Superfund Record of Decision: California Gulch, OU 10, Leadville, CO (8/8/1997)


EPA  Superfund
       Record of Decision:
       California Gulch, OU 10
       Leadville, CO
        8/8/1997
                                 PB97-964402
                                 EPA/541/R-97/145
                                 January 1998

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                                     389882
                             ADMINISTRATIVE
                                  RECORD

                             SF RLE NUMBER
       RECORD OF DECISION

          OKEGO&GULCH
         OPERABLE UNIT 10
CALIFORNIA GULCH SUPERFUND
                 COLORADO
             Augustl997:
      U.S. Envirdnoicntal Protection Agency
          99918th Street, Suite 500   .
          Demger, Colorado 80202  ', /
                                  /• ---t • ~
                              .... > . -....; .•—"?••;

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wDIVI  Federal Programs Corporation
             1526 Cole Boulevard. Suite 150
             Golden. Colorado 80401
             Tel: 303 232-0131 Fax:303232-0904
             August 12, 1997
                                                 ADMINISTRATIVE
                                                       RECORD
             Ms. Rebecca Thomas                                                     ,
             U.S. Environmental Protection Agency
             Region VIII, Mail Code (8EPR-SR)
             999 18th Street, Suite 500
             Denver, CO 80202-2466

             Project:       RAC Region VIII, Contract No. 68-W5-0022
                          Work Assignment No. 013-RS-BD-08-29

             DCN:         3280-013-RT-DECD-01300

             Subject:       Transmittal of Final Record of Decision for Operable Unit 10.

             Dear Ms. Thomas:

             Enclosed please find one unbound copy and four bound copies of the Final Record of
             Decision for Operable Unit 10. This version incorporates the signature page which you
             sent me on August 11, 1997.  If you have additional questions or comments, please
             contact me.

             Sincerely,

             COM FEDERAL PROGRAMS CORPORATION
             Ken Black, R.G.
             Project Manager

             Enclosure
             cc:
DCN
             P -3280-01 J\OUIO'.FrNALROD'.FrN2TRANLTR

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RECORD OF DECISION

OREGON GULCH OPERABLE UNIT 10
CALIFORNIA GULCH SUPERFUND SITE
LEADVILLE, COLORADO

The U.S. Environmental Protection Agency (EPA), with the concurrence of the Colorado
Department of Public Health and Environment (CDPHE), presents this Record of Decision
(ROD) for the Oregon Gulch Operable Unit 10 (OU10) of the California Gulch Superfund Site in
Leadville, Colorado. The ROD is based on the Administrative Record for Oregon Gulch OU10,
including the Remedial Investigation/Feasibility Study (RI/FS), the Proposed Plan, the public
comments received, including those from the potentially responsible parties (PRPs), and EPA
responses. The ROD presents a brief summary of the RI/FS, actual and potential risks to human
health and the environment, and the Selected Remedy. EPA followed the Comprehensive
Environmental Response, Compensation, and Liability Act, as amended, the National
Contingency Plan (NCP), and appropriate guidance in preparation of the ROD. The three
purposes of the ROD are to:

1. Certify that the remedy selection process was carried out in accordance with the
requirements of the Comprehensive Environmental Response, Compensation,
and Liability Act, 42 U.S.C. 9601 et seq., as amended by the Superfund
Amendments and Reauthorization Act (collectively, CERCLA), and, to the extent
practicable, the National Contingency Plan (NCP);

2. Outline the engineering components and remediation requirements of the Selected
Remedy; and

3. Provide the public with a consolidated source of information about the history,
characteristics, and risk posed by the conditions of Oregon Gulch OU10, as well
as a summary of the cleanup alternatives considered, their evaluation, the
rationale behind the Selected Remedy, and the agencies' consideration of, and
responses to, the comments received..

The ROD is organized into three distinct sections:

1. The Declaration section functions as an abstract for the key information
contained in the ROD and is the section of the ROD signed by the EPA Regional
Administrator and the CDPHE Director.

2. The Decision Summary section provides an overview of the OU10
characteristics, the alternatives evaluated, and the analysis of those options. The
Decision Summary also identifies the Selected Remedy and explains how the
remedy fulfills statutory requirements; and
Record of Decision
Oregon Gulch OU 10
8497P 3280-OU OUIO'FINALROI>OLMOROD.WPD

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        3.     The Responsiveness Summary section addresses public comments received on
               the Proposed Plan, the RJ/FS, and other information in the Administrative Record.
Record of Decision
Oregon Gulch OHIO
8497P J280-OU'OU10 FINALROD'.OUIOROD.WPD

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                                        DECLARATION
Record of Decision
Oregon Gulch OU10
8497P 3:80-013 OUIO FINALROD OUIOROD.WPD

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DECLARATION
SITE NAME AND LOCATION

Oregon Gulch Operable Unit 10
California Gulch Superfund Site
Leadville, Colorado

STATEMENT OF BASIS AND PURPOSE

This decision document presents the Selected Remedy for Oregon Gulch OU10 within the
California Gulch Superfund Site in Leadville, Colorado. EPA, with the concurrence of CDPHE,
selected the remedy in accordance with CERCLA and the NCP.

This decision is based on the Adn. nistrative Record for Oregon Gulch OU10 within the
California Gulch Superfund Site. The Administrative Record (on microfilm) and copies of key
documents are available for review at the Lake County Public Library, located at 1115 Harrison
Avenue in Leadville, Colorado, and at the Colorado Mountain College Library, in Leadville,
Colorado. The complete Administrative Record may also be reviewed at the EPA Superfund
Record Center, located at 999 18th Street, 5th Floor, North Terrace in Denver, Colorado.

The State of Colorado concurs with the Selected Remedy, as indicated by signature.

ASSESSMENT OF THE SITE

Actual or threatened releases of hazardous substances at and from Oregon Gulch OU10, 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.

DESCRIPTION OF THE SELECTED REMEDY

The Selected Remedy is the second response action to be taken at Oregon Gulch OU10 of the
California Gulch Superfund Site. The first action taken at Oregon Gulch OU10 was completed
in October 1996. This removal action implemented the Action Memorandum (EPA, 1995) for
miscellaneous tailings and stream sediment in Oregon Gulch and involved excavation of
approximately 3,500 cubic yards of sediment and soil from the channel and floodplain of Oregon
Gulch downstream of the Oregon Gulch Tailings Impoundment. The excavated material was
then placed on top of the impoundment. Following sediment removal, a channel capable of
conveying a 100-year flood event was constructed by mixing limestone in the first foot of subsoil
underlying the channel, installing a geotextile, and placing riprap. The area outside the 100-year
channel and within the 500-year floodplain was stabilized by placing a 12-inch thick layer of fill
in the excavated area, regrading the excavated area, amending the soil, and revegetating. A
sedimentation pond was constructed in Oregon Gulch downstream of the toe of the tailings
Record of Decision
Oregon Gulch OU 10 _ .
8497P .3280-013'OUIO'FINALROD-OUIOROD.WPD L)-'

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impoundment to reduce sediment load in runoff from the tailings embankment. This removal
action is consistent with the Selected Remedy which is described below.

The Selected Remedy for addressing the Oregon Gulch Tailings Impoundment is a Multi-Layer
Rock and Soil Cover with a Geosynthetic Barrier as presented in the Final Focused Feasibility
Study for Oregon Gulch Operable Unit 10 (SMI/TerraMatrix, 1997) as Alternative 5. The
Focused Feasibility Study (FFS) evaluated and screened remedial alternatives retained in the site-
wide Screening Feasibility Study (EPA, 1993) for impounded tailings, stream sediment, and
fluvial tailings within OU10. The FFS used a comparative analysis to evaluate five alternatives
and identify the advantages and disadvantages of each. The Selected Remedy for the tailings
impoundment will consist of regrading the impoundment surface to provide positive drainage
and flattening the embankment side slopes to 3:1 or less. A geosynthetic barrier will be installed
to control infiltration over the entire regraded impoundment (top and side slopes), followed by a
geocomposite drainage layer. An 18-inch-thick vegetated soil layer will be placed on the top of
the geocomposite drainage layer. On the side slopes, an 18-inch-thick layer of random fill
overlain with an erosion-resistant 6-inch-thick gravel layer would be placed over the
geocomposite drainage layer. In addition, lined diversion ditches will be constructed to divert
potential run-on from the tailings and convey runoff from the covered tailings surface. Adjacent
to the impoundment, the diversion ditches will be constructed with a low-permeability lining to
eliminate infiltration. A groundwater cut-off trench will also be installed in the Oregon Gulch
paleo-channel upgradient of the impoundment to further prevent shallow groundwater from
potentially infiltrating the tailings.

The Selected Remedy includes active managment of the seep currently discharging at the toe of
the Oregon Gulch Tailing Impoundment during the interim period from implementation until the
seep does not negatively impact surface water quality. Active management of the seep discharge
will be performed during non-freezing conditions and will include collection and either pumping
or transport of the collected flow to the Yak Tunnel Treatment Plant or other suitable treatment
options. Design of the Selected Remedy will include a drain system at the toe of the
embankment to allow the seep discharge to flow unrestricted and to be collected in a controlled
manner.

The Selected Remedy is protective of human health and the environment through the following:

1. The cover will eliminate airborne transport of tailings particles and limit the potential for
contact of precipitation and surface water with tailings material;

2. Ponding of water on the tailings surface will be minimized, reducing infiltration into the
impoundment;

3. Infiltration through the tailings will be greatly reduced due to the geosynthetic barrier.

4. Erosion and transport of tailings will be eliminated by vegetated and gravel surface
treatments;
Record of Decision
Oreuon Gulch OU10 -^ _
g-WP'JigO-OIS'OUIO'FINALROD'OUIOROD.WPD \J-2.

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 5.      Stability of the side slopes \vill be increased by. regrading to flatten existing slopes prior
        to constructing the soil cover.

 STATUTORY DETERMINATIONS

 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.  Given the type of waste present at this site, this remedy uses
 permanent solutions (e.g., engineered covers) to the maximum extent practicable and satisfies the
 preference for remedies that reduce toxicity, mobility, or volume as a principal element. Because
 this remedy may result in hazardous substances remaining on site above health-based levels, a
 review will be conducted within five years after commencement of remedial action to ensure that
 the remedy continues to provide adequate protection of human health and the environment.  Thi~
 remedy is acceptable to both the State of Colorado and the community of Leadville.
 Max H. Dodson                                              Date
 Assistant Regional Administrator
 Ecosystems Protection and Remediation
 U.S. Environmental Protection Agency, Region VIII
Rccot: oi'Dccinon
Oregon Guich OU10                                __ ^
''1'f 3:33-01 j OLIO FIN/U.RODOUIORODUTD              LJ-J

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                                      DECISION SUMMARY
Record of Decision
Oreton Gulch OU10
8407P: J280-OI3 OU'lO FtNALROD'OUIOROD.WPD

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TABLE OF CONTENTS

SECTION PAGE

1.0 SITE NAME, LOCATION, AND DESCRIPTION DS-1

2.0 OPERABLE UNIT HISTORY AND ENFORCEMENT ACTIVITIES DS-3

3.0 HIGHLIGHTS OF COMMUNITY PARTICIPATION DS-7

4.0 SCOPE AND ROLE OF OPERABLE UNIT DS-9

5.0 SUMMARY OF SITE CHARACTERISTICS DS-11
5.1 PHYSICAL CHARACTERISTICS DS-11
5.2 GEOTECHNICAL EVALUATION DS-11
5.3 NATURE AND EXTENT OF CONTAMINATION DS-12
5.3.1 SURFACE AND SUBSURFACE SOIL AND TAILINGS DS-12
5.3.2 SURFACE WATER DS-13
5.3.3 GROUNDWATER DS-15
5.3.3.1 Groundwater-Surface Water Interaction DS-18
5.3.4 STREAM SEDIMENTS DS-18
5.3.5 AIR DS-19
5.4 HISTORIC AND CULTURAL RESOURCES DS-19

6.0 SUMMARY OF SITE RISKS DS-21
6.1 HUMAN HEALTH RISKS DS-21
6.2 ECOLOGICAL RISKS DS-21
6.2.1 CONTAMINANT IDENTIFICATION DS-21
6.2.2 EXPOSURE ASSESSMENT DS-22
6.2.3 RISK CHARACTERIZATION DS-23
6.3 SUMMARY DS-24

7.0 DESCRIPTION OF ALTERNATIVES :.. DS-26

8.0 SUMMARY OF COMPARATIVE ANALYSIS OF ALTERNATIVES DS-30
8.1 NCP EVALUATION AND COMPARISON CRITERIA DS-30
. 8.1.1 THRESHOLD CRITERIA DS-30
8.1.2 PRIMARY BALANCING CRITERIA DS-30
8.1.3 MODIFYING CRITERIA DS-31
8.2 WAMP PERFORMANCE CRITERIA DS-31
8.3 EVALUATING THE ALTERNATIVES WITH THE NCP CRITERIA .. DS-34
8.3.2 COMPLIANCE WITH APPLICABLE OR RELEVANT AND
APPROPRIATE REQUIREMENTS (ARARs) DS-35
Record of Decision
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8.3.3 LONG-TERM EFFECTIVENESS AND PERMANENCE DS-35
8.3.4 REDUCTION OF TOXICITY, MOBILITY, OR VOLUME
THROUGH TREATMENT DS-36
8.3.5 SHORT-TERM EFFECTIVENESS DS-36
8.3.6 IMPLEMENTABILITY DS-36
8.3.7 COST DS-37
8.3.8 STATE ACCEPTANCE DS-37
8.3.9 COMMUNITY ACCEPTANCE DS-37
8.4 EVALUATING THE ALTERNATIVES WITH THE WAMP
CRITERIA DS-38
8.4.1 SURFACE EROSION STABILITY DS-38
8.4.2 SLOPE STABILITY . :. DS-38
8.4.3 FLOW CAPACITY AND STABILITY DS-38
8.4.4 SURFACE WATER AND GROUND WATER LOADING
REDUCTION DS-39
8.4.5 TERRESTRIAL ECOSYSTEM EXPOSURE DS-39
8.4.6 NON-RESIDENTIAL SOILS DS-39

9.0 SELECTED REMEDY DS-40
9.1 REMEDY FOR THE OREGON GULCH TAILINGS
IMPOUNDMENT DS-41
9.2 CONTINGENCY MEASURES DS-43

10.0 STATUTORY DETERMINATIONS DS-44
10.1 PROTECTION OF HUMAN HEALTH AND THE ENVIRONMENT ... DS-44
10.2 COMPLIANCE WITH ARARs DS-44
•10.3 COST EFFECTIVENESS DS-44
10.4 UTILIZATION OF PERMANENT SOLUTIONS AND ALTERNATIVE
TREATMENT TECHNOLOGIES (OR RESOURCE RECOVERY
TECHNOLOGIES) TO THE MAXIMUM EXTENT POSSIBLE DS-45
10.5 PREFERENCE FOR TREATMENT AS A PRINCIPAL ELEMENT .... DS-45

11.0 DOCUMENTATION OF SIGNIFICANT CHANGES DS-46

12.0 REFERENCES DS-47
APPENDIX A APPLICABLE OR RELEVANT AND APPROPRIATE
REQUIREMENTS (ARARs)
Record of Decision
Oregon Gulch OU10 p.- ..
&497p;.j280-0n OUIO FINALROD OUIOROD WPD U5-I1
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LIST OF FIGURES

FIGURE

I GENERAL LOCATION MAP. CALIFORNIA GULCH SUPERFUND SITE,
LEADVILLE, COLORADO
2 CALIFORNIA GULCH SUPERFUND SITE AND OPERABLE UNITS,
LEADVILLE, COLORADO
3 SITE MAP - OREGON GULCH OPERABLE UNIT 10
4 OREGON GULCH INVESTIGATIONS BOREHOLE AND TEST PIT
LOCATIONS
5 OREGON GULCH GROUNDWATER, SURFACE WATER, AND SEDIMENT
SAMPLING LOCATIONS
6 ALTERNATIVE 5 MULTI-LAYER ROCK AND SOIL COVER WITH
GEOSYNTHETIC BARRIER
7 OREGON GULCH PROPOSED SURFACE CONFIGURA1 iON SELECTED
REMEDY
Record of Decision
Orcton Gulch OU10 __ ...
849TP 3:80-013 OUIOJINALROD'OUIOROD.WPD JJS-111
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LIST OF TABLES

TABLE

1 OREGON GULCH TAILINGS IMPOUNDMENT SOIL SAMPLE
LABORATORY RESULTS SUMMARY
2 OREGON GULCH POND WATER QUALITY
3 OREGON GULCH SEEP WATER QUALITY
4 OREGON GULCH DIVERSION DITCH WATER QUALITY
5 OREGON GULCH SURFACE WATER QUALITY (OG-1)
6 INTERMEDIATE ALLUVIAL AQUIFER WATER QUALITY (MG/L)
7 TAILINGS IMPOUNDMENT PORE WATER QUALITY .
8 PERCHED AQUIFER WATER QUALITY - OGITMW3
9 LOADING TO CALIFORNIA GULCH FROM OREGON GULCH SHALLOW
GROUNDWATER
10 SEDIMENT SAMPLE ANALYSIS RESULTS
11 STREAM SEDIMENT SAMPLE ANALYSIS RESULTS
12 HAZARD INDICES FOR TERRESTRIAL RECEPTORS FROM EXPOSURE
TO CONTAMINANTS IN TAILINGS, SURFACE WATER AND
SEDIMENTS (OU10)
13 HAZARD QUOTIENTS FOR AQUATIC LIFE EXPOSED TO SURFACE
WATER FROM OREGON GULCH
14 HAZARD QUOTIENT FOR AQUATIC LIFE EXPOSED TO SEDIMENT
FROM OREGON GULCH
15 HAZARD INDICES FOR SURFACE MEDIA BY RECEPTOR FOR OU10
16 COMPARISON OF ALTERNATIVES FOR THE OREGON GULCH TAILINGS
IMPOUNDMENT - NCP CRITERIA
17 COST SUMMARY: ALTERNATIVE 2 - VEGETATED SIMPLE COVER
18 COST SUMMARY: ALTERNATIVE 3 - COVER WITH CLAY LAYER
19 COST SUMMARY: ALTERNATIVE 4 - SOIL COVER WITH
GEOSYNTHETIC BARRIER
20 COST SUMMARY: ALTERNATIVE 5 - MULTI-LAYER ROCK AND SOIL
COVER WITH A GEOSYNTHETIC BARRIER
21 COMPARISON OF ALTERNATIVES FOR THE OREGON GULCH
TAILINGS IMPOUNDMENT - WAMP CRITERIA
Record of Decision
Oregon Gulch OL' 10
8-497P 3280-013 OUIOFINALRODOUIORODV/PD
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LIST OF ACRONYMS AND ABBREVIATIONS
AMSL
AOC
AWQC
BARA
CD
CDPHE
CERCLA
COCs
CPT
CZL
EE/CA
EPA
ERA
FFS
HI
HQ
NCP
NRHP
OGDD
OGPD
OGS
OGUP
OU
PERAOG
PRPs
RJ/FS
RME
ROD
RUSLE
SFS
SPT
TDS
TSS
UAO
WAMP
Above Mean Sea Level
Administrative Order on Consent
Ambient Water Quality Criteria
Baseline Aquatic Ecological Risk Assessment
Consent Decree
Colorado Department of Public Health and Environment
Comprehensive Environmental Response, Compensation and Liability Act
Contaminants of Concern
Cone Penetrometer Test
Colorado Zinc-Lead
Engineering Evaluation/Cost Analysis
Environmental Protection Agency
Ecological Risk Assessment
Focused Feasibility Study
Hazard Index
Hazard Quotient
National Oil and Hazardous Substances Pollution Contingency Plan
National Register of Historic Places
Oregon Gulch Drainage Ditch
Oregon Gulch Pond
Oregon Gulch Seep
Oregon Gulch Upgradient
Operable Unit
Preliminary Ecological Risk Assessment for Oregon Gulch
Potentially Responsible Parties
Remedial Investigation/Feasibility Study
Reasonable Maximum Exposure
Record of Decision
Revised Universal Soils Loss Equation
Screening Feasibility Study
Standard Penetration Test
Total Dissolved Solids
Total Suspended Solids
Unilateral Administrative Order
Work Area Management Plan
Record of Decision
OiCL'on Gulch OU 10
84TP 3:80-013 OUIOFINALRODOUIORODWPD
DS-v
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1.0 SITE NAME, LOCATION, AND DESCRIPTION
Oregon Gulch Operable Unit 10
California Gulch Superfund Site
Leadville, Colorado

The California Gulch Superfund Site is located in Lake County, Colorado, in the upper Arkansas
River basin, approximately 100 miles southwest of Denver (see Figure 1). The study area at the
Site encompasses approximately 16.5 square miles and includes the towns of Leadville and
Stringtown, a portion of the Leadville Historic Mining District, and the portion of the Arkansas
River from its confluence with California Gulch downstream to the Lake Fork Creek confluence.
Oregon Gulch is an ephemeral tributary to California Gulch that flows only during the spring
runoff event and during summer storms. The Oregon Gulch watershed drains approximately 185
acres including the 15.8-acre area of OU10. The California Gulch Superfund Site has been
organized into 12 operable units (OUs). Figure 2 shows the Site study area boundaries and the
location of OU10 within the California Gulch Superfund Site.

OU10 is defined as the 500-year floodplain of Oregon Gulch from its headwaters to its
confluence with California Gulch (USDC, 1994). Sources of metal loading within OU10 include
the Oregon Gulch Tailings Impoundment and miscellaneous tailings and stream sediment
contained within the 500-year floodplain of lower Oregon Gulch. Lower Oregon Gulch is
defined as the portion of the gulch downstream of the tailings impoundment.

The Oregon Gulch Tailings Impoundment and the 500-year floodplain of Oregon Gulch
comprise approximately 14.2 acres and 1.6 acres, respectively, of the area of OU10. Oregon
Gulch is a small V-shaped valley with surface water flowing in a northwesterly direction. The
gulch extends approximately one mile from its headwaters, at an elevation of approximately
10,400 feet above mean sea level (AMSL), to the confluence with California Gulch, at an
elevation of approximately 10,025 feet AMSL. The tailings impoundment is located
approximately 1/2 mile upstream of the confluence of Oregon and California gulches and
contains approximately 485,000 cubic yards of tailings. Based on analysis of tailings samples
collected from the impoundment, the tailings represent a source of inorganic metals including
arsenic, cadmium, copper, lead, silver, and zinc. A perennial seep discharges at the toe of the
tailings impoundment and represents a source of acidic water and metals loading to surface water
and groundwater in lower Oregon Gulch (SMI/TerraMatrix, 1997).

Lake County is relatively small (380 square miles) and is predominately rural, with a 1990
population of 6,007 (U.S. Department of Commerce, 1990). About half of this population
resides within the City of Leadville. The population of Lake County has fluctuated with the
mining industry. The population increased to about 9,000 between 1960 and 1981 and then
declined throughout the 1980's. About two-thirds of the land in Lake County is federally owned
and is either part of San Isabel National Forest or managed by the Bureau of Land Management.
Record of Decision
Oregon Gulch OU 10
8497P;.J280-OI3 OUIO'FINALROD'.OUIOROD.WPD
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Land surrounding and within California Gulch is predominately dedicated to mining,
commercial, and residential uses (SMl/TerraMatrix, 1997).

Land within OU10 is privately owned by either the Res-Asarco Joint Venture or Resurrection
Mining Company, except for County Road 6, which is owned by Lake County and two small
parcels of federally owned land managed by the Bureau of Land Management. County Road 6
crosses Oregon Gulch approximately 90 feet upstream of its confluence with California Gulch.
A corrugated metal culvert conveys surface flow under County Road 6. A dirt road extends from
County Road 6 near the confluence of Oregon and California Gulches to the tailings
impoundment. The dirt road was extended past the impoundment and to the southwest to re-
connect with County Road 6 during construction in 1995. No other improvements or structures
exist in Oregon Gulch (SMI/TerraMatrix, 1997).

The climate of Lake County is dry, but otherwise typical of most alpine regions in the southern
Rocky Mountains. The average annual maximum temperature in the Leadville area is 50.5
degrees Fahrenheit and the average annual minimum temperature is 21.9 degrees Fahrenheit,
with an annual mean temperature of 37.3 degrees Fahrenheit. The south-central portion of the
county, at an elevation near 9,000 feet AMSL, receives about 10 inches of precipitation annually.
Wind is predominantly from the northwest, with speeds typically from 0 to 30 miles per hour
(mph) (WCC, 1994). Populated areas of Leadville are predominantly upwind of OU10
(SMI/TerraMatrix, 1997).
Record or Decision
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2.0 OPERABLE UNIT HISTORY AND ENFORCEMENT ACTIVITIES

The California Gulch Superfund Site is located in the highly mineralized Colorado Mineral Belt
of the Rocky Mountains. Mining, mineral processing, and smelting activities have produced
gold, silver, lead, and zinc for more than 130 years in the Leadville area. Mining and its related
industries continue to be a source of income for both Leadville and Lake County. The Leadville
Historic Mining District includes an extensive network of underground mine workings in a
mineralized area of approximately 8 square miles located around Breece Hill. Mining in the
District began in 1860, when placer gold was discovered in California Gulch. As the placer
deposits were exhausted, underground workings became the principle method for removing gold,
silver, lead, and zinc ore. As these mines were developed, waste rock was excavated along with
the ore and placed near the mine entrances. Ore was crushed and separated into metallic
concentrates at mills, with mill tailings generally siurried into tailings impoundments.

