United States
Environmental Protection
Agency
Office of Water and
Waste Management
Washington DC 2046O
SW-867
September 1980
C3
. r»-
cxEPA
Evaluating Cover
Systems for Solid
and Hazardous Waste
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EVALUATING COVER SYSTEMS FOR SOLID AND HAZARDOUS WASTE
by
R. J. Lutton
U. S. Army Engineer Waterways Experiment Station
Vicksburg, Mississippi 39180
Interagency Agreement No. EPA-IAG-D7-01097
Project Officer
Robert E. Landreth
Solid and Hazardous Waste Research Division
Municipal Environmental Research Laboratory
Cincinnati, Ohio 45268
MUNICIPAL ENVIRONMENTAL RESEARCH LABORATORY
OFFICE OF RESEARCH AND DEVELOPMENT
U. S. ENVIRONMENTAL PROTECTION AGENCY
CINCINNATI, OHIO 45268
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DISCLAIMER
This report has been reviewed by the Municipal Environmental Research
Laboratory, U. S. Environmental Protection Agency and approved for publica-
tion. Approval does not signify that the contents necessarily reflect the
views and policies of the U. S. Environmental Protection Agency, nor does
mention of trade names or commercial products constitute endorsement or
recommendation for use.
ii
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Permit Writers Guidance Manual/Technical Resource Document
Preface
The land disposal of hazardous waste is subject to the requirements
of Subtitle C of the Resource Conservation and Recovery Act of 1976.
This Act requires that the treatment, storage, or disposal of hazardous
wastes after November 19, 1980, be carried out in accordance with a
permit. The one exception to this rule is that facilities in existence
as of November 19, 1980 may continue operations until final administrative
dispostion is made of the permit application (providing that the facility
complies with the Interim Status Standards for disposers of hazardous
waste in 40 CFR Part 265). Owners or operators of new facilities must
apply for and receive a permit before beginning operation of such a
facility.
The Interim Status Standards (40 CFR Part 265) and some of the
administrative portions of the Permit Standards (40 CFR Part 264) were
published by EPA in the Federal Register on May 19, 1980. EPA will soon
publish technical permit standards in Part 264 for hazardous waste
disposal facilities. These regulations will ensure the protection of
human health and the environment by requiring evaluations of hazardous
waste management facilities in terms of both site-specific factors and
the nature of the waste that the facility will manage.
The permit official must review and evaluate permit applications to
determine whether the proposed objectives, design, and operation of a
land disposal facility will be in compliance with all applicable pro-
visions of the regulations (40 CFR 264).
EPA is preparing two types of documents for permit officials
responsible for hazardous waste landfills, surface impoundments, and
land treatment facilities: Permit Writers Guidance Manuals and Technical
Resource Documents. The Permit Writers Guidance Manuals provide guidance
for conducting the review and evaluation of a permit application for
site-specific control objectives and designs. The Technical Resource
Documents support the Permit Writers Guidance Manuals in certain areas
(i.e. liners, leachate management, closure, covers, water balance) by
describing current technologies and methods for evaluating the performance
of the applicant's design. The information and guidance presented in
these manuals constitute a suggested approach for review and evaluation
based on best engineering judgments. There may be alternative and
equivalent methods for conducting the review and evaluation. However,
-------
if the results of these methods differ from those of the EPA method,
their validity may have to be validated by the applicant.
In reviewing and evaluating the permit application, the permit
official must make all decisions in a well defined and well documented
manner. Once an initial decision is made to issue or deny the permit,
the Subtitle C regulations (40 CFR 124.6, 124.7 and 124.8) require
preparation of either a statement of basis or a fact sheet that discusses
the reasons behind the decision. The statement of basis or fact sheet
then becomes part of the permit review process specified in 40 CRF
124.6-124.20.
These manuals are intended to assist the permit official in arriving
at a logical, well-defined, and well-documented decision. Checklists and
logic flow diagrams are provided throughout the manuals to ensure that
necessary factors are considered in the decision process. Technical data
are presented to enable the permit official to identify proposed designs
that may require more detailed analysis because of a deviation from suggested
practices. The technical data are not meant to provide rigid guidelines for
arriving at a decision. References are cited throughout the manuals to pro-
vide further guidance for the permit official when necessary.
IV
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FOREWORD
The Environmental Protection Agency was created because of increasing
public and governmental concern about the dangers of pollution to the health
and welfare of the American people. Noxious air, foul water, and spoiled
land are tragic testimony to the deterioration of our natural environment.
The complexity of the environment and the interplay between its components
require a concentrated and integrated attack on the problem.
Research and development is the first necessary step in problem solution;
it involves defining the problem, measuring its impact, and searching for
solutions. The Municipal Environmental Research Laboratory develops new and
improved technology and systems to prevent, treat, and manage wastewater and
the solid and hazardous waste pollutant discharges from municipal and community
sources; to preserve and treat public drinking water supplies; and to minimize
the adverse economic, social, health and aesthetic effects of pollution. This
publication is one of the products of that researcha vital communications
link between the researcher and the user community.
This report is to be used as a tool for evaluating various landfill
cover systems. This data information can be used in determining cover design
requirements for compliance with the current regulations.
Francis T. Mayo, Director
Municipal Environmental Research
Laboratory
v
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ABSTRACT
A critical part of the sequence of designing, constructing, and
maintaining an effective cover over solid and hazardous waste is the
evaluation of engineering plans. Such evaluation is an important function
of regulating agencies, and accompanying documentation can form one basis
for issuing or denying a permit to the owner/operator of the waste disposal
facility. This manual describes 36 steps in evaluation of plans submitted
for approval. Generally, the evaluator considers available soils, site
conditions, details of cover design, and post-closure maintenance and
contingencies.
This report was submitted in fulfillment of Phase III of Interagency
Agreement No. EPA-IAG-D7-01097 between the U. S. Environmental Protection
Agency and the U. S. Army Engineer Waterways Experiment Station (WES).
Work for this manual was conducted during the period December 1979 to
July 1980, and work was completed in July 1980. Dr. R. J. Lutton,
Geotechnical Laboratory, WES, was principal investigator and author.
Director of WES during the work period was COL Nelson P. Conover, CE.
Technical Director was Mr. F. R. Brown.
VI
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CONTENTS
Preface iii
Foreword v
Abstract vi
Metric Conversion Table viii
1. Introduction 1
Purpose and scope 1
Procedures of evaluation 1
2. Examination of Data 3
Test data review procedure (Steps 1-3) 3
Topographical data review procedure (Step 4) 13
Climatological data review procedure (Steps 5-7) .... 16
3. Steps in Evaluation 20
Cover composition evaluation procedure (Step 8) .... 20
Thickness evaluation procedure (Steps 9-13) 24
Placement evaluation procedure (Steps 14-17) 28
Configuration evaluation procedure (Steps 18-19) .... 36
Drainage evaluation procedure (Steps 20-22) 43
Vegetation evaluation procedure (Steps 23-29) 45
4. Post-closure Plan 52
Maintenance evaluation procedure (Steps 30-32) 52
Contingency plan evaluation procedure (Steps 33-36). . . 54
References 56
vii
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METRIC CONVERSION TABLE
Multiply
By
To Obtain
acres
cubic feet per second
degrees (angle)
feet
gallons (U. S. liquid)
inches
pounds (mass)
pounds (mass) per acre
pounds (mass) per cubic foot
square feet
tons (short, mass)
tons (mass) per acre
4046.856
0.02831685
0.01745329
0.3048
0.003785412
0.0254
0.4535924
0.1120851
16.01846
0.09290304
907.1847
0.2241702
square meters
cubic meters per second
radians
meters
cubic meters
meters
kilograms
grams per square meter
kilograms per cubic meter
square meters
kilograms
kilograms per square meter
viii
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SECTION 1
INTRODUCTION
Growing concern for the preservation of a healthful environment, now
and in the future, was the major impetus to the enactment of Public Law
94-580, "Resource Conservation and Recovery Act of 1976" (21 October 1976).
An important part of solid and hazardous waste management is the regulatory
control exercised by the Environmental Protection Agency (EPA) regional
offices and corresponding agencies in state governments. In turn, a major
facet of this regulatory function is the evaluation of the adequacy of
closure covers over the wastes.
PURPOSE AND SCOPE
This manual presents a procedure for evaluating closure covers proposed
for solid and hazardous wastes. The manual is written principally for staff
members in the Regional EPA offices and/or state offices charged with evalua-
ting applications from owners/operators of solid and hazardous waste disposal
areas. All aspects of cover are addressed in sufficient detail to allow for
a complete evaluation of the entire cover system. For more details on the
subjects covered in this manual, the reader is referred to a recent report
emphasizing design and construction of covers which serves as the backup
document. -"
PROCEDURES OF EVALUATION
The evaluation of cover characteristics and design should be kept in
conformance to applicable regulations. The sequence of procedures is
outlined as follows:
1. Examine soil test data
2. Examine topography
3. Examine climate data
4. Evaluate composition
5. Evaluate thickness
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6. Evaluate placement
7. Evaluate configuration
8. Evaluate drainage
9. Evaluate vegetation
10. Evaluate post-closure maintenance
11. Evaluate contingencies plan
The first three procedures in the evaluation process (presented in
SECTION 2) constitute a careful review of materials and conditions at the
proposed or existing site under consideration. Procedures 4-9 outline
evaluations of the characteristics of the cover system within the con-
straints offered by review procedures 1-3. Procedures 10 and 11 evaluate
the adequacy of the cover system and post-closure plan for future conditions,
both expected and unexpected.
Opportunity will be provided in the evaluation scheme in Section 2 for
consideration of departures from more or less conventional designs. Such
an option is specifically intended for instances where the owner/operator, for
one reason or another, proposes a design based on a special engineering study
or calculations. In evaluating such departures in design, the permitting
authority will find useful the additional technical guidance in Reference 1
or may enlist an experienced consulting firm or other source of technical
assistance to conduct the evaluation.
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SECTION 2
EXAMINATION OF DATA
TEST DATA REVIEW PROCEDURE
Sampling and testing are intended to characterize and delineate all
important soil types, and therefore should be under the direction of an
experienced engineer or geologist having competence in the field of soil
mechanics. Field sampling data and laboratory test results should be
thorough and according to widely accepted procedures. Table 1 summarizes
the tests that may be necessary.
Review Field Sampling of Soils
The objective of Step 1* is to establish that the applicant has satis-
factorily documented the physical characteristics, volume, and spatial
distribution of each of the major, distinguishable soil types to be used as
cover. These data, obtained from test pits or borings in the borrow area,
must be accurate since the adequacy of the cover system and the feasibility
of the covering operation are directly affected.
The evaluation is accomplished by examining a map of soil sampling
locations along with some graphical or tabular presentation of the depths
and nature of the soils at each location. Soil types collected at each
location should be classified as described under Step 2. Soil type should
be identified at regular depth intervals even where the soil is obviously
uniform to the depth of interest. Changes in soil types should be located.
Much of the delineation of soil types is accomplished on the basis of
characteristics observed and used in the field, e.g. color and feel when
rubbed between fingers. Such field characteristics should be explained and
related to the traditional U. S. Department of Agriculture (USDA) soil classes
based on grain size (Figures 1 and 2) where reasonable. Characterization
in terras of the Unified Soil Classification System (USCS) (Figure 3) is
confirmed subsequently in laboratory testing (Step 2).
The owner/operator application should include a brief description of
the field sampling methods besides the observations. The traditional manner
of exploring soil to depths of more than a few feet is by soil boring but
trenching below ground surface or cleaning an existing bluff face or pit wall
*Step 1 may be unnecessary where the plan is to contract for the required
volumes of certain soil types delivered to the waste disposal site.
