EPA Superfund Record of Decision: Sand Creek Industrial EPA Id: COD980717953 OU 04 Commerce City Co


                                    EPA/ROD/R08-94/081
                                    1994
EPA Superfund
     Record of Decision:
     SAND CREEK INDUSTRIAL
     EPA ID: COD980717953
     OU04
     COMMERCE CITY, CO
     04/07/1994

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RECORD OF DECISION
DECLARATION STATEMENT

SITE NAME AND LOCATION

Site-wide groundwater, Operable Unit 4 (OU4), Sand Creek Industrial Superfund Site, Commerce
City, Colorado.

STATEMENT OF BASIS AND PURPOSE

This decision document presents the selected remedy for Operable Unit 4 (OU4), Site-wide
groundwater at the Sand Creek Industrial Superfund Site in Commerce City, Colorado. This remedy
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 administrative record for OU4.

The State of Colorado is expected to concur with the selected remedy.

ASSESSMENT OF THE SITE

The Sand Creek Industrial Superfund Site has an extensive history of industrial use, including
pesticide manufacturing, petroleum refining, acidic waste disposal, municipal landfilling, and
chemical storage and distribution. OU4 addresses groundwater underlying the Site and is
contaminated with volatile organic compounds (VOCs), semi-volatile organic compounds (SVOCs),
pesticides, and metals. OU4 also includes a plume of light non-agueous phase liguid (LNAPL)
floating on the water table beneath the northwest portion of the Site. The migration of
groundwater contaminants tends to be impeded by the presence of impermeable clayey materials.

Although groundwater 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 groundwater since water for residential use is provided through
treated water from either the Denver Water Department or the South Adams County Water and
Sanitation District. However, risks associated with potential future use of groundwater for
domestic purposes are unacceptable. Actual or threatened releases of hazardous substances from
OU4, 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 remedy selected for OU4 will minimize direct contact with and ingestion of groundwater
underlying the Site and prevents further offsite migration of contaminants in excess of federal
and state groundwater standards. The major components of the selected remedy include:

• Implementation of institutional controls that will minimize exposure to
contaminated groundwater at OU4 by limiting groundwater usage to non-domestic
purposes and preventing any usage of highly contaminated groundwater.

• Quarterly groundwater and surface water monitoring to evaluate contaminant
migration and changes in site conditions.

• Removal of the recoverable portion of the LNAPL plume located in the northwest
portion of the Site with a dual vapor extraction (DVE) system. Recovered LNAPL will
be transported off site to a recycling facility.

• Onsite infiltration of treated groundwater removed incidentally by operation of the
DVE system.

• Five-year site reviews will be conducted at OU4 and additional remedial action will
be taken if warranted by a change in site conditions.

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STATUTORY DETERMINATIONS

The selected remedy provides protection to human health by limiting exposure to and preventing
ingestion of contaminated groundwater through institutional controls. This alternative protects
the environment by reguiring groundwater and surface water monitoring to ensure that OU4
contamination does not impact Sand Creek or downgradient aguifers at some future date. Removal
of the recoverable portion of the LNAPL plume will effectively eliminate a source of groundwater
contamination at OU4.

The selected remedy is protective of human health and the environment, complies with federal
and state reguirements 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 this site, but because treatment of
the principal threats of OU4 was not found to be feasible, this remedy does not satisfy the
statutory preference for treatment as a principal element. However, many of the principal
threats at the Site are being addressed under other operable units. Because this remedy will
result in hazardous substances remaining on site, a review will be conducted every five years to
ensure that the remedy continues to provide adeguate protection of human health and the
environment.
William P. Yellowtail Date
Regional Administrator
U.S. Environmental Protection Agency, Region VIII

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                            TABIiE OF CONTENTS

Section                                                                       Page

DECLARATION STATEMENT 	 i

I.      SITE NAME, LOCATION, AND DESCRIPTION 	 1

II.     SITE HISTORY AND ENFORCEMENT ACTIVITIES 	 3

III.    HIGHLIGHTS OF COMMUNITY PARTICIPATION	 5

IV.     SCOPE AND ROLE OF RESPONSE ACTION 	 6
V.     SUMMARY OF SITE CHARACTERISTICS
       A.  Topography	 8
       B.  Geology 	 8
       C.  Hydrogeology 	 9
       D.  Water Diversions 	 12
       E.  Nature and Extent of Contamination 	 12

VI.    SUMMARY OF SITE RISKS	 16

       A.  Contaminants of Concern 	 17
       B.  Exposure Assessment 	 20
       C.  Risk Characterization 	 21
                 1.   Current Human Health Risks 	 21
                 2.   Future Human Health Risks 	 22
                 3.   Environmental Risks 	 24

VII.    DESCRIPTION OF ALTERNATIVES 	 24

           Alternative 1:   No Action 	 25

           Alternative 2:   Monitoring and Institutional Controls 	 25

           Alternative 3:   Monitoring and Institutional Controls
           with LNAPL Removal 	 26

           Alternative 4:   Limited Containment of LNAPL using a Cutoff Wall  ... 26

           Alternative 5:   Localized Pump and Treat with LNAPL
           Containment and Groundwater Treatment by GAG and Air Stripping 	 29

           Alternative 6:   Localized Pump and Treat with LNAPL
           Removal and Groundwater Treatment by GAG and Air Stripping 	 29

           Alternative 7:   Localized Pump and Treat with LNAPL
           Containment and Groundwater Treatment by UV Oxidation 	 30

           Alternative 8:   Localized Pump and Treat with LNAPL
           Removal and Groundwater Treatment by UV Oxidation 	 31

           Alternative 9:   Site-Wide Pump and Treat for Total Groundwater
           Restoration with LNAPL Containment 	 31

           Alternative 10: Site Wide Pump and Treat for Total Groundwater
           Restoration with LNAPL Removal 	 32

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VIII.   SUMMARY OF COMPARATIVE ANALYSIS OF ALTERNATIVES 	 32

       A.  Overall Protection of Human Health and the Environment 	 33

       B.  Compliance with ARARs 	 33

       C.  Long-Term Effectiveness and Permanence 	 37

       D.  Reduction of Toxicity, Mobility, or Volume Through Treatment 	 37

       E.  Short-Term Effectiveness 	 38

       F. Implementability 	 38

       G. Cost	 39

       H. State Acceptance 	 41

       I. Community Acceptance 	 41

IX.     SELECTED REMEDY 	 41

X.     STATUTORY DETERMINATIONS  	 47

       A.  Protection of Human Health and the Environment 	 47

       B.  Compliance with ARARs 	 48

       C.  Cost Effectiveness 	 50

       D.  Utilization of Permanent Solutions and Alternative Treatment
           Technologies (or Resource Recovery Technologies)  to the
           Maximum Extent Practicable 	 50

       E.  Preference for Treatment as a Principal Element 	 51


Appendix A.  RESPONSIVENESS SUMMARY 	 A-l

                                LIST OF FIGURES

1.  Location of Sand Creek Superfund Site and Study Area 	 2
2.  Conceptual Cross-Section of Alluvial Aguifers 	 10
3.  Extent of Aguif ers 0,  1,  and 2 	 11
4.  Occurrence of Trichloroethene in Groundwater 	 13
5.  Occurrence of Tetrachloroethene in Groundwater 	 14
6.  Occurrence of Benzene in Groundwater 	 15
7.  Localized and Site-Wide Extent of Remediation and Proposed
    Vibrating Beam Wall Location 	 27
8.  Detail of Localized Extent of Remediation and Proposed
    Vibrating Beam Wall Location 	 28
9.  Dual Vapor Extraction (DVE)  System	 44

                               LIST OF TABLES

1.  Chemicals of Concern for Groundwater and LNAPL at OU4 	 18
2.  Total Carcinogenic and Noncarcinogenic Risks Calculated for
    Potential Future Exposure to OU4 Contamination 	 23
3.  Selected Potential ARARs and TBCs for Operable Unit 4,
    Sand Creek Industrial Superfund Site 	 35
4.  Costs Associated With Alternatives Developed for OU4 (1994 Dollars) 	 40
5.  Institutional Controls Available for OU4 	 43
6.  Regulatory Standards for Chemicals of Concern at OU4 	 46

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Sand Creek Industrial Superfund Site
Operable Unit 4
Commerce City, Colorado
Record of Decision

I. SITE NAME, LOCATION, AND DESCRIPTION

The Sand Creek Industrial Superfund Site (Site) occupies about 300 acres within portions of
both Commerce City in Adams County, Colorado and the City and County of Denver. The Site is
bounded on the north by Interstate 270, on the south by East 48th Avenue, and on the east by Ivy
Street and the eastern extent of the 48th and Holly Landfill. The western boundary is
approximated by Colorado Boulevard, Vasquez Boulevard, and Dahlia Street (Figure 1). Four
known sources of contamination are present at the Site and all are currently inactive: the
Colorado Organic Chemical Company (COCC) property, the 48th and Holly Landfill, the L.C.
Corporation (LCC) property, and the Oriental Refinery property. Operable Unit 4 (OU4) of the
Sand Creek Industrial Superfund Site addresses groundwater affected by these four sources and is
the focus of this Record of Decision (ROD).

Land use near the Site is primarily industrial and includes trucking firms, 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 Chemical sites. Properties adjacent to the Site are zoned
for light and heavy industrial uses, industrial park, industrial park storage, and agricultural
uses. Fifteen residences housing approximately 25 people are located within a one-mile radius
of the Site. The daytime population reaches several hundred due to local businesses and the
industrial nature of the area.

The Denver portion of the Site is located south of East 52nd Avenue west of Forest Street and
south of East 48th Avenue to the east of Forest Street. This area is zoned for heavy industrial
use. No changes in zoning are anticipated by the City and County of Denver Planning
Administration (CCDPA) in the near future. CCDPA indicates that long-range land-use plans
will depend on the fate of Stapleton International Airport following completion of the new
Denver International Airport. The Commerce City portion of the Site 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 area surrounding OU4 is supplied by the South Adams County Water and
Sanitation District (SACWSD) and the Denver Water Department (DWD). Groundwater produced from
alluvial and bedrock wells located north of 1-270 is a major source of water supplied by SACWSD.
Water supplied by the DWD is obtained primarily from surface-water sources located outside of
the Site area. Residents near the OU4 area are not currently using contaminated groundwater for
domestic purposes.

II. SITE HISTORY AND ENFORCEMENT ACTIVITIES

During the 1970s and early 1980s a variety of environmental contamination was discovered and
identified at the Site by EPA's Field Investigation Team (FIT). This contamination has resulted
from at least four sources: The COCC facility; the LCC property; the Oriental Refinery site;
and the 48th and Holly Landfill. Although the ownership and the operations on these properties
were distinct, they were included together as the Sand Creek Industrial Superfund Site and
placed on the National Priorities List (NPL) in 1982 for cleanup under the Comprehensive
Environmental Response, Compensation, and Liability Act of 1980 (CERCLA), as amended by the
Superfund Amendments and Reauthorization Act of 1986 (SARA). Under the Superfund law, the
Environmental Protection Agency (EPA) is charged with the responsibility of developing and
implementing cleanup remedies that protect human health and the environment.

Oriental Refinery Property. The Oriental Refinery was located on the northwest corner of 52nd
and Dahlia and was gutted by a fire in 1955. As a result of the fire, approximately 48,000
gallons of refined petroleum products may have been released from storage tanks. Plant

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operations and the fire have resulted in groundwater contamination. The Tri-County Health
Department (TCHD) sampled the soils at the old refinery site and found hydrocarbon contaminated
soils to a depth of 28 feet. The FPA Field Investigation Team (FIT) investigated the Site in
1980 and found diesel fuel contamination in several groundwater monitoring wells.

Colorado Organic Chemical Company Property. The COCC plant originally manufactured pesticides
in the 1960s under the name of Times Chemical. The COCC site has been the scene of two fires,
both of which occurred when the facility was operated by Colorado International Corporation
(CIC). In 1968 a fire destroyed three buildings. In December 1977 a fire destroyed the
manufacturing eguipment within the facility. Eight hundred people were evacuated and at least
26 people were treated for the inhalation of toxic parathion fumes. Firefighters sprayed more
than 350,000 gallons of water on the blaze and subsequently washed the pesticide-contaminated
water downhill toward Dahlia Street. After these fires several health agencies found
unacceptable conditions at the plant, including: unsatisfactory waste management practices;
unsatisfactory worker safety conditions; violations in storage and handling of flammable
liquids; and soil containing high levels of thermally altered pesticides and other chemicals.

Immediately after the December 1977 fire, the Colorado Department of Health (CDH) issued an
Emergency Cease and Desist Order to CIC, Western United Resources, Globe Chemical, Chicago, Rock
Island and Pacific Railroad, and Mr. Phillip Mozer. This order stated that the operations on
the Site must be halted, the area contaminated by the fire must be isolated, and among other
tasks, the fire-damaged material must be left intact. Although Western United Resources was
named in the Order, documentation has not been found to indicate that they participated in any
operations relevant to the Site.

A March 1984 report described the COCC facility as an unfenced site consisting of six
structures, ten large above-ground tanks (ranging in size from 2000 to 20,000 gallons), and an
uncovered drum storage area. The six structures contained, among other items, approximately
50 drums and an uncertain quantity of pesticide bags. Of the approximately 100-125 total
drums observed both in the open storage area and in the buildings on site, most were unlabeled
and many were rusted, corroded, bulging, stressed, and leaking. Later in 1984, COCC removed
waste drums and contaminated soil, and constructed a fence around the area in response to an
order from EPA.

Between 1985 and 1990, Remedial Investigation/Feasibility Study (RI/FS) activities occurred at
the COCC property as part of the Sand Creek Superfund Site studies. Treatability studies were
also performed to evaluate the effectiveness of soil washing and bioremediation technologies in
cleaning up soil contamination attributable to the COCC facility. During 1991 and 1992,
approximately 2,000 cubic yards of debris, including four buildings, four rail cars, two
concrete tanks, and 13 steel tanks were removed by a licensed hauler and disposed of in
permitted landfills. Soil vapor extraction (SVE) operations, designed to remove volatile
organic compounds from subsurface soil, began at the COCC property during the summer of 1993.
This remedial action is documented in the Explanation of Significant Differences (BSD, 1992) to
the Operable Unit 1 (OU1) ROD (1989). Low Temperature Thermal Treatment (LTTT) was selected as
the method for cleaning up soils contaminated with pesticides and metals at COCC in the Operable
Unit 5 (OU5) ROD Amendment (1993). Remediation of OU1 and OU5 is expected to be completed in
1994.

