United Slates Office of
Environmental Protection Emergency and
Agency Remedial Response
EPA/ROD/R08-93/072
June 1993
SEPA Superfund
Record of Decision:
Sand Creek Industrial
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50272-101
REPORT DOCUMENTATION '1. REPORT NO. 2. 3. Reclplenh Acc88.lon No.
PAGE EPA/ROD/R08-93/072
4. Title and Subtitle 5. Report D8te
SUPERFUND RECORD OF DECISION 06/30/93
Sand Creek Industrial (Operable Units 3 & 6), CO 6.
Fourth Remedial Action
7. Author(s) 8. Performing Organlutlon Repl. No.
9. Performing Organization Name and Addr... 10 Project TaskJWork Unit No.
11. Contract(C) or Oranl(O) No.
(C)
(0)
12. Sponsoring Organization Name and Addl'88. 13. Type of Report .. Period Conrad
U.S. Environmental Protection Agency
401 M Street, S.W. 800/800
Washington, D.C. 20460 14.
15. Supplementary Note.
PB94-964415
16. Abstract (Limit: 200 word.)
The ISO-acre Sand Creek Industrial (Operable Units 3 & 6) site is an inactive 'landfill
located on the 300-acre Sand Creek Industrial site in Commerce City, Colorado. The
site is situated within the Sand Creek floodplain and borders a I-acre wetlands area.
Land use in the area is predominantly industrial, with some agricultural uses. There
are an estimated 25 people who reside within a one-mile radius of the site, and a
daytime population that reaches several hundred due to the local businesses and
industrial nature of the area. Municipal water is supplied for the metropolitan area
surrounding the site through ground water and surface water from alluvial and bedrock
wells and outside sources. In 1990, a State inventory indicated that only two
properties used private wells for drinking water. Prior to 1967, the site was used
primarily for agricultural purposes, but from 1956 to 1964, the southern boundary of
the landfill was used for sand and gravel mining operations. In 1967, the landfill
began accepting both demolition and domestic refuse. Known hazardous and pathological
wastes reportedly were excluded from disposal at the landfill; however, the method used
to exclude these wastes, and the consistency with which this practice was employed, is
not known. In 1975, the landfill was closed, and the area was revegetated. In 1977, a
State investigation of an explosion at the landfill concluded that methane gas was
(See Attached Page)
17. Document Analys18 a. Dacrlpto..
Record of Decision - Sand Creek Industrial (Operable Units 3 & 6), CO
Fourth Remedial Action
Contaminated Media: gw, sw, air
Key Contaminants: VOCs (benzene, PCE, TCE, toluene), metals (arsenic)
b. Identlflel'llOpen-Ended Terms
c. COSATI FleldIGroup
18. Availability SlIlement 19. Securlly Clus (ThIs Report) 21. No. of Pag..
None 52
20. Security CIa- (ThIs Page) 22. Pries
None
(See ANSI.Z39.18)
S.. Instructions on R.v.1'S8
OPTIONAL FORM 272 (4-77)
(Formerly NTI8-35)
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EPA/ROD/R08-93/072
Sand Creek Industrial (Operable Units 3 & 6), CO
Fourth Remedial Action
Abstract (Continued)
migrating from the landfill. In response, two methane gas venting systems were installed
at the landfill in 1978. In 1981, the State determined that the passive venting system
was ineffective, and as a result, one of the PRPs installed an active venting system that
collected gases and vented them to the surface through three stacks. EPA investigations
conducted from 1982 to 1988 indicated the presence of several VOCs and inorganic compou~ds .
in the ground water and surface water. In 1987, air and soil analyses indicated VOC
contamination in the gas samples, but no indication of contamination in the soil samples
from the landfill cover was found. In 1990, EPA required the PRPs to address the
potential for explosion and health risks associated with gaseous emissions released from
the landfill, as OU6. In 1991, as part of the EPA-initiated removal action for OU6, the
PRPs installed and began operating an active landfill gas-extraction system
. (LFGES),replacing the previously installed systems. Due to the complex nature of the
site, EPA has divided it into six operable units in order to more effectively address
specific contamination problems. A 1989 ROD addressed contaminated soil, buildings, and
tanks, as OU1, and a 1990 ROD addressed contaminated soil at the COC area, as OUS. Other
1993 RODs address OU2 and provide an amendment for OUS. This ROD addresses the
contaminated ground water, surface water, and air at the 48th and Holly Landfill, as OUs 3
and 6. Soil and sediment were eliminated from the original scope since investigations
indicated that they were not contaminated significantly. Future RODs will address
remediation of the ground water at the landfill, if subsequent evaluations determine that
the landfill is responsible for unacceptable ground water contamination. The primary
contaminants of concern affecting the ground water, surface water, and air are VOCs,
including benzene, PCE, TCE, and toluene; and metals, including arsenic.
The selected remedial action for this site includes continuing the operation and
maintenance of the OU6 LFGES, including treating the condensate offsite at a POTW, with
improvements as required during the normal course of operation and maintenance activities;
continuing maintenance of the soil cover system, the.perimeter fence, and the warning
signs; continuing existing institutional controls and implementing additional
institutional controls, as necessary; monitoring ground water and landfill gas; and
conducting periodic site reviews; and providing additional remedial action, as necessary,
if monitoring indicates that the landfill contributes to unacceptable contamination of the
ground water. The estimated present worth cost for this remedial action is $7,283,000,
which includes an estimated annual O&M cost of $240,000 for 30 years.
PERFORMANCE STANDARDS OR GOALS:
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RECORD OF pECISION
DECLARATION STATEMENT
~~~}f
SITE NAME AND LOCATION
48th and Holly Landfill (Operable Units 3 and 6), Sand Creek Industrial
Superfund Site, Commerce City, Colorado
STATEMENT OF BASIS AND PURPOSE
This decision document presents the selected remedial action for Operable Units
3 and 6 (OU3/0U6), the 48th and Holly Landfill (the "Landfillj, at the Sand Creek
Industrial Superfund Site in Commerce City, Colorado. This remedial action has been
developed in accordance with the Comprehensive Environmental Response,
Compensation and liability Act of 1980 (CERClA) as amended by the Superfund
Amendments and Reauthorization Act of 1986 (SARA), applicable state laws, and the
National Oil and Hazardous Substances Pollution Contingency Plan (the National
Contingency Plan (NCP), Title 40 Code of Federal Regulations Part 300). This decision
is based on the admini"trative record for OU3/0U6.
The State of Colorado concurs with the selected remedy.
ASSESSMENT OF THE OU3/0U6
Actual or threatened releases of hazardous substances from the Landfill, if not
addressed by implementing the response action selected in this Record of Decision
(ROD), may present an imminent and substantial endangerment to public health,
welfare, or the environment.
DESCRIPTION OF THE REMEDY
The remedial action selected for OU3/0U6 will address. the principal threats
existing at the Landfill and will ensure that: (1) emissions of landfill gas are controlled to
prevent inhalation at levels that pose an endangerment to human health or the .
environment, (2) accumulation of landfill gas is minimized in order to prevent explosion
hazards, (3) dermal contact with the landfill contents is prevented, and (4) the use of
ground water underlying the Landfill as a drinking water source is prevented.
The major components of the selected remedy include:
.
Continued operation and maintenance of the OU6 landfill gas~ .
exttaction system (LFGES) with improvements as required during
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. ,
_.
.... ,...';'" ,. '-,',
, '.\ .'
.
Continued maintenance of the soil cover system with improvements
as required during the normal course of operation and maintenance
activities;
.
Continued maintenance of the perimeter fence and warning signs;
Continuation of existing institutional controls, and implementation
of additional institutional controls, as necessary;
.
.
Implementation of the OU3 monitoring program and periodic site
reviews.
ST A TIITORY Dc I cRMINA TIONS
, 'The selected remedy is protective of human health and the environment. complies
with Federal and State requirements that are legally applicable or relevant and
appropriate to the remedial action,' and is cost effective. This remedy utilizes permanent
solutions and alternative treatment technologies to the maximum extent practicable for
OU3/0U6. Operation of the LFGES to extract and treat landfill gas addresses the
principal threat at the Landfill and satisfies the statutory preference for treatment as a
principal element. Condensate generated during operation of the LFGES will be treated
by a P01W.
The size of the Landfill and the fact that there are no on-site hot spots that
represent the major sources of cont~min~tion preclude a remedy in which cont~min~nts
could be excavated and treated effectively. However, hazards associated with exposure
to landfill contents will be rninimi7.ed through containment, by maint~ining the soil cover
system. Groundwater cODt~mination attributable to OU3 is not considered to be a
principal threat, and potential exposure pathways for ground water have been addressed
to the extent practicable.
Because this remedy will result in hazardous substances remaining on-site, a
review will be conducted every five years after commencement of remedial action to
ensure that the remedy continues to provide adequate protection of human health and
th environment. .
-cr
Date
. - ".' ..
,
Date'
Thomas P. Looby, Director
Colorado Department of Health
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Section
1.
ll.
m.
IV.
v.
VI.
vn.
TABLE OF CONTENTS
J!aB
SITE NAME, LOCATION, AND DESCRIPTION. . . . . . . . . . . . . . . . . . . .. 1
.
SITE HISTORY AND ENFORCEMENT ACI1VITIES ................ 3
HIGHI..IGHTS OF COMMUNI1Y PARTICIPATION. . . . . . . . . . . . . . . . . 6
"
SCOPE AND ROLE OF RESPONSE ACTION.. . . ~ . . . . . . . . . . . . . . . . . 7
SUMMARY OF SITE CHARACTERISTICS. . . . . . . . .,. . . . . . . . . . . . . .. 9
A Surf'ace Geolog)' ...................................... 9
B. Subsurface Geology. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9
C. " Hydrogeology. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 10
D. Nature and Extent of CODtamination ...................... 10
E. Water Diversions. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 13
SUMMARY OF OU3/0U6 SITE RISKS ...............'........... 13
A Contaminants of Concern. . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 13
B. Exposure Assessment. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 14
C. Risk Characterization. . . . . . . . . . . . . . . . . . . . . . .0'. . . . . . . . . .. 16
1. Current Human Health Risks . . . . . . . . . . . . . . . . . . . . . .. 20
2. Future Human Health Risks. . . . . . . . . . . . . . . ~ . . . . . . .. 20
3. Risk Associated with Methane Gas . . . . . . . . . . . . . . . . . .. 22
4. Environmental Risk .................... . . . . . . . . .. 22
DESCRIPTION OF ALTERNATIVES. . . . . . . . . . . . . . . . . . . . . . . . . . .. 23
A Remedial Actions Already Implemented. . . . . . . . . . . . . . . . . .. 23
,B. Alternatives Developed for the Landfill .................... 24
1. Alternative 1: No Action. . . . . . . . . . . . . . . . . . . . . . . . .. 24
2. Alternative 2: No Further Action' . . . . . . . . . . . . . . . . . .. 24
3. Alternative 3: Engineering and Institutional
Controls. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 25
vm. SUMMARY OF COMPARATIVE ANALYSIS OF ALTERNATIVES.... 26
A Criterion 1: Overall Protection of Human Health
and the Environment. . . . . .-. . . . . . . . . . . . . . .. 26
B. Criterion 2: Compliance with ARARs .... '. . . . . . . . . . . . . . . .. 27
C. Criterion 3: Long-Term Effectiveness and
Pe~ence ...... ~ . . . . . . . . . . ~ . . . . . . . . . ~ -. 28
D. Criterion 4: Reduction 'of Toxicity, Mobility, or ,,'
':' ~lume'Through Treatment. . . . . . . . .'. '~, . :~ . . .. 29
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IX.
X
ADDendix
A
Fi~re
1.
~
1.
2.
TABLE OF CONTENTS
(Continued)
Section
~
E. Criterion 5: Short-Term Effectiveness. . . . . . . . . . . . . . . . . . . .. 30
F. Criterion 6: Implementability ........................... 30
G. Criterion 7: Cost.................................... 31
H. Criterion 8: State Acceptance. . . . . . . . . . . . . . . . . . . . . . . . . .. 32
L Criterion 9: Community Acceptance. . . . . . . . . . . . . . . . . . . . .. 32
SErnCTED RE~D Y . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 32
STATUTORY DETERMINATIONS. . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 36
A Protection of Human Health and the Environment. . . . . . . . . . .. 36
B. Compliance with ARARS .............................. 37
C. Cost Effectiveness. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 41
D. Utilization of Permanent Solutions and Alternative
Treatment (or Resource Recovery) Technologies to the
Maximum Extent Practicable. . . . . . . . . . . . . . . . . . . . . . . . .. 41
E. Preference for Treatment as a Principal Element. . . . . . . . . . . .. 42
~
Summary of Institutional Controls for OU3/0U6 . . . . . . . . . . . . . . . . . . . . . Al
LIST OF FIGURES
~
Location of the 48th and Holly Landfill (OU3/0U6) at the
Sand Creek Industrial Superfund Site, Commerce City, Colorado. . . . . . . . . . 2
LIST OF TABLES
~
Chemicals and Media of Concern for the 48th and Holly
Landfill (OU3 and OU6), Sand Creek Industrial Superfund Site. . . . . . . . ..: 15
". ~
,
Chemicals of Concern and Exposure Point Concentrations. . . . . . . . . . . . .'. 17
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Tabl~
3.
4.
s.
