oEPA
United States
Environmental Protection
Agency
CLOSING SMALL TRIBAL
LANDFILLS AND OPEN DUMPS
How to Design Environmentally Safe Covers
Including additional design guidance for arid regions
EPA-909-R-11-007
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CLOSING SMALL TRIBAL LANDFILLS AND OPEN DUMPS
How to Design Environmentally Safe Covers
Including additional design guidance for arid regions
Page
EXECUTIVE SUMMARY 4
GLOSSARY 4
1.0 APPLICATION OF DESIGN GUIDANCE 7
1.1 INTRODUCTION 9
1.2 CLOSURE DESIGN RISK 9
2.0 COVERDESIGN 11
2.1 EVAPOTRANSPIRATION COVER CONCEPT 12
2.1.1 CLIMATES WELL SUITED FOR EVAPOTRANSPIRATION COVERS 14
2.1.2 CONSIDERATIONS FOR EVAPOTRANSPIRATION COVER 17
2.2 PRESCRIPTIVE COVER CONCEPT 17
2.2.1 CONSIDERATIONS FOR PRESCRIPTIVE COVER PROFILES 19
2.3 EROSION 20
2.4 SURF ACE WATER MANAGMENT 21
2.5 DESIGN STEPS FOR COVER SYSTEM 21
3.0 COVER CONSTRUCTION 25
3.1 SOIL PLACEMENT 25
3.2 QUALITY ASSURANCE (QA) 26
4.0 RECOMMENDED COVER PROFILE 27
5.0 REFERENCES 29
APPENDIX A. EROSION
APPENDIX B. COVER SOIL AND VEGETATION RECOMMENDATIONS
APPENDIX C. ANALYSIS TO DETERMINE MINIMUM EVAPOTRANSPIRATION
COVER THICKNESS
APPENDIX D. QUALITY AS SURANCE
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Figure 1. Typical Evapotranspiration cover profile 12
Figure 2. Typical soil-plant-atmosphere water potential variation 13
Figure 3. United States Climate Map 14
Figure 4. Climate's demand for water vs. supply of water Albuquerque, NM (1998) 15
Figure 5. Climate's demand for water vs. supply of water Liver more, CA 16
Figure 6. Relation between moisture retention parameter and soil texture class 18
Figure 7. Desiccation cracking in clay barrier layer_19
Figure 8. Types of Water Erosion That May Occur on a Cover System 20
Figure 9. Infiltration / Erosion vs. Cover Slope 21
Figure 10. Relation between moisture retention parameter &soil texture class 23
Figure 11. Recommended Cover Profile 27
Cover Photo: An Evapotranspiration cover system at the Rocky Mountain Arsenal site near
Denver, Colorado. September 2010.
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CLOSING SMALL TRIBAL LANDFILLS AND OPEN DUMPS
How to Design Environmentally Safe Covers
Including additional design guidance for arid regions
The purpose of this guidance is to help tribal public works managers, and environmental
managers, and tribal leadership determine an appropriate final cover profile for closing small
landfills and open dump sites on tribal lands. This document includes updated information from
previous guidance documents for closing small landfills and open dump sites within arid regions
on tribal lands.
This document presents design and operation considerations for the closure of small landfills and
open dump sites, that while not recognized as landfills under the federal regulations in 40 CFR
Part 258, should consider additional environmental safeguards. This document further provides
guidance and a recommended design methodology for a final cover profile to close open dumps
and solid waste landfills that meet the requirements set forth in 40 CFR 258.l(f). More
specifically, this applies to small municipal solid waste landfills and open dumps that satisfy
criteria summarized in the Decision Tree contained in Section 1.0 of this Guidance. This
document is intended for facilities on trust land within Indian Country.
GLOSSARY
ASTM is the acronym for the American Society for Testing and Materials. An ASTM testing
method defines the way a test is performed and the precision of the result.
Biodegradation is the chemical dissolution of organic waste material by bacteria or other
biological means.
Biointrusion is the intrusion into the underlying waste through the final cover profile by flora
and/or fauna.
Bulk Density is defined as the mass of soil divided by the total volume it occupies.
CFR is the acronym for the Code of Federal Regulations, the codification of the general and
permanent rules published in the Federal Register by the federal government. 40 CFR 258
covers criteria for municipal solid waste landfills.
Desiccation Cracking is defined as the polygonal-shaped cracking that develops in clay or mud
which has dried out.
ET Cover or evapotranspiration cover is a cover profile composed of soil with native vegetation.
Evapotranspiration (ET) is a term that represents the removal of water from a soil profile by the
combination of evaporation from the soil surface and transpiration by the available plant
community.
Flux is the percolation rate through a cover profile.
Geomembrane is a kind of geosynthetic material made up of an impermeable membrane.
Geomembranes are made of various materials; most commonly low-density polyethylene
(LDPE), high-density polyethylene (HOPE), or polyvinyl chloride (PVC).
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Hydraulic Conductivity is a property of vascular plants, soil or rock, which describes the ease
with which water can move through pore spaces or fractures. It depends on the intrinsic
permeability of the material and on the degree of saturation. Saturated hydraulic conductivity
describes water movement through saturated media.
Infiltration is the process by which water on the ground surface enters the soil.
Landfill is a site for the disposal of waste materials by burial and is the oldest form of waste
treatment.
Matric Potential is also referred to as soil suction. It is that component of the *water potential of
plants and soils that is due to capillary forces. Thus the water potential of cell walls and
intercellular spaces is largely due to matric potential.
Municipal Solid Waste (MSW) commonly known as trash or garbage, is a waste type consisting
of everyday items we consume and discard. It predominantly includes food wastes, yard wastes,
containers and product packaging, and other miscellaneous inorganic wastes from residential,
commercial, institutional, and industrial sources.
Open Dump An uncovered site used for disposal of waste without environmental controls. It
includes any facility or site where solid waste is disposed of which is not a sanitary landfill
which meets the criteria promulgated under section 4004 of the Solid Waste Disposal Act (42
U.S.C. 6944) and which is not a facility for disposal of hazardous waste.
Percolation is water that infiltrates into and through a cover profile into the underlying. The rate
of water percolating through the cover is referred to as the cover's flux.
Permeability is the property of a porous material to permit a liquid or gas to pass through.
Permeability is often interchangeably used with the term saturated hydraulic conductivity.
Plant Transpiration is a process similar to evaporation. It is a part of the water cycle, and it is
the loss of water vapor from parts of plants (similar to sweating), especially in leaves but also in
stems, flowers and roots.
Potential Evapotranspiration (PET) is a measure of the ability of the atmosphere to remove
water from the surface through the processes of evaporation and transpiration assuming no
control on water supply. It is commonly referred to as the climate's demand for water.
Prescriptive Cover is a cover profile that is specifically described by regulatory statue. For
federal application it is described in 40 CFR Part 258. It may also be described in state regions.
RCRA is the acronym for the Resource Conservation and Recovery Act. RCRA was enacted in
1976 and is the public law that creates the framework for the proper management of non-
hazardous and hazardous solid waste.
Resistive Cover is a cover profile that is designed to minimize percolation by restricting or
=resisting' the movement of water through it by the inclusion of a barrier layer with a low
saturated hydraulic conductivity.
Sole Source Aquifer is a sole or principal source aquifer as one which supplies at least fifty
percent (50%) of the drinking water consumed in the area overlying the aquifer. These areas can
have no alternative drinking water source(s) which could physically, legally, and economically
supply all those who depend upon the aquifer for drinking water. For convenience, all designated
sole or principal source aquifers are referred to as "sole source aquifers" (SSA).
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Store and Release Cover, also referred to as an ET Cover, is cover profile that is designed to
store any infiltrated water within its profile until that water can be removed via ET.
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1.0 APPLICATION OF DESIGN GUIDANCE
Use the Decision Tree on page 8 to determine if the Closure Design Guidance in Section 4 (and
the Appendices) applies to each site under consideration. Note that this design guidance applies
only to arid sites where annual precipitation is less than 25 inches.
For sites that do not meet the criteria in the Decision Tree, a prescriptive cover summarized in
Section 2.2 may be an option. An alternative cover such as the recommended cover profile may
still be an option; however it should be evaluated based on site-specific conditions.
This guidance is intended for municipal solid waste landfills and open dump sites that are not
specifically covered by 40 CFR Part 258 and are located on Indian Country (may include all
Federal Lands). A recommended cover profile for managed landfills or open dumps that meet
the criteria summarized in the following Decision Tree is described in Section 4.
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DECISION TREE: Simplified Cover Design Guidance for Closure of
Small Landfills/Open Dumps In Indian Country
CRITERIA
Coordinate Closure
with applicable
State/Local Authority
Determine if hazardous
waste (HW) is present.
If some HW is present,
remove to HW Landfill if
practical. If significant
HW is present, refer to
40 CFR Parts 260 -265
for closure.
Follow Applicable
Guidance in effect in
1991 or prior and
applicable Best
Management Practices
Follow applicable
Tribal and/or
Federal
Regulations
.No
, No
«!
Jo
Located within
Country ir
the boundary of Indian
the United States
Yes
Waste is Municipal Solid Waste and/or
Construction Debris
Yes
Site received Waste after 09/09/1991
Yes
NpJ~
Average Annual Precipitation < 25 inches
JVIo
No
Yes
^^^^m
]
pYes
Qualify as Small Quantity Generator
<
Yes
Site received < 20 tons of municipal
waste per day
Yes
Location poses threat to local
population (e.g. located within or close
to residences or public facilities such as
schools, offices, or hospitals)
;
No
Location poses threat to groundwater
(e.g. located above sole source aquifer
with a depth to groundwater < 100 feet
]
No
Yesl
*~H Location poses threat to surface water
No
Yes
Simplified
Design
Guidance
Applies
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1.1 INTRODUCTION
This Guidance is intended to assist and simplify the design and construction of a final cover
system for closure of managed small landfills and open dumps that pose limited risk to human
health and the environment. Limited risk is summarized in Section 1.2 (below) while the
recommended criteria intended to limit the use of this Guidance is outlined in the Decision Tree
on page 8. This Guidance recommends the use of an Evapotranspiration (ET) Cover for sites
that meet this limited risk criterion. The ET Cover concept is described in Section 2.1 with a
recommended cover provided in Section 4.0. If the criteria outlined in the Decision Tree are not
satisfied and unacceptable risks are present at the site, that site may warrant further
considerations including the possible use of a prescriptive cover as detailed in 40 CFR Part 258
and summarized in Section 2.2. The use of a prescriptive cover at a higher risk site does not
mean that a prescriptive cover is a superior cover; only that the use of an alternative cover
system at such a site may not be acceptable under federal regulations.
Design steps for the ET cover profile are described in Section 2.5. Other design considerations
beyond minimization of water intrusion through the cover and establishment of vegetation
include mitigating soil loss due to erosion and controlling surface water. These issues are
discussed in Section 2.3 and 2.4, respectively.
Design steps for a prescriptive cover system can be found in EPA Publication EPA/625/R-
94/008: Design, Operation, and Closure of Municipal Solid Waste Landfills. Prescriptive
requirements are described in 40 CFR Part 258.
A good design is critical to the successful deployment of a final cover system. Just as important
to the long-term success is the quality of the construction of this cover system. Construction
considerations are described in Section 3.0.
1.2 CLOSURE DESIGN RISK
Controlling risk is a primary goal for environmental remediation efforts. Landfill and large open
dump closures are no exception. Risk, as it relates to solid waste disposal sites, is defined as the
actual or potential threat of adverse effects on human health and the environment by effluents,
emissions, wastes, resource depletion, etc., arising from the landfill's encapsulated waste.
Within the realm of environmental risk, this process involves a multi-staged analysis
characterized by a ^isk assessment", ^4sk characterization" and ^isk management". A risk
assessment is -the evaluation of scientific information on the hazardous properties of
environmental agents, the dose-response relationship, and the extent of human exposure to those
agents". In essence a pollutant is identified and its possible effects on those exposed are
described. The result of this analysis -4s a statement regarding the probability that populations or
individuals so exposed will be harmed and to what degree," also known as a risk
characterization. Once risk has been assessed and characterized, -political, social, economic and
engineering implications together with risk-related information" are gathered -4n order to
develop, analyze and compare management options and select the appropriate managerial
response to a potential chronic health hazard". This process is called risk management. Together
these steps comprise the scientific approach to risk.
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The number of variables to be considered are generally site-specific and too numerous to list all.
However, some common variables to consider when assessing the site's human and
environmental health risks include:
> Proximity to shallow sole source aquifers: considerations should include whether the site
is directly above a sole source aquifer; the depth to groundwater; and the potential of
leachate from the site (quantity and quality) that could adversely affect groundwater.
> Proximity to residences and public facilities: Is there the possibility of growth of nearby
communities toward the site or the possibility of future construction on the site? Risks
associated with this issue include the potential for methane migration into nearby
structures.
> Type of waste: Considerations should include whether the site contains municipal or
hazardous waste; are there any medical or other wastes such as asbestos; is the waste
biodegradable - byproducts of biodegradation include carbon dioxide and methane gas as
well as potential differential settlement. Obviously hazardous waste will create more risk
than waste such as construction debris like broken concrete and wood.
> The size and shape of the trench, pit, or excavated area can determine the potential for
future differential settlement. Differential settlement can result in the creation of
significant surface cracks that allow water flow down through the cover and into the
underlying waste while also allowing the upward escape of methane gas. Additionally,
differential settlement may create surface depressions or low spots that allow for ponding
of surface water and thus increased percolation into the waste. This in turn can lead to
increased methane generation along with the potential for increased leachate production
and thus an increased potential groundwater contamination.
