FIFTH FIVE YEAR REVIEW REPORT FOR CALIFORNIA GULCH SUPERFUND SITE LAKE COUNTY, COLORADO

Fifth Five year Review, California Gulch Superfund Site Betsy Smid r FIFTH FIVE YEAR REVIEW REPORT FOR CALIFORNIA GULCH SUPERFUND SITE LAKE COUNTY, COLORADO Prepared by U S Environmental Protection Ag.

INTRODUCTION

A five-year review (FYR) aims to assess the effectiveness and ongoing protection of a remedy for human health and the environment This process involves documenting the methods, findings, and conclusions in FYR reports, which also highlight any identified issues and provide recommendations for resolution.

The U.S Environmental Protection Agency (EPA) is preparing this FYR pursuant to the Comprehensive

Environmental Response, Compensation, and Liability Act (CERCLA) Section 121, consistent with the National Contingency Plan (NCP) (40 CFR Section 300.430(f)(4)(ii)), and considering EPA policy

The fifth Five-Year Review (FYR) for the California Gulch Superfund Site has been conducted, following the completion of the previous review on September 27, 2012 This assessment is necessary due to the presence of hazardous substances, pollutants, and contaminants at the Site, which remain above levels that permit unlimited use and unrestricted exposure (UU/UE).

The FYR was conducted under the leadership of Linda Kiefer, the EPA remedial project manager for the Site, with project managers Alissa Schultz and Kyle Sandor representing the State of Colorado.

Colorado Department of Public Health and Environment (CDPHE) EPA contractor support was provided by Treat Suomi and Claire Marcussen from Skeo Solutions Inc (Skeo) The review began on 6/28/2016

Located about 100 miles southwest of Denver in Lake County, Colorado, the 18 square mile Site encompasses the City of Leadville, parts of the Leadville Historic Mining District, and a section of the Arkansas River This area features residential housing, commercial businesses, and facilities for recreation, historical tourism, athletics, and mining activities, with zoning designated for industrial mining, business, recreation, and residential use The Parkville Water District provides water to most homes and businesses in the vicinity The Site includes 12 operable units (OUs), all of which are addressed in this FYR.

 OU1 - Yak Tunnel/Water Treatment Plant (WTP)

 OU2 - Malta Gulch Fluvial Tailing/Leadville Corp Mill/Malta Gulch Tailing Impoundments

 OU3 - Denver & Rio Grande Western Railroad Company (D&RGW) Slag Piles/Railroad

 OU5 - American Smelting and Refining Company (ASARCO) Smelters/Slag/Mill Sites

 OU6 -Stray Horse Gulch and Evans Gulch Watersheds

 OU11 - Arkansas River Valley Floodplain

 OU12 – Site-wide Water Quality

Former mining activities have led to significant metals contamination in surface water, groundwater, soil, and sediments The Yak Tunnel Water Treatment Plant in Operable Unit 1 (OU1) primarily addresses the water draining from the Yak Tunnel and OU4 The site features extensive piles of mine tailings, slag, and waste rock, with remedial efforts in OUs 2 through 11 aimed at controlling these sources Continuous water quality monitoring is part of the OU12 remedy, which was selected in 2009 Both the OU12 and OU6 remedies are currently in the remedial action phase, with anticipated completion by 2020.

Remedies for OUs 1 through 10 have been successfully implemented and are currently under monitoring and maintenance, showing effective performance Notably, all OUs, except for OU11, have been partially removed from the National Priorities List (NPL).

Once fully implemented, the remedial actions in OU6 and OU12 are anticipated to function effectively As of May 1, 2017, OU11 has transitioned into the Operations and Maintenance (O&M) phase and requires institutional controls prior to its partial deletion from the National Priorities List (NPL).

FIVE-YEAR REVIEW SUMMARY FORM

SITE IDENTIFICATION Site Name: California Gulch

Region: 8 State: CO City/County: Leadville/Lake County

SITE STATUS NPL Status: Final

Has the Site achieved construction completion?

REVIEW STATUS Lead agency: EPA

Author name: Linda Kiefer, with additional support provided by Skeo

Due date (five years after triggering action date) : 9/27/2017

SITE-WIDE RESPONSE ACTION SUMMARY

Site-Wide Basis for Taking Action

For over 140 years, the site has been engaged in mining, mineral processing, and smelting, yielding valuable resources such as gold, silver, lead, and zinc Various mining techniques have resulted in multiple forms of waste, including waste rock piles, mill tailings, slag, and smelter waste, along with the occurrence of acid rock drainage (ARD).

Before the Site was listed on the National Priorities List (NPL) in 1983, groundwater and surface water studies were conducted by private entities, the United States Geological Survey (USGS), and the EPA due to concerns over heavy metals in soils and waste rock affecting human health and mine drainage impacting surface waters in California Gulch and the Arkansas River The initial Phase I Site-wide remedial investigation (Phase I RI), released in May 1987, revealed that surface water in California Gulch exceeded primary drinking water standards for lead and cadmium, with additional contaminants such as cadmium, copper, lead, and zinc surpassing water quality criteria Furthermore, soils and groundwater were found to have elevated levels of arsenic, zinc, lead, copper, and cadmium, leading to further remedial investigation and feasibility studies (RI/FSs) throughout the early 1990s.

Baseline risk assessments (BRAs) evaluated the potential risks to human health and the environment at the Site under the assumption that no cleanup actions were taken Risk-based numerical cleanup goals were determined based on land use across the populated area A summary of the identified risks and the established cleanup goals is provided below, with numerous BRAs detailed in Appendix C.

Under the 1994 Consent Decree, the evaluation of surface water and groundwater quality at the Site was postponed to OU12, for which the EPA issued a Record of Decision (ROD) in September 2009 Currently, remedial actions are in progress to tackle the contamination in surface water and groundwater The risks associated with the Site, along with the numerical cleanup goals for OUs 2 through 11, focus solely on soils, sediments, and mine wastes.

The BRAs determined that non-lead metals in surface soils and groundwater do not significantly impact resident health, identifying lead as the sole contaminant of concern (COC) in soil Risk evaluations involved calculating action levels of lead concentrations that could pose potential health risks Table 1 summarizes the land use-based lead remediation goals.

Table 1: Land Use-Based Lead Remedial Goals

Remediation Goals Land Use-Based Lead Remedial

Worker 6,100-7,700 Plausible Action Levels BRA Part C, 1995

Residential 3,500 BRA Part A,1996 and OU9

Notes: mg/kg – milligrams per kilogram

The 1995 Aquatic Ecological Risk Assessment examined the potential risks to both terrestrial and aquatic organisms It highlighted concerns for terrestrial receptors, such as plants irrigated with contaminated surface water and herbivores consuming these contaminated plants and soil The assessment revealed that past irrigation practices contributed to risks affecting both ecological receptor pathways.

Contamination from California Gulch has significantly impacted the Upper Arkansas River, particularly at the confluence, with effects diminishing downstream The establishment of the Yak Tunnel Water Treatment Plant in 1992 led to improved water quality within two years, yet concerning levels of metals persisted Among these, zinc posed the highest risk to aquatic life, while cadmium, copper, and lead were less hazardous For more information on ecological receptor risks, refer to Appendix C.

Response actions and status of implementation for each OU are discussed in sections IV through XV below.

PROGRESS SINCE THE LAST REVIEW

Progress since the last FYR, protectiveness determinations from the 2012 FYR, status of recommendations from the 2012 FYR will be discussed below within each individual OU.

FIVE-YEAR REVIEW PROCESS

Community Notification, Involvement & Site Interviews

On July 6 and July 13, 2017, the EPA published a public notice in the Leadville Herald Democrat to announce the initiation of the five-year review (FYR) process for the Site, including contact information for Chris Wardell and Warren Smith from CDPHE, and encouraging community involvement Despite the advertisement, there were no responses from the public; however, the EPA reached out to various public officials and interested parties in Leadville/Lake County, ultimately receiving two responses to the mailed interview questions.

The feedback on the FYR questions was largely positive, highlighting the successful completion of past cleanup efforts, which, while time-consuming, have significantly improved public perception and confidence in the safety of the Site Residents feel reassured that the area no longer poses a threat to the Arkansas River and is now a safer environment for families Additionally, the EPA Project Manager received high praise for her effective communication throughout the process.

Community interviews revealed several key concerns among families who recently relocated to the area, particularly regarding environmental issues linked to their properties and economic challenges related to living near a former Superfund Site Residents expressed doubts about the necessity and cost-effectiveness of certain remediation measures, as well as difficulties in maintaining them There is also widespread confusion about the responsibilities for various remedial activities and their specific functions To address these issues, it was recommended that the EPA enhance communication by providing more updates on ongoing and past cleanup efforts, along with resources for blood-lead-level testing in the community.

Staff from Newmont Mining Company, parent company of the Resurrection Mining Company

On February 14, 2017, the PRP for OUs 1, 4, 8, and 10 reported that remedial activities have successfully reduced heavy metal discharges into the Arkansas River, significantly lowering the risk of future uncontrolled releases These efforts have led to notable improvements in the water quality of the Arkansas River.

Newmont/Resurrection has identified community confusion regarding the operators of the Yak Tunnel water treatment plant and the U.S Bureau of Reclamation’s Leadville Mine Drainage Tunnel Water Treatment Plant Their staff has praised the EPA remedial project manager for being highly competent, accessible, and open to discussing solutions for any site-related concerns that may arise.

On September 13 and 14, 2016, a site inspection was conducted to evaluate the effectiveness of remedies at all Operable Units (OUs) Key attendees included EPA Region 8 RPM Linda Kiefer, Treat Suomi, and Claire Marcussen from EPA contractor Skeo, along with Timothy Runnells from the O&M contractor representing the Potentially Responsible Party (PRP) The primary goal of this inspection was to assess the protectiveness of the implemented remedy.

On September 13, 2016, EPA RPM Linda Kiefer conducted a site inspection of OUs 2, 3, 5, 6, 7, 9, 11, and 12, supported by contractors Treat Suomi and Claire Marcussen from Skeo The primary focus of the inspection was to assess the conditions of capped waste piles, impoundments, diversion structures, and engineering controls at these operational units.

The inspection conducted on September 13, 2016, focused on the completed OU9 removal actions at various residential properties over the past five years During the assessment, several segments of the Arkansas River (OU11) downstream of the site were observed, along with monitoring well locations and surface water monitoring points as part of the Site-wide OU12 evaluation.

On September 14, 2016, key participants including EPA RPM Linda Kiefer, contractor support staff Treat Suomi and Claire Marcussen from Skeo, and Timothy Runnells from the O&M contractor representing Newmont/Resurrection, conducted the second day of a site inspection to evaluate the remedies for Operable Units (OUs) 1, 4, 8, and 10 The group convened at the Yak Tunnel Water Treatment Plant (OU1) before proceeding with tours of OUs 4, 8, and 10.

Sections IV to X outline the site inspections conducted for each Operable Unit (OU), accompanied by a checklist and photos found in Appendices F and G Additionally, a review of the data is included, emphasizing any concerns that may affect current or future protectiveness.

OPERABLE UNIT 1: Yak Tunnel WTP

OPERABLE UNIT 1: RESPONSE ACTION SUMMARY

The EPA's RI/FS results indicated that remediation of surface water, groundwater, and sediment is necessary to safeguard human health and the environment due to contamination from former mining activities Key metals such as copper, zinc, cadmium, and lead have polluted surface water, shallow alluvial groundwater, and stream sediments at OU1, with the surface water exposure pathway identified as the primary concern requiring attention.

The EPA released a FS report in June 1987 and a proposed remedial action plan for the Yak Tunnel in August

In 1987, the Environmental Protection Agency (EPA) issued a Unilateral Administrative Order (UAO) to ASARCO Incorporated, Newmont Mining Corporation, Res-ASARCO Joint Venture, and Resurrection Mining Company for the remedial design and action of the Yak Tunnel This order was amended twice, first on April 30, 1993, and again on June 16, 1993.

The Yak Tunnel's remediation strategies were first outlined in the 1988 Record of Decision (ROD), revised in the 1989 ROD Amendment, and further modified in the 1991 and 2013 Explanations of Significant Differences The primary goal for Operable Unit 1 (OU1) is to minimize the release and potential release of hazardous substances, pollutants, and contaminants from the Yak Tunnel into California Gulch.

The chosen solution involves the installation of a permanent water treatment system to address contaminated groundwater from the Yak Tunnel prior to its discharge into California Gulch Additionally, the plan includes the construction of a surge pond and flow-control bulkhead within the tunnel, along with long-term monitoring and institutional controls The cleanup objectives for OU1 align with the effluent discharge limits specified in the established table.

In accordance with the 2008 Consent Decree for Outfall 001A, the established effluent limits remain in effect Furthermore, the decree mandates semi-annual acute toxicity tests on whole effluent, alternating between aquatic invertebrates and fathead minnows for each test.

Table 2: Effluent Discharge Limits Established in the 2008 Consent Decree

COC Effluent Discharge Limit (àg/L)

Notes: àg/L – micrograms per liter

In August 1987, the EPA proposed a remedial action plan for the Yak Tunnel, followed by a Unilateral Administrative Order (UAO) issued on March 29, 1989, to ASARCO Incorporated, Newmont Mining Corporation, and the Res-ASARCO Joint Venture for the tunnel's remedial design and action The UAO was amended twice, on April 30 and June 16, 1993.

Construction of a surge pond and permanent water treatment plant began in September 1988 and finished in June

In 1991, the construction of the Yak Tunnel Water Treatment Plant (WTP) involved four key components: a surface water conveyance system, a surge pond, a barge transfer system, and gravity filters This facility, designed to treat water from the Yak Tunnel, was completed over a two-year period and has been operational since February 1992.

The Yak Tunnel Bulkhead, built in 1994, effectively manages water surges from the Yak Tunnel, especially during the spring melt Positioned approximately 1,680 feet inside the tunnel from the portal, it plays a crucial role in water control.

1995 and 1996 reduced metals loading into the Arkansas River from ephemeral tributaries

Institutional controls, including environmental covenants, are established for Newmont/Newmont/Resurrection Mining Company properties in OU1, as detailed in Appendix L These controls prohibit the use of untreated groundwater and safeguard remedial components Additionally, the Industrial Mining zoning designation for OU1 necessitates Lake County approval and notification to the EPA and CDPHE for any land use changes All remedial components outlined in the 1988 OU1 ROD, 1989 OU1 AROD, and 1991 OU1 ESD are currently in effect, with an ESD signed on July 29, 2013, mandating these institutional controls.

The 2008 Routine Monitoring Plan (RMP), Contingency Plan (CP), and OU1 Work Plan are essential for the long-term execution of the OU1 remedy, in accordance with the 2008 Consent Decree involving the United States, the State of Colorado, and Newmont/Resurrection These documents are integral components of the consent decree, ensuring compliance and effective management of the remediation efforts.

Routine operation and maintenance (O&M) activities involve repairing grouted areas in structures affected by corrosion, settlement, or other issues Additionally, these tasks include the occasional repair or replacement of monitoring well pumps and surface water monitoring equipment to ensure optimal functionality.

During the FYR period, the Yak Tunnel Water Treatment Plant (WTP) underwent significant software upgrades On October 2, 2014, the EPA granted a temporary modification to the Work Plan, permitting the discharge of effluent at a more alkaline pH level than previously allowed This modification raised the upper limit of the 30-Day Average pH range to 11.0, enhancing the plant's operational flexibility.

Newmont/Resurrection has successfully eliminated the need for sulfuric acid addition in post-treatment, which was previously necessary to maintain the plant effluent pH within the permitted upper limit of 9.0 Initially part of a 30-month trial program under the 2008 Consent Decree Work Plan, this modification has now been extended by an additional twelve months to provide the CDPHE with adequate time to review the data, set to expire in April 2018 Data collected through July 2017 indicates that the OU1 discharge has consistently remained within the established effluent limits.

OPERABLE UNIT 1: PROGRESS SINCE THE LAST REVIEW

This section includes the protectiveness determinations and statements from the previous FYR as well as the recommendations from the previous FYR and the status of those recommendations

Table 3: Protectiveness Determinations/Statements from the 2012 FYR

The OU1 remedy offers short-term protection for human health and the environment by channeling contaminated water from the Yak Tunnel to the Yak Tunnel Water Treatment Plant (WTP) The WTP effectively removes heavy metals and adjusts the water’s pH before it is released into surface water Ongoing operations and maintenance (O&M) will persist for the foreseeable future at OU1, ensuring there are no concerning exposure pathways.

Institutional controls are currently being established to ensure long-term protection The EPA needs to assess the necessity of incorporating these controls into the decision document for OU1 to enhance their effectiveness.

Table 4: Status of Recommendations for OU1 from the 2012 FYR

Institutional controls are not currently required by OU1 decision documents

Review whether a decision document is needed to include the institutional controls at OU1

OPERABLE UNIT 1: FIVE-YEAR REVIEW PROCESS

The following data are collected to determine the status of the Yak Tunnel Hydrologic System and determine if any changes are warranted to optimize the system:

 Water level elevations behind the Yak Tunnel bulkhead, in monitoring wells and piezometers and mine shafts

 Yak Tunnel flow and pump rates

 Piezometer and monitoring well field parameter measurements and water quality

 Yak Tunnel blockage field parameter measurements and water quality analyses

 Semiannual Sampling Event: Field and Water Quality Parameters in monitoring wells BBW-5, BBW-10 and the Yak Tunnel

A water-level control program has been established to manage the rising water levels in the Yak Tunnel blockage through groundwater pumping and treatment at the Yak Tunnel Water Treatment Plant (WTP) Since March 2006, this pumping initiative, which has included occasional maintenance shutdowns, has successfully reduced the blockage water levels Data indicates that even at historic high groundwater elevations, the hydraulic gradient remains directed towards the Yak Tunnel, ensuring that adverse groundwater quality conditions are unlikely as long as the groundwater elevation stays below this historic high.

Semi-annual water-quality sampling is conducted at monitoring wells BBW-5 and BBW-10, as well as the Yak Tunnel blockage, to evaluate bedrock groundwater quality and detect any adverse conditions These monitoring wells are strategically located along faults believed to have hydraulic connections with the Yak Tunnel According to the 2015 Annual Monitoring Report for the Yak Tunnel Operable Unit (OU1), the water quality data from BBW-5 and the Yak Tunnel indicated no significant adverse changes compared to 2014 or historical data.

Water released from the Yak Tunnel Water Treatment Plant (WTP) is directed into Upper California Gulch and must comply with the EPA's surface water quality standards set forth in the 2008 Consent Decree Prior to discharge, effluent is sampled, and the EPA conducts monthly monitoring of these results In 2016, there were no instances of surface water quality standards being exceeded in the effluent discharged from the Yak Tunnel WTP.

