United States
Environmental
Protection Agency
Office of Solid Waste and
Emergency Response
(5102G)
EPA 542-R-98-005a
July 1998
wwwclu-m com
EPA Evaluation of Subsurface Engineered
Barriers at Waste Sites
Volume II
Appendix B
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Appendix B
Site Summaries
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NOTICE
This document was prepared for the U S Environmental Protection Agency's (EPA) Office of
Solid Waste and Emergency Response (OSWER) under Contracts No 68-W5-0055 and No 68-
W4-0007. The work assignments preparing this document were led by the EPA Office of
Research and Development's (ORD) National Center for Environmental Assessment (NCEA), in
cooperation with the EPA Office of Emergency and Remedial Response (OERR)
Reference herein to any specific commercial product, process, or service by trade name,
trademark, manufacturer, or otherwise does not constitute or imply endorsement,
recommendation, or favoring by EPA
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SITE1
1.0 SITE DESCRIPTION AND HISTORY
Earner Type
Remedial
Objective
Performance
SB
SC
Site 1 is located m the northeastern United States The site is bordered on the north by a waterway, to
the east is a sparsely populated area of single-family homes Agricultural and vacant land lies to the
south and west The site covers about 38 acres and is immediately bounded by industrial and
commercial properties, city streets, and recreational facilities
The site historically functioned as a municipal solid waste landfill that received residential, commercial,
and institutional solid wastes Initial investigations identified significant contamination from landfill
leachate that was clearly visible in wetlands and the waterway adjacent to the site
The 38-acre landfill site is contained by a subsurface barrier wall The soil-bentonite wall is about 5,400
feet long, it ranges from about 10 to 20 feet in depth and averages about 15 feet in depth The barrier
was constructed in November 1989 A site plan showing basic site features is shown in Figure 1
2.0 GEOLOGIC AND HYDROGEOLOGIC SETTING
The geologic setting of the site is characteristic of the Kittatmny Valley Sub-Province of the Appalachian
Valley and Ridge Physiographic Province The site lies atop glacial lake deposits The glacial lake
deposits have the following soil sequence, 1 to 2 feet of black, organic topsoil, 2 to 6 feet of peat, and a
70- to 90-foot strata of clay and silt Underlying the clay and silt is Martmsburg Formation shale
bedrock 80 to 100 feet below grade The subsurface barrier wall was keyed into the strata of clay and silt,
which exhibit low hydraulic conductivity
The hydrogeologic setting includes one unconfined, unconsolidated, water-beanng zone and a deeper
bedrock aquifer The unconfined aquifer is limited by the glacial lake clay deposits Groundwater flow
m the unconfined zone is in a northerly direction, while the direction of flow in the deeper zone is
undetermined
3.0 NATURE AND EXTENT OF CONTAMINATION
Wetlands located downgradient of the site were contaminated by leachate from the landfill Both
groundwater and surface water contamination was limited to an area downgradient of the site Indicator
chemicals included metals and volatile organic compounds (VOC) as listed below
• 1,2-Dichloroethene at about 2 mg/L
• 1,1,2,2-Tetrachloroethane at about 6 mg/L
• 1,1,1 -Tnchloroethane at about 4 mg/L
4.0 CONTAINMENT REMEDY
The landfill improvement objectives were to provide (1) source control and (2) reduce the risk of
contamination of groundwater and surface water around the site The implemented remedy involved
active containment and included the following general features
Key SB=Soil Bentonite SC=Source Control Performance Rating 2=Evidence suggests objective may be met
Sitel
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Site 1
Site 1
FIGURE 1
Site Plan
Tetra Tecft EM Inc
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• A sofl-bentomte barrier that is about 5,400 linear feet long, 15 feet deep (on average),
and 3 feet thick and that has a 2-foot soil key
• A leachate collection system pumping to onsite storage and trucked to an offsite
treatment system
• Three groundwater quality monitoring points downgradient of the site and two surface
water monitoring points, one upgradient and one downgradient of the site
• A cap consisting of a compacted clay liner (CCL) on the side slopes, and a geomembrane
(GM) and a drainage layer on the landfill top surface A protective soil cover exists over
the CCL and GM
• An active gas venting system
5.0 PERFORMANCE EVALUATION
Performance monitoring of the containment remedy was established by a state permit to include quarterly
groundwater and surface water quality monitoring for metals, biochemical oxygen demand (BOD), and
chemical oxygen demand (COD) and annual monitoring for VOCs, metals, and base/neutral compounds
The hydraulic head across the barrier was not measured Groundwater quality improved outside the
barrier since 1990, indicating the general effectiveness of the containment Surface water quality
adjacent to the site also unproved, further indicating the general effectiveness of the remedy
The leachate collection system presently removes the amount of leachate predicted during its design,
indicating the effectiveness of both the barrier and the cap.
Containment system performance and contributing factors are described further in the following
subsections
5.1 Design
The barrier design was given a below average rating relative to industry practices as discussed in Section
3, Volume I No design-level groundwater modeling was performed for the barrier
The cap design was also given a below average rating The design included a standard, state-prescribed
cap for landfill closure as described in Section 4 0
Leachate collected from the landfill drams to sumps located at the pumping stations The pumping
system includes conventional piping and pumping stations
5.2 Construction Quality Assurance and Construction Quality Control
Barrier construction quality assurance (CQA) and construction quality control (CQC) were rated slightly
below average Generally, CQA/CQC procedures conformed to established standard protocols The
barrier key was visually confirmed along the alignment during construction The barrier met the
permeability requirement of less than 1 x 10"7 centimeters per second (cm/sec) based on test results for
undisturbed samples collected from the completed barrier every 500 linear feet
Sitel
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SWMU19 and SWMU 20-SWMU 19 is a 0 5-acre lagoon that was breached and used for burning and
disposal of lewisite SWMU 20 consists of two 75 by 300 foot pits that were used as a disposal area for
mustard agent and as a burning yard. Contamination consists of heavy metals (arsenic, cadmium, banum,
mercury, lead, and zinc in a metallic crust), mustard agent, mustard sulfone, and mustard sulfoxide
Media contaminated at these SWMUs include soil and groundwater The primary indicator contaminants
in groundwater are arsenic and mercury which were detected at preremediatton levels of 4 9 and 031
mg/L, respectively.
SWMU 21-SWMU 21 is a 0 5-acre area used for mustard agent demilitarization and burning The
contaminants in this SWMU are similar to those found in SWMUs 19 and 20
SWMU 62-SWMU 62 is a 5-acre site that formerly contained a 15-acre lagoon used for testing smoke
pots and grenades Zinc oxide and hexachloroethane along with metals are the contaminants at this
SWMU Media contaminated at this SWMU include soil, groundwater, and surface water The primary
indicator contaminant in groundwater is hexachloroethane, which was detected at a preremediation level
of 0207 mg/L
SWMU 63-SWMU 63 is a 4-acre site which was used as a dump for munition materials Contaminants
include metals and some volatile organic compounds Media contaminated at this SWMU include soil
and groundwater. The primary indicator contaminant in groundwater is lead, which was detected at a
preremediation concentration of 0 4 mg/L
SWMU 66-SWMU 66 is a 0 25-acre site that was used for disposal of munition wastes and for
production of a paraffin binder Metals and organic compounds contaminate the SWMU No specific
information was available regarding the environmental media contaminated at this SWMU
SWMU 27-SWMU 27 is a 40-acre site that was used in the 1940s to manufacture chlorine
Contaminants at this SWMU include metals and chlorinated organic chemicals Media contaminated
includes soil and groundwater. The primary indicator contaminant in groundwater is lead, which was
detected at a preremediation level of 0 37 mg/L
4.0 CONTAINMENT REMEDY
The objective of the containment remedy for the eight SWMUs was to minimize groundwater
contamination by diverting groundwater around or underneath contaminated materials, thus isolating the
sources of contamination and preventing off-site migration of contaminants The containment remedy
for each SWMU consisted of the following elements
• A circumferential slurry cutoff wall
• A high density polyethylene (HDPE) 60-mil cover overlain by 18 niches of compacted,
random fill and 4 niches of topsoil, seeded
• Groundwater monitoring wells irregularly spaced outside each slurry cutoff wall
The containment systems are passive and involve no active groundwater pumping The slurry cutoff
walls at SWMUs 25,27, 62, 63, and 66 were keyed at least 2 ft into the clay-shale unit The slurry cutoff
walls are at least 30 niches wide, except for SWMUs 19 and 20 where the wall is 36 inches wide The
five keyed slurry cutoff walls were constructed as follows
Stte 3
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SITE 2
1.0 SITE DESCRIPTION AND HISTORY Performance
Barrier Type
Remedial
Objective
SB
Containment
dewatenng
1
Site 2 is a municipal solid waste landfill operated under a state permit The site occupies a total of
230 acres, but only 107 acres is designated for solid waste disposal. The active part of the site is
subdivided into the West Tract, which consists of Phase 1(11 acres) and Phase II (59 acres), and the East
Tract, which contains Phase III (37 acres) Waste disposed of at the site is predominantly residential
solid waste generated within city limits The site was permitted in 1980 From 1980 until 1982,
landfilling occurred in Phase I Construction of Phase II was completed in 1981, and included a soil-
bentonrte cutoff wall The purpose of the wall was to allow dewatenng of the landfill, not to prevent
migration of potential leachate Disposal of waste in Phase II began in 1982 and continues today No
groundwater contamination at this site has been documented Figure 1 shows the layout of the Phase n
cutoff wall
2.0 GEOLOGIC AND HYDROGEOLOGIC SETTING
The site is located on Quaternary alluvial deposits associated with a river located 500 to 2,000 feet south
of the site The river flows from west to east The site is located within the current flood plain of the
nver, although embankment fill around the landfill prevents surface water encroachment onto the site
The alluvial deposits consist of clay, silt, sand, and gravel and generally coarsen with depth The alluvial
deposits are 17 to 27 feet thick at the site The alluvium is fairly permeable, although previous sand and
gravel mining has destroyed much of the original depositional structure
Groundwater is present in a perched alluvial aquifer at shallow depths, typically within 5 to 10 feet of the
ground surface Field testing of the perched alluvial aquifer indicates that the groundwater flows to the
north and northeast at a rate of 0 046 feet per day. Permeability coefficients for the alluvial aquifer at the
site range from 1 x 10-3 to 1 x 1Q-7 cm/sec The quaternary alluvial deposits are underlain by a bluish-
gray, slightly calcareous clay shale The shale formation contains occasional thin beds of bentomte and,
to a lesser extent, limestone and claystone thin beds and stringers The shale formation is about 140 feet
thick in the site area Site investigations have shown that permeability coefficients for the shale average
1 x 10'9 cm/sec A sand aquifer is located under the shale, lying at a depth of about 140 feet below
ground surface (bgs) in the site area The aquifer is separated from the base of the landfill excavation by
about 100 feet of shale
3.0 NATURE AND EXTENT OF CONTAMINATION
No contamination at this site has been documented
4.0 CONTAINMENT REMEDY
Under the original permit, the top of the shale formation was to be the base of the landfill Subsequent
investigations and permit modifications have allowed the landfill floor to be excavated about 50 feet into
the shale Before landfillmg activities could begin, the site had to be dewatered and the alluvial
overburden removed From August to November 1981, a soil-bentomte slurry wall was built around
Key SB=SoiI Bentomte Wall Performance Rating l=Remedial objective was met
Site 2
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0 100' 200
SCALE 1" = 200'
FIGURE 1
SITE PUN
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Phase II to dewater the landfill excavation The intention was to create a cutoff banner m order to
prevent the alluvial groundwater from flowing into the landfill excavation The soil-bentomte slurry wall
surrounds Phase n and extends about 7,100 linear feet The bamer is 3 feet wide and ranges from about
22 to 30 feet bgs in depth After the barrier was built, the landfill excavation was dewatered using three
6-inch-diameter pumps The pumps were placed m the bottom of excavation trenches where water
accumulated The pumps were moved around the site as needed Dewatenng took about 1 year
Compacted soil liners have been installed along the sides of the landfill above the shale When
completed, the landfill will have an engineered clay cap
A second soil-bentomte slurry wall was recently completed around the future Phase IE site, and this area
is currently being dewatered
5.0 PERFORMANCE EVALUATION
As noted in Section 1 0, the slurry wall was designed to allow the landfill excavation to be dewatered,
not to prevent migration of potential leachate The bamer has achieved its design objective, as
construction of the slurry wall around Phase II has allowed the excavation to be successfully dewatered
for landfill construction purposes The slurry wall and shale maintain a head differential of about 60 to
80 feet from the alluvial water table to the landfill base Specific bamer performance attributes are
evaluated in the following subsections
5.1 Design
Evaluation of the bamer design generated a rating slightly above average, based on the criteria outlined
in Section 3 of Volume I The design included a target permeability of 1 x 10"7 cm/sec Significant
positive attributes of the design effort included a thorough geotechmcal and hydrological investigation
and a 3-foot key into a competent, impermeable shale stratum
The overall design investigation was thorough Although the number of soil borings along the bamer
alignment (about one bonng every 300 linear feet) was less than the average evaluation of one boring
every 100 to 200 linear feet, the number of borings along, inside, and outside the alignment was deemed
sufficient Figure 1 shows the distribution of design investigation borings In addition, the alluvial
deposits and shale were thoroughly tested for physical parameters
The design also included an impervious fill cap overlying the cutoff wall The fill cap consisted of a
compacted, impervious fill layer that was placed along the center line of the cutoff wall This layer,
shown in Figure 2, was 14 feet wide and 3 feet deep The excavation for the cutoff wall was dug through
this cap layer
5.2 Construction Quality Assurance and Construction Quality Control
Evaluation of the construction quality assurance (CQA) and construction quality control (CQC)
procedures resulted in an average rating The field and laboratory inspection and testing procedures
included trench bottom soundings every 10 feet and sampling and analysis for sand content, viscosity,
density, filtrate loss, and permeability The testing protocols generally met the evaluation standard,
Site 2
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ILL.
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[XISIIKG LEVEE CHUHIH1HI
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- IOP OF SHALE
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LANDFILL SI IE
SOIL SEH10HIIE StUillH
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SHAU APCEAAS 10 (ORH A POCIII IH AHEA
OF HEHCH SIAIIOH 66>flO 10 7K27
ELtVAIIOII OF IOP OF SHALE VAXES FROM
109 TO 390
Site 2
FIGURE 2
SLURRY WALL CROSS SECTIONS
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however, the testing frequency was generally less than the evaluation standard established in Section 3,
Volume I
Laboratory tests of the trench backfill indicated permeability coefficients ranging from 2 2 x lO"? to
1 2 x 10~9 cm/sec, with an average of 6 3 x 10~8 cm/sec, therefore, the design target permeability was
achieved
5.3 Monitoring
Evaluation of the monitoring program resulted in an above average rating based on the criteria outlined
in Section 3 of Volume I Groundwater elevations in the alluvium adjacent to the landfill range from 405
to 425 feet At the bottom of the landfill where the clay shale is exposed (the approximate elevation is
350 feet), the excavation is dry, indicating that the barrier has achieved its objective of maintaining a
dewatered excavation
Protection of groundwater quality was not a design objective of the Site 2 cutoff wall However,
groundwater monitoring at the site is conducted on a semiannual basis in accordance with the site's
municipal solid waste permit, and available groundwater monitoring data can be used as an indicator of
barrier performance Groundwater samples for the West Tract are collected from one upgradient and
four downgradient monitoring wells and are analyzed for general water quality parameters The data are
then evaluated based on a statistical procedure Groundwater data from April 1981 through April 1993
was reviewed As might be expected for groundwater from 55 to 75 feet higher than the elevation of the
excavation, the excavation has had no discernable effect on groundwater quality.
An electrical resistivity survey has been performed annually since 1982 to evaluate potential leachate
migration from the landfill The survey includes a profile of Wenner array soundings with A-spacings of
15 and 33 feet. The resistivity measurements are made at established stations located outside the
perimeter of the cutoff wall The resistivity surveys conducted from 1982 through 1995 have not
revealed any leachate migration
5.4 Operation and Maintenance
No specific operation and maintenance (O&M) protocols exist for the cutoff wall The top of the wall is
below the perimeter embankment berm and is not visible for inspection Currently, while the shale floor
is exposed, groundwater leakage from the sidewalls or floor would be a visible indicator of cutoff wall
performance When landfillmg at Phase II is completed, and a leachate collection system is operational,
excessive leachate production will indicate problems with barrier performance
5.5 Other Considerations
The 1,100-foot-long cutoff wall cost an estimated $399,000 in 1981 Additionally, an estimated $45,000
in costs were incurred for (1) an engineering firm to provide construction inspection and quality control
testing and (2) the services of the design engineering firm during construction
5.6 Remedy Performance
The cutoff wall at Site 2 has met its design objective Bamer performance has been adequate to allow
dewatenng of the landfill excavation
Site 2 5
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6.0 SUMMARY
The cutoff wall, a soil-bentonite slurry wall, has been in place at Site 2, a municipal solid waste landfill,
for 15 years Construction of the slurry wall around Phase II has allowed the excavation to be
successfully dewatered for landfill construction purposes The slurry wall is about 7,100 feet long and
3 feet wide, 22 to 30 feet in depth, and is keyed into a competent shale formation The cutoff wall and
the shale formation maintain a head differential of about 60 to 80 feet from the alluvial water table to the
landfill base Design, CQA/CQC, and performance monitoring data for the site is well documented
Evaluation of the design and CQA/CQC procedures generated slightly above average and average ratings
respectively. Evaluation of the monitoring program generated an above average rating. The barrier
system includes monitoring components (visual observation, monitoring wells, annual resistivity
surveys, and a leachate collection system) capable of monitoring long-term barrier performance
Site 2
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SITES
1.0 SITE DESCRIPTION AND HISTORY
Barrier Type
Remedial Objective
Performance
SB
SC, Ground-water flow
modification
X
Site 3 is located in the central southern United States in a semirural area The site occupies about
15,000 acres and is bordered on the east by a river and on the west by a bayou Highways border the site
on the south and north The site contains more than 20 solid waste management units (SWMU) of
various sizes Of the more than 20 SWMUs at the site, this evaluation was limited to eight SWMUs that
have perimeter subsurface barrier slurry walls Of those eight, two he within one perimeter subsurface
barrier
The site historically functioned as an Army testing and disposal facility Wastes at the site contained
heavy metals and organic compounds These wastes were either placed in land disposal units or directly
discharged to the ground surface Investigation of contaminated site areas began in the 1960s Site
closures were designed to comply with a consent agreement and a hazardous waste management permit
issued by the U.S Environmental Protection Agency (EPA) and the state
2.0 GEOLOGIC AND HYDROGEOLOGIC SETTING
The site geology is characteristic of the West Gulf Coastal Plain Physiographic Province in the southern
United States The site lies within the Mississippi Embayment Structure, a southerly plunging synchne
filled with sedimentary rocks and sediments ranging in age from Jurassic to Quaternary and reaching a
maximum thickness of about 18,000 feet (ft) in the southern part of the gulf coastal region Soils present
on the site surface are Eocene Period sediments composed of marine and nonmarine sands, silts, and
clays These sediments dip gently east toward the Arkansas River and are about 2,600 fit thick Figure 1
shows the generalized surface geology of Site 3
Three major geologic units are present at the site. Surface soils on the central, eastern edge of the site
consist of recent alluvial deposits from the river flood plain These deposits consist of silts and clays
underlain by higher-plasticity, lower-permeability clays and some silts Low-permeability layers within
these deposits act as confining units that separate perched water from underlying soils
Pleistocene-age Terrace deposits are generally located in the central portion of the site These deposits
are fluvial sediments that consist of silty sands and silts The deposits are a few ft thick along the
western edge of the site and are nearly 60 ft thick at the eastern edge of the site near the Arkansas River
alluvial deposits The river alluvial deposits and the Pleistocene Terrace deposits make up the alluvial
aquifer This aquifer is composed of soils ranging from coarse gravel to clays Groundwater in this
alluvial aquifer tends to be of poor quality (that is, it is high in chlorides, sulfate, and iron), therefore, it
is used only for irrigation purposes
Underneath the alluvial aquifer deposits and outcropping in the western portion of the site are marine and
nonmanne clays deposited during the late Eocene Period These clays are characterized as over
consolidated, laminated clay with silry sand lenses Laboratory testing of this clay revealed an
acceptable permeability of 1 7 x 10~7 centimeters per second (cm/sec) Silt and sand lenses within this
group have an acceptable permeability of 1 x 10~5 cm/sec These clays act as a regional confining unit
preventing perched water in the alluvial aquifer from migrating downward
Key SB=Soil Bentonite Wall SC=Source Control Performance Rating X=Insufficient data to determine if remedial objectives were met
Site 3
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Alluvial Deposits
Pleistocene Deposits
Jackson Group
Site 3
Site 3
FIGURE 1
GEOLOGY OF SITE 3
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Underlying the marine and nonmarme clays is a clay-shale confining unit Under the confining unit is an
unconsohdated water bearing unit This unit is located in a sand formation and is the primary source of
drinking water in the vicinity of the site Wells within tne sands unit are screened 800 to 1,000 ft below
ground surface (bgs)
Groundwater flow across the site is typically toward the southeast, some flow reversal occurs in times of
high river levels Rates of groundwater flow across the site tend to be very low because of a low
hydraulic gradient and low-permeability soils
As stated in Section 1 0, the subsurface barriers associated with eight SWMUs were evaluated Of the
eight SWMUs, two are located within the boundaries of one subsurface barrier wall containment system
Because the eight SWMUs are not grouped together in one area of the site but are located in various
areas across the site, their geologies and hydrogeologies differ Following are summaries of the SWMU-
spewfic geologic and hydrogeologic settings
SWMU 25-This SWMU is underlain by a clay-shale unit The approximate depth to groundwater is
19 ft bgs
SWMU 19 and SWMU 20-These SWMUs are underlain by alluvial Terrace deposits varying in
thickness from 1 to 10 ft The approximate depth to groundwater is 15 ft bgs
SWMU 21-This SWMU is underlain by alluvial Terrace deposits varying in thickness from 1 to 10 ft
These deposits thicken east of the site The approximate depth to groundwater is 21 ft bgs
SWMU 62-This SWMU is located on Terrace deposits that range in depth from 18 to 24 ft in thickness
The approximate depth to groundwater is 24 ft bgs
SWMU 63-This SWMU is located on Terrace deposits consisting of sand and silt with some sandy clay
The approximate depth to groundwater is 30 ft bgs
SWMU 66-This SWMU is underlain by Terrace deposits The perched and permanent groundwater
tables are at approximately 18 and 35 ft depths, respectively
SWMU 27-This SWMU lies within an outcrop area of the marine and nonmarme clays A continuous
clay bed underlies the SWMU at a thickness from 2 to 20 ft The approximate depth to groundwater is
20ft
3.0 NATURE AND EXTENT OF CONTAMINATION
Contamination at this site varies from SWMU to SWMU, depending on the waste management practices
used at each SWMU In general, only the shallow alluvial aquifer is contaminated There is no evidence
that the deep sand aquifer is contaminated Groundwater contamination also appears to be confined
within the boundaries of Site 3 The nature and extent of contamination at each of the SWMUs are
summarized below
SWMU 25-SWMU 25 is a former burning pit for production wastes This area was also used for burial
of barrels, railroad ties, and other debris Contaminants at this SWMU include heavy metals (arsenic,
barium, cadmium, lead, and zinc) Media contaminated at this SWMU include soil and groundwater
The primary indicator contaminants at this SWMU are cadmium and lead, which were detected in
groundwater at preremediation levels of 0 01 and 0 06 mg/L, respectively
SiteS 3
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SWMU19 and SWMU 20-SWMU 19 is a 0 5-acre lagoon that was breached and used for burning and
disposal of lewisite SWMU 20 consists of two 75 by 300 foot pits that were used as a disposal area for
mustard agent and as a burning yard Contamination consists of heavy metals (arsenic, cadmium, banum,
mercury, lead, and zinc in a metallic crust), mustard agent, mustard sulfone, and mustard sulfoxide
Media contaminated at these SWMUs include soil and groundwater The primary indicator contaminants
in groundwater are arsenic and mercury which were detected at preremediation levels of 4 9 and 031
mg/L, respectively
SWMU 21-SWMU 21 is a 0 5-acre area used for mustard agent demilitarization and burning The
contaminants in this SWMU are similar to those found in SWMUs 19 and 20
SWMU 62-SWMU 62 is a 5-acre site that formerly contained a 1 5-acre lagoon used for testing smoke
pots and grenades. Zinc oxide and hexachloroethane along with metals are the contaminants at this
SWMU Media contaminated at this SWMU include soil, groundwater, and surface water The primary
indicator contaminant in groundwater is hexachloroethane, which was detected at a preremediation level
of 0207 mg/L
SWMU 63-SWMU 63 is a 4-acre site which was used as a dump for munition materials Contaminants
include metals and some volatile organic compounds Media contaminated at this SWMU include soil
and groundwater. The primary indicator contaminant in groundwater is lead, which was detected at a
preremediation concentration of 0 4 mg/L
SWMU 66-SWMU 66 is a 0 25-acre site that was used for disposal of munition wastes and for
production of a paraffin binder Metals and organic compounds contaminate the SWMU No specific
information was available regarding the environmental media contaminated at this SWMU
SWMU 27-SWMU 27 is a 40-acre site that was used in the 1940s to manufacture chlorine
Contaminants at this SWMU include metals and chlorinated organic chemicals Media contaminated
includes soil and groundwater The primary indicator contaminant in groundwater is lead, which was
detected at a preremediation level of 0 37 mg/L
4.0 CONTAINMENT REMEDY
The objective of the containment remedy for the eight SWMUs was to minimize groundwater
contamination by diverting groundwater around or underneath contaminated materials, thus isolating the
sources of contamination and preventing off-site migration of contaminants The containment remedy
for each SWMU consisted of the following elements-
• A circumferential slurry cutoff wall
• A high density polyethylene (HDPE) 60-mil cover overlain by 18 inches of compacted,
random fill and 4 inches of topsoil, seeded
• Groundwater monitoring wells irregularly spaced outside each slurry cutoff wall
The containment systems are passive and involve no active groundwater pumping The slurry cutoff
walls at SWMUs 25,27,62,63, and 66 were keyed at least 2 ft into the clay-shale unit The slurry cutoff
walls are at least 30 inches wide, except for SWMUs 19 and 20 where the wall is 36 inches wide The
five keyed slurry cutoff walls were constructed as follows
Site 3
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• SWMU 25-The slurry cutoff wall at this SWMU is a perimeter slurry wall estimated to be
1,675 ft in length This slurry wall vanes in depth from 10 to 20 ft bgs, with an acceptable
depth of 14 ft bgs
• SWMU 27-The slurry cutoff wall at this SWMU is estimated to be 2,000 ft in length The
slurry wall vanes in depth from 5 to 14 ft bgs and has an acceptable depth of 12 ft bgs
• SWMU 62-The slurry cutoff wall at this SWMU is a penmeter slurry wall estimated to be
1,800 ft in length The slurry wall appears to be set at an approximate depth of 16 to
18 ft bgs
• SWMU 63- The slurry cutoff wall at this SWMU is a penmeter slurry wall estimated to be
2,100 ft in length The slurry wall appears to be set at an approximate depth of 15 to
17 ft bgs
• SWMU 66- No mformation was available on the depth or length of the slurry cutoff wall at
this SWMU
Hanging slurry cutoff walls exist at SWMUs 19 and 20 The depths of the hanging slurry cutoff walls
were designed to cut off several mterbedded sand and sandstone lenses The acceptable wall depth of the
hanging slurry cutoff walls at these SWMUs is 40 ft bgs
Design of the closure systems was completed in the mid-1980s, and construction of the closure systems
took place between 1987 and 1989
5.0 PERFORMANCE EVALUATION
The purpose of the momtonng program at the site is to determine the effectiveness of the slurry cutoff
wall containment systems in isolating the sources of contamination Residual groundwater
contamination exists, making containment system effectiveness difficult to determine The results from
the current momtonng program, which tracks trends in groundwater contamination levels across the site
using statistical methods, have been inconclusive, and data gaps may exist for several of the SWMUs A
revised monitoring program that includes the installation of new monitoring wells and revision of
analytical sample collection frequencies is being proposed by the facility Details of the revised program
were not available
Although the current momtonng program does not appear to be adequate, current data show no indication
that leakage of contamination is occurring from any of the closure sites Groundwater quality data
indicates that threshold limit values for certain contaminants are occasionally exceeded, but no trends are
apparent that would indicate potential leakage from any of the closure sites The occasional exceedances
may be attributed to residual groundwater contamination that existed before SWMU closure
Containment system performance and contributing factors are discussed further in the following
subsections
5.1 Design
An evaluation of the design information generated an acceptable ratmg relative to the industry practices
discussed in Section 3, Volume I No design-level groundwater modeling was performed for any of the
barners
SiteS
-------
No information was available on the leachate generation and management practices The design called
for a HDPE cover overlain by 18 inches of topsoil and vegetative cover The cover and walls are not
physically connected
5.2 Construction Quality Assurance and Construction Quality Control
Evaluation of the barrier construction quality assurance (CQA) and construction quality control (CQC)
generated an acceptable rating All the soil-bentomte cutoff walls were installed using standard
trenching and backfilling methods The design called for a wall permeability of 1 x 10~7 cm/sec or less, a
minimum bentomte content of 3 percent, a minimum fines content of 48 percent, and a minimum
plasticity of 7 percent The underlying stratum was tested for thickness and permeability continuity
across each SWMU site Soil borings, that penetrated at least 5 ft into the underlying stratum, were used
to determine continuity. Falling head permeability tests in wells and laboratory tests were used to
determine in situ stratum permeability. The minimum design requirements were a stratum thickness of 5
ft and a permeability of less than 1 x 10"7 cm/sec Soil borings were completed at 100-foot centers along
the alignments of the slurry cutoff walls to ensure that low-permeabihty stratum had been properly keyed
before backfill placement In the case of the hanging slurry cutoff wall, the borings were used to
determine the depths at which the walls would penetrate stratum that was below the contaminated zone
Full time CQA/CQC was completed during the installation of the slurry cutoff walls and caps The
CQA/CQC program used was the standard U.S Army Corps of Engineers Regulation ER-1180-1-6
program
Slurry trench backfill and slurry was tested before and during construction No reference to
postconstruction testing of the slurry wall materials was found in the information reviewed
53 Monitoring
Long-term monitoring was rated below acceptable. Currently monitoring of the SWMUs consists of
semiannual collection of groundwater samples outside the perimeter of the cutoff walls Groundwater is
monitored for quality analysis only
Figure 2 shows groundwater quality data for lead associated with SWMUs 19,20, and 21 The figure
shows periodic increases of lead concentrations for one or more sampling rounds, however, data for
subsequent sampling rounds show decreases or leveling off of contaminant levels This figure is
representative of similar analytical data for the site and an overall site trend of declining or steady
contaminant levels near the SWMUs.
5.4 Operation and Maintenance
An operation and maintenance program is in place at the site, however, no specific information on this
program was available
5.5 Other Considerations
No specific cost information for remedial actions at the eight SWMUs was available
SiteS
-------
SWMU's 19, 20 & 21 - Lead
500
450 --
400
350 --
300 --
250 .-
-
1st Half 89 1st Half 90 1st Half 91 1st Half 92 1stHalf93 1st Halt 94 1st Half 95
2nd Half 89 2nd Half 90 2nd Half 91 2nd Half 92 2nd Half 93 2nd Halt 94
— o— w»nei
•D -H
0- W»II134-D S
* W»II205
D
_^_
W«II208-D
™o^
W»lt207-D — C
J— W»ll 209-0 — £r- V
..H211.U -*-
W*II2S3-U
Site 3
FIGURE 2
LEAD LEVELS AT SWMU's 19. 20 & 21
Tetro Tech EM Inc.
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5.6 Remedy Performance
The overall performance of the containment system could not be determined based on available data
6.0 SUMMARY
Site 3 occupies about 15,000-acres and is part of a U S Army testing and disposal operation The site
geology is characteristic of the West Gulf Coastal Plain Physiographic Province The eight SWMUs
used in this evaluation were land disposal facilities before the 1970s Past disposal operations at these
SWMUs resulted in groundwater contamination with heavy metals, semivolatiles, volatile organics, and
other contaminants Remedial actions at the eight SWMUs consisted of construction of circumferential
slurry cutoff walls overlain by a flexible membrane liner and soil cover Groundwater monitoring wells
were installed to evaluate the effectiveness of the containment systems The remedial design was rated
acceptable, CQA/CQC was rated acceptable, and long-term monitoring was rated below acceptable
There was insufficient data to determine if the remedial objectives had been met
SiteS
-------
SITE 4
1.0 SITE DESCRIPTION AND HISTORY
Earner Type
Remedial
Objective
Performance
SB
~sc~
X
Site 4 is located in the midwestern United States and contains a landfill The site lies in a valley less
than 1 mile from a major river The site has rugged topography with high relief Slopes in the area are
generally steep with narrow ridge tops An earthen dam was constructed near the head of the valley to
contain wastes The dam is about 350 feet long, 16 feet wide at its crest, and 45 feet high The valley
up-slope of the earthen dam was used as a landfill and covers about 3 acres Vegetation over the landfill
consists of poor grass and shrubs The adjacent valley sides are heavily wooded Figure 1 shows the
locations of significant site features
The landfill received solids, liquids, and sludges The landfillmg of wastes started in 1969 and ceased in
1980 Construction activities for a remedial action at the site began in July 1992 and were completed in
August 1993.
The site containment consists of a soil-bentonrte slurry wall above a grout curtain The slurry wall
extends around most of the landfill, with improvements to an earthen dam completing the perimeter
barrier The slurry wall was not keyed-in to the earthen dam The earthen dam improvement included
the building of a granular berm on a 3H IV slope and a terrace at mid-height A Resource Conservation
and Recovery Act (RCRA) Subtitle C cap is tied into the slurry wall
2.0 GEOLOGIC AND HYDROGEOLOGIC SETTING
Site 4 is located in the nonglaciated Central Groundwater Region of the United States The subsurface
stratigraphy within the site boundary generally consists of residual soils, which extend 5 to 10 feet below
ground surface (bgs), grading into partially weathered rock and underlying parent bedrock Typically,
the bedrock lies at a depth of 10 feet bgs and consists of alternating layers of sandstone, shale, and coal
with occasional limestone and iron ore In situ weathering of the parent bedrock has formed the residual
soils Some sedimentary deposits (colluvium) are found along the valley floor
Shallow and deep water-bearing zones exist beneath the site in two sandstone units, one above and the
other below the shale Shale permeability at the site averaged 1 x 10"6 centimeters per second (cm/sec),
and sandstone permeability averaged 1 x 10~5 cm/sec The local groundwater flow is to the west,
however, regional flow is toward the valleys with some component of vertical flow through rock
fractures The slurry wall was keyed into the shale to control lateral flow of groundwater into the
landfill
3.0 NATURE AND EXTENT OF CONTAMINATION
Analyses of landfill wastes revealed 13 volatile organic compounds (VOC), 13 semivolatile organic
compounds (SVOC), 20 metals, four pesticides, and cyanide Soil cleanup required lowering the
concentrations of benzo(a)pyrene, ethylbenzene, phenol, arsenic, manganese, and nickel Groundwater
cleanup required lowering the concentrations of 1,2-dichloroethane (DCA), benzene, phenol, arsenic,
manganese, and nickel Groundwater contained the following concentrations of contaminants
Key SB=Soil Bentonrte Wall SC=Source Control Performance Rating X=Insufficient data to determine if remedial objectives were met
Site 4
-------
MW-07
,MW-07A
MW03B
PIPING FOR
GROUNDWATER
COLLECTION
SYSTEM
MW-01/V
f-01B
LIMITS OF CAP
MW-.02B
+ +
MW-02A
LEGEND
•f MONITORING WELL
• EXTRACTION WELL
Hinnn SOIL BENTONITE SLURRY WALL
-f MW-05B
MW-05A4-
SCALE- 1" = 120'
Site 4
FIGURE 1
SITE LAYOUT
7etrcr Tech EM Inc.
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CONCENTRATION
CONTAMINANT micrograms per liter (//g/L)
Acetone 12
Benzene 5
Carbon disulfide 13
Chloroethane 17
1,4-Dichlorobenzene 10
Aluminum 9,480
Arsenic 5 2
Barium 42 8
Beryllium 3 8
Cobalt 815
Copper 5 3
Iron 13,100
Manganese 2,610
Nickel 108
Vanadium 5 5
Zinc 378
4.0 CONTAINMENT REMEDY
Key components of the implemented remedy included the following
• Collection of leachate using one large-diameter extraction well and of contaminated
groundwater using three extraction wells and eight dual-well clusters
• An on-site leachate and groundwater treatment system
• Containment of on-site wastes using (1) a RCRA cap and (2) barrier wall (about 1,451
feet long and 40 feet deep) with a grout curtain 15 feet below the lowest elevation of the
landfill The barrier wall is keyed into the shale bedrock
• Improvements to the earthen dam located at the western end of the landfill hi order to
increase the factor of safety to greater than or equal to 1 5 and improve drainage
• Excavation of contaminated soils and sediments and their consolidation into the landfill
before capping
5.0 PERFORMANCE EVALUATION
Performance monitoring of the containment includes quarterly groundwater monitoring that began m
1994 The objectives of the containment system are to prevent groundwater flow into the landfilled
materials and to minimize the amount of contaminated groundwater pumped to the treatment plant
Site 4
-------
5.1 Design
The barrier design was rated better than acceptable compared to industry practice as described in
Section 3, Volume I The design for the containment system at the site included improvements to an
earthen dam, a barrier wall extending three-quarters of the way around the landfill, a landfill cover, a
leachate collection system, and a leachate and groundwater treatment system The barrier wall system
consists of a grout curtain extending at least 15 feet below the lowest elevation of the landfill and a soil-
bentomte banner wall in the soils above the grout curtain The grout curtain is not part of the earthen
dam The design calculations, drawings, and specifications indicate that the design effort was slightly
better than acceptable Geotechmcal physical testing was conducted, and borings were aligned along the
barrier at less than 100-foot intervals
5.2 Construction Quality Assurance and Construction Quality Control
The construction quality assurance (CQA) and construction quality control (CQC) for barrier wall
construction were rated better than acceptable The CQA/CQC for grout curtain installation could not be
determined based on available data, however, the U S Army Corps of Engineers performed independent
tests on the grout and grout curtain in addition to the construction engineer's testing of the grout curtain
Inspections of the trench excavation, width, verticahty, and continuity were conducted periodically, and
trench sounding was conducted every 10 to 20 feet The key was confirmed about every 20 feet The
landfill cover geomembranes were independently tested by the installer in addition to the engineer's
destructive testing The CQA/CQC for the landfill cover was rated better than acceptable
§3 Monitoring
Long-term monitoring was rated less than acceptable because it did not include hydraulic stress tests or
paired piezometers along the wall Eight pairs of nested groundwater monitoring wells with screens in
the shallow and deep aquifers are located at the site The water levels in three extraction wells (EW-1,
EW-2, and EW-3) located within the landfill limits and one extraction well (EW-4) located at the base of
the earthen dam are monitored monthly The quantity of water pumped from these wells is also
monitored monthly Water from these wells and from the eight monitoring well nests (MW-1A and
MW-1B through MW-8A and MW-8B) located in and around the landfill is treated in an on-site
treatment plant
Water level measurements in the extraction wells indicate that water levels dropped about 7 feet in
EW-1,2 5 feet in EW-2,4 feet in EW-3, and 1 75 feet in EW-4 from October 1994 to April 1995 No
paired piezometers are located inside and outside the barrier wall Available water level data is not
presented in terms of mean sea level Because of the data deficiencies, the hydraulic gradient across the
wall could not be determined
Groundwater quality downgradient of the barrier wall appears to be improving However, data for only
two sampling rounds was available for this evaluation Contaminant concentrations in downgradient
well MW-6A were plotted to show the changing concentrations of three contaminants over tune (see
Figure 2) The data from this well is representative of downgradient water quality The concentrations
of all three contaminants decreased from the fourth quarter of 1995 to the first quarter
of 1996 MW-6B, the deeper well of the nest, did not have any organic contamination, but the
concentration of nickel increased from 76 to 426
Site 4
-------
Downgradient Monitoring Well 6A
-1,2-DCA(mg/L)
-Phenol (mg/L)
-Nickel (ug/L)
Date
Site 4
FIGURE 2
CONTAMINANT CONCENTRATIONS
retro Tech EM Inc.
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5.4 Operation and Maintenance
Groundwater pumped from the extraction and monitoring wells is treated in an on-site treatment system
consisting of a primary collection tank, a heavy metal removal system, a biological treatment system, and
a sand and carbon filtration system before being discharged to a nearby creek Treatment system effluent
samples are collected weekly in accordance with the site's National Pollution Discharge Elimination
System (NPDES) permit
5.5 Other Considerations
The total cost of the grout curtain, slurry wall, landfill cap, and treatment plant was $6,800,000 The cost
of the slurry wall was about $16 00 per square foot, and the cost of the grout curtain was $265 00 per
linear foot, resulting in a total cost of $850,000
5.6 Remedy Performance
Based on limited evidence available to date, the remedy appears to be performing as planned, and the
barrier wall has reduced the pumping rates of the extraction wells to those rates specified in the design
objective The water quality downgradient of the barrier wall is improving slightly
6.0 SUMMARY
Site 4 is a 3-acre landfill situated in a valley The site has primarily organic contamination in soils and
groundwater. A 1,451-foot-long barrier wall extends around most of the landfill However, the barrier
was not keyed into the 350-foot-long earthen dam The barrier wall system consists of a grout curtain
extending at least 15 feet below the lowest elevation of the landfill and a soil-bentonite barrier wall in the
soils above the grout curtain Three extraction wells are located under a RCRA cap, and one extraction
well is located downgradient of the earthen dam
The design was rated better than acceptable, and barrier CQA/CQC was rated better than acceptable
Long-term monitoring was rated below average No paired piezometers are located at the site, therefore,
the presence of a hydraulic gradient across the wall could not be determined Groundwater quality
downgradient of the barrier wall appears to be improving, but only two rounds of sampling data were
available for evaluation Based on the limited data available, it could not be determined if the remedial
objectives had been met
Site 4
-------
SITES
1.0 SITE DESCRIPTION AND HISTORY
Earner Type
Remedial
Objective
Performance
CC
sc
Site 5 is located in northeastern United States The site is a closed municipal solid waste landfill and
covers about 86 acres The site is bordered on the north by a residential development, on the east and
south by secondary roads, and on the west by a dirt road The site and its basic features are shown in
Figure 1
The township operated the landfill from the mid-1950s until 1968, when it was leased to a solid waste
hauling and disposal company. Seepage from the landfill was detected m late 1977 and early 1978, when
excavation began for the construction of nearby homes The containment system installed at the site
includes a leachate collection drain coupled with a 10-foot-wide, 700-foot-long, rectangular, subsurface
clay barrier extending around the perimeter of the site The barrier was keyed into a formation which
exhibits low hydraulic conductivity
2.0 GEOLOGIC AND HYDROGEOLOGIC SETTING
The site consists of mterbedded layers of sand, silt, and clay along the residential development perimeter
Figure 2 shows the soil layers through which the barner wall was constructed
Groundwater occurs on site as perched groundwater overlying the unweathered clays and as unconfined
groundwater in the deeper sand layers The perched groundwater table aquifer is not present in all
portions of the site The clayey layer overlying the silty sands was used as the low permeability zone for
the barner wall key-in
3.0 NATURE AND EXTENT OF CONTAMINATION
Although the exact extent of contamination was not fully documented, indicator chemicals for leachate
contaminations included heavy metals and volatile organic compounds (VOC)
4.0 CONTAINMENT REMEDY
On the basis of hydrogeologic findings, a leachate collection system and barner cutoff wall were
designed and installed around the perimeter of the site The containment remedy for the site includes the
following
A 7,000-foot-long, 10-foot-wide, 10-foot-deep rectangular, compacted clay barrier wall
and leachate collection system surrounding most of the site
• A leachate management system with an emergency power supply
• A protective soil cap for the area encircled by the wall and a clay cap for the portion of
the landfill not underlain by the clay formation
• Surface water and erosion control systems
• Secunty fencing surrounding the entire site
• An active landfill gas collection and treatment system
Key CC=Compacted Clay SC=Souice Control Performance Rating l=Remedial objective was met
SiteS
-------
H-
rt
Ol
to
B-55pO^^£k£
MONITORING WELL
HONITORIN6 PERCHED WATER ZONE
WITHIN THE MAGOTHY FORMATION
MAGOTHY FORMATION HOMITOWNG
WELL
MERCHANTVIU.E FORMATION MONITORING
WELL
PIEZOMETER
PASSIVE GAS VENTS
GAS MONITORING PROBES
MANHOLE / PASSIVE GAS VENT
LANDFILL PROPERTY BOUNDARY LINE
AND FENCE
LEACHATE COLLECTION SYSTEM AND
COMPACTED CLAY CUTOFF WALL
DRAINAGE CHANNEL
7' HIGH CYCLONE FENCE
4" OIA FORCEMAIN
PROPOSED ACCESS ROADS
PROTECTIVE CLAY CAP
PROTECTIVE SOIL CAP
Site 5
FIGURE 1
SITE PUN
Tetro Tech EM Inc.
