EPA542-R-07-019
unitae SMI** September 2007
-" *« r-ft-|-a": Pn."it«t|
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NOTICE
Work described herein was performed by GeoTrans, Inc. (GeoTrans) for the U.S. Environmental
Protection Agency (U.S. E.P.A). Work conducted by GeoTrans, including preparation of this report, was
performed under EPA contract 68-C-02-092 to Dynamac Corporation, Ada, Oklahoma. Mention of trade
names or commercial products does not constitute endorsement or recommendation for use.
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EXECUTIVE SUMMARY
A Remediation System Evaluation (RSE) involves a team of expert scientists and engineers, independent
of the site, conducting a third-party evaluation of site operations. It is a broad evaluation that considers
the goals of the remedy, site conceptual model, above-ground and subsurface performance, and site
closure strategy. The evaluation includes reviewing site documents, visiting the site for up to 1.5 days,
and compiling a report that includes recommendations to improve the system. Recommendations with
cost and cost savings estimates are provided in the following four categories:
Improvements in remedy effectiveness
Reductions in operation and maintenance costs
Technical improvements
Gaining site closeout
The recommendations are intended to help the site team identify opportunities for improvements. In
many cases, further analysis of a recommendation, beyond that provided in this report, may be needed
prior to implementation of the recommendation. Note that the recommendations are based on an
independent evaluation by the RSE team, and represent the opinions of the RSE team. These
recommendations do not constitute requirements for future action, but rather are provided for the
consideration of all stakeholders.
Clear Creek originates in the mountains near Colorado's Continental Divide and runs 60 miles east and
several thousand feet lower in elevation to Golden, Colorado, a western suburb of Denver, Colorado and
then discharges to the South Platte River north of Denver. The drainage basin encompasses
approximately 400 square miles, including a portion of the Colorado Mineral Belt, which includes several
mining districts in Clear Creek and Gilpin Counties. Due to the rich mineralization, these two counties
became some of the most heavily mined areas of Colorado, with gold and silver accounting for the vast
majority of the mining. As part of ore extraction activities, the miners constructed tunnels. Acidic,
metal-rich water from these mine tunnels has continued to enter Clear Creek and its tributaries at many
locations. The Argo Tunnel and Big Five Tunnel, located in Idaho Springs, Colorado, are two of the
tunnels that EPA and CDPHE have focused on to reduce acid and metals loading to Clear Creek. The
Argo Tunnel Water Treatment Plant (Argo WTP), which is located at the entrance of the Argo Tunnel,
treats the discharge from these two tunnels as well as acidic and metals laden ground water from nearby
Virginia Canyon. Although other sources of acid mine drainage and other remedies comprise this
Superfund Site, the RSE team was specifically asked to focus its review on the Argo WTP.
In general, the RSE team found a competent and attentive operations team that was effectively meeting
the challenges of a complex water treatment system. The observations and recommendations contained in
this report are not intended to imply a deficiency in the work of either the system designers or operators,
but are offered as constructive suggestions in the best interest of the EPA, the public, and the facility.
These recommendations have the benefit of being formulated based on operational data unavailable to the
original designers.
Recommendations are provided in three of the four categories: effectiveness, cost reduction, and technical
improvement. No recommendations are provided regarding site closure. The recommendations for
improving system effectiveness are as follows:
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Further consider the risks associated with future blowouts of the Argo Tunnel and the costs of
implementing blowout control and come to a decision whether or not to move forward with
blowout control. The majority of this recommendation would be implemented by CDPHE and
EPA staff. Contractor support might be on the order of $20,000. If blowout control is
implemented, the costs have been estimated to be on the order of $3 million to $5 million.
Evaluate if the discharge of acidic and metals-rich ground water from Virginia Canyon should be
better controlled during high flow events by either bypassing flow from the Argo Tunnel
discharge or by increasing storage or treatment capacity. The majority of this recommendation
would be implemented by CDPHE and EPA staff. Contractor support might be on the order of
$10,000. Increased storage capacity could be achieved by implementing blowout control.
Monitor the air in the treatment plant and confirm that appropriate medical monitoring of
treatment plant operators is occurring given the potential for high metals dust in the treatment
plant air. This recommendation might cost $2,000 to implement.
Recommendations for cost reduction include the following:
Install a new platform and two new filter presses to facilitate solids handling and reduce operator
labor. The site team has received a cost estimate of $560,000 to make this modification. Making
this change should reduce operator labor and improve plant operations, with an estimated savings
of $100,000 per year.
Realize additional reductions in labor in a few years as a result of improving plant operations and
addressing issues that have resulted from the conversion from caustic to lime. When current
issues associated with the lime feed system, solids handling, filter scaling, and solids build up in
the equalization basin are addressed, labor costs might be further reduced by $50,000 per year.
Capital costs of $100,000 to $350,000 might be needed to address the filter scaling. The capital
costs for other changes are included in the technical improvement recommendations.
Consider improvements to the treatment system that will allow solids recycling as originally
anticipated to improve the density of the clarifier underflow and the filter cake and to reduce lime
and chemical usage. Design and implementation of the change suggested in this report might cost
$75,000 to implement, but might result in $55,000 per year in savings, primarily from reduced
solids transport and disposal costs.
In total, the RSE team identified approximately $205,000 per year in potential savings that could result
from an investment of $960,000. Recommendations for technical improvement include the following:
Reduce discharge of recycled solids and high pH water to equalization basins by modifying the
mounting of the pH probe, improving filter press operations, and piping flow from the underbasin
to the reaction tanks instead of the equalization basin.
Improve the lime feed system by creating a recycling loop for the upper portion of the feed
system and considering changes in metering pump design.
Provide additional compressed air capacity to provide redundancy during high flow periods and
to provide aeration associated with the solids recycling recommendation.
in
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Reduce solids wasting flow rate by reducing air flow to the diaphragm pumps with the use of a
regulator and timer.
Consider construction of an on-site solids disposal repository as a contingency to disposal at a
landfill unless a closer evaluation of costs suggests that more substantial savings can be realized
than suggested in this report.
Consider additional improvements suggested by the site team, including the potential use of an
autosampler for collecting effluent samples, a new turbidity meter for better control of the
treatment process, and reserve lime or caustic storage.
The estimated capital costs for making these technical improvements are approximately $157,000. It is
noted, however, that some of these changes would be needed to realize the above-mentioned additional
reductions in labor in a few years.
A table summarizing the recommendations, including estimated costs and/or savings associated with
those recommendations, is presented in Section 7.0 of this report.
IV
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PREFACE
This report was prepared as part of a project conducted by the United States Environmental Protection
Agency Office of Superfund Remediation and Technology Innovation (U.S. EPA OSRTI) in support of
the "Action Plan for Ground Water Remedy Optimization" (OSWER 9283.1-25, August 25, 2004). The
objective of this project is to conduct Remediation System Evaluations (RSEs) at selected pump and treat
(P&T) systems that are jointly funded by EPA and the associated State agency. The project contacts are
as follows:
Organization
Key Contact
Contact Information
U.S. EPA Office of Superfund
Remediation and Technology
Innovation
(OSRTI)
Charles Sands
2777 South Crystal Drive
5th Floor
Mail Code 5204P
Arlington, VA 22202
phone: 703-603-8857
sands.cliarlcs@cpa.gov
Dynamac Corporation
(Contractor to U.S. EPA)
Daniel F. Pope
Dynamac Corporation
3601 Oakridge Boulevard
Ada, OK 74820
phone: 580-436-5740
fax: 580-436-6496
dpope@dynamac.com
GeoTrans, Inc.
(Contractor to Dynamac)
Doug Sutton
GeoTrans, Inc.