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TABLE 1. LABORATORY TEST METHODS FOR SOIL
Name of Test
Standard or
Preferred
Method*
Properties or
Parameters
Determined
Remarks/Special
Equipment
Requirements
Index and Classification Tests
Gradation Analysis
Percent Fines
Atterberg Limits
Specific Gravity
ASTM D421
D422
D2217
ASTM D1140
ASTM D423
D424
D427
ASTM D854
Soil Description ASTM D2488
Soil Classification ASTM D2487
Particle size
distribution
Percent of weight
of material finer
than No. 200 sieve
Plastic limit, liquid
limit, plasticity
index, shrinkage
factors
Specific gravity or
apparent specific
gravity of soil
solids
Description of soil
from visual-manual
examination
Unified soil classi-
fication
Boiling should
not be used for
de-airing
Moisture-Density Relations
Bulk Unit Weight
Water Content
Relative Density
Compaction
Reference 3
ASTM D2216
D2974
Reference 3
ASTM D698
(or 5- to
15-blow mod-
ification)
Bulk unit weight
(bulk density)
Water content as
percent of dry weight
Maximum and minimum
density of cohesion-
less soils
Optimum water and
maximum density
Modified test may
be substituted
for test with
vibratory table
Method for earth
and rock mixtures
is given in
Reference 3
(Continued)
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TABLE 1. (continued)
Standard or
Preferred
Name of Test Method*
Properties or
Parameters
Determined
Remarks /Special
Equipment
Requirements
Consolidation and Permeability
Consolidation
Permeability
ASTM D2435 One-dimensional
compressibility,
permeability of
cohesive soil
ASTM D2434 Permeability
Physical and Chemical Properties
Mineralogy
Reference 4 Identification
of minerals
Organic Content
Reference 5 Organic and
ASTM D2974 inorganic carbon
content as percent
of dry weight
Soluble salts
Pinhole Test
Reference 6
Concentration of
soluble salts in
soil pore water
Reference 7 Dispersion tendency
in cohesive soils
Requires X-ray
diffraction
apparatus. Dif-
ferential thermal
analysis apparatus
may also be used
Where organic
matter content
is critical,
D2974 results
should be
verified by
wet combustion
tests (Reference 5)
Significant in
evaluation of
potential erosion
or piping
Shear Strength and Deformability
Unconfined
Compression
ASTM D2166
Strength of cohesive
soil in uniaxial
compression
(Continued)
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TABLE 1. (continued)
Name of Test
Direct Shear,
Consolidated-
Drained
Standard or
Preferred
Method*
ASTM D3080
Properties or
Parameters
Determined
Cohesion and angle
of internal friction
under drained
conditions
Remarks/Special
Equipment
Requirements
Triaxial Compres-
sion, Unconsoli-
dated-Undrained
TriaxiaL Compres-
sion, Consolidated-
Undrained
Triaxial Compres-
sion, Consolidated-
Drained
ASTM D2850
Reference 3
Reference 3
Shear strength
parameters; cohesion
and angle of internal
friction for soils of
low permeability
Shear strength
parameters; cohesion
and angle of internal
friction for con-
solidated soil
Shear strength
parameters; cohesion
and angle of internal
friction, for long-
term loading
conditions
Circumferential
drains, if used,
should be slit to
avoid stiffening
test specimen
Circumferential
drains, if used,
should be slit to
avoid stiffening
test specimen
* ASTM standard methods are given in Reference 2.
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100
Sui'd- 70 to 005 mm dcomdet
Sill 0.0? to 000? mm diamelfr
Cluy (molln than 0002 mm. diameter
100 90 80 70 60 50 40 30 20 10
90
100
Figure 1. USDA textural classification chart.
Sieve openings in inches
U,S, Standard Sieve Numbers
3 2 l'/j 1 V, Vi '/. 4 10 20 40 60
200
Ml I I I II I Ml I MIT I ( I 1
USDA
uses
GRAVEL
SAND
Veryl 1
coars^-oarse| Med
GRAVEL
Coarse 1 Fine
,. IVerY
Flne J line
SILT
CLAY
SAND
Coarse
Medium I
Fine
SILT OR CLAY
1 1 i I i nnn MI i Hi
111 LJ
1 / 0.42 0.25 0.1 /
iii I i i
100 50
10
0.42 0.25 0.1 / 0.05 0.02 0.01 0.005
0.5 0.074
Grain size in Millimeters
0.001
Figure 2. Comparison of USCS and USDA particle-size scales.
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Major Divisions
1
J
£
d
B
fa
i!
h
8 v
°i
Vt
O
1
1
£
2
S
i
o
s!
1
i
i
c
7
7
t
!
«
4
1
<
J
*
\
{
i
]
i
j
2
vels
coarae fraction
. U sieve all*.
*ed as equivalent
is s~
3 **
6 i? ^ *
°- £S
Sands
Hore than half of coarse fractloo
is s^sXler thae Mo. U sieve site.
(ror visual classification, the l/<*
to the So. U
!!=
3SC
33
y ,
fl'*
fl o'*'
£>:>* vith
PltkC*
(Appreciable
asssount
of floes)
R *0
O -J
. ^1
i !i
m -1
t SR
J *> a
; 2*
S 3U
Highly Organic Soils
Croup
ymbola
3
CM
OP
QM
cc
su
8?
BM
SC
ML
CL
OL
W
CH
OB
Pt
Typical Kane*
U
Veil-graded gravels, gravel-sand aUcturea,
little or no fines.
Poorly graded gravels or gravel-sand alxtures
little or DO fine*.
Sllty gravel*, gravel-iand-sllt nixture.
Clayey gravels, gravel -aand-clay mixtures.
W«U- graded sand*, gravelly aanda. little or
DO floe*.
Poorly graded aandj or gravelly sands, llttl*
or no floe*.
Sllty sands, sand-lilt mixtures.
Clayey sands, *and-clay mixture*.
Inorganic silt* and very fine aaads, rock
flour, sllty or clayey fin* sand* or
clayey allts vlth light plasticity.
Inorganic clayi of lov to MllY* plasticity,
gravelly clays, aandy clay*, sllty clays,
lean clay*.
Organic silt* and organic *llty clayi of lov
plasticity.
Inorganic ailts, micaceous or diatomaceous
fine sandy or sllty soils, elastic silts.
Inorganic clay* of high plasticity, fat clay*.
Organic clay* of medium to high plasticity,
organic silt*.
Peat and other highly organic soils.
(Excluding p
and basing fr
actions on estliu
edures
han 3 in-
ted weights)
5
Vide range In grain slzea and substantial
amounts of all Intennedlate particle sites.
Predominantly one size or a range of sizes vlth
nf
Bonplastlc fines or fines vith low plasticity
(for Identification procedures see ML below).
Plastic fines (for Identification procedures
see CL below).
Wide range ID grain site and subst&ntlal aaounts
of all Intermediate particle cites.
Predominantly ooe site or a range of size*
vith soae intermediate size* Biasing.
Ronplastlc fine* or fines with low plasticity
(for Identification procedures see ML belov).
Plastic fine* (for Identification procedures
aee CL belov) .
Identification Procedures
on Traction Saaller than Ho. UO Sieve Size
Dry Strength
(Cniahlng
characteristics)
Hone to alight
Medium to high
Slight to
BttdlUS.
Slight to
edluv
High to very
high
Medlx* to high
Dilataocy
(React loo
to abaJting)
Quick tc alow
Hooe to very
lov
Slov
Blow to none
Kone
Rone to very
low
Toughness
(Consistency
near PL)
Itone
Medium
Slight
Slight to
nedi.ua
High
Sllgnt to
medium
Readily identified by color, .odor, spongy feel
and frequently by flbrou* texture.
(1, Sol la posoeaslng characteristics of two groups are designated by combinations of group symbols. Tor exaaplt CW-CC, veil-
graded gravel-sand nlxture vlth clay binder. (?) All sieve slzea on this chart are U. S. standard.
FIELD IDENTIFICATIOH PROCEDURES FOR FIHE-ORAIMED SOILS OR FRACTIOUS (MINUS HO. 1.0 SIEVE)
Screening Js not Intrndrd; simply remove by band *.he coarse particles Chat J.itrrfrre with testa.
Dij*tancy_J_r_e*ctipn to ahaAlng). After renovlng particles larger than No. I'D sieve alie, prepare a pat of moist soil with a volume
of about one-half cubic Inch. Add enough vater If necessary to make the soil soft but not sticky.
horizontally, striking vigorously against the other hand several times. A
ter on the surface of the pat which changes to a livery consistency anti becomes
Ingero, the vater and gloss disappear from the surface, the pat stiffens. &nd
pearanee of vater during shaking and of its disappearance during squeezing
n a soil.
tine', reaction whereas a plastic clay has no resctlon. Inorganic silts, such
eftctlon.
Place the pat In the open pain of one hand and shax
positive reaction consists of the appearance of »
glossy. When the sample Is squeezed between the
finally it crack* or crumbles. The rapidity of a
assist in identifying the character of the fines
Very fine clean sa/ids give the quickest and most di
as a typical rock flour, show a moderately quick
Dry Strength (crushing character.sllcs). After removing particles larger than Ho. ^0 sieve size, mold a pat of soil to the consis-
tency of putty, adding water If necessary. Allov the pat to dry completely by oven, \.\ir., or air-drying, and then test, its
Figure 3. Summary of the USC system.
(continued)
-------
Information Beq'-lred for
Describing Soils
6
For undisturbed soils add information
and dralrAfip sharacterlstlcs.
Give typical naae; ladlcate apprcx innate
percentages of sand and gravel, naxl-
aua size; angularity, surface condi-
tion, and hardness of the coarse
grains; loc*l or geologic naoe and
other pertloer.t descriptive Informa-
tion; and symbol in parentheaet.
Exanple :
Silty sand^ gravtUy; about 2Qll hard,
angular gravel particles 1/2-ic.
OMJClmiD size, rounded aad subangular
and grains, coarae to fine; about 1^%
conpla&tic flats vlth lov dry itrer.gth;
ve^l c cope c ted and BO let In place, al-
luvial sand; (SJl).
For undisturbed soils add infornatior.
OD structure, stratification, con-
sistency Jo uadl3turt>ed and re-
molded states, nolsture and drain-
age conditions.
Give typlcai nane; Indicate degree and
naxlaucD slie of coarse grains; color
in wet condition; odor, If ar.y; local
or geologic naoe &r.d other pertinent
descriptive Information; and symbol
lo parentheses.
Example :
Clayej slit, brovn; slightly plastic;
onail percentAge of fine sand;
numerous vertical root holes; firm
and dry In place; loess; (ML).
laboratory Classlf icatlor.
Criteria
7
§
9
I
a
a
a
e
c
tn
I
S
I
s
^
0 0 S
a =9
-.; I "
;. - s s
451 !
8*1 "1
^ r. a . . S ?
d -* *> K w e ~*
,. 5 *
sss *x*J
-o t " " W = v.
g« - *^ o
'H fc O T] M
i> c « ^ ^ c P
«*., S IIS
O »"
^|6 s5
sis § s*
?2s ^s
x§"s 5i*
s ?2
= 3?
C C b
5 & «
aa
C_^
^\^ Cc
Not net*. I
g Greater than *
^ all gnudatloa requirements for CW
Atterberg ;iclts belcv "A" iiM. Above A" line vith
or PI less than U pj betveen !i and *
are borderline cases
vlth PI greate
C.
Not Evetl
requirlr^ use of dual
r thar. ;
- Greater than 6
11 10
O ?
^ all gradation requiresetus for S1-*
Atterberg Halt* belov "A" line Abovr "A" line vtth
or PI less than U FI betwea 4 and 7
are borderline cases
rearing use of d'jal
Atterberg Halts above "A" line "ywc
vlth PI greater than 7
5o ) 1 1 > 1
w |
Coopa
Tou«
ring Soils at Equal
mess and Dry Stre.'if
i Increasing PLaati
| .__i- .: _::__
S 30 '
o -
10 - v
[ 7 1 1 ' ( ~^~ 1
,. ^%fCL-rtL%i^-ML
I S
0 ^'
Liquid Limit . ... -^'
fth Incrrsse ----- ..^£.
Sty Index ... . . . _^_. -
j - --- cu s*-- \- -
s
s
s -
jS .
S - i»
.. . . .
0 10 ' 20 p 10 50 60 70 80 90 100
UQLTD UXIT
PLASTIC XTf CRAFT
For laboratory classification of fine-grained aoils-
High dry atreng" h la character', si ic or .- ays of ',n*
A '.ypionl ;norRfl:ii silt pos
Toug h ae r, s (c j n r. i s t e no^
3i'fi-i!3-.e:j ;:|, ;-M bi- z; n-ni -. .' ; < :.'.... ,.')><-.- ',/jJ nl : >wt'.! : r ;.-!,-. v ..."-;. n-. ; '.-.re by t-vftpornt ior; - The-') '.he -j;-f.'\stfr. : r- --.>:;
out by hand on a r.noolh surface or between the pains into it '.;:reM ntout one-eighth ir.oh in .iiaseter. ?!:* t.'ircn.'. i ;. r);*:-.
folded sj'.d reroiled repeatedly. During this 3iar.: pulftl icr. Ll;e moisture c-cnter.t IP gradually reduccit nr.A ihc ;.;'-. -irsr:-. n:-.rf
finally lose^ ita plasticity, a.iJ crjables vhen the pins*, u- limit is rewched.
After the thread cruablcs, the pieces should be Itaj-ed together anJ n :ili»cht kr;e«^!ns sv-llo:; ro.':: IRUC* ;i:it:i l.'ic I-JT:;* (.-;;.=: 1
The to-jfjaer the tr.rt-ad near the ^iastic iisit ar,J the s'^irfrr tne '.unp when It finnl'.y ^r-.aiblfi , thv "on- i^iiT.t is (.» .''.;
..'a.' -.-lay '.-actior: in the soil, ^eaAfiess o.' tf;e :f:re«(! ' -he (-:«stic li.riT ir.,J -T^icX i.^ss .-if ,-^.crct^c ,'f '.?:<- J .«[» bei-.-v
plastic lifiit indlciite either inorgnnlc clfty of lov piAS'.inty. or n^vteriils suet: Bb kn.ill r.-ty;-»: ,-'.«ys n:;.l orKdnl,' cinys v
occxir bel«v the A-llne.
Figure 3. (continued)
-------
may be as effective and less costly where on-site equipment is sufficient.
Whatever the method, it should be documented in the application.
