PB97-964405
EPA/541/R-97/195
January 1998
EPA Superfund
Record of Decision:
Rocky Flats Plant (USDOE), OU 1
Golden, CO
2/27/1997
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CORRECTIVE ACTION DECISION/RECORD OF DECISION
DECLARATION
SITE NAME AND LOCATION
Rocky Flats Environmental Technology Site, Operable Unit 1: 881 Hillside Area, Jefferson
County, Colorado
STATEMENT OF BASIS AND PURPOSE
This decision document presents the selected remedial action/corrective action for the
Rocky Flats Environmental Technology Site (Rocky Flats) Operable Unit (OU) 1: 881
Hillside Area, located near Golden, Colorado. The selected remedial action was chosen in
accordance with the Comprehensive Environmental Response Compensation and Liability
Act (CERCLA) of 1980, as amended by the Superfund Amendments and Reauthorization
Act (SARA) of 1986, the Colorado Hazardous Waste Act (CHWA) and to the extent
practicable, the National Oil and Hazardous Substances Pollution Contingency Plan
(NCP). The Resource Conservation and Recovery Act (RCRA) is administered through
the CHWA by the Colorado Department of Public Health and Environment (CDPHE). OU
1 was investigated and a remedial action was selected in compliance with the Federal
Facility Agreement and Consent Order - Interagency Agreement-(IAG) signed by the U.S.
Department of Energy (DOE), the State of Colorado, and the U.S. Environmental
Protection Agency (EPA) on January 22,1991. The selected remedial action is also
consistent with the Federal Facility Agreement and Consent Order - Rocky Flats Cleanup
Agreement (RFCA) signed by DOE, the State of Colorado and EPA on July 19,1996.
RFCA is now the governing cleanup agreement for Rocky Flats, and the selected remedy
for OU 1 will be implemented in accordance with RFCA The remedial action selection is
based on the administrative record file for OU 1, and the State of Colorado concurs on the
selected remedy.
ASSESSMENT OF THE SITE
Actual or threatened releases of hazardous substances from this site, if not addressed by
implementing the response action selected in this Corrective Action Decision/Record of
Decision (CAD/ROD), may present a future threat to public health, welfare, or the
environment.
DESCRIPTION OF THE SELECTED REMEDY
OU 1:881 Hillside Area is one of sixteen geographically defined OUs at Rocky Flats that
are identified in the LAG. RFCA consolidates these sixteen operable units into a fewer
number, but OU 1 remains as a separate operable unit due to the fact that it is farther along
in the administrative process and is nearing completion. OU 1 is composed of eleven
Individual Hazardous Substance Sites (IHSSs). The selected remedy presented in this
CAD/ROD includes three primary components:
1. This action addresses the principal threat posed by OU 1 by excavating subsurface soil
contamination at IHSS 119.1, a former drum and scrap metal storage area, thereby
removing the current source of groundwater contamination. The 'major components of
the selected remedial action at IHSS 119.1 (Soil Excavation and Groundwater
Pumping) include:
• Excavation of approximately one thousand to two thousand cubic yards of
contaminated subsurface soils at IHSS 119.1;
• Extraction and then ultraviolet/hydrogen peroxide and ion-exchange treatment of
contaminated groundwater from the excavation; and
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• Either thermal-treatment and replacement of excavated soil into the original
excavation, disposal of excavated soil in an on-site waste disposal cell, or off-site
disposal of excavated soil.
2. Institutional controls will be maintained throughout the OU 1 area in a manner
consistent with RFCA, the Rocky Flats Vision, and the Action Levels and Standards
Framework (ALF) (Attachment 5 to RFCA). These documents recognize that the
reasonably foreseeable future land use for the OU 1 area is restricted open space. The
institutional controls will ensure that the restricted open space land use is maintained for
the OU 1 area and that domestic use of groundwater within the OU 1 area is prevented.
If the reasonably foreseeable future land use for the OU 1 area changes when final
sitewide land use decisions are made, this remedy will be reexarained to ensure
protection of human health and the environment The specific mechanisms (for
example, deed restrictions) to ensure the implementation and continuity of the necessary
institutional controls have not been included in this CAD/ROD. Currently, these
mechanisms are envisioned to be placed in the Final Sitewide CAD/ROD or in this
CAD/ROD during one of the five-year reviews of this document However, should the
Final CAD/ROD not occur or not include these institutional control mechanisms, this
OU 1 CAD/ROD will be revised to include them, if it does not already include them as a
result of a five-year review. The institutional controls can also be removed at one of the
above times, if it is deemed appropriate to do so by the parties.
3. Because of the groundwater and land use controls, the low amounts of contamination in
OU 1 outside of IHSS 119.1, and the low levels of risk associated with the
contamination, no remedial action will be taken at the remaining ten IHSSs in OU 1.
Any surface soil contamination at OU 1 will be addressed jointly with surface soil
contamination at the 903 Pad, Mound and East Trenches area (formerly OU 2).
STATUTORY DETERMINATIONS
The selected remedy for OU 1 satisfies the statutory requirements of CERCLA Section
121. The selected remedy is protective of human health and the environment complies
with Federal and State requirements that are legally applicable or relevant and appropriate to
the remedial action, and is cost-effective. This remedy utilizes permanent solutions and
alternative treatment technologies to the maximum extent practicable and satisfies the
statutory preference for remedies that employ treatment that reduces toxicity, mobility, or
volume as a principal element Because this remedy will result in hazardous substances
remaining in groundwater, a review will be conducted within five years after
commencement of the remedial action to ensure that the remedy continues to provide
adequate protection of human health and the environment
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Jessie Rotferson, Manage
U.S. Department of Energy, Rocky Flats Field Office
Date
Max H. Dodson, Assistant Regional Administrator
Office of Ecosystem Protection and Remediation
U.S. Environmental Protection Agency, Region VIE
Date
Howard Roitman, Director
Hazardous Materials and Waste Management Division
Colorado Department of Public Health and Environment
Date
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Jessifc/Kboerson, Manager
U.S. Departmeni of Energy, Rocky Flats Field Office
Dale
Max H. Dodson, Assistant Regional Administrator
Office of Ecosystem Protection and Remediation
U.S. Environmental Protection Agency, Region VBI
Date
Howard Roitman, Director
Hazardous Materials and Waste Management Division
Colorado Department of Public Health and Environment
Date
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DECISION SUMMARY
SITE NAME. LOCATION AND DESCRIPTION
The Rocky Flats Environmental Technology Site is located approximately sixteen miles
northwest of downtown Denver, in northern Jefferson County, Colorado. A copy of a site
location map is attached (Figure 1). Most Rocky Flats structures are located within the
industrialized area of Rocky Flats, which occupies approximately four hundred acres and is
surrounded by a buffer zone of approximately 6,150 acres. OU 1 is located adjacent to and
on the south side of the Rocky Flats industrial area, on the hillside south and east of
Building 881 and north of Woman Creek (Figure 2).
Geological Setting
Rocky Flats is located along the eastern edge of the southern Rocky Mountain region,
immediately east of the Colorado Front Range. The site is located on a broad, eastward-
sloping pediment that is capped by alluvial deposits of Quaternary age (i.e.. Rocky Flats
Alluvium). The tops of alluvial-covered pediments are nearly flat but slope eastward at
fifty to two hundred feet per mile. At Rocky Flats, the alluvial-covered pediment surface is
dissected by a series of east-northeast trending stream-cut valleys. The bases of the valleys
containing Rock Creek, North and South Walnut Creeks, and Woman Creek lie fifty to two
hundred feet below the elevation of the older pediment surface. These valleys incise into
the bedrock underlying alluvial deposits, but most bedrock is concealed beneath colluvial
material accumulated along the gentle valley slopes. The highest point in the immediate
vicinity of OU 1 is Building 881, which is approximately six thousand feet above mean sea
level. The lowest point is at Woman Creek, about 5,830 feet above mean sea level.
Surface Water
Rock Creek, North and South Walnut Creeks, and Woman Creek are intermittent streams
that flow generally from west to east at Rocky Flats. Surface water within Woman Creek,
which flows along the base of the Building 881 hillside south of OU 1, and which is not
diverted to Mower Reservoir flows into Woman Creek Reservoir, which is part of the
Standley Lake Protection Project The water in Woman Creek Reservoir is detained and
then pumped to Walnut Creek drainage downstream of Great Western Reservoir. The
South Interceptor Ditch (SID) crosses OU 1 between the security area and Woman Creek.
Land Use
Land use within ten miles of Rocky Flats includes residential, commercial, industrial, parks
and open space, agricultural and vacant, and institutional classifications. Most residential
use within five miles of Rocky Flats is located northeast, east and southeast of Rocky
Flats. Commercial development is concentrated near residential developments north and
southwest of Standley Lake and around Jefferson County Airport, located approximately
three miles northeast of Rocky Flats. Industrial land use within five miles of the site is
primarily quarrying and mining operations. Natural resources associated with the
quarrying and mining activities include sand, gravel and coal. Irrigated and non-irrigated
croplands, producing primarily wheat and barley, are located north and northeast of Rocky
Flats and in scattered parcels adjacent to the east boundary of the site. Several horse
operations and small hay fields are located south of Rocky Flats. Much of the vacant land
adjacent to Rocky Bats is rangeland.