> Site location: considerations include whether the site is susceptible to flooding;
earthquakes; is the site susceptible to substantial erosion due to its shape, slope, etc.; is
the site subject to intrusion by burrowing animals and plant roots that may harm the
effectiveness of the cover system or bring waste to the surface?
> Site climate: considerations can include does the site have excessive precipitation; is
there significant snow; are there high intensity storm events that can create excessive
erosion?
> Soil type: considerations can include - does the underlying soil beneath the waste have a
low permeability such as silt or clay or a high permeability such as sand or gravel; does
the cover soil have adequate storage capacity; is the cover soil capable of maintaining a
quality stand of native vegetation?
> Waste placement: considerations should include - was the waste compacted as it was
placed; was the waste placed dry or wet; was the waste placed in a manner that would
lead to future differential settlement?
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2 0
(fafssiJ \^\J W IJI% I^JLJskJlUlllJ
A final cover system for a solid waste landfill is intended to isolate the underlying waste and thus
reduce its inherent risk to human health and the environment. The final cover may be composed
of a single monolithic soil layer or multiple layers acting as a system. The cover profile should
be designed to address each of the site-specific potential release vectors from the landfill or open
dump. A release vector is a potential pathway for harmful encapsulated waste to be released into
the environment. Examples include:
a. Flux: Water that infiltrates into and through a cover profile to the underlying waste is
referred to as percolation. Percolation rate is referred to as flux. Excessive flux can
lead to significant leachate generation that can potentially escape a landfill and carry
harmful contaminants to groundwater, polluting drinking water supplies.
b. Erosion: Excessive erosion can remove the protective cover or reduce its
effectiveness to isolate the underlying waste. Some erosion can be planned for and
taken into account in the cover design. However, excessive erosion, particularly rill
and gully formation should be avoided.
c. Surface Water: Surface water must be controlled to minimize erosion and potential
release of harmful contaminants. Surface water controls can include controlling the
speed, direction, and volume of water. They can also control surface water generated
upstream of the site from running onto the site and/or running off of the site.
d. Biointrusion: Excessive or unwanted intrusion into the underlying waste through the
final cover profile by flora and/or fauna can be a release vector. A layer of rock such
as cobble can be added as part of the cover, or the cover can simply be made thicker.
e. Gas: Carbon dioxide and methane are the primary gases created during
biodegradation of buried municipal solid waste. Inclusion of a gas collection layer is
a common solution for this issue. A major concern related to methane generation and
transport is the potential accumulation of gas in nearby structures. Methane gas can
accumulate within an enclosed structure and create an explosive threat. If structures
exist near a landfill or large open dump, it is a good idea to monitor for methane
within these structures.
Two types of covers are discussed in this guidance. The first type of cover is referred to as a
=store and release' cover. That is, the cover is designed to store infiltrated water within its
profile until it can be released to the atmosphere via evapotranspiration (ET). The combination
of evaporation from the cover soil surface or through plant transpiration is termed ET. These are
alternative earthen covers designed to take advantage of site-specific conditions such as climates
where the demand for water referred to as potential evapotranspiration (PET) significantly
exceeds the supply of water (precipitation). This is further discussed in Section 2.1.1. The
second type of cover, referred to as a =resistive' cover, attempts to block or resist the downward
movement of water typically with low permeable soil barrier layers and/or geosynthetic materials
such as high density polyethylene membranes. These =resistive'-type barriers are considered
prescriptive covers as detailed in 40CFR258. The prescriptive cover is further discussed in
section 2.2.
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2.1. ET COVER CONCEPT
The ET Cover also referred to as a JStore and Release' Cover is an excellent cover system if
properl}
Decisioi
cover.
optimun
cover is
water ui
availabl
ET,
. \ T t
n ... Transpiration T
Precipitation '
Evaporation
Runoff
Topsoil/Surface Treatment
Soil
Figure 1. Typical ET cover profile
The ET cover concept relies on the cover soil to act like a sponge. Infiltrated water is held in this
=sponge' until it can be removed via ET. Previous research has shown that a simple ET cover can
be very effective at minimizing percolation and erosion, particularly in dry environments
(Hauser et al. 1994, Hakonson et al. 1994, Nyhan et al. 1997, Khire et al. 1997, Dwyer 2001,
Dwyer 2003, Albright et al 2004, Nyhan 2005).
ET provides the mechanism to remove stored water from the cover soil layer. Water can move
upward because of evaporation drying the upper portion of the cover soil layer. Evaporation
from the surface will decrease the water content and thus increasing the matric potential of the
soil, (soil suction) resulting in an upward matric potential gradient and inducing upward flow.
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Plant transpiration also relies upon matric potential gradients to remove water from the cover soil
layer. Figure 2 shows the large matric potential difference between the soil and atmosphere. In
dry environments, the total potential difference between soil moisture and atmospheric humidity
can be up to 1000 atmospheres (bars) (Hillel 1998). The larger the soil-plant-atmospheric
potential gradient, the more effective an ET cover system can be.
Air (up to-1000 bar)
Roots (-3 bar)
Soil Water (-0.3 bar)
Figure 2. Typical Soil-Plant-Atmosphere Water Potential Variation (Hillel 1998)
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2.1.1 CLIMATES WELL SUITED FOR ET COVERS
Sites well suited for an ET Cover include climates where the demand for water or potential
evapotranspiration (PET) is significantly greater than the supply of water or precipitation. One
of the criteria included in the Decision Tree in Section 1.0 applies to climates with 25-in of
annual precipitation or less (Figure 3).
Precipitation: Annual Climatology (1971-2000)
Precipitation (in.)
niS-20 O36-40
1? Q28-32
11- 16 QJ: ::f.
-.: -on
40-50 BIOO-IZO
50-60 QI20-140
|60-70
70-60
Figure 3. United States Climate Map (Natural Resources Conservation Service
http://www.wcc.nrcs.usda.gov/climate/prism.html)
However, more important than the annual precipitation is the ratio of the demand for water or
PET to the climate supply of water. As long as this ratio is significantly large enough, an ET
Cover should be able to minimize flux. Typical climates that extend across much of the United
States where the majority of precipitation occurs during the summer months when PET is at its
peak while precipitation during the winter months is lower also while PET is lower are generally
suited for store and release covers given the average PET is greater than precipitation for each
month of the year. An acceptable ratio of PET: precipitation should be based on site-specific
conditions and risk.
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An example of a typical environment well suited for an ET Cover is Albuquerque, NM. The
PET far exceeds the precipitation for each month of the year (Figure 4) and thus a well designed
ET Cover should provide adequate storage capacity to minimize flux.
Precipitation (in.) n PETnn.)
Figure 4. Climate's demand for water (PET) vs. supply of water (precipitation) Albuquerque, NM (1998)
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An example of a non-typical climate also well suited for an ET Cover includes Livermore,
California, just east of San Francisco. The weather in this area is different than many areas of
the country. It is hot and dry in the summer with much of the vegetation dormant during this
period due to lack of precipitation. The area receives most of its precipitation during the winter
months while the PET for the area is at its lowest levels. Despite this weather pattern, the
average PET exceeds the precipitation for the area for every month of the year (Figure 5).
D Precipitation (in) n PET (in)
Figure 5. Climate's demand for water vs. supply of water Livermore, CA
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2.1.2 CONSIDERATIONS FOR ET COVER
Emphasis during the design and construction of a cover system is placed on achieving the
designated performance goals. Two primary performance goals for a cover system include
minimization of flux through the cover and minimization of soil loss due to erosion.
Performance goals can also include controlling the release of gas and/or biointrusion. For an ET
Cover to successfully minimize flux and erosion, a moderate density in the cover soil should be
achieved. Covers placed too loosely will allow infiltrated water to quickly move down and
potentially through the soil profile not allowing the cover to store the water until the moisture is
removed via ET. Placing the cover too densely subjects the profile to preferential flow resulting
from desiccation cracking described in section 2.2.1 and can adversely affect the establishment
of vegetation. Therefore, the cover soil should be placed with moderate compaction that closely
mimics the natural or Jn-situ' density of the soil in its undisturbed state. Generally, this is about
90% of the maximum dry density using the standard proctor method (ASTM D698). Other
considerations should include limiting the amount of salts in the soil that can adversely affect the
vegetation establishment as well as increase the erodibility of the soil (Appendix B). Adequate
plant nutrients are also important, but cover soil can be amended to increase available plant
nutrients.
2.2 PRESCRIPTIVE COVER CONCEPT
A prescriptive cover also referred to as a =iesistive cover' is designed to limit percolation by
incorporating a barrier layer within its profile. The barrier layer is typically a clay layer with a
low saturated hydraulic conductivity or a geomembrane or a combination of the two. The intent
of the low permeable barrier layer is to =iesist' the movement of water into and thus through it.
Federal prescriptive standards for this profile are described in 40 CFR Part 258 (see below).
Many states have the authority to regulate the closure of landfills and as such have their own
unique prescriptive standards for the cover profile or may have directly adopted the federal
standard.
Regulations for the final cover of a RCRA Subtitle -0" facility are prescriptive. Specifically,
these minimum prescriptive requirements for the final cover system include:
1) have a permeability or saturated hydraulic conductivity less than or equal to that of the
bottom liner or natural subsoils present, or no greater than 1 x 10"5 cm/sec, whichever is
less[40CFR258.60(a)(l)];
2) minimize infiltration through the closed Municipal Solid Waste Landfill (MSWL) by the
use of an infiltration layer containing a minimum 45 cm (18-in) of earthen material [40
CFR258.60(a)(2);and
3) minimize erosion of the final cover by the use of an erosion layer containing a minimum
15 cm (6-in) of earthen material that is capable of sustaining native plant growth
[40CFR258.60(a)(3)].
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These requirements are summarized in a cover profile shown in Figure 6.
ll "
Topsoil
Barrier Layer -/
Waste
' 5 cm
5 cm
Figure 6. RCRA Subtitle D Minimum Cover Profile
Many state and local regulatory authorities have modified the minimum cover requirements set
forth in 40CFR258; generally making the requirements more stringent. Some have altered the
barrier soil layer requirements by requiring a lower saturated hydraulic conductivity requirement,
for example requiring a maximum of 1 x 10"6 cm/sec instead of 1 x 10"5 cm/sec. Others have
required a composite barrier layer comprised of both a clay barrier layer and a synthetic
geomembrane. Local environmental regulations should be consulted for minimum cover profile
requirements.
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2.2.1 CONSIDERATIONS FOR PRESCRIPTIVE COVER PROFILES
As previously discussed, the emphasis of the prescriptive cover profile is to minimize flux by
resisting the movement of water vertically downward. This is achieved via a low saturated
hydraulic conductivity in the barrier layer. There are some drawbacks to using the minimum
profile described in 40CFR258. To achieve the lower saturated hydraulic conductivity in the
barrier layer, the soil is typically installed in a moist condition (generally wet of the optimum
moisture content per ASTM D698) and heavily compacted to achieve a higher density. This
allows for the clay particles to be remolded and lower the initial or =as-built' saturated hydraulic
conductivity of the soil layer. Experience has shown these clay barrier layers to be vulnerable to
such things as near-surface desiccation cracking (Figure 7), especially in drier environments
(Suter et al. 1993, Dwyer 2003).
Figure 7. Desiccation Cracking in Clay Barrier Layer
Desiccation cracking can provide easy pathways for water migration downward and defeats the
purpose of trying to install a relatively impermeable (low saturated hydraulic conductivity)
barrier layer. An EPA design guidance document (EPA 1991) for final landfill covers states: "In
arid regions, a barrier layer composed of clay (natural soil) and a geomembrane is not very
effective. Since the soil is compacted ,wet of optimum ', the layer will dry and crack". Further,
some soil textures cannot meet the low saturated hydraulic conductivity without amendments
(e.g. mixed with bentonite). These amendments significantly increase the cost of construction.
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2.3 EROSION
The minimization of flux through a cover is often the primary concern during the design process
of a final cover system. However, the minimization of erosion has proved to be of significant
concern especially in dry environments. Annual soil loss should be limited to 2 tons/acre/year
(EPA 1991). Perhaps more important, the formation of rills and gullies (Figure 8) in the cover
system should be avoided. The recommended cover profile described in section 4.0 utilizes a
gravel/soil admixture for the surface of the cover to minimize erosion and mitigate the formation
of rills/gullies. Refer to Appendix A for a recommended design methodology for the upper layer
of the cover to minimize erosion.
A cover system's susceptibility to erosion is a function of a number of factors, including slope
angle and length, surface soil characteristics, rainfall intensity and duration, and vegetation
(Figure 8). Vegetation will assist to minimize erosion, however in dry climates; native
vegetation is commonly sparse and unable to form a continuous blanket to completely limit
erosion. Consequently, each cover design should address how to assist vegetation in minimizing
both short and long-term erosion.
i ^i
i
Raindrop Erosion
Sheet Erosion
Rill Erosi
Figure 8. Types of Water Erosion That May Occur on a Cover System
Cover top slopes are generally influenced by the topography of the site. Engineering concerns
such as erosion, settlement, shedding surface water, and final aesthetics all play a role in the
determination of the final cover top slope(s). Side slopes should be minimized and must meet
applicable slope stability requirements.
The determination of the final cover slope can be a balancing act between maximizing slope to
increase runoff and thus decrease infiltration or minimize slope to decrease erosion.
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Unfortunately, erosion and infiltration are inversely related when compared against slope and
slope length (Figure 9).