The evaluator must decide whether the arrangement and spacing of
samples have been adequate to delineate the vertical and lateral extent of
the major soil types. Where the evaluation indicates that sampling intervals
are too large, it may be necessary to require additional samples at inter-
mediate positions. One effective technique is to sample at fairly close
spacing along a single line across the borrow area. Elsewhere in the area
there may be a need for only a few additional borings to confirm that the
stratification (including thicknesses) along the cross section apply else-
where also. A grid pattern may also be definitive. The following example
helps to clarify Step 1.
Example: Suppose an application presents as an inclosure
the plan map in Figure 4. The sampling methods at the
three locations have been reviewed and found to be satis-
factory; a geological technician made depth measurements
and identified and sampled the soil types. The evaluator
observes that one of the three sampling locations is
distinct from the other two. The evaluator therefore
recommends that new sample locations be added to delineate
the extent of the CL soil more confidently since this soil
type is important in design of the particular cover.
o
2
4
j
j
6
8
10
B-1 B-2 B-3
BOUNDARY OF
BORROW AREA
CL
CL
CL
SW
200'
Figure 4. Hypothetical cover soil source.
Check Adequacy of Soil Testing Program
Step 2
Two major aspects of the testing program that need to be evaluated are
the selection of tests and the adequacy of testing facilities and personnel.
10
-------
Tests that might be expected or perhaps even specified as minimum requirements
for all diagnostic samples are as follows:
Grain-Size Distribution (Figure 5)
Percent Fines
Atterberg Limits
Soil Classification
Water Content
90
80
£70
m 60
cc
LU
z
u. 50
h-
2 40
CJ
cc
UJ <-,«
Q. 30
20
10
0
1(
r ' ~= -
' .
SANDY SILTY CLAY (CD
Centidlia, WA
W = in Ret
LL =
PI =
- 40.0%
= 21.0%
= 19.0%
^^^
^x
\
\
\
\
\
\
\
^^
30 10 1 0.1 0.01 0.0
GRAIN SIZE IN MILLIMETERS
Figure 5. Gradation of a landfill cover soil.
The tests may be required in duplicate (or more) for better representation
and checking. These tests are basically indexing tests but also useful for
establishing the uniformity or variability within individual soil types.
Other important tests are compaction (Figure 6) and permeability. Even one
of these additional tests or test series may be adequate to establish
characteristics of the unit as a whole provided that unit is relatively
uniform in its index properties.
The remaining soil tests (Table 1) are assigned only where special
problems of slope stability, consolidation, etc. are anticipated. The need
for these tests may not become apparent until after most of the routine
index testing has been accomplished, sometimes not until the critical review
by the evaluator. Nevertheless, the lack of information from special tests
may occasionally constitute a basis for delaying a permit application.
11
-------
100
I I I I I
SANDY SILTY CLAY (CD
CENTRALIA, WASHINGTON
ZERO AIR
VOID CURVE
OPTIMUM WATER CONTENT 22.2%
MAXIMUM DRY DENSITY 96.7 PCF
93
19 20 21 22 23 24 25 26
WATER CONTENT, PERCENT OF DRY WEIGHT
Figure 6. Standard compaction test results with landfill
cover soil.l
Example: In reviewing a permit application an evaluator
finds that a county soil survey report has been used as
the basis for characterizing the soil at the proposed
borrow area. The applicant has used Atterberg limits,
classification, and grain-size distribution data from
the report for type Grenada 6 soil which has been mapped
over 36 percent of the county and specifically is shown
as underlying the borrow area. After careful considera-
tion, the evaluator requests that several deep soil
boring samples from the borrow area be tested at a quali-
fied testing laboratory to verify or reject the suit-
ability of the data from the general county report for
cover design. These samples will also serve to show how
well the county survey of surficial agricultural soils
represents the soils at depths below a few feet which,
of necessity, will contribute to total cover soil volume.
Check Soil Volumes Available
Step 3
At some stage, not necessarily when the site or borrow area is sampled
and tested, the sufficiency of cover soil volume should be evaluated.
12
-------
Accurate volume calculations depend upon accurate measurements of soil thick-
nesses and areas. Accordingly, the evaluator may recommend additional
sampling locations, not only for a better fix on soil indices and properties
but to allow a better calculation of the volumes. Where the data in the
application have shown a uniformity of soil type, it may only be necessary
to check thicknesses rather than to sample and test also. The following
example illustrates the situation, but also see the example under Step 1.
Example: An applicant has submitted the information shown
in Figure 7 as a basis for his estimates of volumes of soil
types available for use as cover. The evaluator reasons that
there is a possibility of a sizable overestimation of
suitable soils available to complete the closure since
variations of layer thicknesses between the existing
sample locations are a distinct possibility (shown by
dashed line in the figure). In this hypothetical case,
the evaluator chooses to accept the estimated volumes
on the basis of observations he has made in a field
inspection and after consultation with a staff geologist.
An important factor in checking volumes available can be the bulking
factor. Some natural soils, particularly those at depth, have a relatively
high unit weight in situ. After excavation, working, and placement as cover
over solid waste, these soils will have experienced a reduction in unit
weight, i.e., a bulking effect, and available volumes tend to be under-
estimated. In contrast, other soils, particularly those near the surface,
have a relatively low unit weight in situ so that available volumes
are easily overestimated. The evaluator should carefully check the basis
for any bulking factor where soil is in short supply.
TOPOGRAPHICAL DATA REVIEW PROCEDURE
Examine Configuration and Topography Step 4
Next the surface configuration of the cover is examined to assure that
evaluations can be made in regard to slope stability, water erosion, and wind
erosion. Most engineered fills for highways, foundations, and so forth are
designed on thr basis of accurate topography or multiple cross sections, and
the evaluator may reasonably expect some such basic data to accompany the
closure plan. Otherwise, the justification for omitting such basic data
should be convincingly presented in the application or be self evident.
One basic form of data presentation is with cross sections through
the cover extending across the site (see Step 1). Cross sections should
show thickness of the closure cover and solid waste and the limits of natural
soil previously excavated for use as cover. Besides being useful for
engineering design and for evaluation of the design, cross sections are
potentially useful for monitoring changes in configuration that may take
place as a result of settlement in the long term. Preparation of cross
sections is well within the capability of most organizations engaged in
construction and can reasonably be expected as a part of an application.
13
-------
2OO FEET
SP
CH ~~ -
X
V
CL"
SP CL
^'"'
CH
ML
**~SP
-^''
f'-'
CH
"ML ~~[
CL^. ^ -* ~" '
CH
ML
CH
Figure 7. Hypothetical cover soil volume data.
-------
A set of cross sections, often parallel to one another, can be highly
useful. Ordinarily the line of section (the surface trace of the cross
section) should trend downslope. Since many solid waste landfills will be
completed with a somewhat irregular surface configuration approaching natural
hills and swales, it may be necessary for the cross sections to be oblique
to one another rather than parallel. About the only criterion for evaluating
sufficiency in the number of cross sections is whether they present the
important aspects of the surface form, closure cover, and underlying solid
waste.
Example: Suppose that the configuration of a solid waste
landfill is as shown in Figure 8. The owner/operator of
the landfill is seeking permission to place final cover
and move his current operations to an adjacent site. He
has supplied the sketch of the site and the surveyed cross
section as the only graphical information of the actual
layout at the site. In his evaluation, the staff member
of the permitting authority feels there is insufficient
data on the existing configuration, i.e. the base on which
cover will be placed, and he requires the applicant to
provide another cross section based on field measurements
across the west side. The evaluator has reasoned that the
west edge of the landfill near the drainageway is steeper
and otherwise distinct from the large open side on the
south and therefore should be represented accurately and
separately in cross section for special examination.
SURVEY POINTS ON
EXISTING SURFACE
100 FEET
Figure 8. Hypothetical landfill configuration,
15
-------
CLIMATOLOGICAL DATA REVIEW PROCEDURE
Examine Precipitation Records
Step 5
The application should include data on the precipitation to be expected
at the site. A useful record typically gives average amounts for a period
of at least several years in the past, e.g. the average monthly precipita-
tions from the last 20 years or thereabout. Average data can be supplemented
with typical records of rainfall on a daily or even hourly basis for a
better picture of rainfall distribution in detail. The source of all
climatological data should be given also so that verifications can be made.
Figure 9 is a map of average annual precipitation that the evaluator can
use to check roughly the expected annual precipitation provided by the
applicant. Similar information is available for Alaska and Hawaii. In
some mountainous or coastal regions the average rainfall can vary over
short distances, and special care must be exercised in evaluation as
illustrated by the following example.
Figure 9. Average annual precipitation in inches (US Dept of Agriculture)
Example: Precipitation records provided in the permit
application concerning a landfill for a city in the Pacific
Northwest are those compiled from the downtown weather
station. The evaluator recognizes that there is a
difference in the weather at the downtown location (near
16
-------
sea level) and the weather at the landfill which is
located in foothills at the far end of the same county.
Therefore, he requests more representative data or
conclusive evidence that any departures will be on the
conservative side.
Examine Evapotranspiration Estimates
Step 6
Since evapotranspiration operates in an important manner to remove
moisture from the cover, it must be regarded as a major factor in cover
design. Therefore, an applicant should include in documentation an accurate
estimate of monthly evapotranspiration as evidence that this factor has been
included in the design. The source of information should be included also.
Where the evapotranspiration data have been derived through calculations from
other parameters, the calculations should be included and explained, and
references should be made to original sources. Figure 10 is a map of average
annual lake evaporation over the contiguous United States which the evaluator
can use to check roughly the expected annual evapotranspiration. Evapo-
transpiration approximately equals lake evaporation which is about 0.7 x pan
evaporation.
Figure 10. Average annual lake evaporation in inches,
according to the National Weather Service.
17
-------
Examine Design Storms
Closure covers should be designed not only for average
precipitation but also for high rates over short durations. Such information
is readily available in the form of design storms for any locality and it is
reasonable to expect that the documentation accompanying an application recog-
nize several extreme rainfalls for recurrence intervals of possible interest.
For an average size landfill a 1-hour storm and storms of longer duration are
of typical interest. The recurrence interval would likely be 10 or 20 years
but the applicant should present reasons for choosing specific intervals and
storm durations. Figure 11 is an example of summary information available
to the evaluator for checking design storm amounts supplied in an application.
Figure 11. Ten-year 1-hour rainfall in inches (US Weather Bureau)
A sequel to the presentation of design storm data is the calculation of
flood discharges for ditches and other elements of the drainage system. The
calculation in simplest form utilizes the rational equation:
CR01A
18
-------
where Q = peak discharge, cubic feet/second
C = runoff coefficient
i = rainfall intensity, inches//hour
A = area of basin, acres
The formula above incorporates the approximation that 1 inch/hour/acre =
1 cubic foot/second. Roughly approximated, the CRO for vegetated clayey
soils on flats and slopes are about 0.5 and 0.7 respectively and for
vegetated sandy soils on flats and slopes are about 0.2 and 0.4.
19
-------
SECTION 3
STEPS IN EVALUATION
Steps in this section differ from those in Section 2 by involving actual
evaluation of the designs and judgments submitted by the applicant rather than
just the examination and ordering of basic data.
COVER COMPOSITION EVALUATION PROCEDURE
The basis for evaluating the composition of the cover is the collection
of data on quantities and descriptions supplied with the application.
Evaluate Composition Step 8
Referring to Table 2, the evaluator should check the soil composition
for suitability as cover by establishing the soil's strengths and deficiencies
in a general way. Where a soil is rated IV or higher, look for special design
features to compensate for deficiencies (e.g., multilayering to supplement a
vulnerable soil with other types). Higher rating numbers tend to indicate
greater need for special features. There is need, of course, to exercise
good judgment when applying a somewhat subjective ranking as that in the
table.
In the particularly important function of minimizing infiltration, it
may be necessary to reject a simple cover design of one layer and require
inclusion of a clay soil layer or other barrier. This necessity may arise
where the dominant soil proposed as cover is:
a. Designated GW, GP, or SP by testing (see Figure 3)
b. Dispersive and therefore possibly subject to internal erosion (see
Reference 1)
c. Insufficient in volume for cover design
Other options may be to import a more suitable soil type or in some way to
improve characteristics by additional treatments.
