the impoundment.
This means that centrifugal pumps can pump a given discharge over only a given
distance once the dredged slurry has been sucked from the impoundment bottom.
If treatment facilities or spoil disposal areas are located at distances or
elevations greater than this maixmum pumping capability, then one or more
booster pumps (usually centrifugal pumps also) must be installed in the pipe-
line to pump the slurry to the desired location. In general, for pumping from
303
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most portable cutterhead dredge vessels, if the disposal or treatment site is
located at a distance greater than a half mile away over level terrain, then
booster pumps will be required to extend the pumping distance.
The rated discharge capacity of the dredge pump can be used to estimate
the solids output (in cubic yards per hour) of the dredging operation, based
on the discharge distance, the size of the discharge pipeline, and the solids
content (percent by volume) of the pumped slurrygenerally on the order of 10
to 30 percent. Figure 7-12 shows the capacity chart for Ellicott Machine's
FIGURE 7-12
TYPICAL CAPACITY CHART FOR PORTABLE CUTTERHEAD DREDGE
(Source: Ellicott Machine Corp., 1969)
400
ง 350
a.
2 300
o
X
I 250
CO
ฃ 200
5
CO
P 150
ง 100
u
.c
i so
&
O
Dragon Dredge Series 400 Capacity Chart
A. Average Materials
10" Pipeline
B. Average Materials
8" Pipeline
500 1000 1500 2000 3000
Length of Discharge Pipeline in Feet at 10 Ft. Terminal Elevation
305
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Series 400 "Dragon" dredge, which relates solids output (in cubic yards per
hour) to the length of the discharge pipeline at a given terminal elevation.
Such a chart can be developed for a given dredging operation and used to
predict dredged material production over time. Keep in mind, however, that
dredging output may be affected by a number of uncontrolled site-specific
variables, including weather conditions, local topography, and unforeseen
equipment failures or dredging obstacles. These will influence both perform-
ance and cost of the dredging operation.
7.2.3 Advantages and Disadvantages
Advantages and disadvantages of hydraulic dredging of surface impound-
ments are summarized in Table 7-7. The main disadvantage associated with
hydraulic removal of materials from surface impoundments is the necessity of
locating and/or constructing dewatering/disposal areas (or treatment facili-
ties) within economical distances of the dredging site. Spoil containment
facilities must be able to handle large volumes of dredged material in a
liquid slurry form, unless dewatering is performed prior to spoil transport
(which will entail added costs also). Processing equipment to dewater, segre-
gate, or chemically treat the dredged slurry may be desirable prior to land
disposal of spoil from the surface impoundment. Requirements for dredge spoil
dewatering can be kept to a minimum by using the high-solids dredging systems
previously discussed. Treatment and disposal options for dredged slurries are
addressed in Section 9.3.
Where special lagoon pumping systems are used to dredge impounded mate-
rials at in-situ density, spoil dewatering may not be necessary. But these
are applicable only to highly consolidated, viscous materials with a high
solids content, such as settled sludges. Most conventional hydraulic dredging
involves the addition of dilution water to bottom materials to form a pumpable
mixture that makes pumping through a pipeline a feasible transportation al-
ternative; it is not always, however, the least expensive alternative.
7.2.4 Costs
The unit costs associated with representative hydraulic dredging tech-
niques for surface impoundments are given in Table 7-8. Capital purchase
costs and operating costs are given for some of the dredge vessels (and ac-
cessories) discussed in this section, although it is recognized that hydraulic
dredging for local municipalities will most likely be performed by specialty
contractors whose rates may be highly variable from site to site. If a
dredging contractor is to be used, costs of dredging can be estimated at $3-5
per cubic yard of material removed.
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TABLE 7-7
SUMMARY OF EVALUATION OF HYDRAULIC DREDGING OF SURFACE IMPOUNDMENTS
Advantages
Efficient removal of solids/water
mixtures from impoundments
Removes hazardous materials in
readily processed form (slurry)
Suitable for removal of materials
from surface impoundments in wide
range of consistenciesfrom free-
flowing liquids to consolidated/
solidified sludges
Utilizes well-established, widely
available technology
Disadvantages
Necessity of locating spoil
management facilities (de-
watering; disposal; treat-
ment) nearby
Necessitates high volume
handling of solids/water
mixtures
May require booster pumps
for long-distance transport
of dredged slurries
Mobilization and demobiliza-
tion may be time-consuming
and costly
Cannot
(such
as
remove large items
drums)
Other cost considerations that are not included in Table 7-8 are the
following:
Crane rental to launch and retrieve portable dredge vessels
Freight and handling costs for shipping dredge equipment
Transportation of equipment from site to site
Insurance (hull coverage and liability) for purchased vessels
Storage and/or warehouse costs
Sales tax
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TABLE 7-8
UNIT COSTS FOR HYDRAULIC DREDGING OF SURFACE IMPOUNDMENTS
Description Unit cost Source
Vaughan Model 335 Lagoon Pumper, $27,400 each 1
with 100 hp motor and 6-inch
chopper pump; complete platform
assembly including winch (shipping
weight approx. 6,500 Ibs)
Mini-Mud Cat SP-810 with 10-foot $68,720 each 2
boom and submerged pump; less
accessories (12,200 Ibs)
weed auger assembly $1,680 2
auger wheels (for lined ponds) $1,347 2
discharge pipe package, 1,500 $18,811 2
feet of 6-inch polyethylene
pipe (10,106 Ibs)
cable and harnessing equipment $5,374 2
(1,656 Ibs)
extra sections of carrier pipe, $126.20 2
6-inch x 19 feet (56 Ibs)
Mud Cat MC-915 with 15-foot boom; $106,313 each 2
less accessories (21,000 Ibs)
air conditioned cab $1,605 2
weed auger assembly $1,712 2
Ni-hard pump $2,502 2
auger wheels (for lined ponds) $1,766 2
right angle cutting knives, extra $222 2
recessed impeller pump (for heavy $1,766 2
weed or debris applications)
turbocharged engine (high $1,926 2
altitude operation)
--continued
308
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TABLE 7-8 (Continued)
Description
Unit cost
Source
discharge pipeline package, $20,629
1,500 feet of 8-inch polyethylene
pipe with PVC floats (8,911 Ibs)
cable and related harnessing $3,524
equipment (995 Ibs)
extra sections of polyethylene $175.50
carrier pipe, 8-inch x 19 feet,
including couplings and gasket
with float bands and links
(85 Ibs)
booster pump, skid mounted, $31,246
with connector fittings
(7,977 Ibs)
service boat and motor (466 Ibs) $1,774
Lease (towards purchase) of Mud Cat
MC-915 with discharge pipeline
package and cable equipment;
first two months
third month +
Operating costs for Mud Cat
Fuel - 6.5 gal/hr x $1.00/gal
lubricants
repairs (parts and labor)
two operators
Total hourly operating costs
VMI Mini Dredge 815 with standard
equipment (16,000 Ibs)
weed cutting attachment
cable and harness
10-inch PVC carrier pipe
floats for carrier pipe
10-inch flexible industrial
tubing
service boat with motor
$ll,000/month
$ 8*,300/month
$ 6.50/hour
$ 1.00/hour
$ 4.25/hour
$20.00/hour
$31.75/hour
$79,500 each
$895
$3,985
$6.22/foot
$2.00/foot
$55.70/50-ft
$1,325
2
2
2
2
2
2
2
2
2
3
3
3
3
3
--continued--
309
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TABLE 7-8 (Continued)
Description Unit cost Source
Contractor hydraulic dredging $3-5/yd3 4
(suction or cutterhead),
materials pumped 1,000 feet to
shore dump (for inland rivers
in South, deduct 30%)
1Vaughan Co., Inc., 1980.
2National Car Rental Systems, Inc., 1980.
3Vaughn-Maitlen Industries, 1979.
"Godfrey, 1979.
7.3. LAND DISPOSAL
7.3.1 General Description and Applications
Land disposal is the most commonly practiced method for disposal of
industrial and municipal wastes. It includes disposal in secured landfills,
surface impoundments, and land application.
The use of secured landfills for the disposal of hazardous waste may
continue for some time since other ultimate disposal techniques are not yet
well developed. Such landfills are typically constructed with impermeable
natural subsoils or man-made liners that inhibit the movement of leachate to
ground and surface waters. In some cases, impermeable covers are required to
reduce the mobilization of leachate and to reduce the possibility of contami-
nation of surface water runoff. Monitoring, nevertheless, is required in
ground and surface waters around the landfill and this must be continued on a
regular basis in order to provide a gage on the integrity of the liner and
leachate collection system. Because of the notoriety given to improperly
designed landfills or impoundments in the past, the institutional (as well as
political) implications involved in landfill and impoundment siting may be
more time-consuming and difficult than the environmental and engineering
aspects of an acceptable facility.
310
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In some cases, application of hazardous wastes on the land may be fea-
sible. This involves the uniform application of selected wastes to a specific
area and includes mixing with upper soil layers. This is usually done after
the wastes have been converted to environmentally acceptable materials by
means of biological, chemical, or physical treatment. This technique has been
used for the disposal of municipal sludges and petroleum industry wastes. For
those wastes that are resistant to biodegradation, the potential of contami-
nation of surface water runoff and infiltration exists. In addition, uptake
of unaltered materials by vegetation can introduce potentially hazardous
compounds into the food chain.
7.3.2 Design and Considerations
Subtitle C of the Resource Conservation and Recovery Act (RCRA) provides
authority to EPA to promulgate regulations designed to control hazardous waste
disposal. Parts 264 and 265 in the Federal Register, Volume 45, No. 98 (May
19, 1980) are the first phase of EPA's requirements under Section 3004 of RCRA
for owners and operators of hazardous waste disposal sites. The requirements
under Section 264 and 265 are, in some respects, purposely general; EPA's
position is that much additional research is needed to provide more specific
guidance to landfill operators, and such research is currently underway.
Section 264 establishes minimum national standards that define acceptable
management of hazardous wastes. Section 265 establishes requirements appli-
cable during interim status or that period after application for a permit but
before final administrative action on the permit. With the huge number of
applications likely to flood EPA, it may be several years before final admin-
istrative action on all permits is taken. Therefore, landfill owners and
operators will need to thoroughly familarize themselves with the requirements
of Parts 264 and 265.
Owners with interim status are required to meet the following criteria as
well as others specified in Parts 265 and 265. Parts 264 and 265 must be
consulted for additional detail.
Owners must develop and follow a waste analysis plan that specifies
tests to be used and their frequency in order to determine the iden-
tity of incoming wastes.
tests to be used and tn
tity of incoming wastes.
Groundwater monitoring is required at all landfills, impoundments, and
landfarms. Landfarms require, in addition, an unsaturated zone moni-
toring system. Site security requires a 24-hour surveillance system
that monitors and controls entry, an artificial or natural barrier
surrounding the site, and measures to control entry at all times.
Owners or operators must develop and follow a written schedule for
inspection of monitoring equipment, safety and emergency equipment,
and operating and structural equipment. The rate of inspection is
based on equipment deterioration and the probability of a human health
hazard with failure.
311
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Monitoring and maintenance will be required for a post-closure period
of 30 years.
Containers are required to be compatible with the wastes. They must
be inspected on a weekly basis and if leaks are occurring, the wastes
must be transferred to other containers or otherwise properly managed.
Part 265 also establishes some specific requirements for landfills and
surface impoundments.
Runon to landfills must be diverted and runoff must be collected. Wind
dispersal of hazardous wastes from landfills must be controlled. Bulk or
non-containerized hazardous liquid wastes must not be placed in a landfill
unless there is a compatible liner and a leachate collection system or the
liquid waste is treated or stabilized chemically or physically.
For surface impoundments, Part 265 requires that there be sufficient
freeboard to prevent overtopping of the dike by overfilling, wave action, or
storms and that it be at least 2 feet. All earthen dikes are required to have
protective cover such as grass, shale, or rock to minimize wind and water
erosion. Specific slopes of dikes have been recommended and are such as to
insure the integrity of the dike.
Part 265 of RCRA also requires certain monitoring and maintenance activi-
ties after closure of a site that has been used to dispose of hazardous waste.
In particular, EPA requires a 30-year leachate monitoring program after the
site has ceased to accept hazardous wastes, although this requirement could be
lengthened or shortened by review on a case-by-case basis. The most signifi-
cant (and probably the most difficult) aspect of closure involves the funds
necessary to maintain and to monitor the facility over an extended period of
time. Trust funds, expenses drawn out of operating revenues, and private and
public insurance programs have all been considered, but none has permitted the
designation of permanent, specific guidelines. As a result, EPA has set up
interim guidelines to allow administration of land disposal sites to proceed.
These guidelines include:
Notice in Deed to Property - a recording of instructions in the use of
the property after its resale, to ensure that liner or cover integrity
be maintained.
Submission of Closure Plans - to assure that an operating facility has
the proper measures to deal with closure and is building up (or has
adequate) finances for post-closure activities.
Time Allotted for Closure - in order to effect closure within a six-
month to three-year interval after operations have ceased, depending
on a review on a case-by-case basis.
312
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Post Closure Permits - to require owners or operators for closed
facilities to provide a program of access, monitoring, and financial
responsibility.
7.3.3 Advantages and Disadvantages of Land Disposal Methods
Land disposal has generally been the most expedient, economical, and best
understood method of disposing of wastes. RCRA requirements will signifi-
cantly increase the cost of land disposal by requiring more stringent site
security, monitoring, and long-term liability and management. There will be
increased incentive for using waste destruction or recovery techniques that do
not require long-term management and liability.
Nevertheless, land disposal in a site that meets RCRA and state require-
ments will continue to be a viable disposal method, particularly until alter-
native technologies are fully developed and facilities are sufficiently prev-
alent to handle much of the waste currently disposed of by land.
7.3.4 Costs
Costs for hauling of wastes are estimated to range from $2-4 per loaded
mile. Disposal costs approximate $240/ton for very hazardous material, $1207
ton for, flammable wastes, $85/ton for most industrial sludges, and $40-50/ton
for municipal treatment sludges (Cecos International, 1980).
7.4 SOLIDIFICATION
Waste solidification involves a number of techniques designed to seal the
wastes in a hard, stable mass. Nearly all of these techniques are an out-
growth of radioactive waste disposal and a U.S. Department of Transportation
(DOT) regulation forbidding the transportation of liquid radioactive wastes
(Pojasek, 1978). Much of the information on solidification techniques is
proprietary and therefore not included in this discussion.
Waste solidification practices are limited in their applicability to
remedial measures for waste disposal sites. One major reason for this is
cost. In addition to the cost of excavating the wastes (see Section 7.1), the
wastes must undergo a thorough analytical characterization and often a sta-
bilization process to ensure compatibility with the solidification process.
Moreover, these processes are, for the most part, very waste-specific. Since
many solidification techniques evolved from the need to transport non-liquid
radioactive wastes, not all methods result in a solid with long-term sta-
bility. Several methods result in a material that, while easy to handle and
transport, is not meant to secure the wastes over a long period of time.
313
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These restrictions limit the use of solidification as a remedy for radioactive
or highly toxic wastes.
It should be noted that many sludges contain significant concentrations
of organic chemical and hydrocarbon constituents. Therefore, the organic
fixing capacity of the various processes should be carefully reviewed and
compared in regard to potential leachates of such pollutants to form the so-
lidified mass.
Solidification methods can be placed in two main groups based on how the
wastes are held in the solid. Some methods physically surround the waste
particles with the solidifying agent. Other methods chemically fix the wastes
in a reaction with the solidifier. Included in these two broad categories are
the six most commonly used methods:
Cement-based
Lime-based
Thermoplastics
Organic polymers
Self-cementation
Classification
Each of these methods is discussed below:
7.4.1 Cement-Based Solidification
7.4.1.1. General Description
This method involves sealing the wastes in a matrix of Portland cement, a
very common construction material. Most solidication is done with Type I
Portland cement but Types II and V can be used for sulfate or sulfite wastes
(EPA, 1979b). This method physically or chemically solidifies the wastes,
depending upon waste characteristics.
7.4.1.2 Applications
Cement-based solidification techniques are among the most versatile.
They can neutralize and seal acids and can handle strong oxidizers such as
chlorates and nitrates (EPA, 1979b). These methods are also good for solidi-
314
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fying many toxic metals, since at the pH of the cement (pH 9-11), many metals
are insoluble carbonates and hydroxides. Certain wastes can cause problems
with the set, cure, and permanence of the cement waste solid unless the wastes
are pretreated. Some of these incompatible wastes are:
Sodium salts of arsenate, borate, phosphate, iodate, and sulfide
Salts of magnesium, tin, zinc, copper, and lead
Organic matter
Some silts
Some clays
Coal or lignite (EPA, 1979b)
7.4.1.3 Special Considerations
A typical cement-based solidification process results in wastes that are
twice the weight and volume of the original. Basically, this means that
reburial of the solidified wastes would require twice as large an area.
7.4.1.4 Advantages and Disadvantages
Provided this process is used on compatible wastes, the short-term effec-
tiveness can be expected to be quite good. The equipment for cement mixing is
commonplace and the process is quite tolerant of chemical variations. How-
ever, because cement is a porous solid, contaminants can be leached out of the
matrix over time and is, therefore, usually not effective for organic wastes.
Although it is possible to seal the outside of a block of cement-solidified
wastes using styrene, vinyl, or asphalt to prevent leaching, no commercial
systems are available to do this (EPA, 1979b).
7.4.1.5 Costs
Cement costs range from $58 to $80 per ton at the mill (1982) and cement
is added to make a product that is about 130 percent of volume of the original
wastes. However, capital expenditure and transportation will vary widely
depending on the site and the waste. Cost information for specific wastes
should be obtained from vendors. Vendors include: Atcor Washington, Inc.,
Park Mall, Peeksville, New York; and Chemfix, Inc., Kenner, Louisiana.
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7.4.2 Lime-Based Solidification
7.4.2.1 General Description
Lime-based solidification is very similar to cement-based, though the
solidifier is a mixture of a fine-grained siliceous material, lime, and water.
Other wastes, such as fly ash, cement-kiln dust, or ground blast-furnace slag
can be used as the siliceous additive (EPA, 1979b). When used with the right
types of wastes, this method results in a fairly stable, easily transported
solid.
7.4.3.2 Applications
In order to be compatible with lime-based solidification, wastes should
be stable at high pH. The most common use of this technique is to solidify
flue gas cleaning sludge using fly ash from the same plant, along with lime
and other additives (EPA, 1979b).
7.4.2.3 Special Considerations
As with cement solidification, the lime-based method increases the weight
and volume of the wastes. The amount of overall increase is related to the
nature of the original wastes. If, for instance, waste fly ash is added as
the solidifying agent rather than some nonwaste additive, two types of wastes
are included in a solid of the same size and weight.
7.4.2.4 Advantages and Disadvantages
Major advantages of this technique include the ready availability and low
cost of materials and the familiarity of commonly used equipment. A disad-
vantage is that the solid mass resulting from lime-based solidification is
porous. As such, it must either be sealed or placed in a secure landfill to
prevent leaching of contained wastes. Another major disadvantage is that
sludge or wastes containing organics cannot be treated.
7.4.2.5 Costs
Cost of lime fixation should be determined on a case-by-case basis.
Overall costs have been reported to range from $0.03 to $0.15 per gallon of
industrial sludge (Palesh and Gulledge, 1979).
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7.4.3 Themoplastic Solidiflcation
7.4.3.1 General Description
Thermoplastic solidification involves sealing wastes in a matrix such as
asphalt bitumen, paraffin, or polythylene. These substances are solid at
normal temperatures, but liquid when heated.
7.4.3.2 Applications
Thermoplastic compounds should not be considered for solidifying:
Organic solvents
Iron and aluminum salts
Strong oxidizers
Anhydrous salts
Wastes that may break down when heated (EPA, 1979b)
7.4.3.3 Special Considerations
Thermoplastic solidification requires specialty equipment and highly
trained operators to heat and mix the wastes and solidifier. The common range
of operating temperatures is 130ฐ to 230ฐ (EPA, 1979b). The energy intensity
of the operation is increased by the requirement that the wastes be thoroughly
dried before solidification. Certain wastes, such as tetraborates, and iron
and aluminum salts can cause premature solidification, and plug up the mixing
machinery (EPA, 1979b). Some thermoplastic/waste mixtures cure to a very
plastic solid and require some secondary containment, such as a 55-gallon
drum, for handling and disposal.
7.4.3.4 Advantages and Disadvantages
Thermoplastically solidified wastes have been shown to lose contaminants
through leaching at a far slower rate than either cement or lime-solidified
wastes. Also, these thermoplastics are little affected by either water or
microbial attack (EPA, 1979b). In addition, this method may permit some
recovery, may effectively handle some organics, and can reduce landfill vol-
ume. These factors combine to give this method excellent long-term effec-
tiveness. Principal disadvantages include the high cost of equipment and high
energy utilization.
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7.4.3.5 Costs
Capital and operating costs are generally not available for non-radio-
active disposal operations. Vendors should be consulted for specific cost
information. One such vendor is: Werner and Pfleiderer Corp., Waldwick, New
Jersey.
7.4.4 Organic Polymer Solidification
7.4.4.1 General Description
The primary organic polymer use for solidification is urea-formaldehyde,
but others include vinyl ester-styrene and polyester. This physical solidi-
fication method involves mixing the wastes with prepolymers, polymers, and a
catalyst to form the solid mass (EPA, 1979b). In some cases, it is possible
to mix the wastes and the polymers in a 55-gallon drum, add the catalyst, and
have solidification take place in a convenient disposal container.
7.4.4.2 Applications
Since organic polymers do not enter into reactions with the wastes, a
somewhat wider range of wastes can be solidified than with most other methods.
With the most common solidification polymer, urea-formaldehyde, however, the
wastes should be stable at low pH, since the catalyst used is strongly acidic
(EPA, 1979b). Acid-catalyzed polymerization is generally highly exothermic.
Waste encapsulated in inorganic polymers should be devoid of thermally un-
stable or high vapor pressure toxicants that might be emitted to ambient air.
In solidifying wastes with organic polymers, the wastes do not have to be
dried prior to polymerization. Any liquid associated with the waste will
remain after polymerization, if not dried, and the polymer mass must often be
dried before disposal. Significant amounts of residual water may have an
effect on the physical integrity of the polymer structure.
7.4.4.3 Special Considerations
As noted earlier, the catalyst used with urea-formaldehyde polymer is
highly acidic and thus very corrosive. This means that the equipment used to
mix and contain these substances must be made of a corrosion-resistant mate-
rial .
318
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Another point that illustrates the importance of proper waste/polymer
drying is the tendency of the solid to "weep" or release any uncombined water.
The weep water is strongly acidic and often laden with pollutants. Secondary
containment as in a lined 55-gallon drum, can help to control this problem.
7.4.4.4 Advantages and Disadvanges
The long-term effectiveness of the various organic polymers is question-
able. Many of the polymers, and especially urea-formaldehyde, are biodegrad-
able, and so could readily release any contained pollutants. This fact alone
shows that these solidification methods are more for ease of handling than for
security of the wastes. Hazardous or harmful releases may occur from cata-
lysts, "weep" water, and fumes from the resins. One advantage of this process
is that the resin formed is less dense than cement, and transportation costs
are significantly reduced. Little is known about suitable waste types for
some polymer solidification methods.
7.4.4.5 Costs
Since little testing has been done on non-radioactive wastes, cost data
are not widely available. Costs for nuclear wastes have been reported at
$2.75 per gallon (Palesh and Gulledge, 1979). Todd Shipyard Corp., Galveston,
Texas markets an organic polymer called "Safe-T-Set." This vendor and others
should be contacted for specific cost data.
7.4.5 Self-Cementing Solidification
7.4.5.1 General Description and Applications
This process is specific to certain types of wastes, and is similar to
cement-based solidification in that a portion of the wastes (8-10%) are cal-
cined to form a cement. Wastes that can be considered for solidification by
this method are flue gas cleaning or desulfurization sludges that contain a
large amount of calcium sulfate or sulfite (EPA, 1979b) and ion exchanger
regenerant wastes from the utilities industry, since these contain appreciable
amounts of calcium sulfate and sodium sulfate.
7.4.5.2 Special Considerations
The requirement that a portion of the wastes be calcined into cement
necessitates special equipment and specially trained workers to carry out this
process. In addition, the calcining step requires an increased energy input.
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7.4.5.3 Advantages and Disadvantages
Self-cementation of cleaning sludges produces a solid that retains metals
and is stable, non-flammable, and non-biodegradable. However, the process is
limited in applicability in that only high sulfate or sulfite sludges can be
used. The process is also energy-intensive and requires specialized equipment
(EPA, 1979b).
7.4.5.4 Costs
Costs of self-cementing solidification are $2-2.75/ton of sludge (EPA,
1979b).
7.4.6 Classification
7.4.6.1 General Description
According to EPA (1979b), glassification of wastes involves combining the
wastes with molten glass at a temperature of 1,350ฐC or greater. However, the
encapsulation might be done at temperatures significantly below 1,350ฐC (a
simple glass polymer such as boric acid can be poured at 850ฐC). This melt is
then cooled into a stable, non-crystalline solid.
7.4.6.2 Applications
This process is quite costly and so has been restricted to radioactive or
very highly toxic wastes (EPA, 1979b). To be considered for glassification,
the wastes should be either stable or totally destroyed at the process working
temperature.
7.4.6.3 Special Considerations
Glassification of wastes is an extremely energy-intensive operation, and
requires sophisticated machinery and highly trained personnel.
7.4.6.4. Advantages and Disadvantages
Of all the common solidification methods, glassification offers the
greatest degree of containment. Most resultant solids have an extremely low
leach rate. Some glasses, however, such as borate-based glasses, have high
320
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leach
requ i
rates and exhibit some water solubility. The high energy demand and
rements for specialized equipment have limited its use.
7.4.6.5 Costs
No information.
7.5. ENCAPSULATION
7.5.1 Description and Applications
Encapsulation is the process by which hazardous wastes are physically
enclosed by a synthetic encasement to facilitate environmentally sound trans-
port, storage, and disposal of the wastes. As a remedial action, encapsula-
tion may be used to seal particularly toxic or corrosive hazardous wastes that
have been removed from disposal sites. Waste types that may require encapsu-
lation include the following:
Solid hazardous wastes in bulk or particulate form (e.g., severely
contaminated sediments)
Dewatered hazardous sludges
Containerized hazardous wastes (solids, sludge, or liquid) in dam-
aged or corroded drums
Hazardous wastes which that been stabilized through solidification/
cementation (by processes described in Section 7.7)
TRW Systems Group has successfully developed bench-scale processes to (1)
agglomerate and encapsulate toxic and corrosive heavy metal sludges and solu-
ble heavy metal salts; and (2) encapsulate containerized wastes. The ag-
glomeration/encapsulation process involves mixing dried sludges (containing
such hazardous heavy metals as arsenic, lead, mercury, selenium, beryllium,
cadmium, zinc, and chromium) with a binder resin (modified 1,2-polybutadiene)
and thermosetting the mixture in a special mold, while applying moderate
mechanical pressure. The agglomerated material is a hard, tough solid block.
Encapsulating the waste/binder agglomerate with a 1/4-inch seamless jacket of
high density polyethylene (HOPE) is accomplished by packing powdered poly-
ethylene around the block and then fusing the powder in-situ with a second
metal sleeve mold. A schematic diagram of the apparatus used to encapsulate
the agglomerate is shown in Figure 7-13. Figure 7-14 summarizes the agglom-
eration/encapsulation process flow. A commercial-scale encapsulate produced
by this method is expected to be a solid cube, 2 feet on edge, weighing 800 to
1,000 pounds. It would require approximately 8 percent (by weight) of poly-
321
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butadiene resin for its fabrication (Lubowitz and Wiles, 1978). Presumably,
as the technology advances, additional jacket sizes will be available.
The second TRW encapsulation process is designed to enclose and seal
waste containers such as 55-gallon drums (subject to corrosion, rupture,
leaks, and spills) using the same basic mold and fusion apparatus. To provide
load-bearing ability, a 1/8-inch-thick interior casing of fiberglass is used
to reinforce the 1/4-inch-thick HOPE jacket that encapsulates the container.
A commercial-scale, fiberglass-reinforced HOPE encapsulate is envisioned to
provide up to 75 gallons of capacity. The cylindrical jacket and casing would
comprise about 5.3 percent (by volume) of the total encapsulate volume.
Commercially, 1/4-inch-thick HOPE jackets can be fabricated in 30 seconds
(Lubowitz and Wiles, 1978).
Comprehensive laboratory testing of bench-scale encapsulates has demon-
strated their ability to withstand severe mechanical stresses and biological
and chemical degradation. Encapsulates containing wastes of various solu-
bility were exposed to leaching solutions of various corrosivity; results
indicate that the encapsulated wastes were completely isolated from, and
resistant to, simulated disposal environment stresses. The encapsulates were
also found extremely resistant to mechanical deformation and rupture. They
exhibit high compressive strength and outstanding ability to withstand impact,
puncture, and freeze-thaw stresses (Lubowitz et al., 1977).
7.5.2 Design and Construction Considerations
It is important to emphasize that encapsulation techniques have only
recently advanced from the developmental and testing stages, and no large
commercial-scale encapsulation facilities have been designed and operated as
yet. It is likely that, as a remedial action, encapsulation will not be an
economically feasible alternative to other direct waste treatment methods.
However, a central solidification/encapsulating waste processing facility may
be technically and economically feasible as a pre-disposal operation at haz-
ardous waste storage and disposal facilities in the near future.
The fabrication of commercial-scale encapsulates of containerized wastes
under actual field conditions would require an encapsulation unit that is
readily transportable to the storage or disposal site where containerized
wastes reside. Where containerized wastes are of volumes smaller than the
design capacity of the encapsulation unit, sand or soil may be used to fill
voids between the container and encapsulate walls. Where very large volume
waste containers require encapsulation (greater than 55 gallons), it may be
necessary to install compaction operations at the site (Lubowitz and Wiles,
1978).
322
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FIGURE 7-13
ENCAPSULATION PROCESS CONCEPT
(Source: Lubowitz et a"!., 1977)
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Waste/Resin
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7.5.3 Advantages and Disadvantages
The major advantage of encapsulation processes is that the waste material
is completely isolated from leaching solutions, and soluble hazardous mate-
rials such as heavy metal ions and toxic salts can be successfully encapsu-
lated. The impervious HOPE jacket eliminates all leaching into contacting
water (which may infiltrate or flow over disposal sites) and effectively
contains hazardous waste substances that might otherwise migrate offsite.
Other advantages associated with hazardous waste encapsulation include:
The cubic and cylindrical encapsulates allow for efficient space
utilization during transport, storage, and disposal
The hazard of accidental spills during transport is eliminated
HOPE is low in cost, commercially available, very stable chemically,
non-biodegradable, mechanically tough, and flexible
Encapsulated waste materials can withstand the mechanical and chem-
ical stresses of a wide range of disposal schemes (landfill, deep-
well disposal, ocean disposal)
There are, however, major disadvantages associated with encapsulation
techniques. Among these are:
The binding resins required for agglomeration/encapsulation (poly-
butadiene) are expensive
The process requires large expenditures of energy in fusing the
binder and forming the jacket
The system requires large capital investments in equipment
Skilled labor is required to operate molding and fusing equipment
Drying/dewatering of non-containerized waste sludges is required for
agglomeration/encapsulation
The process has yet to be applied on a commercial scale under actual
field conditions
7.5.4 Costs
TRW has developed a process economic model to predict the estimated costs
associated with the commercial-scale operation of an agglomeration/ encapsu-
lation facility. By this model, it was determined that a plant with a 20,000
to 60,000 tons per year processing capacity would require an initial capital
investment of approximately $1.4 million. This represents the total cost of
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installed equipment, which includes raw material storage tanks, a rotary tray
drier for drying sludges, two agglomerate molds, a coating mold, curing oven,
powdered HOPE delivery system, steam boiler, raw material feed pumps, and a
conveyor belt system. Such a plant would incur base operating costs of about
$1.8 million annually; this translates to a $91 per ton overall processing
cost for waste materials encapsulated at the plant (Lubowitz et al., 1977).