03
D
a
less
Cover Slope
Figure 9. Infiltration / Erosion vs. Cover Slope
more
2.4 SURFACE WATER MANAGMENT
Control of surface water runoff at a landfill disposal facility is necessary in order to minimize the
potential for environmental damage to ground and surface waters by direct and indirect effects.
Direct surface water contamination can result from solid waste and other dissolved or suspended
contaminants carried by surface runoff. Uncontrolled surface runoff can also contribute to
leachate and gas generation, thereby increasing the potential for both surface- and ground water
contamination. Surface water courses should be diverted from the landfill and there should be no
uncontrolled hydraulic connection between the landfill and standing or flowing surface water.
2.5 DESIGN STEPS FOR COVER SYSTEM
A set of recommended design steps for a cover system are described in this section. The
following steps should be formally or informally considered when designing a cover system to
meet determined performance and/or risk objectives at each site. These steps are briefly
described below.
Note: Throughout this document, a cover system is referred to instead of merely a cover because
it is very important that the design of a final cover be designed as a system rather than merely as
a group of individual components comprising a cover.
1. Determine the regulatory drivers for closure of each specific site.
2. Determine the design life of the cover system to be deployed based on the applicable
regulations and encapsulated waste. Subtitle D municipal solid waste landfills as defined
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by RCRA typically require a minimum 30-year post-closure monitoring period to ensure
the cover system is working as intended. Sites that are not considered municipal solid
waste landfills under RCRA should determine the length of closure based on site-specific
parameters. See the Decision Tree in Section 1.0 for additional guidance.
3. Determine performance objectives of the cover system. Review, assess, and determine
additional data needs, and design documentation to support the final design. Performance
objectives can include, but are not limited to:
a. Risk. The cover system must be designed to control risks associated with each
specific site.
b. The cover flux (moisture that has moved vertically down through the cover
profile) must be less than that which will produce an adverse risk to groundwater.
Generally, flux should be minimized.
c. Erosion of the cover system. As a minimum, all cover systems should be designed
so that the calculated sheet erosion rate does not exceed 2 tons/acre/year (EPA
1991). Erosion effects due to both wind and water should be taken into account.
Refer to Appendix A.
d. Gas emissions should be taken into account and be controlled where applicable.
e. Control biointrusion if warranted. Biointrusion in a landfill cover system refers to
the flora and fauna interactions or intrusion into the cover system. Uncontrolled
biointrusion may increase contaminant release from a closed site via such things
as burrowing animals and/or insects and root intrusion from plants or grasses
whereby contaminants can be brought to the surface or allow for increased flux
and thus increased potential for groundwater contamination.
f Access control. A closure system may require limited access to the site. A typical
control is the installation of a fence around the site with a locked gate.
g. Aesthetic considerations. Closed sites may require the cover system to be
aesthetically appealing to nearby communities.
h. Future use considerations. A cover system should take into account the potential
future use of the site.
4. Determine site-specific issues that will affect the design of the cover systemthese relate
to those identified in step 3, as well as differential settlement, subgrade considerations,
extent of subsurface contamination, size, slopes, seismic, adjacent facilities, existing
complications such as underground utilities, and surface water management issues.
5. Determine the cover type to be deployed whether it is a prescriptive cover such as the
summarized in section 2.2 or an alternative cover such as an ET Cover. This document
emphasizes the use of an ET Cover. The ET cover is a monolithic soil layer that has
adequate soil-water storage capacity to retain any infiltrated water from the determined
design precipitation event(s) until it can be removed via ET.
6. Identify an acceptable borrow soil to be used in the cover system.
a. For an ET Cover, the soil should have adequate water storage capacity while
having the capability to support native vegetation (refer to Appendix B). The
22
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borrow soil can be excavated soil from a nearby area or purchased off-site and
transported on-site. Nearby, native soils are ideal for use in an ET Cover for
economic reasons and because local vegetation is adapted to them. Refer to
Appendix C to assist in determining whether these soils have adequate water
storage capacity. Loams tend to have good storage capacity and generally
minimize the potential for desiccation cracking that can enable preferential flow
(Figure 10).
0.60
o
LJJ
0.50-
0.40-
0.30 -
Si °-20
0.10-
0.00
SAND SANDY LOAM
LOAM
SILTY CLAY SILTY
LOAM LOAM CLAY
CLAY
Figure 10. Relation between moisture retention parameter & soil texture class (Schroeder et al. 1994)
b. For a Prescriptive Cover similar to that shown in Figure 6, the topsoil properties
should provide an effective rooting medium for native vegetation. However, the
key to the barrier layer soil properties are such that the saturated hydraulic
conductivity is less than the regulatory mandated minimum. To achieve the low
permeability criterion, the soil must have limited rock content and have an
adequate volume of fines - preferably clay. Generally, the higher the clay
content, the lower the soil's saturated hydraulic conductivity. Furthermore, the
soil barrier layer is typically placed =wet of its optimum' moisture content (ASTM
D698) and heavily compacted in an effort to remold the soil and ultimately lower
the initial saturated hydraulic conductivity of the layer. Refer to section 2.2.1 for
pitfalls related to this construction process and soil texture.
If laboratory testing of the soil is to be performed for design analysis, the following
considerations for this testing are offered (Refer to Appendix C):
If the potential cover soil is to be modeled, it is common to test for the soil's
hydraulic properties. It is recommended to test the borrow soil at a remolded
density similar to the intended installation density. That is, any laboratory testing
of the soil to be used in the cover system should be tested at a density similar to
the intended constructed density of the cover. A soil's hydraulic properties are
23
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sensitive to the soil's density and thus any modeling performed should be done
based on hydraulic properties derived at the intended soil density.
Other soil properties that may be tested for include strength characteristics (i.e., if
slope stability is a concern with steep side slopes) or particle size analysis if
erosion is a concern.
7. Cover soil placement density. The density of the cover soil should meet the performance
requirements. If low permeability is required, such as the soil barrier layer of a
prescriptive cover, the soil density will be higher and thus heavy compaction is generally
warranted. The upper topsoil layer in Figure 6, is generally placed without compaction.
If it becomes too dense during the construction process, it is advised that it be disced
prior to seeding to enhance the vegetation establishment. The recommended density for
an ET Cover referred to as the goal density is intended to mimic the natural conditions of
the borrow soil in an undisturbed setting (i.e. in-situ density) because soils tend to
migrate toward this density in the long-term. Furthermore, the density needs to be dense
enough to slow water infiltration to the point where ET can remove the water while not
adversely affecting the water storage capacity of the cover profile. It is recommended to
determine this in-situ density of the undisturbed borrow soils to be used and set this as the
goal density for placement of the cover soil. A tolerance of+/- 5 pounds per cubic foot is
common for this constructed density.
8. Determine the cover profile required layers and depth. For a prescriptive cover, the
minimum requirements are shown in Figure 6. For an ET Cover, determine the
minimum required depth of cover soil required to minimize flux (Appendix C). For a site
that meets the criteria outlined in Section 1.0 that utilizes the recommended cover profile
described in Section 4.0, this step is assumed to be unnecessary. That is, the cover soil
has an adequate quantify of fines and thus has adequate storage capacity for the relatively
dry environment and low risk site. However, a technique is described in Appendix C that
allows for a technical justification for the depth of cover to be deployed to minimize flux
should this analysis be warranted.
9. Perform an analysis to predict soil loss due to both surface water and wind erosion as
required. Any predicted soil loss due to erosion is to be added to the overall cover depth
in addition to the minimum depth estimated in previous steps. Refer to Appendix A.
10. Determine other layers or enhancements to the cover system as required based on
performance and/or risk assessment(s) performed. These may include a bio-barrier, gas
control layer, subgrade structural support layer, or a lateral drainage layer.
11. Determine the vegetation mix to be utilized on the cover system.
12. Evaluate the available field data of similar climatic and soil textural classifications to
determine whether the design is feasible. Compile this data as supporting documentation
in the final design report to be submitted to regulators for final approval and permitting.
This field data will provide short-term data that will justify that the design will perform
as intended.
13. Evaluate applicable natural analogs for all parts of the cover systems such as the
hydraulic storage capacity, as well as for such things as biointrusion, climate scenarios,
erosion control, and vegetation. In this case, natural analog can be defined as an
24
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occurrence of materials or processes which resemble those expected in the proposed
geological waste repository. Natural analogs can help evaluate the long-term
performance of a cover system.
14. Determine the installation requirements, to ensure performance of the cover delivers that
desired per the design. This will be included in the construction documents (design
drawings and specifications).
15. Determine the method to be used to ensure that acceptable materials and construction
methods are used to build the cover system. This should be included in the Quality
Assurance (QA) documentation. Refer to Appendix D.
16. Determine maintenance monitoring criteria (if any), methods and frequencies to be
performed to ensure that cover systems are not degrading. This will be included in the
cover system maintenance plan.
17. After the various design considerations have been evaluated and applicable options
selected, the cover system must be engineered to produce the final cover system details.
Besides selecting the required cover profile described above, the appropriate soils must
be used or amended. Erosion must be minimized. Surface water run-on must be avoided
while surface runoff must be controlled. Cover slopes should be designed to minimize
erosion while shedding surface water. For steeper slopes, stability issues may be of
concern.
3.0 COVER CONSTRUCTION
The quality of construction and materials used is critical to achieving design objectives and
criteria. The borrow source used for cover soil should be well characterized prior to its
acceptance for adequate volume, quality of material, and uniformity of material. A description
of some of the important issues related to cover soil is located in Appendix B.
3.1 SOIL PLACEMENT
An important aspect involved with the construction of a soil cover system is that the soils are
placed at a uniform density. This will help limit preferential flow through the cover. Preferential
flow cannot be avoided, but necessary precautions should be employed to ensure it is minimized.
Cover soils should be placed within an acceptable density range. When possible, cover soil
(water storage layer and surface treatment layers only) should come from the same borrow
source. If there is not adequate borrow soil available from a single source, then soils imported
from multiple borrow sources should all be well characterized and placed within respective
specified ranges.
The upper rock/soil admixture layer should be placed in a loose state without compaction. If this
soil layer becomes compacted or is determined to be too density after its installation, but prior to
seeding, it should be loosened prior to seeding. Care should be taken to ensure the rock to soil
ratio is maintained. The final slope and slope tolerances described in the design should be
maintained. Positive drainage should be maintained at all times during installation of the cover
systems.
25
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3,2
Quality Assurance (QA) of both the construction process and materials used is critical to the
successful installation of a cover system. Paramount to this success is the assignment of a person
or team to ensure that adequate QA is applied to the project. The QA engineer should
understand the design and the ultimate goal for success of the project and help ensure that the
constructed product meets the goal.
A QA Plan specific for the project should be written. This should include any QA testing to be
performed, success or failure criteria for the testing, frequency of testing, equipment or materials
to be used in testing along with applicable ASTM standards. The QA Plan should identify what
documentation is to be completed during the construction process and what individuals or
companies should retain the documented QA process.
Refer to Appendix D for recommendations of information to be included in the QA Plan
including examples of QA testing/frequency/criteria.
26
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4.0 RECOMMENDED COVER PROFILE
This guidance document serves to provide technical assistance in the closure of sites that have
been determined to meet acceptable risk and regulatory requirements by applying a well
designed cover system over them. Figure 11 describes a recommended cover profile for sites
that satisfy the criteria outlined in Section 1.0.
6". min
3-0", mm
Native Vegetation
Surface Treatment -
Rock/Soil Admixture
Cover Soil
Existing Interim
Cover (free of
waste/debris)
Waste Material
Figure 11. Recommended Cover Profile
The basic recommended cover is an ET Cover. The elements of this cover system are described
below:
1. Vegetation. Native vegetation should be established on the cover. Plant cover reduces
the harmful effects of surface erosion resulting from both runoff and wind. It provides
for the removal of infiltrated water through transpiration.
27
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2. Surface treatment layer. An admixture composed of soil and rock is designed to resist
erosion due to both surface water runoff and wind. The admixture also enhances the
vegetation establishment. The soil is to be composed of quality topsoil capable of
sustaining native vegetation. This layer should not be compacted to allow for better plant
establishment and initial growth. A typical mix is 25% rock (nominally %" to 2"
diameter) to 75% topsoil by volume. The mixture should be well mixed prior to final
placement. The rock should be a quality durable rock. Refer to Appendix A for a design
methodology.
3. Cover soil. This layer is composed of quality soil with adequate water storage capacity.
The soil should possess adequate levels of plant-essential nutrients to encourage the
establishment and productivity of non-woody indigenous plants (primarily grasses and
forbs). The amount of slat in the soil should also be limited (Appendix B). Amendments
may be required to achieve this. The soil is to serve as a rooting medium and provide for
storage of infiltrated water until removed via ET. If there is substantial depth to an
interim cover system that contains quality soil and is free of waste and debris, this soil
depth can be included in the final cover depth. The interim cover should be well
characterized prior to its inclusion in the final cover profile. All soil in the final cover
profile should be placed as dry as possible while maintaining dust control and no wetter
than the optimum moisture content for the given soil. This will allow for an increased
initial soil storage capacity and mitigate the potential for desiccation cracking. Refer to
Appendix B for soil quality issues and Appendix C for storage capacity and minimum
cover thickness issues.
4. Subgrade. The subgrade soil for a final cover system should be heavily compacted to
provide a stable foundation for the final cover profile. The upper foot of the subgrade is
also recommended to be dry of its optimum moisture content (ASTM D698). This will
help maintain the initial storage capacity of the cover system.
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5.0
1. Abdal, M.; Suleiman, M.; and Al-Ghawas, S. 2000. Vegetable Production in Calcareous
Soils of Kuwait: Status Report. Journal of Vegetable Crop Production. Volume 6 (2).