2 Paragon Way
Freehold, NJ 07728
phone: 732-409-0344
fax: 732-409-3020
dsutton@gcQtransinc.cQm
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TABLE OF CONTENTS
NOTICE i
EXECUTIVE SUMMARY ii
PREFACE v
TABLE OF CONTENTS vi
1.0 INTRODUCTION 1
1.1 PURPOSE 1
1.2 TEAM COMPOSITION 2
1.3 DOCUMENTS REVIEWED 2
1.4 PERSONS CONTACTED 3
1.5 SITE LOCATION, HISTORY, AND CHARACTERISTICS 3
1.5.1 LOCATION 3
1.5.2 HISTORICAL PERSPECTIVE 4
1.5.3 POTENTIAL SOURCES 4
1.5.4 HYDROGEOLOGIC SETTING 5
1.5.5 POTENTIAL RECEPTORS 5
2.0 SYSTEM DESCRIPTION 6
2.1 SYSTEM OVERVIEW 6
2.2 COLLECTION SYSTEM 6
2.3 TREATMENT SYSTEM 6
2.4 MONITORING PROGRAM 7
3.0 SYSTEM OBJECTIVES, PERFORMANCE, AND CLOSURE CRITERIA 8
3.1 CURRENT SYSTEM OBJECTIVES AND CLOSURE CRITERIA 8
3.2 TREATMENT PLANT OPERATION STANDARDS 8
4.0 FINDINGS AND OBSERVATIONS FROM THE RSE SITE VISIT 9
4.1 FINDINGS 9
4.2 COMPONENT PERFORMANCE 9
4.2.1 COLLECTION SYSTEM 9
4.2.2 EQUALIZATION BASINS 9
4.2.3 LIME STORAGE AND FEED SYSTEM 10
4.2.4 PH ADJUSTMENT 10
4.2.5 CHEMICAL REACTION AND PRECIPITATION SYSTEM 10
4.2.6 MEDIA FILTERS 11
4.2.7 SOLIDS HANDLING 11
4.2.8 CONTROLS 11
4.3 COMPONENTS OR PROCESSES THAT ACCOUNT FORMAJORITY OF ANNUAL COSTS 12
4.3.1 UTILITIES 12
4.3.2 CHEMICALS 12
VI
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4.3.3 LABOR 12
4.3.4 TRANSPORT AND DISPOSAL 13
4.3.5 CHEMICAL ANALYSIS 13
4.4 RECURRING PROBLEMS OR ISSUES 13
4.5 REGULATORY COMPLIANCE 13
4.6 TREATMENT PROCESS EXCURSIONS AND UPSETS, ACCIDENTAL CONTAMINANT/REAGENT
RELEASES 14
4.7 SAFETY RECORD 14
5.0 EFFECTIVENESS OF THE SYSTEM TO PROTECT HUMAN HEALTH AND THE
ENVIRONMENT 15
5.1 GROUND WATER 15
5.2 SURF ACE WATER 15
5.3 AIR 15
5.4 SOIL 15
5.5 WETLANDS AND SEDIMENTS 15
6.0 RECOMMENDATIONS 16
6.1 RECOMMENDATIONS TO IMPROVE EFFECTIVENESS 16
6.1.1 EVALUATE AND DECIDE ON NEED FOR BLOWOUT PREVENTION 16
6.1.2 EVALUATE IMPORTANCE OF COMPLETE COLLECTION AND TREATMENT OF THE
VIRGINIA CANYON GROUND WATER 17
6.1.3 EVALUATE INDOOR AIR QUALITY FOR METALS AND CONFIRM MEDICAL
MONITORING FOR PLANT WORKERS 17
6.2 RECOMMENDATIONS TO REDUCE COSTS 18
6.2.1 INSTALL NEW FILTER PRESSES 18
6.2.2 REALIZE SAVINGS FROM IMPROVED OPERATIONS IN FY09 18
6.2.3 IMPROVE METALS TREATMENT BY SOLIDS RECYCLING 20
6.3 RECOMMENDATIONS FOR TECHNICAL IMPROVEMENT 21
6.3.1 REDUCE DISCHARGE OF RECYCLED SOLIDS AND HIGH pH WATER TO
EQUALIZATION BASINS 21
6.3.2 IMPROVE LIME FEED SYSTEM 22
6.3.3 PROVIDE ADDITIONAL COMPRESSED AIR CAPACITY 23
6.3.4 REDUCE SOLIDS WASTING FLOW RATE 23
6.3.5 CONSIDER CONSTRUCTION OF AN ON-SITE SOLIDS DISPOSAL REPOSITORY AS A
CONTINGENCY TO DISPOSAL AT A LANDFILL 23
6.3.6 ADDITIONAL IMPROVEMENTS 24
6.4 CONSIDERATIONS FOR GAINING SITE CLOSE Our 25
6.5 CONSIDERATIONS FOR IMPLEMENTATION 25
7.0 RECOMMENDATIONS 26
Figures
Figure 1-1 Area Addressed by the Argo WTP
vn
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1.0 INTRODUCTION
1.1 PURPOSE
During fiscal years 2000 and 2001 Remediation System Evaluations (RSEs) were conducted at 20 Fund-
lead pump and treat (P&T) sites (i.e., those sites with pump and treat systems funded and managed by
Superfund and the States). Due to the opportunities for system optimization that arose from those RSEs,
EPA OSRTI has incorporated RSEs into a larger post-construction complete strategy for Fund-lead
remedies as documented in OSWER Directive No. 9283.1-25, Action Plan for Ground Water Remedy
Optimization. OSRTI has since commissioned RSEs at additional Fund-lead sites. An independent EPA
contractor is conducting these RSEs, and representatives from EPA OSRTI are participating as observers.
The RSE process was developed by the US Army Corps of Engineers (USAGE) and is documented on the
following website:
http://www.environmental.usace.arniy.niil/libranr/giiide/rsechk/rsechk.html
An RSE involves a team of expert scientists and engineers, independent of the site, conducting a third-
party evaluation of site operations. It is a broad evaluation that considers the goals of the remedy, site
conceptual model, above-ground and subsurface performance, and site closure strategy. The evaluation
includes reviewing site documents, visiting the site for up to 1.5 days, and compiling a report that
includes recommendations to improve the system. Recommendations with cost and cost savings
estimates are provided in the following four categories:
Improvements in remedy effectiveness
Reductions in operation and maintenance costs
Technical improvements
Gaining site closeout
The recommendations are intended to help the site team (the responsible party and the regulators) identify
opportunities for improvements. In many cases, further analysis of a recommendation, beyond that
provided in this report, may be needed prior to implementation of the recommendation. Note that the
recommendations are based on an independent evaluation by the RSE team, and represent the opinions of
the RSE team. These recommendations do not constitute requirements for future action, but rather are
provided for the consideration of all site stakeholders.
The Clear Creek/Central City Superfund Site Argo Tunnel Water Treatment Plant was selected by EPA
OSRTI based on a recommendation from EPA Region 8 and the Colorado Department of Public Health
and Environment. The site team is primarily looking for cost-reduction strategies that will allow the
system to more cost-effectively maintain its designed level of protectiveness. This report provides a brief
background on the site and current operations, a summary of observations made during a site visit, and
recommendations regarding the remedial approach. The cost impacts of the recommendations are also
discussed.
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1.2 TEAM COMPOSITION
The team conducting the RSE consisted of the following individuals:
Peter Rich, Civil and Environmental Engineer, GeoTrans, Inc.
Doug Sutton, Environmental Engineer, GeoTrans, Inc.
Rodger Hosier, Civil and Environmental Engineer, Tetra Tech RMC, Inc.
David Bohmann, Environmental Engineer, GeoTrans, Inc.
1.3 DOCUMENTS REVIEWED
Author
Thomas R.
Wildeman
Black & Veatch
EPA
COM
EPA
COM
COM
COM
Infilco
Degremont, Inc.
CDPHE
J.E. Reynolds &
Associates
Canadian
Environmental
and
Metallurgical,
Inc.
CDPHE
EPA
EPA
CDPHE
Date
1/1/1983
2/8/1983
9/30/1987
9/21/1990
9/30/1991
1/13/1994
7/25/1994
5/12/1995
1983- 1998
5/28/1999
4/28/2000
5/2001
2002
9/22/2003
9/29/2004
2004
Title
Chemistry of the Argo Tunnel Water, Idaho Springs,
Colorado
Remedial Action Master Plan, Central City, Mines Drainage
Sites
Record of Decision - OU1
Clear Creak Phase II Remedial Investigation
Record of Decision - OU3
Clear Creek Remedial Design: Argo Tunnel Active
Treatment System Treatability Report, Bench-Scale Testing
Draft Technical Memorandum
Clear Creek Remedial Design: Argo Tunnel Active
Treatment System Pre-Pilot Testing Evaluations Draft
Technical Memorandum
Clear Creek Remedial Design: Argo Tunnel Active
Treatment System Additional Bench-Scale Testing Technical
Memorandum
Assorted Instructions for System Installation, Engineering
Drawings, and Communications with Project Team
Regarding Design.
Correspondence to Mr. Cevaal (COM) from CDPHE (Ron
Abel): Summary of Concerns with the Argo Tunnel
Treatment Facility, Items Relating to Design and
Construction Monitoring, 5/19/1999
Engineering Evaluation: Argo Tunnel Active Treatment
Facility, Idaho Springs, Colorado
High Density Sludge Process Pilot Scale Neutralization of
Argo Tunnel Acidic Drainage
Clear Creek/Central City Site Repository: Summary of
Sludge Drying Pilot Tests
Record of Decision Amendment - OU3
Record of Decision - OU4
Five Year Review
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Colder
Associates
Colder
Associates
CDPHE
Colder
Associates
Colder
Associates
Colder
Associates
Colder
Associates
Colder
Associates
Goff Engineering
and Surveying
Colder
Associates
Colder
Associates
Colder
Associates
Colder
Associates
CDPHE
CDPHE
CDPHE
5/15/2006
10/2006
2006
3/24/2006
4/5/2006
10/2006
1 1/2006
12/2006
12/23/2006
1/2007
2/2007
3/2007
4/2007
4/20/2007
2002 to present
2006 to present
Argo Water Treatment Facility O&M Project Annual Report
August 1, 2004 through July 31, 2005
Argo Water Treatment Facility O&M Project Annual Report
August 1, 2005 through July 31, 2006
Lime System Specifications
Clear Creek/Central City Superfund Site, Laboratory Testing
and Material Characterization
Clear Creek/Central City Superfund Site, Repository Ste
Characterization Assessment Cost Estimates Update
Argo Water Treatment Facility O&M Project Monthly Report
September 2006
Argo Water Treatment Facility O&M Project Monthly Report
October 2006
Argo Water Treatment Facility O&M Project Monthly Report
November 2006
Argo Water Treatment Facility - Filter Press Modifications
Structural Engineering Fee Proposal
Argo Water Treatment Facility O&M Project Monthly Report
December 2006
Argo Water Treatment Facility O&M Project Monthly Report
January 2007
Argo Water Treatment Facility O&M Project Monthly Report
February 2007
Argo Water Treatment Facility O&M Project Monthly Report
March 2007
Argo Tunnel Source Control
Argo WTP Effluent Data
Virginia Canyon and Big Five Tunnel Data
1.4 PERSONS CONTACTED
The following individuals associated with the site were present for the visit:
Mary Scott, Project Manager, CDPHE
Mike Holmes, Remedial Project Manager, EPA Region 8
Lee Josselyn, Project Manager, Colder Associates
Victor Wirick, Incoming Project Manager, Colder Associates
1.5 SITE LOCATION, HISTORY, AND CHARACTERISTICS
1.5.1 LOCATION
Clear Creek originates in the mountains near Colorado's Continental Divide and runs 60 miles east and
several thousand feet lower in elevation to Golden, Colorado, a western suburb of Denver, Colorado and
then discharges to the South Platte River north of Denver. The drainage basin encompasses
approximately 400 square miles, including a portion of the Colorado Mineral Belt, which includes several
mining districts in Clear Creek and Gilpin Counties. Due to the rich mineralization, these two counties
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became some of the most heavily mined areas of Colorado, with gold and silver accounting for the vast
majority of the mining. As part of ore extraction activities, the miners constructed tunnels. Acidic,
metal-rich water from these mine tunnels has continued to enter Clear Creek and its tributaries at many
locations. The Argo Tunnel and Big Five Tunnel, located in Idaho Springs, Colorado, are two of the
tunnels that EPA and CDPHE have focused on to reduce acid and metals loading to Clear Creek. The
Argo Tunnel Water Treatment Plant (Argo WTP), which is located at the entrance of the Argo Tunnel
treats the discharge from these two tunnels as well as acidic and metals laden ground water from nearby
Virginia Canyon. Figure 1-1 indicates the locations of the Argo Tunnel, Argo WTP, Big Five Tunnel,
and Virginia Canyon.