The Oregon Gulch Tailings Impoundment received tailings from the Resurrection-Asarco mill in
California Gulch from approximately 1942 through 1957 (Foothill Engineering Consultants
[FEC], 1995). Removal action activities, performed during September and October 1995,
included the relocation of 28,000 cubic yards of tailings and underlying soil from the Colorado
Zinc-Lead (CZL) Tailings Impoundment to the Oregon Gulch Tailings Impoundment
(SMI/TerraMatrix, 1995a). An additional 550 cubic yards of sediment excavated from the
culvert and embankment in California Gulch, on property owned by Dorothy Hayes, within OU8
were deposited on top of the Oregon Gulch Tailings Impoundment in September 1996
(SMI/TerraMatrix, 1997).

The California Gulch Site was placed on the National Priorities List (NPL) in 1983, under the
authority of the Comprehensive Environmental Response, Compensation, and Liability Act
(CERCLA) of 1980. The Site was placed on the NPL because of concerns about the impact of
mine drainage on surface waters in the California Gulch and the impact of heavy metals loading
in the Arkansas River (EPA, 1997). Several subsequent investigations have been conducted
within the California Gulch SUperfund Site that have addressed the Oregon Gulch Tailings
Impoundment (OU10).

The investigation conducted by Dames & Moore (D&M, 1986) was performed to assess the
slope stability of existing tailings impoundments in California Gulch and Oregon Gulch. The
investigation also included development of conceptual remediation plans for the impoundments,
surface water drainage and runoff controls, and addressed erosional concerns related to the
tailings impoundments. With respect to the Oregon Gulch Tailings Impoundment, the
investigation consisted of performing a site reconnaissance, and soil sampling to determine the
engineering characteristics of the tailings and foundation soils (SMI/TerraMatrix, 1997).

Water, Waste and Land, Inc. (WWL) conducted a hydrologic investigation of the California
Gulch drainage for Resurrection Mining Company in 1989 (WWL, 1990). The study included
surface water, groundwater, and sediment sampling, laboratory analysis of samples, and an
inventory' of mine wastes. The primary objectives of the investigation were to characterize the
Record of Decision
Oregon Gulch OU 10
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surface water and groundwater quality and flow patterns, and to identify sources of metal loading
in California Gulch. Surface water was sampled at 49 locations and sediment was sampled at 50
locations in June 1989. Thirty-four locations were sampled for surface water in the fall of 1989.
The sample locations included California Gulch and tributary drainages, including Oregon
Gulch.

In September 1990, EPA and the potentially responsible parties (PRPs) entered into an
Administrative Order on Consent (AOC) for the performance of soils sampling and air
monitoring. EPA issued a Unilateral Administrative Order (UAO) which required Resurrection
to conduct and complete the final Soils Investigation Work Plan. Field work was completed in
1992 (EPA, 1997).

A surface water remedial investigation (Surface Water RI) of the California Gulch Site was
conducted in 1991 and 1992. The final Surface Water RI report was issued in 1996 by Colder
and Associates describing the results of the surface water investigation (Golder, 1996a). The
study included surface water and sediment sampling in the Arkansas River and. its tributaries,
including California Gulch. Oregon Gulch was sampled at one site just upstream of its
confluence with California Gulch. California Gulch was sampled upstream and downstream of
its confluence with Oregon Gulch.

A groundwater remedial investigation (Hydrogeologic RI) at the California Gulch Site was
conducted from the fall of 1991 through the winter of 1992. The study included installation of
monitoring wells and piezometers, water level measurements, and groundwater sampling and
analysis. The final Hydrogeologic RI Report describing the results of the investigation was
issued by Golder and Associates in 1996 (Golder, 1996b). Objectives of the study were to
investigate groundwater quality and flow directions, evaluate potential impacts to surface water
receptors, and to characterize background groundwater quality. Oregon Gulch groundwater was
sampled at six monitoring wells. Additional piezometers and monitoring wells in the vicinity of
the confluence of Oregon Gulch and California Gulch were utilized to evaluate the impacts of
Oregon Gulch surface water and groundwater on California Gulch groundwater.

The Tailings RI (WCC, 1994) performed in the fall of 1991 was a comprehensive investigation
encompassing five major tailings impoundments and seven fluvial tailings deposits at the
California Gulch Site. The field programs related to the Oregon Gulch Tailings Impoundment
consisted of the following activities: (1) collection of surface tailings composite samples for
geochemical analysis; (2) drilling of 11 borings in or near the impoundment for geochemical and
geotechnical testing of subsurface material properties; (3) completion of monitoring wells in
eight of the borings for groundwater level measurements, in-situ permeability tests, and
groundwater sampling; (4) collection of surface water and groundwater samples to characterize
water quality upgradient and downgradient of the impoundment; and (5) collection of water
samples from wells completed within the impoundment to characterize the quality of the tailings
pore water (SMIATerraMatrix, 1997).
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In 1993, the EPA conducted a Screening Feasibility Study (SFS) (EPA, 1993) to initiate the
overall Comprehensive Environmental Response, Compensation, and Liability Act (CERCLA)
FS process at the California Gulch Site. The purpose of the SFS was to develop general response
actions and identify an appropriate range of alternatives applicable to the various contaminant
sources to be considered during feasibility studies for the California Gulch Site. Remedial
alternatives retained in the SFS for impounded tailings, stream sediments, and fluvial tailings in
OU10 were further evaluated and screened during the FFS (SMI/TerraMatrix, 1997).

Resurrection entered into a Consent Decree (CD) (USDC, 1994) with the United States, the State
of Colorado (State), and other potentially responsible parties (PRPs) at the California Gulch Site
on May 4, 1994. In the CD, Resurrection agreed to perform certain remediation work in three
operable units (OU4,OU8, and OU10). The Work Area Management Plan (WAMP), included as
Appendix D to the CD (USDC, 1994), defines the scope of work to be performed by
Resurrection.

As a part of the scope, the cultural resources of OU10 were surveyed by Foothills Engineering
Consultants (FEC) on June 23,1994 and by P-III Associates, Inc. (P-III) on June 28, 1995. FEC
surveyed the area of the tailings impoundment and the channel in lower. Oregon Gulch. P-III
surveyed an additional 30 acres of Oregon Gulch that would potentially be disturbed during
remedial activities, including the proposed borrow area and access road corridors. The areas
surveyed are discussed in greater detail in Final Cultural Resources Survey of Oregon Gulch
Operable Unit JO, California Gulch Superfund Site. Lake County, Colorado (FEC, 1995) and in
Cultural Resource Inventory of Access Roads and a Borrow Location in (he Oregon Gulch Area,
Operable Unit 10, California Gulch, CERCLA Site, Lake County, Colorado (P-III, 1995).

An Engineering Evaluation/Cost Analysis (EE/CA) (SMI/TerraMatrix, 1995b) was prepared to
evaluate and identify a removal action for miscellaneous tailings and stream sediment contained
within the 500-year floodplain of Oregon Gulch. An Action Memorandum (EPA, 1995) was
issued on August 4, 1995 by the EPA to select the removal action. The Action Memorandum
selected the following alternatives for the "-moval action: (1) Channel Alternative - 10-year
channel, (2) Stabilization Alternative - Excavation and Reconstruction, and (3) Cultural Resource
Alternative - Reconstruct Existing Channel. The Final Removal Action Design Report
(SMI/TerraMatrix, 1995c) was submitted to the EPA on August 28, 1995, and the Removal
Action Work Plan (SMI/TerraMatrix, 1995d), which provided an implementation plan, was
submitted on September 8, 1995. Implementation of the removal action was initiated during the
fall of 1995 and was completed in the fall of 1996.

The selected removal action for the miscellaneous tailings and stream sediment in Oregon Gulch
was an interim response. It is consistent with the performance of the final remedial action
selected for OU 10.

In 1994 Resurrection initiated a geotechnical investigation (SMI/TerraMatrix, 1995e) of the
Oregon Gulch Tailings Impoundment. The goals of the investigation were: (1) to better define
the stratigraphic profile of the impoundment, (2) to determine the position of the phreatic surface
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within the impoundment, and (3) to refine the existing characterization of material properties of
the tailings, embankment, and foundation soils. The field program included drilling seven
borings within the impoundment, collection of soil samples for geotechnical analysis, and
installation of piezometers.

Resurrection conducted the FFS for OU10 in order to expedite remediation. The FFS followed
the general FS process (EPA, 1988), but relevant remedial alternatives were screened to produce
a set of alternatives that were then analyzed in detail. A Work Plan for the Focused Feasibility
Study of Oregon Gulch Operable Unit JO (Work Plan) (SMI/TerraMatrix, Inc., 1996b) was
submitted to EPA on January 23,1996. EPA approval of the Work Plan was received by
Resurrection on May 16, 1996. The Work Plan described the tasks to be performed by
Resurrection during the FFS.

In December of 1996, Resurrection submitted the Draft Focused Feasibility Study for Oregon
Gulch Operable Unit JO (SMI/TerraMatrix 1996a), according to the terms of the Consent
Decree. The FFS provided a detailed analysis of the five retained remediation alternatives from
the SFS as applied to the Oregon Gulch Tailings Impoundment and alternatives from the SFS for
stream sediment.

A Proposed Plan describing the EPAs preferred alternative was issued on March 19,1997. The
preferred alternative was Alternative 5, Multi-Layer Rock and Soil Cover with a Geosynthetic
Barrier. The Final Focused Feasibility Study for Oregon Gulch OUJO (SMI/TerraMatrix, 1997)
was issued in June 1997.
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3.0 HIGHLIGHTS OF COMMUNITY PARTICIPATION

Public participation is required by CERCLA Sections 113 and 117. These sections require that
before adoption of any plan for remedial action to be undertaken by EPA, the State, or an
individual (PRP), the lead aeencv shall:
1. Publish a notice and brief analysis of the Proposed Plan and make such plan
available to the public; and

2. Provide a reasonable opportunity for submission of written and oral comments
and an opportunity for a public meeting at or near the site regarding the Proposed
Plan and any proposed findings relating to cleanup standards. The lead agency
shall keep a transcript of the meeting and make such transcript available to the
public. The notice and analysis published under item #1 above shall include
sufficient information to provide a reasonable explanation of the Proposed Plan
and alternative proposals considered.

Additionally, notice of the final remedial action plan set forth in the ROD must be published and
the plan must be made available to the public before commencing any remedial action. Such a
final plan must be accompanied by a discussion of any significant changes to the preferred
remedy presented in the Proposed Plan along with the reasons for the changes. A response
(Responsiveness Summary) to each of the significant comments, criticisms, and new data
submitted in written or oral presentations during the public comment period must be included
with the ROD.

EPA has conducted the required community participation activities through the presentation of
the RI/FS and the Proposed Plan, a 30-day public comment period, a formal public hearing, and
the presentation of the Selected Remedy in this ROD. No comments were received during the
public comment period.

The Proposed Plan for Oregon Gulch OU10 was relez^ed for public comment on March 19,
1997. The RI/FS and the Proposed Plan were made available to the public in the Administrative
Reco:d located at the EPA Superfund Records Center in Denver and the Lake County Public
Library in Leadville. A formal public comment period was designated from March 19, through
April 18, 1997.

On March 19, 1997, the EPA hosted a public meeting to present the Proposed Plan for Oregon
Gulch OU10 of the California Gulch Superfund Site. The meeting was held at 7:00 p.m. in the
Mining Hall of Fame in Leadville, Colorado. Representatives from the Resurrection Mining
Company presented the Proposed Plan. Five alternatives were discussed: No Action, Simple
Vegetated Cover, Clay Layer with a Vegetated Cover, Multi-Layer Soil Cover with a
Geosynthetic Barrier and Multi-Layer Rock and Soil Cover with a Geosynthetic Barrier. The
Multi-Layer Rock and Soil Cover with a Geosynthetic Barrier was presented as EPA's and
Resurrection's preferred alternative. A portion of the hearing was dedicated to accepting formal
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oral comments from the public. Community acceptance of the Selected Remedy is discussed in
Section 8.0, Summary of Comparative Analysis of Alternatives, of this Decision Summary.
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4.0 SCOPE AND ROLE OF OPERABLE UNIT

The California Gulch Superfund Site covers a wide area (Figure 2). EPA has established the
following OUs for the cleanup of geographically-based areas within the Site. The OUs are
designated as:

OU1 Yak Tunnel/Water Treatment Plan
OU2 Malta Gulch Fluvial Tailings/Leadville Corporation Mill/Malta Gulch Tailings
Impoundment
OU3 D&RGW Slag Piles/Railroad Easement/Railroad Yard and Stockpiled Fine Slag
OU4 Upper California Gulch
OUS ASARCO Smelter/Slag/Mill Sites
OU6 Starr Ditch/Penrose Dump/Stray Horse Gulch/Evans Gulch
OU7 Apache Tailings Impoundment
OUS Lower California Gulch
OU9 Residential Populated Areas
OU10 Oregon Gulch
OU11 Arkansas River Valley Floodplain
OU12 Site Water Quality

The purpose of the Oregon Gulch OU10 RJ/FS was to gather sufficient information to support an
informed risk management decision on which remedies are the most appropriate for the sources
within OU 10 (namely the Oregon Gulch Tailings Impoundment and the stream sediments). The
RI/FS was performed in accordance with the National Oil and Hazardous Substances Pollution
Contingency Plan (NCP), 40 Code of Federal Regulations (CFR) Part 300, and CERCLA
Section 104,42 U.S.C. § 9604.

The objectives of the RI/FS were to:

• Characterize the physical nature of the tailings and strearr -ediments, and to evaluate the
potential impacts of tailings and stream sediments to the surface water and groundwater.

Define the potential pathways along which metals can migrate, as well as the physical
processes ciid, to the extent necessary, the chemical processes that control these
pathways;
• Determine risk assessment information including potential receptors, exposure patterns,
and food chain relationships;
• Develop, screen, and evaluate remedial alternatives and predict the consequences of each
remedy;

Analyze each of the FS alternatives against the NCP (40 C.F.R. 300.430) criteria; and

• Compare the relative performance among each alternative with respect to the evaluation
criteria.
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Based on the findings of previous investigations and the results-of the Tailings RJ (WCC, 1994),
the contamination at the Oregon Gulch Tailings Impoundment has been adequately delineated to
evaluate alternatives in the RJ/FS.

This ROD was prepared according to EPA guidance (EPA, 1989). The remedy outlined in this
ROD is intended to be the final remedial action for OU10. The primary objectives of the remedy
presented in this ROD are:

• Control airborne transport of tailings particles;

• Control erosion of tailings materials and deposition into local water courses;

• Control leaching and migration of metals from tailings into surface water; and

• Control leaching and migration of metals from tailings into groundwater.

Remedial actions undertaken within OU10 are intended to be consistent with the remedial action
objectives and goals identified for the entire California Gulch Superfund Site and other OU
investigations.
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5.0 SUMMARY OF SITE CHARACTERISTICS
5.1 PHYSICAL CHARACTERISTICS

Oregon Gulch is an ephemeral tributary to California Gulch that flows only during the spring
runoff event and during summer storms. The Oregon Gulch watershed drains approximately 185
acres, including the 15.8 acre area of OU10. The Oregon Gulch Tailing Impoundment and the
500-year floodplain of Oregon Gulch comprise approximately 14.2 acres and 1.6 acres,
respectively, of the area of OU10. The Oregon Gulch Tailings Impoundment is located
approximately 1/2 mile upstream of the confluence of Oregon and California gulches and
contains approximately 485,000 cubic yards of material (SMI/TerraMatrix, 1997). The
maximum depth of the impoundment is approximately 75 feet. Figure 3 shows the location of
the impoundment and the surrounding area.

Surface water flow upgradient of the impoundment is diverted into one of three diversion ditches
(see Figure 3). The surface of the tailings impoundment slopes at approximately 2 percent from
the impoundment margins toward the interior of the impoundment where precipitation and runoff
water form a shallow pond estimated to be 0.5 to 1 foot deep. The pond exists year-round, but
fluctuates in size with snowmelt and precipitation events. The impoundment surface is covered
by sand-sized and finer tailings that are generally oxidized and are predominately orange to red
in color. A significant amount of un-oxidized pyritic, fine- to medium-grained sized tailings are
present on the impoundment surface. The side slopes of the embankment are generally
comprised of course-grained tailings sand. Slopes vary from 2:1 (horizontalrvertical) to 1.5:1.
Minor surface erosion, caused by snowmelt and precipitation events, has transported materials
down the embankment, resulting in the formation of small gullies along the embankment face
(SMI/TerraMatrix, 1997).

5.2 GEOTECHNICAL EVALUATION

Three separate studies examined the physical and geotechnical properties of the Oregon Gulch
Tailings Impoundment: Report of Stability and Reclamation Evaluation. Abandoned Tailings
Ponds, Leadville Unit, Lead\sl(e, Colorado, for ASARCO Incorporated (Dames & Moore
[D&M], 1986); Final Tailings Disposal Area Remedial Investigation Report, California Gulch
Site. Leadville. Colorado, (Tailings RI; Woodward Clyde Consultants [WCC], 1994); and
Geotechnical Investigation Report. Oregon Gulch Tailings Impoundment Operable Unit 10
(Geotechnical Investigation Report; Shepherd Miller, Inc. (SMI/TerraMatrix, 1995e). Data and
information resulting from these studies provide a comprehensive characterization of the
physical and geotechnical properties of the Oregon Gulch Tailings Impoundment.

Numerous laboratory geotechnical tests were performed on tailings samples collected from the
impoundment including: grain size analyses, hydrometer tests, Atterberg limits, moisture
content, specific gravity, dry density, direct shear tests, consolidation tests, triaxial tests, and
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permeability tests. The results of these tests are summarized in Appendix D of the FFS
(SMIfTerraMatrix, 1997).

Generally, the tailings impoundment is comprised of a combination of: 1) cohesionless granular
fine-grained sand tailings exhibiting a wide range of relative densities and moisture contents, and
2) soft to moderately firm, weakly cohesive silt and clay (slime) tailings. Native alluvium
underlying the Oregon Gulch Tailings Impoundment consists of a mixture of sand, silt, and clay
in varying proportions, along with lesser amounts of gravel. The density of the tailings sand
comprising the embankment ranges from loose to medium dense based on Standard Penetration
Tests (SPT) performed during drilling and the results of the Cone Penetrometer Test (CPT)
investigation (SMI/TerraMatrix, 1995e). This range of density is normal for hydraulically
deposited sands.

5.3 NATURE AND EXTENT OF CONTAMINATION

Media evaluated include surface and subsurface soil, tailings, surface water, groundwater and
stream sediments within and downgradient of OU10. The following sections summarize the
nature and extent of contamination for each of these media.

5.3.1 SURFACE AND SUBSURFACE SOIL AND TAILINGS

As pan of the tailings RI, three surface tailings composite samples (0 to 0.15 feet deep) were
collected from the impoundment. Each composite sample consisted of 10 individual subsamples
collected from: 1) the embankment face, 2) the crest of the embankment, and 3) the interior
surface of the impoundment. Subsurface tailings and alluvial foundation samples were collected
from borings OG1B4, OG1B5, OG1B6, OB1B7, OB1B9, and OG1B10, drilled during the
Tailings RI. The locations of the borings are shown in Figure 4.

Tailings and foundation soil samples collected for Tailings RI were analyzed for arsenic,
cadmium, lead, and zine. Selected samples were also analyzed for the following additional
metals: antimony, barium, beryllium, chromium, copper, manganese, mercury, nickel, silver, and
thallium. A summary of arsenic, cadmium, lead, and zinc concentrations of tailings surface
composite samples, tailings subsurface samples, and foundation soil samples is presented in
Table 1. Surface tailings median concentrations of metals were as follows: arsenic - 747
milligrams per kilogram (mg/kg), cadmium - 9.5 mg/kg, lead - 2,170 mg/kg, and zinc - 1,280
mg/kg, respectively.

Median constituent concentrations in subsurface tailings samples were: arsenic - 439.5 mg/kg,
cadmium - 47.4 mg/kg, lead - 3,475 mg/kg, and zinc - 8,720 mg/kg (Table 1). The highest
concentrations of these metals were: arsenic - 1,430 mg/kg (OG1B6), cadmium - 196 mg/kg
(OG1B9), lead - 13,800 mg/kg (OBIB 10), and zinc - 29,300 mg/kg (OG1B9). Concentrations of
lead and zinc are relatively consistent throughout the tailings profile, while arsenic and cadmium
concentrations tend to decrease with depth.
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Metal concentrations in foundation soils were significantly less than concentrations of tailings
samples collected from the impoundment. Median concentrations of metals in the foundation
soils were: arsenic - 12.8 mg/kg, cadmium - 1.2 mg/kg, lead - 77 mg/kg, and zinc - 185.5 mg/kg
(SMI/TerraMatrix, 1997).

5.3.2 SURFACE WATER

The Oregon Gulch channel downstream of the impoundment is approximately 2,700 feet long,
and drains to the northwest into California Gulch (Figure 3). A perennial seep emerges near the
toe of the tailings impoundment and generally infiltrates into the Oregon Gulch alluvium after
flowing a short distance downstream of the impoundment. A berm along the tailings
embankment crest prevents surface water from overflowing the impoundment. A perennial
surface water pond exists near the southeastern edge of the impoundment. The surface area of
the pond is typically about one acre, but fluctuates seasonally depending on climatic conditions.

Surface water quality in Oregon Gulch is characterized by low pH and elevated metal
concentrations. The Oregon Gulch Tailings Impoundment is the primary source of acidic water
and metals loading in Oregon Gulch. Concentrations of metals in surface water upstream of the
impoundment are lower than in surface water in Oregon Gulch downstream of the impoundment.
The seep discharging near the toe of the Oregon Gulch Tailings Impoundment is acidic and
contains elevated metal concentrations that represent a source of metal loading to Oregon Gulch.
Potential contaminants of concern (COCs) in Oregon Gulch surface waters are total suspended
solids (TSS), metals (arsenic, cadmium, copper, lead and zinc), sulfate, and low pH.

Surface water quality sampling has been conducted at six locations in Oregon Gulch between
1989 and June 1996. The locations, shown on Figure 5, are: 1) ponded water on the tailings
impoundment (OGPD), 2) the tailings impoundment seep (OGS), 3) the sediment pond outlet
(OG-2 - post fall 1995), 4) the south diversion ditch around the southwest perimeter of the
impoundment at the confluence with Oregon Gulch (OGDD), 5) Oregon Gulch upgradient of the
tailings impoundment (OGUP), and 6) Oregon Gulch just upstream of the confluence wit}.
California Gulch (OG-1) (SMFTerraMatrix, 1997).

Tailings Ponded Water Quality The w.uer ponded on top of the Oregon Gulch Tailings
Impoundment was sampled during four events: June 1989, September 1991, June 1995, and
June 1996. Analytical results are included in Table 2. The source of the ponded water is
precipitation and runoff from the surface of the tailings. The water quality of the pond is affected
by dissolution of metals from the tailings. Concentrations of arsenic, cadmium, copper and lead
were elevated as compared to concentrations of surface water in Oregon Gulch at OG-1. Total
constituent concentrations in ponded water were similar to the dissolved concentrations.
Dissolved and total concentrations of arsenic and copper detected in samples of the ponded water
are the highest concentrations observed in any surface water samples collected in OU10.
Seasonal variation in the concentrations can be attributed to dilution by snowmelt in spring and
early summer resulting in lower concentrations and evaporation of ponded water causing higher
concentrations in the fall (SMI/TerraMatrix, 1997).
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Tailings Seep Water Quality The seep emerging from the toe of the Oregon Gulch Tailings
Impoundment has been sampled on thirteen occasions from 1989 through June 1996. Table 3
presents the analytical results and mass loading for selected constituents from the seep samples.
Field pH ranged between 2.64 and 3.21 . For all sampling events except the June 1 , 1995 event,
concentrations of zinc and sulfate vary within a narrow range, while concentrations of other
constituents vary approximately one order of magnitude. The June 1, 1995 sample included
discharge from an abandoned decant line that was draining ponded water from the top of the
tailings impoundment. Seep samples collected on that date had lower concentrations of sulfate,
zinc, total dissolved solids (TDS), and TSS due to dilution by the decant flows.

Dissolved zinc concentrations at the seep typically comprise 90 percent of the total zinc
concentrations. Dissolved concentrations of arsenic, cadmium, and copper were also similar to
the total concentrations. However, total concentrations of lead wtre typically greater than the
dissolved concentrations of lead by at least a factor of 2.