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2. Albright, W.H.; Benson, C.; Gee, G.; Roesler, A.; Abichou, T.; Apiwantragoon, P.;
Lyles, B.F.; Rock, S., 2004. Field water balance of landfill final covers. Journal of
Environmental Quality, s.33.
3. Anderson, C.E., and J.C. Stormont. 1999. Report on soil testing for the Mixed-Waste
Landfill Cover Project, Sandia National Laboratories, Tech Area III. Report prepared for
Sandia National Laboratories by the University of New Mexico, Department of Civil
Engineering.
4. Birkeland, P. W. 1974. Pedology Weathering and Geomorphological Research. New
York Oxford Press.
5. Blatt, H.; Middleton, G.; and Murray, R. 1980. Origin of Sedimentary Rocks, 2nd
edition, Prentice-Hall, Inc. Englewood Cliffs, New Jersey.
6. Brady, N. C. and Weil, R. R. 1994. The Nature and Properties of Soils. Prentice Hall.
New Jersey.
7. Cassel, D. K., and D. R. Nielsen. 1986. Field Capacity and Available Water Capacity,
Methods of Soil Analysis, Part 1, Physical and Mineralogical Methods, Agronomy
Monograph No. 9, 2nd Edition, Soil Society of America, Madison, Wisconsin.
8. DOE. 1989. Remedial action planning and disposal cell design. UMTRA-DOE/AL
400503.0000.
9. Dominguez, R.; Campillo, C. D.; Pena, F.; and Delgado, A. 2001. Effect on Soil
Properties and Reclamation Practices on Phosphorous Dynamics in Reclaimed
Calcareous Marsh Soils from the Guadalquivir Valley, SW Spain. Arid Land Research
and Management. 15:203 -221.
10. Dwyer, S. F. 2001. Finding a Better Cover, in Civil Engineering. Published by ASCE,
Reston, VA. Pp. 58-63. January 2001.
11. Dwyer, S.F., 2003. Water balance measurements and computer simulations of landfill
covers. Dissertation, Univ. of New Mexico.
12. Dwyer, S.F., J.C. Stormont, C.E. Andersen. 1999. Mixed Waste Landfill Design Report.
Sandia Report SAND99-2514. Sandia National Laboratories, Albuquerque, NM
13. Dwyer, SF, R. Rager, and J. Hopkins. 2007. Cover System Design Guidance and
Requirements Document. LA-UR-06-4715, EP2006-0667. Los Alamos National
Laboratory report, Los Alamos, NM.
14. EPA. 1991, Design and Construction of RCRA/CERCLA Final Covers, EPA/625/4-
91/025.
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15. EPA. 1994. Design, Operation, and Closure of MUniciapl Solid Waste Landfills.
EPA/625/R-94/008.
16. Hakonson, T. E., K. L. Maines, R. W. Warren, K. V. Bostick, G. Trujillo, J. S. Kent, AND
L. J. Lane. 1994. Hydrologic Evaluation of Four Landfill Cover Designs at Hill Air Force
Base, Utah. Report LAUR-93-4469, Los Alamos National Laboratory, Los Alamos, NM.
17. Harden, J. W.; Taylor, E. M.; Rheis M. C.; and McFadden L. D. 1991. Calcic Gypsic,
and Siliceous Soil Cronosequence in Arid and Semiarid Environments. Occurrence,
Characteristics and Genesis if Carbonate Gypsum, and Silica Accumulations in Soils.
Soils Science Society of America Special. Publication Number 26. Editor: Nettleton, W.
D.
18. Hauser, V.L., Shaw, M.A., Weand, B.L. 1994. Effectiveness of Soil-Vegetative Covers
for Waste Sites. In SUPERFUND XV: 15th Environmental Conference and Exhibition for
the Hazardous Materials/Hazardous Waste Management Industry, Washington DC, Dec
1994, pp. 368-374.
19. Hillel, D., 1998. Environmental Soil Physics, Massachusetts Academic Press, University
of Massachusetts, Amherst, Massachusetts.
20. ITRC, 2003. -Technical and Regulatory Guidance for Design, Installation and
Monitoring of Alternative Final Landfill Covers," Interstate Technology and Regulatory
Council, Alternative Landfill Technologies Team, Washington, D.C.
21. Jones, Ulysses S. and Suarez, E. L. 1985. Plant Nutrient Loading, pH and Calcium
Carbonate Equivalent of Acid Precipitation. U.S. Technical Bulletin/South Carolina
Agricultural Experiment Station; 1095. Pages 6-7. November.
22. Jones, J. P. and Woltz, S. S. 1996. Effect of Calcium Carbonate and Micronutrients on
the Development of Crown Rot of Tomato. Proceedings of the Florida State
Horticultural Society Annual Meeting of the Florida State Horticultural Society. Volume
109. Pages 182-184.
23. Jury, W. A., W. R. Gardner, and W. H. Gardner. 1991. Soil Physics, 5th Edition, John
Wiley & Sons, Inc., New York, NY.
24. Khire, M. V., C. H. Benson, and P. J. Bosscher. 1997. Water Balance Modeling of
Earthen Final Covers, in ASCE Journal of Geotechnical and Geoenvironmental
Engineering, Vol. 123, No. 8, pp. 744-754.
25. Ligotke, M.W. 1994. -Control of Eolian Soil Erosion from Waste-Site Surface Barriers,"
In-situ Remediation: Scientific Basis for Current and Future Technologies, G.W. Gee and
N.R. Wing (eds.), Batelle Press, Richland, WA, pp. 545-559.
26. Lyles, L. 1975. Possible effects of wind erosion on soil productivity. Journ. Soil and
Water Cons. 30:279-283.
27. Mattson, Earl D., Mark Ankeny, Steve Dwyer, Nancy Hampton, Gretchen Matthern,
Brenda Pace, Alva Parsons, Mitch Plummer, Steve Reese, and Jody Waugh. 2004.
Preliminary Design Criteria and Cover Evaluation for the INEEL Subsurface Disposal
Area (Draft) ICP/EXT-04-00216 Revision B, Idaho Completion Project, Idaho Falls,
Idaho 83415
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nd
28.McCuen, R.H. 1998. ^Jydrologic Analysis and Design," 2 Edition, Prentice Hall
Publishing Co., NJ, 814 p.
29. McGeorge, W. T. 1933. Phosphate Availability in Alkaline Calcareous Soils. Journal
of the American Society of Agronomy. Pages 351-354.
30. Monger, H. C. and Gallegos, R. A. 2000. Biotic and Abiotic Processes and Rates of
Pedogenic Carbonate Accumulation in the Southwestern United States-Relationship to
Atmospheric CC>2 Sequestration. Global Climate Change and Pedogenic Carbonates.
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31. Muramoto, S.; Nisizake, H. and Aoyama, I. 1991. Changes in Concentration of
Cadmium, Zinc and Iron in Glutinous and Non-glutinous Rice for Cadmium Sulfide with
or without Calcium Carbonate. Ber. Ohara Inst Landwirtsch Biol Okayama University
Berichte Des Ohara. Volume 20. . Pages 11-18.
32. NRCS. 2000. -Erosion and Sedimentation on Construction Sites," U.S. Department of
Agriculture, National Resources Conservation Service, Soil Quality Urban Technical
Note No. 1,5 p.
33. Nyhan, J. 2005. A Seven-Year Water Balance Study of an Evapotranspiration Landfill
Cover Varying. Vadose Zone J.2005; 4: 466-480
34. Nyhan, J., T. Schofield, J. Salazar. 1997. A water balance study of four landfill cover
designs varying in slope for semiarid regions. Proceedings 1997 International
Containment Technology Conference, St. Petersburg, FL.
35. Pal, D. K.; Dasog, G. S.; Vadicelu, S.; Ahuja, R. L.; and Bhattacharyya T. 2000.
Secondary Calcium Carbonate in Soils of Arid and Semiarid Regions of India. Global
Climate Change and Pedogenic Carbonates. Editors Lai R., Kimble F. M., Eswarn, H.,
and Stewart, B. A. Lewis. Publishers New York.
36. Pemberton, E. L. and Lara, J. M., 1984, Computing degradation and local scour: U.S.
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37. Rahmatullah, Badr-Uz-Zaman, B., Salim, M. 1998. Plant Utilization and Release of
Boron Distributed in Different Fractions In Calcareous Soils. Arid Soil Research and
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38. Schroeder, P., C. Lloyd and P. Zappi. 1994. The Hydrologic Evaluation of Landfill
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39. Sharma, K. D.; Kumar, S.; and Gough L. P. 2001. Rehabilitation of Gypsum-Mined
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APPENDIX A
EROSION
33
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A.1 SHORT-TERM AND LONG-TERM EROSION
The cover system design should address the potential for short-term erosion (i.e., before a good
stand of vegetation is established), and make use of temporary erosion-control measures as
necessary. The design should also address long-term erosion after vegetation has been
established. Erosion can be damaging not only to the cover system but also to areas into which
eroded soil is deposited. Erosion can spread waste and contaminants. Furthermore, it is
important that constructed erosion-control measures be properly installed and maintained.
The timing for completion of cover system construction can impact the potential for early
vegetation establishment and thus affect the severity of erosion. Ideally the conclusion of cover
construction should be scheduled to allow vegetation to become established as soon as
practicable and before the end of the growing season, if at all possible. Short-term erosion
control materials may be needed to protect the surface layer until vegetation is adequately
established. The design specifications should be written to ensure optimization of vegetation
establishment based on that site's climate seeding and/or planting of native vegetation.
The construction contractor is often made responsible for maintaining temporary erosion control
measures and repairing damage due to erosion during and shortly after construction. However,
the general contractor may only have limited expertise in soil erosion control. Furthermore, the
contractor may not be privy to design decisions that affect the potential for severe short-term
erosion. Thus, caution should be exercised in placing responsibility upon the contractor, who
may be ill-equipped to make informed decisions about appropriate erosion control measures.
The design engineer should consider the potential for and consequences of short-term erosion
and be proactive in specifying appropriate control measures (e.g., silt fences, rolled erosion
control materials, sediment traps, hay bales, etc.) in the construction documents.
The Natural Resources Conservation Service (NRCS) (2000) makes the following
recommendations to limit short-term erosion during construction:
cover disturbed soils as soon as possible with vegetation or other materials (e.g. mulch) to
reduce erosion potential;
divert water from disturbed areas;
control concentrated flow and runoff to reduce the volume and velocity of water and
prevent formation of rills and gullies;
minimize the length and steepness of slopes (e.g., use benches);
prevent off-site sediment transport;
inspect and maintain any structural control measures;
where wind erosion is a concern, plan and install windbreaks;
avoid soil compaction by restricting the use of trucks and heavy equipment to limited
areas after seeding of the cover system; and
scarify or disc the upper 6-inches (15 cm) of cover soil that may have been compacted
during construction activities prior to vegetating or placing sod.
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Long-term erosion is an important consideration in the design of the cover's surface layer. In
spite of the admittedly approximate nature of predictive equations for erosion control, most cover
systems will require an analysis of long-term and, sometimes, short-term erosion. Typical design
criteria are as follows:
The design sheet and rill erosion rate should not be exceeded. Although it is advisable to
select allowable rates of soil erosion on a project-specific basis, all covers should be
designed so that the sheet erosion rates not exceed 2 tons/acre/year (EPA, 1991). This
maximum allowable rate is a result of both wind and runoff erosi on rates.
Using the sheet and rill erosion rate from this calculation, the thickness of cover soil at
the end of the design life should be calculated to verify that there is adequate thickness
remaining and that sheet and rill erosion has not progressed through the cover soil and
into the underlying layers. There should also be sufficient soil thickness to support
vegetation and provide for adequate water storage capacity.
The surface layer should resist gully formation under the tractive forces of runoff from
the site-specific design storm(s).
Wind erosion should also be evaluated.
A.2 EROSION ANALYSIS TOOLS
Some of the more common methods for calculating sheet and rill erosion, gully formation, and
wind erosion are briefly described below.
A.2.1 SHEET AND RILL EROSION DUE TO SURFACE RUNOFF
The Natural Resources Conservation Service (NRCS) in 7 CFR Part 610 describes erosion
measures suggested for highly erodible soils. Specifically, subpart 610.11 sets forth the
equations and rules for utilizing the equations that are used to predict soil erosion due to water
and wind. Section 301 of the Federal Agriculture Improvement and Reform Act of 1996
(FAIRA) and the Food Security Act, as amended, 16 U.S.C. 3801-3813 specified that the
Secretary would publish the universal soil loss equation (USLE) and wind erosion equation
(WEQ) used by the Department within 60 days of the enactment of FAIRA. This subpart sets
forth the equations, definition of factors, and provides the rules under which NRCS will utilize
the USLE, the revised universal soil loss equation (RUSLE), and the WEQ.