OU 1
OU 1 is composed of eleven IHSSs, which are specific locations where solid wastes,
hazardous substances, pollutants, contaminants, hazardous wastes, or hazardous
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constituents may have.been disposed or released to the environment within the Rocky Flats
site at any time. Figure 2 shows the locations of these EHSSs and a description of each
IHSS is provided in Table 1.
SITE HISTORY AND ENFORCEMENT ACTIVITIES
Rocky Flats is a government-owned, contractor operated facility that is part of the
nationwide nuclear weapons complex. The site was operated for the U.S. Atomic Energy
Commission (AEC) from its inception during 1951 until the AEC was dissolved in 1975.
Responsibility for Rocky Flats was then assigned to the Energy Research and Development
Administration (ERDA), which was succeeded by DOE in 1977. Until 1992 operations at
Rocky Flats consisted of fabrication of nuclear weapons components from plutonium,
uranium, stainless steel and beryllium. Building 881, which is adjacent to OU 1, was used
for enriched uranium operations and stainless steel manufacturing. The laboratories in
Building 881 also performed analyses of the materials generated in production. Parts made
at the plant were shipped elsewhere for assembly. Support activities at Rocky Flats
included chemical recovery and purification of recyclable transuranic radionuclides and
research and development in metallurgy, machining, nondestructive testing, coatings,
remote engineering, chemistry and physics. These activities resulted in the generation of
radioactive, hazardous and mixed wastes. On-site storage and disposal of these wastes has
contributed to hazardous and radioactive contamination in soils, surface water and
groundwater. Originally the site was named the Rocky Flats Plant, but in 1994 it was
renamed the Rocky Flats Environmental Technology Site to better reflect its new mission of
environmental restoration and the advancement of new and innovative technologies for
waste management, characterization and remediation.
On January 22,1991, a Federal Facility Agreement and Consent Order (i.e., the IAG) was
signed by DOE, EPA and the State of Colorado. Within the IAG eleven IHSSs were
assigned to OU 1: 102, 103, 104, 105.1, 105.2, 106, 107, 119.1, 119.2, 130 and 145
(see Table 1 for a description of these IHSSs and Figure 2 for the location of each IHSS
within OU 1). The IAG provided guidance and direction for investigating the OU 1
IHSSs. As per the IAG, draft and final Work Plans and a draft and final RCRA Facility
Investigation/Remedial Investigation (RFI/RI) report were prepared and submitted to the
regulatory agencies. The RFI/RI report for OU 1 was prepared for subraittal of
documentation and data necessary to determine if the risk from the OU 1 IHSSs warrants
the need for remedial action.
During 1992, as an interim action, a French Drain was constructed across a portion of OU
1 to protect Woman Creek from contaminated groundwater present in OU 1. The French
Drain, along with an extraction well, collects contaminated groundwater moving towards
Woman Creek. The collected groundwater is transported to an ultraviolet/hydrogen
peroxide and ion-exchange water treatment system located in Building 891. In addition,
during 1994, plutonium contaminated surface soil "hot spots" that were located in IHSSs
119.1 and 119.2 were removed from OU 1. This hot spot removal was conducted under
an Accelerated Response Action per the IAG.
The Proposed Plan and Draft Modification of the Rocky Flats RCRA Permit for OU 1
(Proposed Plan) was prepared and released for public comment in May 1996 pursuant to
the IAG and consistent with the draft RFCA. On July 19,1996, DOE, EPA and the State
of Colorado signed the final RFCA, which has replaced the IAG to become the governing
cleanup agreement for Rocky Flats. Pursuant to the "Operable Unit Consolidation Plan" in
RFCA, OU 1 will continue through the CAD/ROD process with EPA as the lead regulatory
agency.
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HIGHLIGHTS OF COMMUNITY PARTICIPATION
The first Final Phase ffl RFI/RI report for OU 1 was submitted to EPA and CDPHE in
November 1993 and the Revised Final Phase HI RFI/RI report was submitted in June
1994. The Proposed Plan for OU 1 was released to the public in May 1996, and was made
available in both the administrative record and in information repositories maintained at
Front Range Community College, the EPA Superfund Records Center, CDPHE, the
Standley Lake Library and the Citizens Advisory Board. The notice of availability for this
document was published in the Rocky Mountain News on May 13, 1996. A public
comment period on the Proposed Plan was held from May 13 to July 12,1996. A public
hearing was held on June 19,1996. At this hearing, representatives from DOE gave a
presentation that summarized the contamination and risks at OU 1, as well as the preferred
remedial alternative for OU 1. DOE also responded to questions about OU 1. In addition,
public comments on the Proposed Plan and Draft Permit Modification were received and
recorded during the public hearing. This record, as well as responses to the written
comments received during the public comment period, is included in the Responsiveness
Summary, which is part of this CAD/ROD. This decision document presents the selected
remedial action for OU 1: 881 Hillside Area at Rocky Flats, chosen in accordance with
CERCLA, as amended by SARA and to the extent practicable, the NCP. The decision for
OU 1 is based on the administrative record.
SCOPE AND ROLE OF OU 1
Because of the complexity of the Rocky Flats site, the site was divided into sixteen
geographically defined OUs in the IAG. CAD/RODs have already been finalized and
signed for three of these OUs (OU 11, OU 15 and OU 16). In all three cases a No Action
decision was determined to be appropriate. Although many of the remaining thirteen OUs
have been consolidated in RFCA. OU 1 remains as an individual operable unit The
selected remedial action presented in this CAD/ROD includes addressing subsurface soil
contamination at IHSS 119.1, a former drum and scrap metal storage area. This action
addresses the principal threat posed by OU 1 by excavating contamination sources in
subsurface soils, thereby removing the current source of groundwater contamination, and
by extracting and treating contaminated groundwater contained at IHSS 119.1. Based on
the results of the final RFI/RI, DOE has determined that the remaining IHSSs within OU 1
are already in a protective state with regard to human health and the environment Thus, no
further action relative to these remaining IHSSs will be taken. Any surface soil
contamination at OU 1 will be addressed jointly with surface soil contamination at the 903
Pad, Mound and East Trenches area (formerly OU 2, which has been consolidated into the
Buffer Zone OU in RFCA). Any additional groundwater associated with OU 1 will be
managed consistent with the Integrated Water Management Plan. Surface water and
suspended sediments transported from OU 1 have historically flowed into Woman Creek or
the South Interceptor Ditch (SID). Since Woman Creek and the SID are being evaluated as
part of OU 5: Woman Creek Priority Drainage, surface water and associated sediments
originating from OU 1 will be addressed as part of OU 5.
SUMMARY OF SITE CHARACTERISTICS
Geology
Geologic units present at the 881 Hillside Area include the Rocky Flats Alluvium at the top
of the hillside, colluvium and artificial fill along central portions of the hillside, and Woman
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Creek Valley Alluvium at the base. These thin (three to eighteen feet) Quaternary age
surficial units are underlain by thick (six hundred to eight hundred feet) Cretaceous
claystones, siltstones and sandstones of the Laramie Formation. The uppermost portion of
the Laramie Formation is disturbed as a result of slumping on the hillside and also contains
numerous fractures primarily due to weathering. This portion of the Laramie Formation is
often referred to as the weathered claystone and may be up to twenty-five feet thick in some
areas.
Surface Features/Surface Water Hydrology
Several erosional and depositional processes have combined to produce gently rolling to
moderately steep slopes on the 881 Hillside. The terrain has been recontoured in several
areas at various times during the construction of Building 881, the placement of fill and
waste materials in several IHSSs, road grading, and the construction of the SID and French
Drain.
Surface water primarily occurs at OU 1 following precipitation and snow melt events after
the soils have become saturated due to infiltration. Surface runoff generally flows south,
where it is intercepted by the SID, and subsequently flows to the C-2 Pond where it is
batched and sampled before being pumped to the Walnut Creek drainage.
Hvdrogeologv
Groundwater occurs under unconfined conditions within the unconsolidated Rocky Flats
Alluvium, colluvium, fill, and weathered claystone section of the Laramie Formation. This
interval is designated as the Upper Hydrostratigraphic Unit (UHSU). Below this,
groundwater is limited to the more porous beds within the Laramie Formation and is
usually confined. This deeper section of strata is designated as the Lower
Hydrostratigraphic Unit (LHSU).
UHSU groundwater is not present across the entire 881 Hillside (OU 1). Groundwater in
the unconsolidated material typically is confined to northwest-southeast trending erosion
incisions in the bedrock surface, referred to as paleochannels, which are masked by the
overlying materials. The extent of groundwater within these paleochannels varies with
seasonal changes in precipitation rates. UHSU groundwater also occurs sporadically
within the upper portion of the Laramie formation within fractures and along slump block
glide planes. As previously discussed, a French Drain was installed between the 881
Hillside and Woman Creek to intercept this shallow unconfined groundwater, and it
extends to a maximum depth of twenty-eight feet below top of bedrock. The French Drain
acts as an effective hydraulic barrier to horizontal migration of UHSU groundwater into
Woman Creek.