On September 14, 2016, the OU Site inspection was conducted, led by Mr Runnells from Newmont/Resurrection’s O&M contractor, who assessed the treatment system, Yak Tunnel portal, and surge pond The inspection highlighted significant upgrades to the plant, including enhancements in software, electronic control boards, lighting, and treatment systems Notably, in 2014, the EPA approved a temporary modification to the discharge permit, allowing the Yak Tunnel WTP to discharge effluent at a higher pH for 42 months to evaluate the effects of eliminating sulfuric acid on downstream metals concentrations in California Gulch At the time of the inspection, the plant was operating efficiently, with all necessary safety and O&M documents available at the command station Photographs of the site, including the Yak Tunnel WTP, were taken, and an inspection checklist was completed, available in Appendix D.

OPERABLE UNIT 1: TECHNICAL ASSESSMENT

QUESTION A: Is the remedy functioning as intended by the decision documents?

Yes The Site inspection and the review of documents, applicable or relevant and appropriate requirements

The Site’s OU1 remedy has been fully implemented and is functioning as intended, as confirmed by ARARs and risk assumptions The Yak Tunnel Water Treatment Plant (WTP) and its supporting structures were completed in 1992 and have been in continuous operation since, aside from scheduled maintenance and repairs During the current FYR period, the plant has also undergone technological and equipment upgrades.

The waters from the Yak Tunnel pose a significant risk of contamination, which could negatively impact the Arkansas River's water quality if not properly treated Ongoing treatment and monitoring of these waters are crucial According to the 2008 Consent Decree, Newmont/Resurrection is responsible for operating and maintaining the OU1 remedy features, and the EPA issued an ESD in July, emphasizing the necessity of institutional controls.

As of 2013, all necessary institutional controls outlined in the site decision documents have been implemented Procedures are established to inform the EPA and CDPHE if local governments approve any changes in land use Additionally, environmental covenants are in place to ensure compliance and protect the site's integrity.

Newmont/Resurrection’s properties with OU1 remedy features were recorded with the Lake County Clerk and

On July 31 and October 1, 2012, covenants were established to effectively restrict land use activities and safeguard remedy components The Yak Tunnel Water Treatment Plant (WTP), along with its surge pond, is secured by perimeter fencing that is both locked and clearly marked The discharge from the Yak Tunnel portal is directed through piping straight to the WTP In April 2016, the Environmental Protection Agency (EPA) partially removed Operable Unit 1 (OU1) from the National Priorities List (NPL).

QUESTION B: Are the exposure assumptions, toxicity data, cleanup levels and remedial action objectives

(RAOs) used at the time of the remedy selection still valid?

There have been no changes to the Applicable or Relevant and Appropriate Requirements (ARARs) outlined in the Record of Decision (ROD) or since the last Five-Year Review (FYR) Additionally, no new standards have emerged that would challenge the effectiveness of the implemented remedy, as detailed in Appendix H.

QUESTION C: Has any other information come to light that could call into question the protectiveness of the remedy?

No No additional information has come to light that would call into question the protectiveness of the remedy.

OPERABLE UNIT 1: ISSUES/RECOMMENDATIONS

Issues/Recommendations OU(s) without Issues/Recommendations Identified in the FYR:

OPERABLE UNIT 1: PROTECTIVENESS STATEMENT

Operable Unit: Protectiveness Determination: Planned Addendum

The OU1 remedy effectively safeguards human health and the environment, ensuring that the Remedial Action Objectives (RAOs) are achieved Contaminated water from the Yak Tunnel is treated at the Yak Tunnel Water Treatment Plant (WTP) before being safely discharged into surface water Additionally, institutional controls have been established to further enhance protection measures.

OPERABLE UNIT 2: Malta Gulch Fluvial Tailing/Leadville Corp Mill/Malta Gulch Tailing Impoundments 17

In 1993, the EPA conducted an engineering evaluation and cost assessment (EE/CA) of the Site, identifying two principal threats at OU2: the risk of casual contact with tailing materials contaminated with heavy metals, and the potential for heavy metals, cyanide, and sulfates to leach into groundwater during precipitation events Table 5 provides a detailed overview of the contamination types present in various media at OU2.

Table 5: Types of Contamination in Each Media for OU2

Tailing Impoundments Elevated lead and zinc

In September 1991, the EPA and Hecla/Day entered into an Administrative Order on Consent (AOC) to conduct an Engineering Evaluation/Cost Analysis (EE/CA) at the MGTI site, aimed at assessing the nature and extent of environmental releases and identifying suitable response actions.

In January 1993, the EPA established agreements with Hecla/Day and Leadville Silver & Gold to clarify their financial responsibilities for cleanup efforts at the MGTI and MTI sites A subsequent partial Consent Decree with Hecla/Day allocated funds specifically for the OU2 cleanup Additionally, an August 1994 Consent Decree enabled the United States, representing the Ore and Chemical Company, to resolve the company's liabilities at the LMGFT site.

In 1995, four removal and response actions were conducted at OU2, which included the excavation of fluvial tailings from Lower Malta Gulch and their subsequent deposition in the MGTI The material within the MGTI was then consolidated, graded, capped, and revegetated Additionally, forty-two corroded drums were removed from the Leadville site.

Corporation Mill and disposed of appropriately The 1996 removal action at the MTI consolidated the tailing, neutralized acidic leachate, and capped and revegetated the area

The removal actions implemented in OU2 effectively prevent or manage the release of hazardous substances, ensuring no unacceptable risks to human health and the environment Lead is identified as the primary contaminant of concern (COC), and the response measures are specifically designed to control all COCs present in the capped material.

On September 30, 1999, the EPA issued the Record of Decision (ROD) for Operable Unit 2 (OU2), which outlined the removal of hazardous substances at the MGTI, Lower Malta Gulch, and MTI areas The 1999 ROD concluded with a "No Further Action" remedy, contingent on the assumption that the OU would remain designated for Industrial Mining or similar uses, prohibiting residential development To reinforce this decision, the EPA released an Explanation of Significant Differences (ESD) on July 29, 2013, emphasizing the necessity of institutional controls to protect the integrity of engineered features and structures involved in the remediation efforts.

On July 23, 2001, the EPA partially removed OU2 from the National Priorities List (NPL) The Industrial Mining zoning designation for both MGTI and MTI is still effective Any future activities at the mill and impoundment site will necessitate a permit from the Colorado Department of Reclamation and Mining Safety Additionally, Lake County enacted an ordinance in April regarding these operations.

On March 15, 2013, institutional controls were established to safeguard remedy components and enforce best management practices for soil excavation These controls mandate approval from the Colorado Department of Public Health and Environment (CDPHE) for any excavation or earth removal activities exceeding 10 cubic yards or that could affect an engineered remedy.

Surface water and groundwater monitoring in the vicinity of OU2 is being addressed as part of OU12

In addition to the four removal actions, the 1999 ROD specified the following monitoring requirements to maintain the effectiveness of the removal actions:

 Review the zoning definition to ensure consistency with the remedy

 Review the status of the Colorado Division of Mining and Geology permit and use of the mill and impoundments

 Upon termination of the Colorado Division of Mining and Geology permit, ensure that final facility reclamation is protective of human health and the environment

 Monitor groundwater in June of each year at nine locations for metals and other inorganic parameters

CDPHE conducts annual O&M inspections and maintenance activities per the March 20, 2015 O&M Plan O&M activities are performed under an EPA grant funded with Special Account monies As a result of the September

2016 inspection, TetraTech, the State O&M Inspection contractor, made several recommendations for maintenance of remedy features The State will determine which of these recommendations will be conducted as part of O&M.

This section includes the protectiveness determinations and statements from the previous FYR as well as the recommendations from the previous FYR and the current status of those recommendations

The remedy at OU2 effectively safeguards human health and the environment in the short term by significantly reducing or eliminating risks associated with hazardous substances at the Malta Gulch Tailing Impoundment and its surrounding areas Institutional controls, including the Industrial Mining designation and state-required mining permits, further enhance protection To ensure long-term safety, the EPA should evaluate the necessity of additional institutional controls for OU2.

Institutional controls are mentioned in the

ROD as “present ICs” in the form of zoning

Review whether additional institutional controls are needed for at OU2

Completed ESD was issued requiring additional institutional controls

There are no applicable data to review for OU2

On September 13, 2016, an inspection of OU2 was conducted, with participant details provided in Section III of the FYR Report The capped impoundments were found to be intact, and the fencing along with warning signs remained in good condition Photographic documentation of site features, including the impoundments, can be found in Appendix E, while the completed inspection checklist is available in Appendix D.

The site inspection and document review confirm that the remedy is effectively functioning as intended by the OU's removal actions and No Further Action Record of Decision (ROD) All necessary institutional controls outlined in the decision documents are currently implemented In the event of a change in land use approved by local governments, established procedures are in place to promptly notify the EPA and CDPHE.

QUESTION B: Are the exposure assumptions, toxicity data, cleanup levels and RAOs used at the time of the remedy selection still valid?

There have been no changes to the Applicable or Relevant and Appropriate Requirements (ARARs) since the Record of Decision (ROD) or the last Five-Year Review (FYR) Additionally, no new standards have emerged that would challenge the remedy's effectiveness, and there have been no alterations in exposure assumptions or toxicity data that could impact its protectiveness Currently, there are no proposed reuse plans for the OU2 mill that would compromise the remedy's integrity.

No No other information has come to light that could call into question the protectiveness of the remedy.

The remedy implemented at OU2 safeguards human health and the environment by significantly reducing or eliminating risks associated with hazardous substance releases Additionally, institutional controls are in place to protect engineered remedy components, ensuring that any soil excavation is conducted in a manner that prioritizes human health and environmental safety.

OPERABLE UNIT 3: Denver & Rio Grande Western Railroad Company (D&RGW) Slag Piles/Railroad Easement/Railroad Yard

Based on findings from the 1989 and 1992 Remedial Investigations (RI) and the 1993 Screening Feasibility Study (SFS), the EPA identified the fine fraction of stockpiled AV Smelter slag and the risk of particulate release during ballast operations as significant potential human health exposure pathways.

Table 8 indicates the types of contamination found in the OU3 media

Table 8: Contaminated Media at OU3

Slag Elevated levels of zinc, lead, arsenic and cadmium; low acid- generating potential and a neutral-to-basic pH Fine slag (less than 3/8 of an inch) Elevated lead

In May 1996, D&RGW submitted an FS for the stockpiled fine slag at the AV Smelter Slag Pile, in accordance with the terms of the 1993 Consent Decree

EPA issued the Stockpiled Fine Slag – Arkansas Valley Smelter Slag Pile ROD (1998 OU3 ROD) on May 6,

In 1998, the area was designated for industrial and mining uses, requiring no additional action On August 6, 2014, the EPA issued an Explanation of Significant Differences (ESD) to incorporate institutional controls into the OU3 remedy due to contamination levels exceeding Unrestricted Use/Unrestricted Exposure (UU/UE) standards The Record of Decision (ROD) specifically addressed only fine slag from the AV Smelter Slag Pile, which consists of slag particles measuring 3/8 inch or less After thorough analysis of alternatives and public feedback, the EPA concluded that a No Action alternative was suitable, as there were no identified pathways for human or ecological exposure to the fine slag, and the risk of metal leaching was minimal Additionally, the 1998 OU3 ROD allowed for the potential future use of the slag depending on regional market demands for construction materials.

The No Action alternative maintains the stockpiled fine slag in its current state without any cleanup or management efforts However, it does allow for the future use of the slag, provided it is properly encapsulated before being utilized or reused.

Based on the lack of fine slag or leachate generation, the 1998 OU3 ROD did not require remedial action at this location

As part of its ballast operations, Union Pacific (UP) relocated approximately 104,000 cubic yards of slag to the

In March 1998, the AV Smelter Slag Pile was leveled to bring the Harrison Street Slag Pile to grade, exposing soils with elevated lead concentrations This exposure poses significant human health risks if the land is developed for residential purposes Consequently, the property has remained vacant to date.

In accordance with the 1993 Consent Decree, UP proposed a work plan to transform the easement into a section of the paved Mineral Belt Bike Trail, which was completed in the late 1990s Following this development, UP donated the easement's ownership to Lake County through a quitclaim deed.

In the summer and fall of 1997, UP excavated 1,264 cubic yards of fine slag from the rail yard and relocated it to the AV Smelter Slag Pile, exposing soils with high lead concentrations This exposure poses significant health risks for potential future residential development Currently, the land remains undeveloped and vacant.

On August 6, 2014, EPA issued an ESD that required institutional controls on OU3 properties

On February 23, 2009, Lake County enacted an ordinance that established institutional controls for OU3, mandating best management practices for soil excavation This ordinance necessitates approval from the Colorado Department of Public Health and Environment (CDPHE) for any excavation or earth removal activities, as all of OU3 is classified as an engineered remedy.

Leadville adopted a similar ordinance for properties within city limits on May 7, 2013 EPA deleted OU3 from the NPL on April 11, 2016

The 1998 OU3 No Action Record of Decision (ROD) did not mandate the maintenance of fine slag piles According to the 1998 Memorandum of Understanding (MOU) between UP, Lake County, and the EPA, the fine slag located on the rail easement was to be integrated into the Mineral Belt Trail, with Lake County designated as responsible for the long-term maintenance of the trail.

For any future applications of slag, it must be encapsulated to ensure safe reuse This encapsulation can involve incorporating fine slag into concrete or asphalt aggregates, utilizing it as a road base, or employing it as backfill, provided that the slag is either chemically bound or physically separated from exposure by a barrier made of a different material.

The remedy at OU3 is currently effective in safeguarding human health and the environment in the short term, as no complete exposure pathways have been identified However, to ensure long-term protection, further studies are necessary to assess whether additional response actions are required at OU3.

Contaminated soil may be a media of potential concern at

Review whether additional response actions are needed at OU3

Completed The need for institutional controls was included in an ESD for OU3 on August 6,

2014 Institutional controls in the form of ordinances were adopted by Lake County on 3/3/2009 and the City of Leadville on 5/7/2013

The OU3 inspection conducted on September 13, 2016, involved participants detailed in Section III of the FYR Report and yielded no significant findings The Rail Easement/Rail Yard area, known as Poverty Flats, has been sold, with the new owner reaching out to CDPHE as per the Institutional Controls (ICs) CDPHE has approved a material management plan for the proposed development All slag piles from this OU were relocated to the Arkansas Valley South Hillside Slag Pile in 1998 or integrated into the paved Mineral Belt Trail Site features, including slag piles, were documented through photographs (see Appendix E), and an inspection checklist is available in Appendix D The slag piles remained intact and in good condition, while the Mineral Belt Trail was also intact, well-maintained, and actively used by pedestrians, cyclists, and skaters.

Yes The Site inspection and the review of documents, ARARs and risk assumptions indicate that the remedy is functioning as intended by the OU3 No Action ROD

All institutional controls required by Site decision documents are in place EPA and CDPHE will be notified if local governments approve a change in land use

There have been no changes to the Applicable or Relevant and Appropriate Requirements (ARARs) identified in the Record of Decision (ROD) or since the last Five-Year Review (FYR) Additionally, no new standards have emerged that would challenge the effectiveness of the implemented remedy There are also no changes in exposure assumptions or toxicity data that would raise concerns about the remedy's protectiveness Currently, there are no proposed reuse plans at Operable Unit 3 (OU3) that would impact the remedy's effectiveness.

The OU3 ROD primarily addressed fine slag at the AV Smelter Slag Pile, but redevelopment proposals for Harrison Street and Poverty Flats revealed additional contaminated media of concern Consequently, an ESD signed on August 6, 2014, mandated institutional controls The EPA also clarified the term “contingency” regarding fine slag utilization in the 1998 ROD, allowing for its use in future commercial applications under specified requirements Additionally, the City of Leadville enacted an ordinance on May 7, 2013, to limit exposure to slag and contaminated soils, leading to the partial deletion of OU3 from the NPL in 2016.

The OU3 remedy prioritizes the protection of human health and the environment through robust institutional controls These controls safeguard the engineered components of the remedy, ensuring that soil excavations are conducted safely and responsibly.

OPERABLE UNIT 4: Upper California Gulch

The EPA's OU4 1994 RI/FS results indicate that hazardous substances from waste rock and fluvial tailing piles pose an imminent threat to public health and the environment These metals, a legacy of past mining activities, risk leaching into surface water or groundwater through acid rock drainage, necessitating urgent remedial action.

Between 1995 and 1996, Resurrection Mining Company conducted removal activities at the Garibaldi Mine in the Garibaldi Sub-basin, the Agwalt Mine in Whites Gulch, and the Upper California Gulch Surface Water Diversion, prior to the issuance of the Record of Decision (ROD) The ROD subsequently highlighted the necessity for further response activities in several areas, including the Garibaldi Sub-basin, the Printer Girl Waste Pile in Whites Gulch, and waste rock sites at Nugget Gulch, AY Minnie, Iron Hill, and FTS 4/Oro City.

EPA issued the ROD for OU4 on March 31, 1998 The RAOs established in the 1994 OU4 ROD include:

 Control erosion of contaminated materials into local water courses

 Control leaching and migration of metals from contaminated materials into the surface water

 Control leaching and migration of metals from contaminated materials into the groundwater

The selected remedy for OU4 consisted of the following remedial components:

 Garabaldi sub-basin: o Diversion of surface water and selected removal of waste

The Whites Gulch sub-basin project involves the excavation, consolidation, and removal of waste rock from the Printer Girl Waste Rock Pile Additionally, the project includes regrading the excavated areas and constructing diversion ditches to effectively manage surface water runoff to the regraded sections.

The Nugget Gulch sub-basin project involves the excavation and consolidation of waste rock from the Rubie, Adirondack, Colorado No 2 East, and North Mike Waste Rock Piles onto the Colorado No 2 Waste Rock Pile Additionally, it includes regrading and applying a simple rock or vegetated cover over the Colorado No 2 Waste Rock Pile The project also focuses on terracing, soil amendment, and revegetation of the excavated areas, along with the construction of diversion ditches to effectively manage surface water runoff to the terraced and regraded sections.

The AY Minnie sub-basin project involves the construction of diversion ditches to minimize surface water runoff onto the AY Minnie Waste Rock Pile Additionally, Lake County Road 2 will be relocated to create space for a sedimentation pond, enhancing protection against stability failures of timber cribbing while preserving the mining heritage and cultural resources of the area.

 Iron Hill sub-basin: o Regrading and placement of a simple cover (revegetated soil or rock) over the Mab Waste Rock Pile as well as revegetation of surrounding disturbed areas

Oro City is undergoing significant reconstruction and stabilization of the Upper California Gulch stream channel to enhance flood resilience for a 500-year flood event This project includes the regrading and removal of channel spoil material and selected fluvial tailings, as needed Additionally, the construction of eight sediment dams within the channel and the creation of approximately 1.5 acres of wetlands along the channel are key components of this initiative.