A.2.1.1 REVISED UNIVERSAL SOIL LOSS EQUATION (RUSLE)
RUSLE represents a revision of the USLE technology in how the factor values in the equation
are determined. RUSLE is explained in the U.S. Department of Agriculture Handbook 703,
predicting Soil Erosion by Water: A Guide to Conservation Planning with the Revised
Universal Soil Loss Equation (RUSLE).'' The RUSLE is expressed as:
As - RexK xLSxC x Pc Equation A. 1
Where:
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AS = average annual soil loss by sheet and rill erosion in tons per acre caused by
sheet and rill erosion;
Rg = rainfall energy/erosivity factor (dimensionless) and is a measure of rainfall
energy and intensity rather than just rainfall amount;
K = soil credibility factor (dimensionless), is a measure of the relative resistance
of a soil to detachment and transport by water, and varies based on seasonal
temperature and rainfall (adjusts it bi-monthly for the effects of freezing and
thawing, and soil moisture);
LS = slope length and steepness factor (dimensionless). It accounts for the effect
of length and steepness of slope on erosion based on the relationship of rill
to interrill erosion;
*- = vegetative cover and management factor (dimensionless) and is the ratio of
soil loss from land cropped under the specified conditions to the
corresponding loss from clean-tilled, continuous fallow. Estimates the soil
loss ratio at one-half month intervals throughout the year, accounting for the
individual effects of prior land use, crop canopy, surface cover, surface
roughness, and soil moisture.; and
PC = conservation support practice factor (dimensionless) and is the ratio of soil
loss with a specific support practice (such as cross-slope farming, strip
cropping, buffer strips, and terraces) to the corresponding soil loss with
uphill and downhill tillage.
Input values for RUSLE are developed using site-specific information and the database that is
part of the RUSLE computer program. A free Windows based version of RUSLE, Version 2 can
be downloaded from http://www.ars. usda.gov/Research/docs.htm?docid=6010 Using As
computed from Equation A.1, the thickness of cover soil at the end of the cover system design
life can be calculated to verify that there is sufficient cover soil remaining.
A.2.1.2 WATER EROSION PREDICTION PROJECT (WEPP) MODEL
The WEPP erosion model computes soil loss along a slope and sediment yield at the end of a
hillslope (USDA 1995). Interrill and rill erosion processes are considered. Interrill erosion is
described as a process of soil detachment by raindrop impact, transport by shallow sheet flow,
and sediment delivery to rill channels. Sediment delivery rate to rill flow areas is assumed to be
proportional to the product of rainfall intensity and interrill runoff rate. Rill erosion is described
as a function of the flow's ability to detach sediment, sediment transport capacity, and the
existing sediment load in the flow.
The appropriate scales for application are tens of meters for hillslope profiles, and up to hundreds
of meters for small watersheds. For scales greater than 100 meters, a watershed representation is
necessary to prevent erosion predictions from becoming excessively large.
Overland flow processes are conceptualized as a mixture of broad sheet flow occurring in
interrill areas and concentrated flow in rill areas. Broad sheet flow on an idealized surface is
assumed for overland flow routing and hydrograph development. Overland flow routing
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procedures include both an analytical solution to the kinematic wave equations and regression
equations derived from the kinematic approximation for a range of slope steepness and lengths,
friction factors (surface roughness coefficients), soil textural classes, and rainfall distributions.
Because the solution to the kinematic wave equations is restricted to an upper boundary
condition of zero depth, the routing process for strip cropping (cascading planes) uses the
concept of the equivalent plane. Once the peak runoff rate and the duration of runoff have been
determined from the overland flow routing, or by solving the regression equations to
approximate the peak runoff and duration, steady-state conditions are assumed at the peak runoff
rate for erosion calculations. Runoff duration is calculated so as to maintain conservation of mass
for total runoff volume.
The erosion equations are normalized to the discharge of water and flow shear stress at the end
of a uniform slope and are then used to calculate sediment detachment, transport, and deposition
at all points along the hillslope profile. Net detachment in a rill segment is considered to occur
when hydraulic shear stress of flow exceeds the critical shear stress of the soil and when
sediment load in the rill is less than sediment transport capacity. Net deposition in a rill segment
occurs whenever the existing sediment load in the flow exceeds the sediment transport capacity.
In watershed applications, detachment of soil in a channel is predicted to occur if the channel
flow shear stress exceeds a critical value and the sediment load in the flow is below the sediment
transport capacity. Deposition is predicted to occur if channel sediment load is above the flow
sediment transport capacity. Flow shear stress in channels is computed using regression
equations that approximate the spatially-varied flow equations. Channel erosion to a nonerodible
layer and subsequent channel widening can also be simulated. Deposition within and sediment
discharge from impoundments is modeled using conservation of mass and overflow rate
concepts.
The WEPP model was developed in the 1980's when an increasing need for improved erosion
prediction technology was recognized by the major research and action agencies of the United
States Department of Agriculture and Interior, including the Agricultural Research Service
(ARS), Natural Resource Conservation Service (NRCS), Forest Service (FS), and Bureau of
Land Management (BLM). In 1985, these agencies embarked on a 10-year research and
development effort to replace the Revised Universal Soil Loss Equation. Some of the differences
between the WEPP model and the RUSLE are as follows:
The RUSLE equation is based on undisturbed agricultural and rangeland top soil
conditions, whereas any kind of soil can be described with WEPP. Thus, WEPP is well
suited to describe a landfill cover, which is a disturbed condition.
The WEPP model is capable of predicting erosion and deposition in more complex
situations, such as when berms are involved. WEPP can predict the erosion on a cover as
well as the deposition in berm channels in the watershed mode. The WEPP model's
ability to determine runoff and channel flow can also aid in determining stability issues
with berms, such as overtopping. RUSLE can only predict the upland erosion between
berms.
RUSLE can only predict average annual upland erosion. WEPP's climate generator
includes stochastically generated events. This is an important point in arid environments
where there are very few precipitation events annually, but when they occur, they are
often torrential events that have major impacts on the site. Thus, a landfill in an arid
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climate is unlikely to fail in an average year, whereas, it is very likely to fail in a year
when a major storm event has occurred. WEPP can predict the impacts from a major
storm event, but RUSLE cannot.
The windows based version of the WEPP software is available along with additional information
regarding the WEPP model, software, and documentation at:
http://www.ars.usda.gov/Research/docs.htm?docid=6010
A.2.2 TRACTIVE FORCE METHOD
The concentration of runoff under many circumstances encourages the formation of rills, which,
if unchecked, grow into gullies (Figure A-l). This can be the most severe type of erosion of
cover systems soils at landfill and waste remediation sites.
Figure A-l. Gully Formation Measured Over Six-Feet Deep in Albuquerque, NM
The dynamics of gully formation are complex and not completely understood. Gully growth
patterns are cyclic, steady, or spasmodic and can result in the formation of continuous or
discontinuous channels. Gully advance rates have been obtained by periodic surveys,
measurements to steel reference stakes or concrete-filled auger holes, examination of gully
changes from small-scale maps, or from aerial photographs. Studies are producing quantitative
information and some procedures that combine empirically- and physically-based methods have
been advanced. Vanoni (1975) presented six methods used for prediction of gully growth and/or
gully head advance. They all follow some type of multiplicative or power law and are replete
with empirical constants that are generally site specific. McCuen (1998) updated and further
38
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described gully erosion prediction equations with the observation that five factors underlie the
relevant variables of the process: land use, watershed size, gully size, soil type, and runoff
momentum. Having investigated the relevant factors, however, McCuen found that none of the
equations treat all terms. Better methods of evaluating gully formation that are more physically
based are needed. Consequently, all covers should be designed to mitigate gully formation.
The potential for gully development in vegetated soil surface layers has been assessed at landfill
sites using the tractive force method described by Temple et al. (1987) and DOE (1989) and
developed for channel flow. The tractive force method (Temple et al., 1987; DOE, 1989) can be
used to calculate the allowable shear stress of a vegetated surface layer as:
ra = TQ6 x C| > Q.9kPa Equation A.2
Where:
Tab = allowable shear stress for the surface layer with bare soil (kPa); and
C0 = void ratio correction factor (dimensionless).
Temple et al. (1987) and DOE (1989) provide graphs for both Tab and ce values.
The allowable shear stress (Ti°0 (Equation A.3) must be equal to or greater than the effective
shear stress (Tie) applied to the surface layer by the flowing water:
Equation A.3
Where:
Yw = unit weight of water (kN/m3);
D = flow depth (m);
-> = slope inclination (dimensionless);
^F = vegetal cover factor (dimensionless);
n = Manning's roughness coefficient for the considered vegetative cover
(dimensionless); and
ns = Manning's roughness coefficient for the bare soil (dimensionless).
Guidance on the selection of values for the vegetal cover factor and the Manning's coefficients is
provided by Temple et al. (1987) and DOE (1989).
The depth of flow can be calculated using the Manning's equation (Equation A.4) (DOE, 1989):
D =
5°5 ' Equation A.4
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Where:
*? = peak rate of runoff (mP3P/s/m) from the Rational Formula (and
incorporating the flow concentration factor);
n = Manning's roughness coefficient for the considered vegetative cover
(dimensionless);
s = slope inclination (dimensionless);
A.2.3 WIND EROSION EQUATION (WEQ)
Wind erosion physically removes the lighter, less dense soil constituents such as organic matter,
clays, and silts (Figure A-2). Thus it removes the most fertile part of the soil and lowers soil
productivity (Lyles, 1975). During the 1930's, a prolonged drought culminated in dust storms
and soil destruction of disastrous proportions. The Wind Erosion Equation (WEQ) (Equation
A.5) for predicting soil loss due to wind erosion is:
E = f(I K C L V)
Figure A-2. Wind Erosion in Arid Climate
Equation A.5
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Where:
£ = the estimation of average annual soil loss in tons per acre.
f indicates the equation includes functional relationships that are not straight-line
mathematical calculations.
I = the soil erodibility index.
K = the ridge roughness factor.
C = the climatic factor. All climatic factor values are expressed as a percentage of the
value established at Garden City, Kansas. Garden City, Kansas was the location
of early research in the WEQ and established the standard for climatic factors
against which the other locations are measured.
L = the unsheltered distance across an erodible field, measured along the prevailing
wind erosion direction.
V = the vegetative cover factor.
A.3
The erosion analysis tools described above, as well as similar others, are all best suited for
farmlands or uniform watersheds with frequent and average rainfall. They are much less
applicable to desert or dry climates where infrequent storms are the rule. The models are also
better suited for finer grained soils like clay and silt and less so for coarser loams. They are best
suited for larger areas and less accurate for smaller areas. They all state that they can deal with
minor rill development but none can deal with gully formation other than the tractive force
method that estimates the potential for gully erosion. In arid and semi-arid climates, soil loss
due to gully erosion can be orders of magnitude greater than sheet flow erosion. In order to
overcome these shortcomings Anderson and Dwyer (Dwyer et al 1999) developed a gravel/soil
admixture designed to mitigate soil loss on landfill covers. This design was later modified by
Dwyer (et al 2007).
Gravel/soil admixtures provide excellent means to minimize erosion while allowing for
vegetation establishment without a significant reduction in evaporation (Waugh et al 1994,
Dwyer 2003). Erosion (Ligotke 1994) and water balance studies (Waugh 1994) suggest that
moderate amounts of gravel mixed into the cover topsoil will control both water and wind
erosion. As wind and water pass over the landfill cover surface, some winnowing of fines from
the admixture is expected, creating a vegetated erosion-resistant surface sometimes referred to as
a -desert pavement". Figure A-3 shows the results of wind erosion in northwestern New Mexico
on the Navajo Reservation where a prescriptive landfill cover had been installed. The local
native soils were generally a coarser loam material, but to comply with prescriptive regulations -
a soil was imported that contained a significant amount of fines (silt and clay). This soil was
installed to meet the low saturated hydraulic conductivity requirement for a prescriptive barrier
layer. Severe winds eroded the newly installed fine cover soils leaving behind some desiccated
clay and minimal fines stabilized by sparse vegetation roots. Of the two-feet of soil originally
installed as the cover, less than a foot remained after a year.
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Figure A-3. Landfill Cover Located on the Navajo Reservation that experienced significant Wind Erosion
The design of a gravel admixture layer should be based on the need to protect the soil cover from
water and wind erosion. A gravel admixture can effectively protect a cover from long-term wind
erosion. The protection from water erosion will depend on the depth, velocity, and duration of
water flowing across the landfill cover. These flow values can be established from the physical
properties of the cover (slope, convex or concave grading, slope uniformity, and length of flow
paths) and the intensity of the precipitation water (precipitation rates, infiltration vs. runoff
relationships, snowmelt and off-site flows).
Erosion is greatly affected by rainfall intensity. As the intensity increases, the velocity of
subsequent run-off also increases. Thus the erosive energy of the flowing water increases as the
square of the velocity. Consequently, the amount of erosion can increase significantly as the
rainfall intensity increases. Anderson and Stormont (1997) estimated that a single 6-hr, 100-year
storm produces more than ten times the annual average erosion quantity. In response to intense
rainfall, erosion does not occur as a uniform lowering of the surface, but by the formation of rills
that turn into gullies. When run-off is channeled into the developing gullies, the velocity
increases, and thus erosion increases (Figure A-l). For a cover surface, gully formation is
particularly problematic because it can compromise the function of the cover system to isolate
the underlying waste.
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6D
T3
ra
OJ
4D
ID
Erosion
(Detachment)
Deposition
0.1 0.2 0.4 1.0 2.0
Size of Parti cl es (mm)
Figure A-4. Relationship Between Erosion Mechanism (Air or Water), Particle Size and Fluid Velocity (Garrels, 1951 as
referenced by Mitchell, 1993).
Erodibility of soils increases as particle size decreases (Figure A-4). Clay particles, while small,
can possess cohesive strength that resists erosion until they become nearly saturated whereby
their cohesion approaches zero. Silts are generally the most erosive soils. Surface soils have
been modified by the addition of larger particles, e.g. gravel, to increase their resistance to
erosion (Ligotke 1994, Waugh et al 1994, Dwyer et al 1999, Dwyer 2003, Dwyer et al 2007). As
the finer portions of the soil are removed by erosive forces, the larger particles remain behind
and form an -armored" surface sometimes referred to as a -d-esert pavement". This surface is
much more stable and resistant to surface erosion due to both surface water run-off and wind
erosion.