L.C. Corporation Property. The LCC property has been a part of Commerce City industry since
1948. Between 1948 and 1958, part of the property was used as a gravel quarry. In 1968, Shell
Chemical Company contracted with LCC for the disposal of spent acidic wastes from Shell's
chemical plant at the Rocky Mountain Arsenal. LCC was to line its disposal impoundments with an
ethylene propylene copolymer film before disposing of any acidic wastes. A liner was installed,
however, it was breached after acidic wastes were deposited in the pits. Approximately 7,810
tons of sulfuric acid were disposed of in the LCC pits.

In November 1974, TCHD investigated a complaint involving severe chemical burns to livestock
that had strayed onto the LCC property. TCHD found pools of liquids in lined pits on the
property. LCC agreed to clean up the liquid after analysis showed that it was a 30% sulfuric
acid solution with a highly acidic pH of 0.75.

In July 1975, TCHD employees discovered a seep discharging acidic liquid into Sand Creek.
Analyses of the seep liquid and water from Sand Creek in 1976 indicated that both contained a

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sulfone believed to be an intermediate by-product from Shell's manufacture of the herbicide
Planavin.

In 1980, at the request of CDH, LCC used lime to neutralize the pits and filled them with clean
backfill. Sampling indicates that the lime was effective in neutralizing the acid pits, and
that the pits do not pose an unacceptable risk to public health, as documented in the Operable
Unit 2 (OU2) ROD (1993).

48th and Holly Landfill. Waste disposal operations were conducted from 1968 to 1975 at the
48th and Holly Landfill (Landfill). The Landfill accepted both demolition and domestic refuse,
and although known hazardous and pathological wastes were reported to be excluded from disposal,
the method of exclusion and the consistency of its application are unknown.

In 1977, two explosions of combustible gas were traced to the migration of methane gas from
the Landfill. Two passive methane gas venting systems, which proved to be ineffective, were
installed at the Landfill in 1978 and 1980. In 1991, the passive systems were replaced with an
active landfill gas extraction system (LFGES) as part of the Sand Creek Superfund Site
activities at Operable Units 3 and 6 (OU3/OU6). The landfill-gas collected by the LFGES is
burned using an enclosed flare to destroy contaminants and eliminate odors. Condensate produced
within the system is collected, treated, and discharged to a sanitary sewer.

After the Landfill ceased operation in 1975, the site was covered with between 1 to 10 feet of
sandy soil, and re-vegetated. In response to erosion, ponding due to differential compaction
within the refuse, and areas lacking well established vegetative cover, several site improvement
activities were undertaken in 1992. These site improvements included fill placement, erosion
control, and reclamation.

Site-Wide Groundwater. The groundwater underlying the Sand Creek Industrial Superfund Site has
been contaminated from the four onsite sources (the COCC facility; the LCC property; the
Oriental Refinery site; and the 48th and Holly Landfill). In addition, some contaminated
groundwater is moving on site from the Chemical Sales Company Superfund site and unidentified
upgradient source(s). The site-wide groundwater is addressed under this OU4 ROD.

Residuals and breakdown products of chemicals contaminating the soils at the COCC facility have
been found in the groundwater. The soils at the Oriental Refinery have been contaminated with
hydrocarbons and petroleum contamination has been found in monitoring wells. The acid wastes
disposed of in pits on the LCC property impacted both groundwater and surface water in Sand
Creek. Contamination from the Landfill has impacted the groundwater at the Site. At the
present time no known contamination is entering the surface water of Sand Creek from the Site.

III. HIGHLIGHTS OF COMMUNITY PARTICIPATION

Community interest in OU4, specifically, and the Sand Creek Industrial Superfund Site, in
general, has been limited. EPA has undertaken several community relations activities as part
of the recent site history.

Community involvement activities for the Site began in April 1985. EPA 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. EPA also
attended a public meeting organized by the Citizens Against Contamination, a local group from
the area, and compiled a list of property owners for the entire site.

EPA mailed a second fact sheet for the Site in November 1985. This fact sheet provided
additional information on investigation and clean-up activities associated with the Site. During
the same month, EPA provided a groundwater contamination briefing at a second public meeting
held by the Citizens Against Contamination.

In January 1986, EPA contacted property owners and Commerce City officials to inform them of
activities at the Site. In April 1987, EPA surveyed area residents about their water use habits
to determine future outreach efforts.

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An RI report describing the nature and extent of contamination at the Sand Creek Industrial
Superfund Site was released for public review in March 1988.  In May 1988, EPA contacted owners
for permission to sample soils on their property.  In October 1988, EPA met with Commerce City
officials to brief them and solicit their reaction to cleanup plans for the site.

On three occasions in 1990, EPA held public meetings addressing all of the Superfund sites in
South Adams County, excluding the Rocky Mountain Arsenal.  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 parties throughout
government and the local community are also provided.  The revised CRP was released in December
of 1991.  In addition to meeting directly with the public, EPA and the CDH have met with the
TCHD, SACWSD, Rocky Mountain Arsenal personnel, Commerce City/Adams County officials, Metro
Waste Water officials, and Representative Patricia Schroeder's staff to update them on
activities.

EPA issued the Proposed Plan for OU4 on February 14, 1994.  The Proposed Plan and RI reports
were made available to the public through the Administrative Record maintained at the EPA Region
VIII Superfund Records Center in Denver and at the information repository at the Adams County
Library.  A notice of availability of these documents and notification of the public meeting
were published in The Rocky Mountain News on February 14, 1994 and in The Commerce City Express
on February 15, 1994.

The public comment period was open from February 14 to March 16, 1994.  The public meeting was
held on March 1, 1994 at the Commerce City Recreation Center.  EPA explained the alternatives
and responded to guestions.  A transcript of the public meeting has been entered into the
Administrative Record.  A Responsiveness Summary, prepared by EPA to address public comments, is
included as Appendix A of this ROD.

IV.   SCOPE  AND ROLE OF RESPONSE ACTION

Due to the complex nature of the Sand Creek Industrial Superfund Site, EPA has divided it into
six operable units (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, this ROD for OU4
addresses the principal potential threats to humans and the environment resulting from exposure
to contaminated groundwater throughout the Site.  The six operable units at the Site are defined
as follows:

       •      Operable Unit 1:   OU1 addresses  contaminated buildings,  soil contamination greater
              than 1000 parts per million (ppm),  and volatile organic compounds (VOCs)  in the
              subsurface soils.   The OU1 area  includes approximately 15  acres  of the site,
              including the COCC plant property,  the land between COCC and LCC,  and the northern
              portion of the Oriental  Refinery site.   The Explanation of Significant Differences
              (BSD; 1992)  to the OU1 ROD (1989)  selected SVE as the method for removing VOCs from
              soils ranging in depth from 8  to 20 feet at OU1.   The purpose  of the OU1 ROD and BSD
              was to  address the principal threat of contact with contaminated soils by the public
              and Site workers,  and to protect surface water and groundwater resources.   The OU1
              ROD and BSD  called for a cleanup of chloroform,  methylene  chloride,
              tetrachloroethene,  and trichloroethene in the subsurface soils.   In addition,
              demolition and removal of contaminated tanks and buildings located in the area was
              included in  the selected remedy.

       •      Operable Unit 2:   This OU addresses the acid waste disposal pits on the LCC
              property,  just north of  the COCC facility.   The pits located there were used for
              disposal of  acid waste from various chemical manufacturing activities occurring both
              off and on site.   The OU2 ROD  (1993)  selected a No Further Action alternative for
              the acid pits.

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• Operable Unit 3: This OU comprises the 48th and Holly Landfill and specifically
includes contaminated surface water, groundwater, sediment, soil, and air in its
vicinity. The OU3/OU6 ROD (1993) selected a remedial alternative for the Landfill.
The ROD called for both engineering and institutional controls. Engineering controls
included the continued operation and maintenance of the landfill gas extraction
system (LFGES). The ROD also dictated that the landfill cover system be maintained,
and groundwater in the vicinity of the Landfill be monitored for potential releases
of contaminants from the Landfill. In addition, the OU3/OU6 ROD provides that if it
is determined by EPA, in consultation with CDH, that the Landfill is responsible for
a contaminant release to groundwater outside the boundary of OU3, such release(s)
will be addressed under OU3.

• Operable Unit 4: This study area is the focus of this ROD and consists of
contaminated groundwater underlying the Sand Creek Industrial Superfund Site.
However, groundwater beneath the 48th and Holly Landfill and groundwater directly
related to the Landfill is being addressed under the OU3/OU6 ROD. OU4 also includes
the light non-agueous phase liguid (LNAPL) plume floating on the water table beneath
a portion of the Site. Petroleum contamination is generally excluded from CERCLA
investigations due to the Petroleum Exclusion. However, EPA included LNAPL in OU4
because the product is mixed with hazardous substances, the presence of hydrocarbons
in the subsurface adversely affects SVE remediation at OU1, and the LNAPL provides a
continuous source of dissolved-phase contaminants to groundwater. Contaminants
detected in the groundwater include volatile organic compounds (VOCs), semi-volatile
organic compounds (SVOCs), pesticides, metals, and sulfones.

• Operable Unit 5: OU5 includes the same area as OU1 but addresses pesticides and
heavy metals in shallow soils to a depth of 5 feet. These soils have contaminant
concentrations greater than action levels and less than or egual to 1,000 ppm of
halogenated organic compounds (HOCs). The remedy selected in the OU5 ROD (1990)
called for soils at the COCC property with concentrations above action levels to be
excavated and treated on site using a soil washing process. Subseguent to the OU5
ROD, EPA analyzed additional samples of the contaminated soils, performed soil
washing treatability studies, and investigated other cleanup technologies. As a
result of this additional work, EPA selected the use of Low Temperature Thermal
Treatment (LTTT) in the OU5 ROD Amendment (1993) as the method for cleaning up
contaminated soils. It is estimated that approximately 8,000 cubic yards of
contaminated soil will reguire treatment at OU5.

• Operable Unit 6: This OU addresses the gaseous emissions at the 48th and Holly
Landfill. The remedy for OU6 was selected in the OU3/OU6 ROD (see OU3 above) and
called for continued operation of the LFGES installed as part of a removal action in
1991.

V. SUMMARY OF SITE CHARACTERISTICS

The Sand Creek Industrial Superfund Site 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 floodplain, 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 Site is a 1-acre wetland that is fed
by a subsurface drain system and is located immediately north of the Landfill.

This Site is in an area classified as mid-latitude semiarid, indicating an area of high summer
temperatures, cold winters, and sparse rainfall. The average annual precipitation is
approximately 15 inches.

A. Topography

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 corner of the Site to approximately
5,250 feet MSL in the southeastern corner. Interpretation 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

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capping material currently covers the refuse at the Landfill and similar thicknesses of fill
materials occur locally in other parts of the Site. Natural drainage paths have also been
altered by development in much of the area.

B. Geology

The subsurface geology in the vicinity of the Site consists of Quaternary alluvial deposits and
Tertiary bedrock. Alluvial deposits range in thickness from less than 20 feet to more than 100
feet and consist of sand, silt, and clay of the Piney Creek Alluvium, eolian deposits of silt
and clay, and sand and gravel of the Broadway Alluvium. Clay and gravel sediments of the Slocum
Alluvium are also locally present. Bedrock in the area is made up of claystone, shale,
siltstone, and sandstone of the Denver Formation. In the central portion of the Site, a
paleochannel is eroded in the bedrock surface and may influence the occurrence and movement of
groundwater in the area. The Denver Formation is underlain by the Arapahoe Formation, Laramie
Formation, and Fox Hills Sandstone. Outcrops of bedrock are not visible at the Site.

C. Hvdroaeoloav

Three discrete alluvial aguifers (Aguifers 0, 1, and 2) have been identified within the
unconsolidated sediment overlying bedrock in the area. Borehole logs taken from investigations
in the vicinity of the Site show that alluvial deposits are composed of relatively high
permeability sands and gravels interbedded with low permeability clayey and silty material. The
extensive amount of clay material present in the subsurface at the Site tends inhibit
groundwater flow and contaminant migration. A generalized cross-section of the aguifer system
at the Site is provided in Figure 2.

In the southeastern portion of the Site, Aguifer 0 is the only alluvial aguifer present (Figure
3), and it directly overlies bedrock or fine-grained alluvial sediments overlying bedrock. In
the central part of the Site, Aguifer 0 exists under perched conditions above Aguifer 2. The
lateral extent of Aguifer 0 is limited to the northwest. Aguifer 0 is unconfined throughout its
extent and is underlain by a low permeability clayey layer (Aguitard A) , which inhibits downward
movement of groundwater. Within Aguifer 0, groundwater flow is generally toward the north to
northwest. Slug test data from Aguifer 0 wells indicate that the horizontal hydraulic
conductivity typically ranges from 0.6 to 1.0 foot per day (ft/d), but was measured to be as
high as 354 ft/d at one well. The hydraulic gradient of Aguifer 0 ranges from 0.004 to 0.06 foot
per foot (ft/ft). Using an estimated effective porosity of 20%, average flow velocities
calculated by Darcy's Law range from 0.03 to 17.7 ft/d for Aguifer 0.

Aguifer 0 receives recharge from upgradient of the Site and discharges to Aguifer 2 where the
confining unit (Aguitard A) separating these aguifers pinches out in the northwest portion of
the 48th and Holly Landfill. It is believed that Aguifer 0 also discharges to the spring
located north of the Landfill via a finger drain system. The direction of groundwater flow in
Aguifers 0 and 2 is generally consistent with the regional flow direction of the alluvial system
(i.e., northerly toward Sand Creek).

Aguifer 1 is present in the northwestern portion of the Site and northwest of the Site (Figure
3). Aguifer 1 exists under unconfined conditions and is separated from Aguifer 2 by a clayey
impermeable unit (Aguitard B). Groundwater flow within Aguifer 1 is generally toward the
east/northeast. Groundwater may discharge from Aguifer 1 to Aguifer 2 in the area where the
confining unit separating these aguifers pinches out, in the vicinity of the northern boundary
of the Landfill. Data from slug tests performed on Aguifer 1 wells indicate the horizontal
hydraulic conductivity ranges from 0.7 to 273 ft/d. The average hydraulic gradient of Aguifer 1
is 0.006 ft/ft. Using an estimated effective porosity of 20%, average flow velocities
calculated by Darcy's Law range from 0.02 to 8.2 ft/d for Aguifer 1.