Comparison of chemical analyses of the seep with flows at the mouth of Oregon Gulch indicates
that the seep concentrations are higher than surface flow concentrations for each analyte of
concern except cadmium for dates when samples were collected at both sites, but the pH values
are slightly lower at the mouth of Oregon Gulch. Ranges of the (SMI/TerraMatrix, 1997) COC
concentrations vary less for the seep than COC concentration ranges in Oregon Gulch.
Comparisons of chemical analyses of the seep with the ponded water on top of the impoundment
indicate that the seep has higher concentrations of cadmium, zinc, and sulfate, whereas pH values
are lower in the pond (SMI/TerraMatrix, 1997).

South Diversion Ditch Water Quality The south diversion ditch was sampled at its confluence
with Oregon Gulch on June 1, 1995, and May 8 and May 17, 1996. Table 4 presents the COC
concentrations and mass loadings. Dissolved metals concentrations in surface water samples
from the south diversion ditch were significantly lower in comparison with metal concentrations
of the tailings ponded water, tailings seep, and Oregon Gulch surface water at OG-1. Sulfate
concentrations average 60 mg/L and the field pH average 3.8 1 . The TDS concentration average
was 1 06.7 mg/L, while the average TSS concentration was 694 mg/L. Total concentrations of
arsenic, lead, and copper were significantly higher than the dissolved concentrations.
Comparison of dissolved to total concentrations indicates that all of the cadmium was in the
dissolved form, dissolved arsenic was 3.8 percent of the total arsenic, dissolved lead was 2
percent of the total lead, dissolved copper was 30 percent of the total copper, and dissolved zinc
was 68 percent of the total zinc (SMI/TerraMatrix, 1997).

Upgradient Water Quality Surface water in Oregon Gulch was sampled upgradient of the
tailings impoundment on May 8, 1996. The sample was collected in the south diversion ditch
just downstream of the confluence of the east diversion ditch with the Oregon Gulch stream
channel (Figure 5, OGUP). Metals concentrations in the upgradient sample were above detection
but were significantly lower in comparison with metal concentrations in samples from the south
diversion ditch. Dissolved arsenic was <0.001 mg/L, and total arsenic was 0.015 mg/L.
Dissolved cadmium was 6.003 mg/L, and total cadmium was 0.005 mg/L. Dissolved copper was
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0.003 mg/L and total copper was 0.02 mg/L. Dissolved lead was 0.002 mg/L and total lead was
0.201 mg/L. Dissolved zinc was 0.4 mg/L and total zinc was 0.78 mg/L. Field pH was 5.37, and
field conductivity was 50 ^mhos/cm. Sulfate concentration was 10 mg/L. The TDS
concentration was below the detection level of 40 mg/L, while the TSS concentration was 316
mg/L. Total concentrations of COCs were significantly higher than dissolved COC
concentrations.

Oregon Gulch Water Quality Surface water in Oregon Gulch was sampled at the confluence
with California Gulch (OG-1, Figure 5) on 21 occasions between 1991 and June 1996. COC
concentrations and mass loadings are presented in Table 5. Over the seven year sampling period.
the pH of Oregon Gulch surface flows has ranged between 2.20 and 3.49, and TDS
concentrations have ranged from 740 to 37,900 mg/L. For most of the sampling events,
dissolved concentrations of cadmium, copper, and zinc comprise the majority of each metal
present, whereas total concentrations of lead and arsenic are significantly higher than dissolved
concentrations.

The analytical results show general patterns of lower constituent concentrations during high flow
events, presumably due to dilution by runoff. Metals concentrations generally increase with
increased flowrates, then diminish prior to peak flows. Evaluation of the sources of flow within
Oregon Gulch indicate that the south diversion ditch contributes a majority of the flow measured
in Oregon Gulch at OG-1 during the spring runoff event. The relatively higher flows and lower
constituent concentrations of the south diversion ditch tend to dilute the concentrations at OG-1
(SMIATerraMatrix, 1997).

5.3.3 GROUNDWATER

Groundwater in Oregon Gulch is contained in consolidated bedrock, unconsolidated glacial till
and outwash sediments, alluvium, and as pore water within the Oregon Gulch Tailings
Impoundment. Three aquifer systems have been identified in Oregon Gulch. The deepest is the
bedrock aquifer. Overlying the bedrock in unconsolidated alluvial and glacial sediments is an
intermediate alluvial aquifer. A perched aquifer exists downgradient of the tailings
impoundment in the shallow alluvial sediments of Oregon Gulch. A perched saturated zone has
also been identified within the Oregon Gulch Tailinjs Impoundment.

Monitoring wells and piezometers have been completed within the tailings impoundment and
within alluvium in surrounding areas to better characterize the hydrogeologic conditions in
Oregon Gulch. Figure 5 shows the locations of the monitoring wells and the piezometers. The
EPA installed a monitoring well (NW-4) in Oregon Gulch 500 feet downstream of the toe of the
tailings embankment. As part of the Tailings RJ, eight monitoring wells were installed in the
vicinity of OU10: one upstream of the Oregon Gulch Tailings Impoundment, four within the
tailings impoundment, and three downstream of the impoundment in Oregon Gulch. A
monitoring well (OG1TMW9, Figure 4) was installed in Oregon Gulch downstream of the
impoundment in 1994 (SMI/TerraMatrix, 1994). Additional hydrologic data were gathered from
borings and CPTs during a geotechnical investigation of the tailings impoundment
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(SMlTerraMatrix, 1995e). During this investigation, one impoundment boring, OG1TP-1. was
completed as a piezometer. Groundwater levels have been measured in the intermediate alluvial
aquifer monitoring wells, the shallow perched aquifer in Oregon Gulch, and within the tailings
impoundment (SMI/TerraMatrix. 1997).

Groundwater piezometric contour maps and cross-sections have been prepared for the
intermediate alluvial and shallow perched aquifers in the vicinity of Oregon Gulch. Groundwater
elevations in monitoring wells OG1TMW1 and OG1TMW9 (Figure 5), completed in the
intermediate alluvial aquifer, indicate that approximately 100 feet of unsaturated alluvium exists
beneath the tailings impoundment. Water elevations in the intermediate alluvial aquifer
(OG1TMW1, OG1TMW9, PZ6, AP1TMW7, and NW16) on Figure 5 indicate that the hydraulic
gradient is approximately 6 percent to the west. The perched saturated zone within the tailings
extends from the seep at the northwest embankment to within the interior of the impoundment.
Water within the impoundment flows toward the seep at an average gradient of approximately 8
percent. The southwest embankment and a majority of the northern embankment appear to be
unsaturated. The maximum saturated tailings thickness of approximately 35 feet occurs within
the impoundment approximately 200 feet southeast of the embankment crest.

Surface water quality criteria have also been utilized to identify COCs for OU10 groundwater
due to the interaction between shallow groundwater and surface water. The Preliminary
Ecological Risk Assessment for Oregon Gulch (PERAOG) (Weston, 1995a) determined surface
water COCs to be cadmium, copper, and zinc based on potential acute exposure to aquatic life.
Arsenic, cadmium, copper, lead, zinc, and sulfate were also listed based on chronic exposure to
aquatic life. Arsenic, cadmium, copper, lead, zinc and sulfate were identified as COCs in the
FFS for characterization of groundwater for evaluation of remedial action alternatives. The fate
and transport of COCs in groundwater are discussed in the following paragraphs.

Dissolution and mobilization of metals by leaching of tailings or sediments by infiltrating waters
are pathways by which metals can enter groundwater within OU10. Primary sources of metals
within OU10 include the Oregon Gulch Tailings Impoundment, and tailings and stream
sediments contained in the floodplain of Oregon Gulch (SMI/TerraMatrix, 1997).

Groundwater quality data is available for three of the water-bearing zones in OU10: the
intermediate alluvial aquifer, the perched saturated zone within the impoundment, and the
perched alluvial aquifer downgradient of the tailings impoundment.

Table 6 presents water quality data for COCs, pH, and TDS, for the intermediate aquifer based
on samples collected from monitoring wells OG1TMW1 and OG1TMW9 (Figure 5). Metal
concentrations of groundwater samples collected from monitoring well OG1TMW1, located
upgradient of the Oregon Gulch Tailings Impoundment, were below detection limits except for
arsenic which was detected at concentrations of 0.001 mg/L to 0.002 mg/L. The pH ranges from
7.72 to 8.33. Sulfate was detected at concentrations of 6 and 10 mg/L. Groundwater quality at
monitoring well OG1TMW9, located northwest of the tailings impoundment, is also shown in
Table 6. Metal concentrations in groundwater at OG1TMW9 are similar to concentrations
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observed at OG1TMW1. The pH of groundwater at OG1TMW9 was between 7.75 and 7.80
during the three sampling episodes. As shown in Table 6, the quality of the intermediate alluvial
aquifer is characterized by alkaline pH and metal concentrations at or below the laboratory
detection values. Concentrations of the intermediate alluvial aquifer are significantly less than
groundwater concentrations for the perched alluvial aquifer in Oregon Gulch or the pore water
contained within the Oregon Gulch Tailings Impoundment (SMI/TerraMatrix, 1997).

Table 7 provides a summary of water quality data for the perched saturated zone within the
Oregon Gulch Tailings Impoundment, as represented by tailings monitoring wells OG1TMW4,
OG1TMW5, and OG1TMW6A. Figure 5 shows the locations of these monitoring wells. Water
samples collected from these monitoring wells indicate that the tailings pore water is acidic (pH
ranges from 4.1 to 5.4) and contains elevated concentrations of dissolved arsenic, cadmium, lead,
and zinc. Sulfate concentrations ranged from 9,220 mg/L to 30,300 mg/L. Referring to the
water quality of the tailing seep previously provided in Table 3, the pH of the tailings seep
(average pH is 2.9) is less than the pH of the perched water within the tailings (average pH is
4.8); however, average metal concentrations of the tailings seep are less than the tailings pore
water by factors ranging from approximately 3 to 30 depending on the specific metal
(SMI/TerraMatrix, 1997).

Table 8 summarizes the chemical analyses of groundwater samples collected from the perched
alluvial aquifer as represented by monitoring wells OG1TMW8 and OG1TMW3. As shown on
Figure 5, monitoring well OG1TMW8 is located near the toe of the tailings embankment, and
monitoring well OG1TMW3 is located approximately 1,500 feet downstream of the toe of the
embankment. The pH at OG1TMW8 ranged from 4.06 to 4.29, while the pH at OG1TMW3 was
significantly lower ranging from 1.90 to 2.81. Sulfate concentrations at both monitoring wells
were similar and ranged from 22,500 to 39,600 mg/L. Average concentrations of arsenic,
cadmium, copper, and zinc were higher at OG1TMW3 than at OG1TMW8. Lead concentrations
in the perched alluvial aquifer were typically lower at downgradient monitoring well OG1TMW3
as compared to OG1TMW8. Based on the comparison of concentrations at OG1TMW8 and
OG1TMW3, concentrations of metals in the perched alluvial aquifer increased and pH decreased
as groundwater migrated downgradient in Oregon Gulch (SMI/TerraMatrix, 1997).

The groundwater quality of the perched alluvial aquifer was also ".ompared to the water quality
of the tailings seep (Table 3) and tailings pore water within the impoundment (Table 7).
Groundwater average metal concentrations at OG1TMW8, located near the toe of the tailings
impoundment, were lower as compared to the average concentrations of the tailings seep and
tailings pore water. The average pH of groundwater at OG1TMW8 was 4.2 as compared to the
average pH of 2.9 for the tailings seep and 4.8 for the tailings pore water. In contrast, the
average metal concentrations at OG1TMW3, located further downgradient in Oregon Gulch,
were higher than the average metal concentrations of the tailings seep and tailings pore water.
except for dissolved lead.
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5.3.3.1 Groundwater-Surface Water Interaction

As previously discussed, surface water flows in Oregon Gulch are hydraulically connected and
interact with the shallow, perched alluvial aquifer in Oregon Gulch. Portions of California Gulch
have also been identified as losing or gaining stream reaches. Losing reaches are defined as
areas where surface water recharges groundwater. Gaining reaches are defined as locations
where groundwater discharges into surface water.

In the Hydrogeologic RI (Golder, 1996b). a gaining reach was identified in California Gulch
generally from the confluences of Oregon Gulch and Starr Ditch with California Gulch to a
distance of approximately 600 feet downstream. The load contributed from shallow groundwater
in Oregon Gulch to this reach of California Gulch was estimated as discussed below.

Estimated loading for the constituents of concern contributed by groundwater in Oregon Gulch to
California Gulch is presented in Table 9 The constituent loading rates were based on the
average dissolved concentrations from smnples collected from monitoring well OG1TMW3 and
the estimated shallow groundwater discharge rate from Oregon Gulch. The average annual
discharge of shallow Oregon Gulch groundwater to California Gulch surface flows was
calculated in the FFS to be 2.8 gpm. The average loads contributed by Oregon Gulch
groundwater were compared to the average loading at point CG-4 (Figure 5), the surface water
sampling site in California Gulch downstream of the confluence with Oregon Gulch. Available
data from sampling events between 1989 to October 1995 were used to calculate the average
constituent loading rate at point CG-4.

The groundwater flow rate from Oregon Gulch of 2.8 gpm is approximately 0.3 percent of the
average flow at CG-4 of 1,632 gpm. As shown in Table 9, shallow groundwater flow in Oregon
Gulch was estimated to contribute the following percentages of loading at CG-4 in California
Gulch: 50 percent of the arsenic load, 0.5 percent of the cadmium, 3 percent of the copper, 0.003
percent of the lead, 5.2 percent of the zinc, and 6.4 percent of the sulfate (SMI/TerraMatrix,
1997).

5.3.4 STREAM SEDIMENTS

Several studies have been conducted to evaluate the metal content in stream sediments in the
California Gulch drainage. As part of these investigations, stream sediment samples were
collected and analyzed. Sediment samples were collected at various surface water sample
locations with California Gulch. Sediment sampling locations in the vicinity of Oregon Gulch
are shown on Figure 5.

Sources of metal contamination to stream sediments in Oregon Gulch include the deposition of
tailings eroded from the embankment of the Oregon Gulch Tailings Impoundment and the
migration of acidic surface water and groundwater containing inorganic metals. Metals
contained in runoff from the tailings embankment and in the tailings seep have contributed to
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metals loading of the stream sediments in Oregon Gulch. The stream sediments contain tailings
and metal precipitates intermixed with native sediment.

Stream sediments in Oregon Gulch are subject to downstream transport during snowmelt runoff
or storm events. In addition, metals adsorbed to or precipitated onto stream sediments may serve
as secondary sources where changes in the water chemistry cause these sorbed or precipitated
metals to re-dissolve into surface water. Mechanisms for the release of metals from stream
sediment into groundwater include direct leaching of stream sediments by groundwater, and
leaching of metals adsorbed or precipitated in stream sediments by surface water infiltrating into
groundwater (SMI/TerraMatrix, 1997).

Metal concentrations of sediment samples collected in 1989 from Oregon Gulch during the
California Gulch Hydrologic Investigation (WWL, 1990) are summarized in Table 10. Within
Oregon Gulch, metal concentrations in stream sediments were observed to be the highest
immediately downstream of the toe of the embankment where eroded tailings have been
deposited (WWL, 1990). Metals concentrations were also elevated in the upper reaches of the
south diversion ditch immediately downstream of the tailings impoundment where erosion along
the southwest embankment has occurred.

Metal con'centrations of stream sediment samples collected between 1989 and 1994 in Oregon
Gulch and at sites in California Gulch upstream and downstream of Oregon Gulch are provided
in Table 11. Metal concentrations in Oregon Gulch stream sediments at OG-1 were generally
lower than concentrations of stream sediments in California Gulch at sampling locations CG-3
(upstream of Oregon Gulch) and CG-4 (downstream of Oregon Gulch). However, sulfate
concentrations of Oregon Gulch stream sediments were higher than sulfate concentrations of
stream sediments in California Gulch (SMI/TerraMatrix, 1997).

5.3.5 AIR

No air quality data has been collected within OU10. Prevailing winds in the Leadville area are
predominately from the west-northwest and to a lesser extent from the northeast. Consequently,
the predominant wind flow over the Oregon Gulch Tailings Impoundment is away from
populated areas of Leadville (SMI/TerraMatrix, 1997).

5.4 HISTORIC AND CULTURAL RESOURCES

During the survey by Foothill Engineering Consultants (FEC, 1995), three cultural resources
sites were identified within Oregon Gulch: (1) the Oregon Gulch Tailings Impoundment (Site
5LK382), (2) historic trash scatter in Oregon Gulch extending from the east side of County Road
6 to an upstream distance of approximately 470 feet (Site 5LK844), and (3) the gravel check dam
located about 0.2 miles upstream of County Road 6 (Site 5LK850). Based on the results of the
cultural resources survey, EPA determined that Site 5LK.844 was eligible for nomination to the
National Register of Historic Places (NRHP). The Stale Historic Preservation Office concurred
with this determination. The 5LK844 site consists of a large historic trash scatter and
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depressions located in Oregon Gulch east of County Road 6, as shown on Figure 3. Artifacts on
the 5LK844 site include glass, ceramics, tin cans, construction materials, and other miscellaneous
items (FEC, 1995). Site 5LK.844 is heavily disturbed by humafi activities and by the natural
geomorphologic processes of Oregon Gulch. The Midland Railroad extended across the gulch in
the middle portion of the 5LK844 site. A road to Georgia Gulch (to the south) crossed the site
area, and a two-track dirt road also extended up the gulch along the north edge of the drainage.
In addition, the area around the 5LK844 site has been used as a trash dump until the present time
(FEC, 1995). Remedial actions in Oregon Gulch outside the boundaries of Site 5LK844 will not
affect any known resources considered eligible for the NRHP. The Tailings Impoundment (Site
5LK382) and the gravel check dam (Site 5LK850) were determined not individually eligible for
the NRHP (SMIATerraMatrix, 1997).

A cultural resource inventory was also conducted by P-III (P-III, 1995) to survey access roads
and a borrow area to be used during response activities. The survey did not discover historic
sites or artifacts in the areas inventoried. Some modem trash and isolated debris were identified
during the inventory; however, no discernible histon properties were encountered in the
inventoried areas. P-III concluded that ground-disturbing activities in the areas inventoried
would not affect any historic properties.
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6.0 SUMMARY OF SITE RISKS

Baseline human health and ecological risk assessments characterize baseline risks at a site (risks
that would exist if no action were taken). They provide the basis for remedial action and indicate
the exposure pathways to be addressed. The following sections of the ROD summarize risk
assessment information describing exposure pathways, contaminants, and potential risks at
OU10.

6.1 HUMAN HEALTH RISKS

OU10 is zoned for industrial and mining use. There are no residents in OU10. OU10 is not used
for any industrial purposes other than the Oregon Gulch Tailings Impoundment. Neither
commercial or industrial workers are exposed to the tailings. Also, OU10 is private property and
is not currently defined as a recreation area. Therefore, exposure pathways to humans do not
currently exist in OU10.

6.2 ECOLOGICAL RISKS

Several baseline risk assessments have characterized ecological risks at OU10. These reports are
as follows:

• Preliminary Ecological Risk Assessment for Oregon Gulch (OUW) (PERAOG) (Weston
1995a)
• Draft Baseline Aquatic Ecological Risk Assessment, California Gulch NPL Site (BARA)
(Weston 1995b)
• Ecological Risk Assessment for the Terrestrial Ecosystem. California Gulch NPL Site,
Leadville, Colorado (ERA) (Weston 1997)

The PERAOG (Weston 1995a) is a preliminary screening-level assessment of risk to aquatic and
terrestrial ecosystems specifically related to contaminant sources in Oregon Gulch. Impacts of
mine waste contamination on the aquatic ecosystem at the California Gulch NPL Site are
characterized in the BARA (Weston 1995b). The ERA (Weston 1997) identifies potential risks
to the terrestrial ecosystem from mine wastes within the California Gulch NPL Site.

6.2.1 CONTAMINANT IDENTIFICATION

Based on the information available (i.e. Section 5), media evaluated for potential ecological risks
consist of tailings, surface soil associated with the tailings, ponded water, surface water, and
sediments. It is unlikely that ecological receptors would be directly exposed to groundwater;
therefore, groundwater is evaluated only in the context of loadings to surface water. All
inorganic contaminants detected in site media, including arsenic, barium, cadmium, chromium,
copper, lead, manganese, mercury, nickel, silver, thallium, and zinc, were evaluated for potential
ecological risks.
Record of Decision
Oregon Gulch OU 10
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6.2.2 EXPOSURE ASSESSMENT

Five components are generally necessary for exposure to occur:

A source of contamination (i.e., the tailings impoundment)
A mechanism of chemical release (i.e., runoff)
• A retention or transport medium (i.e., surface water)
A point of potential contact of the receptor with the contaminated medium (e.g., plants in
soil)
An exposure route at the contact point (i.e., ingestion, direct contact)

The primary source of metals in OU10 is the Oregon Gulch Tailings Impoundment. Release
mechanisms of metals from the tailings impoundment to surface water and sediment include
erosion of tailings from the embankment, surface water runoff, seep discharge, and loading by
groundwater. Metals from the tailings impoundment are potentially released to groundwater by
leaching and migration. Contaminants in stream sediment are p entially released by dissolution
of metals into surface water and by leaching of metals into groundwater.

Potential terrestrial receptors in OU10 include terrestrial wildlife, birds, plants, and soil fauna.
The stream in Oregon Gulch is generally dry, therefore, aquatic receptors do not exist for OU10.
However, aquatic receptors in California Gulch and the Arkansas River could contact sediments
and surface water impacted by contamination from OU10.

Potential exposure pathways to contaminated media in OU10 include: 1) ingestion of surface
tailings by terrestrial receptors, 2) direct contact of terrestrial receptors to surface tailings and
surface water, 3) ingestion of ponded surface water, surface water from the stream channel and
diversion ditch, and surface water from seeps by terrestrial receptors, and 4) incidental ingestion
of sediment by terrestrial receptors during ingestion of surface water.

Aquatic receptors in California Gulch and the Arkansas River could potentially be exposed to
sediments and surface water impacted by OU10 contamination through 1) ingestion of surface
water, sediments, and contaminated dietary items, and 2) direct contact with surface water and
sedi nents.

The ERA (Weston, 1997) selected several terrestrial receptors to represent exposed terrestrial
populations at the site. Terrestrial receptors selected for use in the ERA were blue grouse,
mountain bluebird, American kestrel, red-tailed hawk, bald eagle, least chipmunk, mule deer, and
red fox. Plants and soil fauna were also evaluated for contact with media.

The PERAOG (Weston 1995a) did not identify specific ecological receptors, rather,
representative receptor groups were selected, consisting of passerine, raptor, small herbivore,
large herbivore, small omnivore, and large omnivore receptors. Aquatic receptors in the
Arkansas River and California Gulch were also evaluated for intake of contaminants from
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undiluted surface water and sediment from Oregon Gulch. Aquatic receptors were evaluated as
one group.

Since aquatic life has not been identified in OU10 due to intermittent flow in Oregon Gulch,
contaminant intake by aquatic receptors was not defined as a pathway for evaluation in the
BARA (Weston 1995b). However, OU10 may contribute to contamination in California Gulch
and the Arkansas River through metal loadings in surface water and sediment. Aquatic receptors
in California Gulch and the Arkansas River may be at increased risk from contaminants
contributed by Oregon Gulch.

Contaminant intake was calculated for representative terrestrial receptors using estimates of
exposure (i.e., ingestion rate) combined with estimates of contaminant exposure point
concentrations (the concentration of contaminant at the point r f exposure). Maximum
contaminant concentrations or the 95th percent upper confidence limit of the arithmetic mean
were used as exposure point concentrations. Estimates of contaminant intake were used to
evaluate potential risk to terrestrial receptors.

6.2.3 RISK CHARACTERIZATION

All of the risk assessments used the hazard quotient (HQ) approach to evaluate risk. In this
approach, the exposure point concentration or the contaminant intake is divided by chemical-
specific toxicity criteria. A HQ less than one indicates there is little potential for adverse effects
to occur from exposure to a specific chemical via the exposure pathway evaluated. A HQ greater
than one indicates a potential for risk but does not necessarily mean that adverse effects will
occur. The sum of the HQs is the hazard index (HI).

For terrestrial receptors, contaminant intake for each receptor was divided by toxicity criteria to
obtain an HQ. Toxicological literature were reviewed to derive acceptable chemical intake
values for birds and mammals, and acceptable media concentrations for plants and soil fauna.
F-'.csuiting benchmark values were used as the toxicity criteria.

Aquatic macroinvertebrates, fish, and aquatic plants were assumed to be exposed directly to
contaminants in surface water and sediments. Contaminant exposure point concentrations in
surface water (dissolved concentrations) and sediments were compared to federal criteria such as
the ambient water quality criteria (AWQC), state standards, or other toxicity criteria. Surface
water and sediment criteria are designed to protect all aquatic species. HQs were obtained by
division of the exposure point concentration by the toxicity criteria.

