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FIVE-YEAR REVIEW REPORT

Third Five-Year Review Report

for

Marshall Landfill Site

Boulder County, Colorado

September 2006

PREPARED BY:

U.S. Environmental Protection Agency, Region 8 Denver, Colorado

Approved by: Max Dodson h h ~ Date:

Assistant Regional Administrator U.S. EPA, Region 8

Marshall Landfill Five-Year Review Report

Five Year Review Report 1

TABLE OF CONTENTS

FIVE-YEAR REVIEW SUMMARY FORM.................................................................................. 6 I. Introduction ........................................................................................................................ 9 II. Site Chronology................................................................................................................ 10 III. Background ...................................................................................................................... 11

Location and Setting......................................................................................................... 11 Site History....................................................................................................................... 11

IV. Remedial Actions ............................................................................................................. 12 Remedy Selection............................................................................................................. 13 Remedy Implementation .................................................................................................. 14 Remedy Operation and Maintenance (2004-Present)....................................................... 15

V. Progress Since Second Five-Year Review ....................................................................... 15 VI. Five-Year Review Process ............................................................................................... 16

Administrative Components............................................................................................. 16 Community Involvement.................................................................................................. 16 Document Review ............................................................................................................ 16 Data Review ..................................................................................................................... 17 Site Inspection .................................................................................................................. 18

VII. Technical Assessment ...................................................................................................... 19 Question A: Is the remedy functioning as intended by the decision documents? ............ 19 Question B: Are the exposure assumptions, toxicity data, cleanup levels, and remedial action objectives used at the time of the remedy selection still valid?............................. 19 Question C: Has any other information come to light that could call into question the protectiveness of the remedy? .......................................................................................... 21 Technical Assessment Summary...................................................................................... 21

VIII. Issues ................................................................................................................................ 21 IX. Recommendations and Follow-Up Actions...................................................................... 22 X. Protectiveness Statement .................................................................................................. 22

Next Review..................................................................................................................... 22



TABLES

Table 1 Chronology of Site Events Table 2 Site Surface and Groundwater Standards Table 3 Issues Identified Table 4 Recommendations and Follow-Up Actions

APPENDICES

Appendix A Site Maps Appendix B Photo Log



LIST OF ACRONYMS

ARARs Applicable or Relevant and Appropriate Requirements

CDPHE Colorado Department of Public Health and Environment

CERCLA Comprehensive Environmental Response, Compensation and Liability Act

CFR Code of Federal Regulations

EPA United States Environmental Protection Agency

ESD Explanation of Significant Difference

ICs Institutional Controls

LGAC Liquid-phase granular activated carbon

NCP National Contingency Plan

NPL National Priorities List

O&M Operation and Maintenance

PCE Perchloroethene

POC Point of Compliance

PRP Potentially Responsible Party

RI/FS Remedial Investigation/Feasibility Study

ROD Record of Decision

TCE Trichloroethene

TDS Total Dissolved Solids

VGAC Vapor-phase granular activated carbon

VOCs Volatile Organic Compounds



Executive Summary

The U.S. Environmental Protection Agency (EPA) Region 8 has conducted a third five-year review of the remedial actions implemented at the Marshall Landfill Site (the Site) in Boulder County, Colorado. The purpose of the five-year review is to determine whether the remedy at the Site is protective of human health and the environment. The trigger action for this review is completion of the second five-year review in September 2001. Because hazardous substances, pollutants or contaminants remain at the Site above levels that allow for unrestricted use and unlimited exposure, another five-year review is required.

The Site is located in southeastern Boulder County, approximately one mile east of the town of Marshall and consists of two adjacent landfills, each comprising approximately 80 acres. The Marshall Landfill, located to the north, began operating in 1965, when the Richland Company, under contract with Boulder County, began a solid waste composting and disposal operation at the Site. In 1974, the Marshall Landfill was abandoned when Urban Waste Resources, along with Mesa Sand and Gravel, opened the Boulder Landfill to the immediate south. Landfill, Inc., a wholly owned subsidiary of Browning-Ferris Industries (BFI), purchased the landfill operation in 1975. The Boulder Landfill closed in January 1992. BFI is now owned by Allied Waste Industries. Throughout the period of landfill operations, the land has been owned by The Cowdrey Corporation.

The Site lies along the north-facing side of Lake Mesa and within the Cowdrey Drainage, which conveys surface water from Cowdrey Reservoir No. 2 approximately 3 miles to South Boulder Creek. The land surrounding Marshall Landfill is largely rural and is used primarily for livestock grazing.

Lake Mesa is a broad, upland pediment surface, consisting of a gravel-capped bedrock erosional surface along the crest, a series of colluvial and terrace deposits along the flanks, and colluvial and weathered soil along Cowdrey Drainage. Refuse in the Marshall Landfill was placed along the bedrock slope north of Cowdrey Drainage, down into Cowdrey Drainage and up along the flank of Lake Mesa.

The uppermost hydrostratigraphic unit is an unconfined aquifer with flow generally to the north and northwest and along Cowdrey Drainage. Deeper hydrostratigraphic units are bedrock aquifers within the Laramie and Fox Hills Formations. These units underlie the shallow alluvial and colluvial deposits that make up the shallow aquifer. The regional groundwater flow direction in the bedrock aquifers is to the east.