The OU4 ROD focused on addressing potential sources of surface water and groundwater contamination at the Site, rather than establishing numeric cleanup standards On March 17, 2004, the EPA issued an ESD to defer remedial activities at FTS 4/Oro City, acknowledging the area's historical significance as an early mining camp, a decision supported by interim monitoring data The OU12 remedy aims to tackle site-wide contamination and assess the effectiveness of source control measures, with the possibility of further remediation if needed Additionally, on July 29, 2013, the EPA added institutional controls to the Site remedy through another ESD.

Response actions at Nugget Gulch, Whites Gulch, AY Minnie and Iron Hill began in 1998 and finished in 2001

On December 22, 2010, Lake County enacted institutional controls (ICs) for OU4 by amending the Land Development Code to safeguard both engineered and non-engineered remedies A best management practice handout is distributed to all applicants for building permits in OU4, and any disturbance of these remedies requires written consent from the Colorado Department of Public Health and Environment (CDPHE) Additionally, the area is zoned Industrial Mining, which restricts land use changes without prior County approval and mandates notification to the EPA and CDPHE.

On July 31 and October 1, 2012, Newmont/Resurrection established environmental covenants on its OU4 properties, which prohibit residential use and limit groundwater utilization Subsequently, the EPA removed OU4 from the National Priorities List (NPL) on October 24, 2014.

Newmont/Resurrection performs inspections as outlined in the Operations and Maintenance Plan for the California Gulch Superfund Site, specifically for OU4, OU8, and OU10, as detailed in Appendix D of the 2008 Consent Decree approved on August 29, 2008 The findings from these inspections are compiled in the Annual Inspection Reports for the California Gulch Superfund Site, which can be obtained by reaching out to EPA Region 8.

The remedy at OU4 effectively safeguards human health and the environment in the short term by controlling exposure pathways that may pose unacceptable risks To ensure long-term protection, the EPA should evaluate the necessity of a decision document to establish institutional controls at OU4.

Review whether a decision document is needed to incorporate institutional controls at OU4

Completed ESD calling for institutional controls was completed

The OU4 inspection was conducted on September 14, 2016, with participant details provided in Section III of the FYR Report Photographs capturing site features, such as monitoring wells and access controls, can be found in Appendix G, while the completed inspection checklist is available in Appendix F.

An unpaved roadway traverses OU4, where previous evaluations led to the installation of wire-covered rock and log-reinforced barriers to combat erosion on the downslope side Most waste piles in OU4 have been either removed and consolidated or revegetated, with some covered in rock and marked with no trespassing signs The area features roadways frequented by local residents and tourists for recreational activities, though unauthorized prospectors have been noted trespassing near Oro City To mitigate this issue, the local police department now conducts regular monitoring of the area.

Under the 2008 Consent Decree, Newmont/Resurrection is responsible for the operation and maintenance of OU4 remedy features, ensuring that all institutional controls mandated by Site decision documents are implemented Procedures are established to notify the EPA and CDPHE in the event of local government land use changes Additionally, environmental covenants have been placed on OU4 properties to enhance the protection of these remedy features, with these covenants officially recorded with the Lake County Clerk and Recorder on July 31, 2012, and October 1, 2012.

There have been no changes to the Applicable or Relevant and Appropriate Requirements (ARARs) since the Record of Decision (ROD) or the previous Five-Year Review (FYR), and no new standards have emerged that could jeopardize the remedy's protectiveness The 1998 OU4 ROD did not set numeric cleanup standards for surface water or groundwater but identified Remedial Action Objectives (RAOs) focused on preventing the erosion of contaminated materials into local waterways and controlling their leaching and migration These RAOs have largely been successfully achieved.

Land use at OU4 has not changed The exposure assumptions used in the development of the 1998 OU4 ROD remain valid

The remedy at OU4 prioritizes human health and environmental protection by managing exposure pathways that pose unacceptable risks This is achieved through the diversion of contaminated surface water and the removal, consolidation, or covering of mine waste Institutional controls are in place to guarantee the safety of engineered remedy components, ensuring that any soil excavation is conducted with health and environmental safeguards in mind Additionally, residential use is restricted in specific areas of OU4.

OPERABLE UNIT 5: ASARCO Smelters/Slag/Mill Sites

From 1991 to 1996, final Site-wide BRAs revealed that slag, non-residential soils, and residential area soils posed potential risks due to contamination Metals such as lead, arsenic, cadmium, copper, and zinc, stemming from past mining activities, were found in soil and air, posing threats to both human health and the environment Lead and arsenic were identified as the primary contaminants of concern, leading to their selection as indicator chemicals for the remedial response The specific contaminated mediums at OU5 are detailed in Table 13.

Medium Area of OU5 Contamination

Results of the soils investigation indicate elevated arsenic, cadmium, lead and zinc levels; the highest levels of contamination were detected in samples from the bag-house area

Soil CZL Elevated lead levels

The Elgin Smelter, Grant/Union Smelter, and Western Zinc Smelter have all been identified as sites with elevated levels of lead and arsenic Additionally, the Arkansas Valley South Hillside Slag Pile also exhibits concerning concentrations of these hazardous substances.

In September 1990, the EPA and ASARCO Incorporated signed an Administrative Order on Consent (AOC) for site sampling Following this, in 1991, the EPA issued a Unilateral Administrative Order (UAO) mandating ASARCO to conduct studies and complete Remedial Investigations (RIs) By August 1994, ASARCO entered a Consent Decree with the United States, the State of Colorado, and other potentially responsible parties (PRPs) to undertake specific remediation efforts in Operable Units (OUs) 5, 7, and 9.

The Environmental Protection Agency (EPA) released two Records of Decision (RODs) for Operable Unit 5 (OU5), with the first ROD addressing the AV/CZL Sites issued on September 29, 2000, and the second ROD for the EGWA Sites issued on October 31, 2000.

The RAOs established in the two RODs for OU5 include:

 Control airborne transport of tailing particles, flue dust and soil

 Control erosion of tailing, flue dust and contaminated materials into local water courses

 Control leaching and migration of metals from tailing, flue dust and soil into surface water

 Control leaching and migration of metals from tailing, flue dust and soil into groundwater

 Control contamination exposure to humans, animals and aquatic life

 Prevent direct exposure of population to elevated contaminant levels in surficial soil

The remedy selected for the AV/CZL Sites consisted of:

 Excavation of flue dust and relocation to a single-lined, fully encapsulated repository

The consolidation of tailing and non-residential soils, followed by the installation of an 18-inch vegetated soil cover, will transform parts of the AV/CZL Site into a permanent waste management area.

 Implementation of institutional controls such as deed notices or deed restrictions to provide notification that a barrier is in place and to restrict land uses incompatible with the remedy

The development of an Operations and Maintenance (O&M) program during the remedial design phase is essential for ensuring the effective management of cover and surface water controls This program should include regular inspections to monitor for signs of erosion, differential settlement of the cover, and the overall adequacy of vegetation.

The remedy selected for the EGWA Sites consisted of:

The implementation of institutional controls is essential for warning against potential hazards and ensuring the effectiveness of remediation efforts These controls work by restricting access to or use of the property, addressing current and future land use scenarios.

The 2000 OU5 Record of Decision (ROD) for the EGWA and AV/CZL Sites lacked numeric cleanup standards, focusing instead on mitigating potential sources of contamination affecting surface water, groundwater, and air quality In contrast, the OU12 remedy targets site-wide contamination in surface water and groundwater to evaluate the effectiveness of source control measures Additionally, the EPA issued a minor ROD Modification on May 16, 2013, to clarify the institutional controls in place.

The implementation of the 2000 OU5 AV/CZL ROD commenced in June 2002, involving the demolition of smelter structures, excavation of flue dust, and transportation of contaminated materials to an on-site repository Tailing and contaminated soil were consolidated and covered with 18 inches of clean soil, which was then vegetated, while diversion ditches were constructed to prevent run-on and ponding Although ASARCO Incorporated initiated remedial actions, they were halted due to the company's bankruptcy, leading the EPA to take over the responsibility for the OU5 remedy through a settlement agreement with ASARCO signed in 2007 The EPA successfully completed the OU5 remedial activities by 2010, with ongoing operation and maintenance activities focused on inspecting and maintaining the covers and surface water controls.

The OU5 RODs for the EGWA and AV/CZL Sites incorporated institutional controls as part of the remedy Due to the infeasibility of the original overlay district concept, an alternative approach was developed during the current FYR period On April 15, 2013, Lake County enacted an ordinance that functions as an institutional control, safeguarding remedy components, enforcing best management practices for soil excavation, and mandating CDPHE approval for any excavation or earth removal exceeding 10 cubic yards Similarly, the City of Leadville adopted an ordinance for OU5 properties within city limits on May 7, 2013 Subsequently, the EPA partially deleted OU5 from the NPL on October 24, 2014.

The O&M Plan was finalized on March 20, 2014 CDPHE conducts annual O&M inspections and maintenance activities, funded through an EPA grant with Special Account monies

Following the September 2016 inspection, TetraTech, the State's O&M Inspection contractor, proposed various maintenance recommendations for remedy features The State will decide which of these recommendations will be implemented in the ongoing operation and maintenance process.

The OU5 remedy provides short-term protection for human health and the environment by effectively addressing source contamination through engineered components and planned institutional controls that limit incompatible land uses The Remedial Action Objectives (RAOs) outlined in the 2000 Records of Decision (RODs) for the EGWA and AV/CZL Sites have been successfully met Furthermore, institutional controls will be implemented to safeguard the effectiveness of the remedies at OU5.

For the remedy to be protective over the long term, the O&M Plan should be updated and implemented

O&M has not occurred as directed by the O&M

Update the O&M Plan from the remedial design and implement as necessary

Completed An O&M plan was created 3/20/2014

Institutional controls are a component of the selected remedy but have not been implemented

Institutional controls have been established to ensure environmental protection, with completed environmental covenants placed on Newmont/Resurrection properties within OU5 on April 15 and May 7, 2013 Additionally, Lake County and the City of Leadville enacted ordinances in 2013 that serve as institutional controls for the entire OU5 area.

On September 13, 2016, an inspection of OU5 was conducted, with participants detailed in Section III of the FYR Report Photographs capturing site features can be found in Appendix F, and the completed inspection checklist is available in Appendix D.

All contaminated materials at OU5 have been consolidated and put under a protective cover The cover was revegetated in 2009 just prior to completion of the engineered remedy at OU5.

The site inspection and document review confirm that the OU5 remedy is effectively operating as outlined in the Site decision documents An 18-inch soil cover has been established over the consolidated waste, designed to enhance drainage and reduce erosion through vegetation Additionally, surface water diversion channels have been implemented to prevent run-on and ponding in the waste management unit The EPA took the lead on remedial and operational activities at OU5 following a 2007 settlement with ASARCO Incorporated, while CPDHE is currently responsible for ongoing operations and maintenance.

In 2010, the EPA finalized the construction of the engineered remedy, ensuring that all institutional controls mandated by site decision documents are effectively implemented Local governments are required to notify the EPA and CDPHE if there are any changes in land use approvals.

In addition, EPA signed a minor ROD Mod on May 16, 2013, that clarified the institutional controls EPA partially deleted OU5 from the NPL on October 24, 2014

The selected remedies for OU5 focus on several Remedial Action Objectives (RAOs), including preventing the erosion of contaminated materials into local waterways, controlling the leaching and migration of contaminants into surface water and groundwater, and managing airborne transport of pollutants Additionally, these measures aim to limit exposure to contaminants for humans, animals, and aquatic life, while also preventing direct contact with elevated contaminant levels in surface soil The successful achievement of these RAOs has been facilitated through the implementation of an engineered remedy.

The ARARs outlined in the OU5 RODs remain unchanged since the last FYR, and no new standards have emerged that would challenge the effectiveness of the implemented remedy.

The OU5 remedy effectively safeguards human health and the environment by addressing source contamination with engineered components Institutional controls are in place to prevent incompatible land uses, ensuring compliance with the remedial action objectives (RAOs) outlined in the 2000 Record of Decisions (RODs) for the EGWA and AV/CZL Sites The Colorado Department of Public Health and Environment (CDPHE) conducts routine operations and maintenance (O&M) activities to ensure the remedy functions as intended Additionally, all necessary institutional controls are established, along with procedures for notifying the EPA and CDPHE if local governments approve any changes in land use.

OPERABLE UNIT 6: Stray horse gulch and evans gulch watersheds

The Site-wide final BRA assessed various contaminants in upland and riparian areas, focusing on soil, slag, waste rock, tailing, and fluvial sediments Key contaminants included arsenic, antimony, barium, beryllium, cadmium, chromium, copper, lead, nickel, manganese, mercury, silver, thallium, and zinc The EPA identified lead and arsenic as primary indicators for cleanup due to their significant human health risks at the Site Contaminated media findings for OU6 are detailed in Table 16.

Sediment Based on data from the 1997 EE/CA for Stray Horse Gulch, elevated metals contamination was found in the sampling stations located along Stray Horse Gulch

The analysis of the Stray Horse Gulch tailing and waste rock piles revealed elevated concentrations of lead and arsenic through x-ray fluorescence testing Surface soil samples showed increased levels of arsenic, lead, cadmium, and zinc, while subsurface and foundation soils exhibited significantly elevated concentrations of arsenic, cadmium, lead, and zinc.

Between 1990 and 2001, the EPA undertook various response actions at OU6 to address contamination from mine wastes before the Record of Decision (ROD) was signed A detailed list of these actions can be found in Table B-9, highlighting the systematic efforts to clean up the affected areas.

 Relocation, consolidation and/or capping of selected mine waste piles

The collection and treatment of acid rock drainage (ARD) from mine waste piles is conducted at a facility managed by the U.S Bureau of Reclamation (BOR), located at the entrance of the Leadville Mine Drainage Tunnel (LMDT).

 Construction of ARD retention ponds and subsequent maintenance

 Diversion of clean surface water around mine wastes

 Rehabilitation of Stray Horse Gulch and Starr Ditch

EPA issued the ROD for OU6 on September 25, 2003 The 2003 OU6 ROD identified the following RAOs for OU6:

 Control erosion of mine waste rock and deposition into local water courses

 Control leaching and migration of metals from mine waste rock into surface water

 Control leaching of metals from mine waste rock into groundwater

 Prevent direct unacceptable exposures to elevated concentrations of contaminants in the soil and waste rock

The OU6 selected remedy consisted of the following elements:

 Maintenance of the existing Response Actions implemented prior to the ROD

 Installation of a bulkhead in the LMDT

 Pumping ARD impounded behind the bulkhead to the surface with conveyance to the U.S Bureau of Reclamation (USBR) treatment plant via a gravity pipeline

 Removal of the Ponsardine mine waste pile with on-site disposal

 Repair of unstable cribbing associated with the Robert Emmet mine Site

 Institutional controls on future changes in land use

EPA modified the 2003 OU6 ROD with an AROD on September 28, 2010, to make the following changes in the remedy:

 Phase 1: Improve the clean water diversion systems along the Mahala, Pyrenees, Greenback, RAM, Old and New Mikado, and Adelaide-Ward Waste Rock Piles

 Phase 2: Selectively cap additional mine waste rock piles to decrease the volume of acid rock drainage generated

 Phase 3: Enlarge and enhance the current acid rock drainage collection system and retention ponds

 Eliminate the use of the Leadville Mine Drainage Tunnel and USBR Leadville Mine Drainage Tunnel Treatment Plant from the OU6 remedy, except in the case of emergencies

 Shift the monitoring of groundwater and water levels in the Leadville Mine Drainage Tunnel to the OU12 Site-wide surface water and groundwater remedy

 Site and construct a Site-wide repository in OU6

 Remove implementation of the Leadville Mine Drainage Tunnel bulkhead from the remedy

 Implement institutional controls to protect engineered remedies and to reduce exposure to contaminants that will remain

The 2003 OU6 Record of Decision (ROD) and the 2010 OU6 Amended Record of Decision (AROD) focused on mitigating potential source materials that could lead to surface water and groundwater contamination, rather than establishing specific numeric cleanup standards In contrast, the OU12 remedy is designed to tackle site-wide contamination of surface water and groundwater, ensuring effective monitoring of the implemented source control remedies.

Since before the 2012 FYR, the following remedy elements of the 2003 OU6 ROD and 2010 OU6 AROD have been implemented:

 Maintenance of the existing response actions implemented prior to the ROD

 Removal of the Ponsardine mine waste pile with on-site disposal

 Repair of unstable cribbing associated with the Robert Emmet mine Site

Numerous tracer studies have been conducted to evaluate the hydraulic connection between the Marion adit and the LMDT, focusing on the quality of this connection These investigations also assessed the effectiveness of the 2000 removal action, which redirected acid rock drainage (ARD) from surface water control structures to the subsurface, facilitating its transport to the USBR water treatment facility.

 Installation of monitoring wells in the LMDT as part of data collection to support remedial design

In 2005, a non-time-critical removal action was undertaken to build an engineered outlet for the Gaw Shaft, which is considered a crucial relief point for the mine pool that is held back by potential blockages in the LMDT.

 Negotiation with USBR for treatment of ARD to be extracted from behind the LMDT bulkhead after its construction

 Installation of a relief well during the 2008 State of Emergency due to high water levels and a blockage in the LMDT

 Pumping the water in the Mikado Pond to the Marion Pond in 2011 to prevent an uncontrolled release into Stray Horse Gulch

 Removal of sediment in the Marion, Greenback, Mikado and Adelaide Ponds, and addition of signage and fencing in 2012

Since the 2012 FYR, the following response activities have occurred:

On May 7, 2013, the City of Leadville adopted an ordinance to implement institutional controls at OU6, aimed at safeguarding remedy components and ensuring best management practices during soil excavation The ordinance mandates Colorado Department of Public Health and Environment (CDPHE) approval for any excavation or earth removal exceeding 10 cubic yards Furthermore, certain areas of OU6 are designated for industrial mining and business activities, and an assessment is underway to determine the necessity for additional institutional controls in portions of OU6 that lie outside city limits.

 In 2014, the Mikado pond was dewatered to prevent overtop; sediments were removed to increase capacity

Since 2015, a crucial removal initiative has been implemented to enhance water management at Greenback Pond This action includes the installation of an additional drainage system for spring runoff, improvements to surface water controls, sediment removal from retention ponds, and pumping from ARD retention ponds to prevent overtopping Additionally, water is being pumped at the GAW Shaft, alongside ongoing monitoring of the mine pool.

 Construction of the repository finished on June 13, 2013; an O&M plan for the repository was written The repository also receives contaminated residential soils removed from OU9 (See Section XII)

The 2010 AROD outlines a phased strategy for minimizing acid rock drainage in OU6, with Phase 1 focusing on the improvement of the diversion ditch located upgradient of the Greenback, RAM, and Old and New Mikado waste rock piles, which has already been completed.

2016 The effectiveness of reducing ARD that needs to be treated by the LMDT treatment plant is being evaluated to determine the need and extend of Phases 2 and 3

An O&M plan for the repository is in place An O&M plan for the remaining components will be prepared as part of implementation of the final remedy.

