PB-239  357
AN EVALUATION OF LANDFILL GAS MIGRATION
AND  A PROTOTYPE  GAS MIGRATION  BARRIER

W ins ton-Salem Department of Public Works
Prepared  for:

Environmental  Protection Agency



1975
                          DISTRIBUTED BY:
                          National Technical Information Service
                          U. S.  DEPARTMENT OF COMMERCE

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I. Title anJ Silt-title
BIULIOCRAPHIC DATA
SNCCT
I. S «,'on N'u.
   r.PA/530/SW-79d
PB   239  357
  An Evaluation of Landfill  Cos Migr.it.ion  and
  A  Prototype Cas Migration Barrier
                                                 S. Krpufi lljiie
                                                        197*
f. Auihatd)
  Cttv of '.'Ingtnn-salca. 'i.C.  anil Enviro-F.ngtncers. Inc.
                                                 B. I'rilnnuiiift Ufpaniz^nun Kept.
                                                   No.
'. I'eifoiiiunji OIIEJIII/AIIUII N.imc anJ AUtlir«s
     Dcpartnont of Public Works, City of  Uinston-Salcm,
     North  Carolina, and Enviro-Engineors,  Inc./Kngincering-
     Science,  Inc., Atlanta,   corgia
                                                 10. I>i0|ret/lasli link Unit No.
                                                             ni No.
                                                        S-801519
12. Sponsotmg Orf.ani/.itu \loiJfc and Document Anal)si*.  17o. Uesciiptuik
     Landfill, Gas Migration, gas  Barriers
17k. Idrntificfs/Opcn-Kndcd Tcims


     Gas





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                NOTICE





THIS DOCUMENT HAS BEEN REPRODUCED FROM THE



BEST  COPY  FURNISHED US  BY THE  SPONSORING



AGENCY.  ALTHOUGH  IT  IS  RECOGNIZED  THAT  CER-



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             AN EVALUATION OF LANDFILL GAS MIGRATION

              AND A  PROTOTYPE GAS MIGRATION  CARRIER
            final report  (SU-?9d)  describes uork performed
         for fie Federal  solid isa.de  nznasenent programs
          dencistration Grant project S-3D2&3P ixta written cv
DEPARTMENT OF PUBLIC WORKS,  CITY OF 1JI1JSTON-SALEH, NORTH CAROLINA
      and EHVI'RO-EHGIMEERS IHC. and,  uith nitior exceptions,
           is reproduced  ae  received  fran the  grantee
              U.S. ENVIRONMENTAL PROTECTION AGENCY

                                1975

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This report as submitted by the grantee or contractor has  not  been
technically reviewed by the U.S. Environmental  Protection  Agency  (EPA).
Publication does not signify that the contents  necessarily reflect  the
views and policies of EPA, nor does mention of  comerclal  products
constitute endorsement or recommendation for use by  the U.S. Government.

An environmental protection publication (SW-79d) In  the solid  waste
management series.
                                 11

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                               CONTENTS



Chapters                                                            Page

I      Sunatuiry                                                      1

II     Introduction                                                 3

III    An  Accoi-nt of tlic Evplosio.i  in the. Winston-Sali-m            10
           National Guard Armory

IV     Rrvii-i: of G.-is> Ciiu-r.itIon  a-»d Kovvr.ient From Solid Waste      23
           Ln:.d fills

V      Star i—of-thc-Art ir.  Gas Control  Technology                  30

VI     Selection, Design  ind  Ir.st.il lation of I'rotoLypc- Gas         AO
           Barrier

VII    bcscripti!" of  Prototype  Has K.-irrier                        75

V11I   P=rfonnajice Evaluation of Prototype Gas Barrier             87

IX     Tocluiiqiu-s  for  r.vjluntin;; Solid Waste Landfills \.'ill>
           Rer,'ir
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                         FIGURES  (continued)



 Mo.                                                                  Page

 1     Final Topofiraphy of Che Lint: Road landfill Site, 1972         14

 4     Cross-sccHons Through Completed Link Road Landfill, 1973     16

 5     Initial Cas .VonUorlns Stations, 1970-1971                    19

 6     Combustible Cas Concentration Distribution in Link Road       45
          Disposal Kite  1973

 7     Soil-Air Prt-ssutc Gradient Toward Amory Prior to Barrier     46
          Operation

 8     Gen. rail *eJ Corimst iMe Gas ConrentraLlons at Several         47
          Stations Near Arnory

 9     Soil Pcrrk-»!»j]liy S.-iqdcs  anil Ass oc In ted l'»obc Locations      fit
          in Vicinity of Proposed Barrier

10     His torlf.il Variations of Coniust 5blc Cas Concent ration  nt     70
          Station 7

11     Historical and Projectt-J Concentration  of CoiAx. :tlMe          71
          G;JS Migraine From Disposal Area at  Station  7

JZ     Location of Carrier fells. Header, Pu/.y and  Vent              76

13     Typical Cas Micratlon Barrier Veil                             77

14     Sampling Locations for OeiceLlon anil Alarn SystcD             80

IS     Probe Locations  Tor Cvis Barrier  Evaluation                     90

16     Prossuro Pro'ui; and Manometer Detail                            92
17     Average Concentration  of  Corbustlblc- Cas on Kiilier Side       96
          of Car. Ilii;rdttoii  Darrirr Trier to and During Operational
          Hodos
                                  Iv

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                           FICUKr.S (continued)

No.                                                                rape

18     Percentage  of Lovi-r Explosive Llnlt al  lndividu.il             98
          Probes  in  and !.Var Buildinc*: 1'rior to and During
          Barrier  Opcration.il Modes

19     Variations  of Baronotric Presr.urc During tlic Barrier         102
          Test Period

20     Drawi'o ,-n Curves Between Barrier Wells 5 and 6 During         10-i
          Barrier  Test Period

21     Relative Pressure at Two D> pths Midpoint Between             105
          Barrier  Wells 5 and 6 During Barrier Test Period

22     Relative Pressure at Various Distances  Fron Barrier          106
          During  the Test Period

23     Fre ;ucncy Analysis of t.'oisc Produced by Vai nun Pututt          109

24     Freqi. ncy Analyst  of Background Noise  Measured Three        110
          Feet from Vermin Purp Gearbox

25     Comparison  of Vin.uuin Pur.ip Noise Levels  Measured at 10        111
          Feel to  the Background Noise Levels  Measured During
          Normal Traffic Conditions

 List of  Tables

 No.

 1    Estimated Costs  of  Alternative Gas  Barrier  Systems            50

 2    Relative Effectiveness  of Alternative Cas Barrier Systems      52

 3    Relative Maintainability  of Alternative  Gas Barrier Systems   52

 4    Relative Controllability  of Alternative  Gas Barrier Systems   53

 5    Relative Environmental  Impact of Alternative Cas Barrier       55
         Systems

 6    Relative Disruption During  Construction  of  Alternative        55
         Cas Barrier Systems

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                           TABLES (continued)



 No..                                                               Page

 7    Relative Novelty of Alternative  Gas Barrier  Systems            56

 8    Summary of Relative Scores for Alternative Gas Barrier         58
         Systems

 9    Particle-Size Distribution and Permeability  of Soils  in       65
         Vicinity of Proposed Barrier

10    Cas Chromatographic Analysis of  Barrier  Pump Discharge  Gases  99

11    Cas Chromatographic Analysis of  Samples  from Selected Probe  100
         Locations

12    Statistical Data on Comparative  Effectiveness of Soil-Air    107
         Pressure Reduction at Various Distances from Barrier
         Under Two Operational Modes

13    Power Requirements and Costs for Gas Migration Barrier        114
         System

14    Comparison of Actual and Estimated Construction Costs of     115
         Gas Barrier System
                                     vl

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                            ACKNOWLEDGMENTS
    The completion of this project In essential fulfillment of most  of
tbe objectives originally conceived, despite the limitations which ensued
(namely, the impractlcallty of obtaining definitive data adequate for
comparative analysis at the sites available and the unforeseen modifica-
tion of the Link Road landfill) Is due In no small measure to the close
liaison and assistance provided by EPA project representatives Keith
Hartley and Truett DeCeare.  They redirec. d the project to changing con-
ditions and barrier design aspects to permit the development, design,
installation and testing of a prototype gas barrier system.
    The Winston-Salem project staff was most diligent in fulfilling its
responsibilities, ana strong support and invaluable assistance were pro-
vided by Joe H. Berrlcr, Director of Public Works, Pat Svann, Assistant
Director of Public Works, and Robert H. Davis, Assistant Superintendent
of Sanitation Division.  A special note of  conmendation is due Frank
Styers, whose intimate knowledge  and understanding of gas-barrier prin-
ciples and his  familiarity with  the Link Road, site resulted  in high-
quality construction  and performance, of  the gas  barrier-.
    Acknowledgment  Is also due  representatives of the North  Carolina
National Guard  for  their close  cooperation, particularly Hajor James  N.
Stoneman.
    Key personnel  from  b'nviro-Engineers,  Inc., an affiliate  of Engineering-
Science, Inc.,  who  participated In this  project  were M. DeVon Bogue.  Pro-
gram  Manager, and Dr. Rahman Sheikh.   The  overall program  was conducted
under the  technical direction of Dr.  Donald L. Fcuerstein.
                                   vll

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                              CHAPTER I
                               SUMMARY

     The Department  of Public Works, City of Uinston-Salea, North
Carolina, assisted by Enviro-Engineers, Inc., cordueted a  study  of gas
hazards associated with the Link Road landfill and nearby  structures,
particularly the North Carolina National Guard Armory,  f«J» August 1972
through June 1974.  The study Included a literature review of landfill
gas generation and movement and of the s:ate-of-tho-art of landfill gas
control technology; a review of the explosion attributed to ignition of
nigrat.ng landfill gas in the Armory on 27 September  1969; the design.
Installation and evaluation of a unique type of active gas barrier between
the landfill and the Armory; and the development of guideline considera-
tions  for gas barrier design and detection of landfill gas migration:
hazards.
     The review of literature- on landfill f.-\. generation and movement
Indicated that information on this subject in sparse.  The state-of-the-
art of landfill gas control  technology is limited In  scope and applica-
tion,  consisting primarily of high-capacity active systems, installed
after  landfills were  convicted and developed without specific considera-
tion of gas  flow principles  or conditions at the site of barrier instal-
lation. The  review of the Armory explosion did not delineate any  likely
causes other than migration!  accumulation and Ignition  in the Armory
rupp]y room  of gases  from  the Link Road  landfill.
     The gas  barrier  system,  designed, installed  and evaluated  at  the
Lluk Road site, was developed on a  rational basis, considering  the
anticipated  generation of  gases In  the landfill,  gas permeability  of

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the adjacent soils, gas  flow principles and sinilar factors.   The  system
Incorporates a« series of gravel-filled veils, each containing a perforated
pipe and valve assembly. A header connects all veils to a snail-capacity
vacuua pump and vent assembly.  The system is monitored by a  gas analyzer
console in the Armory, connected to a aeries of gas probes in the  soil
between the barrier and  the Armor/ and in interior spaces, along with
audible and visual alarms to indicate gas concentrations exceeding 25
percent of the lower explosive  Unit.
     Testing of the installed system Included measurements of gas  concen-
trations on both sides of the barrier and the measurement of  pressure
profiles along and transverse to a section of the barrier. Coob us tittle
gas concentrations were  reduced on the Armory side of the barrier  to
sero or near-zero levels wlttiin several veeks after pumping began, and
have remained at these levels through June 197A at minimal pumping rates.
Ubiquitous negative pressure levels were established in the soJl along
and near the barrier shortly after pumping be Ran and have been maintained
throughout the test period.  It would appear that the efficacy of  the
barrier has been demonstrated.
     Although  the program did not permit  refined or detailed  guidelines
for the detection of gas hazards by simplistic procedures perforoed by
landfill management personnel,  general comments were derived  based on
project experience which may be helpful.

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                               CHAPTER II
                              INTRODUCTION

PROJECT RACKCROt'IJD
     The degradation of burled solid wastes under anaerobic conditions
results In the generation of nethone gas which nay rlgrate through the
soil Into areas peripheral to the landfill and accumulate In explosive
concentrations.  Methane is odorless and cannot be rc.idLly detected with-
out special instruments; consequently, neons are needed not only to de-
termine the node and extent of migration of landfill gas but also to
provide systems to protect buildings and other structures fron gas entry
and accumulation.  This report provides the results of a project to In-
vestigate an explosion attributed to accumulation . nd ignition of land-
fill gas at the National Guard Armory in Winston-Salon, North Carolina;
to investigate gas migration characteristics; to design, install and
evaluate a prototype gas barrier; and to provide criteria and <*tsign
guidelines for gas barriers.  The following sections describe background
clencnts and project objectives.
Armory  Lxplosi on
     tt» 27 September 1969,  at about  8:40 a.m.,  a  flash  fire  or explosion
occurred in the nupply  room of  the North Carolina National Guard Armory
in Uinaton-Salcm, North Carolina.  Twenty-five  guardsmen were injured
and  three died as a  result  of  the accident.
     The nearby Link Road  solid waste  landfill  was considered to he the
source  of explosive-  gases,  which were  thought to have  migrated  through
the  Boll and  into the  building.  An  account  of  the explosion, including
a review of possible contributing  factors, is presented in Chapter III.
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Early Investigations
     Following the explosion, a number of investigations were Bade in
an effort to determine the cause of the incident, the potential for a
recurrence* whether explosive gases were migrating from the landfill
into neighboring areas through the coil and to evaluate the factors de-
termining the migration and accumulation of gases from the landfill.
Those investigations relating to the explosion are detailed in Chapter
111.
     The Winston-Salem Department of Public Iforks then sought the assist-
ance of Enviro-Engineers, inc.  (EE), who had performed investigations of
migration of feas from landfills trv the L«* tofceUs,, California area, to
define and Initiate a gas monitoring prog ran at  the Link Road landfill
for the purpose of determining combustible gas concentrations and migra-
tion potentials.
     Twenty gaa sampling probe  locations, with probes located at l-» 10-,
25-, and 40-foot depths, were established around the northwest periphery
of the landfill and around the Armory.  The probes, patterned after
those used by EE in the Los Angeles studies, were attached to plastic
tubes leading to ground level where they could be connected tP portable
gaa analyzers Cor direct  reading of combustible  gas in percent of  the
lower explosive limit or  in percent by volume.   Gas samples were also taken
for gas chcomatographlc analysis.  Gas concentrations were determined at
those probes nearest  the  Armory once  daily  and  at  the  remaining probes
once weekly.  (Tlicso Initial monitoring probe locations ace shown  in
Figure 5, Chapter III.  In later investigations, additional probes ware
installed.   Some were  destroyed and others  were not used  in some of  the
Investigations.)
     Combustible gas  ton cert rat ions  in airi  near the landfill were  at high
levels throughout  the  surveillance period,  and  relatively high levels  of
combustible  gas were  noted in  those probes  located on  the side of  the
Armory nearest  the  main noay of the landlill.  The probes nearest  the
supply room showed  consistently high levels of  combustible gas at  all

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depths, and probes beneach the building slabs in the  supply and assembly
rooms showed combustible gas concentrations well above the lower explosive
limit most of the time.
     It was generally concluded that conditions existed wherein combus-
tible gas  (primarily methane) was being generated in the landfill in
considerable quantity, that it was migrating through the soil to and
beneath the Armory and that concentrations above the lower explosive
limit could accumulate beneath or in the building, posing a likely hazard
of recurrence of explosions if the Armory were  reoccupled.  (The Armory
was vacated shortly after the explosion.)  It was further concluded that
safe beneficial occupancy and use of the Armory could not be resumed un-
less combustible gas concentrations near and beneath the building could
be brought, and maintained, well below  the lower explosive  limit.  The
extent and results of early investigations are  included in  Chapter III.
Project Development and Funding
     The  Winbton-Salen Department of Public  Works, after  discussions
with U.S. Environmental Protection  Agency  (EPA)  Solid  Waste Program
representatives,  submitted,  in January  1970,  an application for a demon-
stration  grant  to conduct a  study and demonstration  related to the
Armory explosion  and  to design and  evaluate  a gas barrier at  the Link
Road  landfill.
      After several revisions of  the original proposal, which  resulted  in
a considerable  expansion  of the  total  project, a grant award  was made  on
 26 June  1972,  and the project was  initiated by EE to provide  engineering
 consultation,  design  and  evaluation functions.  The project is more fully
 described in the following section  and project findings are embodied in
 the succeeding chapters.
 PROJECT OBJECTIVES
      The project, as finally developed and funded,  included four main
 objectives:  (1) investigations pertaining to a review and report of
 the Armory explosion; (2) a review of  the state-of-the-art of gas migra-
 tion and  gas barriers, a review of gas barrier technology  and designs,
                                    5

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the design of a gas barrier for installation at the Link Road site and
its evaluation; (3) investigations of factors Influencing gas generation
and migration from landfills and development of procedures for detecting
and evaluating gas migration in terms of management guidelines for land
operators; and (4) establishment of design criteria for gas barriers.
     A number of factors, including placement of new soil cover on the
Link Road landfill, resulted in only partial fulfillment of a number of
the tasks and in their termination, with EPA approval.  It was not pos-
sible to accurately define the relationship of settlement, cell structure
and cover thickness, climate and other factors with gas generation and
migration; to evaluate effects of gas on vegetation as an indicator of
gas potentials; or to establish a meaningful "checklist" technology for
landfill operators.  It appears that achievement of these objectives
could best be fulfilled at a landfill where the various parameters could
be more accurately measured rather than at a completed landfill.  The
barrier design and evaluation was reoriented, with EPA approval, toward
the design and testing of a low-flow barrier system rather than the com-
bined high-flow and gravel-trench system originally conceived.  This re-
vision has resulted in the development, evaluation and demonstration of
new technology in gas barriers.
     The project objectives listed below are those pursued in the final
project to completion or to a point where meaningful information or
observations were possible.
Investigation and Report of Armory Explosion
     This objective included the accumulation and assembly of all known
data, facts, accounts and reports on the occurrence and aftermath of
the explosion; assembly and review of all investigations and reports of
conditions at the site before and after the explosion; determination and
description of the development and operation of the landfill; a review
of similar incidents elsewhere; an investigation of the landfill site
and the Armory to document  features which might have contributed to the

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migration of gases and their accumulation and ignition in the Armory; a
determination, if possible, of the cause of the explosion;  and prepara-
tion of a full account of the explosion, investigations and conclusions,
if any.  Chapter III presents a complete account of the fulfillment of
this objective.
Evaluation of Factors Related to Gas Generation and Migration
     This objective included a review of the technical literature on gas
generation and movement to establish those parameters which should be
investigated and which would be most applicable within a checklist meth-
odology for landfill operators in assessing gas migration and hazards.
Other activities included the selection and characterization of appro-
priate test landfills; the design ard installation of monitoring systems
for combustible gas concentrations, settlement, vegetation effects and
climatological factors; collection and analysis of data; development of
gas monitoring techniques; and development of a checklist and rating
system.  These efforts were only partially successful, and effort in
achieving this objective was reduced with EPA approval.  Consequently,
the gas monitoring techniques and the checklist procedure are of a very
preliminary nature.  Findings are presented in Chapter IV, and recom-
mended techniques are given in Chapter IX.
Review of State-of-the-Art in Gas Barrier Design
     The objective included a review and summary of the technical litera-
ture and analysis of the design aspects, functioning and application of
existing or new technology to the conditions of the Link Road landfill.
The review included both active and passive systems and systems incor-
porating features of both, plus assessment or development of new tech-
nology, including high-flow and low-flow systems.  A summary and analysis
of the state of the art is provided in Chapter V.
Data Accumulation and Investigations Related to Barrier Design
     The task  required collection of data  for design purposes, including
gas production potentials, soil characteristics and gas permeability.

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area to be protected, cost, technological and construction considerations,
and monitoring systems.   Findings are presented in Chapter VI.
Selection and Design of Cas Barrier
     The objective required selection of the most appropriate gas barrier and
preparation of detailed design drawings and specifications, including
cost estimates and bid document information.  The details of fulfillment
of this objective are presented in Chapter VI.
Cas Barrier Installation
     The objective included selection of a contractor, equipment pro-
curement and construction supervision.  Details are included in Chapters
VI and VII.
Monitoring Program
     Throughout the project, gas concentrations were monitored at the Link
Road landfill and at two  other landfills (not reported herein) in accor-
dance with the needs of the various objectives.  Monitoring included the
installation of gas probes,  the periodic determination of gas concentra-
tions using a portable combustible gas detector and analysis of samples
by gas chromatography.  In addition, records were collated on rainfall and
other climatologieal data. Monitoring was done on a relatively continuous
basis at the Link Road landfill and was revised (following selection of
the barrier design) to provide base-line data and performance-evaluation
data for the barrier.  Monitoring programs arc described in Chapter III
and in Chapters VI through IX.
Cas Barrier Evaluation
     Prior to installation of the gas barrier, gas probe layout and in-
stallation was devised, along with a detailed program for determining
barrier performance.  The evaluation included monitoring of gas flows In
various parts of the system, determination of pressures in the soils
adjacent to the barrier and determination of gas concentrations on both
aides of the barrier and  inside the Armory by means of portable gas
analyzers, gas chromatography and the installed automatic monitoring
systems.  Evaluation of gas barrier performance Is given in Chapter VIII.
                                    8

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MANAGEMENT OF THE STUDY
     A work plan was developed wherein the accomplishment of the various
tasks required to fulfill each objective was subdivided into subtasks,
and responsibilities were assigned to the Vinston-Salem project staff
and to EE.  For the most part, data collection was perfonrcd by the
Winston-Salem project staff in accordance with EE recommendations.
Data analysis was performed primarily by EE.  Technology reviews, barrier
selection and design were an EE responsibility, along with development
of barrier evaluation programs.  Barrier installation and developnent of
barrier performance data were Winston-Salem responsibilities, whereas
analysis of performance data and development of design guidelines were
done by EE.  The account of the Armory explosion was largely a Vinston-
Salem staff effort with EE's major input being directed toward interpre-
tation of documented investigations and specific further investigations
to complete a technical review of the factors possibly related to the
incident.  EE had the major responsibility for developing and preparing
the technical report.