Several sources of contamination were identified during the Remedial Investigation/Feasibility Study (RI/FS), which was conducted in 1986. These include:

• Areas of saturated refuse within the northern portion of the Boulder Landfill and throughout the Marshall Landfill;

• Trenches used for waste disposal between 1972 and 1974 at the Marshall Landfill; • Small, undefined areas within the Marshall Landfill where industrial wastes,

primarily organic solvents, were disposed along with solid wastes; and • Two unlined leachate lagoons in the southern portion of the Marshall Landfill.



No contamination was detected in surface waters leaving the Site during the RI. However, after completion of the RI, 1,1-dichlorethane was detected at 5 micrograms per liter (μg/L) in surface water from the Cowdrey Drainage. On-Site groundwater within the shallow alluvial aquifer was found to be contaminated with volatile organic compounds, heavy metals, chloride, nitrate and sulfate. No contamination was identified in the deeper bedrock aquifer.

Based on the findings of the RI/FS, EPA selected a preferred remedy, which was described in the 1986 Record of Decision. The Site remedy included a groundwater collection and treatment system, landfill improvements, and environmental monitoring programs. The remedy was considered operational in 1993. The collection and treatment system was placed on a stand-by mode in November 2004.

The results of this five-year review identified several issues that should be addressed. On-Site arsenic and chloride concentrations have been consistently greater than the groundwater performance standards since discontinuation of groundwater collection and treatment in November 2004. Furthermore, there are periodic on-Site exceedances of benzene, ammonia, total dissolved solids, chromium, iron and selenium. However, off-Site groundwater exceedances are rare. Detection limits for many constituents are regularly greater than performance standards. Improved analytical techniques should be employed to resolve this issue.

A 2003 Explanation of Significant Difference updated water quality standards for surface and groundwater. For surface water, a distinction was made between water quality standards for Upper and Lower Cowdrey Drainage. However, the limits of each reach were not identified. This should be clarified so the appropriate standards may be associated with surface water points of compliance.

Given that nearly all exceedences of water quality standards occurred on-Site during the monitoring period, the remedy remains largely protective of human health and the environment. However, if current conditions persist, off-Site contaminant migration may occur. Concentrations of relevant chemical constituents should continue to be monitored and reported on a quarterly basis.


FIVE-YEAR REVIEW SUMMARY FORM

SITE IDENTIFICATION| Site name: Marshall Landfill Site.

EPA ID: COD980499255 Region: 8 State: CO City/County: Boulder County

SITE STATUS NPL status: Final Remediation status: Operating (groundwater extraction/treatment system in stand-by mode) Multiple OUs: No Construction completion date: 5/93

Has site been put into reuse? No

REVIEW STATUS Lead agency: EPA Author name: Rebecca Thomas Author title: Project Manager Author affiliation: U.S.EPA, Region 8 Review period: 8/06 – 9/06

Date(s) of site inspection: 09/13/06 Type of review: Statutory

Review number: 3 (third)

Triggering action: Second Five-Year Review Report Triggering action date: 9/28/01

Due date: 9/06


Five-Year Review Summary Form, cont’d.

Issues:

Item No. Issue Affects Current Protectiveness of

Remedy

Affects Future Protectiveness of

Remedy

1 No distinction made between upper and lower Cowdrey drainage. Potentially Potentially

2

Detection limits reported for some inorganics and metals are higher than relevant surface water quality performance standards.

Potentially Potentially

3 Frequent exceedences of groundwater standards at monitoring location EPA-14.



Five-Year Review Summary Form, cont’d.

Recommendations and Follow-up Actions:

Item No.

Issue Recommendation for Follow Up Party Responsible

Due Date

1 No distinction made between upper and lower Cowdrey drainage.

Clarify which surface water points of compliance are in the upper and lower Cowdrey drainage

EPA 12/06

2


Revise analytical method or document new performance standard in an ESD

EPA or Boulder/BFI 12/06


Continue monitoring in accordance with the Proposal to Terminate Active Remediation System Operation.

Boulder/BFI NA

Protectiveness Statement(s): The remedy is currently protective of human health and the environment. Nearly all exceedences of water quality standards occurred on-Site during the monitoring period and institutional controls remain in force. However, if current conditions persist, off-Site contaminant migration may occur.


Marshall Landfill Site Boulder County, Colorado

Third Five-Year Review Report

I. Introduction The U.S. Environmental Protection Agency (EPA) Region 8 has conducted a third five-year review of remedial actions implemented at the Marshall Landfill Site (the Site) in Boulder County, Colorado. The Site consists of two parcels, the original 80-acre Marshall Landfill and the newer 80-acre Boulder Landfill (Figure 1 - Appendix A). Both landfill operations are inactive. Remedial actions taken primarily to address conditions at the older Marshall Landfill are the focus of this five-year review.

The purpose of the five-year review is to determine whether the remedy at a Site is protective of human health and the environment. The methods, findings and conclusions of the review are documented in this Five-Year Review Report. In addition, the Five-Year Review Report identifies deficiencies found during the review, if any, and identifies recommendations to address them. This third five-year review was conducted during August and September 2006. HDR Engineering, Inc. (HDR) of Denver, Colorado, was retained under a subcontract to Project Resources Inc. (PRI) to prepare this Five-Year Review Report for EPA. PRI was retained by the US Army Corps of Engineers, Omaha District under a Rapid Response Program contract.