Al
A2
A3
LIST OF TABLES
(Continued)
.em
Exposure Assumptions Used to Estimate Risks for MLE and
RME Scenarios. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 19
Total Cancer and Non-Cancer Risk Estimates by Exposure
Pathway for Current and Potential Future Scenarios. . . . . . . . . . . . . . . . . .. 21
Cost Summary for the Selected Remedy. . . . . . . . . . . . . . . . . . . . . . . . . . .. 34
Institutional Controls Currently in Place at OU3/0U6 .. . . . . . . . . . . . . . ... A2
Available Supplemental Institutional Controls. . . . . . . . . . . . . . . . . . . . . . . A3
Potential Additional Supplemental Institutional Controls. . . . . . . . . . . . . . . A4
". "
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48.th AND HOLLY LANDFIL~ (OPERABLE UNITS" 3 AND 6)
SAND CREEK INDUSTRIAL SUPERFUND SITE, COMMERCE CI'lY, COLORADO
RECORD OF DECISION
I.
SITE NAME, LOCATION, AND DESCRIPTION
The Sand Creek Industrial Superfund Site (Figure 1) occupies about 300 acres
within portions of both Commerce City in Adanis County, Colorado and the City and
County of Denver, Colorado. The site is centered near the intersection of 52nd Avenue
and Dahlia Street. U.S. Interstate 270 is directly north of the site. 'Four known sources
of contamin~tion are present at the Sand Creek Industrial Superfund Site, and all are
currently inactive: the Colorado Organic Chemical property, the 48th and Holly Landfill,
the LC. Corporation (LeC) property, and the Oriental Refinery property (a source of
petroleum contamination). The 48th and Holly Landfill (Operable Units 3 and 6;
. OU3/0U6), hereafter referred to as tIthe Landfill." is the focus of this Record of
Decision (ROD) and is located in the southern portion of the Sand Creek Industrial
Superfund Site. The Landfill encompasses an area of approximately 150 acres and is
bordered on the north by East 52nd Avenue, on the south by East 48th Avenue, on the
west by Dahlia Street, and on the east by the intersection of the railroad right-of-way and
East 48th Avenue, approximately one-quarter mile east of Ivy Street.
Land use near the Sand Creek Industrial Superfund Site is primarily industrial
and includes trucking finns, petroleum refining operations, chemical production and
supply companies, warehouses, and small businesses. Several other Superfund sites are
also located in the area, including the Rocky Mountain Arsenal, Chemical Sales
. Company, and Woodbury. Properties adjacent to the site are zoned for light and heavy
indUstrial, industrial park, industrial park storage and agricultural uses. Fifteen.
residences with approximately 25 people are located within a mile radius of the site.
The daytime population reaches several hundred due to the local businesses and
industrial nature of the area. The entire Denver parcel is zoned for heavy industrial use.
No changes in zoning are anticipated by the City and County of Denver Planning
Admini~tration (CCDPA) in the near future. CCDPA indicates that long-range l~d-use
plans will depend on the fate of Stapleton International Airport following completion of
. the new Denver International Airport.
The Commerce City parcel is zoned for agricultural and heavy industrial use.
Commerce City's Comprehensive Plan for 1985 to 2010 indicates that future land use of
this area will be primarily industrial with a recreation/open space designation for the
Sand Creek floodplain.
Municipal water for the metr~politan area surrounding OU3/0U6 is supplie"d by
the South Adams County Water and Sanitation District (SACWSD) and 'the Denver
Water Department (DWD). Ground water produced from alluvial and bedrock wells
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"""'" "" ; . . '. Landlill (OUJ/OU,> at
48th"and Holly rce Qty, Colorado.
Location of the nd'Site, Comme
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2
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-------
located north of 1-270 is a major source of water supplied by SACWSD. Water supplied
by the DWD is obtained primarily from surl'ace-water sources located outside of the
Sand Creek Industrial Superfund Site area.
In 1990, the Tri-County. Health Department (TCHD) prepared an inventory of
private wells within the areas bounded on the north by Sand Creek, on the south by
Interstate 70 (1-70), on the west by Colorado Boulevard, and on the east by Quebec
Street. The Landfill is located within these boundaries and covers most of the western
two-thirds of the survey area. The purpose of the inventory was to identify the locations
and uses of all wells within the study area. Results indicated only two properties where
private wells are used for drinking water and both wells were completed in the Arapahoe
Formation (a bedrock aquifer). .
II.
SITE HISTORY AND ENFORCEMENT ACI1VITIES
Before filling operations began at the Land~ the land was used primarily for
agricultural purposes. A review of aerial photographs taken in 1956 and 1964 shows that
sand and gravel mining operations occurred along the southern boundary of the Landfill.
Aerial photographs also show that in 1967, a finger drain system, consisting of a series of
clay tile lateral collector drains, was reportedly installed along the base of an erosional
escarpment located along the south side of the Landfill near 48th Avenue. The reported
purpose of the drain system was to intercept groundwater seepage from the terrace
deposits forming the escarpment. The drain system routes water beneath the Landfill
through a concrete drainpipe which empties via a corrugated metal drainpipe into a
I-acre wetland area adjacent to the Landfill.
Aerial pbotographs indicate that municipallandfilling operations began at the
portion of the Landfill east of Ivy Street in 1967. In 1968, landfilling operations were
initiated west of Ivy Street. According to the former Landfill operator, fill activities
began at the south end of the Landfill and proceeded to the north in one layer or '1ift."
Daily cover material was graded from on-site areas, and the waste was watered to aid
compaction.
The Landfill accepted both demolition and domestic refuse, and the trash was
sorted before dumping. Metal refuse, such as stoves and refrigerators, was placed under
the Colorado and Eastern Railroad Company right-of-way. Known hazardous and
pathological wastes were reportedly excluded from disposal at the Landfill; however, the
method used to exclude these wastes is not known. In addition, it is not known whether
this reported operating practice was consistently employed The Landfill was closed in
1975, and the area was revegetated... .
. . ".' .
,
In June 1977, two men were killed and five injured in two explosions of .
combustible gases that occurred i,n.a water conduit under construction bY the. DWD
-------
northwest of the intersection of 52nd Avenue ~d Dahlia Street. A subsequent
investigation by the Colorado Department of Health (CDH), Tam, and the South
Adams County Fire Prevention Bureau (SACFPB) concluded that the explosions were
caused by methane gas migrating from the Landfill. In response to the explosions and
the detection of combustible gases migrating offsite, two methane gaS venting systems
were installed at the Landfill. Burlington Northern Railroad (BNR), in cooperation with
TCHD and CDH, installed an experimental passive venting system utilizing wind
turbines along the perimeter of the western 2S-acre portion of the Landfill in 1978. In
early 1980, an additional passive methane-gas venting system was installed in the eastern
portion (east of Ivy Street) of the Landfill. Following the explosion, Tam and
SACFPB also periodically monitored for methane gas in businesses surrounding the .
Landfill. The detection of methane gas in nearby buildings, especially around cracks in
foundations and basement walls, supported the conclusion that methane gas was
migrating offsite of the Landfill. In 1981, TCHD determined that the passive venting
system was ineffective, and as a result, BNR installed an active venting system along the
southwest and northwest edge of the Landfill. Gases collected in this system were .
vented to the surface through three stacks. .
l
I
In 1982, the U.S. EPA Field Investigation Team (FIT) performed an evaluation of
the Sand Creek Industrial Site to see if it should be placed on the National Priorities
List (NPL). A composite migration score (SM) of 59.65 was calculated for the site, and
in December 1982 the Sand Creek Industrial site was added to the NFL. In its
investigation, - FIT conducted groundwater sampling downgradient of the Landfill as well
as soil and surface water sampling in order to assess the degree of contamination in the
area. Analytical results indicated the presence of several volatile organic compounds.
(VOCS) in ground water, including 1,1-dichloroethane (1,1-DCA); 1,2 trans- .
dichloroethene (1,2 trans-DCE); 1,1,1-trichloroethane (1,1,1-TCA); and 1,1-
dichloroethene (1,1-DCE). Inorganic compounds that were detected at concentrations
elevated above background levels included arsenic, cadmium, nickel, and zinc.
In late 1983, BNR installed 12 monitoring wells within and around the Landfill
and collected groundwater and surface-water samples for analysis. Concentrations of
arsenic, selenium, lead, antimony, and phenols exceeded EP A drinking water standards
or clean water standards in the area. In January 1984, EP A resampled these locations in
the northern portion of the Landfill. Elevated levels of volatile organics (benzene;
chloroform; 1,2-DCA; 1,1-DCE; 1,2 trans-DCE; tetrachloroethene (PCE); and 1,1,1-
TCA), heavy. metals (cadmium, iron, and manganese), and one phthalate ester were
noted in ground water.
In April1985~ Camp Dresser & McKee, Inc. (CDM) began preparation of a
Remedial InvestigationfFeasibility S~dy. (RIfFS) for the Sand Creek IndUstrial '.
Superfund Site. The site cbaracterizatl'on'report was completed in 1988. During that.
time, BNR continued to investigate possible groundwater cont8mina.tion in the vicinity of
the Landfill. Four newly installed ~ells and three existing wells were sample~~d
-------
indicated the presence of slightly elevated ~ncentrations of total dissolved solids (IDS)
and iron, and low concentrations of 1,I-DCE and 1,I-DCA downgradient of the Landfill.
In August 1987, Engineering-Science, Ine. (ES) collected and analyzed one air
sample from each of the three active methane gas venting stacks to determine whether
emissions could cause adverse health effects. In addition, ES collected four surficial soil
samples to assess emissions resulting from the upward diffusion of gas through the
Landfill cover. Collectively, sixteen VOCS were detected in the stack vent gas samples.
No indication of contamination was observed in the soil samples from the landfill cover.
On February 8, 1990 EP A issued an Administrative Order on Consent (AOC;
Docket No. CERCLA- vm-90-08) to Landfill, Inc. (U) and BNR to perform an RI/FS
for the 48th and Holly Landfill (OU3). EPA's Statement of Work (SOW) in the OU3
AOC included the existing Landfill, the spring emerging from the toe of the Landfill, and
the associated surface-water drainage to the point where the drainage enters a concrete-
lined ditch. Harding Lawson Associates, Inc. (RIA) on behalf of U and BNR,
completed the draft revised Risk Assessment (RA) in April 1992 and the final OU3 RI
in June 1992. In response to EPA comments and current Superfund guidance, the OU3
RA was revised and finalized in early 1993. The Focused Feasibility Study (FFS) for
OU3 was completed and submitted to EPA in March 1993.
On August 15, 1990 EPA issued a Unilateral Order (Docket No. CERCLA-VIII-
90-20) to U and BNR which delineated the PRPs' role in the OU6 Removal Action.
The OU6 Order addressed explosive and health risks associated with gaseous emissions
released from the Landfill and became effective on August 25, 1990. An amendment
issued in September 1990 to the OU3 AOC provided for the inclusion of gaseous
emissions from the Landfill (i.e., OU6) under OU3 following the full implementation of .
the OU6 Removal Action.
In November 1990, an Engineering Evaluation/Cost Analysis (EE/CA) was
prepared for OU6 at the Landfill. The report described the site conditions which
justified a Removal Action, identified Removal Action objectives, discussed remedial
alternatives, and presented the chosen remedy. EP A prepared an Action Memorandum
to request and document approval of the PRP-financed Removal Action for OU6 in
December 1990. An active landfill gas-extraction system (LFGES) was installed by U
and BNR, which began operation in June 1991 as part of the OU6 Removal Action.
The LFGES replaced the previously installed systems and consists of a series of gas
extraction wells interconnected by gas collection piping. Two centrifugal blowers
connected to a single point in the gas collection system are operated alternately to
induce the flow of gases from the gas extraction wells. The gas is diverted to an
enclosed flare system for treatment.. The enclosed flare system is designee to des1!0Y
odors and toxic components of the . landfill gas. Gas monitoring probes are also installed
around the perimeter of the Landfill to monitor the LFGES performance. The probes
are monitored at least monthly fQr .methane concentrations and gas pressure... .
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III.
IDGHLIGHTS OF COMMUNl1Y PARTICIPATION
The community has expressed limited interest in OU3 and OU6, specifically, and
the Sand Creek Industrial Superfund Site, in general. EP A has undertaken several
community relations activities to keep the public informed of issues related to the
Landfill. .
Community involvement activities for the Sand Creek Industrial Superfund Site
began in April 1985. EP A distributed an introductory fact sheet to area residents,
businesses, and agencies. The fact sheet provided background information about the site
and an explanation of the Superfund process. EP A also attended a public meeting
organized by the Citizens Against Contamination, a local group frpm the ar~ and
compiled a list of property owners for the entire site.
EP A mailed a second fact sheet for the Sand Creek Industrial Superfund Site in
November 1985. This fact sheet provided additional information on investigation and
clean-up activities associated with hazardous waste sites. During the same month, EP A
provided a groundwater contamination briefing at a second public meeting held by the
Citizens Against Contamination.
In January 1986, EP A contacted property owners and Commerce City officials to
inform them of activities at the Sand Creek Industrial Superfund Site- In April 1987,
EPA surveyed area residents about their water-use habits to determine--future outreach
efforts.