Without dewatering, the overall cost of this agglomeration/encapsulation
process can be broken down by source as follows: 50 percent, raw material
requirements; 25 percent, labor costs; and 25 percent, equipment costs. The
cost of commercial agglomerating resins such as polybutadiene account for the
major portion of raw material costs; the use of impure, scrape resins (rather
than virgin, commercial resins) may substantially reduce the $91 per ton
processing cost (Lubowitz et al., 1977). It is also important to note that
these costs are derived for the encapsulation process based on initial agglom-
eration of the waste material. Encapsulation of containerized hazardous
wastes using fiberglass-reinforced HOPE jackets does not require initial
agglomeration, and does not require the use of expensive polybutadiene resin,
and therefore will be much more economically feasible as a direct waste treat-
ment method. Also, the encapsulation can be done by a portable system that
can be transported from disposal site to disposal site.
7.6 IN-SITU TREATMENT
An alternative to the removal and subsequent treatment of land-disposed
wastes is to treat the wastes in-place, without dredging or excavation. A
number of conceptual techniques may be applicable as "in-situ" treatment
methods. These techniques may be feasible for sites where wastes are well
defined, shallow, and the extent of contamination is small. Such limitations
suggest specific applicability to chemical spills; soil contaminated by sur-
face leachate; landspreading operations; dredge spoil containment basins; and
small, shallow industrial surface impoundments where the waste has been well
characterized. These methods are briefly discussed in the following section.
7.6.1 Solution Mining
Solution mining or soil flushing is the process of flooding the land-
disposed waste material or area of contamination with a solvent and collecting
the elutriate with a series of shallow well points. The elutriation process
is based on the concept of mobilizing the contaminant(s) into the solvent
phase via solubility or chemical reaction. .The most probable, feasible, and
cost-effective techniques use water as the base solvent.
Water may be the only material used if the waste or contaminant is
readily soluble. Solutions of sulfuric, hydrochloric, nitric, phosphoric, and
carbonic acid may be used to dissolve basic metal salts (hydroxides, oxides,
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and carbonates). Sulfuric acid is the most widely used in industrial leaching
operations (it is, however, restricted to metals that do not form insoluble
sulfates). Hydrochloric acid is used in conjunction with metal complexing
agents. Carbon dioxide may be used with ammonia in the leaching of copper
and nickel (DeRenzo, 1978). Acid may also serve to flush some basic organics
such as amines, ethers, and anilines (Weininger, 1972).
Sodium hydroxide solutions may also be used to flush certain metals and
organics. Sodium hydroxide is used to dissolve metallic aluminum (OeRenzo,
1978) and can be used as well on zinc, tin, lead, and other metals. It may be
useful in dissolving certain organic sulfur compounds and phenols (Considine,
1974).
Complexing and chelating agents may also find limited use in a solution
mining removal system for heavy metals. Some commonly employed substances are
ammonia and ammonium salts, citric acid, ethylene diamine tetracetic acid
(EDTA), and thiourea (Rogoshewski and Carstea, 1980). Also, the use of sur-
factants may prove useful in dissolving oils and greases, such as those found
in oily sludges from petroleum refineries.
As the above reagents will be used in the field rather than in the con-
trolled conditions of a chemical processing plant, it is important that safety
and pollution control considerations enter into the selection of a particular
reagent. For example, hydrochloric or nitric acid may be unsuitable at con-
centrations where vaporization becomes a problem. It is important to consider
the reaction products that could be formed when selecting solvents. For
example, the use of hydrochloric acid to flush an amine waste could result in
the formation of amine hydroc'nlorides. It has also been suggested that hydro-
chloric acid may be used without complexing agents.
An economically feasible process may involve the recycling of elutriate
through the contaminated material, with make-up solvent being added to the
system while a fraction of the elutriate stream is routed to a portable waste-
water treatment system. The appropriate types of wastewater treatment opera-
tions will depend on waste stream characteristics, and a discussion of their
applications can be found in Appendix 3.
The advantages of the process are that, if the waste is amenable to this
technique and distribution, collection, and treatment costs are relatively
low, solution mining can present an economical alternative to the excavation
and treatment of the wastes. It may be particularly applicable if there is a
high safety and health hazard associated with excavation. Also, the effec-
tiveness and completion of the treatment process can be measured via sampling
prior to wastewater treatment.
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Disadvantages include an uncertainty with respect to adequate contact
with wastes; that is, because the wastes are buried, it is difficult to deter-
mine whether the solvent has contacted all the waste. Also, containerized
waste cannot be treated effectively by this method. Another disadvantage is
that the solution mining solvent or elutriate may become a pollutant itself if
the system has been poorly designed.
Costs for a solution mining clean-up will depend on the amount of waste
material to be flushed, the amount of solvent material required, the well-
point collection system, the solvent/elutriate distribution system, and the
wastewater treatment system. Costs for tile drains and well point dewatering
have been previously given in sections on leachate and groundwater control.
Unit costs for some potential solvents and reagents are given in Table 7-9.
The costs for wastewater treatment can be developed from information given in
Appendix B.
TABLE 7-9
COSTS OF POTENTIAL SOLUTION MINING CHEMICALS
Chemical Unit cost
Hydrochloric acid, 20% acid $69/ton
Nitric acid, up to 42 Be $175/ton
Sulfuric acid, virgin $40 - 65/ton
Sulfuric acid, smelter $6 - 40/ton
Caustic soda, liquid 50$ $150 - 200/ton
Citric acid $0.62 - 0.71/lb
Sodium lauryl sulfate, 30% $0.18 - 22/lb
Source: Schnell, 1980
7.6.2 Neutralization/Detoxification
In-situ neutralization/detoxification is the technique of applying or
injecting into the waste disposal site or contaminated area a substance that
immobilizes or destroys a pollutant. This technique is restricted to contam-
inants that can be degraded, have non-toxic breakdown products, and/or are
328
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convertible to insoluble precipitates. It has been recommended that this
technique be applied to industrial waste disposal sites only, since municipal
landfills would constantly be generating anaerobic decomposition products that
would require neutralization over a long period of time (Tolman et al., 1978).
If the material is present as a solid and is constantly dissolving, a similar
problem exists, and neutralization or detoxification would have to be done
repeatedly over a period of time. Thus, this method is applicable to what is
probably a rare situation, i.e., industrial wastes that are either completely
dissolved or readily mobile. A schematic of the process for detoxification of
cyanide is shown in Figure 7-15.
As with solution mining, in-situ neutralization or detoxification is
highly waste-specific. For example, calcium salt solutions would be used to
precipitate free fluorides (Tolman et al., 1978). Many heavy metals may be
precipitated as insoluble salts by application of alkalis or sulfides. Sodium
hypochloride at 2,500 ppm available chloride has been used to detoxify cyanide
contamination by oxidation resulting from indiscriminate dumping (Farb, 1978).
Other oxidizing agents that may be used are potassium permanganate or hydrogen
peroxide. Hydrogen peroxide has been found to be particularly useful for
oxidizing cyanide aldehydes, dialkyl sulfides, dithionate, nitrogen compounds,
phenols, and sulfur compounds (FMC Corp., 1979). Reducing agents such as
ferrous sulfate may be used in conjunction with hydroxides to insolubilize
hexavalent chromium (Tolman et al., 1978; Metcalf and Eddy, Inc., 1972).
Heterogeneous mixtures of wastes present a difficult problem because different
treatments will be required for different wastes, and treatment for one waste
may be unsuitable for another. A further limitation is then introduced, which
is that'this technique should be used only with well defined, segregated waste
cells.
Many of the environmental, health, and safety considerations that apply
to solution mining also apply here. In contrast to solution mining, in-situ
neutralization/detoxification techniques do not inherently incorporate seepage
collection systems. Therefore, if neutralization/detoxification is unsuccess-
ful, any leachate generated will not have been contained. Therefore, an
additional fail-safe collection system is required, which is a major disad-
vantage. Another disadvantage is that it is difficult to determine the degree
of effectiveness of this treatment technique. Although the technique is very
limited in application, it may prove economically feasible if a known indus-
trial pollutant is dissolved in a disposal site and its location can be well
defined.
Economics for a neutralization/detoxification system include the cost for
well point injection system, chemical and feed system, and costs for probing,
excavation, and drilling. Tolman et al. (1978) has estimated a cost to clean
up a hypothetical 10-acre disposal site that had received a single load of
cyanide salts in drums that, over time, have dissolved. Costs are summarized
in Table 7-10. Costs for other chemicals that may be used in an in-situ
neutralization/ detoxification clean-up are shown in Table 7-11.
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TABLE 7-10
COSTS FOR IN-SITU DETOXIFICATION OF CYANIDE1
Item Cost
Exploratory probing, excavation, and drilling $15,000
Development of water supply well, 27 m (90 ft); 5,000
pump and piping
Installation of 45 well points 10,000
Cost of chemical feed pump 2,000
Cost of chemical (sodium hypochlorite) 5,400
Labor for chemical injection, raising of well points 48,000
to flood successive elevations (assumed 4 wells handled
simultaneously), and general labor (1,600 hours)
Power (assumed electrical supply available) 500
$86,300
1 Assumed 10-acre landfill with a total of 1,566 Ibs of cyanide distributed
within a fill volume of 4.9 million cubic feet. Chemical application rate of
68 gallons per pound of cyanide.
Source: Tolman et al., 1978
TABLE 7-11
COSTS OF POTENTIAL IN-SITU NEUTRALIZATION/
DETOXIFICATION CHEMICALS
Chemical Unit cost
Calcium chloride, 100-1b bags $80/ton
Calcium sulfate $36.20/ton
Potassium permanganate $1.29/kg
Hydrogen peroxide, 50% $0.25/lb
Sodium hydroxide, liquid 50% $150-200/ton
Ferrous sulfate $80/ton
Source: Schnell, 1980.
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7.6.3 Micrpbial Degradation
Seeding a waste material with microorganisms to achieve degradation may
be feasible if the waste has been determined to be biodegradable. Research
with the landfarming of oily sludges has shown that many naturally occurring
bacteria can be adapted to the breakdown of petroleum constituents in soil.
These bacteria include Pseudomonas, Nocardia, Arthrobacter, Flavo bacterium,
and Corynebacterium (Kincannon, 1972). Specialized strains of bacteria have
been developed for the breakdown of specific chemicals (see Appendix B) and
may be ordered in dry bulk quantities (Polybac, 1978). The biodegradation
process is slow relative to other remedial actions discussed in this handbook.
Complete degradation of the waste could take several years and may never be
complete if refractory compounds such as polynuclear aromatics are present
(Kincannon, 1972). This is a major disadvantage, since additional migration
of contaminants can occur during the treatment and even afterwards. For
petroleum sludges, biodegradation is an aerobic process, hence proper aeration
is required. This fact probably applies to other organic wastes as well.
Therefore, this technique is generally limited to those situations where the
waste material or contaminated soil is naturally aerated or where artificial
aeration is feasible. Also, the addition of nutrients such as nitrogen and
phosphorus may be required if the waste material is deficient in these con-
stituents. Lime will be required to maintain proper pH. Thus, further prob-
lems exist, with respect to application and mixing of lime and nutrients. The
above criteria suggest that biodegradation may have very limited application
as a remedial technique for in-situ direct treatment of waste material.
Situations where it could be applied are those where complete mixing and
aeration can be achieved, i.e., a chemical spill or landspreading operation
where the wastes have not migrated below tilling depth (about 12 inches), or a
surface impoundment in which the waste is fluid enough to be mechanically
aerated and pumped for mixing. Unit costs for some components of an in-situ
microbial degradation system are given in Table 7-12.
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TABLE 7-12
UNIT COSTS FOR IN-SITU MICROBIAL DEGRADATION
Component
Polybac microbes, dry bulk
Lime
Fertilizer
Liming (labor & equipment only)
Fertilizing (labor & equipment only)
Seeding (labor & equipment only)
Hydraulic spreading (labor &
equipment only)
Soil cultivation (once per month)
Unit cost
$23.75/lb
$59/acre
$85/acre
$160/acre
$200-270/acre
$115-185/acre
$115/acre
$200/acre-month
Floating mechanical aerators, stainless, installed
10 HP
50 HP
100 HP
$6,300 ea.
$11,600 ea.
$21,600 ea.
Reference
1
2
2
2
2
2
2
3
4, 5
1Polybac Corporation, 1978
2McMahon and Pereira, 1979
3Kincannon, 1972
"Richardson Engineering Services, Inc. 1980
5Godfrey, 1979
As an example, assume that an acre of land adjacent to an oily sludge
surface impoundment has been contaminated by surface seepage. Contamination
has been limited to the top 12 inches of soil due to low soil permeability in
the area. It was determined that microbial seeding, liming, and fertilization
of the area with subsequent cultivation of the soil could degrade the wastes.
If soil was cultivated (aerated) every month and lime and fertilizer were
applied every six months for a two-year period, the costs would be as follows:
Initial Application
Polybac microbes
-- assume an application rate of 100 Ibs/acre
100 Ibs x $23.75/lb = $2,375
333
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Lime and fertilizer materials cost
-- $59/acre + $85/acre = $144
Hydraulic spreading = $115
Soil cultivation = $200
Monthly Soi1 Cultivation
23 months x $200/mo.-acre = $4,600
Semiannual Liming and Fertilization
Cost of liming = $160/acre + $59/acre = $219/acre
Cost of fertilization = $270/acre + $85/acre = $355/acre
Fertilization and liming costs assuming four applications in
two years = 4 x ($219 + $355) = $2,296
Total Costs for In-Situ Microbial Degradation (1 acre)
$2,375 + $144 + $115 + $200 + $4,600 + $2,296 = $9,730
7.7 OTHER DIRECT TREATMENT TECHNIQUES
Besides the techniques already mentioned in previous sections, other
techniques may be used to control waste from refuse sites. These techniques
include:
Molten Salt
Plasma Destruction
7.7.1 Molten Salt
The Molten Salt Process is based on the concept of injecting the waste
below the surface of a molten salt bath. The salt typically consists of 90
percent sodium carbonate and 10 percent sodium sulfate. The molten salt is
placed in a reactor where temperatures are maintained in the range of 1,500ฐF
to 1,800ฐF. Lower temperatures can be obtained by using a salt with a lower
melting point, such as potassium carbonate. Combustion of the wastes may
generate gases such as sulfur dioxide or hydrogen chloride. Sulfur dioxide
then reacts with the salt to form sodium sulfate, and hydrogen chloride reacts
to form sodium chloride.
334
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The molten salt process has the ability to retain participates generated
during the combustion process. Depending on the circumstances, the spent
molten salt may be either regenerated or land-disposed.
This process is applicable to disposal of most organic wastes (EPA,
1975). The residence time is usually an average of 3/4 second. The proposed
investment cost for a portable unit treating 500 Ib/hr is about $500,000 (1975
costs). For a 200 Ib/hr unit with salt regeneration, the cost is $800,000
(EPA, 1975).
7.7.2 Plasma Reduction
Plasma is a partially ionized gas composed of ions, electrons, and neu-
tral species. It has been demonstrated that disposal of wastes can be
achieved by injecting the waste material in a microwave plasma system (EPA,
1975).
The plasma destruction process is based on the concept that a molecular
bond can be broken by transferring the energy of an excited particle to the
bond. In a plasma destruction system, microwave energy is applied to excite
the molecules of the carrier gas, thus raising the energy levels of the free
radicals (EPA, 1975). The excited electron then transfers its energy to break
the bonds of materials located in the near proximity. Thus, essentially any
organic waste regardless of its physical properties (liquid, solid, gas) may
be destroyed by the plasma destruction process.
The residence time within the plasma ranges from 0.1 to 1 second. The
operating temperature is low (300ฐF).
The plasma destruction system is only in the developmental state and has
been limited to gaseous material at laboratory-scale operations. This process
has a very high potential for becoming a waste disposal process if favorable
markets can be developed.
Cost for plasma destruction has been estimated at $.10/lb of waste for
electricity and about $10,000 capital cost (EPA, 1975).
335
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REFERENCES
Barnard, W. 1978. Prediction and control of dredged material dispersion
around dredging and open-water pipeline disposal operations. U.S. Army
Engineer Waterways Experiment Station. Vicksburg, MS.
Brunner D., and D. Keller. 1972. Sanitary landfill design and operation.
EPA Report SW-65 ts. Washington, D.C.: U.S. Government Printing Office.
Carson, A. B. 1961. General excavation methods. F. W. Dodge Corporation,
N.Y.
Cecos International, Inc., Niagara Falls, New York. February/May 1980. Per-
sonal communications with S. Paige and P. Rogoshewski.
Considine, D. (ed.) 1974. Chemical and process technology encyclopedia.
New York: McGraw-Hill Book Company.
Day A. 1973. Construction equipment guide. New York: Wiley-Interscience
Publications.
DeRenzo D. (ed.) 1978. Unit operations for treatment of hazardous industrial
wastes. Noyes Data Corporation, Park Ridge, NJ.
Environmental Concern, Inc. 1980. Scope of services available. St. Michaels,
MD.
Farb D. 1978. Upgrading hazardous waste disposal sites: remedial approaches.
U.S. Environmental Protection Agency, Cincinnati, Ohio. SW-677.
FMC Corporation. 1979. Industrial waste treatment with hydrogen peroxide.
Industrial Chemicals Group. Phildelphia, Pennsylvania.
Godfrey R. (ed.). 1976. Building construction cost data: 1976 cost cata-
logue. Duxbury, MA: Robert Snow Means Co., Inc.
Godfrey R. (ed.). 1979. Building construction cost data, 1980. Kingston,
MA: Robert Snow Means Co., Inc.
Gren G. 1976. Hydraulic dredges, including boosters. In: Proceedings of
the Specialty Conference on Dredging and its Environmental Effects. New
York: American Society of Civil Engineers.
Huston .]., and W. Huston. 1976. Techniques for reducing turbidity associated
with present dredging procedures and operations. Prepared for U.S. Army
Engineer Waterways Experiment Station. Vicksburg, MS. Contract no. DACW
39-75-0073.
Kincannon C. 1972. Oily waste disposal by soil cultivation process. U.S.
Environmental Protection Agency, Washington, D.C. EPA-R2-72-110.
336
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Linsley R., and J. Franzini. 1979. Water-resources engineering, 3d ed.
New York: McGraw-Hill Book Company.
Lubowitz H., R. Derham, L. Ryan, and G. Zakrzewski. 1977. Development of a
polymeric cementing and encapsulating process of managing hazardous
wastes. Prepared under contract 68-03-2037 by TRW Systems Group for
USEPA/ORD Municipal Environmental Research Laboratory, Cincinnati, OH.
Lubowitz H., and C. Wiles. 1978. Encapsulation technique for control of Haz-
ardous Wastes. In: Land disposal of hazardous wastes: Proceedings of
the Fourth Annual Research Symposium. Shultz, D. et al. (eds.). Cin-
cinnati, Ohio: Municipal Environmental Research Laboratory, ORD.
EPA-600-9-78-016.
McMahon, L., and P. Pereira (eds.). 1979. 1980 Dodge guide to public works
and heavy construction costs. New York: McGraw-Hill Information Systems.
Metcalf and Eddy, Inc., 1972. Wastewater engineering: collection, treat-
ment, disposal. New York: McGraw-Hill Book Company.
National Car Rental System Inc., Mudcat Division, Fort Lee, New Jersey. Janu-
ary 1980. Personal communication with P. Rogoshewski.
Palesh and Gulledge, 1979.
Pojasek, R.B. April 1978. Stabilization, solidification of hazardous wastes.
Environmental Science and Technology 12(4):382-386.
Polybac Corporation. 1978. Technical data sheets. Allentown, PA.
Pradt L. A. 1972. Developments in wet air oxidation. Chemical Engineering
Progress 68(12):72-77. [Updated 1976.]
Richardson Engineering Services, Inc. 1980. Process plant construction esti-
mating standards, vol. 1. Sol ana Beach, CA.
Rogoshewski, P.J., and D.D. Carstea. 1980. An evaluation of lime precipita-
tion as a means of treating boiler tube cleaning wastes. U.S. Environ-
mental Protection Agency, Research Triangle Park, NC. EPA-600-7-80-052.
Sato E. 1976. Application of dredging techniques for environmental problems
in dredging: Environmental effects and technology. San Francisco:
WODCON Association.
Schnell Publishing Co. 1980. Chemical Marketing Reporter 217(22): [2 June
issue].
Stubbs F. W. 1959. Handbook of heavy construction, 1st ed. New York: Mc-
Graw-Hill.
337
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Tolman, A., A. Ballestero, W. Beck, and G. Emrich. 1978. Guidance manual for
minimizing pollution from waste disposal sites. U.S. Environmental Pro-
tection Agency, Cincinnati, Ohio. EPA-600/2-78-142.
Vaughan Co., Inc. 1980. Vaughan pumps. Montesano, WA: Vaughan Co., Inc.
Vaughn-Maitlen Industries (VMI), Bethany, OK. March 1979. Personal communica-
tion with P. Rogoshewski.
Weininger, S. 1972. Contemporary organic chemistry. New York: Holt, Rine-
hart, and Winston.
U.S. Environmental Protection Agency. 1980. Hazardous wastes and consoli-
dated permit regulations. Federal Register'45(93):33063-33578.
U.S. Environmental Protection Agency. 1975. Incineration in hazardous waste
management. Office of Solid Waste Management Programs. Municipal Envi-
ronmental Research Laboratory, Cincinnati, OH. SW141.
U.S. Environmental Protection Agency. 1978. Liners for sanitary landfills
and chemical and hazardous waste disposal sites. Cincinnati, OH. PB
293335.
U.S. Environmental Protection Agency. 1979a. Process design manual: munici-
pal sludge treatment and disposal. Municipal Environmental Research
Laboratory, Cincinnati, OH. EPA-625/1-79-011.
U.S. Environmental Protection Agency. 1979b. Survey of solidification/sta-
bilization technology for hazardous industrial wastes. Cincinnati, OH.
EPA-600/2-79-056.
338
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8.0 CONTAMINATED WATER AND SEWER LINES
Sanitary sewers and municipal water mains located down-gradient from
hazardous waste disposal sites may become contaminated by infiltration of
leachate or polluted groundwater through cracks, ruptures, or poorly sealed
joints in piping. Water mains are less susceptible to the inflow of liquid
contaminants, since they are generally full-flowing, pressurized systems
constructed of cast iron piping with high structural integrity. They are much
more resistant to cracking from root intrusion or settlement than are the
vitrified clay pipes (VCP) commonly used for gravity sewer lines. However,
the contamination of municipal mains carrying a potable water supply to com-
mercial and residential consumers has much graver public health consequences
than does the contamination of sewage flowing to a treatment plant.
When contamination of sewers or water lines occurs, two basic remedial
options are available: (1) in-place cleaning and repair, or (2) removal and
replacement. Pipeline rerouting and the construction of impermeable subsur-
face barriers such as grout curtains are expensive preventive measures that
may be implemented when existing sewer and water lines are situated in the
proximity of uncontrolled hazardous waste disposal sites.
In order to assess the success of the remedial action utilized, the
contaminated source must be tested. The overall success is easiest to deter-
mine when results of tests can be evaluated against test results obtained
prior to the remedial action. The last section (Section 8.5) of this chapter
discusses the monitoring of water and sewer lines near waste disposal sites to
assess potential contamination and remedial action effectiveness.
8.1 IN-SITU CLEANING
The methods used to clean, inspect, and repair clogged or leaking sewer
lines are well established and, to a large degree, can be applied to rehabili-
tation of contaminated water lines. Available sewer-cleaning techniques
include mechanical scouring, hydraulic scouring and flushing, bucket dredging,
suction cleaning with pumps or vacuums, chemical absorption, or a combination
of these methods. Access to sewer lines for interior cleaning and repair is
most commonly afforded by manholes. Flushing inlets and unplugged residential
service connections provide additional points of access. Fire hydrant con-
nections allow access to municipal water lines.
339
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8.1.1 Mechanical and Hydraulic Scouring
Mechanical scouring is effective in removing pipeline obstacles such as
roots, stones, and corrosion nodules, greases and sludges. In the case of
sewer lines infiltrated by contaminated groundwater or leachate, interior
scouring may be necessary to loosen or remove solidified masses of toxic
chemical precipitates, which are then flushed or dredged from the line.
Scouring, and internal cleaning, in general, is necessary in small-diameter
pipelines to facilitate the precise locating of inflow leaks by closed-circuit
television inspection. Mechanical scouring techniques include the use of
power rodding machines ("snakes"), which pull or push scrapers, augers, and
brushes through the obstructed line (Figure 8-1). "Pigs" are bullet-shaped
plastic balls lined with scouring strips that are hydraulically propelled at
high velocity through water mains to scrape the interior pipe surface (Paw-
towski, 1980).
Hydraulic scouring of contaminated lines can be achieved by running
high-pressure fire hoses into sewer lines through manholes and flushing out
given sections of the sewer. This technique is often used after mechanical
scouring devices have cleared the line of solid debris or loosened contami-
nated sediments and sludges coating the inner surface of the pipe.
8.1.2 Bucket Dredging and Suction Cleaning
A bucket machine can be used to dredge grit or contaminated soil from a
sewer line (Figure 8-2). Power winches are set up over adjacent manholes with
cable connections to both ends of the collection bucket, which is pulled
through the sewer until loaded with debris. The same technique can be used to
pull "sewer balls" or "porcupine scrapers" through obstructed pipes (Hammer,
1975). Bucket dredging is also useful for collecting samples of contaminated
sediments, groundwater, or leachate that may have infiltrated the lines.
Suction devices such as pumps or vacuum trucks also may be used to clean
sewer lines of toxic liquids and debris. Again, manholes and fire hydrants
provide easy access for the setup and operation of such equipment.
8.1.3 Chemical Treatment
Another method of sewer pipeline cleaning is the use of hydrophilic
polymersfoams and gelsthat absorb and physically bind liquid pollutants in
a solid elastomeric matrix (Johnson, 1980). These polymers are special chem-
ical grout's that can either be applied internally to pipelines or injected
through breaks in the line from the exterior. Once the absorbent grout has
set (solidified), the solid grout/pollutant matrix can be hydraulically
flushed from the line. The applications of many of these hydrophilic grouts,
340
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FIGURE 8-1
POWER ROODING MACHINE
(Source: Hammer, 1975)
Power rodding
machine
Rod reel
inside housing
Guide brace
Cleaning tool
341
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FIGURE 8-2
SCHEMATIC OF BUCKET MACHINE CLEANING
(Source: Hammer, 1975)
Power winch with
loading chute
Power winch
Engine
Cable
Truck for hauling
away debris
Manhole |
-J
Roller braced_
in manhole
I .Sewer
Roller
CL
ฃi :
I
whose formulations are often proprietary, are still in the developmental and
testing stages.
8.1.4 Cleaning Considerations
The choice of cleaning techniques for rehabilitating contaminated sewer
and water lines depends on a number of variables: the extent of contami-
nation, the chemical and physical nature of the infiltrated contaminants, the
costs and availability of different cleaning services, ease of access to con-
taminated areas, the immediacy of any potential public health hazards (water
line vs. sewer), and the specific legal and constitutional issues that may
complicate a given cleanup strategy. Interior cleaning of contaminated pipes
will facilitate the location of cracks and joint failures which ultimately
must be sealed to prevent further infiltration of contaminated soil and water.
In some instances, pipeline scouring and flushing must be performed both
before and after the location and repair of inflow leaks.
8.2 LEAK DETECTION AND REPAIRS
8.2.1 Pipeline Inspection
Inspection of pipelines for leaks or infiltration points may be part of a
regular sewer or water line maintenance program. Methods to detect and locate
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pipeline breaches include the use of dyes and other tracer chemicals, patented
audiophone leak detectors, smoke testing, and installation of pressure gages
along a given length of pipe to monitor changes in hydraulic gradient (Linsley
and Franzini, 1979). Large-diameter pipeline interiors are inspected by
pulling skid-mounted miniaturized closed-circuit television cameras through
the line. The entire inspection can be recorded on videotape for future
reference.
Closed-circuit inspection is often performed in conjunction with interior
pipeline grouting systems to seal leaks from the inside.
8.2.2 Grouting
Once infiltration points have been specifically located, or cracked or
ruptured sections of lines have been discovered, the pipeline can be repaired.
One method of in-place repair is to grout fractures or leaky joints to seal
and waterproof points of infiltration/exfiltration. Chemical grouts for
sealing sewer lines are generally limited to acrylamide resins and silica
gels, which are applied to pipeline cracks or non-watertight joints from the
interior as they are detected by television inspection. A grouting packer is
pulled through the sewer line along with the closed-circuit camera, and as
hydraulic breaks or fissures are detected, the grout packer inflates and
injects a root killer (such as copper sulfate) and plastic gel or resin into
the area, sealing the break (Pawtowski, 1980). Usually, enough chemical grout
will set in the surrounding soil to effect a more permanent seal.
Sewer line leaks can be sealed from the exterior by injecting a grout
"collar" into the soil immediately surrounding the area of infiltration. The
choice of soil grout used for exterior sealing depends largely on the texture,
pH, and water content of the surrounding soil. For coarse sands or gravels,
mixtures of clay or bentonite and cement are recommended. Finer-grained sands
and silty soils are more effectively grouted with dilute silica gels or acry-
lamide resins (AFTES, 1976). The application of exterior soil grouting to
seal leaks generally is limited to gravity sewer lines or storm sewers; full-
flowing pressurized sewer lines or water mains are most effectively sealed by
interior relining (Hudson, 1980).
8.2.3 Pipe Relining and Sleeving
Relining of pipelines is another method of sealing that can inhibit
infiltration and exfiltration in pipelines. Cement mortar and bitumen are
commonly applied as a corrosion-preventative coating in water mains, often by
proprietary lining machine processes that do not require removal of the pipe.
Interior lining of sewers can be performed in addition to chemical grouting to
ensure a high level of pipeline integrity and low future risk of groundwater
or leachate infiltration. Large sections of badly cracked or deteriorating
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sewer lines can be relined with high density polyethylene (PE) piping. Poly-
ethylene is extruded from a special cylinder that is pulled through the lines
on a cable (Figure 8-3). As the plastic is extruded, the cylinder is heated
and the polyethylene is fused onto the inner surface of the pipe. Once the
plastic has cooled and solidified, the cylinder is pulled onto a new section
of the line.
Exterior polyethylene sleeving is another method used for leakproofing
water mains. Sheets of polyethylene plastic are simply wrapped around the
length of pipe sections and taped down. This job is usually performed on new
pipeline used for replacement when sections of old or ruptured line are exca-
vated for repair. Sleeving is usually placed only on cast-iron mains 24
FIGURE 8-3
INTERIOR RELINING WITH PE
inches in diameter or smaller; larger cement mains are not sleeved (Laugle,
1980). The costs of sleeving are minor when compared to the overall costs of
pipeline excavation and replacement; sleeving represents a very simple and in-
expensive sealing technology.
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8.3 REMOVAL AND REPLACEMENT
If the inflow of contaminated liquids or sediments is limited to a single
section of piping, or if chemical analysis reveals that no public health
hazard is posed, and the line is accessible without excavation, then mechan-
ical scouring and/or hydraulic flushing of the interior followed by
cement or bitumen relining may be sufficient. However, if the main has
raptured or is known to be an old line, or if extensive contamination of
several sections of pipeline has occurred, then excavation and replacement
must be performed. Excavation and replacement of contaminated lines is the
most expensive remedial option, but in many cases, it is the only available
choice to protect public health, especially when water mains have ruptured or
have been contaminated by infiltration during pump failures. When water lines
break or when there is reason to suspect possible contamination due to the
infiltration of polluted groundwater or soil, public works officials must:
(1) locate and isolate the affected area(s) of pipeline; (2) shut down pumps
and close valves to dry the affected area(s); (3) evaluate the quantity and
nature of any infiltrated contaminants (a process that may involve sample
collection and analysis), and (4) determine the safest and most economical
corrective measure.