The OU6 remedy is designed to safeguard human health and the environment by effectively managing potential exposure pathways that may pose unacceptable risks Presently, contaminated surface waters are contained within a network of retention ponds and are directed for treatment at the USBR Leadville Mine Drainage Tunnel Treatment Plant through the Leadville Mine Drainage Tunnel.

Remedial design activities are underway for implementation of an amended remedy intended to ensure protectiveness over the long term

There were no issues at OU6 identified in the 2012 FYR.

The chosen remedy for OU6 focuses on source remediation, without specific numerical performance standards outlined in the RAOs In contrast, the remedy for OU12 aims to meet chemical-specific, numerical performance standards for surface water and groundwater across the site Consequently, there is no data available for review regarding OU6.

The OU6 inspection was conducted on September 13, 2016, with participants detailed in Section III of the FYR Report Photographs capturing site features, such as monitoring wells and access controls, are included in Appendix E Additionally, a completed inspection checklist can be found in Appendix D.

The site inspection commenced at the waste soil repository and drainage pond, established in 2013 to manage contaminated residential soil and sediment This area was securely fenced and marked with warning signs The repository was found to be in good condition, with its sloped sides reinforced by rock The inspection also covered various waste rock piles and surface water retention ponds in OU6, including the RAM, Mikado, Greenback, Marion, and Pyrenees sites.

The Ponsardine, Hamms, and Penrose waste rock piles generate contaminated runoff that is managed by a surface water ditch system This system directs the runoff to the Leadville Mine Drainage Tunnel, where it is treated at the USBR plant Additionally, participants noted the conveyance system implemented during the May project.

2015 time-critical removal action that transports drainage from the Greenback Pond and Marion Pond to the Robert Emmet Mine Shaft with ultimate treatment at the LMDT

The 2012 FYR recommended enhancements for protectiveness in OU6, leading the EPA to remove sediment and conduct maintenance in the Marion, Greenback, Mikado, and Adelaide ponds They installed clear signage and fencing, ensuring that the waste pile caps and pond barriers remained in good condition During a site inspection, EPA RPM Linda Kiefer noted instances of trespassing for unauthorized prospecting on private land In response, local police now patrol the area to deter trespassing, effectively reducing human exposure to waste piles.

In 2009, the EPA conducted a pilot study to explore capping methods for waste rock piles, aiming to preserve the historical mining landscape while effectively managing drainage and surface water diversion The demonstration areas from this study are still intact, with educational signs along the Mineral Belt Trail providing information about the project and its various alternatives.

The OU6 remedy is currently being fully implemented, aiming to effectively minimize acid rock drainage that affects surface and groundwater, as outlined in Site decision documents Numerous waste rock piles in OU6 have been addressed, with several capped in the 1990s To manage acid rock drainage, surface water retention and diversion channels have been constructed, along with retention ponds that capture this drainage An overflow system directs contaminated surface water through a series of retention ponds and into the Leadville Mine Drainage Tunnel Treatment Plant (LMDT) for further processing.

The 2010 OU6 AROD introduces a phased strategy for mitigating acid rock drainage (ARD) in OU6, starting with Phase 1, which involved enhancing the diversion ditch upstream of the Greenback, RAM, and Old and New Mikado waste rock piles, completed in 2016 Currently, the effectiveness of this enhancement in reducing ARD that requires treatment by the LMDT treatment plant is under evaluation to assess the necessity and scope of subsequent Phases 2 and 3.

The City of Leadville's 2013 ordinance establishes institutional controls for Starr Ditch, a section of OU6 within the city Certain areas of OU6 are designated for industrial mining or business purposes The EPA is currently assessing the need for further institutional controls in portions of OU6 that lie outside Leadville Additionally, there are established procedures to inform the EPA and CDPHE if local governments approve any changes in land use.

The 2003 OU6 Record of Decision (ROD) did not set numeric cleanup standards for surface water or groundwater, but it identified remedial action objectives (RAOs) such as controlling erosion of contaminated materials, preventing the leaching of contaminants into water sources, and avoiding direct exposure to elevated soil and waste rock contaminants In response to significant acid rock drainage and the ongoing deterioration of mine workings, a 2010 Amended Record of Decision (AROD) revised the remedy to enhance efficiency and ensure long-term maintenance of these objectives Currently, remedial design activities are in progress.

The ARARs outlined in the Record of Decision (ROD) remain unchanged since the last Five-Year Review (FYR), and no new standards have emerged that would challenge the effectiveness of the implemented remedy.

6 Will be Protective Completion Date:

The OU6 remedy aims to safeguard human health and the environment upon its completion Presently, contaminated surface waters are managed within a network of retention ponds and directed for treatment at the USBR Leadville Mine Drainage Tunnel Treatment Plant through the Leadville Mine Drainage Tunnel.

OPERABLE UNIT 7: Apache Tailing Impoundments

The 1991 preliminary risk assessment assessed residential risks associated with exposure to contaminated media Following this assessment, numerous studies were conducted, yielding additional data on contaminant concentrations as well as human and ecological exposures The findings contributed to the 2000 Final Focused Feasibility Study.

The Focused Feasibility Study (FFS) evaluated the conditions of the Apache Tailing Impoundments area, identifying arsenic, cadmium, lead, and zinc as potential contaminants of concern (COCs) in OU7 Arsenic and lead were specifically highlighted as indicator contaminants in the final risk assessment due to their significant contribution to human health risks, as determined by the preliminary risk assessment.

The 1991 preliminary risk assessment pinpointed key sources of metals, their environmental release mechanisms, and affected receptors in a conceptual Site model By 1995, the final risk assessment highlighted soil ingestion as the primary exposure pathway for recreational visitors, while commercial and industrial workers faced risks from ingesting soil and dust Other exposure routes, such as slag piles and dermal contact with soil/dust, were deemed insignificant for both workers and recreational users The identified source materials at OU7, including tailing and foundation soils, are classified as non-principal threat wastes.

Weathered sulfidic tailing on the surface of the North and Main Impoundments contains elevated lead and arsenic concentrations and has a high acid-generating potential

Dark gray sulfidic tailing occurs below the weathered sulfidic tailing on the North and Main Impoundments and contains elevated lead and arsenic concentrations

The Main Impoundment's brown oxide tailing exhibits high lead concentrations, while its arsenic levels are lower than those in sulfidic tailing Additionally, this brown oxide tailing possesses substantial neutralization potential, effectively mitigating the acidic leachate produced by sulfidic tailing.

Soil Foundation soils found at both the Main and North Impoundments contain elevated lead concentrations and slightly elevated arsenic concentrations

Between 1996 and 2000, multiple removal actions were conducted at OU7, including the removal of Tailing Ponds No 2 and No 3 These actions involved consolidating the materials from the removed ponds onto the Main Impoundment and installing erosion protection along the southwest embankment's toe, specifically below the clay-tile culverts and wooden box culvert outfalls.

December 1997 Removal Action Completion Report describes the construction activities in greater detail The removal and remediation activities at the Apache Tailing Impoundments are summarized in Table B-10

On June 6, 2000, the EPA issued the Record of Decision (ROD) for Operable Unit 7 (OU7), detailing a remedy aimed at mitigating risks to human health and the environment This remedy includes the construction of a soil cover with a geosynthetic barrier, followed by revegetation efforts, implementation of institutional controls, and a long-term monitoring plan Additionally, a Minor ROD Modification was signed by the EPA on May 16, 2013, to specify the necessary types of institutional controls.

The RAOs identified in the OU7 ROD for the Apache Tailing Impoundments were:

 Control airborne transport of tailing particles

 Control erosion of tailing materials and deposition into local water courses

 Control leaching and migration of metals from tailing into surface water and groundwater

The selected remedy for OU7 included the following components:

 Surface water controls including the channelization of California Gulch through the southern portion of

The application of source surface controls to impounded tailings involves regrading the impoundment, installing a multi-layer composite cover over the entire tailing area, and revegetating the covered surface to enhance environmental safety and stability.

Institutional controls are essential for alerting individuals to potential hazards and ensuring the ongoing effectiveness of remediation efforts These controls involve strategies that limit access to or use of a property, addressing both current and future scenarios through a combination of temporary and permanent measures.

 A long-term monitoring program to assess the quality of surface water and groundwater following implementation of the remedy

The O&M program, established during the remedial design phase, focuses on inspecting and maintaining the cover and surface water controls, while also identifying areas with signs of erosion or differential settlement Additionally, it includes monitoring vegetation to ensure the integrity of the site.

The 2007 OU7 ROD focused on identifying potential source materials that could lead to contamination of surface water, groundwater, and air, rather than establishing numeric cleanup standards In contrast, the OU12 remedy is designed to tackle site-wide contamination of surface water and groundwater, ensuring effective monitoring of the implemented source control remedies.

Primary remediation activities completed included:

 Installation and maintenance of temporary sediment, diversion and stormwater control structures in accordance with the Storm Water Management Plan and maintenance of such controls during construction activities

 Provision of dust control, as necessary, during all excavating, hauling and placing operations

 Excavation of dispersed tailing and soil adjacent to the Main Impoundment to allow for the construction of temporary sedimentation ponds

 Demolition of existing concrete foundations west of the Main Impoundment

The project involves relocating a segment of the sanitary sewer line surrounding the North Impoundment, connecting it to the existing sewer lines at both the eastern and western ends This includes the installation of two new sewer lateral connections and the abandonment of current manholes and sewer lines.

The project involves the regrading of tailing impoundments as depicted in the provided drawings, along with the strategic placement of excavated materials in the fill areas located between the Main and North Impoundments, as well as on top of the Main Impoundment.

 Removal and replacement of the overhead power line running east and west between the Main and North Impoundments

 Channelization of California Gulch through the southern portion of the Main Impoundment

 Installation of the multi-layer cover system consisting of a geosynthetic clay liner, geocomposite drainage layer, and an 18-inch soil cover over the regraded tailing impoundments

 Construction of permanent diversion ditches, berms and swales with appropriate erosion protection to provide surface water run-on and runoff control

 Extension or abandonment of monitoring wells or piezometers as necessary

 Revegetation of the tailing impoundments and other disturbed areas with specified seed mixture

OU7 achieved Remedial Action Project Completion status on December 17, 2003

On December 22, 2010, Lake County adopted a resolution amending the Land Development Code to implement institutional controls (ICs) at OU7, ensuring the protection of both engineered and non-engineered remedies A best management practice handout is provided to all building permit applicants in OU7, and any disruption of these remedies necessitates written approval from the Colorado Department of Public Health and Environment (CDPHE) Similarly, the City of Leadville enacted an ordinance on May 7, 2013, aligning with these protective measures.

A Minor ROD Modification was signed on May 16, 2013 to clarify the types of ICs needed in OU7 EPA partially deleted OU7 from the NPL on October 24, 2014

The O&M Plan was finalized on March 20, 2014 CDPHE conducts annual O&M inspections and maintenance activities, funded through an EPA grant with Special Account monies

Following the September 2016 inspection, TetraTech, the contractor responsible for State O&M Inspections, provided multiple recommendations for the maintenance of remedy features The State will evaluate these recommendations to decide which will be implemented in the ongoing operations and maintenance (O&M) process.

The remedy at OU7 effectively protects human health and the environment, as there are no identified complete exposure pathways for humans or ecosystems, and institutional controls are established To maintain the long-term effectiveness of the OU7 remedy, it is essential to update and implement the Operations and Maintenance (O&M) Plan.

The O&M Plan needs to be updated and implemented

Update and implement the O&M Plan for OU7

Completed The O&M Plan was updated and implemented

On September 13, 2016, an inspection of OU7 was conducted, with participants detailed in Section III of the FYR Report The evaluation of OU7's conditions was primarily based on observations made by regulatory agency personnel who were present during the inspection Additionally, photographs were captured to document site features, including the Apache Tailing.

The Apache Tailing Impoundments were found to be intact and covered with established vegetation, although some localized areas were identified during the annual O&M inspection that require revegetation An inspection checklist is available in Appendix D, and the O&M contractor is actively working to address these identified issues.

Yes The review of documents and Site inspections indicate that the remedy is functioning as intended by the OU7 ROD

Site-wide surface and groundwater management near OU7 is included in the ongoing efforts of OU12 The annual Operations and Maintenance (O&M) review assesses the remedy's stability, functionality, and protective measures Recommendations from this review are incorporated into regular O&M activities, with the Colorado Department of Public Health and Environment (CDPHE) addressing any issues to maintain the remedy's effectiveness All necessary institutional controls specified in site decision documents are currently implemented Additionally, the EPA and CDPHE will be informed if local governments approve any changes in land use Notably, the EPA partially removed OU7 from the National Priorities List (NPL) on October 24, 2014.

There have been no changes to the Applicable or Relevant and Appropriate Requirements (ARARs) outlined in the Record of Decision (ROD) or since the last Five-Year Review (FYR) Additionally, no new standards have emerged that would challenge the effectiveness of the implemented remedy There have been no alterations in exposure assumptions regarding human health or environmental toxicity data that would jeopardize the remedy's protectiveness Currently, there are no proposed reuse plans for Operable Unit 7 (OU7) that would impact the remedy's effectiveness.

No other information has become available that could call into question the protectiveness of the remedy.

The OU7 remedy is designed to safeguard human health and the environment, with no identified completed exposure pathways for humans or ecological systems Institutional controls are established to maintain safety, and the Colorado Department of Public Health and Environment (CDPHE) conducts regular operations and maintenance activities to ensure the remedy operates effectively.

OPERABLE UNIT 8: Lower California Gulch

The remedy at OU8 effectively safeguards human health and the environment, as there are no identified complete exposure pathways for humans or ecosystems With established institutional controls, the remedy is operating as intended, ensuring ongoing protection.

There were no outstanding issues or recommendations identified at OU8.

No data from OU8 were available for review

The OU8 Site inspection occurred on September 14, 2016, with participants detailed in Section III of this FYR Report Photographs documenting site features, such as monitoring wells and access controls, are included in Appendix E.

An inspection checklist has been completed It is available in Appendix D

OU8 spans the lower reaches of California Gulch, situated between OU1 and OU11 During a site inspection, participants assessed various erosion-control measures, including riprap, along the erosion-prone areas of the channel Most tailing sites appeared stabilized, with reinforced embankments However, construction of a building over Lower California Gulch in the Stringtown Mill Area raised concerns, as some adjacent wetlands were filled for vehicle storage Despite these activities, data indicates no adverse effects on the remedy, with surface water concentrations of zinc and cadmium meeting performance standards at the compliance point where California Gulch meets the Arkansas River (sample location AR-3a).

The site inspection and document review confirm that the OU8 remedy has been successfully completed and is operating as intended, following the Site decision documents The excavation of contaminated materials, including fluvial tailing, waste rock, non-residential soil, and stream sediments, was completed in 2003 Ongoing maintenance and monitoring ensure the stability of excavated piles, preventing any risk of metal contamination in California Gulch All required institutional controls are in place, and the EPA and CDPHE will be notified if local governments approve any land use changes Newmont/Resurrection is responsible for the ongoing operation and maintenance activities for OU8 Following the implementation of all remedial components and the achievement of the required cleanup objectives, the EPA partially deleted OU8 from the National Priorities List on January 12, 2010.

The 2000 OU8 Record of Decision (ROD) identified potential sources of contamination affecting surface water and groundwater at OU8, but it did not establish numeric cleanup standards for these water sources In contrast, the OU12 remedy specifically targets site-wide contamination of both surface water and groundwater.

All Remedial Action Objectives (RAOs) outlined in the 2000 OU8 Record of Decision (ROD) have been successfully met The vegetation covering the contaminated material pile surfaces effectively mitigates airborne transport, erosion, and reduces the risk of exposure to contamination for both animals and aquatic life.

Land use at OU8 has not changed The exposure assumptions used in the development of the 2000 OU8 ROD remain valid

No other information has become available that could call into question the protectiveness of the remedy.

The remedy implemented at OU8 effectively safeguards human health and the environment, with no identified complete exposure pathways for either humans or ecological systems Institutional controls are established, ensuring that the remedy operates as intended.

OPERABLE UNIT 9: Residential Populated Areas

The investigation involved multiple risk assessments to evaluate various remedial actions, including Baseline Human Health Risk Assessments (Parts A, B, and C) and an Ecological Risk Assessment.

Terrestrial Ecosystems; a Surface Water Human Health Risk Assessment; a Groundwater Baseline Human Health Rick Assessment; and a Baseline Aquatic Ecological Risk Assessment

The human health risk assessments determined that lead is the sole contaminant of concern (COC) for OU9, supported by lead models and blood-lead monitoring In contrast, non-lead metals, such as arsenic and manganese, found in residential soils do not present a significant health risk to residents These conclusions are backed by extensive site-specific data.

1) Extensive measurements of lead in soil and dust in residential locations

3) Data on lead levels in water and paint (both interior and exterior)

4) Data on the physical and chemical forms of lead at various locations around the community

5) An informative community-wide blood-lead study involving 314 children (about 65 percent of the total population of children at the Site)

This study utilized data to conduct two parallel assessments regarding lead exposure The first assessment employed the EPA’s Integrated Exposure Uptake and Biokinetic model to estimate the impact of lead in soil and dust on blood-lead levels in local children The second approach involved comparing the measured blood-lead levels in these children with national statistics to evaluate the effects of actual exposure to lead at the site.

In November 1998, Golder Associates completed the Final Residential Soil FS, which assessed seven remedial alternatives to tackle elevated lead levels exceeding 3,500 mg/kg in the residential soils of properties, yards, and open spaces within OU9.

The Lake County Community Health Program (LCCHP) serves as an alternative to the previous Kids First (KF) program, focusing on reducing children's exposure to lead in Leadville and surrounding areas This comprehensive initiative integrates blood-lead monitoring, education, and community awareness, while implementing residence-specific actions to address lead contamination in soil, dust, paint, plumbing fixtures, and dietary sources Key operational and maintenance activities involve the administration of LCCHP Phase 2, which encompasses community outreach, education, blood-lead monitoring, and necessary investigation and remediation efforts.

From October 1995 to April 2000, time-critical removal actions were conducted under the KF program, followed by response actions on various residences, commercial properties, and vacant lots under the LCCHP from April 2000 until the summer of 2009.

From October 1995 to the summer of 2009, a total of 1,040 properties were investigated, leading to soil removal actions at 270 sites Additionally, dust removal or paint repairs were conducted at 40 properties, though it is unclear if they required soil removals The last assessment and response actions by the EPA took place in the summer of 2009, while subsequent investigations and remediations are now managed by the LCCHP Phase 2 Workgroup For a detailed history of the initial response actions, refer to Appendix B, Table B-13.