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5.0 PERFORMANCE
In 1993, after numerous environmental investigations, the state and federal regulatory agencies
determined that no further action except for maintenance and monitoring was needed to supplement the
containment remedy Factors contributing to the performance of the containment remedy are further
discussed below
5.1 Design
The compacted clay barrier wall design was rated acceptable with respect to industry practices described
in Section 3, Volume I The collection system was designed to handle the maximum anticipated flows
from the perched groundwater table so as to provide a preferential hydraulic gradient to the collection
line as opposed to radial discharge from the site
A schematic of the containment remedy is shown in Figure 2 The containment remedy has proven to be
effective in reducing landfill leachate generation and in mitigating lateral migration of leachate
Subsequently, additional remedial measures were constructed at the site, including surface water
management systems, a perimeter security fence, a leachate storage facility that ultimately discharges to
the county wastewater treatment plant, and an active landfill gas extraction and treatment system No
design-level groundwater modeling was performed for the containment
The cap design was rated less than acceptable The design included a state regulatory agency-approved
cap consisting of 1 foot of compacted clay, 6 inches of sand above the compacted clay, and 6 inches of
soil suitable for vegetative growth above the sand
5.2 Construction Quality Assurance and Construction Quality Control
The construction quality assurance (CQA) and construction quality control (CQC) procedures used
during construction of the clay bamer cutoff wall were rated better than acceptable Generally, the
CQA/CQC procedures conformed to established industry practices The wall key was confirmed by
visual inspection of the soil and resistance to excavation at key depths Based on testing of undisturbed
samples collected from the completed wall every 400 linear feet, the wall met the design permeability
requirement of less than 1 x 10"7 centimeters per second (cm/sec)
The permeability of the compacted clay bamer and compacted clay cap was determined through
laboratory testing of undisturbed (shelby tube) samples For the cut-off wall, two types of permeability
tests were performed The first test was used to verify an overall effective permeability of 1 x 10"7 cm/sec
The second test was performed on samples of the key-in material In each test sample of the key-in
material, the permeabilities were less than the maximum horizontal and vertical values of 11 x 10"4 and
2 6 x 10"6 cm/sec, respectively.
Cap CQA/CQC was rated slightly better than acceptable Notably, the clay sources were thoroughly
tested for physical properties, including permeability Also, a small version of the compacted clay layer
was constructed and tested by performing permeability measurements on six undisturbed samples The
final cap permeability test results are consistent with the wall permeability test data
SiteS
-------
LEACHATE LEVEL
PIEZOMETER
-LEACHATE
COLLECTION DRAtN
PIEZOMETER
I—CLAY CUTOFF
WALL PIEZOMETER
I—QUATERNARY SEDIMENTS
PIEZOMETER
GROUNDWATER LEVEL IN
QUATERNARY SEDIMENTS
SOIL COVER
MERCHANTVILLE
DRAINAGE
BACKFILL
FORMATION MONITORING
WELL/PIEZOMETER
CLAY CUTOFF
WALL
FORESTED
WETLANDS
FORESTED
WETLANDS
QUATERNARY
SEDIMENTS
SILTY SAND SEAM
LEACHATE
COtLBdf ION DRAIN
. (SURFACE
OF SILTY SAND SEAM
POTENTIOMETRIC SURFACE
STAGNATION ZONE
FIGURE 2
SCHEMATIC SECTION
retro Tech EM Inc
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53 Monitoring
The performance monitoring of the bamer was rated better than acceptable and involved
postconstruction sampling, paired piezometers across the bamer wall, ample groundwater quality
monitoring, and regular inspections
The results of the groundwater monitoring indicate that organic chemicals detected in groundwater do
not exceed state or federal groundwater quality standards Refer to Figure 3 for a summary plot of
groundwater quality
5.4 Operation and Maintenance
A maintenance plan is used for scheduled preventive maintenance and repair of remedial components to
ensure the continued effectiveness of the site remedy Repairs performed as part of maintenance
activities are summarized in an annual report submitted to the state regulatory agency
5.5 Other
The capital and annual O&M costs for the containment remedy are not available
5.6 Remedy Performance
The overall performance of the containment suggests that the remedial objective was met Hydraulic
head criteria were easily met by the leachate collection and removal system, and groundwater quality
outside the containment has improved significantly relative to original on-site concentrations The
barrier wall was determined to be of low permeability, adequately keyed, continuous, and intact based on
the measurements of groundwater table elevations and groundwater quality data The cap has functioned
effectively and has a proper erosion control system
6.0 SUMMARY
Site 5 is a 86-acre closed landfill contaminated with heavy metals and VOCs The site's hydrogeology
and shallow, pervasive aquitard provided the base for a clay bamer wall The compacted clay bamer
wall was augmented with a leachate collection and management system with an emergency power
supply, a compacted clay cap, surface water and erosion control systems, security fencing, and a
groundwater monitoring system The site containment has met the site's remedial objectives and is
considered a protective remedy
SiteS
-------
SAMPLING
DATE
TVOC (1).(2)
U9/I
MARCH
1991
4.895
NOVEMBER
1993
(3)
APRIL
1994
476.94
OCTOBER
1994
439.58
APRIL.
1995
17320
SEPT/OCT
1995
40.21
000
000
.000
000
000
.000
700
400
300
200
100
70
40
30
20
10
7
4
3
1991
1992
1993
1994
1995
10.000
7.000
4000
3000
2000
NOVEMBER
1993
-OCTOBER
1.000
700
400
300
200
1995
100
70
40
30
20
CFPT /nrvr
1995
10
7
4
3
2
1991
1992
1993
1994
1995
NOTES
1.) TVOC = TOTAL VOLATILE ORGANIC COMPOUNDS.
2.) FOR COMPARISON. DATA PRIOR TO MARCH 1991 WAS NOT USED BECAUSE KETONES
WERE NOT ANALYZED.
Sxte 5
Site 5
FIGURE 3
TOTAL VOC's vs TIME
Tefro Tech EM Inc
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SITE 6
1.0 SITE DESCRIPTION AND HISTORY
Earner Type
Remedial
Objective
Performance
SB
SC, Facilitate
dewatenng
Site 6 is located in the southeastern United States The site is about 5 acres m size and was initially
operated as a borrow area for sand A site plan is shown in Figure 1 When borrow operations ceased,
excavated pits at the site were used for disposal of wastes including construction and demolition debns,
cement kirn dust, battery wastes, waste from an automobile shredder, and household waste Waste
disposal as a business operation ceased at the site in 1976, however, unauthorized dumping of waste
occurred at the site beyond 1976 Waste disposal activities at the site contaminated on- and off-site
groundwater with several metals
The original site remedy included solidification of contaminated soil and noncement waste, extraction
and treatment of contaminated on-site groundwater, extraction and treatment of off-site contaminated
groundwater, and installation of a cap The site remedy did not address solidification of the
contaminated cement kiln dust because it was naturally solidified following disposal when it contacted
water Although not part of the original remedy, a subsurface barrier wall was installed to (1) facilitate
dewatenng during site remediation and (2) minimize long-term migration of groundwater through
solidified materials and cement waste after site remediation The extraction and treatment of off-site
groundwater originally required as part of the site remedy became unnecessary because the quality of off-
site groundwater improved to an acceptable level following installation of the barrier wall and cap in
1993 and 1995, respectively
2.0 GEOLOGIC AND HYDROGEOLOGIC SETTING
The site geology is relatively simple About 15 to 20 feet (ft) of fine- to medium-grained,
undifferentiated sediments form the surficial aquifer These sediments overlie a 9-foot-thick, sandy,
phosphatic clayey deposit, that forms a confining layer beneath the surficial aquifer The confining layer
separates the surficial aquifer from a deeper, regional aquifer that is an artesian aquifer in the site area
and can yield large quantities of fresh water The soil-bentonite barrier wall is keyed into the clayey,
confining layer
The surficial aquifer at the site extends from the water table, which was 3 to 8 ft below ground surface
(bgs) during the design studies, to the top of the clayey, confining layer The hydraulic conductivity of
the surficial aquifer is about 30 ft per day The groundwater in the surficial aquifer flows from the west
to the east and southeast with an average hydraulic gradient of 0 005
During the design studies, the elevation of the potentiometnc surface of the deeper, artesian aquifer m
the site area was about 20 ft below the water table The regional direction of groundwater flow in the
artesian aquifer in the site area is primarily from northeast to southwest
3.0 NATURE AND EXTENT OF CONTAMINATION
The wastes disposed of at the site are classified as cement and noncement wastes The noncement waste
occupied most of the site disposal area and contained antimony, arsenic, cadmium, chromium, lead,
nickel, and PCBs The on-site and off-site groundwater in the surficial aquifer was contaminated
Key SB=Soil Bentomte Wall SC=Source Control Performance Rating l=Remedral objective was met
Site 6
-------
w
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rt
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— !i— HJ — u — 81 — ? — a — y .;„
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PROPERTY LINE -/
STREET
UHWSTimOED AREA
0
KON-CEMENt WASTE AREA 1 '
ADCA WHERE HON-CEUENT WASTE CT
EXISTED ABOVE CEUENT WASTE iv-
CEUENI WASTE AREA
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FIGURE 1
SITE FEATURES
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primarily with chromium and lead On-site groundwater had maximum, unfiltered chromium and lead
concentrations of 560 and 1,600 micrograms per liter (ug/L), respectively The maximum, unfiltered
concentrations of chromium and lead in off-site groundwater were 18 and 16 ug/L, respectively The
groundwater in the artesian aquifer was not contaminated
4.0 CONTAINMENT REMEDY
The containment remedy originally consisted of (1) solidification of contaminated soil and noncement
waste, (2) installation of a composite cap over the solidified, waste and the cement waste, and
(3) extraction and treatment of on- and off-site contaminated groundwater The site remedy did not
address solidification of the contaminated cement waste because it was naturally solidified following
disposal when it contacted water The original site remedy was modified to include installation of a
subsurface barrier wall The final site remedy had the following features
• A soil-bentomte barrier wall that is about 2,100-ft-long, 2 5-ft-thick, is 15 to 25-ft-deep,
is keyed at least 3 ft into the clayey, confining layer and has a design permeability of less
than 1 x 10"7 centimeter per second (cm/sec)
• A composite cap with the following six components (in ascending order) (1) a prepared,
random fill base for site grading and for supporting the soil liner, (2) a 1-foot-thick,
compacted clay liner with a permeability of 1 x 10"7 cm/sec, (3) a 40-mil-thick, high-
density polyethylene geomembrane, (4) a 2 5-foot-thick, sand drainage layer, (5) a 0 5-
foot-thick topsoil layer, and (6) a vegetative cover
• Extraction and treatment of on-site contaminated groundwater in excess of that needed
for solidification of purposes
• Extraction and treatment of off-site groundwater with contaminant concentrations above
the cleanup levels
• A storm water retention basin
5.0 PERFORMANCE EVALUATION
The objectives of the barrier wall design and installation were to (1) facilitate dewatenng of soils and
wastes to be solidified during site remediation and (2) minimize the long-term migration of groundwater
through solidified materials and cement waste after site remediation The objectives of the cap design
and installation were to (1) minimize rainfall infiltration into the solidified materials and (2) promote
drainage from the surface while providing an aesthetic cover that would minimize water and wind
erosion at the site following site remediation
The performance of the containment system was monitored by evaluating the water quality in six off-site
wells The first four rounds of quarterly groundwater monitoring showed significant improvement in off-
site groundwater quality The concentrations of chromium and lead dropped below cleanup levels within
1 5 years of containment system installation, demonstrating that the containment system had achieved its
design objective The improvements in off-site groundwater quality following containment system
installation were the sole reason for not performing the extraction and treatment of off-site groundwater
included in the original site remedy Containment system performance and contributing factors are
discussed further in the following subsections
Site 6
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5.1 Design
The barrier wall design was rated better than acceptable The barrier design was based on the results of
thorough hydrogeologic and geotechnical investigations The bentomte content of the slurry wall was
selected after thorough testing of the permeabilities of several soil-bentorute mixtures However, no
groundwater modeling was performed to support the barrier wall design
The cap design was rated acceptable
5.2 Construction Quality Assurance and Construction Quality Control
The construction quality assurance (CQA) and construction quality control (CQC) for the barrier wall
were rated better than acceptable The trench contractor was experienced, trench excavation was
constantly inspected, and barrier continuity was checked Based on the results of postconstruction
permeability testing of barrier wall samples, the hydraulic conductivity of the barrier wall ranged from
4.0 x 10"8 to 6 3 x 10"7 cm/sec, values below the design hydraulic conductivity of 1 0 x 10~7 cm/sec
The CQA/CQC for cap installation was not available
53 Monitoring
The performance monitoring program for the containment system was rated acceptable and consists of
monitoring wells to collect and analyze groundwater samples downgradient and side gradient of the site
The entire contained area has been solidified and monitoring water levels inside the contained area is
unnecessary.
5.4 Operation and Maintenance
The cap is periodically inspected to evaluate the adequacy of surface water drainage and to identify any
erosion or land subsidence that could affect cap performance Only visual inspections are performed
v
5.5 Other Considerations
Construction and operation and maintenance costs for the barrier wall and cap were not available for
review.
5.6 Remedy Performance
The barner wall; the composite cap, and the natural, clayey deposits that underlie the site form a sound
containment system for the cement and the noncement wastes The containment system in conjunction
with waste solidification has performed effectively, as is indicated by the lowering of contaminant
concentrations in off-site groundwater to below cleanup levels following the installation of the
containment system (see Figure 2)
6.0 SUMMARY
Site 6 is located in the southeastern United States The site is about 5 acres in size and was initially
operated as a borrow area for sand When borrow operations ceased, excavated pits at the site were used
for disposal of wastes, including construction and demolition debns, cement kiln dust, battery wastes,
Site 6
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25
ON-SITE WELLS
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20
15
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CLEAN-UP LEVEL
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MW-2 MW-3
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OFF-SITE WELLS
CLEAN-UP LEVEL
t J
MW-11S MW-12S MW-13S MW-14S MW-15 MW-16 MW-17 MW-18 MW-19 MW-20
D UNRLTEHED S RLTEHED :
Site 6
FIGURE 2
LEAD CONCENTRATION IN
GROUNDWATER SAMPLES
Tetra Tech EM Inc
Site 6
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waste from an automobile shredder, and household waste Waste disposal activities at the site
contaminated on- and off-site groundwater with several metals
A soil-bentomte barrier wall was installed on site in 1993 to encircle the solidified noncement waste and
cement waste A composite cap was installed at the site in 1995 The designs of the barrier wall and cap
were rated better than acceptable and acceptable , respectively The CQA/CQC for the barrier wall was
rated better than acceptable The CQA/CQC for the cap was not evaluated because of lack of
information The performance monitoring program for the site was rated acceptable The barrier wall,
the composite cap; and the natural, clayey deposits that underlie the site form a sound containment
system for the cement and the solidified noncement wastes The containment system has performed
effectively and met the remedial objectives
Site 6
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SITE?
1.0 SITE DESCRIPTION AND HISTORY
Earner Type
Remedial Objective
Performance
SB
SC, Lower
water table
2
Site 7 is located in northeastern United States The site includes a 66-acre refuse area and an 11-acre
stressed vegetation area Both areas he adjacent to a perennial stream that is a tributary to a major nver
The site was originally a sand and gravel quarry and was operated as a landfill from 1963 until 1981
The landfill received indiscriminately dumped municipal, chemical, and hospital wastes This dumping
resulted in contaminated surface water and shallow groundwater A subsurface barrier wall, cap, and
leachate collection and pretreatment system were constructed at the site in 1990 Figure 1 shows the
general features of the site
2.0 GEOLOGIC AND HYDROGEOLOGIC SETTING
The site is located on the Atlantic and Gulf Coastal Plain The site area is underlain by unconsohdated
layers of sands and clays deposited in a relatively extensive horizontal sequence with a gentle
southeastern dip The unconsohdated formations underlying the landfill (in descending order) are the
Mount Laurel Sand and Wenonah, Marshalltown, Enghshtown, Woodbury, Merchantville, and Magothy
and Rantan Formations The adjacent stream valley also contains recently deposited alluvium
The landfill is located within an outcrop of the Mount Laurel Sand and Wenonah Formation The upper
Mount Laurel Sand consists of hght-gray to tan, medium- to coarse-grained, quartz sand with glaucomte
and ranges in thickness from 0 to 65 feet in the area of the site The Marshalltown Formation underlies
the Mount Laurel Sand and has a thickness of about 20 to 30 feet The Marshalltown Formation is
composed of medium to dark ohve-gray, fossilrferous and micaceous, very fine-grained, silty sand and
sandy to clayey silt
Groundwater in the Mount Laurel Sand aquifer flows east under the landfill and discharges to the
adjacent stream The aquifer's hydraulic conductivity ranges from 9 1 x 10"4 to 2 0 x 10"2 centimeters per
second (cm/sec) The amount of groundwater flowing through the site area and discharging to the stream
is about 80,000 gallons per day (gpd)
The Marshalltown Formation's hydraulic conductivity tends to decrease with depth and ranges from
1 8 x 10"4 to 3 9 x 10"4 cm/sec, values of 1 8 x 10"2 cm/sec or less were found m more than half the
samples collected from the formation
The Enghshtown Formation is a confined aquifer whose piezometnc surface lies about 10 feet above the
top of the Marshalltown Formation Groundwater in the Enghshtown Formation flows east and appears
to be unaffected by the adjacent stream hi this formation, the hydraulic gradient across the site area
appears to be constant, and the hydraulic conductivity ranges from 1.2 x 10"2 to 4 2 x 10"3 cm/sec The
amount of groundwater flowing through this formation under the site area is about 101,000 gpd
Because of the piezometnc heads in the Mount Laurel Sand and the Enghshtown Formation, the vertical
leakage from the Mount Laurel Sand through the Marshalltown Formation into the Enghshtown
Key SB=Soil Bentonite Wall
S=Source Control Performance Rating- 2=Evidence suggests objective may be met
Site 7
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Formation under the site is estimated to have been 10,000 gpd before construction of the barrier wall In
the area of the stream, the piezometnc head of the Enghshtown Formation is greater than that of the
Mount Laurel Sand or the stream Therefore, vertical leakage occurs upward from the Enghshtown Sand
through the Marshalltown Formation into the stream valley at an estimated rate of 19,000 gpd
3.0 NATURE AND EXTENT OF CONTAMINATION
The Mount Laurel Sand aquifer is heavily contaminated with organic compounds, including
dichloroethanes, dichloroethenes, tnchloroethanes, tnchloroethenes, benzene, toluene, xylenes, ketones,
and phenols Inorganic chemicals found in the aquifer include arsenic, cobalt, iron, magnesium, sodium,
and calcium Hospital wastes have also been found on site
Indicator analyte concentrations at the site include
• Total volatile organics 400 mg/L
• Total organic carbon 1,200 mg/L
• Total organic halides 65 mg/L
• Chemical oxygen demand 3,900 mg/L
• Chromium 5 4 mg/L
Lead 0197 mg/L
Iron. 300 mg/L
« Nickel 5 4 mg/L
Organic contaminants have been found in the Marshalltown Formation to depths of 40 feet below ground
surface (bgs) No evidence of contamination has been found in the Enghshtown Formation aquifer
4.0 CONTAINMENT REMEDY
The objective of the containment remedy for the site is the prevention or mitigation of the off site
migration of hazardous substances The following remedial measures were implemented
A subsurface barrier wall that is about 8,350 linear feet long, 20 to 70 feet deep, and
3-feet thick and that has a 5-foot key
• A roller-compacted concrete retaining wall
• A leachate collection and pretreatment system
A cap that has a 2-foot clay barrier layer, drainage layer, cover soil, and vegetative layer
• Active landfill gas collection and treatment (one gas collection well per acre)
• Dewatenng, excavation, and filling of lagoons
• Monitoring
Site?
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5.0 PERFORMANCE EVALUATION
The performance of the containment systems was evaluated based on quarterly and annual groundwater
monitoring results
Groundwater quality data has shown that the barrier is functioning as intended Only one downgradient
monitoring well has consistently shown contamination The contaminant levels in this well have been
gradually decreasing over time For example, from September 1994 to June 1995, contaminant levels in
the well decreased as follows
• Benzene 429to3mg/L
• Chlorobenzene 16 to 4 mg/L
• Vinyl chloride- 0 3 to 0 mg/L
• Arsenic 44 to 10 mg/L
By comparison, typical contaminant levels in the leachate within the barrier wall are significantly higher
• Benzene, up to 6,260 mg/L
• Chlorobenzene: up to 23 mg/L
• Vinyl chloride, up to 141 mg/L
• Arsenic, up to 190 mg/L
Containment system performance and contributing factors are described further m the following
subsections
5.1 Design
The barrier design was rated better than acceptable with respect to industry practices as described in
Section 3, Volume I The design followed protocols established by the U.S Army Corps of Engineers
Significant positive features of the design included leachate-backfill compatibility testing The bottom of
the barrier was keyed 5 feet into the Marshalltown Formation Additionally, detailed hydrogeologic
models of the area were completed A roller-compacted concrete retaining wall was constructed along a
steep slope of the site to permit the barner to be constructed
5.2 Construction Quality Assurance and Construction Quality Control
The barrier construction quality assurance (CQA) and construction quality control (CQC) were rated
better than acceptable. Generally, CQA/CQC procedures conformed to established industry practices
Significant positive features of the CQA/CQC program included use of a remote backfill mixing area and
postconstruction bonngs These bonngs showed that the m-place backfill had a permeability in the range
of 1 x 10"8 to 9 x 10'9 cm/sec
53 Monitoring
Monitoring at the site was rated less than acceptable Monitoring wells currently exist only outside the
hydraulic barrier at the downgradient region of the containment, whereas monitoring well pairs are used
at the upgradient region Two wells are sampled quarterly, and the samples are analyzed for volatile and
semivolatile organic compound (VOC and SVOC, respectively), pesticide and PCBs, and inorganic
contaminants. Six additional wells are sampled semiannually, and the samples are analyzed for VOCs
Site? 4
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and arsenic only Surface water in the adjacent stream is sampled quarterly at upstream, midstream, and
downstream locations, and the samples are analyzed for VOCs, SVOCs, pesticide and PCBs, and
inorganic contaminants The leachate is sampled quarterly, and the samples are analyzed for VOCs,
SVOCs, pesticide and PCBs, and inorganic contaminants The filtercake produced by leachate
pretreatment on site is sampled annually, and the samples are analyzed for pH, flashpoint, RCRA metals,
"D" code orgamcs, total cyanide, total sulfide, and PCBs Figure 2 provides a summary plot of select
indicator analyte concentrations in shallow groundwater and changes over time for a typical
downgradient monitoring well
Hydraulic head monitoring of the leachate collection system indicates that water levels in the system are
maintained below the top of the hydraulic barrier
5.4 Operation and Maintenance
Operation and maintenance activities at the site include maintaining the on-site leachate pretreatment
facility and the multilayer cap Cap maintenance includes vegetation and erosion control and repair of
any damage
5.5 Other Considerations
The construction costs of the remedial measures were as follows
• Earner $3,120,885 ($7 81 per square foot of the barrier wall)
Multilayer cap $17,073,616
• Gas collection system $4,154,859
Leachate collection system: $1,833,841
• Roller-compacted concrete wall $3,563,023
5.6 Remedy Performance
Monitoring has shown the concentrations of site contaminants to be decreasing in the shallow
groundwater outside the barrier The leachate collection system is functioning to remove contaminated
groundwater from the site However, one of the objectives of the site remedy was to lower the water
table elevation in the Mount Laurel Sand to substantially reduce the potential for downward vertical
migration through the Marshalltown Formation into the Englishtown Formation Figure 3 shows the
intended impact of containment on water table elevations within the contained area of the site No water
level data was available within the barrier wall Therefore, it is not possible to determine if the
downgradient vertical migration has been reduced. However, the water quality outside the wall indicates
that the remedial objectives may have been met
6.0 SUMMARY
Site 7 is located in northeastern United States The site includes a 66-acre refuse area and an 11-acre
stressed vegetation area Both areas lie adjacent to a perennial stream that is a tributary to a major nver
The Mount Laurel Sand aquifer beneath the site is heavily contaminated with organic compounds,
including dichloroethanes, dichloroethenes, tnchloroethanes, tnchloroethenes, benzene, toluene, xylenes,
ketones, and phenols Inorganic contaminants found in the aquifer include chromium, nickel, and lead
Hospital wastes have also been found on site Organic contaminants have been found in the
Site 7
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50
40
30
O
20
10
benzene
chlorobenzene vinyl chloride
Contaminant
arsenic
first sample s latest sample I
[Note Readings are for a monitonng well outside and downgradient of the barrierJ
Site 7
FIGURE 2
SHALLOW GROUNDWATER CONTAMINANTS
Tetra Tech EM Inc
Site 7
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5
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20
-20
-40
-60
400 800 1200 1600 2000 2400 2800
10 X VERTICAL EXAGGERATION
LEGEND
-^ —. WATER LEVEL IN MT LAUREL/WENONAH PRIOR TO
CAPPING a SLURRY WALL
-R~— WATER LEVELIN MT LAUREL/WENONAH AFTER
CAPPING a SLURRY WALL
-57 ENGLISHTOWN PIEZOMETRIC SURFACE
3200
3600
4000
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FIGURE 3
PIEZOMETRIC LEVELS
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Marshalltown Formation to depths of 40 feet bgs No evidence of contamination has been found in the
Englishtown Formation aquifer To minimize off-site migration of contaminants, a soil-bentonite barrier
was included as part of the overall containment system, which also included a leachate collection and
pretreatment system, a landfill gas collection system, and a multilayer cap
The design and CQA/CQC of the barrier were rated better than acceptable The performance monitoring
of the barrier involved construction inspections, use of piezometers, and leachate monitoring The
performance of the containment in limiting the vertical leakage through Marshalltown Formation into the
Englishtown Formation is not known However, the remedial objective of improving downgradient
water quality may have been met
Site?
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SITES
1.0 SITE DESCRIPTION AND HISTORY
Earner Type
Remedial
Objective
Performance
SP
SC
X
Site 8 is a 22 5-acre tract of land The site area was extensively used for sand mining in the 1950s and
1960s From about 1966 until 1971, the site was permitted by the state to accept industrial waste
material from a variety of generators, including refineries and chemical plants An estimated 80 million
gallons of industrial waste was disposed of in the main waste lagoon, and an estimated 300,000 cubic
yards of contaminated sludge and soil was present on site The site's disposal permit was eventually
revoked, and the site was closed in 1971 The closure settlement required the operator to remove on-site
tankage and other aboveground structures, but the lagoon liquids and sludges were not addressed The
site layout is shown m Figure 1
Site activities and releases have resulted in contamination of the shallow aquifer beneath the site Site
remediation has included in situ bioremediation for the lagoon sludges and shallow alluvial groundwater
A sheet-pile barrier was built in 1989 to control flood waters around the lagoon and to prevent migration
of contamination below the lagoon A second sheet-pile barrier was built in 1994 to contain an area of
known dense nonaqueous-phase liquid (DNAPL)
2.0 GEOLOGIC AND HYDROGEOLOGIC SETTING
The site is located in the flood plain of a large nver and is situated on the associated alluvial soils, which
consist of interbedded clay, silt, and sand that are common throughout the Gulf Coastal Plain The site
was extensively mined for sand in the 1950s and 1960s Three aquifers exist below the site The shallow
alluvial aquifer has been extensively contaminated by waste disposal at the site The shallow aquifer
consists of two permeable zones referred to as the SI (shallower) and INT (intermediate) zones The SI
zone is encountered from about 15 to 30 feet below ground surface (bgs) and has a permeability on the
order of 1 x 10"3 to 1 x 10"4 cm/sec The INT zone is located from approximately 35 to 45 feet bgs and
has a permeability on the order of 1 x 10"4 to 1 x 10"s cm/sec The two units are separated by a
discontinuous clay stratum referred to as Cl that ranges from 0 to 7 feet in thickness Although they are
separated by a clay stratum, aquifer tests have shown that the two units are hydrauhcally connected
Groundwater flows to the south in the two shallow alluvial zones
The second aquifer is the Riverdale sand, which is encountered about 110 feet bgs This aquifer is
separated from the alluvial aquifer by an approximately 70-foot-thick clay stratum referred to as C2 The
sheet piles at Site 8 are keyed into the C2 stratum This zone historically contained low concentrations of
several volatile organic compounds that were attributed to the cracked casing of a monitoring well, which
has since been plugged
The third aquifer is a major aquifer for the region This aquifer is present several hundred feet below the
site and has not been impacted by site activities
Key SP=SheetPile SC=Source Control Performance Rating X=Insufficient data to determine if remedial objectives were met
Site 8
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MONITORING WELLS i^
SCREENED IN SI UNIT . -"^
MONITORING WELLS X"
SCREENED IN INT UNIT /
MONITORING WELLS SCREENED
THROUGH SI a INT UNITS
S2 (DEEP AQUIFER)
MONITORING WELLS
PRODUCTION WELLS SCREENED
IN SI UNIT USED FOR
VERIFICATION MONITORING o too 400
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Site 8
FIGURE 1
SITE PUN
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3.0 NATURE AND EXTENT OF CONTAMINATION
Liquids and sludges disposed of on site contained a wide variety of orgamcs, metals, and polychlonnated
biphenyls (PCB), including the following
« Volatile organic compounds (VOC), including benzene, toluene, ethylbenzene,
chloroform, dichloroethanes, and vinyl chloride (up to 400 mg/L for a single
contaminant)
• Pentachlorophenol (up to 750 mg/L)
• Numerous base/neutral orgamcs (up to 5,000 mg/L)
• Pesticides (up to 20 mg/L)
« Metals (up to 5,000 mg/L for a single metal)
The shallow aquifer is contaminated with dissolved phase and DNAPL to a depth of approximately
50 feet bgs The dissolved-phase plume extends about 1,000 feet off site to the south
4.0 CONTAINMENT REMEDY
A record of decision (ROD) for the site was signed on March 24,1988 The remedy for the site includes
(1) m situ biodegradation of sludges and contaminated soils, (2) recovery and treatment of contaminated
groundwater, (3) flood control measures to isolate the site from the 100-year flood plain of the nearby
river, and (4) a slurry wall to restrict migration of contamination in the shallow aquifer below the main
waste lagoon In 1989, flood waters from the nver inundated the site As a result, plans for flood control
were accelerated A combined flood and migration control wall to be built of steel sheet piling was
designed
The sheet-pile barrier, which surrounds the lagoon as shown in Figure 1, was completed in 1990 and is
referred to as the flood wall The flood wall consists of 16 H-piles for the access gate foundation and
996 sheet-pile pairs for the perimeter The total length of the flood wall is approximately 2,900 feet The
top of the flood wall is 3 feet higher than the 100-year flood level The bottoms of the 65- to 75-foot-
long sheet piles are keyed into the clay stratum underlying the INT zone
In 1993, DNAPL was discovered in recovery well INT-11, which is south and outside of the flood wall
Following this discovery, a focused investigation and feasibility study concluded that a second sheet-pile
wall referred to as the INT-11 area cutoff wall should be built to contain potential DNAPL migration
from this area The second wall, which is shown in Figure 2, is 205 feet long and is keyed a minimum of
5 feet into the C2 stratum underlying the INT zone This wall was completed in June 1994
Remediation of the lagoon sludges has been completed, and in situ bioremediation of the alluvial
groundwater in the S1 and INT zones continues The groundwater remediation system includes a
network of pumping and injection wells located inside and outside both walls, nutrient levels in the
subsurface are maintained through use of the injection wells
Site 8
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PREV SUPPLIED
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TELEPHONE UNE
HOPE PRODUCTION WATER UNE
HOPE INJECTION WATER UNF
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St INJFCIIOII WEtt
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INT INJECTION WELL
INT MONITORINO WELL
IMT PRODUCTION WELL
DESTROYED OR ABANDONED WELL
CONE PENETROHETER (OPT) LOCATION
S1-65
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Site 8
FIGURE 2
INT- II AREA CUTOFF WALL
7etra Tech EM me
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5.0 PERFORMANCE EVALUATION
The primary design objective for the flood wall was flood control, and consequently most of the design
effort was apparently focused on flood control No specific monitoring procedures have been identified
that evaluate the effect of the flood wall on contaminant or DNAPL migration The primary design
objective for the INT-11 area cutoff wall, however, was to prevent DNAPL migration from this area
Focused testing has been conducted to evaluate the performance of the INT-11 area bamer
The following subsections summarize flood wall and INT-11 area cutoff wall performance
5.1 DESIGN
The design of the flood wall was rated below average in terms of being a subsurface containment bamer,
and the INT -11 cutoff wall was rated average with respect to the industry practices described in Section
3, Volume I The design report for the flood wall acknowledges that there are inherent difficulties in
sealing the interlock between piles Thus the designs for both walls did not include sealing of the sheet
interlocks The flood wall design report does not address potential subsurface dissolved-phase or
DNAPL contaminant migration through the sheet-pile interlocks However, the design report does
assume that (1) installation of the sheet piling through the depth of the shallow aquifer would
immediately reduce the flow of groundwater under the lagoon; and (2) within 2 to 4 months, groundwater
flow through the sheet-pile joints would be further reduced to a minimum by the natural rust formation
and silt blockage that would occur in the joints
The design report addresses the corrosion potential of the steel pilings and determines that cathodic
protection would be unnecessary
The flood wall design effort included a thorough geotechmcal investigation involving drilling of soil
bonngs and cone penetrometer testing along the barrier alignment Soil samples were collected and
tested for electrical resistivity, gradation, plasticity, moisture content, undramed shear strength, and
unconsohdated-undrained tnaxial compression The geotechmcal evaluation focused on the following
items
• Lateral stability
• Sheet-pile driveabihty
• Construction considerations
• H-pile foundations
• Earthwork
For the INT-11 area cutoff wall, a target permeability of 1 x 10~7 cm/sec was established
5.2 CONSTRUCTION QUALITY ASSURANCE AND CONSTRUCTION QUAIITY CONTROL
CQA could not be rated from the available information For the flood wall, construction quality control
(CQC) activities consisted of (1) observing the driving of H-piles and sheet piles, including the numbers
of blows, general placement, batter, and vertical alignment, and (2) observing the driving resistance of
the bottom 15 feet of selected sheet-pile pairs (the frequency was not specified) Driving resistances
generally ranged from 50 to 150 blows per foot but were as high as 300 blows per foot in a few rare
cases
Site 8
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The visual observations indicated that the high driving resistances did not appear to cause damage to the
sheet pries However, damage to the top of sheet piles was generally associated with a sheet-pile pair
that had become interlocked with an adjoining sheet In these cases, twisting and bending of the top
6 to 12 inches of the sheet piles were observed
5.3 MONITORING
Monitoring was rated below average because specific monitoring protocols to evaluate the performance
of both walls as migration control barriers do not appear to have been established Monitoring for
DNAPL migration is limited to detection of DNAPL in site wells
Both walls create hydraulic barriers, and water levels are typically lower inside the walls than outside
However, gradient reversals resulting from use of groundwater recovery wells inside and outside both
walls, variable pumping rates, as well as intermittent pumping have been documented
Mobile DNAPL is known to exist in the shallow aquifer within the flood wall, and nonmobile DNAPL
residue exists within the INT-11 area cutoff wall Additionally, the remediation system designers have
acknowledged that additional areas of DNAPL may be identified through normal system operation and
that such areas may require other remedial actions in the future
A permeability certification test was conducted on the INT-11 area cutoff wall after construction was
completed On August 22,1994, all recovery and injection wells within a 120-foot radius of the INT-11
cutoff wall were turned off to establish baseline conditions The test was conducted from August 31
through September 14,1994 Tests were conducted on each of the three sides of the wall (east, south,
and west) For each test, one well near the center of each side was either pumped or injected, and
groundwater elevations on both sides of the wall were monitored Each test consisted of a pumping or
injection phase followed by a recovery phase However, this test was inconclusive because cyclic
pumping at wells outside the 120-foot radius affected groundwater levels in the SI and INT zones during
the test Therefore, a modeling approach was used to evaluate the wall's permeability The field test was
simulated using Visual MODFLOW and by applying a sensitivity analysis for the wall's effective
permeability to determine the best fit for the observed data The modeled permeability certification test
indicated that the effective permeability of the INT-11 area cutoff wall is 1 x 10"10 cm/sec The
certification test further indicated that this result is equivalent to 1 x 10"9 cm/sec for a conventional,
2.5-foot-thick, slurry wall Based on this test, the INT-11 area cutoff wall meets the target permeability
value of 1 x 10"7 cm/sec However, an oversight contractor for the U S EPA reviewed the sensitivity
analysis and determined that (1) the 1 x 10"10 cm/sec result is not necessarily conclusive and (2) a result
of 2 3 x 10"7 cm/sec is also valid but not necessarily conclusive
In June 1995 (five years after installation), a section of the flood wall was exposed by excavation and
inspected using visual and ultrasonic techniques The inspectors reached the following conclusions
• No evidence of seepage was observed at wall joints despite a 103-inch head differential
across the wall
• No evidence of corrosion was observed
• Ultrasonic surveys provided no evidence of wall corrosion
SiteS
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• The wall thickness equaled or exceeded the original wall thickness, in some areas, wall
swelling had been caused by pile driving
5.4 OPERATION AND MAINTENANCE
The corrosion potential of site soils has been evaluated, and it has been determined that the corrosion
potential is not significant However, the remediation system designers have acknowledged that cathodic
protection may be needed m the future
5.5 OTHER CONSIDERATIONS
No other significant performance factors were identified or evaluated
5.6 REMEDY PERFORMANCE
Overall, groundwater chemistry and elevation data indicate that the groundwater remediation system at
the site is successful in terms of both contaminant migration control and contaminant recovery Figure 3
illustrates how VOC concentrations have decreased since groundwater remediation began m 1992 The
site's first 5-year review has been completed, and the 5-year review report indicates that DNAPL and
DNAPL residues are contained by the flood wall and the BSTT-ll area cutoff wall Remediation of the
lagoon sludges and soils is complete The former lagoon has been filled with soil and vegetated The
groundwater remediation system is operating However, future remedial actions may be necessary to
address the continued presence of DNAPL in the subsurface
6.0 SUMMARY
Two sheet-pile walls have been used at the site in conjunction with a groundwater remediation system to
prevent migration of contaminated groundwater and DNAPL away from source areas Overall, the entire
remediation system at this site, of which the barriers are only part, is achieving its objectives However,
there does not appear to be an adequate monitoring system to determine the effectiveness of the barriers
in controlling contaminant migration In addition, the sheet-pile wall designers have acknowledged
inherent difficulties in sealing the underground interlocks, although modeling and visual inspection
indicate low permeability and no evidence of leaking
Sue 8
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START
REMEDIATION
Benzene
Toluene
1.2DCA
Vinyl Chloride
•— Chloroform
-100
100
200 300 400
PROJECT DAY (1=1/09/92)
500
600
700
Site 8
FIGURE 3
VOC REDUCTION IN GROUNDWATER
WELL S-106
Tetra Tech EM Inc
Site 8
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SITE 9
1.0 SITE DESCRIPTION AND HISTORY
Earner Type
Remedial Objective
Performance
SB
SC,
Hydraulic
containment
X
Site 9 is located in northeastern United States and covers about 371 acres. The site is bounded by a
residential community, primary and secondary roadways, and wetlands
The site functions as a sanitary landfill for waste disposal Landfilled materials included vegetable and
animal wastes as well as food processing and industrial wastes Fill was placed at the site from the early
1960s until the mid-1970s The current operating authority began operations at the site in 1980 To
support continued landMhng operations at the site, a subsurface barrier wall and a leachate collection
system were proposed and constructed in 1995 to contain on-site leachate and groundwater The site
location is shown in Figure 1
2.0 GEOLOGIC AND HYDROGEOLOGIC SETTING
The site is located on the Atlantic and Gulf Coastal Plain The site is underlain by Tnassic sedimentary
rocks These rocks consist of reddish-brown sandstone, shale, siltstone, and conglomerate
The regional geology of the site area is characterized by a deep bedrock trough that is about 1 mile wide
in the vicinity of the landfill Glacial fall covers the bedrock over most of the region and averages 25 feet
in thickness Varved silts and clays were deposited over the glacial fall A "sand sheet" of glaciofluvial
sediments lies over the varved silts and clays
The groundwater system in the site area consists of a series of alternating aquifers and aquicludes
conforming to the dip of the bedding planes The water-bearing fractures in each aquifer are generally
continuous, but hydraulic connection between individual aquifers is poor Pumping test data indicates
that the direction of highest hydraulic conductivity parallels the strike of the beds
The average laboratory permeability of the varved silts and clays is 9 x 10"7 centimeters per second
(cm/sec) The average laboratory permeability of the sand sheet is 1 x 10"6 cm/sec
3.0 NATURE AND EXTENT OF CONTAMINATION
Site groundwater contains elevated levels of total dissolved solids, chemical oxygen demand (COD),
chlorides, and metals, as shown below
• Total dissolved solids up to 7,800 mg/L
• COD up to 2,500 mg/L
• Chlorides up to 4,600 mg/L
• Iron up to 89 mg/L
Lead up to 2,000 mg/L
• Copper up to 100 mg/L
Off-site groundwater contamination has not been found at levels requiring remedial action
Key SB=Soil Bentorate Wall SC=Source Control Performance Rating X=Insufiicient data to determine if remedial objectives were met
Site 9
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Site 9
Site 9
FIGURE 1
SITE LOCATION
Tetra Tech EM Inc.
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4.0 CONTAINMENT REMEDY
The remediation objective -was to prevent off-site migration of leachate and groundwater Therefore, a
leachate collection system, pumping station, transfer line, and slurry trench cutoff wall were constructed
at the site in 1995 The implemented remedy involved active containment and had the following general
features
• A subsurface barrier wall that is about 18,000 linear feet; 15 to 45 feet deep, 3 feet wide
and that has a 3-foot key
• A leachate collection system that is about 9 to 17 feet deep and that has a 16- and 20-
inch diameter high density polyethylene (HDPE) pipe
• A leachate transfer line (12-rnch diameter, HDPE pipe)
• A leachate pumping station structure
• Four inclinometers
5.0 PERFORMANCE EVALUATION
The performance of the barrier is not monitored because of the current active status of the landfill The
operating authority is connecting the site leachate collection system to the local wastewater treatment
system Until the connection is completed, leachate will not be collected Containment system
performance and contributing factors are described further in the following subsections
5.1 Design
The barrier design was rated acceptable with respect to industry practices described in Section 3, Volume
I The design generally followed established U S Army Corps of Engineers guidance Significant
positive features of the design effort included constant trench-side inspections of the trench and key
depth Additionally, the backfill was completely composed of off-site soil and sodium montmonllonite
bentomte Backfill was mixed in a mobile pugmill, which was used to optimize the characteristics of the
backfill No cap has been constructed at the site
5.2 Construction Quality Assurance and Construction Quality Control
Earner construction quality assurance (CQA) and construction quality control (CQC) were rated
acceptable Generally, the CQA/CQC procedures conformed to established industry practices. Before
construction, the contractor performed backfill-leachate compatibility testing to determine the optimum
backfill mixture for the site
5.3 Monitoring
For an operating solid waste landfill, site groundwater quality must be monitored according to a plan
approved by the state regulatory agency Monitoring wells have been installed outside the barrier, but no
monitoring of the barrier or groundwater is being performed to assess the containment system's
performance. Leachate is not currently being pumped from the site
Site 9
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5.4 Operation and Maintenance
Cost or any other significant information for the site is not available
5.5 Other Considerations
The operation and maintenance related information of the site is not available
5.6 Remedy Performance
The overall performance of the bamer could not be determined because of the lack of monitoring
6.0 SUMMARY
Site 9 is located in northeastern United States and covers about 371 acres The site functions as a
sanitary landfill for waste disposal Landfilled materials include vegetable and animal waste, as well as
food processing and industrial wastes The site is underlain by Tnassic sedimentary rocks The
groundwater system in the site area consists of a series of alternating aquifers and aquicludes conforming
to the dip of the bedding planes The water-bearing fractures in each tabular aquifer are generally
continuous, but hydraulic connection between individual tabular aquifers is poor Pumping test data
indicates that the direction of highest permeability parallels the stake of the beds Site groundwater
contains elevated levels of total dissolved solids, COD, chlorides, and metals To prevent further
contamination of nearby wetlands and off-site groundwater, a soil-bentomte bamer was installed as part
of a containment system that also included a leachate collection and transfer system The design and
CQA/CQC of the bamer were acceptable Leachate collection and treatment are not yet underway No
performance monitoring of the bamer is currently performed
Site 9
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SITE 10
1.0 SITE DESCRIPTION AND HISTORY
Earner Type
Remedial
Objective
Performance
SB
SC,
Hydraulic
gradient
Site 10 is located on a several thousand acre facility in the western United States Hazardous wastes
have been deposited on 1,750 acres of the facility The facility was established in 1942 and has been
used to manufacture, test, package, and dispose of various chemical warfare agents, and munitions,
rocket fuels, herbicides, and pesticides In 1947, portions of the facility were used for the manufacture of
chlorinated benzenes and the pesticide DDT After 1970, the facility activities focused on activation of
chemical warfare materials by caustic neutralization and incineration Facility operations ended in the
early 1980s
Facility activities resulted in widespread on- and off-site groundwater contamination The site remedy
included installing a hydraulic cutoff wall and a groundwater extraction and recharge system to curtail a
contaminant plume migrating off site at the northwestern site boundary (see Figure 1) The cutoff wall
was installed in 1983 The groundwater extraction and recharge system became operational in 1984 No
cap is present on site
2.0 GEOLOGIC AND HYDROGEOLOGIC SETTING
The site is located in the high plains groundwater region The topographic relief at the site is about
200 feet, and the land surface generally slopes northwest toward a nearby nver The overburden consists
primarily of alluvial clays, sands, silts, gravels, and some cobbles ranging in thickness from 0 to 70 feet
The underlying bedrock units consist of deltaic shales, claystones, sandstones, and conglomerates The
uppermost bedrock formation lies about 250 to 400 feet below the site and contains occasional lignite
beds The bedrock surface reflects the erosional development of a local nver valley during the
Quaternary period. Consequently, the bedrock surface is characterized by isolated bedrock highs and
numerous paleochannels The primary contaminant pathway in the site area coincides with two
intersecting, alluvium-filled paleochannels in the bedrock surface
Groundwater is obtained from alluvial deposits and bedrock aquifers, including the underlying bedrock
formations in the site area Bedrock formations constitute important aquifers in the area and are tapped
by a large number of stock, domestic, and municipal wells The alluvial deposits are capable of yielding
large supplies of water where they are sufficiently thick and saturated The uppermost bedrock unit and
alluvial aquifers are interconnected and act as a single aquifer regionally, although greater
transmissivities generally exist in the alluvial aquifer The bedrock aquifer is frequently under artesian
conditions, causing groundwater in the bedrock to recharge the local alluvial aquifer Flow in the alluvial
aquifers below the site vanes from artesian to semiconfrned to unconfmed The regional groundwater
flow direction is from south to north toward the nver. Primary groundwater flow and contaminant
transport are in an alluvial sand and gravel aquifer overlying the bedrock unit This alluvial aquifer is
5 to 20 feet thick in the site area Transmissivities in the alluvial aquifer range from 33,000 to 405,000
gallons per day per square foot (gpd/ft2) Hydraulic conductivity values in the alluvial aquifer average
2,365 feet per day (ft/day) A slug test conducted in a bedrock sand lens indicated a hydraulic
conductivity of 0 14 ft/day.