A.3.1 SOIL /GRAVEL ADMIXTURE DESIGN METHODOLOGY
An approach to design a soil/gravel admixture to serve as a surface -a-rmor" or -desert
pavement" (Figure A-5) was developed that combines analytical and empirical relationships in a
step-by-step process (Dwyer et al, 1999, Dwyer et al 2007).
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b-JJr JT
*w. ' *»
j? ><
r^-x --- _»
Figure A-5. Gravel recently installed on Superfund closure in Farmington, NM
The following steps are involved in the design methodology:
1. Estimate the design rainfall event;
2. Predict run-off for the given slope characteristics, including slope angle and length;
3. Estimate the channel (gully) geometry in response to estimated run-off;
4. Calculate the particle size that will be displaced by the channel; velocity;
5. Determine the depth of scouring and remaining armored layer.
A.3.1.1 DESIGN RAINFALL EVENT
Use a design rainfall return period that makes sense for the site and the waste encapsulated. A
common design event used is a 100-year return period. Local hydrology requirements should be
met.
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The national method" is one of the simplest and best-known analysis methods routinely applied
in urban hydrology for smaller areas. The rational method (Equation A.6) is based on the
assumption that rainfall occurs uniformly over the watershed and at a constant intensity for
duration equal to the time of concentration. This method is commonly used for areas under 40
hectares in size.
The peak rate of runoff, (Q) in cfs (runoff is actually in acre-inches/hour but is rounded to equate
to cfs), is given by the following expression:
Q=-CIA
Where:
Equation A.6
C = Run-off coefficient (dimensionless)
I = Rainfall intensity (in/hr)
A = Surface area that contributes to run-off (acres)
The appropriate value for =I' in this case where erosional processes are being evaluated is the
peak intensity. The duration of the peak rainfall intensity is often derived from the -time of
concentration," which represents the time for run-off from the most remote portion of the
contributory watershed to exit that watershed. This time of duration is dependent on the slope
angle and length and the surface described by the value =C'. Common values for =C' are listed in
table Al.
Vegetation and
Slope Conditions
Woodland
Flat. 0-5% slope
Rolling, 5-10% slope
Hilly, slope
Pasture
Flat, 0-5% slope
Rolling, 5-10% slope
Hilly, 10-30% slope
Cultivated
Flat. 0-5% slope
Rolling, 5-10% slope
Hilly,
Soil Texture
Open sandy
loam
0.10
0.25
0.30
0.10
0.16
0.22
0.30
0.40
0.52
Clay and silty
loam
0.30
0.35
0.50
0.30
0.36
0.42
0.50
0.60
0.72
Tight clay
0.40
0.50
0.80
0.40
0.55
0.60
0.60
0.70
0.82
The assumed contributory area is found from the following figure A-5.
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%L
1 I I
I I I
\ I /
Channel
Figure A-5. Contributory Area for Gully Formation
The contributory area on a landfill can generally be assumed to be the slope length multiplied by
the width that contributes to the formation of gullies, that is, the lateral gully spacing. The slope
width is assumed to about one quarter that of the slope length based on professional experience
and consultation with experts. Consequently, =A' is equal to
A.3.1.3 CHANNEL GEOMETRY
The channel geometry shown in figure A-6 is that assumed for the gully formation.
b
Figure A-6. Channel Geometry
The geometry of the channel that forms is based on regression equations developed from analysis
of a large number of channels (Simons, Li & Assoc., 1982). The channel width is given by:
°3*
Equation A.7
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Where:
b = width of flow (ft)
Qm = mean annual flow (cfs)
M = percentage of silts and clays in soils
The mean annual flow (Qm) is assumed to be between 10 to 20% of the peak rate of run-off (Q)
(Dwyeretal, 1999).
For the given discharge point of geometry, the hydraulic depth (dh) defined as the flow cross-
sectional area divided by the width of water surface is half of the gully depth (d).
For flows at the critical slope:
fa = 0.5 x F°-< x F-^ x Q°<* Equation A.8
Where:
F = width to depth ration = b/dh
^"t = Froude Number -1.0
These equations can be solved simultaneously to yield the channel width and depth for a given
peak flow rate and percentage of silt and clay. With the channel dimensions, the velocity in the
channel can be found.
A 1 1 4
jrl,,J,JL,1r
The incipient particle size is the particle that is on the brink of movement at the assumed
conditions. Any increase in the erosional forces acting on the particle, due to an increase in
velocity or slope, for example, will cause its movement. This incipient particle size (Dc) can be
calculated using the Shield's Equation:
D = T/
c IFS(YS - y) Equation A.9
Where:
T = total average shear stress (pcf)
Fs = Shield's dimensionless shear stress = 0.047
ys = specific weight of soil (pcf)
y = water density = 62.4 pcf
The total average shear stress is given by:
T = y x dh x 5 Equation A.10
Where:
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S = slope (ft/ft)
A.3.1.5 DEPTH OF SCOUR AND ARMOURING REQUIRED
The incipient particle size defines the maximum size of particle that will be eroded for a given
set of conditions. The material larger than the incipient particle size will not be displaced or
eroded and can form an armoring that will protect the channel from further erosion from similar
or lesser storm events.
The depth of scour (Ys) (Figure A-7) to establish an armor layer is given by (Pemberton and
Lara, 1984):
Equation A. 11
Where:
Ys = scour depth
Ya = armor layer thickness
PC = decimal fraction of material coarser than the incipient particle size.
'Original Surface
New Surface
Figure A-7. Armor Layer Development
Other considerations that should be included in the rock/soil admixture design include:
Rock mixed into the soil/rock admixture on the top slope and side slope should be
durable.
The hydraulic properties of interstitial soil would match the underlying water storage soil
layer.
51. The interstitial soil would be live topsoil with favorable fertility, microbiology,
propagules, and nominal phytotoxicity.
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APPENDIX B
COVER SOIL and VEGETATION
RECOMMENDATIONS
49
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B.I SALT CONTENT IN SOILS
Excessive soil salts can prevent the establishment of vegetation, as well as, precipitate out on the
surface creating a surface crust that reduces or prevents the infiltration of water. Saline soils are
susceptible to concentrated surface water flow and thus gully erosion. It is understood that a primary
goal of a cover system is to limit flux through the cover into the underlying waste. However,
infiltration of water into the cover system is required to maintain the integrity of the cover's
vegetation. Vegetation is essential to ensure the long term integrity of the cover system by
stabilizing the soil and minimizing erosion while removing moisture via transpiration. The lack of
vegetation and/or surface crust increases runoff that can lead to increased erosion as seen in figure
B-l.
Figure B-l. Excessive Gully Erosion on Shallow Slope
Soluble salts in a cover soil can go into solution following a precipitation event or series of events.
As the soil dries, moisture is moved upward by matric potential gradients where the salts in solution
precipitate out at or near the ground surface as the water evaporates. These precipitated salts, in
conjunction with the existing salts present in the upper soil layer, promote the formation of a brittle
surface crust (Figure B-2). Soil water salinity can negatively affect soil physical properties by
promoting the binding of fine mineral particles into larger aggregates. This process may promote the
formation of surface crusts. Surface crusts are essentially impermeable to water when dry. The
reduced permeability promotes higher surface runoff volumes due to decreased water infiltration into
the landfill cover soil. In turn, the higher surface runoff volumes increase the erosion of the landfill
cover.
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Figure B-2. Surface Crack in Brittle Cover Soil
Infiltration in the cover soil is compromised by salt-induced soil dispersion. High salt contents
induce dispersion of soil particles and the dispersed particles plug pores within the soil surface
by two means. First, dispersed soil particles plug underlying pores in the soil thereby constricting
avenues (channels and pores) for water and roots to move through the soil. Secondly, soil
structure promoting favorable water infiltration is disrupted because of this dispersion and a
cement-like surface layer is formed when the soil dries. The hardened upper layer, or surface
crust, further restricts water infiltration and plant establishment on the cover soil.
As described above, excessive salt concentrations of soil in the rooting medium can adversely
affect vegetation that in turn increases erosion. Soil dispersion disrupts natural soil structure and
hardens the soil and blocks water infiltration. Under these conditions, it is difficult for plants to
get established and grow. Saline soils are a problem because high salt concentrations prevent
plant roots from effectively utilizing soil water. Plant roots absorb water from the soil through
the process of osmosis. Osmosis is the process whereby water is moved from an area of lower
salt (higher water) concentration to an area of higher salt (lower water) concentration. The salt
concentration inside a normal plant cell (approximately 1.5%) is relatively high compared to
normally dilute salt concentrations in soil water. Therefore, under -^ormal" soil water salinity
levels water will move into root cells from the surrounding soil. However, under high saline soil
conditions, the concentration of salts in the soil water can rise above 1.5% and may inhibit the
movement of water from the surrounding soil to the plant roots. High salt concentrations in the
soil can in fact cause water to move out of plant roots, thereby dehydrating the plant. High salt
contents in the soil may also induce nutrient deficiencies in existing plants since plants take up
nutrients from the surrounding soil via water intake.
Cover soil can be characterized by the following agronomic characteristic ranges that include:
pH, electrical conductivity (EC), sodium absorption ratio (SAR), exchangeable sodium
percentage (ESP), calcium carbonate equivalent, cation exchange capacity (CEC), percent
organic matter, nitrogen (N), phosphorous (P), and potassium (K).
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Electrical conductivity (EC) estimates the amount of total dissolved salts (TDS), or the total
amount of dissolved ions in the water. EC is measured in micro Siemens/cm or micromhos per
centimeter (l|iS/cm = 1 |imho/cm). The Sodium Adsorption Ratio (SAR) is the proportion of
sodium (Na) ions compared to the concentration of calcium (Ca) plus magnesium (Mg). An
SAR value of 15 or greater indicates an excess of sodium will be adsorbed by the soil clay
particles. Excess sodium can cause soil to be hard and cloddy when dry, to crust badly, and to
take water very slowly. Cation Exchange Capacity (CEC) is a calculated value that is an
estimate of the soils ability to attract, retain, and exchange cation elements. It is reported in
millequivalents per 100 grams of soil (meq/lOOg). The exchangeable sodium percentage (ESP)
refers to the concentration of sodium ions on cation exchange (CEC) sites. An ESP of more than
15 percent is considered the threshold value for a soil classified as sodic. This means that sodium
occupies more than 15 percent of the soil's CEC. Be aware that sensitive plants may show injury
or poor growth at even lower levels of sodium. Table B-l summarizes the tests that evaluate the
salt content in soils with recommended limits for each test.
Table B-l. Soil Requirements to Limit excess Salts
Limits
EC
SAR
ESP
CaCO3
Less than
Less than
Less than
Less than
8 |jS/cm
6
15%(g/g)
10%(g/g)
B.I.I CALCIUM CARBONATE CONTENT IN COVER SOILS
The aforementioned discussion on salt content in soils centered on soluble salts. Less soluble
salts such as calcium carbonate (CaCO3) are also harmful to cover soils in excess. Figure B-3
reveals the difference in vegetation establishment on cover soils based on CaCO3 content.
CaCOs is prevalent in soils in the southwestern United States.
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Soils with Higher than 10% CaCO3 by Weight
Soils with Lower than 10% CaCO3 Content by
Weight
Figure B-3. Negative Impact of High Salt Content on Vegetation on a Cover System (Dwyer 2003)
CaCOs is a salt that can be formed by the reaction of carbon dioxide (an acid-forming oxide),
and calcium oxide (a base-forming oxide). Carbon dioxide produced by root (and soil
microorganism) respiration, in the presence of water, forms H2CO3 (carbonic acid) (Birkland
1974). This formation tends to be most active in the upper soil where biological activity is
highest. Calcium cations from weathering of primary minerals, or from windblown dust, or even
entering the soil in rainwater, tend to stay dissociated in the upper soil where pH tends to be
lower and water tends to be more abundant (Birkland 1974; Jones and Suarez 1985; Monger and
Gallegos 2000). As soil solutions pass to greater depth in the soil, increased pH and less
abundant water drive the equilibrium toward precipitation of CaCOs (Birkeland 1974; Harden
1991; Pal et. al. 2000; Monger and Gallegos 2000). As this process continues over time, CaCOs
accumulates in the lower soil. Soil that contains CaCOs is called calcareous soil. Secondary
accumulations of CaCOs in the subsoil are referred to as calcic horizons. They may exist either
as cemented layers, accretions, or concentrated horizons in lower soil profiles. These features
are often colloquially but incorrectly termed caliche. Caliche (a geologic feature) forms on or
very near the surface of soil in arid and semiarid regions), typically as a result of capillary rise
and evaporation of CaCOs-charged ground water.
Calcic soil horizons, by comparison, are a phenomenon of downward leaching. To a certain
extent, the depth to calcic soil horizons depends on the amount of rainfall. Typically, as rainfall
increases, so too does the depth to a calcic soil horizon. When annual rainfall exceeds 100
centimeters (-39 inches), calcic soil horizons disappear from the soil profile (Blatt et al. 1980).
One of the primary means by which CaCOs affects plant growth is by inhibiting the ability of
plants to absorb nutrients from the soil. CaCOs affects plant uptake of both macronutrients (e.g.,
nitrogen and phosphorus) and micronutrients (e.g., zinc and boron).