On September 2, 1999, the OU9 Record of Decision (ROD) established a remedy to address lead contamination in residential soils, opting for the Lead Contamination Control and Health Protection (LCCHP) program, which includes institutional controls to enhance its effectiveness This decision aimed to replace the previous KF program and was designed to mitigate potential risks to human health and the environment caused by lead concentrations in soil, dust, paint, and water that surpass established trigger criteria.

The Remedial Action Objectives (RAOs) for OU9 were established in the 1999 Record of Decision (ROD), following the 1994 EPA lead guidance This guidance emphasized the importance of minimizing exposure to soil lead levels, ensuring that a typical child or a group of similarly exposed children has no more than a 5% risk of exceeding a blood lead level of 10 µg/dL.

 RAO -1: “No more than 5 percent of children (age 0 to 72 months) who live at this Site, either now or in the future, will have blood lead values exceeding 10 àg/dL.”

To ensure health safety, it is crucial that the highest risk level in any specific area, such as a home yard, maintains a probability of no more than one percent for children aged 0 to 72 months to have blood lead levels exceeding 15 µg/dL.

 Added by FS, “Reduce direct exposure of lead incurred by children, which will result in optimal risk reduction through effective use of resources.”

However, it is worth noting that, in 2016, EPA’s Office of Land and Emergency Management (OLEM) released directive 9200.2-167, which updates the scientific considerations to be used at lead cleanups conducted according to EPA’s 1994 Revised Interim Soil Lead Guidance f or CERCLA Sites and RCRA Corrective Action Facilities (Office of Solid Waste and Emergency Response [OSWER] Directive 9355.4-12) and the 1998 update to the 1994 guidance A copy can be found at https://semspub.epa.gov/work/08/1884174.pdf

Since the issuance of guidance in 1994 and 1998, the EPA has found that addressing lead-contaminated soil is most effective through a multi-pathway approach The 2016 directive emphasizes the use of current scientific methods and risk assessment tools for lead cleanups The EPA also acknowledges that the LCCHP Phase 2 focuses on community-based education and outreach to identify sources of lead and exposure pathways in Leadville.

In the 1990s, the LCCHP was regarded as a pioneering initiative that incorporated several innovative strategies It underwent evaluation by external scientists and included continuous assessments to confirm its effectiveness in safeguarding human health This ongoing review process established performance standards, which, once achieved, would signify the successful completion of the LCCHP and the transition to Operations and Maintenance (O&M) These performance standards were detailed in a July 2002 addendum to the OU9 remedial design and are encapsulated in the 2002 Final Methods and Standards for Evaluating the program.

EPA issued an ESD on September 30, 2009 It included the need for institutional controls for the mine waste piles left in place in OU9 The ESD RAOs are:

 Prevent construction of any type of residential dwelling or facility for human occupancy on the mine waste piles unless appropriate plans are approved by EPA or CDPHE

 Maintain the integrity of current or future remedies

The LCCHP was initiated in accordance with the ROD and the Methods and Standards for Evaluating Program Performance ASARCO carried out the LCCHP until its bankruptcy in July 2005, after which the EPA took over the management of soil investigations and cleanups until 2009 Currently, the program is overseen by the OU9 Work Group.

Since 2002, annual reports have documented data collection to assess the effectiveness of the program aimed at reducing blood-lead levels in children By 2005, the performance standards set by the EPA for the selected remedy were successfully met, as confirmed in the 2005 LCCHP Annual Report published on April 5, 2006 Following this achievement, property owners were offered a final opportunity for property investigation and cleanup In 2009, 199 properties were examined, revealing that 31 properties had lead levels exceeding the 3,500 mg/kg action threshold, which were remediated with the consent of the property owners.

The remedy at OU9 effectively protects human health and the environment, as it operates according to established Site decision documents The exposure assumptions, toxicity data, trigger criteria, and Remedial Action Objectives (RAOs) remain valid, with no new information undermining the remedy's protectiveness Additionally, institutional controls are established, and Operations and Maintenance (O&M) are successfully ongoing, supported by the approval and implementation of the LCCHP Phase 2 Work Plan.

There were no issues or recommendations identified in the 2012 FYR for OU9.

Data from the Lake County Blood Lead Program’s blood-lead testing database was reviewed and compared to the RAOs The results can be found in Table 24

Table 24: Blood-Lead Testing Results, 2012 – 2016

Greater than 10 àg/dL Percentage

Greater than 15 àg/dL Percentage

During the years of 2012 to 2016, the average percentages of children age 0 to 72 months with BLL greater than

10 àg/dL and 15 àg/dL are 1.1% and 0.3% respectively; below the respective percentages of 5% and 1% set in the RAOs

Remediations were conducted on multiple properties to address elevated blood-lead levels, which were also resolved through education, identification, and further evaluations Reports indicated that factors such as consumption of foreign candy, lead-based paint, and family member occupations, along with unrelated soil lead levels, contributed to these elevated blood levels Furthermore, remodeling homes built before 1978, which contain lead-based paint, seems to correlate with increased blood-lead levels in both children and adults.

On September 13, 2016, a site inspection was conducted, with participants detailed in Section III of the FYR Report During the inspection, OU9 was evaluated by driving through the city, visiting various parks, and observing remediated properties in the Lake Fork community Photographic documentation of the site features related to OU9 was captured (see Appendix E), and a completed inspection checklist is provided in Appendix D.

The site inspection and document review confirm that the OU9 remedy is operating as intended according to the 1999 Record of Decision (ROD), 2009 Explanation of Significant Differences (ESD), and 2013 Minor ROD Modification Performance standards were successfully achieved in 2006, and the Long-term Operation and Maintenance (O&M) plan for OU9 is outlined in the LCCHP Phase 2 Work Plan.

According to the Blood-Lead Testing Annual Reports from 2012 to 2015, effective O&M activities have ensured consistent monitoring of blood-lead levels and the remediation of lead contamination in households following OU9 Work Group approval Institutional controls have been established through the extension of planning and zoning codes in Leadville and Lake County, safeguarding the engineered remedies in OU9 Furthermore, the Lake County accepted the LCCHP Phase 2 Work Plan, which serves as the institutional control for OU9 and focuses on community outreach and education to prevent lead exposure.

Yes The exposure assumptions and toxicity data used to develop range of plausible action levels for arsenic, published in the BRA Part B, remain valid

The surface soil lead cleanup levels at the site were set to ensure that a typical child has no more than a 5 percent chance of exceeding a blood lead level (BLL) of 10 micrograms per deciliter (µg/dL) This approach aligns with the Environmental Protection Agency's (EPA) current policy and is based partly on the Centers for Disease Control and Prevention's (CDC) 1991 "level of concern" for blood lead levels.

In 2016, the EPA issued a memorandum urging the consideration of current scientific literature, which indicates that adverse health effects are linked to blood lead levels (BLLs) below 10 µg/dL As a result, the EPA is updating its lead policy based on these recent findings Additionally, EPA Region 8 will assess the necessity for revisions to the LCCHP Phase 2 Work Plan as the agency finalizes its updated lead policy.

The remedy at OU9 effectively safeguards human health and the environment, operating as intended according to site decision documents The exposure assumptions, toxicity data, trigger criteria, and Remedial Action Objectives (RAOs) established during the remedy selection remain valid No new information has emerged to challenge the remedy's protectiveness, and institutional controls are actively maintained Additionally, operations and maintenance (O&M) are progressing successfully with the approval and implementation of the LCCHP Phase 2 Work Plan.

OPERABLE UNIT 10: Oregon Gulch

The EPA concluded that hazardous substances from sediments, soils, tailings, and seep water on OU10 pose an imminent and substantial threat to public health and the environment, necessitating immediate remedial action.

Contaminated media in OU10 are presented in Table 25

Sediments generally display elevated metal concentrations and high concentrations of pyrite

Sediments collected at the mouth of Oregon Gulch contain elevated cadmium, iron, manganese and zinc

Elevated lead and zinc concentrations were found throughout the depth of tailing profiles

Arsenic and cadmium levels decreased as a function of tailing depth

Concentrations in foundation soils underneath the tailing were significantly lower than in the tailing

Seep water continuously flows from the base of the tailing embankment throughout the year, exhibiting poor water quality characterized by low pH levels and high concentrations of dissolved metals.

In accordance with the August 4, 1995 Action Memorandum, Resurrection Mining Company removed approximately 3,500 cubic yards of sediment and soil from Oregon Gulch's channel and floodplain, depositing it on the Oregon Gulch Tailing Impoundment during 1995 and 1996 After the sediment removal, the company constructed a channel designed to effectively manage a 100-year flood event while maintaining stability for a 500-year flood event Additionally, the surrounding area was stabilized and revegetated to enhance environmental restoration.

Company also constructed a sedimentation pond in Oregon Gulch downstream of the toe of the tailing impoundment to reduce sediment load in runoff from the tailing embankment

A historic trash dump located in lower Oregon Gulch has been identified during a cultural resource inventory, starting at the intersection of the gulch and County Road 6 and extending about 500 feet upstream This site has been recommended for nomination to the National Register of Historic Places To protect this historically significant area, both pre-ROD removal and post-ROD remedial actions were carefully designed and implemented to prevent any adverse impacts.

EPA issued the ROD for OU10 on August 8, 1997 The 1997 OU10 ROD established the following RAOs:

 Control airborne transport of tailing particles

 Control erosion of tailing materials and deposition in local water courses

 Control leaching and migration of metals from tailing into surface and groundwater

The selected remedy for OU10 consisted of the following components:

 Regrade the impoundment to provide positive drainage and to flatten embankments

 Install geosynthetic barrier to control infiltration, followed by a geocomposite drainage layer

 Install a soil cap with vegetation on top of impoundment

 Install a soil-and-gravel cap on the side slopes

 Construct lined diversion ditches to divert runoff from tailing to the covered tailing surface

 Install a groundwater cutoff trench to prevent groundwater infiltration

 Actively manage seeps by collecting seep and transporting (pumping) to the Yak Tunnel WTP

EPA issued an ESD on July 29, 2013 It required institutional controls as a remedy component for OU10

The 1997 OU10 ROD lacked specific numeric cleanup standards; however, it outlined necessary removal and containment actions aimed at preventing tailing and stream sediments from contributing to surface and groundwater contamination at the larger site.

In 1996, Resurrection completed the removal actions for the Oregon Gulch Tailing Impoundment, implementing the selected remedy from July to October 1998 This involved regrading the impoundment and installing a geosynthetic membrane over the structural fill to control infiltration An 18-inch-thick soil layer with a vegetated cover was placed over the membrane, while a diversion ditch on the eastern side managed run-on and runoff Additionally, an upgradient groundwater interception trench was constructed to limit groundwater infiltration into the tailing impoundment, and a deep discharge drain system was established to manage seep flow from the impoundment toe.

EPA partially deleted OU10 from the NPL on April 16, 2001

Lake County has designated OU10 for Industrial Mining purposes, while Newmont/Resurrection established environmental covenants on its OU10 properties on July 31 and October 1, 2012 These covenants specifically prohibit residential development and impose restrictions on groundwater usage.

Since September 1999, Newmont/Resurrection has been conducting Operations and Maintenance (O&M) activities at OU10 to ensure the effectiveness of the remedy for the Oregon Gulch Tailing Impoundment This includes regular inspections of the tailing impoundment cap and the associated seep collection and pumping system.

Newmont/Resurrection conducts inspections in accordance with the OU4, 8, 10, Operations and Maintenance Plan, California Gulch Superfund Site, which is Appendix D to the 2008 Consent Decree approved on August 29,

2008 Its findings are documented in the Annual California Gulch Superfund Site OU4, OU8 and OU10

Inspection Reports These reports are available by contacting EPA Region 8

The following areas in OU10 are inspected:

 The toe seep collection system, trench collection system and pump house

 The tailing impoundment surface and embankment

 East and South diversion ditches

During the current fiscal year, maintenance activities have focused on repairing piping, maintaining the vegetated cover, replacing pumps, upgrading electrical equipment, and ensuring the integrity of secured fencing and signage around the pump house and the Oregon Gulch Tailing Impoundment.

The remedy at OU10 effectively protects human health and the environment in the short term by consolidating and containing source contamination, preventing the migration of pollutants Any runoff or seepage is managed through trenches that direct water to the Yak Tunnel Water Treatment Plant All Remedial Action Objectives (RAOs) for OU10 have been met, and Newmont/Resurrection Mining Company is actively conducting operation and maintenance (O&M) activities Institutional controls, established as environmental covenants, are in place to ensure ongoing safety To maintain long-term protectiveness, it is recommended that the EPA assess the need for a decision document to further incorporate these institutional controls.

Review whether a decision document is needed to incorporate the institutional controls for OU10

Completed An ESD that requires institutional controls was issued

The OU10 inspection was conducted on September 14, 2016, with participant details outlined in Section III of the FYR Report Photographs documenting site features, such as monitoring wells and access controls, can be found in Appendix E, while the completed inspection checklist is available in Appendix D.

During the site inspection at OU10, participants received a comprehensive tour of the pump house from Mr Runnells, who highlighted the ongoing operations and maintenance activities The Oregon Gulch tailing pile was noted for its healthy vegetation, while the drainage systems were found to be clear and operational Groundwater and surface water diverted from the impoundment are collected in the pump house and subsequently pumped to the surge pond for treatment.

The site inspection and document review confirm that the OU10 remedy has been successfully completed and is functioning as intended, as outlined in the Site decision documents Excavation of stream sediments was completed by 1996, followed by the consolidation and stabilization of the Oregon Gulch Tailing Impoundment in 1998 Newmont/Resurrection Mining Company continues to perform operation and maintenance activities for OU10 All necessary institutional controls are in place, along with procedures to notify the EPA and CDPHE in the event of local government land use changes Following the implementation of all remedial components and the achievement of all remedial action objectives (RAOs), the EPA partially removed OU10 from the National Priorities List (NPL) on April 16, 2001.

There have been no changes to the Applicable or Relevant and Appropriate Requirements (ARARs) identified in the Record of Decision (ROD) or since the last Five-Year Review (FYR) No new standards have emerged that would challenge the effectiveness of the implemented remedy, as detailed in Appendix H The 1997 ROD for Operable Unit 10 (OU10) did not set numeric cleanup standards for surface water or groundwater, while the remedy for Operable Unit 12 (OU12) addresses water quality across the entire site.

All Remedial Action Objectives (RAOs) established in the 1997 OU10 Record of Decision (ROD) have been successfully met These objectives focused on controlling airborne transport of tailing particles, preventing metal leaching and migration into surface water and groundwater, and mitigating erosion of tailing materials into local waterways The excavation of contaminated stream sediments and consolidation within the Oregon Gulch Tailing Impoundment significantly reduces the risk of erosion and contamination spread Additionally, diversion and interception trenches effectively manage run-on, runoff, and potential seep flows for treatment at the Yak Tunnel Water Treatment Plant (WTP) The implementation of a geosynthetic membrane and vegetated cover further inhibits airborne transport and erosion of tailing materials Importantly, land use at OU10 has remained unchanged, and the exposure assumptions from the 1997 OU10 ROD continue to be relevant.

OU(s) without Issues/Recommendations Identified in the FYR:

The OU10 remedy effectively safeguards human health and the environment by consolidating and containing source contamination to prevent the spread of pollutants Any potential seepage or runoff is managed through trenches that direct water to the Yak Tunnel Water Treatment Plant (WTP) All Remedial Action Objectives (RAOs) for OU10 have been successfully met, and Newmont/Resurrection Mining Company is actively conducting ongoing maintenance and operational activities Additionally, institutional controls, including environmental covenants, have been established to ensure continued protection.

OPERABLE UNIT 11: Arkansas River Valley Floodplain

The EPA's assessments of OU11 revealed that metals in the soils of irrigated meadows and riparian areas pose a potential health threat to herbivores, primarily due to low pH conditions leading to phytotoxicity and poor plant demographics While current human health risks are considered below a level of concern for existing land uses, future residential development in OU11 could elevate these risks beyond acceptable levels.

In 1993 and 1994, the EPA's Removal Program focused on stabilizing eroding banks that contained or safeguarded fluvial deposits Starting in 1996, the program identified and assessed fluvial deposits along nine miles of the Arkansas River, explored management alternatives for the waste, and established removal demonstration areas to evaluate the effectiveness of the chosen solutions.

EPA signed the OU11 ROD on September 28, 2005 The RAOs established in the 2005 OU11 ROD were:

 Minimizing future human exposures to heavy metals as defined in the human health BRA

 Controlling leaching and migration of metals from contaminated materials into groundwater

 Reducing toxins in plants and improving plant demographics in the irrigated meadows, riparian areas and fluvial mines wastes as determined to be necessary

 Reducing exposures of wildlife and livestock to heavy metals in soil and vegetation at toxic concentrations from direct exposure or bioaccumulation

 Minimizing erosion of fluvial mine wastes into the Arkansas River as determined necessary to prevent further harm to aquatic life

Components of the selected remedy in the 2005 OU11 ROD included:

 Treatment and maintenance of irrigated meadows areas Treatment consisted of lime amendment or lime/organic amendment, deep tilling and seeding

 Maintenance of tailing deposits treated during prior response actions, as necessary Maintenance will include inspections and retreatment and/or repairs appropriate to enhance or reestablish vegetation

The treatment and maintenance of remaining tailing deposits involved the application of lime and organic amendments, along with deep tilling This process was followed by seeding to promote the physical stabilization of mine wastes through the establishment of vegetation.

 No active revegetation of the (vegetated) riparian areas, although specific riparian areas may be remediated if deemed appropriate during design

To ensure the protection of irrigated meadows, tailing deposits, and riparian areas, institutional controls must be established These controls will prevent alterations in current land use unless it can be clearly demonstrated that the risks associated with the new land use are below an acceptable level of concern.

In 2007, a Remedial Work Plan was established to outline specific treatments for irrigated meadows, fluvial deposits, and nearby streambanks The plan involved the incorporation of lime, fertilizer, and compost into mine waste and soils, along with the seeding of species suitable for the intended land use.

Cleanup levels were not set as the remedial action failed to lower contaminant concentrations at the site The 2007 Remedial Work Plan outlined performance criteria for treated areas to address contamination risks in OU11, including soil and vegetation standards for irrigated meadows and stability metrics for remediated streambanks Despite several vegetation monitoring events post-remedial action showing documented success and ecological progress, the initially established performance criteria were found to be inaccurate and needed refinement Consequently, these performance criteria were revised in 2013.

In 2005, the Record of Decision (ROD) mandated the implementation of institutional controls on irrigated meadows, tailing deposits, and riparian areas, with the EPA collaborating with CDPHE to establish suitable controls for OU11 Between 2008 and 2009, the EPA conducted a remedial action that involved in-situ treatment of 154 acres of irrigated meadows and 18.5 acres of fluvial deposits, followed by seeding efforts To protect the treated soils and promote vegetation growth, vulnerable stream banks adjacent to the fluvial deposits were reconstructed Additionally, a 40-acre demonstration area, where fluvial deposits were treated with soil amendments from 1998 to 2000 to assess the effectiveness of the selected remedy, is included in the OU11 plan The EPA finalized the Remedial Action Report for bank stabilization on September 19, 2013.