This review is required by statute. The EPA must implement five-year reviews consistent with the Comprehensive Environmental Response, Compensation and Liability Act (CERCLA) and the National Oil and Hazardous Substances Pollution Contingency Plan (NCP). CERCLA 121(c), as amended, states:

If the President selects a remedial action that results in any hazardous substances, pollutants, or contaminants remaining at the site, the President shall review such remedial action no less often than each five years after the initiation of such remedial action to assure that human health and the environment are being protected by the remedial action being implemented.

The NCP, Part 300.430(f)(4)(ii) of the Code of Federal Regulations (CFR), states: If a remedial action is selected that results in hazardous substances, pollutants or contaminants remaining at the site above levels that allow for unlimited use and unrestricted exposure, the lead agency shall review such action no less often than every five years after the initiation of the selected remedial action.

This is the third five-year review of the Site. The trigger action for this review is completion of the second five-year review on September 28, 2001. Because hazardous substances, pollutants or contaminants remain at the Site above levels that allow for unrestricted use and unlimited exposure, another five-year review is required.


II. Site Chronology Table 1

Chronology of Site Events

Date Event

1965 Solid waste management operations begin at the Site under management of Richland Company

1969 Operations purchased by Salvage, Inc., later renamed Urban Waste Resources (UWR)

1970-1974 UWR operated solid waste landfill

1974 UWR abandoned Marshall Landfill and, with Mesa Sand and Gravel, opened the Boulder Landfill to the south

1975 Landfill, Inc., a wholly owned subsidiary of Browning-Ferris Industries (BFI), purchased the operation.

July 1982 EPA proposes Marshall Landfill for NPL.

September 1983 Marshall Landfill included on NPL.

1983 EPA, Landfill, Inc., Boulder County, Colorado Department of Health, City of Louisville and Farmers Reservoir and Irrigation Co. enter into a Cooperative Agreement.

1983 EPA issued order to Landfill, Inc. requiring them to install Community Ditch pipeline by 1984.

1985 RI/FS completed by Landfill, Inc.

September 1986 ROD issued by EPA.

March 1989 Consent Decree finalized and accepted by all parties (EPA, City of Boulder, Landfill, Inc. and landowners).

1989-1990 Additional site investigations performed.

1992 Boulder Landfill closes.

May 1992 Final Design Submittal approved by EPA.

November 1992 Explanation of Significant Differences to ROD issued by EPA.

1993 Remedial action construction considered complete with EPA approval of Final Remedial Measures Implementation Report.

1993 Final O&M Plan approved by EPA.

November 1995 First five-year review completed.

1996 Corrective measures completed to address seepage identified in first five-year review.

1997 Final Revised Off-Site Water Quality Monitoring Plan approved by EPA.

September 2001 Second five-year review completed.

September 2003 Explanation of Significant Differences to ROD issued by EPA.

November 2004 Groundwater collection and treatment system terminated.

November 2004 Water quality monitoring plan implemented.


III. Background Location and Setting The Site is located in southeastern Boulder County, approximately one mile east of the town of Marshall. The Site is south of Colorado Highway 170 and is bounded on the east by South 66th Street. Marshall Lake is located approximately 2,000 feet to the west. Approximately two miles east is the town of Superior. The cities of Boulder and Louisville are three miles to the northwest and northeast, respectively. The area within a one-mile radius of the Site is sparsely populated.

The land surrounding Marshall Landfill is used primarily for livestock grazing. The other adjacent land uses are as follows: (1) storage facility for the National Center for Atmospheric Research on the east side of South 66th St.; (2) an irrigation and municipal drinking water reservoir, Marshall Lake, immediately to the west of the Site; and (3) small, non-food warehouse building to the northeast of the Site that has been previously leased for a variety of storage uses.

The Site lies along the north-facing side of Lake Mesa and within the Cowdrey Drainage, which conveys surface water from Cowdrey Reservoir No. 2 approximately 3 miles to South Boulder Creek (see map in Appendix A). At some times in the past, Cowdrey Drainage flow was diverted to Davidson Ditch where it was used for irrigation. Community Ditch also flows along this drainage, and at various times of the year it carries water from South Boulder Creek to Marshall Lake. Drainage from Marshall Lake flows east to the City of Louisville, where it is used as drinking water and then farther east, where the flow is used as irrigation water. Additionally, two small lagoons, dug by Boulder County in an attempt to collect and contain landfill leachate, were previously located within the Marshall Landfill Site.

Lake Mesa is a broad, upland pediment surface, consisting of a gravel-capped bedrock erosional surface along the crest, a series of colluvial and terrace deposits along the flanks, and colluvial and weathered soil along Cowdrey Drainage. Refuse in the Marshall Landfill was placed along the bedrock slope north of Cowdrey Drainage, down into Cowdrey Drainage and up along the flank of Lake Mesa.