Although other sources of acid mine drainage and other remedies comprise this Superfund Site, the RSE
team was specifically asked to focus its review on the Argo WTP.
1.5.2 HISTORICAL PERSPECTIVE
Occasionally, one of the mine tunnels will produce a "blowout" releasing large quantities of water and
sediment in a short period of time. A blowout can happen when debris, likely fallen from the tunnel roof,
temporarily impounds water. Water pressure behind the debris dam eventually builds to the point where
the dam material and everything behind it are pushed forcefully from the mouth of the tunnel. A blowout
from the Argo Tunnel in 1980 focused EPA's attention on Clear Creek and was a significant factor when,
three years later, EPA included the Site on the Superfund National Priorities List (NPL).
The Site was nominated for listing on the NPL in 1982 and added to the NPL in September 1983.
Initially, EPA anticipated at least six Operable Units (OUs) for the Site: treatment of the acid drainage
from five specific mine tunnels (OU1), remediation of the five tailings and waste rock piles near those
tunnels (OU2), source control at the Argo Tunnel (OUS), blowout control at the Argo Tunnel (OU4),
regional ground water contamination (OUS), and upstream mine tunnel discharges and tailings (OU6).
Later, largely as a result of public comment received on the feasibility study for OU2, EPA combined
OUS and OU4 into a comprehensive remedial investigation and feasibility study of the Argo Tunnel and
OUS and OU6 into what has come to be known as the Phase II remedial investigation and feasibility
study. One Record of Decision (ROD) was signed for both the Argo and Phase II studies. Together these
studies are reflected in EPA planning documents as OUS, an expanded version of the original OUS.
The ROD for OU1 - Acid Mine Drainage Treatment - was signed September 30, 1987. The selected
remedy was treatment of the acid discharges from five mine tunnels using an innovative technology, man-
made wetlands. On June 15, 1988, EPA gave the lead for remedial design for OU1 to CDPHE. The lead
for the Phase II remedial investigation and feasibility study was also given to CDPHE at that time.
The ROD for OUS was signed on September 30, 1991 and amended the OU1 ROD. The OUS ROD
included, among other items, treatment of the Argo Tunnel mine water discharge. The OUS ROD
specified a more conventional treatment plant rather than man-made wetlands because the required large
land area was not available near the Argo Tunnel. No action was specified to control blowouts from any
of the mine tunnels. The Argo WTP began full operation on April 7, 1998 treating the discharge from the
Argo Tunnel. The discharges from the Virginia Canyon ground water and Big Five Tunnel were added to
the Argo WTP influent in 2006.
1.5.3 POTENTIAL SOURCES
The Argo Tunnel, Big Five Tunnel, and Virginia Canyon ground water are considered indefinite sources
of acid mine drainage, requiring source control measures to occur on a continuous and indefinite basis.
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The following table summarizes the flow rates, pH, and concentrations of predominant metals for each of
these sources.
Parameter
Average Flow (gpm)
pH
Iron (mg/L)
Manganese (mg/L)
Aluminum (mg/L)
Zinc (mg/L)
Copper (mg/L)
Argo Tunnel*
200 to 450
3
120
90
20
40
4
Big Five Tunnel*
15 to 40**
5.5
65
30
5
8
1
Virginia Canyon*
5 to 180**
3
3
90
80
92
9
*All values are approximate based on historical data.
**Flows to treatment plant can be controlled
1.5.4
HYDROGEOLOGIC SETTING
The Argo Tunnel is 4.16 miles long and was used for drainage and transporting ore and waste rock to the
mill. The Argo Tunnel reportedly was effective at draining many mines in the area. The drainage from
the tunnel is relatively constant over the course of a year relative to infiltration from rainfall, but may vary
from year to year from as low as 200 gpm to as high as 670 gpm. The lower flow rates of 200 gpm to 300
gpm were prevalent from the beginning of operation through 2006, which the site team reports were
generally dry years. To date, 2007 has reportedly been a relatively wet year, and the flow rates from the
tunnel have been on the higher end, requiring the treatment plant to handle approximately 450 gpm of
influent, with flows from Virginia Canyon controlled to only 25 gpm.
The site team reports two large historic blowouts of the Argo Tunnel plus a few smaller blowouts
(registering approximately 1,000 gpm over a few days). The first recorded blowout was reportedly in
1943 as a result of explosive work that was being conducted in the area. The second blowout occurred in
1980 and had an unknown cause but was presumably related to a partial collapse of the tunnel roof that
blocked water flow and eventually gave way. The larger blowouts reportedly have the capability of large
scale fish kills and interrupting the potable water supply for Golden and other municipalities. The smaller
blowouts reportedly occurred during periods of high flow and were more readily diluted by the high flows
of the creek.
1.5.5
POTENTIAL RECEPTORS
The segment of Clear Creek from the Argo Tunnel to Golden, Colorado is used for recreational (e.g.,
fishing, kayaking, etc.) and industrial uses as well as the potable water supply for Golden and other
municipalities.
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2.0 SYSTEM DESCRIPTION
2.1 SYSTEM OVERVIEW
The Argo WTP began full operation on April 7, 1998 treating the discharge from the Argo Tunnel, and
the facility was deemed Operational and Functional on September 30, 1999. The discharge from the
Virginia Canyon ground water was added to the WTP influent in January 2006 and the Big Five Tunnel
discharge was added to the WTP influent in May 2006. The Argo WTP has had difficulty operating
according to its design parameters and has undergone a number of evaluations in an attempt to improve
performance.
2.2 COLLECTION SYSTEM
Discharge is collected from the Argo Tunnel through a grate located outside of the tunnel entrance that
feeds directly into the WTP equalization basins. Discharges from the Virginia Canyon ground water and
the Big Five Tunnel empty from pipe ends located in front of the Argo Tunnel and drain through the grate
into the equalization basins. Mixing of the different flows therefore occurs immediately prior to the
equalization basins. The ground water in Virginia Canyon is collected in a buried drain and conveyed
from the collection area by gravity through HOPE pipe to the Argo location. The flow can be controlled
by an actuated valve operated from the WTP control system. Flow from the Virginia Canyon collection
can be as high as 180 gpm but during high flow periods is controlled to a lower flow rate so that the total
influent to the WTP is within its treatment capacity. Uncollected ground water in Virginia Canyon
eventually discharges to Clear Creek. The discharge from the Big Five Tunnel feeds by gravity into tanks
at the Big Five Tunnel entrance and is then pumped on an intermittent basis to the Argo location. The
tanks at the Big Five Tunnel location also receive water from a small seep that occurs along the
Department of Transportation right-of-way at the nearby entrance to Interstate 70. Pumping from the Big
Five collection tanks to the Argo location typically occurs six times a day for 40 minutes at 90 gpm, plus
siphoned water on a continuous basis at 10 gpm.
2.3 TREATMENT SYSTEM
The treatment system adjusts pH and removes metals through chemical precipitation. The plant was
originally designed to use caustic for pH adjustment but the caustic addition system was replaced by a
lime feed system in late 2005 to reduce chemical costs. The WTP is divided into two identical treatment
trains. Overall, the WTP has the following primary treatment components:
Two 140,000-gallon equalization basins
One lime storage and feed system
Two rapid mix tanks with mixers
Two pH meters to control lime adjustment
Two Infilco-Degremont, Inc. reaction tank and clarifier units designed for minimum flow of 110
gpm and maximum flow of 350 gpm.
One gravity sand filter with three bays with a total bed area of 240 square feet
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One hydrochloric acid metering system to lower pH after metals removal
Solids handling pumps and two solids thickening tanks (5,000 gallons each)
One 40-cubic foot filter press with automatic start/stop
One 105-cubic foot filter press
One 30 x 30 x 10 foot underbasin to receive backwash and water from floor drains
One 30 x 30 x 10 foot underbasin to serve as a clear well to supply backwash or discharge by
gravity to Clear Creek
One programmable logic controller for the metals precipitation system
One programmable logic controller for the lime feed system
One programmable logic controller for the 40 cubic foot filter press
One programmable logic controller for the balance of the system
The WTP also includes inactive caustic storage tanks and a carbon dioxide addition system that were used
for pH adjustment before conversion to the lime system.