Sewer lines that are clogged, contaminated, or cracked generally are much
easier to access than water lines for in-place cleaning and repair. Excava-
tion and replacement of buried sewer lines is a much more costly alternative
since these are generally laid deeper in the ground than water lines. Also,
in-place rehabilitation methods for sewer lines are well-established. For
pressurized water mains, however, cracks and ruptures represent a much more
serious problem in terms of an interrupted or potentially contaminated public
water supply. Excavation may be necessary to access failed joints in water
pipelines, and ruptured or seriously contaminated lines must be replaced.
8.4 COSTS
A summary of unit costs associated with pipeline cleaning and repair is
presented in Table 8-1.
The costs presented in Table 8-1 represent average unit costs for sewer
and water line rehabilitation techniques. Some of the costs are derived from
sources in specific geographic localities (i.e., Cincinnati and Washington,
D.C.) and may not reflect national averages for the services indicated. Site-
specific complications may -add to these unit costs. For instance, if a
pipeline is situated beneath surface pavement, excavation costs will increase
significantly. Costs for removal of surface pavement vary depending on thick-
ness and type of material. Removal of bituminous driveway and road pavement
costs approximately $1.50 to $2.00 per square yard of material excavated.
Excavation of reinforced concrete (up to 6 inches thick) or sidewalk concrete
will add $3.00 to $4.00 per square yard of removed surface. Excavation through
345
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TABLE 8-1
COSTS FOR CLEANING, REPAIR, AND REPLACEMENT OF
WATER AND SEWER LINES
Remedial technique
Sewers
Hydraulic or mechanical
scouring, 12" VCP line
Television inspection,
12" line
Chemical grout for sewer
line sealing
Clean, T.V. inspect and
grout sewer line
Laying VCP in trench
(not including exca
vation and backfill)
Reinforced concrete pipe
(storm sewer), 8'
lengths, trench exca
vation, pipe placement,
backfill and compaction
Water mains
Ductile iron pipeline
excavation and re
placement (including
polyethylene
sleeving)
In-placing cleaning and
cement re-lining of
pipes
Laying ductile iron
pipe, 13' lengths
(not including exca
vation and backfill)
Cost1
$2.00/ft
$1.00/ft
$10-$15/gal
or $3.00/lb
$5.00/ft
average2
8" pipe: $6/ft
12" pipe: $10/ft
24" pipe: $38/ft
36" pipe: $100/ft
36"
42"
48"
54"
60"
$46/ft
$57/ft
$73/ft
$90/ft
$119/ft
8" pipe: $50/ft
12" pipe: $60/ft
16" pipe: $80/ft
24" concrete
pipe: $100/ft
6-12" pipe: 50%
of replacement
24" pipe: 25-30%
of replacement
8" pipe: $13/ft
12" pipe: $21/ft
16" pipe: $30/ft
24" pipe: $46/ft
Source of cost
information
D.C. area sewer
service contractor
D.C. area sewer
service contractor
Avanti International
acrylamide grout
D.C. area sewer
service contractor
R. Godfrey (ed.),
Building Construction
Cost Data. 1980
1980 Dodge Guide
Cincinnati Water Works
Bids (EPA/MERL)
Cincinnati Water Works
Bids (EPA/MERL)
R. Godfrey (ed).,
Building Construction
Cost Data, 1980
continued
346
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TABLE 8-1 (Continued)
Remed i al techn i que
Trench excavation and
backfill
4 ft. wide trench exca-
vated 4 to 10 ft deep
in sandy loam
Trench backfill by
hand; hand tamp com-
paction
Cost
$2-$3/yd 3
$13-$15/yd
Source of cost
information
R. Godfrey (ed.),
Bui 1ding Construction
Cost Data. 1980
R. Godfrey (ed.),
Bui 1ding Construction
Cost Data, 1980
1Unit costs include materials and labor for
2Cost will vary depending on size of line ahd
larger pipe, higher costs.
services indicated.
amount of grouting required;
thicker layers of concrete may cost more
material (Godfrey, 1979). Dewatering of
diaphragm or centrifugal pumps will increase
depending on pump size required (Godfrey,
than $50 per cubic yard of removed
trenches during excavation using
se costs by $100 to $300 per day
979).
The costs presented above also do net include those for hauling of ma-
terials (e.g., pipeline) to the job site, or the necessary handling and dis-
posal of possibly hazardous debris that may be scoured and flushed from con-
taminated lines. Where soil grouting is to be performed to collar a sewer
line break, the choice of an appropriate grout may require a geotechnical
evaluation of the soils in question, thus presenting another consideration
that may add significantly to total costs.
8.5 MONITORING
A properly planned monitoring program is essential in the determination
of the extent and magnitude of water and sewer line contamination. Collected
data can also be used as an early warning system of contamination as well as
an evaluation tool in the determination of the effectiveness of remedial
actions.
347
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The planning of a monitoring program should address three main criteria:
(1) sampling location, (2) parameters to be measured and analytical considera-
tions and (3) sampling frequency. Those criteria are discussed in more detail
in the following sections.
8.5.1 Sampling Locations
Sampling locations should be strategically located so that the results of
sampling give an accurate description of the extent of contamination as well
as identify the most probable contamination source (i.e., where the contami-
nants are entering the water or sewer lines). Because of the differing nature
of water and sewer lines (usually pressurized versus gravity flow), the access
for sampling locations will also differ.
Sampling of water lines may be most easily accomplished by obtaining
samples from private residences and from commercial and industrial establish-
ments. In most instances, permission to sample these sources can be easily
obtained, especially since there is usually no cost involved for the party
being sampled and since the party generally knows that the program is being
carried out for his benefit. Where municipal sources, such as fire hydrants
are available, these can be utilized also.
In obtaining samples from the sources previously mentioned, it is very
important to establish whether the water has been treated. At private resi-
dences treatment may include removal of iron , neutralization, water soften-
ing, and/or water filtration. Water treatment at industrial locations may be
more complex, depending on the use of the water in the industrial process.
The sample must represent untreated water to insure that none of the contam-
inants has been removed.
In choosing the sampling points, the location of the disposal site in
relationship to groundwater gradients must be assessed. The most effective
program would test the nearest down-gradient water and sewer lines. These are
the ones that would most likely be contaminated first and would provide the
earliest warning. This, of course, is true assuming that these lines are
representative of the condition of other lines nearby. In other words, a new
water or sewer line near a contaminating source may not be contaminated, but a
line in poor condition but further from the source may become contaminated.
Sampling of sewer lines can be accomplished at access points such as man-
holes and at the treatment plant. Treatment plant monitoring is carried out
at most plants on a routine basis. Often it is during the analysis of these
samples that contamination is detected. The results from a treatment plant do
not, however, identify the location of the contaminating source. Therefore,
once contamination has been identified, the system has to be reviewed to
identify the areas most likely to be contaminated. Additional samples should
348
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then be collected from manholes located in the area to pin-point the contami-
nating source.
8.5.2 Parameters to be Measured and Analytical Considerations
The selection of particular parameters to be measured depends upon the
nature of the suspected source. The selection of parameters should assure
that the contamination can be easily detected, and should identify some of the
more toxic species so that potential health effects can be mitigated.
Substances of potential concern in hazardous waste leachate include:
Soluble, oxygen-demanding organics
Soluble substances that cause tastes and odors in water supplies
Color and turbidity
Nutrients such as nitrogen, phosphorus, and carbon
Toxic organic and inorganic substances
Refractory materials
Oil, grease, and immiscible liquids
Acids and alkalis
Substances resulting in atmospheric odors
Suspended and dissolved solids
The final list of parameters chosen for analysis should consider the following
(EPA, 1980):
Electrical conductivity (water and sewer lines)
Turbidity (water lines) -
Settleable, suspended, and total dissolved solids (water!ines)
Volatile solids (water lines)
Oils, greases and immiscible liquids (water and sewer lines)
Odors (water and sewer lines)
pH (water and sewer lines)
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Oxidation Reduction Potential (ORP) (water and sewer lines)
Acidity (water and sewer lines)
Alkalinity (water and sewer lines)
Biochemical Oxygen Demand (BOD) (water and sewer lines)
Chemical Oxygen Demand (COD) (water and sewer lines)
Total Organic Carbon (TOC) (water and sewer lines)
Heavy metals (water and sewer lines)
Other specific inorganic sustances (water and sewer lines)
Nitrogen and phosphorus compounds (water and sewer lines)
Volatile organic acids (water and sewer lines)
Toxicity (water and sewer lines)
Analytical procedures have been suggested by EPA and ASTM. The proper
techniques (acceptable to the regulatory agencies) must be utilized. Among
the factors to be considered in selection of an analytical method are:
Sensitivity, precision and accuracy required
Interferences
Number of samples to be analyzed
Quantity of sample available
Analytical turn-around time
Analytical cost
8.5.3 Sampling Frequency
Sampling frequency is largely dependent on the type of monitoring program
being instituted (e.g., routine detective monitoring, problem identification
monitoring, remedial action effectiveness evaluation monitoring). Within a
single monitoring program there may be a variety of sampling frequencies for
individual sampling locations. The type of sample collected (i.e., grab
sample versus a composite sample) must also be established and should suit the
objectives of the program.
350
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During a routine monitoring program, to detect potential contamination,
samples are often collected monthly (or less frequently). These samples are
usually grab samples. If contamination is noted, then the sampling frequency
and number of sampling locations should be increased to identify the con-
taminating source. If water lines are contaminated, an alternative water
source may have to be instituted until the problem is corrected. Sampling
should be carried out after completion of the remedial action to ensure that
the actions taken were effective and sufficient.
Composite samples should be considered in sewer lines where the com-
position and concentrations display great fluctuation. Along with the com-
posite samples, grab samples should also be collected so that peaks and maxi-
mum concentrations of contaminating parameters may be detected.
351
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REFERENCES '
AFTES (Association Francaise des Travaux en Souterrain). 1975. Recommenda-
tions for the use of grouting in underground construction, trans. G.W.
Clough
Godfrey, 8. (ed.). 1979. Building Construction Cost Data, 1980. Kingston,
MA: Robert Snow Means Co., Inc.
Hammer, M. 1975. Water and waste-water technology. New York: John Wiley
and Sons.
Hudson, !_., Department of Public Works, City of Baltimore, MD. March 1980.
Personal communication with H. Bryson.
Johnson, J., Chemical Research Division, 3M Company. March 1980. Personal
communication with H. Bryson.
Laugle, M. for R. Clark. EPA Municipal Environmental Research Laboratory,
Cincinnati, OH. February 1980. Personal communication to R. Wetzal.
Linsley, R., and J. Franzini. 1979. Water resources engineering, 3d ed.
New York: McGraw-Hill Book Co.
National Association of Sewer Service Companies (NASSCo). 1978-1979. Notes
from Underground. Washington, DC. [1978 and 1979 Newsletters.]
Pawtowski, C., J-P Servorooter, Inc. Rockville, MD. March 1980. Personal
communication with H. Bryson.
U.S. Environmental Protection Agency. 1980. Management of hazardous waste
leachate. R.J. Shuckrow et al., for Municipal Environmental Research
Laboratory, Cincinnati, OH. SW-871.
352
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9.0 CONTAMINATED SEDIMENTS
Uncontrolled waste disposal sites may directly or indirectly contaminate
bottom sediments deposited in streams, creeks, rivers, ponds, lakes, estu-
aries, and other bodies of water. Sediment contamination by waste disposal
sites may occur along several different pathways. Contaminated soil may be
eroded from the surface of hazardous waste disposal sites by natural runoff
and subsequently deposited in nearby watercourses or sediment basins con-
structed downslope of the site. Also, existing sediments along stream and
river bottoms may adsorb chemical pollutants that have been washed into the
watercourse from disposal areas within the drainage basin. Similarly, contam-
inated groundwater may drain to surface watercourses and the transported
pollutants may settle into, or chemically bind with, bottom sediments. Anoth-
er possible source of sediment contamination is direct leakage or spills of
hazardous liquids from damaged or mishandled waste containers; spilled chemi-
cals that are heavier and denser than water will sink to the bottom of natural
waters, coating and mixing with sediments. The precise mechanisms by which
sediments may become contaminated by disposal site pollutants will depend on
site-specific hydrologic variables and the physical characteristics of the
polluting chemical(s).
Contaminated sediments, depending on their quantity and nature, may
severely disrupt aquatic ecosystems and may even affect public drinking water
supplies. Chemicals that settle into the bottom sediments of natural waters
may damage or kill benthic organisms, disrupting the aquatic food chain. Fish
kills may follow, or, if a toxic chemical has become concentrated through
passage along successive trophic levels, people feeding on the contaminated
fish or shellfish may be poisoned. More seriously, if contaminated sediments
are deposited in water supply reservoirs, a direct threat to the consuming
public may result.
Remedial techniques for contaminated sediments generally involve removal
and subsequent disposal or treatment of the sediments. Sediment removal
methods include well-established excavation and dredging techniques. Dredged
materials ("spoil") management includes techniques for drying, physical
processing, chemical treatment, and disposal. Treated sediments, or those
that have not been severely contaminated, may be used as construction fill and
in reclamation projects. Plans to remove and treat contaminated sediments
must be designed and implemented on a site-specific basis. Dredging in wet-
lands may require revegetation of the area.
353
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A knowledge of the physical properties and distribution of contaminated
sediments is highly desirable, if not essential, in selecting a dredging
technique and in planning the dredging operation. Information on grain size,
bed thickness, and source and rate of sediment deposition is particularly
useful in this context. Such information can be obtained through a program of
bottom sampling or core sampling of the affected sediment.
9.1 MECHANICAL DREDGING
9.1.1 Descri pti on and Applications
Mechanical dredging of contaminated sediments should be considered under
conditions of low, shallow flow. Dredging should be used in conjunction with
stream diversion techniques to hydraulically isolate the area of sediment
removal. Under any other conditions, mechanical excavation with draglines,
clamshells, or backhoes may create excessive turbidity and cause uncontrolled
transport of contaminated sediments further downstream. Stream diversions
with temporary cofferdams, followed by dewatering and mechanical excavation of
the contaminated sediments, are typical elements of a mechanical dredging
operation for streams, creeks, or small rivers. Mechanical excavation can
also be used to remove contaminated sediments that have been eroded from
disposal sites during major storms and deposited in floodplains or along river
banks above the level of base flow.
For streams and rivers that are relatively shallow and whose flow veloc-
ity is relatively low, backhoes, draglines or clamshells can be used to exca-
vate areas of the stream bed where sediments are contaminated. The excavated
sediments can be loaded directly onto haul vehicles for transport to pre-
designated disposal areas; however, the excavated material must be suffi-
ciently drained and dried before transport. This consideration represents a
major obstacle in such operations. Drained water may contain contaminated
sediments in suspension and must be handled accordingly. If the sediments are
relatively "young" and unconsolidated, they may be of a consistency that is
hard to handle with draglines or clamshells. Additionally, backhoe and drag-
line operation requires a stable base from which to work. For these reasons,
direct mechanical dredging of contaminated sediments in streams is not recom-
mended except for small streams with stable banks, slow and shallow flow,
underwater structures, and where the contaminated sediments are relatively
consolidated and easily drained. Direct mechanical excavation is also fea-
sible for contaminated sediments deposited on dry river banks or in flood-
plains.
A more efficient mechanical dredging operation with broader application
involves stream or river diversion with cofferdams, followed by dewatering and
excavation of contaminated sediments. Such an operation may prove quite
costly; however, there is little chance of stirring up sediments and creating
354
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downstream contamination. Efficiency of sediment removal is much greater by
this method than by instream mechanical dredging without diversion of flow.
Sheet-pile cofferdams may be installed in pairs across streams to tempo-
rarily isolate areas of contaminated sediiiient deposition and allow access for
dewatering and excavation (Figure 9-1). Alternatively, a single curved or
rectangular cofferdam may be constructed to isolate an area along one bank of
the stream or river (Figure 9-2); this method only partially restricts natural
flow and does not necessitate construction of a temporary diversion (by-pass)
channel to convey entire flow around the area of excavation, as the first
method does.
9.1.2 Design And Construction Considerations
During direct mechanical dredging of stream or river sediments, agitation
of the bed deposits during excavation may generate a floating scum of contam-
inated debris on the water surface, particularly if the chemical contaminant
is oily or greasy in nature. The installation of a silt curtain downstream of
the dredging site will function to trap any contaminated debris so generated;
the debris can then be collected through skimming and hauled to special dis-
posal areas.
Similarly, silt curtains can be employed to minimize downstream transport
of contaminated sediments. A schematic of a silt curtain is shown in Figure
9-3. It is constructed of nylon-reinforced polyvinyl chloride and manufac-
tured in 90-foot sections that can be joined together in the field to provide
the specified length. Silt curtains are usually employed in U-shaped or
circular configurations, as shown in Figure 9-4. Silt curtains are not recom-
mended for flow velocities greater than 1.5 feet per second (Barnard, 1978).
If in-stream mechanical dredging is determined to be technically feasible
and cost-effective, it can be performed most effectively during periods of low
flowthat is, during the driest months of the year for the particular cli-
mate. This generalization will hold true for any mechanical dredging opera-
tion, including those that involve cofferdam construction and stream diver-
sion.
Sheet-pile cofferdams are generally constructed of black steel sheeting,
in thickness from 5- to 12-gage and in lengths from 4 to 40 feet. For addi-
tional corrosion protection, galvanized or aluminized coatings are available
(ARMCO, 1979). Cofferdams may be either single-walled or cellular, earth-
filled in sections. Single-wall cofferdams may be strengthened by an earth
fill on both sides. Cellular cofferdams consist of circular sheet-pile cells
filled with earth, generally a mixture of sand and clay (Linsley and Franzini,
1979).
355
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FIGURE 9-1
STREAMFLOW DIVERSION FOR SEDIMENT EXCAVATION USING
TWO COFFERDAMS AND DIVERSION CHANNEL
Temporary sheet-pile;
remove after pipeline construction
Diversion
channel;
excavate, place
corrugated metal
pipe or similar
conduit
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Sediment
dewatering
and excavatio
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Temporary
sheet-pile
Riprap for
outlet protection
356
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357
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358
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FIGURE 9-4
TYPICAL SILT CURTAIN DEPLOYMENT CONFIGURATIONS
(Source: Barnard, 1978)
Maze (Not Recommended)
Legend:
O Mooring Buoy
i. Anchor
ฃ Single Anchor
or Piling
U-Shaped
In-Stream
Curtain Movement Due
to Reversing Currents
"C"
U-Shaped
Anchored On-Shore
Estuary
"D"
Circular or Elliptical
359
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Single-wall sheet-pile cofferdams are most applicable for shallow water
flows. For depths greater than 5 feet, cellular cofferdams are recommended
(Linsley and Franzini, 1979).
Cofferdams are most easily constructed for flow containment on shallow
streams and rivers, or on those with low velocities of flow. Where flow
velocities exceed 2 feet per second, cofferdam construction is not recommended
because of difficulties in driving sheet pile under such conditions (Staples,
1980). Cofferdam construction may be feasible for relatively wide and deep
rivers, providing the velocity of flow is not excessive; however, contaminated
sediments in very deep bodies of water (greater than 5 to 10 feet deep) may be
most effectively removed using hydraulic (suction) dredging techniques (Sec-
tion 9.2).
For small, narrow streams, sheet-piling can be driven by hand with light
equipment such as a hand maul or a light pneumatic hammer. For wider, deeper
streams or rivers where longer sheeting is required and access may be diffi-
cult, heavy driving equipmenta drop hammer or a pneumatic or steam pile
driverwill be needed (ARMCO, 1979). Preassembled (interlocked) sections of
sheeting are positioned and driven with the use of a crane; for wide, deep
rivers, the crane may be operated from a barge. A preconstruction geologic
site investigation may be necessary to ensure that bedrock or impervious
strata will not interfere with the pile-driving operation.
The length of sheet piling required for cofferdam construction will
depend on the stream depth, velocity of flow, and nature of the soil into
which the sheeting is driven. In general, the ratio of exposed length of
sheeting to driven length (unexposed, anchored into soil) should be about 1:1,
with 1 to 3 feet of freeboard above the water surface (Staples, 1980). For
example, to construct a cofferdam on a 5-foot-deep river would require
sheeting approximately 12 feet long: 5 feet driven, 5 feet exposed to flow,
and 2 feet freeboard. A greater length may be required if a layer of soft,
muddy, unconsolidated sediments overlies the stable soil stratum into which
the sheeting must be driven.
Figures 9-1 and 9-2 illustrate the two basic plans for sediment removal
using cofferdams to contain or divert streamflow. Two cofferdams may be
installed completely across the flow to partition the stream into sections to
be individually dewatered and excavated (Figure 9-1). This operation may be
required for stream- or riverbeds in which contaminated sediments have been
deposited completely across the channel cross-section, along both banks. Such
construction requires that the entire streamflow be temporarily diverted
through the excavation of a by-pass channel and installation of corrugated
metal piping of sufficient diameter to handle streamflow.
To estimate the maximum streamflow that can be handled by corrugated
metal piping of a given diameter, a modified Manning equation for corrugated
360
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pipe
flowing half-full at a maximum grade of 10 percent is given below:
where V = average velocity of flow in feet/second
d = diameter of the pipe in feet
S = slope of the pipeline channel grade (expressed
in decimal form; maximum S for which this
equation holds true = 0.10)
This modified Manning equation is based on a roughness coefficient (n) of
0.022 for corrugated metal pipe (Linsley and Franzini, 1979). Corrugated
metal piping is generally available in sizes up to 6 feet in diameter. Based
on pipe diameter and channel grade, velocity (V) of flow through the pipe can
be calculated using this equation. Multiplying the velocity (V) in feet/
second by the cross-sectional flow area (y*ฃ^ง for half-full flow) in square
feet will yield the maximum streamflow (in cubic feet/second) that can be
handled by the diversion pipeline. For pipeline discharge velocities ex-
ceeding 2.0 feet/ second, it may be necessary to stabilize the pipe outlet
area with stone riprap to prevent excessive scouring of the natural stream
bed.
For excavation of contaminated sediments deposited along only one side of
the channel, a single curved or jointed cofferdam can be installed to isolate
the construction area from streamflow (Figure 9-2). Such an installation will
partially restrict natural flow, creating an increased water level and higher
velocity flow within the restricted area of the channel. To prevent bank
overflow and excessive erosion resulting from this restricted flow, it is
recommended that a sheet-pile containment wall be driven along the channel
bank in the area of restricted flow. Both the cofferdam and sheet-pile rein-
forcement wall can be pulled when sediment excavation has been completed and
re-installed further downstream if additional sediment removal is required.
Areas enclosed by cofferdams may require dewatering if infiltration leaks
occur through poorly joined sections of sheet piling or if excessive precipi-
tation occurs during excavation activities. Dewatering can be accomplished
with single-stage centrifugal pumps, which are available in sizes that can
pump up to 5,000 gallons per minute (Richardson Engineering Services, 1980).
Natural drainage and evaporative drying may be sufficient to dewater small
areas of sediment deposition, but this may require too much time. Streambed
sediments isolated by cofferdams must be sufficiently dewatered before exca-
vation of the contaminated sediments can be performed efficiently.
Mechanical excavation of dewatered, contaminated sediments can be accomp-
lished with backhoes, draglines, or clamshells. Crawler-mounted hydraulic
backhoes can handle (excavate and load) as much as 200-300 cubic yards of
sediment per hour, with bucket capacities as great as 3 1/2 cubic yards.
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Draglines can handle up to 400 cubic yards per hour, with typical bucket
capacities of 2 to 5 cubic yards (McMahon and Pereira, 1979). Clamshells are
generally equipped with buckets from 3/8- to 2-cubic yards in size, and can
handle as much as 50 to 100 cubic yards per hour (Godfrey, 1979). Specific
limitations of each equipment type have been previously discussed in Section
7.1. Mechanical dredging output rates will vary depending on the size and
mobility of the equipment, and on site-specific conditions such as available
working area.
Excavated sediments can be loaded directly into haul trucks on-site for
transport to special disposal areas. Haul truck loading beds should be bot-
tom-sealed and covered with a tarpaulin or similar flexible cover to ensure
that no sediments are lost during transport. The entire loading operation
should be performed carefully to avoid uncontrolled spills of contaminated
sediments. Windy weather should be avoided during loading to prevent off-site
transport of finer sediments and dust. Sediments should not have been de-
watered to the point where they are excessively dry or loose.
9.1.3 Advantages and Disadvantages
The advantages and disadvantages associated with mechanical dredging
techniques are summarized in Tables 9-1 and 9-2. Table 9-1 addresses direct
instream mechanical dredging ("wet excavation"). Cofferdam diversion stream-
flow, with subsequent dewatering and mechanical excavation of contaminated
sediments, is addressed in Table 9-2.
Backhoe Excavation
10 yd3 of sediments x $1.50/yd3 to truck-load with backhoe = $15
Backhoe mobilization and demobilization = approx. $150
Contaminated sediment hauling, 200 miles to secure landfill; bulk density
1 ton/yd3; 200 miles x $4/loaded mile = $800
Disposal costs; $240/ton x 1 ton/yd3 x 10 yd3 = $2400
Additional costs to cover removal of the pipe after use and backfilling
of the trench will be incurred in most cases.
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TABLE 9-1
SUMMARY OF EVALUATION OF INSTREAM MECHANICAL DREDGING OF
CONTAMINATED SEDIMENTS
Advantages
May be cost-effective for slow,
shallow streams or sediments
in dry streambeds or flood-
plains
Also effective for small, isolated
pools or ponds containing contam-
minated sediments
Barge-mounted operations may be
used for larger rivers
Disadvantages
Generates excessive turbidity; may
cause downstream transport of
sediments
Only feasible for low, shallow
flows with stable streambanks
and consolidated sediments
May require special dewatering
methods (clamshell lift and drain
over haul trucks)
Efficiency of removal generally poor
Generally not recommended for hand-
ling contaminated sediments instream
TABLE 9-2
SUMMARY EVALUATION OF COFFERDAM METHOD FOR SEDIMENT REMOVAL
Advantages
High efficiency of removal;
low turbidity
Involves well-established
construction techniques
Structures easily removed and
transported
Cost-effective for slow-flowing
streams and rivers with favorable
access (stable banks; open areas)
Disadvantages
May be quite costly for deep, wide
flows and sites requiring diversion
pipeline
Not feasible for fast stream
flows ( >2 ft/sec)
Not recommended for flows deeper
than 10 feet
Sediment dewatering may be required
continued
363
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TABLE 9-2 (Continued)
Advantages Disadvantages
Access for mechanical excavation
equipment may be difficult
May require large excavation and
loading area
Transportation costs may be
excessive (remote areas)
Geologic substrate may prevent
sheet pile drive
TABLE 9-3
COSTS FOR MECHANICAL DREDGING/EXCAVATION OF CONTAMINATED SEDIMENTS
Description Unit cost Source
Dredging, mobilization and
demobilization; add to total $5,000-20,000 total 1
Barge-mounted dragline or clam-
shell, hopper dumped, pumped
1000' to shore dump $4.50-6.50/yd3 1
Bulk excavation; stockpiled or
truck loaded:
hydraulic backhoe, 1-3*5 yd3 bucket $1.16-1.78/yd3 1
clamshell, 1/2 and 1 yd3 $2.32-3.47/yd3 1
dragline, 3/4 and lh yd3 $1.39-2.06/yd3 1
For wet excavation;
clamshell or dragline add 100% 1
backhoe add 50% 1
clamshell excavation in
sheeting or cofferdam $3.50-13.00/yd3 1
continued
364
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TABLE 9-3 (Continued)
Description Unit cost Source
Mobilization and demobilization
of backhoe or dragline, 1^ yd $150 each 1
Earth hauling, 12 yd3 dump truck;
4-mile roundtrip, 1.6 loads/hr $2.34/yd3 1
Sheet piling, steel, high strength
(55,000 psi); temporary installation
(pull and salvage):
20' deep $8.24/ft2 1
25' deep $6.63/ft2 1
(see also Table 4.5)
Pile driver; mobilize and
demobilize:
50-mile radius $5,700 total 2
100-mile radius $9,450 total 2
Corrugated metal pipe, galva-
nized or aluminized; pipe
placement, not including
excavation and backfill
above top of pipe
12-inch diam.
24-inch diam.
36-inch diam.
48-inch diam.
60-inch diam.
16 ga. $ 6.70/linear ft. 1
14 ga. $12.80/linear ft. 1
12 ga. $28.00/linear ft. 1
12 ga. $39.00/linear ft. 1
10 ga. $60.00/linear ft. 1
Stone riprap; dumped from
trucks for outlet protection $16.65/yd3 1
Portable centrifugal water
pumps (self-priming):
3-inch; 20,000 gph, 8.5 hp $ 78/week 3
4-inch; 40,000 gph, 31 hp $225/week 3
6-inch; 90,000 gph, 64 hp $245/week 3
8-inch discharge $280/week 2
10-inch discharge $380/week 2
12-inch discharge $500/week 2
--continued--
365
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TABLE 9-3 (Continued)
Description Unit cost Source
Pump hose:
3-inch, 20-ft section $20.50/week 3
4-inch, 20-ft section $28.50/week 3
6-inch, 20-ft section $64.25/week 3
Silt curtain: $0.50-2.80/ft2 4
Hauling of contaminated
sediments: $ 2-4/1oaded mile 5
$ 2-4/1oaded mile
Disposal of contaminated
sediments: $240/ton 5
1 Godfrey, 1979
2McMahon and Pereira, 1979
3Richardson Engineering, 1980
4Kepner Plastic Fabrications, 1980
5Cecos International, Inc. 1980
9.1.4 Costs
Unit costs associated with mechanical dredging techniques are presented
in Table 9-3. An example cost calculation using those unit costs for mechan-
ical dredging at a hypothetical site is given below.
Assume that a stream 7.5 feet wide and 2 feet deep with an average flow
velocity of 1 fps (foot per second) contains 10 cubic yards of contaminated
sediments deposited along a 30-foot length of the stream from bank to bank.
Two sheet-pile cofferdams are to be constructed across the stream to partition
the area of deposition, necessitating temporary streamflow diversion with a
corrugated metal pipeline. Stream banks are sparsely vegetated and stable,
providing easy access for a 2-cubic yard hydraulic backhoe, which will exca-
vate and truck-load the sediments for offsite transport to a secure chemical
disposal site 200 miles away. Costs for this operation are derived as
follows:
366
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Cofferdam installation and streamflow diversion
5' deep x 8' wide = 40 ft2 x 2 cofferdams = 80 ft2;
pile drive and pull after operation is complete;
80 ft2 x $8.24/ft2 = $659
Excavation for pipeline (no backfill);
assumed trench cross section of 6 ft ;
30 ft x 6 ft2 x |y- ft3 x $1.78/yd3 = $12
Corrugated metal pipeline, 30' long;
12-inch diameter will handle streamflow;
30 ft x $6.70/ft = $201 to lay pipeline
9.2 LOW-TURBIDITY HYDRAULIC DREDGING
9.2.1 Description and Applications
Instream mechanical dredging (wet excavation) of contaminated sediments
is feasible only for relatively shallow, stagnant flows or for isolated ponds
and basins where streambed agitation and excessive turbidity will not cause
uncontrolled downstream contamination. For contaminated sediments in deep
bodies of water or in those with any appreciable flow, low-turbidity hydraulic
dredging operations are required. Low-turbidity dredging is any hydraulic
dredging operation that uses special equipment (dredge vessels, pumps) or
techniques to minimize the re-suspension of bottom materials and subsequent
turbidity that may occur during the operation. Conventional hydraulic dredg-
ing may cause excessive agitation and re-suspension of contaminated bottom
materials, which decreases sediment removal efficiency and which may lead to
downstream transport of contaminated materials, thereby exacerbating the
original pollution. Low-turbidity hydraulic dredging systems include small
specialty dredge vessels, suction dredging systems, and conventional cutter-
head dredges that are modified using special equipment or techniques for
turbidity control (National Car Rental System, Inc., 1980).
The Mud Cat dredge uses a slow-speed horizontal auger assembly equipped
with a mudshield to increase suction efficiency and reduce turbidity. Oper-
ating characteristics of the Mud Cat dredge are discussed in detail in Section
7.2.1. The Mud Cat system is well suited for operation in shallow harbors and
basins and small rivers where fine-grained sediments have to be dredged and
turbidity is a problem. The Mud Cat dredge was 95 to 99 percent efficient in
removing sediments and simulated hazardous materials from impoundment bottoms
in field tests conducted for the Environmental Protection Agency, with greater
removal efficiencies achieved during backward cuts (Nawrocki, 1976). Somewhat
similar to the Mud Cat are the VMI and the Delta mini-dredges.