The uppermost hydrostratigraphic unit is an unconfined aquifer consisting of: (1) alluvial sands, gravels and clays mantling the top and flank of Lake Mesa; (2) colluvial material along the base of Lake Mesa; (3) weathered bedrock and alluvium along Cowdrey Drainage; and (4) refuse placed in the Marshall Landfill. Underlying the Site, groundwater flow in the shallow alluvial aquifer is generally to the north.

Deeper hydrostratigraphic units are bedrock aquifers within the Laramie and Fox Hills Formations. These units underlie the shallow alluvial and colluvial deposits that make up the shallow aquifer. The regional groundwater flow direction in the bedrock aquifers is to the east.

Site History The Site consists of two adjacent landfills, each comprising approximately 80 acres. The Marshall Landfill, located to the north, began operating in 1965, when the Richland Company, under contract with Boulder County, began a solid waste composting and


disposal operation at the Site. Although the contract specified composting operations, landfilling comprised the majority (80%) of waste handling activities. In 1969, the operation was sold to Salvage, Inc., which was later acquired by a group of local investors and renamed Urban Waste Resources. Between 1969 and 1974, the Marshall Landfill accepted municipal waste, unstabilized sewage sludge and many unknown, potentially hazardous wastes. In 1974, the Marshall Landfill was abandoned when Urban Waste Resources, along with Mesa Sand and Gravel, opened the Boulder Landfill to the immediate south. Landfill, Inc., a wholly owned subsidiary of Browning-Ferris Industries (BFI), purchased the landfill operation in 1975. The Boulder Landfill closed in January 1992. BFI is now owned by Allied Waste Industries. Throughout the period of landfill operations, the land has been owned by The Cowdrey Corporation.

In September 1983, the Marshall/Boulder Landfill was listed on the National Priorities List (NPL) due to the release of contamination to irrigation and drinking water. A major concern was the contamination of water flowing in Community Ditch because it serves as a source of drinking water for the City of Louisville. In response to this concern, a 60-inch pressurized pipeline was installed to convey the water across the inactive landfill.

Several sources of contamination were identified during the Remedial Investigation/Feasibility Study (RI/FS), which was conducted in 1986. These include:

• Areas of saturated refuse within the northern portion of the Boulder Landfill and throughout the Marshall Landfill;

• Trenches used for waste disposal between 1972 and 1974 at the Marshall Landfill; • Small, undefined areas within the Marshall Landfill where industrial wastes,

primarily organic solvents, were disposed along with solid wastes; and • Two unlined leachate lagoons in the southern portion of the Marshall Landfill.

No contamination was detected in surface waters leaving the Site via Cowdrey Drainage and Community Ditch during the RI. However, after completion of the RI, 1,1-dichlorethane was detected at 5 micrograms per liter (μg/L) in surface water from the Cowdrey Drainage. On-Site groundwater within the shallow alluvial aquifer was found to be contaminated, as characterized by elevated levels of:

• Volatile organic compounds (VOCs) such as benzene, trichloroethene (TCE) and perchloroethene (PCE);

• Heavy metals such as barium, iron, manganese and zinc; and • Major ions, such as chloride, nitrate and sulfate.

No contamination was identified in the deeper bedrock aquifer.

Based on the findings of the RI/FS, EPA selected a preferred remedy, which was described in the 1986 ROD.

IV. Remedial Actions The following remedial action objectives for the Marshall Landfill Site were included in the Feasibility Study and ROD:

• Assure that all surface water discharge from the landfills does not adversely impact the current or planned future beneficial uses of the surface waters in this


area or any other waters that it may contact; • Control the generation of contaminated groundwater at the Site; • Assure that any off-Site contaminated groundwater originating at the Site does not

adversely impact possible beneficial uses of groundwaters in this area or any other surface waters and groundwaters it may contact;

• Eliminate or control impacts resulting from leachate seepage in the landfills.

Remedy Selection The remedy described by the ROD involves collection of contaminated groundwater leaving the Site; treatment of the collected groundwater; environmental monitoring; and landfill improvements.

The major components of the remedy selected by the ROD include:

• Elimination of off-Site transport of contaminants emanating from the Site by constructing a drain or series of drains to capture shallow groundwater along the entire southern and eastern Site boundaries;

• Treatment of contaminated groundwater in a facility consisting of equalization/sedimentation basins, an air stripper, and carbon adsorption of air stripper off-gas (vapor-phase granular activated carbon, or VGAC);

• Implementation of an environmental monitoring program to verify the effectiveness of the remedial action and to assure protection of public health;

• Completion of landfill improvements, including regrading, revegetation, perimeter ditches and fences to minimize future environmental and public health impacts from the Site;

• Drainage of existing leachate lagoons and transfer of the liquid to the treatment system; and

• Redirection of the discharge of an existing french drain (installed to collect seepage during landfill operations) to the treatment facility.

A Consent Decree (CD) was entered into on March 29, 1989. Its parties are EPA, Landfill, Inc. (now BFI), City of Boulder and certain landowners. Section IV of the CD requires the responsible parties to design, construct, operate, maintain and monitor the performance of the remedial measures implemented at the Site. Exhibit II (Scope of Work) of the CD details the procedures, tasks and schedule to be followed by the responsible parties in performing the selected remedial action. The remedial action required by the CD is the same as that described by the ROD and consists of the following tasks: Task I-Landfill Improvement; Task II-Groundwater Collection and Treatment; Task III-Monitoring. The CD also established the methods by which remediation standards for water quality would be developed for the Site.