The WTP building has two floors, with treatment system, janitorial closet, workshop, and electrical
control room on the bottom floor and office space, restrooms, and meeting areas on the top floor. An
elevator is present for transportation between the floors.
2.4 MONITORING PROGRAM
Compliance monitoring consists of weekly effluent samples, monthly filter cake samples, and quarterly
influent and stream samples. Effluent results are reported monthly in the Discharge Monitoring Report.
Water samples are analyzed for pH, total suspended solids, hardness, total dissolved solids, and 12
metals. Filter cake samples are analyzed for eight toxic metals. Additional monitoring through Hach kits
and sensors are used for controlling the WTP.
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3.0 SYSTEM OBJECTIVES, PERFORMANCE, AND
CLOSURE CRITERIA
3.1 CURRENT SYSTEM OBJECTIVES AND CLOSURE CRITERIA
The 1991 ROD for OU3 specified a number of objectives for the remedy, including waste piles, slope
stabilization, and other measures. The one objective that applies to the Argo WTP is as follows:
"Reducing contaminant loading from the mine drainage tunnels, for the contaminants of concern at the site,
to levels which will allow state stream standards, and state table value standards (where they have been
determined to be relevant and appropriate) to be met."
This objective pertains to long-term acid mine drainage source control. The parameters of concern that
are monitored for the Discharge Monitoring Report are provided in the following section.
3.2 TREATMENT PLANT OPERATION STANDARDS
The treatment plant has the following discharge requirements.
Constituent
pH
TSS
Hardness
Iron
Arsenic
Nickel
Silver
Zinc
Aluminum
Cadmium
Lead
Copper
Manganese
Calcium
Magnesium
TDS
Units
Ppm
Ppm
Ppb
Ppb
Ppb
Ppb
Ppb
Ppb
Ppb
Ppb
Ppb
Ppb
Ppb
Ppb
Ppm
30-Day Average
20
15800
Report
850
0.02
225
3
4.75
17
800
Daily Limits
6.5-9
30
400
Report
0.62
Report
5
219
35
Report
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4.0 FINDINGS AND OBSERVATIONS FROM THE
RSE SITE VISIT
4.1 FINDINGS
The observations provided below are not intended to imply a deficiency in the work of the system
designers, system operators, or site managers but are offered as constructive suggestions in the best
interest of the EPA and the public. These observations have the benefit of being formulated based upon
operational data unavailable to the original designers. Furthermore, it is likely that site conditions and
general knowledge of acid mine drainage treatment have changed over time.
4.2 COMPONENT PERFORMANCE
4.2.1 COLLECTION SYSTEM
The collection system performs adequately under normal flow conditions but would not be capable of
handling a large blowout from the Argo Tunnel. High flow from even relatively small blowouts (e.g., on
the order of 1,000 gpm for a few days) would likely overwhelm the collection grate and treatment system
capacity, resulting in discharge of untreated water from the Argo Tunnel to Clear Creek.
The RSE team did not evaluate the collection system design for Virginia Canyon. The system is capable
of providing flows of up to 180 gpm. However, the collection system does not appear to be the limiting
factor for this contribution of flow. Rather, the limiting step is the hydraulic capacity of the treatment
plant. During high flow periods, the volume of water from the Argo and Big Five Tunnels requires
reducing the flow from the Virginia Canyon collection system by adjusting a valve. During the RSE visit,
flows were high due to spring runoff, and although the Virginia Canyon collection system was capable of
providing 180 gpm, the flow was controlled to 25 gpm. As a result, approximately 155 gpm of impacted
ground water from Virginia Canyon was discharging to Clear Creek due to a lack of capacity in the
treatment plant and the decision to preferentially collect water from the Argo Tunnel.
4.2.2 EQUALIZATION BASINS
The equalization basins receive acid mine drainage flows from three sources, each with different
chemistries. In addition, they receive water from backwashing the filters, from floor drains, filter press
filtrate, and discharge of approximately 20 gpm of reacted water from between the rapid mix tanks and
the reaction tanks from the pH probe housings. As a result of the mixing of flows with different
chemistries, substantial precipitation occurs within the equalization basins leading to solids settling and
clogging of the lines between the equalization basins and the treatment trains. At the time of the RSE,
one of the valves controlling flow from the equalization basins was open 100% resulting in 300 gpm of
flow to the corresponding treatment train, and the other valve was open 35% resulting in 300 gpm of flow
to its corresponding treatment train. To maintain the 300 gpm of flow through one clogged line during
high flow periods, the level in the equalization basins needs to increase, resulting in less storage and
equalization capacity of these basins.
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4.2.3 LIME STORAGE AND FEED SYSTEM
The lime storage and feed system was installed in June 2005 and fully replaced the caustic system in
November 2005. The lime system includes a silo for storage, a slurry mix tank in the enclosure along
with the silo, piping from the lime enclosure to the WTP, a day tank within the WTP for additional
mixing, and diaphragm metering pumps for addition. An automatic flush is present to address clogging in
the lines from the enclosure to the WTP but manual flushing is utilized for the 1-inch lines from the day
tank to the feed location. Frequent blockages occur in these 1-inch lines resulting in lowered system pH
and reduced metals removal until the blockage is addressed.
Automatic notifications of lime reserves provide little time (2 to 3 days) until lime runs low. The site
team is aware of this and can order lime on a sufficiently frequent basis to maintain reserves; however,
the operators are often hesitant to require lime deliveries at sufficient frequency because it results in less
than a full load of lime being delivered and lime delivery drivers express frustration at delivering
incomplete loads.
Issues with poor lime quality have caused problems with grit accumulating throughout the system. The
grit has clogged lines in the lime feed system and settled in the reaction tanks, requiring additional
maintenance. The site team has tried an alternate vendor but still has inconsistent lime quality.
4.2.4 PH ADJUSTMENT
Lime is added to the rapid mix tanks to increase the pH to 10.1 as determined by pH probes located
between the rapid mix tanks and the reaction tanks. This pH set point has been chosen based on
experience regarding the pH that is needed to reliably meet the manganese discharge limit of 800 ug/L.
The pH probes foul and require cleaning and recalibration every few days. To facilitate this routine
practice, the operators have created a stilling well where the pH probes experience a lower flow rate and
can be pulled for maintenance twice a day without causing an uncontrolled release of process water from
the probe location. This stilling well results in a constant discharge of approximately 10 gpm per
treatment train of process water from between the rapid mix tanks and the reaction tanks. The 20 gpm
(i.e., 10 gpm from each train) is discharged to the flow drain, which drains to one of the building
underbasins and is eventually returned to the equalization basins.
Lime usage varies with flow and averages approximately 55,000 pounds per month. Peak lime usage
occurred in May 2007 with approximately 180,000 pounds used.
4.2.5 CHEMICAL REACTION AND PRECIPITATION SYSTEM
The chemical reaction and precipitation system is a packaged unit designed by Infilco Degremont, Inc.
that includes a reaction tank connected directly upstream of a settling tube clarifier. The reaction tank has
a concentric design such that influent comes in through the bottom center draft tube of the tank, flows
upward past the mixer impeller and polymer feed (where polymer is added to promote flocculation), over
baffles, then down between the baffles and the outer part of the tank, and finally up to the top for
discharge to the clarifier. The inner draft tube in the tank supposedly increases the reaction time and
particle interaction to promote production of a dense floe and reduce the amount of pin floe. This design,
however, results in solids settling prematurely in the outer portion of the reaction tank. Settling solids
include grit from the lime system and metal hydroxide floe. The settling is most pronounced at lower
flows and/or with solids recycling.
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The settling tube design of the clarifier requires frequent cleaning of the settling tubes to prevent flow
paths from becoming restricted. The settling tubes, however, are likely required for effective settling
given the relatively small size of the clarifiers relative to process flow rates.
Solids are wasted from the bottom of the clarifier by air operated diaphragm pumps.
4.2.6 MEDIA FILTERS
The effluent from the clarifiers flows by gravity through a filter comprised of three equally sized cells.
Each cell is 8 feet by 10 feet in horizontal dimensions and is designed for a capacity of 350 gpm (4.375
gpm per square foot). The system is designed for a backwash of 1,200 gpm at 20 psig and a surface wash
at 80 gpm at 80 psig. This backwash rate corresponds to 15 gpm per square foot, which is comparable to
typical filter applications; however, the plant operators report that the filters do not effectively backwash.
During backwash, the filter bed does not expand as anticipated, and during the RSE site visit, the plant
operators were actually bypassing the filters in order to keep the plant running. The plant operators have
tried a number of solutions including adding the hydrochloric acid to decrease the pH prior to the filters
rather than after the filters. They have also tried replacing the filter media and experimenting with the
addition of air scouring to the backwash routine. The air scour attempt, however, was unsuccessful
because the filter material had already consolidated prior to initiating the air scour. In addition, unequal
distribution of the air indicating that the air distributors were not level or clogged.
Although the plant is able to meet discharge standards while bypassing the filters, minor upsets in the
clarifier that would normally be addressed by a filter otherwise result in plant shutdowns or effluent
quality excursions.
4.2.7 SOLIDS HANDLING
Solids are wasted from the sludge bed at the bottom of the clarifiers at 20 gpm through 1.5-inch PVC.