Aguifer 2 is present over the western portion of the Site (Figure 3). Aguifer 2 underlies
Aguifer 0 and Aguifer 1 in areas where present and also overlies fine-grained alluvial sediments
overlying bedrock. The extent of hydraulic communication between Aguifer 2 and Aguifers 0 and 1
is not known, but it is believed that some leakage occurs across the aguitards (A and B) that
separate these aguifers. In addition, the limited extent of the aguitards allows groundwater
from Aguifers 0 and 1 to discharge to Aguifer 2 where the aguitards pinch out. Downward
vertical flow velocities from Aguifer 1 to Aguifer 2 are calculated to range from 0.0009 to 20
ft/d. Aguifer 2 exists under confined conditions to the west and northwest portion of the Site

-------
but is unconfined beneath the Landfill and south of the Site. Groundwater flow within Aquifer 2
is generally toward the north. Slug test data from Aguifer 2 wells indicate the horizontal
hydraulic conductivity ranges from 0.2 to 409 ft/d. The average hydraulic gradient of Aguifer 2
is 0.003 ft/ft. Using an estimated effective porosity of 20%, average flow velocities
calculated by Darcy's Law range from 0.003 to 6.1 ft/d for Aguifer 2.

D. Water Diversions

The rights for surface-water diversion from Sand Creek exist at two separate locations
downstream of the Site. The first diversion point is the proposed Henrylyn Sand Creek
Diversion, which is approximately 1.5 miles downstream of the Site. 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 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 Diversion or the existing Burlington Ditch have not been exercised to date.

E. Nature and Extent of Contamination

Elevated levels of organic and inorganic contaminants have been detected throughout OU4 in
Aguifers 0, 1 and 2. Except for the eastern portion of OU4 near the Chemical Sales Company
Superfund Site (see Figure 1), low levels of organic contaminants have been detected in
upgradient wells used to define background water guality. These include chlorinated VOCs and
benzene in Aguifer 0; benzene, toluene, ethylbenzene, and xylene (i.e., BTEX), acetone and
chlorobenzene in Aguifer 1 and benzene, toluene ketones and chlorinated VOCs in Aguifer 2. High
levels of chlorinated VOCs are present upgradient from the eastern portion of the OU4 study
area. These occurrences are believed to be largely the result of releases from past industrial
activities at the Chemical Sales Company Superfund Site located upgradient of the OU4 study
area. Groundwater remediation at OU1 of the Chemical Sales Company Superfund Site is scheduled
to begin during the summer of 1994 and will address this source of VOC contamination. The
occurrence of trichloroethene (TCE), tetrachloroethene (PCE), and benzene are representative of
the extent of VOC and BTEX in groundwater at OU4. Figures 4, 5, and 6 indicate the extent of
TCE, PCE, and benzene contamination at the Site, respectively.

Groundwater in Aguifer 0 contains VOCs; phenols; naphthalene; 1,4-dichlorobenzene; herbicides
and elevated levels of antimony, barium, iron, lead, manganese and vanadium, as compared to
background concentrations. Most of the organic contaminants such as chlorinated VOCs, ketones,
toluene, ethylbenzene, xylene, phenols, 2-methylnaphthalene and naphthalene were detected
primarily in the southeastern portion of OU4. Benzene and phthalates were detected throughout
Aguifer 0. Elevated levels of styrene, antimony, barium, iron, lead and manganese were detected
within and/or downgradient of the 48th and Holly Landfill.

Contaminants detected in Aguifer 1 include chlorinated VOCs, ketones, BTEX, styrene, phenols,
polyaromatic hydrocarbons (PAHs), chlorinated benzene, pesticides, herbicides, aluminum, iron,
magnesium, manganese, and sulfate. Elevated levels of organic and inorganic constituents have
been detected throughout Aguifer 1, except in the northern and western portions of the aguifer
where there are no Aguifer 1 wells. Generally, the highest concentrations of contaminants were
detected on the COCC and northern Oriental Refinery properties. Pesticide contamination in
groundwater appears to be limited to the same area, which coincides with pesticide
contamination in soil at OU5.

Aguifer 2 groundwater contains chlorinated VOCs, ketones, BTEX compounds, phenols, PAHs and
elevated levels of antimony, barium, iron, sulfate, lead and manganese. Concentrations of
organic contaminants are greatest in two areas: the eastern and southeastern portions of OU4,
which are primarily affected by chlorinated VOCs; and the COCC, Oriental Refinery, and LCC

-------
properties.

The bedrock aquifers underlying the Site, with the exception of the weathered surface of the
Denver Formation, do not appear to have been impacted by groundwater contaminants. The
low-permeability nature of the claystone at the top of the Denver Formation in conjunction with
is depth provides protection for the underlying units from dissolved-phase contaminants. The
weathered surface at the top of the Denver Formation is characterized by extensive fracturing
along bedding planes and behaves hydrologically as part of the overlying alluvial aguifer
system.

A plume of LNAPL is present on the groundwater surface beneath the COCC and LCC properties. The
LNAPL is located in Aguifer 2 and overlying clay layers, and the thickness of the plume ranges
from 1.7 to 4.7 feet. Migration of the LNAPL plume is impeded by the presence of thick, clayey
materials. It is estimated that approximately 190,000 gallons of LNAPL occurs as mobile product
and another 170,000 gallons of residual LNAPL is present in fine-grained materials.
Fingerprinting analysis conducted in 1992 of the LNAPL concluded that it is comprised of two
hydrocarbon products: a light naphtha solvent and a diesel-like fuel oil, which increases in
age from south to north (along the Aguifer 2 hydraulic gradient). In contrast, hydrocarbon-
contaminated soil in the northern portion of the Oriental Refinery property and groundwater
northeast of the Site and north of Sand Creek was found to contain only the solvent, while soil
in the southern portions of the Oriental Refinery and LCC properties contained only the fuel oil
product. The data indicate the presence of at least two LNAPL sources and the northward
migration of the LNAPL plume to its current location. Dissolved-phase groundwater contamination
associated with the LNAPL includes BTEX, and a plume of tetraethyl lead (TEL).

VI. SUMMARY OF SITE RISKS

CERCLA mandates that EPA protect human health and the environment from current and potential
exposures to hazardous substances. Groundwater underlying OU4 was evaluated for potential human
health and environmental risks posed by contaminants in several investigations at the Site.
These evaluations were baseline assessments and evaluate potential risks associated with
exposures to current levels of contamination in the absence of any remedial action at the Site.
The following documents describe these risk evaluations:

• 1988 Preliminary Endangerment Assessment (EA) for the Sand Creek Industrial Site,
Colorado: This document described a site-wide risk assessment that evaluated risks
from contaminated soils, groundwater, surface water, and air at the Site.

1993 48th and Holly Street Landfill (OU3) Risk Assessment (RA): This document
updated and supplemented the 1988 EA by incorporating new data presented in the OU3
RI. The two media evaluated in this RA were groundwater in the vicinity of the
Landfill and landfill gas.

1993 Health Evaluation Update: This document was prepared as part of the OU4 RI/FS.
It updated and supplemented the 1988 EA by incorporating new data collected during
the OU4 RI/FS as well as data collected for the 1993 OU3 RA. Groundwater and the
LNAPL plume were the subjects of this evaluation. Results were compared with the
previous EA study.

A. Contaminants of Concern

The potential human health and environmental hazards associated with OU4 result from exposure
to: contaminated groundwater, the LNAPL plume, and contaminated surface water that could result
from the discharge of groundwater to Sand Creek. The LNAPL plume does not appear to be mobile
due to its presence within a clay layer that thickens to the north. The LNAPL plume, however,
provides a continuous source of mobile, dissolved-phase contaminants such as BTEX and TEL.

The chemicals of concern (COCs) for OU4 include VOCS, SVOCs, pesticides, and metals. All
detected contaminants classified as carcinogens are included in this list. The COCs also include
the contaminants likely to present the greatest hazard to human health and the environment based
on potential noncarcinogenic adverse effects. EPA combined and evaluated the 37 COCs previously
identified in the 1988 site-wide RI, data from the OU4 Free-Phase Plume Investigation, and the

-------
COCs identified in the 1993 OU3 RA to determine if it was necessary to continue to use all 37
COCs, or if it was reasonable to retain only a portion of the total number of COCs for the
development of a site remedy. For example, some of the 37 COCs were detected in only a few
samples, some COCs were present at concentrations at or below normal health-based risk levels,
and some COCs had similar properties, such that one COG could be used to represent other COCs.
All COCs were evaluated and 18 were identified as key contributors to risk at the site based on
concentrations and toxicity. In addition, 2,4-D and 4,4'-DDT, soil contaminants that are
prompting remediation at OU1 and OU5, were included at the request of EPA. The compound
chlorophenylmethylsulfone (CPMSO) was also added to the list of COCs at CDH's request after it
was detected in urine samples from residents livinq near the Rocky Mountain Arsenal, located
north (downqradient) of OU4. CPMSO was detected in soil and qroundwater on the LCC property.
Table 1 lists all of the COCS evaluated for OU4 and identifies the 21 key COCs selected for
development of remedial alternatives in the OU4 FS.

B. Exposure Assessment

Exposure pathways and receptors were identified for OU4 in a conceptual model developed for the
Site. Potential release mechanisms associated with OU4 are discharqe of qroundwater to surface
water and pumpinq qroundwater for residential, agricultural, or industrial use.

A 1990 report prepared by TCHD for EPA and CDH contains the most current information on OU4 area
water use. The report summarizes the findings of a door-to-door well inventory and information
survey. The survey encompassed an area bounded by Sand Creek on the north, Interstate 70 on the
south, Quebec Street on the east, and Colorado Boulevard on the west. (This survey area extends
beyond the boundaries of OU4.) The survey supported CDH and EPA efforts to identify potential
receptors of qroundwater contaminated by several sources, includinq sources at the Site. TCHD
contacted property owners to determine the number, location, depth, construction details, and
current use of wells in the survey area.

TCHD obtained information on water use from 419 of the 420 properties in the survey area.
SACWSD and DWB serve most of the water users in the survey area. However, the survey identified
23 private wells, with nine completed in the shallow alluvium. Data reqardinq the depth of nine
wells were unavailable. Four wells identified as deep ranqed from 560 to 1600 feet depth and,
thus, are not in the shallow alluvial aquifers. Two of the deep wells provided water for
drinkinq. No contamination of the deep bedrock aquifers at the Site has been observed in the
studies performed to date.

Of the wells completed in the shallow alluvium, only five are in use. Three are used for
irriqation and one as a seasonal water supply for livestock. The remaininq well, located at a
business on Oriental Refinery property, provides water for a sanitary waste system. The
potential for human exposure to qroundwater contaminants resultinq from these uses is unknown.
These wells will be sampled and evaluated as part of the OU4 monitorinq proqram to determine the
need for future action. EPA and CDH will notify and provide recommendations to the users if
contamination is detected.

Since current use of shallow alluvial qroundwater is limited to aqricultural and wastewater
uses, exposures for the current scenario were not quantified. Domestic use of contaminated
qroundwater and exposure to the LNAPL, however, were evaluated for potential future exposure
scenarios. Exposure pathways evaluated quantitatively were inqestion of qroundwater, and
inhalation of volatile contaminants durinq showerinq. Dermal exposure to contaminants in
qroundwater durinq showerinq, and exposure to surface water contaminants for aquatic biota were
evaluated qualitatively.

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                                       TABIiE 1
                     CHEMICALS OF CONCERN FOR GROUNDlflATER AND LNAPL AT OU4
  CHEMICAL OF CONCERN
                                    GROUNDWATER
                                                             LNAPL
                                                                                KEY
                                                                            CHEMICAL OF
                                                                              CONCERN
Volatile Organic Compounds

Acetone
Benzene
Chlorobenzene
Chloroform
1,1-Dichloroethene
1,2-Dichloroethene  (total)
Ethylbenzene
Methylene Chloride
Styrene
Tetrachloroethene
Toluene
1,1,1-Trichloroethane
Trichloroethene
trans-1,2-Dichloroethene
Vinyl Chloride
Xylenes

Semi-Volatile Organic Compounds
x
x
x
x
x
x
x
x
x
x

x
x
x
x
x
x
x

x
x
x
x
x
x
Acenaphthene
bis (2-ethylhexyl)phthalate
Dibenzofuran
1,2-Dichlorobenzene
1,4-Dichlorobenzene
Fluoranthene
Fluorene
2-Methylnaphthalene
Naphthalene
Phenanthrene
Pyrene
x
x
                      x
                      x
                      x
                      x
                      x
                      x

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                                           TABLE 1

                     CHEMICALS OF CONCERN FOR GROUNDlflATER AND LNAPL AT OU4

  CHEMICAL OF CONCERN               GROUNDWATER              LNAPL               KEY
                                                                             CHEMICAL OF
                                                                               CONCERN


Pesticides and Herbicides

alpha-BHC                                x                                        x
Dieldrin                                 x                                        x
2,4-D*                                   x                                        x
4,4'-DDT*                                x                                        x
gamma-BHC  (Lindane)                      x                                        x

Metals

Antimony                                 x
Arsenic                                  x                                        x
Cadmium                                  x                                        x
Manganese                                x                                        x
Selenium                                 x
Zinc                                     x

Other

CPMSO*                                   x                                        x
Tetraethyl Lead                                                x                  x

  *2,4-D and 4,4'-DDT, soil contaminants that are prompting  remediation  at  OU1 and  OU5,
  were included at the reguest of EPA.  CPMSO  (p-chlorophenylmethylsulfone)  was added at
  the reguest of CDH.

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Estimated exposures were evaluated for the average case and the reasonable maximum case. The
arithmetic mean concentration of contaminants in groundwater was used for the average case.
Maximum contaminant concentrations detected in groundwater were used for the reasonable maximum
case. A resident weighing 70 kilograms was assumed to ingest 2 liters of water per day for 70
years. The 70 kilogram resident was also assumed to be exposed to contaminants volatilized from
a 10-minute shower and to remain in the shower room for 5 minutes longer for a total exposure
time of 15 minutes. A volatilization model developed by Foster and Chrostowski was used to
estimate air concentrations. These were the same basic assumptions used in the 1988 EA, and
were developed before current guidance regarding the use of reasonable maximum exposures (RMEs)
was issued. Results from the 1988 report provide a conservative estimate of risks that are
essentially eguivalent to risks calculated with current guidance.

C. Risk Characterization

Potential health risks to humans are expressed in two ways: carcinogenic (cancer causing) and
noncarcinogenic. For carcinogens, it is assumes that there is no safe dose, but that the risk
of cancer is reduces as the dose is decreased. Slope factors (SF) are used to estimate excess
lifetime cancer risks associated with exposure to potentially carcinogenic chemicals. Excess
lifetime cancer risk is determined by multiplying the intake by the SF. 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 will develop cancer as a result of exposure to a carcinogen over a
70-year lifetime under specific exposure conditions. In determining the need for remedial
action at Superfund sites, EPA guidance states that the total excess cancer risk for all
contaminants must fall below the range of 1 chance in 10,000 (1E-04) to 1 chance in 1 million
(1E-06).