Additional investigations were carried out in 1989 and 1990 in order to provide information needed to design the collection and treatment systems specified in the ROD and determine the remediation standards. In 1992, based on the findings of these investigations, EPA issued an ESD to the 1986 ROD Remedy. The ESD included four significant modifications to the remedy as originally selected:

• The groundwater collection system was changed to consist of a well array along most of the eastern Site boundary and a collection trench along part of the


southern and eastern Site boundaries instead of the series of drains specified by the ROD;

• Breakpoint chlorination/dechlorination was added to the treatment system to remove ammonia from collected groundwater prior to its discharge;

• In addition to the air stripper and air stripper off-gas carbon adsorption system specified in the ROD, a liquid-phase carbon adsorption system (liquid-phase granular activated carbon, or LGAC) was added to remove VOCs; and

• The effluent limitation for chloride was changed from 280 mg/L to 320 mg/L, after the Colorado Water Quality Control Commission modified the numeric water quality stream standard for chloride to 320 mg/L.

When the ROD was issued, groundwater standards did not exist for several VOCs of concern at the Site. As such, the original Applicable or Relevant and Appropriate Requirements (ARARs) are no longer protective of human health and the environment. In addition, many of the Colorado surface water quality standards have also been updated. In 2003 EPA issued a second ESD to the 1986 ROD Remedy which outlines updated performance standards for surface water and groundwater. However, no points of compliance (POCs) for groundwater or surface water monitoring had been established in this ESD or prior decision documents.

The 2003 ESD also identified Institutional Controls (ICs) that are necessary to ensure long-term protection of the engineered remedy and to prevent future release of contamination. ICs have been implemented for the Site and contain two components. The first component is an informational device that identifies the property as a Superfund Site in the records of Boulder County Planning Department. The device is an electronic map, which identifies the landfill boundary, and which will be referenced if any applications related development or other changes in land are submitted to the county. The second component is a local enforcement device. The device is a prohibition on the development of the Superfund Site pursuant to the Rural Preservation Planning Area land use designation. This land use prohibition is enforceable by Boulder County and all surrounding municipalities through the Intergovernmental Agreement US 36 Interstate Corridor Comprehensive Development Plan effective June 20, 2000. Specifically, the agreement states that the municipalities “shall not grant a permit for development” for all areas with the Rural Preservation Planning Area including the Superfund Site.

Remedy Implementation

The remedy implemented is the remedial action selected in the 1986 ROD, as subsequently modified in the 1992 and 2003 ESDs. In 2004, groundwater collection and treatment were discontinued and these systems were placed in a stand-by mode. In order to assess the impact of the discontinuation of treatment, EPA required 12-quarters of monitoring before plant decommissioning. This monitoring is ongoing.


Remedy Operation and Maintenance (2004-Present) The PRPs are conducting relevant long-term monitoring and maintenance activities in accordance with the Operations and Maintenance Plan (O&M Plan), and Final Environmental/ Performance Monitoring Plan. The primary activities associated with O&M and monitoring of the remedy during the past two years include:

• maintenance of landfill improvements; • piezometric monitoring in the vicinity of the groundwater collection system; and • off-Site and on-Site surface water and groundwater monitoring.

Monitoring results are reported to EPA according to the reporting requirements and schedules in the Final Environmental/Performance Monitoring Plan and subsequent sampling and analysis plans (Final Piezometric Monitoring Plan, Revised Off-Site Water Quality Monitoring Plan, Proposal to Terminate Active Remediation System Operation).

V. Progress Since Second Five-Year Review The concerns identified in the second five-year review and subsequent progresses towards resolution are discussed below.

1. Soil cover missing where landfill debris exposed.

Repairs were made and the cover appeared in good condition during the Site inspection.

2. Sparse vegetation in limited areas with steeper slopes.

Vegetative cover has improved since the previous Five-Year Review and is in good condition with few exceptions (see Photo 1-Appendix B).

3. Limited signage to discourage trespassing.

‘No Trespassing’ signs have been posted around the perimeter of the Site where public access is possible.

4. Failure to report results for 1,2-DCA in Off-Site Water Quality Monitoring Report.

Since discontinuation of the groundwater collection and treatment system operation in 2004, the results of all VOCs have been reported.

5. Detection limits reported for some VOCs in the Off-Site Water Quality Monitoring Reports are higher than relevant water quality standards and remediation standards.

The detection limits for all VOCs have been lower than the relevant standards since discontinuation of the groundwater collection and treatment system.

6. Protectiveness of remediation standards for designated uses of Cowdrey Drainage and South Boulder Creek has not been demonstrated.

As a means to demonstrate protectiveness of remediation standards, ARARs were updated in the 2003 ESD issued by the EPA.


7. Groundwater influent to treatment system meets effluent remediation standards; responsible parties propose to discontinue groundwater collection and treatment.

Groundwater collection and treatment have been discontinued as approved by the EPA on November 18, 2004. Water quality monitoring continues.