The wasted solids are stored temporarily in the sludge storage/thickening tank before being dewatered in
one of the two filter presses. The site team reports that solids wasting flows are too high and that more
water than necessary is extracted from the clarifiers during wasting.
Two filter presses are in operation. One is a 40-cubic foot filter press from the original design. It is
elevated above the plant floor and has an automatic shutoff Although it was designed to dump directly
into a rolloff bin, the addition of a second filter press beneath it requires (due to space constraints) that
this 40-cubic foot filter press dump onto the floor. The other filter press was added after plant startup
when a higher volume of sludge was produced than expected (due to a lower than expected density in the
clarifier underflow and a lower than expected percent solids value in the filter cake). This second filter
press is 105 cubic feet. It is located on the plant floor, requires manual operation, and also dumps to the
plant floor. The pressed solids from the floor (from either press) are thus transported in a labor-intensive
process by a small skid steer and by shovel into a rolloff bin.
Solids are disposed of in the Front Range Landfill located in Erie, Colorado, which is approximately 100
miles round trip from the site. The solids content from the clarifier is approximately 3.5% and the solids
content of the pressed solids is approximately 15%.
4.2.8 CONTROLS
The treatment plant is controlled by the following four independent programmable logic controllers.
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One programmable logic controller for the metals precipitation system
One programmable logic controller for the lime feed system
One programmable logic controller for the 40 cubic foot filter press
One programmable logic controller for the balance of the system
Controls for the Big Five Tunnel are achieved through radio telemetry.
The plant is attended from 7am to 5pm daily. The plant controls include a number of alarms that contact
an operator on call, and the controls are accessible remotely using a project laptop.
4.3 COMPONENTS OR PROCESSES THAT ACCOUNT FOR MAJORITY OF
ANNUAL COSTS
Annual O&M costs are approximately $900,000 to $1,000,000 per year as summarized below.
Item Description
Labor: Oversight and Project Management
Labor: System Operation
Utilities: Electricity
Utilities: Natural Gas and Potable Water
Chemicals
Solids Transport and Disposal
Monitoring Analytical Costs
Routine Maintenance Equipment & Materials
Non-Routine Maintenance Equipment & Materials
Other Supplies
Total Estimated Annual Cost
Estimated Annual Cost
$60,000
$446,000
$35,000
$17,000
$109,000
$139,000
$19,000
$72,000
$60,000
$9,000
$966,000
Notes:
- Excludes cost for CDPHE staff
Chemical cost based on FY07 budget
Transport and disposal costs based on FY06 actual
4.3.1 UTILITIES
Electricity, which is utilized for operating the air compressors, pumps, and other motors within the plant,
comprises the majority of the utility costs. Natural gas for heating costs approximately $12,000 per year,
and city water for mixing polymer costs approximately $5,000 per year. The costs for phones and other
similar services are likely included in the "Other Supplies" category.
4.3.2 CHEMICALS
As currently operated, the budget for chemicals includes $73,000 for lime, $15,000 for polymer, and
$21,000 for hydrochloric acid.
4.3.3 LABOR
Labor for the plant is divided into project management and operator categories. Project management is
limited to less than 10 hours per week, which is reasonable for a plant of this complexity. Operator labor
comprises the rest of the labor budget. A total of approximately 11,000 labor hours are budgeted for the
site each year. The plant is staffed by the following individuals:
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A lead operator that works 8-hour days during the week and has primarily administrative
responsibility, quality control, and technical lead on special maintenance/improvement projects
A maintenance person that assists the lead operator and has responsibilities that are evenly split
between maintenance activities and operations
Two duty operators that each work four 10-hour days per week, with overlap on one of those days
for heavier maintenance items, and responsibility for responding to alarms
One assistant operator/laborer that works each day, primarily operating the filter presses,
conducting janitorial activities, and cleaning up
Two additional employees are brought in for help during high flow periods to allow for 24-hour
coverage.
As indicated, the plant is staffed by four people per day plus an additional person during high flow
periods.
4.3.4 TRANSPORT AND DISPOSAL
Transport and disposal costs for solids disposal are reportedly approximately $9.60 per cubic yard plus
$370 per trip for each 18 cubic yard rolloff bin, plus a markup charged by the contractor on all
reimbursable items.
4.3.5 CHEMICAL ANALYSIS
The chemical analysis costs are for the monitoring required for the NPDES permit equivalent. The costs
represent weekly water samples that are analyzed for pH, total suspended solids, hardness, total dissolved
solids, and 12 metals plus filter cake samples that are analyzed for eight toxic metals.
4.4 RECURRING PROBLEMS OR ISSUES
The site team reports the following recurring problems or issues:
Labor intensive solids handling
Labor intensive cleaning of the backwash underbasin and equalization tanks
Clogging/scaling of filters
Ice build-up on the building roof
Lack of redundant air supply during high flow periods
Poor lime quality and grit that settles throughout system
Blockages in the lime feed system
4.5 REGULATORY COMPLIANCE
The treatment plant generally meets discharge standards. The manganese discharge limit of 800 ug/L is
the most difficult standard for the plant to meet and is the primary cause for the large lime requirements
and large quantity of sludge generated by the treatment process. The plant has exceeded this standard
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occasionally over the past several years as the treatment process has been improved. The plant
occasionally experiences bypasses, including one immediately prior to the RSE site visit that resulted
from a shortage of lime.
4.6 TREATMENT PROCESS EXCURSIONS AND UPSETS, ACCIDENTAL
CONTAMINANT/REAGENT RELEASES
There have been no reported major upsets or accidents since the plant began operation other than the
bypasses mentioned previously.
4.7 SAFETY RECORD
A reportable incident occurred in January 2007 due to snow/ice sliding off of the treatment plant roof.
Administrative controls were in place but were not sufficient to prevent the incident. Engineering
controls are being sought to prevent future incidents. Plant health and safety inspections are conducted on
a bimonthly basis. This frequency is reduced from the original monthly basis after it was determined that
bimonthly was sufficient.
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5.0 EFFECTIVENESS OF THE SYSTEM TO PROTECT HUMAN
HEALTH AND THE ENVIRONMENT
5.1 GROUND WATER
Ground water is addressed by this remedy through the interception of acidic, metal-rich ground water
from Virginia Canyon. However, the purpose of intercepting the ground water is to protect nearby
surface water (i.e., Clear Creek). During high flow periods, the treatment system lacks capacity to
address all of the flow from the two tunnels and from Virginia Canyon. Current practice is to limit the
flow that is accepted from the Virginia Canyon collection system, which means that uncollected water
discharges to Clear Creek. Although the iron concentration in the Virginia Canyon water is substantially
lower than that of the Argo Tunnel water, the manganese and pH are comparable between the two
sources, and the aluminum, zinc, and copper are higher in the Virginia Canyon water.
5.2 SURFACE WATER
Surface water is the primary environmental media of concern at this site. The intent of the remedy is to
protect Clear Creek against acid and metals loading from the abandoned Argo and Big Five Tunnels. The
treatment plant is currently able to intercept and treat this discharge under most conditions. However,
there is no infrastructure to protect against short-lived (e.g., on the order of a day) high flow events that
exceed 700 gpm. Under most high flow events, the flow of Clear Creek will also be high such that a
discharge above standards or a bypass will not likely result in harm to the ecosystem or uses of the water.
Based on discussions during the RSE site visit, large blowouts during low, normal, or high flow periods
would likely result in harm to the ecosystem and a temporary shut down of the water supply system for
Golden, Colorado.
5.3 AIR
Air is not a primary environmental media of concern for the Argo WTP remedy. However, the indoor air
quality of the plant is of interest to the health of the operators. The current solids handling practices result
in substantial metals dust, including iron, manganese, aluminum, zinc, and copper. This dust, when
inhaled, could lead to health concerns for the plant workers.
5.4 SOIL
Not applicable.
5.5 WETLANDS AND SEDIMENTS
Not applicable.
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6.0 RECOMMENDATIONS
Cost estimates provided herein have levels of certainty comparable to those done for CERCLA Feasibility
Studies (-30%/+50%), and these cost estimates have been prepared in a manner consistent with EPA 540-
R-00-002, A Guide to Developing and Documenting Cost Estimates During the Feasibility Study, July,
2000.
6.1 RECOMMENDATIONS TO IMPROVE EFFECTIVENESS
6.1.1 EVALUATE AND DECIDE ON NEED FOR BLOWOUT PREVENTION
Although the treatment plant routinely meets its discharge criteria and reduces discharge of acidic, metal-
rich water to Clear Creek from the Argo Tunnel, Big Five Tunnel, and Virginia Canyon ground water, it
is incapable of handling flows of over 700 gpm. Therefore, bypasses of the treatment system would
likely occur during relatively short-lived flows of 1,000 gpm, such as those that were witnessed in 1995
and 1998. A significant bypass of the treatment plant could also occur during a blowout if debris in the
tunnel were to block the flow of water and then suddenly give way. Site documents indicate that the
volume of such a blowout could be on the order of 71 acre-feet.