An RI repon describing the nature and extent of CODtamination at the Sand
Creek Industrial Superfund Site was released for public review in March 1988. In May
1988, EP A contacted owners for permission to sample soils on their property. In
October 1988, EP A met with Commerce City officials to brief them and solicit their
reaction to clean-up plans for the site.
On three occasions in 1990, EP A held public meetings addressing all of the
Superfund sites in South Adams County, excluding the Rocky Mountain Arsenal. At
each meeting, EP A presented its intentions for the Removal Action at OU6 and
encouraged public panicipation. A public comment period was held from October 9,
1990 to November 9, 1990 for the OU6 EE/CA, and no comments were received by
EPA
..
In the fall of 1991, community interviews were conducted to update the site
Community Relations Plan (CRP) originally issued in December 1984. The CRP
outlines community concerns, EPA's strategy for implementing the Plan. and establiShes
information repositories. A list of contacts. and interested panies throughout government
and the local community are also provided. The CRP was released in Decemb.er of
1991. In addition to meeting directly with .the public, EPA and the CDH have met with
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the Tri-County Health Department staff, South Adams County Water and Sanitation
Distri~ Rocky Mountain Arsenal personnel, Commerce City/Adams County officials,
Metro Waste Water officials, and Representative Patricia Schroeder's staff to update
them on OU3/0U6 activities.
On June 3, 1992 a public meeting was held to discuss the Risk Assessment
prepared for OU3. EPA issued the Proposed Plan for OU3/0U6 to the public on
March 19, 1993. The Proposed Plan as well as the RI. RA, and FFS reports were made
available to the public through the Admini~trative Record maintained at the EP A
Region vm Superfund Records Center in Denver and at the information repository at
the Adams County Ubrary. A notice of availability of these documents and notification
of the public meeting were publiShed in The Rocky Mountain News on March 28, 1993
and in the Commerce City Express on March 30, 1993. -
The public comment period for the OU3/0U6 Proposed Plan was open from
March 22, 1993 to April 21, 1993. The public meeting was held at 5:30 p.m. on March
30, 1993 at the Commerce Oty Recreation Center. EP A explained the alternatives and
responded to questions. A transcript of the public meeting has been entered into the
Arlmini~trative Record. No written or oral commentS were received.
IV. - SCOPE AND ROLE OF RESPONSE AcrION
Due to the complex nature of the Sand Creek Industrial Superfund Site, EP A has
divided it into six OUs, or study areas, in order to more effectively address specific
conTamination problems. The OUs were established based on the types of contaminants
present, the type of media affected, and physical characteristics. As discussed above, two
OUs (3 and 6) pertain specifically to the 48th and Holly Landfill. The six operable units
at the Sand Creek Industrial Superfund Site are as follows:
.
Operable Unit 1: OUI addresses conTaminated buildings, soil
cODtamin,,-tion greater than 1000 parts per million (ppm), and VOCs in the
soils. The OUI area includes approximately 15 acres of the site, including
the Colorado Organic Chemical plant property, the land between Colorado
Organic Chemical and the LC. Corporation, and the northern portion of
the Oriental Refinery site.
.
Operable Unit 2: This au addresses the acid waste disposal pits, just
north of the Colorado Organic Chemical property~ commonly referred to as
the LC. Corporation. It is reponed that pits located there were used for
disposal of acid waste from :various chemical manufacturing activities.-'
occurring both off and .on -'site. - - - - - -
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.
Operable Unit 3: This study area comprises the 48th and Hol.J.y Landfill
and specifically includes contaminated surface water, ground water,
sediment, soil, and air in its vicinity.
Operable Unit 4:. This study area comprises the entire site-wide
contaminated ground water. .
.
.
Operable Unit S: OUS includes the same area as OU1, but addresses
pesticides and heavy metals in soils to a depth of S feet with con~mination
greater than action levels and less than or equal to 1000 ppm. There are
up to approximately 14,000 cubic yards of contaminated soil in OUS.
.
Operable Unit 6: This OU addresses the gaseous emissions at the 48th
and Holly Landfill..
At the present time, RODs have been prepared to address remediation action for
OU1, OU2, and OUS at the Sand Creek InduStrial Superfund Site. A ROD amendment
is currently being developed to address fundamental changes made to the selected
remedy for OUSt and the RIfFS for OU4 will be completed in the summer of 1993.
This ROD addresses the principal potential threats to human~ and the
environment resulting from exposure to the 48th and Holly Landfill (OU3/0U6). As
noted above, an amendment (September 1990) to the OU3 Administr;itive Order for the
RIfFS allowed for the inclusion of gaseous emissions from the Landfill in OU3 after the
OU6 Removal Action had been fully implemented. The OU3 FFS evaluated three
alternatives for reducing exposure to contaminated surface water and landfill gas.
Ground water, sediment, and soil were assessed, but remedial alternatives were not
considered as a result of evaluation of media of concern and potential exposure pathways
addressed under OU3. Specific objectives of the remedial action selected for OU3/0U6
are as follows. Landfill and off-site workers as well as off-site residents will be protected
from the landfill contents and gas by ensuring that: (1) emissions of landfill gas are
controlled to prevent inhalation at levels that pose an endangerment to human health or
the environment, (2) accumulation of landfill gas is minimi7.ed in order to prevent
explosion hazards, (3) dermal contact with the landfill contents is prevented, and (4) the
use of ground water underlying the Landfill as a drinking water source is prevented.
A groundwater monitoring program will be implemented at the site to assess
changing aquifer conditions and to continue evaluating the Landfill's impact on
groundwater ,quality. The groundwater monitoring data will provide inforination for
conducting periodic site reviews. In the future, such as when the remedial action for the
Chemical Sales site is complete, if.it is determined from subsequent evaluations that the
Landfill is responsible for unacceptable. groundwater contamination, remediation at the
ground water at ~e Landfill will be addressed under OU3. . . .
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v.
SUMMARY OF SITE CHARAcrERlSTICS
The Sand Creek Industrial Superfund Site, including the 48th and Holly Lan~
is located in an urban environment that has been extensively modified by industrial
development over the past 50 years. The site lies in an area of low relief within the
Sand Creek flood plain. which is part of the South Platte River system. The on-site
drainage represents less than one-half of one percent of the total drainage to Sand
Creek. The only surface-water feature within the Landfill study area is a I-acre wetland
located immediately north of the Landfill The wetland receives water from a "spring"
that discharges from a corrugated metal pipe. This pipe is connected to finger drains
that were installed before landfilling operations began to divert seeps originating along
the escarpment to the south.
The Landfill is in an area classified as mid-latitude semiari~ indicating an area of
high summer temperatures, cold winters, and sparse rainfall. The average annual
precipitation is approximately 15 inches.
A
Surface Geology
Topography in the area rises gently to the south, with elevations ranging. from
approximately 5,180 feet above mean sea level (MSL) in the northwestern comer of the
site to approximately 5,250 feet MSL in the southeastern comer. Interpre~tion of
natural features is complicated by the extensive amount of fill that has been brought into
the area. Between 2 and 10 feet of soil capping material currently covers the refuse at
the Landfill Natural drainage paths also have been altered by development in much of
the area. Natural surficial deposits consist of ~leistocene and Holocene alluvium, eolian
sediments, and lOess. Alluvial deposits in the vicinity of OU3/0U6 range in thickness
from less than 20 feet to more than 100 feet. The deposits generally consist of
interbedded gravel, san~ silt, clay, and minor amounts of cobbles and pebbles. In
addition, paleochannels eroded in the bedrock may influence the occurrence and
movement of ground water in the area.
B.
~
The subsurface geology in the vicinity of the Landfill consists of Quaternary
alluvial deposits and Tertiary bedrock. Alluvial deposits consist of san~ silt, and clay of
the Piney Creek alluvium, eolian deposits of silt and clay, and sand and gravel of the
Broadway alluvium. Oay and gravel sediments of the Slocum alluvium are also locally
present. Bedrock in the area is mad~ up of claystone, shale, siltstone, and sandston.e of
the Denver formation. The Denver fOrmation is underlain by the Arapahoe fo~tion,
Laramie formation, and Fox Hills sandstone. Outcrops of bedrock are not visible at the
Landfill .
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c.
HydrogeoloeY
Three discrete aquifers (Aquifers 0, 1, and 2) have been identified within the
unconsolidated sediment overlying bedrock in the vicinity of the Landfill. Bore hole logs
taken from investigations in the vicinity of the Landfill show that alluvial deposits are
composed of relatively high permeability sands and gravels interbedded with low.
permeability clayey and silty material.
In the southeastern portion of the Landfill, Aquifer 0 is the only alluvial aquifer
present, and it directly overlies bedrock or fine-grained alluvial sediments overlying
bedrock. In the central part of the Landfill, Aquifer 0 exists under perched conditions
. above Aquifer 2. Aquifer 0 is unconfined throughout the Landfill and is underlain by a
low permeability clayey layer (Aquitard A), which inhibits downward movement of
ground water. Within Aquifer 0, groundwater flow is generally toward the north to
northwest.
Aquifer 0 receives recharge from upgradient of the Landfill and discharges to
Aquifer 2 where the confining unit separating these aquifers pinches out in the northwest
portion of the Landfill. Aquifer 0 also discharges to the spring located north of the
Landfill via the finger drain system. The direction of groundwater flow in AqUifers 0
and 2 is generally consistent with the regional flow direction of the alluvial system.
Aquifer 1 is present northwest of the Landfill, including the extreme northwestern
portion of the Landfill. Aquifer 1 exists under unconfined conditions and is separated
from Aquifer 2 by a clayey impermeable unit (Aquitard B). Groundwater flow within
Aquifer 1 is generally toward the east. Ground water may discharge from Aquifer 1 to
Aquifer 2 in the area where the confining unit separating these aquifers pinches out, in
the vicinity of the northern boundary of the Landfill.
The third alluvial aquifer (Aquifer 2) is present over the western tWo-thirds of the
Landfill. Aquifer 2 underlies Aquifer 0 and Aquifer 1 in areas where present and
overlies fine-grained alluvial sediments overlying bedrock. Aquifer 2 exists under
confined conditions to the west and northwest of the Landfill but is unconfined beneath
the Landfill and south of the site. Groundwater flow within Aquifer 2 is generally
toward the north.
D.
Nature and Extent of Contamination
A site-wide RI completed in 1988 identified several contamin;ints in various
operable units. The sources and ext~!1t ~of contamination were not well establishe
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Landfill. The following media were assesse9 for the presence of contamination in the
vicinity of the Landfill:
. Surficial soil
. Ground water
. Surface water and sediment
. Air /landfill gas
Surficial soil samples collected during previous investigations within OU3 and
during the OU3 investigation of sediment within the spring discharge area indicated that
contaminants are not present in these two media. Therefore, the Landfill is not
considered a contributor of contaminants to surficial soil and sediment.
Several VOCs, including 1,1,I-TCA; 1,I-DCA; 1,I-DCE; 1,2-DCE (total);
chloroform; PCE; and TCE were detected in surface-water samples collected from the
spring discharge area. The VOCs detected in surface water are essentially the same as
those detected upgradient of the Landfill in the Chemical Sales site contaminant plumes
in Aquifer O. Due to the similarity of compounds detected upgradient and downgradient
of the Landfill, and the origin of the water discharged to the spring, the OU3 RI
concluded that the most likely source of surface-water contamination is the contaminated
groundwater plumes in Aquifer 0 that resulted from past releases from the Chemical
Sales site.
"
Groundwater samples collected from Aquifers 0, 1, and 2 and water samples
collected from the landfill gas-extraction wells had detectable levels of a number organic
, and inorganic constituents. VOCS were the most widespread of the organic constituents
detected in groundwater samples and were detected at the highest concentrations. Semi-
volatile organic compounds (SVOCs) were also detected in these samples. The
distribution and range of concentrations for the SVOCs were significantly lower than
those observed for the VOCS.
Major sources of groundwater contamination exist in the vicinity of OU3. These
sources include the Chemical Sales site, located southeast of the Landfill, and the
Colorado Organic Chemical Company and Oriental Refinery sites, located west of the
Landfill. Substantial plumes of VOCS within Aquifer 0, including PCE; TCE; l,l-DCE;
1,I-DCA; cis-l,2-dichloroethene (cis-l,2-DCE); 1,1,1-TCA; vinyl chloride; methylene'
chloride; and carbon tetrachloride emanate from the Chemical Sales site and extend to
the north at least as far as Sand Creek. Concentrations of several VOCs within these
plumes exceed 10,,000 micrograms per liter (~g/l) near the source area. These
contaminated groundwater plumes from the Chemical Sales site pass beneath the eastern
portion of the Landfill and may aff~~ groundwater quality downgradient of OU3/9U6.
. ". . ... .
\ .
Major plumes of hydrocarbon compounds, including benzene, toluene, .
ethylbenzene, xylenes, chlorinated. VOCS, and SVOCs are present within Aquifer 1.
-------
These plumes emanate from the Colorado Organic Chemical Company and/or Oriental
Refinery sites (OUI and OUS) and extend northeast to Sand Creek. The con~minant
plumes may pass beneath the extreme northwestern portion of the Landfill and affect
groundwater quality downgradient of OU3/0U6.