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                              CHAPTER  III
           AN ACCOUNT OF THE EXPLOSION IN THE WINSTON-SALEM
                        NATIONAL GUARD ARMORY

ACCOUNT
     On 27 Septenber 1969.  at approximately  8:40 a.m., a flash fire or
explosion occurred in the supply room  of the North Carolina National
Guard Armory at 2000 Silas  Creek Parkway (formerly Link Road) in Kinston-
Salem, North Carolina.  Of  approximately 25  Guardsoen injured in and
near the Supply Room, 1Z were seriously injured, seven of vhom are now
partially or totally disabled.  Three  Guardsmen died as a result of burns
or subsequent complications.
     The National Guard Armory was built in  1962 adjacent to the Citv's
operating solid waste landfill, whose  continued operation was a condition
of the deed.  In addition to the Armory, the National Guard utilized ad-
joining landfilled property for parking and  servicing a large fleet of
supply vehicles, including  large-capacity fuel tankers.  Other National
Guard structures included a garage/repair building, a small shed and an
underground fuel-storage tank in the parking area, and a prefabricated
steel storage building constructed on  a slab placed over a landfilled area
to the rear of the Armory.   The \rmory was built on a six-inch reinforced
concrete slab and, except for the central drill-hall area, is of one-story
conerote-block construction. A two-story addition to the building,
»>uilt by the City in 1965,  housed Winston-Salem's Police Academy.  The
slab was poured over four inches of crushed  stone.  The site was prepared
by leveling existing topography.  No portion of the building extends over

                                  10

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a landflllcd area and closest proximity to the landfill  (about  30 feet)
is at the rear of the building.   Prior to placing foundations,  it wan
found that soil conditions at the rear of the buildings  did not provide
adequate bearing capacity; consequently, spread footings were used to  a
depth of six feet along the rear of the building.  No nechanized ventila-
tion system was provided for the main building.
     Other structures nearby on  land of or adjacent to the Link Road land-
fill Include an abandoned abattoir (now used for fire training  purposes),
a fire training tower and a peripheral road constructed  around  the fire
training ai°a, developed by the  City for Fire Department use.  The -fire
training tower is built on a landfilled area as is the peripheral road.
Fire hydrants are supplied by a  looped eight-inch water main crossing
beneath the vehicle storage area from Silas Creek Parkway.
     Utility structures include  water and electrical services to the
Armory, a sanitary sewer serving the garage and Armory,  building sever
and drains and a 72-inch storm drain constructed through the landfill
and discharging to Salem Creek.   The stona drain was emplaced during land-
fill construction.  Street drains from the fire training area,  the en-
trance ro£.d and paved areas enter the storm drain.
     Figure 1 provides general details on the Armory, the nearby landfill
and associated facilities.  Figure 2 shows the boundaries of the landfill
and structure and Figure 3 shows final landfill topography (prior to place-
ment of additional cover in July 1973).
     The Link Road landfill was  initiated in 1949 when the City's onsite
incinerator was closed and was near completion in 1969 when the Armory
explosion occurred.  The present vehicle storage area is placed over the
area formerly used to landfill incinerator residue.  Dead animals and
wastes from the abattoir were disposed in trenches close by.  No other
segregation of wastes was practiced (except surface composting of leaves
and vegetative trimmings) and wastes deposited throughout the remainder
of the fill include intermixed domestic, industrial and commercial wastes.
In general, wastes were placed in an organized fashion, compacted to the

                                  11

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                               SANITARY SEWER
                                      V
                    SILAS
         CREEK
 PARKWAY
                           STORM DRAIN
         SANITARY
         SEWER  -
            PAVED
            AREA
                                           \
                                         \Y
                                       ..  i_)
          VEHICLE
    METAL PARKING AREA
   0SHEO  (GRAVEL)
M  J*  H  M  M M  M_M<
                          a         -   v»
                        TOWER/  ( ^~ d&i
                        i   ^  V.*.>-O=-/J>
                           ARMORY
                         SUPPLY
                         ROOM—»T
 ^PAVING  J
/^^ar^llT^
11\    rr^A
 VEHICLE
 PARKING
 (GRAVEL)/
                            SANITARY
                            SEWER .
                                                                             N
                                                                             *
  72"DRAIN
                                                    ---- ~'*
                                                    CONCRETE SLAB
                                                  SEWER MANHOLE
                                                      VENT ASSEMBLY
   VEGETATION


LANDFILL

                             A
                          LANDFILL

                              VEGETATION
                                                      \
                    TO SALEM CREEK
            \
                                                      LEGEND

                                                  — APPROXIMATE EDGE
                                                    OF LANDFILL
                                                    PONDED WATER
                                                                           AREA OF MAJOR
                                                                           SUBSIDENCE
Figure   I:   National  Guard  Armory  and  associated  structures,  1972

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                          SILAS CREEK  PARKWAY
                   PARKING
                  oSHEO
LOCATION OF \
FORMER      I
SEWAGE      /
TREATMENT J
PLANT
       x
                „.	FORMER
                               CONCRETE
                               SLAB
    INCINERATOR
                              LINK
                              ROAD
                              LANDFILL
EXISTING STRUCTURES
APPROXIMATE LANDFILL
BOUNDARY
     Figurt  2:  Link  Rood   landfill  and   associated  structures

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APPROXIMATE LIMIT-
  OF LAND  FILLED
         WASTES
                           nr,7/111 "?•'•'•
           LEGEND
           STRUCTURE
           PAVING
           GRAVEL SURFACE
0 100 200   400
    SCALE
        Figure   3'    Final  topography  of  tht Link  Road  landfill  sift,  1972

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best of ability of equipment provided and covered with  compacted  soil
cover, If not daily,  at frequent Intervals.   Operation  of  the site,
while perhaps not In  strict accordance with  high standards set  for sani-
tary landfills today, was equivalent to or better than  operation  of  its
contemporaries.  Depth of the landfill ranges from 10 to nearly 40 feet
in places.  Inmedlately back of the Arnory.  wastes were packed  along a
steep natural bank (extreme settlement occurred and Is  continuing to
occur at this location).  The landfill is reported to have incorporated
a high ratio of soil  cover to wastes deposited.  Most of the bulk of the
landfill Is saturated from groundwater and surface water.   Total  quantity
of wastes deposited is estimated at 1.4 oillion cubic yards. Figure 4
shows typical cross sections through the landfill.
     In the summer of 1965, a welder installing part of the storm drainage
system near the Armory received minor burns  in a flesh  fire. In  November
of the sane year, a fireman working near one of the street drains In the
fire training area dropped a lighted match into a manhole  and received
minor burns in the resulting minor explosion.  In December 1965,  the Guard's
Executive Officer reported a flash fire while welding downspouting on  the
Armory's roof drain system wnlch he was connecting, to an underground
drainage system extending into the filled area back of  the Armory.   The
Fire Department determined presence of combustible r.as  in  the abattoir
but none in the Armory.  In 1966, representatives of the Federal  Solid
Waste Program investigated conditions in the fire training area and  con-
firmed methane in the storm drains.  In July 1966, following complaints
of strong odors froei the landfill, a blower  was installed  in a  brick
building, surmounted  by a tall vent stack, over a large manhole in  the
stora drain to the rear of the Armory.  This ventinp, system was operated
intermittently thereafter and was apparently affective  in  dispersal  of gas
and odors.  During these early episodes, investigations centered  around
accumulation of combustible gases in sewers, a condition not uncommon  to
sewers, though more common to sanitary sewers than to storm drains.
No detailed investigations were made to determine occurrence or extent of
gas accumulation in the Arnory.

                                  IS

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                                                1200
Figure  4:   Cross-sections  through  completed Link Rood
                       landfill, 1972
                          16

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     Only a week or so before the explosion occurred,  three  to  four feet
of additional cover had been compacted over the landfill Just oack  of  the
Armory, where extensive settlement had occurred.  The  Guard  subsequently
dismantled and removed the prefabricated building nearby, due to extensive
deformation of the building slab caused by settlement  of the landfill  in
this area.
     On 26 September 1969, the day before the tragedy, City  representatives
not with Guard represpntatives to investigate the occurrence of "odors
or gas" from the arms storage vault off the Armory supply room.  No source
of gas, defective systems or other causes were noted.   Arrangements were
cade to have the Fire Department check out the vault (after being closed
several days) with portable gas detection equipment the following week.
Since the vault would be opened during drills, the Guard proceeded with
scheduled drills.  The explosion occurred the following morning.
     Immediately following the explosion, it was conjectured by some that
the "blue flame" explosion or fire was caused by ignition of gas migrating
from the landfill and accumulating in the vault or supply room.  Investiga-
tions did not reveal presence of petroleum products or flammable materials
in the supply room or vault, nor was an ignition source definitely estab-
lished.  It is presumed  that one of the Guardsmen lit a match, despite
posted "No Suoking" regulations.
     The explosion lifted the roof of the supply room at least-six inches
at the southeast corner.  Windows were broken, but it was not known vhether
they were broken by the  occupants or  from  the  force of the  explosion.  The
rear wall and celling were blackened and scorched, but most of the stored
materials  (such as blankets) were undamaged.   A one-half inch horizontal
separation between the  rear wall and  the floor slab was  noted  following
the explosion.
     Combustible gas sampling in the  supply room, drill  hall and pistol
range shortly after the  explosion, using a portable combustible  gas indi-
cator,  revealed combustible  gas concentrations near or above the lower
                                   17

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explosive limit   (LEL) only at  cracks in the slab.  In soils outside the
Armory* readings were above the LEL.  It was thought that soil saturation
by recent heavy rains prevented landfill gas from venting through the
landfill cover, thereby  increasing  lateral gas migration while lack of
ventilation in the building may have contributed to gas accumulation in
the supply room.  Subsequent  readings on 6-9 October 1969 were inconclusive,
but seemed to indicate a significantly higher concentration in the vault
than in the supply room  (but  no concentrations were noted above the LEL).
     Gas sampling was done in nearby sanitary sewers and storm drains on
9-10 October and 21 November  1969.  whereas high combustible gas concentra-
tions were noted in manholes  near and behind the Armory in the early tests
and petroleum vapor was  reported  in two of the manholes, there was no
conclusive evidence of gasoline or  other petroleum vapors entering the
Armory from the sewers,  and all combustible gas concentrations had dimin-
ished by late November 1969.
     A network of 20 holes was  drilled 30- to 40-feet deep around the
Armory in 1970, and gas  sampling  probes were inserted at 1-, 10-, 25-
and 40-foot depths.  The probes,  whose locations are shown on Figure 5,
were connected to plastic tubes leading to the surface from which com-
bustible gas concentrations were  determined periodically with a portable
combustible gas detector. Subslab  sampling points were established by
drilling holes through the floor  slab in the drill hall and supply room.
Combustible gas concentrations  in the range of 30 to 40 percent by volume
were recorded in  the exterior probes over a period of many months.  Con-
centrations in excess of the  LEL  were consistently recorded below the
building slab.  This sampling program verified that combustible gas from
the Link Road landfill was migrating to and beneath the Armory, presenting
a continuing hazard of gas accumulation and explosion.  Concern about
this situation prompted  interest  in developing and demonstrating a gas
barrier between the landfill  and  the Armory.
*For methane,  the LEL is four to five percent by volume  in air.
                                    18

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    H  M  M M I
   '16
           15  J
              il  >ft.M  * K i

   18         .17
   '  H  °lf  M  H   M   MJ»<
r~z
    .
                                 •10
                                                       LEGEND

                                                    •   SAMPLING STATION

                                                  I, 2   PROBE NUMBER
Figure   5 •  Initial gas monitoring stations, 1970-1971

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     The Armory was vacated  shortly after  the explosion and since has
remained vacant.  The  landfill  was completed in March 1970 but continued
use has been made of the  fire training  center and the Guard's vehicle
storage and maintenance area.   Wild vegetation  has grown over most of the
landfill surface.  Except for periodic  monitoring of combustible gas coi -
centrations, little activity was  conducted on site until August 1972,
when Investigations began related to studies of gas migration and develop-
ment of a gas barrier.  A portion of these investigations was directed
toward a review of the Armory explosion and to  possible causes.
FINDINGS
     During the placement of probes in  the landfill for combustible gas
concentration evaluations in 1973, it was  found that high moisture con-
ditions occur throughout  the landfill.   Combustible gas measurements
indicate that the gas  migrates  tnrough  the soil a considerable distance
from the landfill boundary and  occurs beneath the Armory in explosive con-
centrations.  Investigations indicated  that the soil cover, though variable
in consistency and thickness, is  relatively porous, but that saturation
of the surface layers  by  rainfall may increase  lateral migration.  The
landfill is continuing to settle  unevenly, particularly in a large area
immediately back of the Armory  and in an area on the east side of the
fire training area (see Figure  1).  In  the summer of 1973, three to four
feet of new soil cover was placed over  the upper portion of the Armory.
This new soil cover places additional weight on this portion (which con-
tinues to subside) and may further reduce  venting of gas through the
cover or intensify local  gas migration  through  adjoining soils.
     Analysis of soils along the  line of the barrier indicated considerable
variation in the soil's gas  permeability along  the landfill periphery,
with the greatest permeability  being noted back of the Armory.  In early
tests of the gas barrier  in  1974, rapid gas flow was noted into three
of ehe barrier's suctirn  wells, located about midway in the vehicle storage
area. Indicating local areas of high gas permeability in the nearby soils.
Porous incinerator residue underlies this  area.
                                   20

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     Gas flow toward the Armory appears to be greatest immediately to the
rear of the Armory, where the land::! 11 periphery is closest and where major
settlement is continuing.  Significant combustible gas concentrations also
occur on the vest side cf the Armory, indicative either of relatively long-
range but attenuated gas migration from the main body of the landfill oz
of moderate gas flow from wastes landfilled in the incinerator-residue area.
     In 1973, a ditch was dug around the southeast corner of the Armory to
a depth of about eight feet in order to determine if direct channels for
gas migration existed between the landfill and the Armory in this area.
Examination indicated that several types of relatively coarse, sandy soils
were intermixed, with discrete lenses of sandy-micaceous material ocurring
throughout.  No direct conduit or obvious avenue for ready migration of
gases was noted.  Tests on the soil did not indicate presence of petro-
leum products.  At the same time, field test? were made which indicated
that building drains were functioning properly.  It was noted that tile
drains, formerly connected to roof-gutter downspouts, had openings near
the building which would permit venting of any gases entering the drains
before they reached the building.  There was no connection between roof
drains and the Armory interior.
     Inquiries to  the National Guard regarding possible spillage  of  gaso-
line into sewers on nearby soils, with likely entry  into the Armory,  did
not substantiate this possibility.
     In summary, the exact cause  of explosive gas  accumulation  in the
supply  room or vault and its subsequent Ignition has not been determined.
It does not appear that  utility gas or petroleum-vapor sources  were  likely.
No explosive  gas,  other  than combustible  gas migrating from the landfill,
vas discerned and  the Armory was  reasonably veil-protected from accumula-
 tion of gases  from normal sources.  Combustible  gas  was  likely  migrating
 from  the  landfill  through adjoining soil  to  a-.id beneath  the Amory prior
 to the explosion,  but  its presence  or hazard potential had not  been  con-
 firmed.   Early  assumptions  that  combustible  gas  concentrations  were  con-
 fined  to  sewers  were  reasonably  valid,  in the  light  of extant knowledge
 and-practice.   Although  operation and construction of the Link Road  land-
 fill  resulted in conditions  contributing to extensive gas production and
                                   21

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migration, Che nature  and potential hazards of gas migration were not
then well known.  The  landfill was operated in a manner common to landfill
practice prevailing at that  time.
     The Armory explosion has highlighted  (unfortunately with tragic
aftermath) the extreme importance of recognizing the hazardous explosion
potentials from landfill gas migration possibly resulting from operation
of solid waste land disposal sites.  Measures to -minimize gas production
and migration potentials during  and after  landfill operation are in order.
along with the protection of structures nearby from gas accumulation by
structural features and by  active or passive gas barriers.  Such measures
are included in modern guidelines for sanitary landfill design and opera-
tion.
     Litigation following the Armory explosion has apparently been settled.
Tests on  the gas  barrier have thus  far indicated favorable  results.  Gas
concentrations between the  barrier  and  the Armory  have been reduced to
zero or near-zero levels  by operation of  the  gas barrier.   If, after a
suitable  period of operation,  the  gas barrier remains  as  effective as
the preliminary results have indicated,  and the  barrier system is propetu
operated,  regularly monitored and  constantly  maintained at  speci'fied      *
operating levels, normal use and occupancy of the  Armory  should be
possible.
                                   22

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                               CHAPTER IV
     REVIEW OF GAS GENERATION AND MOVEMENT FROM SOLID WASTE LANDFILLS

LITERATURE REVIEW
     The paucity of information on gas generation and movement from
solid waste landfills is attested to by only brief mention In a principal
solid waste disposal reference (Reference 1) and the listing of only 48
articles in the most recent bibliography on the subject (Reference 2).
Many of the articles are of a nontechnical nature and,  in many cases.
discussions of gas generation and movement are only a small part of  the
article listed.  Only a few are based on scientific measurements over a
significant period of time, and several of those containing specific data
are based on observation of simulated landfills, on test refuse cells or
on laboratory-scale experiments.  The most informative of the early
articles, based on field studies, was that reporting studies related to
groundwater and to carbon dioxide production from landfills, conducted by
or for  the California Department  of Water Resources, the California
Water Pollution Control Board  and the California State Water Quality Con-
trol Board.   Studies of gas explosion episodes were limited in  thorough-
ness or scientific approach;  the  most extensive  report being of an
explosion  in  an abandoned power  substation  in Atlanta, Georgia, which was
being converted to a recreation  facility  adjacent to a landfill.   An ex-
tensive study by  Los Angeles County  included a  review of  gas production
and  movement  at 10 landfills in  the  Los Angelas  area and  extensive lab-
oratory studies to determine diffusion  coefficients for  landfill  gas
in a variety  of soils  (Reference 3). The study also presented design and
construction  criteria  for  buildings  on  or near solid waste landfills.
                                  23

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Studii-s of pl'ot  landfills  or  refuse  cells  in  southern California
(References 4, 5, 6  and  7)  have  contributed considerable information on
gas production and migration.  Most of  the  reported work on gas genera-
tion and movement has  been  undertaken in recent  years  (i.e., since
1954); the earliest  article was  published in 1940.
     The literature  review  was supplemented by field inspection and re-
view of information  on existing  solid waste landfills in the Los Angeles,
California area where  a  number of  gas migration  studies or observations
have been made and where gas barrier  systems have been installed.
CAS GENERATION FROM  SOLID WASTE  LANDFILLS
     In ttie early stages of solid  waste decomposition in a landfill,
decomposition takes  place through  processes which utilize the initial
supply of oxygen entrained  in  the  wastes.  In  the first six months to a
year, carbon dloxidn predominates.  Principal  gases produced are carbon
dioxide, hydrogen, nitrogen and  methane. Carbon dioxide and methane
mak£ up over 90 percent  of  the total  gas produced (Reference 8).  Hydro-
gen sulfide iuay be produced in areas  where  salt  water is in contact with
the refuse.  As the  entrained  oxygen  supply diminishes, anaerobic decom-
position ensues and  an increasing  amount of methane is produced while
other gas production diminishes.  Significant  methane production may
occur within six months  to  a year, and  production may continue over long
periods of time.  The  production of gases depends on a number of factors,
including the amount of  oxygen available, the  organic content of the
solid wastes, particle size and  degree  of compaction and the amount of
moisture available.  In  general, high organic  content and moisture will
increase gas production. Smaller  particle  size  (by exposing more of the
refuse to bacterial  action) may  have  a similar effect.  There are some
Indications that  densely compacted refuse will decompose at a slower rate
than loosely compacted refuse  and  that  gas  production may be prolonged
In densely packed landfills (Reference  7).   Several studies of gas produc-
tion have indicated  that from  very moist or saturated "noraal" domestic
re'Juse, carbor, dioxide may  be  produced in quantities of about 0.2 cu ft/lb,
whereas from the  same  type  of  refuse  which  is  relatively dry, the
                                   24

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production is only about 0.04 cu fc/lb (Reference 9).   In a sealed test
chamber of mixed refuse, 2,027 cu ft of decomposition  gases were pro-
duced from 73 cu yd of refuse over 906 days, or about  28 cu ft/cu yd
(Reference 7).  In a similar test, over a 200-day period, gas production
was approximately 28 cu ft/cu yd of refuse, or about 0.04 cu ft/lb
(Reference 7).  Theoretically, a pound of refuse can produce 2.7 cu ft
of carbon dioxide and 3.9 cu ft of methane (Reference 10).  How much of
this potential production will be realized in a particular landfill over
a given period of time will depend on a number of factors which aid or
binder gas production, and the variations in production will be largely
dependent on variations in these factors.
     Anaerobic conditions may occur within a month after wastes are buried
(Reference 11).  Dry landfills apparently produce much less gas than those
which are initially or subsequently saturated with moisture.  Moisture
additions to a landfill can reinitiate or increase carbon dioxide and
methane production.  Under such conditions, once initiated, methane pro-
duction may continue f«r a long period of time.
GAS MIGRATION FROM LANDFILLS
     In studies of migration of decomposition gases from  landfills
(References 4, 8, 12, 13 and 14), it has been noted that  carbon dioxide
and methane migrate upward and downward as well as laterally through
surrounding soils.  Most of the gas produced will migrate upward  through
soil cover.  Field observations have reported explosive concentrations
consistently as far as 600 feet from a landfill  (Reference 15).
     Field observations in a study of a landfill in southern California
(Reference 12) Indicated that carbon dioxide moved vertically  through
the soil cover at more than 10 times the rate it moved downward or  Later-
ally through adjacent soils.  Other studies indicate that 18 to 24  times
the quantity of carbon dioxide and methane, respectively, pass through
the cover than into the surrounding soil  (Reference 13).  Carbon  dioxide
movement rates ranged between 0.22 and 0.8 ft/day vertically and  betvesn
0.24 ft/day and 1.4 ft/day horizontally  (in undisturbed alluvial  soils)

                                  25

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in one study  (Reference  9)  to vertical  and  horizontal velocities of 0.22
ft/day to 0.24  ft/day  in another (Reference 14).
     Little is  known about  gas migration within a  landfill.  In landfills
where well-compacted waste  and cover does not  prevail or where settlement,
groundwater intrusion  or fires have  caused  destruction of cell integrity,
gas will likely migrate  through voids or channels  throughout the nass,
perhaps towards a section of the landfill's periphery where localized
(rather than  general)  gas nigration  may occur.  Numerous instances have
been noted where methane or other gases issue  from surface cracks in
landfills in  large quantity and at considerable velocity.  Maintenance
of a gas-permeable cover or other means of  venting, would appear to be
most important  in insuring  that lateral landfill gas nigration is mini-
nized.  Impermeable  scaling of a landfill surface  at any time will likely
cause a prompt  increase  In  lateral gas  migration  (Reference 16).  Even
If a landfill has been in place for  many years and decomposition of
early-deposited refuse is in an advanced stage (with theoretically de-
clining gas production rates), gas migration controls should consider
characteristics of the more- recently deposited wastes, wherein gas pro-
duction and migration  potentials may be highest.   Critical areas of a
landfill in terms of gas migration would likely be those where the mois-
ture content  is highest, where highly organic  wastes were deposited
(these are often concentrated in one area of the landfill, commonly with
minimal compaction or  cover) and areas  where the landfill surface nay
be most impermeable.
     In addition to  the  general gas  migration  characteristics of a land-
fill, it is apparent that local variations  in  gas  production and migra-
tion occur, perhaps  related to reduced  permeability of soil covet due to
precipitation,  settlement or other phenomena.  Ho  long-range correlation
of gas production and  migration of landfill gases  with precipitation has
beor. documented, but field  observations have indicated a general increase
It. gas migration following  extensive precipitation.  Monitoring of gas
concentrations  related to gas control barriers has indicated daily and
periodic fluctuations  or "excursions" of gas concentrations both above

                                   26

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and below the average.  Consequently, gas migration is likely to be
extremely variable and control systems should be based on theoretical
maximum potentials for gas production and migration.
HAZARDS DUE TO LANDFILL GAS MIGRATION
     The principal hazard from migrating landfill gas is likely to be
from methane.  It has a relatively high production rate in comparison
with other gases, it has a  .cndency to migrate laterally with greater
facility than other gases when venting is impeded and it has a long-term
production potential from landfills.  Its explosive hazard and the in-
ability to detect the presence or concentration of methane without in-
struments further emphasize its prime importance among the migrating
landfill gases.  The tendency of carbon dioxide to migrate downward to
groundwatcr and to acidify it increases the corrosivity of the water.
Methane, by contrast, is relatively insoluble in water.  Maximum produc-
tion of carbon dioxide from a landfill is relatively short-lived, in com-
parison with methane production.  Hydrogen sulfide, because of its noxious
odor, is relatively c&rily detected and is produced primarily in those
relatively few landfills in contact with sulphate-containing sea water.
     Relatively few occasions of explosions or other tragic consequences
from migration of landfill gases have been reported, and only a couple
have been investigated closely.  A survey of 2CS counties in 1965 Indi-
cated that only 21 percent had built on landfills.  In these cases, aany
of  the structures were plagued with settlement and gas problems  (Reference
17).  Fires in San Francisco's waterfront landfill were attributed to land-
fill gas (Reference 18).  A fire in a manhole of a sewer built through a
landfill near Knoxville, Tennessee occurred in 1947, within  two weeks
after the landfill was sealed with soil cover  (Reference 16).  At a  large
landfill near Seattle, Washington, pipes inserted  through the soil cover
were used to vent and burn  off escaping gases and  to partially eliminate
odors  (References 19  and 20).   In the New York City area, gas accumulations
In  a sewer near a landfill  were noted, and an explosion occurred in  a small
building situated on  another  landfill.  More recent explosions include
                                   27

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one at a warming hut at an  above-ground sanitary landfill converted to a
ski slope, an explosion in  a  former power substation being converted to
a recreational facility next  to an active landfill  in Atlanta, Georgia
(Reference 21). and the tragic explosion in the KMnstcn-Salem, North
Carolina National Guard Armory, built close to a landfill just being
completed.  The latter two  episodes resulted in five deaths and in in-
Jury to 12 building occupants.  In the Atlanta incident, methane gas
accumulated in the building from  landfilled refuse  placed against and
under the building and was  ignited hy a workman installing natural-gas
heating facilities.  Ignition of  leaking natural gas from the gas
facilities was ruled out as a cause of the explosion.  In the Hinston-
Salem incident, early flash fires in sewer lines near the landfill had
been attributed to gas migration  from th_ landfill, but gas migration
beneath the Armory had not  been, suspected.  Following the explosion,
presence of methane in the  soil next to the building and beneath the
building's floor slab was detected in explosive concentration.  These and
later investigations, reported in Chapter III of this report, failed to
Indicate a source of explosive gas other than combustible ga& from the
landfill.  The influence of a large storm drain through the landfill,
either as a channel for combustible gases to the Armory or as a con-
tributor of water to the landfill, was not demonstrated,  Monitoring of
gas probes around the site  in recent yars indicates tne continued genera-
tion of combustible gas and its migration to the vicinity of the Armory
in explosive concentrations.
     Host of the explosions have  been attributed to accumulation and
ignition of methane.  Perhaps as  a result of these  other hazardous inci-
dents, construction of buildings  on or near landfills has apparently
dwindled or such development  is done with appropriate precautions.
OBSERVATIONS OF GAS MIGRATION AT  VINSTON-SALEM
     Early investigators attributed the accumulation of combustible gas
in she Armory just prior to the explosion to an antecedent heavy preciplta-
tltitij which reduced venting through the landfill cover with & resultant
increased lateral migration*  and  to a lack of building ventilation.  Gas

                                   28

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permeability •• asurements of soil samples, taken relative to the gas
barrier recently constructed, indicate that the peripheral soil is gen-
erally permeable to gas flow with highest permeability in the soils near
the supply room, where the explosion occurred.  Other possible influences
include extensive settlement near the landfill edge nearest the Armory
and subsequent additional placement of cover soil (shortly before the
explosion).
     It was not possible to make field measurement of gas generation rates
or the relative effects of cover type, thickness or settlement on gas
flow.  It was determined, however, that high moisture occurs throughout
the landfill and that it was actively producing combustible gas, which
migrates readily through the surrounding permeable soils.
     A more detailed account of observations and findings is presented
in Chapter VIII.
                                   29

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                              CHAPTER V
                 STATE-OF-THE-ART  IN GAS CONTROL TECHNOLOGY

INTRODUCTION
    Relatively  little  Investigative work has been performed and reported
in the literature concerning the generation and movement of decomposition
gases from sanitary  landfills.  Nevertheless,  uncontrolled migration of
decoiaposltion gases  from a landfill is recognized to be capable of posing
a great threat  to its  environs  due to pollution of groundwaters, damage
to vegetation or the hazards of gas explosions.  Only in recent years
have active measures been undertaken to investigate and provide means
for controlling the  movement of decomposition  gases from landfills.  The
limited literature on  the subject  of gas control measures makes reference
to procedures which  should or could be utilized to mitigate the problems
of gas migration, but  xt contains  very little  reference to the actual
means for achieving  the desired results.   This is probably due in large
part to the experimental nature of the art of  gas control technology.
Testing and evaluation of the various control  methods are still in progress
in different parts of  the country, and definitive conclusions are yet to
be formulated.  In general, detailed information on design and operation
jf gas control  systems is lacking  in the literature, mainly because this
area is a recent addition in the  field of  landfill design and utilization.
GAS CONTROL SYSTEMS
    This section contains information on gas control systems known to have
been installed, mainly in the western United States, either for experimental
purposes or in  attempts to eliminate existing  problems at particular sites.
Gas control systems  can be categorized into  two major subsystems—pre-
construction systems and post-construction systems.  The pre-constmctlon
                                     30

