PB95-963138
EPA/ESD/R08-93/104
March 1995
EPA Superfund
Explanation of Significant Difference
for the Record of Decision:
Marshall/Boulder Landfill,
Boulder County, CO
11/2/1992
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ADMINISTRATIVE RECORD
RLE PLAN
0
Marshall/Boulder Landfill
EXPLANATION OF SIGNIFICANTDIFFEHENCES
MARSHALL/BOULDER LANDRLLSUPERFUND SITE"
EPA Region VII!
November, 1992
Groundwater underiying the Marshall/Boulder Land-
fill Site (Site) in southeast Boulder County, Colorado, is
contaminated with high levels of organic and inorganic
compounds as a result of surface water and ground-
water leaching through waste material disposed of on
the Site between 1969 and 1974. These concentrations
pose a potential health risk to humans and aquatic life.
Consequently, the Site has been targeted for cleanup
under the Comprehensive Environmental Response,
Compensation and Liability Act (CERCLA), or Super-
fund.
After thorough study and evaluation, the U.S. Environ-
mental Protection Agency (EPA) issued a Record of
Decision (ROD) in September 1986 which described the
remedy chosen by EPA to dean up the Site. Between
1986 and 1990, additional information was obtained
which warrants modifications to the 1986 ROD remedy.
The revisions, which are described in detail in this
Explanation of Significant Differences (ESD), are as
follows:
1. Thegroundwatercollectionsystemwillconsistofa
well array along most of the eastern Site boundary
and a collection trench along part of the southern
and eastern Site boundaries instead of only a series
of drains as previously stipulated.
2. The collected groundwater will be treated to re-
move ammonia using breakpoint chlorinan'on /de-
chlorination prior to discharge.
3. In addition to the air stripper and air stripper off-
gas carbon adsorption system specified in the ROD,
a liquid-phase carbon adsorption system (liquid-
phase granular activated carbon, or LGAC) will be
used to remove volatile organic compounds (VOCs).
4. The effluent limitation for chloride (measured as a
30-day average) will be 320 milligrams per liter
(mg/1) rather than 280 mg/L
Construction of the treatment facility and groundwater
collection system began in September 1992. Operations
will commence after a construction period of approxi-
mately 14 months.
PUBUCCOMMENT
EPA is concerned that the selected remedy meets the
needs of the community and also provides protection of
human health and the environment. EPA encourages
the public to make written or oral comments on the
selectedremedy. TheAdministrativeRecord,FactSheets
and other pertinent documents are available for public
review at the following locations:
EPA Superfund Records Center (303)293-1807
999-18th Street
5th Floor - North Podium
Denver, CO 80202-2405
Boulder Public Library
llth & Arapahoe
Boulder, CO 80302
Louisville Public Labrary
950 Spruce Street
Louisville, CO 80027
(303)441-3100
(303)666-6037
Questions and comments regarding this ESD may be
directed to:
Paula Schmittdiel (303)293-1527
Remedial Project Manager
Mary Hagan, (303) 294-1160
Community Relations Coordinator
EPA maintains a mailing list of groups and individuals
who are interested in the Marshall/Boulder landfill
Superfund Site. If you did not receive this ESD by mail
and would like to be added to our mailing list, please
send yourname,affiliation,addressand telephone num-
ber to:
Mary Hagan
U.S. EPA (80EA)
999 -18th Street, Suite 500
Denver, Colorado 80202-2405
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INTRODUCTION
This BSD has been prepared by EPA to explain the
significant differences between the 1986 ROD Remedy
and the remedy delineated in the Final Design Remedy
dated September6,1991,attheMarshall/Boulder Land-
fill Site. EPA is the lead agency for overseeing deanup
of the Site and the Colorado Department of Health
(CDH) is the support agency.
Section 117(c)of CERCLAandSection300.435(c)(2)(i)of
the National Oil and Hazardous Substances Pollution
Contingency Plan (NCP) require EPA to publish an ESD
when the remedy implemented differs significantly
from that remedy described in the ROD. This ESD
provides a brief summary of the background of the Site,
a description of the remedial design, and a comparison
of the 1986 ROD Remedy to the Final Design Remedy.