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The waterless dredge has the capability of pumping slurries with a solids
content of 30 to 50 percent by weight, with little generation of turbidity.
It works best in unconsolidated thixotrophic materials. A bucket wheel type
dredge, recently developed by Ellicott Machine Corporation, is capable of
digging highly consolidated material and has the ability of controlling the
solids content in the slurry stream.
An Italian dredging system, Pneuma, uses two-stage vacuum suction to
remove sediments in batches with minimal turbidity. This pumping system is
highly applicable in confined areas, where conventional dredge equipment
cannot be used (Huston, 1976). Other pump dredging systems that require small
dilution volumes and minimize turbidity include the Mud Cat SP-810 pumping
platform and the Vaughan Company's Lagoon Pumper, both discussed in greater
detail in Section 7.2.1. These systems are applicable for removal of high
viscosity materials such as sludges, thick muds and consolidated, fine-grained
bottom sediments deposited at depths less than 15 feet.
A Japanese construction firm has developed a dredging system for removal
of high-density sludges called the "oozer pump" which may have applications in
very deep bodies of water such as large rivers or harbors. This system uti-
lizes vacuum suction and air compression to efficiently remove muddy sediments
(silt and clay) and sludges with low turbidity (Nishi, 1976).
Another Japanese suction dredge, the "Clean Up," (Figure 9-5) uses a
hydraulically driven, ladder-mounted submerged centrifugal pump to "vacuum"
muddy bottom sediments (fine-grained; high water content) from depths as great
as 75 feet, with very low turbidity. This system can pump very dense mixtures
(40 to 50 percent solids by volume) at constant flow rates as great as 500,000
gallons per hour, removing up to 900 cubic yards of sediment per hour. A
dredge vessel equipped with this pumping system may be used to remove con-
taminated sediments from large rivers or harbors in depths as shallow as 16
feet, with minimal pollution of the surrounding environment from dredge-
generated turbidity (Sato, 1976).
Low-turbidity sediment removal can also be accomplished with conventional
cutterhead pipeline dredges (such as the Ellicott Dragon series discussed in
Section 7.2.1), if they are modified by cutter removal or the addition of
auxiliary pumps. Cutter removal essentially converts the dredge into a suc-
tion dredge. With the cutter removed, the suction mouth can be placed direct-
ly on the bottom material; this increases suction efficiency, maximizes dredge
production, and minimizes turbidity. However, this technique is applicable
only for the removal of soft, unconsolidated sediments where cutterhead action
is not required to cut and loosen the bottom material. Jets and Ladder-
mounted pumps can be installed on conventional cutterhead dredges to increase
the head available for lifting bottom material, thereby increasing dredge
output and minimizing turbidity. The jet nozzle, usually mounted at or near
the suction mouth, increases lifting energy by injecting a high-velocity
368
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stream of water into the suction. The use of a jet may increase dredgin
efficiency to the extent that cutter removal is feasible (Huston, 1976)
FIGURE 9-5
THE JAPANESE SUCTION DREDGE "CLEAN UP"
(Source: Sato, 1976)
Submerged Pump
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9.2.2 Design and Construction Considerations
There are certain procedures that all sediment dredging operations may
follow to minimize streambed agitation and control turbidity. Where cutter-
head dredges are being used, a reduction in the speed of the spiral cutter (in
terms of revolutions per minute) will generally result in lower turbidity
levels in the immediate vicinity of the cutter (Huston, 1976). Cutter speed
reduction may adversely affect dredge production, however, particularly in
hardened, irregular sediments.
When dredging in areas of strong currents and natural turbulence, the
dredging operation should proceed upstream, into the current, because any
turbidity generated must pass around and under the dredge. This will increase
the tendency of any suspended material to flocculate and settle. Downstream
dredging will allow turbid water to spread ahead of the dredge vessel uninter-
rupted (Huston, 1976). The effect of controlling turbidity through upstream
dredging is greatest when operating in shallow flows.
Another consideration for turbidity reduction is the timing of dredging
operations. If dredging is to be done for contaminated sediments in aqueous
environments, projects should be scheduled for periods of low flow and dry,
calm weather whenever possible. Natural stream turbidity and current turbu-
lence will be minimal at such times and will not contribute to dredge-
generated turbidity. Timely dredging also allows for easy visual monitoring
of any dredge-generated turbidity.
When preparing dredging contracts for contaminated sediment removal where
turbidity control is essential, contract provisions should specify the use of
special low-turbidity dredge vessels or auxiliary equipment and techniques
designed to minimize turbidity generation (Huston, 1976). The bidder should
be made to specify minimum sediment removal volumes and maximum allowable
turbidity levels in the downstream environment to ensure an effective dredging
operation.
Other important considerations for hydraulic dredging operations are
discussed in Section 7.2.2.
9.2.3 Advantages and Disadvantages
Advantages and disadvantages associated with hydraulic dredging tech-
niques are discussed in Section 7.2.3. Low-turbidity hydraulic dredging may
entail extra costs when time-consuming modifications are made (such as cutter
speed reduction or installation of jets) for purposes of turbidity control.
These extra costs are generally balanced, however, by the environmental bene-
fits derived from efficient removal of contaminated sediments.
370
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9.2.4 Costs
Unit costs for hydraulic dredging, including special low-turbidity dredge
vessels such as the Mud Cat, have been previously presented in Table 7-8.
9.3 DREDGE SPOIL MANAGEMENT
Contaminated dredge spoil management includes methods for dewatering,
transporting, storing, treating, and disposing of con tain ina ted sediments after
they have been mechanically or hydraul ically dredged from the area of deposi-
tion. Related spoil management techniques, which will not be addressed here,
include the possible reuse of treated sediments as construction fill in vari-
ous applications and the treatment of contaminated effluent separated from
dredge slurry streams. The most technically and economically effective strat-
egy to handle contaminated sediments removed from a given dredge site will
depend on many site-specific variables, which include the following:
Method of dredging used - hydraulic vs. mechanical
Method of spoil transport - pipeline vs. truck or hopper
barge
Physical nature of removed spoil - consistency (solids/water
content) and grain size distribution
Volume of removed spoil
Nature and quantity of contamination; physical and chemical
characteristics of contaminant; hazard/toxicity level of
contamination
Proximity of acceptable treatment, storage, or disposal
facilities
Available land area for construction of treatment or con-
tainment facilities
There are several well-establ ished techniques for the processing and
reuse or disposal of uncontaminated dredge spoil. Techniques- for managing
contaminated dredge spoil, however, are influenced by the possibly hazardous
nature of the spoil material. Special consideration must be given to handling
these sediments in a safe, efficient manner. Contaminated spoil treatment and
disposal options may be limited because of this fundamental consideration.
371
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9.3.1 Dewatering and Transport
Mechanical dredging generally removes contaminated sediments in discrete,
bulk quantities with relatively low water content. Sediments excavated from
dry riverbanks, floodplains, or diverted streambeds may be easily truck-loaded
without dewatering. For coarse-grained sand and gravel sediments removed by
instream mechanical dredging (wet excavation), dewatering is readily accom-
plished through gravity drainage. Gravity drainage may be performed by drag-
line or clamshell operators, who simply lift the excavated load and allow any
contained water to drain freely over special collection bins. These collec-
tion bins are necessary for dewatering of contaminated spoil, since finer-
grained contaminated sediments may remain in suspension in the drained water;
the bins may be flatbed truck- or trailer-mounted for easy transport to treat-
ment or disposal areas.
Protection of groundwater from contamination by water draining from
dredge spoil is a major concern in the handling of this material. Dewatering,
storage, and disposal facilities must be designed so as to prevent the infil-
tration of contaminated water into groundwater. This may involve the use of
impermeable liners, underdrains, and collection systems, as described in
Chapter 5.
Fine-grained muddy sediments (silt and clay) do not readily drain and
generally have a much higher water content than sand and gravel spoil. Be-
cause of time considerations, dewatering of these fine-grained sediments
generally cannot be accomplished at the dredge site. If their consistency is
too dilute, they must be mechanically dredged with special care and truck-
loaded for transport to spoil containment areas or processing facilities.
Dewatering of mechanically dredged sediments with a high water content is
frequently necessary before the sediments can be economically transported to
final disposal areas. Where spoil containment basins are not located at the
dredge site and when small quantities of fine-grained spoil are mechanically
dredged in dilute form, temporary sand drying beds may be used to dewater the
spoil. These are small diked containment areas with a surface layer of 6 to
12 inches of coarse sand underlain by layers of graded gravel. The earthen
bottom (preferably of clay) is sloped slightly to vitrified clay tile under-
drains placed in trenches. Spoil filling depths are from 2 to 5 feet (Hammer,
1975). Dewatering is accomplished by gravity drainage and air drying (evapo-
ration). The drained water, collected in the tile underdrains, may be
gravity-discharged to sanitary sewer lines if sampling indicates low levels of
contamination. Alternatively, if high concentrations of a contaminant are
detected, the drained water may be collected by sump pumping to portable
treatment works. The dewatered soil can be removed from the drying bed by a
front-end loader and truck-loaded for transport.
372
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Where large quantities of dilute spoil are mechanically dredged from
riverbeds, clamshell or dragline loading onto hopper barges is a transporta-
tion option that may be more feasible than truck loading. Hydraulically
dredged spoil slurries, usually consisting of about 10 to 30 percent solids
(by volume), may also be pumped onto hopper barges for both dewatering and
long-distance transport to disposal sites.
9.3.2 Storage and Disposal
Conventional dredged material containment basins serve two basic func-
tions: the removal of dredged solids by sedimentation (settling); and the
short-term storage or long-term disposal of these removed solids (Mallory and
Nawrocki, 1974). Spoil containment basins can be formed by constructing
perimeter berms or dikes around natural topographic depressions. The basins
are used to contain spoil slurries pumped through pipelines from hydraulic
dredging vessels. Within the basin, sedimentation is the principal process
that functions to remove suspended solids from the slurry stream. The surface
area and depth of the containment facility, the detention time, the rate at
which the dredge pumps into the basin, the solids content of the slurry, and
the grain-size distribution of the dredged material are important factors in
determining the quantity of solids retained and the resultant effluent water
quality (Mallory and Nawrocki, 1974). All these factors, of course, will vary
from site to site.
Conventional spoil containment basins are constructed with sluices and
overflows to release effluent to natural watercourses in which suspended
solids concentrations are low enough to meet state or local water quality
criteria. Containment basins designed and constructed to receive spoil
slurries containing contaminated sediments must discharge overflow either to
sanitary sewer lines (for eventual treatment) or to a secondary containment
basin, a clay- or synthetic membrane-lined impoundment with no overflow struc-
tures for either permanent or temporary storage.
The required settling area for spoil containment basins is theoretically
determined by dividing the settling velocity of the smallest particle to be
retained into the basin overflow rate, as previously described in Section
3.4.7 on sedimentation basins. For continuous operations, the basin overflow
rate will be equal to the dredge pumping rate. A particle's ideal settling
velocity from water is dependent upon the particle's diameter and specific
gravity. The real settling velocity of particles is influenced by the temper-
ature and salinity of the water in which they are suspended, the shape of the
particles, and the turbulence of flow (Mallory and Nawrocki, 1974).
The settling of fine particles can be somewhat improved with the use of
coagulants or polyelectrolytes. Coagulants include metal salts and hydroxides
such as ferric sulfate, ferric chloride, and calcium hydroxide. Polyelectro-
lytes are high molecular weight synthetic polymers that may be either anionic,
cationic, or neutral in charge. Polyelectrolytes can be easily injected into
373
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the dredge pipeline before the slurry is discharged into the containment basin
or barge.
If the dredge site is near a large navigable body of water, it may be
possible to employ hopper barges to serve as floating containment basins.
Such a system would be especially applicable where land restrictions would
prohibit the construction of a containment area. The dredge spoil can be
stored and possibly settled if the waterway from which it was removed was
relatively quiescent. The injection of a flocculant prior to discharge into
the barge would enhance settling. The capacity of the hopper barges and the
required amount of settling time would determine the number of barges needed
for disposal. A tug boat would also be needed to move barges into position
and for transport to a transfer area, where supernatant could be decanted and
settled solids could be excavated.
The dredge pumping rate must be adequate to maintain the largest spoil
particle present in suspension. Figure 9-6 shows dredging rates typically
required to transport various size sediments through different size discharge
lines. Figure 9-7 presents typical grain size distributions for dredge sedi-
ments of three different classes, based upon the aquatic environment in which
they are deposited. The distributions shown are representative of the fol-
lowing situations: Class I, a flowing river; Class II, a harbor with moderate
flow or tidal action; and Class III, a relatively still lake (Mallory and
Nawrocki, 1974).
When spoil containment facilities attain their maximum storage capacity
and they are to be reused, secondary dredging or excavation is necessary to
remove the spoil. Contaminated spoil, if it has been sufficiently dewatered,
can be mechanically dredged from containment basins with draglines or clam-
shells and truck-loaded for transport to secured landfills or other suitable
disposal areas. Dewatering of contaminated spoil deposited in containment
basins may be accomplished through natural drying, the use of sub-spoil sand/
gravel drainage layers, vacuum pumping with well-points, or electroosmotic
pumping (expensive, but very effective for dewatering fine-grained materials).
For recently deposited spoil with a high water content or for secondary
impoundments containing decanted supernatant, hydraulic dredging with a Mud
Cat or similar dredge vessel is the most effective means of secondary removal.
The dredged spoil would be pumped through overland pipeline to a secondary
containment basin for storage permanently or prior to processing facilities.
For mechanically dredged contaminated sediments that are transported in
dry, bulk quantities, the most feasible disposal alternative is disposal in a
secured landfill -- a facility designed and operated to safely handle wastes
that may be toxic, corrosive, ignitable, or chemically unstable. For sedi-
ments containing only very low levels of a given contaminant, it may be fea-
374
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sible to dispose of mechanically dredged sediments in a conventional municipal
solid waste landfill.
9.3.3 Treatment
Physical processing of dredged sediments to selectively remove contami-
nated particle fractions or to recover uncontaminated fractions from dredge
slurry streams may be a feasible spoil management option. Chemical contami-
nants are oftentimes associated with the fine-grained particles of dredged
material; therefore, physical treatment methods such as particle size segrega-
tion can serve to isolate contaminated portions of dredged material with a
substantial reduction of volume. Processing facilities can be designed that
use equipment commercially available in the sand, gravel, and mineral proces-
sing industries. These equipment types include hydraulic scalpers, classi-
fiers, thickeners, hydrocyclones, sieves and screens, filters, clarifiers,
inclined tube settlers, and flotation separation units. Hydraulic scalpers
and classifiers can be used to hydraulically separate sand and gravel (parti-
cles greater than 74 microns in diameter) from dredge slurries; when these
sediment fractions are uncontaminated, they can be further processed (sized,
washed, and blended) to meet construction specifications. The selection of
equipment types and combinations for liquid/solids separation, filtration, and
sedimentation will depend upon the primary dredge size, the slurry discharge
rate, the grain size distribution of the dredge spoil, the total quantity of
spoil removed, and the nature of spoil contamination (Mallory and Nawrocki,
1974).
It may be feasible to design and install portable processing systems at
the dredging site to remove hazardous particulate material from the dredge
discharge stream. Figure 9-8 is a schematic of such a processing system that
may be applicable for handling 1500 gpm flows typical of the Mud Cat dredge.
Such a system would be totally portable and would be capable of processing a
wide range of hazardous materials (in particulate form) hydraulically dredged
from a pond or other surface impoundment (Nawrocki, 1976).
In this system, initial solids/water separation is achieved by portable
seal ping-classifying tanks that hydraulically separate sand-size and coarser
particles from the dredge slurry. Spiral classifiers use a large-diameter
sand screw to collect, convey, and deposit the removed solids to a discharge
pile outside the tank. Overflow from the scalping-classifying tank will go to
the secondary separation portion of the system, where removal of fine-grained
materials (less than 74 microns in diameter) will be achieved. This may be
performed most efficiently with a Uni-Flow filter, a series of banks of
hanging polypropylene hoses. The overflow is pumped into and through the
hoses, which filter out fine-grained materials in suspension. The sludge that
collects on the inside of the hoses is periodically flushed into a collection
trough beneath the filter. Chemical coagulants are added to this backflush
sludge and the effluent from this process is recycled back into the system for
final solids removal. An included tube settler, in conjunction with coagulant
377
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FIGURE 9-8
PORTABLE CONTAMINATED SPOIL PROCESSING SYSTEM
(Source: Nawrocki, 1976)
Initial Separation
Portable Scalping-Classifying
Tank and Spiral Classifiers
Secondary Separation
Uni-Flow Filter
Backflush Sludge
Removed Solids
Final Separation
Inclined Tube Settler
Coagulant Feeder
Removed Solids Effluent
Return
Water
to Pond
Removed Solids
the
settler influent, will achieve final separation by removing
microns in diameter and smaller, ensuring a high quality return
addition to
particles 6
flow to the impoundment (Nawrocki, 1976).
Sizing and selection of the individual components of such a processing
system should be performed on a site-by-site basis, depending on system flow
rate, the grain-size distribution of the solids, and the suspended solids
concentration of the dredge slurry. The total costs of such a system would
depend on equipment sizes and operating efficiency of the system.
In its simplest form, dredge slurry treatment might consist of adding
chemical coagulants (long-chain synthetic polymers or polyelectrolytes) to
dredge slurry streams or containment basin materials in order to enhance
settling. Coagulation is most effective with very fine clay-sized particles,
and it can reduce required containment basin areas by speeding up the sedimen-
tation process (Mailory and Meccia, 1974).
In addition to separating solids from the dredge spoil, it is possible
that solids may be further processed to remove the contaminants by leaching
with the appropriate organic or inorganic solvent. A hypothetical organic
solvent would be hexane, because of its low cost, while an inorganic leaching
378
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solution may be either hydrochloric or sulfuric acid (for most metals) or
sodium hydroxide (for phenols and some metals). The cleaned sediments may
then be disposed of in a normal landfill or possibly returned to their origin.
9.3.4 Design and Cost Considerations
The total costs of a given spoil management strategy must be determined
on a case-by-case basis. However, some examples of costs and some general
economic considerations are discussed here.
The land area required for construction of conventional spoil containment
basins, for settling of both primary and secondary effluent, is an important
cost consideration in selecting a method to manage dredge spoil. Where new
land must be acquired for containment basin construction, local real estate
values will determine initial capital requirements. When existing land dis-
posal sites are located within economic pumping or truck-hauling distances,
the major cost consideration will be transportation and handling costs. In
general, when fine-grained solids are removed from containment basins by
secondary dredging to provide additional spoil storage volume, pipeline trans-
port of a concentrated slurry using booster pumps is less costly than truck
loading and transport of the same quantity of dry solids (Mailory and Naw-
rocki, 1974). Secondary dredging of containment basins, coagulant addition to
dredge slurry streams, and sand and gravel removal from slurry streams by
processing equipment are three effective methods of reducing required contain-
ment basin area, and thereby decreasing capital outlay required for a spoil
management project.
If hopper barges are considered as an alternative to containment basins,
costs of barge and tug rental for the period of dredging, plus costs for fuel
and crew will have to be considered.
When processing equipment is used to recover uncontaminated fractions of
-sand and gravel from dredged sediments, and the sand and gravel is washed and
blended to meet construction specifications, then processing systems will
actually help pay for themselves to a limited extent. Processing also serves
to reduce required containment basin area and facilitates handling and dis-
posal of dredge spoil through dewatering and classifying sediments. There-
fore, when dredged sediments are not severely contaminated or when only par-
ticle fractions of a given grain size are contaminated, processing systems are
economically more feasible than the exclusive use of conventional containment
basins to store or dispose of dredge spoil. Portable processing systems may
therefore represent an economically attractive alternative to conventional
spoil management by containment basin settling alone.
Processing facilities and/or containment bains should be constructed as
close as possible to the dredging operation. However, existing land disposal
379
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sites or processing facilities, although they may be located at considerable
distances from the dredge site, will generally preclude new construction of
such facilities; pipeline pumping or truck hauling costs to existing sites
will not be as great as new construction costs, unless the existing facilities
are located at very great distances from the dredging site and there are
massive quantities of sediments requiring treatment and/or disposal.
Frequently, the most effective spoil management strategy from both a
technical and economic viewpoint will combine several of the techniques dis-
cussed in this section. An integrated spoil management system might include
the following:
A portable processing system for preliminary sand and gravel
removal
A small containment basin for temporary storage of contami-
nated fine-grained sediments
Coagulant addition to the containment basin to enhance
settling
A well point dewatering system to dry the impounded sedi-
ments and facilitate mechanical excavation and offsite
transport of the sediments to suitable land disposal sites
so that the containment basin can be reused
Secondary hydraulic dredging of the fine-grained sediments
and subsequent pipeline pumping to a suitable disposal
impoundment (to allow for primary containment basin reuse)
Again, the most cost-effective spoil management strategy will depend on many
site-specific variables: the dredge pumping rate; suspended solids content of
the dredge slurry; total quantity of solids to be handled; available land area
and proximity to dredging site; extent of sediment contamination; form of
removed sediments (mechanical dredging - dry solids; hydraulic dredging-dilute
slurry); and proximity of existing land disposal or processing facilities.
Some unit costs are presented in Table 9-4, which provides a general
picture of the costs associated with dredge spoil management. These data
should be used only for conceptual design and planning studies, and equipment
manufacturers should be consulted for more detailed cost estimates. Costs for
constructing dredge spoil containment basins are presented in Figure 9-9.
Excavation and disposal costs can be found in Section 9.1. No cost informa-
tion was developed for advanced spoil treatment such as solvent extraction.
Annual indices presented in Appendix C can be used to update costs based on
earlier years.
380
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TABLE 9-4
UNIT COSTS ASSOCIATED WITH DREDGE SPOIL MANAGEMENT
Item
Portable seal ping-classify-
ing tank combined with
spiral classifiers
Uni-Flow filter
Hydroclones (5)
Inclined tube setter
Coagulant feeder, piping
pumps
Low boy trailer
Semi trailers
Land purchase cost
(estimated)
Polymer cost @ 5 ppm
Tug rental (with crew)
Barge rental (12,000 bbl )
Unit/capacity
1500 gpm
1500 gpm
1500 gpm
1500 gpm
1500 gpm
ea.
ea.
acre
1000 yds
day
day
Cost
$84,000
$20,000
$14,000
$ 7,600
$21,000
$12,000
$12,000
$10,000
$ 12
$ 3,000
$ 300
Base jear
19751
19751
19732
19751
19751
19751
19751
-
1979 3
19804
19804
1Nawrocki, 1976
2 Mai lory and Nawrocki, 1974
3Betz Laboratories, 1979
4C.J. Tippido Co., 1980
Some costing examples using the unit costs presented in Table 9-4 are
given below.
Assume that an area is being dredged at a rate of 1,500 gpm at 20 percent
from a contaminated river (Class I sediments). An estimated area of 500,000
square feet must be dredged down about one foot.
381
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Some basic calculations set up the time frame, which in many cases may
affect selection of techniques for dredge spoil management:
Total amount of material to be dredged = 500,000 ft2 x 10
ft = 500,000 ft3
Total dredge discharge to remove sediment at 20% solids (by
volume) =
500,000 ft3 T 0.20 = 2,500,000 ft3
Total dredging time required =
x 7'gal - 1,500 gpm = 12,470 minutes = 210 hours
Assuming a 6-hour working day for actual dredging for 5 days a week (30
hours dredging per week), it would take approximately seven weeks to complete
dredging operations. For this relatively small amount of dredge spoil, it may
be feasible to construct a zero-discharge lined containment basin. The size
requirement for a 10-foot-deep zero-discharge basin would be as follows:
Area = 2,500,000 ft3 * 10 ft * 43,560 ft/acre = 6 acres
Costs of a lined based can now be estimated:
Estimated land cost = 6 acres x $10,000/acre = $60,000
Construction costs (excluding liner) =
6 acres x 43,560 = 261.360 ft2
acre
From Figure 9.9, the construction cost in 1973 would
be about $40,000.
The ENR Construction Index (Appendix C) is used to
update costs
$40,000 (1973) x = $66,700
Costs for clay liner (2 ft thick) at $8.50 per cubic yard
(see Table 3-2).
$8.50/yd3 * 27 ft3/yd3 = $0.31/ft3
261,360 ft2 x 2 ft x $0.31/ft3 = $162,000
The total cost for a 6-acre clay-lined containment basin is:
$60,000 + $66,700 + $162,000 = $288,700
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An alternative to constructing a sediment basin is to use hopper barges
as temporary containment structures. The hopper barge system would be fea-
sible only if a navigable river was located near the site and a feasible
treatment scenario could be implemented to dispose of dredge spoil super-
natant, i.e., discharge to a sanitary sewer. With a slightly reduced flow of
about 14,000 gpm at 6 hours of dredging time per day, one 12, 000-barrel -capac-
ity hopper barge would be required to contain one day of dredge output. The
required settling time to produce an acceptable supernatant would dictate the
total number of hopper barges needed in the system. For the purpose of
costing, it is assumed that 5 days are required for settling if flocculants
are used. Thus, at least 5 hopper barges will be needed for the containment
system, plus a tug for maneuvering and transport. It is assumed that after
settling, the supernatant will be pumped to a sanitary sewer and the settled
dredge spoil will be draglined into trucks for hauling to a secure landfill.
Rental of hopper barges and the tug will depend on projected time to complete
dredging. Again, if the total dredge discharge to remove sediment at 20
percent solids is 2,500,000 ft3, the required time to complete the operation
will be as follows:
Total dredging time =
2,500,000 ft3 x 7'^3ga1 1400 gpm = 13,360 minutes = 223 hours
Again, assuming a 30-hour week for actual dredging time, it would take
slightly less than 8 weeks for dredging, thus the tug and barges must be
rented for 40 days assuming a 5-day work week. Costs for the barge system are
as follows:
Tug rental (with crew) = - x 40 days = $120,000
Barge rental = 5 barges x x 40 days = $ 60,000
Polymer addition = . x - x 2,500,000 ft3 = $1,110
.
Dragline from barge to dumptrucks (from Table 7-6)
Assumed sediment specific gravity of 75 lbs/ft3
Dragline excavation =
x 750,000 ft3 = $38,600
Hauling and disposal costs
Assumed sediment gravity of 75 lbs/ft3
383
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Total tonnage =
750,000^x^X2^^=28,130
Hauling costs (from Section 7.3);
assume 100 miles transport tons =
28,130 tons x t^c^^d x 4^- x 100 miles = $422,000
o Disposal costs (from Section 7.3) =
28,130 tons x ~ = $6,751,200
The total costs for the barge dredge spoil, not including hauling and dis-
posal, are $219,000. The costs including disposal in a secure chemical land-
fill would bring the costs to well over $7 million.
It is difficult to compare the two options without a more thorough know-
ledge of the toxicity of the sediment. It may be possible to dispose of
sediments in a municipal landfill, which would reduce disposal costs for the
barge system significantly. Also, if the wastes are highly toxic, the con-
structed containment basin would have to be made more secure or the wastes
would have to be excavated and placed in a secured landfill, which would
significantly increase the costs of this approach.
The above considerations and associated costs demonstrate the enormous
problems encountered when dealing with dredging contaminated sediments, since
large capital outlays are required to handle large volumes of waste material
within a relatively short time. Also, if dredge spoil supernatant is severely
contaminated and cannot be discharged to sanitary or industrial sewerage, the
on-site treatment of wastewater becomes a major problem. The best way to
circumvent these high containment costs is to reduce the spoil volume by, (1)
dredging slowly to decrease liquid entrainment; and (2) using one of the un-
conventional dredging systems that is capable of pumping a high solids stream.
9.4 REVEGETATION
When dredging contaminated sediments in wetlands environments such as
tidal marshes and estuaries, an important construction consideration is the
possible reclamation of the dredged area with special fill and revegetation
techniques. This consideration applies to marshes dredged both hydraulically
384
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oo
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and mechanically. In many instances, a suitable fill material for marshlands
is uncontaminated dredge spoil transported from another area of the marsh or
from inland sources. Marshland restoration involves subgrading the dredged
area with clean fill and resurfacing the area with stockpiled, naturally
vegetated marsh materials. Alternatively, the restoration area can be devel-
oped to the original grade with inorganic sediments (sands) between one- and
two-feet in depth, and then seeded or transplanted with appropriate marsh
plants such as cordgrass (Spartina alterniflora) and saltmarsh hay (Spartina
patens). Fertilizers may be required if inorganic sediments are used (Envi-
ronmental Concern, Inc., 1981). Wave action and salt stresses are the most
important factors limiting vegetative establishment in tidal marshes, and
timely seeding of tolerant plant species is necessary for successful marshland
restoration. A successfully restored marsh will support coastal fisheries and
other wildlife populations, will provide effective and inexpensive natural
control of shoreland erosion, and will provide flood control for coastal
floodplains (Environmental Concern, Inc. 1980).
Unit costs associated with the revegetation of wetlands areas are pre-
sented in Table 9-5. An example cost calculation using these unit costs for
revegetation is given below.
Assume a wetlands area of 20 feet by 400 feet has been dredged to remove
2 feet of contaminated sediments. Thus an excavated column of 16,000 ft must
be filled and revegetated.
Cost of replacement fill:
16,000 ft3 x 27y(jSt3 x $5.30/yd3 = $3,141
Cost for revegetation by contractor:
400 ft x $8/ft = $3,200
Total cost for revegetation = $3,141 + $3,200 = $6,341
386
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TABLE 9-5
UNIT COSTS FOR DREDGED MARSHLAND RESTORATION ACTIVITIES1
Description
Plant delivery to restoration site
up to 1,500 4-inch peat-potted
plants
up to 5,000 1 3/4 inch peat-
potted plants
1,500 to 4,500 4-inch peat
potted plants
5,000 to 15,000 1 3/4-inch
peat-potted plant
bare root seedlings, springs
and seed
Plant material
seeds (viable), up to 20,000
50,000 - 500,000
>500,000
dormant tubers, bulbs and
rhizomes
dormant sprigs
seedlings, bare root,
1-month old
seedlings, bare root,
3-month old
peat-potted seedlings,
3 to 5 month old'
peat-potted seedlings,
5-months old
Unit cost
$0.55/mile (roundtrip)
$0.75/mile (roundtrip)
packing and mailing costs FOB
St. Michaels, MD
$5.00/1,000 seeds
$150/50,000 seeds
$1,000/500,000 seeds
$0.65 - 0.75 each
$0.10 - 0.12 each
$0.03
$0.13
$0.45
$0.60
0.05 each
0.15 each
0.55 each
0.70 each
continued
387
-------
TABLE 9-5 (Continued)
Description Unit cost
Replacement fill: bank sand $5.30/cubic yard
hauled 2 miles, placed and (Godfrey, 1979)
spread
Total marshland seeding or trans- $6 - 8/1inear foot of shoreline
planting contractor cost (includ- (for areas up to 20 feet wide)
ing initial fertilization)
Consulting rates; marine biologist, $13/hour
plant ecologist, or environmental
scientist
Environmental Concern, Inc., 1980.
388
-------
REFERENCES
ARMCO, 1979
Barnard W. 1978. Prediction and control of dredged material dispersion around
dredging and open-water pipeline disposal operations. U.S. Army Engineer
Waterways Experiment Station. Vicksburg, Mississippi.
Betz Laboratories, Treuose, PA. June 1979. Personal communication with
P. Rogoshewski.
C.J. Tippido Co., Houston, TX. March 1980. Personal communication with P.
Rogoshewski.
Cecos International, Inc., Niagara Falls, NY. February/May 1980. Personal
communications with S. Paige and P. Rogoshewski.
Environmental Concern, Inc. 1980. Scope of services available. St. Michaels,
MD.
Environmental Concern, Inc., St. Michaels, MD. 1981. Personal communication
with P. Rogoshewski.