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systems consist of measures that arc incorporated into the design of the
landfill to mitigate the movement of gases from the landfill.  Integrated
design measures taken to prevent the entry of gases into structures
constructed on or adjacent to landfills are also included under the heading
of pre-construction systems.  Post-construction systems include all of
those facilities which are designed and constructed after completion of
the landfill or construction of structures or. or near the landfill.
Post-construction systems are developed as a solution for the problems
created by uncontrolled landfills.  Host gas control systems in existence
today are of the latter type.
Pre-Construction Systems
    Pre-construction systems are relatively recent innovations and their
development has come about as a result of the increased awareness and
knowledge on the hazards of landfill-generated gases.  Various gas con-
trol methods nay be utilized in the pre-construction stage.  These methods
are classified as "permeable methods" and "impermeable methods."  Some
permeable methods include the use of gravel vents or gravel-filled trenches
to provide a more permeable path for the escape of- gases from the land-
fill to the atmosphere.  In this fashion, decomposition gases are Inter-
cepted and prevented from migrating beyond the Units of the fill.  Other
permeable methods consist of a system of gravel-filled trenches and/or
wells, with vent pipes and collecting laterals inserted in the trenches
and the wells for conveyance of gases out and away from the fill and ad-
jacent structures.
     Impermeable methods are based on the use of natural or synthetic bar-
rier materials to prevent gases from migrating beyond the fill limits.  A
venting system is usually utilized along with the physical barrier system
in order to prevent the buildup of positive gas pressure within the con-
fines of the fill.  Such venting would particularly be required if the
surface of the landfill is later sealed by paving or by the use of some
other impermeable cover materi*?..  The barrier system may consist of clay.
synthetic membrane, concrete, asphalt or other bituminous material.
                                 31

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     It has.beep suggested  (Reference 22} that the most conaon, and pos-
sibly the most practical, impermeable barrier method involves the use of
compacted clay, either as a liner  in the bottom and sides of the fill or
as a curtain wall to block  underground  gas movement.  It was concluded from
laboratory experiments (Reference  23),  which were conducted to,determine
toe thane diffusion coefficients  for various soils with differing particle
size under varying  conditions of noisturr and pressures, that soils with
a high percentage of clay can act  as a  gas barrier under favorable soil
moisture conditions.  However,  the impermeable soil barrier method still
remains relatively  untested. Some synthetic membranes have been utilized
in landfill construction, but these have been used primarily for the pur-
pose of controlling the  flow of leachates.
     The literature contains very  little  reference to pre-construction
gas control systems constructed in conjunction with sanitary landfills.
It is probable, however, that much of the work in this area is still in
progress and has not been publicized or reported.  One example of such a
system  (Reference 24) is a  sanitary landfill located in Kansas City,
Kansas, which was initiated by  the Kid-American Regional Council, Kansas
City, Missouri.  The project is supported in part by a demonstration grant
from the Office of  Solid Haste  Management Programs, U.S. Environmental
Protection  Agency.  The  completed  site  is to be utilized for a regional
park, which .will include several public buildings and recreational facili-
ties.  Several homes are also located adjacent to the landfill site.
Becognizing the potential dangers  to these structures from landfill gen-
erated combustible  gas,  a combination permeable and impermeable system
for gas venting is  being constructed as part  of the landfill.  A soil
blanket under  the fill,  laid primarily  to control downward flow of
leachates,  also will provide a  relatively impermeable barrier  to the
downward movement of gases. To allow ventilation of gases from the fill,
a portion of the one-foot thick daily soil  cover of each lift  of the fill
at the site perimeter is being  removed  to allow  gases to pass  readily up-
ward through each  lift.   A  trench two to three feec deep will  t«» ex-
cavated and backfilled with gravel at  tne top of the fill in the final
                                   32

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earth cover around the site edge.  A permeable channel is  thereby  pro-
vided through which landfill gases  can travel  readily  and  vent to  the
atmosphere.  The effectiveness of this method  of gas control has not
been established.
     More common pre-construction systems are  those that are designed  and
constructed for protection of structures which are erected on or adjacent
to a completed landfill.  Numerous examples of these gas control systems
are in existence, although reported cases in the literature are rather
limited (Reference 25) and include examples of techniques  used to  protect
various structures such as school buildings, a market  building and a
residential area.  In most cases the control systems involve vent  pipes
around the perimeter of the structure or within the building itself,
gravel trenches, impermeable barriers around the foundations and under
the floor slabs, or a combination of these.
     Observations of some recent gas barrier installations in  southern
California were obtained from interviews with designers, developers and
public agency personnel.  Information from these interviews is presented
below.
     For protection of a public market located on natural ground adjacent
to a landfill, a series of trenches were excavated in the subgrade under
the building and backfilled with gravel.  The trenches were spaced approxi-
mately 12  to 15 feet on center and were 12 inches deep and 12 inches
wide.  These trenches extend the full width of the building,  terminating
at the foundation walls.  Two-inch diameter vertical vent pipes were
placed in  the walls of  the building and connected  to each gravel  trench
at tne perimeter of the building.  As an additional precaution,  the entire
subgrade beneath the floor slab was covered with a protective impermeable
10-ttll polyethylene membrane which was laid on a two-inc*  sand bed.
Venting of the trenches and subgrade area occurs by natural ventilation
only, and no provisions were made for forced ventilation.   Periodic
measurements of gas concentrat. >is have not detected the presence of
                                   33

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combustible  gas within  the confines  of  the building, indicating that the
precautions  taken  are satisfactorily venting  the  combustible gases from
beneath the  building.
     At the  site of  a new  apartment  building  complex located adjacent to
an old 70 to 130 feet deep  landfill  which was formerly a dlatomaceous earth
mine, a gas  interceptor trench was employed as a means to channel land-
fill generated gases away  from the building complex.  The trench extends
the full width of  the development and was installed in natural material
between the  fill and the buildings.   The trench is approximately 18 feet
deep and 24  inches wide, and  is  filled  with gravel.  To vent the trench,
which will eventually be sealed  over with pavement, four-inch diameter
pipes were Installed vertically  at intervals  of 30 to 40 feet.
     The public agency  that constructed this  fill also utilized a similar
gravel filled cut-off trench  in  a different location to intercept the
gases that might flow from the fill  to  adjacent private property and
home sites.  In this case,  the trench was 30  inches wide, 20 feet deep
and 1,050 feet long. This trench was left open to the atmosphere for
venting purposes and has successfully arrested all gas migration to the
endangered properties.  Recent measurements of gas concentrations on both
sides of the venting crench indicate that the trench is still acting
as a satisfactory  deterrent to migration of the gases.
     A more  sophisticated  gas control system  will be used for a public
service building complex  to be constructed adjacent to a former landfill
where monitoring has Indicated the presence of combustible gas.  The entire
construction area  is being filled with  earth  cover  for a depth of approxi-
mately SO feet to  bring the level  of the  completed surface to that of the
adjacent developments.   Prior to filling, a trench was excavated in the
original ground  in which a six-inch  diameter  perforated gas collector
pipe was placed.   The  trench  is  seven feet deep  and two  feet wide and is
backfilled with  gravel and sealed  at the  top  with a plastic membrane.
The total control  system extends for a  distance  of  approximately 850 feet

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and consists of two separate segments.   The first segment, which is 450
feet long, consists of a gravel trench,  perforated pipe and  four vertical
gravel-filled wells, which extend upward from the trench  to  the surface
of the new fill.  A four-inch diameter perforated vent pipe  was installed
in each 24-inch diameter vertical well and connected to the  perforated
collector pipe.  These pipes extend 10 feet above the finished surface.
Each extended vent pipe, which is nonperforated, is capped with a
gas burn-off device.  The second segment, which extends for  approximately
400 feet, consists of the gravel trench, six-inch diameter perforated
collector pipe and five 24-inch diameter gravel-filled wells.  These  wells
are approximately SO feet deep and contain a four-inch diameter perforated
pipe connected to a six-inch diameter collector pipe. This  segment con-
tains only one four-inch diameter vent pipe which is connected to  the
collector pipe and extends upward through the new fill, terminating  10
feet above the finished surface.  In the middle of the  control system,
each collector pipe is connected to a six-inch diameter nonperforated
riser pipe, which extends vertically to the surface and is capped.  If
needed these two pipes can be utilized for forced ventilation of gases
by installing a vacuum pump on the system.  A series of gas  monitoring
probes are also being installed as part of this system for measurement
of gas concentration at various depths and for continual monitoring and
evaluation of the system.
     Other examples, which are mostly of similar design (but for which
little definitive  information  is available), exist and consist of gravel-
filled wells, gravel-filled  trenches or both.  Some  control systems employ
forced ventilation  in conjunction with gravel-filled wells and trenches,
whereas  others  rely entirely upon natural  ventilation.  The permeable
method for  gas  control  appears  to be more  commonly employed because such
systems  arc  known to have performed satisfactorily  and are  relatively
inexpensive  and simple  to install.
                                    35

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     Examples of pre-construction systems utilized elsewhere in the nation
are few.  One of these systems is located near Boston, Massachusetts at
the site of the new  university of Massachusetts Columbia Point Campus in
Boston Harbor (Reference 26).  The seven-building University complex is
being constructed on a completed dump site where substantial quantities
of methane gas and some hydrogen sulfide have been detected.  To assure
safe beneficial occupancy of the buildings after completion, an elaborate
gas detection and control system has been designed and installed for each
building at this site.  Each system consists of a network of perforated
pipes laid in a gravel blanket beneath the floor of the building.  The
perforated pipes are connected to collector pipes which convey the gases
to a vertical venting system existing above roof level.  The gravel blanket
Is overlain with an  impermeable gas barrier (40-rail polyvinyl chloride
membrane) placed over a concrete mudsill, and all subterranean utility
entries to the building are sealed.  Each piping network is of varying
size, predicated upon quantities of gas flow and head losses in the system.
Automatic gas analyzers and control panels in each system provide con-
tinual printout readings of combustible gas concentrations beneath the
buildings and from occupiable interior spaces.  The control panels activate
the gas-evacuation pumps and air-inlet valves when combustible gas con-
centrations reach a  pre-set level.  All such systems vill be monitored
at a central console and may be separately monitored and controlled.
One building at a lower grade is protected with a membrane-enclosed
rock blanket filled  with nitrogen under pressure, and a sub-ramp space
is constantly purged by means of a blower and pipe network.  Performance
checks of the University of Massachusetts systems are underway, and all
systems appear to be performing satisfactorily.
Post-Construction Systems
     As mentioned previously, the majority of the gas control systems
reported in the literature are of the post-construction type and have
been constructed to  eliminate an existing and potentially dangerous con-
dition.  Many of these systems have been experimental in nature and are
the forerunners of many of the pre-construction systems discussed above.

                                    36

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     Three expi-riiaental post-construction  gas  control systeas have been
developed and tested in Los  Angeles  County as  part of a  three-year
research study (Reference 3).
     The system that has been most extensively tested and evaluated con-
sists of five wells which are spaced 40 feet apa^t and are  constructed In
natural ground adjacent to the landfill Interface.  Each veil Is  30 inches
in diameter and 60 feet deep.   The wells are divided into three separate
levels.  A six-inch diameter perforated pipe is installed to the  bottom
wf each level of the gravel-filled well.  Each level Is  topped with a
layer of concrete to eliminate short-circuiting -within the  well during
pumping fro.ii various levels.  The three perforated pipes from each
well arc connected to an vij>ht-inch dianeter header pipe that is  connected
to a 25-horsepover exhaust blower.
     An extensive testing and monitoring program was conducted to ex-
amine the relative effectiveness of this gas control system in reducing
or preventing gas migration beyond the vertical plane  of the well system
to the adjacent properties.   The basic conclusions drawn fron the program
were that natural ventilation of the wells did not provide  an effective
barrier to gas migration; that some forced ventilation across the plane
of the wells is necessary to arrest gas migration; and that with  con-
tinuous pumping at the rate of 80 scfn per well, well spacinge of 150
to 200 feet nay be sufficient for the control  of migrating  gases.  It
should be noted, however, that these conclusions arc  for the particular
test installation described and reported upon, and nay not  be exactly
applicable to other areas with different soil  and other  environmental
conditions.
     An extensive post-construction system has been employed by  the City
of Los Angeles for controlling the migration of gases  from an active  land-
fill Into an adjacent residential area and a school building  complex
(Reference 27).  Several test systems were constructed and  evaluated prior
to installation of the principal permanent system.  The  basic permanent
system consists of 17 ventilation welle 25 feet deep,  spaced  on  150-foot
centers with a design withdrawal rate of 200 scfm from each well.  It
                                    37

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had been determined  from earlier test prograas conducted on three  of  these
wells that the spacing of  the wells, and thus the zone of influence of
each well, was a function  of the withdrawal rate froo each veil, and  that
the depth of the well was  not a significant factor in tlie overall  effec-
tiveness of the control  system.  These criteria were used in designing
the main system.  The City chose a 25-foot depth, which was considered
to be sufficient.  The wells were placed along two sides of the 125  to
ISO feet deep fill only  (opposite the residential area on one side and
the school area on the other side).  The other two sides of the former
gravel pit had previously  been lined with a clay barrier, placed as the
fill progressed, to  prevent water intrusion from adjacent spreading grounds.
It was expected that the clay liner would also serve as a gas barrier,
and therefore no forced  ventilation system was installed on those  two
sides.  In recent  (1974) observations, it is apparent that gas is
migrating beneath  the wells.  Installation of additional wells, 100  feet
deep, is planned.
     The wells in  the above system are two feet in diameter and are  drilled
in natural ground.   A six-inch diameter perforated polyvinyl chloride
pipe was placed in each  well, and the wells were backfilled with gravel.
Each well pipe is  connected to a vitrified clay header pipe that runs
three-fourths of a mile  to a 15-horsepower blower.  The blower feeds  an
induced draft vapor  rume incine.-ator that uses natural gas as a supple-
mentary fuel.  To  date,  tests have indicated that gas migration has been
controlled by this ventilation system and that odors can be controlled
by the fume coL-_ustion chamber.  However, further tests are being  con-
ducted to determine  optimum flow rates, effective areas of influence of
each well, the total amount of gas produced and the rate of gas produc-
tion with respect  to time.
     A system similar to that being used by the City of Los Angeles  (as
described above) was utilized by the County Sanitation Districts of  Los
Angeles County to  control  the movement of gases from the completed por-
tion of one of their active sanitary landfills.  The fill Is adjoined

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would not migrate Co these areas,  a series  of 18  24-inch wells, varying
in depth from 30 to 40 feet and spaced 100  feet  apart,  have been  drilled
to date (1974).  A six-inch diameter polyvinyl chloride perforated pipe
was placed in each well, after which the wells were backfilled with  gravel
to within eight feet of the surface.  Each  well was capped  with a layer
of driller's mud and three feet of concrete,  and  was  then backfilled with
earth to the finished surface.  Each well pipe was connected to a header
pipe, which was connected to a S-horsepower suction blower.  Two  locally-
fabricated burners, each receiving 400- to  625-scfm gas flow, are in-
stalled on piping assemblies from the blower  exhaust  and  operated in
parallel.  Although gas flow is less than the design  value, preliminary
results indicate that gas movement into the adjacent  properties  are
being arrested by this control system.  It  became necessary, however, to
install seven additional wells to the original 11-well system.   The
burners, equipped with automatic pilot lights, operate continuously.
     A gas control system utilizing natural ventilation was installed by
a manufacturing company to protect its building coirplex.  The system was
installed approximately 150 feet from the edge of an  old  landfill in con-
junction with the construction of an addition to an existing building and
extended the full length of the complex bordering upon an old landfill
site.  The installation consists of a series  of gravel-filled wells spaced
20 feet on centers and a gravel-filled trench five feet in depth.  Each
veil is two feet in diameter and 40 feet In depth. A four-inch  diameter
perforated pipe was placed in the trench to collect  the gases from the
veils and the trench area.  Vertical risers,  four inches  in diameter and
connected to the trench pipe at a spacing of  approximately  100 feet,
extend up the wall of the building  for emission of gases  above the top
of the buildings.  The effectiveness of this  control system is  presently
unknown.
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                                CHAPTER VI
        SELECTION. DESI3J  AND INSTALLATION OF PROTOTYPE CAS BARRIER

HISTORY OF SITE DEVELOPMENT
     Development of  the Link Road landfill, ..he Armory ano other facili-
ties on or near the  landfill Is described in Chapter II.  Primary features
of Interest with regard to design and installation of the gas barrier
included an escinatc of the gas production potential of the landfill's
contf-its, the permeability of the adjacent soils, the history of com-
bustible gas concentrations and migration, the proximity to the landfill
of buildings and facilities to be protected and the location of under-
ground facilities.
     In 1973, the Link Road landfill was 24 years old, the last refuse
having been placed near the Armory In September 1969.  Extensive settle-
neat had occurred just back of the Armory and the fire training area.
Settlement was continuing, the landfill surface was covered with weeds
and landfill-generated gases were venting from the soil cover through
extensive cracks in  a number of areas.
     In July 1973. over 100,000 cubic yards, or approximately 162,000
Sons, of new soil cover were placed over the old cover throughout most
of tne undeveloped upper portions of she landfill to restore final grade
and to fill settlement areas.  This represents an additional load on the
upper surface of the landfill of over 500 pounds per square foot.  Depth
jf nev cover placement back of tr.e Armory was three to four feet.

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SITE DESCRIPTION
Physical Features
Topography- -
     The landfill occupies approximately 40 acres  of a 60-acre  tract
in the southeast portion of Winston-Salem.   The perimeter  of  the  landfill
extends about 5,600 feet.
     Originally, the site consisted of a relatively steep  hillside In
the vicinity of the present Armory, with a ravine  running  easterly along
the present line of the 72-inch storm drain.  A small stream  ran  through
this area and in the flat portion of the site, near Salem  Creek,  the
stream bed contained fairly extensive swampy areas.  The terrain  slopes
generally southeast from the highest elevations near the eastern  boundary
of the landfill site towards Salem Creek, which is about 70 feet  lower.
Final topography and typical cross-sections are shown in Figures  3 and
4.  As landfilling progressed, wastes were Initially deposited  in the
areas near Salem Creek.  Drainage ditches were used  to dewater  the flat
areas and work progressed up slope, finally terminating near  original
grade in the vicinity of the Armory.  During operation of  the abattoir,
highly organic slaughterhouse wastes and dead animals were burled nearby.
A small amount of refuse was also compacted over a limited section of  the
incinerator residue area and covered prior to conversion of this  area
into a parking and maintenance area.
     The present fire training area is grassed and relatively flat,
 sloping gently  to  the  center  of  the  main landfilled area.   Some  settlement
 areas  still  exist  in which water stands.   Surface cracks  are evident.  The
 peripheral  road  drains  through a storm-sewer  system to the 72-inch main
 storm  drain.  Most  of  the parking and maintenance area is surfaced with
 a 12-  to 18-inch thick well-packed layer of crushed stone.  A  small por-
 tion is paved with  asphalt, and  street  drains divert runoff  to the main
 atorm  drain.  The  entry road  and the immediate area around the Armory are
 paved  with  asphalt  and drain  to  the  main storm drain.  Relatively shallow
 sanitary sewers  cross  the parking area  from Forsyth Technical  Institute

                                   41

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and connect with  sewers  entering the property from Silas Creek Partway
and passing southeastward  by  the Armory.  Sewers and drains fron
the Armory connect to  this sewer.  A looped eight-inch hater main passes
through the parking area to serve the hydrants in the fire training area.
     The upper surface of  the completed landfill is relatively flat,
but beyond the fire training area and to the east of the Armory, it begins
sloping rapidly towards  Salem Creek.  Surface drainage is to the south-
east, and no severe surface drainage problems have been noted.
Soils—
     The soils at the  base of the landfill are primarily sandy, with  a
relatively low clay content.  Soil information obtained during preliminary
testing for foundation design in the vicinity of the Armory indicated
a rather sandy soil, with  unsuitable bearing capacity for building con-
struction in some areas.  The cover material obtained on site  was generally
of a sandy nature with relatively low clay content.  Varying amounts
of soil cover material were brought in from time to time from a number
of sources during the  development of the landfill, and there is no con-
sistent pattern of soil  cover by type.
Climate—
     The Wins ton-Salem area has a relatively moderate climate character-
istic of inland areas  of the  Piedmont.  Average annual precipitation
is about 42 inches with  a  major amount of precipitation occurring in
the early summer  and early winter months.  Temperatures in summer rarely
exceed the mid-90's.   Winter  weather is generally moderate with snow
and subfreezing weather  of relatively light intensity and duration.
Hydrology—
     Boring logs  of subsurface explorations, placement of probes and
excavation for the prototype  gas barrier indicated that the groundwater
table is between  25 and  30 feet below the surface along the line of the
barrier, i.e., outside the land ."ill at the higher elevations.  Similar
exploration in the landfill,  nowev^r, indicated water levels within three

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to five feet of the surface toward the center of the  fill.  These findings
indicate occurrence of saturated areas throughout the landfill due either
to water penetrating the soil cover or emanating from subterranean springs,
with most occurrences in settlement areas.   It is apparent  that most  of
the mass of the landfill has reached field  saturation,  a condition con-
ducive to maximum gas production.
Deposited Refust
     Field checks indicated that wastes buried in the landfill had an
average density of about 26 pounds per cubic foot.  The average depth of
fill was considered, for design purposes, to be 35 feet.   As  reported by
Winston-Salem officials, the refuse to cover ratio was 2 to 1.
Other Features —
     The principal areas of concern with regard to gas migration and
potential hazards at the Link "oad site are along the boundaries between
the landfill and its most elevated periphery.  Here the major construc-
tion of facilities has  taken place, and the facilities are in the upgrade
zone of gas migration.  In the fire training area, deposition of highly
organic wastes and  lack of compaction may be resulting in high gas genera-
tion and migration  toward the parking area and the Armory.  Gas was not
found above the periphery road in early investigations, however.
     The placement  of roads, buildings, crushed  stone, sidewalks and
paved parking and access areas in the general vicinity of the Armory
has  reduced vertical venting of  gases from underlying refuse  and has
directed migration  of gases toward the Armory.   The surface seal afforded
by the  paving and  crushed stone  will, however, serve a useful function
 In the  operation of the gas barrier since short-circuiting of air
 through the soil into  the active barrier system  will be reduced.