Noncarcinogenic risks are calculated by assuming there is a dose below which no adverse health
effects will occur. This level is called the reference dose (RfD) and is used to estimate the
hazard guotient (HQ) associated with the potential exposure to noncarcinogens. HQs are
determined by calculating the ratio of the estimated intake level to the RfD. A hazard index
(HI) can be generated by adding the HQs for all chemicals with similar target organs or critical
effects within a medium, and by adding HQs across all media to which a population may reasonably
be expected to be exposed. The HI provides a useful reference point for evaluating the potential
significance of multiple contaminant exposures within a single medium or across media. An HI of
1 is identified in the NCP as a Superfund site remediation goal.

Risks estimated for OU4 indicate that actual or threatened releases of hazardous substances from
OU4 groundwater, 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.
Current and potential future human health risks as well as environmental risks attributable to
OU4 are discussed below:

1. Current Human Health Risks

Currently, shallow alluvial groundwater is not used for domestic purposes. There are five wells
completed in the shallow alluvium in the OU4 vicinity and they are used for agricultural or
sanitary waste purposes. Estimates of current risks were not calculated due to the lack of
sampling data for these wells and the absence of completed exposure pathways. As mentioned
previously, these wells will be sampled and evaluated as part of the OU4 groundwater monitoring
program, and EPA and CDH will notify and provide recommendations to the users if contamination
is detected.

2. Future Human Health Risks

The contaminants of concern and exposure factors used to calculate risks for the 1993 OU3 RA and
1993 Health Evaluation Update were identical to those used in the 1988 site-wide RI and,
therefore, the risk values generated in these three evaluations can therefore be directly
compared. This comparison illuminates differences and similarities in the contaminant and risk
profile for shallow alluvial groundwater in 1988, 1991, and 1992. However, there were
significant differences in sample size for each aguifer and each investigation, which
potentially affects the results (i.e., fewer samples and fewer wells sampled may result in data
that do not represent aguifer contamination). In addition, only some of the samples collected

-------
in 1991 were analyzed for pesticides, and the 1992 investigation did not include analysis for
metals. The 1992 Aquifer 0 data are considered inadequate for risk evaluation because of the
small sample size. Similarly, the data collected in 1991 are considered inadequate to evaluate
the risks associated with Aquifer 1.

The calculated total risks for individual aquifers and specific data bases are presented in
Table 2 and are all based on the maximum detected concentration from the sample data for each
aquifer, rather than on an average concentration. Generally, the 1991 and 1992 data indicate
risks similar to those calculated from data collected for the 1988 site-wide RI. The risk
values indicate that groundwater in all three aquifers, and the LNAPL plume have total excess
cancer risks (ranging from 1E-02 to IE-OS) that are above EPA's acceptable risk range.

The greatest risks are associated with ingestion of groundwater. However, inhalation of VOCs
during showering contributes significantly to risk in several cases. The primary contaminants
contributing to cancer risk in groundwater are arsenic, benzene, and vinyl chloride, all
classified as known human, or "Class A", carcinogens. For the LNAPL, benzene alone contributes
the total cancer risk of greater than 1 in 100 (1E-02) when ingestion is considered. The high
concentrations of contaminants in the LNAPL make ingestion unlikely due to odor, bad taste, and
visible contamination. The LNAPL is likely to be acutely toxic. It should be noted that the
difference in risks calculated for the individual aquifers versus the OU4 collective data is
primarily attributable to the exclusion of benzene and other petroleum-related compounds from
the aquifer-by-aquifer analysis in the 1988 EA.

The primary contributors to noncarcinogenic risk in groundwater are the chlorinated solvents
tetrachloroethene and 1,2-dichloroethene (critical effects: liver and kidney damage), the metals
manganese (critical effect: neurological disorders) and arsenic (critical effect: skin
lesions), the polyaromatic hydrocarbon naphthalene (critical effect: interference with
developmental weight gain), and the insecticide dieldrin (critical effect: liver damage).
Tetraethyl lead (critical effect liver damage and central nervous system disorders) is the
primary contributor to noncarcinogenic risk for the LNAPL.

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                                             TABIiE 2
             TOTAL CARCINOGENIC AND NONCARCINOGENIC RISKS CALCULATED FOR POTENTIAL
                              FUTURE EXPOSURE TO OU4 CONTAMINATION.
EXPOSURE PATHWAY-                AQUIFER 0               AQUIFER 1
TOTAL RISKS
             AQUIFER 2
AQUIFERS
  0 & 1
                           1988    1991    1992    1988    1991    1992    1988    1991    1992     1991     1992
Ingestion of Groundwater

- Total Cancer Risk         4E-3    4E-3      -     9E-3

- Hazard Index               23        -      5

Inhalation of Volatile COCs in Groundwater While Showering

- Total Cancer Risk         9E-4    3E-3      -     7E-4
3E-5    2E-3    8E-4    3E-3    3E-2    1E-2
- Hazard Index
                                     0.9
0.06
                                                                    5E-7
                                                                    0.03
                                 44
                                                                            4E-4
                                                                             0.4
                                                                                    1E-3
                                                                                    0.05
                                                                                            4E-4
                                                                                             0.4
Note:  The year indicated refers to a values reported in a specific risk assessment report or values calculated from  a
specific data base.  1988 = Risks calculated using 1986 and 1987 RI data and reported in the 1988 Preliminary
Endangerment Assessment.  1991 and 1992 = Risks calculated using groundwater data collected in 1991 and  1992.

Data collected in 1991 and 1992 are considered to be too limited to evaluate risks associated with Aquifer  1 and Aguifer
0, respectively.

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3. Environmental Risks

The potential hazards to environmental receptors were qualitatively evaluated in the 1988 EA and
the 1993 OU3 RA. Terrestrial and aquatic habitats present at the Site were described and
individual species known to occur in the vicinity were identified. No federal or state
threatened or endanqered plant or animal species are known to be present on the Site.

The likelihood of exposure of terrestrial receptors to COCs in qroundwater is considered remote
because qroundwater is not accessible except at the point of discharqe into a marsh near the
landfill. The maximum concentrations of COCs in surface water collected at the marsh were
compared to federal ambient water quality criteria (AWQC) and state water quality standards for
protection of aquatic life. Maximum surface water concentrations at the marsh were lower
than AWQC and state standards for all COCs havinq an established standard. These results aqreed
with previous similar comparisons for the 1988 EA. Because of the low potential for exposure to
qroundwater contaminants for terrestrial receptors and the low concentrations of contaminants
found in surface water, environmental risks are currently expected to be minimal.

VII. DESCRIPTION OF ALTERNATIVES

In the OU4 FS, a ranqe of options were developed for addressinq qroundwater and LNAPL
contamination at OU4. Ten remedial alternatives were retained for OU4 followinq the
development, screeninq, and detailed analysis of alternatives in the FS. EPA decided to
include alternatives involvinq containment or full-scale treatment of the LNAPL plume because:
(1) the LNAPL plume poses a potential threat to human health or the environment throuqh
discharqe to Sand Creek, the Denver Metro sanitary sewer lines, and downqradient wells; (2) the
LNAPL plume represents a continual source of contaminants and therefore affects qroundwater
treatment options; and (3) the presence of the LNAPL interferes with operation of the soil vapor
extraction (SVE) system constructed for remediation of OU1. As discussed previously, petroleum
contamination is qenerally excluded from CERCLA investiqations due to the Petroleum Exclusion,
which exempts pure product from CERCLA response actions. However, EPA has response authority to
address the LNAPL at OU4 because the product is mixed with hazardous substances. Removal of the
recoverable portion of the LNAPL plume beneath the COCC property would occur under OU1 remedial
action, but it is considered to be a component of the alternatives developed for OU4 since many
of the treatment options for OU4 would contain or treat the LNAPL as well as dissolved-phase
qroundwater contamination.

Five-year site reviews would be conducted for all alternatives developed for OU4. Except for
the "No-Action" alternative, each alternative also includes the followinq common elements:

Groundwater and Surface Water Monitorinq - Existinq and future qroundwater monitorinq wells
(approximately 16) would be sampled and analyzed periodically throuqhout OU4 to assess the
effectiveness of the selected alternative and chanqes in natural conditions. Monitorinq points
would be located upqradient of the Site (to detect contamination enterinq the Site), within the
LNAPL plume (to track movement of the LNAPL), downqradient from OU4 (to detect dissolved-phase
and LNAPL plume miqration off site), within Sand Creek (to assess the possible discharqe of
contaminated qroundwater to surface water), and immediately north of Sand Creek (to detect any
miqration of contaminants under the creek). Samples will initially be collected quarterly, but
may be collected less frequently if data indicate that site conditions are not chanqinq
siqnificantly on a quarterly basis. In addition, the five private wells that are completed in
the shallow alluvium in the vicinity of OU4 will be sampled and evaluated as part of the OU4
qroundwater monitorinq proqram. EPA and CDH will notify and provide recommendations to the
users if contamination is detected.

Institutional Controls - EPA and CDH will coordinate with local officials and property owners,
and will request the use and implementation of institutional controls at the Site. Zoninq
restrictions, includinq recommendations aqainst well usaqe for domestic purposes, will be
proposed in order to minimize potential future human exposure to contaminated qroundwater
underlyinq the site. These objectives are already achieved in part throuqh state advisories
aqainst the construction of water wells in areas with known contamination. Additional
institutional controls that may be implemented as necessary include subdivision requlations,
buildinq permits, recordinq requirements, state statutes, local ordinances, and deed
restrictions and notices implemented by current property owners.

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Alternative 1: No Action

The Superfund program requires that the "No-Action" alternative be considered at every site.
The No Action alternative establishes a baseline for comparison of other alternatives. Under
this alternative, EPA would not remove, treat, or contain the LNAPL plume or contaminated
groundwater. However, groundwater contamination levels may be reduced over the long-term
through natural attenuation. EPA could set specific action levels and take remedial action at
OU4 in the future if warranted by a change in site conditions.

Alternative 2: Monitoring and Institutional Controls

As with Alternative 1, EPA would take no action to remove, treat, or contain the LNAPL plume or
contaminated groundwater. However, steps would be taken to limit human exposure to contaminated
groundwater through the implementation of local institutional controls. In addition, monitoring
of groundwater and surface water at the Site would be performed to evaluate changes in site
conditions. Natural attenuation processes would reduce contaminant concentrations in
groundwater over the long-term. As with Alternative 1, EPA could set specific action levels and
implement remedial action in the future if warranted by a change in site conditions.

Alternative 3: Monitoring and Institutional Controls with LNAPL Removal

Alternative 3 is similar to Alternative 2, with the addition of removal of the LNAPL plume.
The principal elements of this alternative are:

• Dual vapor extraction (DVE) wells would be installed in the LNAPL plume area. LNAPL
vapors and liquids removed from the subsurface would pass through an air/liquid
separator, and the resulting liquid stream would flow through an oil/water separator
to recover free-phase LNAPL. Recovered LNAPL would be transported off site to a
recycling facility. Water from the oil/water separator would be transported to an
on-site groundwater treatment facility. LNAPL vapors from the air/liquid separator
would be transported by pipeline to the soil vapor extraction (SVE) system in
operation at OU1 for treatment by the existing catalytic oxidation unit.

• Water received at the treatment facility from the DVE system oil/water separator
would first be pre-treated for metals removal using chemical precipitation followed
by sedimentation. Groundwater pretreatment for metals is necessary to prevent
potential fouling and clogging of the air stripper. The water would then pass
through an air stripper where volatile contaminants would be removed. In
particular, air stripping would remove vinyl chloride and methylene chloride which
would tend to pass through the granular activated carbon (GAG) unit. Treatment of
the off-gas from the air stripper may be required depending upon the level of
emissions. Liquid phase GAG would follow as the final treatment process, however, a
detailed engineering evaluation could result in a re-sequencing of the air stripping
and GAG treatment processes. Spent GAG would be regenerated off site.

• Treated groundwater would be injected on site, upgradient of the extraction wells.
EPA permitting (SDWA UIC Class 5 permit) and testing prior to injection would occur
as necessary.

Alternative 4: Limited Containment of LNAPL using a Cutoff Wall

Alternative 4 is similar to Alternative 3 with the exception that the LNAPL plume would be
contained, rather than removed. The principal elements of this alternative are:

• A vibrating beam wall would be constructed along the northern and eastern edges of
the LNAPL plume (Figures 7 and 8) to contain and prevent further migration of the
LNAPL plume and associated dissolved-phase groundwater contamination, and therefore
prevent further degradation of the groundwater.

• A series of extraction wells would be constructed upgradient and adjacent to the
vibrating beam wall. Groundwater would be pumped, only as necessary, to reduce the
pressure and prevent flow around the wall.

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• Extracted groundwater would be transported by pipeline to an on-site treatment
facility.

• Groundwater would be treated to reduce concentrations of metals and organic
compounds, as described under Alternative 3. Any LNAPL withdrawn with the
groundwater would be separated out with an oil/water separator prior to groundwater
treatment and be transported off site to a recycling center.

• Treated groundwater would be injected on site, downgradient of the vibrating beam
wall. EPA permitting (Safe Drinking Water Act (SDWA) Underground Injection Control
(UIC) Class 5 permit) and testing prior to injection would occur as necessary.

• No additional removal, treatment or containment of the groundwater would occur
except for the removal and treatment necessary to maintain the integrity and
effectiveness of the containment system.

Alternative 5: Localized Pump and Treat with LNAPL Containment and Groundwater Treatment by GAC
and Air Stripping

In this alternative, as well as the following alternatives dissolved phase contaminants in
groundwater are specifically targeted for remediation. The LNAPL plume is contained as
described in Alternative 4. The major elements of this alternative are:

• A series of extraction wells would be constructed within the localized extent of
groundwater remediation area defined on Figures 7 and 8.

• Limited containment of the LNAPL plume (vibrating beam wall), as described in
Alternative 4, would be implemented in conjunction with the pump and treat system.

• Groundwater would be pumped and transported by pipeline to an on-site treatment
facility. The contaminated groundwater would be treated to reduce levels of metals
and organic compounds, as described under Alternative 3.

• Treated groundwater would be injected downgradient of the vibrating beam wall. EPA
permitting (SDWA UIC Class 5 permit) and testing prior to injection would occur as
necessary.