Godfrey, R. (ed.). 1979. Building Construction cost data, 1980. Kingston,
MA: Robert Snow Means Co., Inc.
Hammer M. 1975. Water and waste-water technology. New York: John Wiley &
Sons, Inc.
Huston J., and W. Huston. 1976. Techniques for reducing turbidity associated
with present dredging procedures and operations. Prepared for U.S. Army
Engineer Waterways Experiment Station. Vicksburg, MS. Contract no. DACW
39-75-0073.
Kepner Plastic Fabricators, Torres, CA. May 1980. Personal communication
with P. Rogoshewski.
Linsley R., and J. Franzini. 1979. Water-resources engineering, 3d ed.
New York: McGraw-Hill Book Company.
Mallory C., and R. Meccia. 1974. Concepts for the reclamation of dredged
material. Columbia, MD: Hittman Associates, Inc.
Mallory C., and M. Nawrocki. 1974. Containment area facility concepts for
dredged material separation, drying, and rehandling. Final report. Pre-
pared by Hittman Associates, Inc. for U.S. Army Engineer Waterways
Experiment Station. Vicksburg, MS. Contract report D-74-6.
McMahon, L., and P. Pereira (eds.). 1979. 1980 Dodge guide to public works
and heavy construction costs. New York: McGraw-Hill Information Sys-
tems.
389
-------
National Car Rental System, Inc., Mud Cat Division, Fort Lee, NJ. January
1980. Personal communication with P. Rogoshewski.
Nawrocki, M. 1976. Removal and separation of spilled hazardous materials from
impoundment bottoms. Prepared under contract no. 68-03-0304 by Hittman
Associates, Inc. for U.S. EPA/ORD, Industrial Environmental Research
Laboratory. Cincinnati, Ohio. EPA-600/2/76-245.
Nipak, 1980. Sewer Rehabilitation with Nipak Polyetheylene Pipe. Appeared
in February 15, 1980 Advertisement.
Nishi, K. 1976. Dredging of high-density sludge using oozer pump. In: Dredg-
ing: environmental effects and technology. San Francisco: WODCON Asso-
ciation.
Richardson Engineering Services, Inc. 1980. Process plant construction esti-
mating standards, vol. 1. Solana Beach, CA.
Sato, E. 1976. Application of dredging techniques for environmental problems.
In: Dredging: environmental effects and technology. San Francisco:
WODCON Association.
Staples, G., JRB Associates, Inc., McLean, VA. April 1980. Personal Com-
munication with P. Le.
390
-------
APPENDIX A
MONITORING SYSTEMS
INTRODUCTION
Once design and construction of a remedial action has been completed, it
will be necessary to monitor the various environmental media (groundwater,
air, surface water). The basic objectives of a monitoring system are to:
Measure the effectiveness of the implementive remedial action by
providing long-term verification;
Act as an "early warning" system for possible breakdown of the
remedial action program;
Protect groundwater and surface water users from potential harm.
The following sections provide a brief description of the considerations
necessary to implement monitoring of the various environmental media. It must
be emphasized that an all-encompassing description of monitoring programs is
not presented here. However, the necessary background and types of consider-
ations are discussed in sufficient detail to provide the user with an under-
standing of monitoring systems.
GROUNDWATER MONITORING
The major steps necessary in establishing a groundwater sampling network
include:
Establish background
Well placement
391
-------
Well design
Sampling program
Laboratory analysis
Data interpretation
Establishing a background level of groundwater quality is of primary
importance in answering the question "what was the groundwater quality before
it entered the landfill site," and "what j_s_ the groundwater quality now?" The
background well can provide information on groundwater contamination that is
not attributable to the landfill site. Many times, high concentrations of
nutrients, iron, or pH can be linked to agriculture or mining operations that
are located in an aquifer recharge zone. It is therefore necessary to estab-
lish a solid groundwater quality background data base to ensure that chemical
analysis of monitoring wells is interpreted properly.
Well Placement
A typical monitoring well placement scheme is shown in Figure A-l. Well
"A" is the background monitoring well and is located far enough upgradient
from the site to insure that the landfill will have no effect on the hydraulic
condition at the wall.
Well "B" is located on-site, and is placed in a location where migrating
contamination can be detected entering the groundwater. The "B" well will
also serve as a first indicator of the effectiveness of the remedial action
program. If water quality in the monitoring well does not indicate a steady
improvement over time (allowing for program stabilization), it will indicate
the need for further remedial action considerations. This well must be very
carefully constructed and sealed, in order to prevent vertical migration of
contaminants down the well casing.
Well "C" is located downgradient from the site, at a position close
enough to detect changes in groundwater quality as soon as possible. These
wells should also, over a period of time after the "B" wells, show a similar
trend of improvement of groundwater quality. These wells should be screened
over the entire distance of the aquifer to ensure that a leachate plume is not
passing under the well system.
Well Design
The design of the wells installed at the designated locations will depend
upon the number and extent of the water-bearing zones to be monitored. If
392
-------
FIGURE A-l
TYPICAL MONITOR WELL NETWORK, AREAL VIEW
(Source: EPA/530/SW-616)
Legend:
A, B, C - Monitoring Wells
393
-------
only one aquifer system is to be monitored, a single well designed in the
configuration shown in Figure A-2 could be used. It is important to note
that, if a remedial action program is being monitored for a chemical landfill
site that contains organic solvents, PVC casing should not be used. It can be
replaced with either case hard steel or plated steel casing.
If more than one aquifer or water bearing zone is to be monitored, a well
cluster system will be required at each well location. A typical well cluster
system is shown in Figure A-3.
Table A-l shows typical costs associated with monitoring well instal-
lation.
Sampling
There are three basic ways in which a sample can be extracted from a
monitoring well:
Installation of permanent pumps is only advisable for long-term
monitoring.
Portable pumps can be carried from well to well for each sampling
effort, although the pump must be properly cleaned between each
sample.
The airlift method uses compressed gases to force water up a
sampling tube. The airlift method is preferable to a pump for pre-
venting cross-contamination between samples and wells.
The choice of a groundwater sampling method will depend upon:
Frequency of sampling
The number of monitoring wells
Site-specific conditions
The type of laboratory analyses to be performed for each sample will be
dictated by the types of wastes contained at the site. Costs for each sample
to be analyzed can range from a few dollars to $5,000 depending upon the
number and complexity of the contaminants within each sample.
394
-------
FIGURE A-2
TYPICAL MONITORING WELL SCREENED OVER A SINGLE VERTICAL INTERVAL
(Source: EPA/530/SW-616)
Land Surface
Borehole
Schedule 40 PVC
Casing
Slotted Schedule
40 PVC Screen
Cap
Low Permeability
Backfill
Water Table
395
-------
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SURFACE WATER MONITORING
If clean-up of a contaminated surface water body is part of the remedial
action program, periodic monitoring of the surface water quality will be
necessary.
As with groundwater monitoring, the establishing of background water
quality is important for determination of the effectiveness of the remedial
action program. A location far enough upstream to be unaffected by the land-
fill site is necessary to ensure proper baseline data quality.
Three stream sampling sites should be adequate to determine the effec-
tiveness of the remedial action program on stream water quality. These are:
Background upstream
Closest stream point to landfill site
Location downstream from landfill site (1/2-mile radius)
There are many different types of surface water samplers. The choice
among them is a function of many factors, including the size of the water body
to be sampled, the type of sampling being conducted, and the number of samples
to be taken. This section discusses three types of surface water samplers and
one type of runoff sampler:
A Nansen bottle is used in deep surface water. It takes a water
sample over a depth interval roughly equivalent to its length, and
is activated by remote control.
The Van Dorn Bottle operates on the same principle as a Nansen
bottle, but does not reverse. It is more commonly used because it
is less cumbersome. Van Dorn bottles are constructed to take
samples in a horizontal or vertical orientation, depending on the
depth of the water. A vertical Van Dorn sampler is shown in
Figure A-4.
A grab sampler can be used with a peristaltic pump for sampling at
shallow depths. This sample will not allow for specific depth
sampling, but is highly effective for quick sampling and is well
suited for a preliminary investigation.
A plus sampler is used for collecting storm water runoff. These
samplers should be made of polyethylene, or preferably, Teflon (see
Figure A-4). A network of plugs is driven into the ground so that
the top face of each plug is just below the surface of the surround-
ing material. Overland runoff enters each plus through a screen in
the top that removes large particles but permits smaller suspended
399
-------
particulates to enter. These plugs may also be used to collect soil
moisture through channels around the side surface by covering the
openings in the top faces.
FIGURE A-4
SURFACE WATER SAMPLING EQUIPMENT
Groundwater
Seepage
Surface Water
Entrance
Vertical
Van Dorn/Nansen Sampler
Storm Water Runoff
Sampling Plug Collector
GAS MONITORING
sary
type
Prior to the installation of
to determine if the landfill
of information needed to make
Waste type
Method of disposal
Age of facility
a gas monitoring system, it will be neces-
site is capable of generating gases. The
this determination includes:
Landfill facilities that have never received organic wastes will more
than likely not be producing gas. Methane gas production requires an anaero-
400
-------
bic environment. Therefore, sites that are very young will not have had the
time necessary to produce gas. In addition, any sites using a landspreading
disposal method will not produce gas.
Volatile toxic substances, however, may produce hazardous gases in rela-
tively young landfills. Reactions between substances in landfills may also
form gases that constitute a hazard.
Monitoring Points
It is recommended that there be at least two monitoring points along the
property boundaries located in such areas as dry sand or gravel, alignment
with an off-site point of concern, proximity of the waste deposit, areas where
there is dead or unhealthy vegetation that might be due to gas migration, and
areas where underground construction might have created a natural path for gas
flow (EPA-SW 828).
On the average, sampling points should be approximately 3 feet in depth.
A diagram showing a typical gas probe placement is shown in Figure A-5.
It may be necessary to measure gas concentrations at multiple levels at
one point. This can be accomplished by the use of a multi-level gas sampling
probe, as shown in Figure A-6.
Sampling of gas is accomplished by using a standard gas monitoring appa-
ratus. Measurements are taken directly from the probes in the field by
pumping a sample through the gas explosion meter and obtaining a measurement
level.
401
-------
FIGURE A-5
TYPICAL GAS PROBE PLACEMENT
(Source: EPA-SW 828)
Masking Tape Over
End of Probe
D
Cloth to be Wrappe
and Tied Around
Perforated End of ^
Tubing
Back Filled
Material
i
epi
Pro
J
"-
\* **
f " *
*"
* 1
*
**
*
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be
\
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*-
/
)
j
^*>.
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SN,
* *
* N
* 4
*
' I
i
Y
/
i
Depth and Identification of Probe
Marked on Tape with Waterproof
Ink Pen, then Wrap with Clear Tape
Cement Plug
Perforations 1' Min. (Can Use
Hand Drill, Knife Point, or
Other Sharp Instrument to
Perforate Tube End)
Weight (a Rock or Lead Weight
Can be Taped or Tied to
Bottom of Probe)
402
-------
FIGURE A-6
TYPICAL MULTI-LEVEL GAS SAMPLING PROBE INSTALLATION
(Source: EPA-SW 828)
Gas Sampling
H h-13"
Dia.
Ground Surface
Gas Probe
Typical Section
(No Scale)
Source: SCS Engineers
403
-------
APPENDIX A
REFERENCES
JRB Associates, Inc. 1980. Training Manual for Hazardous Waste Site
Investigations. Prepared for the U.S. Environmental Protection
Agency. McLean, Virginia.
U.S. Environmental Protection Agency. 1977. Procedures manual for ground-
water monitoring at solid waste disposal facilities. EPA/530/SW-616.
Office of Solid Waste, Washington, D.C.
U.S. Environmental Protection Agency. 1980. Classifying solid waste disposal
facilities: a guidance manual. SW-828. Office of Solid Waste,
Washington, D.C.
404
-------
APPENDIX B
WASTEWATER TREATMENT MODULES
This appendix presents a discussion of various treatment modules that may
be applicable to leachate treatment. Each treatment module is discussed in
terms of applicability to various waste types and strengths. Major design and
construction parameters, advantages and disadvantages, and costs are consi-
dered. Cost curves were generally prepared to show 1976 costs and may be
updated using the table in Appendix C.
The following treatment modules have been considered:
Flow equalization
Precipitation, flocculation, and sedimentation
Biological treatment
air-activated sludge
pure oxygen-activated sludge
trickling filters
rotating biological discs
biological seeding
stabilization ponds/aerated lagoons
Carbon adsorption
Ion exchange
Liquid ion exchange
Ammonia stripping
Wet air oxidation
Chiorination
405
-------
1.0 FLOW EQUALIZATION
1.1 GENERAL DESCRIPTION AND APPLICATIONS
The primary objective of flow equalization basins is to dampen the flow
and concentration fluctuations. Both biological and physical/chemical
processes operate more effectively if composition and volume are fairly con-
stant. Because of the high variability in leachate, equalization basins will
almost invariably be required to increase the stability of biological and
physical/ chemical unit operations.
1.2 DESIGN AND CONSTRUCTION CONSIDERATIONS
In computing equalization volume requirements for leachate treatment
systems, it will be necessary to use the water balance equation to determine
flow and to design for annual peak rainfall or near peak flow volume of the
area. In sizing the equalization basin, the designer will need to determine
the amount of fluctuation that the other unit operations in the treatment
process can handle without impairing performance, and provide equalization
volumes to ensure that fluctuation does not exceed that amount. Equalization
basins can be designed for either sideline equalization, where water in excess
of the daily flow is equalized, or for in-line equalization where the entire
daily flow is equalized. Because of large fluctuations in the concentrations
of pollutants, leachate treatment will require inline equalization.
Factors that require consideration in design of the equalization basin
include:
Degree of flow rate and organic loading equalization required to
ensure reliable and efficient performance of other process units.
Aeration and mixing equipment
Pumping and discharge flow rate control
Feasible alternative treatment component size for peak flows
Aeration and mixing equipment need to be carefully selected. As a guide-
line, the minimum mixing required to prevent deposition of solids in municipal
treatment systems (at 200 mg/ SS) ranges from about 0.02 to 0.04 hp/1000 gal.
Minimum aeration required to prevent septic conditions is about 1.25 to 2.0
cfm/1000 gal.
Because of the large variation in hydraulic head necessary for operation
of equalization tanks, pumping is normally required. If a pumping station is
406
-------
required in the headworks, pumps can be designed for the additional head
needed for equalization basin operation.
1.3 ADVANTAGES AND DISADVANTAGES
Equalization basins are generally reliable and can be easily designed to
achieve the objective. They can dramatically increase the stability of flow
and/or concentration of sensitive operations such as carbon adsorption, bio-
logical treatment, precipitation, and ion exchange. The only disadvantage is
that an equalization basin may require a considerable amount of land area to
handle peak flows.
1.4 COSTS
1976 costs for concrete basins with a detention time of one day are shown
in Figures B-l and B-2 (EPA, 1978).
FIGURE B-l
1976 CONSTRUCTION COSTS FOR
CONCRETE EQUALIZATION
BASINS
FIGURE B-2
1976 O&M COSTS FOR
CONCRETE EQUALIZATION
BASINS
CONSTRUCTION COST
OPERATION & MAINTENANCE COST
10
1 0
I
B
1 0
001
01
1 0 10
Wastewaler Flow. Mgal/d
100
(*)
(0
0
D 0 1
O
ง
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8
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407
-------
2.0 PRECIPITATION, FLOCCULATION AND SEDIMENTATION
2.1 GENERAL DESCRIPTION AND APPLICATION
Precipitation, flocculation, and sedimentation are well-developed pro-
cesses that have been applied to the treatment of various industrial waste-
waters containing particulates and/or soluble heavy metals.
Precipitation removes a substance from solution and transforms it into a
solid particle. Flocculation promotes particle growth of suspended solids so
that they can be more easily removed, and sedimentation removes suspended
particles from the liquid.
The processes of precipitation, flocculation, and sedimentation are
suitable treatment methods whenever it is necessary to remove precipitable
soluble substances and/or suspended solids. The most common applications
suitable for hazardous waste sites will include:
Settling of suspended solids from surface water runoff
Removal of soluble and insoluble toxic metals
Removal of soluble inorganics natural to groundwater supplies
Many toxic metals, including cadmium, lead, arsenic, and chromium, are
successfully removed from wastewater by precipitation, flocculation, and
sedimentation.
There is no upper limit on the concentrations that can be treated by
these processes. The lower limit for removal of soluble species is generally
governed by the solubility product of the particular ion, although this method
of predicting removal efficiency is not very reliable.
2.2 DESIGN AND CONSTRUCTION CONSIDERATION
The major features to consider in the design of a sedimentation basin or
clarifier are the hydraulic flow, chemical requirements, and dosages based on
concentrations of suspended matter and precipitable soluble species and the
settling rate. The three processes can be carried out in separate basins as
shown in Figure B-3, or as Figure B-4 illustrates, a clarifier may be used
with separate zones for chemical mixing, precipitation, flocculation, and
sedimentation.
408
-------
FIGURE B-3
REPRESENTATIVE CONFIGURATION EMPLOYING PRECIPITATION,
FLOCCULATION, AND SEDIMENTATION
(Source: DeRenzo, 1978)
Precipitation
Precipitating Flocculation
Chemicals ~
Flocculating .
Agents 1
Inlet Liquid-*-
Stream
A Sedimentation
/
ซ4
1
Rapid Mix Tank
t
C
IH
) C
> C
41 OH
)
^-
4]
Flocculation Chamber
i
Outlet Liquid
Stream
jiymJUIIi iii ii"
m
Sedimentation Basin
FIGURE B-4
TYPICAL SOLIDS CONTACT CHEMICAL TREATMENT SYSTEM
(Source: Azad 1976)
See Copyright Notice, Page 497
Lime Makeup
Solids-contact Unit
Chemical Feed
Turbine
/ Water Level
Sludge Pipe
Gravity Thickener
"k Effluent
Recarbonation
(Neutralization)
Multiple-hearth
Lime Recalciner
Lime Cooler
Recalcined Lime
409
-------
In applying the processes of precipitation, coagulation, and sedimenta-
tion, laboratory tests are available to determine the degree of precipitation
along with reaction time and required chemical dosage, the type of flocculant
that must be used, and the settling rate.
2.2.1 Precipitation
The two most common precipitation reactions applicable to leachate treat-
ment are addition of a compound, such as sulfide, that will react directly
with the hazardous metal to form a sparingly soluble compound and change in
the equilibrium, especially by pH adjustment with lime, so that a soluble
compound becomes insoluble and precipitates.
Precipitation of metals is governed by the solubility product of the
metal ion. However, actual efforts to precipitate metals usually do not
achieve effluent concentrations equal to the theoretical solubility. Explan-
ations for this include:
Many metals form complexes with organo-metallics. These ions are,
in some cases, more soluble than the ion itself and may prevent
precipitation.
Cyanide ions or other ions in the wastewater may complex with
metals, making them difficult to precipitate as the hydroxide or
sulfide (DeRenzo, 1978).
Although lime precipitation is the most widely used method for precipita-
ting heavy metals, there are problems with the process that the user should be
aware of. Many metals reach a minimum solubility at a specific pH, but
further addition of lime causes the metal to become soluble again. Therefore,
the dosage needs to be accurately controlled. However, the fluctuating leach-
ate quantities and concentrations of metals will make it very difficult to
control the lime dosage to obtain ideal precipitation; jar tests will need to
be conducted frequently.
Lime dosage requirements for municipal leachate may be considerably
higher than those used for municipal wastewater treatment; whereas municipal
systems require dosages of about 250-400 mg/l to obtain a pH of 10.5, de-
pending on alkalinity of the water, the GROWS landfill leachate treatment
system requires about 6,000 mg/i to obtain a pH of 10 (EPA, 1977a). Also,
some metals require very high pH for precipitation as the hydroxide, and the
effluent must then be neutralized before it can meet discharge pH limitations
or be at an acceptable pH for biological treatment.
410
-------
Precipitation as the metal sulfide is an alternative that has not been
used widely. As shown in Table B-l, metal sulfides are less soluble than
hydroxides, and generally the metal can be reduced to lower concentrations.
TABLE B-l
APPROXIMATE SOLUBILITIES OF METALS (ppm IN PURE WATER)
Metal
As hydroxide
As sulfide
_ . Solubility as hydroxide
hacror - Solub11ity as su1fide
Source: Permutit, 1977
2.2.2 Coagu1 a t iion/Fl qccu 1 a t i on
Factor
1
Iron
Zinc
Cadmium
Nickel
Copper
Lead
Mercury
Silver
Chromium
9
1
2
7
2
2
4
1
8
x
x
X
X
X
X
X
X
X
10"
10ฐ
10"
10"
10"
10ฐ
10"
io1
1
5
3
2
4
io"4
3
2
7
7
6
4
9
7
x
x
X
x
X
X
x
X
(No
10
10
10
10
10
10
10
10
-5
-7
-10
-1
- 13
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-20
12
3
5
3
1
3
5
4
1
x
x
x
x
x
X
X
X
io4
IO6
IO4
io5
NT
!04,
10
10
precip.)
Settling of suspended solids depends upon gravitational and/or inertial
forces to remove solid particles. Coagulation and flocculation are intended
to overcome repulsion forces of individual particles, causing them to agglom-
erate into larger particles (DeRenzo, 1978). Chemicals used for coagulation
and flocculation include alum, ferric chloride, ferric sulfide, lime (coagu-
lants), and polyelectr.olytes (flocculants). The effectiveness of a particular
coagulant varies in different applications, and in a given application each
coagulant has an optimum concentration and pH range. The processes of coagu-
lation and flocculation require rapid mixing followed by a slow and gentle
mixing to allow contact between small particles and agglomeration into larger
particles. Coagulants must be completely dispersed into water immediately.
This is especially true for inorganic coagulants such as alum that precipitate
immediately. For lime treatment, it is useful to disperse the lime throughout
the wastewater in the presence of recycled sludge to provide an abundance of
411
-------
surface area on which the precipitate can form (Azad, 1976). Rapid mix is
usually accomplished in 10-60 seconds. A mean temporal velocity gradient in
excess of 300 ft/(sec)(ft) is recommended (Azad, 1976; Liptak, 1974).
The required dosage of coagulant depends upon pH, alkalinity, phosphate
levels, and mode of mixing; dosage can be determined by jar tests and zeta
potential tests. Typical chemical dosages used in industrial treatment pro-
cesses are listed in Table B-2. The hydraulic loading, also listed in Table
B-2, is used as a basis for determining suspended solids removal efficiencies.
The hydraulic loadings shown are intended to achieve 80-90 percent suspended
solids removal (Azad, 1976).
TABLE B-2
CHEMICAL TREATMENT OF INDUSTRIAL WASTEWATER BY COAGULATION
Criteria Fed 3 Alum Ca(OH)2
Dose, mg/1 80-120 100-150 350-500
Hydraulic loading, gpm/sq ft1 0.3-0.4 0.2-0.4 0.5-0.8
Chemical sludge production,
Ib/million gal 350-700 250-500 4,000-7,000
1Without use of polyelectrolytes
Source: Azad, 1976
See Copyright Notice, Page 497.
After achieving effective mix, promotion of particle growth by floccula-
tion is the next step. The addition of flocculants is usually made downstream
from the coagulant addition point because the rapid mixing can break up the
floe (Liptak, 1974).
Flocculation is accomplished in 15-30 minutes. Mean temporal velocity
gradients of 40-80 ft/(sec)(ft) are recommended. The lower value is for
fragile floe (aluminum or iron), and the higher value is for lime (Azad,
1976).
412
-------
2.2.3 Sedimentation
As indicated previously, sedimentation may be carried out in a separate
basin from precipitation and coagulation, or all three processes may be
carried out in the same basin. When the operations are carried out in combi-
nation, two design configurations are available. In the conventional system,
rapid mix is completed "in-line" before water enters the large settler where
flocculating and clarification are completed. In the sludge-blanket type
units, coagulation, mixing, flocculation, and settling all take place in a
single unit (Liptak, 1974).
Criteria for sizing settling basins are overflow rate (surface settling
rate), tank depth at the side walls, and detention time. For municipal treat-
ment systems, depths average 10 - 12 feet, detention time usually averages 1-3
hours, and surface loading rates average 360-600 gal/d/ft2 for alum floe,
540-1,200 gal/d/ft2 for lime floe, and 700-800 gal/d/ft2 for FeCl3 (EPA,
1978a). Design is considered in detail in Section 3.4.7 for sedimentation
basins, and these parameters are generally applicable to clarifiers as well.
In selecting the particular tank shape, proportions, equipment, etc., the
designer should:
1. Provide for even inlet flow distribution in a manner that
minimizes inlet velocities and short circuiting.
2. Minimize outlet currents and their effects by limiting weir
loadings and by proper weir placement.
3. Provide sufficient sludge storage depths to permit desired
thickening of sludge. Solids concentrations of 2 to 7 percent
should be obtained.
4. Provide sufficient wall height to give a minimum of 18 inches
of freeboard.
5. Reduce wind effects on open tanks by providing wind screens and
by limiting fetch of wind on tank surface with baffles, weirs
or launders.
6. Consider economy of alternative layouts that can be expected
to provide equivalent performance.
7. Maintain equal flow to parallel units. This is most important
and often forgotten. Equal flow distribution between settling
units is generally obtained by designing equal resistances into
parallel inlet flow ports or by flow splitting in symmetrical
weir chambers (EPA, 1975).
413
-------
2.2.4 Advantages and Disadvantages
Major advantages and disadvantages of these processes as applied to
hazardous wastes are listed in Table B-3.
TABLE B-3
ADVANTAGES AND DISADVANTAGES OF PRECIPITATION, COAGULATION, AND FLOCCULATION
Advantages
Process can be economically
applied to very large volumes of
wastewater
Processes have been widely used,
equipment is relatively simple
Processes have very low energy
consumption
There is no upper limit to concen-
trations that can be treated
Disadvantages
Process often yields incomplete
removal of many hazardous compounds
Large quantities of sludge may be
generated
Metal precipitate sludges may be
an environmental hazard
Equipment may be difficult to obtain
for flows of less than vlO.OOO gpd
Because of continually changing
leachate quality, required dosages
of precipitants and coagulants
will continuously change
2.3 Costs
Figure B-5 shows costs for construction, operation, and maintenance of a
primary clarifier based on the design criteria listed below.
Costs for chemicals and their storage are not included. However, costs
for storage, handling, and feed of lime and alum are shown in Figures B-6 and
B-7. Dosages used for these cost estimates are typical for municipal treat-
ment systems but may not be adequate for leachate treatment.
414
-------
FIGURE B-5
1976 CONSTRUCTION AND O&M COSTS FOR A PRIMARY CLARIFIER
(Source: EPA, 1978)
10
1 0
0 1
CONSTRUCTION COST
0011
0 1
OPERATION 4 MAINTENANCE COST
1 0 10
Wastewater Flow Mgal/d
1 0
at
3
i| 01
s =
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000001
415
-------
FIGURE B-6
COSTS FOR LIME STORAGE, HANDLING, AND FEED (1976 COSTS)
(Source: EPA, 1978)
1 0
0 1
o
o
3 001
CONSTRUCTION COSTS
0001
.1
1.0 10
Wastewซt*r Flow, Mgal/d
100
1 Or
Q 01
o
001
0001
0
OPERATION & MAINTENANCE COST
10 10
Wastewater flow. Mgal/d
100
416
-------
FIGURE B-7
COSTS FOR ALUM STORAGE, HANDLING, AND FEED (1976 COSTS)
(Source: EPA, 1978)
10
10
i
o
i 01
001
0
MM
BM
a*
200
= :
1
mg/1
[CONSTRUCTION COST~
.."
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V
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10 IO
I1
i
01
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0 1
001
0001
=;
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^
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10
100
Wastewater Flow. Mgal/d
Wastewater Flow. Mgal/d
417
-------
Package plants suitable for coagulation, flocculation, sedimentation, and
filtration are available for small flows (10,000 gpd to 2 mgd) as factory-pre-
assembled modules. Construction, operation, and maintenance costs for 1978
are shown in Figures B-8 and B-9. The costs are detailed in Tables B-4 and
B-5.
These plans, which are available either as factory-preassembled units or
field-assembled modules, significantly reduce the cost of small facilities.
The units are automatically controlled and require only minimal operator
attention. The package plant is illustrated in Figure B-10.
Cost estimates were developed for standard manufactured units incorpo-
rating 20 minutes of flocculation, tube settlers rated at 150 gpd/ft2, mixed-
media filters rated at 2 and 5 gpm/ft2 , and a media depth of 30 inches. The
costs include premanufactured treatment plant components, mixed media, chemi-
cal feed facilities (storage tanks and feed pumps), flow measurement and con-
trol devices, pneumatic air supply (for plants of 200 gpm and larger) for
valve and instrument operation, effluent and backwash pumps, all necessary
controls for a complete and operable unit, and building. The three smaller
plants utilize low-head filter effluent transfer pumps and are to be used with
an above-grade clearwell. The larger plants gravity discharge to a below-
grade clearwell.
Raw water intake and pumping facilities, clearwell storage, high-service
pumping, and sitework, exclusive of foundation preparations, are not included
in the costs.
Complete treatment package plants (coagulation, flocculation, sedimenta-
tion, and filtration) are designed for essentially unattended operationthat
is, they backwash automatically on the basis of headloss or excessive filtered
water turbidity, and then return to service (EPA, 1979).
3.0 BIOLOGICAL TREATMENT
3.1 GENERAL DESCRIPTION AND APPLICATIONS
Most organic chemicals are biodegradable, although the relative ease of
biodegradation varies widely. With properly acclimated microbial populations,
adequate detention time, and equalization to ensure uniform flow, biological
treatment can be used to treat a wide variety of organics. There is con-
siderable flexibility in biological treatment because there are a variety of
available processes and microorganisms are remarkably flexible. Several
generalizations can be made with regard to the ease of treatability of organ-
ics by biological treatment.
418
-------
FIGURE 8-8
CONSTRUCTION COST FOR PACKAGE COMPLETE TREATMENT PLANTS AT FILTRATION
RATES OF 2 AND 5 gpm/ft (1977 COSTS)
(Source: EPA, 1979)
1,000,000
9
?
6
5
4
*- 3
v>
o
o
g 100,000
o 8
-^ 7
* 6
O
10,000
2GPM
FT
5 iปPM
F-2
10 234 56789JOO 234 567891000 234 56789
CAPACITY - gpm '0'00ฐ
-H
10
CAPACITY-liters/sec
-H
100
4V
-------
FIGURE B-9
OPERATION AND MAINTENANCE REQUIREMENTS FOR PACKAGE COMPLETE TREATMENT PLANTS -
LABOR AND TOTAL COSTS AT FILTRATION RATES OF 2 AND 5 gpm/ft (1977 COSTS)
(Source: EPA, 1979)
100,000
9
w 8
ฃ 7
-^ 6
I 5
8 3
I2
10,000 10,000
9F~
8
7
m
IOOC
10
TOTAL
tAfr(>R-Hi-P*hป
COit"
T>
i
Vil.
2GPM,
COST
FT':
LABOR-5GPIV/FT2
'FT
3 4 56789100 234 567891000
PLANT FLOW RATE-gpm
-ป-
3 456 789
10,000
10 100
PLANT FLOW RATE-liters/sec
420
-------
FIGURE B-10
TYPICAL PACKAGE WATER TREATMENT PLANT FOR PRECIPITATION, FLOCCULATION,
AND SEDIMENTATION
(Source: EPA, 1979)
Floccula-
tion
compartment
Compressed
air supply
Feed pumps^ assembly
Polyelectrolyte
feed assembly
Chemical storage
PLAN VIEW
Filtered water to
storage
Package treat-
ment plant -->
Washwater sewer -
ELEVATION VIEW
421
-------
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Non-aromatics or cyclic hydrocarbons are preferred over aromatics
Materials with unsaturated bonds such as alkenes are preferred over
materials with saturated bonds.
Stereochemistry affects the susceptibility of certain compounds to
attack.
Soluble organics are usually more readily degraded than insoluble
materials. Biological treatment is more efficient in removing
dissolved or colloidal materials, which are more readily attacked by
enzymes. This is not the case, however, for trickling filters or
other fixed media treatment systems, which preferentially treat
suspended matter.