Results of risk characterization in the PERAOG indicated that terrestrial wildlife and birds are at
risk from exposure to contaminants in tailings, surface water, and sediments in OU10. Table 12
summarizes the His for terrestrial receptors at OU10 for all exposure pathways and all
contaminants. As indicated by risk estimates in the PERAOG. His based on average exposure
range from 33 for large omnivores to 2,160 for passerines. For reasonable maximum exposure
(RME), His range from 46 for large omnivores to 3.601 for passerines. Although not all HQs
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exceed one, all His are greater than one, indicating that all terrestrial receptors are at potential
risk from exposure to one or more contaminants at OU10.

Table 13 summarizes the HQs presented in the PERAOG for aquatic life in California Gulch
and/or the Arkansas River exposed to undiluted contaminant concentrations in surface water
from Oregon Gulch. As shown in Table 13, several HQs exceed one for both average and RME
intake. The maximum HQ from comparison of acute AWQC to average intake is 3,715 for zinc.
The maximum HQ from comparison of chronic AWQC to average intake is 4,053 for zinc. HQs
based on RME intake are correspondingly greater. The maximum HQs from comparison of
acute and chronic AWQC to RME intake is 6,313 and 6,887 (both for zinc), respectively. These
HQs indicate that aquatic receptors in California Gulch and/or the Arkansas River are at potential
risk from exposure to contaminants in undiluted surface water from Oregon Gulch.

Table 14 provides the HQs presented in the PERAOG for aquatic life in California Gulch and/or
the Arkansas River exposed to undiluted contaminant concentrations in sediments from Oregon
Gulch. As shown in this table, several HQs exceed one for both average and RME intake. The
maximum HQ for average exposure is 14, for copper. The maximum HQ for RME intake is 27,
for arsenic. These HQs indicate that aquatic receptors in California Gulch and/or the Arkansas
River are at potential risk from exposure to contaminants in sediments from Oregon Gulch.

The characterization of risks presented in the ERA indicated that terrestrial wildlife and birds are
at risk from exposure to contaminants in tailings, surface water, and sediments in OU10. Table
15 summarizes the His presented in the ERA for terrestrial receptors at OU10 for all exposure
pathways and all contaminants. His exceed one for the blue grouse, mountain bluebird,
American kestrel, and least chipmunk. This indicates there is potential risk to terrestrial
receptors at OU10 from exposure to contaminants.

The BARA identifies the impact of mine waste contamination on the aquatic ecosystem at the
California Gulch Superfund Site. Mine waste, including waste rock, tailings piles, and smelter
wastes in the form of slag, flue dust, and stack emissions have caused increased metal loadings to
surface water and sediments in the California Gulch area and the Arkansas River. The physical
limitations of Oregon Gulch preclude the support of aquatic life, therefore, risk evaluations in the
BARA were focused on California Gulch and the Arkansas River. Risk to aquatic life was not
calculated for Oregon Gulch. Surface water and sediment data presented in the BARA indicate
that Oregon Gulch is a contributing source to the ongoing metal pollution of surface water and
sediment in California Gulch and the Arkansas River. Contaminants in surface water and
sediments in California Gulch and the Arkansas River present a risk to aquatic receptors. Oregon
Gulch contributes to this risk; however, the portion contributed by Oregon Gulch was not defined
in the BARA.

6.3 SUMMARY

The results of the risk assessments pertinent to OU10 indicate the following media and exposure
pathways present potential risk to terrestrial and/or aquatic receptors:
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• Ingestion of surface tailings by terrestrial receptors

Direct exposure of plants and soil fauna to surface tailings

Ingestion of surface water and accompanying incidental ingestion of sediment by terrestrial
receptors

Direct exposure of aquatic receptors to surface water downstream of OU10

• Direct exposure of aquatic receptors to sediment downstream of OU 10

The following conclusions may be reached from results presented in the ERA, BARA, and
PERAOG:

• The tailings pile presents a potential risk to terrestrial receptors and to downstream aquatic
receptors through runoff, etc.

Surface water presents a potential risk to terrestrial receptors and to the aquatic ecosystem
downstream of OU 10

• Sediment presents a potential risk to terrestrial receptors and to the aquatic ecosystem
downstream of OU 10

• OU 10 is a contributing source of contaminants to downstream surface water and sediment
and therefore contributes to the potential risk in California Gulch.
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7.0 DESCRIPTION OF ALTERNATIVES

A wide range of cleanup options were considered in the Screening Feasibility Study (SFS) (EPA,
1993). Some of the alternatives were eliminated during preliminary screening because they
would not effectively address contamination, could not be implemented, or would have had
excessive costs. Remedial action alternatives for OU10 that were retained after screening
alternatives from the SFS for stream sediments were evaluated in the EE/CA and the alternatives
for the impounded tailings were evaluated in the FFS. All of the alternatives were evaluated
using the nine criteria required by the NCP and six additional performance criteria required by
the WAMP as a pan of the CD. This evaluation is described in the next section.

Three categories of alternatives were evaluated in the EE/CA for Oregon Gulch Stream Sediment
(SMI/TerraMatrix, 1995b): (1) channel alternatives, (2) floodplain stabilization alternatives, and
(3) cultural resource alternatives. Two channel alternatives, a 500-year channel and a 10-year
channel, were evaluated for their potential to stabilize the channel in Oregon Gulch below the
tailing impoundment. Four floodplain stabilization alternatives were considered to address the
area outside the newly constructed channel. These alternatives are: (1) stabilization in place, (2)
cover in place, (3) excavation and reconstruction, and (4) treatment in place. Four remedial
action alternatives were developed to address the remediation at Cultural Resource Site 5LK844
while avoiding adverse impacts to the site. These alternatives are: (1) no action, (2) avoidance,
(3) covering, and (4) reconstructing the existing channel. In conjunction with these alternatives,
a sediment control pond was proposed for construction in Oregon Gulch downstream of the toe
of the tailing impoundment to protect the stream channel from eroded tailing and sediment.

A brief description of the five clean up alternatives that were considered in the FFS for the
Oregon Gulch OU10 impounded tailings (SMI/TerraMatrix, 1997) is provided below.

Alternative 1: No Action

Estimated capital and operating cost: SO
Implementation time: Immediate

No remediation would take place under this alternative. This is the "no action" alternative
required under CERCLA and is used as a baseline against which other alternatives are evaluated.
The existing impoundment is susceptible to erosion and migration of tailings as well as leaching
of metals from tailings. Existing diversion ditches reduce the amount of run-on to the tailings
surface. A sediment control dam, built as part of the Oregon Gulch Stream Sediment EE/CA
(SMI/TerraMatrix, 1995b), captures sediment from runoff from the northwest embankment.

Alternative 2: Simple Vegetated Cover

Estimated capital and operating cost: $1,830,000
Implementation time: 1 to 2 years
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This alternative would consist of regrading the tailings impoundment surface and embankment,
and placing a soil cover. The simple soil cover would consist of a structural fill layer comprised
of regraded tailings and borrow soil followed by a 3-inch-thick layer of granular limestone. The
limestone would be overlain by an 18-inch-thick growth media layer, including soil amendments.
The cover would be revegetated with a mixture of native and introduced species adapted to the
location (SMI/TerraMatrix, 1997).

Alternative 3: Clay Layer Vegetated Cover

Estimated capital and operating cost: $1,980,000
Implementation time: 1 to 2 years

This alternative would consist of regrading the tailings impoundment surface and embankment,
and placement of a vegetated cover with a low-permeability clay layer on the top of the
impoundment and a simple vegetated cover on the embankment side slopes. The low-
permeability clay cover placed on the top of the impoundment would consist of a structural fill
layer made up of regraded tailings and borrow soil, a 12-inch-thick low-permeability clay layer, a
6-inch-thick sand drainage layer, a geotextile, an 18-inch-thick random fill layer, and a vegetated
12-inch-thick growth media layer with soil amendments. The cover placed on the embankments
would be similar to the cover used with Alternative 2. This cover would consist of 3 inches of
granular limestone overlain by an 18-inch-thick growth media layer, including soil amendments
and vegetation (SMI/TerraMatrix, 1997).

The tailings embankments would be regraded to a slope of 2.75:1 or flatter to increase stability
and meet WAMP criteria (USDC, 1994). The final design of the regraded embankment slope
would be determined during the remedial design based on available data that may be
supplemented by laboratory testing of site soils. The tailings impoundment surface would be
regraded to eliminate ponding and achieve positive drainage into a low-permeability diversion
ditch located adjacent to the east side of the impoundment. The diversion ditch located adjacent
to the east side of the impoundment would drain to the south diversion ditch. To reduce the
potential for groundwater entering the tailing impoundment, an upgradient groundwater
interceptor trench would be constructed in the Oregon Gulch channel upstream of the tailing
impoundment. Collected groundwater would drain to the south diversion ditch. This alternative
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also includes a provision to collect and treat the seep currently discharging at the toe of the
impoundment until the seep no longer impacts surface water quality.

Alternative 4: Soil Cover with Geosynthetic Barrier

Estimated capital and operating cost: $2.270.000
Implementation time: 1 to 2 years

This alternative would consist of regrading the tailings impoundment surface and embankments,
and placement of a soil cover with a geosynthetic barrier layer on the top of the impoundment
and a simple vegetated cover on the tailings embankments. The tailings embankments would be
regraded to a slope of 2.75:1 or flatter to increase stability and meet WAMP criteria (USDC,
1994). The final design of the regraded embankment slope would be determined during the
remedial design based on available data that may be supplemented by laboratory testing of site
soils (SMin~erraMatrix, 1997).

The impoundment top surface would be regraded to achieve positive drainage from the surface
into a low-permeability diversion ditch located adjacent to the east side of the impoundment.
The diversion ditch located adjacent to the east side of the impoundment would drain to the south
diversion ditch. The cover placed on the top of the impoundment would consist of a structural
fill layer consisting of regraded tailings or borrow soil, a geosynthetic barrier, a sand drainage
layer, a geotextile, and an 18-inch-thick layer of plant growth media layer.

The simple cover placed on the embankments would be similar to the cover specified in
Alternative 2. This simple cover would consist of 3 inches of granular limestone placed over the
regraded tailings followed by an 18-inch-thick growth media layer, including soil amendments
and establishing vegetation.

To reduce the potential for groundwater entering the tailing impoundment, an upgradient
groundwater interceptor trench would be constructed in the Oregon Gulch channel upstream of
the tailing impoundment. Collected groundwater would drain to the south diversion ditch. This
alternative also includes a provision to collect and treat the seep currently discharging at the toe
of the impoundment until the seep no longer impacts surface water quality.

Alternative 5: Multi-Layer Rock and Soil Cover with Geosynthetic Barrier .

Estimated capital and operating cost: $2.540,000
Time to implement: 1 to 2 years

This alternative includes regrading the tailings impoundment surface and embankments, and
placement of a multi-layer cover with a geosynthetic barrier layer. The tailings embankments
would be regraded to slopes of 3:1 or flatter to enhance stabilization, and the top of the
impoundment surface would be regraded to achieve positive drainage from the surface into a
low-permeability diversion ditch located adjacent to the east side of the impoundment. The
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diversion ditch located adjacent to the east side of the impoundment would drain to the south
diversion ditch. The cover placed on the impoundment (including the embankments) would
consist of structural fill consisting of borrow or suitable tailings, a geosynthetic barrier layer, and
a geocomposite drainage layer. An 18-inch-thick layer of plant growth media would be placed
on the top of the impoundment over the geocomposite drainage layer. On the embankments, an
18-inch-thick layer of random fill overlain with an erosion-resistant, 6-inch-thick gravel layer
would be placed over the geocomposite drainage layer. The regraded and covered surface would
eliminate ponding on the impoundment and allow runoff to drain into the diversion ditch.

The tailings embankment would be regraded to a 3:1 slope or flatter to increase stability and
meet WAMP criteria (USDC, 1994). The final design of the regraded embankment slope would
be determined during the remedial design based on available data which may be supplemented
by laboratory testing of site soils and samples of specific geosynthetic cover components
(SMI/TerraMatrix, 1997). The top surface of the tailings would be regraded to a slope of 2
percent towards the diversion ditch located on the east side.

Section 300.430(e)(9) of the NCP requires that the EPA evaluates and compares the remedial
cleanup alternatives based on the nine criteria listed below. The first two criteria, (I) overall
protection of human health and the environment and (2) compliance with applicable or relevant
and appropriate requirements (ARARs) in Appendix A, are threshold criteria that must be met
for the Selected Remedy. The Selected Remedy must then represent the best balance of the
remaining primary balancing and modifying criteria. In addition the cleanup alternatives were .
evaluated using six performance criteria specified in the WAMP (USDC, 1994) to assist in
evaluating the effectiveness of each alternative.

8.1 NCP EVALUATION AND COMPARISON CRITERIA

8.1.1 THRESHOLD CRITERIA

1. Overall protection of human health and the environment addresses whether or not a
remedy provides adequate protection and describes how potential risks posed through
each pathway are eliminated, reduced, or controlled through treatment, engineering
controls, or Institutional Controls.

2. Compliance with ARARs addresses whether or not a remedy will comply with identified
federal and state environmental and siting laws and regulations.

8.1.2 PRIMARY BALANCING CRITERIA

3. Long-term effectiveness and permanence refers to the ability of a remedy to maintain
reliable protection of human health and the environment over time.

4. Reduction of toxicitv. mobility and volume through treatment refers to the degree that the
remedy reduces toxicity, mobility, and volume of the contamination.

5. Short-term effectiveness addresses the period of time needed to complete the remedy and
any adverse impact on human health and the environment that may be posed during the
construction and implementation period until cleanup goals are achieved.

6. Implementability refers to the technical and administrative feasibilities of a remedy,
including the availability of materials and services needed to carry out a particular option.

7. Cost evaluates the estimates capital costs, operation and maintenance (O&M) costs, and
present worth costs of each alternative.
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8.1.3 MODIFYING CRITERIA

8. State acceptance indicates whether the State (CDPHE), based on its review of the
information, concurs with, opposes, or has no comment on the preferred alternative.

9. Community acceptance is based on whether community concerns are addressed by the
Selected Remedy and whether or not the community has a preference for a remedy.

8.2 WAMP PERFORMANCE CRITERIA

Additional site-specific criteria beyond the required NCP criteria have been developed for
evaluating remedial alternatives for OU10. These criteria are described in the WAMP attached
as Appendix D to the Consent Decree for the California Gulch Site. The six WAMP (USDC,
1994) criteria described below have assisted in the evaluation of the effectiveness of each
proposed alternative:

1. Surface Erosion Stability: Remedial alternatives for source material will ensure surface
erosion stability through the development of surface configurations and implementation
of erosion protection measures. The remedial design will meet the following criteria:

a. Erosional releases of waste material are predicted by use of all or some of the
following procedures: the Revised Universal Soils Loss Equation (RUSLE), wind
erosion soil loss equation (Woodruff and Siddoway, 1965), and the procedures set
forth in the U.S. Nuclear Regulatory Commission's Staff Technical Position.
Design of Erosion Protection Covers for Stabilization of Uranium Mill Tailings
Sites (NRC, 1990) for site-specific storm flow conditions set forth in l.b below.

b. Remediated surfaces located within the 500-year floodplain will be stable under
500-year, 24-hour, and 2-hour storm events. Remediated surfaces located outside
the 500-year floodplain will be s j >le under 100-year, 24-hour, and 2-hour storm
events. On source embankments or where the slope of the reconstructed source is
steeper than 5:1 (Horizontal-.Vertical), surface flow will be concentrated by a
factor of 3 for purposes of evaluating erosion stability.

2. Slope Stability: Source remediation alternatives will ensure geotechnical stability
through the development of embankments or slope contours. The remedial design will
meet the following criteria:

a. Impounding embankments will be designed with a Factor of Safety (Safety
Factor) of 1.5 for static conditions and 1.0 for pseudo-static conditions.

b. Recontoured slopes will be designed with a Safety Factor of 1.5 for static
conditions and 1.0 for pseudo-static conditions.
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c. Analysis of geotechnical stability will be performed using an acceptable computer
model. Material and geometry input parameters will be obtained from available
data.

3. flow Capacity and Stability: Remedial alternatives utilizing retaining structures,
diversion ditches, or reconstructed stream channels will ensure sufficient capacity and
erosional stability of those structures. The remedial design will meet the following
criteria:

a. Capacity: Diversion ditches will be sized to convey the 100-year, 24-hour, and 2-
hour storm events. Reconstructed stream channels will be sized to convey flow
equal to or greater than the flow capacity immediately upstream of the
reconstruci:on.

b. Stability: Erosional release of waste material from ditches, stream channels, or
retaining structures will be determined by either or both of the following models:
U.S. Army Corps of Engineers Hydrologic Engineering Center HEC-1 (COE,
1991) and HEC-2 (COE, 1990) models.

1) Diversion Ditches and Reconstructed Stream Channels: Remedial
surfaces located within the California Gulch 500-year floodplain will be
designed to be stable under flows resulting from 500-year, 24-hour, and 2-
hour storm events. Remedial construction outside the 500-year floodplain
will be designed to withstand flows resulting from the 100-year, 24-hour,
and 2-hour storm events. Reconstructed team channels will be configured
to the extent practicable to replicate naturally occurring channel patterns.

2) Retaining Structures: Structures such as gabions, earth dikes, or riprap
will be designed to be stable under the conditions stated above under item
3.b. 1 for the diversion ditch or stream channel with which the structure is
associated. If riprap is to be placed in stream channels or ditches, the
riprap will be sized utilizing one of the following methods:

U.S. Army Corps of Engineers (COE, 1991);
Safety Factor Method (Stevens and Simons, 1971);
Stephenson Method (Stephenson, 1979);
Abt/CSU Method (Abt, et. al., 1988).

Selection of one of these methods will be based on the site-specific flow
and slope conditions encountered.

4. Surface and Groundwater Loading Reduction: Remedial alternatives will ensure
reduction of mass loading of COCs (including TSS and sulfate), as defined in the Draft
Final Terrestrial Risk Assessment (see WAMP [USDC, 1994]), and change in pH,
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resulting from run-on, run-off, and infiltration from source areas. The FFS will
incorporate the following:

. a. For each source of contamination evaluated in the FFS, the present mass loading
of COCs (including TSS and sulfate) will be calculated for both surface and
groundwater using scientifically accepted methods. Present pH measurements
will also be calculated.

b. For each source of contamination evaluated in the FFS, the net loading reduction
of COCs (including TSS and sulfate) and change in pH resulting from
implementation of each remedial alternative shall be calculated for surface and
groundwater using scientifically accepted methods.

5. Terrestrial Ecosystem Exposure: Evaluation of remedial action alternatives with respect
to reduction of risk to the terrestrial ecosystems within each OU should be based on area-
wide estimates of risk to receptor populations. Exposure estimates for assessing this risk
should consider factors that affect the frequency and duration of contact with
contaminated media, such as: (1) the concentrations and area! extent of contamination,
and (2) the effect of home range on the amount of time a given species will spend in
contact with contaminated media. For each source of contamination evaluated in the
FFS, the reduction of the potential exposure predicted to result from the implementation
of each remedial action alternative will be compared to the present potential exposure
predicted by the terrestrial ecosystem risk assessment, as follows:

a. For each source of contamination evaluated in the FFS, the present risk due to
exposure as defined in the terrestrial ecosystem risk assessment will be estimated
for soil, each source of contamination, and ponded surface water associated with
each source of contamination.

b. For each source of contamination evaluated ii he FFS, reduction of exposure and
ecological risk resulting from the implementation of each remedial alternative will
be estimated for soil and the media types above. The potential exposure predicted
to result from implementation of each remedial alternative will be compared to the
present potential baseline exposure predicted by the terrestrial ecosystem risk
assessment.

6. Non-residential Soils: Non-residential soils will be addressed in the FFS. These non-
residential soils are in areas zone agricultural/forest, highway/business, and
industrial/mining. The non-residential areas xvithin the OU will be evaluated in the FFS
consistent with current and likely future land use.
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8.3 EVALUATING THE ALTERNATIVES WITH THE NCP CRITERIA

A comparative analysis of the channel and floodplairi remedial action alternatives for the stream
sediments in Oregon Gulch was performed in the EE/CA and subsequently summarized in the
Action Memorandum (EPA, 1995). The EE/CA found that the 10-year channel alternative and
the 500-year channel alternative would both achieve RAOs and comply with ARARs. The long-
term effectiveness and permanence of the two channel alternatives would also be similar. The
10-year channel alternative, however, is less costly and less difficult to implement than the 500-
year channel alternative.

The EE/CA and Action Memorandum also evaluated four floodplain alternatives. The four
alternatives achieve RAOs to varying degrees. The excavation and reconstruction alternative
offered the greatest degree of overall protection to the environment in controlling erosion and
reducing leaching of metals to groundwater and surface water. The excavation and
reconstruction alternative also provided greater longterm effectiveness and permanence since
sediments and miscellaneous tailing within the 500-year floodplain would be removed. All four
floodplain alternatives would provide similar performance based on implementability. The
estimated cost of the floodplain alternatives in conjunction with the 10-year channel alternative
ranged from $112,000 for the stabilization in place alternative to $154,00 for the treatment in
place alternative.

Of the cultural resource alternatives analyzed in the EE/CA, reconstructing the existing channel
offered the greatest degree of overall protection to the environment by eliminating erosion and
leaching of metals to groundwater and surface water and is less costly and less difficult to
construct than either the avoidance or covering alternatives. The no action alternative was
presented as a baseline for comparison the other three alternatives.

What follows is a brief summary of the evaluation and comparison of the Oregon Gulch Tailings
Impoundment alternatives. Additional details evaluating the alternatives are presented in the
FFS. This section evaluates the Oregon Gulch OU10 tailings impoundment alternatives against
the nine NCP criteria. Table 16 provides a comparison of the five remedial action alternatives
and the nine NCP criteria. Information for this section was obtained from the FFS for Oregon
Gulch OU10(SMI/TerraMatrix, 1997).

8.3.1 OVERALL PROTECTION OF HUMAN HEALTH AND THE ENVIRONMENT

This criterion is based on the level of protection of human health and the environment afforded
by each alternative. All of the alternatives, except Alternative 1 (No Action), would provide
adequate protection of human health and the environment. Because the "no action" alternative is
not protective of human health and the environment, it is not considered further in this analysis
as an option for this site.
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Although tailings materials and contaminated soils would remain on site, residual risks would be
reduced under all action alternatives (except No Action) to achieve protection of human health
via:

• The use of engineered covers to provide a barrier to wastes; and/or

• The use of revegetated treatment techniques to reduce the surface erosion.

Alternatives 2 through 5 provide overall protection of human health and the environment by
meeting the following remedial action objectives (RAOs) defined for impounded tailings in the
SFS:

• Control airborne transport of tailings particles;

• Control erosion of tailings materials and deposition in local water courses;

• Control leaching and migration of metals from tailings into surface water; and

• Control leaching and migration of metals from tailings into groundwater.

The primary difference between the alternatives is the increased protectiveness provided by
covers with a geosynthetic barrier (Alternatives 4 and 5). Alternatives 4 and 5 would provide a
higher level of infiltration reduction than the other alternatives. Alternative 5 would offer the
greatest erosional stability and the greatest reduction in infiltration since the geosynthetic barrier
would be installed over the entire area of the regraded impoundment (top surface and
embankment slopes), as compared to only on the top surface for Alternative 4.

8.3.2 COMPLIANCE WITH APPLICABLE OR RELEVANT AND APPROPRIATE
REQUIREMENTS (ARARs)

This criterion is based on compliance with the ARARs presented in Appendix A. Alternatives 2
through 5 would comply with all of the ARARs.

8.3.3 LONG-TERM EFFECTIVENESS AND PERMANENCE

Depending on the specific remedial action alternative, Alternatives 2 through 5 would provide
good to excellent long-term effectiveness and permanence. All of the surfaces for Alternative 2
through 5 provide for positive drainage from the surface to the diversion ditches and would be
resistant to erosion. In comparison to the other alternatives. Alternative 5 would provide the
highest level of permanence and long-term effectiveness. The rock cover surface on the
embankment slopes for Alternative 5 would be erosion resistant, and long-term maintenance
requirements would be minimal.
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8.3.4 REDUCTION OF TOXICITY, MOBILITY, OR VOLUME THROUGH
TREATMENT

This criterion is based on the treatment process used; the amount of contamination destroyed or
treated; the reduction of toxicity, mobility, and volume; the irreversible nature of the treatment;
the type and quantity of residuals remaining; and the statutory preference for treatment.
Alternatives 2 through 5 would all greatly reduce the mobility of the tailings (and metals) by
regrading the surface and constructing the cover. However, toxicity and volume of the tailings
would be unaffected by these alternatives. In addition these alternatives would not comply with
the statutory preference for treatment.

8.3.5 SHORT-TERM EFFECTIVENESS

This criterion is based on the degree of community and worker protection offered, the potential
environmental impacts of the remediation, and the time until the remedial action is completed.
Additional risk to the community during implementation of Alternatives 2 through 5 may result
from dust emissions and increased road traffic. The topography surrounding the remediation
area and the prevailing wind directions in the area (predominantly from the northwest) are
conducive to natural abatement of short-term risk to the community from these alternatives.
Furthermore, short-term risk factors could be effectively managed with standard engineering
controls during construction. Dust abatement is a commonly practiced construction method.
Additional traffic would be light and limited to private roads in the immediate vicinity of Oregon
Gulch. The borrow source for construction materials is adjacent to the impoundment thus
minimizing the haul distance.