 COMBUSTIBLE CAS CONCENTRATION'S AT LINK ROAD DISPOSAL SITE
 Areal  Distribution
     The concentration of explosive gases in soil voids within and ad-
 jacent to the landfill area is  a positive Indication of sources of gas
                                   43

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generation and general  direction of long-tern movement.  Because of the
vide fluctuations observed  in gas  concentrations from day to day, average
annual gas concentrations  from  the deep  (25  feet) sampling probes were used
to obtain the combustible  gas concentration  contour map shown on Figure 6.
High concentrations were observed  throughout the landfill, with rela-
tively abrupt declines  at  the peripheries.  Near the Armory gas concen-
trations persist for a  considerable distance from the landfill edge, which
is an indication of the relative ease  of gas passage through the media
lying between the fill  and  the building.  Gas contour gradients between
the fill and the truck  parking area and the  garage are somewhat larger,
indicating lower gas permeability  in the soils.  Relatively high concen-
trations persist at the outermost  probe at the landfill edge nearest the
abattoir.
     The observation of a  relatively gentle  gas concentration gradient,
i.e., low resistance to flow, in the direction of the Armory in 1973 is
coupled with the observation of a  soil-air relative-pressure gradient in
the same direction.  Manometers connected to pressure probes installed in
the peripheral area of  the  landfill in a line extending toward the Armory
(Figure 15) consistently recorded  decreasing pressures in the direction
of the building over a  one-month period of measurements in early 1974*
as shown in Figure  7.   Gauge pressure  readings within the landfill reached
as high as 200-mra water column, whereas  those nearest the building vas-
cillated near zero.  Thus,  the pressure  and  the concentration gradients
along this particular direction induced both mass flow and the diffusion
of combustible gas  toward  the building prior to the construction of the
barrier.
Temporal Variations
     Monitoring of  combustible  gas concentrations from a large number
of probes in the Armory was conducted  during the period 1970 to early
1974.  The large quantity  of data  obtained were plotted, general'.zed
and a number of representative  or  critical stations were selected for
presentation in Figure  8.
                                   44

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    GARAGE
                                                                            •S5
                               CONTOUR INTERVAL: 10 PERCENT CH* BY VOLUME
Rgure  6:   Combustible  909  concentration distribution in Link  Rood  disposal  site,
                                        1973

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 §
 0
 ••
 o
 9

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 E
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 V)


 S


 Ul

 CO
 o
 u
 u
 o
 u
 c
 111
          • BARRIER  EVALUATION  INITIATED
          •GAS MIGRATION  BARRIER SYSTEM CONSTRUCTED
•W*cu yd ADDITIONAL SOIL COVER PLACED OVER LANDFILL
          • TRENCH ALONG S AND E SIDES OF ARMORY BUILDING
           EXCAVATED AND NEW ANALYZER  DEPLOYED
            IU NtW ANALT£e.n Utr-LUItU            N


            I I I I  I I  I (  I I  I I  I I I I I  I M I  I I  ill  I I I I I 1
  §  »-
                                               1972


Figure  8:  Generalized  combustible  gas concentrations  at several  stations  near

                                       Armory

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     Rigorous attempts at  correlating combustible gas concentrations with
rainfall and temperature variations failed to demonstrate any  regular
patterns.  However, it can be  observed from Figure 8 that a steadv decline
of combustible gas concentration had been occurring over the period of
monitoring, before barrier construction, at all stations in the vicinity
of the Armory  (Stations  7, 8,  9, 10 and  11, Figure 5).
     The sudden  rise  in  concentration of explosive gases noted in late
1972 coincides with  the  excavation of an L-shaped trench along the south
and east sides of the Armory.   It  is believed  that backfilling of this
trench with  loose material caused migrating combustible gas from areas of
higher concentrations to move more readily  toward the probe stations than
was possible previously.  At about the  same time  that the  trench was
dug, a new gas analyzer was purchased and  deployed by the  monitoring
personnel.   It was a few months later that the new gas  analyzer was found
Co be  reading five to 10 percentage points higher than  the previously-
used analyzor.  The COL ji nation of these two events  tend to explain the
sudovn  rise in gas concentrations that occurred in late 1972.   Soon after
 the  ,udden rise, a gradual decline was observed with a rate somewhat
 higher than that observed  in  the early part of the monitor ing period.
     Altogether, trends shown in Figures 6, 7 and 8 confirm the specific
 conclusions reached earlier about gradual gas concentration reductions
 over time,  the  response of the concentration  at a given peripheral point
 to permeability of wdia  between  that point and the landfill, and the ex-
 istence of  an overwhelming mass flow component in the migration of gases
 away from the landfill.
 EVALUATION  OF ALTERNATIVE GAS BARRIER SYSTEMS
      Three  alternative  gas barrier systems were evaluated for the purpose
 cf selecting a  suitable method of gas  control for the Link Road disposal
 site.  The  alternatives considered were forced ventilation, natural
 ventilation and impervious membrane.   Three modes of operation of the
 forced ventilstion method were considered:  high-flow  0-100 scfm/well)
 ventilation, low-flow (MO scfm/well)  ventilation corfeined with  the use
                                    48

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of a surface seal and lew-flow (ilO scfin/well)  ventilation without  the
use of surface seal.
     The objectives and functions of high-flow, forced-ventilation  and
low-flow, forced-ventilation systems are quite  different.  The objective
of the high-flow, forced-ventilation system is  to create a relatively
large bulk flow of soil-air gases, which Includes a substantial amount
of overlying atmospheric air that is pulled through the surface of the
landfill, from the area of influence of each well.  Therefore, in addi-
tion to providing an effective barrier against  migration of  landfill-
generated gases, this system effects a dilution of combustible gases in
the soil-air on the landfill side in the vicinity of the barrier.  There-
fore, in this sytsm, no attempt is made to exclude atmospheric air, ex-
cept in the immediate vicinity of each well.  The objective of the low-
flow, forced-ventilation system is to create a vertical plane, or barrlert
of ubiquitous negative pressure between wells which will  intercept land-
fill-generated gases naturally migrating toward  the barrier and cause
them to flow  to a well due  to the  induced negative pressure gradient.
In this system, a minimum amount of  landfill-generated gases,  I.e., only
that necessary to create the barrier of negative pressure, is extracted
from the area of influence  of each well.  To be  effective, this system
requires that the inflow of overlying atmospheric air  into the landfill
in  the  vicinity  of  the barrier be  kept  to an absolute  minimum.
     As described in Chapter  V,  the  state-of-the-art of gas  control  tech-
nology  is by  and  large experimental  at  this point in time.   The experi-
mental  and  demonstration projects  involving gas  migration barriers have
generally  failed to provide universal design criteria. However, existing
 systems of  gas  migration  control have demonstrated the feasibility of
 controlling the flow of  gases from landfills.   Furthermore,  the limited
 experience  has  provided  some  field data on the mode of operation and
 effectiveness of several gas  ventilation methods.  These data are of
 value for developing new design criteria for conditions other than those
 for which direct experience is available.

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     Several criteria were considered in evaluating the various methods
of gas migration control.  The methods considered were ranked under each
criterion and given an appropriate score in accordance with the quantita-
tive or subjective information presently available.  The judgement on
the final ranking of the systems may be more readily Justifiable  in some
cases than in others where performance data are scarce or inapplicable.
Nevertheless, it is believed  tnat a fair and impartial evaluation of
each system was obtained with the scoring system used.
Cost
     Total annual costs were  obtained from estimates of capital cost
and operation and maintenance cost for each alternative, and are  shown
In Table 1.  All capital costs were amortized over a 10-year period at
an interest rate of aix percent.  As indicated in Table 1, the highest
rank or score of five was  assigned to the system with the least total
annual cost and a score of one to the most expensive.  Detailed informa-
tion on capital cost requirements for forced ventilation systems,
natural ventilation systems and  impermeable barrier systems is pre-
sented in Appendix A.
      Table 1.  ESTIMATED COSTS  OF ALTERNATIVE GAS BARRIER SYSTEMS
                                (dollars)
                               Total       Annual      Total      Rank/
Alternative system         capital cose  04M cost   annual cose  Score
Forced ventilation
a. High flow
b. Low flow with seal
c. Low flow without seal
Natural ventilation
Impermeable barrier

52,000
73.600
37,600
10,000
24,500

3,000
1.200
850
0
500

10,000
11,500
6,100
1.400
4.000

2
1
3
5
4
                                   50

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Effectiveness
     Because effectiveness is the primary factor of concern in the selec-
tion of a gas control system, this parameter was assigned a weight of
three.  Thus in a one-to-five relative ranking of the alternatives (with
the highest rank assigned to the most effective method), the score for
effectiveness of an alternative system vould range from three to IS.
Experience with existing systems Indicates that forced-ventilation systems,
as a group, are far more effective than either the natural ventilation or
the impermeable barrier systems.  Natural ventilation systems have gener-
ally been least effective in preventing gas migration from a disposal site.
because high-flow, forced-ventilation barrier systems have proven to be
effective, this alternative was assigned the highest score.
     Low-flow, forced-ventilation barrier systems have not been tested to
date as a means of preventing gas migration.  Therefore, their relative
ranking is based upon theoretical fluid flow behavior which clearly
indicates that the low-flow, forced-ventilation system would be far more
effective than natural ventilation or Impermeable barrier methods.  By
the same token, it is surmised that the effectiveness of low-flow, forced-
ventilation methods may be somewhat lower than high-flow, forced-ventila-
tion systems.  Theoretical considerations also imply that the use o£
a surface seal, as discussed in the sections below, would Increase the
effectiveness of  low-flow, forced-ventilation systems in intercepting
migrating gas.
     The assigned  rank and score  of alternative  systems from the viewpoint
of  effectiveness  is presented  in  Table  2.
 Maintainability
      Maintainability is  important because It bears directly upon the
 reliability of and continuous safety'provided by a given barrier system.
 Generally, the simpler the system the more maintainable it will be.   Con-
 versely, the more complicated and larger the barrier appurtenances,  the
 greater are chances for  breakdown and the need for maintenance.   There-
 fore, the natural ventilation and the impermeable barriers would be  more
 maintainable than those  requiring pipelines, pumps and control structures.

                                     51

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    Table 2.  RELATIVE EFFECTIVENESS OF ALTERNATIVE GAS BARRIER SYSTEMS
Alternative system
Forced ventilation
a. High flow
b. Low flow with seal
c. Low flow without seal
Natural ventilation
Impermeable barrier
Rank

5
4
3
1
2
Score

IS
12
9
3
6
The rank and  score  for the five  alternative systems with respect to
maintainability  is  presented in  Table  3.
   Table 3.  RELATIVE MAINTAINABILITY OF ALTERNATIVE CAS BARRIER SYSTEMS
                                     Possible naintenance          Rank/
    Alternative systems                    problems                Score


 Forced ventilation

   a.  High flow              Pump failure, control mechanisms       1
                                maintenance, short-circuiting
                                of air flow

   b.  Low flow wich seal     Pump failure, control mechanisms,      2
                                seal breakage

   c.  Low flow without seal  Pump failure, control mechanisms,      3
                                short-circuiting

 Natural ventilation          Plugging of porous material by         4
                                surface drainage

 Impermeable barrier          Seal breakage                          5
                                     52

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Controllability
     This criterion is a measure of the ability of operators to adjust
the operation of a system in accordance with the feedback provided by the
monitoring system.  Thus, in a highly controllable system, working with
100 percent effectiveness, operating costs can be lowered by reducing
flow rates or decreasing purapage periods, or both.  The energy input to
the same system nay be increased to intercept any gases upon the incep-
tion or Increase in gas migration.  The rank and score of the five alter-
native systems with respect to controllability is shown in Table 4.

  Table 4.  RELATIVE CONTROLLABILITY OF ALTERNATIVE CAS BARRIER SYSTEMS

Alternative system                Control feature             Rank/Score

Forced ventilation
  a.  High flow             Flow  rate  (decreasable),               3
                              well spacing
  b.  Low flow with seal    Flow  rate  (wide range of varia-        5
                              tion), well spacing, strip
                              width
  c.  Lou flow without  seal Flow  rate  (wide range of varia-        4
                              tion), well spacing
Natural ventilation                  Hone                          1
Impermeable barrier                  More                          1

Environmental Effects
      The  most noticeable  environmental effects  of disposal site  gas  migra-
 tion barrier systems  are noise, odor,  options  for final use of the site
 end the  aesthetic appearance  of system appurtenances.   Noise and odor are
 primarily caused by  the forced-ventilation  systems  involving use of motors
 and the  discharge of  pumped refuse gases into the atmosphere from a con-
 centrated point source.  The  high-flew, forced-ventilation systems,  by
 za'.ure.  pose the greatest noif level and the highest discharges of
 malodorous  gases.  The low-flow, forced-ventilation systems, on the other

                                   53

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hand, are relatively quiet and contribute much smaller volumes of landfill
gases to the surrounding areas.  The existence or absence of surface seal
does not appear to contribute significantly and in a direct manner to
change in either noise  level or odor dispersal.  Indirectly, however,  it
may reduce total punpage flow requirement, which would lower noise and
rates of malodorous gas extraction.  Both natural ventilation and imper-
meable barrier systems  are completely noise free.  The natural ventila-
tion systems conceivably can contribute more naladorous gases along the
barrier by providing  freer venting access than can the impermeable barrier
system.
   '  From the point of  view  of options  for final use of the disposal
site, the forced-ventilation systems  are  favored over the others due
to the  fact  that such systems would more  readily enable beneficial uses
of areas on  and adjacent  to  the  completed disposal sites due to their
greater effectiveness.   Such uses  include public parks and recreation
sites and other  facilities which nay  be developed upon the completed
fill areas.
  rj  Aesthetically,  the impermeable barrier system is completely innocuous
after construction is completed, whereas  the  natural ventilation system
will have some protruding vent pipes.  The  forced-ventilation systems.
on  the  other hand, pose structural unsightliness  in proportion to the
magnitude of pumpage and surface sealing. To the extent that  these
features  detract  from the natural open-space  setting,  the forced
ventilation systems would be aesthetically more objectionable.  The rating
scores  given each alternative barrier system with respect to environmental
 effects are presented in Table 5.
Disturbance Due to Construction
      In the course of  constructing new gas migration  barrier systems,  a
 certain amount of earth excavation, well drilling, pipeline installation
 and other activities are certain  to disturb the site  for the duration of
 const'.-uction work.  Placement of  either  a natural ventilation system or
 en impermeable membrane will require a large amount of excavation and
 b&ckfilling work with  the attendant stockpiling of fill material as well as
                                    54

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disposal of excavated soil.  These disruptions are monumental relative to
well drilling and surface seal application required in the forced-ventila-
tion systems.  The assigned scores for disruption due to construction of
the alternative systems are presented in Table 6.

Table 5.  RELATIVE ENVIRONMENTAL I Iff ACT OF ALTERNATIVE GAS BARRIER SYSTE11S
Rank/Score

Alternative system
Forced ventilation
a. High flow
b. Low flow with seal
c. Low flow without seal
Natural ventilation
Impermeable barrier

Noise

1
3
2
5
5

Odor

1
3
2
4
5
Final use
options

3
5
£
2
1

Aesthetics

2
2
3
4
5
           Table 6.  RELATIVE DISRUPTION DURING CONSTRUCTION
                     OF ALTERNATIVE GAS BARRIER SYSTEMS
    Alternative system
Rank/Score
 Forced ventilation
   a.  High flow
   b.  Low flow with seal
   c.  Low flow without seal
 Natural vcncilation
 Impermeable barrier
    5
    4
    5
    1
    1
                                    55

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Experimentation and  Innovation
    Because of the paucity  of information presently available on the
entire problem of gas migration control, it is deemed important to
emphasize innovation and experimentation in this field.  Furthermore,  a
system with built-in flexibility, allowing variation of the independent
parameters (pumpagc  rate, strip width, etc.), is considered to be a
great advantage.  The advantages are twofold.  First it allows the system
to be "tuned" to the particular peculiarities of the site, and secondly
it provides data for use in design and operation of similar gas migration
barriers at other locations.  The innovative character of each system
and its flexibility  are judged on the basis of past experience or lack
thereof with the respective systems.  The impermeable barrier system  is
one of the oldest concepts, followed closely by the natural ventilation
alternative.  On the contrary, application of a surface seal and a low-
flow, forced-ventilation barrier is the most novel concept in gas migra-
tion control.  High-flow,  forced-ventilation systems have been in use in
several locations for some  time and are thus ranked intermediate among the
other alternative systems  insofar as experimentation and innovation are
concerned.  The ranking and scoring of the alternative systems from this
respect are summarized in  Table 7.

      Table 7.  RELATIVE NOVELTY OF ALTERNATIVE GAS BARRIER SYSTEMS

   Alternative system              Novelty feature          Rank/Score

Forced ventilation
  a.  High flow                         None                    3
  b.  Low flow with  seal        Low flow, surface seal          5
  c.  Low flow, without seal           Low flow                 4
Natural ventilation                     None                    2
Impermeable barrier                     None                    1
                                   56

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SELECTION OF THE GAS BARRIER SYSTEM
     A summary of the scores assigned each alternative gas control system
is presented in Table 8.   The low-flow, forced-ventilation system with
a surface seal received the highest cumulative score, followed by the
low-flow sysLem without the surface seal.   The high-flow, forced-venti-
lation system has the next highest  score,  followed by the impermeable
barrier system.  The natural ventilation system has the  lowest total
score.
     On the basis of these scores,  the low-flow, forced-ventilation
system with surface seal was selected for design to provide  a barrier
against migrating gases from the Link Road landfill.
THEORETICAL CONSIDERATIONS
     Laminar flow of fluids through porous oedia is governed by  Darcy's
law.  In order to be able to use analytic tools to describe  the  movement
of landfill gases toward outlying areas, it is necessary to  make certain
justifiable simplifying assumptions concerning the fluids (air-methane
mixture), the porous media  (refuse, fill and undisturbed soils  adjacent
to the landfill) and the flow process.  These assumptions and the justi-
fications therefor are given, in some  length, before a presentation of
the  theoretical  considerations tor the design of a low-flow, forced-venti-
lation system with surface  seal.
Assumptions
Laminar Flow—
     Darcy's law has been experimentally  found valid for all flows in
the  laminar range, i.e., with Reynold's numbers below unity.  Because
the  kinematic  visocity of air is about  10  times greater than that of
uatev, the  law allows  an air flow  10  times that of water within the
applicability  of Darcy's  law.  Therefore,  inasmuch  as Darcy's law is
universally used successfully to describe groundwater movement under
most conditions, laminar  flow should  prevail  for  all gas movement pro-
blems  encountered  in barrier system design and related analyses.

                                   57

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                        Table 8.   SUMMARY OF RELATIVE SCORES FOR ALTERNATIVE GAS BARRIER SYSTEMS
wn
oo
Total
Alternative annual
systems cost
Forced ventilation
a. High flow
b. Low flow
with seal
c. Low flow
without seal
Natural ventilation
Impenieable barrier

2
1
3
5
4
Effec-
tiveness

15
12
9
3
6
Maintain-
ability

1
2
3
4
5
Control-
lability

3
5
4
1
1
Con
struction
disturbance

5
4
5
1
1
Environ-
mental
effects

7
13
11
15
16
Experimen-
tation &
innovation

3
5
4
2
1
Total
score

3fi
4?
39
3)
34

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Isotropic Media—
     Mechanics of fluit1 flow in porous media almost universally  assume
isotropicity of the medium.  Flows  occurring. In a well-type barrier system
are in fact three-dimensional, even though the principal  direction  of
movement of gas is perpendicular to the barrier.   The  only anisotropicity
of significance may be due to the various horizons developed  during the
soil-forming process.  As long as flow along the vertical dimension is
minimal and differentiation of soil horizons is not highly exaggerated,
the assumption of isotropicity is not expected to limit the  applicability
of Darcy's law co flow situations under consideration.  Generally,  the
effects of anisottopic media upon flow conditions are  only  of theoretical
significance.  In practical applications these effects are  subordinated
by the scale of the flow parameters.
Homogeneous Media—
     The assumption of homogeneity of soils along and in the vicinity
of the gas migration barrier led to the use of a single representative
permeability factor for the entire length of the gas barrier.  The  super-
ficial fallacy of this assumption is evident In the range of perraeabilities
measured for the air-dried samples taken from various points In the vicin-
ity of the barrier.  Soil permeability variations are an common within
relatively short distances  that unless a great number of samples are
obtained, It is not safe to assign the results of one test to the zone
of Influence of a number of wells.  Thus a single representative per-
aeability value was judiciously selected for use in the  design of the
entire barrier systea.  Natural soil  variations will  generally be averaged
out  for  the entire system,  as well as  for each well,  resulting in flows
close Lo theoretical derivations.  The problem of lack of homogeneity
Is dimilarly handled in groundwater  flow analyses successfully.
Steady-State  Flow—
     At  the begi.i.iing  of thi.  operation of  the  gas migration barrier sys-
tem, a  transient  flow  condition will exist wish  complex  flow and pressure
distribution  patterns  in the  vicinity of the barrier. This  time-variant

                                  59

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condition will  last  until streamlines and the pressure distribution net-
work finally become  stabilized  La  a steady-state pattern closely resen-
bling those predicted by the equations.  During periods of wetting and
drying of the soil surfaces  (such  as at  the  onset of the wet and the
dry seasons) nonsready-state gas flour will prevail due to changing soil
permeability in those periods.  A  Ions-terra  decrease in gas generation
rate In the disposal area vil.1.  impose an additional transitory character
to the gas flow parameters.
     The effects that the nonsteady character of flow axe liable to exert
upon flow conditions arc all such  that design based upon a steady-state
assumption is biased toward providing a  conservative system.
Constant Gas Density—
     In the range of negative pressures  produced by the pumping.equinment
proposed for the barrier system (less than 0.01 atra), pas densities should
not vary by no re than one percent. Snail variations will not affect the
accuracy of predicted flows  to  a significant or measurable degree.
Analytical Relationships
     For the condition  under consideration,  namely the presence of a
lower confinement to gaseous flew  in the forn of the groundwater table
which is relatively  impermeable cocpdred to  the overlying unsaturated
soil and an upper confinement in th? form of paving or other appropriate
seal, the flow  of gas tovard any well in the barrier is given by the
Thietn equation  for radial flow  of  fluids in  a confined aquifer  (an
adaptation of Darcy's Law);  viz.,
                              -2 ir h k AP
                           q   u In (re/rw>                         (1)
where:      q ** flow to each well  (cfs)
            h » depth La groundwater table  (ft)
            k " Intrinsic soil  permeability  (ft2)
           &p •* imposed pressure differential between well and  Unit
                 of  influence,  re  (psf)
             li " average gas viscosity  (lb-sec/ft2)
        re/rv B ratio of radius of influence of well to radius  of well

                                   60

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     In order to intercept all gases moving toward the protected area.
wells should be spaced along the barrier so that pumpage from all wells
in the barrier equals gas movement toward the barrier.  Flow from each
side of the barrier may be calculated by using Darcy's equation directly,

                       «-*»oS                            (2)
where:       Q = total gas flow front each side to the gas barrier (cfs)
             L « length of barrier (ft)
            &? » average pressure differential between the barrier ant
                an orthogonal distance AX away  (psf)
            AX - distance over which AP acts (ft)
Accurate estimation of the pressure gradient, AP/AX, is the key to the
usefulness of liquation 2.  Because the negative  pressure along the barrier,
indicated by Ap, will vary from a maxima at the  wells to a minima at mid-
points between the wells, the effective negative pressure at the barrier
is assumed to be about 0.5 Ap.  Therefore,
                             nP - 0.5 fip                          (3)

     The total system  flow is equal to 2Q and the number of wells along
the barrier, n,  may be determined by dividing the total flow from both
sides of the barrier by pumpage rate from each well; viz.,

                              • -V                             m
     Spacing bntwecn wells, S, is obtained by dividing the length of the
barrier system by  the nuiaber of required wells;  i.e.,

                              S " n                               (5)
Spacing between  wells can also be determined independently cf most: system
variables by substituting Equations 1, 2, 3 an.i  4 into Equation 5; viz.,
                              ,      2» AX
                                   In <.-r)                      (6)
                                  61

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     To assure  confined aquifer  conditions, the width of seal along the
barrier, W, must  be  only sufficient  to provide the pressure gradient
AP/AX.  Therefore,
                             W = 2 AX                               (7)
Cost Minimization
     The economic trade off; between the width of the sealed barrier and
the number of wells  along the  barrier can be evaluated using the relation:
                             C - CQ  + Cx + C2                       (8)
where:      C   =  total  cost of the barrier
            CQ  =  costs  independent of number of wells and spacing
            C^  "  costs  associated with the number of wells in the
                  system «* Kj n
            KI  =  cost of each  well and appurtenances thereto
            C2  -  costs  associated with the sealed strip = 2 K2 L AX
            K2  »  cost of paving  a unit width along the entire length of
                  the strip
     A minimum  total cost solution can be obtained if C Is related to
AX by substituting Equations 1,  2, 3 and 4 into Equation 8; i.e.,
                         L In (rc/rw) Kj
                C  ' C0 + —TVAX	 + 2 K2 L AX                 (9)
Differentiating C with  respect to AX gives:

                                          2 K, L
                _dC	L ln (re/rw>  Kl
                           2 TI  (AX)2
Setting  dC   equal  tc  zero to obtain  the minimum cost solution gives:
        d(AX)
                 AX  =
The first multiplicand  is  a physical constant  for a given system and the
second can be determined from  prevailing unit  costs of the various
elements of the barrier system.

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CAS BARRIER DESIGN
Widtn of Surface Seal
     The nost economical AX is determined from Equation 10.   Tor a well
radius, r  , of one foot and an assumed radtus of influence,  r , of 100 feet:
                      AX - \/ln (100/1) /An

                         - 0.605X^/1(2                            (11)

 Choice of an appropriate numerical value  for  r   depends,  to a  certain
 extent, upon the expected final value  of  the  width, W,  of the  sealed
 strip along the barrier.  The width of seal will determine the approxi-
 mate radius of Influence of the well by imposing a  lower  limit of AX
 feet upon the path that the air stream will traverse horizontally before
 arriving at the intake perforations of the wells.   Thl; assignment,
 arbitrary as it may appear, is not too critical in  the  solution of Equa-
 tion 10, because of the logarithmic and square  root function  In which
 r  appears.  (A 50 or 100 percent error in estimation of  r will result
 in only a 4.6 or 8.4 percent error, respectively, in  the  value of AX.)
      The unit cost of wells, K., is comprised of the  costs of drilling,
 piping, gravel placencnt and monitoring and control devices  for each
 well.  These costs, under the existing conditions,  and  for a  30-feet  well
 depth are:
              Drilling 0 $20/ft             -    $600/well
              Piping   @   3/ft             =      90/well
              Gravel   @   2/ft             -      60/well
              Monitoring  (orifice meter)     -     350/well
              Control (butterfly valve)      -     150/well

                   TOTAL                 RX  -  $1,250/we 11

 The  unit cost of  sealing the barrier strip,  K_, is the unit cost of
 placing sealant on each square foot of the barrier.  Cost of sealant is
 estimated  to be S0.10/ft".

                                     63

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Replacing K^ and KZ in Equation 11 gives:
                       flX - 0.605 >/i."250/0. IB = 50 ft
Tills value of  AX is  Chen used  as  a basis  for Che computation of flow
Coward wells,  spacing of wells and actual strip width.
     The  resulting width of the paved strip alone, the line of well is:

                             H - 2 AX - 100 ft

Flow Rote and  Capacity
    An important  parameter in  the computation of flow toward the barrier
and inco  tlio wells is  soil permeability,  k.  Thirteen soil samples from
eight different  locations along the proposed barrier and at two depths
In five locations were analyzed in the  laboratory.  A nonste,-\
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  Table 9. PARTICLE-SIZE DISTRIBUTION AND PERMEABILITY OF SOILS IN VICINITY OF PROPOSED BARRIER
Probe*
1
2
3
8

25

33

54

55

g
Location
Southwest of Armory supply
Sample
depth,
ft
room 6
South of Armory supply room 5
Southeast of Armory supply
South of Armory building0

West of Armory building0

East of Armory building6

South of truck park area

South of metal shed

room 6
4 to 6
14 to 16
4 to 6
14 to 16
4 to 6
14 to 16
4 to 6
14 to 16
4 to 6
17 to 19
Sieve analysis of soils.
percentage passing sieve
No. 4
4760u
86.5
100.0
99.3
98.4
99.4
99.6
97.1
98.7
99.4
97.0
97.9
85.3
98.4
No. 10
2000u
59.5
100.0
94.2
95.6
97.8
95.8
88.6
95.2
97.5
93.0
93.6
76.9
95.1
No. 40
417u
21.7
62.4
54.6
63.1
68.8
66.8
60.6
73.2
69.0
69.2
68.9
53.7
80.6
No. 200
74u
5.3
15.9
9.8
22.5
28.6
19.5
18.5
37.4
35.1
33.1
35.4
24.3
35.0
Permeability,
io-12 ft2
425
37.8
160
126
61.2
33.4
43.2
95.5
110
76.5
54.0
2.16
81.0
  Figure 9 shows location of probes in the waste disposal site and vicinity.
b Samples were collected from the bottom of a trench dug along the southern wall of the supply room.
c Core samples were obtained from the given depths using standard sampling techniques (Reference 28).