The presence of key functional groups at certain locations can make
compounds more or less amenable to degradation. Alcohols, for
example, are more easily degraded than their alkane or alkene homo-
logues. On the other hand, addition of a Cl group or an N02 group,
increases resistance to biodegradation (EPA, 1979b).
Despite the fact that industrial wastes may be refractory to biological
treatment for any of the above reasons, microorganisms can be acclimated to
degrade many compounds that are initially refractory. Similarly, while heavy
metals are inhibitory to biological treatment, the biomass can also be ac-
climated, within limits, to tolerate higher concentrations of metals. Table
B-6 lists concentrations of metals above which treatment efficiency of acti-
vated sludge may be inhibited. The remainder of this discussion on biological
treatment addresses the general design criteria, advantages and disadvantages,
and costs of various biological treatment methods in handling hazardous waste-
waters. The treatment methods considered include:
Air activated sludge and high purity oxygen activated sludge
Trickling filter
Rotating biological disc
Bacterial seeding
Anaerobic/aerobic and facultative lagoons
424
-------
TABLE B-6
THRESHOLD CONCENTRATION FOR VARIOUS METALS IN THE AIR-ACTIVATED SLUDGE PROCESS
Metal ion
Concentration (mg/e)
Type activated sludge experiment
Silver
Vanadium
Zinc
Nickel
Chromium,
Chromium,
Lead
Iron (Ferric)
Copper
Cadmium
.03
10.0
2.0
5-10
1.0
1.0-2.5
1.0
2.0
10.0
1.0
10.0
1.0
10.0
10
15
1.0-10.0
1.0
2.0
1.0
5.0
Carbonaceous
Carbonaceous
Carbonaceous
Carbonaceous
Nitrification
Carbonaceous
Nitrification
Nitrification
Carbonaceous
Nitrification
Nitrification
Nitrification
Carbonaceous
Carbonaceous
Carbonaceous
Carbonaceous
Nitrification
Nitrification
Carbonaceous
Nitrification
Source: De Renzo, 1978
3.2 AIR ACTIVATED SLUDGE/PURE OXYGEN ACTIVATED SLUDGE
3.2.1 Applications
The air activated sludge process has been proven effective in the treat-
ment of industrial wastewaters from refineries and coke plants, of pharma-
ceutical wastes, PVC wastes, and food processing wastes (EPA, 1979; Azad,
1976). Conventional activated sludge has treated petroleum wastes with a
BOD5as high as 10,000 ppm (Azad, 1976). The process has also been reasonably
well demonstrated for the treatment of leachate from municipal landfills. At
the GROWS landfill in Bucks County, Pennsylvania, BOD removal of over 98
percent was achieved for an influent concentration of almost 5,000
425
-------
Treatment included physical/chemical as well as biological treatment (EPA,
1977a). Experiments have shown that activated sludge is generally well suited
to treatment of high strength leachates containing high concentrations of
fatty acids. As the landfill stabilizes, the ratio of BOD/COD decreases and
the wastes become less amenable to biological treatment (EPA, 1977a).
The activated sludge process is sensitive to suspended solids and oil and
grease. It is recommended that suspended solids be less than one percent (Oe
Renzo, 1978). Oil and grease must be less than 75 mg/ฃ, and preferably less
than 50 mg/ฃ, for effective treatment (Azad, 1976).
3.2.2 Design and Construction Considerations
Key design parameters for activated sludge include (1) aeration period or
detention time; (2) BOD loading per unit volume, usually expressed in terms of
Ib BOD applied per day per 1,000 ft3 of aeration basin; and (3) the food-to-
microorganism ratio (F/M), which expresses BOD loading with regards to micro-
bial mass (mixed liquor volatile suspended solids-MLVSS). There are several
modifications of the activated sludge process that may be used depending upon
the BOD loading and the required treatment efficiency. Table B-7 summarizes
the loading and operational parameters for aeration processes that may be
applicable to treatment of hazardous leachate.
Even though conventional treatment has limitations such as a poor toler-
ance for shock loads, a tendency towards producing bulking sludge that results
in high suspended solids in the effluent, and low acceptable BOD loadings,
these problems can be alleviated to varying extents with variations in process
design. The completely mixed activated sludge process (Table B-7) is the most
widely used for treatment of wastewaters with relatively high organic loads.
The advantages of this system are:
Less variation in organic loading, resulting in more uniform oxygen
demand and effluent quality
Dilution of the incoming wastewater into the entire basin, resulting
in reduced shock loads
Use of the entire contactor contents at all times because of com-
plete mixing (Azad, 1976).
The extended aeration process involves long detention times and a low F/M
ratio (0.1). Process design at this low F/M ratio results in a high degree of
oxidation and a minimum of excess sludge. The contact stabilization process,
in which biological solids are contacted with the wastewater for short periods
of time, then separated and finally reaerated to degrade sorbed organics, has
shown some success for industrial wastes with a high content of suspended and
colloidal organics (Ford and Tischler, 1977). Pure oxygen systems have re-
solved several major drawbacks of conventional treatment. Pure oxygen systems
426
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show increased bacterial activity, decreased sludge volume, reduced aeration
tank volume, and improved sludge settling (EPA, 1979b). The pure oxygen pro-
cess has been demonstrated to be applicable to a wide range of wastes at high
F/M ratios. Such wastestreams include: petrochemical, dye, pharmaceutical,
and pesticide wastes (EPA, 19795).
In addition to protess variations, there are several measures available
for minimizing process upsets and maximizing stability:
The deleterious effects of hydraulic and organic load variations can
be minimized by equalization preceding biological treatment.
A commonly used method for providing increased biodegradation is to
increase the inventory of biological solids in the aeration basin by
increasing the sludge-recycle ratio or reducing sludge wasteage.
However, there is usually a trade-off to such an approach. Higher
sludge quantities lead to increased need for food and air. Also,
old heavy sludge tends to become mineralized and devoid of oxygen,
creating a less active floe. The rate of return sludge may vary
from 35 to 50 percent in systems carrying a low MISS concentration
(^2,000 mg/ฃ) and from 75 to 100 percent in systems carrying higher
MISS (Azad, 1976).
Suspended solids should be reduced as much as possible by sedimen-
tation or filtration.
Since kinetics of biological degradation are concentration-depen-
dent, dilution can minimize process upsets under some conditions.
Sludge bulking, which leads to poor effluent quality, can be con-
trolled by pH control, sufficient aeration, and adequate nutrient
supply. An important consideration for leachate treatment is that
microbial growth is a function of the limiting nutrient. Some
leachates may be phosphorus or nitrogen-limited. Requirements for
nitrogen and phosphorus are generally:
N = 5 lb/100 Ib BOD5 removed
P = 1 lb/100 BOD5 removed
(Azad, 1976; Hammer, 1975; Metcalf and Eddy, 1972)
Equipment used for activated sludge treatment varies considerably but the
major types of aerators are mechanical surface aeration, diffuse air, and
sparged turbine aeration.
Mechanical surface aerators are considerably cheaper than diffused
aerators, with slow speed mechanical aerators being the cheapest means for
oxygenation.
429
-------
Compressed air diffusion in activated sludge reactors is achieved by two
major types of units: fine air diffusers and coarse air bubble diffusers.
The operator can increase or decrease oxygenation and mixing by changing the
air-blower output. Changes greater than 50 percent are better effected by
changing the number of diffusers.
Sparged turbines are mechanically diffused air units. This form of
diffused air is very fine and benefits from improved gas transfer kinetics.
However, the sparged turbine is generally not as efficient in gas transfer as
is the mechanical aerator (Azad, 1976; Metcalf and Eddy, 1972; Hammer, 1975).
Secondary clarifiers are used to separate activated sludge solids from
the mixed liquor and to produce concentrated solids for the return flow re-
quired to sustain biological treatment. Where multiple tanks are required, it
will probably be preferable to use rectangular tanks rather than circular
tanks since they require less area. Average hydraulic loading varies from 400
to 800 gal/day/ft2 and peak loadings range from 700 to 1200 gal/day/ft2,
depending on MLSS concentration and percent sludge recycle. Average solids
loading of 0.6 to 1.2 lb/h/ft2 and peak loadings of 1.25 to 2.0 lb/h/ft2 are
typical for activated sludge plants. Depths are normally 12 to 15 feet.
3.2.3 Advantages and Disadvantages
Advantages and disadvantages of activated sludge and pure oxygen treat-
ment are summarized in Table B-8.
3.2.4 Costs
Treatment costs are dependent upon oxygen requirements, detention time,
volumetric loadings, and food-to-microorganisms ratios.
1976 construction and maintenance costs are shown in Figures B-ll and
B-12 for conventional treatment using mechanical aeration (EPA, 1978). Costs
were based on the following criteria:
Design Basis: ENR Index = 2475
1. Construction cost includes aeration basins. Clarifier and recycle
pumps are not included.
2. Volumetric loading = 32 Ib B005/d/l,000 ft.
3. 1.1 Ib 02 supplied/lb BOD5 removed.
4. MLSS = 2,000 mg/1.
430
-------
TABLE B-8
ADVANTAGES AND DISADVANTAGES OF ACTIVATED SLUDGE AND
PURE OXYGEN ACTIVATED SLUDGE
Advantages
Activated sludge has been widely
used in industrial wastewater
treatment
There are a number of process
variations which allow for high
degree of flexibility
Process reliability is good
(although not well known for
pure oxygen activated sludge)
Can tolerate higher organic
loads than most biological
treatment process
Disadvantages
Capital costs are high
Process is sensitive to suspended
solids and metals
Generates sludge which can be high
in metals and refractory organics
Subject to upsets from shock loads
Fairly energy intensive
5. F/M = 0.25 Ib BOD5/d/lb MLSS.
6. Detention time = 6 hours (based on average daily flow).
431
-------
FIGURE B-ll
CONSTRUCTION COSTS FOR CONVENTIONAL
ACTIVATED SLUDGE TREATMENT
(1976 COSTS)
(Source: EPA, 1978)
FIGURE B-12
O&M COSTS FOR CONVENTIONAL
ACTIVATED SLUDGE TREATMENT
(1976 COSTS)
(Source: EPA, 1978)
10
01
ODI
CpNSTRUCTIpM COS
01 IO 10
Wastewater Flow, Mqal/d
100
1.0
0.01
009
s
X
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Wastewater Flow, Mqal/d
Figures B-13 and B-14 show 1976 construction and maintenance costs for extended
aeration package plants for low flows of less than 0.1 MGD.
COSTS - Construction cost includes comminutor, aeration
basin, clarifier, chlorine contact chamber, aerobic di-
gester, chlorine feed facility, building, fencing for
extended aeration package plants between 0.01 and 0.1
Mgal/d. Detention time: 24 hours (based on average daily
flow).
432
-------
FIGURE B-13
CONSTRUCTION COSTS FOR AN
EXTENDED AERATION PACKAGE PLANT
(1976 COSTS)
(Source: EPA, 1978)
CONSTRUCTION COST
1.0
Iff
kl
(fl
O 0.1
10
O
0.01
Ixt
s
ei
^
ide
^4
^
d
A
^
era
tioi
( 1
1
Pac
k
a?
;e
| 1 1 M
PI
ant
0.01 0.1 1.0
Wastewater Flow, Mgal/d
FIGURE B-14
O&M COSTS FOR AN EXTENDED
AERATION PACKAGE PLANT
(Source: EPA, 1978)
OPERATION AND MAINTENANCE COST
^ 0.01
o
en
0
g
h-
w
8
0.0001
^
^
/
J>
s
K
fa
j**
s
/s
s
A
f
'
,
{
.-'
- ;
'
^ 5
; To
i Lai
. Ua
i "M
I Pฐ
i Cr
tal
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te
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'
tal*
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emtcals
o.oi o.i
Wastewater Flow, Mgai/d
Figures B-15 and B.16 shows 1979 construction, maintenance and operating costs
for pure oxygen activated sludge (carbonaceous oxidation) based on the
following criteria.
COSTS - Construction cost includes oxygenation basins and
covers, dissolution equipment, oxygen generators and liquid
oxygen feed/storage facilities, instrumentation (where
applicable), and licensing fees, ENR Index = 2872. Oxygen
was assumed to be delivered as liquid oxygen for plants from
0.1 to 1 Mgal/d size. For plants from 1.0 to 100 Mgal/d,
oxygen was assumed to be generated on-site. 1.2 Ib 09
supplier per 1 Ib BODf. removed. MLVSS = 3,100 mg/1. F/M =
0.5 Ib BOD5/d/lb MLVSS. Detention time = 2 h (based on
average daily flow), volumetric loading = 97 Ib BODr/d/
100 ft. Oxygen transfer rate (OTR) differs depending upon
type of oxygen generator:
o Liquid oxygen generator; OTR = 6.5 02/hph
o Pressure swing adsorption (PSA); OTR = 2.0 Ib 0?/hph
o Cryogen oxygen generator, OTR = 2.5 Ib 0?/hph
433
-------
FIGURE B-15
CONSTRUCTION COSTS FOR
PURE OXYGEN-ACTIVATED SLUDGE
(Source: EPA, 1978)
FIGURE B-16
O&M COSTS FOR PURE OXYGEN-
ACTIVATED SLUDGE
(Source: EPA, 1978)
100
CONSTRUCTION COST
10
1 0
01
0
**
^
/
ft
S
Liqui
1'S
ฃ
?
d 0>
1 10
~^L
,''n
ygen
1
c
^
ry<
^
39
enic
10 101
Wastewater Flow Mgal/d
OPERATION & MAINTENANCE COST
1 O
ง 01
5
001
Liquid Oxygen
0001
;*=
535
PSA
>^
R=
Cryogenic^
01
10 10
Wastewaler Flow. Mgal/d
100
Figures B-17 and B-18 show 1976 construction and O&M costs for rectangular
secondary clarifiers based on the following design considerations.
COSTS -
Service Life: 40 years. ENR - 2475 (Sept. 1976), Power
Cost: $0.32/kwn.
1. Flocculator-type clarifier: 600 gal/d/ft2
2. Costs include sludge return and waste pumps. Sludge
concentration of 1 percent solids. Pump TDH at
10 ft. Spare pumps included as necessary, (non-clog
centrifugal pumps).
3. To adjust capital cost for alternative flow rates,
enter the curve at effective flow (Qa) = Q DESIGN*
400 gal/d/ft2 x (I/New Design Overflow Rate).
434
-------
FIGURE B-17
CONSTRUCTION COSTS FOR
RECTANGULAR CLARIFIERS
SECONDARY CLARIFIERS
(1976 COSTS)
FIGURE B-18
O&M COSTS FOR RECTANGULAR
SECONDARY CLARIFIERS
CONSTRUCTION COST
OPERATION & MAINTENANCE COST
0
Q
0
1 0
0 1
001
0
f
t=
s
1
ซx
,
x
s
~,''
1 0
^
I
X
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10 100
งi
ii
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2 001
0001
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'.
100
Wastewater Flow Mgal/d
Wastewa'sr Fiow. Mgal/d
3.3 TRICKLING FILTERS
3.3.1 Applications
Trickling filters are well suited to treatment of low flow waste streams
and are usually used as roughing filters to reduce organic loads to a level
suitable for activated sludge treatment. Trickling filters are currently used
in conjunction with other treatment methods to treat wastewaters from refin-
eries, Pharmaceuticals, pulp and paper mills, etc. (EPA, 1979; Azad, 1976).
Efficiency of tricklirvg filters in the treatment of refinery and petrochemical
wastes ranges from 10 to 20 percent when used as a roughing filter to 50 to 90
percent when used for secondary treatment (Azad, 1976). The process is more
effective for removal of colloidal and suspended materials than it is for
removal of soluble matter.
Because of the
biodegradation along
short hydraulic residence time on the filter material,
the filter media is generally insufficient as the sole
435
-------
means of biological treatment. For concentrated wastes, a high rate of recir-
culation would be required for significant reduction of organics. The short
residence time, however, has the advantage of allowing greater variations in
influent waste composition as compared to activated sludge or anaerobic diges-
tion. By placing a trickling filter in sequence with activated sludge treat-
ment, the filters could be used to even out loading variations while the
activated sludge would achieve the high removal efficiencies needed (De Renzo,
1978; Liptak, 1974).
3.3.2 Design and Construction Considerations
The variables that influence design and performance of the trickling
filter include: organic and hydraulic load, media type, nature of the waste,
pH, and temperature.
Trickling filters are classified according to their ability to handle
hydraulic and organic loads. Typical acceptable loads for low and high rate
filters are shown in Table B-9. Use of plastic media filters, with low bulk
density, has resulted in increased organic and hydraulic loading rates over
those achieved with rock media filters (Table B-9).
Plastic media filters have generally shown good performance under high
BOD loading conditions that would not be tolerated by a conventional type
system because of clogging problems (Azad, 1976).
Recirculation is generally required to provide uniform hydraulic loading
as well as to dilute high strength wastewaters. However, there is a limit to
the advantage achievable with recirculation. Generally recirculation rates
greater than four times the influent rate do not increase treatment efficiency
(Liptak, 1974). Several recirculation patterns are available. One of the
most popular is gravity return of the underflow from the final clarifier to a
wet well during periods of low flow and direct recirculation by pumping filter
discharge back to the influent as shown in Figure B-19.
Several formulas have been proposed which predict BOD removal efficiency
based on waste type, influent BOD, hydraulic load and other factors related to
performance. Problems with these models include the need to determine treat-
ability on a case by case basis and the fact that the models are usually
applicable for only very specific conditions. The reader is referred to
articles by Velz, 1960; Germain, 1966; Schulze, 1960; and Eckenfelder, 1963
for these models.
436
-------
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437
-------
FIGURE B-19
TRICKLING FILTER RECIRCULATION
(Source: Hammer, 1975)
Direct recirculation, Q~
Lift
pumps
Influent
Q*
Prin
^
r
rf" ""Tr""""""-*
> CUH.
*"**"" Q + Q + Q
1
1
1
1 O + OB O
,)^ ^ I 1 >i
J T Final 1 Effluent
Sludge
Recirculation
pumps
Wet well
3.3.3 Advantages and Disadvantages
Table B-10 summarizes the advantages and disadvantages of trickling
filters as compared to other biological treatment methods and non-biological
methods for removal of organics.
TABLE B-10
ADVANTAGES AND DISADVANTAGES OF TRICKLING FILTERS
Advantages
Because of short hydraulic
residence times, process is not
highly sensitive to shock loads
Suitable for removal of suspended
or colloidal matter
Has good applicability as a
roughing filter to even out
organic loads
Disadvantages
Vulnerable to below freezing
temperatures
Limited treatment capability in
a single stage operation
Potential for odor problem
Has limited flexibility and control
Requires long recovery time if dis-
rupted
438
-------
3.3.4 Costs
1977 costs for a high rate trickling filter, rock media plant are shown
in Figure B.20 and B.21 for the following design basis.
COSTS Assumptions: ENR = 2494.
1. Construction cost (January 1977 dollars) based on:
bed depth = 5 ft; organic loading = 20 1b BODr/d/
1000 ft ; recirculation ratio = 4.0 (@ average daily
flow) to 0.4 (@ peak daily flow, assumed to equal
3.5 times average daily flow) to maintain average
hydraulic loading .75 gal/min/ft2.
2. Cost includes rock media, underdrains, distributors,
and reinforced concrete containment structures.
Clarifier and recirculation equipment not included.
3. Operation and maintenance cost includes labor @ $7.50/h
and materials. Does not include energy costs.
Water Quality: Filter Influent (mg/1) Effluent (mg/1)
BOD 130 45
Suspended Solids 100 40
3.4 ROTATING BIOLOGICAL DISCS
3.4.1 Description and Applications
The process is similar to the trickling filter in that the wastes are
treated by a fixed-film biological growth. A series of disks are mounted on
a horizontal shaft and are place in a countour bottom tank and immersed
approximately 40 percent. When rotated out of the tank, the liquid trickles
out of the void space and the biomass is aerated. One such process, Bio-
surf, is illustrated in Figure B-22.
439
-------
FIGURE B-20
CONSTRUCTION COSTS FOR TRICKLING
FILTER PACKAGE PLANT (1976 COSTS)
(Source: EPA, 1978)
CONSTRUCTION COST
FIGURE B-21
O&M COSTS FOR TRICKLING FILTER
PACKAGE PLANT (1976 COSTS)
(Source: EPA, 1978)
OPERATION & MAINTENANCE COST
100
10
1.0
0.1
i
Y*
S
p*
z:ฃ
_ij
f
/
f
U4--
krrj
10
rr*-
T
_i_L .
1
100
0.01
0.001
X
*
L
>
S
^
S
k^
V
s
? r
j_-
s
'l*
.f
Y^
10
^
^
^
S
x1
s. .
^
/
^
x'
--)t
1 1
later]
II
.1 _ j
I
......
. ,
W~
\ i;
als "
100
_L
Wastewater Flow. Mgal/d
Wastewater Flow. Mgal/d
FIGURE B-22
BIO-SURF PROCESS SCHEMATIC
(Source: Autotrol, 1978)
Bio-Surf Units
Primary Treatment
Secondary Clarifier
440
-------
Rotating biological discs are currently being used at full scale to treat
wastewaters from the manufacture of herbicides, Pharmaceuticals, petroleum,
pulp and paper, and pigments (Autotrol, 1978). The process has only been used
in the United States since 1969 and is not widespread. However, its modular
construction, low hydraulic head loss, and adaptability to existing plants
have resulted in growing use (EPA, 1978a). The process can be used for
roughing, nitrification, or secondary treatment.
3.4.2 Design and Construction Considerations
For adequate treatment it is recommended that the process include four
stages (discs) per train and the use of at least two parallel trains.
Typical design criteria include:
Organic loading: 30 - 60 lbBOD/1,000 ft3 media (without nitrification)
15 - 20 lbBOD/1,000 ft3 media (with nitrification)
Hydraulic loading: 0.75 to 1.5 gal/d/ft2 (without nitrification)
0.3 - 0.6 gal/d/ft2 (with nitrification)
Detention time: 40 - 90 minutes (without nitrification)
90 - 230 minutes (with nitrification)
(Source: EPA, 1978a)
Based on the design criteria, rotating biological discs can handle or-
ganic loads similar to a high rate trickling filter.
3.4.3 Advantages and Disadvantages
Table B-ll summarizes advantages and disadvantages of rotating biological
discs as compared to trickling filters and activated sludge.
3.4.4 Costs
1976 costs for rotating biological discs are shown in Figure B-23 and
B-24 for flow rates of 0.1 to 10 MGD. Costs are based on the following:
COSTS - (ENR Index = 2475)
1. Construction cost includes RBC shafts (standard
media, 100,000 ft2/shaft, motor drives (5 hp/shaft),
441
-------
molded fiberglass covers, and reinforced concrete
basins.
2.
3.
4.
Cost does not include primary or secondary clarifiers
Loading rate - 1.0 gal/d/ft2.
Treatment for carbonaceous oxidation.
TABLE B-ll
ADVANTAGES AND DISADVANTAGES OF ROTATING BIOLOGICAL DISCS
Advantages
Process has considerably more
flexibility than trickling filters;
both the intensity of contact
between biomass and wastewater and
the aeration rate can be easily
controlled by the rotational speed
of the discs
Wastewater retention time can be
controlled by selecting appropriate
tank size; thus higher degrees
of treatment can be obtained than
with trickling filters
In contrast to the trickling
filter, biological discs rarely
clog since shearing forces contin-
uously and uniformly strip excess
growth
As compared to activated sludge,
rotating biological discs can
handle large flow variations
and high organic shock loads
Modular construction provides
flexibility to meet increases
or decreased treatment needs
Disadvantages
Vulnerable to climate changes
not covered
if
High organic loads may result in
first stage septicity and supple-
mental aeration may be required
Odor may be a problem if septic
conditions develop
As with trickling filters, biomass
will be slow to recover if disrupted
Can handle only relatively low
strength wastes as compared to
activated sludge
442
-------
FIGURE B-23
CONSTRUCTION COSTS FOR ROTATING
BIOLOGICAL DISCS
(Source: EPA, 1978)
FIGURE B-24
O&M COSTS FOR ROTATING
BIOLOGICAL DISCS
(Source: EPA, 1978)
100
10
m
s
8
5
c
o
3 10
01
.
/
/
*~ ฃ
X
"1
t
/I
<
'
0(
Pd/
f 2
54
? J.
I!
si
o
i
01 10 10
Wastewater Flow, Mgal/d
10
01
001
0001
s
-^
"^
OPERATION 8 MAINTENANCE
^ "
^ ,'
. ^
.-''
,-"
)
.
-
.
^
^/
^
'
u ~ *"
/-'
^ - -
COST
Totol.
S-Pm
L*1
, Labor
. : Ma
r
all
- -
001
OOOOI
01 10 10
Wastewater Flow, Mgal/d
3.5 BIOLOGICAL SEEDING
3.5.1 Description and Applications
Biological seeding involves addition of acclimated or mutant bacteria
that will hasten biodegradation of refractory compounds. As was mentioned
previously, it is possible to acclimate bacteria to a wide range of organics.
Many organisms are known to induce enzymes needed to degrade "refractory"
organics if they are gradually exposed to increasingly higher levels of the
"refractory" compound. Thus biomass that has treated petrochemical wastes for
a period of time will be more suited to degrading benzenes, naphthalene, and
phenols in leachate than would biomass from a municipal treatment process.
The Polybac Corporation offers a freeze-dried, biochemical preparation
containing mutant bacteria and substances to enhance their growth. The prod-
uct was developed for degradation of benzene derivatives, phenols and cresols,
naphthalenes, gasolines, kerosene, cyanides (properly diluted), and other
toxic wastes from refineries, pesticides, pulp mills, steel mills, and textile
and food processing plants (Polybac, 1978). The product offers some advan-
tages over acclimated bacteria taken directly from treatment plants. Starting
443
-------
with acclimated bacteria, Polybac uses radiation to increase the genetic
diversity of microorganisms. The strains resulting from radiation processes
are further exposed to selected compounds in order to isolate those organisms
with enhanced abilities to degrade specific compounds (Zitrides, 1978).
Phenobac or other acclimated cultures may be added to conventional
systems to increase process stability, initiate recovery from shock loads,
provide faster startup, and increase the capacity to handle variations in
organic loads.
Mobay Chemical Corporation recently used Phenobac in order to recover
biological activity after a down time period that occurred during extremely
cold weather. The activated sludge process, treating mixed organic chemical
intermediates, was brought back into operation after 15 days.
Use of Phenobac was also found to enhance biological treatment stability
at an Exxon Chemical Company Plant treating petrochemical wastewaters (Poly-
bac, 1978).
3.5.2 Design and Construction Considerations
Phenobac or other acclimated cultures are used as the biomass in conven-
tional or pure oxygen treatment systems, or in landfarming applications.
Application rates are determined on a case-by-case basis.
3.5.3 Advantages and Disadvantages
Table B-12 summarizes the advantages and disadvantages of treatment with
acclimated cultures.
3.5.4 Costs
Freeze-dried cultures available through Polybac Corp. cost $23.75/lb
rehydrated. Fifty-five gallons of water are generally used to rehydrate 25
Ibs (Krupka, 1980). All other costs are the same as those encountered for
conventional or pure oxygen-activated sludge.
444
-------
TABLE B-12
ADVANTAGES AND DISADVANTAGES OF TREATMENT WITH ACCLIMATED BACTERIA
Advantages
Use of acclimated cultures can
decrease start-up time
Provides increased resistance
to shock loads
Increases process stability
Disadvantages
May require continuous seeding
where there are other microbial
predators, excessive washout, or
adverse environmental conditions
such as presence of toxic metals
Increased materials costs for
operation of activated sludge or
high oxygen systems
3.6 ANAEROBIC, AEROBIC, AND FACULTATIVE LAGOONS
3.6.1 General Description and Applications
Lagoons or waste stabilization ponds are large shallow basins that rely
on long retention times and natural aeration to decompose the waste. The
aerated lagoon is a variation in which the wastes are artificially aerated
with diffused air or mechanical aerators. It differs from activated sludge
processes in that there is no sludge biomass recycle. Waste stabilization
ponds are more sensitive to high concentrations of inorganics and suspended
solids than are other biological methods. Since there is no mixing, suspended
solids would settle in the pond, creating an excessive load which inhibits
benthic microorganisms and creates a sludge blanket along the bottom of the
pond.
Waste stabilization ponds have been used to treat low strength industrial
wastes or as a polishing step for certain waste types. This treatment module
is employed in food processing industries, paper and pulp
mills, refineries, and petrochemical plants (De
445
and
Renzo, 1978;
mills, textile
Nemerow, 1978).
-------
3.6.2 Design and Construction Considerations
Each subtype of waste stabilization pond utilizes a different type of
bacteria but is of similar construction, with an earthen pit and earthen side
levees. Treatment of leachates requires that the pond be lined. The designs
of various waste stabilization ponds and aerobic lagoons differ significantly.
Table B-13 summarizes the major design criteria. The criteria indicate that,
in general, lagoons can treat only low strength waste and therefore will be
best suited as a polishing step used in conjunction with other treatment
methods.
As Table B-13 indicates, the aerobic lagoon requires the greatest surface
area to treat an equivalent waste load. Oxygen transfer depends on the ratio
of lagoon surface area to volume (length to wide ratio should be less than
3:1), temperature, turbulence, and bacterial oxygen uptake. The system has
the least tolerance for high organic loads but benefits from a short detention
time (EPA, 1979; Liptak, 1974).
Anaerobic stabilization ponds require significantly less surface area and
can handle substantially higher organic loads. Deep lagoons benefit from
better heat retention, and an effluent length-to-width ratio of 2:1 is recom-
mended.
Sludge buildup is much less for the anaerobic pond than for the aerobic;
for every pound of BOD destroyed by the anaerobic process, about 0.1 Ib of
solids is formed, as compared to 0.5 Ib for the aerobic lagoon. The major
disadvantage of the anaerobic lagoon is that it produces strong odors unless
the sulfate concentration is maintained below 100 mg/i (Liptak, 1974).
The facultative lagoon benefits from having an aerobic layer that oxi-
dizes hydrogen sulfide gas to eliminate odors. It can handle BOD loads inter-
mittently between the anaerobic and aerobic lagoon.
Artificial aeration with mechanical or diffused aerators allows for
deeper basins and higher organic loads than those obtained in aerobic lagoons.
The basins are designed for partial mixing only, and anaerobic decomposition
occurs on the bottom. Operating costs are significantly less than for acti-
vated sludge, but the system cannot withstand the organic loads tolerated by
activated sludge.
In general, the use of several lagoons in series is more efficient than
one lagoon since it can reduce short-circulation and lead to increased organic
removal efficiency.
446
-------
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en
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447
-------
3.6.3 Advantages and Disadvantages
Table B-14 summarizes advantages and disadvantages of waste stabilization
ponds and aerated lagoons.
TABLE B-14
ADVANTAGES AND DISADVANTAGES OF STABILIZATION PONDS AND AERATED LAGOONS
Advantages
Operating costs are low compared
to other biological treatment
methods
Cost-effective treatment for
polishing effluent
Waste stabilization ponds require
minimal energy
Disadvantages
Tolerate low strength wastes only
Intolerant of suspended solids and
metals
Require large land areas
Performance markedly affected by
temperature, and treatment method
is not suitable for freezing
temperatures
System has limited flexibility
Volatile gases may be emitted
from processes
3.6.4 Costs
1976 costs for anaerobic and facultative stabilization ponds and aerated
lagoons are shown in the following figures based upon the design criteria
listed.
448
-------
Anaerobic Lagoons (Figures B-25 and B-26)
COSTS -
Service Life: 50 years
Average detention time = 35 days; January 1979 dollars; ENR
Index = 2872; depth = 10 ft; BOD5 loading = 466 Ib/acre/d.
Construction cost includes excavating, grading and other
earthwork and service roads. Costs do not include land and
pumping. Liner cost not included in estimate.