Example: According to the testing results accompanying
the permit application, cover at a solid waste disposal
site will consist of gravelly sand classified SW according
to the USCS. The permitting authority has previously
assigned a high priority to impeding water percolation
into the solid waste. The evaluator, therefore, notifies
20
-------
TABLE 2. RANKING OF USCS SOIL TYPES ACCORDING TO PERFORMANCE OF COVER FUNCTIONS
Trafficability Water Percolation (i.-i:» X:,-r:itioii
USCS
Symbol
CW
GP
GM
GC
SW
SP
SM
SC
ML
Typical Soils
Go-No Go Stickiness
(PC! Value)* (Clay, 7,)
We 11 -graded gravels, gravel-sand
mixtures, little or no fines
Poorly graded gravels, gravel-
sand mixtures, little or no
fines
Silty gravels, gravel-sand-silt
mixtures
Clayey gravels, gravel-sand-clay
mixtures
Well-graded sands, gravelly
sands, little or no fines
Poorly graded sands, gravelly
sands, little or no fines
Silty sands, sand-silt mixtures
Clayey sands, sand-clay mixtures
Inorganic silts and very fine
I
( >200 )
I
(>200)
III
(177)
V
(150)
I
(>200)
I
(>200)
II
(179)
IV
(157)
IX
sands, rock flour, silty or (lOU)
I
(0-5)
I
(0-5)
III
(0-20)
VI
(10-50)
II
(0-10)
II
(0-10)
IV
(0-20)
VII
(10-50)
V
(0-20)
clayey fine sands, or clayey
silts with slight plasticity
CL
OL
MH
CH
OH
Inorganic clays of low to
plasticity, gravelly clays
sandy clays, silty clays,
clays
Organic silts and organic
clays of low plasticity
Inorganic silts, micaceous
diatociaceous fine sandy or
soils, elastic silts
Inorganic clays of high
plasticity, fat clays
Organic clays of medium to
plasticity, organic silts
medium
,
lean
silty
or
silty
high
VII
(111)
X
(61.)
VIII
(107)
VI
(H.5)
XI
(62)
VIII
(10-50)
V
(0-20)
IX
(50-100)
X
(50-100)
SJ ipperiness Impede Assist inpcau A::., ijt
(Sand-Gravel, %) (> , cir./s)» (:-:, cn/:;)» (ll., c:-;)» (H., c.-,)»
I y
(95-100) do"'2) m
I XII
(95-100) do"1)
III VII . VI
(60-95) (5 x 10"")
V V. VIII
(50-90) (10"') g
II IX IV a
(95-100) (ID"'1) o
o
t.
II XI II n.
(95-100) (5 x 10 ) £
IV VIII v *
(60-95) (10"-j) i.
o
4)
vi vi vii a
(50-90) (2 x 10 ') ~
o
VII IV,. IX '
(0-60) (10"') a
tn
4;
3
CO
VIII II . XI >
(0-55) (3 x 10"°) *
{'-
m
VII
(0-60)
IX III X
(0-50) (10 1
X I XII
(0-50) (io"y)
_
(6)
ix i:
VII IV
(6U)
IV VI:
VI II HI -2
(60) a
ti
vii ;v 5
in
a
0
VI V o
(112) g
V VI
i,
O
in vin S
(130) «
S
cC
"*
11 IX "'
(idO) 4,
§
to
I X
(200-i.00+)
Pt
Peat and other highly organic
soils
XII
(continued)
-------
TABLE 2. (continued)
N3
tsj
Ero.
USCS Fire Water
Symbol Resistance (K- Factor)*
GW
GP
GM
GC
SW
SP J
2
t.
SM j!
"
s
sc ^
o
5
ML "
m
CL I
tn
OL
MH
CH
OH
Pt
I
(< -05)
I
-
IV
Ill
II
(.05)
II
VI
(-12-. 27)
VII
(-1U-.27)
XIII
(.60)
XII
(.28-. 1.8)
XI
(.21-. 29)
X
(.25)
IX
( .13-. 29)
VIII
V
(.13)
;ion Control
Reduce
Wind Dust Fast Freeze
(Sand-Gravel, %1 Control (H , en}"
I
(95-100)
I
(95-100)
III
(60-95)
V o
(50-90) 5
§
II
(95-100) |
m
ii Z
(95-100) u
a
e
iv S
(60-95) ..
S
VI ra
(50-90) "
in
V
vii 3
(0-60) ?
T3
VIII §
(0-55) «>
c
VII 5
(0-60) S,
V
IX §
(0-50) M
X
(0-50)
X
IX
VII
IV
VIII
VII
VI
V
III
II
I
Freeze Action
Saturation
(Heave, ran/day)
I
(0.1-3)
I
(0.1-3)
IV
(O.li-i.)
VII
(1-8)
II
(0.2-2)
II
(0.2-2)
V
(0.2-7)
VI
(1-7)
X
(2-27)
VIII
(1-6)
VIII
IX
Ill
(0.8)
Crack
Resistance
( Expansion, %}
I
(0)
I
(0)
III
V
I
(0)
I
(0)
II
IV
VI
VIII
(1-10)
VII
IX
X
(>10)
IX
(continued)
-------
TABLE 2. (continued)
uses
Symbol
Side Slope
Stability
Seepage
Drainage
Discourage
Burrovinc
Irapede
Vector
r-r.ergence
Discourage
Birds
Support
Vegetation
Future U:;e
Natural Koundat ic:;
CW
GP
GM
GC
SW
SP
SM
SC
vni
TX
iA
VII
iv
IX
IX
II
10
ML
VI
CL
OL
a
>
a
in
VI
viz
IV
MH
I
w
o
CO
ii
IV
CH
VIII
OH
VIII
Pt
III
* RCI is rating cone index, k is coefficient of permeability, H is capillary head, and K-Factor is the soil erodibility factor.
The ratings I to XIII are for best through poorest in performing the specified cover function.
-------
the applicant that the SW soil (well graded sand) is
unacceptable (ranked IX in Table 2) in a single-layer
configuration and that it will be rejected unless a
layered system with a barrier layer is incorporated.
Example: The applicant at a site has proposed to use a
clayey silt for closure cover. The applicant had previously
been asked to obtain at his own expense a series of tests
on the soil to determine its tendency towards dispersion.
The area has a high rainfall, and its low topography can
conceivably cause a detention of runoff with increased
opportunity for infiltration. Internal erosion that can
affect dispersive soils would conceivably lead to a
deterioration of the cover by migration of soil particles
into the solid waste below. The laboratory test report
in the second submittal of the application confirms
that the silty soil has a modest tendency for dispersion.
The evaluator concludes that inclusion of a clay barrier
is advisable. However, the evaluator goes on to explain
that other solutions to the potential problem may be inves-
tigated also since the applicant has indicated an interest
in treating the dispersive soils with lime in order to
flocculate clay particles and reduce their tendency towards
dispersion.
The susceptibility of particular soil types to erosion can also be
evaluated according to a useful erosion loss equation (see Step 18).
THICKNESS EVALUATION PROCEDURE
The evaluation of closure cover thickness is often of primary importance
and the evaluator should devote considerable attention to it. Thickness in
excess of a certain established minimum* may be governed by one or more of
the following factors:
a. Coverage
b. Infiltration
c. Gas migration
d. Trafficability and support requirements
e. Freeze/thaw or dry/soak effects
This list may be extended by addition of other factors of possible concern
such as:
*Miniraura cover thickness requirements vary from state to state according
to experience.
-------
f. Cracking (factors f,g,h,i are discussed in reference 1)
g. Differential settlement and offset
h. Membrane protection
i. Vegetative requirements
Evaluate coverage Step 9
The closure cover functions basically to cover solid waste completely,
and therefore, some guidance is in order to evaluate for factor a_ above.
A reasonable criterion of adequacy for coverage over irregular solid waste
can be offered as follows:
T >2R
where T is cover thickness and R is relief. The relief is defined for
this criterion as the vertical distance from high point to low point of irreg-
ularities on the top surface of the solid waste. The size of the area over
which this vertical distance should be measured corresponds roughly to the
size of the equipment used for placing closure cover. Where intermediate
size dozers are to be used, the area within which the relief is measured
would be on the order of 20 by 20 feet. In large covering operations where
pans or other large pieces of equipment are to be used, the area size could
be on the order of 50 feet across.
The applicant may choose to circumvent the requirement of increasing
thickness above the established minimum to compensate for relief by smoothing
the upper surface of solid waste. Where sand fill is abundantly available,
it can be mixed with heterogenous solid waste in roughly equal proportions
for a more workable material to achieve a smoother top surface. The sand-
waste mixture thus forms a buffer-*- that can improve the performance and
longevity of the cover placed above.
Evaluate Thickness for Infiltration Step 10
Logically, the next criterion to be examined in the evaluation concerns
infiltration, ]> above. Adequacy against infiltration can be evaluated by
use of a water balance technique in which input of water on a monthly or
daily basis is compared with expected losses from surface runoff and evapo-
transpiration. Excesses beyond storage capacity of the cover soil are
considered to pass through the cover as percolation. The evaluator is
referred to another manual" in which the details of a recommended computer-
ized procedure are outlined step by step.
For purposes of evaluating the thickness of the cover, a somewhat
abbreviated water balance technique may be useful also. This method has
been suggested for predicting percolation by EPA,9 and its utility in
evaluating or designing cover has been reviewed.1 The water balance
25
-------
technique serves to check the effect of increased thickness for providing
increased water storage in the cover soil and consequent decrease in
percolation. The example below illustrates the technique and its use.
Example: Using a 30-year climate record, the evaluatcr
analyzes the effectiveness of a 2-foot silty sand cover
with grass at Chippewa Falls, Wisconsin. Table 3 shows
the water balance tabulation. The average annual perco-
lation is calculated to be 3.88 inches. The evaluatcr
next expands this analysis to explore the effects of a
much thicker cover on percolation. The result is shown
in Table 4. A storage capacity of 8 inches (representing
greatly increased thickness) is substituted for the
storage of 1.05 inches used in Table 3. The overall
effect on cumulative percolation is small, with a reduc-
tion by only about 20 percent to an annual percolation
of 3.13 inches. His analysis indicates to the evaluator
that increasing cover thickness is not an efficient way
of reducing percolation in this area.
Evaluate Thickness for Gas Migration Step 11
Thickening the cover may be a direct and effective procedure for
reducing gas migration through the cover, especially to the extent that
increased thickness enhances maintenance of a high moisture content. The
technique is especially attractive for remedial work where problems are
localized. Increasing thickness of coarse-grained soils affects gas
discharge inversely. In fine-grained soils the open pore space necessary
for migration is at least intermittently blocked by the included pore water,
and the evaluator must consider this complication critically in arriving
at his recommendations.
Example: The cover proposed for a solid waste disposal
site in a high-rainfall area consists of a fine-grained
soil that basically functions to exclude most percolation.
Anticipating eventual problems with gas migration through
this cover, the evaluator considers recommending thickening
of the cover design. However, after careful consideration,
the evaluator concludes that adjustments of the thickness
will not have a dramatic effect because the soil usually
retains considerable moisture (depending on the complications
of rainfall history and evapotranspiration-'-) and is already
blocking most of the gas movement. The evaluator learns that
the applicant believes that thickening the cover to reduce
the remaining intermittent, uncontrolled gas discharge will
also not be cost-effective and, therefore, thickening
is not favored by the applicant. He then concentrates
his immediate attention on considering other options such
as gas vents though it may be necessary to return later to
the thickening technique despite its low cost-effectiveness.
26
-------
TABLE 3. MONTHLY WATER BALANCE ANALYSIS
IN INCHES FOR CHIPPEWA FALLS, WISCONSIN1
Parameter Jan Feb Mar Apr Hay Jun Jul Aug Sep Oct i.'ov Dec Ann.
Average Precipitation 0.39+ 0.71 + 0.77* 0.67* 1.00* L.0~
(P) 0.77* 2-55 3.73 '..19 3.65 3.56 3.37 2.0u 0.67* 2^.^3
Runoff (RO) 0.05 0.17 T.?li 0.27 0.2u 0.."3 0.2? 0.13 0.0'" 1.59
Moisture available for.
infiltration (l)
'0.00 0.00 0.72 2-38 3.1.9 3-92 3.^1 3.'?3 3-15 1.91 0.63 0.00 22.9"
(I - PET) 0.00 0.00 0.72 1.28 0.99 0.02 -1.19-0.67 0.^5 0.71 0.63 0.00
(T. neR (I - PET)) (0) -1.19-1.86
1-°5 1'°3 1'05§ 1'°5 1"°5 i'°5 0'2T °'13 0'53 ]-°5 1'°5 °'05
(AST) 0.00 0.00 0.00 0.00 0.00 0.00 -0.73-0..lk +0.''5 +O.U7 O.OO 0.00
°-°° °-°° °-°° l'l° 2'5° 3"9° l'19 3-'T 2'7° '-20 °-°° °-°° 1O-°
Percolation (PRC) 0.00 0.00 0.72 1.28 0-99 0.02 0.00 0.00 0.00 0.21* 0.63 0.00 3.65
t Precipitation between November 16 and March 15 is listed as snow but is changed to runoff at
spring thaw.
* Precipitation in November and March is divided into half rain, half snow.
§ Water-holding capacity is assumed to be at maximum in March when snow melts.
TABLE 4. MONTHLY WATER BALANCE ANALYSIS IN INCHES WITH THICK COVER*
Parameter Jan Feb Mar Apr "ay Jun Jul Aug Sep Oct i!uv Dec Ann.