Alternative 6: Localized Pump and Treat with LNAPL Removal and Groundwater Treatment by GAC and
Air Stripping

Alternative 6 is identical to Alternative 5 with the exception that the LNAPL plume would be
removed, rather than contained. The major components of this alternative are:

• A series of extraction wells would be constructed within the localized area defined
on Figure 7. Groundwater would be pumped and transported by pipeline to an on-site
treatment facility, where it would be treated to reduce concentrations of metals and
organic compounds, as described under Alternative 3.

• DVE wells would be installed in the LNAPL plume area. LNAPL vapors and liguids
removed by the DVE wells would pass through an air/liguid separator, and the
resulting liquids stream would flow through an oil/water separator to recover
free-phase LNAPL. Recovered LNAPL would be transported off site to a recycling
facility. Water from the oil/water separator would be transported to an on-site
groundwater treatment facility where it would be treated with groundwater removed by
the localized extraction system. LNAPL vapors from the air/liguid separator would
be transported by pipeline for treatment by the catalytic oxidation unit in
operation at the OU1 SVE system.

• Treated groundwater would be injected back into the shallow aguifer. EPA permitting
(SDWA UIC Class 5 permit) and testing prior to injection would occur as necessary.

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Alternative 7: Localized Pump and Treat with LNAPL Containment and Groundwater Treatment by UV
Oxidation

Alternative 7 is similar to Alternative 5 with the primary difference being the groundwater
treatment method. This alternative would use UV oxidation, rather than air stripping and GAG
filtration for treatment of contaminated groundwater. Since UV oxidation is an innovative and
unproven technology, a treatability study would be performed prior to implementation of
Alternative 7 to verify the effectiveness of the treatment process at OU4. The principal
components of Alternative 7 are:

• A series of extraction wells would be constructed within the localized extent of
groundwater remediation area defined on Figures 7 and 8.

• Limited containment of the LNAPL plume (vibrating beam wall), as described in
Alternative 4, would be implemented in conjunction with the pump and treat system.

• Groundwater would be pumped and transported by pipeline to an on-site treatment
facility.

• Any LNAPL withdrawn with the groundwater would be separated out with an oil/water
separator and transported off site to a recycling center. The groundwater treatment
process would consist of pre-treatment for metals using chemical precipitation
followed by sedimentation. The water would then pass through a UV oxidation unit to
remove VOCs. If ozone is used in the treatment process, off-gas from the treatment
process would pass through an ozone decomposer before air venting.

• Treated groundwater would be injected downgradient of the vibrating beam wall. EPA
permitting (SDWA UIC Class 5 permit) and testing prior to injection would occur as
necessary.

Alternative 8: Localized Pump and Treat with LNAPL Removal and Groundwater Treatment by UV
Oxidation

This alternative is similar to Alternative 7 in that it includes a localized pump and treat
system and the use of UV oxidation in treating contaminated groundwater. The main difference is
that Alternative 8 provides for removal of the LNAPL plume, rather than containment. As with
Alternative 7, a treatability study would need to be performed prior to implementation of the
alternative to verify the effectiveness of UV oxidation in treating contaminated groundwater at
OU4. The primary elements of this alternative include:

• A series of extraction wells would be constructed within the localized area defined
on Figures 7 and 8. Groundwater would be pumped and transported by pipeline to an
on-site treatment facility.

• A DVE system would be installed in the LNAPL plume area and operated as described
under Alternative 3.

• Water received at the treatment facility from both the groundwater extraction
system and the dual vapor extraction system would treated as described under
Alternative 7.

• Treated groundwater would be injected back into the shallow aguifer. EPA
permitting (SDWA UIC Class 5 permit) and testing prior to injection would occur as
necessary.

Alternative 9: Site-Wide Pump and Treat for Total Groundwater Restoration with LNAPL Containment

Alternative 9 consists of the same basic elements as Alternative 5 except that the scope of the
remedial action is more comprehensive. In this alternative a site-wide groundwater extraction
system would be constructed, rather than focusing only on the most highly contaminated area
near the COCC and LCC properties.

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• A series of extraction wells would be constructed throughout the entire site (see
site-wide extent of groundwater remediation on Figure 7).

• Limited containment of the LNAPL plume (vibrating beam wall), as described in
Alternative 4, would be implemented in conjunction with the pump and treat system.

• Groundwater would be pumped and transported by a conveyance system (pipelines) to an
on-site treatment facility. Groundwater treatment for metals and organic compounds
would occur as described in Alternative 3.

• Treated groundwater would be injected downgradient of the vibrating beam wall. EPA
permitting (SDWA UIC Class 5 permit) and testing prior to injection would occur as
necessary.

Alternative 10: Site-Wide Pump and Treat for Total Groundwater Restoration with LNAPL Removal

This alternative is similar to Alternative 9 in that site-wide remediation would occur, but the
LNAPL plume would be removed rather than contained. Following completion of the remedial
action, the Site would be available for unrestricted commercial and/or industrial use. The
principal components of this alternative are:

• A series of extraction wells would be constructed throughout the entire Site, as
indicated in Figure 7. Groundwater would be pumped and transported by pipeline to
an on-site treatment facility.

• A DVE system would be installed in the LNAPL plume area, as described in
Alternative 3.

• Contaminated water received at the treatment facility from both the groundwater
extraction system and the dual vapor extraction system would treated for metals
and organic compounds as described under Alternative 3.

• Treated groundwater would be injected back into the shallow aguifer. EPA permitting
(SDWA UIC Class 5 permit) and testing prior to injection would occur as necessary.

VIII. SUMMARY OF COMPARATIVE ANALYSIS OF ALTERNATIVES

In this section, alternatives developed for OU4 are evaluated and compared to each other using
the nine evaluation criteria reguired by the National Oil and Hazardous Substances Pollution
Contingency Plan (NCP; 40 CFR § 300.430) 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 Reguirements (ARARs);
3. Long-Term Effectiveness and Permanence;
4. Reduction of Toxicity, Mobility, or Volume Through Treatment;
5. Short-Term Effectiveness;
6. Implementability;
7. Cost;
8. State Acceptance; and
9. Community Acceptance.

The NCP defines the first two criteria as threshold criteria which must be met by the
alternative. The succeeding five criteria, termed balancing criteria, form the primary criteria
on which the detailed analysis of alternatives is based. The last two criteria are modifying
criteria and were evaluated after public comment on the Proposed Plan is received.

A. Overall Protection of Human Health and the Environment

This criterion assesses the protection afforded by each alternative, considering the magnitude
of the residual risk remaining at the Site after the remedial action has been completed.

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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.

Although groundwater 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 groundwater because water for residential use is provided through
treated water from either the DWD or SACWSD.

Alternative 10 is the most protective of human health and the environment and would allow future
commercial/industrial use of the Site without engineering or institutional controls and without
limitations on the exposures for human and environmental receptors. Alternative 1 provides the
least protection to human health and the environment of the ten alternatives. Contaminant
levels would only be reduced through natural attenuation under Alternatives 1 and 2, and the
LNAPL and dissolved contaminant plumes are not contained or treated. Remedial action could be
taken under Alternatives 1 and 2, however, if future information indicates that the
contamination migrates to either Sand Creek or the underlying aguifers. Alternatives 2 through
10 would provide overall protection to human health through the use of institutional controls
which would limit human exposure to contaminated media. Migration of the LNAPL plume which could
potentially threaten Sand Creek, Metro sanitary sewer lines, or downgradient wells is prevented
by the installation of a vibrating beam wall in Alternatives 4, 5, 7, and 9. However,
Alternatives 3, 6, 8, and 10 would provide relatively greater protection from potential effects
from exposure to the LNAPL by removing the recoverable LNAPL from the Site, rather than
containing it. Site-wide groundwater remediation included in Alternatives 9 and 10 would
provide relatively greater protection of human health and the environment at OU4 than the
localized groundwater remediation proposed under Alternatives 5 through 8.

B. Compliance with ARARs

Section 121(d) of SARA mandates that for all remedial actions conducted under CERCLA, cleanup
activities must be conducted in a manner that complies with ARARs, or if ARARs cannot be
attained a justifiable waiver must be obtained. The NCP and SARA have defined applicable
reguirements and relevant and appropriate reguirements as follows:

• Applicable reguirements are those federal and state reguirements that would be
legally applicable, either directly, or as incorporated by a federally authorized
state program.

• Relevant and appropriate reguirements are those federal and state reguirements that,
while not legally "applicable," are designed to apply to problems sufficiently
similar to those encountered at CERCLA sites that their application is appropriate.
Reguirements may be relevant and appropriate if they would otherwise be
"applicable," except for jurisdictional restrictions associated with the
reguirement.

• Other reguirements to be considered are federal and state non-regulatory
reguirements, 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 situation, 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 treatment levels. Location-specific ARARs govern natural features
such as wetlands and floodplains, and man-made features such as archeological and historic
areas. Action-specific ARARs are technology- or activity-based reguirements that set
restrictions on particular kinds of actions at CERCLA sites.

Table 3 summarizes the potential ARARs and guidance, advisories, and criteria to be considered
(TBCs) for OU4. All alternatives would likely comply with pertinent chemical-, action- and
location-specific ARARs. Alternatives which involve withdrawal, treatment, and injection of

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groundwater (Alternatives 3 through 10) will be reguired to achieve Safe Drinking Water Act
Maximum Contaminant Levels (SDWA MCLs) and/or state standards prior to groundwater injection.
Contaminated groundwater attributable to the Site would also be reguired to meet SDWA MCLs
and/or state groundwater standards at the downgradient (i.e., northern) Site boundary. There
are no chemical-specific ARARs for Alternative 1 since no activity would occur.

Wells installed for monitoring and/or extraction and injection systems in Alternatives 2 through
10 would be subject to the reguirements of the Colorado Department of Natural Resources, State
Engineer's Office. Additional action-specific ARARs that Alternatives 3 through 10 must comply
with include: state air regulations for emissions from the LNAPL and groundwater treatment
systems; the Hazardous Materials Transportation Act (HMTA) and the Resource Conservation and
Recovery Act (RCRA) for the off-site transport of treatment residuals; and RCRA for waste
disposal, reuse, and recycling. There are no action-specific ARARs for Alternative 1 since no
activity would occur.

Compliance with location-specific ARARs for alternatives that include the vibrating beam wall,
extraction and injection systems, or treatment facilities (i.e., Alternatives 3 through 10)
would depend on the location of these components. However, no protected properties have been
identified in the immediate vicinity of OU4.

Guidance regarding ambient air levels of toxic air pollutants (National Ambient Air Quality
Standards, NAAQSs) should be considered for designing air pollution controls for the Site. The
EPA Reference Concentrations and Slope Factors would be used to calculate the hazard indices and
the risk levels. The State of Colorado considers the Massachusetts Ambient Air Level standards
as important guidance. EPA has issued a policy statement regarding air emission controls for
air strippers located in ozone non-attainment areas and believes that this policy is a TBC
because Denver is an ozone non-attainment area (OSWER Directive 9355.0-28). Other TBCs
identified for OU4 are the CERCLA Petroleum Exclusion, and EPA guidance regarding land disposal
restrictions.

C. Long-Term Effectiveness and Permanence

The focus of this criterion 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;

• Adeguacy and reliability of long-term management controls providing continued
protection from residuals; and

• Associated risks in the event the technology or permanent facilities must be
replaced.

Alternative 10 would provide the greatest degree of long-term effectiveness since contaminants
would be permanently removed from the Site and no residual risks would remain. Alternatives 2
through 9 would be effective at limiting contact with and ingestion of contaminated groundwater
in the long term provided that institutional controls are effective. The No-Action alternative
would not provide long-term effectiveness. Alternatives 3 through 10 effectively prevent the
spread of the LNAPL plume and a portion of the dissolved contaminant plumes in the long term
provided the integrity of the vibrating beam wall is maintained or the dual extraction system
operates satisfactorily. The long-term effectiveness of groundwater remediation in Alternatives
5 through 10 depends upon continual remediation since re-contamination of the site would occur
due to upgradient sources once the OU4 pump and treat system was shut down.

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          Regulation
                       TABIiE 3
        SEIiECTED POTENTIAL ARARs AND TBCs FOR
OPERABIiE UNIT 4, SAND CREEK INDUSTRIAL SUPERFUND SITE

                   Citation
                     ARARs
       Comments
Resource Conservation and Recovery
Act
Safe Drinking Water Act -
Underground Injection Control
Regulations

Primary Drinking Water Regulations
Colorado Classification and Water
Quality Control Act
             42 USC § 6901
             40 CFR Parts 260-268
             42 USC § 300 (g)
             40 CFR Parts 144 - 147
             42 USC §  (300)  (f)
             40 CFR Part 141
             5 CCR 1002-E
ARAR if Remedial Action
involves hazardous waste or

sufficiently similar material.

ARAR if Remedial Action
includes injection of
ground water.

Includes final maximum
contaminants levels  (MCLs)
and MCL goals  (MCLGs)
greater than zero.  May serve
as treatment level prior to
injection.

May serve as clean-up and/or
treatment levels.  Contains
allowance for variance at
CERCLA sites.
Colorado Basic Standards for
Groundwater
             5 CCR 1002-E
May serve as clean-up and/or
treatment levels.  Contains
allowance for variance at
CERCLA sites.
Hazardous Materials Transportation
Act

Clean Air Act

              NSPS
              PSD reguirements
              NESHAPs
             49 § 1801 et. seg.
             49 CFR Parts 107, 171, 172

             42 USC § 7412 et. seg.

               40 CFR Part 60


               40 CFR Part 52


               40 CFR Part 61
ARAR if hazardous materials
are transported off site.
  ARAR if Remedial Action
 involves regulated new source(s)

  ARAR if RA involves major
 new source(s)  of S02 or N02.

  ARAR if RA involves emission
 of a regulated pollutant from
 a regulated source.

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Colorado Air Pollution Control
Regulations

       •      Regulation 1
5 CCR 1001-1 et. seg.
  5  CCR 1001-3
  Regulations emission of S02,
 particulates and smoke.
              Regulation 2
  5  CCR 1001-4
  Regulates odorous emissions
 from a single source.
              Regulation 3
  5  CCR 1001-5
  Sets permitting reguirements,
 only substantive reguirements
 may be ARARs.
              Regulation 6
  5  CCR 1001-8
                                           Sets  performance  standards
                                          for new emissions  sources.
              Regulation 7
  5  CCR 1001-9
  Regulates VOC emissions.
Colorado Revised and Amended Rules
and Regulations of the Board of
Examiners of Water Well Construction
and Pump Installation Contractors
2 CCR 402-2
                                         ARAR for groundwater
                                         monitoring well installation
                                         and abandonment activities.
Executive Order on Floodplain
Management
Executive Order 11988
40 CFR Part 6.302(b)
ARAR if designated floodplain
is affected.
Executive Order on Protection of
Wetlands
Executive Order 11990
40 CFR Part 6.302(a)
ARAR if designated wetland
is affected.