VI. Five-Year Review Process This is the third five-year review of the Site.

Administrative Components The five-year review team was lead by Rebecca Thomas, the EPA Project Manager, and included technical staff from EPA's contractor, HDR. Rob Henneke of EPA acted as the Community Involvement Coordinator.

The review was initiated on August 21, 2006 and included the following components:

• Community Involvement, • Local Interviews, • Document Review, • Data Review, • Site Inspection and • Five-Year Review Report Development and Review

The schedule for the review extended through September 2006.

Community Involvement A notice that the five-year review was in progress was placed in the Boulder Daily Camera on August 21, 2006. The notice invited members of the public to submit their input regarding the review to EPA.

EPA interviewed two Marshall Landfill area residents on August 24 and 29, 2006. The residents expressed no personal or community concerns about the Site or remedy. One resident, who followed the progress of groundwater treatment, believes the remedy is successful. The same person kept other area residents informed and confirmed their confidence in the remedy. The other resident is a member of local government and has not received any concerns from constituents. Both residents expressed their desire that the land remain open space as called for in existing zoning regulations. The land has rural preservation status that is to be maintained by Boulder County.

Following completion of the five-year review, a notice will be placed in the Boulder Daily Camera announcing that the review has been completed and that copies of the report are available for the public to review at the EPA Superfund Records Center in Denver, CO and Boulder Public Library in Boulder, CO.

Document Review

In preparing this Five-Year Review Report, the following documents were reviewed:

• EPA ROD, 1986 • ESD, 1992 • First Five-Year Review for Marshall Landfill Site, 1995


• Second Five-Year Review for Marshall Landfill Site, 2001 • ESD, 2003 • Approval letter of discontinuation of groundwater collection and treatment, 2004

Interviews were conducted with the following individuals to provide supplemental technical information:

• Fonda Apostolopoulos (Colorado Department of Public Health and Environment (CDPHE).

Data Review The remedy includes a monitoring program designed to track groundwater levels and to evaluate groundwater and surface water quality. Each monitoring component has specific objectives for demonstrating the performance of the remedy.

Prior to the suspension of groundwater collection/treatment in November 2004, the major elements of the monitoring program were piezometric monitoring in the vicinity of the groundwater collection system, monitoring of the collection/treatment system inflow, off-Site surface water and groundwater monitoring, and monitoring of the water treatment system effluent. However, surface and ground water POCs were not defined until first proposed in 2004.

In their proposal to discontinue collection and treatment of groundwater, the responsible parties identified two off-Site surface water POCs (CDO and CDPO) along with one on-Site groundwater POC (EPA-14) and one off-Site groundwater POC (EPA-18) (see Figure 2-Appendix A).

In preparing this Five-Year Review Report, the following monitoring documents were reviewed:

• Technical Memorandum: Proposal to Terminate Active Remediation System Operation, ARCADIS, October, 2004

• Quarter 1 Water Quality Monitoring Results, ARCADIS, May 2005 • Quarters 3 and 4 Water Quality Monitoring Results, Herst &Associates, Inc.,

December 2005 and February 2006 • Notification of Arsenic and Chloride Exceedances at POC Well EPA-14, Herst

&Associates, Inc., February 2006 • Quarters 1 and 2 Water Quality Monitoring Results, Herst &Associates, Inc.,

April and July 2006

A summary of these data and their interpretation for demonstrating remedy performance is provided below.

Technical Memorandum: Proposal to Terminate Active Remediation System Operation

This memorandum proposes termination of groundwater collection and treatment. The memorandum concludes that concentrations of VOCs in treatment facility influent have been declining since 1997 and that inorganic compounds were not occurring above naturally-occurring levels. Furthermore, concentrations of certain species of VOCs have been below the Colorado Groundwater Quality Standards since June of 2000 with a few exceptions. In each case, the exceptions to this trend are attributed to drought conditions.


Given these findings, it was proposed that collection and treatment of groundwater be discontinued.

In order to assess the impact of the discontinuation of treatment, the memorandum proposed a 12-quarter monitoring plan involving sample collection from seven groundwater wells and two surface water sites. Additionally, two of the monitoring wells (EPA-14 and EPA-18) and the two surface water sampling locations (CDO and CDPO) were defined as POCs (see Figure 2-Appendix A). The memorandum states that if an exceedance at a POC is observed, the location will be re-sampled within a two-week period. If the exceedance is reproducible and attributed to a change down-gradient from the landfill, EPA is to be notified and will determine if additional actions are required.

Water Quality Monitoring Results

Examination of the VOC data reveals that between March 2005 and May 2006 there were no exceedances of VOC concentrations at either of the surface water POCs. However, it should be noted that on four of the six sampling dates monitoring location CDO was dry and monitoring location CDPO was dry on two of the six sampling dates. Benzene concentrations exceeded the groundwater performance standard on three of the six dates at EPA-14.

Concentrations of inorganics at the two surface water POCs were below the surface water performance standards on all six dates. However, detection limits for ammonia are greater than surface water performance standards by a factor of 25. Ammonia, chloride, and TDS at monitoring location EPA-14 exceeded their respective groundwater performance standards on every sampling date. At EPA-14, ammonia ranged in concentration from 33.4 to 140 milligrams per liter (mg/L) (groundwater standard = 0.21 mg/L), reported concentrations of chloride ranged from 400 to 900 mg/L (groundwater standard = 250 mg/L), and TDS ranged in concentration from 2730 to 4300 mg/L (groundwater standard = 650 mg/L).