Pesticides and herbicides were generally not detected in ground water in the
vicinity of the Landfill. The inorganic constituents detected in groundwater samples
were generally consistent upgradient and downgradient of the Landfill. However, a
limited number of inorganic constituents appeared to be slightly elevated in
downgradient monitoring wells relative to the range of concentrations observed in
upgradient wells. The inorganic constituents detected most frequently at significantly
elevated concentrations include iron and manganese. A few additional inorganics
including antimony, barium, cadmium, calcium, cobalt, magnesium, nickel, potassium,
sodium, and chloride, were detected downgradient of the Landfill at slightly elevated
levels.
Water samples were collected from selected landfill gas-extraction wells during
construction of the LFGES to assess the presence of contaminants within the Landfill.
The most frequently detected organic constituents include ketones, benzene,
ethylbenzene, toluene, total xylenes, and several chlorinated VOCs. The ketones were
detected in the highest concentrations, ranging as high as 5600 ~g/l for 2-bu~one.
Chlorinated VOCS were detected less frequently and at generally lower concentrations.
The compou~ds detected most frequently in samples from landfill gas~xtraction wells
were generally not detected in monitoring wells located downgradient of the Landfill.
Inorganic constituents were detected in samples from landfill gas-extraction wells at
concentrations significantly exceeding background concentrations in Aquifer O.
As discussed in the OU3 ~ the chemical data for the various media indicate that
the Landfill is not contributing significantly to organic and inorganic contamination
downgradient of the Landfill. Other source areas in the vicinity of the Landfill are
clearly contributing substantial levels of organic constituents to ground water, both
upgradient and downgradient of the Landfill. The Chemical Sales site appears to be the
source for most of the chlorinated VOCs that are detected in the ground water.
The inorganic analytical data indicate that iron and manganese may originate in
the Landfill. These constituents are elevated in the landfill gas-extraction well water
samples and are also observed at elevated levels downgradient of the Landfill.
Air samples were collected from stack vents associated .with landfill gas-collection
systems formerly operating at the Landfill. Analytical results for these samples showed
the presence of several VOCs, incluQ,ing benzene; chloroform; 1,I-DCE; PCE; and yinyl
chloride. Most concentrations were less than 10 mg/m3. In additio~' the methane gas
explosions that occurred near the Landfill"in 1977 indicated that landfill'gas is capable of
migrating from the Landfill. The LFGES installed at the Landfill in 1991"35 part of the
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OU6 Removal Action is designed to prevent the migration of landfill gas from the
Landfill. .
E.
Water Diversions
The rights for surface-water diversion from Sand Creek exist at two separate
locations downstream of the Landfill. The first diversion point is the proposed Henrylyn
Sand Creek Diversio~ which is approximately 1.5 miles downstream of the Sand Creek
Industrial Superfund Site on the northeast quarter of Section 12, Township 3 South,
Range 68 West (TIS,. R68W). Diversions from this location could reach 250 cubic feet
per second of water for direct irrigation and storage in existing and planned reservoirs.
The second diversion' point is approximately 2 miles downstream of the Sand Creek
Industrial Superfund Site where the Burlington Ditch intersects Sand Creek. A
maximum of 250 cubic feet per second of water is appropriated for irrigation and
domestic use at this location. According to a representative of the Burlington Ditch
Company, water rights along the proposed Henrylyn Sand Creek Diversi<;m or the
existing Burlington Ditch have not been exercised to date.
VI.
SUMMARY OF OU3/0U6 SITE RISKS
CERClA mandates that EP A protect human health and the enviroJUIlent from
current and potential exposures to hazardous substances at the 48th and Holly Landfill.
Therefore, a Risk Assessment (RA) was prepared for OU3 to evaluate potential human
health and environmental baseline risks associated with contamination at the site. in the
absence of any remedial action. The OU3 RA supplements and updates a previous RA
prepared in 1987 for the Landfill by incorporating data collected during the OU3 RI.
The OU3 RA also addresses risks posed by baseline conditions present at OU6 prior to
implementation of the Removal Action. Two primary types of hazards are associated
with the Landfill: the potential health hazard posed by contamination related to the
Landfill, and the potential explosive hazard associated with methane gas generated
within the Landfill.
A
Contaminants of Concern
. Ground water in Aquifers 0, 1, and 2, surface water, and air were identified as
media of concern in the OU3 RI. Soil and sediment were eliminated since investigations
indicated that they were not significantly contaminated. . Analytical data collected from
1986 through 1991 for the media of~oncem were evaluated according to EP A da~
validation aiteria, a concentration toXicity screen was performed, and the fate and
transport properties of individual chemicals were examined in developing a list of ".
chemicals of concern (COC) for tJIe Landfill. The 23 COCS selected include VOCs,
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SVOCs, and metals. These .contaminants represent all the carcinogenic chemicals
detected in media of concern and the non-c:arcinogenic chemicals present that are the
most likely to pose the greatest relative risk to humam, and the environment. Chemicals
detected in stack vent air samples and used as indicator chemicals in the previous RA
'are also considered as COCS for the air medium. A list of COCS for specific media of
concern is presented in Table 1.
B.
Exposure Assessment
Exposure pathways and receptors were identified based on the aU3 site
conceptual modeL Potential release mechanisms associated with the Landfill include
leaching of chemicals in refuse and their subsequent movement into ground water, and
volatilization of landfill gas. Although an active LFGES is currently operating at the
Lan~ baseline conditions that were present before remedial measures were
implemented were considered in assessing risk associated with the Landfill. Transpon
processes at the Landfill include groundwater flow and withdrawal, groundwater
discharge to surface water, and dispersion of VOCs from the Landfill.
Exposure pathways that were quantitatively evaluated for the current land-use
. scenario in the aU3 RA are: inhalation of ambient air for local residents, nearby
workers, nearby neighborhoods, and the nearest school; and dermal exposure to surface
water for children potentially wading in the spring discharge area. EnVironmental
receptors (Le., plants and wildlife) potentially exposed to COCs in surface water were
also qualitatively assessed. Under the current land-use scenario, no human receptors are
known to be exposed to chemicals at the Landfill via the domestic use of ground. water.
The ground water beneath the Landfill is classified by the State of Colorado as a
potential drinking water supply, and the South Adams County Water and Sanitation
District (SACWSD) draws municipal supplies from the area north of the Landfill. There
is currently a limited use of ground water for crop irrigation and livestock watering in the
area. The SACWSD, irrigation, and livestock watering pathways will be assessed as pan
of the entire Sand Creek Industrial Superfund Site under OU4.
Exposure pathways that were quantitatively evaluated for loc:a1 residents under the
potential future land-use scenario are: ingestion of groundwater contaminants in drinking
water, inhalation of VOCS from ground water while showering, dermal exposure to .
irrigation water derived from ground water, dermal exposure to surface water for
children potentially wading in the spring discharge area, and inhalation. of ambient air
from vapors emanating from the Landfill. Risks associated with aquatic life coming into
direct contact with surface water were also quantitatively assessed for the hypothetical
future scenario. .
. "...
,
Estimated current and potential future risks were based on an average or most
likely exposure concentration (MLE) and'.a reasonable maximum exposure concentration
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.,
Table 1.
Chemicals and Media of Cpncem for the 48th and Holly Land~ll
(OU3 and OU6), Sand Creek Industrial Superfund Site.
CHEMICALS OF CONCERN SURFACEWAl'ER GROUND WATER AIR
VOlATILE ORGANICS:
Benzene X X X
Chloroform X X X
1,2-Dichloroethaae (l,2-DCA) X X
l,l-Dichloroethene (l.l-DCE) X X X
1,2.DichIoroethene (1,2-DCE) X X
1,2-Dichloropropaae X X
Tetraehloroethene (PeE) X X X
1.1.I-Trich\olOethane (l.l.l-TCA) X X
Tric:hloroethene (TeE) X X
1.1,2-Tric:bloroethane (l,l,2-TCA) X X
Vinyl Qloride X X X
SEMIVOlA11LE ORGANICS:
Naphthalene X X
INORGANlCS:
Antimony X X
Arsenic: X X
Barium X X
Cadmium X X
Auoride X X
Manganese X X
Mercuty X X
Nickel X X
Vanadium X X
ADDmONAL VOlATILE ORGANICS
FOR AIR
Chlorobell=ne ." .. X
,
Toluene .. X
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(RME) using concentrations of COCS in ground water and surface water. Because of
limited numbers of groundwater samples for each well location and the need to compute
exposure point concentrations for each individual well, RME concentration values were
established as the maximum detection on a per well basis. The MLE concentrations
were computed as the arithmetic mean of the data collected for each well. For air,
maximum concentrations modeled for the previous RA were used as exposure point
concentrations, since the OU3 RA does not consider operation of the OU6 LFGES.
The exposure point concentrations for COCS in ground water, surface water, and air are
presented in Table 2.
I
I
t,
I
;
Intakes of COCS for each of the exposure scenarios were calculated separately by
exposure route and then summed. The exposure assessment was structured to address
potentially sensitive subpopulations, including children. Exposure assumptionS used to
estimate risk associated with MLE and RME exposure scenarios are presented in Table
3.
C.
Risk Characterization
Potential health risks to humans are expressed in two ways: carcinogenic (cancer
causing) and non-carcinogenic. For carcinogens, it is assumed that there is no safe dose,
but that the risk of cancer lessens as the dose decreases. Cancer potency factors (CPFs)
or slope factors are used for estimating excess lifetime cancer risks associated with
exposure to potentially carcinogenic chemicals. Excess lifetime cancer risk is determined
by multiplying the intake level by the CPF. These risks are probabilities and are
generally expressed as excess cancer risks. An excess lifetime cancer risk indicates the
chance, over and above the background average risk (approximately one in four), that ,an
individual has of developing cancer as a result of exposure to a carcinogen over a 7~year
lifetime under specific exposure conditions. In determining the need for remedial action
at Superfund sites, EP A guidance states that the total excess cancer risk for all
contamin~nts must fall below the range of one chance in ten thousand (1.0E-04) to one
chance in one million (1.0E-06).
Non-carcinogenic risks are calculated by assuming that there is a dose below
which no adverse health effects will occur. This dose is referred to as the reference dose
(RID) and is used to estimate the hazard quotient (HQ) associated with the potential
exposure to non-carcinogens. HQs are determined by calculating the ratio of the
estimated intake level to the RID. A hazard index (HI) can be generated by adding the
HOs for all chemicals having similar target organs or critical effects within a medium., or
by adding HOs across all the media to which a population may reasonably be' exposed.
The III provides a useful' reference point for evaluating the potential significance of
multiple contaminant exposures witbih, a single medium or across meoia. An III cjf 1 is
identified in the NCP as a Superfund site'remediation goal. ' , "
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Tnhle 2. Cbemiculs or Concern nnd Exposure Point Conccntrutlons
-
.....
SlIltFACI! WA1Ht (,.IGfI.) AUt (Rlglm') cmOIlND WA1T:n ("e/I.t'
CIIEMICAIS011 CONCERN MI.I:. RME- @IO rcet' @600 reel' @0.75 mile!>" @1.25 milc!>" MI.P. mllx" RMI! mou'
VOlA TlI.r: ORGANICS:
lIenzcnc 0.3 0.5 4.00r:.5 6.301:.0S S.60E.05 1.32E.04 303 540
Chlorororm 11.8 1.0 2.S71!.1I4 1.6 m.04 8.401:.0S S.60E.OS 37.0 37.0
1,2-I)ichlnrocth:lnt (1,2.DCA) O.S 0.5 ... ... ... ... 11.5 2S.0
1,1.l>ichloroclhcnc (I,I.DCI!) 13.7 15.0 0.001:.06 O.OIlE.06 4.101:.05 2.741!.04 1500 ISOO
1,2.l>ichlnrncthl'llc (1.2-I)CI!t 46.3 no ... ... --- ... 443 920
1 ,2. Dichloropropanc . O.S n.s ... ... ... ...' 10.S 25.0
Tctrachlnrntthcnc (I'CE{: 21.0 23.0 1.231:.04 2.371:.04 1.9]1:.04 4.02E.1I4 3700 ssno
1.I,I.Trichlllroctli:lllc (I,I,I.TCA) 13.7 15.0 ... ... ... ... 3177 721111
.
Trichloroclhenc: (TCE) 10.0 11.0 ... ... ... ... 13S0 2400
1,I,2.Trichloroc:thanc CI,I,2.1'CA) 0.5 O.S .n ... ... ... 10.S 2S.0
Vinyl Chillride 1.0 1.0 6.ool!.06 4.2111:.05 2.7/11:.0S 8.001:.06 30.0 S/I./I
SEMIVOI.A111.E OnOANICS:
Napillhalcnc 511 5.0 ... 'n .n ... 130 1411
INOROANICS:
Antimony 12.0 12.0 ... ... n. ... 57.9 87.1
Arsenic 1.5 1.9 ... ... n. ... 4U 81.7
Rarium .' 411.9 48.9 ... ... -.. n. 1090 1090
Cadmium I.S 1.5 ... '" ... ... 9.1 13.1
Fluoride I!J1MI.O 1900.0 'n ... '" ... 14,000 14,000
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l'uhle 2. Chemiculs or Concern und Exposure Point Concentrullons
(ConUnued)
Mercnry 0.9 1.1 ... ... ... ... 0.7 1.7
Niel;d li.O 6.0 n ... n. ... 1918 3830
Vanadium 5.1 5.1 .-. ... ... ... 28.0 I 28.0
ADOmONAI. VOl A Tn.l! ORGANICS
FOR Allt
Chlornbcnzenc ... ... 0.001!-06 3.001!.06 5.00E.06 2.101!-OS ... ...