Average Precipitation 0.89t 0.71+ 0.77* 0.67* l.OOt 1. .0^
(P) 0.77* 2.55 3.73 <4.19 3.65 3.56 3.37 2.0t 0.67* 2'..53
Runoff (RO) 0.05 0.17 0.2". 0.27 0.2.4 0.23 0.22 0.13 O.Ofe 1.59
Moisture available for 0_OQ , , h ^ ,_91 fi Q ?2 ^
infiltration (I)
Potential evapotrans- Q 0_QO Q QQ itg0i,_00 ?.70 U20 0.00 0.00 20.00
piration (PET)
(I - PET) 0.00 0.00 0.72 1.28 0.99 0.02 -1.19-0.67 0.1.5 0.71 0.63 0.00
(£ neg (T - PET)) (0) -1.19-1.86
Soil moisture 8_QO 8_OQ g_00§ 8_QO Q^Q &^QQ 6_gQ 6_33 6_7g ?_Ug 8_OQ g_00
storage 1ST)
(AST) 0.00 0.00 0.00 0.00 0.00 0.00 -1.11-0.56 +0.145 +0.71 +0.51 0.00
ti n
Percolation (PRC) 0.00 0.00 0.72 1.28 0.99 0.02 0.00 0.00 0.00 0.00 0.12 0-00 3.13
* Compare with Table 3.
t Precipitation between November l6 and March 15 is listed as snow but is changed to runoff at
spring thaw.
* Precipitation in November and March is divided into half rain, half snow.
§ Water-holding capacity is assumed to be at maximum in March when snow melts.
27
-------
Evaluate Support Requirements Step 12
The low bearing capacity of some solid waste landfills can be circum-
vented by increasing soil thickness above waste. In this way the relatively
strong soil resists punching and rotational shear. The thickness of soil
should be at least 1.5 x the width of footings. However, any proposal to
superimpose buildings on the cover should receive particularly critical
reviews and would ordinarily be rejected for a hazardous waste site.
Past experience with buildings on landfills is replete with cases of
structural damage from differential settlement and unnecessary hazard
from accumulation of methane and other gases.
Consider Freeze/Thaw and Dry/Soak Effects Step 13
In cold regions of the country, special attention may need to be
directed to disturbing effects of freezing. Similarly in semiarid areas
subject to periods of sustained drying conditions, equal concern may be
warranted in regard to excessive drying and cracking. The reasons for
concern have been summarized elsewhere.1
The evaluator may check for adequacy of the cover thickness by use of
Figure 12 or similar summary. In case of a need for greater detail or in
locations of mountainous terrain where the depth of freezing can vary over
short distances, the evaluator should seek information on depth of freezing
from a local agricultural agency. The depth of drying to be expected over
extended droughty periods can similarly be estimated on the basis of
experience in the region.
Example: An applicant has proposed to use 3 feet of soil
in the northern Great Plains where the average annual
maximum depth of freezing is 3 feet. To avoid disturbance
of the cover to its full thickness the evaluator recommends
that cover thickness be increased to 4 feet.
Before requiring substantial modification by thickening the cover, the
evaluator would ordinarily obtain a consensus among selected local
engineers that the disturbance of the cover could be significant.
PLACEMENT EVALUATION PROCEDURE
After selection of the material and appropriate thickness for cover,
efforts should be directed to the most effective placement and treatment.
Cover can be improved in several ways as it is constructed. Materials may be
added for better gradation, hauling and spreading equipment can be operated
beneficially, and certain layering can be introduced.
Evaluate Cover Compaction Step 14
Some compaction is almost always accomplished during the spreading of
cover soil; and this densification is highly effective in producing benefits,
28
-------
Figure 12. Regional depth of frost penetration in inches.
11
principally increasing strength and reducing permeability. Figures 13 and 14
illustrate these effects and provide the evaluator some guidance on what can
be achieved. The laboratory compaction test provides a useful data base on
which the evaluator can judge the effects of compaction of the cover under
consideration. It has been found-'- that soil compacted routinely over soft
waste (municipal wastes) falls below standard compaction curves such as
obtained in ASTM D698 (Table 1). The differences in field compaction
results over spongy solid waste versus those over a hard base can be
compensated approximately by using laboratory test procedures with fewer
than the "standard" 25 blows of the compacting hammer. Keep in mind that
the objective of the laboratory tests is to model actual field compaction
of cover soil with dozers and other compacting equipment.
Approximate general guidance (Figure 15) has been derived regarding
the field compaction effort necessary in 6 to 12 inches of soil cover on
municipal solid waste. Field dry density of the cover can be predicted
from measured placement water contents by using laboratory compaction curves
at appropriately light compaction effort. For example, where a dozer raakes
four passes on the average, a 5-blow compaction curve should be determined
29
-------
45
40
v>
IK
U
at
C
L*STtC fines
a.js
POROSITY, n (fO* 6*2
MS 0* ffJK
KATIO. if OH 6 «
«**5 4404
20
100 110 120
DRY UNIT WEIGHT (y0), PCF
Figure 13. Relation of effective angle of internal
friction to dry unit weight (US Navy).
10"" 10
10 ° 10"5 10"
PERMEABILITY. CM;SEC
Figure 14. Coefficient of permeability of materials as affected
by degree of compaction.
30
-------
105
15 20 25
WATER CONTENT, 1, OF DRY WEIGHT
35
Figure 15. Schematic guidance for predicting cover compaction
results with intermediate-size dozers on municipal
solid waste using laboratory test results.
by laboratory testing and be used for predictions. The curves shown in
Figure 15 appear generally valid, but relations between field compaction
and laboratory curves should be determined site-specifically if cover
density data are deemed necessary;1 the evaluator may need to make this
judgment under Step 2. A reasonable goal for which one might strive,
particularly in the compaction of barrier layers, is 90 percent of maximum
dry density according to 5- or 15-blow compaction tests. On the other
hand, when compacting on a solid base, e.g., on a granular soil-like
solid waste, one might strive for 90 percent of maximum dry density by
standard 25-blow tests.
Example: In his second submission of an application,
an owner/operator has included results of 15-blow compaction
tests conducted on the cover soil by a certified testing
laboratory (Figure 16). It is claimed later that approxi-
mately 90 percent of maximum dry density will be achieved
31
-------
with six passes of the compacting equipment. The natural
water content is approximately 10 percent. The evaluator
notes that the cover soil is to be excavated and hauled and
placed directly. He therefore asks the applicant to
expand on his intentions as far as manipulating the
water content of the soil closer to optimum in order
to reasonably expect 90 percent of maximum dry density.
100
95
90
85
80
75
OPTIMUM WATER
CONTENT = 27%
10 15 20 25 30
WATER CONTENT. %
35
40
Figure 16, Hypothetical cover soil compaction.
Evaluate Internal Layering
Step 15
Layering is a promising technique for final solid waste cover. By
combining two or three distinct materials in layers (Figure 17) the designer
may mobilize favorable characteristics of each together at little extra
expense. The following descriptionsl should help to guide the evaluation
of layered cover designs.
The primary feature in layered systems is usually the barrier. This
layer functions to restrict passage of water or gas. Barrier layers are
almost always composed of clayey soil that has inherently low permeability;
USCS types CH, CL, and SC (Figure 3) are recommended. Soil barriers are
susceptible to deterioration by cracking when exposed at time surface, so
that a buffer layer above is recommended to protect the clayey soil from
excessive drying.
32
-------
LOAM IFOR VEGETATION)
oooooooooooooo
oooooooooooooooooo
ocoooooooooooooooo
oooooooooooooooooo
" oooooooooooooooooo
r'HANNFL) JOOOOOOOOCOOOOOOOO
^_nMINnJC.U_l jooOOOOOOOOOOOOOOO
LOAM:
7//////////, CL AY Vfwin7?//////////.
i i i 1 M 1 1 1 1 i i
SILT ( FILTER)
SAND (BUFFER)
Figure 17. Typical layered cover systems.
Synthetic membranes of butyl or neoprene rubber, hypalon, polyolefin,
polyvinyl chloride, etc. may be considered in place of soil barriers.
Usually a sheet thickness of at least 20 mils is required. Some membranes
should be spread carefully over a smooth base to lie in a relaxed state
or a 5-percent slack may be necessary; usually the manufacturers provide
directions. Soils immediately above and below a membrane can constitute
critical components of the layered cover since irregularities and hard
pieces impinging on the membrane can cause damage, particularly during
subsequent compaction. Therefore, the application should address
thoroughly the question of preserving the integrity of the impermeable
membrane during construction. Manufacturer's recommendations for splicing
the membrane in the field should be followed and should be detailed in the
application. Provide a trench at least 8 inches deep or other anchorage
at the top of any slope. The evaluation of synthetic membranes in layered
cover systems may benefit from related guidance on basal liner systems
presented in another manual; particularly in regard to reactivity between
waste and membrane.
Barrier layers may also be constructed by adding certain additives or
cements to the available soil. Addition of bentonite clay is a proven means
33
-------
of reducing permeability, but homogenizing the mixture can present
difficulties and may need to be confirmed by laboratory tests, post-
placement examination, or other means identified in the permit
application. Other additions to soil, such as lime, portland cement, and
bituminous cement, may require an even more conservative stance on the
part of the evaluator since experiences with these materials in layered
covers are quite limited.
Layered cover systems should include buffer soil layers1 where a
buffer layer may be described as a random layer having a subordinate
covering function. Buffers serve to protect the barrier layer or membrane
sheet from tears, cracks, offsets, punctures, and other deterioration.
Below a barrier or the main cover soil a buffer also provides a smooth,
regular base. Any soil type will serve as a buffer ordinarily, but it
should be free of clods. A properly placed buffer filling voids around
barrels of waste serves to minimize settlement and disruption of the
final capping cover.
Where layers with grossly discordant grain sizes are joined, there may
be a tendency for fine particles to penetrate the coarser layer. As a result,
the effectiveness of coarse layers that may be used for water drainage can be
reduced by clogging of the pores. Removals from the fine layer may promote
additional bad effects, such as internal erosion and settlement. Similar
problems can develop around pipe drains buried in the cover system. Such
problems are confronted in construction and agriculture, and procedures have
been established for choosing grain size for a filter. A widely used criter-
ion is written
D (filter soil)
< 4 to 5
85(protected soil)
where D^ and Dg^ refer to the grain sizes for which 15 and 85 percent by
weight of the soils are finer, respectively. Common filter soils are SP, SM,
ML, and MH (Figure 3); filter fabric or cloth may be considered in place of
a soil filter layer.
Example: Suppose that grain-size distribution curves have
been submitted with the application to represent soils to
be used in a layered system. The evaluator locates the
D-jc and Dg5 grain sizes at the points shown in Figure 18.
Since the ratio of these sizes does not meet the criterion,
the application is returned for modification of design.
A water drainage layer, blanket, or channel may be designed into cover
in numerous ways to provide a path for water to exit rapidly. Well sorted
(poorly graded) sand and gravel are recommended as effective drainage
materials, i.e. soils classified GP and SP. Drainage channels and layers
may be associated with a system of buried pipe drains but the expense of
this combined system ordinarily limits its applicability to high-priority
disposal areas.
34
-------
100
1 0.1
GRAIN SIZE IN MILLIMETERS
0.01
0.001
Figure 18. Hypothetical size gradation of ineffective
filter soil.
Gas drainage layer and vents may have granular consistency and inter-
connections and general configuration similar to those of the water drainage
layer or channel. Both layer types function to transmit preferentially.
The position in the cover system is a main distinction. The gas drainage
layer is placed on the lower side to intercept gases rising from waste cells
whereas the drain for water is positioned on the upper side to intercept
water percolating from the surface. Figure 19 illustrates a passive gas
tronw
Vented gal
Vegetation
Riser
Final cover material
Gravel
Perforated lateral
Cell
Figure 19. Passive collecting and venting system
of laterals in gravel trenches above
waste cell.
35
-------
vent design concept, but the pressure-induced draft systems are preferred
to passive vents in most cases. Details of the systems should be included
in the permit application.
Evaluate Top Soil Step 16
A top soil or a subsoil made amenable to supporting vegetation fre-
quently forms the top of a layered cover system. Untreated subsoils are
seldom suitable directly, so it has been necessary frequently to supplement
subsoil with fertilizers, conditioners, etc., as explained elsewhere
(Steps 24-26) to obtain the desired result. Loams or USCS types GM, GC, SM,
SC, ML, and CL (Figure 3) are recommended but agronomic considerations
usually prevail. The upper lift should be placed in a loose condition
and not compacted.
Review Proposed Construction Techniques Step 17
The application should be carefully reviewed for conformance to the
following general recommendations! for layering (from the bottom up):
a. Make buffer layer below barrier thick and dense enough to provide
smooth, stable base for compacting in c^. below.
b. Compact all layers except topsoil and top lift of upper buffer.
c. In barrier layer, consider striving for 90 percent of maximum
dry density according to 5- or 15-blow compaction test where solid waste
is soft or according to standard 25-blow compaction test where solid
waste is granular and soil-like.
d. Cover barrier layer soon enough to prevent excessive drying
and cracking.
e. Provide sufficient design thickness to assure performance of layer
function; specifying a 6- to 12-inch minimum should prevent excessively thin
spots resulting from poor spreading techniques.
f. Construct in plots small enough to allow rapid completion.
g. Consider seeding topsoil at time of spreading.