There were no exceedances of metal concentrations at the surface water POCs over the course of the six sampling dates. However, detection limits for silver and mercury were greater than the performance standards by a factor of 20. At monitoring location EPA-14, arsenic concentrations exceeded the groundwater performance standard of 10 µg/L on 9 of 10 sampling dates (note: the number of sampling dates is greater than six due to the fact that re-sampling events are required when exceedences are measured). On these nine dates arsenic concentrations range from 31 to 43 µg/L. Chromium, iron, and selenium were also reported to have exceeded performance standards at EPA-14 on at least one sampling date.

Site Inspection

A site inspection was performed on September 13th, 2006 by representatives of USEPA, CDPHE and HDR. The site inspection objectives were to observe vegetative and soil cover on the landfill as well as to inspect the perimeter of the Site for the presence of signage to discourage trespassing.

Previous concerns regarding the condition of landfill improvements appear to have been addressed. The vegetative and soil cover is in good condition with the exception of a small area of thin vegetative cover on the south end of the landfill (Photo 1-Appendix B).


At the time of the inspection, no seepage was observed within the landfill boundary. However, areas of lush vegetation were observed (Photo 2-Appendix B).

The Marshall Landfill is surrounded by a barbed-wire fence, but the Site can be easily accessed by trespassers (Photo 3-Appendix B). There are multiple signs posted adjacent to public access areas indicating the area is private property.

VII. Technical Assessment Question A: Is the remedy functioning as intended by the decision documents? Landfill Improvements

Several years were required to establish sufficient vegetation to stabilize and reduce erosion of the soil cover by wind and runoff. Vegetative cover is sparse on several small areas, but there is no current evidence of soil cover erosion that would reduce the overall effectiveness of landfill improvements.

Compliance with Surface and Groundwater Performance Standards

One of the remedial action objectives of the ROD is to assure that surface drainage from the Site does not adversely impact beneficial uses of nearby surface waters. Surface water monitoring demonstrates that applicable water quality standards are generally maintained in Cowdrey Drainage and Community Ditch. The exceptions always involve detection limits being much higher than the surface water quality performance standards. It should also be noted that the surface water POCs have been dry during many of the recent sampling events.

Groundwater monitoring has identified multiple exceedances of VOCs, inorganic constituents and metals at monitoring location EPA-14. Arsenic, chloride, ammonia and TDS concentrations have been consistently greater than the groundwater performance standards since discontinuation of groundwater collection and treatment. Furthermore, there are periodic exceedances at EPA-14 of benzene, chromium, iron and selenium. However, exceedances at EPA-18 (off-Site station) are rare.

Institutional Controls

According to the 2003 ESD, the ICs are in force.

Given nearly all exceedences of water quality standards occurred on-Site during the monitoring period and the ICs are in force, the remedy remains largely protective of human health and the environment. However, if current conditions persist, off-Site contaminant migration may occur.

Question B: Are the exposure assumptions, toxicity data, cleanup levels, and remedial action objectives used at the time of the remedy selection still valid? There have been no changes in the physical conditions of the Site or surrounding land uses that would change the exposure assumptions, cleanup levels or remedial action objectives for the Site. All performance standards are ARARs-based and therefore there is no need to assess exposure assumptions or toxicity data.


Changes in ARARs

ARARs were updated in the 2003 ESD issued by the EPA. Since that time there have been no changes to ARARs. ARAR-based surface and groundwater standards are shown in Table 2.

Table 2 Site Surface and Groundwater Standards

Parameter Ground Water Performance

Standard

Surface Water Performance Standard for the Upper Cowdrey (Hardness=50)

Surface Water Performance Standard for the Lower Cowdrey (Hardness=50)

TDS (mg/L) 6501 Chloride (mg/L) 250 3202 320 Sulfate (mg/L) 250 Existing as of 01-01-00 or 250

whichever is less restrictive Existing as of 01-01-00 or 250

whichever is less restrictive Ammonia (mg/L) 0.213 N/A 0.02 Nitrate (as N) (mg/L) 10 10 10 Nitrite (as N) (mg/L) 1 1.0 0.05 Arsenic (mg/L) 0.01 0.05 0.05 Barium (mg/L) 2 -- Cadmium (mg/L) 0.005 0.01 Acute=.002

Chronic=.0013 Chromium (mg/L) 0.1 0.05 0.011 Copper (mg/L) 1.0 1.0 Acute=0.007

Chronic=0.005 Iron (mg/L) 101 Existing as of 01-01-00 or

300ug/l whichever is less restrictive

Same

Lead (mg/L) 0.05 Acute=0.05 Acute=0.03 Chronic=0.0012

Manganese (mg/L) 11 Existing as of 01-01-00 or 50 ug/l whichever is less restrictive

(dissolved)

Same

Mercury (mg/L) 0.002 Acute=0.002 Chronic=0.00001 Nickel (mg/L) 0.1 N/A Acute=0.26