Toluenc .-. n' 1.861!.04 3.48E.04 2.241!.04 1.71JP.-04 ... ...
,
.,..,.
.....
00
.
MU! . Must likely cXI}()sure concentration
RME . Reasonahle milximum exposure concenlratlon
Ambient air exposure point concentrations were modeled (!!S. 1987). Values shown are maximum concentrations estimaled for recelltors Illhe indicated distance from Ihe source.
Olslance!ltc:ceplor: 10 feel" Iresp.,ssen; 600 fcel .. local residcnts or nearby worl;ers; 0.75 mile = nearest developed neighborhood; 1.25 miles... nearest school.
Groundwater conccntrntions Ire from 31 wells wllhin, upgradienl, and tlowngradicnl of the landfill. Wells Included Rlay be affected by chemicals from other sources.
MJ.f! concentrali"ns were ealcul.lled fnr indlv!.!unl wells. The vulne shown is the hlshest gronndwaler MI.E conl:cnlralinn reported.
IttoIE oonccntmliolls were calculatcd fnr individnal wells. 111c vallie shnwn is the highest groundwater UM[£ conccnlratlnn repnrtetl.
Source: OU3 itA (III.A, 19')3)
. .
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Table 3. Exposure Assumptions Used to Estimate Risks for MLE and RME Scenarios
PARAMETER UNITS MLE RME
Averaging Tune days 25,550 (carcinogens/adult) 25,550 (carcinogens/adult)
3,285 (noncarcinogens/adult) 10,950 (noncarcinogens/adult)
3,285 (noncarcinogens/ child) 3,285 (noncarcinogensl child)
Body Weight leg 70 (adult) 70 (adult)
18 (child) 18 (child)
Dermal Swface Area an2/evcnt 3,000 (adult) 3,000 (adult)
(swface water) 1,500 (child) 1,soo (child)
Exposure Frequency days/year 350 (adult) 350 (adult)
(non-swface water) . 350 (child) 350 (child)
Exposure Frequency events/year 7 (adult) 62 (adult)
(swface water) 7 (child) 62 (child)
Exposure Duration years 9 (adult) 30 (adult)
9 (child) 9 (child) .
Exposure Tune hours/day 2.0 (adult) 2.6 (adult)
(surface water) 2.0 (child) 2.6 (child)
Ingestion Rate l/day 1.4 (adult) 2.0 (adult)
(water) 0.7 (child) 1.0 (child)
Inhalation Rate m3/day 20 (adult) 20 (adult)
(air) 5 (child) 5 (child)
Source: aU3 RA (HLA, 1993).
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The RME and MLE cancer and non-cancer risk estimates by exposure pathways
for current and potential future land-use scenarios at the study area are presented in
Table 4.
1.
Current Human fiealth Risks
Under the assumption that the LFGES is no longer functioning and nearby
residents are exposed to maximum concentrations of chemicals in air, the inhalation of
ambient air is the greatest contributor to carcinogenic risk "for the current land-use
scenario. Total mean RME and MLE cancer risk estimates for dermal exposure to
surface water and inhalation of vapors from ambient air are both approximately 4.0E-OS.
This total RME and MLE cancer risk for the current scenario does not exceed the
highest acceptable risk of 1.0E-04 but exceeds the point of departure for assessing the
need for remedial action of 1.0E-06, as defined by the NCP. For the current land-use
scenario the total In is less than 1 and indicates there are no unacceptable potential
adverse non-carcinogenic health effects. .
Though ground water in the area is classified as a potential drinking water supply
by the State of Colorado, there is no unacceptable current health-risk due to ingestion,
inhalation, or skin contact with contaminated ground water since water for residential
use is provided through treated water from either the Denver Water Department or
SACWSD. The operation of the LFGES currently eliminates emissions from the
Landfill. However, if the LFGES was riot operating, the estimated cancer risk for
inhalation of landfill gas vapors would ~e approximately four people in 100,000.
2.
Future Human Health Risks
As part of the human health risk assessment for the potential .future land-use
" scenario, the domestic use of ground water was evaluated. Individual cancer risks and
hazard indices were calCulated for 31 well locations within the study area for the
hypothetical future groundwater-use scenario. Estimated risk levels for this scenario
indicate that RME cancer risk exceeds 1.0E-04 near the southeast and northwest
portions of the Landfill, and that 1,1-DCE, vinyl chloride, and arsenic are the primary
contributors to the total carcinogenic risk in these areas. These values represent risks
posed to humans using alluvial ground water for domestic purposes. The total site-wide
RME cancer risk of 3.0E-03 for the potential future land-use scenario is greater than the
target risk range of 1.0E-06 to 1.0E-04. Similarly, the total MLE cancer risks for the
potential future land-use scenario of 4.0E-04 also exceeds the target risk range. The
pathway contributing the most to th~"overa11 cancer risk for the potential future-us~
scenario is the domestic use of groun«} Water. Cancer risk associated "with inhalation of
gas vapors in the future could be as high "as 2.0E-06 risk for children and 9.0E-07 risk for
adults assuming continuous exposure to rilaximum chemical concentrations. "
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Table 4. Total Cancer and Non-Cancer Risk Estimates by Exposure Pathway for Current and Potential Future Scenarios.
N
.....
CANCER RISKS NON-CANCER RISKS
EXPOSURE PATHWAY MLE RME' MLE. RME
Currenl Use
. Dermal Exposure 10 Surface Waler
(Child) S.OE-09 6.0E-08 <1
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For non-carcinogenic contaminants, th~ potential future land-use scenario exhibits
total HIs in excess of 1 (see Table 4). These elevated HIs are associated with the
hypothetical domestic use of ground water and are attribu~ed to the individual
exceedances of HQs for PeE (critical effect: liver), antimony (critical effect: blood),
manganese (critical effects: the central nervous and respiratory systems), fluoride (critical
effect: tooth enamel), and nickel (critical effect: body weight).
In snmmary, the risk analysis indicates that the greatest contributing pathway to
the total cancer risk for a potential residential future land-use scenario would be the
domestic use of ground water. Potential cancer risks for this pathway range from one
person in one thousand to one person in one hundred at OU3/0U6. The risk (above
background) of contracting cancer from ground water in the vicinity of the site is
currently estimated to be highest southeast and northwest of the Landfill The risk
calculations also indicate that there is a potential for adverse health effects resulting
from exposure to non-carcinogenic contaminants through groundwater ingestion.
3.
Risk Associated with Methane Gas
Methane, the component of landfill gas that presents the greatest explosion risk, is
combustible when present in air at concentrations between 5 percent and 15 percent.
Potential explosive risks were virtually eliminated with the installation of the LFGES
during the spring of 1991. However, if the LFGES were to malfunction, fail, or- cease
operating outside of the normal cOurse of O&M activities, then explosive conditions
could occur at the Landfill. It is not possible to quantitatively predict health risks that
could be associated with failure of the system.
4.
Environmental Risk
The potential hazards to environmental receptors were qualitatively evaluated in
the OU3 RA Terrestrial and aquatic habitats present at the Landfill were described
and individual species known to occur in the vicinity were identified. No federally
threatened or endangered plant or animal species are known to be present at the
Landfill.
Exposure of terrestrial receptors to COCS in ground water is considered remote
because ground water is not accessible except at the point of discharge. into the marsh.
Exposure point concentrations and maximum concentrations of COCS in SUrface water
collected at the marsh were compared to federal ambient water quality criteria (A WQC)
and state water quality standards for protection of aquatic life. Maximum surface water
concentrations were lower than A Wac and state standards for all COCS having a:Ii
established standard. Based on the expected chemical fate, incomplete exposure' ,
pathways, low chemical concentra~ons, and comparison of COC concentrations in
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surface water to aquatic life protection criteria, environmental impacts associated with
the Landfill are expected to be minimal. .
In conclusion, the OU3 RA indicates that actual or threatened releases of
hazardous substances from this Landfill, if not addressed by implementing the response
action selected in this ROD, may present an imminent and substantial endangerment to .
public health, welfare, or the environment.
VII.
DESCRIPTION OF ALTERNATIVES
A.
Remedial Actions Alrea~ Implemented
Remedial actions that have already been implemented at the Landfill under the
OU6 Removal Action include soil cover improvementS, installation and operation of the
LFGES, and construction of a perimeter fence and warning signs. In 1992, a soil cover
system improvement program was initiated to address erosion, poor drainage, and lack of
vegetative cover. Approximately 62,000 cubic yards of fill was placed in designated areas
of the Landfill to provide a minimum cover depth of 2 feet. The soil cover was graded
to improve runoff characteristics and revegetated to promote evapotranspiration and
control erosion.
An active gas extraction system was installed. in 1991 to control the accumulation
of landfill gas and eliminate odors and toxic gas emissions. The LFGES consists of a
series of 75 gas extraction wells interconnected by over 15,700 feet of piping. Two
centrifugal blowers alternately operate to induce the flow of gases from the gas
extraction wells. The extracted gas is conveyed to a 50-foot high enclosed flare system
for treatment before release to the atmosphere. Condensate generated by the gas
extraction system is collected in 4 sumps and conveyed to a 10,000 gallon storage tank.
The condensate is discharged from the storage tank to a sanitary sewer for treatment in
a publicly owned treatment works (P01W) operated by the City and County of Denver.
Twenty-two gas monitoring probes (in addition to the 6 previously existing probes) were
installed around the perimeter of the Landfill to monitor the performance of the
LFGES. These probes are sampled monthly to monitor. methane concentrations and gas
pressure. The system is operated so that the concentration of methane within the probes
. does not exceed 5% by volume.
In an effort to limit human access to the Landfill, a 3-strand, smooth wire fence
was erected around the perimeter of the Landfill in 1991. Signs are posted on the fence
to warn against trespassing and hazardous conditions. In addition, EP A has issued an'
Access Order to Colorado Paint Co~pany (CPC), which allows EP A, U, and BNR .to
control the activities that can be condtlcted on the Landfill for a period of up to 25 years
in order to protect the integrity of the response action. EP A has entered into an access
agreement with the Colorado and ;Eastern Railroad Company (CERC) which allows
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EP A and authorized representatives to conduct and maintain response actions on the
CERC property. As discussed previously, EP A has also issued a Unilateral Order for
OU6 that provides for implementing, operating, and maintaining the LFGES.
B.
Alternatives Developed for the Landfill
The detailed analyses of remedial alternatives, presented in the Focused
Feasibility Study (FFS) for OU3, resulted in the development of three alternatives for
site remediation. These alternatives are summarized below:
1.
Alternative 1: No Action
The Superfund program requires that the "No-Action" alternative be considered at
every'site. Under this alternative, EP A would take no action to control the source of
contamination. However, groundwater monitoring and a site review would be conducted
at least every five years.
Under this alternative, the operation of the LFGES would be discontinued. The
landfill soil cover system and existing institutional conU'ols would not be maintained, and
the perimeter fence would not be repaired or maintained. Alternative 1 would therefore
not provide for any additional remediation of affected media within QY3/0U6. Ceasing
operation of the LFGES would likely result in an accumulation of landfill gas beneath
the Landfill. Erosion would degrade the integrity of the landfill soil cover system.
Natural fate processes, including degradation and attenuation, would continue to reduce
contaminant concentrations in ground water over time. A groundwater monitoring
program would be implemented, and periodic site reviews would also be conducted.
2.
Alternative 2: No Further Action
'The major components of this alternative are: continued operation and
maintenance of the LFGES, continued maintenance of the landfill soil cover system,
continuation of existing institutional controls, continued maintenance of the perimeter
fence and warning signs, implementation of a groundwater and landfill gas monitoring
program, and periodic site reviews.
Under this alternative, the LFGES would continue to extract and treat landfill gas
and maintenance would be performed as necessary. A landfill gas monitoring program
would be used to assess the operatio~ performance of the LFGES.
. ~. . .-
,
The landfill soil cover system would be maintained. Revegetation' and soil cover
maintenance would be perfonned ~ necessary to maintain landfill appeari.ri~e, promote
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evapotranspiration, control runon and runoff, prevent excessive erosion of soil cover, and
provide a barrier to direct contact with landfill contents.
Alternative 2 would include continued maintenance of the OU6 Administrative
Order, OU6 Access Order, and the CERC access agreement The perimeter fence and
warning signs would be maintained in order to control access to the Landfill. Repairs
would be made as necessary to the fence, and signs would be replaced if damaged or
stolen to prevent trespassing.
Natural fate processes, including degradation and attenuation, would continue to
reduce contaminant concentrations with time in ground water. A groundwater and
landfill gas monitoring program would be implemented and periodic site reviews would
also be conducted.
3.
Alternative 3: En~neerini and Institutional Controls
Under Alternative 3, a combination of institutional and engineering controls
would be" implemented in the vicinity of the Landfill to limit exposure to affected media.
The major components of Alternative 3 are: continued operation and maintenance of the
LFGES and continued maintenance of the soil cover system, with improvements to both
as required during the normal course of operation and maintenance (O&M) activities;
continued maintenance of the perimeter fence and warning signs; continuation of existing
institutional controls; implementation of additional institutional controls, as necessary;
implementation of a groundwater and landfill gas monitoring program; and periodic site
reviews. .H warrante~ remedial action will be taken at OU3/0U6 if new information
obtained from the groundwater monitoring program indicates that the Landfill
contributes unacceptable levels of contamination to the ground water.