Vertical migration between the UHSU and the LHSU is limited by the extremely low
hydraulic conductivity of the claystones within the Laramie Formation. The hydraulic
conductivity of these claystones (1 x 10"' cm/sec) is approximately three orders of
magnitude less than that of the overlying unconsolidated sediments (1 x Iff5 cm/sec), and
as a result the vertical component of migration is extremely small compared to the
horizontal component. In addition, the porous saturated sandstones of the LHSU are
laterally discontinuous, with intervening claystone aquitards effectively limiting horizontal
migration within the LHSU.
Recharge to the UHSU is minimal, and occurs primarily through infiltration of
precipitation. Infiltration rates range from approximately two inches per hour for initial
infiltration to as little as one half inch per hour for final (saturated) infiltration. Discharge
occurs largely through evapotranspiration and surface discharge at seeps and into the SID.
Total volumes of UHSU groundwater at OU 1 varies annually and seasonally, but the Final
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Phase HI RFI/RI report (June 1994) estimated the volume to be approximately 5.0 to 5.8
acte-feet
Flora /Fauna
Grassland habitats are dominant at OU 1, representing about 82% of the total area. Nine
percent is either developed or disturbed; marsh habitat occupies 4%; woodland habitat
constitutes 4%; and shrub habitats account for the remaining 1%. A restored wetlands was
created to mitigate damages resulting from installing the French Drain. Wildlife species are
typical of those in similar habitats throughout the foothills area. As a result of limited
ephemeral surface water, aquatic species with short life cycles and small habitats, such as
bentnic macroinvertebrates, have developed as opposed to fish populations.
Site Contamination
A detailed methodology was developed during the Phase HI RFI/RI for determining the
nature and extent of contamination at OU 1. Using this methodology, analytes within the
following chemical classes were analyzed: volatile organic compounds (VOCs),
semivolatile organic compounds (SVOCs), pesticides, polychlorinated biphenyls (PCBs),
metals, and radionuclides. The following media were assessed for the presence of
contamination: surface soil, subsurface soil, groundwater, surface water/seeps, and
sediments. Based on this analysis, VOCs, SVOCs, metals, and radionuclides were
identified as contaminants at OU 1 (see Table 2). Note that the data in Table 2 does not
reflect the 1994 surface soil hotspot removal.
From this and other data collected, the Phase HI RFI/RI concluded that in OU 1 only IHSS
119.1 contains a significant source of contamination in the subsurface soil. The primary
contaminants identified at IHSS 119.1 are as follows: carbon tetrachloride; 1,1-
dichloroethene;tetrachloroethene; l,l,l-trichloroethane;trichloroethene; and selenium. No
radioactive contamination was identified in the subsurface soil at IHSS 119.1. Also, based
on the data collected during the Phase HI RFI/RI, the other IHSSs in OU 1 were not found
to be contamination source areas and do not contribute significantly to groundwater
contamination. Therefore, the other IHSSs do not warrant any further remedial action,
and, as previously stated in the "Scope and Role of OU 1" section of this CAD/ROD, the
selected remedial action for OU 1 addresses subsurface soil contamination and groundwater
contamination at IHSS 119.1.
Groundwater in OU 1 is contaminated by VOCs and metals (see Table 2). Releases of
VOCs within IHSS 119.1 are presumed to have occurred in the form of dense non-aqueous
phase liquids (DNAPLs). This conclusion is based on the fact that drums at this IHSS
contained unknown quantities and types of solvents, coupled with the presence of
chlorinated solvent concentrations in groundwater at levels approaching 7% of the
solubility limits of the substances. The presence of mobile or residual DNAPL at this
location is inferred only, since DNAPL has not been directly observed, and maximum
measured concentrations of VOCs in subsurface soil is less than 2.0 mg/1. Table 3 lists
monitoring wells in the vicinity of IHSS 119.1 and their contaminant concentration range
for the Contaminants of Concern (COCs) for the years 1987 through 1995. The locations
of these wells are shown on Figure 3. Only two of the wells (974 and 4387) have
concentrations exceeding 1% of the compound solubility.
The lateral extent of groundwater contamination is generally limited to an area north of the
SID. The occurrence of contaminants in LHSU groundwater is limited to relatively low
levels of VOCs (less than 100 jig/l) and localized occurrences of metals, particularly
selenium (concentrations ranging from below background to fifteen times the background
levelofSOpg/l).
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A soil gas survey was conducted during early 1996 to more accurately define the extent and
approximate volume of contaminated subsurface soil that will be excavated at IHSS 119.1.
Based on this soil gas survey, two potential subsurface soil contamination source areas
were identified (see Figure 3), resulting in an approximate total volume of subsurface soil
to be excavated between one thousand and two thousand cubic yards.
Fate and Transport
In general, contaminant migration at the site was evaluated in terms of the identified
pathways at OU 1. Migration of VOCs and metals in groundwater at IHSS 119.1 is
restricted to northwest-southeast oriented channel features incised on the bedrock surface.
The observed extent of groundwater contamination originating from IHSS 119.1 was
compared with the predicted extent to confirm the accuracy of the hydrogeologic conceptual
model. Contaminant transport rates were estimated by calculating groundwater seepage
velocity and contaminant-specific retardation factors (see Table 3). The observed migration
distance of VOC and metal contamination originating from IHSS 119.1 (approximately
three hundred feet) falls within the predicted range. After implementation of the subsurface
soil removal action presented in this CAD/ROD, the present source of this groundwater
contamination will be eliminated.
Radionuclides and SVOCs in surface soils are susceptible to redistribution by wind or
surface water erosion events. Surface soils at OU 1 were contaminated with windblown
low-level radionuclides transported from the 903 Pad area, and any remaining surface soil
contamination will be addressed jointly with surface soil contamination at the 903 Pad area.
Surface water is intercepted by the SID and will be addressed as part of OU 5.
SUMMARY OF SITE RISKS
As part of the Phase El RFI/RI conducted for OU 1, a Baseline Risk Assessment (BRA)
was prepared to identify any current or potential future risks to human health and the
environment The BRA evaluated health risks from surface soil, subsurface soil,
groundwater, surface water, and sediments within the OU 1 boundaries.
The surface soil hot spot removal action conducted at OU 1 for plutonium, americium and
uranium contamination reduced the risk from this contaminant group and medium by 100
times. The risk from surface soils was reduced to 1 in 100,000 (10"s) after the OU 1 hot
spot removal was completed. This contaminant group contributed the highest risk to a
human receptor in the OU 1 BRA. With respect to subsurface soils and groundwater, the
primary contaminants identified in the Phase ID RFI/RI were: carbon tetrachloride; 1,1-
dichloroethene; tetrachloroethene; 1,1,1-trichloroethane; trichloroethene; and selenium.
The BRA identified potential health risks from these contaminants associated with current
and possible future exposure scenarios at OU 1. The scenarios originally examined in the
OU 1 BRA are as follows: current on-site commercial/industrial; current off-site
residential; future on-site commercial/industrial; future on-site ecological reserve; and future
on-site residential. However, not all of these scenarios are considered valid or currently
possible.
The Rocky Flats Future Site Use Working Group, consisting of participants from DOE,
EPA, CDPHE, and major stakeholders, recommended in the June 1995 "Future Site Use
Recommendations" report that the future on-site residential land use scenario not be
considered. The commercial/industrial exposure scenario was recommended for use within
the industrial area of the plant and the open space exposure scenario was recommended for
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the buffer zone. These recommendations are consistent with the conceptual land uses in the
ALF and with the Rocfy Flats Vision. The OU 1 area lies on the border between these two
anticipated land uses. DOE has not yet made a final determination regarding the future land
uses for OU 1. This determination will be consistent with RFC A and the Rocky Flats
Vision and will take into consideration the fact that the hillside at OU 1 has shown the
potential for landslides and slumping. This would make the construction of structures at
OU 1 complicated and problematic. In addition, as stated in the ALP, domestic use of
groundwater will be prevented through institutional controls.
There are no health risks associated with the future open space park exposure scenario from
OU 1 subsurface soil or groundwater since there are no exposure routes available from
either medium. The carcinogenic risk calculated in the OU 1 BRA for the future on-site
commercial/industrial worker in the industrial area from subsurface soils and groundwater
is 2.4 x Iff4. This risk is slightly above EPA's acceptable risk range of KT4 to 10"*.
The Phase HI RFI/RI identified no significant environmental risk; therefore, environmental
risks warrant no further examination.
In conclusion, actual or threatened releases of hazardous substances from this site, if not
addressed by implementing the response action selected in this CAD/ROD, may present an
imminent and substantial endangerment to public health, welfare, or the environment.
DESCRIPTION OF ALTERNATIVES
Six candidate remedial alternatives were compiled from the treatment technologies that
passed a detailed screening process conducted during the Corrective Measures
Study/Feasibility Study (CMS/FS), including the No Action alternative. A description of
each remedial alternative is given below. The six remedial alternatives are: No Action
(Alternative 0), Institutional Controls with the French Drain (Alternative 1), Groundwater
Pumping and Soil Vapor Extraction (Alternative 2), Groundwater Pumping and Soil Vapor
Extraction with Thermal Enhancement (Alternative 3), Hot Air Injection with Mechanical
Mixing (Alternative 4), and Soil Excavation with Groundwater Pumping (Alternative 5).