The treated areas were monitored from 2009 through 2012, in accordance with the Site’s Monitoring and

In 2014 and 2015, CPW restored fish habitats along the Arkansas River and subsequently performed maintenance to reestablish shoring rock displaced by high water in 2015 The implemented remedy is functioning as anticipated, and ongoing monitoring results will guide future maintenance needs, assess compliance with Remedial Action Objectives (RAOs), determine the maturity and self-sustainability of the remediated areas, and support the EPA’s Five-Year Review process.

Recent maintenance efforts have focused on re-treating specific sections of demonstration areas, reseeding areas with bare or sparse vegetation, repairing constructed stream banks, and stabilizing native stream banks that were affected during the process.

2011 extreme runoff conditions, and removal of construction roads

The remedy for OU11 was determined to be Operational and Functional on April 25, 2017, starting the O&M phase O&M is conducted by CDPHE through a special account funded grant.

The remedy at OU11 is anticipated to safeguard human health and the environment once fully implemented, while current measures are in place to manage exposure pathways that may pose unacceptable risks.

Institutional controls are a component of the selected remedy but have not been implemented

The remedial action for OU11 was completed in 2013, while the remedy for OU12 aims to meet specific chemical performance standards for both surface water and groundwater across the site Consequently, a summary of the relevant data for OU11 is provided in Section XV.3 of the data review for OU12.

The OU11 Site inspection conducted on September 13, 2016, involved various participants and included a tour along the Arkansas River and surrounding ranches, as detailed in Section III of the FYR Report Photographs of site features, such as monitoring wells and access controls, are included in Appendix E Observations indicated that the Arkansas River floodplain is functioning effectively downstream from the confluence with California Gulch, with no impediments to flow During the inspection, CPW informed the EPA about past high water levels that had displaced large boulders into the river, which were subsequently relocated to stabilize the banks Some erosion was noted during periods of high water, but overall, the Arkansas River is showing signs of recovery downstream from Leadville The inspection findings and maintenance reports confirm that the OU11 remedy has been implemented as intended.

The site inspection and document review confirm that the remedy is effectively functioning as intended, meeting the requirements outlined in the decision document and design specifications In 2013, the EPA stabilized the stream banks, while CPW successfully restored fish habitat along the Arkansas River.

In 2014 and 2015, significant high water events caused by snow melts impacted the area, leading to a transition of O&M responsibilities for OU11 to CDPHE in May 2017 As part of the OU12 Site-wide remedy, ongoing monitoring of surface water, sediment, and biota is being conducted.

There have been no changes in exposure assumptions regarding human health and the environment, nor in toxicity data, that would undermine the effectiveness of the remedy Additionally, there are no proposed alterations to the reuse plans at OU11 that would impact the remedy's protective measures.

No No information has come to light that calls into question the protectiveness of the remedy.

Issues and Recommendations Identified in the FYR:

OU(s): 11 Issue Category: Institutional Controls

Issue: Institutional controls are a component of the selected remedy but have not yet been implemented

No Yes EPA/State EPA 12/31/2018

11 Short-term Protective Completion Date:

The current remedy at OU11 effectively safeguards human health and the environment by stabilizing streambanks to reduce erosion, exposure, and chemical migration To maintain long-term protection, it is essential to implement institutional controls that ensure ongoing safety and effectiveness.

OPERABLE UNIT 12: Site-Wide Water Quality

In the mid-1990s, the EPA's human health risk assessments indicated that contaminants in site-wide surface water and groundwater could present significant health risks if consumed by humans These risks are primarily attributed to mine wastes that produce acid rock drainage, leading to potential future health hazards.

In the 1990s, the EPA identified mine wastes at Upper California Gulch (OU4), Stray Horse Gulch (OU6), Apache Tailing Impoundments (OU7), and Oregon Gulch (OU10) as major contributors to acid rock drainage (ARD) at the Site Since then, various measures have been implemented to mitigate the impacts of these contaminated areas.

The 1995 Baseline Risk Assessment and the 2004 OU12 Characterization of Risks to Aquatic Receptors highlight zinc and cadmium as the contaminants of concern (COCs) for trout and macroinvertebrates in the Upper Arkansas River Given that brown trout are the most prevalent species in this ecosystem, the EPA has directed its primary focus towards assessing the risks associated with this particular species.

In 2004, the EPA found that historical zinc and cadmium concentrations below California Gulch likely reduced the survival rates of brown trout fry, contributing to lower fish densities in that area Recently, the predicted risk to fish has decreased, and fish populations have begun to increase, suggesting that remedial efforts at the Site may have reduced harmful releases into the Arkansas River However, further observation is necessary to confirm whether this trend is due to decreased Site releases or other influencing factors.

The EPA has determined that elevated levels of zinc and cadmium, commonly found in the spring below California Gulch, may negatively impact the survival and reproduction of certain benthic macroinvertebrates, particularly sensitive species like mayflies Consequently, there is a noticeable decline in the numbers of these taxa in the river downstream of the confluence with California Gulch compared to upstream Despite this, the overall density and diversity of the benthic community remains largely unaffected, suggesting that the availability of benthic prey is sufficient to support fish populations.

Risk to herbivores and plants along the Arkansas River, although caused by historical irrigation by Site-wide surface water, were remediated under the remedy for OU11

Current EPA risk assessments do not evaluate the risks to terrestrial receptors from consuming potentially contaminated aquatic prey However, this is not deemed a significant oversight, as the metals of concern at the site do not significantly accumulate in aquatic species like fish or invertebrates Studies from other mining sites suggest that terrestrial receptor exposure is primarily influenced by the ingestion of contaminated soils or sediments rather than aquatic prey Table 30 outlines the contaminants of concern (COCs) by medium for OU12 Among the various COCs, zinc and cadmium serve as effective indicator parameters for assessing groundwater, surface water, human health, and environmental conditions in the OU12 area.

Cadmium Copper Lead Zinc Ecological Receptors Cadmium

Arsenic Cadmium Lead Manganese Zinc

Investigations at the site commenced in the mid-1980s and continued until 2012, with a comprehensive list of relevant reports available in the OU12 RI Report and Administrative Record By fall 2003, response actions aimed at reducing metal contamination in surface and groundwater were implemented across all major sources, including waste rock piles and mill tailings These efforts, conducted under various Records of Decision (RODs) and action memoranda, led to significant improvements in water quality both within individual operable units (OUs) and site-wide In 2009, the EPA selected the OU12 remedy, which involved institutional controls and long-term monitoring of water quality, alongside a technical impracticability waiver for shallow groundwater, allowing for the adjustment of maximum contaminant levels (MCLs).

The RAOs for OU12, as listed in the 2009 ROD, include:

 Prevent unacceptable exposure of aquatic organisms in the Arkansas River to COCs

 Prevent unacceptable human exposure to COCs in surface and groundwater

 No action (no additional active remediation) for Site-wide surface or groundwater

Institutional controls are implemented to limit the use of surface and groundwater, effectively reducing the risk of negative health impacts from consuming contaminated site water Since the Arkansas River water complies with drinking water standards, these controls do not apply to it.

 Collection and review of long-term monitoring data

 a technical impracticability waiver for shallow groundwater (e.g., waiving the maximum contaminant levels, or MCLs)

A summary of the cleanup goals for surface water, which correspond to Colorado’s 2009 Water Quality Standards for segments of the Upper Arkansas River) are below presented in Table 31

Table 31: Surface water COC Cleanup Goals

COC Season 2009 OU12 ROD Cleanup Goals for Arkansas River Segments

Acute: 1.136672-[ln(hardness) x 0.041838] x e0.915[ln(hardness)]-3.6236)

Chronic: 1.101672-[ln(hardness) x 0.041838] x e0.7998[ln(hardness)]-3.1725)

WQS Seasonal Modification (April-May)

WQS (June-March) Acute: 0.978 x e0.8537[ln(hardness)]+2.2178

WQS Seasonal Modification (April-May) 649 (àg/L)

Notes: a Criteria listed in 2009 OU12 ROD, pages DS-48 and DS-49 àg/L – micrograms per liter

OU12 has been under remedial action until 2020, with the EPA and CDPHE conducting long-term monitoring as part of the remedy This includes annual sampling events based on the 2009 California Gulch Superfund Site Final Field Sampling Plan, which commenced after the EPA approved the April 2015 Remedial Design Report This report outlines the monitoring strategy for surface water, groundwater, and aquatic organisms, updating the previous sampling plan According to the 2009 Record of Decision (ROD), it is anticipated that long-term monitoring will demonstrate continued improvements in surface and groundwater quality as remediation efforts progress across the other 11 operable units (OUs) Despite the removal of seasonal modifications to water quality standards for cadmium and zinc in the Arkansas River segments 2b and 2c in 2014, current standards for these metals are still being met The EPA is also in the process of finalizing the remaining institutional controls for OU12.

The April 2015 Remedial Design Report contains the long-term monitoring plan for sampling surface water, groundwater and aquatic organisms This plan also serves as the O&M plan for OU12.

The OU12 remedy's effectiveness was not assessed in the 2012 FYR, which identified no issues or recommendations for this area The remedial design was finalized on April 29, 2015, and the ongoing remedial action is anticipated to be completed by September 2020.

The OU12 remedy is currently in the remedial action phase, focusing on long-term monitoring of groundwater and surface water, with the remedial action set to conclude in 2020 In collaboration, the EPA, CDPHE, and Tetra Tech developed the 2015 Remedial Design Report, which outlines a comprehensive monitoring strategy that includes a Surface Water Monitoring Program, a Groundwater Monitoring Program, a Fluvial Sediment Sampling Program, and an Aquatic Life Monitoring Program within the California Gulch and Upper Arkansas River watersheds The data collected from these programs is continuously reviewed by the EPA and CDPHE.

Routine surface water sampling is conducted along California Gulch, Stray Horse Gulch/Starr Ditch, and the Arkansas River to analyze various metals This summary highlights zinc and cadmium, as these metals are the primary contributors to aquatic risks in the area.

The results indicate that water quality standards for cadmium and zinc are being met in segments 2b and 2c of the Arkansas River See Appendix I for data analysis trends

Table 32 outlines the surface water quality locations in the Arkansas River, highlighting the point of compliance (POC) at station AR-3A and the reference location at station AR-1.

Table 32: Arkansas River Surface Water Quality Locations

AR-1 About a quarter-mile downstream of Tennessee Creek (Segment 2a)

About a half-mile downstream of California Gulch (Segment 2b)

AR-4 About a half-mile downstream of Lake Fork (Segment 2c)

Segment 2c of the AR-5 area is located upstream of Empire Gulch and approximately a quarter-mile downstream from the Hwy 24 bridge For more comprehensive information, please refer to the Site’s Annual Monitoring Reports, which cover surface water, groundwater, fluvial sediment, and biological assessments.

In 2009, the Technical Impracticability (TI) Waiver exempted the maximum contaminant levels (MCLs) for metals, specifically cadmium and lead, in certain areas of the OU12 shallow groundwater, as outlined in the TI Waiver boundary map within the 2009 OU12 Record of Decision (ROD) Groundwater quality is monitored through semi-annual sampling of 17 shallow alluvial wells in the vicinity of source areas, conducted in spring and fall Additionally, 19 wells near engineered remedies, such as Malta, Apache, and CZL Tailing Impoundments, are evaluated once every five years to assess remedy effectiveness for the Five-Year Review (FYR) Spring sampling captures groundwater influenced by high-flow surface water from snowmelt, while fall sampling reflects conditions with minimal surface water impact.

Fluvial sediment samples collected from California Gulch and the Arkansas River revealed peak zinc concentrations at Stations CG-1, CG-3, and CG-5 in 2015 Notably, the concentrations of metals in the fluvial sediment remained stable from 2006 to 2015.

In 2015, the CPW conducted monitoring of brown trout populations in the Arkansas River and Lake Fork The findings revealed a decline in trout populations upstream of the compliance point from 2014 to 2015, while downstream, brown trout populations experienced an increase during the same timeframe.

In 2015, Colorado State University (CSU) conducted a study on macroinvertebrate populations in the Arkansas River and California Gulch The research revealed that springtime macroinvertebrate abundance and diversity were consistent across all Arkansas River sites However, in the fall, diversity declined below California Gulch compared to other locations along the river Notably, California Gulch exhibited significantly lower macroinvertebrate abundance and diversity than the Arkansas River Additionally, data on Brown Trout density showed a variable but overall increasing trend over the years.

The OU12 inspection occurred on September 13 and 14, 2016, with participants detailed in Section III of this FYR Report The inspection included photographs of site features, such as monitoring wells and access controls.

An inspection checklist has been finalized and can be found in Appendix D The monitoring locations, including wells, were assessed and found to be in good condition, secured with locks Additionally, surface water monitoring locations were examined and were free from obstructions.

The OU12 remedy is currently being implemented and is expected to function as outlined in the Site decision documents This remedy includes ongoing long-term monitoring and the establishment of institutional controls, which are still in progress While routine monitoring of surface water and groundwater is taking place, showing a general decline or stability in contaminant levels, some exceptions remain The EPA and the State are actively working to finalize the necessary institutional controls.

Yes The exposure assumptions, toxicity data, cleanup levels and RAOs used at the time of remedy selection are still valid

The 2009 Technical Impracticability (TI) Waiver exempted the Maximum Contaminant Levels (MCLs) for metals, particularly cadmium and lead, in designated areas of the OU12 shallow groundwater, as illustrated in the TI Waiver boundary map from the 2009 OU12 Record of Decision (ROD) The chosen remedy adheres to all action-specific Applicable or Relevant and Appropriate Requirements (ARARs), and since it does not involve construction, location-specific ARARs are not applicable Additionally, Colorado has eliminated the seasonal restrictions.

In 2014, modifications were made to the Water Quality Standards (WQS) for Segments 2b and 2c As these updated standards are currently being met, there are no newly established standards that would challenge the effectiveness of the selected remedy.

No No information has come to light that calls into question the protectiveness of the remedy.

12 Will be Protective Completion Date:

The OU12 remedy aims to safeguard human health and the environment upon its completion Current monitoring of surface water and groundwater at the site indicates that zinc and cadmium levels in surface water comply with Colorado Water Quality standards A technical impracticability waiver for groundwater contamination was established by the 2009 Record of Decision (ROD) To ensure the long-term effectiveness of the OU12 remedy, it is essential to implement institutional controls.

NEXT REVIEW

The next FYR Report for the California Gulch Superfund Site is required five years from the completion date of this review

2008-2009 Monitoring and Maintenance Report, Operable Unit 11 California Gulch Superfund Site, Leadville, Colorado Prepared by URS Operating Services, Inc for EPA Region 8 June 20, 2011

The 2015 Monitoring Report for Surface Water, Groundwater, Fluvial Sediment, and Biological assessment at the California Gulch Superfund Site in Leadville, Colorado, was prepared by Tetra Tech for the Colorado Department of Public Health and Environment's Hazardous Materials and Waste Management Division in February 2017.

The Action Memorandum for the Stray Horse Gulch OU6 Site in Leadville, CO, outlines removal actions conducted in November 2014 and June 2016 Additionally, the Action Memorandum OU9 details the removal action for three residential properties in Leadville, CO, completed in September 2016 Furthermore, the Action Memorandum OU6/12 addresses removal actions for the Stray Horse Gulch OU6/12 Site, also carried out in June 2016.

Amending the Lake County Land Development Code and Adopting Regulations Concerning Institutional

Controls for Operable Units Within the California Gulch Superfund Site County of Lake and State of Colorado February 2009

Annual Blood-Lead Program Report - 2012 and 2013 Lake County Colorado Prepared by Lake County Public Health Agency February 2013

Annual Blood-Lead Program Report - 2014 Lake County Colorado Prepared by Lake County Public Health Agency March 2015

Annual Monitoring Report - 2015, Yak Tunnel Operable Unit 1 California Gulch Superfund Site, Leadville Colorado March 2016

Baseline Human Health Risk Assessment, California Gulch Superfund Site, Leadville, Colorado, Part A, Risks to Residents from Lead EPA Region 8 June 2, 1996

Baseline Human Health Risk Assessment, California Gulch Superfund Site, Leadville, Colorado, Part B, Risks to Residents from Contaminants other than Lead EPA Region 8 January 2, 1996

Baseline Human Health Risk Assessment, California Gulch Superfund Site, Part C, Evaluation of Worker

Scenario Roy F Weston, Inc April 1995

Best Management Practices for Managing Lead, Arsenic and Cadmium Containing Soils in Lake County,

Colorado Lake County Building and Land Use Department May 2009

California Gulch Superfund Site Operations and Maintenance Plan Operable Units 2, 5 and 7 Prepared by

CERCLA Information System Site Information accessed from website https://cumulis.epa.gov/supercpad/cursites/csitinfo.cfm?id01478 Accessed October 21, 2016

In May 2013, the City of Leadville, Colorado, enacted Ordinance 3, Series 2013, amending the Leadville Municipal Code to establish regulations for institutional controls affecting Operable Units 3, 5, 6, 7, 8, and 9 within the California Gulch Superfund Site This ordinance aims to ensure compliance with environmental safety standards and protect public health in the designated areas.