Wastewater Characteristics:
BODq Influent, mg/1
D 600
Effluent mg./l
240
To adjust costs for other BODr and /or detention times, enter
curve at effective flow (QE)
QE = Q[)esiqn x (466 Ib/acre/d) (new detention time)
y (new design loading) (35 days)
FIGURE B-25
1976 CONSTRUCTION COST FOR
ANAEROBIC LAGOONS
(Source: EPA, 1978)
FIGURE B-26
O&M COSTS FOR ANAEROBIC LAGOONS
(Source: EPA, 1978)
I
o
10 c
0.1
0.01
01
CONSTRUCTION COST
10 10
Wastewater Flow. Mgal/d
100
OPERATION ซ MAINTENANCE COST
0,1
0.01
0001
0
I
f
^
^
s
---
f. '..
1
1
>
/
\
f>
*
10
" .^
^
f
10
' '
10
Wastewater I low Mgal/d
449
-------
Facultative Lagoons (Figures B-27 and B-28)
COSTS-
1. Warm climate - Lagoon loading = 40 Ib BOD5/acre/d.
2. Cool climate (northern U.S.) - Lagoon loading = 20 Ib
BODg/acre/d.
3. Water depth = 4 ft.
4. Construction cost includes excavating, grading, and
other earthwork required for normal subgrade prepara-
tion and service roads. Costs do not include land
and pumping.
5. Process performance:
Wastewater Characteristics
^Jl Out
BOD5, mg/ฃ 210 30
COD, mg/ฃ 400 100
TSS, mg/ฃ 230 60
Total-P, mg/ฃ 11 8
NH -N, mg/ฃ 20 15 (cool climate)
1 (warm climate)
6. No liner included in cost estimate.
7. ENR Index = 2475
Adjustment Factor: To adjust costs for loadings other
than those above, enter curve at effective flow (QE).
450
-------
FIGURE B-27
CONSTRUCTION COSTS FOR FACULTATIVE
LAGOONS (1976 COSTS)
(Source: EPA, 1978)
FIGURE B-28
O&M COSTS FOR FACULTATIVE
LAGOONS (1976 COSTS)
(Source: EPA, 1978)
CONSTRUCTION COST
OPERATION 4 MAINTENANCE COST
1 0
01
001
0
.
^
/
/
/
^>
J
Cc
/
*
=--;
---
K-H
ol
<'
/
/
1
ft=
-U
4rH
Clim
\
x
x^
, '
at
V
s
e
x
/
4
w
/
^
,
/'
arm
I
1 0
" !
'
x
/
Clim
/
/*
fit
/
.e
10 10
Wastewaler Flow, Mgal/d
1 0
D 0 1
001
0001
0 1
1 0 10
Wastewater Flow Mgal/d
100
Aerated Lagoons (Figures B-29 and B-30)
COSTS -
1. Service Life: 30 years; ENR Index = 2475
2.
3.
Theoretical detention time = 7 d; 15-ft water depth;
floating mechanical aerators.
Horsepower required = 36 hp/Mgal of capacity; power
@ $.02/kWh.
4. Construction cost includes excavation, embankment,
and seeding of lagoon/slopes (3 cells); service road
and fencing; riprap enbankment protection; hydraulic
control works; aeration equipment; and electrical
equipment.
451
-------
Wastewater Characteristics
BOD 5, mg/l
COD, mg/l
TSS, mg/l
Total-P, mg/l
NH3 -N, mg/l
In
210
400
230
11
20
Out
25
50
40
8
18
To adjust construction cost for detention time other than
above, enter curve at effective flow (QE).
FIGURE B-29
CONSTRUCTION COSTS FOR
AERATED LAGOONS
FIGURE B-30
O&M COSTS FOR AERATED LAGOONS
10
10
M
Millions of Dolla
1 2
ป
iM
^
7 days
CONSTRUCTION COST:
^
-
S
' ,
s
^-
/
'--
,
01 IO 10
Wastewater Flow. Mgal/d
100
IO
01
001
OOOI
0
*
X
^
^
:OPERATION a
t
0*
*~
1
1
'
, '
OK
s
-f
MAINTENANCE COST ~J[P
/
L-lii
j 7 1 '
RM
10
r I
^
' **
<
.^
**&
<^F~
* i .
ซ
i
_ -
X '
10
. QOOC*
100
Wastewater Flow, Mgal/d
452
-------
4.0 CARBON ADSORPTION
4.1 GENERAL DESCRIPTION
The process of carbon adsorption involves contacting a waste stream with
carbon, which selectively adsorbs hazardous materials by physical and/or
chemical forces. When carbon reaches its ultimate capacity for adsorption,
that is, when rate of adsorption and desorption are equal, the carbon is
removed for disposal, destruction, or regeneration.
4.2 APPLICATIONS
The suitability of carbon adsorption for treatment of wastewater asso-
ciated with disposal sites depends upon the influent characteristics, the
extent of pretreatment. and the required effluent quality. The highest con-
centration of solute in the influent stream that has been treated on a con-
tinuous basis is 10,000 ppm TOC, and a 1 percent solution is currently con-
sidered as the upper limit (De Renzo, 1978).
Concentrations of oil and grease in the influent should be limited to 10
ppm. Concentrations of suspended solids should be less than 50 ppm in upflow
systems; downflow systems can handle concentrations as high as 2000 ppm,
although frequent backwashing would be required. Removal of inorganics by
carbon generally requires concentrations of less than 1,000 ppm and preferably
less than 500 ppm (De Renzo, 1978).
The suitability of using activated carbon for removal of a certain
solute(s) depends upon molecular weight, structure, and solubility. Table
B-15 summarizes the influence of molecular structure and other properties of
organics on their adsorbability. Table B-16 summarizes the potential for
removal of inorganics by activated carbon.
As would be expected from the information in Table B-15, activated carbon
has been proven effective in the removal of a variety of chlorinated hydro-
carbons, organic phosphorus, carbonates, PCB's, phenols, and benzenes.
Specific hazardous organics that are effectively removed include aldrin,
dieldrin, endrin, ODD, DDE, DDT, toxaphene, and 2 aroclors (Gulp, 1978).
Activated carbon treatment has not been shown to be suitable for treat-
ment of municipal landfill leachates from young landfills; carbon shows poor
adsorption capacity for fatty acids, which are prevalent in municipal landfill
leachate. Carbon adsorption is generally not effective for wastes with high
BOD/COD and COD/TOC ratios (EPA, 1977).
453
-------
TABLE B-15
EFFECTS OF MOLECULAR STRUCTURE AND OTHER FACTORS ON
ADSORPTION BY ACTIVATED CARBON
1. Aromatic compounds are generally more adsorbable than aliphatic compounds
of similar molecular size.
2. Branched chains are usually more adsorbable than straight chains.
3. Substituent groups affect adsorbability:
Substituent group Nature of influence
Hydroxyl Generally reduces adsorbability; extent of
decrease depends on structure of host
molecule
Amino Effect similar to that of hydroxyl but
somewhat greater. Many ami no acids are
not adsorbed to any appreciable extent
Carbonyl Effect varies according to host molecule;
glyoxylic and more adsorbable than acetic
but similar increase does not occur when
introduced into higher fatty acids
Double bonds Variable effect
Halogens Variable effect
Sulfonic Usually decreases adsorbability
Nitro Often increases adsorbability
4. An increasing solubility of the solute in the liquid carrier decreases
its adsorbability.
5. Generally, strongly ionized solutions are not as adsorbable as weakly
ionized ones; i.e., undissociated molecules are, in general, preferen-
tially adsorbed.
6. The amount of hydrolytic adsorption depends on the ability of the
hydrolysis to form an adsorbable acid or base.
7. Unless the screening action of the carbon pores intervene, large mole-
cules are more sorbable than small molecules of similar chemical nature.
This is attributed to more solute carbon chemical bonds being formed,
making desorption more difficult.
Source: Azad 1976
See Copyright Notice, Page 497
454
-------
TABLE B-16
POTENTIAL FOR REMOVAL OF INORGANIC MATERIAL BY ACTIVATED CARBON
Constituents
Metals of high sorption potential
Antimony
Arsenic
Bismuth
Chromium
Tin
Metals of good sorption potential
Silver
Mercury
Cobalt
Zirconium
Elements of fair-to-good sorption
potential
Lead
Nickel
Titanium
Vanadium
Iron
Elements of low or unknown
sorption potential
Copper
Cadmium
Zinc
Beryllium
Barium
Selenium
Molybdenum
Manganese
Tungsten
Potential for
removal by carbon
Highly sorbable in some solutions
Good in higher oxidation states
Very good
Good, easily reduced
Proven very high
Reduced on carbon surface
CH3HgCl sorbs easily
Metal filtered out
Trace quantities readily sorbed,
possibly as complex ions
Good at low pH
Good
Fair
Good
Variable 2+
""* good, FE poor, but may
oxidize
FE
Slight, possibly good if
complexed
Slight
Slight
Unknown
Very low
Slight
Slight at pH 6-8, good as
complex ion
Not likely, except as Mn04
Slight
continued
455
-------
TABLE B-16 (Continued)
Constituents
Miscellaneous inorganic water
constituents
Phosphorus
P, free element
3-
P04phosphate
Free halogens
F2 fluorine
C12 chlorine
Br2 bromine
I2 iodine
Hal ides
F" flouride
Cl", Br", I"
Potential for
removal by carbon
Not likely to exist in reduced
form in water
Not sorbed but carbon may induce
precipitation Ca3(P04)2 or
Will not exist in water
Sorbed well and reduced
Sorbed strongly and reduced
Sorbed very strongly, stable
May sorb under special conditions
Not appreciably sorbed
Source: Gulp, 1978
See Copyright Notice, Page 497.
4.3 DESIGN AND CONSTRUCTION CONSIDERATIONS
Critical design criteria are organic load, hydraulic load, contacting
method, contact time, and regeneration requirements.
The approximate carbon requirements for a specific organic load, and the
residual organic levels can be estimated from adsorption removal kinetics
conducted on a batch basis. An isotherm can be used as a functional expres-
sion for variation of adsorption with concentration of adsorbate in bulk
solution. The isotherm is expressed in terms of removal of impurity (i.e.,
BOD, COD, or color).
J5J- = KC 1/n
where: X = impurity adsorbed
M = weight of carbon
C = equilibrium concentration of impurity
K,n = constant (Gulp, 1978)
456
-------
Isotherms are a useful approximation of treatability, but generally give
a falsely high estimate of continuous carbon performance.
There are four basic ways that waste streams can be contacted, and the
choice of the appropriate method depends upon influent characteristics,
effluent criteria, flow rate, and economics. Table B-17 summarizes these
available methods and Figure B-31 illustrates them.
Upflow beds have the advantage over downflow beds in that they more closely
approach continuous countercurrent contact operations, which results
in minimal use of carbon. Also, upflow beds can be designed to allow for
removal of spent carbon and addition of fresh carbon while the columns remain
in operation. Downflow columns have the advantage that they can handle higher
suspended solids concentrations, although backwashing requirements may be
frequent.
FIGURE B-31
ADSORBER CONFIGURATIONS
(Source: DeRenzo, 1978)
Moving Bed Down Flow in Series Down Flow in Parallel Upflow-Expanded in Series
out
in
out
out in
Typical operating parameters for carbon adsorption systems are summarized
in Table B-18. The parameters are based on system operations for physical/
chemical and tertiary treatment systems.
457
-------
TABLE B-17
SUMMARY OF ACTIVATED CARBON CONTACTING METHODS
Method
Downflow adsorbers
parallel
in
Downflow adsorbers in
series
Moving bed
Upflow-expanded
Comments
For high volume applications
Can handle higher than average suspended
solids (^65-70 ppm)
Relatively low capital costs
Effluents from several columns blended,
therefore less suitable where effluent
limitations are low
2-10 gpm/ft2 flow rate
Large volume systems
Countercurrent carbon use
Effluent concentrations relatively low
Can handle higher than average suspended
solids (M55-70 ppm) if downflow
Capital costs higher than for parallel
systems
2-10 gpm/ft2 flow rate
Countercurrent carbon use (most
efficient use of carbon)
Suspended solids must be low (<10 ppm)
Capital and operating costs relatively high
Can use such beds in parallel or series
2-7 gpm/ft2 flow rate
Countercurrent carbon use (if in series)
Can handle high suspended solids (they
are allowed to pass through)
High flows in bed (M5 gpm/ft2)
Minimum pretreatment
Minimum headloss
Source: DeRenzo, 1978
458
-------
TABLE B-18
OPERATING PARAMETERS FOR CARBON ADSORPTION
Parameter
Contact time
Hydraulic load
Backwash rate
Carbon loss
during
regeneration
Weight of COD
Removed per
weight of
carbon
Carbon require-
ments
PCT plant
Tertiary
plant
Bed depth
Regin' rements
Generally 10-50 min; may be
as high as 2 hours for some
industrial wastes
2-15 gpm/ft2 depending on
type of contact system; see
Table 3-17
Rates of 20-30 gpm/ft2 usually
produce 25-50 percent bed
expansion
4-9 percent
2-10 percent
0.2 - 0.8
Sources
Gulp, 1978
liptak, 1974
Liptak, 1974
DeRenzo, 1978
Liptak, 1974
Gulp, 1978
DeRenzo, 1978
500 - 1800 lb/106 gal.
200 - 500 lb/106 gal.
10 - 30 feet
Gulp, 1978
EPA, 1978a
The decision to regenerate and reuse granular carbon or to use it on a
once-through basis is based primarily on economics. For plants requiring less
than 200 Ib/day of carbon (less than approximately 0.8 mgd), regeneration is
probably not economical. Most leachate treatment facilities will fall within
this range.
459
-------
Use of electric furnaces, rather than multiple hearth furnaces, may make
it possible to regenerate activated carbon economically for plants using less
than 200 Ib/day (Gulp, 1978). Regeneration needs can be determined on the
basis of COD adsorbed per pound of carbon or required carbon dosage in terms
of total flow.
4.4 ADVANTAGES AND DISADVANTAGES
B-19.
Advantages and disadvantages of carbon adsorption are summarized in Table
TABLE B-19
ADVANTAGES AND DISADVANTAGES OF ACTIVATED CARBON
Advantages
High flexibility in operation
and design
Suitable for treatment of a
wide range of organics that
do not respond to biological
treatment
Has high adsorption potential
for some highly hazardous
inorganics (i.e., CR, CN)
Tolerant of some fluctuations
in concentrations and flow
Disadvantages
Intolerant of high suspended solids
levels
Requires pretreatment for oil and
grease removal where concentrations
are greater than 10 ppm
Not suitable for removal of low
molecular weight organics, highly
soluble or highly ionized organics
Limited in practice to wastes with
less than 10,000 ppm organics
O&M costs are high
4.5 COSTS
Costs for 1976 are shown in Figures B-32 and B-33 for tertiary granular
activated carbon adsorption. The costs are based on the following criteria:
460
-------
COSTS - ENR Index = 2475
1. Construction cost includes vessels, media, pumps,
carbon storage tanks, controls, and operations
building; loading rate = 30 Ib/Mgal; contact time =
30 min; disposal costs not included.
2. O&M cost includes pumping ($0.02/kWh), labor
($7.50/h, including fringes) and maintenance.
3. No regeneration is included; therefore, above 3
Mgal/d, cost curves are extrapolated.
FIGURE B-32
CONSTRUCTION COSTS FOR TERTIARY
ACTIVATED CARBON TREATMENT
(1976 COSTS)
(Source: EPA, 1978)
FIGURE B-33
O&M COSTS FOR TERTIARY
ACTIVATED CARBON TREATMENT
(1976 COSTS)
(Source: EPA, 1978)
CONSTRUCTION COST
100
10
o
i
1 0
0 1
0.1
1.0 10
Wastewater Flow. Mgal/d
100
OPERATION & MAINTENANCE COST
10
1 0
0 1
001
0.1
^
^
s
ft
-r
'
^
/
*
till
s J
1.0
1
1
' "-
f>
/
J
s
10 10
Wastewater Flow, Mgal/d
461
-------
5.0 ION EXCHANGE
5.1 GENERAL DESCRIPTION
Ion exchange resins are insoluble solids containing fixed cations and
anions capable of reversible exchange with mobile ions of the opposite sign in
solutions with which they are brought into contact. The direction and extent
of the reaction are governed by the relative insolubilities of the salts that
can be formed and the equilibrium constants (De Renzo 1978).
5.2 APPLICATIONS
Ion exchange is considered applicable for removal of the following
classes of chemicals:
All soluble metallic elements, either cationic or anionic
Anions such as halides, cyanides, and nitrate
Acids such as carboxylics, sulfonics, and some phenols at pH suffic-
iently alkaline to give the ions
However, there are certain limitations on the ion exchange capability of
various resins, and these must be considered in determining the feasibility of
ion exchange and its pretreatment requirements. The upper concentration limit
for exchangeable ions for efficient operations is about 2,500 mg/ฃ expressed
as calcium carbonate, or 0.05 equivalents/liter. This upper limit is due
primarily to the fact that high concentrations of exchangeable ions result in
a rapid exhaustion of the resin during the process and costs for regeneration
become prohibitively high (DeRenzo, 1978). Also, the effectiveness of ion
exchange resins can be decreased by the presence of certain waste constit-
uents. Suspended matter must be very low so as not to foul the resins.
Oxidizing agents such as chromic or nitric acid can be damaging to resins as
well. Finally, some organics, especially aromatics, can be irreversibly
adsorbed by' the resin, resulting in decreased capacity. (DeRenzo, 1978).
This problem can sometimes be solved by prefiltering the wastewater or by
using scavenger exchange resins (Metcalf and Eddy, 1972).
Ion exchange is currently being used in a number of industrial treatment
processes, which suggests that it may be suited for treatment of some haz-
ardous waste leachates. Notably, ion exchange is widely used in the elec-
troplating industry to remove impurities from rinse water. Rinse waters
are usually fairly dilute solutions of chromium, nickel, and cyanides. Ion
exchange is generally used as a polishing step in treatment of electroplating
wastes and is also widely used as a final treatment method for metal fin-
ishing wastewaters for removal of cyanides, zinc, chromium, and other metals.
462
-------
Another application is for removal of valuable metals such as copper, molybde-
num, cobalt, and nickel from dilute leach liquors from tailing or dump piles
(Nemerow, 1978; De Renzo, 1978).
5.3 DESIGN AND CONSTRUCTION CONSIDERATIONS
The major design considerations for ion exchange treatment include selec-
tion of the appropriate resin, based on organic loads, hydraulic load, selec-
tion of the appropriate operating mode, and consideration of backwashing and
regeneration requirements.
5.3.1 Selection of the Resin
The extent to which removal of anions and/or cations occurs depends on
the equilibrium that is established between the ions in the aqueous phase and
those in the solid phase. For instance, the equilibrium for the removal of
sodium from solution is defined as follows:
[H] x RNa ..
[NaJ x RH = KH * Na
where: KH -> Na = selectivity coefficient
x RH = mole fraction of hydrogen on the exchange resin
x RNa = mole fraction of sodium on exchange resin
[ ] = concentration in the solution phase
The selectivity coefficient depends on the nature and volume of the ion, the
type of resin and its saturation and the ion concentration in wastewater
(Metcalf and Eddy, 1972). Since the stability of the salts formed by the ions
and exchangers can be highly variable, it is important to make a knowledgeable
choice of the exchange material so that it will allow for the selective sepa-
ration. Exchange resins can be selected and compared by the following crite-
ria:
Functionality, which refers to the kinds of ions that are exchanged
Exchange capacity, which is a measure of the total uptake of spe-
cific ions
Selectivity, which refers to the preference of one kind of exchange-
able ion over another (De Renzo, 1978)
Table B-20 lists some available resin types that may be well-suited to leach-
ate treatment.
463
-------
TABLE B-20
COMMON REACTIVE GROUPS FOR ION EXCHANGE RESIN1
Reactive group
Strong acid (sulfonic)
Weak acid (carboxylic)
Weak acid (phenolic)
Strong base (quaternary amine)
Weak base (tertiary and secondary
amine)
Chelating (varied, may be imino-
diacetate or oximine groups)
Exchangeable ions
Cations in general
Cations in general
Cesium and polyvalent cations
All anions, especially used for
anions of weak acids (cyanide,
caronate, silicate, etc.)
Anions of strong acids (sulfate,
chloride, etc.)
Cations, especially transition and
heavy elements
'Differences in the particular starting materials and preparation route fre-
quently give rise to differences in handling properties, stability and re-
action kinetics between resins that have the same polymer backbone, function-
al groups, and exchange capacity. Hence it is important to test a variety of
resins for a particular application.
Source: DeRenzo, 1978
5.3.2 Mode of Operation
Ion exchange may be carried out as a batch or continuous operation.
Where a continuous operation is practiced, there are three possible operating
modes: cocurrent fixed bed, countercurrent fixed bed, and countercurrent
continuous. Table B-21 presents a summary comparison of the three processes
(De Renzo, 1978).
Commonly used variations of the fixed bed exchange mode include mixed
beds and use of exchange columns in series. Mixed beds (Figure B-34) give a
larger driving force and yield higher removal of efficiencies than the same
amount of resin used in separate beds (Vermuelen, 1977). Where a number of
beds are used in series (Figure B-35), it is possible to detach the upstream
bed, regenerate it, and reattach it at the downstream end, thereby making it
more similar to a countercurrent stream.
464
-------
5.3.3 Regeneration
Continued contact of the exchange resin with the solution containing the
ions to be removed results in eventual exhaustion of the active sites on the
resins. It is generally advisable to regenerate the resins before all active
sites are exhausted. Table B-22 summarizes the types of regenerants and
dosage ranges. Optimum regenerant quantities and conditions will vary with
the process involved and can be determined experimentally.
TABLE B-21
COMPARISON OF ION EXCHANGE OPERATING MODES
Capacity for high
feed flow & Cone.
Effluent quality
Regenerant and
rinse require-
ments
Equipment
complexity
Equipment for
continous
operation
Relative costs
(per unit volume)
Investment
Operating
Cocurrent
fixed bed
Least
Fluctuates
with bed
exhaustion
Highest
Simplest;
can use
manual
operation
Multiple
beds, single
regeneration
equipment
Least
Highest
chemicals &
labor; high-
est resin
inventory
Countercurrent
fixed bed
Middle
High, minor
fluctuations
Somewhat less
than cocurrent
More complex;
automatic con-
trols for re-
generation
Multiple beds,
single regen-
eration equip-
ment
Middle
Less chemicals,
water & labor
than concurrent
Countercurrent
continuous
Highest
High
Least, yields
most cone, re-
generant waste
Most complex;
completely auto-
mated
Provides con-
tinous service
Highest
Least chemical
& labor; lowest
resin inventory
Source: DeRenzo, 1978
465
-------
FIGURE B-34
MIXED BED OPERATING CYCLE SHOWING (A) SERVICE PERIOD,
(B) BACKWASH WITH RESIN SEGREGATION, (C) REGENERATION, AND (D) RESIN RE-MIXING
(Source: Vermuelen, 1977)
See Copyright Notice, Page 497
Raw Water
Drain
Treated
Alkali
Air Out
Raw Water
(a)
(b)
(c)
(d)
FIGURE B-35
CYCLIC MULTIBED SYSTEM, EACH STEP HAVING TWO BEDS IN PROCESS USE
(1 AHEAD OF 2) AND ONE BED OFFSTREAM FOR REGENERATION
(Source: Vermuelen, 1977)
See Copyright Notice, Page 497
in
O
1
O
ง
j"t=
R
__.
|
2
f-
|
1
1
TJ
^- " ' ง
ป 1^11 m
2
~
ฑ=.-.i
.4
1
-*
4
R
ss Connectio
(ซ
h-
1
-
^4
R
-H
2
=d
466
-------
TABLE B-22
EXAMPLES OF REGENERANTS AND DOSAGE RANGES
Desired
Resin type Io nic form Regenerant 1b/ft3 Concentration
Cationic H* HC1 4-10 2-10%
H H2S04 5-12 2-10%
Na NaCl 5-10 6-25%
Strong basic anionic OH" NaoH 4-8 2-10%
Weakly basic anionic NH3 Free base 1-2 2-4%
NaOH Free base 2-4 1-2%
5.4 ADVANTAGES AND DISADVANTAGES
Advantages and disadvantages of ion exchange for treatment of leachate
are summarized in Table B-23.
5.5 COSTS
Costs of ion exchange vary widely, depending upon stream size and concen-
tration of contaminants. Treatment costs have been estimated to be on the
order of $6/103 gal. for dilute, complex waste streams (DeRenzo, 1978).
To give the reader an idea of the costs associated with ion exchange, two
examples have been used. Example 1 presents 1978 costs associated with ion
exchange removal of nitrate, sulfate, and other anions for a range of flows
from 70,000 gpd to 830,000 gpd. Construction, operation, and maintenance
costs are shown in Tables B-24 and B-25 for the following conditions:
Nitrate and sulfate concentrations of 100 mg/ฃ and 80 mg/l respect-
tively, other anions, 120 mg/ฃ
Strongly basic anionic exchange resin
467
-------
TABLE B-23
ADVANTAGES AND DISADVANTAGES OF ION EXCHANGE
Advantages
Suitable for removal of soluble
inorganics not removed by pre-
cipitation/sedimentation
Technology is reasonably well
demonstrated for electroplating
wastes, metal, and pickling
liquors
Process energy requirements
are low
Disadvantages
Not suitable for removal of high
concentrations
Pretreatment is required for sus-
pended solids, certain organics
(especially aromatic), and
oxidants
Operation and maintenance costs
are high compared to most treat-
ment processes
Spent regenerant has potential
for containing high concentra-
tions of contaminants
Bed-depth of 6 feet
Regenerate requirements: 15 Ib resin/ft3
Contact vessel of prefabricated steel with the conceptual designs
shown in Table B-24.
Regeneration time and backwash time of 54 min. and 10 min., respec-
tively
Costs for spent regenerant excluded
Costs for treatment of a complex, dilute waste containing heavy metal
cations may differ significantly from the costs presented above for treatment
of a dilute waste containing anions. The major variables that may affect the
costs include the number of contactors needed, the types of resins required,
and regeneration requirements. Strongly basic anion exchange resins used to
cost the treatment system described above tend to be the most expensive. Cost
ranges for the various types of resins are summarized below:
468
-------
Strongly basic anion exchangers: $140-280/ft3
Strongly acid cation exchangers: $ 50- 70/ft3
Weakly basic anion exchangers: $130-170/ft3
Weakly acid cation exchangers: $100-120/ft3
(Rohm and Haas, 1979)
Unit costs for various regenerants are as follows:
HCL - $ 38/ton
H2S04 - $ 39-66/ton
NaCL - $ 67/ton
NaOH - $200/ton
NH3 - $155-195/ton
Source: Chemical Market Reporter, 1980
The second example was costed by Arthur D. Little from 1976 cost data.
The stream is a dilute mixed waste stream from a metal finishing operation.
Fixed Stream to Process: dilute mixed aqueous waste from metal
finishing, 80,000 gallons/day (303m3/day) containing:
zinc 15 mg/ฃ
copper 0.5 mg/ฃ
cyanide (total) 19 mg/l
chromium 22 mg/l
pH 10 (approximately)
TABLE B-24
CONCEPTUAL DESIGN FOR PRESSURE ION EXCHANGE NITRATE REMOVAL
Plant capacity
(gpd)
70,000
270,000
425,000
610,000
830,000
(Source: EPA, 1979)
469
Number
of contactors
2
2
2
2
2
Diameter of
contactors (ft)
2
4
5
6
7
Housing
ft2
132
210
255
304
357
-------
TABLE B-25
1978 CONSTRUCTION COST FOR PRESSURE ION EXCHANGE NITRATE REMOVAL
Plant capacity (gpd)
Cost category
Excavation and sitework:
Manufactured equipment
Equipment
Media
Concrete
Steel
Labor
Pipe and valves
Electrical and instru-
mentation
Housing
SUBTOTAL
Misc. and contingency
TOTAL
70,000
$50
11,860
5,460
280
420
4,770
9,650
18,390
7,600
58,480
8,770
67,250
270,000
$110
16,500
21,860
490
680
5,990
12,440
21,460
8,900
88,430
13,260
101,690
452,000
$140
19,090
34,160
550
950
6,880
13,600
23,070
9,800
108,240
16,240
124,480
610,000
$170
21,660
49,200
740
1,110
7,590
15,360
23,720
10,700
130,250
19,540
149,790
830,000
$200
25,920
66,960
880
1,300
9,250
18,350
24,360
11,600
158,820
23,820
182,640
Source: EPA, 1979
Treatment Objective: to provide effluent that meets discharge require-
ments for zinc (
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TABLE B-27
ION EXCHANGE COST ESTIMATE (1976 DOLLARS)
Annual Cost per Annual
quantity unit quantity cost
Variable costs
Operating labor 2,200 MM $12/hour $26,400
Chemicals
Resin replacement (20%/yr) 2,800
- NaOH (70%) 175 tons $60/ton 28,000
- H2S04 (98%) 48 tons $53.25/ton 2,600
Total chemicals $33,000
Utilities (electricity) 75,000 kWh $0.02/kWh 1,500
Maintenance (3% of investment) 12,000
Total variable costs $73,300
Fixed costs
Taxes & insurance (2% of investment)1 $ 8,000
Capital recovery (10 years @ 10%)1 64,700
Total fixed costs $72,700
Unit costs ($/103 gallons) $ 5.21
Estimated Capital Investment $400.00
Source: DeRenzo, 1978
6.0 LIQUID ION EXCHANGE
6.1 GENERAL DESCRIPTION AND APPLICATIONS
Liquid Ion Exchange (LIE) involves the selective removal and/or separa-
tion of free and complexed metal ions and other inorganics from aqueous
streams. In this process, the inorganic(s) of interest are transferred from
the aqueous phase to an immiscible organic phase. This organic phase is then
contacted with a second aqueous phase whose composition is such that the
inorganics now transfer to that phase. The basic principle underlying the
liquid ion exchange reaction is the concept of distribution or partition
between phases. In the liquid ion exchange process, a water-soluble, ionic
472
-------
species is caused to become more soluble in an organic solvent (by salt forma-
tion, complexation, etc.), thus promoting the partition or extraction of that
species into the solvent (DeRenzo, 1978).
LIE is competitive with conventional ion exchange and can be used to
treat much higher concentrations than the conventional process. The process
is applicable to any aqueous waste stream containing extractable species and
to any wastes containing inorganics that can be dissolved in aqueous acid on
alkali to yield extractable species. Virtually all soluble cations can be
removed, although commercially available extractants preferentially extract
heavy polyvalent metals. Soluble but undissociated species such as mercuric
chloride, anions, and metal oxyanions, and weak acids such as hydrofluoric
acid can also be extracted. (DeRenzo 1978). The process is sensitive to
certain wastewater contaminants. The presence of surfactants causes changes
in phase separation. Oxidants tend to cause degradation of functional groups
of extractants, and the presence of suspended matter in excess of 0.1 percent
may have detrimental effects on the process.
Although in theory there is no limit to the concentrations that can be
treated by this process, the volume of extractants that must be used places
practical limitations on the concentrations. Commercial processes for extrac-
tion of cobalt and nickel treat solutions up to 10 g/i and this is probably a
typical upper!imit concentration (DeRenzo, 1978).
There are several commercial and near-commercial applications for removal
of various inorganics by LIE. Some examples include:
Recovery of nitric, hydrofluoric, and molybdic acid from metal
pickling liquors
Recovery of copper from spent alkaline etchant solutions and from
ammonia/ammonium carbonate leaching of metallic copper scrap
Recovery of iron, zinc, copper, nickel, and chromium from alkali
hydroxide sludges
Removal of cyanide and zinc from electroplating rinse water
(DeRenzo, 1978)
6.2 DESIGN AND CONSTRUCTION CONSIDERATIONS
Liquid ion exchange is a steady state process because of its dependence
on a constant distribution coefficient and on proper time for phase separa-
tion. The contacting process should provide intimate mixing to maximize mass
transfer. Therefore, the process should be run on a continuous basis rather
than as a batch operation.