The Administrative Order for the OU6 LFGES, the Colorado Paint" Company
(CPC) Access Order, and the CERC access agreement already preclude certain activities
at the site that would be inconsistent with or interfere with the response actions for
OU6. Current zo~ng prohibits residential development on most of the Landfill (Le., the
CPC and BNR portions of the site). Additional institutional controls may be utilized as
necessary in Alternative 3 to supplement the controls that are already in place to ensure
that the response action remains effective. Furthermore, EP A would have continuing
oversight authority over response actions at the Landfill. EP A approval may be required
for activities at the site beyond continued O&M of the LFGES, the soil cover system,
and fencing/warning signs to the extent that such activities would interfere with or be
inconsistent with the response action. The primary purposes of the institutional controls
would be: (1) to protect the integrity of the soil cover system in order to prevent d.ermal
or direct contact with the landfill contents, (2) to prevent the use of ground water"
underlying the Landfill as a drinking water source, and (3) to protect the LFGES." " "
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VIII. SUMMARY OF COMPARATIVE ANALYSIS OF ALTERNATIVES
In this section, alternatives developed for OU3/0U6 of the Sand Creek Industrial
Superfund Site are evaluated and compared to each other using the nine evaluation
criteria required by the National Oil and Hazardous Substances Pollution Contingency
Plan (NCP) to identify the alternative that provides the best balance among the criteria.
The relative performance of the alternatives is summarized by highlighting the key
differences among the alternatives in relation to the following criteria:
1. Overall Protection of Human Health and the Environment
2. Compliance with Applicable, or Relevant and Appropriate Requirements
(ARARs)
3. Long-Term Effectiveness and Performance
4. Reduction of Toxicity, Mobility, or Volume Through Treatment
S. Short-Term Effectiveness
6. Implementability
7. Cost
8. State Acceptance
9. Community Acceptance
A
. Criterion 1: Overall Protection of Human Health and the Environment
- -
This criterion is categorized as a threshold criterion (Le., alternatives must pass
this criterion to remain in the evaluation). This criterion assesses the protection afforded
by each alternative, considering the magnitude of the residual risk remaining at the site
after the response objectives have been met. Protectiveness is determined by evaluating
how site risks from each exposure route are eliminated, reduced, or controlled by the
specific alternative. The evaluation also takes into account short-term or cross-media
impacts that result from implementation of the alternative remedial activity.
Overall protection of human health and the environment would be provided by
Alternatives 2 and 3. Alternative 1, the No-Action alternative, would not provide
adequate protection of human health and the environment, because (1) ceasing
operation of the LFGES would increase the likelihood of explosion and increase the
potential for inhalation of landfill gas and (2) discontinuing maintenance of the soil
cover system and the perimeter fence with warning signs would increase the potential for
direct contact with landfill contents. Alternative 3 would provide even greater overall
protection of human health and the environment than the current sufficient protection
afforded by Alternative 2 because the implementation of additional institutional con~ols,
as necessary, within OU3 would further ~educe the risks associated with (1) potential
future use of ground water and (2) pot~ntial for direct contact with landfill contentS. In
addition, Alternative 3 includes a provision for making improvements to the LFGES. and
. ~ '.
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soil cover system, as required, to ensure ad~quate protection of human health and the
environment.
B.
CriteriQn 2: Compliance with ARARs
This criterion is also a threshold criterion in that all alternatives must attain
ARARs to be considered as site remedies or, if ARARs are not attained a justifiable
ARARs waiver must be obtained. Section 121(d) of the Superfund Amendments and
Reauthorization Act (SARA) mandates that for all remedial actions conducted under
cERCLA, cleanup activities must be conducted in a manner that complies with ARARs.
The NCP and SARA have defined both applicable requirements and relevant and
appropriate requirements as follows:
.
Applicable requirements are those federal and state requirements that
would be legally applicable, either directly, or as incorporated by a
federally authorized state program.'
Relevant and appropriate requirements are those federal and state
requirements that, while not legally "applicable," are designed to apply to
problems sufficiently similar to those encountered at CERCLA sites, that
their application is appropriate. Requirements may be relevant and
appropriate if they would otherwise be "applicable," except f~n jurisdictional
restrictions associated with the requirement.
.
Other requirements to be considered are federal and state non-regulatory
" requirements, such as guidance documents or criteria. Advisories or
guidance documents do not have the status of potential ARARs. However,
where there are no specific ARARs for a chemical or situatio~ or where
such ARARs are not sufficient to be protective, guidance or advisories
should be identified and used to ensure that a remedy is protective.
, Federal and state ARARs which must be considered include those that are:
chemical-specific, location-specific, and action-specific. Chemical-specific ARARs govern
the extent of site cleanup in terms of actual cleanup levels. For example, Colorado
Interim Organic Pollutant Standards (ClOPS) for stream segments classified for aquatic
life and/or water supply are chemical-specific ARARs for the site. Location-specific
ARARs govern natural site features such as wetlands, floodplains, and man-made
features such as archeological and historic areas. Action-specific ARARs are technology
or activity-based requirements that set restrictions on particular kinds of action at '
CERClA sites.
. ''''.' .
,
Alternatives 1, 2, and 3 would comply with ARARs. Since no remedial action
would be implemented under the ,No-Action alternative, there are no action-specific
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ARARs for Alternative 1. Analyses of sampl~s collected in the spring discharge area
during the OU3 RI indicate that the ClOPS are not exceeded. The investigation of QU3
also revealed that there are no listed archeological or historic properties, or endangered
or threatened species present at the Landfill. In addition, it is not expected that the
remedial activities associated with OU3/0U6 would adversely impact any wetlands at or
near the Landfill.
The next five criteria are designated as balancing criteria. These criteria are used
to measure the positive and negative aspects of performance, implementability, and cost
for each alternative.
C.
Criterion 3: Lone-Term Effectiveness and Permanence
The focus of this evaluation is to determine the effectiveness of each alternative
with respect to the risk posed by treatment of residuals and/or untreated wastes after the
cleanup criteria have been achieved. Several components were addressed in making the
determinations, including:
Magnitude of residual risk from the alternative.
Likelihood that the alternative will meet process efficiencies and
performance specifications.
Adequacy and reliability of long-term management controls providing
continued protection from residuals.
Associated risks in the event the technology or permanent facilities must be
replaced.
Comparison of alternatives with respect to long-term effectiveness and
permanence indicates that Alternative 3 would provide the most effective and permanent
remedial solution for OU3/0U6. Alternative 1 would not reduce the residual risk at the
Landfill since it does not include provisions to maintain existing controls that would
manage untreated materials at the Landfill. Under Alternative 1, hypothetical risks
would likely increase after ceasing operation of the LFGES and discontinuing
maintenance of the soil cover system. Alternative 3 is more effective and permanent
than Alternative 2. Alternative 3 includes additional institutional controls, as necessary,
and provisions for improvements to the LFGES and the soil cover system, as required.
Therefore, Alternative 3 provides m~re. reliable controls for future management of.
untreated materials at the Landfill. trim Alternative 2. . . .
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D.
Criterion 4: ~ Toxicity. ~ty. or Volume ThroueQ...Jreatment
This criterion evaluates the ability of the alternatives to significantly achieve.
reduction of the toxicity, inobility, or volume of the contaminants or wastes at the site,
through treatment. The criterion is a principal statutory requirement of CERCl.A. This
analysis evaluates the quantity of contaminants treated and destroyed, the degree of
expected reduction in toxicity, mobility, or volume measured as a percentage of
reduction, the degree to which the treatment will .be irreversible, the type and quantity of
residuals produced, and the manner in which the principal threat will be addressed
through treatment. The risk posed by residuals will be considered in determining the
adequacy of reduced toxicity and mobility achieved by each alternative. .
Alternatives 2 and 3 would reduce the toxicity, mobility, or volume of landfill gas
through extraction and treatment while landfill gas cac concentrations, mobility, and
volume would likely increase under Alternative 1. Maintenance of the soil cover system
would continue to reduce the mobility of landfill contents under Alternatives 2 and 3.
The provision in Alternative 3 for modifications of the LFGES and the soil cover system,
as required, ensures that reductions in toxicity, mobility and volume of landfill gas and
reduction in the mobility of landfill contents would be maintained in the event of
changing conditions at the Landfill. However, under present conditions, Alternatives 2
and 3 are essentially equivalent with respect to reducing toxicity, mobility, or volume.
Under Alternatives 2 and 3, the toxicity of landfill gas would be significantly
reduced by the flare system, which incinerates the extracted gas. The mobility of landfill
gas would be controlled through capture and extraction by the LFGES. Review of 1992
gas monitoring probe data indicates that the mobility of methane bas been substantially
reduced since operation of the LFGES began. The volume of landfill gas would be
reduced through extraction and treatment by the LFGES. Currently, approximately
700,000 cubic feet of landfill gas per day are collected and treated by the LFGES.
The mobility of the landfill contents would be reduced through continued
maintenance of the soil cover system and would thereby minimize the potential for direct
contact with landfill contents. The soil cover system prevents transport of refuse by
animals as well as by wind and erosion. The soil cover system does not contribute to a
reduction in the toxicity or volume of the landfill contents. However, the toxicity of the
landfill contents may be reduced by natural biodegradation.
Alternatives 2 and 3 would not provide a reduction in the toxicity, mobility, or
volume of contaminated ground water beyond those processes occurring naturally.
Reductions in toxicity as a result of natural attenuation and biodegradation processes
may occur in ground water. Volatilization of organic compounds may result in a minor
reduction in volume. . ,- . ". .
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Alternative 1 would not reduce the toxicity, mobility, or volume of landfill gas,
ground water, or landfill contents beyond what would occur through natural degradation
and attenuation processes.
E.
Criterion 5: Short-Term Effectiveness
The short-term effectiveness of each alternative was assessed based on the risk
associated with the implementation of the remedial action to the community, workers,
and environment and the time required to achieve the response objectives. Measures to
mitigate releases and provide protection are central to this determination.
The evaluation of the alternatives indicate that all three are essentially equivalent
with respect to short-term adverse environmental impacts and protection of the
community and workers. With the exception of the groundwater monitoring program
and additional institutional controls, as necessary, all remedial actions associated with
Alternatives 2 and 3 have already been implemented. Alternative 3 may involve future
improvements to the LFGES and soil cover system, but adverse short-term impacts
should be minimized through standard engineering controls and adherence to standard
health and safety practices. Because no remedial actions are proposed under Alternative
1, no potential short-term exposure to the community, construction workers, or additional
impacts to the environment would occur as a result of implementing a remedial action.
F.
Criterion 6: Implementability
This criterion analyzes technical feasibility, administrative feasibility, and the
availability of services and materials. Technical feasibility assesses the difficulty of
construction or operation of a particular alternative and unknowns associated with .
process technologies. The reliability of the technologies based on the likelihood of
technical problems that would lead to project delays is critical in this determination. The
ability to monitor the effectiveness of the alternative is also considered.
Admini"trative feasibility assesses the ease or difficulty of obtaining permits or .
rights-of-way for construction. Availability of se~ces and materials evaluates the need
for off-site treatment, storage, or disposal services, and the availability of such services.
Necessary equipment, specialists, and additional resources are also evaluated in
determining ~e ease by which these needs could fulfilled.
Each of the alternatives evaluated would be technically feasible. No additional
construction, maintenance, or operations beyond those already existing would be .
required under any of the alternatives,with the exception of Alternative 3, which may
require improvements to existing systems~. These improvements are expected to be .
readily implementable because no. pnplementation difficulties were experience~. during
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the installation of the LFGES and improvement of the soil cover system. The
groundwater monitoring program included 'in Alternatives 1, 2, and 3 is technically
implementable because existing groundwater monitoring wells would be utilized to
accomplish the proposed monitoring. The off-site monitoring of landfill gas included in
Alternatives 2 and 3 is also technically implementable since existing monitoring probes
would be used. .
. It is unlikely that the regulatory agencies or the public would accept shutdown of
the LFGES as proposed under Alternative 1. Alternative 2 would be admini"tratively
feasible. Institutional controls, as necessary, in Alternative 3 would require additional
legal effort to be implemented and would be dependent in certain instances on
cooperation of property owners and municipalities or other governmental entities, and
satisfaction of legal requirements. Alternative 2 would likely be the easiest to implement
with respect to admini"trauve feasibility because no additional actions would be required.
G.
Criterion 7: Cost
Alternatives are evaluated for cost in terms of both capital costs and long-term
O&M costs necessary to ensure continued effectiveness of the alternatives. Capital costs
include the sum of the direct capital costs (materials, equipment, labor, land purchases)
and indirect capital costs (engineering, licenses, or permits). Long-term O&M costs
include labor, materials, energy, equipment replacement, disposal, and sampling
necessary to implement the alternative. The objective of the cost analysis is to eliminate
those alternatives that (1) do not provide measurably greater protection of human health
and the environment, and. (2) include costs that are substantially greater than those of
other alternatives.
The present worth ~ysis is used to evaluate expenditures that would occur
during different time periods. By discounting all costs to a common base year (Le.,
1992), the costs could be compared on the basis of a single figure for each alternative.
Total present worth costs were calculated by multiplying the capital and O&M cost
incurred during each year by the present worth factor. An interest rate of 5 % and a
project duration. of 30 years was used in accordance with EP A guidance.