Completedocumentation of the remedial design isavail-
able for public review at the EPA Superfund Records
Center in Denver, Colorado.
SUMMARY OF SITEfflSTORY AND
CONTAMINATION PROBLEM
Site History
The Marshall/Boulder Landfill is located in southeast
Boulder County,eastof the town ofMarshall (Exhibit 1).
The Site is south of Colorado Highway 170 and is
bounded on the east by South 66th Street Marshall Lake
is located approximately 2,000 feet to the west Ap-
proximately two miles to the east is the town of Supe-
rior. The cities of Boulder and Louisville are three miles
to the northwest and northeast, respectively.
Surface water flows from southwest to northeast through
two parallel drainages on the Site. Cowdrey Drainage
carries water from Cowdrey Reservoir No. 2 to South
Boulder Creek; in the past someof this intermittentflow
was diverted to Davidson Ditch, where it was used for
irrigation. South of Cowdrey Drainage is Community
Ditch, which carries water from Marshall Take to the
Cityof Louisville Water TreatmentPlant Groundwater
in theshallowaquifer flows toward Cowdrey Drainage,
or generally to the north on most of the Site and to the
south in the northern part of the Site.
The Site consists of two adjacent landfills, each compris-
ing approximately 80 acres. The Marshall Landfill,
located to the north, began official operation in 1965,
when the Richland Company, under contract with Boul-
der County, began a solid waste composting and dis-
posal operation at the Site. Although the contract speci-
fied composting operations, landfilling comprised the
majority (80%) of waste handling activities. In 1969, the
operation was sold to Salvage, Inc., which was later
acquired by a group of local investors and renamed
Urban Waste Resources. Between 1969 and 1974, the
Marshall Landfill accepted municipal waste,
unstabilized sewage sludge and many unknown .and
potentially hazardous wastes. In 1974, the Marshall
Landfill was abandoned when Urban Waste Resources,
along with Mesa Sand and Gravel, opened the Boulder
Landfill to the south. T.andfillr Inc., a wholly-owned
subsidiary of Browning-Ferris Industries, purchased
the landfill operation in 1975. The Boulder landfill
dosed in January 1992.
In September 1983, the Marshall/Boulder Landfill was
included on the National Priorities List due to the re-
lease of contamination to irrigation and drinking water.
A major concern was the contamination of water flow-
ingin Community Ditch,because itserves asa sourceof
drinking water for the City of Louisville. In response to
this concern, a 60-inch pressurized pipeline was in-
stalled to convey the water across the inactive landfill
The potential for contamination of shallow and deep
groundwater is being addressed by this remedy.
Contamination Problems
Several sources of contamination were identified dur-
ing the Remedial Investigation/Feasibility Study (RI/
FS), which was conducted in 1986. These include
•S> Areas of saturated refuse within the northern por-
tion of the Boulder Landfill and throughout the
Marshall Landfill;
Small, undefined areas within the Marshall Landfill
where industrial wastes, primarily organicsolvents,
were disposed of along with solid wastes; and
•& Two unlined leachate lagoons in the southern por-
tion of the Marshall Landfill.
Detected on-site contamination is characterized by el-
evated levels of:
<3> Volatile organic compounds (VOCs) such as ben-
zene, trichloroethyiene and tetrachloroethylene;
•S Heavymetalssuchasbarium,iron,manganeseand
zinc and
<£> Major ions such as chloride, nitrate and sulfate.
Based on the findings of the RI/FS, EPA selected a
preferred remedy, which was described in 1986 ROD.
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SUMMARY OF THE 1986 ROD REMEDY
The 1986 ROD Remedy involves the collection of con-
taminated groundwater leaving the Site; treatment of
the collected groundwater; environmental monitoring;
andlandfUlimprovements. The 1986 ROD Remedy also
includes off-site monitoring to determine the existence
and detrimental effect of off-site sources of contamina-
tion to the area.