Short-lived periods of flow over 700 gpm might occur on a fairly regular basis during the snow melt
season, especially if the full volume of intercepted ground water from Virginia Canyon is considered
(rather than controlled by a valve). These high flow discharge events would likely occur during periods
of high flow for Clear Creek such that the environmental impacts would be reduced. However, a large
blowout could occur during any season and could have significant impacts on the ecology of the creek
and on downstream public water systems that draw water from Clear Creek. Therefore, the site
stakeholders should come to agreement on how to address the potential for future blowouts. One side of
the argument stresses that historic blowouts have occurred infrequently, and it is uncertain as to how
many decades may pass before another blowout occurs. This side of the argument suggests that the $3
million to $5 million might be better spent on other aspects of the site. The other side of the argument
stresses the severity impacts to the Clear Creek ecosystem and to the temporary shut down of the Golden,
Colorado public water supply if a blowout occurs. Immediate harm to the public could also occur if the
creek is being used for recreational purposes (e.g., fishing, kayaking, etc.) near the tunnel when a large
blowout occurs.
This RSE has focused on the water treatment plant operation, and it is beyond the scope of the RSE to
fully consider the risks associated with potential tunnel blowouts. However, it is important to note that
the reported estimated capital costs for controlling future blowouts (and controlling tunnel flow in
general), is only equal to 3 to 5 years of treatment plant O&M and likely comparable to the design and
construction costs of the treatment plant. Therefore, the costs of this improvement would be relatively
low compared to the long-term costs for this site. If the risks are substantial, the reported estimated
capital cost is likely worth the investment. Control of tunnel blowouts was a component of the original
ROD and one of the primary aspects of the site that gained the attention of CDPHE and EPA.
This evaluation will likely primarily involve interaction of EPA and CDPHE staff and management.
Contractor costs to support this evaluation might be on the order of $20,000 for a limited paper review
and meeting attendance.
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6.1.2 EVALUATE IMPORTANCE OF COMPLETE COLLECTION AND TREATMENT OF THE
VIRGINIA CANYON GROUND WATER
During the high flow season, the treatment plant operators need to partially close the valve that controls
flow from Virginia Canyon so that the treatment plant can accommodate the flow from the Argo and Big
Five Tunnels. This approach, however, means that the Virginia Canyon collection system is effectively
bypassed and acidic and metal-rich ground water in Virginia Canyon discharges to Clear Creek. As
indicated in Section 1.5.3 of this report, the metals concentrations for aluminum, zinc, and copper are
higher in the Virginia Canyon ground water than they are in the Argo Tunnel water. It is recommended
that the site team evaluate the need to completely collect and treat the impacted ground water from
Virginia Canyon. The RSE team sees the following potential outcomes of such an evaluation:
Bypasses of the Virginia Canyon ground water collection system occur during periods of high
flow in Clear Creek and are sufficiently diluted such that there are no adverse impacts to human
health or the environment.
The water quality of the Virginia Canyon ground water is worse than that of the Argo Tunnel
such that during periods of high flow all of the Virginia Canyon ground water should be collected
and treated and the Argo Tunnel water should be bypassed, if necessary.
The loadings to Clear Creek from Virginia Canyon, the Argo Tunnel, and Big Five Tunnel are
unacceptable, and modifications should be made to allow complete capture of all sources during
the typical snowmelt season.
If the evaluation results in the third potential outcome, then one of the modifications that might be
appropriate is including flow control for the Argo Tunnel such that the discharge of the Argo Tunnel
could be stored while the flow from Virginia Canyon is addressed. If 100 gpm of discharge from the
Argo Tunnel were to be stored for a period of 60 days, the total stored volume would be 8.6 million
gallons or 26.5 acre-feet of water. This is approximately one third of the volume that would need to be
controlled for a large blowout. Therefore, there is additional benefit to constructing a bulkhead for the
Argo Tunnel for blowout/flow control.
Implementation of this recommendation is likely accomplished by CDPHE and EPA staff evaluating the
flows from all of these acid mine drainage sources against the existing the NPDES permit equivalent and
loading calculations. Further effort by CDPHE and EPA might be needed to prepare an Explanation of
Significant Differences if the evaluation resulted in a different treatment strategy than is currently in
place. Contractor support for this evaluation would likely be limited to organizing and preparing data for
CDPHE and EPA to review. The cost for this support might be $10,000.
6.1.3 EVALUATE INDOOR AIR QUALITY FOR METALS AND CONFIRM MEDICAL
MONITORING FOR PLANT WORKERS
The currently used solids handling process results in accumulation of solids on the floor and process
equipment. When it dries, fine metal oxide dust can be produced that can negatively impact indoor air
quality and work safety. It is recommended that indoor air quality be tested and compared to OSHA
standards and that project managers confirm that medical monitoring of plant workers is being conducted
to test blood levels of appropriate metals. This recommendation should cost less than $2,000 to
implement.
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6.2 RECOMMENDATIONS TO REDUCE COSTS
6.2.1 INSTALL NEW FILTER PRESSES
The current approach to dewatering solids is labor intensive and inefficient for two primary reasons.
First, the large filter press is located on the floor and dumps the filter cake on the floor such that the filter
cake needs to be manually placed in rolloff bins. Second, the large filter press does not have an
automated shutoff, which requires additional operator attention and prevents the staff from starting a run
before leaving for the evening. The site team has been considering a capital improvement to the plant that
would involve extending the elevated platform where the current smaller filter press sits and replacing
both filter presses with new automated 80 cubic-foot presses. Both presses would sit on the elevated
platform and would dump into rolloff bins. The estimated capital cost is approximately $560,000 for this
improvement. Although the cost is relatively high compared to annual costs, the modification should
result in one less full time employee for operations at a projected annual savings of approximately
$100,000 per year. In addition, by directly dumping to the rolloff bins, less solids will be on the floor,
which will reduce the amount of metal dust in the plant and the amount of solids that are washed down
drains to the underbasin and eventually to the equalization basin. This should improve indoor air quality
(health and safety) and facilitate plant maintenance.
The RSE team recommends that this capital improvement be implemented. The estimated capital costs
appear reasonable. Competitive bids should be obtained if they have not been already.
6.2.2 REALIZE SAVINGS FROM IMPROVED OPERATIONS IN FY09
Implementing Recommendation 6.2.1 should help reduce labor costs from $506,000 to approximately
$406,000. Given the complexity of plant operations, maximum additional savings would likely be limited
to an additional $50,000 per year if major recurring issues are resolved and labor can be reduced by one
full-time worker to a half-time worker such that the plant operates with 3.5 employees during most of the
year and 4 or 4.5 employees during the high flow season. The major issues to be addressed include
installing the filter presses mentioned above, addressing the lime grit problem, addressing the filter
scaling problem, and addressing other items listed in this RSE. Together, problems with the lime feed
system and filter scaling have dominated the operations notes since August 2006 indicating that
substantial operator and project management time has been devoted to addressing these issues. For
example, activities regarding filter modifications and repair were noted on 12 days during January 2007,
17 days during February 2007, and 8 days during March 2007. Both of these issues result from
conversion of caustic to lime and will eventually be resolved. The RSE team expects that these time-
consuming issues will continue or new issues will arise in FY08 but that by FY09, the issues will be
addressed and potential labor reductions might be possible. The lime problems are currently being
addressed by the site team, and an additional suggested item for improvement is provided in Section 6.3
of this report. Below are three approaches to addressing the problems with the filters beyond those that
are being attempted by the site team.
Approach #1 - Replace Filter Media in All Three Filter Cells and Implement Well-Designed Air Scour
The implementation of a well-designed air scour system is likely critical for future filter use. Even if anti-
scaling agents or other improvements are made to the process water, air scour improves expansion of the
filter bed and reduces the amount of water used for backwashing. Although air scour has been attempted,
a well-designed system with effective air distribution on new, unconsolidated media has not been
attempted. This approach involves replacing the filter media in each filter cell and installing effective air
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scour systems to be used with backwashing for all three cells. This modification, if feasible, might be
accomplished for $100,000.
Approach #2 -Replace Filters with New Units that Have Integrated Air Scour for Backwashing
If the current filters cannot be modified to include effective air scour, the site team might consider
installing new filter units that include effective air scour. This approach might cost $200,000 to remove
the existing filters, replace them with other units, and provide additional air compressors/blowers for air
scouring. Due to the increased capital cost, this approach should only be used if the modification of the
current filter cells is not feasible or not practical.
Approach #3 - Precipitate Metals at a Lower pH and Remove Remaining Manganese with Potassium
Permanganate and Greensand Filters
Potassium permanganate addition and greensand filters were considered earlier in the design but were
eliminated from consideration due to the cost of reagents. The estimated cost for potassium
permanganate was over $400,000 per year to achieve oxidation of the manganese. However, this analysis
was done on the treatment system influent and the amount of potassium permanganate was based on the
total influent of manganese to the plant rather than the manganese that was present in the effluent of the
clarifier. The site team currently operates the metals removal system at pH 10.1 and has tried to reduce it
in the past but could not meet the manganese discharge standard of 800 ug/L at a lower pH. Under this
approach, the site team would reduce the pH to various set points and monitor the manganese levels in the
clarifier effluent. As the pH decreases, less lime will be required, less sludge will be generated, and less
scaling will occur on the filters. However, the manganese levels will increase requiring an increased level
of potassium permanganate and greensand. The savings associated with this approach are difficult to
calculate. Testing may indicate that savings in reduced sludge disposal, lime usage, and hydrochloric acid
usage are offset by potassium permanganate costs. A 90% reduction in the manganese concentrations by
metals precipitation would result in permanganate costs of $40,000 per year. The costs of permanganate
would likely offset the savings from reduced lime usage and sludge generation.