The total present worth costs are identical ($7,283,000) for Alternatives 2 and 3
. since the additional expenditures required for Alternative 3 (Le., additional institutional
controls and required improvements to the LFGES and soil cover system, as necessary)
cannot be estimated. A total present worth cost of $4,316,000 is estimated for
Alternative 1. Operation and maintenance costs incurred to date were included for
Alternative 1, but future O&M for ~e LFGES and soil cover system were exclude<;l since
this alternative proposed discontinuation of these systems~ Total annual O&M costs for
Alternative 1 include only the implementation of a groundwater monitoring program and
periodic site reviews and are esti~ted at $47,000. For both Alternatives 2 and 3, total
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estimated capital costs and annual O&M costs, are 53,170,000 and $240,000, respectively.
However, capital costs for Alternative 3 are likely to be somewhat higher than indicated
due to costs associated with additional institutional controls, if necessary. .
H.
Criterion 8: State Acceptance
This modifying criterion evaluates technical and administrative issues that may be
raised by the State. EP A has involved CDH throughout the RIfFS and remedy selection
process. The State of Colorado concurs with EPA's selected alternative, as presented in
Section IX.
i
i
.,
I.
Criterion 9: Communi\y Acceptance
This modifying criterion evaluates questions and comments on the Proposed Plan
received from members of the community. It appears that the community supports
EPA's selected remedy, as presented in Section IX. No comments on the Proposed Plan
were received by EP A during the public comment period. Therefore, preparation of a
Responsiveness Summary for this ROD was not necessary.
IX.
SELEcrED REMEDY
Based on consideration of the requirements of CERCLA and the detailed analysis
of alternatives,. EP A with the concurrence of the State of Colorado has determined that
Alternative 3, Engineering and InstitUtional Controls, is the most appropriate remedy for
OU3/0U6 of the Sand Creek Industrial Superfund Site. This remedy includes extraction
and treatment of landfill gas; maintenance of the soil cover system and LFGES with
improvements, as required; maintenance of the perimeter fence and warning signs;
implementation of additional institutional controls, as necessary; implementation of a
monitoring program and site reviews; and additional remedial action, as necessary, if
.monitoring indicates that the Landfill contributes to unacceptable contamination of
ground water. The PRPs will be responsible for maintenance of each component of the
remedy. .
The detailed analysis of alternatives shows that for overall protection of human
health and the environment; effectiveness; and reduction of toxicity, mobility or volume,
the selected alternative is superior to Alternatives 1 and 2. The selected remedy and
Alternative 2 are essentially equivalent in terms of technical and admini"trative
feasibility, although cooperation of land~wners or governmental entities may be ..
necessary for implementation of certaiQ additional institutional controls under the .
selected alternative. Costs for the selected remedy and Alternative 2 are. also similar,
however, there may be additional C
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associated with additional institutional conn:ol implementation, if necessary, and any
improvements required to the LFGES and soil cover system during the normal course of
O&M activities.
The selected remedy incorporates removal, treatment, and containment
technologies. The principal components of the selected alternative are described below
in greater detail. Capital and annual O&M costs for these components are presented in
Table S.
, ~ndfiIl Gas-Extraction System: The LFGES was installed within the boundaries
of the Landfill during the spring of 1991 as part of the OU6 landfill gas Removal Action.
The LFGES has the following primary components: seventy-five landfill gas-extraction
wells; gas collection piping, consisting of a main header and 13 subheaders; four
condensate sumps, piping, and a knockout pot; a 10,OOO-gallon condensate storage tank;
two gas-extraction blowers and ancillary equipment; an enclosed gas flare system and a
blower building; and 22 gas monitoring probes. Condensate collected in the storage tank
is discharged via a sanitary sewer to the. Denver Metro Central Treatment Plant. The
LFGES is designed to capture as much of the landfill gas within the Landfill as possible
and minimi7.e its vertical and lateral migration via the extraction wells and gas collection
piping. The enclosed flare system .destroys odors and toxic components of the landfill
gas. The gas monitoring probe network monitors the' LFGES performance. Based on
results from the gas monitoring probes and extraction wells sampled weekly and
evaluated quarterly, the LFGES is adequately capturing methane and mitigating off-site
gas migration. The preferred alternative provides for improvements or upgrades to the
LFGES, as required. .
Soil Cover System: Site improvements were undertaken at the Landfill during the
spring of 1992 to enhance the integrity of the soil cover system and improve general
erosion control and site appearance. The site improvements were also expected to
improve O&M of the LFGES by reducing infiltration of ambient air into the Landfill.
The site improvements consisted of: (1) the placement, grading, and compaction of
approximately 62,000 cubic yards of fill material; (2) the placement of fill in low/eroded
areas and the construction of terraces and straw bale dikes to control surface-water
runoff; and (3) the revegetation of approximately 30 acres and interseeding of 8 acres of
the Landfill. Under the preferred alternative, the soil cover system will be maintained
. (i.e., mowing the grass and spot reseeding as necessary) and improved as conditions at
the Landfill warrant. The need for additional improvements to the soil cover system will
be based on visual indications, such as surface erosion or a lack of vegetation. . .
Fencini: The Landfill is currently fenced with a 3-strand smooth wire fence that
was installed in August 1991. Warning signs are posted around the entire perimete.r of
the fence. Maintaining the wooden fence posts, repairing broken. striinds of wire, 'and
replacing warning signs as required will ensure that the fence will contiIiue to be ail
effective deterrent to public acce~:to the. Landfill. ..' .
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Table 5. Cost Summary for the Selected Remedya
Capital Costs:
. Landfill Gas Extraction System
. Landfill Soil Cover System
. Perimeter Fence
. Groundwater Monitorine Program Desi~
TOTAL CAPITAL COSTS
Estimated Annual O&M Costs:
. Landfill Gas Extraction System
. Landfill. Soil Cover System
. Groundwater Monitoring Program
. Periodic Site Assessment
TOTAL ANNUAL O&M COSTS
TOTAL PRESENT WORTIi (1992 $)b
- $2,470,000
- $ 673,000
- $ 16,000
- $ 11.000
$3,170,000
- $ 152,000
- $ 40,000
- $ 36,000
- $ 11.400
- $ 240,00> (rounded)
- $7,283,000 (rounded)
a The capital costs of the selected remedy are likely to be. higher than indicated due to
costs associated with implementation of additional institutional controls, as necessary.
However, these costs were not included because of uncertainties in estimating costs
associated with negotiating and implementing the additional institutional controls.
b Total present worth costs assume an annual discount rate of 5% and a project duration
of 30 years.
Source: OU3 FFS (HLA, 1993).
. ". .
,
34
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Institutional Controls: The purposes of the institutional controls component of
the selected alternative are (1) to protect the'integrity of the soil cover system to prevent
dermal or direct .contact with the landfill contents, (2) to prevent the use of ground water
underlying the Landfill as a drinking water source, and (3) to protect the LFGES
operating at the LandfilL These objectives are already achieved in part through EP A
oversight of the response action; state restrictions on permitting and constructing water
wells in areas of known contamination; and maintenance of the existing controls under
the OU6 Order, the CPC Access Order, and the Consent for Access on CERC property.
Additional institutional controls that may be implemented as necessary include further
EP A Orders issued pursuant to CERCLA f 106, judicial Consent Decrees under
CERCLA i 122, zoning and subdivision regulations, building permits, recording
requirements, state statutes, and local ordinances. Institutional controls currently in
place at OU3/0U6 as well as available and potential supplemental institutional controls
are summarized in Appendix A. .
aU3 Monitorine Prowam: The OU3 monitoring program consists of groundwater
and landfill gas monitoring components. Under the preferred alternative, both
components will be implemented or continued. The duration of the OU3 monitoring
program will be established in a Unilateral Order. The groundwater monitoring
component is designed to assess changing conditions in Aquifers 0 and 2, . and to continue
evaluation of the Landfill's impact on groundwater quality. Key elements .of the
monitoring program include: annual sampling of 3 existing upgradient wells, annual
sampling of 6 existing downgradient wells, annual sampling of one location ~t the spring
discharge area, and proposed target analytes based on the results of the OU3 RI.
The landfill gas monitoring component was implemented with the startup of the
LFGES in the spring of 1991. The perimeter netWork of 22 gas monitoring probes will
continue to be monitored to evaluate the performance of the LFGES. In addition, six
gas monitoring probes existing on the northwest perimeter of the Landfill prior to the
OU6 Removal Action will also continue to be monitored to provide additional
information regarding system performance and the migration of landfill gas. The
LFGES is operated so that the concentration of methane within the monitoring probes
does not exceed 5% by volume.
Data from both components of the OU3 monitoring program will support
assessment of landfill conditions and LFGES performance as well as the need for
improvements as provided for under the selected remedy. In addition, the data will be
used to assess the site and ongoing activities during the periodic site review. In the
future, if it is determined that the Laridfill is responsible for unacceptable groundwater.
contamination, the remediation of ground water at the Landfill will be addressed under
003.
. ", .
,
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x.
STATUTORY DETERMINATIONS
EP A's primary responsibility at Superfund sites is to undertake remedial actions
that achieve adequate protection of human health and the environment. In addition,
Section 121 of CERClA establishes several other statutory requirements and
preferences. These specify that when complete, the selected remedial action for a site
must comply with applicable or relevant and appropriate environmental standards
established under federal and state environmental laws unless a statutory waiver is
justified. The selected remedy must also be cost effective and utilize. permanent
. solutions and alternative treatment technologies or resource recovery technologies to the
maximum extent practicable. Finally, the statute includes a preference for remedies that
employ treatments that permanently and significantly reduce the volume, toxicity, or
mobility of hazardous wastes as their principal element. The following discussion
addresses how the selected remedy meets these statutory requirements.
.A
Protection of Human Health and the Environment
EPA's Guidance for Conducting Remedial Investigations and Feasibility Studies
Under CERCLA (1988) indicates that protectiveness may be achieved by reducing.
exposure. through actions such as containment, limiting access, or providing an alternate
water supply. The remedial actions described for the selected remedy will permanently
address the principal threats to human health and the environment for OU3/0U6
through treatment to reduce the toxicity, mobility, and volume of landfill gas and
containment of landfill contents. Concentrations of contaminants of concern in the
spring discharge area do not exceed preliminary remediation goals, so remedial action
objectives for aquatic life. have been achieved. The risks associated with potential future
activities at the Landfill will be addressed by the implementation of additional
institutional controls, if necessary.
Though CERCLA favors active remediation, institutional controls may be
implemented under CERCLA in appropriate circumstances. As provided by the
Preamble to the NCP (55 Federal Register 8666, 8706 [March 8, 1990]):
Examples of institutional controls, which generally limit human activities at or
near facilities where hazardous substances, pollutan~ or contaminants exist or
will remain onsite, include land and resource use and deed restrictioIlS,. well
drillin~ prohibitions, building permits, and well use advisories and deed notices.
EP A oelieves ...that.institutiOIial controls have a valid role in remediation and are
allowed under CERCLA (e.g., Section 121(d)(2)(B)(ii) appears to contemplate
such C9ntrols). Institutio.n3:l ~ontrols are a necess~ sUPJ?lem~nt whe~ some
waste IS left m place, as It IS m most response actions. Also, m some mstances
where the balancing of tradeoffs among alternatives during selection of remedy
process indicates no practicable way to active!>, remediate a site, institutional
controls such as deed restrictions or well-drillfng prohibitions are. the only means
available to provide protection of.human healtli. ... .. .
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Institutional controls are particularly ~uited for application at municipal landfills.
For example, as provided in EPA's Conducting Remedial Investigation/Feasibility Studies
for CERCLA Municipal Landfill Sites (1991):
For municipal landfill sit~ the major purpose of deed restrictions is to protect
the integrity of the cap. The restrictive covenant should liinit subsurface
development (excavauonlj excessive vehicular traffic (including off-road vehicles),
and groundwater use. Aaditional deed restrictions may be reQuired for effective
implementation of other technologies. The permissible uses/limitations for the
specific landfill p'ropc::m' should be identified based on the nsk the site poses and
the remedial actions liKely to be implemented.
B.
Compliance with ARARs
All federal and state ARARs will be met by the selected remedy. Federal and
state ARARs which must be considered include those that are: chemical-specific,
loeation-specific, and action-specific. Potential ARARs identified for OU3/0U6 are
. provided below.
Chemical-Specific ARARs:
. . Colorado Interim Organic Pollutant Standards (ClOPS) for Stream
Segments Oassified for Aquatic Life.
Sampling data from OU3 indicates that none of these standards are
exceeded. Therefore, the selected alternative complies with this potential
ARAR.
Location-Specific ARARs:
. Archeological and Historic Preservation Act, 16 USC ~ 469;40 CFR ~
6.301(c).
The investigations of OU3 have not revealed any data that would trigger
the effect of the Act or its regulations. The selected remedy will comply.
with this potential ARAR.
. National Historic Preservation Act (NHPA), 16 USC ~ 470; 40 CFR ~
6.301(b); 36 CFR Part 800.
Studies of OU3 have. ndt revealed any historic properties that would .trigger
the effect of this Actor its regulations. The selected alternative will
comply with this pot~ntial ARAR.
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. Colorado Register of Historic Places, Colo. Rev. Stat. fi 24-80.1.101, ~
~ 8 CCR 1504-5.