Key SB=Soil Bentomte Wall SC=Source Control Performance Rating 2=Evidence suggests objective may be met
Site 10
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LEGEND
A EXISTING EXTRACTION Y/ELL
U EXISTING INJECTION ,YLLL
Site 10
Site 10
FIGURE 1
SITE FEATURES
Tetra Tech EM Inc.
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3.0 NATURE AND EXTENT OF CONTAMINATION
Wastes generated from various military and industrial operations were routinely discharged into several
unlined evaporation ponds at the facility This practice continued until 1956 when an evaporation basin
with an asphalt liner was constructed Solid wastes have been burned at various site locations Chemical
spills have occurred in and around the site These actions have resulted m widespread contamination of
groundwater by a host of inorganic and organic contaminants, such as chloride, fluoride,
dusopropylmethyl phosphonate (DIMP), dicyclopentadiene (DCPD), dibromochloropropane (DBCP),
organosulfur compounds, organichlonne pesticides, volatile aromatic compounds, and volatile
organohalogen compounds
In 1980, a groundwater study indicated that a narrow plume of groundwater containing several
contaminants, including DIMP, DBCP, chloride, fluoride, endrrn, and dieldrrn, was leaving the site from
its northern and northwestern areas Although the contaminants detected m the plume could not be
traced back to a particular source on site, they were known to be associated with operation of the disposal
basins, chemical manufacturing plants, and waste handling systems
4.0 CONTAINMENT REMEDY
The remedial objective at the site was to capture and remove organic contaminants, particularly DBCP,
from the groundwater crossing the site boundary A combination of groundwater extraction and
recharge system and a 1,425-foot-long, 3-foot-wide soil-bentorute cutoff wall was installed along the
northwestern site boundary to intercept the contaminated groundwater The cutoff wall is keyed at least
5 feet into the unfractured and unweathered shale of the bedrock Any sandstone encountered below the
alluvium was removed The average depth of the cutoff wall was about 52 feet below ground surface
(bgs) Groundwater is pumped from a row of extraction wells on the northwestern side of the site,
treated by a carbon adsorption system, and returned to the aquifer through recharge wells
A total of 15 wells are used to extract groundwater Ten extraction wells have a design pumping rate of
100 gallons per minuet (gpm) each The remaining extraction wells are designed to pump at 25 gpm
each A total of 21 recharge wells are drilled 5 feet into bedrock The cutoff wall was installed in 1983
The groundwater extraction and recharge system became operational in 1984
In 1989, low concentrations of contaminants were detected in off-site groundwater near the cutoff wall
Field investigations conducted in 1990 revealed that (1) an alluvial channel was acting as a pathway for
groundwater in the alluvial aquifer to move around the cutoff wall and (2) a plume containing low
concentrations of dieldnn was present southwest of the cutoff wall As a result, the existing cutoff wall
was extended about 650 feet to the northeast in 1990, and two additional extraction wells were installed
south of the cutoff wall in 1991 The cutoff wall extension was 3 feet wide and was keyed at least 5 feet
into the underlying bedrock (or less if the bedrock could not be excavated to this depth) Pumping rates
for the two additional extraction wells averaged about 1 and 2 gpm.
5.0 PERFORMANCE EVALUATION
The cutoff wall and the groundwater extraction, treatment, and recharge system were jointly designed to
intercept and treat contaminated and potentially contaminated groundwater that flows toward and across
the northwestern site boundary and to return treated groundwater to the aquifer Groundwater quality
data indicates that the initial systems were only partially effective- contaminants were flowing around
the wall and off site Modifications to the systems appear to have halted off site migration of
contaminants Containment system performance and contributing factors are described further in the
following subsections
Site 10 3
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5.1 Design
The cutoff wall design was rated acceptable based on industry standards discussed in Section 3, Volume
I Evaluation of the groundwater extraction and recharge system is not within the scope of this study,
however, the design of the groundwater extraction and recharge system appears to be acceptable The
design of the cutoff wall and the groundwater extraction and recharge system was based on the results of
a groundwater modeling effort
5.2 Construction Quality Assurance and Construction Quality Control
The construction quality assurance (CQA) and construction quality control (CQC) of the cutoff wall were
rated better than acceptable Backfill slump and gradation testing were measured once for every 300
cubic yards. Trench depth soundings were conducted every 10 feet Bentonite slurry density, filtration,
slump, and sand content were measured at least twice each day A slump of 3 to 6 inches was considered
acceptable. Slurry viscosity was determined once or twice each day with a minimum required reading of
40 seconds Backfill's hydraulic conductivity was measured every 200 feet
S3 Monitoring
The performance monitoring program was rated acceptable Groundwater elevation is measured in 150
wells, groundwater quality data is obtained for 21 monitoring wells located on both sides of the cutoff
wall. Both groundwater elevation and quality data is collected quarterly
5.4 Operation and Maintenance
No information on operation and maintenance activities and associated costs was available for review
5.5 Other Considerations
The construction cost estimate for the 650-foot cutoff wall extension was $242,000 The construction
costs for the original cutoff wall were not available
5.6 Remedy Performance
The original containment remedy system—a combination of groundwater extraction and recharge wells
and a 1,425-foot-long cutoff wall—was only partially effective Site investigations following
implementation of the original containment remedy revealed (1) an alluvial channel that was allowing
contaminants to flow around the existing wall and off site and (2) an additional dieldnn plume located
southwest of the groundwater extraction wells Modifications to the original containment remedy—
including extension of the cutoff wall 650 feet to the northeast—appear to have halted contaminant
migration off site
6.0 SUMMARY
Site 10 is located on a 17,000-acre facility that was used to manufacture, test, package, and dispose of
various warfare agents and munitions as well as to manufacture chlorinated benzenes and pesticide Past
waste disposal practices resulted in widespread on- and off-site groundwater contamination with a host of
inorganic and organic compounds The site containment remedy included installation of a 1,425-foot-
long cutoff wall and a series of groundwater extraction and recharge wells Groundwater extracted from
the site was treated in a carbon adsorption system before its remjection The cutoff wall was installed in
1983, and the groundwater extraction treatment system became operational in 1984 In 1989,
Site 10 4
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contaminants were detected off-site groundwater near the northwestern site boundary, site investigations
revealed an additional dieldnn plume southwest of the extraction wells as well as an alluvial channel
around the northeastern edge of the cutoff wall The containment remedy was expanded m 1990 to
extend the cutoff wall 650-feet to the northeast and again in 1991, to add two extraction wells The
cutoff wall design and the performance monitoring program were rated about average The CQA/CQC
was rated above average. Contaminant plume migration around the cutoff wall has been controlled
through the addition of the northeast wall extension, and recent groundwater quality and hydraulic data
indicates that the wall is performing as intended
Site 10
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SITE 11
1.0 SITE DESCRIPTION AND HISTORY
Earner Type
Remedial
Objective
Performance
SB,CB
SC
X
Site 11 is a Superfund site located in northeastern United States The site, which contains a landfill,
covers about 60 acres The landfill occupies about 30 acres m roughly an I^shape. The site is bounded
to the east by a creek and to the north and west by an operating solid waste complex A site plan
showing basic site features is included in Figure 1
The landfill operated from 1973 through late 1981 as a municipal solid waste landfill During its
operation, the landfill was permitted to accept sanitary and nonchermcal industrial wastes, including
sewage sludge In 1975, an investigation by a state regulatory agency disclosed landfilling of about
95 tons of hazardous chemicals, including heavy metals, phthalates, and vinyl chloride monomers
The selected remedy for the site includes a composite cap, a subsurface barrier wall, an upgradient
groundwater interceptor, a leachate collection and treatment system, disposal of lagoon liquids and
sediments, and a gas collection and treatment system Installation of the containment system was
completed in fall 1992
2.0 GEOLOGIC/HYDROGEOLOGIC SETTING
The geologic setting of the site is characteristic of the Atlantic Coastal Plain Physiographic Province and
consists of Pleistocene deposits, the Merchantville Formation, and the Rantan-Magothy Formation
During the remedial design, soil borings were drilled at 100-foot intervals along the proposed barrier wall
alignment to define subsurface conditions Three main formations were encountered along the wall
alignment From the ground surface to 10 to 25 feet below ground surface (bgs), a silty clay to clayey
sand fill was encountered The fill was underlain by a 10- to 15-foot-thick, natural alluvial deposit of
sandy silt clay to clayey sand Below this soil was a hard, low-hydraulic-conductivity clay of the
Merchantville Formation ranging up to 68 feet in thickness The subsurface barrier wall was keyed into
this clay
The hydrogeology of the site is characterized by a dual aquifer system consisting of a shallow, water
table aquifer in Pleistocene deposits separated from a deep, regional aquifer m the Rantan-Magothy
Formation by a relatively impermeable layer of Merchantville Formation The general flow direction of
groundwater within the Rantan-Magothy Formation aquifer is southeast Because the Merchantville
Formation acts as a confining layer, the hydraulic head within the Rantan-Magothy aquifer is artesian,
and the potentiometnc surface occurs in the Merchantville Formation The water observed in the
Pleistocene deposits was found to occur 12 to 30 feet above mean sea level (msl), and the potentiometnc
surface in the Rantan-Magothy Formation occurred 2 to 7 feet above msl However, because the
hydraulic conductivity of the Merchantville Formation is low and its thickness is up to 68 feet, any
significant hydraulic interconnection between the shallow and deep aquifers was considered unlikely
3.0 NATURE AND EXTENT OF CONTAMINATION
The mam source of environmental concern related to the landfill has been the reported deposition of
about 95 tons of hazardous chemicals at the site, including heavy metals, phthalates, and vinyl chlonde
Key SB=Soil Bentorute Wall CB=Cement Bentomte Wall SC=Source Control Performance Rating X=Insufficient
data to determine if remedial objectives were met
Site 11
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rt
(D
FIGURE 1
SITE PLAN
-------
monomers Sampling and analysis of leachate in landfill wells indicated the presence of volatile organic
compounds (VOC) and heavy metals Leachate seeps have been observed m several areas of the site
Monitoring wells screened for Pleistocene deposit contained VOCs at concentrations ranging from 3 to
232 g/L, m addition, several inorganic constituents were detected at elevated levels However,
monitoring wells screened in the Rantan-Magothy Formation aquifer exhibited groundwater quality
similar to that of regional wells, indicating that the overall water quality in the Rantan-Magothy
Formation had not been impacted by the waste in the landfill A limited air quality investigation was
performed to determine whether VOCs were being emitted from the site Two surveys performed to
monitor on-site manholes, monitoring wells, and leachate lagoons indicated the presence of total VOCs
in air at concentrations ranging from 0 to 40 parts per million (ppm)
4.0 CONTAINMENT REMEDY
The selected remedy for the site involved active containment and had the following general features
• A soil-bentomte barrier that is about 5,240 linear feet long; 20 feet deep (on average),
and 3 feet thick and that has a 3-foot soil key
• A soil-cement-bentomte (SCB) barrier that is about 300 linear feet long, 20 feet deep (on
average), and 3 feet thick and that has a 3-foot soil key
• An upgradient groundwater interceptor system
• A manhole network supplemented by four wells drilled into the landfill to reduce
leachate levels near the slurry wall
• Removal and disposal of lagoon liquids and sediments
• Landfill gas collection and treatment
• A geomembrane standard RCRA-type cap consisting of compacted clay, a geonet, and
protective soil cover
5.0 PERFORMANCE
The performance monitoring plan for the containment is currently being reviewed and is awaiting
approval to be implemented The postconsrruction monitoring plan includes initial, quarterly
groundwater quality monitoring followed by annual groundwater quality monitoring
Surface water quality adjacent to the site has improved since installation of the containment system,
indicating the general effectiveness of the remedy
The leachate collection system presently removes the amount of leachate predicted after the completion
of the containment system, indicating the effectiveness of the barrier wall and the cap
Containment system performance and contributing factors are described further in the following
subsections
Site 11
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5.1 Design
The bamer design was rated acceptable compared to industry practices described in Section 3, Volume I
The barrier wall consists of 300 feet of SCB wall along the 10 percent grade alignment and 5,240 feet of
soil-bentonite wall around the rest of the site along the alignment grade of less than 2 percent During
SCB wall construction, panels were designed to maintain slurry levels. SCB material is self-hardening,
while soil-bentonite materials remain soft and plastic Significant positive features of the design
included installation of alignment borings at 100-foot intervals, testing of more than 54 soil samples, use
of a 3-foot soil key, and thorough compatibility testing No design-level groundwater modeling was
performed Tests of hydraulic conductivity of the backfill material were performed for both the soil-
bentonite and SCB walls
The cap design was rated acceptable The design included a standard RCRA-type cap Significant
positive aspects of the cap design included installation of enough on-site borings to characterize the fall
and its stability and settlement potential
The pumping system design effort involved conventional piping and pumping design activities
5.2 Construction Quality Assurance and Construction Quality Control
Barrier construction quality assurance (CQA) and construction quality control (CQC) were rated better
than acceptable The bamer was constructed using centralized mixing and a computerized pugmill to
feed and monitor backfill mix components For the soil-bentonite wall, confirmation testing included
drilling and collecting one undisturbed sample for each 100 feet of wall installed For the SCB wall, one
confirmation sample was collected for each 50 feet of wall installed Based on testing of undisturbed
samples collected from the completed bamer, the soil-bentonite and SCB walls met the permeability
requirement of less than 1 x 10" cm/sec.
53 Monitoring
The performance monitoring plan for the site was not evaluated because no formal monitoring of
groundwater, surface water, or sediment is currently conducted at the site. The postconstruction
containment monitoring plan is presently under review by the state regulatory organization
5.4 Operation and Maintenance
The operation and maintenance (O&M) plan for the site is being reviewed by the state regulatory
organization.
SJS Other
The costs for the containment totaled $8,900,000 The estimated annual O&M costs total about
$1,200,000
5.6 Remedy Performance
Based on limited evidence, it appears that the remedial objectives may be met The bamer was
determined to be of low permeability, adequately keyed, continuous, and intact based on available
CQA/CQC data. Visual surface water monitoring has indicated improvement since bamer completion.
The cap has functioned effectively to minimize infiltration The long-term performance of the
Site 11 4
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containment system can only be evaluated after extended hydraulic head and groundwater quality
monitoring is performed
6.0 SUMMARY
Site 11 is the 60-acre site that includes a 30-acre, former municipal solid waste landfill Various heavy
metals, phthalates, and vinyl chloride monomers contaminate site soils, surface water, and groundwater
and some contamination is present in off-site groundwater The site lies in the Atlantic Coastal Plain
Physiographic Province and the geology consists of Pleistocene deposits, the Merchanrville Formation,
and the Rantan-Magothy Formation The containment remedy consisted of a soil-bentomte and SCB
barrier, a composite cap, a leachate collection and removal system, landfill gas collection and treatment,
and groundwater collection and monitoring The design and CQA/CQC of the barrier were rated
acceptable and better than acceptable, respectively No data is available on CQA/CQC of the cap
Performance monitoring of the barrier has involved a minimal effort to date only postconstruction
sampling and visual inspection of surface water quality have been performed The remedy's long-term
protectiveness can only be measured through future monitoring efforts
Site 11
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SITE 12
1.0 SITE DESCRIPTION AND HISTORY
Earner Type
Remedial
Objective
Performance
VBG
SC, Reduce
leachate generation
Site 12 is located on a 17,000-acre facility in the western United States The facility was established in
1942 and has been used to manufacture, test, package, and dispose of various chemical warfare agents
and munitions In 1947, portions of the facility were used for the manufacture of chlorinated benzenes
and the pesticide (DDT) After 1970, primary activities focused on demilitarization of chemical warfare
materials Site operations ceased in the early 1980s
Site 12 covers a portion of about 1,750 acres of the facility The site consists of trenches that were used
from 1952 to 1965 to dispose of liquid and solid wastes generated from the manufacture of pesticide
Waste disposal m trenches resulted in widespread, on- and off-site groundwater contamination A cap
and a barrier wall were installed at the site in 1991 as a temporary remedy to limit off-site migration of
contaminated groundwater The barrier wall was installed using a vibrating beam technique The final
remedy for the site has not yet been selected The general site layout, including the locations of the
barrier wall and groundwater quality monitoring wells, is shown in Figure 1
2.0 GEOLOGIC AND HYDROGEOLOGIC SETTING
The site is located within the High Plains Groundwater Region The topographic relief at the site is
about 200 feet, and the land surface generally slopes northwest toward a nearby nver. The overburden
consists primarily of alluvial clays, sands, silts, gravels, and some cobbles ranging in thickness from 0 to
as much as 70 feet In some places the alluvium is overlain in places by more recent deposits of
windblown silt and sands The underlying bedrock units consist of deltaic shales, claystones, sandstones,
and conglomerates The bedrock displays a gentle regional dip to the southeast
Groundwater is obtained from alluvial deposits and bedrock aquifers in the region Bedrock formations
constitute important aquifers in the area and are tapped by several thousand stock, domestic, and
municipal wells. The alluvial deposits are capable of yielding large supplies of water where they are
sufficiently thick and saturated The regional groundwater flow direction is from south to north toward a
nearby nver
The site is underlain by up to 10 feet of moderately well sorted, fine-grained, unconsohdated sand of
eohan origin This eolian sand unit is underlain by about 8 to 15 feet of silty clay of eluvial origin The
eluvial clay unit forms a low-permeability layer underlying the eohan sand unit Bedrock underlies the
eluvial clay unit and is composed of siltstones and claystones The depth to bedrock along the barrier
wall ranges from 19 to 26 feet below ground surface The barrier wall is keyed into the clay unit or the
bedrock
3.0 NATURE AND EXTENT OF CONTAMINATION
Wastes generated from various military and industrial operations were routinely discharged into several
unlined evaporation ponds at the facility This practice continued until 1956, when an evaporation basin
with an asphalt hner was constructed Solid wastes have been burned at various site locations Chemical
spills have occurred in and around the site manufacturing complexes These actions have resulted in
widespread introduction of a host of organic and inorganic contaminants The organic contaminants
detected on site include volatile organic compounds (VOC) such as (1) benzene, (2) ethylbenzene,
Key VGB=Vibrating Beam Groutwall SC=Source Control Performance Rating 2=Evidence suggests objective may be met
Site 12
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DOWNGRADED
UPGRADIENT
LEGEND
Monitoring Well
Alluvial
Piezometer
D,rUU>ad
Surface Topography
MBO " (Contour Interval =
05 feel)
SCALE 1 3000
0 Ti ISO FEBf
l-j M~T=T~l-4 M I
Site 12
FIGURE 1
SITE FEATURES
letro Tech EM Inc.
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(3) chlorobenzene, (4) xylenes, (5) toluene, (6) 1,1-dichloroethane and 1,2-dichlorethane, (7) methyl
chloride, (8) methylene chlonde, (9) chloroform, and (10) tnchoroethene
Other site contaminants uiclude chlonde, fluoride, diisopropylmethyl phosphonate, dicyclopentadiene,
dibromochloropropane, organosulfur compounds, and organochlonne pesticides
4.0 CONTAINMENT REMEDY
A passive containment system was selected as a temporary site remedy with the objective of reducing
generation and lateral migration of leachate from the trenches A final site remedy has not yet been
selected The passive containment system consists of a barrier wall encircling the disposal trenches and a
cap over the area encircled by the barrier wall The passive containment system has the following
features
• A subsurface barrier wall that is about 2,500 feet long, 19 to 29 feet deep, and 4 inches thick
To minimize generation of strong odors associated with excavation of trenches for installing
a subsurface barrier, the barrier wall was constructed using the vibrating beam technique
The southern side and the southern half of the eastern side of the barrier wall were keyed at
least 3 feet into the eluvial clay unit, and the rest of the wall was keyed into bedrock to a
depth beyond which the vibrating beam could not penetrate.
• A soil and vegetative cover cap for the area encircled by the barrier wall The cap has about
12 inches of compacted soil fill overlain by 20 inches of uncompacted soil planted with
crested wheat grass The intent of the vegetative cover was to reduce erosion and
consumptively utilize soil moisture
No groundwater extraction or recharge wells are present within the contained area Construction of the
containment system was completed in 1991
5.0 PERFORMANCE EVALUATION
The objective of the cap and barrier wall are to reduce generation and off-site, lateral migration of
leachate from the wastes disposed of in the trenches The performance of the containment system is
monitored using five pairs of piezometers (PW1A/PW1B through PW5A/PW5B) and several
groundwater quality monitoring wells located upgradient and downgradient of the contained area.
The water level within the contained area has risen because groundwater is not extracted from the
contained area Groundwater levels in piezometer pairs indicate an inward gradient along the southern
side of the barrier wall and an outward gradient along the northern side (see Figure 2) The extent of
groundwater mounding against the northern side of the bamer wall vanes depending on whether the wall
intercepts the eolian sand or the eluvial clay Groundwater quality data for locations upgradient of,
within, and downgradient of the bamer wall shows little change in contaminant concentrations over time
The presence of stable contaminant concentrations downgradient of the wall, and mounding of the
groundwater against the northern bamer wall suggest that the cap and wall are limiting the generation
and migration of leachate across the site Containment system performance and contnbuting factors are
discussed further in the following subsections
Site 12
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PIEZOMETER PAIR 1A/1B
5240
Jun-94
Aug-94 Sep-94 Od-34 Nov-94 Deo-94 Jan-95 Fe6-95 Mar-95 Apr-95 May-95 Jun-95 Juf-95
DATE
524O
5239-
o
i
LLJ
111
CD
CC
HI
5238- -
5237-
5236-
5235-
•
5234-
5233-
5232-
5231-
PIEZOMETER PAIR 3A/3B
- i : i "" • "" 7" ; « | ""
I . OUTSIDE SLURRY WALL^
I::,:.- «
! i : : : 1 : '.'.'•
May-94 Jun-94 JufS4 Aug-94 Sep-94 Od-94 Nov-94 Dec-34 Jan-95 Fei-95 Mar-95 Apr-95 May-95 Jun-95 JuI95
DATE
Site 12
FIGURE 2
WATER TABLE ELEVATIONS
VERSUS TIME
Tetra Tech EM Inc
Site 12
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5.1 Design
The bamer wall design was rated acceptable A geophysical screening survey was conducted to
determine a barrier wall alignment that would minimize the chance of encountering unexploded ordnance
or subsurface obstructions during construction Borings along the alignment appear to have been drilled
at spacings of less than 100 feet, based on review of the engineering drawings The barrier wall was
constructed using the vibrating beam technique The slurry consisted of a stable, colloidal suspension of
IMPERMIX, a self-hardening grout The barrier wall was keyed (1) into bedrock on the northern side,
western side, and northern half of the eastern side of the bamer wall to a depth beyond which the
vibrating beam could not penetrate, and (2) at least 3 feet into the eluvial clay unit on the southern side
and southern half of the eastern side of the bamer wall No information was available on (1)
geotechnical testing, (2) groundwater modeling, or (3) protection from surface loading
Insufficient data was available to evaluate the design of the soil and vegetative cap The cap over the
area surrounded by the barrier wall was constructed using compacted fill for the bottom 12 inches
overlain by 20 inches of uncompacted soil suitable for supporting vegetation No geomembrane barriers
were used The compacted soil layer was placed before the bamer wall was constructed The
uncompacted soil layer was placed after barrier wall construction was completed, the 20-inch,
uncompacted soil layer covers the bamer wall
5.2 Construction Quality Assurance and Construction Quality Control
The construction quality assurance (CQA) and construction quality control (CQC) for the barrier wall
were rated better than acceptable The wall's continuity and depth were checked by pulling a steel bar
(that extended to the bottom of the bamer wall) horizontally during wall installation Slurry density and
viscosity were measured every 2 hours during wall construction, and filtrate loss in the slurry was tested
once each day Hydraulic conductivity was determined at minimum wall spacings of 200 feet No as-
built records for the bamer wall were available for review
The CQA/CQC for the cap was not evaluated because of lack of inf ormation
53 Monitoring
The monitoring program for the site was rated better than acceptable The monitoring program consists
of 11 groundwater monitoring wells and soil moisture, soil erosion, and vegetation monitoring Water
table elevations and groundwater quality are monitored to evaluate the effectiveness of the bamer wall m
minimizing lateral flow of contaminated groundwater Water level measurements from the piezometers
paired across the barrier wall are used to determine hydraulic gradients across the wall at five locations
The paired piezometers are located about 10 feet inside and outside the bamer wall In addition, six soil
moisture monitoring stations have been installed inside and outside the wall to evaluate variations in soil
moisture in the plant root zone. Soil erosion and vegetation development are monitored because
consumption of soil moisture by vegetation is the primary means of minimizing water infiltration at the
site
5.4 Operation and Maintenance
Visual inspections are periodically conducted at the site to evaluate the adequacy of surface water
drainage and to identify any erosion or land subsidence that could affect the performance of the cap
Sue 12
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5.5 Other Considerations
The capital cost of installing the barrier wall, cap, and monitoring wells as well as associated road work
is estimated to be $1,775,000 The cost of installing the barrier wall is estimated to be $456,000, the cost
of installing the cap is estimated to be $432,000 Annual monitoring and maintenance costs, including
the costs of sample collection and analysis, water table monitoring, data reporting, health and safety
supplies, vegetative cover maintenance, and waste handling, are estimated at $59,000
5.6 Remedy Performance
Substantial head differences have been established across the northern side of the barrier wall, indicating
that the area enclosed by the barrier wall is hydraulically isolated from its surroundings Although water
quality data shows no observable change in the distributions and concentrations of groundwater
contamination, water level data suggests that the barrier wall is reducing lateral migration of
contaminants emanating from the trenches
6.0 SUMMARY
Site 12, which is located in the western United States, is part of a 17,000-acre facility that was used to
manufacture, test, package, and dispose of various chemical warfare agents and munitions and to
manufacture chlorinated benzenes and pesticide The site consists of trenches that were used from 1952
to 1965 to dispose of liquid and solid wastes generated from pesticide manufacturing In 1991, a
containment system consisting of a barrier wall surrounding the trenches and a vegetated soil cap over
the area inside the barner wall was installed.
The design and CQA/CQC of the barner wall were rated acceptable and better than acceptable,
respectively. The design and CQA/CQC of the cap were not evaluated because of lack of information
The performance monitoring program for the site was rated better than acceptable Soil moisture data
indicates that the cap is appropriate for this climate and is preventing water infiltration into the trenches
Water quality data does not indicate any reductions in contaminant concentrations in groundwater
downgradient of the barner wall, however, water level data indicates that the bamer wall is reducing
lateral migration of contaminants emanating from the trenches, which was the principal objective of the
containment system
Site 12
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SITE 13
1.0 SITE DESCRIPTION AND HISTORY
Earner Type
Remedial
Objective
Performance
SB
SC
Site 13 is located in the northeastern United States The site occupies approximately 16 acres of a former
gravel pit
Between 1958 and 1971, household wastes, liquid and semi-solid chemical wastes, and other industrial
wastes were buned at the site The landfill was closed by the State in 1971 The site is bordered on two
sides by streams The wastes have leached out of the embankments of the streams contaminating the
surface waters and marsh areas around the streams and the lake into which they discharge A subsurface
barrier wall, cap, and groundwater flushing and treatment system were constructed at the site between
1983 and 1992 Figure 1 shows the general features on the site
2.0 GEOLOGIC/HYDROLOGIC SETTING
The site is located in the Atlantic and Gulf Coastal Plain The landfill is underlain by unconsolidated to
poorly consolidated fluvial and marine deposits of Cretaceous and Tertiary age The surficial geologic
material is of Upper Miocene age and belongs to the Cohansey Sand Formation Flow through the
Cohansey Sands into the adjacent stream is in the range of 20,000 to 62,000 gallons per day This layer
ranges in thickness from 16 to 55 feet and is separated into the upper and lower Cohansey at the site
Underlying this formation are the silty and clayey sands of Middle Miocene age known as the Kirkwood
Formation This layer is approximately 51 feet thick. Between the two sand units and serving as the top
member of the Kirkwood Formation is a dense silty clay zone known as the Kirkwood Clay Hydraulic
conductivity of this layer is approximately 2 8 x 10"4 feet/day. This layer ranges in thickness from 9 to 17
feet and dips to the southeast
3.0 NATURE AND EXTENT OF CONTAMINATION
The unlmed landfill is reported to have received millions of gallons of toxic and hazardous wastes
including solvents, paint thinners, formaldehyde, paints, phenol and amine wastes, dust collector
residues, resin, and ester press cakes The contaminants of concern are various volatile organic
compounds, semi-volatile organic compounds, and heavy metals
4.0 CONTAINMENT REMEDY
The remedial design outlined by the United States Environmental Protection Agency (USEPA) in their
Record of Decision (ROD) called for the mitigation and minimization of the migration of hazardous
substances The following remedial measures were implemented
Slurry wall (-8,350 If, -20 - 70 ft deep, ~ 3 ft thick, 2 ft. minimum key),
• Groundwater flushing/treatment system, Cap (40 mil HDPE, drainage layer, cover soil,
vegetative layer),
Key SB=Soil Bentomte Wall SOSource Control Performance Rating 2=Evidence suggests objective may be met
Site 13
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Not To Seal*
RELOCATED RUN
BRANCH
EXISTING SHALLOW DRAIN
BRANCH DIVERSION CHANNEL
[FD01, FD02. FD03]
LEGEND:
E - Ertredlon W«!l
C - Cohanitv Wtll
SW - Surfaot WqtV Sample
FO - Franeh Drain SampU
Site 13
FIGURE 1
SITE MAP
7etra Tech EM Inc.
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• Collector system (for seeps and shallow groundwater)
The system was designed to contain waste and allow extraction of contaminated groundwater, treatment,
and flushing of the landfill contents with water The flushing process was intended to accelerate waste
degradation and reduce contained source material
5.0 PERFORMANCE
The performance of the containment system will be determined based on the quarterly and annual
groundwater monitoring program of both inside and outside monitoring locations
The containment system performance and contributing criteria are described further in the following
sections
5.1 Design
Barrier design achieved an average rating relative to established standards The design followed protocol
established by the U S Army Corps of Engineers (COE) and was performed by a consultant Some
significant positive features of the design included backfill compatibility testing utilizing site leachate
Additionally, a detailed hydrogeologic investigation of the area was performed The key at the bottom of
the barrier was two feet into the clay layer
Earner and containment design were complicated by the site's elevation change and potential differential
hydraulic heads across the barrier The design considered the eventual upgradient mounded water,
creating an inward gradient and the down slope outward gradient, creating potential leakage Head
differential was also a design concern because of impacts associated with groundwater extraction and
flushing
Additionally, several remediation systems have been installed outside the barrier to capture leakage
French drain and trench drain systems were installed northeast of the landfill area to capture
contaminated groundwater downgradient and outside the barrier The french dram system replaced an
earlier well point system The french dram was installed to limit the movement of contaminated
groundwater into the adjacent marsh area The french dram captures groundwater from the Lower
Cohansey Sands, and as such, shallow groundwater is seeping to the surface along the slope northeast of
the containment area A separate trench drain was installed to capture seepage in the Upper Cohansey
and shallow subsurface soils
The flushing and treatment system removes contaminated groundwater from extraction wells located in
the containment area Water is pumped from the a local clean aquifer and is used to flush the
contaminants from the site This clean water is injected into the contained landfill through injection
wells and infiltration trenches Subsequently, water is extracted and treated at the onsite facility This
water is discharged to the local sanitary sewer The onsite treatment includes precipitation, flocculation,
settling, clarification and filtration for removal of metals, air stripping for removal of volatile organic
compounds, and carbon polishing of the liquid stream to remove the remaining less volatile organic
compounds
The cap consists of an HDPE membrane with a drainage layer directly above A layer of cover soil and
top soil were then placed Access roads are surfaced with crushed stone
Site 13
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5.2 CQA/CQC
Barrier CQA/CQC was rated slightly above average Generally, the procedures conformed to the
established standard protocol CQA was performed by the COE Some significant positive features of
the CQA program included backfill sampling performed at a frequency of one per 100 lineal feet of
trench, or one sample per 324 cubic yards of backfill. This is an above average frequency for backfill
testing Additionally, preconstruction borings were completed by the Contractor on 100 foot maximum
centers along the centerlrne of the trench alignment However, slurry viscosity was permitted to be used
at 35 seconds, which is less than the industry standard of 40 seconds
Cap CQA was rated average The HDPE geomembrane and cover soil cap were installed based on an
industry standard specification Destructive and non-destructive testing was performed to verify the
seaming of the geomembrane.
53 Monitoring
Monitoring at the site includes quarterly and annual monitoring of wells and surface water locations
Groundwater is tested for metals, volatiles, and senuvolatiles Water in the pumping system is tested
daily or weekly at various sampling points for VOAs and BNAs Figure 2 provides a summary plot of
select indicator compounds and changes over time These are maximum values for the series of wells
sampled The data show a general decrease in contaminant concentrations over time in the zone
immediately outside the containment system This suggests that dissolved contaminant mass outside the
containment system has decreased over time and that contaminant migration from the containment
system has been limited
The hydraulic head monitoring indicated an inward gradient is being maintained on the west side of the
site. However, an outward gradient is evident on the east side of the site The outward gradient is
primarily due to the site topography and the use of the groundwater flushing system The flushing
system artificially raises the interior groundwater levels, which are subsequently lowered during
groundwater extraction. Groundwater levels are measured continuously using a computer system
connected to paired piezometers Figure 3 presents a summary of the hydraulic head across the barrier
for select monitoring locations during periods of high hydraulic head differential
5.4 Operation and Maintenance
Operation and Maintenance at the site consists of maintaining the groundwater flushing and treatment
system and the associated equipment. Regular maintenance of the cap consists of vegetation and erosion
control and repair of any damage No barrier maintenance is performed
5.5 Cost
Design cost for the barrier and cap was $1.45 million Construction costs were $3 09 million
Site 13
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60
40
.o
Q.
Q.
g
&
S
o
o
O
•§
20
I
Methylene chlonde
Chloroform
Benzene Arsenic
1,2-Dichloroethane
Contaminant
Zinc
Chromium
11985 11995
Site 13
FIGURE 2
CONTAMINANT CONCENTRATION vs TIME
fetro Tech EM Inc
Site 13
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LO
Tt
m
o
m
CO
1
m
Measurement, feet
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5.6 Remedy Performance
The monitoring system was rated slightly better than acceptable Monitoring has shown the
concentration of site contaminants to be decreasing in the shallow groundwater outside of the barrier
while the groundwater flushing and treatment system is functioning to remove contaminated groundwater
from the site The contaminant levels have been gradually decreasing over time as shown above
Decreases are shown on Figure 2 Groundwater head differentials across the barrier are apparently
greater than anticipated and have created some operational restrictions and perhaps increased barrier
leakage Groundwater extraction rates have not achieved predicted rates Reduced groundwater
extraction may lengthen predicted cleanup time needed to flush the landfill Seeps and leakage down
gradient from the barrier have been greater than expected but have been controlled with drain systems
Despite operational difficulties, the containment and flushing system continues to manage contamination
offsite and slowly reduce contaminants inside the barrier.
6.0 SUMMARY
Site 13 is located in New Jersey and occupies approximately 16 acres of former gravel pit Between
1958 and 1971, household wastes, liquid and semi-solid chemical wastes, and other industrial wastes
were buned at the site The landfill is reported to have received a variety of hazardous wastes including
solvents, paint thinners, formaldehyde, paints, phenol and amine wastes, dust collector residues, resin,
and ester press cakes The landfill was closed by the State in 1971. The remedial design, which called
for the mitigation and minimization of the migration of hazardous substances, included a slurry wall,
groundwater flushing/treatment system, and cap Additional groundwater collection systems have been
installed outside the barrier to prevent further offsite contamination Design was acceptable and
CQA/CQC of the barrier involved a slightly above acceptable effort The cap CQA rated average
Despite operational difficulties, the containment and flushing system continues to manage contamination
offsite and slowly reduce contaminants inside the barrier
Site 13
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SITE 14
1.0 SITE DESCRIPTION AND HISTORY
Earner Type
Remedial
Objective
Performance
PC
Hydraulic
cutoff
The site is an open pit mine in British Columbia, Canada The depth of the open pit was 850 feet, and
was scheduled to reach 1,000 feet The south pit wall was adjacent to the shore line Waste rock from
the mining operation was disposed in the sea inlet, thereby extending the shore line out up to 3,000 feet
The mine operator wanted to find a way to mine the body of ore behind the south pit wall in order to
extend the mining operation This would require moving the south pit wall through the highly pervious
rock waste dump
2.0 GEOLOGIC AND HYDROLOGIC SETTING
At the location of the remedy, the site geological formations consist of
• Waste rock dump, with a very an extremely variable matrix from clay size to 4 to 5 feet
in diameter The thickness of this layer was approximately 60 feet
• Beach deposits of 5 to 10 feet thick
• A glacial till layer, approximately 40 feet thick The very dense till consisted mostly of
impervious clay silt material, with some pervious outwash ream
• The bedrock, a massive tuff
The waste fill was extremely pervious. In some zones, its permeability was in the range of
1 x 10 2cm/sec
3.0 NATURE AND EXTENT OF CONTAMINATION
No known contamination existed at the site
4.0 CONTAINMENT REMEDY
The extension of the mining operation southward toward the inlet required the design and installation of
a vertical barrier to control seepage into the open pit through the highly pervious waste fill and the
somewhat pervious outwash
The mine operators considered using the grouting or slurry wall technology and after extensive review
with specialty designers and contractors decided to control the seepage by means of a slurry wall The
design was based on pushing back the south wall of the pit by 300 feet, thereby allowing the recovery of
an additional 83 million tons or ore The final pit depth was 1,200 feet below sea level (or the lowest
point in the world)
Key PC=Plastic Concrete Wall Performance Rating l=Remedial objective was met
Site 14
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The physical characteristics of the seepage barrier were
Type of wall Plastic concrete built by the panel method
Length- 4,100 feet
Depth' 73 feet average, 110 feet maximum
Thickness 30 inches
Key. 15% of the wall was built on the top of bedrock, the remaining had an 8 foot key m the till
material
5.0 PERFORMANCE EVALUATION
5.1 Design
In view of the complexity of the project and the risk involved relative to a safe operation of the mine, the
design effort was very extensive Factors to consider were the stability of the south slope and its
deformation, the deformabihty of the barrier, the nsk of piping or blowout through the wall where it was
installed through very porous waste, and the overall seepage (in case the wall would fissure as a result of
the anticipated slope movement) In addition, the design needed to address the constructability of the
wall with respect to the very difficult site conditions The design included
• Deformation analysis performed using a finite element analysis stress-strain model (A
onsite test pad was used to determine the elastic modules to use for the loose waste rock
dump.) The deflection and settlement of the top of the bamer were determined to be on the
order of 1 to 2 and 0 5 inches, respectively
• Seepage analysis
• An extensive backfill mix design including special testing designed to subject the backfill to
erosion testing
Final design consisted of the selection of a low strength plastic concrete slurry wall, (28 day unconfined
compressive strength of 220 psi), down to bedrock, or with an 8 foot key into the impervious till
53 CQA/CQC
The cutoff wall was installed by a specialized slurry wall contractor, after a very extensive selection
process. Severe slurry losses were expected during the wall installation through the very pervious fill
Special procedures were developed and tested in the laboratory as well as in the field prior to the wall
installation
Compatibility tests between the bentorute slurry, mixed with fresh water, and the sea water were
conduced prior to the start of the project
The quality control program during installation of the wall was very extensive to ensure the success of
the project, and involved for each slurry wall panel
• Frequent testing of the new and trench slurry to ensure trench stability
• Control of the verticality and thickness of the wall
Site 14
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• Control of the minimum joint thickness between adjacent panels
• Cleaning of joints between panels
• Examination of the cuttings to ensure proper key
• Cleanliness of the trench bottom prior to backfilling the excavated panels
• Control of the mixing and placement process of the backfill
• Testing of the backfill (for strength, defonnabihty, and permeability)
5.3 Monitoring
The vertical barrier was heavily instrumented including
• Inclinometers
• Vibrating wire and standpipe piezometers
• Settlement/movement monitoring of the top of the wall and slope
• Measurement of the rates and flow to pump the water from the bottom of the pits
4.4 Performance
This exceptional project was successfully completed The waste material and beach sand were
dewatered m approximately 2 months, corresponding to a drawdown between 40 and 50 feet Deflection
of the barrier and settlement of its top compared with the design predictions The excavation slope as
well as the water flow remained stable during the life of the project
5.0 SUMMARY
This site is a nonhazardous project
A highly deformable low strength plastic concrete wall was installed to a maximum depth of 110 feet
through very difficult subsurface conditions to prevent sea seepage into a 1,200 feet deep open pit mine
The slurry wall performed as expected for the four year life of the project
Site 14
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SITE 15
1.0 SITE DESCRIPTION AND HISTORY
Earner Type
Remedial
Objective
Performance
SB
SC
1
Site 15 is a sanitary landfill located in the northeastern United States It is bounded on the south by a gas
pipeline and electrical towers and on the north by railroad tracks and electrical towers The landfill
occupies about 137 acres A site plan showing basic site features is presented in Figure 1
The site lies within the Sawmill Creek Basin, which drains into a river located a little over 1 mile east of
the site Originally the entire site was composed of tidal wetlands and mud flats, but portions of the site
have been filled over the years The site vicinity is generally composed of lagoons, mud flats, and
marshes
Phase I of a two-phase landfill improvement program was completed in June 1984 and included
construction of the soil-bentonite barrier along the northern, eastern, and southern perimeter of the
landfill, leachate drains parallel to the cutoff wall, two leachate pump stations, and a stormwater
management system Phase II of the landfill improvements, which was completed in July 1989, included
completion of the barrier, completion of the leachate drain parallel to the wall, and installation of
groundwater monitoring wells, piezometers, and inclinometers
2.0 GEOLOGIC AND HYDROGEOLOGIC SETTING
Subsurface conditions at the site are the result of at least three glacial advances, the last of which created
a lake as the glacier melted and retreated northward Sands and silts were deposited on the bed of the
lake, with the fine-grained, suspended clay settling out The nature of the on-site strata is as follows
Stratum 1 Fill on-site is refuse such as paper products, plastics, textiles, and rubber This fill is 78
to 110 feet thick at the top of the landfill, tapering off to between 9 and 23 feet thick
around the landfill Beyond the limits of the landfill, the first 5 to 12 feet is made up of
fill containing primarily soil (sand, silt, gravel, and organic silt) with concrete, bnck,
wood, and cinder debns
Stratum 2 This stratum contains black-brown organic silt, peat, and varying amounts of fibrous
material It is about 15 feet thick Strata 1 and 2 are often intermixed, as the fill sinks
into Stratum 2 because of its softness
Stratum 3 This stratum contains gray-silty to clayey sand varying in thickness from 0 to 23 feet
Stratum 4 This stratum contains gray-brown varved clay and silt, silty clay, and silt and vanes in
thickness from 100 to more than 180 feet This stratum is medium to very stiff 20 feet
below mean seal level (msl), medium stiff from 20 to 40 feet below msl, and soft or very
soft beneath 60 feet below msl
Key SB=Soil Bentomte Wall
SC = Source Control
Performance Rating 1 = Remedial objective was met
Site 15
-------
X
s s: = -? |
I- II i =-\ »
i*!uii
|
cc a.
i y
Site 15
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The subsurface cutoff wall was keyed into the Stratum 4 varved clay, which exhibits low hydraulic
conductivity Based on 25 tests, the vertical permeability of Stratum 4 is 1 x 10~7 centimeters per second
(cm/sec)
The hydrogeologic setting includes a water-bearing zone overlying the varved clay in Stratum 4
Groundwater flow in Strata 3 is m a westerly direction Eleven groundwater monitoring wells are
installed at the site, some of these are shallow wells, while the rest extend to or into the underlying clay
layer The highest gradient for leachate is m a westerly direction because of the existence of Stratum 3,
which is in contact with the landfill refuse
3.0 NATURE AND EXTENT OF CONTAMINATION
A landfill investigation report evaluated subsurface geology at the site and made recommendations for
construction of landfill improvements One such recommendation included construction of a leachate
management system, with a cutoff wall and leachate drain Also, the state required the site owner to
construct landfill improvements in order to contain leachate within the landfill and minimize leachate
migration Significant leachate contaminants include ammonia, arsenic, and some volatile organic
compounds (VOC) which are present at levels higher than state groundwater standards
The primary improvements consisted of measures for leachate management, landfill expansion, and
landfill closure, including gas venting and groundwater monitoring The landfill expansion involved
excavating an existing lagoon to about 40 feet below existing grades and raising existing landfill grades
4.0 CONTAINMENT REMEDY
The remedy for the site consists of achieving an inward gradient and prevent migration of site
contaminants The 3-foot-thick cutoff wall is keyed into the varved clay in Stratum 4 The leachate
collection drain is below the normal water level in the adjacent meadowlands The leachate collection
drain was designed to maintain an inward gradient along the perimeter of the landfill and act as a
hydraulic barrier to outward movement of leachate The implemented remedy involved active
containment and the following general features
• A soil-bentonite cutoff wall that is 11,230 linear feet long, 20 feet deep, and 3 feet thick
and that has a 2-foot soil key
• A leachate collection system
• Clusters of three piezometers installed both inside and outside the wall at five locations
to determine the groundwater response to leachate collection and pumping
• Eleven groundwater monitoring wells, some of which are shallow while the rest extend
to or into the underlying clay layer
5.0 PERFORMANCE EVALUATION
Laboratory tests conducted on the cutoff wall samples showed that its permeability meets the
1 x 10"7 cm/sec requirement of the state regulatory organization Similarly, the subsurface clay that
constitutes the base of the landfill meets the permeability requirement of the state regulatory
Site 15
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organization The cutoff wall also is keyed 2 feet into an impervious stratum as required by the state
regulatory organization
The perimeter leachate drain, located inside the cutoff wall, captures leachate and conveys it to a
pumping station, which is connected to a sanitary sewer system and treatment plant The leachate drain
creates an inward gradient relative to the surrounding waters Pumping records indicate that the volume
of leachate handled at the pumping station is consistent with the design of the system
5.1 Design
The barrier design was rated acceptable relative to industry practices discussed m Section 3, Volume I
No design-level groundwater modeling was performed for the containment
The closure and postclosure plan for the landfill proposes a final cover layer of 1- to 2-foot thick soil
Vegetation support is to be installed over 88 acres of the side slopes of the landfill
52 Construction Quality Assurance and Construction Quality Control
Barrier construction quality assurance (CQA) and construction quality control (CQC) was rated better
than acceptable Cutoff wall and leachate drain construction was completed along the perimeter of the
landfill. In addition, installation of groundwater monitoring wells, piezometers, and inclinometers was
completed.