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                                                  TABIiE 3
                                   SEIiECTED POTENTIAL ARARs AND TBCs FOR
                           OPERABIiE UNIT 4, SAND CREEK INDUSTRIAL SUPERFUND SITE
        Regulation
    Citation
                                              Comments
                                              TBCs
Clean Air Act-
National Ambient Air Quality
Standards  (NAAQS)
42 USC § 7401
40 CFR Part 50
ARAR if more than 250
tons/year of S02, or N02, or
100 tons/year of PM-10, CO or
03 are emitted from RA
treatment facility.
Massachusetts Allowable
Ambient Levels
Code of Massachusetts Regulations
Title 310 § 6.04
The State of Colorado
considers these air guality
standards a TBC.
Safe Drinking Water Act National
Primary Drinking Water Standards-
Proposed
42 USC § 300 (f)
40 CFR Parts 141.11 and 141.16
May serve as clean-up level
for treating groundwater prior
to injection.
Colorado Interim Organic Pollutant
Standards
5 CCR 1002-E
                                         May serve as clean-up level
                                         for treating groundwater prior
                                         to injection.
Superfund LDR Guide #5
EPA OSWER Directive 9347.3-05FS
Guidance for on-site disposal
of hazardous waste.
Superfund LDR Guide #7
EPA OSWER Directive 9347.3-08FS
Guidance for on-site disposal
of hazardous waste.
EPA Guidance Document
EPA OSWER Directive 9355.0-28
Guidance for control of
emissions from air strippers at
Superfund sites.
CERCLA Petroleum Exclusion Clause
                                        42 USC § 101  (4)
                                        42 USC § 104  (a)
                                         Limits CERCLA authority and
                                         funding for removal and
                                         treatment of petroleum
                                         product.
Adams County Zoning Regulations
                                         May affect institutional controls.

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D. Reduction of Toxicitv, Mobility, or Volume Through Treatment

This criterion evaluates the ability of the alternatives to significantly achieve reduction
of the toxicity, mobility, or volume of the contaminants or wastes at the site through
treatment. The criterion is a principal statutory reguirement of CERCLA. This analysis
evaluates the guantity 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 guantity of residuals produced, and the manner in
which the principal threat will be addressed through treatment. The risk posed by residuals is
considered in determining the adeguacy of reduced toxicity and mobility achieved by each
alternative.

Alternative 10, followed by Alternative 9, provide the greatest reduction in toxicity,
mobility and volume of contamination through total restoration of groundwater (versus localized
groundwater remediation under Alternatives 5 through 8) at the Site. Removal of the LNAPL plume
in Alternatives 3, 6, 8, and 10 would reduce the volume of LNAPL, rather than simply reduce its
mobility as would be accomplished with the vibrating beam wall in Alternatives 4, 5, 7, and 9.
No reduction in contaminant toxicity, mobility, or volume, other than by natural processes,
would occur under Alternatives 1 and 2. Alternative 4 reduces the mobility of the LNAPL plume,
but would provide only a minimal reduction in contaminant toxicity and volume by treatment only
of groundwater extracted to maintain the integrity of the vibrating beam wall. Upgradient
sources would provide a continuous source of contaminants (LNAPL and VOCs) to the OU4 area under
all the alternatives.

E. 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 reguired to achieve the response objectives. Measures to mitigate releases and provide
protection are central to this determination.

All of the alternatives except for Alternative 1 would provide a similar degree of short-term
effectiveness by protecting the community, workers, and environment through adeguate
preventative measures. These preventative measures include items such as establishing exclusion
zones during remedial activities, use of personal protective eguipment for onsite workers, and
dust control practices. The greater scope of construction activities associated with site-wide
groundwater remediation in Alternatives 9 and 10 would result in slightly higher short-term
risks as compared with the localized treatment or containment actions included in the other
alternatives. However, standard engineering controls and adherence to standard health and safety
practices would minimize potential adverse short-term impacts. Alternative 1 would provide the
least amount of short-term effectiveness. The time until the response objectives are achieved
for Alternatives 5 through 10 is unknown because the duration of remediation at OU4 is largely
dependent on removing upgradient sources of contamination (LNAPL and upgradient contaminated
groundwater). For costing purposes, it was assumed that at least 30 years would be necessary.

F. Implementabilitv

This criterion analyzes technical and administrative feasibility, and the availability of
services and materials. Technical feasibility assesses the difficulty of construction or
operation of a particular alternative and uncertainties 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.

Administrative feasibility assesses the ease or difficulty of obtaining permits or rights-of-
way for construction. Availability of services and materials evaluates the need for off-site
treatment, storage, or disposal services, and the availability of such services.

Necessary eguipment, specialists, and additional resources are also evaluated in determining the
ease by which these needs could be fulfilled.

All of the alternatives under consideration, except those involving site-wide remediation
(Alternatives 9 and 10), are both technically and administratively feasible, although

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implementation of Alternative 1 is unlikely from an administrative standpoint. It is
doubtful that regulatory agencies or the public would accept a No Action alternative for OU4.
Alternative 2 is the easiest to implement because relatively little construction would be
involved. Alternatives 3 through 6, 9 and 10 involve the utilization of readily available,
proven technologies. Alternatives 7 and 8 would be more difficult to implement because they
incorporate an innovative, unproven technology (i.e., UV oxidation) reguiring a treatability
study. The larger scope of the remedial effort under Alternatives 9 and 10 and the presence of
upgradient contaminant sources would make implementation of these alternatives much more
difficult than that associated with alternatives involving localized or no groundwater
remediation.

G. 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, eguipment, labor, land purchases) and indirect capital
costs (engineering, licenses, or permits). Long-term O&M costs include labor, materials,
energy, eguipment 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 analysis is used to evaluate expenditures that would occur during different
time periods. By discounting all costs to a common base year (i.e., 1994), the costs can 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 EPA guidance.

The estimated costs associated with each alternative are shown in Table 4. The total present
worth costs range from $22,300 for Alternative 1 to $ 22,312,400 for Alternative 10.
Alternatives that include site-wide groundwater treatment have high capital and O&M costs,
whereas alternatives that address localized contamination have medium capital and O&M costs.
However it should be noted that the 30-year estimate for project duration may not be accurate
for those alternatives involving groundwater treatment. It is not expected that groundwater
upgradient of OU4 will attain MCLs in the foreseeable future, nor is it known if the groundwater
pump and treat component of Alternatives 5 through 10 will be capable of removing all
groundwater contamination in a 30-year period. Therefore, costs associated with Alternatives
may be significantly higher than estimates provided in Table 4. Alternatives that incorporate
removal of the LNAPL plume, rather than containment of the plume, have relatively lower present
worth costs. Cost savings in those alternatives that include LNAPL removal (Alternatives 3, 6,
8, and 10) are anticipated by utilizing the existing OU1 SVE system and treatment facilities as
well as associated O&M activities, as opposed to building and operating new facilities.

H. State Acceptance

This criterion evaluates technical and administrative issues that may be raised by the State.
EPA has involved CDH throughout the RI/FS and remedy selection process. The State of Colorado
concurs with EPA's selected alternative, as presented in Section IX.

I. Community Acceptance

This criterion evaluates guestions and comments on the Proposed Plan received from members of
the community. Few comments were received on the OU4 Proposed Plan, and it appears that
community accepts EPA's selected remedy, as presented in Section IX. EPA's responses to oral
and written comments are provided in the Responsiveness Summary of this ROD (Appendix A).

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                      TABIiE 4

COSTS ASSOCIATED WITH ALTERNATIVES DEVELOPED FOR OU4
                   (1994 DOLLARS)
ALTERNATIVE
NO.
1
2
3
4
5
6
7
8
9
10
CAPITAL
COSTS
$0
$37,300
$256,200
$2, 683,200
$2,847, 600
$448, 600
$3,146, 600
$1,435,800
$5,158,500
$5,202,100
ANNUAL
O&M COSTS
$8,000
$186,200
$241,400
$359,000
$392,700
$250,700
$567,200
$484,300
$1,117,500
$1,119, 600
TOTAL PRESENT
WORTH
$22,300
$2,799,000
$3,866,500
$8,101,300
$8,783,700
$4,201,900
$11,765,200
$8,780,000
$22,236, 600
$22,312,400

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IX. SELECTED REMEDY

EPA has selected Alternative 3 as the remedy for OU4. The remedial action selected for OU4 will
restrict direct contact with and ingestion of groundwater underlying the Site and will protect
currently uncontaminated groundwater. Five-year reviews of the Site will be reguired because
contaminants will remain at OU4 following completion of the remedial action. This remedy is
comprised of the following components:

Groundwater and Surface Water Monitoring - Existing and future groundwater monitoring wells (a
total of approximately 16) will be sampled and analyzed periodically throughout OU4 to assess
the effectiveness of ongoing remedial activities or changes in natural conditions. Samples will
be analyzed for the presence of VOCs, semi-volatile compounds, pesticides, and metals.
Monitoring points wiil be located upgradient of the Site (to detect contamination from other
sources), downgradient of the LNAPL plume (to track potential plume movement), downgradient from
OU4 (to detect contaminant migration off site), within Sand Creek (to assess the impacts of
contaminated groundwater possibly discharging to surface water) and immediately north of Sand
Creek (to detect any potential migration of contaminants under the creek). Samples will
initially be collected guarterly for at least one year but may be collected less freguently
(i.e., semi annually or annually) if data indicate that site conditions are not changing
significantly on a guarterly basis. For costing purposes, it was assumed that guarterly
monitoring would be conducted for a period of 30 years. However, actual monitoring will
continue for as long as contaminant concentrations in groundwater at the Site boundary exceed
SDWA MCLs or state groundwater standards. In addition, the five private wells that are
completed in the shallow alluvium in the vicinity of OU4 will be sampled once and evaluated as
part of the OU4 groundwater monitoring program. EPA and CDH will notify and provide
recommendations to the users if contamination is detected.

Institutional Controls - EPA and CDH will coordinate with local officials and property owners,
and will reguest the implementation of institutional controls at the Site. Zoning restrictions,
including recommendations against well usage for domestic purposes, will be implemented to the
extent possible to prevent future human exposure to contaminated groundwater underlying the
site. These objectives are already achieved in part through state advisories against the
construction of water wells in areas with known contamination. Additional institutional
controls that may be implemented as necessary include subdivision regulations, building permits,
recording reguirements, state statutes, local ordinances, and deed restrictions and notices
implemented by current property owners. Table 5 provides additional information on the
institutional controls available for OU4.

LNAPL Removal - A DVE system (Figure 9) will be used to remove both LNAPL vapors and liguids
from the subsurface. Vapors will be extracted by applying a vacuum to the well, as in SVE. The
applied vacuum will also create a hydraulic gradient toward the well, causing LNAPL and
groundwater to flow to the extraction well. LNAPL can then be recovered without creating a
drawdown of the water table.

Higher overall removal rates can be achieved using a DVE system, as opposed to pumping liguids
only. The greater removal efficiency is achieved by extracting vapors from the LNAPL plume as
well as liguids. In addition, drawing air through the subsurface enhances biodegradation of
additional LNAPL in situ, further expediting remediation. By combining liguids extraction,
volatilization, and biodegradation, a DVE system is considered to be significantly more
effective than a liguids only extraction system. It is expected that the excess capacity of the
catalytic oxidation unit in operation at the OU1 SVE system can be used for treating vapors
removed by the DVE wells, thereby reducing construction time and costs.

Approximately twenty DVE wells will be installed in the center of the LNAPL plume area shown in
Figures 7 and 8. The location of the wells will be restricted based on planned OU5 excavation
activities. LNAPL vapors and liguid removed from the subsurface will pass through an air/liguid
separator, and the resulting liguids stream will flow through an oil/water separator to recover
free-phase LNAPL. Recovered LNAPL will be transported off site to a recycling facility. Water
from the oil/water separator will be piped to an on-site groundwater treatment facility. LNAPL
vapors from the air/liguids separator will be transported by pipeline to the SVE system in
operation at OU1 for treatment by the existing catalytic oxidation unit.

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Water received at the treatment facility from the DVE oil/water separator will first be
pre-treated for metals removal using chemical precipitation followed by sedimentation.
Groundwater pretreatment for metals is necessary to prevent potential fouling and clogging of
the air stripper. The water will then pass through the air stripper where volatile contaminants
will be removed. In particular, air stripping will remove vinyl chloride and methylene chloride
which would tend to pass through the GAG unit. Treatment of the off-gas from the air stripper
with a thermal or catalytic oxidation unit may be required depending upon the level of
emissions. Liguid phase GAG will follow as the final treatment process. However, a detailed
engineering evaluation could result in a re-seguencing of the air stripping and GAG treatment
processes. Spent GAG will be regenerated off site.

Figure 9. Dual Vapor Extraction (DVE) System
Treated groundwater will be injected upgradient of the extraction wells. EPA permitting (SDWA
UIC Class 5 permit) and testing prior to injection will occur as necessary.

Remediation Goals and Performance Standards. Remedial action objectives (RAOs) developed for
OU4 are:

• Prevent direct contact with and ingestion of groundwater; and

• Protect uncontaminated groundwater for current and future use by preventing further
migration of contaminants (both LNAPL and dissolved phase) in excess of federal and
state drinking-water standards.

The DVE system will be designed to remove the mobile portion of the LNAPL plume located near the
COCC and LCC properties in the northwest portion of OU4. The current estimated extent of this
plume is indicated in Figures 7 and 8. Approximately 50% (190,000 gallons) of the total LNAPL
volume at OU4 is estimated to be mobile under normal fluid flow, but a greater amount of LNAPL
recovery is expected due to the addition of residual LNAPL removal through volatilization by the
DVE system. The initial vapor-phase LNAPL removal rate is expected to be equivalent to
approximately 200 gallons per day. The initial liquid-phase LNAPL removal rate is more
difficult to estimate due to the lack of sufficient pump test data and uncertainties regarding
the actual LNAPL plume thickness. However, an estimated removal rate of approximately 25 to 75
gallons per day of liquid LNAPL appears reasonable based on the limited data.