Studies of OU3 have not revealed any historic properties that would trigger
the effect of this Act or its regulations. The selected alternative will
comply with this potential ARAR.
. Endangered Species Act, 16 USC fi 1531, et seQ.; 50 CFR Part 17; 40
CFR fi 6.302(h).
Studies of OU3 have not indicated the presence of any listed species that
would trigger the effect of this Act or its regulations. The selected
alternative will comply with this potential ARAR.
. Non-Game Endangered or Threatened Species Conservation Act, Colo.
Rev. Stat. fi 32.101, et seq.; 2 CCR 406-8.
Studies of OU3 have not indicated the presence of any listed species that
would trigger the effect of this Act or its regulations. The selected
alternative will comply with this potential ARAR.
. Executive Order on Protection of Wetlands, Executive Order No. 11990;
40 CFR fi 6.302(a).
.The U.S. Fish and Wildlife Service does not believe that the remedial
activities associated with OU3 will adversely impact any wetland that may
be present at or near the Landfill (letter dated June 6, 1991 from the U.S.
Department of the Interior). Therefore, the Executive Order and its
regulations are not ARARs for OU3. In the event that the OU3 remedial
activities adversely impact any wetlands at aU3, the Executive Order and
regulations may be ARARs.
Action-Specific ARARs ~d Guidance To Be Considered (THC):
. Conducting Remedial Investigatio~/Feasibility Studies for CERClA
Municipal Landfill Sites (EPA, 1991).
EP A has provided gUid~Ce specifically intended to address the
remediation of municipal landfills. In particular, the guidance addresses
the type of cover su~ested -for municipal landfills and reco~ .a soil
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cover as sufficient to prevent dermal contact with landfill contents. It is
apparent that EPA's municipal landfill guidance is not an ARAR (see
NCP, 40 CFR f 300.400(g)(3». However, as an Agency guidance, it may
be a THC for OU3.
. Potential Action-Specific ARARs Pertinent to Operation of the Gas
Collection System at dU6, as set forth in the Sand Creek Industrial
Superfund Site OU6 EE/CA (~ 1990).
Gas Collection System:
. 'Oean Air Act, 42 USC ff 7401 et seQ.. National Ambient Air
Quality Standards (NAAQS).
NAAQS are ARARs for the Landfill. The landfill area is an attainment
area for sulfur dioxide, nitrogen dioxide, and lead, and a non-attainment
area for particulates, carbon, monoxide, and ozone. However, since the
gas collection system is not expected to exceed NAAQS levels during
the remedial action, this requirement is relevant and appropriate.
.
Colorado Air Pollution Control Regulations, 5 CCR 1001-1 et seQ.
Based on experience with other similar gas removal systems and the
performance of the OU6 LFGES to date, it is not expected that the
LFGES will qualify as a major stationary source. However, if the gas
collection system should ever qualify as a major stationary source, the
pertinent substantive requirements applicable to major stationary
sources in the Colorado Air Pollution Control Regulations would be
potential ARARs. '
.
Colorado Solid Waste Disposal Sites and Facilities Regulations, 6
CCR 1007-2, Section 2. '
These regulations include requirements concerning explosive gas
concentrations at solid waste disposal facilities. Section 2.2.5 requires
that explosive gas concentrations be monitored regularly. Section 2.2.6
limits explosive gas concentrations for solid waste facilities and 'requires
that the concentragon,of explosive gases must not exceed 1% by volume
of air within facility"structures or 5% by volume of air at the site" ,
boundary. Section 2.4.4 'provides that concentrations of explosive' gases
generated by the facilitY for solid waste disposal shall not exceed 5% in
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the air at the site boundary after closure. These requirements are
potential ARARs for the gas collection system. .
Condensate Mana~ement:
.
RCRA Subtitle C Requirements, 6 CCR 1007-3.
The condensate generated from operation of the LFGES should not be
a hazardous waste because it is not a listed waste and it is not derived
from a listed hazardous waste. Based on. sampling of condensate from
the LFGES and past experience with landfill condensate, it is not
expected that concentration limits set forth in the TCLP rule will be
exceeded or that the condensate will otherwise exhibit a characteristic
of hazardous waste. Therefore, RCRA Subtitle C requirements should
not be ARARs for the management of condensate. In the unlikely
event that (1) the condensate exhibits a characteristic of a hazardous
waste, and (2) the condensate is not managed in a manner excluded
from RCRA Subtitle C regulation, requirements pertinent to the
management of the condensate would be potential ARARs.
.
Compliance with Colorado Discharge Permit System Regulations, S
CCR 1002-2.
Substantive provisions of these regulations would be potential ARARs
in the event that management of the condensate involved a point source
discharge to Sand Creek. However, condensate will be stored in a
10,QOO-gallon storage tank and discharged to a POTW.
.
Federal Pretreatment Regulations
Colorado has adopted the federal General Pretreatment Regulations for
Existing and New Sources of Pollution, 40 CPR Part 403, as amended
SS Fed. Reg. 30082 (July 24, 1990)~ Therefore, Colorado regulations
will not be more stringent than federal regulations, which are potential
ARARs since the condensate will be discharged to a POTW.
.
Local Pretreatment. Rules
- ". .
\
Section 121( d) of CERCLA does not require CERCLA response actionS
to comply with lo.~ laWs (Le., local laws by themselves are. nc;>t
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ARARs). While local pretreatment requirements. technically are not
considered to be ARARs, the LFGES is expected to comply with
applicable provisions of these requirements. .
.
c.
Cost Effectiveness
The selected alternative is cost-effective in its approach to remediating landfill
gas, containment of landfill contents, and restricting access to the site. The aU3
monitoring program will allow assessment of the conditions at the Landfill relative to (1)
groundwater contamination attributable to the site and (2) accumulation and migration
of landfill gas. The analysis of sampling data collected will allow for cost-effective
decisions regardirig any future improvements that may be required for the remedial
systems. Total capital. annual O&M, and present worth costs for the selected remedy
are 53,170,000; $240,000; and $7,283,000; respectively. However, if implementation of
. additional institutional controls are necessary, capital costs for the selected remedy are
likely to be higher than indicated.
D.
Utilization of Permanent Solutions and Alternative Treatment (or Resource
_Recovery) Technologies to the Maximum Extent Practicable
The selected remedy utilizes permanent solutions and treatment technologies to
the maximum extent practicable for the 48th and Holly Landfill. Specifica1fy, the use of
the LFGES to extract and treat landfill gas results in a permanent reduction in methane
and concentrations of COCS in landfill gas through thermal destruction. Condensate
generated by the operation of the LFGES will be treated by a P01W. Because no hot
spots ,were located within the Landfill, it was considered impractical and unnecessary to
remediate landfill contents. Direct contact with landfill contents will be eliminated by
containing the refuse beneath the landfill cap.
Of the alternatives that are protective of human health and the environment and
comply with ARARs, EP A believes that the selected remedy provides the best balance in
terms of long-term effectiveness and permanence; reduction in toxicity, mobility, or
volume achieved through treatment; short-term effectiveness; implementability; cost; and
the statutory preference for treatment as a principal element. Overall protection of
human health and the environment, and long-term effectiveness and permanence were.
the most decisive criteria in selecting Alternative 3 as the preferred remedy.
The selected remedy offers greater overall protection of human health and the
environment than afforded by Alternatives 1 or 2 because future potential exposure
pathways for ground water are addiess~d through additional institutional controls, as .
necessary. Alternative 1 would not b~ protective of human health or the environment.
The preferred alternative provides .~e greatest long-term effectiveness by inclu~ng
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provisions for future modifications and improvements to the LFGES and soil cover
system as required during the normal course of O&M activities. The selected remedy
and Alternative 2 are essentially equivalent with respect to the evaluation of compliance
with ARARs; reduction of toxicity, mobility, or volume; shon-term effectiveness; and
implementability. Alternative 1 would not reduce residual risk associated with landfill
gas, landfill contents, or groundwater exposure pathways; nor would it employ any
treatment options that would reduce the toxicity, mobility, or volume of cont:.min:.nts in
the media of concern. Alternative 1 is also not likely to be admini"tratively feasible.
The additional capital expenditure for the selected alternative associated with
implementation of additional institutional controls, as necessary, is not expected to be
significant in comparison to Alternative 2.
E.
Preference for Treatment as a Principal Element
The selected remedy satisfies the statutory preference for treatment as a principal
element and is fully consistent with the NCP. Operation of the LFGES to extract and
treat landfill gas addresses the principal threat posed by landfill gas. The LFGEs will
reduce the potential for explosion and inhalation hazards by mitigating the migration and
accumulation of landfill gases. Combustible and toxic components of the landfill gas will
be permanently destroyed through thermal destruction by the flare system. Condensate
generated from the extraction of landfill gas will be treated by the Denver Metro P01W.
The size of the Landfill and the fact that there are no on-site liot spots that
represent the major sources of contamination preclude a remedy in which cont:.min:.nts
could be excavated and treated effectively. However, hazards associated with exposure
to landfill contents will be minimized through containment by maintaining the soil cover
system. Groundwater contamination attributable to the Landfill is not considered to be
a principal threat, and potential exposure pathways for ground water have been
addressed to the extent practicable.
Because this rexnedy will result in hazardous substances reJTI:.ining on-site, a
review will be conducted every five years after commencement of remedial action to
ensure that the remedy continues to provide adequate protection of human health and
the environment.
. . .,,,. .
,
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APPENDIX A
SUMMARY OF INSTITUTIONAL CONTROLS FOR OU3/0U6
. ,... .
,
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Table At. Institutional Controls Currently in Place at OU3/0U6.
.
OU6 Order
Access Order
Consent for Access
EP A Oversight Activity
State of Colorado's Office of
State EngiDeers, State Board
of Examiners of Water Well
Construction and Pump
Installation Contractors
(revised effective July 30,
1988), Rule 10.2.2
Requires implementation of methane gas recovery
system; restricts activities to the extent that such
activities conflict with response actions at OU6, and
requires continued maintenance of response action.
Allows access to CPC property by BN, LI and EPA in
order to allow such parties to conduct OU6 removal
action on CPC property; restricts present and future
activities on CPC property which would interfere with
removal action.
Provides access for Response Actions to be conducted
by EP A and its authorized representatives on CERC
property.
Precludes activities at site that would interfere with
response actions, unless approved by EP A
Precludes permitting and construction of wells in
areas of known contamination. -
,- .
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Table A2. Available Supplemental Institutional Controls.
.
.Lt~%i~lt. 1IIIIjTj\rtl..il'Blil
Commerce City Zoning Limits the types of development allowed in the CERC
"AG" property.
Commerce City Zoning "1-3" Prohibits residential development on CPC property,
and consequently prohibits water wells serving the
residential development.
Denver Zo~g "1-2" Prohibits residential development on Burlington
Northern property, and consequently prohibits water
wells serving the residential development.
.0
Denver and Commerce City Requires title check and review of proposed
Subdivision Regulations subdivision by various government agencies which
should disclose any recorded information relating to
the prior use of the Site as a landfill or any methane
hazards disclosed therein.
Commerce City Subdivision Requires water sampling in order to preveont use of
Regulations unpotable water, if any, under the Site.
Denver and Commerce City Requires soil borings and/or excavations to determine
Building content of soils under proposed development site;
Departments/Uniform prohibits issuance of building permits where
Building Code dangerous conditions exist.
Denver and Commerce City Requires recording in the appropriate county records
Subdivision of any existing or future Unilateral Order or Consent
Regulations/Recording of Decree affecting the Site. Such recording be
other Documents in disclosed by any title search required by the
Appropriate Real Property Subdivision Regulations and inform reviewing
Records agencies of the prior use of the Site as landfill and/or
any existing methane hazards.
,- 0
. '.'
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.
Table A3. Potential Additional Supplemental Institutional Controls
.
.
:'.' ',','" ,":"',"," '.. ,"", . ,"', .
. .... ...... ...:::::::.:/IriStitutional
.: ...:::/:.:.::::::.:\/i:(: COntrol."... ..
.,., . ","," ""
. .
..
Funher EP A Orders issued
pursuant to CERCLA ~ 106
Judicial Consent Decree under
CERCLA's ~ 122
Correspondence to Colorado
Land Use Commission and local
governments requesting
designation of Site as "Area of
Interest" under the Land Use Act
Ordinances adopted by
Commerce City and/or Denver
under their police powers.
Easement in Gross
Colorado Excavation
Statute/filing of appropriate
notices with Denver and Adams
County Oerk and Recorder
. .
.. ..
. .. .... . . .
" . "...... . . ..... H'
......... . ....PUrposesof:. ..,.....:.. .
:..j;:(:... . ..:.:~~nitiona1 ~hif8j.:..::.:.:::i.!...1...:.::.;.::.:.:::::.:'-::;. .... ..
May serve itself as institutional control and
provide further use restrictions against property
owners as necessary for response actions.
May serve itself as institutional control and
provide funher use restrictions against property
owners as necessary for response actions.
To obtain a designation of the Site as a "Area of
Interest" under the Colorado Land Use Act,
requiring all potential developers to obtain a
permit prior to development of any portion of
the Site.
To adopt well bans.
-"
Voluntary landowner control granted to restrict
development of property.
To require any potential developer on the
property to provide notification of any proposed
excavation on the Site.
. " .
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