Permeability tests were conducted on samples of the soil-bentonite mix during construction and on
undisturbed samples from the completed wall A total of 135 soil-bentonite mix permeability tests were
performed, and an average permeability of 3 4 x 10"8 cm/sec was obtained Also, a total of 50
permeability tests were performed on undisturbed soil-bentonite wall samples, but one test was
performed in the varved clay below the key The average permeability of undisturbed soil-bentonite wall
samples was 5.3 x 10"8 cm/sec
S3 Monitoring
Performance monitoring of the barrier conducted since 1990 was rated better than acceptable
Piezometers were installed at five locations At each location, a cluster of three piezometers was
installed inside the cutoff wall, and a cluster of three was installed outside the cutoff wall Based on
measurements taken, an inward gradient existed to inhibit leachate flow through the soil-bentorute cutoff
wall. With the exception of one location, both the shallow and intermediate piezometers showed an
inward gradient through the cutoff wall (see Figure 2)
The deep piezometers in the varved clay showed about 1-foot-higher head inside the landfill than outside,
indicating an outward flow condition This higher head in the varved clay inside the landfill also caused
an upward flow condition from the base of the landfill and was attributed to excess pore pressure in the
clay stratum, which is higher than the leachate mound However, the outward flow seems to be very
limited and the impact on 1he deeper groundwater is being studied
Eleven groundwater monitoring wells were installed, some of the wells are shallow wells, while the rest
extend to or into the underlying clay layer Groundwater quality monitoring data for only one period is
available Ammonia;, arsenic, and VOCs were detected at levels higher than the groundwater standards
set by the state regulatory organization, however, their concentrations have decreased from their initial
levels
Site 15
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11+00
30+00
50+00
Well Location
55+00
61+00
Site 15
FIGURE 2
HEAD DIFFERENCE ACROSS BARRIER
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5.4 Operation and Maintenance
Operation and maintenance (O&M) requirements for the containment system involved monthly site
inspections, quarterly effluent sampling and well water level readings, and annual well water sampling
since 1990
Leachate levels in the manholes are monitored weekly, while all pipes, manholes, and cleanout risers,
and the leachate force main are inspected monthly
5.5 Other Considerations
No information on cost was available
5.6 Remedy Performance
Remedy objectives regarding hydraulic head were easily met, and groundwater quality outside the
containment is improving The barrier was determined to be of low permeability, adequately keyed,
continuous, and intact based on available data
6.0 SUMMARY
Site 15 is a 137-acre former sanitary landfill Leachate and groundwater are mixed in three strata
overlying a varved clay stratum that vanes in thickness from 100 to over 180 feet The containment
remedy consisted of a soil-bentomte barrier, leachate collection and removal system, and monitoring
The design and CQA/CQC of the barrier were rated acceptable and slightly better than acceptable,
respectively Performance monitoring of the barrier was rated better than acceptable and involved post
construction sampling, installation of clustered piezometers across the barrier, ample groundwater quality
monitoring, and regular inspections The site containment generally met closure plan requirements
Groundwater quality outside the barrier has unproved, and gradients are inward except at one location in
the varved clay layer; however, the low permeabilities at this location make the outward flow negligible
Site 15
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SITE 16
1.0 SITE DESCRIPTION AND HISTORY
Earner Type
Remedial
Objective
Performance
CB
SC, contain
DNAPL
Site 16 is located m a hghtly industrialized setting in the glaciated portion of the Appalachian Mountains
The site covers about 12 acres and is located at the confluence of two shallow nvers The site
topography is relatively flat except for flood control levees constructed along the nvers
The site is the location of a former manufactured gas plant A variety of waste by-products were
generated by coal gasification conducted at the site These were stored in on-site lagoons The waste by-
products are tarlike, dense non aqueous phase liquid (DNAPL) substances that caused contamination in
the on-site soils, groundwater, and adjacent surface water bodies Contamination was identified in 1980
during repairs of the flood control levees along the nvers Starting in 1981, the site underwent a senes of
emergency actions, investigations, and subsequent remediation to remove and control migration of the
DNAPL A cement-bentonite hydraulic cutoff wall was constructed at the site in 1981 to impede the
flow of DNAPL and allow DNAPL extraction by pumping DNAPL extraction by enhanced recovery
techniques as well as further investigation were subsequently conducted at the site A site plan with
basic site features is shown in Figure 1
2.0 GEOLOGIC/HYDROLOGIC SETTING
The local geologic setting consists of unconsolidated glacial and fluvial soils overlying Devonian-age
bedrock The bedrock shale and underlying limestone of this region is characterized by intense, broad,
structural folds with associated minor folding The unconsolidated sods generally consists of varying
fluvial deposits of sands and gravels underlying glacial outwash sands and gravels, a fine-grained, sand
to silt layer with some clay attnbuted to glacial lake deposition, and finally a dense till above bedrock
The permeable gravels extend to about 20 to 40 feet below grade before the lower-permeability, silty
sands are encountered The silty sand unit forms the relatively low-permeability unit below the site and
provided the suitable matenal for keying the cutoff wall
The unconsolidated soils above the till act as a single, unconfined unit transmitting flow from upland
areas to the adjoining nvers The preremediation flow pattern was from west to east and has been
significantly altered by the remedial measures Bedrock hydraulic heads indicate an upward flow into the
unconsolidated aquifer The upper fluvial and glacial sands and gravels have hydraulic conductivities on
the order of 1 x 10"2 to 1 x 10"3 centimeters per second (cm/sec) This is in contrast to the underlying silty
sand, which has conductivities orders of magnitude lower, making the basal silty sand an impediment to
flow but not a confining interval or bottom However, the silty sand interval is believed to be a barner to
DNAPL migration
3.0 NATURE AND EXTENT OF CONTAMINATION
On-site soil and groundwater and off-site groundwater are contaminated with free-phase, tar-like
DNAPLs, BTEX compounds, and several metals such as arsenic These contaminants have been
grouped, for purposes of groundwater remediation, into free-phase and dissolved-phase constituents
This report addresses containment of the free-phase (DNAPL) contaminants at the site
Key CB=Cement Bentomte Wall SC=Source Control Performance Rating 2-Evidence suggests objective may be met
Site 16
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Ground water sampling and level measurement
Site 16
FIGURE 1
SITE PUN
Tetro Tech EM Inc.
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Coal tar was disposed of on-site in a shallow tar pit, providing a source of DNAPL contamination in the
shallow and permeable sands and gravels DNAPL migrated by gravity flow and either was contained in
a minor subsurface depression on the silty sand layer or migrated to discharge to the adjoining nver
Contamination therefore existed on site and off site in subsurface soils, groundwater, and adjacent
surface water and sediments Partial analysis of the coal tar compounds yielded the following
composition
Naphthalenes 36% • Phenanthrene 23%
Acenaphthenes 0 72 % • Anthracene 23%
Fluoranthene "32% • Dimethyl naphthalenes 215 %
Identification of the contamination in 1981 prompted emergency remedial action to cut off the flow of
DNAPL to the adjacent nver and to contain the DNAPL within the site boundary, for later removal
4.0 CONTAINMENT REMEDY
The remedial objective was to intercept the DNAPL by active containment before its discharge to the
adjacent nver The active containment includes installation of a hydraulic cutoff wall, excavation of
some source matenal, and active pumping of DNAPL The remedy was implemented as an emergency
removal action The implemented remedy included the following general features
• A hanging cement-bentomte hydraulic cutoff wall that is 650 linear feet long, 23 feet
deep, and 1 foot thick and that has a 2-foot soil key
• Four DNAPL extraction well nests
• Four pairs of groundwater level momtonng locations paired across the wall
• Several groundwater quality momtonng locations upgradient and downgradient
• Multiple surface water quality momtonng points along the adjacent waterways
• Select on-site source excavation
The hydraulic cutoff wall is notable in several respects The cutoff wall is not circumferential It is
effectively a hanging wall, being keyed into silty sands of moderate permeability. The cutoff wall is tied
to an existing sheet-pile bamer at one end and is connected to the clay core of a flood levee with a grout
curtain on the opposite end The cutoff wall was constructed using a specially designed, 12-inch-wide
backhoe arm and bucket to reduce quantities of contaminated spoil
5.0 PERFORMANCE
Based on the head difference measurements across the wall, the containment system at the site appears to
be effective m limiting migration of DNAPL to the adjacent nver Monitored groundwater quality and
surface water quality do not show discernible trends from 1982 to 1995 The cutoff wall has allowed
extraction of upgradient DNAPL by preventing migration beyond the wall
Site 16
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5.1 Design
The barrier design effort was rated acceptable with respect to industry practices discussed in Section 3,
Volume I Several hydrogeologic and feasibility studies were performed before barrier construction
The barrier mix was designed and tested to achieve a maxrmum permeability of less than or equal to
1 x 10"6 cm/sec target permeability. A thick, earthen cover was placed over the top of the barrier (No
cap was installed at the site ) No known groundwater modeling was performed at the site before
construction to forecast the eventual major changes to groundwater flow patterns The barrier is only
12 inches thick, however, the cement-bentonite mixture provided sufficient strength Detailed
specifications for construction testing were not available and, if not prepared, would be considered a
shortcoming of the design
5.2 Construction Quality Assurance and Construction Quality Control
Overall, the barrier construction quality assurance (CQA) and construction quality control (CQC) were
rated less than acceptable CQA/CQC information was limited, due probably in part to the installation
being an emergency action The contractor possessed significant experience, and the trench sounding
and key confirmation were acceptable. As a cement-bentonite wall was installed, backfill CQA
parameters are not applicable. A possible problem associated with CQA/CQC for this site was that the
construction of the barrier had to be interrupted when a gas hue was encountered, requiring hand
excavation. Also, no postconstruction sampling or testing was identified
53 Monitoring
The postconstruction monitoring effort relative to DNAPL containment was better than acceptable in
several respects Many DNAPL and groundwater quality monitoring points were installed Four pairs of
wells were located across the barrier to monitor hydraulic head and groundwater quality Geophysical
methods were used in an attempt to characterize barrier integrity Also, adjacent surface water quality
was monitored over time
Head measurements were taken across the bamer wall at the four paired monitoring locations over time
Those data are displayed in Figure 2 for biweekly intervals in 1988 and 1989 and for more recent
periods The data indicate that the head loss across the wall was between 1 to 4 feet through the
measured period While this is not a conclusive measure of the wall's integrity, it does indicate the
consistent effectiveness of the wall in impeding groundwater flow
Groundwater quality was measured and reviewed over the past 7 years The results of these
measurements, shown in Figure 3, show no conclusive trend indicating a decline in downgradient
concentrations. However, the objective of the wall was not to contain dissolved-phase contamination but
rather to intercept gravity-driven DNAPL contamination
An attempt was made to measure physical integrity of the wall using self-potential geophysical methods
The streaming self-potential method was used This method measures changes in electrical potential as a
result of ions in solution passing through a porous medium The survey was performed on 25-foot
centers along the cutoff wall and was intended to measure leakage Background noise and poor response
resulted in inconclusive data In areas believed to have some possible leakage based on geophysical
findings, hydraulic head measurements revealed no unusual head loss, and presumably no leakage
Site 16
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10/06/88 10/18/88 11/02/88 11/09/88 11/22/88 12/12/88 01/27/89 02/17/89 03/29/89 04/14/89 06/01/93 11/01/95
DATE
-a- Pair A -o- PairB -&- PairC -B- PairD I
Site 16
FIGURE 2
HEAD DIFFERENCE vs TIME
Tetra Tech EM Inc
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10/88
12/95
10/88
12/95
a Inside
Q Outside
& Inside
0 Outside
Site 16
FIGURE 3
CONCENTRATION vs TIME
Tetro Tech EM Inc.
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5.4 Operation and Maintenance
No operation and maintenance (O&M) information was available O&M of the active portions of the
remediation is not addressed in this evaluation
5.5 Other
Costs for cutoff wall construction and associated work exceeded the original estimates Originally, the
estimate for cutoff wall construction, select excavation, and monitoring well installation and associated
work totaled $180,000 to $280,000 Subsequently, increased excavation and disposal costs increased the
overall cost to about $500,000 Also, the cost to install the cutoff wall (including a 50-foot grout curtain
and monitoring wells) increased to $290,000 because of wider trench widths than expected, additional
handling of material, and the additional cement and bentonite used This makes the total project cost
equal to about $25 per square foot of the wall
5.6 Remedy Performance
The objective of the remedy to cut off DNAPL migration was met The cutoff wall impeded
groundwater flow, prevented further DNAPL migration to the nver, and allowed subsequent DNAPL
extraction by other means.
6.0 SUMMARY
Site 16 is a 12-acre, former manufactured gas plant with DNAPL contamination in site soils and
groundwater The site's location adjacent to two nvers, the absence of an impermeable bottom, and the
need to stop DNAPL migration led to the use of a noncircumferential, hanging cutoff wall This partial
containment was augmented by select excavation of source material, and DNAPL extraction Cutoff wall
installation was performed as an emergency action
The design was rated acceptable and CQA/CQC of the cutoff wall was rated less than acceptable
However, the hydraulic, chemical, and physical monitoring of the cutoff wall involved better than
acceptable efforts Measurements of hydraulic head over time have shown consistently lower head inside
the wall The groundwater quality data does not show discernible trends and actually shows increased
concentrations downgradient of the cutoff wall at some locations, presumably because of the presence of
source material and dissolved constituents Overall, the cutoff wall and associated elements appear to
have been effective in meeting the original objectives of intercepting DNAPL migration and allowing
free-phase DNAPL removal by other means
Site 16
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SITE 17
1.0 SITE DESCRIPTION AND HISTORY
Earner Type
Remedial
Objective
Performance
SB
SC
Site 17 is located in the northeastern United States Site 17 is a 57-acre landfill that rises about 45 feet
above the natural grade and is located on a 144-acre property, a nver runs north of and adjacent to the site
(see Figure 1) The landfill began operation in 1959 and was closed by a state regulatory agency in 1979
During its operation, the landfill accepted more than 17,000 drums of chemical waste, municipal refuse,
and millions of gallons of bulk liquid chemical wastes
Remedial activities at Site 17 included the construction of a soil-bentomte slurry wall and a multi-layer
cap The remedial objective for the containment system was to prevent migration of contaminants from the
site by limiting horizontal and vertical flow of precipitation and groundwater through the landfill
2.0 GEOLOGIC AND HYDROGEOLOGIC SETTING
Site 17 lies m the northern part of the Atlantic Coastal Plain physiographic province It lies on relatively
flat land that gradually slopes toward the nver to the north The surrounding terrain is predominantly
gently rolling coastal plain with marshes and small ndges Beneath the site area he the following geologic
formations (in ascending order) Bedrock, the Potomac Group, Rarttan Formation, Enghshtown Formation,
Marshalltown Formation, Wenonah Formation, Mount Laurel Sand, Navesink Formation, Red Bank Sand,
Hornerstown Sand, and Vincetown Formation Site remedial activities did not involve investigation of
units deeper than the Red Bank Sand
The Red Bank Sand, which is 50 to 60 feet thick in the Site 17 area, is a complex formation containing
four units The lowest unit is a massive, silty, fine-grained sand that is 10 to 20 feet thick This unit is
overlain by a poorly sorted, medium- to coarse-grained sand that is the principal water-yielding layer in the
Red Bank Sand This layer is overlain by the Trnton Sand, which is a 5- to 10-foot-thick, compact,
cemented sandstone with a high percentage of coarse-grained detritus The upper unit of the Red Bank
Sand is an 8- to 12-foot-thick, partially cemented, silty, fine sand The Hornerstown Sand overlies the Red
Bank Sand and is generally considered to be a confimng layer The slurry wall is keyed into the
Hornerstown Sand This layer is an approximately 12-foot-thick, silty, fine sand that has various amounts
of clay The uppermost formation in the landfill area is the Vincetown Formation, a medium-grained sand
that ranges in thickness from a few inches just north of the landfill to about 30 feet on the south side of the
landfill
Two primary aquifers exist in the area around Site 17, one shallow and one deep The uppermost saturated
units (the Vincetown and the Hornerstown Sand Formations) comprise what is referred to as the Water
Table Aquifer The horizontal flow direction in the Water Table Aquifer is north from Site 17 toward the
nver The calculated groundwater flow velocity from Site 17 to the nver ranges from 80 to 740 feet per
year The horizontal flow direction in the underlying Red Bank Aquifer is also north from Site 17 toward
the nver, and the calculated groundwater flow velocity ranges from 12 to 91 feet per year Vertical
groundwater flow in the vicinity of Site 17 is downward from the Water Table Aquifer to the
Key SB=Sod Bentomte Wall SC=Source Control Performance Rating 2+=Evidence suggests objective may be met
Site 17
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II I
-DEP-04
•P-4
DEP-07
PRB-3
LEGEND
SHALLOW PIEZOMETER IN THE VlNCENTOWN
FORMATIOM ANOW WASTE
PLF-4-*!
-J£ Av W p-ia
?*, W
P-8
PRB-3— O PIE20METER W THE RED BANK FORMATION
MONITOTWG mi DESIGNATED FOR
HYDRAULIC MONITORING. (OU1 IMPLEMEMTATtON
WORK PLAN - HYDRAULIC GROUNDWATER
MONITORING - AW)
* NOTE: P-7 TO BE INSTALLED AT FUTURE DATE
P~10
400
600
SCALE IN FEET
Site 17
FIGURE 1
SITE LAYOUT
fetro Tech EM /nc.
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Red Bank Aquifer beneath the landfill and is upward m the valley of the nver Over the entire site area,
vertical groundwater flow is also upward from the Navesmk Formation to the Red Bank Aquifer
3.0 NATURE AND EXTENT OF CONTAMINATION
Groundwater samples collected from monitoring wells located at Site 17 and screened in the Water Table
Aquifer contained a large number of volatile organic compounds (VOC) The dominant VOCs present at
the site, with the maximum concentration reported, are as follows
2-Butanone 190,000
Methylene chloride 125,
« Acetone 1,000 fig/L
Toluene 1,000 (xg/L
• 1,2-Dichloroethane 1,000 ng/L
• Benzene 1,000 pg/L
• Tnchloroethene 1,000 pg/L
Metals including aluminum, chromium, barium, cadmium, cobalt, copper, iron, lead, nickel, manganese,
zinc, vanadium, arsenic, antimony, mercury, and tin have also been found in groundwater samples from
on-site wells
Monitoring results indicate that off-site groundwater contamination in the Water Table Aquifer is confined
to (1) a narrow zone north and northeast of Site 17 between the site and the nver with a total area of about
20 acres and (2) a very narrow zone along the eastern perimeter of Site 17 In the deeper Red Bank
Aquifer, off-site groundwater contamination is found only in the zone north and northeast of the landfill
between the landfill and the nver No groundwater contamination was found in wells completed m the
lower part of the Red Bank Sand below the Red Bank Aquifer
4.0 CONTAINMENT KEMEDY
The U S Environmental Protection Agency (EPA) signed a record of decision (ROD) for the site in
September 1984 The remedial objective for the site as stated in the ROD is to contain site contaminants
and clean up contaminated groundwater and leachate directly below the landfill A hydraulic gradient
performance catena for maintaining a gradient of -0 5 feet inward gradient was also included in the ROD
Remedial construction began in July 1991 and included the following features
• A slurry wall that is approximately 5,965 feet long, 15 to 33-1/2 feet deep, and 3feet thick
with a 2-foot soil key depth
• A leachate collection trench that is about 5,800 feet long; 2 feet wide, and 10 to 18 feet
deep
• Leachate collection wells (21 wells installed at approximately 300 foot intervals)
• A methane gas collection system and methane gas flare
• A water treatment plant
Sue 17
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• A interceptor drain that is approximately 2,800 feet long and extraction wells to collect
contaminated groundwater from the shallow and deep aquifers respectively
• A 57-acre, rmiltalayered cap consisting of a prefabricated bentomte mat, a 40-mil, very low
density polyethylene (VLDPE) geomembrane, a coarse sand drainage layer, filter fabric,
an 18-inch soil cover, and at least 6 inches of topsoil
• A perimeter drainage system
• A hydraulic monitoring system which is described in detail below
Six pairs of piezometers were installed inside and outside the perimeter of the slurry wall These
piezometers were screened in the Vincetown Formation, the waste, or both A Red Bank Aquifer
piezometer was also installed outside the slurry wall at each of the six locations The diameter of each
Vincetown Formation and waste piezometer is 4 niches each, and the Red Bank Formation piezometer was
installed with 2-inch-diameter screen and riser pipe Four piezometers were installed in the central landfill
area and are screened in the Vincetown Formation, the waste, or both
Six monitoring wells are located in or near the central landfill area and are being used to monitor water
levels to above the top of the Hornerstown Formation within the landfill material Two additional
monitoring wells are located beyond the landfill slurry wall and are being used for hydraulic monitoring
All eight wells are screened in either the waste or the Vincetown Formation
5.0 PERFORMANCE EVALUATION
The groundwater monitoring program was designed to monitor the effectiveness of the barrier containment
system by (1) determining the piezometnc level of the shallow water-beanng zone within the landfill
material along the landfill perimeter and outside the slurry wall barrier and (2) monitoring the upward
gradient underneath the landfill by determining the piezometnc level within the Red Bank Aquifer in the
central area of the landfill
Monthly monitoring of the hydraulic head across the barrier indicates that an inward gradient exists A
groundwater status report dated December 28,1995, indicates that inward hydraulic gradients were present
at all paired monitoring points around the landfill In addition, the inward hydraulic gradients at all pairs
exceeded the performance criterion of less than -0 5 feet Particularly significant inward gradients of -8 9
feet were observed at pairs P9-P10 and P11-P12
The leachate collection system presently removes the amount of leachate predicted, and according to the
remedial project manager, the leachate level has dropped since the system began operation
5.1 Design
The barrier containment system design was given an acceptable rating relative to industry practices as
described in Section 3, Volume I The containment system was designed to contain and recover
contaminated groundwater within the landfill A 15-foot wide by 3-foot deep clay bench was installed
around the landfill along the centerhne of the slurry wall Before the slurry wall construction began,
27 soil borings were drilled at about 200-foot intervals along the alignment of the slurry wall to obtain
native soil samples for use in the design of the slurry wall mix and to better define the depth to and
elevation of the Hornerstown Sand The slurry wall is keyed into the Hornerstown Sand The appropriate
soil-bentomte backfill mix was established by laboratory testing The approved slurry mix was 62 percent
Site 17 4
-------
excavated soil, 35 percent borrowed clay, 2 percent dry bentomte, and percent bentomte The mix,
which had a permeability of 1 x 107 centimeter per second (cm/sec) or less, was blended beside the trench
using a power harrow mixer attached to a backhoe and was further blended usmg with a bulldozer to
obtain the specified composition
The cap design was given an acceptable rating relative to industry practices The 57-acre, multilayered cap
was constructed over the entire landfill The cap consists of a prefabricated bentomte mat overlain by a 40-
mil, VLDPE geomembrane Two types of VLDPE were employed for the project based on friction angle
measurements of the material interfaces, which were measured in the laboratory A smooth geomembrane
was installed in areas having a slope no steeper than 15 1 (horizontal to vertical), and a textured
geomembrane was installed on slopes steeper than 15 1 but no steeper than 6 1 In areas where slopes
exceeded 6 1, a 2-foot-thick, compacted clay liner was constructed Once the liner system was completed,
a coarse sand drainage layer, filter fabric, 18 inches of soil cover, and at least 6 inches of topsoil to support
vegetation were installed
5.2 Construction Quality Assurance and Construction Quality Control
Barrier construction quality assurance (CQA) and construction quality control (CQC) were given a better
than acceptable rating relative to industry practices Notably, various tests of the slurry and backfill were
performed For example, tests were conducted on the bentomte powder (one test per shipment), the
bentomte slurry-plant (fourtests per day for viscosity and density and one test per day for filtrate loss and
pH), the mix water (one test per source for chemical analysis), the bentomte slurry-trench (four tests per
day for viscosity and density), and the backfill (three tests per day for slump and density, one test per 2000
cubic yards for gradation, and three tests per 400 feet for permeability). All test results indicated
permeabilities equal to or less than the required 1 x 107 cm/sec
The slurry wall backfill profile was measured and recorded at the end of each workday and at the
beginning of the next workday to verify that the trench had not caved in over the backfill The slope of the
backfill in the trench was typically 10 1 After the completion of the slurry wall, a drill ng was used to
obtain samples of the placed backfill for permeability analysis Laboratory results indicated that all
samples had permeabilities equal to or less than 1 x 107 cm/sec.
Cap CQA/CQC was given a better than acceptable relative to industry practices The rigorous CQC
program used during liner installation included both field testing (destructive and nondestructive) of
production welding and laboratory testing of production welding at all seams All seams were subjected to
100 percent CQC testing, and only one 100-foot seam failed the CQC testing and required reseamrng No
vehicular traffic was permitted on the geomembrane at any time after its installation The drainage layer
was compacted to a minimum relative density of 65 percent Testing was performed at a frequency of five
tests per acre to verify proper drainage layer compaction All seaming operations for the filter fabric were
inspected for compliance with specifications Testing was also performed to verify proper compaction of
the 18-inch-thick soil cover layer
53 Monitoring
The groundwater monitoring program for the site was given an acceptable rating relative to industry
practices The monitoring program was intended to evaluate the hydraulic performance of the landfill cap,
the slurry wall, and the leachate collection system with respect to groundwater quality, leachate generation
rates, and the maintenance of an inward hydraulic gradient Twelve piezometers located inside and outside
the containment wall are used to determine water levels in the shallow water-beanng zone within the
landfill material along the landfill perimeter and outside the slurry wall Information provided by the RPM
Site 17
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for the site indicates that an inward gradient exists and that the slurry wall is containing on-site
contamination The RPM also stated that the leachate level inside the landfill has dropped, which indicates
that the system is operating correctly
Another objective of the groundwater monitoring program was to monitor the upward gradient underneath
the landfill by determining the piezometnc levels within the Red Bank Aquifer and within the shallow
water-bearing zone in the central area of the landfill. No information pertaining to this objective was
available for review
5.4 Operation and Maintenance
The mam operation and maintenance (O&M) manual for the site includes O&M activities for the leachate
collection system, the multilayered cap, and other systems, but no information detailing barrier O&M was
available Monthly monitoring of groundwater levels and quarterly monitoring of groundwater quality are
performed.
5.5 Other Considerations
According to EPA, the cost of remedy design and the remedy for both the landfill and downgradient
contaminated groundwater outside of the slurry wall was $55 million to $60 million
5.6 Remedy Performance
Groundwater levels inside and outside the containment indicate that an inward gradient exists Leachate
levels reportedly have dropped inside the landfill indicating that the wall and the leachate extraction
systems are operating as designed.
6.0 SUMMARY
Site 17 is located in the northeastern United States. The site is a 57-acre landfill contained by a soil-
bentomte bamer and a multilayered cap. The site operated as a landfill from 1959 to 1979 and received
various amounts of municipal and chemical wastes, which resulted in VOC, semivolatile organic
compounds (SVOC), and metal contamination The geology of the site includes the Homerstown Sand
Formation, which is considered to be a confimng layer and which the bamer wall is keyed into This layer
is about 12 feet thick and contains silty, fine-grained sand with varying amounts of clay. Extraction
pumping inside the landfill has created an inward gradient of less than -0 5 feet (the performance criteria)
to control off-site migration of contaminants Monitoring results and post-construction evaluations also
indicate that the bamer containment has been successful in reducing leachate volume to levels predicted
during the system design phase
Site 17
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SITE 18
1.0 SITE DESCRIPTION AND HISTORY
Earner Type
Remedial
Objective
Performance
SB
SC
Site 18 is located in the midwestern United States The site is a former sand and gravel borrow pit
covering about 4 acres The site was used for disposal of industrial and municipal wastes from 1945 to
1977 In 1979 and 1980, the site was capped with compacted clay as an interim measure Construction
of a barrier wall was completed in December 1994 and a permanent site cap was completed in July 1995
Pumping of groundwater from PW-1 and PW-2, which are located outside the barrier wall, began in
September 1995 Pumping of groundwater from PW-3 and PW-4 began in July 1995 Figure 1 shows
the significant features of the site.
2.0 GEOLOGIC AND HYDROGEOLOGIC SETTING
Site 18 is located in the Central Groundwater Region of the United States The site consists of alluvial
deposits of gravel, sand, and silt over bedrock The alluvial deposits are about 90 feet thick, and the
bedrock consists of sandstone, siltstone, and shale The sand and gravel materials are fairly continuous
across the site
The saturated thickness of the sand and gravel aquifer beneath the site vanes from 30 to 45 feet The
sand and gravel aquifer materials range in permeability from 1 x 10"2 to 1 x 10"4 centimeters per second
(cm/sec) The water table is 35 to 40 feet below ground surface (bgs), and groundwater flows to the
southwest toward a major nver Bedrock permeability vanes from 4.4 x 10"5 to 9 5 x 10"5 cm/sec
3.0 NATURE AND EXTENT OF CONTAMINATION
The site contains anthracene residue, salts, and miscellaneous process wastes from an adjoining tar plant,
foundry sand containing heavy metals, phenols, and oils, and other wastes Site contaminants consist
primarily of benzene, toluene, ethylbenzene, and xylene (BTEX), polynuclear aromatic hydrocarbons
(PAH), nonaqueous-phase substances (NAPS), and arsenic The contaminants have moved off site
through the unconfined sand and gravel horizon The concentrations of selected contaminants in the
groundwater are as follows
• Benzene 750 - 5,600
Toluene 1,400 - 3,500
• Ethylbenzene 440 - 1,000 jxg/L
Xylene 990 - 3,200 ng/L
• Arsenic 12 - 59 p,g/L
4.0 CONTAINMENT REMEDY
The penmeter bamer forms a closed loop around the 4-acre waste disposal area The bamer is intended
to enclose the capped wastes and provide a low-permeability bamer to groundwater flow. During bamer
construction, excavated on-site soil was mixed with imported clay and bentomte slurry to make the soil-
bentorute mix that was placed in the excavated trench General features of the corrective action include
the following
Key SB=Soil Bentomte Wall SC=Source Control Performance Rating 2=Evidence suggests objective may be met
Site 18 I
-------
i MW-
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"
'
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m-m**m**»mm*tm***^^ \.
DISPOSAL
AREA BOUNDARY
LEGEND
MONITORING WELL OR
OBSERVATION WELL
PUMPING WELL
75" 0 75' 150'
SCALE 1" = 150'
SITE 18
FIGURE 1
SITE LAYOUT
Tetra Tech EM Inc.
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• A soil-bentomte perimeter barrier that is about 2,000 linear feet long, 80 to 86 feet deep,
and 30 inches thick with a 0 1-foot key into bedrock
• Resource Conservation and Recovery Act (RCRA) Subtitle C Cap consisting of a
12-mch thick layer of soil overlain by a geosyntheuc clay liner, a 40-mil high density
polyethylene liner, geonet and 24-inch thick soil cover
• Four groundwater extraction wells (two inside and two outside the barrier)
• 24 wells to monitor remedial action performance, however, only 9 wells are being used
• Delineation of the NAPS layer
Groundwater pumped from the four extraction wells is treated in an on-site treatment plant
5.0 PERFORMANCE EVALUATION
The objectives for the containment system were to maintain a slight inward groundwater gradient into the
barrier wall and to minimize the pumping rate for contaminated groundwater The performance of the
containment system is evaluated in the following subsections
5.1 Design
The design was rated better than acceptable compared to the standard industry practice as discussed in
Section 3, Volume I Seventeen soil bonngs (about one bonng every 100 feet) were installed along the
barrier wall alignment to define the subsurface stratigraphy and top-of-bedrock profile The trench slurry
compatibility was tested to determine the effect of the viscous, oily NAPS fluids on the backfill
materials Based on the testing results, borrow clay with a plasticity of up to 25 percent was mixed with
0 21 to 0 91 percent dry bentomte and uncontamrnated excavated trench and soils The RCRA Subtitle C
cap is connected to the barrier
5.2 Construction Quality Assurance and Construction Quality Control
Barrier construction quality assurance (CQA) and construction quality control (CQC) were rated better
than acceptable, but there were several problems The verification of the key-in depth was insufficient
during trench excavation and backfilling A total of 23 bonngs were advanced along the centerline of the
wall It was determined that the bedrock key-in was not accomplished from stations 1+00 through 5+00,
and several sand seams and lenses were present along the rest of the wall In situ soil mixing (ISSM) was
performed along the entire length of the wall to incorporate the sand into the backfill After the ISSM
operations, 28 backfill samples were collected These samples met the 1 x 10"7 cm/sec permeability
requirement of the design Sediment erosion control measures were not well maintained during
construction of the wall, possibly allowing sediments to run into the trench and causing permeable zones
along the bottom of the wall
53 Monitoring
Long-term monitoring was rated better than acceptable compared to standard industry practice The
monitoring program includes measuring groundwater elevations, monitoring for the presence of NAPS,
and sampling and analysis of the groundwater A total of 24 wells are installed at the site to monitor
groundwater elevations, five of these wells are also used for NAPS monitoring Groundwater samples
Site 18 3
-------
are collected from nine well locations on a quarterly basis and analyzed for BTEX, PAH, total petroleum
hydrocarbon (TPHC), pH, total and amenable cyanide, total phenols, ammonia-nitrogen, and arsenic
Data for four pairs of wells was compared to determine the existence of an inward gradient MW-2/OW-
4, OW-5/MW-3, OW-6/OW-7, and OW-8/MW-12 are located at the "corners" of the perimeter wall, with
one well of each pair located inside the barrier and the other located outside Figure 2 shows the water
level elevations in well pair OW-5/MW-3 beginning on May 8,1995 (to represent conditions before
pumping began), and continuing with monthly measurements from July 1995 through March 1996
Figure 2 demonstrates that an inward gradient has developed across the barrier wall The site contractor
noted that the rising groundwater levels inside and outside the containment area between December 1995
and February 1996 was likely due to higher than expected leakage into the containment area
The groundwater monitoring program at the site includes sampling at two well locations inside and seven
well locations outside the perimeter barrier The two interior wells are PW-3 and PW-4, the wells
located outside the barrier wall are PW-1, PW-2, MW-2, and four others
The groundwater quality in the pumping wells inside the wall show an increase in contaminant
concentrations, except for a 50 percent decrease in naphthalene concentration The quality of water from
pumping wells outside the wall has improved slightly The concentration of contaminants has decreased
slightly in MW-2, located just outside the barrier wall These water quality results, coupled with the
inward gradient discussed earlier, indicate that the containment system is performing as designed
5.4 Operation and Maintenance
Operation and maintenance (O&M) activities at the site include measuring groundwater levels, and
sampling groundwater wells and gas vents Groundwater pumped from outside the barrier is treated
using an activated carbon filter and is then discharged off site Groundwater pumped from within the
bamer is treated in an off-site wastewater treatment faculty
5.5 Other Considerations
The approximate costs associated with design and construction of the bamer wall, cap, and pump and
treat system were $5 5 million., $2 7 million, and $13 million, respectively O&M costs are minimal for
the barrier wall, $10,000 per year for the cap, and $500,000 per year for the pump and treat system
5.6 Remedy Performance
The remedy is performing as designed, with pumping from the extraction well operating at design rates
An inward gradient has developed, and will be maintained through pumping the wells within the barrier
wall. The water quality in pumping and monitoring wells outside the bamer wall are improving
Site 18
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Well Pair MW-3 and OW-5
Water Level Elevations
5205
5195
5185
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5175
517
5165
516
05/08/95 07/24/95 08/15/95 09/12/95 10/17/95
11/14/95
Date
12/20/95
01/22/96
2/19/96
3/18/96
3/25/96
Site 18
FIGURE 2
GROUNDWATER ELEVATIONS
retro Tech EM Inc.
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6.0 SUMMARY
Site 18 is a 4-acre, former sand and gravel borrow pit in the midwestern United States that was used for
disposal of industrial and municipal wastes BTEX, PAHs, NAPS, and arsenic are the primary site
contaminants. A 2,000-foot soil-bentomte barrier wall and a RCRA Subtitle C cap was constructed to
control the source of contamination. Groundwater is extracted from inside the barrier wall using two
wells and is treated using a bioremediation process Groundwater from outside the barrier is pumped
using two wells and treated with activated carbon
The design, CQA/CQC, and long-term monitoring were rated above average An inward gradient was
established and maintained at the site, although the water level within the barrier has fluctuated with
water levels outside the barrier, indicating slight leakage Water quality monitoring of the pumping wells
indicates that contaminant concentrations are decreasing, while monitoring well concentrations do not
show any particular trends Based on the results of two water quality monitoring events, the barrier wall
cap and associated water management system appear to be effective m meeting the containment and
remediation objectives
SUe 18
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SITE 19
1.0 SITE DESCRIPTION AND HISTORY
Earner Type
Remedial
Objective
Performance
SB
SC,zero
gradient
Site 19 covers about 32 acres and is located in the northeastern United States The site was a sand and
gravel pit that later became the repository for various household and hazardous wastes The site received
wastes for at least 20 years until the early 1980s, when complaints about volatilizing compounds
emanating from an adjacent stream caused alarm among local residents Another stream located
downgradient drains to the surrounding city's water supply reservoir
The site is bordered by two streams, and a nver is located within 1 mile of the site A municipal solid
waste landfill is operating adjacent to and just upgradient from the site. Mobile home communities
border the site on its remaining sides
The selected site remedy called for containment of a 20-acre area by hydrodynamic isolation, including a
subsurface barrier wall and a pump and treat system with recharge The barrier wall was constructed m
1982, and a geomembrane cap was installed as well One year later, the pump and treat system was
installed to augment the containment The site remedy was evaluated between 1990 and 1993 for
compliance with regulatory requirements Recent studies have been performed to evaluate the
effectiveness of the remedy. Figure 1 shows the site and basic features
The site represents a good application of containment in a difficult hydrogeologic environment without
the advantage of a pervasive, confining layer or bottom The barrier and recirculation approach was a
pragmatic method of controlling source migration and evaluating off-site contamination in a phased
fashion
2.0 GEOLOGIC/HYDROLOGIC SETTING
The site lies in the Glaciated Appalachian Region of the United States, and the site geology reflects
recent glaciation. The site area is underlain by a sequence of fine to coarse sands and lenses of silts and
silty, fine sands that are outwash and glacial lake deposits This unconsohdated sequence is underlain by
dense glacial till, which is generally thin and not always continuous Although it is low in permeability,
the till is an imperfect aquiclude The till is founded on a bedrock of weathered schist of varying
competency and permeability The bedrock's shallower layers are highly fractured
The unconsohdated sands range in permeability from 10"5 to 10"1 centimeters per second (cm/sec) and
have an average hydraulic conductivity of about 10"2 cm/sec The lower till permeability is on the order
of 10"5 cm/sec The rock has widely varying hydraulic conductivities within a range of 10"3 to
10"5 cm/sec, some rock testing has revealed hydraulic conductivities as high as 10"1 cm/sec
The regional groundwater flow direction is east to west, and discharge occurs downgradient into the
streams and the nver near the site. This flow was interrupted by the installation of the circumferential
bamer wall, which significantly altered the local flow pattern After the bamer wall was installed and
before any groundwater was pumped, groundwater rose 2 to 3 feet, mounding against the upgradient
(eastern) portion of the bamer, a general east to west gradient in the containment and a downgradient
outward flow condition In addition, intenor shallow water levels within the contained area were
Key SB=Soil Bentorate Wall SOSource Control Performance Rating 3=Evidence suggests objective may not be met
Site 19
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Site 19
FIGURE 1
SITE PLAN
EHT Tetro Tech EM Inc.
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artificially higher than underlying intervals, causing downward gradients However, water levels m the
wells screened in the bedrock both inside and outside the containment area were similar, implying the
presence of permeable bedrock Gradient values and the corresponding flow through the containment
varied depending on subsequent pumping activities
3.0 NATURE AND EXTENT OF CONTAMINATION
The site received household and hazardous wastes for at least 20 years Reportedly, tanker trucks
dumped liquids in open pits at the site Consequently, the site displayed elevated concentrations of
several compounds, but volatile organic compounds (VOC) were most prevalent Total VOC
concentrations were as high as 2,000 mg/L Of the VOCs detected, tetrahydrofuran (THF) was the most
common In samples containing VOCs, over 90 percent could be attributed to THF Therefore, THF
became the indicator compound for the site
Before the remedial action, the concentrations of THF at the site ranged from detection limits to about
170 mg/L The highest concentrations were detected downgradient toward the adjoining streams
Concentrations were highest in the shallow, overburden soils After the remedial action, the
concentrations were generally lower but the distribution of THF had changed
4.0 CONTAINMENT REMEDY
The site remedy consists of an active containment system consisting of a circumferential hydraulic
barrier wall, a pumping system, a site-wide cap, and a monitoring program General features of the
remedy included-
• A soil-bentomte hydraulic barrier wall that is about (on average) 4,000 linear
feet long; to 110 feet deep (50 foot average), 3-foot thick, and keyed into
weathered rock (with minimal penetration)
• Eight recharge and extraction wells
• Six recharge trenches at two locations
• Several pairs of groundwater level monitoring locations paired across the barrier
• Many groundwater quality monitoring wells upgradient and downgradient
* More than three surface water quality monitoring locations along the adjacent
waterways
• A cap (geomembrane)
0 A treatment system
It was determined that the original 6-acre source area and an additional 14 acres were underlain by the
contaminant plume to be contained An early feasibility study determined that neither hydraulic isolation
alone nor containment alone would be practical or effective in containing the contamination, primarily
because of the local geology and the absence of a suitable and pervasive confining bottom at the site
Therefore, the remedy called for hydrodynamic isolation or active containment and a "zero net gradient"
Site 19
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condition across the bamer wall It was also realized that controlling the inward gradient condition
might not be feasible in all cases and that the effectiveness of the containment should be re-evaluated
5.0 PERFORMANCE
Overall remedy performance has been the subject of several studies during and after remedial
construction Performance was measured based on groundwater quality and maintenance of a zero net
gradient across the barrier wall Generally the containment has been successful in reducing shallow
groundwater contamination on site However, barrier underflow and off-site bedrock contamination may
have been exacerbated by the remedy
Containment system performance and contributing factors are described further in the following
subsections
5.1 Design
The barrier design was rated slightly better than acceptable with respect to industry practices described in
Section 3, Volume I. The feasibility of implementing different systems was studied, adequate numbers
of borings were drilled along the bamer wall alignment, significant compatibility testing was performed,
a geophysical survey was performed along the entire bamer alignment, and detailed bamer and testing
specifications were developed The bamer construction specifications were both performance- and
design-based The barrier was designed to incorporate excavated material and was constructed using
trench-side mixing Feasibility study- and design-level groundwater modeling were performed
However, modeling and keying requirements apparently underestimated the impact of groundwater flow
in the bedrock and under the key
The geomembrane cap consisted of 40-mil HDPE material Insufficient design information was available
to evaluate the cap design
5.2 Construction Quality Assurance and Construction Quality Control
Earner construction quality assurance (CQA) and construction quality control (CQC) were rated slightly
better than acceptable because of the thorough and detailed controls placed on construction The bamer
was continuously inspected during construction Rigorous testing was performed, including parallel
fixed-ring and flexible-wall permeameter studies as well as testing using bentonite content methylene
blue titration Periodic, documented testing of groundwater quality and measurement of hydraulic head
were performed during and after construction In addition, postconstruction peizocone testing was
performed for window detection, undisturbed bamer samples were collected and tested, pump testing
across the bamer was performed, and geophysical methods were used to measure bamer integrity
Insufficient information was available to evaluate cap CQA/CQC
53 Monitoring
The monitoring program for Site 19 involved a better than acceptable effort Groundwater and surface
water quality was measured periodically to assess plume migration and the effectiveness of the pumping
and recirculation system Hydraulic head was also measured at nested piezometers inside and outside the
bamer to evaluate the pumping system's effectiveness in maintaining a zero gradient condition, not only
for lateral flow but also for vertical flow and bamer underflow.