473
-------
Three types of contactors
differential contactors, and cen
simplest and most commonly used,
least able to respond to changes
tion. These units require a long
trifugal contactors have a very
phase separation. They are able
complex and require an intricate
are currently available: mixed settlers,
trifugal contactors. Mixed settlers are the
but they are least flexible in that they are
in process conditions such as feed composi-
time for contact and phase separation. Cen-
short detention time, and provide excellent
to respond quickly to process changes but are
control system (DeRenzo, 1978).
Extraction reagents are classified according to differences in the nature
of stripping chemistry. The reagents are used as dilute solutions (5-30
percent). Classes of reactants include:
Basic extractants such as ketones, ethers, and amines react with
acids or metallic ions to form salts or complexes soluble in organic
solvents
Acidic extractants, such as carboxylic acids, and naphthalenes and
alkylnaphalene sulfonic acids react with bases or salts by exchange
of cations.
Chelating extractants for stable chelate complexes with metal ions
Ionic extractants form o-rganic extractable ion pairs with anions or
cations (DeRenzo 1978)
The process yields two aqueous streams, the cleaned stream and the second
aqueous stream termed the stripping liquor. Both will contain small amounts
of the extraction solvent. The "cleaned" aqueous stream may require further
treatment by adsorption prior to stream discharge. The stripping liquor will
contain hazardous wastes at high concentrations (see Figure B-36) and must be
treated to render the hazardous compounds innocuous (DeRenzo 1978).
FIGURE B-36
LIQUID ION EXCHANGE OF METAL FINISHING WASTES
Feed (80,000 gpd) Solvent
f 1 (5,000 god) t [
Extraction
(Two Stages)
Stripping
(Two Stages)
Effluent (~ 150 gpd. Zinc ~ 7,800 mg/8
Cyanide ~ 13,400 mg/8
Chromium ~ 11,700 mg/8
Copper ? (not known)
Raffinate
Stripping Solution
474
-------
6.3 ADVANTAGES AND DISADVANTAGES
Advantages and disadvantages of liquid ion exchange are summarized in
Table B-28.
TABLE B-28
ADVANTAGES AND DISADVANTAGES OF LIQUID ION EXCHANGE
Advantages
Applicable for treatment of most
dissolved ionized and un-ionized
inorganics in aqueous streams
Process has been proven reliable
in treatment of pickling liquor
and electroplating wastes
Process can treat higher inorganic
concentrations than conventional
ion exchange
Disadvantages
Process is sensitive to the presence
of oxidants, surfactants, and sus-
pended solids
There is a potential for water pol-
lution unless reclaimed extractants
are stripped from discharge stream
The regeneration solution into which
hazardous components are stripped
from the extraction solvent will
contain hazardous components at
high concentrations. These must
be rendered innocuous
6.4 COSTS
Few economic studies have been done on the treatment of dilute waste
streams. Costs appear to be comparable or somewhat less than conventional ion
exchange. A rough idea of costs can be determined from the example presented
in Table B-29.
475
-------
TABLE B-29
LIQUID ION EXCHANGE COST EXAMPLE OPERATING COST
ESTIMATES FOR LIQUID ION EXCHANGE (1976 COSTS)
Annual Cost per Annual
quantity unit quantity cost
Variable costs
Operating Labor 2,200 MM $12/hour $26,400
Electricity 80,000 kWh 0.02/kWh 1,600
Chemicals
Kerosene 330/gal 0.45/gal 150
Triaecyl alcohol 700/1 bs 0.37/lb 260
Aliquat 90/lbs 1.40/lb 130
Caustic (70%) 70/tons 180/ton 12,600
Total chemicals
Maintenance (3% of investment)1
Total variable costs
Fixed costs
Taxes & insurance (2% of investment)1
Capital recovery (10 years @ 10%)
Total fixed costs
Unit costs ($/10 gallons)
$33,000
12,000
$53,140
$ 6,000
48,860
$108,000
$ 4.09
1 Estimated capital investment $300.00.
Source: DeRenzo, 1976
This cost estimate does not include further treatment of the "cleaned"
stream to remove any extractant solvent.
7.0 AMMONIA STRIPPING
7.1 GENERAL DESCRIPTION
Ammonia stripping is a mass transfer operation which, at high pH, can
decrease ammonia concentrations in water by bringing it into intimate contact
with air. At a pH of about 12, only ammonia gas will be present, and ammonia
is readily stripped.
476
-------
7.2 APPLICATION
Ammonia stripping will be desirable for treatment of any leachate where
ammonia is present in sufficiently high concentrations to exhibit toxicity to
biomass in biological treatment or to create such environmental problems as
toxicity to fish or high oxygen demand following steam discharge.
Leachate from municipal refuse can exhibit widely varying ammonia concen-
trations. A range of 2 mg/l to about 1000 mg/l was reported for leachate from
13 municipal fills (EPA, 1977).
7.3 DESIGN AND CONSTRUCTION CONSIDERATIONS
Ammonia stripping can be carried out either in a stripping lagoon or in a
packed column. Schematics of an ammonia stripping lagoon and packed tower are
illustrated in Figures B-37 and B-38. The major factors affecting performance
and design include pH, temperature, air flow, hydraulic loading, and tower
packing depth and spacing (Gulp 1978). Cost and performance are relatively
independent of influent ammonia concentrations (Gulp, 1978).
The pH must be raised to a point where all or nearly all ammonia is
converted to gas. The pH for efficient operations ranges varies from about
10.8-11.5. Where lime precipitation is part of a treatment scheme, it is
advantageous to locate the ammonia stripping unit after lime precipitation to
take advantage of the high pH in the clarifier effluent.
As water temperature decreases, it becomes more difficult to remove
ammonia by stripping. The amount of air per gallon must be increased to
maintain removal as temperature decreases. It is impractical to heat strip-
ping units when the temperature reaches freezing (Gulp, 1978).
The hydraulic loading rate in a packed tower is a critical factor in
determining performance. If hydraulic loading becomes too high, good droplet
formation needed for efficient stripping is disrupted. If the rate is too
low, packing may not be properly wetted, resulting in poor performance and
formation of scale. Optimum hydraulic load for a packed tower is about 1 to 2
gpm/ft2. Optimum air flow rates for packed towers have been shown to be
300-500 ftVgal. for 90-95 percent removal.
Where ammonia concentrations are high (in excess of 100 mg/l), it may be
attractive both economically and environmentally to recover the ammonia in an
adsorption tower. With good countercurrent contact, 90-95 percent of the
ammonia can be transferred to the absorption solution. Figure B-39 illus-
trates the ammonia removal and recovery process.
477
-------
FIGURE B-37
AMMONIA STRIPPING LAGOON
(Source: Gulp, 1978)
See Copyright Notice, Page 497
Air Spraying of Recycled Pond Water
Clarified Lime
Treated Wastewater
pH = 11.0
Out pH = 10.8 ฑ
FIGURE B-38
AMMONIA STRIPPING TOWER
(Source: Gulp, 1978)
See Copyright Notice, Page 497
Air Outlet
t
Water
Inlet
Water
Inlet
Air
Inlet
Water
Outlet
^Collection Basin
Cross-Flow Tower
Air Outlet
Water
Inlet
Air Inlet
Drift
Eliminators
Distribution
System
Air Inlet
Water
^-Collecting
Basin
Countercurrent Tower
478
-------
FIGURE B-39
SCHEMATIC OF AMMONIA REMOVAL AND RECOVERY SYSTEM
(Source: U.S. EPA, 1978)
Wastewater Containing
Dissolved Ammonia (NH
g
JH3)
A
c
\
A ."v /
- Stripp
Uni
Gas Stream with Ammonia Increased ;
^ A
ng
I*-
\Rec
.
r
s Stream-ammonia
uced by Absorptior^
A
i ' 1
A A A A
Absorption
Unit
1 4 L1!!
I
t
w**t^t+
v
Wastewater Stripped of Nearly
,~ ^^^^_ iVioloi
Fan >> r-i
\
y
l_J
- Ducting (Typical)
Acid and
Water Makeup
Recycled
" Absorbent
Liquid
Pump
ป Ammonium Salt Blowdowr
or Discharge to Stripper
7.4 ADVANTAGES AND DISADVANTAGES
Table B-30 summarizes the advantages and disadvantages of ammonia strip-
ping.
TABLE B-30
ADVANTAGES AND DISADVANTAGES OF AMMONIA STRIPPING
Advantages
Can reduce ammonia levels below
toxic level to biomass in bio-
logical treatment
Process is relatively indepen-
dent of ammonia concentration
Disadvantages
Cost prohibitive to operation at
temperatures below freezing
Sensitive to pH, temperature,
and to fluxes in hydraulic load
Releases ammonia to air unless
recovery is implemented
479
-------
7.5 COSTS
Figures 8-40 and B-41 summarize the capital, operating, and maintenance
costs for ammonia stripping towers designed to treat flows ranging from 0.01 -
10 mgd.
FIGURE B-40
CAPITAL COSTS OF AMMONIA STRIPPING
SYSTEM, INCLUDING RELATED YARDWORK
ENGINEERING, LEGAL, FISCAL, AND
FINANCING COSTS DURING CONSTRUCTION
AND EXCLUDING COST OF pH ADJUSTMENT.
BASED ON 1 gpm/sf OF TOWER PACKING,
24 ft PACKING DEPTH. INCLUDES
INFLUENT PUMPING (TDH = 50 ft).
FIGURE B-41
OPERATION AND MAINTENANCE
COSTS OF AMMONIA STRIPPING
SYSTEM, EXCLUDING COST OF
pH ADJUSTMENT; LABOR FIXED
(3 59/HOUR, POWER 9 50.02/kwh,
Construction Cost
Operation & Maintenance Cost
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480
-------
8.0 WET AIR OXIDATION
8.1 GENERAL DESCRIPTION AND APPLICATIONS
Wet air oxidation is based on the concept that any substance capable of
burning can be oxidized in the presence of air at elevated pressure and
moderate temperature. As Figure B-42 illustrates, wastewater containing some
oxidizable material is mixed with air and pumped through an exchanger. It is
then pumped to a reactor, where oxygen in air reacts with organic matter in
wastes.
FIGURE B-42
WET AIR OXIDATION FLOW SCHEMATIC
High
Pressure
Pump
Exchanger
Reactor
Separator
Compressor
, Steam
ปป Oxidized Liquid
Oxidation is accompanied by temperature rise, and the heat produced can
be used to sustain the process. After the reaction phase, gas and liquid are
separated and liquid is used to heat the incoming material (Pradt, 1976).
Wet Air Oxidation (WAO) may be applied to a wide class of wastewaters
such as those from the manufacture of pesticides, petrochemicals, pharmaceuti-
481
-------
cals, or other industrial chemicals (Zimpro, 1979). The process generally
treats wastes with a high COD, ranging from 5-150 g/ฃ and, in general, is only
suitable for high strength wastes.
The performance of WAO has been well demonstrated for the treatment of
acrylonitrile wastes with high concentrations of cyanide and for the treatment
of scrubbing liquor from coke oven gas clean-up, which contains cyanides,
thiocyanates, and thiosulfates. Treatment of these wastes is currently prac-
ticed on an industrial scale (Zimpro 1979).
WAO has also been shown to effectively oxidize a number of toxic organics
on a bench-scale level. Table B-31 shows the results of 1 hour WAO of 10
organics of temperatures of 320ฐC and 275ฐC. The maximum operating conditions
for most installations is 275ฐC; most of the wastes were effectively treated
at this temperature, although a catalyst may be required to achieve the de-
sired degree of oxidation.
8.2 DESIGN AND CONSTRUCTION CONSIDERATIONS
Wet air oxidation takes place by a family of related oxidation and hy-
drolysis reactions. These reactions lead to partially oxidized intermediate
products and, if reactor residence time and temperature permit, eventually to
carbon dioxide and water. Hence, the degree of oxidation is primarily a
function of reaction temperature and residence time (Zimpro, 1979). Actual
operating conditions vary from about 350ฐF and 350 psig to 610ฐF and 3000 psig
(Wilhelmi and Knopp, 1979). At temperatures of about 300ฐF, about 5-10 per-
cent of the COD will be oxidized. Nearly complete oxidation occurs for most
substances at temperatures of 610ฐF (Pradt, 1979).
Although WAO alone may be used as the complete treatment process, it is
often uneconomical for achieving the high degree of oxidation required for ef-
fluent discharge. Zimpro has developed a two-step process whereby WAO is used
to accomplish 40-95 percent COD reduction, with a biological or biophysical
polishing step following. During WAO, the higher molecular weight compounds
are preferentially oxidized to lower molecular weight intermediates such as
methanol and formaldehyde, which can be easily degraded in biological treat-
ment. The biophysical process involves addition of powdered activated carbon
(PAC) to the activated sludge in concentrations in excess of 10,000 to 20,000
mg/l. PAC acts as a flocculating agent promoting settling, and as a toxic
sink for substances that might have survived WAO. It also allows for higher
MLVSS concentrations than normally allowed with activated sludge (Wilhelmi and
Ely, 1979). A combination of low-pressure oxidation and biological treatment
was shown to be effective for a Louisville, KY sewage treatment plant's toxic
sludges (Wilhelmi and Ely, 1979).
482
-------
TABLE B-31
WET AIR OXIDATION OF TOXIC ORGANICS
1-Hour Wet Oxidations
Compound
Acenaphthene
Acrolein
Acrylonitrile
2-Chlorophenol
2.4-Dimethylphenol
2.4-Dinitrotoluene
1.2-Diphenylhydrazine
4-Nitrophenol
Pentachlorophenol
Phenol
Starting
concen-
tration1
% Starting material destroyed
320ฐC
7.0 g/1 99.96%
8.41 g/1 >99.96%*
8.06 g/1 99.91%
12.41 g/1 99.86%
8.22 g/1 99.99%
10.0 g/1 99.88%
5.0 g/1 99.98%
10.0 g/1 99.96%
5.0 g/1 99.88%
10.0 g/1 99.97%
275ฐC 275ฐC/Cu11
99.99%
99.05%
99.00% 99.50%
94.96% 99.88%
99.99%
99.74%
99.98%
99.60%
81.96% 97.30%
99.77%
1The concentration remaining was less than the detection limit of 3 mg/ฃ.
Source: Zimpro, 1979
WAO can be thermally self-sustaining, requiring no additional fuel on
feed COD's as low as 15,000 ppm. By comparison, incineration requires concen-
trations of 300,000 to 400,000 ppm (Zimpro, 1979) to be self-sustaining. The
following equation can be used to determine the maximum waste COD (g/l) which
can be oxidized by the previously selected air to waste ratio (Liptak, 1974).
COD = 27.8 x (ratio of air to waste)
483
-------
8.3 ADVANTAGES AND DISADVANTAGES
B.32
Advantages and disadvantages of the WAO process are summarized in Table
TABLE B-32
ADVANTAGES AND DISADVANTAGES OF WET AIR OXIDATION
Advantages
Process can handle high waste
concentrations of 5-150 g/ฃ
Reactor can be thermally self-
sustaining at COD concentra-
tions of 15,000 ppm, thus
reducing operating costs
Creates no air pollution
problems
Disadvantages
Stainless steel equipment leads
to higher capital costs than
for incineration
Additional heat source will
be needed when organic load
is less than 15,000 ppm COD
Requires well trained opera-
tors
8.4 COSTS
The costs of WAO are proportional to the volume of the waste stream, the
required pressure, and the amount of air and auxiliary steam required. No
cost curves were available for the wet air oxidation process. However, Tables
B-33, B-34, and B-35 provide an idea of the associated costs.
484
-------
TABLE B-33
FEED WASTE CHARACTERISTICS ASSUMED FOR COST OF WET AIR OXIDATION
Flow, gal/min 20
m/s 0.000126
pH 1.
COD 70,000
Chloride 32,000
Total solids 118,000
Ash 23,000
TOC 30,000
Calcium 400
Magnesium 40
Sulfur 500
Source: Wilhelmi, 1979
TABLE B-34
PERFORMANCE/OPERATING CRITERIA FOR WET AIR OXIDATION
Temperature, ฐC 279
COD reduction, % 80
Effluent COD, mg/L 14,000
Effluent BOD, mg/L 8,000
Effluent pH 1
Source: Wilhelmi, 1979
485
-------
TABLE B-35
COST OF WAO (1979 DOLLARS)
Installed capital cost,
$ millions
Operating costs, $:
Fuel
Power
Steam
Maintenance
Labor
Additional treatment
Surcharge
Chemicals
Total Operating Cost, $
Source: Wilhelmi and Knopp, 1979
WAO
1.8
56,000
45,000
(same)
31,500
(same)
$132,000
9.0 CHLORINATION
9.1 GENERAL DESCRIPTION AND APPLICATIONS
Chlorine is widely used in wastewater treatment for disinfection, odor
control, and BOD reduction. It combines with water-forming hypochlorous acid
which, in turn, can ionize to the hypochlorite ion.
pH 8
C12 + H20 > HCL + HOCL > H + OCL
-------
9.2 DESIGN AND CONSTRUCTION CONSIDERATIONS
The effectiveness of wastewater chlorination depends upon pH, tempera-
ture, time of contact, degree of mixing, and presence of interfering sub-
stances (Liptak, 1974).
Temperature and pH: The extent to which hypochlorous acid ionizes to
form the weaker oxidizing hypochlorite ion depends on pH and temperature.
Figure B-43 illustrates the extent of ionization as a function of these two
variables.
Since hypochlorous acid is a more powerful oxidant, it is desirable to
maintain a pH of less than 7.5.
Time of Contact: The rate of bacterial kill increases with time of
exposure to chlorine. A detention time of 15 to 30 minutes is generally
required in a baffled closed tank (Liptak, 1974).
Mixing; Complete and uniform mixing of chlorine with wastewater is
important to disinfection. Any measurable short-circuiting can be ruinous to
the process efficiency and, therefore, tank shape mixing and proper baffling
are critical (Gulp, 1978).
It has also been shown that rapid initial mixing may be important; the
residuals formed initially are apparently more bactericidal than compounds
formed later (Culp, 1978).
Interfering Compounds: Chlorine reacts readily with ammonia in water to
form chloramines, which are much less effective oxidizing agents. Chlorine
also oxidizes ferrous iron, sulfides, and nitrates. Presence of these species
increases the chlorine demand (i.e., the amount of chlorine that will combine
with various chemicals before it begins to appear as free chlorine residual)
and increases the required dosage (Liptak, 1974).
The size of the .chlorinator is based on the chlorine demand of the water
and on its flow rate. Typical chlorine dosages for disinfection are 3-15
mg/l for trickling filter effluent and 2-8 mg/l for activated sludge effluent
(Metcalf and Eddy, 1972).
The chlorinator is equipped with a feed control system. The simplest and
least expensive is a manual device for feed control. Automatic ratio control
devices are available that can adjust the chlorine dosage to changes in flow
rate. A more sophisticated control system can include a residual chlorine
487
-------
FIGURE B-43
EXTENT OF HYPOCHLOROUS ACID (HOC!) IONIZATION INTO OCL"
AS A FUNCTION OF pH AND TEMPERATURE
(Source: Liptak, 1974)
See Copyright Notice, Page 497
100| 1 IV I 1 1 1 1 1 0
S.
90
80
70
60
50
40
30
20
10
25
0ฐC
10
20
30
40
T)
CD
50 I
O
o
60 -~
70
80
90
100
10
456789
pH
analyzer, which controls the chlorine dosage based on residual chlorine levels
(Liptak, 1974).
The most common chlorine compounds used in wastewater treatment are
chlorine gas and calcium and sodium hypochlorite. The latter two are used in
small treatment plants where simplicity and safety are more important than
cost. Because calcium hypochlorite granules are readily soluble in water and
are relatively stable under proper storage conditions, they are often favored
(Metcalf and Eddy, 1972). Chlorine gas is risky to both store and use.
9.3 ADVANTAGES AND DISADVANTAGES
Table B-36 summarizes the advantages and disadvantages of chlorination.
488
-------
TABLE B-36
ADVANTAGES AND DISADVANTAGES OF CHLORINATION
Advantages
Markedly reduces concentrations
of harmful organisms
Process is very reliable
Less expensive than alternative
means of disinfection such as
ozone
Disadvantages
May cause formation of
chlorinated hydrocarbons
Chlorine gas is hazardous and
requires careful handling
Chlorine reacts with certain
chemicals in water, leaving
only the residual for disin-
fection
9.4 COSTS
Figures B-44 and B-45 show 1976 construction, operation, and maintenance
costs for chlorination based on the parameters listed below:
COSTS -
1. Service life: 15 years
2. Equipment: Including chlorine supply, chlorinator,
and contact chamber
3. Dosage = 10 mg/1; contact time = 30 minutes
4. Labor rate = $7.50/hr, including benefits
5-. Power cost = $.02/kWh; chlorine cost = $160/ton
6. Index: ENR = 2475, September 1976.
489
-------
FIGURE B-44
CONSTRUCTION COSTS FOR CHLORINATION
(Source: EPA, 1978)
FIGURE B-45
O&M COSTS FOR CHLORINATION
(Source: EPA, 1978)
I
01
001
0
CONSTRUCTION COST;
10 10
Wastewater Flow. Mgal/d
100
ll Coil, Millions 01 Dollar.
( Total, Chmcato, Labor)
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925
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490
-------
REFERENCES
Autotrol Corp. 1978. Autotrol wastewater treatment systems: design manual.
Autotrol Biosystems Division. Milwaukee, WI.
Azad, Hardam (ed.). 1976. Industrial wastewater management handbook. New
York: McGraw-Hill Book Co.
Gulp, R.L. et al. 1978. Handbook of advanced wastewater treatment. New
York: Van Nostrand Reinhold Company.
DeRenzo, D.H. 1978. Unit operations for treatment of hazardous industrial
wastes. Noyes Data Corp., Park Ridge, NJ.
Dow Chemical Co. 1971. A laboratory manual on ion exchange. No. 177-1207-
77.
Eckenfelder, W.W. 1963. Trickling filter design and performance. Trans-
actions of the American Society of Civil Engineers 128 (Part III):371.
Ford, D.L. and L.F. Tischler. 1977. Guide to wastewater treatment. Chemical
Engineering. August 1977.
Germain, J.E. 1966. Economical treatment of domestic waste by plastic-medium
trickling filters. J. Water Pollution Control Federation 28:192.
Hammer, J. J. 1975. Water and wastewater technology. New York: John Wiley
& Sons, Inc.
JRB Associates, Inc. 1980. Training manual for hazardous waste site
investigations. Prepared for the U.S. Environmental Protection Agency.
McLean, Virginia.
Krupka, M. May 1980. Personal communication with K. Wagner.
Liptak, B.G. (ed.). 1974. Environmental engineers' handbook, vol. 1: water
pollution. Radnor, PA: Chilton Book Company.
Metcalf and Eddy, Inc. 1972. Wastewater engineering: collection, treatment,
and disposal. New York: McGraw-Hill Book Company.
Nemerow, N.L. 1978: Industrial water pollution: origin, characteristics,
and treatment. Reading, MA: Addison-Wesley Publishing Co.
Permutit. 1977. Sulfex heavy metals waste treatment process. Technical Bul-
letin 13:6.
Polybac Corporation. 1978. Phenobac mutant bacterial hydrocarbon degrader.
New York, NY.
Pradt, L.A. 1972. Developments in wet air oxidation. Chemical Engineering
Progress 68 (12):72-77. [Updated 1976.]
491
-------
Rohm and Haas Company. 1979. Fluid process chemicals consumer price sched-
ule. Independence Mall, Philadelphia.
Schulze, K.L. 1960. Conference on biological waste treatment. Manhattan
College, April 1960.
U.S. Environmental Protection Agency. 1975. Process design manual for sus-
pended solids removal. Technology Transfer Office, Washington, D.C.
EPA-625/l-75-003a.
U.S. Environmental Protection Agency. 1977a. Demonstration of a leachate
treatment plant. By Steiner, Keenan and Fungaroli for Office for Solid
Wastes. Washington, D.C. PB-269-502.
U.S. Environmental Protection Agency. 1977b. Evaluation of leachate treat-
ment, vol. 1: characterization of leachate; vol. 2: biological and
physical/chemical processes. By E.S. Chian and F.B. Dewalle for Munici-
pal Environmental Research Laboratory. EPA-600/2-77-186a.
U.S. Environmental Protection Agency. 1977. Wastewater treatment facilities
for sewered small communities. Technology Transfer Division. Washing-
ton, D.C. EPA-625/1-77-009.
U.S. Environmental Protection Agency. 1978a. Innovative and alternative
technology assessment manual. Office of Water Program Operations.
EPA-430/9-78-009.
U.S. Environmental Protection Agency. 1978. State of the art report - pesti-
cide disposal research. By Midwest Research Institute for Municipal
Environmental Research Laboratory, Cincinnati, OH. EPA-600/2-78-183.
U.S. Environmental Protection Agency. 1979a. Estimating waste treatment
costs, vol. 3: Cost curves applicable to 2,500 gpd to 1.0 mgd treatment
plants. Municipal Environmental Research Laboratory, Cincinnati, OH.
EPA-600/2-79-162C.
U.S. Environmental Protection Agency. 1979b. Selected biodegradation tech-
niques for treatment and ultimate disposal of organic materials. Munici-
pal Environmental Research Laboratory. EPA-600/2-79-006.
Velz, C.J. 1960. A basic law for performance of biological beds. Sewage
Works Journal 20:245.
Vermuelen, T. 1977. Process arrangements for ion exchange and adsorption.
Chemical Engineering Progress Vol. 73(10):57-61
Wilhelmi, A.R., and R.B. Ely. 1979. The treatment of toxic industrial waste-
waters by a two-step process. 30th Annual Purdue Industrial Waste Con-
ference.
Wilhelmi, A.R., and P.V. Knopp. 1979. Wet air oxidationan alternative to
incineration. Chemical Engineering Progress [Reprint].
492
-------
Zimpro. 1979. Industrial pollution control systems. Zimpro Environmental
Control Systems. Rothschild, WI.
Zitrides, T. 1978. Mutant bacteria for the disposal of hazardous
organic wastewaters. Presented at: Pesticide disposal research and
development symposium. Reston, VA., 6-7 September 1978.
493
-------
APPENDIX C
COST INDICES (Average Per Year)
Year
1950
1951
1952
1953
1954
1955
1956
1957
1958
1959
1960
1961
1962
1963
1964
1965
1966
1967
1968
1969
1970
1971
1972
1973
1974
1975
Marshall &
Stevens
Installed
Equipment
Indices
1926=100
All
Industry
168
180
181
183
185
191
209
224
229
235
238
237
239
239
242
245
252
263
273
285
303
321
332
344
398
444
Engineering
News-Record
Construction
Index
1913=100
510
543
569
600
628
660
690
724
759
797
824
847
872
901
936
971
1,021
1,070
1,155
1,269
1,395
1,581
1,753
1,895
2,020
2,212
Engineering
News-Record
Building Cost
Index
1913=100
375
400
416
431
446
465
491
509
525
548
559
568
580
594
612
627
650
672
721
790
836
948
1,048
1,138
1,204
1,306
continued
494
Chemical
Engineering
Plant
Construction
Index
1957-1959=100
74
80
81
85
86
88
94
99
100
101
102
101
102
102
103
104
107
110
114
119
126
132
137
144
165
182
EPA
Sewage
Treatment
Plant
Construction
Index
1957-1959=100
102
104
105
106
107
109
110
112
116
119
123
132
143
160
172
182
217
250
-------
COST INDICES (Average Per Year) (continued)
Year
1976
1977
1978
1979
1980
1981
Marshall &
Stevens
Installed
Equipment
Indices
1926=100
All
Industry
472
505
545
599
660
721
Engineering
News-Record
Construction
Index
1913=100
2,401
2,577
2,776
3,003
3.1591
3,705a
Engineering
News-Record
Building Cost
Index
1913=100
1,425
1,545
1,674
1,819
1,918*
1,184'
Chemical
Engineering
Plant
Construction
Index
1957-1959=100
192
204
219
239
261
2731
EPA
Sewage
Treatment
Plant
Construction
Index
1957-1959=100
262
278
305
335
3582
1 Based on December of year.
*Based on March of year.
495
-------
COPYRIGHT NOTICE
Figure 3-4 From WATER RESOURCES ENGINEERING, 3rd ed. by Ray
K. Linsley and Joseph B. Franzini, Copyright (c)
1979, by McGraw-Hill, Inc. Used by permission of
McGraw-Hill Book Company.
Figure 4-11 From GROUNDWATER, by R. Allan Freeze and John A.
Cherry, Copyright (c) 1979, p. 328. Reprinted by
permission of Prentice-Hall, Inc., Englewood
Cliffs, N.J.
Table 4-12 From GROUNDWATER, by R. Allan Freeze and John A.
Cherry, Copyright (c) 1979, p. 318. Reprinted by
permission of Prentice-Hall, Inc., Englewood
Cliffs, N.J.
From "Love Canal aftermath: Learning from a
tragedy," by R. S. Glaubinger, Excerpted by
special permission from CHEMICAL ENGINEERING,
Oct. 22, 1979, Copyright (c), by McGraw-Hill,
Inc., New York, N.Y. 10020.
From "Pipe flow chart for turbulent flow."
Reprinted by special permission from CHEMICAL
& METALLURGICAL ENGINEERING, May 1937, Copyright
(c) 1937, by McGraw-Hill, Inc., New York, N.Y.
10020.
From CHEMICAL ENGINEERS' HANDBOOK, 5th ed. by
RobertH. Perry and Cecil H. Chilton, ed.
Copyright (c) 1973, McGraw-Hill, Inc. Used
by permission of McGraw-Hill Book Company.
From Table 6.29g, from THE ENVIRONMENTAL
ENGINEERS HANDBOOK, Volume II, entitled Air
Pollution and edited by Bela G. Liptdk.
Copyright 1974 by the authors. Reprinted with
the permission of the publisher, CHILTON BOOK
COMPANY, Radnor, PA.
Figure 7-2 From HANDBOOK OF HEAVY CONSTRUCTION, by F.W.
Figure 7-4 Stubbs, Copyright (c) 1959, McGraw-Hill, Inc.
Used by permission of McGraw-Hill Book Company.
Figure 5-3
Figure 5-4
Figure 6-10
Table 6-4
Table 6-6
496
-------
COPYRIGHT NOTICE (Continued)
Figure 7-5
Figure 7-7b
Figure 7-9
Table B-2
Table B-4
Table B-15
Table B-16
Figure B-34
Figure B-35
Figure B-37
Figure B-38
Figure B-43
From GENERAL EXCAVATION METHODS, by A.B.
Carson, Copyright (c) 1961, F.W. Dodge
Corporation. Used by permission of McGraw-
Hill Book Company.
From WATER RESOURCES ENGINEERING by Ray K.
Linsley and Joseph B. Franzini, Copyright
(c) 1979, by McGraw-Hill, Inc. Used by
permission of Ellicott Machine Corporation,
Baltimore, Maryland.
From WATER RESOURCES ENGINEERING, by Ray K.
Linsley and Joseph B. Franzini, Copyright (c)
1979, by McGraw-Hill, Inc. Used by permission
of McGraw-Hill Book Company.
From INDUSTRIAL WASTEWATER MANAGEMENT HAND-
BOOK, by Hardam S. Azad, ecL, Copyright (c)
1976 by McGraw-Hill, Inc. Used by permission
of McGraw-Hill Book Company.
Reprinted from JOURNAL American Water Works
Association, Volume 64, Number 6 (June, 1972),
by permission. Copyright 1972, the American
Water Works Association.
From CHEMICAL ENGINEERS' HANDBOOK by Robert H.
Perry and Cecil H. Chi!ton, ed. Copyright (c)
1973, McGraw-Hill, Inc. Used by permission
of McGraw-Hill Book Company.
From HANDBOOK OF ADVANCED WASTE WATER TREAT-
MENT, 2nd ed., by Russel L. Culp et. al.
Copyright T^f) 1978 by Van Nostrand Reinhold
Company. Reprinted by permission of the
publisher.
From Figure 5.23c, from THE ENVIRONMENTAL EN-
GINEERS HANDBOOK, Volume I, entitled Water
Pollution and edited by Bฃla G. Liptdk. Copy-
right 1974 by the author,?. Reprinted with
permission of'the publisher, CHILTON BOOK
COMPANY, Radnor, PA.
497
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-------