Risk to workers during implementation of those alternatives may result from dust inhalation,
contact with contaminated materials, and other industrial safety hazards. Dust generation would
be mitigated using standard construction site watering and dust control practices. Contact with
tailings by trained remediation workers would be minimal, because appropriate safety measures
would be utilized.

Impacts to the environment during implementation of these remedial actions could potentially
result from accidental discharge of runoff with suspended solids from tailings disturbed during
construction. Potential problems would be minimized through the use of sediment control
measures, including the existing sediment control pond downstream of the impoundment.

8.3.6 IMPLEMENTABILITY

This criterion is based on the ability to perform construction and implement administrative
actions. The construction technologies used in Alternatives 2 through 5 are commonly used and
widely accepted. Materials and personnel would be readily available for this type of work. The
geosynthetic installation (Alternatives 4 and 5) may require specialized equipment and trained
personnel.
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The administrative feasibility of these alternatives would be good. Compliance with statutory
limits would not be necessary since the selected remedial action would not be CERCLA fund-
financed. Construction permits would not be necessary since all the work would occur on site.
Res- Asarco joint venture and Resurrection own a majority of the land area within OU10
including the adjacent haul road and the majority of the borrow area (BLM has jurisdiction of a
small portion), so obtaining access from land owners would not be an issue.

8.3.7 COST

This criterion evaluates the estimated capital, O&M and present worth costs of each alternative.
Present worth costs range from $1.83 million (Alternative 2) to $2.54 million (Alternative 5).
The present worth of post-removal site control costs for a 30-year period were calculated
assuming a 7 percent discount rate.

Alternative 2: Simple Vegetated Cover

The estimated cost for this alternative would be $1.83 million. Estimated cost details are
summarized in Table 17.
o
Alternative 3: Clay Layer Vegetated Cover

The estimated cost for this alternative would be $1.98 million. Estimated cost details are
summarized in Table 18.

Alternative 4: Soil Cover with. Geosynthetic Barrier

The estimated cost for this alternative would be $2.27 million. Estimated cost details are
summarized in Table 19.

Alternative 5: Muhi-Laver Rock and Soil Cover with Geosvnthetic Barrier

The estimated cost for this alternative would be $2.54 million. Estimated cost details are
summarized in Table 20.

8.3.8 STATE ACCEPTANCE

The State has been consulted throughout this process and concurs with the Selected Remedy.

8.3.9 COMMUNITY ACCEPTANCE

Public comment on the RI/FS and Proposed Plan was solicited during a formal public comment
period extending from March 19 to April 18, 1997. It is assumed that the community is
generally supportive of EPA's Multi-Layer Rock and Soil Cover with Geosynthetic Barrier
alternative since no comments were received during the formal public comment period.
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8.4 EVALUATING THE ALTERNATIVES WITH THE WAMP CRITERIA

A comparative analysis of the channel and floodplairi remedial action alternatives for the stream
sediments in Oregon Gulch using the WAMP criteria was performed in the FFS. The Action
Memorandum implemented the Removal Action for the stream sediments (EPA, 1995).

All channel, floodplain, and cultural resource alternatives would comply with WAMP criteria for
surface erosion stability. The loading reduction for the channel alternatives were determined to
be similar. Of the four floodplain alternatives, the cover in place alternative and the excavation
and reconstruction alternative is predicted to provide a slightly higher predicted reduction in
surface and groundwater flows. The cover in place alternative and the excavation and
reconstruction alternative would also eliminate the risk to the terrestrial ecosystem by covering
or removing the miscellaneous tailing and stream sediment. The predicted loading reductions
and reduction in terrestrial ecosystem are similar for the cultural resource alternatives. Non-
residential soils have not been identified as a source of contamination within OU10.
What follows is a brief summary of the agencies' evaluation and comparison of Oregon Gulch
Tailings Impoundment alternatives against the six WAMP criteria. Additional details evaluating
the alternatives are presented in the FFS. Table 21 presents a comparison of the ability of the
five remedial action alternatives to achieve WAMP criteria. Information for this section was
obtained from the FFS for Oregon Gulch OU10 (SMI/TerraMatrix, 1997).

8.4.1 SURFACE EROSION STABILITY

This criterion evaluates surface erosion stability through the development of surface
configurations and implementation of erosion protection. All of the alternatives, except
Alternative 1 (No Action), would achieve the erosional stability criteria, defined by the WAMP,
with vegetative or rock covers and would reduce the existing loading of metals to surface or
groundwater. Because the "no action" alternative does not provide erosional stability, it is not
evaluated further in this analysis as an option for this site. Alternative 5 would provide the
highest level of erosional stability.

8.4.2 SLOPE STABILITY

This criterion evaluates geotechnical stability through the development of embankments or slope
contours to meet factors of safety criteria defined by the WAMP. Alternatives 2 through 4 would
provide embankment slopes regraded to 2.75:1 or flatter to meet WAMP criteria. Alternatives 5
would provide embankment slopes regraded to 3:1 or flatter to meet WAMP criteria.

8.4.3 FLOW CAPACITY AND STABILITY

This criterion evaluates the capacity and erosional stability of retained structures, diversion
ditches, or reconstructed stream channels. Alternatives 2 through 5 would provide diversion
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ditches around the perimeter of the impoundment to be sized to convey the 100-year, 24-hour
storm and be erosionally stable according to WAMP criteria. The channels would be stabilized
using vegetation, riprap, concrete, or several manufactured channel reinforcement products.

8.4.4 SURFACE WATER AND GROUNDWATER LOADING REDUCTION

This criterion evaluates the extent to which an alternative would ensure the reduction of mass
loading of COCs resulting from run-on, run-off, and infiltration from source areas.

The predicted reductions in surface water loading and groundwater loading were calculated for
each alternative, and are summarized in Table 21. The reduction of loading was calculated by
comparing existing conditions to predicted conditions for each alternative. The covers would
reduce lo iding by reducing or eliminating surface water contact with tailings and by reducing
infiltration.

Alternatives 2 through 5 would provide a similar reduction in surface water loading. For
Alternatives 2 through 5, surface water loading is predicted to be reduced from current loading
conditions by approximately 89 percent to 100 percent, depending on the contaminant of
concern. As shown in Table 21, the predicted reduction in groundwater loading ranges from 84.4
percent for Alternative 2 to 99.8 percent for Alternative 5 since each alternative reduces
infiltration by a different amount.

8.4.5 TERRESTRIAL ECOSYSTEM EXPOSURE

This criterion evaluates the ability of each alternative to reduce risk to the terrestrial ecosystem
within OU10. Each of the covers for Alternatives 2 through 5 would virtually eliminate the risk
to the terrestrial ecosystem by isolating the tailings and removing the existing surface water
pond.

8.4.6 NON-RESIDENTIAL SOILS

This criterion is not applicable. The sources of contamination at OU10 are miscellaneous
tailings and stream sediment, not non-residentL! soils. Non-residential soils are not a source of
contamination within OU10.
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9.0 SELECTED REMEDY
An Action Memorandum (EPA, 1995) was issued on August 4, 1995 by the EPA that selected
the following as the removal action for stream sediments within OU10:

Channel Alternative: 10-Year Channel. This alternative consists of constructing a
channel capable of conveying the 10-year flood and stabilizing both the channel and the
overbank area inundated during the 500-year flood. Channel construction will include
excavating sediment to an average depth of 1.5 feet, mixing limestone in the first foot of
subsoil underlying the channel, installing a geotextile, and placing riprap.

Stabilization Alternative: Excavation and Reconstruction. This alternative controls
the release of contaminants by stabilizing the area outside the 100-year channel within the
500-year flood plain of Oregon Gulch. This alternative consists of: (1) excavating a 1-
foot-thick layer of sediment, (2) transporting the excavated sediment to the Oregon Gulch
Tailing Impoundment, and (3) re-establishing the excavated area of the gulch by
regrading, placement of a 1-foot-thick layer of fill in the excavated area, amending the
soil, and revegation.

Cultural Resource Alternative: Reconstruct Existing Channel. This alternative
consists of removing stream sediment in the existing channel within Site 5LK.844 to an
average depth of 1.5 feet, mixing limestone in the first foot of subsoil underlying the
channel, and stabilizing the channel with riprap for the 500-year flood. Excavation
within the disturbed area of the existing channel will not disturb cultural resources.

A Final Removal Action Design Report (SMI/TerraMatrix, 1995c) was submitted to the EPA on
August 28, 1995, and a Removal Action Work Plan (SMI/TerraMatrix, 1995d) providing an
implementation plan was submitted on September 8,1995. Implementation of the removal
action was initiated during the fall of 1995 and was completed in the fall of 1996.

Based upon consideration of CERCLA requirements, the detailed analysis of alternatives, and
public comments, EPA has determined that the Multi-Layer Rock and Soil Cover with a
Geosynthetic Barrier alternative presented in the Proposed Plan, with no modifications, is the
appropriate remedy for the Oregon Gulch Tailings Impoundment within OU10. This Selected
Remedy will reduce risk to human health and the environment through the following:

• Provides the highest level of permanence and long-term effectiveness with the greatest
reduction of infiltration into the tailings impoundment.

• Meets or exceeds all of the stability requirements predicated in the WAMP and
minimizes the present risk to the terrestrial ecosystem. In addition, the cover proposed in
the Selected Remedy exceeds the other alternatives in its ability to reduce the loading of
contaminants to the surface water and the groundwater.
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• Eliminates airborne transport of tailings particles and minimizes both the erosion of
tailings materials and deposition into local water courses and the leaching and migration
of metals into groundwater and surface water.

• Controls the risks defined by the risk assessment including ingestion of surface tailings
by terrestrial wildlife, contact of plants and soil fauna with surface tailings, and ingestion
of surface water by wildlife.

The Selected Remedy best meets the entire range of selection criteria and achieves, in EPA's
determination, the appropriate balance considering site-specific conditions and criteria identified
in CERCLA, the NCP and the WAMP, as provided in Section 10.0, Statutory Determinations.

9.1 REMEDY FOR THE OREGON GULCH TAILINGS IMPOUNDMENT

The Selected Remedy would consist of regrading the impoundment surface to provide positive
drainage and flattening the embankment side slopes to 3:1 or milder. A geosynthetic barrier
would be installed over a structural fill layer to control infiltration over the entire regraded
impoundment (top and side slopes), followed by a geocomposite drainage layer (Figure 6). An
18-inch-thick vegetated soil layer will be placed on the top of the geocomposite drainage layer.
On the side slopes, an 18-inch-thick layer of random fill overlain with an erosion-resistant 6-
inch-thick gravel layer would placed over the geocomposite drainage layer.

The structural fill layer would consist of borrow soil or sandy tailings free of debris. This layer
would be placed and compacted on top of the regraded tailings in areas of soft tailings and in
areas requiring fill. The purpose of this layer is to achieve trafficability for heavy equipment to
all areas of the tailings and provide a firm base free from protruding rocks and debris on which
the overlying geosynthetic and soil layers would be placed. In areas of firm tailings, located
primarily in the embankment area, the structural fill layer may not be required. The thickness of
this layer would also depend on the regraded surface configuration.

An infiltration barrier consisting of a geosynthetic barrier layer would be placed over the
structural fill layer. The geosynthetic barrier would have a permeability of 3x10'9 cm/sec or less,
based on manufacturer's data. A geocomposite drainage layer, consisting of drainage netting
covered on both sides with a geotextile, would be installed over the geosynthetic barrier. This
layer would provide a lateral drainage pathway for any infiltration that may accumulate on the
geosynthetic barrier. The geotextile would allow water to infiltrate the drainage netting, but
would prevent migration of fine soil particles that may plug openings in the netting
(SMI/TerraMatrix, 1997).

An 18-inch-thick layer of plant growth media would be placed over the geocomposite drainage
layer on the top of the impoundment. The plant growth media would consist of borrow soil
screened to remove oversized rocks and amended, as required, with nutrients, manure, and/or
organic matter to help establish and sustain vegetation. The amount and types of nutrients would
Record of Decision
Oreeon Gulch OUIO
8497P 3280-013 OUIO'FINALROD'OUIOROD.WPD
-------
be based on the analysis of the borrow material comprising this layer. The seed mixture for
revegetation of the cover would contain both native and introduced grasses and forbs that would
produce a self-sustaining plant community that would not require irrigation or nutrient
supplements.

On the embankments of the impoundment, an 18-inch-thick layer of random fill would be placed
over the geocomposite drainage layer. A 6-inch-thick gravel layer would be placed over the
random fill layer to provide erosion protection.

The East Diversion Ditch would be constructed on the east side of the impoundment to convey
runoff from the impoundment and to divert potential run-on flow away from the impoundment.
This ditch would be built with a low-permeability lining to reduce infiltration (Figure 7). The
discharge from the East Diversion Ditch, along with runoff from upstream Oregon Gulch, would
flow to the South Diversion Ditch. This ditch would also be built with a low-permeability lining
to minimize infiltration where the ditch is adjacent to the tailings impoundment. The South
Diversion Ditch would follow its CVL -;nt alignment to a point approximately 100 feet northwest
of the impoundment, where it would be directed through a drop channel to empty into the
Oregon Gulch channel just upstream of the existing Sediment Control Pond. The existing South
Diversion Ditch alignment downstream of the drop channel would be reclaimed by regrading the
channel sideslopes to 3:1 or flatter and revegetating (SMI/TerraMatrix, 1997).

To reduce the potential for groundwater entering the tailings impoundment, an upgradient
groundwater interceptor trench would be constructed in the Oregon Gulch channel upstream of
the tailings impoundment (Figure 7). Collected groundwater would drain to the South Diversion
Ditch. The Oregon Gulch channel upstream of the impoundment would also be lined from its
confluence with the South Diversion Ditch to just upstream of the groundwater interceptor trench
to minimize infiltration.

Temporary erosion and sediment control measures would be used around the perimeter of the site
until the multi-layer cover is installed on the regraded embankment and impoundment surface;
these measures may include silt fencing, straw bales, and possibly erosion control matting. A
temporary sediment control dam, built as part of the Oregon Gulch Stream Sediment EE/CA will
capture sediment from runoff from the northwest embankment. Following installation of the
cover, the sediment control dam would not be needed and could be removed (SMI/TerraMatrix,
1997).

The Selected Remedy will include active managment of the seep currently discharging at the toe
of the Oregon Gulch Tailing Impoundment during the interim period from implementation of the
selected alternative until the seep does not negatively impact surface water quality. Active
management of the seep discharge will be performed during non-freezing conditions and will
include collection and either pumping or transport of the collected flow to the Yak Tunnel
Treatment Plant or other suitable treatment options. Design of the Selected Remedy will include
a drain system at the toe of the embankment to allow the seep discharge to flow unrestricted and
to be collected in a controlled manner. After implementation of the Selected Remedy, seep flow
Record of Decision
Oregon Gulch 01! 10 __
SJ'TP JISO-OIJOUIO'FINAl-RODOL'IOROD.WPD Ub-42
-------
rates are anticipated to decrease, lessening any potential water quality impacts during winter
months.

9.2 CONTINGENCY MEASURES

Specific water quality goals for surface streams and heavy metals contamination have not been
established at this time. EPA has agreed to establish specific surface and groundwater
requirements at a later date when EPA, CDPHE, and the PRPs have reached agreement on the
allowable heavy-metals contaminant loadings for each of the contributing source areas (operable
units) for the entire California Gulch Superfund Site.

Existing data will be compared to water quality and sediment data collected after the Selected
Remedy has been implemented. An evaluation of the degree of surface water-quality
improvement will be made by EPA and CDPHE at that time. If the improvement in Oregon
Gulch surface water quality is not considered sufficient then additional response actions may be
performed.

The Selected Remedy will be designed to minimize active maintenance requirements. Post-
closure maintenance of the impermeable cap and vegetative or rock armor cover will be used to
ensure that the integrity and permance of the cap is maintained. Provisions for surveillance and
repair will be established.

Because the Oregon Gulch Tailings Impoundment will remain on site, the Selected Remedy will
require a five-year review under Section 121(c) of CERCLA and Section 300.430(0(4)(ii) of the
NCP. The five-year review includes a review of the groundwater and surface water monitoring
data, inspection of the integrity of the cap, and an evaluation as to how well the Selected Remedy
is achieving the RAOs and ARARs that it was designed to meet.
Record of Decision
Oeton Gulch OU10
sj'):p: j:go-on-OL'io FINALROD OUIOROD WPD
-------
10.0 STATUTORY DETERMINATIONS

Under CERCLA Section 121, EPA must select a remedy that is protective of human health and
the environment; that complies with ARARs; is cost effective; and utilizes permanent solutions,
and alternative treatment technologies, or resource recovery technologies to the maximum extent
practicable. In addition, CERCLA includes a preference for remedies that include treatment
which permanently and significantly reduces the volume, toxicity, or mobility of hazardous
wastes as a principal element. The Selected Remedy does not satisfy the statutory preference for
treatment as a principal element of the remedy. In narrowing the focus of the FFS, treatment of
the Oregon Gulch Tailings Impoundment was determined to be impracticable. The following
sections discuss how the Selected Remedy meets statutory requirements. A similar
determination was made in selecting the Removal Action for the stream sediments as presented
in the Action Memorandum (EPA, 1995).

10.1 PROTECTION OF HUMAN HEALTH AND THE ENVIRONMENT

The Selected Remedy protects human health and the environment through the prevention of
direct contact with contaminants at the site. The Selected Remedy uses engineered covers to
effectively reduce direct contact, ingestion, and inhalation of all contaminants. The reduction in
total loading of COCs to groundwater is estimated to be 99.8 percent resulting from
implementation of the Selected Remedy. Loading of COCs to surface water runoff from the
tailings was estimated to be reduced by 89 percent for lead, 96 percent for cadmium, 97 percent
for TSS, and 99 percent or greater for arsenic, copper, zinc, and sulfate. Due to the significant
reduction in infiltration resulting from the Selected Remedy, the Oregon Gulch Tailings
Impoundment seep is predicted to stop flowing in less than approximately 7 years after
implementation of this alternative, resulting in further reduction in surface water loading
(SMIATerraMatrix, 1997).

Potential risk to the terrestrial ecosystem due to ingestion or exposure to tailings would be
eliminated by the Selected Remedy since the impoundment would be covered. Potential risk due
to ingestion of ponded surface water on the tailings would be eliminated since the pond would
not exist after regrading the tailings surface.

10.2 COMPLIANCE WITH ARARs

The Selected Remedy will comply with all ARARs identified in Appendix A to this ROD. No
waiver of ARARs is expected to be necessary. Final performance standards will not include
ARARs for Site-wide surface and ground waters or require a specified decrease in point or
nonpoint source loadings of COCs to Site-wide surface and groundwaters (USCD, 1994).

10.3 COST EFFECTIVENESS

EPA has determined that the Selected Remedy is cost effective in mitigating the principal risks
posed by contaminated tailings. Section 300.430(f)(ii)(D) of the NCP requires evaluation of cost
Record of Decision
Oreuon Gulch OU10
840-p 3:80-013 OUIOFINALRODOUIOROD.Vm) Ub-44
-------
effectiveness. Overall effectiveness is determined by the following three balancing criteria:
long-term effectiveness and permanence; reduction of toxicity, mobility, and volume through
treatment; and short-term effectiveness. Overall effectiveness is then compared to cost to ensure
that the remedy is cost effective. The Selected Remedy meets the criteria and provides for
overall effectiveness in proportion to its cost. The estimated cost for the Selected Remedy is
$2.54 million. The cost estimate includes periodic inspection of the cover.

To the extent that the estimated cost of the Selected Remedy exceeds the cost for other
alternatives, the difference in cost is reasonable when related to the greater overall effectiveness
achieved by the Selected Remedy.

10.4 UTILIZATION OF PERMANENT SOLUTIONS AND ALTERNATIVE
TREATMENT TECHNOLOGIES iQR RESOURCE RECOVERY
TECHNOLOGIES! TO THE MAXIMUM EXTENT POSSIBLE

EPA has determined that the Selected Remedy represents the maximum extent to which
permanent solutions can be utilized in a cost effective manner at the Oregon Gulch Tailings
Impoundment.

Of those alternatives that are protective of human health and the environment and comply with
ARARs, EPA has determined that the Selected Remedy for the Oregon Gulch Tailings
Impoundment provides the best balance in terms of long-term effectiveness and permanence,
treatment, implementability, cost, and state and community acceptance.

While the Selected Remedy for the tailings impoundment does not utilize the most permanent
solution treatment or removal, the use of engineered covers provides a long-term effective and
permanent barrier to contaminated waste materials, thus reducing risk to.an equivalent extent.
Because the tailings impoundment will remain on site with no treatment, the Selected Remedy
will require a five-year review under Section 121(c) of CERCLA and Section 300.430(f)(4)(ii) of
theNCP.

10.5 PREFERENCE FOR TREATMENT AS A PRINCIPAL ELEMENT

Various treatment options for impounded tailings were considered early in the FS process;
however, due to the nature and size of the impounded tailings, these options were determined to
be either technically impracticable and/or not cost-effective (EPA, 1993).
Record of Decision
Oregon Gulch OL' 10 —.^ .-
840Tp 3280-01 3 OUIO'FrNALRODOUIORODWPD Ub-4D
-------
11.0 DOCUMENTATION OF SIGNIFICANT CHANGES

The Selected Remedy is the second response action to be taken at OU10 of the California Gulch
Superfund Site. The first action implemented the Action Memorandum (EPA, 1995) for
miscellaneous tailings and stream sediment in Oregon Gulch and was completed in October
1996. This removal action is consistent with the Selected Remedy for the Oregon Gulch Tailings
Impoundment.

The Proposed Plan for the Oregon Gulch Tailings Impoundment was released for public
comment on March 19, 1997. The Proposed Plan identified Alternative 5, Multi-Layer Rock and
Soil cover with a Geosynthetic Barrier as the preferred alternative. No comments were received
during the public comment period. Subsequently, the EPA determined that no significant
changes to the remedy, as it was originally identified in the Proposed Plan, were necessary.
Record of Decision
Ocron Gulch OU10
84'1-|. .1:80-0;:! OUO RNALRODOUOROD WPD DS-46
-------
12.0 REFERENCES

Abt, S.R., R.J. Wittier, J.F. Ruff, D.L. LaGrone, M.S: Khattak, J.D. Nelson, N.E. Hinkle, and
D. W. Lee. 1988. Development of Riprap Design Criteria by Riprap Testing in Flumes.
Phase II. U.S. Nuclear Regulatory Commission, Office of Nuclear Material Safety and
Safeguards NUREG/CR-4651, Vol. 2.

Dames and Moore. 1986. Report, Stability and Reclamation Evaluations, Abandoned Tailings
Ponds, Leadville Unit, Leadville Colorado, for Asarco, Incorporated. February.

Foothill Engineering Consultants, Inc. (FEC). 1995. Final Cultural Resources Survey of
Oregon Gulch Operable Unit 10, California Gulch Super fund Site, Lake County,
Colorado. September 8.

Golder. 1996a. Final Surface Water Remedial Investigation Report, California Gulch Site,
Leadville, Colorado. May.

Golder. 1996b. Final Hydrogeologic Remedial Investigation Report, California Gulch Site,
Leadville, Colorado. May.

P-III Associates, Inc. 1995. Cultural Resource Inventory of Access Roads and a Borrow
Location in the Oregon Gulch Area, Operable Unit 10, California Gulch, CERCLA Site,
Lake County, Colorado. Cultural Resources Report 5058-01-9508. July 14.
Shepherd Miller Inc./TerraMatrix (SMI/TerraMatrix). 1997. Final Focused Feasibility Study for
Oregon Gulch Operable Unit 10, California Gulch Site, prepared for Resurrection Mining
Company, June.

Shepherd Miller Inc./TerraMatrix (SMI/TerraMatrix). 1996a. Draft Focused Feasibility Study
for Oregon Gulch Operable Unit 10, California Gulch Site, prepared for Resurrection
Mining Company, December.

Shepherd Miller, Inc./TerraMatrix (SMI/TerraMatrix). 1996b. Work Plan for the Focused
Feasibility Study for Oregon Gulch Operable Unit 10. January 23.

Shepherd Miller, Inc./TerraMatrix (SMI/TerraMatrix). 1995a. Final Engineering
Evaluation/Cost Analysis for Colorado Zinc-Lead Tailings Area Within Lower California
Gulch Operable Unit 8. July.

Shepherd Miller, Inc./TerraMatrix (SMI/TerraMatrix). 1995b. Final Engineering
Evaluation/Cost Analysis for Stream Sediment with Oregon Gulch Operable Unit 10.
June.
Record of Decision
Oregon Gulch OU10
841'P .3280-013 OU10'FINAJLROD OUIOROD.WPD
-------
Shepherd Miller, Inc./TerraMatrix (SMI'TerraMatrix). 1995c. Final Removal Action Design
Report, Engineering Evaluation Cost Analysis for Stream Sediments within Oregon
Gulch Operable Unit 10. August.