Site 19
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70000
1985 1986 1987 1988 1989 1990
YEAR
1991
1992
1993
1994
Site 19
FIGURE 2
AVG. CONCENTRATION - TOTAL VOCs
INSIDE BARRIER WALL
Tetro Tech EM Inc.
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Groundwater quality data for overburden monitoring wells within the bamer, summed to display total
VOC concentrations over fame, is shown graphically in Figure 2 The figure shows the dramatic decrease
in shallow overburden concentrations However, groundwater quality monitoring outside the bamer wall
and downgradient has indicated increasing concentrations of VOCs m bedrock Increasing VOC
concentrations in bedrock were detected in some places for several years immediately after installation of
the bamer, and more recently were detected in an area downgradient of the bamer At some
downgradient locations, interior bedrock concentrations are greater than two orders of magnitude more
than the overlying shallow concentrations, and the bedrock concentrations of VOCs outside the bamer
are two to three times higher than the bedrock concentrations inside the bamer
Additional barrier performance monitoring was conducted during a regulatory agency-required remedial
action evaluation study This monitoring is described in Section 5 4
5.4 Operation and Maintenance
The O&M activities of the remedial action conducted since 1983 were examined in detail by revisiting
the containment system 10 years after its installation and evaluating bamer integrity, groundwater
quality, and the overall effectiveness of the remedy The study involved extensive monitoring of
hydraulic head for horizontal and vertical gradients at the bamer, pumping tests at the bamer, drilling of
11 barrier confirmation borings to test for extent of the bamer and physical parameters, and an
evaluation of groundwater flow and impact on the surrounding area The results of the study are
discussed in Section 5.6
S3 Other
The capital cost of the containment as estimated in a predesign document is outlined below
• Slurry wall $2,100,000 (about $10 per square foot of the barrier wall)
Cap $436,000
WeHs- $50,000
Gas Vents- $65,000
• Groundwater treatment $1,644,000
Postconstruction documents indicate that the bamer wall construction cost was actually $4 65 per square
foot. Annual O&M costs were not available for the site
5.6 Remedy Performance
Early performance monitoring conducted since installation in 1982 was rigorous in attempting to define
the effectiveness of the containment system The site's lack of a pervasive, low-permeability aqmtard
layer has caused difficulties in meeting the initial zero net gradient objective
Recent investigation has shown that about one-third of the bamer is subject to outward flow.
Undisturbed sample collection and testing indicates that the current bamer permeability is about one
order of magnitude above the constructed values, and chemical results indicate the possibility of
bentomte degradation, although the data is not conclusive More importantly, the additional flow occurs
by underflow beneath the barrier in the bedrock Recent head measurements and groundwater quality
data indicate that a downward gradient exists in places from the shallow aquifer to the bedrock
Contaminants are apparently migrating through fractured bedrock and under the bamer, these
contaminants may present a risk to downgradient receptors
Site 19 6
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The barrier, geomembrane cap, and recirculation system have proven effective m reducing contaminant
concentrations in the shallow overburden soils Downward gradients and migration of contamination in
the bedrock apparently result in contamination moving outside the containment Impacts of such
migration may be evaluated by establishing a groundwater management zone Further monitoring is
likely in the future
6.0 SUMMARY
Site 19, located in the northeastern United States, has a 20-acre area contained by a soil-bentomte barrier
wall, and is equipped with a geomembrane cap and pumping system The site is a former sand and gravel
pit that received various municipal and hazardous wastes, resulting in VOC contamination. The geology
of the site consists of permeable, glacial sands and gravel overlying fractured schist with locally high
permeability Recirculation (extraction and infiltration) pumping has attempted to achieve a zero
gradient condition to control off-site migration of contaminants Monitoring and postconstruction
evaluations indicate that the containment has been successful in significantly reducing shallow
groundwater contaminant concentrations However, downward groundwater flow and permeable
fractured bedrock have created conditions under which site contaminants can apparently migrate to
bedrock downgradient of the barrier Therefore, the containment has been only partially effective in
meeting the remedial objectives The site is undergoing further evaluation that may lead to establishing a
groundwater management zone and conducting further monitoring
Site 19
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SITE 20
1.0 SITE DESCRIPTION AND HISTORY
Earner Type
Remedial
Objective
Performance
SB
'scf
Site 20 is located in the eastern United States The site covers 20 acres in an area of industrial,
commercial, and warehousing operations on a peninsula near a river estuary
For more than a century, the site was used to process chromium ore to produce a number of chromium-
containing chemical compounds Chromium ore processing at the site generated large quantities of
process residuals containing soluble chromium These process residuals were used as fill material
enlarging the peninsula upon which at the site is located Perimeter bulkheads stabilize the site at the
water's edge In addition, large quantities of water were used for processing and plant housekeeping
A subsurface hydraulic barrier was completed at the site in 1996, and cap and groundwater pumping
system construction has begun The site and basic site features are shown in Figure 1
2.0 GEOLOGIOTYDROLOGIC SETTING
The site is located on the Atlantic and Gulf Coastal Plain The site is underlain by Precambnan rock
overlain by a layer of Lower Cretaceous sediments (the Patuxent Formation) The Cretaceous sediments
form the central core of the peninsula where the site lies Above this core are layers of coarse-grained
Pleistocene sediments, marine silts, and heterogeneous fill materials The top fill layer on which the
industrial facilities were built consists of construction debns, brick, wood fragments, silts, and sands
Contamination was found at the site in two groundwater-yielding layers, one shallow and one deep The
shallow, unconfined groundwater lies above low-permeabihty silts near the site perimeter and flows
radially off the site through the perimeter bulkheads to the north, west, and south Deep, partially
confined groundwater lies within the Cretaceous sands, it flows from northwest of the site to the
southeast Precambnan rock underlies the site soils The uppermost layer of rock extends beneath the
entire site and ranges in thickness from 5 to 20 feet This layer is made up of decomposed rock and
consists of clayey, fine to coarse sand The permeabilities of this material ranges from 3 8 x 10"4 to 3 8 x
10"7 centimeters per second (cm/sec) The next lower rock layer consists of fine to coarse sand in a clay
silt matrix with a high quantity of feldspar and biotite, and the next lower layer is a weathered to
medium-hard gneiss with quartz seams. The barrier wall was keyed a minimum of 3 feet and up to 6 feet
into the uppermost layer of rock
3.0 NATURE AND EXTENT OF CONTAMINATION
The site soils and groundwater were contaminated primarily with chromium Chromium levels in
groundwater were found to range from 0 01 to 14,500 mg/L Computer modeling of contaminant
migration from the site indicated that about 62 pounds per day of chromium was released into adjacent
surface water and groundwater The deep groundwater flow has resulted in off-site groundwater
contaminant concentrations of up to 200 mg/L
It was determined that reducing recharge of the deep groundwater from above would reduce chromium
migration from the shallow groundwater to the deep groundwater. Additionally, it was determined that
Key SB=Soil Bentomte Wall SC=Scmrce Control Performance Rating 2=Evidence suggests objective may be met
Site 20
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I >
PAIRED
PIEZOMETERS-
EXTRACTION WELL-
S-B BARRIER-\
80' 160'
SCALE 1" = 160'
Site 20
FIGURE 1
SITE FEATURES
Tetra Tech EM Inc
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the site soils would not be excavated, but rather would remain in place and be contained by the remedial
measures This was the intent in constructing the containment barriers at the site
4.0 CONTAINMENT REMEDY
The containment remedy had the following general features-
• A rock outboard embankment to allow waterside soil-bentonite barrier construction
• A subsurface barrier wall that is about 3,200 linear feet long; 65 to 80 feet deep, 3 feet
thick and that has a 3-foot rock key
• A cap (including a capillary break, geomembrane clay liner, FML 60 mil low density
polyethylene [LDPE], geonet, cover)
• Groundwater extraction system consisting of 12 perimeter deep wells and 4 landside
shallow wells
• Monitoring (hydraulic head, groundwater quality, and surface water quality)
The rock embankment constructed around the waterside perimeter of the site reinforced the bulkheads
and provided a structural platform for constructing the soil-bentonite barrier The embankment also
provided some reduction of groundwater flow off site
The multilayer geosynthefac cap was designed to facilitate future use of the site for residential,
commercial, or recreational purposes
The groundwater monitoring system for the site includes 32 piezometers paired at 12 locations Four of
these locations have nested, paired piezometers in shallow and deep aquifers whereas the remaining eight
locations have paired piezometers only in deep aquifers Each piezometer pair has one piezometer
installed on the inner side of the banner and one piezometer on the outer side of the barrier Sixteen
extraction wells will remove groundwater from the two aquifers The water will be pumped to an on-site
transfer station, where it will be stored until it is transported to a treatment facility Groundwater levels
inside the barrier must be kept at 0 01 foot lower than the outside groundwater levels (based on averaged
hourly readings) The system will be operated by an on-site computer system capable of changing
pumping rates to accommodate changes in groundwater levels
The multimedia cap and groundwater extraction system have not yet been constructed
5.0 PERFORMANCE
The long-term performance of the barrier will be determined based on periodic monitoring of hydraulic
head, groundwater quality, and surface water quality
Hydraulic head across the banner has been significantly influenced by the installation of the barrier
After the completion of the barrier wall, groundwater levels inside the barrier rose by several feet
Because the groundwater extraction system had not been constructed, the groundwater rise was managed
using a series of sumps Excess groundwater was pumped to an on-site treatment facility
Site 20
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Containment system performance and contributing factors are described further in the following
subsections.
5.1 Design
The barrier design was rated better than acceptable based on industry practice as discussed in Section 3,
Volume I The design specifications generally followed the guidance established by the U.S Army
Corps of Engineers Significant positive features of the design included rigorous compatibility testing of
both slurry and backfill with on-site groundwater and the brackish surface water surrounding the site A
salt water-resistant bentomte was used as a dry addition to the backfill in order to counteract potential
effects of the brackish surface water The slurry used in the trench was a conventional, untreated
bentomte. Borings were drilled every 90 feet along the barrier alignment Trench stability analysis was
performed to determine an acceptable depth for the slurry above the groundwater table elevation because
of the tidal surface water fluctuation Additionally, planned barrier penetrations and vehicle crossing
slabs, as well as surface capping details and the cap interface were all designed before barrier
construction.
The cap design was rated better than acceptable The site is planned for development after the remedial
construction is complete A significant positive feature of the cap design is its inclusion of future utility
locations in preparation for development This feature will allow cap layers to be removed in only those
areas where utility or development construction is necessary
5.2 Construction Quality Assurance and Construction Quality Control
Earner construction quality assurance (CQA) and construction quality control (CQC) were rated better
than acceptable Significant positive features of the CQA/CQC program included constant inspection of
trench excavation and backfilling Inspections included sounding of the trench bottom and verification of
key depth. Backfill mixing was inspected constantly, and testing was performed to determine the
permeability, slump, and gradation of each batch of backfill (200 to 500 cubic yards) before its
placement. Backfill was mixed in a central location Slurry was tested both before and after placement
in the trench. The viscosity and sand content of the slurry were tested, and modifications were made as
necessary Backfill testing was performed by the design engineer A minimum of one permeability and
gradation test was performed for each batch Slurry testing was performed by the contractor with
random, duplicate testing by the design engineer, duplicate testing was performed daily at the discretion
of the design engineer
As part of CQA/CQC monitoring, the slurry levels in the trench were closely inspected to determine
whether slurry was being lost to the adjacent surface water Because the barrier was being constructed
within a previously constructed rock embankment, slurry loss through the larger stones in the base of the
embankment was a possibility Slurry loss occurred at one location during bamer construction, and a
plugging agent was used to seal the leak The bamer alignment was shifted slightly at this location to
avoid additional leakage No additional slurry loss occurred at this location during construction
A construction completion report was written detailing the various aspects of the construction,
CQA/CQC, as-built plans, modifications, and final data
The CQA/CQC for cap is not evaluated because the cap is yet to be constructed
Site 20
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5.3 Monitoring
Hydraulic head monitoring was performed at least weekly and often three to four times weekly during
construction Monitoring of this site has been performed since 1988 as part of the remedial action
Existing monitoring wells both inside and outside the barrier were used As part of the construction
contract, an additional 16 pairs of piezometers were installed Monitoring of these piezometers revealed
an increase in the groundwater level inside the barrier after the barrier was completed The increase was
due to infiltration of precipitation and the lack of a groundwater extraction system Sumps were
installed at several locations around the perimeter of the site to manage the elevated groundwater until
the permanent groundwater extraction system became operational
Hydraulic head measurements were plotted over time This plot details the rise in shallow groundwater
levels within the barrier over time as the barrier was constructed As the groundwater levels after the
completion of the barrier indicate, groundwater pumping was not being performed during this period
Continuous monitoring of water levels was performed at several paired piezometer locations around the
site to compare tidal influence inside and outside the barrier Shallow locations showed no tidal
influence inside the barrier, indicating barrier integrity However, deep locations inside the barrier
showed minor, dampened tidal response, presumably because of pressure waves emanating from the
underlying, tidally influenced rock
Hydraulic testing was also performed at several locations around the site perimeter to measure distance-
drawdown response inside the barrier and check for impact outside the barrier At each location tested,
the outside piezometer showed no pumprng-induced influence, even when head differentials were on the
order of 20 to 30 feet during active pumping Such testing confirmed the integrity of the barrier in the
immediate vicinity of the locations tested
Groundwater quality was monitored around the site perimeter on a quarterly basis before, during, and
immediately after construction Quarterly data showed no distinct decrease in contaminant
concentrations outside the barrier, in fact, some concentrations increased This finding has been
attributed to changes in groundwater flow during construction and the flow equilibration processes after
construction This well is located about 15 feet outside and downgradient of the barrier
Surface water lies immediately adjacent to the barrier along 2,200 feet of its alignment. Surface water
samples from several locations, including locations along the barrier were sampled and analyzed for total
chromium Sample results showed an immediate improvement in water quality at some locations upon
barrier completion Since completion of the barrier, average chromium concentrations in surface water
have been below the 0 050-mg/L standard
5.4 Operation and Maintenance
Operation and maintenance (O&M) activities consisted of observing the barrier for signs of settlement,
erosion, or other damage Settlement plates were installed in the surface of the barrier during
construction and were surveyed to determine whether settlement had occurred No abnormal settlement
has occurred to date Ongomg future O&M for the barrier will include review of pumping and
monitoring data
Site 20
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5.5 Other
The construction cost of the containment is estimated to be about $28,000,000 Earner construction,
excluding embankment construction, cost about $5,000,000, or $22 per square foot of wall Annual
O&M costs, excluding water treatment costs, for the completed containment are estimated to be
$400,000.
5.6 Remedy Performance
Water levels inside and outside the barrier were at significantly different hydraulic heads upon barrier
completion Minimal postconstructaon monitoring has been performed However, testing and monitoring
indicate that no leakage is occurring and that when an active, inward gradient is maintained, no leakage
will occur. Long-term monitoring will be used to track containment performance
6.0 SUMMARY
Site 20 is a 20-acre site located in eastern United States For more than a century, chromium ore was
processed at the site to produce many chromium-contaimng chemical compounds Contamination was
found at the site in two groundwater-yielding layers, one shallow and one deep The shallow
groundwater lies above low-permeability silts near the site perimeter and flows radially off the site
through bulkheads to the north, west, and south Deep groundwater within Cretaceous sands flows from
northwest of the site to the southeast To minimize further contamination of the adjacent harbor and off-
site groundwater, a soil-bentonite barrier was designed as part of the overall containment system, which
also included a groundwater extraction system and a multilayer cap
The design and CQA/CQC of the barrier were rated better than acceptable Performance monitoring of
the barrier was also rated better than acceptable involving intensive construction inspection,
postconstruction sampling, installation of paired piezometers across the barrier, and extensive
groundwater quality monitoring Early results indicate that the barrier is a protective remedy The
effectiveness of the entire containment will be determined based on future monitoring data
Site 20
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SITE 21
1.0 SITE DESCRIPTION AND HISTORY
Earner Type
Remedial
Objective
Performance
SB, DSM
Inward
gradient
X
Site 21 is located in the Midwestern United States The site covers about 60 acres and contains three
waste disposal areas (see Figure 1) The Old Site, which operated from 1967 to 1974, covers 5 acres and
is the disposal area described in this site summary The New Site, which was operated from 1974 to
1983, covers 40 acres and was closed in 1983 The low-level radioactive waste (LLRW) site operated
from 1967 to 1978, and closure activities were completed in 1989 The tritium plume associated with the
LLRW site has been remediated, and the chemically contaminated plume is being monitored by the U S
Environmental Protection Agency
The Old and New Sites were investigated from 1985 to 1989, and a remedial plan was selected in 1990
In 1994, construction of the barrier wall and a Resource Conservation and Recovery Act (RCRA)-type
cap to cover the areas bounded by the barrier wall was completed for the Old Site A groundwater
extraction system from within the containment area began operating in 1996 Extracted groundwater is
treated at an on-site treatment plant
2.0 GEOLOGIC AND HYDROGEOLOGICAL SETTING
Site 21 is in the Glaciated Central Region of the United States. Overburden soils in the area consist of
glacial drift (till and outwash), loess, dune sand, and alluvium The thickness of the overburden soils
ranges from 20 to 75 feet The Toulon Sand member of the Glasford Formation is an average of 15 feet
thick at the site and forms an unconfmed aquifer at the site. The low-permeability till units underlying
the sand member impede vertical groundwater flow and contaminant migration through the till unit
Bedrock underlying the soils is about 65 feet deep and consists of interlayered and weathered Silunan-
age shale, siltstone, limestone, sandstone, and coal The upper surface of the bedrock has been altered by
glacial erosion and excavation activities associated with site construction and coal mining The lateral
continuity of the Toulon Sand provides a preferential pathway for groundwater flow to a lake located
southeast of the site The average hydraulic conductivity of the aquifer is 24 feet per day Fractured
zones in the bedrock also provide pathways for contaminant migration from the site
3.0 NATURE AND EXTENT OF CONTAMINATION
The plume associated with the old disposal area contains tnchloroethene, chloroform, benzene;
tetrachloroethene, 1,1-dichloroethane, 1,2-dichloroethane, 1,2-dichloropropane, methylene chloride,
xylene, and arsenic Analysis of groundwater samples collected within the glacial formation beneath the
Old Site indicates organic and inorganic contaminants in the following concentrations
• Tnchloroethene 200 to 7,800 micrograms per liter
• Chloroform: 410 to 100,
• Benzene. 340 to 10,000
Tetrachloroethene- 100 to 50,
• 1,1-Dichloroethane 7tol70//g/L
Key SB=Soil Bentonrte Wall Performance Rating 3=Evidence suggests objective may not be met
Site 21 1
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(CHEMICAL WASTE
TRENCHES)
(BAMOACTIVe WAtTC tnCNCHIft)
ROAO
Site 21
FIGURE 1
SITE LAYOUT
Tetro Tech EM Inc.
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1,2-Dichloroethane. 1,400 to 10,000 /zg/L
• 1,2-Dichloropropane 6 to 110
• Methylene chlonde 200 to 40,
Xylene 10to210yUg/L
• Arsenic 10 to 70 //g/L
4.0 CONTAINMENT REMEDY
The selected corrective measures for source control at Site 21 consist of the following components
• Placement of soil-bentomte barrier walls around the Old Site that are 2,900 feet long, 40
to 70 feet deep, and 3 feet wide with a 3-foot key
• Construction of a RCRA Subtitle C cap over the Old Site consisting of a geosynthetic
clay liner, 40-mil high density polyethylene liner, geonet, and cover soils
• Installation of extraction wells within areas encircled by the barrier walls
Deep soil mixing technology was used to construct the soil-bentomte barrier walls. The barrier was
keyed into till or shale bedrock
5.0 PERFORMANCE EVALUATION
The objective of the containment system is to maintain an inward groundwater gradient at the Old Site
Performance monitoring began at the site in April 1996 and consists of monthly water-level monitoring
of paired monitoring wells within and outside the barrier walls Also, beginning m 1992, quarterly water
quality was monitored m wells located outside the wall within the contaminated plume
An evaluation of containment system design, construction quality assurance and construction quality
control (CQA/CQC), monitoring, operation and maintenance, other considerations, and remedy
performance are discussed m the following subsections
5.1 Design
The hydrogeologic investigation and geotechmcal design investigation for the site was better than
acceptable with respect to industry practices described in Section 3, Volume I, with borings spaced
100 feet apart along the barrier wall alignment Groundwater modeling, trench slurry compatibility, and
the backfill permeability testing were conducted by the engineer in coordination with the contractor The
cap design was thorough, with the provision for erosion control measures
5.2 Construction Quality Assurance and Construction Quality Control
The CQA/CQC was rated better than acceptable The specialty contractor selected for the barrier wall
construction had completed more than 10 such comparable projects, and conducted all the standard tests
to ensure that the slurry mix was within the design specifications Post construction barrier sampling and
testing was conducted to verify the depth of the key-in and the permeability of the bamer wall The EPA
provided oversight of the CQA/CQC activities, and independently verified the depth of the key-in
Site 21
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S3 Monitoring
The monitoring for the site was rated less than acceptable Monitoring consists of four pairs of
monitoring wells, with one well in each pair located within the barrier wall and the other located outside
the waU. Monitoring of water quality downgradient of the barrier wall is conducted quarterly However,
hydraulic stress tests, settlement monitoring and barrier wall movement monitoring was not done Figure
2 shows a downgradient well pair where the water level within the barrier wall has been 0 35 to 14 feet
higher than the outside water level However, results are available for only 2 months, continued pumping
is expected to produce an inward gradient
Figure 3 shows the concentrations of two organic compounds detected in the influent to the on-site
wastewater treatment plant. Groundwater from a series of wells located in the contaminant plume is
collected and treated in the on-site treatment plant After peaking between August 1993 and January
1995, contaminant concentrations have stabilized at lower concentrations
5.4 Operation and Maintenance
The extraction wells and the treatment plant are properly maintained The influent and effluent
groundwater concentrations are monitored monthly at the treatment plant
5.5 Other Considerations
The cost for the containment system was approximately $4,300,000 Barrier wall costs equaled
$3,000,000 Operation and maintenance costs are approximately $10,000 per year for the cap
5.6 Remedy Performance
Because the extraction system just started operating in April 1996, there is not yet convincing evidence
that an inward groundwater gradient has developed
6.0 SUMMARY
Site 21 consists of three disposal areas, two of which received hazardous chemical wastes and occupy a
total of about 60 acres. In 1994, construction of a soil-bentonite barrier wall and RCRA Subtitle C cap
was completed. A contaminated groundwater plume containing organic compounds at concentrations
near or above 10,000 g/L is associated with the Old Site Six extraction wells are located within the
plume, and four are located within the barrier wall. Currently, water from all extraction wells is treated
in an on-site treatment plant Design and CQA/CQC of the barrier wall were both determined to be
significantly above average Monitoring of the barrier wall was rated below average Monthly
measurements of groundwater levels do not indicate that an inward gradient has been established at the
site yet.
Groundwater quality data is collected quarterly and indicates that contaminant concentrations are
decreased rapidly after construction of the wall and cap, but remain in the mg/L range Overall, there is
insufficient data to determine if remedial objectives had been met
Site 21
-------
Downgradient Well Pair
7305
lfarefv? •»»!„.'3r*K
-------
IZ
Concentration (ug/L)
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o
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if
m
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SITE 22
1.0 SITE DESCRIPTION AND SUMMARY
Earner Type
Remedial
Objective
Performance
SB
SC
Site 22 is located in northeastern United States The site is a corner property bound by a road on the south,
a highway on the west, a creek on the north, and an industrial facility on the east The site was first used
for solvent refining and recovery and then was used to process industrial wastes before it was shut down in
1980 In 1991, the site was assigned two operable units (OU) for remediation purposes OU1 is the
designation given to the 5 9-acre site currently contained within a slurry wall OU1 includes contaminated
soils and groundwater above the clay layer at the site OU2 refers to all other areas on and off site that
require remediation Each OU has its own record of decision (ROD)
An initial feasibility study (FS) for OU1 was conducted in 1989 The FS evaluated remediation and
treatabihty alternatives for OU1 groundwater and soil or sludge A total of nine monitoring wells were
installed off site m 1988. five shallow monitoring wells (MW-8S to MW-12S) were screened in the fill,
and four deeper monitoring wells were installed (MW-8D, MW-11D, MW-12D, and MW-13D) A deep
bedrock monitoring well (MW-2R) was installed on site in 1989 Also, 23 test pits were excavated in July
1989 to evaluate the nature of the fill material. Figure 1 shows the site layout
2.0 GEOLOGIC AND HYDROGEOLOGIC SETTING
Site 22 is located within the Atlantic and Gulf Coastal Plain and the Piedmont Geologic Province of New
Jersey The area is underlain by the Tnassic-age Newark Supergroup bedrock, which is predominantly
shales and sandstones The advancing ice front of the Wisconsinan Glacial event eroded valleys into
underlying rocks As the glacier retreated, a glacial lake formed between the ice front and the terminal
moraine Fine-grained sediments were deposited in this lake, and till was deposited over the scoured
bedrock Overlying the glacial sediments is a sequence of moraines and marsh sediments Fill was placed
above the marsh deposits to develop the land where the site is located
Based on information collected from soil borings, the stratigraphy at he site is as follows (in descending
order) fill, peat, gray silt, varved clay, till, and bedrock. The fill is composed of soil mixed with
construction fill The fill is thinnest near an on-site creek and increases in thickness toward the road that
borders the south side of the site The fill thickness ranges from 3 to 11 feet and averages about 8 4 feet
The peat is the youngest of the naturally occurring materials at the site Its thickness decreases from the
creek that borders the north side of the site to the road that borders the south side of the site In some
places, the peat is completely absent This could be the result of the high water content of peat, which
causes the peat to be displaced when fill is placed over it The peat's thickness ranges from 0 to 7 feet and
averages 1 8 feet At one location, fine sand that appears to be natural overlies the peat, indicating the
occurrence of localized channel scouring and filling
The gray silt is about 2 feet thick across the site Bedding is not present except for rare laminations The
material is extensively mottled, indicating reduced conditions
The varved clay layer is a wedge-shaped clay unit that is thickest toward the creek that borders the north
side of the site and thinner toward the road that borders the south side of the site The unit's thickness
ranges from 0 to 18 feet The unit's upper surface is horizontal, while the lower surface is inclined From
the creek to the road, the varved clay yields to a massive red clay unit and a sand unit that is 0 to 8 feet
thick
Key SB=So2 Bentorate Wall SC=Source Control Performance Rating 3=Evidence suggests objective may not be met
Site 22
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*
MW-13D
H.69)
Site 22
NOT TO SCALE
Site 22
FIGURE 1
SITE LAYOUT
Tetro Tech EM /nc.
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The Wisconsuuan till is 20 feet thick and is the deepest unconsohdated unit in the strata It is composed of
three members (1) clean sand, (2) massive clay, and (3) sand and gravel The bedrock is reddish-brown
shale of the Brunswick Formation A seismic study was conducted to determine the approximate depth of
the bedrock its depth was estimated to be 59 6 feet
Three aquifer systems are present at the site They are (in descending order) the water table aquifer
(shallow), the till aquifer (intermediate), and the bedrock aquifer (deep). The water table aquifer is very
shallow, usually lying 1 to 2 feet below ground surface (bgs), and occurs under perched conditions on the
underlaying clay Its lateral flow is toward the center of the site as well as toward the creek, the highway,
the road, and the adjoining property to the east The fall aquifer is thought to be connected to the water
table aquifer because of the presence of unconsohdated recent and Holocene-age fluvial deposits and the
underlying glacial deposits The bedrock aquifer in the site is generally confined by the overlying mantle
of unconsohdated deposits However, the possibility exists that all three aquifers beneath the site are
connected Not enough information was available to reach a definition conclusion in this regard
3.0 NATURE AND EXTENT OF CONTAMINATION
On-site operational areas included a tank farm, drum storage areas, a still and boiler house, a staging
platform, and a thin-film evaporator The tank farm had an unlined containment area that was depressed 1
to 2 feet with respect to the surrounding surface elevations At one time the farm contained 18 tanks, but
only one tank remains on site This tank contains sludge with extremely high polychonnated biphenyl
(FOB) levels The structural integrity of the tank is suspect because of discoloration observed on the
outside of the tank
During the remedial investigation (RI), various contaminants, including volatile organic compounds
(VOC), acid extractable compounds, base neutral compounds, PCBs, metals, petroleum hydrocarbons, and
pesticides, were detected at high levels at all soil depths sampled
4.0 CONTAINMENT REMEDY
A baseline nsk assessment (BRA) for the site was conducted in 1990 for the U S Environmental
Protection Agency (EPA) The BRA followed the EPA guidance for conducting nsk assessments that was
current at the time On September 14,1990, EPA issued a ROD selecting an interim remedy for OU1
based on the RI/FS and BRA The ROD defined OU1 as "contaminated soils and groundwater above the
clay layer" and selected a remedy composed of the following elements a slurry wall that encompasses the
entire site, an infiltration barrier to be placed over the site, a groundwater extraction and collection system
for OU1, and off-site treatment and disposal of extracted groundwater
The design of the interim remedy was presented in the interim remedy remedial design report (IRRDR) in
1991 The construction of the interim remedy began in August 1991 and was completed in June 1992 As
part of the design effort, 18 soil bonngs were installed to evaluate subsurface conditions in the vicinity of
the proposed slurry wall
An "upgraded" slurry wall was installed at the site in August 1991, and a steel sheet-pile wall was
constructed along the creek to facilitate installation of the slurry wall An upgraded slurry wall is a soil-
bentomte slurry wall with a high-density polyethylene (HDPE) membrane inserted vertically through the
center of the completed wall The purpose of this liner is to ensure a slurry wall permeability of less than 1
x 10"7 centimeters per second (cm/sec)
Site 22
-------
The total length of the slurry wall installed at the site is 1,890 feet The depth of the slurry wall ranges
from 11 8 to 18 8 feet bgs The width of the slurry wall is 36 inches, which allowed sufficient space for
installation of the vertical HDPE membrane The slurry wall is keyed into a gray silt or varved clay-red
clay unit that has a permeability of 7 6 x 10s cm/sec After the completion of the slurry wall, a temporary
cap made of HDPE was installed The total area of cap coverage is 238,285 square feet
A dewatenng system was installed to manage the groundwater within OU1 The is being extracted by the
dewatenng system to achieve and then maintain the required water level in OU1 The collected
groundwater is transported to a facility in southern New Jersey for treatment and disposal The total
amount of groundwater extracted from the site between June 1992 and March 1996 is about 278,280
gallons.
5.0 PERFORMANCE EVALUATION
As part of the interim remedy for OU1, a slurry wall was installed adjacent to and inside the perimeter of
the 5.9-acre site The wall extends from the ground surface into the silt and clay layers A sheet-pile
retaining wall was installed along the on-site creek A temporary infiltration barrier was installed across
the entire surface of the area surrounded by the slurry wall The backfill mix of off-site soil and bentomte
was designed to achieve and maintain a permeability of no more than 1 x 107 cm/sec After 3 years of
pumping, the water level within the slurry wall had not decreased significantly compared to the water
levels outside the wall
5.1 Design
The design was assigned an average rating Hydrogeologic and FSs were performed Geotechmcal
physical testing was performed, and test borings were spaced between 100 and 200 feet apart In addition,
groundwater design performance modeling was performed Backfill permeability was tested, but the
number of tests performed is unknown
5.2 Construction Quality Assurance and Construction Quality Control
Barrier construction quality assurance (CQA) and construction quality control (CQC) were assigned a
slightly above average rating as a result of an 18-hour slurry mixing period and the trench, slurry, and
backfill testing, which was performed However, although CQA and CQC testing was performed, the
results of that testing were not available For example, sand was added to the slurry mixture, but the final
sand content is not known
53 Monitoring
The site monitoring program involves sampling of 13 groundwater wells and four surface water sampling
points in the on-site creek. Target analytes are tested for annually, and VOCs are tested for quarterly
Quarterly sampling reports are generated for the site Sampling data has shown that an inward gradient
exists at the site, but this gradient has been sporadic and sometimes insignificant The exact location and
extent of site contamination are still under investigation Since the slurry wall was installed, no
performance or stress tests have been conducted on it
The site monitoring program was assigned a slightly below average rating because (1) no hydraulic stress
tests were performed and (2) no physical samples were collected and no permeability tests were performed
after the wall was installed
Site 22
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5 4 Operation and Maintenance
No information was available concerning operation and maintenance of the slurry wall containment system
at the site
5.5 Other Considerations
Following is a breakdown of the estimated cost for implementing the interim remedy based on the OU1
ROD The actual cost of the interim remedy is unknown because it was facilitated by a potentially
responsible party group and EPA does not have the actual cost information
Conceptual Items Cost Estimates in Thousands of Dollars
Total construction cost: 2,097,000
Engineering and construction oversight 460,000
Monitoring (quarterly for 3 years) 109.000
Subtotal: 2,666,000
Contingency (about 10 percent) 267,000
TOTAL COST: $2,933,000
5.6 Remedy Performance
Overall, remedial objectives have not been met because of the low or nonexistent inward gradient provided
by the pumping system
6.0 SUMMARY
Site 22 is a 5.9-acre site with an "upgraded" slurry wall (an HDPE membrane was inserted vertically
through the center of the wall). The site was used for industrial waste processing from 1971 to 1980, when
a court order shut down the site The geology of the site consists (in descending order) of fill, peat, gray
silt, varved clay, till, and bedrock The slurry wall is keyed into the gray silt and varved clay layers A
pumping system was installed to induce an inward gradient, but after 3 years, the water level inside the
slurry wall had not decreased significantly compared to the water levels outside the wall
Site 22
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SITE 23
1.0 SITE DESCRIPTION AND HISTORY
Earner Type
Remedial
Objective
Performance
SB
SC
2+
Site 23 is located in the northeastern United States The site is adjacent to a nver to the north, a river to
the east, undeveloped land to the south, and a road to the west The road provides access to the site along
its western border A site map showing basic site features is provided in Figure 1
The site covers about 315 acres and contains an active municipal waste landfill fully surrounded by a
soil-bentonite subsurface barrier wall The wall was designed and built for subsurface leachate
containment The wall was constructed in two phases and completed in late 1984 The barrier wall is
about 3 miles long and ranges from about 10 to 60 feet deep, averaging about 38 feet in depth Other site
features include a leachate collection and disposal system, withdrawal wells, piezometers, and
groundwater monitoring wells The existing leachate management system includes a perimeter and
intenor leachate collection system.
2.0 GEOLOGIC/HYDROGEOLOGIC SETTING
The landfill is located near the western edge of the Atlantic Coastal Plain At the landfill, the geology is
generally composed of the following six strata (in descending order)
• Fill from 40 years of sanitary landfill operations and from general improvements at the
landfill perimeter (for example, roads, caps, and berms)
• Organic marine tidal marsh deposits consisting of organic silts and clays with
interbedded peat (meadow mat) near the surface and frequently under the fill
• A sand unit, which typically has only a small amount of fines and is consequently very
permeable
• A clay unit, which acts to inhibit the flow of water (The subsurface barrier wall was
keyed into this low hydraulic conductivity clay unit and into the underlying residual soil)
• Residual soil, typically a dense, clayey soil with weathered rock fragments
• Shale bedrock
The sand unit and the bedrock form two distinct aquifers separated by the clay unit The sand aquifer is a
major groundwater resource in the region and the groundwater flows pnmanly to the southeast toward
the adjacent rivers
The bedrock aquifer system is not considered to be a major source of water in the site area Water in the
bedrock aquifer is stored in and transmitted through fissures and fractures in the bedrock The general
flow directions of the groundwater in the bedrock aquifer are north toward the nver and east toward the
other nver Pump tests conducted at the site have indicated that the upper bedrock is not highly fractured
and has low hydraulic conductivity, thus it yields little or no water
Key SB = Soil Bentomte SC = Source Control Performance Rating 2+ = Evidence suggests objective may be met
Site 23
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J)MW-23S
V ^
'STATION 76*oo
* LOCATION OF HONITOBIHO VfUS
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3.0 NATURE AND EXTENT OF CONTAMINATION
The landfill had been constructed within a marshland environment located directly above the outcrop
area of the sand aquifer Several volatile organic compounds (VOC) were detected in groundwater from
the sand and bedrock aquifers (for example, 1,1,1-tnchloroethane at 400 ug/L)
4.0 CONTAINMENT REMEDY
The barrier wall was designed as part of the overall hydraulic containment system, which also includes
the leachate collection system The objective of the containment system was to prevent possible leachate
migration from the landfill into the surrounding groundwater The containment system has the following
general features
• A soil-bentomte subsurface barrier wall that is about 15,480 linear feet long, 38 feet deep
(on average), and 3 feet thick and that has a 3-foot soil key
• A leachate collection system
• 21 piezometers installed both inside and outside of the wall to determine the
groundwater response to pumping
« 15 groundwater monitoring wells screened in the sand aquifer adjacent to the barrier wall
5.0 PERFORMANCE
The evaluation of the barrier wall's integrity was based on its (1) physical presence, (2) conformance to
design specifications, (3) performance as a hydraulic barrier, and (4) effect on surrounding groundwater
quality
The physical presence of the barrier wall was investigated after construction and was verified at all tested
locations except one reach A physical and geotechmcal investigation was conducted using piezocone
testing as well as pumping tests at three locations along the wall to assess the wall's overall hydraulic
effectiveness Generally, the results of hydraulic testing showed the wall to be hydraulically adequate
Available groundwater quality data does not indicate any contaminant plume emanating from the area
enclosed by the barrier wall One potentially problematic area was located where a leak was detected
during the postconstruction investigation This area had experienced some difficulties during
construction because of trench failure New soil-bentomte backfill was used to fill the failed area The
trench was reexcavated for more than 600 feet No contaminants were found to have migrated through
this portion of the barrier wall
Future installation of a slot dram and withdrawal well system to maintain an inward, 1-foot hydraulic
head differential across the barrier wall is planned in order to provide adequate leachate collection
throughout the contaminated area
Site 23
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5.1 Design
The barrier design was rated average with respect to industry practices as discussed in Section 3,
Volume I The design generally followed the requirements of the governing state organization
The wall was designed to (1) be 3 feet wide, (2) consist of a soil-bentomte backfill mixture capped with
soil, and (3) extend vertically from the ground surface to at least 3 feet into clay or bedrock The soil-
bentomte wall is about 3 miles long and ranges from about 10 to 60 feet deep, averaging about 38 feet m
depth.
Because the landfill is currently operating, the cap has not been designed
5.2 Construction Qualify Assurance and Construction Qualify Control
Barrier construction quality assurance (CQA) and construction quality control (CQC) were rated better
than acceptable Based on testing of undisturbed barrier samples collected every 500 linear feet, the
barrier met the design permeability requirement of less than 1 x 10"7 cm/sec
Piezocone testing was performed at approximately 400-foot intervals along the centerline of the barrier
wall to provide overall profiling coverage of the wall Seventeen dissipation tests were performed during
profiling to estimate the in situ permeability of the wall The estimated permeability ranged from 1 x 10"7
to 1 x 10"9 cm/sec, indicating that the soil-bentomte backfill material met the design objective with
respect to hydraulic conductivity
53 Monitoring
Containment monitoring was rated slightly better than acceptable The monitoring involved taking
quarterly readings of hydraulic head at 21 pairs of monitoring locations around the barrier and on either
side of the barrier An additional 15 monitoring locations outside the barrier were sampled quarterly
(samples were analyzed for metals, BOD, and COD) and annually (samples were analyzed for metals,
VOCs, and semivolatile organic compounds)
The quarterly groundwater hydraulic head data available for several years showed that in most cases, the
head differential was maintained at greater than a 1-foot difference across the barrier, thereby achieving
inward flow.
Pumping tests were conducted at three piezometer locations along the outside of the wall These
locations were selected based on the findings of the piezocone testing, test bonng information, and
construction records At two of the three piezometer locations, piezometers located inside the wall
showed no change in static head, while at the third location, the piezometer located inside the wall
indicated a hydraulic connection between the inside and outside of the wall. The results of the testing are
summarized in Figure 2
5.4 Operation and Maintenance
Operation and maintenance (O&M) requirements for the containment involved monthly site inspections,
quarterly effluent sampling and well water level readings, and annual well water sampling since 1984
Site 23
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0)
P-15ID
P-4ID
Well Name
P-5ID
Note1 Data shows drawdown in wells located across the
barrier from the pumped well
Site 23
FIGURE 2
DRAW DOWN ACROSS BARRIER
fetro Tech EM Inc
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5.5 Other
No additional information about the site, including the capital and O&M costs, is available
5.6 Remedy Performance
The overall remedy is performing as designed Hydraulic head objectives were easily met using the
leachate collection and pumping system Groundwater quality outside the containment has improved
significantly based on the decrease in contaminant concentrations The barrier was determined to be of
low permeability, adequately keyed, continuous, and intact based on the groundwater table elevation
measurements
6.0 SUMMARY
Site 23 is a 315-acre active municipal solid waste landfill The landfill was constructed within a
marshland environment located directly above the outcrop area of an aquifer, which serves as a major
groundwater resource in the region To prevent possible migration of leachate into the aquifer, a barrier
wall and leachate collection system were designed as part of the overall containment system The
containment remedy consisted of a soil-bentonite barrier and a leachate collection system
The design and CQA/CQC of the barrier were rated acceptable and better than acceptable, respectively
The performance monitoring of the barrier was rated better than acceptable involving postconstruction
sampling, use of the piezometers paired across the barrier, ample groundwater quality monitoring, and
regular inspections The site containment has met containment objectives
Site 23
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SITE 24
1.0 SITE DESCRIPTION AND HISTORY
Earner Type
Remedial
Objectives
Performance
SW
SC
Site 24 is an abandoned refinery that manufactured biphenyl, polychlonnated biphenyls (PCB), phenyl
phenol, naphtha, and fuel oils from 1967 until the early 1980s The site occupies about 13 acres, and the
nearest residences he 50 feet from the site Site activities have resulted in contamination of the shallow
groundwater-beanng zones under the site The remedy outlined in the 1986 record of decision (ROD)
includes construction of a soil-bentomte slurry wall around the site and a groundwater pump and treat
system for the shallow groundwater-beanng zone Figure 1 presents a current site plan
2.0 GEOLOGIC AND HYDROGEOLOGIC SETTING
Site 24 is located within the Gulf Coastal Plain and overlies an outcrop of Pleistocene-age alluvial
sediments These sediments are composed of clays and silts with occasional sand zones Two shallow
groundwater-beanng zones have been identified at the site the 30-foot sand and the 100-foot sand The
30-foot zone is a sandy silt and silty sand layer that occurs from about 10 to 40 feet below ground surface
(bgs) at the site and has an estimated permeability of 1 x 10"4 to 1 x 10"5 cm/sec The transmissivity of this
zone is estimated to be 2 to 3 square feet per day The groundwater in the 30-foot zone is unusable and has
a chlonde content ranging from 2,000 to 10,000 mg/L Groundwater in this zone flows east toward an
adjacent flood control channel at a rate of about 5 feet per year
The 100-foot sand is a well-sorted sand that occurs from about 50 to 140 feet bgs This 100-foot sand is
separated from the 30-foot sand by a 13- to 27-foot-thick clay stratum with a permeability on the order of
1 x 10"9 cm/sec (based on laboratory permeability tests of three samples) The slurry wall around the site
penmeter is keyed into this stratum The 100-foot sand contains the shallowest usable groundwater in the
site vicinity This groundwater is used locally on a limited basis by residents and industry Groundwater
in this zone flows to the west and southwest at a rate of about 20 to 30 feet per year
A remedial investigation (RI) report for the site suggests that the 30-foot and 100-foot sands may be
connected as a result of growth faulting in the south half of the site Although this hypothesis was not
specifically investigated dunng the RI, or illustrated on any cross sections or maps reviewed, it was used to
explain (1) features of the potentiometnc surface of the 30-foot sand and (2) the presence of contaminants
in the 100-foot sand
Before 1967, petroleum production was common in the area, and oil production wells were known to be
present on site However, the number, age, and location of on-site oil wells are not known One former
on-site oil well was investigated and found to be plugged and abandoned in accordance with state
requirements However, it is not known whether any other on-site oil wells were adequately plugged and
abandoned The site area still contains several active oil wells The depth of the shallowest oil-producing
zone is not known
Key SW = Slurry Wall SC = Source Control Performance Rating X = Insufficient data to determine if remedial objectives were met
Site 24
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MW-24 D OMW-26 DITCH
^
COUNTY aOOO CONTROL UNIT C 105-03-00 (CKWNEL)
it— 1|(
LECEHD
• OttTH) BWIWWe KliS (tf)
Q DtttM} WMTOflMa kOU (t40r)
Q K» uxmwa wu (iw)
0 w KOMKT wu (M)
^ KW ttOMXT K1U (1W)
Site 24
FIGURE 1
SITE PUN
Tefro Tech EM Inc.