Completion Report, Yak Tunnel Monitoring Wells, California Gulch Superfund Site, Leadville, Colorado

Consent Decree California Gulch Superfund Site, Leadville, Colorado United States District Court May 1994

Construction Completion Report, Apache Tailing Impoundments, Operable Unit 7, California Gulch Superfund Site, Leadville, Colorado MFG, Inc December 2003

Construction Completion Report, California Gulch Operable Unit 11, Remedial Action Frontier Environmental Services, Inc January 2011

Construction Completion Report, Yak Tunnel Operable Unit, California Gulch Superfund Site, Leadville,

Colorado Res-ASARCO Joint Venture February 1993

Direct Final Notice of Partial Deletion of Operable Unit 8, California Gulch Superfund Site, Lake County,

Direct Final Notice of Partial Deletion of Operable Unit 9, California Gulch Superfund Site, Leadville, Colorado EPA Region 8 January 2002

Direct Final Notice of Partial Deletion of Operable Unit 9, California Gulch Superfund Site, Leadville, Colorado EPA Region 8 May 2011

Draft Monitoring and Maintenance Plan, Operable Unit 11, California Gulch Superfund Site, Leadville, Colorado U.S EPA Region 8 March 16, 2010

Ecological Risk Assessment for the Terrestrial Ecosystem, California Gulch Superfund Site, Leadville, Colorado EPA Region 8 January 1997

Explanation of Significant Differences, Operable Unit 4, California Gulch Superfund Site, Leadville, Colorado July 2013

Explanation of Significant Differences, Operable Unit 10, California Gulch Superfund Site, Leadville, Colorado EPA Region 8 July 2013

Explanation of Significant Differences, D&RGW Slag Piles and Easement, Operable Unit 3, California Gulch Superfund Site, Leadville, Colorado EPA Region 8 August 2014

Explanation of Significant Differences, Malta Gulch Fluvial Tailing/Leadville Corporation Mill/Malta Gulch Tailing Impoundments, Operable Unit 2 California Gulch Superfund Site, Lake County, CO July 2013

Explanation of Significant Differences, Residential Populated Areas Operable Unit 9, California Gulch Superfund Site, Lake County, Colorado EPA Region 8 September 2009

Explanation of Significant Differences, Upper California Gulch, Operable Unit 4, California Gulch Superfund Site, Leadville, CO March 2004

Explanation of Significant Differences, Yak Tunnel, Operable Unit 1, California Gulch Superfund Site, Leadville, Colorado EPA Region 8 October 1991

Explanation of Significant Differences, Yak Tunnel, Operable Unit 1, California Gulch Superfund Site Lake County, Colorado July 2013

Final Focused Feasibility Study, Operable Unit 7, Apache Tailing Impoundments, California Gulch Superfund Site, Leadville, Colorado MFG, Inc January 17, 2000

Final Focused Feasibility Study for Upper California Gulch Operable Unit 4, California Gulch Superfund Site, Leadville, Colorado TerraMatrix and Shepherd Miller Incorporated January 1998

Final Modification of 1994 Consent Decree with ASARCO U.S Department of Justice June 2008

First Five-Year Review Report for California Gulch Superfund Site EPA Region 8 February 2, 1996

Focused Feasibility Study, Operable Unit 6, California Gulch Superfund Site, Leadville, Colorado HDR

Focused Feasibility Study, Operable Unit 12, California Gulch Superfund Site, Leadville, Colorado, HDR November 2007

Fourth Five-Year Review Report for California Gulch Superfund Site, Leadville, Colorado EPA Region 8 September 2012

Lake County Blood-Lead Program 2010 Blood-Lead Testing Annual Report Lake County Public Health Agency

Lake County Ordinance, Resolution 2013-3 Amending the Lake County Land Development Code and Adopting Regulations Concerning Institutional Control for Operable Units 2 and 5 within the California Gulch Superfund Site April 2013

Memorandum of Understanding Between Union Pacific Railroad, Lake County, and EPA on the Mineral Belt Trail Project Union Pacific Railroad and Lake County Board of Commissioners July 1998

Minor ROD Modification, OU5 California Gulch Superfund Site, Leadville, Colorado EPA Region 8 May

Minor ROD Modification, OU9 California Gulch Superfund Site, Leadville, Colorado EPA Region 8 May

Monitoring and Maintenance Report, Operable Unit 11 California Gulch Superfund Site, Leadville, Colorado URS Operating Services, Inc June 20, 2011

National Oil and Hazardous Substances Pollution Contingency Plan; National Priorities List: Partial Deletion of the California Gulch Superfund Site OU4, 5 and 7 October 24, 2014

Notice of Intent to Partial Delete Operable Unit 2, California Gulch Superfund Site, EPA Region 8 May 24,

Operations and Maintenance Facility 2016 Inspection for Operable Units 2, 5 and 7 Prepared by Tetra Tech February 23, 2017

Operations & Maintenance Plan for Operable Units 4, 8 and 10; Rebecca Thomas' Comments; MGF, Inc October

Overflow Contingency Plan, Leadville Drainage Tunnel – Remedial Mikado Pond, Operable Unit 6, California Gulch Superfund Site, Leadville, Colorado US EPA Region 8

The Environmental Protection Agency announced the partial deletion of the California Gulch Superfund Site, specifically targeting Operable Unit 1 (Yak Tunnel/Water Treatment Plant) and Operable Unit 3 (Denver & Rio Grande Western Railroad Company Slag Piles/Railroad Easement/Railroad Yard), as documented in the Federal Register, Volume 81, Number 26, dated February 9, 2016.

Partial Deletion of the California Gulch Superfund Site OU02 by the Environmental Protection Agency Federal Register/Vol 66, No 99 May 22, 2001

Partial Deletion of the California Gulch Superfund Site OUs 4, 5 and 7 by the Environmental Protection Agency Federal Register/Vol 79, No 206/Friday, October 24, 2014

Partial Deletion of the California Gulch Superfund Site OU 8 by the Environmental Protection Agency Federal Register/Vol 74, No 218 November 13, 2009

Partial Deletion of the California Gulch Superfund Site OU09 - subunits A and B, residential waste rock piles, and the parks and playgrounds by the Environmental Protection Agency Federal Register/Vol 67, No 34

Partial Deletion of the California Gulch Superfund Site OU10 by the Environmental Protection Agency Federal Register/Vol 66, No 32 February 15, 2001

Partial Deletion of the of the California Gulch Superfund Site Remaining portions of OU 9 by the Environmental Protection Agency Federal Register/Vol 76, No 183 September 21, 2011

Pollution Report, Operable Unit 2 Leadville Corporation Lab, California Gulch Superfund Site, Leadville, Lake County, Colorado EPA Region 8 June 2004

Pollution/Situation Report, Acid Rock Drainage Controls, Operable Unit 6, California Gulch Superfund Site, Leadville, Colorado EPA Region 8 October 29, 2014

Pollution/Situation Report, Stray Horse Gulch, Operable Unit 6, California Gulch Superfund Site, Leadville, Colorado EPA Region 8 December 16, 2013

Record of Decision, Operable Unit 1, California Gulch Superfund Site, Leadville, Colorado EPA Region 8 March 29, 1988

Record of Decision, Operable Unit 2, California Gulch Superfund Site, Leadville, Colorado EPA Region 8 September 1999

Record of Decision, Operable Unit 3, California Gulch Superfund Site, Leadville, Colorado EPA Region 8 May

Record of Decision, Operable Unit 4, California Gulch Superfund Site, Leadville, Colorado EPA Region 8 March 31, 1998

Record of Decision, Operable Unit 5, AV/CZL Sites, California Gulch Superfund Site, Leadville, Colorado EPA Region 8 September 2000

Record of Decision, Operable Unit 5, EGWA Sites, California Gulch Superfund Site, Leadville, Colorado EPA Region 8 October 31, 2000

Record of Decision, Operable Unit 6, California Gulch Superfund Site, Leadville, Colorado, EPA Region 8 September 2003

Record of Decision, Operable Unit 7, California Gulch Superfund Site, Leadville, Colorado EPA Region 8 June

Record of Decision, Operable Unit 10, California Gulch Superfund Site, Leadville, Colorado EPA Region 8 August 8, 1997

Record of Decision Amendment, Operable Unit 6 Record of Decision for the Stray Horse Gulch California Gulch Superfund Site EPA Region 8 September 2010

Record of Decision Modification, Yak Tunnel Operable Unit, California Gulch Superfund Site, Leadville,

Remedial Action Completion Report, Operable Unit 6, Stray Horse Gultch, California Gulch Superfund Site, Leadville, Colorado US EPA Region 8 June 2013

Remedial Action Completion Report, Operable Unit 10, California Gulch Superfund Site, Leadville, Colorado Shepherd Miller, Inc and Montgomery Watson Mining Group November 1999

Remedial Action Completion Report Record of Preparation Review and Approval, California Gulch Superfund Site Operable Unit 9, Populated Residential Areas EPA Region 8 January 2011

Remedial Action Construction Activities for Operable Unit 4 are now complete, California Gulch Superfund Site, Leadville, Colorado EPA Region 8 Letter December 2003

Remedial Action Report, Operable Unit 11, California Gulch Superfund Site, Leadville, Colorado EPA Region 8 June 13, 2013

Remedial Action Report, Revision 1, Remedial Action, California Gulch, Operable Unit 5, Arkansas Valley / Colorado Zinc Lead Sites, Lake County, Colorado Pacific Western Technologies, LTD February 2010

Remedial Design Report, Operable Unit 12, California Gulch Superfund Site, Leadville, Colorado Tetra Tech April 2015

Resolution Amending the Lake County Land Development Code and Adopting Regulations Concerning

In December 2009, the Board of County Commissioners for Lake County, Colorado, addressed the implementation of institutional controls for the seventeen mine waste piles situated in Operable Unit 9 of the California Gulch Superfund Site These controls aim to manage and mitigate potential environmental and health risks associated with the site, ensuring the safety of the surrounding community.

Routine Monitoring Plan, Yak Tunnel Operable Unit, California Gulch Superfund Site, Leadville, Colorado Prepared by MFG, Inc for EPA Region 8 April 2008

Second Amendment to Administrative Order for Yak Operable Unit Remedial Design/Remedial Action, California Gulch Superfund Site, Leadville, Colorado EPA Region 8 June 16, 1993

Second Five-Year Review Report for California Gulch Superfund Site Prepared for EPA Region 8 by

Third Five-Year Review Report for California Gulch Superfund Site, Leadville, Colorado Prepared for EPA Region 8 by HDR Engineering, Inc September 28, 2007

Transmittal of First Amendment to Administrative Order for Yak Tunnel Operable Unit Remedial

Design/Remedial Action (With Unilateral Administrative Order 89-20 Attached), California Gulch Superfund Site, Leadville, Colorado EPA Region 8 April 30, 1993

Work Plan for the Lake County Community Health Program Phase 2 Lake County Board of County

Commissioners, Lake County Public Health Agency, Colorado Department of Public Health and

Environment, and EPA Region 8 February 2009

Superfund Enterprise Management System (SEMS) document numbers are included in the tables below for reference SEMS is EPA’s internal document system Some documents are publicly available at https://cumulis.epa.gov/supercpad/SiteProfiles/index.cfm?fuseaction=second.scs&id01478 If documents are not available on the website, contact EPA Region 8’s Information Service Center at https://www.epa.gov/aboutepa/epa-region-8s-environmental-information-service-center

Placer gold discovered in California Gulch and mining began in the District 1859

The Harrison Reduction Works, located at the intersection of Harrison Avenue and Elm Street, was the only smelter known to have processed gold ores in OU3 Established in 1877, it operated until its closure in 1893.

The Grant Smelter in operation 1878-1882

Berdell and Witherell Smelter operated near the La Plata slag pile in OU3 1878-1887

OU2 area developed with placer claims 1879-1882

The Cummings and Finn Smelter Works commenced operations in Big Evans Gulch in 1879, also known as the Fryer Hill Smelting Company, before being dismantled in 1886 Additionally, the Big Evans Gulch area hosted other smelters, including the Ohio and Missouri Smelter and the Gage Smelter.

Hagaman Smelter, and the Raymond, Sherman and McKay Smelter

The Elgin Smelter operated intermittently 1879-1903

The Elgin, Grant, and Arkansas Valley Smelters in OU5 were constructed The Arkansas Valley (AV)

Smelter processed lead ore and reprocessed slag to produce lead, silver and other metals and operated until 1961 1879-1961

AV Smelter operated in OU5 1882-1960

The Union Smelter was in operation 1892-1900

Between 1892 and 1900, the Bimetallic Smelting Company leased the La Plata area in OU3 for the pyritic smelting of low-grade ores From 1893 to 1902, the Elgin Smelter works in OU5 were leased and operated by various companies In 1895, the Yak Tunnel was driven to dewater mines and facilitate mineral exploration and development in OU1 In 1900, the American Smelting and Refining Company acquired the La Plata works in OU3.

The Western Zinc Mining and Reducing Company constructed a smelter to the west of the City of

Leadville in OU5 that extracted zinc from ores 1914-1926

Harrison Recovery Works was established to rework the Harrison Street slag pile in OU3 1917

Last extension to Yak Tunnel occurred – total length of tunnel measures 3-1/2 to 4 miles into Iron Hill and Breece Hill in OU1 1923

The CZL Site operated a flotation mill that processed zinc-lead ores sporadically between 1925 and 1940

The tailing impoundment at the CZL Site is only tailing impoundment in OU8 1925-1940

The Colorado Zinc-Lead Mill in OU5 utilized a specialized flotation process to extract zinc, lead, gold, silver, and copper from ores Although the mill ceased operations in 1930, it underwent renovations afterward.

Between 1935 and 1938, the mill processed ores from various local mines and waste dumps until its permanent closure The history of the AV or Grant/Union smelters reveals the disposal of slag at this site.

The mill responsible for producing the tailings deposited in the Main Impoundment and potentially the North Impoundment in OU7 was situated on the hillside to the northeast of the North Impoundment.

Venir Mill, the California Gulch Mill and the ASARCO Leadville Milling unit 1939-1956

Ore & Chemical Company used OU2 as a disposal Site 1943-1946

The Oregon Gulch Tailing Impoundment in OU10 received tailing from the Newmont/Resurrection-

ASARCO mill in California Gulch 1945-1957

Hecla Mining Company, which later purchased Day Mines (Hecla/Day), leased OU2 property 1947-1987 D&RGW purchased the AV Smelter slag pile in OU3 from ASARCO for use as ballast 1961

Leadville Corporation purchased OU2 property 1968

D&RGW purchased the La Plata Slag Pile in OU3 from the Leadville Sanitation District in 1970 1970 The Apache Mill began operations in the late 1970s and continued operations into the 1980s 1970s-1980s

A mill facility utilized a cyanide leach process to extract silver from ore obtained from the Sherman and

Diamond Newmont/Resurrection mines The mill was purchased by Leadville Corporation in the early

1980s It continued operations until the mill closed in 1986 1970s-1986

D&RGW purchased the Harrison Street Slag Pile in OU3 from NL Industries for use as a ballast production 1983

Leadville Silver & Gold operated a pyrite recovery process at OU2 1983-1988

EPA listed the Site on the National Priorities List (NPL) 9/8/1983

Record of Decision (ROD) signed for OU1 Yak Tunnel 3/29/1988

Modifications of the OU1 ROD signed 3/23/1989

Explanation of Significant Differences (ESD) for OU1 signed 10/22/1991

Yak Tunnel Water Treatment Plant (WTP) began treating Yak Tunnel discharge 1992

Site-wide Consent Decree – SEMS#303506 5/16/1994

First Five-Year Review (FYR) signed 2/2/1996

ROD signed for OU10 – Oregon Gulch 8/8/1997

ROD signed for OU4 – Upper California Gulch 3/31/1998

ROD signed for OU3 – D&RGW Railroad Slag Piles, Easement, Yard, and the Mineral Belt Trail 5/6/1998

ROD signed for OU2 – Malta Gulch 9/30/1999

ROD signed for OU7 – Apache Tailing Impoundments 6/6/2000

ROD signed for OU8 – Lower California Gulch 9/29/2000

ROD signed for OU5 – slag and soils for Elgin Smelter, Grant/Union Smelter, Western Zinc Smelter and

Arkansas Valley South Hillside Slag Sites 9/29/2000

ROD signed for OU5 – tailing, flue dust and non-residential soils for Arkansas Valley Smelter and CZL mill Sites 10/31/2000

OU10 partially deleted from the NPL 4/16/2001

Notice of Partial Deletion of OU2 from the NPL 7/23/2001

Notice of Partial Deletion of the parks and playgrounds, residential mine waste rock piles, and Subunits A and B in OU9 from the NPL 4/22/2002

OU7 Apache Tailing Impoundments capped 6/24/2002

ROD signed for OU6 encompassing previous removal actions 9/25/2003

ROD signed for OU11 – Arkansas River Floodplain 9/28/2005

Various response actions performed by parties to the Consent Decree 1994-2006

Lake County has declared a State of Emergency due to rising water levels in the LMDT area as of February 1, 2008 In response, a relief well was installed to pump excess water to the LMDT treatment plant by March 1, 2008 Additionally, the second EPA-led site-wide technical assistance grant was successfully completed on May 1, 2008.

Site-wide claim in ASARCO bankruptcy proceeding 5/1/2008

Final Consent Decree with Newmont USA and Newmont/Resurrection Mining Company 6/26/2008

Final Modification of 1994 Consent Decree with ASARCO 7/2/2008

Site-Wide Water Quality (OU12) ROD signed 9/22/2009

Lower California Gulch (OU8) partially deleted from the NPL 1/12/2010

ROD Amendment for OU6 signed 9/28/2010

Residential areas (OU9) partially deleted from NPL 9/21/2011

On May 16, 2013, several minor Record of Decision (ROD) modifications were made, including the ASARCO Smelters/Slag/Mill Sites (OU5), Apache Tailing Impoundments (OU7), Lower California Gulch (OU8), and Residential Soils (OU9), with respective SEMS numbers 1261492, 1261491, 1261490, and 1261489 Additionally, on June 13, 2013, the repository completion for Stray Horse Gulch (OU6) was documented under SEMS#1265520.

ESD signed Yak Tunnel (OU1) – SEMS#1267311 7/29/2013

ESD signed Malta Gulch Fluvial Tailing/Leadville Corporation Mill/Malta Gulch Tailing Impoundments

ESD Upper California Gulch (OU4) – SEMS#1267313 7/29/2013

ESD Oregon Gulch (OU10) – SEMS#1267314 7/29/2013

ESD D&RGW Slag Piles and Easement (OU3) – SEMS#1286501 8/6/2014

Upper California Gulch (OU4), ASARCO Smelters/Slag/Mill Sites (OU5) and Apache Tailing

Impoundments (OU7) partially deleted from NPL – SEMS#1310757 10/24/2014 Yak Tunnel (OU1) and DR&G Slag Piles (OU3) partially deleted from NPL 4/11/2016

Table B-2: Chronology of OU1 Events

California Gulch Superfund Site placed on the NPL 9/8/1983

Phase I Remedial Investigation (RI) Report released – SEMS#325440, 308998, 309003 5/1987

Feasibility Study (FS) Report released – SEMS#314983 6/1/1987

Proposed Remedial Action Plan released for OU1 – SEMS#333922 12/7/1987

Began Surge Pond and Interim Treatment Plant remedy 9/1988

Modification of ROD (AROD) – SEMS#316277 3/23/1989

Unilateral Administrative Order (UAO 89-20) – SEMS#304436 3/29/1989

Construction of Yak Tunnel WTP began 2/1990

Completed Surge Pond and Interim Treatment Plant remedy 6/1991

Completion of Yak Tunnel Monitoring Wells – SEMS#2041904 2/1/1992

Completion of the Yak Tunnel WTP facility – SEMS#320890-96 2/1992 to

First amendment to UAO 89-20 – SEMS#309585 4/30/1993

Second amendment to UAO 89-20 – SEMS#318526 6/16/1993

Yak Tunnel Bulkhead remedy began 3/1994

Consent Decree with ASARCO – SEMS#303506 5/16/1994

Completion of Yak Tunnel Bulkhead Remedy 11/1994

Rising water levels detected in Yak Tunnel 5/2002

Dewatering of Black Cloud Mine underway 3/2006

EPA and the potentially responsible parties (PRPs) signed a Consent Decree for performance of remedy and operation and maintenance (O&M) – SEMS#1073144 (this Consent Decree replaced UAO 89-20) 6/26/2008 Environmental Covenants placed – SEMS#1242260-62

ESD added institutional controls – SEMS#1267311 7/29/2013

OU partial deletion from NPL 4/11/2016

California Gulch Superfund Site placed on NPL 9/8/1983

Administrative Order on Consent (AOC) for Engineering Evaluation/Cost Assessment (EE/CA) at the

Malta Gulch Tailing Impoundment (MGTI) – SEMS#318530 9/1991

Partial Consent Decree with Hecla Mining Company to settle Hecla’s Site-wide liabilities –

1/6/1993 and 8/17/1994 Partial Consent Decree with Leadville Silver and Gold Company to settle its Site-wide liabilities –

EE/CA issued for the MGTI – SEMS#309834 8/2/1993

An Action Memorandum was issued for the removal action at MGTI (SEMS#315870) on September 10, 1993 Subsequently, a time-critical removal action was authorized at LMGFT (SEMS#317241) on August 14, 1995, with the actual removal action commencing on September 5, 1995.