The major components of the 1986 ROD Remedy in-
clude:
v> Elimination of off-site transport of contaminants
emanating from the Site by constructing a drain or
series of drains to capture shallow groundwater
along the entire southern and eastern Site bound-
aries;
*> Treatment of contaminated groundwater in a facil-
ity consisting of equalization/sedimentation ba-
sins, an air stripper, and carbon adsorption of air
stripper off-gas (vapor-phase granular activated
carbon, or VGAC);
Implementation of an environmental monitoring
program to verify the effectiveness of the remedial
action and to assure protection of public health;
LandfiUimprovements,indudingregrading,reveg-
etation, perimeter ditches and fences to minimize
future environmental and public health impacts
from the Site;
Drainage of the existing leachate lagoons and trans-
fer of the liquid to the treatment system; and
Redirection of the discharge of the existing french
drain to the treatment facility.
WELL ARRAY
tVVWW COLLECTION TRENCH
....... FENCE
EXHIBIT 1
WITH FINAL DESIGN REMEDY
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JUSTIFICATION FOR CHANGES
In order to design the collection and treatment systems
described in the 1986 ROD Remedy, additional infor-
mation was obtained during several sampling events in
1989 and 1990 and thatinformation was summarized in
the Additional Studies Final Report and two addenda.
These reports are part of the Administrative Record.
Based on the findings of these investigations and fur-
ther work on the remedial design, the 1986 ROD Rem-
edy is being modified to maximize its efficiency and
protectiveness. The new findings are summarized in
Exhibitl
/
/
French Drain
I Extraction Wells
Collection Trencn
oon Drainage
j Seepage Control Drain
EQUALIZATION /
• TANKS /
souos
/
OXIDATION
/
/
/
pH ADJUSTMENT
/
/
RAPID MKWG/FIOC- /SQUOS
CULATONSEmjNQ /
imUtnman /
OEWATERMQ
OFSUJDGE
FILTRATION
/
FINAL OH
ADJUSTMENT
AIR
•>
r
LAND DISPOSAL
OF DRUMMED
SOUOS
(VOC
_v/ VQAC
~J (VOCMmoMi)
/
/
/
LOAC
(aaMMVOCM
Je.
BREAKPOINT
CXLOfOMATION
RELEASE OF
AIR EMISSIONS
OECHLOHNAHON
(MMMICBIUIIar.iru.Ml
EXHIBITS
TREATMENT PROCESS FLOW DIAGRAM AS PER FINAL DESIGN
3> Shallow^groundwaterwasnotencounteredinwells
drilled at the western extent of the southern Site
boundary and the northern end of the eastern Site
boundary. Additionally, the base of the shallow
aquifer along part of the eastern Site boundary is
deeper than me original estimation. The saturated
thickness in this area is greater than originally de-
termined as well
S> Estimated ammonia concentrations in the treat-
ment facility influent were revised to reflect the
higher concentrations found in certain groundwa-
ter wells and in the discharge at the seepage face,
where landfill leachate flows to the surface.
3- During remedial design it was determined mat an
air stripper and VGAC may not consistently re-
move detected levels of volatile and semi-volatile
organic compounds (SVOCs). Icing of the air strip-
per and VGAC may occur during the winter months
which would reduce their efficiency.
«S "The numeric chloride water quality stream stan-
dard for Cowdrey Drainage was amended from 250
mg/1 to 320 mg/1 by the Colorado Water Quality
Control Commission.
DESCRIPTION OF SIGNmCANTDIFFERENCES
AND BASIS FOR THE CHANGES
There are four significant modifications to the 1986
ROD Remedy based on new information obtained since
the ROD was issued. They are as follows:
o- Change in type and extent of groundwater collec-
tion system;
S- Additionoftreatmentforammoniainwastestream;
3> Additioitof liquid-phase carbon adsorption; and
o- Revision of me effluent limitation for chloride.
Change in Type and Extotf of GroundvvaterCoIlecticaiSystan
The 1986RODRemedyrequiresthecollectionof ground-
water using a drain or series of drains along the south-
ern and eastern Site boundaries. A collection trench as
originally conceived is not feasible along the southern
portion of the eastern boundary given the revised thick-
ness and overall depth of the base of the saturated zone.