For Alternatives 2,3,4 and 5, the volume of soil to be remediated was estimated, from the
results of a recent soil gas survey performed at OU 1, to be between one thousand and two
thousand cubic yards of soil (approximately a fifty feet by fifty feet by twelve feet deep
excavation). During implementation of the remedy, confirmatory soil sampling will be
performed to determine where the excavation can be terminated, based on cleanup levels
identified in the ALF.
Alternative 0: No Action
The No Action alternative is required by CERCLA as a baseline alternative with which to
compare other alternatives. The No Action alternative uses results of the Baseline Risk
Assessment to define exposure levels to human and environmental receptors at the site
under existing conditions, and specifically excludes remedial activities.
Use of the existing French Drain groundwater collection system would be discontinued
under this alternative. Groundwater would, therefore, flow toward Woman Creek. The
only activity associated with the No Action alternative is groundwater monitoring to detect
changes in contaminant concentrations or migration patterns. Monitoring would begin
immediately and would continue until a determination could be made that monitoring is no
longer required. Existing wells no longer deemed necessary would be abandoned as
appropriate.
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No remedial time frame is established for this alternative since the alternative relies solely
on natural contaminant degradation and attenuation processes to meet Remedial Action
Objectives (RAOs). A thirty year monitoring time frame is assumed, in accordance with
EPA guidance. It is estimated that it will cost approximately $1.9 million to implement this
remedial alternative and continue monitoring groundwater for thirty years.
Alternative 1: Institutional Controls with the French Drain
Alternative 1 seeks to achieve RAOs by restricting access to wells impacted by OU 1
contaminants through institutional controls, while continuing to treat groundwater collected
by the existing French Drain at the Building 891 water treatment system. Institutional
controls would also be employed to prevent domestic groundwater use at OU 1. Further
degradation of groundwater would be minimized by continued containment and treatment
of the groundwater. Subsurface contamination sources would eventually be depleted by
dissolution to groundwater, although the length of time for this to occur would be quite
extensive.
The existing French Drain and Building 891 treatment system would continue to operate
until no longer deemed necessary based on contaminant concentrations in the groundwater.
Groundwater monitoring would continue for as long as required to verify that contaminant
concentrations in groundwater have been permanently reduced below appropriate limits.
Wells no longer deemed necessary for monitoring would be abandoned as appropriate.
No remediation time frame is defined for Alternative 1 since the French Drain system is
currently operational and would continue to operate until acceptable contaminant
concentrations are achieved. Based on current operations of the existing French Drain
system, it is reasonable to assume that due to the slow groundwater collection rate,
operation of the French Drain system would be required for an extensive period of time
before RAOs are achieved. Experience with similar remedial actions at similar sites
suggests that extremely long time frames are required for complete contaminant depletion.
For the purpose of preparing a cost estimate, a thirty year time frame for remedial activities
is assumed, based on EPA guidance. Based on this time frame, the estimated cost for
completion of Alternative 1 is $17.5 million.
Alternative 2; Groundwater Pumping and Soil Vapor Extraction
Alternative 2 seeks to achieve RAOs by dewatering the identified IHSS 119.1 source area
using conventional pumping techniques, and by implementing a localized soil vapor
extraction (SVE) system. Risk from contaminated groundwater would be eliminated by
extraction and treatment, while further degradation of groundwater would be minimized by
removal of contaminant sources through SVE.
SVE would enhance volatilization and subsequent contaminant recovery from saturated
soils, unsaturated soils and groundwater at OU 1. SVE targets contaminants that have
partitioned to the aqueous phase, have adsorbed onto subsurface soils, exist in a free phase
or occupy soil pore spaces in a vapor phase. Discrete pools of groundwater located in
IHSS 119.1 would be extracted via the existing French Drain and one to three additional
recovery wells. Collected groundwater would be treated by the existing Building 891
water treatment system or other appropriate facility. These same areas, once desaturated,
would be subjected to SVE to enhance the removal of any residual contaminants.
SVE can be significantly influenced by site geology and contaminant characteristics.
Geological factors that can influence the success of SVE include depth to groundwater,
subsurface soil/rock type and surface permeability. At OU 1, the subsurface soils contain
large amounts of clay which would inhibit the effectiveness of this technology.
Contaminants that are effectively recovered by SVE exhibit a vapor pressure of 1.0 mm of
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mercury or more at 20.degrees Celsius and which have a dimensionless Henry's Law
constant greater than 0.01. The contaminants identified at OU 1 would be amenable to
recovery by SVE.
It is also assumed that the vapor extraction wells in IHSS 119.1 would be approximately
two to six inches in diameter. The wells would be operated cyclically to enhance recovery
and would be used in combination with a granular activated carbon (GAC) unit to treat
extracted vapors. The existing French Drain and Building 891 treatment system would
continue to operate during the remedial activities, but after remediation of the source is
complete the French Drain would be decommissioned and groundwater collection and
treatment would cease. Groundwater monitoring would be performed consistent with the
Integrated Water Management Plan after completion of the remedial action.
The remediation time frame, which is considered to be the time until protection is achieved
by the remedial action, is estimated to be approximately five years for Alternative 2. Based
on this time frame and other technical information defining this alternative, the estimated
cost for completion of Alternative 2 is $8.1 million.
Alternative 3; Groundwater Pumping and SVE with Thermal Enhancement
Alternative 3 seeks to achieve RAOs by combining SVE as described in Alternative 2 with
thermal recovery enhancement techniques. Groundwater extraction and treatment would be
employed to address groundwater contamination, while SVE with thermal enhancement
would be used to remove contamination sources. This alternative considers two innovative
treatment technologies that can effect an increase in subsurface soil temperatures and thus
enhance SVE: radio frequency heating and electrical resistance (ohmic) heating. These
technologies are discussed in detail in the OU 1 CMS/FS report In general, these thermal
enhancement techniques enhance the success of the SVE by increasing the temperature in
the subsurface soil which allows more complete and faster volatilization, and thus
recovery, of organic constituents in the soil. The increase in temperature of the subsurface
soil also assists in dewatering the area by vaporizing pore space moisture.
As in Alternative 2, the existing French Drain and Building 891 treatment system would
continue to operate until remediation of the contamination source is complete, at which time
the French Drain would be decommissioned and groundwater collection and treatment
would cease. Groundwater monitoring would be performed consistent with the Integrated
Water Management Plan after completion of the remedial action.
The remediation time frame for Alternative 3 is estimated to be three years. Based on this
time frame and other technical information defining this alternative, the estimated cost for
completion of Alternative 3 is $7.5 million.
Alternative 4: Hot Air Injection with Mechanical Mixing
Alternative 4 seeks to achieve RAOs through an in-situ technology that combines hot air
stripping with vigorous mixing of subsurface media. Contaminated groundwater at IHSS
119.1 would be remediated through extraction and treatment in the Building 891 facility,
and the IHSS 119.1 subsurface soil contamination source would be addressed with hot air
injection and mechanical mixing.
This technology operates under the same basic principles of SVE and thermal enhancement
discussed previously, but combines these principles with vigorous mechanical mixing to
increase the effectiveness of the subsurface soil treatment. The primary treatment system in
this alternative would consist of a caterpillar mounted drill rig with specialized drilling
equipment The drill equipment is capable of delivering treatment reagents, such as hot air
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or steam, via piping in a hollow drill bit shaft that has mixing/cutting blades four to twelve
feet in diameter.
Groundwater extraction wells would be placed in previously treated soil columns.
Dewatering of a small area prior to treating the initial soil column would be accomplished
via an extraction well drilled with conventional drilling equipment. Extracted groundwater
would be treated in the existing Building 891 treatment system. The treatment columns, or
drill shafts, would overlap by thirty percent to ensure adequate treatment throughout the
entire site. Four to six columns can be treated per day, depending on site conditions.
The existing French Drain and Building 891 treatment system would continue to operate
during the remedial activities, but after remediation of the source is complete the French
Drain would be decommissioned and groundwater collection and treatment would cease.
Groundwater monitoring would be performed consistent with the Integrated Water
Management Plan after completion of the remedial action.
The remediation time frame for Alternative 4 is estimated to be two years. Based on this
time frame and other technical information defining this alternative, the estimated cost for
completion of Alternative 4 is $4.3 million.
Alternative 5: Soil Excavation with Groundwater Pumping
Alternative 5 is intended to achieve RAOs through excavation of contaminated subsurface
soils and contaminated groundwater beneath IHSS 119.1. Based on the report of a recent
soil gas survey that was performed at IHSS 119.1 ("Sampling and Analysis Report -
Identification and Delineation of Contaminant Source Area for Excavation Design
Purposes", April 1996), the estimated volume of soil that will be excavated from IHSS
119.1 is one thousand to two thousand cubic yards (approximately fifty feet by fifty feet by
twelve feet deep).
Contaminated groundwater would be extracted from the excavation and treated in the
Building 891 water treatment system. The excavated subsurface soils would either be
treated on-site with a thermal desorption unit and returned to the excavation, disposed in an
on-site disposal cell, or disposed off-site.
The existing French Drain and Building 891 treatment system would continue to operate
during the remedial activities, but after remediation of the source is complete the French
Drain would be decommissioned and groundwater collection and treatment would cease.