Shepherd Miller, Inc./TerraMatrix (SMI TerraMatrix). 1995d. Final Removal Action Workplan.
Engineering Evaluation/Cost Analysis for Stream Sediments within Oregon Gulch
Operable Unit 10. September.

Shepherd Miller, Inc./TerraMatrix (SMI/TerraMatrix). 1995e. Geotechnical Investigation
Report, Oregon Gulch Tailing Impoundment Operable Unit 10. December.

Shepherd Miller, Inc./TerraMatrix (SMI/TerraMatrix). 1994. Draft Monitoring Well Installation
Report for Wells Installed in California and Oregon Gulches. November.

Stephenson, D. 1979. Rockfill in Hydraulic Engineering, Developments in Geotechnical
Engineering, 27. E.T. Sevier, Scientific Publishing Co.

Stevens, M.A. and D.B. Simmons. 1971. River Mechanics, edited by Shen, H.W. Fort Collins,
Colorado: H.W. Shen.

U.S. Army Corps of Engineers (COE). 1991. Flood Hydrograph Package, HEC-l. Hydrologic
Engineering Center.

U.S. Army Corps of Engineers (COE). 1990. Computation of Water Surface Profiles, HEC-2.
Hydrologic Engineering Center.

U.S. Department of Commerce. 1990. Selected Population and Housing Characteristics.
Bureau of the Census.

U.S. District Court (USDC), District of Colorado. 1994. Civil Action No. 83-C-2388, Consent
Decree with ASARCO, Inc., Resurrection Mining Company, Newmont Mining
Corporation, and the Res-ASARCO Joint Venture, Appendix D: Work Area
Management Plan for the California Gulch Superfund Site, Implementation by
Resurrection Mining Company. May.

U.S. Environmental Protection Agency (EPA). 1997. Proposed Plan for Oregon Gulch Operable
Unit 10, California Gulch Superfund Site, Leadville, Colorado. March.

U.S. Environmental Protection Agency (EPA). 1995. Action Memorandum for PRP Financed
Removal Action at the Oregon Gulch Stream Sediments Site, Operable Unit 10. 8H WM-
SR. August 4.
Record of Decision
Orcfon Gulch OU10 _
8J<>:p J280-01J OL/'IO FINALROD'OUIOROD WPD L/b-4o
-------
U.S. Environmental Protection Agency (EPA). 1993. Final Screening Feasibility Study far
Remediation Alternatives at the California Gulch NPL Site. Leadville, Colorado.
September.

U.S. Environmental Protection Agency (EPA). 1989. Guidance on Preparing Superfund
Decision Documents: The Proposed Plan, the Record of Decision, Explanation of
Differences, the Record of Decision Amendment. Interim Final. EPA/540/G-89/007.
July.

U.S. Environmental Protection Agency (EPA). 1988. Guidance for Conducting Remedial
Investigations and Feasibility Studies Under CERCLA. EPA/540/G-89/004. Office of
Emergency and Remedial Response, Washington D.C. October.

U.S. Nuclear Regulatory Commission (NRC). 1990. Final Staff Technical Position, Design of
Erosion Protection Covers for Stabilization of Uranium Mill Tailings Sites.

Water, Waste, and Land, Inc. (WWL). 1990. California Gulch Hydrologic Investigation,
Leadville, Colorado. August.

Weston, Inc. and Terra Technologies. 1997. Ecological Risk Assessment for the Terrestrial
Ecosystem. California Gulch NPL Site. Leadville, Colorado. January 1997.

Weston, Roy F., Inc. 1995a. Preliminary Ecological Risk Assessment For Oregon Gulch
(OU10). January.

Weston, Roy F., Inc. 1995b. Final Baseline Aquatic Ecological Risk Assessment (BARA).
California Gulch, NPL Site. September.

Woodruff, N.P. and F.H. Siddoway, 1965. A Wind Erosion Equation, Soil Science Society of
America Proceedings 29(5):602-608.

Woodward Clyde Consultants (WCC). 1994. Final Tailings Disposal Area Remedial
Investigation Report, California Gulch Site, Leadville. Colorado. January.
Record of Decision
Oregon Gulch OUIO
S497P j:80-OU OUIO FINALROI>OU10ROD.WPD
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FIGURES
Record of Decision
Oregon Gulch OHIO
WPTP^SO-OiyOUIO'FINALROD-OinORODWPD
-------
\ACAORI2\DWG\3280-OI5\FIGI 03/24/97
C O L\0 R) A D C
CALIFORNIA GULCH
SUPER FUND SITE
Source: SMI/TerraMalrix 1996a
Rgure 1
California Qulch
Superfund Site
General Location Map
Leadvllle, Colorado
-------
California Gulch
Stipertund Site
And Operable Units
Leadville. Colorado
-------
OPERABLE UNIT ID BOUNDARY
600 YEAR FLOOOPUUN

|| BORROW AREA

/DIVERSION DITCH
1 "^ .'. • . \ 1
:J\"V
rs. \ \ .
Suurci! :iMI/lt:MaM.tlnii 1(.)Mli,i
Rgure 3
Oregon Gulch
OporableUnH 10
Leadvllle, Colorado
-------
• DAMES A MOORE (1088)
• TAILINGS R.I. (WCC. 1894)
« GEOTECHNICAL INVESTIGATION
(SMI/ TMI. 1905)
* MONITORING WELL INSTALLATION REPORT
(SMI/IMI. 1994)
Source: SMI/TerraMalrix. 1996a
Rgure 4
Oregon Gulch
Investigations
Borehole And Test Pit Locations
Leadvllle, Colorado
-------
CONTOUR INTERVAL = 25 FEET

-••• GROUND SURFACE CONTOURS

SURFACE WATCR DRAINAGE

MONITORING WELL

SURFACE WATER SAMPLE Si IT
SURFACE WATER AND
SEDIMENT SAMPLE SITE
OREGON
.-TAILING
IMPOUNDMENT
x- -TREATMENT
>—-~ v PLANT:;;
Oregon Gulch
Ground Water, Surface Wolor
& Sediment Sampling Locations
Leadvllle. Colorado
-------
SLOPE 2-3%
3 (MINIMUM)
PUNT GROWTH MEDIA
BORROW/TAILING
STRUCTURAL FILL
(THICKNESS VARIES)
Source: SMI/TerraMatrix. 1996a
Figure 6
Alternative 5
Multi-Layer Rock And Soil
Cover With Geosynthetic Barrier
Leadvllle, Colorado
-------
Oregon Gulch
Proposed Surface
Configuration
Selected Remedy
ooict K«tuii«ilion Muling Cuiiipuni. Mui I'J'J/
-------
TABLES
Record of Decision
Oregon Gulch OU10
W97P-J280-013.OU10 FINALROCMDUIOROD.WPD
-------
TABLE 1
OREGON GULCH TAILINGS IMPOUNDMENT SOIL SAMPLE
LABORATORY RESULTS SUMMARY
CONSTITUENT
Arsenic

Cadmium

Lead

Zinc

Sample
Type
STC
FS
T
STC
FS
T
STC
FS
T
STC
FS
T
Number of
Samples
3
10
24
3
10
24
3
9
24
3
10
24
Average
(mg/Kg)
762.7
13.4
486. 1
12.6
1.6
55.3
1.960.7
83.4
4.587.9
1.740
284.8
II. 027.1
Median
(mg/Kg)
747
12.8
439.5
9.5
1.2
47.4
2.170
77
3.475
1.280
185.5
8.720
Standard
Deviation
(mg/Kg)
79.7
7.6
245.6
8.7
1.6
36.9
1.000.6
57.3
2.814.7
1.302.4
271.9
5.635.6
Minimum
-------
TAULE 2
OREGON GULCH POND WATER QUALITY
Concentrations (mg/L)
Date
Field pll (std. units)
Arsenic (diss.)
Arsenic (tot.)
Cadmium (diss.)
Cadmium (lot.)
Copper (diss.)
Copper (tot.)
Lead (diss.)
Lead (tot.)
Zinc (diss.)
Zinc (tot.)
Sulfatc
TDS
6/7/89
2.24
0.90
0.88
0.082
0.085
3.4
3.7
0.012
0.021
16
15
4,300
4,600
9/17/91
1.91
3.41 B
5.30
0.272
0.225
15.10
12.2
R
46.8
39.0
36.3
9,820 J
8,560 J
6/2/95
2.60
0.30
0.29
0.029
0.022 B
0.96
0.89
0.29
0.32
3.95
4.20
880
1,150
6/6/96
3.3
0.002 B
0.007
1.280
1.210
0.84
0.96
1.52
1.63
181.0
172.0
1,760
2,710
Average
2.51
1.15
1.62
0.42
1.54
5.07
17.75
0.61
12.12
59.99
56.88 .
4,190
4,255
Minimum
1.91
0.002
0.007
0.03
0.02
0.84
0.89
0.01
0.02
3.95
4.20
880
1,150
Mnximnm
3.3
3.41
5.30
1.28
1.21
15.10
12.20.
1.52
'16.80
. 181
172
9,820
8,560
Note: All values in milligrams per Liter except pH, U = Non-detect, B = Between method detection and instrument detection limit,
J = Estimated through validation, R = Rejected through validation, Averages include non-dctect values as the detection liniii

SOURCE: SMl/TcrraMalrix, 1996a
lOvHODVI'AIII.I-J.WI'l)
-------
TABLE 3
OREGON GULCH SEEP WATER QUALITY
Concentrations (mg/L)
Dale
Flow (gpm)
Field pi 1 (sltl. units)
Arsenic (cliss.)
Arsenic (tot.)
Cadmium (diss.)
Cadmium (tot.)
Copper (cliss.)
Copper (tot.)
Lead (diss.)
Lend (tot.)
Zinc (diss.)
Zinc (tot.)
Sulfaie
IDS
TSS
6/7/89
1.35
2.9
0.036
0.038
0.09
0.08
2
2.3
0.08
0.09
930
940
35,000
51,000
86
10/25/89
1.80
2.81
0.05 U
0.12
0.053
0.07
0.32
0.62
0.07
0.68
730
790
30.000
49,000
560
9/17/91
0.90
2.76
0.120 B
0.0412 BJ
0.282
0.278
0.482 B
1.19 BJ
R
0.193
1.130
1,090
27.700 J
12.900
862
6/2/94
3.14
2.75
0.104
0.093
0.028
0.31
0.5 U
1.75
0.088
0.175
780
780
27,000
46,100
NM
10/5/94
1.14
2.96
0.048
0.072
0.009
1.05
0.5 U
0.5 U
0.136
0.29
1.030
990
35,274
58,096
NM
6/1/95
41.3
2.76
0.28
0.29
0.05
0.04
1.15
1.05
0.3
0.37
15.4
14
1,230
1,420
16
6/27/9^
1.92
2.64
0.2
0.2
0.5
0.6
2.9
2.8
0.114
0.171
672
718
34.400
47,300
224
Note: Constituent concentrations in milligrams per Liter (mg/L), flow in gallons per minute (gpm), U = Non-detcct,
J = Estimated concentration, R = Rejected through validation, NM = Not Measured, B = Between method detection-
limit and instrument detection limit

SOURCE: SMI/TerraMatrix. 1996a
i'Yi:sooivnuiovHoi>\TA«i.i!.v\vri>
-------
TABLE 3 (continued)
OREGON GULCH SEEP WATERQUALITY
Loading (Ibs/day)
Date
Flow (gpm)
Arsenic (diss.)
Arsenic (tot.)
Cadmium
Cadmium (tot.)
Copper (diss.)
Copper (tot.)
Lead (diss.)
Lead (tot.)
Zinc (diss.)
Zinc (tot.)
Sulfatc
TDS
TSS
6/7/89
1.35
0.00058
0.00061
0.0015
0.0013
0.032
0.037
0.0013
0.0015
15
15
570
830
1.4
10/25/89
1.80
0.00054 U
0.0026
0.0011
0.0015
0.0069
0.013
0.0015
0.015
16
17
650
1.100
12
9/17/91
0.90
0.0013 D
0.00044 BJ
0.0030
0.0030
0.0052 B
0.013 BJ
R
0.0021
12
12
300 J
140
NM
6/2/94
3.14
0.0039
0.0035
0.0011
0.012
0.019
0.033 U
0.0033
0.0066
29
29
1.000
1,700
NM
10/5/94
1.14
0.00066
0.00099
0.00012
0.014
0.0034 U.
0.0034 U
0.0019
0.0040
14
14
490
800
NM
6/1/95
41.3
0.14
0.14
0.025
0.020
0.57
0.52
0.15
0.18
7.6
6.9
610
700
-7.9
6/27/95
1. 92
0.0046
.0.0046
0.012
0.014
0.067
0.064
0.0026
0.0039
15
17
790
1.100
5.2
Note: Constituent loadings in pounds per day (Ibs/day), flow in gallons per minute (gpm), U = Non-detect concentration data.
J = Estimated concentration data, R = Loading not calculated due to rejected data, NM = Not Measured. B = Between
method detection limit and instrument detection limit. Average loading calculated using non-detecl and estimated
concentrations at values shown.

SOURCE: SMI/TeiiaMaliix, I996a
I'V'.'SOj
-------
TABLE 3 (continued)
OREGON GULCH SEEP WATER QUALITY
Concentmtions (mg/L)
Date
Flow (gpm)
Field pll (std.
Arsenic (diss.)
Arsenic (tot.)
Cadmium (diss.)
Cadmium (lot.)
Copper (diss.)
Copper (tot.)
Lead (diss.)
Lead (tot.)
Zinc (diss.)
Zinc (lot.)
Sul Fate
TDS
TSS
7/26/95
0.85
2.82
0.14
0.128
0.16
0.6
3.9
2.9
0. 155
0.13
740
742
3 1 .400
36,500
198
8/31/95
1.92
2.97
0.08
0.155
0.7
0.54
3.1
3.6
0.12
1.23
835
818
31,500
49,800
136
9/27/95 .
1.17
2.95
0.13
0.116
1 B
0.59
3
3.6
0.14
0.32
938
918
32.900
52,300
216
10/26/95
3.08
2.95
0.09
0.23
I.I B
1
0.94
0.95
0.18
0.86
884
1,100
34,400
61,700
646
5/17/96
4.49
2.7
0.078
0.08
0.33
1.3
1.7
1.54
0.05
0.11
488
479
18,400
28,290
86
6/6/96
1.34
3.21
0.11
5
0.30
1.9
1.5
1.56
0.14
0.14
825
790
29,700
49,500
202
Average
4.95
2.86
0.11
0.50
0.23
0.64
1.69
1.87
0.13
0.37
769
783
28,377
41,838
294
Maximum
41.3
3.21
0.28
5
0.7
1.90
3.90
3.60
0.3
1.23
1,130
1.100
35,274
61,700
862
Minimum
0.85
2.64
0.036
0.03S
0.009
0.04
0.32
0.50
0.05
0.09
15.4
14.0
1,230
1.420
16
Note: Constituent concentrations in milligrams per Liter (mg/L), Flow in gallons per minuter (gpm), U = Non-detect, J = Estimated
concentration data, R = Rejected through validation, NM = Not Measured, B = Between method detection limit and instrument
detection limit

SOURCE: TerraMatrix. I996a
i'v':xoui.«ouiu\K(>i>vr.\m.i-:j wi-u
-------
TABLE 3 (concluded)
OREGON GULCH SEEP WATER QUALITY
Loading (Ib/day)
Date
Flow (gpm)
Arsenic (diss.)
Arsenic (tot.)
Cadmium
Cadmium (lot.)
Copper (diss.)
Copper (tot.)
Lead (diss )
Lead (lot )
Zinc (iliss )
Zinc (lot.)
Sul fate
TDS
TSS
7/26/95
0.85
0.0014
0.0013
0.0016
0.0061
0.040
0.030
0.0016
00013
76
7.6
320
370
2.0
8/31/95 |
1.92
0.0018
0.0036
0.016
0.012
0.071
0.083
0.0028
0.028
19
19
730
1,100
3.1
9/27/95 |
1.17
0.0018
0.001 6 B
0.014
0.0083
0.042
0.051
0.0020
0.0045
13
13
460
730
3.0
10/26/95
3.08
0.0033
0.0085 B
0.041
0.037
0.035
0.035
0.0067
0.032
33
41
1.300
2,300
24
5/17/96 \
4.49
0.0042
0.0043
0.018
0.070
0.092
0.081
0.003
0.006
26
26
990
1,500
4.6
6/6/96
1.35
0.002
0.081
0.005
0.031
0.024
0.025
0.002
0.002
13
13
480
800
3.3
Average
4.95
0.013
0.022
0.011
0.018
0.077
0.076
0.015
0.022
17
18
670
1000
6.7
Maximum
41.3
0.14
0.14
0.041
0.07
0.57
0.52
0.15
0.18
33
41
1.300
2.300
24
Minimum
0.85
0.00054
0.00044
^0.00012
0.0013
0.0034
0.0034
0.0013
0.0013
7.6
6.9
300
140
1.4
Note: Consiiuicni loadings in pounds per day (Ibs/day), flow in gallons per minute (gpm), U = Non-detect concentration data, J =
Estimated concentration data. R = Loading not calculated due to rejected data, NM = Not Measured, B = Between method
detection limit and instrument detection limit. Average loading calculated using non-detect and estimated concentrations at
values shown.

SOURC1-: SMI/TcmiMatrix. I996a
JIUMtODM All! \.\ Wl't)
-------
TABLE 4
OREGON GULCH SOUTH DIVERSION DITCH WATER QUALITY

Date
Flow (gpm)
Field pH (std. units)
Arsenic (diss.) -
Arsenic (tot.)
Cadmium (diss.)
Cadmium (tot.)
Copper (diss.)
Copper (tot.)
Lead (diss.)
Lead (tot.)
Zinc (diss.)
Zinc (lot.)
Sulfate
TDS
TSS
Concentration
(mg/L)
6/1/95
565.5
4.08
0.001 U
0.026
0.008
0.008
0.014
0.046
0.007
0.38
0.94
1.38
40 U
60
1,750
Loading
(Ib/day)
6/1/95
565.5
NA
0.003 U
0.177
0.054
0.054
0.095
0.312
0.048
2.58
6.38
. 9.37
135.8U
407
11,885
Concentration
(mg/L)
5/8/96
1391.4
. 4.11
0.00 IU
0.047
0.006
0.007
0.019
0.043
0.014
0.35
0.83
0.98
30
100
326
Loading
(Ib/day)
5/8/96
1391.4
NA
0.017
0.787
0.100
0.117
0.318
0.719
0.23
5.85
13.8
16.41
502.2
1,674
5.457.3
Concentration
(mg/L)
. 5/17/96
40.4
3.24
0.001
0.002
0.016
. 0014
0.054
0.049
0.023
0.037
1.83
1.92
no
160
6.0
Loading
(Ib/day)
5/17/96
> 40.4
NA
0.0005
0.001
0.008
0.007
0.026
0.024
0.011
0.018
0.89
0.93
53.5
77.8
2.92
Note: U - Non-detect at concentration value shown,
concentration.
NA - Not Applicable.