A well array consisting of 30 extraction wells will re-
place the collection trench from a point approximately
600 feet north from the southeast comer of the Site to a
pointapprcodmately 4/WO feet to thenorth,as shown in
Exhibit 1. The well array will be designed to remove
contaminated groundwater from the entire saturated
thickness of the shallow aquifer in a more efficient and
4 effective manner.
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The groundwater collection system will not extend
along the entire length of the southern and eastern Site
boundaries,ascailedforintheROD,fortworeasons: 1)
the-alluvium near the southwestern and northeastern
corners of the Site is apparently unsaturated and 2)
existing piezometric data indicate that shallow ground-
water along the western 700 feet of the southern Site
boundary, if present, would migrate northward onto
the Site. The in tent of the 1986 remedy was to collect and
treat groundwater leaving, rather than entering, the
Site. The collection trench will be approximately 1,200
feet in length, beginning approximately 600 feet west of
the southeastern corner of the Site and extending ap-
proximately 600 feet north to the well array, as shown in
Exhibit 1. The western extent of the collection trench is
midway between a well in which groundwater was
encountered and a well in which groundwater was not
encountered.
During the monitoringprogram, both water quality and
piezometric data will be collected along the entire south-
em and eastern Site boundaries to confirm the presence
of groundwater and the direction of groundwater flow.
The collectionsystem will be extended if shallowground-
water is detected in areas not included in the collection
system. The revised configuration of the groundwater
collection system is shown in Exhibit 1.
Addition of Treatment for Ammonia in Waste Stream
The 1986 ROD Remedy did not address treatment for
ammonia since ammonia levels were not believed to
exist in concentrations which exceeded discharge stan-
dards. In September 1990, several on-site wells, the
seepage face and French Drain were sampled and ana-
lyzed for ammonia. These data resulted in higher
estimated ammonia concentrations, which could cause
the treatment facility effluent to intermittently exceed
the discharge standard for ammonia if not treated.
Breakpoint chlorination and dechlorination are being
added to the treatment process to remove ammonia.
During breakpoint chlorination, ammonia is oxidized
to nitrogen gas by the addition of chlorine Residual
chlorine is then removed by adding sulfur dioxide.
Dechlorination will be the final treatment step before
discharge.
Addition of Liquid-Phase Carbon Adsorption
The 1986 ROD Remedy calls for the removal of VOCs
with an air stripper and air stripper off-gas carbon
adsorption. During remedial design, the Potentially
Responsible Parties proposed adding an LGAC after
they determined mat discharge standards for VOCs
maynotbeconsistentlymet Bypassingtheairstripper
outflow through an LGAC, increased removal of VOCs
and SVOCs would be achieved, assuring compliance
with the discharge standards. Another benefit of the
LGAC is its capacity to remove a wide range of organic
compounds. Exhibit 2 shows the treatment process as
revised by the modifications described in this ESD.
Revision of the Effluent Limitation for Chloride
At a public hearing on May 5,1992, the City of Boulder
and Landfill, Inc. requested mat the Colorado Water
Quality Control Commission permanently modify the
chloride water quality stream standard on Upper and
Lower Co wdrey Drainage. In response to this request,
the numeric standard was changed from 250 mg/1 to
320 mg/1, measured as a 30-day average. This change
should not pose any threat to human health or the
environment A monitoring plan for chloride will be
implemented to ensure that the water supply use clas-
sification for Cowdrey Drainage is protected at the
higher limit
SUMMARY OF SIGNIFICANT L)li*HKENCES
Original 1986 ROD Remedy Final Design Remedy
Gioundwater collection
alongeatire southern and
a drain or series of drains.
most of the southern and east-
ern site boundaries using a
ooDttlkmtnaich andweUanay.