Completion of removing the recoverable LNAPL will be determined based on monitoring of vapor
emissions from the DVE system. Sampling of vapors will occur under equilibrium conditions and
will be conducted on a monthly basis. Cleanup of the recoverable LNAPL will be considered
completed when the LNAPL vapor removal rate of the DVE system becomes asymptotic. The specific
criteria that must be met for completion of LNAPL removal are: (1) a greater than 90% reduction
from initial vapor concentrations must be achieved, and (2) the LNAPL removal rate must be less
than 10% per month for a three consecutive month period.

Groundwater and surface water monitoring at OU4 will be performed indefinitely until
concentrations of contaminants meet applicable or relevant and appropriate federal and state
standards. The duration of the OU4 monitoring program will be largely dependent on remediation
of upgradient groundwater contamination. Remedial action at the Chemical Sales Company
Superfund Site, located immediately southeast of the 48th and Holly Landfill, is expected to
begin during the summer of 1994 and will address a source of the VOC contamination present in
the eastern portion of OU4.

The points of compliance at OU4 will be groundwater and surface water at Sand Creek along the
northern (downgradient) boundary of the Site, and at the groundwater injection wells.
Contaminated groundwater attributable to the Site will be required to meet SDWA MCLs and more
stringent state groundwater standards at the points of compliance. Contaminant levels in
groundwater monitoring wells at the Site will be evaluated and compared with upgradient (i.e.,
background) contaminant. Table 6 presents the action levels for those COCs at OU4 that have an
established federal or state drinking-water standard.

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Zoning and
Deed
Restrictions
                                           TABLE 5

                           INSTITUTIONAL CONTROLS AVAILABLE FOR OU4

                Purpose                                 Measures
Limit or prohibit certain  uses  of
the property  (deed restrictions,
easements, covenants).

Alert potential  future  buyers  of
property to site risks  (deed
notice).
Deed restrictions,
deed notices,
easements,
covenants,
permits.
                                                                Existing/Available Institutional Controls
The OU4 site area  falls within  an area already zoned
for industrial use under  the  existing Commerce City
Zoning Ordinance.  Existing laws  prohibit residential
development in those portions of  the site designated
as 1-2 or 1-3.  Colorado  Rev. Status 30-38-114 gives
the Adams County Commissioner authority to
enforce zoning by  issuing fines and imprisonment for
violators.  County zoning, however,  could be revised
to change the current  zoning  of the OU4 site area in
the future.

Existing Commerce  City Subdivision Regulations
allow the city council to prohibit,  control or restrict
subdivision/development of property that could place
present or future  inhabitants of  the area at risk.  The
regulations also require  a title  check that should
disclose any recorded  information relating to past site
use and hazards.
EPA could negotiate a CERCLA
Section 122 Consent Decree with
OU4 potentially responsible  parties
(PRPs) restricting OU4  land  use.
EPA may include in Section 122
Consent Decrees penalty
provisions for violation  of  the
decree.
                                                                                                                                                EPA could petition the  Colorado
                                                                                                                                                Land Use Commission to  require a
                                                                                                                                                hearing to decide i f  OU4  should  be
                                                                                                                                                designated as an "Area  of Interest"
                                                                                                                                                under the Land Use Act.   Such a
                                                                                                                                                designation would require any
                                                                                                                                                potential developer to  obtain a
                                                                                                                                                permit prior to the development  of
                                                                                                                                                any portion of the site.
Municipal       Minimi ze  the  use  of OU4
Water Supply    groundwater as  a
                domestic/potable  water source.
                                        Require use of
                                        existing municipal
                                        water supply.
                                                                                 EPA could negotiate a settlement with  the  PRPs
                                                                                 which includes attaching a deed notice  or  restriction
                                                                                 to property owned by the PRPs.
                         Existing zoning laws contribute to prevention  of  use
                         of  OU4  groundwater for domestic purposes  (OU4
                         groundwater is currently not being used for domestic
                         purposes).

                         Existing Commerce City subdivision regulations
                         require the collection and analysis of water samples
                         prior  to subdivision or development of the property
                         for both residential and non-residential  development.
                         Any such sampling at OU4 would disclose the
                         contaminated state of the groundwater and prevent,
                         by  law,  a developer from using the groundwater  for
                         drinking purposes if the proposed development  site
                         is  underlain by contaminated groundwater,
                         Commerce City would require an agreement  from
                         SACWSD,  or the Denver Water Department if
                         applicable regarding the supply of municipal water  to
                         the new development.
                                                               Persuade  the  record owners of
                                                               OU4 property  by deed to create an
                                                               Easement  in Gross  to restrict
                                                               development of  their property.

                                                               EPA could negotiate a CERCLA
                                                               122 Consent Decree with OU4
                                                               PRP's restricting  groundwater use.
                                                               EPA could petition the Colorado
                                                               State Engineer  to  advise against
                                                               the drilling  of new wells in the
                                                               OU4 site  area.

                                                               The City  Council of Commerce
                                                               City has  the  authority under
                                                               Colorado  Rev. Statute 31-15-708  (1)
                                                                (c) to enact  an ordinance
                                                               prohibiting the drilling or use of
                                                               wells in  area in which the
                                                               groundwater is  deemed inj urious
                                                               to health.  Commerce City has the
                                                               authority under Colorado Rev.
                                                               Statute 31-16-101  to enforce
                                                               ordinances such as well restriction
                                                               ordinances with fines and
                                                               imprisonment.

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                                   TABIiE 6
             REGULATORY STANDARDS FOR CHEMICALS OF CONCERN AT OU4
       OU4 Chemical of Concern
Concentration (mg/1)
                                                                 Source
Benzene
Chlorobenzene
Chloroform
CPMSO
2,4-D
4,4-DDT
1,2-Dichlorobenzene
1,4-Dichlorobenzene
1,1-Dichloroethene
trans-1,2-Dichloroethene
Dieldrin
Ethylbenzene
Methylene Chloride
Lindane (gamma-BHC)
Styrene
Tetrachloroethene
Toluene
1,1,1-Trichloroethane
Trichloroethene
Vinyl Chloride
Xylenes (total)
Antimony
Arsenic
Selenium
0.005
0.100
0.006
0.02
0.07
0.0001
0.6
0.075
0.007
0.1
0.000002
0.680
0.005
0.0002
0.1
0.005
1
0.2
0.005
0.002
10
0.006
0.05
0.01
CIOPS
CIOPS
CIOPS
EPA
SDWA MCL
CIOPS
SDWA MCL
SDWA MCL
SDWA MCL
SDWA MCL
CIOPS
CIOPS
SDWA MCL
SDWA MCL
SDWA MCL
SDWA MCL
SDWA MCL
SDWA MCL
SDWA MCL
SDWA MCL
SDWA MCL
SDWA MCL
SDWA MCL
CIOPS
 CIOPS          Colorado Interim Organic Pollutants Standards
 SDWA MCL       Safe Drinking Water Act Maximum Contaminant Level
 EPA            EPA Memorandum on Toxicity of p-Chlorophenylmethyl Sulfide and
                its Oxidation Products; from Robert Benson, Ph. D., Toxicologist
                to Larry Diede (January 21,1994).

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The groundwater standard for CPMSO was established based on a toxicological study performed by
EPA. Concentrations of COCs that do not have a federal or state drinking-water standard will
also be monitored, and potential risks associated with detected concentrations of these
contaminants will be evaluated.

X. STATUTORY DETERMINATIONS

EPA's primary responsibility at Superfund sites is to undertake remedial actions that achieve
adeguate protection of human health and the environment. In addition, CERCLA § 121 establishes
several other statutory reguirements 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 reguirements.

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 alternative water supply. A containment system
does not appear to be necessary at OU4 at this tune because the LNAPL and dissolved-phase
contaminant plumes are not migrating significantly. This is due to a relatively flat hydraulic
gradient at the Site and the presence of impermeable days that inhibit contaminant transport.

Since groundwater is not currently used for drinking water or other domestic uses, there is
presently not a significant health risk at OU4 because of a lack of completed exposure pathways.
The risks associated with potential future exposure scenarios are adeguately addressed in the
selected remedy by the implementation of LNAPL removal, institutional controls, and monitoring.
Removal of the recoverable LNAPL will minimize potential discharges to Sand Creek, the Metro
Waste Water sanitary sewer system, downgradient water supply wells, and will eliminate a
potential source of groundwater contamination. Groundwater and surface-water monitoring will
allow for evaluating the performance of the selected remedy and the need for additional action.
The monitoring program conducted for the 48th and Holly Street Landfill under the OU3 Unilateral
Order will also provide information on changes in groundwater guality at OU4.

Short-term and cross media impacts due to implementation of the selected remedy are expected to
be minimal. Potential risks to human health and environment through exposure to contaminated
groundwater and soil during well installation and construction of the DVE system will be
minimized by the use of appropriate preventative and protective measures. Potential cross media
impacts will be minimized by proper well construction methods.

Due to the presence of upgradient contamination, including petroleum product which is exempt
from remediation under CERCLA, and the residual LNAPL contamination that is likely to remain at
the Site, institutional controls must be used at OU4. The institutional controls will minimize
risks associated with potential future use of contaminated groundwater. Although 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, pollutants, or contaminants exist or
will remain onsite, include land and resource use and deed restrictions, well
drilling prohibitions, building permits, and well use advisories and deed notices.
EPA believes ...that institutional controls have a valid role in remediation and
are allowed under CERCLA (e.g., Section 121(d)(2)(B)(ii) appears to contemplate
such controls). Institutional controls are a necessary supplement when some
waste is left in place, as it is in most response actions. Also, in some instances
where the balancing of tradeoffs among alternatives during selection of remedy

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process indicates no practicable way to actively remediate a site, institutional
controls such as deed restrictions or well-drilling prohibitions are the only means
available to provide protection of human health.

B. Compliance with ARARs

The selected remedy will comply with all federal and state ARARs. ARARs which must be
considered include those that are chemical-, action-, and location-specific. Potential ARARs
identified for OU4 were described in Table 3 and are listed below for the selected alternative:

Chemical-specific: For compliance with pertinent chemical-specific ARARs, contaminated
groundwater attributable to the Site will be reguired to meet applicable SDWA MCLs (40 CFR Part
141) and applicable state groundwater standards such as the Colorado Classification and Water
Quality Control Act and the Colorado Basic Standards for Groundwater (5 CCR 1002-8) at the
downgradient Site boundary. Contaminant levels in groundwater monitoring wells at the Site will
be evaluated and compared with upgradient (i.e., background) contaminant concentrations.
Groundwater that is removed incidentally by the DVE system and subseguently treated will also
need to meet these groundwater standards prior to injection. The groundwater treatment facility
included in the selected remedy will be capable of achieving these applicable regulatory
standards.

Action-specific: Treatment residuals from the LNAPL removal system will be transported off site
in compliance with HMTA (applicable) and RCRA (applicable) reguirements if the residuals are
considered to be hazardous. Disposal of any hazardous treatment residuals will occur off site
at a RCRA Subtitle C treatment, storage, or disposal (TSD) facility. Wells installed for the
OU4 monitoring program and the abandonment of existing unneeded wells will be subject to the
Colorado Revised and Amended Rules and Regulations of the Board of Examiners of Water Well
Construction and Pump Installation Contractors (2 CCR 402-2) . EPA permitting (SDWA Underground
Injection Control Regulations, Class 5 permit) and testing prior to injection of groundwater
will occur as necessary.

Most of the air ARARs depend on emission sources and, therefore, are action specific. Because
there are no major sources of emissions at OU4, these ARARs pertain to activities associated
with the selected remedy, rather than to existing conditions. The selected remedy will comply
with the following air ARARs:

• National Ambient Air Quality Standards (NAAQS) - Particulate emissions will be
controlled during construction activities, and VOC emissions, which act as a
precursor to ozone formation, will be managed during remedial action. The
selected remedy will not cause or contribute to violations of the NAAQS.

• Colorado Ambient Air Quality Standards - The selected remedy will comply with
state-specific standards for lead and total suspended particulate matter.

>• Regulation 1 - The selected remedy will comply with provisions regarding
opacity limitations and control of particulate emissions that apply to
construction activities.

>• Regulation 2 - All actions taken at OU4 will be in compliance with state
odor regulations.

>• Regulation 3 - Air Pollution Emission Notices (APENs) will be filed for each
stage of activity, including construction, and operation of the DVE system and
water treatment eguipment.

>• Regulation 6 and Federal New Source Performance Standards - 40 CFR Part 60,
Subpart FF contains provisions relating to VOC emissions from petroleum
refinery wastewater systems. The selected remedy will meet relevant and
appropriate portions of Regulation 6 and the New Source Performance Standards.

>• Regulation 7 - Reasonably Available Control Technology (RACT) for VOC
sources within Colorado will be applied to the selected remedy.

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>• Colorado Regulation 8 - limitations on beryllium and lead emissions will
be met during construction if contaminated soils are disturbed. Relevant
and appropriate limitations on mercury emissions will be attained if water
treatment system sludge is dried. Relevant and appropriate provisions
involving vinyl chloride emissions from specific types of eguipment will also
be met.

• National Emissions Standards for a Hazardous Air Pollutants (NESHAPs) - The selected
remedy will meet relevant and appropriate portions of the NESHAPs (i.e., Subpart FF
of 40 CFR Part 61).

Location-specific: Location-specific ARARs include the Executive Orders on Floodplain
Management and Protection of Wetlands. Only a relatively small portion of the Site is located
within the Sand Creek floodplain. Compliance with location-specific ARARs depends on the
location of the treatment facility, monitoring wells, DVE wells, and groundwater injection
wells. No protected properties have been identified in the immediate vicinity of OU4 and, the
selected remedy will comply with location-specific ARARs.

Other Guidance, Criteria, or Advisories to be Considered (TBCs): Guidance regarding ambient air
levels of toxic air pollutants (National Ambient Air Quality Standards, NAAQSs) will be
considered for designing air pollution controls for the Site. The State of Colorado considers
the Massachusetts Ambient Air Level standards as important guidance. EPA has issued a policy
statement regarding air emission controls for air strippers at Superfund sites located in ozone
non-attainment areas and considers this policy a TBC because Denver is an ozone non-attainment
area (OSWER Directive 9355.0-28). The CERCLA Petroleum Exclusion which limits CERCLA authority
and funding for removal and treatment of petroleum product is also identified as a TBCC for the
selected remedy.

C. Cost Effectiveness

The selected remedy has been determined to provide overall effectiveness proportional to its
costs and is therefore considered cost effective. The OU4 monitoring program will allow
assessment of groundwater contamination attributable to the Site. The analysis of sampling data
collected will provide information necessary for making cost-effective decisions regarding the
need for future action at the Site. The alternative selected includes removal of the
recoverable LNAPL which is less expensive than containment and provides a relatively greater
degree of protectiveness. Total capital, annual O&M, and present worth costs for the selected
remedy are $256,200; $241,400; and $3,866,500; respectively. The selected alternative is the
third least expensive option of the ten alternatives developed for OU4.