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3.0 NATURE AND EXTENT OF CONTAMINATION
The principal sources of contaminants at the site include waste lagoons and ponds, buried drums, landfills,
landspreading areas, waste piles, and spill areas. The main contaminants include PCBs, solvents,
chlorinated solvents, and polynuclear aromatic hydrocarbons (PAH) In soil, PCBs were present at levels
up to 12,000 mg/kg Former oil production wells on and near the site may also have been a source of site
contaminants or migration pathways between groundwater zones
The 30-foot sand was estimated to contain 23 to 41 million gallons of groundwater containing the
following contaminants
PCBs (up to
benzene (610 |xg/L)
ethylbenzene (1,500 \igfL)
toluene (17 \ngfL)
xylene (4,300 ng/L)
tnchloroethene (TCE) (420ng/L)
naphthalene (720 ng/L)
fluorene
The 100-foot sand was estimated to contain at least 6 million gallons of groundwater contaminated with
TCE, but the extent of contamination in the 100-foot sand is not known
4.0 CONTAINMENT REMEDY
On September 18, 1986, EPA issued a ROD for the site that specifies preventing further degradation of the
30-foot sand as one of the remedial objectives The ROD describes the containment portion of the selected
remedy to include a slurry trench cutoff wall, cap, and a groundwater recovery and treatment system. The
implemented remedy includes the following elements
• A perimeter slurry wall that is about 3,300 feet long, 35 feet deep, and 2 5 feet wide and
that has a key depth of 5 feet
• A permanent, multilayer surface cap including 3f eet of compacted clay overlain by 60-
mil HDPE, a 2-foot-thick sand drainage layer, and 2 feet of vegetated topsoil
• A TCE-contaminated groundwater recovery and treatment system consisting of nine
recovery wells in the 30-foot sand and one recovery well in the 100-foot sand
• A monitoring network of three monitoring wells in the 30-foot sand outside the slurry
wall, and four monitoring wells in the 100-foot sand
Site 24
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The sluiry wall was designed to be a containment barrier that prevents off-site migration of contaminants
by maintaining a negative inward gradient The barrier is keyed 5 feet into the clay aqmtard between the
30- and 100-foot aquifers to prevent leakage In addition to the slurry wall, a groundwater recovery system
was designed to recover contaminated groundwater for treatment and to provide a lower hydraulic head
within the perimeter slurry wall than outside it, thus maintaining a horizontal gradient into the containment
area. However, no performance standard (minimum negative gradient across the wall) was specified.
The construction activities for the slurry wall were certified on September 21,1990 According to the
certification report, all quality control tests and parameters were in accordance with the quality assurance
plan However, the groundwater monitoring and recovery system was not placed in operation until May
1993.
The Resource Conservation and Recovery Act (RCRA) cap, which was completed in April 1990, consisted
(from bottom to top) of (1) a 3-foot-thick, clay layer, (2) a 60-mil high density polyethylene (HOPE) liner,
(3) a 2-foot thick, sand drainage layer, and (4)2 feet of topsoil with a vegetative cover The cap slopes
gently away from the center of the site. The cap covers the entire site, including the slurry wall
5.0 PERFORMANCE EVALUATION
Groundwater elevations in the monitoring and recovery wells are monitored monthly Groundwater
samples for chemical and water quality parameter analyses have been collected quarterly since the
groundwater monitoring and recovery system became operational in May 1993 The following subsections
summarize containment system performance.
5.1 Design
Based on the criteria outlined in Section 3, Volume I, the barrier design evaluation generated an average
rating, but it was based on limited design information Most of the available design information was
associated with the groundwater extraction system, not with the slurry wall The slurry wall design
objective was to maintain a negative inward gradient in conjunction with the 30-foot sand recovery wells
No specific performance standard was identified Positive attributes of the design included a --foot key
into the clay aquitard below the 30-foot sand and the construction quality control (CQQ sampling
Negative attributes included limited collection of geotechmcal design data along the barrier alignment
Also, no information regarding slurry compatibility testing or analysis of long-term chloride degradation of
the bentomte was found
The cap design was evaluated as being above average Positive attributes of the cap design include the
following (1) the cap covers the waste disposal areas and slurry wall, and (2) the cap components (Sfeet
of compacted clay overlain by 60-mil HDPE, a 2-foot-thick sand drainage layer, and 2 feet of vegetated
topsoil) are substantial
5.2 Construction Quality Assurance and Construction Quality Control
Evaluation of the construction quality assurance (CQA) and construction quality control (CQC)
information generated an average rating CQA/CQC documents indicated that field testing of slurry trench
materials was conducted in accordance with the project CQA/CQC plans The backfill was tested for
liquid limit, gradation, and permeability The slurry was tested for slump, density, Marsh viscosity, and
filtrate loss Samples were collected from the completed trench for permeability testing No
documentation was available to establish the adequacy of the key depth.
Site 24
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53 Monitoring
The groundwater monitoring system was evaluated to be below average based on the criteria described in
Section 3, Volume I Three groundwater monitoring wells are located approximately 30 feet outside the
barrier in the 30-foot sand zone MW-26 is located on the east side of the site between the slurry wall and
the drainage ditch, MW-10 is located on the west side of the site, and MW-11 is located near the
northwest corner of the site Before remedial activities began, the groundwater gradient was determined
to be to the east toward the flood control channel next to the site Only one monitoring well, MW-26, is
located on this side of the site Therefore, downgradient groundwater monitoring appears to be
inadequate
The monitoring system is also deficient because no monitoring wells or piezometers are located within the
containment barrier perimeter Groundwater elevations are monitored monthly in the nine 30-foot sand
recovery wells, all of which are located within the barrier perimeter The use of recovery wells to monitor
interior groundwater elevations may not generate data that is representative of hydraulic conditions at the
barrier interface These conditions would be best monitored by well or piezometer pairs straddling the
barrier.
Figure 2 illustrates groundwater elevation data for monitoring well MW-26 and recovery well RW-4
These two wells are located about 100 feet apart along the east side of the site The data shows that a
outward gradient was present from December 1994 through March 1995 The cause of the outward
gradient is not known, although it may be associated with the surface water level in the adjacent flood
control channel The 30-foot sand zone is believed to be in hydraulic communication with the surface
water in the channel
Figure 3 illustrates groundwater elevation data for monitoring well MW-11 and recovery well RW-8
These two wells are located about 50 feet apart on the north side of the site Available data from May
1993 through December 1995 shows that an inward gradient existed between these two wells
Monitoring wells MW-26 and MW-10 were located in areas of known contamination TCE
concentrations in groundwater have not changed significantly since the recovery system began operation
in 1993 Groundwater samples collected from MW-26 have consistently contained about 100 u.g/L TCE,
and in December 1995, a concentration of 3,000 ug/L PCB was detected (see Figure 4 and 5)
5.4 Operation and Maintenance
No operation and maintenance (O&M) specific procedures for the slurry wall are specified in the O&M
plan The slurry wall is covered by the edge of the cap and is therefore not accessible for visual
inspection However, the O&M plan indicates that the hydraulic gradient across the slurry wall will be
evaluated after each monthly monitoring event to confirm the presence of an inward gradient
The O&M plan specifies cap maintenance procedures that include (1) quarterly visual inspections of the
vegetative cover and side slopes for erosion, (2) quarterly inspections of the cap for surface water ponding
and infiltration, (3) annual benchmark surveys to detect potential cap subsidence, and (4) mowing of the
vegetative cover on a monthly basis from April to October and on an as-needed basis during the rest of the
year
Site 24
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Gl
EC
I
§
0
GROUNDWATER ELEVATION COMPARISON
RW-4 AND MW-26
30
CO
5 25
ts
UJ
20
15
10
May 93 Dec 94 Apr 95 Jun95 Aug95 Oct95 Dec 95
Oct94 Mar 95 May 95 Jul95 Sep95 Nov95
SAMPLE DATE [Figure 21
Site 24
FIGURE 2
GROUNDWATER ELEVATION COMPARISON
7etro Tech EM Inc
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35
30
w
s.
I'"
DJ 20
GROUDWATER
en o en
m
GROUNDWATER ELEVATION COMPARISON
*
• ""--•
\
• RW-8
® MW-11
i i i
RW-8 AND MW-11
^ ~4*
\
\
X
I
\ / •-
1 I 1 1 1 1 1 1
^
1
May 93 Oct94 Dec 94 Mar 95 Apr 95 May 95 Jun95 Jul95 Aug95 Sep95 Oct95 Nov95 Dec 95
SAMPLE DATE [Figure 3 1
Site 24
FIGURE 3
GROUNDWATER ELEVATION COMPARISON
Tetro Tech EM Inc.
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— MW10
+ MW25
+ MW1 1 '
-A-MW26 '
^ MW22 •*• MW23 •
*• MW8 0 MW1 7 •
^MW24
^MW101
Site 24
FIGURE 4
MONITORING WELL TCE (ppb)
CHEMICAL ANALYSIS SUMMARY
fetro Tech EM Inc.
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3,500
3,000
2,500
2,000
1,500
1,000
500
93
* * *
4144 i
MW10
MW25
MW11 -*-MW22 -»-MW23 *- MW24
Site 24
FIGURE 5
MONITORING WELL PCB (ppb)
CHEMICAL ANALYSIS SUMMARY
Tetra Tech EM Inc.
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5.5 Other Considerations
The installed quantity of slurry wall was 101,668 89 ft2 The total cost was $374,142 52
5.6 Remedy Performance
Because there is only one downgradient monitoring well and no monitoring wells are located within the
containment barrier perimeter, it is impossible to evaluate the performance of the remedy
6.0 SUMMARY
Site 24 is an abandoned refinery that manufactured biphenyl, PCBs, phenyl phenol, naphtha, and fuel oils
from 1967 until the early 1980s Site activities have resulted in contamination of the shallow groundwater-
bearing zones under the site The remedy outlined in the 1986 ROD included construction of a soil-
bentonite slurry cutoff wall around the site and a groundwater pump and treat system for the shallow
groundwater-beanng zone. The slurry wall is approximately 3,300 feet long, 35 feet deep, and 2 5 feet
wide and has a key depth of 5 feet into a clay aquitard Evaluation of the design and CQA/CQC generated
average ratings The site's monitoring system was rated below average because (1) there is insufficient
downgradient monitoring, and (2) interior groundwater elevations are monitored using active recovery
wells, not well or piezometer parrs From December 1994 through March 1995, an outward gradient was
observed between monitoring well MW-26 and recovery well KW-4 that may have been associated with
the hydraulic interconnection of the 30-foot sand and the flood control channel adjacent to the site The
limitations of the monitoring system precluded further evaluation of this condition
Site 24 10
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SITE 25
1.0 SITE DESCRIPTION AND HISTORY
Barrier Type
Remedial
Objective
Performance
SB
"scT
Site 25 is located in the Alluvial Basins ground-water region in the Pacific Northwest The site is
composed of a 12 3-acre property, and seven off-property remedial action areas totaling 18 acres located
adjacent to or near the property The site has been divided into ten remedial action areas for
management and tracking purposed (see Figure 1), the barrier wall encircles Areas I, II, IX, and X Past
activities at this site include recycling and reprocessing of solid and liquid waste materials from over 300
industries and other businesses located primarily in the Pacific Northwest
Site operations ceased in 1983 Remediation of site soil and groundwater contamination also began m
1983 Surface removal of contaminated material was completed in 1985 Remediation of subsurface and
groundwater began in 1987 and continues to date Subsurface remediation has included construction of
(1) monitoring wells, (2) a groundwater extraction and treatment system, and (3) a subsurface barrier
wall to a depth of about 40 feet (ft) below ground surface (bgs) around the site Portions of the site have
been capped The rest of the site is scheduled to be capped by 1999
2.0 GEOLOGIC AND HYDROGEOLOGIC SETTING
The site is underlain by fill, alluvial, and postglacial unconsohdated deposits consisting of sand, gravel,
silt, and clay Fill occurs in localized areas of the site to a depth of about 15 ft bgs Underlying soils
extending from the base of the fill to depths of about 50 ft are primarily composed of silty sand, silt, clay,
and peat At depths greater than 50 ft bgs, the soils are typically poorly graded sand with some silt
Water-bearing zones beneath the site are referred to as Zones A, B, C, and D that are identified by their
respective depths, 10 to 30 ft, 40 to 60 ft, 80 to 100 ft, and 120 to 140 ft Aquitards are generally present
between these zones, however, they tend to be discontinuous Zone A, the uppermost aquifer, is
unconfined, Zone B is semi-confined to confined, and Zones C, and D are confined Groundwater at and
near the site occurs 5 to 10 ft bgs within the unconfined, upper alluvial aquifer Groundwater within this
aquifer flows predominantly to the northwest at a rate of about 100 ft per year No known water supply
wells he within the immediate vicinity of the site The local municipality obtains a portion of its
drinking water from a deep artesian aquifer located more than 1 mile upgradient from the site, this
aquifer is hydrauhcally isolated from the shallow and intermediate-depth aquifers beneath the site
3.0 NATURE AND EXTENT OF CONTAMINATION
Site investigations conducted by state, federal, and private organizations identified the presence of more
than 80 priority pollutants in the soil and groundwater at the site Three volatile organic compounds
(VOC) —the solvents trichloroethene (TCE), czs-l,2-dichloroethene and vinyl chloride—and six heavy
metals—cadmium, chromium, copper, nickel, lead, and zinc—are currently considered to be the most
important contaminants because of their concentrations, toxicities, and potential effects on human health
and the environment The VOCs of concern are primarily sorbed onto soil particles, and are to a lesser
degree dissolved m groundwater Heavy metals are primarily dissolved in groundwater, but are also
adsorbed on soil particles
Key SB = Soil Bentomte SC = Source Control Performance Rating 2 = Evidence suggests objective may be met
Site 25
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Remedial Action Area
Identification
Cell Number Identification
Shallow Piezometer
(~35 ft deep) Location
and Designation
Deep Piezometer
(- 45 ft deep) Location
and Designation
Ground Water
Quality Well
P31 «*S> P33
in
FIGURE 1
SITE FEATURES
Tetra Tech EM Inc
Site 25
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The initial contaminant sources were the on-site tanks, drums, waste piles, and impoundments that were
present at the tune the site ceased operations in 1983 These sources were removed in 1984 However,
contaminants that remained in the soil leached into the shallow groundwater and migrated further to an
adjacent creek, a drain, and deeper off-site groundwater units
4.0 CONTAINMENT REMEDY
Remediation efforts at the site have thus far included the following (1) excavation and off-site disposal
of 21,900 cubic yards (yd3) of contaminated soil and sludge, (2) removal of 24,000 pounds (Ib) of VOCs
and 78,000 Ib of metals from groundwater via groundwater extraction and treatment, (3) elimination of
storm water runoff from contaminated portions of the site, (4) removal of contaminated sediments from
the creek, and (5) containment of contamination remaining at the site through installation of a slurry wall
and maintenance of an inward gradient through groundwater pumping
The original groundwater extraction system consisted of 206 well points (each 30 ft deep) connected by
header pipes This vacuum-operated system was organized into seven cells for operational efficiency
The extraction system was expanded twice after 1988 in 1992, two extraction wells were installed
between the barrier wall and the creek, and in 1994, 80 well points were installed on 10-foot centers
between the slurry wall and the east drain adjacent to Cells 3, 4, and 6 The infiltration system, which
was also installed in 1988, consists of about 13,000 linear ft of buned, perforated pipe through which
varying amounts of water can be infiltrated to enhance flushing of the site Since 1988, the groundwater
extraction system has pumped over 600 million gallons of contaminated groundwater Extraction rates
averaged about 200 gallons per minute (gpm) during 1994
The barrier wall serves as a flow control device for the extraction system by restricting lateral flow of
water from the creek and surrounding areas and intercepting water within Zone A In addition, the wall
isolates the area of highest contamination By blocking inward lateral flow from outside the
contaminated area, the wall substantially increases the efficiency of the pump and treat system While
contaminated groundwater is being extracted, relatively uncontammated groundwater from outside the
wall is drawn inward underneath the wall, this effect forms a hydraulic barrier that prevents
contaminants from migrating away from the contained area The barrier wall is not keyed into a
subsurface horizon but is designed to extend into or through a silt and clay layer near the base of the
wall This layer is generally present between 10 ft below mean sea level (msl) and the base of the wall at
22 ft below msl The wall is a 4,400-ft-long, 40- to 50-ft-deep, 30-mch-thick hanging wall that surrounds
the site Construction of the slurry wall was completed m 1989
5.0 PERFORMANCE EVALUATION
The site remedy calls for creation of an inward gradient in the water-bearing Zone A An inward
gradient is considered to exist under the following conditions (1) the piezometnc heads in the shallow
and deep piezometers outside the wall are higher than the piezometnc heads in the corresponding
piezometers inside the barrier wall, (2) each deep piezometer inside the wall has a higher piezometnc
head than its corresponding shallow piezometer, and (3) the piezometnc heads in the shallow
piezometers and well points in the western part of Area V are higher than those in the eastern part of
Area V The locations of piezometers PI through P48 are shown in Figure 1
Based on the established inward gradient and groundwater quality data, the containment system has been
successful in containing and reducing the contamination m on-site shallow groundwater Figure 2
displays TCE concentrations m groundwater from an off-site monitoring well, the location of this well is
Site 25 3
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to
H-
rt
(D
S3
TRICHLOROETHENE CONCENTRATION
WELL7M26B
I I If If I If I I If I If If I If I If I If I I
1(91 MM
SAMPLE DATE
Site 25
FIGURE 2
TRICHLOROETHENE CONCENTRATION
fetro Tech EM Inc
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shown in Figure 1 Containment system performance and contributing factors are described further in
the following subsections
5.1 Design
The barrier design was rated slightly better than acceptable with respect to industry practices as
described m Section 3, Volume I More than 3 tests were performed to determine the long-term
compatibility of backfill with the contaminated groundwater However, the wall protection from surface
loading or subsurface breach was either below standard or nonexistent No information was available on
any hydrogeologic investigation, groundwater modeling, or trench stability analysis
5.2 CQA/CQC
Earner construction quality assurance and construction quality control (CQA/CQC) were rated better
than acceptable Backfill slump testing and slope testing was performed on every 250 to 300 yd3 of
backfill However, although a desander was used to control slurry sand content, slurry sand percentages
ranged from 17 to as much as 40 percent Trench sounding was done up to 10 times per day, daily
profiles of trench bottom were obtained, slurry was tested continuously, and backfill permeability
samples were obtained for every 100 If of the wall
Backfill samples were initially tested for permeability using the rigid wall permeameter Permeabilities
for six of the first nine samples tested were higher than the 1 x 10~7 cm/sec specification As a result, the
amount of dry bentonite added to the backfill was immediately increased to decrease backfill
permeability Three backfill samples were then tested using the flexible wall permeameter, and were
found to meet the 1 x 10'7 cm/sec specification All further testing was done using the flexible wall
permeameter
53 Monitoring
Long-term monitoring was rated slightly better than acceptable Groundwater and surface water quality
samples are routinely collected in numbers that exceed the industry standard Piezometer pairs across
the wall are located at reasonably spaced intervals The railroad embankment parallel to the eastern side
of the wall was monitored for settlement by using monuments evenly spaced along the 1,700-ft length of
the embankment No movement of the embankment was detected during construction of the barrier wall
Based on a 1994 annual evaluation report, requirements of maintaining an inward gradient across the
barrier wall has been consistently met at all measuring points since August 1989 except in two deep
piezometer pairs (P15-P16 and P19-P20) located in the northwestern portion of the site These
piezometer pairs, each made up of one piezometer located inside and one outside the slurry wall, have
historically displayed either predominantly neutral or outward gradients Piezometer pair P15-P 16
displayed exclusively outward gradients in 1994 compared with 63 percent outward gradients (with 37
percent neutral gradients) in 1993 and 88 percent outward gradients (with 12 percent neutral gradients) m
1992 Piezometer pair P19-P20 showed a predominantly neutral gradient in both 1994 and 1993,
however, inward gradients were displayed more frequently than outward gradients in this piezometer pair
m 1994 This indicates a change m conditions from 1993, when outward gradients occurred more
frequently than inward gradients However, upward gradients have been consistently measured at these
locations
Piezometer data collected on May 8, 1996, indicates that an inward gradient continues to exist at most
monitoring points along the wall However, outward gradients are present at piezometer pairs P18-P17
Site 25 5
-------
and P28-P27 (shallow), and at pairs P16-P15 and P46-P45 (deep) The lack of a consistent inward
gradient around these piezometers may be related to (1) groundwater withdrawal rates, which were
reduced in these areas because of lower concentrations of groundwater contaminants, or (2) possible
leaks in the barrier caused by several underground pipelines that pass through the slurry wall in this area
As a result of low concentrations of groundwater contaminants in the northern portion of the site, the
organizations conducting site remediation have proposed to remove the barrier wall around Cell 7 and
construct a new northern barrier wall segment
5.4 Operation & Maintenance
The slurry wall is covered by a mounded fill for run-on and run-off control Current operations and
maintenance costs are estimated to exceed 5 million dollars per year
5.5 Other
The as-built barrier wall consists of over 192,000 square ft of excavation and backfill About
1,788,000 pounds of dry bentonite was added directly to the backfill Wall construction costs were not
available
5.6 Remedy Performance
In spite of the presence of a neutral or outward gradient at certain piezometers, the barrier wall appears
to have achieved its intended purpose of assisting in contaminant removal from groundwater The site
owners seek to change the remediation system at the site, from active to passive by (1) cappmg the site,
(2) installing about 15 extraction wells, and (3) abandoning the well point system The long-term goals
are to stop treating the metals in the groundwater, and to reduce the volume of groundwater being
pumped
6.0 SUMMARY
Site 25 is primarily made up of a 12 3-acre property that was used to recycle and reprocess solid and
liquid waste materials Past waste management practices at the site resulted in widespread contamination
of site soil and groundwater with more than 80 priority pollutants., including VOCs and heavy metals
Contamination has also been detected in the adjacent creek and in off-site groundwater units Cleanup
actions have included installation of monitoring wells, a groundwater extraction and treatment system,
and a 4,400-ft-long barrier wall that completely surrounds the site Although this 30-mch-thick wall
penetrates a siity clay layer near its base, it is considered to be a hanging wall This wall serves as a flow
control device that (1) enhances the efficiency of the extraction system by restricting inward lateral flow
of water from the creek and surrounding areas, (2) intercepts lateral, off-site, migration of contaminated
groundwater within the shallow aquifer, and (3) isolates the area of highest contamination The design,
CQA/CQC of the barrier, and monitoring activities were rated better than acceptable Piezometer pairs
have generally displayed inward and upward gradients except along the northwestern portion of the
barrier wall, where neutral or outward gradients have been documented The neutral and outward
gradients are considered to be a result of very low groundwater extraction rates in these areas, high
extraction rates are localized in areas of the site with relatively high contaminant concentrations
Limited groundwater quality data indicates that contaminant concentrations are decreasing over time
Overall, the barrier wall appears to be meeting its objectives
Site 25
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SITE 26
1.0 SITE DESCRIPTION AND HISTORY
Earner Type
Remedial
Objective
Performance
SB
Hydraulic
containment
Site 26 is located at the northern boundary of a large facility in the western United States Hazardous
wastes have been deposited on 1,750 acres of the 17,000-acre facility The topographic relief is about
200 feet (ft), with the land surface generally sloping northwest toward a nearby river The facility was
established in 1942 and has been used by both government and industry to manufacture, test, package,
and dispose of various chemical warfare agents, rocket fuels, herbicides, pesticides, nerve gases, mustard
gases, and incendiary munitions In 1947, portions of the facility were used for the manufacture of
chlorinated benzenes and the pesticide, DDT After 1970, primary activities at the facility focused on
demilitarization of chemical warfare materials by caustic neutralization and incineration The last
military operation at the facility ended in the early 1980s
The site remedy included a hydraulic cutoff wall and a withdrawal-recharge system to curtail a
contaminant plume migrating across the north boundary No cap is present on site
2.0 GEOLOGIC AND HYDROGEOLOGIC SETTING
There are two major geologic units at Site 26 an alluvial unit and a bedrock unit The alluvium consists
of about 15 ft of fine-grained eohan silt and clay deposits that mantle a 0- to 15-ft-thick lower unit of
well sorted fluvial sand and gravel The maximum alluvial thickness in the area is about 30 ft The
bedrock units consist of deltaic shales, claystones, sandstones, and conglomerates The uppermost
bedrock unit below the site is about 250 to 400 ft thick and contains occasional lignite beds The bedrock
surface reflects the erosional development of a local river valley during the Quaternary period
Consequently the bedrock surface is characterized by isolated bedrock highs and numerous
paleochannels Three significant, alluvium-filled paleochannels can be traced throughout the site area
Groundwater occurs in alluvial deposits and bedrock aquifers, including the underlying bedrock
formations Bedrock formations are important aquifers in the area, where they are tapped by several
thousand stock, domestic, and municipal wells Where they are sufficiently thick and saturated, the
alluvial deposits are capable of yielding large supplies of water The uppermost bedrock unit and the
alluvial aquifers are interconnected and act as a single aquifer regionally, although greater
transmissivities generally exist in the alluvial aquifer Transmissivities in the alluvial aquifer range from
6,000 to as high as 79,000 gallons per day per ft (gpd/ft), hydraulic conductivities range from 84 7 to
7,500 gpd/ft2 Transmissiviry and hydraulic conductivity values in the bedrock aquifer ranges from 0 16
to 1,022 gpd/ft and from 0 04 to 256 gpd/ft2, respectively The bedrock aquifer is frequently under
artesian conditions, causing groundwater in the aquifer to recharge the local alluvial aquifer
Groundwater flow in the alluvial aquifers below the site vanes from artesian to semiconfined to
unconfined The regional groundwater flow direction is from south to north toward the river The
primary groundwater flow and contaminant transport are in the alluvial sand and gravel aquifer overlying
bedrock The total groundwater flow in the site area ranges from 250 to 325 gallons per minute (gpm)
Estimates of the average linear groundwater velocity in the site area range from 1 5 to 10.0 ft/day The
saturated thickness of the alluvial aquifer vanes from 0 to 30 ft in the site area.
Key SB=Soil Bentonrte Wall Performance Rating 2=Evidence suggests objective may be met
Sue 26
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3.0 NATURE AND EXTENT OF CONTAMINATION
Wastes generated from various military and industrial operations were routinely discharged into several
unlined evaporation ponds located on site This practice continued until 1956, when a basin was
constructed with an asphalt liner Solid wastes have been burned at various on-srte locations Chemical
spills have occurred in and around the site manufacturing complexes These actions have resulted in
widespread introduction of a host of organic and inorganic contaminants such as chloride, fluoride,
dhsopropylmethyl phosphonate (DIMP), dicyclopentadiene (DCPD), dibromochloropropane,
organosulfur compounds, organochlonne pesticides, volatile aromatic compounds, and volatile
organohalogen compounds to the on- and off-site groundwater In the mid-1970s, DIMP and DCPD as
well as other organic compounds were detected in groundwater migrating across the north boundary of
the site
The present pattern of contaminant distribution in groundwater extends from south to north along
existing paleochannels (see Figure 1) Downgradient of the site area, the contaminant flow path splits
into two separate pathways as a result of the presence of an area of unsaturated alluvium
4.0 CONTAINMENT REMEDY
To curtail migration of site contaminants across the site's northern boundary, the North Boundary
Containment System (NBCS) was constructed The objective of the system was to provide hydraulic
containment using a soil-bentonite cutoff wall and a series of extraction and recharge wells The system
was assembled in two phases The first phase involved a pilot system that began operation in June 1978
The pilot system consisted of a 1,500-ft-long, soil-bentonite cutoff wall, six dewatenng wells, and 12
recharge wells The cutoff wall ranged in depth from 23 to 27 ft and was designed to be keyed 2 ft into
bedrock
The second phase involved expansion of the pilot system to its present configuration, the expanded
system began operation in January 1982 The extensions of the cutoff wall were constructed in 1981 as
wings to the original pilot system wall and extend 3,840 ft due east and 1,400 ft to the west-southwest
The extended portions of the cutoff wall are about 3 ft wide and up to 45 ft deep
The completed NBCS consists of the following elements (1) a series of 54 groundwater withdrawal
wells to extract contaminated groundwater; (2) a 6,740-ft-long, soil-bentonite cutoff wall to impede
groundwater flow and separate contaminated and treated groundwater, (3) a carbon adsorption treatment
system to remove organic contaminants from groundwater, and (4) a recharge system of 38 wells to
return treated groundwater to the alluvial aquifer The withdrawal wells are divided into three collection
manifolds designated as A, B, and C, the wells discharge water to a common sump before its treatment
The average flow through the system is 200 to 300 gpm
Thirty-five of the withdrawal wells are screened in the alluvium, and 19 wells are screened in the Denver
Formation sandstone units The Denver Formation dewatenng wells have not been used since the
autumn of 1984 because their operation was suspected of inducing contamination in the formation In
October 1988, the NBCS recharge trenches interim response action was implemented to increase the
recharge capacity of the system A total of 10 trenches, each 160 ft long, were installed downgradient of
the west section of the barrier In 1991, five additional trenches were constructed along the east portion
of the bamer system All 15 trenches (Tl through T15) recharge treated water into the alluvial aquifer
Site 26
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• i, > ""~;r^ • •
' .• ' •,. '< •
'l». ;- VI%. 4y.,i :•
I- V ,~SOIL-BENTONITE BARRIER
LEGEND
ISOCONCFNTDATION LINE
ISOCONCENtnATION LIME
MONITORING W6CL
UNSATUHATEO ALLUVIUM
0 400 800
Site 26
FIGURE 1
SITE PUN AND DBCP
CONCENTRATION DISTRIBUTION
fetro Tech EM Inc.
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5.0 PERFORMANCE EVALUATION
The NBCS was designed to intercept, treat, and discharge contaminated and potentially contaminated
groundwater that flows toward and across the northern boundary of the site Groundwater quality and
hydraulic data indicate that the cutoff wall was ineffective during its first 10 years of operation
Insufficient recharge capacity created a large hydraulic gradient across the cutoff wall, which allowed
contamination to move under or through the pilot system portion of the wall Subsequent system
modifications to the recharge system appear to have reduced the gradient to zero or less, which should
reduce or prevent further off-site migration Containment system performance and contributing factors
are described further in the following subsections
5.1 Design
Design procedures used generally exceeded the established industry standards as discussed in Section 3,
Volume I, and the design was rated better than acceptable The existing soil-bentomte cutoff wall is
6,470 ft long; is about 3 ft wide, has a design conductivity of 1 x 10"7 centimeters per second (cm/sec) or
less, and ranges from 20 to more than 45 ft bgs in depth The bottom of the entire cutoff wall was keyed
into the bedrock The east and west extensions were keyed into bedrock at their ends, where the alluvial
aquifer was unsaturated The extensions were also keyed into the existmg pilot system section of the
cutoff wall The entire barrier was covered with a 1 5-ft-thick, clay cover
A report completed in February 1989 evaluates the soil-bentomte cutoff wall and concludes that the most
critical deficiency of the cutoff wall design was the depth of the pilot system portion of the barrier The
pilot system barrier was designed to penetrate about 2 ft into bedrock The presence of high hydraulic
gradients across the barrier in this area was considered to be likely to promote flow underneath the
barrier wall through highly weathered claystone and sandstone in the upper bedrock Groundwater flow
through the bedrock directly beneath the extensions of the cutoff wall was considered to be negligible
because these sections were keyed an average of 12 ft into bedrock and because head differences across
these sections are less than those across the pilot system wall The depth of the weathered bedrock is
generally considered to be less than 12 ft bgs Contractors were hired to fracture hard bedrock zones
using explosives during trenching operations However, the use of explosives may have increased the
secondary permeability of the upper bedrock beneath the barrier Also, the ground vibrations caused by
use of explosives may have sloughed material into the slurry trench
5.2 Construction Quality Assurance and Construction Quality Control
No information was available on the following factors (1) the inspection frequency during trench
excavation, (2) trench bottom cleaning, (3) trench key confirmation, (4) mixing and testing of slurry,
(5) the sand content of the slurry, (6) backfill slump and permeability testing, and (7) as-built records
Without this data, the adequacy of the construction quality assurance (CQA) and construction quality
control (CQC) methods used cannot be evaluated
According to the response action assessment final report, the subcontractor performing trench backfilling
operations during construction of the barrier extensions changed the procedure used for gradation testing
without the knowledge of the site owner Subsequent testing of the barrier revealed many backfill
gradation values significantly outside of the specified range In some areas, more than 50 percent of the
backfill was finer than the 200 sieve size In addition, the water used for slurry mixing during the barrier
extension project consisted of treated sewage water from the site treatment plant It is not known what
effect the use of this water had on the final hydraulic conductivity of the extended cutoff wall
Site 26 4
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5.3 Monitoring
Long-term monitoring was rated acceptable Groundwater samples are routinely collected m numbers
that exceed the industry standard Ten equally spaced, alluvial piezometers were installed about 25 ft
from the cutoff wall to monitor water levels on both sides of the wall Hydraulic conductivities measured
in wall samples averaged 3 x 10"7 cm/sec for the pilot system wall and 2 x 10"8 cm/sec for the extensions
Although laboratory hydraulic conductivity tests indicate that the design permeability has been achieved
in many zones of the barrier, hydrologic data suggests that the overall hydraulic conductivity of the
barrier could be as much as two orders of magnitude higher, or about 2 x 10~5 cm/sec This maximum
value was determined based on aquifer tests performed within 300 ft of the cutoff wall No information
on settlement, movement, geophysical integrity, or dessication or earth stress was available
Comparison of contaminant distributions prepared for DIMP and DCPD for September 1977 (presystem
conditions) and for spring and summer 1987 indicates that the distribution patterns of these compounds
upgradient of the NBCS have not been significantly altered by the presence of the NBCS Similarly,
based on comparison of 1979 data and the distributions observed in 1987, the pattern of DBCP
distribution seems to have been relatively unaffected (see Figure 1) Using DIMP, DBCP, and DCPD as
indicators, the upgradient distribution of contaminants has not been dramatically altered by the presence
of the NBCS
Head differences of up to 9 ft have developed across the cutoff wall since the pilot system was installed
in 1977 (see Figure 2) These head differences have created the potential for northward groundwater
flow through the cutoff wall and the upper bedrock beneath the wall (see Figure 2) The head differences
were attributed to problems with the recharge wells located near the western side of the pilot system,
including limited recharge capacity and inadequate recharge distribution
By 1991, the recently constructed recharge trenches were reducing the large outward gradient within the
alluvial and bedrock aquifers Water level data collected during 1993—the most recent available
monitoring data—indicates that a reverse gradient was established along the entire barrier during most of
this monitoring period (see Figure 3) Water level data collected from well pairs drilled in 1993 proved
for the first time that a reverse gradient was also present in the upper bedrock across the west part of the
cutoff wall Water level hydrographs for alluvium and upper bedrock well pairs indicate a hydraulic
connection between the units along the western and eastern parts of the wall Therefore, if a reverse
gradient is maintained in the alluvium, a reverse gradient should also be present in the upper bedrock,
and contamination movement underneath the cutoff wall should be significantly reduced
5.4 Operation and Maintenance
Problems have been encountered with both the withdrawal and recharge systems at this site The
performance problems of the withdrawal system were attributed to adverse weather conditions and poor
well placement, certain wells were located in partially cemented or clayey sands, which have diminished
dewatermg capacity The buildup of a large hydraulic head across the cutoff wall was attributed to an
inadequate recharge system These problems were addressed through modification of the withdrawal
wells and addition of 15 recharge trenches
5.5 Other Considerations
No cost information was available for the NBCS at the site
Sue 26
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V)
H-
rt
n>
O\
SOUTH
NORTH
Head difference across barrier ~ 70 Feet
SOIL-BENTONITE
BARRIER
! Weathered
Clayshale
LEGEND
«*• IDEALIZED GROUND-WATER FLOW PATH BENEATH BARRIER
Z WATER LEVEL MEASURED SPRING 1987
-- WATER TABLE
5180
5160
5140
-5120
5100
0 100 200
Scale In Feet
Site 26
FIGURE 2
GENERALIZED NORTH-SOUTH CROSS
SECTION SHOWING POTENTIAL
GROUND-WATER FLOW PATH
fetro Tech EM Inc.
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LU
ui
in
CO
I
m
I
uj
S
I
LU
LU
CO
i
LU
LU
m
I
LU
QC
LU
I
5,150-
5,148-
5,146-
5.144-
5.142-
5.140-
5.138-
5,136-
5.134-
5.132-
5.130-
5,128-
5,126-
5,124—
North Boundary Water Levels: Across Barrier
Alluvial Wells
~J Tl T3 T4 T5 TS 77 T8 T9 TIP Til TO T13 TM T15
Sample Date 05/11/93
5,150-
5.148-
5,146-
5.144-
5.142-
5J40-
5,138-
5,136-
5.134-
5,132-
5,130-
5,128-
5,126-
5,124-
i I i I I I I i i
Wefl Location
c Wells South « Wells North
of Cutoff Wall of Cutoff Wall
North Boundary Water Levels: Across Bauier
Allimal Wells
Tl 72 TS T4 T5 T6 17 T3 T9 TIP Til TO TI3 T14 T15
Sample Date. 09/17/93
519
I
I
Well Location
a Wells South o Wells North
of Cutoff Wall of Cutoff Wall
Site 26
FIGURE 3
VARIATION IN WATER TABLE
ELEVATIONS WITH TIME
Tetrcr Tech EM Inc.
Site 26
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5.6 Remedy Performance
The original NBCS, including both the pilot system and its extensions, was not effective in preventing
groundwater contamination from migrating off site because of groundwater recharge system deficiencies
Through addition of recharge trenches and other modifications of the NBCS, the large outward gradient
across the barrier was reduced to zero or reversed to an inward gradient by 1993 If a reverse gradient is
maintained in the alluvium, a reverse gradient should also be present m the upper bedrock, and
contamination movement underneath the cutoff wall should be significantly reduced
6.0 SUMMARY
Site 26 is part of a 17,000-acre facility that was used to manufacture, test, package, and dispose of
various chemical warfare agents, rocket fuels, herbicides, pesticides, nerve gases, mustard gases, and
incendiary munitions Past waste management practices at the site resulted m widespread, on- and
off-site groundwater contamination with a host of organic and inorganic compounds Cleanup actions
involved the installation of monitoring wells and a groundwater extraction and treatment system, which
included a 6,740-ft-long cutoff wall The treatment system was designed to intercept, treat, and
discharge contaminated and potentially contaminated groundwater that was flowing toward and across
the northern boundary of the site
Design performance was rated better than acceptable CQA/CQC could not be evaluated because of lack
of information regarding trench, slurry, and backfill testing Long-term monitoring was rated acceptable
Contaminant plume migration under and through the pilot system wall have been controlled though
addition of recharge trenches that appear to have reduced the large outward hydraulic gradient across the
cutoff wall. Although no recent groundwater quality data was available, the cutoff wall and its
associated treatment system appear to be performing as intended
Site 26
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SITE 27
1.0 SITE DESCRIPTION AND HISTORY
Barrier Type
Remedial
Objectives
Performance
SB
SC
2+
Site 27 is located in eastern United States The site covers about 10 acres and is bounded by industrial
and commercial properties, city streets, and recreational facilities
The site functioned as a burning ground and a landfill for wastes from about 1962 to 1984 The site
received household, construction, and industrial wastes, including over 1,000 drums of various materials
Initial site investigations identified significant contamination, and a removal action was performed m
1984 The site's active containment remedy consists of a soil-bentonite subsurface barrier wall, a
multimedia cap, and a two-well groundwater extraction system Remedial construction was completed at
the site in 1990 A site plan showing basic site features is presented in Figure 1
2.0 GEOLOGIC/HYDROGEOLOGIC SETTING
The site is underlain by about 20 to 40 feet of fill and silty clay to clayey silt This shallow interval
includes lenses of sand typical of the area The base of this shallow stratum includes a clay-silt interval
that forms the key for the subsurface barrier wall, and forms the base of the uppermost water-bearing
zone The aquifer is underlain by a 25- to 80-foot thick clay-silt aquitard Underlying the clay-silt
aqmtard are unconsohdated, sand and silt-clay sequences that continue to crystalline bedrock 100 to 200
feet below grade.
The hydrogeologic setting includes three water-bearing zones The uppermost, unconfined zone is
limited in areal extent and is not a potential source of drinking water because of its insufficient yield
The underlying two zones are either current or potential sources of drinking water The groundwater
flow direction in the upper zone is northeasterly, the direction of flow in the deep zone is to the east-
south east The typical hydraulic conductivity of the shallow zone soils ranges from 1 x 10~3 to 1 x 10-5
centimeters per second (cm/sec) The horizontal gradient in the uppermost zone is about 0 05
3.0 NATURE AND EXTENT OF CONTAMINATION
The on-site soil and groundwater as well as off-site groundwater were contaminated with several organic
compounds and metals Groundwater contamination was limited to the shallow and intermediate water
bearing zones Contaminants included benzene, toluene, ethylbenzene, and xylene (BTEX), vinyl
chloride, tnchloroethene (TCE), dichloroethene (DCE), beryllium, chromium, and nickel The ranges of
concentrations of those contaminants were reported as follows
• TCE 0 to 3,000 y
• DCE 0 to 20,000 ,ug/L
• Chromium 0 to 1 ,600 £ig/L
• Nickel Oto750^g/L
Key SB = Soil Bentomte Wall SC = Source Control Performance Rating 2+ = Evidence suggests objective may be met
Site 27 1
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Also, although the emergency removal action included removal of many of the drums from the site,
wastes remaining on site were a significant source of contaminants
4.0 CONTAINMENT REMEDY
The objectives of the containment remedy are to provide source control and prevent further
contamination of groundwater in the off-site, intermediate water-bearing zone Therefore, the site
remedy required hot spot removal, a subsurface diversion or containment structure, a multilayer cap,
surface drainage control, and periodic groundwater monitoring The implemented remedy involved
active containment and had the following general features
• A soil-bentonite barrier that is about 2,200 liner feet long, 25 feet deep (on average), and
3 feet thick and that has a 5-foot soil key
• Two shallow extraction wells pumping groundwater for off-site treatment
• Eight water level monitoring locations with wells paired across the barrier
• Five additional groundwater quality monitoring locations on site
• A cap with compacted clay liner (CCL) side slopes and geomembrane (GM) on the top,
a drainage layer, and a protective soil cover
• An active gas venting system
5.0 PERFORMANCE
The performance monitoring requirements for the containment include quarterly groundwater quality
monitoring for the first year after construction and annual monitoring thereafter as well as quarterly
measurement of groundwater table elevations to check the gradient across the barrier wall at designated
locations
The hydraulic gradient across the barrier wall was maintained in excess of the natural hydraulic gradient
present Prior to barrier construction, based on the rationale that as long as this original gradient could
be maintained the containment would function A head differential greater than 1 foot was easily
maintained across the barrier wall by the two-well extraction system In fact, the pumping required to
maintain the needed head differential significantly decreased over time
Groundwater contaminant concentrations decreased outside the containment and increased inside the
containment over time, indicating the general effectiveness of the containment
A 5-year regulatory review required for the site indicated that containment performance was adequate
and that the remedy was protective of human health and the environment
Containment system performance and contributing factors are described further in the following
subsections
Site 27
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5.1 Design
The barrier wall design was rated better than acceptable with respect to industry practices described m
Section 3, Volume I The design generally followed established U S Army Corps of Engineers
guidance Significant positive features of the design effort included drilling of alignment borings at less
than 100-foot intervals, testing of more than 60 soil samples, use of a 5-foot soil key, and thorough
compatibility testing No design-level groundwater modeling was performed for the containment The
banner was constructed using trench-side mixing
The cap design was rated slightly less than acceptable The design included a standard RCRA-type cap
as described in Section 4 0 Significant positive aspects of the design effort included ample use of on-
site borings to characterize the fill and its stability and settlement potential Drawbacks of the design
included neglect of seismic considerations in the stability analysis, lack of interface friction testing to
evaluate interface stability, and failure to include a leachate management system
53, Construction Quality Assurance and Construction Quality Control
Barrier wall construction quality assurance (CQA) and construction quality control (CQC) were rated
better than acceptable Generally, the CQA/CQC procedures used conformed to established standard
protocols The barrier key was deepened during construction based on the results of confirmation
sampling every 25 linear feet, resulting in another 3 to 5 feet of excavation over about 60 percent of the
alignment Based on testing of undisturbed samples collected from the completed barrier at 250-foot
intervals, the barrier met the permeability requirement of less than 1 x 10"? cm/sec The average
permeability from confirmation permeability tests was about 2 x 10"^ cm/sec
Cap CQA/CQC was rated slightly better than acceptable Notably, the CCL clay sources were
thoroughly tested for physical properties, including permeability A CCL test pad was constructed and
tested, one sealed, double-ring infitrometer (SDRI) and six undisturbed samples were used for
permeability measurements Compaction-permeability relationships were confirmed in the field
CQA/CQC requirements for installing the geomembrane liner generally followed industry standards
Notably, all extrusion seams were vacuum box-tested, and double-wedge welded seams were air
pressure-tested Shear and peel destructive testing was performed for every 750 feet of seam
53 Monitoring
Containment monitoring was rated slightly better than acceptable The monitoring involved taking
quarterly measurements of groundwater table elevations at eight pairs of monitoring wells spaced about
every 300 feet around the barrier and about 10 feet on either side of the barrier An additional five
monitoring locations inside and outside the barrier were sampled to assess groundwater quality, quarterly
for the first year after construction and then annually Two wells inside the barrier were used to monitor
pumping activities In addition, the amount of groundwater extracted was monitored and reported along
with the water quality data to the receiving publicly-owned treatment works (POTW) No separate
monitoring of the cap other than periodic inspection was performed
The quarterly measurements of groundwater table elevations were available for several years including
the period of groundwater extraction This data showed that in most cases the hydraulic head differential
was maintained above the specified 1-foot difference across the barrier to achieve the design gradient of
greater than 0 05 However, maintaining this hydraulic head differential allowed both inward (negative)
and outward (positive) gradients across the barrier Hydraulic head changes were generally as expected
Site 27 4
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pairs showed outward gradients and a trend toward decreasing water levels as the downgradient recharge
from groundwater flow was interrupted by the barrier Upgradient monitoring well pairs showed inward
gradients and fluctuating exterior water levels but not much mounding against the barrier wall Summary
plots of water levels are shown in Figure 2
Figure 3 shows groundwater quality data collected immediately after construction and for several
consecutive quarters thereafter The wells outside the containment showed generally decreasing
contaminant concentrations while some wells inside the barrier show stabihzing or increasing
concentrations In two cases where monitoring after barrier construction showed contamination outside
the barrier, the wells were located on the downgradient side of the containment, in an area where positive
gradients existed across the barrier
5.4 Operation and Maintenance
Operation and Maintenance (O&M) requirements for the containment involved monthly site inspections,
quarterly effluent sampling and well water level readings, and annual well water sampling since 1991
Earner O&M was designed to respond to any breaching or degradation revealed by water level
monitoring According to the 5-year regulatory review, required O&M activities included correcting
surface erosion problems with the cap and adjusting pumping requirements One significant O&M
problem involved addressing increasing constituent concentrations in extracted groundwater, a carbon
pretreatment process had to be installed in order to meet POTW permit requirements
5.5 Other
The containment has performed well and has been cost-effective The capital cost of the containment
was about $4,500,000 Annual O&M costs were estimated to total about $30,000
5.6 Remedy Performance
The hydraulic gradient design criterion was easily met by the pumping system, and groundwater quality
outside the containment has improved in some cases relative to the original on-site concentrations The
barrier was determined to be of low permeability, adequately keyed, continuous, and intact based on
hydraulic head monitoring and pumping quantities The cap also functioned effectively, only typical
erosion concerns were raised during the 5-year regulatory review
6.0 SUMMARY
Site 27 is the 10-acre site of a former landfill Various chlorinated solvents and metals are present in the
on-site soils and groundwater, and contamination is present in off-site groundwater The sites
hydrogeology and shallow, aquitard allowed for containment of contaminated soil and groundwater on
site The containment remedy consisted of installing a soil-bentomte barrier, a cap, active pumping using
two on-site wells, and monitoring The design and CQA/CQC of the barrier involved a better than
acceptable effort, but the cap design effort was rated less than acceptable Cap CQA/CQC rated slightly
better than acceptable based on the limited data available The pumping system was a conventional
installation
The performance monitoring of the barrier involved post construction sampling of barrier use of paired
piezometers across the barrier, ample groundwater quality monitoring, and regular inspections
Containment performance was consistent with remedial objectives of the remedy, and the containment is
considered to be a protective remedy
Site 27 5
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08/90
GW Table Elevations versus Time
11/90
Down Gradient Well Pair
02/91 05/91 11/91
SAMPLE DATE
02/93
07/93
•Well A (IN) -s>. Well A (OUT)
74
172
§ 70
LU
68
m
I
66
64
08/90
GW Table Elevations versus Time
Up Gradient Well Pair
11/90
02/91 05/91 11/91
SAMPLE DATE
Well B (IN) •«- Well B (OUT)
02/93
07/93
Site 27
Site 27
FIGURE 2
GW TABLE ELEVATIONS versus TIME
Jetra Tech EM Inc.