Groundwater monitoring would be performed consistent with the Integrated Water
Management Plan after completion of the remedial action.
The remediation time frame for Alternative 5 is estimated to be four to six months. Based
on this time frame and other technical information defining this alternative, the estimated
costs for completion of Alternative 5, depending on how the excavated soil is managed, is
as follows: if the soil is treated on-site and returned to the excavation the cost is
approximately $3.5 million; if the soil is disposed off-site the cost is approximately $3.9
million; and if the soil is disposed in an on-site disposal cell without treatment the cost is
approximately $3.3 million.
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SUMMARY OF THE COMPARATIVE ANALYSIS OF ALTERNATIVES
Threshold Criteria
Overall Protection of Human Health and the Environment: Alternative 5 provides the best
overall protection of human health and the environment by providing the largest reduction
in exposure potential within the shortest amount of time through removal of the
contamination source. Alternatives 2,3 and 4 provide the next best level of overall
protection of human health and the environment, based on the fact that they are designed to
reduce exposure potential through in place remediation of the contamination source at IHSS
119.1. However, these alternatives involve technologies that are not proven to be effective
in the clay soils that are present at IHSS 119.1. Therefore, they would not be as thorough
in removing the contamination source as Alternative 5, and they also involve longer
remediation timeframes. Alternative 1 protects human health and the environment by
collecting and treating contaminated groundwater, as well as by implementing certain
institutional controls to reduce exposure to the contaminants, but it does not address the
contamination in the subsurface soil and, therefore, is not as protective as the previously
discussed alternatives. Finally, Alternative 0 offers the least amount of protection to human
health and the environment because it does not involve any source removal, containment or
other controls.
Compliance with Applicable or Relevant and Appropriate Requirements f ARARs): The
ARARs that have been identified and analyzed for each alternative for the contaminants of
concern at IHSS 119.1 are as follows:
• Classifications and Numeric Standards (5 CCR 1002-8,3.8, So. Plane River Basin)
• Colorado Basic Standards for Surface Water (5 CCR 1002-8,3.1, Segment 4a of Big
Dry Creek):
carbon tetrachloride 0.25 ng/L
1,1-dichloroethene 0.057 ng/L
tetrachloroethene 0.8 pig/L
1,1,1 -trichloroethane 200 jlg/L
trichloroethene 2.7 Hg/L
selenium 20 Hg/L (acute); 5 jig/L (chronic)
• Colorado Hazardous Waste Regulations (6 CCR 1007-3 Parts 264 and 268)
• Colorado Air Pollution Control Regulations (5 CCR 1001-5, Regulation 7)
• Colorado Nongame, Endangered or Threatened Species Conservation Act (CRS 33-2-
101).
The State contends that 5 CCR 1002-8,3.12 (Site Specific Water Quality Classifications
and Standards for Ground Water) and 5 CCR 1002-8,3.11 (Basic Standards for Ground
Water) are ARARs. DOE disagrees with this contention. Both parties reserve their
respective rights to raise this issue and supporting arguments in any relevant forum. The
parties do not anticipate that this disagreement will ripen into a formal dispute because 5
CCR 1002-8, 3.12 adopts the standards set forth in 5 CCR 1002-8, 3.1 and 3.8, and these
standards are consistent with the enforceable standards set forth in the ALE In addition, 5
CCR 1002-8, 3.11 contains standards which are generally consistent with or less stringent
than the standards set forth in 5 CCR 1002-8,3.1 and 3.8.
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Alternatives 2,3,4 and 5 are expected to meet all of the above identified ARARs, while
Alternatives 0 and 1 are expected to meet all ARARs except that they may not meet the
Colorado Basic Standards for Surface Water. Therefore, Alternatives 0 and 1 rank low
under this criterion.
Primary Balancing Criteria
Long-Term Effectiveness and Permanence: Alternative 5 provides the highest level of
long-term effectiveness and permanence since it removes both groundwater contamination
and subsurface soil contamination sources in IHSS 119.1, and thereby prevents any further
contamination of groundwater. Alternatives 2,3 and 4 also remove groundwater
contamination, but are not as effective at removing subsurface soil contamination sources
because the technologies used in these alternatives have not been proven effective in the
clay soils at IHSS 119.1. Alternative 1 provides even less long-term effectiveness and
permanence since it only removes groundwater contamination, but not subsurface soil
contamination sources. Alternative 0 provides the lowest level of long-term effectiveness
and permanence since it does not treat or remove any contamination at IHSS 119.1.
Reduction of Toxicitv. Mobility, or Volume Through Treatment: Alternative 5 provides the
highest reduction of mobility because it removes the primary source of contamination and
treats contaminated groundwater, thereby preventing any further migration of
contaminants. In addition, if the excavated soil is treated, as discussed in the "Description
of Alternatives" section, Alternative 5 also provides the highest reduction of toxicity and
volume through treatment Alternatives 2,3 and 4 provide the next highest level of
toxicity, mobility and volume reduction since they involve groundwater treatment as well as
in place treatment of the subsurface soil contamination source. Alternative 1 provides less
reduction of toxicity, mobility and volume through treatment because it treats only
contaminated groundwater and does not address the subsurface soil contamination.
Alternative 0 ranks lowest in this category because it treats neither groundwater nor
subsurface soil contamination, and thus provides no reduction in toxicity, mobility or
volume through treatment.
$hort-Term Effectiveness: This criterion evaluates community, environmental and site
worker protection during the implementation of the remedy. It also evaluates the
effectiveness and reliability of protective measures during implementation and the time until
RAOs are achieved.
Alternatives 0 and 1 rank highest under the community, environmental and site worker
protection during implementation portion of this criterion because they involve no
disturbance of the existing site and little or no worker involvement Alternatives 2,3,4
and 5 involve some site disturbance, but the disturbance is not expected to create a
significant impact on the community, the environment or site workers. Alternative 3 has
the potential to present increased hazards to site workers due to the heating of the
subsurface soil.
For the effectiveness and reliability of protective measures during implementation and for
the time until RAOs are achieved, Alternative 5 ranks the highest. Excavation has been
proven to be the most effective and reliable of the technologies presented here when applied
to clay soils. In addition, DOE anticipates that it will take only four to six months for
RAOs to be achieved once implementation of Alternative 5 has begun. The amount of time
until RAOs are achieved for Alternatives 2,3 and 4, once implementation of the alternative
has begun, is five years, three years and two years, respectively. Alternatives 0 and 1 are
the least effective and reliable since they do not address the subsurface soil contamination
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source. Also, the amount of time until RAOs are achieved for these two alternatives is
unknown, but likely to be quite extensive, since they rely on natural degradation of the
contaminants.
Implementabilitv: This criterion evaluates the technical and administrative feasibility of
implementing the alternatives including the availability of materials and services needed
during implementation, as well as the ability to monitor the effectiveness of the remedy.
Alternative 1 is the most easily implementable because it represents the current condition at
OU 1. The only additional work that it would involve would be to implement institutional
controls at OU 1 and perform groundwater monitoring. Alternative 0 is the next most
easily implementable alternative because it involves only decommissioning the French
Drain and performing groundwater monitoring. Alternative 5 is the next most
implementable alternative. Excavation has been proven to be effective and implementable
in clay soils, and the equipment necessary to perform the excavation is readily available.
Also, the effectiveness of Alternative 5 can be easily monitored.
Alternatives 2,3 and 4 use intrusive treatment methods that may pose technical problems,
and are, therefore, less implementable than the other alternatives. For example, soil vapor
extraction (Alternatives 2 and 3) cannot be reliably conducted in clay soils. Alternative 3 is
even more difficult to implement than Alternative 2 because it is still an experimental
technology. Alternative 4 is the most difficult option to implement because of the sloping,
unstable hillside that the drill rig would have to work on, and because of the Limited supply .
of the specialized equipment that is needed.
Cost: This criterion evaluates the capital cost for each alternative, long-term operation and
maintenance (O&M) expenditures required to sustain it, and post-closure costs occurring
after the completion of remediation. Future expenditures are adjusted to present worth
amounts by discounting all costs to a common base year using present worth cost analysis.
Alternative 0 is the least costly since it involves only decommissioning the French Drain
and performing groundwater monitoring for thirty years. The total estimated cost of
Alternative 0 is $1.9 million. Alternative 5 is the next least costly alternative, with the
following estimated costs of completion: $3.3 million if the excavated soil is placed
directly into an on-site waste disposal cell, $3.5 million if the excavated soil is treated on-
site with a thermal desorption unit and placed back into the original excavation, and $3.9
million if the excavated soil is disposed off-site. The cost estimates are based on an
excavation volume of 1000 to 2000 cubic yards of soil (50 feet by 50 feet by 12 feet deep
excavation), which was estimated as the appropriate soil excavation volume in the recent
soil gas survey at IHSS 119.1. These cost estimates include all costs of soil excavation,
handling and management of the soil, operation of the French Drain and groundwater
treatment plant for one year (or until the soil has been excavated), and groundwater
monitoring for thirty years.