The macronutrient most affected by the presence of CaCOs is phosphorus. Phosphorous is
absorbed by plants in two forms: H2P(V, and HPO42". Of these, H2PO4" is most readily available
to plants, whereas plants do not readily absorb HPO42". In fact, McGeorge (1933) considered the
monovalent form the only form of phosphorus that influenced plant growth and nutrition. In
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order for phosphorus to be absorbed by the root, the solution or film around the root must have a
pH of 7.6, which is more difficult to attain in higher pH soil (McGeorge 1933). The abundance
of these forms of phosphorous available to plants depends upon the pH of the soil (McGeorge
1933). In low pH (acidic) soil H2P(V is most abundant, whereas HPC>42" is most abundant in
high pH (alkaline) soil. The presence of H^PCV is greatly reduced in calcareous soil with pH
between 8.0 and 8.5 (McGeorge 1933; Sharma et al. 2001). In addition, phosphorus can react
with CaCOs in soil to form calcium carbonate phosphate (McGeorge 1933; Dominguez 2001), a
form unavailable to plants.
The uptake of micronutrients by plants is also affected by the presence of CaCOs. The
micronutrients whose absorption by plants is most affected by the presence of CaCOs are boron,
zinc, iron, copper, and manganese (Brady and Weil 1994; Jones and Woltz 1996; Abdal et al.
2000). Reactions with CaCOs, water, and carbon dioxide in soil can transform these
micronutrients into forms unavailable for plants (Muramoto et al. 1991; Wang and Tzou 1995;
Jones and Woltz 1996). One of the most common micronutrient deficiencies in plants is boron
(Brady and Weil 1994). In calcareous soil, boron is fixed or bound by soil colloids (Brady and
Weil 1994; Rahmatullah et al. 1998). For example, a study on sunflowers found that, as soil
concentrations of CaCOs increased, the dry weight of sunflower shoots decreased, and correlated
with decreasing concentrations of boron in the plant tissue (Rahmatullah et al. 1998).
Concentrated CaCOs in soil also increases the potential for crusting, thereby reducing water
infiltration and inhibiting root penetration (West et al. 1988; Abdal et al. 2000; Dominguez et al.
2001; Sharma et al. 2001). In other words, physical changes of the soil caused by higher
concentrations ofCaCOs can cause reductions in plant production.
In addition to inhibiting plant growth, increasing CaCOs concentrations in soil have also been
linked to decreases in soil microfauna populations (Sharma et al. 2001). The affected
microfauna include fungi, bacteria and actinomycetes, and azotobacter (Sharma et al. 2001).
Microfauna are critical to the conversion of soil nitrogen into forms available to plants.
Mycorrhizal associations (a symbiotic relationship between the root and fungi) can be critical for
plants to increase uptake and harvesting of nutrients, especially phosphorus, and water.
The maximum allowable calcium content levels for cover soil in the rooting zone (upper 3-feet
[91 cm]) should be less than 10% by weight (Dwyer 2003).
B.2 SOIL NUTRIENT REQUIRMENTS
Just as important to limit the amount of salts in a cover soil is that the soil used have adequate
nutrients to allow for a quality stand of native vegetation. Adequate soil nutrients must be
available to adequately establish native vegetation on the cover surface. The parameters
considered for acceptable nutrients for a given borrow soil are: cation exchange capacity (CEC),
percent organic matter, nitrogen (N), phosphorus (P), and potassium (K+). The following soil
nutrients values are required in the upper 3-feet (91 cm) of all cover soil installed. Table B-2
summarizes the recommended tests to be performed on soils to determine the appropriate
nutrients levels with their recommended acceptable ranges.
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Table B-2. Soil Nutrient Requirements for Covers
Test
CEC
Percent organic matter
N
P
K
Limits
Greater than 15
Greater than 2% (g/g)
Greater than 6 parts per million
(ppm)
4 to 7ppm
61 to 120 ppm
The disadvantages of a low CEC obviously include the limited availability of mineral nutrients to
the plant and the soil's inefficient ability to hold applied nutrients.
Organic matter makes up only a small part of the soil. Even in small amounts, organic matter is
very important. Soil organic matter has several parts: The living microbes in the soil (like
bacteria and fungi), which break down very rapidly when they die. Partially decayed plant
material and microbes, for instance, plant material you mix in or manure. The stable material
formed from decomposed plants and microbes. This material is called humus, and is broken
down very slowly.
Organic matter affects both chemical and physical properties of the soil:
Chemical Effects: Organic matter releases many plant nutrients as it is broken down in
the soil, including nitrogen (N), phosphorus (P) and sulfur (S). It is also one of two
sources of CEC in the soil. (Clay is the other major source.) CEC represents the sites in
the soil that can hold positively charged nutrients like calcium (Ca++), magnesium (Mg+)
and potassium (K+). If CEC is increased, the soil can hold more nutrients and release
them for plant growth. To increase CEC, you have to increase organic matter.
Physical Effects: Organic matter loosens the soil, which increases the amount of pore
space. This has several important effects. The density of the soil goes down (it becomes
less compacted) and the soil structure improves. This means that the sand, silt and clay
particles in the soil stick together, forming aggregates or crumbs. Because there is more
pore space, the soil is able to hold more water and more air. Plants grown on healthy soils
won't be as stressed by drought or excess water. Water also flows into the soil from the
surface more quickly. With less compaction, it is also easier for plant roots to grow
through the soil.
There are many ways to add organic matter to soils. Compost and manure may add larger
amounts of organic matter. Compost is very similar in composition to soil organic matter. It
breaks down slowly in the soil and is very good at improving the physical condition of the soil.
Manure may break down quickly, releasing nutrients for plant growth, but it may take longer to
improve the soil using this material. Whatever matter is chosen to amend the soil, it should meet
the environmental standards of the site.
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A major consideration when selecting plants for a site is provided in Executive Order 13148,
which promotes the use of native species on revegetated sites. EPA defines native plants as
plants that have evolved over thousands of years in a specific region and have adapted to the
geography, hydrology, and climate (see http://www.epa.gov/greenacres/). Native plants found in
the surrounding natural areas have the best chance of success, require the least maintenance, and
are the most cost-effective in the long term. Ideally, revegetation of a site will create natural
conditions that encourage re-population by native animal species and are consistent with the
surrounding land. Using non-native plants located close to native plant environments could
displace the native plants; therefore, it is important to check the invasive nature of the proposed
plants (Executive Order 13112). Plant succession must be considered; for example, the original
species planted may not survive but may attract local wildlife to the area that will disperse the
seed and aid in the overall revegetation of the site.
A key element in the stability and performance of an ET cover system is vegetation. Native
grasses are desired on landfill and open dump covers because they stabilize the surface soil and
reduce erosion, transpire stored soil-water, and have relatively shallow thin roots that generally
do not result in preferential flow paths (EPA 1991).
Landfill cover vegetation goals (Waugh et al. 2002):
are well adapted to the engineered soil habitat,
are capable of high transpiration rates,
limit soil erosion, and
are structurally and functionally resilient.
Diverse mixtures of native and naturalized plants will maximize water removal and remain more
resilient given variable and unpredictable changes in the environment resulting from pathogen
and pest outbreaks, disturbances (overgrazing, fire, etc.), and climatic fluctuations. Local
indigenous ecotypes that have been selected over thousands of years are usually best adapted. In
contrast, the exotic grass plantings common on engineered covers are genetically and structurally
rigid, are more vulnerable to disturbance or eradication by single factors, and will require
continual maintenance (Mattson et al. 2004).
Selection of plant species is an important consideration in the design of a vegetated surface layer.
The vegetation serves several functions (Mattson et al. 2004):
Plant leaves intercept some of the rain before it impacts the surface layer, thereby
reducing the energy of the water and the potential for erosion.
Plant vegetation also helps dissipate wind energy.
The shallow root system of plants enhances the surface layer resistance to water and wind
erosion.
Plants promote ET of water, which increases the available water storage capacity of the
cover soils and decreases drainage from these soils.
A well-vegetated surface layer is generally considered more natural and esthetically
pleasing than an unvegetated surface layer.
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In selecting the appropriate vegetation for a site, the following general recommendations are
offered:
Locally-adapted, low-growing grasses and shrubs that are herbaceous or woody
perennials should be selected.
The plants should survive drought and temperature extremes.
The plants should contain roots that will penetrate deep enough to remove moisture from
beneath the surface but not so deep as to disrupt the drainage layer, hydraulic barrier, or
gas collection layer.
The plants should be capable of thriving with minimal addition of nutrients.
The plant population should be sufficiently diverse to provide erosion protection under a
variety of conditions.
The plants should not be an attractant to burrowing wildlife.
The vegetative cover should be capable of surviving and functioning with little or no
maintenance (e.g., without irrigation other than for initial plant establishment,
fertilization, and mowing).
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APPENDIX C
ANALYSIS TO DETERMINE MINIMUM ET
COVER THICKNESS
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Determine the minimum required depth of cover soil for an ET Cover required to minimize
flux. For a site that meets the criteria outlined in Section 1.0 that utilizes the recommended
cover profile described in Section 4.0. this step is assumed to be unnecessary. That is, the
cover soil has an adequate quantify of fines (greater than 20% pass the number 200 sieve)
and thus has adequate storage capacity for the relatively dry environment and low risk site.
The following steps may be performed if this is not the case.
a. Identify the design infiltration event(s). This can be dependent on design life.
Utilizing average climatic conditions is often used. Other possibilities include the
simulation of extreme or stress conditions such as wet years or extreme
precipitation events.
b. A first-order estimate of required cover thickness can be determined from
estimates of the water-holding or storage capacity of the soil and the amount of
infiltrated water that has to be stored. The design strategy for an ET cover system
is to ensure the storage capacity is sufficient to store the -worst-case" infiltration
quantity resulting from the design precipitation event until it can be removed via
ET. The maximum water content a soil can hold after all drainage downward
resulting from gravitational forces is referred to as its field capacity. Field
capacity is often arbitrarily reported as the water content at about 330 cm of
matric potential head (Jury et al. 1991). Below field capacity, the hydraulic
conductivity is often assumed to be so low that gravity drainage becomes
negligible and the soil moisture is held in place by suction or matric potential. The
storage capacity of a soil layer is thus calculated by multiplying its field capacity
by the soil layer thickness. This assumes a consistent field capacity. However, not
all of this stored water can be removed via transpiration (by plants). Vegetation is
generally assumed to reduce the soil moisture content to the permanent wilting
point, which is typically defined as the water content at 15,000 cm of matric
potential head (Cassel and Nielsen 1986). Evaporation from the soil surface can
further reduce the soil moisture below the wilting point to the residual saturation,
which is the water content ranging from below 15,000 cm to an infinite matric
potential. If water is only removed by plants, Stormont and Morris (1998)
reported that the net storage capacity, also referred to as the available water-
holding capacity, of a soil layer can be approximated by:
NSC = (FC- PWP) b Equation C.I
where:
NSC = net storage capacity
FC = field capacity
PWP = permanent wilting point
b = soil layer thickness
For example, the water content at field capacity from a representative soil
sample is estimated to be 16% while the permanent wilting point is
assumed to be about 6%. Thus the net storage capacity for this soil is
about 10% of its thickness.
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It is important to note that the use of field capacity and permanent wilting
point here is arbitrary and ignores other factors that affect the amount of
moisture retained in a soil layer (e.g., Jury et al. 1991, Cassel and Nielsen
1986). Nevertheless, these are simple and commonly used concepts and
are applicable for approximating the water storage capacity of a soil layer.
Model the cover system given desired vegetation characteristics and determined
climatic conditions. Model the cover profile for a deeper than desired depth. If a
unit gradient bottom boundary condition is used, place it below any significant
transient soil-moisture activity. Determine the minimum depth required based on
the Dwyer Pont of Diminishing Returns Method (Dwyer et al. 2007).
A more detailed method to determine the minimum cover soil depth required to
minimize flux utilizes an accepted unsaturated flow software package based on
the Richards' Equation (ITRC 2003). The Dwyer Point of Diminishing Returns
Method (Dwyer et al. 2007) should be utilized. This method simply determines
the cover depth at which flux has been minimized. That is, the cover soil depth
where an additional increment of soil will no longer decrease flux (Figure C-l) is
determined to be the point of diminishing return for soil depth. A cover profile
should be modeled with the expected cover and waste layers included. The
monolithic soil-water storage from the ET cover should be modeled at a depth
greater than the minimum expected depth. If a capillary barrier is introduced into
the cover profile resulting from the addition of a bio-barrier or other underlying
coarse soil layer, multiple model runs will be required to determine the minimum
cover soil required for storage capacity to minimize flux. The effect of the
capillary barrier on the storage capacity of the cover profile may be ignored
resulting in an added factor of safety (FS) in the cover's water storage capacity.
The model output of predicted percolation at various points within the cover
profile is then plotted against the cover depth. Generally, in arid and semiarid
climates, the point of diminishing returns is when the estimated flux approaches
zero or actually produces a negative flux (upward movement of moisture). The
cover soil depth that produces the minimum flux or -point of diminishing returns"
is the minimum depth required for water storage capacity only.
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Annual Flux
Cover Depth where flux has
been minimized
Figure C-l. Cover depth vs. annual percolation
Perform sensitivity modeling of the cover profile as required during the final
design process. Examples of model sensitivities include variances in soil
properties, optional layer additions, and climatic and vegetation variations. These
sensitivity analyses may increase the thickness of the cover soil layer or help
determine the best choice(s) for optional layers such as bio-barriers and drainage
layers.
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APPENDIX D
QUALITY ASSURANCE
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D.I CONSTRUCTION QUALITY ASSURANCE
Quality Assurance (QA) is a planned system of activities that provides the owner / operator and
permitting agency confidence that the facility was constructed as specified in the design. QA is
generally the responsibility of the owner and often designated to the design engineer(s) or other
designated party. Quality control (QC) is a planned system of inspections used to directly
monitor and control the quality of the construction process and materials used. QC is generally
the responsibility of the contractor building the facility. Recommendations and considerations to
be included in a QA Plan and in the QA process are included below. It is understood that the
size and complexity of the project will dictate the extent of the QA process.