SOURCE: SMirTcrraMatrix, 1996a
loading labeled with U are calculated using non-detect
P.JiSO-OIJOUIO'JlOD'.TADLE-l.WPD
-------
TABLE 5
OREGON GULCH SURFACE WATER QUALITY (OG-1)
Concentrations (mg/L)
Date
Flow (gpm)
Field pi 1 (std. units)
Arsenic (diss.)
Arsenic (tot.)
Cadmium (diss.)
Cadmium (lot.)
Copper (diss.)
Copper (lot.)
Lead (diss.)
Lead (lot.)
Zinc (diss.)
Zinc (tot.)
Sulfate
TDS
TSS
5/2/91
216
3.33
O.OIS8 BJ
0.245
0.11 J
0.0895 J
0.893 J
10.2 J
0.0473 R
25.5 J
114 J
1,110 J
3,300
6.010
522 J
6/12/91
0.45
2.32
R
0.0336 DJ
0.555
0.557 J
8.42
7.8
R
R
644
634 J
7.480
29,600
80
7/24/91
0.27
2.55
0.268
0.601
0.664
0.549
2.27
2.34
0.001 U
3.6
557
559 J
R
9,430
490 J
5/17/94
4.5
2.45
0.006
0.005
0.15
0.15
2.2
2.15
0.01
0.006
205
192
5,840
10,100
NM
5/26/94
0.45
2.25
0.008
0.008
0.0135
0.215
3.3
2.9
0.005
0.018
297
285
9300
15,400
NM
5/4/95
1.35
2.20
0.015
0.049
0.43
0.41
3.88
3.7
0.012
0.31
712
717
24,300
37.900
330
5/16/95
259
2.51
0.089
0.47
0.35
O.'l
2.2
2.22
0.03
2.7
252
255
10,000
13,800
1,260
Note: All constituent concentrations in milligrams per Liter (mg/L), U = Non-detect, J = Estimated concentration. R = Rejected through
validation, NM = Not measured 0 = Between method dcction limit and instrument detection limit
SOUI
SMI/TerraMalri.x. I996;i
l'.\)2IO.OI)\OUIO\HUI)UAltl.h> \vn>
-------
TAHLE5(con(inucd)
OREGON GULCH SURFACE WATER QUALITY (OG-1)
Loading (Ib/dny)
Date
Flow (gpm)
Arsenic (diss.)
Arsenic (tot.)
Cadmium (diss.)
Cndinium (tot.)
Copper (diss.)
Copper (lot.)
Lend (diss.)
Lead (tot.)
Zinc (diss.)
Zinc (tot.)
Snlfate
TDS
TSS
5/2/91
216
0.041 DJ
0.64
0.29 J
0.23 J
2.3 J
26 J
0.12
66 J
300 J
2,900 J
8,600
16,000
1,300 J
6/12/91
0.45
R
I.8E-04 BJ
0.0030
0.0030 J
0.045
0.042
R
R
3.5
3.4 J
40
160
0.43
7/24/91
0.27
0'.00087
0.0019
0.0022
0.0018
0.0073
0.0076
I.6E-06 U
0.012
1.8
1.8 J
R
30
1.6 J
5/17/94
4.49
0.00032
0.00027
0.0081
0.0081
0.12
0.12
0.00054
0.00032
II
10
320
540
NM
5/26/94
0.45 .
4.3E-05
4.3E-05
7.3E-05
0.0012
0.018
0.016
2.7E-05
0.00010
1.6
1.5
50.4
83
NM
5/4/95
1.35
0.00024
0.00079
0.0070
0.0066
0.063
0.060
0.00019
0.0050
12
12
390
610
5.3
5/16/95
259
0.28
1.5
I.I
1.3
6.9
6.9
0.093
8.4
790
790
31,000
43,000
3,900
Note: All constituent loadings in pounds per dny (Ibs/day), flow in gallons per minute (gpm), U = Non-detect concentration data, J =
Estimated concentration data, R = Loading not calculated due to rejected data, NM = Not Measured, B = Between method detection
limit and instrument detection limit. Average loading calculated using non-dctect anc? estimated concentrations at values shown.
SOURCE: SMI/TerraMatrix, I996a
PAUIO.ODVOUIOMtOUvrAIII.O.VVI-l)
-------
TABLE 5 (continued)
OREGON GULCH SURFACE WATER QUALITY (OG-1)
Concentrations (mg/L)
Date
Flow (gpm)
Field pi 1 (sld. units)
Arsenic (diss.)
Arsenic (lot.)
Cadmium (diss.)
Cadmium (tut.)
Copper (diss.)
Copper (tot.)
Lead (diss.)
Lead (tot.)
Zinc (diss.)
Zinc (lot.)
Sulfnte
TDS
TSS
5/23/95
956
3.02
0.062
0.23
0.09
0.11
0.62
0.75
0.03
1.28
50.9
50.2
1,900
3.030
524 J
6/1/95
646
2.9
0.012
0.11
0.05
0.04
0.35
0.28
0.023
0.48
26
25.2
990
1.310
476
6/7/95
350
3.4
0.002
0.058
0.023
0.029
0.25
0.239
0.04
0.6
14.8
14.7
510
740
962
6/14/95
5.97
2.65
0.012
0.012
0.04
0.19
1.8
2.1
0.024
0.067
136
140
4.800
7,070
26
6/27/95
7.6
2.49
0.009
0.01 U
0.3
0.2
2.5
2.7
0.03
0.032
196
211
8,200
12.300
46
7/26/95
0.63
2.49
0.06
0.044
0.18
0.5
4.5
3.4
0.06
0.039
596
590
24.500
36.800
132
5/7/96
1504
3.39
0.003
0.23
0.06
0.129
0.3
0.43
0.038
1.75
31.7
30.5
1130
1760
884
Note: All constituent concentrations in milligrams per Liter (mg/L). U = Non-deled. J = Estimated conccn.ration, R =
NM = Not measured D = Between method dection limit and instrument detection limit U = Non-dctccl through
J = P.slimatcd through validation. II = Rejected through validation, NM = Not measured
Rejected through validation,
validation at value shown.
SOURCE: SMI/TcrraMatrix, I996a
r.v3280.oij\ouiu\itoi>viAiii.i:s.wm
-------
TABLE 5 (continued)
OREGON GULCH SURFACE WATER QUALITY (OG-J)
Loading (Ib/day)
Dale
Flow (gpm)
Arsenic (diss.)
Arsenic (tot.)
Cadmium (diss.)
Cadmium (lol.)
Copper (diss.)
Copper (lot.)
Lend (diss.)
Lead (lol.)
Zinc (diss.)
Zinc (lot.)
Sulfale
TDS
TSS
5/23/95
956
0.71
2.6
1.0
1.3
7.1
8.6
0.34
15
580
580
22,000
35,000
6,000 J
6/1/95
646
0.093
0,85
0.39
0.31
2.7
2.2
0.18
3.7
200
200
7,700
10,000
3,700
6/7/95
350
0.0084
0.24
0.097
0.12
I.I
1.0
0.17
2.5
62
62
2,100
3,100
4,000
6/14/95
5.97
8.6E-04
8.6E-04
0.0029
0.014
0.13
0.15
0.0017
0.0048
9.7
10
340
510
1.9
6/27/95
7.58
8.2E-04
4.6E-04 U
0.027
0.018
0.23
0.25
0.0027
0.0029
18
19
750
1,100
4.2
7/26/95
0.63
4.5E-04
3.3E-04
0.0014
0.0038
0.034
0.026
4.5E-04
2.9E-04
4.5
4.5
190
280
1.0
5/7/96
1504
0.054
4.2
I.I
23
5.4
7.8
'0.68
130
570
550
20,000
32,000
16,000
Note: All constituent loadings in pounds per day (Ibs/day), flow in gallons per minute (gpm), U = Non-detect concentration data, J =
Estimated concentration data, R = Loading not calculated due to rejected data, NM = Not Measured, B - Between method detection
limit and instrument detection limit. Average loading calculated using non-detcct and estimated concentrations at values shown.
SOURCE: SMI/TcrraMairix, I996a
P:O2SO-OI3\OUIO\ROO\TAI)l.rS.WI>0
-------
TABLE 5 (continued)
OREGON GULCH SURFACE WATER QUALITY (OG-1)
Concentrations (nig/L)
Date
Flow (gpm)
Field pi 1
Arsenic (diss.)
Arsenic (lol.)
Cadmium (diss.)
Cadmium (lot.)
Copper (diss.)
Copper (lot.)
Lead-(diss.)
Le;id (tot.)
Zinc (diss.)
Zinc (tot.)
Sul Pnte
IDS
TSS
5/8/96
1526
3.49
0.0010 B
0.05
0.032
0.067
0.15
0.19
0.046
0.57
15.9
16.1
530
880
830
5/17/96
63
3.38
0.007
0.004
0.09
0.09
0.7
0.64
0.026
0.027
68.4
66
2400
3630
10
6/6/96
3.1
3.09
0.005 U
0.005 B
0.15
0.26
1.7
1.7
0.02
0.03
133
133
5190
8710
54
Average
326
2.82
0.04
0.13
0.19
0.23
2.1
2.6
0.028
2.3
238
296
6738
11,675
442
Maximum
1526
3.49
0.27
0.60
0.66
0.56
8.42
10.20
0.060
25.50
712
1,110
24,500
37,900
1,260
Minimum
0.27
2.20
0.001
0.004
0.014
0.029
0.15
0.19
0.001
0.006
14.8
M.7
510
740
10
Note: All constituent concentrations in milligrams per Liter (nig/L), U = Non-dctect through validation at value shown, J = Estimated
through validation, R - Rejected through validation, NM = Not measured
SOURCE: SMI/TerraMatrix, I996a
l':U!«0-OI3\OUICKK01>UAIII.i:S Wl'l)
-------
TABLE 5 (concluded)
OREGON GULCH SURFACE WATER QUALITY (OG-1)
Loading (Ib/d.iy)
Dale
Flow (gpm)
Arsenic (cliss.)
Arsenic (tot.)
Cadmium (diss.)
Cadmium (tot.)
Copper (diss.)
Copper (tot.)
Lead (diss.)
Lead (tot.)
Zinc (diss.)
Zinc (tot.)
Sulfalc
TDS
TSS
5/8/96
1256
0.02 D
0.92
0.59
1.2
2.8
3.5
0.85
10
2,900
300
9,700
16,000
15,000
5/17/96
63
0.005
0.003
0.068
0.068
0.53
0.48
0.02
0.02
«
52
50
1.800
2,700
7.6
6/6/96
3.1
0.0002 U
0.0002
0.006
0.01
0.064
0.064
0.001
0.001
5.0
5.0
200
330
2.0
Average
310
0.08
0.64
0.28
0.40
1.7
3.4
0.15
15
350
320
7,000
9,500
3300
Maximum
1504
0.71
4.2
I.I
2.3
7.1
26
0.85
130
2,900
2,900
31,000
43,000
16,000
Minimum
0.27
0.00004
0.00004
0.00007
0.0012
0.007
0.008
0.000002
0.0001
1.6
1.5
40
30
0.43
Note: All constituent loadings in pounds per day (Ibs/day), flow in gallons per minute (gpm), U = Non-delect concentration data, J =
Estimated concentration data, R = Loading not calculated due to rejected data, NM = Not Measured, B = Between method detection
limit and instrument detection limit. Average loading calculated using non-detect and estimated concentrations at values shown.
SOURCE: SMI/TcrraMatrix, 1996a
li:UJ80-OIJ\OUItW(OI)\TAIII.i:S.WI'IJ
-------
TABLE 6
INTERMEDIATE ALLUVIAL AQUIFER WATE'R QUALITY (mg/L)
Location
Dme
Source
Field pVI
Arsenic (diss.)
Cadmium (diss.)
Copper (diss.)
Lead (diss.)
Zinc (diss.)
Sulfate
TDS
OG1TMW1
10/31/91
wcc
7.72
0.01 U
0.005 U
0.025 U
0003U
0.02 U
1749 U
1901
OG1TMW1
6/1/94
SMI
7.75
0.001
0.0001 U
0.01 U
0.001 U
0.0 1 U
10 U
12')
OG1TMW1
10/12/94
SMI
8.33
0.001
0.0001 U
0.01 U
0.001 U
0.01 U
6
140
OG1TMW9
10/11/94
SMI
7.80
0.002
0.0002
0.01 U
0.001 U
0.01 U
315
620
OG1TMW9
1/26/95
SMI
7.75
0.001
0.000 1
0.01 U
0.001 U
0.01 U
414
684
OG1TMW1
6/6/96
SMI
8.1
0.002 D
0.0005 U
0.001 U
0.001 U
0.01 U
10
130
OG1TMW9
6/6/96
SMI
7.8
0.0020
0.0005 U
0.001 U
0.001 U
O.I
490
820
Average Minimum Maximum
7.89
0.00
0.001 1
0.01 3 U
0.0014 U
0.027 U
208
387.6
7.72
0.001
0.0001 U
0.01 U
0.001 U
0.001 U
6
129
8.33
0.002
0.0002
0.00 IU
0.001 U
O.I
'100
820
Note: All constituent concentrations in milligrams/Liter (mg/L) unless otherwise noted.
Sources: 1991 sample concentration data: llydrogcolngic R.I. (Colder. I996b)
I "0-1 ihtougli June 1096 data: Water Sampling Program Data Transmitials SMI/TMI (1994. 1995. 1996)
U = Non-deled. J = Estimated through validation. K = Rejected through validation
1) = llciwccn method detection limit (MDL) and instrument detection lintil (IDL). NM = Not Measured
IUMU)l>M'Atll.i:6 Wl'l)
-------
TABLE 7
TAILING IMPOUNDMENT PORE WATER QUALITY
Location
Date
Source
Field jjll
Arsenic (diss.)
Cadmium (diss.)
Copper (diss.)
Lead (diss.)
Zinc (diss.)
Sullale
TDS
OG1TMW4
10/30/91
wcc
4.14
1 U
0.5 U
2.5 U
0.432
52H
30.300
60.400
ocmviws
10/30/91
wcc
5.22
1 U
0.5 U
2.5 U
0.339
214
14,400
24.000
OG1TMW5
6/2/94
SMI
5.35
0.021
0.082
5U
1.22
272
16.300
23.200
OG1TMW5
10/6/94
SMI
4.9
0.043
0.0165
0.01 U
1.98
178
9.220
14.400
OG1TMW6A
10/31/91
SMI
5.10
1.0 UJ
0.5 U
2.5 U
4.66
1.150
29.900
23.400
OG1TMW6A
6/5/96
SMI
4.24
0.01 U
0.032
0.01 U
0.95
580
23.900
37.300
Average Minimum Minimum
4.82
0.03
0.27
2.5 U
1.59
487
20.670
30.450
4.14
0.021
0.0165
0.01 U
0.339
178
9.220
60.400
5.35
0.043
0.082
5U
4.66
1150
30.300
14.400
Note: All constituent concentrations in milligrams/Liter (mg/L) except pi I.
Sources: 1991 sample concentration data: Ilydrogcologic R.I. (Colder. 1996b)
1994 through June 1996 data: Wnlcr Sampling Program Data Transmiitalj SMI/TMI (1994. 1995. 1996)
U = Non-doled. J = Estimated through validation. K = Rejected through validation. I) = Dclwccn method detection limit (MOL) and instrument detection limit
(IDL). NM = Not Measured
r 0340-01 J\OUIOVROI)\TAlll.l:.7. WI'D
-------
TABLE 8
PERCHED AQUIFER WATER QUALITY - OG1TMW3
Dole
Source
Field pH
Arsenic (diss.)
Cadmium (diss.)
Copper (diss.)
Lend (diss.)
Zinc (diss.)
Sulfale
TDS
10/31/9!
\VCC
2.15
1 UJ
0.568
8.08
0.3 U
K6I
29.400
45.300
10/21/93
SMI
2.25
0.02
0.37
4.94
0.005
760
28.647
39.710
6/2/94
SMI
2.58
0.033
0.26
4.4
0.05 U
812
24.600
44.600
10/6/94
SMI
1.90
0.02
0.052
5.15
0.001 U
735
25.519
39.000
1/25/95
SMI
2.27
0.04
0.56
6.4
0.001 U
880
29.700
46.300
6/1/95
SMI
2.52
0.01
0.6
5.5
0.001
961
33.400 J
49.800
9/26/95
SMI
LJ.59
0.25
0.6
4.4
0.01
585
22.500
34.700
6/6/96
SMI
2.81
0.02
0.5
4.2
0.005 U
746
26,600
43.700
Average
2.38
0.17
0.5
5.6
0.005
792
27.545
42.888
Minimum
1.90
0.008
0.26
4.4
0.001 U
585
22,500
34.700
Maximum
2.81
0.25
0.568
R.08
0.01
961
33,400
49.XOO
Note: All constituent concentrations in milligrams/Liter (mg/L) except pll.
Somcc*. 1991 sample concentration dala: llydrogcologic R.I. (Colder, 19961))
1994 through June 1996 data- water Sampling Program DaiaTransmiuals SM1/TMI (1994. 1995. 1996)
U = Nun-delect. J = Estimated concentration, R = Rejected through validation D = Between method detection limit (MDL) and instrument
detection limit (IDL), NM = Not Measured
'O.'SI
lUMtODM AlllJ.3 Wl'l)
-------
TABLE 8 (concluded)
PERCHED AQUIFER WATER QUALITY - OGITMW8
Dale
Source
Field pM
Arsenic (diss.)
Cadmium (diss.)
Copper (diss.)
Lead (diss.)
Zinc (diss.)
Siilfate
TDS
10/31/91
wcc
4.06
I UJ
0.5 U
2.5 U
0.3 U
672
30.000
50,600 J
6/2/94
SMI
4.29
0.006
O.I
5U
0.005
745
27.000
50.700
10/11/94
SMI
4.20
0.007
0.117
1 U
0.003
610
35.200
46,100
1/25/95
SMI
4.06
0.005
0.12
0.4 U
0.018
672
32.700
47.300
6/1/95
SMI
4.24
0.002
0.13
0.004
0.009
812
39.600
61,200
9/26/95
SMI
L_ 4.11
0.02
0.13
0.1
0.012
525
30.000 J
45.800
Average
4.16
0.0 1
0.119
0.05
0.009
673
32.400
50.300
Minimum
4.06
0.002
O.I
0.004
0.005
525
27.000
45.800
Maximum
L_ 4.29
0.016
0.13
O.I
0.018
812
39.600
61.200
Note: All conslitucnt concentrations in milligrams/Liter (mg/L) except pH.
Sources: 1991 snmplc concentration data: Hydrogcologic R.I. (Colder. I996b)
1994 through June 1996 data: Water Sampling Program Data Transmiltals SMI/TMI (1994. 1995. 1996)
U = Non-deled. J = Estimated concentration, R = Rejected through validation D = Between method detection limit (MDL) and instrument
detection limit (IDL). NM = Not Measured
r.Vi:il(M>l.l\OUIO\KOI>\TAllU:.S WI'O
-------
TABLE 9
LOADING TO CALIFORNIA GULCH FROM OREGON GULCH SHALLOW GROUND WATER
Locution
Flow (gpm)
Field pH (std. units)
Arsenic (diss.)
Cadmium (diss.)
Copper (diss.)
Lead (diss.)
Zinc (diss.)
Sulfate
OG1TMW3
Average
Concentrations
2.8*
2.38
0.17
0.50
5.6
0.005
792
27.545
OG1TMW3
Average Loading
(Ibs/day)

0.02
0.01
0.19
0.0002
26.9
933
CG-4 Average
Concentrations
1,632
4.97
0.002
0.11
0.31
0.31
26.5
750
CG-4
Average Loading
(Ibs/day)

0.04
2.14
6.05
6.05
517
14,645
OG1TMW3
Loading as %
of CG-4
0.31%

50%
0.5%
3.1%
0.003%
5.2% .
6.4%
Note: All constituent concentrations in milligrams/Liter (mg/L) except pH, Flow in gallons per minute (gpm). All loading in
pounds per day (Ibs/day).
Sources: 1991 sample concentration and (low measurement data: Hydrogeologic R.I. (Colder, 1996b)
1994 through June 1996 data: Water Sampling Program Data Transmittals SM1/TM1 (1994, 1995, 1996)

* Flow estimated in Appendix C, Section C.4 of the FFS (SMl/TerraMatrix 1996a).
IU'1 INAl.KoDvlAIILI.1; W|'l>
-------
TABLE 10
SEDIMENT SAMPLE ANALYSIS RESULTS (WWL SAMPLING EVENT, JUNE 1989)
Analytes
Pyritic Sulfur
Silver (total)
Arsenic (total)
Cadmium (total)
Chromium (total)
C opper (total)
iron (total)
Manganese (total)
Lead (total)
Zinc (total)
Units
°/0
mg/kg
mg/kg
mg/kg
mg/kg
mg/kg
%
mg/kg
mg/kg
mg/kg
OG-1
(Just above confluence
with California Gulch)
4.3
13
200
5.8
4.5
380
8.7
1,500
750
1,800
OG-2
(Seep at toe of
impoundment)
1.2
22
79
19
5.8
550
8.7
3,200
3,900
6,900
OG-3
(S. diversion ditch
downstream of
impoundment)
12
23
220
10
2.1
540
17
600
1,600
1,500
SOURCE: SMinerraMatrix, 1996a
P. J:SO-OI) OUIO^ROD'TAOLEIO.WPD
-------
TABLE 11
STREAM SEDIMENT SAMPLE ANALYSIS RESULTS

Arsenic (mg/kg)
Jun-89
May-91
Jul-91
Sep-91
Mar-92
Oct-93
May-94
Cadmium (mg/kg)
Jun-89
May-9 1
Jul-91
Sep-91
Mar-92
Oct-93
May-94
Copper (mg/kg)
Jun-89
Jul-91
Sep-91
Mar-92
Oct-93
May-94
Iron (mg/kg)
May-91
Jul-9!
Sep-9 1
Mar-92
California Gulch
CC-3

190
290
214
152
199
104
150

28
26.9
18
13.2
24.8
10
7

720
1,070
1,260
895
406
484

93,500
82,700
80.000
84,700
Starr Ditch
SD-1

190
147
2.8

48.05

28
438
19.8

7.6

450
296

91.9

44.100
46.500

17.500
Oregon Gulch
OG-1

200
152
2.3

5.8
1.5
4.6

380
109

53.900
47.000

California Gulch
CG-4

20
146
61.5
56.7
116
169
70

16
17.3
8.5
9.9
11.3
12
7

610
593
319
319
494
296

75.400
- 3 1 .000
30.000
47,300
Note: 1989 sample sites were re-designated with name of nearest current site.

SOURCE: SMI/TerraMatrix, 1996a
P:j:SO-OI3 OUIO'RO[>TABLEII.WPD
-------
TABLE 11 (concluded)
SEDIMENT SAMPLE ANALYSIS RESULTS
1
J Oct-93
May-94
J| Lead (mg/kg)
Jun-89
May-91
Jul-91
Sep-9!
Mar-92
Oct-93
May-94
Sulfate (mg/kg)
May-91
Jul-91
Sep-9 1
Mar-92
j| Zinc (mg/kg)
Jun-89
May-91
Jul-91
Sep-9 1
Mar-92
Oct-93
j May-94
California Gulch
CG-3
59,600
55,600

2,000

2,130
2,180
2,620
1,320
1,680

816
1,060
270
362

6,000

3,710
5.210
6.100
3,480
3.130
Starr Ditch
SD-I

4,200

2.380

578

324
1.960

6.400

6.410

1.680

Oregon Gulch
OC-I

750

633

3.570
6.920

1.800
1.820
683

California Gulch
CG-4
71,800
46.300

3.200

1,220
1,170
2,150
3.170
1,830

1.690
450
410
262

4400

2.530
3.040
4,190
5,060
2.750
Note: 1989 sample sites were re-designated with name of nearest current site.

SOURCE: SMI/TerraMatrix, 1996a
P 3:80-013 OL'IO'ROD'TABLEll V-TD
-------
TABLE 12
HAZARD INDICES FOR TERRESTRIAL RECEPTORS FROM EXPOSURE TO
CONTAMINANTS IN TAILINGS, SURFACE WATER, AND SEDIMENTS
PRELIMINARY ECOLOGICAL RISK ASSESSMENT FOR OREGON GULCH (OU10)
Receptor
Passerine
Raptor
Small herbivore
Large herbivore
Small omnivore
Large omnivore
HI Average Intake
2160.23
1991.01
97.26
35.2
111.68
32.78
HI Reasonable
Maximum Intake
3606.21
3296.88
139.91
54.47
155.59
45.66
.OU Iff ROD-TABLE! J.WPD
-------
TABLE 13
HAZARD QUOTIENTS FOR AQUATIC LIFE EXPOSED
TO SURFACE WATER FROM OREGON' GULCH
Analyte
Aluminum
Antimony
Arsenic
Barium
Beryllium
Cadmium
Chromium
Copper
Iron
1 Lead
Mercury
Manganese
Nickel
Selenium
Silver
Thallium
Zinc
Acute AWQC
Average
NA
NA
0.41
NA
NA
133.63
0.09
252.35
NA
0.01
0.05
NA
0.45
0.33
0.13
NA
3715.69
RME
NA
NA
0.78
NA
NA
200.30
0.17
550.33
NA
0.31
0.05
NA
0.77
0.50
0.19
NA
6313.73
Chronic AWQC
Average -
NA
NA
0.79
NA
NA
473.80
0.71
378.53
NA
0.01
9.80
NA
3.94
1.33
NA
NA
4053.48
RME
NA
NA
1.48
NA
NA
710.16
1.40
825.49
NA
0.31
9.80
NA
6.74
2.00
NA
NA
6887.70
Note: Cd, Cu, Pb, Ni, Zn are hardness dependent;
based on EPA Acute and Chronic Criteria.
a hardness of 100 mg/f was used to calculate the AWQC. HQs
SOURCE: Preliminary Ecological Risk Assessment for Oregon Gulch (OU10), Weston, 1995a
P J2SO-OI3 OUIO'JIOD'TABLEIJ WTD
-------
TABLE 14
HAZARD QUOTIENT FOR AQUATIC LIFE
EXPOSED TO SEDIMENT FROM OREGON GULCH
Analyte
Aluminum
Antimony
Arsenic
Barium
Beryllium
Cadmium
Chromium
Copper
Iron
Lead
Mercury
Manganese
Nickel
Selenium
Silver
Thallium
Zinc
Average
NA
NA
13.90
4.50
. NA
1.04
0.41
14.29
6.77
9.59
0.60
0.81
0.29
NA
NA
NA
NA
RME
NA
NA
27.39
6.25
NA
1.58
0.56
14.29
7.24
9.59
0.60
0.87
0.39
NA
NA
NA
NA
NA = Not Available
SOURCE: Preliminary Ecological Risk Assessment for Oregon Gulch (OU10), Weston, 1995a
P:U:SO-OI3'OUIO'JIODVTABLEI4.W.TD
-------
TABLE 15
HAZARD INDICES FOR SURFACE MEDIA BY RECEPTOR FOR OUIO
!ou
OUIO
Blue
Grouse
10
Mtn.
Bluebird
252
American
Kestrel
2
Red-tail
Hawk
0
Bald
Eagle
0
Least
Chipmunk
25
Mule
Deer
0
Red
Fox
0
SOURCE: Weston, Inc. and Terra Technologies, 1997.
P O^O-OI 3iOL'IOVP.OD\TABLE 15 WPD
-------
TADLE 16 I
COMI'ARfSON OF ALTERNATIVES FOR THE OREGON GULCH TAILING IMPOUNDMENT - NCP CRITERIA

Overall Protection of
lutiinn Health iiiul (he
environment
This criterion includes
whether the remcdinl aclion
)bjeclives |RAOsJ would
>e met)
Compliance with AllAlli
^ong-Tcrm EfJcclivcneii
:iiul Permanence
(eilueliun of Tojicily,
Mobility, or Volume
through Treatment
Short-Term LfTecllveiien
mplemcntablllty
Cost
A Rcncy Acceptance
Comniunilv Acceptance
Altcrnnllve 1
No Action
Does not meet HA Os.
Allows continued
contamination of ground
and surface water.
Continued erosion or tailing
from the existing
embankment slopes.
Not an issue-
No long-term effectiveness.
Treatment not applicable.
No disturbance lo the
community. Nol effective in
reducing short-term risk lo
ihe environment.
Not an issue.
SO
Not Likely.
Nol Likely.
Alternative 2
Simple Vegetated Cover
Good overall protection.
Meets RAOs:
Controls airborne releases
Controls erosion
-Controls releases lo
surface water
-Reduces releases lo
groundwalcr
Complies with all ARARs.
Good long-lenn
effectiveness and
wnnancncc.
vlobility reduced, treatmenl
iiol applicable.
Some short-term risk lo the
community due lo dust
emissions, increased (raffle.
and lo workers rcgrading
ihe tailing surface.
Relatively easy lo
implement.
SI. 83 Million
Possibly.
Possibly.
Alternative 3
Clay Layer Vegetated
Cover
Good overall protection.
Meets RAOs:
-Controls airborne releases
-Controls erosion
•Controls releases to
surface water
-Further reduces releases to
groundwater
Complies with all ARARs.
Good long-term
effectiveness and
permanence.
Mobility reduced, treatmenl
not applicable.
Some short-term risk to die
community due lo dust
emissions, increased traffic,
and lo workers regrading
the tailing surface.
Relatively easy lo
implement.
SI. 98 Million
Possibly.
Possibly.
Alternative 4
Soil Cover with
Ccojynthetlc Barrier
Very good overall
protection. Meets RAOs:
-Controls airborne releases
-Controls erosion
-Controls releases to
surface water
-Provide: high level of
protection to groundwater
C*Mnplies with all ARARs.
Very good long-term
effectiveness and
permanence.
Mobility reduced, treatmenl
not applicable.
Some short-term risk to the
community due lo dust
emissions, increased traffic,
and lo workers rcgrading
the tailing surface.
Geosynthetic installation
may require specialized
equipment and manpower.
S2.27 Million
Likely.
Likely.
Alternative S
Multi-Layer Rock and
Soil Cover with
Gcn.ivnlhetlc Harriet
Excellent overall protection
Meels RAOs.
-Controls airborne releases
-Controls erosion
-Controls releases lo surface
water
•Provides highest level of
groundwalcr protection
Complies with all AKAKs,
Excellent long-lemi
effectiveness and
pennnncncc.
Mobility reduced, ticalmenl
not applicable.
Some sliorHcnn nsk to the
community due to dust
emissions, increased traffic,
and to workers rcgniding
the tailing surface.
Geosynihctrc installation
may require spccinlixed
equipment and manpower.
$2.54 Million
Most Likely.
Most Likely.
SOURCE: SMI/TcrrnMnlrix, I996a
I' vKlu 01 JiOUIlM INAiKUlM A1ILLI6 VVI'O
-------
TABLE 17
COST SUMMARY: ALTERNATIVE 2 - VEGETATED SIMPLE COVER
Cai>r«r«u Cukn NPL S...
OHO
Culch T«il
DIRECT CAPITAL COSTS
Conpoocni
RfCOVTOURING
Cul * Fill Tallin*
Move Wei Tailing
Snctural Backfill