Alternative 4 is more costly than Alternatives 0 and 5, with an estimated total cost of $4.3
million. This estimate is based on the same volume of soil as Alternative 5 (1000 to 2000
cubic yards), and includes all costs of performing the hot air injection and mechanical
mixing, operation of the French Drain and groundwater treatment plant for two years, and
groundwater monitoring for thirty years.
Alternative 3 is more costly than the previously discussed alternatives, with an estimated
total cost of $7.5 million, which is also based on a soil volume of 1000 to 2000 cubic yards
for tteatment. This cost estimate includes all costs of performing the soil vapor extraction
with thermal enhancement, operation of the French Drain and groundwater treatment plant
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for three years, and groundwater monitoring for thirty years. Alternative 2 is even more
costly, with an estimated total cost of $8.1 million. Again, this cost estimate is based on a
soil volume of 1000 to 2000 cubic yards for treatment It includes all costs of performing
the soil vapor extraction, operation of the French Drain and groundwater treatment plant for
five years, and groundwater monitoring for thirty years.
Alternative 1 is the most expensive alternative, with an estimated total cost of $17.5
million, which is based on the long-term operation of the French Drain and the water
treatment plant for thirty years and groundwater monitoring for thirty years.
Modifying Criteria
State Acceptance: This criterion addresses the State's comments and concerns regarding
the appropriateness of the selected remedy. The State of Colorado was represented on the
Dispute Resolution Committee that selected the preferred remedial alternative for OU 1 and
agrees with the selection. The State has no outstanding, significant comments or concerns
with the selected remedy.
*•
Community Acceptance: This criterion evaluates the selected remedy in terms of issues and
concerns raised by the public through the public involvement process. At the public
hearing for the OU 1 Proposed Plan on June 19,1996, DOE received one comment from
the public that was supportive of the preferred remedial alternative. During the public
comment period for the OU 1 Proposed Plan, DOE received one set of written comments
from the public, which, in general, expressed concern for funding and timing of the
selected remedy, and requested clarification on several issues in the Proposed Plan. These
comments are addressed in the attached Responsiveness Summary.
Anticipated Damages to Natural Resources: Alternatives 2,3,4 and 5 will not result in any
irreversible damages to natural resources and will improve the quality of soil and
groundwater by excavation and treatment Alternative 1 will not result in any irreversible
damages to natural resources and will improve the quality of groundwater by treatment
Alternative 0 will not result in any irreversible damages to natural resources, but will
continue to degrade the quality of groundwater since the alternative does not involve any
remedial activity. Measures to control and reduce the risk of damages to natural resources
will be considered prior to beginning the remedial activity.
THE SELECTED REMEDY
The selected remedy for OU 1 includes three primary components:
1. Excavating subsurface soil contamination at IHSS 119.1, a former drum and scrap
metal storage area, thereby removing the current source of groundwater contamination.
The major components of the selected remedial action at IHSS 119.1, described in
detail below, include:
• Excavation of approximately one thousand to two thousand cubic yards of
contaminated subsurface soils at IHSS 119.1;
• Extraction and then ultraviolet/hydrogen peroxide and ion-exchange treatment of
contaminated groundwater from the excavation; and
• Either thermal treatment and replacement of excavated soil into the original
excavation, disposal of excavated soil in an on-site waste disposal cell, or off-site
disposal of excavated soil.
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This portion of thejelected remedy for OU 1 was chosen by the Dispute Resolution
Committee (DRC)~bn August 25,1995, as part of the dispute resolution process that is
defined in the IAG, which was the governing cleanup agreement at the time of the
decision. At that time, the DRC was composed of DOE's Assistant Manager for
Environmental Restoration, EPA's Federal Facilities Branch Chief, and CDPHE's
Program Manager for the Hazardous Waste Control Program. In choosing the remedial
action for IHSS 119.1, the DRC was interested in controlling groundwater
contamination through source removal. The DRC determined that Alternative 5, Soil
Excavation with Groundwater Pumping, is the most appropriate remedial action for
IHSS 119.1. This remedial action includes excavation of approximately one thousand
to two thousand cubic yards of contaminated subsurface soils at IHSS 119.1; extraction
and then ultraviolet/hydrogen peroxide and ion-exchange treatment of contaminated
groundwater at IHSS 119.1; either thermal treatment and replacement of excavated soil
into the original excavation, disposal of excavated soil in an on-site waste disposal cell,
or off-site disposal of the excavated soil; and groundwater monitoring consistent with
the Integrated Water Management Plan.
The comparative analysis of alternatives shows that Alternative 5 rates best for overall
protection of human health and the environment; compliance with ARARs; long-term
effectiveness and permanence; and reduction of tbxicity, mobility, or volume through
treatment Alternative 5 rates higher than the other alternatives for short-terra
effectiveness, and rates good for implementability and anticipated damages to natural
resources. Alternative 5 is expected to take the least amount of time to achieve
protection at IHSS 119.1 (four to six months), and is the least expensive alternative
except for Alternative 0, which is to perform no remedial action. In addition,
Alternative 5 satisfies the CERCLA statutory preference for remedies that employ
treatment as a principal element and achieves the Remedial Action Objectives set for OU
The principal components of the IHSS 119.1 remedial action selected to meet these
RAOs and remediation goals are described below:
Excavation of soil: Excavation of contaminated subsurface soils will begin at IHSS
119.1 in the two contamination source areas identified during the recent soil gas
survey. The location of these two areas can be found on Figure 3. From the soil gas
survey results, it is estimated that the amount of soil that will be excavated is
approximately one thousand to two thousand cubic yards. During the excavation,
sampling will be performed to confirm the point at which all contaminated subsurface
soil has been removed, in accordance with the ALF. In addition, during
implementation of the selected remedy, DOE will perform confirmatory soil sampling
downgradient of IHSS 119.1 to verify that a contamination source does not exist there.
A detailed sampling and analysis plan for both of these confirmatory sampling activities
will be prepared as part of the Remedial Design for OU 1. A detailed soil excavation
plan will also be prepared as part of the Remedial Design.
Groundwater extraction and treatment: Groundwater will be extracted from the
excavation and will be transferred to the existing Building 891 ultraviolet/hydrogen
peroxide and ion-exchange water treatment system for final treatment and discharge.
After all contaminated subsurface soil has been excavated and all contaminated
groundwater has been extracted from the excavation, the French Drain system will be
decommissioned and its use will be discontinued. The final details of the groundwater
extraction and the decommissioning of the French Drain will be presented in the
Remedial Design for OU 1.
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Handling and management of excavated soil: DOE is considering three options for
managing the excavated soil: on-site treatment and placement back into the original
excavation, disposal in an on-site waste disposal cell, or off-site disposal. DOE's
preferred method of managing the excavated soil is to treat the soil on-site in a thermal
desorption unit to levels that will be identified and approved in the Remedial Design.
The treated soil would then be placed back into the original excavation. Again, the final
details of how the excavated soil will be handled and managed will be prepared as part
of the Remedial Design and will be in accordance with RFC A.
Groundwater monitoring! DOE anticipates that groundwater monitoring will be
performed at IHSS 119.1, consistent with the Integrated Water Management Plan, after
the remedial action is complete. The details of this groundwater monitoring will be
presented in the Remedial Design.
It is possible that changes to the remedial activities described above may be made as a
result of the remedial design and construction processes. Any such changes, in
general, would reflect modifications resulting from the engineering design process.
2. Institutional controls will be maintained throughout the OU 1 area in a manner
consistent with RFCA, the Rocky Rats Vision, and the ALF. These documents
recognize that the reasonably foreseeable future land use for the OU 1 area is restricted
open space. The institutional controls will ensure that the restricted open space land
use is maintained for the OU 1 area and that domestic use of groundwater within the
OU 1 area is prevented. If the reasonably foreseeable future land use for the OU 1 area
changes when final sitewide land use decisions are made, this remedy will be
reexamined to ensure protection of human health and the environment The specific
mechanisms (for example, deed restrictions) to ensure the implementation and
continuity of the necessary institutional controls have not been included in this
CAD/ROD. Currently, these mechanisms are envisioned to be placed in the Final
Sitewide CAD/ROD or in this CAD/ROD during one of the five-year reviews of this
document However, should the Final CAD/ROD not occur or not include these
institutional control mechanisms, this OU 1 CAD/ROD will be revised to include them,
if it does not already include them as a result of a five-year review. The institutional
controls can also be removed at one of the above times, if it is deemed appropriate to do
so by the parties.
3. Because of the groundwater and land use controls, the low amounts of contamination in
OU 1 outside of IHSS 119.1, and the low levels of risk associated with the
contamination, no remedial action will be taken at the remaining ten IHSSs in OU 1.
Implementing the selected remedy will not result in any irreversible damages to natural
resources. Wetlands will not be injured; flood elevations will not be affected; soil and
groundwater will be temporarily disturbed during excavation activities, but will not be
permanently impacted; and no permanent displacement or loss of wildlife will result from
the implementation of the selected remedy.
The selected remedy will achieve the Remedial Action Objectives set for OU 1, which were
identified in the CMS/FS report as follows:
• Prevent the inhalation of, ingestion of, and/or dermal contact with VOCs and inorganic
contaminants in OU 1 groundwater that would result in a total excess cancer risk greater
than 10"4 to 10"* for carcinogens, and/or a Hazard Index greater than or equal to one for
non-carcinogens.