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LOCATIONS SHOWN ON
TABLE 9



/- SANITARY
# SEWER


^

jsigo
••E^^MHBES
0 50

                                                                             200
Figure   9:   Soil  permeability  samples  and  associated probe  locations  in
                        vicinity  of  proposed  barrier

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    The choice of a viscosity value tor gases flowing In the vicinity
of the proposed barrier was made with full cognizance of pressure and
temperature Influences, as well as metnane concentration, upon the gas
mixture.  The pressure dependence of the gas-mixture viscosity, in the
pressure ranges encountered, is negligible.  The value chosen for vis-
cosity of the gas mixture allows for the most conservative computation
of flows in the temperature and methane concentration ranges expected
to be experienced under various operating circumstances.
      Cas viscosity decreases with decreasing temperature and  with increas-
 ing methane concentration.   The lowest  probable soil-air temperature is
 about 10°C at the depths where gas flow under forced ventilation will
 occur.  The estimated ncthane concentration  of the  f»as  being generated
 in the landfill is expected to be about 29 percent  in 1973, the time
 that the barrier system will become operational (see Figure 11).  Linear
 Interpolation of reported values for viscosity of air and of methane at
 standard temperatures results in a design value for the methane-air nix-
 Lure of 157 micropoises.
      Using fquation 1 to calculate flow toward each well, and using the
 following data:
              h • 30 ft, as measured in the field from ground surface
                  to the groundwater table along the proposed barrier
                           — 12   2
              k = 69.9 x 10    ft , selected representative intrinsic
                  permeability based upon laboratory tests
             Ap = 0.01 atmosphere (.21.2 psf), selected vacuum to be  imposed
                  by pump
              p - 157 micropoises (3.28 10~7 lb-scc/ft2)
             r  = 100 ft, assumed radius of influence of a well
             r  • 1 ft, a design parameter

 the flow to each well will be:
                                  _i i
                  2 ir
                     3.28*10~7(4.61)
                                    67

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     Using Equation  2  to compute  the  total flow from each orthogonad
direction toward the gas migration  barrier, and the additional appropriate
data:
             L - 1.000 ft,  the length of  the main legs of the barrier
            AP • 0.5&P - Q.OOS atm  (10.6  psf)
            AX « 50  ft, as  determined from cost analysis

 the total flow from one side of the barrier will  be:
            Q . -6.99.10-11(30>
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     It is logical to presume that combustible gas generation rate is
in some direct fashion related to combustible gas concentration in the
surrounding areas to the disposal site.  Such a relation would exist
whether gas transport were by diffusion or advectlon.  Although com-
bustible gas generation data are not available, combustible gas concen-
tration values have been obtained at the Link Road disposal site over
the past three years at several sampling locations.  Individual sampling
data were plotted and smoothed to eliminate the day-to-day variations
in the  concentration of the  coafcustlble gases.  A  plot of combustible
gas concentrations  for one typical  sampling station  is presented  in
Figure  10.  To  obtain a reasonable  estimate of  the pseudo-equilibrium
gas generation  rate suggested by  Figure 10, a few  logical assumptions
are required  regarding the quantitative nature  of  the events  and  con-
   Li
ditJlons at  the  Link Road  disposal site.
      It has been reported (Reference  10)  that a pound of refuse will
ultimately  produce  3.9  ft of methane  gas  upon  complete  biochemical
decomposition.   For conservative  design purposes,  this  value  of refuse
conversion  to methane  is  assumed  to apply  at  the Link Road  disposal  site.
      The density of conpactcd  refuse  at  the  Link  Road disposal site  is
estimated to  average  about  26  Ib/ft .
      The volume of the entire  disposal site  was estimated  from cross-
sectional profiles of the filled  area determined  by  field  surveys.  A
 total volume  of abcut  1.4 x 10  yd  has been filled  with refuse  and cover
material.  The  refuse:cover ratio was estimated at 4:1  to  be  conservative
 in the design (the City has  indicated a ratio of 2:1).   The perimeter of
 the disposal  site was measured at about 5,600 ft  and the average  fill
 depth was determined  from actual borings  to be about 35 ft.
      A semi-logarithmic plot of combustible  gas concentrations at
 Station 7 (see Figure 5 for location) versus time, which is shown in
 Figure 11, indicates the  following relationship:
                                    69

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         I 70
         o
         O
         o
         
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     IOO
      50
J3
5
       !O
   o
   <§
   o
   in
   o
   u    I
   00
   00

   u
      0.5
       O.I
        1970
                                   -0.288t
                1975       I98O       1985
                               YEAR
1990
1995
  Figure   IT-   Historical  and  projected  concentration of
combustible  gas   migrating  from   disposal  area  at  station 7
                                 71

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                                  -0.288 t
                          C -  C0C
where C- and C  are  combustible gas  concentrations  initially  (t » 0) and
at time, t, respectively.   Figure  11 was based  on  onlv one sampling
."Cation because it  provided the largest number  of  data and,  of all
sampling stations,  it is located in the closest proximity of the Armory
supply room where the flaeh fire occurred.
     Assuming  that  gas generation rate is  proportional to gas concentra-
tion at the periphery of the landfill during tht decomposition period,
Equation  12 can be rewritten for gas generation rates; viz.,

                            r _„ _  -0.288 t
where F_ and F are  gas  generation  rates during  the  initial year and at
some later year,  t,  after completion  of the  disposal operation.  The
value of F can be computed by integrating  gas generation rate over the
life of the  landfill and equating it  to total gas production expected
from a pound of  refuse; i.e.,

                         F dt - 3.9 ft3/lb

This procedure yields FQ = 1.082 ft  CH./lb  in  the  initial year after
disposal  operations have been completed.   Thus* Equation  13 becomes:
 In laid- 1973, when the barrier presumably will become operational,  the
 annual gas generation will amount to 0.222 ft  Cll./lb.
      On this basis, the average CH^ flow rate during 1973 across a 1,000
 feet long vertical cross-section of the landfill periphery will he:

        x l.AxlO6 yd3 x 26     x 27     x 0.222       x 5.256 x 105

                                                        5600    9"* cfln
                                     72

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 The various simplifying assumptions  made  to  arrive  at this value are of
 such a nature as  to make it  a  conservatively high estimate, particularly
 since no allowance was given to vertical  venting through  the  surface of
 the disposal site, which may only be approached during periods when the
-disposal site surface is made  nearly impermeable to upward  gas movement
 due to precipitation, confining it to lateral migration.  The 59  cfn
 maximum gas migration rate computed above is far below  the  design  value
 of 163 cfm for the main branch (1,000 feet)  of the  low-flow,  forced-
 ventilation system, which provides for a  reasonable factor  of safety.
 Pipe  Sizes
       For a maximum allowable  total  dynamic  head (friction)  loss in the
 system of  10 Inches of water  column and  a design total flow  rate of 196
 ficfm,  the  suction header pipe should be  four inches in diameter.  A con-
 stant diameter suction  header is  provided throughout the system to simplify
 procurement  and  installation.
       For the reasons  discussed  in che  next  section, the underground
 piping, consisting of the wells and suction header, was sized to  accom-
 modate a high-flow system,  should it be  required.   In this case,  for  the
 sane  maximum allowable Lotal  dynamic head loss in  the system of 10 inches
 of water column  and a design  total  flow  rate of about 1,800  scfm, the
 suction header pipe should  be eight inches  in diameter throughout.
 Because  the flow in each short-section of well pipe will be  relatively
 small and  the concomitant  head loss negligible, the well pipes were
 sized at  four inches in diameter to allow  for greater ease of perfora-
  tion in  the field.
 CONSTRUCTION STRATEGY
       Due to the  relatively high estimated cost of the  surface  seal
  (about 45  percent of the total system cost) and the possibility that
  the existing surface may provide an adequate seal, a step-wise con-
  struction strategy was employed.
                                     73

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     Because any of  the  three  forced-ventilation systems are considered
to be acceptable for controlling  gas migration  from the Link Road dis-
posal site, the two  low-flow,  forced-ventilation systems can be designed
to provide a backup  capability by sizing the  pipelines for maximum flows
required In a high-flow,  forced-ventilation system.
Preferred System;  Low-Flow. Forced-Ventilation Without Surface Seal
     Low-flow operation without surface  seal was rated next-to-highest
in total score in Table  8.  However, because  it is the least expensive
of the forced-ventilation alternatives,  it was chosen as the first system
to be tested, and to be  used if proven effective.  Should the testing
program indicate that satisfactory  gas migration control is achieved
with the low-flow system without  a  surface seal, no further construction—
and additional expenses—would be necessary.
Contingency Plan 1;    Low-Flow. Forced-Ventilation With Surface Seal
     If the low-flow system without a seal does not prove effective during
the test period, a surface  seal would be applied along the barrier,
with width and other parameters specified in  later sections.  The pro-
vision of surface seal should  assure gas migration control with the Low
flows predicated in  the  theoretical considerations.
Contingency Plan lit  High-Flow.  Forced-Ventilation
     In the unllkelv event  that the testing program reveals gas migration
beyond the barrier system while the low-flow, forced-ventilation system
Is in operation, flows can  be  increased  by installation of much larger
pumping capacity so  that adequate protection  is provided.
     The initial design  of  the pipelines and  pumpage facilities for the
proposed barrier are carried out  with the necessary provisions for con-
version to high-flow puim>agc rates  of the magnitude already proved effec-
tive in other ateas  close to solid  waste disposal sites.  Thus, if the
low flows prove not  to be wholly  effective  (as judged by the testing
program), pumpage rates  can be increased without incurring excessive
pipeline head losses.

                                    74

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                              CHAPTER VII
                  DESCRIPTION  OF  PROTOTYPE CAS BARRIER

PLANS AND SPECIFICATIONS
     Detailed plans and specifications were  prepared prior to construc-
tion of the gas barrier system.   A brief description of the various
components of the barrier system  is presented herein in order to maintain
adequate reference for the evaluation of the system performance, given
in Chapter VIII.
     The gas migration barrier is essentially a  curtain of negative
pressures, in relation to the  atmosphere, maintained indefinitely by
pumpage of gases from a series of wells  along  the  curtain.  Continuous
maintenance of negative pressure  at every point  along the barrier—placed
between the refuse disposal area and the Armory—is the key to  provision
of protection to the occupants.   The line of wells, in relation to the
landfill and the building, is  presented in Figure  12.
BARRIER WELLS
     Barrier wells, which provide  the means for creation of negative
relative pressure, are all similar to the one  shown on  Figure 13.
The wells arc all interconnected through an eight-inch  diameter polyvinyl
chloride header pipe,  laid underground along the entire  length  of the
barrier.  A butterfly  valve, installed between each well head and the
header, controls  flow  from each well.  This provision is important  for
balancing system  flow  and equalizing pressure drop along the barrier.
Veil heads are  also equipped with  quick-disconnect assemblies for field
measurement of  vacuum created in each well during operation.  The valve

                                   75

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15    14   13    12
        FIRE  LAB
                                          PUMP
                                               NEW  FILL
NEW


  FILL
N
A
                           LEGEND


                           BARRIER  WELL

                           HEADER
                                                             SCAU - r«r
                                                           0   SO  100   ISO
                                     2S   7S   123
   Figure  12:  Location of  barrier  wells,  header, pump and  vent

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              QUICK DISCONNECT
              VACUUM  GAUGE
                                     GROUND  SURFACE
 MANHOLE
                                                HEADER
 SEAL
15  FEET OF
COMPACTED
FILL  OR
CONCRETE
   SLOTTED
   PIPE (PVC)
                                           CONDENSATE
                                           DRAIN  AT
                                           LOW  POINTS
    BUTTERFLY
    VALVE
                                          ROCK  FILL
2- FOOT DIAMETER HOLE
~30-FEET DEEP
                            CAPPED
Figure  13:   Typical  gas  migration  barrier  well
                         77

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and pressure gauge connection are located in accessible manholes.  The
wells consist of slotted  four-inch diameter polyvinyl chloride pipes
surrounded by coarse gravel.  A 15-foot length of the unslotted section
is lamed lately below the  ground surface and at least 10 feet of the
slotted section is above  the groundwater table.
VACUUM PUMP
     In order to produce  .1 continuous  relative negative pressure  along
the barrier, a positive-displacement,  lobe-type vacuum pump,  capable
of pumping 250 scfro  (the  nearest  available to design capacity of  196  ecfra)
of air-methane mixture  at a vacuum of  10 inches of water column was
provided.  The pump was installed on the northwest corner of  the  Aitnory,
and its suction pipe was  connected to  the northern leg of the harrier,
as shown on  Figure  12.  A variable-speed drive system, consisting of
a variable-type sheave, companion pulley and belt, was provided in order
to afford a  capability  for testing system performance undar different
flow conditions.
CAS MONITORING AND SIGNALLING SYSTEM
     The purpose of  the monitoring and signalling system is twofold:
(1) to provide the  occupants of  the National Guard Armory with  an early
warning of intrusion of refuse-generated  combustible  gas into the space
between the  Armory  and  the barrier and into the building and <2) to
determine the  long-term effectiveness  of  the gas  migration barrier.
     Because failure  in a coob-jstible  gas barrier system could result
in a threat  to human  life and property, it  is  Imperative that the gas
control system be  provided with  a fail-safe monitoring and signalling
system designed  to detect dangerous  gas build-up  in  the building and
to warn the  occupants.   Data obtained  from the long-term monitoring
program will supplement intensive test data which were obtained at the
beginning of the operation of the barrier system. Valuable additional
datat pertaining to the effectiveness  of the  selected system, can thus
bo acquired  while  at the same time  ensuring the safety of the building's
occupants.

                                   78

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Selected System Design Criteria and  Characteristics
     Components of the monitoring and  signalling system must meet
certain functional requirements to satisfy  the system objectives.  These
components include the sampling network,  the detection system and the
signalling system.
Sampling Network--
     Sampling point locations were selected to ensure that gas will not
accumulate unnoticed in the Armory.  The  network consists of probes
located within the building and in the ground between the building
and the gas migration barrier.  Probes within the Armory provide a direct
measurement of the parameter of concern,  namely the presence of minute
amounts of combustible gas in the Armory.  Probes located in the ground
between the Armory and the barrier provide a warning of  the presence
of gas passing the barrier toward the  Armory.  Such an event will
allow Implementation of remedial measures prior to detection of any
explosive gas within the Armory.
     Sampling points between the Armory and the gas migration barrier
are located in such a manner as to intercept the most probable pathways
for gas movement, namely midway between the gas extraction wells.  The
sampling points within the ground are  located adequately remote  from
the Armory so that early warning of gas migration  toward the Armory will
allow remedial action, if deemed necessary.  Gas samples are withdrawn
at a depth which will provide an indication of maximum prevalent com-
bustible gas concentrations.
     Cas sampling points within the Arnory arc  installed in locations
where landfill gas might be expected to infiltrate  or  accumulate  in the
building.  Possible danger points are deformation  cracks in the below-
grade structure of the building and unventilated high  points  in rooms
or confined spaces.
     The selected sampling network  consist:, of four interior sampling
points  and six exteri^i sampling wells.  Locations  of sampling points
are shown in Figure 14.  Choice of  locations of sample probes  was based

                                  79

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        NORTH-
        LEG
ee
o
                          -PUMP
i
? ,'
9 '
WNT
NORTH
^ 	 ANALYZER PANEL AND
S AUDIBLE ALARM
1 	 .
CAROLINA ^^
NATIONAL GUARD ^-^
ARMORY

0
BUILDING Q






^x
        WEST
        LEG
        CONTINUES
                                                                            EAST
                                                                            LEG
                                                                            CONTINUES
^
*
                       GAS
                                                                *
                                                                 ^
NOTE: PROBE NUMBERS DO NOT CONFORM TO
     THE NUMBERING SYSTEM USED FOR
     PROBES IN PRIOR SYSTEMS.
              Figure  14:    Sampling  locations  for detection and alarm system

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on the results of the sampling program conducted  during four years
(1970 to 1974; and the predicted Impact of the control measures on gas
migration.
     Interior gas sarpling points are located near the ceiling in the
supply room, vault, wool room and at the ground floor of the Police
Academy in the southwest portion of the Armory.  The exterior sampling
veils will provide gas concentration data from 10 feet deep probes
located approximately h ilfway between the gas control barrier and  the
Armory and spaced about midway between the gas extraction  wells.  This
configuration and sampling depth will ensure best interception  of  the
most probable pathways of gas migration, should any gases  cross the
barrier and  provide adequate warning of increasing p.as  concentrations
before hazardous  levels arc reached near any potential  entry  point.
Detection System--
     The  combustible  gas analyzer selected for use In the pas monitoring
system  is relatively  simple and  robust and of a  type common to mining and
other gas detection  applications.   Extreme accuracy in analysis is
of less importance  than dependability  of  service.  The selected system
Is designed to function reliably with  minimal attendance, because techni-
cal staff is not expected  to  be  available for frequent maintenance or
testing of the equipment  after the  initial evaluation program.
      Host of the available combustible gas detection devices have been
developed for the mining  industry.   They  consist of an electrically heated
 coil (sensor), the resistance of which varie:  in proportion to the heat
 of combustion generated by the burning of a  gas  mixture ignited by the
 coll, and a device for measuring the coil resistance.  Where several
 locations are to be sampled and analyzed, it Is  both economical and
 convenient  from the point of view of operation to centralize measurement
 and recording.  In the selected system, samples  arc pumped from the
 various probe sources to a single sensor located at a  central  monitor-
 ing station.
                                     81

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     The detection system, includes a MSA Model F gas  analyzer, a 10-
point recorder, sample pump and visual and audible alarms, mounted in a
console located within the Armory (Figure 14).  A continuously pumped
sampling system with a centrally located gas sensor was  considered pre-
ferential to individual sensors at every sampling veil because pimping
of the sample assures positive displacement of gas across the sensor.
Each exterior sampling well is provided with an access point for COD-
bustiblc gas injection 10 test the function of the system, whereby known
concentrations of test gas may be introduced into the  well and monitored
at the gas monitoring console.

     Samples are withdrawn continuously from each interior and exterior
campling point and monitored sequentially in a step-wise manner.  Gas
from each interior sampling point is passed sequentially across the
probe for a three-ninutc period; thus the interval between routine
measurements of combustible gas from a particular point  within the
Armory is 12 minutes.  This sequence is interrupted every  two hours
when gases withdrawn from the exterior sampling points are passed
sequentially across the probe [or a three-minute period. This lapse of
time between exterior samplings Is deemed adequate in light  of the
results of the evaluation program presented in ChfDter VIII. Thus,
monitoring of interior samples is interrupted for a period of  18 minutes
while exterior sanples are being measured.  Analyzed gas samples and
surplus by-pass gas are vented to the atmosphere  above the roof of  the
Armory.
     Measurements of percent of lower explosive limit of combustible
gas are made and  recorded on a 10-point recorder located in  the monitoring
console.
Signalling Sygtem--
     The signalling system was designed to warn immediately all occupants
of the Armory should explosive gas concentrations be approached within
the confines of the building.  An alarm,  audible in all parts  of the
Armory, is provided,  together with visual signals at the central monitoring

                                    82

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station.  In addition, visual signals arc provided at  the central
measuring station if combustible gas is detected at  any exterior sam-
pling probe.
     The detection system is also provided with audible and visual alarms
to warn Anaory occupants of electrical or mechanical failure of any of
the system components.
     The visual and audible alarms are activated at  a pre-set combustible
gas concentration of 25 percent of the lower explosive limit (LEL).  This
level Is well within the analyzer's capability for accurate analysis and
sufficiently below the LEL to rllow necessary action long before the LEL
is approached.
OPLRATLNC PROCEDURES
     Based upon preliminary results of the evaluation program, a set
of operating procedures has been developed for use by field personnel
during the active life of the landfill and the beneficial occupancy of the
Armory.  These procedures are divided into routine  procedures, system tests
and maintenance.  It is crucial to the safety of the Armory premises that
these procedures be followed regularly and precisely, and that any irregu-
larities be promptly and properly corrected.
Routine Procedures
     The pump is to be operated continuously at the  lowest speed practi-
cable (about 600 rpm) with the drive system provided.  This speed of
rotation should provide the necessary protection with minimal equipment
wear.  The regular operation of the system will, in  the long tern, re-
sult In breakdowns and failure of parts.  Replacement parts and repair
facilities must be readily available to minimize down time and prevent
the possibility of gas movement into the vicinity of the  Armory during
these periods.
     The recorder charts must be carefully reviewed  by operating person-
nel at the time that they are changed.  Any time that readings above zero
percent lower explosive limit are obtained, time, date and concentration
should be permanently recorded in a special book.  This will allow ready
                                   83

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reference and appropriate decision on the necessity for changing opera-
tional node of the system.  Although pressure readings need not be  ob-
tained as.part of the routine procedures, it is important that access to
and operation of the pressure probes (Ml through M10, Figure 15) be Main-
tained and their destruction be avoided.  Should future testing become
necessary, existence of  these probes will be of vital importance.
System Tests
     Periodic  tests  of  the  integrity of the various system components
are necessary  to minimize  repair and down time as veil as to maximize
reliability of the monitoring and signalling systcn.  For major equip-
ment, such as puop,  motor,  analyzer, recorder, etc., the instructions
specified by the manufacturers should be followed carefully and strictly.
     Once every  six  months, test gas with a known concentration of
methane shouldtbe injected  into  the exterior sampling wells through the
access points provided,  while the system is placed on manual control for
testingrsamples  from .a  particular well. The volume of injected gas
should be sufficient to fill the well  casing and the volume immediately
adjacent  to it,  or  at  least enough to  effec* a response at the monitoring
panel.  .This quantity will  be ascertained *-. field personnel through
experience.  Response of the analyzer  to these tests should be noted
in :the special monitoring book kept near the analyzer panel.
     -After.every shutdown  (for repair,  replacements, etc.), the record
of the analyzer  should  be  critically viewed for possible gas Intrusion.
System Maintenance
     All  manufacturers'  recommended maintenance procedures must be
followed  for pump,  motor,  analyzer,  recorder and other equipment used
for .the Link Road landfill  gas barrier system.  Breakdowns and  failures
oust be  imraediajtely attended and repaired.
SAFETY FEATURES
     There are a number of safety features  Incorporated in the design,
operational procedures  and contingency provisions  of the gas migration

                                    84

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barrier system.  The design of the barrier involves  gas-well  spacing and
flow specification which together Include provisions amounting  to a very
hlj»;> factor of safety.  While this margin may appear excessive, it  should
be noted that gas migration barrier design is still  evolving  and  that
human life may be jeopardized without provision of excess  capability.
The pump as well as the analyzer sampling units are  designed  to be ex-
plosion-proof, and excess combustible gases are vented to  the atmosphere
at a level above the roof of the Armory.
     Operational procedures, described above, also include ample  safetv
features which, if followed faithfully, should prevent any possibility of
failure or danger to occupants.
     Any mechanical system upon which safety of humans is  based needs
back-up contingency provisions.  The gas barrier Is  no exception.  There-
fore, a series of back-up safety provisions are available  for implementa-
tion upon indication of need.  These provisions—none of which  will
probably ever be needed—are:
     (1)  If at any time the lowest speed of pump operation fails to
intercept gas movement across  the barrier, pump speed can  be  increased
gradually until gas concentrations at the exterior probes  (Probes 5
through 10, Figure 14) drop to zero.
     (2)  If provision (1) does not provide the necessary  protection, all
butterfly valves on Wells 9 through 15  (western leg of the barrier, shown
on Figure 12}  should be shut off.  This action will almost double  the flow
 from the  wells immediately  surrounding the  building and should inter-
 cept any  gas  movement  across  the  barrier.
      (3)  If both provisions  (1)  and  (2) fail to provide protection, a
surface seal  (asbestos-cement, concrete, asphalt, bentonite, plastic
sheeting, etc.  as may be determined when and if the need arises) should be
placed  to a width of  100 feet  along  the barrier.  This provision will
prevent movement of atmospheric air  along the barrier Into the wells.
The  net effect will be the  creation of a substantially greater vacuum
midway between wells  and hence a  far  greater assurance of interception
of gases  moving toward the  building.
                                   85

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     (4)  Ultimately,  if  all  the above provisions fail, the vacuum pump
should be replaced with a larger pump with higher capacity.  The veils
and headers are sized  such that the pumpage rates can be increased to
as high as 10  to 20  times the rate which Is expected to be satisfactory.
Thus, there is no conceivable possibility that any provisions beyond
this step need be implemented.
                                     86

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                               CHAPTER VIII
             PERFORMANCE EVALUATION OF PROTOTYPE GAS BARRIER

INTRODUCTION
     Protection of tmcan lite, property and the environment  in and around
the facilities near che Link Road waste disposal site has been the prin-
cipal objective of constructing the gas migration barrier system.   An
indisputable assurance of its reliable and safe operation—over  extended
periods of rime—is necessary befoie there can be safe  occupancy and
regular use of the buildings.  A carefully planned,  systematic and
rigorous testing program has been conducted, and the results thoroughly
examined and evaluated.  These results were favorable,  and indicate
that, if the system continues to operate at the tested  level,  safe
occupancy of the Armory peraises can be anticipated  in  the relatively
near future.
     The primary objective of the testing and evaluation program was
to aid in the selection oE the most cost-effective mode of operation
for the barrier system.  The test sequence was planned  to permit evalua-
tion of each mode of operation independently and under  similar conditions,
insofar as prevailing constraints allowed.  The program was  designed
to tfst and evaluate least-cost methods at the outset and to progress
to mare costly modes of operation only if the lower-cost methods failed
to provide the necessary protection.
     A secondary objective was to accumulate data and experience for
better understanding of gas-flow ohenomena near solid waste  land disposal
sites under the influence of the forced-ventilation  gas barrier  system.
                                   87