D.I.I QA PLAN
A written QA Plan should precede any field construction activities. This plan should consider
standards recommended in the EPA Technical Guidance Document -Quality Assurance and
Quality Control for Waste Containment Facilities" (EPA, 1994).
A copy of the site-specific plans and specifications, QA plan, and QA documentation reports
should be retained at the facility by the QA engineer. The plans, specifications, and QA
documents can be the chief means for the facility owner/operator to demonstrate to the
regulatory agency that QA objectives for a project have been met.
The QA plan should include a detailed description of all QA activities to be used during
materials inspection and construction to manage the installed quality of the covers and associated
facilities. The QA plan should be tailored to each specific project with all important guidelines
and standards integrated into the project plans and specifications.
D.1.2 PERSONNEL QUALIFICATIONS
An important factor in assessing the quality of a cover system installation is the degree to which
key personnel involved in the process are qualified to perform the required tasks. QA personnel
must be familiar with:
1. the proj ect' s design including plans and specifications;
2. proj ect lay out;
3. materials to be used;
4. drainage control features;
5. soil borrow materials;
6. construction procedures, complications, schedule, and equipment;
7. material placement techniques and requirements;
8. equipment to be used and its capabilities; and
9. site specific complications/concerns.
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Key individuals involved in the QA process during the construction of cover systems and their
minimum recommended qualifications are listed in Table D.I.
Table D.I. Minimum Personnel Qualifications (EPA, 1994)
Individual
Design Engineer(s)
Minimum Qualifications
Registered Professional Engineer with
adequate job-specific experience.
QA Personnel/Inspectors) - Designated
Representative(s)
The individual(s) designated by the
appropriate authority with knowledge of
the project, and its plans, specifications,
and QA documents. Employed separately
from the contractor(s) building the facility.
QA Engineer -Designated Representative
QA Certifying Engineer. Representative or
Designated Individual(s)
QC Personnel
The individual in charge of the daily QA
process. Employed separately from the
contractor(s) building the facility.
Adequate experience and technical
knowledge of cover system design and
construction process and requirements.
Individual with intimate knowledge of the
project, and its plans, specifications, and
QA documents. Employed separately from
the contractor(s) building the facility.
Employed by the general contractor,
installation contractor, or earthwork
contractor involved in the waste
containment facilities; appropriately
trained.
QC Officer
The individual specifically designated by
the general contractor, manufacturer or
fabricator in charge of quality control
activities.
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D.1.3 DOCUMENTATION
In addition to insuring the correct installation of the cover system, another major intent of the
QA process is to provide documentation of the construction process.
D.l.3.1 DAILY INSPECTION REPORTS
Daily reporting and documentation procedures should be required. The QA engineer should
prepare daily written inspection reports that are to be included in the final QA documentation.
The daily reports should include information about the work accomplished, tests performed and
observations made, along with descriptions of the adequacy of the work completed.
D.l.3.2 DAILY SUMMARY REPORTS
A daily written summary is to be prepared by the QA engineer. These reports provide a
chronological framework for identifying and recording all other reports and aids in tracking what
activities/tasks were completed and by whom. At a minimum, the daily summary reports should
include the following:
Date, project name, location, waste containment unit under construction, personnel
involved in major activities, and other relevant identification information.
Description of weather conditions, including temperature, cloud cover, and precipitation.
Summaries of any meetings held and actions recommended or taken.
Specific work units and locations of construction under way during that particular day.
Equipment and personnel being utilized in each work task, including subcontractors.
Identification of areas or units of work being inspected.
Unique identifying sheet number of geomembranes for cross-referencing and document
control.
Description of off-site materials received, including any quality control data provided by
the supplier.
Calibrations or recalibrations of test equipment, including actions taken as a result of
recalibration.
Decisions made regarding approval (or disapproval) of units of material or of work
and/or corrective actions to be taken in instances of substandard or suspect quality.
Inspection data sheets and/or problem reporting and corrective measures used to
substantiate any QA decisions described in the previous item.
Signature of the QA engineer.
Any other pertinent information.
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D.l.3.3 INSPECTION AND TESTING REPORTS
All observations, results of field tests, and results of laboratory tests performed on- or off-site
should be recorded on a data sheet. Recorded observations and test results can take the form of
notes, charts, sketches, or photographs, or a combination of these.
At a minimum, the inspection data sheets should include the following information:
Description or title of the inspection activity.
Location of the inspection activity or location from which the sample was taken.
Type of inspection activity and procedure used (reference to standard method when
appropriate or specific method described in QA plan).
Unique identifying geomembrane sheet number for cross-referencing and document
control.
Recorded observation or test data.
Results of the inspection activity (pass/fail); comparison with specification requirements.
In addition to the individual preparing the data sheet, identification of all personnel
involved in the inspection.
Signature of the QA inspector and review signature by the QA engineer.
D.l.3.4 PROBLEM IDENTIFICATION AND CORRECTIVE MEASURES
REPORTS
A problem is defined as material or workmanship that does not meet the requirements of the
plans, specifications, or QA plan for a project or any obvious defect in material or workmanship
(even if there is conformance with plans, specifications, and the QA plan). At a minimum,
problem identification and corrective measures reports contain the following information:
Location of the problem.
Description of the problem (in sufficient detail and with supporting sketches or
photographic information where appropriate) to adequately describe the problem.
Unique identifying geomembrane sheet number for cross-referencing and document
control.
Probable cause for the problem.
How and when the problem was identified (reference to inspection data sheet or daily
summary report by inspector).
Where relevant, estimation of how long the problem existed.
Any disagreement noted by the inspector between him/her-self and contractor about
whether or not a problem existed or the cause of the problem.
Suggested corrective measure(s).
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Documentation of correction, if corrective action was taken and completed prior to
fmalization of the problem, and completed corrective measures report (reference to
inspection data sheet, where applicable).
Where applicable, outline of suggested methods to prevent similar problems in the future.
Signature of the QA inspector and review signature of QA engineer.
D.l.3.5 DRAWINGS OF RECORD
Drawings of record (better known as -a-s-built" drawings) should be prepared to document the
actual lines, grades, and conditions of each component of the covers/facilities. For the cover soil
components, the record drawings should include survey data that identifies lower and upper
elevations of a particular component (layer), the plan dimensions of the component, and
locations of all destructive and nondestructive test sampling sites.
D.l.3.6 FINAL DOCUMENTATION AND CERTIFICATION
Upon completion of the project, the QA engineer should prepare a final documentation and
certification report. This report is to include all daily inspection reports, the daily QA engineer's
summary reports, inspection data sheets, problem identification and corrective measures reports,
other documentation (such as quality control data provided by manufacturers or fabricators,
laboratory test results, photographs, as-built drawings, internal QA memoranda or reports with
data interpretation or analyses), and design changes made by the design engineer during
construction. The document should be certified to be correct by the QA certifying engineer.
D.l.3.7 DOCUMENT CONTROL
The QA documents should be maintained under a document control procedure. Any
modifications to the documents should be reported to and agreed upon by all parties involved.
An indexing procedure should be developed for conveniently replacing pages in the QA plan
when modifications became necessary; the replacement pages detail the revision status.
D.l.3.8 STORAGE OF RECORDS
During construction, the QA engineer should be responsible for all QA documents including
copies of the design criteria, specifications, plan revisions, and originals of all data sheets and
reports. Duplicate records should be kept at a separate location to prevent the loss of this
valuable information if the originals were inadvertently destroyed.
D.1.4 MEETINGS
Pre-designated meetings included a pre-bid meeting held prior to bidding of the contract. Also, a
pre-construction meeting that can be held in conjunction with a resolution meeting after the
contract has been awarded, but prior to the start of construction activities.
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D.l.4.1 PRE-BID MEETING
The intent of this meeting is to discuss the QA plan and to resolve differences of opinion among
the various concerned parties before the project was let for bidding. Holding the pre-bid meeting
before formal construction bids are prepared can allow the companies bidding on the
construction to better understand the level of QA required on the project. Also, if the bidders
identify problems with the QA plan, they can be corrected early on in the process.
D.l.4.2 RESOLUTION MEETING
The objectives of the resolution meeting are to establish lines of communication, review
construction plans and specifications, emphasize the critical aspects of the project needed to
achieve proper quality, begin planning and coordination of tasks, and identify potential factors
that might cause difficulties or delays in construction. The meeting should be attended by
appropriate personnel including the project's design engineer, representatives of the general
contractor and major subcontractors, the QA engineer, and the QA certifying engineer.
The resolution meeting can cover the following activities:
An individual should be assigned to take minutes.
Individuals can be introduced to one another along with their project responsibilities (or
potential responsibilities) can be identified.
Copies of the project plans and specifications should be made available for group
discussion.
The QA plan can be distributed.
Copies of any special permit restrictions that are relevant to construction or QA should be
distributed.
The plans and specifications should be described, along with unique design features (so
the contractors would understand the rationale behind the general design), potential
construction problems, and allow for questions from any of the parties concerning the
construction.
The QA plan should be reviewed and discussed, with the QA engineer and QA certifying
engineer outlining their expectations and identifying the most critical components of their
proj ect parti ci pati on.
Procedures for Manufacturing Quality Control (MQC) and Construction Quality Control
(CQC) proposed by installers and contractors should be reviewed and discussed.
Corrective actions to resolve potential construction problems should be discussed.
Procedures for documentation and distribution of documents should be discussed.
Each organization's responsibility, authority, and lines of communication should be
discussed.
Suggested modifications to the QA plan that would improve quality management on the
project should be solicited.
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Climatic variables (e.g., precipitation, wind, temperature) that might affect the
construction schedule should be discussed.
Familiarizing all project participants with inspection and testing procedures and the criteria for
pass/fail decisions (including the resolution of test data outliers) is a key objective of this
meeting. Additionally, it is imperative that all parties understand the key problems QA
personnel have identified and that each party fully understands their roles and responsibilities
and the procedures regarding problem resolution.
D.l.4.3 PRE-CONSTRUCTION MEETING
The pre-construction meeting can be held in conjunction with the resolution meeting if desired.
The meetings should be scheduled after the general construction contracts have been awarded
and the major subcontractors and material suppliers have been established. The purpose of the
pre-construction meeting is to review the details of the QA plan, to ensure that the responsibility
and authority of each individual is clearly understood, to reach agreement on the established
procedures to resolve construction problems, and to establish a foundation of cooperation in
quality management. The pre-construction meeting should be attended by the design engineer,
representatives of the general contractor and major subcontractors, the QA engineer, and the QA
certifying engineer.
The pre-construction meeting should include the following activities:
Assignment of an individual to take meeting minutes.
Introduce parties and identify their responsibilities and authority.
Distribute the QA plan, identify any revisions made after the resolution meeting, and
answer any questions about the Q A plan, procedures, or related documentation.
Discuss lines of project communication.
Discuss reporting procedures, distribution of documents, the schedule for routine project
meetings, and resolution of construction problems.
Review site requirements and logistics, including safety procedures.
Review the project design, discuss the most critical construction aspects, and discuss
scheduling and sequencing issues.
Discuss MQC procedures to be employed by the fabricators contracted to the general
contractor.
Discuss CQC procedures to be employed by the installer or contractor.
Compile a list of action items requiring resolution and assign responsibilities for these
items.
D.l.4.4 PROGRESS MEETINGS
Weekly progress meetings should be held at the job site. At times, additional progress meetings
can be called at the discretion of the Construction Quality Assurance engineer. Meeting
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attendees should be those involved in the specific issues being discussed. These meetings should
be helpful in maintaining lines of communication, resolving problems soon after they are
developed, identifying action items, and improving overall quality management. The QA
engineer or his/her designated representative should be present at all meetings.
D.1.5 SAMPLE CUSTODY
All samples should be identified and described in the QA plan. Whenever a sample is taken, a
chain of custody record should be made for that sample. If the sample is transferred to another
individual or laboratory, records of the transfer should be established so that chain of custody can
be traced. The purpose for the records of sample custody is to assist in tracing the cause of
anomalous test results or other testing problems, and to minimize the potential for accidental
sample loss.
D.1.6 WEATHER
Weather can play a significant factor on construction activities and material placement during
cover installation. The contractor or installer is responsible for complying with the contract plans
and specifications (along with the MQC/CQC plans for the various components of the cover
system). Specifications should include restrictions on weather conditions for certain construction
activities such as soil placement where dry soil placement is critical. The contractor or installer
is responsible for insuring that these weather restrictions are observed during construction.
D.1.7 WORK STOPPAGES
Unexpected work stoppages can result from a variety of causes. The QA engineer should be
careful during any work stoppages to determine: (1) whether in-place materials were covered and
protected from damage, (2) whether partially covered materials were adequately protected, and
(3) whether manufactured materials were properly stored and properly or adequately protected
from the elements. In essence, the cessation of construction during work stoppages does not
mean that QA inspection and documentation temporarily ceases.
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EPA Region 9 Waste Management Division contact information:
Office Manager
U.S. Environmental Protection Agency
Office of Pollution Prevention and Solid Waste
75 Hawthorne Street
Mail Code WST-7
San Francisco, CA 94105
Email: baker.michelle@epa.gov
Webpage: http://www.epa.gov/region9/waste/tribal/index.html
EPA Region 9, Waste Management Division Office Receptionist
415-947-8708
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