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• Prevent migration of contaminants from subsurface soils to groundwater that would
result in groundwater contamination in excess of potential groundwater ARARs for OU
1 contamination.
• . Prevent migration of contaminants in OU 1 groundwater from adversely impacting
surface water quality in Woman Creek.
These RAOs were selected to address the primary risk exposure pathways identified for
OU 1, which are groundwater and subsurface soil pathways. The preliminary remediation
goals (PRGs) for these RAOs dealing with groundwater and subsurface soils were
identified in the CMS/FS report by examining both risk-based and ARAR-based values.
The exposure route of groundwater ingestion resulted in the highest potential risk to a
future on-site resident, so the Colorado Basic Standards for Groundwater, found in 5 CCR
1002-8, 3.11.5 and 3.11.6 were selected as appropriate PRGs for OU 1.
Subsequent to the selection of PRGs in the CMS/FS report, however, RFCA was finalized
and is currently the governing cleanup agreement for Rocky Flats. The remediation goals
in RFCA are based on the protection of surface water and are specified in the ALF.
Therefore, the remediation goals for the contaminants at OU 1 are based on the ALF.
RFCA also identifies points of compliance for all remedial activities conducted at Rocky
Flats, which will be used for the remediation of OU 1.
DOCUMENTATION OF SIGNIFICANT CHANGES
The OU 1 Proposed Plan for Rocky Rats was released for public comment on May 13,
1996. The Proposed Plan identified Alternative 5, Soil Excavation with Groundwater
Pumping, as the preferred remedial alternative. DOE reviewed all written and verbal
comments submitted during the public comment period. Upon review of these comments,
it was determined that no significant changes to the remedy, as it was originally identified
in the Proposed Plan, were necessary.
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RESPONSIVENESS SUMMARY
OVERVIEW
The Proposed Plan for OU 1 was available for public review and comment from May 13,
1996, through July 12,1996. In addition, a public hearing was held on June 19, 1996, at
which oral and written comments were solicited. This Responsiveness Summary provides
a summary of the comments on the OU 1 Proposed Plan that were received during the
public comment period, as well as DOE's responses to the public's concerns. All
comments received during the public comment period were considered in the final selection
of the remedial alternative for OU 1.
SUMMARY OF COMMENTS RECEIVED DURING PUBLIC COMMENT
PERIOD AND DOE RESPONSES
DOE solicited written and oral comments from the public on the OU 1 Proposed Plan
during the public comment period and at the public hearing. A summary of the comments
that were received and DOE's responses are provided below:
Comment: A member of the community at the public hearing stated that the selection of
the preferred remedial alternative was logical and looked like it would move Rocky Flats
forward toward cleanup and closure.
Response: No response necessary.
Comment: A written comment was received that expressed concern over the apparent
lack of funding for the implementation of the selected remedy, considering that the
remediation of JHSS 119.1 is ranked number 12 on the Environmental Restoration (ER)
Ranking in RFCA The commenter was concerned that the remedial action must be
conducted with fifteen months of completing the Remedial Investigation/Feasibility Study
(RI/FS), according to CERCLA.
Response; First, while DOE is faced with significant budget cuts that will affect the
activities that can be completed at Rocky Flats in FY97, final decisions on site priorities and
funding for FY97 have not yet been made. The ER Ranking is intended to be a guide to
funding and remediating the top priority IHSSs on-site, based on various factors including
available funding, timing and project status. The IHSSs do not have to be remediated in
the exact order that they appear on the ranking list Therefore, DOE is not certain that this
remedial action will not be funded in FY97. Second, the section of CERCLA quoted in the
written comment (CERCLA Section 120(e)(2)) refers to the entire site, not specifically to
any particular operable unit In addition, cleanup at Rocky Flats has been governed by an
enforceable agreement (first the IAG and now RFCA) since 1991. EPA has said that DOE
is in compliance with CERCLA time frames as long as it is in compliance with this
enforceable agreement. Therefore, the remedial action presented in this CAD/ROD does
not have to be implemented within fifteen months of the final CAD/ROD.
Comment: A written comment was received that expressed concern over the management
of the excavated soils in Alternative 5. Because three options were listed for the
management of the soils, the commenter was concerned that a complete evaluation of the
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alternatives could not have been accomplished. Also, the commenter questioned the option
of on-site disposal of the excavated soil and stated that more detail should be given on the
management of the excavated soil.
Response: Although three options are presented in the Proposed Plan for managing the
excavated soil, the fundamentals of Alternative 5, as compared to the other alternatives
under the nine criteria required by CERCLA, are the same under each option, and the
comparison results are also the same. For example, regardless of the method of handling
the excavated soil, provided it is in compliance with all applicable laws and regulations,
Alternative 5 is still overall the most protective of human health and the environment, based
on the removal of the contamination source in the subsurface soil. The evaluation of
alternatives was not dependent on the method of managing the excavated soil to show that
Alternative 5 is the most appropriate alternative. In addition, separate cost estimates were
provided in the Proposed Plan for each different option of soil management under
Alternative 5. In all three cases Alternative 5 is the least expensive alternative, other than
the No Action alternative.
The intent of the on-site disposal option for the excavated soil is to dispose of the soil in a
permitted on-site waste disposal cell, if such a unit exists on-site at the time that this
remedial action is performed. Both the disposal unit and the soil would meet all applicable
requirements before on-site disposal would occur. If such a disposal unit does not exist
on-site, one of the other two options will be employed. As stated in the CAD/ROD, it is -
currently DOE's preference to treat the excavated soil on-site in a thermal desorption unit
and place it back into the excavation, provided that the treated soil meets soil put-back
requirements established by RFCA. The details for managing the excavated soil, including
necessary treatment, required permits, and applicable laws and regulations, will be included
in the Remedial Design, along with all of the details of implementing the selected remedy.
Comment: A written comment was received that questioned whether a health assessment
by the Agency for Toxic Substances and Disease Registry (ATSDR) has been or will be
performed at Rocky Flats.
Response: A health assessment by ATSDR is scheduled for Rocky Flats by the year
2002. This is based on available resources at ATSDR and the prioritized needs of the
whole DOE complex for health assessments to be performed. DOE is using the results of
the Baseline Risk Assessment for OU 1, which includes a Public Health Evaluation and an
Environmental Evaluation, to move forward with this remedial action.
Comment: Written comments were received that expressed concern over vague language
in the Proposed Plan regarding the conclusions in the RFI/RI on the extent of
contamination and the need for remedial action at OU 1.
Response: The RFI/RI report, which is available for review in the Administrative Record
and public reading rooms, does definitively determine the need for further remedial action
at each IHSS in OU 1 and presents in detail the information used to make those
determinations. The RFI/RI concluded that only IHSS 119.1 contributes significantly to
groundwater contamination and contains subsurface soil contamination at levels that
warrant a remedial action. Based on the data contained in the report, the RFI/RI also
concluded that the remainder of the IHSSs at OU 1 are already in a protective state (i.e., do
not contribute significantly to groundwater contamination and do not contain contamination
at levels that warrant a remedial action). Due to the limited scope of the Proposed Plan, a
summary of these conclusions and data was presented and references were made to the
22
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RFI/RI in the Proposed Plan, rather than repeat in detail the information already presented
in the RFI/RI report For the characterization of IHSS 104, the Proposed Plan only
referred to a review of documentation. However, conclusions on the characterization of
IHSS 104 were also based on investigation data, as presented in the RFI/RI report.
Comment: A written comment was received that expressed concern over the requirement
in the IAG to incorporate actions that are completed pursuant to CERCLA authority into the
Rocky Hats RCRA permit.
Response: RFCA now requires that CDPHE incorporate only final corrective action
decisions into the Rocky Flats RCRA permit in order to satisfy the requirement to include a
corrective action element in the permit In addition, RFCA states that activities required
under any concurrence CAD/ROD (where both EPA and CDPHE concur with the
CAD/ROD) will not require permits.
Comment: Written comments were received that questioned whether RCRA listed
hazardous wastes were disposed at OU 1, based on the contaminants of concern that were
identified in the Proposed Plan. The commenter questioned whether the excavated soil
should be handled as a RCRA listed hazardous waste.
Response: Based on the RFI/RI, DOE does not have any information to indicate that
spent solvents, which would have been RCRA listed hazardous wastes, were disposed at
OU 1. Rather, the VOCs listed in the Proposed Plan were identified as contaminants of
concern based on sampling and analysis of the groundwater and soil that was conducted at
OU 1 during the RFI/RI. DOE cannot conclusively say that these VOC contaminants are
the result of the disposal of spent solvents (i.e., RCRA listed hazardous waste), therefore,
the RCRA hazardous waste listing does not apply to the contaminants, and the soil does not
contain a listed hazardous waste.
The Remedial Design will describe in detail how the excavated soil will be managed. At
this point, it is anticipated that the excavated soil, which itself is not a waste, would be
considered environmental media containing hazardous constituents that exhibit a hazardous
waste characteristic for VOCs. The excavated soil would be treated in a thermal desorption
unit Following this treatment the soil would be sampled and analyzed to verify the
successful removal of VOCs from the excavated soil. At that point the excavated soil
would no longer contain hazardous constituents that exhibit a hazardous waste
characteristic. Therefore, land disposal restrictions (LDR) and minimum technological
requirements (MTR) would not apply to the excavated soils.