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80
•§.60
a.
8
20
GROUNDWATER QUALITY
Total VOCs in Downgradlent Well Pair
u
07/90 11/90 02/91 05/91 08/91 11/91 02/92 05/92 08/92
SAMPLE DATE
I Hair
Smouuutju
w Inside O Outside
15
10
GROUNDWATER QUALITY
Total Metals In Downgradlent Well Pair
07/90 11/90 02/91 05/91 08/91 11/91 02/92 05/92 08/92
SAMPLE DATE
HS Inside a Outside
12
,-, 10
£
S 8
GROUNDWATER QUALITY
Total VOCs In Upgradlent Well Pair
07/90 11/90 02/91
05/91 08/91 11/91
SAMPLE DATE
02/92 05/92 08/92
H3 Inside ra Outside
Q.
"5" «
o c
S 2
O
GROUNDWATER QUALITY
Total Metals In Upgradlent Well Pair
07/90 11/90 02/91 05/91 08/91 11/91 02/92 05/92 08/92
SAMPLE DATE
03 Inside a Outside
Site 27
FIGURE 3
GROUNDWATER QUALITY versus TIME
fetro Tech EM Inc.
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SITE 28
1.0 SITE DESCRIPTION AND HISTORY
Earner Type
Remedial
Objective
Performance
SB
~SC~
2+
Site 28 is located immediately upgradient from a drinking water well field in the western United States
The site spans about 22 acres The site formerly held a manufacturing facility that generated waste
solvents Release of waste solvents from a failed storage tank contaminated site soils and groundwater in
the early 1980s
A soil-bentomte barrier wall encircling about 175 acres of the site and a groundwater extraction system
to maintain an inward hydraulic gradient across the wall were installed m 1986 as an interim remedy
Components of the final remedy included excavation and off-site disposal of highly contaminated soil,
soil vapor extraction (SVE), maintenance of an inward hydraulic gradient across the wall, and extraction,
treatment, and off-site disposal of on-site groundwater from a deep aquifer
The layout of the barrier wall and the locations of site monitoring wells are shown in Figure 1
2.0 GEOLOGIC AND HYDROGEOLOGIC SETTING
Alluvial deposits extend from the ground surface to the bedrock, which lies about 330 to 360 feet below
ground surface (bgs) Within the alluvium, sand and gravel layers form four aquifers that are generally
separated by aquitards formed by silt and silly clay layers For the purposes of this evaluation, the
aquifers are referred to as Aquifers 1 through 4, and the aquitards are referred to as Aquitards 1-2,2-3,
and 3-4 Aquifer 1 is the topmost aquifer and is separated from Aquifer 2 by Aquitard 1-2, Aquitard 2-3
separates Aquifer 2 from Aquifer 3, and Aquitard 3-4 separates Aquifer 3 from Aquifer 4 At some site
locations, Aquifer 1 either merges with Aquifer 2 or is absent
Aquifer 1 is about 15 to 20 feet thick, is located about 35 to 40-feet bgs, and is absent at some site
locations Aquitard 1-2 is about 5 to 30 feet thick Aquifer 2 spans the site and is located between 60
and 120 feet bgs The barrier wall is keyed into Aquitard 2-3, which spans the site and is about 40 feet
thick Aquifer 3 also spans the entire site and is located between 150 and 190 feet bgs Aquitard 3-4 and
Aquifer 4 are not continuous across the site Aquifer 4, where it is distinguishable from Aquifer 3, is
located between 220 and 270 feet bgs
Aquifer 1 has generally been dry since the installation of the barrier wall Aquifers 2, 3, and 4 are all
high-yielding aquifers Based on aquifer performance tests, the average hydraulic conductivities are
0 014 centimeters per second (cm/sec) for Aquifer 1, 0 33 cm/sec for Aquifer 2, and about 0 20 cm/sec
for Aquifers 3 and 4 The general groundwater flow direction m all the aquifers is northwesterly
Before the barrier wall installation, the hydraulic gradient in Aquifer 2 ranged from 0 0016 to
0 0020 foot/foot Following the barrier wall installation, the hydraulic gradient within the contained area
became 0 foot/foot, while outside the wall it varied between 0 006 and 0 025 foot/foot
Aquifers 2,3, and 4 were confined aquifers before installation of the barrier wall However, following
the barrier wall installation and pumping of groundwater to maintain an inward hydraulic gradient across
Key SB=Soil Bentomte Wall SC=Source Control Performance Rating. 2+=Evidence suggests objective may be met
SUe 28 1
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CO
H-
rt
(t>
K>
00
to
LEGEND'
MOfiUOT UNC
KKCC UNC
• — 9LUMT WAIL
A OBSERVATION
' WELL
Site 28
FIGURE 1
SITE FEATURES
retro Tech EM Inc.
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the barrier wall, Aquifer 2 became unconfined The downward vertical gradient from Aquifer 2 to
Aquifer 3 ranges from 0 063 to 0 160 foot/foot The net vertical gradient between Aquifers 3 and 4 is 0
foot/foot
3.0 NATURE AND EXTENT OF CONTAMINATION
Following the release of waste solvents from the failed storage tank, site soils and groundwater were
contaminated, primarily with tnchloroethane (TCA), 1,1-dichloroethene (1,1-DCE), acetone, isopropyl
alcohol (IPA), xylenes, Freon-113, and tetrachloroethene (PCE) The groundwater in Aquifer 1 had the
highest concentrations of contaminants, including 1,900 ug/L TCA, 76,000 ng/L xylenes, 99,000 ug/L
acetone, and 45,000 jj,g/L IPA TCA was the primary contaminant m on- and off-site groundwater in
Aquifer 2 with a maximum on-site concentration of 670 mg/L and a maximum off-site concentration of
about 1 ug/L On-site groundwater contamination in Aquifer 3 was limited, this aquifer's highest TCA
concentration was about 7 ug/L However, contaminant concentrations in off-site groundwater in
Aquifer 3 were higher, indicating that contaminants had migrated from Aquifer 2 to Aquifer 3 at
locations off site Aquifer 4 was not sampled
4.0 CONTAINMENT REMEDY
The containment remedy includes the following features
« A soil-bentomte barrier wall that is about 3,425 feet long, 3 feet thick, 100 to 180 feet
deep, and keyed at least 2 feet into Aquitard 2-3
• Extraction of groundwater from Aquifers 1 and 2 to maintain an inward hydraulic
gradient across the barrier wall
• Treatment and off-site disposal of extracted groundwater
• Excavation and off-site disposal of highly contaminated soil
• SVE
The containment remedy did not include installation of a cap to reduce infiltration into the contained
area However, infiltration is expected to be very low in the contained area because (1) over one-third of
the contained area is covered by buildings, driveways, and parking lots, (2) one-third of the contained
area is covered by an approximately 1-foot-thick layer of soil-bentomte mixture resulting from soil-
bentomte mixing operations for barrier wall installation, and (3) the rest of the contained area is covered
by vegetation that removes soil moisture via evapotranspiration
5.0 PERFORMANCE EVALUATION
The objectives for the containment system design and installation were to (1) contain the most
contaminated, on-site groundwater and (2) reduce the volume of off-site groundwater to be remediated
and its remediation time by substantially reducing downgradient migration of on-site contaminants
The performance of the containment system was evaluated by monitoring (1) the water levels m 10 pairs
of piezometers almost equally spaced along the length of the barrier wall and (2) the quality of off-site
groundwater The water table elevation measurements from all piezometer parrs indicated an inward
Site 28
-------
gradient across the slurry wall The maximum differences in water level between piezometers located
outside and inside the barrier wall ranged from less than 1 foot (downgradient of the barrier) to about
16 feet (upgradient of the barrier) The concentrations of contaminants in off-site groundwater
downgradient of the barrier wall decreased significantly after installation of the containment system
Containment system performance and contributing factors are further discussed in the following
subsections
5.1 Design
The containment system design was rated better than acceptable with respect to industry practices
described in Section 3, Volume I The design was based on a thorough investigation of the site geology
and hydrogeology Extensive groundwater monitoring was used to support the design effort, and the
trench-slurry compatibility was investigated Grain size analyses of more than 50 soil samples and
laboratory tests of soil permeability were performed to determine the composition of the soil-bentonite
mix used in the slurry trenches The design considered the seismic stability of the slurry wall, the
potential impact of the barrier wall on the foundations of structures expected to be built in the vicinity of
the bamer wall, and the maximum allowable head difference across the barrier wall The groundwater
extraction system design was based on the results of groundwater modeling
5.2 Construction Quality Assurance and Construction Quality Control
The construction quality assurance (CQA) and construction quality control (CQC) of the containment
system were rated better than acceptable After construction, the integrity of the barrier wall was
evaluated using a hydraulic stress test The test was conducted within the contained area, and it lasted
for more than 1 year During the test, the water levels were measured in 20 paired piezometers located
inside and outside the bamer wall at 10 almost equally spaced locations. The water level measurements
indicated an inward hydraulic gradient across the bamer wall at all 10 locations
53 Monitoring
The performance monitoring program was rated better than acceptable because in addition to periodic
monitoring of water table elevations and water quality across the bamer wall, a pump test was conducted
for more than 1 year to stress the wall for performance evaluation purposes
5.4 Operation and Maintenance
Following the performance evaluation stress test, pumping of groundwater was continued to maintain an
inward gradient across the bamer wall Periodic measurement of water table elevations in paired
monitoring wells has been ongoing since 1987
5.5 Other Considerations
The construction and operation and maintenance costs for the containment remedy were not available for
review.
Site 28
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5.6 Remedy Performance
The containment system achieved its design objectives and performed well Its effectiveness was
demonstrated (1) during a performance evaluation pump test conducted for more than 1 year and (2) by
improvements in off-site groundwater quality
6.0 SUMMARY
Site 28 is located immediately upgradient from a drinking water well field in the western United States
The site spans about 22 acres The site formerly held a manufacturing facility that generated waste
solvents Release of waste solvents from a failed storage tank contaminated site soils and groundwater in
the early 1980s A soil-bentomte barrier wall encircling about 175 acres of the site and a groundwater
extraction system to maintain an inward hydraulic gradient across the wall were installed in 1986 as an
interim remedy. Components of the final remedy included excavation and off-site disposal of highly
contaminated soil, SVE, maintenance of an inward hydraulic gradient across the wall; and extraction,
treatment, and off-site disposal of on-site groundwater from a deep aquifer
The design, CQA/CQC, and performance monitoring program for Site 28 were rated better than
acceptable After construction, the integrity of the barrier wall was evaluated using a pump test that
lasted for more than 1 year The containment system at Site 28 achieved its design objectives and
performed well Its effectiveness was demonstrated (1) during the performance evaluation pump test and
(2) by improvements in off-site groundwater quality
Site 28
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SITE 29
1.0 SITE DESCRIPTION AND HISTORY
Earner Type
Remedial
Objective
Performance
SB
SC
Site 29 is located in the northeastern United States The site is bordered on the south by a road and on
the east, north, and west by wetlands lying along the stream channels of two creeks Industrial and
sermresidential lands surround the site, which is 15 acres in size Historically the site was used to house
a hazardous waste incineration facility The facility contained a high-temperature liquid waste
incinerator, storage tanks, drums, and lagoons Figure 1 shows the site layout
Initial remedial investigations (RI) identified significant contamination at the site In 1982, a state
environmental agency performed a surficial cleanup at the site, which included removal of about 80,000
gallons of liquid chemical waste from 10 bulk storage tanks, demolition of the incinerator, and closure of
the lagoons
The 15-acre site is contained by a subsurface barrier wall installed in 1986 The soil-bentomte slurry
wall is 2,700 feet (ft) long, 4 ft thick, and 14 to 16 ft deep
2.0 GEOLOGIC AND HYDROGEOLOGIC SETTING
The site is located in the Ene-Ontano Plain subsection of the glaciated central region of the Great Lakes
Physiographic Province The topography m the site area reflects the glaciation that most of the glaciated
central region underwent during the Pleistocene epoch
Site 29 lies near the crest of a large drumhn The uppermost soil at the site consists of a variety of fill
and refuse materials Below these materials is a sequence of glacial drift Pleistocene-age glacial lake
deposits make up the youngest unit The clay and silt content of this unit increases to the west as the unit
extends into an rnterdrumhn lowland This unit is underlain by a discontinuous mantle of ablation
(oxidized) toll that has been removed by erosion m the southeastern section of the site Underlying the
ablation till is a variably thick layer of dense lodgement (reduced) till
Localized areas of outwash have also been intercepted in site borings The extent and configuration of
the outwash channels are quite variable, and the outwash sand and gravel are as much as 20 ft thick in the
central portion of the site Glaciolacustnne sediments have also been found overlying the outwash at the
site These sediments are as much as 15 ft thick
The bedrock in the site area consists of nearly flat-lying Ordovician- and Silunan-age sedimentary rocks
The average bedrock dip is about 40 ft per mile Site-specific investigations have involved drilling of
borings through at least the upper 40 ft of the Oswego Sandstone, which is suspected to be at least 400 ft
thick
The hydrogeologic setting includes overburden units with large groundwater yields in localized channel-
in filling stratified outwash sand and gravel Most of the large industrial and commercial wells in the site
area are located within this outwash unit The ablation till is used for residential wells in the site area,
has permeabilities ranging from 1 2 x 10"4 to 4 x 10"5 centimeters per second (cm/sec), and extends from
the surface to 15 ft below ground surface (bgs) The lodgement till and the glaciolacustnne
Key SB=Soil Bentomte Wall SOSouice Control Performance Rating 2=Evidence suggests objective may be met
Site 29
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SCALE
LEACKATE COLLECTION DRAIN
LOW
LEA: HATE
COLLECTION
TANK
Site 29
FIGURE 1
SITE FEATURES
Tetra Tech EM Inc.
Site 29
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sediments are the poorest aquifers and serve locally as aqmtards, their permeabilities range from 7 x 10"5
to 6 x 10~6 cm/sec, and they he from 15 to 36 ft bgs The bedrock aquifer is not very useful as a
water-beanng unit and it lies at depths beneath 36 ft bgs The sandstone bedrock has very low
permeability, although fractures within this unit slightly increase its permeability
Groundwater in the unconsolidated aquifer flows west in the western portion of the site and north in the
northeastern portion of the site A horizontal hydraulic gradient of about 0 01 ft/ft exists in the bedrock
aquifer to the northwest, and a downward hydraulic gradient ranging from 0 004 to 0 19 ft/ft exists
between the water table zone and the upper bedrock zone
3.0 NATURE AND EXTENT OF CONTAMINATION
Liquid waste spills and lagoon overflow into a nearby creek are the primary sources of groundwater and
surface water contamination, respectively Contamination at the site includes metals, volatile organic
compounds, and semivolatile organic compounds Indicator chemicals at the site include the following
• Benzene at between 5 and 6 mg/L
• Toluene at about 16 mg/L
• Ethylbenzene at about 5 mg/L
• Xylene at about 36 mg/L
• Methylene chloride at about 120 mg/L
• Nickel at about 11 mg/L
• Cyanide at about 7 mg/L
Soil contamination is widespread and nonumform across the site During the initial RIs, groundwater
contamination was identified in areas of the overburden aquifer that he outside the current containment
system Therefore, at the time of slurry wall construction, impacted overburden groundwater was not
completely enclosed by the containment system
4.0 CONTAINMENT REMEDY
The objectives for the remedy were to provide source control and minimize or prevent migration of the
existing contaminant plume The primary design considerations for the slurry wall were the following
(1) use of slurry wall components that were compatible with the groundwater, (2) alignment of the wall
in a manner that would provide containment of the contaminant plume, (3) reduction of the leaching
potential of contaminants inside the containment structure by preventing infiltration or precipitation with
a Resource Conservation and Recovery Act (RCRA) cap, and (4) attainment of a permeability of 1 x 10"7
cm/sec for slurry wall materials The implemented remedy involved active containment and included
installation of the following features
• A soil-bentomte barrier wall that is about 2,700 ft long, is keyed a mimmum of 2 ft into
the lodgement till layer, and is 3 to 11 ft thick The top of the wall lies 3 ft below the
existing site grade The wall was constructed using the trench and backfill method to
achieve the design permeability of 1 x 10"7 cm/sec
• A leachate collection sump system within the barrier wall
• A RCRA Subtitle C cap consisting of a 2-foot-thick clay layer, a 40-mil high density
polyethylene (HDPE) liner, and 3 ft of cover soil
Site 29
-------
• Groundwater monitoring well nests at six locations around the site Each nest consists
of two wells, one inside the barrier and one outside the barrier
• Paired piezometers to monitor water levels at six locations surrounding the barrier
Implementation of the remedy was completed in 1986 At that time, it was suspected that the barrier wall
as designed and installed did not enclose all of the existing contaminant plume
5.0 PERFORMANCE EVALUATION
Remedial activities were completed at the site in 1986 shortly after completion of the barrier system At
that tune, the U S Environmental Protection Agency (EPA) reported that contaminants had been detected
outside the slurry wall and that contamination was present in the bedrock aquifer system A
supplemental RI and feasibility study (FS) were completed to determine whether the barrier wall was
intact This supplemental study showed that the permeability of the barrier wall was consistently less
than the maximum design permeability of 1 x 10-7 cm/sec The study concluded that a vertical gradient
may exist at the site and that a stratigraphic depression near the center of the site may permit migration of
contaminants from the site
In order to control contaminant migration, the state environmental agency intermittently removed
leachate from 1986 through 1990 Beginning in May 1991, the potentially responsible party (PRP) for
the site assumed responsibility for leachate removal and disposal From February 1992 through March
1993, leachate was removed from the site at a rate of 20,000 gallons per month The leachate removal
rate was increased to 30,000 gallons per month in April 1993 and remains at that level The pumping
rate is sufficient to maintain an inward gradient at the site
5.1 Design
The barrier design was rated acceptable relative to industry practices described m Section 3, Volume I
Limited groundwater modeling was completed before the design of the barrier
The cap design was also given an acceptable rating The cap design involved a standard RCRA
composite cap as described in Section 4 0, Containment Remedy
5.2 Construction Quality Assurance and Construction Quality Control
Trench sounding, backfill slump, and backfill permeability tests were performed No detailed
information was available on other aspects of construction quality assurance and construction quality
assurance (CQA/CQC)
53 Monitoring
Containment system monitoring was rated acceptable relative to the standard for active containment Six
paired monitoring wells and six pairs of piezometers are used to collect water quality samples and water
level measurements Groundwater data in quarterly sampling reports indicates that contaminant
concentrations inside the slurry wall are being reduced, and an inward groundwater gradient has been
established and maintained for more than 3 years
Site 29
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5.4 Operation and Maintenance
No information was available on operation and maintenance (O&M) activities for the barrier system
5.5 Other Considerations
No information was available on the costs associated with construction and O&M of the barrier system
5.6 Remedy Performance
An inward gradient has been consistently maintained for more than 3 years In addition, groundwater
quality data has shown a decrease in contaminant levels within the barrier wall, contaminant
concentrations in groundwater outside the barrier wall have also decreased The banner appears to be
properly keyed, of sufficiently low permeability, continuous, and intact based on available data The
maintenance of an inward hydraulic gradient by means of pumping appears to be effective in preventing
formation of a vertical hydraulic gradient and migration of contaminants under the site Therefore, the
remedy is performing as designed
6.0 SUMMARY
Site 29 is located m the northeastern United States At the 15-acre site, a soil-bentomte slurry wall was
constructed using a trench and backfill method The wall is keyed at least 2 ft into lodgement till, and a
RCRA Subtitle C cap has been installed at the site A pumping system was installed, and an inward
gradient has been maintained for more than 3 years Barrier design, CQA/CQC, and containment system
monitoring were rated acceptable based on the evaluation criteria The site containment generally met
the remedial objectives Groundwater quality outside the barrier has improved
Site 29
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SITE 30
1.0 SITE DESCRIPTION AND HISTORY
Earner Type
Remedial
Objective
Performance
SB
SC, contain
LNAPL
Site 30, a former dump, is located in the Midwestern United States During the 1970s the site accepted
dry industrial, construction, chemical, and demolition wastes Industrial wastes accepted at the site
included waste oil, resins, flammable materials, caustics, and arsenic-contaminated materials Land use
before dumping began at the site has not been documented A soil-bentomte slurry wall encompasses the
17-acre site to surround the known area of contamination An intermediate slurry wall, located within
the primary wall, separates the primary containment area (PCA) from surface water ponds and wetlands
located on the west and south sides of the site within the primary slurry wall The intermediate wall was
installed after it was determined that not all of the area within the primary slurry wall was contaminated
and that consequently not all of the area needed to be capped
When the primary slurry wall was constructed in 1991, eight clusters of four groundwater monitoring
wells were located equidistant around the site at 400-foot intervals Each cluster consisted of two well
nests one inside and one outside the slurry wall Each well nest consisted of a shallow and a deep well
The wells were located approximately 10 feet from the slurry wall centerline The shallow wells were
screened at the water table and the deep wells were screened at the base of the aquifer directly above the
clay till formation Fourteen pumping wells were located at the site in a pumping well field Eight pairs
of piezometers were also located along the slurry wall midway between the monitoring well pairs.
Currently, only six monitoring wells outside of the barrier wall and two pumping wells remain at the site
All interior monitoring wells and piezometers have been removed Figure 1 shows the locations of the
monitoring wells, pumping wells, and piezometers when the barrier walls were first constructed
Figure 2 shows the current site layout
Groundwater from the PCA was treated in an on-site treatment plant to remove nonaqueous-phase liquids
(NAPL), inorganics, and organics Effluent from the treatment system was returned to the PCA through
an infiltration gallery to flush NAPLs and contamination from the soil and fill
Construction of the primary slurry wall, pumping well field, and treatment plant was completed in
November 1991 Extraction and treatment of oil and groundwater within the PCA began in February
1992 Surface water from the ponds outside of the PCA was also extracted, treated, and discharged off
site intermittently from April 1992 through December 1995 Ten rounds of groundwater sampling were
conducted from April 1992 through October 1995 In February 1995, oil and groundwater extraction was
discontinued A Resource Conservation and Recovery Act (RCRA)-type cap and soil vapor extraction
(SVE) system was installed in the PCA in August 1995, and the SVE system began operating in October
1995
2.0 GEOLOGIC AND HYDROGEOLOGIC SETTING
Site 30 is located in an area of the Glaciated Central Groundwater Region which is characterized by east-
west trending sandy ndges and dunes separated by marshy lowlands. The ndge complexes are
predominantly composed of well sorted fine- to medium-grained sand and occasionally contain minor
amounts of coarse sand, gravel, and silt These sand deposits are 20 to 30 feet thick in the site area
Key SB=So»l Bentonite Wall SG=Source Control Performance Rating 3=Evidence suggests objective may not be met
Site 30 1
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TREATVENT
PLANT
SITE PERIMETER FENCE
PRIMARY
CONTANIMENT
AREA (PCA)
I
' VlNFILTRATION
PVV_S | / GALLERY
»*£-
SURFACE
WATER
AND
WETLANDS
LEGEND
sc OIL/GROUNDWATER
— RECOVERY PUMPING WELL
® PERIMETER MONITORING WELL
0 PIEZOMETER
—— PRIMARY WALL
100 0 100' 200
SCALE 1 ' = 200'
— INTERMEDIATE WALL
SOURCE: MODIFIED FROM FLUOR DANiEL ENGINEERING 199S
Site 30
Site 30
FIGURE 1
FORMER SITE LAYOUT
Tetro Tech EM Inc
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—v; v< -
TREATMENT
PLANT
SITE PERIMETER FENCE
PRIMARY
CONTANIMENT
AREA (PCA)
SURFACE
WATER
AND
WETLANDS
LEGEND
CflL/GROUNDWATER
RECOVERY PUMPING WELL
PERIMETER MONITORING WELL
PRIMARY WALL
100 0 TOO' 200
SCALE 1" = 200'
— INTERMEDIATE WALL
SOURCE. MODIFIED FROM FLUOR DANIEL ENGINEERING 1995
Site 30
Site 30
FIGURE 2
CURRENT SITE LAYOUT
Tetra Tech EM Inc
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The sand deposits are underlain by a gray, argillaceous till that occasionally contains cobbles or pebbles
The till layer is approximately 100 feet thick and directly overlies bedrock in the area
Bedrock hi site area is predominantly composed of the Late Silurian Racine Dolomite Formation, which
is characterized by relatively flat lying, massive, thick-bedded dolomite that contains very few fractures
The sand deposits below the site form an unconfined aquifer that is separated from the deeper, bedrock
aquifers by the till layer. The unconfined aquifer extends from a river south of the site to a major, fresh
water lake north of the site The unconfined aquifer is generally saturated within 10 feet of the ground
surface, making it highly susceptible to contamination Groundwater flow in the immediate vicinity of
Site 30 is generally to the northeast, and groundwater discharges into the fresh water lake and a regional
river South of the site, a local groundwater high divides the unconfined aquifer Flow north of the
groundwater high appears to be toward a major regional river, and flow south of the groundwater high
appears to be toward a river south of the site
The shallow depth to groundwater and the numerous ponds m the site area combine to provide localized
influences on groundwater flow The unconfined aquifer is generally not used for water supply purposes,
however, the aquifer is used for limited industrial and residential purposes Deeper bedrock aquifers are
generally used for high-capacity industrial purposes
3.0 NATURE AND EXTENT OF CONTAMINATION
The primary contaminants of concern affecting groundwater are benzene, trichloroethene, toluene,
polynuclear aromatic hydrocarbons (PAH), and lead The concentrations of these contaminants in the
pumping wells during Round 1 of sampling conducted in April 1992 are as follows
Benzene 130 to 1,900 micrograms per liter (ug/L)
Trichloroethene 230 to 1,700 fj.gfL
Toluene 21 to 20,000 //g/L
PAHs 15 to 6,910 /ig/L
Lead 4 to 60 /zg/L
4.0 CONTAINMENT REMEDY
The containment remedy consists of the following general features
• A soil-bentonite slurry wall about 3,400 feet long, 3 feet wide, and 30 feet deep keyed
3 feet into the clay till formation
• Fourteen pumping wells for extracting groundwater (reduced to two pumping wells)
• An on-site groundwater treatment plant (not operational since February 1995)
• Thirty-two groundwater monitoring wells (currently reduced to six monitoring wells) and
groundwater monitoring
• RCRA-type cap (installed in 1994)
• SVE system and monitoring (installed in 1995)
SUe 30
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5.0 PERFORMANCE EVALUATION
The design goals for the containment system include confinement of the floating hydrocarbon layer and
containment or recovery of groundwater that poses a risk to humans of greater than 1 in 100,000 The
primary design considerations include the following
• Low permeability and compatibility with the contaminated groundwater
• Alignment to confine contaminated groundwater
• Interface with the RCRA cap and underlying till aquiclude
The barrier design, construction quality assurance and construction quality control (CQA/CQC),
monitoring, operation and maintenance, other considerations, and remedy performance are discussed
below
5.1 Design
The barrier design was rated above average compared to industry practices as described in Section 3,
Volume I The primary slurry wall was constructed using trenching-and-backfill method The
intermediate slurry wall was constructed using a vibrating beam method The Waterways Experiment
Station of the U S Army Corps of Engineers conducted a compatibility study of two soil-bentomte slurry
wall backfill mixtures Geophysical testing was conducted and borings were drilled along the barrier
alignment at a frequency of approximately one boring per 100 to 200 feet Suitable clay borrow material
was obtained and mixed with bentonite slurry and, if necessary, dry bentomte to produce a soil-bentomte
backfill mix The backfill was mixed in batches of 100 cubic yards and transported by dump truck to the
trench
The RCRA Subtitle C cap consisted of a 2-foot-thick clay layer, a 40-mil high-density polyethylene liner,
and 3 feet of cover soil The cap covers the site area enclosed by the intermediate slurry wall (the PCA)
5.2 CQA/CQC
Barrier CQA/CQC was rated slightly above average The CQA Plan for the site discusses the following
elements, work platform, slurry preparation, trench excavation, backfill preparation and placement, clay
cap over the slurry wall, and sampling and testing after slurry wall completion The CQA plan was
reviewed by U S Army Corps of Engineers personnel Sampling and testing of the backfill materials
after primary slurry wall completion consisted of obtaining undisturbed Shelby tube samples at 400-foot
intervals along the wall and testing the permeability of samples obtained near the water table, near the
bottom, and from midway between these two samples
5.3 Monitoring
Long-term monitoring was rated average compared to standard industry practice Groundwater elevation
measurements were compared to determine the existence of an inward gradient Figure 3 shows water
level elevations in down- and upgradient perimeter wells, in a pumping well within the PCA under the
RCRA cap, and in the ponds beginning in January 1992
Site 30
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1/9/92 3/18/92 5/21/92 7/6/92 9/24/92 11/19/922/23/93 5/25/93 7/22/93 9/23/93 2/14/94 8/2S/94 10/21/9412/27/94 2/17/95 5/18/95 7/12/9510/20/9512/10/95
2/7/92 4/25/92 6/18/92 8/11/92 10/6/92 1/4/93 3/31/93 6/25/93 6/31/93 10/21/83 5/16/94 9/20/94 11/17/94 V20/SS 3/29/95 6/21/95 9/18/95 11/16/95 1/04/95
DATE
• PCA * Upgrad-out(W61S)
& Pond * Dwngrad-out(W21SR)
Site 30
FIGURE 3
GROUNDWATER ELEVATIONS
lug Tetra Tech EM Inc.
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The figure shows that an inward gradient has not been established across the site Water levels within
the slurry wall were higher than those outside the wall after slurry wall completion and before pumping
began
The water level elevations in the upgradient well located outside of the slurry wall reflect an inward
gradient beginning in August 1994 and remaining through March 1996 monitoring The downgradient
well does not indicate an inward gradient except perhaps between October 1994 and July 1995. The
graph clearly shows that once groundwater extraction was stopped in February 1995, the water level
within the PCA rebounded or leveled out Figure 4 shows the water levels for a downgradient well pair
Again, this figure shows that an inward gradient was not established The infiltration gallery and the
existence of surface water in on-site ponds and wetlands may influence the water level within the PCA
The surface water level in the ponds and wetlands fluctuated between 595 5 to 600 feet above mean sea
level from January 1992 to October 1995
Benzene, total PAHs, lead, and nickel were selected to represent on-site contamination because
groundwater was analyzed for these chemicals during all sampling rounds and they represent several
primary contaminants of concern Figure 5 shows the concentration of contaminants detected in well
W21S, the downgradient well outside the barrier Well W21S is located along the primary slurry wall
(only one banner between the pumping well field and W21S) Benzene concentrations appear to be
declining since January 1993, and total PAHs remained below detection limits until October 1995 Lead
levels, when detected, are stable Nickel concentrations vary from below detection limits to 183 y-g/L,
with no apparent correlation with tune Additional results from sampling round 10 indicate no
significant changes in groundwater chemistry outside of the primary slurry wall
5.4 Operation and Maintenance
Site 30 operation and maintenance components include routine operation, monitoring, and maintenance
of the SVE system, inspections of the RCRA cap, measurements of surface water and groundwater
elevations, control of water levels in the on-site pond, and sampling of groundwater, surface water (for
National Pollutant Discharge Elimination System permit), and soil gas
5.5 Other Considerations
Approximate costs for the design and construction of the slurry wall and treatment systems are presented
below
Activity Approximate Cost
Design $5,900,000
Construction $8,300,000
Subtotal $14,200,000
Operation and Maintenance (for a
2-year operational period) $4,450,000
Total $18,650,000
Site 30
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Well Pair W21S and W23S
Downgradient - Northeast
Oct-95
-W21S(out)
.W23S(in)
.FW-6(PCA)
Site 30
FIGURE 4
GROUNDWATER ELEVATIONS
Tetra Tech EM Inc
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Apr-92
W21S Contaminants
Downgradient - Northeast
2 120
D)
S 100
80
Jan-93
May-94
Benzene
PAHs
(total)
Lead
Nickel
Date
Site 30
FIGURE 5
CONTAMINANT CONCENTRATIONS
Tetro Tech EM Inc
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5.6 Remedy Performance
Although primary bamer CQA/CQC testing indicates that barrier wall design specifications were met,
the remedy is not yet performing as designed An inward gradient has not developed downgradient of the
site and after 10 rounds of sampling over 2 5 years, contaminant levels outside of the bamer wall have
not decreased. The primary reason for the absence of an inward gradient downgradient of the site seems
to be related to the stoppage of pumping The soil vapor extraction system is still being evaluated as part
of the overall remedy for the site
6.0 SUMMARY
Site 30 is a 17-acre hazardous waste landfill that accepted waste oil, resin, flammable materials, caustics,
and arsenic-contaminated wastes, as well as industrial, construction, chemical, and demolition wastes
The primary groundwater contaminants are benzene, tnchloroethene, toluene, PAHs, and lead at
concentrations of up to 20,000 ug/L A 3,400-foot-long soil-bentomte barrier wall encompasses the site,
and an intermediate bamer wall separates an uncontarmnated wetland from the PCA The PCA has a
RCRA cap that was installed in 1994 An extraction system operated from February 1992 through
February 1995 to remove contaminated groundwater for subsequent on-site treatment The treated water
was recirculated through an infiltration gallery until August 1994
Design and CQA/CQC objectives were both rated above average, long-term monitoring was rated
average Hydraulic head monitoring was conducted monthly and indicates that an inward gradient has
not yet developed or been maintained consistently across the PCA Water quality monitoring conducted
quarterly or annually has not shown any significant change in contaminant concentration outside of the
primary barrier wall
Site 30 10
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SITE 31
1.0 SITE DESCRIPTION AND HISTORY
Earner Type
Remedial
Objective
Performance
SB
SC
Site 31 is located within the northern Rocky Mountains in the Western Mountain Ranges groundwater
region The site began operation in 1886 and treated railroad ties and other wood products until 1983
Wood preserving agents used at the site included (1) zinc chloride, (2) a creosote and oil mixture, and
(3) pentachlorophenol (PCP) Process wastes were initially disposed of in a number of locations in the
vicinity of the site plant, including low areas and sloughs immediately north and west of the plant This
occurred until two evaporation ponds were constructed on site in 1958. Solid wastes generated from
retort cleaning were reportedly buned south of the plant Contamination outside the evaporation ponds
was discovered in 1981 during groundwater monitoring
The groundwater beneath about 140 acres of the 700-acre site property contains numerous polynuclear
aromatic hydrocarbons (PAH), including PCP Contaminated groundwater is prevented from moving off
site by a subsurface barrier wall and collection drains A 10,410-foot-long barrier wall surrounds the site
and is keyed into the underlying bedrock (see Figure 1) Contaminated groundwater within the barrier
wall is collected in horizontal drains, remediated by an on-site activated carbon treatment system, and
discharged into an adjacent river No cap is present at this site
2.0 GEOLOGIC AND HYDROGEOLOGIC SETTING
The site stratigraphy consists of a thin, surficial layer of recent alluvial flood plain deposits that directly
overlie the bedrock units beneath the site The alluvial deposits consist of unconsokdated silts, sands,
and gravels that are typically 5 to 12 feet thick The hydraulic conductivities of these deposits range
from 0 1 to 5 x 10-3 centimeters per second (cm/sec) The underlying bedrock dips about 4 degrees to
the west-northwest, which results in three bedrock units (the Morrison, Sundance, and Chugwater units)
subcropping directly beneath the alluvium within the site boundary (see Figure 2)
The Momson unit consists of siltstones, shales, and fine sandstones with individual beds typically less
than 10 feet thick Beneath the site, the thickness of the Momson unit ranges from 0 (at the subcrop
margin) to about 70 feet thick The western segment of the barrier wall was installed through the
Momson unit to cut off dense nonaqueous-phase liquid (DNAPL) migration along these joints
According to aquifer tests, hydraulic conductivities in the Morrison unit range from 1 x 10"4 to 1 x 10"2
cm/sec
The Sundance unit contains well sorted, massive, fine- to medium-grained sandstone that is poorly to
moderately consolidated Because of the dips of the beds beneath the site, the thickness of the Sundance
unit ranges from 0 (at the subcrop margin) to about 120 feet Hydraulic conductivities m this unit range
from 1 x 10"4 to 1 x 10"3 cm/sec
The Chugwater unit consists of shale with sandstone, limestone, and gypsum interbeds The Chugwater
unit is about 900 feet thick beneath the site, where it serves as an extensive confining layer for the high
artesian heads present in the underlying Casper aquifer Based on aquifer tests, the hydraulic
conductivity of the Chugwater unit beneath the site ranges from 1 x 10"6 to 1 x 10"4 cm/sec The Casper
aquifer is considered to be the primary source of groundwater in the region and is found at a depth of
over 900 feet below ground surface (bgs).
Key SB=Soil Bentonite Wall SC=Source Control Performance Rating 2=Evidence suggests objective may be met
Site 31 1
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Site 31
FIGURE 1
SITE LAYOUT
retro Tech EM Inc.
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Morrison Free Phase
Contaminant Plume
Pump
Station A
Oily
Contamination Plume
Sundance & Chugwater
Contaminant Plume
MCWS
Withdrawal
Well
Contaminant Stringer
-Morrison
Contaminant
Plumq Dissolved
Plume"
Site 31
FIGURE 2
CONCEPTUAL SITE CROSS SECTION
SHOWING ESTIMATED BEDROCK
CONTAMINANT PLUMES
fetro Tech EM Inc.
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As a result of the low topographic position of the alluvium along the adjacent river, water in the
Morrison, Sundance, and Chugwater units discharges to the alluvium and then to the river in the vicinity
of the site Local precipitation and losses from the river during periods of high flow also contribute
water to the alluvium.