COVER
»imntenc
Surface
Embankment

Surface
Embankment

RE VEGETATION
Rnvfrtarionw/amend.
Surface
Embankment
Efotito Count Masuig
en the Embankment
SEE? MANAGEMENT
Sera Coltrcnm SyMm
Sony and Omfloo SyHcm
Pipeline u Yak Timnux Plant
liiiii
cu. yd.
eu.yd.
otyd.
«.yd.
tu.yd.

cu.yd.
cu.yd.
14. yd
LS
LS
OTHER IMPROVEMENTS
L'pcradietu CrauM) Wam teeittfaw Tmc*
and Dmn « Eau and Saudi Di«k«
Cellcnor OUUMMH - Eaai Side
unaii Oi«ca»«
OimCawrol
ScotiMi Camel

TOTAL DIRECT CAPITAL COSTS

IN DIRECT CAPITAL com
u
LS
'M()%oTdinc!)
Rciulaiery Cm ()% efdirca)
Mebiliiaiian and Oi«n> limnii (10%)
EPA frti (20% el enf nvcria,. 5% »f dirtct)

TOTAL INDIRECT CAPITAL COSTS

TOTAL CAPITAL COSTS

POST REMOVAL SITE CONTROL COST
Quantity
41000
5.000
20.000
j.xn
I.6U
21.000
10.000
1.7
4.0
I*.-MO
I
I
1.000
TOV.
IM Eaci

DIRECT OPERATION AND MAINTENANCE COSTS
lUpCCIUXI INMT I
Ereiien Repjiri acfft 12
Vegetation Maintenance acn 12
llrctncity for Pumping LS r
Pump and plumbing iMmmunce LS I

TOTAL

NDIRr.CT OPERATION AND MAINTENANCE COSTS
•kdVniniu>«iien(}V.d«Kt) LS I
feci(5V.ofduetl) LS I
ae«r>e(:S%ef duett) LS I

TOTAL

OPERATION AND MAINTENANCE PRESENT WORTH (JO YEARS)
Tsui Ce«i
J2J7.0JO
JWJ.OJ7
SMUM
JI2JO
SI1UJ
SIO.TJO
SU.*M
Jl}.*»7
S)UM
SI01*IO
XU.OOO
S4I.74:
WI.742
ML1)*
EaxMy?
JIJTIJJ4
MOM
MOM
fl.500
ii4.*«o

»7*»

i;.'4»
Von
JO
JO
10
50
JO
JO
JO-
JO
CR \NOTOTAI.
*«r*
JU.W4
$74.4W
SIMM
n.ni
till. 117
J».2*t
W.2M
u*.-t7:

U1.06I
SOURCE: SMI/TerraMairi.x. I996a
J:S3-OIJOUIO FINALRO[>TAOLEl'.WPD
-------
TABLE 18
COST SUMMARY: ALTERNATIVE 3 - COVER WITH CLAY LAYER
Califernij Culch *Pl Sin
OlMO Feasibility Send/ • Orefori Culch Tailrat, lm»ne«tiin
Md Dae* • EaM and SM* Oiartwi
.•aUcno>CkMH<
Oi inin Oinlm
DIRECT CAPITAL COSTS
UCONTOCRING
Cut £ Fill Tailinj
\tO»'C Wet Tailing
Structural Backfill

COVER
Compacted Screened - CUf Layer
Drainage Layer
Surface
Drainpipe
Geomiil* Fatric
nil
Sate*
ScreeMC) Cover Material
Surface
Unit

cu.yd
cu.yd.
cu.jrd.
e..,*.
cu-rd.
tin A.
«->*
u VEGETATION
Emtankmcw
M CoMral Ma
M i*> EmhmkiMM

SEEP MANAGEMENT
ittf C^Oftotm Sjruoi
• YakTn

OTHER IMPROVEMEXTS
I* ft.
Time*
U
It
OTAL DIRECT CAPITAL COSTS

.VDIBECT CAPITAL COSTS
(|il Fn (
cgvUtwy Con (5% of «nct)
oMlitMMn M4 Oii.itilimi»« ( 10%)
PA rrr. (J0% *t rafJMnMf. J% oT «na)

TOTAL I.VOIRECT CAPITAL COSTS

'OTAL CAPITAL COSTS
POST RC.MOVAL SITt CONTROL COST
7.0K
UM
IBCCT OPERATION A.VD MAI.VTC.NA.SCC COSTS
ration Rrpjirt acre
(riauo* Maimraanct acn
Iccmcify for Pumping L5
ump and l*1iunb«A| MaMwiiancc L5

OTAL

NDinrCT'bPF.RATIO.S A>0 MAI.VTt.XA.NCE COSTS
dminitmiioit ( 3% direct) LS
IIK. fm (5% of direct) LS
rKrvc(:)%ofitircci| LS

OTAL
Ouafliiry

J i.OOO
S.OOO
20.000
Subcoul
1 4.000

7.000
1.000
HO.OOO

21.000

14.000
10.000
17
4.0
l«.400
I
I
1.000
Sukagcal
Eack
I
i:
i:
>PCRATIO.N A.NO MAI.VTC.NA.NCt PRESENT WORTH I JO VCARS)
ToulCou
5IU4J
SI2.I31
JIO.t»
HJ.*4«
SIAlflO
SM.OOO
1^.000
SI07.47I
UI.U4
U1.1M
SI07..7I
I7JJ70
Eack/yr
JI.0-Ta.TI i
PrcwM
s*ooo
MOOO
SI.WO
j:oo

SI4.0U
JT41
(741
SJ.74J
)0
;o
10
itltt
tl.l*4
SO i^
CROOTOTVI
SOURCE: SMIATerraMatrix, !996a
i er>r>T.\ni.ElS WPO
-------
TABLE 19
COST SUMMARY: ALTERNATIVE 4 - SOIL COVER WITH GEOSYNTHETIC BARRIER
C»ifg"»« CuKh NPL Sn< -10 FAukiKry Study • Onf*n Culch
DIRIC: C*'.T*L COSTS
Comaofici" L'nii Quaniily Toul Cot"
C«:£ ' ' Ti.,.»j Cuyd. J 1.000
Vj.t v« Tailing Cu >U J.OOO
CrMI S«r?j£» <4 yd. 4J.JJO '
Smviwai Backfill cv.jnl 70.000
Svbcoul UN.MJ
COV£«
Lifltrtio"* • C"**aflJcnnM cu.)ri. 1.425
Or>i>wMnt Samct - Suffer 14 ft. JSO.OOO
Sunact «>* 7.000
Ottna.pr lii> fu 1.000
Gvwwuir Faanc H-ft. 310.000
Scrm>t< CCOT MMfial
Swfatf c*-)^- 21,000
EMMHUWIII c«.yd 10.000
WVECETATION
S^facc acm f.7
f«»Mi>iii«i acn 4.0
lit ini 1 SMJJM
SEEP MANAGEMENT
Srr* C«urf\c(2r.ordirml LS 1 1 1)111
TOTAL
OrtK.sT^ AND MAl.NTENANCF PRESENT WOKTII (JO VCARS)

JUli.rrj

ST7&JI4
sun.m

Yon *•"»
JO SIJIH
JO S74.4JJ
JO S74.JM
7 MOU
7 . JI.07I
S17J..M
jo Jrrw
M J9 ?9^
JO H6 J72
US.06I
CR.\NJ>TOT.II. i:.:«'.:u
SOtRCt SMlTerr»M3ln«.
P J2S"-0: ;• 0- : ^ Fjv.v.ROO TABLE!1) WHO
-------
TABLE 20
ALTERNATIVE 5: MULTI-LAYER ROCK AND SOIL COVER
WITH A GEOSYNTHETIC BARRIER LAYER
1
California Culch NPL Site
OU-IO Fmtibiliry Sludr - Orct»" Cukh Tailing Impoundment
DIRECT CAPITAL COSTS

RECONTOURING
Cut <& Fill Tailing
More Wet Tailing
Grading, prep, for liner
Structural Backfill
COVER
^cotynthetic Barrier
Surface £ Embankment
Geecompe«iie Drainage Net
Surface £ Embankment
Cover Material
Surface • If Screened
Embankment • If Pit-ma
Embankment • A* of rock
Revegciatc Surface
SEEP MANAGEMENT
ieep Collection Syucm
itimp and Overflow Syifem
Pipeline to Yak Treatment Plant
OTHER IMPROVEMENTS
.'pgradkal Ground Water Interceptor Trench
and the Upgradient
Collector Channel
Mvcnion Ditchci
Dun Control
Sediment Control

OTAL DIRECT CAPITAL COSTS.

NDIRECT CAPITAL COSTS

ngineering and detign (10% of direct)
ontingcncy (25% of direct)
egil Fee (5% of direct)
tcgulaiory Cou (5% of direct)
lobilizalion and Demobilization (10%)
PA rm (20% ofcnginetring. 5% ofdirett)

OT _ INDIRECT CAPITAL COSTS

OTAL CAPITAL COSTS

POST REMOVAL SITE CO.TTROL COST
Discount Rate: 7.0%

omponenl
Unit Quantity Tout Cou

cu.yd.

cu.yd.
46.500
5.000
62.000
lt.000
SJ5I.77)
•O..IX

cu.yd.
cu.yd.
cu.yd.
•cm
575.000

575.000

20.000
11.000
3.700
t.1
Subtotal
LS I
lin. ft 1.000
Subtotal
LS
LS
SI7S.700
U2.MI
SI2.S51
SI0.750
J33.HI
JI5.W3

J3I.230
1102.910
no.ooo
125.000
JI47.79*
SI.4T7.t75
J7J.I-W
S73.I99
JIJ7.T9I
1101.451
Unit
IRECT OPERATION AND MAI.VTC.NANCC COSTS
n»pcctiori hour
rotion Repairi acre
rgeunon Mitntenance acre
lectriciry for Pumping LS
ump and plumbing maintenance LS

OTAL

VDIRECT OPERATION AND MAINTENANCE COSTS
dminmrllion (5% direct) LS
IIK. fce»(3*'.ofdirect) LS
cvcrvc(:5%of direct) LS
Each
Each/yr
• 4
I
S/>Tar
S2.500
u.ooo
SI.500
s:oo

S9.4IO '
JJ74
JU74
Vean
PreMtil
Worth
30
30
30
7
7
30
30
30
SD.IU
S3I.O:3
{41.636
Si.OU
II. 071

JIOV7CH
ss.st:
jssi:
OTAL

DERATION AND MAINTE.NA.NCt: PRESENT WORTH (JO YEARS)
(4I.I7J

SOURCE: SMI/TerraMairix. I996a
P JJSO.OU OUIO-FINALROO-.TADLEIO.WPD
-------
TABLE 21
COMPARISON OF ALTERNATIVES FOR THE OREGON GULCH TAILING IMPOUNDMENT - WAMP CRITERIA

Surface Erosion Stability
Slope Stability
•"low Capacity itiul
Stability
Surface Water (SW) and
Cruiimlwiitcr (CW)
Contaminant Loading
{eduction
I'errestrial Ecosystem
I*! x pus tin*
Non-Residential Soils
Allernntive 1
No Action
No crosional stability
neasurcs would be taken.
•mbankmenls do not meet
WAMP criteria.
The existing embankment
slopes do not meet WAMP
criteria.
Existing diversion ditches-
have the capacity lo carry
the 100-yr. 2-l-hr flood, but
do not meet WAMP
stability criteria.
No reduction in loading;
seep flow would continue.
Continued risk to Icrrcslria
ecosystem exists from
ingcslion of contaminated
surface water and tailing.
Not applicable. Non-
residential soils do not
exist on the tailing
impoundment.
Alternative!
Simple Vcgetntcd Cover
All surfaces would be
tabilizcd with vegetation
o meet WAMP criteria.
lie embankment slopes
vould be rcgradcd to
2.75:1 or flatter to meet
WAMP criteria.
Diversion ditches and
channels would be si/cd
and stabilized for (he 100-
yr, 24-hr Rood to meet
WAMP criteria.
84.4% GW loading
reduction; 89% to 100%
SW loading reduction;
seep may continue lo flow
The risk to terrestrial
ecosystem is minimized.
Not applicable. Non-
residential soils do not
exist on the tailing
impoundment.
Alternatives
Clay Layer Vegetated
Cover
All surfaces would be
labilized with vegetation
omeet WAMP criteria.
The embankment slopes
would be regraded to
2.75:1 or flatter lo meet
WAMP criteria.
Diversion ditches and
channels would be sized
and stabilized for the 100-
frt 24-hr flood lo mcel
WAMP criteria.
93.3% OW loading
reduction; 89% to 100%
SW loading reduction.
The risk (o terrestrial
ecosystem is minimized.
Not applicable. Non-
residential soils do not
exist on (he tailing
impoundment.
Alternative 4
Soil Cover with
Gcosynthellc Barrier
All surfaces would be
stabilized with vegetation
omeet WAMP criteria.
The embankment slopes
would be regraded (o
2.75:1 or flatter lo meet
WAMPcriieria.
Diversion ditches and
channels would be sized
and stabilized for the 100-
yr. 24-hr flood lo meet
WAMP criteria.
96.6% GW loading
reduction; 89% to 100%
SW loading reduction.
The risk to terrestrial
ecosystem is minimized.
Not applicable. Non-
residential soils do not
exist on the tailing
impoundment.
Alternative S
Multl-Lnycr Rock and
Soil Cover with
Gcojynthctic Harrier
•mbankmenl stabilized
vilh rock and top surfaces
stabilized with vegetation
o meet WAMP criteria.
Die embankment slopes
would be regraded lo
2.75:1 or flatter lo rtieel
WAMPcrileiia.
Diversion ditches and
channels would lie si/cd
and slabili/ed for the 100-
yr, 2't-hr Hood to meet
WAMPcriieria.
99.8% GW loading
reduction; 89% (o 100%
SW loading reduction.
The risk to terrestrial
ecosystem is minimized.
Not applicable. Non-
residential soils do not
exist on the tailing
impoundment.
SOURCE: SMI/TerniMalrix, I996a
I- V»?SO-OI.)\OUIU\KOI>\TAW.I-::I.\VTI>
-------
APPENDIX A

ARARs
Record of Decision
OefonOulchOUlO
S4»7P:'j:80-OI3.OUIO>nNALROt*OUIOROD.WPD
-------
SUMMARY OF FEDERAL AND STATE LOCATION-SPECIFIC ARARS FOR OU10
Statute* RajtuttKOt CritoC*
or Limitation
}»»*&\ *"- *»~^*1&SMSlt*9s*
CH^io, **• ^
r-t <; v*;

Appropriate
^^4^^*^^<^*<^^- • "»»3!!v*vwfc,
PescfUjuofi
FEDERAL
Endangered Species Act
Fish and Wildlife Coordination
Act
Wilderness Act
Executive Order No 11988
Floodplain Management
Executive Order No. 11990
Protection of Wetlands
Section 404. Clean Water Act
(CWA)
16 USC §1531 ej j$g
50 CFR § J 200 and 402
16 USC §661 £ 33.
40 CFR § 6 302
16 USC 131 1.16 USC 668
50 CFR 53, 50 CFR 27
40 CFR § 6 302 A
Appendix A
40 CFR §6.302(1) and
Appendix A
33 USC 125 lei sea
33 CFR Part 330
No
No
No
Yes
Yea
Yes
No
No
No
...
...

Provides protection for threatened and endangered species
and their habitats. However, site-specific studies did not
document the presence of threatened or endangered species.
If threatened or endangered species are encountered during
remedial activities in OU10. then requirements of Act would
be applicable.
Requires coordination with federal and state agencies to
provide protection offish and wildlife in water resource
development programs; regulates actions that impound,
divert, control, or modify any body of water. However.
proposed remedial action activities in OUIO will not affect
fish or wildlife. If it appears that remedial activities may
impact wildlife resources, EPA will coordinate with both the
U.S. Fish and Wildlife Service and the Colorado Department
of Natural Resources.
Limits activities within areas designated as wilderness areas
or National Wildlife Refuge Systems.
Pertains to floodpliin management and construction and
impoundments in such areas.
Minimizes adverse impacts on areas designated as wetlands.
^
Regulates discharge of dredged >T fill materials into waters of
the United States. Substantive requirements of portions of
Nationwide Permit No. 38 (General and Specific Conditions)
are applicable to OUIO remedial activities conducted within
watei j of the United Stales.
AAODIOARAR FNL
-------
SUMMARY OF FEDERAL AND STATE LOCATION-SPECIFIC ARARS FOR OU10 (Continued)
st^wMi^tii^
orunjiwioii *
The Hislonc and Archaeological
Data Preservation Act of 1 974
National Historic Preservation
Acl(NHPA)
Executive Order 1 IS93
Protection and Enhancement of
the Cultural Environment
Historic Sites Act of I93S
The Archeologica) Resources
Protection Act of 1 979
Resource Conservation and
Recovery Act (RCRA).
Subtitle D
^^^L^mM^N^^
^ '*% ^ ** ?•* Jfc**1- v<- -uAwaivLa. *(,> «oS'S^> v
nLiiBMfB ^--f ^"-
•• , - ~>?*;x; * ^~i t^^J'T^f? - - \,v ^o
Eslablishes procedures to preserve historical and
archeological data that might be destroyed through alteration
of terrain as a result of a federal construction project or a
federally licensed activity program A cultural resource
survey was completed in OU 1 0 to identify historic properties
which may be affected by remedial activity.
Expands historic preservation programs; requires
preservation of resources included in or eligible for listing on
the National Register for Historic Places.
Directs federal agencies to institute procedures to ensure
programs contribute to the preservation and enhancement of
non-federally owned historic resources. Consultation with
the Advisory Council on Historic Preservation is required if
remedial activities should threaten cultural resources.
Preserves for public use historic sites, buildings, and objects
of natural significance.
Requires a permit for any excavation or removal of
archeological resources from public lands or Indian lands
Maybe relevant and appropriate if archeological resources
are encountered during remedial action activity.
Provides general classification criteria for solid waste
disposal facilities pertaining to floodplahu

. ' - ; STATE OF COLORADO ' • ..•*! -V^:-'*
Nongame, Endangered or
Threatened Species Act
CRS §§33-2-101 to 108
No
No
Standards for regulation of nongame wildlife and threatened
and endangered species. Site-specific studies did not
document the presence of threatened or endangered species.
If threatened or endangered species are encountered during
remedial activities in OUIO, then requirements of Act will be
applicable.
A:\OUIOARARFNL
-------
SUMMARY OF FEDERAL AND STATE LOCATION-SPECIFIC ARARS FOR OUIO (Continued)
or limitation

Colorado Register of Historic
Places
CRS§§ 24-801 -101 to 108
No
No
Authorizes the Slate Historical Society to nominate properties
for inclusion on the State Register of Historic Places.
Applicable only if remedial action activities impact an area
listed on the Register.
Colorado Historical.
Prehisloncal. and Archaeological
Resources Act
CRS 55 24-80-401 to 4 10
1301 to 1305
No
Yes
Concerns historical, prehistorical, and archaeological
resources; applies only to areas owned by the State or its
political subdivisions. May be relevant and appropriate if
remedial action impacts an archaeological site.
Colorado Species of Special
Concern and Species of
Undetermined Status
Colorado Division of
Wildlife Administrative
Directive E-1, 1985.
modified
No
No
Protects species listed on the Colorado Division of Wildlife
generated list. Urges coordination with the Division of
Wildlife if wildlife species are to be impacted. No evidence
of species of special concern have been identified at this site
Colorado Natural Areas
Colorado Revised Statutes.
Title 33 Article 33.
Section 104
No
No
Maintains a list of plant species of "special concern."
Although not protected by State statue, coordination with .
Division of Parks and Outdoor Recreation is recommended if
activities will impact listed species.
Colorado Solid Waste Disposal
Sites and Facilities Act.
6 CCR 1007-2

6 CCR 1007-2. Part I
No
No
Establishes regulations for solid waste management facilities,
including location standards. Proposed remedial action in
OUIO will not establish a solid waste management facility.
A.M1UIOARAR KNL
-------
SUMMARY OF FEDERAL AND STATE ACTION-SPECIFIC ARARS FOR OU10
1 ISWtfW^^I??^^ iMm^M^l^ ™*,»**j&
* " ^
-------
SUMMARY OF FEDERAL AND STATE ACTION-SPECIFIC ARARS FOR OUIO (Continued)
Si^Beqi^lA®
orliratatioB
Colorado Noise Abatement Act
Regulations on the Collection of
Aquatic Life
Colorado Hazardous Waste
Regulations
Colorado Air Pollution
Prevention and Control Act
Colorado Air Pollution
Prevention and Control Act

CRS §§25-12-101 to 108
2CCR406-8.Cb.13,
Article III. Sec 1316
6 CCR 1007-3, Put 264:
Section 264.301. (g).(h).(i).
andfl);
Section 264.3 10, («XI)
through (aX4);
Section 264.3 10, (bXI) and
(bXS)
5 CCR 1001 -4
Regulation 2
Odors
5 ~CR 1001-5
Regulation 3
APENs
*lffiPP^PiSSijaS'^^'^
$
Yes
No
No
Yes
Yes
!~> i5*8B"*
" • 9F»3qfiSfw ;
...
No
Yes
...
~
^^^j^m^^^^m^^^^^ -
< \ * >>§ (^\ t « R«ri|?fwi
Establishes maximum permissible noise levels for particular
time periods and land use related to construction projects.
Requirements governing the collection of wildlife for
scientific purposes. Remedial action activities within OUIO
will not include biological monitoring.
These specific provisions of the hazardous waste regulations
may be relevant and appropriate for conducting remedial
actions in OU 1 0. Specific provisions of Section 264.30 1
concern run-on control, run-off control, management of run-
on and run-off control systems, and wind dispersal. Specific
provisions of Section 264.3 10 concern placement of a cover
to minimize infiltration, minimize maintenance, promote
drainage and minimize erosion, and accommodate settling
Applicable only if remedial action activities cause
objectionable odors. Remedial action in OUIO is not
expected to produce odors.
Substantive provisions of APENs will be met.
AXHIIOARAR KNL
-------
SUMMARY OF FEDERAL AND STATE CHEMICAL-SPECIFIC ARARS FOR OUIO
Standard Iteniaquait Criteril:' '
or Limitation

Clean Air Act.
National Primary and Secondary
Ambient Air Quality Standards

RCRA Land Disposal
Restrictions (LDRs)
?*&9s v^V" Vv^fc^^^SW&P**.
- •* citation * "
"TiTw^j

40CFRPU1SO

40 CFR Part 268
•%£&&&&• —•. -.*Ai^M"V> !^ i >-.»> •••: »
DcscnpUoo

National ambient air quality standards (NAAQS) are
implemented through the New Source Review Program and
State Implementation Plans (SIPs). The federal New Source
Review program address only major sources. Emissions
associated with proposed remedial action in OUIO will be
limited to fugitive dust emissions associated with earth
moving activities during construction. These activities will
not constitute a major source. Therefore, attainment and
maintenance of NAAQS pursuant to the New Source Review
Program are not ARARs. See Colorado Air Pollution
Prevention and Control Act concerning applicability of
requirements implemented through the SIP.
RCRA LDRs are not applicable because the materials in issue
hav- been identified as extraction or beneficiaiion wastes that
are «|4cu1caHy exempted from the definition of a hazardous
waste. Not relevant and appropriate, see Superfund LDR
Guide f7
A.tOUIOARAR FNL
-------
SUMMARY OF FLDERAL AND STATE CHEMICAL-SPECIFIC ARARS FOR OUIO (Continued)
Standard, Requiitroci^ CrHenli,
or Limitation
* *>* «•
Applicable
Appropriate
Description
STATE OF COLORADO
Colorado Air Pollution
Prevention and Control Act
SCCRIOOI-M

5CCR 1001-10
PartC (I) 4(10
Regulations
Yes
Pursuant to the Colorado Air Pollution Prevention and
Control Act applicants for construction permits are required
to evaluate whether the proposed source will exceed NAAQS
Applicants are also required to evaluate whether the proposed
activities would cause the Colorado ambient standard for TSP
to be exceeded. Construction activities associated with the
proposed remedial action in OU10 will be limited to
generation of fugitive dust emissions. Colorado regulates
fugitive emissions through Regulation No. I. Compliance
with applicable provisions of the Colorado air quality
requirements will be achieved by adhering to a fugitive
emissions control plan prepared in accordance with
Regulation No I

Regulation 8 sets emission limits for lead and hydrogen
sulfide. Applicants are required to evaluate whether the
proposed activities would result in the Regulation 8 lead
standard being exceeded. The proposed remedial action in
OUIO is not projected to exceed the emission levels for lead
or Hydrogen sulfide, although some lead emissions may occur.
Compliance with Regulation 8 will be achieved by adhering
to a fugitive emissions control plan prepared in accordance
with Regulation No 1.
A \OUIOARAR KNL
-------