Comment: A written question was received concerning the levels of radioactivity that
must be met before placement of soils contaminated with radionuclides is allowed.
Response; Information from the RFI/RI for OU 1 indicates that radionuclide
contamination is not expected in the subsurface soils at OU 1. However, as required by
RFCA, a working group consisting of representatives from DOE, EPA and the State of
Colorado are working on developing site specific radionuclide clean-up and put-back levels
for soil The proposal by this working group will be available for public comment from
September 1, 1996, through October 4, 1996. A final decision on this issue is expected to
be made by October 18, 1996.
23
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iqure
Generol Locolion ol
Rocky Flols Environmenlol
Technology Sile
24
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NA/AHOOUS SUBSiANCt S'tC (inSS)
ANO MIS OCSiCNATiON. OtSxtO WHCRC 0'S'O=BtO
CON]T
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Table 1
Individual Hazardous Substance Site.Descriptions
IHSS
Number
IHSS Name
Description
102
Oil Sludge
Pic Site
Approximately 40 x 70 ft1, area located approximately 180 feet touch of Building 881 where
30 to SO drums of non-ndioactive oily sludge were emptied in the Uie 1950s. The sludge
was from the cleaning of two No. 6 fuel oil tanks, designated as IHSSs 10S.I and 10S.2, and
was backfilled when disposal operations ceased
103
Chemical
Burial Site
Approximately 50 feet in diameter (2,000 ft.1), the pit is circular is shape, and is located
approximately ISO feet southeast of Building 881 on 1963 aerial photographs. Area was
reportedly used to bury unknown chemicals.
104
Liquid
Dumping
Site
Reportedly a former (pre-1969) liquid waste disposal pond in area east of Building 881 - no
exact location or dimensions of pit - location is uncertain due to poor quality of 1965 aenal
photograph. Approximate dimensions are 50 x SO ft*.
105.1.
10S.2
Out-of-
Service Fuel
Oil Tank
Sites
Located immediately couth of Building 881, thece were storage tanks for No. 6 fuel oil.
Suspected leaks in 1972. Tank* closed in place through filling with asbestos-containing
material and cement. IHSS 107, the Hillside Oil Leak Site, may have been caused by leakage
from these tanks.
106
Outfall Site
Overflow line from the sanitary sewer sump in Building 887. The outfall was used for
discharge of untreated sanitary wastes in the 1950s and 1960s. Due to concern about
discharges from (he outfall entering Woman Creek, several small retention ponds and an
interceptor ditch were built in 1955 and 1979, respectively, to divert the outfall water to
Pond C-2.
107
Hillside Oil
Leak Site
Site of 1972 fuel oil spill from Budding 881 foundation drain outfall. A concrete skimming
pond was built below the foundation drain outfall to contain the oil flowing from the
foundation drain, and an interceptor ditch was constructed to prevent oil-contaminated water
from reaching Woman Creek.
119.1,
119.2
Multiple
Solvent Spill
Sites
Former drum storage areas east of Building 881 along the southern perimeter road. IHSS
119.1 is the larger western drum and scrap metal storage area, and appears to have contained
mostly drums in the southern part of the IHSS and mostly scrap metal in the northern pan.
although material was moved around frequently as documented by aerial photographs. IHSS
119.2 is the smaller eastern drum and scrap metal storage area and appears to have contained
mostly scrap metal. The drums contained unknown quantities and types of solvents and
wastes. The scrap metal may have been coated with residual oils and/or hydraulic coolants.
130
Radioactive
Site - 800
Area*)
Area east of Building 881. Used between 1969 and 1972 to dispose of soil and asphalt
contaminated with low levels of plutonium and uranium. IHSS 130 is referred to as the
Contaminated Soil Disposal Area Bast of Building 881 in the HRR to better milch the history
of waste disposal: the site is included in the discussion of the 900 area at RFETS in that
report. IHSS 130 contains approximately 320 tons or 250 cubic yards which came from three
sources: I) plutonium-conlaminaled soil and asphalt, placed in September of 1969. 2) road
asphalt and soil red contaminated by leaking drum in transit and 3) 60 cu. yds. of plutonium-
contaminated soil removed from around the Building 774 process waste tanks in 1972.
145
Sanitary
Waste Line
Leak
Six-inch cast-iron sanitary sewer line that originates at the Building 887 lift station and that
leaked on the hillside south of Building 881. The line had conveyed sanitary wastes and low-
evel radioactive laundry effluent to the sanitary treatment plant from about 1969 to 1973.
27
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Table 2: Summary of Contaminants at OU1
Surface
Soil
Subsurface
Soil
Groundwater
Surface Water/
Seeps
Sediments
Inorganic Analytes
Selenium
Vanadium
Plutonium
Americium
Uranium
X*
X
X'
X*
X*
X*
X
X
X**
X**
X**
X"
Volatile Organic Compounds
1,1.1-Trichloroethane
Trichloroethenc
Tetrachloroethene
Carbon Tetrachloride
1,2-Dichloroethane
Chloroform
1.1-Dichloroethene
1,2-Dichloroethene
cis- 1 ,2-Dichlorocihene
1.1,2-Trichloroe thane
1,1-Dichlorocthanc
Toluene
Total Xylenes
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
Semivolatile Organic Compounds
Pol/nuclear Aromatic
Hydrocarbons
Aroclor-1254
Aroclor-1248
X
X
X
X
X
X
• Presence in these media is based on hoc spot data.
*• Presumed to be present as a contaminant of these media because of the widespread nature of the contamination originating from
an off-site source.
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Table 3: Summary of VOC Concentrations in Groundwater, IHSS 119.1,1987-1995
Well No.
0974
1074
0487
4387
37891
37991
32591
Compound
ecu
1,1 -DCE
TCA
PCE
TCE
ecu
1,1-DCE
TCA
PCE
TCE
ecu
1,1-DCE
TCA
PCE
TCE
ecu
l.l-DCE
TCA
PCE
TCE
ecu
l.l-DCE
TCA
PCE
TCE
ecu
l.l-DCE
TCA
PCE
TCE
ecu
l.l-DCE
TCA
PCE
TCE
Range of Concentrations (ug/L)
5U - 2,800
500U - 48,000
1,220-30,250
430- 13.200
1 .500 -72,000
2.500E - 5.000
42J - 120
SOU - 390
100U - 49
790 - 3.600
46 - 2.600
2U- 12
3.2 - 20
14-590
220 - 9.500
40U-2.IOO
1,400- 11.000
1.700-20,000
61 - 7.590
100- 15.540
0.2U
0.2U
0.1U
0.1U-7.IB
0.1U- 1.3
O.lU-0.2
0.2U
0.1U
O.IU- 16
0.1U-3.3
O.I
0.68 - 6
0.4-2
1 -3
5U- MOO
Note: Well 0587 had 12 ug/L TCE on (8/92). well 33491 had I
not sampled. U=not detected at or above method detection limit
J=estimaied value.
ug/L TCE (11/94). and wells 33691, and 38291 were
. B=appeared in method blank. E=estimated value, and
Summary of VOC Physical Characteristics
Compound
ecu
l.l-DCE
TCA
PCE
TCE
Solubility
(mg/L)
800
400
1360
150
MOO
Specific Density
(20°)
(g/cc)
1.59
1.22
1.34
1.62
1.46
LogK^.
Octanol Water
Coefficient
2.83
2.13
2.47
2.60
2.53
Henry's Law
Constant
(aim-mVmol)
0.0302
0.021
0.018
0.0153
0.0091
Compiled from Cohen. R.M.. Mercer. J.W.. and Mathews. J.. 1993. DNAPL Site Evaluation: C.K. Smoley. Publisher.
29
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Department of Energy
ROCKY FLATS FIELD OFFICE
P.O.BOX 928
GOLDEN. COLORADO 80402-0028
MAR 2 ° — 97-DOE-05168
Mr. Tim Rehder, Manager
Rocky Flats Project
U. S. Environmental Protection Agency, Region VIII
999 18th Street, Suite 500
Denver, Colorado 80202-2466
Mr. Joseph Schieffelin, Permitting and Compliance Unit Leader
Federal Facilities Program
Hazardous Materials and Waste Management Division
Colorado Department of Public Health and Environment
4300 Cherry Creek Drive South
Denver, Colorado 80222- 1 5 30
Dear Mr. Rehder and Mr. Schieffelin:
Enclosed is a copy of the final Corrective Action Decision/Record of Decision for Operable
Unit 1, 881 Hillside, including the signatures of all parties, for your records. Thank you
for your cooperation during the finalization of this important decision document
If you have any questions, please contact Sandi MacLeod at 966-3367.
Sincerely,
Gail Hill, Acting Group Lead
Regulatory Liaison Group
Enclosure
cc w/Enc:
G. Kleeman, EPA
C. Spreng, CDPHE
Administrative Record
cc w/o Enc:
J. Legare, AMEC, RFFO
S. MacLeod, ERWM, RFFO
N. Castaneda, ERWM, RFFO
J. Rampe, PLD, RFFO
T. Howell, OCC, RFFO
A. Sieben, KH
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