CONFIGURATION EVALUATION PROCEDURE
The concern for the configuration of the cover surface is driven mostly
by a concern to avoid excessive erosion or excessive infiltration. Not only
is erosion objectionable in itself but erosion can degrade the cover and
seriously reduce its effectiveness.
36
-------
Evaluate Erosion Potential
Step 18
The USDA universal soil loss equation (USLE) is a convenient tool for
use in evaluating erosion potential. The USLE predicts average annual soil
loss as the product of six quantifiable factors. The equation is:
A = RKLSCP
where A = average annual soil loss, in tons/acre
R = rainfall and runoff erosivity index
K = soil erodibility factor, tons/acre
L = slope-length factor
S = slope-steepness factor
C = cover/management factor
P = practice factor
The data necessary as input to this equation are available to the evaluator
in a figure and tables included below. Note that the evaluations in Step 8
on soil composition and Steps 23-29 on vegetation all impact on the evalu-
ation of erosion also.
Factor R in the USLE can be calculated empirically from climatological
data. For average annual soil loss determinations, however, R can be obtained
directly from Figure 20. Factor K, the average soil loss for a given soil in
i5
Figure 20. Average annual values of rainfall-erosivity factor R .
37
11
-------
a unit plot, pinpoints differences in erosion according to differences in soil
type. Long-term plot studies under natural rainfall have produced K values
generalized in Table 5 for the USDA soil types.
TABLE 5. APPROXIMATE VALUES OF FACTOR K FOR
USDA TEXTURAL CLASSES11
Texture class
Sand
Fine sand
Very fine sand
Loamy sand
Loamy fine sand
Loamy very fine sand
Sandy loam
Fine sandy loam
Very fine sandy loam
Loam
Silt loam
Silt
Sandy clay loam
Clay loam
Silty clay loam
Sandy clay
Silty clay
Clay
Organic
0.5$
K
0.05
.16
.1+2
.12
.2U
.UU
.27
35
.1*7
.38
.1*8
.60
.27
.28
.37
.1U
.25
matter
2%
K
0.03
.ll»
.36
.10
.20
.38
.2U
.30
.ia
3U
.1*2
.52
.25
.25
.32
.13
.23
0.13-0.
content
h%
K
0.02
.10
.28
.08
.16
.30
19
.2»»
.33
.29
.33
.k2
.21
.21
.26
.12
.19
29
The values shown are estimated averages of broad
ranges of specific-soil values. When a texture is
near the borderline of two texture classes, use
the average of the two K values.
The evaluator must next consider the shape of the slope in terms of
length and inclination. The appropriate LS factor is obtained from Table 6.
A nonlinear slope may have to be evaluated as a series of segments, each
with uniform gradient. Two or three segments should be sufficient for most
engineered landfills, provided the segments are selected so that they are
also of equal length (Table 6 can be used, with certain adjustments). Enter
Table 6 with the total slope length and read LS values corresponding to the
percent slope of each segment. For three segments, multiply the chart LS
values for the upper, middle, and lower segments by 0.58, 1.06, and 1.37,
38
-------
TABLE 6. VALUES OF THE FACTOR LS FOR SPECIFIC
COMBINATIONS OF SLOPE LENGTH AM) STEEPNESS11
'"c Slope
0.5
1
2
3
4
5
6
8
10
12
14
16
18
20
25
30
40
50
60
Slope length (t'ect)
25
0.07
0.09
0.13
0.19
0.23
0.27
0.34
0.50
0.69
0.90
1.2
1.4
1.7
2.0
3.0
4.0
6.3
8.9
12.0
50
0.08
0.10
0.16
023
0.30
0.38
0.48
0.70
0.97
1.3
1.6
2.0
2.4
2.9
4.2
56
9.0
13.0
16.0
75
0.09
0.12
0.19
0.26
0.36
0.46
100
0.10
0.13
0.20
0.29
040
0.54
j
0.58
0.86
1.2
1.6
2.0
2.5
3.0
35
S.I
6.9
11.0
15.0
20.0
0.67
0.99
1.4
1.8
2.3
2.8
3.4
4.1
5.9
8.0
13.0
18.0
23.0
150
0.11
0.15
0.23
200
'0.12
0.16
0.25
i
0.33
0.47
0.66
0.82
1.2
1.7
2.2
2.8
3.5
4.2
5.0
7.2
9.7
16.0
22.0
28.0
0.35
0.53
0.76
0.95
1.4
1.9
2.6
3.3
4.0
4.9
5.8
8.3
11.0
18.0
25.0
300
0.14
0.18
0.28
0.40
400
0.15
0.20
0.31
0.44
0.62 | 0.70
0.93
1.7.
1.7
1.1
1.4
2.0
2.4 i 2.7
1
3.1
4.0
4.9
6.0
7.1
10.0
140
22.0
31.0
3.6
4.6
5.7
6.9
8.2
12.0
16.0
25.0
500
0.16
0.21
0.33
0.47
0.76
1.2
1.5
2.2
3.1
4.0
5.1
6.4
7.7
9.1
13.0
18.0
28.0
600
0.17
0.22
0.34
0.49
0.82
1.3
1.7
2.4
3.4
4.4
5.6
7.0
8.4
10.0
14.0
200
31.0
800 i 1 000
i
0.19
0.24
0.38
0.54
0.92
1.5
1.9
28
3.9
5.1
6.5
8.0
9.7
12.0
17.0
23.0
0.20
0.26
0.40
(1.57
1.0
1.7
2.1
3.1
4.3
5.7
7 .1
9.0
11.0
13.0
19.0
25.0
Values given for slopes longer than 300 leet or steeper than 18% are extrapolations beyond the range of the research data and.
therefore, less certain than the others.
respectively. The average of the three products is a good estimate of the
overall effective LS value. If two segments are sufficient, multiply by 0.71
and 1.29.
Factor C in the USLE is the ratio of soil loss from land cropped under
specified conditions to that from clean-tilled, continuous fallow. Therefore,
C combines effects of vegetation, crop sequence, management, and agricultural
(as opposed to engineering) erosion-control practices. On landfills, freshly
covered and without vegetation or special erosion-reducing procedures of cover
placement, C will usually be about unity. Where there is vegetative cover or
significant amounts of gravel, roots, or plant residues or where cultural
practices increase infiltration and reduce runoff velocity, C is much less
than unity. Estimate C by reference to Table 7 for cover management condi-
tions anticipated in the application, and consider changes that may take
place in time. See Reference 1 for additional guidance.
Factor P in the USLE is similar to C except that it accounts for addi-
tional erosion-reducing effects of land management practices that are
superimposed on the cultural practices, e.g., contouring, terracing, and
39
-------
TABLE 7. GENERALIZED VALUES OF FACTOR C FOR STATES
EAST OF THE ROCKY MOUNTAINS11
Oop, rotation, and management
Base value: continuous fallow, tilled up and down slope
CORN
C. Rd R. fall TP, conv
C, RdR, spring TP, conv
C. RdL. fall TP, conv
C. RdR, we seeding, spring TP. conv
C, RdL, standing, spring TP, conv
C-W-M-M. RdL, T P for C, disk lot W
C-W-M-M-M. RdL. TP for C, disk for W
C, no-till pi in c-k sod, 95-80% re
COTTON
Cot. conv (Western Plains)
Cot. eonv (South)
MLADOW
Crass & Legume mix
Alfalfa, lespcdeza or Sencia
Sweet clover
SORGHUM, GRAIN (Western Plains)
RdL. spring TP, conv
No-lill pi mshicdded 70-50% re
SOYBEANS
B, RdL, spring TP, conv
C-B, TP annually, conv
B, no-till pi
C-B. no-till pi, fall shred C stalks
WHKAT
W-F, fallTPafte; W
W-r, stubble mulch, 500 Ibs re
W-F, stubble mulch, 1000 Ibs re
Productivity level
High
Mod.
C value
1.00
0.54
.50
.42
.40
.38
.039
.032
.017
0.42
.34
0.004
.020
.025
0.43
.11
0.48
.43
.22
.18
0.38
.32
.21
1.00
0.62
.59
.52
.49
.48
.074
.061
.053
0.49
.40
0.01
0.53
.18
0.54
.51
.28
.22
Abbreviations defined:
B soybeans
C - corn
e-k chemically killed
conv- conventional
cot - cotton
F - fallow
M - grass & legume hay
pi - plant
W - wheat
we - winter cover
Ibs re - pounds of crop residue per acre remaining on surface after new crop seeding
% re percentage of soil surface covered by residue mulch after new crop seeding
70-50% re 707< cover for C values in first column; 5095 for second column
RdR - residues (corn stover, straw, etc.) removed or burned
RdL all residues left on field (on surface or incorporated)
TP - turn plowed (upper 5 or more inches of soil inverted, covering residues)
40
-------
contour strip-cropping. Approximate values of P, related only to slope
steepness, are listed in Table 8. These values are based on rather
limited field data, but P has a narrower range of possible values
than the other five factors.
TABLE 8. VALUES OF FACTOR P
11
Practice
Contouring (Pt-l
Contour strip cropping I
R-R-M-M1
R-\\-M-M
R-R-W-M
R-W
R-O
(PC1)
Contour terracing (P()2
No support practice
e
planting
Land slope (percent)
1.1-2
2.1-7
7.1-12
12.1-18
18.1-24
(Factor P)
0.60
0.30
0.30
0.45
0.52
0.60
0.30
3 0.6K/T
1.0
0.50
0.25
0.25
0.38
0.44
3.50
0.25
0.5/\/n"
1.0
0.60
0.30
0.30
0.45
0.52
0.60
0.30
0.6/\7rT
1.0
0.80
0.40
0.40
0.60
0.70
0.80
0.40
0.8/x/rT
1.0
0.90
0.45
0.45
0.68
0.90
0.90
0.45
0.9/x/rT
1.0
1 R = rowcrop, \V = fall-seeded grain. O = spring-seeded grain. M = meadow. The crops are grown in rotation and so arranged on
the field that rowcrop strips are always separated by a meadow or winter-grain strip.
2 These Pt values estimate the amount of soil eroded to the terrace channels and arc used for conservation planning. For prediction
of off-field sediment, the P, values are multiplied by 0.2.
3 n = number of approximately equal-length intervals into which the field slope is divided by the terraces. Tillage operations must
be parallel to the terraces.
Example: An owner/operator proposes to close one section
of his small landfill with a sandy clay subsoil cover
having the surface configuration shown in Figure 21.
The factor R has been established as 200 for this locality.
The evaluator questions anticipated erosion along the
steep side and assigns the following values to the
other factors in the USLE after inspecting Tables 5
through 8:
K = 0.14 LS = 8.3
1.00
P = 0.90
The rate of erosion for the steep slope of the landfill
is calculated as follows:
A = 200 (0.14 tons/acre) (8.3) (1.00) (0.90) = 209 tons/acre
This erosion not only exceeds a limit recommended by the
permitting authority but also indicates a potential
41
-------
exposure of solid waste in that side of the landfill.
The evaluator therefore recommends that the owner/operator
review his plan of closure to reduce the potential erosion.
One way that the operator might accomplish this reduction
in erosion is by placing additional solid waste along the
steep slope in an overlapping wedge as indicated in the figure.
Although the new cover would have a greater slope length,
the overall effect is to reduce the factor LS and the amount
of erosion.
AS PROPOSED
100 FEET
to
Figure 21. Hypothetical landfill configuration and modification.
Evaluate Surface Slope Inclination
Step 19
Rainfall runoff is increased by increases in inclination of the surface,
and accordingly, infiltration decreases. Since erosion also increases with
increasing inclination (Step 18), the balance between these opposing consider-
ations often must be carefully evaluated. On slopes of less than 3 percent,
the irregularities of the surface and vegetation commonly act as traps for
detention of runoff. The value 5 percent has been suggested and used in
grounds maintenance^ as an approximation of an inclination sufficient to
facilitate runoff without risking excessive erosion. A quantitative evalua-
tion of the erosional effect of inclination is outlined for factor LS under
Step 18.
Slope inclination becomes more critical as inclination is increased.
Not only is erosion more serious, but slope mass stability can become a factor
on relatively steep side slopes of landfills and surface impoundments.
Usually the evaluator will do well to seek assistance from technical agencies
experienced in analyzing slope stability since varied strength properties and
seepage conditions can greatly complicate the mass stability. As a rough
guide, however, the evaluator can usually count on the rule of thumb that
not exceeding IV (vertical) on 4H (horizontal) or other inclination shown by
experience or analysis to be relatively stable would assure satisfactory
slope performance in most cases.
42
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The vulnerability of knoll-like configurations to wind erosion can be
evaluated by the use of Figure 22. An adjustment factor is obtained as an
erosion loss percentage of 100 or more in comparison with erosion loss from a
similar flat surface. This factor should be used to estimate the effects of
sides of landfills that may present a knoll-like configura'ion toward the
prevailing winds.
700
600
500
ui
o
tr
£300
in
in
250
200
150
100
1-5 2 25 3 456
WINDWARD KNOLL SLOPE (PERCENT)
8 10
Figure 22. Knoll adjustment (a) from top
of knoll and (b) from upper
third of slope.13 (Reproduced
by permission of Soil Science
Society of America.)