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The information will aid in designing other gas barrier systems  in
similar circumstances.
     Measuring the zone of influence of individual wells and of  the
whole barrier under actual operating conditions was a key element in
the program.  This parameter helps determine the maximum well spacing
which assures pressure reduction along barriers in future systems.  Other
parameters determined include noise levels at the pumps and flow dis-
tribution among  the wells under different pumpage rates.
TEST EQUIPMENT AND INSTRUMENTATION
     Some of the equipment used in the test program was similar  to or
identical with equipment  Installed for the continuous monitoring and
signalling system.   In addition, gas concentrations were determined
using portable combustible gas analyzers.  Soil-air pressures were
determined from  probes placed near the barrier.  Atmospheric pressure
was obtained  from the meteorological station at the Greensboro,  North
Carolina, Airport approximately 35 miles  from  the Armory.
Flow Meter
     A  cumulative flow  meter was  installed on  the discharge manifold of
the vacuum pump.  Cumulative flow  over a  known period  of time was read
and recorded,  including the  date  and time at which  readings were
obtained.
Gas Probes
     The ultimate purpose of the gas barrier is to reduce  gas concentra-
tions  in the immediate vicinity  of the protected  facilities  sufficiently
below  the lower explosive limit  to assure their safe use.  This para-
meter  is a primary criterion for the barrier system's  success under each
mode of operation.  Measurements of explosive gas concentration can be
correlated with such independent variables  as flew rate, duration of
 flow  and weather conditions for the purposes of future design considera-
 tions .
                                    88

-------
     It is not sufficient to measure gas  concentrations in terns of
percentage of the lower explosive limit.   Concentrations may exceed LEL
at the beginning of barrier operation or  when test  flow rates are too
low to reduce all concentrations  below the explosive  limit.  A portable
gas analyzer unit (J-W Gas Kit, Model HPK) was used to determine explosive
gas concentrations, in percent by volume.  When gas concentrations in
probes not connected to the barrier monitoring and  signalling system
fell below the lower explosive limit, readings in terms of percent lover
explosive limit were taken with  the portable unit.  This allowed more
sensitivity to variations of concentration at the lower ranges of con-
centration.  The installed gas monitoring and signalling system  (con-
sisting of a sampling system, combustible gas analyzer, programmer,
control and signal devices and a  10-point recorder) were used to deter-
mine gas concentrations (in terms of LEL) from the  probe  locations
serving the system.  Locations of probes  serving the  iLonitoring and
signalling system, as well as those for supplemental  evaluations, are
shown in Figure 15.  Subterranean Probes 5 through  10 (see Figure 14)
consist of standard wo11 points  driven 10 feet below  grade,  connected
permanently by copper sample lines to the gas analyzer.   Access  is pro-
vided through water-meter-type enclosures.
Pressure Probes
     Maintenance of a ubiquitous  negative pressure  in the vicinity of
the barrier is an essential requirement;  consequently,  it is important
to verify the ubiquity of the negative pressure and to measure  its varia-
tions.  Relations between pressure distribution and pressure variation
in the soil and with system flow rate and atmospheric conditions help
describe the effects of soil properties and gas movement  at  the Link
Road site.  Probes were installed to permit pressure  determinations  at
10- and 20-foot depths at locations shown in Figure 15.
     Specially constructed U-tube manometers were used to measure sub-
terranean soil-air pressures at  each pressure probe.   A schematic drawing
of a typical pressure probe installation and manometer is shown in

                                   89

-------
                                                        ANALYZER  PANEL
GARAGE

            FIRE LAB
                        JL GA$  EXTRACTION  WELL
                         • GAS  ANALYZER PROBE, EXTERIOR
                         0 GAS  ANALYZER PROBE, INTERIC <
                         O GAS  CONCENTRATION  PROBE
                         A GAS  PRESSURE  PROBE
N
            .29
                                                                       IZS
           Figure  15:   Probe  locations  for gas barrier  evaluation

-------
Figure 16.  In this instance,  manometer assemblies were fabricated locally
and permanently mounted on plyboard.   The  manometer assembly was mounted
on a cart for transport to each sampling point.
Vacuum Gauges and Taps
     Each well is equipped with a vacuum gauge  tap so that flow among
the barrier wells may be equalized (uniform vacuum) by use of butterfly
throttling valves.  Consistent recording of vacuum readings and of valve
settings at each well are required to provide information for operational
and test regimes.
TEST PROCEDURES
     Ease levels of gas concentration and  pressures in the soils were
established before any pumping (even for equipment testing) took place.
These tests were perfonuod regularly for approximately one month prior
to the first activation and operation of the pump.  The on-going gas
monitoring program continued uninterrupted and  readings were obtained
on a regular, daily (5 day/wk) schedule, coinciding with gas concentra-
tion readings throughout the test period.
Mode 7;  Low-Flow Pumpage without Surface  Seal
     The vacuum pump was operated at the lowest flow  rate of 160 scfm
(corresponding to lowest available speed setting of 585  rpm) for about
two weeks.  This period was not enough to  produce an  equilibrium pres-
sure distribution in the soils along the barrier; however, most para-
meters were approaching steady-state, as shown  later  under discussion
of results.  During this period, gas concentration, pressure,  flow rate
and cumulative volume of gases removed were recorded.
Modes II. Ill and IV;   Varying Flow Pumpage without  Surface Seal
     After it was ascertained that the system was satisfactorily effective
at the minimum pumpage rate, pump speeds were increased  for  a  similar
length of time.  This sequence could be repeated, if  necessary, by step
increases In the pump spec*' (745, 905 and 1,065 rpm)  until the pump's
ultimate capacity Is reached.  System flow rates at  these pump (settings

                                   91

-------
     1/2  PLYBOARO
  1/8" POLYPROPYLENE
       TUBING
   GLASS TUBING
        VULVES
  1/8"  POLYPROPYLENE
        TUBING
     1/2  STONE
  PERFORATED   PROBE
     1/2  STONE-
METER  STICK


   GLASS  WOOL



-GLASS  TUBING
                                   COLORED  WATER
                                    (p= 100 g/ee)
                                 MANOMETER
                                     SOIL  SURFACE
                                     7?3ZV~

                                      CEMENT  SEAL
—CEMENT  SEAL

     PRESSURE
      PROBE
                          \*—+\— 6" TO 8" DIAMETER
                                 DRILLED HOLE
Figure  I6:    Pressure   probe  and  manometer  detail
                           92

-------
were 168, 210 and 250 scfm, respectively.    Throughout  each test sequence,
all parameters were measured and recorded.
     Maintenance of a ubiquitous negative pressure  and  no  passage of
landfill gas Co the protected side of the barrier (when the barrier is
operating ac low flow with no sealants)  was  used as a positive  criterion
of successful performance.
Mode V;  Contingency Tests for Surface Seal  with Varying Flow
     An ultimate back-up provision, the necessity for which appears
highly unlikely, is application of the designed surface seal along  the
barrier.  Application of the surface seal will make it  possible to  effect
confined flow conditions, with no flow of  atmospheric gases into or
between wells along the barrier.  Standard  asphalt  paving  is considered
nost appropriate as a seal, bul application  of a seal was  not required
or tested in the evaluations conducted and  reported herein.
     The test progr.in for such a contingency condition  was designed to
give the maximum amount of data for future  design purposes as well  as
to effectively evaluate this unique feature, not connon to existing
barriers.  While the seal is being installed, pumping should continue
at the lowest design rate and complete data collection  should be con-
ducted.  A chronicle ot Che progress of seal applications  should be kept
to correlate the time of seal placement with the reductions  in  gas  con-
centrations or increases in negative pressure.
     The seal can be placed in successively increasing widths  and  lengths
(e.g., exclude western  leg), allowing sufficient tine between  dimensional
Increments to permit equilibration of the flow and pressures.   Incremental
seal application and concurrent lapses of Lime will be  dependent on
available test results, equipment availability and logistics.
     In the highly unlikely event that the low-flow and surface-seal
combination system proves unsatisfactory (under some severe  combination
of conditions, certainly not expected at the Link Road site),  high-flow
pumps  may be installed  and their performance tested in much  the same
general pattern t's prescribed above  for the low-flow ays ten.   The success

                                   93

-------
of high-flow ventilation barriers, has  already been demonstrated else-
where (Reference-27).
NoiseSurvey
     Noise levels resulting from operation  of the vacuum pump equipment
Installed for  gas evacuation were measured  by R. J. Reynolds Tobacco
Company personnel on  15  Hay 1974 for the  City of Wins ton-Salem.  The
objectives of  the survey were to determine  if the vacuum pump produced
noise levels which would be annoying and  generate objectionable complaints
and to determine  if the  noise levels during operation were hazardous to
human hearing.  On chat  basis, the  procedure used was to measure the
noise levels produced by the vacuum pump  and to measure the prevailing
daytime background noise levels with the  vacuum pump off.
     The following instruments were used  during the noise survey:  General
RaJlo Octave-Band Noise  Analyzer, Type 1558-BP, Serial No. 2155; and
General Radio  Piezoelectric Microphone Assembly, Type 1560-P6, Serial-
No. 1614.
     The A-weighted sound  level and octave-band sound pressure levels
were measured  at  two  positions. The pump speed was 1,065 rpm (motor
speed 1,750  rpm).  All measurements were  taken at a height of  four feet
above the ground.  The first measurement  was  taken close to the pump.
The microphone was located three feet  north of the vacuum pump gearbox.
The second measurement was taken 10 feet  north of  the vacuum  punp gear-
box at the sidewalk.   Kith the vacuum pump off, background noise levels
were alea measured three feet north of the vacuum pun? gearbox during
normal and peak traffic  conditions  on Silas Creek Parkway.
     The A-weighted sound  levels obtained were used  to evaluate noise  in-
duced hearing  hazard. The A-weighting network has a  frequency character-
istic similar  to that of the human  ear, i.e., both  arc more sensitive
to middle  frequencies than very high  or very  low  frequencies.  The. octave-
band frequency analysis, i.e.., the  distribution of sound pressure level
in the nine  preferred octave bands  with center frequencies  from  31.5  to
6(000 Hz provides additional information  concerning  the character of

                                    94

-------
the noise and for estimating subjective annoyance effects  such as
speech interference.
RESULTS
     A large volume of data on gas concentrations and  pressures was
generated during the course of system testing and evaluation,  under
two modes of operation, lasting about three months.  These data
firmly corroborate the theoretical computations which  were used as
a basis for the conceptual design of the gas migration barrier.
Because most data are confirmatory, only representative samples of
data showing trends over time and space are presented  In this  section.
The remainder of the data are not graphlcallv presented in order to
maintain simplicity and prevent repetition and confusion of the pre-
sentation.
     Records obtained  from flow rate meters, gas concentration probes
and pressure probes, and those obtained less frequently from other instru-
ments were analyzed and evaluated promptly.  Because many decisions  re-
garding additional construction and operation of the barrier system had
to be based upon these  results, prompt and proper analysis and careful
evaluation of data were conducted as the data were collected and as system
operation continued during the test period.  Overall evaluation criteria
on each of the pararicturs are outlined below.
Combustible Gas Concentrations
     The most Important parameter, from the point of view of human safety
from explosion hazard.1;, is concentration of explosive gases on the protected
side of the barrier.  Early results, after Initiation of pumping, Indica-
ted a definitive trend, with gas concentrations in the protected areas
rapidly falling with Line.  The trends continued ai  all probe locations
with a firm trend toward zero readings throughout the monitoring period.
Trends of average combustible go., concentrations are shown on Figure 17
for shallow (10 feet) probes and deep  (15 feet) probes on both sides of the
barrier.  In order to maintain comparability of the two sets of data, only
                                   95

-------
    to
    <
    O

    UJ
    _l
    CD

    t-
    «n

    CD
    2
    O
    O

    u.
    O
100



90



80


70
                         DAYS  AFTER  START  OF PUMPING

           -25 -20  -15   -10  -50    5    10   15   20   25   30  38   40  45
    ~                              LEGEND
PROTECTED JIDE OF BARRIER


    DEEP L° 115 ft° "   """""

LANDFILL  SIDE OF BARRIER
                                                            ond 17
                                                   prob«l2,l4,l5ondl8
                                                 j
    z
    UJ
    O

    O
    u

    UJ
    cr
    UJ
                                                L11
          20  25   90
           MARCH
                       10   15   20   25  90
                          APRIL

                               DATE - 1974
                       10   15   20   25   30
                           MAY
Figure
 17:   Average  concentration  of  combustible  gas on either  side  of  gas
migration   barrier  prior  to  ond   during   operational   modes

-------
those data obtained from Probes 11, 13, 16 and 17 (Armory side)  and 12,  14.
15 and 18 (landfill side) were utilized to obtain the averages plotted on
Figure 17.  Other data present a similar picture.  From probes  located
inside the Buildings, readings of percent of the lower explosive limit
(i.e., percentage of five percent methane by volume in air),  recorded
with automatic equipment, verc obtained and plotted as shown  on  Figure
18.  Percent lower explosive limit (LED is a very sensitive  and hip.hly
refined measure of safety or lack, of it in an occupied space.   (For example,
25 percent of LEL, at which point alarm systems are activated, corresponds
to a methane concentration in air of only 1.25 percent by volume.)
     Gas chromatographic analyses of combustible and other gases sampled
at the pump discharge and at selected probes provided additionil data
durlnc the evaluation period.  Concentrations of oxygen, nitrogen,  methane
and carbon d oxide in these samples were measured.  Table 10  shows  the
chroaatographic analysis for the pump discharge and Table 11  for other
selected probes from the deep (15 feet) access points.  As expected, the
gas mixture pumped from the volume of soil on both sides of the  barrier
was rich in methane and carbon dioxide at the beginning of the operation.
As pumping continued, evacuation of combustible gas from the  protected
side of the barrier and admission of atmospheric- air from both sides caused
a gradual decline of CH. and CO. concentrations with a simultaneous in-
crease in 02 and N^ concentrations. A similar trend from t?as  chromatograph
concentrations at the selected probes was not as evident during  the brief
tine and limited extent of gas chromatographic analyses, in the  early
period of barrier operation, but pronounced reduction in concentrations
at probes near tha barrier were verified by gas analyzer readings as
pumping continued.  Concentrations at most probes had declined  to or near
zero levels, with lowered gas concentrations persisting at a  few deep
probes, primarily on the landfill side.
Flow from Individual Wells
     A primary parameter in the operation of the barrier system at  the
Link Road site is rate of flow of the gas mixture.  It is imperative
that flow from Individual wells be maintained uniform along the  entire

-------
   100

 390
 $5
  .80
 O
 5 TO
 a:

 S60
 o

 I50
 v>
 g40

 330
 0
 oa

 O 10
 o
                      DAYS  AFTER START OF  PUMPING
                      •tO   -5   0510620       30354045
  r'5   '*P   .'?.  .P.  m5T   '°    g.   2Q.  2S.   ff   35.  -40.  i45
            j\ I I I I I I njll M I I I I I I! II H I I I I I I H I I I I t II I I I I I I M t I I



PERCENT      n

S 5,6,7,8,9,10  J\     j   j
> ^ n. . _ t        I • •
 'IT Mf1
_/
 [       PERCENT
 ^-P
PROBES 5
  (EXTERIOR)
BACKGROUND
                  KI
                    \  i
                           -\-MOK I-
                                      •MODE M-
                                   NOTE - PROBE NUMBERS
                                     REFER TO LOCATIONS
                                     SHOWN  ON  FIGURE 14
                    I
                             \
                         '. n
                          H  I
        /-PROBES I,Z,3,<»  I \[
        f    (INTERIOR)      If
    iJniilu        ili.  iiL^-Ji

                        \-fc-PROBE 5

                            PROBE 9
                         j^ PROBE 6
                            PROBES 1,2,3,4,
                                3,9,10
*
                                                 -ALL PROBES

                                                        • L,
                                                                      nil
      20   25   30
        MARCH
                             25   30
                   10    IS   20
                      APRIL
                         DATE-1974
                                      10    15   20  25   30
                                          MAY
Figure 18:  Percentage  of  lower  explosive limit at individual probes  in  and
     near buildings  prior  to and  during barrier operational  modes.

-------
Table 10.  CAS CHROMATOCKAPHIC ANALYSIS




   OF BARRIER PUMP DISCHARGE  CASES
DATE
16
18
19
22
23
24
25
26
29
30
1
2
3
6
8
10
13
IS
17
Apr
Apr
Apr
Apr
Apr
Apr
Apr
Apr
Apr
Apr
May
May
May
May
May
May
May
May
May
74
74
74
74
74
74
74
74
74
74
74
74
74
74
74
74
74
74
74
Cos coiqiosition , Z by
°2 N2 CH4
7.
3.
7.
9.
7.
5.
5.
5.
3.
IS
12
6
4
4
0
6
1
5
8
1
.2
.5
10.7
21
20
18
19
8
9
13

.4
.4
.4
.6
.0
.5
44
43
47
48
51
54
54
50
61
63
62
73
78
76
76
75
68
67
74
.7
.4
.4
.5
.2
.3
.5
.0
.0
.0
.9
.6
24.
31.
20.
20.
19.
20.
19.
22.
14.
11.
7.
8.
4
1
3
6
8
6
8
8
4
2
5
1
Trace
.8





1.
2.
2.
11.
11.
7.
2
6
6
8
3
0
volume
C02
23
24
24
29
20
2C
20
22
20
8
17
10
.0
.7
.6
.5
.7
.0
.8
.2
.6
.8
.0
.0
Trace
1
2
2
11
11
6
.0
.4
.2
.1
.9
.7
                 99

-------
              Table 11.  GAS CHROMATOGRAPHIC ANALYSIS

              OF SAMPLES FROM SELECTED PROBE LOCATIONS*


                         Gas composition, % by volume
             DATE         0     N        CB      C0
Probe 11D
24
30
2
Apr
Apr
May
74
74
74
9.
2.
6.
2
8
3
30.
18.
35.
2
7
2
37
45
30
.0
.1
.5
22
33
28
.8
.0
.0
                              .Probe 12D
3 May 74
-6 May 74
4.1
5.1
10.6
20
53.1
43.8
31.3
30.7
                              Probe 24D
18 Apr 74
19 Apr 74
22 Apr 74
23 Apr 74
25 Apr 74
26 Apr 74
1 May 74
4.0
-5.2
.1.2
8.6
3.0
4.5
3.8
13.9
9.1
10.1
35.0
20.4
26.8
33.1
53.8
55.0
62.8
35.7
52.9
46.5
36.4
25.6
30.4
26.0
20..2
-24.7
71.6
26.1
*Probe .locations  12 and .24 are on the landfill  side  of  Che barrier.
 Probe .11 is in  the gravel-surfaced parking lot,  inside the barrier
 and west of the .Armory.   See  Figure 15.
                                100

-------
barrier for the duration of its operation.   An unusually  high  Clow  In
a well usually indicates leakage of air or a relatively high-permeability
medium surrounding the well.  In such cases, the valve at the  well  head
was partially or totally throttled so that the well would not  interfere
with the operation of other wells.  An unusually low flow may  Indicate
a low permeability medium around the well.   Such an observation was not
recorded during the conduct of the test procedure.
     Direct flow measurement on each well head was  not practical.   How-
ever, an indirect, though accurate, measure of flrw was obtained  from
relative vacuum readings.  A portable vacuum gauge  was used on quick-con-
nect nipples provided on each well head.  Excessively low vacuum  readings
were encountered on three wells (Wells 11, 12 and 13, Figure 12)  located
in an area where higher soil permeabilities were suspected from earlier
soil tests.  The rushing sound of air moving through these particular
well heads emphatically corroborated that excessive flows were taking
place from those wells.  Therefore, in order to maintain  as high  a vacuum
as possible and to preserve the uniformity of flow from other wells, the
valves on the three wells were closed.  While this  modification may reduce
effectiveness of the barrier in the vicinity of the wells, flow at the
remaining wells is increased thereby.  No potential for hazardous gas
accumulation existed nearby so further modification, such as application
of a surface seal, was not attempted.
     Flow rates from the entire system were 160 and 250  scfn during op-
erational Modes I and II, respectively.  These  flows correspond to aver-
ag?. flows per well of 11 and 17 scfm, respectively.  It  should be noted
that the flow rates found satisfactory in the tests are  far lover than
those reported for other existing forced-ventilation operating systems.
Pressure Distribution
     All pressure measurements were made relative  to the atmosphere.
It was found that atmospheric pressure variations were experienced almost
immediately at the depths manometer probes were Installed.  In view of
the wide atmospheric pressure variations encountered, as shown In Figure
19, and because flow, in &  given  area, occurs in direct  response to
                                   101

-------
   770
   760
E
E
 .  750
UJ

I
UJ

-------
gradients of relative pressure, use of absolute pressures was  avoided.
Typical draw-down curves between wells were obtained before  and during  Che
test period as pumping progressed.   Pressure distributions at  20-foot depth
between Wells 5 and 6 at selected points In time are shown on  Figure 20.
It Is noteworthy that a ubiquitous  negative pressure at all  points  along
the barrier was obtained immediately after r—>lng began at  the 160-scfm
rate and that the negative pressures at all points between wells, partic-
ularly midway, continued to increase significantly, particularly at the
250-scfm rate.
     The increases in negative pressure with time at the deep  probe level
at the H6 through M10 stations at a point midway between wells and  at
increasing distances from the line of wells are illustrated  in Figures
21 and 22, respectively.  The significance of the drop in pressure  over
time is dramatically exhibited in a statistical test of the  differences
between average pressure before pumping and that during each mode of
operation of the barrier system.  The range, average, standard deviation
and statistical significance test of the differences for each  mode  of
operation throughout its duration are shown on Table 12.  It is noted
that the influence of the barrier significantly extends to a distance
of at least 18 meters (about 60 feet) from the barrier in  both operating
nodes (160 and 250 scfn).
Noise Levels
     The Federal Occupational Safety and Health Act of 1970  (OSHA),
using the Walsh-Healy Public Contracts Act, paragraph 50.204.10, Safety
and Health Standards for Federal Supply Contracts, specifier the maximum
number of hours per day an employee may be exposed as a function of the
A-veighted sound level when measured with the A-network of a standard
sound level meter at slow response.
     According to the regulation, the noise level  limit is 90 dB(A) for
an eight hour per day exposure  over a working  lifetime.  For  noise levels
lower than 90 dB(A), longer exposure times are permitted.   The converse
IB also true.

                                   103

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                 MANOMETER  STATION
                  M2     M3      M4     MS
WELL 6    MI
                                            DAr    —
                                            MINUS IS
                                            DAY    ~~
                                            MINUS 5 —
                                           DAY  I  —
  IO            5           0           5           10
     DISTANCE  FROM MIDPOINT  BETWEEN WELLS, m
Figure  20:  Drawdown  curves  between  barrier  wells
            5 and 6 during barrier test period
                       104

-------
o
*

E
E
(E
O
CO

UJ
a:
a.
I
 10


 0


 10


20


30


40


50


60


70


80
O
to
   -90
  -100
-25  -20  -
                      DAYS  AFTER  START  OF PUMPING

                  15   -10  -5   0    5   10   15   20   25
                           MODE I
                          (iBOscfm)
                                                      30   3S  40   45
                           i
-MODE JT-
 (25Oscfm)
                                             x-SHALLOW  PROBE (10 FEET)
                                                    ill
                                     „	DEEP  PROBE  (20 FEET)
                                                                i
       20   25   30
        MARCH
                  10   15   20  25   30   5
                     APRIL
                                                 10   15   20   25   30
                                                     MAY
                                  DATE - 1974

Figure  21:   Relative  pressure  at   two  depths   midpoint  between  barrier
                      wells 5 and 6 during barrier test  period

-------
          DAYS AFTER  START  OF PUMPING
                                      25  30  36  40  45
20  25  30
 MARCH
                    6  20
                   APRIL
                                                    30
                      DATE- 1974
NOTE:  PRESSURE READINGS WERE OBTAINED FROM MANOMETER PROBE
      LOCATIONS M6 THROUGH MIO (FIGURE 15), ESTABLISHED AT  6-
      METER INTERVALS, IN A LINE PERPENDICULAR TO THE LINE OF
      THE BARRIER AND EXTENDING  INTO THE LANDFILL  FROM A
      POINT MIDWAY  BETWEEN WELLS  5 AND 6
Figure 22'-  Relative  pressure at  various  distances
         from  barrier during the  test  period
                       106

-------
                     Table 12.  STATISTICAL DATA ON COMPARATIVE EFFECTIVENESS OF SOIL-AIR  1'RESSURE
                        REDUCTION AT VARIOUS DISTANCES FROM BARRIER UNDER  TWO OPERATIONAL  MODES.'





M
S

static-.
Ml
MS
M7
MS
X9
SIO
Distance fros
barrier.
•s ft
0
6
12
IS
24
30
0
19.7
39. i
59.0
78.7
98.4
Frinsurc raise, — 1'2°
«.-.rt,-n.n'
+7 to -22
0 to -8
+12 to 0
+30 to 8
+214 to -18
+116 to -44
v«!e I
-2 to -72
-14 tc -47
0 to -25
0 to -3
+157 to -155
+33 to -17
"efe II '
-71 to -124
-43 to -97
-i: to -54
-9 to -47
+156 to -13
+105 to +7
"c.ir r-
lll^-OU-
-2
.4
5
6
95
27
e^jre. rr- )!20
1 vo-lc I
-42
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Str-t!tca-.tly difCerc-t fron baekprojrd coriiltloiR at the °9 percent level of centlder.cc.
Net •Igntflcnntly different fron bnc*jrc-jrd conditions at tbc 99 pcrcc-.t level of confidence.