Treatment to reduce ammonia -Removal of ammonia using
notaddxessed. breakpoint chloriiuilioiL
Removal of VOCs from collected Removal of VOCs from
ground water with an air rnflgrtprl groundwater withan
stripper andairstripperoff-gaa air stripper, off-gas carbon
carbon adsorption. adsorption and LGAC
Proposed chloride effluent
modified to 320 mg/L
SUPPORT AGENCY COMMENTS
CDH has reviewed the Final Design Remedy described
in this ESD and has provided comments to EPA. These
comments have been incorporated into this ESD to the
maximum extent practicable CDH supports imple-
mentation of the Final Design Remedy as presented in
mis ESD.
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STATUTORY DETERMINATIONS
The changes to the 1986 ROD Remedy were made in
accordance with all applicable regulatory and statutory
requirements, as required by Section 121 of CERCLA.
Considering the new information that has been devel-
oped and the changes mat have been made to the
selected remedy, EPA and COH believe that the Final
Design Remedy remains protective of human health
and the environment, complies with federal and state
requirements that were identified in the ROD as appli-
cable or relevant and appropriate to this remedial ac-
tion at the time the original ROD was signed and is cost-
effective, m addition, the revised Final Design Remedy
utilizes permanent solutions and alternative treatment
technologies to the maximum extentpracticableon this
Site.
U.S. Environmental Protection Agency
Office of External Affairs
99918th Street, Suite 500
Denver Colorado 80202-2405
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i
UNITED STATES ENVIRONMENTAL PROTECTION AGENCY
REGION VIII
999 18th STREET • SUITE 500
DENVER. COLORADO 80202-2466 '
681254
Ref: 8HWM-SR
MEMORANDUM
OCT 2 6 1992
ADMINISTRATIVE RECORD
FILE PLAN
3
Jack W. McGraw, Acting Regional Administrator
Robert L. Duprey, Direct
Hazardous Waste Manag
TO:
FROM:
SUBJECT: BSD - Marshall-Boulder Landfi-1
Attached to this memorandum for your approval is an
Explanation of Significant Differences (BSD) to the 1986 Record
of Decision (ROD) for the Marshall-Boulder Landfill. This BSD
documents changes made to the remedy during the remedial design.
process. The changes are considered significant but not
fundamental to the original remedy selected in the ROD.
The specific changes include 1) a change in the type and
extent of ground water collection; 2) the addition of treatment
for ammonia in the waste stream; 3) the addition of liquid-phase
carbon absorption, and 4) revision of the effluent limitation for
chloride based on an administrative change by the Colorado Water
Quality Control Commission. .
The changes to the remedy were made in accordance with all
applicable regulatory and statutory requirements, as required by
CERCLA section 121. The remedy remains protective of human
health and the environment, complies with federal and state
requirements identified in the 1986 ROD, and remains cost-
effective. BPA Headquarters has been consulted and has concurred
on the BSD. Likewise, both the Office of Regional Counsel and
the State of Colorado Department of Health have reviewed the BSD
and had only minor comments, which have been addressed.
The final remedial design has been approved and the PRPs
have begun construction of the remedy. The Hazardous Waste
Management Division recommends approval of the BSD as proposed.
._ • ^
cci Diana Shannon, SRB
Marc Alston, SRB
Paula Schmittdiel, SRB
Wendy Silver, ORC
John Cordova, CDH
Printtd on Rtoyeltd Ptp"
I
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ADMINISTRATIVE RECORD
EXPLANATION OF SIGNIFICANT DIFFERENCES
BSCOBD O9 CHCTSTOM fBflDl - MAKSHAUi-BOTTIiDBR
DBCIABATION8
TILE PLAN
3
Considering the new information that has been developed and the
change* that have been aade to the selected remedy chosen in the
September, 1986 HOD, SPA has determined that the remedy remains
protective of human health and the environment, complies with
Federal and State requirements that are applicable or relevant
and appropriate to this remedial action, except those for which a
waiver is invoked, and is cost-effective. In addition, the
revised remedy utilises permanent solution* and alternative
treatment technologies to the mairiamn extent practicable for this
Site.
Jack w.
Acting Regional Adminis
Date/
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