14
Finally, another general rule of thumb provides that IV on 2H is the
maximum slope on which vegetation can be established and maintained, assuming
ideal soil with low erodibility and adequate moisture-holding capacity. In
soils less than ideal, maximum vegetative stability cannot be attained on
slopes steeper than about IV on 3H. Optimum vegetative stability generally
requires slopes of IV on 4H or flatter.
DRAINAGE EVALUATION PROCEDURE
Check Overall Drainage System
Step 20
Examine the documentation to establish that drainage of surface runoff
from the covered area and surroundings has been thoroughly addressed. Maps
presenting topography or other descriptions of surface configuration should
be carefully reviewed to see that rainfall or snow melt on any part of the
site is free to move downs lope without encountering obstacles that might
lead to ponding or excessive erosion. At the same time, a check should be
made to see that the slope is not anywhere in excess of the slopes for
43
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flat surfaces and for ditches provided in the regulations. In those
places such as the edge of the landfill where slopes may of necessity be
relatively steep, a check for adverse effects in the form of excessive
erosion should be made as explained elsewhere (Step 18).
Evaluate Ditch Design Step 21
To confirm the adequacy of drainage ditches, the evaluator should for-
mally check the hydraulic calculations on which design for ditch cross
sections are based. This step can be important but for many landfills may
only be necessary where diversion ditches convey runoff from beyond the site
around its edge. Calculation should not usually be necessary on the landfill
cover itself unless an overflow situation would have serious consequences.
Design (and evaluation) of a ditch is routinely accomplished using
the Rational equation (Step 7) and Manning's equation. It was explained in
Section 2 that calculations of discharge Q for design storm or storms should
be included with the documentation supplied with the application for closure.
Q in cubic feet/second is used to calculate ditch cross sections in
Manning's equation:
2/3 1/2
Q = 1.486 AR /J S '
where n = coefficient of roughness
A = area, square feet
R = hydraulic radius, feet
S = energy gradient, feet/foot
The Manning n value is usually obtained from a table and that authori-
tative reference should be cited in the application to facilitate checking.
For a rough check, use n = 0.02. The S in the equation is simply the
longitudinal inclination of the ditch.
The design amounts to a manipulation of the remaining unknowns A and
R within certain constraints. Numerous tables have been developed and are
available for assistance in design; again these references should be identi-
fied when used. The cross sectional area A of the waterfilled ditch is
affected by the choice of shape, e.g., between triangular and trapezoidal.
The hydraulic radius R is also affected since it is by definition the area
divided by the wetted perimeter formed by the ditch. A final constraint is
the requirement that erosion in the ditch be limited by limiting discharge
velocity Q/A to an appropriate maximum from among those determined as
critical for the range of soil types (Table 9).
Evaluate Culvert Design Step 22
Evaluations of culverts and other closed structures that may occasion-
ally be used as a part of the drainage system are approached in approximately
44
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TABLE 9. THRESHOLD VELOCITY FOR EROSION IN DITCHES
Soil max, feet/second
GP
GW, GC
GM
SC
SM
SW, SP
CL, CH
ML, MH
7-8
5-7
2-5
3-4
2-3
1-2
2-3
3-5
the same way as Step 21. An added complication is the capacity of the struc-
ture to transmit the water. Where the capacity is too small, water will back
up and form a pond, at least temporarily.
VEGETATION EVALUATION PROCEDURE
Rapid establishment and maintenance of vegetation can be accomplished
on soil covering solid waste only by carefully addressing soil type, nutrient
and pH levels, climate, species selection, mulching, and seeding time.-'-
Fertile soils, if available at all for landfill cover, are usually cost-
prohibitive, so that nonproductive soils or subsoils often have to be used.
County agricultural agents may be able to provide guidance.
Evaluate Soil Suitability for Vegetation Step 23
Soil composed of a mixture of clay, silt, and sand such that none of
the components dominates is called a loam. The stickiness of the clay and
the floury nature of the silt are balanced by the nonsticky and mealy or
gritty characteristics contributed by the sand. A loam is rated overall best
for supporting vegetation as it is easily kept in good physical condition and
is conducive to good seed germination and easy penetration by roots.
Clay-rich soils may be productive when in good physical condition, but
they require special management methods to prevent puddling or breaking down
of the clay granules. Silt-rich soils lack the cohesive properties of clay
and the grittiness of sand, are water retentive, and usually are easily kept
in good condition. Soils made up largely of sand can be productive if suffi-
cient organic matter is present internally or as a surface mulch to hold
nutrients and moisture; sandy soils tend to dry out very rapidly and lose
nutrients by leaching.
45
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Remember that worthwhile steps in establishing vegetation may be to
stockpile and then to reuse the original topsoil. The less fertile under-
lying soil will be available as daily or intermediate cover. As the operation
nears completion, the stockpiled topsoil can be used in the final cover to
facilitate rapid growth of grasses and/or shrubbery. The original topsoil
must be significantly more fertile than underlying soil strata; otherwise,
stockpiling is not practical or economical.
Evaluate pH Level Step 24
Tests should be made to determine pH and buffering capacity (usually
stated as tons/acre of lime necessary to adjust the soil pH to around 6.5).
The amount of lime necessary to neutralize a given soil depends upon soil
pore-water pH and "reserve acidity." The reserve acidity is a single factor
which incorporates several variables; soils with high levels of organic
matter and/or clay require higher amounts of lime for pH adjustment. The
pH of subsoil (where appreciable in the cover) also influences lime require-
ments; acidic subsoils require higher levels and repetitive applications of
lime. Some buried landfill wastes act much like acid subsoils making higher
lime application levels or more frequent liming intervals necessary for
adequate pH control.
Evaluate Nitrogen and Organic Matter Step 25
Nitrogen is of special importance in establishing vegetation because
it is needed in relatively large amounts during vigorous growth but is easily
lost from the soil. Nitrogen fertilizer requirements depend upon the amount
of organic matter present (higher organic matter levels requiring higher
application rates), the soil texture (more is required on sandy soils), and
the seed mixture chosen (more is required for grasses than legumes). Gener-
ally 50 to 85 Ib/acre of nitrogen are recommended. Fertilizers are rated by
the amount of nitrogen they contain per weight of fertilizer (e.g. 6 percent
nitrogen). To calculate the amount of fertilizer necessary to furnish the
recommended amount of nitrogen, simply divide the recommended application by
the fractional amount of nitrogen the fertilizer to be used contains. For
example, to apply 50 Ib/acre nitrogen using fertilizer which is 6 percent
nitrogen, divide 50 by 0.06 to get 833 Ib/acre fertilizer required. Table 10
indicates typical ranges of organic matter in different soil types and a rough
range of nitrogen levels present in a typical loam with moderate levels of
organic matter.
Evaluate Other Nutrients Step 26
Necessary levels of phosphorus in soil are shown in Table 10. Unlike
nitrogen, phosphorus is not mobile in the soil and thus is lost very slowly
to leaching. It is possible to give enough phosphorus in one application to
last several growing seasons. Generally at least 15 Ib/acre of phosphorus*
*In calculating on the basis of P2°r> remember that percent P 0 is 2.3 times
an equivalent percent phosphorus.
-------
TABLE 10. RELATIVE LEVELS OF ORGANIC MATTER AND MAJOR NUTRIENTS IN SOILS15
Organic Matter,
Relative
Level*
Very low
Low
Medium
High
Very
high
Sand,
Loamy
Sand
<0.6
0.6-1.5
1.6-2.5
2.6-3.5
>3.5
Sandy Loam,
Loam,
Silt Loam
<1.6
1.6-3.0
3.1-14.5
14.6-5.5
>5.5
percent
Clay Loam,
Sandy Clay,
Clay
<2.6
2.6-U.5
l;.6-6.5
6.6-T.5
>7.5
Nitrogen
It/acre
<20
20-50
50-85
85-125
>125
Phosphorus
Ib/acre
<6
6-10
11-20
21-30
>30
Potassium
Ib/acre
260
* Medium level is typical of agricultural loam soil. Low levels need supple-
mental fertilization; high levels need no fertilization under normal
circumstances.
is recommended as a starter. The availability of phosphorus to the plant is
quite dependent on pH. At optimum pH values (6.2-6.8) amounts of 50 Ib/acre
are usually adequate; at pH values below 6.2 or between 6.9 and 7.5, about
80 Ib/acre is needed for optimum growth. Under very alkaline conditions (pH
greater than 7.5), phosphorus levels of 110 Ib/acre are required. These
recommendations are for raw subsoils, or for sandy or high clay soils of low
organic material content.
Potassium is much less important in grass establishment than in legume
establishment and maintenance; thus the rate of application depends upon both
test results and species to be seeded. A minimum application of 26 Ib/acre
potassium (32 Ib/acre 1^0) as a starter is recommended under any circum-
stances. Applications can run as high as 230 Ib/acre potassium (277 Ib/acre
KoO) on impoverished soils where legumes are to be seeded. Potassium is
moderately mobile in the soil and is slowly leached out, but one heavy
application should be adequate for several growing seasons.
Evaluate Species Selection
Step 27
Each species of grass, legume, shrub, or tree has its own environmental
and biological strengths and limitations. Moisture, light, temperature, ele-
vation, aspect, balance and level of nutrients, and competitive cohabitants
are all parameters which favor or restrict plant species. The selection of
the best plant species for a particular site depends upon knowledge of
adapted plants that have the desired characteristics. Table 11 gives the
major parameters usually important to species selection and examples of
grasses and legumes exhibiting the parameters. Characteristics which almost
universally should be given precedence are: low growing and spreading from
rhizomes or stolons; rapid germination and development; and resistance to
fire, insects, and disease. Plants which are poisonous or are likely to
escape the site and become noxious should be avoided.
47
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TABLE 11. IMPORTANT CHARACTERISTICS OF GRASSES AND LEGUMES
Characteristic
Degree *
Common Examples
Texture
Growth height
Growth habit
Reproduction
Annual
Perennials
Maintenance
Shallow rooted Weak
Deep rooted
Moisture
Temperature
Fine Kentucky bluegrass., bentgrass, red fescue
Coarse Smooth bromegrass, reed canarygrass,
timothy
Short Kentucky bluegrass, buffalograss, red fescue
Medium Redtop, perennial ryegrass
Tall Smooth bromegrass, timothy, switchgrass
Bunch Timothy, big bluester., sand dropseed,
perennial ryegrass
Sod foiuer Quackgrass, smooth bromegrass, Kentucky
bluegrass, switch'grass
Seed Red and alsike clover, sand dropseed, rye,
perennial ryegrass, field bromegrass
Vegetative Prairie cordgrass, some bentgrasses
Seed and White clover, crownvetch, quackgrass,
vegetative Kentucky bluegrass, smooth bromegrass
Summer Rabbit clover, oats, soybeans, corn,
sorghum
Winter Rye, hairy vetch, field bromegrass
Short-lived Timothy, perennial ryegrass, red and
white clover
Long-lived Birdsfoot trefoil, crovmvetch, Kentucky
bluegrass, smooth bromegrass
Difficult Tall fescue, reed canarygrass, timothy,
alfalfa
Moderate Kentucky bluegrass, smooth bromegrass
Easy Crownvetch, white clover, birdsfoot
trefoil, big bluestem
Sand dropseed, crabgrass, foxtail, white
clover
Strong Timothy, Kentucky bluegrass
Weak Many weeds
Strong Big bluestem, switchgrass, alfalfa, reed
canarygrass
Dry Sheep fescue, sand dropseed, smooth
bromegrass
Moderate Crested wheatgrass, red clover
Wet Reed canarygrass, bentgrass
Hot Lehman lovegrass, fourwing saltbush,
ryegrass
Moderate Orchard grass, Kentucky bluegrass, white
clover
Cold Alfalfa, hairy vetch, smooth bromegrass,
slender wheatgrass
*Variety, specific characteristic, subcharacteristic, or
favored condition.
48
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A very large number of species of grasses and legumes are available
for reclamation use. Species that find wide and frequent application are
described in Tables 12 and 13. A local agronomist should be consulted for
recommendation of locally adapted plant varieties.
Evaluate Time of Seeding
Step 28
Probably the most critical of all decisions in the successful establish-
ment of vegetative cover on poor soils is the time of seeding. The optimum
time of seeding depends on the species selected and the local climate. Best
seeding time under normal circumstances is presented in Tables 12 and 13 for
the recommended grasses and legumes. A local county agent or seed house
should be consulted for more specific local information.
Most perennials require a period of cool, moist weather to become
established to the extent that they can withstand a cold winter freeze or
hot summer drought. Early fall (late August in the north through October
in the south) usually allows enough time for the plants to develop to the
stage that they can withstand a hard winter. Plants then have a good start
for early spring growth and can reach full development before any summer
drought. Spring planting is usually second choice for all but a few of the
more rapidly developing perennials. Germination and early development are
TABLE 12. GRASSES COMMONLY USED FOR REVEGETATION*
Variety
Best
Seeding Seed Densityt
Time seeds/ft2
Important Characteristics
Areas/Conditions
of Adaptation
Redtop bentgrass
Smooth bromegrass
Field bromegrass
Kentucky bluegrass
Tall fescue
Meadow fescue
Orchard grass
Fall
Spring
Spring
Fall
Fall
Fall
Spring
lli
2.9
6.1.