Start date for Removal Action at the MGTI (9/10/1993 Action Memorandum) 10/5/1995 Action Memorandum issued for time-critical removal action at the MTI – SEMS#321257 8/9/1996

Start Date for time-critical removal action at the MGTI (8/9/1996 Action Memorandum) 9/4/1996

Discovery of drums at the Leadville Mill 11/7/1997

Completion of removal actions identified in Action Memoranda dated 9/10/1993, 8/14/1995 and

Action Memorandum issued for time-critical removal action of Leadville Mill drums – SEMS#346866 4/15/1998

Time-critical drum removal action completed 7/2/1998

Final Pollution Reports on 9/10/1993, 8/14/1995, 8/9/1996 Action Memorandum – SEMS#323615,

Notice of intent to partial delete OU2 from the NPL – SEMS#493090, 493091 2/12/2001

Partial deletion from the NPL – SEMS#1249430 7/23//2001

EPA issued a lien on the PRPs property 9/23/2002

Lake County passed ordinance that acts as an institutional control – SEMS #1261487 4/15/2013

ESD signed adding institutional controls – SEMS #1267312 7/29/2013

Table B-4: Chronology of Removal Actions Performed at OU2

Date Removal Action Taken Start

 Grade and revegetate contiguous fluvial tailing

 Removal non-contiguous pockets of fluvial tailing and dispose of the material in the MGTI

 Provide for long-term maintenance and monitoring

 Grade and revegetate contiguous fluvial tailing

 Removal non-contiguous pockets of fluvial tailing and dispose of the material in the MGTI

 Provide for long-term maintenance and monitoring

 Grade, compact and revegetate the impoundments

 Dispose of pyritic materials from the Apache Energy &

 Provide for long-term maintenance and monitoring of the vegetated cap/cover

 Stage 42 drums in a secure location

 Dispose or recycle oily liquids in accordance with Standards for the Management of Used Oil, 40 CFR

Transport hazardous wastes to a Resource Conservation and Recovery Act (RCRA)-approved treatment or disposal facility

EPA’s contractor sampled the three slag piles as part of the Site RI 1986

Soils investigation conducted that included sampling of slag from the Harrison Street pile, La

Plata pile, and an area west of Leadville (AV Smelter Slag Pile not included) 1988

EPA conducted second sampling of slag to determine the concentrations of metals in three

D&RGW slag piles and to evaluate potential of migration 5/1989

AOC with D&RGW for remedial investigation/feasibility study (RI/FS) of slag piles –

RI/FS completed for seven major lead slag piles and a zinc slag pile – SEMS#305053, 303054,

Site-Wide Screening Feasibility Study (SFS) completed – SEMS #301445 9/1/1993 AOC with D&RGW for completion of investigation and remediation activities – SEMS#301431 9/15/1993 EPA, State and D&RGW enter into Consent Decree – SEMS#318593 12/1993

D&RGW submitted ballast operations plan to EPA 7/1995

D&RGW submitted a feasibility study for the stockpiled fine slag at the AV Smelter slag pile according to Consent Decree terms – SEMS #320758 5/13/1996

Union Pacific Railroad Company (UP) assumed D&RGW’s responsibilities at the Site 1996

ROD signature for OU3 (addressed only the fine slag stockpiled as a subpile of the AV Smelter

Request for Partial Deletion of the Mineral Belt Trail from the State of Colorado to EPA –

Lake County adopts ordinance that acts as an institutional control – SEMS#1100390 3/3/2009 City of Leadville adopts ordinance that acts as an institutional control – SEMS#1265522 5/7/2013

ESD requiring institutional controls signed – SEMS#1286501 8/6/2014

OU3 partially deleted from the NPL 4/11/2016

Final Yak Tunnel/California Gulch RI 1986

OU12 DATA ANALYSIS TRENDS I-1

Figure I-1: Flow and Dissolved Zinc Surface Water Concentrations at AR-1

Figure I-2: Flow and Dissolved Cadmium Surface Water Concentrations in AR-1

Figure I-3: Flow and Dissolved Zinc Surface Water Concentrations at AR-3A

Figure I-4: Flow and Dissolved Cadmium Surface Water Concentrations in AR-3A

• Oisso \oed Zinc (rrg,1 ) ã Meets StandYd • Dissolved Zinc (mgil) ã Exceeds Sbncbird - - -Tef11> Modified Std {0.649 rrg,1.)

- -20ll-2015ARã l Avg O,JyFlow (c:is) -His 10ricAR-1 Avg Daily Ao.v(ds )

• OisS,eo ~i:lmlum (/':'l)IL) ã Mt ~ 3 ~:,r,

- - -Te.no- Mo:11\e'-} • u xeeo:S ;sQn(l,)J'O

California Gulch Superfund Site Five-Year Review Interview Form

Site Name: California Gulch EPA ID No.: COD980717938

Subject Name: Lawrence Fiske Affiliation: Newmont/Resurrection

Interview Format: In Person Phone Mail Other: Email

Interview Category: Potentially Responsible Parties (PRPs)

1 What is your overall impression of the remedial activities at the Site?

Newmont/Resurrection has made significant progress in its remedial activities, leading to a reduction in the discharge of zinc, iron, and other metals As a result, the likelihood of the event that prompted the Superfund listing occurring again is very low Overall, the efforts by Newmont/Resurrection are viewed positively.

Newmont/Resurrection's remedial efforts have significantly improved visual aspects, eliminating issues like red water and erosion In contrast, some remedial activities conducted by other parties lack visual appeal and may not provide the same level of protection Overall, these efforts have led to enhanced water quality in the Arkansas River, delivering a positive environmental impact.

2 What have been the effects of the Site on the surrounding community, if any?

Improved public perception, and confidence that the Site is no longer impairing the Arkansas River and is a safer area to raise families

3 What is your assessment of the current performance of the remedy in place at the Site?

While the overall effectiveness of the measures implemented was satisfactory, a retrospective analysis suggests that some remedies may have been unnecessary or disproportionately costly compared to the benefits gained, and many of these solutions are also expensive and challenging to sustain over time.

4 Are you aware of any complaints or inquiries regarding environmental issues or the remedial action from residents since implementation of the cleanup?

Public confusion exists regarding the responsibilities and functions of various remedial activities, particularly concerning Newmont/Resurrection Questions have arisen about the LMDT blockage, the specific treatment processes of the Yak Water Treatment Plant (WTP), and the water quality management in Evans and Stray Horse Gulches.

5 Do you feel well-informed regarding the Site’s activities and remedial progress? If not, how might EPA convey site-related information in the future?

We do not receive much information on activities occurring in the OUs that are not

6 Do you have any comments, suggestions or recommendations regarding the management or operation of the Site’s remedy?

The EPA remedial project manager is very competent, readily available, and always willing to discuss questions for improving or modifying the remedy and other issues that come up

7 Do you consent to have your name included along with your responses to this questionnaire in the FYR report?

California Gulch Superfund Site Five-Year Review Interview Form

Site Name: California Gulch EPA ID No.: COD980717938

Subject Name: Sarah Dallas Affiliation: City of Leadville

Subject Contact Information: 800 Harrison Ave

Leadville, CO 80461 719-486-2092 adminservices@leadville-co.gov

Interview Format: In Person Phone Mail Other: Email

1 What is your overall impression of the remedial activities at the Site?

Recent efforts have significantly reduced contaminated water runoff, especially during the spring season, addressing previous concerns about brown and red runoff Additionally, the integrity of most, if not all, known caps remains intact, indicating that reclamation initiatives are yielding positive results.

2 What have been the effects of this Site on the surrounding community, if any?

Concerns about environmental contamination continue to affect newly located families near the former superfund site, as they express worries about potential correlations to elevated lead levels in children under six Additionally, the community faces ongoing economic challenges stemming from its previous classification as a superfund site.

3 What is your assessment of the current performance of the remedies in place at the Site?

There has not been much, or any, public information and governmental information sent to the City for review I am not currently educated to discuss my assessment without more information

4 Are you aware of any complaints or inquiries regarding environmental issues or the remedial action from residents since implementation of the cleanup?

Residents on the East side near South Toledo Street have expressed concerns about potential development disturbing remediated soils, which could lead to re-contamination Additionally, property owners are eager to proceed with development in previously remediated areas The city of Leadville and Lake County have established best management practices for soil removal to address these issues However, there seems to be a need for increased public awareness and informative follow-up regarding these regulations.

5 Do you feel well-informed regarding the Site’s activities and remedial progress? If not, how might EPA convey site-related information in the future?

I feel that regular updates, either bi-annually or annually, would enhance communication with elected officials and keep the public informed It is also crucial to have clear information regarding the future plans and stages of former superfund sites Establishing clear expectations and understanding is essential for fostering transparency and trust.

6 Do you have any comments, suggestions or recommendations regarding the management or operation of the Site’s remedy?

Again, reiteration of ongoing communication from the EPA with the City of Leadville

Figure K-1: 2009 County Institutional Control for Operable Units 3 and 8

PROCJ!fDINO OF THE BOARD 01' COUNTY COMMISSIONERS COUNTY OF I.AXE AND STAT£ OF COLORADO lWIOUJ'llON~

A 'RESOLlmON AMENDING Tim LAKE COUNTY LAND DEVELOPMEl'lI' CODE AND ADOPTING R.EOULATIONS CONCERMNO INSTrrunONAL CONTROLS FOR OPE.UBL£ UNITS WITHIN THE CALIFORNIA OUICH SUPF.RFUND SITE

The Board of County Commissioners of Lake County, Colorado, is responsible for managing the affairs of the county in accordance with state regulations.

WHEREAS, Ibo Boad bas initialed a Land U11e and Developmcn1 Applicallon, file number 01-41, proposing that 1be Lab Comity lA:id Dnclopll*lt Code (LDC) be amended to

The EPA's Records of Decision or Action Memo highlight the need for institutional controls at the California Gulch Superfund Site to prevent improper handling of contaminated materials These measures are essential for assisting the EPA in delisting the California Gulch Superfund Site from the National Priorities List (NPL).

WHEREAS, bccause the ameudment 10 the LDC was initialc4 by the Board, no application fee: wa.s JCquired to be peid; and

WHEIU!AS, the Lake County Land P ,elo~ Code docs DOI CU!ffllllY coulain provbiom NWlilbuJa in:iti1\1tioul COl1llb for Ille California O\llcb Superfuod Site; and

The 111 amendment to the Leko Company's Land Development Code is essential to incorporate guidelines for reviewing and defining institutional controls related to the California Gulch Superfund Site.

WHER.EAS, 1be Lake County Plann!oc C o ~ 811d the Board of County Coalmlaionen held a joint public llMillg 011 this lliatter on 1lle M. day o f ~ 2009; md

WHEREAS, the Bcmd of County Commiasioncra bu comidcRd the ,-,IJIIXlC1lG8lion ã of the Lake CoUDty 1.-t U1e ~ and Iba Plannin& CommiJaioG; 1111d

The Board of County Commissioners finds that the proposed amendments to the Lake County Land Development Code align with the goals and objectives of the Lake County Comprehensive Plan These changes do not require adjustments to social values, planning concepts, or other economic conditions, and are expected to enhance public health, safety, and welfare for the citizens of Lake County.

NOW Timl.EFOlE BE IT RE.SOLVED lbat:

~ This Resolutioo iJ comistai\, whh \be goals, objectivem, poli

Tiêu đề	Fifth Five-Year Review Report For California Gulch Superfund Site Lake County, Colorado
Tác giả	U.S. Environmental Protection Agency Region 8
Người hướng dẫn	Betsy Smidã r, Assistant Regional Administrator, Office of Ecosystems Protection and Remediation
Trường học	U.S. Environmental Protection Agency
Chuyên ngành	Environmental Science
Thể loại	report
Năm xuất bản	2023
Thành phố	Denver

Định dạng
Số trang	320
Dung lượng	38,17 MB

FIFTH FIVE YEAR REVIEW REPORT FOR CALIFORNIA GULCH SUPERFUND SITE LAKE COUNTY, COLORADO

INTRODUCTION

SITE-WIDE RESPONSE ACTION SUMMARY

PROGRESS SINCE THE LAST REVIEW

FIVE-YEAR REVIEW PROCESS

OPERABLE UNIT 1: Yak Tunnel WTP

OPERABLE UNIT 1: RESPONSE ACTION SUMMARY

OPERABLE UNIT 1: PROGRESS SINCE THE LAST REVIEW

OPERABLE UNIT 1: FIVE-YEAR REVIEW PROCESS

OPERABLE UNIT 1: TECHNICAL ASSESSMENT

OPERABLE UNIT 1: ISSUES/RECOMMENDATIONS

OPERABLE UNIT 1: PROTECTIVENESS STATEMENT

OPERABLE UNIT 2: Malta Gulch Fluvial Tailing/Leadville Corp Mill/Malta Gulch Tailing Impoundments 17

OPERABLE UNIT 2: RESPONSE ACTION SUMMARY

OPERABLE UNIT 2: PROGRESS SINCE THE LAST REVIEW

OPERABLE UNIT 2: FIVE-YEAR REVIEW PROCESS

OPERABLE UNIT 2: TECHNICAL ASSESSMENT

OPERABLE UNIT 2: ISSUES/RECOMMENDATIONS

OPERABLE UNIT 2: PROTECTIVENESS STATEMENT

OPERABLE UNIT 3: Denver & Rio Grande Western Railroad Company (D&RGW) Slag Piles/Railroad Easement/Railroad Yard

OPERABLE UNIT 3: RESPONSE ACTION SUMMARY

OPERABLE UNIT 3: PROGRESS SINCE THE LAST REVIEW

OPERABLE UNIT 3: FIVE-YEAR REVIEW PROCESS

OPERABLE UNIT 3: TECHNICAL ASSESSMENT

OPERABLE UNIT 3: ISSUES/RECOMMENDATIONS

OPERABLE UNIT 3: PROTECTIVENESS STATEMENT

OPERABLE UNIT 4: Upper California Gulch

OPERABLE UNIT 4: RESPONSE ACTION SUMMARY

OPERABLE UNIT 4: PROGRESS SINCE THE LAST REVIEW

OPERABLE UNIT 4: FIVE-YEAR REVIEW PROCESS

OPERABLE UNIT 4: TECHNICAL ASSESSMENT

OPERABLE UNIT 4: ISSUES/RECOMMENDATIONS

OPERABLE UNIT 4: PROTECTIVENESS STATEMENT

OPERABLE UNIT 5: ASARCO Smelters/Slag/Mill Sites

OPERABLE UNIT 5: RESPONSE ACTION SUMMARY

OPERABLE UNIT 5: PROGRESS SINCE THE LAST REVIEW

OPERABLE UNIT 5: FIVE-YEAR REVIEW PROCESS

OPERABLE UNIT 5: TECHNICAL ASSESSMENT

OPERABLE UNIT 5: ISSUES/RECOMMENDATIONS

OPERABLE UNIT 5: PROTECTIVENESS STATEMENT

OPERABLE UNIT 6: Stray horse gulch and evans gulch watersheds

OPERABLE UNIT 6: RESPONSE ACTION SUMMARY

OPERABLE UNIT 6: PROGRESS SINCE THE LAST REVIEW

OPERABLE UNIT 6: FIVE-YEAR REVIEW PROCESS

OPERABLE UNIT 6: TECHNICAL ASSESSMENT

OPERABLE UNIT 6: ISSUES/RECOMMENDATIONS

OPERABLE UNIT 6: PROTECTIVENESS STATEMENT

OPERABLE UNIT 7: Apache Tailing Impoundments

OPERABLE UNIT 7: RESPONSE ACTION SUMMARY

OPERABLE UNIT 7: PROGRESS SINCE THE LAST REVIEW

OPERABLE UNIT 7: FIVE-YEAR REVIEW PROCESS

OPERABLE UNIT 7: TECHNICAL ASSESSMENT

OPERABLE UNIT 7: ISSUES/RECOMMENDATIONS

OPERABLE UNIT 7: PROTECTIVENESS STATEMENT

OPERABLE UNIT 8: Lower California Gulch

OPERABLE UNIT 8: PROGRESS SINCE THE LAST REVIEW

OPERABLE UNIT 8: FIVE-YEAR REVIEW PROCESS

OPERABLE UNIT 8: TECHNICAL ASSESSMENT

OPERABLE UNIT 8: ISSUES/RECOMMENDATIONS

OPERABLE UNIT 8: PROTECTIVENESS STATEMENT

OPERABLE UNIT 9: Residential Populated Areas

OPERABLE UNIT 9: RESPONSE ACTION SUMMARY

OPERABLE UNIT 9: PROGRESS SINCE THE LAST REVIEW

OPERABLE UNIT 9: FIVE-YEAR REVIEW PROCESS

OPERABLE UNIT 9: TECHNICAL ASSESSMENT

OPERABLE UNIT 9: ISSUES/RECOMMENDATIONS

OPERABLE UNIT 9: PROTECTIVENESS STATEMENT

OPERABLE UNIT 10: Oregon Gulch

OPERABLE UNIT 10: RESPONSE ACTION SUMMARY

OPERABLE UNIT 10: PROGRESS SINCE THE LAST REVIEW

OPERABLE UNIT 10: FIVE-YEAR REVIEW PROCESS

OPERABLE UNIT 10: TECHNICAL ASSESSMENT

OPERABLE UNIT 10: ISSUES/RECOMMENDATIONS

OPERABLE UNIT 10: PROTECTIVENESS STATEMENT

OPERABLE UNIT 11: Arkansas River Valley Floodplain

OPERABLE UNIT 11: RESPONSE ACTION SUMMARY

OPERABLE UNIT 11: PROGRESS SINCE THE LAST REVIEW

OPERABLE UNIT 11: FIVE-YEAR REVIEW PROCESS

OPERABLE UNIT 11: TECHNICAL ASSESSMENT

OPERABLE UNIT 11: ISSUES/RECOMMENDATIONS