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     By way of comparison,  the  A-weighted sound  levele measured at three
and 10 feet from  the  vacuum pump gearbox operating at maximum speed  (1,065
(1,065 rpra) were 86 dB(A) and 75 dB(A), respectively.  Results of the
noise analysis are  presented in Figures 23 and 24.  Thus, operation of
the vacuum pump does  not  present a serious hazard to human hearing.
Since the  pump operator  is  not  required to spend a considerable length
of tide near  the  unit, personal ear protective devices, such as ear plup.s
and ear muffs, are  not  required.
     A further evaluation of the pump noise  levels at  the sidewalk vas
made due to the possibility of  annoyance when the vacuum pump noise
Interferes with speech intelligibility.  The Preferred Speech Inter-
ference Level (PS1L)  is  a good  guide to the  interfering effect of an
intruding  noise on  speech.
     The extent co  which a steady  continuous noise interferes with
speech communication  depends upon  the distance between the speaker and
listener at various levels of voice effort.   The PSIL  is the arithmetic
average of the sound  pressure levels in the  three octave bands, with
center frequencies  at 500, 1,000  and 2,000  Hz.   The  interference  levels
are for average male  voices with  speaker  and listener  facing eachn
other, using  unexpected  word material.  It  is assumed  there are no
nearby reflecting surfaces that aid the  speech sounds.
     The PSIL of  the noise produced by the  vacuum pump at  the  sidewalk
is 70 dB.   The average person would need  to shout to Bake  himself" under-
stood at a distance of six feet with the  vacuum pump in  operation.  A
comparison of the PSIL produced by the vacuum pump (70 dB) and the PSIL
of the prevailing background noise in the area during normal traffic  con-
ditions  (54 dB)  Indicates that the average person would  be understood
at a  distance up  to about six feet using a normal conversational voice
level with the vacuum pump off, as shown in Figure 25.
                                   108

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    100
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    60
                                   AT IO-FEET\
50
40
    30
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       Figure 23!   Frequency  analysis of noise  produced  by

                                  vacuum pump
                                109

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    100
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                             FREQUENCY, Hr
                                                            10000 dB(A)
 Figure  24:  Frequency analysis of background noise measured

                      three  feet  from vacuum pump gearbox
                                 no

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    IOO
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 1
     zo
                                                             10000  PSIL
                               Frequency, Hz
 Figure  25'  Comporison  of vacuum pump noise  levels measured  at
              10 feet  to the background  noise  levels measured during
                            normal  traffic  conditions
                                 111

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EVALUATION OF RESULTS
Safety for Occupancy
     The combustible gas  concentration profiles, presented ii. Figures 17
and 18. show conclusively that  the system is providing and maintaining gas
concentrations at  or near zero  inside the barrier and In occupied spaces
under the least  Intensive operating  mode.   If careful monitoring confirms
that these conditions continue  to obtain over a period of months, the
Armory should then be free from explosion hazards and suitable for normal
occupancy and use. That  adequate protection is apparently provided
Is best evidenced  by  the  plot of percent lower explosive Unit at all
inside monitoring  probe locations before and after  the start of the
system, as shown on Figure 18.  Probes  loceted inside the Armory (Probes
1, 2, 3 and  4)  consistently recorded zero LEL readings throughout the
test period.  Whereas  combustible  gas concentrations were uniformly above
100 percent  LEL before  the start  of  the system at all probes outside the
Armory, they  dropped precipitously upon start of  the pumping process.
The sharp, but  ephemeral, resurgence of gas concemrations at two outside
probes  (Probes  5 and 9) after the initial  drop,  is  Attributed to the
arrival of gases that had previously moved  under and beyond'the Aratory.
It is expected  that after all the explosive gas  on the protected side
is extracted there will be no more source  of supply of gas. north of the
barrier,  to  give  rise to any further such  peaks.   With the pumpage rates
of 160  to 250 scfia used, it Is estimated  that complete  removal was accom-
plished in the  duration  of the test period.
      A  comparison of average combustible  gas concentrations  on  both  sides
of  the  barrier at two depths, as shown in Figure 17,  is  revealing.   Whfle
combustible gas concentrations at both depths (10 and 15 feet  from the sur-
 face) declined to zero on  the protected side of the barrier,  those on
 the  landfill side declined to values above zero.  This  trend is  wholly
expected  due to the continuous generation of combustible gas  in the  land-
 fill.  The decline in concentration is due to admixture  of progressively
 greater anouni.s of air entering from the surface.  This  phenomenon also
 explains  the faster rate of  decline of combustible gas concentration from
 the shallower probes than from the  deeper ones on both sides of the
                                    112

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barrier. Afcer several months, when equilibriun conditions  are  fully
established, the average concentration of cocibustiblc  gas  froa  the probes
on the landfill side of the barrier—at any given punpage  rate—nay be
used as an index to the approximate gas generation rates in the fill.
Barrier Effectivcnesa
     While gas concentration data help establish the effective  operation of
the system, pressure distributions reveal the degree of success of the
barrier, its extent of influence and the need, if any, for its  improvement.
The "draw-down" curves in Figure 20 show the gradual lowering of  pressure
(increasing negative pressures) at all points between  wells. While a
minimal pressure drop of a few millimeters of water at the midpoint be-
tween wells would be sufficient Lo ascertain protection, i.egative pressures
of above 100 nllllmetcrr. water obtained under Mode II  operation of the
barrier provide a very high factor of safety.  The pressure decline o'er
the test period at the critical midpoint between wells is  illustrated
on Figure 21.  The high negative pressures obtained virtually guarantee
existence of ubiquitous negative pressures throughout  the  length  and  dcoth
of the construction barrier.
Extent of Influence of Barrier
     A very significant question in the design of new  barrier systems
is the radius of Influence oz wells along the barrier.  Thij parameter
helps establish maximum spacing of wells, flow rates to be employed  and.
In some cases, the need for a surface seal along the barrier.  The extent
of influence of the barrier can be readily visualized  from Figure 22  in
which declines in pressure are illustrated as a function of time from
Che start of operations and distance from the barrier.  Although only
the pressure readings at the deeper (20 feet) probe locations are shown,
the trends  arc the same for the shallow probes, albeit, more pronounced.
It is evident from Figure 22 and from statistical analysis presented in
Table 12 that the influence of the barrier extends to at least  Station
M8, approximately 60  feet from the barrier.  Thus, it  may be rurmised
thac under  existing flow conditions, a well spacing greater than the

                                    113

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existing 67-foot interval nay be permissible.  Conversely, it  is  evident
that lover flow rates  can be effective in providing the necessary pro-
tection vith the existing spacing.
Noise Levels
     The pump motor  does not present a hearing hazard and does not  con-
tribute any additional neighborhood noise at the property line, located
more than 50 iset  from the  pump.  There is some noise at the sidewalk
directly in front  of the pump.  However, this should not present  a  public
hazard because people  are not expected to be working for Ions  periods
In that area.  The only person who would be clc e to the pump  at  any time
1  the operator.   That person is not required to spend a considerable
length of time near  the equipment during normal operation.
Fover Requireman c  and  Cos t
     The major component of the barrier system requiring power is the
motor driving the  vacuum pump via the variable-speed sheave and pulley
system.  Power requirement  for the pump was computed directly, using
actual voltage and current  measurements during operation at the two extremes
of the pinup speed  range.  Power requirement for the gas analyzer sampling
pump is relatively minor.   It was calculated using a similar procedure.
Unit power cost at the time of these computations was $0.0251/kw-Jhr.
The power required and its  cost at  the  two speed extremes are  presented
in Table 13.

Table 13.  POWER REQUIREMENTS AND COSTS FOR GAS MIGRATION BARRIER SYSTEM
Unit
Hot or
Analyzer
Total
700
Power,
kw
3.229
0.918
4.147
Pump spee-J,
Cost,
S/vr
697
198
895
rpm
1050
Power,
kw
4. 835
0.918
5.753

Cost,
S/vr
1,044
198
1,242
                                   114

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Barrier System Cost
    The total construction cost for the barrier system was $88,100,
which consisted of $64,400 for the barrier and $23,700 for the monitoring
equipment.
    The itemized costs for various elements of the gas barrier system,
as constructed, are presented in Table 14, which also indicates the
corresponding estimated costs used in the evaluation of alternatives.

Table 14.  COMPARISON OF ACTUAL AND ESTIMATED CONSTRUCTION COSTS OF
                          GAS BARRIER SYSTEM
Element
Gas wells
Manholes
Suction header, 8 in.
Vacuum pump
Monitoring system
Total barrier
Cost,
Actual
19,800
7,380
24,970
12,250
(23,700)
64,400
dollars
Estimated
17,000
6,100
8,900
8,000
-
40,000
     The  greatest  discrepancy  between  actual and  estimated costs  is  the
 much higher (more than twofold)  actual  cost of the eight-inch  dia-
 meter polyvinyl chloride  suction header.   The higher actual costs in
 all other elements of  the system can  be attributed to  the high rate
 of inflation that occurred between the  time of estimation and  the time
 of procurement and construction.
                                   115

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                              CHAPTER IX
              TECHNIQUES FOR EVALUATING SOLID WASTE LANDFILLS
                     WITH REGARD TO CAS MIGRATION

MINIMIZING ADVERSE EFFECTS OF GAS PRODUCTION AND MIGRATION
     Decomposition gases are a normal, expected consequence of land dis-
posal of solid wastes.  Sanitary landfill procedures will necessarily
establish anaerobic  conditions; consequently, provisions should be made
to control the migration of the gases, particularly methane.  Certain
precautions or provisions can be taken to minimize adverse effects by
proper site selection and by the design, construction and operation of
the sanitary landfill.  In general, open burning dumps pose lesser pro-
blems from gas production and migration then do sanitary landfills since
dumps usually afford ample ventilation and organic content is reduced by
burning.  However, any  buried refuse whether in A dump or landfill nay
produce gases which  may migrate to and accumulate in structures.
Site Selection
     To minimize  gas production from landfilled wastes, they should be
kept as dry as possible.  Consequently, the site for a sanitary Landfill
should be selected so as  to minimize entry of surface water or grounrtwater.
Locations with high  elevation, low water table and adequate natural sur-
face drainage features  are preferable.  Sites should be selected so as
to be least affected by nearby development which would increase surface
runoff onto the landfill.  To minimize effects of migrating gases,  sites
should be chosen  which  are remote from nearby existing structures or froa
likely future development  on nearby land.  The determination of proper
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separation between landfill  sites  and  nearby  development should be based
on engineering evaluations,  including  gas  permeability of soils. Sites
in areas designated for open-space,  recreational  or similar nonconstructlon
uses are generally perferable, although adequate  barriers can  be constructed
to permit on-site or nearby  development in some cases.  Sites  should be
selected so that the soil cover obtained on site  will be sufficiently
permeable to allow venting of gases  through the cover, yet not so permeable
that gases will easily migrate from the landfill  periphery.  Sandy soils
and those with voids and rocks, etc. are likely to have high permeability
for gas.  Clay and similar soils would have low permeability.  In general,
sites should be selected which require a minimal  amount of construction
(such as surface drainage, barriers  for gas controls, etc.) in order  to
minimize costs.
Landfill Design
     A number of design features are important for the control of gases.
If natural surface-drainage  features are minimal, the landfill design
should include a permanent surface drainage system to divert  surface  water
away from the landfill.  If groundwater levels are high,  a membrane or
other Impermeable barrier should be required to exclude  groundwater,
or wastes should be deposited above ground.  The landfill's  final grade
should be at least one percent to drain surface water without erosion
of landfill soil cover.  Landfill-edge slopes should also be protected
against erosion.  The operational plan should require adequate daily
compaction and covering of incoming wastes so that voids are reduced and
water entry during deposition is minimized.  The area of solid wastes
exposed to precipitation should be minimized by  limiting the size of the
working face.  The design may also include installation of gravel-filled
trenches, membranes  or other  permeable barriers  or areas of undisturbed
soil between waste deposits as natural barriers or vents (depending on
soil permeability).   The  design should also stipulate the ultimate antic-
ipated  use of  the  completed landfill.   If  construction is to be pemitted
on site or nearby, developers should  follow  construction precautions to
minimize  potential for gas  accumulation.   Undisturbed areas of soil nay

                                    117

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be left for future building sites, utility conduits and roads.   If soil
permeability permits extensive lateral gas migration, it may be necessary
to leave undisturbed an extensive peripheral area around each area where
wastes are buried, within which building will be prohibited or restricted.

Landfill Construction and Operation
     It Is important that design and operational plans be closely  follow.-4
during operation  r; the landfill and that any deviations therefrom be
undertaken with caution and be recorded.  In developing the landfill, it
is important to Dininize  the proportion of the site which will be  subject
to receiving precipitation  runoff and  to conduct operations so that  proper
grade and cover will be restored as soon as possible.  Natural cover and
beneficial runoff characteristics should be retained as long as possible.
Every effort should be nade to insure  prompt, maximum contraction and
covering of the wastes within a minimal space.  The highest and dryest
portion of the site should be reserved for the placement of liquid and
highly organic wastes, and  they should be disposed so that surface drainage
will be away from the main body of  the deposited wastes.  Absorption
of liquids by spreading such wastes over  the main body of drier wastes
will serve only to accelerate gas production therein, over a wider area.
Records should be kept on the  location and character of special-waste
deposition areas  such as  animal carcasses, sludges, etc., so that unusual
gas-migration suspect areas will be demarcated.  Such special-waste areas
should be  located in  those  parts  of  the landfill where on-slte or nearby
construction is least  likely  to occur. Such areas may be enclosed by
impermeable or other  gas  migration  barriers.  Use  of water  for dust con-
trol should be kept  to  a minimum,  and  water should not be added to the
wastes  to  aid in  compaction.  Pre-construct!on  of  trenches  and stock-
piling  of  cover materials should  be  minimized in order  to reduce ponding
of water and interference with  proper  drainage.  Portable pumps should
be used to drain  ponded water rapidly, and  finished  areas of the landfill
should  be  regraded  and  additional cover applied as necessary to eliminate
ponding due  to  settlement and to  restore  cover  integrity,   finished areas
                                    118

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of the landfill should be revegetated as  soon  as possible in order  to
restore proper runoff, retain cover and stabilize slopes.
Ultimate Use
     Development of the completed site should  follow  the designed plan.
The finished site should be recorded in property records with  a  proper
description of Its conversion from prior  condition  to finished landfill,
its intended use, zoning and use restrictions. Until ultimate-use  plans
are implemented, the finished site should be maintained so  as  to minimize
water entry.  Such maintenance will possibly Include  regrading,  filling
or revegetation of the site and the maintenance of  surface  or  subsurface
drainage.
GAS MONITORING PRACTICE
     It has not been common practice to design or install systems  at
solid waste land disposal sites to detect or to measure the concentration
of decomposition gases escaping from the  surface of the landfill or
migrating into adjacent areas.  It has been shown  that for  landfills where
initial or subsequent moisture in the wastes is limited, production and
migration of gases will be relatively low and  the need for  monitoring
gas migration will be minimal.  Many landfills, particularly those con-
structed wholly or partially above original ground  level, will have one
or more edges, plus the landfill surface, exposed  to the  atmosphere,
and monitoring will be required only where migration through ad.lacent
soils will likely occur.
NEED FOR GAS MONITORING
     For landfills where peripheral venting systems or barriers (active
or passive) have been installed, monitoring needs will be  minimal, and
consist primarily of checking the effectiveness of the venting system
or barriers.  The principal need for monitoring will be at  those landfills
where:
     (1)  field saturation of the landfilled wastes occurs  or is expected
          to occur at any time,

                                   119

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     (2)  subterranean utilities arc installed nearby,
     (3)  buildings or other structures are constructed on or near the
          landfill (dependent on gas permeability of the soil),
     (4)  permit requirements or regulations require monitoring  for
          migrating gases, or
     (5)  the landfill surface cover permeability is reduced by  paving
          or other sealants, either during operation or following land-
          fill closure.
     Monitoring would not generally be required for landfills where
ultimate use will be for open space, agriculture or other uses where
utilities or enclosed structures will not be required.  Suitable pre-
cautions should be taken, however, when and if utilities or structures
are installed and in any instance where site-use plans are modified to
uses which require on-site or nearby construction.
     Tho&e landfills whose cover materials are of high permeability will
likely have high permeability soils adjacent, If the cover material was
obtained on site.  Nevertheless those landfills where adjacent soils are
highly permeable to gas  flow are most in need of monitoring. Even
though the landfill will Likely vent gases rapidly through the permeable
cover, surface water may easily infiltrate the cover  to expedite p.as
production.  Periodic saturation of the soil cover will at least period-
ically reduce cover permeability for brief periods, possibly resulting
In brief subsequent episodes of lateral gas migration.  Consequently, Ras
monitoring will likely be most important following heavy precipitation
episodes.
     In those instances where landfills have highly permeable soil  cover
but relatively impermeable surrounding soils cr impermeable barriers,
there will be minimal need for gas monitoring.
     Xt has been noted  that  landfills will produce decomposition gases,
particularly methane,  for  30  to 40 years.  Also if conditions change,
such as introduction of  groundwater or surface water, so that moisture
increases occur in a formerly dry  landfill, gas production may be
                                    120

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reinitiated.   Consequently,  it  cannot  be  safely assumed  that a vintage
landfill will no longer produce gas,  and  some form  of  monitoring  or  sur-
veillance may be required indefinitely.
PHYSICAL OBSERVATIONS
     The operator or manager of a solid waste land  disposal  facility, or
those examining a site with  regard to ultimate use  or  nearby construction
can, through observation of  some physical features, sometimes  gauge  the
potential for gas migration  or detect signs of gas  migration occurring.
Recording of such observations during the active  lifetine of a sanitarv
landfill will provide some guidance to future development of gas  migra-
tion problems.  Physical observations, performed  without dependence  en
expensive instruments, may serve as an early warning of potential problems
from gas migration which can be followed up with  instrumented  surveil-
lance.  Early warning signs  of potential problems include observation
of unusual settlement, effects on vegetation, occurrence of gas  in sewers
or other subterranean structures  (which may require Instrumented sur-
veillance), odors or gas bubbles in water accumulations.  Observations
on these phenomena at the Link Koad facility, as  related to gas  production
and migration, are noted in the following sections.
Settlement
     Whereas  the surface of the Link Road landfill is generally  flat,
a number of random undulations occur throughout, indicating that local
settlement has occurred.  Over most of the landfill,  the settlement
observed was  similar  to  that occurring in most landfills of its  type (i.e.,
moderate but  not extensive).  Two specific areas of extensive and dramatic
settlement were  in  the area just  back of the  Armory where wastes were
deposited along a steep  natural bank and in  the  fire  training area.  The
peripheral  road  is  undulating,  indicative of  settlement  throughout.  Just
above  the  lower peripheral  road,  large depressions were  overgrown with
cattails (a water-loving plant)  and after rains, all  depressions held
water  for  long periods  of time.   Similar cattail and  water-filled areas
were noted  just north of the  concrete slab back  of the Arnory.   Extensive
                                  121

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 cracking of  the soil cover was  noted in the  fire training area and in
 a  line paralleling the bank  crest back of  the Armory, indicative of
 BetClement and  local infiltration of surface water.
     After nev  cover was  applied in  the summer of 1973, it was noted that
 rapid settlement was continuing back of the Armory and that a crack was
 re-established  along the  bank crest.
     Settlement plates placed throughout the fill were lost when the new
 cover was placed,  and only a minimal amount of settlement was noted for
 the  few months  they were  in  place.   The landfill is settling slowly in
 general, but  rapidly in a few locations.  The settlement areas are gener-
 ally characterized by relatively high comb.-stible gas concentrations.
 The  rate of settlement immediately prior to  the Armory explosion and the
 effect of settlement in increasing gas migration at that time could not
 be established.  Obviously,  the rate of settlement in the fire training
 area and in the area back of the Armory is much faster than nearby areas
 of the landfill.
     As at Link Road, rapid-settlement areas in most landfills are often
 those where the highest gas  concentrations occur.  Where settlement is
 the result of rapid decomposition of wastes in the immediate acea, rapid
 gas evolution is to be expected and  its migration through nearby soils
 results both froia  internal pressures caused by shifting oC the mass and
 from increasing gas pressure.   Additionally, channels may be created
 through disruption of cell integrity, soil-cover displacement and erosion
 processes by surface water entry through which gas escapes readily.  These
 processes arc likely all  combined in the Link Road landfill's fire train-
 ing area.
     In the settlement area  back of  the Armory, the deposited wastes are
 not likely to produce gas at as high a rate as those in the fire training
 area because the wastes placed  near  ihc Armory were less putrescible.
 Consequently, the  settlement is likely due to physical causes, primarily
 the sliding of  the wastes down  the natural slope, hastened by the entry
 of water from ponding and cracking and the weight of additional cover
material.  From these observations,  it can be confirmed that settlement
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areas in landfills arc likely locations  where gas  is  rapidly being gen-
erated or gas migration Is being hastened and abetted by  physical pro-
cesses.  In cither situation, observations of settlement  are a means  of
discerning locations of high gas migration potential  for  further observa-
tion.
     Visual features associated with settlement areas include, in addition
to the differences in elevation, which may not be apparent for moderate
settlement, specific types of vegetation and surface  cracking.  Water-
loving vegetation such as cattails nay grow in settlement areas which
frequently hold water.  In grassy areas, grass docs not grow in the
Immediate vicinity of the crack so that cracks in the soil cover are
readily visible when the grass is short and dormant but are less visible
when the grass is long or growing vigorously.
Vegetation
     A preliminary assessment was made at the Link Road landfill of che
potential for visual effects of gas damage to vegetation serving as a
monitoring aid for detection of gas migration.  A report of this assess-
ment is included  in Appendix B.
     Vegetative growth at  the Link Road  landfill was heterogeneous but
had  no apparent correlation with areas of high or low gas concentration
 (neither was there a  discemable pattern of  gas concentration  at the Land-
 fill surface indicating consistently hif.h and  low j>as concentration
 areas).  Vegetation at other landfills  in  the  area was either too  sparse
 or too recently established  to  permit meaningful  observations.
     Areas  peripheral to  the Link Road  landfill where gas data were  avail-
 able were not  vegetated,  being  covered with  either asphalt or crushed stone.
     The  one area where  visible effects  on vegetation were noted was in
 the fire  training area.   It  appears  that in  the  immediate vicinity (one
 to two inches) of a crack from  which pas is  ernerRing, vegetation does
 noi grow.   This effect may be  due  to the drying effect of the gases  In
 the grass1  root zone. On either side  of the bare area along  the cracks,
 the grass appeared to be growing well,  with  no gradation in color or

                                   123

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growth rate being observable.  Grass (fescue) at the Link Road landfill
is apparently not a sensitive vegetative indicator of gas migration.
Nevertheless, plantings of  grass on the perimeter of a landfill and into
adjoining areas might aid in increasing the visibility of any cracks or
openings in the surface from which gas may be emerging.
     In some areas, it has  been  reported that certain ornamental plants
have been killed by gas migrating from landfills and that it is difficult
at some landfills to maintain grass cover or plantings because of gas.
The potential for gross observation of effects on vegetation to serve
as an indicator of gas migration remains undefined.
Other
     It has been noted in  the literature that at some  landfills, bubbles
of emerging gas can be noted in  surface-ponded areas after a rain.  This
phenomenon was noted by one observer at the Link Road  landfill in the
ponded water filling settlement  depressions in the fire  training area.
     In general, occurrence of a local strong concentration of odor might
be taken as an indicator  of gas  migration, but it would  likely be difficult
to distinguish the precise  location or to gauge the concentration.  Methane
is odorless and could not be detected in this manner.  Other gas
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INSTRUMENTED SURVEILLANCE
     Gas concentrations at the Link Road landfill were  determined  through
Instrumented surveillance, taking gas  samples  fron installed probes.
A review of these procedures and findings follows.
Gas Probe Layouts
     A series of probes were installed at the  Link Road landfill and at
two other landfills in order to determine gas  concentrations.  The probes
were of the Los Angeles type (Reference 23), consisting of a short length
of perforated plastic tubing attached to snail-diameter plastic tubing.
The probes were placed at various depths (1, 10 and 25  feet, normally) in
six-Inch diameter holes at various sampling  locations,  and the holes were
back-filled with soil  'between probe placements) to the ground surface.
Each probe tubing lead was marked according  to probe depth. For the
earlier studies, probes were established around the Arnorv. Later, addi-
tional sampling locations vere installed on  a  grid patter, extending
several hundred feet outward in the landfill.   In many  of these locations,
water uas encountered within two to three feet of the landfill surface.
Upon installation of the gas barrier,  additional sampling locations were
established on either side of the barrier.  In addition, well-point-type
probes were established inside the barrier and connected to the gas mon-
itor.  Four occupied-space interior probes were connected to the monitor
installed inside the Armory.  The various probes and their locations are
described in Figures 5, 6, 14 and 15.
     In order to determine pressure differentials in the soils along the
barrier and between wells, 10 sampling locations (Figure 15) were  estab-
lished along a portion of the barrier back of  the Armory supply room.
Probes were established at two depths  at each  location, and pressure
readings were taken by use of a mobile manometer (Figure It).
Instrument Use
     Two portable conbustibl  gas detectors  (J-W Gas Kit, Model HPK) were
used to determine gas concentrations fron the  probes at each sampling
                                   125

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point.  This Instrument  Is  calibrated to show combustible gas concen-
trations In percent by volume  in air.  In use, the operator Inserts
the instrument's metal probe into the probe tubing at  the sampling point
and permits the Instrument's vacuum pump to evacuate the tubing until
a proper sample Is obtained.  The steady-state concentration reading is
recorded for each probe  and sampling station.  During the studies., concen-
trations were .determined daily in sone instances, and at weekly intervals
on others.  The instrument  was calibrated against standard gases and was
checked for "zero" (acmospheric) readings frequently.
     In addition to the  gas concentration data obtained by use of the
portable gas detector, samples were also analyzed by gas chronatography.
Samples were obtained from  the probes by using evacuated flasks connected
to the probe tubing, following evacuation of the tubing with the portable
instrument's vacuum pump.
SIGNIFICANCE OF FINDINGS
Sampling Pattern
     The  distance  between sampling stations  ranged  from about 10 to
over  100  feet.  The  original  aeries  was dispersed in accordance with
the need  to establish  gas concentration profiles around the Armory,  with
closest spacing nearest  the Armory supply room.  Outlying sampling
points were established  to determine concentrations  in presumed high gas
areas (such  as  those in  the fire  training area) or  to determine the
boundaries or -extent of  gas migration potential.  Shallow probes of one-
foot depth were established to determine if  gas was emerging through the
soil surface, whereas  the deep probes were established  at the approximate
level equivalent  to  the  base of the landfill.
      In general,  the concentrations at  the  lowest probe of  a sample loca-
tion were highest  while  Chose at  mid-depth were  somewhat  lower.  Concen-
trations  at the one-foot probes were erratic and are  considered unreliable.
Gas Migration
      Typical combustible gas concentration  profiles arc shown  in Figures
6.  17 and 18.