50
5.5
5.3
12
Strong, rhizonatous roots,
perennial
Long-lived perennial
Annual, fibrous roots,
winter rapid growth
Alkaline soils, rapid grower,
perennial
Slow to establish, long-lived
perennial, good seeder
Smaller than tall, susceptible
to leaf rust
More heat tolerant but less
Wet, acid soils, warm
season
Damp, cool summers,
drought resistant
Cornbelt eastward
North, humid, U.S.
south to Tennessee
Widely adapted, damp
soils
Cool to warm regions,
widely adapted
Temperate U.S.
Annual ryegrass
Timothy
Reed canarygrass
Fall
Fall
Late
summer
cold resistant than smooth
bromegrass or Kentucky bluegrass
5.6 Not winter hardy, poor dry
land grass
30 Shallow roots, bunch grass
13 Tall coarse, sod former,
perennial, resists flooding
and drought
Moist southern U.S.
Northern U.S., cool,
humid areas
Northern U.S., wet,
cool areas
* Taken from many sources, but especially 15 and 16.
t Number of seeds per square foot when applied at 1 Ib/acre.
49
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TABLE 13. LEGUMES COMMONLY USED FOR REVEGETATION
Variety
Alfalfa (many varieties)
Birdsfoot trefoil
Sweet clover
Red clover
Alslke clover
Korean lespedeza
Sericea lespedeza
Hairy vetch
White clover
Crownvetch
Best
Seeding
Time
Late
summer
Spring
Spring
Early
spring
Early
spring
Early
spring
Early
spring
Fall
Early
fall
Early
fall
Seed Densityt
seeds /ft2
5.2
9.6
6.0
6.3
16
5.2
8.0
0.5
18
2.7
Important Characteristics
Good on alkaline loara, re-
quires good management
Good on infertile soils,
tolerant to acid soils
Good pioneer on non-acid soils
Not drought resistant,
tolerant to acid soils.
Similar to red clover
Annual, widely adapted
Perennial, tall erect plant,
widely adapted
Winter annual, survives belov
0°F, widely adapted
World-wide, many varieties,
does well on moist, acid soils
Perennial, creeping stems and
rhizomes, acid tolerant
Areas/Conditions
of Adaptation
Widely adapted
Moist, temperate
U.S.
Widely adapted
Cool, moist areas
Cool, moist areas
Southern, U.S.
Southern, U.S.
All of U.S.
All of U.S.
Northern U.S.
* Taken from many sources but mainly 15 and 16.
t Number of seeds per square foot when applied at 1 Ib/acre.
slowed due to the cool early spring weather. Late frosts often severely
damage the young plants. Late spring planting does not allow enough time
for most perennials to mature before summer and annuals will usually out-
compete the preferred perennials.
Annuals generally are best planted in spring and early summer. Growth
is completed quickly before the summer heat and the soil moisture is used up.
During this period annuals easily out-compete the perennials. Annuals can,
however, be planted any time the soil is damp and warm when a quick plant
cover is desired and often will provide an acceptable mulch for fall seeded
perennials.
Evaluate Seed and Surface Protection
Step 29
Bare soil as a seeding medium suffers from large temperature and
moisture fluctuations and from rapid degeneration due to wind and water
erosion. Mulches provide temporary protection against these influences and
therefore the use of mulch should be expected in the plan for closure cover.
Almost any material spread, formed or simply left on the soil surface
will act as a mulch, e.g., straw and other crop residues, sawdust, wood chips,
wood fiber, bark, manure, brush, jute or burlap, gravel, stones, peat, paper,
leaves, plastic film, and various organic and inorganic liquids. For straw
used where erosion is not anticipated, an application of 1.5 tons/acre is
50
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recommended. On slopes or elsewhere where erosion threatens, 2 tons/acre
produces better results. Application rates over 2.5 tons/acre often result
in reduced germination and emergence and such high rates should be avoided.
Rapid growing, summer cover crops can be used to advaitage as living
mulches if final grade work is finished in late spring or early summer when
chances of successful perennial grass-legume seedings are low. Coarse
grasses such as Sudan grass or a local equivalent are good choices as they
are widely adaptable and the tall, stiff stalks are most effective as a mulch.
Petroleum-based products such as asphalt and resins are often suitable
and are frequently used as mulching materials. Specially formulated emulsions
of asphalt under various trade names have been used throughout the world to
prevent erosion, reduce evaporation, promote seed germination, and warm the
soil to advance the seeding date. The film clings to but does not deeply
penetrate the soil; it is not readily destroyed by wind and rain and remains
effective from 4 to 10 weeks. Application rates of 1000-1200 gallons/acre
are usually required to control erosion. Asphalt mulches cost about twice
the applied cost of a straw mulch.
51
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SECTION 4
POST-CLOSURE PLAN
Provisions for maintenance and for contingencies after site closure
should follow a logical plan.
MAINTENANCE EVALUATION PROCEDURE
Some cover deterioration like erosion can be tolerated where the post-
closure plan has provisions for frequent, regular maintenance. Elsewhere
regular maintenance of the cover may be planned on a less frequent interval,
in which case a more conservative cover design is necessary at the start.
Evaluate Design/Maintenance Balance jtep 30
Check to see that the plan for closure covering generally achieves a
reasonable balance between initial design and plans for monitoring, mainte-
nance, and repair. So many specific factors (climate, waste type, soil,
vegetation, etc.) are involved in evaluating this balance that little
detailed guidance can be offered; nevertheless the assessment is important
and should be performed with care and diligence. The following example
helps clarify the general nature of the problem and the recommended
philosophy.
Example: In a late modification, the applicant formally
proposes to reduce the frequency of post-closure monitoring
inspection visits to a remote hazardous waste site by
overdesigning the closure cover at the start. A certain
period between inspection visits has become more or less
standard in the region on the basis of experience, but
the applicant now proposes to double this period. The
overdesign amounts to prescribing a thicker cover than
might ordinarily be considered sufficient. In this case
the evaluator rejects the proposed modification of less
frequent inspections. He reasons that emergency condi-
tions such as from wind or water erosion or from cover
cracking can compound and intensify the problem in a
short period in this region and therefore frequent
inspections are imperative and necessary.
Evaluate Maintenance of Vegetation Step 31
After vegetation is established on a landfill, maintenance is necessary
to keep less desirable, native species from taking over and weak areas in the
52
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cover from developing. In most areas judicious, twice-yearly mowing will
keep down weed and brush species. Annual fertilization (and liming if
necessary) will generally allow desirable species to out-compete the weedy
species of lower quality. Occasional use of selective herbicides usually
controls noxious invaders, but care must be taken to avoid injuring or
weakening the desirable species, lest more harm than benefit results in the
long run. In rare circumstances, large insect populations may threaten the
stand of vegetation so that insecticide application becomes desirable. The
evaluator should review the intermediate and long-range plans for maintaining
vegetation with cognizance of plant needs in establishment (and reestablish-
ment) as outlined in Steps 24-29.
Landfill cover soils are usually shallow and of low quality for growing
high-quality vegetation. This problem is greatly compounded if an impervious
clay or plastic barrier is incorporated in the cover. Such a barrier makes
the plant-root zone susceptible'to swamping after moderate rains since
vertical drainage is impeded. Upon saturation, the soil becomes anaerobic
and roots in the system are threatened. Short periods of swamping will
weaken the vegetation; longer periods may cause a complete loss. Swamping
tolerant species (such as Reed canary grass) and surface drainage will
lessen these problems.
On the other extreme, the thin soil dries excessively during dry
periods. No deep soil moisture is available to tide the plants over even
moderate droughts. Plants which have been weakened by prior waterlogging
or that are not drought-tolerant are especially vulnerable. Irrigation
may be necessary during prolonged dry spells to preclude complete loss of
plant cover.
Landfills may continue to produce gases and soluble organic decomposi-
tion products for years after closure, and vegetation can be damaged. An
impervious cover over the landfill may shield the plant roots from these
products and also keeps the landfill dry so that gas production is low or
nonexistent. Deep-rooted shrubs or trees are usually not recommended on
landfills since roots will tend to penetrate into the waste zone.
Evaluate Provisions for Condition Surveys Step 32
Applications for closures should include plans for monitoring the site
in the future. An annual site visit by a technical person qualified to eval-
uate the condition of the cover may be considered sufficient by the permitting
authority for some sites. Elsewhere, however, it may be judged that more
frequent inspections are necessary. Provisions should be made in the applica-
tion for collecting documentation during the site visit. The documentation
and inspection reports should be kept on site by the owner/ operator or at
some other location where it can be examined conveniently. Copies of the
reports including all significant observations or conclusions should be
kept in the applicant's file for review on request by the overseeing agency.
53
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Example: The evaluator has reviewed an application for
closing a site and found that there is sufficient planning
to monitor site conditions over an extended period. He
notes, however, that the site visits are to be made by a
representative of the owner/operator with no provision for
a state or EPA representative to accompany the inspector.
Among changes he requires in this application, therefore,
is the stipulation in the post-closure plan that the state
agency (or EPA) will be notified five days before the site
visit so that they may send a representative.
CONTINGENCY PLAN EVALUATION PROCEDURE
Evaluate Plan for Erosion Damage Repair Step 33
Long-term maintenance helps to avoid erosion problems. However, unusual
climate conditions and shortcomings in the design occasionally cause excessive
erosion by wind or water even on well-maintained covers.
Factors that need to be considered in the plan include the future source
of supply of fill soil for repair and the ability of someone to undertake the
repair work. The extent of repair work should be detailed in words to the
effect that repair work will bring lines and grades at least to their original
configuration. It is also appropriate to expect that the remedial work will
involve redesign where excessive erosion indicates that the original design
was deficient. Some of the many options that might be mentioned for consid-
eration in the case of a necessity for repair would include construction of
berms, protection of slopes and channels by riprap, and the use of other
special energy dissipators such as check dams.
In anticipation of major problems of sheet erosion across entire sur-
faces such methods as terracing might be identified, provided their effect on
infiltration is not excessively adverse.
In those regions where wind erosion can present a serious problem, the
post-closure plan should include specific statements on correcting wind erosion
problems. The following example is illustrative of the recommended attitude.
Example: Consider a site in the southern Great Plains.
An applicant proposes to dispose of waste in a trench
operation in which soil excavated from the trench will
be used as final cover. Since a considerable mound
will have been formed upon closure, the evaluator
foresees the possibility of eventual wind erosion.
No provision with specifics for timely repair addresses
this possible erosion problem, so the evaluator
recommends that the applicant develop contingencies
accordingly. The evaluator offers for consideration
the use of snow fences as one quick response technique.
54
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Evaluate Plan for Vegetation Repair Step 34
Waste disposal areas have long-lived potential for negative impact
and permanent vegetative cover should be maintained. Once a cover of
vegetation is started and stabilized, extensive root systems develop and
decomposition processes form a layer of humus capable of perpetuating
the cover of vegetation. However, erosion forces, burrowing animals, etc.,
may damage parts of this cover of soil, humus, and vegetation. Provisions
should be made for repairing such damage, specifically for transplanting
grass sod, planting the new seeds or shrubs, and replacing eroded soil
during the inactive life of the area.
The principal part of the application documents that the evaluator
should carefully review is that part dealing with measures to return damaged
vegetation to a state such as originally planned (see VEGETATION EVALUATION
PROCEDURES, SECTION 2). One additional facet of the plan for maintenance of
vegetation is the fact that deterioration of the vegetative cover is often
widespread; swampiness or droughtiness, nutrient starvation, or methane migra-
tion in the cover quickly affects the entire vegetation system. Exceptions
are problems induced by erosion, and repair in this case should be of less
concern. Because of this potential widespread impact the applicant's plans
for maintaining or for repairing the vegetation should be closely tied to the
monitoring plan and should be adequate to respond quickly to the early stages
of a major problem.
Evaluate Plan for Drainage Renovation Step 35
The principal part of the applicant's plan for drainage renovation
should include sufficient details to assure that the drainage system for the
site as designed will be restored quickly to its original condition. In
addition to this, the plan for repair should provide for such additional work
as becomes necessary after a period of operations. Such additional work might
include placement of riprap along a slope subjected to more erosive action
than anticipated in the original drainage design. Except for such unexpected
problems, the maintenance of drainage should amount to fairly straightforward
cleaning of ditches and cutting of brush.
Evaluate Provisions for Other Cover Deterioration Step 36
Contingency planning should include making provisions for all forms of
cover deterioration other than erosion and distress of the vegetation, covered
elsewhere. Such deterioration might result from excessive root penetration,
cracking, disturbance by cold weather, seepage, and slope instability. The
evaluator should consider the likely effectiveness of post-closure plans to
addressing such problems in a timely manner. His evaluation should, of course,
be made in the context of policies established by state agencies and/or EPA.
Such policies need not necessarily assign responsibility for correcting such
unanticipated problems to the owner/operator.
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