The primary reduction in sludge volume would likely result from a decrease in the production of
magnesium hydroxide. Sludge volumes have not increased as a result of the transition from using caustic
to lime, suggesting that the use of lime is not adding to sludge volume. It is noted that magnesium
concentrations decrease from approximately 120 mg/L in the influent to approximately 40 mg/L in the
effluent. Because magnesium hydroxide typically forms at a higher pH, a reduced pH should decrease the
amount formed. The primary reduction in scaling would result from lower calcium concentrations in the
clarifier effluent. The product of the current calcium and sulfate concentrations exceed the solubility
product for calcium sulfate, suggesting that it may be contributing to filter scaling. Furthermore, scaling
was not an issue when caustic was used for pH adjustment.
The cost for implementing this approach may be as high as $350,000 to pilot this approach, remove the
existing filters and replace them with greensand filters with a total hydraulic capacity of over 700 gpm,
and add air scour capability for backwashing. Given the substantial capital cost and the negligible
savings, this approach should only be considered if other approaches to resolving the filter scaling are
unsuccessful or if the site team is confident that substantially lower permanganate use would be required
than assumed here.
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6.2.3
IMPROVE METALS TREATMENT BY SOLIDS RECYCLING
After labor, solids transport and disposal and chemicals represent the next largest cost categories. In
FY06, solids transport and disposal cost approximately $140,000. As indicated in Recommendation
6.3.6, the on-site repository may not provide substantial savings. Therefore, reduction in this cost
category will need to result from either decreased solids production or increased solids density. The cost
for chemicals is mostly for lime. Together, the hydrochloric acid and polymer are half the cost of the
lime. No alternatives for hydrochloric acid or polymer are suggested. For decreasing pH after solids
removal, sulfuric acid would increase sulfate concentrations and carbon dioxide would increase carbonate
concentrations, further increasing the potential for scaling. As a result, reductions in lime and other
chemical usage, if it is going to occur, will need to result from removing metals at a lower pH. This
would reduce lime usage, reduce hydrochloric acid usage, and reduce solids generation. The RSE team
provides the following approach for consideration.
The WTP was originally conceived to use solids recycling, but the design has seemingly prevented this
from being implemented. Convincing small scale pilot tests conducted at the plant, however, suggest that
solids recycling in a high density sludge (HDS) configuration can substantially reduce lime usage and
increase sludge density. The site team has reportedly attempted solids recycling previously at relatively
low flow rates (e.g., 5% of influent flow), but efforts have been complicated by solids settling in the
chimney of the reaction chamber and blocking the flow to the clarifier. Effective solids recycling likely
needs to be conducted at a higher flow rate to increase the solids concentration and the flow in the
reaction chamber. It is also apparent that modifications would need to be made to the reaction chamber to
prevent solids from settling in the chimney between the reaction tank and the clarifier.
With the current reaction tank design, water must flow up past the impeller in the center of the tank, over
a baffle into the outer portion of the tank, down to the bottom of the tank, and then up the entire height of
the tank over a baffle into the clarifier (see figure below).
CLARIFIER
CHIMNEY
REACTION
TANK [
INFLUENT
PATH OF
WATER
This is a relatively tortuous path for the solids-laden water to travel. Typically, a baffle is provided to
prevent the turbulence associated with mixing from affecting the clarifier; however, this design appears to
include additional separation. Solids settling within the chimney might be greatly reduced if the inner
walls of the reaction tank were removed and the baffle between the tank and the chimney was
raised/shortened so that the mixing of the impeller would prevent solids from settling in the tank and the
upward path to the clarifier is shortened. The influent location and impeller and mixer design may need
to be modified to provide adequate mixing in this larger tank volume. A figure of the potential revised
design is shown below.
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REACTION
TANK
INFLUENT
IMPELLER-"""^
CLARIFIER
CHIMNEY
PATH OF
WATER
If this approach is not possible, the site team might consider adding additional mixing or turbulence to the
existing chimney area to prevent settling.
An effective solids recycle ratio and other parameters might be taken from the results of the previous pilot
test, but it is acknowledged that the pilot test was conducted before the contributions from the Big Five
Tunnel and Virginia Canyon were added. With aeration, the pilot tests suggested that increased sludge
density and manganese removal could be achieved with pH 9.5. A reduction in lime and hydrochloric
acid usage is expected but is hard to predict. It appears reasonable to assume that sludge density in the
clarifier underflow might double and that pressed sludge volumes might decrease by half due to the lesser
mass of solids (less lime and precipitate from a lower operating pH) and likely a drier filter cake. If this is
the case, the number of press pulls would be reduced, which would help operate the plant at reduced labor
(See Recommendation 6.2.2), and the cost to dispose of sludge would decrease by $70,000 per year. The
reduced pH and improved solids settling would theoretically help reduce the solids loading or scaling on
the filters. The above savings would be partially offset by the cost of aeration, which might require a 20
horsepower compressor as indicated in the pilot test report. The cost of electricity to operate this
compressor might be $15,000 per year, reducing the potential savings from solids recycling to $55,000
per year.
The capital costs for implementing this change might include $75,000 for design and implementation of
the change to the reaction tanks and aeration. The capital cost of additional aeration is included in
Recommendation 6.3.3. The selection and testing of system parameters (e.g., solids recycling ratio, pH
set point, etc.) would be determined by testing from the current project management team and plant
operators. It is assumed that once the lime and filter issues are addressed that the current level of staffing
could conduct the necessary testing and work out operational issues by FY09.
6.3 RECOMMENDATIONS FOR TECHNICAL IMPROVEMENT
6.3.1 REDUCE DISCHARGE OF RECYCLED SOLIDS AND HIGH pH WATER TO
EQUALIZATION BASINS
The project team reports solids build up in the equalization basins that require a substantial level of effort
to clean. During the RSE site visit, the line from the equalization basin for treatment train #1 was fouling.
The valve controlling flow from the basin to the treatment train was 100% open with 300 gpm of process
flow. By comparison, the value for train #2 was only 35% open with 300 gpm of process flow. This
fouling will eventually require that solids be removed from the equalization basin and the pipe. If this
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cleaning is necessary during the high flow period when both trains are needed, a bypass would likely
occur due to insufficient capacity.
The solids build up and fouling of the equalization basins is likely primarily the result of high solids and
high pH water being returned to the equalization basins from a number of sources including the floor
drains, filter backwashing, filter press filtrate, and a constant drain of 10 gpm from each of the pH probe
mounting locations. The solids settle in the equalization basin, and the high pH of this post rapid-mix
process water reacts with the metals laden acidic water from the tunnels and Virginia Canyon forming
additional solids. In March 2007, this post rapid-mix process water was approximately 13% of the
volume of acid mine drainage entering the equalization basins. At a pH of 10.1, substantial solids
generation can occur within the equalization basins. There are two primary suggestions for reducing the
return of this high pH water to the equalization basins.
Modify Mounting of pH Probes
The pH probes are currently mounted in a "still well" type configuration in which approximately 10 gpm
of process water from between the rapid mix tank and reaction tank for each treatment train is drained
through a 3 inch pipe where the probe is mounted. The project team conveyed that this configuration was
used to facilitate removal of the pH probe and to reduce the flow velocity around the probe to reduce
fouling. The flow velocity around the pH probe can be reduced by branching off of and returning to the
main process line rather than discharging 10 gpm of water to the floor drain. Easy insertion and removal
of the valve could be accomplished by isolating the mounting area on this branched line with two valves
or by using an insertion and removal type mounting that allows the probe to be inserted/removed without
interrupting process flow. This modification to both treatment trains could likely be made for under
$5,000.
Pipe Return from Underbasin to Rapid Mix Tanks Rather than Equalization Tanks
The high solids and pH water from the underbasin could be piped back to the rapid mix tank instead of
the equalization tank. The underbasin would serve to equalize flow, and a variable speed drive and flow
meter could be installed in the line to maintain a relatively constant flow from the underbasin to keep the
treatment trains in equilibrium. This modification would likely cost $20,000 to implement.
6.3.2 IMPROVE LIME FEED SYSTEM
Clogging of the lime feed system has been a recurring problem. The RSE team recommends the
following improvement.
Lime feed systems are usually designed to constantly circulate slurry in a looped system in order to
minimize the formation of obstructions in pipes, valves, and pumps carrying the slurry. The lime feed
systems at the Argo WTP do not include this feature. Instead, piping between the mix tank below the
lime silo and the day tank in the WTP building is cleaned with an automatic water flush. For pipes,
pumps, and valves between the day tank and points of application, only a manual flushing system is
available. Because flow rates through these components are lower and manual flushing can be
overlooked (or omitted during evening hours), more frequent blockages occur.
The upper lime feed system could be modified to constantly circulate flow in a loop from the slurry
mixing tank to the treatment building and back. Slurry would circulate constantly at flow rates greater
than the peak needed for pH control. The circulation line would need to be adequately sized to provide
lime to both treatment trains or two separate recirculation lines (one per train) would be needed.
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Peristaltic hose pumps might prove to be less maintenance intensive than other pump types for this
service.
For the lower system, metering pumps could withdraw slurry directly from the circulating pipe system
(thus eliminating the need for the existing day tank). In a manner similar to the existing operations, the
metering pumps would then inject lime slurry into the influent flow at rates paced to maintain the desired
pH. If clogging of the currently installed diaphragm style chemical metering pumps and appurtenances
continues to be problematic after the grit removal system is installed, variable speed peristaltic hose
pumps could be a viable alternative.
The above modifications, including purchasing of new metering pumps for both the upper and lower feed
systems, might be accomplished for $20,000. Improved operation, a reduction in maintenance, and fewer
alarm callouts should result.