                                    126

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     Cas concentrations in the landfill were generally  only  slightly
higher than those in probes between the landfill and  the Armory,
indicative of the relative ease with which gas migrates through  the
peripheral soil.  Concentrations above the LEL were noted in  the  parking
lot northeast o£  the Armory at considerable distance  from  the landfill;
but north of the  Armory, concentrations vere at zero  levels.
     The findings indicate that gas migrates readily  to the  Armory am!
at considerable distance from the main landfill across  the former incin-
erator-residue area.  Where the gas apparently encounters  undisturbed
soil, as at the northern boundary of the fire training  area, the undis-
turbed soils near the front of the Ar..iory and the parking  area southeast
of the Anaory, it is more rapidly attenuated.  These  areas,  however,  are
at considerable distance from the landfill boundary,  and attenuation  nay
be attributed as  much to distance as to decreasing soil permeability.
     The gas samples consisted primarily of methane,  as the  gas  chromato-
graphic analyses  attests (Tables 10 and .'!).
     Cas production and migration from the Link Road  landfill continues
year-round at a singlficant rate, though it is steadily declining.  At
the present rate, significant gas production may continue  10 years or
more.  Seasonal variations in gas production and migration have  been
noted, with peaks occurring in February or March and  declining through the
Bumaer months to  lows in mid-winter.  Combustible gas concentrations  In
the 40-percent range are still occurring near the landfill boundary,  and
explosive-concentration accumulations arc a potential for  years  to cone.
There appears to be a short-range increase in gas migration  occurring
after rainfall episodes; consequently, there is a need  to  be concerned
with gas migration problems at this site on a relatively continuous basis.
     The Link Road landfill seems to have the following characteristics,
with regard to gas migration and explosive hazards:
                                   127

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      (1)   the  landfill  is largely saturated and is producing methane gas
           steadily with both seasonal peaks and periodic increases
           following  precipitation episodes;
      (2)   gas  migrates  readily  through  the soil to nearby structures,
           due  to high gas permeability  of the intervening soil;
      (3)   major structures  are  in close proximity to the landfill or
           are  built  on  site and until recently have had no means to
           prevent gas entry;
      (4)   major settleaent  is continuing to occur in areas of the
          JLandfill closest  to stuctures and permeable soil strata; and
      (5)  -gas  migration appears to  be attenuated below the LEL within
           200  feet of the  landfill  boundary when passing through un-
           disturbed  soil.
      It appears likely  that despite the high production of gas at this
site  and  the relatively permeable nature of the soil, normal building
construction could have been  followed for structures built on natural
.ground 100 to  200  feet  from the landfill boundaries (though not on the
incinerator-residue  portion).
GAS DETECTION
Observations in Subterranean  Structures
      In retrospect,  the occurrence  of the flash  fires in sewer drains
•and roof  gutters could  have served  as adv.need warnings of gas migration.
In fact,  the fires  in the sewers of the fixe  training area were assumed
to be associated with the entry of  landfill  gas.  Occurrence of gas in
sanitary  sewers, as  noted in a later investigation, is  less definitive.
Rapid settlement in both heavy-settlement areas  was noted, but its possible
relation  to lateral gas migration was not suspected.  There were no ob-
served effects on  vegetation indicative of gas  migration or of gas bubbles
In ponded water.
                                    128

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Physical Phenomena
     At this site, physical phenomena related to gas migration were
either not of sufficient magnitude, could not be properly  observed or
were associated with factors net related to gas  migration  to the Armory.
Instrumented Surveillance at Shallow Depths
     It has been suggested that sampling for gas with  a portable instru-
ment at shallow (1 foot) depths in the soil adjacent  to a  landfill boundary
could serve as an early warning of gas migration.  The erratic  nature
of data fron the one-foot probes in the initial gas sampling network
indicates that this is an unreliable procedure per se.  It was  observed
Chat any sampling from an unclosed system wherein air  may  be entrained
with the gas sample gives erratic results.  Any such  system should be
based on the sampling of permanently installed probes  installed at least
three feet below the surface.
Sampling Patterns
     The placement of sampling stations to monitor gas migration should
be based on some knowledge of the soil permeability.   If gas pemeability
tests of peripheral soils indicate low permeability,  it would probably
suffice to place sampling stations at 100-foot intervals along and 25
to 50 feet  from the landfill edge.  At landfills adjoined by highly per-
meable soils, stations should be at 50-foot  intervals or less with a second
line of stations 100  feet from the landfill edge.  The nature and extent
of the pattern will depend  in large measure  on the gas permeability of
the soil and proximity of the facilities  to  be protected.  Intervals
suggested herein  are  admittedly  arbitrary.   At landfills where peripheral
soils are relatively  impermeable,  it might only be necessary to install
monitoring  probe networks in the near vicinity of areas of the landfill
where high  gas production is anticipated  (i.e., wet-waste disposal, sludpe
disposal, animal  carcass  disposal, etc.).   In general, where the likelihood
of gas  migration  is greatest and the  resultant hazards are most significant,
the  gas monitoring network  should  be  of  greater  sophistication.
                                    129

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ROUTINE OBSERVATIONS
     Relatively simple  observations should be  required of landfill oper-
ators- to provide early  warning of  potential gas migration.  These include
recording:
     (1): occurrence  of rapid or extensive settlement;
     (2)  occurrence  of extensive  cracking in  landfill cover or nearby
          soils;
     (3)  occurrence  of vegetation browning or die-off in peripheral
          areas;.
     (4)  concentration of odors;
     (5).- occurrence  of. flash fires or minor flares on or off site; and
     (60- occurrence  of bubbles in ponded water on'landfill periphery.

INSTRUMENTED OBSERVATIONS AND RECORDS
     If- any of the crude observations or a combination thereof indicates
that gas migration may  be occurring,  landfill  supervisors should institute
surveillance based*on use of portable gas detectors and  relatively shallow,
but' per&anent&y installed, probes. This should include:
     (1)  installation of a.suitable  probe network in the suspect areas,
          probes'being established at least  three feet deep; and
     (2)  sampling and recording combustible  gas, using  a portable gas
          detector, according  to the  following schedule:
           (a)S  weekly, during spring  and early summer;
           (b))  daily follovlr   .teavy  precipitation; and
           (c)3  at  regular two-week or monthly  intervals  during winter
                and fall months.

FOLLOH^-UP GAS, MONITORING
     If concentrations are  found near the explosive  range,  additional
probes, placed at  10- to 15-foot depths will aid in determining  the extent
                                   130

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and range of gas migration.  The range of probe placement  should be ex-
tended if gas concentrations continue to occur at the  outer edge, in order
to determine extent of migration.  If levels continue  or are in the high
range, it will be necessary to consider barrier Installation or prohibi-
tion of construction within the near vicinity of the  landfill.
GAS MONITORING INSTRUMENTS
     Relatively simple, low-cost portable gas detectors are available
which indicate presence of combustible gas and are calibrated to read
gas concentrations in percent of the lower explosive  limit (LEL).  Gas
readings near or in excess of the LEL (52 by volume of methane in air)
would indicate the possible necessity of follow-up monitoring, using a
nore expensive portable Instrument calibrated to read higher combustible
gas concentrations directly in percent by volume.
     Instruments of this type are commonly used by utility companies, pub-
lic works departments and fire departments.  Arrangements  could probably
be made with such agencies for routine nonitoring and reporting of pas
concentrations in subterranean facilities near landfills.
     Gas samples can be taken from inexpensive subsurface probes in
evacuated flasks for gas chronatographlc analysis in commercial  labora-
tories.  Many water and sewer department laboratories can perform  such
analyses at minima] cost.
SUMMA
     In summary, careful selection, design and operation of sanitary  land-
fills will usually minimize gas production and migration.  Gas production
and emergence through soil cover is to be expected in a sanitary landfill,
but on-site or nearby structures should be protected from gas migration
or accumulation by structural  features, distance or by passive or  active
gas barriers.
     During landfill operation, careful observation and recording  of
physical  features such as  settlement, damage  to nearby vegetation, flash
fires, odor occurrences, gas in subterranean  facilities, etc. will provide
                                   131

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early warning of potential  gas migration.  Use of portable gas detectors
to sample combustible  gas concentrations fron permanently installed probes
can verify gas migration problems,  and  follow-up monitoring with more
sensitive instruments  will  aid in  the decision to control gas migration
or restrict use of  the area of gas  migration.
     Observations at  the Link Road landfill  verified  the utility of settle-
ment and subterranean-facility  gas determinations as  indicators of gas
problems but did not  afford opportunity to verify utility of vegetation
effects as a gas migration  indicator.   Shallow sampling of soils with
a portable gas detector is  unreliable.   Probes three  co 10 feet deep
will provide, reliable indication of gas movement.  Gas  production and
migration at the Link Road  site  peaked  in  the spring  months, declined
through the summer  and increased through the fall months.
     Monitoring of  landfill gas  migration  should be based on soil permeabil-
ity, proxitaity o£ nearby structures and knowledge of  the location and
extent of high gas  production areas.  In some landfills, monitoring may
be  restricted to known high gas  production areas.
                                    132

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                            CHAPTER X

                            REFERENCES


1.  Municipal Refuse Disposal.  American  Public \Iorks Association, 2nd ed.,
    Chicago, Public Administration Service,  p. 128-132,  134,  135  (1*»66).

2.  "Landfill Decomposition Gases - An Annotated Bibliography," Ceyer,
    Janes A., National Environmental Research Center,  Environmental
    Protection Agency, SW-72-1-1, 28 pp.  (June 1972).

3.  Development of construction and use  criteria for  sanitary landfills,;
    final report on a solid waste management denonstration grant.
    Department of County Engineer, County of Los \npeles,  and Engineering-
    Science, Inc.  Environmental Protection Publication SW-19d.  U.S.
    Environmental Protection Agency, 1973. [511 p.]  (Distributed
    by National Technical Information Service, Springfield, Va.
    as Pn-218 672.)

4.  Merz. R. C., and R. Stone.   Gas production in a sanitary landfill.
    Public Works. 95(2):84-87,  174-175,  Feb. 1964.

5.  "Quantitative  Study of Gas Produced by Decomposing Refuse," Merz, R.C.
    and  Stone, R.,  Public Works. 99(ll):86-87 (November 1968).

6.  "Sanitary  Landfill Behavior  in an Aerobic Environment," Merz, R.C.
    and  Stone, R.,  Public Works. 97(1):67-70  (January 1966).

7.  Herz, R. C., and  R. Stone.   Special studies of a  sanitary  landfill.
    Environmental  Protection Publication  SU-8rg.  Rockville, lid.,
    U.S. Department of Health, Education, and Welfare, 1970.   (Distri-
    buted by National Technical  Information Service,  Springfield, Va.,
    as PB-196  148.   [222 p.])

8.   In-situ Investigation  of Movements  of Cases  Produced  from Decomposing
    Refuse. California State Water Quality  Control Board,  Final  Report-,
    Publication  No.  35,  Sacramento (1967).

9.   "Effect of Solid Waste Disposal  on  Ground Water Quality," Coe,  J.J.,
    Journal of the American Water Works Association.  62:776-783  (Dec-
    enber  1970).

10.  "Gas Generation and Movement in Landfills," Anderson,  D.R. and Callinan,
    J.P.,  In Proceedings;   National Industrial  Solid  Wastes Management
    Conference.  Houston,  (March 1970).
                                   133

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11.  California  State Water  Pollution  Control  Board.  Report on
     the  investigation  of  leaching of  a sanitary  landfill.  Publication
     No.  10.   Sacramento,  1954.   [92 p]

12.  "Water Pollution Hazards  from Refuse-Produced Carbon Dioxid««,"
     Bishop, U.D., Carter, R.C., and Ludwig, H.F., Journal of Water
     Pollution Control  Federation.  38(3):328-329  (March 1966).

13.  In-situ Investigation of  Movements  of Cases Produced fron Pcconposintt
     Refuse. California State  Mater Quality Control Board, Publicatio.i
     No.  31,. Sacramento (1965).

14.  "Gas Movement in Landfilled Rubbish," Bishop, W.D., Carter, R.C.,
     and  Ludwig, H.F.,  Public  Works. 96(11):64-68  (November 1965).

IS.  Eliassen, R. , F. N. O'llara, and E.  C. Monahan.  Sanitary landfill.
     gas  control.  American  City.  72(12):115-117,  December 1957.

16.  "Gas Fire in Sewer Manhole Traced to Sanitary Fill Operation,"
     Engineering News-Record.  139(26):51 (25 December 1947).

17.  How  to  use  your completed landfills.  American City. 80(R):91-94,
     August  1965.

18.  "Gas Fires  in a Sanitary  Fill," Engineering News-Record. 140(2):86-87
     (8 January  1948).

19.  "Landfill Gas Burned  for  Odor Control," Dunn, W.L., Civil Engineering.
     27(11):60-61  (November  1957).

20.  "Storm  Drainage and Gas Burning at Refuse Disposal Sites," Dunn, W.L.,
     Civil Engineering. 30(8):68-69 (August  1960).

21.  "Methane Gas Explosions Delay Building  on a  Landfill," Solid V'astes
     Management  - Refuse Removal Jou-nal,  12(7):20 (July  1969).

22.  Brunner,  D. R., and D.  J. Keller.  Sanitary  landfill design and
     operation.  Environmental Protection  Publication SW-65ts.
     Washington, U.S. Government  Printing  Office, 1972.  59 p.

23.  Development of  construction  and use criteria for sanitarv  landfills:
     an interim  report. County of Los Angeles, Denartment of County
     Engineers,  Los  Angeles, and. Engineering-Science. Inc.  Cincinnati,
     U.S. Department of Health, Education, and Welfare,  1969.   [267 p.]
                                   134

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24.   "Model Sanitary Landfill in Kansas City. Kansas." Gerald A.  Neely
     and Nicholas S. Artz, Civil Engineering (October 1972).

25.   "Gas Explosion Hazards in Sanitary Landfills.  I.e.  MacFarlane, Public
     Works (May 1970).                                                	

26.   "A Gas Monitoring  and Control System," Public Works. 101 (12), p. 39
     (December 1970).

 27.  The  Desl&n  and  Installation of A  Cas Migration Control  System
     for  A Sanitary  Landfill. C.P. Callal.an  and R.H.  Curske,  Bureau
     of Sanitation.  City  of  Los Angeles  (May 1971).

 28.  Methods  of  Soil Analysis - Part i.  American  Society of  Agronomy,
     Madison, pp.  520-528 (1965).
                                    135

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                       APPENDIX A
     COST ESTIMATES FOR FORCED VENTILATION,  NATURAL




VENTfLATION AND IMPERMEABLE MEMBRANE GAS CONTROL SYSTEMS
                           136

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                  PRELIMINARY COST ESTIMATES FOR FORCED

                    VENTILATION CAS CONTROL SYSTEMS
                               (dollars)
I leu
18 Gas wells3
Construction
Butterfly valves
Fittings
Precast boxes
Suction header
Pipe, fittings, etc.
High-flow
system
13.500
2,500
1,000
6,100
8,900
Low-flow
system with-
out seal
13.500
2,500
1,000
6,100
2,500
Low-flow
system with
seal
13.500
2.500
1,000
6,100
2,500
Vacuum pump & fittings

   Pump, valves, electrical
      panels, fldme traps,
      etc.                    16,000         8,000           8.000

Surface seal                    —            —            36,000

Contingency                    A.OOP         4.000           A.OOP

   TOTAL                      52,000        37,600          73,600


 Includes 15 wells in the main branch and three wells in the small
 branch of the gas control system.
                                  137

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             COST CALCULATIONS  FOR NATURAL VENTILATION AND
                                                       *
                IMPERMEABLE  MEMBRANE CAS CONTROL SYSTEMS
ASSUMPTIONS
     The  following assumptions were made  for calculating capital costs
of the natural  ventilation and impermeable membrane gas control systems:
       (1)  A dragline can excavate 81.6 yd /hr at the rate of $45/hr.
       (2)  A 20 feet deep trench  2 feet wide can be excavated for the
           natural ventilation system.
       (3)  Gravel will cost about- $2.25/ton delivered on site.
       (4)  A side slope of 1.5 vertical to 1 horizontal will be re-
           quired for impervious  membrane trench when clay is used
           as' the barrier material.
       (5)  The impervious membrane will consist of a dry core 2' feet
           vide and 20 feet deep.
       (6)  Clay will cost $4.25/ton delivered  on site.
                                                3
       (7)  Clay tamping will cost about $0.80/yd  .
       (8)  Clay and gravel have  a density of  2.20 ton/yd .
COST BREAKDOWN
Natural Ventilation  System
             Excavation cost      •   $    800
             Gravel materials      -     7,400
             Other costs          •     1.800
               Total costs-          $10,000
 *Costs will, vary somewhat, by location
                                   138

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Impermeable Membrane
            Excavation cost      •   $ 6,200
            Clay materials       -    14,000
            Clay tamping         "     1,150
            Other costs          -     3.200
               Total costs           $24,550
VOLUME CALCULATIONS
Natural Ventilation
     1,000-foot trench x 20 feet deep x 2 feet wide = 40,000 ft
           Trench volume • 1,480 yd
Impermeable Membrane
     1,000-foot trench x ?0 feet depth x 15.32 feet average width
for side slope of 1.5 vertical to 1 horizontal
     Total volume - 306,400 ft3  -  11,400 yd3
     Clay volume  -  40,000 ft3  •   1,480 yd
                                  139

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                        APPENDIX  B
           EVALUATION OP EFFECTS ON VEGETATION
REGARDfNG SANITARY LANDFILLS AT WINSTON-SALEM. NORTH CAROLINA
                            140

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             Report
   Co Engineering-Science, Inc.
             on the
        Detailed Work Plan
               for
Evaluation Effects on Vegetation
           Regarding
       Sanitary Landfills
                at
 Winston-Salcm, North Carolina
          19 April 1973
      Caythcr 1.. Plunmu-r, Ph.D.
         995 Timothy Road
         Athens, Georgia
                141

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     The purpose of the work plan was to "Obtain ana Review Data on
Effects cf Gas on Vegetation."
     A general ^crusal of the work plan gives the initial impression
that the project is well conceived, well organized, having clearly de-
fined objectives, good control characteristics, and the problem to be
solved is simple, straight forward with potentially clear-cut results.
The problem looks challenging partly because the nature of the objec-
tives have an intriguing origin and partly because the concept of
identifying sentinel plants to indicate an impact of mankind on the
environment is relatively underfined.
     The work plan calls for the derivation tl diversity indices to
relate to gas potentials aiiH to effects on sentinel plants.  This part
of the work plan seemed to have some inherent difficulties built into
it having been designed without first-hand knowledge of the way di-
versity indices are interpreted bared upon field conditions.  To
devise the indices would be no problem, but to relate the meaning of
that information to the objectives of t'.ie project are obstacles that
appeared to be difficult to achieve.
     A trip to Winston-Salcm, North Carolina, and to the landfills
was undertaken in conjunction witli a student in the Botany Department
at the University of Georgia to determine the feasibility of completing
the work plan to the satisfaction of Engineering-Science, Inc.  We
vent on the weekend of 6-8 April 1973.  A day and a half were spent
in the field.  Both the Link Road site and the Overdale sites were
visited under the guidance of Mr. Robert Davis.
     Communications with Engineering-Science, Inc. advised me that
methane gas was a principal component of those emitted from the old
city dump.  A very brief search of the literature revealed also that
carbon dioxide, hydrogen, sulfur dioxide, and hydrogen sulfide were
among the possible kinds.  The effects of gas on vegetation would be
complicated, therefore, by mixtures of gases of unknown composition
and of unknown concentrations.  At L'IO site it was easy to learn that
age of the fill and time difference.-, in decomposition rates were added
complications.
                                  142

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     The soil was cracked in placed,  sometimes  around subsidence  pits,
so gases Immcrgcd from place to place according to  the distribution
and kinds of subterranean materials.
     Vegetation on the old city dump  also varied from place  to  place.
Some was of the onc-ycar-old abandoned field type,  that  is crabgrass
and ragweed steins.  Others were of the six-  to  eight-year-old field
type--Coldcn rods, Asters, etc.  Yet  others, wetland Cattails,  and
dryland Hroomedgc grass, grew side by side--an  unnatural situation
brought aljut by physical changes in  the level  of the land.  Diversity
indices related to site quality arc not meaningful  indicators of  effects
of gas on vegetation.
     Gas oozed from pools of water in the pits  as out body weights
shifted from place to place.  It became conclusive, therefore,  that
changes in atmospheric pressure of one inch  could change the load
factor on gas emission by approximately two tons in a pit covering about
300 square feet.  This means that cloudy ueathcr and a  pressure drop
would probably cause gases to accumulate internally whereas  sunny skies
and high pressures would cause these  gases to be forced  out.
     Soils differed greatly within one square meter.  Some places the
clayey soils were tough enough to exclude all root  penetration; in
other places the sandy soils allowed  good plant growth.   Chalky alkali
sites evidently excluded some species.  High nitrogen places occurred,
as did nitrogen-deficient sites.
     Within the chain-linked fence at the Link  Koad site, the fescue
grass was growing poorly in some places and excellently in others.   It
seemes to have been planted uniformly.  It also seemed  to have  been
affected by poor growth in a small area where odors of  certain  gases
were almost suffocating to us.  Bermuda grass,  however,  grew very well
where fescue did not.  The ground was cracked in placed, odors  came
from the cracks, and all grasses within four to five  inches  on each
side of the cracks were dead.  This small situation (and there  «rore
several lines of such features) was the only place  in which  vegetation
was obviously affected by something that came apparently from the cracks.

                                   143

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Otherwise, there was absolutely no doubt that soil textures and  fertility
were responsible for most other variations in the vegetation.  The  cer-
tainty of harmful effects of gas along these cracks cannot be  demon-
strated clearly without further study.
     One plant, the Chickwcek, was yellowed in certain situations but
not in others.  Careful examination showed that the lower leaves were
in fact dead.  Other leaves had yellow spots on them similar to-such  de-
fects as those caused by sulfur dioxide in other plants.  This sign of
yellowness suggests the possibility of a sentinel plant.  Because the
manifestations were very localized and not widely spread raises  some
doubts about  the real indicator values o£ such "effects."  There is no
doubt in my mind that other plants can be affected similarly,  and
probably arc.  But the Interpretation and meaning of these facts must
be tested under experimental conditions before any useful indicator
values of sentinel plants can be suggested more particularly.  To com-
pare these effects with concentrations of gases in the  field would  be
nearly impossible, especially without knowledge of the way in which a
single kind of gas injures a plant species.  The hopeful thing about
all this is that detrimental effects do occur, but they do not seem
to be widely  spread.
     The assumption all along seems to be that detrimental effects  are
the chief manifestations of gas concentrations.  Perhaps this stems from
Crocker's bood Growth of Plants in which  the affects of gases on plants
arc treated as extensively as was knowledge about  the subject until
1946.  On the other hand, beneficial effects could be possible because
methane  fumes arc  known to stimulate the  growth of potato buds  (see
Biol. Ahst. 1972,  item 33720).  Marsh gas, of which methane if the prime
constituent,  is  commonly associated with  plants.   No doubt many plants
have become quite  tolerant to methane.  Hydrogen  sulfide is not really
very toxic  to plants, but it is to animals.  A very good possibility
exists  that the  vegetation on a sanitary  landfill, or any  old dump,
could be enhanced  in  places by  the totality  of the  local environment.
                                   144

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     The Overdale situ is a marvelous example  of what  landfills  ought
to be.  The fescue plantings added acceptability of  the  site.  That
grass did have several unusually green patches growing hc>*e  and  there—
probably from dung piles dropped by stray dogs,  perhaps  urine  spots,
etc.  In general, the grass looked nitrogen deficient, but uniformly
so.  Obviously, the site was more homogeneous  than the old dump.  No
detrimental conditions were outstanding.   The  question was raised:
What sentinel plants would indicate gas at different concentrations
here?  The assumption was cither that gases would ooze from  the  ground
uniformly, or that they would move laterally and come  out near some
pre-existing harrier.
     A search for such a plant is underway. Perhaps one can be  found,
such as Chickvecd, but it is more likely to be an annual rather  than
a perennial; it would probably be a temporary  rather than permanent
resident on the site; and it would be seasonal in its  responsive indi-
cator qualities.  When that plant, 
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