3.0 NATURE AND EXTENT OF CONTAMINATION
The contaminants found at the site result from its historical use for wood preserving operations
Compounds associated with creosote and PCP wood preserving agents are found in soils and in the
alluvial and bedrock groundwater systems beneath the site The wood preserving wastes largely consist
of an immiscible, heavier-than-water mixture of creosote and PCP in earner oil Contamination at the
site ranges from oil-saturated sands and gravel to groundwater contamination in the parts per billion
range, site contaminants have been discharged to the river
DNAPLs have been observed in the alluvium and in portions of the Momson and Sundance units at the
site No evidence exists that the contamination has entered the Chugwater unit The largest mass of
DNAPL resides in the alluvium, where as much as 7 million gallons has been estimated to have
contaminated an area of about 90 acres Most of the potential 7 million gallons is considered to be
present at residual, immobile saturations The thickness of DNAPL in the alluvium ranges from less than
a. few inches to about 4 5 feet Individual pools are perched above the Momson and Sundance units at
various locations around the site The DNAPL generally resides in the coarser-grained alluvial gravels
and sands
Relative to the large DNAPL mass in the alluvium, the amount of contamination within the underlying
bedrock is limited Discrete, thin layers of DNAPL have been identified in the lower portion of the
Morrison unit, where DNAPL has migrated along select joints that occur within a siltstone layer near the
base of the unit Because of DNAPL movement along the slope of the beds, the contamination has
migrated a lateral distance of about 850 feet from the likely source, the DNAPL contamination is about
60 feet bgs at this point DNAPL contamination within the Momson unit has been observed to extend
just beyond the western alignment of the barrier wall, this contamination lies within the capture zone of
three Momson unit groundwater extraction wells
DNAPL in the Sundance unit occurs in two distinct patterns Localized DNAPL penetration has
occurred within the top 2 feet of the unit, although the depth is more commonly limited to 1 inch or less
The second pattern of Sundance unit contamination consists of occasional, discrete, thin stringers
oriented parallel to the bedding The Sundance unit stringers have been observed at a lateral distance of
about 1,100 feet from the source area Because their lateral migration follows the slope of the beds, the
stringers have been observed as deep as 70 feet bgs
4.0 CONTAINMENT REMEDY
Wood-preserving operations at the site ceased in 1983, and the site was placed on the National Priorities
List (NPL) in the same year Also in 1983, a dike was built along the river to isolate the site from the
100-year flood plain In fell 1983, a section of sheet pile was installed to cut off the flow of oil from the
site into the nver along a subsurface flow path Surface impoundments containing hazardous waste were
remediated, and the site plant was demolished in 1984 The removal actions involved processing more
than 700,000 gallons of wood preserving oils and treating about 250,000 gallons of contaminated pond
water
Site 31
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The EPA selected an interim remedy in 1986 to control the source of contamination and to provide for
groundwater cleanup The objective of this remedy, called the Contaminant Isolation System (CIS), is to
prevent contaminant migration to the river using a barrier wall, and to extract and treat contaminated
water within the banner wall Because the contamination extended up to and beneath the river, the nver
channel had to be relocated about 150 feet to the west to allow the barrier wall to be installed around this
contamination
The barrier consists of a 10,410-foot-long, soil-bentomte wall that encloses an area of about 144 acres
In the areas where the Sundance and Chugwater units subcrop, the wall was extended completely through
the alluvium and at least 2 feet into bedrock. The typical depth of the barrier wall in these areas is 10 to
15 feet below the original ground surface In areas where the Morrison unit subcrops, the wall's depth
was extended through the alluvium, and the Morrison unit, and into the upper 2 feet of the underlying
Sundance unit In these areas, the wall extends as much as 77 feet bgs
Alluvial groundwater levels are managed by a series of horizontal collection dramlines This collection
system consists of about 18,000 feet of buned, horizontal drainlines, three pump stations, and two
discharge points to the nver (see Figure 1) The purpose of the drainlines is to ensure that water levels
inside the barrier wall are lower than levels outside the wall The reverse gradient is monitored through
collection of about 100 water level measurements each month from the alluvium, Sundance, and
Chugwater units (see Figure 3) Water collected within the internal drainlines is treated by a series of
activated carbon columns that adsorb contaminants About 57 million gallons of water had been treated
after the first year of system operation The treatment system is capable of processing contaminated
water at flow rates up to 400 gpm The treated water is then discharged to the nver under a National
Pollutant Discharge Elimination System (NPDES) permit
Contaminated bedrock groundwater, which is considered to be limited in occurrence, is located both on
and off site On-site DNAPL contamination is contained by the CIS and the upward gradients within the
bedrock units Off-site contamination is being removed by three withdrawal wells and treated in the CIS
activated carbon water treatment plant Twenty-one wells and piezometers are monitored as part of this
system six inside the wall and 15 outside the wall Data on water levels, groundwater flow paths,
gradients, and the capture zone is evaluated monthly This data shows that the capture zone extends
beyond the limits of the groundwater contaminant plume
5.0 PERFORMANCE EVALUATION
The objective of the alluvial water level monitoring program is to confirm that the water management
system is maintaining an inward flow gradient at the bamer wall. The water level monitoring network
includes paired piezometers located immediately inside and outside the bamer wall to allow direct
observations of water levels near the wall Since CIS startup, potentiometnc maps have shown lower
alluvial water levels inside the bamer wall and alluvial groundwater flowing into the ulterior drams (see
Figure 4) Water level gauging and potentiometnc surface maps for the alluvium are generated on either
a monthly or quarterly basis As long as inward groundwater flow gradients are maintained within the
water management system, additional alluvial water quality monitoring is not performed However,
limited sampling of nver sediments and fish tissue is conducted In addition, NPDES samples are
collected from the north and south drains on a weekly basis
The containment system has been successful in reducing on-site levels of contamination and in
preventing contaminants from reaching the nver Specific performance factors are evaluated in the
following subsections
Site 31
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Pill
Site 31
FIGURE 3
PUN VIEW SHOWING CIS ALLUVIAL
WATER LEVEL MONITORING WELLS
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39
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SAMPLE DATE
Inside Well (P-1 23)
Outside Well (P-1 24)
Site 31
FIGURE 4
WEST WALL HYDROGRAPHS
Tetro Tech EM Inc
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5.1 Design
The barrier design was rated acceptable as compared to established industry practices described m
Section 3, Volume I The design objectives for the barrier wall were to provide a (1) physical barrier that
reduces the potential for outward movement of contamination and (2) hydraulic barrier that reduces the
flow of water into the containment area On average, less than one preconstructoon soil bonng was
installed every 200 feet along the barrier alignment, except along the western wall, where the bonng
density increased to about one every 75 feet because of the proximity of the river. The top of the barrier
wall is protected from damage and desiccation by 2-foot-thick, protective fill The fill is a granular soil
separated from the wall by a geotextile fabric A gravel road was constructed on top of the barrier wall
on the western two-thirds of the site to allow access and maintenance The barrier wall is composed of a
mixture of the following (1) up to 85 percent by weight selected backfill material consisting of suitable
on-site-excavated sand, gravel, and bedrock fragments and imported sand and gravel, (2) not less than 10
percent by weight imported silt and clay, and (3) not less than 2 5 percent by weight commercial
bentorute Compatibility tests were conducted to evaluate the effect of contact between the soil-bentomte
mixture and contamination on the permeability of the wall materials
5.2 Construction Quality Assurance and Construction Quality Control
Barrier construction quality assurance (CQA) and construction quality control (CQC) were rated better
than acceptable because the procedures used generally exceeded the established standard protocols The
permeability of the soil-bentomte backfill was measured as 1 x 10"7 cm/sec (fixed-ring), and 6 x 10"8
cm/sec (triaxial), which met the design criteria The depth of the completed trench before backfilling
was measured at 25-foot intervals Visual analysis of trench bottom samples along with evaluation of
subsurface data verified that the wall was keyed into the specified geologic formations
53 Monitoring
Long-term monitoring was rated acceptable as compared to established standard protocols Hydraulic
head measurements are routinely collected from at least eight sets of paired piezometers However,
information regarding barrier settlement, movement, continuity, and integrity is generally not collected
Alluvial water level data from December 1986 indicates that water levels were higher inside the barrier
wall than outside along the western and most of the northern segments of the wall This finding reflects
conditions before the startup of the CIS By April 1987, groundwater elevations had dropped along the
southern, northern, and western segments of the wall, as a result of CIS operation An inward gradient
was detected at three of the eight alluvial monitoring well pairs straddling the barrier wall Groundwater
levels measured during May 1987 indicate the presence of an inward gradient at all eight alluvial
monitoring well pairs straddling the barrier wall. According to quarterly monitoring reports, this inward
gradient has been maintained through the most recent sampling date (June 15,1995) The most recent
alluvial potentiometnc map shows groundwater at the site flowing toward the interior drains and shows
lower alluvial water levels inside the barrier wall than outside
Alluvial water quality data collected to meet NPDES permit conditions suggests that no organic
contamination concentrations above the method detection limits are leaving the site Inorganic
concentrations in groundwater being discharged from the site are within the range specified in the
NPDES permit In addition, sampling and analysis of river sediment indicated no statistical difference
between contaminant concentrations upstream of and adjacent to the site The results of 1987 and 1988
fish sampling events generally show nondetectable or trace levels of PAHs in whole fish samples, and no
contaminants were detected in fish fillet samples collected during this period
Site 31 8
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Bedrock groundwater elevations measured in May 1987 indicated that water levels within the Morrison
unit inside the barrier wall were lower than outside the wall Water levels in the Sundance and
Chugwater units are higher than in the alluvium, suggesting a potential for upward flow from the
Chugwater unit, through the Sundance unit, into the alluvium Except for Morrison unit removal wells,
contamination was detected in only two Morrison unit wells (BR-29 and BR-35) and one Sundance unit
well (BR-5)
5.4 Operation and Maintenance
Contaminated site areas are surrounded by a barbed-wire fence and locked gates Once each week, the
site facilities are inspected for damage, evidence of intrusion, and other problems The inspection
includes examination of the fence and gates, pump stations, and buildings Each month, the entire length
of the barrier wall is inspected for signs of damage or erosion, including the following (1) excessive
settlement at the ground surface, (2) rodent or beaver holes in the flood-plain dike, (3) nearby erosion,
and (4) broken or leaking water lines The top of the barrier wall is protected from damage and
desiccation by a 2-foot-thick, protective fill The fill is granular soil separated from the wall by
geotextile fabric In addition, the river channel is inspected for signs of erosion
5.5 Other Considerations
The construction and CQA/CQC costs for the barrier wall totaled about $2 5 million
5.6 Remedy Performance
Based on almost 10 years of monitoring data, the CIS (including the barrier wall) appears to be
preventing contaminant migration from the site to the surrounding alluvium and the river CQA/CQC
testing performed during and after barrier wall construction indicated that the design specifications were
met Monthly monitoring of the water management system has demonstrated that alluvial water levels
are consistently lower inside the barrier wall, thus providing a reverse-gradient hydraulic barrier to help
prevent contaminant migration to the river Since the CIS was installed, contaminant concentrations m
the river have been about one to two orders of magnitude below proposed sediment criteria for protection
of aquatic life and concentrations corresponding to ambient water quality criteria
6.0 SUMMARY
Site 31 is a 700-acre wood treatment facility where past operations have caused widespread DNAPL
contamination of soil and groundwater Site contamination ranges from oil-saturated sands and gravels
to groundwater contamination in the parts per billion range, and discharged to the adjacent river A
10,410-foot-long, soil-bentonite barrier wall was constructed around the contaminated portion of the site
to control the source of contamination and prevent further contaminant discharges to the river To
remediate the groundwater, a system was installed to collect, manage, and treat contaminated
groundwater within the barrier wall
The barrier wall design was rated acceptable, and CQA/CQC was rated better than acceptable Long-
term monitoring was rated acceptable Hydraulic head monitoring is conducted monthly to quarterly, but
available water quality data is limited to the bedrock aquifers Alluvial hydrographs for paired
piezometers along the barrier wall indicate that a continuous inward gradient has been maintained since
the treatment system was put in operation Three groundwater extraction wells appear to be limiting the
movement and reducing the levels of contamination in the bedrock aquifers outside the barrier wall
Overall, the barrier wall and associated water management system appear to be meeting the remediation
objectives
Site 31
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SITE 32
1.0 SITE DESCRIPTION AND HISTORY
Earner Type
Remedial
Objective
Performance
SB
Isc"
Site 32 is a 35-acre former sand and gravel quarry that was subsequently used as a landfill The site is
located in the northwestern United States Landfilling operations at the site, including open burning of
refuse, started in the early 1960s The layout of the site is shown in Figure 1
2.0 GEOLOGIC AND HYDROGEOLOGIC SETTING
No site investigation was performed before the start of the landfilhng operations However, a geologic
and hydrologic investigation was performed later to support selection of the remedial action and closure
requirements The site stratigraphy is summarized below (in descending order)
« Upper soils consisting of very permeable sand and gravel The thickness of this deposit
ranges from 4 to 30 feet
• Some very dense glacial till lenses (silly sands)
• A very dense layer of silry, sandy gravel that ranges from 12 to 30 feet in thickness
• Older, undifferentiated deposits consisting of layers of sand, gravel, and silt
A shallow aquifer exists in the sand and gravel deposits During the rainy season, this aquifer rises and
saturates the lower zone of landfill refuse, thereby generating leachate This shallow aquifer is perched
on top of the older, undifferentiated deposits Groundwater m the aquifer flows southwest toward a river
The vertical permeability of the older, undifferentiated deposits is less than or equal to 1 x 10-6
centimeters per second (cm/sec) A deep aquifer also exists below the site at a depth of 130 to 150 feet
below ground surface
3.0 NATURE AND EXTENT OF CONTAMINATION
No information exists on the nature and quantities of refuse deposited in the landfill until 1977
Approximately 270,000 tons of municipal solid waste were received between 1977 and 1993 when final
closure took place Sixteen monitoring wells have been installed throughout the site Organic
compounds were detected in the shallow aquifer downgradient of the landfill Concentrations of iron and
manganese in the aquifer exceeded secondary drinking water standards Benzene was also detected in
the shallow aquifer at concentrations in excess of 5 micrograms per liter Sampling of off-site, domestic
wells revealed no groundwater contamination m the shallow aquifer No contaminants were detected in
the deep aquifer
4.0 CONTAINMENT REMEDY
The containment remedy for the site includes the following features
• A soil-bentomte cutoff wall that is 4,750 feet long, 3 feet wide, and 50 feet deep on
average
Key SB=Soil Bentomte Wall SC=Source Control Performance Rating l=Remedial objective was met
Site 32 1
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• A leachate extraction well system and pump station
• A leachate aeration basin
• A gas control and disposal system
• A geomembrane final cover system that includes a 60-miI, high-density polyethylene
liner and a 3-foot thick soil section
5.0 PERFORMANCE EVALUATION
The cutoff wall and leachate extraction facilities were designed to maintain the groundwater level inside
the containment at least 3 feet below the deepest refuse (to minimize the amount of leachate generated)
and at least 1 5 feet below the groundwater level outside the containment Extracted leachate is pumped
first to an aeration basin then to a wastewater treatment facility through a new, 6-inch-diameter, 8-mile-
long force main to an existing treatment plant
5.1 Design
Several remedies were evaluated based on their technical adequacy and cost Soil borings were drilled
along the cutoff alignment at 2-foot intervals The design of the selected remedy was (at least) rated
acceptable relative to industry practices discussed in Section 3, Volume I Hydraulic modeling was done
to estimate the drawdown and pumping requirements for the system The cutoff wall was designed to be
keyed 3 feet into the layer of low-permeability, older, undifferentiated deposits This layer is continuous
beneath the site The design permeability was less than or equal to 1 x 10-7 cm/sec
The design included a final cover (high density polyethylene geomembrane) and a landfill gas system
The system of leachate extraction wells was designed for an initial drawdown of 30 million gallons of
leachate and then a maintenance rate of 80 gallons per minute (gpm) After full closure of the landfill,
the pumping rate was expected to drop to 20 gpm The extracted leachate was to be pumped through the
force main to an existing treatment plant A typical cross section of the site is shown in Figure 2
5.2 Construction Qualify Assurance and Construction Quality Control
No rating for construction quality assurance (CQA) and construction quality control (CQC) was assigned
because no CQA or CQC data was available for our review
Installation of the cutoff wall was performed by a slurry wall specialty contractor Excavation was more
difficult than expected The contractor claimed that a very hard, cemented layer not shown in the soil
boring logs was present The engineer and owner maintained that the logs indicated the presence of a
very dense layer with a blow count in excess of 100 per 6 inches In any case, all parties agreed that the
work was more difficult than anticipated, and an agreement was reached to extend the work schedule and
increase the contract value To increase the rate of excavation, the contractor prednlled 28-inch-diameter
holes at 10 foot centers
The cap was constructed in two phases The northern part of the landfill, approximately 15 acres was
covered in 1989, and the remaining 20 acres in 1994
SUe 32
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The three leachate extraction wells were tested to evaluate their capacity and the drawdown before
extraction operations began
5.3 Monitoring
Monitoring was given an above average rating Piezometers and monitoring wells were installed inside
and outside the containment area Ten wells outside the barrier wall, seven in the shallow aquifer, and
three m the deep one are presently, (almost 7 years of operation), monitored quarterly They were
monitored daily upon the start of operation Samples are analyzed for about 150 chemical parameters In
addition, the elevation of the groundwater is monitored inside and outside the wall (see Figure 3)
5.4 Operation and Maintenance
A particularity of this site is the installation of an automatic control system for the operation of the
extraction wells The system is controlled by one of the piezometers which is instrumented A remote
monitoring system has also been installed for the landfill gas control system These systems are
connected to the owner operation centers via modem, eliminating the need for a site attendant Hence,
past closure care and reporting are automated, ensuring continuous monitoring of the groundwater levels,
leachate extraction flow rates, and flare temperature
5.5 Other Considerations
No cost uiformation was available about either barrier installation or O&M The closure cost was
estimated at $110,000 per acre
5.6 Remedy Performance
Initial drawdown occurred faster than expected After 3 months of system operation, the water table
inside the containment had been lowered 8 feet During the same period, the water table outside the
containment rose to 5 feet as a result of rainfall Only 9 5 million gallons of leachate was pumped to
achieve the 8-foot lowering of the water table inside the containment instead of the expected 30 million
gallons This indicates that the soil was much less porous than anticipated
After the initial drawdown, leachate extraction took place only as required to maintain the level of the
water table inside the containment 3 feet below the refuse
In a recent publication, after analysis of the available data, representatives of the operators concluded that
the inward hydraulic gradient has been maintained as per design objective and that the groundwater
monitoring shows "ten statistically significant reductions in the selected leachate indicator parameters,
two increases (neither statistically significant) and are unchanged condition", thereby demonstrating that
"the shallow aquifer remediations have reduced off-site migration"
6.0 SUMMARY
Site 32 is a former sand and gravel quarry that was subsequently used as a landfill Organic compounds
were detected in the shallow aquifer downgradient of the landfill The deep aquifer was not
contaminated A remediation plan was implemented to contain contaminated leachate and maintain the
level of the water table within the containment below the waste The remedy consisted of a soil-
bentomte cutoff wall around the landfill, a cap, and a leachate extraction system The leachate is pumped
to a municipal treatment plant 8 miles away Water quality in the shallow aquifer has improved and is
presently good Future increase of contamination is not expected with continued operation and
maintenance of the remedial system
Site 32
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FIGURE 3
GROUNDWATER DRAWDOWN ELEVATIONS
Tetra Tech EM Inc
Site 32
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SITE 33
1.0 SITE DESCRIPTION AND HISTORY
Earner Type
Remedial
Objective
Performance
FG
SC, msitu
treatment
Site 33 is located in the western United States A single-story structure occupies 20,000 square feet of
the 1 5-acre site The site is bounded by industrial and commercial properties and a city street
Semiconductors were manufactured on site from the late 1970s to 1983 Volatile organic compound
(VOC) contamination of site soil and groundwater occurred as a result of manufacturing operations A
groundwater extraction and treatment system approved as a final remedy for the site by the state has been
in operation since 1987 The in situ treatment system was installed in late 1994 and early 1995 (see
Figure 1)
2.0 GEOLOGIC AND HYDROGEOLOGIC SETTING
The site investigation identified two water-yielding zones Zone A consists of fine- to medium-grained
sands and silly sands lying 10 to 15 feet below ground surface (bgs) Groundwater in this shallow
aquifer flows northwest A low-permeability layer of silt and clay that is about 65 feet thick separates
Zone A from the deep aquifer, Zone B
3.0 NATURE AND EXTENT OF CONTAMINATION
VOCs were detected in Zone A groundwater beneath the site These VOCs include tnchloroethene,
czs-l,2-dichloroethene, and Freon 113 No VOCs were detected in Zone B groundwater
4.0 CONTAINMENT REMEDY
The objective of the bamer wall was to provide a cheaper treatment alternative than the existing
groundwater extraction and treatment system at the site An in situ treatment process based on
metal-enhanced dehalogenation of VOCs was selected for further study and implementation The
remedy had the following features
• Construction of a cement-bentonite wall on one side and a soil-bentonite wall on the
other side of the site The purpose of these bamer walls was to channel (or "funnel")
contaminated groundwater toward a permeable reactive bamer
• Construction of a 38-foot-long, 22-foot-deep, permeable reactive barrier, also known as a
treatment wall (or "gate")
• Installation of monitoring wells inside and outside the treatment wall
5.0 PERFORMANCE EVALUATION
The in situ treatment system was installed in late 1994 and early 1995 The treatment wall has been in
operation since January 1995 Subsequent monitoring indicated that the chemical concentrations in the
influent to the treatment wall were higher than those anticipated in the design effort However, the
contaminant concentrations in the effluent downgradient of the treatment wall were below regulatory
levels
Key FG=Funnel Gate SC=Source Control Performance Rating 2=Evidence suggests objective may be met
Site 33
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Site 33
FIGURE 1
PUN VIEWS AND GROUNDWATER
FLOW MODELING OF TREATMENT WALL
Tetra Tech EM Inc
Site 33
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5.1 Design
The design of the containment system rated better than acceptable relative to industry practices discussed
in Section 3, Volume I The design effort included evaluation of the in situ treatment process
Laboratory tests indicated that the VOCs in the site groundwater were degrading in the presence of
granular iron In addition, a 9-mne month, pilot-scale test was conducted on site during which site
groundwater was pumped through a 7-foot-high canister filled with granular iron These tests
demonstrated that complete degradation of the influent VOCs occurred when the groundwater flowed
through the iron pellets
The design effort also included a geotechmcal investigation and design of the funnel and treatment wall
system The geotechmcal investigation was substantial 49 cone penetration tests were performed to
develop a geotechmcal model This model was used to determine the alignment of the slurry wall and its
depth In addition, the design laboratory evaluated and optimized cement-bentomte slurry mixes Long-
term compatibility tests were performed on selected cement-bentomte slurry mixes
A numerical groundwater flow model was developed to determine the maximum flow velocity through
the in situ treatment wall The model was calibrated using historical hydraulic data Hydraulic and
bench-scale tests provided the data required to determine the dimensions of the treatment wall.
Trenchabihty was thoroughly evaluated to select the type of barriers to be installed as well as the location
of the braced excavation for the treatment wall
5.2 Construction Quality Assurance and Construction Quality Control
The construction quality assurance (CQA) and construction quality control (CQC) program was rated
better than acceptable The barrier installation work was done by a specialty slurry wall contractor A
CQA/CQC program was established by the contractor before the start of the project The program
included the following activities
• Continuous visual inspection of the cuttings to ensure at least 2 feet of penetration into
the aquitard
• Depth sounding at 25-foot intervals
• Certification of materials
• Daily testing of the bentonite and cement-bentomte slurries
• Daily testing of the soil-cement backfill before backfilling
• Unconfmed, compressive testing and tnaxial permeability testing of the soil-cement
backfill and hardened cement-bentomte The specified unconfined, compressive strength
was 17 5 pounds per square inch at 28 days, and the required permeability was less than
or equal to 5 x 10"6 cm/sec
The treatment wall was installed inside a temporary, sheet-pile cofferdam with temporary bracing A
temporary form system was installed inside the cofferdam to ensure that the iron pellets and pea-gravel
filter would not mix together during backfilling operations Some permanent sheet piles were left in
Site 33
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place to connect the slurry walls with the treatment wall, thereby ensuring that no contaminated
groundwater would flow on the edges of the wall
53 Monitoring
The monitoring system at the site was rated acceptable and included the following elements
• Four monitoring wells in the iron filter at the downgradient edge of the treatment wall
• Two piezometers in the upgradient pea-gravel filter
• One monitoring well upgradient of the treatment wall to measure chemical
concentrations Groundwater samples collected from this well contained some chemicals
at concentrations higher than expected
5.4 Operation and Maintenance
No operation and maintenance data was available
5.5 Other Considerations
No cost data was available
5.6 Remedy Performance
Groundwater samples collected downgradient of the treatment wall show that contaminant concentrations
have been reduced to below regulatory levels The treatment performance is notable because influent
contaminant concentrations have been higher than planned for in the design
6.0 SUMMARY
Site 33 is believed to be the first commercial application of a subsurface reactive barrier for treating
groundwater contaminated with VOCs Based on the monitoring performed for 1 5 years after the
installation of the system, the in situ treatment wall has met the remedial objectives
Site 33
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SITE 34
1.0 SITE DESCRIPTION AND HISTORY
Earner Type
Remedial
Objective
Performance
SB
Hydraulic
Bamer
Site 34 involved the construction of reservoir facilities at a site in the mid-atlantic United States In 1987
and 1988, an earthen dam and a dike were constructed using a soil-bentonite slurry wall extending through
the dam and dike embankments and through the site overburden This wall was intended to serve as the
barrier to seepage through the previous embankment and overburden. The reservoir covers about 760
acres, and its storage capacity is close to 4 2 billion gallons
2.0 GEOLOGIC AND HYDROGEOLOGIC SETTINGS
As shown in Figure 1, the dams and dike are underlain by Coastal Plain sediments consisting of the
following formations in descending order
« The upper Kirkwood Formation is predominantly a sandy formation lying above the lower
Kirkwood Formation, which consists of interlayer silt, clay, and sand
• The Manasquan Formation, which lies below the Kirkwood Formation, is the major clay
layer below the reservoir It contains highly plastic, glaucomtic clay at its top and
becomes sandy toward its bottom
• The Vincentown Formation is mostly sandy
Acidic soils exist within all of these formations The level of the groundwater table within the Kirkwood
Formation varies greatly depending surface topography The hydraulic conductivity of the Kirkwood
Formation varies from 1 x 106 to 5 x 10~7 cm/sec The Vincentown Formation is the mam regional aquifer
present below the reservoir. Some artesian conditions exist in the vicinity of the dam
3.0 NATURE AND EXTENT OF CONTAMINATION
No known contamination exists at the site
4.0 CONTAINMENT REMEDY
The containment design was unique as it incorporated a soil-bentonite cutoff wall for the initial
construction of the impervious dam core Several other alternatives for the impervious core were studied,
including a cement-bentonite cutoff wall and a clay core The soil-bentonite cutoff wall was more
economical than the cement-bentonite cutoff wall and the clay core No economical source of clay for the
clay core was available locally The embankment fill material for the dam and dike consisted mostly of
fine sand from the Upper Kirkwood formation obtained from on-site borrow areas This material was
mostly sandy (classified as SW, SP-SM, and SM) The soil-bentomte wall is subject to a very high
gradient, particularly at the lower elevation of the valley across which the dam was installed This gradient
warranted an increase in the thickness of the soil-bentonite wall in this deep zone The soil-bentomte
Key SB=Soil Bentonrte Wall Performance Rating l=Remedial objective was met
Site 34
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120
too
teo
•0
40
M
UOWCT tWWSQUMI SMB
0 500 FT
0 SCM£ «« M
FIGURE 1A-PROFILE ALONG AXIS OF 0AM
OIBANKUENT
FU.IH UIHED MttA
lMr
DAM CftEST EL 34 U (111 FT)
UPPER STACe PUTFORH
STACC puirow
vp a orot-svsiai vmuum
WIRE PtEZOUCItR
40 VP • aoscD-SYsmi vmunm
MIN. I tU (SFT) */^/OPPCT HNWSQUIW CUY/\
se •
TOTAL SIHtSS COL
^K/MB
FIGURE I b- TYPICAL DAM SECTION (STA is + so) o '^ • u
33
30
Site 34
FIGURE 1
DAM CROSS SECTIONS
Tetro Tech EM Inc.
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wall also extended below the dam through the previous overburden The soil-bentomte cutoff wall is about
4,000 feet long, is 3 to 4 feet thick, has a maximum depth of 76 feet with a key depth of 5 feet, and has an
area of 333,000 square feet
5.0 PERFORMANCE
Barrier performance and contributing factors are discussed further in the following subsections
5.1 Design
The design was rated better than acceptable relative to industry practices described in Section 3, Volumt
A site soil investigation and the design of the soil-bentonite cutoff wall were performed by a geotechmcal
engineer A thorough investigation of the site, including the subsurface conditions along the barrier
alignment, was performed The design effort included hydraulic simulations as well as stability settlement
analyses of the dam and overburden The design was based on a long-term permeability of less than or
equal to 1 x 10"6 cm/sec for the cutoff wall The design key in the Manasquan Formation clay was 5 feet
An extensive laboratory study of the soil-bentomte backfill was performed that included the following
activities
• Testing of various soil-bentomte backfill mixes and site materials representing all
expected soil conditions through which the excavation would take place
« Compatibility testing of backfill mixes and the site groundwater, which was acidic
» A study of the compressibility of the backfill
* Evaluation of the potential for hydraulic fracturing of the cutoff wall in view of the high
gradient
5.2 Construction Quality Assurance and Construction Quality Control
Construction quality assurance (CQA) and construction quality control (CQC) was rated better than
acceptable The installation of the soil-bentomte cutoff wall was performed by a specialized slurry wall
contractor Because the soil-bentomte wall was a critical element for the long-term stability of the dam, its
installation was subjected to stringent procedures The installation of the key material into the aquitard
was continuously inspected by the slurry wall contractor and a representative of the owner
Samples of the bottom of the trench and of the interface of the slurry and backfill were collected every day
before the trench was backfilled This sampling was performed to ensure that no sand deposit was present
in the key (Most of the trench excavation took place in sand materials )
Slurry properties were monitored two or three tunes per 8-hour shift, both in the storage ponds for new
slurry and in the trench In addition, the trench slurry was desanded continuously
The backfill mixed along the trench with a bulldozer was subjected to daily gradation density and slump
testing Fixed wall permeability tests were conducted by the contractor every day Flexible-wall tnaxial
testing was performed by an independent laboratory twice each week The slope of the backfill in the
trench was also measured on a daily basis
Site 34
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53 Monitoring
An extensive monitoring system was implemented at the site resulting in a better than acceptable rating
The system included the following elements
• Settlement plates in the soil-bentomte backfill
• Piezometers upstream of, downstream of, and inside the soil-bentomte barrier (vibrating
wire)
• Inclinometers
• Stress cells, including cells inside the soil-bentomte barrier
• Flow measuring devices to measure seepage through the dam
In addition, an automated data acquisition system was installed to provide fast and efficient collection and
interpretation of the monitoring data
5.4 Operation and Maintenance
Because the monitoring system is automated and measurements are taken continuously, operation and
maintenance is largely restricted to dram clean out and embankment slope repair following particularly
heavy rains
5.5 Other Considerations
The construction of the cutoff wall (exclusive of design costs) was approximately $6 per square foot
5.6 Remedy Performance
All monitoring instruments were monitored manually before and during the initial filling of the reservoir m
1990 and automatically thereafter The results of the monitoring system indicate that
• No appreciable settlement of the top of the backfill has been noted
• The total flow rate of seepage measured at the flow weirs at the base of the dam has
remained below 12 gallons per minute This flow rate did not increase as the reservoir
was filled
• The piezometers have registered a head drop across of nearly 30 feet across the wall
Typical piezometer and horizontal stress readings are shown m Figures 2 and 3, respectively
6.0 SUMMARY
Site 34 is an earthen dam and dike located in the mid-atlantic United States The design for the dam and
dike incorporated a soil-bentomte cutoff wall for the impervious dam core The success of the project was
ensured by a thorough design and an intensive CQA/CQC program during cutoff wall construction
Postconstruction monitoring, which has been performed for more than 7 years, indicates that the cutoff
wall has been very effective m minimizing seepage through the sandy embankment and its foundation
Site 34
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CO
H>
ft
tt>
00
U/f OT 8-8 WALL (VP-30)
D/t OP SHI WML (VP-SJ)
UNDER BLANKET DRAIN
AND VP-M)
SONOJFUAUJJ ASONOJFUAU
TOE. MOXTH
Site 34
FIGURE 2
PIEZOMETRIC HEADS AT STA. 19+50
fetro Tech EM Inc.
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CO
H-
rt
R>
co
- 9,000
k
SON 0 J F M A U J J AS 0 N 0 J FMAM
1ML MONTH
Site 34
FIGURE 3
TOTAL HORIZONTAL STRESSES IN S-B WALL
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SITE 35
1.0 SITE DESCRIPTION AND HISTORY
Earner Type
Remedial
Objective
Performance
PC
Seepage
control
Site 35 is located in the south central United States adjacent to a river and a flood control dam built by the
U S Army Corps of Engineers in 1962 The barrier well was constructed in 1994 as a prerequisite for a
deep excavation for the construction of a hydroelectric power plant
2.0 GEOLOGIC AND HYDROGEOLOGIC SETTING
The site is located within the flood plain of the river and is underlain by recent alluvial sediments made up
of clays, silts, and predominantly fine-grained sands The alluvial sediments are underlain by a gravel
layer lying above the Tertiary-age Jackson Formation The Jackson Formation is made up of indurated,
highly plastic clay of low permeability The soil strata are summarized below (in descending order)
• Sandy clay fill (about 9 feet thick)
• Silty sand (48 to 65 feet thick)
• Clay (3 to 10 feet thick)
• Fine sand (32 feet thick)
• Gravel (2 feet thick)
• Tertiary-age dense clay
The water table is approximately 20 feet below ground surface (bgs)
3 0 NATURE AND EXTENT OF CONTAMINATION
No contamination exists on site
40 CONTAINMENT REMEDY
A dry excavation., about 100 feet in depth, was required within a few hundred feet of a large river for tiie
construction of the hydroelectric power plant The project included installation of a deep cutoff wall on
the perimeter of the excavation and a deep dewatenng system inside the excavation
The cutoff wall is made of plastic concrete and is 3,810 feet long, is 2 feet, 8 inches thick, averages 138
feet m depth, and has an area of 564,000 square feet A 140-foot deep remforced-concrete slurry wall was
installed within the cutoff wall to support the 90-foot-deep mass excavation, thereby drastically decreasing
the volume of the excavation Tiebacks provided lateral support of the concrete slurry wall Some soil-
bentonite sections were also installed on the back of the cutoff wall as protection agamst wall penetration
at locations where the tiebacks would be drilled through the plastic concrete
The dewatenng system, which is shown in Figure 1, included 16 wells installed to a depth of 130 feet and
sand drains installed to a depth of 110 feet bgs The purpose of the drains was to allow drainage of the
upper water table through the intermediate clay layer and to allow dewatenng from the lower pumped
interval
Key PC=Plastic Concrete Wall Perfoimance Rating 1-Remedial objective was met
Site 3 5 1
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FIGURE 1
LOCATION FOR DEWATERING WELLS
AND SAND DRAINS
Tetro Tech EM Inc.
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5.0 PERFORMANCE EVALUATION
The dewatermg flow rate indicates excellent performance by the cutoff wall The pumping system inside
the excavation uses conventional deep wells
5.1 Design
The design was rated better than acceptable based on industry standards discussed in Section 3,
Volume I A specialized geotechmcal engineering firm assisted the structural engineer in the design of the
dewatermg and excavation support systems The site was thoroughly investigated to ensure the continuity
of the aquitard and determine the geotechmcal characteristics of the soil formations Modelmg was
performed to determine the dimensions of the pumping system as well as to predict the deformation of the
reinforced-concrete slurry wall during mass excavation The characteristics of the plastic concrete were
specified, including slump, the nature of the aggregate and cement, strength after 7 days of pressure equal
to or greater than 200 pounds per square inch (psi), and a permeability less than or equal to 1 x 10"7
centimeters per second (cm/sec)
5.2 Construction Quality Assurance and Construction Quality Control
The construction quality assurance (CQA) and construction quality control (CQC) for the cutoff wall were
rated better than acceptable Prior to the start of the project, the plastic concrete mix was designed and
tested with the materials and mixing plant to be used for the slurry wall construction The plastic concrete
cutoff wall was installed using the panel method, that is, the wall consists of 136 panels whose lengths
vary from 9 to 35 feet The cutoff wall was installed by a specialized slurry wall contractor An extensive
CQA/CQC program was developed to ensure the following
• The quality of the bentomte slurry during excavation and before plastic concrete mixing
• A slurry storage capacity sufficient to handle large slurry losses
• The vertically of panel installation in the aquitard (the contractor had to maintain panel
verticality within 0 15 percent)
• Cleaning of the joints between the panels
• Cleaning and probing of the bottom of each panel before plastic concrete pouring
• The quality of the plastic concrete and of the tremie placement
In addition, a test plastic concrete panel was installed using the same equipment, materials, and
methodology as were to be used for the remaining panels This test was performed to demonstrate that the
contractor could maintain the verticality tolerance and construct the wall in accordance with the
specifications
5.3 Monitonng
Monitoring for Site 35 was rated better than acceptable A monitoring plan was implemented to monitor
the following items
Site 3 5
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• Head across the plastic concrete cutoff wall
• Dewatenng rates
• Deformation of the remforced-concrete slurry wall during and after mass excavation
• Tieback loads
Flow through the cutoff wall and underlying aquitard and the performance of the overall system after
rainfall are closely monitored with a network of piezometers installed inside and outside the wall
(see Figure 2) Groundwater contours inside the perimeter of the cutoff wall are shown in Figure 3
5.4 Remedy Performance
The cutoff wall was completed in mid-1994 Dewatenng has been performed for more than 1 5 years
The water table inside the cutoff wall has been lowered 95 feet The average pumping rate has stabilized
at about 100 gallons per minute, reflecting the excellent performance of the cutoff wall
6.0 SUMMARY
Site 35 contains no contamination A 150-foot-deep, plastic concrete cutoff wall was required at the site
to allow a 90-foot excavation in the immediate vicinity of a large river The design, CQA/CQC, and
monitoring of the cutoff wall were rated better than acceptable The pumping system inside the
excavation employs conventional deep wells The plastic concrete cutoff wall is subject to a 95-foot head
The mass excavation was completed by January 1996 The dewatenng flow rate meets the designed rate,
and indicates excellent performance by the cutoff wall.
SOe 35
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V
\
FIGURE 2
PIEZOMETER LAYOUT
fetro Tech EM Inc.
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/
-•^
t
OF RIGHT 8AM
__3JENT AREA
DWC.C002 AND
COOS FOH DETAILS.
EOSTKG CORPS OF EHC3EERS'
" 0AM
PERMANENT BENCH UAJBC HQ.1
DUG CQ19
s4 " ~- VfJff 7'~ T "r" "^ **1T' 'f" *"~^S
%> x-^vl'iTi^Jr i
PERMANENT BENCH HARK. NO. 2
NOTE. DUE TO THE SMALL AMOUNT OF PIEZOMETER DATA
AVAILABLE, THP CENTER SEEPAGE CUT-OFF WALL
WAS NOTTAKEN INTO ACCOUNT WHEN DEVELOPING
GROUNDWATER CONTOURS
Site 35
FIGURE 3
GROUNDWATER CONTOURS INSIDE
THE PERIMETER SEEPAGE
CUT-OFF WALL (4/5/96)
Tetra Tech EM Inc
Site 35
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SITE 36
1.0 SITE DESCRIPTION AND HISTORY
Earner Type
Remedial
Objective
Performance
CC
Minimize Infiltration
of Precipitation
X
Site 36, which is located in the northeastern United States, was evaluated as a'cap only site The site is
made up of a landfill and landfill expansion areas The original landfill began operation in 1958 and was
initially used for processing and disposal of municipal waste Industrial wastes were also disposed of in
the landfill during the late 1960s and early 1970s The landfill ceased operation m April 1986 The
original landfill has an area of about 65 acres and is unlined The landfill has an elevation of 240 feet
above mean sea level, (msl) and the bottom of the landfill is estimated to be 80 feet above msl Landfill
expansion began in 1977 The landfill expansion areas were lined and provided with leachate collection
systems
In 1977, new state regulations were passed mat required the site to implement a program to determine the
quality of groundwater below the landfill, this program was later expanded to assess the effect of the
landfill on the surrounding area After contamination was found m the groundwater below the landfill,
Site 36 underwent partial capping and installation of a leachate and gas control system was completed
The site was placed on the National Priority List (NPL) in September 1983, and the remedy was
implemented in 1992 and 1993
2.0 GEOLOGIC AND HYDROGEOLOGIC SETTING
The site is located in an area underlain by four hydrogeologic units the Glacial Formation, Magothy
Aquifer, Rantan Clay, and Lloyd Aquifer These units rest on a bedrock surface that lies about 1,100 feet
(ft) below msl at the site and dips to the southeast toward the Atlantic Ocean
The Glacial Formation occurs from directly below the landfill to about 20 ft below msl at the site The
Glacial Formation is made up of irregular deposits of gravel, sand, sandy clay, and clay Because they vary
in permeability, thickness, and extent, these deposits have great influence on recharge and movement of
groundwater Deposits of clay impede infiltration and percolation of water, thus creating perched water
conditions locally, whereas permeable beds of sand and gravel offer little resistance to water
The upper formation of the Magothy Aquifer ranges from about 200 to more than 120 ft below msl This
formation consists chiefly of interbedded, gray, buff, and white fine-grained sand and clayey sand, and of
black, gray, white, buff, and red clay Gravely zones are common near the bottom of the formation but are
rare in the upper part
The water table occurs m the Glacial Formation at approximately 40 to 70 ft above msl This water-
bearing stratum is commonly referred to as the Upper Glacial Aquifer Groundwater under the landfill
flows to the south-southeast Water level data collected from walls upgradient of the landfill does not
indicate components of groundwater flow north and west of the site
Key CC=Composite Cap
Performance Rating X=InstifBcient data to determine if remedial objectives were met
Site 36
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3.0 NATURE AND EXTENT OF CONTAMINATION
Contamination was identified below the original landfill, and an off-site landfill leachate plume extendmg
about 4,000 feet and having a maximum width of 3,000 feet was also identified The approximate vertical
extent of the landfill leachate plume is about 160 feet below msl The primary contaminants of concern in
groundwater on and off site are 1,2-dichloroethene, 1,1-dichloroethane, vinyl chloride, methylene chloride,
trichloroethene, and chloroethene
4.0 CONTAINMENT REMEDY
In 1979, several investigations revealed problems involving volatile organic compounds (VOCs) in
groundwater and landfill leachate The site was placed on the NPL on September 8, 1983 Remedial
activities were already underway at the site, including capping of a 29-acre portion of the landfill A
record of decision (ROD) for the site was signed on March 18,1988 The ROD called for the following
measures to be taken at the site
• Installation of eight diffusion (reuyection) wells for treated groundwater
• Completion of a 35-acre cap consisting of an 18-inch layer of compacted clay and 18
inches of soil cover
• Improvement of the landfill gas collection and leachate control systems
• Installation of five groundwater recovery wells with a design flow of 1 5 million gallons
per day and screened to intersect both the shallow and deep
• Installation of an air stripper to treat VOCs in the groundwater
A landfill gas collection system was installed at the site in 1992, and a leachate control system was
installed and has operated since 1993 on 12 acres of the site The groundwater remediation program
involves use of five groundwater recovery wells installed at the leading edge of the VOC plume The
combined flow from all the wells is directed through common transmission piping to an air stripper
Treated groundwater is discharged to eight diffusion wells located in a recharge basin that lies
hydraulically upgradient of the landfill at the western perimeter of the site
5.0 PERFORMANCE EVALUATION
Hydraulic monitoring is conducted quarterly to verify hydraulic containment of the plume by the recovery
well system Water level measurements are required until equilibrium and appropriate drawdown have
been established Groundwater quality monitoring is to be conducted until groundwater quality criteria
defined by the consent decree have been met
Hydraulic monitoring has indicated that the current plume capture zone was developed soon after the
startup of the groundwater recovery walls, and that the size and shape of the capture zone have remained
relatively stable over 14 operating quarters Water level data indicates that water levels in the vicinity of
the capture zone initially declined about 10 to 12 feet as a result of pumping
Site 3 6
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Ground-water quality data indicates no significant change in the VOC plume However, reductions m total
VOC concentrations in some monitoring wells over time indicate that groundwater quality may be
improving as a result of the groundwater remediation program
The on-site treatment plant has displayed an average treatment efficiency of 99 42 percent since its startup
Treated groundwater is discharged to the diffusion wells
Remedy performance and contributing factors are discussed further m the following subsections
Localized mounding may be occurring in the vicinity of the recharge basin This mounding may have a
minimal effect on groundwater flow directions
5.1 Design
The landfill cap design was shghtlybetter than acceptablebased on the criteria described in Section 3,
Volume I State regulations require that the capping process include regradmg the slopes of the landfill to
a slope of 3 horizontal to 1 vertical The lowest portion of the cap consists of an 18-inch, compacted clay
layer The clay cap was constructed in 6- to 8-mch-thick lifts (after compaction) and had to meet the
following specifications
• Permeability. 1 x Iff7 cm/sec or less
• Gram size P200 content of 50 percent by weight or greater
• Liquid limits 25 percent or greater
• Plasticity index 10 percent or greater
• Compaction 90 percent modified proctor density or greater
• Moisture content varying between optimum and 25 percent of wet optimum
5.2 Construction Quality Assurance and Constriction Quality Control
The construction quality assurance (CQA) and construction quality control (CQC) for the cap were rated
acceptable relative to industry practices discussed in Section 3, Volume I^ccording to the bid
specification for the capping and closure of Site 36 CQA/CQC measures were implemented during
construction of the landfill cap
An independent testing laboratory was used to test the clay seal m place The parameters tested were
permeability, grain size, liquid limits, plasticity index, compaction, and moisture content In situ
compaction was tested using a nuclear densiometer at the intersection points of a 100-foot grid, and the
grid was to be offset for each lift of in-place material One undisturbed sample per acre per lift of clay was
collected and analyzed for hydraulic conductivity One sample for each 500 cubic yards of clay placed was
analyzed for gram size distribution, dry density, and moisture content A qualified soil technician or
engineer was present during construction of the cap to provide visual inspection and to direct sampling and
testing
The cover soil (located above the clay seal) was also tested during construction for the following
parameters pH, particle size, liquid limits, plasticity index, moisture content, and unconfined compression
strength The cover soil was placed and compacted to 85 percent of its maximum dry density. Placement
was completed in two or more lifts of 6-inch maximum thickness as necessary to achieve the line grade
specified
Site 36
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53 Monitoring
A monitoring program was designed and implemented to meet a requirement for ensuring that (1) the off-
site leachate plume was being hydrauhcally controlled and (2) contaminated groundwater was meeting
cleanup criteria. Baseline monitoring was conducted from July 30 through August 2,1991
The monitoring program is rated acceptable The cap is inspected quarterly Quarterly hydraulic
monitoring is conducted (1) to verify that equilibrium and appropriate drawdown of the plume is being
established to prevent further expansion of the plume and (2) to determine the extent of mounding in the
recharge basin area and the effect of that mounding, if any, on local groundwater flow patterns Review of
a third quarter 1995 groundwater sampling report indicates that the current plume capture zone was
developed soon after the startup of the groundwater remediation system, and that the size and shape of the
capture zone have remained relatively stable over 14 operating quarters The average flow from the five
recovery wells has varied from about 0 90 to 1 44 million gallon per day
Quarterly monitoring of groundwater quality is being conducted for the leachate plume until the
termination criteria are met Review of quarterly groundwater monitoring results indicates no significant
change in the dimensions of the VOC plume Reductions in total VOC concentrations in some monitoring
wells over tame indicate that groundwater may be improving as a result of the groundwater remediation
program
Monitoring of the on-site treatment plant influent and effluent is conducted monthly to meet requirements
The treatment plant is also equipped with a gas chromatograph, allowing monitoring of the day-to-day
treatment efficiency of the plant Samples are collected from recovery wells for VOC analysis The
treatment plant is also equipped to monitor water quality parameters for the influent and effluent analysis
5.4 Operation and Maintenance
A document entitled "Post Closure Operation and Maintenance Manual for the Capping Coverage,
Drainage and Roadway System? was prepared This manual presents a protocol for postclosure
monitoring and maintenance of the landfill and for corrective measures The subjects discussed in this
manual include the cover system, drainage system, access roads, gabion wall, and materials and equipment
required for routine maintenance No summary reports detailing the results of the operation and
maintenance program were available for review
5.5 Other Considerations
The final costs for the design and construction of the landfill cap are $13,800,000 These costs do not
include the costs for the portion of the landfill that was capped in 1983
5.6 Remedy Performance
The overall performance of the containment remedy appears to be meeting the remedial objectives The
off-site leachate plume appears to have remained relatively stable over 14 operating quarters Groundwater
quality data indicate no significant change in the VOC plume, but reductions in total VOC concentrations
have been observed at some monitoring wells The on-site treatment plant has an average treatment
efficiency of 99.42 percent. Localized mounding may be occurring in the vicinity of the upgradient
recharge basin.
Site 36
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6.0 SUMMARY
The original landfill at Site 36 began operation in 1958 The landfill initially accepted municipal waste,
but industrial wastes were also disposed of m the landfill during the late 1960s and early 1970s Site 36
was placed on the NPL on September 8,1983 The landfill ceased operations in April 1986 An
investigation of groundwater contamination at and around the landfill begun in 1979 revealed
contamination in groundwater below the landfill and in a leachate plume that had migrated about 4,000
feet from the site The containment remedy consisted of a clay cap, landfill and gas collection and leachate
control systems, five groundwater recovery wells, a groundwater treatment plant, and eight diffusion wells
for recovered water The cap design effort was ratedbetter than acceptable, and CQA/CQC of the cap was
rated acceptable
Site 36
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