6.3.3 PROVIDE ADDITIONAL COMPRESSED AIR CAPACITY
The plant operators and project manager stated that the maximum compressed air capacity is used by the
treatment plant during high flow periods. Some processes need to be timed appropriately to have
sufficient capacity. Given the importance of compressed air in operating the plant (metering pumps, filter
presses, wasting pumps, etc.), the plant would need to run at reduced capacity during a high flow period if
one of the air compressors needed service. This would likely result in a plant bypass. Additional
compressed air capacity should be provided for redundancy. Additional capacity would likely cost
$60,000 for an additional 40 horsepower of compressed air capacity.
6.3.4 REDUCE SOLIDS WASTING FLOW RATE
During the site visit, the plant operators indicated that the flow rate of the diaphragm wasting pumps was
too high and entrained more water than necessary. The RSE team suggests that this flow be controlled by
reducing the air flow rate to the pumps with regulators and by adding timers to waste sludge periodically
rather than continuously. This modification can be implemented at a cost of about $2,000.
6.3.5 CONSIDER CONSTRUCTION OF AN ON-SITE SOLIDS DISPOSAL REPOSITORY AS A
CONTINGENCY TO DISPOSAL AT A LANDFILL
The site team has been considering the construction of an on-site repository near the former Druid Mine
for solids disposal from this and other operable units for the site. Efforts to date have focused on the
constructability of the material anticipating that the repository would include both below grade and above
grade sections. The consistency of dewatered solids, however, does not have the properties necessary for
above grade construction. The estimated costs for the repository include an HOPE liner, leachate
collection system, HDPE cover, and revegetation. The RSE team agrees with the concept of the on-site
repository as a contingency to landfill disposal but has some suggestions with regard to design.
The RSE team recommends the use of a below grade repository only for the solids from the WTP. It is
suggested that the repository consist of an excavated area that can be backfilled with solids and then
covered with excavated material and revegetated. Above ground portions of the repository are not
recommended, and the HDPE liner and leachate collection system are not necessary in the opinion of the
RSE team. The repository will be built within the area drained by the Argo Tunnel such that any water
that does drain from the solids will be recaptured by the tunnel and WTP. The amount of water retained
in the solids that could potentially drain is very low compared to the amount of precipitation that may
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infiltrate. As such, the liner and leachate collection system are added features that will create additional
work without providing much benefit.
A repository could be built each year for that year's anticipated solids disposal volume and covered at the
end of each season. Due to potential access issues, use of the repository may not be appropriate in winter,
but for the greatest return on investment, the repository should be accessible during the spring for the high
flow snow melt season. For the winter months that the repository is not accessible, disposal could
continue at the landfill. Assuming 25% of the solids generated from the plant each year would be taken to
a landfill, approximately 2,700 cubic yards of disposal volume in a repository may be required for the
remainder of the solids. Assuming a depth of 6 feet, this translates to an area of approximately 12,000
square feet or 0.28 acres. The cost to construct and close a repository of this size should be less than
$50,000. Initial costs for road improvements might cost $25,000 based on estimates provided by the site
contractor, who has presumably reviewed the current conditions.
The savings from avoiding landfill disposal at current rates would be similar. Current transport and
disposal costs are reported as $370 per load of 18 cubic yards for transport, $9.60 per cubic yard for
disposal, and a markup by the site contractor for reimbursable costs. Including the markup, the unit rates
are closer to $450 per load of 18 cubic yards for transport and $11.50 per cubic yard for disposal. The
disposal costs would be eliminated, and because of the closer proximity of the on-site repository, the
transport cost might be $300 instead of $450 per load. The savings would therefore be approximately
$54,000 per year. As a result, the RSE team recommends that the on-site repository, in the manner
described here, be considered as a contingency if transport and disposal rates for the landfill increase
substantially or repository construction and closure can be accomplished for under $40,000.
6.3.6 ADDITIONAL IMPROVEMENTS
The site team had other suggestions for improvements that could facilitate plant operations. Some of
these that the RSE team supports include the following:
Autosampler - Currently, six four-hour composite effluent samples are collected on weekly basis
for the discharge monitoring report. This can be time consuming, and if efforts are going to be
made to reduce labor in the future, an autosampler would be appropriate.
Turbidity meter - The plant operators and project managers indicated that the current turbidity
meter is not effective at detecting the small pin floe in the clarifier effluent that typically signals
sludge baulking will occur. A different turbidity meter might provide a better warning so that the
treatment process can be adjusted. One potential option is the SOLITAX turbidity and suspended
solids analyzer by Hach, which costs approximately $5,000.
Additional lime storage - The site team also suggested the need for additional lime storage given
that a bypass recently occurred as a result of a lime shortage. During high flow periods, the
current lime storage capacity provides little time between alarms and coordinating the next lime
shipment. Lime is currently delivered to the site in 45,000-pound loads, which is sufficient for 20
days of normal operation but only seven or eight days during high flow periods. The site team
could consider either additional lime storage or a backup supply of caustic to use while a new
shipment of lime is expected.
The RSE team suggests that $25,000 might be appropriate to acquire/install the above items.
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6.4 CONSIDERATIONS FOR GAINING SITE CLOSE OUT
No recommendations provided in this category.
6.5 CONSIDERATIONS FOR IMPLEMENTATION
The RSE team provides the following suggestions for implementing the above recommendations.
Priority should be given to those recommendations that could be implemented relatively quickly and can
result in a significant improvement to plant operation. Recommendations 6.1.3 (air quality and medical
monitoring), 6.2.1 (new filter presses), 6.3.1 (reducing solids and caustic discharge to equalization
basins), 6.3.2 (improving lime feed system), and 6.3.4 (reduce solids wasting rate) could be implemented
immediately. Recommendations 6.1.2 (evaluate discharge from Virginia Canyon) and 6.3.3 (additional
compressed air capacity) should be implemented before the next snow melt season. Recommendation
6.2.2 should be considered during the low flow period during the summer and early fall of 2008, and
recommendations 6.1.1 and 6.2.3 should be considered after these other recommendations have been
addressed.
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7.0 RECOMMENDATIONS
The observations and recommendations contained in this report are not intended to imply a deficiency in
the work of either the system designers or operators, but are offered as constructive suggestions in the
best interest of the EPA and the public. These recommendations have the benefit of being formulated
based upon operational data unavailable to the original designers.
Recommendations are provided in three of the four categories: effectiveness, cost reduction, and technical
improvement. Table 7-1 summarizes the costs and cost savings associated with each recommendation.
Capital costs, the change in annual costs, and the change in life-cycle costs are presented for each
recommendation.
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Table 7-1. Cost Summary Table
Recommendation
6.1.1 Evaluate and Decide on
Need for Blowout Prevention
6. 1.2 Evaluate Importance of
Complete Collection and
Treatment of the Virginia
Canyon Ground Water
6. 1.3 Evaluate Indoor Air
Quality for Metals And Confirm
Medical Monitoring for Plant
Workers
6.2.1 Install New Filter Presses
6.2.2 Realize Savings from
Improved Operations in FY09
6.2.3 Improve Metals Treatment
by Solids Recycling
6.3.1 Reduce Discharge of
Recycled Solids and High pH
Water to Equalization Basins
6.3.2 Improve Lime Feed
System
6.3.3 Provide Additional
Compressed Air Capacity
6.3.4 Reduce Solids Wasting
Flow Rate
6.3.5 Consider Construction of
an On-Site Solids Disposal
Repository as a Contingency to
Disposal at a Landfill
6.3.6 Additional Improvements
Reason
Effectiveness
Effectiveness
Effectiveness
Cost Reduction
Cost Reduction
Cost Reduction
Technical
Improvement
Technical
Improvement
Technical
Improvement
Technical
Improvement
Technical
Improvement
Technical
Improvement
Additional
Capital
Costs
($)
$20,000
$10,000
$,2000
$560,000
$100,000
To
$350,000
$75,000
$25,000
$20,000
$60,000
$2,000
$25,000
$25,000
Estimated
Change in
Annual
Costs
($/yr)
$0
$0
$0
($100,000)
($50,000)
($55,000)
$0
$0
$0
$0
$4,000
$0
Estimated
Change in
Life-Cycle
Costs
$*
$20,000
$10,000
$2,000
($2,440,000)
($1,400,000)
To
($1,150,000)
($1,575,000)
$25,000
$20,000
$60,000
$2,000
($95,000)
$25,000
Estimated
Change in
Life-Cycle
Costs (net
present
value)
$**
$20,000
$10,000
$2,000
($1,054,000)
($707,000)
To
($457,000)
($812,000)
$25,000
$20,000
$60,000
$2,000
($40,000)
$25,000
Costs in parentheses imply cost reductions
* assumes 5 years of operation with a discount rate of 0% (i.e., no discounting)
** assumes 5 years of operation with a discount rate of 5% and no discounting in the first year
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FIGURES
-------
FIGURE 1-1. MAP OF AREA ADDRESSED BY THE ARGO WTP.
:' 5"~ '" ' ''' *.,-«-- '!*>""---- ' >','' ' '' «"'<.<'. '
VIRGINIA CANYON
GROUND WATER
, :-~ ;iw:;;aq#s-;
', --T~'-;... "- x\ -:;.;-/.* ;-^-^- :' :w,>. "-^-m-
: > '--...-,. '.;':- - - '"'- *-.'- =?''t/-^ * - .//i£c." --, .^^^S-v.r^Ci'fcsi&a
0 3000
SCALE IN FEET
6000
(Note: Based on Clear Creek/Central City Superfund Site,
Five Year Review Report, Figure 3.)
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