Chronic=0.029 Selenium (mg/L) 0.05 Chronic=0.01 Acute=0.018

Chronic=0.005 Silver (mg/L) 0.05 Acute=0.05 Acute=0.065

Chronic=0.066 Zinc (mg/L) 5 Chronic=5.0 Same Phenols (mg/L) 4.2 Water Standard (WS)=4.2 Same 1,1-dichloroethane (mg/L) 0.007 WS=0.007 Same Trans 1,2-dichloroethylene (mg/L) 0.1 WS=0.1 Same 1,1,1-trichloroethane (mg/L) 0.2 WS=0.2 Same Tetrachlorethylene (mg/L) 0.005 WS=0.005 Same 1,1-dichlorothylene (mg/L) 0.007 WS=0.007 Same Ethylbenzene (mg/L) 0.680 WS=0.7 Same Toluene (mg/L) 1 WS=1.0 Same Benzene (mg/L) 0.005 WS=0.0012 Same Trichloroethylene (mg/L) 0.005 WS=0.05 Same

1 Alternate Background Standards are allowable pursuant to the Consent Decree and documented in the “Technical Memorandum:

Review of Remediation Standards” dated July 29, 2002. 2

ESD, 1992 USEPA which documented Colorado Water Quality modified the chloride water quality stream standard for Upper and Lower Cowdrey Drainage to 320 (mg/L). This does not impact the standard for groundwater. 3

Risk Based Concentration Table value, For a single contaminant in a single medium, the RBC corresponds to the target risk or hazard quotient, EPA 4/2/2002.


Progress of Remedy

Since discontinuation of the groundwater collection and treatment system, surface water samples indicate that applicable water quality standards are generally being met. However, only data from the previous six quarters has been reported. Furthermore, detection limits for many constituents are much greater than the performance standards for surface water.

Quarterly groundwater sampling reveals that most constituents are below the performance standards outlined in Table 2. However, as outlined in the previous section, there are consistent exceedances of arsenic and chloride and periodic exceedences of other constituents

Institutional Controls

The ICs outlined above are still relevant and valid.

Question C: Has any other information come to light that could call into question the protectiveness of the remedy? Protection of surface water for all beneficial uses cannot be confirmed at this time because several parameters monitored in off-Site surface water (silver, mercury, ammonia) have surface water quality standards that are lower than their reported detection limits in recent monitoring reports. The fact that monitoring locations CDO and CDPO have been dry four of the last six and two of the last six sampling dates, respectively, makes confirmation that surface waters are being protected difficult to determine.

All ICs are functioning as intended.

There is no other information that calls into question the protectiveness of the remedy.

Technical Assessment Summary According to the data reviewed, the site inspection and interviews, the remedy is largely functioning as intended by the ROD, as modified by the ESDs. There have been no changes to the physical conditions of the Site or surrounding land uses that would affect the protectiveness of the remedy. Since the discontinuation of the groundwater collection and treatment system groundwater standards for certain constituents are exceeded on a regular basis at the on-Site POC. Furthermore, detection limits for various constituents are too high to accurately asses if the all performance standards are being met.

Given that nearly all exceedences of water quality standards occurred on-Site during the monitoring period, the remedy remains largely protective of human health and the environment. However, if current conditions persist, off-Site contaminant migration may occur. Concentrations of relevant chemical constituents should continue to be monitored and reported on a quarterly basis.

VIII. Issues Based on the information collected during the second Five-Year Review Report, the following issues were identified:


Table 3 Issues Identified

Item No. Issue Affects Current Protectiveness of

Remedy

Affects Future Protectiveness of

Remedy

1 No distinction made between upper and lower Cowdrey drainage. Potentially Potentially

2





IX. Recommendations and Follow-Up Actions Table 4

Recommendations and Follow-Up Actions

Item No. Issue Recommendation for Follow Up Party

Responsible Due Date

1 No distinction made between upper and lower Cowdrey drainage.

Clarify which surface water points of compliance are in the upper and lower Cowdrey drainage

EPA 12/06

2


Revise analytical method or document new performance standard in an ESD

EPA or Boulder/BFI 12/06


Continue monitoring in accordance with the Proposal to Terminate Active Remediation System Operation.

Boulder/BFI NA

X. Protectiveness Statement The remedy is currently protective of human health and the environment. Nearly all exceedences of water quality standards occurred on-Site during the monitoring period and institutional controls remain in force. However, if current conditions persist, off-Site contaminant migration may occur.

Next Review This Site requires ongoing five-year reviews in accordance with CERCLA §121(c). The next five-year review for the Marshall Landfill Site will be performed by September 2011, five years from the date of completion of this review.

APPENDICES

APPENDIX A

APPENDIX B

Photo Log

Picture 1

Thin vegetation at south end of landfill looking west.

Picture 2

Looking southwest at lush vegetation in area of possible shallow groundwater (on north facing slope).

Picture 3

Looking southeast at water treatment plant.

Picture 4

Looking northwest at northwest corner of landfill.

Picture 5 South part of landfill looking southwest.

Picture 6

Cowdrey Creek drainage looking west.

report for marshall landfill site - semspub.epa.gov · marshall landfill five-year review report...

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