D. Utilization of Permanent Solutions and Alternative Treatment Technologies (or Resource
Recovery Technologies) to the Maximum Extent Practicable

The selected remedy utilizes permanent solutions and treatment technologies to the maximum
extent practicable at OU4. Site-wide remediation of OU4 was found not to be feasible because
groundwater is not currently being used for domestic purposes, the existence of upgradient
contaminant source(s), the inability of a groundwater pump and treat system to extract all of
the residual contamination, and high cost of treating all groundwater beneath the Site. Removal
of the recoverable LNAPL will permanently eliminate a potential source of groundwater
contamination to OU4. Implementation and continued enforcement of institutional controls will
minimize the potential for exposure to contaminated groundwater. However, the effectiveness of
institutional controls is largely dependent on the continued cooperation of property owners,
municipalities, and other governmental entities. The OU4 groundwater monitoring program will
allow for evaluation of changes in groundwater guality, the detection of any offsite migration
of contaminated groundwater, and the need for further action at the Site.

Of the alternatives that are protective of human health and the environment and comply with
ARARs, EPA 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; and cost. Overall protection of human
health and the environment, and cost were the most decisive criteria in selecting Alternative 3
as the preferred remedy.

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E.  Preference for Treatment as a Principal Element

Treatment of the principal threats at OU4 was found not to be attainable due to the presence of
upgradient contaminant sources and limitations in EPA's response authority due to the Petroleum
Exclusion.  Therefore, the selected remedy does not satisfy the statutory preference for
treatment as a principal element.  However, many of the principal threats at the Site are being
addressed under remedial actions occurring at other OUs and ultimately will eliminate or control
sources of groundwater contaminants affecting the Site.  LNAPL vapors removed by the DVE system
will be permanently destroyed by a thermal or catalytic oxidation unit, and groundwater removed
during operation of the DVE system will treated to SDWA MCLs or more stringent state
drinking-water standards.

Because the selected 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 adeguate protection of human health and the environment.

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                                   APPENDIX A

                              RESPONSIVENESS SUMMARY
               SAND CREEK INDUSTRIAL SUPERFUND SITE, OPERABLE UNIT 4
                              COMMERCE CITY, COLORADO
1.   OVERVIEW
The U.S. Environmental Protection Agency  (EPA) established a public comment period from
February 14, 1994 through March 16, 1994 for interested parties to comment on the Feasibility
Study  (FS)  report and the Proposed Plan for Operable Unit 4  (OU4)  of the Sand Creek Industrial
Superfund Site in Commerce City, Colorado.  EPA also held a public meeting at 5:30 p.m. on March
1, 1994 at the Commerce City Recreation Center to outline the proposed remedy for OU4.   The
preferred alternative includes monitoring and institutional controls with light non-agueous
phase liguid (LNAPL) removal.

The Responsiveness Summary, reguired by the NCP (40 CFR Part 300.430(f)(3)(i)(F)), provides a
summary of comments received from the community during the public comment period,  as well as
EPA's responses to public concerns.  All comments received during the public comment period were
considered in EPA's final selection of a remedial alternative for OU4.

2.  BACKGROUND ON COMMUNITY INVOLVEMENT

Most of the community involvement at the Sand Creek Site Industrial Site has stemmed from local
officials and neighboring businesses.  In the past, concern about liability and property values
has been high in this community.  Site-specific concerns identified through recent community
interviews include credibility of the government,  publicity and economic issues, the Superfund
process, remedial activities, and health effects.

The following discussions identify the general nature of the concerns expressed by the community
and indicate specific concerns where appropriate.

Credibility of the Government:  Reportedly, a distrust of local, state, and federal government
persists in this community.  This distrust is attributed to contradictory statements made by
government representatives and what some people feel is a historical cover-up of environmental
problems.  In addition, the tremendous amount of environmental contamination that has occurred
in this community has made residents of Commerce City and the surrounding area feel like
"governmental and scientific guinea pigs," according to one resident.

On one occasion, some individuals who work near the Sand Creek site reguested information from
the EPA about water and soil guality in the area.   According to those interviewed, the EPA
response was that the water was fine but there was a problem with soils at the Sand Creek
Superfund Site.  Because these individuals worked uphill from the Site, they were told at they
were not at risk.  The workers did not believe the EPA and have feelings of distrust toward the
Agency.

Publicity and Economic Concerns:  Residents of Commerce City feel that bad publicity has stifled
the economy of the community and destroyed the area's ability to attract new business.  A primary
concern of local officials is that contamination in the area has been associated solely with
Commerce City although area Superfund sites are also located in Denver and unincorporated Adams
County.

Residents and business owners in the area are very concerned about property values.  One local
business owner said that he is unable to use his land for collateral and the property is
virtually unsalable.  Homeowners feel that a decline in property values can be attributed to the
presence of Superfund sites in the area.  Liability under Superfund has been a major concern
during the history of the Sand Creek Site, but the issue has not been raised by the community
recently.

The Superfund Process:  Local officials, residents, and business owners expressed concern about
the amount of time it takes to cleanup a site.  Specifically, one individual said that by the
time a remedy is about to be implemented, the treatment or disposal alternative that was
selected in the ROD may not be appropriate for the site.  Another concern is that contamination

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may have an opportunity to migrate while studies are being conducted and a remedy is being
designed.

Several interviewees felt that the Superfund process was inefficient. One individual said that
the Superfund process has become ineffective because a substantial portion of the Superfund
money has been spent on legal fees.

Remedial Activities: Lack of information about environmental sampling, remedial activities, and
protective clothing tends to intimidate and frighten people who work near the Site area. In
addition, local employees expressed a desire to know the schedule of sampling and remedial
activities in advance. Dusts generated during cleanup are a primary concern associated with
remedial activity. The people want to be assured that the proper preventative measures are
taken to limit the generation of dust, and that air quality near the Site is monitored
adequately during cleanup work.

Health Effects: Some of the individuals interviewed associate personal physical problems with
contamination in the area. The risks to pregnant women who work near the Site are of
particular concern to local employees. The community is also concerned about the overall air,
water, and soil quality in the area.

EPA General Response: The Community Relations Program for the Sand Creek Industrial Superfund
Site is improving the community's understanding of the data and the potential hazards associated
with the site, as well as the Superfund process. The community has been kept informed of
ongoing activities conducted at the Sand Creek site through mailings, newspaper announcements,
and public meetings. A notice of availability of the OU4 Proposed Plan, RI, and FS reports and
notification of the public meeting were published in The Rocky Mountain News on February 14,
1994 and in The Commerce City Express on February 15, 1994. The public comment period for the
OU4 Proposed Plan was open from February 14 to March 16, 1994, and the public meeting was held
on March 1, 1994 at the Commerce City Recreation Center. EPA explained the alternatives
developed for OU4, presented its preferred remedy, and responded to questions. In addition, EPA
has established an information repository at the Adams County Library and the EPA Superfund
Records Center in Denver, Colorado where materials relevant to the community's concerns and
interests may be reviewed. Documents pertaining to OU4 which are stored at the repository
include: the RI/FS reports, risk assessments, and related documents) and the Proposed Plan.

Because remedial actions for contaminated groundwater at Superfund sites often use similar
technologies and approaches, EPA has developed guidelines designed specifically for addressing
contaminated groundwater at these sites (EPA/540/G-88/003). This focused approach was adopted
in conducting the RI/FS for OU4. Use of these guidelines helped to expedite the RI/FS and
center the remedy selection on proven and widely used technologies, which ultimately resulted in
a more efficient use of time and resources. By streamlining the RI/FS process EPA: (1)
improves the efficiency and effectiveness of decision making at these sites; (2) provides
consistency among the EPA Regions in their approach to conducting an RI/FS and selecting a
remedy; and (3) facilitates more effective remedial designs.

The Comprehensive Environmental Response, Compensation, and Liability Act (CERCLA) mandates that
EPA protect human health and the environment from current and potential exposures to hazardous
substances. Groundwater underlying OU4 was evaluated for potential human health and
environmental risks posed by contaminants in several investigations at the Site. These studies
evaluated baseline risks and potential future risks associated with exposures to current levels
of contamination at OU4. The following documents describe risk evaluations performed at the
Site:

1993 48th and Holly Street Landfill (OU3) Risk Assessment: This document updated
and supplemented the 1988 EA by incorporating new data presented in the OU3 RI. The
two media evaluated in this risk assessment were groundwater in the vicinity of the
Landfill and landfill gas.

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              1993 Health Evaluation Update:   This document was prepared as part of the OU4  RI/FS.
              It updated and supplemented the 1988 EA by incorporating new data collected during
              the OU4 RI/FS as well as data collected for the 1993 OU3 risk assessment.
              Groundwater and the LNAPL plume were the subjects of this evaluation.   Results were
              compared with the previous EA study.

Protection of the community during remedial action is a primary concern of EPA.  The preferred
remedy for OU4 will meet all applicable or relevant and appropriate federal and state
reguirements.   Monitoring will be performed during construction activities to evaluate the air
guality, adeguate controls will be used to suppress dust generation, and appropriate measures
will be taken to protect workers and residents during remedial action.

3.  SUMMARY OF COMMENTS RECEIVED DURING PUBLIC COMMENT PERIOD AND EPA RESPONSES

EPA solicited written and oral comments from the community on the OU4 Proposed Plan during the
public comment period and at the public meeting.  A summary of comments received and EPA's
responses are provided below:

Comment:  One participant at the public meeting wanted to know how many wells are in the Sand
Creek Superfund site area, regardless of whether they were used for drinking water or
agricultural purposes.  He also wanted to know if the wells had been tested over a period of
time.

EPA Response:   A 1990 report prepared by Tri-County Health Department  (TCHD; 1990)for EPA and
the Colorado Department of Health  (CDH) contains the most current information on OU4 area water
use.  The report summarizes the findings of a door-to-door well inventory and information
survey.  The survey encompassed an area bounded by Sand Creek on the north, Interstate 70 on the
south, Quebec Street on the east, and Colorado Boulevard on the west.   (This survey area extends
beyond the boundaries of OU4.)  The survey supported CDH and EPA efforts to identify potential
receptors of groundwater contaminated by several sources, including sources at the Site.  TCHD
contacted property owners to determine the number, location, depth, construction details, and
current use of wells in the survey area.

TCHD obtained information on water use from 419 of the 420 properties in the survey area.  South
Adams County Water and Sanitation District and Denver Water Board serve most of the water users
in the survey area.  However, the survey identified 23 private wells, with nine completed in the
shallow alluvium.  Data regarding the depth of nine wells were unavailable.  Four wells
identified as deep ranged from 560 to 1600 feet depth, and thus are not in the shallow OU4
aguifers.  Two of the deep wells provided water for drinking.

Of the wells completed in the shallow alluvium, five are in use.  Three are used for irrigation
and one as a seasonal water supply for livestock.  The remaining well, located at a business on
Oriental Refinery property, provides water for a sanitary waste system. These wells have not
been sampled by EPA in the past, but will be included in the OU4 monitoring program.

Within the OU4 site boundary, there are approximately 80 groundwater monitoring wells.  EPA
intends to permanently abandon those monitoring wells that will not be sampled in the OU4 and
OU3 groundwater monitoring programs.

Comment:  A city council member at the public meeting felt that the proposed remedy for OU4 was
primarily a monitoring function and was not sufficient because it addressed only a limited
geographic area.  He believed that this has a direct effect on the marketability and economics
of the area, the willingness of the people to invest in the area, and establishing permanent
commercial and industrial use of the land.

EPA Response:   Groundwater underlying the Sand Creek site does not appear to be migrating due to
the nature of the aguifer system and the presence of clays.  EPA believes that monitoring is an
appropriate response for the conditions at the Site.  The proposed remedy for OU4 also includes
the implementation of institutional controls which will minimize potential exposure to
contaminated groundwater.  The dual vapor extraction  (DVE) system will be used for removing
LNAPL, a potential source of groundwater contamination.  The groundwater monitoring component of
the preferred alternative will not interfere with industry in the area and will provide
protection by detecting any offsite migration of contaminants and the need for further action at

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the Site.

Remedial action is underway at other nearby Superfund sites, and collectively these activities
will reduce risks associated with contamination in the area. By cleaning up these sites, the
potential environmental liability associated with the affected properties is reduced, the
property values increase, and the marketability of the area is enhanced.

Comment: A community member at the public meeting wanted to know what would be done with the
groundwater that will be removed during operation of the DVE system.

EPA Response: Contaminated groundwater that is extracted along with the LNAPL by the DVE system
will be treated at the site for the removal of organic and metal contaminants and will be
returned to the alluvial aguifer system by onsite groundwater re-injection or infiltration.
Specific engineering details of the groundwater treatment and re-injection system will be
developed during the remedial design phase of the project. It is currently estimated the
groundwater removal rate during operation of the DVE system will be approximately 20 gallons per
minute (ppm).

Comment: A written comment was received indicating concern that groundwater issues that have
been evaluated and addressed under OU3 are not explicitly excluded from coverage under OU4 in
the Proposed Plan. The author asked EPA to clarify in the OU4 ROD that groundwater in the
vicinity of the 48th and Holly Landfill has been addressed under the OU3/OU6 Remedial
Design/Remedial Action (RD/RA) as specified in the Statement of Work to the OU3/OU6 Unilateral
Administrative Order (UA) for RD/RA.

EPA Response: Due to the limited available space and the scope of the Proposed Plan, only a
general overview of OU3/OU6 activities was provided. The OU4 ROD indicates that groundwater
beneath the Landfill and related to the Landfill is addressed in the OU3/OU6 ROD.

Comment: Another written comment was received concerning Table 2 (Remedial Alternative
Screening Matrix) of the OU4 Proposed Plan. The author believed that the long-term
effectiveness and permanence of Alternative 2 (i.e., monitoring and institutional controls)
should be designated as "limited" rather "none" because these actions provide reliable controls
for future management of untreated materials and thereby reduce the residual risk associated
with the Sand Creek Superfund Site.

EPA Response: Compared with the other alternatives developed for OU4, Alternative 2 provides
the second lowest degree of long-term effectiveness and permanence. Alternative 2 is largely
dependent on the willingness of property owners and local governments to implement and enforce
institutional controls. EPA has little authority with respect to establishing and enforcing
institutional controls. However, the proposed remedy for OU4 (Alternative 3) combines LNAPL
removal with institutional controls and groundwater monitoring and, therefore, provides a
greater degree of long-term effectiveness and permanence.

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